,,the ,,principles ,,of ,,chemistry ,by ,d4 ,,mendel,,eff ,,translated ,,from ,,the ,,russian 7,,sixth ,,edition7 ,,by ,,george ,,kamensky1 ,a4,r4,s4,m4 ,,of ,,the ,,imperial ,,mint1 ,,st ,,petersburg3 ,,member ,,of ,,the ,,russian ,,physico-,,chemical ,,society ,,edited ,,by ,t4 ,a4 ,,lawson1 ,b4,sc4 ,,ph4,d4 ,,examiner ,,in ,,coal-,,tar ,,products ,,to ,,the ,,city ,,and ,,guilds ,,of ,,london ,,institute ,,fellow ,,of ,,the ,,institute ,,of ,,chemistry ,,in ,,two ,,volumes ,,volume ,,ii4 ,,longmans1 ,,green1 ,,and ,,co #ci ,,paternoster ,,row1 ,,london ,,new ,,york ,,and ,,bombay #ahig ,all rights reserved 99 99 99 99 99 ,,table ,,iii4 ,the periodic dependence of the composition of the simplest compounds and properties of the simple bodies upon the atomic weights of the elements4 ---------------------------------------- ----------------- ,molecular composition of the higher hydrogen and ,atomic weights of the elements metallo-organic compounds ---------------------------------------- ----------------- ,e,,ch#c1 ,c#b;,h#e1 c4 #a #b #c #d #e #f ,,hh ,h #a1jje 7mean7 ,li #gjb 7,stas7 ,be #ia 7,nilson ,pettersson7 ,,be#c -- -- ,b #aaj 7,ramsay ,ashton7 ,,ch#d ,c#b;,h#f ,c#b;,h#d ,c#b;,h#b ,c #abjj 7,roscoe7 ,,nh#c ,n#b;,h#d -- ,n #adjd 7,stas7 ,,oh#b -- ,o #af 7conventional7 ,,fh ,f #aij 7,christiansen7 ,na,e ,na #bcjd 7,stas7 ,mg,e#b -- ,mg #bdc 7,burton7 ,al,e#c -- -- ,al #bga 7,mallet7 ,si,h#d ,si#b;,e#f -- -- ,si #bhd 7,thorpe ,young7 ,,ph#c ,p#b;,h#d -- ,p #caj 7v4 d4 ,plaats7 ,,sh#b -- ,s #cbjf 7,stas7 ,cl,h ,cl #cede 7,stas7 ,k #ciae 7,stas7 ,ca #djj 7,dumas7 ,sc #ddj 7,nilson7 ,ti #dha 7,thorpe7 ,v #eab 7,roscoe7 ,cr #eba 7,rawson7 ,mn #eea 7,marignac7 ,fe #efj 7,dumas7 ,co #ehi 7,zimmermann7 ,ni #eid 7,winkler7 ,cu #fc4f 7,richards7 ,zn,e#b -- ,zn #fec 7,marignac7 ,ga,e#c -- -- ,ga #fii 7,boisbaudran7 ,ge,e#d -- -- -- ,ge #gbc 7,winkler7 ,as,h#c -- -- ,as #gej 7,dumas7 ,se,h#b -- ,se #gij;,a 7,pettersson7 ,br,h ,br #giie 7,stas7 ,rb #hee 7,godeffroy7 ,sr #hgf 7,dumas7 ,y #hi 7,clve7 ,zr #ijf 7,bailey7 ,nb #id 7,marignac7 ,mo #ifa 7,maas7 ,unknown metal ,ru #ajag 7,joly7 ,rh #ajbg 7,seubert7 ,pd #ajfd 7,keller ,smith7 ,ag #ajgib 7,stas7 ,cd,e#b -- ,cd #aaba 7,lorimer ,smith7 ,in,e#c -- -- ,in #aacf 7,winkler7 ,sn,e#d -- -- -- ,sn #aaia 7,classen7 ,sb,h#c -- -- ,sb #abjd 7,schneider7 ,te,h#b -- ,te #abea 7,brauner7 ,cs #acbg 7,godeffroy7 ,ba #acgd 7,richards7 ,la #achb 7,brauner7 ,ce #adjb 7,brauner7 ,ta #ahbg 7,marignac7 ,w #ahdj 7,waddel7 ,unknown element4 ,ir #aicc 7,joly7 ,pt #aifj 7,dittmar ,mc,arthur7 ,au #aige 7,mallet7 ,hg,e#b -- ,hg #bjje 7,erdmann ,mar47 ,tl,e#c -- -- ,tl #bjda 7,crookes7 ,pb,e#d -- -- -- ,pb #bjfij 7,stas7 ,bi,e#c -- -- ,bi #bjhi 7,classen7 ,five unknown elements4 ,th #bcbd 7,krss ,nilson7 ,unknown element4 ,u #bcic 7,zimmermann7 ---------------------------------------- ----------------- ---------------------------------------- ------------------------------ ,composition of the saline compounds1 ,x ,cl ---------------------------------------- ------------------------------ ,br1 7,,no#c71 #a_/b ,o1 #a_/b 7,,so#d71 ,,oh1 7,,om7 ,z1 where ,m ,k1 #a_/b ,ca1 #a_/c ,al1 c4 ,form ,,rx ,,rx#b ,,rx#c ,,rx#d ,,rx#e ,,rx#f ,,rx#g ,,rx#h ,oxi- ,r#b,o ,,ro ,r#b,o#c ,,ro#b ,r#b,o#e ,,ro#c ,r#b,o#g ,,ro#d des #g #h #i #aj #aa #ab #ac #ad ,x or ,h#b,o i,x -- ,be,x#b -- -- ,,bx#c -- ,,co -- ,,coz#b ,n#b,o ,,no ,,noz ,,no#b ,,no#b,z -- ,,ox#b ,,fz ,na,x -- ,mg,x#b -- -- ,al,x#c -- -- -- ,si,o,z#b -- -- ,,px#c -- ,,poz#c -- ,,sx#b -- ,,soz#b -- ,,so#b,z#b ,cl,z -- ,cl,o,z -- ,cl,o#b,z -- ,cl,o#c,z ,,kx -- ,ca,x#b -- -- ,sc,x#c -- ,ti,x#b ,ti,x#c ,ti,x#d -- ,,vo ,,vox -- ,,voz#c -- ,cr,x#b ,cr,x#c ,cr,o#b -- ,cr,o#b,z#b -- ,mn,x#b ,mn,x#c ,mn,o#b -- ,mn,o#b,z#b ,mn,o#c,z -- ,fe,x#b ,fe,x#c -- -- ,fe,o#b,z#b -- ,co,x#b ,co,x#c ,co,o#b -- ,ni,x#b ,ni,x#c ,cu,x ,cu,x#b -- ,zn,x#b -- -- ,ga,x#c -- ,ge,x#b -- ,ge,x#d -- ,as,s ,as,x#c ,as,s#b ,as,o#b,z -- -- -- ,se,o,z#b -- ,se,o#b,z#b ,br,z -- ,br,o,z -- ,br,o#b,z -- ,br,o#c,z ,rb,x -- ,sr,x#b -- -- ,,yx#c -- -- -- ,zr,x#d -- -- ,nb,x#c -- ,nb,o#b,z -- -- ,mo,x#c ,mo,x#d -- ,mo,o#b,z#b 7eka-manganese1 ,em #ii74 ,em,o#c,z ,ru,o#d -- ,ru,x#b ,ru,x#c ,ru,x#d -- ,ru,o#b,z#b ,ru,o#c,z -- ,rh,x#b ,rh,x#c ,rh,x#d -- ,rh,o#b,z#b ,pd,x ,pd,x#b -- ,pd,x#d ,ag,x -- ,cd,x#b -- ,in,x#b ,in,x#c -- ,sn,x#b -- ,sn,x#d -- -- ,sb,x#c -- ,sb,o#b,z -- -- -- ,te,o,z#b -- ,te,o#b,z#b ,,iz -- ,,iz#c -- ,,io#b,z -- ,,io#c,z ,cs,x -- ,ba,x#b -- -- ,la,x#c -- -- ,ce,x#c ,ce,x#d ,little known ,di #adb4a and ,yb #agc4b1 and over #ae unknown elements4 -- -- -- -- ,ta,o#b,z -- -- -- ,,wx#d -- ,,wo#b,z#b ,os,o#d -- -- ,os,x#c ,os,x#d -- ,os,o#b,z#b -- -- -- ,ir,x#c ,ir,x#d -- ,ir,o#b,z#b -- ,pt,x#b -- ,pt,x#d ,au,x -- ,au,x#c ,hg,x ,hg,x#b ,tl,x -- ,tl,x#c -- ,pb,x#b -- ,pb,o,z#b -- -- ,bi,x#c -- ,bi,o#b,z -- -- -- ,th,x#d -- -- -- ,,uo#b -- ,,uo#b,x#b ,,uo#d ---------------------------------------- ------------------------------ ---------------------------------------- --------------------------- ,lower ,simple bodies ,molecular composition of hydrogen ------------------- the higher hydrogen and ,peroxides com- ,sp4 ,sp4 ,melting metallo-organic compounds pounds gr vol4 point ---------------------------------------- ------------------------- ,e,,ch#c1 ,c#b;,h#e1 c4 #a #b #c #d #ae #af #ag #ah #ai ,,hh,h#b,o#b -- 99#jje #bj -#bej8 -- -- #jei #aai #ahj -- ,be,h #afd #ee #ijj8 ,,be#c -- -- -- -- #be #dd #a1cjj8 ,,ch#d ,c#b;,h#f ,c#b;,h#d ,c#b;,h#b ,c#b,o#e99 -- 99#ai #fc #b1fjj8 ,,nh#c ,n#b;,h#d --,n#b,o#f99 ,n#c;,h 99#jf #bc -#bjc ,,oh#b --,o#c -- 99#ji #ah -#bcj8 ,,fh -- -- 8#aj #ai 8 ,na,e,na,o ,na#b;,h #jih #bce #if ,mg,e#b -- -- ,mg,h #agd #ad #ejj ,al,e#c -- -- -- -- #bf #aa #fjj ,si,h#d ,si#b;,e#f -- -- -- -- #bc #ab #a1cjj8 ,,ph#c ,p#b;,h#d -- -- ,p#b;,h #bb #ad #dd ,,sh#b --,s#b,o#g -- #bjg #ae #aad ,cl,h -- -- 99#ac #bg -#ge ,,ko#b ,k#b;,h #jhg #de #eh ,ca,o#b ,ca,h #aef #bf #hjj -- -- 8#be 8#ah #a1bjj8 ,ti,o#c -- #cf #ac #b1ejj8 -- -- #ee #i #c1jjj8 ,cr#b,o#g -- #fg #gg #b1jjj8 -- -- #ge #gc #a1ejj -- ,fen,h99 #gh #gb #a1dej -- -- #hf #fh #a1djj -- ,nin,h #hg #fh #a1cej ,cu#b,o#e99 ,cu,h #hh #gb #a1jed ,zn,e#b --,zn,o#b -- #ga #ib #dah ,ga,e#c -- -- -- -- #eif #aag #cj ,ge,e#d -- -- -- -- -- #edg #acb #ijj ,as,h#c -- -- -- ,as#d;,h99 #efe #acc #ejj ,se,h#b -- -- -- #dh #af #bag ,br,h -- -- #ca #bf -#g ,rb,o ,rb#b;,h99 #ae #eg #ci ,sr,o#b ,sr,h #be #ce #fjj8 -- -- 99#cd 99#bf #a1jjj8 -- ,zr#dn,h99 #da #bb #a1ejj8 -- ,nbn,h99 #ga #ac #a1hjj8 ,mo#b,o#g -- #hf #aa #b1bjj8 -- -- -- -- -- -- ,run,h99 #abb #hd #b1jjj8 -- ,rhn,h99 #aba #hf #a1ijj8 -- ,pd#b;,h #aad #hc #a1ejj ,ag,o -- #aje #ajc #iej ,cd,e#b --,cd,o#b -- #hf #ac #cbj ,in,e#c -- -- -- -- #gd #ad #agf ,sn,e#d -- -- --,sn,o#c -- #gb #af #bcb ,sb,h#c -- -- -- -- #fg #ah #dcb ,te,h#b -- -- -- #fd #bj #dee ,,ih -- -- #di #bf #aad -- ,cs#b;,h99 #bcg #ef #bg ,ba,o#b ,ba,h #cge #cf 8 -- -- #fa #bc 8 -- -- #ff #ba #gjj8 -- ,tan,h99 #ajd #ah 8 ,w#b,o#g -- #aia #if #b1fjj -- -- #bbe #he #b1gjj8 -- ,irn,h99 #bbd #hf #b1jjj -- ,ptn,h99 #bad #ib #a1gge -- -- #aic #aj #a1jde ,hg,e#b -- -- -- #acf #ae -#ci ,tl,e#c -- -- -- -- #aah #ag #bid ,pb,e#d -- -- -- -- -- #aac #ah #cbh ,bi,e#c -- -- -- -- #ih #ba #bfi -- -- #aaa #ba 8 -- -- #ahg #ac #b1djj8 ---------------------------------------- ------------------------- ,a ,from analogy there is reason for thinking that the atomic weight of selenium is really slightly less than #gij4 ,columns #a1 #b1 #c1 and #d give the molecular composition of the hydrogen and metallo-organic compounds1 exhibiting the most characteristic forms assumed by the elements4 ,the first column contains only those which correspond to the form ,,rx#d1 the second column those of the form ,,rx#c1 the third of the form ,,rx#b1 and the fourth of the form ,,rx1 so that the periodicity stands out clearly 7see ,column #af74 ,column #e contains the symbols of all the more or less well-known elements1 placed according to the order of the magnitude of their atomic weights4 ,column #f contains the atomic weights of the elements according to the most trustworthy determinations4 ,the names of the investigators are given in parenthesis4 ,the atomic weight of oxygen1 taken as #af1 forms the basis upon which these atomic weights were calculated4 ,some of these have been recalculated by me on the basis of ,stas's most trustworthy data 7see ,chapter ,,xxiv4 and the numbers given by ,stas in the table1 where they are taken according to van der ,plaats and ,thomsen's calculations74 ,columns #g-ad contain the composition of the saline compounds of the elements1 placed according to their forms1 ,,rx1 ,,rx#b to ,,rx#h 7in the #adth column74 ,if the element ,r has a metallic character like ,h1 ,li1 ,be1 c41 then ,x represents ,cl1 ,,no#c1 #a_/b ,,so#d1 c41 haloid radicles1 or 7,,oh7 if a perfect hydrate is formed 7alkali1 aqueous base71 or #a_/b ,o1 #a_/b ,s1 c4 when an anhydrous oxide1 sulphide1 c4 is formed4 ,for instance1 ,na,cl1 ,mg7,,no#c7b1 ,al#b7,,so#d7c1 correspond to ,na,x1 ,mg,x#b1 and ,al,x#c2 so also ,na7,,oh71 ,mg7,,oh7#b1 ,al7,,oh7#c1 ,na#b,o1 ,mg,o1 ,al#b,o#c1 c4 ,but if the element1 like ,c or ,n1 be of a metalloid or acid character1 ,x must be regarded as 7,,oh7 in the formation of hydrates2 7,,om7 in the formation of salts1 where ,m is the equivalent of a metal1 #a_/b ,o in the formation of an anhydride1 and ,cl in the formation of a chloranhydride2 and in this case 7i4e4 in the acid compounds7 ,z is put in the place of ,x2 for example1 the formul ,,coz#b1 ,,no#b,z1 ,,mno#b,z1 ,fe,o#b,z#b1 and ,,iz#c correspond to ,,co7,na,o7#b ,na#b;,,co#c1 ,c,o,cl#b1 ,,co#b1 ,,no#b7,na,o7 ,na,n,o#c1 ,,no#b;,cl1 ,,no#b7,,oh7 ,,hno#c2 ,mn,o#c7,,ok7 ,k,mn,o#d1 ,i,cl1 c4 ,the #aeth column gives the compositions of the peroxides of the elements1 taking them as anhydrous4 ,an asterisk 7997 is attached to those of which the composition has not been well established1 and a dash 7--7 shows that for a given element no peroxides have yet been obtained4 ,the peroxides contain more oxygen than the higher saline oxides of the same elements1 are powerfully oxidising1 and easily give peroxide of hydrogen4 ,this latter circumstance necessitates their being referred to the type of peroxide of hydrogen1 if bases and acids are referred to the type of water 7see ,chapter ,,xv41 ,note #g and #aa bis74 ,the #afth column gives the composition of the lower hydrogen compounds like ,n#c;,h and ,na#b;,h4 ,they may often be regarded as alloys of hydrogen1 which is frequently disengaged by them at a comparatively moderate temperature4 ,they differ greatly in their nature from the hydrogen compounds given in columns #a-d 7see ,note #ab74 ,column #ag gives the specific gravity of the elements in a solid and a liquid state4 ,an asterisk 7997 is placed by those which can either only be assumed from analogy 7for example1 the sp4 gr4 of fluorine and hydrogen1 which have not been obtained in a liquid state71 or which vary very rapidly with a variation of temperature and pressure 7like oxygen and nitrogen71 or physical state 7for instance1 carbon in passing from the state of charcoal to graphite and diamond74 ,but as the sp4 gr4 in general varies with the temperature1 mechanical condition1 c41 the figures given1 although chosen from the most trustworthy sources1 can only be regarded as approximate1 and not as absolutely true4 ,they clearly show a certain periodicity2 for instance1 the sp4 gr4 diminishes from ,al on both sides 7,al1 ,mg1 ,na1 with decreasing atomic weight2 and ,al1 ,si1 ,p1 ,s1 ,cl1 with increasing atomic weight1 it also diminishes on both sides from ,cu1 ,ru1 and ,os47 ,the same remarks refer to the figures in the #ahth column1 which gives the so-called atomic volumes of the simple bodies1 or the quotient of their atomic weight and specific gravity4 ,for ,na1 ,k1 ,rb1 and ,cs the atomic volume is greatest among the neighbouring elements4 ,for ,ni1 ,pd1 and ,os it is least1 and this indicates the periodicity of this property of the simple bodies4 ,the last 7#aith7 column gives the melting points of the simple bodies4 ,here also a periodicity is seen1 i4e4 a maximum and minimum value between which there are intermediate values1 as we see1 for instance1 in the series ,cl1 ,k1 ,ca1 ,sc1 and ,ti1 or in the series ,cr1 ,mn1 ,fe1 ,co1 ,ni1 ,cu1 ,zn1 ,ga1 and ,ge4 99 99 99 99 99 ,,chapter ,,xv ,,the ,,grouping ,,of ,,the ,,elements ,,and ,,the ,,periodic ,,law ,it is seen from the examples given in the preceding chapters that the sum of the data concerning the chemical transformations proper to the elements 7for instance1 with respect to the formation of acids1 salts1 and other compounds having definite properties7 is insufficient for accurately determining the relationship of the elements1 inasmuch as this may be many-sided4 ,thus1 lithium and barium are in some respects analogous to sodium and potassium1 and in others to magnesium and calcium4 ,it is evident1 therefore1 that for a complete judgment it is necessary to have1 not only qualitative1 but also quantitative1 exact and measurable1 data4 ,when a property can be measured it ceases to be vague1 and becomes quantitative instead of merely qualitative4 ,among these measurable properties of the elements1 or of their corresponding compounds1 are3 7a7 isomorphism1 or the analogy of crystalline forms2 and1 connected with it1 the power to form crystalline mixtures which are isomorphous2 7b7 the relation of the volumes of analogous compounds of the elements2 7c7 the composition of their saline compounds2 and 7d7 the relation of the atomic weights of the elements4 ,in this chapter we shall briefly consider these four aspects of the matter1 which are exceedingly important for a natural and fruitful grouping of the elements1 facilitating1 not only a general acquaintance with them1 but also their detailed study4 ,historically the first1 and an important and convincing1 method for finding a relationship between the compounds of two different elements is by isomorphism4 ,this conception was introduced into chemistry by ,mitscherlich 7in #ahbj71 who demonstrated that the corresponding salts of arsenic acid1 ,h#c;,as,o#d1 and phosphoric acid1 ,h#c,,po#d1 crystallise with an equal quantity of water1 show an exceedingly close resemblance in crystalline form 7as regards the angles of their faces and axes71 and are able to crystallise together from solutions1 forming crystals containing a mixture of the isomorphous compounds4 ,isomorphous substances are those which1 with an equal number of atoms in their molecules1 present an analogy in their chemical reactions1 a close resemblance in their properties1 and a similar or very nearly similar crystalline form3 they often contain certain elements in common1 from which it is to be concluded that the remaining elements 7as in the preceding example of ,as and ,p7 are analogous to each other4 ,and inasmuch as crystalline forms are capable of exact measurement1 the external form1 or the relation of the molecules which causes their grouping into a crystalline form1 is evidently as great a help in judging of the internal forces acting between the atoms as a comparison of reactions1 vapour densities1 and other like relations4 ,we have already seen examples of this in the preceding pages4#a ,it will be sufficient to call to mind that the compounds of the alkali metals with the halogens ,,rx1 in a crystalline form1 all belong to the cubic system and crystallise in octahedra or cubes--for example1 sodium chloride1 potassium chloride1 potassium iodide1 rubidium chloride1 c4 ,the nitrates of rubidium and csium appear in anhydrous crystals of the same form as potassium nitrate4 ,the carbonates of the metals of the alkaline earths are isomorphous with calcium carbonate--that is1 they either appear in forms like calc spar or in the rhombic system in crystals analogous to aragonite4#a bis ,furthermore1 sodium nitrate crystallises in rhombohedra1 closely resembling the rhombohedra of calc spar 7calcium carbonate71 ,ca,c,o#c1 whilst potassium nitrate appears in the same form as aragonite1 ,ca,c,o#c1 and the number of atoms in both kinds of salts is the same3 they all contain one atom of a metal 7,k1 ,na1 ,ca71 one atom of a non-metal 7,c1 ,n71 and three atoms of oxygen4 ,the analogy of form evidently coincides with an analogy of atomic composition4 ,but1 as we have learnt from the previous description of these salts1 there is not any close resemblance in their properties4 ,it is evident that calcium carbonate approaches more nearly to magnesium carbonate than to sodium nitrate1 although their crystalline forms are all equally alike4 ,isomorphous substances which are perfectly analogous to each other are not only characterised by a close resemblance of form 7homeomorphism71 but also by the faculty of entering into analogous reactions1 which is not the case with ,,rno#c and ,,rco#c4 ,the most important and direct method of recognising perfect isomorphism--that is1 the absolute analogy of two compounds--is given by that property of analogous compounds of separating from solutions in homogeneous crystals1 containing the most varied proportions of the analogous substances which enter into their composition4 ,these quantities do not seem to be in dependence on the molecular or atomic weights1 and if they are governed by any laws they must be analogous to those which apply to indefinite chemical compounds4#b ,this will be clear from the following examples4 ,potassium chloride and potassium nitrate are not isomorphous with each other1 and are in an atomic sense composed in a different manner4 ,if these salts be mixed in a solution and the solution be evaporated1 independent crystals of the two salts will separate1 each in that crystalline form which is proper to it4 ,the crystals will not contain a mixture of the two salts4 ,but if we mix the solutions of two isomorphous salts together1 then1 under certain circumstances1 crystals will be obtained which contain both these substances4 ,however1 this cannot be taken as an absolute rule1 for if we take a solution saturated at a high temperature with a mixture of potassium and sodium chlorides1 then on evaporation sodium chloride only will separate1 and on cooling only potassium chloride4 ,the first will contain very little potassium chloride1 and the latter very little sodium chloride4#c ,but if we take1 for example1 a mixture of solutions of magnesium sulphate and zinc sulphate1 they cannot be separated from each other by evaporating the mixture1 notwithstanding the rather considerable difference in the solubility of these salts4 ,again1 the isomorphous salts1 magnesium carbonate1 and calcium carbonate are found together--that is1 in one crystal--in nature4 ,the angle of the rhombohedron of these magnesia-lime spars is intermediate between the angles proper to the two spars individually 7for calcium carbonate1 the angle of the rhombohedron is #aje #h2 magnesium carbonate1 #ajg #cj2 ,ca,mg7,,co#c7b1 #ajf #aj74 ,certain of these isomorphous mixtures of calc and magnesia spars appear in well-formed crystals1 and in this case there not unfrequently exists a simple molecular proportion of strictly definite chemical combination between the component salts--for instance1 ,ca,c,o#c1,mg,c,o#c--whilst in other cases1 especially in the absence of distinct crystallisation 7in dolomites71 no such simple molecular proportion is observable3 this is also the case in many artificially prepared isomorphous mixtures4 ,the microscopical and crystallo-optical researches of ,professor ,inostrantzoff and others show that in many cases there is really a mechanical1 although microscopically minute1 juxtaposition in one whole of the heterogeneous crystals of calcium carbonate 7double refracting7 and of the compound ,ca,mg,c#b,o#f4 ,if we suppose the adjacent parts to be microscopically small 7on the basis of the researches of ,mallard1 ,weruboff1 and others71 we obtain an idea of isomorphous mixtures4 ,a formula of the following kind is given to isomorphous mixtures3 for instance1 for spars1 ,,rco#c1 where ,r ,mg1 ,ca1 and where it may be ,fe1,mn 4441 c4 ,this means that the ,ca is partially replaced by ,mg or another metal4 ,alums form a common example of the separation of isomorphous mixtures from solutions4 ,they are double sulphates 7or seleniates7 of alumina 7or oxides isomorphous with it7 and the alkalis1 which crystallise in well-formed crystals4 ,if aluminium sulphate be mixed with potassium sulphate1 an alum separates1 having the composition ,k,al,s#b,o#h1ab;,h#b,o4 ,if sodium sulphate or ammonium sulphate1 or rubidium 7or thallium7 sulphate be used1 we obtain alums having the composition ,r,al,s#b,o#h1ab;,h#b,o4 ,not only do they all crystallise in the cubic system1 but they also contain an equal atomic quantity of water of crystallisation 7#ab;,h#b,o74 ,besides which1 if we mix solutions of the potassium and ammonium 7,,nh#d;,al,s#b,o#h1ab;,h#b,o7 alums together1 then the crystals which separate will contain various proportions of the alkalis taken1 and separate crystals of the alums of one or the other kind will not be obtained1 but each separate crystal will contain both potassium and ammonium4 ,nor is this all2 if we take a crystal of a potassium alum and immerse it in a solution capable of yielding ammonia alum1 the crystal of the potash alum will continue to grow and increase in size in this solution--that is1 a layer of the ammonia or other alum will deposit itself upon the planes bounding the crystal of the potash alum4 ,this is very distinctly seen if a colourless crystal of a common alum be immersed in a saturated violet solution of chrome alum1 ,k,cr,s#b,o#h1ab;,h#b,o1 which then deposits itself in a violet layer over the colourless crystal of the alumina alum1 as was observed even before ,mitscherlich noticed it4 ,if this crystal be then immersed in a solution of an alumina alum1 a layer of this salt will form over the layer of chrome alum1 so that one alum is able to incite the growth of the other4 ,if the deposition proceed simultaneously1 the resultant intermixture may be minute and inseparable1 but its nature is understood from the preceding experiments2 the attractive force of crystallisation of isomorphous substances is so nearly equal that the attractive power of an isomorphous substance induces a crystalline superstructure exactly the same as would be produced by the attractive force of like crystalline particles4 ,from this it is evident that one isomorphous substance may induce the crystallisation#d of another4 ,such a phenomenon explains1 on the one hand1 the aggregation of different isomorphous substances in one crystal1 whilst1 on the other hand1 it serves as a most exact indication of the nearness both of the molecular composition of isomorphous substances and of those forces which are proper to the elements which distinguish the isomorphous substances4 ,thus1 for example1 ferrous sulphate or green vitriol crystallises in the monoclinic system and contains seven molecules of water1 ,fe,s,o#d1g;,h#b,o1 whilst copper vitriol crystallises with five molecules of water in the triclinic system1 ,cu,s,o#d1e;,h#b,o2 nevertheless1 it may be easily proved that both salts are perfectly isomorphous2 that they are able to appear in identically the same forms and with an equal molecular amount of water4 ,for instance1 ,marignac1 by evaporating a mixture of sulphuric acid and ferrous sulphate under the receiver of an air-pump1 first obtained crystals of the hepta-hydrated salt1 and then of the penta-hydrated salt ,fe,s,o#d1e;,h#b,o1 which were perfectly similar to the crystals of copper sulphate4 ,furthermore1 ,lecoq de ,boisbaudran1 by immersing crystals of ,fe,s,o#d1g;,h#b,o in a supersaturated solution of copper sulphate1 caused the latter to deposit in the same form as ferrous sulphate1 in crystals of the monoclinic system1 ,cu,s,o#d1g;,h#b,o4 #a ,for instance the analogy of the sulphates of ,k1 ,rb1 and ,cs 7,chapter ,,xiii41 ,note #a74 #a bis ,the crystalline forms of aragonite1 strontianite1 and witherite belong to the rhombic system2 the angle of the prism of ,ca,c,o#c is #aaf #aj1 of ,sr,c,o#c #aag #ai1 and of ,ba,c,o#c #aah #cj4 ,on the other hand the crystalline forms of calc spar1 magnesite1 and calamine1 which resemble each other quite as closely1 belong to the rhombohedral system1 with the angle of the rhombohedra for ,ca,c,o#c #aje #h1 ,mg,c,o#c #ajg #aj1 and ,zn,c,o#c #ajg #dj4 ,from this comparison it is at once evident that zinc is more closely allied to magnesium than magnesium to calcium4 #b ,solutions furnish the commonest examples of indefinite chemical compounds4 ,but the isomorphous mixtures which are so common among the crystalline compounds of silica forming the crust of the earth1 as well as alloys1 which are so important in the application of metals to the arts1 are also instances of indefinite compounds4 ,and if in ,chapter ,i41 and in many other portions of this work1 it has been necessary to admit the presence of definite compounds 7in a state of dissociation7 in solutions1 the same applies with even greater force to isomorphous mixtures and alloys4 ,for this reason in many places in this work ,i refer to facts which compel us to recognise the existence of definite chemical compounds in all isomorphous mixtures and alloys4 ,this view of mine 7which dates from the sixties7 upon isomorphous mixtures finds a particularly clear confirmation in ,b4 ,roozeboom's researches 7#ahib7 upon the solubility and crystallising capacity of mixtures of the chlorates of potassium and thallium1 ,k,cl,o#c and ,tl,cl,o#c4 ,he showed that when a solution contains different amounts of these salts1 it deposits crystals containing either an excess of the first salt1 from #ih p4c4 to #ajj p4c41 or an excess of the second salt1 from #fcg to #ajj p4c42 that is1 in the crystalline form1 either the first salt saturates the second or the second the first1 just as in the solution of ether in water 7,chapter ,i472 moreover1 the solubility of the mixtures containing #cfc and #ih p4c4 ,k,cl,o#c is similar1 just as the vapour tension of a saturated solution of water in ether is equal to that of a saturated solution of ether in water 7,chapter ,i41 ,note #dg74 ,but just as there are solutions miscible in all proportions1 so also certain isomorphous bodies can be present in crystals in all possible proportions of their component parts4 ,van 't ,hoff calls such systems 'solid solutions4' ,these views were subsequently elaborated by ,nernst 7#ahib71 and ,witt 7#ahia7 applied them in explaining the phenomena observed in the coloration of tissues4 #c ,the cause of the difference which is observed in different compounds of the same type1 with respect to their property of forming isomorphous mixtures1 must not be looked for in the difference of their volumetric composition1 as many investigators1 including ,kopp1 affirm4 ,the molecular volumes 7found by dividing the molecular weight by the density7 of those isomorphous substances which do give intermixtures are not nearer to each other than the volumes of those which do not give mixtures2 for example1 for magnesium carbonate the combining weight is #hd1 density #cjf1 and volume therefore #bg2 for calcium carbonate in the form of calc spar the volume is #cg1 and in the form of aragonite #cc2 for strontium carbonate #da1 for barium carbonate #df2 that is1 the volume of these closely allied isomorphous substances increases with the combining weight4 ,the same is observed if we compare sodium chloride 7molecular volume #bg7 with potassium chloride 7volume #cg71 or sodium sulphate 7volume #ee7 with potassium sulphate 7volume #ff71 or sodium nitrate #ci with potassium nitrate #dh1 although the latter are less capable of giving isomorphous mixtures than the former4 ,it is evident that the cause of isomorphism cannot be explained by an approximation in molecular volumes4 ,it is more likely that1 given a similarity in form and composition1 the faculty to give isomorphous mixtures is connected with the laws and degree of solubility4 #d ,a phenomenon of a similar kind is shown for magnesium sulphate in ,note #bg of the last chapter4 ,in the same example we see what a complication the phenomena of dimorphism may introduce when the forms of analogous compounds are compared4 ,hence it is evident that isomorphism--that is1 the analogy of forms and the property of inducing crystallisation--may serve as a means for the discovery of analogies in molecular composition4 ,we will take an example in order to render this clear4 ,if1 instead of aluminium sulphate1 we add magnesium sulphate to potassium sulphate1 then1 on evaporating the solution1 the double salt ,k#b,mg,s#b,o#h1f;,h#b,o 7,chapter ,,xiv41 ,note #bh7 separates instead of an alum1 and the ratio of the component parts 7in alums one atom of potassium per #b,,so#d1 and here two atoms7 and the amount of water of crystallisation 7in alums #ab1 and here #f equivalents per #b,,so#d7 are quite different2 nor is this double salt in any way isomorphous with the alums1 nor capable of forming an isomorphous crystalline mixture with them1 nor does the one salt provoke the crystallisation of the other4 ,from this we must conclude that although alumina and magnesia1 or aluminium and magnesium1 resemble each other1 they are not isomorphous1 and that although they give partially similar double salts1 these salts are not analogous to each other4 ,and this is expressed in their chemical formul by the fact that the number of atoms in alumina or aluminium oxide1 ,al#b,o#c1 is different from the number in magnesia1 ,mg,o4 ,aluminium is trivalent and magnesium bivalent4 ,thus1 having obtained a double salt from a given metal1 it is possible to judge of the analogy of the given metal with aluminium or with magnesium1 or of the absence of such an analogy1 from the composition and form of this salt4 ,thus zinc1 for example1 does not form alums1 but forms a double salt with potassium sulphate1 which has a composition exactly like that of the corresponding salt of magnesium4 ,it is often possible to distinguish the bivalent metals analogous to magnesium or calcium from the trivalent metals1 like aluminium1 by such a method4 ,furthermore1 the specific heat and vapour density serve as guides4 ,there are also indirect proofs4 ,thus iron gives ferrous compounds1 ,fe,x#b1 which are isomorphous with the compounds of magnesium1 and ferric compounds1 ,fe,x#c1 which are isomorphous with the compounds of aluminium2 in this instance the relative composition is directly determined by analysis1 because1 for a given amount of iron1 ,fe,cl#b only contains two-thirds of the amount of chlorine which occurs in ,fe,cl#c1 and the composition of the corresponding oxygen compounds1 i4e4 of ferrous oxide1 ,fe,o1 and ferric oxide1 ,fe#b,o#c1 clearly indicates the analogy of the ferrous oxide with ,mg,o and of the ferric oxide with ,al#b,o#c4 ,thus in the building up of similar molecules in crystalline forms we see one of the numerous means for judging of the internal world of molecules and atoms1 and one of the weapons for conquests in the invisible world of molecular mechanics which forms the main object of physico-chemical knowledge4 ,this method#e has more than once been employed for discovering the analogy of elements and of their compounds2 and as crystals are measurable1 and the capacity to form crystalline mixtures can be experimentally verified1 this method is a numerical and measurable one1 and in no sense arbitrary4 #e ,the property of solids of occurring in regular crystalline forms--the occurrence of many substances in the earth's crust in these forms--and those geometrical and simple laws which govern the formation of crystals long ago attracted the attention of the naturalist to crystals4 ,the crystalline form is1 without doubt1 the expression of the relation in which the atoms occur in the molecules1 and in which the molecules occur in the mass1 of a substance4 ,crystallisation is determined by the distribution of the molecules along the direction of greatest cohesion1 and therefore those forces must take part in the crystalline distribution of matter which act between the molecules2 and1 as they depend on the forces binding the atoms together in the molecules1 a very close connection must exist between the atomic composition and the distribution of the atoms in the molecule on the one hand1 and the crystalline form of a substance on the other hand2 and hence an insight into the composition may be arrived at from the crystalline form4 ,such is the elementary and a priori idea which lies at the base of all researches into the connection between composition and crystalline form4 ,hay in #ahaa established the following fundamental law1 which has been worked out by later investigators3 ,that the fundamental crystalline form for a given chemical compound is constant 7only the combinations vary71 and that with a change of composition the crystalline form also changes1 naturally with the exception of such limiting forms as the cube1 regular octahedron1 c41 which may belong to various substances of the regular system4 ,the fundamental form is determined by the angles of certain fundamental geometric forms 7prisms1 pyramids1 rhombohedra71 or the ratio of the crystalline axes1 and is connected with the optical and many other properties of crystals4 ,since the establishment of this law the description of definite compounds in a solid state is accompanied by a description 7measurement7 of its crystals1 which forms an invariable1 definite1 and measurable character4 ,the most important epochs in the further history of this question were made by the following discoveries3--,klaproth1 ,vauquelin1 and others showed that aragonite has the same composition as calc spar1 whilst the former belongs to the rhombic and the latter to the hexagonal system4 ,hay at first considered that the composition1 and after that the arrangement1 of the atoms in the molecules was different4 ,this is dimorphism 7see ,chapter ,,xiv41 ,note #df74 ,beudant1 ,frankenheim1 ,laurent1 and others found that the forms of the two nitres1 ,,kno#c and ,na,n,o#c1 exactly correspond with the forms of aragonite and calc spar2 that they are able1 moreover1 to pass from one form into another2 and that the difference of the forms is accompanied by a small alteration of the angles1 for the angle of the prisms of potassium nitrate and aragonite is #aai1 and of sodium nitrate and calc spar1 #abj2 and therefore dimorphism1 or the crystallisation of one substance in different forms1 does not necessarily imply a great difference in the distribution of the molecules1 although some difference clearly exists4 ,the researches of ,mitscherlich 7#ahbb7 on the dimorphism of sulphur confirmed this conclusion1 although it cannot yet be affirmed that in dimorphism the arrangement of the atoms remains unaltered1 and that only the molecules are distributed differently4 ,leblanc1 ,berthier1 ,wollaston1 and others already knew that many substances of different composition appear in the same forms1 and crystallise together in one crystal4 ,gay-,lussac 7#ahaf7 showed that crystals of potash alum continue to grow in a solution of ammonia alum4 ,beudant 7#ahag7 explained this phenomenon as the assimilation of a foreign substance by a substance having a great force of crystallisation1 which he illustrated by many natural and artificial examples4 ,but ,mitscherlich1 and afterwards ,berzelius and ,henry ,rose and others1 showed that such an assimilation only exists with a similarity or approximate similarity of the forms of the individual substances and with a certain degree of chemical analogy4 ,thus was established the idea of isomorphism as an analogy of forms by reason of a resemblance of atomic composition1 and by it was explained the variability of the composition of a number of minerals as isomorphous mixtures4 ,thus all the garnets are expressed by the general formula3 7,,ro7#c,m#b,o#c7,si,o#b7c1 where ,r ,ca1 ,mg1 ,fe1 ,mn1 and ,m ,fe1 ,al1 and where we may have either ,r and ,m separately1 or their equivalent compounds1 or their mixtures in all possible proportions4 ,but other facts1 which render the correlation of form and composition still more complex1 have accumulated side by side with a mass of data which may be accounted for by admitting the conceptions of isomorphism and dimorphism4 ,foremost among the former stand the phenomena of homeomorphism--that is1 a nearness of forms with a difference of composition--and then the cases of polymorphism and hemimorphism--that is1 a nearness of the fundamental forms or only of certain angles for substances which are near or analogous in their composition4 ,instances of homeomorphism are very numerous4 ,many of these1 however1 may be reduced to a resemblance of atomic composition1 although they do not correspond to an isomorphism of the component elements2 for example1 ,cd,s 7greenockite7 and ,ag,i1 ,ca,c,o#c 7aragonite7 and ,,kno#c1 ,ca,c,o#c 7calc spar7 and ,na,n,o#c1 ,ba,s,o#d 7heavy spar71 ,k,mn,o#d 7potassium permanganate71 and ,k,cl,o#d 7potassium perchlorate71 ,al#b,o#c 7corundum7 and ,fe,ti,o#c 7titanic iron ore71 ,fe,s#b 7marcasite1 rhombic system7 and ,fe,s,as 7arsenical pyrites71 ,ni,s and ,ni,as1 c4 ,but besides these instances there are homeomorphous substances with an absolute dissimilarity of composition4 ,many such instances were pointed out by ,dana4 ,cinnabar1 ,hg,s1 and susannite1 ,pb,s,o#dc,pb,c,o#c appear in very analogous crystalline forms2 the acid potassium sulphate crystallises in the monoclinic system in crystals analogous to felspar1 ,k,al,si#c,o#h2 glauberite1 ,na#b;,ca7,,so#d7b1 augite1 ,r,si,o#c 7,r ,ca1 ,mg71 sodium carbonate1 ,na#b;,,co#c1aj;,h#b,o1 ,glauber's salt1 ,na#b,,so#d1aj;,h#b,o1 and borax1 ,na#b;,br,o#g1aj;,h#b,o1 not only belong to the same system 7monoclinic71 but exhibit an analogy of combinations and a nearness of corresponding angles4 ,these and many other similar cases might appear to be perfectly arbitrary 7especially as a nearness of angles and fundamental forms is a relative idea7 were there not other cases where a resemblance of properties and a distinct relation in the variation of composition is connected with a resemblance of form4 ,thus1 for example1 alumina1 ,al#b,o#c1 and water1 ,h#b,o1 are frequently found in many pyroxenes and amphiboles which only contain silica and magnesia 7,mg,o1 ,ca,o1 ,fe,o1 ,mn,o74 ,scheerer and ,hermann1 and many others1 endeavoured to explain such instances by polymetric isomorphism1 stating that ,mg,o may be replaced by #c;,h#b,o 7for example1 olivine and serpentine71 ,si,o#b by ,al#b,o#c 7in the amphiboles1 talcs71 and so on4 ,a certain number of the instances of this order are subject to doubt1 because many of the natural minerals which served as the basis for the establishment of polymeric isomorphism in all probability no longer present their original composition1 but one which has been altered under the influence of solutions which have come into contact with them2 they therefore belong to the class of pseudomorphs1 or false crystals4 ,there is1 however1 no doubt of the existence of a whole series of natural and artificial homeomorphs1 which differ from each other by atomic amounts of water1 silica1 and some other component parts4 ,thus1 ,thomsen 7#ahgd7 showed a very striking instance4 ,the metallic chlorides1 ,r,cl#b1 often crystallise with water1 and they do not then contain less than one molecule of water per atom of chlorine4 ,the most familiar representative of the order ,r,cl#b1b;,h#b,o is ,ba,cl#b1b;,h#b,o1 which crystallises in the rhombic system4 ,barium bromide1 ,ba,br#b1b;,h#b,o1 and copper chloride1 ,cu,cl#b1b;,h#b,o1 have nearly the same forms3 potassium iodate1 ,,kio#d2 potassium chlorate1 ,k,cl,o#d2 potassium permanganate1 ,k,mn,o#d2 barium sulphate1 ,ba,s,o#d2 calcium sulphate1 ,ca,s,o#d2 sodium sulphate1 ,na#b,,so#d2 barium formate1 ,ba,c#b;,h#b,o#d1 and others have almost the same crystalline form 7of the rhombic system74 ,parallel with this series is that of the metallic chlorides containing ,r,cl#b1d;,h#b,o1 of the sulphates of the composition ,,rso#d1b;,h#b,o1 and the formates ,,rc#b;,h#b,o#d1b;,h#b,o4 ,these compounds belong to the monoclinic system1 have a close resemblance of form1 and differ from the first series by containing two more molecules of water4 ,the addition of two more molecules of water in all the above series also gives forms of the monoclinic system closely resembling each other2 for example1 ,ni,cl#b1f;,h#b,o and ,mn,s,o#d1d;,h#b,o4 ,hence we see that not only is ,r,cl#b1b;,h#b,o analogous in form to ,,rso#d and ,,rc#b;,h#b,o#d1 but that their compounds with #b;,h#b,o and with #d;,h#b,o also exhibit closely analogous forms4 ,from these examples it is evident that the conditions which determine a given form may be repeated not only in the presence of an isomorphous exchange--that is1 with an equal number of atoms in the molecule--but also in the presence of an unequal number when there are peculiar and as yet ungeneralised relations in composition4 ,thus ,zn,o and ,al#b,o#c exhibit a close analogy of form4 ,both oxides belong to the rhombohedral system1 and the angle between the pyramid and the terminal plane of the first is #aah #g1 and of the second #aah #di4 ,alumina1 ,al#b,o#c1 is also analogous in form to ,si,o#b1 and we shall see that these analogies of form are conjoined with a certain analogy in properties4 ,it is not surprising1 therefore1 that in the complex molecule of a siliceous compound it is sometimes possible to replace ,si,o#b by means of ,al#b,o#c1 as ,scheerer admits4 ,the oxides ,cu#b,o1 ,mg,o1 ,ni,o1 ,fe#c,o#d1 ,ce,o#b1 crystallise in the regular system1 although they are of very different atomic structure4 ,marignac demonstrated the perfect analogy of the forms of ,k#b,zr,f#f and ,ca,c,o#c1 and the former is even dimorphous1 like the calcium carbonate4 ,the same salt is isomorphous with ,r#b,nb,o,f#e and ,r#b,,wo#b;,f#d1 where ,r is an alkali metal4 ,there is an equivalency between ,ca,c,o#c and ,k#b,zr,f#f1 because ,k#b is equivalent to ,ca1 ,c to ,zr1 and ,f#f to ,o#c1 and with the isomorphism of the other two salts we find besides an equal contents of the alkali metal--an equal number of atoms on the one hand and an analogy to the properties of ,k#b,zr,f#f on the other4 ,the long-known isomorphism of the corresponding compounds of potassium and ammonium1 ,,kx and ,,nh#d,x1 may be taken as the simplest example of the fact that an analogy of form shows itself with an analogy of chemical reaction even without an equality in atomic composition4 ,therefore the ultimate progress of the entire doctrine of the correlation of composition and crystalline forms will only be arrived at with the accumulation of a sufficient number of facts collected on a plan corresponding with the problems which here present themselves4 ,the first steps have already been made4 ,the researches of the ,geneva savant1 ,marignac1 on the crystalline form and composition of many of the double fluorides1 and the work of ,wyruboff on the ferricyanides and other compounds1 are particularly important in this respect4 ,it is already evident that1 with a definite change of composition1 certain angles remain constant1 notwithstanding that others are subject to alteration4 ,such an instance of the relation of forms was observed by ,laurent1 and named by him hemimorphism 7an anomalous term7 when the analogy is limited to certain angles1 and paramorphism when the forms in general approach each other1 but belong to different systems4 ,so1 for example1 the angle of the planes of a rhombohedron may be greater or less than #ij1 and therefore such acute and obtuse rhombohedra may closely approximate to the cube4 ,hausmannite1 ,mn#c,o#d1 belongs to the tetragonal system1 and the planes of its pyramid are inclined at an angle of about #aah1 whilst magnetic iron ore1 ,fe#c,o#d1 which resembles hausmannite in many respects1 appears in regular octahedra--that is1 the pyramidal planes are inclined at an angle of #aji #bh4 ,this is an example of paramorphism2 the systems are different1 the compositions are analogous1 and there is a certain resemblance in form4 ,hemimorphism has been found in many instances of saline and other substitutions4 ,thus1 ,laurent demonstrated1 and ,hintze confirmed 7#ahgc71 that naphthalene derivatives of analogous composition are hemimorphous4 ,nickls 7#ahdi7 showed that in ethylene sulphate the angle of the prism is #abe #bf1 and in the nitrate of the same radicle #abf #ie4 ,the angle of the prism of methylamine oxalate is #aca #bj1 and of fluoride1 which is very different in composition from the former1 the angle is #acb4 ,groth 7#ahgj7 endeavoured to indicate in general what kinds of change of form proceed with the substitution of hydrogen by various other elements and groups1 and he observed a regularity which he termed morphotropy4 ,the following examples show that morphotropy recalls the hemimorphism of ,laurent4 ,benzene1 ,c#f;,h#f1 rhombic system1 ratio of the axes #jhia 3 #a 3 #jgii4 ,phenol1 ,c#f;,h#e7,,oh71 and resorcinol1 ,c#f;,h#d7,,oh7#b1 also rhombic system1 but the ratio of one axis is changed--thus1 in resorcinol1 #jiaj 3 #a 3 #jedj2 that is1 a portion of the crystalline structure in one direction is the same1 but in the other direction it is changed1 whilst in the rhombic system dinitrophenol1 ,c#f;,h#c7,,no#b7b7,,oh7 ,o#hcc 3 #a 3 #jgec2 trinitrophenol 7picric acid71 ,c#f;,h#b7,,no7#c7,,oh7 #jicg 3 #a 3 #jigd2 and the potassium salt #jidb 3 #a 3 #aced4 ,here the ratio of the first axis is preserved--that is1 certain angles remain constant1 and the chemical proximity of the composition of these bodies is undoubted4 ,laurent compares hemimorphism with architectural style4 ,thus1 ,gothic cathedrals differ in many respects1 but there is an analogy expressed both in the sum total of their common relations and in certain details--for example1 in the windows4 ,it is evident that we may expect many fruitful results for molecular mechanics 7which forms a problem common to many provinces of natural science7 from the further elaboration of the data concerning those variations which take place in crystalline form when the composition of a substance is subjected to a known change1 and therefore ,i consider it useful to point out to the student of science seeking for matter for independent scientific research this vast field for work which is presented by the correlation of form and composition4 ,the geometrical regularity and varied beauty of crystalline forms offer no small attraction to research of this kind4 ,the regularity and simplicity expressed by the exact laws of crystalline form repeat themselves in the aggregation of the atoms to form molecules4 ,here1 as there1 there are but few forms which are essentially different1 and their apparent diversity reduces itself to a few fundamental differences of type4 ,there the molecules aggregate themselves into crystalline forms2 here1 the atoms aggregate themselves into molecular forms or into the types of compounds4 ,in both cases the fundamental crystalline or molecular forms are liable to variations1 conjunctions1 and combinations4 ,if we know that potassium gives compounds of the fundamental type ,,kx1 where ,x is a univalent element 7which combines with one atom of hydrogen1 and is1 according to the law of substitution1 able to replace it71 then we know the composition of its compounds3 ,k#b,o1 ,,kho1 ,k,cl1 ,,nh#b,k1 ,,kno#c1 ,k#b,,so#d1 ,,khso#d1 ,k#b,mg7,,so#d7b1f;,h#b,o1 c4 ,all the possible derivative crystalline forms are not known4 ,so also all the atomic combinations are not known for every element4 ,thus in the case of potassium1 ,,kch#c1 ,k#c,p1 ,k#b,pt1 and other like compounds which exist for hydrogen or chlorine1 are unknown4 ,only a few fundamental types exist for the building up of atoms into molecules1 and the majority of them are already known to us4 ,if ,x stand for a univalent element1 and ,r for an element combined with it1 then eight atomic types may be observed3-- ,,rx1 ,,rx#b1 ,,rx#c1 ,,rx#d1 ,,rx#e1 ,,rx#f1 ,,rx#g1 ,,rx#h4 ,let ,x be chlorine or hydrogen4 ,then as examples of the first type we have3 ,h#b1 ,cl#b1 ,h,cl1 ,k,cl1 ,na,cl1 c4 ,the compounds of oxygen or calcium may serve as examples of the type ,,rx#b3 ,,oh#b1 ,o,cl#b1 ,o,h,cl1 ,ca,o1 ,ca7,,oh7#b1 ,ca,cl#b1 c4 ,for the third type ,,rx#c we know the representative ,,nh#c and the corresponding compounds ,n#b,o#c1 ,,no7,,oh71 ,,no7,,ok71 ,p,cl#c1 ,p#b,o#c1 ,,ph#c1 ,sb,h#c1 ,sb#b,o#c1 ,b#b,o#c1 ,b,cl#c1 ,al#b,o#c1 c4 ,the type ,,rx#d is known among the hydrogen compounds4 ,marsh gas1 ,,ch#d1 and its corresponding saturated hydrocarbons1 ,cn,h#bn #b1 are the best representatives4 ,also ,,ch#c;,cl1 ,c,cl#d1 ,si,cl#d1 ,sn,cl#d1 ,sn,o#b1 ,,co#b1 ,si,o#b1 and a whole series of other compounds come under this class4 ,the type ,,rx#e is also already familiar to us1 but there are no purely hydrogen compounds among its representatives4 ,sal-ammoniac1 ,,nh#d;,cl1 and the corresponding ,,nh#d7,,oh71 ,,no#b7,,oh71 ,cl,o#b7,,ok71 as well as ,p,cl#e1 ,p,o,cl#c1 c41 are representatives of this type4 ,in the higher types also there are no hydrogen compounds1 but in the type ,,rx#f there is the chlorine compound ,w,cl#f4 ,however1 there are many oxygen compounds1 and among them ,,so#c is the best known representative4 ,to this class also belong ,,so#b7,,oh7#b1 ,,so#b;,cl#b1 ,,so#b7,,oh7,cl1 ,cr,o#c1 c41 all of an acid character4 ,of the higher types there are in general only oxygen and acid representatives4 ,the type ,,rx#g we know in perchloric acid1 ,cl,o#c7,,oh71 and potassium permanganate1 ,mn,o#c7,,ok71 is also a member4 ,the type ,,rx#h in a free state is very rare2 osmic anhydride1 ,os,o#d1 is the best known representative of it4#f #f ,the still more complex combinations--which are so clearly expressed in the crystallo-hydrates1 double salts1 and similar compounds--although they may be regarded as independent1 are1 however1 most easily understood with our present knowledge as aggregations of whole molecules to which there are no corresponding double compounds1 containing one atom of an element ,r and many atoms of other elements ,,rxn4 ,the above types embrace all cases of direct combinations of atoms1 and the formula ,mg,s,o#d1g;,h#b,o cannot1 without violating known facts1 be directly deduced from the types ,mg,xn or ,,sxn1 whilst the formula ,mg,s,o#d corresponds both with the type of the magnesium compounds ,mg,x#b and with the type of the sulphur compounds ,,so#b,x#b1 or in general ,,sx#f1 where ,x#b is replaced by 7,,oh7#b1 with the substitution in this case of ,h#b by the atom ,mg1 which always replaces ,h#b4 ,however1 it must be remarked that the sodium crystallo-hydrates often contain #aj;,h#b,o1 the magnesium crystallo-hydrates #f and #g;,h#b,o1 and that the type ,pt,m#b,x#f is proper to the double salts of platinum1 c4 ,with the further development of our knowledge concerning crystallo-hydrates1 double salts1 alloys1 solutions1 c41 in the chemical sense of feeble compounds 7that is1 such as are easily destroyed by feeble chemical influences7 it will probably be possible to arrive at a perfect generalisation for them4 ,for a long time these subjects were only studied by the way or by chance2 our knowledge of them is accidental and destitute of system1 and therefore it is impossible to expect as yet any generalisation as to their nature4 ,the days of ,gerhardt are not long past when only three types were recognised3 ,,rx1 ,,rx#b1 and ,,rx#c2 the type ,,rx#d was afterwards added 7by ,cooper1 ,kekul1 ,butleroff1 and others71 mainly for the purpose of generalising the data respecting the carbon compounds4 ,and indeed many are still satisfied with these types1 and derive the higher types from them2 for instance1 ,,rx#e from ,,rx#c--;as1 for example1 ,p,o,cl#c from ,p,cl#c1 considering the oxygen to be bound both to the chlorine 7as in ,h,cl,o7 and to the phosphorus4 ,but the time has now arrived when it is clearly seen that the forms ,,rx1 ,,rx#b1 ,,rx#c1 and ,,rx#d do not exhaust the whole variety of phenomena4 ,the revolution became evident when ,wrtz showed that ,p,cl#e is not a compound of ,p,cl#c ,cl#b 7although it may decompose into them71 but a whole molecule capable of passing into vapour1 ,p,cl#e like ,,pf#e and ,si,f#d4 ,the time for the recognition of types even higher than ,,rx#h is in my opinion in the future2 that it will come1 we can already see in the fact that oxalic acid1 ,c#b;,h#b,o#d1 gives a crystallo-hydrate with #b;,h#b,o2 but it may be referred to the type ,,ch#d1 or rather to the type of ethane1 ,c#b;,h#f1 in which all the atoms of hydrogen are replaced by hydroxyl1 ,c#b;,h#b,o#db;,h#b,o ,c#b7,,oh7#f 7see ,chapter ,,xxii41 ,note #ce74 ,the four lower types ,,rx1 ,,rx#b1 ,,rx#c1 and ,,rx#d are met with in compounds of the elements ,r with chlorine and oxygen1 and also in their compounds with hydrogen1 whilst the four higher types only appear for such acid compounds as are formed by chlorine1 oxygen1 and similar elements4 ,among the oxygen compounds the saline oxides which are capable of forming salts either through the function of a base or through the function of an acid anhydride attract the greatest interest in every respect4 ,certain elements1 like calcium and magnesium1 only give one saline oxide--for example1 ,mg,o1 corresponding with the type ,mg,x#b4 ,but the majority of the elements appear in several such forms4 ,thus copper gives ,cu,x and ,cu,x#b1 or ,cu#b,o and ,cu,o4 ,if an element ,r gives a higher type ,,rxn1 then there often also exist1 as if by symmetry1 lower types1 ,,rxn-#b1 ,,rxn-#d1 and in general such types as differ from ,,rxn by an even number of ,x4 ,thus in the case of sulphur the types ,,sx#b1 ,,sx#d1 and ,,sx#f are known--for example ,,sh#b1 ,,so#b1 and ,,so#c4 ,the last type is the highest1 ,,sx#f4 ,the types ,,sx#e and ,,sx#c do not exist4 ,but even and uneven types sometimes appear for one and the same element4 ,thus the types ,,rx and ,,rx#b are known for copper and mercury4 ,among the saline oxides only the eight types enumerated below are known to exist4 ,they determine the possible formul of the compounds of the elements1 if it be taken into consideration that an element which gives a certain type of combination may also give lower types4 ,for this reason the rare type of the suboxides or quaternary oxides ,r#d,o 7for instance1 ,ag#d,o1 ,ag#b;,cl7 is not characteristic2 it is always accompanied by one of the higher grades of oxidation1 and the compounds of this type are distinguished by their great chemical instability1 and split up into an element and the higher compound 7for instance1 ,ag#d,o #b;,ag ,ag#b,o74 ,many elements1 moreover1 form transition oxides whose composition is intermediate1 which are able1 like ,n#b,o#d1 to split up into the lower and higher oxides4 ,thus iron gives magnetic oxide1 ,fe#c,o#d1 which is in all respects 7by its reactions7 a compound of the suboxide ,fe,o with the oxide ,fe#b,o#c4 ,the independent and more or less stable saline compounds correspond with the following eight types3-- ,r#b,o2 salts ,,rx1 hydroxides ,,roh4 ,generally basic like ,k#b,o1 ,na#b,o1 ,hg#b,o1 ,ag#b,o1 ,cu#b,o2 if there are acid oxides of this composition they are very rare1 are only formed by distinctly acid elements1 and even then have only feeble acid properties2 for example1 ,cl#b,o and ,n#b,o4 ,r#b,o#b or ,,ro2 salts ,,rx#b1 hydroxides ,r7,,oh7#b4 ,the most simple basic salts ,r#b,,ox#b or ,r7,,oh7,x2 for instance1 the chloride ,zn#b,o,cl#b2 also an almost exclusively basic type2 but the basic properties are more feebly developed than in the preceding type4 ,for example1 ,ca,o1 ,mg,o1 ,ba,o1 ,pb,o1 ,fe,o1 ,mn,o1 c4 ,r#b,o#c2 salts ,,rx#c1 hydroxides ,r7,,oh7#c1 ,,ro7,,oh71 the most simple basic salts ,,rox1 ,r7,,oh7,x#c4 ,the bases are feeble1 like ,al#b,o#c1 ,fe#b,o#c1 ,tl#b,o#c1 ,sb#b,o#c4 ,the acid properties are also feebly developed2 for instance1 in ,b#b,o#c2 but with the non-metals the properties of acids are already clear2 for instance1 ,p#b,o#c1 ,p7,,oh7#c4 ,r#b,o#d or ,,ro#b2 salts ,,rx#d or ,,rox#b1 hydroxides ,r7,,oh7#d1 ,,ro7,,oh7#b4 ,rarely bases 7feeble71 like ,zr,o#b1 ,pt,o#b2 more often acid oxides2 but the acid properties are in general feeble1 as in ,,co#b1 ,,so#b1 ,sn,o#b4 ,many intermediate oxides appear in this and the preceding and following types4 ,r#b,o#e2 salts principally of the types ,,rox#c1 ,,ro#b,x1 ,,ro7,,oh7#c1 ,,ro#b7,,oh71 rarely ,,rx#e4 ,the basic character 7,x1 a halogen1 simple or complex2 for instance1 ,,no#c1 ,cl1 c47 is feeble2 the acid character predominates1 as is seen in ,n#b,o#e1 ,p#b,o#e1 ,cl#b,o#e2 then ,x ,,oh1 ,,ok1 c41 for example ,,no#b7,,ok74 ,r#b,o#f or ,,ro#c2 salts and hydroxides generally of the type ,,ro#b,x#b1 ,,ro#b7,,oh7#b4 ,oxides of an acid character1 as ,,so#c1 ,cr,o#c1 ,mn,o#c4 ,basic properties rare and feebly developed as in ,,uo#c4 ,r#b,o#g2 salts of the form ,,ro#c,x1 ,,ro#c7,,oh71 acid oxides2 for instance1 ,cl#b,o#g1 ,mn#b,o#g4 ,basic properties as feebly developed as the acid properties in the oxides ,r#b,o4 ,r#b,o#h or ,,ro#d4 ,a very rare type1 and only known in ,os,o#d and ,ru,o#d4 ,it is evident from the circumstance that in all the higher types the acid hydroxides 7for example1 ,h,cl,o#d1 ,h#b,,so#d1 ,h#c,,po#d7 and salts with a single atom of one element contain1 like the higher saline type ,,ro#d1 not more than four atoms of oxygen2 that the formation of the saline oxides is governed by a certain common principle which is best looked for in the fundamental properties of oxygen1 and in general of the most simple compounds4 ,the hydrate of the oxide ,,ro#b is of the higher type ,,ro#bb;,h#b,o ,,rh#d,o#d ,r7,,ho7#d4 ,such1 for example1 is the hydrate of silica and the salts 7orthosilicates7 corresponding with it1 ,si7,,mo7#d4 ,the oxide ,r#b,o#e1 corresponds with the hydrate ,r#b,o#ec;,h#b,o #b,,rh#c,o#d #b,,ro7,,oh7#c4 ,such is orthophosphoric acid1 ,,ph#c,o#c4 ,the hydrate of the oxide ,,ro#c is ,,ro#c;,h#b,o ,,rh#b,o#d ,,ro#b7,,oh7#b--;for instance1 sulphuric acid4 ,the hydrate corresponding to ,r#b,o#g is evidently ,,rho ,,ro#c7,,oh7--for example1 perchloric acid4 ,here1 besides containing ,o#d1 it must further be remarked that the amount of hydrogen in the hydrate is equal to the amount of hydrogen in the hydrogen compound4 ,thus silicon gives ,si,h#d and ,si,h#d,o#d1 phosphorus ,,ph#c and ,,ph#c,o#d1 sulphur ,,sh#b and ,,sh#b,o#d1 chlorine ,cl,h and ,cl,h,o#d4 ,this1 if it does not explain1 at least connects in a harmonious and general system the fact that the elements are capable of combining with a greater amount of oxygen1 the less the amount of hydrogen which they are able to retain4 ,in this the key to the comprehension of all further deductions must be looked for1 and we will therefore formulate this rule in general terms4 ,an element ,r gives a hydrogen compound ,,rhn1 the hydrate of its higher oxide will be ,,rhn,o#d1 and therefore the higher oxide will contain #b,,rhn,o#d - n,h#b,o ,r#b,o#h - n4 ,for example1 chlorine gives ,cl,h1 hydrate ,cl,h,o#d1 and the higher oxide ,cl#b,o#g4 ,carbon gives ,,ch#d and ,,co#b4 ,so also1 ,si,o#b and ,si,h#d are the higher compounds of silicon with hydrogen and oxygen1 like ,,co#b and ,,ch#d4 ,here the amounts of oxygen and hydrogen are equivalent4 ,nitrogen combines with a large amount of oxygen1 forming ,n#b,o#e1 but1 on the other hand1 with a small quantity of hydrogen in ,,nh#c4 ,the sum of the equivalents of hydrogen and oxygen1 occurring in combination with an atom of nitrogen1 is1 as always in the higher types1 equal to eight4 ,it is the same with the other elements which combine with hydrogen and oxygen4 ,thus sulphur gives ,,so#c2 consequently1 six equivalents of oxygen fall to an atom of sulphur1 and in ,,sh#b two equivalents of hydrogen4 ,the sum is again equal to eight4 ,the relation between ,cl#b,o#g and ,cl,h is the same4 ,this shows that the property of elements of combining with such different elements as oxygen and hydrogen is subject to one common law1 which is also formulated in the system of the elements presently to be described4#g #g ,the hydrogen compounds1 ,r#b;,h1 in equivalency correspond with the type of the suboxides1 ,r#d,o4 ,palladium1 sodium1 and potassium give such hydrogen compounds1 and it is worthy of remark that according to the periodic system these elements stand near to each other1 and that in those groups where the hydrogen compounds ,r#b;,h appear1 the quaternary oxides ,r#d,o are also present4 ,not wishing to complicate the explanation1 ,i here only touch on the general features of the relation between the hydrates and oxides and of the oxides among themselves4 ,thus1 for instance1 the conception of the ortho-acids and of the normal acids will be considered in speaking of phosphoric and phosphorous acids4 ,as in the further explanation of the periodic law only those oxides which give salts will be considered1 ,i think it will not be superfluous to mention here the following facts relative to the peroxides4 ,of the peroxides corresponding with hydrogen peroxide1 the following are at present known3 ,h#b,o#b1 ,na#b,o#b1 ,s#b,o#g 7as ,,hso#d871 ,k#b,o#d1 ,k#b,o#b1 ,ca,o#b1 ,ti,o#c1 ,cr#b,o#g1 ,cu,o#b7871 ,zn,o#b1 ,rb#b,o#b1 ,sr,o#b1 ,ag#b,o#b1 ,cd,o#b1 ,cs,o#b1 ,cs#b,o#b1 ,ba,o#b1 ,mo#b,o#g1 ,sn,o#c1 ,w#b,o#g1 ,,uo#d4 ,it is probable that the number of peroxides will increase with further investigation4 ,a periodicity is seen in those now known1 for the elements 7excepting ,li7 of the first group1 which give ,r#b,o1 form peroxides1 and then the elements of the sixth group seem also to be particularly inclined to form peroxides1 ,r#b,o#g2 but at present it is too early1 in my opinion1 to enter upon a generalisation of this subject1 not only because it is a new and but little studied matter 7not investigated for all the elements71 but also1 and more especially1 because in many instances only the hydrates are known--for instance1 ,mo#b;,h#b,o#h--;and they perhaps are only compounds of peroxide of hydrogen--for example1 ,mo#b;,h#b,o#h #b,mo,o#c ,h#b,o#b--since ,prof4 ,schne has shown that ,h#b,o#b and ,ba,o#b possess the property of combining together and with other oxides4 ,nevertheless1 ,i have1 in the general table expressing the periodic properties of the elements1 endeavoured to sum up the data respecting all the known peroxide compounds whose characteristic property is seen in their capability to form peroxide of hydrogen under many circumstances4 ,in the preceding we see not only the regularity and simplicity which govern the formation and properties of the oxides and of all the compounds of the elements1 but also a fresh and exact means for recognising the analogy of elements4 ,analogous elements give compounds of analogous types1 both higher and lower4 ,if ,,co#b and ,,so#b are two gases which closely resemble each other both in their physical and chemical properties1 the reason of this must be looked for not in an analogy of sulphur and carbon1 but in that identity of the type of combination1 ,,rx#d1 which both oxides assume1 and in that influence which a large mass of oxygen always exerts on the properties of its compounds4 ,in fact1 there is little resemblance between carbon and sulphur1 as is seen not only from the fact that ,,co#b is the higher form of oxidation1 whilst ,,so#b is able to further oxidise into ,,so#c1 but also from the fact that all the other compounds--for example1 ,,sh#b and ,,ch#d1 ,s,cl#b and ,c,cl#d1 c4--are entirely unlike both in type and in chemical properties4 ,this absence of analogy in carbon and sulphur is especially clearly seen in the fact that the highest saline oxides are of different composition1 ,,co#b for carbon1 and ,,so#c for sulphur4 ,in ,chapter ,,viii4 we considered the limit to which carbon tends in its compounds1 and in a similar manner there is for every element in its compounds a tendency to attain a certain highest limit ,,rxn4 ,this view was particularly developed in the middle of the present century by ,frankland in studying the metallo-organic compounds1 i4e4 those in which ,x is wholly or partially a hydrocarbon radicle2 for instance1 ,x ,,ch#c or ,c#b;,h#e c4 ,thus1 for example1 antimony1 ,sb 7,chapter ,,xix47 gives1 with chlorine1 compounds ,sb,cl#c and ,sb,cl#e and corresponding oxygen compounds ,sb#b,o#c and ,sb#b,o#e1 whilst under the action of ,,ch#c;,i1 ,c#b;,h#e;,i1 or in general ,,ei 7where ,e is a hydrocarbon radicle of the paraffin series71 upon antimony or its alloy with sodium there are formed ,sb,e#c 7for example1 ,sb7,,ch#c7c1 boiling at about #ha71 which1 corresponding to the lower form of combination ,sb,x#c1 are able to combine further with ,,ei1 or ,cl#b1 or ,o1 and to form compounds of the limiting type ,sb,x#e2 for example1 ,sb,e#d;,cl corresponding to ,,nh#d;,cl with the substitution of nitrogen by antimony1 and of hydrogen by the hydrocarbon radicle4 ,the elements which are most chemically analogous are characterised by the fact of their giving compounds of similar form ,,rxn4 ,the halogens which are analogous give both higher and lower compounds4 ,so also do the metals of the alkalis and of the alkaline earths4 ,and we saw that this analogy extends to the composition and properties of the nitrogen and hydrogen compounds of these metals1 which is best seen in the salts4 ,many such groups of analogous elements have long been known4 ,thus there are analogues of oxygen1 nitrogen1 and carbon1 and we shall meet with many such groups4 ,but an acquaintance with them inevitably leads to the questions1 what is the cause of analogy and what is the relation of one group to another8 ,if these questions remain unanswered1 it is easy to fall into error in the formation of the groups1 because the notions of the degree of analogy will always be relative1 and will not present any accuracy or distinctness ,thus lithium is analogous in some respects to potassium and in others to magnesium2 beryllium is analogous to both aluminium and magnesium4 ,thallium1 as we shall afterwards see and as was observed on its discovery1 has much kinship with lead and mercury1 but some of its properties appertain to lithium and potassium4 ,naturally1 where it is impossible to make measurements one is reluctantly obliged to limit oneself to approximate comparisons1 founded on apparent signs which are not distinct and are wanting in exactitude4 ,but in the elements there is one accurately measurable property1 which is subject to no doubt--namely1 that property which is expressed in their atomic weights4 ,its magnitude indicates the relative mass of the atom1 or1 if we avoid the conception of the atom1 its magnitude shows the relation between the masses forming the chemical and independent individuals or elements4 ,and according to the teaching of all exact data about the phenomena of nature1 the mass of a substance is that property on which all its remaining properties must be dependent1 because they are all determined by similar conditions or by those forces which act in the weight of a substance1 and this is directly proportional to its mass4 ,therefore it is most natural to seek for a dependence between the properties and analogies of the elements on the one hand and their atomic weights on the other4 ,this is the fundamental idea which leads to arranging all the elements according to their atomic weights4 ,a periodic repetition of properties is then immediately observed in the elements4 ,we are already familiar with examples of this3-- ,f #ai1 ,cl #cee1 ,br #hj1 ,i #abg1 ,na #bc1 ,k #ci1 ,rb #he1 ,cs #acc1 ,mg #bd1 ,ca #dj1 ,sr #hg1 ,ba #acg4 ,the essence of the matter is seen in these groups4 ,the halogens have smaller atomic weights than the alkali metals1 and the latter than the metals of the alkaline earths4 ,therefore1 if all the elements be arranged in the order of their atomic weights1 a periodic repetition of properties is obtained4 ,this is expressed by the law of periodicity1 the properties of the elements1 as well as the forms and properties of their compounds1 are in periodic dependence or 7expressing ourselves algebraically7 form a periodic function of the atomic weights of the elements4#h ,table ,i4 of the periodic system of the elements1 which is placed at the very beginning of this book1 is designed to illustrate this law4 ,it is arranged in conformity with the eight types of oxides described in the preceding pages1 and those elements which give the oxides1 ,r#b,o and consequently salts ,,rx1 form the #ast group2 the elements giving ,r#b,o#b or ,,ro as their highest grade of oxidation belong to the #bnd group2 those giving ,r#b,o#c as their highest oxides form the #crd group1 and so on2 whilst the elements of all the groups which are nearest in their atomic weights are arranged in series from #a to #ab4 ,the even and uneven series of the same groups present the same forms and limits1 but differ in their properties1 and therefore two contiguous series1 one even and the other uneven--for instance1 the #dth and #eth--form a period4 ,hence the elements of the #dth1 #fth1 #hth1 #ajth1 and #abth1 or of the #crd1 #eth1 #gth1 #ith1 and #aath1 series form analogues1 like the halogens1 the alkali metals1 c4 ,the conjunction of two series1 one even and one contiguous uneven series1 thus forms one large period4 ,these periods1 beginning with the alkali metals1 end with the halogens4 ,the elements of the first two series have the lowest atomic weights1 and in consequence of this very circumstance1 although they bear the general properties of a group1 they still show many peculiar and independent properties4#i ,thus fluorine1 as we know1 differs in many points from the other halogens1 and lithium from the other alkali metals1 and so on4 ,these lightest elements may be termed typical elements4 ,they include-- ,h4 ,li1 ,be1 ,b1 ,c1 ,n1 ,o1 ,f4 ,na1 ,mg4444 ,in the annexed table all the remaining elements are arranged1 not in groups and series1 but according to periods4 ,in order to understand the essence of the matter1 it must be remembered that here the atomic weight gradually increases along a given line2 for instance1 in the line commencing with ,k #ci and ending with ,br #hj1 the intermediate elements have intermediate atomic weights1 as is clearly seen in ,table ,,iii41 where the elements stand in the order of their atomic weights4 ,i4 ,,ii4 ,,iii4 ,,iv4 ,v4 ,,vi4 ,,vii4 ,i4 ,,ii4 ,,iii4 ,,iv4 ,v4 ,,vi4 ,,vii4 ,even ,series4 ,mg ,al ,si ,p ,s ,cl ,k ,ca ,sc ,ti ,v ,cr ,mn ,fe ,co ,ni ,cu ,zn ,ga ,ge ,as ,se ,br ,rb ,sr ,y ,zr ,nb ,mo -- ,ru ,rh ,pd ,ag ,cd ,in ,sn ,sb ,te ,i ,cs ,ba ,la ,ce ,di8 -- -- -- -- -- -- -- -- -- -- -- -- -- -- ,yb -- ,ta ,w -- ,os ,ir ,pt ,au ,hg ,tl ,pb ,bi -- -- -- -- -- ,th -- ,u ,uneven ,series ,the same degree of analogy that we know to exist between potassium1 rubidium1 and csium2 or chlorine1 bromine1 and iodine2 or calcium1 strontium1 and barium1 also exists between the elements of the other vertical columns4 ,thus1 for example1 zinc1 cadmium1 and mercury1 which are described in the following chapter1 present a very close analogy with magnesium4 ,for a true comprehension of the matter#aj it is very important to see that all the aspects of the distribution of the elements according to their atomic weights essentially express one and the same fundamental dependence--periodic properties4#aa ,the following points then must be remarked in it4 #h ,the periodic law and the periodic system of the elements appeared in the same form as here given in the first edition of this work1 begun in #ahfh and finished in #ahga4 ,in laying out the accumulated information respecting the elements1 ,i had occasion to reflect on their mutual relations4 ,at the beginning of #ahfi ,i distributed among many chemists a pamphlet entitled ',an ,attempted ,system of the ,elements1 based on their ,atomic ,weights and ,chemical ,analogies1' and at the ,march meeting of the ,russian ,chemical ,society1 #ahfi1 ,i communicated a paper ',on the ,correlation of the ,properties and ,atomic ,weights of the ,elements4' ,the substance of this paper is embraced in the following conclusions3 7#a7 ,the elements1 if arranged according to their atomic weights1 exhibit an evident periodicity of properties4 7#b7 ,elements which are similar as regards their chemical properties have atomic weights which are either of nearly the same value 7platinum1 iridium1 osmium7 or which increase regularly 7e4g4 potassium1 rubidium1 csium74 7#c7 ,the arrangement of the elements or of groups of elements in the order of their atomic weights corresponds with their so-called valencies4 7#d7 ,the elements1 which are the most widely distributed in nature1 have small atomic weights1 and all the elements of small atomic weight are characterised by sharply defined properties4 ,they are therefore typical elements4 7#e7 ,the magnitude of the atomic weight determines the character of an element4 7#f7 ,the discovery of many yet unknown elements may be expected4 ,for instance1 elements analogous to aluminium and silicon1 whose atomic weights would be between #fe and #ge4 7#g7 ,the atomic weight of an element may sometimes be corrected by aid of a knowledge of those of the adjacent elements4 ,thus the combining weight of tellurium must lie between #abc and #abf1 and cannot be #abh4 7#h7 ,certain characteristic properties of the elements can be foretold from their atomic weights4 ,the entire periodic law is included in these lines4 ,in the series of subsequent papers 7#ahgj-gb1 for example1 in the ,transactions of the ,russian ,chemical ,society1 of the ,moscow ,meeting of ,naturalists1 of the ,st4 ,petersburg ,academy1 and ,liebig's ,annalen7 on the same subject we only find applications of the same principles1 which were afterwards confirmed by the labours of ,roscoe1 ,carnelley1 ,thorpe1 and others in ,england2 of ,rammelsberg 7cerium and uranium71 ,l4 ,meyer 7the specific volumes of the elements71 ,zimmermann 7uranium71 and more especially of ,c4 ,winkler 7who discovered germanium1 and showed its identity with ekasilicon71 and others in ,germany2 of ,lecoq de ,boisbaudran in ,france 7the discoverer of gallium ekaaluminium72 of ,clve 7the atomic weights of the cerium metals71 ,nilson 7discoverer of scandium ekaboron71 and ,nilson and ,pettersson 7determination of the vapour density of beryllium chloride7 in ,sweden2 and of ,brauner 7who investigated cerium1 and determined the combining weight of tellurium #abe7 in ,austria1 and ,piccini in ,italy4 ,i consider it necessary to state that1 in arranging the periodic system of the elements1 ,i made use of the previous researches of ,dumas1 ,gladstone1 ,pettenkofer1 ,kremers1 and ,lenssen on the atomic weights of related elements1 but ,i was not acquainted with the works preceding mine of ,de ,chancourtois 7vis tellurique1 or the spiral of the elements according to their properties and equivalents7 in ,france1 and of ,j4 ,newlands 7,law of ,octaves--for instance1 ,h1 ,f1 ,cl1 ,co1 ,br1 ,pd1 ,i1 ,pt form the first octave1 and ,o1 ,s1 ,fe1 ,se1 ,rh1 ,te1 ,au1 ,th the last7 in ,england1 although certain germs of the periodic law are to be seen in these works4 ,with regard to the work of ,prof4 ,lothar ,meyer respecting the periodic law 7,notes #ab and #ac71 it is evident1 judging from the method of investigation1 and from his statement 7,liebig's ,annalen1 ,supt4 ,band #g1 #ahgj1 #ced71 at the very commencement of which he cites my paper of #ahfi above mentioned1 that he accepted the periodic law in the form which ,i proposed4 ,in concluding this historical statement ,i consider it well to observe that no law of nature1 however general1 has been established all at once2 its recognition is always preceded by many hints2 the establishment of a law1 however1 does not take place when its significance is recognised1 but only when it has been confirmed by experiment1 which the man of science must consider as the only proof of the correctness of his conjectures and opinions4 ,i therefore1 for my part1 look upon ,roscoe1 ,de ,boisbaudran1 ,nilson1 ,winkler1 ,brauner1 ,carnelley1 ,thorpe1 and others who verified the adaptability of the periodic law to chemical facts1 as the true founders of the periodic law1 the further development of which still awaits fresh workers4 #i ,this resembles the fact1 well known to those having an acquaintance with organic chemistry1 that in a series of homologues 7,chapter ,,viii47 the first members1 in which there is the least carbon1 although showing the general properties of the homologous series1 still present certain distinct peculiarities4 #aj ,besides arranging the elements 7a7 in a successive order according to their atomic weights1 with indication of their analogies by showing some of the properties--for instance1 their power of giving one or another form of combination--both of the elements and of their compounds 7as is done in ,table ,,iii4 and in the table on p4 #cf71 7b7 according to periods 7as in ,table ,i4 at the commencement of volume ,i4 after the preface71 and 7c7 according to groups and series or small periods 7as in the same tables71 ,i am acquainted with the following methods of expressing the periodic relations of the elements3 7#a7 ,by a curve drawn through points obtained in the following manner3 ,the elements are arranged along the horizontal axis as absciss at distances from zero proportional to their atomic weights1 whilst the values for all the elements of some property--for example1 the specific volumes or the melting points1 are expressed by the ordinates4 ,this method1 although graphic1 has the theoretical disadvantage that it does not in any way indicate the existence of a limited and definite number of elements in each period4 ,there is nothing1 for instance1 in this method of expressing the law of periodicity to show that between magnesium and aluminium there can be no other element with an atomic weight of1 say1 #be1 atomic volume #ac1 and in general having properties intermediate between those of these two elements4 ,the actual periodic law does not correspond with a continuous change of properties1 with a continuous variation of atomic weight--in a word1 it does not express an uninterrupted function--and as the law is purely chemical1 starting from the conception of atoms and molecules which combine in multiple proportions1 with intervals 7not continuously71 it above all depends on there being but few types of compounds1 which are arithmetically simple1 repeat themselves1 and offer no uninterrupted transitions1 so that each period can only contain a definite number of members4 ,for this reason there can be no other elements between magnesium1 which gives the chloride ,mg,cl#b1 and aluminium1 which forms ,al,x#c2 there is a break in the continuity1 according to the law of multiple proportions4 ,the periodic law ought not1 therefore1 to be expressed by geometrical figures in which continuity is always understood4 ,owing to these considerations ,i never have and never will express the periodic relations of the elements by any geometrical figures4 7#b7 ,by a plane spiral4 ,radii are traced from a centre1 proportional to the atomic weights2 analogous elements lie along one radius1 and the points of intersection are arranged in a spiral4 ,this method1 adopted by ,de ,chancourtois1 ,baumgauer1 ,e4 ,huth1 and others1 has many of the imperfections of the preceding1 although it removes the indefiniteness as to the number of elements in a period4 ,it is merely an attempt to reduce the complex relations to a simple graphic representation1 since the equation to the spiral and the number of radii are not dependent upon anything4 7#c7 ,by the lines of atomicity1 either parallel1 as in ,reynolds's and the ,rev4 ,s4 ,haughton's method1 or as in ,crookes's method1 arranged to the right and left of an axis1 along which the magnitudes of the atomic weights are counted1 and the position of the elements marked off1 on the one side the members of the even series 7paramagnetic1 like oxygen1 potassium1 iron71 and on the other side the members of the uneven series 7diamagnetic1 like sulphur1 chlorine1 zinc1 and mercury74 ,on joining up these points a periodic curve is obtained1 compared by ,crookes to the oscillations of a pendulum1 and1 according to ,haughton1 representing a cubical curve4 ,this method would be very graphic did it not require1 for instance1 that sulphur should be considered as bivalent and manganese as univalent1 although neither of these elements gives stable derivatives of these natures1 and although the one is taken on the basis of the lowest possible compound ,,sx#b1 and the other of the highest1 because manganese can be referred to the univalent elements only by the analogy of ,k,mn,o#d to ,k,cl,o#d4 ,furthermore1 ,reynolds and ,crookes place hydrogen1 iron1 nickel1 cobalt1 and others outside the axis of atomicity1 and consider uranium as bivalent without the least foundation4 7#d7 ,rantsheff endeavoured to classify the elements in their periodic relations by a system dependent on solid geometry4 ,he communicated this mode of expression to the ,russian ,chemical ,society1 but his communication1 which is apparently not void of interest1 has not yet appeared in print4 7#e7 ,by algebraic formul3 for example1 ,e4 ,j4 ,mills 7#ahhf7 endeavours to express all the atomic weights by the logarithmic function ,a #ae7n - #jicget71 in which the variables n and t are whole numbers4 ,for instance1 for oxygen n #b1 t #a2 hence ,a #aeid2 for antimony n #i1 t #j2 whence ,a #abj1 and so on4 n varies from #a to #af and t from #j to #ei4 ,the analogues are hardly distinguishable by this method3 thus for chlorine the magnitudes of n and t are #c and #g2 for bromine #f and #f2 for iodine #i and #i2 for potassium #c and #ad2 for rubidium #f and #ah2 for csium #i and #bj2 but a certain regularity seems to be shown4 7#f7 ,a more natural method of expressing the dependence of the properties of elements on their atomic weights is obtained by trigonometrical functions1 because this dependence is periodic like the functions of trigonometrical lines1 and therefore ,ridberg in ,sweden 7,lund1 #ahhe7 and ,f4 ,flavitzky in ,russia 7,kazan1 #ahhg7 have adopted a similar method of expression1 which must be considered as worthy of being worked out1 although it does not express the absence of intermediate elements--for instance1 between magnesium and aluminium1 which is essentially the most important part of the matter4 7#g7 ,the investigations of ,b4 ,n4 ,tchitchrin 7#ahhh1 ,journal of the ,russian ,physical and ,chemical ,society7 form the first effort in the latter direction4 ,he carefully studied the alkali metals1 and discovered the following simple relation between their atomic volumes3 they can all be expressed by ,a7#b - #jjdbh;,an71 where ,a is the atomic weight and n #a for lithium and sodium1 #d_/h for potassium1 #c_/h for rubidium1 and #b_/h for csium4 ,if n always #a1 then the volume of the atom would become zero at ,a #df-b_/c1 and would reach its maximum when ,a #bc-a_/c1 and the density increases with the growth of ,a4 ,in order to explain the variation of n1 and the relation of the atomic weights of the alkali metals to those of the other elements1 as also the atomicity itself1 ,tchitchrin supposes all atoms to be built up of a primary matter2 he considers the relation of the central to the peripheric mass1 and1 guided by mechanical principles1 deduces many of the properties of the atoms from the reaction of the internal and peripheric parts of each atom4 ,this endeavour offers many interesting points1 but it admits the hypothesis of the building up of all the elements from one primary matter1 and at the present time such an hypothesis has not the least support either in theory or in fact4 ,besides which the starting-point of the theory is the specific gravity of the metals at a definite temperature 7it is not known how the above relation would appear at other temperatures71 and the specific gravity varies even under mechanical influences4 ,l4 ,hugo 7#ahhd7 endeavoured to represent the atomic weights of ,li1 ,na1 ,k1 ,rb1 and ,cs by geometrical figures--for instance1 ,li #g represents a central atom #a and six atoms on the six terminals of an octahedron2 ,na1 is obtained by applying two such atoms on each edge of an octahedron1 and so on4 ,it is evident that such methods can add nothing new to our data respecting the atomic weights of analogous elements4 #aa ,many natural phenomena exhibit a dependence of a periodic character4 ,thus the phenomena of day and night and of the seasons of the year1 and vibrations of all kinds1 exhibit variations of a periodic character in dependence on time and space4 ,but in ordinary periodic functions one variable varies continuously1 whilst the other increases to a limit1 then a period of decrease begins1 and having in turn reached its limit a period of increase again begins4 ,it is otherwise in the periodic function of the elements4 ,here the mass of the elements does not increase continuously1 but abruptly1 by steps1 as from magnesium to aluminium4 ,so also the valency or atomicity leaps directly from #a to #b to #c1 c41 without intermediate quantities1 and in my opinion it is these properties which are the most important1 and it is their periodicity which forms the substance of the periodic law4 ,it expresses the properties of the real elements1 and not of what may be termed their manifestations visually known to us4 ,the external properties of elements and compounds are in periodic dependence on the atomic weight of the elements only because these external properties are themselves the result of the properties of the real elements which unite to form the 'free' elements and the compounds4 ,to explain and express the periodic law is to explain and express the cause of the law of multiple proportions1 of the difference of the elements1 and the variation of their atomicity1 and at the same time to understand what mass and gravitation are4 ,in my opinion this is still premature4 ,but just as without knowing the cause of gravitation it is possible to make use of the law of gravity1 so for the aims of chemistry it is possible to take advantage of the laws discovered by chemistry without being able to explain their causes4 ,the above-mentioned peculiarity of the laws of chemistry respecting definite compounds and the atomic weights leads one to think that the time has not yet come for their full explanation1 and ,i do not think that it will come before the explanation of such a primary law of nature as the law of gravity4 ,it will not be out of place here to turn our attention to the many-sided correlation existing between the undecomposable elements and the compound carbon radicles1 which has long been remarked 7,pettenkofer1 ,dumas1 and others71 and reconsidered in recent times by ,carnelley 7#ahhf71 and most originally in ,pelopidas's work 7#ahhc7 on the principles of the periodic system4 ,pelopidas compares the series containing eight hydrocarbon radicles1 ,cn,h#bn #a1 ,cn,h#bn c41 for instance1 ,c#f;,h#ac1 ,c#f;,h#ab1 ,c#f;,h#aa1 ,c#f;,h#aj1 ,c#f;,h#i1 ,c#f;,h#h1 ,c#f;,h#g1 and ,c#f;,h#f--with the series of the elements arranged in eight groups4 ,the analogy is particularly clear owing to the property of ,cn,h#bn#a to combine with ,x1 thus reaching saturation1 and of the following members with ,x#b1 ,x#c 444 ,x#h1 and especially because these are followed by an aromatic radicle--for example1 ,c#f;,h#e--;in which1 as is well known1 many of the properties of the saturated radicle ,c#f;,h#ac are repeated1 and in particular the power of forming a univalent radicle again appears4 ,pelopidas shows a confirmation of the parallel in the property of the above radicles of giving oxygen compounds corresponding with the groups in the periodic system4 ,thus the hydrocarbon radicles of the first group--for instance1 ,c#f;,h#ac or ,c#f;,h#e--;give oxides of the form ,r#b,o and hydroxides ,,rho1 like the metals of the alkalis2 and in the third group they form oxides ,r#b,o#c and hydrates ,,ro#b;,h4 ,for example1 in the series ,,ch#c the corresponding compounds of the third group will be the oxide 7,,ch7#b,o#c or ,c#b;,h#b,o#c--that is1 formic anhydride and hydrate1 ,,cho#b;,h1 or formic acid4 ,in the sixth group1 with a composition of ,c#b1 the oxide ,,ro#c will be ,c#b,o#c1 and hydrate ,c#b;,h#b,o#d--that is1 also a bibasic acid 7oxalic7 resembling sulphuric1 among the inorganic acids4 ,after applying his views to a number of organic compounds1 ,pelopidas dwells more particularly on the radicles corresponding with ammonium4 ,with respect to this remarkable parallelism1 it must above all be observed that in the elements the atomic weight increases in passing to contiguous members of a higher valency1 whilst here it decreases1 which should indicate that the periodic variability of elements and compounds is subject to some higher law whose nature1 and still more whose cause1 cannot at present be determined4 ,it is probably based on the fundamental principles of the internal mechanics of the atoms and molecules1 and as the periodic law has only been generally recognised for a few years it is not surprising that any further progress towards its explanation can only be looked for in the development of facts touching on this subject4 #a4 ,the composition of the higher oxygen compounds is determined by the groups3 the first group gives ,r#b,o1 the second ,r#b,o#b or ,,ro1 the third ,r#b,o#c1 c4 ,there are eight types of oxides and therefore eight groups4 ,two groups give a period1 and the same type of oxide is met with twice in a period4 ,for example1 in the period beginning with potassium1 oxides of the composition ,,ro are formed by calcium and zinc1 and of the composition ,,ro#c by molybdenum and tellurium4 ,the oxides of the even series1 of the same type1 have stronger basic properties than the oxides of the uneven series1 and the latter as a rule are endowed with an acid character4 ,therefore the elements which exclusively give bases1 like the alkali metals1 will be found at the commencement of the period1 whilst such purely acid elements as the halogens will be at the end of the period4 ,the interval will be occupied by intermediate elements1 whose character and properties we shall afterwards describe4 ,it must be observed that the acid character is chiefly proper to the elements with small atomic weights in the uneven series1 whilst the basic character is exhibited by the heavier elements in the even series4 ,hence elements which give acids chiefly predominate among the lightest 7typical7 elements1 especially in the last groups2 whilst the heaviest elements1 even in the last groups 7for instance1 thallium1 uranium7 have a basic character4 ,thus the basic and acid characters of the higher oxides are determined 7a7 by the type of oxide1 7b7 by the even or uneven series1 and 7c7 by the atomic weight4#aa bis ,the groups are indicated by ,roman numerals from ,i4 to ,,viii4 #b4 ,the hydrogen compounds being volatile or gaseous substances which are prone to reaction--such as ,h,cl1 ,h#b,o1 ,h#c,n1 and ,h#d;,c#ab--;are only formed by the elements of the uneven series and higher groups giving oxides of the forms ,r#b,on1 ,,ro#c1 ,r#b,o#e1 and ,,ro#b4 #c4 ,if an element gives a hydrogen compound1 ,,rxm1 it forms an organo-metallic compound of the same composition1 where ,x ,cn,h#bn #a2 that is1 ,x is the radicle of a saturated hydrocarbon4 ,the elements of the uneven series1 which are incapable of giving hydrogen compounds1 and give oxides of the forms ,,rx1 ,,rx#b1 ,r,x#c1 also give organo-metallic compounds of this form proper to the higher oxides4 ,thus zinc forms the oxide ,zn,o1 salts ,zn,x#b and zinc ethyl ,zn7,c#b;,h#e7b4 ,the elements of the even series do not seem to form organo-metallic compounds at all2 at least all efforts for their preparation have as yet been fruitless--for instance1 in the case of titanium1 zirconium1 or iron4 #d4 ,the atomic weights of elements belonging to contiguous periods differ approximately by #de2 for example1 ,k,rb1 ,cr,mo1 ,br,i4 ,but the elements of the typical series show much smaller differences4 ,thus the difference between the atomic weights of ,li1 ,na1 and ,k1 between ,ca1 ,mg1 and ,be1 between ,si and ,c1 between ,s and ,o1 and between ,cl and ,f1 is #af4 ,as a rule1 there is a greater difference between the atomic weights of two elements of one group and belonging to two neighbouring series 7,ti-,si ,v-,p ,cr-,s ,mn-,cl ,nb-,as1 c4 #bj72 and this difference attains a maximum with the heaviest elements 7for example1 ,th-,pb #bf1 ,bi-,ta #bf1 ,ba-,cd #be1 c474 ,furthermore1 the difference between the atomic weights of the elements of even and uneven series also increases4 ,in fact1 the differences between ,na and ,k1 ,mg and ,ca1 ,si and ,ti1 are less abrupt than those between ,pb and ,th1 ,ta and ,bi1 ,cd and ,ba1 c4 ,thus even in the magnitude of the differences of the atomic weights of analogous elements there is observable a certain connection with the gradation of their properties4#ab bis #e4 ,according to the periodic system every element occupies a certain position1 determined by the group 7indicated in ,roman numerals7 and series 7,arabic numerals7 in which it occurs4 ,these indicate the atomic weight1 the analogues1 properties1 and type of the higher oxide1 and of the hydrogen and other compounds--in a word1 all the chief quantitative and qualitative features of an element1 although there yet remain a whole series of further details and peculiarities whose cause should perhaps be looked for in small differences of the atomic weights4 ,if in a certain group there occur elements1 ,r#a1 ,r#b1 ,r#c1 and if in that series which contains one of these elements1 for instance ,r#b1 an element ,q#b precedes it and an element ,t#b succeeds it1 then the properties of ,r#b are determined by the properties of ,r#a1 ,r#c1 ,q#b1 and ,t#b4 ,thus1 for instance1 the atomic weight of ,r#b #a_/d7,r#a ,r#c ,q#b ,t#b74 ,for example1 selenium occurs in the same group as sulphur1 ,s #cb1 and tellurium1 ,te #abe1 and1 in the #gth series ,as #ge stands before it and ,br #hj after it4 ,hence the atomic weight of selenium should be #a_/d7cb #abe #ge #hj7 #gh1 which is near to the truth4 ,other properties of selenium may also be determined in this manner4 ,for example1 arsenic forms ,h#c;,as1 bromine gives ,h,br1 and it is evident that selenium1 which stands between them1 should form ,h#b,se1 with properties intermediate between those of ,h#c;,as and ,h,br4 ,even the physical properties of selenium and its compounds1 not to speak of their composition1 being determined by the group in which it occurs1 may be foreseen with a close approach to reality from the properties of sulphur1 tellurium1 arsenic1 and bromine4 ,in this manner it is possible to foretell the properties of still unknown elements4 ,for instance in the position ,,iv1 #e--that is1 in the ,i,vth group and #eth series--an element is still wanting4 ,these unknown elements may be named after the preceding known element of the same group by adding to the first syllable the prefix eka-1 which means one in ,sanskrit4 ,the element ,,iv1 #e1 follows after ,,iv1 #c1 and this latter position being occupied by silicon1 we call the unknown element ekasilicon and its symbol ,es4 ,the following are the properties which this element should have on the basis of the known properties of silicon1 tin1 zinc1 and arsenic4 ,its atomic weight is nearly #gb1 higher oxide ,es,o#b1 lower oxide ,es,o1 compounds of the general form ,es,x#d1 and chemically unstable lower compounds of the form ,es,x#b4 ,es gives volatile organo-metallic compounds--for instance1 ,es7,,ch#c7d1 ,es7,,ch#c7c;,cl1 and ,es7,c#b;,h#e7d1 which boil at about #afj1 c42 also a volatile and liquid chloride1 ,es,cl#d1 boiling at about #ij and of specific gravity about #ai4 ,es,o#b will be the anhydride of a feeble colloidal acid1 metallic ,es will be rather easily obtainable from the oxides and from ,k#b;,es,f#f by reduction1 ,es,s#b will resemble ,sn,s#b and ,si,s#b1 and will probably be soluble in ammonium sulphide2 the specific gravity of ,es will be about #ee1 ,es,o#b will have a density of about #dg1 c4 ,such a prediction of the properties of ekasilicon was made by me in #ahga1 on the basis of the properties of the elements analogous to it3 ,,iv1 #c1 ,si1 ,,iv1 #g ,sn1 and also ,,ii1 #e ,zn and ,v1 #e ,as4 ,and now that this element has been discovered by ,c4 ,winkler1 of ,freiberg1 it has been found that its actual properties entirely correspond with those which were foretold4#ac ,in this we see a most important confirmation of the truth of the periodic law4 ,this element is now called germanium1 ,ge 7see ,chapter ,,xviii474 ,it is not the only one that has been predicted by the periodic law4#ad ,we shall see in describing the elements of the third group that properties were foretold of an element ekaaluminium1 ,,iii1 #e1 ,el #fh1 and were afterwards verified when the metal termed 'gallium' was discovered by ,de ,boisbaudran4 ,so also the properties of scandium corresponded with those predicted for ekaboron1 according to ,nilson4#ae #aa bis ,true peroxides 7see ,note #g71 like ,h#b,o#b1 ,ba,o#b1 ,s#b,o#g 7,chapter ,,xx471 must not be confused with true saline oxides even if the latter contain much oxygen 7for instance1 ,n#b,o#e1 ,cr,o#c1 c47 although one and the other easily oxidise4 ,the difference between them is seen in their fundamental properties3 the saline oxides correspond to water1 while the peroxides correspond in their reactions and origin to peroxide of hydrogen4 ,this is clearly seen in the difference between ,na#b,o and ,na#b,o#b 7,chapter ,,xii474 ,therefore the peroxides should also have their periodicity4 ,an element ,r1 giving a highest degree of oxidation1 ,r#b,on1 may give both a lower degree of oxidation1 ,r#b,on - m 7where m is evidently less than n71 and peroxides1 ,r#b,on #a1 ,r#b,on #b1 or even more oxygen4 ,this class of oxides1 to which attention has only recently been turned 7,berthelot1 ,piccini1 c471 may perhaps on further study give the possibility of generalising the capability of the elements to give unstable complex higher forms of combination1 such as double salts1 and in my opinion should in the near future be the field of new and important discoveries4 ,and in contemporary chemistry1 salts1 saline oxides1 hydrogen compounds1 and other combinations of the elements corresponding to them constitute an important and very complex problem for generalisation1 which is satisfied by the periodic law in its present form1 to which it has risen from its first state1 in which it gave the means of foreseeing 7see later on7 the existence of unknown elements 7,ga1 ,sc1 and ,ge71 their properties1 and many details respecting their compounds4 ,until those improvements in the periodic system which have been proposed by ,prof4 ,flavitzky 7of ,kazan7 and ,prof4 ,harperath 7of ,cordoba1 in the ,argentine ,republic71 ,ugo ,alvisi 7,italy71 and others give similar practical results1 ,i think it unnecessary to discuss them further4 #ab ,the hydrides generalised by the periodic law are those to which metallo-organic compounds correspond1 and they are themselves either volatile or gaseous4 ,the hydrogen compounds like ,na#b;,h1 ,ba,h1 c4 are distinguished by other signs4 ,they resemble alloys4 ,they show 7see end of last chapter7 a systematic harmony1 but they evidently should not be confused with true hydrides1 any more than peroxides with saline oxides4 ,moreover1 such hydrides have1 like the peroxides1 only recently been subjected to research1 and have been but little studied4 ,the best known of these compounds are given in the #afth column of ,table ,,iii41 and it will be seen that they already exhibit a periodicity of properties and composition4 #ab bis ,the relation between the atomic weights1 and especially the difference #af1 was observed in the sixth and seventh decades of this century by ,dumas1 ,pettenkofer1 ,l4 ,meyer1 and others4 ,thus ,lothar ,meyer in #ahfd1 following ,dumas and others1 grouped together the tetravalent elements carbon and silicon2 the trivalent elements nitrogen1 phosphorus1 arsenic1 antimony1 and bismuth2 the bivalent oxygen1 sulphur1 selenium1 and tellurium2 the univalent fluorine1 chlorine1 bromine1 and iodine2 the univalent metals lithium1 sodium1 potassium1 rubidium1 csium1 and thallium1 and the bivalent metals beryllium1 magnesium1 strontium and barium--observing that in the first the difference is1 in general #af1 in the second about #df1 and the last about #hg-ij4 ,the first germs of the periodic law are visible in such observations as these4 ,since its establishment this subject has been most fully worked out by ,ridberg 7,note #aj71 who observed a periodicity in the variation of the differences between the atomic weights of two contiguous elements1 and its relation to their atomicity4 ,a4 ,bazaroff 7#ahhg7 investigated the same subject1 taking1 not the arithmetical differences of contiguous and analogous elements1 but the ratio of their atomic weights2 and he also observed that this ratio alternately rises and falls with the rise of the atomic weights4 ,i will here remark that the relation of the eighth group to the others will be considered at the end of this work in ,chapter ,,xxii4 #ac ,the laws of nature admit of no exceptions1 and in this they clearly differ from such rules and maxims as are found in grammar1 and other inventions1 methods1 and relations of man's creation4 ,the confirmation of a law is only possible by deducing consequences from it1 such as could not possibly be foreseen without it1 and by verifying those consequences by experiment and further proofs4 ,therefore1 when ,i conceived the periodic law1 ,i 7#ahfi-ahga1 ,note #i7 deduced such logical consequences from it as could serve to show whether it were true or not4 ,among them was the prediction of the properties of undiscovered elements and the correction of the atomic weights of many1 and at that time little known1 elements4 ,thus uranium was considered as trivalent1 ,u #abj2 but as such it did not correspond with the periodic law4 ,i therefore proposed to double its atomic weight--,u #bdj1 and the researches of ,roscoe1 ,zimmermann1 and others justified this alteration 7,chapter ,,xxi474 ,it was the same with cerium 7,chapter ,,xviii47 whose atomic weight it was necessary to change according to the periodic law4 ,i therefore determined its specific heat1 and the result ,i obtained was verified by the new determinations of ,hillebrand4 ,i then corrected certain formul of the cerium compounds1 and the researches of ,rammelsberg1 ,brauner1 ,clve1 and others verified the proposed alteration4 ,it was necessary to do one or the other--either to consider the periodic law as completely true1 and as forming a new instrument in chemical research1 or to refute it4 ,acknowledging the method of experiment to be the only true one1 ,i myself verified what ,i could1 and gave every one the possibility of proving or confirming the law1 and did not think1 like ,l4 ,meyer 7,liebig's ,annalen1 ,supt4 ,band #g1 #ahgj1 #cfd71 when writing about the periodic law that 'it would be rash to change the accepted atomic weights on the basis of so uncertain a starting-point4' 7',es wrde voreilig sein1 auf so unsichere ,anhaltspunkte hin eine ,aenderung der bisher angenommenen ,atomgewichte vorzunehmen4'7 ,in my opinion1 the basis offered by the periodic law had to be verified or refuted1 and experiment in every case verified it4 ,the starting-point then became general4 ,no law of nature can be established without such a method of testing it4 ,neither ,de ,chancourtois1 to whom the ,french ascribe the discovery of the periodic law1 nor ,newlands1 who is put forward by the ,english1 nor ,l4 ,meyer1 who is now cited by many as its founder1 ventured to foretell the properties of undiscovered elements1 or to alter the 'accepted atomic weights1' or1 in general1 to regard the periodic law as a new1 strictly established law of nature1 as ,i did from the very beginning 7#ahfi74 #ad ,when in #ahga ,i wrote a paper on the application of the periodic law to the determination of the properties of hitherto undiscovered elements1 ,i did not think ,i should live to see the verification of this consequence of the law1 but such was to be the case4 ,three elements were described--ekaboron1 ekaaluminium1 and ekasilicon--and now1 after the lapse of twenty years1 ,i have had the great pleasure of seeing them discovered and named ,gallium1 ,scandium1 and ,germanium1 after those three countries where the rare minerals containing them are found1 and where they were discovered4 ,for my part ,i regard ,l4 de ,boisbaudran1 ,nilson1 and ,winkler1 who discovered these elements1 as the true corroborators of the periodic law4 ,without them it would not have been accepted to the extent it now is4 #ae ,taking indium1 which occurs together with zinc1 as our example1 we will show the principle of the method employed4 ,the equivalent of indium to hydrogen in its oxide is #cgg--that is1 if we suppose its composition to be like that of water2 then ,in #cgg1 and the oxide of indium is ,in#b,o4 ,the atomic weight of indium was taken as double the equivalent--that is1 indium was considered to be a bivalent element--and ,in #b #cgg #ged4 ,if indium only formed an oxide1 ,,ro1 it should be placed in group ,,ii4 ,but in this case it appears that there would be no place for indium in the system of the elements1 because the positions ,,ii41 #e ,zn #fe and ,,ii41 #f ,sr #hg were already occupied by known elements1 and according to the periodic law an element with an atomic weight #ge could not be bivalent4 ,as neither the vapour density nor the specific heat1 nor even the isomorphism 7the salts of indium crystallise with great difficulty7 of the compounds of indium were known1 there was no reason for considering it to be a bivalent metal1 and therefore it might be regarded as trivalent1 quadrivalent1 c4 ,if it be trivalent1 then ,in #c #cgg #aac1 and the composition of the oxide is ,in#b,o#c1 and of its salts ,in,x#c4 ,in this case it at once falls into its place in the system1 namely1 in group ,,iii4 and #gth series1 between ,cd #aab and ,sn #aah1 as an analogue of aluminium or dvialuminium 7dvi #b in ,sanskrit74 ,all the properties observed in indium correspond with this position2 for example1 the density1 cadmium #hf1 indium #gd1 tin #gb2 the basic properties of the oxides ,cd,o1 ,in#b,o#c1 ,sn,o#b1 successively vary1 so that the properties of ,in#b,o#c are intermediate between those of ,cd,o and ,sn,o#b or ,cd#b,o#b and ,sn#b,o#d4 ,that indium belongs to group ,,iii4 has been confirmed by the determination of its specific heat1 7#jjeg according to ,bunsen1 and #jjee according to me7 and also by the fact that indium forms alums like aluminium1 and therefore belongs to the same group4 ,the same kind of considerations necessitated taking the atomic weight of titanium as nearly #dh1 and not as #eb1 the figure derived from many analyses4 ,and both these corrections1 made on the basis of the law1 have now been confirmed1 for ,thorpe found1 by a series of careful experiments1 the atomic weight of titanium to be that foreseen by the periodic law4 ,notwithstanding that previous analyses gave ,os #aiig1 ,ir #aih1 and ,pt #ahg1 the periodic law shows1 as ,i remarked in #ahga1 that the atomic weights should rise from osmium to platinum and gold1 and not fall4 ,many recent researches1 and especially those of ,seubert1 have fully verified this statement1 based on the law4 ,thus a true law of nature anticipates facts1 foretells magnitudes1 gives a hold on nature1 and leads to improvements in the methods of research1 c4 #f4 ,as a true law of nature is one to which there are no exceptions1 the periodic dependence of the properties on the atomic weights of the elements gives a new means for determining by the equivalent the atomic weight or atomicity of imperfectly investigated but known elements1 for which no other means could as yet be applied for determining the true atomic weight4 ,at the time 7#ahfi7 when the periodic law was first proposed there were several such elements4 ,it thus became possible to learn their true atomic weights1 and these were verified by later researches4 ,among the elements thus concerned were indium1 uranium1 cerium1 yttrium1 and others4 #g4 ,the periodic variability of the properties of the elements in dependence on their masses presents a distinction from other kinds of periodic dependence 7as1 for example1 the sines of angles vary periodically and successively with the growth of the angles1 or the temperature of the atmosphere with the course of time71 in that the weights of the atoms do not increase gradually1 but by leaps2 that is1 according to ,dalton's law of multiple proportions1 there not only are not1 but there cannot be1 any transitive or intermediate elements between two neighbouring ones 7for example1 between ,k #ci and ,ca #dj1 or ,al #bg and ,si #bh1 or ,c #ab and ,n #ad1 c47 ,as in a molecule of a hydrogen compound there may be either one1 as in ,,hf1 or two1 as in ,h#b,o1 or three1 as in ,,nh#c1 c41 atoms of hydrogen2 but as there cannot be molecules containing #b-a_/b atoms of hydrogen to one atom of another element1 so there cannot be any element intermediate between ,n and ,o1 with an atomic weight greater than #ad or less than #af1 or between ,k and ,ca4 ,hence the periodic dependence of the elements cannot be expressed by any algebraical continuous function in the same way that it is possible1 for instance1 to express the variation of the temperature during the course of a day or year4 #h4 ,the essence of the notions giving rise to the periodic law consists in a general physico-mechanical principle which recognises the correlation1 transmutability1 and equivalence of the forces of nature4 ,gravitation1 attraction at small distances1 and many other phenomena are in direct dependence on the mass of matter4 ,it might therefore have been expected that chemical forces would also depend on mass4 ,a dependence is in fact shown1 the properties of elements and compounds being determined by the masses of the atoms of which they are formed4 ,the weight of a molecule1 or its mass1 determines1 as we have seen1 7,chapter ,,vii4 and elsewhere7 many of its properties independently of its composition4 ,thus carbonic oxide1 ,,co1 and nitrogen1 ,n#b1 are two gases having the same molecular weight1 and many of their properties 7density1 liquefaction1 specific heat1 c47 are similar or nearly similar4 ,the differences dependent on the nature of a substance play another part1 and form magnitudes of another order4 ,but the properties of atoms are mainly determined by their mass or weight1 and are in dependence upon it4 ,only in this case there is a peculiarity in the dependence of the properties on the mass1 for this dependence is determined by a periodic law4 ,as the mass increases the properties vary1 at first successively and regularly1 and then return to their original magnitude and recommence a fresh period of variation like the first4 ,nevertheless here as in other cases a small variation of the mass of the atom generally leads to a small variation of properties1 and determines differences of a second order4 ,the atomic weights of cobalt and nickel1 of rhodium1 ruthenium1 and palladium1 and of osmium1 iridium1 and platinum1 are very close to each other1 and their properties are also very much alike--the differences are not very perceptible4 ,and if the properties of atoms are a function of their weight1 many ideas which have more or less rooted themselves in chemistry must suffer change and be developed and worked out in the sense of this deduction4 ,although at first sight it appears that the chemical elements are perfectly independent and individual1 instead of this idea of the nature of the elements1 the notion of the dependence of their properties upon their mass must now be established2 that is to say1 the subjection of the individuality of the elements to a common higher principle which evinces itself in gravity and in all physico-chemical phenomena4 ,many chemical deductions then acquire a new sense and significance1 and a regularity is observed where it would otherwise escape attention4 ,this is more particularly apparent in the physical properties1 to the consideration of which we shall afterwards turn1 and we will now point out that ,gustavson first 7,chapter ,x41 ,note #bh7 and subsequently ,potilitzin 7,chapter ,,xi41 ,note #ff7 demonstrated the direct dependence of the reactive power on the atomic weight and that fundamental property which is expressed in the forms of their compounds1 whilst in a number of other cases the purely chemical relations of elements proved to be in connection with their periodic properties4 ,as a case in point1 it may be mentioned that ,carnelley remarked a dependence of the decomposability of the hydrates on the position of the elements in the periodic system2 whilst ,l4 ,meyer1 ,willgerodt1 and others established a connection between the atomic weight or the position of the elements in the periodic system and their property of serving as media in the transference of the halogens to the hydrocarbons4#af ,bailey pointed out a periodicity in the stability 7under the action of heat7 of the oxides1 namely3 7a7 in the even series 7for instance1 ,cr,o#c1 ,mo,o#c1 ,,wo#c1 and ,,uo#c7 the higher oxides of a given group decompose with greater ease the smaller the atomic weight1 while in the uneven series 7for example1 ,,co#b1 ,ge,o#b1 ,sn,o#b1 and ,pb,o#b7 the contrary is the case2 and 7b7 the stability of the higher saline oxides in the even series 7as in the fourth series from ,k#b,o to ,mn#b,o#g7 decreases in passing from the lower to the higher groups1 while in the uneven series it increases from the ,ist to the ,i,vth group1 and then falls from the ,i,vth to the ,v,i,ith2 for instance1 in the series ,ag#b,o1 ,cd,o1 ,in#b,o#c1 ,sn,o#b1 and then ,sn,o#b1 ,sb#b,o#e1 ,te,o#c1 ,i#b,o#g4 ,k4 ,winkler looked for and actually found 7#ahij7 a dependence between the reducibility of the metals by magnesium and their position in the periodic system of the elements4 ,the greater the attention paid to this field the more often is a distinct connection found between the variation of purely chemical properties of analogous substances and the variation of the atomic weights of the constituent elements and their position in the periodic system4 ,besides1 since the periodic system has become more firmly established1 many facts have been gathered1 showing that there are many similarities between ,sn and ,pb1 ,b and ,al1 ,cd and ,hg1 c41 which had not been previously observed1 although foreseen in some cases1 and a consequence of the periodic law4 ,keeping our attention in the same direction1 we see that the most widely distributed elements in nature are those with small atomic weights1 whilst in organisms the lightest elements exclusively predominate 7hydrogen1 carbon1 nitrogen1 oxygen71 whose small mass facilitates those transformations which are proper to organisms4 ,poluta 7of ,kharkoff71 ,c4 ,c4 ,botkin1 ,blake1 ,brenton1 and others even discovered a correlation between the physiological action of salts and other reagents on organisms and the positions occupied in the periodic system by the metals contained in them4#ag #af ,meyer1 ,willgerodt1 and others1 guided by the fact that ,gustavson and ,friedel had remarked that metalepsis rapidly proceeds in the presence of aluminium1 investigated the action of nearly all the elements in this respect4 ,for example1 they took benzene1 added the metals to be experimented on to it1 and passed chlorine through the liquid in diffused light4 ,when1 for instance1 sodium1 potassium1 barium1 c4 are taken1 there is no action on the benzene2 that is1 hydrochloric acid is not disengaged2 but if aluminium1 gold1 or1 in general1 any metal having this power of aiding chlorination 7,halogen-bertrger7 is employed1 then the action is clearly seen from the volumes of hydrochloric acid evolved 7especially if the metallic chloride formed is soluble in benzene74 ,thus1 in group ,i41 and in general among the even and light elements1 there are none capable of serving as agents of metalepsis2 but aluminium1 gallium1 indium1 antimony1 tellurium1 and iodine1 which are contiguous members in the periodic system1 are excellent transmitters 7carriers7 of the halogens4 #ag ,the periodic relations enumerated above appertain to the real elements1 and not to the elements in the free state as we know them2 and it is very important to note this1 because the periodic law refers to the real elements1 inasmuch as the atomic weight is proper to the real element1 and not to the 'free' element1 to which1 as to a compound1 a molecular weight is proper4 ,physical properties are chiefly determined by the properties of molecules1 and only indirectly depend on the properties of the atoms forming the molecules4 ,for this reason the periods1 which are clearly and quite distinctly expressed--for instance1 in the forms of combination--become to some extent involved 7complicated7 in the physical properties of their members4 ,thus1 for instance1 besides the maxima and minima corresponding with the periods and groups1 new molecules appear2 thus1 as regards the melting-point of germanium1 a local maximum appears1 which was1 however1 foreseen by the periodic law when the properties of germanium 7ekasilicon7 were forecast4 ,as1 from the necessity of the case1 the physical properties must be in dependence on the composition of a substance1 i4e4 on the quality and quantity of the elements forming it1 so for them also a dependence on the atomic weight of the component elements must be expected1 and consequently also on their periodic distribution4 ,we shall meet with repeated proofs of this in the further exposition of our treatise1 and for the present will content ourselves with citing the discovery by ,carnelley in #ahgi of the dependence of the magnetic properties of the elements on the position occupied by them in the periodic system4 ,carnelley showed that all the elements of the even series 7beginning with lithium1 potassium1 rubidium1 csium7 belong to the number of magnetic 7paramagnetic7 substances2 for example1 according to ,faraday and others1#ag bis ,c1 ,n1 ,o1 ,k1 ,ti1 ,cr1 ,mn1 ,fe1 ,co1 ,ni1 ,ce1 are magnetic2 and the elements of the uneven series are diamagnetic1 ,h1 ,na1 ,si1 ,p1 ,s1 ,cl1 ,cu1 ,zn1 ,as1 ,se1 ,br1 ,ag1 ,cd1 ,sn1 ,sb1 ,i1 ,au1 ,hg1 ,tl1 ,pb1 ,bi4 #ag bis ,the relation of certain elements 7for instance1 the analogues of ,pt7 among diamagnetic and paramagnetic bodies is sometimes doubtful 7probably partly owing to the imperfect purity of the reagents under investigation74 ,this subject has been studied in some detail by ,bachmetieff in #ahhi4 ,carnelley also showed that the melting-point of elements varies periodically1 as is seen by the figures in ,table ,,iii4 7nineteenth column71#ah where all the most trustworthy data are collected1 and predominance is given to those having maximum and minimum values4#ai #ah ,it is evident that many of the figures1 especially those exceeding #ajjj1 have been determined with but little exactitude1 and some1 placed in ,table ,,iii4 with the sign 7871 ,i have only given on the basis of rough and comparative determinations1 calculated from the melting-points of silver and platinum1 now established by many observers4 ,in ,table ,,iii41 besides the large periods whose maxima correspond with carbon1 silicon1 titanium1 ruthenium 7871 and osmium 7871 there are also small periods in the melting-points1 and their maxima correspond with sulphur1 arsenic1 antimony4 ,the minima correspond with the halogens and metals of the alkalis4 ,a distinct periodicity is also seen in taking the coefficients of linear expansion 7chiefly according to ,fizeau72 for instance1 in the vertical series 7according to the magnitude of the atomic weight71 ,fe1 ,co1 ,ni1 ,cu1 the linear expansion in millionths of an inch #ab1 #ac1 #ag1 and #bi2 for ,rh1 ,pd1 ,ag1 ,cd1 ,in1 ,sn1 and ,sb the coefficients are #h1 #ab1 #ai1 #ca1 #df1 #bf1 and #ab1 so that a maximum is reached at ,in4 ,in the series ,ir 7#g71 ,pt 7#e71 ,au 7#ad71 ,hg 7#fj71 ,tl 7#ca71 ,pb 7#bi71 and ,bi 7#ad71 the maximum is at ,hg and the minimum at ,pt4 ,raoul ,pictet expressed this connection by the fact that he found the product alpha7t #bgc7croot7,a_/d7 to be nearly constant for all elements in the free state1 and nearly equal to #jjde1 and being the coefficient of linear expansion1 t #bgc1 the melting-point calculated from the absolute zero 7-#bgc71 and #croot7,a_/d71 the mean distance between the atoms1 if ,a is the atomic weight and d the sp4 gr4 of an element4 ,although the above product is not strictly constant1 nevertheless ,pictet's rule gives an idea of the bond between magnitudes which ought to have a certain connection with each other4 ,de ,heen1 ,nadeschdin1 and others also studied this dependence1 but their deductions do not give a general and exact law4 #ai ,carnelley found a similar dependence in comparing the melting-points of the metallic chlorides1 many of which he redetermined for this purpose4 ,the melting-points 7and boiling-points1 in brackets7 of the following chlorides are known1 and a certain regularity is seen to exist in them1 although the number 7and degree of accuracy7 of the data is insufficient for a generalisation3-- ,li,cl #eih ,be,cl#b #fjj ,b,cl#c -#bj ,na,cl #ggb ,mg,cl#b #gjh ,al,cl#c #ahg ,k,cl #gcd ,ca,cl#b #gai ,sc,cl#c 8 ,cu,cl #dcd ,zn,cl#b #bfb ,ga,cl#c #gf 7#iic7 7#fhj7 7#bag7 ,ag,cl #dea ,cd,cl#b #eda ,in,cl#c 8 ,tl,cl #dbg ,pb,cl#b #dih ,bi,cl#c #bbg 7#gac7 7#ijh7 ,we will also enumerate the following data given by ,carnelley1 which are interesting for comparison3 ,h,cl -#aab 7-#ajb72 ,rb,cl #gaj1 ,sr,cl#b #hbe1 ,cs,cl #fca1 ,ba,cl#b #hfj1 ,sb,cl#c #gc 7#bbc71 ,te,cl#b #bji 7#cbg71 ,i,cl #bg1 ,hg,cl#b #bgf 7#cjc71 ,fe,cl#c #cjf1 ,nb,cl#e #aid 7#bdj71 ,ta,cl#c #baa 7#bdb71 ,w,cl#f #aij4 ,the melting-points of the bromides and iodides are higher or lower than those of the corresponding chlorides1 according to the atomic weight of the element and number of atoms of the halogen1 as is seen from the following examples3--#a4 ,k,cl #gcd1 ,k,br #fii1 ,,ki #fcd2 #b4 ,ag,cl #ded1 ,ag,br #dbg ,ag,i #ebg2 #c4 ,pb,cl#b #dih 7#ijj71 ,pb,br#b #dii 7#hfa71 ,pb,i#b #chc 7#ijf72 #d4 ,sn,cl#d below -#bj 7#aad71 ,sn,br#b #cj 7#bja71 ,sn,i#d #adf 7#bie7 7see ,chapter ,,ii4 ,note #bg1 and ,chapter ,,xi4 ,note #dg;bis1 c47 ,laurie 7#ahhb7 also observed a periodicity in the quantity of heat developed in the formation of the chlorides1 bromides1 and iodides 7fig4 #gi71 as is seen from the following figures1 where the heat developed is expressed in thousands of calories1 and referred to a molecule of chlorine1 ,cl#b1 so that the heat of formation of ,k,cl is doubled1 and that of ,sn,cl#d halved1 c43 ,na #aie 7,ag #ei1 ,au #ab71 ,mg #aea 7,zn #ig1 ,cd #ic1 ,hg #fc71 ,al #aag1 ,si #gi 7,sn #fd71 ,k #baa 7,li #ahg71 ,ca #agj 7,sr #ahe1 ,ba #aid71 whence it is seen that the greatest amount of heat is evolved by the metals of the alkalis1 and that in each period it falls from them to the halogens1 which evolve very little heat in combining together4 ,richardson1 by comparing the heats of formation of the fluorides also came to the conclusion that they are in periodic dependence upon the atomic weights of the combined elements4 ,illustration3 ,,fig4 #gi4--,laurie's diagram for expressing the periodic variation of the heat of formation of the chlorides4 ,the absciss give the atomic weights from #j to #baj1 and the ordinates the amounts of heat from #j to #bbj thousand calories evolved in the combination with ,cl#b1 7i4e4 with #ga parts of chlorine74 ,the apices of the curve correspond to ,li1 ,na1 ,k1 ,rb1 ,cs1 and the lower extremities to ,f1 ,cl1 ,br1 and ,i4 ,in this respect it may not be superfluous to remark 7#a7 that ,thomsen1 whose results ,i have employed above1 observed a correlation in the calorific equivalents of analogous elements1 although he did not remark their periodic variation2 7#b7 that the uniformity of many thermochemical deductions must gain considerably by the application of the periodic law1 which evidently repeats itself in calorimetric data2 and if these data frequently lead to true forecasts1 this is due to the periodicity of the thermal as well as of many other properties1 as ,laurie remarked2 and 7#c7 that the heat of formation of the oxides is also subject to a periodic dependence which differs from that of the heat of formation of the chlorides1 in that the greatest quantity corresponds with the bivalent metals of the alkaline earths 7magnesium1 calcium1 strontium1 barium71 and not with the univalent metals of the alkalis1 as is the case with chlorine1 bromine1 and iodine4 ,this circumstance is probably connected with the fact that chlorine1 bromine1 and iodine are univalent elements1 and oxygen bivalent 7compare1 for instance1 ,chapter ,,xi41 ,note #ac1 ,chapter ,,xxii41 ,note #dj1 ,chapter ,,xxiv41 ,note #bh;bis1 c47 ,keyser 7#ahib71 in investigating the spectra of the alkali metals and metals of the alkaline earths1 came to the conclusion that in this respect also there is a regularity of a periodic character in dependence upon the atomic weights4 ,probably a closer and systematic study of many of the properties of the elements and of complex and simple bodies formed by them will more and more frequently lead to similar conclusions1 and to extending the range of application of the periodic law4 ,there is no doubt that many other physical properties will1 when further studied1 also prove to be in periodic dependence on the atomic weights1#ai bis but at present only a few are known with any completeness1 and we will only refer to the one which is the most easily and frequently determined--namely1 the specific gravity in a solid and liquid state1 the more especially as its connection with the chemical properties and relations of substances is shown at every step4 ,thus1 for instance1 of all the metals those of the alkalis1 and of all the non-metals the halogens1 are the most energetic in their reactions1 and they have the lowest specific gravity among the adjacent elements1 as is seen in ,table ,,iii41 column #ag4 ,such are sodium1 potassium1 rubidium1 csium among the metals1 and chlorine1 bromine1 and iodine among the non-metals2 and as such less energetic metals as iridium1 platinum1 and gold 7and even charcoal or the diamond7 have the highest specific gravity among the elements near to them in atomic weight2 therefore the degree of the condensation of matter evidently influences the course of the transformations proper to a substance1 and furthermore this dependence on the atomic weight1 although very complex1 is of a clearly periodic character4 ,in order to account for this to some extent1 it may be imagined that the lightest elements are porous1 and1 like a sponge1 are easily penetrated by other substances1 whilst the heavier elements are more compressed1 and give way with difficulty to the insertion of other elements4 ,these relations are best understood when1 instead of the specific gravities referring to a unit of volume1#bj the atomic volumes of the elements--that is1 the quotient ,a_/d of the atomic weight ,a by the specific gravity d--are taken for comparison4 ,as1 according to the entire sense of the atomic theory1 the actual matter of a substance does not fill up its whole cubical contents1 but is surrounded by a medium 7ethereal1 as is generally imagined71 like the stars and planets which travel in the space of the heavens and fill it1 with greater or less intervals1 so the quotient ,a_/d only expresses the mean volume corresponding to the sphere of the atoms1 and therefore #croot,a_/d is the mean distance between the centres of the atoms4 ,for compounds whose molecules weigh ,m1 the mean magnitude of the atomic volume is obtained by dividing the mean molecular volume ,m_/d by the number of atoms n in the molecule4#ba ,the above relations may easily be expressed from this point of view by comparing the atomic volumes4 ,those comparatively light elements which easily and frequently enter into reaction have the greatest atomic volumes3 sodium #bc1 potassium #de1 rubidium #eg1 csium #ga1 and the halogens about #bg2 whilst with those elements which enter into reaction with difficulty1 the mean atomic volume is small2 for carbon in the form of a diamond it is less than #d1 as charcoal about #f1 for nickel and cobalt less than #g1 for iridium and platinum about #i4 ,the remaining elements having atomic weights and properties intermediate between those elements mentioned above have also intermediate atomic volumes4 ,therefore the specific gravities and specific volumes of solids and liquids stand in periodic dependence on the atomic weights1 as is seen in ,table ,,iii41 where both ,a 7the atomic weight7 and d 7the specific gravity71 and ,a_/d 7specific volumes of the atoms7 are given 7column #ah74 #ai bis ,probably1 besides thermo-chemical data 7,note #ai71 the refractive index1 cohesion1 ductility1 and similar properties of corresponding compounds or of the elements themselves will be found to exhibit a dependence of the magnitude of the atomic weight upon the periodic law4 #bj ,having occupied myself since the fifties 7my dissertation for the degree of ,m4,a4 concerned the specific volumes1 and is printed in part in the ,russian ,mining ,journal for #ahef7 with the problems concerning the relations between the specific gravities and volumes1 and the chemical compositions of substances1 ,i am inclined to think that the direct investigation of specific gravities gives essentially the same results as the investigation of specific volumes1 only that the latter are more graphic4 ,table ,,iii4 of the periodic properties of the elements clearly illustrates this4 ,thus1 for those members whose volume is the greatest among the contiguous elements1 the specific gravity is least--that is1 the periodic variation of both properties is equally evident4 ,in passing1 for instance1 from silver to iodine we have a successive decrease of specific gravity and successive increase of specific volume4 ,the periodic alternation of the rise and fall of the specific gravity and specific volume of the free elements was communicated by me in ,august #ahfi to the ,moscow ,meeting of ,russian ,naturalists4 ,in the following year 7#ahgj7 ,l4 ,meyer's paper appeared1 which also dealt with the specific volume of the elements4 #ba ,in my opinion the mean volume of the atoms of compounds deserves more attention than has yet been paid to it4 ,i may point out1 for instance1 that for feebly energetic oxides the mean volume of the atom is generally nearly #g2 for example1 the oxides ,si,o#b1 ,sc#b,o#c1 ,ti,o#b1 ,v#b,o#e1 as well as ,zn,o1 ,ga#b,o#c1 ,ge,o#b1 ,zr,o#b1 ,in#b,o#c1 ,sn,o#b1 ,sb#b,o#e1 c41 whilst the mean volume of the atom of the alkali and acid oxides is greater than #g4 ,thus we find in the magnitudes of the mean volumes of the atom in oxides and salts both a periodic variation and a connection with their energy of essentially the same character as occurs in the case of the free elements4 ,thus we find that in the large periods beginning with lithium1 sodium1 potassium1 rubidium1 csium1 and ending with fluorine1 chlorine1 bromine1 iodine1 the extreme members 7energetic elements7 have a small density and large volume1 whilst the intermediate substances gradually increase in density and decrease in volume--that is1 as the atomic weight increases the density rises and falls1 again rises and falls1 and so on4 ,furthermore1 the energy decreases as the density rises1 and the greatest density is proper to the atomically heaviest and least energetic elements2 for example1 ,os1 ,ir1 ,pt1 ,au1 ,u4 ,in order to explain the relation between the volumes of the elements and of their compounds1 the densities 7column ,s7 and volumes 7column ,m_/s7 of some of the higher saline oxides arranged in the same order as in the case of the elements are given on p4 #cf4 ,for convenience of comparison the volumes of the oxides are all calculated per two atoms of an element combined with oxygen4 ,for example1 the density of ,al#b,o#c #dj1 weight ,al#b,o#c #ajb1 volume ,al#b,o#c #bee4 ,whence1 knowing the volume of aluminium to be #aa1 it is at once seen that in the formation of aluminium oxide1 #bb volumes of it give #bee volumes of oxide4 ,a distinct periodicity may also be observed with respect to the specific gravities and volumes of the higher saline oxides4 ,thus in each period1 beginning with the alkali metals1 the specific gravity of the oxides first rises1 reaches a maximum1 and then falls on passing to the acid oxides1 and again becomes a minimum about the halogens4 ,but it is especially important to call attention to the fact that the volume of the alkali oxides is less than that of the metal contained in them1 which is also expressed in the last column1 giving this difference for each atom of oxygen4#bb ,thus #b atoms of sodium1 or #df volumes1 give #bd volumes of ,na#b,o1 and about #cg volumes of #b,na,h,o--that is1 the oxygen and hydrogen in distributing themselves in the medium of sodium have not only not increased the distance between its atoms1 but have brought them nearer together1 have drawn them together by the force of their great affinity1 by reason1 it may be presumed1 of the small mutual attraction of the atoms of sodium4 ,such metals as aluminium and zinc1 in combining with oxygen and forming oxides of feeble salt-forming capacity1 hardly vary in volume1 but the common metals and non-metals1 and especially those forming acid oxides1 always give an increased volume when oxidised--that is1 the atoms are set further apart in order to make room for the oxygen4 ,the oxygen in them does not compress the molecule as in the alkalis2 it is therefore comparatively easily disengaged4 #bb ,the volume of oxygen 7judging by the table on p4 #cf7 is evidently a variable quantity1 forming a distinctly periodic function of the atomic weight and type of the oxide1 and therefore the efforts which were formerly made to find the volume of the atom of oxygen in the volumes of its compounds may be considered to be futile4 ,but since a distinct contraction takes place in the formation of oxides1 and the volume of an oxide is frequently less than the volume in the free state of the element contained in it1 it might be surmised that the volume of oxygen in a free state is about #ae1 and therefore the specific gravity of solid oxygen in a free state would be about ,o#i4 ,s ,m_/s ,volume of ,oxygen ,h#b,o #aj #ah 8- #bb ,li#b,o #bj #ae - #i ,be#b,o#b #cjf #af #bf ,b#b,o#c #ah #ci #ajj ,c#b,o#d #af #ee #ajf ,n#b,o#e #afd #ff 8 #d ,na#b,o #bf #bd - #bb ,mg#b,o#b #ce #bc - #de ,al#b,o#c #dj #bf #ac ,si#b,o#d #bfe #de #eb ,p#b,o#e #bci #ei #fb ,s#b,o#f #aif #hb #hg ,cl#b,o#g 8#aib #ie #f ,k#b,o #bg #ce - #ce ,ca#b,o#b #cbe #cd - #h ,sc#b,o#c #chf #ce 8 #j ,ti#b,o#d #db #ch #c ,v#b,o#e #cdi #eb #fg ,cr#b,o#f #bgd #gc #ie ,cu#b,o #ei #bd #if ,zn#b,o#b #eg #bc #dh ,ga#b,o#c 8#ea #cf #d ,ge#b,o#d #dg #dd #de ,as#b,o#e #da #ef #fj ,sr#b,o#b #dg #dd - #ac ,y#b,o#c #ej #de 8- #b ,zr#b,o#d #ee #dd #j ,nb#b,o#e #dg #eg #f ,mo,o#f #dd #fe #fh ,ag#b,o #ge #ca #aa ,cd#b,o#c #hj #cb #c ,in#b,o#c #gah #ch #bg ,sn#b,o#d #g,o #dc #bg ,sb#b,o#e #fe #di #bf ,te,o#f #ea #fh #dg ,ba#b,o#b #eg #eb - #aj ,la#b,o#c #fe #ej #a ,ce#b,o#d #fgd #ej #b ,ta#b,o#e #ge #ei #df ,w#b,o#f #fh #fh #hb ,hg#b,o#b #aaa #ci #de ,pb#b,o#d #hi #ec #db ,th#b,o#d #ihf #ed #b ,as the volumes of the chlorides1 organo-metallic and all other corresponding compounds1 also vary in a like periodic succession with a change of elements1 it is evidently possible to indicate the properties of substances yet uninvestigated by experimental means1 and even those of yet undiscovered elements4 ,it was possible by following this method to foretell1 on the basis of the periodic law1 many of the properties of scandium1 gallium1 and germanium1 which were verified with great accuracy after these metals had been discovered4#bc ,the periodic law1 therefore1 has not only embraced the mutual relations of the elements and expressed their analogy1 but has also to a certain extent subjected to law the doctrine of the types of the compounds formed by the elements3 it has enabled us to see a regularity in the variation of all chemical and physical properties of elements and compounds1 and has rendered it possible to foretell the properties of elements and compounds yet uninvestigated by experimental means2 thus it has prepared the ground for the building up of atomic and molecular mechanics4#bd #bc ,as an example we will take indium oxide1 ,in#b,o#c4 ,its sp4 gr4 and sp4 vol4 should be the mean of those of cadmium oxide1 ,cd#b,o#b1 and stannic oxide1 ,sn#b,o#d1 as indium stands between cadmium and tin4 ,thus in the seventies it was already evident that the volume of indium oxide should be about #ch1 and its sp4 gr4 about #gb1 which was confirmed by the determinations of ,nilson and ,pettersson 7#gagi7 made in #ahhj4 #bd ,as the distance between1 and the volumes of1 the molecules and atoms of solids and liquids certainly enter into the data for the solution of the problems of molecular mechanics1 which as yet have only been worked out to any extent for the gaseous state1 the study of the specific gravity of solids1 and especially of liquids1 has long had an extensive literature4 ,with respect to solids1 however1 a great difficulty is met with1 owing to the specific gravity varying not only with a change of isomeric state 7for example1 for silica in the form of quartz #bfe1 and in tridymite #bb7 but also directly under mechanical pressure 7for example1 in a crystalline1 cast1 and forged metal71 and even with the extent to which they are powdered1 c41 which influences are imperceptible in liquids4 ,compare ,chapter ,,xiv41 ,note #ee;bis4 ,without going into further details1 we may add to what has been said above that the conception of specific volumes and atomic distances has formed the subject of a large number of researches1 but as yet it is only possible to lay down a few generalisations given by ,dumas1 ,kopp1 and others1 which are mentioned and amplified by me in my work cited in ,note #bj1 and in my memoirs on this subject4 #a4 ,analogous compounds and their isomorphs have frequently approximately the same molecular volumes4 #b4 ,other compounds1 analogous in their properties1 exhibit molecular volumes which increase with the molecular weight4 #c4 ,when a contraction takes place in combination in a gaseous state1 then contraction is in the majority of instances also to be observed in the solid or liquid state--that is1 the sum of the volumes of the reacting substances is greater than the volume of the resultant substance or substances4 #d4 ,in decomposition the reverse takes place to that which occurs in combination4 #e4 ,in substitution 7when the volumes in a state of vapour do not vary7 a very small change of volume generally takes place--that is1 the sum of the volumes of the reacting substances is almost equal to the sum of the resultant substances4 #f4 ,hence it is impossible to judge the volume of the component substances from the volume of a compound1 although it is possible to do so from the product of substitution4 #g4 ,the replacement of ,h#b by sodium1 ,na#b1 and by barium1 ,ba1 as well as the replacement of ,,so#d by ,cl#b1 scarcely changes the volume1 but the volume increases with the replacement of ,na by ,k1 and decreases with the replacement of ,h#b1 by ,li#b ,cu1 and ,mg4 #h4 ,there is no need for comparing volumes in a solid and liquid state at the so-called corresponding temperatures--that is at temperatures at which vapour tension is equal in each case4 ,the comparison of volumes at the ordinary temperature is sufficient for finding a regularity in the relations of volumes 7this deduction was developed with particular detail by me in #ahef74 #i4 ,many investigators 7,perseau1 ,schrder1 ,lwig1 ,playfair and ,joule1 ,baudrimont1 ,einhardt7 have sought in vain for a multiple proportion in the specific volumes of solids and liquids4 #aj4 ,the truth of the above is seen very clearly in comparing the volumes of polymeric substances4 ,the volumes of their molecules are equal in a state of vapour1 but are very different in a solid and liquid state1 as is seen from the close resemblance of the specific gravities of polymeric substances4 ,but as a rule the more complex polymerides are denser than the simpler4 #aa4 ,we know that the hydroxides of light metals have generally a smaller volume than the metals1 whilst that of magnesium hydroxide is considerably greater1 which is explained by the stability of the former and instability of the latter4 ,in proof of this we may cite1 besides the volumes of the true alkali metals1 the volume of barium 7#cf7 which is greater than that of its stable hydroxide 7sp4 gr4 #de1 sp4 vol4 #cj74 ,the volumes of the salts of magnesium and calcium are greater than the volume of the metal1 with the single exception of the fluoride of calcium4 ,with the heavy metals the volume of the compound is always greater than the volume of the metal1 and1 moreover1 for such compounds as silver iodide1 ,ag,i 7d #eg71 and mercuric iodide1 ,hg,i#b 7d #fb1 and the volumes of the compounds #da and #gc71 the volume of the compound is greater than the sum of the volumes of the component elements4 ,thus the sum of the volumes ,ag ,i #cf1 and the volume of ,ag,i #da4 ,this stands out with particular clearness on comparing the volumes ,k ,i #ga with the volume of ,,ki1 which is equal to #ed1 because its density #cjf4 #ab4 ,in such combinations1 between solids and liquids1 as solutions1 alloys1 isomorphous mixtures1 and similar feeble chemical compounds1 the sum of the reacting substances is always very nearly that of the resulting substance1 but here the volume is either slightly larger or smaller than the original2 speaking generally1 the amount of contraction depends on the force of affinity acting between the combining substances4 ,i may here observe that the present data respecting the specific volumes of solid and liquid bodies deserve a fresh and full elaboration to explain many contradictory statements which have accumulated on this subject4 ,,chapter ,,xvi ,,zinc1 ,,cadmium1 ,,and ,,mercury ,these three metals give1 like magnesium1 oxides ,,ro1 which form feebly energetic bases1 and like magnesium they are volatile4 ,the volatility increases with the atomic weight4 ,magnesium can be distilled at a white heat1 zinc at a temperature of about #icj1 cadmium about #ggj1 and mercury about #cea4 ,their oxides1 ,,ro1 are more easily reducible than magnesia1 and mercuric oxide is the most easily reducible4 ,the properties of their salts ,,rx#b are very similar to the properties of ,mg,x#b4 ,their solubility1 power of forming double and basic salts1 and many other qualities are in many respects identical with those of ,mg,x#b4 ,the greater or less ease with which they are oxidised1 the instability of their compounds1 the density of the metals and their compounds1 their scarcity in nature1 and many other properties gradually change with the increase of atomic weight1 as might be expected from the periodicity of the elements4 ,their principal characteristics1 as contrasted with magnesium1 find a general expression in the fact that zinc1 cadmium1 and mercury are heavy metals4 ,zinc stands nearest to magnesium in atomic weight and in properties4 ,thus zinc sulphate1 or white vitriol1 easily crystallises with seven molecules of water1 ,zn,s,o#d1g;,h#b,o4 ,it is isomorphous with ,epsom salts1 and parts with difficulty with the last molecule of water2 it forms double salts--for instance1 ,zn,k#b7,,so#d7b1f;,h#b,o--exactly as magnesium sulphate does4#a ,zinc oxide1 ,zn,o1 is a white powder1 almost insoluble in water1#b like magnesia1 from which1 however1 it is distinguished by its solubility in solutions of sodium and potassium hydroxides4#c ,zinc chloride#d is decomposed by water1 combines with ammonium chloride1 potassium chloride1 c41 just like magnesium chloride1 forms an oxychloride1 and also combines with zinc oxide4#d bis #a ,zinc sulphate is often obtained as a by-product--for instance1 in the action of galvanic batteries containing zinc and sulphuric acid4 ,when the anhydrous salt is heated it forms zinc oxide1 sulphurous anhydride1 and oxygen4 ,the solubility in #ajj parts of water at ,o #dc1 #bj #ec1 #dj #fc-a_/b1 #fj #gd1 #hj #hd-a_/b1 #ajj #ie parts of anhydrous zinc sulphate--that is to say1 it is closely expressed by the formula #dc #jebt4 ,an admixture of iron is often found in ordinary sulphate of zinc in the form of ferrous sulphate1 ,fe,s,o#d1 isomorphous with the zinc sulphate4 ,in order to separate it1 chlorine is passed through the solution of the impure salt 7when the ferrous salt is converted into ferric71 the solution is then boiled1 and zinc oxide is afterwards added1 which1 after some time has elapsed1 precipitates all the ferric oxide4 ,ferric oxide of the form ,r#b,o#c is displaced by zinc oxide of the form ,,ro4 #b ,zinc oxide is obtained both by the combustion and oxidation of zinc1 and by the ignition of some of its salts--for instance1 those of carbonic and nitric acids2 it is likewise precipitated by alkalis from a solution of ,zn,x#b in the form of a gelatinous hydroxide4 ,the oxide produced by roasting zinc blende 7by burning in the air1 when the sulphur is converted into sulphurous anhydride7 contains various impurities4 ,for purification1 the oxide is mixed with water1 and the sulphurous anhydride formed by roasting the blende is passed through it4 ,zinc bisulphite1 ,zn,s,o#c1;,h#b,,so#c1 then passes into solution4 ,if a solution of this salt be evaporated1 and the residue ignited1 zinc oxide1 free from many of its impurities1 will remain4 ,zinc oxide is a light white powder1 used as a paint instead of white lead2 the basic salt1 corresponding with magnesia alba1 is used for the same purpose4 ,v4 ,kouriloff 7#ahij7 by boiling the hydrate of the oxide with a #c p4c4 solution of peroxide of hydrogen obtained ,zn#b;,h#b,o#d or the hydrate of the peroxide 7 ,zn,o#b,zn,h#b,o#b or a compound of #b,zn,o with ,h#b,o#b71 which did not part with its oxygen at #ajj1 but only above #abj4 ,cadmium gives a similar compound of a yellow colour4 ,magnesium1 although it does form such a compound1 does so with great difficulty4 #c ,for the solution of one part of the oxide #ee1djj parts of water are required4 ,nevertheless1 even in such a weak solution1 zinc oxide 7hydroxide1 ,zn,h#b,o#b7 changes the colour of red litmus paper4 ,zinc oxide is obtained in the wet way by adding an alkali hydroxide to a solution of a zinc salt--for instance3 ,zn,s,o#d #b;,,hko ,k#b,,so#d ,zn,h#b,o#b4 ,the gelatinous precipitate of zinc hydroxide is soluble in an excess of alkali1 which clearly distinguishes it from magnesia4 ,this solubility of zinc hydroxide in alkalis is due to the power of zinc oxide to form a compound1 although an unstable one1 with alkalis--that is to say1 points to the fact that zinc oxide already partly belongs to the intermediate oxides4 ,the oxides of the metals above mentioned 7except ,be,o7 do not show this property4 ,the property which metallic zinc itself has of dissolving in caustic alkali with the disengagement of hydrogen 7the solution is facilitated by contact with platinum or iron7 depends on the formation of such a compound of the oxides of zinc and the alkali metals4 ,the solution of zinc hydroxide1 ,zn,h#b,o#b1 in potash 7in a strong solution71 proceeds when these hydrates are taken in proportion to ,zn,h#b,o#b ,,kho4 ,if such a solution be evaporated to dryness1 water extracts only caustic potash from the fused residue4 ,when a solution of zinc hydroxide in strong alkali is mixed with a large mass of water1 nearly all the oxide of zinc is precipitated2 and1 therefore1 in weak solutions1 a large quantity of the alkali is required to effect solution1 which points to the decomposition of the zinc-alkali compounds by water4 ,if strong alcohol be added to a solution of zinc oxide in sodium hydroxide1 the crystallo-hydrate1 #b,zn7,,oh77,o,na71#g;,h#b,o1 separates4 #d ,zinc chloride1 ,zn,cl#b1 is generally employed in the arts in the form of a solution obtained by dissolving zinc in hydrochloric acid4 ,this solution is used for soldering metals1 impregnating wood1 c4 ,the reason why it is thus employed may be understood from its properties4 ,when evaporated it first parts with its water of crystallisation2 on being further heated1 however1 it loses all traces of water1 and forms an oily mass of anhydrous salt which solidifies on cooling4 ,this substance melts at #bej1 commences to volatilise at about #djj1 and boils at #gcj4 ,the soldering of metals--that is1 the introduction of an easily fusible metal between two contiguous metallic objects--is hindered by any film of oxide upon them2 and1 as heated metals easily oxidise1 they are naturally difficult to solder4 ,zinc chloride is used to prevent the oxidation4 ,it fuses on being heated1 and1 covering the metal with an oily coating1 prevents contact with the air2 but even if any oxide has formed1 the free hydrochloric acid generally existing in the zinc chloride solution dissolves it1 and in this way the metallic surface of the metals to be soldered is preserved fit for the adhesion of the liquid solder1 which1 on cooling1 binds the objects together4 ,much zinc chloride is used also for steeping wood 7telegraph-posts and railway-sleepers7 in order to preserve it from decaying quickly2 this preservative action is in all probability mainly due to the poisonous character of zinc salts 7corrosive sublimate is still more poisonous1 and a still better agent to preserve wood from decay71 since decay is due to the action of lower organisms4 ,the specific gravity of solutions containing p per cent4 of zinc chloride1 ,zn,cl#b1 is as follows3 p #aj #bj #cj #dj #ej #ae_/d #ajic #aahd #abic #adaa #aeed ds_/dt -#c -#e -#g -#h -#i ,the last line shows the change of specific gravity for #a in ten-thousandth parts for temperatures near #ae4 ,more accurate determinations of ,cheltzoff1 personally communicated by him1 led him to conclude that solutions of zinc chloride follow the same laws as the solutions of sulphuric acid1 which will be considered in ,chapter ,,xx43 7#a7 from ,h#b,o to ,zn,cl#b1abj;,h#b,o s ,s#j #ibhep #jagdhp#b2 7#b7 from thence to ,zn,cl#b1dj;,h#b,o s ,s#j #icifp - #jjabfp#b2 7#c7 thence to ,zn,cl#b1be;,h#b,o s #aadhae #ifde7p - #aehi7 #jdefg7p - #aehi7b2 7#d7 thence to ,zn,cl#b1aj;,h#b,o s #abbaba #ajdhb7p - #bcba7 #jgiib7p - #bcba7b2 7#e7 thence to p #fe p4c4 s #adfjfc #adjif7p - #dcje7 #adije7p - #dcje7b1 where s is the specific gravity of the solution at #ae1 containing p p4c4 of ,zn,cl#b by weight1 taking water at #d #ajjjj1 and where ,s#j #iiiaf 7specific gravity of water at #ae74 ,the compound of zinc chloride with hydrochloric acid has been mentioned in ,vol4 ,i4 ,chapter ,x4 ,zinc chloride has a great affinity for water2 it is not only soluble in it1 but in alcohol1 and on being dissolved in water becomes considerably heated1 like magnesium and calcium chlorides4 ,zinc chloride is capable of taking up water1 not only in a free state1 but also in chemical combination with many substances4 ,thus1 for instance1 it is used in organic researches for removing the elements of water from many of the organic compounds4 #d bis ,when mixed with zinc oxide it forms1 with remarkable ease1 a very hard mass of zinc oxychloride1 which is applied in the arts2 for instance1 in painting1 to resist the action of water1 or for cementing such objects as are destined to remain in water4 ,zinc oxychloride1 ,zn,cl#b1c,zn,o1#b;,h#b,o 7 ,zn#b,o,cl#b1b,zn,h#b,o#b71 is also formed from a solution of zinc chloride by the action of a small quantity of ammonia on it after heating the precipitate obtained with the liquid for a considerable time2 the admixture of ammonium salts with a mixture of a strong solution of zinc chloride with its oxide makes a similar mass1 which does not solidify so rapidly1 and is therefore more useful for some purposes4 ,moisture and cold do not change the hardened mass of oxychloride1 and it also resists the action of many acids1 and a temperature of #cjj1 which makes it a useful cement for many purposes4 ,a solution of magnesium chloride with magnesium oxide forms a similar oxychloride4 ,the mass solidifies best when there are equal quantities by weight of zinc in the chloride and oxide1 and therefore when it has the composition ,zn#b,o,cl#b ,in preparing such a cement1 naturally zinc oxide alone may be taken1 and the requisite quantity of hydrochloric acid added to it4 ,the capacity of ,zn,cl#b to combine with water1 ,zn,o1 and ,h,cl 7and also with other metallic chlorides7 indicates its property to combine with molecules of other substances1 and therefore its compounds with ,,nh#c1 and especially a compound1 ,zn,cl#bb,,nh#c1 similar to sal-ammoniac1 might be expected 7i4e4 #b,,nh#d;,cl1 in which ,h#b is replaced by ,zn74 ,and indeed it has long been known that ,zn,cl#b absorbs ammonia and gives solid substances capable of dissociating with the disengagement of ,,nh#c4 ,among these compounds ,isambert and ,v4 ,kouriloff 7#ahid7 obtained ,zn,cl#bf,,nh#c1 ,zn,cl#bd,,nh#c1 ,zn,cl#bb,,nh#c1 and ,zn,cl#b,,nh#c4 ,the dissociation tension of the two last-mentioned compounds at #bah is equal to #dcf mm4 and #fg mm4 ,cd,cl#b also forms similar compounds with ,,nh#c 7,kouriloff1 #ahid74 ,zinc1 like many heavy metals1 is often found in nature in combination with sulphur1 forming the so-called zinc blende1#e ,zn,s4 ,it sometimes occurs in large masses1 often crystallised in cubes2 it is frequently translucent1 and has a metallic lustre1 although this is not so clearly developed as in many other metallic sulphides with which we shall hereafter become acquainted4 ,the ores of zinc also comprise the carbonate1 calamine1 and silicate1 siliceous calamine4 #e ,this mineral has been given the name of 'mock-ore1' on account of its having the appearance 7considerable density1 #djf1 c47 of ordinary metallic ores2 it deceived the first miners1 because it did not1 like other ores1 give metal when simply roasted in air and fused with charcoal4 ,the white zinc oxide1 formed by burning the vapours of zinc1 was also called 'nihil album1' or 'white nothing1' on account of its lightness4 ,illustration3 ,,fig4 #hj4--;,distillation of zinc in a crucible placed in a furnace4 o c1 tube along which the vapour passes and condenses4 ,metallic zinc 7spelter7 is most frequently obtained from the ores containing the carbonate#f--that is1 from calamine1 which is sometimes found in thick veins3 for instance1 in ,poland1 ,galicia1 in some places on the banks of the ,rhine1 and in considerable masses in ,belgium and ,england4 ,in ,russia beds of zinc ore are met with in ,poland and the ,caucasus1 but the output is small4 ,in ,sweden1 as early as the fifteenth century1 calamine was worked up into an alloy of zinc and copper 7brass71 and ,paracelsus produced zinc from calamine2 but the technical production of the metal itself1 long ago practised in ,china1 only commenced in ,europe in #ahjg--;in ,belgium1 when the ,abb ,donnet discovered that zinc was volatile4 ,from that time the production increased until it is now about #aej million kilograms in ,germany alone4 #f ,it may be here mentioned that by the word ore is meant a hard1 heavy substance dug out of the earth1 which is used in metallurgical works for obtaining the usual heavy metals long known and used4 ,the natural compounds of sodium1 or magnesium1 are not called ores1 because magnesium and sodium have not been long obtainable in quantity4 ,the heavy metals1 those which are easily reduced and do not easily oxidise1 are exclusively those which are directly applied in manufactures4 ,ores either contain the metals themselves 7for instance1 ores of silver or bismuth71 and the metals are then said to be in a native state1 or else their sulphur compounds 7blende1 mock-ore1 pyrites--as1 for example1 galena1 ,pb,s2 zinc blende1 ,zn,s2 copper pyrites1 ,cu,fe,s7 or oxides 7as the ores of iron71 or salts 7calamine1 for instance74 ,zinc is incomparably rarer than magnesium1 and is only well known because it is transformed from its ores into a metal which finds direct use in many branches of industry4 ,the reduction of metallic zinc from its ores is based on the fact that zinc oxide#g is easily reduced by charcoal at a red heat3 ,zn,o ,c ,zn ,,co4 ,the zinc thus obtained is in a finely divided state and impure1 being mixed with other metals reduced with it1 but the greater portion is converted into vapour1 from which it easily passes into a liquid or solid state4 ,the reduction and distillation are carried on in earthenware retorts1 filled with a mixture of the divided ore and charcoal4 ,the vapours of zinc and gases formed during the reaction escape by means of a pipe leading downwards1 and are led to a chamber where the vapours are cooled4 ,by this means they do not come into contact with the air1 because the neck of the retort is filled with gaseous carbonic oxide1 and therefore the zinc does not oxidise2 otherwise its vapour would burn in the air4#g bis ,the vapours of zinc1 entering into the cooling chamber1 condense into white zinc powder or zinc dust4 ,when the neck of the retort is heated the zinc is obtained in a liquid state1 and is cast into plates1 in which form it is generally sold4 #g ,ores1 when extracted from the earth by the miners1 are often enriched by sorting1 washing1 and other mechanical operations4 ,the sulphurous ores 7and likewise others7 are then generally roasted4 ,roasting an ore means heating it to redness in air4 ,the sulphur then burns1 and passes off in the form of sulphurous anhydride1 ,,so#b1 and the metal oxidises4 ,the roasting is carried on in order to obtain an oxide instead of a sulphur compound1 the oxide being reducible by charcoal4 ,these methods1 introduced ages ago1 are met with in nearly all metallurgical works for practically all ores4 ,for this reason the preparatory treatment of zinc blende furnishes zinc oxide3 this is already contained in calamine4 #g bis with very impure ores1 especially such as contain lead 7,pb,s often accompanies zinc71 the vapour of the reduced zinc is allowed to pass directly into the air4 ,it burns and gives ,zn,o1 which is used as a pigment4 ,commercial zinc is generally impure1 containing a mixture of lead1 particles of carbon1 iron1 and other metals carried over with the vapours1 although they are not volatile at a temperature approaching #ajjj4 ,if it be required to obtain pure zinc from the commercial article1 it is subjected to a further distillation in a crucible with a pipe passing through the bottom1 the vapours formed by the heated zinc only having exit through the pipe cemented into the bottom of the crucible4 ,passing through this pipe1 the vapours condense to a liquid1 which is collected in a receiver4 ,zinc thus purified is generally re-melted and cast into rods1 and in this form is often used for physical and chemical researches where a pure article is required4#h #h ,this zinc1 although homogeneous1 still contains certain impurities1 to remove which it is necessary to prepare some salt of zinc in a pure state and transform it into carbonate1 which latter is then distilled with charcoal2 and1 as thin sheets of zinc can only be obtained from very pure metal1 they are frequently made use of in cases where pure zinc is required4 ,in order to remove the arsenic from zinc1 it was proposed to melt it and mix it with anhydrous magnesium chloride1 by which means vapours of zinc chloride and arsenic chloride are formed4 ,perfectly pure zinc is made 7,v4 ,meyer and others7 by decomposing1 by means of the galvanic current1 a solution of zinc sulphate to which an excess of ammonia has been added4 ,the zinc used for ,marsh's arsenic test 7,chapter ,,xix47 is purified from ,as by fusing it with ,,kno#c and then with ,zn,cl#b4 ,metallic zinc has a bluish-white colour2 its lustre1 compared with many other metals1 is insignificant4 ,when cast it exhibits a crystalline structure4 ,its specific gravity is about #g--that is1 varies from #fh to #gb1 according to the degree of compression 7by forging1 rolling1 c47 to which it has been subjected4 ,it is very ductile1 considering its hardness4 ,for this reason it chokes up files when being worked4 ,its malleability is considerable when pure1 but in the ordinary impure condition in which it is sold1 it is impossible to roll it at the ordinary temperature1 as it easily breaks4 ,at a temperature of #ajj1 however1 it easily undergoes such operations1 and can then be drawn into wire or rolled into sheets4 ,if heated further it again becomes brittle1 and at #bjj may be even crushed into powder1 so completely does it lose its molecular cohesion4 ,it melts at #dah1 and distils at #icj4 ,zinc does not undergo any change in the atmosphere4 ,even in very damp air it only becomes slowly coated with a very thin white coating of oxide4 ,for this reason it is available for all objects which are only in contact with air4 ,therefore sheet zinc may be used for roofing and many other purposes4#i ,this great unchangeability of zinc in the air shows its slight energy with regard to oxygen compared with the metals already mentioned1 which are capable of reducing zinc from solutions4 ,but zinc plays this part with regard to the remaining metals--for example1 it reduces salts of lead1 copper1 mercury1 c4 ,although zinc is an almost unoxidisable metal at the ordinary temperature1 it burns in the air on being heated1 particularly when in the form of shavings or in the condition of vapour4 ,at the ordinary temperature zinc does not decompose water--at any rate1 if the metal be in a dense mass4 ,but even at a temperature of #ajj zinc begins little by little to decompose water2 it easily displaces the hydrogen of acids at the ordinary temperature1 and of alkalis on being heated4 #i ,cornices and other architectural ornaments1 remarkable for their lightness and beauty1 are stamped out of sheet zinc4 ,zinc-roofing does not require painting1 but it melts during a conflagration1 and even burns at a strong heat4 ,many iron vessels1 c41 are covered with zinc 7'galvanised'7 in order to prevent them from rusting4 ,in this respect the action of zinc varies a great deal with the degree of its purity4 ,weak sulphuric acid 7corresponding with the composition ,h#b,,so#d1h;,h#b,o7 at the ordinary temperature does not act at all on chemically pure zinc1 and even a stronger solution acts very slowly4 ,if the temperature be raised1 and particularly if the zinc be previously slightly heated1 so as to cover the surface with a film of oxide1 chemically pure zinc acts on sulphuric acid4 ,thus1 for example1 one cubic centimetre of zinc in sulphuric acid having a composition ,h#b,,so#d1f;,h#b,o at the ordinary temperature in two hours only dissolves to the extent of #jjah gram1 and at a temperature of #ajj about #ce grams4 ,if we compare this slow action with that rapid evolution of hydrogen which occurs in the case of commercial zinc1 we see that the influence of those impurities in the zinc is very great4 ,every particle of charcoal or iron introduced into the mass of the zinc1 and likewise the connection of the zinc with a piece of another electro-negative metal1 assists such a dissolution4 ,the slowness of the action of sulphuric acid on pure zinc 7and likewise on amalgamated zinc7 may also be explained by the fact that a layer of hydrogen#aj collects on the surface of the metal1 preventing contact between the acid and the metal4#aj bis #aj ,veeren 7#ahia7 proved this by simple experiments1 finding that in vacuo the solution proceeds far more rapidly for both pure and commercial zinc1 and still more rapidly in the presence of oxidising agents 7which absorb the hydrogen7 like ,cr,o#c and ,h#b,o#b4 #aj bis ,the addition of cupric sulphate1 or1 better still1 a few drops of platinic chloride 7the metals become reduced71 to the sulphuric acid greatly accelerates the evolution of the hydrogen1 because in this case1 as with commercial zinc1 galvanic couples are formed locally by the copper or platinum and the zinc1 under the influence of which the zinc rapidly dissolves4 ,the action of acids on metallic zinc of various degrees of purity has been the subject of many investigations1 particularly important with reference to the application of zinc in galvanic batteries1 whilst some investigations have direct significance for chemical mechanics1 although from many points of view the matter is not clear4 ,i consider it useful to mention certain of these investigations4 ,calvert and ,johnson made the following series of observations on the action of sulphuric acid of various degrees of concentration on #b grams of pure zinc during two hours4 ,in the cold the concentrated acid1 ,h#b,,so#d1 does not act1 ,h#b,,so#d1b;,h#b,o dissolves about #jjjb gram1 but principally forms hydrogen sulphide1 which is obtained also when the dilution reaches ,h#b,,so#d1g;,h#b,o1 when #jjce gram of zinc is dissolved4 ,when largely diluted with water1 pure hydrogen begins to be disengaged4 ,h#b,,so#d1b;,h#b,o at #acj gives a mixture of hydrogen sulphide and sulphurous anhydride dissolving #jaef gram of zinc4 ,bouchardat showed that if in a vessel made of glass or sulphur dilute sulphuric acid acting on a piece of zinc liberates one part of hydrogen1 then the same acid with the same piece of zinc in the same time will liberate #d parts of hydrogen if the vessel be made of tin--that is1 zinc forms a galvanic couple with tin2 in a leaden vessel #i parts of hydrogen are set free1 with a vessel of antimony or bismuth #ac parts1 silver or platinum #ch parts1 copper #ej parts1 iron #dc parts4 ,if a salt of platinum be added to the dilute sulphuric acid 7#a part of acid and #ab parts of water71 ,millon determined that the rapidity of the action on the zinc is increased #adi times1 and by the addition of copper sulphate is rendered #de times greater than the action of pure sulphuric acid4 ,the salts which are added are reduced to metals by the zinc1 their contact serving to promote the reaction because they form local galvanic currents4 ,according to the observations of ,cailletet1 if1 at the ordinary pressure1 sulphuric acid with zinc liberates #ajj parts of hydrogen1 then with a pressure of #fj atmospheres #dg parts will be liberated and #a part at a pressure of #abj atmospheres4 ,with a reduced pressure under the receiver of an air-pump #afh parts are liberated4 ,helmholtz showed that a reduced pressure also exercises its influence on galvanic elements4 ,debray1 ,lwel1 and others showed that zinc liberates hydrogen and forms basic salts and zinc oxide with solutions of many salts--for instance1 ,m,cln1 aluminium sulphate1 and alum1 ,sodium and potassium carbonates scarcely act1 because they form carbonates4 ,the salts of ammonia act more strongly than the salts of potassium and sodium2 the zinc remains bright4 ,it is evident that this action is founded on the formation of double salts and basic salts4 ,the variation with concentration in the rate of the action of sulphuric acid on zinc 7containing impurities7 under otherwise uniform conditions is in evident connection with the electrical conductivity of the solution and its viscosity1 although1 when largely diluted1 the action is almost proportional to the amount of acid in a known volume of the solution4 ,forging1 casting the molten metal1 and similar mechanical influences change the density and hardness of zinc1 and also strongly influence its power of liberating hydrogen from acids4 ,kayander showed 7#ahha7 that when magnesium is submitted to the action of acids3 7a7 the action depends1 not on the nature of the acid1 but on its basicity2 7b7 the increase of the action is more rapid than the growth of the concentration2 and 7c7 there is a decrease of action with the increase of the coefficient of internal friction and electrical conductivity4 ,spring and ,aubel 7#ahhg7 measured the volume of hydrogen disengaged by an alloy of zinc and a small quantity of lead 7#jf p4c471 because the action of acids is then uniform4 ,in order to deal with a known surface1 spheres were taken 7#ie millimetres diameter7 and cylinders 7#ag mm4 dia471 the sides of which were covered with wax in order to limit the action to the end surfaces4 ,during the commencement of the action of a definite quantity of acid the rapidity increases1 attains a maximum1 and then declines as the acid becomes exhausted4 ,the results for #e1 #aj1 and #ae per cent4 of hydrochloric acid are given below4 ,h denotes the number of cubic centimetres of hydrogen1 ,d the time in seconds elapsing after the zinc spheres have been plunged into the acid4 ,at #ae were obtained3 ,h #ej #ajj #bjj #djj #fjj #hjj #ajjj #e p4c4 ,d #gad #aaeb #agee #bgca #cijh #fbcd #aedfb #aj p4c4 ,d #cja #dee #fdi #iie #aegc #bgdf #fgdh #ae p4c4 ,d #ajf #aea #bcc #ddj #hbf #afjd #dbhi ,at #ce3 #e p4c4 ,d #dfb #gje #ajeh #agjj #bebe #dacb #hdii #aj p4c4 ,d #if #adh #bci #dfj #hce #aeid #cgce #ae p4c4 ,d #dd #fd #aab #bee #eje #ajaa #bdeg ,at #ee3 #e p4c4 ,d #agh #bgf #djh #fii #aafd #baje #ejic #aj p4c4 ,d #cd #fj #aac #beh #dia #igj #bdeg #ae p4c4 ,d #bd #ce #eh #acf #bci #faj #aeic ,in consequence of the complex character of the phenomenon1 the authors themselves do not consider their determinations as being conclusive1 and only give them a relative significance2 and in this connection it is remarkable that hydrobromic acid under similar conditions 7with an equivalent strength7 gives a greater 7from #b to #e times7 rapidity of action than hydrochloric acid1 but sulphuric acid a far smaller velocity 7nearly #be times smaller74 ,it is also remarkable that during the reaction the metal becomes much more heated than the acid4 ,it may be mentioned that zinc dust and zinc itself1 when heated with hydrated lime and similar hydrates1 disengages hydrogen3 this method has even been proposed for obtaining hydrogen for filling war balloons4 ,the action of zinc on acids1 and the consequent formation of zinc salts1 interferes with its application in many cases1 particularly for the preservation of liquids either containing or capable of developing acid4 ,for this reason zinc vessels ought not to be used for the preparation or preservation of food1 as this often contains acids which form poisonous salts with the zinc4 ,even ordinary water1 containing carbonic acid1 slowly attacks zinc4 ,finely divided zinc1 or zinc dust1 obtained in the distillation of the metal when the receiver is not heated up to the melting point1 on account of its presenting a large surface of contact and containing foreign matter 7particularly zinc oxide71 has in the highest degree the property of decomposing acids1 and even water1 which it easily decomposes1 particularly if slightly heated4 ,on this account zinc dust is often used in laboratories and factories as a reducing agent4 ,a similar influence of the finely divided state is also noticed in other metals--for instance1 copper and silver--which again shows the close connection between chemical and physico-mechanical phenomena4 ,we must first of all turn to this close connection for an explanation of the widely spread application of zinc in galvanic batteries1 where the chemical 7latent1 potential7 energy of the acting substances is transformed into 7evident1 kinetic7 galvanic energy1 and through this latter into heat1 light1 or mechanical work4 ,hermann and ,stromeyer1 in #ahai1 showed that cadmium is almost always found with zinc1 and in many respects resembles it4 ,when distilled the cadmium volatilises sooner1 because it has a lower boiling point4 ,sometimes the zinc dust obtained by the first distillation of zinc contains as much as #e per cent4 of cadmium4 ,when zinc blende1 containing cadmium1 is roasted1 the zinc passes into the state of oxide1 and the cadmium sulphide in the ore oxidises into cadmium sulphate1 ,cd,s,o#d1 which resists tolerably well the action of heat2 therefore if roasted zinc blende be washed with water1 a solution of cadmium sulphate will be obtained1 from which it is very easy to prepare metallic cadmium4 ,hydrogen sulphide may be used for separating cadmium from its solutions2 it gives a yellow precipitate of cadmium sulphide1 ,cd,s 7according to the equation ,cd,s,o#d ,h#b,s ,h#b,,so#d ,cd,s71#aa which1 on account of its characteristic colour1 is used as a pigment4#aa bis ,cadmium sulphide1 when strongly heated in air1 leaves cadmium oxide1 from which the metal may be obtained in precisely the same way as in the case of zinc4 #aa ,it may be here remarked that sulphate of zinc 7especially in the presence of mineral acids7 does not give a precipitate of sulphide of zinc1 or is only slightly precipitated by sulphuretted hydrogen4 #aa bis ,sulphide of cadmium appears in two varieties of a similar chemical but different physical character3 one is of a lemon colour1 and the other bright red4 ,kloboukoff 7#ahij7 studied the physical properties of these varieties more closely4 ,the sp4 gr4 of the former is #cijf1 and of the latter #deac4 ,they belong to different crystallographic systems4 ,the first variety may be converted into the second by friction or pressure1 but the second cannot be converted into the first variety by these means4 ,cadmium is a white metal1 and when freshly cut is almost as white and lustrous as tin4 ,it is so soft that it may be easily cut with a knife1 and so malleable that it can be easily drawn into wire1 rolled into sheets1 c4 ,its specific gravity is #hfg1 melting point #cbj1 boiling point #ggj2 its vapours burn1 forming a brown powder of the oxide4#ab ,next to mercury it is the most volatile metal2 hence ,deville determined the density of its vapours compared with hydrogen1 and found it to be equal to #ega2 therefore the molecule contains one atom whose weight #aab4 ,v4 ,meyer found the like for zinc2 the molecule of mercury also contains one atom4 #ab ,amongst the compounds of cadmium very closely allied to the compounds of zinc1 we must mention cadmium iodide1 ,cd,i#b1 which is used in medicine and photography4 ,this salt crystallises very well3 it is prepared by the direct action of iodine1 mixed with water1 on metallic cadmium4 ,one part of cadmium iodide at #bj requires for its solution #ajh part of water4 ,it may be remarked that cadmium chloride at the same temperature requires #jga part of water to dissolve it1 so that the iodine compound of this metal is less soluble than the chloride1 whilst the reverse relation holds in the case of the corresponding compounds of the alkali or alkaline earthy metals4 ,cadmium sulphate crystallises well1 and has the composition #c;,cd,s,o#d1h;,h#b,o1 thus differing from zinc sulphate4 ,cadmium oxide is soluble1 although sparingly1 in alkalis1 but in the presence of tartaric and certain other acids the alkaline solution of cadmium oxide does not change when boiled1 whilst a diluted solution in that case deposits cadmium oxide3 this may also serve for separating zinc compounds from those of cadmium4 ,cadmium is precipitated from its salts by zinc1 which fact may also be taken advantage of for separating cadmium2 for this reason1 in an alloy of zinc and cadmium1 acids first of all extract the zinc4 ,cadmium is in all respects less energetic than zinc4 ,thus1 for instance1 it decomposes water with difficulty1 and this only when strongly heated4 ,it even acts but slowly on acids1 but then displaces hydrogen from them4 ,it is necessary here to call attention to the fact that for alkali and alkaline earthy metals 7of the even series7 the highest atomic weight determines the greatest energy2 but cadmium 7of the uneven series71 whilst having a larger atomic weight than zinc1 is less energetic4 ,the salts of cadmium are colourless1 like those of zinc4 ,de ,schulten obtained a crystalline oxychloride1 ,cd7,,oh7,cl by heating marble with a solution of cadmium chloride in a sealed tube at #bjj4 ,mercury resembles zinc and cadmium in many respects1 but presents that distinction from them which is always noticed in all the heaviest metals 7with regard to atomic weight and density7 compared with the lighter ones--namely1 that it oxidises with more difficulty1 and its compounds are more easily decomposed4#ab bis ,besides compounds of the usual type ,,rx#b1 it also gives those of the lower type1 ,,rx1 which are unknown for zinc and cadmium4#ac ,mercury therefore gives salts of the composition ,hg,x 7mercurous salts7 and ,hg,x#b 7mercuric salts71 the oxides having the formul ,hg#b,o and ,hg,o respectively4 #ab bis ,according to its atomic weight1 mercury follows gold in the periodic system1 just as cadmium follows silver and zinc follows copper3-- ,ni #ei ,cu #fc ,zn #fe ,pd #ajf ,ag #ajh ,cd #aab ,pt #aif ,au #aih ,hg #bjj ,eventually we shall see the near relation of platinum1 palladium1 and nickel1 and also of gold1 silver1 and copper1 but we will now point out the parallelism between these three groups4 ,the relation between the physical and also chemical properties is here strikingly similar4 ,nickel1 palladium1 and platinum are very difficult to fuse 7far more so than iron1 ruthenium1 and osmium1 which stand before them74 ,copper1 silver1 and gold melt far more easily in a strong heat than the three preceding metals1 and zinc1 cadmium1 and mercury melt still more easily4 ,nickel1 palladium1 and platinum are very slightly volatile2 copper1 silver1 and gold are more volatile2 and zinc1 cadmium1 and mercury are among the most volatile metals4 ,zinc oxidises more easily than copper1 and is reduced with more difficulty1 and the same is true for mercury as compared with gold4 ,these properties for cadmium and silver are intermediate in the respective groups4 ,relations of this kind clearly show the nature of the periodic law4 #ac ,thus thallium1 lead1 and bismuth1 following mercury according to their atomic weights1 form1 besides compounds of the highest types1 ,tl,x#c1 ,pb,x#d1 and ,bi,x#e1 also the lower ones ,tl,x1 ,pb,x#b1 and ,bi,x#c4 ,mercury is found in nature almost exclusively in combination with sulphur 7like zinc and cadmium1 but is still rarer than them7 in the form known as cinnabar1 ,hg,s 7,chapter ,,xx41 ,note #bi74 ,it is far more rarely met with in the native or metallic condition1 and this in all probability has been derived from cinnabar4 ,mercury ore is found only in a few places--namely1 in ,spain 7in ,almaden71 in ,idria1 ,japan1 ,peru1 and ,california4 ,about the year #ahhj ,minenkoff discovered a rich bed of cinnabar in the ,bahmout district 7near the station of ,nikitovka71 in the ,government of ,ekaterinoslav1 so that now ,russia even exports mercury to other countries4 ,cinnabar is now being worked in ,daghestan in the ,caucasus4 ,mercury ores are easily reduced to metallic mercury1 because the combination between the metal and the sulphur is one of but little stability4 ,oxygen1 iron1 lime1 and many other substances1 when heated1 easily destroy the combination4 ,if iron is heated with cinnabar1 iron sulphide is formed2 if cinnabar is heated with lime1 mercury and calcium sulphide and sulphate are formed1 #d;,hg,s #d;,ca,o #d;,hg #c;,ca,s ,ca,s,o#d4 ,on being heated in the air1 or roasted1 the sulphur burns1 oxidises1 forming sulphurous anhydride1 and vapours of metallic mercury are formed4 ,mercury is more easily distilled than all other metals1 its boiling point being about #cea1 and therefore its separation from natural admixtures1 decomposed by one of the above-mentioned methods1 is effected at the expense of a comparatively small amount of heat4 ,the mixture of mercury vapour1 air1 and products of combustion obtained is cooled in tubes 7by water or air71 and the mercury condenses as liquid metal4#ad #ad ,during the condensation of the vapours of mercury in works1 a part forms a black mass of finely-divided particles1 which gives metallic mercury when worked up in centrifugal machines1 or on pressure1 or on re-distillation4 ,in mercury we observe a tendency to easily split up into the finest drops1 which are difficult to unite into a dense mass4 ,it is sufficient to shake up mercury with nitric and sulphuric acids in order to produce such a mercury powder4 ,the mercury separated 7for instance1 reduced by substances like sulphurous anhydride7 from solutions1 forms such a powder4 ,according to the experiments of ,nernst1 this disintegrated mercury when entering into reactions develops more heat than the dense liquid metal--that is to say1 the work of disintegration reappears in the form of heat4 ,this example is instructive in considering thermochemical deductions4 ,mercury1 as everybody knows1 is a liquid metal at the ordinary temperature4 ,in its lustre and whiteness it resembles silver4#ae ,at -#ci mercury is transformed into a malleable crystalline metal2 at #j its specific gravity is #aceif1 and in the solid state at -#dj it is #adci4af ,mercury does not change in the air--that is to say1 it does not oxidise at the ordinary temperature--but at a temperature approaching the boiling-point1 as was stated in the ,introduction1 it oxidises1 forming mercuric oxide4 ,both metallic mercury and its compounds in general produce salivation1 trembling of the hands1 and other unhealthy symptoms which are found in the workmen exposed to the influence of mercurial vapours or the dust of its compounds4 #ae ,mercury may sometimes be obtained in a perfectly pure state from works 7in iron bottles holding about #ce kilos71 but after being used in laboratories 7for baths1 calibration1 c47 it contains impurities4 ,it may be purified mechanically in the following way3 a paper filter with a fine hole 7pricked with a needle7 is placed in a glass funnel and mercury is poured into it1 which slowly trickles through the hole1 leaving the impurities upon the filter4 ,sometimes it is squeezed through chamois leather or through a block of wood 7as in the well-known experiment with the air-pump74 ,it may be purified from many metals by contact with dilute nitric acid1 if small drops of mercury are allowed to pass through a long column of it 7from the fine end of a funnel72 or by shaking it up with sulphuric acid in air4 ,mercury may be purified by the action of an electric current1 if it be covered with a solution of ,hg,n,o#c4 ,but the complete purification of mercury for barometers and thermometers can only be attained by distillation1 best in a vacuum 7the vapour-tension of mercury is given in ,chapter ,,ii41 ,note #bg74 ,for this purpose ,weinhold's apparatus is most often used4 ,the principle of this apparatus is very ingenious1 the distillation being effected in a ,torricellian vacuum continuously supplied with fresh mercury1 whilst the condensed mercury is continuously removed4 ,this process of distillation requires very little attention1 and gives about one kilo of pure mercury per hour4 #af ,if the volume of liquid mercury at #j be taken as #ajjjjjj1 then1 according to the determinations of ,regnault 7recalculated by me in #ahge71 at t it will be #ajjjjjj #ahjat #jjbt#b4 ,as many of the compounds of mercury decompose on being heated--for instance1 the oxide or carbonate#ag--;and as zinc1 cadmium1 copper1 iron1 and other metals separate mercury from its salts1#ah it is evident that mercury has less chemical energy than the metals already described1 even than zinc and cadmium4 ,nitric acid1 when acting on an excess of mercury at the ordinary temperature1 gives mercurous nitrate1 ,hg,n,o#c4ai ,the same acid1 under the influence of heat and when in excess 7nitric oxide being liberated71 forms mercuric nitrate1 ,hg7,,no#c7b4 ,this1#bj both in its composition and properties1 resembles the salts of zinc and cadmium4 ,dilute sulphuric acid does not act on mercury1 but strong sulphuric acid dissolves it1 with evolution of sulphurous anhydride 7not hydrogen71 and on being slightly heated with an excess of mercury it forms the sparingly soluble mercurous sulphate1 ,hg#b,,so#d2 but if mercury be strongly heated with an excess of the acid1 the mercuric salt1 ,hg,s,o#d1ba is formed4 ,alkalis do not act on mercury1 but the non-metals chlorine1 bromine1 sulphur1 and phosphorus easily combine with it4 ,they form1 like the acids1 two series of compounds1 ,hg,x and ,hg,x#b4 ,the oxygen compound of the first series is the suboxide of mercury1 or mercurous oxide1 ,hg#b,o1 and of the second order the oxide ,hg,o1 mercuric oxide4 ,the chlorine compound corresponding with the suboxide is ,hg,cl 7calomel71 and with the oxide ,hg,cl#b 7corrosive sublimate or mercuric chloride74 ,in the compounds ,hg,x1 mercury resembles the metals of the first group1 and more especially silver4 ,in the mercuric compounds there is an evident resemblance to those of magnesium1 cadmium1 c4 ,here the atom of mercury is bivalent1 as in the type ,,rx#b4bb ,every soluble mercurous compound 7corresponding with the type of the suboxide of mercury71 ,hg,x1 forms a white precipitate of calomel1 ,hg,cl1 with hydrochloric acid or a metallic chloride1 because ,hg,cl is very slightly soluble in water1 ,hg,x ,m,cl ,hg,cl ,,mx4 ,in soluble mercuric compounds1 ,hg,x#b1 hydrochloric acid and metallic chlorides do not form a precipitate1 because corrosive sublimate1 ,hg,cl#b1 is soluble in water4 ,alkali hydroxides precipitate the yellow mercuric oxide from a solution of ,hg,x#b1 and the black mercurous oxide from ,hg,x4 ,potassium iodide forms a dirty greenish precipitate1 ,hg,i1 with mercurous salts1 ,hg,x1 and a red precipitate1 ,hg,i#b1 with the mercuric salts1 ,hg,x#b4 ,these reactions distinguish the mercuric from the mercurous salts1 which latter represent the transition from the mercuric salts to mercury itself1 #b;,hg,x ,hg ,hg,x#b4 ,the salts1 ,hg,x1 as well as ,hg,x#b1 are reduced by nascent hydrogen 7e4g4 from ,zn ,h#b,,so#d71 by such metals as zinc and copper1 and also by many reducing agents--for example1 hypophosphorous acid1 the lowest grade of oxidation of phosphorus1 by sulphurous anhydride1 stannous chloride1 c4 ,under the action of these reagents the mercuric salts are first transformed into the mercurous salts1 and the latter are then reduced to metallic mercury4 ,this reaction is so delicate that it serves to detect the smallest quantity of mercury2 for instance1 in cases of poisoning1 the mercury is detected by immersing a copper plate in the solution to be tested1 the mercury being then deposited upon it 7more readily on passing a galvanic current74 ,the copper plate1 on being rubbed1 shows a silvery white colour2 on being heated1 it yields vapours of mercury1 and then again assumes its original red colour 7if it does not oxidise74 ,the mercurous compounds1 ,hg,x1 under the action of oxidising agents1 even air1 pass into mercuric compounds1 especially in the presence of acids 7otherwise a basic salt is produced71 #b;,hg,x #b;,,hx ,o #b;,hg,x#b ,h#b,o2 but the mercuric compounds1 when in contact with mercury1 change more or less readily1 and turn into mercurous compounds1 ,hg,x#b ,hg #b;,hg,x4 ,for this reason1 in order to preserve solutions of mercurous salts1 a little mercury is generally added to them4 #ag ,all salts of mercury1 when mixed with sodium carbonate and heated1 give mercurous or mercuric carbonates2 these decompose on being heated1 forming carbonic anhydride1 oxygen1 and vapours of mercury4 #ah ,spring 7#ahhh7 showed that1 solid dry ,hg,cl is gradually decomposed in contact with metallic copper4 ,according to the determinations of ,thomsen1 the formation of a gram of mercurial compounds from their elements develops the following amounts of heat 7in thousands of units73 ,hg#b ,o1 #db2 ,hg ,o1 #ca2 ,hg ,s1 #ag2 ,hg ,cl1 #da2 ,hg ,br1 #cd2 ,hg ,i1 #bd2 ,hg ,cl#b1 #fc2 ,hg ,br#b1 #ea2 ,hg ,i#b1 #cd2 ,hg ,c#b,n#b1 #ai4 ,these numbers are less than the corresponding ones for potassium1 sodium1 calcium1 barium1 and for zinc and cadmium--for instance1 ,zn ,o1 #he2 ,zn ,cl#b1 #ig2 ,zn ,br#b1 #gf2 ,zn ,i#b1 #di2 ,cd ,cl#b1 #ic2 ,cd ,br#b1 #ge2 ,cd ,i#b1 #di4 #ai ,this salt easily forms the crystallo-hydrate ,hg,n,o#c1;,h#b,o1 corresponding with ortho-nitric acid1 ,h#c,,no#d 7the terms ortho-1 pyro-1 and meta-acids are explained in the chapter on ,phosphorus71 with the substitution of ,hg for ,h4 ,in an aqueous solution this salt can only be preserved in the presence of free mercury1 otherwise it forms basic salts1 which will be mentioned hereafter 7,chapter ,,vi41 ,note #ei74 #bj ,mercuric nitrate1 ,hg7,,no#c7b1h;,h#b,o1 crystallises from a concentrated solution of mercury in an excess of boiling nitric acid4 ,water decomposes this salt2 at the ordinary temperature crystals of a basic salt of the composition ,hg7,,no#c7b1;,hg,o1#b;,h#b,o are formed1 and with an excess of water the insoluble yellow basic salt ,hg7,,no#c7b1;,h#b,o1#b;,hg,o4 ,these three salts correspond with the type of ortho-nitric acid1 7,h#c,,no#d7b1 in which mercury is substituted for #a1 #b and #c times ,h#b4 ,as all these salts still contain water1 it is possible that they correspond with the tetrahydrate ,n#b,o#e #d;,h#b,o ,n#b,o7,,oh7#h if ortho-nitric acid ,n#b,o#e #c;,h#b,o #b,,no7,,oh7#c4 #ba ,to obtain the mercuric salt a large excess of strong sulphuric acid must be taken and strongly heated4 ,with a small quantity of water colourless crystals of ,hg,s,o#d1;,h#b,o may be obtained4 ,an excess of water1 especially when heated1 forms the basic salt 7as in ,note #bj71 ,hg,s,o#d1b;,hg,o1 which corresponds with trihydrated sulphuric acid1 ,,so#c #c;,h#b,o ,s7,,oh7#f1 with the substitution of ,h#f by #c;,hg1 which in mercuric salts is equivalent to ,h#f4 ,le ,chatelier 7#ahhh7 gives the following ratio between the amounts of equivalents per litre3 ,hg,s,o#d #jcah #jhij #ahj #bjb ,,so#c #jgeb #adb #baj #bdj --that is1 the relative amount of free acid decreases as the strength of the solution increases4 #bb ,the question of the molecular weight of calomel--that is1 whether the mercury in the salts of the suboxide is monatomic or diatomic--long occupied the minds of chemists1 although it is not of very great importance4 ,it is only recently 7#ahid7 that this question can be considered as answered1 thanks to the researches of ,v4 ,meyer and ,harris1 in favour of diatomicity--that is1 that calomel is analogous to peroxide of hydrogen and contains ,hg#b;,cl#b 7like ,o#b;,h#b7 in its molecule if corrosive sublimate contains ,hg,cl#b 7like water ,,oh#b74 ,as a matter of fact1 direct experiment gives the vapour density of calomel as about #aah--that is1 indicates that its molecule contains ,hg,cl1 whilst the molecule of the sublimate1 judging also by the vapour density 7nearly #acf71 contains ,hg,cl#b2 it might therefore be concluded that the mercury in the suboxide is not only monovalent 7corresponding to ,h7 but also monatomic1 whilst in the oxide it is divalent and diatomic4 ,instances of a variable atomicity1 as shown by the vapour density1 are known in ,n#b,o1 ,,no1 and ,,nh#c1 ,,co and ,,co#b1 ,p,cl#c and ,p,cl#e1 and it might therefore be supposed that the present was a similar instance4 ,but there are also instances of a variable equivalency which do not correspond to a variation of atomicity--for example1 ,,oh#b 7water7 and ,,oh 7peroxide of hydrogen71 ,,ch#d 7methane71 ,c#b;,h#e 7ethyl71 and ,,ch#b 7ethylene71 c4 ,here1 according to the law of substitution1 the residues of ,,oh#b and ,,ch#d combine together and give molecules2 ,,ohoh ,o#b;,h#b 7peroxide of hydrogen7 and ,,ch#c;,,ch#c ,c#b;,h#f 7ethane71 c4 ,the same may be assumed also to be the relation of calomel to sublimate2 the residue ,hg,cl1 which is combined with ,cl in sublimate1 corresponds to ,hg,cl#b1 and in calomel it may be supposed that this residue is combined with itself1 forming the molecule ,hg#b;,cl#b4 ,on this view of the composition of the molecule of calomel it would follow that in the state of vapour it breaks up into two molecules1 ,hg,cl#b and ,hg1 when the vapour density would be about #aah 7because that of sublimate is about #acf and that of mercury about #ajj71 and that in cooling this mixture 7like a mixture of ,h,cl and ,,nh#c7 again gives ,hg#b;,cl#b4 ,it was therefore necessary to prove that calomel is decomposed in the state of vapour4 ,this was not effected for a long time1 although ,odling1 as far back as the thirties1 showed that gold becomes amalgamated 7i4e4 absorbs metallic mercury7 in the vapour of calomel1 but not in the vapour of sublimate4 ,recently1 however1 ,v4 ,meyer and ,harris 7#ahid7 have shown that a greater amount of the vapour of mercury than of calomel passes 7at about #dfe7 through a porous clay cell1 containing calomel4 ,this proves that the vapour of calomel contains a mixture of the vapours of ,hg and ,hg,cl#b1 as would follow from the second hypothesis4 ,moreover1 on introducing a heated piece of ,,kho into the vapour of calomel1 ,meyer observed the formation1 not of suboxide 7black71 but of oxide of mercury 7yellow74 ,therefore the molecular formula of calomel must be taken as ,hg#b;,cl#b 7and not ,hg,cl74 ,the lowest oxygen compound of mercury--that is1 mercurous oxide1 ,hg#b,o--does not seem to exist1 for the substance precipitated in the form of a black mass by the action of alkalis on a solution of mercurous salts gradually separates on keeping into the yellow mercuric oxide and metallic mercury1 as does also a simple mechanical mixture of oxide1 ,hg,o1 with mercury 7,guibourt1 ,barfoed74 ,the other compound of mercury with oxygen is already known to us as mercuric oxide1 ,hg,o1 obtained in the form of a red crystalline substance by the oxidation of mercury in the air1 and precipitated as a yellow powder by the action of sodium hydroxide on solutions of salts of the type ,hg,x#b4 ,in this case it is amorphous and more amenable to the action of various reagents 7,chap4 ,,xi41 ,note #cb7 than when it is in the crystalline state4 ,indeed1 on trituration1 the red oxide is changed into a powder of a yellow colour4 ,it is very sparingly soluble in water1 and forms an alkaline solution which precipitates magnesia from the solution of its salts4 ,mercury combines directly with chlorine1 and the first product of combination is calomel or mercurous chloride1 ,hg#b;,cl#b4 ,this is obtained1 as above stated1 in the form of a white precipitate by mixing solutions of mercurous salts with hydrochloric acid or with metallic chlorides4 ,a precipitate of calomel is also obtained by reducing a boiling aqueous solution of corrosive sublimate1 ,hg,cl#b1 with sulphurous anhydride4 ,it is likewise produced by heating corrosive sublimate with mercury4#bb bis ,calomel may be distilled 7although in so doing it decomposes and recombines on cooling from a state of vapour72 its vapour density equals #aah compared with hydrogen 7 #a7 7see ,note #bc74 ,in the solid state its specific gravity is #gj2 it crystallises in rhombic prisms1 is colourless1 but has a yellowish tint1 turns brown from the action of light1 and when boiled with hydrochloric acid decomposes into mercury and corrosive sublimate4 ,it is used as a strong purgative4 ,corrosive sublimate or mercuric chloride1 ,hg,cl#b1 can be obtained from or converted into calomel by many methods4#bc ,an excess of chlorine 7for instance1 aqua regia7 converts calomel and also mercury into corrosive sublimate4 ,it owes its name corrosive sublimate to its volatility1 and1 in medicine up to the present day1 it is termed ,mercurius sublimatus seu corrosivus4 ,the vapour density1 compared with hydrogen 7 #a7 is #ace2 therefore its molecule contains ,hg,cl#b4 ,it forms colourless prismatic crystals of the rhombic system1 boils at #cjg1 and is soluble in alcohol4 ,it is usually prepared by subliming a mixture of mercuric sulphate with common salt1 ,hg,s,o#d #b,na,cl ,na#b,,so#d ,hg,cl#b4 ,corrosive sublimate combines with mercuric oxide1 forming an oxychloride or basic salt1#bc bis of the composition ,hg,cl#b1b;,hg,o 7magnesium and zinc form similar compounds74 ,this compound is obtained by mixing a solution of corrosive sublimate with mercuric oxide or with a solution of sodium bicarbonate4 ,in general1 with both mercurous and mercuric salts1 there is a marked tendency to form basic salts4#bd #bb bis ,calomel 7in ,japanese ',keyfun'7 has been prepared in ,japan 7and ,china7 for many centuries1 by heating mercury in clay crucibles with sea salt1 which contains ,mg,cl#b and gives ,h,cl4 ,the vapour of the mercury reacts with this ,h,cl and the oxygen of the air and forms calomel3 #b;,hg #b;,h,cl ,o ,hg#b;,cl#b ,h#b,o4 ,the calomel collects on the lid of the crucible in the form of a sublimate 7,divers1 #ahid74 #bc ,hg,cl#b is partially converted into calomel even in the act of dissolving in ordinary water1 especially under the action of light4 #bc bis ,as feebly energetic bases 7for instance1 the oxides ,mg,o1 ,zn,o1 ,pb,o1 ,cu,o1 ,al#b,o#c1 ,bi#b,o#c1 c471 mercuric oxide 7see ,notes #bj1 #ba7 and mercurous oxide easily give basic salts1 which are usually directly formed by the action of water on the normal salt1 according to the general equation 7for mercuric compounds1 ,,rx#b73 n,,rx#b m,h#b,o #bm,,hx 7n-m7,,rx#bm,,ro neutral salt water acid basic salt or else are produced directly from the normal salt and the oxide or its hydroxide4 ,thus mercurous nitrate1 when treated with water1 forms basic salts of the composition #f7;,hg,n,o#c71;,hg#b,o1,h#b,o1 #b7;,hg,n,o#c71;,hg#b,o1,h#b,o1 and #c7;,hg,n,o#c71;,hg#b,o1,h#b,o1 the first two of which crystallise well4 ,naturally it is possible either to refer similar salts to the type of hydrates--for instance1 the second salt to the hydrate ,n#b,o#e1d;,h#b,o--or to view it as a compound1 ,hg,n,o#c1;,hg,h,o1 but our present knowledge of basic salts is not sufficiently complete to admit of generalisations4 ,however1 it is already possible to view the subject in the following aspects3 7#a7 basic salts are principally formed from feeble bases2 7#b7 certain metals 7mentioned above7 form them with particular ease1 so that one of the causes of the formation of many basic salts must depend on the property of the metal itself2 7#c7 those bases which readily form basic salts as a rule also readily form double salts2 7#d7 in the formation of basic salts1 as also everywhere in chemistry1 where sufficient facts have accumulated1 we clearly see the conditions of equally balanced heterogeneous systems1 such as we saw1 for instance1 in the formation of double salts1 crystallo-hydrates1 c4 ,the mercuric salts often form double salts 7confirming the third thesis71 and mercuric chloride easily combines with ammonia1 forming ,hg7,,nh#d7b;,cl#d1 or in general ,hg,cl#bn,m,cl4 ,if a mixture of mercurous and potassium sulphates be dissolved in dilute sulphuric acid1 the solution easily yields large colourless crystals of a double salt of the composition ,k#b,,so#d1c;,hg,s,o#d1b;,h#b,o4 ,boullay obtained crystalline compounds of mercuric chloride with hydrochloric acid1 and mercuric iodide with hydriodic acid2 and ,thomsen describes the compound ,hg,br#b1;,h,br1#d;,h#b,o as a well-crystallised salt1 melting at #ac1 and having1 in a molten state1 a specific gravity #cag and a high index of refraction4 ,moreover1 the capacity of salts for forming basic compounds has been considerably cleared up since the investigation 7by ,wrtz1 ,lorenz1 and others7 of glycol1 ,c#b;,h#d7,,oh7#b 7and of polyatomic alcohols resembling it71 because the ethers ,c#b;,h#d,x#b1 corresponding with it1 are capable of forming compounds containing ,c#b;,h#d,x#bn,c#b;,h#d,o4 ,on the other hand1 there is reason to think that the property of forming basic salts is connected with the polymerisation of bases1 especially colloidal ones 7see the chapter on ,silica1 ,lead ,salts1 and ,tungstic ,acid74 #bd ,mercuric iodide1 ,hg,i#b1 is obtained first as a yellow1 and then as a red1 precipitate on mixing solutions of mercuric salts and potassium iodide1 and is soluble in an excess of the latter 7in consequence of the formation of the double salt1 ,hg,k,i#c72 of ammonium chloride 7for a similar reason71 c4 ,it crystallises at the ordinary temperature in square prisms of a red colour4 ,on being heated1 these change into yellow rhombic crystals1 isomorphous with mercuric chloride4 ,this yellow form of mercuric iodide is very unstable1 and when cooled and triturated easily again assumes the more stable red form4 ,when fused1 a yellow liquid is obtained4 ,mercuric cyanide1 ,hg7,,cn7#b1 forms one of the most stable metallic cyanides4 ,it is obtained by dissolving mercuric oxide in prussic acid1 and by boiling ,prussian blue with water and mercuric oxide1 ferric oxide being then obtained in the precipitate4 ,mercuric cyanide is a colourless crystalline substance1 soluble in water1 and distinguished by its great stability2 sulphuric acid does not liberate prussic acid from it1 and even caustic potash does not remove the cyanogen 7a complex salt is probably produced71 but the halogen acids disengage ,,hcn4 ,like the chloride1 it combines with mercuric oxide1 forming the oxycyanide1 ,hg#b,o7,,cn7#b1 and it shows a very marked tendency to form double compounds--for example1 ,k#b;,hg7,,cn7#d4 ,the alkali chlorides and iodides form similar compounds--for instance1 the salt ,hg,k,i7,,cn7#b crystallises very well1 and is produced by directly mixing solutions of potassium iodide and mercuric cyanide4 ,wells 7#ahhi7 and ,vare obtained and investigated many such double salts1 and showed the possibility of the formation1 not only of ,hg,cl#b,m,cl and ,hg,cl#bb,m,cl where ,m is a metal of the alkalis--for example1 ,cs--but also of ,hg,cl#bc,m,cl1#b7;,hg,cl#b7,m,cl1 and in general n,hg,x#bm,,mx1 where ,x stands for various haloids4 ,mercury has a remarkable power of forming very unstable compounds with ammonia1 in which the mercury replaces the hydrogen1 and1 if a mercuric compound be taken1 its atom occupies the place of two atoms of the hydrogen in the ammonia4 ,thus ,plantamour and ,hirtzel showed that precipitated mercuric oxide dried at a gentle heat1 when continuously heated 7up to #ajj-aej7 in a stream of dry ammonia1 leaves a brown powder of mercuric nitride1 ,n#b;,hg#c1 according to the equation #c;,hg,o #b,,nh#c ,n#b;,hg#c #c;,h#b,o4#bd bis ,this substance1 which is attacked by water1 acids1 and alkalis 7giving a white powder71 is very explosive when struck or rubbed1 evolving nitrogen1 proving that the bond between the mercury and the nitrogen is very feeble4#be ,by the action of liquefied ammonia on yellow mercuric oxide ,weitz also obtained an explosive compound1 dimercurammonium hydroxide1 ,n#b;,hg#d,o1 which corresponds with an ammonium oxide1 7,,nh#d7b,o1 in which the whole of the hydrogen is replaced by mercury4 ,a solution of ammonia reacts with mercuric oxide1 forming the hydroxide1 ,n,hg#b4,,oh1 to which a whole series of salts1 ,n,hg#b,x1 correspond2 these are generally insoluble in water and capable of decomposing with an explosion4 ,but salts of the same type1 but with one atom of mercury1 ,,nh#b;,hg,x1 are more frequently and more easily formed2 they were principally studied by ,kane1 although known much earlier4 ,thus1 if ammonia be added to a solution of corrosive sublimate 7or1 still better1 in reverse order71 a precipitate is obtained known as white precipitate 7,mercurius prcipitatus albus7 or mercurammonium chloride1 ,,nh#b;,hg,cl1 which may also be regarded not only as sal-ammoniac with the substitution of ,h#b by mercury1 but also as ,hg,x#b1 where one ,x represents ,cl and the other ,x represents the ammonia radicle1 ,hg,cl#b #b,,nh#c ,,nh#b4;,hg,cl ,,nh#d;,cl4 ,when heated1 mercurammonium chloride decomposes1 yielding mercurous chloride2 when heated with dry hydrochloric acid it forms ammonium chloride and mercuric chloride4 ,other simple and double salts of mercurammonium1 ,,nh#b;,hg,x1 are also known4 ,pici 7#ahij7 showed that all the compounds ,hg,h#b,,nx may be regarded as compounds of the above-named ,hg#b,,nx with ,,nh#d,x because their sum equals #b;,hg,h#b,x4#be bis #bd bis ,see ,chapter ,,xix41 ,note #f bis3 ,hg#c,p#b4 ,in studying the metallic nitrides it is necessary to keep the corresponding phosphides in mind4 #be ,hg#c,n#b is similar in composition to ,mg#c,n#b1 c4 7,chapter ,,xiv47 ,the readiness with which mercuric nitride explodes shows that the connection between the nitrogen and the mercury is very unstable1 and explains the circumstance that the so-called mercury fulminate1 or fulminating mercury1 is an exceedingly explosive substance4 ,this substance is prepared in large quantities for explosive mixtures2 it enters into the composition of percussion caps1 which explode when struck1 and ignite gunpowder4 ,mercury fulminate was discovered by ,howard1 and from that time has been prepared in the following way3 one part of mercury is dissolved in twelve parts of nitric acid1 of sp4 gr4 #acf1 and when the whole of the mercury is dissolved1 #ee parts of #ij p4c4 alcohol are added1 and the mass is shaken4 ,a reaction then commences1 accompanied by a rise in temperature due to the oxidation of the alcohol4 ,as a matter of fact1 many oxidation products are produced during the action of the nitric acid on the alcohol 7glycolic acid1 ethers1 c47 ,when the reaction becomes tolerably vigorous1 the same quantity of alcohol is added as at the commencement1 when a grey precipitate of the fulminate separates4 ,this salt has the composition ,c#b;,hg7,,no#b7,n4 ,it explodes when struck or heated4 ,the mercury in it may be replaced by other metals--for instance1 copper or zinc1 and also silver4 ,the silver salt1 ,c#b;,ag#b7,,no#b7,n1 is obtained in a precisely analogous manner1 and is even more explosive4 ,under the action of alkali chlorides1 only half the silver is replaced by the alkali metal1 but if the whole of the silver be replaced by an alkali metal1 then the salt decomposes4 ,this is evidently because combinations of this kind proceed in virtue of the formation of substances in which mercury1 and metals akin to it1 are connected in an unstable way with nitrogen4 ,potassium and other light metals are incapable of entering into such connection and therefore1 the substitution of potassium for mercury entails the splitting-up of the combination4 ,investigations of the fulminates were carried on by ,gay-,lussac and ,liebig1 but only the investigations of ,l4 ,n4 ,shishkoff fully cleared up the composition and relation of these substances to the other carbon compounds4 ,shishkoff showed that fulminates correspond with the nitro-acid1 ,c#b;,h#b7,,no#b7,n4 ,the explosiveness of the group depends partly on its containing at the same time ,,no#b and carbon2 we already know that all such nitrogen compounds are explosive4 ,if we imagine that the ,,no#b is replaced by hydrogen1 we shall have a substance of the composition ,c#b;,h#c,n4 ,this is acetonitrile--that is1 acetic acid ,,nh#c - #b;,h#b,o1 or ethenyl nitrile1 as shown in ,chapter ,,vi4 ,the formation of an acetic compound by the action of nitric acid on alcohol is easily understood1 because acetic acid is produced by the oxidation of alcohol1 and the production of the elements of ammonia1 indispensable for the formation of a nitrile1 is accounted for by the fact that nitric acid under the action of reducing substances in many cases forms ammonia4 ,moreover a certain analogy has been found between fulminating acid and hydroxylamine1 but details upon this subject must be looked for in works on organic chemistry4 ,the explosiveness of fulminating mercury1 the rapidity of its decomposition 7gunpowder1 and even guncotton1 burn more slowly and explode less violently71 and the force of its explosion1 are such that a small quantity 7loosely covered7 will shatter massive objects4 ,the investigations of ,abel on the communication of explosion from one substance to another are remarkable4 ,if guncotton be ignited in an open space1 it burns quietly2 but if fulminating mercury be exploded by the side of it1 the decomposition of the guncotton is effected instantaneously1 and it then shatters the objects upon which it lies1 so rapid is the decomposition4 ,abel explains this by supposing that the explosion of the fulminating salt brings the molecules of guncotton into a uniform or as it were harmonious state of vibration1 which causes the rapid decomposition of the whole mass4 ,this rapid decomposition of explosive substances defines the distinction between explosion and combustion4 ,besides this1 ,berthelot showed that from that form of powerful molecular concussion which takes place during the explosion of fulminating mercury1 the state of strain and stability of equilibrium of substances which are endothermal1 or capable of decomposing with the disengagement of heat--for instance1 cyanogen1 nitro compounds1 nitrous oxide1 c4--is generally destroyed4 ,thorpe showed that carbon bisulphide1 ,,cs#b1 also an endothermal substance1 decomposes into sulphur and charcoal1 when fulminating mercury is exploded in contact with it4 #be bis ,the capacity for replacing hydrogen in chloride of ammonium by metals also belongs to ,zn and ,cd4 ,kvasnik 7#ahib71 by the action of ammonia upon alcoholic solutions of ,cd,cl#b and ,zn,cl#b1 obtained substances of the general formula ,m7,,nh#c;,cl7#b1 formed as it were from two molecules of sal-ammoniac by the substitution of two atoms of hydrogen by a diatomic metal4 ,these substances appear as white1 finely crystalline powders4 ,under the action of heat half the ammonia passes off1 and a compound of the composition ,m,cl,n,h#c;,cl is formed4 ,the compounds of cadmium and zinc are distinguished from each other by the former being more volatile than the latter4 ,we may further remark that in the series ,mg1 ,zn1 ,cd1 and ,hg the capacity to form double salts of diverse composition increases with the atomic weight4 ,thus1 according to ,wells and ,walden's observations 7#ahic71 the ratio n 3 m for the type n,m,clm,r,cl#b 7,m ,k1 ,li1 ,na 444 ,r ,mg1 ,zn 4447 is for ,mg #a 3 #a1 for ,zn #c 3 #a1 #b 3 #a1 and #a 3 #a2 for ,cd1 besides this1 salts are known with the ratio #d 3 #a1 and for ,hg #c 3 #a1 #b 3 #a1 #a 3 #a1 #b 3 #c1 #a 3 #b1 and #a 3 #e4 ,mercury as a liquid metal is capable of dissolving other metals and forming metallic solutions4 ,these are generally called 'amalgams4' ,the formation of these solutions is often accompanied by the development of a large amount of heat--for instance1 when potassium and sodium are dissolved 7,chapter ,,xii41 ,note #ci72 but sometimes heat is absorbed1 as1 for instance1 when lead is dissolved4 ,it is evident that phenomena of this kind are exceedingly similar to the phenomena accompanying the dissolution of salts and other substances in water1 but here it is easy to demonstrate that which is far more difficult to observe in the case of salts3 the solution of metals in mercury is accompanied by the formation of definite chemical compounds of the mercury with the metals dissolved4 ,this is shown by the fact that when pressed 7best of all in chamois leather7 such solutions leave solid1 definite compounds of mercury with metals4 ,it is1 however1 very difficult to obtain them in a pure state1 on account of the difficulty of separating the last traces of mercury1 which is mechanically distributed between the crystals of the compounds4 ,nevertheless1 in many cases such compounds have undoubtedly been obtained1 and their existence is clearly shown by the evident crystalline structure and characteristic appearance of many amalgams4 ,thus1 for instance1 if about #b-a_/b p4c4 of sodium be dissolved in mercury1 a hard1 crystalline amalgam is obtained1 very friable and little changeable in air4 ,it contains the compound ,na,hg#e 7,chapter ,,xii41 ,note #ci74 ,water decomposes it1 with the evolution of hydrogen1 but more slowly than other sodium amalgams1 and this action of water only shows that the bond between the sodium and the mercury is weak1 just like the connection between mercury and many other elements--for instance1 nitrogen4 ,mercury directly and easily dissolves potassium1 sodium1 zinc1 cadmium1 tin1 gold1 bismuth1 lead1 c41 and from such solutions or alloys it is in most cases easy to extract definite compounds--thus1 for instance1 the compounds of mercury and silver have the compositions ,hg,ag and ,ag#b;,hg#c4 ,objects made of copper when rubbed with mercury become covered with a white coating of that metal1 which slowly forms an amalgam2 silver acts in the same way1 but more slowly1 and platinum combines with mercury with still greater difficulty4 ,this metal only readily forms an amalgam when in the form of a fine powder4 ,if salts of platinum in solution are poured on to an amalgam of sodium1 the latter element reduces the platinum1 and the platinum separated is dissolved by the mercury4 ,almost all metals readily form amalgams if their solutions are decomposed by a galvanic current1 where mercury forms the negative pole4 ,in this way an amalgam may even be made with iron1 although iron in a mass does not dissolve in mercury4 ,some amalgams are found in nature--for instance1 silver amalgams4 ,amalgams are used in considerable quantities in the arts4 ,thus the solubility of silver in mercury is taken advantage of for extracting that metal from the ore by means of amalgamation1 and for silvering by fire4 ,the same is the case with gold4 ,tin amalgam1 which is incapable of crystallising and is obtained by dissolving tin in mercury1 composes the brilliant coating of ordinary looking-glasses1 which is made to adhere to the surface of the polished glass by simply pressing by mechanical means sheets of tin foil bathed in mercury on to the cleansed surface of the glass4#bf 7,see ',the ,nature of ,amalgams1' by ,w4 ,l4 ,dudley2 ,toronto1 #ahhi47 #bf ,i consider it appropriate here to call attention to the want of an element 7ekacadmium7 between cadmium and mercury in the periodic system 7,chapter ,,xv47 ,but as in the ninth series there is not a single known element1 it may be that this series is entirely composed of elements incapable of existing under present conditions4 ,however1 until this is proved in one way or another1 it may be concluded that the properties of ekacadmium will be between those of cadmium and mercury4 ,it ought to have an atomic weight of about #aee1 to form an oxide ,ec,o1 a slightly stable oxide ,ec#b,o4 ,both ought to be feeble bases1 easily forming double and basic salts4 ,the volume of the oxide will be nearly #age1 because the volume of cadmium oxide is about #af1 and that of mercuric oxide #ai4 ,therefore the density of the oxide will approach #aga #age #ig4 ,the metal ought to be easily fusible1 oxidising when heated1 of a grey colour1 with a specific volume1 about #ad 7cadmium #ac1 mercury #ae71 and1 therefore1 its specific gravity 7#aee #ad7 will nearly #aa4 ,such a metal is unknown4 ,but in #ahgi ,dahl1 in ,norway1 discovered in the island of ,oter1 not far from ,krager1 in a vein of ,iceland spar in a nickel mine1 traces of a new metal which he called norwegium1 and which presented a certain resemblance to ekacadmium4 ,perfect purity of the metal was not attained1 and therefore the properties ascribed to norwegium must be regarded as approximate1 and likely to undergo considerable alteration on further study4 ,a solution of the roasted mineral in acid was twice precipitated by sulphuretted hydrogen1 and again ignited2 the oxide obtained was easily reduced4 ,when the metal was dissolved in hydrochloric acid largely diluted with water1 and the solution boiled1 the basic salt was precipitated1 and thus freed from the copper which remained in the solution4 ,the reduced metal had a density #idd1 and easily oxidised4 ,if the composition ,ng,o be assigned to the oxide1 then ,ng #adei4 ,it fused at #bed2 the hydroxide was soluble in alkalis and potassium carbonate4 ,in any case1 if norwegium is not a mixture of other metals1 it belongs to the uneven series1 because the heavy metals of the even series are not easily reducible4 ,brauner thinks that norwegium oxide is ,ng#b,o#c1 the atom ,ng #bai1 and places it in ,group ,,vi41 series #aa1 but then the feebly acid higher oxide1 ,ng,o#c1 ought to be formed4 ,amongst the metals accompanying zinc which have been named1 but not authentically separated1 must be included the actinium of ,phipson 7#ahha74 ,he remarked that certain sorts of zinc give a white precipitate of zinc sulphide which blackens on exposure to light and then becomes white in the dark again4 ,its oxide1 closely resembling in many ways cadmium oxide1 is insoluble in alkalis1 and it forms a white metallic sulphide1 blackening on exposure to light4 ,as no further mention has been made of it since #ahhb1 its existence must be regarded as doubtful4 ,,chapter ,,xvii ,,boron1 ,,aluminium1 ,,and ,,the ,,analogous ,,metals ,,of ,,the ,,third ,,group ,if the elements of small atomic weight which we have hitherto discussed be placed in order1 it will be clearly seen that1 judging by the formul of their higher compounds1 one element is wanting between beryllium and carbon4 ,for lithium gives ,li,x1 beryllium forms ,be,x#b1 and then comes carbon giving ,,cx#d4 ,evidently to complete the series we must look for an element forming ,,rx#c1 and having an atomic weight greater than #i and less than #ab4 ,and boron is such a one2 its atomic weight is #aa1 and its compounds are expressed by ,,bx#c4 ,lithium and beryllium are metals2 carbon has no metallic properties2 boron appears in a free state in several forms which are intermediate between the metals and non-metals4 ,lithium gives an energetic caustic oxide1 beryllium forms a very feeble base2 hence one would expect to find that the oxide of boron1 ,b#b,o#c1 has still more feeble basic properties and some acid properties1 all the more as ,,co#b and ,n#b,o#e1 which follow after ,b#b,o#c in their composition and in the periodic system1 are acid oxides4 ,and1 indeed1 the only known oxide of boron exhibits a feeble basic character1 together with the properties of a feeble acid oxide4 ,this is even seen from the fact that a solution of boron oxide reddens blue litmus and acts on turmeric paper as an alkali1 and these reactions may be used for determining the presence of ,b#b,o#c in solutions4 ,by themselves the alkali borates have an alkaline reaction1 which clearly indicates the feeble acid character of boric acid4 ,if they are mixed in solution with hydrochloric acid1 boric acid is liberated1 and if a piece of turmeric paper be immersed in this solution and then dried1 the excess of hydrochloric acid volatilises1 while the boric acid remains on the paper and communicates a brown coloration to it1 just like alkalis4 ,boron trioxide or boric anhydride enters into the composition of many minerals1 in the majority of cases in small quantities as an isomorphous admixture1 not replacing acids but bases1 and most frequently alumina 7,al#b,o#c71 for as a rule the amount of alumina decreases as that of the boric anhydride increases in them4 ,this substitution is explained by the similarity between the atomic composition of the oxides of aluminium 7alumina7 and boron4 ,the subdivision of oxides into basic and acid can in no way be sharply defined1 and here we meet with the most conclusive proof of the fact1 for the oxides of boron and aluminium belong to the number of intermediate oxides1 closely approaching the limit separating the basic from the acid oxides4 ,their type 7,chapter ,,xv47 ,r#b,o#c is intermediate between those of the basic oxides ,r#b,o and ,,ro and those of the acid oxides ,r#b,o#e and ,,ro#c4 ,if we turn our attention to the chlorides1 we remark that lithium chloride is soluble in water1 is not volatile1 and is not decomposed by water2 the chlorides of beryllium and magnesium are more volatile1 and although not entirely1 still are decomposed by water2 whilst the chlorides of boron and aluminium are still more volatile and are decomposed by water4 ,thus the position of boron and aluminium in the series of the other elements is clearly defined by their atomic weights1 and shows us that we must not expect any new and distinct functions in these elements4 ,boron was originally known in the form of sodium borate1 ,na#b;,b#d,o#g1aj;,h#b,o1 or borax1 or tincal1 which was exported from ,asia1 where it is met with in solution in certain lakes of ,thibet2 it has also been discovered in ,california and ,nevada1 ,u4,s4,a4#a ,boric acid was afterwards found in sea-water and in certain mineral springs4#b ,its presence may be discovered by means of the green coloration which it communicates to the flame of alcohol1 which is capable of dissolving free boric acid4#c ,many of the boron compounds employed in the arts are obtained from the impure boric acid which is extracted in ,tuscany from the so-called suffioni4 ,in these localities1 which present the remains of volcanic action1 steam mixed with nitrogen1 hydrogen sulphide1 small quantities of boric acid1 ammonia1 and other substances1 issue from the earth4#c bis ,the boric acid partially volatilises with the steam1 for if a solution of boric acid be boiled1 the distillate will always contain a certain amount of this substance4#d #a ,borax is either directly obtained from lakes 7the ,american lakes give about #b1jjj tons and the lakes of ,thibet about #a1jjj tons per annum71 or by heating native calcium borate 7see ,note #b7 with sodium carbonate 7about #d1jjj tons per annum71 or it is obtained 7up to #b1jjj tons7 from the ,tuscan impure boric acid and sodium carbonate 7carbonic anhydride is evolved74 ,borax gives supersaturated solutions with comparative ease 7,gernez71 from which it crystallises1 both at the ordinary and higher temperatures1 in octahedra1 containing ,na#b;,b#d,o#g1e;,h#b,o4 ,its sp4 gr4 is #aha4 ,but if the crystallisation proceeds in open vessels1 then at temperatures below #ef1 the ordinary prismatic crystallo-hydrate ,b#d,na#b,o#g1aj;,h#b,o is obtained4 ,its sp4 gr4 is #aga1 it effloresces in dry air at the ordinary temperature1 and at #j #ajj parts of water dissolve about #h parts of this crystallo-hydrate1 at #ej #bg parts1 and at #ajj #bja parts4 ,borax fuses when heated1 loses its water and gives an anhydrous salt which at a red heat fuses into a mobile liquid and solidifies into a transparent amorphous glass 7sp4 gr4 #bcg71 which before hardening acquires the pasty condition peculiar to common molten glass4 ,molten borax dissolves many oxides and on solidifying acquires characteristic tints with the different oxides2 thus oxide of cobalt gives a dark blue glass1 nickel a yellow1 chromium a green1 manganese an amethyst1 uranium a bright yellow1 c4 ,owing to its fusibility and property of dissolving oxides1 borax is employed in soldering and brazing metals4 ,borax frequently enters into the composition of strass and fusible glasses4 #b ,we may mention the following among the minerals which contain boron3 calcium borate1 7,ca,o7#c7;,b#b,o#c77;,h#b,o7#f1 found and extracted in ,asia ,minor1 near ,brusa2 boracite 7stassfurtite71 7,mg,o7#f7;,b#b,o#c7h1,mg,cl#b1 at ,stassfurt1 in the regular system1 large crystals and amorphous masses 7specific gravity #bie71 used in the arts2 eremeffite 7,damour71 ,al,b,o#c or ,al#b,o#c;,b#b,o#c1 found in the ,adulchalonsk mountains in colourless1 transparent prisms 7specific gravity #cbh7 resembling apatite2 datholite1 7,ca,o7#b7,si,o#b7b;,b#b,o#c1;,h#b,o2 and ulksite1 or the boron-sodium carbonate from which a large quantity of borax is now extracted in ,america 7,note #a74 ,as much as #aj p4c4 of boric anhydride sometimes enters into the composition of tourmalin and axinite4 #c ,this green coloration is best seen by taking an alcoholic solution of volatile ethyl borate1 which is easily obtained by the action of boron chloride on alcohol4 #c bis ,p4 ,chigeffsky showed in #ahhd 7at ,geneva7 that in the evaporation of saline solutions many salts are carried off by the vapour--for instance1 if a solution of potash containing about #ag-bj grams of ,k#b;,,co#c per litre be boiled1 about #e milligrams of salt are carried off for every litre of water evaporated4 ,with ,li#b;,,co#c the amount of salt carried over is infinitesimal1 and with ,na#b;,,co#c it is half that given by ,k#b;,,co#c4 ,the volatilisation of ,b#b,o#c under these circumstances is incomparably greater--for instance1 when a solution containing #ad grams of ,b#b,o#c per litre is boiled1 every litre of water evaporated carries over about #cej milligrams of ,b#b,o#c4 ,when ,chigeffsky passed steam through a tube containing ,b#b,o#c at #djj1 it carried over so much of this substance that the flame of a ,bunsen's burner into which the steam was led gave a distinct green coloration2 but when1 instead of steam1 air was passed through the tube there was no coloration whatever4 ,by placing a tube with a cold surface in steam containing ,b#b,o#c1 ,chigeffsky obtained a crystalline deposit of the hydrate ,b7,,oh7#c on the surface of the tube4 ,besides this1 he found that the amount of ,b#b,o#c carried over by steam increases with the temperature1 and that crystals of ,b7,,oh7#c placed in an atmosphere of steam 7although perfectly still7 volatilise1 which shows that this is not a matter of mechanical transfer1 but is based on the capacity of ,b#b,o#c and ,b7,,oh7#c to pass into a state of vapour in an atmosphere of steam4 #d ,how it is that these vapours containing boric acid are formed in the interior of the earth is at present unknown4 ,dumas supposes that it depends on the presence of boron sulphide1 ,b#b,s#c 7others think boron nitride71 at a certain depth in the earth4 ,this substance may be artificially prepared by heating a mixture of boric acid and charcoal in a stream of carbon bisulphide vapour1 and by the direct combination of boron and the vapour of sulphur at a white heat4 ,the almost non-crystalline compound ,b#b,s#c1 sp4 gr4 #aee1 thus obtained is somewhat volatile1 has an unpleasant smell1 and is very easily decomposed by water1 forming boric acid and hydrogen sulphide1 ,b#b,s#c #c;,h#b,o ,b#b,o#c #c;,h#b,s4 ,it is supposed that a bed of boron sulphide lying at a certain depth below the surface of the earth comes into contact with sea water which has percolated through the upper strata1 becomes very hot1 and gives steam1 hydrogen sulphide1 and boric acid4 ,this also explains the presence of ammonia in the vapours1 because the sea water certainly passes through crevices containing a certain amount of animal matter1 which is decomposed by the action of heat and evolves ammonia4 ,there are several other hypotheses for explaining the presence of the vapours of boric acid1 but owing to the want of other known localities the comparison of these hypotheses is at present hardly possible4 ,the amount of boric anhydride in the vapours which escape from the ,tuscan fumerolles and suffioni is very inconsiderable1 less than one-tenth per cent41 and therefore the direct extraction of the acid would be very uneconomical1 hence the heat contained in the discharged vapours is made use of for evaporating the water4 ,this is done in the following manner4 ,reservoirs are constructed over the crevices evolving the vapours1 and the water of some neighbouring spring is passed into them4 ,the vapours are caused to pass through these reservoirs1 and in so doing they give up all their boric acid to the water and heat it1 so that after about twenty-four hours it even boils2 still this water only forms a very weak solution of boric acid4 ,this solution is then passed into lower basins and again saturated by the vapours discharged from the earth1 by which means a certain amount of the water is evaporated and a fresh quantity of boric acid absorbed2 the same process is repeated in another reservoir1 and so on until the water has collected a somewhat considerable amount of boric acid4 ,the solution is drawn from the last reservoir ,a into settling vessels ,b ,d1 and then into a series of vessels a1 b1 c4 ,in these vessels1 which are made of lead1 the solution is also evaporated by the vapours escaping from the earth1 and attains a density of #aj to #aa ,baum4 ,it is allowed to settle in the vessel ,c1 in which it cools and crystallises1 yielding 7not quite pure7 crystalline boric acid4 ,at temperatures above #ajj1 for instance1 with superheated steam1 boric acid volatilises with steam very easily4 ,illustration3 ,,fig4 #ha4--;,extraction of boric acid in ,tuscany4 ,if boric acid be introduced into an excess of a strong hot solution of sodium hydroxide1 then1 on slowly cooling1 the salt ,na,b,o#b1d;,h#b,o crystallises out4 ,this salt contains an equivalent of ,na#b,o to one equivalent ,b#b,o#c4 ,it might be termed a neutral salt did it not possess strongly alkaline reactions and easily split up into the alkali and the more stable borax or biborate of sodium mentioned above1 which contains #b;,b#b,o#c to ,na#b,o4#e ,this salt is prepared by the action of boric acid on a solution of sodium carbonate4 ,borax may be perfectly purified by crystallisation4 ,if a saturated and hot solution of borax be mixed with strong hydrochloric acid1 common salt and a normal crystalline hydrate of boric acid are formed4 ,the composition of this hydrate is ,b7,,ho7#c1 according to the form ,,bx#c--that is1 of the composition ,b#b,o#c1c;,h#b,o4 ,this is the easiest method of obtaining pure boric acid4 ,the water is easily expelled from this hydrate2 it loses half at #ajj and the remainder on further heating1 and the remaining ,b#b,o#c or boric anhydride fuses at #ehj 7according to ,carnelley71 forming at first a ductile 7easily drawn out into threads71 tenacious mass and then a colourless liquid solidifying to a transparent glass1 which absorbs moisture from the atmosphere and then becomes cloudy4#f ,only the alkaline salts of boric acid are soluble in water1 but all borates are soluble in acids1 owing to their easy decomposability and the solubility of boric acid itself4 ,although boric anhydride1 ,b#b,o#c1 absorbs #c;,h#b,o from damp air1 still in the presence of water it always#g combines with a less quantity of bases 7borax only contains #a_/f74 ,however1 fused boric anhydride forms a crystalline compound with magnesium of the same type as the hydrate 7,mg,o7#c;,b#b,o#c 7,ebelmann71 and even with sodium it forms 7,na#b,o7#c;,b#b,o#c or ,na#c;,,bo#c 7,benedict74 ,as a rule1 the salts of boric acid contain less base1 although they are all able to form saline compounds with bases when fused4 ,generally1 vitreous fluxes are formed by this means1#h which when fused recall ordinary aqueous solutions in many respects4 ,some of them crystallise on solidifying1 and then they have1 like salts1 a definite composition4 ,the property of boric anhydride of forming higher grades of combination with basic oxides when fused explains the power of fused borax to dissolve metallic oxides1 and the experiments of ,ebelmann on the preparation of artificial crystals of the precious stones by means of boric anhydride4 ,boric anhydride is1 although with difficulty1 volatile at a high temperature1 and therefore if it dissolves an oxide1 it may be partially driven off from such a solution by prolonged and powerful ignition2 in which case the oxides previously in solution separate out in a crystalline form1 and frequently in the same forms as those in which they occur in nature--for example1 crystals of alumina1 which by itself fuses with difficulty1 have been obtained in this manner4 ,it dissolves in molten boric anhydride1 and separates out in natural rhombohedric crystals4 ,in this way ,ebelmann also obtained spinel--that is1 a compound of magnesium and aluminium oxides which occurs in nature4#i #e ,metals1 like ,na1 ,k1 ,li1 give salts of the type of borax1 ,,mbo#b or ,,mh#b;,,bo#c4 ,a solution of borax1 ,na#b;,b#d,o#g1 has an alkaline reaction1 decomposes ammonia salts with the liberation of ammonia 7,bolley71 absorbs carbonic anhydride like an alkali1 dissolves iodine like an alkali 7,georgiewics71 and seems to be decomposed by water4 ,thus ,rose showed that strong solutions of borax give a precipitate of silver borate with silver nitrate1 whilst dilute solutions precipitate silver oxide1 like an alkali4 ,georgiewics even supposes 7#ahhh7 boric anhydride to be entirely void of acid properties2 for all acids1 on acting on a mixture of solutions of potassium iodide and iodate1 evolve iodine1 but boric acid does not do this4 ,with dilute solutions of sodium hydroxide ,berthelot obtained a development of heat equal to #aa-a_/b thousand calories per equivalent of alkali 7#dj grams sodium hydroxide7 when the ratio ,na#b,o 3 #b;,b#b,o#c 7as in borax7 was taken1 and only #d thousand calories when the ratio was ,na#b,o 3 ,b#b,o#c1 whence he concludes that water powerfully decomposes those sodium borates in which there is more alkali than in borax4 ,laurent 7#ahdi7 obtained a sodium compound1 ,na#b,o1#d;,b#b,o#c1aj;,h#b,o1 containing twice as much boric anhydride as borax1 by boiling a mixture of borax with an equivalent quantity of sal-ammoniac until the evolution of ammonia entirely ceased4 ,hence it is evident that feeble acids are as prone to1 and as easily1 form acid salts 7that is1 salts containing much acid oxide7 as feeble bases are to give basic salts4 ,these relations become still clearer on an acquaintance with such feeble acids as silicic1 molybdic1 c4 ,this variety of the proportions in which bases are able to form salts recalls exactly the variety of the proportions in which water combines with crystallo-hydrates4 ,but the want of sufficient data in the study of these relations does not yet permit of their being generalised under any common laws4 ,with respect to the feeble acid energy of boric anhydride ,i think it useful to add the following remarks4 ,carbonic anhydride is absorbed by a solution of borax1 and displaces boric anhydride2 but it is also displaced by it1 not only on fusion1 but also on solution1 as the preparation of borax itself shows4 ,sulphuric anhydride is absorbed by boric acid1 forming a compound ,b7,,hso#d7c1 where ,,hso#d is the radicle of sulphuric acid 7,d',ally74 ,with phosphoric acid1 boric acid forms a stable compound1 ,,bpo#d1 or ,b#b,o#c,p#b,o#e1 undecomposable by water1 as ,gustavson and others have shown4 ,with respect to tartaric acid1 boric anhydride is able to play the same part as antimonious oxide4 ,mannitol1 glycerol1 and similar polyhydric alcohols also seem able to form particularly characteristic compounds with boric anhydride4 ,all these aspects of the subject require still further explanation by a method of fresh and detailed research4 #f ,ditte determined the sp4 gr43-- #j #ab #hj ,b#b,o#c #ahgff #ahdgj #afihh ,b7,,oh7#c #aedfc #aeagb #achbh ,solubility #aie #bib #afhb ,the last line gives the solubility1 in grams1 of boric acid1 ,b7,,oh7#c1 per #ajj c4c4 of water1 also according to the determinations of ,ditte4 #g ,it is evident that1 in the presence of basic oxides1 water competes with them1 which fact in all probability determines both the amount of water in the salts of boric acid as well as their decomposition by an excess of water4 ,in confirmation of the above-mentioned competing action between water and bases1 ,i think it useful to point out that the crystallo-hydrate of borax containing #e;,h#b,o may be represented as ,b7,,ho7#c1 or rather as ,b#b7,,oh7#f1 with the substitution of one atom of hydrogen by sodium1 since ,na#b;,b#d,o#g1e;,h#b,o #b;,b#b7,,oh7#e7,o,na74 ,the composition of the acid boric salts is very varied1 as is seen from the fact that ,reychler 7#ahic7 obtained 7,cs#b,o7#c;,b#b,o#c1 7,rb#b,o7#b;,b#b,o#c 7corresponding to borax7 and 7,li#b,o7,b#b,o#c1 and that ,le ,chatelier and ,ditte obtained1 for ,ca,o1 ,mg,o1 c41 7,,ro7,b#b,o#c1 7,,ro7#bc;,b#b,o#c1 7,,ro7#b;,b#b,o#c1 7,,ro7#b;,b#b,o#c1 and even 7,,ro7#c;,b#b,o#c4 #h ,a glass can only be formed by those slightly volatile oxides which correspond with feeble acids1 like silica1 phosphoric and boric anhydrides1 c41 which themselves give glassy masses1 like quartz1 glacial phosphoric acid1 and boric anhydride4 ,they are able1 like aqueous solutions and like metallic alloys1 to solidify either in an amorphous form or to yield 7or even be wholly converted into7 definite crystalline compounds4 ,this view illustrates the position of solutions amongst the other chemical compounds1 and allows all alloys to be regarded from the aspect of the common laws of chemical reactions4 ,i have therefore frequently recurred to it in this work1 and have since the year #ahej introduced it into various provinces of chemistry4 #i ,if boric acid in its aqueous solutions proves to be exceedingly feeble1 unenergetic1 and easily displaced from its salts by other acids1 yet in an anhydrous state1 as anhydride1 it exhibits the properties of an energetic acid oxide1 and it displaces the anhydrides of other acids4 ,this of course does not mean that the acid then acquires new chemical properties1 but only depends on the fact that the anhydrides of the majority of acids are much more volatile than boric anhydride1 and therefore the salts of many acids--even of sulphuric acid--are decomposed when fused with boric anhydride4 ,by itself boric acid is used in the arts in small quantity1 chiefly for the preservation of meat and fish 7which must be afterwards well washed in water7 and of milk1 and for soaking the wicks of stearin candles2 the latter application is based on the fact that the wicks1 which are made of cotton twist1 contain an ash which is infusible by itself but which fuses when mixed with boric acid4 ,free boron was obtained 7#ahji7 by ,davy1 ,gay-,lussac1 and ,thnard when they obtained the metals of the alkalis1 for boric anhydride when fused with sodium gives up its oxygen to the sodium1 and free boron is liberated as an amorphous powder like charcoal4#aj ,it is of a brown colour1 specific gravity #bde 7,moissan71 and when dry does not alter in the air at the ordinary temperature2 but it burns when ignited to #gjj1 and in so doing combines not only with the oxygen of the air1 but also with the nitrogen4 ,however1 the combustion is never complete1 because the boric anhydride formed on the surface covers the remaining mass of the boron1 and so preserves it from the action of the oxygen4 ,acids1 even sulphuric 7forming ,,so#b7 and phosphoric 7forming phosphorus71 easily oxidise amorphous boron1 especially when heated1 converting it into boric acid4 ,alkalis have the same action on it1 only in this case hydrogen is evolved4 ,boron decomposes steam at a red heat1 also with evolution of hydrogen4 #aj ,amorphous boron is prepared by mixing #ajj parts of powdered boric anhydride with #ej parts of sodium in small lumps2 this mixture is thrown into a powerfully heated cast-iron crucible1 covered with a layer of ignited salt1 and the crucible covered4 ,reaction proceeds rapidly2 the mass is stirred with an iron rod1 and poured directly into water containing hydrochloric acid4 ,the action is naturally accompanied by the formation of sodium borate1 which is dissolved1 together with the salt1 by the water1 whilst the boron settles at the bottom of the vessel as an insoluble powder4 ,it is washed in water1 and dried at the ordinary temperature4 ,magnesium1 and even charcoal and phosphorus1 are also able to reduce boron from its oxide4 ,boron1 in the form of an amorphous powder1 very easily passes through filter-paper1 remains suspended in water1 and colours it brown1 so that it appears to be soluble in water4 ,sulphur precipitated from solutions shows the same 7colloidal7 property4 ,when borax is fused with magnesium powder1 it gives a brown powder of a compound of boron and magnesium1 ,mg#b;,b 7,winkler1 #ahij71 but when a mixture of #a part of magnesium and #c parts of ,b#b,o#c is heated to redness 7,moissan1 #ahib71 it forms amorphous boron in the form of a chestnut-coloured powder1 which1 after being washed with water1 hydrochloric and hydrofluoric acids1 is fused again with ,b#b,o#c in an atmosphere of hydrogen in order to prevent the access of the nitrogen of the air1 which is easily absorbed by incandescent amorphous boron4 ,sabatier 7#ahia7 considers that a certain amount of gaseous hydride of boron is evolved in the action of hydrochloric acid upon the alloys of magnesium and boron1 because the gas disengaged burns with a green flame4 ,still1 the existence of hydride of boron cannot be regarded as certain4 ,under the action of the heat of the electric furnace boron forms with carbon a carbide1 ,,bc1 as ,mhlhuser and ,moissan showed in #ahic4 ,amorphous boron1 like charcoal1 dissolves in certain molten metals4 ,the property of fused aluminium of dissolving boron in considerable quantity is very striking2 on cooling such a solution1 the boron partially combined with the aluminium separates out in a crystalline form1 and its properties are then exceedingly remarkable4 ,the crystalline boron may be obtained by heating 7to #a1cjj7 the pulverulent boron with aluminium in a well-closed crucible1 the access of air being prevented as far as possible4 ,after cooling1 crystals are observed on the surface of the aluminium1 and may easily be separated by dissolving the latter in hydrochloric acid1 which does not act on the crystals4 ,the specific gravity of the crystals is #bfh2 they are partially transparent1 but are for the most part coloured dark brown2 they contain about #d p4c4 of carbon and up to #g p4c4 of aluminium1 so that they cannot be considered as pure boron4 ,nevertheless1 the properties of this crystalline substance1 which was obtained by ,whler and ,deville1 are very remarkable4 ,it most closely resembles the diamond in its properties--in fact1 these crystals have the lustre and high refracting power proper to the diamond only1 whilst their hardness competes with that of the diamond4 ,their powder polishes even the diamond1 and like the diamond scratches the sapphire and corundum4 ,crystalline boron is much more stable with respect to chemical reagents than the amorphous variety1 and as it resembles the diamond1 so amorphous boron1 on the other hand1 distinctly recalls certain of the properties of charcoal2 thus a certain resemblance exists between boron and carbon in a free state1 which is further justified by the proximity of their positions in the periodic system4 ,among the other compounds of boron1 those with nitrogen and the halogens are the most remarkable4 ,as already mentioned above1 amorphous boron combines directly with nitrogen at a red heat4 ,if it be heated in a glass tube in a stream of nitric oxide1 perfect combustion takes place1 #e;,b #c,,no ,b#b,o#c #c;,,bn4 ,if the residue be treated with nitric acid1 the boric anhydride dissolves1 whilst the boron nitride remains#aa as an extremely light white powder1 which is sometimes partially crystalline and greasy to the touch1 like talc4 ,it is infusible and unchanged1 even at the melting-point of nickel4 ,in general1 it is remarkable for its great stability with respect to chemical reagents4 ,nitric and hydrochloric acids1 as well as alkaline solutions1 and hydrogen and chlorine at a red heat1 have no action on it4 ,when fused with potash1 it evolves ammonia1 and when ignited in steam it also yields ammonia3 #b;,,bn #c;,h#b,o ,b#b,o#c #b,,nh#c4ab #aa ,at first boron nitride was obtained by heating boric acid with potassium cyanide or other cyanogen compounds4 ,it may be more simply prepared by heating anhydrous borax with potassium ferrocyanide1 or by heating borax with ammonium chloride4 ,for this purpose one part of borax is intimately mixed with two parts of dry ammonium chloride1 and the mixture heated in a platinum crucible4 ,a porous mass is formed1 which after crushing and treating with water and hydrochloric acid1 leaves boron nitride4 ,boron fluoride1 ,,bf1 is known1 corresponding to ,,bn2 this body was obtained by ,besson and ,moissan 7#ahia74 ,the action of phosphorus upon iodide of boron1 ,,bi#c1 forms ,,pbi#b1 and when heated to #ejj in hydrogen it forms ,,bp1 which gives ,,ph#c with fused ,,kho4 #ab ,when fused with potassium carbonate it forms potassium cyanate1 ,,bn ,k#b;,,co#c ,,kbo#b ,,kcno4 ,all this shows that boron nitride is a nitrile of boric acid1 ,,bo7,,oh7 ,,nh#c - #b;,h#b,o ,,bn4 ,the same is expressed by saying that boron nitride is a compound of the type of the boron compounds ,,bx#c1 with the substitution of ,x#c by nitrogen1 as the trivalent radicle of ammonia1 ,,nh#c4 ,no less remarkable is the compound of boron with fluorine--boron fluoride1 ,,bf#c4 ,it is produced in many instances when compounds of boron and of fluorine are brought together4#ac ,the most convenient method of preparing it is by heating a mixture of calcium fluoride with boric anhydride and sulphuric acid1 #c;,ca,f#b ,b#b,o#c #c;,h#b,,so#d #c;,ca,s,o#d #c;,h#b,o #b;,,bf#c4ad ,it is a colourless liquefiable gas 7the liquid boils at -#ajj71 which on coming into contact with damp air forms white fumes1 owing to its combining with water4 ,one volume of water dissolves as much as #a1jej volumes of this gas 7,bazaroff71 forming a liquid which disengages boron fluoride when heated1 and distils over unaltered4 ,boron fluoride chars organic matter1 owing to its taking up the water from it1 and in this respect it acts like sulphuric acid4 ,the behaviour of boron fluoride with water must be understood as a reversible reaction1 since with water it yields hydrofluoric and boric acids1 whilst they1 acting on one another1 re-form boron fluoride and water4 ,a state of equilibrium is set up between these four substances 7and between two reversible reactions7 which is distinctly dependent on the mass of the water4#ad bis ,when boron fluoride is in great excess1 the equilibrated system1 which is capable of distilling over 7sp4 gr4 of the liquid #agg71 has a composition ,,bf#c1b;,h#b,o 7or ,b#b,o#c1;,h#b,o1#f;,,hf74 ,it has also its corresponding salts4#ae ,it is a caustic liquid1 having the properties of a powerful acid2 but it does not act on glass1 which shows that there is no free hydrofluoric acid present4 ,under the action of water this system changes1 with the formation of boric acid and hydroborofluoric acid 7,,hbf#d7 according to the equation #d;,,bf#c;,h#d,o#b #c;,,hbf#d ,,bh#c,o#c #e;,h#b,o4#af ,this hydroborofluoric acid has its corresponding salts--for instance1 ,,kbf#d4 ,on evaporating the aqueous solution this free acid decomposes1 with the evolution of hydrofluoric acid1 and a stable system is again obtained3 #b;,,hbf#d #e;,h#b,o ,b#b;,f#f;,h#aj,o#e #b;,,hf4 ,the resultant solution 7containing #b;,,bf#c1e;,h#b,o1 sp4 gr4 #aeh71 which is identical with that formed by the evaporation of a solution of boric acid with hydrofluoric acid1 again only contains a compound of boron fluoride with water4 ,probably there are various other possible and more or less stable states of equilibrium and definite compounds of boron fluoride1 hydrofluoric acid1 and water4 #ac ,boron fluoride is frequently evolved on heating certain compounds occurring in nature containing both boron and fluorine4 ,if calcium fluoride is heated with boric anhydride1 calcium borate and boron fluoride are formed1 and the latter1 as a gas1 is volatilised3 #b;,b#b,o#c #c;,ca,f#b #b;,,bf#c ,ca#c;,b#b,o#f4 ,the calcium borate1 however1 retains a certain amount of calcium fluoride4 #ad ,in order to avoid the formation of silicon fluoride the decomposition should not be carried on in glass vessels1 which contain silica1 but in lead or platinum vessels4 ,boron fluoride by itself does not corrode glass1 but the hydrofluoric acid liberated in the reaction may bring a part of the silica into reaction4 ,boron fluoride should be collected over mercury1 as water acts on it1 as we shall see afterwards4 #ad bis ,it appears to me that from this point of view it is possible to understand the apparently contradictory results of different investigators1 especially those of ,gay-,lussac 7and ,thnard71 ,davy1 ,berzelius1 and ,bazaroff4 ,in the form in which the reaction of ,,bf#c on water is given here1 it is evident that the act of solution in water is accompanied by complex but direct chemical transformations1 and ,i think that this example should prove the justness of those observations upon the nature of solutions which are given in ,chapter ,i4 #ae ,they are called fluoborates4 ,they may be prepared directly from fluorides and borates4 ,such compounds of halogens with oxygen salts are known in nature 7for instance1 apatite and boracite71 and may be artificially prepared4 ,the composition of the fluoborates--for example1 ,k#d;,,bf#c,o#b--may be expressed as that of a double salt1 ,,bo7,,ok71#c,,kf4 ,if an excess of water decomposes them 7,bazaroff71 this does not prove that they do not exist as such1 for many double salts are decomposed by water4 #af ,fluoboric acid contains boron fluoride and water1 hydrofluoboric acid1 boron fluoride1 and hydrofluoric acid4 ,it is evident that on the one side the competition between water and hydrofluoric acid1 and1 on the other hand1 their power to combine1 are among the forces which act here4 ,from the fact that hydroborofluoric acid1 ,,hbf#d1 can only exist in an aqueous solution1 it must be assumed that it forms a somewhat stable system only in the presence of #c;,h#b,o4 ,nothing of this kind occurs with boron chloride1 because hydrochloric acid does not act on boric acid4 ,however1 amorphous boron at #djj burns in chlorine1 and at #daj forms boron chloride1 ,b,cl#c4 ,the boron burns in the chlorine1 forming a gas which1 in a freezing mixture1 condenses into a liquid boiling at #ag1 and gives up its excess of chlorine1 if there be any1 to mercury4 ,the specific gravity of this liquid is #adb at #f4 ,boron chloride may also be directly obtained from boric anhydride by the simultaneous action of charcoal and chlorine at a high temperature3 ,b#b,o#c #c;,c #c;,cl#b #b;,b,cl#c #c;,,co4 ,it is also obtained by the action of phosphoric chloride on boric anhydride in a closed tube at #bjj ,it is completely decomposed by water1 like the chloranhydride of an acid1 boric acid being formed2 hence it fumes in the air3 #b;,b,cl#c #f;,h#b,o #b;,,bh#c,o#c #f;,h,cl4 ,boron forms with bromine a similar compound1 ,b,br#c1 specific gravity at #f #bfd1 boiling at #ij4 ,the vapour densities of the fluoride1 chloride1 and bromide of boron show that they contain three atoms of the halogen in the molecule--that is1 that boron is a trivalent element forming ,,bx#c4af bis #af bis ,iodide of boron1 ,,bi#c1 was obtained by ,moissan 7#ahia71 by heating a mixture of the vapours of ,,hi and ,b,cl#c in a tube1 or by the action of iodine vapour 7at #gej7 or ,,hi upon amorphous boron4 ,,bi#c is a solid substance which dissolves in benzol and ,,cs#b1 reacts with water1 melts at #dc1 boils at #baj1 has a density #cc at #ej1 and partially decomposes in the light4 ,besson 7#ahia7 obtained ,b,i,br#b 7boiling at #abe71 and ,,bi#b;,br 7boiling at #ahj7 by heating 7#cjj-djj7 a mixture of the vapours of ,,hi and ,b,br#c1 and showed that ,,nh#c combines with ,b,br#c and ,,bi#c in various proportions4 ,as in the first group lithium is followed by sodium1 giving a more basic oxide1 so in the second group beryllium is followed by magnesium1 and so also in the third group there is1 besides the lightest element1 boron1 whose basic character is scarcely defined1 aluminium1 ,al #bg1 whose oxide1 alumina1 has somewhat distinct basic properties1 which1 although not so powerful as in magnesium oxide1 are more distinct than in boric anhydride4 ,among the elements of the third group1 aluminium is the most widely distributed in nature2 it will be sufficient to mention that it enters into the composition of clay to demonstrate the universal distribution of aluminium in the earth's crust4 ,alumina is so named from its being the metal of alums 7alumen74 ,clay1 which is so widely distributed and familiar to everybody1 is the insoluble residue obtained after the action of water containing carbonic acid on many rocks1 and especially on the felspars contained in some of them4 ,felspar is a compound containing potash or soda1 alumina1 and silica4 ,the primary rocks1 like granite1 contain many similar compounds 7see ,chapter ,,xviii43 ,felspars74 ,felspar is acted on by water containing carbonic acid1 all the alkalis 7potash and soda71 and a portion of the silica passing into the water as substances which are soluble and carried away by it1 whilst the alumina and silica left from the felspar remain on the spot where the solution has taken place4 ,this is the original method of the formation of clay in its primary deposits among rocks along whose crevices the atmospheric water has permeated4 ,such primary deposits often contain a white pure clay1 termed kaolin or porcelain clay4 ,but such clay is a rarity1 because the conditions for its formation are rarely met with4 ,the water1 whilst acting chemically on rocks1 at the same time destroys them mechanically1 and carries off the finely divided residues of disintegration with it4 ,clay is most easily subjected to this mechanical action of water1 because it is composed of grains of exceedingly small size and void of any visible crystalline structure1 which easily remain suspended in water4 ,the cloudy water of running mountain streams generally contains particles of clay in suspension1 owing to the above-described chemical and mechanical action of the water on the minerals contained in the mountain rocks4 ,together with these minute particles of clay the water carries away the coarser components on which it is not able to act--for example1 splinters of rock1 grains of mica1 quartz1 c4 ,they were originally held together by those minerals which form clay4 ,when the water acts on these binding minerals1 a sandy mass is formed which water bears away4 ,the cloudy water in which the particles of clay and sand are held in suspension carries them to1 and deposits them at1 the estuaries of rivers1 lakes1 seas1 and oceans4 ,the coarser particles are first deposited and form sand and similar disintegrated rocky matter1 whilst the clay1 owing to its finely divided state1 is carried on further1 and is only deposited in the still parts of the rivers1 lakes1 c4 ,such disintegrations of rocks and separations of clay from sand have been gradually going on during the millions of years of the earth's existence1 and are now proceeding1 and have been the cause of the formation of the immense deposits of sandstone and clay now forming a part of the earth's strata4 ,such beds of clay may have been transferred by currents and streams from one locality to another1 so that we must distinguish between primary and secondary deposits of clay4 ,in places these beds of clay have1 owing to long exposure under water1 and perhaps partially owing to the action of heat1 undergone compression1 and have formed the rocky masses known as clay slates and schists1 which sometimes form entire mountains4 ,roofing slates belong to this class of rocks4 ,from what has been said above it will be evident that these deposits can never consist of a chemically pure and homogeneous substance1 but will contain all kinds of extraneous insoluble finely divided matter1 and especially sand--that is1 fragments of rock1 chiefly quartz 7,si,o#b74 ,it is1 however1 possible to considerably purify clay from these impurities1 owing to the fact that they are the result of mechanical disintegration1 whilst the clay has been formed as a residue of the chemical alteration of rocky matter1 and therefore its particles are incomparably more minute than the particles of sand and other rock fragments mixed with it4 ,this difference in the size of the grains causes the clay to remain longer in suspension when shaken up in water than the coarser grains of sand4 ,if clay be shaken up in water1 and especially if it be previously boiled in it1 and if after the first portion has settled the cloudy water be decanted1 it will give a deposit of a very much purer clay than the original4 ,this method is employed for purifying kaolin designed for the manufacture of the best kinds of china1 earthenware1 c4 ,a similar method is also employed in the investigation of earths for determining the composition of soils chiefly composed of a mixture of sand1 clay1 limestone1 and mould4 ,the limestone is soluble in dilute acids1 but neither the clay nor sand passes into solution by this means1 and therefore the limestone is easily separated in the investigation of soils4 ,the clay is separated from the sand by a mechanical method similar to that described above1 and termed levigation4#ag #ag ,the process of levigation is based on the difference in the diameters of the particles of clay and sand4 ,in density these particles differ but little from each other1 and therefore a stream of water of a certain velocity can only carry away the particles of a certain diameter1 whilst the particles of a larger diameter cannot be borne away by it4 ,this is due to the resistance to falling offered by the water4 ,this resistance to substances moving in it increases with the velocity1 and therefore a substance falling into water will only move with an increasing velocity until its weight equals the resistance offered by the water1 and then the velocity will be uniform4 ,and as the weight of the minute particles of clay is small1 the maximum velocity attained by them in falling is also small4 ,a detailed account of the theory of falling bodies in liquid1 and of the experiments bearing on this subject1 may be found in my work1 ,concerning the ,resistance of ,liquids and ,aeronautics1 #ahhj4 ,the minute particles of clay remain suspended longer in water1 and take longer to fall to the bottom4 ,heavy particles1 although of small dimensions1 fall more quickly1 and are borne away by water with greater difficulty than the lighter4 ,in this way gold and other heavy ores are washed free from sand and clay1 and the coarser portions and heavier particles are left behind4 ,a current of water of a certain velocity cannot carry away with it particles of more than a definite diameter and density1 but by increasing the velocity of the current a point may be arrived at when it will bear away larger particles4 ,a description of apparatus for the observation of phenomena of this kind is given by ,schne in his memoir in the ,transactions of the ,moscow ,society of ,natural ,sciences for #ahfg4 ,in order to be able accurately to vary the velocity of the current of water1 a cylinder is employed in which the earth to be experimented on is placed1 and water is introduced through the conical bottom of the cylinder4 ,the rate at which the water rises in the cylinder will vary according to the quantity of water flowing per unit of time into the vessel1 and consequently particles of various sizes will be carried away by the water flowing over the upper edges of the vessel4 ,schne showed by direct experiment that a current of water having a velocity of #ja mm4 per second will carry away particles having a diameter of not more than #jjjge mm41 that is1 only the most minute2 with a velocity v #jb mm4 per second1 particles having a diameter d #jjaa mm4 are carried away2 with v #jc mm41 d #jjadf mm42 with v #jd mm41 d #jjag mm42 with v #je mm41 d #jjb mm42 with v #a mm41 d #jjc mm42 with v #d mm41 d #jjg mm42 with v #aj mm41 d #jacg mm42 with v #ab mm41 d #jae mm42 and therefore if the current does not exceed one of these velocities1 it will only carry away or wash away particles having a diameter less than that indicated4 ,the sand and other particles mixed with the clay will then remain in the vessel4 ,the very minute particles obtained after levigation are all considered as clay1 although not only clay but other rock residue may also exist in it as very fine particles4 ,however1 this is very seldom the case1 and the fine mud separated from all clays has practically the same composition as the purest kinds of kaolin4 ,the relation between the amounts of clay and sand in soils used for the cultivation of plants is very important1 because a soil rich in clay is denser1 heavier1 shrinks up under the action of heat1 and does not readily yield to the plough in dry or wet weather1 whilst a soil rich in sand is friable1 crumbling1 easily parts with its moisture and dries rapidly1 but is comparatively easily worked4 ,neither crumbling sand nor pure clay can be regarded as a good cultivating soil4 ,the difference in the amounts of clay and sand in a soil has also a purely chemical signification4 ,sand is easily permeated by the air1 because its particles are not closely packed together4 ,hence the chemical change of manures proceeds very easily in sandy soils4 ,but on the other hand such soils do not retain the nutritious principles contained in the manure1 nor the water necessary for the nourishment of plants by means of their roots4 ,solutions of nutritious substances1 containing salts of potassium1 phosphoric acid1 c41 when passed through sand only leave a portion moistening the surface of its particles4 ,the sand has only to be washed with pure water and all the adhering films of solution are washed away4 ,it is not so with clay4 ,if the above solutions be passed through a layer of clay the retention of the nutritive substances of these solutions will be very marked2 this is partly because of the very large surface which the minute particles of clay expose4 ,the nutritive elements dissolved in water are retained by the particles of clay in a peculiar manner--that is1 the absorptive power of clay is very great compared to that of sand--and this has a great significance in the economy of nature 7,chapter ,,xiii41 p4 #edg74 ,it is evident that for cultivation the most convenient soils in every respect will be those containing a definite mixture of clay and sand1 and indeed the most fertile soils have this composition4 ,the study of fertile soils1 which is so important for a knowledge of the natural conditions for the application of fertilisers1 belongs1 strictly speaking1 to the province of agriculture4 ,in ,russia the first foundation of a scientific fertilisation has been laid by ,dokuchaeff4 ,as an example only1 we will give the composition of four soils2 7#a7 ,the black earth of the ,simbirsk ,government2 7#b7 a clay soil from the ,smolensk ,government2 7#c7 a more sandy soil from the ,moscow ,government2 and 7#d7 a peaty soil from near ,st4 ,petersburg4 ,these analyses were made in the laboratory of the ,st4 ,petersburg ,university about #ahfj1 in connection with experiments on fertilisation 7conducted by me7 by the ,imperial ,free ,economical ,society4 #aj1jjj grams of air-dried soil contain the following quantities 7in grams7 of substances capable of dissolving in acids1 and of serving for the nourishment of plants4 7#a7 7#b7 7#c7 7#d7 ,na#b,o #aa #e #d #d ,k#b,o #eh #aj #g #e ,mg,o #ib #cc #ai #g ,ca,o #acd #ag #ad #aa ,p#b,o#e #g #a #g #c ,n #dd #aa #ac #af ,s #ac #g #g #f ,fe#b,o#c #cda #aee #aaa #df ,by chemical and mechanical analysis1 the chief component parts per #ajj parts of air-dried soil are ,clay #df #bi #ab #aj ,sand #dj #fg #hf #hd ,organic matter #cg #ag #jf #da ,hygroscopic water #fc #ac #jh #ai ,weight of a litre in grams #aaej #abgj #acej #ifj ,the black earth excels the other soils in many respects1 but naturally its stores are also exhausted by cultivation if nothing be returned to it in the form of fertilisers2 and the improvement of a soil 7for instance1 by the addition of marl or peat1 and by drainage and watering71 and its fertilisation1 if carried on in conformity with its composition and with the properties of the plants to be cultivated1 are capable of rendering not only every soil fit for cultivation1 but also of improving its value1 so that in the course of time whole countries 7like ,holland7 may clearly improve their agricultural position1 whilst under the ordinary rgime of continued exhaustion of the soil1 entire regions 7as1 for instance1 many parts of ,central ,asia7 may be rendered unfit for any agriculture4 ,by treating clay with strong sulphuric acid1 which dissolves the alumina in it1 and then 7by means of an alkaline carbonate7 dissolving the silica which was combined with the alumina in the clay 7but not that occurring in the form of sand1 c41 which is hardly dissolved by carbonate of soda solution at all even on boiling71 we may form an idea of the proportion between the component parts of a clay2 and by igniting it at a high temperature1 we may determine the amount of water held in it4 ,in the purer sorts of clay dried at #ajj 7sp4 gr4 of pure kaolin is about #be7 this proportion is about #b,si,o#b 3 #b;,h#b,o 3 ,al#b,o#c4 ,in this case the conversion of felspar into kaolin is expressed by the equation3-- ,k#b,o1,al#b,o#c1f,si,o#b ,al#b,o#c1b,si,o#b ,k#b,o1#d,si,o#b2 ,felspar ,kaolin the compound ,k#b,o1#d,si,o#b passes into solution4 ,but as a rule clays contain from #de to #fj p4c4 of silica1 from #bj to #cj p4c4 of alumina1 and about #ab p4c4 of water2 and it cannot be supposed that clays are always homogeneous1 because they are an aggregation of residues 7of silico-aluminous compounds7 which are unacted on by water4 ,nevertheless1 clays always contain a hydrous compound of alumina and silica1 which is able to give up the alumina contained by it as a base to strong sulphuric acid1 forming aluminium sulphate1 which is soluble in water4 ,after this treatment the silica remains1 and is soluble in a solution of an alkaline carbonate4#ah #ah ,everyone knows that a mixture of clay and water is endowed with the property of taking a given form when subjected to a moderate pressure4 ,this plasticity of clay renders it an invaluable material for practical purposes4 ,from clay are moulded and manufactured a variety of objects1 beginning with the common brick and ending with the most delicate china works of art4 ,this plasticity of clay increases with its purity4 ,when articles made of clay are dried1 the well-known hard mass is obtained2 but water washes it away1 and furthermore1 the cohesion of its particles is not sufficiently great for it to resist the impression of blows1 shocks1 c4 ,if such an article be subjected to the action of heat1 its volume first decreases1 then it begins to lose water1 and it shrinks still further 7in the case of a compact mass approximately by #a_/e of its linear measurement74 ,on the other hand1 a great coherence of particles is obtained1 and thus burnt clay has the hardness of stone4 ,pure clay1 however1 shrinks so considerably when burnt that the form given to it is destroyed and cracks easily form2 such vessels are also porous1 so that they will not hold water4 ,the addition of sand--that is1 silica in fine particles--or of chamotte--that is1 already burnt and crushed clay--renders the mass much more dense and incapable of cracking in the furnace4 ,nevertheless1 such clay articles 7bricks1 earthenware vessels1 c47 are still porous to liquids after being burnt1 because the clay in the furnace is only baked and does not fuse4 ,in order to obtain articles impervious to water the clay must either be mixed with substances which form a glassy mass in the furnace1 permeating the clay and filling up its pores1 or else only the surface of the article is covered with such a glassy fusible substance4 ,in the first case the purest kinds of clay give what is known as china1 in the second case porcelain or 'faence4' ,so1 for instance1 by covering the surface of clay articles with a layer of the oxides of lead and tin1 the well-known white glaze is obtained1 because the oxides of these metals give a white gloss when fused with silica and clay4 ,in the preparation of china1 fluor spar and finely ground silica is mixed up into the clay2 these ingredients give a mass which is infusible but softens in the furnace1 so that all the particles of the clay cohere in this softened mass1 which hardens on cooling4 ,a glaze composed of glassy substances1 which only fuse at a high temperature1 is also applied to the surface of china articles4 ,clay is the source from which alumina1 ,al#b,o#c1 and the majority of the compounds of aluminium are prepared4 ,among these compounds the most important are the alums--that is1 the double sulphates of potassium 7and allied metals7 and aluminium1 ,al,k7,,so#d7b1ab;,h#b,o4 ,when clay is treated with sulphuric acid diluted with a certain amount of water1 aluminium sulphate1 ,al#b7,,so#d7c1 is formed2 and if potassium carbonate or sulphate be added to this solution1 a double salt or alum is obtained in solution4 ,the alums crystallise easily1 and are prepared on a very large manufacturing scale owing to their being employed in the process of dyeing4 ,alums are soluble in water1 and1 on the addition of ammonia to their solutions1 they give hydrous alumina1 or aluminium hydroxide1 as a white gelatinous precipitate1 which is insoluble in water but easily soluble in acids1 even when dilute1 and in aqueous soda or potash4 ,the solubility of alumina in acids indicates the basic character of the oxide1 and its solubility in alkalis and its power of forming compounds with them shows the weakness of this basic character4 ,however1 the feeblest acids1 even carbonic acid1 take up the alkali from such a solution1 and the alumina then separates out in a precipitate as the hydroxide4 ,it must also be remembered as characteristic of the salt-forming properties of alumina that it does not combine with such feeble acids as carbonic1 sulphurous1 or hypochlorous1 c4--that is1 its compounds with these acids are decomposed by water4 ,it is also important to observe that the hydroxide is not soluble in aqueous ammonia4 ,alumina1 ,al#b,o#c--that is1 the anhydrous aluminium oxide--is met with in nature1 sometimes in a somewhat pure state1 having crystallised in transparent crystals1 which are often coloured by impurities 7chromic1 cobaltic1 and ferric compounds74 ,such are the ruby and sapphire1 the former red and the latter blue4 ,they have a specific gravity #dj1 are distinguished by their very great hardness1 which is second only to that of the diamond1 and they represent the purest form of alumina4 ,they are found in ,ceylon and other islands of the ,indian ,archipelago1 embedded in a rock matrix4#ah bis ,corundum is the same crystallised anhydrous alumina coloured brown by a trace of oxide of iron4 ,a very much larger portion of this impurity occurs in emery1 which is found in crystalline masses in ,asia ,minor and in ,massachusetts1 and owing to its extreme hardness is employed for polishing stones and metals4 ,in this anhydrous and crystalline state the aluminium oxide is a substance which very powerfully resists the action of reagents1 and is insoluble both in solutions of the alkalis and in strong acids4 ,it is only capable of passing into solution after being fused with alkalis4#ai ,alumina may be obtained in this form by artificial means if the hydroxide be ignited and then fused in the oxyhydrogen flame4#bj ,alumina also occurs in nature in combination with water--as1 for instance1 in the rather rare minerals hydrargillite 7sp4 gr4 #bc71 ,al#b,o#c1c;,h#b,o #b;,al7,,ho7#c1 and diaspore1 ,al#b,o#c1;,h#b,o #b;,al,o7,,ho7 7sp4 gr4 #cd74 ,a less pure hydrate1 mixed with ferric oxide1 sometimes occurs in masses 7at ,baux in the south of ,france7 and is termed bauxite2 it contains ,al#b,o#c1b;,h#b,o ,al#b,o7,,ho7#d 7sp4 gr4 #bf74 ,when bauxite is ignited with sodium carbonate1 carbonic anhydride is liberated and the alumina then combines with the sodium oxide1 forming a saline aluminate of the oxides of aluminium and sodium4 ,this is taken advantage of in practice for the preparation of pure alumina compounds on a large scale1 for bauxite is found in large masses 7in the ,south of ,france1 in ,austria1 and in ,carolina in ,south ,america71 and the resultant compound of alumina and sodium is soluble in water and does not contain ferric oxide4 ,this solution when subjected to the action of carbonic anhydride gives a precipitate of aluminium hydroxide1#ba which with acids forms aluminium salts4 ,if aqueous ammonia be added to a solution of aluminium sulphate a gelatinous precipitate is formed1 which at first remains suspended in the liquid and then on settling forms a gelatinous mass1 which itself indicates the colloidal property of aluminium hydroxide4 ,the following points are characteristic of this colloidal state3 7#a7 in an anhydrous state such a colloidal substance is insoluble in water1 as alumina is2 7#b7 in the hydrated state1 it is gelatinous and insoluble in water2 and 7#c7 it is also capable of existing in solutions1 from which it separates out in a non-crystalline state1 forming a substance resembling glue4 ,these different states of colloids were distinguished by ,graham1 who gave them the following very characteristic names4 ,he called the gelatinous form of the hydrate hydrogel1 i4e4 a gelatinous hydrate1 and the soluble form of the aqueous compound1 hydrosol1 from the ,latin for a soluble hydrate4 ,alumina readily and frequently assumes these states4 ,the gelatinous hydrate of alumina is its hydrogel4 ,it is1 as has been already mentioned1 insoluble in water1 and1 like all similar hydrogels1 shows not the faintest sign of crystallisation2 it is apt to vary in many of its properties with the amount of water it contains1 and loses its water on ignition1 leaving a white powder of the anhydrous oxide4 ,the hydrogel of alumina is soluble both in acids and alkalis4 ,it may also be obtained by the evaporation of its solutions in such feebly energetic acids as volatile acetic acid4 ,these properties are very frequently made use of in the arts1 and especially in the processes of dyeing1 because the hydrogel of alumina in precipitating attracts a number of colouring matters from their solutions1 the precipitate being thus coloured by the dyes attracted4#bb ,the preparation of fixed dyes and the employment of aluminous compounds 7mordants7 in the processes of dyeing are founded on this fact4#bc ,when precipitated upon the fibres of tissues 7calicoes1 linens1 c47 the aluminium hydroxide renders them impermeable to water2 this may be taken advantage of for the preparation of waterproof tissues4 #ah bis ,frmy 7#ahij7 obtained transparent rubies1 which crystallised in rhombohedra1 and resembled natural rubies in their hardness1 colour1 size1 and other properties4 ,he heated together a mixture of anhydrous alumina containing more or less caustic potash1 with barium fluoride and bichromate of potassium4 ,the latter is added to give the ruby its colour1 and is taken in small quantity 7not more than #d parts by weight to #ajj parts of alumina74 ,the mixture is put into a clay crucible1 and heated 7for from #ajj hours to #h days7 in a reverberatory furnace at a temperature approaching #a1ejj4 ,at the end of the experiment the crucible was found to contain a crystalline mass1 and the walls were covered with crystals of the ruby of a beautiful rose colour4 ,it was found that the access of moist air was indispensable for the reaction4 ,according to ,frmy1 the formation of the ruby may be here explained by the formation of fluoride of aluminium which under the action of the moist air at the high temperature of the furnace gives the ruby and hydrofluoric acid gas4 #ai ,the effects of purely mechanical subdivision on the solubility of alumina are evident from the fact that native anhydrous alumina1 when converted into an exceedingly fine powder by means of levigation1 dissolves in a mixture of strong sulphuric acid and a small quantity of water1 especially when heated in a closed tube at #bjj1 or when fused with acid sulphate of potassium 7see ,chapter ,,xiii41 ,note #i74 #bj ,the preparation of crystallised alumina is given on p4 #fe1 and in ,note #ah bis4 ,when alumina1 moistened with a solution of cobalt salt1 is ignited1 it forms a blue mass called ,thnard's salt4 ,this coloration is taken advantage of not only in the arts1 but also for distinguishing alumina from other earthy substances resembling it4 #ba ,the treatment of bauxite is carried on on a large scale1 chiefly in order to obtain alumina from alkaline solutions1 free from ferric oxide1 because in dyeing it is necessary to have salts of aluminium which do not contain iron4 ,but this end1 it would seem1 may also be obtained by igniting alumina containing ferric oxide in a stream of chlorine mixed with hydrocarbon vapours1 as ferric chloride then volatilises4 ,k4 ,bayer observed that in the treatment of bauxite with soda1 about #d molecules of sodium hydroxide pass into solution to #a molecule of alumina1 and that on agitating this solution 7especially in the presence of some already precipitated aluminium hydroxide71 about two-thirds of the alumina is precipitated1 so that only #a molecule of alumina to #ab molecules of sodium hydroxide remains in solution4 ,this solution is evaporated directly1 and used again4 ,he therefore treats bauxite directly with a solution of ,na,h,o at #agj in a closed boiler1 and on cooling adds hydrated alumina to the resultant solution4 ,the greater part of the dissolved alumina then precipitates on this hydrated alumina1 and the solution is used over again4 ,the hydroxide which separates from the alkaline solution contains ,al7,,oh7#c4 ,all these properties bear a great resemblance to those of boric acid4 ,it may be taken for granted that the relation between sodium hydroxide and alumina in solution varies with the mass of water4 ,if lime be added to a solution of alumina in alkali 7sodium aluminate7 calcium aluminate is precipitated1 from which acids first extract the lime1 leaving aluminium hydroxide1 which is easily soluble in acids 7,loewig74 ,when sodium aluminate is mixed with a solution of sodium bicarbonate1 a double carbonate of the alkali and aluminium is precipitated1 which is easily soluble in acids4 #bb ,these coloured precipitates of alumina are termed lakes1 and are employed in dyeing tissues and in the formation of various pigments--such as pastels1 oil colours1 c4 ,thus1 if organic colouring matters1 such as logwood1 madder1 c41 are added to a solution of any aluminium salt1 and then an alkali is added1 so that alumina may be precipitated1 these pigments1 which are by themselves soluble in water1 will come down with the precipitate4 ,this shows that alumina is able to combine with the colouring matter1 and that this compound is not decomposed by water4 ,the dyes then become insoluble in water4 ,if a dye be mixed with starch paste and aluminium acetate1 and then1 by means of engraved blocks having a design in relief1 we transfer this mixture to a fabric which is then heated1 the aluminium acetate will leave the hydrogel of alumina which binds the colouring matter1 and water will no longer be able to wash the pigment from the material--that is1 a so-called 'fixed' dye is obtained4 ,in the case of dyeing a fabric a uniform tint1 it is first soaked in a solution of aluminium acetate and then dried1 by which means the acetic acid is driven off1 while the hydrogel of alumina adheres to the fibres of the material4 ,if the latter be then passed through a solution of a dye in water1 the former will be attracted to the portions covered with alumina1 and closely adhere to them4 ,if certain parts of the material be protected by the application of an acid1 such as tartaric1 ,c#d;,h#f,o#f1 oxalic1 citric1 c4 7these acids being non-volatile71 the alumina will be dissolved in those parts1 and the pigment will not adhere1 so that after washing1 a white design will be obtained on those parts which have been so protected4 ,in dye-works the aluminium acetate is generally obtained in solution by taking a solution of alum1 and mixing it with a solution of lead acetate4 ,in this case lead sulphate is precipitated and aluminium acetate remains in solution1 together with either acetate or sulphate of potassium1 according to the amount of acetate of lead first taken4 ,the complete decomposition will be as follows3 ,k,al7,,so#d7b #b,pb7,c#b;,h#c,o#b7b ,,kc#b;,h#c,o#b ,al7,c#b;,h#c,o#b7c #b,pb,s,o#d1 or the less complete decomposition1 #b,k,al7,,so#d7b #c,pb7,c#b;,h#c,o#b7b #b;,al7,c#b;,h#c,o#b7c ,k#b,,so#d #c,pb,s,o#d4 ,if the resultant solution of aluminium acetate be evaporated or further boiled1 the acetic acid passes off and the hydrogel of alumina remains4 ,as the salt of potassium obtained in the solution passes away with the water used for washing1 and the salt of lead precipitated has no practical use1 this method for the preparation of aluminium acetate cannot be considered economical2 it is retained in the process of dyeing mainly because both the salts employed1 alum and sugar of lead1 easily crystallise1 and it is easy to judge of their degree of purity in this form4 ,indeed1 it is very important to employ pure reagents in dyeing1 because if impurity is present--such as a small quantity of an iron compound--the tint of the dye changes2 thus madders give a red colour with alumina1 but if oxide of iron be present the red changes into a violet tint4 ,the aluminium hydroxide is soluble in alkalis1 whilst ferric oxide is not4 ,therefore sodium aluminate--that is1 the dissolved compound of alumina and caustic soda--obtained1 as already described1 from bauxite1 is sometimes employed in dyeing4 ,every aluminium salt gives a solution containing sodium aluminate free from iron1 when it is mixed with excess of caustic soda4 ,this solution1 when mixed with a solution of ammonium chloride1 gives a precipitate of the hydrogel of alumina3 ,al7,,oh7#c #c,na,h,o #c,,nh#d;,cl ,al7,,oh7#c #c,na,cl #c,,nh#d,,oh4 ,there was originally free soda1 and on the addition of sal-ammoniac there is free ammonia1 and this does not dissolve alumina1 therefore the hydrogel of the latter is precipitated4 #bc ,another direct method for the preparation of pure aluminium compounds consists in the treatment of cryolite containing aluminium fluoride together with sodium fluoride1 ,al,na#c;,f#f4 ,this mineral is exported from ,greenland1 and is also found in the ,urals4 ,it is crushed and heated in reverberatory furnaces with lime1 and the resultant mass is treated with water2 sodium aluminate is then obtained in solution1 and calcium fluoride in the precipitate ,al,na#c;,f#f #c;,ca,o #c;,ca,f#b ,al,na#c,o#c4 ,the hydrosol of alumina--i4e4 the soluble aluminium hydroxide--is more difficult to obtain4#bd ,in order to obtain this soluble variety of alumina1 ,graham took a solution of its hydrogel in hydrochloric acid--that is1 a solution of aluminium chloride1 which is able to dissolve a still further quantity of the hydrogel of alumina1 forming a basic salt having probably one of the compositions ,al7,,ho7,cl#b or ,al7,,ho7#b;,cl4 ,when such a solution1 considerably diluted with water1 is subjected to dialysis--that is1 to diffusion through a membrane#be--the hydrochloric acid diffuses through the membrane and leaves the alumina in the form of hydrosol4 ,the resultant solution1 even when only containing two or three per cent4 of alumina1 passes into the hydrogel state with such facility that it is sufficient to transfer it from one vessel to another which has not been previously washed with water1 for the entire mass to solidify into a jelly4 ,but a solution containing not more than one-half per cent4 of alumina may even be boiled without coagulating2 however1 after the lapse of several days this solution will of its own accord yield the hydrogel of alumina4#be bis #bd ,crum first prepared a solution of basic acetate of alumina--that is1 a salt containing as large as possible an excess of aluminium hydroxide with as small as possible a quantity of acetic acid4 ,the solution must be dilute--that is1 not contain more than one part of alumina per #bjj of water--and if this solution be heated in a closed vessel 7so that the acetic acid cannot evaporate7 to the boiling point of water1 for one and a half to two days1 then the solution1 which apparently remains unaltered1 loses its original astringent taste1 proper to solutions of all the salts of alumina1 and has instead the purely acid taste of vinegar4 ,the solution then no longer contains the salt1 but acetic acid and the hydrosol of alumina in an uncombined state2 they may be isolated from each other by evaporating the acetic acid in shallow vessels at the ordinary temperature1 and with a thin layer of liquid the alumina does not separate as a precipitate4 ,when the acid vapours cease to come off there remains a solution of the hydrosol of alumina1 which is tasteless and has no action on litmus paper4 ,when concentrated1 this solution acquires a more and more gluey consistency1 and when completely evaporated over a water-bath it leaves a non-crystalline glue-like hydrate1 whose composition is ,al#b;,h#d,o#e ,al#b,o#c1b;,h#b,o4 ,the smallest quantity of alkalis1 and of many acids and salts1 will convert the hydrosol into the hydrogel of alumina--that is1 convert the aluminium hydroxide from a soluble into an insoluble form1 or1 as it is said1 cause the hydrate to coagulate or gelatinise4 ,the smallest amount of sulphuric acid and its salts will cause the alumina to gelatinise--that is1 cause the hydrogel to separate4 ,many such colloidal solutions are known 7,vol4 ,i4 p4 #ih1 ,note #eg74 #be ,in a dialyser1 ,vol4 ,i4 p4 #fc1 ,note #ah4 #be bis ,the different states in which the hydrates of alumina occur and are prepared resemble similar varieties of the hydrates of the oxides of iron and chromium1 of molybdic and tungstic acids1 as well as of phosphoric and silicic acids1 of many sulphides1 proteid substances1 c4 ,we shall therefore have occasion to recur to this subject in the further course of this work4 ,the most remarkable peculiarity of ,graham's solution is that it solidifies on litmus paper1 and leaves a blue ring on it1 which shows the alkaline--that is1 basic--character of the alumina in such a solution4 ,if in the dialysis the basic hydrochloric acid salt be replaced by a similar acetic acid salt1 a hydrosol of alumina is obtained which does not act upon litmus4 ,with respect to alumina as a base1 it is very important to observe that it is not only capable of combining with other bases#bf but that it does not give salts with feeble volatile acids 7like carbonic and hypochlorous72 it forms salts which are easily decomposed by water1 especially when heated1#bg as well as double and basic salts1#bh so that it forms a clear example of a feeble base4#bi ,to these characteristics of alumina we must add that it not only gives compounds of the type ,al,x#c1 but also the polymeric type ,al#b,x#f1 even when ,x is a simple univalent haloid like chlorine4 ,deville and ,troost showed 7#aheg7 that the vapour density of aluminium chloride 7at about #djj7 is #icg with respect to air--that is1 nearly #ace with respect to hydrogen1 and therefore the formula of its molecule is expressed by ,al#b;,cl#f1 and not ,al,cl#c1cj although in the case of boron1 arsenic1 and antimony1 which give oxides ,r#b,o#c of the same composition as ,al#b,o#c1 the chlorine compounds form non-polymeric molecules1 ,b,cl#c1 ,as,cl#c1 ,sb,cl#c4ca ,this duplication 7polymerisation7 of the form ,al,x#c is connected with the facility with which the salts of aluminium combine with other salts to form double salts and with aluminium hydroxide itself to form basic salts4 #bf ,compounds of alumina with bases 7aluminates1 see ,note #ba7 are sometimes met with in nature4 ,such are spinel 7see p4 #fe71 ,mg,o1,al#b,o#c ,mg,al#b,o#d1 chrysoberyl1 ,be,al#b,o#d1 and others4 ,magnetic oxide of iron1 ,fe,o1,fe#b,o#c ,fe#c,o#d1 and compounds like it1 belong to the same class4 ,here we evidently have a case of combination 'by analogy1' as in solutions and alloys1 accompanied by the formation of strictly definite saline compounds1 and such instances form a clear transition from so-called solutions and certain mixtures to the type of true salts4 #bg ,not only aluminium acetate 7,note #bd71 but also every other aluminium salt with a volatile acid1 parts with its acid on heating an aqueous solution--that is1 is decomposed by water1 and forms either basic salts or a hydrate of alumina4 ,by dissolving aluminium hydroxide in nitric acid we may easily obtain a well-crystallising aluminium nitrate1 ,al7,,no#c7c1i;,h#b,o1 which fuses at #gc without decomposing 7,ordway71 gives a basic salt1 #b;,al#b,o#c1f;,,hno#c1 at #ajj1 and at #adj leaves the aluminium hydroxide perfectly free from the elements of nitric acid4 ,but the solutions of this salt1 like those of the acetate1 are also able to yield aluminium hydroxide4 ,from all this it is evident that we must suppose that the solutions of this and similar salts contain an equilibrated dissociated system1 containing the salt1 the acid1 and the base1 and their compounds with water1 as well as partly the molecules of water itself4 ,such examples much more clearly confirm those conceptions of solutions which are given in the first chapter than a general preliminary acquaintance with the subject can do4 #bh ,as an example of native basic salts we may cite alunite1 or alum-stone 7sp4 gr4 #bf71 which sometimes occurs in crystals1 but more frequently in fibrous masses4 ,it has been found in masses in the ,caucasus 7at ,zaglik1 forty versts distance from ,elizabetpol71 and at ,tolfa1 near ,rome4 ,its composition is ,k#b,o1#c;,al#b,o#c1d,,so#c1f;,h#b,o 7alunite contains #i;,h#b,o74 ,it is soluble in water but not decomposed by it1 but after being slightly ignited it gives up alum to it4 ,it may be artificially prepared by heating a mixture of alum with aluminium sulphate in a closed tube at #bcj4 #bi ,as the colloidal properties are particularly sharply developed in those oxides 7,al#b,o#c1 ,si,o#b1 ,mo,o#c1 ,sn,o#b1 c47 which show 7like water also7 the properties of feeble bases and feeble acids1 there is probably some causal reason for this coincidence1 all the more so since among organic substances--gelatins1 albumins1 c4--the representatives of the colloids also have the property of feebly combining with bases and acids4 #cj ,since ,deville's experiments the question of the density of aluminium chloride has been frequently re-investigated4 ,the subject has more especially occupied the attention of ,nilson1 ,pettersson1 ,friedel and ,crafts1 and ,v4 ,meyer and his collaborators4 ,in general1 it has been found that at low temperatures 7up to #ddj7 the density is constant1 and indicates a molecule ,al#b;,cl#f2 whilst depolymerisation probably 7although it is not yet certain7 takes place at higher temperatures1 and the molecule ,al,cl#c is obtained4 ,along with this there has been1 and still is1 a difference of opinion as to the vapour density of aluminium ethyl and methyl--whether for instance1 ,al7,,ch#c7c or ,al#b7;,,ch#c7f expresses the molecule of the latter4 ,the interest of these researches is intimately connected with the question of the valency of aluminium1 if we hold to the opinion that elements in their various compounds have a constant and strictly definite valency4 ,in this case the formula ,al,cl#c or ,al7,,ch#c7c would show that ,al is trivalent1 and that consequently the compounds of aluminium are ,al7,,oh7#c1 ,al,o#c;,al1 and1 in general1 ,al,x#c4 ,but if the molecule be ,al#b;,cl#f1 it is--for the followers of the doctrine of the invariable valency of the elements--incompatible with the idea of the trivalency of aluminium1 and they assume it to be quadrivalent like carbon1 likening ,al#b;,cl#f to ethane ,c#b;,h#f ,,ch#c;,,ch#c1 although this does not explain why ,al does not form ,al,cl#d1 or1 in general1 ,al,x#d4 ,in this work another supposition is introduced2 according to this1 although aluminium1 as an element of group ,,iii41 gives compounds of the type ,al,x#e1 this does not exclude the possibility of these molecules combining with others1 and consequently with each other--that is1 forming ,al#b,x#f2 just as the molecules of univalent elements exist either as ,h#b1 ,cl#b1 c41 or as ,na1 and the molecules of bivalent elements either as ,zn1 or as ,s#b1 or even ,s#f4 ,in the first place it must be recognised that the limiting form does not exhaust all power of combination1 it only exhausts the capacity of the element for combining with ,x's1 but the saturated substance may afterwards combine with whole molecules1 which fact is best proved by the capacity of substances to form crystalline compounds with water1 ammonia1 c4 ,but in some substances this faculty for further combinations is less developed 7for instance1 in carbon tetrachloride1 ,c,cl#d71 whilst in others it is more so4 ,al,x#c combines with many other molecules4 ,now if a limiting form1 which does not combine with new ,x's1 nevertheless combines with other whole molecules1 it will naturally in some instances combine with itself1 will polymerise4 ,in this manner the mind clearly grasps the idea that the same forces which cause ,s#b to unite itself to ,cl#b1 or ,c#b;,h#d to ,cl#b1 c41 also unite molecules of a similar kind together2 thus polymerisation ceases to be an isolated fragmentary phenomenon1 and chemical combinations 'by analogy' acquire a particular and important interest4 ,in conformity with these views the following proposition may be made concerning the compounds of aluminium4 ,they are of the type ,al,x#c in the limit1 like ,,bx#c1 but those limiting forms are still able to combine to form ,al,x#c1,,rz1 and the aluminium chloride is a compound of this kind--i4e4 7,al,x#c7b4 ,in boron1 for example1 in ,b,cl#c1 this tendency to form further compounds is less developed4 ,hence boron chloride appears as ,b,cl#c1 and not 7,b,cl#c7b4 ,polymerisation is not only possible when a substance has not attained the limit 7although it is more probable then71 but also when the limiting form has been reached1 if only the latter has the faculty of combining with other whole molecules4 ,we may therefore conclude that aluminium1 like boron1 is trivalent in the same sense that lithium and sodium are univalent1 magnesium bivalent1 and carbon tetravalent4 ,in a word1 there is no reason to consider that aluminium is capable of forming compounds ,al,x#d1 and in that way to explain the existence of the molecule ,al#b;,cl#f4 ,furthermore1 there are many reasons for thinking that ,al,f#c1 ,al#b,o#c1 and other empirical formul do not express the molecular weights of these compounds1 but that they are much higher3 ,aln,f#cn1 ,al#bn,o#cn4 ,in recent years convincing proofs of the truth of the above statements have been obtained1 and of the independent existence of ,al,x#c in a state of vapour2 for ,comb has determined the vapour density of the volatile acetyl of aluminium acetate ,al7,c#c;,h#g,o#b7c 7which melts at #aic1 boils at #cae1 and distils without a trace of decomposition71 and has found that it exactly corresponds to the above molecular composition4 ,on the other hand1 ,louise and ,roux 7#ahhi7 by employing the method of 'freezing point depression' of solutions 7,chapter ,i41 ,note #di7 found that the molecules ,al#b7;,c#b;,h#e7f and ,al#b7;,c#e;,h#aa7f1 c41 correspond to the type ,al#b,x#f4 ,thus it may now be accepted that the molecular composition of the compounds of aluminium in their simplest form is ,al,x#c1 but that they may polymerise and give ,al#b,x#f or1 in general1 ,al#b,x#cn4 #ca ,in the case of gallium1 as a close analogue of aluminium1 ,lecoq de ,boisbaudran 7#ahhj7 showed that probably the molecule gallium chloride contains ,ga#b;,cl#f at low temperatures and high pressures1 and that it dissociates into ,ga,cl#c at high temperatures and low pressures4 ,the molecule of indium chloride seems to exist only in the simplest form1 ,in,cl#c4 ,aluminium sulphate1 ,al#b7,,so#d7c1 which is obtained by treating clay or the hydrates of alumina with sulphuric acid1 crystallises in the cold with #bg;,h#b,o1 or at the ordinary temperature in pearly crystals1 which are greasy to the touch and contain #af;,h#b,o4#cb ,its solutions act like sulphuric acid--for instance1 they evolve hydrogen with zinc1 forming basic salts1 which are sometimes met with in nature 7aluminite1 ,al#b,o#c1,,so#c1i;,h#b,o1 alumiane1 ,al#b,o#c1b,,so#c1 and others71 and may be obtained by the decomposition of normal salts and by the direct solution of the hydroxide in normal salts3 these exhibit a varying composition1 7,al#b,o#c7n7,,so#c7m7,h#b,o7q1 where m_/n is less than #c4 ,aluminium sulphate is now prepared 7from the pure hydrate obtained from bauxite1 ,note #ba7 in large quantities for dyeing purposes 7instead of alums7 as a mordant4 ,with solutions of the alkali sulphates 7potassium1 sodium1 ammonium1 rubidium1 and csium sulphates71 the normal salt easily forms double salts1 termed alums--for example1 the ordinary crystalline alum contains ,k,al7,,so#d7b1ab;,h#b,o1 or ,k#b,,so#d1;,al#b7,,so#d7c1bd;,h#b,o4 ,in the ammonium alums 7which leave a residue of alumina when ignited7 the potassium is replaced by ammonium 7,,nh#d74 ,alums are used in large quantities1 because there is scarcely any other salt which crystallises so easily4 ,in this respect the alums formed by potassium and ammonium are equally convenient to purify1 because they present a considerable difference in their solubility at the ordinary and higher temperatures4 ,if the crystallisation be conducted rapidly1 the salt separates in minute crystals1 but if it be slowly deposited1 especially in large masses1 as in factories1 then crystals several centimetres long are sometimes obtained4 ,at a higher temperature alums are very much more soluble1 and crystallise with greater difficulty1 and are therefore less easily freed from impurities2 at #j #ajj parts of water dissolve #c parts1 at #cj #bb parts1 at #gj #ij parts1 and at #ajj #ceg parts of potassium alum4#cc ,the solubility of ammonium alum is slightly less4 ,the specific gravity of potassium alum is #agd1 of ammonium alum #afc1 and of sodium alum #afj4 ,alums easily part with their water of crystallisation2 thus potash alum partially effloresces when exposed to the air1 and loses #i mol4 ,h#b,o under the receiver of an air-pump4 ,at #ajj1 dry air passed over alums takes up nearly all their water4 ,as we have already mentioned 7,chapter ,,xv471 the law of isomorphous substitutions exhibits itself more clearly in the alums than in any other salts1 and all alums not only contain the same amount of water of crystallisation1 ,,mr7,,so#d7b1ab;,h#b,o 7where ,m ,k1 ,,nh#d1 ,na2 ,r ,al1 ,fe1 ,cr71 and appear in crystals whose planes are inclined at equal angles1 but they also give every possible kind of isomorphous mixture4 ,the aluminium in them is easily replaced by iron1 chromium1 indium and sometimes by other metals1 whilst the potassium may be substituted by sodium1 rubidium1 ammonium1 and thallium1 and the sulphuric acid may be replaced by selenic and chromic acids4 #cb ,the pure salt 7#af;,h#b,o7 is not hygroscopic4 ,in the presence of impurities the amount of water increases to #ah;,h#b,o1 and the salt becomes hygroscopic4 #cc ,the common form of crystals of alums is octahedral1 but if this solution contains a certain small excess of alumina above the ratio #b;,al7,,oh7#c to ,k#b,,so#d1 and not more sulphuric acid than #c;,h#b,,so#d to #b;,al7,,oh7#c1 then it easily forms combinations of the cube and octahedron1 and these alums are called 'cubic' alums4 ,they are valued by the dyer because they can contain no iron in solution1 for oxide of iron is precipitated before alumina1 and if the latter be in excess there can be no oxide of iron present4 ,these alums were long exported from ,italy1 where they were prepared from alunite 7,note #bh74 ,aluminium chloride1 ,al#b;,cl#f1 is obtained1 like other similar chlorides1 7for instance ,mg,cl#b7 either directly from chlorine and the metal1 or by heating to redness an intimate mixture of the amorphous anhydrous oxide and charcoal in a stream of dry chlorine4#cc bis ,the resultant sublimate is very volatile1#cd and forms a crystalline1 easily fusible mass1 which deliquesces in the air and easily dissolves in water1 with the evolution of a large amount of heat4#cd bis ,on evaporating this solution1 hydrochloric acid and aluminium hydroxide are liberated4 ,but if the solution be heated in a closed tube1 with an excess of hydrochloric acid1 then1 on cooling1 crystals of ,al,cl#c1f;,h#b,o are obtained--that is1 aluminium chloride both combines with water and is decomposed by it4 ,and the faculty of the type ,al,x#c for combining with other molecules is seen in the compounds of ,al,cl#c with many other chlorine compounds4 ,thus1 for example1 a mixture of aluminium chloride with sulphur tetrachloride gives ,al#b;,cl#f1,s,cl#d1 under the action of chlorine1 whilst with phosphorus pentachloride it forms ,al,cl#c1,p,cl#e2 it also combines with ,n,o,cl4 ,thus1 the compounds ,al,cl#c1,n,o,cl1 ,al,cl#c1,p,o,cl#c1 ,al,cl#c1c,,nh#c1 ,al,cl#c1,k,cl1 ,al,cl#c1,na,cl are known4#ce ,the compound of aluminium and sodium chlorides1 ,al,na,cl#d1 is very fusible and much more stable in the air than aluminium chloride itself4 ,it seems to be of the same type as the alums4 ,this compound1 ,al,na,cl#d1 is employed in the extraction of metallic aluminium1 as we shall presently proceed to describe4 ,aluminium bromide1 which is obtained by the direct combination of metallic aluminium with bromine1 closely resembles the chloride2 it melts at #ij1 volatilises at #bgj1 and its vapour density indicates the formula ,al#b;,br#f4 ,aluminium iodide is obtained by heating iodine with finely divided aluminium in a closed tube2 it is so easily decomposed by oxygen that its vapour even explodes when mixed with it4#cf #cc bis ,it is also formed by the action of hydrochloric acid upon metallic aluminium 7,nilson and ,pettersson71 by heating alumina in a mixture of the vapours of naphthaline and ,h,cl 7,faure1 #ahhi71 and by the action of dry ,h,cl upon an alloy of #ad p4c41 or more of ,al and copper 7,mobery74 #cd ,aluminium chloride fuses at #agh1 boils at #ahc 7pressure #gee mm41 at #afh under a pressure of #bej mm41 and at #bac under #b1bgh mm471 according to ,friedel and ,crafts1 so that it boils immediately after fusion4 ,according to ,seubert and ,pallard 7#ahib71 ,al#b;,cl#f fuses at #aic4 ,aluminium bromide fuses at about #ib1 and the iodide at #ahe according to ,weber1 at #abe according to ,deville and ,troost4 ,all these halogen compounds of aluminium are soluble in water4 ,aluminium fluoride1 ,al,f#c 7,aln,f#cn71 is insoluble in water4 ,it is obtained by dissolving alumina in hydrofluoric acid2 a solution is then formed1 but it contains an excess of hydrofluoric acid4 ,when this solution is evaporated1 crystals containing ,al#b;,f#f1;,,hf1,h#b,o are obtained4 ,they are also insoluble in water4 ,by saturating the above solution with a large quantity of alumina1 and then evaporating1 we obtain crystals having the composition ,al#b;,f#f1g;,h#b,o4 ,all these compounds1 when ignited1 leave insoluble anhydrous aluminium fluoride4 ,it forms colourless rhombohedra1 which are non-volatile1 of sp4 gr4 #ca1 and are decomposed by steam into alumina and hydrofluoric acid4 ,the acid solution apparently contains a compound which has its corresponding salts2 by the addition of a solution of potassium fluoride1 a gelatinous precipitate of ,al,k#c;,f#f is obtained4 ,a similar compound occurs in nature--namely1 ,al,na#c;,f#f1 or cryolite1 sp4 gr4 #cj4 #cd bis ,in this respect aluminium chloride resembles the chloranhydrides of the acids1 and probably in the aqueous solution the elements of the hydrochloric acid are already separated1 at least partially1 from the aluminium hydroxide4 ,the solution may also be obtained by the action of aluminium hydroxide on hydrochloric acid4 #ce ,here we see an instance in confirmation of what has been said in ,note #cj--;i4e4 the action of the molecule ,al,cl#c4 ,we will cite still another instance confirming the power of alumina to enter into complex combinations4 ,alumina1 moistened with a solution of calcium chloride1 gives1 when ignited1 an anhydrous crystalline substance 7tetrahedral71 which is soluble in acids1 and contains 7,al#b,o#c7f7;,ca,o7#aj;,ca,cl#b4 ,even clay forms a similar stony substance1 which might be of practical use4 ,among the most complex compounds of aluminium1 ultramarine1 or lapis lazuli1 must be mentioned4 ,it occurs in nature near ,lake ,baikal1 in crystals1 some colourless and others of various tints--green1 blue1 and violet4 ,when heated it becomes dull and acquires a very brilliant blue colour4 ,in this form it is used for ornaments 7like malachite71 and as a brilliant blue pigment4 ,at the present time ultramarine is prepared artificially in large quantities1 and this process is one of the most important conquests of science2 for the blue tint of ultramarine has been the object of many scientific researches1 which have culminated in the manufacture of this native substance4 ,the most characteristic property of ultramarine is that when placed in sulphuric acid it evolves hydrogen sulphide and becomes colourless4 ,this shows that the blue colour of ultramarine is due to the presence of sulphides4 ,if clay be heated in a furnace with sodium sulphate and charcoal 7forming sodium sulphide7 without access of air1 a white mass is obtained1 which becomes green when heated in the air1 and when treated with water leaves a colourless substance known as 'white ultramarine4' ,when ignited in the air it absorbs oxygen and turns blue4 ,the coloration is ascribed to the presence of metallic sulphides or polysulphides1 but it is most probable that silicon sulphide1 or its oxysulphide1 ,si,o,s1 is present4 ,at all events the sulphides play an important part1 but the problem is not yet quite settled4 ,the formula ,na#h;,al#f,si#f,o#bd,s is ascribed to white ultramarine4 ,the green probably contains more sulphur1 and the blue a still larger quantity4 ,the last is supposed to contain ,na#h;,al#f,si#f,o#bd,s#c4 ,it is more probable 7according to ,guckelberger1 #ahhb7 that the composition of the blue varies between ,si#ah;,al#ah,na#bj,s#f,o#ga and ,si#ah;,al#ab,na#bj,s#f,o#fi4 ,the latter may be expressed as 7,al#b,o#c7f7,si,o#b7ah7,na#b,o7#aj,s#f, o#e1 which would indicate the presence of insufficiently-oxidised sulphur in ultramarine4 #cf ,at the ordinary temperature aluminium does not decompose water1 but if a small quantity of iodine1 or of hydriodic acid and iodine1 or of aluminium iodide and iodine1 is added to the water1 then hydrogen is abundantly evolved4 ,it is evident that here the reaction proceeds at the expense of the formation of ,al#b;,i#f1 and that this substance1 with water1 gives aluminium hydroxide and hydriodic acid1 which1 with aluminium1 evolves hydrogen4 ,aluminium probably belongs to those metals having a greater affinity for oxygen than for the halogens 7,note #cf tri74 ,metallic ,aluminium was first prepared by ,whler in #ahbb as a grey powder by the action of potassium on aluminium chloride4 ,he afterwards 7in #ahde7 obtained it as a white compact metal1 unoxidisable in the air1 and only slowly attacked by acids4 ,owing to the vast and wide occurrence of clay1 many efforts have been made in investigating in detail the methods for the extraction of this metal4 ,these efforts were brought to a successful issue 7#ahed7 by ,sainte-,claire ,deville1 who is also renowned for his doctrine of dissociation4 ,experiments on a large scale have proved that metallic aluminium1 although possessed of great lightness1 strength1 and durability1 is not so generally suitable for technical purposes as was at first thought4 ,nitric and many other acids1 indeed1 do not act on it1 but the alkalis1 alkaline substances1 and even salts--for instance1 moist table salt--humidity1 c41#cf bis tarnish it1 and hence objects made of aluminium suffer at the surfaces1 alter1 and cannot1 as was hoped1 replace the precious metals1 from which it differs in its extreme lightness4 ,but the alloys made with aluminium 7especially with copper1 for example aluminium bronze7 are very valuable in their properties and applications4 #cf bis ,as an example we may mention that if mercury comes in contact with metallic aluminium and especially if it be rubbed upon the surface of aluminium moistened with a dilute acid1 the ,al becomes rapidly oxidised 7,al#b,o#c being formed74 ,the oxidation is accompanied by a very curious appearance1 as it were of wool 7or fur7 formed by threads of oxide of aluminium growing upon the metal4 ,this was first pointed out by ,cass in #ahgj1 and subsequently by ,a4 ,sokoleff in #ahib4 ,this interesting and curious phenomenon has not to my knowledge been further studied4 ,i think it necessary1 however1 to add that according to ,lubbert and ,rascher's researches 7#ahia71 wine1 coffee1 milk1 oil1 urine1 earth1 c41 have no more action upon aluminium vessels than upon copper1 tin1 and other similar articles4 ,in the course of four months ordinary vinegar dissolved #jce grm4 of ,al per sq4 centimetre1 whilst a #e per cent4 solution of common salt dissolved about #jje grm4 of aluminium4 ,ditte 7#ahij7 showed that ,al is acted upon by nitric and sulphuric acids1 although only slowly 7owing to the formation of a layer of gas1 as in ,chapter ,,xvi41 ,note #aj7 and that the reaction proceeds much more rapidly in vacuo or in the presence of oxidising agents4 ,al is even oxidised by water on the surface1 but the thin coating of alumina formed prevents further action4 ,in the course of twelve hours nitric acid sp4 gr4 #achc dissolved at #ag about #bj grms4 of aluminium 7containing only a small amount of ,si1 #a-a_/d p4c47 from a sq4 metre of surface 7,le ,rouart1 #ahia74 ,the ,deville method for the preparation of metallic aluminium is based on the decomposition of the above-mentioned compound of sodium and aluminium chlorides by metallic sodium4 ,the compound is obtained by passing the vapour of aluminium chloride 7evolved from a mixture of alumina1 extracted from bauxite or cryolite1 with charcoal ignited in a stream of chlorine7 over red-hot salt1 when the compound ,al,na,cl#d1 is itself volatilised1 and may in this manner be obtained pure4 ,a mixture of this compound with salt and fluor spar1 or with cryolite1 is heated with a certain excess of sodium1 cut into small lumps4 ,on a large scale this operation is carried on in special furnaces with a small access of air and at a high temperature4 ,the decomposition takes place chiefly according to the equation ,na,al,cl#d #c,na #d,na,cl ,al4 ,neither charcoal nor zinc will reduce the oxygen compounds of aluminium2 even sodium and potassium do not act on alumina4 ,moreover1 metallic aluminium1 like magnesium1 is able to reduce even the metals of the alkalis from their oxygen compounds4 ,this is connected with the fact that the atom of oxygen evolves more heat in combining with ,al 7and ,mg7 than it does in combining with other metals2 whilst on the other hand1 chlorine 7and the other halogens7 evolve more heat in combining with the metals of the alkalis4#cf tri #cf tri ,in addition to the data given in ,chapters ,,xi41 ,,xiii41 and in ,chapter ,,xv41 ,note #ai1 the following are the amounts of heat in thousands of units1 evolved in the formation of the oxides and chlorides from the metals taken in gram-atomic quantities3 ,na#b,o #ajj2 ,mg,o #adj992 #a_/c;,al#b,o#c #abj992 #a_/c;,fe#b,o#c #fc992 ,na#b;,cl#b #aie2 ,mg,cl#b #aea2 #a_/c;,al#b;,cl#f #ajg2 #a_/c;,fe#b;,cl#f #fd4 ,the asterisks following the oxides of ,mg1 ,al and ,fe call attention to the fact that the existing data refer to the formation of the hydrates of these metals1 from which the heat of formation of the anhydrous oxides may easily be assumed1 because the heat of hydration 7for example1 ,mg,o ,h#b,o7 has not yet been determined4 ,since the close of the eighties the metallurgy of aluminium has taken a new direction1 based upon the action of an electric current upon cryolite at a high temperature1#cg and the solution of oxide of aluminium 7obtained from bauxite or in the form of corundum7 in it2 under these conditions metallic aluminium is reduced at the negative pole 7cathode7 in a sufficiently pure state1 and if the cathode be copper1 forms alloys with it4 ,such are ,hall's and ,cowle's 7both in the ,united ,states7 and the ,neuhausen process 7where the current is obtained from a dynamo worked by the ,falls of the ,rhine at ,schaffhausen74 ,as an example1 we will describe 7in the words of ,prof4 ,d4 ,p4 ,konovaloff1 who became acquainted with this process at the ,chicago ,exhibition71 ,hall's process as applied near ,pittsburg1 where it gives about #a1ejj kilos of ,al a day4 ,an iron box 7about #a metre long and #a_/b metre wide71 provided with a well rammed down charcoal lining1 is charged with a mixture of cryolite and ,al#b,o#c 7from bauxite71 over which salt is strewn1 and a current of #e1jjj ampres at #bj volts is passed through the mixture4 ,the anode is composed of a carbon cylinder 7about #i cm4 in diameter71 while the charcoal lining forms the cathode4 ,when the temperature inside the box is raised to a red heat by the current1 the mixture fuses and the ,al#b,o#c begins to decompose4 ,the ,al liberated collects at the bottom of the box1 whilst the oxygen evolved burns the charcoal anode4 ,when the decomposition is at an end1 and the resistance of the mass increases1 a fresh quantity of ,al#b,o#c is added1 and this is continued until the amount of impurities accumulated in the furnace and passing into the metal becomes too great4#cg bis #cg ,cryolite under the action of the current at about #a1jjj gives off the vapour of ,na which reduces the ,al1 but it recombines with the liberated fluorine and again passes into the fused mass4 ,it is important to obtain aluminium at as low a temperature as possible1 but the action proceeds far more easily with the solution 7alloy7 of oxide of aluminium in cryolite4 #cg bis ,the cost of working this process can be brought as low as #bj cents per lb4 or about #b-a_/b fcs4 per kilo4 ,in ,england1 ,castner1 prior to the introduction of the electric method1 obtained ,al by taking a mixture of #a1bjj parts of the double salt ,na,al,cl#d1 #fjj parts of cryolite1 and #cej parts of ,na1 and obtained about #abj parts of ,al1 so that the cost of this process is about #a-a_/b time that of the electric method4 ,buchner found that sulphide of aluminium1 ,al#b,s#c1 is more suitable for the preparation of ,al by the electrolytic method than ,al#b,o#c1 but since the formation of ,al#b,s#c by heating a mixture of ,al#b,o#c1 and charcoal in sulphur vapour proceeds with difficulty1 ,gray 7#ahid7 proposed to prepare ,al#b,s#c by heating a mixture of charcoal1 sulphate of aluminium1 and sodium fluoride4 ,the resultant molten mixture of ,na,f and ,al#b,s#c gives aluminium directly under the action of an electric current4 ,aluminium has a white colour resembling that of tin--that is1 it is greyer than silver and has the feebly dull lustre of tin1 but compared to tin and pure silver1 aluminium is very hard4 ,its density is #bfg--that is1 it is nearly four times lighter than silver and three times lighter than copper4 ,it melts at an incipient red heat 7#fjj71 and in so doing is but slightly oxidised4 ,at the ordinary temperature it does not alter in the air1 and in a compact mass it burns with great difficulty at a white heat1 but in thin sheets1 into which it may be rolled1 or as a very fine wire1 it burns with a brilliant white light1 since it forms an infusible and non-volatile oxide4 ,aluminium itself is non-volatile at a furnace heat4 ,these properties render ,al a very good reducing agent1 and ,n4 ,n4 ,beketoff showed that it reduces the oxides of the alkali metals 7,chapter ,,xiii41 ,note #db bis74 ,dilute sulphuric acid has scarcely any action on it1 but the strong acid dissolves it1 especially with the aid of heat4 ,nitric acid1 dilute or strong1 has no action whatever on it4 ,on the other hand1 hydrochloric acid dissolves aluminium with great ease1 as do also solutions of caustic soda and potash4 ,in the latter cases hydrogen is evolved4#ch #ch ,aluminium1 when heated to the high temperature of the electric furnace1 dissolves carbon and forms an alloy which1 according to ,moissan1 when rapidly treated with cold hydrochloric acid leaves a compound ,c#c;,al#d in the form of a yellow crystalline transparent powder1 sp4 gr4 #bcf 7see ,chapter ,,viii4 ,note #ab bis74 ,this carbide of aluminium ,c#c;,al#d corresponds to methane ,,ch#d1 for ,al replaces ,h#c and carbon ,o#b or ,h#d1 that is1 it is equal to three molecules of ,,ch#d with the substitution of twelve atoms of ,h in it by four of ,al1 or1 what is the same thing1 it is the duplicated molecule of ,al#b,o#c with the substitution of ,o#f by ,c#c4 ,and indeed ,c#c;,al#d under the action of water forms marsh gas and hydrate of alumina3 ,c#c;,al#d #ab;,h#b,o #c;,,ch#d #d;,al7,,oh7#c4 ,this decomposition gives a new aspect of the synthesis of hydrocarbons1 and quite agrees with what should follow from the action of water upon the metallic carbides as applied by me for explaining the origin of naphtha 7,chapter ,,viii41 ,notes #eg1 #eh1 and #ei74 ,frank 7#ahid7 by heating ,al with carbon obtained a similar although not quite pure compound1 which 7like ,ca,c#b7 evolves acetylene with hydrochloric acid i4e4 probably has the composition ,al,c#c4 ,aluminium forms alloys with different metals with great ease4 ,among them the copper alloy is of practical use4 ,it is called aluminium bronze4 ,this alloy is prepared by dissolving #aa p4c4 by weight of metallic aluminium in molten copper at a white heat4 ,the formation of the alloy is accompanied by the development of a considerable quantity of heat1 so that it glows to a bright white heat4 ,this alloy1 which corresponds with the formula ,al,cu#c1 presents an exceedingly homogeneous mass1 especially if perfectly pure copper be taken4 ,it is distinguished for its capacity to fill up the most minute impressions of the mould into which it may be cast1 and by its extraordinary elasticity and toughness1 so that objects cast from it may be hammered1 drawn1 c41 and at the same time it is fine-grained and exceedingly hard1 takes an excellent polish1 and1 what is most important1 its surface then remains almost unchangeable in the air1 and has a colour and lustre which may be compared to that of gold alloys4 ,hence aluminium bronze is much used in the arts for making spoons1 watches1 vessels1 forks1 knives1 and for ornaments1 c4 ,no less important is the fact that the admixture of one-thousandth part of aluminium with steel renders its castings homogeneous 7free from cavities7 to an extent that could not be arrived at by other means1 nor does the quality of the steel in any respect deteriorate by this admixture1 but rather is it improved4 ,in a pure state1 aluminium is only employed for such objects as require the hardness of metals with comparative lightness1 such as telescopes and various physical apparatus and small articles4 ,according to the periodic system of the elements1 the analogues of magnesium are zinc1 cadmium1 and mercury in the second group4 ,so also in the third group1 to which aluminium belongs1 we find its corresponding analogues gallium1 indium1 and thallium4 ,they are all three so rarely and sparingly met with in nature that they could only be discovered by means of the spectroscope4 ,this fact shows that they are partially volatile1 as should be the case according to the property of their nearest neighbours1 the very volatile zinc1 cadmium and mercury4 ,as with them1 in gallium1 indium1 and thallium the density of the metal1 decomposability of compounds1 c41 rises with the atomic weight4 ,but here we find a peculiarity which does not exist in the second group4 ,in the latter1 the fusibility increases with the atomic weight of magnesium1 zinc1 cadmium1 and mercury2 indeed1 the heaviest metal--mercury--is a liquid4 ,in the third group it is not so4 ,in order to understand this it is sufficient to turn our attention to the elements of the further groups of the uneven series--for instance1 to group ,v41 containing phosphorus1 arsenic1 and antimony1 or to group ,,vi41 with sulphur1 selenium1 and tellurium1 and also to group ,,vii41 where chlorine1 bromine and iodine are situated4 ,in all these instances the fusibility decreases with a rise of atomic weight2 the members of the higher series1 the elements of a high atomic weight1 fuse with greater difficulty than the lighter elements4 ,the representatives of the uneven series of group ,,iii41 aluminium1 gallium1 indium1 thallium1 forming1 as they do1 a transition1 all show an intermediate behaviour4 ,here the most fusible of all is the medium metal gallium1#ch bis which fuses at the heat of the hand2 whilst indium1 thallium1 and aluminium fuse at much higher temperatures4 #ch bis ,the same is the case in group ,,iv4 of the uneven series1 where tin is the most fusible4 ,thus the temperature of fusion rises on both sides of tin 7silicon is very infusible2 germanium1 #ijj2 tin1 #bcj2 lead1 #cbf72 as it also does in group ,,iii41 starting from gallium1 for indium fuses at #agf1 less easily than gallium but more easily than thallium 7#bid74 ,aluminium also fuses with greater difficulty than gallium4 ,zinc 7group ,,ii471 which has an atomic weight #fe1 should be followed in group ,,iii4 by an element with an atomic weight of about #fi4 ,it will be in the same group as ,al and should consequently give ,r#b,o#c1 ,r,cl#c1 ,r#b7,,so#d7c1 alums and similar compounds analogous to those of aluminium4 ,its oxide should be more easily reducible to metal than alumina1 just as zinc oxide is more easily reduced than magnesia4 ,the oxide ,r#b,o#c should1 like alumina1 have feeble but clearly expressed basic properties4 ,the metal reduced from its compounds should have a greater atomic volume than zinc1 because in the fifth series1 proceeding from zinc to bromine1 the volume increases4 ,and as the volume of zinc #ib1 and of arsenic #ah1 that of our metal should be near to #ab4 ,this is also evident from the fact that the volume of aluminium #aa1 and of indium #ad1 and our metal is situated in group ,,iii41 between aluminium and indium4 ,if its volume #aae and its atomic weight be about #fi1 then its density will be nearly #ei4 ,the fact that zinc is more volatile than magnesium gives reason for thinking that the metal in question will be more volatile than aluminium1 and therefore for expecting its discovery by the aid of the spectroscope1 c4 ,these properties were indicated by me for the analogue of aluminium in #ahga1 and ,i named it 7see ,chapter ,,xv47 eka-aluminium4 ,in #ahge1 ,lecoq de ,boisbaudran1 who had done much work in spectrum analysis1 discovered a new metal in a zinc blende from the ,pyrenees 7,pierrefitte74 ,he recognised its individuality and difference from zinc1 cadmium1 indium1 and the other companions of zinc by means of the spectroscope2 but he only obtained some fractions of a centigram of it in a free state4 ,consequently only a few of its reactions were determined1 as1 for instance1 that barium carbonate precipitates the new oxide from its salts 7alumina1 as is known1 is also precipitated74 ,lecoq de ,boisbaudran named the newly discovered metal gallium4 ,as one would expect the same properties for eka-aluminium as were observed in gallium1 ,i pointed out this fact at the time in the ,memoirs of the ,paris ,academy of ,sciences4 ,all the subsequent observations of ,lecoq de ,boisbaudran confirmed the identity between the properties of gallium and those indicated for eka-aluminium4 ,immediately after this the ammonium alum of gallium was obtained1 but the most convincing proof of all was found in the fact that the density of gallium although first apparently different 7#dg7 from that indicated above1 afterwards1 when the metal was carefully purified from sodium 7which was first used as a reducing agent71 proved to be just that 7#ei7 which would have been looked for in the analogue of aluminium2 and1 what was very important1 the equivalent 7#bcc7 and atomic weight 7#fih7 determined by the specific heat 7#jjh7 were shown by experiment to be such as would be expected4 ,these facts confirmed the universality and applicability of the periodic system of the elements4 ,it must be remarked that previous to it there was no means of either foretelling the properties or even the existence of undiscovered elements4#ci #ci ,the spectrum of gallium is characterised by a brilliant violet line of wave-length #dag millionths of a millimetre4 ,the metal can be separated from the solution1 containing a mixture of the many metals occurring in the zinc blende1 by making use of the following reactions3 it is precipitated by sodium carbonate in the first portions2 it gives a sulphate which1 on boiling1 easily decomposes into a basic salt1 very slightly soluble in water2 and it is deposited in a metallic state from its solutions by the action of a galvanic current4 ,it fuses at #cj1 and1 when once fused1 remains liquid for some time4 ,it oxidises with difficulty1 evolves hydrogen from hydrochloric acid and from potassium hydroxide1 and1 like all feeble bases 7for instance1 alumina and indium oxide71 it easily forms basic salts4 ,the hydroxide is soluble in a solution of caustic potash1 and slightly so in caustic ammonia4 ,gallium forms volatile ,ga,cl#c and ,ga,cl#b 7,nilson and ,pettersson74 ,much more light has been thrown on that element of the aluminium group which follows after cadmium 7its position in the periodic system is ,,iii41 #g1 that is1 it is in group ,,iii4 in the #gth series74 ,this is indium1 ,in1 which also occurs in small quantities in certain zinc ores4 ,it was discovered 7#ahfc7 by ,reich and ,richter 7and more fully investigated by ,winkler7 in the ,freiberg zinc ores1 and was named indium from the fact that it gives to the flame of a gas-burner a blue coloration1 owing to the indigo blue spectral lines proper to it4 ,the equivalent 7see ,chapter ,,xv41 ,note #ae71 specific heat1 and other properties of the metal confirm the atomic weight ,in #aac4dj #dj ,the vapour density of indium chloride1 ,in,cl#c 7,note #ca71 determined by ,nilson and ,pettersson1 confirms this atomic weight4 ,indium is separated from zinc and cadmium1 with which it occurs1 by taking advantage of the fact that its hydroxide is insoluble in ammonia1 that the solutions of its salts give indium when treated with zinc 7hence indium is dissolved after zinc by acids7 and that they give a precipitate with hydrogen sulphide even in acid solutions4 ,metallic indium is grey1 has a sp4 gr4 of #gdb1 fuses at #agf1 and does not oxidise in the air2 when ignited1 it first gives a black suboxide1 ,in#d,o#c1 then volatilises and gives a brown oxide1 ,in#b,o#c1 whose salts1 ,in,x#c1 are also formed by the direct action of acids on the metal1 hydrogen being evolved4 ,caustic alkalis do not act on indium1 from which it is evident that it is less capable of forming alkaline compounds than aluminium is2 however1 with potassium and sodium hydroxides1 solutions of indium salts give a colourless precipitate of the hydroxide1 which is soluble in an excess of the alkali1 like the hydroxides of aluminium and zinc4 ,its salts do not crystallise4 ,nilson and ,pettersson 7#ahhi71 by the action of ,h,cl upon ,in1 obtained volatile crystalline1 ,in,cl#b1 and by treating this compound with ,in1 ,in,cl also4 ,inasmuch as we found among the analogues of magnesium in group ,,ii4 a metal1 mercury1 heavier and more easily reduced than the rest1 and giving two grades of oxidation1 so we should expect to find a metal among the analogues of aluminium in group ,,iii4 which would be heavy1 easily reduced1 and give two grades of oxidation1 and would have an atomic weight greater than #bjj4 ,such is thallium4 ,it forms compounds of a lower type1 ,tl,x1 besides the higher unstable type ,tl,x#c1 just as mercury gives ,hg,x#b and ,hg,x4 ,in the form of the thallic oxide1 ,tl#b,o#c1 the base is but feebly energetic1 as would be expected by analogy with the oxides ,al#b,o#c1 ,ga#b,o#c1 and ,in#b,o#c1 whilst in thallous oxide1 ,tl#b,o1 the basic properties are sharply defined1 as might be expected according to the properties of the type ,r#b,o 7,chapter ,,xv474 ,thallium was discovered in #ahfa by ,crookes and by ,lamy in certain pyrites4 ,when pyrites are employed in the manufacture of sulphuric acid1 they are burned1 and give besides sulphurous anhydride the vapours of various substances which accompany the sulphur1 and are volatile4 ,among these substances arsenic and selenium are found1 and together with them1 thallium4 ,these substances accumulate in a more or less considerable quantity in the tubes through which the vapours formed in the combustion of the pyrites have to pass4 ,when the methods of spectrum analysis were discovered 7#ahfj71 a great number of substances were subjected to spectroscopic research1 and it was observed that those sublimations which are obtained in the combustion of certain pyrites contained an element having a very sharply-defined and characteristic spectrum--namely1 in the green portion of the spectra it gave a well-defined band 7wave-length #ece millionth millimetres7 which did not correspond with any then known element4#da #da ,thallium was afterwards found in certain micas and in the rare mineral crookesite1 containing lead1 silver1 thallium1 and selenium4 ,its isolation depends on the fact that in the presence of acids thallium forms thallous compounds1 ,tl,x4 ,among these compounds the chloride and sulphate are only slightly soluble1 and give with hydrogen sulphide a black precipitate of the sulphide ,tl#b,s1 which is soluble in an excess of acid1 but insoluble in ammonium sulphide4 ,under the action of a galvanic current solutions of thallium salts deposit the metal in the form of a heavy powder4 ,it is of a grey colour like tin1 is soft like sodium1 and has a metallic lustre4 ,its specific gravity is #aah1 it melts at #bij1 and volatilises at a high temperature4 ,when heated slightly above its melting point it forms an insoluble 7in water7 higher oxide1 ,tl#b,o#c1 as a dark-coloured powder1 generally however accompanied by the lower oxide ,tl#b,o1 which is also black but soluble in water and alcohol4 ,this solution has a distinctly alkaline reaction4 ,this thallous oxide1 melts at #cjj1 and is easily obtained from the hydroxide ,tl,h,o by igniting it without access of air 7in the presence of air the incandescent thallous oxide partly passes into thallic oxide74 ,thallous hydroxide1 ,tl,o,h1 crystallises with one molecule ,h#b,o in yellow prisms which are very easily soluble in water4 ,metallic thallium may be used for its preparation1 as the metal in the presence of water attracts oxygen from the air and forms the hydroxide4 ,but metallic thallium does not decompose water1 although it gives a hydroxide which is soluble in water4#da bis ,all the other data for the chemical and physical properties of thallium1 of its two grades of oxidation and of their corresponding salts1 are expressed by the position occupied by this metal in virtue of its atomic weight ,tl #bjd1 between mercury ,hg #bjj1 and lead ,pb #bjf4 #da bis ,the best method of preparing thallous hydroxide1 ,tl,o,h1 is by the decomposition of the requisite quantity of baryta by thallous sulphate1 which is slightly soluble in water2 barium sulphate is then obtained in the precipitate and thallous hydroxide in solution4 ,this solubility of the hydroxide is exceedingly characteristic1 and forms one of the most important properties of thallium4 ,these lower 7thallous7 compounds are of the type ,tl,x1 and recall the salts of the alkalis4 ,the salts ,tl,x are colourless1 do not give a precipitate with the alkalis or ammonia1 but are precipitated by ammonium carbonate1 because thallous carbonate1 ,tl#b;,,co#c1 is sparingly soluble in water4 ,platinic chloride gives the same kind of precipitate as it does with the salts of potassium--that is1 thallous platinochloride1 ,pt,tl#b;,cl#f4 ,all these facts1 together with the isomorphism of the salts ,tl,x with those of potassium1 again point out what an important significance the types of compounds have in the determination of the character of a given series of substances4 ,although thallium has a greater atomic weight and greater density than potassium1 and although it has a less atomic volume1 nevertheless thallous oxide is analogous to potassium oxide in many respects1 for they both give compounds of the same type1 ,,rx4 ,we may further remark that thallous fluoride1 ,tl,f1 is easily soluble in water as well as thallous silicofluoride1 ,si,tl#b;,f#f1 but that thallous cyanide1 ,tl,c,n1 is sparingly soluble in water4 ,this1 together with the slight solubility of thallous chloride1 ,tl,cl1 and sulphate1 ,tl#b,,so#d1 indicates an analogy between ,tl,x and the salts of silver1 ,ag,x4 ,as regards the higher oxide or the thallic oxide1 ,tl#b,o#c1 the thallium is trivalent in it--that is1 it forms compounds of the type ,tl,x#c4 ,the hydroxide1 ,tl,o7,,oh71 is formed by the action of hydrogen peroxide on thallous oxide1 or by the action of ammonia on a solution of thallic chloride1 ,tl,cl#c4 ,it is obtained as a brown precipitate1 insoluble in water but easily soluble in acids1 with which it gives thallic salts1 ,tl,x#c4 ,thallic chloride1 which is obtained by cautiously heating the metal in a stream of chlorine1 forms an easily fusible white mass1 which is soluble in water and able to part with two-thirds of its chlorine when heated4 ,an aqueous solution of this salt yields colourless crystals containing one equivalent of water4 ,it is evident from the above that all the thallic salts can easily be reduced to thallous salts by reducing agents such as sulphurous anhydride1 zinc1 c4 ,besides these salts1 thallic sulphate1 ,tl#b7,,so#d7c1g;,h#b,o1 thallic nitrate ,tl7,,no#c7c1d;,h#b,o1 c41 are known4 ,these salts are decomposed by water1 like the salts of many feeble basic metals--for example1 aluminium4 ,gallium1 indium1 and thallium belong to the uneven series1 and there should be elements of the even series in group ,,iii4 corresponding with calcium1 strontium1 and barium in group ,,ii4 ,these elements should in their oxides ,r#b,o#c present basic characters of a more energetic kind than those shown by alumina1 just as calcium1 strontium1 and barium give more energetic bases than magnesium1 zinc1 and cadmium4 ,such are yttrium and ytterbium1 which occur in a rare ,swedish mineral called gadolinite1 and are therefore termed the gadolinite metals4 ,to these belong also the metal lanthanum1 which accompanies the two other metals cerium and didymium in the mineral cerite1 and it therefore belongs to the cerite metals4 ,all these metals and certain others accompanying them1 give basic oxides ,r#b,o#c4 ,at first their formula was supposed to be ,,ro1 but the application of the periodic system required their being counted as elements of groups ,,iii4 and ,,iv41 which was also confirmed by the determination of the specific heats of these metals1#db and better still by the fact that ,nilson and ,clve1 in their researches on the gadolinite metals 7#ahgi71 discovered that they contain a peculiar and very rare element1 scandium1 which by the magnitude of its atomic weight1 ,sc #dd1 and in all its properties1 exactly corresponds with the metal 7previously foretold on the basis of the periodic system7 ekaboron1 whose properties were determined by taking the cerite and gadolinite metals as forming oxides ,r#b,o#c4dc #db ,the specific heat of cerium determined 7#ahgj7 by me1 and afterwards confirmed by ,hillebrand1 corresponds with that atomic weight of cerium according to which the composition of two oxides should be ,ce#b,o#c and ,ce,o#b4 ,hillebrand also obtained metallic lanthanum and didymium by decomposing their salts by a galvanic current1 and he found their specific heats to be near that of cerium and about #jjd1 and it is therefore justifiable to give them an atomic weight near that of cerium1 as was done on the basis of the periodic law4 ,up to #ahgj yttrium oxide was also given the formula ,,ro4 ,having re-determined the equivalent of yttrium oxide 7with respect to water71 and found it to be #gdf1 ,i considered it necessary to also ascribe to it the composition ,y#b,o#c1 because then it falls into its proper place in the periodic system4 ,if the equivalent of the oxide to water be #gdf1 it contains #ehf of metal per #af of oxygen1 and consequently one part by weight of hydrogen replaces #bic of yttrium1 and if it be regarded as bivalent 7oxide ,,ro71 it would not1 by its atomic weight #ehf1 find a place in the second group4 ,but if it be taken as trivalent--that is1 if the formula of its oxide be ,r#b,o#c and salts ,,rx#c--then ,y #hh1 and a position is open for it in the third group in the sixth series after rubidium and strontium4 ,these alterations in the atomic weights of the cerite and gadolinite metals were afterwards accepted by ,clve and other investigators1 who now ascribe a formula ,r#b,o#c to all the newly discovered oxides of these metals4 ,but still the position in the periodic system of certain elements--for example of holmium1 thulium1 samarium1 and others--has not yet been determined for want of a sufficient knowledge of their properties in a state of purity4 #dc ,so1 for example1 in #ahga1 in the ,journal of the ,russian ,physico-,chemical ,society 7p4 #de7 and in ,liebig's ,annalen1 ,supt4 ,band viii4 #aih1 ,i deduced1 on the basis of the periodic law1 an atomic weight #dd for ekaboron1 and ,nilson in #ahhh found that of scandium1 which is ekaboron1 to be ,sc #ddjc1 ,the periodic law showed that the specific gravity of the ekaboron oxide would be about #he1 that it would have decided but feeble basic properties and that it would give colourless salts4 ,and this proved to be the case with scandium oxide4 ,in describing scandium1 ,clve and ,nilson acknowledge that the particular interest attached to this element is due to its complete identity with the expected element ekaboron4 ,and this accurate foretelling of properties could only be arrived at by admitting that alteration of the atomic weights of the cerite and gadolinite metals which was one of the first results of the application of the periodic system of the elements to the interpretation of chemical facts4 ,in my first memoirs1 namely1 in the ,bulletin of the ,st4 ,petersburg ,academy of ,sciences1 vol4 viii4 7#ahgj71 and in ,liebig's ,annalen 7l4 c4 p4 #afh7 and others1 ,i particularly insisted on the necessity of altering the then accepted atomic weights of cerium1 lanthanum1 and didymium4 ,clve1 ,hglund1 ,hillebrand and ,norton1 and more especially ,brauner1 and others accepted the proposed alteration1 and gave fresh proofs in favour of the proposed alterations of these atomic weights4 ,the study of the fluorides was particularly important4 ,placing cerium in the fourth group1 the composition of its highest oxide would then be ,ce,o#b1 and its compounds ,ce,x#d and the lower oxide1 ,ce#b,o#c or ,ce,x#c4 ,brauner obtained the fluoride ,ce,f#d1;,h#b,o corresponding with the first1 and a double crystalline salt1 #c,,kf1#b;,ce,f#d1b;,h#b,o1 without any admixture of compound of the lower grade ,ce,x#c1 which generally occur together with the majority of salts corresponding with ,ce,x#d4 ,it will be seen from these formul and from the tables of the elements1 that cerium and didymium do not belong to the third group1 which is now being described1 but we mention them here for convenience1 as all the cerite and gadolinite metals have much in common4 ,these metals1 which are rare in nature1 resemble each other in many respects1 always accompany each other1 are with difficulty isolated from each other1 and stand together in the periodic system of the elements2 they have acquired a peculiar interest owing to their having been in #ahgj the objects of the study of ,marignac1 ,delafontaine1 ,soret1 ,lecoq de ,boisbaudran1 ,brauner1 ,clve1 ,nilson1 the professors of ,upsala1 and others4 ,the cerite and gadolinite metals occur in rare siliceous minerals from ,sweden1 ,america1 the ,urals1 and ,baikal1 such as cerite 7in ,sweden71 gadolinite1 and orthite2 and in still rarer minerals formed by titanic1 niobic1 and tantalic acids1 such as euxenite in ,norway and ,america1 and samarskite in ,norway1 the ,urals and ,america1 and in a few rare fluorides and phosphates4 ,among the latter1 monazite is found in somewhat considerable quantities in ,brazil and ,north ,carolina2 this contains the phosphate of cerium1 ,ce,p,o#d 7 ,ce#b,o#c,p#b,o#c71 together with didymium1 thorium and lanthanum 7according to ,w4 ,edron and ,shapleigh's analyses71 and is now used for preparing that mixture of the oxides of the rare metals 7especially ,th,o#b1 ,ce#b,o#c1 ,la#b,o#c1 c471 which is employed for incandescent burners 7,auer von ,welsbach71 as it has been found by experiment that these oxides when raised to incandescence in a non-luminous gas flame1 give a far more brilliant flame with a smaller consumption of gas1 besides being suitable for such non-luminous gases as water gas4 ,the insufficiency of material to work upon1 and the difficulty of separating the oxides from each other1 are the chief reasons why the composition of the compounds of these rare metals is so imperfectly known4 ,cerite is the most accessible of these minerals4 ,besides silica it contains more than #ej p4c4 of the oxides of cerium1 lanthanum 7from #d p4c471 and didymium4 ,the decomposition of its powder by sulphuric acid gives sulphates1 all of which are soluble in water4 ,the other minerals mentioned above are also decomposed in the same manner4 ,the solution of sulphates is precipitated with free oxalic acid1 which forms salts insoluble in water and dilute acids with all the cerite and gadolinite oxides4 ,the oxides themselves are obtained by igniting the oxalates4 ,when ignited in the air the cerium passes from its ordinary oxide ,ce#b,o#c into the higher oxide ,ce,o#b1 which is so feeble a base that its salts are decomposed by water1 and it is insoluble in dilute nitric acid4 ,therefore it is always possible to remove all the cerium oxide by repeated ignitions and solutions in sulphuric acid4 ,the further separation of the metals is mainly based on four methods employed by many investigators4 7a7 ,a solution of the mixed salts is treated with an excess of solid potassium sulphate4 ,double salts1 such as ,ce#b7,,so#d7c1c,k#b,,so#d1 are thus formed4 ,the gadolinite metals1 namely yttrium1 ytterbium1 and erbium1 then remain in solution--that is1 their double salts are soluble in a solution of potassium sulphate1 whilst the cerite metals--namely1 cerium1 lanthanum1 and didymium--are precipitated1 that is1 their double salts are insoluble in a saturated solution of potassium sulphate4 ,this ordinary method of separation1 however1 appears from the researches of ,marignac to be so untrustworthy that a considerable amount of didymium and the other metals remain in the soluble portion1 owing to the fact that1 although individually insoluble1 they are dissolved when mixed together4 ,thus erbium and terbium occur both in the solution and precipitate4 ,nevertheless1 beryllium1 yttrium1 erbium1 and ytterbium belong to the soluble1 and scandium1 cerium1 lanthanum1 didymium1 and thorium to the insoluble portion4 ,the insoluble salt of scandium1 for example 7i4e4 insoluble in a solution of potassium sulphate71 has a composition ,sc#b7,,so#d7c1c,k#b,,so#d4 7b7 ,the oxides obtained by the ignition of the oxalates are dissolved in nitric acid 7the nitrates of the cerite metals easily form double salts with those of the alkali metals1 and as some--for example1 the ammonio-lanthanum salt--crystallise very well1 they should be studied and applied to the analytical separation of these metals71 the solution is then evaporated to dryness1 and the residue fused4 ,all nitrates are destroyed by heat2 those of aluminium and iron1 c41 very easily1 those of the cerite and gadolinite metals also easily 7although not so easily as the above7 but in different degrees and sequence2 so that by carrying on the decomposition carefully from the beginning it is possible to destroy the nitrate of only one metal without touching the others1 or leaving them as insoluble basic salts4 ,this method1 like the preceding and the two following1 must be repeated as many as seventy times to attain a really constant product of fixed properties1 that is1 one in which the decomposed and undecomposed portions contain one and the same oxide4 ,this method1 due to ,berlin and worked out by ,bunsen1 has given in the hands of ,marignac and ,nilson the best results1 especially for the separation of the gadolinite metals1 ytterbium and scandium4 7c7 ,a solution of the salts is partially precipitated by ammonia2 that is1 the solution is mixed with a small quantity of ammonia insufficient for the precipitation of the entire quantity of the bases 7fractional precipitation74 ,thus1 the didymium hydroxide is first precipitated from a mixture of the salts of didymium and lanthanum4 ,a partial separation may be effected by repeating the solution of the precipitate and fractional precipitation1 but a perfectly pure product is scarcely attainable4 7d7 ,the formates having different degrees of solubility 7lanthanum formate #dbj parts of water per one of salt1 didymium formate #bba1 cerium formate #cfj1 yttrium and erbium formates easily soluble7 give a possible means of separating certain of the gadolinite metals from each other by a method of fractional solution and precipitation1 as ,bunsen1 ,bahr1 ,clve1 and others have pointed out4 7e7 ,crookes 7#ahic7 took advantage of the fractional precipitation of alcoholic solutions of the chlorides by amylene1 and by this means separated1 for example1 erbium1 terbium1 and others4 7f7 ,lastly1 oxide of thorium ,th,o#b 7,chapter ,,viii41 ,note #ei7 is separated by means of its solubility in a solution of sodium carbonate4 ,a good method of separating these metals is not known1 for they are so like each other4 ,there are also only a few methods of distinguishing them from each other1 and we can only add the following four to the above4 a ,the faculty of oxidising into a higher oxide4 ,this is very characteristic for cerium1 which gives the oxides ,ce#b,o#c and ,ce,o#b or ,ce#b,o#d4 ,didymium also gives one colourless oxide1 ,di#b,o#c1 which is capable of forming salts 7of a lilac colour71 and another1 according to ,brauner1 ,di#b,o#e which is dark brown and does not form salts1 so far as is known1 and 7like ceric oxide7 acts as an oxidising agent1 like the higher oxides of tellurium1 manganese1 lead1 and others4 ,lanthanum1 yttrium1 and many others are not capable of such oxidation4 ,the presence of the higher oxides may be recognised by ignition in a stream of hydrogen1 by which means the higher oxides are reduced to the lower1 which then remain unaltered4 b ,the majority of the salts of the gadolinite and cerite metals are colourless1 but those of didymium and erbium are rose-coloured1 the salts of the higher oxide of cerium1 ,ce,x#d1 yellow1 of the higher oxide of terbium1 yellow1 c4 ,thus1 the first metals obtained from gadolinite were yttrium1 giving colourless1 and erbium1 giving rose-coloured1 salts4 ,afterwards it was found that the salts of erbium of former investigators contained numerous colourless salts of scandium1 ytterbium1 c41 so that a coloration sometimes indicates the presence of a small impurity1 as was long known to be the case in minerals1 and therefore this point of distinction cannot be considered trustworthy4 c ,in a solid state and in solutions1 the salts of didymium1 samarium1 holmium1 c41 give characteristic absorption spectra1 as we pointed out in ,chapter ,,xiii41 and this naturally is connected with the colour of these salts4 ,the most important point is1 that those metals which do not give an absorption spectrum--for example1 lanthanum1 yttrium1 scandium1 and ytterbium--may be obtained free from didymium1 samarium1 and the other metals giving absorption spectra1 because the presence of the latter may be easily recognised by means of the spectroscope1 whilst the presence of the former in the latter cannot be distinguished1 and therefore the purification of the former can be carried further than that of the latter4 ,we may further remark that the sensitiveness of the spectrum reaction for didymium is so great that it is possible with a layer of solution half a metre thick to recognise the presence of #a part of didymium oxide 7as salt7 in #dj1jjj parts of water4 ,cossa determined the presence of didymium 7together with cerium and lanthanum7 in apatites1 limestones1 bones1 and the ashes of plants by this method4 ,the main group of dark lines of didymium correspond with wave-lengths of from #ehj to #egj millionths mm42 and the secondary to about #ebj1 #gcj1 #dhj1 c4 ,the chief absorption bands of samarium are #dgb-dhf1 #dag1 #ejj1 and #eei4 ,besides which1 ,crookes applied the investigation of the spectra of the phosphorescent light which is emitted by certain earths in an almost perfect vacuum1 when an electric discharge is passed through it1 to the discovery and characterisation of these rare metals4 ,but it would seem that the smallest admixture of other oxides 7for example1 bismuth1 uranium7 so powerfully influences these spectra that the fundamental distinctions of the oxides cannot be determined by this method4 ,besides which1 the spectra obtained by the passage of sparks through solutions or powders of the salts are determined and applied to distinguishing the elements1 but as spectra vary with the temperature and elasticity 7concentration7 this method cannot be considered as trustworthy4 d ,the most important point of distinction of individual metallic oxides is given by the direct determination of their equivalent with respect to water--that is1 the amount of the oxide by weight which combines 7like water7 with #hj parts by weight of sulphuric anhydride1 ,,so#c1 for the formation of a normal salt4 ,for this purpose the oxide is weighed and dissolved in nitric acid1 sulphuric acid is then added1 and the whole is evaporated to dryness over a water-bath and then heated over a naked flame sufficiently strongly to drive off the excess of sulphuric acid1 but so as not to decompose the salt 7the product would in that case not be perfectly soluble in water72 then1 knowing the weight of the oxide and of the anhydrous sulphate1 we can find the equivalent of the oxide4 ,the following are the most trustworthy figures in this connection3 scandium oxide #dece 7,nilson71 yttrium oxide #geg 7,clve2 according to my determination1 #ahga--gdf71 cerous oxide--that is1 the lower form of oxidation of cerium1 according to various investigators 7,bunsen1 ,brauner1 and others7 from #ajh to #aaa1 the higher oxide of cerium from #he to #hg1 lanthanum oxide1 according to ,brauner1 #ajh1 didymium oxide 7in salts of the ordinary lower form of oxidation7 about #aab 7,marignac1 ,brauner1 ,clve71 samarium oxide about #aaf 7,clve71 ytterbium oxide #acac 7,nilson74 ,it may not be superfluous here to draw attention to the fact that the equivalent of the oxides of all the gadolinite and cerite metals for water distribute themselves into four groups with a somewhat constant difference of nearly #cj4 ,in the first group is scandium oxide with equivalent #de1 in the second1 yttrium oxide #gf1 in the third1 lanthanum1 cerium1 didymium1 and samarium oxides with equivalent about #aaj1 and1 in the fourth1 erbium1 ytterbium1 and thorium oxides with equivalent about #aca4 ,the common difference of period is nearly #de4 ,and if we ascribe the type ,r#b,o#c to all the oxides--that is1 if we triple the weight of the equivalent of the oxide--we shall obtain a difference of the groups nearly equal to #ij1 which1 for two atoms of the metal1 forms the ordinary periodic difference of #de4 ,if one and the same type of oxide ,r#b,o#c be ascribed to all these elements 7as now generally accepted1 in many cases there being insufficiently trustworthy data71 then the atomic weights should be ,sc #dd1 ,y #hi1 ,la #ach1 ,ce #adj1 ,di #add1 7neodymium #adj1 praseodymium #add71 ,sm #aej1 ,yb #agc1 also terbium #adg1 holmium #afb1 alphayttrium #aeg1 erbium #aff1 thulium #agj1 decipium #aga4 ,it should be observed that there may be instances of basic salts4 ,if1 for example1 an element with an atomic weight #ij gave an oxide ,,ro#b1 but salts ,,rox#b1 then by counting its oxide as ,r#b,o#c its atomic weight would be #aei4 ,all the points distinguishing many gadolinite and cerite elements have not been sufficiently well established in certain cases 7for example1 with decipium1 thulium1 holmium1 and others74 ,at present the most certain are yttrium1 scandium1 cerium1 and lanthanum4 ,in the case of didymium1 for example1 there is still much that is doubtful4 ,didymium1 discovered in #ahdb by ,mosander after lanthanum1 differs from the latter in its absorption spectrum and the lilac-rose colour of its salts4 ,delafontaine 7#ahgh7 separated samarium from it4 ,welsbach showed that it contains two particular elements1 neodymium 7salts bluish-red7 and praseodymium 7salts apple-green71 and ,becquerel 7#ahhg7 by investigating the spectra of crystals1 recognised the presence of six individual elements4 ,probably1 therefore1 many of the now recognised elements contain a mixture of various others1 and as yet there is not enough confirmation of their individuality4 ,as regards yttrium1 scandium1 cerium1 and lanthanum1 which have been established without doubt1 ,i think that1 owing to their great rarity in nature and chemical art1 it would be superfluous to describe them further in so elementary a work as the present4 ,we may add that ,winkler 7#ahia7 obtained a hydrogen compound of lanthanum1 whose composition 7according to ,brauner7 is ,la#b;,h#c1 as would be expected from the composition of ,na#b;,h1 ,mg#b;,h#b1 c4 ,c4 ,winkler 7#ahia71 on reducing ,ce,o#b with magnesium1 also remarked a rapid absorption of hydrogen1 and showed that a hydride of cerium1 ,ce,h#b1 corresponding to ,ca,h1 and the other similar hydrides of metals of the alkaline earths1 is formed 7,chapter ,,xiv41 ,note #fc74 ,the brevity of this work and the great rarity of the above-mentioned elements will give me the right to exclude their description1 all the more as the principles of the periodic system enable many of their properties to be foreseen1 and as their practical uses 7cerium oxalate is used in medicine1 and didymium oxide in the manufacture of glass1 a mixture of the oxides of lanthanum and similar metals is employed for giving a bright light1 as this mixture emits a brilliant white light when brought to incandescence7 are very limited1 by reason of their great rarity in nature1 and the difficulty of separating them from one another4 ,,chapter ,,xviii ,,silicon ,,and ,,the ,,other ,,elements ,,of ,,the ,,fourth ,,group ,carbon1 which gives the compounds ,,ch#d1 and ,,co#b1 belongs to the fourth group of elements4 ,the nearest element to carbon is silicon1 which forms the compounds ,si,h#d and ,si,o#b2 its relation to carbon is like that of aluminium to boron or phosphorus to nitrogen4 ,as carbon composes the principal and most essential part of animal and vegetable substances1 so is silicon almost an invariable component part of the rocky formations of the earth's crust4 ,silicon hydride1 ,si,h#d1 like ,,ch#d1 has no acid properties1 but silica1 ,si,o#b1 shows feeble acid properties like carbonic anhydride4 ,in a free state silicon is also a non-volatile1 slightly energetic non-metal1 like carbon4 ,therefore the form and nature of the compounds of carbon and silicon are very similar4 ,in addition to this resemblance1 silicon presents one exceedingly important distinction from carbon3 namely1 the nature of the higher degree of oxidation4 ,that is1 silica1 silicon dioxide1 or silicic anhydride1 ,si,o#b is a solid1 non-volatile1 and exceedingly infusible substance1 very unlike carbonic anhydride1 ,,co#b1 which is a gas4 ,this expresses the essential peculiarity of silicon4 ,the cause of this distinction may be most probably sought for in the polymeric composition of silica compared with carbonic anhydride4 ,the molecule of carbonic anhydride contains ,,co#b1 as seen by the density of this gas4 ,the molecular weight and vapour density of silica1 were it volatile1 would probably correspond with the formula ,si,o#b1 but it might be imagined that it would correspond to a far higher atomic weight of ,sin,o#bn1 principally from the fact that ,si,h#d is a gas like ,,ch#d1 and ,si,cl#d is a liquid and volatile1 boiling at #eg--that is1 even lower than ,c,cl#d1 which boils at #gf4 ,in general1 analogous compounds of silicon and carbon have nearly the same boiling points if they are liquid and volatile4#a ,from this it might be expected that silicic anhydride1 ,si,o#b1 would be a gas like carbonic anhydride1 whilst in reality silica is a hard non-volatile substance1#a bis and therefore it may with great certainty be considered that in this condition it is polymeric with ,si,o#b1 as on polymerisation--for instance1 when cyanogen passes into paracyanogen1 or hydrocyanic acid into cyanuric acid 7,chapter ,,ix47--very frequently gaseous or volatile substances change into solid1 non-volatile1 and physically denser and more complex substances4#b ,we will first make acquaintance with free silicon and its volatile compounds1 as substances in which the analogy of silicon with carbon is shown1 not only in a chemical but also in a physical sense4#c #a ,chloroform1 ,c,h,cl#c1 boils at #fj1 and silicon chloroform1 ,si,h,cl#c1 at #cd2 silicon ethyl1 ,si7,c#b;,h#e7d1 boils at about #aej1 and its corresponding carbon compound1 ,c7,c#b;,h#e7d1 at about #abj2 ethyl orthosilicate1 ,si7,,oc#b;,h#e7d1 boils at #afj1 and ethyl orthocarbonate1 ,c7,,oc#b;,h#e7d1 at #aeh4 ,the specific volumes in a liquid state--that is1 those of the silicon compounds--generally are slightly greater than those of the carbon compounds2 for example1 the volumes of ,c,cl#d #id1 ,si,cl#d #aab1 ,c,h,cl#c #ha1 ,si,h,cl#c #hb1 of ,c7,,oc#b;,h#e7d #ahf1 and ,si7,,oc#b;,h#e7d #bja4 ,the corresponding salts have also nearly equal specific volumes2 for example1 ,ca,c,o#c #cg1 ,ca,si,o#c #da4 ,it is impossible to compare ,si,o#b and ,,co#b1 because their physical states are so widely different4 #a bis ,but silica fuses and volatilises 7,moissan7 in the heat of the electric furnace1 about #cjjj1 ,si,o#b is also partially volatile at the temperature attained in the flame of detonating gas 7,cremer1 #ahib74 #b ,a property of intercombination is observable in the atoms of carbon1 and a faculty for intercombination1 or polymerisation1 is also seen in the unsaturated hydrocarbons and carbon compounds in general4 ,in silicon a property of the same nature is found to be particularly developed in silica1 ,si,o#b1 which is not the case with carbonic anhydride4 ,the faculty of the molecules of silica for combining both with other molecules and among themselves is exhibited in the formation of most varied compounds with bases1 in the formation of hydrates with a gradually decreasing proportion of water down to anhydrous silica1 in the colloid nature of the hydrate 7the molecules of colloids are always complex71 in the formation of polymeric ethereal salts1 and in many other properties which will be considered in the sequel4 ,having come to this conclusion as to the polymeric state of silica since the years #ahej-ahfj1 ,i have found it to be confirmed by all subsequent researches on the compounds of silica1 and1 if ,i mistake not1 this view has now been very generally accepted4 #c ,it was only after ,gerhardt1 and in general subsequently to the establishment of the true atomic weights of the elements 7,chapter ,,vii471 that a true idea of the atomic weight of silicon and of the composition of silica was arrived at from the fact that the molecules of ,si,cl#d1 ,si,f#d1 ,si7,,oc#b;,h#e7d1 c41 never contain less than #bh parts of silicon4 ,the question of the composition of silica was long the subject of the most contradictory statements in the history of science4 ,in the last century ,pott1 ,bergmann1 and ,scheele distinguished silica from alumina and lime4 ,in the beginning of the present century ,smithson for the first time expressed the opinion that silica was an acid1 and the minerals of rocks salts of this acid4 ,berzelius determined the presence of oxygen in silica--namely1 that #h parts of oxygen were united with #g of silicon4 ,the composition of silica was first expressed as ,si,o 7and for the sake of shortness ,s only was sometimes written instead74 ,an investigation in the amount of silica present in crystalline minerals showed that the amount of oxygen in the bases bears a very varied proportion to the amount of oxygen in the silica1 and that this ratio varies from #b 3 #a to #a 3 #c4 ,the ratio #a 3 #a is also met with1 but the majority of these minerals are rare4 ,other more common minerals contain a larger proportion of silica1 the ratio between the oxygen of the bases and the oxygen of the silica being equal to #a 3 #b1 or thereabouts2 such are the augites1 labradorites1 oligoclase1 talc1 c4 ,the higher ratio #a 3 #c is known for a widely distributed series of natural silicates--for example1 the felspars4 ,those silicates in which the amount of oxygen in the bases is equal to that in the silica are termed monosilicates2 their general formula will be 7,,ro7#b,si,o#b or 7,r#b,o#c7b7,si,o#b7c4 ,those in which the ratio of the oxygen is equal to #a 3 #b are termed bisilicates1 and their general formula will be ,r,o,si,o#b or ,r#b,o#c7,si,o#b7c4 ,those in which the ratio is #a 3 #c will be trisilicates1 and their general formula 7,,ro7#b7,si,o#b7c or 7,r#b,o#c7b7,si,o#b7i4 ,in these formul the now established composition of ,si,o#b--that is1 that in which the atom of ,si #bh--;is employed4 ,berzelius1 who made an accurate analysis of the composition of felspar1 and recognised it as a trisilicate formed by the union of potassium oxide and alumina with silica1 in just the same manner as the alums are formed by sulphuric acid1 gave silica the same formula as sulphuric anhydride--that is1 ,si,o#c4 ,in this case the formula of felspar would be exactly similar to that of the alums--that is1 ,k,al7,si,o#d7b1 like the alums1 ,k,al7,,so#d7b4 ,if the composition of silica be represented as ,si,o#c1 the atom of silicon must be recognised as equal to #db 7if ,o #af2 or if ,o #h1 as it was before taken to be1 ,si #ba74 ,the former formul of silica1 ,si,o 7,si #ad7 and ,si,o#c 7,si #db71 were first changed into the present one1 ,si,o#b 7,si #bh71 on the basis of the following arguments3--,an excess of silica occurs in nature1 and in siliceous rocks free silica is generally found side by side with the silicates1 and one is therefore led to the conclusion that it has formed acid salts4 ,it would therefore be incorrect to consider the trisilicates as normal salts of silica1 for they contain the largest proportion of silica2 it is much better to admit another formula with a smaller proportion of oxygen for silica1 and it then appears that the majority of minerals are normal or slightly basic salts1 whilst some of the minerals predominating in nature contain an excess of silica--that is1 belong to the order of acid salts4 ,at the present time1 when there is a general method 7,chapter ,,vii47 for the determination of atomic weights1 the volumes of the volatile compounds of silica show that its atomic weight ,si #bh1 and therefore silica is ,si,o#b4 ,thus1 for example1 the vapour density of silicon chloride with respect to air is1 as ,dumas showed 7#ahfb71 #eid1 and hence with respect to hydrogen it is #hee1 and consequently its molecular weight will be #aga 7instead of #agj as indicated by theory74 ,this weight contains #bh parts of silicon and #adb parts of chlorine1 and as an atom of the latter is equal to #cee1 the molecule of silicon chloride contains ,si,cl#d4 ,as two atoms of chlorine are equivalent to one of oxygen1 the composition of silica will be ,si,o#b--that is1 the same as stannic oxide1 ,sn,o#b1 or titanic oxide1 ,ti,o#b1 and the like1 and also as carbonic and sulphurous anhydrides1 ,,co#b and ,,so#b4 ,but silica bears but little physical resemblance to the latter compounds1 whilst stannic and titanic oxides resemble silica both physically and chemically4 ,they are non-volatile1 crystalline insoluble1 are colloids1 also form feeble acids like silica1 c41 and they might therefore be expected to form analogous compounds1 and be isomorphous with silica1 as ,marignac 7#ahei7 found actually to be the case4 ,he obtained stannofluorides1 for example an easily soluble strontium salt1 ,sr,sn,f#f1b;,h#b,o1 corresponding with the already long known silicofluorides1 such as ,sr,si,f#f1b;,h#b,o4 ,these two salts are almost identical in crystalline form 7monoclinic2 angle of the prism1 #hc for the former and #hd for the latter2 inclination of the axes1 #ajc #df for the latter and #ajc #cj for the former71 that is1 they are isomorphous4 ,we may here add that the specific volume of silica in a solid form is #bbf1 and of stannic oxide #bae4 ,free silicon can be obtained in an amorphous or crystalline state4 ,amorphous silicon is produced1 like aluminium1 by decomposing the double fluoride of sodium and silicon 7sodium silicofluoride7 by means of sodium3 ,na#b,si,f#f #d,na #f,na,f ,si4 ,by treating the mass thus obtained with water the sodium fluoride may be extracted and the residue will consist of brown1 powdery silicon4 ,in order to free it from any silica which might be formed1 it is treated with hydrofluoric acid4 ,this silicon powder is not lustrous2 when heated it easily ignites1 but does not completely burn4 ,it fuses when very strongly heated1 and has then the appearance of carbon4#d ,crystalline silicon is obtained in a similar way1 but by substituting an excess of aluminium for the sodium3 #c,na#b,si,f#f #d;,al #f,na,f #d;,al,f#c #c,si4 ,the part of the aluminium remaining in the metallic state dissolves the silicon1 and the latter separates from the solution on cooling in a crystalline form4 ,the excess of aluminium after the fusion is removed by means of hydrochloric and hydrofluoric acid4 ,the best silicon crystals are obtained from molten zinc2 #ae parts of sodium silicofluoride are mixed with #bj parts of zinc and #d parts of sodium1 and the mixture is thrown into a strongly heated crucible1 a layer of common salt being used to cover it2 when the mass fuses it is stirred1 cooled1 treated with hydrochloric acid1 and then washed with nitric acid4 ,silicon1 especially when crystalline1 like graphite and charcoal1 does not in any way act on the above-mentioned acids4 ,it forms black1 very brilliant1 regular octahedra having a specific gravity of #bdi2 it is a bad conductor of electricity1 and does not burn even in pure oxygen 7but it burns in gaseous fluorine74 ,the only acid which acts on it is a mixture of hydrofluoric and nitric acids2 but caustic alkalis dissolve in it like aluminium1 with evolution of hydrogen1 thus showing its acid character4 ,in general silicon strongly resists the action of reagents1 as do also boron and carbon4 ,crystalline silicon was obtained in #ahee by ,deville1 and amorphous silicon in #ahbf by ,berzelius4#d bis #d ,a similar form of silicon is obtained by fusing ,si,o#b with magnesium1 when an alloy of ,si and ,mg is also formed 7,gattermann74 ,warren 7#ahhh7 by heating magnesium in a stream of ,si,f#d obtained silicon and its alloy with magnesium4 ,winkler 7#ahij7 found that ,mg#e,si#c and ,mg#b,si are formed when ,si,o#b and ,mg are heated together at lower temperatures1 whilst at a high temperature ,si only is formed4 #d bis ,it is very remarkable that silicon decomposes carbonic anhydride at a white heat1 forming a white mass which1 after being treated with potassium hydroxide and hydrofluoric acid1 leaves a very stable yellow substance of the formula ,si,c,o1 which is formed according to the equation1 #c,si #b;,,co#b ,si,o#b #b,si,c,o4 ,it is also slowly formed when silicon is heated with carbonic oxide4 ,it is not oxidised when heated in oxygen4 ,a mixture of silicon and carbon when heated in nitrogen gives the compound ,si#b;,c#b,n1 which is also very stable4 ,on this basis ,schtzenberger recognises a group1 ,c#b,si#b1 as capable of combining with ,o#b and ,n1 like ,c4 ,we may add that ,troost and ,hautefeuille1 by heating amorphous silicon in the vapour of ,si,cl#d1 obtained crystalline silicon1 and probably at the same time lower compounds of ,si and ,cl were temporarily formed4 ,in the vapour of ,ti,cl#d under the same conditions crystalline titanium is formed 7,levy1 #ahib74 ,silicon hydride1 ,si,h#d1 analogous to marsh gas was obtained first of all in an impure state1 mixed with hydrogen1 by two methods3 by the action of an alloy of silicon and magnesium on hydrochloric acid1#e and by the action of the galvanic current on dilute sulphuric acid1 using electrodes of aluminium1 containing silicon4 ,in these cases silicon hydride is set free1 together with hydrogen1 and the presence of the hydride is shown by the fact that the hydrogen separated ignites spontaneously on coming into contact with the air1 forming water and silica4 ,the formation of silicon hydride by the action of hydrochloric acid on magnesium silicide is perfectly akin to the formation of phosphuretted hydrogen by the action of hydrochloric acid on calcium phosphide1 to the formation of hydrogen sulphide by the action of acids on many metallic sulphides1 and to the formation of hydrocarbons by the action of hydrochloric acid on white cast iron4 ,on heating silicon hydride--that is1 on passing it through an incandescent tube1 it is decomposed into silicon and hydrogen1 just like the hydrocarbons1 but the caustic alkalis1 although without action on the latter1 react with silicon hydride according to the equation3 ,si,h#d #b,,kho ,h#b,o ,si,k#b,o#c #d;,h#b4 #e ,this alloy1 as ,beketoff and ,cherikoff showed1 is easily obtained by directly heating finely divided silica 7the experiment may be conducted in a test tube7 with magnesium powder 7,chapter ,,xiv41 ,notes #ag1 #ah74 ,the substance formed1 when thrown into a solution of hydrochloric acid1 evolves spontaneously inflammable and impure silicon hydride1 so that the self-inflammability of the gas is easily demonstrated by this means4 ,in #ahej-fj ,whler and ,buff obtained an alloy of silicon and magnesium by the action of sodium on a molten mixture of magnesium chloride1 sodium silicofluoride1 and sodium chloride4 ,the sodium then simultaneously reduces the silicon and magnesium4 ,friedel and ,ladenburg subsequently prepared silicon hydride in a pure state1 and showed that it is not spontaneously inflammable in air1 at the ordinary pressure1 but that1 like ,,ph#c1 and like the mixture prepared by the above methods1 it easily takes fire in air under a lower pressure or when mixed with hydrogen4 ,they prepared the pure compound in the following manner3 ,whler showed that when dry hydrochloric acid gas is passed through a slightly heated tube containing silicon it forms a very volatile colourless liquid1 which fumes strongly in air2 this is a mixture of silicon chloride1 ,si,cl#d1 and silicon chloroform1 ,si,h,cl#c1 which corresponds with ordinary chloroform1 ,c,h,cl#c4 ,this mixture is easily separated by distillation1 because silicon chloride boils at #eg1 and silicon chloroform at #cf4 ,the formation of the latter will be understood from the equation ,si #c;,h,cl ,h#b ,si,h,cl#c4 ,it is an anhydrous inflammable liquid of specific gravity #af4 ,it forms a transition product between ,si,h#d and ,si,cl#d1 and may be obtained from silicon hydride by the action of chlorine and ,sb,cl#e1 and is itself also transformed into silicon chloride by the action of chlorine4 ,gattermann obtained ,si,h,cl#c by heating the mass obtained after the action 7,note #d7 of ,mg upon ,si,o#b1 in a stream of chlorine 7with ,h,cl7 at about #dgj4 ,friedel and ,ladenburg1 by acting on anhydrous alcohol with silicon chloroform1 obtained an ethereal compound having the composition ,si,h7,,oc#b;,h#e7c4 ,this ether boils at #acf1 and when acted on by sodium disengages silicon hydride1 and is converted into ethyl orthosilicate1 ,si7,,oc#b;,h#e7d1 according to the equation #d,si,h7,,oc#b;,h#e7c ,si,h#d #c,si7,,oc#b;,h#e7d 7the sodium seems to be unchanged71 which is exactly similar to the decomposition of the lower oxides of phosphorus1 with the evolution of phosphuretted hydrogen4 ,if we designate the group ,c#b;,h#e1 contained in the silicon ethers by ,et1 the parallel is found to be exact3 #d,,pho7,,oh7#b ,,ph#c #c,,po7,,oh7#c2 #d,si,h7,o,et7#c ,si,h#d #c,si7,o,et7#d4 ,silicon chloride1 ,si,cl#d1 is obtained from amorphous anhydrous silica 7made by igniting the hydrate7 mixed with charcoal1#f heated to a white heat in a stream of dry chlorine--that is1 by that general method by which many other chloranhydrides having acid properties are obtained4 ,silicon chloride is purified from free chlorine by distillation over metallic mercury4 ,free silicon forms the same substance when treated with dry chlorine4 ,it is a volatile colourless liquid1 which boils at #ei and has a specific gravity of #aeb4 ,it fumes strongly in air1 has a pungent smell1 and in general has the characteristic properties of the acid chloranhydrides4 ,it is completely decomposed by water1 forming hydrochloric acid and silicic acid1 according to the equation3 ,si,cl#d #d;,h#b,o ,si7,,oh7#d #d;,h,cl4#g #f ,the amorphous silica is mixed with starch1 dried1 and then charred by heating the mixture in a closed crucible4 ,a very intimate mixture of silica and charcoal is thus formed4 ,in ,chapter ,,xi41 ,note #ac1 we saw that elements like silicon disengage more heat with oxygen than with chlorine1 and therefore their oxygen compounds cannot be directly decomposed by chlorine1 but that this can be effected when the affinity of carbon for oxygen is utilised to aid the action4 ,when the mass obtained by the action of ,mg upon ,si,o#b is heated to #cjj in a current of chlorine1 it easily forms ,si,cl#d 7,gattermann73 besides which two other compounds1 corresponding to ,si,cl#d1 are formed1 namely3 ,si#b;,cl#f1 which boils at #ade and solidifies at -#a1 and ,si#c;,cl#h1 which boils at about #bab4 ,these substances1 which answer to corresponding carbon compounds 7,c#b;,h#f and ,c#c;,h#h71 act upon water and form corresponding oxygen compounds2 for instance1 ,si#b;,cl#f #d;,h#b,o 7,si,o#b;,h7#b #f;,h,cl gives the analogue of oxalic acid 7,,co#b;,h7#b4 ,this substance is insoluble in water1 decomposes under the action of friction and heat with an explosion1 and should be called silico-oxalic acid1 ,si#b;,h#b,o#d 7see later1 ,note #aa bis74 #g ,silicon chloride shows a similar behaviour with alcohol4 ,this is accompanied by a very characteristic phenomenon2 on pouring silicon chloride into anhydrous alcohol a momentary evolution of heat is observed1 owing to a reaction of double decomposition1 but this is immediately followed by a powerful cooling effect1 due to the disengagement of a large amount of hydrochloric acid--that is1 there is an absorption of heat from the formation of gaseous hydrochloric acid4 ,this is a very instructive example in this respect2 here two processes occurring simultaneously--one chemical and the other physical--are divided from each other by time1 the latter process showing itself by a distinct fall in temperature4 ,in the majority of cases the two processes proceed simultaneously1 and we only observe the difference between the heat developed and absorbed4 ,in acting on alcohol1 silicon chloride forms ethyl orthosilicate1 ,si,cl#d #d;,,hoc#b;,h#e #d;,h,cl ,si7,,oc#b;,h#e7d4 ,this substance boils at #afj1 and has a specific gravity #jid4 ,another salt1 ethyl metasilicate1 ,si,o7,,oc#b;,h#e7b1 is also formed by the action of silicon chloride on anhydrous alcohol2 it volatilises above #cjj1 having a sp4 gr4 #ajh4 ,it is exceedingly interesting that these two ethereal salts are both volatile1 and both correspond with silica1 ,si,o#b3 the first ether corresponds to the hydrate ,si7,,oh7#d1 orthosilic acid1 and the second to the hydrate ,si,o7,,oh7#b1 metasilicic acid4 ,as the nature of hydrates may be judged from the composition of salts1 so also1 with equal right1 can ethereal salts serve the same purpose4 ,the composition of an ethereal salt corresponds with that of an acid in which the hydrogen is replaced by a hydrocarbon radicle--for instance1 by ,c#b;,h#e4 ,and1 therefore1 it may be truly said that there exist at least the two silicic acids above mentioned4 ,we shall afterwards see that there are really several such hydrates2 that these ethereal salts actually correspond with hydrates of silica is clearly shown from the fact that they are decomposed by water1 and that in moist air they give alcohol and the corresponding hydrate1 although the hydrate which is obtained in the residue always corresponds with the second ethereal salt only--that is1 it has the composition ,si,o7,,oh7#b2 this form corresponds also to carbonic acid in its ordinary salts4 ,this hydrate is formed as a vitreous mass when the ethyl silicates are exposed to air1 owing to the action of the atmospheric moisture on them4 ,its specific gravity is #agg4 ,silicon bromide1 ,si,br#d1 as well as silicon bromoform1 ,si,h,br#c1 are substances closely resembling the chlorine compounds in their reactions1 and they are obtained in the same manner4 ,silicon iodoform1 ,si,h,i#c1 boils at about #bbj1 has a specific gravity of #cd1 reacts in the same manner as silicon chloroform1 and is formed1 together with silicon iodide1 ,si,i#d1 by the action of a mixture of hydrogen and hydriodic acid on heated silicon4 ,silicon iodide is a solid at the ordinary temperature1 fusing at about #abj2 it may be distilled in a stream of carbonic anhydride1 but easily takes fire in air1 and behaves with water and other reagents just like silicon chloride4 ,it may be obtained by the direct action of the vapour of iodine on heated silicon4 ,besson 7#ahia7 also obtained ,si,cl#c;,i 7boils at #aac71 ,si,cl#b;,i#b 7#agb71 and ,si,cl,i#c 7#bbj71 and the corresponding bromine compounds4 ,all the halogen compounds of ,si are capable of absorbing #f,,nh#c and more4 ,besides which ,besson obtained ,si,s,cl#b by heating ,si in the vapour of chloride of sulphur2 this compound melts at #gd1 boils at #ahe1 and gives with water the hydrate of ,si,o#b1 ,h,cl1 and ,h#b,s4 ,the most remarkable of the haloid compounds of silicon is silicon fluoride1 ,si,f#d4 ,it is a gaseous substance only liquefied by intense cold1 -#ajj1 and is obtained 7,chapter ,,xi47 directly by the action of hydrofluoric acid on silica and its compounds 7,si,o#b #d;,,hf #b;,h#b,o ,si,f#d71 and also by heating fluorspar with silica 7#b;,ca,f#b #c,si,o#b #b;,ca,si,o#c ,si,f#d74h ,in order to prepare silicon fluoride1 sand or broken glass is mixed with an equal quantity by weight of fluorspar and #f parts by weight of strong sulphuric acid1 and the mixture is gently heated4 ,it fumes strongly in air1 reacting with the aqueous vapours1 although it is produced from silica and hydrofluoric acid with the separation of water4 ,it is evident that a reverse reaction occurs here2 that is to say1 the water reacts with the silicon fluoride1 but the reaction is not complete4 ,this phenomenon is similar to that which occurs when water decomposes aluminium chloride1 but at the same time hydrochloric acid dissolves aluminium hydroxide and forms the same aluminium chloride4 ,the relative amount of water present 7together with the temperature7 determines the limit and direction of the reaction4 ,the faculty which silicon fluoride has of reacting with water is so great that it takes up the elements of water from many substances--for instance1 like sulphuric acid1 it chars paper4 ,water dissolves about #cjj volumes of this gas1 but in this case it is not a common dissolution which takes place1 but a reaction4 ,during the first absorption of silicon fluoride by water1 silicic acid is separated in the form of a jelly1 but a certain quantity of the silicon fluoride also remains in the liquid1 because the hydrofluoric acid formed dissolves the other part of the silica#i and forms the so-called hydrofluosilicic acid3 ,h#b,si,f#f ,si,f#d #b;,,hf ,si,h#b,o#c #f;,,hf - #c;,h#b,o4 ,that is to say1 a metasilicic acid1 ,si,h#b,o#c1 in which ,o#c is replaced by ,f#f4 ,this view of the composition of hydrofluosilicic acid may be admitted1 because it forms a whole series of crystallisable and well defined salts4 ,in general1 the whole reaction of water on silicon fluoride may be expressed by the equation3 #c,si,f#d #c;,h#b,o ,si,o7,,oh7#b #b,si,h#b;,f#f4 ,hydrofluosilicic acid and silicic acid resemble each other as much1 and differ as much1 in their chemical character as water and hydrofluoric acid4 ,for this reason silicic acid is a feebler acid than hydrofluosilicic acid1 and in addition to this the former is insoluble1 and the latter soluble1 in water4#aj ,hydrofluosilicic acid is also formed if silicic acid be dissolved in a solution of hydrofluoric acid4 ,it is incapable of volatilising without decomposition1 and on heating the concentrated acid silicon fluoride is evolved1 leaving an aqueous solution of hydrofluoric acid4 ,this is the reason why solutions of hydrofluosilicic acid corrode glass4 ,this decomposition may be further accelerated by the addition of sulphuric acid1 or even of other acids4 ,hydrofluosilicic acid1 when acting on potassium and barium salts1 gives precipitates1 because the salts of these metals are but sparingly soluble in water3 thus #b,,kx ,h#b,si,f#f #b;,,hx ,k#b,si,f#f4 ,the potassium salt is obtained in the form of very fine octahedra1 but the precipitate does not form quickly1 and at first appears as a jelly4 ,nevertheless1 the decomposition is complete1 and it is taken advantage of for obtaining their corresponding acids from salts of potassium4#aj bis #h ,this property of calcium fluoride of converting silica into a gas and a vitreous fusible slag of calcium silicate is frequently taken advantage of in the laboratory and in practice in order to remove silica4 ,the same reaction is employed for preparing silicon fluoride on a large scale in the manufacture of hydrofluosilicic acid 7see sequel74 #i ,the amount of heat developed by the solution of silicic acid1 ,si,o#bn,h#b,o1 in aqueous hydrofluoric acid1 x,,hfn,h#b,o1 increases with the magnitude of x and normally equals x#e1fjj heat units1 where x varies between #a and #h4 ,however1 when x #aj the maximum amount of heat is developed 7 #di1ejj units71 and beyond that the amount decreases 7,thomsen74 #aj ,in reality1 however1 it would seem that the reaction is still more complex1 because the aqueous solution of silicon fluoride does not yield a hydrate of silica1 but a fluo-hydrate 7,schiff71 ,si#b,o#c7,,oh7,f1 corresponding to the 7pyro7 hydrate ,si#b,o#c7,,oh7#b1 equal to ,si,o7,,oh7#b,si,o#b1 so that the reaction of silicon fluoride on water is expressed by the equation3 #e,si,f#d #d;,h#b,o #c,si,h#b;,f#f ,si#b,o#c7,,oh7,f ,,hf4 ,however1 ,berzelius states that the hydrate1 when well washed with water1 contains no fluorine1 which is probably due to the fact that an excess of water decomposes ,si#b,o#c7,,oh7,f1 forming hydrofluoric acid and the compound ,si#b,o#c7,,oh7#b4 ,water saturated with silicon fluoride disengages silicon fluoride and hydrofluoric acid when treated with hydrochloric acid1 the gelatinous precipitate being simultaneously dissolved4 ,it may be further remarked that hydrofluosilicic acid has been frequently regarded as ,si,o#b1f;,,hf1 because it is formed by the solution of silica in hydrofluoric acid1 but only two of these six hydrogens are replaced by metals4 ,on concentration1 solutions of the acid begin to decompose when they reach a strength of #f;,h#b,o per ,h#b,si,f#f1 and therefore the acid may be regarded as ,si7,,oh7#d1b;,h#b,o1#f;,,hf1 but the corresponding salts contain less water1 and there are even anhydrous salts1 ,r#b,si,f#f1 so that the acid itself is most simply represented as ,h#b,si,f#f4 ,if gaseous silicon fluoride be passed directly into water1 the gas-conducting tube becomes clogged with the precipitated silicic acid4 ,this is best prevented by immersing the end of the tube under mercury1 and then pouring water over the mercury2 the silicon fluoride then passes through the mercury1 and only comes into contact with the water at its surface1 and consequently the gas-conducting tube remains unobstructed4 ,the silicic acid thus obtained soon settles1 and a colourless solution with a pleasant but distinctly acid taste is procured4 ,mackintosh1 by taking #i p4c4 of hydrofluoric acid1 observed that in the course of an hour its action on opal attained #gg p4c4 of the possible1 and did not exceed #a-a_/b p4c4 of its possible action on quartz during the same time4 ,this shows the difference of the structure of these two modifications of silica1 which will be more fully described in the sequel4 #aj bis ,the sodium salt is far more soluble in water1 and crystallises in the hexagonal system4 ,the magnesium salt1 ,mg,si,f#f1 and calcium salt are soluble in water4 ,the salts of hydrofluosilicic acid may be obtained not only by the action of the acid on bases or by double decompositions1 but also by the action of hydrofluoric acid on metallic silicates4 ,sulphuric acid decomposes them1 with evolution of hydrofluoric acid and silicon fluoride1 and the salts when heated evolve silicon fluoride1 leaving a residue of metallic fluoride1 ,r#b;,f#b4 ,silicon1 having so much in common with carbon1 is also able to combine with it in the proportion given by the law of substitution1 that is1 it forms a carbide of silicon ,c,si1 called carborundum and obtained by ,mhlhuser and ,acheson in the ,united ,states1 and by ,moissan in ,france 7#ahia71 and others1 by reducing silica with carbon in the electrical furnace at a temperature of about #bejjaa1 i4e4 by the action of an electrical current upon a mixture of carbon and ,si,o#b with ,na,cl4 ,after treating the resultant mass with acids and washing with water1 carborundum is obtained in transparent1 lustrous grains of a greenish color1 possessing great hardness 7greater than corundum7 and therefore used for polishing the hardest kinds of steel and stones4 ,the specific gravity is about #ca4 ,carborundum does not alter at a red heat1 does not burn1 and apparently approaches the diamond in its properties4 7,moissan obtained1 #ahid1 a similar very hard compound for boron1 ,b#f;,c1 sp4 gr4 #be47 #aa ,see ,note #d bis4 ,probably ,schtzenberger had already obtained ,c,si in his researches together with other silicon compounds4 ,an amorphous1 less hard compound of the same alloy is also obtained together with the hard crystalline ,c,si4 ,according to the principle of substitution1 if silicon forms ,si,h#d1 a series of hydrates1 or hydroxyl derivatives1 ought to exist corresponding to it4 ,the first hydrate of an alcoholic character ought to have the composition ,si,h#c7,,oh72 the second hydrate ,si,h#b7,,oh7#b2 the third1 ,si,h7,,oh7#c2aa bis and the last1 ,si7,,oh7#d4 ,the last is a hydrate of silica1 because it is equal to ,si,o#b #b;,h#b,o72 and it is formed by the action of water on silicon chloride1 when all four atoms of chlorine are replaced by four hydroxyl groups4 ,it does not1 however1 remain in this state1 but easily loses part of its water4 #aa bis ,the following consideration is very important in explaining the nature of the lower hydrates which are known for silicon4 ,if we suppose water to be taken up from the first hydrates 7just as formic acid is ,,ch7,,oh7#c1 minus water71 we shall obtain the various lower hydrates corresponding with silicon hydride4 ,when ignited they should1 like phosphorous and hypophosphorous acids1 disengage silicon hydride1 and leave a residue of silica behind--i4e4 of the oxide corresponding to the highest hydrate--just as organic hydrates 7for example1 formic acid with an alkali7 form carbonic anhydride as the highest oxygen compound4 ,such imperfect hydrates of silicon1 or1 more correctly speaking1 of silicon hydride1 were first obtained by ,whler 7#ahfc7 and studied by ,geuther 7#ahfe71 and were named after their characteristic colours4 7,see ,note #f74 ,leucone is a white hydrate of the composition ,si,h7,,oh7#c4 ,it is obtained by slowly passing the vapour of silicon chloroform into cold water3 ,si,h,cl#c #c;,h#b,o ,si,h7,,oh7#c #c;,h,cl4 ,but this hydrate1 like the corresponding hydrate of phosphorus or carbon1 does not remain in this state of hydration1 but loses a portion of its water4 ,the carbon hydrate of this nature1 ,,ch7,,oh7#c1 loses water and forms formic acid1 ,,cho7,,oh72 but the silicon hydrate loses a still greater proportion of water1 #b,si,h7,,oh7#c1 parting with #c;,h#b,o1 and consequently leaving ,si#b;,h#b,o#c4 ,this substance must be an anhydride2 all the hydrogen previously in the form of hydroxyl has been disengaged1 two remaining hydrogens being left from ,si,h#d4 ,the other similar hydrate is also white1 and has the composition ,si#c;,h#b,o 7nearly74 ,it may be regarded as the above white hydrate ,si,o#b4 ,a yellow hydrate1 known as chryseone 7silicone71 is obtained by the action of hydrochloric acid on an alloy of silicon and calcium2 its composition is about ,si#f;,h#d,o#c4 ,most probably1 however1 chryseone has a more complex composition1 and stands in the same relation to the hydrate ,si,h#b7,,oh7#c as leucone does to the hydrate ,si,h7,,oh7#c1 because this very simply expresses the transition of the first compound into the second with the loss of water1 ,si,h#b7,,oh7#c - ,h#b ,h#b,o ,si,h7,,oh7#c4 ,when these lower hydrates are ignited without access of air1 they are decomposed into hydrogen1 silicon1 and silica--that is1 it may be supposed that they form silicon hydride 7which decomposes into silicon and hydrogen7 and silica 7just as phosphorous and hypophosphorous acids give phosphoric acid and phosphuretted hydrogen74 ,when ignited in air1 they burn1 forming silica4 ,they are none of them acted on by acids1 but when treated with alkalis they evolve hydrogen and give silicates2 for example1 leucone3 ,si,h#b,o#c #d,,kho #b,si,k#b,o#c ,h#b,o #b;,h#b4 ,they have no acid properties4 ,silica or silicic anhydride1 both in the free state and in combination with other oxides1 enters into the composition of most of the rocky formations of the earth's crust4 ,these silicious compounds are substances varying so much in their properties1 crystalline forms1 and relations to one another that they are comprised in a special branch of natural science 7like the carbon compounds71 and are treated of in works on mineralogy2 so that1 in dealing with them further1 we shall only give a short description of these various compounds4 ,it is first of all necessary to turn to the description of silica itself1 especially as it is not unfrequently met with in nature in a separate state1 and often forms whole masses of rocky formations1 called 'quartz4' ,in an anhydrous condition silica appears in the greatest variety of natural forms--sometimes in well-formed crystals1 hexagonal prisms1 terminated by hexagonal pyramids4 ,if the crystals are colourless and transparent1 they are called rock crystal4 ,this is the purest form of silica4 ,prismatic crystals of rock crystal sometimes attain considerable size1 and as they are remarkable for their unchangeability1 great hardness1 and high index of refraction1 they are used for ornaments1 for seals1 making necklaces1 c4#ab ,rock crystal coloured with organic matter in contact with which it has been produced has a brown or greyish colour1 and then bears the name of cairngorm or smoky quartz4 ,in this form it has the same uses as rock crystal1 especially as it is often found in large masses4 ,the same mineral1 frequently occurs1 coloured red or pink by manganese or iron oxides1 especially in aqueous formations1 and is then known as amethyst4 ,when finely coloured the amethyst is used as a precious stone1 but amethysts most frequently occur as small crystals in the cavities formed in other rocky formations1 and especially in those formed in silica itself4 ,a similar anhydrous silica is often found in transparent non-crystalline masses1 having the same specific gravity as rock crystal itself 7#bff74 ,in this case it is called quartz4 ,sometimes it forms complete rocky formations1 but more often penetrates or is interspersed through other rocky formations1 together with other siliceous compounds4 ,thus1 in granite1 quartz is mixed with felspar and similar substances4 ,sometimes the colouring of quartz is so considerable that it is hardly transparent in thin sheets1 but it is often found in transparent masses slightly coloured with various tints4 ,the existence in nature of enormous masses of quartz proves that it resists the action of water4 ,when water destroys rocky formations1 the siliceous minerals which they contain are partly dissolved and partly transformed into clay1 c4 ,but the quartz remains untouched1 in the form of grains in which it existed in the rocky formation2 sometimes1 when crushed1 it is carried away by the water and deposited4 ,this is the nature of sand4 ,naturally1 sometimes other rocky substances which are not changed by water1 or only slightly acted on by it1 are found in sand2 but as these latter are more or less changed by the continuous action of water1 it is not unusual to find sand which consists almost entirely of pure quartz4 ,common sand is generally coloured yellow or reddish-brown by foreign mineral matter1 consisting principally of ferruginous minerals and clays4 ,the purest or so-called quartz sand is1 however1 rarely found1 and is recognised by the absence of colour1 and also by the test that when shaken in water it does not form any turbidity3 this shows the absence of clay2 when fused with bases it forms a colourless glass1 and on this account is a valuable material for the manufacture of glass4 ,sands were formed at all periods of the earth's existence2 the ancient ones1 compressed by strata of more recent formation and permeated with various substances 7deposited from the infiltrating water71 are sometimes solidified into rock1 called sandstone1 composing1 in some places1 whole mountain chains1 and serviceable as a most excellent building material1 on account of the slight change it undergoes under the influence of atmospheric agencies1 and on account of the facility with which it may be wrought from rocky formations into immense regularly-shaped flags--the latter property is due to the primary laminar structure of the sand formations deposited1 as above-mentioned1 by water4 ,many grindstones and whetstones are made from such rocks4 #ab ,two modifications of rock crystal are known4 ,they are very easily distinguished from each other by their relation to polarised light2 one rotates the plane of polarisation to the right and the other to the left--in the one the hemihedral faces are right and in the other they are left2 this opposite rotatory power is taken advantage of in the construction of polarisers4 ,but1 with this physical difference--which is naturally dependent on a certain difference in the distribution of the molecules--there is not only no observable difference in the chemical properties1 but not even in the density of the mass4 ,perfectly pure rock crystal is a substance which is most invariable with respect to its specific gravity4 ,the numerous and accurate determinations made by ,steinheil on the specific gravity of rock crystal show that 7if the crystal be free from flaws7 it is very constant and is equal to #bff4 ,perfectly pure anhydrous silica is not only known in the condition of rock crystal and quartz having a specific gravity of #bf1 but also in another special form1 having other chemical and physical properties4 ,this variety of silica has a specific gravity of #bb1 and is formed by fusing rock crystal or heating silicic acid4#ab bis ,silicic acid1 when heated to a dull red heat1 parts entirely with the water it contains1 and leaves an exceedingly fine amorphous mass of silica 7easily levigated1 but difficult to moisten72 it is characterised by such excessive friability that1 when lightly blown on1 a large mass of it rises into the air like a cloud of dust4 ,a mass of anhydrous silica maybe poured in this way from one vessel to another like a liquid1 and like the latter it takes a horizontal position in the vessel containing it4#ac ,anhydrous silica1 like quartz1 does not fuse in the heat of a furnace1 but it fuses in the oxyhydrogen flame to a colourless glassy mass exactly similar to that formed in the same way from rock crystal4 ,in this condition silica has a specific gravity of #bb4ac bis ,both forms of silica are insoluble in ordinary acids1 and even when they are in the state of powder1 alkalis in solution act very slowly and feebly on them2 rock crystal offers much greater resistance to the action of alkalis than the powder obtained by heating the hydrate4 ,the latter is quite soluble1 although but slowly1 in hot alkaline solutions4 ,this last property appertains in a greater degree to anhydrous silica having a specific gravity of #bb than to that which has a specific gravity of #bf4 ,hydrofluoric acid more easily transforms the former into silicon fluoride than it does the latter4 ,both varieties of silica1 when taken in the form of powder1 easily combine with bases1 forming1 on being fused with an alkali1 a vitreous slag1 which is a salt corresponding with silica4 ,glass is such a salt1 formed of alkalis and alkaline earthy bases2 if the glass does not contain any of the latter--that is1 if only alkaline glass be taken--a mass soluble in water is obtained4 ,in order to obtain such soluble glass1 potassium or sodium carbonates1 or better a mixture of the two 7fusion mixture71 is fused with fine sand4 ,a still better and further saturation of the alkalis with silica is effected by the action of alkaline solutions on the silicon hydrate met with in nature2 for instance1 an alkaline solution is often made use of to act on the so-called tripoli1 or collection of siliceous skeletons of the lowest microscopical infusoria1 which is sometimes found in considerable layers in the form of a sandy mass4 ,tripoli is used for polishing1 not only on account of the considerable hardness of the silica1 but also because the microscopic bodies of the infusoria have a pointed shape1 which1 however1 is not angular1 so that they do not scratch metals like sand4#ad ,the alkaline solutions of silica obtained by boiling tripoli with caustic soda under pressure contain various proportions of silica and alkali4#ad bis ,in order that it may contain the greatest amount of silica1 silicic acid should be added to the heated solution4 ,silicic acid is formed by taking any solution containing silica and alkali1 and adding to it1 by degrees1 some acid--for instance1 sulphuric or hydrochloric2 if the experiment be carried on carefully and the solution be concentrated1 the whole mass thickens to a jelly1 due to the gelatinous form of the silicic acid separated from the salt by the action of the acid4 ,the decomposition may be expressed by the following equation3 ,si7,o,na7#d #d;,h,cl #d,na,cl ,si7,,oh7#d4 ,the hydrate separated1 ,si7,,oh7#d1 easily loses part of the water and forms a jelly1 the whole mass gelatinising if the solution be strong enough4#ae #ab bis ,several other modifications are known as minute crystals4 ,for example1 there is a particular mineral first found in ,styria and known as tridymite4 ,its specific gravity #bc and form of crystals clearly distinguish it from rock crystal2 its hardness is the same as that of quartz--that is1 slightly below that of the ruby and diamond4 #ac ,there is a distinct rise of temperature 7about #d7 when amorphous silica is moistened with water4 ,benzene and amyl alcohol also give an observable rise of temperature4 ,charcoal and sand give the same result1 although to a less extent4 #ac bis ,silica also occurs in nature in two modifications4 ,the opal and tripoli 7infusorial earth7 have a specific gravity of about #bb1 and are comparatively easily soluble in alkalis and hydrofluoric acid4 ,chalcedony and flint 7tinted quartzose concretions of aqueous origin71 agate and similar forms of silica of undoubted aqueous origin1 although still containing a certain amount of water1 have a specific gravity of #bf1 and correspond with quartz in the difficulty with which they dissolve4 ,this form of silica sometimes permeates the cellulose of wood1 forming one of the ordinary kinds of petrified wood4 ,the silica may be extracted from it by the action of hydrofluoric acid1 and the cellulose remains behind1 which clearly shows that silica in a soluble form 7see sequel7 has permeated into the cells1 where it has deposited the hydrate1 which has lost water1 and given a silica of sp4 gr4 #bf4 ,the quartzose stalactites found in certain caves are also evidently of a similar aqueous origin2 their sp4 gr4 is also #bf4 ,as crystals of amethyst are frequently found among chalcedonies1 and as ,friedau and ,sarrau 7#ahgi7 obtained crystals of rock crystal by heating soluble glass with an excess of hydrate of silica in a closed vessel1 there is no doubt but that rock crystal itself is formed in the wet way from the gelatinous hydrate4 ,chroustchoff obtained it directly from soluble silica4 ,thus this hydrate is able to form not only the variety having the specific gravity #bb but also the more stable variety of sp4 gr4 #bf2 and both exist with a small proportion of water and in a perfectly anhydrous state in an amorphous and crystalline form4 ,all these facts are expressed by recognising silica as dimorphous1 and their cause must be looked for in a difference in the degree of polymerisation4 #ad ,deposits of perfectly white tripoli have been discovered near ,batoum1 and might prove of some commercial importance4 #ad bis ,alkaline solutions1 saturated with silica and known as soluble glass1 are prepared on a large scale for technical purposes by the action of potassium 7or sodium7 hydroxide in a steam boiler on tripoli or infusorial earth1 which contains a large proportion of amorphous silica4 ,all solutions of the alkaline silicates have an alkaline reaction1 and are even decomposed by carbonic acid4 ,they are chiefly used by the dyer1 for the same purposes as sodium aluminate1 and also for giving a hardness and polish to stucco and other cements1 and in general to substances which contain lime4 ,a lump of chalk when immersed in soluble glass1 or better still when moistened with a solution and afterwards washed in water 7or better in hydrofluosilicic acid1 in order to bind together the free alkali and make it insoluble71 becomes exceedingly hard1 loses its friability1 is rendered cohesive1 and cannot be levigated in water4 ,this transformation is due to the fact that the hydrate of silica present in the solution acts upon the lime1 forming a stony mass of calcium silicate1 whilst the carbonic acid previously in combination with the lime enters into combination with the alkali and is washed away by the water4 #ae ,the equation given above does not express the actual reaction1 for in the first place silica has the faculty of forming compounds with bases1 and therefore the formula ,si,na#d,o#d is not rightly deduced1 if one may so express oneself4 ,and1 in the second place1 silica gives several hydrates4 ,in consequence of this1 the hydrate precipitated does not actually contain so high a proportion of water as ,si7,,oh7#d1 but always less4 ,the insoluble gelatinous hydrate which separates out is able 7before1 but not after1 having been dried7 to dissolve in a solution of sodium carbonate4 ,when dried in air its composition corresponds with the ordinary salts of carbonic acid--that is1 ,si,h#b,o#c1 or ,si,o7,,oh7#b4 ,if gradually heated it loses water by degrees1 and1 in so doing1 gives various degrees of combination with it4 ,the existence of these degrees of hydration1 having the composition ,si,h#b,o#cn,si,o#b1 or1 in general1 n,si,o#bm,h#b,o1 where m n1 must be recognised1 because most varied degrees of combination of silica with bases are known4 ,the hydrate of silica1 when not dried above #cj1 has a composition of nearly ,h#d,si#c,o#h 7,h#b,si,o#c7b,si,o#b1 but at #fj contains a greater proportion of silica--that is1 it loses still more water2 and at #ajj a hydrate of the composition ,si,h#b,o#cb,si,o#b1 and at #bej a hydrate having approximately a composition ,si,h#b,o#cg,si,o#b is obtained4 ,these data show the complexity of the molecules of anhydrous silica4 ,the hydrates of silica easily lose water and give the hydrates 7,si,o#b7n7,h#b,o7m1 where m becomes smaller and smaller than n4 ,in the natural hydrates1 this decrement of water proceeds quite consecutively1 and1 so to say1 imperceptibly1 until n becomes incomparably greater than m1 and when the ratio becomes very large1 anhydrous silica of the two modifications #bf and #bb is obtained4 ,the composition 7,si,o#b7aj1;,h#b,o still corresponds with #bi p4c4 of water1 and natural hydrates often contain still less water than this4 ,thus some opals are known which contain only #a p4c4 of water1 whilst others contain #g and even #aj p4c4 ,as the artificially prepared gelatinous hydrate of silica when dried has many of the properties of native opals1 and as this hydrate always loses water easily and continually1 there can be no doubt that the transition of 7,si,o#b7n7,h#b,o7m into anhydrous silica1 both amorphous and crystalline 7in nature1 chalcedony71 is accomplished gradually4 ,this can only be the case if the magnitude of n be considerable1 and therefore the molecule of silica in the hydrate is undoubtedly complex1 and hence the anhydrous silica of sp4 gr4 #bb and #bf does not contain ,si,o#b1 but a complex molecule1 ,sin,o#bn--that is1 the structure of silica is polymeric and complex1 and not simple as represented above by the formula ,si,o#b4 ,neither of the two varieties of anhydrous silica1 nor the various natural gelatinous hydrates1 are directly soluble in water4 ,there is1 however1 a condition of silica known which is soluble in water1 soluble silica1 and silica is found in this state in nature4 ,small quantities of soluble silica are met with in all waters4 ,certain mineral springs1 and especially hot springs--of which the best known are the ,geysers of ,iceland and those in the ,north ,american ,national ,park 7,yellowstone ,valley7--contain a considerable amount of silica in solution4 ,such water1 permeating the objects it meets with--for instance1 wood--penetrates into them and deposits silica inside them1 that is1 transforms them into a petrified condition4 ,siliceous stalactites1 and also many 7if not all7 forms of silica are formed by such water4 ,the absorption of silica by plants by means of their roots1 and also by the lower organisms having siliceous bodies1 is due also to their nourishing themselves with the solutions containing silica continually formed in nature4 ,thus1 in plants1 in the straws of the grasses1 in hard shave-grass1 and especially in the knots of bamboo and other straw-like plants1 a considerable quantity of silica is deposited1 which must previously have been absorbed by the plants4 ,silicic acid is a colloid4 ,the gelatinous silicon hydrate is its hydrogel1 the soluble hydrate is the hydrosol 7,chapter ,,xii47 ,both varieties may be easily obtained from the alkaline silicates and from water-glass4 ,the very same substances--that is1 aqueous solutions of soluble glass and acid--taken in the same proportion1 may produce either the gelatinous or the soluble silica1 according to the way these solutions are mixed together4 ,if the acid be added little by little to the alkaline silicate1 with continuous stirring1 a moment arrives when the whole mass thickens to a jelly1 hydrogel2 in this case the silicic acid is formed in the midst of the alkaline solution and becomes insoluble4 ,but if the mixing be done in the reverse order--that is1 if the soluble glass be added to the acid1 or if a quantity of acid be rapidly poured into the solution of the salt--then the separation of the silica takes place in the midst of the acid liquid1 and it is obtained in the form of the soluble hydrate1 the hydrosol4#af #af ,the presence of an excess of acid aids the retention of the silica in the solution1 because the gelatinous silica obtained in the above manner1 but not heated to #fj--that is1 containing more water than the hydrate ,h#b,si,o#c--;is more soluble in water containing acid than in pure water4 ,this would seem to indicate a feeble tendency of silica to combine with acids1 and it might even have been imagined that in such a solution the hydrate of silica is held in combination by an excess of acid1 had ,graham not obtained soluble silica perfectly free from acid1 and if there were not solutions of silica free from any acid in nature4 ,at all events a tolerably strong solution of free silica or silicic acid may be obtained from soluble glass diluted with water4 ,the solution1 besides silica1 will contain sodium chloride and an excess of the acid taken4 ,if this solution remains for some time exposed to the air1 or in a closed vessel1 and under various other conditions1 it is found that1 after a time1 insoluble gelatinous silica separates out--that is1 the soluble form of silica is unstable1 like the soluble form of alumina4 ,the analogous forms of molybdic or tungstic acids may be heated1 evaporated1 and kept for a long period of time without the soluble form being converted into the insoluble4 ,the hydrosol of silica prepared by mixing an excess of hydrochloric acid with a solution of sodium silicate1 may be freed from the admixtures both of hydrochloric acid and salt1 sodium chloride1 by means of dialysis1#ag as ,graham showed 7in #ahfa7 in enquiring into the nature of colloids 7,chapter ,i471 and making many other important chemical investigations4 ,the solution1 containing the acid1 salt1 and silica1 all dissolved in water1 is poured into a dialyser--that is1 a vessel with a porous diaphragm surrounded by water4 ,certain substances pass more easily through the diaphragm than others4 ,this may be represented thus3 the passage through the diaphragm proceeds in both directions1 and if the solutions on each side of the diaphragm be equally strong1 there will be equal numbers of molecules of the soluble substance passing into either side in a given time1 some passing quickly and others slowly4 ,the metallic chlorides and hydrochloric acid belong to the series of crystalloids which easily pass through a diaphragm1 and therefore the hydrochloric acid and sodium chloride contained in the above-mentioned dialyser pass from the solution through the diaphragm into the water of the external vessel with considerable rapidity4 ,the aqueous solution of colloidal silica also penetrates through the diaphragm1 but very much more slowly4 ,but if the amount of the substance dissolved is not equal on either side of the diaphragm1 the whole system strives to attain a state of equilibrium2 that is1 the given substance penetrates through the diaphragm from the side where it is in excess to the part where there is a smaller quantity of it4 ,all substances which are soluble in water have the faculty of penetrating through a membrane swollen in water1 but the velocity of penetration is not equal1 and in this respect the dialyser separates substances like a sieve4 ,the silica passes less rapidly through the diaphragm than the sodium chloride and hydrochloric acid1 so that by repeatedly changing the external water it is easy to effect the extraction of the chlorine compounds from the dialyser1 which will finally only contain a solution of silica4 ,this extraction 7of ,h,cl and ,na,cl7 may be so complete that the liquid taken from the dialyser will not give any precipitate with a solution of silver nitrate4 ,graham obtained in this way soluble silica having a distinctly acid reaction1 which1 however1 disappeared on the addition of a very minute quantity of alkali2 for ten parts of silica in the solution it was sufficient to take one part of alkali in order to give the liquid an alkaline reaction1 so slightly energetic are the acid properties of silicic acid4 ,the solution of silica obtained by this method becomes gelatinous on standing1 on being heated1 or on evaporation under the receiver of an air-pump1 c4 ,the hydrosol is transformed into the hydrogel1 the soluble hydrate into the gelatinous4 #ag ,see ,chapter ,i41 ,note #ah4 ,a solution of water-glass mixed with an excess of hydrochloric acid is poured into the dialyser1 and the outer vessel is filled with water1 which is continually renewed4 ,the water carries off the sodium chloride and hydrochloric acid1 and the hydrosol remains in the dialyser4 ,thus in addition to the gelatinous form of the silicic acid1 there exists also a variety of this substance1 soluble in water1 as is the case with alumina4 ,such variation in properties and exactly the same relations with regard to water characterise an immense series of other substances having a great significance in nature4 ,the number of such substances is especially great among organic compounds1 and particularly in those classes of them which compose the principal material of the bodies of animals and plants4 ,it is sufficient to mention1 for instance1 the gelatin which is familiar to all as carpenter's and other glues1 and in the form of size and jelly4 ,the same substance is also known in the solution which is used to join objects together4 ,in a peculiar insoluble condition it enters into the composition of hides and bones4 ,these various forms of gelatin differ in the same way as the different varieties of silica4 ,the property of forming a jelly is exactly the same as in silica1 and the adhesiveness of the solutions of both substances is identical2 soluble silica adheres like a solution of gelatin4 ,the same properties are again shown by starch1 rosin1 and albumin1 and by a series of similar substances4 ,the diaphragms used in dialysis are also insoluble1 gelatinous1 forms of colloids4 ,the bodies of animals and plants consist largely of similar matter1 insoluble in water1 corresponding with the gelatinous or insoluble silicon hydrate1 or with glue4 ,the albumin which coagulates when eggs are boiled is a typical form of the gelatinous condition of such substances in the body4 ,these slight indications are sufficient in order to show how great is the significance of those transformations which are so well marked in silica4 ,the facts discovered by ,graham in #ahfa-ahfd comprise the most essential acquisitions in the general association of these phenomena of nature in the history of organic forms4 ,the facility of transit from hydrogel to hydrosol is the first condition of the possibility of the development of organisms4 ,the blood contains hydrosols1 and the hydrogels of the same substances are contained in the muscles and tissues1 and especially on the surface1 of the body4 ,all tissues are formed from the blood1 and in that case the hydrosols are converted into hydrogels4#ah ,the absence of crystallisation1 the property1 apparently under the influence of feeble agencies1 of passing from the soluble condition to the insoluble1 to the gelatinous condition of the hydrogel1 constitute the fundamental properties of all colloids4#ai #ah ,a similar process occurs in plants--for example1 when they secrete a store of material for the following year in their bulbs1 roots1 c4 7for instance1 the potato in its tubers71 the solutions from the leaves and stems penetrate into the roots and other parts in the form of hydrosols1 where they are converted into hydrogels--that is1 into an insoluble form1 which is acted on with difficulty and is easily kept unaltered until the period of growth--for example1 until the following spring--when they are reconverted into hydrosols1 and the insoluble substance re-enters into the sap1 and serves as a source of the hydrogels in the leaves and other portions of plants4 #ai ,as regards their chemical composition the colloids are very complex--that is1 they have a high molecular weight and a large molecular volume--in consequence of which they do not penetrate through membranes1 and are easily subject to variation in their physical and chemical properties 7owing to their complex structure and polymerism87 ,they have but little chemical energy1 and are generally feeble acids1 if belonging to the order of oxides or hydrates1 such as the hydrates of molybdic and tungstic acids 7,chapter ,,xxi474 ,but now the number of substances capable1 like colloids1 of passing into aqueous solutions and of easily separating out from them1 as well as of appearing in an insoluble form1 must be supplemented by various other substances1 among which soluble gold and silver 7,chapter ,,xxiv47 are of particular interest4 ,so that now it may be said that the capacity of forming colloid solutions is not limited to a definite class of compounds1 but is1 if not a general1 at all events1 an exceedingly widely distributed phenomenon4 ,silica1 as regards its salt forming properties1 stands in the series of oxides on the boundary line on the side of the acids in just such a place as alumina occupies on the side of the bases--that is1 aluminium hydroxide is the representative of the feeblest bases and silicic acid is the least energetic of acids 7at least in the presence of water--that is1 in aqueous solutions72 in alumina1 however1 the basic properties are distinctly expressed1 while in silica the acid properties preponderate4 ,like all feeble acid oxides it is capable of forming1 with other acids1 saline compounds which are but slightly stable and are very easily decomposed in the presence of water4 ,the chief peculiarity of the silicates consists in the number of their types4 ,the salts formed with nitric or sulphuric acid exist in one1 two1 and three tolerably stable forms1 but for acids like silicic acid the number of forms is very great1 almost unlimited4 ,the natural silicates in particular furnish proof of this fact2 they contain various bases in combination with silica1 and for one and the same base there often exist various degrees of combination4 ,as feeble bases are capable of forming basic salts in addition to normal salts--that is1 a compound of a normal salt with a feeble base 7either the hydroxide or the oxide7--so the feeble acid oxides 7although not all7 form1 in addition to normal salts1 highly acid salts--that is1 normal salts plus acid 7hydrate or anhydride74 ,such acids are boric1 phosphoric1 molybdic1 chromic1 and especially silicic1 acid4 ,in order to explain these relations it is necessary first to recollect the existence of the various hydrates of silica1 or silicic acids1#bj and then to turn our attention to the similarity between silicon compounds and metallic alloys4 ,silica is an oxide having the appearance of1 and in many respects the same properties as1 those oxides which combine with it1 and if two metals are capable of forming homogeneous alloys in which there exist definite or indefinite compounds1 it is permissible to assume a similar power of forming alloys in the case of analogous oxides4 ,such alloys are found in indefinite1 amorphous masses in the form of glass1 lava1 slags1 and a number of similar siliceous compounds which do not contain any definite types of combination1 but nevertheless are homogeneous throughout their mass4 ,by slow cooling1 or under other circumstances1 definite crystalline compounds may--and sometimes do--separate from this homogeneous mass1 as also sometimes definite crystalline alloys separate from metallic alloys4 #bj ,this is in accordance with the generally-accepted representation of the relations between salts and the hydrates of acids1 but it is of little help in the study of siliceous compounds4 ,generally speaking1 it becomes necessary to explain the property of 7,si,o#b7n to combine with 7,,ro7m1 where n may be greater than m1 and where ,r may be ,h#b1 ,ca1 c4 ,here we are aided by those facts which have been attained by the investigation of carbon compounds1 especially with respect to glycol4 ,glycol is a compound having the composition ,c#b;,h#f,o#b1 only differing from alcohol1 ,c#b;,h#f,o1 by an extra atom of oxygen4 ,this hydrate contains two hydroxyl groups1 which may be successively replaced by chlorine1 c4 ,hence the composition of glycol should be represented as ,c#b;,h#d7,,oh7#b4 ,it has been found that glycol forms so-called polyglycols4 ,their origin will be understood from the fact that glycol as a hydrate has a corresponding anhydride of the composition ,c#b;,h#d,o1 known as ethylene oxide4 ,this substance is ethane1 ,c#b;,h#f1 in which two hydrogens are replaced by one atom of oxygen4 ,ethylene oxide is not the only anhydride of glycol1 although it is the simplest one1 because ,c#b;,h#d,o ,c#b;,h#d7,,oh7#b - ,h#b,o4 ,various other anhydrides of glycol are possible1 and have actually been obtained1 of the composition n,c#b;,h#d7,,oh7#b - 7n - #a7;,h#b,o 7,c#b;,h#d7n,on - #a7,,oh7#b4 ,these imperfect anhydrides of glycol1 or polyglycols1 still contain hydroxyls like glycol itself1 and therefore are of an alcoholic character in the same sense as glycol itself4 ,they are obtained by various methods1 and1 amongst others1 by the direct combination of ethylene oxide with glycol1 because ,c#b;,h#d7,,oh7#b 7n - #a7;,c#b;,h#d,o 7,c#b;,h#d7n,on - #a7,,oh7#b4 ,the most important circumstance1 from a theoretical point of view1 is that these polyglycols may be distilled without undergoing decomposition1 and that the general formula given above expresses their actual molecular composition4 ,hence we have here a direct combination of the anhydride with the hydrate1 and1 moreover1 a repeated one4 ,the formula ,an,h#b,o may be used to express the composition of glycol and polyglycols with respect to ethylene oxide in the most simple manner1 if ,a stand for ethylene oxide4 ,when n #a we have glycol1 when n is greater than #a a polyglycol4 ,such also is the relationship of the salts of hydrate of silica1 if ,a stand for silica1 and if we imagine that ,h#b,o may also be taken m times4 ,such a representation of the polysilicic acids corresponds with the representation of the polymerism of silica4 ,laurent supposed the existence of several polymeric forms1 ,si#b,o#d1 ,si#c,o#f1 c41 besides silica1 ,si,o#b4 ,the formation of crystalline rocks in nature is partly of such a nature4 ,by aqueous or igneous agency1 but in any case in a liquid condition1 those oxides which form the earth's crust and her crystalline minerals came into mutual contact4 ,first of all they formed a shapeless mass1 of which lava1 glass1 slags and solutions are examples1 but little by little1 or else suddenly1 some definite compounds of certain oxides existing in this alloy or in the shapeless mass were formed4 ,this is entirely similar to two metals forming a homogeneous alloy1#ba and under known circumstances 7for instance1 on cooling the alloy1 or in the case of aqueous solution when the two metals are simultaneously liberated from the solution71 definite crystalline compounds are separated4 ,in any case there is no doubt that there is less distinction between silica and bases1 than between bases and such anhydrides as1 for instance1 sulphuric or nitric1 or even carbonic1 as is seen on comparing the physical and chemical properties of silica and various kinds of oxides4 ,alumina1 especially1 is exceedingly near akin to silica2 not only in the hydrated state1 but also in the anhydrous condition1 there exists a certain similarity between the crystalline forms of alumina and silica1 in the uncombined state4 ,both are very hard1 transparent1 inactive1 non-volatile1 infusible1 and crystallise in the hexagonal system--in a word1 they are remarkably similar1 and for this reason they are capable1 like two kindred metals1 of entering into many different degrees of combination4 ,isomorphous mixtures--that is1 differing by the substitution of oxides akin both in their physical and chemical characters--are very frequently met with among minerals1 and the study of the latter gave the principal impetus to the study of isomorphism4 ,thus1 in a whole series of minerals1 lime and magnesia are found in variable and interchangeable proportions4 ,exactly the same may be said of potassium and sodium1 of alumina and ferric oxide1 of manganous1 ferrous1 magnesium oxides1 c4 ,such isomorphism does not1 however1 extend without change of form and properties beyond certain rather narrow limits4#bb ,what ,i mean by this is that lime is not always replaced totally1 but often only in small quantities1 by magnesia1 or by the manganous and ferrous oxides1 without changing the crystalline form4 ,the same may be observed with regard to potassium and lithium1 which may be in part1 but not completely1 replaced by sodium4 ,on the total substitution of one metal for another1 often 7although not invariably7 the entire nature of the substance is changed2 for instance1 enstatite 7or bronzite7 is a magnesium bisilicate with a small isomorphous substitution of calcium for magnesium2 its composition is expressed by the formula ,mg,si,o#c1 it belongs to the rhombic system4 ,on the entire substitution of calcium1 wollastonite1 ,ca,si,o#c1 of the monoclinic system1 is obtained2 when manganese is substituted1 rhodonite1 of the triclinic system1 is produced2 but in all of them the angles of the prism are #hf to #hh4bc #ba ,for us the latter have not a saline character1 only because they are not regarded from this point of view1 but an alloy of sodium and zinc is1 in a broad sense1 a salt in many of its reactions1 for it is subject to the same double decompositions as sodium phosphide or sulphide1 which clearly have saline properties4 ,the latter 7sodium phosphide71 when heated with ethyl iodide1 forms ethyl phosphide1 and the former--i4e4 the alloy of zinc and sodium--gives zinc ethyl2 that is1 the element 7,p1 ,s1 ,zn7 which was united with the sodium passes into combination with the ethyl3 ,r,na ,et,i ,r,et ,na,i4 ,by combining sodium successively with chlorine1 sulphur1 phosphorus1 arsenic1 antimony1 tin1 and zinc1 we obtain substances having less and less the ordinary appearance of salts1 but if the alloy of sodium and zinc cannot be termed a salt1 then perhaps this name cannot be given to sodium sulphide1 and the compounds of sodium with phosphorus4 ,the following circumstance may also be observed3 with chlorine1 sodium gives only one compound 7with oxygen1 at the most three71 with sulphur five1 with phosphorus probably still more1 with antimony naturally still more1 and the more analogous an element is to sodium1 the more varied are the proportions in which it is able to combine with it1 the less are the alterations in the properties which take place by this combination1 and the nearer does the compound formed approach to the class of compounds known as indefinite chemical compounds4 ,in this sense a siliceous alloy1 containing silica and other acids1 is a salt4 ,the oxide to a certain extent plays the same part as the sodium1 whilst the silica plays the part of the acid element which was taken up successively by zinc1 phosphorus1 sulphur1 c41 in the above examples4 ,such a comparison of the silica compounds with alloys presents the great advantage of including under one category the definite and indefinite silica compounds which are so analogous in composition--that is1 brings under one head such crystalline substances as certain minerals1 and such amorphous substances as are frequently met with in nature1 and are artificially prepared1 as glass1 slags1 enamels1 c4 ,if the compounds of silica are substances like the metallic alloys1 then 7#a7 the chemical union between the oxides of which they are composed must be a feeble one1 as it is in all compounds formed between analogous substances4 ,in reality such feeble agencies as water and carbonic acid are able1 although slowly1 to act on and destroy the majority of the complex silica compounds in rocks1 as we saw in the preceding chapter2 7#b7 their formation1 like that of alloys1 should not be accompanied by a considerable alteration of volume2 and this is actually the case4 ,for example1 felspar has a specific gravity of about #bf1 and therefore1 taking its composition to be ,k#b,o1,al#b,o#c1f,si,o#b1 we find its volume1 corresponding with this formula1 to be #eefh4 #bf #bad1 the volume of ,k#b,o #ce1 of ,al#b,o#c #bf1 and of ,si,o#b #bbf4 ,hence the sum of the volumes of the component oxides1 #ce #bf #f #bbf #aif1 which is very nearly equal to that of the felspar2 that is1 its formation is attended by a slight expansion1 and not by contraction1 as is the case in the majority of other cases when combinations determined by strong affinities are accomplished4 ,in the case in question the same phenomenon is observed as in solutions and alloys--that is1 as in cases of feeble affinities4 ,so also the specific gravity of glass is directly dependent on the amount of those oxides which enter into its composition4 ,if in the preceding example we take the sp4 gr4 of silica to be1 not #bfe1 but #bb1 its volume #bgc1 and the sum of the volumes will be #bbd--that is1 greater than that of orthoclase4 #bb ,it is1 however1 easy to imagine1 and experience confirms the supposition1 that in a complex siliceous compound containing for instance sodium and calcium1 the whole of the sodium may be replaced by potassium1 and at the same time the whole of the calcium by magnesium1 because then the substitution of potassium for the sodium will produce a change in the nature of the substance contrary to that which will occur from the calcium being replaced by magnesium4 ,that increase in weight1 decrease in density1 increase of chemical energy1 which accompanies the exchange of sodium for potassium will1 so to speak1 be compensated by the exchange of calcium for magnesium1 because both in weight and in properties the sum of ,na ,ca is very near to the sum of ,k ,mg4 ,pyroxene or augite can be taken as an example2 its composition may be expressed by the formula ,ca,mg,si#b,o#f2 that is1 it corresponds with the acid ,h#b,si,o#c2 it is a bisilicate4 ,in many respects it closely resembles another mineral called 'spodumene' 7they are both monoclinic74 ,this latter has the composition ,li#f;,al#h,si#ae,o#de4 ,on reducing both formul to an equal contents of silica the following distinction will be observed between them3 spodumene 7,li#b,o7#f7;,al#b,o#c7hcj,si,o#b2 augite 7,ca,o7#ae7,mg,o7#aecj,si,o#b4 ,that is1 the difference between them consists in the sum of the magnesia and lime 7,mg,o7#ae 7,ca,o7#ae replacing the sum of the lithium oxide and alumina 7,li#b,o7#f 7,al#b,o#c7h2 and in the chemical relation these sums are near to one another1 because magnesium and calcium1 both in forms of oxidation and in energy 7as bases71 in all respects occupy a position intermediate between lithium and aluminium1 and therefore the sum of the first may be replaced by the sum of the second4 ,if we take the composition of spodumene1 as it is often represented to be1 ,li#b,o1,al#b,o#c1d,si,o#b1 the corresponding formula of augite will be 7,ca,o7#b17,mg,o7#b1d,si,o#b1 and also the amount of oxygen in the sum of ,li#b,o,al#b,o#c will be the same as in 7,ca,o7#b7,mg,o7#b4 ,i may remark1 for the sake of clearness1 that lithium belongs to the first1 aluminium to the third group1 and calcium and magnesium to the intermediate second group2 lithium1 like calcium1 belongs to the even series1 and magnesium and aluminium to the uneven4 ,the representation of the substitutions of analogous compounds here introduced was first deduced by me in #ahef4 ,it finds much confirmation in facts which have been subsequently discovered--for example1 with respect to tourmalin4 ,wlfing 7#ahhh71 on the basis of a number of analyses 7especially of those by ,rggs71 states that all varieties contain an isomorphous mixture of alkali and magnesia tourmalin2 into the composition of the former there enters #ab,si,o#b1c;,b#b,o#c1h;,al#b,o#c1b,na#b ,o1#d;,h#b,o1 and of the latter #ab,si,o#b1c;,b#b,o#c1e;,al#b,o#c1ab,mg, o1#c;,h#b,o4 ,hence it is seen that the former contains in addition the sum of #c;,al#b,o#c1b,na#b,o1,h#b,o1 whilst in the latter this sum of oxides is replaced by #ab,mg,o1 in which there is as much oxygen as in the sum of the more clearly-defined base #b,na#b,o and less basic #c;,al#b,o#c;,h#b,o--that is1 the relation is just the same here as between augite and spodumene4 #bc ,with respect to the silica compounds of the various oxides1 it must be observed that only the alkali salts are known in a soluble form2 all the others only exist in an insoluble form1 so that a solution of the alkali compounds of silica1 or soluble glass1 gives a precipitate with a solution of the salts of the majority of other metals1 and this precipitate will contain the silica compounds of the other bases4 ,the maximum amount of the gelatinous hydrate of silica1 which dissolves in caustic potash1 corresponds with the formation of a compound1 #b,k#b,o1#i,si,o#b4 ,but this compound is partially decomposed1 with the precipitation of hydrate of silica1 on cooling the solution4 ,solutions containing a smaller amount of silica may be kept for an indefinite time without decomposing1 and silica does not separate out from the solution2 but such compounds crystallise from the solutions with difficulty4 ,however1 a crystalline bisilicate 7with water7 has been obtained for sodium having the composition ,na#b,o1,si,o#b--;i4e4 corresponding to sodium carbonate4 ,the whole of the carbonic acid is evolved1 and a similar soluble sodium metasilicate is obtained on fusing #ce parts of sodium carbonate with #b parts of silica4 ,if less silica be taken a portion of the sodium carbonate remains undecomposed2 however1 a substance may then be obtained of the composition ,si7,o,na7#d1 corresponding with orthosilicic acid4 ,it contains the maximum amount of sodium oxide capable of combining with silica under fusion4 ,it is a sodium orthosilicate1 7,na#b,o7#b1,si,o#b4 ,calcium carbonate1 and the carbonates of the alkaline earths in general1 also evolve all their carbonic acid when heated with silica1 and in some instances even form somewhat fusible compounds4 ,lime forms a fusible slag of calcium silicate1 of the composition ,ca,o1,si,o#b and #b;,ca,o1#c,si,o#b4 ,with a larger proportion of silica the slags are infusible in a furnace4 ,the magnesium slags are less fusible than those with lime1 and are often formed in smelting metals4 ,many compounds of the metals of the alkaline earths with silica are also met with in nature4 ,for instance1 among the magnesium compounds there is olivine1 7,mg,o7#b1,si,o#b1 sp4 gr4 #cd1 which occurs in meteorites1 and sometimes forms a precious stone 7peridote71 and occurs in slags and basalts4 ,it is decomposed by acids1 is infusible before the blow-pipe1 and crystallises in the rhombic system4 ,serpentine has the composition #c,mg,o1#b,si,o#b1b;,h#b,o2 it sometimes forms whole mountains1 and is distinguished for its great cohesiveness1 and is therefore used in the arts4 ,it is generally tinted green2 its specific gravity is #be2 it is exceedingly infusible1 even before the blowpipe4 ,it is acted on by acids4 ,among the magnesium compounds of silica1 talc is very widely used4 ,it is frequently met with in rocks which are widely distributed in nature1 and sometimes in compact masses2 it can be used for writing like a slate pencil or chalk1 and being greasy to the touch1 is also known as steatite4 ,it crystallises in the rhombic system1 and resembles mica in many respects2 like it1 it is divisible into lamin1 greasy to the touch1 and having a sp4 gr4 #bg4 ,these lamin are very soft1 lustrous1 and transparent1 and are infusible and insoluble in acids4 ,the composition of talc approaches nearly to #f,mg,o1#e,si,o#b1b;,h#b,o4 ,among the crystalline silicates the following minerals are known3--,wollastonite 7tabular-spar71 crystallises in the monoclinic system2 sp4 gr4 #bh2 it is semi-transparent1 difficultly fusible1 decomposed by acids1 and has the composition of a metasilicate1 ,ca,o,si,o#b4 ,but isomorphous mixtures of calcium and magnesium silicates occur with particular frequency in nature4 ,the augites 7sp4 gr4 #cc71 diallages1 hypersthenes1 hornblendes 7sp4 gr4 #ca71 amphiboles1 common asbestos1 and many similar minerals1 sometimes forming the essential parts of entire rock formations1 contain various relative proportions of the bisilicates of calcium and magnesium partially mixed with other metallic silicates1 and generally anhydrous1 or only containing a small amount of water4 ,in the pyroxenes1 as a rule1 lime predominates1 and in the amphiboles 7also of the monoclinic system7 magnesia predominates4 ,details upon this subject must be looked for in works upon mineralogy4 ,the most remarkable complex siliceous compounds are the felspars1 which enter into nearly all the primary rocks like porphyry1 granite1 gneiss1 c4 ,these felspars always contain1 in addition to silica and alumina1 oxides presenting more marked basic properties1 such as potash1 soda1 and lime4 ,thus the orthoclase 7adularia71 or ordinary felspar 7monoclinic7 of the granites1 contains ,k#b,o1,al#b,o#c1f,si,o#b2 albite contains the same substances1 only with ,na#b,o instead of ,k#b,o 7it already appertains to the triclinic system72 anorthite contains lime1 and its composition is ,ca,o1,al#b,o#c1b,si,o#b4 ,on expressing the two last as containing equal quantities of oxygen1 we have3-- ,albite ,na#b ,al#b ,si#f ,o#af ,anorthite ,ca#b ,al#d ,si#d ,o#af ,it is then evident that on the conversion of albite into anorthite1 ,na#b,si#b is replaced by ,ca#b;,al#b1 and this sum1 both in chemical energy and in the form of oxide1 may be considered as corresponding with the first1 because sodium and silicon are extreme elements in chemical character 7from groups ,i4 and ,,iv471 and calcium and aluminium are means between them 7from groups ,,ii4 and ,,iii471 and actually both these felspar minerals are not only of one 7triclinic7 system1 but form 7,tchermak1 ,schuster7 all possible kinds of definite compounds 7isomorphous mixtures7 between themselves1 as indicated by their composition and all their properties4 ,thus oligoclase1 andesine1 labradorite1 c4 7plagioclases71 are nothing more than mutual combinations of albite and anorthite4 ,labradorite consists of albite1 in combination with #a to #b molecules of anorthite4 ,the class of zeolites corresponds to the felspars2 they are hydrated compounds of a similar composition to the felspars4 ,thus natrolite contains ,na#b,o1,al#b,o#c1c,si,o#b1b;,h#b,o1 and analcime presents the same composition1 but contains #d,si,o#b instead of #c,si,o#b4 ,in general1 the felspars and zeolites contain ,,ro1,al#b,o#c1n,si,o#b1 where n varies considerably4#bd #bd ,the majority of the siliceous minerals have now been obtained artificially under various conditions4 ,thus ,n4 ,n4 ,sokoloff showed that slags very frequently contain peridote4 ,hautefeuille1 ,chroustchoff1 ,friedel1 and ,sarasin obtained felspar identical in all respects with the natural minerals4 ,the details of the methods here employed must be looked for in special works on mineralogy2 but1 as an example1 we will describe the method of the preparation of felspar employed by ,friedel and ,sarasin 7#ahha74 ,from the fact that felspar gives up potassium silicate to water even at the ordinary temperature 7,debray's experiments71 they concluded that the felspar in granites had an aqueous origin 7and this may be supposed to be the case from geological data72 then1 in the first place1 its formation could not be accomplished unless in the presence of an excess of a solution of potassium silicate4 ,in order to render this argument clear ,i may mention1 as an example1 that carnallite is decomposed by water into easily soluble magnesium chloride and potassium chloride1 and therefore if it is of aqueous origin it could not be formed otherwise than from a solution containing an excess of magnesium chloride1 and1 in the second place1 from a strongly-heated solution2 again1 felspar itself and its fellow-components in granites are anhydrous4 ,on these facts were based experiments of heating hydrates of silica with alumina and a solution of potassium silicate in a closed vessel4 ,the mixture was placed in a sealed platinum tube1 which was enclosed in a steel tube and heated to dull redness4 ,when the mixture contained an excess of silica the residue contained many crystals of rock crystal and tridymite1 together with a powder of felspar1 which formed the main product of the reaction when the proportion of hydrate of silica was decreased1 and a mixture of a solution of potassium silicate with alumina precipitated together with the silica by mixing soluble glass with aluminium chloride was employed4 ,the composition1 properties1 and forms of the resultant felspar proved it to be identical with that found in nature4 ,the experiments approach very nearly to the natural conditions1 all the more as felspar and quartz are obtained together in one mixture1 as they so often occur in nature4 ,such complex silicates are generally insoluble in water1#be and if they undergo change in it1 it is but very slow1 and more often only in the presence of carbonic acid4 ,some of the silicates which are insoluble in water are easily and directly decomposed by acids2 for instance1 the zeolites and those fused silicates which contain a large quantity of energetic bases--such as lime4 ,many of the silicates1 like glass1#bf are hardly changed by acids1 particularly if they contain much silica1 whilst fusion with alkalis leads to the formation of compounds rich in bases1 after which acids decompose the alloys formed4#bg #be ,the application of cements is based on this principle2 they are those sorts of 'hydraulic' lime which generally form a stony mass1 which hardens even under water1 when mixed with sand and water4 ,the hydraulic properties of cements are due to their containing calcareous and silico-aluminous compounds which are able to combine with water and form hydrates1 which are then unacted on by water4 ,this is best proved1 in the first place1 by the fact that certain slags containing lime and silica1 and obtained by fusion 7for example1 in blast-furnaces71 solidify like cements when finely ground and mixed with water2 and1 in the second place1 by the method now employed for the manufacture of artificial cements 7formerly only peculiar and comparatively rare natural products were used74 ,for this purpose a mixture of lime and clay is taken1 containing about #be p4c4 of the latter2 this mixture is then heated1 not to fusion1 but until both the carbonic anhydride and water contained in the clay are expelled4 ,this mass when finely ground forms ,portland cement1 which hardens under water4 ,the process of hardening is based on the formation of chemical compounds between the lime1 silica1 alumina1 and water4 ,these substances are also found combined together in various natural minerals--for example1 in the zeolites1 as we saw above4 ,in all cases cement which has set contains a considerable amount of water1 and its hardening is naturally due to hydration--that is1 to the formation of compounds with water4 ,well-prepared and very finely-ground cement hardens comparatively quickly 7in several days1 especially after being rammed down71 with #c parts 7and even more7 of coarse sand and with water1 into a stony mass which is as hard and durable as many stones1 and more so than bricks and limestone4 ,hence not only all maritime constructions 7docks1 ports1 bridges1 c471 but also ordinary buildings1 are made of ,portland cement1 and are distinguished for their great durability4 ,a combination of ironwork 7ties1 girders7 and cement is particularly suitable for the construction of aqueducts1 arches1 reservoirs1 c4 ,arches and walls made of such cements may be much less thick than those built up of ordinary stone4 ,hence the production and use of cement rapidly increases from year to year4 ,the origin of accurate data respecting cements is chiefly due to ,vicat4 ,in ,russia ,professor ,schuliachenko has greatly aided the extension of accurate data concerning ,portland cement4 ,many works for the manufacture of cement have already been established in various parts of ,russia1 and this industry promises a great future in the arts of construction4 #bf ,glass presents a similar complex composition1 like that of many minerals4 ,the ordinary sorts of white glass contain about #ge p4c4 of silica1 #ac p4c4 of sodium oxide1 and #ab p4c of lime2 but the inferior sorts of glass sometimes contain up to #aj p4c4 of alumina4 ,the mixtures which are used for the manufacture of glass are also most varied4 ,for example1 about #cjj parts of pure sand1 about #ajj parts of sodium carbonate1 and #ej of limestone are taken1 and sometimes double the proportion of the latter4 ,ordinary soda-glass contains sodium oxide1 lime1 and silica as the chief component parts4 ,it is generally prepared from sodium sulphate mixed with charcoal1 silica1 and lime 7,chapter ,,xii471 in which case the following reaction takes place at a high temperature3 ,na#b,,so#d ,c ,si,o#b ,na#b,si,o#c ,,so#b ,,co4 ,sometimes potassium carbonate is taken for the preparation of the better qualities of glass4 ,in this case a glass1 potash-glass1 is obtained containing potassium oxide instead of sodium oxide4 ,the best-known of these glasses is the so-called ,bohemian glass or crystal1 which is prepared by the fusion of #ej parts of potassium carbonate1 #ae parts of lime1 and #ajj parts of quartz4 ,the preceding kinds of glass contain lime1 whilst crystal glass contains lead oxide instead4 ,flint glass--that is1 the lead glass used for optical instruments--is prepared in this manner1 naturally from the purest possible materials4 ,crystal-glass--i4e4 glass containing lead oxide--is softer than ordinary glass1 more fusible and has a higher index of refraction4 ,however1 although the materials for the preparation of glass be most carefully sorted1 a certain amount of iron oxides falls into the glass and renders it greenish4 ,this coloration may be destroyed by adding a number of substances to the vitreous mass1 which are able to convert the ferrous oxide into ferric oxide2 for example1 manganese peroxide 7because the peroxide is deoxidised to manganous oxide1 which only gives a pale violet tint to the glass7 and arsenious anhydride1 which is deoxidised to arsenic1 and this is volatilised4 ,the manufacture of glass is carried on in furnaces giving a very high temperature 7often in regenerative furnaces1 ,chapter ,,ix474 ,large clay crucibles are placed in these furnaces1 and the mixture destined for the preparation of the glass1 having been first roasted1 is charged into the crucibles4 ,the temperature of the furnace is then gradually raised4 ,the process takes place in three separate stages4 ,at first the mass intermixes and begins to react2 then it fuses1 evolves carbonic acid gas1 and forms a molten mass2 and1 lastly1 at the highest temperature1 it becomes homogeneous and quite liquid1 which is necessary for the ultimate elimination of the carbonic anhydride and solid impurities1 which latter collect at the bottom of the crucible4 ,the temperature is then somewhat lowered1 and the glass is taken out on tubes and blown into objects of various shapes4 ,in the manufacture of window-glass it is blown into large cylinders1 which are then cut at the ends and across1 and afterwards bent back in a furnace into the ordinary sheets4 ,after being worked up1 all glass objects have to be subjected to a slow cooling 7annealing7 in special furnaces1 otherwise they are very brittle1 as is seen in the so-called ',rupert's drops1' formed by dropping molten glass into water2 although these drops preserve their form1 they are so brittle that they break up into a fine powder if a small piece be knocked off them4 ,glass objects have frequently to be polished and chased4 ,in the manufacture of mirrors and many massive objects the glass is cast and then ground and polished4 ,coloured glasses are either made by directly introducing into the glass itself various oxides1 which give their characteristic tints1 or else a thin layer of a coloured glass is laid on the surface of ordinary glass4 ,green glasses are formed by the oxides of chromium and copper1 blue by cobalt oxide1 violet by manganese oxide1 and red glass by cuprous oxide and by the so-called purple of ,cassius--i4e4 a compound of gold and tin--which will be described later4 ,a yellow coloration is obtained by means of the oxides of iron1 silver1 or antimony1 and also by means of carbon1 especially for the brown tints for certain kinds of bottle-glass4 ,from what has been said about glass it will be understood that it is impossible to give a definite formula for it1 because it is a non-crystalline or amorphous alloy of silicates2 but such an alloy can only be formed within certain limits in the proportions between the component oxides4 ,with a large proportion of silica the glass very easily becomes clouded when heated2 with a considerable proportion of alkalis it is easily acted on by moisture1 and becomes cloudy in time on exposure to the air2 with a large proportion of lime it becomes infusible and opaque1 owing to the formation of crystalline compounds in it2 in a word1 a certain proportion is practically attained among the component oxides in order that the glass formed may have suitable properties4 ,nevertheless1 it may be well to remark that the composition of common glass approaches to the formula ,na#b,o1,ca,o1#d,si,o#b4 ,the coefficient of cubical expansion of glass is nearly equal to that of platinum and iron1 being approximately #jjjjjbg4 ,the specific heat of glass is nearly #jah1 and the specific gravity of common soda glass is nearly #be1 of ,bohemian glass #bd1 and of bottle glass #bg4 ,flint glass is much heavier than common glass1 because it contains the heavier oxide of lead1 its specific gravity being #bi to #cb4 #bg ,it must be recollected that although acids seem to act only feebly on the majority of silicates1 nevertheless a finely-levigated powder of siliceous compounds is acted on by strong acids1 especially with the aid of heat1 the basic oxides being taken up and gelatinous silica left behind4 ,in this respect sulphuric acid heated to #bjj with finely-divided siliceous compounds in a closed tube acts very energetically4 ,according to the periodic law1 the nearest analogues of silicon ought to be elements of the uneven series1 because silicon1 like sodium1 magnesium1 and aluminium1 belongs to the uneven series4#bh ,immediately after silicon follows ekasilicon or germanium1 ,ge #gb1 whose properties were predicted 7#ahga7 before ,winkler 7#ahhf7 in ,freiberg1 ,saxony 7,chapter ,,xv4 #e71 discovered this element in a peculiar silver ore called argyrodite1 ,ag#f;,ge,s#e4bi ,easily reduced from the oxide by heating with hydrogen and charcoal1 and separated from its solutions by zinc1 metallic germanium proved to be greyish white1 easily crystallisable 7in octahedra71 brittle1 fusible 7under a coating of fused borax7 at about #ijj1 and easily oxidisable2 the specific gravity #edfi1 the atomic weight #gbc1 and the specific heat #jjgf1cj as might be expected for this element according to the periodic law4 ,the corresponding germanium dioxide1 ,ge,o#b1 is a white powder having a specific gravity of #dgjc2 water1 especially when boiling1 dissolves this dioxide 7#a part of ,ge,o#b requires for solution #bdg parts of water at #bj1 #ie parts at #ajj74 ,it forms soluble salts with alkalis and is but sparingly soluble in acids4#ca ,in a stream of chlorine the metal forms germanium chloride1 ,ge,cl#d1 which boils at #hf1 and has a specific gravity of #ahhg at #ah2 water decomposes it1 forming the oxide4 ,all these properties#cb of germanium1 showing its analogy to silicon and tin1 form a most beautiful demonstration of the truth of the periodic law4#cc #bh ,such elements as silicon1 tin1 and lead were only brought together under one common group by means of the periodic law1 although the quadrivalency of tin and lead was known much earlier4 ,generally silicon was placed among the non-metals1 and tin and lead among the metals4 #bi ,at first 7,february #ahhf7 the want of material to work on1 the absence of a spectrum in the ,bunsen's flame1 and the solubility of many of the compounds of germanium1 presented difficulties in the researches of ,professor ,winkler1 who1 on analysing argyrodite by the usual method1 obtained a constant loss of #g p4c41 and was thus led to search for a new element4 ,the presence of arsenic and antimony in the accompanying minerals also impeded the separation of the new metal4 ,after fusion with sulphur and sodium carbonate1 argyrodite gives a solution of a sulphide which is precipitated by an excess of hydrochloric acid2 germanium sulphide is soluble in ammonia and then precipitated by hydrochloric acid1 as a white precipitate1 which is dissolved 7or decomposed7 by water4 ,after being oxidised by nitric acid1 dried and ignited germanium sulphide leaves the oxide ,ge,o#b1 which is reduced to the metal when ignited in a stream of hydrogen4 #cj ,g4 ,kobb determined the spectrum of germanium1 when the metal was taken as one of the electrodes of a powerful ,ruhmkorff's coil4 ,the wave-lengths of the most distinct lines are #fjb1 #ehc1 #eah1 #eac1 #dha1 #dgd1 millionths of a millimetre4 #ca ,if germanium or germanium sulphide be heated in a stream of hydrochloric acid1 it forms a volatile liquid1 boiling at #gb1 which ,winkler regarded as germanium chloride1 ,ge,cl#b1 or germanium chloroform1 ,ge,h,cl#c4 ,it is decomposed by water1 forming a white substance1 which may perhaps be the hydrate of germanious oxide1 ,ge,o1 and acts as a powerfully reducing agent in a hydrochloric acid solution4 #cb ,under certain circumstances germanium gives a blue coloration like that of ultramarine1 as ,winkler showed1 which might have been expected from the analogy of germanium with silicon4 #cc ,winkler expressed this in the following words 7,jour4 f4 pract4 ,chemie1 #ahhf #b1 #cd1 #ahb-ahc73 '444 es kann keinem ,zweifel mehr unterliegen1 dass das neue ,element nichts ,anderes1 als das vor fnfzehn ,jahren von ,mendeleff prognosticirte ,ekasilicium ist4' ',denn einen schlagenderen ,beweis fr die ,richtigkeit der ,lehre von der ,periodicitt der ,elemente1 als den1 welchen die ,verkrperung des bisher hypothetischen ,ekasilicium in sich schliesst1 kann es kaum geben1 und er bildet in ,wahrheit mehr1 als die blosse ,besttigung einer khn aufgestellten ,theorie1 er bedeutet eine eminente ,erweiterung des chemischen ,gesichtfeldes1 einen mchtigen ,schritt in's ,reich der ,erkenntniss4' ,the increase of atomic weight from silicon #bh to germanium #gb is #dd--that is1 about the same difference as there is in the atomic weights of chlorine and bromine2 between germanium and its next analogue1 tin 7,sn #aah71 the difference is #df--that is1 almost as much as the amount by which the atomic weight of iodine exceeds that of bromine4 ,metallic tin is rarely met with in nature2 it occurs in the veins of ancient formations1 almost exclusively in the form of oxide1 ,sn,o#b1 called tin-stone4 ,the best known tin deposits are in ,cornwall and in ,malacca4 ,in ,russia1 tin ores have been found in small quantities on the shores of ,lake ,ladoga1 in ,pitkarand4 ,the crushed ore may easily be separated from the earthy matter accompanying it by washing on inclined tables1 as the tin-stone has a specific gravity of #fi1 whilst the impurities are much lighter4 ,tin oxide is very easily reduced to metallic tin by heating with charcoal4 ,for this reason tin was known in ancient times1 and the ,phoenicians brought it from ,england4 ,metallic tin is cast into ingots of considerable weight or into thin sticks or rods4 ,tin has a white colour1 rather duller than that of silver4 ,it fuses easily at #bcb1 and crystallises on cooling4 ,its specific gravity is #gbi4 ,the crystalline structure of ordinary tin is noticed in bending tin rods1 when a peculiar sound is heard1 produced by the fracture of the particles of tin along the surfaces of crystalline structure4 ,when pure tin is cooled to a low temperature it splits up into separate crystals1 the bond between the particles is lost1 the tin assumes a grey colour1 becomes less brilliant--in a word1 its properties become changed1 as ,fritzsche showed4 ,this depends on the peculiar structure which the tin then acquires1 and is particularly remarkable because it is effected by cold in a solid4#cc bis ,if such tin be fused1 or even simply heated1 it becomes like ordinary tin1 but is again changed when cooled4 ,when in this condition tin has a specific gravity of #gai4 ,similarly1 tin is obtained by the action of the galvanic current on a solution of tin chloride2 it then appears in crystals of the cubic system1 and has a specific gravity of #gah--that is1 the same as when cooled4#cd #cc bis ,emilianoff 7#ahij7 states that in the cold of the ,russian winter #cj out of #bjj tin moulds for candles were spoilt through becoming quite brittle4 #cd ,the tin deposited by an electric current from a neutral solution of ,sn,cl#b easily oxidises and becomes coated with ,sn,o 7,vignon1 #ahhi74 ,tin is softer than silver and gold1 and is only surpassed by lead in this respect4 ,in addition to this it is very ductile1 but its tenacity is very slight1 so that wire made from it will bear but little strain4 ,in consequence of its ductility it is easily worked1 by forging and rolling into very thin sheets 7tin foil71 which are used for wrapping many articles to preserve them from moisture1 c4 ,in this case1 however1 and in many others1 lead is mixed with the tin1 which1 within certain limits1 does not alter the ductility4 ,whilst so soft at the ordinary temperatures tin becomes brittle at #bjj1 before fusing4 ,tin powder may be easily obtained if the metal be fused and then stirred whilst cooling4 ,at a white heat tin may be distilled1 but with more difficulty than zinc4 ,if molten tin comes into contact with oxygen1 it oxidises1 forming stannic oxide1 ,sn,o#b1 and its vapour burns with a white flame4 ,at ordinary temperatures tin does not oxidise1 and this very important property of tin allows it to be applied in many cases for covering other metals to prevent their oxidising4 ,this is termed tinning4 ,iron and copper are frequently tinned4 ,iron and steel sheets1 coated with tin1 bear the name of tin plate 7for the most part made in ,england71 and are used for numerous purposes4 ,tin plate is prepared by immersing iron sheets1 previously thoroughly cleansed by acid and mechanical means1 into molten tin4#cd bis #cd bis ,if after this the coating of tin be rapidly cooled--for instance1 by dashing water over it--it crystallises into diverse star-shaped figures1 which become visible when the sheets are first immersed in dilute aqua regia and then in a solution of caustic soda4 ,the coating of iron by tin1 guards it against the direct access of air1 but it only preserves the iron from oxidation so long as it forms a perfectly continuous coating4 ,if the iron is left bare in certain places1 it will be powerfully oxidised at these spots1 because the tin is electro-negative with respect to the iron1 and thus the oxidation is confined entirely to the iron in the presence of tin4 ,hence a coating of tin over iron objects only partially preserves them from rusting4 ,in this respect a coating of zinc is more effectual4 ,however1 a dense and invariable alloy is formed over the surface of contact of the iron and tin1 which binds the coating of tin to the remaining mass of the iron4 ,tin may be fused with cast iron1 and gives a greyish-white alloy1 which is very easily cast1 and is used for casting many objects for which iron by itself would be unsuitable owing to its ready oxidisability and porosity4 ,the coating of copper objects by tin is generally done to preserve the copper from the action of acid liquids1 which would attack the copper in the presence of air and convert it into soluble salts4 ,tin is not acted on in this manner1 and therefore copper vessels for the preparation of food should be tinned4 ,tin with copper forms bronze1 an alloy which is most extensively used in the arts4 ,bronze has various colours and a variety of physical properties1 according to the relative amount of copper and tin which it contains4 ,with an excess of copper the alloy has a yellow colour2 the admixture of tin imparts considerable hardness and elasticity to the copper4 ,an alloy containing #gh parts of copper and about #bb per cent4 of tin is so elastic that it is used for casting bells1 which naturally require a very elastic and hard alloy4#ce ,for casting statues and various large or small ornamental articles alloys containing #b to #e p4c4 of tin1 #aj to #cj p4c4 of zinc1 and #fe to #he p4c4 of copper are used4#cf ,tin is also often used alloyed with lead1 for making various objects--for instance1 drinking vessels4 #ce ,the ancient ,chinese alloys1 containing about #bj p4c4 of tin 7specific gravity of alloys about #hi71 which have been rapidly cooled1 are distinguished for their resonance and elasticity4 ,these alloys were formerly manufactured in large quantities in ,china for the musical instruments known as tom-toms4 ,owing to their hardness1 alloys of this nature are also employed for casting guns1 bearings1 c41 and an alloy containing about #aa p4c4 of tin 7corresponding with the ratio ,cu#ae,sn7 is known as gun-metal4 ,the addition of a small quantity of phosphorus1 up to #b p4c41 renders bronze still harder and more elastic1 and the alloy so formed is now used under the name of phosphor-bronze4 ,the alloy ,sn,cu#c is brittle1 of a bluish colour1 and has nothing in common with either copper or tin in its appearance or properties4 ,it remains perfectly homogeneous on cooling1 and acquires a crystalline structure 7,riche74 ,all these signs clearly indicate that the alloy ,sn,cu#c is a product of chemical combination1 which is also seen to be the case from its density1 #hia4 ,had there been no contraction1 the density of the alloy would be #hba4 ,it is the heaviest of all the alloys of tin and copper1 because the density of tin is #gbi and of copper #hh4 ,the alloy ,sn,cu#d1 specific gravity #hgg1 has similar properties4 ,all the alloys except ,sn,cu#c and ,sn,cu#d split up on cooling2 a portion richer in copper solidifies first 7this phenomenon is termed the liquation of an alloy71 but the above two alloys do not split up on cooling4 ,in these and many similar facts we can clearly distinguish a chemical union between the metals forming an alloy4 ,the alloys of tin and copper were known in very remote ages1 before iron was used4 ,the alloys of zinc and tin are less used1 but alloys composed of zinc1 tin1 and copper frequently replace the more costly bronze4 ,concerning the alloys of lead see ,note #df4 #cf ,an excellent proof of the fact that alloys and solutions are subject to law is given1 amongst others1 by the application of ,raoult's method 7,chapter ,i41 ,note #di7 to solutions of different metals in tin4 ,thus ,heycock and ,neville 7#ahhi7 showed that the temperature of solidification of molten tin 7#bbfd7 is lowered by the presence of a small quantity of other metals in proportion to the concentration of the solution4 ,the following were the reductions of the temperature of solidification of tin obtained by dissolving in it atomic proportions of different metals 7for example1 #fe parts of zinc in #aa1hjj parts of tin72 ,zn #bec1 ,cu #bdg1 ,ag #bfg1 ,cd #baf1 ,pb #bbb1 ,hg #bc1 ,sb #b rise1 ,al #acd4 ,as ,raoult's method 7,chapter ,,vii47 enables the molecular weight to be determined1 the almost perfect identity of the resultant figures 7except for aluminium7 shows that the molecules of copper1 silver1 lead1 and antimony contain one atom in the molecule1 like zinc1 mercury1 and cadmium4 ,they obtained the same result 7#ahij7 for ,mg1 ,na1 ,ni1 ,au1 ,pd1 ,bi and ,in4 ,it should here be mentioned that ,ramsay 7#ahhi7 for the same purpose 7the determination of the molecular weight of metals on the basis of their mutual solution7 took advantage of the variation of the vapour tension of mercury 7see ,vol4 ,i41 p4 #acd71 containing various metals in solution1 and he also found that the above-mentioned metals contain but one atom in the molecule4 ,tin decomposes the vapour of water when heated with it1 liberating the hydrogen and forming stannic oxide4 ,sulphuric acid1 diluted with a considerable quantity of water1 does not act1 or at all events acts very slightly1 on tin1 but tin reduces hot strong sulphuric acid1 when not only sulphurous anhydride but also sulphuretted hydrogen is evolved4 ,hydrochloric acid acts very easily on tin1 with evolution of hydrogen and formation of stannous chloride1 ,sn,cl#b1 in solution1 which1 with an excess of hydrochloric acid and access of air1 is converted into stannic chloride3 ,sn,cl#b #b;,h,cl ,o ,sn,cl#d ,h#b,o4#cf bis ,nitric acid diluted with a considerable quantity of water dissolves tin at the ordinary temperature1 whilst the nitric acid itself is reduced1 forming1 amongst other products1 ammonia and hydroxylamine4 ,here the tin passes into solution in the form of stannous nitrate4 ,stronger nitric acid 7also more dilute1 when heated7 transforms the tin into its highest grade of oxidation1 ,sn,o#b1 but the latter then appears as the so-called metastannic acid1 which does not dissolve in nitric acid1 and therefore the tin does not pass into solution4 ,feeble acids--for instance1 carbonic and organic acids--do not act on tin even in the presence of oxygen1 because tin does not form any powerful bases4 #cf bis ,the action of a mixture of hydrochloric acid and tin forms an excellent means of reducing1 wherein both the hydrogen liberated by the mixture 7at the moment of separation7 and the stannous chloride act as powerful reducing and deoxidising agents4 ,thus1 for instance1 by this mixture nitro-compounds are transformed into amido-compounds--that is1 the elements of the group ,,no#b are reduced to ,,nh#b4 ,it is important to remark as a characteristic of tin that it is reduced from its solutions by many metals which are more easily oxidised1 as1 for instance1 by zinc4 ,in combination1 tin appears in the two types1 ,sn,x#d and ,sn,x#b1cg compounds of the intermediate type1 ,sn#b,x#f1 being also known1 but these latter pass with remarkable facility in most cases into compounds of the higher and lower types1 and therefore the form ,sn,x#c cannot be considered as independent4 #cg ,many volatile compounds of tin are known1 whose molecular weights can therefore be established from their vapour densities4 ,among these may be mentioned stannic chloride1 ,sn,cl#d1 and stannic ethide1 ,sn7,c#b;,h#e7d 7the latter boils at about #aej74 ,but ,v4 ,meyer found the vapour density of stannous chloride1 ,sn,cl#b1 to be variable between its boiling point 7#fjf7 and #aajj1 owing1 it would seem1 to the fact that the molecule then varies from ,sn#b;,cl#d to ,sn,cl#b1 but the vapour density proved to be less than that indicated by the first and greater than that shown by the second formula1 although it approaches to the latter as the temperature rises--that is1 it presents a similar phenomenon to that observed in the passage of ,n#b,o#d into ,,no#b4 ,stannous oxide1 ,sn,o1 in an anhydrous condition is obtained by boiling solutions of stannous salts with alkalis1 the first action of the alkali being to precipitate a white hydrate of stannous oxide1 ,sn7,,oh7#b,sn,o4 ,the latter when heated parts with water as easily as the hydrate of copper oxide4 ,in this form stannous oxide is a black crystalline powder 7specific gravity #fg7 capable of further oxidation when heated4 ,the hydrate is freely soluble in acids1 and also in potassium and sodium hydroxides1 but not in aqueous ammonia4#ch ,this property indicates the feeble basic properties of this lower oxide1 which acts in many cases as a reducing agent4#ci ,among the compounds corresponding with stannous oxide the most remarkable and the one most frequently used is stannous chloride or chloride of tin1 ,sn,cl#b1 also called proto-chloride of tin 7because it is the lowest chloride1 containing half as much ,cl as ,sn,cl#d74 ,it is a transparent1 colourless1 crystalline substance1 melting at #bej and boiling at #fjf4 ,water dissolves it1 without visible change 7in reality partial decomposition occurs1 as we shall see presently74 ,it is also soluble in alcohol4 ,it is obtained by heating tin in dry hydrochloric acid gas1 the hydrogen being then liberated1 or by dissolving metallic tin in hot strong hydrochloric acid and then evaporating quickly4 ,on cooling1 crystals of the monoclinic system are obtained having the composition ,sn,cl#b1b;,h#b,o4 ,an aqueous solution of this substance absorbs oxygen from the atmosphere1 and gives a precipitate containing stannic oxide4 ,from this it follows that a solution of stannous chloride will act as a reducing agent1 a fact frequently made use of in chemical investigations--for example1 for reducing metals from their solutions--since even mercury may be reduced to a metallic state from its salts by means of stannous chloride4 ,this reducing property is also employed in the arts1 especially in the dyeing industry1 where this substance in the form of a crystalline salt finds an extensive application1 and is known as tin salt or tin crystals4 #ch ,when rapidly boiled1 an alkaline solution of stannous oxide deposits tin and forms stannic oxide1 #b,sn,o ,sn ,sn,o#d1 which remains in the alkaline solution4 #ci ,weber 7#ahhb7 by precipitating a solution of stannous chloride with sodium sulphite 7this salt as a reducing agent prevents the oxidation of the stannous compound7 and dissolving the washed precipitate in nitric acid1 obtained crystals of stannous nitrate1 ,sn7,,no#c7b1bj;,h#b,o1 on refrigerating the solution4 ,this crystallo-hydrate easily melts1 and is deliquescent4 ,besides this1 a more stable anhydrous basic salt1 ,sn7,,no#c7b1,sn,o1 is easily formed4 ,in general1 stannous oxide as a feeble base easily forms basic salts1 just as cupric and lead oxides do4 ,for the same reason ,sn,x#b easily forms double salts4 ,thus a potassium salt1 ,sn,k#b;,cl#d1;,h#b,o1 and especially an ammonium salt1 ,sn7,,nh#d7b;,cl#d1;,h#b,o1 called pink salt1 are known4 ,some of these salts are used in the arts1 owing to their being more stable than tin salts alone4 ,stannous bromide and iodide1 ,sn,br#b and ,sn,i#b1 resemble the chloride in many respects4 ,among other stannous salts a sulphate1 ,sn,s,o#d1 is known4 ,it is formed as a crystalline powder when a solution of stannous oxide in sulphuric acid is evaporated under the receiver of an air-pump4 ,the feeble basic character of the stannous oxide is clearly seen in this salt4 ,it decomposes with extreme facility1 when heated1 into stannic oxide and sulphurous anhydride1 but it easily forms double salts with the salts of the alkali metals4 ,in gaseous hydrochloric acid1 stannous chloride1 ,sn,cl#b1b;,h#b,o1 forms a liquid having the composition ,sn,cl#b1;,h,cl1#c;,h#b,o 7sp gr4 #bb1 freezes at -#bg71 and a solid salt1 ,sn,cl#b1;,h#b,o 7,engel74 ,stannic oxide1 ,sn,o#b1 occurring in nature as tinstone1 or cassiterite1 is formed during the oxidation or combustion of heated tin in air as a white or yellowish powder which fuses with difficulty4 ,it is prepared in large quantities1 being used as a white vitreous mixture for coating ordinary tiles and similar earthenware objects with a layer of easily fusible glass or enamel4 ,acid solutions of stannic oxide treated with alkalis1 and alkaline solutions treated with acids1 give a precipitate of stannic hydroxide1 ,sn7,,oh7#d1 also known as stannic acid1 which1 when heated1 gives up water and leaves the anhydride1 ,sn,o#b1 which is insoluble in acids1 clearly showing the feebleness of its basic character4 ,when fused with alkali hydroxides 7not with their carbonates or acid sulphates71 an alkaline compound is obtained which is soluble in water4 ,stannic hydroxide1 like the hydrates of silica1 is a colloidal substance1 and presents several different modifications1 depending on the method of preparation1 but having an identical composition2 the various hydroxides have also a different appearance1 and act differently with reagents4 ,for instance1 a distinction is made between ordinary stannic acid and metastannic acid4 ,stannic acid is produced by precipitation by soda or ammonia from a freshly-prepared solution of stannic chloride1 ,sn,cl#d1 in water2 on drying the precipitate thus obtained1 a non-crystalline mass is formed1 which is freely soluble in strong hydrochloric or nitric acids1 and also in potassium and sodium hydroxides4 ,this ordinary stannic acid may be still better obtained from sodium stannate by the action of acids4 ,metastannic acid is insoluble in sulphuric and nitric acids4 ,it is obtained in the form of a heavy white powder by treating tin with nitric acid2 hydrochloric acid does not dissolve it immediately1 but changes it to such an extent that1 after pouring off the acid1 water extracts the stannic chloride1 ,sn,cl#d1 already formed4 ,dilute alkalis not only dissolve metastannic acid1 but also transform it into salts1 which1 slowly1 yet completely1 dissolve in pure water1 but are insoluble even in dilute alkali hydroxides4 ,dilute hydrochloric acid1 especially when boiling1 changes the ordinary hydrate into metastannic acid4 ,on this depends1 by the way1 the formation of a white precipitate1 stannic hydroxide1 from solutions of stannous and stannic chlorides diluted with water4 ,the stannic oxide first dissolved changes under the influence of hydrochloric acid into metastannic acid1 which is insoluble in water in the presence of hydrochloric acid4 ,solutions of metastannic acid differ from solutions of ordinary stannic acid1 and in the presence of alkali they change into solutions of ordinary acid1 so that metastannic acid corresponds principally with the acid compounds of stannic oxide1 and ordinary stannic acid with the alkaline compounds4#dj ,graham obtained a soluble colloidal hydroxide2 it is subject to the same transformations that are in general peculiar to colloids4 #dj ,frmy supposes the cause of the difference to consist in a difference of polymerisation1 and considers that the ordinary acid corresponds with the oxide ,sn,o#b1 and the meta-acid with the oxide ,sn#e,o#aj1 but it is more probable that both are polymeric but in a different degree4 ,stannic acid with sodium carbonate gives a salt of the composition ,na#b,sn,o#c4 ,the same salt is also obtained by fusing metastannic acid with sodium hydroxide1 whilst metastannic acid gives a salt1 ,na#b,sn,o#c1d,sn,o#b 7,frmy71 when treated with a dilute solution of alkali2 moreover1 stannic acid is also soluble in the ordinary stannate1 ,na#b,sn,o#c 7,weber71 so that both stannic acids 7like both forms of silica7 are capable of polymerisation1 and probably only differ in its degree4 ,in general1 there is here a great resemblance to silica1 and ,graham obtained a solution of stannic acid by the direct dialysis of its alkaline solution4 ,the main difference between these acids is that the meta-acid is soluble in hydrochloric acid1 and gives a precipitate with sulphuric acid and stannous chloride1 which do not precipitate the ordinary acid4 ,vignon 7#ahhi7 found that more heat is evolved in dissolving stannic acid in ,,kho than metastannic4 ,stannic oxide shows the properties of a slightly energetic and intermediate oxide 7like water1 silica1 c472 that is to say1 it forms saline compounds both with bases and with acids1 but both are easily decomposed1 and are but slightly stable4 ,but still the acid character is more clearly developed than the basic1 as in silica1 germanic oxide1 and lead dioxide4 ,this determines the character of the compounds ,sn,x#d1 corresponding to stannic chloride1 ,sn,cl#d 7also called tetrachloride of tin74 ,it is obtained in an anhydrous condition by the direct action of chlorine on tin1 and is then easily purified1 because it is a liquid boiling at #aad1 and therefore can be easily distilled4 ,its specific gravity is #bbh 7at #j71 and it fumes in the open air 7spiritus fumans libavii71 reacting on the moisture of the air1 thus showing the properties of a chloranhydride4 ,water however does not at first decompose it1 but dissolves it1 and on evaporation gives the crystallo-hydrate ,sn,cl#d1e;,h#b,o4 ,if but little water be taken1 crystals containing ,sn,cl#d1c;,h#b,o are formed1 which part with one-third of the water when placed under the receiver of the air-pump4 ,a large quantity of water however1 especially on heating1 causes a precipitate of metastannic acid#da and formation of ,h,cl4 #da ,the formation of the compound ,sn,cl#d1c;,h#b,o is accompanied by so great a contraction that these crystals1 although they contain water1 are heavier than the anhydrous chloride ,sn,cl#d4 ,the penta-hydrated crystallo-hydrate absorbs dry hydrochloric acid1 and gives a liquid of specific gravity #aiga1 which at #j yields crystals of the compound ,sn,cl#d1b;,h,cl1#f;,h#b,o 7it corresponds with the similar platinum compound71 which melt at #bj into a liquid of specific gravity #aibe 7,engel74 ,stannic chloride combines with ammonia 7,sn,cl#d1d,,nh#c71 hydrocyanic acid1 phosphoretted hydrogen1 phosphorus pentachloride 7,sn,cl#d1,p,cl#e71 nitrous anhydride and its chloranhydride 7,sn,cl#d1,n#b,o#c and ,sn,cl#d1b,n,o,cl71 and with metallic chlorides 7for example1 ,k#b,sn,cl#f1 7,,nh#d7b,sn,cl#f1 c47 ,in general1 a highly-developed faculty for combination is observed in it4 ,tin does not combine directly with iodine1 but if its filings be heated in a closed tube with a solution of iodine in carbon bisulphide1 it forms stannic iodide1 ,sn,i#d1 in the form of red octahedra which fuse at #adb and volatilise at #bie4 ,the fluorine compounds of tin have a special interest in the history of chemistry1 because they give a series of double salts which are isomorphous with the salts of hydrofluosilicic acid1 ,si,r#b;,f#f1 and this fact served to confirm the formula ,si,o#b for silica1 as the formula ,sn,o#b was indubitable4 ,although stannic fluoride1 ,sn,f#d1 is almost unknown in the free state1 its corresponding double salts are very easily formed by the action of hydrofluoric acid on alkaline solutions of stannic oxide2 thus1 for example1 a crystalline salt of the composition ,sn,k#b;,f#f1;,h#b,o is obtained by dissolving stannic oxide in potassium hydroxide and then adding hydrofluoric acid to the solution4 ,the barium salt1 ,sn,ba,f#f1c;,h#b,o1 is sparingly soluble like its corresponding silicofluoride4 ,the more soluble salt of strontium1 ,sn,sr,f#f1b;,h#b,o1 crystallises very well1 and is therefore more important for the purposes of research2 it is isomorphous with the corresponding salt of silicon 7and titanium72 the magnesium salt contains #f;,h#b,o4 ,stannic sulphide1 ,sn,s#b1 is formed1 as a yellow precipitate1 by the action of sulphuretted hydrogen on acid solutions of stannic salts2 it is easily soluble in ammonium and potassium sulphides1 because it has an acid character1 and then forms thiostannates 7see ,chapter ,,xx474 ,in an anhydrous state it has the form of brilliant golden yellow plates1 which may be obtained by heating a mixture of finely-divided tin1 sulphur1 and sal-ammoniac for a considerable time4 ,it is sometimes used in this form under the name of mosaic gold1 as a cheap substitute for gold-leaf in gilding wood articles4 ,on ignition it parts with a portion of its sulphur1 and is converted into stannous sulphide ,sn,s4 ,it is soluble in caustic alkalis4 ,hydrochloric acid does not dissolve the anhydrous crystalline compound1 but the precipitated powdery sulphide is soluble in boiling strong hydrochloric acid1 with the evolution of hydrogen sulphide4 ,the alkali compounds of stannic oxide--that is1 the compounds in which it plays the part of an acid1 corresponding in this respect to the compounds of silica and other anhydrides of the composition ,,ro#b--;are very easily formed and are used in the arts4 ,their composition in most cases corresponds with the formula ,sn,m#b,o#c--that is1 ,sn,o7,,mo7#b1 similar to ,,co7,,mo7#b1 where ,m ,k1 ,na4 ,acids1 even feeble acids like carbonic1 decompose the salts1 like the corresponding compounds of alumina or silica4 ,in order to obtain potassium stannate1 which crystallises in rhombohedra1 and has the composition ,sn,k#b,o#c1c;,h#b,o1 potassium hydroxide 7#h parts7 is fused1 and metastannic acid 7#c parts7 gradually added4 ,sodium stannate is prepared in practice in large quantities by heating a solution of caustic soda with lead oxide and metallic tin4 ,in this last case an alkaline solution of lead oxide is formed1 and the tin acts on the solution in such a way as to reduce the lead to the metallic state1 and itself passes into solution4 ,it is very remarkable that lead displaces tin when in combination with acids1 whilst tin1 on the contrary1 displaces lead from its alkali compounds4 ,by dissolving the mass obtained in water1 and adding alcohol1 sodium stannate is precipitated1 which may then be dissolved in water and purified by re-crystallisation4 ,in this case it has the composition ,sn,na#b,o#c1c;,h#b,o if separated from strong solutions1 and ,sn,na#b,o#c1aj;,h#b,o when crystallised at a low temperature from dilute solutions4 ,in the arts this salt is used as a mordant in dyeing operations4 ,with a cold solution of sodium hydroxide metastannic acid forms a salt of the composition 7,na,h,o7#b1e,sn,o#b1c;,h#b,o1 from which ,frmy drew his conclusions concerning the polymerism of metastannic acid4 ,tin1 like other metals and many metalloids1 gives a peroxide form of combination or perstannic oxide4 ,this substance was obtained by ,spring 7#ahhi7 in the form of a hydrate1 ,h#b,sn#b,o#g #b7,sn,o#c7;,h#b,o1 by mixing a solution of ,sn,cl#b1 containing an excess of ,h,cl1 with freshly prepared peroxide of barium4 ,a cloudy liquid is then obtained1 and this after being subjected to dialysis leaves a gelatinous mass which on drying is found to have the composition ,sn#b;,h#b,o#g4 ,above #ajj this substance gives off oxygen and leaves ,sn,o#b4 ,it is evident that ,sn,o#c bears the same relation to ,sn,o#b as ,h#b,o#b to ,h#b,o or ,zn,o#b to ,zn,o1 c4 ,tin occupies the same position amongst the analogues of silicon as cadmium and indium amongst the analogues of magnesium and aluminium respectively1 and as in each of these cases the heavier analogues with a high atomic weight and a special combination of properties--namely1 mercury and thallium--are known1 so also for silicon we have lead as the heaviest analogue 7,pb #bjf71 with a series of both kindred and special properties4 ,the higher type1 ,pb,x#d--;for instance1 ,pb,o#b--;is in a chemical sense far less stable than the lower type1 ,pb,x4 ,the ordinary compounds of lead correspond with the latter1 and in addition to this1 ,pb,o1 although not particularly energetic1 is still a decided base easily forming basic salts1 ,pb,x#b7,pb,o7n4 ,although the compounds ,pb,x#d1 are unstable they offer many points of analogy with the corresponding compounds of tin ,sn,o#b2 this is seen1 for instance1 in the fact that ,pb,o#b is a feeble acid1 giving the salt ,pb,k#b,o#c1 that ,pb,cl#d is a liquid like ,sn,cl#d which is not affected by sulphuric acid1 and that ,pb,f#d gives double salts1 like ,sn,f#d or ,si,f#d 7,brauner #ahid4 ,see ,chapter ,,ii41 ,note #di bis72 ,pb7,c#b;,h#e7d also resembles ,sn7,c#b;,h#e7d c4 ,all this shows that lead is a true analogue of tin1 as ,hg is of cadmium4#da bis #da bis ,although this has long been generally recognised from the resemblance between the two metals1 still from a chemical point of view it has only been demonstrated by means of the periodic law4 ,lead is found in nature in considerable masses1 in the form of galena1 lead sulphide1 ,pb,s4#db ,the specific gravity of galena is #geh1 colour grey2 it crystallises in the regular system1 and has a fine metallic lustre4 ,both the native and artificial sulphides are insoluble in acids 7hydrogen sulphide gives a black precipitate with the salts ,pb,x#b74db bis ,when heated1 lead melts1 and in the open air is either totally or partially transformed into white lead sulphate1 ,pb,s,o#d1 as it also is by many oxidising agents 7hydrogen peroxide1 potassium nitrate74 ,lead sulphate is also insoluble in water1#dc and lead is but rarely met with in this form in nature4 ,the chromates1 vanadates1 phosphates1 and similar salts of lead are also somewhat rare4 ,the carbonate1 ,pb,c,o#b1 is sometimes found in large masses1 especially in the ,altai region4 ,lead sulphide is often worked for extracting the silver which it contains2 and as the lead itself also finds manifold industrial applications1 this work is carried out on an exceedingly large scale4 ,many methods are employed4 ,sometimes the lead sulphide is decomposed by heating it with cast iron4 ,the iron takes up the sulphur from the lead and forms easily-fusible iron sulphide1 which does not mix with the heavier reduced lead4 ,but another process is more frequently used3 the lead ore 7it must be clean2 that is1 free from earthy matter1 which may be easily removed by washing7 is heated in a reverberatory furnace to a moderate temperature with a free access of air4 ,during this operation part of the lead sulphide oxidises and forms lead sulphate1 ,pb,s,o#d1 and lead oxide4 ,when the oxidation of part of the lead has been attained1 it is necessary to shut off the air supply and increase the temperature1 then the oxidised compounds of the lead enter into reaction with the remaining lead sulphide1 with formation of sulphurous anhydride and metallic lead4 ,at first from ,pb,s ,o#c1 ,pb,o ,,so#b are formed1 and also from ,pb,s ,o#d lead sulphate ,pb,s,o#d1 and then ,pb,o and ,pb,s,o#d react with the remaining ,pb,s1 according to the equations #b,pb,o ,pb,s #c,pb ,,so#b and also ,pb,s,o#d ,pb,s #b,pb #b,,so#b4dd #db ,mixed ores of copper compounds together with ,pb,s and ,zn,s are frequently found in the most ancient primary rocks4 ,as the separation of the metals themselves is difficult1 the ores are separated by a method of selection or mechanical sorting4 ,such mixed ores occur in ,russia1 in many parts of the ,caucasus1 and in the ,donetz district 7at ,nagolchik74 #db bis ,lead sulphide in the presence of zinc and hydrochloric acid is completely reduced to metallic lead1 all the sulphur being given off as hydrogen sulphide4 #dc ,lead sulphate1 ,pb,s,o#d1 occurs in nature 7anglesite7 in transparent brilliant crystals which are isomorphous with barium sulphate1 and have a specific gravity of #fc4 ,the same salt is formed on mixing sulphuric acid or its soluble salts with solutions of lead salts1 as a heavy white precipitate1 which is insoluble in water and acids1 but dissolves in a solution of ammonium tartrate in the presence of an excess of ammonia4 ,this test serves to distinguish this salt from the similar salts of strontium and barium4 #dd ,according to ,j4 ,b4 ,hannay 7#ahid7 the last named decomposition 7,pb,s ,pb,s,o#d #b,pb #b,,so#b7 is really much more complicated1 and in fact a portion of the ,pb,s is dissolved in the ,pb1 forming a slag containing ,pb,o1 ,pb,s and ,pb,s,o#d1 whilst a portion of the lead volatilises with the ,,so#b in the form of a compound ,pb,s#b,o#b1 which is also formed in other cases1 but has not yet been thoroughly studied4 ,besides these methods for extracting lead from ,,pbs in its ores1 roasting 7the removal of the ,s in the form of ,,so#b7 and smelting with charcoal with a blast in the same manner as in the manufacture of pig iron 7,chapter ,,xxii47 are also employed4 ,we may add that ,pb,s in contact with ,zn and hydrochloric acid 7which has no action upon ,pb,s alone7 entirely decomposes1 forming ,h#b,s and metallic lead3 ,pb,s ,zn #b;,h,cl ,pb ,zn,cl#b ,h#b,s4 ,as lead is easily reduced from its ores1 and the ore itself has a metallic appearance1 it is not surprising that it was known to the ancients1 and that its properties were familiar to the alchemists1 who called it ',saturn4' ,hence metallic lead1 reduced from its salts in solution by zinc1 having the appearance of a tree-like mass of crystals1 is called 'arbor saturni1' c4 ,the appearance of lead is well known2 its specific gravity is #aac2 the bluish colour and well-marked metallic lustre of freshly-cut lead quickly disappear when exposed to the air1 because it becomes coated with a layer--although a very thin layer--of oxide and salts formed by the moisture and acids in the atmosphere4 ,it melts at #cbj1 and crystallises in octahedra on cooling4 ,its softness is apparent from the flexibility of lead pipes and sheets1 and also from the fact that it may be cut with a knife1 and also that it leaves a grey streak when rubbed on paper4 ,on account of its being so soft1 lead naturally cannot be applied in many cases where most metals may be used2 but on the other hand it is a metal which is not easily changed by chemical reagents1 and as it is capable of being soldered and drawn into sheets1 c41 lead is most valuable for many technical uses4 ,lead pipes are used for conveying water#de and many other liquids1 and sheet lead is used for lining all kinds of vessels containing liquids--7acids1 for instance7 which act on other metals4 ,this particularly refers to sulphuric and hydrochloric acids1 because at a low temperature they do not act on lead1 and if they form lead sulphate1 ,pb,s,o#d1 and chloride1 ,pb,cl#b1 these salts being insoluble in water and in acids1 cover the lead and protect it from further corrosion4#df ,all soluble preparations of lead are poisonous4 ,at a white heat lead may be partially distilled2 the vapours oxidise and burn4 ,lead may also be easily oxidised at low temperatures4 ,lead only decomposes water at a white heat1 and does not liberate hydrogen from acids1 with the exception only of very strong hydrochloric acid and then only when boiling4 ,sulphuric acid diluted with water does not act on it1 or only acts very feebly at the surface2 but strong sulphuric acid1 when heated1 is decomposed by it1 with the evolution of sulphurous anhydride4 ,the best solvent for lead is nitric acid1 which transforms it into a soluble salt1 ,pb7,,no#c7b4 #de ,freshly laid new lead pipes contaminate the water with a certain amount of lead salts1 arising from the presence of oxygen1 carbonic acid1 c41 in the water4 ,but the lead pipes under the action of running water soon become coated with a film of salts--lead sulphate1 carbonate1 chloride1 c4--which are insoluble in water1 and the water pipes then become harmless4 #df ,lead is used in the arts1 and owing to its considerable density1 it is cast1 mixed with small quantities of other metals1 into shot4 ,a considerable amount is employed 7together with mercury7 in extracting gold and silver from poor ores1 and in the manufacture of chemical reagents1 and especially of lead chromate4 ,lead chromate1 ,pb,cr,o#d1 is distinguished for its brilliant yellow colour1 owing to which it is employed in considerable quantities as a dye1 mainly for dyeing cotton tissues yellow4 ,it is formed on the tissue itself1 by causing a soluble salt of lead to react on potassium chromate4 ,lead chromate is met with in nature as 'red lead ore4' ,it is insoluble in water and acetic acid1 hut it dissolves in aqueous potash4 ,the so-called pewter vessels often consist of an alloy of #e parts of tin and #a part of lead1 and solder is composed of #a to #b parts of tin with #a_/b part of lead4 ,amongst the alloys of lead and tin1 ,rudberg states that the alloy ,pb,sn#c stands out from the rest1 since1 according to his observations1 the temperature of solidification of the alloy is #ahg4 ,although acids thus have directly but little effect on lead1 and this is one of its most important practical properties1 yet when air has free access1 lead 7like copper7 very easily reacts with many acids1 even with those which are comparatively feeble4 ,the action of acetic acid on lead is particularly striking and often applied in practice4 ,if lead be plunged into acetic acid it does not change at all and does not pass into solution1 but if part of the lead be immersed in the acid1 and the other part remain in contact with the air1 or if lead be merely covered with a thin layer of acetic acid in such a way that the air is practically in contact with the metal1 then it unites with the oxygen of the air to form oxide1 which combines with the acetic acid and forms lead acetate1 soluble in water4 ,the formation of lead oxide is especially marked from the fact that with a sufficient quantity of air not only is the normal lead acetate formed but also the basic salts4#dg #dg ,the normal lead acetate1 known in trade as sugar of lead1 owing to its having a sweetish taste1 has the formula ,pb7,c#b;,h#c,o#b7b1c;,h#b,o4 ,this salt only crystallises from acid solutions4 ,it is capable of dissolving a further quantity of lead oxide or of metallic lead in the presence of air4 ,a basic salt of the composition ,pb7,c#b;,h#c,o#b7b1,pb,h#b,o#b is then formed which is soluble in water and alcohol4 ,as in this salt the number of atoms is even and the same as in the hydrate of acetic acid1 ,c#b;,h#d,o#b1;,h#b,o ,c#b;,h#c7,,oh7#c1 it may be represented as this hydrate in which two of hydrogen are replaced by lead--that is1 as ,c#b;,h#c7,,oh77,o#b,pb74 ,this basic salt is used in medicine as a remedy for inflammation1 for bandaging wounds1 c41 and also in the manufacture of white lead4 ,other basic acetates of lead1 containing a still greater amount of lead oxide1 are known4 ,according to the above representation of the composition of the preceding lead acetate1 a basic salt of the composition 7,c#b;,h#c7b7,o#b,pb7#c would be also possible1 but what appear to be still more basic salts are known4 ,as the character of a salt also depends on the property of the base from which it is formed1 it would seem that lead forms a hydroxide of the composition ,h,o,pb,o,h1 containing two water residues1 one or both of which may be replaced by the acid residues4 ,if both water residues are replaced1 a normal salt1 ,x,pb,x1 is obtained1 whilst if only one is replaced a basic salt1 ,x,pb,o,h1 is formed4 ,but lead does not only give this normal hydroxide1 but also polyhydroxides1 ,pb7,,oh71n,pb,o1 and if we may imagine that in these polyhydroxides there is a substitution of both the water residues by acid residues1 then the power of lead for forming basic salts is explained by the properties of the base which enters into their composition4 ,when oxidising in the presence of air1#dh when heated or in the presence of an acid at the ordinary temperature1 lead forms compounds of the type ,pb,x#b4 ,lead oxide1 ,pb,o1 known in industry as litharge1 silbergltte 7this name is due to the fact that silver is extracted from the lead ores of this kind7 and massicot4 ,if the lead is oxidised in air at a high temperature1 the oxide which is formed fuses1 and on cooling is easily obtained in fused masses which split up into scales of a yellowish colour1 having a specific gravity of #ic2 in this form it bears the name of litharge4 ,litharge is principally used for making lead salts1 for the extraction of metallic lead1 and also for the preparation of drying oils--for instance1 from linseed oil4#di ,when oxidised carefully and slightly heated1 lead forms a powdery 7not fused7 oxide known under the name of massicot4 ,it is best prepared in the laboratory by heating lead nitrate1 or lead hydroxide4 ,it has a yellow colour1 and differs from litharge in the greater difficulty with which it forms lead salts with acids4 ,thus1 for instance1 when massicot is moistened with water it does not attract the carbonic acid of the air so easily as litharge does4 ,it may1 however1 be imagined that the cause of the difference depends only on the formation of dioxide on the surface of the lead oxide1 on which the acids do not act4 ,in any case lead oxide is comparatively easily soluble in nitric and acetic acids4 ,it is but slightly soluble in water1 but communicates an alkaline reaction to it1 since it forms the hydroxide4 ,this hydroxide is obtained in the shape of a white precipitate by the action of a small quantity of an alkali hydroxide on a solution of a lead salt4 ,an excess of alkali dissolves the hydroxide separated1 which fact demonstrates the comparatively indistinct basic properties of lead oxide4 ,the normal lead hydroxide1 which should have the composition ,pb7,,oh7#b1 is unknown in a separate state1 but it is known in combination with lead oxide as ,pb7,,oh7#b1b,pb,o or ,pb#c,o#b7,,oh7#b4 ,the latter is obtained in the form of brilliant1 white1 octahedral crystals when basic lead acetate is mixed with ammonia and gently heated4 ,the basic qualities of this hydroxide are shown distinctly by its absorbing the carbonic anhydride of the air4 ,when an alkaline solution of the hydroxide is boiled1 it deposits lead oxide in the form of a crystalline powder4 #dh ,few compounds are known of the lower type ,pb,x1 and still fewer of the intermediate type ,pb,x#c4 ,to the first type belongs the so-called lead suboxide1 ,pb#b,o1 obtained by the ignition of lead oxalate1 ,c#b,pb,o#d1 without access of air4 ,it is a black powder1 which easily breaks up under the action of acids1 and even by the simple action of heat1 into metallic lead and lead oxide4 ,this is the character of all suboxides4 ,they cannot be regarded as independent salt-forming oxides1 neither can those forms of oxidation of lead which contain more oxygen than the oxide of lead1 ,pb,o1 and less than the dioxide1 ,pb,o#b4 ,as we shall see1 at least two such compounds are formed4 ,thus1 for example1 an oxide having the composition ,pb#b,o#c is known1 but it is decomposed by the action of acids into lead oxide1 which passes into solution1 and lead dioxide1 which remains behind4 ,such is red lead4 7,see further on47 #di ,in the boiling of drying oils1 the lead oxide partially passes into solution1 forming a saponified compound capable of attracting oxygen and solidifying into a tar-like mass1 which forms the oil paint4 ,perhaps1 however1 glycerine partially acts in the process4 ,ossovetsky by saturating drying oil with the salts of certain metals obtained oil colours of great durability4 ,a mixture of very finely-divided litharge with glycerine 7#ej parts of litharge to #e c4c4 of anhydrous glycerine7 forms a very quick 7two minutes7 setting cement1 which is insoluble in water and oils1 and is very useful in setting up chemical apparatus4 ,the hardening is based on the reaction of the lead oxide with glycerine 7,moraffsky74 ,lead oxide forms but few soluble salts--for instance1 the nitrate and the acetate4 ,the majority of its salts 7sulphate1 ,pb,s,o#d2 carbonate1 ,pb,c,o#c2 iodide1 ,pb,i#b1 c47 are insoluble in water4 ,these salts are colourless or light yellow if the acid be colourless4 ,in lead oxide the faculty of forming basic salts1 ,pb,x#bn,pb,o or ,pb,x#bn,pb,h#b,o#b1 is strongly developed4 ,a similar property was observed in magnesium and also in the salts of mercury1 but lead oxide forms basic salts with still greater facility1 although double salts are in this case more rarely formed4#ej #ej ,it is very instructive to observe that lead not only easily forms basic salts1 but also salts containing several acid groups4 ,thus1 for example1 lead carbonate occurs in nature and forms compounds with lead chloride and sulphate4 ,the first compound1 known as corneous lead1 phosgenite1 has the composition ,pb,c,o#c1,pb,cl#b2 it occurs in nature in bright cubical crystals1 and is prepared artificially by simply boiling lead chloride with lead carbonate4 ,a similar compound of normal salts1 ,pb,s,o#d1,pb,c,o#c1 occurs in nature as lanarkite in monoclinic crystals4 ,leadhillite contains ,pb,s,o#d1c,pb,c,o#c1 and also occurs in yellowish1 monoclinic1 tabular crystals4 ,we will turn our attention to these salts of lead1 because it is very probable that their formation is allied to the formation of the basic salts1 and the following considerations may lead to the explanation of the existence of both4 ,in describing silica we carefully developed the conception of polymerisation1 which it is also indispensable to recognise in the composition of many other oxides4 ,thus it may be supposed that ,pb,o#b is a similar polymerised compound to ,si,o#b--;i4e4 that the composition of lead peroxide will be ,pbn,o#bn1 because lead methyl1 ,pb,me#d1 and lead ethyl1 ,pb,et#d1 are volatile compounds1 whilst ,pb,o#b is non-volatile1 and is very like silica in this respect1 and not in the least like carbonic anhydride4 ,still more should a polymeric structure1 ,pbn,on1 be ascribed to lead oxide1 since it differs as little from lead dioxide in its physical properties as carbonic oxide does from carbonic anhydride1 and being an unsaturated compound is more likely to be capable of intercombination 7polymerisation7 than lead dioxide4 ,these considerations respecting the complexity of lead oxide could have no real significance1 and could not be accepted1 were it not for the existence of the above-mentioned basic and mixed salts4 ,the oxide apparently corresponds with the composition ,pbn,x#bn1 and since1 according to this representation1 the number of ,x's in the salts of lead is considerable1 it is obvious that they may be diverse4 ,when a part of these ,x's is replaced by the water residue 7,,oh7 or by oxygen1 ,x#b ,o1 and the other parts by an acid residue1 ,x1 then basic salts are obtained1 but if a part of the ,x's is replaced by acid residues of one kind1 and the other part by acid residues of another kind1 then those mixed salts about which we are now speaking are formed4 ,thus1 for example1 we may suppose1 for a comparison of the composition of the majority of the salts of lead1 that n #ab1 and then the above-mentioned compounds will present themselves in the following form3--,lead oxide1 ,pb#ab,o#ab1 its crystalline hydrate1 ,pb#ab,o#h7,,oh7#h1 lead chloride1 ,pb#ab;,cl#bd1 lead oxychloride1 ,pb#ab;,cl#ab,o#f1 the other oxychloride1 ,pb#ab7,,oh7#h;,cl#f,o#f1 mendipite 7see ,note #ea71 ,pb#ab;,cl#h,o#h1 normal lead carbonate1 ,pb#ab7;,,co#c7ab1 crystalline basic salt1 ,pb#ab7,,oh7#f7;,,co#c7f1 white lead1 ,pb#ab7;,,co#c7h7;,,ho7#h1 corneous lead1 ,pb#ab;,cl#ab7;,,co#c7f1 lanarkite1 ,pb#ab7;,,co#c7f7,,so#d7f1 leadhillite1 ,pb#ab7;,,co#c7i7,,so#d7c1 c4 ,the number #ab is only taken to avoid fractional quantities4 ,possibly the polymerisation is much higher than this4 ,the theory of the polymerisation of oxides introduced by me in the first edition of this work 7#ahfi7 is now beginning to be generally accepted4 ,amongst the soluble lead salts1 that best known and most often applied in practical chemistry is lead nitrate1 obtained directly by dissolving lead or its oxide in nitric acid4 ,the normal salt1 ,pb7,,no#c7b1 crystallises in octahedra1 dissolves in water1 and has a specific gravity of #de4 ,when a solution of this salt acts on white lead or is boiled with litharge1 the basic salt1 having a composition ,pb7,,oh77,,no#c71 is formed in crystalline needles1 sparingly soluble in cold water but easily dissolved in hot water1 and therefore in many respects resembling lead chloride4 ,when the nitrate is heated1 either lead oxide is obtained or else the oxide in combination with peroxide4 ,lead chloride1 ,pb,cl#b1 is precipitated from the soluble salts of lead when a strong solution is treated with hydrochloric acid or a metallic chloride4 ,it is soluble in considerable quantities in hot water1 and therefore if the solutions be dilute or hot1 the precipitation of lead chloride does not occur1 and if a hot solution be cooled1 the salt separates in brilliant prismatic crystals4 ,it fuses when heated 7like silver chloride71 but is insoluble in ammonia4 ,this salt is sometimes met with in nature1 and when heated in air is capable of exchanging half its chlorine for oxygen1 forming the basic salt or lead oxychloride1 ,pb,cl#b,pb,o1 which may also be obtained by fusing ,pb,cl#b and ,pb,o together4 ,the reaction of lead chloride with water vapour leads to the same conclusion1 showing the feeble basic character of lead #b,pb,cl#b ,h#b,o ,pb,cl#b1,pb,o #b;,h,cl4 ,when ammonia is added to an aqueous solution of lead chloride a white precipitate is formed1 which parts with water on being heated1 and has the composition ,pb7,,oh7,cl1,pb,o4 ,this compound is also formed by the action of metallic chlorides on other soluble basic salts of lead4#ea #ea ,a similar basic salt having a white colour1 and therefore used as a substitute for white lead1 is also obtained by mixing a solution of basic lead acetate with a solution of lead chloride4 ,its formation is expressed by the equation3 #b,pb,x7,,oh71,pb,o ,pb,cl#b #b,pb7,,oh7,cl1,pb,o ,pb,x#b4 ,similar basic compounds of lead are met with in nature--for instance1 mendipite1 ,pb,cl1#b,pb,o1 which appears in brilliant yellowish-white masses4 ,the ignition of red lead with sal-ammoniac results in similar polybasic compounds of lead chloride1 forming the ,cassel's1 or mineral yellow of the composition ,pb,cl#bn,pb,o4 ,lead iodide1 ,pb,i#b1 is still less soluble than the chloride1 and is therefore obtained by mixing potassium iodide with a solution of a lead salt4 ,it separates as a yellow powder1 which may be dissolved in boiling water1 and on cooling separates in very brilliant crystalline scales of a golden yellow colour4 ,the salts ,pb,br#b1 ,pb,f#b1 ,pb7,,cn7#b1 ,pb#b;,fe7,,cn7#f are also insoluble in water1 and form white precipitates4 ,lead carbonate1 or white lead1 is the most extensively used basic lead salt4 ,it has the valuable property of 'covering1' which only to a certain extent appertains to lead sulphate and other white powdery substances used as pigments4 ,this faculty of 'covering' consists in the fact that a small quantity of white lead mixed with oil spreads uniformly1 and if such a mixture be spread over a surface 7for instance1 of wood or metal7 the surface is quickly covered--that is1 light does not penetrate through even a very thin layer of superposed white lead2 thus1 for example1 the grain of the wood remains invisible4#eb ,white lead1 or basic lead carbonate1 after being dried at #abj1 has a composition ,pb7,,oh7#b1b,pb,c,o#c4ec ,it may be obtained by adding a solution of sodium carbonate to a solution of one of the basic salts of lead--for instance1 the basic acetate--and likewise by treating this latter with carbonic acid4 ,for this purpose the solution of basic acetate is poured into the vessel f2 it is prepared in the vat ,a1 containing litharge1 into which the pump ,p delivers the solution of the acetate1 which remains after the action of carbonic anhydride on the basic salt4 ,in ,a a basic salt is formed having a composition approaching to ,pb#d7,,oh7#f7;,c#b;,h#c,o#b7b2 carbonic anhydride1 #b;,,co#b1 is passed through this solution and precipitates white lead1 ,pb#b7,,oh7#b7;,,co#c7b1 and normal lead acetate1 ,pb7,c#b;,h#c,o#b7b1 remains in the solution1 and is pumped back into the vat ,a containing lead oxide1 where the normal salt is again 7on being agitated7 converted into the basic salt4 ,this is run into the vessel ,e1 and thence into f4 ,into the latter carbonic anhydride is delivered from the generator ,d1 and forms a precipitate of white lead4#ec bis #eb ,it is remarkable that a peculiar kind of attraction exists between boiled linseed oil and white lead1 as is seen from the following experiments4 ,white lead is triturated in water4 ,although it is heavier than water1 it remains in suspension in it for some time and is thoroughly moistened by it1 so that the trituration may be made perfect2 boiled linseed oil is then added1 and shaken up with it4 ,a mixture of the oil and white lead is then found to settle at the bottom of the vessel4 ,although the oil is much lighter than the water it does not float on the top1 but is retained by the white lead and sinks under the water together with it4 ,there is not1 however1 any more perfect combination nor even any solution4 ,if the resultant mass be then treated with ether or any other liquid capable of dissolving the oil1 the latter passes into solution and leaves the white lead unaltered4 #ec ,it may be regarded as a salt corresponding with the normal hydrate of carbonic acid1 ,c7,,oh7#d1 in which three-quarters of the hydrogen is replaced by lead4 ,a salt is also known in which all the hydrogen of this hydrate of carbonic acid is replaced by lead--namely1 the salt containing ,,co#d,pb#b4 ,this salt is obtained as a white crystalline substance by the action of water and carbonic acid on lead4 ,the normal salt1 ,pb,c,o#c1 occurs in nature under the name of white lead ore 7sp4 gr4 #fdg71 in crystals1 isomorphous with aragonite1 and is formed by the double decomposition of lead nitrate with sodium carbonate1 as a heavy white precipitate4 ,thus both these salts resemble white lead1 but the first-named salt is exclusively used in practice1 owing to its being very conveniently prepared1 and being characterised by its great covering capacity1 or 'body1' due to its fine state of division4 #ec bis ,one of the many methods by which white lead is prepared consists in mixing massicot with acetic acid or sugar of lead1 and leaving the mixture exposed to air 7and re-mixing from time to time71 containing carbonic acid1 which is absorbed from the surface by the basic salt formed4 ,after repeated mixings 7with the addition of water71 the entire mass is converted into white lead1 which is thus obtained very finely divided4 ,illustration3 ,,fig4 #hb4--,manufacture of white lead4 ,in order to mark the transition from lead oxide1 ,pb,o1 into lead dioxide ,pb,o#b 7plumbic anhydride71 it is necessary to direct our attention to the intermediate oxide1 or red lead1 ,pb#c,o#d4ed ,in the arts it is used in considerable quantities1 because it forms a very durable yellowish-red paint used for colouring the resins 7shellac1 colophony1 c47 composing sealing wax4 ,it also forms a very good cheap oil paint1 used especially for painting metals1 more particularly because drying oils--for instance1 hemp seed1 linseed oils--very quickly dry with red lead and with lead salts4 ,red lead is prepared by slightly heating massicot1 for which purpose two-storied stoves are used4 ,in the lower story the lead is turned into massicot1 and in the higher one1 having the lower temperature 7about #cjj71 the massicot is transformed into red lead4 ,frmy and others showed the instability of red lead prepared by various methods1 and its decomposition by acids1 with formation of lead dioxide1 which is insoluble in acids1 and a solution of the salts of lead oxide4 ,the artificial production 7synthesis7 of red lead by double decomposition was most important4 ,for this purpose ,frmy mixed an alkaline solution of potassium plumbate1 ,k#b,pb,o#c 7prepared by dissolving the dioxide in fused potash71#ed bis with an alkaline solution of lead oxide4 ,in this way a yellow precipitate of minium hydrate is formed1 which1 when slightly heated1 loses water and turns into bright red anhydrous minium ,pb#c,o#d4 #ed ,if lead hydroxide be dissolved in potash and sodium hypochlorite be added to the solution1 the oxygen of the latter acts on the dissolved lead oxide1 and partially converts it into dioxide1 so that the so-called lead sesquioxide is obtained2 its empirical formula is ,pb#b,o#c4 ,probably it is nothing but a lead salt--i4e4 is referable to the type of dioxide of lead1 or its hydroxide1 ,pb,o7,,oh7#b1 in which two atoms of hydrogen are replaced by lead1 ,pb,o7,o#b,pb74 ,the brown compound precipitated by the action of dilute acids--for example1 nitric--splits up1 even at the ordinary temperature1 into insoluble lead dioxide and a solution of a lead salt4 ,this compound evolves oxygen when it is heated4 ,it dissolves in hydrochloric acid1 forming a yellow liquid1 which probably contains compounds of the composition ,pb,cl#b and ,pb,cl#d1 but even at the ordinary temperature the latter soon loses the excess of chlorine1 and then only lead chloride1 ,pb,cl#b1 remains4 ,in order to see the relation between red lead and lead sesquioxide1 it must be observed that they only differ by an extra quantity of lead oxide--that is1 red lead is a basic salt of the preceding compound1 and if the compound ,pb#b,o#c may be regarded as ,pb,o#c,pb1 then red lead should be looked on as ,pb,o#c,pb1,pb,o--that is1 as basic lead plumbate4 #ed bis ,frmy obtained potassium plumbate in the following manner4 ,pure lead dioxide is placed in a silver crucible1 and a strong solution of pure caustic potash is poured over it4 ,the mixture is heated and small quantities are removed from time to time for testing1 which consists in dissolving in a small quantity of water and decomposing the resultant solution with nitric acid4 ,there is a certain moment during the heating when a considerable amount of insoluble lead dioxide is precipitated on the addition of the nitric acid2 the solution then contains the salt in question1 and the heating must be stopped1 and a small amount of water added to dissolve the potassium plumbate formed4 ,on cooling the salt separates in somewhat large crystals1 which have the same composition as the stannate--that is1 ,pb,o7,,ko7#b1c;,h#b,o4 ,minium is the first and most ordinary means of producing lead dioxide1 or plumbic anhydride1 ,pb,o#b1ee because when red lead is treated with dilute nitric acid it gives up lead oxide1 and ,pb,o#b remains1 on which dilute nitric acid does not act4 ,the composition of minium is ,pb#c,o#d1 and therefore the action of nitric acid on it is expressed by the equation3 ,pb#c,o#d #d;,,hno#c ,pb,o#b #b,pb7,,no#c7b #b;,h#b,o4 ,the dioxide may also be obtained by treating lead hydroxide suspended in water with a stream of chlorine4 ,under these conditions the chlorine takes up the hydrogen from the water1 and the oxygen passes over to the lead oxide4#ef ,when a strong solution of lead nitrate is decomposed by the electric current1 the appearance of crystalline lead dioxide is also observed upon the positive pole2 it is also found in nature in the form of a black crystalline substance having a specific gravity of #id4 ,when artificially produced it is a fine dark powder1 resisting the action of acids1 but nevertheless when treated with strong sulphuric acid it evolves oxygen and forms lead sulphate1 and with hydrochloric acid it evolves chlorine4 ,the oxidising property of lead dioxide depends of course on the facility of its transition into the more stable lead oxide1 which is easily understood from the whole history of lead compounds4 ,in the presence of alkalis it transforms chromium oxide into chromic acid1 whilst lead chromate1 ,pb,cr,o#d1 is formed1 remaining1 however1 in solution1 on account of its being soluble in caustic alkalis4 ,the oxidising action of lead dioxide on sulphurous anhydride is most striking1 as it immediately absorbs it1 with formation of lead sulphate4 ,this is accompanied by a change of colour and development of heat1 ,pb,o#b ,,so#b ,pb,s,o#d4 ,when triturated with sulphur the mixture explodes1 the sulphur burning at the expense of the oxygen of the lead dioxide4 ,tetrachloride of lead1 ,pb,cl#d1 belongs to the same class of lead compounds as ,pb,o#b4 ,this chloride is formed by the action of strong hydrochloric acid upon ,pb,o#b1 or1 in the cold1 by passing a stream of chlorine through water containing ,pb,cl#b in suspension4 ,the resultant yellow solution gives off chlorine when heated4 ,with a solution of sal ammoniac 7,nicolukin1 #ahhe7 it gives a precipitate of a double salt1 7,,nh#d7b,pb,cl#f 7very slightly soluble in a solution of sal ammoniac71 which when treated with strong sulphuric acid 7,friedrich1 #ahij7 gives ,pb,cl#d as a yellow liquid sp4 gr4 #cah1 which solidifies at -#ah1 and when heated gives ,pb,cl#b ,cl#b4 ,it is not acted upon by ,h#b,,so#d like ,sn,cl#d4 ,tetrafluoride of lead 7,brauner7 belongs to the same class of compounds1 it easily forms double salts and decomposes with the evolution of fluorine 7,chapter ,,ii41 ,note #di bis74#ef bis #ee ,lead dioxide is often called lead peroxide1 but this name leads to error1 because ,pb,o#b does not show the properties of true peroxides1 like hydrogen or barium peroxides1 but is endowed with acid properties--that is1 it is able to form true salts with bases1 which is not the case with true peroxides4 ,lead dioxide is a normal salt-forming compound of lead1 as ,bi#b,o#e is for bismuth1 ,ce,o#b for cerium1 and ,te,o#c for tellurium1 c4 ,they all evolve chlorine when treated with hydrochloric acid1 whilst true peroxides form hydrogen peroxide4 ,the true lead peroxide1 if it were obtained1 would probably have the composition ,pb#b,o#e1 or1 in combination with peroxide of hydrogen1 ,h#b,pb#b,o#g ,h#b,o#b ,pb#b,o#e1 judging from the peroxides corresponding with sulphuric1 chromic1 and other acids1 which we shall afterwards consider4 ,as a proof of the fact1 that the form ,pb,o#b1 or ,pb,x#d1 is the highest normal form of any combination of lead1 it is most important to remark that it might be expected that the action of lead chloride1 ,pb,cl#b1 on zinc-ethyl1 ,zn,et#b1 would result in the formation of zinc chloride1 ,zn,cl#b1 and lead-ethyl1 ,pb,et#b1 but that in reality the reaction proceeds otherwise4 ,half of the lead is set free1 and lead tetrethyl1 ,pb,et#d1 is formed as a colourless liquid1 boiling at about #bjj 7,butleroff1 ,frankland1 ,buckton1 ,cahours1 and others74 ,the type ,pb,x#d is not only expressed in ,pb,et#d and ,pb,o#b1 but also in ,pb,f#d1 obtained by ,brauner4 #ef ,according to ,carnelley and ,walker1 the hydrate 7,pb,o#b7c1;,h#b,o is then formed2 it loses water at #bcj4 ,the anhydrous dioxide remains unchanged up to #bhj1 and is then converted into the sesquioxide1 ,pb#b,o#c1 which again loses oxygen at about #djj1 and forms red lead1 ,pb#c,o#d4 ,red lead also loses oxygen at about #eej1 forming lead oxide1 ,pb,o1 which fuses without change at about #fjj1 and remains constant as far as the limit of the observations made 7about #hjj74 ,the best method for preparing pure lead dioxide consists in mixing a hot solution of lead chloride with a solution of bleaching powder 7,fehrman74 #ef bis ,the plumbates of ,ca and other similar metals1 mentioned in ,chapter ,,iii41 ,note #g1 also belong to the form ,pb,x#d4 ,amongst the elements of the second and third groups it was observed that the elements were more basic in the even than in the uneven series4 ,it is sufficient to remember calcium1 strontium1 and barium in the even1 and magnesium1 zinc1 and cadmium in the uneven series4 ,in addition to this1 in the even series1 as the atomic weight increases1 in the same type of oxidation the basic properties increase 7the acid properties decrease72 for example1 in the second group1 calcium1 strontium1 barium4 ,the same also appears in the fourth and all the following groups4 ,in the even series of the fourth group titanium1 zirconium1 cerium1 and thorium are found4 ,all their highest oxides1 ,,ro#b1 even the lightest1 titanic oxide1 ,ti,o#b1 have more highly developed basic properties than silica1 ,si,o#b1 and in addition to this the basic properties are more distinctly seen in zirconium dioxide1 ,zr,o#b1 than in titanic oxide1 ,ti,o#b1 although the acid property of combining with bases still remains4 ,in the heaviest oxides1 cerium dioxide1 ,ce,o#b1 and thorium dioxide1 ,th,o#b1 no acid properties are observed1 these being both purely basic oxides4 ,in ,chapter ,,xvii4 7,note #dc7 we already pointed out this higher oxide of cerium4 ,as the above-mentioned elements are rather rare in nature1 have but little practical application1 and do not present any new forms of combination1 it is unadvisable to dwell on them in this treatise4 ,titanium is found in nature in the form of its anhydride or oxide1 ,ti,o#b1 mixed with silicon in many minerals1 but the oxide is also found separately in the form of semi-metallic rutile 7sp4 gr4 #db74 ,another titanic mineral is found as a mixture in other ores1 known as titanic iron ore 7in the ,thuensky mountains of the southern ,ural2 it is known as thuenite71 ,fe,ti,o#c4 ,this is a salt of ferrous oxide and titanic anhydride4 ,it crystallises in the rhombohedric system1 has a metallic lustre1 grey colour1 sp4 gr4 #de4 ,the third mineral in which titanium is found in considerable quantities in nature is sphene or titanite1 ,ca,ti,si,o#e ,ca,o1,si,o#b1,ti,o#b1 sp4 gr4 #ce1 colour yellow1 green1 or the like1 crystallises in tablets4 ,the fourth1 but rare1 titanic mineral is peroffskite1 calcium titanate1 ,ca,ti,o#c2 it forms blackish-grey or brown cubic crystals1 sp4 gr4 #djb1 and occurs in the ,ural and other localities4 ,it may be prepared artificially by fusing sphene in an atmosphere of water vapour and carbonic anhydride4 ,at the end of the last century ,klaproth showed the distinction between titanic compounds and all others then known4#eg #eg ,the compounds of titanium are generally obtained from rutile2 the finely-ground ore is fused with a considerable amount of acid potassium sulphate1 until the titanic anhydride1 as a feeble base1 passes into solution4 ,after cooling1 the resultant mass is ground up1 dissolved in cold water1 and treated with ammonium hydrosulphide2 a black precipitate then separates out from the solution4 ,this precipitate contains ,ti,o#b 7as hydrate7 and various metallic sulphides--for example1 iron sulphide4 ,it is first washed with water and then with a solution of sulphurous anhydride until it becomes colourless4 ,this is due to the iron sulphide contained in the precipitate1 and rendering it black1 being converted into dithionate by the action of the sulphurous acid4 ,the titanic acid left behind is nearly pure4 ,the considerable volatility of titanium chloride may also be taken advantage of in preparing the compounds of titanium from rutile4 ,it is formed by heating a mixture of rutile and charcoal in dry chlorine2 the distillate then contains titanium chloride1 ,ti,cl#d4 ,it may be easily purified1 owing to its having a constant boiling point of #acf4 ,its specific gravity is #agf2 it is a colourless liquid1 which fumes in the air1 and is perfectly soluble in water if it be not heated4 ,when hot water acts on titanic chloride1 a large proportion of titanic acid separates out from the solution and passes into metatitanic acid4 ,a similar decomposition of acid solutions of titanic acid is accomplished whenever they are heated1 and especially in the presence of sulphuric acid1 just as with metastannic acid1 which titanic acid resembles in many respects4 ,on igniting the titanic acid a colourless powder of the anhydride1 ,ti,o#b1 is obtained4 ,in this form it is no longer soluble in acids or alkalis1 and only fuses in the oxyhydrogen flame2 but1 like silica1 it dissolves when fused with alkalis and their carbonates2 as already mentioned1 it dissolves when fused with a considerable excess of acid potassium sulphate--that is1 it then reacts as a feeble base4 ,this shows the basic character of titanic anhydride2 it has at once1 although feebly developed1 both basic and acid properties4 ,the fused mass1 obtained from titanic anhydride and alkali when treated with water1 parts with its alkali1 and a residue is obtained of a sparingly-soluble poly-titanate1 ,k#b,ti,o#cn,ti,o#b4 ,the hydrate1 which is precipitated by ammonia from the solutions obtained by the fusion of ,ti,o#b with acid potassium sulphate1 when dried forms an amorphous mass of the composition ,ti7,,oh7#d4 ,but it loses water over sulphuric acid1 gradually passing into a hydrate of the composition ,ti,o7,,oh7#b1 and when heated it parts with a still larger proportion of water2 at #ajj the hydrate ,ti#b,o#c7,,oh7#b is obtained1 and at #cjj the anhydride itself4 ,the higher hydrate1 ,ti7,,oh7#d1 is soluble in dilute acid1 and the solution may be diluted with water2 but on boiling the sulphuric acid solution 7though not the solution in hydrochloric acid71 all the titanic acid separates in a modified form1 which is1 however1 not only insoluble in dilute acids1 but even in strong sulphuric acid4 ,this hydrate has the composition ,ti#b,o#c7,,oh7#b1 but shows different properties from those of the hydrate of the same composition described above1 and therefore this modified hydrate is called metatitanic acid4 ,it is most important to note the property of the ordinary gelatinous hydrate 7that precipitated from acid solutions by ammonia7 of dissolving in acids1 the more so since silica does not show this property4 ,in this property a transition apparently appears between the cases of common solution 7based on a capacity for unstable combination7 and the case of the formation of a hydrosol 7the solubility of germanium oxide1 ,ge,o#b1 perhaps presents another such instance74 ,if titanium chloride be added drop by drop to a dilute solution of alcohol and hydrogen peroxide1 and then ammonia be added to the resultant solution1 a yellow precipitate of titanium trioxide1 ,ti,o#c;,h#b,o1 separates out1 as ,piccini1 ,weller1 and ,classen showed4 ,this substance apparently belongs to the category of true peroxides4 ,titanium chloride absorbs ammonia and forms a compound1 ,ti,cl#d1d,,nh#c1 as a red-brown powder which attracts moisture from the air and when ignited forms titanium nitride1 ,ti#c,n#d4 ,phosphuretted hydrogen1 hydrocyanic acid1 and many similar compounds are also absorbed by titanium chloride1 with the evolution of a considerable amount of heat4 ,thus1 for example1 a yellow crystalline powder of the composition ,ti,cl#d1b;,,hcn is obtained by passing dry hydrocyanic acid vapour into cold titanium chloride4 ,titanium chloride combines in a similar manner with cyanogen chloride1 phosphorus pentachloride1 and phosphorus oxychloride1 forming molecular compounds1 for example ,ti,cl#d1,p,o,cl#c4 ,this faculty for further combination probably stands in connection1 on the one hand1 with the capacity of titanium oxide to give polytitanates1 ,ti,o7,,mo7#b1n,ti,o#b2 on the other hand1 it corresponds with the kindred faculty of stannic chloride for the formation of poly-compounds 7,note #da71 and lastly it is probably related to the remarkable behaviour of titanium towards nitrogen4 ,metallic titanium1 obtained as a grey powder by reducing potassium titanofluoride1 ,k#b,ti,f#f1 7sp4 gr4 #cee ,k4 ,hofman #ahic71 with iron in a charcoal crucible1 combines directly with nitrogen at a red heat4 ,if titanic anhydride be ignited in a stream of ammonia1 all the oxygen of the titanic oxide is disengaged1 and the compound ,ti,n#b is formed as a dark violet substance having a copper-red lustre4 ,a compound ,ti#e,n#f is also known2 it is obtained by igniting the compound ,ti#c,n#d in a stream of hydrogen1 and is of a golden-yellow colour with a metallic lustre4 ,to this order of compounds also belongs the well-known and chemically historical compound known as titanium nitrocyanide2 its composition is ,ti#e;,,cn#d4 ,this substance appears as infusible1 sometimes well-formed1 cubical crystals of sp4 gr1 #dc1 and having a red copper colour and metallic lustre2 it is found in blast furnace slag4 ,it is insoluble in acids but is acted on by chlorine at a red heat1 forming titanium chloride4 ,it was at first regarded as metallic titanium2 it is formed in the blast furnace at the expense of those cyanogen compounds 7potassium cyanide and others7 which are always present1 and at the expense of the titanium compounds which accompany the ores of iron4 ,whler1 who investigated this compound1 obtained it artificially by heating a mixture of titanic oxide with a small quantity of charcoal1 in a stream of nitrogen1 and thus proved the direct power for combination between nitrogen and titanium4 ,when fused with caustic potash1 all the nitrogen compounds of titanium evolve ammonia and form potassium titanate4 ,like metals they are able to reduce many oxides--for example1 oxides of copper--at a red heat4 ,among the alloys of titanium1 the crystalline compound ,al#d,ti is remarkable4 ,it is obtained by directly dissolving titanium in fused aluminium2 its specific gravity is #caa4 ,the crystals are very stable1 and are only soluble in aqua regia and alkalis4 ,the comparatively rare element zirconium1 ,zr #ij1 is very similar to titanium1 but has a more basic character4 ,it is rarer in nature than titanium1 and is found principally in a mineral called zircon1 ,zr,si,o#d ,zr,o#b4,si,o#b1 crystallising in square prisms1 sp4 gr4 #de4 ,it has considerable hardness and a characteristic brownish-yellow colour1 and is occasionally found in the form of transparent crystals1 as a precious stone called hyacinth4#eh ,metallic zirconium was obtained1 by ,berzelius and ,troost1 by the action of aluminium on potassium zirconofluoride in the same way that silicon is prepared2 it forms a crystalline powder1 similar in appearance to graphite and antimony1 but having a very considerable hardness1 not much lustre1 sp4 gr4 #dae4 ,in many respects it resembles silicon2 it does not fuse when heated1 and even oxidises with difficulty1 but liberates hydrogen when fused with potash4 ,when fused with silica it liberates silicon4 ,with carbon in the electrical furnace it forms ,zr,c#b1 with hydrogen it gives ,zr,h#b 7like ,ca,h#b1 ,winkler1 ,vol4 ,i41 p4 #fba72 hydrochloric and nitric acids act feebly on it1 but aqua regia easily dissolves it4 ,it is distinguished from silicon by the fact that hydrofluoric acid acts on it with great facility1 even in the cold and when diluted1 whilst this acid does not act on silicon at all4 #eh ,the formula ,zr,o was first given to the oxide of zirconium as a base1 in this case ,zr #de whilst the present atomic weight is ,zr #ij--that is1 the formula of the oxide is now recognised as being ,zr,o#b4 ,the reasons for ascribing this formula to the compounds of zirconium are as follows4 ,in the first place1 the investigation of the crystalline forms of the zirconofluorides--for example1 ,k#b,zr,f#f1 ,mg,zr,f#f1e;,h#b,o--which proved to be analogous in composition and crystalline form with the corresponding compounds of titanium1 tin1 and silicon4 ,in the second place1 the specific heat of ,zr is #jjfg1 which corresponds with the combining weight #ij4 ,the third and most important reason for doubling the combining weight of zirconium was given by ,deville's determination of the vapour density of zirconium chloride1 ,zr,cl#d4 ,this substance is obtained by igniting zirconium oxide mixed with charcoal in a stream of dry chlorine1 and is a colourless1 saline substance which is easily volatile at #ddj4 ,its density referred to air was found to be #hae1 that is #aag in relation to hydrogen1 as it should be according to the molecular formula of this substance above-cited4 ,it exhibits1 however1 in many respects1 a saline character and that of an acid chloranhydride1 for zirconium oxide itself presents very feebly developed acid properties but clearly marked basic properties4 ,thus zirconium chloride dissolves in water1 and on evaporation the solution only partially disengages hydrochloric acid--resembling magnesium chloride1 for example4 ,zirconium was discovered and characterised as an individual element by ,klaproth4 ,pure compounds of zirconium are generally prepared from zircon1 which is finely ground1 but as it is very hard it is first heated and thrown into cold water1 by which means it is disintegrated4 ,zircon is decomposed or dissolved when fused with acid potassium sulphate1 or still more easily when fused with acid potassium fluoride 7a double soluble salt1 ,k#b,zr,f#f1 is then formed72 however1 zirconium compounds are generally prepared from powdered zircon by fusing it with sodium carbonate and then boiling in water4 ,an insoluble white residue is obtained consisting of a compound of the oxides of sodium and zirconium1 which is then treated with hydrochloric acid and the solution evaporated to dryness4 ,the silica is thus converted into an insoluble form1 and zirconium chloride obtained in solution4 ,ammonia precipitates zirconium hydroxide from this solution1 as a white gelatinous precipitate1 ,zr,o7,,oh7#b4 ,when ignited this hydroxide loses water and in so doing undergoes a spontaneous recalescence and leaves a white infusible and exceedingly hard mass of zirconium oxide1 ,zr,o#b1 having a specific gravity of #ed 7in the electrical furnace ,zr,o#b fuses and volatilises like ,si,o#b1 ,moissan74 ,owing to its infusibility1 zirconium oxide is used as a substitute for lime and magnesia in the ,drummond light4 ,this oxide1 in contradistinction to titanium oxide1 is soluble1 even after prolonged ignition1 in hot strong sulphuric acid4 ,the hydroxide is easily soluble in acids4 ,the composition of the salts is ,zr,x#d1 or ,zr,o,x#b1 or ,zr,o,x#b1,zr,o#b1 just as with those of its analogues4 ,but although zirconium oxide forms salts in the same way with acids1 it also gives salts with bases4 ,thus it liberates carbonic anhydride when fused with sodium carbonate1 forming the salts ,zr7,na,o7#d1 ,zr,o7,na,o7#b1 c4 ,water1 however1 destroys these salts and extracts the soda4 ,the very similar element thorium 7,th #bcb7 was distinguished by ,berzelius from zirconium4 ,it is very rarely met with1 in thorite and orangeite1 ,th,si,o#d1b;,h#b,o4 ,the latter is isomorphous with zircon 7sp4 gr4 #dh74ei #ei ,thorium has also been found in the form of oxide in certain pyrochlores1 euxenites1 monazites1 and other rare minerals containing salts of niobium and phosphates4 ,the compounds of thorium are prepared by decomposing thorite or orangeite with strong sulphuric acid at its boiling point2 this renders the silica insoluble1 and the thorium oxide passes into solution when the residue is treated with cold water1 after having been previously boiled with water 7boiling water does not dissolve the oxide of thorium74 ,lead and other impurities are separated by passing sulphuretted hydrogen through the solution1 and the thorium hydroxide is then precipitated by ammonia4 ,if this hydroxide be dissolved in the smallest possible amount of hydrochloric acid1 and oxalic acid be then added1 thorium oxalate is obtained as a white precipitate1 which is insoluble in an excess of oxalic acid2 this reaction is taken advantage of for separating this metal from many others4 ,it1 however1 resembles the cerite metals 7,chapter ,,xvii41 ,note #dc7 in this and many other respects4 ,the thorium hydroxide is gelatinous2 on ignition it leaves an infusible oxide1 ,th,o#b1 which1 when fused with borax1 gives crystals of the same form as stannic oxide or titanic anhydride2 sp4 gr4 #ihf4 ,but the basic properties are much more developed in thorium oxide than in the preceding oxides1 and it does not even disengage carbonic acid when fused with sodium carbonate--that is1 it is a much more energetic base than zirconium oxide4 ,the hydrate1 ,th,o#b1 however1 is soluble in a solution of ,na#b;,,co#c 7,chapter ,,xvii41 ,note #dc74 ,thorium chloride1 ,th,cl#d is obtained as a distinctly crystalline sublimate when thorium oxide1 mixed with charcoal1 is ignited in a stream of dry chlorine4 ,when heated with potassium1 thorium chloride gives a metallic powder of thorium having a sp4 gr4 #aaa4 ,it burns in air1 and is but slightly soluble in dilute acids4 ,the atomic weight of thorium was established by ,chydenius and ,delafontaine on the basis of the ismorphism of the double fluorides4 ,,chapter ,,xix ,,phosphorus ,,and ,,the ,,other ,,elements ,,of ,,the ,,fifth ,,group ,nitrogen is the lightest and most widely distributed representative of the elements of the fifth group1 which form a higher saline oxide of the form ,r#b,o#e1 and a hydrogen compound of the form ,,rh#c4 ,phosphorus1 arsenic1 bismuth1 and antimony belong to the uneven series of this group4 ,phosphorus is the most widely distributed of these elements4 ,there is hardly any mineral substance composing the mass of the earth's crust which does not contain some--it may be a small--amount of phosphorus compounds in the form of the salts of phosphoric acid4 ,the soil and earthy substances in general usually contain from one to ten parts of phosphoric acid in #aj1jjj parts4 ,this amount1 which appears so small1 has1 however1 a very important significance in nature4 ,no plant can attain its natural growth if it be planted in an artificial soil completely free from phosphoric acid4 ,plants equally require the presence of potash1 magnesia1 lime1 and ferric oxide1 among basic1 and of carbonic1 sulphuric1 nitric1 and phosphoric anhydrides1 among acid oxides4 ,in order to increase the fertility of a more or less poor soil1 the above-named nutritive elements are introduced into it by means of fertilisers4 ,direct experiment has proved that these substances are undoubtedly necessary to plants1 but that they must be all present simultaneously and in small quantities1 and that an excess1 like an insufficiency1 of one of these elements is necessarily followed by a bad harvest1 or an imperfect growth1 even if all the other conditions 7light1 heat1 water1 air7 are normal4 ,the phosphoric compounds of the soil accumulated by plants pass into the organism of animals1 in which these substances are assimilated in many instances in large quantities4 ,thus the chief component part of bones is calcium phosphate1 ,ca#c,p#b,o#h1 and it is on this that their hardness depends4#a #a ,dry bones contain about one-third of gelatinous matter and about two-thirds of ash1 chiefly calcium phosphate4 ,the salts of phosphoric acid are also found in the mass of the earth as separate minerals2 for example1 the apatites contain this salt in a crystalline form1 combined with calcium chloride or fluoride1 ,ca,r#b1c;,ca#c7,,po#d7b1 where ,r ,f or ,cl1 sometimes in a state of isomorphous mixture4 ,this mineral often crystallises in fine hexagonal prisms2 sp4 gr4 #cag to #cbb4 ,vivianite is a hydrated ferrous phosphate1 ,fe#c7,,po#d7b1h;,h#b,o4 ,phosphates of copper are frequently found in copper mines2 for example1 tagilite1 ,cu#c7,,po#d7b1;,cu7,,oh7#b1b;,h#b,o4 ,lead and aluminium form similar salts4 ,they are nearly all insoluble in water4 ,the turquoise1 for instance1 is hydrated phosphate of alumina1 7,al#b,o#c7b1,p#b,o#ee;,h#b,o1 coloured with a salt of copper4 ,sea and other waters always contain a small amount of phosphates4 ,the ash of sea-plants1 as well as of land-plants1 always contains phosphates4 ,deposits of calcium phosphate are often met with2 they are termed phosphorites and osteolites1 and are composed of the fossil remains of the bones of animals2 they are used for manure4 ,of the same nature are the so-called guano deposits from ,baker's ,island1 and entire strata in ,spain1 ,france1 and in the ,governments of ,orloff and ,kursk in ,russia4 ,it is evident that if a soil destined for cultivation contain very little phosphoric acid1 the fertilisation by means of these minerals will be beneficial1 but1 naturally1 only if the other elements necessary to plants be present in the soil4 ,phosphorus was first extracted by ,brand in #affi1 by the ignition of evaporated urine4 ,after the lapse of a century ,scheele1 who knew of the existence of a more abundant source of phosphorus in bones1 pointed out the method which is now employed for the extraction of this element4 ,calcium phosphate in bones permeates a nitrogenous organic substance1 which is called ossein1 and forms a gelatin4 ,when bones are treated exclusively for the extraction of phosphorus1 neglecting the gelatin1 they are burnt1 in which case all the ossein is burnt away4 ,when1 however1 it is desired to preserve the gelatin1 the bones are immersed in cold dilute hydrochloric acid1 which dissolves the calcium phosphate and leaves the gelatin untouched2 calcium chloride and acid calcium phosphate1 ,ca,h#d7,,po#d7b1 are then obtained in the solution4 ,when the bones are directly burnt in an open fire their mineral components only are left as an ash1 containing about #ij per cent4 of calcium phosphate1 ,ca#c7,,po#d7b1 mixed with a small amount of calcium carbonate and other salts4 ,this mass is treated with sulphuric acid1 and then the same substance is obtained in the solution as was obtained from the unburnt bones immersed in hydrochloric acid--i4e4 the acid calcium phosphate soluble in water1 in which reaction naturally the chief part of the sulphuric acid is converted into calcium sulphate3 ,ca#c7,,po#d7b #b;,h#b,,so#d #b;,ca,s,o#d ,ca,h#d7,,po#d7b4 ,ca#c7,,po#d7b #d;,h,cl #b;,ca,cl#b ,ca,h#d7,,po#d7b4 ,on evaporating the solution1 crystallisable acid calcium phosphate is obtained4 ,the extraction of the phosphorus from this salt consists in heating it with charcoal to a white heat4 ,when heated1 the acid phosphate1 ,ca,h#d7,,po#d7b1 first parts with water1 and forms the metaphosphate1 ,ca7,,po#c7b1 which for the sake of simplicity may be regarded1 like the acid salt1 as composed of pyrophosphate and phosphoric anhydride1 #b;,ca7,,po#c7b ,ca#b,p#b,o#g ,p#b,o#e4 ,the latter1 with charcoal1 gives phosphorus and carbonic oxide1 ,p#b,o#e #e;,c ,p#b #e;,,co4 ,so that in reality a somewhat complicated process takes place here1 yielding ultimately products according to the following equation3 #b;,ca,h#d7,,po#d7b #e;,c #d;,h#b,o ,ca#b,p#b,o#g ,p#b #e;,,co4 ,after the steam has come over1 phosphorus and carbonic oxide distil over from the retort and calcium pyrophosphate remains behind4#a bis #a bis ,by subjecting the pyrophosphate to the action of sulphuric or hydrochloric acid it is possible to obtain a fresh quantity of the acid salt from the residue1 and in this manner to extract all the phosphorus4 ,it is usual to take burnt bones1 but mineral phosphorites1 osteolites1 and apatites may also be employed as materials for the extraction of phosphorus4 ,its extraction for the manufacture of matches is everywhere extending1 and in ,russia1 in the ,urals1 in the ,government of ,perm1 it has attained such proportions that the district is able to supply other countries with phosphorus4 ,a great many methods have been proposed for facilitating the extraction of phosphorus1 but none of them differ essentially from the usual one1 because the problem is dependent on the liberation of phosphoric acid by the action of acids1 and on its ultimate reduction by charcoal4 ,thus the calcium phosphate may be mixed directly with charcoal and sand1 and phosphorus will be liberated on heating the mixture1 because the silica displaces the phosphoric anhydride1 which gives carbonic oxide and phosphorus with the charcoal4 ,it has also been proposed to pass hydrochloric acid over an incandescent mixture of calcium phosphate and charcoal2 the acid then acts just as the silica does1 liberating phosphoric anhydride1 which is reduced by the charcoal4 ,it is necessary to prevent the access of air in the condensation of the vapours of phosphorus1 because they take fire very easily2 hence they are condensed under water by causing the gaseous products to pass through a vessel full of water4 ,for this purpose the condenser shown in fig4 #hc is usually employed4 ,illustration3 ,,fig4 #hc4--,preparation of phosphorus4 ,the mixture is calcined in the retort c4 ,the vapours of phosphorus pass through a into water without coming into contact with air4 ,the phosphorus condenses in the water1 and the gases accompanying it escape through i4 ,as phosphorus melts at about #dj1 it condenses at the bottom of the receiver in a molten liquid mass1 which is cast under water in tubes1 and is sold in the form of sticks4 ,this is common or yellow phosphorus4 ,it is a transparent1 yellowish1 waxy substance1 which is not brittle1 almost insoluble in water1 and easily undergoes change in its external appearance and properties under the action of light1 heat1 and of various substances4 ,it crystallises 7by sublimation or from its solution in carbon bisulphide7 in the regular system1 and#b 7in contradistinction to the other varieties7 is easily soluble in carbon bisulphide1 and also partially in other oily liquids4 ,in this it recalls common sulphur4 ,its specific gravity is #ahd4 ,it fuses at #dd1 and passes into vapour at #bij2 it is easily inflammable1 and must therefore be handled with great caution2 careless rubbing is enough to cause phosphorus to ignite4 ,its application in the manufacture of matches is based on this4#b bis ,it emits light in the air owing to its slow#c oxidation1 and is therefore kept under water 7such water is phosphorescent in the dark1 like phosphorus itself74 ,it is also very easily oxidised by various oxidising agents and takes up the oxygen from many substances4#c bis ,phosphorus enters into direct combination with many metals and with sulphur1 chlorine1 c41 with development of a considerable amount of heat4 ,it is very poisonous although not soluble in water4 #b ,vernon 7#ahia7 observed that ordinary 7yellow7 phosphorus is dimorphous4 ,if it be melted and by careful cooling be brought in a liquid form to as low a temperature as possible1 it gives a variety which melts at #dec 7the ordinary variety fuses at #ddc71 sp4 gr4 #ahbg 7that of the ordinary variety is #ahah7 at #ac1 crystallises in rhombic prisms 7instead of in forms belonging to the cubical system74 ,this is similar to the relation between octahedral and prismatic sulphur 7,chapter ,,xx474 #b bis ,according to ,herr ,irinyi 7an ,hungarian student71 the first phosphorus matches were made in ,austria at ,roemer's works in #ahce4 #c ,the absorption of the oxygen of the atmosphere at a constant ordinary temperature by a large surface of phosphorus proceeds so uniformly1 regularly1 and rapidly1 that it may serve1 as ,ikeda 7,tokio1 #ahic7 has shown1 for demonstrating the law of the velocity 7rate7 of reaction1 which is considered in theoretical chemistry1 and shows that the rate of reaction is proportional to the active mass of a substance--i4e4 dx_/dt k7,a - x7 where t is the time1 ,a the initial mass of the reacting substance--in this case oxygen--x the amount of it which has entered into reaction1 and k the coefficient of proportionality4 ,ikeda took a test-tube 7diameter about #aj mm471 and covered its outer surface with a coating of phosphorus 7by melting it in a test-tube of large diameter1 inserting the smaller test-tube1 and1 when the phosphorus had solidified1 breaking away the outer test-tube71 and introduced it into a definite volume of air1 contained in a ,woulfe's bottle 7immersed in a water bath to maintain a constant temperature71 one of whose orifices was connected with a mercury manometer showing the fall of pressure1 x4 ,knowing that the initial pressure of the oxygen 7in air nearly #gej #jbji7 was about #aee mm4 ,a1 the coefficient of the rate of reaction k is given1 by the law of the variation of the rate of reaction with the mass of the reacting substance1 by the equation3 k 7#a_/t7log7,a_/7,a - x771 where t is the time1 counting from the commencement1 of the experiment in minutes4 ,when the surface of the phosphorus was about #aa sq4 cm41 the following results were actually obtained4 t #aj #bj #cj #dj #ej #fj minutes x #aje #bae #caa #djg #dia #egc mm #aj1jjj k #cb #cb #cb #cc #cc #cc ,the constancy of k is well shown in this case4 ,the determination takes a comparatively short time1 so that it may serve as a lecture experiment1 and demonstrates one of the most important laws of chemical mechanics4 #c bis ,not only do oxidising agents like nitric1 chromic1 and similar acids act upon phosphorus1 but even the alkalis are attacked--that is1 phosphorus acts as a reducing agent4 ,in fact it reduces many substances1 for instance1 copper from its salts4 ,when phosphorus is heated with sodium carbonate1 the latter is partially reduced to carbon4 ,if phosphorus be placed under water slightly warmed1 and a stream of oxygen be passed over it1 it will burn under the water4 ,besides this1 there is a red variety of phosphorus1 which differs considerably from the above4 ,red phosphorus 7sometimes wrongly called amorphous phosphorus7 is partially formed when ordinary phosphorus remains exposed to the action of light for a long time4 ,it is also formed in many reactions2 for example1 when ordinary phosphorus combines with chlorine1 bromine1 iodine1 or oxygen1 a portion of it is converted into red phosphorus4 ,schrtter1 in ,vienna1 investigated this variety of phosphorus1 and pointed out by what methods it may be produced in considerable quantities4 ,red phosphorus is a powdery red-brown opaque substance of specific gravity #bad4 ,it does not combine so energetically with oxygen and other substances as yellow phosphorus1 and evolves less heat in combining with them4#d ,common phosphorus easily oxidises in the air2 red phosphorus does not oxidise at all at the ordinary temperature2 hence it does not phosphoresce in the air1 and may be very conveniently kept in the form of powder4 ,it does not1 like yellow phosphorus1 fuse at #dd4 ,after being converted into vapour at #bij or #cjj1 it again passes into the ordinary variety when slowly cooled4 ,red phosphorus is not soluble in carbon bisulphide and other oily liquids1 which permits of its being freed from any admixture of the ordinary phosphorus4 ,it is not poisonous1 and is used in many cases for which the ordinary phosphorus is unsuitable or dangerous2 for example1 in the manufacture of matches1 which are then not poisonous or inflammable by accidental friction1 and therefore the red variety has now replaced the ordinary phosphorus4#d bis #d ,the thermochemical determinations for phosphorus and its compounds date from the last century1 when ,lavoisier and ,laplace burnt phosphorus in oxygen in an ice calorimeter4 ,andrews1 ,despretz1 ,favre1 and others have studied the same subject4 ,the most accurate and complete data are due to ,thomsen4 ,to determine the heat of combustion of yellow phosphorus1 ,thomsen oxidised it in a calorimeter with iodic acid in the presence of water1 and a mixture of phosphorous and phosphoric acids was thus formed 7was not any hypophosphoric acid formed8--,salzer71 and the iodic acid converted into hydriodic acid4 ,it was first necessary to introduce two corrections into the calorimetric result obtained1 one for the oxidation of the phosphorous into phosphoric acid1 knowing their relative amounts by analysis1 and the other for the deoxidation of the iodic acid4 ,the result then obtained expresses the conversion of phosphorous into hydrated phosphoric acid4 ,this must be corrected for the heat of solution of the hydrate in water1 and for the heat of combination of the anhydride with water1 before we can obtain the heat evolved in the reaction of ,p#b with ,o#e in the proportion for the formation of ,p#b,o#e4 ,it is natural that with so complex a method there is a possibility of many small errors1 and the resultant figures will only present a certain degree of accuracy after repeated corrections by various methods4 ,of such a kind are the following figures determined by ,thomsen1 which we express in thousands of calories3--,p#b ,o#e #cgj2 ,p#b ,o#c #c;,h#b,o #djj2 ,p#b ,o#e a mass of water #dje4 ,hence we see that ,p#b,o#e #c;,h#b,o #cj2 #b,,ph#c,o#d an excess of water #e4 ,experiment further showed that crystallised ,,ph#c,o#d1 in dissolving in water1 evolves #bg thousand calories1 and that fused 7#ci7 ,,ph#c,o#d evolves #eb thousand calories1 whence the heat of fusion of ,h#c,,po#d #be thousand calories4 ,for phosphorous acid1 ,h#c,,po#c1 ,thomsen obtained ,p#b ,o#c #c;,h#b,o #bej1 and the solution of crystallised ,h#c,,po#c in water -#jac1 and of fused ,h#c,,po#c #bi4 ,for hypophosphorous acid1 ,h#c,,po#b1 the heats of solution are nearly the same 7-#jag and #ba71 and the heat of formation ,p#b ,o #c;,h#b,o #ge2 hence its conversion into #b;,h#c,,po#c evolves #age thousand calories1 and the conversion of #b;,h#c,,po#c into #b;,h#c,,po#d #aej thousand calories4 ,for the sake of comparison we will take the combination of chlorine with phosphorus1 also according to ,thomsen1 per #b atoms of phosphorus1 ,p#b #c;,cl#b #aea1 ,p#b #e;,cl#b #baj thousand calories4 ,in their reaction on an excess of water 7with the formation of a solution71 #b,p,cl#c #acj1 #b,p,cl#e #bdg1 and #b,p,o,cl#c #adb thousand calories4 ,besides which we will cite the following data given by various observers3 heat of fusion for ,p 7that is1 for #ca parts of phosphorus by weight7 -#jae thousand calories2 the conversion of yellow into red phosphorus for ,p1 from #ai to #bg thousand calories2 ,p ,h#c #dc1 ,,hi ,,ph#c #bd1 ,,ph#c ,h,br #bb thousand calories4 ,at the ordinary temperature 7#bj ,c47 phosphorus is not oxidised by pure oxygen2 oxidation only takes place with a slight rise of temperature1 or the dilution of the oxygen with other gases 7especially nitrogen or hydrogen71 or a decrease of pressure4 #d bis ,ordinary phosphorus takes fire at a temperature 7#fj7 at which no other known substance will burn4 ,its application to the manufacture of matches is based on this property4 ,in order to illustrate the easy inflammability of common 7yellow7 phosphorus1 its solution in carbon bisulphide may be poured over paper2 this solvent quickly evaporates1 and the free phosphorus spread over a large surface takes fire spontaneously1 notwithstanding the cooling effect produced by the evaporation of the bisulphide4 ,the majority of phosphorus matches are composed of common phosphorus mixed with some oxidising substance which easily gives up oxygen1 such as lead dioxide1 potassium chlorate1 nitre1 c4 ,for this purpose common phosphorus is carefully triturated under warm water containing a little gum2 lead dioxide and potassium nitrate are then added to the resultant emulsion1 and the match ends1 previously coated with sulphur or paraffin1 are dipped into this preparation4 ,after this the matches are dipped into a solution of gum and shellac1 in order to preserve the phosphorus from the action of the air4 ,when such a match containing particles of yellow phosphorus is rubbed over a rough surface1 it becomes 7especially at the point of rupture of the brittle gummy coating7 slightly heated1 and this is sufficient to cause the phosphorus to take fire and burn at the expense of the oxygen of the other ingredients4 ,the heads of the 'safety' matches do not contain any phosphorus1 but only substances capable of burning and of supporting combustion4 ,red phosphorus is spread over a surface on the box1 and it is the friction against this phosphorus which ignites the matches4 ,there is no danger of the matches taking fire accidentally1 nor are they poisonous4#e ,this red phosphorus is prepared by heating the ordinary phosphorus at #bcj to #bgj2 it is evident that this must be done in an atmosphere incapable of supporting combustion--for example1 in nitrogen1 carbonic anhydride1 steam1 c4 ,on a large scale1 ordinary phosphorus is placed in closed iron vessels1#e bis and immersed in a bath of different proportions of tin and lead1 by which means the temperature of #bej necessary for the conversion is easily attained4 ,it is kept at this temperature for some time4 ,the temperature is at first cautiously raised1 and the air is thus partially expelled by the heat1 and also by the evolution of steam 7the phosphorus is damp when put in71 whilst the remaining oxygen is also partially absorbed by the phosphorus1 so that an atmosphere of nitrogen is produced in the iron vessel4 ,red phosphorus enters into all the reactions proper to yellow phosphorus1 only with greater difficulty and more slowly2#f and1 as its vapour tension 7volatility7 is less than that of the yellow variety1 it may be supposed that a polymerisation takes place in the passage of the yellow into the red modification1 just as in the passage of cyanogen into paracyanogen1 or of cyanic acid into cyanuric acid 7,chapter ,,ix4 ,notes #ci bis and #dh74 #e ,in the so-called 'safety' or ,swedish matches 7which are not poisonous1 and do not take fire from accidental friction7 a mixture of red phosphorus and glass forms the surface on which the matches are struck1 and the matches themselves do not contain any phosphorus at all1 but a mixture of antimonious sulphide1 ,sb#b,s#c 7or similar combustible substances7 and potassium chlorate 7or other oxidising agents74 ,the combustion1 when once started by contact with the red phosphorus1 proceeds by itself at the expense of the inflammatory and combustible elements contained in the tip of the match4 ,the mixture applied on the match itself must not be liable to take fire from a blow or friction4 ,the mixture forming the heads of the 'safety' matches has the following approximate composition3 #ee-fj parts of chlorate of potassium1 #e-aj parts of peroxide of manganese 7or of ,k#b;,cr#b,o#g71 about #a part of sulphur or charcoal1 about #a part of pentasulphide of antimony1 ,sb#b,s#e1 and #cj-dj parts of rouge and powdered glass4 ,this mixture is stirred up in gum or glue1 and the matches are dipped into it4 ,the paper on which the matches are struck is coated with a mixture of red phosphorus and trisulphide of antimony1 ,sb#b,s#c1 stirred up in dextrine4 #e bis ,phosphorus only acts on iron at a red heat4 ,the boiler is provided with a safety valve and gas-conducting tube1 which is immersed in mercury or other liquid to prevent the admission of air into the boiler4 #f ,the specific heat of the yellow variety is #jahi--that is1 greater than that of the red variety1 which is #jagj4 ,the sp4 gr4 of the yellow is #ahd1 and of the red prepared at #bfj #bae1 and of that prepared at #ehj and above 7i4e4 'metallic' phosphorus1 see below7 #bcd4 ,at #bcj the pressure of the vapour of ordinary phosphorus #ead millimetres of mercury1 and of the red #j--that is to say1 the red phosphorus does not form any vapour at this temperature2 at #ddg the vapour tension of ordinary phosphorus is at first #eejj mm41 but it gradually diminishes1 whilst that of red phosphorus is equal to #afcf mm4 ,hittorf1 by heating the lower portion of a closed tube containing red phosphorus to #ecj and the upper portion to #ddg1 obtained crystals of the so-called 'metallic' phosphorus at the upper extremity4 ,as the vapour tensions 7according to ,hittorf1 at #ecj the vapour tension of yellow phosphorus #hjdj mm41 of red #faci mm41 and of metallic #dacj mm47 and reactions are different1 metallic phosphorus may be regarded as a distinct variety4 ,it is still less energetic in its chemical reaction than red phosphorus1 and it is denser than the two preceding varieties3 sp4 gr4 #bcd4 ,it does not oxidise in the air2 is crystalline1 and has a metallic lustre4 ,it is obtained when ordinary phosphorus is heated with lead for several hours at #djj in a closed vessel1 from which the air has been exhausted4 ,the resultant mass is then treated with dilute nitric acid1 which first dissolves the lead 7phosphorus is electro-negative to lead1 and does not1 therefore1 act on the nitric acid at first7 and leaves brilliant rhombohedral crystals of phosphorus of a dark violet colour with a slight metallic lustre1 which conduct an electric current incomparably better than the yellow variety2 this also is characteristic of the metallic state of phosphorus4 ,the researches of ,lemoine partially explain the passage of yellow 7ordinary7 phosphorus into its other varieties4 ,he heated a closed glass globe containing either ordinary or red phosphorus1 in the vapour of sulphur 7#ddj71 and then determined the amount of the red and yellow varieties after various periods of time1 by treating the mixture with carbon bisulphide4 ,it appeared that after the lapse of a certain time a mixture of definite and equal composition is obtained from both--that is1 between the red and yellow varieties a state of equilibrium sets in like that of dissociation1 or that observed in double decompositions4 ,but at the same time1 the progress of the transformation appeared to be dependent on the relative quantity of phosphorus taken per volume of the globe 7i4e4 upon the pressure74 ,neglecting the latter1 we will cite as an example the amounts of the red phosphorus transformed into the ordinary1 and of the ordinary not converted into red1 per #cj grams of red or yellow taken per litre capacity of the globe1 heated to #ddj4 ,when red phosphorus was taken1 #dge grams of yellow phosphorus were formed after two hours1 four grams after eight hours1 three grams after twenty-four hours1 and the last limit remained constant on further heating4 ,when thirty grams of yellow phosphorus were taken1 five grams remained unaltered after two hours1 four grams after eight hours1 and after twenty-four hours and more three grams as before4 ,troost and ,hautefeuille showed that liquid phosphorus in general changes more easily into the red than does phosphorus vapour1 which1 however1 is able1 although slowly1 to deposit red phosphorus4 ,the question presents itself as to whether phosphorus in a state of vapour is the ordinary or some other variety8 ,hittorf 7#ahfe7 collected many data for the solution of this problem1 which leave no doubt that 7as experimental figures show7 the density of the vapour of phosphorus is always the same1 although the vapour tension of the different varieties and their mixtures is very variable4 ,this shows that the different varieties of phosphorus only occur in a liquid and solid state1 as indeed is implied in the idea of polymerisation4 ,strictly speaking1 the vapour of phosphorus is a particular state of this substance1 and the molecular formula ,p#d refers only to it1 and not to any other definite state of phosphorus4 ,but ,raoult's solution method showed that in a benzene solution the fall of the freezing point indicates for ordinary phosphorus a molecule ,p#d1 judging by the determinations of ,paterno and ,nasini 7#ahhh71 ,hirtz 7#ahij71 and ,beckmann 7#ahia71 who obtained for sulphur by the same method a molecular weight ,s#f1 in conformity with the vapour density4 ,further research in this direction will perhaps show the possibility of finding the molecular weight of red phosphorus1 if a means be discovered for dissolving it without converting it into the yellow variety4 ,i think it will not be out of place here to draw the reader's attention to the fact that red phosphorus1 which we must recognise as polymeric with the yellow1 stands nearer to nitrogen1 whose molecule is ,n#b1 in its small inclination towards chemical reactions1 although judging by its small vapour tension it must be more complex than ordinary 7yellow and white7 phosphorus4 ,the vapour of phosphorus is colourless2 its density remains constant between #cjj and #ajjj 7,dumas1 #ahcc2 ,mitscherlich1 ,deville1 and ,troost1 #ahei1 and others74 ,the density with respect to air has been determined as from #dc to #de4 ,hence1 referred to hydrogen1 it is #dd #add #fc1 corresponding with a molecular weight #abd1 i4e4 the molecule of phosphorus in a state of vapour contains ,p#d4 ,the reader will remember that the molecule of nitrogen contains ,n#b1 of sulphur ,s#f or ,s#b1 and of oxygen ,o#b or ,o#c4 ,the chemical energy of phosphorus in a free state more nearly approaches that of sulphur than nitrogen4 ,phosphorus is combustible and inflames at #fj2 but having in the act of combination parted with a portion of its energy in the form of heat it becomes analogous to nitrogen1 so long as there is no question of its reduction back again into phosphorus4 ,nitric acid is easily reduced to nitrogen1 whilst phosphoric acid is reduced with very much greater difficulty4 ,all the compounds of phosphorus are less volatile than those of nitrogen4 ,nitric acid1 ,,hno#c1 is easily distilled2 metaphosphoric acid1 ,,hpo#c1 is generally said to be non-volatile2 triethylamine1 ,n7,c#b;,h#e7c1 boils at #ij1 and triethylphosphine1 ,p7,c#b;,h#e7c1 at #abg4 ,phosphorus not only combines easily and directly with oxygen1 but also with chlorine1 bromine1 iodine1 sulphur1 and with certain metals1 and red phosphorus when heated combines with hydrogen also4#f bis ,so1 for instance1 when fused with sodium under naphtha1 phosphorus gives the compound ,na#c,p#b4 ,zinc1 absorbing the vapour of phosphorus1 gives the phosphide ,zn#c,p#b 7sp4 gr4 #dgf72 tin1 ,sn,p2 copper1 ,cu#b,p2 even platinum combines with phosphorus 7,pt,p#b1 sp4 gr4 #hgg74f tri ,iron1 when combined even with a small quantity of phosphorus1 becomes brittle4#g ,some of these compounds of phosphorus are obtained by the action of phosphorus on the solutions of metallic salts1 and by the ignition of metallic oxides in the vapour of phosphorus1 or by heating mixtures of phosphates with charcoal and metals4 ,phosphides do not exhibit the external properties of salts1 which are so clearly seen in the chlorides and still distinctly observable in the sulphides4 ,the phosphides of the metals of the alkalis and of the alkaline earths are even immediately and very easily decomposed by water1 whereas this is found to be the case with only a very few sulphides1 and still more rarely and indistinctly with the chlorides4 ,we may take calcium phosphide as an example4#g bis ,phosphorus is laid in a deep crucible1 and covered with a clay plug1 over which lime is strewn4 ,at a red heat the vapours of phosphorus combine with the oxygen of the lime and form phosphoric anhydride1 which forms a salt with another portion of the lime1 whilst the liberated calcium combines with the phosphorus and forms calcium phosphide4 ,its composition is not quite certain2 it may be ,ca,p 7corresponding with liquid phosphuretted hydrogen74 ,this substance is remarkable for the following reaction3 if we take water--or1 better still1 a dilute solution of hydrochloric acid--and throw calcium phosphide into it1 bubbles of gas are evolved1 which take fire spontaneously in the air and form white rings4 ,this is owing to the fact that the liquid hydrogen phosphide1 ,,ph#b1 is first formed1 thus1 ,ca,p #b;,h,cl ,ca,cl#b ,,ph#b1 which1 owing to its instability1 very easily splits up into the solid phosphide1 ,p#b;,h1 and gaseous phosphide1 ,,ph#c2 #e,,ph#b ,p#b;,h #c,,ph#c2 the latter corresponds with ammonia4 ,the mixture of the gaseous and liquid phosphides takes fire spontaneously in the air1 forming phosphoric acid4 ,the same hydrogen phosphides are formed when water acts on sodium phosphide 7,p#b,na#c74 ,a similar mixture of gaseous liquid and solid phosphuretted hydrogen 7,retgers #ahid7 is formed by heating 7in a glass tube7 red phosphorus in a stream of dry hydrogen4 ,hence we see that there are three compounds of phosphorus with hydrogen4 7#a7 ,the first or solid yellow phosphide1 ,p#b;,h 7more probably ,p#d;,h#b71 is obtained by the action of strong hydrochloric acid on sodium phosphide2 it takes fire when struck or at #age4 7#b7 ,the liquid1 ,,ph#b1 or more correctly expressed as the molecule1 ,p#b;,h#d1 is a colourless liquid which takes fire spontaneously in the air1 boils at #cj1 is very unstable1 and is easily decomposed 7by light or hydrochloric acid7 into the two other phosphides of hydrogen4 ,it is prepared by passing the gases evolved by the action of water on calcium phosphide through a freezing mixture4#h ,and1 lastly1 7#c71 gaseous hydrogen phosphide1 phosphine1 ,,ph#c1 which is distinguished as being the most stable4 ,it is a colourless gas1 which does not take fire in the air4 ,it has an odour of garlic1 and is very poisonous4 ,it resembles ammonia in many of its properties4#h bis ,it is easily decomposed by heat1 like ammonia1 forming phosphorus and hydrogen2 but it is very slightly soluble in water1 and does not saturate acids1 although it forms compounds with some of them which resemble ammonium salts in their form and properties4 ,among them the compound with hydriodic acid1 ,,ph#d;,i1 analogous to ammonium iodide1 is remarkable4 ,this compound crystallises on sublimation in well-formed cubes1 like sal-ammoniac1 which it resembles in many respects4 ,however1 this compound does not enter into those reactions of double decomposition which are proper to sal-ammoniac1 because its saline properties are very feebly developed4 ,phosphuretted hydrogen also combines1 like ammonia1 with certain chloranhydrides2 but they are decomposed by water1 with the evolution of phosphine4 ,ogier 7#ahhj7 showed that hydrochloric acid also combines with phosphine under a pressure of #bj atmospheres at #ah1 and under the ordinary pressure at -#ce1 forming the crystalline phosphonium chloride ,,ph#d;,cl1 corresponding to sal-ammoniac4 ,hydrobromic acid does the same with greater ease1 and hydriodic acid with still greater facility1 forming phosphonium iodide1 ,,ph#d;,i4#i #f bis ,retgers 7see further on7 showed this in #ahid1 and observed that ,as when heated also combines with hydrogen4 #f tri ,the capacity of mercury 7,chapter ,,xvi41 ,note #be bis7 to give unstable compounds with nitrogen gives rise to the supposition that similar compounds exist with phosphorus also4 ,such a compound was obtained by ,granger 7#ahib7 by heating mercury with iodide of phosphorus in a closed tube at #bge-cjj4 ,after removing the iodide of mercury formed1 there remain fine rhombic crystals having a metallic lustre1 and composition ,hg#c,p#b4 ,this compound is stable1 does not alter at the ordinary temperature and only decomposes at a red heat2 when heated in air it burns with a flame4 ,nitric and hydrochloric acids do not act upon it1 but it is easily decomposed by aqua regia4 ,a phosphide of copper1 ,cu#b,p#b1 was obtained by ,granger 7#ahic7 by heating a mixture of water1 finely divided copper and red phosphorus in a sealed tube to #acj4 ,the excess of copper was afterwards washed away by a solution of ,,nh#c in the presence of air4 #g ,the metallic compounds of phosphorus possess a great chemical interest1 because they show a transition from metallic alloys 7for instance1 of ,sb1 ,as7 to the sulphides1 halogen salts1 and oxides1 and on the other hand to the nitrides4 ,although there are already many fragmentary data on the subject1 the interesting province of the metallic phosphides cannot yet be regarded as in any way generalised4 ,the varied applications 7phosphor-iron1 phosphor-bronze1 c471 which the phosphides have recently acquired should give a strong incentive to the complete and detailed study of this subject1 which would1 in my opinion1 help to the explanation of chemical relations beginning with alloys 7solutions7 and ending with salts and the compounds of hydrogen 7hydrides71 because the phosphor-metals1 as is proved by direct experiment1 stand in the same relation to phosphuretted hydrogen as the sulphides do towards sulphuretted hydrogen1 or as the metallic chlorides to hydrochloric acid4 #g bis ,many other compounds of phosphorus are also capable of forming phosphuretted hydrogen4 ,thus ,,bp also gives ,,ph#c 7see ,chapter ,,xvii41 ,note #ab74 ,according to ,lpke 7#ahij7 phosphuretted hydrogen is formed by phosphide of tin4 ,the latter is prepared by treating molten tin covered with a layer of carbonate of ammonium1 with red phosphorus2 #bjj-cjj c4c4 of water are then poured into a flask1 #c-e grams of this phosphide of tin dropped in1 and after driving out the air by a stream of carbonic acid1 hydrochloric acid 7sp4 gr4 #aajd7 is poured in4 ,the disengagement of phosphuretted hydrogen takes place on heating the flask in a water bath4 ,the following is another easy method for preparing ,,ph#c4 ,a mixture of #a part of zinc dust 7fume7 and #b parts of red phosphorus are heated in an atmosphere of hydrogen 7the mixture burns in air74 ,combination takes place accompanied by a flash1 and a grey mass of ,zn#c,p#b is formed which gives ,,ph#c when treated with dilute ,h#b,,so#d4 #h ,the spontaneous inflammability of the hydride ,,ph#b in air is very remarkable1 and it is particularly interesting that its analogues in composition1 ,p7,c#b;,h#e7b 7the formula must be doubled7 and ,zn7,c#b;,h#e7b1 also take fire spontaneously in air4 #h bis ,the analogy between ,,ph#c and ,,nh#c is particularly clear in the hydrocarbon derivatives4 ,just as ,,nh#b,r1 ,,nhr#b1 and ,,nr#c1 where ,r is ,,ch#c1 and other hydrocarbon radicles1 correspond to ,,nh#c1 so there are actually similar compounds corresponding to ,,ph#c4 ,these compounds form a branch of organic chemistry4 #i ,the periodic law and direct experiment 7the molecular weight7 show that ,,ph#c is the normal compound of ,p and ,h and that it is more simple than ,,ph#b or ,p#b;,h#d1 just as methane1 ,,ch#d1 is more simple than ethane1 ,c#b;,h#f1 whose empirical composition is ,,ch#c4 ,the formation of liquid phosphuretted hydrogen may be understood from the law of substitution4 ,the univalent radicle of ,,ph#c is ,,ph#b1 and if it is combined with ,h in ,,ph#c it replaces ,h in liquid phosphuretted hydrogen1 which thus gives ,p#b;,h#d4 ,this substance corresponds with free amidogen 7hydrazine71 ,n#b;,h#d 7,chapter ,,vi47 ,probably ,p#b;,h#d is able to combine with ,,hi1 and perhaps also with #b;,,hi1 or other molecules--that is1 to give a substance corresponding to phosphonium iodide4 ,phosphonium iodide1 ,,ph#d;,i1 may be prepared1 according to ,baeyer1 in large quantities in the following manner3--#ajj parts of phosphorus are dissolved in dry carbon bisulphide in a tubulated retort3 when the mixture has cooled1 #age parts of iodide are added little by little1 and the carbon bisulphide is then distilled off1 this being done towards the end of the operation in a current of dry carbonic anhydride at a moderate temperature4 ,the neck of the retort is then connected with a wide glass tube1 and the tubulure with a funnel furnished with a stopcock1 and containing #ej parts of water4 ,this water is added drop by drop to the phosphorous iodide1 and a violent reaction takes place1 with the evolution of hydriodic acid and phosphonium iodide4 ,the latter collects as crystals in the glass tube and the retort itself4 ,it is purified by further distillations2 more than #ajj parts may be obtained4 ,baeyer expresses the reaction by the equation ,p#b;,i #b;,h#b,o ,,ph#d;,i ,,po#b2 and the compound ,,po#b may be represented as phosphorous phosphoric anhydride3 ,p#b,o#e ,p#b,o#c #d,,po#b4 ,as a better proportion we may take #djj grams of phosphorus1 #fhj grams of iodine1 and #bdj grams of water1 and express the formation thus3 #ac,p #i;,i #ba;,h#b,o #c;,h#d,p#b,o#g #g,,ph#d;,i #b;,,hi 7,chapter ,,xi41 ,note #gg74 ,phosphonium iodide and even phosphine act as reducing agents in solutions of many metallic salts4 ,cavazzi showed that with a solution of sulphurous anhydride phosphine gives sulphur and phosphoric acid4 ,phosphuretted hydrogen1 or phosphine1 ,,ph#c1 is generally prepared by the action of caustic potash on phosphorus4#aj ,small pieces of phosphorus are dropped into a flask containing a strong solution of caustic potash and heated4 ,potassium hypophosphite1 ,h#b,,kpo#b1 is then obtained in solution2 gaseous phosphuretted hydrogen is evolved3 ,p#d #c,,kho #c;,h#b,o #c7,,kh#b,,po#b7 ,,ph#c4 ,liquid phosphuretted hydrogen 7and free hydrogen7 is also formed1 together with the phosphine1 so that the gaseous product1 on escaping from the water into the air1 takes fire spontaneously1 forming beautiful white rings of phosphoric acid4 ,in this experiment1 as in that with calcium phosphide1 it is the liquid1 ,p#b;,h#d1 that takes fire2 but the phosphine set light to by it also burns1 ,,ph#c ,o#d ,,ph#c,o#d4 ,the same phosphuretted hydrogen1 ,,ph#c1 may be obtained pure1 and not spontaneously combustible1 by igniting the hydrates of phosphorous acid 7#d,,ph#c,o#c ,,ph#c #c,,ph#c,o#d7 and hypophosphorous acid 7#b,,ph#c,o#b ,,ph#c ,,ph#c,o#d72 or1 more simply1 by the decomposition of calcium phosphide by hydrochloric acid1 because then all the liquid phosphide1 ,p#b;,h#d1 is decomposed into non-volatile ,p#b;,h and gaseous ,,ph#c4 ,pure phosphine liquefies when cooled to -#ij1 boils at -#he1 and solidifies at -#ace 7,olszewski74 ,when phosphorus burns in an excess#aj bis of dry oxygen1 then only phosphoric anhydride1 ,p#b,o#e is formed4 ,it is prepared by dropping pieces of phosphorus through a wide tube1 fixed into the upper neck of a large glass globe1 on to a cup suspended in the centre of the globe4 ,these lumps are set alight by touching them with a hot wire1 and the phosphorus burns into ,p#b,o#e4 ,the dry air necessary for its combustion is forced into the globe through a lateral neck1 and the white flakes of phosphoric anhydride formed are carried by the current of air through a second lateral neck into a series of ,woulfe's bottles1 where they settle as friable white flakes4 ,phosphoric anhydride may also be formed by passing dry air through a solution of phosphorus in carbon bisulphide4 ,all the materials for the preparation of this substance must be carefully dried1 because it combines with great eagerness with water1 at the same time developing a large amount of heat and forming metaphosphoric acid1 ,,hpo#c1 from which the water cannot be separated by heat4 ,phosphoric anhydride is a colourless snow-like substance1 which attracts moisture from the air with the utmost avidity4 ,it fuses at a red heat1 and then volatilises4 ,its affinity for water is so great that it takes it up from many substances4 ,thus it converts sulphuric acid into sulphuric anhydride1 and carbohydrates 7wood1 paper7 are carbonised1 and give up the elements of water when brought into contact with it4 #aj ,the air must first be expelled from the flask by hydrogen1 or some other gas which will not support combustion1 as otherwise an explosion might take place owing to the spontaneous inflammability of the phosphuretted hydrogen4 ,the combustion of phosphuretted hydrogen in oxygen also takes place under water when the bubbles of both gases meet1 and it is very brilliant4 ,the phosphuretted hydrogen obtained by the action of phosphorus on caustic potash always contains free hydrogen1 and often even the greater part of the gas evolved consists of hydrogen4 ,pure phosphuretted hydrogen 7not containing hydrogen or liquid or solid phosphides7 is obtained by the action of a solution of potash on phosphonium iodide3 ,,ph#d;,i ,,kho ,,ph#c ,,ki ,h#b,o 7in just the same way as ammonia is liberated from ammonium chloride74 ,the reaction proceeds easily1 and the purity of the gas is seen from the fact that it is entirely absorbed by bleaching powder and is not spontaneously inflammable4 ,its mixture with oxygen explodes when the pressure is diminished 7,chapter ,,xviii41 ,note #h74 ,the vapours of bromine1 nitric acid1 c41 cause it to again acquire the property of inflaming in the air2 that is1 they partially decompose it1 forming the liquid hydride1 ,p#b;,h#d4 ,oppenheim showed that when red phosphorus is heated at #bjj with hydrochloric acid in a closed tube it forms the compound ,p,cl#c7;,h#c,,po#c71 together with phosphine4 #aj bis ,if there be a deficiency of oxygen1 phosphorous anhydride ,p#b,o#c is formed4 ,it was obtained by ,thorpe and ,tutton 7#ahij7 and is easily volatilised1 melts at #bbe1 boils without change 7in an atmosphere of ,n#b or ,,co#b7 at #agc1 and is therefore easily separated from ,p#b,o#c1 which volatilises with difficulty4 ,the vapour density shows that the molecular weight is double1 i4e4 ,p#d,o#f 7like ,as#b,o#c74 ,although colourless1 phosphorous anhydride 7its density in a state of fusion at #bd #aicf7 turns yellow and reddens in sun-light 7possibly red phosphorus separates out 871 and decomposes at #djj forming hypophosphorous anhydride ,p#b,o#d 7,note #aa7 and phosphorus4 ,it passes into ,p#b,o#e in air and oxygen1 and when slightly heated in oxygen becomes luminous1 and ultimately takes fire4 ,cold water slowly transforms ,p#b,o#c into phosphoric acid1 but hot water gives an explosion and leads to the formation of ,,ph#c1 7,p#d,o#f #f;,h#b,o ,,ph#c #c,,ph#c,o#d74 ,alkalis act in the same manner4 ,it takes fire in chlorine and forms ,p,o,cl#c and ,,po#b;,cl1 and combines with sulphur at #afj1 forming ,p#b,s#b,o#c 7the molecular formula is double this7 a substance which volatilises in vacuo and is decomposed by water into ,h#b,s and phosphoric acid1 i4e4 it may be regarded as ,p#b,o#e1 in which ,o#b has been replaced by two atoms of sulphur4 ,judging from the above1 the mixture of ,p#b,o#c and ,p#b,o#e formed in the combustion of phosphorus in air is transformed into ,p#b,o#e in an excess of oxygen4 ,when moist phosphorus slowly oxidises in the air1 it not only forms phosphorous and phosphoric acids1 but also hypophosphoric acid1 ,h#d,p#b,o#f1 which when in a dry state easily splits up at #fj into phosphorous and metaphosphoric acids 7,h#d,p#b,o#f ,h#c,,po#c ,,hpo#c71 but differs from a mixture of these acids in that it forms well-characterised salts1 of which the sodium salt1 ,h#b,na#b,p#b,o#f1 is but slightly soluble in water 7the sodium salts of phosphoric and phosphorous acids are easily soluble71 and that it does not act as a reducing agent1 like mixtures containing phosphorous acid4#aa #aa ,salzer proved the existence of hypophosphoric acid 7it is also called subphosphoric acid71 in which many chemists did not believe4 ,drawe 7#ahhh7 and ,rammelsberg 7#ahib7 investigated its salts4 ,it may be obtained in a free state by the following method4 ,the solution of acid produced by the slow oxidation of moist phosphorus is mixed with a solution 7#be p4c47 of sodium acetate4 ,a salt1 ,na#b;,h#b,p#b,o#f1f;,h#b,o1 crystallises out on cooling2 it is soluble in #de parts of water1 and gives a precipitate of ,pb#b,p#b,o#f with lead salts 7,ag#d,p#b,o#f with salts of silver74 ,the lead salt is decomposed by a current of hydrogen sulphide1 when lead sulphide is precipitated1 while the solution1 evaporated under the receiver of an air-pump1 gives crystals of ,h#d,p#b,o#f1b;,h#b,o1 which easily lose water and give ,h#d,p#b,o#f4 ,the salts in which the ,h#d is replaced by ,ni#b1 or ,ni,na#b1 or ,cd,na#b1 c41 are insoluble in water4 ,in order to see the relation between phosphoric acid and hypophosphoric acid which does not contain the elements of phosphorous acid 7because it does not reduce either gold or mercury from their solutions71 but which nevertheless is capable of being oxidised 7for example1 by potassium permanganate7 into phosphoric acid1 it is simplest to apply the law of substitution4 ,this clearly indicates the relation between oxalic acid1 7,,cooh7#b1 and carbonic acid1 ,,oh7,,cooh74 ,the relation between the above acids is exactly the same if we express phosphoric acid as ,,oh7,,poo#b;,h#b71 because in this case ,p#b;,h#d,o#f1 or 7,,poo#b;,h#b7c1 will correspond with it just as oxalic does with carbonic acid4 ,a similar relationship exists between hyposulphuric or dithionic acid1 7,,so#b,,oh7#b1 and sulphuric acid1 ,,oh7,,so#b,,oh71 as we shall find in the following chapter4 ,dithionic acid corresponds with the anhydride ,s#b,o#e1 intermediate between ,,so#b and ,,so#c2 oxalic acid with ,c#b,o#c1 intermediate between ,,co and ,,co#b2 hypophosphoric acid corresponds with the anhydride ,p#b,o#d1 intermediate between ,p#b,o#c and ,p#b,o#e1 and the analogue of ,n#b,o#d4 ,judging by the general law of the formation of acids 7,chapter ,,xv471 the series of phosphorus compounds should include the following ortho-acids and their corresponding anhydrides1 answering to phosphuretted hydrogen1 ,h#c,p3-- ,h#c,,po#d1 phosphoric acid1 and ,p#b,o#e1 anhydride1 ,h#c,,po#c1 phosphorous acid1 and ,p#b,o#c1 anhydride1 ,h#c,,po#b1 hypophosphorous acid1 and ,p#b,o1 anhydride4#ab ,the last of these 7the analogue of ,n#b,o7 is almost unknown4 ,phosphoric anhydride 7,p#b,o#e7 with a small quantity of water does not at first give orthophosphoric acid1 ,,ph#c,o#d1 but a compound ,p#b,o#e1;,h#b,o1 or ,,pho#c1 whose composition corresponds with that of nitric acid2 this is metaphosphoric acid4 ,even with an excess of water1 combining with phosphoric anhydride1 this metaphosphoric acid1 and not the ortho-1 passes at first into solution4 ,metaphosphoric acid in solution only passes into orthophosphoric acid when the solution is heated or after a lapse of time4 #ab ,besides the hydrates enumerated1 a compound1 ,,ph#c,o1 should correspond with ,,ph#c4 ,this hydrate1 which is analogous to hydroxylamine1 is not known in a free state1 but it is known as triethylphosphine oxide1 ,p7,c#b;,h#e7c,o1 which is obtained by the oxidation of triethylphosphine1 ,p7,c#b;,h#e7c4 ,it must be observed that there may also be lower oxides of phosphorus corresponding with ,,ph#c1 like ,n#b,o and ,,no1 and there are even indications of the formation of such compounds1 but the data concerning them cannot be considered as firmly established4 ,orthophosphoric acid#ac is obtained by oxidising phosphorus with nitric acid until the phosphorus entirely passes into solution and the lower oxides of nitrogen cease to be evolved4 ,the reaction takes place best with dilute nitric acid1 and when aided by heat4 ,the resultant solution is evaporated to a syrup4 ,if a weighed quantity of phosphorus 7dried in a current of dry carbonic anhydride7 be taken1 a crystalline mass of the acid can be obtained by evaporating the solution until it consists only of the quantity#ad of phosphoric acid corresponding with the amount of phosphorus taken 7from #ca parts of ,p1 #ih parts of solution74 ,the acid fuses at #ci2 specific gravity of the liquid #ahh4 ,phosphorus pentachloride1 ,p,cl#e1 and oxychloride1 ,p,o,cl#c 7see further on71 give orthophosphoric acid and hydrochloric acid with water4 ,the two other varieties of phosphoric acid1 with which we shall presently become acquainted1 give the same ortho-acid when under the influence of acids1 with particular ease when boiled and more slowly in the cold4 ,by itself orthophosphoric acid 7either in solution or when dry7 does not pass into the other varieties2 it does not oxidise1 and therefore presents the limiting and stable form4 ,when heated to #cjj1 it loses water and passes into pyrophosphoric acid1 #b;,h#c,,po#d ,h#b,o ,h#d,p#b,o#g1 whilst at a red heat it loses twice as much water and is converted into metaphosphoric acid1 ,h#c,,po#d ,h#b,o ,,hpo#c4 ,in aqueous solution orthophosphoric acid differs clearly from pyro- or metaphosphoric acids1 because the solutions of these latter acids give different reactions3 thus orthophosphoric acid does not precipitate albumin1 does not give a precipitate with barium chloride1 and forms a yellow precipitate of silver orthophosphate1 ,ag#c,,po#d1 with silver nitrate 7in the presence of alkalis1 but not otherwise72 whilst a solution of pyrophosphoric acid1 ,h#d,p#b,o#g1 although it does not precipitate albumin or barium chloride1 gives a white precipitate of silver pyrophosphate1 ,ag#d,p#b,o#g1 with silver nitrate2 and a solution of metaphosphoric acid1 ,,hpo#c1 precipitates both albumin and barium chloride1 and gives a white precipitate of silver metaphosphate1 ,ag,p,o#c1 with silver nitrate4 ,these points of distinction were studied by ,graham1 and are exceedingly instructive4 ,they show that the solution of a substance does not determine the maximum of chemical combination with water1 that solutions may contain various degrees of combination with water1 and that there is a clear difference between the water serving for solution and that entering into chemical combination4 ,graham's experiments also showed that the water whose removal or combination determines the conversion of ortho- into meta- and pyrophosphoric acids differs distinctly from water of crystallisation1 for he obtained the salts of ortho-1 meta-1 and pyrophosphoric acids with water of crystallisation1 and they differed in their reactions1 like the acids themselves4 ,this water of crystallisation was expelled with greater ease than the water of constitution of the hydrates in question4#ad bis #ac ,phosphoric acid1 being a soluble and almost non-volatile substance1 cannot be prepared like hydrochloric and nitric acids by the action of sulphuric acid on the alkali phosphates1 although it is partially liberated in the process4 ,for this purpose the salts of barium or lead may be taken1 because they give insoluble salts1 thus ,ba#c7,,po#d7b #c;,h#b,,so#d #c;,ba,s,o#d #b;,h#c,,po#d4 ,bone ash contains1 besides calcium phosphate1 sodium and magnesium phosphates1 and fluorides and other salts1 so that it cannot give directly a pure phosphoric acid4 #ad ,if this is not done the orthophosphoric acid1 ,,ph#c,o#d1 loses a portion of its water1 and then1 as with an excess of water1 it does not crystallise4 #ad bis ,the difference between the reactions of ortho-1 meta- and pyrophosphoric acids1 established by ,graham 7see p4 #afc71 is of such importance for the theory of hydrates and for explaining the nature of solutions1 that in my opinion its influence upon chemical thought has been far from exhausted4 ,at the present time many such instances are known both in organic 7for instance1 the difference between the reactions of the solutions of certain anhydrides and hydrates of acids71 and inorganic chemistry 7for example1 the difference between the rose and purple cobalt compounds1 ,chapter ,,xxii4 c47 ,they essentially recall the long known and generalised difference between ,c#b;,h#d 7ethylene71 ,c#b;,h#f,o 7ethyl alcohol ethylene water71 and ,c#d;,h#aj,o 7ethyl ether #b ethylene water #b alcohol - water72 but to the present day the numerous analogous phenomena existing among inorganic substances are only considered as a simple difference in degrees of affinity1 distinguishing the water of constitution 7hydration71 crystallisation1 and solution without penetrating into the difference of the structure or distribution of the elements1 which exists here and gives rise to a distinct isomerism of solutions4 ,in my opinion the progress of chemistry1 especially with regard to solutions1 should make rapid strides when the cause of the isomerism of solutions1 for instance1 of ortho- and pyrophosphoric acids1 has become as clear to us as the cause of many well-studied instances of the isomerism1 polymerism1 and metamerism of organic compounds4 ,here it forms one of those many important problems which remain for the chemistry of the future in a state of only indistinct presentiments and in the form of facts empirically known but insufficiently comprehended4 ,orthophosphoric acid has a pleasant acid taste and a distinctly acid reaction2 it is used as a medicine1 and is not poisonous 7phosphorous acid is poisonous74 ,alkalis1 like sodium1 potassium1 and ammonium hydroxides1 saturate the acid properties of phosphoric acid when taken in the ratio #b,na,h,o 3 ,h#c,,po#d--that is1 when salts of the composition ,h,na#b,,po#d are formed4 ,when taken in the ratio ,na,h,o 3 ,h#c,,po#d1 a solution having an acid reaction is obtained1 and when #c,na,h,o 3 ,h#c,,po#d--that is1 when the salt ,na#c,,po#d is formed--an alkaline reaction is obtained4 ,hence many chemists 7,berzelius7 even regarded the salts of composition ,r#b;,,hpo#d as normal1 and considered phosphoric acid to be bibasic4 ,but the salt ,na#b;,,hpo#d also shows a feeble alkaline reaction1 so that it is impossible to judge the characteristic peculiarities of acids by the reactions on litmus paper1 as we already know from many examples4 ,orthophosphoric acid is tribasic1 because it contains three equivalents of hydrogen replaceable by metals1 forming salts1 such as ,na,h#b,,po#d1 ,na#b;,,hpo#d1 and ,na#c,,po#d4 ,it is also tribasic1 because with silver nitrate its soluble salts always give ,ag#c,,po#d1ae a salt with three equivalents of silver1 and because by double decomposition with barium chloride it forms a salt of the composition ,ba#c7,,po#d7b1 and silver and barium hardly ever give basic salts4 ,with the metals of the alkalis1 phosphoric acid forms soluble salts1 but the normal salts of the metals of the alkaline earths1 ,r#c7,,po#d7b and even ,r#b;,h#b7,,po#d71 are insoluble in water1 but dissolve in feeble acids1 such as phosphoric and acetic1 because they then form soluble acid salts1 especially ,,rh#d7,,po#d7b4af #ae ,silver orthophosphate1 ,ag#c,,po#d1 is yellow1 sp4 gr4 #gcb1 and insoluble in water4 ,when heated it fuses like silver chloride1 and if kept fused for some length of time it gives a white pyrophosphate 7the decomposition which causes this is not known74 ,it is soluble in aqueous solutions of phosphoric1 nitric1 and even acetic acids1 of ammonia1 and many of its salts4 ,if silver nitrate acts on a dimetallic orthophosphate--for instance1 ,na#b;,,hpo#d--;it still gives ,ag#c,,po#d1 nitric acid being disengaged3 ,na#b;,,hpo#d #c;,ag,n,o#c ,ag#c,,po#d #b,na,n,o#c ,,hno#c4 ,when alcohol is added to silver orthophosphate1 ,ag#c,,po#d1 dissolved in syrupy phosphoric acid1 it precipitates a white salt 7the alcohol takes up the free phosphoric acid7 having the composition ,ag#b;,,hpo#d1 which is immediately decomposed by water into the normal salt and phosphoric acid4 #af ,the researches of ,thomsen showed that in very dilute aqueous solutions the majority of monobasic acids--nitric1 acetic1 hydrochloric1 c4 7but hydrofluoric acid more and hydrocyanic less7--,,hx evolve the following amounts of heat 7in thousands of calories7 with caustic soda3 ,na,h,o #b;,,hx #ad2 ,na,h,o ,,hx #ad2 #b,na,h,o ,,hx #ad2 that is1 if n be a whole number n,na,h,o ,,hx #ad and ,na,h,o n,,hx #ad4 ,hence reaction here only takes place between one molecule of ,na,h,o and one molecule of acid1 and the remaining quantity of acid or alkali does not enter into the reaction4 ,in the case of bibasic acids1 ,h#b,r 7sulphuric1 dithionic1 oxalic1 sulphuretted hydrogen1 c471 ,na,h,o #b;,h#b,r #ad2 ,na,h,o ,h#b,r #ad2 #b,na,h,o ,h#b,r #bh2 n,na,h,o ,h#b,r #bh2 that is1 with an excess of acid 7,na,h,o #b;,h#b,r7 #ad thousand units of heat are developed1 and with an excess of alkali #bh4 ,when phosphoric acid is taken 7but not all tribasic acids--for instance1 not citric7 the general character of the phenomenon is similar to the preceding1 namely1 ,na,h,o #b;,h#c,,po#d #adg2 ,na,h,o ,h#c,,po#d #adh2 #b,na,h,o ,h#c,,po#d #bga2 #c,na,h,o ,h#c,,po#d #cdj2 #f,na,h,o ,h#c,,po#d #cec2 or1 in general terms1 ,na,h,o n,h#c,,po#d #ad 7approximately7 and n,na,h,o ,h#c,,po#d #ce and not #db1 which shows a peculiarity of phosphoric acid4 ,in the case of energetic acids1 when one equivalent 7#bc grams7 of sodium 7in the form of hydroxide7 replaces one equivalent 7#a gram7 of hydrogen 7with the formation of water and in dilute solutions71 #ad1jjj heat units are evolved2 and this is true for phosphoric acid when in ,h#c,,po#d1 ,na or ,na#b replaces ,h or ,h#b1 but when ,na#c replaces ,h#c less heat is developed4 ,this will be seen from the following scheme based on the preceding figures3 ,h#c,,po#d ,na,h,o #adh2 ,na,h#b,,po#d ,na,h,o #abc2 ,na#b;,,hpo#d ,na,h,o #ei2 with ,na#c,,po#d ,na,h,o1 a very small amount of heat is evolved1 as may be judged from the fact that ,na#c,,po#d #c,na,h,o #ac1 but still heat is evolved4 ,it must be supposed that in acting on phosphoric acid in the presence of a large quantity of water1 a certain portion of the sodium hydroxide remains as alkali uncombined with the acid4 ,thus1 on increasing the mass of the alkali1 heat is still evolved1 and a fresh interchange between ,na and ,h takes place4 ,hence water shows a decomposing action on the alkali phosphates4 ,the same decomposing action of water is seen1 but to a less extent1 with ,na#b;,,hpo#d1 as may be judged both from the reactions of this salt and from the amount of heat developed by ,na,h#b,,po#d with ,na,h,o4 ,such an explanation is in accordance with many facts concerning the decomposition of salts by water already known to us4 ,recent researches made by ,berthelot and ,louguinine have confirmed the above deductions made by me in the first edition 7#ahga7 of this work4 ,at the present time views of this nature are somewhat generally accepted1 although they are not sufficiently strictly applied in other cases4 ,as regards ,,ph#c,o#d it may be said that3 on the substitution of the first hydrogen this acid acts as a powerful acid 7like ,h,cl1 ,,hno#c1 ,h#b,,so#d72 on the substitution of the second hydrogen as a weaker acid 7like an organic acid72 and on the substitution of the third1 as an alcohol1 for instance phenol1 having the properties of a feeble acid4 ,phosphoric anhydride1 or any of its hydrates1 when ignited with an excess of sodium hydroxide1 carbonate1 c41 forms normal or trisodium orthophosphate1 ,na#c,,po#d1 but when a solution of sodium carbonate is decomposed by orthophosphoric acid1 only the salt ,na#b;,,hpo#d is formed2 and when an excess of sodium chloride is ignited with orthophosphoric acid1 hydrochloric acid is evolved1 and the acid salt ,h#b,na,p,o#d alone is formed4 ,these facts clearly indicate the small energy of phosphoric acid with respect to the formation of the tri-metallic salt1 which is seen further from the fact that the salt ,na#c,,po#d has an alkaline reaction1 decomposes in the presence of water and carbonic acid1 forming ,na#b;,,hpo#d1 corrodes glass vessels in which it is boiled or evaporated1 just like solutions of the alkalis1 disengages1 like them1 ammonia from ammonium chloride1 and crystallises from solutions1 as ,na#c,,po#d1ab;,h#b,o1 only in the presence of an excess of alkali4 ,at #ae the crystals of this salt require five parts of water for solution2 they fuse at #gg4 ,disodium orthophosphate1 or common sodium phosphate1 ,na#b;,,hpo#d1 is more stable both in solution and in the solid state4 ,as it is used in medicine and in dyeing1 it is prepared in considerable quantities1 most frequently from the impure phosphoric acid obtained by the action of sulphuric acid on bone ash4 ,the solution thus formed--which contains1 besides phosphoric and sulphuric acids1 salts of sodium1 calcium1 and magnesium--is heated1 and sodium carbonate added so long as carbonic anhydride is disengaged4 ,a precipitate is formed containing the insoluble salts of magnesium and calcium1 whilst the solution contains sodium phosphate1 ,na#b;,,hpo#d1 with a small quantity of other salts1 from which it may be easily purified by crystallisation4 ,at the ordinary temperature its solutions1 especially in the presence of a small amount of sodium carbonate1 give finely-formed inclined prismatic crystals1 ,na#b;,,hpo#d1ab;,h#b,o2 when the crystallisation takes place above #cj they only contain #g;,h#b,o4 ,the former crystals even lose a portion of their water of crystallisation at the ordinary temperature 7the salt effloresces71 and form the second salt with #g;,h#b,o2 whilst under the receiver of an air-pump and over sulphuric acid they also part with this water4#ag ,when ignited they lose the last molecule of water of constitution1 and give sodium pyrophosphate1 ,na#d,p#b,o#g4 #ag ,na#b;,,hpo#d1ab;,h#b,o has a sp4 gr4 #aec4 ,poggiale determined the solubility in #ajj parts of water 7#a7 of the anhydrous ortho-salt ,na#b;,,hpo#d1 and 7#b7 of the corresponding pyro-salt ,na#d,p#b,o#g3-- #j #bj #dj #hj #ajj ,i4 #ae #aaa #cji #ha #ajh ,,ii4 #cb #fb #ace #cj #dj ,at temperatures of #bj to #ajj the ortho-salt is so very much less soluble that this difference alone already indicates the deeply-seated alteration in constitution which takes place in the passage from the ortho- to the pyro-salts4 ,monosodium orthophosphate1 ,na,h#b,,po#d1 crystallises with one equivalent of water2 its solution has an acid reaction4 ,at #ajj the salt only loses this water of crystallisation1 and at about #bjj it parts with all its water1 forming the metaphosphate ,na,p,o#c4 ,it is prepared from ordinary sodium phosphate by adding phosphoric acid until the solution does not give a precipitate with barium chloride1 and then evaporating and crystallising the solution4 ,the solution of this salt does not absorb carbonic anhydride1 and does not give a precipitate with salts of calcium1 barium1 c4#ah #ah ,the ammonium orthophosphates resemble the sodium salts in many respects1 but the instability of the di- and tri-metallic salts is seen in them still more clearly than in the sodium salts2 thus 7,,nh#d7c,,po#d1 and even 7,,nh#d7b;,,hpo#d1 lose ammonia in the air 7especially when heated1 even in solutions72 ,,nh#d;,h#b,,po#d alone does not disengage ammonia and has an acid reaction4 ,the crystals of the first salt contain #c;,h#b,o1 and are only formed in the presence of an excess of ammonia2 both the others are anhydrous1 and may be obtained like the sodium salts4 ,when ignited these salts leave metaphosphoric acid behind2 for example1 7,,nh#d7b;,,hpo#d #b,,nh#c ,h#b,o ,,hpo#c4 ,ammonia also enters into the composition of many double phosphates4 ,ammonium sodium orthophosphate1 or simply phosphate1 ,,nh#d,na,h,p,o#d1d;,h#b,o1 crystallises in large transparent crystals from a mixture of the solutions of disodium phosphate and ammonium chloride 7in which case sodium chloride is obtained in the mother liquid71 or1 better still1 from a solution of monosodium phosphate saturated with ammonia4 ,it is also formed from the phosphates in urine when it ferments4 ,this salt is frequently used in testing metallic compounds by the blow-pipe1 because when ignited it leaves a vitreous metaphosphate1 ,na,p,o#c1 which1 like borax1 dissolves metallic oxides1 forming characteristic tinted glasses4 ,when a solution of trisodium phosphate is added to a solution of a magnesium salt it gives a white precipitate of the normal orthophosphate ,mg#b7,,po#d7b1g;,h#b,o4 ,if the trisodium salt be replaced by the ordinary salt1 ,na#b;,,hpo#d1 a precipitate is also formed1 and ,mg,h,p,o#d1g;,h#b,o is obtained4 ,it might be thought that the normal salt ,mg#c7,,po#d7b would be precipitated if disodium phosphate was added to ammonia and a salt of magnesium1 but in reality ammonium magnesium orthophosphate1 ,mg,n,h#d,,po#d1f;,h#b,o1 is precipitated as a crystalline powder1 which loses ammonia and water when ignited1 and gives a pyrophosphate1 ,mg#b,p#b,o#g4 ,this salt occurs in nature as the mineral struvite1 and in various products of the changes of animal matter4 ,if we consider that the above salt parts with ammonia with difficulty1 and that the corresponding salt of sodium is not formed under the same conditions 7,mg,na,p,o#d1i;,h#b,o is obtained by the action of magnesia on disodium phosphate71 if we turn our attention to the fact that the salts of calcium and barium do not form double salts as easily as magnesium1 and remember that the salts of magnesium in general easily form double ammonium salts1 we are led to think that this salt is not really a normal1 but an acid salt1 corresponding with ,na#b;,,hpo#d1 in which ,na#b is replaced by the equivalent group ,,nh#c,mg4 ,the common normal calcium phosphate1 ,ca#c7,,po#d7b1 occurs in minerals1 in animals1 especially in bones1 and also probably in plants1 although the ash of many portions of plants1 as a rule1 contains less lime than the formation of the normal salt requires4 ,thus #ajj parts of the ash 7from #e1jjj parts of grain7 of rye grain contain #dge of phosphoric anhydride and only #bg of lime1 and even the ash of the whole of the rye 7including the straw7 contains twice as much phosphoric anhydride as lime1 and the normal salt contains almost equal weights of these substances4 ,only the ash of grasses1 and especially of clover1 and of trees1 contains in the majority of cases more lime than is required for the formation of ,ca#c,p#b,o#h4 ,this salt1 which is insoluble in water1 dissolves even in such feeble acids as acetic and sulphurous1 and even in water containing carbonic acid4 ,the latter fact is of immense importance in nature1 since by reason of it rain water is able to transfer the calcium phosphates in the soil into solutions which are absorbed by plants4 ,the solubility of the normal salt in acids takes place by virtue of the formation of an acid salt1 which is evident from the quantity of acid required for its solution1 and more especially from the fact that the acid solutions when evaporated give crystalline scales of the acid calcium phosphate1 ,ca,h#d7,,po#d7b1 soluble in water4 ,this solubility of the acid salt forms the basis of the treatment by acids of bones1 phosphorites1 guano1 and other natural products containing the normal salt and employed for fertilising the soil4 ,the perfect decomposition requires at least #b;,h#b,,so#d to ,ca#c7,,po#d7b1 but in reality less is taken1 so that only a portion of the normal salt is converted into the acid salt4 ,hydrochloric acid is sometimes used4 7,in practice such mixtures are known as superphosphates74 ,certain experiments1 however1 show that a thorough grinding1 the presence of organic1 and especially of nitrogenous1 substances1 and the porous structure of some calcium phosphates 7for example1 in burnt bones71 render the treatment of phosphoric manures by acids superfluous--that is1 the crop is not improved by it4 ,as a hydrate1 orthophosphoric acid should be expressed1 after the fashion of other hydrates1 as containing three water residues 7hydroxyl groups71 i4e4 as ,,po7,,oh7#c4 ,this method of expression indicates that the type ,,px#e1 seen in ,,ph#d;,i1 is here preserved1 with the substitution of ,x#b by oxygen and ,x#c by three hydroxyl groups4 ,the same type appears in ,p,o,cl#c1 ,p,cl#e1 ,,pf#e1 c4 ,and if we recognise phosphoric acid as ,,po7,,oh7#c1 we should expect to find three anhydrides corresponding with it3 7#a7 ,,po7,,oh7#bb,o1 in which two of the three hydroxyls are preserved2 this is pyrophosphoric acid1 ,h#d,p#b,o#g4 7#b7 ,,po7,,oh7,o1 where only one hydroxyl is preserved4 ,this is metaphosphoric acid4 7#c7 7,,po7#b,o#c or ,p#b,o#e1 that is1 perfect phosphoric anhydride4 ,therefore1 pyro- and metaphosphoric acids are imperfect anhydrides 7or anhydro-acids7 of orthophosphoric acid4#ai #ai ,in this sense the ortho-acid itself might be regarded as an anhydro-acid1 counting ,p7,,ho7#e as the perfect hydrate1 if ,,ph#e existed2 but as in general the normal hydrates correspond with the existing hydrogen compounds with the addition of up to #d atoms of oxygen1 therefore ,,ph#c,o#d is the normal acid1 just as ,,sh#b,o#d and ,cl,h,o#d2 while ,,nho#c1 ,,ch#b,o#c are meta-acids1 or higher normal acids 7,,nh#c,o#d and ,,ch#d,o#d7 with the loss of a molecule of water4 ,in order to see the relation between the ortho-1 pyro-1 and metaphosphoric acids1 the first thing to remark in them is that the anhydride ,p#b,o#e is combined with #c1 #b1 and #a molecules of water4 ,in the absence of data for the molecular weight of ortho- and pyrophosphoric acids it is necessary to mention that all existing data for metaphosphoric acid indicate 7,note #ba7 that its molecule is much more complex and contains at least ,h#c,p#c,o#i or ,h#f,p#f,o#ah4 ,the explanation of the problems which here present themselves can1 it seems to me1 be only looked for after a detailed study of the phenomena of the polymerisations of mineral substances1 and of those complex acids1 such as phosphomolybdic1 which we shall hereafter describe 7,chapter ,,xxi47 ,a similar instance is exhibited in the solubility of hydrate of silica 7produced by the action of silicon fluoride on water7 in fused metaphosphoric acid1 with the formation1 on cooling1 of an octahedral compound 7sp4 gr41 #ca7 containing ,si,o#b1,p#b,o#e4 ,a certain indication 7but no proof7 that ordinary orthophosphoric acid is polymerised is given by ,staudenmaier 7#ahic71 who obtained a salt1 ,k#e;,h#d,p#c,o#ab1 by the action of a solution of ,,kh#b,,po#d upon ,k#b;,,co#c2 and a compound1 ,,kh#c,p#b,o#h1 corresponding to the doubled molecule of ,h#c,,po#d1 by the action of ,,kh#b,,po#d upon ,h#c,,po#d itself4 ,pyrophosphoric acid1 ,h#d,p#b,o#g1 is formed by heating orthophosphoric acid to #bej when it loses water4#ai bis ,its normal salts are formed by igniting the dimetallic salts of orthophosphoric acid of the types ,,hm#b,,po#d4 ,thus from the disodium salt we obtain sodium pyrophosphate1 ,na#d,p#b,o#g 7it crystallises from water with #aj;,h#b,o1 is very stable1 fuses when heated1 has an alkaline reaction1 and does not form ortho-salts when its solution is boiled73 and from the monosodium salt ,na,h#b,,po#d the acid salt ,na#b;,h#b,p#b,o#g 7easily soluble in water7 is formed2 this has an acid reaction1 and when ignited further gives the meta-salt4#bj #ai bis ,according to ,watson 7#ahic7 the ortho-acid is partially transformed into the pyro-acid at #bcj1 whilst at #bfj the latter begins to volatilise4 ,at #cjj the meta-acid only is formed4 #bj ,the method of preparation of the acid itself consists in converting the sodium salt1 ,na#d,p#b,o#g1 by double decomposition with water and a salt of lead1 into insoluble lead pyrophosphate1 ,pb#b,p#b,o#g1 which is then suspended in water and decomposed by sulphuretted hydrogen2 lead sulphide is thus precipitated1 and pyrophosphoric acid remains in solution4 ,this solution cannot be heated1 or the pyro-acid will pass into the ortho-1 but must be evaporated under the receiver of an air-pump4 ,it concentrates to a syrup and crystallises1 and when ignited in this form loses water1 and forms metaphosphoric acid4 ,it resembles orthophosphoric acid in many respects2 its salts with the alkalis are also soluble1 and the others insoluble in water but soluble in acids4 ,when heated in solution with acid it gives orthophosphoric acid1 as well as when fused with an excess of alkali4 ,witt heated ammonium chloride with phosphoric acid 7hydrochloric acid was evolved71 ignited the residue to drive off ammonia1 and obtained pyrophosphoric acid in the residue4 ,metaphosphoric acid1 ,,hpo#c 7the analogue of nitric acid71 is formed by the ignition of the pyro- and ortho-acids 7or1 better1 of their ammonium salts71 as a vitreous1 hygroscopic1 fused mass 7glacial phosphoric acid1 acidum phosphoricum glaciale71 soluble in water and volatilising without decomposition4 ,it is also formed in the first slow action of cold water on the anhydride1 but metaphosphoric acid gradually changes into the ortho-acid when its solution is boiled1 or when it is kept for any length of time1 especially in the presence of acids4#ba #ba ,as when using phenolphthalein as an indicator in neutralising by an alkali metaphosphoric acid is monobasic1 and orthophosphoric acid is bibasic1 it is possible by means of this difference to follow the transition of meta- into orthophosphoric acid4 ,sabatier 7#ahhh7 carried on an investigation of this nature1 and found that the rate of transformation is dependent on the temperature1 and is subject to the general laws of the rate of chemical transformations which belongs to physical chemistry4 ,metaphosphoric acid has a particular interest in respect to the variations to which its salts are subject4 ,the metaphosphates are formed by the ignition of the acid orthophosphates1 ,,mh#b,,po#d1 or ,,mnh#d;,,hpo#d1 or of the acid pyrophosphates1 ,m#b;,h#b,p#b,o#g1 or ,m#b7,,nh#d7b,p#b,o#g1 water and ammonia being given off in the process4 ,the properties of the metaphosphates1 which have a similar composition to nitrates--for instance1 ,na,p,o#c1 or ,ba7,,po#c7b--vary according to the duration of the ignition to which the ortho-1 or pyrophosphates from which they are prepared have been subjected4 ,when the salts ,na,h#b,,po#d or ,,nh#d,na,h,p,o#d are strongly ignited1 a salt ,na,p,o#c is formed1 which deliquesces in the air1 and gives a gelatinous precipitate with salts of the alkaline earths4 ,but1 as ,graham 7in #ahcj-dj71 and many others1 especially ,fleitmann and ,henneberg 7in #ahdj-ej71 and ,tamman 7in the nineties71 observed1 under other conditions the salts of the same composition acquire other properties4 ,the above chemists recognise five polymeric forms of metaphosphates1 7,,hpo#c7n4 ,we will follow the nomenclature and researches of ,fleitmann4 ,monometaphosphoric acid4 ,the salts are distinguished for their insolubility in water2 even the salts ,na,p,o#c1 ,,kpo#c1 are insoluble4 ,they are obtained by igniting the monometallic orthophosphates--for example1 ,,rh#b,,po#d--up to the temperature at which all water is evolved 7#caf71 but not to fusion4 ,no double salts are known4 ,dimetaphosphoric acid1 on the contrary1 easily forms double salts--for example1 ,k,na,p#b,o#f1 and also the copper potassium salt1 c4 ,the copper salt is obtained by evaporating a solution of copper oxide in orthophosphoric acid4 ,a blue ortho-salt1 ,cu,r,h,o#d1 first separates from the solution1 then a light-blue pyro-salt1 ,cu#b,p#b,o#g2 and above #cej1 when metaphosphoric acid itself begins to volatilise1 the dimetaphosphate1 ,cu,p#b,o#f1 is formed4 ,the residue is washed with water1 and decomposed with a hot solution of sodium sulphide1 when the sodium salt1 ,na#b,p#b,o#f1 is obtained in solution4 ,this salt1 when evaporated with alcohol1 gives crystals containing #b mol4 ,h#b,o1 which1 however1 retain their solubility 7in #g parts of water7 after the water is driven off at #ajj4 ,when fused1 these crystals give a deliquescent salt 7hexa-metaphosphate74 ,the solution of the salt has a neutral reaction1 which only after prolonged boiling becomes acid1 owing to the formation of orthophosphate1 ,na,h#b,,po#d4 ,the soluble salts of dimetaphosphoric acid give the insoluble silver salt1 ,ag#b,p#b,o#f1 with silver nitrate1 and a precipitate of ,ba,p#b,o#fb;,h#b,o with barium chloride4 ,trimetaphosphoric acid is obtained as the sodium salt ,na#c,p#c,o#i when any other metaphosphate of sodium is fused and slowly cooled1 then dissolved in a slight excess of warm water1 and the resultant solution evaporated4 ,the crystals contain #f mol4 ,h#b,o1 and dissolve in four parts of water4 ,an acid reaction is only obtained1 as with the preceding salt1 after prolonged boiling with water4 ,the acid is a true analogue of nitric acid1 because all its metallic salts are soluble4 ,hexametaphosphoric acid4 ,fleitmann so named the ordinary metaphosphoric acid 7glacial7 which attracts moisture4 ,the deliquescent sodium salt is obtained1 like the trimetaphosphate1 only by rapid cooling4 ,it is also formed by fusing silver oxide with an excess of phosphoric acid4 ,the sodium salt is soluble in water1 and gives viscous1 elastic precipitates with salts of ,ba1 ,ca1 and ,mg4 ,lubert 7#ahic7 obtained salts of ,ag1 ,pb1 c4 ,jawein and ,thillot 7#ahhi71 who investigated the sodium salts of metaphosphoric acid by ,raoult's method1 came to the conclusion that the salts of di- and tri-metaphosphoric acid behave in such a manner that their molecule must be represented as non-polymerised ,na,p,o#c1 whilst those of hexametaphosphoric acid behave as 7,na,p,o#c7d4 ,at all events1 the series of salts which ,fleitmann and ,henneberg regard as monometaphosphates--i4e4 as non-polymerised--are most probably the most polymerised1 because they are insoluble4 ,according to ,tamman's researches1 vitreous metaphosphoric acid contains a mixture consisting chiefly of two varieties1 differing in the solubility and degree of stability of their salts4 ,the least stable corresponds to ,fleitmann's hexa-acid1 and gives three isomeric salts4 ,tamman came to the conclusion that there exist polymers also in the form of penta-1 ortho-1 and deca-metaphosphoric acids4 ,without going into details upon this subject1 ,i do not think it superfluous to point out that the undoubted capability of metaphosphoric acid to polymerise should be connected with its faculty of combining with water1 whilst the degree of polymerisation and the number of polymeric forms cannot yet be considered as sufficiently explained4 ,in order to see the relation between phosphoric acid and the lower acids of phosphorus1 it is simplest to imagine the substitution of hydroxyl in ,h#c,,po#d or ,,po7,,oh7#c by hydrogen4 ,then from orthophosphoric acid1 ,,po7,,oh7#c1 we shall obtain phosphorous acid1 ,,poh7,,oh7#b1 and hypophosphorous acid1 ,,poh7,,oh72 and1 furthermore1 phosphorous acid should be bibasic if orthophosphoric acid was tribasic1 and hypophosphorous acid should be monobasic4 ,this conclusion#ba bis is1 in fact1 true1 and hence all the acids of phosphorus may be referred to one common type1 ,,px#e1 whose representatives are ,,ph#d;,i and ,p,cl#e1 ,p,o,cl#c1 ,p,cl#b;,f#c1 c4 #ba bis ,the bibasity of ,h#c,,po#c1 established by ,wrtz1 has been proved by many direct experiments 7see1 for instance1 ,note #bb71 among which we may mention that ,amat 7#ahib7 took a mixture of the aqueous solutions of ,na#b;,,hpo#c and ,na,h,o and added absolute alcohol to it4 ,two layers were formed2 the upper1 alcoholic1 contained all the excess of ,na,h,o1 whilst the lower only contained the salt ,na#b;,,hpo#c1 which was therefore unable to react with the excess of ,na,h,o4 ,amat also obtained ,na,h#b,,po#c by saturating ,h#c,,po#c with soda until he obtained a neutral reaction with methyl-orange4 ,the replacement of one atom of ,h by sodium here1 as in phosphoric acid 7,note #af71 gives more heat than the replacement of the second atom4 ,for the third atom there is no formation of a salt1 and therefore no evolution of heat4 ,the monometallic salts--for example1 ,na,h#b,,po#c--or the ammonia salts1 when heated to #afj1 give1 as ,amat had previously shown1 a salt of bibasic pyrophosphorous acid1 ,na#b;,h#b,p#b,o#e4 ,phosphorous acid1 ,,ph#c,o#c1 is generally obtained from phosphorus trichloride1 ,p,cl#c1 by the action of water3 ,p,cl#c #c;,h#b,o #c;,h,cl ,,ph#c,o#c4 ,both acids formed are soluble in water1 but are easily separated1 because hydrochloric acid is volatile whilst phosphorous acid volatilises with difficulty1 and if a small amount of water be originally taken the hydrochloric acid nearly all passes off directly4 ,concentrated solutions of phosphorous acid give crystals of ,h#c,,po#c1 which fuse at #gj1 attract moisture from the air1 and deliquesce when ignited1 giving phosphine and phosphoric acid1#bb and are oxidised into orthophosphoric acid by many oxidising agents4 ,in its salts only two hydrogen atoms are replaced by metals 7,wrtz72 the salts of the alkaline metals are soluble1 and give precipitates with salts of the majority of other metals4 #bb ,phosphorous acid1 when subjected to the action of nascent hydrogen 7zinc and sulphuric acid71 evolves phosphine1 and when boiled with an excess of alkali it evolves hydrogen 7,,ph#c,o#c #c,,kho ,,pk#c,o#d #b;,h#b,o ,h#b72 owing to its liability to oxidation1 it is a reducing agent--for instance1 it reduces cupric chloride to cuprous chloride1 and precipitates silver from the nitrate and mercury from its salts4 ,these reactions are perhaps connected with the fact that in this acid one atom of hydrogen should be considered as in the same condition as in phosphuretted hydrogen1 which is expressed by the formula ,,pho7,,oh7#b1 if we represent it as ,,ph#d,x1 with the substitution of two of the hydrogen atoms by oxygen and of ,,hx by two of hydroxyl4 ,the direct passage of phosphorous chloride into phosphorous acid would1 however1 indicate that all the three atoms of hydrogen in it occur in the form of hydroxyl1 because no difference is known between the three atoms of chlorine in ,p,cl#c--they all react alike1 as a rule4 ,however1 ,menschutkin1 by acting on alcohol1 ,c#b;,h#e,,oh1 with phosphorous chloride1 obtained hydrochloric acid and a substance ,p7,c#b;,h#e,o7,cl#b1 and from it by the action of bromine he obtained ethyl bromide1 ,c#b;,h#e;,br1 and a compound ,p,br,o,cl#b1 which proves1 to a certain extent1 the existence of a difference between the three atoms of chlorine in phosphorous chloride4 ,if we turn our attention to the formation of phosphine by the ignition of phosphorous acid1 we see that #d,,ph#c,o#c only evolve #c;,h in the form of ,,ph#c1 and therefore the residue--that is1 #c,,ph#c,o#d--will still contain one hydrogen of the same nature as in phosphine1 because in #d,,ph#c,o#c we should recognise four such hydrogens as in phosphine4 ,we arrive at the same conclusion by examining the decomposition of hypophosphorous acid1 #b,,ph#c,o#b ,,ph#c ,,ph#c,o#d4 ,in the two molecules of the monobasic hypophosphorous acid taken1 there are only two atoms of hydrogen replaceable by metals1 whilst in the molecule of the resultant phosphoric acid there are three4 ,perhaps relations of this nature determine the relative stability of the dimetallic salts of orthophosphoric acid4 ,the monobasic hypophosphorous acid1 ,,ph#c,o#b1 gives salts ,,ph#b,o#b,na1 7,,ph#b,o#b7b;,ba1 c42 the two remaining atoms of hydrogen 7which exist in the same form as in phosphine1 ,,ph#c7 are not replaceable by metals1 and this determines the property of these salts of evolving phosphuretted hydrogen when heated 7especially with alkalis74 ,in acting on substances liable to reduction it is this hydrogen which acts1 and1 for example1 reduces gold and mercury from the solutions of their salts1 or converts cupric into cuprous salts4 ,in all these instances the hypophosphorous acid is converted into phosphoric acid4 ,under the action of zinc and sulphuric acid it gives phosphine1 ,,ph#c4 ,nevertheless1 neither hypophosphorous acid nor its dry salts absorb oxygen from the air4 ,the salts of hypophosphorous acid are more soluble than those of the preceding acids of phosphorus4 ,thus the sodium salt ,p,na,h#b,o#b does not give a precipitate with barium chloride1 and the salts of calcium1 barium1 and many other metals are soluble4#bc ,the hypophosphites are prepared by boiling an alkali with phosphorus so long as phosphuretted hydrogen is evolved4 ,the acid itself is obtained from barium hypophosphite 7prepared in the same manner by boiling phosphorus in baryta water71 by decomposing its solution with sulphuric acid4 ,by concentration of the solution of hypophosphorous acid 7it must not be heated above #acj1 at which temperature it decomposes7 a syrup is formed which is able to crystallise4 ,in the solid state hypophosphorous acid fuses at #ag1 and has the properties of a clearly defined acid4 #bc ,calcium hypophosphite is used in medicine4 ,according to ,cavazzi1 a mixture of sodium hypophosphite1 ,na,h#b,,po#b1 and sodium nitrate explodes violently4 ,the types ,,px#c and ,,px#e1 which are evident for the hydrogen and oxygen compounds of phosphorus1 are most clearly seen in its halogen compounds1#bd to the consideration of which we will proceed1 fixing our attention more especially on the chlorine compounds1 as being the most important from the historical1 theoretical1 and practical point of view4 #bd ,fluorine and bromine give ,,px#c and ,,px#e1 like chlorine4 ,with respect to iodine ,,pi#e is1 in a chemical sense1 a very unstable substance1 and generally phosphorus tri-iodide only is formed 7from yellow or red phosphorus and iodine in the requisite proportions74 ,it is a red crystalline substance1 fuses at #ee1 is easily decomposed by water1 forming phosphorous and hydriodic acids1 and when heated it evolves iodine vapours and forms phosphorus di-iodide1 ,,pi#b4 ,this substance may be obtained in the same manner as the preceding by taking a smaller proportion of iodine 7#h parts of iodine to #a part of phosphorus1 whilst the tri-iodide requires #abc72 it also forms red crystals1 which melt at #aaj4 ,when decomposed by water it not only gives phosphorous and hydriodic acids1 but also phosphine and a yellow substance 7a lower oxide of phosphorus74 ,in its composition di-iodide of phosphorus corresponds with liquid phosphuretted hydrogen1 ,,ph#b1 and probably its molecular weight is much higher3 ,p#b;,i#d or ,p#c;,i#f1 c4 ,as the iodine compounds of phosphorus give hydriodic and phosphorous acids with water1 and as both these substances are reducing agents in the presence of water 7and hydrates71 iodide of phosphorus also acts as a reducing agent4 ,phosphorus burns in chlorine1 forming phosphorous chloride1 ,p,cl#c1 and with an excess of chlorine1 phosphoric chloride1 ,p,cl#e4 ,the oxychloride1 ,p,o,cl#c1 as the simplest chloranhydride according to the type ,,px#e1 and also phosphoric chloride1 correspond with orthophosphoric acid1 ,,po7,,oh7#c1 while phosphorous chloride1 ,p,cl#c1 corresponds with phosphorous acid and the type ,,px#c4 ,phosphoric oxychloride1 ,p,o,cl#c1 is a colourless liquid1 boiling at #aaj4 ,phosphorus trichloride is also a colourless liquid1 boiling at #gf1be whilst phosphoric chloride is a solid yellowish substance1 which volatilises without melting at about #afh4 ,they are all heavier than water1 and form types of the chloranhydrides or chlorine compounds of the non-metallic elements whose hydrates are acids1 just as ,na,cl or ,ba,cl#b are types of halogen metallic salts4 #be ,in a liquid state the density of phosphorous chloride at #aj #aeig1 and therefore its molecular volume #acge_/aeig #hfj1 and that of phosphorus oxychloride is equal to #aece_/afic #ijg2 hence the addition of oxygen has produced considerable increase in volume1 just as in the conversion of sulphur dichloride1 ,s,cl#b1 into sulphuryl chloride1 ,s,o,cl#b1 the volume changes from #fd to #ga4 ,it is the same with the boiling-points2 phosphorus trichloride boils at #gj1 the oxychloride at #ajj1 sulphur dichloride at #fd1 and sulphuryl chloride at #gh--that is1 the addition of oxygen raises the boiling points4 ,the vapour density of phosphorus trichloride and oxychloride corresponds with their formul 7,cahours1 ,wrtz7--namely1 is equal to half the molecular weight referred to hydrogen4 ,but it is not so with phosphorus pentachloride4 ,cahours showed that the vapour density of phosphorus pentachloride referred to air #cfe1 to hydrogen #ebf1 whilst according to the formula ,p,cl#e it should be #ajdb4 ,hence this formula corresponds with four1 and not with two1 molecules4 ,this shows that the vapour of phosphoric chloride contains two and not one molecule1 that in a state of vapour it splits up1 like sal-ammoniac1 sulphuric acid1 c4 ,the products of disruption must here be phosphorous chloride1 ,p,cl#c1 and chlorine1 ,cl#b1 bodies which easily re-form phosphoric chloride1 ,p,cl#e1 at a lower temperature4 ,this decomposition of phosphoric chloride in its conversion into vapour is confirmed by the fact that the vapour of this almost colourless substance shows the greenish-yellow colour proper to chlorine4 ,this dissociation of phosphoric chloride has been considered by some chemists as a sign that phosphorus1 like nitrogen1 does not give volatile compounds of the type ,,px#e1 and that such substances are only obtained as unstable molecular compounds which break up when distilled2 for example1 ,,ph#c1;,,hi1 ,p,cl#c1;,cl#b1 ,,nh#c1;,h,cl1 c4 ,to prove that the molecule ,p,cl#e actually exists1 ,wrtz in #ahgj observed that when mixed with the vapour of phosphorous chloride the vapour of phosphoric chloride distils over 7from #afj to #aij7 perfectly colourless1 and has a density which is really near to the formula--namely1 to #ajd--;and the same density was determined for the pentachloride in an atmosphere of chlorine4 ,hence at low temperatures and in admixture with one of the products of dissociation1 there is no longer that decomposition which occurs at higher temperatures--that is1 we have here a case of dissociation proceeding at moderate temperatures4 ,an important proof in favour of the type ,,px#e is exhibited by phosphorus pentafluoride ,,pf#e1 obtained by ,thorpe as a colourless gas which only corrodes glass after the lapse of time2 it may be kept over mercury1 and has a normal density4 ,it is formed when liquid arsenic trifluoride1 ,as,f#c1 is added to phosphoric chloride surrounded by a freezing mixture3 #c,p,cl#e #e;,as,f#c #c,,pf#e #e;,as,cl#c4 ,in general1 fluorine and phosphorus give stable compounds3 ,,pf#c1 ,,pof#c1 and ,,pf#e1 as would be expected from the fact that in passing from ,cl to ,i 7i4e4 as the atomic weight of the halogen increases7 the stability of the compounds with ,p and the tendency to give ,,px#e 7,note #bd7 decreases4 ,phosphorus trifluoride is obtained by heating a mixture of ,zn,f#b and ,p,br#c1 by the action of ,as,f#c upon ,p,cl#c1 by heating phosphide of copper with ,pb,f#b1 c4 ,it is a strong-smelling gas1 which liquefies at -#aj under a pressure of #dj atmospheres1 giving a colourless liquid4 ,it dissolves easily in 7is absorbed by1 reacts with7 water1 and acts upon glass2 when mixed with ,cl#b it combines with it 7,poulenc1 #ahia71 forming ,p,cl#b;,f#c1 a colourless gas of normal density1 which is transformed into a liquid at #h1 decomposes into ,,pf#c ,cl#b at #bej1 and1 with a small amount of water1 gives oxy-fluoride of phosphorus1 ,,pof#c 7with a large amount of water it gives ,,ph#c,o#d71 which ,moissan 7#ahia7 obtained by the action of dry ,,hf upon ,p#b,o#e1 and ,thorpe and ,tutton 7#ahij7 by heating a mixture of cryolite and ,p#b,o#e4 ,it is a gas of normal density1 like ,,pf#c1 and was obtained by ,moissan by the action of fluorine upon ,,pf#c 7,,psf#c1 see ,chapter ,,xx41 ,note #bj74 ,thus the forms ,,px#c and ,,px#e not only exist in many solid and non-volatile substances1 but also as vapours4 ,if a piece of phosphorus be dropped into a flask containing chlorine1 it burns when touched with a red-hot wire1 and combines with the chlorine4 ,if the phosphorus be in excess1 liquid phosphorus trichloride1 ,p,cl#c1 is always formed1 but if the chlorine be in excess the solid pentachloride is obtained4 ,the trichloride is generally prepared in the following manner4 ,dry chlorine 7passed through a series of ,woulfe's bottles containing sulphuric acid7 is led into a retort containing sand and phosphorus4 ,the retort is heated1 the phosphorus melts1 spreads through the sand1 and gradually forms the trichloride1 which distils over into a receiver1 where it condenses4 ,phosphoric chloride or phosphorus pentachloride1 ,p,cl#e1 is prepared by passing dry chlorine into a vessel containing phosphorus trichloride 7purified by distillation74 ,phosphorous chloride combines directly with oxygen1 but more rapidly with ozone or with the oxygen of potassium chlorate 7#c,p,cl#c ,k,cl,o#c #c,p,o,cl#c ,k,cl71 forming phosphorus oxychloride1 ,p,o,cl#c 7,brodie74 ,this compound is also formed by the first action of water on phosphoric chloride2 for example1 if two vessels1 one containing phosphoric chloride and the other water1 are placed under a bell jar1 after a certain time the crystals of the chloride disappear and hydrochloric acid passes into the water4 ,the aqueous vapour acts on the pentachloride1 and the following reaction occurs3 ,p,cl#e ,h#b,o ,p,o,cl#c #b;,h,cl1 the result being that liquid phosphorus oxychloride is found in one vessel1 and a solution of hydrochloric acid in the other4 ,however1 an excess of water directly transforms phosphoric chloride into orthophosphoric acid1 ,p,cl#e #d;,h#b,o ,,ph#c,o#d #e;,h,cl1#bf since ,p,o,cl#c reacts with water 7#c;,h#b,o71 forming #c;,h,cl and phosphoric acid ,,po7,,oh7#c4 #bf ,phosphorus oxychloride is obtained by the action of phosphoric chloride on hydrates of acids 7because alkalis decompose phosphorus oxychloride71 according to the equation ,p,cl#e ,,rho ,p,o,cl#c ,r,cl ,h,cl1 where ,,rho is an acid4 ,the reaction only proceeds according to this equation with monobasic acids1 but then ,r,cl is volatile1 and therefore a mixture is obtained of two volatile substances1 the acid chloride and phosphorus oxychloride1 which are sometimes difficult to separate2 whilst if the hydrate be polybasic the reaction frequently proceeds so that an anhydride is formed3 ,,rh#b,o#b ,p,cl#e ,,ro ,p,o,cl#c #b;,h,cl4 ,if the anhydride be non-volatile 7like boric71 or easily decomposed 7like oxalic71 it is easy to obtain pure oxychloride4 ,thus phosphorus oxychloride is often prepared by acting on boric or oxalic acid with phosphoric chloride4 ,it is also formed when the vapour of phosphoric chloride is passed over phosphoric anhydride1 ,p#b,o#e #c,p,cl#e #e,p,o,cl#c4 ,this forms an excellent example in proof of the fact that the formation of one substance from two does not necessarily show that the resultant compound contains the molecules of these substances in its molecule4 ,but other oxychlorides of phosphorus are also formed by the interaction of phosphoric anhydride and chloride2 thus at #bjj the chloranhydride1 ,,po#b;,cl1 or chloranhydride of metaphosphoric acid1 is formed 7,gustavson74 ,the chloranhydride of pyrophosphoric acid1 ,p#b,o#c;,cl#d1 was obtained 7,hayter and ,michaelis71 together with ,n,o,cl1 c41 by the action of ,,no upon cold ,p,cl#c1 as a fuming liquid boiling at #baj4 ,the above chlorine compounds serve not only as a type of the chloranhydrides1 but also as a means for the preparation of other acid chloranhydrides4 ,thus the conversion of acids ,,xho into chloranhydrides1 ,x,cl1 is generally accomplished by means of phosphorus pentachloride4 ,this fact was discovered by ,chancel1 and adopted by ,gerhardt as an important method for studying organic acids4 ,by this means organic acids1 containing1 as we know1 ,,rcooh 7where ,r is a hydrocarbon group1 and where carboxyl may repeat itself several times by replacing the hydrogen of hydrocarbon compounds71 are converted into their chloranhydrides1 ,r,c,o,cl4 ,with water they again form the acid1 and resemble the chloranhydrides of mineral acids in their general properties4 ,since carbonic acid1 ,,co7,,oh7#b1 contains two hydroxyl groups1 its perfect chloranhydride1 ,c,o,cl#b1 carbonic oxychloride1 carbonyl chloride or phosgene gas1 contains two atoms of chlorine1 and differs from the chloranhydrides of organic acids in that in them one atom of chlorine is replaced by the hydrocarbon radicle ,r,c,o,cl1 if ,r be a monatomic radicle giving a hydrocarbon ,,rh4 ,it is evident1 on the one hand1 that in ,r,c,o,cl the hydrogen is replaced by the radicle ,c,o,cl1 which is also able to replace several atoms of hydrogen 7for example1 ,c#b;,h#d7;,c,o,cl7#b corresponds with the bibasic succinic acid72 and1 on the other hand1 that the reactions of the chloranhydrides of organic acids will answer to the reactions of carbonyl chloride1 as the reactions of the acids themselves answer to those of carbonic acid4 ,carbonyl chloride is obtained directly from dry carbon monoxide and chlorine#bg exposed to the action of light1 and forms a colourless gas1 which easily condenses into a liquid1 boiling at #h1 specific gravity #adc1 and having the suffocating odour belonging to all chloranhydrides4 ,like all chloranhydrides1 it is immediately decomposed by water1 forming carbonic anhydride1 according to the equation ,c,o,cl#b ,h#b,o ,,co#b #b;,h,cl1 and thus expresses the type proper to all chloranhydrides of both mineral and organic acids4#bh #bg ,the direct action of the sun's rays1 or of magnesium light1 is necessary to start the reaction between carbonic oxide and chlorine1 but when once started it will proceed rapidly in diffused light4 ,an excess of chlorine 7which gives its coloration to the colourless phosgene7 aids the completion of the reaction1 and may afterwards be removed by metallic antimony4 ,porous substances1 like charcoal1 aid the reaction4 ,phosgene may be prepared by passing a mixture of carbonic anhydride and chlorine over incandescent charcoal4 ,lead or silver chloride1 when heated in a current of carbonic oxide1 also partially form phosgene gas4 ,carbon tetrachloride1 ,c,cl#d1 also forms it when heated with carbonic anhydride 7at #djj71 with phosphoric anhydride 7#bjj71 and most easily of all with sulphuric anhydride 7#b,,so#c ,c,cl#d ,c,o,cl#b ,s#b,o#e;,cl#b1 this is pyrosulphuryl chloride74 ,chloroform1 ,c,h,cl#c1 is converted into carbonyl chloride when heated with ,,so#b7,,oh7,cl 7the first chloranhydride of sulphuric acid72 ,c,h,cl#c ,,so#c;,h,cl ,c,o,cl#b ,,so#b #b;,h,cl 7,dewar71 and when oxidised by chromic acid4 ,among the reactions of phosgene we may mention the formation of urea with ammonia1 and of carbonic oxide when heated with metals4 #bh ,we are already acquainted with some of the chloranhydrides of the inorganic acids--for instance1 ,b,cl#c1 and ,si,cl#d--;and here we shall describe those which correspond with sulphuric acid in the following chapter4 ,it may be mentioned here that when hydrochloric acts on nitric acid 7aqua regia1 ,vol4 ,i4 p4 #dfg7 there is formed1 besides chlorine1 the oxychlorides ,n,o,cl and ,,no#b;,cl1 which may be regarded as chloranhydrides of nitric and nitrous acids 7nitrogen chloride1 ,vol4 ,i4 p4 #dgf74 ,the former boils at -#e1 the latter at #e1 the specific gravity of the first at -#ab #adaf1 and at -#ah #adcc 7,geuther71 and of the second #ac2 the first is obtained from nitric oxide and chlorine1 the second from nitric peroxide and chlorine1 and also by the action of phosphoric chloride on nitric acid4 ,if the gases evolved by aqua regia be passed into cold and strong sulphuric acid1 they form crystals of the composition ,,nhso#c 7like chamber crystals71 which melt at #hf1 and with sodium chloride form acid sodium sulphate and the oxychloride ,n,o,cl4 ,this chloranhydride of nitric acid is termed nitrosyl chloride4 ,cyanogen chloride1 ,c,n,cl1 is the gaseous chloranhydride of cyanic acid2 it is formed by the action of chlorine on aqueous mercury cyanide1 ,hg7,,cn7#b #b;,cl#b ,hg,cl#b #b;,c,n,cl4 ,when chlorine acts on cyanic acid1 it forms not only this cyanogen chloride1 but also polymerides of it--a liquid1 boiling at #ah1 and a solid1 boiling at #aij4 ,the latter corresponds with cyanuric acid1 and consequently contains ,c#c,n#c;,cl#c4 ,details concerning these substances must be looked for in works on organic chemistry4 ,in order to show the general method for the preparation of acid chloranhydrides1 we will take that of acetic acid1 ,,ch#c;,,cooh1 as an example4 ,phosphorus pentachloride is placed in a glass retort1 and acetic acid poured over it2 hydrochloric acid is then evolved1 and the substance distilling over directly after is a very volatile liquid1 boiling at #ej1 and having all the properties of the chloranhydrides4 ,with water it forms hydrochloric and acetic acids4 ,the reaction here taking place may be explained thus3 the substitution of the oxygen taken from the acetic acid 7from its carboxyl7 by two atoms of chlorine from the ,p,cl#e should be as follows3 ,,ch#c;,,cooh ,p,cl#e ,,ch#c;,c,o,h,cl#b ,p,o,cl#c4 ,but the compound ,,ch#c;,c,o,h,cl#b does not exist in a free state 7because it would indicate the possibility of the formation of compounds of the type ,,cx#f1 and carbon only gives those of the type ,,cx#d72 it therefore splits up into ,h,cl and the chloranhydride ,,ch#c;,c,o,cl4 ,the general scheme for the reaction of phosphorus pentachloride with hydrates ,,roh is exactly the same as with water2 namely1 ,,roh with ,p,cl#e1 gives ,p,o,cl#c ,h,cl ,r,cl--that is a chloranhydride4#bh bis #bh bis ,this reaction indeed proceeds very easily and completely with a number of hydroxides1 if they do not react on hydrochloric acid and phosphorus oxychloride1 which is the case when they have alkaline properties4 ,when the hydroxide is bibasic and is present in excess1 it not unfrequently happens that the elements of water are taken up3 ,r7,,oh7#b ,p,cl#e ,,ro #b;,h,cl ,p,o,cl#c4 ,the anhydride ,,ro may then be converted into chloranhydride1 ,,ro ,p,cl#e ,r,cl#b ,p,o,cl#c--that is1 phosphorus pentachloride brings about the substitution of ,o by ,cl#b4 ,thus carbonyl chloride1 ,c,o,cl#b1 boron chloride1 #b;,b,cl#c1 and succinic chloride1 ,c#d;,h#d,o#b;,cl#b1 c41 are respectively obtained by the action of phosphoric chloride on carbonic1 boric1 and succinic anhydrides4 ,phosphorus pentachloride reacts in a similar manner on the aldehydes1 ,,rcho1 forming ,r,c,h,cl#b1 and on the chloranhydrides themselves--for example1 with acetic chloride1 ,,ch#c4;,c,o,cl 7when heated in a closed tube71 it forms a substance having the composition ,,ch#c;,c,cl#c4 ,phosphorus trichloride and oxychloride act in a similar manner to phosphoric chloride4 ,when phosphorus trichloride acts on an acid1 #c,,rho ,p,cl#c #c,r,cl ,p7,,ho7#c4 ,if a salt is taken1 then by the action of phosphorus oxychloride a corresponding chloranhydride and salt of orthophosphoric acid are easily formed3 #c,r7,,ko7 ,p,o,cl#c #c,r,cl ,,po7,,ko7#c4 ,the chloranhydride ,r,cl is always more volatile than its corresponding acid1 and distils over before the hydrate ,,rho4 ,thus acetic acid boils at #aag1 and its chloranhydride at #ej4 ,phosphoric and phosphorous acids are very slightly volatile1 whilst their chloranhydrides are comparatively easily converted into vapour4 ,the faculty of the chloranhydrides to react at the expense of their own chlorine determines their great importance in chemistry4 ,for instance1 suppose we require to know the molecular formula of some hydrate which does not pass into a state of vapour and does not give a chloranhydride with hydrochloric acid--that is1 which has not any basic or alkaline properties2 we must then endeavour to obtain this chloranhydride by means of phosphoric chloride1 and it frequently happens that the corresponding chloranhydride is volatile4 ,the resultant chloranhydride is then converted into vapour1 and its composition is determined2 and if we know its composition we are able to decide that of its corresponding hydrate4 ,thus1 for example1 from the formula of silicon chloride1 ,si,cl#d1 or of boron chloride1 ,b,cl#c1 we can judge the composition of their corresponding hydrates1 ,si7,,ho7#d1 ,b7,,ho7#c4 ,having obtained the chloranhydride ,r,cl or ,r,cln1 it is possible by its means to obtain many other compounds of the same radicle ,r according to the equation ,,mx ,r,cl ,m,cl ,,rx4 ,m may be ,h1 ,k1 ,ag1 or other metal4 ,the reaction proceeds thus if ,m forms a stable compound with chlorine--for example1 silver chloride1 hydrochloric acid1 and ,r1 an unstable substance4 ,hence1 a chloranhydride is frequently employed for the formation of other compounds of a given radicle2 for instance1 with ammonia they form amides ,,rnh#b1 and with salts ,,rok1 with anhydrides ,r#b,o1 c4 ,containing1 as they do1 chlorine1 which easily reacts with hydrogen1 phosphorus pentachloride1 trichloride1 and oxychloride enter into reaction with ammonia1 and give a series of amide and nitrile compounds of phosphorus4 ,thus1 for example1 when ammonia acts on the oxychloride we obtain sal-ammoniac 7which is afterwards removed by water7 and an orthophosphoric triamide1 ,,po7,,nh#b7c1 as a white insoluble powder on which dilute acids and alkalis do not act1 but which1 when fused with potassium hydroxide1 gives potassium phosphate and ammonia like other amides4 ,when ignited1 the triamide liberates ammonia and forms the nitrile ,,pon1 just as urea1 ,,co7,,nh#b7b1 gives off ammonia and forms the nitrile ,,conh4 ,this nitrile1 called monophosphamide1 ,,pon1 naturally corresponds with metaphosphoric acid1 namely1 with its ammonium salt4 ,,nh#d,,po#c - ,h#b,o ,,po#b,,nh#b1 an as yet unknown amide1 and ,,po#b,,nh#b - ,h#b,o gives the nitrile ,,pon4 ,this relation is confirmed by the fact that ,,pon1 moistened with water1 gives metaphosphoric acid when ignited4 ,it is the analogue of nitrous oxide1 ,,non4 ,it is a very stable compound1 more so than the preceding4#bi #bi ,the reaction of ammonia on phosphorus pentachloride is more complex than the preceding4 ,this is readily understood3 to the oxychloride1 ,p,o,cl#c1 tere corresponds a hydrate ,,po7,,oh7#c1 and a salt ,,po7,,nh#d,o7#c1 and consequently also an amide ,,po7,,nh#b7c1 whilst the pentachloride1 ,p,cl#e1 has no corresponding hydrate ,p7,,oh7#e1 and therefore there is no amide ,p7,,nh#b7e4 ,the reaction with ammonia will be of two kinds3 either instead of #e mol4 ,,nh#c1 only #c mol4 ,,nh#c or still less will act2 i4e4 ,p,cl#b7,,nh#b7c1 ,p,cl#c7,,nh#b7b1 c4 are formed2 or else the pentachloride will act like a mixture of chlorine with the trichloride1 and then as the result there will be obtained the products of the action of chlorine on those amides which are formed from phosphorus trichloride and ammonia4 ,it would appear that both kinds of reaction proceed simultaneously1 but both kinds of products are unstable1 at all events complex1 and in the result there is obtained a mixture containing sal-ammoniac1 c4 ,the products of the first kind should react with water1 and we should obtain1 for example1 ,p,cl#c7,,nh#b7b #b;,h#b,o #c;,h,cl and ,,po7,,ho77,,nh#b7b4 ,this substance has not actually been obtained1 but the compound ,,ponh7,,nh#b7 derived from it by elimination of the elements of water is known1 and is termed diphosphamide2 it is1 however1 more probable that it is a nitrile than an amide1 because only amides contain the group ,,nh#b4 ,it is a colourless1 stable1 insoluble powder1 which possibly corresponds with pyrophosphoric acid1 more especially since when heated it evolves ammonia and gives and leaves phosphoryl nitride1 ,,pon--that is1 the nitrile of metaphosphoric acid4 ,the amide corresponding with the pyrophosphate ,p#b,o#c7,,nh#d,o7#d should be ,p#b,o#c7,,nh#b7d1 and the nitriles corresponding to the latter would be ,p#b,o#b,n7,,nh#b7c1 ,p#b,,on#b7,,nh#b7b1 and ,p#b,n#c7,,nh#b74 ,the composition of the first is the same as that of the above diphosphamide4 ,the third pyrophosphoric nitrile has a formula ,p#b,n#d;,h#b1 and this is the composition of the body known as phospham1 ,,phn#b 7in a certain sense this is the analogue of ,n#c;,h polymerised1 ,chapter ,,vi47 ,indeed1 phospham has been obtained by heating the products of the action of ammonia on phosphoric chloride1 as an insoluble and alkaline powder1 which gives ammonia and phosphoric acid when subjected to the action of water4 ,the same substance is obtained by the action of ammonium chloride on phosphoric chloride 7,p,n,cl#b is first formed1 and reacts further with ammonia1 forming phospham71 and by igniting the mass which is formed by the action of ammonia on phosphorus trichloride4 ,formerly the composition of phospham was supposed to be ,,phn#b1 now there is reason to think that its molecular weight is ,p#c;,h#c,n#f4 ,the above compounds correspond with normal salts1 but nitriles and amides corresponding to acid salts are also possible1 and they will be acids4 ,for example1 the amide ,,po7,,ho7#b7,,nh#b71 and its nitrile1 will be either ,,pn7,,ho7#b or ,,po7,,ho77,,nh71 but at all events of the composition ,,pnh#b,o#b1 and having acid properties4 ,the ammonium salt of this phosphonitrilic acid 7it is called phosphamic acid71 ,,pnh7,,nh#d7,o#b1 is obtained by the action of ammonia on phosphoric anhydride1 ,p#b,o#e #d,,nh#c ,h#b,o #b,,pnh7,,nh#d7,o#b4 ,a non-crystalline soluble mass is thus formed1 which is dissolved in a dilute solution of ammonia and precipitated with barium chloride1 and the resultant barium salt is then decomposed with sulphuric acid1 and thus a solution of the acid of the above composition is obtained4 ,it is evident from the theory of the formation of amides and nitriles 7,chapter ,,ix47 that very many compounds of this kind can correspond with the acids of phosphorus2 but as yet only a few are known4 ,the easy transitions of the ortho-1 meta-1 and pyrophosphoric acids1 by means of the hydrogen of ammonia1 into the lower acids1 and conversely1 tend to complicate the study of this very large class of compounds1 and it is rarely that the nature of a product thus obtained can be judged from its composition2 and this all the more that instances of isomerism and polymerism1 of mixture between water of crystallisation and of constitution1 c41 are here possible4 ,many data are yet needed to enable us to form a true judgment as to the composition and structure of such compounds4 ,as the best proof of this we will describe the very interesting and most fully investigated compound of this class1 ,p,n,cl#b1 called chlorophosphamide1 or nitrogen chlorophosphorite4 ,it is formed in small quantities when the vapour of phosphoric chloride is passed over ignited sal-ammoniac4 ,besson 7#ahib7 heated the compound ,p,cl#eh,,nh#c 7which is easily and directly formed from ,p,cl#e and ,,nh#c7 under a pressure of about #ej mm4 7of mercury7 to #bjj1 and obtained brilliant crystals of ,p,n,cl#b1 which melted at #ajf 7in the residue after the distillation of sal-ammoniacal phospham74 ,the chlorine in it is very stable--quite different from that in phosphoric chloride4 ,indeed1 the resultant substance is not only insoluble in water 7though soluble in alcohol and ether71 but it is not even moistened by it1 and distils over1 together with steam1 without being decomposed4 ,in a free state it easily crystallises in colourless prisms1 fuses at #aad1 boils at #bej 7,gladstone1 ,wichelhaus71 and when fused with potash gives potassium chloride and the amidonitrile of phosphoric acid4 ,judging from its formula and the simplicity of its composition and reactions1 it might be thought that the molecular weight of this substance would be expressed by the formula ,p,cl#b,n1 that it corresponds with ,,pon and with ,p,cl#e 7like ,p,o,cl#c71 with the substitution of ,cl#c by ,n1 just as in ,p,o,cl#c two atoms of chlorine are replaced by oxygen2 but all these surmises are incorrect1 because its vapour density 7referred to hydrogen--,gladstone1 ,wichelhaus7 #ahb--that is1 the molecular formula must be three times greater1 ,p#c,n#c;,cl#f4 ,the polymerisation 7tripling7 is here of exactly the same kind as with the nitriles4 ,the most important analogue of phosphorus is arsenic1 the metallic aspect of which and the general character of its compounds of the types ,as,x#c and ,as,x#e at once recall the metals4 ,the hydrate of its highest oxide1 arsenic acid 7ortho-arsenic acid71 ,h#c;,as,o#d1 is an oxidising agent1 and gives up a portion of its oxygen to many other substances2 but1 nevertheless1 it is very like phosphoric acid4 ,mitscherlich established the conception of isomorphism by comparing the salts of these acids4#cj #cj ,it is necessary to remark that1 although arsenic is so closely analogous to phosphorus 7especially in the higher forms of combination1 ,,rx#c and ,,rx#e71 at the same time it exhibits a certain resemblance and even isomorphism with the corresponding compounds of sulphur 7especially the metallic compounds of the type ,m,as1 corresponding with ,,ms74 ,thus compounds containing metals1 arsenic1 and sulphur are very frequently met with in nature4 ,sometimes the relative amounts of arsenic and sulphur vary1 so that an isomorphous substitution between the arsenides and sulphides must be recognised4 ,besides ,fe,s#b 7ordinary pyrites71 and ,fe,as#b1 iron forms an arsenical pyrites containing both sulphur and arsenic1 which from its composition1 ,fe,as,s or ,fe,s#b;,fe,as#b1 resembles the two preceding4 ,arsenic occurs in nature1 not only combined with metals1 but also1 although rarely1 native and also in combination with sulphur in two minerals--one red1 realgar1 ,as#b,s#b1 and the other yellow1 orpiment1 ,as#b,s#c 7,chapter ,,xx41 ,note #bi74 ,arsenic occurs1 but more rarely1 in the form of salts of arsenic acid--for instance1 the so-called cobalt and nickel blooms1 two minerals which are found accompanying other cobalt ores1 are the arsenates of these metals4 ,arsenic is also found in certain clays 7ochres7 and has been discovered in small quantities in some mineral springs1 but it is in general of rarer occurrence in nature than phosphorus4 ,arsenic is most frequently extracted from arsenical pyrites1 ,fe,s,as1 which1 when roasted without access of air1 evolves the vapour of arsenic1 ferrous sulphide being left behind4 ,it is also obtained by heating arsenious anhydride with charcoal1 in which case carbonic oxide is evolved4 ,in general1 the oxides and other compounds are very easily reduced4 ,solid arsenic is a steel-grey brittle metal1 having a bright lustre and scaly structure4 ,its specific gravity is #eg4 ,it is opaque and infusible1 but volatilises as a yellow vapour which on cooling deposits rhombohedral crystals4#cj bis ,the vapour density of arsenic is #aej times greater than that of hydrogen--that is1 its molecule1 like that of phosphorus1 contains #d atoms1 ,as#d4 ,when heated in the air1 arsenic easily oxidises into white arsenious anhydride1 ,as#b,o#c1 but even at the ordinary temperature it loses its lustre 7becomes dull71 owing to the formation of a coating of a lower oxide4 ,the latter appears to be as volatile as arsenious anhydride1 and it is probable that it is owing to the presence of this compound that the vapours of arsenious compounds1 when heated with charcoal 7for example1 in the reducing flame of a blow-pipe71 have the characteristic smell of garlic1 because the vapour of arsenic itself has not this odour4 #cj bis ,according to ,retgers 7#ahic7 the arsenic mirror 7see further on7 is an unstable variety of metallic arsenic1 whilst the brown product which is formed together with it in ,marsh's apparatus is a lower hydride ,as,h4 ,schuller and ,mc,leod 7#ahid71 however1 recognise a peculiar yellow variety of arsenic4 ,arsenic easily combines with bromine and chlorine2#ca nitric acid and aqua regia also oxidise it into the higher oxide1 or rather its hydrate1 arsenic acid4#cb ,as far as is known1 it does not decompose steam1 and it acts exceedingly slowly on those acids1 like hydrochloric1 which are not capable of oxidising4 #ca ,hydrochloric acid dissolves arsenious anhydride in considerable quantities1 and this is probably owing to the formation of unstable compounds in which the arsenious anhydride plays the part of a base4 ,a compound called arsenious oxychloride1 having the composition ,as,o,cl1 is even known4 ,it is formed when arsenious anhydride is added little by little to boiling arsenic trichloride1 ,as#b,o#c ,as,cl#c #c;,as,o,cl4 ,it is a transparent substance1 which fumes in air1 and combines with water to form a crystalline mass having the composition ,as#b7,,oh7#d;,cl#b4 ,when heated it decomposes into arsenious chloride and a fresh oxychloride of a more complex composition1 ,as#f,o#h;,cl#b ,arsenic trichloride1 when treated with a small quantity of water1 forms the crystalline compound1 ,as#b7;,,ho7#d;,cl#b1 mentioned above4 ,these compounds resemble the basic salts of bismuth and aluminium4 ,the existence of these compounds shows that arsenic is of a more metallic or basic character than phosphorus4 ,nevertheless arsenic trichloride1 ,as,cl#c1 resembles phosphorus trichloride in many respects4 ,it is obtained by the direct action of chlorine on arsenic1 or by distilling a mixture of common salt1 sulphuric acid1 and arsenious anhydride4 ,the latter mode of preparation already indicates the basic properties of the oxide4 ,arsenious chloride is a colourless oily liquid1 boiling at #acj1 and having a sp4 gr4 of #bbj4 ,it fumes in air like other chloranhydrides1 but it is much more slowly and imperfectly decomposed by water than phosphorus trichloride4 ,a considerable quantity of water is required for its complete decomposition into hydrochloric acid and arsenious anhydride4 ,it forms an excellent example of the transition from true metallic chlorides to true chloranhydrides of the acids4 ,it hardly combines with chlorine1 i4e4 if ,as,cl#e is formed it is very unstable4 ,arsenic tribromide1 ,as,br#c1 is formed as a crystalline substance1 fusing at #bj and boiling at #bbj1 by the direct action of metallic arsenic on a solution of bromine in carbon bisulphide1 the latter being then evaporated4 ,the specific gravity of arsenic tribromide is #ccf4 ,crystalline arsenic tri-iodide1 ,as,i#c1 having a sp4 gr4 #dci1 may be obtained in a like manner2 it may be dissolved in water1 and on evaporation separates out from the solution in an anhydrous state--that is1 it is not decomposed--and consequently behaves like metallic salts4 ,arsenic trifluoride1 ,as,f#c1 is obtained by heating fluor spar and arsenious anhydride with sulphuric acid4 ,it is a fuming1 colourless1 and very poisonous liquid1 which boils at #fc and has a sp4 gr4 of #bgc4 ,it is decomposed by water4 ,it is very remarkable that fluorine forms a pentafluoride of arsenic also1 although this compound has not yet been obtained in a separate state1 but only in combination with potassium fluoride4 ,this compound1 ,k#c;,as,f#h1 is formed as prismatic crystals when potassium arsenate1 ,k#c;,as,o#d1 is dissolved in hydrofluoric acid4 #cb ,arsenic acid1 ,h#c;,as,o#d1 corresponding with orthophosphoric acid1 is formed by oxidising arsenious anhydride with nitric acid1 and evaporating the resultant solution until it attains a sp4 gr4 of #bb2 on cooling it separates in crystals having the above composition4 ,this hydrate corresponds with the normal salts of arsenic acid2 but on dissolving in water 7without heating71 and on cooling a strong solution1 crystals containing a greater amount of water1 namely1 7,as,h#c,o#d7b1;,h#b,o1 separate4 ,this water1 like water of crystallisation1 is very easily expelled at #ajj4 ,at #abj crystals having a composition identical with that of pyrophosphoric acid1 ,as#b;,h#d,o#g1 separate1 but water1 on dissolving this hydrate with the development of heat1 forms a solution in no way differing from a solution of ordinary arsenic acid1 so that it is not an independent pyroarsenic acid that is formed4 ,neither is there any true analogue of metaphosphoric acid1 although the compound ,as,h,o#c is formed at #bjj1 and on solidifying forms a mass having a pearly lustre and sparingly soluble in cold water2 but on coming into contact with warm water it becomes very hot1 and gives ordinary orthoarsenic acid in solution4 ,arsenic acid forms three series of salts1 which are perfectly analogous to the three series of orthophosphates4 ,thus the normal salt1 ,k#c;,as,o#d1 is formed by fusing the other potassium arsenates with potassium carbonate2 it is soluble in water and crystallises in needles which do not contain water4 ,di-potassium arsenate1 ,k#b;,h,as,o#d1 is formed in solution by mixing potassium carbonate and arsenic acid until carbonic anhydride ceases to be evolved2 it does not crystallise1 and has an alkaline reaction2 hence it corresponds perfectly with the sodium phosphate4 ,as was mentioned above1 arsenic acid itself acts as an oxidising agent2 for example1 it is used in the manufacture of aniline dyes for oxidising the aniline1 and it is prepared in large quantities for this purpose4 ,when sulphuretted hydrogen is passed through its solution1 sulphuric acid and arsenious anhydride are obtained in solution4 ,arsenic acid is very easily soluble in water1 and its solution has an exceedingly acid reaction1 and when boiled with hydrochloric acid evolves chlorine1 like selenic1 chromic1 manganic1 and certain other higher metallic acids4 ,arsenic anhydride1 ,as#b,o#e1 is produced when arsenic acid is heated to redness4 ,it must be carefully heated1 as at a bright red heat it decomposes into oxygen and arsenious anhydride4 ,arsenic anhydride is an amorphous substance almost entirely insoluble in water1 but it attracts moisture from the air1 deliquesces1 and passes into the acid4 ,hot water produces this transformation with great ease4 ,arseniuretted hydrogen1 arsine1 ,as,h#c1 resembles phosphuretted hydrogen in many respects4 ,this colourless gas1 which liquefies into a mobile liquid at -#dj1 has a disagreeable garlic-like odour1 is only slightly soluble in water1 and is exceedingly poisonous4 ,even in a small quantity it causes great suffering1 and if present to any considerable amount in air it even causes death4 ,the other compounds of arsenic are also poisonous1 with the exception of the insoluble sulphur compound and some compounds of arsenic acid4 ,arseniuretted hydrogen1 ,as,h#c1 is obtained by the action of water on the alloy of arsenic and sodium1 sodium hydroxide and arseniuretted hydrogen being formed4 ,it is also formed by the action of sulphuric acid on the alloy of arsenic and zinc3 ,zn#c;,as#b #c;,h#b,,so#d #b;,as,h#c #c,zn,s,o#d4cc ,the oxygen compounds of arsenic are very easily reduced by the action of hydrogen at the moment of its evolution from acids1 and the reduced arsenic then combines with the hydrogen2 hence1 if a certain amount of an oxygen compound of arsenic be put into an apparatus containing zinc and sulphuric acid 7and thus serving for the evolution of hydrogen71 the hydrogen evolved will contain arseniuretted hydrogen4 ,in this case it is diluted with a considerable amount of hydrogen4 ,but its presence in the most minute quantities may be easily recognised from the fact that it is easily decomposed by heat 7#bjj according to ,brunn7 into metallic arsenic and hydrogen1 and therefore if such impure hydrogen he passed through a moderately-heated tube metallic arsenic will be deposited as a bright layer on the part of the tube which was heated 7see ,note #cj bis74 ,this reaction is so sensitive that it enables the most minute traces of arsenic to be discovered2 hence it is employed in medical jurisprudence1 as a test in poisoning cases4 ,it is easy to discover the presence of arsenic in common zinc1 copper1 sulphuric and hydrochloric acids1 c4 by this method4 ,it is obvious that in testing for poison by ,marsh's apparatus it is necessary to take zinc and sulphuric acid quite free from arsenic4 ,the arsenic deposited in the tube may be driven as a volatile metal from one place to another in the current of hydrogen evolved1 owing to its volatility4 ,this forms a distinction between arseniuretted and antimoniuretted hydrogen1 which is decomposed by heat in just the same way as arseniuretted hydrogen1 but the mirror given by ,sb is not so volatile as that formed by ,as4 ,illustration3 ,,fig4 #hd4--;,formation and decomposition of arseniuretted hydrogen4 ,hydrogen is evolved in the ,woulfe's bottle1 and when the gas comes off1 a solution containing arsenic is poured through the funnel4 ,the presence of ,as,h#c is recognised from the deposition of a mirror of arsenic when the gas-conducting tube is heated4 ,if the escaping hydrogen be lighted1 and a porcelain dish be held in the flame1 a film of arsenic is deposited on it4 ,the gas is dried by passing through the tube containing calcium chloride4 ,this apparatus is used for the detection of arsenic by ,marsh's test4 #cc ,the formation of arseniuretted hydrogen is accompanied by the absorption of #cg1jjj heat units1 while phosphine evolves #ah1jjj 7,ogier71 and ammonia #bg1jjj4 ,sodium 7#jf p4c47 amalgam1 with a strong solution of ,as#b,o#c1 gives a gas containing #hf vols4 of arsenic and #ad vols4 of hydrogen 7,cavazzi74 ,if hydrogen contains arseniuretted hydrogen1 it also gives metallic arsenic when it burns1 because in the reducing flame of hydrogen the oxygen attracted combines entirely with the hydrogen and not with the arsenic1 so that if a cold object1 such as a piece of china1 be held in the hydrogen flame the arsenic will be deposited upon it as a metallic spot4#cd #cd ,this spot1 or the metallic ring which is deposited on the heated tube1 may easily be tested as to whether it is really due to arsenic or proceeds from some other substance reduced in the hydrogen flame--for instance1 carbon or antimony4 ,the necessity for distinguishing arsenic from antimony is all the more frequently encountered in medical jurisprudence1 from the fact that preparations of antimony are very frequently used as medicine1 and antimony behaves in the hydrogen apparatus just like arsenic1 and therefore in making an investigation for poisoning by arsenic it is easy to mistake it for antimony4 ,the best method to distinguish between the metallic spots of arsenic and antimony is to test them with a solution of sodium hypochlorite1 free from chlorine1 because this will dissolve arsenic and not antimony4 ,such a solution is easily obtained by the double decomposition of solutions of sodium carbonate and bleaching powder4 ,a solution of potassium chlorate acts in the same manner1 only more slowly4 ,further particulars must be looked for in analytical works4 ,arseniuretted hydrogen1 like phosphuretted hydrogen1 is only slightly soluble in water1 has no alkaline properties--that is1 it does not combine with acids--and acts as a reducing agent4 ,when passed into a solution of silver nitrate it gives a blackish brown precipitate of metallic silver1 the arsenic being oxidised4 ,if acting on copper sulphate and similar salts1 arseniuretted hydrogen sometimes forms arsenides--i4e4 it reduces the metallic salt with its hydrogen1 and is itself reduced to arsenic4 ,sulphuric1 and even hydrochloric1 acid reduces arseniuretted hydrogen to arsenic1 and it is still more easily decomposed by arsenious chloride1 and with phosphorous chloride it gives the compound ,p,as4 ,arseniuretted hydrogen gives metallic arsenic with an acid solution of arsenious anhydride 7,tivoli74 ,the most common compound of arsenic is the solid and volatile arsenious anhydride1 ,as#b,o#c1 which corresponds with phosphorous and nitrous anhydrides4 ,this very poisonous1 colourless1 and sweet-tasting substance is generally known under the name of arsenic1 or white arsenic4 ,the corresponding hydrate is as yet unknown2 its solutions1 when evaporated1 yield crystals of arsenious anhydride4 ,it is chiefly prepared for the dyer1 and is also used as a vermin killer1 and sometimes in medicine2 it is a product from which all other compounds of arsenic can be prepared4 ,it is obtained as a by-product in roasting cobalt and other ores containing arsenic4 ,arsenical pyrites are sometimes purposely roasted for the extraction of arsenious anhydride4 ,when arsenical ores are burnt in the air1 the sulphur and arsenic are converted into the oxides ,as#b,o#c and ,,so#b4 ,the former is a solid at the ordinary temperature1 and the latter gaseous1 and therefore the arsenious anhydride is deposited as a sublimate in the cooler portion of the flues through which the vapours escape from the furnace4 ,it collects in condensing chambers especially constructed in the flues4 ,the deposit is collected1 and after being distilled gives arsenious anhydride in the form of a vitreous non-crystalline mass4 ,this is one of the varieties of arsenious anhydride1 which is also known in two crystalline forms4 ,when sublimed--i4e4 when it rapidly passes from the state of vapour to the solid state--it appears in the regular system in the form of octahedra4#ce ,it is obtained in the same form when it is crystallised from acid solutions4 ,the specific gravity of the crystals is #cg4 ,the other crystalline form 7in prisms7 belongs to the rhombohedral system1 and is also formed by sublimation when the crystals are deposited on a heated surface1 or when it is crystallised from alkaline solutions4#cf #ce ,according to ,mitscherlich's determination1 the vapour density of arsenious anhydride is #aii 7,h #a7--that is1 it answers to the molecular formula ,as#d,o#f4 ,probably this is connected with the fact that the molecule of free arsenic contains ,as#d4 ,v4 ,meyer and ,biltz1 however1 showed 7#ahhi7 that at a temperature of about #a1gjj the vapour density of arsenic corresponds with the molecule ,as#b1 and not ,as#d1 as at lower temperatures4 #cf ,arsenious anhydride is obtained in an amorphous form after prolonged heating at a temperature near to that at which it volatilises1 or1 better still1 by heating it in a closed vessel4 ,it then fuses to a colourless liquid1 which on cooling forms a transparent vitreous mass1 whose specific gravity is only slightly less than that of the crystalline anhydride4 ,on cooling1 this vitreous mass undergoes an internal change1 in which it crystallises and becomes opaque1 and acquires the appearance of porcelain4 ,the following difference between the vitreous and opaque varieties is very remarkable3 when the vitreous variety is dissolved in strong and hot hydrochloric acid it gives crystals of the anhydride on cooling1 and this crystallisation is accompanied by the emission of light 7which is visible in the dark71 and the entire liquid glows as the crystals begin to separate4 ,the opaque variety does not emit light when the crystals separate from its hydrochloric acid solution4 ,it is also remarkable that the vitreous variety passes into the opaque form when it is pounded--that is1 under the action of a series of blows4 ,thus1 several varieties of arsenious anhydride are known1 but as yet they are not characterised by any special chemical distinctions1 and even differ but little in their specific gravities1 so that it cannot be said that the above differences are due to any isomeric transformation--that is1 to an arrangement of the atoms in the molecule--but probably only depend on a difference in the distribution of the molecules1 or1 in other terms1 are physical and not chemical variations4 ,one part of the vitreous anhydride requires twelve parts of boiling water for its solution1 or twenty-five parts at the ordinary temperature4 ,the opaque variety is less soluble1 and at the ordinary temperature requires about seventy parts of water for its solution4 ,solutions of arsenious anhydride have a sweet metallic taste1 and give a feeble acid reaction4 ,its solubility increases with the admixture of acids and alkalis4 ,this shows the property of arsenious anhydride of forming salts with acids and alkalis4 ,and in fact compounds of it with hydrochloric acid 7,note #ca71 sulphuric anhydride 7see further on71 and with the alkali oxides are known4#cg ,if silver nitrate be added to a solution of arsenious anhydride1 it does not give any precipitate unless a certain amount of the arsenious anhydride is saturated with an alkali--for instance1 ammonia4 ,it then gives a precipitate of silver arsenite1 ,ag#c;,as,o#c4 ,this is yellow1 soluble in an excess of ammonia1 and anhydrous2 it distinctly shows that arsenious acid is tribasic1 and that it differs in this respect from phosphorous acid1 in which only two atoms of hydrogen can be replaced by metals4#ch ,the feeble acid character of arsenious anhydride is confirmed by the formation of saline compounds with acids4 ,in this respect the most remarkable example is the anhydrous compound with sulphuric acid1 having the composition ,as#b,o#c1,,so#c4 ,it is formed in the roasting of arsenical pyrites in those spaces where the arsenious anhydride condenses1 a portion of the sulphurous anhydride being converted into sulphuric anhydride1 ,,so#c1 at the expense of the oxygen of the air4 ,the compound in question forms colourless tabular crystals1 which are decomposed by water with formation of sulphuric acid and arsenious anhydride4#ci #cg ,arsenious anhydride does not oxidise in air1 either in a dry state or in solution1 but in the presence of alkalis it absorbs oxygen from the air1 and acts as an excellent reducing agent4 ,this probably is connected with the fact that arsenic acid is much more energetic than arsenious acid1 and that it is arsenic acid which is formed by the oxidation of the latter in the presence of alkalis4 ,arsenious anhydride is easily reduced to arsenic by many metals1 even by copper4 #ch ,the feebleness of the acid properties of arsenious anhydride is seen in the fact that if it be dissolved in ammonia water1 and then a still stronger solution of ammonia be added1 prismatic crystals separate having the composition of ammonium metarsenite1 ,,nh#d;,as,o#c4 ,this ammonium salt deliquesces in air1 and loses all its ammonia4 ,the magnesium salt is tri-metallic1 ,mg#c7;,as,o#c7b2 it is insoluble in water1 and is formed by mixing an ammoniacal solution of arsenious anhydride with an ammoniacal solution of a magnesium salt4 ,it is insoluble even in ammonia1 although it dissolves in an excess of acids4 ,magnesium hydroxide gives the same salt with arsenious solutions1 and hence magnesia is one of the best antidotes for arsenic poisoning4 ,the arsenites of copper are much used in the manufacture of colours1 more especially of pigments4 ,they are distinguished by their insolubility in water and by their remarkably vivid green colour1 but at the same time by their poisonous character4 ,not only do such pigments applied to wall papers or other materials easily dust off from them1 but they give exhalations containing ,as,h#c4 ,the cupric salts1 ,cu,x#b1 when mixed with an alkaline solution of arsenious acid1 give a green precipitate of a copper salt called ,scheele's green4 ,its composition is probably ,cu,h,as,o#c4 ,ammonia dissolves it1 and gives a colourless solution1 containing cuprous arsenate--that is1 the cupric compound is reduced and the arsenic subjected to a further oxidation4 ,the so-called ,schweinfurt green was still more used1 especially in former times2 it is an insoluble green cupric salt1 which resembles the preceding in many respects1 but has a different tint4 ,it is prepared by mixing boiling solutions of arsenious acid and cupric acetate4 ,arsenious acid forms an insoluble compound with ferric hydroxide1 resembling the phosphate2 and this is the reason why freshly precipitated oxide of iron is employed as an antidote for arsenic4 ,the freshly precipitated oxide of iron1 taken immediately after poisoning by arsenic1 converts the arsenious acid into an insoluble state1 by forming a compound on which the acids of the stomach have no action1 so that the poisoning cannot proceed4 ,it is remarkable that the inhabitants of certain mountainous countries accustom themselves to taking arsenic1 as a means which1 according to their experience1 helps to overcome the fatigue of mountain ascents4 ,arsenious anhydride and certain of its salts are also used in medicine1 naturally only in small quantities4 ,when taken internally arsenic passes into the blood1 and is mainly excreted by the urine4 #ci ,adie 7#ahhi7 obtained compounds of ,as#b,o#c with #a1 #b1 #d1 and #h ,,so#c by the direct action of ordinary and ,nordhausen sulphuric acid upon ,as#b,o#c4 ,weber had previously obtained ,as#b,o#c,,so#c 7which disengages ,,so#c at #bbe71 and also other ,as#b,o#cn,,so#c 7where n #c1 #f1 and #h71 by the action of the vapours of ,,so#c upon ,as#b,o#c at a definite temperature4 ,the compound ,as#b,o#c1h,,so#c loses ,,so#c at #ajj4 ,oxide of antimony1 ,sb#b,o#c1 gives similar compounds4 ,adie 7#ahia7 also obtained 7by the action of ,,so#c upon ,h#c,,po#d7 a compound ,h#c,,po#dc,,so#c in the form of a viscous liquid decomposed by water4 ,antimony 7stibium71 ,sb #abj1 is another analogue of phosphorus4 ,in its external appearance and the properties of its compounds it resembles the metals still more closely than arsenic4 ,in fact1 antimony has the appearance1 lustre1 and many of the characteristic properties of the metals4 ,its oxide1 ,sb#b,o#c1 exhibits the earthy appearance of rust or of lime1 and has distinctly basic properties1 although it corresponds with nitrous and phosphorous anhydride1 and is able1 like them1 to give saline compounds with bases4 ,at the same time antimony presents1 in the majority of its compounds1 an entire analogy with phosphorus and arsenic4 ,its compounds belong to the type ,sb,x#c and ,sb,x#e4 ,it is found in nature chiefly in the form of sulphide1 ,sb#b,s#c4 ,this substance sometimes occurs in large masses in mineral veins and is known in mineralogy under the name of antimony glance or stibnite1 and commercially as antimony 7,chapter ,,xx41 ,note #bi74 ,the most abundant deposits of antimony ore occur in ,portugal 7near ,oporto on the ,douro74 ,besides which antimony partially or totally replaces arsenic in some minerals2 thus1 for example1 a compound of antimony sulphide and arsenic sulphide with silver sulphide is found in red silver ore4 ,but in every case antimony is a rather rare metal found in few localities4 ,in ,russia it is known to occur in ,daghestan in the ,caucasus4 ,it is extracted chiefly for the preparation of alloys with lead and tin1 which are used for casting printing type4#dj ,some of its compounds are also used in medicine1 the most important in this respect being antimony pentasulphide1 ,sb#b,s#e 7sulfur auratum antimonii71 and tartar emetic1 which is a double salt derived from tartaric acid and has the composition ,c#d;,h#d,k7,sb,o7,o#f4 ,even the native antimony sulphide is used in large quantities as a purgative for horses and dogs4 ,metallic antimony is extracted from the glance1 ,sb#b,s#b1 by roasting1 when the sulphur burns away and the antimony oxidises1 forming the oxide ,sb#b,o#c1 which is then heated with charcoal1 and thus reduced to a metallic state4 ,the reduction may be carried on in the laboratory on a small scale by fusing the sulphide with iron which takes up the sulphur4#dj bis #dj ,printers' type consists of an alloy known as 'type-metal1' containing usually about #ae parts of antimony to #he parts of lead2 sometimes 7for example1 for stereotypes7 from #aj to #ae per cent4 ,bi or #h per cent4 ,sn and even ,cu is added4 ,the hardness of the alloy1 which is essential for printing1 evidently depends upon the presence of antimony1 but an excess must be avoided1 since this renders the alloy brittle1 and the type after a time loses its sharpness4 #dj bis ,antimony is prepared in a state of greater purity by heating with charcoal the oxide obtained by the action of nitric acid on the impure commercial metallic antimony4 ,this is based on the fact that by the action of the acid1 antimony forms the oxide ,sb#b,o#c1 which is but slightly soluble in water4 ,the arsenic1 which is nearly always present1 forms soluble arsenious and arsenic acids1 and remains in solution4 ,the purest antimony is easily obtained from tartar emetic1 by heating it with a small quantity of nitre4 ,metallic antimony also occurs1 although rarely1 native2 and as it is very easily obtained1 it was known to the alchemists of the fifteenth century4 ,very pure metallic antimony may be deposited by the electric current from a solution of antimonious sulphide in sodium sulphide after the addition of sodium chloride to the solution4 ,metallic antimony has a white colour and a brilliant lustre2 it remains untarnished in the air1 for the metal does not oxidise at the ordinary temperature4 ,it crystallises in rhombohedra1 and always shows a distinctly crystalline structure which gives it quite a different aspect from the majority of the metals yet known4 ,it is most like tellurium in this respect4 ,antimony is brittle1 so that it is very easily powdered2 its specific gravity is #fg1 it melts at about #dcb1 but only volatilises at a bright red heat4 ,when heated in the air--for instance1 before the blow-pipe--it burns and gives white odourless fumes1 consisting of the oxide4 ,this oxide is termed antimonious oxide1 although it might as well be termed antimonious anhydride4 ,it is given the first name because in the majority of cases its compounds with acids are used1 but it forms compounds with the alkalis just as easily4 ,antimonious oxide1 like arsenious anhydride1 crystallises either in regular octahedra or in rhombic prisms2 its specific gravity is #eef2 when heated it becomes yellow and then fuses1 and when further heated in air it oxidises1 forming an oxide of the composition ,sb#b,o#d4 ,antimonious oxide is insoluble in water and in nitric acid1 but it easily dissolves in strong hydrochloric acid and in alkalis1 as well as in tartaric acid or solutions of its acid salts4 ,when dissolved in the latter it forms tartar emetic4 ,it is precipitated from its solutions in alkalis and acids 7by the action of acids on the former and alkalis on the latter74 ,it occurs native but rarely4 ,as a base it gives salts of the type ,sb,o,x 7as if the basic salts ,sb,x#c1 ,sb#b,o#c7 and hardly ever forms salts1 ,sb,x#c4 ,in the antimonyl salts1 ,sb,o,x1 the group ,sb,o is univalent1 like potassium or silver4 ,the oxide itself is 7,sb,o7#b,o1 the hydroxide1 ,sb,o7,,oh71 c42 tartar emetic is a salt in which one hydrogen of tartaric acid is replaced by potassium and the other by antimonyl1 ,sb,o4 ,antimonious oxide is very easily separated from its salts by any base1 but it must be observed that this separation does not take place in the presence of tartaric acid1 owing to the property of tartaric acid of forming a soluble double salt--i4e4 tartar emetic4#da #da ,as antimonious oxide answers to the type ,sb,x#c1 it is evident that compounds may exist in which antimony will replace three atoms of hydrogen2 such compounds have been to some extent obtained1 but they are easily converted by water into substances corresponding with the ordinary formul of the compounds of antimony4 ,thus tartar emetic1 ,c#d;,h#d7,sb,o7,,ko#f1 loses water when heated1 and forms ,c#d;,h#b,sb,k,o#f--that is1 tartaric acid1 ,c#b;,h#f,o#f1 in which one atom of hydrogen is replaced by potassium and three by antimony4 ,but this substance is reconverted into tartar emetic by the action of water4 ,a similar compound is seen in that intermediate oxide of antimony which is formed when antimonious oxide is heated in air3 its composition is ,sb,o#b or ,sb#b,o#d4 ,this oxide may be regarded as orthantimonic acid1 ,sb,o7,,ho7#c1 in which three atoms of hydrogen are replaced by antimony in that state in which it occurs in oxide of antimony--i4e4 ,sb,o7,sb,o#c7 ,sb#b,o#d4 ,oxide of antimony is also formed when antimonic acid is ignited2 it then loses water and oxygen1 and gives this intermediate oxide as a white infusible powder1 of sp4 gr4 #fg4 ,it is somewhat soluble in water1 and gives a solution which turns litmus paper red4 ,if metallic antimony1 or antimonious oxide1 be oxidised by an excess of nitric acid and the resultant mass be carefully evaporated to dryness1 metantimonic acid1 ,sb,h,o#c1 is formed4 ,its corresponding potassium salt1 #b,sb,k,o#c1e;,h#b,o1 is prepared by fusing metallic antimony with one-fourth its weight of nitre and washing the resultant mass with cold water4 ,this potassium salt is only slightly soluble in water 7in #ej parts7 and the sodium salt is still less so4 ,an ortho-acid1 ,sb,h#c,o#d1 also appears to exist2#da bis it is obtained by the action of water on antimony pentachloride1 but it is very unstable1 like the pentachloride1 ,sb,cl#e1 itself1 which easily gives up ,cl#b1 leaving antimony trichloride1 ,sb,cl#c1 and this is decomposed by water1 forming an oxychloride--,sb,o,cl1 only slightly soluble in water4 ,when antimonic acid is heated to an incipient red heat1 it parts with water and forms the anhydride1 ,sb#b,o#e1 of a yellow colour and specific gravity #fe4db #da bis ,beilstein and ,blaese 7#ahhi71 after preparing many salts of antimonic acid1 came to the conclusion that it is monobasic1 but all the salts still contain water1 so that their general type is mostly3 ,m,sb,o#cc;,h#b,o1 for example1 ,m ,li1 ,hg 7salts of the suboxide71 #a_/b ,pb1 c4 ,the type of the ortho-salts1 ,m#b,sb,o#d1 is quite unknown1 although it is reproduced in the thio-compounds1 for instance1 ,schlippe's salt1 ,na#b,sb,s#d1 but this salt also contains water of crystallisation1 #i;,h#b,o 7,chapter ,,xx41 ,note #bi74 #db ,among the other compounds of antimony1 antimoniuretted hydrogen1 ,sb,h#c1 resembles arseniuretted hydrogen in its mode of formation and properties 7it splits up at #aej1 ,brunn #ahij2 when liquified1 it boils at -#fe and solidifies at -#ib71 whilst the halogen compounds differ in many respects from those of arsenic4 ,when chlorine is passed over an excess of antimony powder1 it forms antimony trichloride1 ,sb,cl#c1 but if the chlorine be in excess it forms the pentachloride1 ,sb,cl#e4 ,the trichloride is a crystalline substance which melts at #gb and distils at #bcj1 whilst the pentachloride is a yellow liquid1 which splits up into chlorine and the trichloride when heated2 at #adj it begins to give off chlorine abundantly1 carrying away the vapour of the trichloride with it2 and at #bjj the decomposition is complete1 and pure antimonious chloride only passes over4 ,this property of antimony pentachloride has caused it to be applied in many cases for the transference of chlorine2 all the more that when it has given up its chlorine1 it leaves the trichloride1 which is able to absorb a fresh amount of chlorine2 and therefore many substances which are unable to react directly with gaseous chlorine do so with antimony pentachloride1 and in the presence of a small quantity of it chlorine will act on them1 just as oxygen is able1 in the presence of nitrogen oxides1 to oxidise substances which could not be oxidised by means of free oxygen4 ,thus carbon bisulphide is not acted on by chlorine at low temperatures--this reaction requires a high temperature--but in the presence of antimony pentachloride its conversion into carbon tetrachloride takes place at low temperatures4 ,antimony tri- and pentachloride1 having the character of chloranhydrides1 fume in air1 attract moisture1 and are decomposed by water1 forming antimonious and antimonic acids4 ,but in the first action of water the trichloride does not evolve all its chlorine as hydrochloric acid1 which is intelligible in view of the fact that antimonious anhydride is also a base1 and is therefore able to react with acids2 indeed antimony sulphide dissolved in an excess of hydrochloric acid 7hydrogen sulphide is evolved7 gives an aqueous solution of antimony trichloride1 which1 when carefully distilled1 even gives the anhydrous compound4 ,antimony trichloride is only decomposed by an excess of water1 and then not completely1 for with a large quantity of water it forms powder of algaroth--i4e4 antimony oxychloride4 ,the first action of water consists in the formation of oxychloride1 ,sb,o,cl--that is1 a salt corresponding to oxide of antimony as a base4 ,if antimony oxide or antimony chloride be dissolved in an excess of hydrochloric acid1 and the solution diluted with a considerable amount of water1 then this same powder of algaroth is precipitated4 ,the composition varies with the relative amount of water2 namely1 between the limits ,sb,o,cl and ,sb#d,o#e;,cl#b4 ,the latter compound is1 as it were1 a basic salt of the former1 because its composition #b7,sb,o,cl7,sb#b,o#c4 ,with bromine and iodine1 antimony forms compounds similar to those with chlorine4 ,antimonious bromide1 ,sb,br#c1 crystallises in colourless prisms1 melts at #id1 and boils at #bgj2 antimonious iodide1 ,sb,i#c1 forms red crystals of sp4 gr4 #ej2 antimony trifluoride1 ,sb,f#c separates from a solution of antimonious oxide in hydrofluoric acid1 and ,sb,f#e is formed by a similar treatment of antimonic acid4 ,the latter gives easily-soluble double salts with the fluorides of the metals of the alkalis4 ,de ,han 7#ahhg7 obtained very stable double soluble salts1 ,sb,f#c1,k,cl 7#ajj parts of water dissolve #eg parts of salt71 ,sb,f#c1,k#b,,so#d1 c41 which he proposed to make use of in the arts as very easily crystallisable and soluble salts of antimony4 ,engel1 by passing hydrochloric acid gas into a saturated solution of antimonious chloride at #j1 obtained a compound ,h,cl1#b,sb,cl#c1b;,h#b,o1 and with the pentachloride a compound ,sb,cl#e1e;,h,cl1#aj;,h#b,o4 ,bismuth trichloride1 ,bi,cl#c1 gives a similar compound4 ,saunders 7#ahib7 obtained #e,rb,cl1#c,sb,cl#c and ,rb,cl1,sb,cl#c4 ,ditte and ,metzner 7#ahib7 showed that ,sb and ,bi dissolve in hydrochloric acid only owing to the participation of the oxygen of the air or of that dissolved in the acid4 ,the heaviest analogue of nitrogen and phosphorus is bismuth1 ,bi #bjh4 ,here1 as in the other groups1 the basic1 metallic1 properties increase with the atomic weight4 ,bismuth does not give any hydrogen compound and the highest oxide1 ,bi#b,o#e1 is a very feeble acid oxide4 ,bismuthous oxide1 ,bi#b,o#c1 is a base1 and bismuth itself a perfect metal4 ,to explain the other properties of bismuth it must further be remarked that in the eleventh series it follows mercury1 thallium and lead1 whose atomic weights are near to that of bismuth1 and that therefore it resembles them and more especially its nearest neighbour1 lead4 ,although ,pb,o and ,pb,o#b1 represent types different from ,bi#b,o#c and ,bi#b,o#e1 they resemble them in many respects1 even in their external appearance1 moreover the lower oxides both of ,pb and ,bi are basic and the higher acid1 which easily evolve oxygen4 ,but judging by the formula1 ,bi#b,o#c is a more feeble base than ,pb,o4 ,they both easily give basic salts4 ,bismuth forms compounds of two types1 ,bi,x#c and ,bi,x#e1dc which entirely recall the two types we have already established for the compounds of lead4 ,just as in the case of lead1 the type ,pb,x#b1 is basic1 stable1 easily formed1 and passes with difficulty into the higher and lower types1 which are unstable1 so also in the case of bismuth the type of combination ,bi,x#c is the usual basic form4 ,the higher type of combination1 ,bi,x#e1dd in fact behaves toward this stable type1 ,bi,x#c1 in exactly the same manner as lead dioxide does to the monoxide2 and bismuthic acid is obtained by the action of chlorine on bismuth oxide suspended in water1 in exactly the same way as lead dioxide is obtained from lead oxide4 ,it is an oxidising agent like lead dioxide1 and even the acid character in bismuthic acid is only slightly more developed than in lead dioxide4 ,here1 as in the case of lead 7minium71 intermediate compounds are easily formed in which the bismuth of the lower oxide plays the part of a base combined with the acid which is formed by the higher form of the oxidation of bismuth4 #dc ,metallic bismuth is very easily obtained when the compounds of the oxide are reduced by powerful reducing agents1 but when less powerful reducing agents--for example1 stannous oxide--are taken1 bismuth suboxide is formed as a black crystalline powder4 ,it is a compound of the type ,bi,x#b1 its composition being ,bi,o2 it is decomposed by acids into the metal and oxide1 which passes into solution4 #dd ,the type ,bi,x#e is represented by the pentoxide1 ,bi#b,o#e1 its metahydrate1 ,bi#b,o#e1;,h#b,o1 or ,bi,h,o#c1 known as bismuthic acid1 and the pyrohydrate1 ,bi#b;,h#d,o#g4 ,bismuth pentoxide is obtained by the prolonged passage of chlorine through a boiling solution of potassium hydroxide 7sp4 gr4 #ach71 containing bismuth oxide in suspension2 the precipitate is washed with water1 with boiling nitric acid 7but not for long1 as otherwise the bismuthic acid is decomposed71 then again with water1 and finally the resultant bright red powder of the hydrate ,bi,h,o#c is dried at #abe4 ,the prolonged action of nitric acid on bismuthic anhydride1 ,bi#b,o#e1 results in the formation of the compound ,bi#b,o#d1;,h#b,o1 which decomposes in moist air1 forming ,bi#b,o#c4 ,the density of bismuthic anhydride is #eaj1 of the tetroxide1 ,bi#b,o#d1 #cfj1 and of bismuthic acid1 ,bi,h,o#c1 #ege4 ,pyrobismuthic acid1 ,bi#b;,h#d,o#g1 forms a brown powder1 which loses a portion of its water at #aej1 and decomposes on further heating1 with the evolution of oxygen and water4 ,it is obtained by the action of potassium cyanide on a solution of bismuth nitrate4 ,the meta-salts of bismuthic acid are known1 for example ,k,bi,o#c4 ,they generally occur1 however1 in combinations with metabismuthic acid itself4 ,thus ,andr 7#ahia7 took a solution of the double salt of ,bi,br#c and ,k,br1 treated it with bromine after adding ammonia1 and obtained a red-brown precipitate1 which after being washed 7for several weeks7 had the composition ,k,bi,o#c1;,h,bi,o#c ,when washed with dilute nitric acid this salt gave bismuthic acid4 ,illustration3 ,,fig4 #he4--;,furnace used for the extraction of bismuth from its ores4 ,in nature1 bismuth occurs in only a few localities and in small quantities1 most frequently in a native state1 and more rarely as oxide and as a compound of bismuth sulphide with the sulphides of other metals1 and sometimes in gold ores4 ,it is extracted from its native ores by simple fusion in the furnace shown in fig4 #he4 ,this furnace contains an inclined iron retort1 into the upper extremity of which the ore is charged1 and the molten metal flows from the lower extremity4 ,it is refined by re-melting1 and the pure metal may be obtained by dissolving in nitric acid1 decomposing the resultant salt with water1 and reducing the precipitate by heating it with charcoal4 ,bismuth is a metal which crystallises very well from a molten state4 ,its specific gravity is #ih2 it melts at #bfi1 and if it be melted in a crucible1 allowed to cool slowly1 and the crust broken and the remaining molten liquid poured out1 perfect rhombohedral crystals of bismuth are obtained on the sides of the crucible4#dd bis ,it is brittle1 has a grey-coloured fracture with a reddish lustre1 is not hard1 and is but very slightly ductile and malleable2 it volatilises at a white heat and easily oxidises4 ,it recalls antimony and lead in many of its properties4 ,when oxidised in air1 or when the nitrate is ignited1 bismuth forms the oxide1 ,bi#b,o#c1 as a white powder which fuses when heated and resembles massicot4 ,the addition of an excess of caustic potash to a solution of a bismuthous salt gives a white precipitate of the hydroxide1 ,bi,o7,,oh71 which loses its water and gives the anhydrous oxide when boiled with a solution of caustic potash4 ,both the hydroxide and oxide easily dissolve in acids and form bismuthous salts4 #dd bis ,hrard 7#ahhi7 obtained a peculiar variety of bismuth by heating pure crystalline bismuth to a bright red heat in a stream of nitrogen4 ,a greenish vapour was deposited in the cooler portions of the apparatus in the form of a grey powder1 which under the microscope had the appearance of minute globules4 ,an atmosphere of nitrogen is necessary for this transformation1 other gases such as hydrogen and carbonic oxide do not favour the transition4 ,the resultant amorphous bismuth fuses at #daj 7the crystalline variety at #bfi71 sp4 gr4 #idhc4 7,does it not contain a nitride87 ,bismuthous oxide1 ,bi#b,o#c1 is a feeble and unenergetic base4 ,the normal hydroxide of the oxide ,bi#b,o#c is ,bi7,,oh7#c2 it parts with water and forms a metahydroxide 7bismuthyl hydroxide71 ,bi,o7,,oh74 ,both of these hydroxides have their corresponding saline compounds of the composition ,bi,x#c and ,bi,o,x4 ,and the form ,bi,o,x is nothing else but the type of the basic salt1 because #c,,rox ,,rx ,r#b,o#c4 ,it is evident that in the type ,bi,x#c the bismuth replaces three atoms of hydrogen4 ,and indeed with phosphoric acid solutions of the bismuthous salts give a precipitate of the composition ,bi,p,o#d4 ,on the other hand1 in the form of compounds ,bi,o,x or ,bi7,,oh7#b,x1 the univalent group 7,bi,o7 or 7,bi,h#b,o#b7 is combined with ,x4 ,many bismuth salts are formed according to the type ,bi,o,x4 ,for instance the carbonate1 7,bi,o7#b;,,co#c1 which corresponds with the other carbonates ,m#b;,,co#c4 ,it is obtained as a white precipitate when a solution of sodium carbonate is added to a solution of a bismuth salt4#de ,the compound radicle ,bi,o is not a special natural grouping1 as it was formerly represented to be2 it is simply a mode of expression for showing the relation between the compound in question and the compounds of other oxides4 #de ,basic bismuth carbonate is employed for whitening the skin 7veloutine1 c47 ,three salts of nitric acid are known containing bismuthous oxide4 ,if metallic bismuth or its oxide be dissolved in nitric acid1 it forms a colourless transparent solution containing a salt which separates in large transparent crystals containing ,bi7,,no#c7c1e;,h#b,o4 ,when heated at #hj these crystals melt in their water of crystallisation1 and in so doing lose a portion of their nitric acid together with water1 forming a salt whose empirical formula is ,bi#b,n#b;,h#b,o#i4 ,if the preceding salt belongs to the type ,bi,x#c1 this one should belong to the form ,bi,o,x1 because it ,bi,o7,,no#c7 ,bi7,h#b,o#b77,,no#c74 ,this salt may be heated to #aej without change4 ,when the first colourless crystalline salt dissolves in water it is decomposed4 ,there is no decomposition if an excess of acid be added to the water--that is to say1 the salt is able to exist in an acid solution without decomposing1 without separation of the so-called basic salt--but by itself it cannot be kept in solution2 water decomposes this salt1 acting on it like an alkali4 ,in other words the basic properties of bismuthic oxide are so feeble that even water acts by taking up a portion of the acid from it4 ,here we see one of the most striking facts1 long since observed1 confirming that action of water on salts about which we have spoken in ,chapter ,x4 and elsewhere4 ,this action on water may be expressed thus3--,bi,x#c #b;,h#b,o ,bi7,,oh7#b,x #b,,xh4 ,a salt of the type ,bi7,,oh7#b,x is obtained in the precipitate4 ,but if the quantity of acid1 ,,hx1 be increased1 the salt ,bi,x#c is again formed and passes into solution4 ,the quantity of the salt ,bi,o,x which passes into solution on the addition of a given quantity of acid depends indisputably on the amount 7mass7 of water 7,muir74 ,the solution1 which is perfectly transparent with a small amount of water1 becomes cloudy and deposits the salt of the type ,bi,o,x1 when diluted4 ,the white flaky precipitate of ,bi7,,oh7#b,,no#c formed from the normal salt ,bi7,,no#c7c by mixing it with five parts of water1 and in general with a small amount of water1 is used in medicine under the name of magistery of bismuth4#df #df ,with an excess of water a further quantity of acid is separated and a still more basic salt formed4 ,the ultimate product1 on which an excess of water has apparently no action whatever1 is a substance having the composition ,bi,o7,,no#c74;,bi,o7,,oh74 ,in the latter salt we see the limit of change1 and this limit appears to show that the type of the saline compounds of bismuthic oxide is of the form ,bi#b,x#f1 and not ,bi,x#c2 but it is very probable1 on the basis of the examples which we considered in the case of lead1 that this type should be still further polymerised in order to give a correct idea of the type of the bismuthous compounds4 ,if we refer all the bismuthous compounds to this type1 ,bi#b,x#f1 we shall obtain the following expression for the composition of the nitrates3 normal salt1 ,bi#b7,,no#c7f1 first basic salt1 ,bi#b,o7,,oh7#b7,,no#c7b1 magistery of bismuth1 ,bi#b7,,oh7#d7,,no#c7b1 and the limiting form ,bi#b,o#b7,,oh77,,no#c74 ,the general character of bismuthous oxide in its compounds is well exemplified in the nitrate2 bismuthous chloride1 ,bi,cl#c1 which is obtained by heating bismuth in chlorine1 or by dissolving it in aqua regia1 and then distilling without access of air1 is also decomposed by water in exactly the same manner1 and forms basic salts--for instance1 first1 ,bi,o,cl1 like the above salt of nitric acid4 ,bismuth chloride boils at #ddg and probably its formula is ,bi,cl#c4 ,polymerisation may take place in some compounds and not in others4 ,a volatile compound of the composition ,bi7,c#b;,h#e7c is also known as a liquid which is insoluble in water and decomposes with explosion when heated at #acj4 ,double salts containing chloride of bismuth are3 #b7,k,cl7,bi,cl#cb;,h#b,o 7from a solution of ,bi#b,o#c and ,k,cl in hydrochloric acid7 and ,k,cl,bi,cl#c;,h#b,o4 ,bigham 7#ahib7 also obtained ,k,br7,,so#d7b in tabular crystals by treating the above-named double salt with strong sulphuric acid4 ,the composition of this salt recalls that of alum4 ,metallic bismuth is used in the preparation of fusible alloys4 ,the addition of bismuth to many metals renders them very hard1 and at the same time generally lowers their melting point to a considerable extent4 ,thus ,wood's metal1 which contains one part of cadmium1 one part of tin1 two parts of lead1 and four parts of bismuth1 fuses at about #fj1 and in general many alloys composed of bismuth1 tin1 lead1 and antimony melt below or about the boiling point of water4#dg #dg ,as the metals contained in alloys like the above 7bismuth1 lead1 tin1 cadmium7 are difficultly volatile and their alloys are fusible1 they may be employed in the place of mercury in many physical experiments conducted at or above #gj1 and they offer the advantage that they do not give any vapour having an appreciable tension 7mercury at #ajj1 #jge mm47 ,bismuth expands in passing into a molten state1 but it has a temperature of maximum density4 ,according to ,luedeking the mean coefficient of expansion of liquid bismuth is #jjjjjddb 7between #bgj and #cjc71 and of solid bismuth #jjjjjdaa4 ,just as in group ,,ii41 side by side with the elements zinc1 cadmium1 and mercury in the uneven series1 we found calcium1 strontium1 and barium in the even series2 and as in group ,,iv41 parallel to silicon1 germanium1 tin1 and lead1 we noticed thallium1 zirconium1 cerium1 and thorium2 so also in group ,v4 we find1 beside those elements of the uneven series just considered by us1 a series of analogues in the even series1 which1 with a certain degree of similarity 7mainly quantitative1 or relative to the atomic weights71 also present a series of particular 7qualitative7 independent points of distinction4 ,in the even series are known vanadium1 which stands between titanium and chromium1 niobium1 between zirconium and molybdenum1 and tantalum1 situated near tungsten 7an element of group ,,vi4 like chromium and molybdenum74 ,just as bismuth is similar in many respects to its neighbour lead1 so also do these neighbouring elements resemble each other1 even in their external appearance1 not to mention the quality of their compounds1 naturally taking into account the differences of type corresponding with the different groups4 ,the occurrence in group ,v4 determines the type of the oxides1 ,r#b,o#c and ,r#b,o#e1 and the development of an acid character in the higher oxides4 ,the occurrence in the even series determines the absence of volatile compounds1 ,,rh#c1 for these metals1 and a more basic character of the oxides of a given composition than in the uneven series1 c4#dh ,vanadium1 niobium1 and tantalum belong to the category of rare metals1 and are exceedingly difficult to obtain pure1 more especially owing to their similarity to1 and occurrence with1 chromium1 tungsten and other metals1 and also in combination among themselves2 therefore it is natural that they have been far from completely studied1 although since #ahfj chemists have devoted not a little time to their investigation4 ,the researches carried out by ,marignac1 at ,geneva1 on niobium1 and by ,sir ,henry ,roscoe1 at ,manchester1 on vanadium deserve special attention4 ,the undoubted external resemblance of the compounds of chromium and vanadium1 as well as the want of completeness in the knowledge of the compounds of vanadium1 long caused its oxides to be considered analogous in atomic composition to those formed by chromium4 ,the higher oxide of vanadium was therefore supposed to have the formula ,,vo#c4 ,but the fact of the matter is1 that the chemical analogy of the elements does not hold in one direction only2 vanadium is at one and the same time the analogue of chromium1 and consequently of the elements like sulphur of group ,,vi1 and also the analogue of phosphorus1 arsenic1 and antimony2 just as bismuth stands in respect to lead and antimony4 ,investigation has shown that the compounds of vanadium are always accompanied by those of phosphorus as well as of iron1 and that it is even more difficult to separate it from the compounds of phosphorus than from those of iron and tungsten4 ,we should have to extend our description considerably if we wished to give the complete history1 even of vanadium alone1 not to mention niobium and tantalum1 all the more as questions would not unfrequently arise concerning the compounds of these elements which have not yet been fully elucidated4 ,we shall therefore limit ourselves to pointing out the most important features in the history of these elements1 the more so since the minerals themselves in which they occur are exceedingly rare and only accessible to a few investigators4 #dh ,although1 guided by ,brauner1 who showed that didymium gives a higher oxide1 ,di#b,o#e1 ,i place this element in the fifth group1 still ,i am not certain as to its position1 because ,i consider that the questions relating to this metal are still far from being definitely answered4 ,an important point in the history of the members of this group is the circumstance that they form volatile compounds with chlorine1 similar to the compounds of the elements of the phosphorus group1 namely1 of the type ,,rx#e4 ,the vapour densities of the compounds of this kind were determined1 and served as the most important basis for the explanation of the atomic composition of these molecules4 ,in this we see the power of general and fundamental laws1 like the law of ,avogadro-,gerhardt4 ,an oxychloride1 ,v,o,cl#c1 is known for vanadium1 which is the perfect analogue of phosphorus oxychloride4 ,it was formerly considered to be vanadium chloride1 for just as in the case of uranium 7,chapter ,,xxi471 its lower oxide1 ,,vo1 was considered to be the metal1 because it is exceedingly difficultly reduced--even potassium does not remove all the oxygen1 besides which it has a metallic appearance1 and decomposes acids like a metal2 in a word1 it simulates a metal in every respect4 ,vanadium oxychloride is obtained by heating the trioxide1 ,v#b,o#c1 mixed with charcoal1 in a current of hydrogen2 the lower oxide of vanadium is then formed1 and this1 when heated in a current of dry chlorine1 gives the oxychloride ,v,o,cl#c as a reddish liquid which does not act on sodium and may be purified by distillation over this metal4 ,it fumes in the air1 giving reddish vapours2 it reacts on water1 forming hydrochloric and vanadic acids2 hence1 on the one hand it is very similar to phosphorus oxychloride1 and on the other hand to chromium oxychloride1 ,cr,o#b;,cl#b 7,chapter ,,xxi474 ,it is of a yellow colour1 its specific gravity is #ahc1 it boils at #abj1 and its vapour density is #hf with respect to hydrogen2 therefore the above formula expresses its molecular weight4#di #di ,when the vapours of vanadium oxychloride are heated with zinc in a closed tube at #djj1 they lose a portion of their chlorine and form a green crystalline mass of sp4 gr4 #bhh1 which is deliquescent in air and has the composition ,v,o,cl#b4 ,only its vapour density is unknown1 and it would be extremely important to determine whether its molecular composition is that given above1 or whether it corresponds with the formula ,v#b,o#b;,cl#d4 ,another less volatile oxychloride1 ,v,o,cl1 is formed with it as a brown insoluble substance1 which is1 however1 soluble in nitric acid like the preceding4 ,roscoe obtained a still less chlorinated substance1 namely1 7,,vo7#b;,cl2 but it may only consist of a mixture of ,,vo and ,v,o,cl4 ,at all events1 we here find a graduated series such as is met with in the compounds of very few other elements4 ,vanadic anhydride1 ,v#b,o#e1 is obtained either in small quantities from certain clays where it accompanies the oxides of iron 7hence some sorts of iron contain vanadium7 and phosphoric acid1 or from the rare minerals3 volborthite1 ,cu,h,v,o#d1 or basic vanadate of copper2 vanadinite1 ,pb,cl#bc,pb#c7,,vo#d7b2 lead vanadate1 ,pb#c7,,vo#d7b1 c4 ,the latter salts are carefully ignited for some time with one-third of their weight of nitre2 the fused mass thus formed is powdered and boiled in water3 the yellow solution obtained contains potassium vanadate4 ,the solution is neutralised with acid1 and barium chloride added2 a meta-salt1 ,ba7,,vo#c7b1 is then precipitated as an almost insoluble white powder1 which gives a solution of vanadic acid when boiled with sulphuric acid4 7,the precipitate is at first yellow1 as long as it remains amorphous1 but it afterwards becomes crystalline and white47 ,the solution thus obtained is neutralised with ammonia1 which thus forms ammonium 7meta7 vanadate1 ,,nh#d,,vo#c1 which1 when evaporated1 gives colourless crystals1 insoluble in water containing sal-ammoniac2 hence this salt is precipitated by adding solid sal-ammoniac to the solution4 ,ammonium vanadate1 when ignited1 leaves vanadic acid behind4 ,in this it differs from the corresponding chromium salt1 which is deoxidised into chromium oxide when ignited4 ,in general1 vanadic acid has but a small oxidising action4 ,it is reduced with difficulty1 like phosphoric or sulphuric acid1 and in this differs from arsenic and chromic acids4 ,vanadic acid1 like chromic acid1 separates from its solution as the anhydride ,v#b,o#e1 and not in a hydrous state4 ,vanadic anhydride1 ,v#b,o#e1 forms a reddish-brown mass1 which easily fuses and re-solidifies into transparent crystals having a violet lustre 7another point of resemblance to chromic acid72 it dissolves in water1 forming a yellow solution with a slightly acid reaction4#ej #ej ,strong acids and alkalis dissolve vanadic anhydride in considerable quantities1 forming yellow solutions4 ,when it is ignited1 especially in a current of hydrogen1 it evolves oxygen and forms the lower oxides2 ,v#b,o#d 7acid solutions of a green colour1 like the salts of chromic oxide71 ,v#b,o#c1 and the lowest oxide1 ,,vo4 ,the latter is the metallic powder which is obtained when the vanadium oxychloride is heated in an excess of hydrogen1 and was formerly mistaken for metallic vanadium4 ,when a solution of vanadic acid is treated with metallic zinc it forms a blue solution1 which seems to contain this oxide4 ,it acts as a reducing agent 7and forms a close analogue to chromous oxide1 ,cr,o74 ,metallic vanadium can only be obtained from vanadium chloride which is quite free from oxygen4 ,moissan 7#ahic7 obtained it by reducing the oxide with carbon in the electric furnace1 and considered it to be most infusible of the metals in the series ,pt1 ,cr1 ,mo1 ,u1 ,w1 and ,v 7he also obtained a compound of vanadium and carbon74 ,the specific gravity of this metal is #ee4 ,it is of a grey-white colour1 is not decomposed by water1 and is not oxidised in air1 but burns when strongly heated1 and can be fused in a current of hydrogen 7forming perhaps a compound with hydrogen74 ,it is insoluble in hydrochloric acid1 but easily dissolves in nitric acid1 and when fused with caustic soda it forms sodium vanadate4 ,as regards the salts of vanadic acid1 three different classes are known2 the first correspond with metavanadic acid1 ,,vmo#c ,m#b,,ov#b,o#e1 the second correspond with the dichromates--that is1 have the composition ,v#d,m#b,o#aa1 which is equal to ,m#b,o #b,v#b,o#e--;and the third correspond with orthovanadic acid1 ,,vm#c,o#d or #c,m#b,o ,v#b,o#e4 ,the latter are formed when vanadic anhydride is fused with an excess of an alkaline carbonate4 ,vanadic acid gives the so-called 'complex' acids 7which are considered more fully in ,chapter ,,xxi4 in speaking of ,mo and ,w7--i4e4 acids formed of two acids assimilated into one4 ,thus ,friedheim 7#ahij7 obtained phosphor-vanadic acid1 and ,schmitz-,dumont 7#ahij7 a similar arseno-vanadic acid4 ,the former is obtained by heating ,v#b,o#e with sirupy phosphoric acid4 ,the resultant golden-yellow tabular crystals have the composition ,h#b,,ov#b,o#e,p#b,o#ei;,h#b,o1 and there are corresponding salts--for example1 7,,nh#d7b,v#b,o#e,p#b,o#e with #c and #g;,h#b,o1 c4 ,these salts cannot be separated by crystallisation1 so that there are 'complexes' of these acids in a whole series of salts 7and also in nature74 ,it may be supposed 7,friedheim7 that ,v#b,o#e here1 as it were1 plays the part of a base1 or that those acids may be looked upon as double salts4 ,among the true double salts of vanadium 7,nb and ,ta7 very many are known among the fluorides1 such as ,,vf#cb,,nh#d;,f1 ,,vof#bb,,nh#d;,f1 ,,vo#b;,f1#c,,nh#d;,f1 c4 7,pettersson1 ,piccini1 and ,georgi1 #ahij-ib74 ,vanadium was discovered at the beginning of this century by ,del-,rio1 and afterwards investigated by ,sefstrm1 but it was only in #ahfh that ,roscoe established the above formul of the vanadic compounds4 ,niobium and tantalum#ea occur as acids in rare minerals1 and are mainly extracted from tantalite and columbite1 which are found in ,bavaria1 ,finland1 ,north ,america1 and in the ,urals4 ,these minerals are composed of the ferrous salts of niobic and tantalic acids2 they contain about #ae per cent4 of ferrous oxide in isomorphous mixture with manganous oxide1 in combination with various proportions of tantalic and niobic anhydrides4 ,these minerals are first fused with a considerable amount of potassium bisulphate1 and the fused mass is boiled in water1 which dissolves the ferrous and potassium salts and leaves an insoluble residue of impure niobic and tantalic acids4 ,this raw product is then treated with ammonium sulphide1 in order to extract the tin and tungsten1 which pass into solution4 ,the residue containing the acids 7according to ,marignac7 is then treated with hydrofluoric acid1 in which it entirely dissolves1 and potassium fluoride is added to the resultant hot solution2 on cooling1 a sparingly soluble double fluoride of potassium and tantalum separates out in fine crystals1 while the much more soluble niobium salt remains in solution4 ,the difference in the solubility of these double salts in water acidified with hydrofluoric acid 7in pure water the solution becomes cloudy after a certain time7 is so great that the tantalum compound requires #aej parts of water for its solution1 and the niobium compound only #ac parts4 ,the ,greenland columbite 7specific gravity #ecf7 only contains niobic acid1 and that from ,bodenmais1 ,bavaria 7specific gravity #fjf7 almost equal quantities of tantalic and niobic acids4 ,having isolated tantalic and niobic salts1 ,marignac found that the relation between the potassium and fluorine in them is very variable--that is1 that there exist various double salts of fluoride of potassium1 and of the fluorides of the metals of this group1 but that with an excess of hydrofluoric acid both the tantalum and niobium compounds contain seven atoms of fluorine to two of potassium1 whence it must be concluded that the simplest formula for these double salts will be ,k#b,,rf#g ,,rf#e1b,,kf2 that is1 that the type of the higher compounds of niobium and tantalum is ,,rx#e1 and hence is similar to phosphoric acid4 ,a chloride1 ,ta,cl#e1 may be obtained from pure tantalic acid by heating it with charcoal in a current of chlorine4 ,this is a yellow crystalline substance1 which melts at #baa1 and boils at #bda2 its vapour density with respect to hydrogen is #ahj1 as would follow from the formula ,ta,cl#e4 ,it is completely decomposed by water into tantalic and hydrochloric acids4 ,niobium pentachloride may be prepared in the same manner2 it fuses at #aid1 and boils at #bdj4 ,when treated with water this substance gives a solution containing niobic acid1 which only separates out on boiling the solution4 ,delafontaine and ,deville found its vapour density to be #ic 7air #a71 as is shown by its formula ,nb,cl#e4eb #ea ,the researches made by ,roscoe were preceded by those of ,marignac in #ahfe1 on the compounds of niobium and tantalum1 to which were also ascribed different formul from those now recognised4 ,tantalum was discovered simultaneously with vanadium by ,hatchett and ,ekeberg1 and was afterwards studied by ,rose1 who in #ahdd discovered niobium in it4 ,notwithstanding the numerous researches of ,hermann 7in ,moscow71 ,kobell1 ,rose1 and ,marignac1 still there is not yet any certainty as to the purity of1 and the properties ascribed to1 the compounds of these elements4 ,they are difficult to separate from each other1 and especially from the cerite metals and titanium1 c41 which accompany them4 ,before the investigations of ,rose the highest oxide of tantalum was supposed to belong to the type ,ta,x#f--that is1 its composition was taken as ,ta,o#c1 and to the lower oxide was ascribed a formula ,ta,o#b4 ,rose gave the formula ,ta,o#b to the higher oxide1 and discovered a new element called niobium in the substance previously supposed to be the lower oxide4 ,he even admitted the existence of a third element occurring together with tantalum and niobium1 which he named pelopium1 but he afterwards found that pelopic acid was only another oxide of niobium1 and he considered it probable that the higher oxide of this element is ,nb,o#b1 and the lower ,nb#b,o#c4 ,hermann found that niobic acid which was considered pure contained a considerable quantity of tantalic acid1 and besides this he admitted the existence of another special metallic acid1 which he called ilmenic acid1 after the locality 7the ,ilmen mountains of the ,urals7 of the mineral from which he obtained it4 ,v4 ,kobell recognised still another acid1 which he called dianic acid1 and these diverse statements were only brought into agreement in the sixties by ,marignac4 ,he first of all indicated an accurate method for the separation of tantalic and niobic compounds1 which are always obtained in admixture4 #eb ,if niobic acid be mixed with a small quantity of charcoal and ignited in a stream of chlorine1 a difficultly-fusible and difficultly-volatile oxychloride1 ,nb,o,cl#c separates4 ,the vapour density of this compound with respect to air is #ge1 and this vapour density perfectly confirms the accuracy of the formul given by ,marignac1 and indicates the quantitative analogy between the compounds of niobium and tantalum1 and those of phosphorus and arsenic1 and consequently also of vanadium4 ,in their qualitative relations 7as is evident also from the correspondence of the atomic weights71 the compounds of tantalum and niobium exhibit a great analogy with the compounds of molybdenum and tungsten4 ,thus zinc1 when acting on acid solutions of tantalic and niobic compounds1 gives a blue coloration1 exactly as it does with those of tungsten and molybdenum 7also titanium74 ,these acids form the same large number of salts as those of tungsten and molybdenum4 ,the anhydrides of the acids are also insoluble in water1 but as colloids are sometimes held in solution1 just like those of titanic and molybdic acids4 ,furthermore1 niobium is in every respect the nearest analogue of molybdenum1 and tantalum of tungsten4 ,niobium is obtained by reducing the double fluoride of niobium and sodium1 with sodium4 ,it is difficult to obtain in a pure state4 ,it is a metal on which hydrochloric acid acts with some energy1 as also does hydrofluoric acid mixed with nitric acid1 and also a boiling solution of caustic potash4 ,tantalum1 which is obtained in exactly the same way1 is a much heavier metal4 ,it is infusible1 and is only acted on by a mixture of hydrofluoric and nitric acids4 ,rose in #ahfh showed that in the reduction of the double fluoride1 ,nb,f#e1b,,kf1 by sodium1 a greyish powder is obtained after treating with water4 ,the specific gravity of this powder is #fh1 and he considers it to be niobium hydride1 ,nb,h4 ,neither did he obtain metallic niobium when he reduced with magnesium and aluminium1 but an alloy1 ,al#c,nb1 having a sp4 gr4 of #de4 ,niobium1 so far as is known1 unites in three proportions with oxygen4 ,nb,o1 which is formed when ,nb,o,f#c1b,,kf is reduced by sodium2 ,nb,o#b1 which is formed by igniting niobic acid in a stream of hydrogen1 and niobic anhydride1 ,nb#b,o#e1 a white infusible substance1 which is insoluble in acids1 and has a specific gravity of #de4 ,tantalic anhydride closely resembles niobic anhydride1 and has a specific gravity of #gb4 ,the tantalates and niobates present the type of ortho-salts--for example1 ,na#b;,h,nb,o#d1f;,h#b,o1 and also of pyro-salts1 such as ,k#c;,h,nb#b,o#g1f;,h#b,o1 and of meta-salts--for example1 ,k,nb,o#c1b;,h#b,o4 ,and1 besides these1 they give salts of a more complex type1 containing a larger amount of the elements of the anhydride2 thus1 for instance1 when niobic anhydride is fused with caustic potash it forms a salt which is soluble in water1 and crystallises in monoclinic prisms1 having the composition ,k#h,nb#f,o#ai1af;,h#b,o4 ,there is a perfectly similar isomorphous salt of tantalic acid4 ,tantalite is a salt of the type of metatantalic acid1 ,fe7,ta,o#c7b4 ,the composition of ,yttrotantalite appears to correspond with orthotantalic acid4 ,,chapter ,,xx ,,sulphur1 ,,selenium1 ,,and ,,tellurium ,the acid character of the higher oxides ,,ro#c of the elements of group ,,vi4 is still more clearly defined than that of the higher oxides of the preceding groups1 whilst feeble basic properties only appear in the oxides ,,ro#c of the elements of the even series1 and then only for those elements having a high atomic weight--that is1 under those two conditions in which1 as a rule1 the basic characters increase4 ,even the lower types ,,ro#b and ,r#b,o#c1 c41 formed by the elements of group ,,vi41 are acid anhydrides in the uneven series1 and only those of the elements of the even series have the properties of peroxides or even of bases4 ,sulphur is the typical representative of group ,,vi41 both on account of the fact that the acid properties of the group are clearly defined in it1 and also because it is more widely distributed in nature than any of the other elements belonging to this group4 ,as an element of the uneven series of group ,,vi41 sulphur gives ,h#b,s1 sulphuretted hydrogen1 ,,so#c1 sulphuric anhydride1 and ,,so#b1 sulphurous anhydride4 ,and in all of them we find acid properties--,,so#c and ,,so#b are anhydrides of acids1 and ,h#b,s is an acid1 although a feeble one4 ,as an element sulphur has all the properties of a true non-metal2 it has not a metallic lustre1 does not conduct electricity1 is a bad conductor of heat1 is transparent1 and combines directly with metals--in short it has all the properties of the non-metals1 like oxygen and chlorine4 ,furthermore1 sulphur exhibits a great qualitative and quantitative resemblance to oxygen1 especially in the fact that1 like oxygen1 it combines with two atoms of hydrogen1 and forms compounds resembling oxides with metals and non-metals4 ,from this point of view sulphur is bivalent1 if the halogens are univalent4#a ,the chemical character of sulphur is expressed by the fact that it forms a very slightly stable and feebly energetic acid with hydrogen4 ,the salts corresponding with this acid are the sulphides1 just as the oxides correspond to water and the chlorides to hydrochloric acid4 ,however1 as we shall afterwards see more fully1 the sulphides are more analogous to the former than to the latter4 ,but although combining with metals1 like oxygen1 sulphur also forms chemically stable compounds with oxygen1 and this fact impresses a peculiar character on all the relations of this element4#b #a ,the character of sulphur is very clearly defined in the organo-metallic compounds4 ,not to dwell on this vast subject1 which belongs to the province of organic chemistry1 ,i think it will be sufficient for our purpose to compare the physical properties of the ethyl compounds of mercury1 zinc1 sulphur and oxygen4 ,the composition of all of them is expressed by the general formula 7,c#b;,h#e7b,r1 where ,r ,hg1 ,zn1 ,s1 or ,o4 ,they are all volatile3 mercury ethyl1 ,hg7,c#b;,h#e7b1 boils at #aei1 its sp4 gr4 is #bddd1 molecular volume #ajf2 zinc ethyl boils at #aah1 sp4 gr4 #ahhb1 volume #aja2 ethyl sulphide1 ,s7,c#b;,h#e7b1 boils at #ij1 sp4 gr4 #jhbe1 volume #ajg2 common ether1 or ethyl oxide1 ,o7,c#b;,h#e7b1 boils at #ce1 sp4 gr4 #jgcf1 volume #aja1 in addition to which diethyl itself1 7,c#b;,h#e7b ,c#d;,h#aj1 boils about #j1 sp4 gr4 about #jfb1 volume about #id4 ,thus the substitution of ,hg1 ,s1 and ,o scarcely changes the volume1 notwithstanding the difference of the weights2 the physical influence1 if one may so express oneself1 of these elements1 which are so very different in their atomic weights1 is almost alike4 #b ,therefore in former times sulphur was known as an amphid element4 ,although the analogy between the compounds of sulphur and oxygen has been recognised from the very birth of modern chemistry 7owing1 amongst other things1 to the fact that the oxides and sulphides are the most widely spread metallic ores in nature71 still it has only been clearly expressed by the periodic system1 which places both these elements in group ,,vi4 ,here1 moreover1 stands out that parallelism which exists between ,,so#b and ozone ,,oo#b1 between ,k#b,,so#c and peroxide of potassium ,k#b,o#d 7,volkovitch in #ahic again drew attention to this parallelism74 ,sulphur belongs to the number of those elements which are very widely distributed in nature1 and occurs both free and combined in various forms4 ,the atmosphere1 however1 is almost entirely free from compounds of sulphur1 although a certain amount of them should be present1 if only from the fact that sulphurous anhydride is emitted from the earth in volcanic eruptions1 and in the air of cities1 where much coal is burnt1 since this always contains ,fe,s#b4 ,sea and river water generally contain more or less sulphur in the form of sulphates4 ,the beds of gypsum1 sodium sulphate1 magnesium sulphate1 and the like are formations of undoubtedly aqueous origin4 ,the sulphates contained in the soil are the source of the sulphur found in plants1 and are indispensable to their growth4 ,among vegetable substances1 the proteds always contain from one to two per cent4 of sulphur4 ,from plants the albuminous substances1 together with their sulphur1 pass into the animal organism1 and therefore the decomposition of animal matter is accompanied by the odour of sulphuretted hydrogen1 as the product into which the sulphur passes in the decomposition of the albuminous substances4 ,thus a rotten egg emits sulphuretted hydrogen4 ,sulphur occurs largely in nature1 as the various insoluble sulphides of the metals4 ,iron1 copper1 zinc1 lead1 antimony1 arsenic1 c41 occur in nature combined with sulphur4 ,these sulphides frequently have a metallic lustre1 and in the majority of cases occur crystallised1 and also very often several sulphides occur combined or mixed together in these crystalline compounds4 ,if they are yellow and have a metallic lustre they are called pyrites4 ,such are1 for example1 copper pyrites1 ,cu,fe,s#b1 and iron pyrites1 ,fe,s#b1 which is the commonest of all4 ,they are all also known as glances or blendes if they are greyish and have a metallic lustre--for example1 zinc blende1 lead glance1 ,pb,s1 antimony glance1 ,sb#b,s#c1 c4 ,and1 lastly1 sulphur occurs native4 ,it occurs in this form in the most recent geological formations in admixture with limestone and gypsum1 and most frequently in the vicinity of active or extinct volcanoes4 ,as the gases of volcanoes contain sulphur compounds--namely1 sulphuretted hydrogen and sulphurous anhydride1 which by reacting on one another may produce sulphur1 which also frequently appears in the craters of volcanoes as a sublimate--it might be imagined that the sulphur was of volcanic origin4 ,but on a nearer acquaintance with its mode of occurrence1 and more especially considering its relation to gypsum1 ,ca,s,o#d1 and limestone1 the present general opinion leads to the conclusion that the 'native' sulphur has been formed by the reduction of the gypsum by organic matter and that its occurrence is only indirectly connected with volcanic agencies4 ,near ,tetush1 on the ,volga1 there are beds containing gypsum1 sulphur1 and asphalt 7mineral tar74 ,in ,europe the most important deposits of sulphur are in the south of ,sicily from ,catania to ,girgenti4#c ,there are very rich deposits of sulphur in ,daghestan near ,cherkai and ,cherkat in ,khyut1 near ,mount ,kanabour-bam1 near ,petrovsk1 and in the ,kira ,koumski steppes in the ,trans-,caspian provinces1 which are able to supply the whole of ,russia with this mineral4 ,abundant deposits of sulphur have also been found in ,kamtchatka in the neighbourhood of the volcanoes4 ,the method of separation of the sulphur from its earthy impurities is based on the fact that sulphur melts when it is heated4 ,the fusion is carried on at the expense of a portion of the sulphur1 which is burnt1 so that the remainder may melt and run from the mass of the earth4 ,this is carried on in special furnaces called calcaroni1 built up of unhewn stone in the neighbourhood of the mines4#d #c ,when in ,sicily1 ,i found1 near ,caltanisetta1 a specimen of sulphur with mineral tar4 ,in the same neighbourhood there are naphtha springs and mud volcanoes4 ,it may be that these substances have reduced the sulphur from gypsum4 ,the chief proof in favour of the origin of sulphur from gypsum is that in treating the deposits for the extraction of the sulphur it is found that the proportion of sulphur to calcium carbonate never exceeds that which it would be had they both been derived from calcium sulphate4 #d ,naturally only those ores of sulphur which contain a considerable amount of sulphur can be treated by this method4 ,with poor ores it is necessary to have recourse to distillation or mechanical treatment in order to separate the sulphur1 but its price is so low that this method in most cases is not profitable4 ,the sulphur obtained by the above-described method still contains some impurities1 but it is frequently made use of in this form for many purposes1 and especially in considerable quantities for the manufacture of sulphuric acid1 and for strewing over grapes4 ,for other purposes1 and especially in the preparation of gunpowder1 a purer sulphur is required4 ,sulphur may be purified by distillation4 ,the crude sulphur is called rough1 and the distilled sulphur refined4 ,the arrangement given in fig4 #hf is employed for refining sulphur4 ,the rough sulphur is melted in the boiler d1 and as it melts it is run through the tube ,f into an iron retort ,b heated by the naked flame of the furnace4 ,here the sulphur is converted into vapour1 which passes through a wide tube into the chamber ,g1 surrounded by stone walls and furnished with a safety-valve ,s4 ,illustration3 ,,fig4 #hf4--,refining sulphur by sublimation4 ,sulphur is purified by distillation in special retorts 7see fig4 #hf7 by passing the vapour into a chamber ,g built of stone4 ,the first portions of the vapour entering into the condensing chamber are condensed straightway from the vapour into a solid state1 and form a fine powder known as flowers of sulphur4#e ,but when the temperature of the receiver attains the melting point of sulphur1 it passes into a liquid state and is cast into moulds 7like sealing wax71 and is then known under the name of roll sulphur4#f #e ,flowers of sulphur always contain a certain amount of the oxides of sulphur4 #f ,sulphur may be extracted by various other means4 ,it may be extracted from iron pyrites1 ,fe,s#b1 which is very widely distributed in nature4 ,from #ajj parts of iron pyrites about half the sulphur contained1 namely1 about #be parts1 may be extracted by heating without the access of air1 a lower sulphide of iron1 which is more stable under the action of heat1 being left behind4 ,alkali waste 7,chapter ,,xii471 containing calcium sulphide and gypsum1 ,ca,s,o#d1 may be used for the same purpose1 but native sulphur is so cheap that recourse can only be had to these sources when the calcium sulphide appears as a worthless by-product4 ,the most simple process for the extraction of sulphur from alkali waste1 in a chemical sense1 consists in evolving sulphuretted hydrogen from the calcium sulphide by the action of hydrochloric acid4 ,the sulphuretted hydrogen when burnt gives water and sulphurous anhydride1 which reacts on fresh sulphuretted hydrogen with the separation of sulphur4 ,the combustion of the sulphuretted hydrogen may be so conducted that a mixture of #b;,h#b,s and ,,so#b is straightway formed1 and this mixture will deposit sulphur 7,chapter ,,xii41 ,note #ad74 ,gossage and ,chance treat alkali waste with carbonic anhydride1 and subject the sulphuretted hydrogen evolved to incomplete combustion 7this is best done by passing a mixture of sulphuretted hydrogen and air1 taken in the requisite proportions1 over red-hot ferric oxide71 by which means water and the vapour of sulphur are formed3 ,h#b,s ,o ,h#b,o ,s4 ,in an uncombined state sulphur exists in several modifications1 and forms a good example of the facility with which an alteration of properties can take place without a change of composition--that is1 as regards the material of a substance4 ,common sulphur has the well-known yellow colour4 ,this colour fades as the temperature falls1 and at -#ej sulphur is almost colourless4 ,it is very brittle1 so that it may be easily converted into a powder1 and it presents a crystalline structure1 which1 by the way1 shows itself in the unequal expansion of lumps of sulphur by heat4 ,hence when a piece of sulphur is heated by the warmth of the hand1 it emits sounds and sometimes cracks1 which probably also depends on the bad heat-conducting power of this substance4 ,it is easily obtained in a crystalline form by artificial means1 because although insoluble in water it dissolves in carbon bisulphide1 and in certain oils4#g ,solutions of sulphur in carbon bisulphide when evaporated at the ordinary temperature yield well-formed transparent crystals of sulphur in the form of rhombic octahedra1 in which form it occurs native4 ,the specific gravity of these crystals is #bjde4 ,fused sulphur1 cast into moulds and cooled1 has1 after being kept a long time1 a specific gravity #bjff2 almost the same as that of the crystalline sulphur of the above form1 which shows that common sulphur is the same as that which crystallises in octahedra4 ,the specific heat of octahedral sulphur is #jag2 it melts at #aad1 and forms a bright yellow mobile liquid4 ,on further heating1 the fused sulphur undergoes an alteration1 which we shall presently describe1 first observing that the above octahedral state of sulphur is its most stable form4 ,sulphur may be kept at the ordinary temperature in this form for an indefinite length of time1 and many other modifications of sulphur pass into this form after being left for a certain time at ordinary temperature4 #g ,one hundred parts of liquid carbon bisulphide1 ,,cs#b1 dissolve #afe parts of sulphur at -#aa1 #bd parts at #j1 #cg parts at #ae1 #df parts at #bb1 and #aha parts at #ee4 ,the saturated solution boils at #ee1 whilst pure carbon bisulphide boils at #dg4 ,the solution of sulphur in carbon bisulphide reduces the temperature1 just as in the solution of salts in water4 ,thus the solution of #bj parts of sulphur in #ej parts of carbon bisulphide at #bb lowers the temperature by #e2 #ajj parts of benzene1 ,c#f;,h#f1 dissolves #jife part of sulphur at #bf1 and #dcgg parts at #ga2 chloroform1 ,c,h,cl#c1 dissolves #ab part of sulphur at #bb1 and #afce parts at #agd4 ,if sulphur be melted and then slightly cooled1 so that it forms a crust on the surface and over the sides of the crucible1 while the internal mass remains liquid1 then the sulphur takes another crystalline form as it solidifies4 ,this may be seen by breaking the crust1 and pouring out the remaining molten sulphur4#h ,it is then found that the sides of the crucible are covered with prismatic crystals of the monoclinic system2 they have a totally different appearance from the above-described crystals of rhombic sulphur4 ,the prismatic crystals are brown1 transparent1 and less dense than the crystals of rhombic sulphur1 their specific gravity being only #aic1 and their melting point higher--about #abj4 ,these crystals of sulphur cannot be kept at the ordinary temperature1 which is indeed evident from the fact that in time they turn yellow2 the specific gravity also changes1 and they pass completely into the ordinary modification4 ,this is accompanied by a considerable development of heat1 so that the temperature of the mass may rise #ab4 ,thus sulphur is dimorphous--that is1 it exists in two crystalline forms1 and in both forms it has independent physical properties4 ,however1 no chemical reactions are known which distinguish the two modifications of sulphur1 just as there are none distinguishing aragonite from calcspar4#i #h ,if the experiment be made in a vessel with a narrow capillary tube1 the sulphur fuses at a lower temperature 7occurs1 as it were1 in a supersaturated state71 and solidifying at #ij1 appears in a rhombic form 7,schtzenberger74 #i ,if sulphur be cautiously melted in a ,u tube immersed in a salt bath1 and then gradually cooled1 it is possible for all the sulphur to remain liquid at #ajj4 ,it will now be in a state of superfusion2 thus also by careful refrigeration water may be obtained in a liquid state at -#aj1 and a lump of ice then causes such water to form ice1 and the temperature rises to #j4 ,if a prismatic crystal of sulphur be thrown into one branch of the ,u tube containing the liquid sulphur at #ajj1 and an octahedral crystal be thrown into the other branch1 then1 as ,gernez showed1 the sulphur in each branch will crystallise in the corresponding form1 and both forms are obtained at the same temperature2 therefore it is not the influence of temperature only which causes the molecules of sulphur to distribute themselves in one or another form1 but also the influence of the crystalline parts already formed4 ,this phenomenon is essentially analogous to the phenomena of supersaturated solutions4 ,if molten sulphur be heated to #aeh it loses its mobility and becomes thick and very dark-coloured1 so that the crucible in which it is heated may be inverted without the sulphur running out4 ,when heated above this temperature the sulphur again becomes liquid1 and at #bej it is very mobile1 although it does not acquire its original colour1 and at #ddj it boils4 ,these modifications in the properties of sulphur depend not only on the variations of temperature1 but also on a change of structure4 ,if sulphur1 heated to about #cej1 be poured in a thin stream into cold water1 it does not solidify into a solid mass1 but retains its brown colour and remains soft1 may be stretched out into threads1 and is elastic1 like guttapercha4 ,but in this soft and ductile state1 also1 it does not remain for a long time4 ,after the lapse of a certain period this soft transparent sulphur hardens1 becomes opaque1 passes into the ordinary yellow modification of sulphur1 and in so doing develops heat1 just as in the conversion of the prismatic into the octahedral variety4 ,the soft sulphur is characterised by the fact that a certain portion of it is insoluble in carbon bisulphide4 ,when soft sulphur is immersed in this liquid1 only a portion of common sulphur passes into solution1 whilst a certain portion is quite insoluble and remains so for a long time4 ,the maximum proportion of insoluble sulphur is obtained by heating slightly above #agj4 ,it melts at #aad4 ,an exactly similar insoluble amorphous sulphur is obtained in certain reactions in the wet way1 when sulphur separates out from solutions4 ,thus sodium thiosulphate1 ,na#b,s#b,o#c1 when treated with acids1 gives a precipitate of sulphur1 which is insoluble in carbon bisulphide4 ,the action of water on sulphur chloride also gives a similar modification of sulphur4 ,certain sulphides1 when treated with nitric acid1 also yield sulphur in this form4#aj #aj ,a certain amount of insoluble sulphur remains for a long time in the mass of soft sulphur1 changing into the ordinary variety4 ,freshly-cooled soft sulphur contains about one-third of insoluble sulphur1 and after the lapse of two years it still contains about #ae p4c4 ,flowers of sulphur1 obtained by the rapid condensation of sulphur from a state of vapour1 also contains a certain amount of insoluble sulphur4 ,rapidly distilled and condensed sulphur also contains some insoluble sulphur4 ,hence a certain amount of insoluble sulphur is frequently found in roll sulphur4 ,the action of light on a solution of sulphur converts a certain portion into the insoluble modification4 ,insoluble sulphur is of a lighter colour than the ordinary variety4 ,it is best prepared by vaporising sulphur in a stream of carbonic anhydride1 hydrochloric acid1 c41 and collecting the vapour in cold water4 ,when condensed in this manner it is nearly all insoluble in carbon bisulphide4 ,it then has the form of hollow spheroids1 and is therefore lighter than the common variety3 sp4 gr4 #ahb4 ,an idea of the modifications taking place in sulphur between #aaj and #bej may be formed from the fact that at #aej liquid sulphur has a coefficient of expansion of about #jjjje1 whilst between #aej and #bej it is less than #jjjjc4 ,engel 7#ahia71 by decomposing a saturated solution of hyposulphite of sodium 7,note #db7 with ,h,cl in the cold 7the sulphur is not precipitated directly in this case71 obtained1 after shaking up with chloroform and evaporation1 crystals of sulphur 7sp4 gr4 #bace71 which1 after several hours1 passed into the insoluble 7in ,,cs#b7 state1 and in so doing became opaque1 and increased in volume4 ,but if a mixture of solution of ,na#b,s#b,o#c and ,h,cl be allowed to stand1 it deposits sulphur1 which1 after sufficient washing1 is able to dissolve in water 7like the colloid varieties of the metallic sulphides1 alumina1 boron1 and silver71 but this colloid solution of sulphur soon deposits sulphur insoluble in ,,cs#b4 ,when a solution of sulphuretted hydrogen in water is decomposed by an electric current the sulphur is deposited on the positive pole1 and has therefore an electro-negative character1 and this sulphur is soluble in carbon bisulphide4 ,when a solution of sulphurous acid is decomposed in the same manner1 the sulphur is deposited on the negative pole1 and is therefore electro-positive1 and the sulphur so deposited is insoluble in carbon bisulphide4 ,the sulphur which is combined with metals must have the properties of the sulphur contained in sulphuretted hydrogen1 whilst the sulphur combined with chlorine is like that which is combined with oxygen in sulphurous anhydride4 ,hence ,berthelot recognises the presence of soluble sulphur in metallic sulphides1 and of the insoluble modification of amorphous sulphur in sulphur chloride4 ,cloez showed that the sulphur precipitated from solutions is either soluble or insoluble1 according to whether it separates from an alkaline or acid solution4 ,if sulphur be melted with a small quantity of iodine or bromine1 then on pouring out the molten mass it forms amorphous sulphur1 which keeps so for a very long time1 and is insoluble1 or nearly so1 in carbon bisulphide4 ,this is taken advantage of in casting certain articles in sulphur1 which by this means retain their tenacity for a long time2 for example1 the discs of electrical machines4 ,at temperatures of #ddj to #gjj the vapour density of sulphur is #ff referred to air--i4e4 about #if referred to hydrogen4 ,hence1 at these temperatures the molecule of sulphur contains six atoms1 it has the composition ,s#f4 ,the agreement between the observations of ,dumas1 ,mitscherlich1 ,bineau1 and ,deville confirms the accuracy of this result4 ,but in this respect the properties of sulphur were found to be variable4 ,when heated to higher temperatures1 that is to say1 above #hjj1 the vapour density of sulphur is found to be one-third of this quantity1 i4e4 about #cb referred to hydrogen4 ,at this temperature the molecule of sulphur1 like that of hydrogen1 oxygen1 nitrogen1 and chlorine1 contains two atoms2 hence the molecular formula is then ,s#b4 ,this variation in the vapour density of sulphur evidently corresponds with a polymeric modification1 and may be likened to the transformation of ozone1 ,o#c1 into oxygen1 ,o#b1 or better still1 of benzene1 ,c#f;,h#f1 into acetylene1 ,c#b;,h#b4aa #aa ,here1 however1 it is very important to remark that both benzene and acetylene can exist at the ordinary temperature1 whilst the sulphur molecule ,s#b only exists at high temperatures2 and if this sulphur be allowed to cool1 it passes first into ,s#f and then into a liquid state4 ,were it possible to have sulphur at the ordinary temperature in both the above modifications1 then in all probability the sulphur in the state ,s#b would present totally different properties from those which it has in the form ,s#f1 just as the properties of gaseous acetylene are far from being similar to those of liquid benzene4 ,sulphur1 in the form of ,s#b1 is probably a substance which boils at a much lower temperature than the variety with which we are now dealing4 ,paterno and ,nasini 7#ahhh71 following the method of depression or fall of the freezing-point in a benzene solution1 found that the molecule of sulphur in solution contains ,s#f4 ,one must here call attention to the fact that sulphur1 with all its analogy to oxygen 7which also shows itself in its faculty to give the modification ,s#b71 is also able to give a series of compounds containing more atoms of sulphur than the analogous oxygen compounds do of oxygen4 ,thus1 for instance1 compounds of #e atoms of sulphur with #a atom of barium1 ,ba,s#e1 are known1 whereas with oxygen only ,ba,o#b is known4 ,on every side one cannot but see in sulphur a faculty for the union of a greater number of atoms than with oxygen4 ,with oxygen the form of ozone1 ,o#c1 is very unstable1 the stable form is ,o#b2 whilst with sulphur ,s#f is the stable form1 and ,s#b is exceedingly unstable4 ,furthermore1 it is remarkable that sulphur gives a higher degree of oxidation1 ,h#b,,so#d1 corresponding1 as it were1 with its complex composition1 if we suppose that in ,s#f four atoms of sulphur are replaced by oxygen and one by two atoms of hydrogen4 ,the formul of its compounds1 ,k#b,,so#d1 ,k#b,s#b,o#c1 ,k#b,s#e1 ,ba,s#e1 and many others1 have no analogues among the compounds of oxygen4 ,they all correspond with the form ,s#f 7one portion of the sulphur being replaced by oxygen and another by metals71 which is not attained by oxygen4 ,in this faculty of sulphur to hold many atoms of other substances the same forces appear which cause many atoms of sulphur to form one complex molecule4 ,in its faculty for combination1 sulphur most closely resembles oxygen and chlorine2 like them1 it combines with nearly all elements1 with the development of heat and light1 forming sulphur compounds1 but as a rule this only takes place at a high temperature4 ,at the ordinary temperature it does not enter into reactions1 owing1 amongst other things1 to the fact that it is a solid4 ,in a molten state it acts on most metals and on the halogens4 ,it burns in air at about #cjj1 and with carbon at a red heat1 but it does not combine with nitrogen4 ,fine wires1 or the powders of the greater number of metals1 burn in the vapour of sulphur4 ,the direct combination of hydrogen with sulphur is restricted by a limit--that is1 at a given temperature and under other given conditions it does not proceed unrestrictedly2 there is no explosion or recalescence4 ,sulphuretted hydrogen1 ,h#b,s1 decomposes at its temperature of combination--that is1 it is easily dissociated4#ab ,the same phenomenon is repeated here as with water1 except that the temperatures at which the attraction of hydrogen for sulphur begins and ceases are much lower than in the case of oxygen and hydrogen4 ,the temperature at which combination takes place is here1 as in many other instances1 nearly the same as that at which dissociation begins4 ,hence sulphuretted hydrogen is formed in a small quantity by the direct ignition of a mixture of the vapour of sulphur and hydrogen4 ,however1 the temperature must not be high1 because otherwise the whole of the sulphuretted hydrogen is decomposed2 but at lower temperatures a small amount of sulphuretted hydrogen is formed by direct combination4#ac ,sulphuretted hydrogen however1 like all other hydrogen compounds1 may be easily obtained by the double decomposition of its corresponding metallic compounds1 the replacement of the metal by hydrogen being effected by the action of acids on the sulphides4 ,the metallic sulphides are1 as a rule1 easily formed4 ,a sulphide1 when mixed with a non-volatile acid1 may give1 by double decomposition1 a salt of the acid taken and sulphuretted hydrogen1 ,m#b,s ,h#b,,so#d ,h#b,s ,m#b,,so#d4 ,however1 it is not all sulphides nor solutions of all acids that will evolve sulphuretted hydrogen1 which fact is exceedingly characteristic1 because1 for example1 all carbonates evolve carbonic anhydride when treated with any acid4 ,sulphuric acid will only evolve sulphuretted hydrogen from those sulphides which contain a metal capable of decomposing the acid with the evolution of hydrogen4 ,thus zinc1 iron1 calcium1 magnesium1 manganese1 potassium1 sodium1 c41 form sulphides which evolve sulphuretted hydrogen when treated with sulphuric acid1 and the metals themselves evolve hydrogen with acids4#ad ,the sulphides of those metals which do not liberate hydrogen from acids do not generally act on acids--that is1 do not form sulphuretted hydrogen with them2 such are1 for example1 the sulphides of lead1 silver1 copper1 mercury1 tin1 c4 ,therefore1 the modus operandi of the formation of sulphuretted hydrogen by the action of acids on metallic sulphides may be looked on as a phenomenon of the combination of hydrogen1 at the moment of its evolution1 with the sulphur1 which is combined with the metal4 ,such a representation is all the more simple as all the circumstances under which sulphuretted hydrogen is formed are exactly similar to the conditions of the formation of hydrogen itself4 ,thus the usual mode of preparing sulphuretted hydrogen is by the action of sulphuric acid on ferrous sulphide1 in which the same apparatus and method are employed as in the preparation of hydrogen1 only replacing the metallic iron or zinc by ferrous sulphide or zinc sulphide4 ,the reaction between sulphide of iron and sulphuric acid takes place at the ordinary temperature1 and is accompanied by just as small a development of heat as in the liberation of hydrogen itself1 ,fe,s ,h#b,,so#d ,fe,s,o#d ,h#b,s4#ae #ab ,in the formation of potassium sulphide1 ,k#b,s 7that is1 in the combination of #cb parts of sulphur with #gh parts of potassium71 about #ajj thousand heat units are developed4 ,nearly as much heat is developed in the combination of an equivalent quantity of sodium2 about #ij thousand heat units in the formation of calcium or strontium sulphide2 about #dj thousand for zinc or cadmium sulphide1 and about #bj thousand for iron1 cobalt1 or nickel sulphide4 ,less heat is evolved in the combination of sulphur with copper1 lead1 and silver4 ,according to ,thomsen1 sulphur develops heat with hydrogen in solutions4 ,the reaction ,i#b1;,aq1,h#b,s #ba1hcj calories4 ,but1 as the reaction ,i#b ,h#b ,aq develops #bf1hdb calories1 it follows that the reaction ,h#b ,s develops #d1eab calories4 #ac ,if sulphur be melted in a flask and heated nearly to its boiling point1 as ,lidoff showed1 the addition1 drop by drop 7from a funnel with a stopcock7 of heavy 7#ji7 naphtha oil 7of lubricating oleonaphtha71 c41 is followed by a regular evolution of sulphuretted hydrogen4 ,this is analogous to the action of bromine or iodine on paraffin and other oils1 because hydrobromic or hydriodic acid is then formed 7,chapter ,,xi47 ,a certain amount of hydrogen sulphide is even formed when sulphur is boiled with water4 #ad ,however1 the matter is really much more complicated4 ,thus zinc sulphide evolves sulphuretted hydrogen with sulphuric or hydrochloric acids1 but does not react with acetic acid and is oxidised by nitric acid4 ,ferrous sulphide evolves sulphuretted hydrogen with acids1 whilst the bisulphide1 ,fe,s#b1 does not react with acids of ordinary strength4 ,this absence of action depends1 among other things1 on the form in which the native iron pyrites occurs2 it is a crystalline1 compact1 and very dense substance2 and acids in general react with great difficulty on such metallic sulphides4 ,this is seen very clearly in the case of zinc sulphide2 if this substance is obtained by double decomposition1 it separates as a white precipitate1 which evolves sulphuretted hydrogen with great ease when treated with acids4 ,zinc sulphide is obtained in the same form when zinc is fused with sulphur1 but native zinc sulphide--which occurs in compact masses of zinc blende1 and has a metallic lustre--is not decomposed or scarcely decomposed by sulphuric acid4 ,another source of complication in the behaviour of the metallic sulphides towards acids depends on the action of water1 and is shown in the fact that the action varies with different degrees of dilution or proportion of water present4 ,the best known example of this is antimonious sulphide1 ,sb#b,s#c1 for strong hydrochloric acid1 containing not more water than corresponds with ,h,cl1#f;,h#b,o1 even decomposes native antimony glance1 with evolution of sulphuretted hydrogen1 whilst dilute acid has no action1 and in the presence of an excess of water the reaction #b,sb,cl#c #c;,h#b,s ,sb#b,s#c #f;,h,cl occurs1 whilst in the presence of a small amount of water the reaction proceeds in exactly the opposite direction4 ,here the participation of water in the reaction and its affinity are evident4 ,the facts that lead sulphide is insoluble in acids1 that zinc sulphide is soluble in hydrochloric acid but insoluble in acetic acid1 that calcium sulphide is even decomposed by carbonic acid1 c4--all these peculiarities of the sulphides are in correlation with the amount of heat evolved in the reaction of the oxides with hydrogen sulphide and with acids1 as is seen from the observations of ,favre and ,silberman1 and from the comparisons made by ,berthelot in the ,proceedings of the ,paris ,academy of ,sciences1 #ahgj1 to which we refer the reader for further details4 #ae ,ferrous sulphide is formed by heating a piece of iron to an incipient white heat1 and then removing it from the furnace and bringing it into contact with a piece of sulphur4 ,combination then proceeds1 accompanied by the development of heat1 and the ferrous sulphide formed fuses4 ,the sulphide of iron thus formed is a black1 easily-fusible substance1 insoluble in water4 ,when damp it attracts oxygen from the air1 and is converted into green vitriol1 ,fe,s,o#d4 ,if all the iron does not combine with the sulphur in the method described above1 the action of sulphuric acid will evolve hydrogen as well as hydrogen sulphide4 ,we will not describe the details of the preparation of sulphuretted hydrogen employed as a reagent in the laboratory1 because1 in the first place1 the methods are essentially the same as in the preparation of hydrogen1 and1 in the second place1 because the apparatus and methods employed are always described in text-books of analytical chemistry4 ,ferrous sulphide may be advantageously replaced by calcium sulphide or a mixture of calcium and magnesium sulphides4 ,a solution of magnesium hydrosulphide1 ,mg,s1,h#b,s1 is very convenient1 as at #fj it evolves a stream of pure hydrogen sulphide4 ,a paste1 consisting of ,cu,s with crystals of ,mg,cl#b and water1 may also be employed1 since it only evolves ,h#b,s when heated 7,habermann74 ,in nature sulphuretted hydrogen is formed in many ways4 ,the most usual mode of its formation is by the decomposition of albuminous substances containing sulphur1 as mentioned above4 ,another method is by the reducing action of organic matter on sulphates1 and by the action of water and carbonic acid on the sulphides formed by this reduction4 ,volcanic eruptions are a third source of sulphuretted hydrogen in nature4 ,although sulphuretted hydrogen is formed in small quantities everywhere1 it nevertheless soon disappears from the atmosphere1 owing to its being easily decomposed by oxidising agencies4 ,many mineral waters contain sulphuretted hydrogen1 and smell of it2 they are called 'sulphur waters4' ,sulphuretted hydrogen1 at the ordinary temperature1 is a colourless gas1 having a very unpleasant odour4 ,it has1 as its composition ,h#b,s shows1 a specific gravity seventeen times greater than hydrogen1 and therefore it is somewhat heavier than air4 ,sulphuretted hydrogen liquefies at about -#gd1 and at the ordinary temperature when subjected to a pressure of #aj to #ae atmospheres2 at -#he it is converted into a solid crystalline mass4#ae bis ,the easy liquefaction of sulphuretted hydrogen is evidently allied to its solubility4 ,one volume of water at #j dissolves #dcg volumes of sulphuretted hydrogen1 at #aj #ceh volumes1 and at #bj #bi volumes4#af ,the solutions impart a very feeble red coloration to litmus paper4 ,this gas is poisonous4 ,one part in fifteen hundred parts of air will kill birds4 ,mammalia die in an atmosphere containing #a_/bjj of this gas4 #ae bis ,liquid sulphuretted hydrogen is most easily obtained by the decomposition of hydrogen polysulphide1 which we shall presently describe1 by the action of heat1 and in the presence of a small amount of water4 ,if poured into a bent tube1 like that described for the liquefaction of ammonia 7,chapter ,,vi471 the hydrogen polysulphide is decomposed by heat1 in the presence of water1 into sulphur and sulphuretted hydrogen1 which condenses in the cold end of the tube into a colourless liquid4 #af ,sulphuretted hydrogen is still more soluble in alcohol than in water2 one volume at the ordinary temperature dissolves as much as eight volumes of the gas4 ,the solutions in water and alcohol undergo change1 especially in open vessels1 owing to the fact that the water and alcohol dissolve oxygen from the atmosphere1 which1 acting on the sulphuretted hydrogen1 forms water and sulphur4 ,the solution may be so altered in this manner that every trace of sulphuretted hydrogen disappears4 ,solutions of sulphuretted hydrogen in glycerine change much more slowly1 and may therefore be kept for a long time as reagents4 ,de ,forcrand obtained a hydrate1 ,h#b,s1#af;,h#b,o1 resembling the hydrates given by many gases4 ,sulphuretted hydrogen is very easily decomposed into its component parts by the action of heat or a series of electric sparks4 ,hence it is not surprising that sulphuretted hydrogen undergoes change under the action of many substances having a considerable affinity for hydrogen and oxygen4 ,very many metals#ag evolve hydrogen with sulphuretted hydrogen1 so that in this respect it presents the property of an acid2 for instance1 #b;,h#b,s ,sn #b;,h#b ,sn,s#b4 ,this may be taken advantage of for determining the composition of sulphuretted hydrogen1 because a given volume then leaves the same volume of hydrogen4 ,on the other hand1 oxygen1#ah chlorine1#ai and even iodine decompose sulphuretted hydrogen1 removing the hydrogen from it and leaving free sulphur1 so that in this reaction the sulphur is replaced by the above-named elements2 for example1 ,h#b,s ,br#b #b;,h,br ,s4 ,in no other hydrogen compound is it so easy to show the substitution1 both of hydrogen and of the element combined with it1 as in hydrogen sulphide4 ,this clearly proves the feeble union between the elements forming this gas4 ,compounds containing a considerable amount of oxygen1 with which they easily part1 can accomplish the separation of the sulphur very easily4 ,such are1 for instance1 nitrous acid1 chromic acid1 and even ferric oxide and the higher oxides like it4 ,thus1 if sulphuretted hydrogen be passed into a solution of chromic acid or an acid solution of ferric oxide1 water is formed1 and the sulphur is separated in a free state4 ,thus1 sulphuretted hydrogen acts as a reducing agent1 in virtue of the hydrogen it contains4 ,salts of iodic1 chlorous1 chloric1 and other acids are reduced by sulphuretted hydrogen1 their oxygen acting mainly on its hydrogen2 but in the presence of an excess of a powerful oxidising agent a portion of the sulphur may also be oxidised to sulphurous anhydride4 ,the reducing action of sulphuretted hydrogen is frequently applied in chemical manipulations for the preparation of lower oxides1 and for the conversion of certain oxygen compounds into hydrogen compounds3 thus1 the higher oxides of nitrogen are converted into ammonia by it1 and in the presence of alkalis the nitro-compounds are converted into ammonia derivatives4 ,the reaction of sulphuretted hydrogen on sulphurous anhydride belongs to this class of phenomena1 the chief products of which are sulphur and water1 #b;,h#b,s ,,so#b #b;,h#b,o ,s#c4 #ag ,some metals evolve hydrogen from sulphuretted hydrogen at the ordinary temperature4 ,for example1 the light metals1 and copper and silver 7especially with the access of air87 among the heavy metals4 ,hence articles made of silver turn black in the presence of vapours containing sulphuretted hydrogen1 because silver sulphide is black4 ,zinc and cadmium act at a red heat1 but not completely4 #ah ,if sulphuretted hydrogen escapes from a fine orifice into the air1 it will burn when lighted1 and be transformed into sulphurous anhydride and water4 ,but if it burns in a limited supply of air--for instance1 when a cylinder is filled with it and lighted--then only the hydrogen burns1 which has1 judging from the amount of heat developed in its combustion and from all its properties1 a greater affinity for oxygen than sulphur4 ,in this respect the combustion of sulphuretted hydrogen resembles that of hydrocarbons4 #ai ,hence bleaching powder and chlorine destroy the disagreeable smell of sulphuretted hydrogen4 7,for the reaction of hydrogen sulphide and iodine1 see ,chapter ,,xi4 p4 #ejd47 ,the acid character of sulphuretted hydrogen is clearly seen in its action on alkalis and salts4#ai bis ,thus lead oxide and its salts in the presence of sulphuretted hydrogen form water or an acid1 and sulphide of lead3 ,pb,x#b ,h#b,s ,pb,s #b;,,hx4 ,this reaction takes place even in the presence of powerful acids1 because lead sulphide is one of those sulphides which are unacted on by acids1 and in solutions the reaction is a complete one4 ,this reaction is taken advantage of for the preparation of many acids1 by first converting into a lead salt1 and then submitting this salt to the action of sulphuretted hydrogen4 ,for example1 lead formate with sulphuretted hydrogen gives formic acid4 ,sulphuretted hydrogen in acting on a number of metallic acid substances in solution or in an anhydrous state also forms corresponding sulphates3 7#a7 if it does not reduce the acid2 7#b7 if the sulphur compound corresponding with the anhydride of the acid be insoluble in water1 the reaction proceeds in solutions2 7#c7 if the sulphuretted hydrogen and the acid taken do not come in contact with an alkali1 on which they would be able to act first2 and 7#d7 if the sulphur compound be not decomposed by water4 ,thus solutions of arsenious acid give a precipitate of arsenious sulphide1 ,as#b,s#c1 with sulphuretted hydrogen4 ,this reaction proceeds not only in the presence of water1 but also of acids1 because the latter do not decompose the resultant sulphur compounds4 ,the type of the decomposition is the same as with bases--that is1 the sulphur and oxygen change places3 ,,ron n,h#b,s ,,rsn n,h#b,o4 ,some sulphides corresponding with acid anhydrides are decomposed by water1 and therefore are not formed in the presence of water4 ,such1 for example1 are the sulphides of phosphorus4#bj #ai bis ,perfectly dry ,h#b,s 7,hughes #ahib7 has no action upon perfectly dry salts1 just as dry ,h,cl does not react with dry ,,nh#c or metals 7,chapter ,,ix41 ,note #bi74 #bj ,the sulphide ,p#d,s is obtained by cautiously fusing the requisite proportions of common phosphorus and sulphur under water2 it is a liquid which solidifies at #j1 and may be distilled without undergoing change1 but it fumes in air and easily takes fire4 ,the higher sulphide1 ,p#b,s1 has similar properties4 ,but little heat is evolved in the formation of these compounds1 and it may be supposed that they are formed by the direct conjunction of whole molecules of phosphorus and sulphur2 but if the proportion of sulphur be increased1 the reaction is accompanied by so considerable a rise of temperature that an explosion takes place1 and for the sake of safety red phosphorus must be used1 mixed as intimately as possible with powdered sulphur and heated in an atmosphere of carbonic anhydride4 ,the higher compounds are decomposed by water4 ,by increasing the proportion of sulphur1 the following compounds have been obtained3 ,p#d,s#c as prisms 7fuses at #afe1 ,rebs71 soluble in carbon bisulphide1 and unaltered by air and water2 phosphorus trisulphide1 ,p#b,s#c1 is the analogue of ,p#b,o#c2 it is a light yellow crystalline compound only slightly soluble in carbon bisulphide1 fusible and volatile1 decomposed into hydrogen sulphide and phosphorous acid by water1 and1 like the highest compound of sulphur and phosphorus1 ,p#b,s#e1 it forms thio-salts with potassium sulphide1 c4 ,this phosphorus pentasulphide corresponds with phosphoric anhydride2 like the trisulphide it gives hydrogen sulphide and phosphoric acid with an excess of water4 ,it reacts in many respects like phosphoric chloride4 ,the sulphide ,,ps#b is also known2 the vapour density of this compound seems to indicate a molecule ,p#c,s#f4 ,phosphorus sulphochloride1 ,p,s,cl#c1 corresponds with phosphorus oxychloride4 ,it is a colourless1 pleasant-smelling liquid1 boiling at #abd1 and of sp4 gr4 #afc2 it fumes in air and is decomposed by water3 ,p,s,cl#c #d;,h#b,o ,,ph#c,o#d ,h#b,s #c;,h,cl4 ,it is obtained when phosphoric chloride is treated with hydrogen sulphide1 hydrochloric acid being also formed2 it is also produced by the action of phosphoric chloride on certain sulphides--for example1 on antimonious sulphide1 also by the 7cautious7 action of phosphorus on sulphur chloride3 #b,p #c,s#b;,cl#b #b,p,s,cl#c #d,s1 by the action of ,p,cl#e upon certain sulphides1 for example1 ,sb#b,s#c1 by the reaction3 #c,m,cl ,p#b,s#e ,p,s,cl#c ,m#c,,ps#d 7,glatzel1 #ahic71 and in the reaction #c,p,cl#c ,s,o,cl#b ,p,cl#e ,p,o,cl#c ,p,s,cl#c1 showing the reducing action of phosphorus trichloride1 which is especially clear in the reaction ,,so#c ,p,cl#c ,,so#b ,p,o,cl#c4 ,thorpe and ,rodger 7#ahhi71 by heating #c,pb,f#b or ,bi,f#c with phosphorus pentasulphide 7and also by heating ,as,f#c and ,p,s,cl#c to #aej71 obtained thiophosphoryl fluoride as a colourless1 spontaneously inflammable gas 7see further on1 ,note #gd bis1 and ,chapter ,,xix41 ,note #be74 ,the action of ,p,s,cl#c upon ,na,h,o gives a salt of monothiophosphoric acid 7,wrtz1 ,kubierschky71 ,h#c,,pso#c1 which gives soluble salts of the alkalis4 ,the metallic sulphides corresponding with the metallic oxides have either a feeble alkaline or a feeble acid character1 according to the character of the corresponding oxide1 and therefore by combining together they are able to form saline substances--that is1 salts in which the oxygen is replaced by sulphur4 ,thus sulphuretted hydrogen having the properties of a feeble acid#ba has1 at the same time1 the properties of water1 and forms the type of the sulphur derivatives1 which may also be formed by means of sulphuretted hydrogen1 just as the oxides may be formed by the aid of water4 ,but as sulphuretted hydrogen has acid properties1 it combines more easily with the basic metallic sulphides4 ,hence1 for instance1 there exists a compound of sulphuretted hydrogen with potassium sulphide1 potassium hydrosulphide1 #b,,khs ,k#b,s ,h#b,s1 just as there are potassium hydroxides2 but there are scarcely any compounds of sulphuretted hydrogen with the sulphides corresponding with acids4 ,thus the sulphides of the metals may be regarded either as salts of sulphuretted hydrogen or as oxides of the metals in which the oxygen is replaced by sulphur4 ,in general terms the sulphides exhibit the same degrees of difference with respect to their solubility in water as do the oxides4 ,thus the oxides of the alkali metals1 and of some of the metals of the alkaline earths1 are soluble in water1 whilst those of nearly all the other metals are insoluble4 ,the same may be said as to the sulphides2 the sulphides of the metals of the alkalis and certain of the alkaline earths are soluble in water1 whilst those of the other metals are insoluble4 ,those metals1 like aluminium1 whose oxides--for example1 ,al#b,o#c--;have intermediate properties and do not form compounds with feeble acids1 at least in a wet way1 also do not form sulphides by this method1 although these may be obtained indirectly4 ,and in general the sulphides of the metals are easily formed in a wet way1 and with particular ease if they are insoluble in water4 ,in this case their salts enter into double decomposition with sulphuretted hydrogen1 or with soluble sulphides1 and give an insoluble sulphide--for instance1 a salt of lead gives lead sulphide with sulphuretted hydrogen4 ,by the action of sulphuretted hydrogen on a salt of a metal1 a free acid must be formed besides the metallic sulphide4 ,thus if a metal ,m be in a state of combination ,,mx#b1 then by the action of sulphuretted hydrogen there will be formed1 besides ,,ms1#bb an acid #b;,,hx4 ,it is evident that sulphuretted hydrogen will not precipitate an insoluble sulphide from the salts of those metals whose sulphides react with free acid1 such as zinc1 iron1 manganese1 c4 ,the reaction ,fe,cl#b ,h#b,s ,fe,s #b;,h,cl1 and the like1 do not take place because the acid acts on the ferrous sulphide4 ,antimonious sulphide is not acted on by dilute hydrochloric acid1 but it is decomposed by strong acid1 and therefore in presence of an excess of hydrochloric acid antimonious chloride does not entirely react with hydrogen sulphide1 whilst the reaction #b,sb,cl#c #c;,h#b,s ,sb#b,s#c #f;,h,cl is a complete one in a dilute solution and with a small quantity of acid4 ,those metallic sulphides which are decomposed by acids may be obtained in a wet way by the double decomposition of the salts of the metals1 not with hydrogen sulphide1 but with soluble metallic sulphides1 such as sulphide of ammonium or of potassium1 because then no free acid is formed1 but a salt of the metal 7potassium or ammonium7 which was taken as a soluble sulphide4 ,so1 for example1 ,fe,cl#b ,k#b,s ,fe,s #b,k,cl4#bc #ba ,sulphuretted hydrogen does not saturate the alkaline properties of alkali hydroxides1 so that a solution of potassium hydroxide will not under any circumstances give a neutral liquid with sulphuretted hydrogen4 ,in this case the sulphuretted hydrogen forms in solution only an acid salt with the potassium3 ,,kho ,h#b,s ,,khs ,h#b,o4 ,it must be supposed that the normal salt is not formed in the solution--that is1 that the reaction #b,,kho ,h#b,s ,k#b,s #b;,h#b,o does not take place4 ,this is seen from the fact that a development of heat1 depending on the formation of potassium hydrosulphide1 ,,khs1 is remarked when as much hydrogen sulphide is passed into a solution of potassium hydroxide as it will absorb4 ,but if a further quantity of potassium hydroxide be added to the resultant solution1 heat is not developed1 whilst if alkali be added to potassium acid sulphate or sodium acid carbonate1 heat is developed4 ,it must not be concluded from this that ,h#b,s is a monobasic acid1 for here there is a question of the decomposing action of water upon ,k#b,s2 ,k#b,s and ,h#b,o in reacting on each other should absorb heat if the reaction of ,,khs upon ,,kho evolves heat4 ,furthermore1 it must be taken into account that potassium oxide1 ,k#b,o1 and the anhydrous oxides like it1 also do not exist in solutions1 for whenever they are formed they immediately react with the water1 forming caustic potash1 ,,kho1 c4 ,in the same way1 directly potassium sulphide1 ,k#b,s1 is formed in water it is decomposed into potassium hydroxide and hydrosulphide3 ,k#b,s ,h#b,o ,,kho ,,khs4 ,potassium sulphide1 ,k#b,s1 in a solid state corresponds with ,k#b,o1 although neither can exist in solution4 #bb ,during recent years 7beginning with ,schulze1 #ahhb7 it has been found that many metallic sulphides which were considered totally insoluble do1 under certain circumstances1 form very unstable solutions in water1 as already mentioned in ,chapter ,i41 ,note #eg4 ,arsenic sulphide is very easily obtained in the form of a solution 7hydrosol74 ,solutions of copper and cadmium sulphides may also be easily obtained by precipitating their salts ,cu,x#b1 or ,cd,x#b1 with ammonium sulphide1 and washing the precipitate2 but they are re-precipitated by the addition of foreign salts4 #bc ,in reality the preceding reaction should be expressed thus3 ,fe,cl#b #b,,khs ,fe,s #b,k,cl ,h#b,s 7,note #ba71 because in the presence of water not ,k#b,s but ,,khs reacts4 ,but as the sulphuretted hydrogen takes no part in the reaction1 it is usual to express the formation of such sulphides without taking the hydrogen sulphide proceeding from the potassium or ammonium hydrosulphides into account4 ,it is not usual to employ potassium sulphide but ammonium sulphide--or1 to speak more accurately1 ammonium hydrosulphide--in order to avoid the formation of a non-volatile salt of potassium and to have1 together with the formation of the sulphide1 a salt of ammonium which can always be driven off by evaporating the solution and igniting the residue--for instance3 ,fe,cl#b 7,,nh#d7b,s ,fe,s #b,,nh#d;,cl4 ,thus the metallic sulphides may be divided into three chief classes3 7#a7 those soluble in water1 7#b7 those insoluble in water but reacting with acids1 and 7#c7 those insoluble both in water and acids4 ,the third class may be easily subdivided into two groups2 to the first group belong those sulphides which correspond with bases or basic oxides1 and are therefore unable to play the part of an acid with the sulphides of the alkalis1 and are insoluble in ,,nh#d;,,hs1 whilst the sulphides of the second group are of an acid character1 and give soluble thio-salts with the sulphides of the alkaline metals1 in which they play the part of an acid4 ,to this group belong those metals whose corresponding oxides have acid properties4 ,it must be observed1 however1 that not all metallic acids have corresponding sulphides1 partly owing to the fact that certain acids are reducible by sulphuretted hydrogen1 especially when their lower degrees of oxidation are of a basic character4 ,such are1 for instance1 the acids of chromium1 manganese1 c4 ,sulphuretted hydrogen converts them into lower oxides1 having the properties of bases4 ,those bases which do not combine with feeble acids1 such as carbonic acid and hydrogen sulphide1 give a precipitate of hydroxide with ammonium sulphide--for example1 aluminium salts react in this manner4 ,this difference of the metals in their behaviour towards sulphuretted hydrogen gives a very valuable means of separating them from each other1 and is taken advantage of in analytical chemistry4 ,if1 for instance1 the metals of the first and third groups occur together1 it is only necessary to convert them into soluble salts1 and to act on the solution of the salts with sulphuretted hydrogen2 this will precipitate the metals of the third group in the form of sulphides1 whilst the metals of the first group will not be in the least acted on4 ,such a method of separating the metals is considered more fully in analytical chemistry1 and we will therefore limit ourselves here to pointing out to which groups the most common metals belong1 and the colour which is proper to the sulphide precipitated4 ,metals which are precipitated by sulphuretted hydrogen1 as sulphides from a solution of their salts1 even in the presence of free acid3 ,the precipitate is soluble in ammonium sulphide3 ,platinum 7dark brown7 ,antimony 7orange7 ,gold 7dark brown7 ,arsenic 7yellow7 ,tin 7yellow and brown7 ,the precipitate is insoluble in ammonium sulphide3 ,copper 7black7 ,mercury 7black7 ,silver 7black7 ,lead 7black7 ,cadmium 7yellow7 ,metals which are precipitated by ammonium sulphide from neutral solutions1 but not precipitated from acid solutions by sulphuretted hydrogen3 ,the sulphide precipitated is soluble in hydrochloric acid3 ,zinc 7white7 ,manganese 7rose colour7 ,iron 7black7 ,the sulphide precipitated is not soluble in dilute hydrochloric acid3 ,nickel 7black7 ,cobalt 7black7 ,a hydroxide1 and not a sulphide1 is precipitated3 ,chromium 7green7 ,aluminium 7white7 ,the metals of the alkalis and of the alkaline earths are not precipitated either by sulphuretted hydrogen or ammonium sulphide4 ,the metals of the alkaline earths when in acid solutions in the form of phosphates and many other salts are precipitated by ammonium sulphide1 because the latter neutralises the free acid1 with formation of an ammonium salt of the acid and evolution of sulphuretted hydrogen4 ,metallic sulphides may be obtained by many other means besides the action of sulphuretted hydrogen on salts and oxides1 or by the simple combination of metals with sulphur when heated or fused4 ,thus they may also be formed by the reduction of sulphates by heating them with charcoal or other means4 ,charcoal takes up the oxygen from many sulphates1 leaving corresponding sulphides4 ,thus sodium sulphate1 ,na#b,,so#d1 when heated with charcoal1 forms sodium sulphide1 ,na#b,s4 ,besides which metallic sulphides are also obtained by heating metals or their oxides in the vapours of many sulphur compounds--for example1 in the vapour of carbon bisulphide1 ,,cs#b1 when the carbon takes up the oxygen and the sulphur combines with the metal4 ,the sulphides formed in this manner are often crystalline1 and often appear with those properties and in that crystalline form in which they occur in nature4 ,besides which we must mention that many of the sulphides of the metals are oxidised in air at the ordinary1 and especially at a higher1 temperature1 forming either ,,so#b and the oxide of the metal or sulphates4 ,this oxidation proceeds with particular ease1 even at the ordinary temperature1 when a metallic sulphide is precipitated from its solutions1 as a fine powder containing water4 ,the sulphides of iron and manganese1 c41 are very easily oxidised in this manner4 ,but if these hydrates be ignited1 they lose their water 7the ignition must be carried on in a stream of hydrogen to prevent their oxidation during the process71 become denser1 and are no longer oxidised at the ordinary temperature4 ,those sulphides whose corresponding sulphates are decomposed by heat part with their sulphur in the form of sulphurous anhydride when they are ignited in air1 and the metal1 as a rule1 remains behind as oxide4 ,this is taken advantage of in the treatment of sulphurous ores4 ,the process is called roasting4 ,hydrogen not only forms sulphuretted hydrogen with sulphur1 but it also combines with it in several other proportions1 just as it combines with oxygen1 forming not only water but also hydrogen peroxide4 ,moreover these polysulphides of hydrogen are also unstable1 like hydrogen peroxide1 and are also obtained from the corresponding polysulphides of the metals of the alkaline earths1 just as hydrogen peroxide is obtained from barium peroxide4 ,thus calcium forms not only calcium sulphide1 ,ca,s1 but also as bi-1 tri-1 and pentasulphide1 ,ca,s#e1 and all these compounds are soluble in water4 ,sodium also combines with sulphur in the same proportions1 forming sulphides from ,na#b,s to ,na#b,s#e4 ,if an acid be added to a solution of a polysulphide1 it gives sulphur1 sulphuretted hydrogen1 and a salt of the metal4 ,for instance1 ,,ms#e1 #b;,h,cl ,m,cl#b ,h#b,s #d,s4 ,if we reverse the operation1 and pour a solution of a polysulphide into an acid1 sulphur is not precipitated1 but an oily liquid is formed which is heavier than water and insoluble in it4 ,this is the polysulphide of hydrogen3 ,,ms#e #b;,h,cl ,m,cl#b ,h#b,s#e4 ,as ,rebs showed 7#ahhh71 whatever polysulphide be taken--of sodium1 for instance--it always gives one and the same hydrogen pentasulphide1#bd of specific gravity #aga 7#ae74 ,it can only be preserved in the absence of water and at low temperatures1 and then not for long3 for1 especially in the presence of alkalis and when slightly warmed1 it splits up very easily into sulphuretted hydrogen and sulphur4#be #bd ,rebs took di-1 tri-1 tetra-1 and pentasulphides of sodium1 potassium1 and barium1 which he prepared by dissolving sulphur in solutions of the normal sulphides2 on adding hydrochloric acid he always obtained hydrogen pentasulphide1 whence it is evident that #d;,h#b,sn 7n - #a7;,h#b,s#e 7#e - n7,h#b,s4 ,for example1 if ,h#b,s#b were formed1 it would decompose according to the equation #d;,h#b,s#b ,h#b,s#e #c;,h#b,s4 ,the hydrogen pentasulphide formed breaks up into hydrogen sulphide and sulphur when brought into contact with water4 ,previous to ,rebs' researches many chemists stated that all polysulphides gave the bisulphide ,h#b,s#b1 and ,hofmann recognised only hydrogen trisulphide1 ,h#b,s#c4 #be ,the formation of the polysulphides of hydrogen1 ,h#b,sn is easily understood from the law of substitution1 like that of the saturated hydrocarbons1 ,cn,h#bn #b1 knowing that sulphur gives ,h#b,s1 because the molecule of sulphuretted hydrogen may be divided into ,h and ,,hs4 ,this radicle1 ,,hs1 is equivalent to ,h4 ,by substituting this radicle for hydrogen in ,h#b,s we obtain 7,,hs7,,hs ,h#b,s#b1 7,,hs77,,hs7,s ,h#b,s#c1 c41 in general ,h#b,sn4 ,the homologues of ,,ch#d1 ,cn,h#bn #b are formed in this manner from ,,ch#d1 and consequently the polysulphides ,h#b,sn are the homologues of ,h#b,s4 ,the question arises why in ,h#b,sn the apparent limit of n is #e--that is1 why does the substitution end with the formation of ,h#b,s#e8 ,the answer appears to me to be clearly because in the molecule of sulphur1 ,s#f1 there are six atoms of sulphur 7,note #aa74 ,the forces in one and the other case are the same4 ,in the one case they hold ,s#f together1 in the other ,s#e and ,h#b2 and1 judging from ,h#b,s1 the two atoms of hydrogen are equal in power and significance to the atom of sulphur4 ,just as hydrogen peroxide1 ,h#b,o#b1 expresses the composition of ozone1 ,o#c1 in which ,o is replaced by ,h#b1 so also ,h#b,s#e corresponds with ,s#f4 ,the soluble sulphides and polysulphides of the metals of the alkalis and alkaline earths--for example1 of ammonium1#bf potassium1#bg and calcium1#bh--;have the appearance and properties of salts1 just as the hydrated oxides have1 whilst the sulphides of the metals of the higher groups resemble their oxides and have not at all the appearance of salts1 and this is more especially the case with regard to the crystalline forms in which they frequently occur in nature4#bi #bf ,ammonium sulphide1 7,,nh#d7b,s1 may be prepared by passing sulphuretted hydrogen into a vessel full of dry ammonia1 or by passing both dry gases together into a very cold receiver4 ,in the latter case it is necessary to prevent the access of air1 and to have an excess of ammonia4 ,under these circumstances1 two volumes of ammonia combine with one volume of sulphuretted hydrogen1 and form a colourless1 very volatile1 crystalline substance1 having a very unpleasant odour1 which is very poisonous and exceedingly unstable4 ,when exposed to the air it absorbs oxygen and acquires a yellow colour1 and then contains oxygen and polysulphide compounds 7because a portion of the hydrogen sulphide gives water and sulphur74 ,it is soluble in water and forms a colourless solution1 which1 however1 in all probability contains free ammonia and the acid salt--that is1 ammonium hydrosulphide1 ,,nh#d;,,hs1 or 7,,nh#d7b1,s1,h#b,s4 ,this salt is formed when dry ammonia is mixed with an excess of dry sulphuretted hydrogen4 ,the compound contains equal volumes of the components ,,nh#c ,h#b,s 7,,nh#d7;,,hs4 ,it crystallises in an anhydrous state in colourless plates1 and may be easily volatilised 7dissociating like ammonium chloride71 even at the ordinary temperature2 it has an alkaline reaction1 absorbs oxygen from the air1 is soluble in water1 and its solution is usually prepared by saturating an aqueous solution of ammonia with sulphuretted hydrogen4 ,according to the ordinary rule1 these salts1 like other ammonium salts1 split up into ammonia and sulphuretted hydrogen when they are distilled4 ,a solution of ammonium sulphide is able to dissolve sulphur1 and it then contains compounds of hydrogen polysulphide and ammonia4 ,some of these compounds may be obtained in a crystalline form4 ,thus ,fritzsche obtained a compound of ammonia with hydrogen pentasulphide1 or ammonium pentasulphide1 7,,nh#d7b,s#e1 in the following manner3 ,he saturated an aqueous solution of ammonia with sulphuretted hydrogen1 added powdered sulphur to it1 and passed ammonia gas into the solution1 which then absorbed a fresh amount4 ,after this he again passed sulphuretted hydrogen into the solution1 and then added sulphur1 and then again ammonia4 ,after repeating this several times1 orange-yellow crystals of 7,,nh#d7b,s#e separated out from the liquid4 ,these crystals melted at #dj to #ej1 and were very unstable4 ,when a solution of ammonium hydrosulphide1 prepared by saturating a solution of ammonia with sulphuretted hydrogen1 is exposed to the air1 it turns yellow1 owing to the presence of an ammonium polysulphide1 whose formation is due to the sulphuretted hydrogen being oxidised by the air and converted into water and sulphur1 which is dissolved by the ammonium sulphide4 ,in certain analytical reactions it is usual to employ a solution of ammonium sulphide which has been kept for some time and acquired a yellow colour4 ,this yellow sulphide of ammonium deposits sulphur when saturated with acids1 whilst a freshly-prepared solution only evolves sulphuretted hydrogen4 ,the yellow solution furthermore contains ammonium thiosulphate1 which is derived not only from the oxidation of the ammonium sulphide1 but also from the action of the liberated sulphur on the ammonia1 just as an alkaline salt of thiosulphuric acid and a sulphide are formed by the action of sulphur on a solution of a caustic alkali4 #bg ,potassium sulphide1 ,k#b,s1 is obtained by heating a mixture of potassium sulphate and charcoal to a bright-red heat4 ,it may be prepared in solution by taking a solution of potassium hydroxide1 dividing it into two equal parts1 and saturating one portion with sulphuretted hydrogen so long as it is absorbed4 ,this portion will then contain the acid salt ,,khs 7,note #ba74 ,the two portions are then mixed together1 and potassium sulphide will then be obtained in the solution4 ,this solution has a strongly alkaline reaction1 and is colourless when freshly prepared1 but it very easily undergoes change when exposed to the air1 forming potassium thiosulphate and polysulphides4 ,when the solution is evaporated at low temperatures under the receiver of an air-pump1 it yields crystals containing ,k#b,s1#e;,h#b,o 7heated at #aej1 they part with #c mol4 ,h#b,o1 and at higher temperatures they lose nearly all their water without evolving sulphuretted hydrogen74 ,when they are ignited in glass vessels they corrode the glass4 ,when a solution of caustic potash1 completely saturated with sulphuretted hydrogen1 is evaporated under the receiver of an air-pump it forms colourless rhombohedra of potassium hydrosulphide1 #b7,,khs71,h#b,o1,k#b,s1,h#b,s1,h#b,o4 ,these crystals are deliquescent in the air1 but do not change in a vacuum when heated up to #agj1 and at higher temperatures they lose water but do not evolve sulphuretted hydrogen4 ,the anhydrous compound1 ,,khs1 fuses at a dark-red heat into a very mobile yellow liquid1 which gradually becomes darker in colour and solidifies to a red mass4 ,it is remarkable that when a solution of the compound ,,khs is boiled it somewhat easily evolves half its sulphuretted hydrogen1 leaving potassium sulphide1 ,k#b,s1 in solution2 and a solution of the latter in water is also able to evolve sulphuretted hydrogen on prolonged boiling1 but the evolution cannot be rendered complete1 and1 therefore1 at a certain temperature1 a solution of potassium sulphide will not be capable of absorbing sulphuretted hydrogen at all4 ,from this we must conclude that potassium hydroxide1 water1 and sulphuretted hydrogen form a system whose complex equilibrium is subject to the laws of dissociation1 depends on the relative mass of each substance1 on the temperature1 and the dissociation pressure of the component elements4 ,potassium sulphide is not only soluble in water1 but also in alcohol4 ,berzelius showed that in addition to potassium sulphide there also exist potassium bisulphide1 ,k#b,s#b2 trisulphide1 ,k#b,s#c2 tetrasulphide1 ,k#b,s#d2 and pentasulphide1 ,k#b,s#e4 ,according to the researches of ,schne1 the last three are the most stable4 ,these different compounds of potassium and sulphur may be prepared by fusing potassium hydroxide or carbonate with an excess of sulphur in a porcelain crucible in a stream of carbonic anhydride4 ,at about #fjj potassium pentasulphide is formed2 this is the highest sulphur compound of potassium4 ,when heated to #hjj it loses one-fifth of its sulphur and gives the tetrasulphide1 which at this temperature is stable4 ,at a bright-red heat--namely1 at about #ijj--the trisulphide is formed4 ,this compound may be also formed by igniting potassium carbonate in a stream of carbon bisulphide1 in which case a compound1 ,k#b;,,cs#c1 is first formed corresponding to potassium carbonate1 and carbonic anhydride is evolved4 ,on further ignition this compound splits up into carbon and potassium trisulphide1 ,k#b,s#c4 ,the tetrasulphide may also be obtained in solution if a solution of potassium sulphide be boiled with the requisite amount of sulphur without access of air4 ,this solution yields red crystals of the composition ,k#b,s#d1b;,h#b,o when it is evaporated in a vacuum4 ,these crystals are very hygroscopic1 easily soluble in water1 but very sparingly in alcohol2 when ignited they give off water1 sulphuretted hydrogen1 and sulphur4 ,if a solution of potassium sulphide be boiled with an excess of sulphur it forms the pentasulphide1 which1 however1 is decomposed on prolonged boiling into sulphuretted hydrogen and potassium thiosulphate3 ,k#b,s#e #c;,h#b,o ,k#b,s#b,o#c #c;,h#b,s4 ,a substance called liver of sulphur was formerly frequently used in chemistry and medicine4 ,under this name is known the substance which is formed by boiling a solution of caustic potash with an excess of flowers of sulphur4 ,this solution contains a mixture of potassium pentasulphide and thiosulphate1 #f,,kho #ab,s #b,k#b,s#e ,k#b,s#b,o#c #c;,h#b,o4 ,the substance obtained by fusing potassium carbonate with an excess of sulphur was also known as liver of sulphur4 ,if this mixture be heated to an incipient dark-red heat it will contain potassium thiosulphate1 but at higher temperatures potassium sulphate is formed4 ,in either case a polysulphide of potassium is also present4 ,the sulphides of sodium1 for example ,na#b,s1 ,na,h,s1 c41 in many respects closely resemble the corresponding potassium compounds4 #bh ,the metals of the alkaline earths1 like those of the alkalis1 form several compounds with sulphur2 thus calcium forms compounds with one and with five atoms of sulphur4 ,there are doubtless also intermediate sulphides4 ,if sulphuretted hydrogen be passed over ignited lime it forms water and calcium sulphide1 which may also be formed by heating calcium sulphate with charcoal1 whilst if sulphur be heated with lime or with calcium carbonate1 then naturally oxygen compounds 7calcium thiosulphate and sulphate7 are formed at the same time as calcium sulphide4 ,the prolonged action of the vapour of carbon bisulphide1 especially when mixed with carbonic anhydride1 on strongly ignited calcium carbonate entirely converts it into sulphide4 ,calcium sulphide is generally obtained as an almost colourless1 opaque1 brittle mass1 which is infusible at a white heat1 and is soluble in water4 ,the act of solution 7as with ,k#b,s1 ,note #ba7 is partly accompanied by a double decomposition with the water4 ,when heated1 dry calcium sulphide does not absorb oxygen from the air4 ,an excess of water decomposes it1 like many other metallic sulphides1 precipitating lime 7as a product of the decomposition the lime hinders the action of the water upon the ,ca,s2 see soda refuse1 ,chapter ,,xii41 ,note #ab71 and forming a hydrosulphide1 ,ca,h#b,s#b1 in solution4 ,this compound is also formed by passing sulphuretted hydrogen through an aqueous solution of calcium sulphide or lime4 ,its solution1 like that of calcium sulphide1 has an alkaline reaction4 ,it decomposes when evaporated1 and absorbs oxygen from the air4 ,calcium pentasulphide1 ,ca,s#e1 is not known in a pure state1 but may be obtained in admixture with calcium thiosulphate by boiling a solution of lime or calcium sulphide with sulphur3 #c;,ca,h#b,o#b #ab,s #b;,ca,s#e ,ca,s#b,o#c #c;,h#b,o4 ,a similar compound in an impure form is formed by the action of air on alkali waste1 and is used for the preparation of thiosulphates4 ,many of the sulphides of the metals of the alkaline earths are phosphorescent--that is1 they have the faculty of emitting light1 after having been subjected to the action of sunlight1 or of any bright source of light 7,canton phosphorus1 c474 ,the luminosity lasts some time1 but it is not permanent1 and gradually disappears4 ,this phosphorescent property is inherent1 in a greater or less degree1 to nearly all substances 7,becquerel71 but for a very short time1 whilst with calcium sulphide it is comparatively durable1 lasting for several hours1 and ,dewar 7#ahid7 showed that it is far more intense at very low temperatures 7for instance1 in bodies cooled in liquid oxygen to -#ahb74 ,it is due to the excitation of the surfaces of substances by the action of light1 and is determined by those rays which exhibit a chemical action4 ,hence daylight or the light of burning magnesium1 c41 acts more powerfully than the light of a lamp1 c4 ,warnerke has shown that a small quantity of magnesium lighted near the surface of a phosphorescent substance rapidly excites the greatest possible intensity of luminosity2 this enabled him to found a method of measuring the intensity of light--i4e4 to obtain a constant unit of light--and to apply it to photography4 ,the nature of the change which is accomplished on the surface of the luminous substance is at present unknown1 but in any case it is a renewable one1 because the experiment may be repeated for an infinite number of times and takes place in a vacuum4 ,the intensity and tint of the light emitted depend on the method of preparation of the calcium sulphide1 and on the degree of ignition and purity of the calcium carbonate taken4 ,according to the observations of ,becquerel1 the presence of compounds of manganese1 bismuth1 c41 sodium sulphide 7but not potassium sulphide71 c41 although in minute traces1 is perfectly indispensable4 ,this gives reason for thinking that the formation 7in the dark7 and decomposition 7in light7 of double salts like ,mn,s1,na#b,s perhaps form the chemical cause of the phenomena4 ,compounds of strontium and barium have this property to even a greater extent than calcium sulphide4 ,these compounds may be prepared as in the following example3 ,a mixture of sodium thiosulphate and strontium chloride is prepared2 a double decomposition takes place between the salts1 and1 on the addition of alcohol1 strontium thiosulphate1 ,sr,s#b,o#c1 is precipitated1 which1 when ignited1 leaves strontium sulphide behind4 ,the strontium sulphide thus prepared emits 7when dry7 a greenish yellow light4 ,it contains a certain amount of sulphur1 sodium sulphide1 and strontium sulphate4 ,by ignition at various temperatures1 and by different methods of preparation1 it is possible to obtain mixtures which emit different coloured lights4 #bi ,as examples1 we will describe the sulphides of arsenic1 antimony1 and mercury4 ,arsenic trisulphide1 or orpiment1 ,as#b,s#c1 occurs native1 and is obtained pure when a solution of arsenious anhydride in the presence of hydrochloric acid comes into contact with sulphuretted hydrogen 7there is no precipitate in the absence of free acid74 ,a beautiful yellow precipitate is then obtained3 ,as#b,o#c #c;,h#b,s #c;,h#b,o ,as#b,s#c2 it fuses when heated1 and volatilises without decomposition4 ,as#b,s#c is easily obtained in a colloid form 7,chapter ,i41 ,note #eg74 ,when fused it forms a semi-transparent1 yellow mass1 and it is thus that it enters the market4 ,the specific gravity of native orpiment is #cd1 and that of the artificially-fused mass is #bg4 ,it is used as a yellow pigment1 and owing to its insolubility in water and acids it is less injurious than the other compounds corresponding to arsenious acid4 ,according to the type ,as,x#b1 realgar1 ,as,s1 is known1 but it is probable that the true composition of this compound is ,as#d,s#d--that is1 it presents the same relation to orpiment as liquid phosphuretted hydrogen does to gaseous4 ,realgar 7,sandaraca7 occurs native as brilliant red crystals of specific gravity #cei1 and may be prepared artificially by fusing arsenic and sulphur in the proportions indicated by its formul4 ,it is prepared in large quantities by distilling a mixture of sulphur and arsenical pyrites4 ,like orpiment it dissolves in calcium sulphide1 and even in caustic potash4 ,it is used for signal lights and fireworks1 because it deflagrates and gives a large and very brilliant white flame with nitre4 ,with antimony1 sulphur gives a tri- and a pentasulphide4 ,the former1 ,sb#b,s#c1 which corresponds with antimonious oxide1 occurs native 7,chapter ,,xix47 in a crystalline form2 its sp4 gr4 is then #di1 and it presents brilliant rhombic crystals of a grey colour1 which fuse when heated4 ,a substance of the same composition is obtained as an amorphous orange powder by passing sulphuretted hydrogen into an acid solution of antimonious oxide4 ,in this respect antimonious oxide again reacts like arsenious acid1 and the sulphides of both are soluble in ammonium and potassium sulphides1 and1 especially in the case of arsenious sulphide1 are easily obtained in colloidal solutions4 ,by prolonged boiling with water1 antimonious sulphide may be entirely converted into the oxide1 hydrogen sulphide being evolved 7,elbers74 ,native antimony sulphide1 or the orange precipitated trisulphide when fused with dry1 or boiled with dissolved1 alkalis1 forms a dark-coloured mass 7,kermes mineral7 formerly much used in medicine1 which contains a mixture of antimonious sulphide and oxide4 ,there are also compounds of these substances4 ,a so-called antimony vermilion is much used as a dye2 it is prepared by boiling sodium thiosulphate 7six parts7 with antimony trichloride 7five parts7 and water 7fifty parts74 ,this substance probably contains an oxysulphide of antimony--that is1 a portion of the oxygen in the oxide of antimony in it is replaced by sulphur4 ,red antimony ore1 and antimony glass1 which is obtained by fusing the trisulphide with antimonious oxide1 have a similar composition1 ,sb#b,,os#b4 ,in the arts1 the antimony pentasulphide1 ,sb#b,s#e1 is the most frequently used of the sulphur compounds of antimony4 ,it is formed by the action of acids on the so-called ,schlippe's salt1 which is a sodium thiorthantimonate1 ,sb,s7,na,s7#c1 corresponding with 7,chapter ,,xix41 ,note #da bis7 orthantimonic acid1 ,sb,o7,,oh7#c1 with the replacement of oxygen by sulphur4 ,it is obtained by boiling finely-powdered native antimony trisulphide with twice its weight of sodium carbonate1 and half its weight of sulphur and lime1 in the presence of a considerable quantity of water4 ,the processes taking place are as follows3--,the sodium carbonate is converted into hydroxide by the lime1 and then forms sodium sulphide with the sulphur2 the sodium sulphide then dissolves the antimony sulphide1 which in this form already combines with the greatest amount of sulphur1 so that a compound is formed corresponding with antimony pentasulphide dissolved in sodium sulphide4 ,the solution is filtered and crystallised1 care being taken to prevent access of air1 which oxidises the sodium sulphide4 ,this salt crystallises in large1 yellowish crystals1 which are easily soluble in water and have the composition ,na#c,sb,s#d1i;,h#b,o4 ,when heated they lose their water of crystallisation and then fuse without alteration2 but when in solution1 and even in crystalline form1 this salt turns brown in air1 owing to the oxidation of the sulphur and the breaking up of the compound4 ,as it is used in medicine1 especially in the preparation of antimony pentasulphide1 it is kept under a layer of alcohol1 in which it is insoluble4 ,acids precipitate antimony pentasulphide from a solution of this salt1 as an orange powder1 insoluble in acids and very frequently used in medicine 7sulfur auratum antimonii74 ,this substance when heated evolves vapours of sulphur1 and leaves antimony trisulphide behind4 ,mercury forms compounds with sulphur of the same types as it does with oxygen4 ,mercurous sulphide1 ,hg#b,s1 easily splits up into mercury and mercuric sulphide4 ,it is obtained by the action of potassium sulphide on mercurous chloride1 and also by the action of sulphuretted hydrogen on solutions of salts of the type ,hg,x4 ,mercuric sulphide1 ,hg,s1 corresponding with the oxide1 is cinnabar2 it is obtained as a black precipitate by the action of an excess of sulphuretted hydrogen on solutions of mercuric salts4 ,it is insoluble in acids1 and is therefore precipitated in their presence4 ,if a certain amount of water containing sulphuretted hydrogen be added to a solution of mercuric chloride1 it first gives a white precipitate of the composition ,hg#c,s#b;,cl#b--that is1 a compound ,hg,cl1#b;,hg,s1 a sulphochloride of mercury like the oxychloride4 ,but in the presence of an excess of sulphuretted hydrogen1 the black precipitate of mercuric sulphide is formed4 ,in this state it is not crystalline 7the red variety is formed by the prolonged action of polysulphides of ammonium upon the black ,hg,s71 but if it be heated to its temperature of volatilisation it forms a red crystalline sublimate which is identical with native cinnabar4 ,in this form its specific gravity is #hj1 and it forms a red powder1 owing to which it is used as a red pigment 7vermilion7 in oil1 pastel1 and other paints4 ,it is so little attacked by reagents that even nitric acid has no action on it1 and the gastric juices do not dissolve it1 so that it is not poisonous4 ,when heated in air1 the sulphur burns away and leaves metallic mercury4 ,on a large scale cinnabar is usually prepared in the following manner3 #cjj parts of mercury and #aae parts of sulphur are mixed together as intimately as possible and poured into a solution of #ge parts of caustic potash in #dbe parts of water1 and the mixture is heated at #ej for several hours4 ,red mercury sulphide is thus formed1 and separates out from the solution4 ,the reaction which takes place is as follows3 ,a soluble compound1 ,k#b;,hg,s#b1 is first formed2 this compound is able to separate in colourless silky needles1 which are soluble in the caustic potash1 but are decomposed by water1 and at #ej2 this solution 7perhaps by attracting oxygen from the air7 slowly deposits ,hg,s in a crystalline form4 ,spring conducted an interesting research 7at ,lige1 #ahid7 upon the conversion of the black amorphous sulphide of mercury1 ,hg,s1 into red crystalline cinnabar4 ,this research formed a sequel to ,spring's classical researches on the influence of high pressures upon the properties of solids and their capacity for mutual combination4 ,he showed1 among other things1 that ordinary solids and even metals 7for instance1 ,pb71 after being considerably compressed under a pressure of #bj1jjj atmospheres1 return on removal of the pressure to their original density like gases4 ,but this is only true when the compressed solid is not liable to an allotropic variation1 and does not give a denser variety4 ,thus prismatic sulphur 7sp4 gr4 #ai7 passes under pressure into the octahedral 7sp4 gr4 #bje7 variety4 ,black ,hg,s 7precipitated from solution7 has a sp4 gr4 #gf1 while that of the red variety is #hb1 and therefore it might be expected that the former would pass into the latter under pressure1 but experiments both at the ordinary and a higher temperature did not give the looked-for result1 because even at a pressure of #bj1jjj atmospheres the black sulphide was not compressed to the density of cinnabar 7a pressure of as much as #ce1jjj atmospheres was necessary1 which could not be attained in the experiment74 ,but ,spring prepared a black ,hg,s1 which had a sp4 gr4 of #hj1 and this1 under a pressure of #b1ejj atmospheres1 passed into cinnabar4 ,he obtained this peculiar black variety of ,hg,s 7sp4 gr4 #hj7 by distilling cinnabar in an atmosphere of ,,co#b1 when the greater portion of the ,hg,s is redeposited in the form of cinnabar4 ,under the action of a solution of polysulphide of ammonium1 this variety of ,hg,s passes more slowly into the red variety than the precipitated variety does1 while under pressure the conversion is comparatively easy4 ,it is worthy of remark1 that ,linder and ,picton obtained complex compounds of many of the sulphides of the heavy metals 7,ca1 ,hg1 ,sb1 ,zn1 ,cd1 ,ag1 ,au7 with ,h#b,s1 for example ,h#b,s1#g;,cu,s 7by the action of ,h#b,s upon the hydrate of oxide of copper71 ,h#b,s1#i;,cu,s 7in the presence of acetic acid and with an excess of ,h#b,s71 c4 ,probably we have here a sort of 'solid' solution of ,h#b,s in the metallic sulphides4 ,as the acids derived from chlorine1 phosphorus1 and carbon are the oxidised hydrogen compounds of these elements1 so also we can form an idea of the acid hydrates of sulphur1 or of the normal acids of sulphur1 by representing them as the oxidised products of sulphuretted hydrogen-- ,h,cl ,h#b,s ,h#c,p ,h#d;,c ,h,cl,o ,h#b,,so787 ,h#c,,po787 ,h#d;,,co ,h,cl,o#b ,h#b,,so#b787 ,h#c,,po#b ,h#d;,,co#b ,h,cl,o#c ,h#b,,so#c ,h#c,,po#c ,h#d;,,co#c ,h,cl,o#d ,h#b,,so#d ,h#c,,po#d ,h#d;,,co#dcj ,in the case of chlorine1 if not all the hydrates1 at all events salts of all the normal hydrates are known1 whilst in the case of sulphur only the acids ,h#b,s1 ,h#b,,so#c and ,h#b,,so#d are known4 ,but1 on the other hand1 the latter are obtained not only as hydrates but also as stable anhydrides1 ,,so#b and ,,so#c1 which are formed with the evolution of heat from sulphur and oxygen2 #cb parts of sulphur in combining with #cb parts of oxygen--that is1 in forming ,,so#b--;evolve #ga1jjj heat units1#ca and if the oxidation proceeds to the formation of ,,so#c1 #ajc1jjj heat units are evolved4 ,these figures may be compared with those which correspond with the passage of carbon into ,,co and ,,co#b1 when #bi1jjj and #ig1jjj units of heat are evolved4 ,this determines the stability of the higher oxides of sulphur1 and also expresses the peculiarity of sulphur as an element which1 although an analogue of oxygen1 forms stable compounds with it1 and thus fundamentally differs from chlorine4 ,the higher and lower oxides of chlorine are powerful oxidising agents1 whilst the higher oxide of sulphur1 ,,so#c1 has but feeble oxidising powers1 and the lower oxide1 ,,so#b1 frequently acts as a reducing agent1 and is formed by the direct combustion of sulphur1 just as carbonic anhydride1 ,,co#b1 proceeds from the combustion of carbon4 ,in the combustion of sulphur1 and also in the oxidation 7roasting7 of the sulphides and polysulphides by their ignition in air1 sulphurous oxide1 or sulphurous anhydride1 or sulphur dioxide1 ,,so#b1ca bis is exclusively formed4 ,it is prepared on a large scale by burning sulphur or roasting iron pyrites or other sulphides#cb for the manufacture of sulphuric acid 7,chapter ,,vi471 and for direct application in the manufacture of wine or for bleaching tissues and other purposes4 ,in the latter instances its application is based on the fact that sulphurous anhydride acts on certain vegetable matters1 and has the property of a reducing and feeble acid4#cb bis #cj ,,ch#d gives ,,ch#d,o or ,,ch#c7,,oh71 wood spirit2 ,,ch#d,o#b or ,,ch#b7,,oh7#b1 which decomposes into water and ,,ch#b,o--that is1 methylene oxide or formaldehyde2 ,,ch#d,o#c ,,ch7,,oh7#c ,h#b,o ,,cho7,,oh71 or formic acid2 and ,,ch#d,o#d ,c7,,oh7#d #b;,h#b,o ,,co#b4 ,there are four typical hydrogen compounds1 ,,rh1 ,,rh#b1 ,,rh#c1 and ,,rh#d1 and each of them has its typical oxide4 ,beyond ,h#d and ,o#d combination does not proceed4 #ca ,rhombic sulphur1 #ga1jhj heat units2 monoclinic sulphur1 #ga1gbj units1 according to ,thomsen4 #ca bis ,however1 when sulphur or metallic sulphides burn in an excess of air1 there is always formed a certain1 although small1 amount of ,,so#c1 which gives sulphuric acid with the moisture of the air4 #cb ,the enormous amount of sulphuric acid now manufactured is chiefly prepared by roasting native pyrites1 but a considerable amount of the ,,so#b for this purpose is obtained by roasting zinc blende 7,zn,s7 and copper and lead sulphides4 ,a certain amount is also procured from soda refuse 7,note #f7 and the residues obtained from the purification of coal gas4 #cb bis ,sulphurous anhydride is also obtained by the decomposition of many sulphates1 especially of the heavy metals1 by the action of heat2 but this requires a very powerful heat4 ,this formation of sulphurous anhydride from sulphates is based on the decomposition proper to sulphuric acid itself4 ,when sulphuric acid is strongly heated 7for instance1 by dropping it upon an incandescent surface7 it is decomposed into water1 oxygen1 and sulphurous anhydride--that is1 into those compounds from which it is formed4 ,a similar decomposition proceeds during the ignition of many sulphates4 ,even so stable a sulphate as gypsum does not resist the action of very high temperatures1 but is decomposed in the same manner1 lime being left behind4 ,the decomposition of sulphates by heat is accomplished with still greater facility in the presence of sulphur1 because in this case the liberated oxygen combines with the sulphur and the metal is able to form a sulphide4 ,thus when ferrous sulphate 7green vitriol7 is ignited with sulphur1 it gives ferrous sulphide and sulphurous anhydride3 ,fe,s,o#d #b,s ,fe,s #b,,so#b1 and this reaction may even be used for the preparation of this gas4 ,at #djj sulphuric acid and sulphur give an extremely uniform stream of pure sulphurous anhydride1 so that it is best prepared on a manufacturing scale by this method4 ,iron pyrites1 ,fe,s#b1 when heated to #aej with sulphuric acid 7sp4 gr4 #age7 in cast-iron vessels also gives an abundant and uniform supply of sulphurous anhydride4 ,in the laboratory--that is1 on a small scale--sulphurous anhydride is best prepared by deoxidising sulphuric acid by heating it with charcoal1 or copper1 sulphur1 mercury1 c4 ,charcoal produces this decomposition of sulphuric acid at but moderately high temperatures2 it is itself converted into carbonic anhydride1#cb tri and therefore when sulphuric acid is heated with charcoal it evolves a mixture of sulphurous and carbonic anhydrides3 ,c #b;,h#b,,so#d ,,co#b #b,,so#b #b;,h#b,o4 ,the metals which are unable to decompose water1 and which do not1 therefore1 expel hydrogen from sulphuric acid1 are frequently capable of decomposing sulphuric acid1 with the evolution of sulphurous anhydride1 just as they decompose nitric acid1 forming the lower oxides of nitrogen4 ,these metals are silver1 mercury1 copper1 lead1 and others4 ,thus1 for example1 the action of copper on sulphuric acid may be expressed by the following equation3 ,cu #b;,h#b,,so#d ,cu,s,o#d ,,so#b #b;,h#b,o4 ,in the laboratory this reaction is carried on in a flask with a gas-conducting tube1 and does not take place unless aided by heat4#cc #cb tri ,mellitic acid is formed at the same time 7,verneuille74 #cc ,the thermochemical data connected with this reaction are as follows3 ,a molecule of hydrogen ,h#b1 in combining with oxygen 7,o #af7 develops about #fi1jjj heat units1 whilst the molecule of ,,so#b1 in combining with oxygen only develops about #cb1jjj heat units--that is1 about half as much--and therefore those metals which cannot decompose water may still be able to deoxidise sulphuric into sulphurous acid4 ,those metals which decompose water and sulphuric acid with the evolution of hydrogen1 evolve in combining with sixteen parts by weight of oxygen more heat than hydrogen does--for example1 ,k#b1 ,na#b1 ,ca develop about or more than #ajj1jjj heat units2 ,fe1 ,zn1 ,mn about #gj1jjj to #hj1jjj heat units2 whilst those metals which neither decompose water nor evolve hydrogen from sulphuric acid1 but are still capable of evolving sulphurous anhydride from it1 develop less heat with oxygen than hydrogen1 but nearly the same amount1 if not more than1 sulphurous anhydride develops--for example1 ,cu and ,hg develop about #dj1jjj and ,pb about #ej1jjj heat units4 ,in its physical and chemical properties sulphurous anhydride presents a great resemblance to carbonic anhydride4 ,it is a heavy gas1 somewhat considerably soluble in water1 very easily condensed into a liquid2 it forms normal and acid salts1 does not evolve oxygen under the direct action of heat1#cd although such metals as sodium and magnesium burn in it1 just as in carbonic anhydride4 ,it has a suffocating odour1 which is well known owing to its being evolved when sulphur or sulphur matches are burnt4 ,in characterising the properties of sulphurous anhydride1 it is very important to remember 7,chapter ,,ii47 also that it is more easily liquefied 7at -#aj1 or at #j under two atmospheres pressure7 than carbonic anhydride 7thirty-six atmospheres at #j71ce that it is more soluble than carbonic anhydride 7,vol4 ,i4 p4 #gi72 at #j1 #ajj vols4 of water dissolve #ahj vols4 of carbonic anhydride and #fhh vols4 of sulphuric anhydride71 that the molecular weight of ,,so#b #fd and of ,,co#b #dd1 and that the density of liquid sulphurous anhydride at #j #adc 7molecular volume #de7 and of carbonic anhydride #jie 7molecular volume #di74 ,although sulphur dioxide is the anhydride of an acid1 nevertheless1 like carbonic anhydride1 it does not form any stable compounds with water1 but gives a solution from which it may be entirely expelled by the action of heat4#cf ,the acid character of sulphurous anhydride is clearly expressed by the fact that it is entirely absorbed by alkalis1 with which it forms acid and normal salts easily soluble in water4 ,with salts of barium1 calcium1 and the heavy metals1 the normal salts of the alkalis1 ,m#b,,so#c1 give precipitates exactly like those formed by the carbonates4 ,in general1 the salts of sulphurous acid are closely analogous to the corresponding carbonates4 #cd ,that is1 it only dissociates and re-forms the original product on cooling4 #ce ,at a given temperature the pressure of this gas evolved from any salt will be less than that of carbonic anhydride1 if we compare the separation of a gas from its salts with the phenomenon of evaporation1 as was done in discussing the decomposition of calcium carbonate4 ,liquid sulphurous anhydride is used on a large scale 7,pictet7 for the production of cold4 #cf ,de la ,rive1 ,pierre1 and more especially ,roozeboom1 have investigated the crystallo-hydrate which is formed by sulphurous anhydride and water at temperatures below #g under the ordinary pressure1 and in closed vessels 7at temperatures below #ab74 ,its composition is ,,so#b1g;,h#b,o1 and density #ab4 ,this hydrate corresponds with the similar hydrate ,,co#b1h;,h#b,o obtained by ,wroblewsky4 ,acid sodium sulphite1 ,na,h,s,o#c1 may be obtained by passing sulphurous anhydride into a solution of sodium hydroxide4 ,it is also formed by saturating a solution of sodium carbonate with the gas 7carbonic anhydride is then given off71 and as the solubility of the acid sulphite is much greater than that of the carbonate1 a further quantity of the latter may be dissolved after the passage of the sulphurous anhydride1 so that ultimately a very strong solution of the sulphite may be formed in this manner1 from which it may be obtained in a crystalline form1 either by cooling and evaporating 7without heating1 for then the salt would give off sulphurous anhydride7 or by adding alcohol to the solution4 ,when exposed to the air this salt loses sulphurous anhydride and attracts oxygen1 which converts it into sodium sulphate4 ,the acid sulphites of the alkali metals are able to combine not only with oxygen1 but also with many other substances--for example1 a solution of the sodium salt dissolves sulphur1 forming sodium thiosulphate1 gives crystalline compounds with the aldehydes and ketones1 and dissolves many bases1 converting them into double sulphites4 ,having the faculty of attracting or absorbing oxygen1 acid sodium sulphite is also able to absorb chlorine1 and is therefore employed1 like sodium thiosulphate1 for the removal of chloride 7as an antichlor71 especially in the bleaching of fabrics1 when it is necessary to remove the last traces of the chlorine held in the tissues1 which might otherwise have an injurious effect on them4 ,if a solution of an alkali hydroxide be divided into two parts1 and one half is saturated with sulphurous anhydride1 and then the other half added to it1 a normal salt will be obtained in the solution1 having an alkaline reaction1 like a solution of sodium carbonate4 ,the acid salt has a neutral reaction4#cf bis ,like sodium carbonate1 normal sodium sulphite has the composition ,na#b,,so#c1aj;,h#b,o1 and its maximum solubility is at #cc--;in a word1 it very closely resembles sodium carbonate4 ,although this salt does not give off sulphurous anhydride from its solution1 it is able1 like the acid salt1 to absorb oxygen from the air1 and is then converted into sodium sulphate4#cg #cf bis ,schwicker 7#ahhi7 by saturating ,na,h,s,o#c with potash1 or ,,khso#c with soda1 obtained ,na,k,s,o#c1 in the first instance with ,h#b,o1 and in the second instance with #b;,h#b,o1 probably owing to the different media in which the crystals are formed4 ,in general sulphurous acid easily forms double salts4 #cg ,the normal salts of calcium and magnesium are slightly1 and the acid salts easily1 soluble in water4 ,these acid sulphites are much used in practice2 thus calcium bisulphite is employed in the manufacture of cellulose from sawdust1 for mixing with fibrous matter in the manufacture of paper4 ,besides the acid character we must also point out the reducing character of sulphurous anhydride4 ,the reducing action of sulphurous acid1 its anhydride and salts1 is due to their faculty of passing into sulphuric acid and sulphates4 ,the reducing action of the sulphites is particularly energetic1 so that they even convert nitric oxide into nitrous oxide3 ,k#b,,so#c #b,,no ,k#b,,so#d ,n#b,o4 ,the salts of many of the higher oxides are converted into those of the lower--for example1 ,fe,x#c into ,fe,x#b1 ,cu,x#b into ,cu,x1 ,hg,x#b into ,hg,x2 thus #b;,fe,x#c ,,so#b #b;,h#b,o #b;,fe,x#b ,h#b,,so#d #b;,,hx4 ,in the presence of water1 sulphurous anhydride is oxidised by chlorine 7,,so#b #b;,h#b,o ,cl#b ,h#b,,so#d #b;,h,cl71 iodine1 nitrous acid1 hydrogen peroxide1 hypochlorous acid1 chloric acid1 and other oxygen compounds of the halogens1 chromic1 manganic1 and many other metallic acids and higher oxides1 as well as all peroxides4 ,free oxygen in the presence of spongy platinum is able to oxidise sulphurous anhydride even in the absence of water1 in which case sulphuric anhydride ,,so#c is formed1 so that the latter may be prepared by passing a mixture of sulphurous anhydride and oxygen over incandescent spongy platinum1 or1 as it is now prepared on a large scale in chemical works1 by passing this mixture over asbestos or pumice stone moistened with a solution of platinum salt and ignited4 ,sulphurous anhydride is completely absorbed by certain higher oxides--for instance1 by barium peroxide and lead dioxide 7,pb,o#b ,,so#b ,pb,s,o#d74ch #ch ,this reaction is taken advantage of in removing sulphurous anhydride from a mixture of gases4 ,lead dioxide1 ,pb,o#b1 is brown1 and when combined with sulphurous anhydride it forms lead sulphate1 ,pb,s,o#d1 which is white1 so that the reaction is evident both from the change in colour and development of heat4 ,sulphurous anhydride is slowly decomposed by the action of light1 with the separation of sulphur and formation of sulphuric anhydride4 ,this explains the fact that sulphurous anhydride prepared in the dark gives a white precipitate of silver sulphite1 ,ag#b,,so#c1 with silver chlorate1 ,ag,cl,o#d1 but when prepared in the light1 even in diffused light1 it gives a dark precipitate4 ,this naturally depends on the fact that the sulphur liberated then forms silver sulphide1 which is black4 ,there are1 however1 cases where sulphurous anhydride acts as an oxidising agent--that is1 it is deoxidised in the presence of substances which are capable of absorbing oxygen with still greater energy than the sulphurous anhydride itself4 ,this oxidising action proceeds with the formation of sulphuretted hydrogen or of sulphides1 while the reducing agent is oxidised at the expense of the oxygen of the sulphurous anhydride4 ,in this respect1 the action of stannous salts is particularly remarkable4 ,stannous chloride1 ,sn,cl#b1 in an aqueous solution gives a precipitate of stannic sulphide1 ,sn,s#b1 with sulphurous anhydride--that is1 the latter is deoxidised to sulphuretted hydrogen1 while ,sn,x#b is oxidised into ,sn,x#d4 ,a solution of sulphurous anhydride has also an oxidising action on zinc4 ,the zinc passes into solution1 but no hydrogen is evolved1#ci because a salt of hydrosulphurous acid1 ,zn,s#b,o#d1 is formed4 ,the free acid is still less stable than the salt4 #ci ,schnebein observed that the liquid turns yellow1 and acquires the faculty of decolorising litmus and indigo4 ,schtzenberger showed that this depends on the formation of a zinc salt of a peculiar and very powerfully-reducing acid1 for with cupric salts the yellow solution gives a red precipitate of cuprous hydrate or metallic copper1 and it reduces salts of silver and mercury entirely4 ,an exactly similar solution is obtained by the action of zinc on sodium bisulphite without access of air and in the cold4 ,the yellow liquid absorbs oxygen from the air with great avidity1 and forms a sulphate4 ,if the solution be mixed with alcohol1 it deposits a double sulphite of zinc and sodium1 ,zn,na#b7,,so#c7b1 which does not decolorise litmus or indigo4 ,the remaining alcoholic solution deposits colourless crystals in the cold1 which absorb oxygen with great energy in the presence of water1 but are tolerably stable when dried under the receiver of an air-pump4 ,the solution of these crystals has the above-mentioned decolorising and reducing properties4 ,these crystals contain a sodium salt of a lower acid2 their composition was at first supposed to be ,h,na,s,o#b1 but it was afterwards proved that they do not contain hydrogen1 and present the composition ,na#b,s#b,o#d 7,bernthsen74 ,the same salt is formed by the action of a galvanic current on a solution of sodium bisulphite1 owing to the action of the hydrogen at the moment of its liberation4 ,if ,,so#b resembles ,,co#b in its composition1 then hyposulphurous acid ,h#b,s#b,o#d resembles oxalic acid ,h#b;,c#b,o#d4 ,perhaps an analogue of formic acid ,,sh#b,o#b will be discovered4 ,the faculty of sulphurous anhydride of combining with various substances is evident from the above-cited reactions1 where it combines with hydrogen and with oxygen1 and this faculty also appears in the fact that1 like carbonic oxide1 it combines with chlorine1 forming a chloranhydride of sulphuric acid1 ,,so#b;,cl#b1 to which we shall afterwards return4 ,the same faculty for combination also appears in the salts of sulphurous acid1 in their liability to oxidation and in the exceedingly characteristic formation of a peculiar series of salts obtained by ,pelouze and ,frmy4 ,at a temperature of -#aj or below1 nitric oxide ,,no is absorbed by alkaline solutions of the alkali sulphites1 forming a peculiar series of nitrosulphates4 ,at a higher temperature these salts are not formed but the nitric oxide is reduced to nitrous oxide4 ,but in the cold the liquid saturated with nitric oxide after a certain time gives prismatic crystals resembling those of nitre4 ,the composition of the potassium salt is ,k#b,,sn#b,o#c--that is1 the salt contains the elements of potassium sulphite and of nitric oxide4#dj #dj ,the instability of this salt is very great1 and may be compared to that of the compound of ferrous sulphate with nitric oxide1 for when heated under the contact influence of spongy platinum1 charcoal1 c41 it splits up into potassium sulphate and nitrous oxide4 ,at #acj the dry salt gives off nitric oxide1 and re-forms potassium sulphite4 ,the free acid has not yet been obtained4 ,these salts resemble the series of sulphonitrites discovered by ,frmy in #ahde4 ,they are obtained by passing sulphurous anhydride through a concentrated and strongly alkaline aqueous solution of potassium nitrite4 ,they are soluble in water1 but are precipitated by an excess of alkali4 ,the first product of the action has the composition ,k#c,,ns#c;,,ho#i4 ,it is then converted by the further action of sulphurous anhydride1 cold water1 and other reagents into a series of similar complex salts1 many of which give well-formed crystals4 ,one must suppose that the chief cause of the formation of these very complex compounds is that they contain unsaturated compounds1 ,,no1 ,,kno#b1 and ,,khso#c1 all of which are subject to oxidation and further combination1 and therefore easily combine among each other4 ,the decomposition of these compounds1 with the evolution of ammonia1 when their solutions are heated is due to the fact that the molecule contains the deoxidant1 sulphurous anhydride1 which reduces the nitrous acid1 ,,no7,,oh71 to ammonia4 ,in my opinion the composition of the sulphonitrites may be very simply referred to the composition of ammonia1 in which the hydrogen is partly replaced by the radicle of the sulphates4 ,if we represent the composition of potassium sulphate as ,,ko4,,kso#c1 the group ,,kso#c will be equivalent 7according to the law of substitution7 to ,,ho and to hydrogen4 ,it combines with hydrogen1 forming the potassium acid sulphite1 ,,khso#c4 ,hence the group ,,kso#c may also replace the hydrogen in ammonia4 ,judging by my analysis 7#ahgj7 the extreme limit of this substitution1 ,n7,,hso#c7c1 agrees with that of the sulphonitrite1 which is easily formed1 simultaneously with alkali1 by the action of potassium sulphite on potassium nitrite1 according to the equation #c,k7,,kso#c7 ,,kno#b #b;,h#b,o ,n7,,kso#c7c #d;,,hko4 ,the researches of ,berglund1 and especially of ,raschig 7#ahhg71 fully verified my conclusions1 and showed that we must distinguish the following types of salts1 corresponding with ammonia1 where ,x stands for the sulphonic group1 ,,hso#c1 in which the hydrogen is replaced by potassium2 hence ,x ,,kso#c3 7#a7 ,,nh#b,x1 7#b7 ,,nhx#b1 7#c7 ,,nh#c1 7#d7 ,n7,,oh7,,xh1 7#e7 ,n7,,oh7,x#b1 7#f7 ,n7,,oh7#b,x1 just as ,,nh#b7,,oh7 is hydroxylamine1 ,,nh7,,oh7#b1 is the hydrate of nitrous oxide1 and ,n7,,oh7#c is orthonitrous acid1 as follows from the law of substitution4 ,this class of compounds is in most intimate relation with the series of sulphonitrous compounds1 corresponding with 'chamber crystals' and their acids1 which we shall consider later4 ,there are also several other substances1 formed by the oxides of nitrogen and sulphur1 which belong to this class of complex and1 under some circumstances1 unstable compounds4 ,in the manufacture of sulphuric acid1 both these classes of oxides come into contact with each other in the lead chambers1 and if there be insufficient water for the formation of sulphuric acid they give crystalline compounds1 termed chamber crystals4 ,as a rule1 the composition of the crystals is expressed by the formula ,,nhso#c4 ,this is a compound of the radicles ,,no#b of nitric acid1 and ,,hso#c of sulphuric acid1 or nitro-sulphuric acid1 ,,no#b4,,sho#c1 if sulphuric acid be expressed as ,,oh4,,sho#c and nitric by ,,no#b4,,oh4 ,the tabular crystals of this substance fuse at about #gj1 are formed both by the direct action of nitrous anhydride or nitric peroxide 7but not ,,no1 which is not absorbed by sulphuric acid7 on sulphuric acid 7,weltzien and others71 and especially on sulphuric acid containing an anhydride and the lower oxides of sulphur and nitric acid4#da #da ,in the sulphuric acid chambers the lower oxides of nitrogen and sulphur take part in the reaction4 ,they are oxidised by the oxygen of the air1 and form nitro-sulphuric acid--for example1 #b,,so#b ,n#b,o#c ,o#b ,h#b,o #b,,nhso#e4 ,this compound dissolves in strong sulphuric acid without changing1 and when this solution is diluted 7when the sp4 gr4 falls to #ae71 it splits up into sulphuric acid and nitrous anhydride1 and by the action of sulphurous anhydride is converted into nitric oxide1 which by itself 7in the absence of nitric acid or oxygen7 is insoluble in sulphuric acid4 ,these reactions are taken advantage of in retaining the oxides of nitrogen in the ,gay-,lussac coke-towers1 and for extracting the absorbed oxides of nitrogen from the resultant solution in the ,glover tower4 ,although nitric oxide is not absorbed by sulphuric acid1 it reacts 7,rose1 ,brning7 on its anhydride1 and forms sulphurous anhydride and a crystalline substance1 ,n#b,s#b,o#i #b,,no #c,,so#c - ,,so#b ,n#b,o#cb,,so#c4 ,this may be regarded as the anhydride of nitro-sulphuric acid1 because ,n#b,s#b,o#i #b,,nhso#e - ,h#b,o2 like nitro-sulphuric acid1 it is decomposed by water into nitro-sulphuric acid and nitrous anhydride4 ,since boric and arsenious anhydrides1 alumina and other oxides of the form ,r#b,o#c are able to combine with sulphuric anhydride to form similar compounds decomposable by water1 the above compound does not present any exceptional phenomenon4 ,the substance ,n,o,cl,s,o#c obtained by ,weber by the action of nitrosyl chloride upon sulphuric anhydride belongs to this class of compounds4 ,thiosulphuric acid1 ,h#b,s#b,o#c--that is1 a compound of sulphurous acid and sulphur--also belongs to the products of combination of sulphurous acid4 ,in the same way that sulphurous acid1 ,h#b,,so#c1 gives ,h#b,,so#d with oxygen1 so it gives ,h#b,s#b,o#c with sulphur4 ,in a free state it is very unstable1 and it is only known in the form of its salts proceeding from the direct action of sulphur on the normal sulphites2 if endeavours be made to separate it in a free state1 it immediately splits up into those elements from which it might be formed--that is1 into sulphur and sulphurous acid4 ,the most important of its salts is the sodium thiosulphate 7known as hyposulphite71 ,na#b,s#b,o#c1e;,h#b,o1 which occurs in colourless crystals1 and is unacted on by atmospheric oxygen either when in a dry state or in solution4 ,many other salts of this acid are easily formed by means of this salt1#da bis although this cannot be done with all bases1 for such bases as alumina1 ferric oxide1 chromium oxide1 and others do not give compounds with thiosulphuric acid1 just as they do not form stable compounds with carbonic acid4 ,whenever these salts might be formed1 they 7like the acid7 split up into sulphurous acid and sulphur1 and furthermore the elements of thiosulphuric acid in many cases act in a reducing manner1 forming sulphuric acid and taking up the oxygen from reducible oxides4 ,thus when treated with a thiosulphate the soluble ferric salts give a precipitate of sulphur and form ferrous salts4 ,the thiosulphates of the metals of the alkalis are obtained directly by boiling a solution of their sulphites with sulphur3 ,na#b,,so#c ,s ,na#b,s#b,o#c4 ,the same salts are formed by the action of sulphurous anhydride on solutions of the sulphides2 thus sodium sulphide dissolved in water gives sulphur and sodium thiosulphate when a stream of sulphurous anhydride is passed through it3 #b,na#b,s #c,,so#b #b,na#b,s#b,o#c ,s4 ,the polysulphides of the alkali metals when left exposed to the air attract oxygen and also form thiosulphates4#db #da bis ,many double salts of thiosulphuric acid are known1 for instance1 ,pb,s#b,o#c1c,na#b,s#b,o#c1ab;,h#b,o2 ,ca,s#b,o#c1c,k#b,s#b,o#c1e;,h#b,o1 c4 7,fortman1 ,schwicker1 ,fock1 and others74 #db ,thus when alkali waste1 which contains calcium sulphide1 undergoes oxidation in the air it first forms a calcium polysulphide1 and then calcium thiosulphate1 ,ca,s#b,o#c4 ,when iron or zinc acts on a solution of sulphurous acid1 besides the hyposulphurous acid first formed1 a mixture of sulphite and thiosulphate is obtained 7,note #ci71 #c,,so#b ,zn#b ,zn,s,o#c ,zn,s#b,o#c4 ,in this case1 as in the formation of hyposulphurous acid1 there is no hydrogen liberated4 ,one of the most common methods for preparing thiosulphates consists in the action of sulphur on the alkalis4 ,the reaction is accomplished by the formation of sulphides and thiosulphates1 just as the reaction of chlorine on alkalis is accompanied by the formation of hypochlorites and chlorides2 hence in this respect the thiosulphates hold the same position in the order of the compounds of sulphur as the hypochlorites do among the chlorine compounds4 ,the reaction of caustic soda on an excess of sulphur may be expressed thus3 #f,na,h,o #ab,s #b,na#b,s#e ,na#b,s#b,o#c #c;,h#b,o4 ,thus sulphur is soluble in alkalis4 ,on a large scale sodium thiosulphate1 ,na#b,s#b,o#c1 is prepared by first heating sodium sulphate with charcoal1 to form sodium sulphide1 which is then dissolved in water and treated with sulphurous anhydride4 ,the reaction is complete when the solution has become slightly acid4 ,a certain amount of caustic alkali is added to the slightly acid solution2 a portion of the sulphur is thus precipitated1 and the solution is then boiled and evaporated when the salt crystallises out4 ,the saturation of the solution of sodium sulphide by sulphurous anhydride is carried on in different ways--for example1 by means of coke-towers1 by causing the solution of sulphide to trickle over the coke1 and the sulphurous anhydride1 obtained by burning sulphur1 to pass up the coke-tower from below4 ,an excess of sulphurous anhydride must be avoided1 as otherwise sodium trithionate is formed4 ,sodium thiophosphate is also prepared by the double decomposition of the soluble calcium thiosulphate with sodium sulphate or carbonate1 in which case calcium sulphate or carbonate is precipitated4 ,the calcium thiosulphate is prepared by the action of sulphurous anhydride on either calcium sulphide or alkali waste4 ,a dilute solution of calcium thiosulphate may be obtained by treating alkali waste which has been exposed to the action of air with water4 ,on evaporation1 this solution gives crystals of the salt containing ,ca,s#b,o#c1e;,h#b,o4 ,a solution of calcium thiosulphate must be evaporated with great care1 because otherwise the salt breaks up into sulphur and calcium sulphide4 ,even the crystallised salt sometimes undergoes this change4 ,the crystals of sodium thiosulphate are stable1 do not effloresce and at #j dissolve in one part of water1 and at #bj in #jf part4 ,the solution of this salt does not undergo any change when boiled for a short time1 but after prolonged boiling it deposits sulphur4 ,the crystals fuse at #ef1 and lose all their water at #ajj4 ,when the dry salt is ignited it gives sodium sulphide and sulphate4 ,with acids1 a solution of the thiosulphate soon becomes cloudy and deposits an exceedingly fine powder of sulphur 7,note #aj74 ,if the amount of acid added be considerable1 it also evolves sulphurous anhydride3 ,h#b,s#b,o#c ,h#b,o ,s ,,so#b4 ,sodium thiosulphate has many practical uses2 it is used in photography for dissolving silver chloride and bromide4 ,its solvent action on silver chloride may be taken advantage of in extracting this metal as chloride from its ores4 ,in dissolving1 it forms a double salt of silver and sodium3 ,ag,cl ,na#b,s#b,o#c ,na,cl ,ag,na,s#b,o#c4 ,sodium thiosulphate is an antichlor--that is1 a substance which hinders the destructive action of free chlorine owing to its being very easily oxidised by chlorine into sulphuric acid and sodium chloride4 ,the reaction with iodine is different1 and is remarkable for the accuracy with which it proceeds4 ,the iodine takes up half the sodium from the salt and converts it into a tetrathionate2 #b,na#b,s#b,o#c ,i#b #b,na,i ,na#b,s#d,o#f1 and hence this reaction is employed for the determination of free iodine4 ,as iodine is expelled from potassium iodide by chlorine1 it is possible also to determine the amount of chlorine by this method if potassium iodide be added to a solution containing chlorine4 ,and as many of the higher oxides are able to evolve iodine from potassium iodide1 or chlorine from hydrochloric acid 7for example1 the higher oxides of manganese1 chromium1 c471 it is also possible to determine the amounts of these higher oxides by means of sodium thiosulphate and liberated iodine4 ,this forms the basis of the iodometric method of volumetric analysis4 ,the details of these methods will be found in works on analytical chemistry4 ,on adding a solution of a lead salt gradually to a solution of sodium thiosulphate a white precipitate of lead thiosulphate1 ,pb,s#b,o#c1 is formed 7a soluble double salt is first formed1 and if the action be rapid1 lead sulphide74 ,when this substance is heated at #bjj1 it undergoes a change and takes fire4 ,sodium thiosulphate in solution rapidly reduces cupric salts to cuprous salts by means of the sulphurous acid contained in the thiosulphate1 but the resultant cuprous oxide is not precipitated1 because it passes into the state of a thiosulphate and forms a double salt4 ,these double cuprous salts are excellent reducing agents4 ,the solution when heated gives a black precipitate of copper sulphide4 ,the following formul sufficiently explain the position held by thiosulphuric acid among the other acids of sulphur3 ,sulphurous acid ,,so#b;,h7,,oh7 ,sulphuric acid ,,so#b,,oh7,,oh7 ,thiosulphuric acid ,,so#b,,sh7,,oh7 ,hyposulphurous acid ,,so#b;,h7,,so#b;,h7 ,dithionic acid ,,so#b,,oh7,,so#b,,oh7 ,at one time it was thought that all the salts of thiosulphuric acid only existed in combination with water1 and it was then supposed that their composition was ,h#d,s#b,o#d1 or ,h#b,,so#b1 but ,popp obtained the anhydrous salts4 ,although sulphur1 oxidising at a high temperature1 only forms a small quantity of sulphuric anhydride1 ,,so#c1 and nearly all passes into sulphurous anhydride1 still the latter may be converted into the higher oxide1 or sulphuric anhydride1 ,,so#c1 by many methods4 ,sulphuric anhydride is a solid crystalline substance at the ordinary temperature2 it is easily fusible 7#ae71 and volatile 7#df71 and rapidly attracts moisture4 ,although it is formed by the combination of sulphurous anhydride with oxygen1 it is capable of further combination4 ,thus it combines with water1 hydrochloric acid1 ammonia1 with many hydrocarbons1 and even with sulphuric acid1 boric and nitrous anhydrides1 c41 and also with bases which burn directly in its vapour1 forming sulphates in the presence of traces of moisture 7see ,chapter ,,ix41 ,note #bi74 ,the oxidation of sulphurous anhydride1 ,,so#b1 into sulphuric anhydride1 ,,so#c1 is effected by passing a mixture of the former and dry oxygen or air over incandescent spongy platinum4 ,an increase of pressure accelerates the reaction 7,hanisch74 ,if the product be passed into a cold vessel1 crystalline sulphuric anhydride is deposited upon the sides of the vessel1 but as it is difficult to avoid all traces of moisture it always contains compounds of its hydrates3 ,h#b,s#b,o#g and ,h#b,s#d,o#ac1 whose presence so modifies the properties of the anhydride 7,weber7 that formerly two modifications of the anhydride were recognised4 ,the same sulphuric anhydride may be obtained from certain anhydrous sulphates1 or those which are almost so1 which are decomposed by heat1 whilst an impure but perfectly anhydrous anhydride is formed by distillation over phosphoric anhydride4 ,for instance1 acid sodium sulphate1 ,na,h,s,o#d1 and the pyro- or di-sulphate1 ,na#b,s#b,o#g 7,chapter ,,xii47 formed from it1 when ignited evolve sulphuric anhydride4 ,green vitriol--that is1 ferrous sulphate1 ,fe,s,o#d--;belongs to the number of those sulphates which easily give off sulphuric anhydride under the action of heat4 ,it contains water of crystallisation and parts with it when it is heated1 but the last equivalent of water is driven off with difficulty1 just as is the case with magnesium sulphate1 ,mg,s,o#dg;,h#b,o2 however1 when thoroughly heated1 this evolution of sulphuric anhydride does take place1 although not completely1 because at a high temperature a portion of it is decomposed by the ferrous oxide 7,,so#c #b;,fe,o71 which is converted into ferric oxide1 ,fe#b,o#c1 and in consequence part of the sulphuric anhydride is converted into sulphurous anhydride4 ,thus the products of the decomposition of ferrous sulphate will be3 ferric oxide1 ,fe#b,o#c1 sulphurous anhydride1 ,,so#b1 and sulphuric anhydride1 ,,so#c1 according to the equation3 #b;,fe,s,o#d ,fe#b,o#c ,,so#b ,,so#c4 ,as water still remains with the ferrous sulphate when it is heated1 the result will partially consist of the hydrate ,h#b,,so#d1 with anhydride1 ,,so#c1 dissolved in it4 ,sulphuric acid was for a long time prepared in this manner2 the process was formerly carried on on a large scale in the neighbourhood of ,nordhausen1 and hence the sulphuric acid prepared from ferrous sulphate is called fuming ,nordhausen acid4 ,at the present time the fuming acid is prepared by passing the volatile products of the decomposition of ferrous sulphate through strong sulphuric acid prepared by the ordinary method4 ,the sulphurous anhydride is insoluble in it1 but it absorbs the sulphuric anhydride4 ,sulphuric anhydride may be prepared not only by igniting ,fe,s,o#d or sodium pyrosulphate1 ,na#b,s#b,o#g 7the decomposition proceeds at #fjj71 but also by heating a mixture of the latter and ,mg,s,o#d 7,walters72 in the former case a stable double salt ,mg,na#b7,,so#d7b finally remains4 ,it is also obtained by the direct combination of ,,so#b and ,o under the action of spongy platinum or asbestos coated with platinum black 7,c4 ,winkler's process74 ,nordhausen sulphuric acid fumes in air1 owing to its containing and easily giving off sulphuric anhydride1 and it is therefore also called fuming sulphuric acid2 these fumes are nothing but the vapour of sulphuric anhydride combining with the moisture in the air and forming non-volatile sulphuric acid 7hydrate74#dc #dc ,nordhausen sulphuric acid may serve as a very simple means for the preparation of sulphuric anhydride4 ,for this purpose the ,nordhausen acid is heated in a glass retort1 whose neck is firmly fixed in the mouth of a well-cooled flask4 ,the access of moisture is prevented by connecting the receiver with a drying-tube4 ,on heating the retort the vapours of sulphuric anhydride will pass over into the receiver1 where they condense2 the crystals of anhydride thus prepared will1 however1 contain traces of sulphuric acid--that is1 of the hydrate4 ,by repeatedly distilling over phosphoric anhydride1 it is possible to obtain the pure anhydride1 ,,so#c1 especially if the process be carried on without access of air in a closed vessel4 ,the ordinary sulphuric anhydride1 which is imperfectly freed from the hydrate1 is a snow-white1 exceedingly volatile substance1 which crystallises 7generally by sublimation7 in long silky prisms1 and only gives the pure anhydride when carefully distilled over ,p#b,o#e4 ,freshly prepared crystals of almost pure anhydride fuse at #af into a colourless liquid having a specific gravity at #bf #aia1 and at #dg #aha2 it volatilises at #df4 ,after being kept for some time the anhydride1 even containing only small traces of water1 undergoes a change of the following nature3 ,a small quantity of sulphuric acid combines by degrees with a large proportion of the anhydride1 forming polysulphuric acids1 ,h#b,,so#d1n,,so#c1 which fuse with difficulty 7even at #ajj1 ,marignac71 but decompose when heated4 ,in the entire absence of water this rise in the fusing point does not occur 7,weber71 and then the anhydride long remains liquid1 and solidifies at about #ae1 volatilises at #dj1 and has a specific gravity #aid at #af4 ,we may add that ,weber 7#ahha71 by treating sulphuric anhydride with sulphur1 obtained a blue lower oxide of sulphur1 ,s#b,o#c4 ,selenium and tellurium also give similar products with ,,so#c1 ,se,s,o#c1 and ,te,s,o#c4 ,water does not act upon them4 ,nordhausen sulphuric acid contains a peculiar compound of ,,so#c and ,h#b,,so#d1 or pyrosulphuric acid2 an imperfect anhydride of sulphuric acid1 ,h#b,s#b,o#g1 analogous in composition with the salts ,na#b,s#b,o#g1 ,k#b;,cr#b,o#g1 and bearing the same relation to ,h#b,,so#d that pyrophosphoric acid does to ,h#c,,po#d4 ,the bond holding the sulphuric acid and anhydride together is unstable4 ,this is obvious from the fact that the anhydride may easily be separated from this compound1 by the action of heat4 ,in order to obtain the definite compound1 the ,nordhausen acid is cooled to #e1 or1 better still1 a portion of it is distilled until all the anhydride and a certain amount of sulphuric acid have passed over into the distillate1 which will then solidify at the ordinary temperature1 because the compound ,h#b,,so#d1,,so#c fuses at #ce4 ,although this substance reacts on water1 bases1 c41 like a mixture of ,,so#c ,h#b,,so#d1 still since a definite compound1 ,h#b,s#b,o#g1 exists in a free state and gives salts and a chloranhydride1 ,s#b,o#e;,cl#b1dd we must admit the existence of a definite pyrosulphuric acid1 like pyrophosphoric acid1 only that the latter has a far greater stability and is not even converted into a perfect hydrate by water4 ,further1 the salts ,m#b,s#b,o#g dissolved in water react in the same manner as the acid salts ,,mhso#d1 whilst the imperfect hydrates of phosphoric acid 7for example1 ,,pho#c1 ,h#d,p#b,o#g7 have independent reactions even in an aqueous solution which distinguish them and their salts from the perfect hydrates4 #dd ,pyrosulphuric chloranhydride1 or pyrosulphuryl chloride1 ,s#b,o#e;,cl#b1 corresponds to pyrosulphuric acid1 in the same way that sulphuryl chloride1 ,,so#b;,cl#b1 corresponds to sulphuric acid4 ,the composition ,s#b,o#e;,cl#b ,,so#b;,cl#b ,,so#c4 ,it is obtained by the action of the vapour of sulphuric anhydride on sulphur chloride3 ,s#b;,cl#b #e,,so#c #e,,so#b ,s#b,o#e;,cl#b4 ,it is also formed 7and not sulphuryl chloride1 ,,so#b;,cl#b1 ,michaelis7 by the action of phosphorus pentachloride in excess on sulphuric acid 7or its first chloranhydride1 ,,sho#c;,cl74 ,it is an oily liquid1 boiling at about #aej1 and of sp4 gr4 #ah4 ,according to ,konovaloff 7,chapter ,,vii471 its vapour density is normal4 ,it should be noticed that the same substance is obtained by the action of sulphuric anhydride on sulphur tetrachloride1 and also on carbon tetrachloride1 and this substance is the last product of the metalepsis of ,,ch#d1 and therefore the comparison of ,s,cl#b and ,s#b;,cl#b with products of metalepsis 7see later7 also finds confirmation in particular reactions4 ,rose1 who obtained pyrosulphuryl chloride1 ,s#b,o#e;,cl#b1 regarded it as ,s,cl#f1e,,so#c1 for at that time an endeavour was always made to find two component parts of opposite polarity1 and this substance was cited as a proof of the existence of a hexachloride1 ,s,cl#f4 ,pyrosulphuryl chloride is decomposed by cold water1 but more slowly than chlorosulphuric acid and the other chloranhydrides4 ,the relation between pyrosulphuric acid and the normal acid will be obvious if we express the latter by the formula ,,oh7,,so#c;,h71 because the sulphonic group 7,,so#c;,h7 is then evidently equivalent to ,,oh1 and consequently to ,h1 and if we replace both the hydrogens in water by this radicle we shall obtain 7,,so#c;,h7#b,o--that is1 pyrosulphuric acid4 ,illustration3 ,,fig4 #hg4--;,concentration of sulphuric acid in glass retorts4 ,the neck of each retort is attached to a bent glass tube1 whose vertical arm is lowered into a glass or earthenware vessel acting as a receiver for the steam which comes over from the acid1 as the former still contains a certain amount of acid4 ,sulphuric acid1 ,h#b,,so#d1 is formed by the combination of its anhydride1 ,,so#c1 and water1 with the evolution of a large amount of heat2 the reaction ,,so#c ,h#b,o develops #ba1cjj heat units4 ,the method of its preparation on a large scale1 and most of the methods employed for its formation1 are dependent on the oxidation of sulphurous anhydride1 and the formation of sulphuric anhydride1 which forms sulphuric acid under the action of water4 ,the technical method of its manufacture has been described in ,chapter ,,vi4 ,the acid obtained from the lead chambers contains a considerable amount of water1 and is also impure owing to the presence of oxides of nitrogen1 lead compounds1 and certain impurities from the burnt sulphur which have come over in a gaseous and vaporous state 7for example1 arsenic compounds74 ,for practical purposes1 hardly any notice is taken of the majority of these impurities1 because they do not interfere with its general qualities4 ,most frequently endeavours are only made to remove1 as far as possible1 all the water which can be expelled4#de ,that is1 the object is to obtain the hydrate1 ,h#b,,so#d1 from the dilute acid 7#fj per cent471 and this is effected by evaporation by means of heat4 ,every given mixture of water and sulphuric acid begins to part with a certain amount of aqueous vapour when heated to a certain definite temperature4 ,at a low temperature either there is no evaporation of water1 or there can even be an absorption of moisture from the air4 ,as the removal of the water proceeds1 the vapour tension of the residue decreases for the same temperature1 and therefore the more dilute the acid the lower the temperature at which it gives up a portion of its water4 ,in consequence of this1 the removal of water from dilute solutions of sulphuric acid may be easily carried on 7up to #ge p4c4 ,h#b,,so#d7 in lead vessels1 because at low temperatures dilute sulphuric acid does not attack lead4 ,but as the acid becomes more concentrated the temperature at which the water comes over becomes higher and higher1 and then the acid begins to act on lead 7with the evolution of sulphuretted hydrogen and conversion of the lead into sulphate71 and therefore lead vessels cannot be employed for the complete removal of the water4 ,for this purpose the evaporation is generally carried on in glass or platinum retorts1 like those depicted in figs4 #hg and #hh4 #de ,the removal of the water1 or concentration to almost the real acid1 ,h#b,,so#d1 is effected for two reasons3 in the first place to avoid the expense of transit 7it is cheaper to remove the water than to pay for its transit71 and in the second place because many processes--for instance1 the refining of petroleum--require a strong acid free from an excess of water1 the weak acid having no action4 ,when in the manufacture of chamber acid1 both the ,gay-,lussac tower 7cold1 situated at the end of the chambers7 and the ,glover tower 7hot1 situated at the beginning of the plant1 between the chambers and ovens for the production of ,,so#b7 are employed1 a mixture of nitrose 7i4e4 the product of the ,gay-,lussac tower7 and chamber acid containing about #fj p4c4 ,h#b,,so#d1 is poured into the ,glover tower1 where under the action of the hot furnace gases containing ,,so#b1 and the water held in the chamber acid 7#a7 ,n#b,o#c is evolved from the nitrose2 7#b7 water is expelled from the chamber acid2 7#c7 a portion of the ,,so#b is converted into ,h#b,,so#d2 and 7#d7 the furnace gases are cooled4 ,thus1 amongst other things1 the ,glover tower facilitates the concentration of the chamber acid 7removal of ,h#b,o71 but the product generally contains many impurities4 ,illustration3 ,,fig4 #hh4--;,concentration of sulphuric acid in platinum retorts4 ,the concentration of sulphuric acid in glass retorts is not a continuous process1 and consists of heating the dilute #ge per cent4 acid until it ceases to give off aqueous vapour1 and until acid containing #ic-ih per cent4 ,h#b,,so#d 7#ff ,baum7 is obtained--and this takes place when the temperature reaches #cbj and the density of the residue reaches #ahdg 7#ff ,baum74#df ,the platinum vessels designed for the continuous concentration of sulphuric acid consist of a still ,b1 furnished with a still head ,e1 a connecting pipe ,e ,f1 and a syphon tube ,h ,r1 which draws off the sulphuric acid concentrated in the boiler4 ,a stream of sulphuric acid previously concentrated in lead retorts to a density of about #fj ,baum--i4e4 to #ge per cent4 or a sp4 gr4 of #ag--runs continuously into the retort through a syphon funnel ,e4 ,the apparatus is fed from above1 because the acid freshly supplied is lighter than that which has already lost water1 and also because the water is more easily evaporated from the freshly supplied acid at the surface4 ,the platinum retort is heated1 and the steam coming off#dg is condensed in a worm ,f ,g1 whilst as fresh dilute acid is supplied to the boiler the acid already concentrated is drawn off through the syphon tube ,h ,b1 which is furnished with a regulating cock by means of which the outflow of the concentrated acid from the bottom of the retort can be so regulated that it will always present one and the same specific gravity1 corresponding with the strength required4 ,for this purpose the acid flowing from the syphon is collected in a receiver ,r1 in which a hydrometer1 indicating its density1 floats2 if its density be less than #ff ,baum1 the regulating cock is closed sufficiently to retard the outflow of sulphuric acid1 so as to lengthen the time of its evaporation in the retort4#dh #df ,the difficulty with which the last portions of water are removed is seen from the fact that the boiling becomes very irregular1 totally ceasing at one moment1 then suddenly starting again1 with the rapid formation of a considerable amount of steam1 and at the same time bumping and even overturning the vessel in which it is held4 ,hence it is not a rare occurrence for the glass retorts to break during the distillation2 this causes platinum retorts to be preferred1 as the boiling then proceeds quite uniformly4 #dg ,according to ,regnault1 the vapour tensions 7in millimetres of mercury7 of the water given off by the hydrates of sulphuric acid1 ,h#b,,so#d1n,h#b,o1 are-- t#e #ae #cj n #a #ja #ja #jb #b #jd #jg #ae #c #ji #af #da #d #ac #bh #gj #e #ba #db #ajg #g #cb #fb #aef #i #da #hj #aif #aa #dd #ij #bbb #ag #ee #ajf #bfa ,according to ,lunge1 the vapour tension of the aqueous vapour given off from solutions of sulphuric acid containing p per cent4 ,h#b,,so#d1 at t1 equals the barometric pressure #gbj to #gcj mm4 p #aj #bj #cj #dj #ej #fj #gj #hj #he #ij #ie t #ajb #aje #ajh #aad #abd #ada #agj #bjg #bcc #bfb #bie ,the latter figures give the temperature at which water is easily expelled from solutions of sulphuric acid of different strengths4 ,but the evaporation begins sooner1 and concentration may be carried on at lower temperatures if a stream of air be passed through the acid4 ,kessler's process is based upon this 7,note #dh74 #dh ,the greatest part of the sulphuric acid is used in the soda manufacture1 in the conversion of the common salt into sulphate4 ,for this purpose an acid having a density of #fj ,baum is amply sufficient4 ,chamber acid has a density up to #aeg #ej to #ea ,baum2 it contains about #ce per cent4 of water4 ,about #ae per cent4 of this water can be removed in leaden stills1 and nearly all the remainder may be expelled in glass or platinum vessels4 ,acid of #ff ,baum1 #ahdg1 contains about #if per cent4 of the hydrate ,h#b,,so#d4 ,the density falls with a greater or less proportion of water1 the maximum density corresponding with #ig-a_/b per cent4 of the hydrate ,h#b,,so#d4 ,the concentration of ,h#b,,so#d in platinum retorts has the disadvantage that sulphuric acid1 upwards of #ij per cent4 in strength1 does corrode platinum1 although but slightly 7a few grams per tens of tons of acid74 ,the retorts therefore require repairing1 and the cost of the platinum exceeds the price obtained for concentrating the acid from #ij per cent4 to #ih per cent4 7in factories the acid is not concentrated beyond this by evaporation in the air74 ,this inconvenience has lately 7#ahia1 by ,mathey7 been eliminated by coating the inside of the platinum retorts with a thin 7#ja to #jjb mm47 layer of gold which is #dj times less corroded by sulphuric acid than platinum4 ,ngrier 7#ahij7 carries on the distillation in porcelain dishes1 ,blond by heating a thin platinum wire immersed in the acid by means of an electric current1 but the most promising method is that of ,kessler 7#ahia71 which consists in passing hot air over sulphuric acid flowing in a thin stream in stone vessels1 so that there is no boiling but only evaporation at moderate temperatures3 the transference of the heat is direct 7and not through the sides of the vessels71 which economises the fuel and prevents the distilling vessels being damaged4 ,when1 by evaporation of the water1 sulphuric acid attains a density of #ff ,baum 7sp4 gr4 #ahd71 it is impossible to concentrate it further1 because it then distils over unchanged4 ,the distillation of sulphuric acid is not generally carried on on a large scale1 but forms a laboratory process1 employed when particularly pure acid is required4 ,the distillation is effected either in platinum retorts furnished with corresponding condensers and receivers1 or in glass retorts4 ,in the latter case1 great caution is necessary1 because the boiling of sulphuric acid itself is accompanied by still more violent jerks and greater irregularity than even the evaporation of the last portions of water contained in the acid4 ,if the glass retort which holds the strong sulphuric acid to be distilled be heated directly from below1 it frequently jerks and breaks4 ,for greater safety the heating is not effected from below1 but at the sides of the retort4 ,the evaporation then does not proceed in the whole mass1 but only from the upper portions of the liquid1 and therefore goes on much more quietly4 ,the acid may be made to boil quietly also by surrounding the retort with good conductors of heat--for example1 iron filings1 or by immersing a bunch of platinum wires in the acid1 as the bubbles of sulphuric acid vapour then form on the extremities of the wires4 ,strictly speaking1 sulphuric acid is not volatile1 and at its so-called boiling-point it really decomposes into its anhydride and water2 its boiling-point 7#cch7 being nothing else but its temperature of decomposition4 ,the products of this decomposition are substances boiling much below the temperature of the decomposition of sulphuric acid4 ,this conclusion with regard to the process of the distillation of sulphuric acid may be deduced from ,bineau's observations on the vapour-density of sulphuric acid4 ,this density referred to hydrogen proved to be half that which sulphuric acid should have according to its molecular weight1 ,h#b,,so#d1 in which case it should be #di1 whilst the observed density was equal to #bde4 ,besides which1 ,marignac showed that the first portions of the sulphuric acid distilling over contain less of the elements of water than the portion which remains behind1 or which distils over towards the end4 ,this is explained by the fact that on distillation the sulphuric acid is decomposed1 but a portion of the water proceeding from its decomposition is retained by the remaining mass of sulphuric acid1 and therefore at first a mixture of sulphuric acid and sulphuric anhydride--i4e4 fuming sulphuric acid--is obtained in the distillate4 ,it is possible by repeating the distillation several times and only collecting the first portions of the distillate1 to obtain a distinctly fuming acid4 ,to obtain the definite hydrate ,h#b,,so#d it is necessary to refrigerate a highly concentrated acid1 of as great a purity as possible1 to which a small quantity of sulphuric anhydride has been previously added4 ,sulphuric acid containing a small quantity 7a fraction of a per cent4 by weight7 of water only freezes at a very low temperature1 while the pure normal acid1 ,h#b,,so#d1 solidifies when it is cooled below #j1 and therefore the normal acid first crystallises out from the concentrated sulphuric acid4 ,by repeating the refrigeration several times1 and pouring off the unsolidified portion1 it is possible to obtain a pure normal hydrate1 ,h#b,,so#d1 which melts at #ajd4 ,even at #dj it gives off distinct fumes--that is1 it begins to evolve sulphuric anhydride1 which volatilises1 and therefore even in a dry atmosphere the hydrate ,h#b,,so#d becomes weaker1 until it contains #a-a_/b p4c4 of water4#di #di ,thus it appears that so common1 and apparently so stable1 a compound as sulphuric acid decomposes even at a low temperature with separation of the anhydride1 but this decomposition is restricted by a limit1 corresponding to the presence of about #a-a_/b p4c4 of water1 or to a composition of nearly ,h#b,o1#ab;,h#b,,so#d4 ,now there is no reason for thinking that this substance is a definite compound2 it is an equilibrated system which does not decompose under ordinary circumstances below #cch4 ,dittmar carried on the distillation under pressures varying between #cj and #b1adj millimetres 7of mercury71 and he found that the composition of the residue hardly varies1 and contains from #iib to #ihb per cent4 of the normal hydrate1 although at #cj mm4 the temperature of distillation is about #baj and at #b1adj mm4 it is #chb4 ,furthermore1 it is a fact of practical importance that under a pressure of two atmospheres the distillation of sulphuric acid proceeds very quietly4 ,sulphuric acid may be purified from the majority of its impurities by distillation1 if the first and last portions of the distillate be rejected4 ,the first portions will contain the oxides of nitrogen1 hydrochloric acid1 c41 and the last portions the less volatile impurities4 ,the oxides of nitrogen may be removed by heating the acid with charcoal1 which converts them into volatile gases4 ,sulphuric acid may be freed from arsenic by heating it with manganese dioxide and then distilling4 ,this oxidises all the arsenic into non-volatile arsenic acid4 ,without a preliminary oxidation it would partially remain as volatile arsenious acid1 and might pass over into the distillate4 ,the arsenic may also be driven off by first reducing it to arsenious acid1 and then passing hydrochloric acid gas through the heated acid4 ,it is then converted into arsenious chloride1 which volatilises4 ,in a concentrated form sulphuric acid is commercially known as oil of vitriol1 because for a long time it was obtained from green vitriol and because it has an oily appearance and flows from one vessel into another in a thick and somewhat sluggish stream1 like the majority of oily substances1 and in this clearly differs from such liquids as water1 spirit1 ether1 and the like1 which exhibit a far greater mobility4 ,among its reactions the first to be remarked is its faculty for the formation of many compounds4 ,we already know that it combines with its anhydride1 and with the sulphates of the alkali metals2 that it is soluble in water1 with which it forms more or less stable compounds4 ,sulphuric acid1 when mixed with water1 develops a very considerable amount of heat4#ej #ej ,the amount of heat developed by the mixture of sulphuric acid with water is expressed in the diagram on p4 #gg1 ,volume ,i41 by the middle curve1 whose absciss are the percentage amounts of acid 7,h#b,,so#d7 in the resultant solution1 and ordinates the number of units of heat corresponding with the formation of #ajj cubic centimetres of the solution 7at #ah74 ,the calculations on which the curve is designed are based on ,thomsen's determinations1 which show that #ih grams or a molecular amount of sulphuric acid1 in combining with m molecules of water 7that is1 with m#ah grams of water71 develop the following number of units of heat1 ,r3-- m #a #b #c #e #i ,r #fcgi #idah #aaacg #acajh #adieb c #jdcb #jdgj #jejj #jegf #jgja ,t #abg #adi #adf #aba #hb m #ai #di #ajj #bjj ,r #afbef #affhd #afhei #agjff c #jhba #jiad #jied #jige ,t #ade #ai #i #e c stands for the specific heat of ,h#b,,so#dm,h#b,o 7according to ,marignac and ,pfaundler71 and ,t for the rise in temperature which proceeds from the mixture of ,h#b,,so#d with m,h#b,o4 ,the diagram shows that contraction and rise of temperature proceed almost parallel with each other4 ,besides the normal hydrate ,h#b,,so#d1 another definite hydrate1 ,h#b,,so#d1;,h#b,o 7#hddh per cent4 of the normal hydrate1 and #aeeb per cent4 of water7 is known2 it crystallises#ej bis extremely easily in large six-sided prisms1 which form above #j--namely1 at about #he2 when heated to #baj it loses water4#ea ,if the hydrates ,h#b,,so#d and ,h#b,,so#d1;,h#b,o exist at low temperatures as definite crystalline compounds1 and if pyrosulphuric acid1 ,h#b,,so#d,,so#c1 has the same property1 and if they all decompose with more or less ease on a rise of temperature1 with the disengagement of either ,,so#c or ,h#b,o1 and in their ordinary form present all the properties of simple solutions1 it follows that between sulphuric anhydride1 ,,so#c1 and water1 ,h#b,o1 there exists a consecutive series of homogeneous liquids or solutions1 among which we must distinguish definite compounds1 and therefore it is quite justifiable to look for other definite compounds between ,,so#c and ,h#b,o1 beyond the conditions for a change of state4 ,in this respect we may be guided by the variation of properties of any kind1 proceeding concurrently with a variation in the composition of a solution4 #ej bis ,pickering 7#ahij7 showed 7a7 that dilute solutions of sulphuric acid containing up to ,h#b,,so#d #aj;,h#b,o deposit ice 7at -#jab when there is #b1jjj;,h#b,o per ,h#b,,so#d1 at -#jbc when there is #a1jjj;,h#b,o1 at -#ajd when there is #bjj;,h#b,o1 at -#bab when there is #ajj;,h#b,o1 at -#de when there is #ej;,h#b,o1 at -#aeg when there is #bj;,h#b,o1 and at -#fa when the composition of the solution is ,h#b,,so#d #aj;,h#b,o72 7b7 that for higher concentrations crystals separate out at a considerable degree of cold1 having the composition ,h#b,,so#dd;,h#b,o1 which melt at -#bde1 and if either water or ,h#b,,so#d be added to this compound the temperature of crystallisation falls1 so that a solution of the composition #ab;,h#b,,so#d #ajj;,h#b,o gives crystals of the above hydrate at -#gj1 #ae;,h#b,,so#d #ajj;,h#b,o at -#dg1 #cj;,h#b,,so#d #ajj;,h#b,o at -#cb1 #dj;,h#b,,so#d #ajj;,h#b,o at -#eb2 7c7 that if the amount of ,h#b,,so#d be still greater1 then a hydrate ,h#b,,so#d;,h#b,o separates out and melts at #he1 while the addition of water or sulphuric acid to it lowers the temperature of crystallisation so that the crystallisation of ,h#b,,so#d;,h#b,o from a solution of the composition ,h#b,,so#d #agc;,h#b,o takes place at -#bb1 ,h#b,,so#d #ae;,h#b,o at -#fe1 ,h#b,,so#d #ab;,h#b,o at #cg1 ,h#b,,so#d #jge;,h#b,o at #bh1 ,h#b,,so#d #je;,h#b,o at -#af2 7d7 that when there is less than #dj;,h#b,o per #ajj;,h#b,,so#d1 refrigeration separates out the normal hydrate ,h#b,,so#d1 which melts at #ajce1 and that a solution of the composition ,h#b,,so#d #jce;,h#b,o deposits crystals of this hydrate at -#cd1 ,h#b,,so#d #ja;,h#b,o at -#da1 ,h#b,,so#d #jje;,h#b,o at #di1 while fuming acid of the composition ,h#b,,so#d #jje,,so#c deposits ,h#b,,so#d at about #g4 ,thus the temperature of the separation of crystals clearly distinguishes the above four regions of solutions1 and in the space between ,h#b,,so#d ,h#b,o and #be;,h#b,o a particular hydrate ,h#b,,so#dd;,h#b,o separates out1 discovered by ,pickering1 the isolation of which deserves full attention and further research4 ,i may add here that the existence of a hydrate ,h#b,,so#dd;,h#b,o was pointed out in my work1 ,the ,investigation of ,aqueous ,solutions1 p4 #abj 7#ahhg71 upon the basis that it has at all temperatures a smaller value for the coefficient of expansion k in the formula ,st ,s#j_/7a - kt7 than the adjacent 7in composition7 solutions of sulphuric acid4 ,and for solutions approximating to ,h#b,,so#daj;,h#b,o in their composition1 k is constant at all temperatures 7for more dilute solutions the value of k increases with t and for more concentrated solutions it decreases74 ,this solution 7with #aj;,h#b,o7 forms the point of transition between more dilute solutions which deposit ice 7water7 when refrigerated and those which give crystals of ,h#b,,so#dd;,h#b,o4 ,according to ,r4 ,pictet 7#ahid7 the solution ,h#b,,so#daj;,h#b,o freezes at -#hh 7but no reference is made as to what separates out71 i4e4 at a lower temperature than all the other solutions of sulphuric acid4 ,however1 in respect to these last researches of ,r4 ,pictet 7for #hhhh p4c4 ,h#b,,so#d -#ee1 for ,h#b,,so#d;,h#b,o #ce1 for ,h#b,,so#db;,h#b,o -#gj1 for ,h#b,,so#dd;,h#b,o -#dj1 c47 it should be remarked that they offer some quite improbable data2 for example1 for ,h#b,,so#dge;,h#b,o they give the freezing point as #j1 for ,h#b,,so#dcjj;,h#b,o #de1 and even for ,h#b,,so#dajjj;,h#b,o #je1 although it is well known that a small amount of sulphuric acid lowers the temperature of the formation of ice4 ,i have found by direct experiment that a frozen solidified solution of ,h#b,,so#d #cjj;,h#b,o melted completely at #j4 #ea ,with an excess of snow1 the hydrate ,h#b,,so#d1;,h#b,o1 like the normal hydrate1 gives a freezing mixture1 owing to the absorption of a large amount of heat 7the latent heat of fusion74 ,in melting1 the molecule ,h#b,,so#d absorbs #ifj heat units1 and the molecule ,h#b,,so#d;,h#b,o #c1fhj heat units4 ,if therefore we mix one gram molecule of this hydrate with seventeen gram molecules of snow1 there is an absorption of #ah1jhj heat units1 because #ag;,h#b,o absorbs #ag #a1dcj heat units1 and the combination of the monohydrate with water evolves #i1hjj heat units4 ,as the specific heat of the resultant compound ,h#b,,so#d1ah;,h#b,o #jhac1 the fall of temperature will be -#ebf4 ,and1 in fact1 a very low temperature may be obtained by means of sulphuric acid4 ,but only a few properties have been determined with sufficient accuracy4 ,in those properties which have been determined for many solutions of sulphuric acid1 it is actually seen that the above-mentioned definite compounds are distinguished by distinctive marks of change4 ,as an example we may cite the variation of the specific gravity with a variation of temperature 7namely ,k ds_/dt1 if s be the sp4 gr4 and t the temperature74 ,for the normal hydrate1 ,h#b,,so#d1 this factor is easily determined from the fact that-- s #ahebh - #ajfet #jjact#b1 where s is the specific gravity at t 7degrees ,celsius7 if the sp4 gr4 of water at #d #aj1jjj4 ,therefore ,k #ajfe - #jjbft4 ,this means that at #j the sp4 gr4 of the acid ,h#b,,so#d decreases by #ajfe for every rise of a degree of temperature1 at #aj by #ajci1 at #bj by #ajac1 at #cj by #ihg4eb ,and for solutions containing slightly more anhydride than the acid ,h#b,,so#d 7i4e4 for fuming sulphuric acid71 as well as for solutions containing more water1 ,k is greater than for the acid ,h#b,,so#d4 ,thus for the solution ,,so#c1b;,h#b,,so#d1 at #aj ,k #aaj4 ,on diluting the acid ,h#b,,so#d ,k again increases until the formation of the solution ,h#b,,so#d1;,h#b,o 7,k #aaa at #aj71 and then1 on further dilution with water1 it again decreases4 ,consequently both hydrates ,h#b,,so#d and ,h#b,,so#d1;,h#b,o are here expressed by an alteration of the magnitude of ,k4 #eb ,for example1 if it be taken that at #ai the sp4 gr4 of pure sulphuric acid is #ahccj1 then at #bj it is #ahccj - 7#bj - #ai7ajac #ahcbj4 ,illustration3 ,,fig4 #hi4--;,diagram showing the variation of the factor 7ds_/dp7 of the specific gravity of solutions of sulphuric acid4 ,the percentage quantities of the acid1 ,h#b,,so#d1 are laid out on the axes of absciss4 ,the ordinates are the factors or rises in sp4 gr4 7water at #d #aj1jjj7 with the increase in the quantity of ,h#b,,so#d4 ,this shows that in liquid solutions it is possible by studying the variation of their properties 7without a change of physical state7 to recognise the presence or formation of definite hydrate compounds1 and therefore an exact investigation of the properties of solutions1 of their specific gravity for instance1 should give direct indications of such compounds4#ec ,the mean result of the most trustworthy determinations of this nature is given in the following tables4 ,the first of these tables gives the specific gravities 7in vacuo1 taking the sp4 gr4 of water at #d #a71 at #j 7column #c71 #ae 7column #d71 and #cj 7column #e71ec bis for solutions having the composition ,h#b,,so#d n,h#b,o 7the value of n is given in the first column71 and containing p 7column #b7 per cent4 7by weight in vacuo7 of ,h#b,,so#d4ec tri n p #j #ae #cj #ajj #eaf #ajcgd #ajcda #ajbib #ej #ihb #ajgag #ajfff #ajfjc #be #aghh #aaccg #aabeg #aaagc #ae #bffc #abjdj #aaici #aahcg #aj #cebe #abgeh #abfdi #abedj #h #djej #acbbc #acaaj #abiih #f #dgeg #achfe #acgdh #acfbb #e #ebac #adcja #adahj #adjfb #d #egfe #adhha #adgee #adfca #c #fddg #aefce #aeeja #aecgj #b #gcac #affdh #afejj #afcei #a #hddh #agidj #agggb #agfjh #je #iaei #ahdde #ahbhd #ahabh ,h#b,,so#d #ajj #ahebi #ahcgb #ahbba #ec ,unfortunately1 notwithstanding the great number of fragmentary and systematic researches which have been made 7by ,parks1 ,ure1 ,bineau1 ,kolbe1 ,lunge1 ,marignac1 ,kremers1 ,thomsen1 ,perkin1 and others7 for determining the relation between the sp4 gr4 and composition of solutions of sulphuric acid1 they contain discrepancies which amount to1 and even exceed1 #jjjb in the sp4 gr4 ,for instance1 at #aed the solution of composition ,h#b,,so#dc;,h#b,o has a sp4 gr4 #aedic according to ,perkin 7#ahhf71 #aeeja according to ,pickering 7#ahij71 and #aeebe according to ,lunge 7#ahij74 ,the cause of these discrepancies must be looked for in the methods employed for determining the composition of the solutions--i4e4 in the inaccuracy with which the percentage amount of ,h#b,,so#d is determined1 for a difference of #a p4c4 corresponds to a difference of from #jjjgj 7for very weak solutions7 to #jjaah 7for a solution containing about #gc p4c47 in the specific gravity 7that is the factor ds_/dp7 at #ae4 ,as it is possible to determine the specific gravity with an accuracy even exceeding #jjjjb1 the specific gravities given in the adjoining tables are only averages and most probable data in which the error1 especially for the #cj-hj p4c4 solutions cannot be less than #jjjaj 7taking water at #d as #a74 #ec bis ,judging from the best existing determinations 7of ,marignac1 ,kremers1 and ,pickering7 for solutions of sulphuric acid 7especially those containing more than #e p4c4 ,h#b,,so#d7 within the limits of #j and #cj 7and even to #dj71 the variation of the sp4 gr4 with the temperature t may 7within the accuracy of the existing determinations7 be perfectly expressed by the equation ,st ,s#j ,at ,bt#b4 ,it must be added that 7#a7 three specific gravities fully determine the variation of the density with t2 7#b7 ds_/dt ,a #b;,bt--i4e4 the factor of the temperature is expressed by a straight line2 7#c7 the value of ,a 7if p be greater than #e p4c47 is negative1 and numerically much greater than ,b2 7#d7 the value of ,b for dilute solutions containing less than #be p4c4 is negative2 for solutions approximating to ,h#b,,so#dc;,h#b,o in their composition it is equal to #j1 and for solutions of greater concentration ,b is positive2 7#e7 the factor ds_/dp for all temperatures attains a maximum value about ,h#b,,so#d;,h#b,o2 7#f7 on dividing ds_/dt by ,s#j1 and so obtaining the coefficient of expansion k 7see ,note #ec71 a minimum is obtained near ,h#b,,so#d and ,h#b,,so#dd;,h#b,o1 and a maximum at ,h#b,,so#d;,h#b,o for all temperatures4 #ec tri ,these data 7as well as those in the following table7 have been recalculated by me chiefly upon the basis of ,kremer's1 ,pickering's1 ,perkin's1 and my own determinations2 all the requisite corrections have been introduced1 and ,i have reason for thinking that in each of them the probable error 7or difference from the true figures1 now unknown7 of the specific gravity does not exceed #jjjjg 7if water at #d #a7 for the #be-hj p4c4 solutions1 and #jjjjb for the more dilute or concentrated solutions4 ,in the second table the first column gives the percentage amount p 7by weight7 of ,h#b,,so#d1 the second column the weight in grams 7,s#ae7 of a litre of the solution at #ae 7at #d the weight of a litre of water #a1jjj grams71 the third column1 the variation 7d,s_/dt7 of this weight for a rise of #a1 the fourth column1 the variation d,s_/dp of this weight 7at #ae7 for a rise of #a per cent4 of ,h#b,,so#d1 the fifth column1 the difference between the weight of a litre at #j and #ae 7,s#j - ,s#ae71 and the sixth column1 the difference between the weight of a litre at #ae and #cj 7,s#ae - ,s#cj74 p ,s#ae d,s#ae_/;dt d,s#ae_/;dp ,s#j- ,s#ae- ,s#ae ,s#cj #j #iiiae #jadh #gj #jg #cd #e #ajccj #jbg #fh #ca #ej #aj #ajfgg #jch #ga #eb #fd #bj #aadai #jeh #gg #hf #hi #cj #abbac #jfi #hb #ajd #ajd #dj #acjff #jge #hh #aac #aab #ej #acigi #jgi #ii #aai #aah #fj #aejab #jhf #ajh #acj #abg #gj #afaca #jic #aaf #ada #ach #hj #agcad #ajd #aaj #aeh #aed #ij #ahaii #ajh #ed #afd #afj #ie #ahcgf #ajc #ag #aeh #aea #ajj #ahcgb #ajc -#aied #aeg #aea ,the figures in these tables give the means of finding the amount of ,h#b,,so#d contained in a solution from its specific gravity1#ee and also show that 'special points' in the lines of variation of the specific gravity with the temperature and percentage composition correspond to certain definite compounds of ,h#b,,so#d with ,,oh#b4 ,this is best seen in the variation of the factors 7d,s_/dt and d,s_/dp7 with the temperature and composition 7columns #c1 #d1 second table74 ,we have already mentioned how the factor of temperature points to the existence of hydrates1 ,h#b,,so#d and ,h#b,,so#d1;,h#b,o4 ,as regards the factor d,s_/dp 7giving the increase of sp4 gr4 with an increase of #a per cent4 ,h#b,,so#d7 the following are the three most salient points3 7#a7 ,in passing from #ih per cent4 to #ajj per cent4 the factor is negative1 and at #ajj per cent4 about -#jjjai 7i4e4 at #ii per cent4 the sp4 gr4 is about #ahcia1 and at #ajj per cent4 about #ahcgb1 at #ae1 the amount of ,h#b,,so#d has increased whilst the sp4 gr4 has decreased71 but as soon as a certain amount of ,,so#c is added to the definite compound ,h#b,,so#d 7and 'fuming' acid formed7 the specific gravity rises 7for example1 for ,h#b,,so#d #jacf ,,so#c the sp4 gr4 at #ae #ahff71 that is the factor becomes positive 7and1 in fact1 greater by #jja71 so that the formation of the definite hydrate ,h#b,,so#d is accompanied by a distinct and considerable break in the continuity of the factor#ee bis2 7#b7 ,the factor 7d,s_/dp7 in increasing in its passage from dilute to concentrated solutions1 attains a maximum value 7at #ae about #jjab7 about ,h#b,,so#db;,h#b,o1 i4e4 at about the hydrate corresponding to the form ,,sx#f2 proper to the compounds of sulphur1 for ,s7,,oh7#f ,h#b,,so#db;,h#b,o2 the same hydrate corresponds to the composition of gypsum ,ca,s,o#db;,h#b,o1 and to it also corresponds the greatest contraction and rise of temperature in mixing ,h#b,,so#d with ,h#b,o 7see ,chapter ,i41 ,note #bh72 7#c7 ,the variation of the factor 7d,s_/dp7 under certain variations in the composition proceeds so uniformly and regularly1 and is so different from the variation given under other proportions of ,h#b,,so#d and ,h#b,o1 that the sum of the variations of d,s_/dp is expressed by a series of straight lines1 if the values of p be laid along the axis of absciss and those of d,s_/dp along the ordinates4#ef ,thus1 for instance1 for #ae1 at #aj per cent4 d,s_/dp #jjjga1 at #bj per cent4 #jjjgg1 at #cj per cent4 #jjjhb1 at #dj per cent4 #jjjhh1 that is1 for each #aj per cent4 the factor increases by about #jjjjf for the whole of the above range1 but beyond this it becomes larger1 and then1 after passing ,h#b,,so#db;,h#b,o1 it begins to fall rapidly4 ,such changes in the variation of the factor take place apparently about definite hydrates1#ef bis and especially about ,h#b,,so#dd;,h#b,o1 ,h#b,,so#db;,h#b,o and ,h#b,,so#d;,h#b,o4 ,all this indicating as it does the special chemical affinity of sulphuric acid for water1 although of no small significance for comprehending the nature of solutions 7see ,chapter ,i4 and ,chapter ,,vii471 contains many special points which require detailed investigation1 the chief difficulty being that it requires great accuracy in a large number of experimental data4 #ed ,the factor d,s_/dp passes through #j1 that is1 the specific gravity attains a maximum value at about #ih p4c4 ,this was discovered by ,kohlrausch1 and confirmed by ,chertel1 ,pickering1 and others4 #ee ,naturally under the condition that there is no other ingredient besides water1 which is sufficiently true4 ,for commercial acid1 whose specific gravity is usually expressed in degrees of ,baum's hydrometer1 we may add that at #ae ,specific gravity #a #aa #ab #ac #ad #ae #af #ag #ah ,degree ,baum #j #ac #bd #ccc #dab #dha #eda #eie #fdb #ff ,baum 7the strongest commercial acid or oil of vitriol7 corresponds to a sp4 gr4 #ahd4 ,by employing the second table 7by the method of interpolation7 the specific gravity1 at a given temperature 7from #j to #cj7 can be found for any percentage amount of ,h#b,,so#d1 and therefore conversely the percentage of ,h#b,,so#d can be found from the specific gravity4 #ee bis ,whether similar 7even small7 breaks in the continuity of the factor d,s_/dp exist or not1 for other hydrates 7for instance1 for ,h#b,,so#d;,h#b,o and ,h#b,,so#dd;,h#b,o7 cannot as yet be affirmed owing to the want of accurate data 7,note #ec74 ,in my investigation of this subject 7#ahhg7 ,i admit their possibility1 but only conditionally2 and now1 without insisting upon a similar opinion1 ,i only hold to the existence of a distinct break in the factor at ,h#b,,so#d1 being guided by ,c4 ,winkler's observations ond the specific gravities of fuming sulphuric acid4 #ef ,in #ahhg1 on considering all the existent observations for a temperature #j1 ,i gave the accompanying scheme 7p4 #bdc7 of the variation of the factor ds_/dp at #j4 ,i did not then 7#ahhg7 give this scheme an absolute value1 and now after the appearance of two series of new determinations 7,lunge and ,pickering in #ahij71 which disagree in many points1 ,i think it well to state quite clearly3 7#a7 that ,lunge's and ,pickering's new determinations have not added to the accuracy of our data respecting the variation of the specific gravity of solutions of sulphuric acid2 7#b7 that the sum total of existing data does not negative 7within the limit of experimental accuracy7 the possibility of a rectilinear and broken form for the factors ds_/dp2 7#c7 that the supposition of 'special points' in ds_/dp1 indicating definite hydrates1 finds confirmation in all the latest determinations2 7#d7 that the supposition respecting the existence of hydrates determining a break of the factor ds_/dp is in in way altered if1 instead of a series of broken straight lines1 there be a continuous series of curves1 nearly approaching straight lines2 and 7#e7 that this subject deserves 7as ,i mentioned in #ahhg7 new and careful elaboration1 because it concerns that foremost problem in our science--solutions--and introduces a special method into it--that is1 the study of differential variations in a property which is so easily observed as the specific gravity of a liquid4 #ef bis ,these hydrates are3 7a7 ,h#b,,so#d ,,so#c;,h#b,o 7melts at #ajd72 7b7 ,h#b,,so#d;,h#b,o ,,so#cb;,h#b,o 7crystallo-hydrate1 melts at #he72 7c7 ,h#b,,so#db;,h#b,o 7is apparently not crystallisable72 7d7 one of the hydrates between ,h#b,,so#df;,h#b,o and ,h#b,,so#dc;,h#b,o1 most probably ,h#b,,so#dd;,h#b,o ,,so#ce;,h#b,o1 for it crystallises at -#bde 7,note #ej bis72 and 7e7 a certain hydrate with a large proportion of water1 about ,h#b,,so#daej;,h#b,o4 ,the existence of the last is inferred from the fact that the factor ds_/dp first falls1 starting from water1 and then rises1 and this change takes place when p is less than #e p4c4 ,certainly a change in the variation of ds_/dp or ds_/dt does take place in the neighbourhood of these five hydrates 7,pickering1 #ahij1 recognised a far greater number of hydrates74 ,i think it well to add that if the composition of the solutions be expressed by the percentage amount of molecules--r#a,,so#c 7#ajj - r#a7;,h#b,o we find that for ,h#b,,so#d1 r#a #ej1 for ,h#b,,so#db;,h#b,o r#a #be #ej_/b1 for ,h#b,,so#d;,h#b,o1 r#a #ccccc #ej #b_/c1 while for ,h#b,,so#dd;,h#b,o1 r#a #affff #ej #a_/c--;i4e4 that the chief hydrates are distributed symmetrically between ,h#b,o and ,h#b,,so#d4 ,besides which ,i may mention that my researches 7#ahhg7 upon the abrupt changes in the factor for solutions of sulphuric acid1 and upon the correspondence of the breaks of ds_/dp with definite hydrates1 received an indirect confirmation not only in the solutions of ,,hno#c1 ,h,cl1 ,c#b;,h#f,o1 ,c#c;,h#h,o1 c41 which ,i investigated 7in my work cited in ,chapter ,i41 ,note #ai71 but also in the careful observations made by ,professor ,cheltzoff on the solutions of ,fe,cl#c and ,zn,cl#b 7,chapter ,,xvi41 ,note #d7 which showed the existence in these solutions of an almost similar change in ds_/dp as is found in sulphuric acid4 ,the detailed researches 7#ahic7 made by ,tourbaba on the solutions of many organic substances are of a similar nature4 ,besides which1 ,h4 ,crompton 7#ahhh71 in his researches on the electrical conductivity of solutions of sulphuric acid1 and ,tammann1 in his observations on their vapour tension1 found a correlation with the hydrates indicated as above by the investigation of their specific gravities4 ,the influence of mixtures of a definite composition upon the chemical relations of solutions is even exhibited in such a complex process as electrolysis4 ,v4 ,kouriloff 7#ahia7 showed that mixtures containing about #c p4c41 #dg p4c4 and #gc p4c4 of sulphuric acid--i4e4 whose composition approaches that of the hydrates ,h#b,,so#daej;,h#b,o1 ,h#b,,so#df;,h#b,o and ,h#b,,so#db;,h#b,o--exhibit certain peculiarities in respect to the amount of peroxide of hydrogen formed during electrolysis4 ,thus a #c p4c4 solution gives a maximum amount of peroxide of hydrogen at the negative pole1 as compared with that given by other neighbouring concentrations4 ,starting from #c p4c41 the formation of peroxide of hydrogen ceases until a concentration of #dg p4c4 is reached4 ,the great affinity of sulphuric acid for water is also seen from the fact that when the strong acid acts on the majority of organic substances containing hydrogen and oxygen 7especially on heating7 it very frequently takes up these elements in the form of water4 ,thus strong sulphuric acid acting on alcohol1 ,c#b;,h#f,o1 removes the elements of water from it1 and converts it into olefiant gas1 ,c#b;,h#d4 ,it acts in a similar manner on wood and other vegetable tissues1 which it chars4 ,if a piece of wood be immersed in strong sulphuric acid it turns black4 ,this is owing to the fact that the wood contains carbohydrates which give up hydrogen and oxygen as water to the sulphuric acid1 leaving charcoal1 or a black mass very rich in it4 ,for example1 cellulose1 ,c#f;,h#aj,o#e1 acts in this manner4#eg #eg ,cellulose1 for instance unsized paper or calico1 is dissolved by strong sulphuric acid4 ,acid diluted with about half its volume of water converts it 7if the action be of short duration7 into vegetable parchment 7,chapter ,i41 ,note #ah74 ,the action of dilute solutions of sulphuric acid converts it into hydro-cellulose1 and the fibre loses its coherent quality and becomes brittle4 ,the prolonged action of strong sulphuric acid chars the cellulose while dilute acid converts it into glucose4 ,if sulphuric acid be kept in an open vessel1 the organic matter of the dust held in the atmosphere falls into it and blackens the acid4 ,the same thing happens if sulphuric acid be kept in a bottle closed by a cork2 the cork becomes charred1 and the acid turns black4 ,however1 the chemical properties of the acid undergo only a very slight change when it turns black4 ,sulphuric acid which is considerably diluted with water does not produce the above effects1 which clearly shows their dependence on the affinity of the sulphuric acid for water4 ,it is evident from the preceding that strong sulphuric acid will act as a powerful poison2 whilst1 on the other hand1 when very dilute it is employed in certain medicines and as a fertiliser for plants4 ,we have already had frequent occasion to notice the very energetic acid properties of sulphuric acid1 and therefore we will now only consider a few of their aspects4 ,first of all we must remember that1 with calcium1 strontium1 and especially with barium and lead1 sulphuric acid forms very slightly soluble salts1 whilst with the majority of other metals it gives more easily soluble salts1 which in the majority of cases are able1 like sulphuric acid itself1 to combine with water to form crystallo-hydrates4 ,normal sulphuric acid1 containing two atoms of hydrogen in its molecule1 is able for this reason alone to form two classes of salts1 normal and acid1 which it does with great facility with the alkali metals4 ,the metals of the alkaline earths and the majority of other metals1 if they do form acid sulphates1 do so under exceptional conditions 7with an excess of strong sulphuric acid71 and these salts when formed are decomposable by water--that is1 although having a certain degree of physical stability they have no chemical stability4 ,besides the acid salts ,,rhso#d1 sulphuric acid also gives other forms of acid salts4 ,an entire series of salts having the composition ,,rhso#d1;,h#b,,so#d1 or for bivalent metals ,,rso#d1c;,h#b,,so#d1eh has been prepared4 ,such salts have been obtained for potassium1 sodium1 nickel1 calcium1 silver1 magnesium1 manganese4 ,they are prepared by dissolving the sulphates in an excess of sulphuric acid and heating the solution until the excess of sulphuric acid is driven off2 on cooling1 the mass solidifies to a crystalline salt4 ,besides which1 ,rose obtained a salt having the composition ,na#b,,so#d1,na,h,s,o#d1 and if ,h,na,s,o#d be heated it easily forms a salt ,na#b,s#b,o#g ,na#b,,so#d1,,so#c2 hence it is clear that sulphuric anhydride combines with various proportions of bases1 just as it combines with various proportions of water4 #eh ,weber 7#ahhd7 obtained a series of salts ,r#b,o1#h,,so#cn,h#b,o for ,k1 ,rb1 ,cs1 and ,tl4 ,we have already learned that sulphuric acid displaces the acid from the salts of nitric1 carbonic1 and many other volatile acids4 ,berthollet's laws 7,chapter ,x47 explain this by the small volatility of sulphuric acid2 and1 indeed1 in an aqueous solution sulphuric acid displaces the much less soluble boric acid from its compounds--for instance1 from borax1 and it also displaces silica from its compounds with bases2 but both boric anhydride and silica1 when fused with sulphates1 decompose them1 displacing sulphuric anhydride1 ,,so#c1 because they are less volatile than sulphuric anhydride4 ,it is also well known that with metals1 sulphuric acid forms salts giving off hydrogen 7,fe1 ,zn1 c471 or sulphur dioxide 7,cu1 ,hg1 c474#eh bis #eh bis ,ditte 7#ahij7 divides all the metals into two groups with respect to sulphuric acid2 the first group includes silver1 mercury1 copper1 lead1 and bismuth1 which are only acted upon by hot concentrated acid4 ,in this case sulphurous anhydride is evolved without any by-reactions4 ,the second group contains manganese1 nickel1 cobalt1 iron1 zinc1 cadmium1 aluminium1 tin1 thallium1 and the alkali metals4 ,they react with sulphuric acid of any concentration at any temperature4 ,at a low temperature hydrogen is disengaged1 and at higher temperatures 7and with very concentrated acid7 hydrogen and sulphurous anhydride are simultaneously evolved4 ,the reactions of sulphuric acid with respect to organic substances are generally determined by its acid character1 when the direct extraction of water1 or oxidation at the expense of the oxygen of the sulphuric acid1#ei or disintegration does not take place4 ,thus the majority of the saturated hydrocarbons1 ,cn,h#bm1 form with sulphuric acid a special class of sulphonic acids1 ,cn,h#bm-#a7;,,hso#c72 for example1 benzene1 ,c#f;,h#f1 forms benzenesulphonic acid1 ,c#f;,h#e4,,so#c;,h1 water being separated1 for the formation of which oxygen is taken up from the sulphuric acid1 for the product contains less oxygen than the sulphuric acid4 ,it is evident from the existence of these acids that the hydrogen in organic compounds is replaceable by the group ,,so#c;,h1 just as it may be replaced by the radicles ,cl1 ,,no#b1 ,,co#b;,h and others4 ,as the radicle of sulphuric acid or sulphoxyl1 ,,so#b,,oh or ,,sho#c1 contains1 like carboxyl 7,vol4 ,i41 p4 #cie71 one hydrogen 7hydroxyl7 of sulphuric acid1 the resultant substances are acids whose basicity is equal to the number of hydrogens replaced by sulphoxyl4 ,since also sulphoxyl takes the place of hydrogen1 and itself contains hydrogen1 the sulpho-acids are equal to a hydrocarbon ,,so#c1 just as every organic 7carboxylic7 acid is equal to a hydrocarbon ,,co#b4 ,moreover1 here this relation corresponds with actual fact1 because many sulphonic acids are obtained by the direct combination of sulphuric anhydride3 ,c#f;,h#e17,,so#c;,h7 ,c#f;,h#f ,,so#c4 ,the sulphonic acids give soluble barium salts1 and are therefore easily distinguished from sulphuric acid4 ,they are soluble in water1 are not volatile1 and when distilled give sulphurous anhydride 7whilst the hydroxyl previously in combination with the sulphurous anhydride remains in the hydrocarbon group2 thus phenol1 ,c#f;,h#e4,,oh1 is obtained from benzenesulphonic acid71 and they are very energetic1 because the hydrogen acting in them is of the same nature as in sulphuric acid itself4#fj #ei ,for example1 the action of hot sulphuric acid on nitrogenous compounds1 as applied in ,kjeldahl's method for the estimation of nitrogen 7,volume ,i4 p4 #bdi74 ,it is obvious that when sulphuric acid acts as an oxidising agent it forms sulphurous anhydride4 ,the action of sulphuric acid on the alcohols is exactly similar to its action on alkalis1 because the alcohols1 like alkalis1 react on acids2 a molecule of alcohol with a molecule of sulphuric acid separates water and forms an acid ethereal salt--that is there is produced an ethereal compound corresponding with acid salts4 ,thus1 for example1 the action of sulphuric acid1 ,h#b,,so#d1 on ordinary alcohol1 ,c#b;,h#e,,oh1 gives water and sulphovinic acid1 ,c#b;,h#e;,,hso#d--that is1 sulphuric acid in which one atom of hydrogen is replaced by the radicle ,c#b;,h#e of ethyl alcohol1 ,,so#b7,,oh77,,oc#b;,h#e71 or1 what is the same thing1 the hydrogen in alcohol is replaced by the radicle 7sulphoxyl7 of sulphuric acid1 ,c#b;,h#e,o4,,so#b7,,oh74 #fj ,we will mention the following difference between the sulphonic acids and the ethereal acid sulphates 7,note #ei73 the former re-form sulphuric acid with difficulty and the latter easily4 ,thus sulphovinic acid when heated with an excess of water is reconverted into alcohol and sulphuric acid4 ,this is explained in the following manner4 ,both these classes of acids are produced by the substitution of hydrogen by ,,so#c;,h1 or the univalent radicle of sulphuric acid1 but in the formation of ethereal acid sulphates the ,,so#c;,h replaces the hydrogen of the hydroxyl in the alcohol1 whilst in the formation of the sulphonic acids the ,,so#c;,h replaces the hydrogen of a hydrocarbon4 ,this difference is clearly evidenced in the existence of two acids of the composition ,,so#d;,c#b;,h#f4 ,the one1 mentioned above1 is sulphovinic acid or alcohol1 ,c#b;,h#e4,,oh1 in which the hydrogen of the hydroxyl is replaced by sulphoxyl ,c#b;,h#e4,,oso#c;,h1 whilst the other is alcohol1 in which one atom of the hydrogen in ethyl1 ,c#b;,h#e1 is replaced by the sulphonic group--that is 7,c#b;,h#d7,,so#c;,h,,oh4 ,the latter is called isethionic acid4 ,it is more stable than sulphovinic acid4 ,the details as to these interesting compounds must be looked for in works on organic chemistry1 but ,i think it necessary to note one of the general methods of formation of these acids4 ,the sulphites of the alkalis--for example1 ,k#b,,so#c--when heated with the halogen products of metalepsis1 give a halogen salt and a salt of a sulphonic acid4 ,thus methyl iodide1 ,,ch#c;,i1 derived from marsh gas1 ,,ch#d1 when heated to #ajj with a solution of potassium sulphite1 ,k#b,,so#c1 gives potassium iodide1 ,,ki1 and potassium methylsulphonate1 ,,ch#c,,so#c,k--that is a salt of the sulphonic acid4 ,this shows that the sulphonic acid may be referred to sulphurous acid1 and that there is a resemblance between sulphuric and sulphurous acid1 which clearly reveals itself here in the formation of one product from them both4 ,sulphuric acid1 as containing a large proportion of oxygen1 is a substance which frequently acts as an oxidising agent3 in which case it is deoxidised1 forming sulphurous anhydride and water 7or even1 although more rarely1 sulphuretted hydrogen and sulphur74 ,sulphuric acid acts in this manner on charcoal1 copper1 mercury1 silver1 organic and other substances1 which are unable to evolve hydrogen from it directly1 as we saw in describing sulphurous anhydride4 ,although the hydrate of a higher saline form of oxidation 7,chapter ,,xv471 sulphuric anhydride is capable of further oxidation1 and forms a kind of peroxide1 just as hydrogen gives hydrogen peroxide in addition to water1 or as sodium and potassium1 besides the oxides ,na#b,o and ,k#b,o1 give their peroxides1 compounds which are in a chemical sense unstable1 powerfully oxidising1 and not directly able to enter into saline combinations4 ,if the oxides of potassium1 barium1 c41 be compared to water1 then their peroxides must in like manner correspond to hydrogen peroxide1#fa not only because the oxygen contained in them is very mobile and easily liberated1 and because their reactions are similar1 but also because they can be mutually transformed into each other1 and are able to form compounds with each other1 with bases and with water1 and indeed form a kind of peroxide salts4#fb ,this is also the character of persulphuric acid1 discovered in #ahgh by ,berthelot1 and its corresponding anhydride or peroxide of sulphur ,s#b,o#g4 ,it is formed from #b,,so#c ,o with the absorption of heat 7-#bg thousand heat units71 like ozone from ,o#b ,o 7-#bi thousand units of heat71 or hydrogen peroxide from ,h#b,o ,o 7-#ba thousand heat units74 #fa ,the reaction ,ba,o ,o develops #ab1jjj heat units1 whilst the reaction ,h#b,o ,o absorbs #ba1jjj heat units4 #fb ,schne obtained a compound of peroxide of barium with peroxide of hydrogen4 ,if barium peroxide be dissolved in hydrochloric 7or acetic7 acid1 or if a solution of hydrogen peroxide be diluted with a solution of barium hydroxide1 a pure hydrate is precipitated having the composition ,ba,o#b1h;,h#b,o 7sometimes the composition is taken as ,ba,o#b1f;,h#b,o74 ,this fact was already known to ,thnard4 ,schne showed that if hydrogen peroxide be in excess1 a crystalline compound of the two peroxides1 ,ba,o#b;,h#b,o#b1 is precipitated4 ,schne also obtained small well-formed crystals of the same composition by adding a solution of ammonia to an acid solution of barium peroxide 7containing a barium salt and hydrogen peroxide or a compound of ,ba,o#b with the acid74 ,thus barium peroxide combines with both water and hydrogen peroxide4 ,this is a very important fact for the comprehension of the composition of other peroxides4 ,moreover1 if the peroxides are able to give hydrates they can also form corresponding salts1 i4e4 they can combine with bases and acids1 as was afterwards found to be the case on further research into this subject4 ,peroxide of sulphur is produced by the action of a silent discharge upon a mixture of oxygen and sulphurous anhydride4#fc ,with water ,s#b,o#g gives persulphuric acid1 ,h#b,s#b,o#h4 ,the latter is obtained more simply by mixing strong sulphuric acid 7not weaker than ,h#b,,so#d1b;,h#b,o7 directly with hydrogen peroxide1 or by the action of a galvanic current on sulphuric acid mixed with a certain amount of water1 and cooled1 the electrodes being platinum wires1 when persulphuric acid naturally appears at the positive pole4#fd ,when an acid of the strength ,h#b,,so#d1f;,h#b,o is taken1 at first the hydrate of the sulphuric peroxide1 ,s#b,o#g1;,h#b,o only is formed2 but when the concentration about the positive pole reaches ,h#b,,so#d1c;,h#b,o1 a mixture of hydrogen peroxide and the hydrate of sulphuric peroxide begins to be formed4 ,dilute solutions of sulphuric peroxide can be kept better than more concentrated solutions1 but the latter may be obtained containing as much as #abc grams of the peroxide to a litre4 ,it is a very instructive fact that hydrogen peroxide is always formed when strong solutions of persulphuric acid break up on keeping4 ,so that the bond between the two peroxides is established both by analysis and synthesis3 hydrogen peroxide is able to produce ,s#b;,h#b,o#h1 and the latter to produce hydrogen peroxide4 ,a mixture of sulphuric peroxide with sulphuric acid or water is immediately decomposed1 with the evolution of oxygen1 either when heated or under the action of spongy platinum4 ,the same thing takes place with a solution of baryta1 although at first no precipitate is formed and the decomposition of the barium salt1 ,ba,s#b,o#h1 with the formation of ,ba,s,o#d1 only proceeds slowly1 so that the solution may be filtered 7the barium salt of persulphuric acid is soluble in water74 ,mercury1 ferrous oxide1 and the stannous salts1 are oxidised by ,s#b;,h#b,o#h4 ,these are all distinct signs of true peroxides4 ,the same common properties 7capacity for oxidising1 property of forming peroxide of hydrogen1 c47 are possessed by the alkali salts of persulphuric acid1 which are obtained by the action of an electric current upon certain sulphates1 for instance ammonium or potassium sulphate4 ,the ammonium salt of persulphuric acid1 7,,nh#d7b,s#b,o#h1 is especially easily formed by this means1 and is now prepared on a large scale and used 7like ,na#b,o#b and ,h#b,o#b7 for bleaching tissues and fibres4#fe #fc ,anhydrous sulphuric peroxide1 ,s#b,o#g1 is obtained by the prolonged 7#h to #aj hours7 action of a silent discharge of considerable intensity on a mixture of oxygen and sulphurous anhydride2 the vapour of sulphuric peroxide1 ,s#b,o#g1 condenses as liquid drops1 or after being cooled to #j in the form of long prismatic crystals1 resembling those of sulphuric anhydride4 ,the anhydrous compound ,s#b,o#g 7and also the hydrated compound7 cannot be preserved long1 as it splits up into oxygen and sulphuric anhydride4 ,direct experiment shows that a mixture of equal volumes of sulphurous anhydride and oxygen leaves a residue of a quarter of the oxygen taken1 or half of the whole volume1 which indicates the formula ,s#b,o#g4 ,this substance is soluble in water1 and it then gives a hydrate1 probably having the composition ,s#b,o#g1;,h#b,o #b,,sho#d4 ,this solution oxidises the salts ,sn,x#b1 potassium iodide1 and others1 which renders it possible to prove that the solution actually contains one atom of oxygen capable of effecting oxidation to two molecules of sulphuric anhydride4 ,in order to fully demonstrate the reality of a peroxide form for acids1 it should be mentioned that some years ago ,brodie obtained the so-called acetic peroxide1 7,c#b;,h#b,o7#b,o#b1 by the action of barium peroxide on acetic anhydride1 7,c#b;,h#c,o7#b,o4 ,its corresponding hydrate is also known4 ,this shows that true peroxides and their hydrates1 with reactions similar to those of hydrogen peroxide1 are possible for acids4 ,a similar higher oxide has long been known for chromium1 and ,berthelot obtained a like compound for nitric acid 7,chapter ,,vi41 ,note #bf74 #fd ,when an acid of the strength ,h#b,,so#df;,h#b,o is taken1 at first only the hydrate of the sulphuric peroxide1 ,s#b,o#g;,h#b,o1 is formed1 but when the concentration at the positive pole reaches ,h#b,,so#dc;,h#b,o1 a mixture of hydrogen peroxide and the hydrate of sulphuric peroxide begins to be formed4 ,a state of equilibrium is ultimately arrived at when the amounts of these substances correspond to the proportion ,s#b,o#g 3 #b;,h#b,o#b1 which1 as it were1 answers to a new hydrate1 ,s#b,o#ib;,h#b,o4 ,but its existence cannot be admitted because the sulphuric peroxide can be easily distinguished from the hydrogen peroxide in the solution owing to the fact that the former does not act on an acid solution of potassium permanganate1 whilst the hydrogen peroxide disengages both its own oxygen and that of the permanganic acid1 converting it into manganous oxide4 ,their common property of liberating iodine from an acid solution of the potassium iodide enables the sum of the active oxygen in them both to be determined4 #fe ,if a solution of sulphuric acid which has been first subjected to electrolysis be neutralised with potash or baryta1 the salt which is formed begins to decompose rapidly with the evolution of oxygen 7,berthelot1 #ahij74 ,on saturating with caustic baryta1 the solution of the salt formed may be separated from the sulphate of barium1 and then the composition of the resultant compound1 ,ba,s#b,o#h1 may be determined from the amount of oxygen disengaged4 ,marshall 7#ahia7 studied the formation of this class of compounds more fully2 he subjected a saturated solution of bisulphate of potassium to electrolysis with a current of #c-c-a_/b ampres2 before electrolysis dilute sulphuric acid is added to the liquid surrounding the negative pole1 and during electrolysis the solution at the anode is cooled4 ,the electrolysis is continued without interruption for two days1 and a white crystalline deposit separates at the anode4 ,to avoid decomposition1 the latter is not filtered through paper1 but through a perforated platinum plate1 and dried on a porous tile4 ,the mother liquor1 with the addition of a fresh solution of bisulphate of potassium1 is again subjected to electrolysis and the crystals formed at the anode are again collected1 c4 ,the salt so obtained may be recrystallised by dissolving it in hot water and rapidly cooling the solution after filtration2 a small proportion of the salt is decomposed by this treatment4 ,rapid cooling is followed by the formation of small columnar crystals2 slow cooling gives large prismatic crystals4 ,the composition of the salt is determined either by igniting it1 when it forms sulphate of potassium1 or else by titrating the active oxygen with permanganate3 its composition was found to correspond to the salt of persulphuric acid1 ,k#b,s#b,o#h4 ,the solution of the salt has a neutral reaction1 and does not give a precipitate with salts of other metals4 ,k#b,s#b,o#h is the most insoluble of the salts of persulphuric acid4 ,with nitrate of silver it forms persulphate of silver1 which gives peroxide of silver under the action of water according to the equation ,ag#b,s#b,o#h #b;,h#b,o ,ag#b,o#b #b;,h#b,,so#d4 ,with an alkaline solution of a cupric salt 7,fehling's solution7 it forms a red precipitate of peroxide of copper4 ,manganese and cobalt salts give precipitates of ,mn,o#b and ,co#b,o#c4 ,ferrous salts are rapidly oxidised1 potassium iodide slowly disengages iodine at the ordinary temperature4 ,all these reactions indicate the powerful oxidising properties of ,k#b,s#b,o#h4 ,in oxidising in the presence of water it gives a residue of ,,khso#d4 ,the decomposition of the dry salt begins at #ajj but is not complete even at #bej4 ,the freshly prepared salt is inodorous1 but after being kept in a closed vessel it evolves a peculiar smell different from that of ozone4 ,the ammonium salt of persulphuric acid1 7,,nh#d7b,s#b,o#h1 is obtained in a similar manner4 ,it is soluble to the extent of #eh parts per #ajj parts by weight of water4 ,the decomposition of the ammonium salt by the hydrated oxide of barium gives the barium salt1 ,ba,s#b,o#hd;,h#b,o1 which is soluble to the extent of #ebb parts in #ajj parts of water at #j4 ,the crystals do not deliquesce in the air and decompose in the course of several days2 they decompose most rapidly in perfectly dry air4 ,solutions of the pure salt decompose slowly at the ordinary temperature2 on boiling barium sulphate is gradually precipitated1 oxygen being liberated simultaneously4 ,to completely decompose this salt it is necessary to boil its solution for a long time4 ,alcohol dissolves the solid salt2 the anhydrous salt does not separate from the alcoholic solution1 but a hydrate containing one molecule of water1 ,ba,s#b,o#h;,h#b,o1 which is soluble in water but insoluble in absolute alcohol4 ,solid barium persulphate decomposes even when slightly heated4 ,the free acid1 which may serve for the preparation of other salts1 is obtained by treating the barium salt with sulphuric acid4 ,the lead salt1 ,pb,s#b,o#h1 has been obtained from the free acid2 it crystallises with two or three molecules of water4 ,it is soluble in water1 deliquesces in the air1 and with alkalis gives a precipitate of the hydrated oxide which rapidly oxidises into the binoxide4 ,traube1 before ,marshall's researches1 thought that the electrolysis of solutions of sulphuric acid did not give persulphuric acid but a persulphuric oxide having the composition ,,so#d4 ,on repeating his former researches 7#ahib7 ,traube obtained a persulphuric oxide by the electrolysis of a #gj per cent4 solution of sulphuric acid1 and he separated it from the solution by means of barium phosphate4 ,analysis showed that this substance corresponded to the above composition ,,so#d1 and therefore ,traube considers it very likely that the salts obtained by ,marshall corresponded to an acid ,h#b,,so#d ,,so#d1 i4e4 that the indifferent oxide1 ,,so#d1 can combine with sulphuric acid and form peculiar saline compounds4 ,in order to understand the relation of sulphuric peroxide to sulphuric acid we must first remark that hydrogen peroxide is to be considered1 in accordance with the law of substitution1 as water1 ,h7,,oh71 in which ,h is replaced by 7,,oh74 ,now the relation of ,h#b,s#b,o#h to ,h#b,,so#d is exactly similar4 ,the radicle of sulphuric acid1 equivalent to hydrogen1 is ,,hso#d2fe bis it corresponds with the 7,,oh7 of water1 and therefore sulphuric acid1 ,h7,,sho#d71 gives 7,,sho#d7b or ,s#b;,h#b,o#h1 in exactly the same manner as water gives 7,,ho7#b--;i4e4 ,h#b,o#b4ff #fe bis ,or one of those supposed ions which appear at the positive pole in the decomposition of sulphuric acid by the action of a galvanic current4 #ff ,if this be true one would expect the following peroxide hydrates3 for phosphoric acid1 7,h#b,,po#d7b ,h#d,p#b,o#h #b;,h#b,o #b,,po#c2 for carbonic acid1 7,,hco#c7b ,h#b;,c#b,o#f ,h#b,o ,c#b,o#e2 and for lead the true peroxide will be also ,pb#b,o#e1 c4 ,judging from the example of barium peroxide 7,note #fb71 these peroxide forms will probably combine together4 ,it seems to me that the compounds obtained by ,fairley for uranium are very instructive as elucidating the peroxides4 ,in the action of hydrogen peroxide in an acid solution on uranium oxide1 ,,uo#c1 there is formed a uranium peroxide1 ,,uo#d1d;,h#b,o 7,u #bdj71 but hydrogen peroxide acts on uranium oxide in the presence of caustic soda2 on the addition of alcohol a crystalline compound containing ,na#d,,uo#h1d;,h#b,o is precipitated1 which is doubtless a compound of the peroxides of sodium1 ,na#b,o#b1 and uranium1 ,,uo#d4 ,it is very possible that the first peroxide1 ,,uo#d1d;,h#b,o1 contains the elements of hydrogen peroxide and uranium peroxide1 ,u#b,o#g1 or even ,u7,,oh7#f1;,h#b,o#b1 just as the peroxide form lately discovered by ,spring for tin perhaps contains ,sn#b,o#c1;,h#b,o#b4 ,the largest part of the sulphuric acid made is used for reacting on sodium chloride in the manufacture of sodium carbonate2 for the manufacture of the volatile acids1 like nitric1 hydrochloric1 c41 from their corresponding salts2 for the preparation of ammonium sulphate1 alums1 vitriols 7copper and iron71 artificial manures1 superphosphate 7,chapter ,,xix41 ,note #ah7 and other salts of sulphuric acid2 in the treatment of bone ash for the preparation of phosphorus1 and for the solution of metals--for example1 of silver in its separation from gold--for cleaning metals from rust1 c4 ,a large amount of oil of vitriol is also used in treatment of organic substances2 it is used for the extraction of stearin1 or stearic acid1 from tallow1 for refining petroleum and various vegetable oils1 in the preparation of nitro-glycerine 7,chapter ,,vi41 ,notes #cg and #cg bis71 for dissolving indigo and other colouring matters1 for the conversion of paper into vegetable parchment1 for the preparation of ether from alcohol1 for the preparation of various artificial scents from fusel oil1 for the preparation of vegetable acids1 such as oxalic1 tartaric1 citric1 for the conversion of non-fermentable starchy substances into fermentable glucose1 and in a number of other processes4 ,it would be difficult to find another artificially-prepared substance which is so frequently applied in the arts as sulphuric acid4 ,where there are not works for its manufacture1 the economical production of many other substances of great technical importance is impossible4 ,in those localities which have arrived at a high technical activity the amount of sulphuric acid consumed is proportionally large2 sulphuric acid1 sodium carbonate1 and lime are the most important of the artificially-prepared agents employed in factories4 ,besides the normal acids of sulphur1 ,h#b,,so#c1 ,h#b,,so#c,s1 and ,h#b,,so#d1 corresponding with sulphuretted hydrogen1 ,h#b,s1 in the same way that the oxy-acids of chlorine correspond with hydrochloric acid1 ,h,cl1 there exists a peculiar series of acids which are termed thionic acids4 ,their general composition is ,sn,h#b,o#f1 where n varies from #b to #e4 ,if n #b1 the acid is called dithionic acid4 ,the others are distinguished as trithionic1 tetrathionic1 and pentathionic acids4 ,their composition1 existence1 and reactions are very easily understood if they be referred to the class of the sulphonic acids--that is1 if their relation to sulphuric acid be expressed in just the same manner as the relation of the organic acids to carbonic acid4 ,the organic acids1 as we saw 7,chapter ,,ix471 proceed from the hydrocarbons by the substitution of their hydrogen by carboxyl--that is1 by the radicle of carbonic acid1 ,,ch#b,o#c - ,,ho ,,cho#b4 ,the formation of the acids of sulphur by means of sulphoxyl may be represented in the same manner1 ,,hso#c ,h#b,,so#d - ,,ho4 ,therefore to hydrogen ,h#b1 there should correspond the acids ,h4,,sho#c1 sulphurous1 and ,,sho#c4,,sho#c ,s#b;,h#b,o#f1 or dithionic2 to ,,sh#b there should correspond the acids ,,sh7,,sho#c7 ,h#b,s#b,o#c 7thiosulphuric71 and ,s7,,sho#c7b ,h#b,s#c,o#f 7trithionic72 to ,s#b;,h#b the acids ,s#b;,h7,,sho#c7 ,h#b,s#c,o#b 7unknown71 and ,s#b7,,sho#c7b ,h#b,s#d,o#f 7tetrathionic72 to ,s#c;,h#b the acids ,s#c;,h7,,sho#c7 and ,s#c7,,sho#c7b ,h#b,s#e,o#f 7pentathionic74 ,we know that iodine reacts directly with the hydrogen of sulphuretted hydrogen and combines with it1 and if thiosulphuric acid contains the radicle of sulphuretted hydrogen 7or hydrogen united with sulphur7 of the same nature as in sulphuretted hydrogen1 it is not surprising that iodine reacts with sodium thiosulphate and forms sodium tetrathionate4 ,thus1 thiosulphuric acid1 ,,hs7,,sho#c71 when deprived of ,h1 gives a radicle which immediately combines with another similar radicle1 forming the tetrathionate ,s#b7,,so#b;,,ho7#b4 ,on this view#fg of the structure of the thionic acids and salts1 it is also clear how all the thionic acids1 like thiosulphuric acid1 easily give sulphur and sulphides1 with the exception only of dithionic acid1 ,h#b,s#b,o#f1 which1 judging from the above1 stands apart from the series of the other thionic acids4 ,dithionic acid stands in the same relation to sulphuric acid as oxalic acid does to carbonic acid4 ,oxalic acid is dicarboxyl1 7,,cho#b7b ,c#b;,h#b,o#d1 and so also dithionic acid is disulphoxyl1 7,,sho#c7b ,s#b;,h#b,o#f4 ,oxalic acid when ignited decomposes into carbonic anhydride and carbonic oxide1 ,,co1 and dithionic acid when heated decomposes into sulphuric anhydride and sulphurous anhydride1 ,,so#b1 and ,,so#b stands in the same relation to ,,so#c as ,,co to ,,co#b4 ,this also explains the peculiarity of the calcium1 barium1 and lead1 c4 salts of the thionic acids being easily soluble 7although the corresponding salts of ,h#b,,so#c1 ,h#b,,so#d1 and ,h#b,s dissolve with difficulty71 because the former are similar to the salts of the sulphonic acids1 which are also soluble in water4 ,thus the thionic acids are disulphonic acids1 just as many dicarboxylic acids are known--for example1 ,,ch#b7;,,co#b;,h7#b1 ,c#f;,h#d7;,,co#b;,h7#b4fh #fg ,this view was communicated by me in #ahgj to the ,russian ,chemical ,society4 #fh ,dithionic acid1 ,h#b,s#b,o#f1 is distinguished among the thionic acids as containing the least proportion of sulphur4 ,it is also called hyposulphuric acid1 because its supposed anhydride1 ,s#b,o#e1 contains more ,o than sulphurous oxide1 ,,so#b or ,s#b,o#d1 and less than sulphuric anhydride1 ,,so#c or ,s#b,o#f4 ,dithionic acid1 discovered by ,gay-,lussac and ,welter1 is known as a hydrate and as salts1 but not as anhydride4 ,the method for preparing dithionic acid usually employed is by the action of finely-powdered manganese dioxide on a solution of sulphurous anhydride4 ,on shaking1 the smell of the latter disappears1 and the manganese salt of the acid in question passes into solution2 ,mn,o#b #b,,so#b ,mn,s#b,o#f4 ,if the temperature be raised1 the dithionate splits up into sulphurous anhydride and manganese sulphate1 ,mn,s,o#d4 ,generally owing to this a mixture of manganese sulphate and dithionate is obtained in the solution4 ,they may be separated by mixing the solution of the manganese salts with a solution of barium hydroxide1 when a precipitate of manganese hydroxide and barium sulphate is obtained4 ,in this manner barium dithionate only is obtained in solution4 ,it is purified by crystallisation1 and separates as ,ba,s#b,o#f1b;,h#b,o2 this is then dissolved in water1 and decomposed with the requisite amount of sulphuric acid4 ,dithionic acid1 ,h#b,s#b,o#f1 then remains in solution4 ,by concentrating the resultant solution under the receiver of an air-pump it is possible to obtain a liquid of sp4 gr4 #acdg1 but it still contains water1 and on further evaporation the acid decomposes into sulphuric acid and sulphurous anhydride3 ,h#b,s#b,o#f ,h#b,,so#d ,,so#b4 ,the same decomposition takes place if the solution be slightly heated4 ,like all the thionic acids1 dithionic acid is readily attacked by oxidising agents1 and passes into sulphurous acid4 ,no dithionate is able to withstand the action of heat1 even when very slight1 without giving off sulphurous anhydride3 ,k#b,s#b,o#f ,k#b,,so#d ,,so#b4 ,the alkali dithionates have a neutral reaction 7which indicates the energetic nature of the acid7 are soluble in water1 and in this respect present a certain resemblance to the salts of nitric acid 7their anhydrides are3 ,n#b,o#e and ,s#b,o#e74 ,klss 7#ahhh7 described many of the salts of dithionic acid4 ,langlois1 about #ahdj1 obtained a peculiar thionic acid by heating a strong solution of acid potassium sulphite with flowers of sulphur to about #fj1 until the disappearance of the yellow coloration first produced by the solution of the sulphur4 ,on cooling1 a portion of the sulphur was precipitated1 and crystals of a salt of trithionic acid1 ,k#b,s#c,o#f 7partly mixed with potassium sulphate71 separated out4 ,plessy afterwards showed that the action of sulphurous acid on a thiosulphate also gives sulphur and trithionic acid3 #b,k#b,s#b,o#c #c,,so#b #b,k#b,s#c,o#f ,s4 ,a mixture of potassium acid sulphite and thiosulphate also gives a trithionate4 ,it is very possible that a reaction of the same kind occurs in the formation of trithionic acid by ,langloid's method1 because potassium sulphite and sulphur yield potassium thiosulphate4 ,the potassium thiosulphate may also be replaced by potassium sulphide1 and on passing sulphurous anhydride through the solution thiosulphate is first formed and then trithionate3 #d,,khso#c ,k#b,s #d,,so#b #c,k#b,s#c,o#f #b;,h#b,o4 ,the sodium salt is not formed under the same circumstances as the corresponding potassium salt4 ,the sodium salt does not crystallise and is very unstable3 the barium salt is1 however1 more stable4 ,the barium and potassium salts are anhydrous1 they give neutral solutions and decompose when ignited1 with the evolution of sulphur and sulphurous anhydride1 a sulphate being left behind1 ,k#b,s#c,o#f ,k#b,,so#d ,,so#b ,s4 ,if a solution of the potassium salt be decomposed by means of hydrofluosilicic or chloric acid1 the insoluble salts of these acids are precipitated and trithionic acid is obtained in solution1 which however very easily breaks up on concentration4 ,the addition of salts of copper1 mercury1 silver1 c41 to a solution of a trithionate is followed1 either immediately or after a certain time1 by the formation of a black precipitate of the sulphides whose formation is due to the decomposition of the trithionic acid with the transference of its sulphur to the metal4 ,tetrathionic acid1 ,h#b,s#d,o#f1 in contradistinction to the preceding acids1 is much more stable in the free state than in the form of salts4 ,in the latter form it is easily converted into trithionate1 with liberation of sulphur4 ,sodium tetrathionate was obtained by ,fordos and ,glis1 by the action of iodine on a solution of sodium thiosulphate4 ,the reaction essentially consists in the iodine taking up half the sodium of the thiosulphate1 inasmuch as the latter contains ,na#b,s#b,o#c1 whilst the tetrathionate contains ,na,s#b,o#c or ,na#b,s#d,o#f1 so that the reaction is as follows3 #b,na#b,s#b,o#c ,i#b #b,na,i ,na#b,s#d,o#f4 ,it is evident that tetrathionic acid stands to thiosulphuric acid in exactly the same relation as dithionic acid does to sulphurous acid2 for the same amount of the other elements in dithionate1 ,,kso#c1 and tetrathionate1 ,,ks#b,o#c1 there is half as much metal as in sulphite1 ,k#b,,so#c1 and thiosulphate1 ,k#b,s#b,o#c4 ,if in the above reaction the sodium thiosulphate be replaced by the lead salt ,pb,s#b,o#c1 the sparingly-soluble lead iodide ,pb,i#b and the soluble salt ,pb,s#d,o#f are obtained4 ,moreover the lead salt easily gives tetrathionic acid itself 7,pb,s,o#d is precipitated74 ,the solution of tetrathionic acid may be evaporated over a water-bath1 and afterwards in a vacuum1 when it gives a colourless liquid1 which has no smell and a very acid reaction4 ,when dilute it may be heated to its boiling-point1 but in a concentrated form it decomposes into sulphuric acid1 sulphurous anhydride1 and sulphur3 ,h#b,s#d,o#f ,h#b,,so#d ,,so#b ,s#b4 ,pentathionic acid1 ,h#b,s#e,o#f1 also belongs to this series of acids4 ,but little is known concerning it1 either as hydrate or in salts4 ,it is formed1 together with tetrathionic acid1 by the direct action of sulphurous acid on sulphuretted hydrogen in an aqueous solution2 a large proportion of sulphur being precipitated at the same time3 #e,,so#b #e;,h#b,s ,h#b,s#e,o#f #e,s #d;,h#b,o4 ,if1 as was shown above1 the thionic acids are disulphonic acids1 they may be obtained1 like other sulphonic acids1 by means of potassium sulphite and sulphur chloride4 ,thus ,spring demonstrated the formation of potassium trithionate by the action of sulphur dichloride on a strong solution of potassium sulphite3 #b,,kso#c,k ,s,cl#b ,s7,,so#c,k7#b #b,k,cl4 ,if sulphur chloride be taken1 sulphur also is precipitated4 ,the same trithionate is formed by heating a solution of double thiosulphates2 for example1 of ,ag,k,s#b,o#c4 ,two molecules of the salts then form silver sulphide and potassium trithionate4 ,if the thiosulphate be the potassium silver salt ,,so#c,k7,ag,s71 then the structure of the trithionate must necessarily be 7,,so#c,k7#b,s4 ,previous to ,spring's researches1 the action of iodine on sodium thiosulphate was an isolated accidentally discovered reaction2 he1 however1 showed its general significance by testing the action of iodine on mixtures of different sulphur compounds4 ,thus with iodine1 ,i#b1 the mixture ,na#b,s ,na#b,,so#c forms #b,na,i ,na#b,s#b,o#c1 whilst the mixture ,na#b,s#b,o#c ,na#b,,so#c ,i#b gives #b,na,i ,na#b,s#c,o#f--that is1 trithionic acid stands in the same relation to thiosulphuric acid as the latter does to sulphuretted hydrogen4 ,we adopt the same mode of representation3 by replacing one hydrogen in ,h#b,s by sulphuryl we obtain thiosulphuric acid1 ,,hso#c4;,,hs1 and by replacing a second hydrogen in the latter again by sulphuryl we obtain trithionic acid1 7,,hso#c7b,s4 ,furthermore1 ,spring showed that the action of sodium amalgam on the thionic acids causes reverse reactions to those above indicated for iodine4 ,thus sodium thiosulphate with ,na#b gives ,na#b,s ,na#b,,so#c1 and ,spring showed that the sodium here is not a simple element taking up sulphur1 but itself enters into double decomposition1 replacing sulphur2 for on taking a potassium salt and acting on it with sodium1 ,,kso#c7,,sk7 ,na,na ,,kso#c,na 7,,sk7,na4 ,in a similar way sodium dithionate with sodium gives sodium sulphite3 7,na,s,o#c7b ,na#b #b,na,s,o#c,na2 sodium trithionate forms ,na,s,o#c,na and ,na,s,o#c4,s,na1 and tetrathionate forms sodium thiosulphate1 7,na,s,o#c7,s#b7,na,s,o#c7 ,na#b #b7,na,s,o#c77,na,s74 ,in all the oxidised compounds of sulphur we may note the presence of the elements of sulphurous anhydride1 ,,so#b1 the only product of the combustion of sulphur1 and in this sense the compounds of sulphur containing one ,,so#b are-- ,h ,,ho ,c#f;,h#e ,,hs ,,so#b ,,so#b ,,so#b ,,so#b ,,ho ,,ho ,,ho ,,ho ,sulphurous ,sulphuric ,benzene sulphonic ,thiosulphuric acid acid acid acid while1 according to this mode of representation1 the thionic acids are-- ,,ho ,,ho ,,ho ,,ho ,,so#b ,,so#b ,,so#b ,,so#b ,s ,s#b ,s#c ,,so#b ,,so#b ,,so#b ,,so#b ,,ho ,,ho ,,ho ,,ho ,dithionic ,trithionic ,tetrathionic ,pentathionic ,hence it is evident that ,,so#b has 7whilst ,,co#b has not7 the faculty for combination1 and aims at forming ,,so#b,x#b4 ,these ,x#b can ,o1 and the question naturally suggests itself as to whether the ,o#b which occurs in ,,so#b is not of the same nature as this oxygen which adds itself to ,,so#b--that is1 whether ,,so#b does not correspond with the more general type ,,sx#d1 and its compounds with the type ,,sx#f8 ,to this we may answer ',yes' and ',no'--',yes' in the general sense which proceeds from the investigation of the majority of compounds1 especially metals1 where ,,ro corresponds with ,r,cl#b1 ,,rx#b2 ',no' in the sense that sulphur does not give either ,,sh#d1 ,,sh#f1 or ,s,cl#f1 and therefore the stages ,,sx#d and ,,sx#f are only observable in oxygen compounds4 ,with reference to the type ,,sx#f a hydrate1 ,s7,,ho7#f1 might be expected1 if not ,s,cl#f4 ,and we must recognise this hydrate from a study of the compounds of sulphuric acid with water4 ,in addition to what has been already said respecting the complex acids formed by sulphur1 ,i think it well to mention that1 according to the above view1 still more complex oxygen acids and salts of sulphur may be looked for4 ,for instance1 the salt ,na#b,s#d,o#h obtained by ,villiers 7#ahhh7 is of this kind4 ,it is formed together with sodium trithionate and sulphur1 when ,,so#b is passed through a cold solution of ,na#b,s#b,o#c1 which is then allowed to stand for several days at the ordinary temperature3 #b,na#b,s#b,o#c #d,,so#b ,na#b,s#d,o#h ,na#b,s#c,o#f ,s4 ,it may be assumed here1 as in the thionic acids1 that there are two sulphoxyls1 bound together not only by ,s1 but also by ,,so#b1 or what is almost the same thing1 that the sulphoxyl is combined with the residue of trithionic acid1 i4e4 replaces one aqueous residue in trithionic acid4 ,sulphur exhibits an acid character1 not only in its compounds with hydrogen and oxygen1 but also in those with other elements4 ,the compound of sulphur and carbon has been particularly well investigated4 ,it presents a great analogy to carbonic anhydride1 both in its elementary composition and chemical character4 ,this substance is the so-called carbon bisulphide1 ,,cs#b1 and corresponds with ,,co#b4 ,the first endeavours to obtain a compound of sulphur with carbon were unsuccessful1 for although sulphur does combine directly with carbon1 yet the formation of this compound requires distinctly definite conditions4 ,if sulphur be mixed with charcoal and heated1 it is simply driven off from the latter1 and not the smallest trace of carbon bisulphide is obtained4 ,the formation of this compound requires that the charcoal should be first heated to a red heat1 but not above1 and then either the vapour of sulphur passed over it or lumps of sulphur thrown on to the red-hot charcoal1 but in small quantities1 so as not to lower the temperature of the latter4 ,if the charcoal be heated to a white heat1 the amount of carbon bisulphide formed is less4 ,this depends1 in the first place1 on the carbon bisulphide dissociating at a high temperature4#fi ,in the second place1 ,favre and ,silberman showed that in the combustion of one gram of carbon bisulphide 7the products will be ,,co#b #b,,so#b7 #c1djj heat units are evolved--that is1 the combustion of a molecular quantity of carbon bisulphide evolves #beh1djj heat units 7according to ,berthelot1 #bdf1jjj74 ,from a molecule of carbon bisulphide in grams we may obtain #ab grams of carbon1 whose combustion evolves #if1jjj heat units1 and #fd grams of sulphur1 evolving by combustion 7into ,,so#b7 #adj1hjj heat units4 ,hence we see that the component elements separately evolve less heat by their combustion 7#bcg1jjj heat units7 than carbon bisulphide itself--that is1 that heat should be evolved 7at the ordinary temperature7 and not absorbed in its decomposition1 and therefore that the formation of carbon bisulphide from charcoal and sulphur is in all probability accompanied by an absorption of heat4#gj ,it is therefore not surprising that1 like other compounds produced with an absorption of heat 7ozone1 nitrous oxide1 hydrogen peroxide1 c471 carbon bisulphide is unstable and easily converted into the original substances from which it is obtained4 ,and indeed if the vapour of carbon bisulphide be passed through a red-hot tube1 it is decomposed--that is1 it dissociates--into sulphur and carbon4 ,and this takes place at the temperature at which this substance is formed1 just as water decomposes into hydrogen and oxygen at the temperature of its formation4 ,in this absorption of heat in the formation of carbon bisulphide is explained the facility with which it suffers reactions of decomposition1 which we shall see in the sequel1 and its main difference from the closely analogous carbonic anhydride4 ,illustration3 ,,fig4 #ij4--;,apparatus for the manufacture of carbon bisulphide4 #fi ,even light decomposes carbon bisulphide1 but not to the extent of separating carbon2 under the action of the sun's rays it is decomposed into sulphur and solid substance which is considered to be carbon monosulphide2 it is of a red colour1 and its sp4 gr4 is #aff4 7,the formation of a red liquid compound ,c#c,s#b has also been remarked47 ,thorpe 7#ahhi7 observed a complete decomposition of carbon bisulphide under the action of a liquid alloy of potassium and sodium2 it is accompanied by an explosion and the deposition of carbon and sulphur4 ,a similar complete decomposition of carbon bisulphide is also accomplished by the action of mercury fulminate 7,chapter ,,xvi41 ,note #bf71 and is due to the fact that at the ordinary temperature 7at which carbon bisulphide is not produced7 the decomposition of carbon bisulphide takes place with the development of heat--that is1 it presents an exothermal reaction1 like the decomposition of all explosives4 ,it is very possible that at a higher temperature1 when carbon bisulphide is formed1 the combination of carbon with sulphur is also an exothermal reaction--that is1 heat is developed4 ,if this should be the case1 carbon bisulphide would present a most instructive example in thermochemistry4 #gj ,the fact should not be lost sight of that sulphur and charcoal are solids at the ordinary temperature1 whilst carbon bisulphide is a very volatile liquid1 and consequently1 in the act of combination1 referred to the ordinary temperature 7,note #fi71 there is1 as it were1 a passage into a liquid state1 and this requires the absorption of heat4 ,and furthermore1 the molecule of sulphur contains at least six atoms1 and the molecule of carbon in all probability 7,chapter ,,viii47 a very considerable number of atoms2 thus the reaction of sulphur on charcoal may be expressed in the following manner3 #c;,cn n,s#f #cn,,cs#b--that is1 from n #c molecules there proceed #cn molecules1 and as n must be very considerable1 #cn must be greater than #c n1 which indicates a decomposition in the formation of carbon bisulphide1 although the reaction at first sight appears as one of combination4 ,this decomposition is seen also from the volumes in the solid and liquid states4 ,carbon bisulphide has a sp4 gr4 of #abi2 hence its molecular volume is #ei4 ,but the volume of carbon1 even in the form of charcoal1 is not more than #f1 and the volume of ,s#b is #cj2 hence #cf volumes after combination give #ei volumes--an expansion takes place1 as in decompositions4 ,in the laboratory carbon bisulphide is prepared as follows3 ,a porcelain tube is luted into a furnace in an inclined position1 the upper extremity of the tube being closed by a cork1 and the lower end connected with a condenser4 ,the tube contains charcoal1 which is raised to a red heat1 and then pieces of sulphur are placed in the upper end4 ,the sulphur melts1 and its vapour comes into contact with the red-hot charcoal1 when combination takes place2 the vapours condense in the condenser1 carbon bisulphide being a liquid boiling at #dh4 ,on a large scale the apparatus depicted in fig4 #ij is employed4 ,a cast-iron cylinder rests on a stand in a furnace4 ,wood charcoal is charged into the cylinder through the upper tube closed by a clay stopper1 whilst the sulphur is introduced through a tube reaching to the bottom of the cylinder4 ,pieces of sulphur thrown into this tube fall on to the bottom of the cylinder1 and are converted into vapour1 which passes through the entire layer of charcoal in the cylinder4 ,the vapour of carbon bisulphide thus formed passes through the exit tube first into a ,woulfe's bottle 7where the sulphur which has not entered into the reaction is condensed71 and then into a strongly-cooled condenser or worm4#ga #ga ,carbon bisulphide1 as prepared on a large scale1 is generally very impure1 and contains not only sulphur1 but1 more especially1 other impurities which give it a very disagreeable odour4 ,the best method of purifying this malodorous carbon bisulphide is to shake it up with a certain amount of mercuric chloride1 or even simply with mercury1 until the surface of the metal ceases to turn black4 ,after this the carbon bisulphide must be poured off and distilled over a water-bath1 after mixing with some oil to retain the impurities4 ,pure carbon bisulphide is a colourless liquid1 which refracts light strongly1 and has a pure ethereal smell2 at #j its specific gravity is #abic1 and at #ae #abga4 ,if kept for a long time it seems to undergo a change1 especially when it is kept under water1 in which it is insoluble4 ,it boils at #dh1 and the tension of its vapour is so great that it evaporates very easily1 producing cold1#gb and therefore it has to be kept in well-stoppered vessels2 it is generally kept under a layer of water1 which hinders its evaporation and does not dissolve it4#gc #gb ,if carbon bisulphide be evaporated under the receiver of an air-pump1 or by means of a current of air1 it is possible to obtain a temperature as low as -#fj1 and the carbon bisulphide does not solidify at this temperature4 ,however1 if a series of air-bubbles be passed through it by means of bellows1 a crystalline white substance remains which volatilises below #j3 this a hydrate1 ,h#b,o1#b;,,cs#b2 it easily decomposes into water and carbon bisulphide4 ,it is formed in the above experiment by the moisture held in the air passed through the carbon bisulphide1 and the fall of temperature4 #gc ,strong alcohol is miscible in all proportions with carbon bisulphide1 but dilute alcohol only in a definite amount1 owing to its diminished solubility from the presence of the water in it4 ,ether1 hydrocarbons1 fatty oils1 and many other organic substances are soluble with great ease in carbon bisulphide4 ,this is taken advantage of in practice for extracting the fatty oils from vegetable seeds1 such as linseed1 palm-nuts1 or from bones1 c4 ,the preparation of vegetable oils is usually done by pressing the seeds under a press1 but the residue always contains a certain amount of oil4 ,these traces of oil can1 however1 be removed by treatment with carbon bisulphide4 ,in this manner a solution is obtained which when heated easily parts with all the carbon bisulphide1 leaving the non-volatile fatty oil behind1 so that the same carbon bisulphide may be condensed and used over again for the same purpose4 ,it also dissolves iodine1 bromine1 indiarubber1 sulphur1 and tars4 ,carbon bisulphide1 especially at high temperatures1 very often acts by its elements in a manner in which carbon and sulphur alone are not able to react1 which will be understood from what has been said above respecting its endothermal origin4 ,if it be passed over red-hot metals--even over copper1 for instance1 not to mention sodium1 c4--it forms a sulphide of the metal and deposits charcoal1 and if the vapour be passed over incandescent metallic oxides it forms metallic sulphides and carbonic anhydride 7and sometimes a certain amount of sulphurous anhydride74 ,lime and similar oxides give under these circumstances a carbonate and a sulphide--for example1 ,,cs#b #c;,ca,o #b;,ca,s ,ca,c,o#c4 ,the sulphides obtained by this means are often well crystallised1 like those found in nature--for example1 lead and antimony sulphides4 ,carbon bisulphide enters into many combinations1 which are frequently closely analogous to the compounds of carbonic anhydride4 ,in this respect it is a thio-anhydride--i4e4 it has the character of the acid anhydrides1#gc bis like carbonic anhydride1 with the difference that the oxygen of the latter is replaced by sulphur4 ,by thio-compounds in general are understood those compounds of sulphur which differ from the compounds of oxygen as carbon bisulphide does from carbonic anhydride--that is1 which correspond with the oxygen compounds1 but with substitution of sulphur for oxygen4 ,thus thiosulphuric acid is monothiosulphuric acid--that is1 sulphuric acid in which one atom of sulphur replaces one atom of oxygen4 ,with the sulphides of the alkalis and alkaline earths1 it forms saline substances corresponding with the carbonates1 and these compounds may be termed thiocarbonates4 ,for example1 the composition of the sodium salt ,na#b;,,cs#c is exactly like that of sodium carbonate4 ,they are formed by the direct solution of carbon bisulphide in aqueous solutions of the sulphides2 but they are difficult to obtain in a crystalline form1 because they are easily decomposable4 ,when the solutions of these salts are highly concentrated they begin to decompose1 with the evolution of sulphuretted hydrogen and the formation of a carbonate1 water taking part in the reaction--for example1 ,k#b;,,cs#c #c;,h#b,o ,k#b;,,co#c #c;,h#b,s4#gd #gc bis ,and just as ,c,o,cl#b corresponds to ,,co#b1 so also the chloranhydride1 ,c,s,cl#b1 or thiophosgene1 corresponds to ,,cs#b4 #gd ,if instead of a sulphide we take an alkali hydroxide1 a thiocarbonate is also formed1 together with a carbonate--thus1 #c;,ba,h#b,o#b #c;,,cs#b #b;,ba,c,s#c ,ba,c,o#c #c;,h#b,o4 ,from the instability of the thiocarbonates of the alkaline metals we can clearly see the reason of the difficulty with which the salts of the heavier metals are formed1 whose basic properties are incomparably weaker than those of the alkali metals4 ,however1 these salts may be obtained by double decomposition4 ,ammonia in reacting on carbon bisulphide gives1 besides products like those formed by other alkalis1 a whole series of products of as complex a structure as those substances which are produced by the action of carbonic anhydride on ammonia4 ,in the ninth chapter we examined the formation of the ammonium carbonates1 and saw the transition from them into the cyanides4 ,it is not surprising after this that the action of carbon bisulphide on ammonia not only produces the above-mentioned salts1 but also amidic compounds corresponding with them1 in which the oxygen is wholly or partially replaced by sulphur4 ,thus ammonium dithiocarbamate is very easily obtained if carbon bisulphide be added to an alcoholic solution of ammonia1 and the mixture cooled in a closed vessel4 ,the salt then separates out in minute yellow crystals1 ,,cn#b;,h#f,s#b4 ,carbon bisulphide not only forms compounds with the metallic sulphides1 but also with sulphuretted hydrogen--that is1 it forms thiocarbonic acid1 ,h#b;,,cs#c4 ,this is obtained by carefully mixing solutions of thiocarbonates with dilute hydrochloric acid4 ,it then separates in an oily layer1 which easily decomposes in the presence of water into sulphuretted hydrogen and carbon bisulphide1 just as the corresponding carbonic acid 7hydrate7 decomposes into water and carbonic anhydride4 ,carbon bisulphide combines not only with sodium sulphide1 but also with the bisulphide1 ,na#b,s#b1 not1 however1 with the trisulphide1 ,na#b,s#c4 ,the relation of carbon bisulphide to the other carbon compounds presents many most interesting features which are considered in organic chemistry4 ,we will here only turn our attention to one of the compounds of this class4 ,ethyl sulphide1 7,c#b;,h#e7b,s1 combines with ethyl iodide1 ,c#b;,h#e;,i1 forming a new molecule1 ,s7,c#b;,h#e7c;,i4 ,if we designate the hydrocarbon group1 for instance ethyl1 ,c#b;,h#e1 by ,et1 the reaction would be expressed by the following equation 3 ,et#b,s ,et,i ,s,et#c;,i4 ,this compound is of a saline character1 corresponds with salts of the alkalis1 and is closely analogous to ammonium chloride4 ,it is soluble in water2 when heated it again splits up into its components ,et,i and ,et#b,s1 and with silver hydroxide gives a hydroxide1 ,et#c,s,,oh1 having the property of a distinct and energetic alkali1 resembling caustic ammonia4 ,thus the compound group ,s,et#c combines1 like potassium or ammonium1 with iodine1 hydroxyl1 chlorine1 c4 ,the hydroxide ,s,et#c,,oh is soluble in water1 precipitates metallic salts1 saturates acids1 c4 ,hence sulphur here enters into a relation towards other elements similar to that of nitrogen in ammonia and ammonium salts1 with only this difference1 that nitrogen retains1 besides iodine1 hydroxyl1 and other groups1 also ,h#d or ,et#d 7for example1 ,,nh#d;,cl1 ,n,et#c;,,hi1 ,n,et#d;,i71 whilst sulphur only retains ,et#c4 ,compounds of the formula ,,sh#c,x are however unknown1 only the products of substitution ,s,et#c,x1 c4 are known4 ,the distinctly alkaline properties of the hydroxide1 triethylsulphine hydroxide1 ,s,et#c,,oh1 and also the sharply-defined properties of the corresponding hydroxide1 tetraethylammonium hydroxide1 ,n,et#d,,oh1 depend naturally not only on the properties of the nitrogen and sulphur entering into their composition1 but also on the large proportion of hydrocarbon groups they contain4 ,judging from the existence of the ethylsulphine compounds1 it might be imagined that sulphur forms a compound1 ,,sh#d1 with hydrogen2 but no such compound is known1 just as ,,nh#e is unknown1 although ,,nh#d;,cl exists4 ,a remarkable example#gd bis of the thio-compounds is found in thiocyanic acid--i4e4 cyanic acid in which the oxygen is replaced by sulphur1 ,,hcns4 ,we know 7,chapter ,,ix47 that with oxygen the cyanides of the alkaline metals ,,rcn give cyanates ,,rcno2 but they also combine with sulphur1 and therefore if yellow prussiate of potash be treated as in the preparation of potassium cyanide1 and sulphur be added to the mass1 potassium thiocyanate1 ,,kncs1 is obtained in solution4 ,this salt is much more stable than potassium cyanate2 it dissolves without change in water and alcohol1 forming colourless solutions from which it easily crystallises on evaporation4 ,it may be kept exposed to air even when in solution2 in dissolving in water it absorbs a considerable amount of heat1 and forms a starting-point for the preparation of all the thiocyanates1 ,,rcns1 and organic compounds in which the metals are replaced by hydrocarbon groups4 ,such1 for example1 is volatile mustard oil1 ,c#c;,h#e;,,csn 7allyl thiocyanate71#ge which gives to mustard its caustic properties4 ,with ferric salts the thiocyanates give an exceedingly brilliant red coloration1 which serves for detecting the smallest traces of ferric salts in solution4 ,thiocyanic acid1 ,,hcns1 may be obtained by a method of double decomposition1 by distilling potassium thiocyanate with dilute sulphuric acid4 ,it is a volatile colourless liquid1 having a smell recalling that of vinegar1 is soluble in water1 and may be kept in solution without change4#ge bis #gd bis ,thorpe and ,rodger 7#ahhi71 by heating a mixture of lead fluoride and phosphorus pentasulphide to #bej in an atmosphere of dry nitrogen1 obtained gaseous phosphorus fluosulphide1 or thiophosphoryl fluoride1 ,,psf#c1 corresponding with ,p,o,cl#c4 ,this colourless gas is converted into a colourless liquid by a pressure of eleven atmospheres2 it does not act on dry mercury1 and takes fire spontaneously in air or oxygen1 forming phosphorus pentafluoride1 phosphoric anhydride1 and sulphurous anhydride4 ,it is soluble in ether1 but is decomposed by water3 ,,psf#c #d;,h#b,o ,h#b,s ,h#c,,po#d #c;,,hf 7,note #bj74 #ge ,although mustard oil may be obtained from the thiocyanates1 it is only an isomer of allyl thiocyanate proper1 as is explained in ,organic ,chemistry4 #ge bis ,sulphur can only replace half the oxygen in ,,co#b1 as is seen in carbon oxysulphide1 or monothiocarbonic anhydride ,,cos4 ,this substance was obtained by ,than1 and is formed in many reactions4 ,a certain amount is obtained if a mixture of carbonic oxide and the vapour of sulphur be passed through a red-hot tube4 ,when carbon tetrachloride is heated with sulphurous anhydride1 this substance is also formed2 but it is best obtained in a pure form by decomposing potassium thiocyanate with a mixture of equal volumes of water and sulphuric acid4 ,a gas is then evolved containing a certain amount of hydrocyanic acid1 from which it may be freed by passing it over wool containing moistened mercuric oxide1 which retains the hydrocyanic acid4 ,the reaction is expressed by the equation3 #b,,kcns #b;,h#b,,so#d #b;,h#b,o ,k#b,,so#d 7,,nh#d7b,,so#d #b;,,cos4 ,it is also formed by passing the vapour of carbon bisulphide over alumina or clay heated to redness 7,gautier2 silicon sulphide is then formed74 ,,cos is also formed by passing phosgene over a long layer of asbestos mixed with cadmium sulphide at #bgj2 ,cd,s ,c,o,cl#c ,cd,cl#b ,,cos 7,nuricsn1 #ahib74 ,the pure gas has an aromatic odour1 is soluble in an equal volume of water1 which1 however1 acts on it1 so that it must be collected over mercury4 ,when slightly heated1 carbon oxysulphide decomposes into sulphur and carbonic oxide4 ,it burns in air with a pale blue flame1 explodes with oxygen1 and yields potassium sulphide and carbonate with potassium hydroxide3 ,,cos #d,,kho ,k#b;,,co#c ,k#b,s #b;,h#b,o4 ,the sulphur compounds of chlorine ,cl#b,s and ,cl#b,s#b may be regarded on the one hand as products of the metalepsis of the sulphides of hydrogen1 ,h#b,s and ,h#b,s#b2 and on the other hand of the oxygen compounds of chlorine1 because chloride of sulphur1 ,cl#b,s1 resembles chlorine oxide1 ,cl#b,o1 whilst ,cl#b,s#b corresponds with the higher oxide of chlorine2 or thirdly1 we may see in these compounds the type of the acid chloranhydrides1 because they are all decomposed by water1 forming hydrochloric acid1 and sulphur tetrachloride1 ,s,cl#d1 is decomposed with the formation of sulphurous anhydride4#gf #gf ,there is no reason for seeing any contradiction or mutual incompatibility in these three views1 because every analogy is more or less modified by a change of elements4 ,thus1 for instance1 it cannot be expected that the product of the metalepsis of hydrogen sulphide would resemble the corresponding products of water in all respects1 because water has not the acid properties of hydrogen sulphide4 ,in the days of dualism and electrical polarity it was supposed that the sulphur varied in its nature3 in hydrogen sulphide or potassium sulphide it was considered to be negative1 and in sulphurous anhydride or sulphur dichloride positive4 ,it then appeared evident that sulphur dichloride would have no point of analogy with potassium sulphide4 ,but metalepsis1 or its expression in the law of substitution1 necessitates such opinions being laid aside4 ,if we can compare ,,co#b1 ,,ch#d1 ,c,cl#d1 ,c,h,cl#c1 ,,ch#c7,,oh7 with each other1 we cannot recognise any difference in the sulphur in ,,sh#b1 ,s,cl#b1 ,,sk#b1 or in general ,,sx#b1 for otherwise we should have to acknowledge as many different states of sulphur1 carbon1 or hydrogen as there are compounds of sulphur1 carbon1 or hydrogen4 ,the essential truth of the matter is that all the elements in a molecule play their part in the reactions into which it enters4 ,often this appears to be contradicted in the result--for example1 hydrogen alone may be replaced2 but it is not this hydrogen alone that has determined the reaction2 all the elements present have participated in it4 ,this may be made clearer by the following rough illustration4 ,supposing two regiments of soldiers were fighting against each other1 and that several men were lost by one of the regiments2 no one could say that it was only these men who took part in the engagement4 ,the other men fired and the bullets flew over the heads of their opponents4 ,it was not only those who fell who fought1 although they only were removed from the field of battle2 the fighting proceeded among the masses1 but only those few were disabled who went forward and were more conspicuous c42 not that the remainder did not take part in the action2 they also fought and were an object of attack1 only they remained sound and unhurt4 ,hydrogen is lighter than other elements and its atoms more mobile2 it subjects itself more frequently and easily to reactions2 but it is not it alone which reacts1 it is even less liable to attack than other elements4 ,it participates in exceedingly diverse reactions1 not indeed because the hydrogen itself varies1 but because one atom of it puts itself forward1 another is hidden1 one is united with carbon1 another feebly held by sulphur1 one stands or moves in the neighbourhood of oxygen1 another is joined to a hydrocarbon4 ,all hydrogen atoms are equal1 and equally serve as an object of attack for the atoms of molecules encountering them1 but those only are removed from the sphere of action which are nearer the surface of a molecule1 which are more mobile1 or held by a less sum of forces4 ,so also sulphur is one and the same in sulphur dichloride1 in sulphurous or sulphuric anhydride1 in hydrogen sulphide1 in potassium sulphide1 but it reacts differently1 and those elements which are with it also vary in their reactions because they are with it1 and it varies its reactions because it is with them4 ,it is possible to seize on a character common to substances quantitatively and qualitatively analogous to each other4 ,it may be admitted that an element in certain forms is not able to enter into reactions into which in other forms it enters willingly1 if only the requisite conditions are encountered2 but it must not therefore be concluded that an element changes its essential quality in these different cases4 ,the preceding remarks touch on questions which are subject to much argument among chemists1 and ,i mention them here in order to show the treatment of those most important problems of chemistry which lie at the basis of this treatise4 ,illustration3 ,,fig4 #ia4--;,apparatus for the preparation of sulphur chloride1 and similar volatile compounds prepared by combustion in a stream of chlorine4 ,the compounds of sulphur with chlorine are prepared in the apparatus depicted in fig4 #ia4 ,as sulphur chloride is decomposed by water1 the chlorine evolved in the flask ,c must be dried before coming into contact with the sulphur4 ,it is therefore first passed through a ,woulfe's bottle1 ,b1 containing sulphuric acid1 and then through the cylinder ,d containing pumice stone moistened with sulphuric acid1 and then led into the retort ,e1 in which the sulphur is heated4 ,the compound which is formed distils over into the receiver ,r4 ,a certain amount of sulphur passes over with the sulphur chloride1 but if the resultant distillate be re-saturated with chlorine and distilled no free sulphur remains1 the boiling-point rises to #add1 and pure sulphur chloride1 ,s#b;,cl#b1 is obtained4 ,it has this formula because its vapour density referred to hydrogen is #fh4 ,it is also obtained by heating certain metallic chlorides 7stannous1 mercuric7 with sulphur2 both the metal and chlorine then combine with the sulphur4 ,sulphur chloride is a yellowish-brown liquid1 which boils at #add1 and has a specific gravity of #agj at #j4 ,it fumes strongly in the air1 reacting on the moisture contained therein1 and has a heavy chloranhydrous odour4 ,it dissolves sulphur1 is miscible with carbon bisulphide1 and falls to the bottom of a vessel containing water1 by which it is decomposed1 forming sulphurous anhydride and hydrochloric acid2 but it first forms various lower stages of oxidation of sulphur1 because the addition of silver nitrate to the solution gives a black precipitate4 ,with hydrogen sulphide it gives sulphur and hydrochloric acid1 and it reacts directly with metals--especially arsenic1 antimony1 and tin--forming sulphides and chlorides4 ,in the cold1 it absorbs chlorine and gives sulphur dichloride1 ,s,cl#b4 ,the entire conversion into this substance requires the prolonged passage of dry chlorine through sulphur chloride surrounded by a freezing mixture4 ,the distillation of the dichloride must be conducted in a stream of chlorine1 as otherwise it partially decomposes into sulphur chloride and chlorine4 ,pure sulphur dichloride is a reddish-brown liquid1 which resembles the lower chloride in many respects2 its specific gravity is #afb2 its odour is more suffocating than that of sulphur chloride2 it volatilises at #fd4gg #gg ,the observed vapour density of sulphur dichloride referred to hydrogen is #ecc1 and that given by the formula is #eae4 ,the smaller molecular weight explains its boiling point being lower than that of sulphur chloride1 ,s#b;,cl#b4 ,the reactions of both these compounds are very similar4 ,sulphur converts the dichloride1 ,s,cl#b1 into the monochloride1 ,s#b;,cl#b4 ,in one point the dichloride differs distinctly from the monochloride--that is1 in its capacity for easily giving up chlorine and decomposing4 ,even light decomposes it into chlorine and the monochloride4 ,hence it acts on many substances in the same manner as chlorine1 or substances which easily part with the latter1 such as phosphoric or antimonic chloride4 ,in distinction to these1 however1 sulphur dichloride would appear to distil without any considerable decomposition1 judging by the vapour density4 ,but this is not a valid conclusion1 for if there be a decomposition1 then #b,s,cl#b ,s#b;,cl#b ,cl#b2 now the density of sulphur chloride #fge1 and of chlorine #cee1 and consequently a mixture of equal volumes of the two #eae1 just the same as an equal volume of sulphur dichloride4 ,therefore the distillation of sulphur dichloride is probably nothing but its decomposition4 ,hence the compound ,s,cl#b1 which is stable at the ordinary temperature1 decomposes at #fd4 ,in the cold it absorbs a further amount of chlorine1 corresponding to ,s,cl#d1 but even at -#aj a portion of the absorbed chlorine is given off--that is1 dissociation takes place4 ,thus the tetrachloride is even less stable than the dichloride4 ,thionyl chloride1 ,s,o,cl#b1 may be regarded as oxidised sulphur dichloride2 it corresponds with sulphur chloride1 ,s#b;,cl#b1 in which one atom of sulphur is replaced by oxygen4 ,at the same time it is chlorine oxide 7hypochlorous anhydride1 ,cl#b,o7 combined with sulphur1 and also the chloranhydride of sulphurous acid--that is1 ,,so7,,ho7#b1 in which the two hydroxyl groups are replaced by two atoms of chlorine1 or sulphurous anhydride1 ,,so#b1 in which one atom of oxygen is replaced by two atoms of chlorine4 ,all these representations are confirmed by reactions of formation1 or decompositions2 they all agree with our notions of the other compounds of sulphur1 oxygen1 and chlorine2 hence these definitions are not contradictory to each other4 ,thus1 for instance1 thionyl chloride was first obtained by ,schiff1 by the action of dry sulphurous anhydride on phosphorus pentachloride4 ,on distilling the resultant liquid1 thionyl chloride comes over first at #hj1 and on continuing the distillation phosphorus oxychloride distils over at above #ajj1 ,p,cl#e ,,so#b ,p,o,cl#c ,s,o,cl#b4 ,this mode of preparation is direct evidence of the oxychloride character of ,s,o,cl#b4 ,wrtz obtained the same substance by passing a stream of chlorine oxide through a cold solution of sulphur in sulphur chloride2 the chlorine oxide then combined directly with the sulphur1 ,s ,cl#b,o ,s,o,cl#b1 whilst the sulphur chloride remained unchanged 7sulphur cannot be combined directly with chlorine oxide1 as an explosion takes place74 ,thionyl chloride is a colourless liquid1 with a suffocating acrid smell2 it has a specific gravity at #j of #afge1 and boils at #gh4 ,it sinks in water1 by which it is immediately decomposed1 like all chloranhydrides--for example1 like carbonyl chloride1 which corresponds with it3 ,s,o,cl#b ,h#b,o ,,so#b #b;,h,cl4#gg bis #gg bis ,hartog and ,sims 7#ahic7 obtained thionyl bromide1 ,s,o,br#b1 by treating ,s,o,cl#b with sodium bromide2 it is a red liquid1 sp4 gr4 #bfb1 and decomposes at #aej4 ,normal sulphuric acid has two corresponding chloranhydrides2 the first1 ,,so#b7,,oh7,cl1 is sulphuric acid1 ,,so#b7;,,ho7#b1 in which one equivalent of ,,ho is replaced by chlorine2 the second has the composition ,,so#b;,cl#b--that is1 two ,,ho groups are substituted by two of chlorine4 ,the second chloranhydride1 or the compound ,,so#b;,cl#b1 is called sulphuryl chloride1 and the first chloranhydride1 ,,so#b;,h,o,cl1 may be called chlorosulphonic acid1 because it is really an acid2 it still retains one hydroxyl of sulphuric acid1 and its corresponding salts are known4 ,thus1 potassium chloride absorbs the vapour of sulphuric anhydride1 forming a salt1 ,,so#c,k,cl1 corresponding with ,,so#c;,h,cl as acid4 ,in acting on sodium chloride it forms hydrochloric acid and the salt ,na,s,o#c;,cl4 ,this first chloranhydride of sulphuric acid1 ,,so#b;,h,o,cl1 discovered by ,williamson1 is obtained either by the action of phosphorus pentachloride on sulphuric acid 7,p,cl#e ,h#b,,so#d ,p,o,cl#c ,h,cl ,,hso#c;,cl71 or directly by the action of dry hydrochloric acid on sulphuric anhydride1 ,,so#c ,h,cl ,,hso#c;,cl4 ,the most easy and rapid method of its formation is by direct saturation of cold ,nordhausen acid with dry hydrochloric acid gas 7,,so#c ,h,cl ,,hso#c;,cl71 and distillation of the resultant solution2 the distillate then contains ,,hso#c;,cl4 ,it is a colourless fuming liquid1 having an acrid odour2 it boils at #aec 7according to my determination1 confirmed by ,konovaloff71 and its specific gravity at #ai is #aggf4 ,it is immediately decomposed by water1 forming hydrochloric and sulphuric acids1 as should be the case with a true chloranhydride4 ,in the reactions of this chloranhydride we find the easiest means of introducing the sulphonic group ,,hso#c into other compounds1 because it is here combined with chlorine4 ,the second chloranhydride of sulphuric acid1 or sulphuryl chloride1 ,,so#b;,cl#b1 was obtained by ,regnault by the direct action of the sun's ray on a mixture of equal volumes of chlorine and sulphurous oxide4 ,the gases gradually condense into a liquid1 combining together as carbonic oxide does with chlorine4 ,it is also obtained when a mixture of the two gases in acetic acid is allowed to stand for some time4 ,the first chloranhydride1 ,,so#c;,h,cl1 decomposes when heated at #bjj in a closed tube into sulphuric acid and sulphuryl chloride4 ,it boils at #gj1 its specific gravity is #ag1 it gives hydrochloric and sulphuric acids with water1 fumes in the air1 and1 judging by its vapour density1 does not decompose when distilled4#gh #gh ,pyrosulphuryl chloride1 ,s#b,o#e;,cl#b4 ,see ,note #dd4 ,thorpe and ,kirman1 by treating ,,so#c with ,,hf1 obtained ,,so#b7,,oh7,f1 as a liquid boiling at #afc1 but which decomposed with greater facility and then gave ,,so#b;,f#b4 ,the acids of sulphur naturally have their corresponding ammonium salts1 and the latter their amides and nitriles4 ,it will be readily understood how vast a field for research is presented by the series of compounds of sulphur and nitrogen1 if we only remember that to carbonic and formic acids there corresponds1 as we saw 7,chapter ,,ix471 a vast series of derivatives corresponding with their ammonium salts4 ,to sulphuric acid there correspond two ammonium salts1 ,,so#b7;,,ho77,,nh#d,o7 and ,,so#b7,,nh#d,o7#b2 three amides3 the acid amide ,,so#b7;,,ho77,,nh#b71 or sulphamic acid1 the normal saline compound ,,so#b7,,nh#d,o77,,nh#b71 or ammonium sulphamate1 and the normal amide ,,so#b7,,nh#b7b1 or sulphamide 7the analogue of urea72 then the acid nitrile1 ,,son7,,ho71 and two neutral nitriles1 ,,son7,,nh#b7 and ,,sn#b4 ,there are similar compounds corresponding with sulphurous acid1 and therefore its nitriles will be1 an acid1 ,,sn7,,ho71 its salt1 and the normal compound1 ,,sn7,,nh#b74 ,dithionic and the other acids of sulphur should also have their corresponding amides and nitriles4 ,only a few examples are known1 which we will briefly describe4 ,sulphuric acid forms salts of very great stability with ammonia1 and ammonium sulphate is one of the commonest ammoniacal compounds4 ,it is obtained by the direct action of ammonia on sulphuric acid1 or by the action of the latter on ammonium carbonate2 it separates from its solutions in an anhydrous state1 like potassium sulphate1 with which it is isomorphous4 ,hence1 the composition of crystals of ammonium sulphate is 7,,nh#d7b,,so#d4 ,this salt fuses at #adj1 and does not undergo any change when heated up to #ahj4 ,at higher temperatures it does not lose water1 but parts with half its ammonia1 and is converted into the acid salt1 ,,hnh#d,,so#d2 and this acid salt1 on further heating1 undergoes a further decomposition1 and splits up into nitrogen1 water1 and acid ammonium sulphite1 ,,hnh#d,,so#c4 ,at the ordinary temperature the normal salt is soluble in twice its weight of water and at the boiling-point of water in an equal weight4 ,in its faculty for combinations this salt exhibits a great resemblance to potassium sulphate1 and1 like it1 easily forms a number of double salts2 the most remarkable of which are the ammonia alums1 ,,nh#d;,al,s#b,o#h1ab;,h#b,o1 and the double salts formed by the metals of the magnesium group1 having1 for example1 the composition 7,,nh#d7b,mg,s#b,o#h1f;,h#b,o4 ,ammonium sulphate does not give an amide when heated1 perhaps owing to the faculty of sulphuric anhydride to retain the water combined with it with great force4 ,but the amides of sulphuric acid may be very conveniently prepared from sulphuric anhydride4 ,their formation by this method is very easily understood because an amide is equal to an ammonium salt less water1 and if the anhydride be taken it will give an amide directly with ammonia4 ,thus1 if dry ammonia be passed into a vessel surrounded by a freezing mixture and containing sulphuric anhydride1 it forms a white powdery mass called sulphatammon1 having the composition ,,so#c1b;,h#c,n1 and resembling the similar compound of carbonic acid1 ,,co#b1b,,nh#c4 ,this substance is naturally the ammonium salt of sulphamic acid1 ,,so#b7,,nh#d,o7,,nh#b4 ,it is slowly acted on by water1 and may therefore be obtained in solution1 in which it slowly reacts with barium chloride1 which proves that with water it still forms ammonium sulphate4 ,if this substance be carefully dissolved in water and evaporated1 it yields well-formed crystals1 whose solution no longer gives a precipitate with barium chloride4 ,this is not due to the presence of impurities1 but to a change in the nature of the substance1 and therefore ,rose calls the crystalline modification parasulphatammon4 ,platinum chloride only precipitates half the nitrogen as platinochloride from solutions of sulphat- and parasulphatammon1 which shows that they are ammonium salts1 ,,so#b7,,nh#d,o77,,nh#b74 ,it may be that the reason of the difference in the two modifications is connected with the fact that two different substances of the composition ,n#b;,h#d,,so#b are possible3 one is the amide ,,so#b7,,nh#b7b corresponding with the normal salt1 and the other is the salt of the nitrile acid corresponding with acid ammonium sulphate--that is1 ,,son7,,onh#d7 corresponds with the acid ,,son7,,oh7 ,,so#b7,,nh#d,o7,,oh - #b;,h#b,o4 ,hence there may here be a difference of the same nature as between urea and ammonium cyanate4 ,up to the present1 the isomerism indicated above has been but little investigated1 and might be the subject of interesting researches4 ,if in the preceding experiment the ammonia1 and not the sulphuric anhydride1 be taken in excess1 a soluble substance of the composition #b,,so#b1c,,nh#c is formed4 ,this compound1 obtained by ,jacqueline and investigated by ,voronin1 doubtless also contains a salt of sulphamic acid--that is1 of the amide corresponding with the acid ammonium sulphate ,,hnh#d,,so#d - ,h#b,o 7,,nh#b7,,so#b7,,oh74 ,probably it is a compound of sulphatammon with sulphamic acid4 ,thus it has an acid reaction1 and does not give a precipitate with barium chloride4 ,with normal sulphate of ammonium1 an amide of the composition ,n#b;,h#d,,so#b should correspond1 which should bear the same relation to sulphuric acid as urea bears to carbonic acid4 ,this amide1 known as sulphamide1 is obtained by the action of dry ammonia on the sulphuryl chloride1 ,,so#b;,cl#b1 just as urea is obtained by the action of ammonia on carbonyl chloride1 ,,so#b;,cl#b #d,,nh#c ,n#b;,h#d,,so#b #b,,nh#d;,cl4 ,the ammonium chloride is separated from the resultant sulphamide with great difficulty4 ,cold water1 acting on the mixture1 dissolves them both2 the cold solution does not gives precipitate with barium chloride4 ,alkalis act on it slowly1 as they do on urea2 but on boiling1 especially in the presence of alkalis or acids1 it easily recombines with water1 and gives an ammonium salt4 ,v4 ,traube 7#ahib7 obtained sulphamide by the reaction of sulphuryl1 dissolved in chloroform1 upon ammonia4 ,the resultant precipitate dissolves when shaken up with water1 and the solution 7after boiling with the oxides or lead or silver7 is evaporated1 when a syrupy liquid remains4 ,with nitrate of silver the latter gives a solid compound1 which1 when decomposed by hydrochloric acid1 gives free sulphamide in large colourless crystals1 having the composition ,,so#b7,,nh#b7b4 ,this substance fuses at #ha1 begins to decompose below #ajj1 and is entirely decomposed above #bej2 it is soluble in water1 and the solution has a neutral reaction and bitter taste4 ,when heated with acids1 sulphamide gradually decomposes1 forming sulphuric acid and ammonia4 ,if the silver compound obtained by the action of sulphamide on nitrate of silver be heated at #agj-ahj until ammonia is no longer evolved1 and the residue be extracted with water acidulated with nitric acid1 a salt separates out from the solution1 answering in its composition to sulphamide1 ,,so#b,n,ag1 which the amide - ,,nh#c ,,so#b,n#b;,h#d - ,,nh#c ,,so#b,,nh4 ,the action of sulphuryl chloride 7and of the other chloranhydrides of sulphur7 on ammonium carbonate always1 as ,mente showed 7#ahhh71 results in the formation of the salt ,,nh7,,so#c,,nh#d7b4 ,the nitriles corresponding with sulphuric acid are not as yet known with any certainty4 ,the most simple nitrile corresponding with sulphuric acid should have the composition ,n#b;,h#h,,so#d - #d;,h#b,o ,n#b,s4 ,this would be a kind of cyanogen corresponding with sulphuric acid4 ,on comparing sulphurous acid with carbonic acid1 we saw that they present a great analogy in many respects1 and therefore it might be expected that nitrile compounds having the composition ,,nhs and ,n#b,s#b would be found4 ,the latter of these compounds is well known1 and was obtained by ,soubeiron1 by the action of dry ammonia on sulphur chloride4 ,this substance corresponds with cyanogen 7paracyanogen71 and is known as nitrogen sulphide1 ,n#b,s#b4 ,it is formed according to the equation #c,s,cl#b #h,,nh#c ,n#b,s#b ,s #f,,nh#d;,cl4 ,the free sulphur and nitrogen sulphide are dissolved by acting on the product with carbon bisulphide1 the nitrogen sulphide being much less soluble than the sulphur4 ,it is a yellow substance1 which is excessively irritating to the eyes and nostrils4 ,it explodes when rubbed with a hard substance1 being naturally decomposed with the evolution of nitrogen2 but when heated it fuses without decomposing1 and only decomposes with explosion at #aeg4 ,it is insoluble in water1 and only slightly so in alcohol1 ether1 and carbon bisulphide2 #ajj parts of the latter dissolve #ae part of nitrogen sulphide at the boiling point4 ,this solution on cooling deposits it in minute transparent prisms of a golden yellow colour4 ,in the group of the halogens we saw four closely analogous elements--fluorine1 chlorine1 bromine1 and iodine--and we meet with the same number of closely allied analogues in the oxygen group2 for besides sulphur this group also includes selenium and tellurium3 ,o1 ,s1 ,se1 ,te4 ,these two groups are very closely allied1 both in respect to the magnitudes of their atomic weights and also in the faculty of the elements of both groups for combining with metals4 ,the distinct analogy and definite degree of variance known to us for the halogens1 also repeat themselves in the same degree for the elements of the oxygen group4 ,amongst the halogens fluorine has many peculiarities compared to ,cl1 ,br and ,i which are more closely analogous1 whilst oxygen differs in many respects from ,s1 ,se1 ,te1 which possess greater similarities4 ,the analogy in a quantitative respect is perfect in both cases4 ,thus the halogens combine with ,h1 and the elements of the oxygen group with ,h#b1 forming ,h#b,o1 ,h#b,s1 ,h#b,se1 ,h#b,te4 ,the hydrogen compounds of selenium and tellurium are acids like hydrogen sulphide4 ,selenium1 by simple heating in a stream of hydrogen1 partially combines with it directly1 but seleniuretted hydrogen is more readily decomposable by heat than sulphuretted hydrogen1 and this property is still more developed in telluretted hydrogen4 ,hydrogen selenide and telluride are gases like sulphuretted hydrogen1 and1 like it1 are soluble in water1 form saline compounds with alkalis1 precipitate metallic salts1 are obtained by the action of acids on their compounds with metals1 c4 ,selenium and tellurium1 like sulphur1 give two normal grades of combination with oxygen1 both of an acid character1 of which only the forms corresponding to sulphurous anhydride--namely1 selenious anhydride1 ,se,o#b1 and tellurous anhydride1 ,te,o#bgi--;are formed directly4 ,these are both solids1 obtained by the combustion of the elements themselves and by the action of oxidising agents on them4 ,they form feebly energetic acids1 having distinct bibasic properties2 however1 a characteristic difference from ,,so#b is observable both in the physical properties of these compounds and in their stability and capacity for further oxidation1 just as in the series of the halogens already known to us1 only in an inverse order2 in the latter we saw that iodine combines more easily than bromine or chlorine with oxygen1 forming more stable oxygen compounds1 whereas here1 on the contrary1 sulphurous anhydride1 as we know1 is difficultly decomposed1 parts with its sulphur with difficulty1 and is easily oxidised and especially in its salts1 while selenious and tellurous anhydrides are oxidised with difficulty and easily reduced1 even by means of sulphurous acid4 #gi ,selenious anhydride1 ,se,o#b1 is a volatile solid1 which crystallises in prisms soluble in water4 ,it is best procured by the action of nitric acid on selenium4 ,the well-known researches of ,nilson 7#ahgd7 showed that the salts of selenious acid easily form acid salts1 and are so characteristic in many respects that they may even serve for judging the analogy of types of oxides4 ,thus the oxides of the composition ,,ro give normal salts of the composition ,r,se,o#c1b;,h#b,o1 where ,r ,mn1 ,co1 ,ni1 ,cu1 ,zn4 ,the salts of magnesium1 barium1 and calcium contain a different quantity of water1 as do also the salts of the oxides ,r#b,o#c4 ,we here turn attention to the fact that beryllium gives a normal salt1 ,be,se,o#c1b;,h#b,o1 and not a salt analogous to those of aluminium1 scandium1 ,sc#b7,se,o#c7c1;,h#b,o1 yttrium1 ,y#b7,se,o#c7b1ab;,h#b,o1 and other oxides of the form ,r#b,o#c1 which speaks in favour of the formula ,be,o4 ,tellurous anhydride is also a colourless solid1 which crystallises in octahedra2 it also1 when heated1 first fuses and then volatilises4 ,it is insoluble in water1 and the decomposition of its salts gives a hydrate1 ,h#b,te,o#c1 which is insoluble4 ,it is a very characteristic circumstance that selenious and tellurous anhydrides are very easily reduced to selenium and tellurium4 ,this is not only effected by metals like zinc1 or by sulphuretted hydrogen1 which are powerful deoxidisers1 but even by sulphurous anhydride1 which is able to precipitate selenium and tellurium from solutions of the selenites and tellurites1 and even of the acids themselves1 which is taken advantage of in obtaining these elements and separating them from sulphur4 ,sulphuric acid1 as we know1 rarely acts as an oxidising agent4 ,it is otherwise with selenic and telluric acids1 ,h#b,se,o#d and ,h#b,te,o#d1 which are powerful oxidising agents--that is1 are easily reduced in many circumstances either into the lower oxide or even to selenium and tellurium4 ,a powerful oxidising agent is required in order to convert selenious and tellurous anhydrides into selenic and telluric anhydrides1 and1 moreover1 it must be employed in excess4 ,if chlorine be passed through a solution of potassium selenide1 ,k#b,se1 telluride1 ,k#b,te1 selenite1 ,k#b,se,o#c1 or tellurite1 ,k#b,te,o#c1 it acts as an oxidiser in the presence of the water1 forming potassium selenate1 ,k#b,se,o#d1 or tellurate1 ,k#b,te,o#d4 ,the same salts are formed by fusing the lower oxides with nitre4 ,these salts are isomorphous with the corresponding sulphates1 and cannot therefore be separated from them by crystallisation4 ,the salts of potassium1 sodium1 magnesium1 copper1 cadmium1 c4 are soluble like the sulphates1 but those of barium and calcium are insoluble1 in perfect analogy with the sulphates4 ,when copper selenate1 ,cu,se,o#d1 is treated with sulphuretted hydrogen 7,cu,s is precipitated71 selenic acid remains in solution4 ,on evaporation and drying in vacuo at #ahj it gives a syrupy liquid1 which may be concentrated to almost the pure acid1 ,h#b,se,o#d1 having a specific gravity of #bf4 ,cameron and ,macallan 7#ahia7 showed that pure ,h#b,se,o#d only remains liquid in a state of superfusion whilst the solidified acid melts at #eh1 the solid acid crystallises well1 its sp4 gr4 is then #bie4 ,the hydrate ,h#b,se,o#d1;,h#b,o melts at #be4 ,the acid in a superfused state has a sp4 gr4 #bcf and the solid #bfc4 ,like sulphuric acid strong selenic acid attracts moisture from the atmosphere2 it is not decomposed by sulphurous acid1 but oxidises hydrochloric acid 7like nitric1 chromic1 and manganic acids71 evolving chlorine and forming selenious acid1 ,h#b,se,o#d #b;,h,cl ,h#b,se,o#c ,h#b,o ,cl#b4 ,telluric acid1 ,h#b,te,o#d1 is obtained by fusing tellurous anhydride with potassium hydroxide and chlorate2 the solution1 containing potassium tellurate1 is then precipitated with barium chloride1 and the barium tellurate1 ,ba,te,o#d obtained in the precipitate is decomposed by sulphuric acid4 ,a solution of telluric acid is thus obtained1 which on evaporation yields colourless prisms1 soluble in water1 and containing ,te,h#b,o#d1b;,h#b,o4 ,two equivalents of water are driven off at #afj2 on further heating the last equivalent of water is expelled1 and then oxygen is given off4 ,it also gives chlorine with hydrochloric acid1 like selenic acid4 ,its salts also correspond with those of sulphuric acid4 ,it must1 however1 be remarked that telluric and selenic acids are able to give poly-acid salts with much greater ease than sulphuric acid4 ,thus1 for example1 there are known for telluric acid not only ,k#b,te,o#d1e;,h#b,o and ,k,h,te,o#d1c;,h#b,o1 but also ,k,h,te,o#d1;,h#b,te,o#d1;,h#b,o ,k#b,te,o#d1c;,h#b,te,o#d1b;,h#b,o4 ,this salt is easily obtained from acid solutions of the preceding salts and is less soluble in water4 ,as selenious anhydride is volatile and gives similar poly-salts1 it may be surmised that selenious1 tellurous1 selenic1 and telluric anhydrides are polymeric as compared with sulphurous and sulphuric anhydrides1 for which reason it would be desirable to determine the vapour density of selenious anhydride4 ,it would probably correspond with ,se#b,o#d or ,se#c,o#f4 ,in order to show the very close analogy of selenium to sulphur1 ,i will quote two examples4 ,potassium cyanide dissolves selenium1 as it does sulphur1 forming potassium selenocyanate1 ,k,c,n,se1 corresponding with potassium thiocyanate4 ,acids precipitate selenium from this solution1 because selenocyanic acid1 ,h#b;,c,n,se1 when in a free state is immediately decomposed4 ,a boiling solution of sodium sulphite dissolves selenium1 just as it would sulphur1 forming a salt analogous to thiosulphate of sodium1 namely1 sodium selenosulphate1 ,na#b,s,se,o#c4 ,selenium is separated from a solution of this salt by the action of acid4 ,selenium was obtained in #ahag by ,berzelius from the sublimate which collects in the first chamber in the preparation of sulphuric acid from ,fahlun pyrites4 ,certain other pyrites also contain small quantities of selenium4 ,some native selenides1 especially those of lead1 mercury1 and copper1 have been found in the ,hartz ,mountains1 but only in small quantities4 ,pyrites and blendes1 in which the sulphur is partially replaced by selenium1 still remain the chief source for its extraction4 ,when these pyrites are roasted they evolve selenious anhydride1 which condenses in the cooler portions of the apparatus in which the pyrites are roasted1 and is partially or wholly reduced by the sulphurous anhydride simultaneously formed4 ,the presence of selenium in ores and sublimates is most simply tested by heating them before the blowpipe1 when they evolve the characteristic odour of garlic4 ,selenium exhibits two modifications1 like sulphur3 one amorphous and insoluble in carbon bisulphide1 the other crystalline and slightly soluble in carbon bisulphide 7in #a1jjj parts at #de and #f1jjj at #j71 and separating from its solutions in monoclinic prisms4 ,if the red precipitate obtained by the action of sulphurous anhydride on selenious anhydride be dried1 it gives a brown powder1 having a specific gravity of #dbf1 which when heated changes colour and fuses to a metallic mass1 which gains lustre as it cools4 ,the selenium acquires different properties according to the rate at which it is cooled from a fused state2 if rapidly cooled1 it remains amorphous and has the same specific gravity 7#dbh7 as the powder1 but if slowly cooled it becomes crystalline and opaque1 soluble in carbon bisulphide1 and has a specific gravity of #dhj4 ,in this form it fuses at #bad and remains unchanged1 whilst the amorphous form1 especially above #hj1 gradually passes into the crystalline variety4 ,the transition is accompanied by the evolution of heat1 as in the case of sulphur2 thus the analogy between sulphur and selenium is clearly shown here4 ,in the fused amorphous form selenium presents a brown mass1 slightly translucent1 with a vitreous fracture1 whilst in the crystalline form it has the appearance of a grey metal1 with a feeble lustre and a crystalline fracture4#gi bis ,selenium boils at #gjj1 forming a vapour whose density is only constant at a temperature of about #a1djj1 when it is equal to #gid 7referred to hydrogen7--that is1 the molecular formula is then ,se#b1 like sulphur at an equally high temperature4 #gi bis ,muthmann1 in his researches upon the allotropic forms of selenium1 pointed out 7#ahhi7 a peculiar modification1 which appears1 as it were1 as a transition between crystalline and amorphous selenium4 ,it is obtained together with the crystalline variety by slowly evaporating a solution of selenium in bisulphide of carbon1 and differs from the crystalline variety in the form of its crystals2 it passes into the latter modification when heated4 ,schultz also obtained selenium 7like ,ag1 see ,chapter ,,xxiv47 in a soluble form1 but these researches are not so conclusive as those upon soluble silver1 and we shall therefore not consider them more fully4 ,tellurium is met with still more rarely than selenium 7it is known in ,saxony7 in combination with gold1 silver1 lead1 and antimony in the so-called foliated tellurium ore4 ,bismuth telluride and silver telluride have been found in ,hungary and in the ,altai4 ,tellurium is extracted from bismuth telluride by mixing the finely-powdered ore with potassium and charcoal in as intimate a mixture as possible1 and then heating in a covered crucible4 ,potassium telluride1 ,k#b,te1 is then formed1 because the charcoal reduces potassium tellurite4 ,as potassium telluride is soluble in water1 forming a red-brown solution which is decomposed by the oxygen of the atmosphere 7,k#b,te ,o ,h#b,o #b,,kho ,te71 the mass formed in the crucible is treated with boiling water and filtered as rapidly as possible1 and the resultant solution exposed to the air1 by which means the tellurium is precipitated4#hj ,in a free state tellurium has a perfectly metallic appearance2 it is of a silver-white colour1 crystallises very easily in long brilliant needles2 is very brittle1 so that it can be easily reduced to powder2 but it is a bad conductor of heat and electricity1 and in this respect1 as in many others1 it forms a transition from the metals to the non-metals4 ,its specific gravity is #fah1 it melts at an incipient red heat1 and takes fire when heated in air1 like selenium and sulphur1 burning with a blue flame1 evolving white fumes of tellurous anhydride1 ,te,o#b1 and emitting an acrid smell if no selenium be present2 but if it be1 the odour of the latter preponderates4 ,alkalis dissolve tellurium when boiled with it1 potassium telluride1 ,k#b,te1 and potassium tellurite1 ,k#b,te,o#c1 being formed4 ,the solution is of a red colour1 owing to the presence of the telluride1 ,k#b,te2 but the colour disappears when the solution is cooled or diluted1 the tellurium being all precipitated3 #b,k#b,te ,k#b,te,o#c #c;,h#b,o #f,,kho #c,te4#ha #hj ,the tellurium thus prepared is impure1 and contains a large amount of selenium4 ,the latter may be removed by converting the mixture into the salts of potassium1 and treating this with nitric acid and barium nitrate1 when barium selenate only is precipitated1 whilst the barium tellurate remains in solution4 ,this method does not1 however1 give a pure product1 and it appears to be best to separate the selenium from the tellurium in a metallic form2 this is done by boiling the impure potassium tellurate with hydrochloric acid1 which converts it into potassium tellurite1 from which the tellurium is reduced by sulphurous anhydride4 ,the metal thus obtained is then fused and distilled in a stream of hydrogen2 the selenium volatilises first1 and then the tellurium1 owing to its being much less volatile than the former4 ,nevertheless1 tellurium is also volatile1 and may be separated in this manner from less volatile metals1 such as antimony4 ,brauner determined the atomic weight of pure tellurium1 and found it to be #abe1 but showed 7#ahhi7 that tellurium purified by the usual method1 even after distillation1 contains a large amount of impurities4 #ha ,the decomposition proceeds in the above order in the cold1 but in a hot solution with an excess of potassium hydroxide it proceeds inversely4 ,a similar phenomenon takes place when tellurium is fused with alkalis1 and it is therefore necessary in order to obtain potassium telluride to add charcoal4 ,selenium and tellurium form higher compounds with chlorine with comparative ease4 ,for selenium1 ,se,cl#b and ,se,cl#d are known1 and for tellurium ,te,cl#b and ,te,cl#d4 ,the tetrachlorides of selenium and tellurium are formed by passing chlorine over these elements4 ,selenium tetrachloride1 ,se,cl#d1 is a crystalline1 volatile mass which gives selenious anhydride and hydrochloric acid with water4 ,tellurium tetrachloride is much less volatile1 fuses easily1 and is also decomposed by water4 ,both elements form similar compounds with bromine4 ,tellurium tetrabromide is red1 fuses to a brown liquid1 volatilises1 and gives a crystalline salt1 ,k#b,te,br#f1c;,h#b,o1 with an aqueous solution of potassium bromide4 ,,chapter ,,xxi ,,chromium1 ,,molybdenum1 ,,tungsten1 ,,uranium1 ,,and ,,manganese ,sulphur1 selenium1 and tellurium belong to the uneven series of the sixth group4 ,in the even series of this group there are known chromium1 molybdenum1 tungsten1 and uranium2 these give acid oxides of the type ,,ro#c1 like ,,so#c4 ,their acid properties are less sharply defined than those of sulphur1 selenium1 and tellurium1 as is the case with all elements of the even series as compared with those of the uneven series in the same group4 ,but still the oxides ,cr,o#c1 ,mo,o#c1 ,,wo#c1 and even ,,uo#c1 have clearly defined acid properties1 and form salts of the composition ,,mo1n,,ro#c with bases ,,mo4 ,in the case of the heavy elements1 and especially of uranium1 the type of oxide1 ,,uo#c1 is less acid and more basic1 because in the even series of oxides the element with the highest atomic weight always acquires a more and more pronounced basic character4 ,hence ,,uo#c shows the properties of a base1 and gives salts ,,uo#b,x#b4 ,the basic properties of chromium1 molybdenum1 tungsten1 and uranium are most clearly expressed in the lower oxides1 which they all form4 ,thus chromic oxide1 ,cr#b,o#c1 is as distinct a base as alumina1 ,al#b,o#c4 ,of all these elements chromium is the most widely distributed and the most frequently used4 ,it gives chromic anhydride1 ,cr,o#c1 and chromic oxide1 ,cr#b,o#c--two compounds whose relative amounts of oxygen stand in the ratio #b 3 #a4 ,chromium is1 although somewhat rarely1 met with in nature as a compound of one or the other type4 ,the red chromium ore of the ,urals1 lead chromate or crocoisite ,pb,cr,o#d1 was the source in which chromium was discovered by ,vauquelin1 who gave it this name 7from the ,greek word signifying colour7 owing to the brilliant colours of its compounds2 the chromates 7salts of chromic anhydride7 are red and yellow1 and the chromic salts 7from ,cr#b,o#c7 green and violet4 ,the red lead chromate is1 however1 a rare chromium ore found only in the ,urals and in a few other localities4 ,chromic oxide1 ,cr#b,o#c1 is more frequently met with4 ,in small quantities it forms the colouring matter of many minerals and rocks--for example1 of some serpentines4 ,the commonest ore1 and the chief source of the chromium compounds1 is the chrome iron ore or chromite1 which occurs in the ,urals#a and ,asia ,minor1 ,california1 ,australia1 and other localities4 ,this is magnetic iron ore1 ,fe,o1,fe#b,o#c1 in which the ferric oxide is replaced by chromic oxide1 its composition being ,fe,o1,cr#b,o#c4 ,chrome iron ore crystallises in octahedra of sp4 gr4 #dd2 it has a feeble metallic lustre1 is of a greyish-black colour1 and gives a brown powder4 ,it is very feebly acted on by acids1 but when fused with potassium acid sulphate it gives a soluble mass1 which contains a chromic salt1 besides potassium sulphate and ferrous sulphate4 ,in practice the treatment of chrome iron ore is mainly carried on for the preparation of chromates1 and not of chromic salts1 and therefore we will trace the history of the element by beginning with chromic acid1 and especially with the working up of the chrome iron ore into potassium dichromate1 ,k#b;,cr#b,o#g1 as the most common salt of this acid4 ,it must be remarked that chromic anhydride1 ,cr,o#c1 is only obtained in an anhydrous state1 and is distinguished for its capacity for easily giving anhydro-salts with the alkalis1 containing one1 two1 and even three equivalents of the anhydride to one equivalent of base4 ,thus among the potassium salts there is known the normal or yellow chromate1 ,k#b;,cr,o#d1 which corresponds to1 and is perfectly isomorphous with1 potassium sulphate1 easily forms isomorphous mixtures with it1 and is not therefore suitable for a process in which it is necessary to separate the salt from a mixture containing sulphates4 ,as in the presence of a certain excess of acid1 the dichromate1 ,k#b;,cr#b,o#g #b,k#b;,cr,o#d #b;,,hx - #b,,kx - ,h#b,o1 is easily formed from ,k#b;,cr,o#d1 the object of the manufacturer is to produce such a dichromate1 the more so as it contains a larger proportion of the elements of chromic acid than the normal salt4 ,finely-ground chrome iron ore1 when heated with an alkali1 absorbs oxygen almost as easily 7,chapter ,,iii41 ,note #g7 as a mixture of the oxides of manganese with an alkali4 ,this absorption is due to the presence of chromic oxide1 which is oxidised into the anhydride1 and then combines with the alkali ,cr#b,o#c ,o#c #b;,cr,o#c4 ,as the oxidation and formation of the chromate proceeds1 the mass turns yellow4 ,the iron is also oxidised1 but does not give ferric acid1 because the capacity of the chromium for oxidation is incomparably greater than that of the iron4 #a ,the working of the ,ural chrome iron ore into chromium compounds has been firmly established in ,russia1 thanks to the endeavours of ,p4 ,k4 ,ushakoff1 who constructed large works for this purpose on the river ,kama1 near ,elabougi1 where as much as #b1jjj tons of ore are treated yearly1 owing to which the importation of chromium preparations into ,russia has ceased4 ,a mixture of lime 7sometimes with potash7 and chrome iron ore is heated in a reverberatory furnace1 with free access of air and at a red heat for several hours1 until the mass becomes yellow2 it then contains normal calcium chromate1 ,ca,cr,o#d1 which is insoluble in water in the presence of an excess of lime4#a bis ,the resultant mass is ground up1 and treated with water and sulphuric acid4 ,the excess of lime forms gypsum1 and the soluble calcium dichromate1 ,ca,cr#b,o#g1 together with a certain amount of iron1 pass into solution4 ,the solution is poured off1 and chalk added to it2 this precipitates the ferric oxide 7the ferrous oxide is converted into ferric oxide in the furnace7 and forms a fresh quantity of gypsum1 while the chromic acid remains in solution--that is1 it does not form the sparingly-soluble normal salt 7#a part soluble in #bdj parts of water74 ,the solution then contains a fairly pure calcium dichromate1 which by double decomposition gives other chromates2 for example1 with a solution of potassium sulphate it gives a precipitate of calcium sulphate and a solution of potassium dichromate1 which crystallises when evaporated4#b #a bis ,but the calcium chromate is soluble in water in the presence of an excess of chromic acid1 as may be seen from the fact that a solution of chromic acid dissolves lime4 #b ,there are many variations in the details of the manufacturing processes1 and these must be looked for in works on technical chemistry4 ,but we may add that the chromate may also be obtained by slightly roasting briquettes of a mixture of chrome iron and lime1 and then leaving the resultant mass to the action of moist air 7oxygen is absorbed1 and the mass turns yellow74 ,potassium dichromate1 ,k#b;,cr#b,o#g1 easily crystallises from acid solutions in red1 well-formed prismatic crystals1 which fuse at a red heat and evolve oxygen at a very high temperature1 leaving chromic oxide and the normal salt1 which undergoes no further change3 #b,k#b;,cr#b,o#g #b,k#b;,cr,o#d ,cr#b,o#c ,o#c4 ,at the ordinary temperature #ajj parts of water dissolve #aj parts of this salt1 and the solubility increases as the temperature rises4 ,it is most important to note that the dichromate does not contain water1 it is ,k#b;,cr,o#d ,cr,o#c2 the acid salt corresponding to potassium acid sulphate1 ,,khso#d1 does not exist4 ,it does not even evolve heat when dissolving in water1 but on the contrary produces cold1 i4e4 it does not form a very stable compound with water4 ,the solution and the salt itself are poisonous1 and act as powerful oxidising agents1 which is the character of chromic acid in general4 ,when heated with sulphur or organic substances1 with sulphurous anhydride1 hydrogen sulphide1 c41 this salt is deoxidised1 yielding chromic compounds4#b bis ,potassium dichromate#c is used in the arts and in chemistry as a source for the preparation of all other chromium compounds4 ,it is converted into yellow pigments by means of double decomposition with salts of lead1 barium1 and zinc4 ,when solutions of the salts of these metals are mixed with potassium dichromate 7in dyeing generally mixed with soda1 in order to obtain normal salts71 they are precipitated as insoluble normal salts2 for example1 #b;,ba,cl#b ,k#b;,cr#b,o#g ,h#b,o #b;,ba,cr,o#d #b,k,cl #b;,h,cl4 ,it follows from this that these salts are insoluble in dilute acids1 but the precipitation is not complete 7as it would be with the normal salt74 ,the barium and zinc salts are of a lemon yellow colour2 the lead salt has a still more intense colour passing into orange4 ,yellow cotton prints are dyed with this pigment4 ,the silver salt1 ,ag#b;,cr,o#d1 is of a bright red colour4 #b bis ,the oxidising action of potassium dichromate on organic substances at the ordinary temperature is especially marked under the action of light4 ,thus it acts on gelatin1 as ,poutven discovered2 this is applied to photography in the processes of photogravure1 photo-lithography1 pigment printing1 c4 ,under the action of light this gelatin is oxidised1 and the chromic anhydride deoxidised into chromic oxide1 which unites with the gelatin and forms a compound insoluble in warm water1 whilst where the light has not acted1 the gelatin remains soluble1 its properties being unaffected by the presence of chromic acid or potassium dichromate4 #c ,ammonium and sodium dichromates are now also prepared on a large scale4 ,the sodium salts may be prepared in exactly the same manner as those of potassium4 ,the normal salt combines with ten equivalents of water1 like ,glauber's salt1 with which it is isomorphous4 ,its solution above #cj deposits the anhydrous salt4 ,sodium dichromate crystals contain ,na#b;,cr#b,o#g1b;,h#b,o4 ,the ammonium salts of chromic acid are obtained by saturating the anhydride itself with ammonia4 ,the dichromate is obtained by saturating one part of the anhydride with ammonia1 and then adding a second part of anhydride and evaporating under the receiver of an air-pump4 ,on ignition1 the normal and acid salts leave chromic oxide4 ,potassium ammonium chromate1 ,,nh#d,k,cr,o#d1 is obtained in yellow needles from a solution of potassium dichromate in aqueous ammonia2 it not only loses ammonia and becomes converted into potassium dichromate when ignited1 but also by degrees at the ordinary temperature4 ,this shows the feeble energy of chromic acid1 and its tendency to form stable dichromates4 ,magnesium chromate is soluble in water1 as also is the strontium salt4 ,the calcium salt is also somewhat soluble1 but the barium salt is almost insoluble4 ,the isomorphism with sulphuric acid is shown in the chromates by the fact that the magnesium and ammonium salts form double salts containing six equivalents of water1 which are perfectly isomorphous with the corresponding sulphates4 ,the magnesium salt crystallises in large crystals containing seven equivalents of water4 ,the beryllium1 cerium1 and cobalt salts are insoluble in water4 ,chromic acid dissolves manganous carbonate1 but on evaporation the solution deposits manganese dioxide1 formed at the expense of the oxygen of the chromic acid4 ,chromic acid also oxidises ferrous oxide1 and ferric oxide is soluble in chromic acid4 ,one of the chromates most used by the dyer is the insoluble yellow lead chromate1 ,pb,cr,o#d 7,chapter ,,xviii41 ,note #df71 which is precipitated on mixing solutions of ,pb,x#b with soluble chromates4 ,it easily forms a basic salt1 having the composition ,pb,o1,pb,cr,o#d1 as a crystalline powder1 obtained by fusing the normal salt with nitre and then rapidly washing in water4 ,the same substance is obtained1 although impure and in small quantity1 by treating lead chromate with neutral potassium chromate1 especially on boiling the mixture2 and this gives the possibility of attaining1 by means of these materials1 various tints of lead chromate1 from yellow to red1 passing through different orange shades4 ,the decomposition which takes place 7incompletely7 in this case is as follows3 #b,pb,cr,o#d ,k#b;,cr,o#d ,pb,cr,o#d1,pb,o ,k#b;,cr#b,o#g--that is1 potassium dichromate is formed in solution4 ,when potassium dichromate is mixed with potassium hydroxide or carbonate 7carbonic anhydride being disengaged in the latter case7 it forms the normal salt1 ,k#b;,cr,o#d1 known as yellow chromate of potassium4 ,its specific gravity is #bg1 being almost the same as that of the dichromate4 ,it absorbs heat in dissolving2 one part of the salt dissolves in #age part of water at the ordinary temperature1 forming a yellow solution4 ,when mixed even with such feeble acids as acetic1 and more especially with the ordinary acids1 it gives the dichromate1 and ,graham obtained a trichromate1 ,k#b;,cr#c,o#aj ,k#b;,cr,o#d1b;,cr,o#c1 by mixing a solution of the latter salt with an excess of nitric acid4 ,chromic anhydride is obtained by preparing a saturated solution of potassium dichromate at the ordinary temperature1 and pouring it in a thin stream into an equal volume of pure sulphuric acid4#d ,on mixing1 the temperature naturally rises2 when slowly cooled1 the solution deposits chromic anhydride in needle-shaped crystals of a red colour sometimes several centimetres long4 ,the crystals are freed from the mother liquor by placing them on a porous tile4#d bis ,it is very important at this point to call attention to the fact that a hydrate of chromic anhydride is never obtained in the decomposition of chromic compounds1 but always the anhydride1 ,cr,o#c4 ,the corresponding hydrate1 ,cr,o#d;,h#b1 or any other hydrate1 is not even known4 ,nevertheless1 it must be admitted that chromic acid is bibasic1 because it forms salts isomorphous or perfectly analogous with the salts formed by sulphuric acid1 which is the best example of a bibasic acid4 ,a clear proof of the bibasicity of ,cr,o#c is seen in the fact that the anhydride and salts give 7when heated with sodium chloride and sulphuric acid7 a volatile chloranhydride1 ,cr,o#b;,cl#b1 containing two atoms of chlorine as a bibasic acid should4#e ,chromic anhydride is a red crystalline substance1 which is converted into a black mass by heat2 it fuses at #aij1 and disengages oxygen above #bej1 leaving a residue of chromium dioxide1 ,cr,o#b1f and1 on still further heating1 chromic oxide1 ,cr#b,o#c4 ,chromic anhydride is exceedingly soluble in water1 and even attracts moisture from the air1 but1 as was mentioned above1 it does not form any definite compound with water4 ,the specific gravity of its crystals is #bg1 and when fused it has a specific gravity #bf4 ,the solution presents perfectly defined acid properties4 ,it liberates carbonic anhydride from carbonates2 gives insoluble precipitates of the chromates with salts of barium1 lead1 silver1 and mercury4 #d ,the sulphuric acid should not contain any lower oxides of nitrogen1 because they reduce chromic anhydride into chromic oxide4 ,if a solution of a chromate be heated with an excess of acid--for instance1 sulphuric or hydrochloric acid--oxygen or chlorine is evolved1 and a solution of a chromic salt is formed4 ,hence1 under these circumstances1 chromic acid cannot be obtained from its salts4 ,one of the first methods employed consisted in converting its salts into volatile chromium hexafluoride1 ,cr,f#f4 ,this compound1 obtained by ,unverdorben1 may be prepared by mixing lead chromate with fluor spar in a dry state1 and treating the mixture with fuming sulphuric acid in a platinum vessel3 ,pb,cr,o#d #c;,ca,f#b #d;,h#b,,so#d ,pb,s,o#d #c;,ca,s,o#d #d;,h#b,o ,cr,f#f4 ,fuming sulphuric acid is taken1 and in considerable excess1 because the chromium fluoride which is formed is very easily decomposed by water4 ,it is volatile1 and forms a very caustic1 poisonous vapour1 which condenses when cooled in a dry platinum vessel into a red1 exceedingly volatile liquid1 which fumes powerfully in air4 ,the vapours of this substance when introduced into water are decomposed into hydrofluoric acid and chromic anhydride3 ,cr,f#f #c;,h#b,o ,cr,o#c #f;,,hf4 ,if very little water be taken the hydrofluoric acid volatilises1 and chromic anhydride separates directly in crystals4 ,the chloranhydride of chromic acid1 ,cr,o#b;,cl#b 7,note #e71 is also decomposed in the same manner4 ,a solution of chromic acid and a precipitate of barium sulphate are formed by treating the insoluble barium chromate with an equivalent quantity of sulphuric acid4 ,if carefully evaporated1 the solution yields crystals of chromic anhydride4 ,fritzsche gave a very convenient method of preparing chromic anhydride1 based on the relation of chromic to sulphuric acid4 ,at the ordinary temperature the strong acid dissolves both chromic anhydride and potassium chromate1 but if a certain amount of water is added to the solution the chromic anhydride separates1 and if the amount of water be increased the precipitated chromic anhydride is again dissolved4 ,the chromic anhydride is almost all separated from the solution when it contains two equivalents of water to one equivalent of sulphuric acid4 ,many methods for the preparation of chromic anhydride are based on this fact4 #d bis ,they cannot be filtered through paper or washed1 because the chromic anhydride is reduced by the filter-paper1 and is dissolved during the process of washing4 #e ,berzelius observed1 and ,rose carefully investigated1 this remarkable reaction1 which occurs between chromic acid and sodium chloride in the presence of sulphuric acid4 ,if #aj parts of common salt be mixed with #ab parts of potassium dichromate1 fused1 cooled1 and broken up into lumps1 and placed in a retort with #bj parts of fuming sulphuric acid1 it gives rise to a violent reaction1 accompanied by the formation of brown fumes of chromic chloranhydride1 or chromyl chloride1 ,cr,o#b;,cl#b1 according to the reaction3 ,cr,o#c #b,na,cl ,h#b,,so#d ,na#b,,so#d ,h#b,o ,cr,o#b;,cl#b4 ,the addition of an excess of sulphuric acid is necessary in order to retain the water4 ,the same substance is always formed when a metallic chloride is heated with chromic acid1 or any of its salts1 in the presence of sulphuric acid4 ,the formation of this volatile substance is easily observed from the brown colour which is proper to its vapour4 ,on condensing the vapour in a dry receiver a liquid is obtained having a sp4 gr4 of #ai1 boiling at #aah1 and giving a vapour whose density1 compared with hydrogen1 is #gh1 which corresponds with the above formula4 ,chromyl chloride is decomposed by heat into chromic oxide1 oxygen1 and chlorine3 #b;,cr,o#b;,cl#b ,cr#b,o#c #b;,cl#b ,o2 so that it is able to act simultaneously as a powerful oxidising and chlorinating agent1 which is taken advantage of in the investigation of many1 and especially of organic1 substances4 ,when treated with water1 this substance first falls to the bottom1 and is then decomposed into hydrochloric and chromic acids1 like all chloranhydrides3 ,cr,o#b;,cl#b ,h#b,o ,cr,o#c #b;,h,cl4 ,when brought into contact with inflammable substances it sets fire to them2 it acts thus1 for instance1 on phosphorus1 sulphur1 oil of turpentine1 ammonia1 hydrogen1 and other substances4 ,it attracts moisture from the atmosphere with great energy1 and must therefore be kept in closed vessels4 ,it dissolves iodine and chlorine1 and even forms a solid compound with the latter1 which depends upon the faculty of chromium to form its higher oxide1 ,cr#b,o#g4 ,the close analogy in the physical properties of the chloranhydrides1 ,cr,o#b;,cl#b and ,,so#b;,cl#b1 is very remarkable1 although sulphurous anhydride is a gas1 and the corresponding oxide1 ,cr,o#b1 is a non-volatile solid4 ,it may be imagined1 therefore1 that chromium dioxide 7which will be mentioned in the following note7 presents a polymerised modification of the substance having the composition ,cr,o#b2 in fact1 this is obvious from the method of its formation4 ,if three parts of potassium dichromate be mixed with four parts of strong hydrochloric acid and a small quantity of water1 and gently warmed1 it all passes into solution1 and no chlorine is evolved2 on cooling1 the liquid deposits red prismatic crystals1 known as ,peligot's salt1 very stable in air4 ,this has the composition ,k,cl1,cr,o#c1 and is formed according to the equation ,k#b;,cr#b,o#g #b;,h,cl #b,k,cl1,cr,o#c ,h#b,o4 ,it is evident that this is the first chloranhydride of chromic acid1 ,h,cr,o#c;,cl1 in which the hydrogen is replaced by potassium4 ,it is decomposed by water1 and on evaporation the solution yields potassium dichromate and hydrochloric acid4 ,this is a fresh instance of the reversible reactions so frequently encountered4 ,with sulphuric acid ,peligot's salt forms chromyl chloride4 ,the latter circumstance1 and the fact that ,geuther produced ,peligot's salt from potassium chromate and chromyl chloride1 give reason for thinking that it is a compound of these two substances3 #b,k,cl1,cr,o#c ,k#b;,cr,o#d ,cr,o#b;,cl#b4 ,it is also sometimes regarded as potassium dichromate in which one atom of oxygen is replaced by chlorine--that is1 ,k#b;,cr#b,o#f;,cl#b1 corresponding with ,k#b;,cr#b,o#g4 ,when heated it parts with all its chlorine1 and on further heating gives chromic oxide4 #f ,this intermediate degree of oxidation1 ,cr,o#b1 may also be obtained by mixing solutions of chromic salts with solutions of chromates4 ,the brown precipitate formed contains a compound1 ,cr#b,o#c1;,cr,o#c1 consisting of equivalent amounts of chromic oxide and anhydride4 ,the brown precipitate of chromium dioxide contains water4 ,the same substance is formed by the imperfect deoxidation of chromic anhydride by various reducing agents4 ,chromic oxide1 when heated1 absorbs oxygen1 and appears to give the same substance4 ,chromic nitrate1 when ignited1 also gives this substance4 ,when this substance is heated it first disengages water and then oxygen1 chromic oxide being left4 ,it corresponds with manganese dioxide1 ,cr#b,o#c1;,cr,o#c #c;,cr,o#b4 ,krger treated chromium dioxide with a mixture of sodium chloride and sulphuric acid1 and found that chlorine gas was evolved1 but that chromyl chloride was not formed4 ,under the action of light1 a solution of chromic acid also deposits the brown dioxide4 ,at the ordinary temperature chromic anhydride leaves a brown stain upon the skin and tissues1 which probably proceeds from a decomposition of the same kind4 ,chromic anhydride is soluble in alcohol containing water1 and this solution is decomposed in a similar manner by light4 ,chromium dioxide forms ,k#b;,cr,o#d when treated with ,h#b,o#b in the presence of ,,kho4 ,the action of hydrogen peroxide on a solution of chromic acid or of potassium dichromate gives a blue solution1 which very quickly becomes colourless with the disengagement of oxygen4 ,barreswill showed that this is due to the formation of a perchromic anhydride1 ,cr#b,o#g1 corresponding with sulphur peroxide4 ,this peroxide is remarkable from the fact that it very easily dissolves in ether and is much more stable in this solution1 so that1 by shaking up hydrogen peroxide mixed with a small quantity of chromic acid1 with ether1 it is possible to transfer all the blue substance formed to the ether4#f bis #f bis ,now that persulphuric acid ,h#b,s#b,o#h is well known it might be supposed that perchromic anhydride1 ,cr#b,o#g1 would correspond to perchromic acid1 ,h#b;,cr#b,o#h1 but as yet it is not certain whether corresponding salts are formed4 ,pchard 7#ahia7 on adding an excess of ,h#b,o#b and baryta water to a dilute solution of ,cr,o#b 7#h grm4 per litre71 observed the formation of a yellow precipitate1 but oxygen was disengaged at the same time and the precipitate 7which easily exploded when dried7 was found to contain1 besides an admixture of ,ba,o#b1 a compound ,ba,cr,o#e1 and this ,ba,o#b ,cr,o#c1 and does not correspond to perchromic acid4 ,the fact of its decomposing with an explosion1 and the mode of its preparation1 proves1 however1 that this is a similar derivative of peroxide of hydrogen to persulphuric acid 7,chapter ,,xx47 ,with oxygen acids1 chromic acid evolves oxygen2 for example1 with sulphuric acid the following reaction takes place3 #b;,cr,o#c #c;,h#b,,so#d ,cr#b7,,so#d7c ,o#c #c;,h#b,o4 ,it will be readily understood from this that a mixture of chromic acid or of its salts with sulphuric acid forms an excellent oxidising agent1 which is frequently employed in chemical laboratories and even for technical purposes as a means of oxidation4 ,thus hydrogen sulphide and sulphurous anhydride are converted into sulphuric acid by this means4 ,chromic acid is able to act as a powerful oxidising agent because it passes into chromic oxide1 and in so doing disengages half of the oxygen contained in it3 #b;,cr,o#c ,cr#b,o#c ,o#c4 ,thus chromic anhydride itself is a powerful oxidising agent1 and is therefore employed instead of nitric acid in galvanic batteries 7as a depolariser71 the hydrogen evolved at the carbon being then oxidised1 and the chromic acid converted into a non-volatile product of deoxidation1 instead of yielding1 as nitric acid does1 volatile lower oxides of offensive odour4 ,organic substances are more or less perfectly oxidised by means of chromic anhydride1 although this generally requires the aid of heat1 and does not proceed in the presence of alkalis1 but generally in the presence of acids4 ,in acting on a solution of potassium iodide1 chromic acid1 like many oxidising agents1 liberates iodine2 the reaction proceeds in proportion to the amount of ,cr,o#c present1 and may serve for determining the amount of ,cr,o#c1 since the amount of iodine liberated can be accurately determined by the iodometric method 7,chapter ,,xx41 ,note #db74 ,if chromic anhydride be ignited in a stream of ammonia1 it gives chromic oxide1 water1 and nitrogen4 ,in all cases when chromic acid acts as an oxidising agent in the presence of acids and under the action of heat1 the product of its deoxidation is a chromic salt1 ,cr,x#c1 which is characterised by the green colour of its solution1 so that the red or yellow solution of a salt of chromic acid is then transformed into a green solution of a chromic salt1 derived from chromic oxide1 ,cr#b,o#c1 which is closely analogous to ,al#b,o#c1 ,fe#b,o#c1 and other bases of the composition ,r#b,o#c4 ,this analogy is seen in the insolubility of the anhydrous oxide1 in the gelatinous form of the colloidal hydrate1 in the formation of alums1#g of a volatile chloride of chromium1 c4#g bis #g ,as a mixture of potassium dichromate and sulphuric acid is usually employed for oxidation1 the resultant solution generally contains a double sulphate of potassium and chromium--that is1 chrome alum1 isomorphous with ordinary alum--,k#b;,cr#b,o#g #d;,h#b,,so#d #bj;,h#b,o ,o#c ,k#b;,cr#b7,,so#d7d1bd;,h#b,o or #b7,k,cr7,,so#d7b1ab;,h#b,o74 ,it is prepared by dissolving potassium dichromate in dilute sulphuric acid2 alcohol is then added and the solution slightly heated1 or sulphurous anhydride is passed through it4 ,on the addition of alcohol to a cold mixture of potassium dichromate and sulphuric acid1 the gradual disengagement of pleasant-smelling volatile products of the oxidation of alcohol1 and especially of aldehyde1 ,c#b;,h#d,o1 is remarked4 ,if the temperature of decomposition does not exceed #ce1 a violet solution of chrome alum is obtained1 but if the temperature be higher1 a solution of the same alum is obtained of a green colour4 ,as chrome alum requires for solution #g parts of water at the ordinary temperature1 it follows that if a somewhat strong solution of potassium dichromate be taken 7#d parts of water and #a-a_/b of sulphuric acid to #a part of dichromate71 it will give so concentrated a solution of chrome alum that on cooling1 the salt will separate without further evaporation4 ,if the liquid1 prepared as above or in any instance of the deoxidation of chromic acid1 be heated 7the oxidation naturally proceeds more rapidly7 somewhat strongly1 for instance1 to the boiling-point of water1 or if the violet solution already formed be raised to the same temperature1 it acquires a bright green colour1 and on evaporation the same mixture1 which at lower temperatures so easily gives cubical crystals of chrome alum1 does not give any crystals whatever4 ,if the green solution be kept1 however1 for several weeks at the ordinary temperature1 it deposits violet crystals of chrome alum4 ,the green solution1 when evaporated1 gives a non-crystalline mass1 and the violet crystals lose water at #ajj and turn green4 ,it must be remarked that the transition of the green modification into the violet is accompanied by a decrease in volume 7,lecoq de ,boisbaudran1 ,favre74 ,if the green mass formed at the higher temperature be evaporated to dryness and heated at #cj in a current of air1 it does not retain more then #f equivalents of water4 ,hence ,lwel1 and also ,schrtter1 concluded that the green and violet modifications of the alum depend on different degrees of combination with water1 which may be likened to the different compounds of sodium sulphate with water and to the different hydrates of ferric oxide4 ,however1 the question in this case is not so simple1 as we shall afterwards see4 ,not chrome alum alone1 but all the chromic salts1 give two1 if not three1 varieties4 ,at least1 there is no doubt about the existence of two--a green and a violet modification4 ,the green chromic salts are obtained by heating solutions of the violet salts1 the violet solutions are produced on keeping solutions of the green salts for a long time4 ,the conversion of the violet salts into green by the action of heat is itself an indication of the possibility of explaining the different modifications by their containing different proportions 7or states7 of water1 and1 moreover1 by the green salts having a less amount of water than the violet4 ,however1 there are other explanations4 ,chromic oxide is a base like alumina1 and is therefore able to give both acid and basic salts4 ,it is supposed that the difference between the green and violet salts is due to this fact4 ,this opinion of ,krger is based on the fact that alcohol separates out a salt from the green solution which contains less sulphuric acid than the normal violet salt4 ,on the other hand1 ,lwel showed that all the acid cannot be separated from the green chromic salts by suitable reagents1 as easily as it can be from the same solution of the violet salts2 thus barium salts do not precipitate all the sulphuric acid from solutions of the green salts4 ,according to other researches the cause of the varieties of the chromic salts lies in a difference in the bases they contain--that is1 it is connected with a modification of the properties of the oxide of chromium itself4 ,this only refers to the hydroxides1 but as hydroxides themselves are only special forms of salts1 the differences observed as yet in this direction between the hydroxides only confirm the generality of the difference observed in the chromic compounds 7see ,note #g bis74 ,the salts of chromic oxide1 like those of alumina1 are easily decomposed1 give basic and double salts1 and have an acid reaction1 as chromic oxide is a feeble base4 ,potassium and sodium hydroxides give a precipitate of the hydroxide with chromic salts1 ,cr,x#c4 ,the violet and green salts give a hydroxide soluble in an excess of the reagent2 but the hydroxide is held in solution by very feeble affinities1 so that it is partially separated by heat and dilution with water1 and completely so on boiling4 ,in an alkaline solution1 chromic hydroxide is easily converted into chromic acid by the action of lead dioxide1 chlorine1 and other oxidising agents4 ,if the chromic oxide occurs together with such oxides as magnesia1 or zinc oxide1 then on precipitation it separates out from its solution in combination with these oxides1 forming1 for example1 ,zn,o1,cr#b,o#c4 ,viard obtained compounds of ,cr#b,o#c with the oxides of ,mg1 ,zn1 ,cd1 c47 ,on precipitating the violet solution of chrome alum with ammonia1 a precipitate containing ,cr#b,o#c1f;,h#b,o is obtained1 whilst the precipitate from the boiling solution with caustic potash was a hydrate containing four equivalents of water4 ,when fused with borax chromic salts give a green glass4 ,the same coloration is communicated to ordinary glass by the presence of traces of chromic oxide4 ,a chrome glass containing a large amount of chromic oxide may be ground up and used as a green pigment4 ,among the hydrates of oxide of chromium ,guignet's green forms one of the widely-used green pigments which have been substituted for the poisonous arsenical copper pigments1 such as ,schweinfurt green1 which formerly was much used4 ,guignet's green has an extremely bright green colour1 and is distinguished for its great stability1 not only under the action of light but also towards reagents2 thus it is not altered by alkaline solutions1 and even nitric acid does not act on it4 ,this pigment remains unchanged up to a temperature of #bej2 it contains ,cr#b,o#c1b;,h#b,o1 and generally a small amount of alkali4 ,it is prepared by fusing #c parts of boric acid with #a part of potassium dichromate2 oxygen is disengaged1 and a green glass1 containing a mixture of the borates of chromium and potassium1 is obtained4 ,when cool this glass is ground up and treated with water1 which extracts the boric acid and alkali and leaves the above-named chromic hydroxide behind4 ,this hydroxide only parts with its water at a red heat1 leaving the anhydrous oxide4 ,the chromic hydroxides lose their water by ignition1 and in so doing become spontaneously incandescent1 like the ordinary ferric hydroxide 7,chapter ,,xxii474 ,it is not known1 however1 whether all the modifications of chromic oxide show this phenomenon4 ,the anhydrous chromic oxide1 ,cr#b,o#c1 is exceedingly difficultly soluble in acids1 if it has passed through the above recalescence4 ,but if it has parted with its water1 or the greater part of it1 and not yet undergone this self-induced incandescence 7has not lost a portion of its energy71 then it is soluble in acids4 ,it is not reduced by hydrogen4 ,it is easily obtained in various crystalline forms by many methods4 ,the chromates of mercury and ammonium give a very convenient method for its preparation1 because when ignited they leave chromic oxide behind4 ,in the first instance oxygen and mercury are disengaged1 and in the second case nitrogen and water3 #b;,hg#b;,cr,o#d ,cr#b,o#c ,o#e #d;,hg or 7,,nh#d7b;,cr#b,o#g ,cr#b,o#c #d;,h#b,o ,n#b4 ,the second reaction is very energetic1 and the mass of salt burns spontaneously if the temperature be sufficiently high4 ,a mixture of potassium sulphate and chromic oxide is formed by heating potassium dichromate with an equal weight of sulphur3 ,k#b;,cr#b,o#g ,s ,k#b,,so#d ,cr#b,o#c4 ,the sulphate is easily extracted by water1 and there remains a bright green residue of the oxide1 whose colour is more brilliant the lower the temperature of the decomposition4 ,the oxide thus obtained is used as a green pigment for china and enamel4 ,the anhydrous chromic oxide obtained from chromyl chloride1 ,cr,o#b;,cl#b1 has a specific gravity of #eba1 and forms almost black crystals1 which give a green powder4 ,they are hard enough to scratch glass1 and have a metallic lustre4 ,the crystalline form of chromic oxide is identical with that of the oxide of iron and alumina1 with which it is isomorphous4 #g bis ,the most important of the compounds corresponding with chromic oxide is chromic chloride1 ,cr#b;,cl#f1 which is known in an anhydrous and in a hydrated form4 ,it resembles ferric and aluminic chlorides in many respects4 ,there is a great difference between the anhydrous and the hydrated chlorides2 the former is insoluble in water1 the latter easily dissolves1 and on evaporation its solution forms a hygroscopic mass which is very unstable and easily evolves hydrochloric acid when heated with water4 ,the anhydrous form is of a violet colour1 and ,whler gives the following method for its preparation3 an intimate mixture is prepared of the anhydrous chromic oxide with carbon and organic matter1 and charged into a wide infusible glass or porcelain tube which is heated in a combustion furnace2 one extremity of the tube communicates with an apparatus generating chlorine which is passed through several bottles containing sulphuric acid in order to dry it perfectly before it reaches the tube4 ,on heating the portion of the tube in which the mixture is placed and passing chlorine through1 a slightly volatile sublimate of chromic chloride1 ,cr,cl#c or ,cr#b;,cl#f1 is formed4 ,this substance forms violet tabular crystals1 which may be distilled in dry chlorine without change1 but which1 however1 require a red heat for their volatilisation4 ,these crystals are greasy to the touch and insoluble in water1 but if they be powdered and boiled in water for a long time they pass into a green solution4 ,strong sulphuric acid does not act on the anhydrous salt1 or only acts with exceeding slowness1 like water4 ,even aqua regia and other acids do not act on the crystals1 and alkalis only show a very feeble action4 ,the specific gravity of the crystals is #bii4 ,when fused with sodium carbonate and nitre they give sodium chloride and potassium chromate1 and when ignited in air they form green chromic oxide and evolve chlorine4 ,on ignition in a stream of ammonia1 chromic chloride forms sal-ammoniac and chromium nitride1 ,cr,n 7analogous to the nitrides ,,bn1 ,al,n74 ,mosberg and ,peligot showed that when chromic chloride is ignited in hydrogen1 it parts with one-third of its chlorine1 forming chromous chloride1 ,cr,cl#b--that is1 there is formed from a compound corresponding with chromic oxide1 ,cr#b,o#c1 a compound answering to the suboxide1 chromous oxide1 ,cr,o--just as hydrogen converts ferric chloride into ferrous chloride with the aid of heat4 ,chromous chloride1 ,cr,cl#b1 forms colourless crystals easily soluble in water1 which in dissolving evolve a considerable amount of heat1 and form a blue liquid1 capable of absorbing oxygen from the air with great facility1 being converted thereby into a chromic compound4 ,the blue solution of chromous chloride may also be obtained by the action of metallic zinc on the green solution of the hydrated chromic chloride2 the zinc in this case takes up chlorine just as the hydrogen did4 ,it must be employed in a large excess4 ,chromic oxide is also formed in the action of zinc on chromic chloride1 and if the solution remain for a long time in contact with the zinc the whole of the chromium is converted into chromic oxychloride4 ,other chromic salts are also reduced by zinc into chromous salts1 ,cr,x#b1 just as the ferric salts ,fe,x#c are converted into ferrous salts ,fe,x#b by it4 ,the chromous salts are exceedingly unstable and easily oxidise and pass into chromic salts2 hence the reducing power of these salts is very great4 ,from cupric salts they separate cuprous salts1 from stannous salts they precipitate metallic tin1 they reduce mercuric salts into mercurous and ferric into ferrous salts4 ,moreover1 they absorb oxygen from the air directly4 ,with potassium chromate they give a brown precipitate of chromium dioxide or of chromic oxide1 according to the relative amounts of the substances taken3 ,cr,o#c ,cr,o #b;,cr,o#b or ,cr,o#c #c;,cr,o #b;,cr#b,o#c4 ,aqueous ammonia gives a blue precipitate1 and in the presence of ammoniacal salts a blue liquid is obtained which turns red in the air from oxidation4 ,this is accompanied by the formation of compounds analogous to those given by cobalt 7,chapter ,,xxii474 ,a solution of chromous chloride with a hot saturated solution of sodium acetate1 ,c#b;,h#c,na,o#b1 gives1 on cooling1 transparent red crystals of chromous acetate1 ,c#d;,h#f;,cr,o#d1;,h#b,o4 ,this salt is also a powerful reducing agent1 but may be kept for a long time in a vessel full of carbonic anhydride4 ,the insoluble anhydrous chromic chloride ,cr,cl#c very easily passes into solution in the presence of a trace 7#jjjd7 of chromous chloride ,cr,cl#b4 ,this remarkable phenomenon was observed by ,peligot and explained by ,lwel in the following manner3 chromous chloride1 as a lower stage of oxidation1 is capable of absorbing both oxygen and chlorine1 combining with various substances4 ,it is able to decompose many chlorides by taking up chlorine from them2 thus it precipitates mercurous chloride from a solution of mercuric chloride1 and in so doing passes into chromic chloride3 #b;,cr,cl#b #b;,hg,cl#b ,cr#b;,cl#f #b;,hg,cl4 ,let us suppose that the same phenomenon takes place when the anhydrous chromic chloride is mixed with a solution of chromous chloride4 ,the latter will then take up a portion of the chlorine of the former1 and pass into a soluble hydrate of chromic chloride 7hydrochloride of oxide of chromium71 and the original anhydrous chromic chloride will pass into chromous chloride4 ,the chromous chloride re-formed in this manner will then act on a fresh quantity of the chromic chloride1 and in this manner transfer it entirely into solution as hydrate4 ,this view is confirmed by the fact that other chlorides1 capable of absorbing chlorine like chromous chloride1 also induce the solution of the insoluble chromic chloride--for example1 ferrous chloride1 ,fe,cl#b1 and cuprous chloride4 ,the presence of zinc also aids the solution of chromic chloride1 owing to its converting a portion of it into chromous chloride4 ,the solution of chromic chloride in water obtained by these methods is perfectly identical with that which is formed by dissolving chromic hydroxide in hydrochloric acid4 ,on evaporating the green solution obtained in this manner1 it gives a green mass1 containing water4 ,on further heating it leaves a soluble chromic oxychloride1 and when ignited it first forms an insoluble oxychloride and then chromic oxide2 but no anhydrous chromic chloride1 ,cr#b;,cl#f1 is formed by heating the aqueous solution of chromic chloride1 which forms an important fact in support of the view that the green solution of chromic chloride is nothing else but hydrochloride of oxide of chromium4 ,at #ajj the composition of the green hydrate is ,cr#b;,cl#f1i;,h#b,o1 and on evaporation at the ordinary temperature over ,h#b,,so#d crystals are obtained with #ab equivalents of water2 the red mass obtained at #abj contains ,cr#b,o#c1d;,cr#b;,cl#f1bd;,h#b,o4 ,the greater portion of it is soluble in water1 like the mass which is formed at #aej4 ,the latter contains ,cr#b,o#c1b;,cr#b;,cl#f1i;,h#b,o #c7;,cr#b,o,cl#d1c;,h#b,o7--that is1 it presents the same composition as chromic chloride in which one atom of oxygen replaces two of chlorine4 ,and if the hydrate of chromic chloride be regarded as ,cr#b,o#c1f;,h,cl1 the substance which is obtained should be regarded as ,cr#b,o#c1d;,h,cl combined with water1 ,h#b,o4 ,the addition of alkalis--for example1 baryta--to a solution of chromic chloride immediately produces a precipitate1 which1 however1 re-dissolves on shaking1 owing to the formation of one of the oxychlorides just mentioned1 which may be regarded as basic salts4 ,thus we may represent the product of the change produced on chromic chloride under the influence of water and heat by the following formul3 first ,cr#b,o#c1f;,h,cl or ,cr#b;,cl#f1c;,h#b,o is formed1 then ,cr#b,o#c1d;,h,cl1,h#b,o or ,cr#b,o,cl#d1c;,h#b,o1 and lastly ,cr#b,o#c1b;,h,cl1#b;,h#b,o or ,cr#b,o#b;,cl#b1c;,h#b,o4 ,in all three cases there are #b equivalents of chromium to at least #c equivalents of water4 ,these compounds may be regarded as being intermediate between chromic hydroxide and chloride2 chromic chloride is ,cr#b;,cl#f1 the first oxychloride ,cr#b7,,oh7#b;,cl#d1 the second ,cr#b7,,oh7#d;,cl#b1 and the hydrate ,cr#b7,,oh7#f--that is1 the chlorine is replaced by hydroxyl4 ,it is very important to remark two circumstances in respect to this3 7#a7 ,that the whole of the chlorine in the above compounds is not precipitated from their solutions by silver nitrate2 thus the normal salt of the composition ,cr#b;,cl#f1i;,h#b,o only gives up two-thirds of its chlorine2 therefore ,peligot supposes that the normal salt contains the oxychloride combined with hydrochloric acid3 ,cr#b;,cl#f #b;,h#b,o ,cr#b,o#b;,cl#b1d;,h,cl1 and that the chlorine held as hydrochloric acid reacts with the silver1 whilst that held in the oxychloride does not enter into reaction1 just as we observe a very feebly-developed faculty for reaction in the anhydrous chromic chloride2 and 7#b7 if the green aqueous solution of ,cr,cl#c be left to stand for some time1 it ultimately turns violet2 in this form the whole of the chlorine is precipitated by ,ag,n,o#c1 whilst boiling re-converts it into the green variety4 ,lwel obtained the violet solution of hydrochloride of chromic oxide by decomposing the violet chromic sulphate with barium chloride4 ,silver nitrate precipitates all the chlorine from this violet modification2 but if the violet solution be boiled and so converted into the green modification1 silver nitrate then only precipitates a portion of the chlorine4 ,recoura 7#ahij-ahic7 obtained a crystallohydrate of violet chromium sulphate1 ,cr#b7,,so#d7c1 with #ah or #ae ,h#b,o4 ,by boiling a solution of this crystallohydrate1 he converted it into the green salt1 which1 when treated with alkalis1 gave a precipitate of ,cr#b,o#c1b;,h#b,o1 soluble in #b;,h#b,,so#d 7and not #c71 and only forming the basic salt1 ,cr#b7,,oh7#b7,,so#d7b4 ,he therefore concludes that the green salts are basic salts4 ,the cryoscopic determinations made by ,a4 ,speransky 7#ahib7 and ,marchetti 7#ahib7 give a greater 'depression' for the violet than the green salts1 that is1 indicate a greater molecular weight for the green salts4 ,but as tard1 by heating the violet sulphate to #ajj1 converted it into a green salt of the same composition1 but with a smaller amount of ,h#b,o1 it follows that the formation of a basic salt alone is insufficient to explain the difference between the green and violet varieties1 and this is also shown by the fact that ,ba,cl#b precipitates the whole of the sulphuric acid of the violet salt1 and only a portion of that of the green salt4 ,a4 ,speransky also showed that the molecular electro-conductivity of the green solutions is less than that of the violet4 ,it is also known that the passage of the former into the latter is accompanied by an increase of volume1 and1 according to ,recoura1 by an evolution of heat also4 ,piccini's researches 7#ahid7 throw an important light upon the peculiarities of the green chromium trichloride 7or chromic chloride72 he showed 7#a7 that ,ag,f 7in contradistinction to the other salts of silver7 precipitates all the chlorine from an aqueous solution of the green variety2 7#b7 that solutions of green ,cr,cl#c1f;,h#b,o in ethyl alcohol and acetone precipitate all their chlorine when mixed with a similar solution of ,ag,n,o#c2 7#c7 that the rise of the boiling-point of the ethyl alcohol and acetone green solutions of ,cr,cl#c1f;,h#b,o 7,chapter ,,vii41 ,note #bg bis7 shows that i in this case 7as in the aqueous solutions of ,mg,s,o#d and ,hg,cl#b7 is nearly equal to #a1 that is1 that they are like solutions of non-conductors2 7#d7 that a solution of green ,cr,cl#c in methyl alcohol at first precipitates about #g_/h of its chlorine 7an aqueous solution about #b_/c7 when treated with ,ag,n,o#c1 but after a time the whole of the chlorine is precipitated2 and 7#e7 that an aqueous solution of the green variety gradually passes into the violet1 while a methyl alcoholic solution preserves its green colour1 both of itself and also after the whole of the chlorine has been precipitated by ,ag,n,o#c4 ,if1 however1 in an aqueous or methyl alcoholic solution only a portion of the chlorine be precipitated1 the solution gradually turns violet4 ,in my opinion the general meaning of all these observations requires further elucidation and explanation1 which should be in harmony with the theory of solutions4 ,recoura1 moreover1 obtained compounds of the green salt1 ,cr#b7,,so#d7c1 with #a1 #b1 and #c molecules of ,h#b,,so#d1 ,k#b,,so#d1 and even a compound ,cr#b7,,so#d7c;,h#b;,cr,o#d4 ,by neutralising the sulphuric acid of the compounds of ,cr#b7,,so#d7c and ,h#b,,so#d with caustic soda1 ,recoura obtained an evolution of #cc thousand calories per each #b,na,h,o1 while free ,h#b,,so#d only gives #cjh thousand calories4 ,recoura is of opinion that special chromo sulphuric acids1 for instance 7,cr,s,o#d7;,h#b,,so#d #a_/b;,cr#b7,,so#d7c;,h#b,,so#d1 are formed4 ,with a still larger excess of sulphuric acid1 ,recoura obtained salts containing a still greater number of sulphuric acid radicles1 but even this method does not explain the difference between the green and violet salts4 ,these facts must naturally be taken into consideration in order to arrive at any complete decision as to the cause of the different modifications of the chromic salts4 ,we may observe that the green modification of chromic chloride does not give double salts with the metallic chlorides1 whilst the violet variety forms compounds ,cr#b;,cl#f1b,r,cl 7where ,r an alkali metal71 which are obtained by heating the chromates with an excess of hydrochloric acid and evaporating the solution until it acquires a violet colour4 ,as the result of all the existing researches on the green and violet chromic salts1 it appears to me most probable that their difference is determined by the feeble basic character of chromic oxide1 by its faculty of giving basic salts1 and by the colloidal properties of its hydroxide 7these three properties are mutually connected71 and moreover1 it seems to me that the relation between the green and violet salts of chromic oxide best answers to the relation of the purpureo to the luteo cobaltic salts 7,chapter ,,xxii41 ,note #ce74 ,this subject cannot yet be considered as exhausted 7see ,note #g74 ,we may here observe that with tin the chromic salts1 ,cr,x#c1 give at low temperatures ,cr,x#b and ,sn,x#b1 whilst at high temperatures1 on the contrary1 ,cr,x#b reduces the metal from its salts ,sn,x#b4 ,the reaction1 therefore1 belongs to the class of reversible reactions 7,beketoff74 ,poulenc obtained anhydrous ,cr,f#c 7sp4 gr4 #cgh7 and ,cr,f#b 7sp4 gr4 #daa7 by the action of gaseous ,,hf upon ,cr,cl#b4 ,a solution of fluoride of chromium is employed as a mordant in dyeing4 ,recoura 7#ahij7 obtained green and violet varieties of ,cr#b;,br#f1f;,h#b,o4 ,the green variety can only be kept in the presence of an excess of ,h,br in the solution2 if alone its solution easily passes into the violet variety with evolution of heat4 ,chromic oxide1 ,cr#b,o#c1 rarely found1 and in small quantities1 in chrome ochre1 is formed by the oxidation of chromium and its lower oxides1 by the reduction of chromates 7for example1 of ammonium or mercuric chromate7 and by the decomposition 7splitting up7 of the saline compounds of the oxide itself1 ,cr,x#c or ,cr#b,x#f1 like alumina1 which it resembles in forming a feeble base easily giving double and basic salts1 which are either green or violet4 ,the reduction of chromic oxide--for instance1 in a solution by zinc and sulphuric acid--leads to the formation of chromous oxide1 ,cr,o1 and its salts1 ,cr,x#b1 of a blue colour 7see ,notes #g and #g bis74 ,the further reduction#h of oxide of chromium and its corresponding compounds gives metallic chromium4 ,deville obtained it 7probably containing carbon7 by reducing chromic oxide with carbon1 at a temperature near the melting point of platinum1 about #agej1 but the metal itself does not fuse at this temperature4 ,chromium has a steel-grey colour and is very hard 7sp4 gr4 #ei71 takes a good polish1 and dissolves in hydrochloric acid1 but cold dilute sulphuric and nitric acids have no action upon it4 ,bunsen obtained metallic chromium by decomposing a solution of chromic chloride1 ,cr#b;,cl#f1 by a galvanic current1 as scales of a grey colour 7sp4 gr4 #gc74 ,whler obtained crystalline chromium by igniting a mixture of the anhydrous chromic chloride ,cr#b;,cl#f 7see ,note #g bis7 with finely-divided zinc1 and sodium and potassium chlorides1 at the boiling-point of zinc4 ,when the resultant mass has cooled the zinc may be dissolved in dilute nitric acid1 and grey crystalline chromium 7sp4 gr4 #fha7 is left behind4 ,frmy also prepared crystalline chromium by the action of the vapour of sodium on anhydrous chromic chloride in a stream of hydrogen1 using the apparatus shown in the accompanying drawing1 and placing the sodium and the chromic chloride in separate porcelain boats4 ,the tube containing these boats is only heated when it is quite full of dry hydrogen4 ,the crystals of metallic chromium obtained in the tube are grey cubes having a considerable hardness and withstanding the action of powerful acids1 and even of aqua regia4 ,the chromium obtained by ,whler by the action of a galvanic current is1 on the contrary1 acted on under these conditions4 ,the reason of this difference must be looked for in the presence of impurities1 and in the crystalline structure4 ,but in any case1 among the properties of metallic chromium1 the following may be considered established3 it is white in colour1 with a specific gravity of about #fg1 is extremely hard in a crystalline form1 is not oxidised by air at the ordinary temperature1 and with carbon it forms alloys like cast iron and steel4 #h ,the reduction of metallic chromium proceeds with comparative ease in aqueous solutions4 ,thus the action of sodium amalgams upon a strong solution of ,cr#b;,cl#f gives 7first ,cr,cl#b7 an amalgam of chromium from which the mercury may be easily driven off by heating 7in hydrogen to avoid oxidation71 and there remains a spongy mass of easily oxidizable chromium4 ,plaset 7#ahia71 by passing an electric current through a solution of chrome alum mixed with a small amount of ,h#b,,so#d and ,k#b,,so#d1 obtained hard scales of chromium of a bluish-white colour possessing great hardness and stability 7under the action of water1 air1 and acids74 ,glatzel 7#ahij7 reduced a mixture of #b,k,cl ,cr#b;,cl#f by heating it to redness with shavings of magnesium4 ,the metallic chromium thus obtained has the appearance of a fine light-grey powder which is seen to be crystalline under the microscope2 its sp4 gr4 at #af is #fgbhd4 ,it fuses 7with anhydrous borax7 only at the highest temperatures1 and after fusion presents a silver-white fracture4 ,the strongest magnet has no action upon it4 ,moissan 7#ahic7 obtained chromium by reducing the oxide ,cr#b,o#c with carbon in the electrical furnace 7,chapter ,,viii41 ,note #ag7 in #i-aj minutes with a current of #cej ampres and #ej volts4 ,the mixture of oxide and carbon gives a bright ingot weighing #ajj-aaj grams4 ,a current of #ajj ampres and #ej volts completes the experiment upon a smaller quantity of material in #ae minutes2 a current of #cj ampres and #ej volts gave an ingot of #aj grams in #cj-dj minutes4 ,the resultant carbon alloy is more or less rich in chromium 7from #hgcg-iag p4c474 ,to obtain the metal free from carbon1 the alloy is broken into large lumps1 mixed with oxide of chromium1 put into a crucible and covered with a layer of oxide4 ,this mixture is then heated in the electric furnace and the pure metal is obtained4 ,this reduction can also be carried on with chrome iron ore ,fe,o,cr#b,o#c which occurs in nature4 ,in this case a homogeneous alloy of iron and chromium is obtained4 ,if this alloy be thrown in lumps into molten nitre1 it forms insoluble sesquioxide of iron and a soluble alkaline chromate4 ,this alloy of iron and chromium dissolved in molten steel 7chrome steel7 renders it hard and tough1 so that such steel has many valuable applications4 ,the alloy1 containing about #c p4c4 ,cr and about #ac p4c4 carbon1 is even harder than the ordinary kinds of tempered steel and has a fine granular fracture4 ,the usual mode of preparing the ferrochromes for adding to steel is by fusing powdered chrome iron ore under fluxes in a graphite crucible4 ,illustration3 ,,fig4 #ib4--;,apparatus for the preparation of metallic chromium by igniting chromic chloride and sodium in a stream of hydrogen4 ,the two analogues of chromium1 molybdenum and tungsten 7or wolfram71 are of still rarer occurrence in nature1 and form acid oxides1 ,,ro#c1 which are still less energetic than ,cr,o#c4 ,tungsten occurs in the somewhat rare minerals1 scheelite1 ,ca,w,o#d1 and wolfram2 the latter being an isomorphous mixture of the normal tungstates of iron and manganese1 7,mn,fe7,,wo#d4 ,molybdenum is most frequently met with as molybdenite1 ,mo,s#b1 which presents a certain resemblance to graphite in its physical properties and softness4 ,it also occurs1 but much more rarely1 as a yellow lead ore1 ,pb,mo,o#d4 ,in both these forms molybdenum occurs in the primary rocks1 in granites1 gneiss1 c41 and in iron and copper ores in ,saxony1 ,sweden1 and ,finland4 ,tungsten ores are sometimes met with in considerable masses in the primary rocks of ,bohemia and ,saxony1 and also in ,england1 ,america1 and the ,urals4 ,the preliminary treatment of the ore is very simple2 for example1 the sulphide1 ,mo,s#b1 is roasted1 and thus converted into sulphurous anhydride and molybdic anhydride1 ,mo,o#c1 which is then dissolved in alkalis1 generally in ammonia4 ,the ammonium molybdate is then treated with acids1 when the sparingly soluble molybdic acid is precipitated4 ,wolfram is treated in a different manner4 ,most frequently the finely-ground ore is repeatedly boiled with hydrochloric and nitric acids1 and the resultant solutions 7of salts of manganese and iron7 poured off1 until the dark brown mass of ore disappears1 whilst the tungstic acid remains1 mixed with silica1 as an insoluble residue2 it is treated also with ammonia1 and is thus converted into soluble ammonium tungstate1 which passes into solution and yields tungstic acid when treated with acids4 ,this hydrate is then ignited1 and leaves tungstic anhydride4 ,the general character of molybdic and tungstic anhydrides is analogous to that of chromic anhydride2 they are anhydrides of a feebly acid character1 which easily give polyacid salts and colloid solutions4#h bis #h bis ,the atomic composition of the tungsten and molybdenum compounds is taken as being identical with that of the compounds of sulphur and chromium1 because 7#a7 both these metals give two oxides in which the amounts of oxygen per given amount of metal stand in the ratio #b 3 #c2 7#b7 the higher oxide is of the latter kind1 and1 like chromic and sulphuric anhydrides1 it has an acid character2 7#c7 certain of the molybdates are isomorphous with the sulphates2 7#d7 the specific heat of tungsten is #jjccd1 consequently the product of the atomic weight and specific heat is #fae1 like that of the other elements--it is the same with molybdenum1 #ifj #jjgbb #fi2 7#e7 tungsten forms with chlorine not only compounds ,w,cl#f1 ,w,cl#e1 and ,w,o,cl#d1 but also ,,wo#b;,cl#b1 a volatile substance the analogue of chromyl chloride1 ,cr,o#b;,cl#b1 and sulphuryl chloride1 ,,so#b;,cl#b4 ,molybdenum gives the chlorine compounds1 ,m,o,cl#b1 ,m,o,cl#c7871 ,m,o,cl#d 7fuses at #aid1 boils at #bfh2 according to ,debray it contains ,m,o,cl#e71 ,mo,o,cl#d1 ,mo,o#b;,cl#b1 and ,mo,o#b7,,oh7,cl4 ,the existence of tungsten hexachloride1 ,w,cl#f1 is an excellent proof of the fact that the type ,,sx#f appears in the analogues of sulphur as in ,,so#c2 7#f7 the vapour density accurately determined for the chlorine compounds ,mo,cl#d1 ,w,cl#f1 ,w,cl#e1 ,w,o,cl#d 7,roscoe7 leaves no doubt as to the molecular composition of the compounds of tungsten and molybdenum1 for the observed and calculated results entirely agree4 ,tungsten is sometimes called scheele in honour of ,scheele1 who discovered it in #agha and molybdenum in #aggh4 ,tungsten is also known as wolfram2 the former name was the name given to it by ,scheele1 because he extracted it from the mineral then known as tungsten and now called scheelite1 ,ca,w,o#d4 ,the researches of ,roscoe1 ,blomstrand and others have subsequently thrown considerable light on the whole history of the compounds of molybdenum and tungsten4 ,the ammonium salts of tungsten and molybdic acids when ignited leave the anhydrides1 which resemble each other in many respects4 ,tungsten anhydride1 ,,wo#c1 is a yellowish substance1 which only fuses at a strong heat1 and has a sp4 gr4 of #fh4 ,it is insoluble both in water and acid1 but solutions of the alkalis1 and even of the alkali carbonates1 dissolve it1 especially when heated1 forming alkaline salts4 ,molybdic anhydride1 ,mo,o#c1 is obtained by igniting the acid 7hydrate7 or the ammonium salt1 and forms a white mass which fuses at a red heat1 and solidifies to a yellow crystalline mass of sp4 gr4 #dd2 whilst on further heating in open vessels or in a stream of air this anhydride sublimes in pearly scales--this enables it to be obtained in a tolerably pure state4 ,water dissolves it in small quantities--namely1 #a part requires #fjj parts of water for its solution4 ,the hydrates of molybdic anhydride are soluble also in acids 7a hydrate1 ,h#b,mo,o#d1 is obtained from the nitric acid solution of the ammonium salt71 which forms one of their distinctions from the tungstic acids4 ,but after ignition molybdic anhydride is insoluble in acids1 like tungstic anhydride2 alkalis dissolve this anhydride1 easily forming molybdates4 ,potassium bitartrate dissolves the anhydride with the aid of heat4 ,none of the acids yet considered by us form so many different salts with one and the same base 7alkali7 as molybdic and tungstic acids4 ,the composition of these salts1 and their properties also1 vary considerably4 ,the most important discovery in this respect was made by ,marguerite and ,laurent1 who showed that the salts which contain a large proportion of tungstic acid are easily soluble in water1 and ascribed this property to the fact that tungstic acid may be obtained in several states4 ,the common tungstates1 obtained with an excess of alkali1 have an alkaline reaction1 and on the addition of sulphuric or hydrochloric acid first deposit an acid salt and then a hydrate of tungstic acid1 which is insoluble both in water and acids2 but if instead of sulphuric or hydrochloric acids1 we add acetic or phosphoric acid1 or if the tungstate be saturated with a fresh quantity of tungstic acid1 which may be done by boiling the solution of the alkali salt with the precipitated tungstic acid1 a solution is obtained which1 on the addition of sulphuric or a similar acid1 does not give a precipitate of tungstic acid at the ordinary or at higher temperatures4 ,the solution then contains peculiar salts of tungstic acid1 and if there be an excess of acid it also contains tungstic acid itself2 ,laurent1 ,riche1 and others called it metatungstic acid1 and it is still known by this name4 ,those salts which with acids immediately give the insoluble tungstic acid have the composition ,r#b,,wo#d1,,rhwo#d1 whilst those which give the soluble metatungstic acid contain a far greater proportion of the acid elements4 ,scheibler obtained the 7soluble7 metatungstic acid itself by treating the soluble barium 7meta7 tetratungstate1 ,ba,o1#d,,wo#c1 with sulphuric acid4 ,subsequent research showed the existence of a similar phenomenon for molybdic acid4 ,there is no doubt that this is a case of colloidal modifications4 ,many chemists have worked on the various salts formed by molybdic and tungstic acids4 ,the tungstates have been investigated by ,marguerite1 ,laurent1 ,marignac1 ,riche1 ,scheibler1 ,anthon1 and others4 ,the molybdates were partially studied by the same chemists1 but chiefly by ,struv and ,svanberg1 ,delafontaine1 and others4 ,it appears that for a given amount of base the salts contain one to eight equivalents of molybdic or tungstic anhydride2 i4e4 if the base have the composition ,,ro1 then the highest proportion of base will be contained by the salts of the composition ,,rowo#c or ,r,o,mo,o#c--that is1 by those salts which correspond with the normal acids ,h#b,,wo#d and ,h#b,mo,o#d1 of the same nature as sulphuric acid2 but there also exist salts of the composition ,,ro1#b,,wo#c1 ,,ro1#c,,wo#c 444 ,,ro1#h,,wo#c4 ,the water contained in the composition of many of the acid salts is often not taken into account in the above4 ,the properties of the salts holding different proportions of acids vary considerably1 but one salt may be converted into another by the addition of acid or base with great facility1 and the greater the proportion of the elements of the acid in a salt1 the more stable1 within a certain limit1 is its solution and the salt itself4 ,the most common ammonium molybdate has the composition 7,,nh#d;,,ho7#f1;,h#b,o1#g,mo,o#c 7or1 according to ,marignac and others1 ,,nh#d;,h,mo,o#d71 and is prepared by evaporating an ammoniacal solution of molybdic acid4 ,it is used in the laboratory for precipitating phosphoric acid1 and is purified for this purpose by mixing its solution with a small quantity of magnesium nitrate1 in order to precipitate any phosphoric acid present1 filtering1 and then adding nitric acid and evaporating to dryness4 ,a pure ammonium molybdate free from phosphoric acid may then be extracted from the residue4 ,phosphoric acid forms insoluble compounds with the oxides of uranium and iron1 tin1 bismuth1 c41 having feeble basic and even acid properties4 ,this perhaps depends on the fact that the atoms of hydrogen in phosphoric acid are of a very different character1 as we saw above4 ,those atoms of hydrogen which are replaced with difficulty by ammonium1 sodium1 c41 are probably easily replaced by feebly energetic acid groups--that is1 the formation of particular complex substances may be expected to take place at the expense of these atoms of the hydrogen of phosphoric acid and of certain feeble metallic acids2 and these substances will still be acids1 because the hydrogen of the phosphoric acids and metallic acids1 which is easily replaced by metals1 is not removed by their mutual combination1 but remains in the resultant compound4 ,such a conclusion is verified in the phosphomolybdic acids obtained 7#ahhh7 by ,debray4 ,if a solution of ammonium molybdate be acidified1 and a small amount of a solution 7it may be acid7 containing orthophosphoric acid or its salts be added to it 7so that there are at least #dj parts of molybdic acid present to #a part of phosphoric acid71 then after a period of twenty-four hours the whole of the phosphoric acid is separated as a yellow precipitate1 containing1 however1 not more than #c to #d p4c4 of phosphoric anhydride1 about #c p4c4 of ammonia1 about #ij p4c4 of molybdic anhydride1 and about #d p4c4 of water4 ,the formation of this precipitate is so distinct and so complete that this method is employed for the discovery and separation of the smallest quantities of phosphoric acid4 ,phosphoric acid was found to be present in the majority of rocks by this means4 ,the precipitate is soluble in ammonia and its salts1 in alkalis and phosphates1 but is perfectly insoluble in nitric1 sulphuric1 and hydrochloric acids in the presence of ammonium molybdate4 ,the composition of the precipitate appears to vary under the conditions of its precipitation1 but its nature became clear when the acid corresponding with it was obtained4 ,if the above-described yellow precipitate be boiled in aqua regia1 the ammonia is destroyed1 and an acid is obtained in solution1 which1 when evaporated in the air1 crystallises out in yellow oblique prisms of approximately the composition ,p#b,o#e1bj,mo,o#c1bf;,h#b,o4 ,such an unusual proportion of component parts is explained by the above-mentioned considerations4 ,we saw above that molybdic acid easily gives salts ,r#b,on,mo,o#cm,h#b,o1 which we may imagine to correspond to a hydrate ,mo,o#b7;,,ho7#bn,mo#cm,h#b,o4 ,and suppose that such a hydrate reacts on orthophosphoric acid1 forming water and compounds of the composition ,mo,o#b7;,,hpo#d7n,mo,o#cm,h#b,o or ,mo,o#c7;,h#b,,po#d7bn,mo,o#cm,h#b,o2 this is actually the composition of phosphomolybdic acid4 ,probably it contains a portion of the hydrogen replaceable by metals of both the acids ,h#c,,po#d and of ,h#b,mo,o#d4 ,the crystalline acid above is probably ,h#c,mo,p,o#g1i,mo,o#c1ab;,h#b,o4 ,this acid is really tribasic1 because its aqueous solution precipitates salts of potassium1 ammonium1 rubidium 7but not lithium and sodium7 from acid solutions1 and gives a yellow precipitate of the composition ,r#c,mo,p,o#g1i,mo,o#c1h;,h#b,o1 where ,r ,,nh#d4 ,besides these1 salts of another composition may be obtained1 as would be expected from the preceding4 ,these salts are only stable in acid solutions 7which is naturally due to their containing an excess of acid oxides71 whilst under the action of alkalis they give colourless phosphomolybdates of the composition ,r#c,mo,p,o#c1,mo,o#b1c;,h#b,o4 ,the corresponding salts of potassium1 silver1 ammonium1 are easily soluble in water and crystalline4 ,phosphomolybdic acid is an example of the complex inorganic acids first obtained by ,marignac and afterwards generalised and studied in detail by ,gibbs4 ,we shall afterwards meet with several examples of such acids1 and we will now turn attention to the fact that they are usually formed by weak polybasic acids 7boric1 silicic1 molybdic1 c471 and in certain respects resemble the cobaltic and such similar complex compounds1 with which we shall become acquainted in the following chapter4 ,as an example we will here mention certain complex compounds containing molybdic and tungstic acids1 as they will illustrate the possibility of a considerable complexity in the composition of salts4 ,the action of ammonium molybdate upon a dilute solution of purpureocobaltic salts 7see ,chapter ,,xxii47 acidulated with acetic acid gives a salt which after drying at #ajj has the composition ,co#b,o#caj,,nh#cg,mo,o#cc;,h#b,o4 ,after ignition this salt leaves a residue having the composition #b;,co,o#g,mo,o#c4 ,an analogous compound is also obtained for tungstic acid1 having the composition ,co#b,o#caj,,nh#caj,,wo#ci;,h#b,o4 ,in this case after ignition there remains a salt of the composition ,co,o#e,,wo#c 7,carnot1 #ahhi74 ,professor ,kournakoff1 by treating a solution of potassium and sodium molybdates1 containing a certain amount of suboxide of cobalt1 with bromine obtained salts having the composition3 #c,k#b,o,co#b,o#cab,mo,o#cbj;,h#b,o 7light green7 and #c,k#b,o,co#b,o#caj,mo#caj;,h#b,o 7dark green74 ,pchard 7#ahic7 obtained salts of the four complex phosphotungstic acids by evaporating equivalent mixtures of solutions of phosphoric acid and metatungstic acid 7see further on73 phosphotrimetatungstic acid ,p#b,o#eab,,wo#cdh;,h#b,o1 phosphotetrametatungstic acid ,p#b,o#eaf,,wo#cfi;,h#b,o1 phosphopentametatungstic acid ,p#b,o#ebj,,wo#c;,h#b,o1 and phosphohexametatungstic acid ,p#b,o#ebd,,wo#cei;,h#b,o4 ,kehrmann and ,frankel described still more complex salts1 such as3 #c;,ag#b,o#d;,ba,o,p#b,o#ebb,,wo#c;,h#b, o1#e;,ba,o#b ,k#b,,op#b,o#cbb,,wo#cdh;,h#b,o4 ,analogous double salts with #bb,,wo#c were also obtained with ,k,sr1 ,k,hg1 ,ba,hg1 and ,,nh#d,pb4 ,kehrmann 7#ahib7 considers the possibility of obtaining an unlimited number of such salts to be a general characteristic of such compounds4 ,mahom and ,friedheim 7#ahib7 obtained compounds of similar complexity for molybdic and arsenic acids4 ,for tungstic acid there are known3 7#a7 ,normal salts--for example1 ,k#b,,wo#d2 7#b7 the so-called acid salts have a composition like #c,k#b,o1#g,,wo#c1f;,h#b,o or ,k#f;,h#h7,,wo#d7g1b;,h#b,o2 7#c7 the tritungstates like ,na#c,o1#c,,wo#c1c;,h#b,o ,na#b;,h#d7,,wo#d7c1;,h#b,o4 ,all these three classes of salts are soluble in water1 but are precipitated by barium chloride1 and with acids in solution give an insoluble hydrate of tungstic acid2 whilst those salts which are enumerated below do not give a precipitate either with acids or with the salts of the heavy metals1 because they form soluble salts even with barium and lead4 ,they are generally called metatungstates4 ,they all contain water and a larger proportion of acid elements than the preceding salts2 7#d7 the tetratungstates1 like ,na#b,o1#d,,wo#c1aj;,h#b,o and ,ba,o1#d,,wo#c1i;,h#b,o for example2 7#e7 the octatungstates--for example1 ,na#b,o1#h,,wo#c1bd;,h#b,o4 ,since the metatungstates lose so much water at #ajj that they leave salts whose composition corresponds with an acid1 #c;,h#b,o1#d,,wo#c--that is1 ,h#f,w#d,o#ae--whilst in the meta salts only #b hydrogens are replaced by metals1 it is assumed1 although without much ground1 that these salts contain a particular soluble metatungstic acid of the composition ,h#f,w#d,o#ae4 ,as an example we will give a short description of the sodium salts4 ,the normal salt1 ,na#b,,wo#d1 is obtained by heating a strong solution of sodium carbonate with tungstic acid to a temperature of #hj2 if the solution be filtered hot1 it crystallises in rhombic tabular crystals1 having the composition ,na#b,,wo#d1b;,h#b,o1 which remain unchanged in the air and are easily soluble in water4 ,when this salt is fused with a fresh quantity of tungstic acid1 it gives a ditungstate1 which is soluble in water and separates from its solution in crystals containing water4 ,the same salt is obtained by carefully adding hydrochloric acid to the solution of the normal salt so long as a precipitate does not appear1 and the liquid still has an alkaline reaction4 ,this salt was first supposed to have the composition ,na#b,w#b,o#g1d;,h#b,o1 but it has since been found to contain 7at #ajj7 ,na#f,w#g,o#bd1af;,h#b,o--that is1 it corresponds with the similar salt of molybdic acid4 7,if this salt be heated to a red heat in a stream of hydrogen1 it loses a portion of its oxygen1 acquires a metallic lustre1 and turns a golden yellow colour1 and1 after being treated with water1 alkali1 and acid1 leaves golden yellow leaflets and cubes which are very like gold4 ,this very remarkable substance1 discovered by ,whler1 has1 according to ,malaguti's analysis1 the composition ,na#b,w#c,o#i2 that is1 it1 as it were1 contains a double tungstate of tungsten oxide1 ,,wo#b1 and of sodium1 ,na#b,,wo#d1,,wo#b,,wo#c4 ,the decomposition of the fused sodium salt is best effected by finely-divided tin4 ,this substance has a sp4 gr4 #ff2 it conducts electricity like metals1 and like them has a metallic lustre4 ,when brought into contact with zinc and sulphuric acid it disengages hydrogen1 and it becomes covered with a coating of copper in a solution of copper sulphate in the presence of zinc--that is1 notwithstanding its complex composition it presents to a certain extent the appearance and reactions of the metals4 ,it is not acted on by aqua regia or alkaline solutions1 but it is oxidised when ignited in air47 ,the ditungstate mentioned above1 deprived of water 7having undergone a modification similar to that of metaphosphoric acid71 after being treated with water1 leaves an anhydrous1 sparingly soluble tetratungstate1 ,na#b,,wo#d1c,,wo#c1 which1 when heated at #abj in a closed tube with water1 passes into an easily soluble metatungstate4 ,it may therefore be said that the metatungstates are hydrated compounds4 ,on boiling a solution of the above-mentioned salts of sodium with the yellow hydrate of tungstic acid they give a solution of metatungstate1 which is the hydrated tetratungstate4 ,its crystals contain ,na#b,w#d,o#ac1aj;,h#b,o4 ,after the hydrate of tungstic acid 7obtained from the ordinary tungstates by precipitation with an acid7 has stood a long time in contact with a solution 7hot or cold7 of sodium tungstate1 it gives a solution which is not precipitated by hydrochloric acid2 this must be filtered and evaporated over sulphuric acid in a desiccator 7it is decomposed by boiling74 ,it first forms a very dense solution 7aluminium floats in it7 of sp4 gr4 #cj1 and octahedral crystals of sodium metatungstate1 ,na#b,w#d,o#ac1aj;,h#b,o1 sp4 gr4 #che1 then separate4 ,it effloresces and loses water1 and at #ajj only two out of the ten equivalents of water remain1 but the properties of the salt remain unaltered4 ,if the salt be deprived of water by further heating1 it becomes insoluble4 ,at the ordinary temperature one part of water dissolves ten parts of the metatungstate4 ,the other metatungstates are easily obtained from this salt4 ,thus a strong and hot solution1 mixed with a like solution of barium chloride1 gives on cooling crystals of barium metatungstate1 ,ba,w#d,o#ac1i;,h#b,o4 ,these crystals are dissolved without change in water containing hydrochloric acid1 and also in hot water1 but they are partially decomposed by cold water1 with the formation of a solution of metatungstic acid and of the normal barium salt ,ba,w,o#d4 ,in order to explain the difference in the properties of the salts of tungstic acid1 we may add that a mixture of a solution of tungstic acid with a solution of silicic acid does not coagulate when heated1 although the silicic acid alone would do so2 this is due to the formation of a silicotungstic acid1 discovered by ,marignac1 which presents a fresh example of a complex acid4 ,a solution of a tungstate dissolves gelatinous silica1 just as it does gelatinous tungstic acid1 and when evaporated deposits a crystalline salt of silicotungstic acid4 ,this solution is not precipitated either by acids 7a clear analogy to the metatungstates7 or by sulphuretted hydrogen1 and corresponds with a series of salts4 ,these salts contain one equivalent of silica and #h equivalents of hydrogen or metals1 in the same form as in salts1 to #ab or #aj equivalents of tungstic anhydride2 for example the crystalline potassium salt has the composition ,k#h,w#ab,si,o#db1ad;,h#b,o #d,k#b,o1#ab,,wo#c1,si,o#b1ad;,h#b,o4 ,acid salts are also known in which half of the metal is replaced by hydrogen4 ,the complexity of the composition of such complex acids 7for example1 of the phosphomolybdic acid7 involuntarily leads to the idea of polymerisation1 which we were obliged to recognise for silica1 lead oxide1 and other compounds4 ,this polymerisation1 it seems to me1 may be understood thus3 a hydrate ,a 7for example1 tungstic acid7 is capable of combining with a hydrate ,b 7for example1 silica or phosphoric acid1 with or without the disengagement of water71 and by reason of this faculty it is capable of polymerisation--that is1 ,a combines with ,a--combines with itself--just as aldehyde1 ,c#b;,h#d,o1 or the cyanogen compounds are able to combine with hydrogen1 oxygen1 c41 and are liable to polymerisation4 ,on this view the molecule of tungstic acid is probably much more complex than we represent it2 this agrees with the easy volatility of such compounds as the chloranhydrides1 ,cr,o#b;,cl#b1 ,mo,o#b;,cl#b1 the analogues of the volatile sulphuryl chloride1 ,,so#b;,cl#b1 and with the non-volatility1 or difficult volatility1 of chromic and molybdic anhydrides1 the analogues of the volatile sulphuric anhydride4 ,such a view also finds a certain confirmation in the researches made by ,graham on the colloidal state of tungstic acid1 because colloidal properties only appertain to compounds of a very complex composition4 ,the observations made by ,graham on the colloidal state of tungstic and molybdic acids introduced much new matter into the history of these substances4 ,when sodium tungstate1 mixed in a dilute solution with an equivalent quantity of dilute hydrochloric acid1 is placed in a dialyser1 hydrochloric acid and sodium chloride pass through the membrane1 and a solution of tungstic acid remains in the dialyser4 ,out of #ajj parts of tungstic acid about #hj parts remain in the dialyser4 ,the solution has a bitter1 astringent taste1 and does not yield gelatinous tungstic acid 7hydrogel7 either when heated or on the addition of acids or salts4 ,it may also be evaporated to dryness2 it then forms a vitreous mass of the hydrosol of tungstic acid1 which adheres strongly to the walls of the vessel in which it has been evaporated1 and is perfectly soluble in water4 ,it does not even lose its solubility after having been heated to #bjj1 and only becomes insoluble when heated to a red heat1 when it loses about #b-a_/b p4c4 of water4 ,the dry acid1 dissolved in a small quantity of water1 forms a gluey mass1 just like gum arabic1 which is one of the representatives of the hydrosols of colloidal substances4 ,the solution1 containing #e p4c of the anhydride1 has a sp4 gr4 of #ajdg2 with #bj p4c41 of #abag2 with #ej p4c41 of #ahj2 and with #hj p4c41 of #cbd4 ,the presence of a polymerised trioxide in the form of hydrate1 ,h#b,,ow#c,o#i or ,h#b,o#d,,wo#c1 must then be recognised in the solution3 this is confirmed by ,sabaneeff's cryoscopic determinations 7#ahhi74 ,a similar stable solution of molybdic acid is obtained by the dialysis of a mixture of a strong solution of sodium molybdate with hydrochloric acid 7the precipitate which is formed is re-dissolved74 ,if ,mo,cl#d be precipitated by ammonia and washed with water1 a point is reached at which perfect solution takes place1 and the molybdic acid forms a colloid solution which is precipitated by the addition of ammonia 7,muthmann74 ,the addition of alkali to the solutions of the hydrosols of tungstic and molybdic acids immediately results in the re-formation of the ordinary tungstates and molybdates4 ,there appears to be no doubt but that the same transformation is accomplished in the passage of the ordinary tungstates into the metatungstates as takes place in the passage of tungstic acid itself from an insoluble into a soluble state2 but this may be even actually proved to be the case1 because ,scheibler obtained a solution of tungstic acid1 before ,graham1 by decomposing barium metatungstate 7,ba,o#d,,wo#c1i;,h#b,o7 with sulphuric acid4 ,by treating this salt with sulphuric acid in the amount required for the precipitation of the baryta1 ,scheibler obtained a solution of metatungstic acid which1 when containing #dcge p4c4 of acid1 had a sp4 gr4 of #afcd1 and with #bgfa p4c4 a sp4 gr4 of #acbg--that is1 specific gravities corresponding with those found by ,graham4 ,pchard found that as much heat is evolved by neutralising metatungstic acid as with sulphuric acid4 ,questions connected with the metamorphoses or modifications of tungstic and molybdic acids1 and the polymerisation and colloidal state of substances1 as well as the formation of complex acids1 belong to that class of problems the solution of which will do much towards attaining a true comprehension of the mechanism of a number of chemical reactions4 ,i think1 moreover1 that questions of this kind stand in intimate connection with the theory of the formation of solutions and alloys and other so-called indefinite compounds4 ,hydrogen 7which does not directly form compounds with ,cr1 ,mo1 and ,w7 reduces molybdic and tungstic anhydride at a red heat2 and this forms the means of obtaining metallic molybdenum and tungsten4 ,both metals are infusible1 and both under the action of heat form compounds with carbon and iron 7the addition of tungsten to steel renders the latter ductile and hard74#i ,molybdenum forms a grey powder1 which scarcely aggregates under a most powerful heat1 and has a specific gravity of #he4 ,it is not acted on by the air at the ordinary temperature1 but when ignited it is first converted into a brown1 and then into a blue oxide1 and lastly into molybdic anhydride4 ,acids do not act on it--that is1 it does not liberate hydrogen from them1 not even from hydrochloric acid--but strong sulphuric acid disengages sulphurous anhydride1 forming a brown mass1 containing a lower oxide of molybdenum4 ,alkalis in solution do not act on molybdenum1 but when fused with it hydrogen is given off1 which shows1 as does its whole character1 the acid properties of the metal4 ,the properties of tungsten are almost identical2 it is infusible1 has an iron-grey colour1 is exceedingly hard1 so that it even scratches glass4 ,its specific gravity is #aia 7according to ,roscoe71 so that1 like uranium1 platinum1 c41 it is one of the heaviest metals4#i bis ,just as sulphur and chromium have their corresponding persulphuric and perchromic acids1 ,h#b,s#b,o#h and ,h#b;,cr,o#h1 having the properties of peroxides1 and corresponding to peroxide of hydrogen1 so also molybdenum and tungsten are known to give permolybdic and pertungstic acids1 ,h#b,mo#b,o#h and ,h#b,w#b,o#h1 which have the properties of true peroxides1 i4e4 easily disengage iodine from ,,ki and chlorine from ,h,cl1 easily part with their oxygen1 and are formed by the action of peroxide of hydrogen1 into which they are readily reconverted 7hence they may be regarded as compounds of ,h#b,o#b with #b,mo,o#c and #b,,wo#c71 c4 ,their formation 7,boerwald #ahhd1 ,kemmerer #ahia7 is at once seen in the coloration 7not destroyed by boiling71 which is obtained on mixing a solution of the salts with peroxide of hydrogen1 and on treating1 for instance1 molybdic acid with a solution of peroxide of hydrogen 7,pchard #ahib74 ,the acid then forms an orange-coloured solution1 which after evaporation in vacuo leaves ,mo#b;,h#b,o#hd;,h#b,o as a crystalline powder1 and loses #d;,h#b,o at #ajj1 beyond which it decomposes with the evolution of oxygen4#i tri #i ,moissan 7#ahic7 studied the compounds of ,mo and ,w formed with carbon in the electrical furnace 7they are extremely hard7 from a mixture of the anhydrides and carbon4 ,poleck and ,grtzner obtained definite compounds ,fe,w#b and ,fe,w#b;,c#c for tungsten4 ,metallic ,w and ,mo displace ,ag from its solutions but not ,pb4 ,there is reason for believing that the sp4 gr4 of pure molybdenum is higher than that 7#he7 generally ascribed to it4 #i bis ,we may conclude our description of tungsten and molybdenum by stating that their sulphur compounds have an acid character1 like carbon bisulphide or stannic sulphide4 ,if sulphuretted hydrogen be passed through a solution of a molybdate it does not give a precipitate unless sulphuric acid be present1 when a dark brown precipitate of molybdenum trisulphide1 ,mo,s#c1 is formed4 ,when this sulphide is ignited without access of air it gives the bisulphide ,mo,s#b2 the latter is not able to combine with potassium sulphide like the trisulphide ,mo,s#c1 which forms a salt1 ,k#b,mo,s#d1 corresponding with ,k#b,mo,o#d4 ,this is soluble in water1 and separates out from its solution in red crystals1 which have a metallic lustre and reflect a green light4 ,it is easily obtained by heating the native bisulphide1 ,mo,s#b1 with potash1 sulphur1 and a small amount of charcoal1 which serves for deoxidising the oxygen compounds4 ,tungsten gives similar compounds1 ,r#b,,ws#d1 where ,r ,,nh#d1 ,k1 ,na4 ,they are decomposed by acids1 with the separation of tungsten trisulphide1 ,,ws#c1 and molybdenum trisulphide1 ,mo,s#c4 ,rideal 7#ahib7 obtained ,w#b,n#c by heating ,,wo#c in ,,nh#c4 ,this compound exhibited the general properties of metallic nitrides4 #i tri ,when peroxide of hydrogen acts upon a solution of potassium molybdate well-formed yellow crystals belonging to the triclinic system separate out in the cold4 ,when these crystals are heated in vacuo they first lose water and then decompose1 leaving a residue composed of the salt originally taken4 ,they are soluble in water but insoluble in alcohol4 ,their composition is represented by the formula ,k#b,mo#b,o#hb;,h#b,o4 ,an ammonium salt is obtained by evaporating peroxide of hydrogen with ammonium molybdate4 ,the following salts have also been obtained by the action of peroxide of hydrogen upon the corresponding molybdates3 ,na#b,mo#b,o#ff;,h#b,o--in yellow prismatic crystals2 ,mg,mo#b,o#haj;,h#b,o--stellar needles2 ,ba,mo,o#hb;,h#b,o--in microscopic yellow octahedra4 ,a corresponding sodium pertungstate has been obtained by ,pchard by boiling sodium tungstate with a solution of peroxide of hydrogen for several minutes4 ,the solution rapidly turns yellow1 and no longer gives a precipitate of tungstic anhydride when treated with nitric acid4 ,when evaporated in vacuo the solution leaves a thick syrupy liquid from which ray-like crystals separate out2 these crystals are more soluble in water than the salt originally taken4 ,when heated they also lose water and oxygen4 ,their composition answers to the formula ,m#b,w#b,o#hb;,h#b,o1 where ,m ,na1 ,,nh#d1 c4 ,the permolybdates and pertungstates have similar properties4 ,when treated with oxygen acids they give peroxide of hydrogen1 and disengage chlorine and iodine from hydrochloric acid and potassium iodide4 ,piccini 7#ahia7 showed that peroxide of hydrogen not only combines with the oxygen compounds of ,mo and ,w1 but also with their fluo-compounds1 among which ammonium fluo-molybdate ,mo,o#b;,f#bb,,nh#d and others have long been known4 7,a few new salts of similar composition have been obtained by ,f4 ,moureu in #ahic47 ,the action of peroxide of hydrogen upon these compounds gives salts containing a larger amount of oxygen2 for instance1 a solution of ,mo,o#b;,f#bb,,kfh#b,o with peroxide of hydrogen gives a yellow solution which after cooling separates out yellow crystalline flakes of ,mo,o#c;,f#bb,,kfh#b,o1 resembling the salt originally taken in their external appearance4 ,by employing a similar method ,piccini also obtained3 ,mo,o#c;,f#bb,rb,f,h#b,o--yellow monoclinic crystals2 ,mo,o#c;,f#b1b;,cs,f,h#b,o1--yellow flakes1 and the corresponding tungstic compounds4 ,all these salts react like peroxide of hydrogen4 ,in speaking of these compounds ,i for my part think it may be well to call attention to the fact that1 in the first place1 the composition of ,piccini's oxy-fluo compounds does not correspond to that of permolybdic and pertungstic acid4 ,if the latter be expressed by formul with one equivalent of an element1 they will be ,h,mo,o#d and ,,hwo#d1 and the oxy-fluo form corresponding to them should have the composition ,mo,o#c;,f and ,,wo#c;,f while it contains ,,mo#c;,f#b and ,,wo#c;,f#b1 i4e4 answers as it were to a higher degree of oxidation1 ,mo,h#b,o#c and ,w#c;,,ho#c4 ,but if permolybdic acid be regarded as #b,mo,o#c ,h#b,o#b1 i4e4 as containing the elements of peroxide of hydrogen1 then ,piccini's compound will also be found to contain the original salts ,h#b,o2 for example1 from ,mo,o#b;,f#bb,,kfh#b,o there is obtained a compound ,mo,o#b;,f#bb,,kfh#b,o#b1 i4e4 instead of ,h#b,o they contain ,h#b,o#b4 ,in the second place the capacity of the salts of molybdenum and tungsten to retain a further amount of oxygen or ,h#b,o#b probably bears some relation to their property of giving complex acids and of polymerising which has been considered in ,note #h bis4 ,there is1 however1 a great chemical interest in the accumulation of data respecting these high peroxide compounds corresponding to molybdic and tungstic acids4 ,with regard to the peroxide form of uranium1 see ,chapter ,,xx41 ,note #ff4 ,uranium1 ,u #bdj1 has the highest atomic weight of all the analogues of chromium1 and indeed of all the elements yet known4 ,its highest salt-forming oxide1 ,,uo#c1 shows very feeble acid properties4 ,although it gives sparingly-soluble yellow compounds with alkalis1 which fully correspond with the dichromates--for example1 ,na#b,u#b,o#g ,na#b,o1#b,,uo#c1aj--yet it more frequently and easily reacts with acids1 ,,hx1 forming fluorescent yellowish-green salts of the composition ,,uo#b,x#b1 and in this respect uranic trioxide1 ,,uo#c1 differs from chromic anhydride1 ,cr,o#c1 although the latter is able to give the oxychloride1 ,cr,o#b;,cl#b4 ,in molybdenum and tungsten1 however1 we see a clear transition from chromium to uranium4 ,thus1 for example1 chromyl chloride1 ,cr,o#b;,cl#b1 is a brown liquid which volatilises without change1 and is completely decomposed by water2 molybdenum oxychloride1 ,mo,o#b;,cl#b1 is a crystalline substance of a yellow colour1 which is volatile and soluble in water 7,blomstrand71 like many salts4 ,tungsten oxychloride1 ,,wo#b;,cl#b1 stands still nearer to uranyl chloride in its properties2 it forms yellow scales on which water and alkalis act1 as they do on many salts 7zinc chloride1 ferric chloride1 aluminium chloride1 stannic chloride1 c471 and perfectly corresponds with the difficultly volatile salt1 ,,uo#b;,cl#b 7obtained by ,peligot by the action of chlorine on ignited uranium dioxide1 ,,uo#b71 which is also yellow and gives a yellow solution with water1 like all the salts ,,uo#b,x#b4 ,the property of uranic oxide1 ,,uo#c1 of forming salts ,,uo#b,x#b is shown in the fact that the hydrated oxide of uranium1 ,,uo#b7;,,ho7#b1 which is obtained from the nitrate1 carbonate1 and other salts by the loss of the elements of the acid1 is easily soluble in acids1 as well as in the fact that the lower grades of oxidation of uranium are able1 when treated with nitric acid1 to form an easily crystallisable uranyl nitrate1 ,,uo#b7,,no#c7b1f;,h#b,o2 this is the most commonly occurring uranium salt4#aa #aj ,uranium trioxide1 or uranic oxide1 shows its feeble basic and acid properties in a great number of its reactions4 7#a7 ,solutions of uranic salts give yellow precipitates with alkalis1 but these precipitates do not contain the hydrate of the oxide1 but compounds of it with bases2 for example1 #b,,uo#b7,,no#c7b #f,,kho #d,,kno#c #c;,h#b,o ,k#b,u#b,o#g4 ,there are other urano-alkali compounds of the same constitution2 for example1 7,,nh#d7b,u#b,o#g 7known commercially as uranic oxide71 ,mg,u#b,o#g1 ,ba,u#b,o#g4 ,they are the analogues of the dichromates4 ,sodium uranate is the most generally used under the name of uranium yellow1 ,na#b,u#b,o#g4 ,it is used for imparting the characteristic yellow-green tint to glass and porcelain4 ,neither heat nor water nor acids are able to extract the alkali from sodium uranate1 ,na#b,u#b,o#g1 and therefore it is a true insoluble salt1 of a yellow colour1 and clearly indicates the acid character 7although feeble7 of uranic oxide4 7#b7 ,the carbonates of the alkaline earths 7for instance1 barium carbonate7 precipitate uranic oxide from its salts1 as they do all the salts of feeble bases2 for example1 ,r#b,o#c4 7#c7 ,the alkaline carbonates1 when added to solutions of uranic salts1 give a precipitate1 which is soluble in an excess of the reagent1 and particularly so if the acid carbonates be taken4 ,this is due to the fact that 7#d7 the uranyl salts easily form double salts with the salts of the alkali metals1 including the salts of ammonium4 ,uranium1 in the form of these double salts1 often gives salts of well-defined crystalline form1 although the simple salts are little prone to appear in crystals4 ,such1 for example1 are the salts obtained by dissolving potassium uranate1 ,k#b,u#b,o#g1 in acids1 with the addition of potassium salts of the same acids4 ,thus1 with hydrochloric acid and potassium chloride a well-formed crystalline salt1 ,k#b7,,uo#b7;,cl#d1b;,h#b,o1 belonging to the monoclinic system1 is produced4 ,this salt decomposes in dissolving in pure water4 ,among these double salts we may mention the double carbonate with the alkalis1 ,r#d7,,uo#b77;,,co#c7c 7equal to #b,r#b;,,co#c ,,uo#b;,,co#c72 the acetates1 ,r7,,uo#b77;,c#b;,h#c,o#b7c--;for instance1 the sodium salt1 ,na7,,uo#b77;,c#b;,h#c,o#b7c1 and the potassium salt1 ,k7,,uo#b77;,c#b;,h#c,o#b7c1;,h#b,o2 the sulphates1 ,r#b7,,uo#b77,,so#d7c1b;,h#b,o1 c4 ,in the preceding formula ,r ,k1 ,na1 ,,nh#d1 or ,r#b ,mg1 ,ba1 c4 ,this property of giving comparatively stable double salts indicates feebly developed basic properties1 because double salts are mainly formed by salts of distinctly basic metals 7these form1 as it were1 the basic element of a double salt7 and salts of feebly energetic bases 7these form the acid element of a double salt71 just as the former also give acid salts2 the acid of the acid salts is replaced in the double salts by the salt of the feebly energetic base1 which1 like water1 belongs to the class of intermediate bases4 ,for this reason barium does not give double salts with alkalis as magnesium does1 and this is why double salts are more easily formed by potassium than by lithium in the series of the alkali metals4 7#e7 ,the most remarkable property1 proving the feeble energy of uranic oxide as a base1 is seen in the fact that when their composition is compared with that of other salts those of uranic oxide always appear as basic salts4 ,it is well known that a normal salt1 ,r#b,x#f1 corresponds with the oxide ,r#b,o#c1 where ,x ,cl1 ,,no#c1 c41 or ,x#b ,,so#d1 ,,co#c1 c42 but there also exist basic salts of the same type where ,x ,,ho or ,x#b ,o4 ,we saw salts of all kinds among the salts of aluminium1 chromium1 and others4 ,with uranic oxide no salts are known of the types ,,ux#f 7,u,cl#f1 ,u7,,so#d7c1 alums1 c41 are not known71 nor even salts1 ,u7,,ho7#b,x#d or ,,uox#d1 but it always forms salts of the type ,u7,,ho7#d,x#b1 or ,,uo#b,x#b4 ,judging from the fact that nearly all the salts of uranic oxide retain water in crystallising from their solutions1 and that this water is difficult to separate from them1 it may be thought to be water of hydration4 ,this is seen in part from the fact that the composition of many of the salts of uranic oxide may then be expressed without the presence of water of crystallisation2 for instance1 ,u7,,ho7#d,k#b;,cl#d 7and the salt of ,,nh#d1 ,u7,,ho7#d,k#b7,,so#d7b1 ,u7,,ho7#d7;,c#b;,h#c,o#b7b4 ,sodium uranyl acetate however does not contain water4 #aa ,uranyl nitrate1 or uranium nitrate1 ,,uo#b7,,no#c7b1f;,h#b,o1 crystallises from its solutions in transparent yellowish-green prisms 7from an acid solution71 or in tabular crystals 7from a neutral solution71 which effloresce in the air and are easily soluble in water1 alcohol1 and ether1 have a sp4 gr4 of #bh1 and fuse when heated1 losing nitric acid and water in the process4 ,if the salt itself 7,berzelius7 or its alcoholic solution 7,malaguti7 be heated up to the temperature at which oxides of nitrogen are evolved1 there then remains a mass which1 after being evaporated with water1 leaves uranyl hydroxide1 ,,uo#b7;,,ho7#b 7sp4 gr4 #eic71 whilst if the salt be ignited there remains the dioxide1 ,,uo#b1 as a brick-red powder1 which on further heating loses oxygen and forms the dark olive uranoso-uranic oxide1 ,u#c,o#h4 ,the solution of the nitrate obtained from the ore is purified in the following manner3 sulphurous anhydride is first passed through it in order to reduce the arsenic acid present into arsenious acid2 the solution is then heated to #fj1 and sulphuretted hydrogen passed through it2 this precipitates the lead1 arsenic1 and tin1 and certain other metals1 as sulphides1 insoluble in water and dilute nitric acid4 ,this liquid is then filtered and evaporated with nitric acid to crystallisation1 and the crystals are dissolved in ether4 ,or else the solution is first treated with chlorine in order to convert the ferrous chloride 7produced by the action of the hydrogen sulphide7 into ferric chloride1 the oxides are then precipitated by ammonia1 and the resultant precipitate1 containing the oxides ,fe#b,o#c1 ,,uo#c1 and compounds of the latter with potash1 lime1 ammonia1 and other bases present in the solution 7the latter being due to the property of uranic oxide of combining with bases71 is washed and dissolved in a strong1 slightly-heated solution of ammonium carbonate1 which dissolves the uranic oxide but not the ferric oxide4 ,the solution is filtered1 and on cooling deposits a well-crystallising uranyl ammonium carbonate1 ,,uo#b7,,nh#d7d7;,,co#c7c1 in brilliant monoclinic crystals which on exposure to air slowly give off water1 carbonic anhydride1 and ammonia2 the same decomposition is readily effected at #cjj1 the residue then consisting of uranic oxide4 ,this salt is not very soluble in water1 but is readily so in ammonium carbonate2 it is obvious that it may readily be converted into all the other salts of oxides of uranium4 ,uranium salts are also purified in the form of acetate1 which is very sparingly soluble1 and is therefore directly precipitated from a strong solution of the nitrate by mixing it with acetic acid4 ,we may also mention the uranyl phosphate1 ,,hupo#f1 which must be regarded as an orthophosphate in which two hydrogens are replaced by the radicle uranyl1 ,,uo#b1 i4e4 as ,h7,,uo#b7,,po#d4 ,this salt is formed as a hydrated gelatinous yellow precipitate1 on mixing a solution of uranyl nitrate with disodium phosphate4 ,the precipitation occurs in the presence of acetic acid1 but not in the presence of hydrochloric acid4 ,if moreover an excess of an ammonium salt be present1 the ammonia enters into the composition of the bright yellow gelatinous precipitate formed1 in the proportion ,,uo#b,,nh#d,,po#d4 ,this precipitate is not soluble in water and acetic acid1 and its solution in inorganic acids when boiled entirely expels all the phosphoric acid4 ,this fact is taken advantage of for removing phosphoric acids from solutions--for instance1 from those containing salts of calcium and magnesium4 ,uranium1 which gives an oxide1 ,,uo#c1 and the corresponding salt ,,uo#b,x#b and dioxide ,,uo#b1 to which the salts ,,ux#d correspond1 is rarely met with in nature4 ,uranite or the double orthophosphate of uranic oxide1 ,r7,,uo#b7;,h#b,p#b,o#h1g;,h#b,o1 where ,r ,cu or ,ca1 uranium-vitriol ,u7,,so#d7b1;,h#b,o1 samarakite1 and schynite1 are very rarely found1 and then only in small quantities4 ,of more frequent and abundant occurrence is the non-crystalline1 earthy brown uranium ore known as pitchblende 7sp4 gr4 #gb71 which is mainly composed of the intermediate oxide1 ,u#c,o#h ,,uo#b1b,,uo#c4 ,this ore is found at ,joachimsthal in ,bohemia and in ,cornwall4 ,it usually contains a number of different impurities1 chiefly sulphides and arsenides of lead and iron1 as well as lime and silica compounds4 ,in order to expel the arsenic and sulphur it is roasted1 ground1 washed with dilute hydrochloric acid1 which does not dissolve the uranoso-uranic oxide1 ,u#c,o#h1 and the residue is dissolved in nitric acid1 which transforms the uranium oxide into the nitrate1 ,,uo#b7,,no#c7b4 ,it must be observed that the oxide of uranium1 first distinguished by ,klaproth 7#aghi71 was for a long time regarded as able to give metallic uranium under the action of charcoal and other reducing agents 7with the aid of heat74 ,but the substance thus obtained was only the uranium dioxide1 ,,uo#b4 ,the compound nature of this dioxide1#ab or the presence of oxygen in it1 was demonstrated by ,peligot 7#ahda71 by igniting it with charcoal in a stream of chlorine4 ,he thus obtained a volatile uranium tetrachloride1 ,u,cl#d1ac which1 when heated with sodium1 gave metallic uranium as a grey metal1 having a specific gravity of #ahg1 and liberating hydrogen from acids1 with the formation of green uranous salts1 ,,ux#d1 which act as powerful reducing agents4#ad #ab ,uranium dioxide1 or uranyl1 ,,uo#b1 which is contained in the salts ,,uo#b,x#b1 has the appearance and many of the properties of a metal4 ,uranic oxide may be regarded as uranyl oxide1 7,,uo#b7,o1 its salts as salts of this uranyl2 its hydroxide1 7,,uo#b7;,h#b,o#b1 is constituted like ,ca,h#b,o#b4 ,the green oxide of uranium1 uranoso-uranic oxide 7easily formed from uranic salts by the loss of oxygen71 ,u#c,o#h ,,uo#b1b,,uo#c1 when ignited with charcoal or hydrogen 7dry7 gives a brilliant crystalline substance of sp4 gr4 about #aaj 7,urlaub71 whose appearance resembles that of metals1 and decomposes steam at a red heat with the evolution of hydrogen2 it does not1 however1 decompose hydrochloric or sulphuric acid1 but is oxidised by nitric acid4 ,the same substance 7i4e4 uranium dioxide ,,uo#b7 is also obtained by igniting the compound 7,,uo#b7,k#b;,cl#d in a stream of hydrogen1 according to the equation ,,uo#b,k#d;,cl#d ,h#b ,,uo#b #b;,h,cl #b,k,cl4 ,it was at first regarded as the metal4 ,in #ahda ,peligot found that it contained oxygen1 because carbonic oxide and anhydride were evolved when it was ignited with charcoal in a stream of chlorine1 and from #bgb parts of the substance which was considered to be metal he obtained #chb parts of a volatile product containing #adb parts of chlorine4 ,from this it was concluded that the substance taken contained an equivalent amount of oxygen4 ,as #adb parts of chlorine correspond with #cb parts of oxygen1 it followed that #bgb - #cb #bdj parts of metal were combined in the substance with #cb parts of oxygen1 and also in the chlorine compound obtained with #adb parts of chlorine4 ,these calculations have been made for the now accepted atomic weight of uranium 7,u #bdj1 see ,note #ad74 ,peligot took another atomic weight1 but this does not alter the principle of the argument4 #ac ,uranium tetrachloride1 uranous chloride1 ,u,cl#d1 corresponds with uranous oxide as a base4 ,it was obtained by ,peligot by igniting uranic oxide mixed with charcoal in a stream of dry chlorine3 ,,uo#c #c;,c #b;,cl#b ,u,cl#d #c;,,co4 ,this green volatile compound 7,note #ab7 crystallises in regular octahedra1 is very hygroscopic1 easily soluble in water1 with the development of a considerable amount of heat1 and no longer separates out from its solution in an anhydrous state1 but disengages hydrochloric acid when evaporated4 ,the solution of uranous chloride in water is green4 ,it is also formed by the action of zinc and copper 7forming cuprous chloride7 on a solution of uranyl chloride1 ,,uo#b;,cl#b1 especially in the presence of hydrochloric acid and sal-ammoniac4 ,solutions of uranyl salts are converted into uranous salts by the action of various reducing agents1 and among others by organic substances or by the action of light1 whilst the salts ,,ux#d are converted into uranyl salts1 ,,uo#b,x#b1 by exposure to air or by oxidising agents4 ,solutions of the green uranyl salts act as powerful reducing agents1 and give a brown precipitate of the uranous hydroxide1 ,,uh#d,o#d1 with potash and other alkalis4 ,this hydroxide is easily soluble in acids but not in alkalis4 ,on ignition it does not form the oxide ,,uo#b1 because it decomposes water1 but when the higher oxides of uranium are ignited in a stream of hydrogen or with charcoal they yield uranous oxide4 ,both it and the chloride ,u,cl#d1 dissolve in strong sulphuric acid1 forming a green salt1 ,u7,,so#d7b1b;,h#b,o4 ,the same salt1 together with uranyl sulphate1 ,,uo#b7,,so#d71 is formed when the green oxide1 ,u#c,o#h1 is dissolved in hot sulphuric acid4 ,the salts obtained in the latter instance may be separated by adding alcohol to the solution1 which is left exposed to the light2 the alcohol reduces the uranyl salt to uranous salt1 an excess of acid being required4 ,an excess of water decomposes this salt1 forming a basic salt1 which is also easily produced under other circumstances1 and contains ,,uo7,,so#d71b;,h#b,o 7which corresponds to the uranic salt74 #ad ,the atomic weight of uranium was formerly taken as half the present one1 ,u #abj1 and the oxides ,u#b,o#c1 suboxide ,,uo1 and green oxide ,u#c,o#d1 were of the same types as the oxides of iron4 ,with a certain resemblance to the elements of the iron group1 uranium presents many points of distinction which do not permit its being grouped with them4 ,thus uranium forms a very stable oxide1 ,u#b,o#c7,u #abj71 but does not give the corresponding chloride ,u#b;,cl#f 7,roscoe1 however1 in #ahgd obtained ,u,cl#e1 like ,mo,cl#e and ,w,cl#e71 and under those circumstances 7the ignition of oxide of uranium mixed with charcoal1 in a stream of chlorine71 when the formation of this compound might be expected1 it gives 7,u #abj7 the chloride ,u,cl#b1 which is characterised by its volatility2 this is not a property1 to such an extent1 of any of the bichlorides1 ,r,cl#b1 of the iron group4 ,the alteration or doubling of the atomic weight of uranium--i4e4 the recognition of ,u #bdj--was made for the first time in the first 7,russian7 edition of this work 7#ahga71 and in my memoir of the same year in ,liebig's ,annalen1 on the ground that with an atomic weight #abj1 uranium could not be placed in the periodic system4 ,i think it will not be superfluous to add the following remarks on this subject3 7#a7 ,in the other groups 7,k--,rb--,cs1 ,ca--,sr--,ba1 ,cl--,br--,i7 the acid character of the oxides decreases and their basic character increases with the rise of atomic weight1 and therefore we should expect to find the same in the group ,cr--,mo--,w--,u1 and if ,cr,o#c1 ,mo,o#c1 ,,wo#c be the anhydrides of acids then we indeed find a decrease in their acid character1 and therefore uranium trioxide1 ,,uo#c1 should be a very feeble anhydride1 but its basic properties should also be very feeble4 ,uranic oxide does indeed show these properties1 as was pointed out above 7,note #aj74 7#b7 ,chromium and its analogues1 besides the oxides ,,ro#c1 also form lower grades of oxidation ,,ro#b1 ,r#b,o#c1 and the same is seen in uranium2 it forms ,,uo#c1 ,,uo#b1 ,u#b,o#c and their compounds4 7#c7 ,molybdenum and tungsten1 in being reduced from ,,ro#c1 easily and frequently give an intermediate oxide of a blue colour1 and uranium shows the same property2 giving the so-called green oxide which1 according to present views1 must be regarded as ,u#c,o#h ,,uo#bb,,uo#c1 analogous to ,mo#c,o#h4 7#d7 ,the higher chlorides1 ,r,cl#f1 possible for the elements of this group1 are either unstable 7,w,cl#f7 or do not exist at all 7,cr72 but there is one single lower volatile compound1 which is decomposed by water1 and liable to further reduction into a non-volatile chlorine product and the metal4 ,the same is observed in uranium1 which forms an easily volatile chloride1 ,u,cl#d1 decomposed by water4 7#e7 ,the high sp4 gr4 of uranium 7#ahf7 is explained by its analogy to tungsten 7sp4 gr4 #aia74 7#f7 ,for uranium1 as for chromium and tungsten1 yellow tints predominate in the form ,,ro#c1 whilst the lower forms are green and blue4 7#g7 ,zimmermann 7#ahha7 determined the vapour densities of uranous bromide1 ,u,br#d1 and chloride1 ,u,cl#d 7#aid and #acb71 and they were found to correspond to the formul given above--that is1 they confirmed the higher atomic weight ,u #bdj4 ,roscoe1 a great authority on the metals of this group1 was the first to accept the proposed atomic weight of uranium1 ,u #bdj1 which since ,zimmermann's work has been generally recognised4 ,as the salts of uranic oxide are reduced in the absence of organic matter by the action of light1 and as they impart a characteristic coloration to glass1#ae they find a certain application in photography and glass work4 #ae ,uranium glass1 obtained by the addition of the yellow salt ,k#b,u#b,o#g to glass1 has a green yellow fluorescence1 and is sometimes employed for ornaments2 it absorbs the violet rays1 like the other salts of uranic oxide--that is1 it possesses an absorption spectrum in which the violet rays are absent4 ,the index of refraction of the absorbed rays is altered1 and they are given out again as greenish-yellow rays2 hence1 compounds of uranic acid1 when placed in the violet portion of the spectrum1 emit a greenish-yellow light1 and this forms one of the best examples 7another is found in a solution of quinine sulphate7 of the phenomenon of fluorescence4 ,the rays of light which pass through uranic compounds do not contain the rays which excite the phenomena of fluorescence and of chemical transformation1 as the researches of ,stokes prove4 ,if we compare together the highly acid elements1 sulphur1 selenium1 and tellurium1 of the uneven series1 with chromium1 molybdenum1 tungsten1 and uranium of the even series1 we find that the resemblance of the properties of the higher form ,,ro#c does not extend to the lower forms1 and even entirely disappears in the elements1 for there is not the smallest resemblance between sulphur and chromium and their analogues in a free state4 ,in other words1 this means that the small periods1 like ,na1 ,mg1 ,al1 ,si1 ,p1 ,s1 ,cl1 containing seven elements1 do not contain any near analogues of chromium1 molybdenum1 c41 and therefore their true position among the other elements must be looked for only in those large periods which contain two small periods1 and whose type is seen in the period containing3 ,k1 ,ca1 ,sc1 ,ti1 ,v1 ,cr1 ,mn1 ,fe1 ,co1 ,ni1 ,cu1 ,zn1 ,ga1 ,ge1 ,as1 ,se1 ,br4 ,these large periods contain ,ca and ,zn1 giving ,,ro1 ,sc1 and ,ga of the third group1 ,ti and ,ge giving ,,ro#b1 ,v and ,as forming ,r#b,o#e1 ,cr and ,se of the sixth group1 ,mn and ,br of the seventh group1 and the remaining elements1 ,fe1 ,co1 ,ni1 form connective members of the intermediate eighth group1 to the description of the representatives of which we shall turn in the following chapters4 ,we will now proceed to describe manganese1 ,mn #ee1 as an element of the seventh group of the even series1 directly following after ,cr #eb1 which corresponds with ,br #hj to the same degree that ,cr does with ,se #gi4 ,for chromium1 selenium1 and bromine very close analogues are known1 but for manganese as yet none have been obtained--that is1 it is the only representative of the even series in the seventh group4 ,in placing manganese with the halogens in one group1 the periodic system of the elements only requires that it should bear an analogy to the halogens in the higher type of oxidation--i4e4 in the salts and acids--whilst it requires that as great a difference should be expected in the lower types and elements as there exists between chromium or molybdenum and sulphur or selenium4 ,and this is actually the case4 ,the elements of the seventh group form a higher salt-forming oxide1 ,r#b,o#g1 and its corresponding hydrate1 ,,hro#d1 and salts--for example1 ,k,cl,o#d4 ,manganese in the form of potassium permanganate1 ,k,mn,o#d1 actually presents a great analogy in many respects to potassium perchlorate1 ,k,cl,o#d4 ,the analogy of the crystalline form of both salts was shown by ,mitscherlich4 ,the salts of permanganic acid are also nearly all soluble in water1 like those of perchloric acid1 and if the silver salt of the latter1 ,ag,cl,o#d1 be sparingly soluble in water1 so also is silver permanganate1 ,ag,mn,o#d4 ,the specific volume of potassium perchlorate is equal to #ee1 because its specific gravity #bed2 the specific volume of potassium permanganate is equal to #eh1 because its specific gravity #bga4 ,so that the volumes of equivalent quantities are in this instance approximately the same whilst the atomic volumes of chlorine 7#cee_/ac #bg7 and manganese 7#ee_/ge7 are in the ratio #d 3 #a4 ,in a free state the higher acids ,h,cl,o#d and ,h,mn,o#d are both soluble in water and volatile1 both are powerful oxidisers--in a word1 their analogy is still closer than that of chromic and sulphuric acids1 and those points of distinction which they present also appear among the nearest analogues--for example1 in sulphuric and telluric acids1 in hydrochloric and hydriodic acids1 c4 ,besides ,mn#b,o#g manganese gives a lower grade of oxidation1 ,mn,o#c1 analogous to sulphuric and chromic trioxides1 and with it corresponds potassium manganate1 ,k#b,mn,o#d1 isomorphous with potassium sulphate4#af ,in the still lower grades of oxidation1 ,mn#b,o#c and ,mn,o1 there is hardly any similarity to chlorine1 whilst every point of resemblance disappears when we come to the elements themselves--i4e4 to manganese and chlorine--for manganese is a metal1 like iron1 which combines directly with chlorine to form a saline compound1 ,mn,cl#b1 analogous to magnesium chloride4#ag #af ,the comparison of potassium permanganate with potassium perchlorate1 or of potassium manganate with potassium sulphate1 shows directly that many of the physical and chemical properties of substances do not depend on the nature of the elements1 but on the atomic types in which they appear1 on the kind of movements1 or on the positions in which the atoms forming the molecule occur4 #ag ,if1 however1 we compare the spectra 7,vol4 ,i4 p4 #efe7 of chlorine1 bromine1 and iodine with that of manganese1 a certain resemblance or analogy is to be found connecting manganese both to iron and to chlorine1 bromine1 and iodine4 ,manganese belongs to the number of metals widely distributed in nature1 especially in those localities where iron occurs1 whose ores frequently contain compounds of manganous oxide1 ,mn,o1 which presents a resemblance to ferrous oxide1 ,fe,o1 and to magnesia4 ,in many minerals magnesia and the oxides allied to it are replaced by manganous oxide2 calcspars and magnesites--i4e4 ,r,,co#c in general--are frequently met with containing manganous carbonate1 which also occurs in a separate state1 although but rarely4 ,the soil also and the ash of plants generally contain a small quantity of manganese4 ,in the analysis of minerals it is generally found that manganese occurs together with magnesia1 because1 like it1 manganous oxide remains in solution in the presence of ammoniacal salts1 not being precipitated by reagents4 ,the property of this manganous oxide1 ,mn,o1 of passing into the higher grades of oxidation under the influence of heat1 alkalis1 and air1 gives an easy means not only of discovering the presence of manganese in admixture with magnesia1 but also of separating these two analogous bases4 ,magnesia is not able to give higher grades of oxidation1 whilst manganese gives them with great facility4 ,thus1 for instance1 an alkaline solution of sodium hypochlorite produces a precipitate of manganese dioxide in a solution of a manganous salt3 ,mn,cl#b ,na,cl,o #b,na,h,o ,mn,o#b ,h#b,o #c,na,cl2 whilst magnesia is not changed under these circumstances1 and remains in the form of ,mg,cl#b4 ,if the magnesia be precipitated owing to the presence of alkali1 it may be dissolved in acetic acid1 in which manganese dioxide is insoluble4 ,the presence of small quantities of manganese may also be recognised by the green coloration which alkalis acquire when heated with manganese compounds in the air4 ,this green coloration depends on the property of manganese of giving a green alkaline manganate3 ,mn,cl#b #d,,kho ,o#b ,k#b,mn,o#d #b,k,cl #b;,h#b,o4 ,thus the faculty of oxidising in the presence of alkalis forms an essential character of manganese4 ,the higher grades of oxidation containing ,mn#b,o#g and ,mn,o#c are quite unknown in nature1 and even ,mn,o#b is not so widely spread in nature as the ores composed of manganous compounds which are met with nearly everywhere4 ,the most important ore of manganese is its dioxide1 or so-called peroxide1 ,mn,o#b1 which is known in mineralogy as pyrolusite4 ,manganese also occurs as an oxide corresponding with magnetic iron ore1 ,mn,o1,mn#b,o#c ,mn#c,o#d1 forming the mineral known as hausmannite4 ,the oxide ,mn#b,o#c also occurs in nature as the anhydrous mineral braunite1 and in a hydrated form1 ,mn#b,o#c1;,h#b,o1 called manganite4 ,both of these often occur as an admixture in pyrolusite4 ,besides which1 manganese is met with in nature as a rose-coloured mineral1 rhodonite1 or silicate1 ,mn,si,o#c4 ,very fine and rich deposits of manganese ores have been found in the ,caucasus1 the ,urals1 and along the ,dnieper4 ,those at the ,sharapansky district of the ,government of ,kutais and at ,nicopol on the ,dnieper are particularly rich4 ,a large quantity of the ore 7as much as #ajj1jjj tons yearly7 is exported from these localities4 ,thus manganese gives oxides of the following forms3 ,mn,o1 manganous oxide1 and manganous salts1 ,mn,x#b1 corresponding with the base1 which resembles magnesia and ferrous oxide in many respects2 ,mn#b,o#c1 a very feeble base1 giving salts1 ,mn,x#c1 analogous to the aluminium and ferric salts1 easily reduced to ,mn,x#b2 ,mn,o#b1 dioxide1 generally called peroxide1 an almost indifferent oxide1 or feebly acid2#ah ,mn,o#c1 manganic anhydride1 which forms salts resembling potassium sulphate2#ah bis ,mn#b,o#g1 permanganic anhydride1 giving salts analogous to the perchlorates4 #ah ,the name 'peroxide' should only be retained for those highest oxides 7and ,mn,o#b stands between ,mn,o and ,mn,o#c7 which either by a direct method of double decomposition are able to give hydrogen peroxide or contain a larger proportion of oxygen than the base or the acid1 just as hydrogen peroxide contains more oxygen than water4 ,their type will be ,h#b,o#b1 and they are exemplified by barium peroxide1 ,ba,o#b1 and sulphur peroxide1 ,s#b,o#g1 c4 ,such a dioxide as ,mn,o#b is1 in all probability1 a salt--that is1 a manganous manganate1 ,mn,o#c,mn,o1 and also1 as a basic salt of a feeble base1 capable of combining with alkalis and acids4 ,hence the name of manganese peroxide should be abandoned1 and replaced by manganese dioxide4 ,pb,o#b is better termed lead dioxide than peroxide4 ,bisulphide of manganese1 ,mn,s#b1 corresponding to iron pyrites1 ,fe,s#b1 sometimes occurs in nature in fine octahedra 7and cube combinations71 for instance1 in ,sicily2 it is called ,hauerite4 #ah bis ,on comparing the manganates with the permanganates--for example1 ,k#b,mn,o#d with ,k,mn,o#d--we find that they differ in composition by the abstraction of one equivalent of the metal4 ,such a relation in composition produced by oxidation is of frequent occurrence--for instance1 ,k#d;,fe7,,cn7#f in oxidising gives ,k#c;,fe7,,cn7#f2 ,h#b,,so#d in oxidising gives persulphuric acid1 ,,hso#d1 or ,h#b,s#g,o#h2 ,h#b,o forms ,,ho or ,h#b,o#b1 c4 ,all the oxides of manganese when heated with acids give salts1 ,mn,x#b1 corresponding with the lower grade of oxidation1 manganous oxide1 ,mn,o4 ,manganic oxide1 ,mn#b,o#c1 is a feebly energetic base2 it is true that it dissolves in hydrochloric acid and gives a dark solution containing the salt ,mn,cl#c1 but the latter when heated evolves chlorine and gives a salt corresponding with manganous oxide ,mn,cl#b--;i4e4 at first3 ,mn#b,o#c #f;,h,cl #c;,h#b,o ,mn#b;,cl#f1 and then the ,mn#b;,cl#f decomposes into #b,mn,cl#b ,cl#b4 ,none of the remaining higher grades of oxidation have a basic character1 but act as oxidising agents in the presence of acids1 disengaging oxygen and passing into salts of the lower grade of oxidation of manganese1 ,mn,o4 ,owing to this circumstance1 the manganous salts are often obtained2 they are1 for instance1 left in the residue when the dioxide is used for the preparation of oxygen and chlorine4#ai #ai ,in the preparation of oxygen from the dioxide by means of ,h#b,,so#d1 ,mn,s,o#d is formed2 in the preparation of chlorine from ,h,cl and ,mn,o#b1 ,mn,cl#b is obtained4 ,these two manganous salts may be taken as examples of compounds ,mn,x#b4 ,manganous sulphate generally contains various impurities1 and also a large amount of iron salt 7from the native ,mn,o#b71 from which it cannot be freed by crystallisation4 ,their removal may1 however1 be effected by mixing a portion of the liquid with a solution of sodium carbonate2 a precipitate of manganous carbonate is then formed4 ,this precipitate is collected and washed1 and then added to the remaining mass of the impure solution of manganous sulphate2 on heating the solution with this precipitate1 the whole of the iron is precipitated as oxide4 ,this is due to the fact that in the solution of the manganese dioxide in sulphuric acid the whole of the iron is converted into the ferric state 7because the dioxide acts as an oxidising agent71 which1 as an exceedingly feeble base precipitated by calcium carbonate and other kindred salts1 is also precipitated by manganous carbonate4 ,after being treated in this manner1 the solution of manganous sulphate is further purified by crystallisation4 ,if it be a bright red colour1 it is due to the presence of higher grades of oxidation of manganese2 they may be destroyed by boiling the solution1 when the oxygen from the oxides of manganese is evolved and a very faintly coloured solution of manganous sulphate is obtained4 ,this salt is remarkable for the facility with which it gives various combinations with water4 ,by evaporating the almost colourless solution of manganous sulphate at very low temperatures1 and by cooling the saturated solution at about #j1 crystals are obtained containing #g atoms of water of crystallisation1 ,mn,s,o#d1g;,h#b,o1 which are isomorphous with cobaltous and ferrous sulphates4 ,these crystals1 even at #aj1 lose #e p4c4 of water1 and completely effloresce at #ae1 losing about #bj p4c4 of water4 ,by evaporating a solution of the salt at the ordinary temperature1 but not above #bj1 crystals are obtained containing #e mol4 ,h#b,o1 which are isomorphous with copper sulphate2 whilst if the crystallisation be carried on between #bj and #cj1 large transparent prismatic crystals are formed containing #d mol4 ,h#b,o 7see ,nickel74 ,a boiling solution also deposits these crystals together with crystals containing #c mol4 ,h#b,o1 whilst the first salt1 when fused and boiled with alcohol1 gives crystals containing #b mol4 ,h#b,o4 ,graham obtained a monohydrated salt by drying the salt at about #bjj4 ,the last atom of water is eliminated with difficulty1 as is the case with all salts like ,mn,s,o#dn,h#b,o4 ,the crystals containing a considerable amount of water are rose-coloured1 and the anhydrous crystals are colourless4 ,the solubility of ,mn,s,o#d1d;,h#b,o 7,chapter ,i41 ,note #bd7 per #ajj parts of water is3 at #aj1 #abg parts2 at #cge1 #adi parts2 at #ge1 #ade parts2 and at #aja1 #ib parts4 ,whence it is seen that at the boiling-point this salt is less soluble than at lower temperatures1 and therefore a solution saturated at the ordinary temperature becomes turbid when boiled4 ,manganous sulphate1 being analogous to magnesium sulphate1 is decomposed1 like the latter1 when ignited1 but it does not then leave manganous oxide1 but the intermediate oxide1 ,mn#c,o#d4 ,it gives double salts with the alkali sulphates4 ,with aluminium sulphate it forms fine radiated crystals1 whose composition resembles that of the alums--namely1 ,mn,al#b7,,so#d7d1bd;,h#b,o4 ,this salt is easily soluble in water1 and occurs in nature4 ,manganous chloride1 ,m,cl#b1 crystallises with #d mol4 ,h#b,o1 like the ferrous salt1 and not with #f mol4 ,h#b,o like many kindred salts--for example1 those of cobalt1 calcium1 and magnesium2 #ajj parts of water dissolve #ch parts of the anhydrous salt at #aj and #ee parts at #fb4 ,alcohol also dissolves manganous chloride1 and the alcoholic solution burns with a red flame4 ,this salt1 like magnesium chloride1 readily forms double salts4 ,a solution of borax gives a dirty rose-coloured precipitate having the composition ,mn,h#d7;,,bo#c7b;,h#b,o1 which is used as a drier in paint-making4 ,potassium cyanide produces a yellowish-grey precipitate1 ,mn,c#b,n#b1 with manganous salts1 soluble in an excess of the reagent1 a double salt1 ,k#d,mn,c#f,n#f1 corresponding with potassium ferrocyanide1 being formed4 ,on evaporation of this solution1 a portion of the manganese is oxidised and precipitated1 whilst a salt corresponding to ,gmelin's red salt1 ,k#c1,mn,c#f,n#f 7see ,chapter ,,xxii471 remains in solution4 ,sulphuretted hydrogen does not precipitate salts of manganese1 not even the acetate1 but ammonium sulphide gives a flesh-coloured precipitate1 ,mn,s2 at #cbj this sulphide of manganese passes into a green variety 7,antony74 ,oxalic acid in strong solutions of manganous salts gives a white precipitate of the oxalate1 ,mn,c#b,o#d4 ,this precipitate is insoluble in water1 and is used for the preparation of manganous oxide itself because it decomposes like oxalic acid when ignited 7in a tube without access of air71 with the formation of carbonic anhydride1 carbonic oxide1 and manganous oxide4 ,manganous oxide thus obtained is a green powder1 which however oxidises with such facility that it burns in air when brought into contact with an incandescent substance1 and passes into the red intermediate oxide ,mn#c,o#d4 ,in solutions of manganous salts1 alkalis produce a precipitate of the hydroxide ,mn,h#b,o#b1 which rapidly absorbs oxygen in the presence of air and gives the brown intermediate oxide1 or1 more correctly speaking1 its hydrate4 ,manganous oxide1 besides being obtained by the above-described method from manganous oxalate1 may also be obtained by igniting the higher oxides in a stream of hydrogen1 and also from manganese carbonate4 ,the manganous oxide ignited in the presence of hydrogen acquires a great density1 and is no longer so easily oxidised4 ,it may also be obtained in a crystalline form1 if during the ignition of the carbonate or higher oxide a trace of dry hydrochloric acid gas be passed into the current of hydrogen4 ,it is thus obtained in the form of transparent emerald green crystals of the regular system1 and in this state is easily soluble in acids4 ,manganous oxide in oxidising gives the red oxide of manganese1 ,mn#e,o#d4 ,this is the most stable of all the oxides of manganese2 it is not only stable at the ordinary but also at a high temperature--that is1 it does not absorb or disengage oxygen spontaneously4 ,when ignited1 all the higher oxides of manganese pass into it by losing oxygen1 and manganous oxide by absorbing oxygen4 ,this oxide does not give any distinct salts1 but it dissolves in sulphuric acid1 forming a dark red solution1 which contains both manganous and manganic 7of the oxide1 ,mn#b,o#c7 sulphates4 ,the latter with potassium sulphate gives a manganese alum1 in which the alumina is replaced by its isomorphous oxide of manganese4 ,but this alum1 like the solution of the intermediate oxide in sulphuric acid1 evolves oxygen and leaves a manganous salt when slightly heated4 ,manganese dioxide is still less basic than the oxide1 and disengages oxygen or a halogen in the presence of acids1 forming manganous salts1 like the oxide4 ,however1 if it be suspended in ether1 and hydrochloric acid gas passed into the mixture1 which is kept cool1 the ether acquires a green colour1 owing to the formation of tetrachloride of manganese1 ,mn,cl#d1 corresponding with the dioxide which passes into solution4 ,it is however very unstable1 being exceedingly easily decomposed with the evolution of chlorine4 ,the corresponding fluoride1 ,mn,f#d1 obtained by ,nickls is much more stable4 ,at all events1 manganese dioxide does not exhibit any well-defined basic character1 but has rather an acid character1 which is particularly shown in the compounds ,mn,f#d and ,mn,cl#d just mentioned1 and in the property of manganese dioxide of combining with alkalis4 ,if the higher grades of oxidation of manganese be deoxidised in the presence of alkalis1 they frequently give the dioxide combined with the alkali--for example1 in the presence of potash a compound is formed which contains ,k#b,o1#e,mn,o#b1 which shows the weak acid character of this oxide4 ,when ignited in the presence of sodium compounds manganese dioxide frequently forms ,na#b,o1#h,mn,o#b and ,na#b,o1#ab,mn,o#b1 and lime when heated with ,mn,o#b gives from ,ca,o1#c,mn,o#b to 7,ca,o7#b1,mn,o#b 7,rousseau7 according to the temperature4 ,besides which1 perhaps1 ,mn,o#b is a saline compound1 containing ,mn,o,mn,o#c or 7,mn,o7#c,mn#b,o#g1 and there are reactions which support such a view 7,spring1 ,richards1 ,traube1 and others72 for instance it is known that manganous chloride and potassium permanganate give the dioxide in the presence of alkalis4 ,manganese dioxide may be obtained from manganous salts by the action of oxidising agents4 ,if manganous hydroxide or carbonate be shaken up in water through which chlorine is passed1 the hypochlorite of the metal is not formed1 as is the case with certain other oxides1 but manganese dioxide is precipitated3 #b,mn,o#b;,h#b ,cl#b ,mn,cl#b ,mn,o#b1;,h#b,o ,h#b,o4 ,owing to this fact1 hypochlorites in the presence of alkalis and acetic acid when added to a solution of manganous salts give hydrated manganese dioxide1 as was mentioned above4 ,manganous nitrate also leaves manganese dioxide when heated to #bjj4 ,it is also obtained from manganous and manganic salts of the alkalis1 when they are decomposed in the presence of a small amount of acid2 the practical method of converting the salts ,mn,x#b into the higher grades of oxidation is given in ,chapter ,,ii41 ,note #f4 ,as the salts of manganous oxide ,mn,x#b closely resemble 7and are isomorphous with7 the salts of magnesia ,mg,x#b in many respects 7with the exception of the fact that ,mn,x#b are rose coloured and are easily oxidised in the presence of alkalis71 we will not dwell upon them1 but limit ourselves to illustrating the chemical character of manganese by describing the metal and its corresponding acids4 ,the fact alone that the oxides of manganese are not reduced to the metal when ignited in hydrogen 7whilst the oxides of iron give metallic iron under these circumstances71 but only to manganous oxide1 ,mn,o1 shows that manganese has a considerable affinity for oxygen--that is1 it is difficult to reduce4 ,this may be effected1 however1 by means of charcoal or sodium at a very high temperature4 ,a mixture of one of the oxides of manganese with charcoal or organic matter gives fused metallic manganese under the powerful heat developed by coke with an artificial draught4 ,the metal was obtained for the first time in this manner by ,gahn1 after ,pott1 and more especially ,scheele1 had in the last century shown the difference between the compounds of iron and manganese 7they were previously regarded as being the same74 ,manganese is prepared by mixing one of its oxides in a finely-divided state with oil and soot2 the resultant mass is then first ignited in order to decompose the organic matter1 and afterwards strongly heated in a charcoal crucible4 ,the manganese thus obtained1 however1 contains1 as a rule1 a considerable amount of silicon and other impurities4 ,its specific gravity varies between #gb and #hj4 ,it has a light grey colour1 a feebly metallic lustre1 and although it is very hard it can be scratched by a file4 ,it rapidly oxidises in air1 being converted into a black oxide2 water acts on it with the evolution of hydrogen--this decomposition proceeds very rapidly with boiling water1 and if the metal contain carbon4#bj #bj ,other chemists have obtained manganese by different methods1 and attributed different properties to it4 ,this difference probably depends on the presence of carbon in different proportions4 ,deville obtained manganese by subjecting the pure dioxide1 mixed with pure charcoal 7from burnt sugar71 to a strong heat in a lime crucible until the resultant metal fused4 ,the metal obtained had a rose tint1 like bismuth1 and like it was very brittle1 although exceedingly hard4 ,it decomposed water at the ordinary temperature4 ,brunner obtained manganese having a specific gravity of about #gb1 which decomposed water very feebly at the ordinary temperature1 did not oxidise in air1 and was capable of taking a bright polish1 like steel2 it had the grey colour of cast iron1 was very brittle1 and hard enough to scratch steel and glass1 like a diamond4 ,brunner's method was as follows3 ,he decomposed the manganese fluoride 7obtained as a soluble compound by the action of hydrofluoric acid on manganese carbonate7 with sodium1 by mixing these substances together in a crucible and covering the mixture with a layer of salt and fluor spar2 after which the crucible was first gradually heated until the reaction began1 and then strongly heated in order to fuse the metal separated4 ,glatzel 7#ahhi7 obtained #be grms4 of manganese1 having a grey colour and sp4 gr4 #gci1 by heating a mixture of #ajj grms4 of ,mn,cl#b with #bjj grms4 ,k,cl and #ae grms4 ,mg to a bright white heat4 ,moissan and others1 by heating the oxides of manganese with carbon in the electric furnace1 obtained carbides of manganese--for example1 ,mn#c;,c--and remarked that the metal volatilised in the heat of the voltaic arc4 ,metallic manganese is1 however1 not prepared on a large scale1 but only its alloys with carbon 7they readily and rapidly oxidise7 and ferro-manganese or a coarsely crystalline alloy of iron1 manganese and carbon1 which is smelted in blast-furnaces like pig-iron 7see ,chapter ,,xxii47 ,this ferro-manganese is employed in the manufacture of steel by ,bessemer's and other processes 7see ,chapter ,,xxii47 and for the manufacture of manganese bronze4 ,however1 in ,america1 ,green and ,wahl 7#ahie7 obtained almost pure metallic manganese on a large scale4 ,they first treat the ore of ,mn,o#b with #cj p4c4 sulphuric acid 7which extracts all the oxides of iron present in the ore71 and then heat it in a reducing flame to convert it into ,mn,o1 which they mix with a powder of ,al1 lime and ,ca,f#b 7as a flux71 and heat the mixture in a crucible lined with magnesia2 a reaction immediately takes place at a certain temperature1 and a metal of specific gravity #gc is obtained1 which only contains a small trace of iron4 ,manganese gives two compounds with nitrogen1 ,mn#e,n#b and ,mn#c,n#b4 ,they were obtained by ,prelinger 7#ahid7 from the amalgam of manganese ,mn#b;,hg#e 7obtained on a mercury anode by the action of an electric current upon a solution of ,mn,cl#b72 the mercury may be removed from this amalgam by heating it in an atmosphere of hydrogen1 and then metallic manganese is obtained as a grey porous mass of specific gravity #gdb4 ,if this amalgam be heated in dry nitrogen it gives ,mn#e,n#b 7grey powder1 sp4 gr4 #feh71 but if heated in an atmosphere of ,,nh#c it gives 7as also does ,mn#e,n#b7 ,mn#c,n#b1 7a dark mass with a metallic lustre1 sp4 gr4 #fba71 which1 when heated in nitrogen is converted into ,mn#e,n#b1 and if heated in hydrogen evolves ,,nh#c and disengages hydrogen from a solution of ,,nh#d;,cl4 ,at all events1 manganese is a metal which decomposes water more easily than iron1 nickel1 and cobalt4 ,it has been shown above that if manganese dioxide1 or any lower oxide of manganese1 be heated with an alkali in the presence of air1 the mixture absorbs oxygen1#ba and forms an alkaline manganate of a green colour3 #b,,kho ,mn,o#b ,o ,k#b,mn,o#d ,h#b,o4 ,steam is disengaged during the ignition of the mixture1 and if this does not take place there is no absorption of oxygen4 ,the oxidation proceeds much more rapidly if1 before igniting in air1 potassium chlorate or nitre be added to the mixture1 and this is the method of preparing potassium manganate1 ,k#b,mn,o#d4 ,the resultant mass dissolved in a small quantity of water gives a dark green solution1 which1 when evaporated under the receiver of an air-pump over sulphuric acid1 deposits green crystals of exactly the same form as potassium sulphate--namely1 six-sided prisms and pyramids4 ,the composition of the product is not changed by being redissolved1 if perfectly pure water free from air and carbonic acid be taken4 ,but in the presence of even very feeble acids the solution of this salt changes its colour and becomes red1 and deposits manganese dioxide4 ,the same decomposition takes place when the salt is heated with water1 but when diluted with a large quantity of unboiled water manganese dioxide does not separate1 although the solution turns red4 ,this change of colour depends on the fact that potassium manganate1 ,k#b,mn,o#d1 whose solution is green1 is transformed into potassium permanganate1 ,k,mn,o#d1 whose solution is of a red colour4 ,the reaction proceeding under the influence of acids and a large quantity of water is expressed in the following manner3 #c,k#b,mn,o#d #b;,h#b,o #b,k,mn,o#d ,mn,o#b #d,,kho4 ,if there is a large proportion of acid and the decomposition is aided by heat1 the manganese dioxide and potassium permanganate are also decomposed1 with formation of manganous salt4 ,exactly the same decomposition as takes place under the action of acids is also accomplished by magnesium sulphate1 which reacts in many cases like an acid4 ,when water holding atmospheric oxygen in solution acts on a solution of potassium manganate1 the oxygen combines directly with the manganate and forms potassium permanganate1 without precipitating manganese dioxide1 #b,k#b,mn,o#d ,o ,h#b,o #b,k,mn,o#d #b,,kho4 ,thus a solution of potassium manganate undergoes a very characteristic change in colour and passes from green to red2 hence this salt received the name of chameleon mineral4#bb #ba ,volume ,i4 p4 #aeg1 ,note #g4 #bb ,it was known to the alchemists by this name1 but the true explanation of the change in colour is due to the researches of ,chevillot1 ,edwards1 ,mitscherlich1 and ,forchhammer4 ,the change in colour of potassium manganate is due to its instability and to its splitting up into two other manganese compounds1 a higher and a lower3 #c,mn,o#c ,mn#b,o#g ,mn,o#b4 ,manganese trioxide is really decomposed in this manner by the action of water 7see later73 #c,mn,o#c ,h#b,o #b,mn,h,o#d ,mn,o#b 7,franke1 ,thorpe1 and ,humbly74 ,the instability of the salt is proved by the fact of its being deoxidised by organic matter1 with the formation of manganese dioxide and alkali1 so that1 for instance1 a solution of this salt cannot be filtered through paper4 ,the presence of an excess of alkali increases the stability of the salt2 when heated it breaks up in the presence of water1 with the evolution of oxygen4 ,the method of preparing potassium permanganate will be understood from the above4 ,there are many recipes for preparing this substance1 as it is now used in considerable quantities both for technical and laboratory purposes4 ,but in all cases the essence of the methods is one and the same3 a mixture of alkali with any oxide of manganese 7even manganous hydroxide1 which may be obtained from manganous chloride7 is first heated in the presence of air or of an oxidising substance 7for the sake of rapidity1 with potassium chlorate72 the resultant mass is then treated with water and heated1 when manganese dioxide is precipitated and potassium permanganate remains in solution4 ,this solution may be boiled1 as the liquid will contain free alkali2 but the solution cannot be evaporated to dryness1 because a strong solution1 as well as the solid salt1 is decomposed by heat4 ,by adding a dilute solution of manganous sulphate to a boiling mixture of lead dioxide and dilute nitric acid1 the whole of the manganese may be converted into permanganic acid 7,crum74 ,potassium permanganate1 ,k,mn,o#d1 crystallises in well-formed1 long red prisms with a bright green metallic lustre4 ,in the arts the potash is frequently replaced by soda1 and by other alkaline bases1 but no salt of permanganic acid crystallises so well as the potassium salt1 and therefore this salt is exclusively used in chemical laboratories4 ,one part of the crystalline salt dissolves in #ae parts of water at the ordinary temperature4 ,the solution is of a very deep red colour1 which is so intense that it is still clearly observable after being highly diluted with water4 ,in a solid state it is decomposed by heat1 with evolution of oxygen1 a residue consisting of the lower oxides of manganese and potassium oxide being left4#bb bis ,a mixture of permanganate of potassium1 phosphorous and sulphur takes fire when struck or rubbed1 a mixture of the permanganate with carbon only takes fire when heated1 not when struck4 ,the instability of the salt is also seen in the fact that its solution is decomposed by peroxide of hydrogen1 which at the same time it decomposes4 ,a number of substances reduce potassium permanganate to manganese dioxide 7in which case the red solution becomes colourless74#bc ,many organic substances 7although far from all1 even when boiled in a solution of permanganate7 act in this manner1 being oxidised at the expense of a portion of its oxygen4 ,thus1 a solution of sugar decomposes a cold solution of potassium permanganate4 ,in the presence of an excess of alkali1 with a small quantity of sugar1 the reduction leads to the formation of potassium manganate1 because #b,k,mn,o#d #b,,kho ,o #b,k#b,mn,o#d ,h#b,o4 ,with a considerable amount of sugar and a more prolonged action1 the solution turns brown and precipitates manganese dioxide or even oxide4 ,in the oxidation of many organic bodies by an alkaline solution of ,k,mn,o#d generally three-eighths of the oxygen in the salt are utilised for oxidation3 #b,k,mn,o#d ,k#b,o #b,mn,o#b ,o#c4 ,a portion of the alkali liberated is retained by the manganese dioxide1 and the other portion generally combines with the substance oxidised1 because the latter most frequently gives an acid with an excess of alkali4 ,a solution of potassium iodide acts in a similar manner1 being converted into potassium iodate at the expense of the three atoms of oxygen disengaged by two molecules of potassium permanganate4 #bb bis ,the solution of this salt with an excess of impure commercial alkali generally acquires a green tint4 #bc ,a solution of potassium permanganate gives a beautiful absorption spectrum 7,chapter ,,xiii47 ,if the light in passing through this solution loses a portion of its rays in it 7if one may so account for it71 this is partially explained by the increased oxidising power which the solution then acquires4 ,we may here also remark that a dilute solution of permanganate of potassium forms a colourless solution with nickel salts1 because the green colour of the solution of nickel salts is complementary to the red4 ,such a decolorised solution1 containing a large proportion of nickel and a small proportion of manganese1 decomposes after a time1 throws down a precipitate1 and re-acquires the green colour proper to the nickel salts4 ,the addition of a solution of a cobalt salt 7rose-red7 to the nickel salt also destroys the colour of both salts4 ,in the presence of acids1 potassium permanganate acts as an oxidising agent with still greater energy than in the presence of alkalis4 ,at any rate1 a greater proportion of oxygen is then available for oxidation1 namely1 not #c_/h1 as in the presence of alkalis1 but #e_/h1 because in the first instance manganese dioxide is formed1 and in the second case manganous oxide1 or rather the salt1 ,mn,x#b1 corresponding with it4 ,thus1 for instance1 in the presence of an excess of sulphuric acid1 the decomposition is accomplished in the following manner3 #b,k,mn,o#d #c;,h#b,,so#d ,k#b,,so#d #b,mn,s,o#d #c;,h#b,o #e,o4 ,this decomposition1 however1 does not proceed directly on mixing a solution of the salt with sulphuric acid1 and crystals of the salt even dissolve in oil of vitriol without the evolution of oxygen1 and this solution only decomposes by degrees after a certain time4 ,this is due to the fact that sulphuric acid liberates free permanganic acid from the permanganate1#bd which acid is stable in solution4 ,but if1 in the presence of acids and a permanganate1 there is a substance capable of absorbing oxygen--for instance1 capable of passing into a higher grade of oxidation--then the reduction of the permanganic acid into manganous oxides sometimes proceeds directly at the ordinary temperature4 ,this reduction is very clearly seen1 because the solutions of potassium permanganate are red whilst the manganous salts are almost colourless4 ,thus1 for instance1 nitrous acid and its salts are converted into nitric acid and decolorise the acid solution of the permanganate4 ,sulphurous anhydride and its salts immediately decolorise potassium permanganate1 forming sulphuric acid4 ,ferrous salts1 and in general salts of lower grades of oxidation capable of being oxidised in solution1 act in exactly the same manner4 ,sulphuretted hydrogen is also oxidised to sulphuric acid2 even mercury is oxidised at the expense of permanganic acid1 and decolorises its solution1 being converted into mercuric oxide4 ,moreover1 the end point of these reactions may easily be seen1 and therefore1 having first determined the amount of active oxygen in one volume of a solution of potassium permanganate1 and knowing how many volumes are required to effect a given oxidation1 it is easy to determine the amount of an oxidisable substance in a solution from the amount of permanganate expended 7,marguerite's method74 #bd ,if sulphuric acid is allowed to act on potassium permanganate without any special precautions1 a large amount of oxygen is evolved 7it may even explode and inflame71 and a violet spray of the decomposing permanganic acid is given off4 ,but if the pure salt 7i4e4 free from chlorine7 be dissolved in pure well-cooled sulphuric acid1 without any rise in temperature1 a green-coloured liquid settles at the bottom of the vessel4 ,this liquid does not contain any sulphuric acid1 and consists of permanganic anhydride1 ,mn#b,o#g 7,aschoff1 ,terreil74 ,it is impossible to prepare any considerable quantity of the anhydride by this method1 as it decomposes with an explosion as it collects1 evolving oxygen and leaving red oxide of manganese4 ,permanganic anhydride1 ,mn#b,o#g1 in dissolving in sulphuric acid1 gives a green solution1 which 7according to ,franke1 #ahhg7 contains a compound ,mn#b,,so#aj 7,mn,o#c7b,,so#d--that is1 sulphuric acid in which both hydrogens are replaced by the group ,mn,o#c1 which is combined with ,,ok in permanganate of potassium4 ,this mixture with a small quantity of water gives ,mn#b,o#g1 according to the equation3 7,mn,o#c7b,,so#d ,h#b,o ,h#b,,so#d ,mn#b,o#g1 and when heated to #cj it gives manganese trioxide1 7,mn,o#c7b,,so#d ,h#b,o #b,mn,o#b ,h#b,,so#d ,o4 ,pure manganese trioxide is obtained if the solution of 7,mn,o#c7b,,so#d be poured in drops on to sodium carbonate4 ,then1 together with carbonic anhydride1 a spray of manganese trioxide passes over1 which may be collected in a well-cooled receiver1 and this shows that the reaction proceeds according to the equation3 7,mn,o#c7b,,so#d ,na#b;,,co#c ,na#b,,so#d #b,mn,o#c ,,co#b ,o 7,thorpe74 ,the trioxide is decomposed by water1 forming manganese dioxide and a solution of permanganic acid3 #c,mn,o#c ,h#b,o ,mn,o#b #b;,h,mn,o#d4 ,the same acid is obtained by dissolving permanganic anhydride in water4 ,barium permanganate when treated with sulphuric acid gives the same acid4 ,this barium salt may be prepared by the action of barium chloride on the difficultly soluble silver permanganate1 ,ag,mn,o#d1 which is precipitated on mixing a strong solution of the potassium salt with silver nitrate4 ,the solution of permanganic acid forms a bright red liquid which reflects a dark violet tint4 ,a dilute solution has exactly the same colour as that of the potassium salt4 ,it deposits manganese dioxide when exposed to the action of light1 and also when heated above #fj1 and this proceeds the more rapidly the more dilute the solution4 ,it shows its oxidising properties in many cases1 as already mentioned4 ,even hydrogen gas is absorbed by a solution of permanganic acid2 and charcoal and sulphur are also oxidised by it1 as they are by potassium permanganate4 ,this may be taken advantage of in analysing gunpowder1 because when it is treated with a solution of potassium permanganate1 all the sulphur is converted into sulphuric acid and all the charcoal into carbonic anhydride4 ,finely-divided platinum immediately decomposes permanganic acid4 ,with potassium iodide it liberates iodine 7which may afterwards be oxidised into iodic acid7 7,mitscherlich1 ,fromherz1 ,aschoff1 and others74 ,ammonia does not form a corresponding salt with free permanganic acid1 because it is oxidised with evolution of nitrogen4 ,the oxidising action of permanganic acid in a strong solution may be accompanied by flame and the formation of violet fumes of permanganic acid2 thus a strong solution of it takes fire when brought into contact with paper1 alcohol1 alkaline sulphides1 fats1 c4 ,we may add that1 according to ,franke1 #a part of potassium permanganate with #ac parts of sulphuric acid at #ajj gives brown crystals of the salt ,mn#b7,,so#d7c1;,h#b,,so#d1d;,h#b,o1 which gives a precipitate of hydrated manganese dioxide1 ,h#b,mn,o#c ,mn,o#b;,h#b,o1 when treated with water4 ,spring1 by precipitating potassium permanganate with sodium sulphite and washing the precipitate by decantation1 obtained a soluble colloidal manganese oxide1 whose composition was the mean between ,mn#b,o#c and ,mn,o#b--namely1 ,mn#b,o#c1d7,mn,o#b;,h#b,o74 ,the oxidising action of ,k,mn,o#d1 like all other chemical reactions1 is not accomplished instantaneously1 but only gradually4 ,and1 as the course of the reaction is here easily followed by determining the amount of salt unchanged in a sample taken at a given moment1#be the oxidising reaction of potassium permanganate1 in an acid liquid1 was employed by ,harcourt and ,esson 7#ahfe7 as one of the first cases for the investigation of the laws of the rate of chemical change#bf as a subject of great importance in chemical mechanics4 ,in their experiments they took oxalic acid1 ,c#b;,h#b,o#d1 which in oxidising gives carbonic anhydride1 whilst1 with an excess of sulphuric acid1 the potassium permanganate is converted into manganous sulphate1 ,mn,s,o#d1 so that the ultimate oxidation will be expressed by the equation3 #e;,c#b;,h#b,o#d #b,mn,k,o#d #c;,h#b,,so#d #aj;,,co#b ,k#b,,so#d #b,mn,s,o#d #h;,h#b,o4 ,the influence of the relative amount of sulphuric acid is seen from the annexed table1 which gives the measure of reaction p per #ajj parts of potassium permanganate1 taken four minutes after mixing1 using n molecules of sulphuric acid1 ,h#b,,so#d1 per #b,k,mn,o#d #e;,c#b;,h#b,o#d3 n #b #d #f #h #ab #af #bb p #bb #cf #ea #fc #gg #hf #ib showing that in a given time 7#d minutes7 the oxidation is the more perfect the greater the amount of sulphuric acid taken for given amounts of ,k,mn,o#d and ,c#b;,h#b,o#d4 ,it is obvious also that the temperature and relative amount of every one of the acting and resulting substances should show its influence on the relative velocity of reaction2 thus1 for instance1 direct experiment showed the influence of the admixture of manganous sulphate4 ,when a large proportion of oxalic acid 7#ajh molecules7 was taken to a large mass of water and to #b molecules of permanganate #ad molecules of manganous sulphate were added1 the quantity x of the potassium permanganate acted on 7in percentages of the potassium permanganate taken7 in t minutes 7at #af7 was as follows3 t #b #e #h #aa #ad #dd #dg #ec #fa #fh x #eb #aba #ahg #bea #cac #fhd #gag #geh #gih #hcj ,these figures show that the rate of reaction--that is1 the quantity of permanganate changed in one minute--decreases proportionally to the decrease in the amount of unchanged potassium permanganate4 ,at the commencement1 about #bf per cent4 of the salt taken was decomposed in the course of one minute1 whilst after an hour the rate was about #je per cent4 ,the same phenomena are observed in every case which has been investigated1 and this branch of theoretical or physical chemistry1 now studied by many1#bg promises to explain the course of chemical transformations from a fresh point of view1 which is closely allied to the doctrine of affinity1 because the rate of reaction1 without doubt1 is connected with the magnitude of the affinities acting between the reacting substances4 #be ,for rapid and accurate determinations of this kind1 advantage is taken of those methods of chemical analysis which are known as 'titrations' 7volumetric analysis71 and consist in measuring the volume of solutions of known strength required for the complete conversion of a given substance4 ,details respecting the theory and practice of titration1 in which potassium permanganate is very frequently employed1 must be looked for in works on analytical chemistry4 #bf ,the measurements of velocity and acceleration serve for determining the measure of forces in mechanics1 but in that case the velocities are magnitudes of length or paths passed over in a unit of time4 ,the velocity of chemical change embodies a conception of quite another kind4 ,in the first place1 the velocities of reactions are magnitudes of the masses which have entered into chemical transformations2 in the second place1 these velocities can only be relative quantities4 ,hence the conception of 'velocity' has quite a different meaning in chemistry from what it has in mechanics4 ,their only common factor is time4 ,if dt be the increment of time and dx the quantity of a substance changed in this space of time1 then the fraction 7or quotient7 dx_/dt will express the rate of the reaction4 ,the natural conclusion1 come to both by ,harcourt and ,esson1 and previously to them 7#ahej7 by ,wilhelmj 7who investigated the rate of conversion1 or inversion1 of sugar in its passage into glucose71 consists in establishing that this velocity is proportional to the quantity of substances still unchanged--i4e4 that dx_/dt ,c7,a - x71 where ,c is a constant coefficient of proportionality1 and where ,a is the quantity of a substance taken for reaction at the moment when t #j and x #j--that is1 at the beginning of the experiment1 from which the time t and quantity x of substance changed is counted4 ,on integrating the preceding equation we obtain log7,a_/7,a - x77 kt1 where k is a new constant1 if we take ordinary 7and not natural7 logarithms4 ,hence1 knowing ,a1 x1 and t1 for each reaction1 we find k1 and it proves to be a constant quantity4 ,thus from the figures cited in the text for the reaction #b,k,mn,o#d #ajh;,c#b;,h#b,o#d #ad,mn,s,o#d1 it may be calculated that k #jjaad2 for example1 t #dd1 x #fhd 7,a #ajj71 whence kt #jejjd and k #jjaad1 7see also ,chapter ,,xiv41 ,note #c1 and ,chapter ,,xvii41 ,note #be bis74 #bg ,the researches made by ,hood1 ,van't ,hoff1 ,ostwald1 ,warder1 ,menschutkin1 ,konovaloff1 and others have a particular significance in this direction4 ,owing to the comparative novelty of this subject1 and the absence of applicable as well as indubitable deductions1 ,i consider it impossible to enter into this province of theoretical chemistry1 although ,i am quite confident that its development should lead to very important results1 especially in respect to chemical equilibria1 for ,van't ,hoff has already shown that the limit of reaction in reversible reactions is determined by the attainment of equal velocities for the opposite reactions4 ,,chapter ,,xxii ,,iron1 ,,cobalt1 ,,and ,,nickel ,judging from the atomic weights1 and the forms of the higher oxides of the elements already considered1 it is easy to form an idea of the seven groups of the periodic system4 ,such are1 for instance1 the typical series ,li1 ,be1 ,b1 ,c1 ,n1 ,o1 ,f1 or the third series1 ,na1 ,mg1 ,al1 ,si1 ,p1 ,s1 ,cl4 ,the seven usual types of oxides from ,r#b,o to ,r#b,o#g correspond with them 7,chapter ,,xv47 ,the position of the eighth group is quite separate1 and is determined by the fact that1 as we have already seen1 in each group of metals having a greater atomic weight than potassium a distinction ought to be made between the elements of the even and uneven series4 ,the series of even elements1 commencing with a strikingly alkaline element 7potassium1 rubidium1 csium71 together with the uneven series following it1 and concluding with a haloid 7chlorine1 bromine1 iodine71 forms a large period1 the properties of whose members repeat themselves in other similar periods4 ,the elements of the eighth group are situated between the elements of the even series and the elements of the uneven series following them4 ,and for this reason elements of the eighth group are found in the middle of each large period4 ,the properties of the elements belonging to it1 in many respects independent and striking1 are shown with typical clearness in the case of iron1 the well-known representative of this group4 ,iron is one of those elements which are not only widely diffused in the crust of the earth1 but also throughout the entire universe4 ,its oxides and their various compounds are found in the most diverse portions of the earth's crust2 but here iron is always found combined with some other element4 ,iron is not found on the earth's surface in a free state1 because it easily oxidises under the action of air4 ,it is occasionally found in the native state in meteorites1 or aerolites1 which fall upon the earth4 ,meteoric iron is formed outside the earth4#a ,meteorites are fragments which are carried round the sun in orbits1 and fall upon the earth when coming into proximity with it during their motion in space4 ,the meteoric dust1 on passing through the upper parts of the atmosphere1 and becoming incandescent from friction with the gases1 produces that phenomenon which is familiar under the name of falling stars4#b ,such is the doctrine concerning meteorites1 and therefore the fact of their containing rocky 7siliceous7 matter and metallic iron shows that outside the earth the elements and their aggregation are in some degree the same as upon the earth itself4 #a ,the composition of meteoric iron is variable4 ,it generally contains nickel1 phosphorus1 carbon1 c4 ,the schreibersite of meteoric stones contains ,fe#d,ni#b,p4 #b ,comets and the rings of ,saturn ought now to be considered as consisting of an accumulation of such meteoric cosmic particles4 ,perhaps the part played by these minute bodies scattered throughout space is much more important in the formation of the largest celestial bodies than has hitherto been imagined4 ,the investigation of this branch of astronomy1 due to ,schiaparelli1 has a bearing on the whole of natural science4 ,the question arises as to why the iron in meteorites is in a free state1 whilst on earth it is in a state of combination4 ,does not this tend to show that the condition of our globe is very different from that of the rest8 ,my answer to this question has been already given in ,volume ,i4 p4 #cgg1 ,note #eg4 ,it is my opinion that inside the earth there is a mass similar in composition to meteorites--that is1 containing rocky matter and metallic iron1 partly carburetted4 ,in conclusion1 ,i consider it will not be out of place to add the following explanations4 ,according to the theory of the distribution of pressures 7see my treatise1 ,on ,barometrical ,levelling1 #ahgf1 pages #dh et seq47 in an atmosphere of mixed gases1 it follows that two gases1 whose densities are d and d#a1 and whose relative quantities or partial pressures at a certain distance from the centre of gravity are h and h#a1 will1 when at a greater distance from the centre of attraction1 present a different ratio of their masses x 3 x#a--that is1 of their partial pressures--which may be found by the equation d#a7log7h7 - log7x77 d7log7h#a7 - log7x#a774 ,if1 for instance1 d 3 d#a #b 3 #a1 and h h#a 7that is to say1 the masses are equal at the lower height7 #ajjj1 then when x #aj the magnitude of x#a will not be #aj 7i4e4 the mass of a gas at a higher level whose density #a will not be equal to the mass of a gas whose density #b1 as was the case at a lower level71 but much greater--namely1 x#a #ajj--that is1 the lighter gas will predominate over a heavier one at a higher level4 ,therefore1 when the whole mass of the earth was in a state of vapour1 the substances having a greater vapour density accumulated about the centre and those with a lesser vapour density at the surface4 ,and as the vapour densities depend on the atomic and molecular weights1 those substances which have small atomic and molecular weights ought to have accumulated at the surface1 and those with high atomic and molecular weights1 which are the least volatile and the easiest to condense1 at the centre4 ,thus it becomes apparent why such light elements as hydrogen1 carbon1 nitrogen1 oxygen1 sodium1 magnesium1 aluminium1 silicon1 phosphorus1 sulphur1 chlorine1 potassium1 calcium1 and their compounds predominate at the surface and largely form the earth's crust4 ,there is also now much iron in the sun1 as spectrum analysis shows1 and therefore it must have entered into the composition of the earth and other planets1 but would have accumulated at the centre1 because the density of its vapour is certainly large and it easily condenses4 ,there was also oxygen near the centre of the earth1 but not sufficient to combine with the iron4 ,the former1 as a much lighter element1 principally accumulated at the surface1 where we at the present time find all oxidised compounds and even a remnant of free oxygen4 ,this gives the possibility not only of explaining in accordance with cosmogonic theories the predominance of oxygen compounds on the surface of the earth1 with the occurrence of unoxidised iron in the interior of the earth and in meteorites1 but also of understanding why the density of the whole earth 7over #e7 is far greater than that of the rocks 7#a to #c7 composing its crust4 ,and if all the preceding arguments and theories 7for instance the supposition that the sun1 earth1 and all the planets were formed of an elementary homogeneous mass1 formerly composed of vapours and gases7 be true1 it must be admitted that the interior of the earth and other planets contains metallic 7unoxidised7 iron1 which1 however1 is only found on the surface as aerolites4 ,and then assuming that aerolites are the fragments of planets which have crumbled to pieces so to say during cooling 7this has been held to be the case by astronomers1 judging from the paths of aerolites71 it is readily understood why they should be composed of metallic iron1 and this would explain its occurrence in the depths of the earth1 which we assumed as the basis of our theory of the formation of naphtha 7,chapter ,,viii41 ,notes #eg-fj74 ,the most widely diffused terrestrial compound of iron is iron bisulphide1 ,fe,s#b1 or iron pyrites4 ,it occurs in formations of both aqueous and igneous origin1 and sometimes in enormous masses4 ,it is a substance having a greyish-yellow colour1 with a metallic lustre1 and a specific gravity of #ej2 it crystallises in the regular system4#b bis #b bis ,immense deposits of iron pyrites are known in various parts of ,russia4 ,on the river ,msta1 near ,borovitsi1 thousands of tons are yearly collected from the detritus of the neighbouring rocks4 ,in the ,governments of ,toula1 ,riazan1 and in the ,donets district continuous layers of pyrites occur among the coal seams4 ,very thick beds of pyrites are also known in many parts of the ,caucasus4 ,but the deposits of the ,urals are particularly vast1 and have been worked for a long time4 ,amongst these ,i will only indicate the deposits on the ,soymensky estate near the ,kishteimsky works2 the ,kaletinsky deposits near the ,virhny-,isetsky works 7containing #a-b p4c4 ,cu72 on the banks of the river ,koushaivi near ,koushvi 7#c-e p4c4 ,cu71 and the deposits near the ,bogoslovsky works 7#c-e p4c4 ,cu74 ,iron pyrites 7especially that containing copper which is extracted after roasting7 is now chiefly employed for roasting1 as a source of ,,so#b1 for the manufacture of chamber sulphuric acid 7,vol4 ,i4 p4 #bia71 but the remaining oxide of iron is perfectly suitable for smelting into pig iron1 although it gives a sulphurous pig iron 7the sulphur may be easily removed by subsequent treatment1 especially with the aid of ferro-manganese in ,bessemer's process74 ,the great technical importance of iron pyrites leads to its sometimes being imported from great distances2 for instance1 into ,england from ,spain4 ,besides which1 when heated in closed retorts ,fe,s#b gives sulphur1 and if allowed to oxidise in damp air1 green vitriol1 ,fe,s,o#d4 ,the oxides are the principal ores used for producing metallic iron4 ,the majority of the ores contain ferric oxide1 ,fe#b,o#c1 either in a free state or combined with water1 or else in combination with ferrous oxide1 ,fe,o4 ,the species and varieties of iron ores are numerous and diverse4 ,ferric oxide in a separate form appears sometimes as crystals of the rhombohedric system1 having a metallic lustre and greyish steel colour2 they are brittle1 and form a red powder1 specific gravity about #ebe4 ,ferric oxide in type of oxidation and properties resembles alumina2 it is1 however1 although with difficulty1 soluble in acids even when anhydrous4 ,the crystalline oxide bears the name of specular iron ore1 but ferric oxide most often occurs in a non-crystalline form1 in masses having a red fracture1 and is then known as red hmatite4 ,in this form1 however1 it is rather a rare ore1 and is principally found in veins4 ,the hydrates of ferric oxide1 ferric hydroxides1#c are most often found in aqueous or stratified formations1 and are known as brown hmatites2 they generally have a brown colour1 form a yellowish-brown powder1 and have no metallic lustre but an earthy appearance4 ,they easily dissolve in acids and diffuse through other formations1 especially clays 7for instance1 ochre72 they sometimes occur in reniform and similar masses1 evidently of aqueous origin4 ,such are1 for instance1 the so-called bog or lake and peat ores found at the bottom of marshes and lakes1 and also under and in peat beds4 ,this ore is formed from water containing ferrous carbonate in solution1 which1 after absorbing oxygen1 deposits ferric hydroxide4 ,in rivers and springs1 iron is found in solution as ferrous carbonate through the agency of carbonic acid3 hence the existence of chalybeate springs containing ,fe,c,o#c4 ,this ferrous carbonate1 or siderite1 is either found as a non-crystalline product of evidently aqueous origin1 or as a crystalline spar called spathic iron ore4 ,the reniform deposits of the former are most remarkable2 they are called spherosiderites1 and sometimes form whole strata in the jurassic and carboniferous formations4 ,magnetic iron ore1 ,fe#c,o#d ,fe,o1,fe#b,o#c1 in virtue of its purity and practical uses1 is a very important ore2 it is a compound of the ferrous and ferric oxides1 is naturally magnetic1 has a specific gravity of #ea1 crystallises in well-formed crystals of the regular system1 is with difficulty soluble in acids1 and sometimes forms enormous masses1 as1 for instance1 ,mount ,blagodat in the ,ural4 ,however1 in most cases--for instance1 at ,korsak-,mogila 7to the north of ,berdiansk and ,nogaiska1 near the ,sea of ,azov71 or at ,krivoi ,rog 7to the west of ,ekaterinoslav7--the magnetic iron ore is mixed with other iron ores4 ,in the ,urals1 the ,caucasus 7without mentioning ,siberia71 and in the districts adjoining the basin of the ,don1 ,russia possesses the richest iron ores in the world4 ,to the south of ,moscow1 in the ,governments of ,toula and ,nijninovgorod1 in the ,olonetz district1 and in the ,government of ,orloffsky 7near ,zinovieff in the district of ,kromsky71 and in many other places1 there are likewise abundant supplies of iron ores amongst the deposited aqueous formations2 the siderite of ,orloffsky1 for instance1 is distinguished by its great purity4#d #c ,the hydrated ferric oxide is found in nature in a dual form4 ,it is somewhat rarely met with in the form of a crystalline mineral called gthite1 whose specific gravity is #dd and composition ,fe#b;,h#c,o#d1 or ,fe,h,o#b--that is1 one of oxide of iron to one of water1 ,fe#b,o#c1;,h#b,o2 frequently found as brown ironstone1 forming a dense mass of fibrous1 reniform deposits containing #b;,fe#b,o#c1c;,h#b,o--that is1 having a composition ,fe#d;,h#f,o#i4 ,in bog ore and other similar ores we most often find a mixture of this hydrated ferric oxide with clay and other impurities4 ,the specific gravity of such formations is rarely as high as #dj4 #d ,the ores of iron1 similarly to all substances extracted from veins and deposits1 are worked according to mining practice by means of vertical1 horizontal1 or inclined shafts which reach and penetrate the veins and strata containing the ore deposits4 ,the mass of ore excavated is raised to the surface1 then sorted either by hand or else in special sorting apparatus 7generally acting with water to wash the ore71 and is subjected to roasting and other treatment4 ,in every case the ore contains foreign matter4 ,in the extraction of iron1 which is one of the cheapest metals1 the dressing of an ore is in most cases unprofitable1 and only ores rich in metal are worked--namely1 those containing at least #bj p4c4 ,it is often profitable to transport very rich and pure ores 7with as much as #gj p4c4 of iron7 from long distances4 ,the details concerning the working and extraction of metals will be found in special treatises on metallurgy and mining4 ,iron is also found in the form of various other compounds--for instance1 in certain silicates1 and also in some phosphates2 but these forms are comparatively rare in nature in a pure state1 and have not the industrial importance of those natural compounds of iron previously mentioned4 ,in small quantities iron enters into the composition of every kind of soil and all rocky formations4 ,as ferrous oxide1 ,fe,o1 is isomorphous with magnesia1 and ferric oxide1 ,fe#b,o#c1 with alumina1 isomorphous substitution is possible here1 and hence minerals are not unfrequently found in which the quantity of iron varies considerably2 such1 for instance1 are pyroxene1 amphibole1 certain varieties of mica1 c4 ,although much iron oxide is deleterious to the growth of vegetation1 still plants do not flourish without iron2 it enters as an indispensable component into the composition of all higher organisms2 in the ash of plants we always find more or less of its compounds4 ,it also occurs in blood1 and forms one of the colouring matters in it2 #ajj parts of the blood of the highest organisms contain about #jje of iron4 ,the reduction of the ores of iron into metallic iron is in principle very simple1 because when the oxides of iron are strongly heated with charcoal1 hydrogen1 carbonic oxide1 and other reducing agents1#e they easily give metallic iron4 ,but the matter is rendered more difficult by the fact that the iron does not melt at the heat developed by the combustion of the charcoal1 and therefore it does not separate from those mechanically mixed impurities which are found in the iron ore4 ,this is obviated by the following very remarkable property of iron3 at a high temperature it is capable of combining with a small quantity 7from #b to #e p4c47 of carbon1 and then forms cast iron1 which easily melts in the heat developed by the combustion of charcoal in air4 ,for this reason metallic iron is not obtained directly from the ore1 but is only formed after the further treatment of the cast iron2 the first product extracted from the ore being cast iron4 ,the fused mass disposes itself in the furnace below the slag--that is1 the impurities of the ore fused by the heat of the furnace4 ,if these impurities did not fuse they would block up the furnace in which the ore was being smelted1 and the continuous smelting of the cast iron would not be possible2#f it would be necessary periodically to cool the furnace and heat it up again1 which means a wasteful expenditure of fuel1 and hence in the production of cast iron1 the object in view is to obtain all the earthy impurities of the ore in the shape of a fused mass or slag4 ,only in rare cases does the ore itself form a mass which fuses at the temperature employed1 and these cases are objectionable if much iron oxide is carried away in the slag4 ,the impurities of the ores most often consist of certain mixtures--for instance1 a mixture of clay and sand1 or a mixture of limestone and clay1 or quartz1 c4 ,these impurities do not separate of themselves1 or do not fuse4 ,the difficulty of the industry lies in forming an easily-fusible slag1 into which the whole of the foreign matter of the ore would pass and flow down to the bottom of the furnace above the heavier cast iron4 ,this is effected by mixing certain fluxes with the ore and charcoal4 ,a flux is a substance which1 when mixed with the foreign matter of the ore1 forms a fusible vitreous mass or slag4 ,the flux used for silica is limestone with clay2 for limestone a definite quantity of silica is used1 the best procedure having been arrived at by experiment and by long practice in iron smelting and other metallurgical processes4#g #e ,the reduction of iron oxides by hydrogen belongs to the order of reversible reactions 7,chapter ,,ii471 and is therefore determined by a limit which is here expressed by the attainment of the same pressure as in the case where hydrogen acts on iron oxides1 and as in the case where 7at the same temperature7 water is decomposed by metallic iron4 ,the calculations referring to this matter were made by ,henri ,sainte-,claire ,deville 7#ahgj74 ,spongy iron was placed in a tube having a temperature t1 one end of which was connected with a vessel containing water at #j 7vapour tension #df mm47 and the other end with a mercury pump and pressure gauge which determined the limiting tension attained by the dry hydrogen p 7subtracting the tension of the water vapour from the tension observed74 ,a tube was then taken containing an excess of iron oxide4 ,it was filled with hydrogen1 and the tension p#a observed of the residual hydrogen when the water was condensed at #j4 t #bjj #ddj #hfj #ajdj p #iei #beh #abh #ib mm4 p#a -- -- #abh #id mm4 ,the equality of the pressure 7tension7 of the hydrogen in the two cases is evident4 ,the hydrogen here behaves like the vapour of iron or of its oxide4 ,by taking ferric oxide1 ,fe#b,o#c1 ,moissan observed that at #cej it passed into magnetic oxide1 ,fe#c,o#d1 at #ejj into ferrous oxide1 ,fe,o1 and at #fjj into metallic iron4 ,wright and ,luff 7#ahgh71 whilst investigating the reduction of oxides1 found that 7a7 the temperature of reaction depends on the condition of the oxide taken--for instance1 precipitated ferric oxide is reduced by hydrogen at #he1 that obtained by oxidising the metal or from its nitrate at #age2 7b7 when other conditions are the same1 the reduction by carbonic oxide commences earlier than that by hydrogen1 and the reduction by hydrogen still earlier than that by charcoal2 7c7 the reduction is effected with greater facility when a greater quantity of heat is evolved during the reaction4 ,ferric oxide obtained by heating ferrous sulphate to a red heat begins to be reduced by carbonic oxide at #bjb1 by hydrogen at #bfj1 by charcoal at #dcj1 whilst for magnetic oxide1 ,fe#c,o#d1 the temperatures are #bjj1 #bij1 and #dej respectively4 #f ,the primitive methods of iron manufacture were conducted by intermittent processes in hearths resembling smiths' fires4 ,as evidenced by the uninterrupted action of the steam boiler1 or the process of lime burning1 and the continuous preparation and condensation of sulphuric acid or the uninterrupted smelting of iron1 every industrial process becomes increasingly profitable and complete under the condition of the continuous action1 as far as possible1 of all agencies concerned in the production4 ,this continuous method of production is the first condition for the profitable production on the large scale of nearly all industrial products4 ,this method lessens the cost of labour1 simplifies the supervision of the work1 renders the product uniform1 and frequently introduces a very great economy in the expenditure of fuel and at the same time presents the simplicity and perfection of an equilibrated system4 ,hence every manufacturing operation should be a continuous one1 and the manufacture of pig iron and sulphuric acid1 which have long since become so1 may be taken as examples in many respects4 ,a study of these two manufactures should form the commencement of an acquaintance with all the contemporary methods of manufacturing both from a technical and economical point of view4 #g ,the composition of slag suitable for iron smelting most often approaches the following3 #ej to #fj p4c4 ,si,o#b1 #e to #bj ,al#b,o#c1 the rest of the mass consisting of ,mg,o1 ,ca,o1 ,mn,o1 ,fe,o4 ,thus the most fusible slag 7according to the observations of ,bodeman7 contains the alloy ,al#b,o#c1d;,ca,o1#g,si,o#b4 ,on altering the quantity of magnesia and lime1 and especially of the alkalis 7which increases the fusibility7 and of silica 7which decreases it71 the temperature of fusion changes with the relation between the total quantity of oxygen and that in the silica4 ,slags of the composition ,,ro1,si,o#b are easily fusible1 have a vitreous appearance1 and are very common4 ,basic slags approach the composition #b,,ro1,si,o#b4 ,hence1 knowing the composition and quantity of the foreign matter in the ore1 it is at once easy to find the quantity and quality of the flux which must be added to form a suitable slag4 ,the smelting of iron is rendered more complex by the fact that the silica1 ,si,o#b1 which enters into the slag and fluxes is capable of forming a slag with the iron oxides4 ,in order that the least quantity of iron may pass into the slag1 it is necessary for it to be reduced before the temperature is attained at which the slags are formed 7about #ajjj71 which is effected by reducing the iron1 not with charcoal itself1 but with carbonic oxide4 ,from this it will be understood how the progress of the whole treatment may be judged by the properties of the slags4 ,details of this complicated and well-studied subject will be found in works on metallurgy4 ,thus the following materials have to be introduced into the furnace where the smelting of the iron ore is carried on3 7#a7 the iron ore1 composed of oxide of iron and foreign matter2 7#b7 the flux required to form a fusible slag with the foreign matter2 7#c7 the carbon which is necessary 7a7 for reducing1 7b7 for combining with the reduced iron to form cast iron1 7c7 principally for the purpose of combustion and the heat generated thereby1 necessary not only for reducing the iron and transforming it into cast iron1 but also for melting the slag1 as well as the cast iron--and 7#d7 the air necessary for the combustion of the charcoal4 ,the air is introduced after a preparatory heating in order to economise fuel and to obtain the highest temperature4 ,the air is forced in under pressure by means of a special blast arrangement4 ,this permits of an exact regulation of the heat and rate of smelting4 ,all these component parts necessary for the smelting of iron must be contained in a vertical1 that is1 shaft furnace1 which at the base must have a receptacle for the accumulation of the slag and cast iron formed1 in order that the operation may proceed without interruption4 ,the walls of such a furnace ought to be built of fireproof materials if it be designed to serve for the continuous production of cast iron by charging the ore1 fuel1 and flux into the mouth of the furnace1 forcing a blast of air into the lower part1 and running out the molten iron and slag from below4 ,the whole operation is conducted in furnaces known as blast furnaces4 ,the annexed illustration1 fig4 #ic 7which is taken by kind permission from ,thorpe's ,dictionary of ,applied ,chemistry71 represents the vertical section of such a furnace4 ,these furnaces are generally of large dimensions--varying from #ej to #ij feet in height4 ,they are sometimes built against rising ground in order to afford easy access to the top where the ore1 flux1 and charcoal or coke are charged4#h #h ,the section of a blast furnace is represented by two truncated cones joined at their bases1 the upper cone being longer than the lower one2 the lower cone is terminated by the hearth1 or almost cylindrical cavity in which the cast iron and slag collect1 one side being provided with apertures for drawing off the iron and slag4 ,the air is blown into the blast furnace through special pipes1 situated over the hearth1 as shown in the section4 ,the air previously passes through a series of cast-iron pipes1 heated by the combustion of the carbonic oxide obtained from the upper parts of the furnace1 where it is formed as in a 'gas-producer4' ,the blast furnace acts continuously until it is worn out2 the iron is tapped off twice a day1 and the furnace is allowed to cool a little from time to time so as not to be spoilt by the increasing heat1 and to enable it to withstand long usage4 ,blast furnaces worked with charcoal fuel are not so high1 and in general give a smaller yield than those using coke1 because the latter are worked with heavier charges than those in which charcoal is employed4 ,coke furnaces yield #bj1jjj tons and over of pig iron a year4 ,in the ,united ,states there are blast furnaces #cj metres high1 and upwards of #fjj cubic metres capacity1 yielding as much as #acj1jjj tons of pig iron1 requiring a blast of about #gej cubic metres of air per minute1 heated to #fjj1 and consuming about #jhe part of coke per #a part of pig iron produced4 ,at the present time the world produces as much as #cj million tons of pig iron a year1 about #i_/aj of which is converted into wrought iron and steel4 ,the chief producers are the ,united ,states 7about #aj million tons a year7 and ,england 7about #i million tons a year72 ,russia yields about #a-a_/e million tons a year4 ,the world's production has doubled during the last #bj years1 and in this respect the ,united ,states have outrun all other countries4 ,the reason of this increase of production must be looked for in the increased demand for iron and steel for railway purposes1 for structures 7especially ship-building71 and in the fact that3 7a7 the cost of pig iron has fallen1 thanks to the erection of large furnaces and a fuller study of the processes taking place in them1 and 7b7 that every kind of iron ore 7even sulphurous and phosphoritic7 can now be converted into a homogeneous steel4 ,illustration3 ,,fig4 #ic4--,vertical section of a modern ,cleveland blast furnace capable of producing #cjj to #a1jjj tons of pig iron weekly4 ,the outer casing is of riveted iron plates1 the furnace being lined with refractory fire-brick4 ,it is closed at the top by a 'cap and cone' arrangement1 by means of which the charge can be fed into the furnace at suitable intervals by lowering the moveable cone4 ,in order to more thoroughly grasp the chemical process which takes place in blast furnaces1 it is necessary to follow the course of the material charged in at the top and of the air passing through the furnace4 ,from #ej to #bjj parts of carbon are expended on #ajj parts of iron4 ,the ore1 flux1 and coke are charged into the top of the furnace1 in layers1 as the cast iron is formed in the lower parts and flowing down to the bottom causes the whole contents of the furnace to subside1 thus forming an empty space at the top1 which is again filled up with the afore-mentioned mixture4 ,during its downward course this mixture is subjected to increasing heat4 ,this rise of temperature first drives off the moisture of the ore mixture1 and then leads to the formation of the products of the dry distillation of coal or charcoal4 ,little by little the subsiding mass attains a temperature at which the heated carbon reacts with the carbonic anhydride passing upwards through the furnace and transforms it into carbonic oxide4 ,this is the reason why carbonic anhydride is not evolved from the furnace1 but only carbonic oxide4 ,as regards the ore itself1 on being heated to about #fjj to #hjj it is reduced at the expense of the carbonic oxide ascending the furnace1 and formed by the contact of the carbonic anhydride with the incandescent charcoal1 so that the reduction in the blast furnace is without doubt brought about by the formation and decomposition of carbonic oxide and not by carbon itself--thus1 ,fe#b,o#c #c;,,co ,fe#b #c;,,co#b4 ,the reduced iron1 on further subsidence and contact with carbon1 forms cast iron1 which flows to the bottom of the furnace4 ,in these lower layers1 where the temperature is highest 7about #a1cjj71 the foreign matter of the ore finally forms slag1 which also is fusible1 with the aid of fluxes4 ,the air blown in from below1 through the so-called tuyeres1 encounters carbon in the lower layers of the furnace1 and burns it1 converting it into carbonic anhydride4 ,it is evident that this develops the highest temperature in these lower layers of the furnace1 because here the combustion of the carbon is effected by heated and compressed air4 ,this is very essential1 for it is by virtue of this high temperature that the process of forming the slag and of forming and fusing the cast iron are effected simultaneously in these lower portions of the furnace4 ,the carbonic acid formed in these parts rises higher1 encounters incandescent carbon1 and forms with it carbonic oxide4 ,this heated carbonic oxide acts as a reducing agent on the iron ore1 and is reconverted by it into carbonic anhydride2 this gas meets with more carbon1 and again forms carbonic oxide1 which again acts as a reducing agent4 ,the final transformation of the carbonic anhydride into carbonic oxide is effected in those parts of the furnace where the reduction of the oxides of iron does not take place1 but where the temperature is still high enough to reduce the carbonic anhydride4 ,the ascending mixture of carbonic oxide and nitrogen1 ,,co#b1 c41 is then withdrawn through special lateral apertures formed in the upper cold parts of the furnace walls1 and is conducted through pipes to those stoves which are used for heating the air1 and also sometimes into other furnaces used for the further processes of iron manufacture4 ,the fuel of blast furnaces consists of wood charcoal 7this is the most expensive material1 but the pig iron produced is the purest1 because charcoal does not contain any sulphur1 while coke does71 anthracite 7for instance1 in ,pennsylvania1 and in ,russia at ,pastouhoff's works in the ,don district71 coke1 coal1 and even wood and peat4 ,it must be borne in mind that the utilisation of naphtha and naphtha refuse would probably give very profitable results in metallurgical processes4 ,the process just described is accompanied by a series of other processes4 ,thus1 for instance1 in the blast furnace a considerable quantity of cyanogen compounds are formed4 ,this takes place because the nitrogen of the air blast comes into contact with incandescent carbon and various alkaline matters contained in the foreign matter of the ores4 ,a considerable quantity of potassium cyanide is formed when wood charcoal is employed for iron smelting1 as its ash is rich in potash4 ,the cast iron formed in blast furnaces is not always of the same quality4 ,when slowly cooled it is soft1 has a grey colour1 and is not completely soluble in acids4 ,when treated with acids a residue of graphite remains2 it is known as grey or soft cast iron4 ,this is the general form of the ordinary cast iron used for casting various objects1 because in this state it is not so brittle as in the shape of white cast iron1 which does not leave particles of graphite when dissolved1 but yields its carbon in the form of hydrocarbons4 ,this white cast iron is characterised by its whitish-grey colour1 dull lustre1 the crystalline structure of its fracture 7more homogeneous than that of grey iron71 and such hardness that a file will hardly cut it4 ,when white cast iron is produced 7from manganese ore7 at high temperatures 7and with an excess of lime71 and containing little sulphur and silica but a considerable amount of carbon 7as much as #e p4c471 it acquires a coarse crystalline structure which increases in proportion to the amount of manganese1 and it is then known under the name of 'spiegeleisen' 7and 'ferro-manganese'74#i #i ,the specific gravity of white cast iron is about #ge4 ,grey cast iron has a much lower specific gravity1 namely1 #gj4 ,grey cast iron generally contains less manganese and more silica than white2 but both contain from #b to #c p4c4 of carbon4 ,the difference between the varieties of cast iron depends on the condition of the carbon which enters into the composition of the iron4 ,in white cast iron the carbon is in combination with the iron--in all probability1 as the compound ,c,fe#d 7,abel and ,osmond and others extracted this compound1 which is sometimes called 'carbide1' from tempered steel1 which stands to unannealed steel as white cast iron does to grey71 but perhaps in the state of an indefinite chemical compound resembling a solution4 ,in any case the compound of the iron and carbon in white cast iron is chemically very unstable1 because when slowly cooled it decomposes1 with separation of graphite1 just as a solution when slowly cooled yields a portion of the substance dissolved4 ,the separation of carbon in the form of graphite on the conversion of white cast iron into grey is never complete1 however slowly the separation be carried on2 part of the carbon remains in combination with the iron in the same state in which it exists in white cast iron4 ,hence when grey cast iron is treated with acids1 the whole of the carbon does not remain in the form of graphite1 but a part of it is separated as hydrocarbons1 which proves the existence of chemically-combined carbon in grey cast iron4 ,it is sufficient to re-melt grey cast iron and to cool it quickly to transform it into white cast iron4 ,it is not carbon alone that influences the properties of cast iron2 when it contains a considerable amount of sulphur1 cast iron remains white even after having been slowly cooled4 ,the same is observed in cast iron very rich in manganese 7#e to #g p4c471 and in this latter case the fracture is very distinctly crystalline and brilliant4 ,when cast iron contains a large amount of manganese1 the quantity of carbon may also be increased4 ,crystalline varieties of cast iron rich in manganese are in practice called ferro-manganese 7p4 #caj71 and are prepared for the ,bessemer process4 ,grey cast iron not having an uniform structure is much more liable to various changes than dense and thoroughly uniform white cast iron1 and the latter oxidises much more slowly in air than the former4 ,white cast iron is not only used for conversion into wrought iron and steel1 but also in those cases where great hardness is required1 although it be accompanied by a certain brittleness2 for instance1 for making rollers1 plough-shares1 c4 ,cast iron is a material which is either suitable for direct application for casting in moulds or else for working up into wrought iron and steel4 ,the latter principally differ from cast iron in their containing less carbon--thus1 steel contains from #a p4c4 to #je p4c4 of carbon and far less silicon and manganese than cast iron2 wrought iron does not generally contain more than #jbe p4c4 of carbon and not more than #jbe p4c4 of the other impurities4 ,thus the essence of the working up of cast iron into steel and wrought iron consists in the removal of the greater part of the carbon and other elements1 ,s1 ,p1 ,mn1 ,si1 c4 ,this is effected by means of oxidation1 because the oxygen of the atmosphere1 oxidising the iron at a high temperature1 forms solid oxides with it2 and the latter1 coming into contact with the carbon contained in the cast iron1 are deoxidised1 forming wrought iron and carbonic oxide1 which is evolved from the mass in a gaseous form4 ,it is evident that the oxidation must be carried on with a molten mass in a state of agitation1 so that the oxygen of the air may be brought into contact with the whole mass of carbon contained in the cast iron1 or else the operation is effected by means of the addition of oxygen compounds of iron 7oxides1 ores1 as in ,martin's process74 ,cast iron melts much more easily than wrought iron and steel1 and1 therefore1 as the carbon separates1 the mass in the furnace 7in puddling7 or hearth 7in the bloomery process7 becomes more and more solid2 moreover the degree of hardness forms1 to a certain extent1 a measure of the amount of carbon separated1 and the operation may terminate either in the formation of steel or wrought iron4#aj ,in any case1 the iron used for industrial purposes contains impurities4 ,chemically pure iron may be obtained by precipitating iron from a solution 7a mixture of ferrous sulphate with magnesium sulphate or ammonium chloride7 by the prolonged action of a feeble galvanic current2 the iron may be then obtained as a dense mass4 ,this method1 proposed by ,bttcher and applied by ,klein1 gives1 as ,r4 ,lenz showed1 iron containing occluded hydrogen1 which is disengaged on heating4 ,this galvanic deposition of iron is used for making galvanoplastic clichs1 which are distinguished for their great hardness4 ,electro-deposited iron is brittle1 but if heated 7after the separation of the hydrogen7 it becomes soft4 ,if pure ferric hydroxide1 which is easily prepared by the precipitation of solutions of ferric salts by means of ammonia1 be heated in a stream of hydrogen1 it forms1 first of all1 a dull black powder which ignites spontaneously in air 7pyrophoric iron71 and then a grey powder of pure iron4 ,the powdery substance first obtained is an iron suboxide2 when thrown into the air it ignites1 forming the oxide ,fe#c,o#d4 ,if the heating in hydrogen be continued1 more water and pure iron1 which does not ignite spontaneously1 will be obtained4 ,if a small quantity of iron be fused in the oxyhydrogen flame 7with an excess of oxygen7 in a piece of lime and mixed with powdered glass1 pure molten iron will be formed1 because in the oxyhydrogen flame iron melts and burns1 but the substances mixed with the iron oxidise first4 ,the oxidised impurities here either disappear 7carbonic anhydride7 in a gaseous form1 or turn into slag 7silica1 manganese1 oxide1 and others7--that is1 fuse with the glass4 ,pure iron has a silvery white colour and a specific gravity of #ghd2 it melts at a temperature higher than the melting-points of silver1 gold1 nickel1 and steel1 i4e4 about #adjj-aejj and below the melting point of platinum 7#agej74aa ,but pure iron becomes soft at a temperature considerably below that at which it melts1 and may then be easily forged1 welded1 and rolled or drawn into sheets and wire4#aa bis ,pure iron may be rolled into an exceedingly thin sheet1 weighing less than a sheet of ordinary paper of the same size4 ,this ductility is the most important property of iron in all its forms1 and is most marked with sheet iron1 and least so with cast iron1 whose ductility1 compared with wrought iron1 is small1 but it is still very considerable when compared with other substances--such1 for instance1 as rocks4#ab #aj ,this direct process of separating the carbon from cast iron is termed puddling4 ,it is conducted in reverberatory furnaces4 ,the cast iron is placed on the bed of the furnace and melted2 through a special aperture1 the puddler stirs up the oxidising mass of cast iron1 pressing the oxides into the molten iron4 ,this resembles kneading dough1 and the process introduced in ,england became known as puddling4 ,it is evident that the puddled mass1 or bloom1 is a heterogeneous substance obtained by mixing1 and hence one part of the mass will still be rich in carbon1 another will be poor1 some parts will contain oxide not reduced1 c4 ,the further treatment of the puddled mass consists in hammering and drawing it out into flat pieces1 which on being hammered become more homogeneous1 and when several pieces are welded together and again hammered out a still more homogeneous mass is obtained4 ,the quality of the steel and iron thus formed depends principally on their uniformity4 ,the want of uniformity depends on the oxides remaining inside the mass1 and on the variable distribution of the carbon throughout the mass4 ,in order to obtain a more homogeneous metal for manufacturing articles out of steel1 it is drawn into thin rods1 which are tied together in bundles and then again hammered out4 ,as an example of what may be attained in this direction1 imitation ,damascus steel may be cited2 it consists of twisted and plaited wire1 which is then hammered into a dense mass4 7,real damascened wootz steel may be made by melting a mixture of the best iron with graphite 7#a_/ab7 and iron rust2 the article is then corroded with acid1 and the carbon remains in the form of a pattern47 ,steel and wrought iron are manufactured from cast iron by puddling4 ,they are1 however1 obtained not only by this method but also by the bloomery process1 which is carried out in a fire similar to a blacksmith's forge1 fed with charcoal and provided with a blast2 a pig of cast iron is gradually pushed into the fire1 and portions of it melt and fall to the bottom of the hearth1 coming into contact with an air blast1 and are thus oxidised4 ,the bloom thus formed is then squeezed and hammered4 ,it is evident that this process is only available when the charcoal used in the fire does not contain any foreign matter which might injure the quality of the iron or steel--for instance1 sulphur or phosphorus--and therefore only wood charcoal may be used with impunity1 from which it follows that this process can only be carried on where the manufacture of iron can be conducted with this fuel4 ,coal and coke contain the above-mentioned impurities1 and would therefore produce iron of a brittle nature1 and thus it would be necessary to have recourse to puddling1 where the fuel is burnt on a special hearth1 separate from the cast iron1 whereby the impurities of the fuel do not come into contact with it4 ,the manufacture of steel from cast iron may also be conducted in fires2 but1 in addition to this1 it is also now prepared by many other methods4 ,one of the long-known processes is called cementation1 by which steel is prepared from wrought iron but not from cast iron4 ,for this process strips of iron are heated red-hot for a considerable time whilst immersed in powdered charcoal2 during this operation the iron at the surface combines with the charcoal1 which however does not penetrate2 after this the iron strips are re-forged1 drawn out again1 and cemented anew1 repeating this process until a steel of the desired quality is formed--that is1 containing the requisite proportion of carbon4 ,the ,bessemer process occupies the front rank among the newer methods 7since #ahef72 it is so called from the name of its inventor4 ,this process consists in running melted cast iron into converters 7holding about #f tons of cast iron7--that is1 egg-shaped receivers1 fig4 #id1 capable of revolving on trunnions 7in order to charge in the cast iron and discharge the steel71 and forcing a stream of air through small apertures at a considerable pressure4 ,combustion of the iron and carbon at an elevated temperature then takes place1 resulting from the bubbles of oxygen thus penetrating the mass of the cast iron4 ,the carbon1 however1 burns to a greater extent than the iron1 and therefore a mass is obtained which is much poorer in carbon than cast iron4 ,as the combustion proceeds very rapidly in the mass of metal1 the temperature rises to such an extent that even the wrought iron which may be formed remains in a molten condition1 whilst the steel1 being more fusible than the wrought iron1 remains very liquid4 ,in half an hour the mass is ready4 ,the purest possible cast iron is used in the ,bessemer process1 because sulphur and phosphorus do not burn out like carbon1 silicon1 and manganese4 ,illustration3 ,,fig4 #id4--;,bessemer converter1 constructed of iron plate and lined with ganister4 ,the air is carried by the tubes1 ,l1 ,o1 ,d to the bottom1 ,m1 from which it passes by a number of holes into the converter4 ,the converter is rotated on the trunnion d by means of the rack and pinion ,h1 when it is required either to receive molten cast iron from the melting furnaces or to pour out the steel4 ,the presence of manganese enables the sulphur to be removed with the slag1 and the presence of lime or magnesia1 which are introduced into the lining of the converter1 facilitates the removal of the phosphorus4 ,this basic ,bessemer process1 or ,thomas ,gilchrist process1 introduced about #ahhj1 enables ores containing a considerable amount of phosphorus1 which had hitherto only been used for cast iron1 to be used for making wrought iron and steel4 ,naturally the greatest uniformity will be obtained by re-melting the metal4 ,steel is re-melted in small wind furnaces1 in masses not exceeding #cj kilos2 a liquid metal is formed1 which may be cast in moulds4 ,a mixture of wrought and cast iron is often used for making cast steel 7the addition of a small amount of metallic ,al improves the homogeneity of the castings1 by facilitating the passage of the impurities into slag74 ,large steel castings are made by simultaneous fusion in several furnaces and crucibles2 in this way1 castings up to #hj tons or more1 such as large ordnance1 may be made4 ,this molten1 and therefore homogeneous1 steel is called cast steel4 ,of late years the ,martin's process for the manufacture of steel has come largely into use2 it was invented in ,france about #ahfj1 and with the use of regenerative furnaces it enables large quantities of cast steel to be made at a time4 ,it is based on the melting of cast iron with iron oxides and iron itself--for instance1 pure ores1 scrap1 c4 ,there the carbon of the cast iron and the oxygen of the oxide form carbonic oxide1 and the carbon therefore burns out1 and thus cast steel is obtained from cast iron1 providing1 naturally1 that there is a requisite proportion and corresponding degree of heat4 ,the advantage of this process is that not only do the carbon1 silicon1 and manganese1 but also a great part of the sulphur and phosphorus of the cast iron burn out at the expense of the oxygen of the iron oxides4 ,during the last decade the manufacture of steel and its application for rails1 armour plate1 guns1 boilers1 c41 has developed to an enormous extent1 thanks to the invention of cheap processes for the manufacture of large masses of homogeneous cast steel4 ,wrought iron may also be melted1 but the heat of a blast furnace is insufficient for this4 ,it easily melts in the oxyhydrogen flame4 ,it may be obtained in a molten state directly from cast iron1 if the latter be melted with nitre and sufficiently stirred up4 ,considerable oxidation then takes place inside the mass of cast iron1 and the temperature rises to such an extent that the wrought iron formed remains liquid4 ,a method is also known for obtaining wrought iron directly from rich iron ores by the action of carbonic oxide3 the wrought iron is then formed as a spongy mass 7which forms an excellent filter for purifying water71 and may be worked up into wrought iron or steel either by forging or by dissolving in molten cast iron4 ,everybody is more or less familiar with the difference in the properties of steel and wrought iron4 ,iron is remarkable for its softness1 pliability1 and small elasticity1 whilst steel may be characterised by its capability of attaining elasticity and hardness if it be cooled suddenly after having been heated to a definite temperature1 or1 as it is termed1 tempered4 ,but if tempered steel be re-heated and slowly cooled1 it becomes as soft as wrought iron1 and can then be cut with the file and forged1 and in general can be made to assume any shape1 like wrought iron4 ,in this soft condition it is called annealed steel4 ,the transition from tempered to annealed steel thus takes place in a similar way to the transition from white to grey cast iron4 ,steel1 when homogeneous1 has considerable lustre1 and such a fine granular structure that it takes a very high polish4 ,its fracture clearly shows the granular nature of its structure4 ,the possibility of tempering steel enables it to be used for making all kinds of cutting instruments1 because annealed steel can be forged1 turned1 drawn 7under rollers1 for instance1 for making rails1 bars1 c471 filed1 c41 and it may then be tempered1 ground and polished4 ,the method and temperature of tempering and annealing steel determine its hardness and other qualities4 ,steel is generally tempered to the required degree of hardness in the following manner3 ,it is first strongly heated 7for instance1 up to #fjj71 and then plunged into water--that is1 hardened by rapid cooling 7it then becomes as brittle as glass74 ,it is then heated until the surface assumes a definite colour1 and finally cooled either quickly or slowly4 ,when steel is heated up to #bbj1 its surface acquires a yellow colour 7surgical instruments72 it first of all becomes straw-coloured 7razors1 c471 and then gold-coloured2 then at a temperature of #bej it becomes brown 7scissors71 then red1 then light blue at #bhe 7springs71 then indigo at #cjj 7files71 and finally sea-green at about #cdj4 ,these colours are only the tints of thin films1 like the hues of soap bubbles1 and appear on the steel because a thin layer of oxides is formed over its surface4 ,steel rusts more slowly than wrought iron1 and is more soluble in acids than cast iron1 but less so than wrought iron4 ,its specific gravity is about #gf to #gi4 ,as regards the formation of steel1 it was a long time before the process of cementation was thoroughly understood1 because in this case infusible charcoal permeates unfused wrought iron4 ,caron showed that this permeation depends on the fact that the charcoal used in the process contains alkalis1 which1 in the presence of the nitrogen of the air1 form metallic cyanides2 these being volatile and fusible1 permeate the iron1 and1 giving up their carbon to it1 serve as the material for the formation of steel4 ,this explanation is confirmed by the fact that charcoal without alkalis or without nitrogen will not cement iron4 ,the charcoal used for cementation acts badly when used over again1 as it has lost alkali4 ,the very volatile ammonium cyanide easily conduces to the formation of steel4 ,although steel is also formed by the action of cyanogen compounds1 nevertheless it does not contain more nitrogen than cast or wrought iron 7#jja p4c471 and these latter contain it because their ores contain titanium1 which combines directly with nitrogen4 ,hence the part played by nitrogen in steel is but an insignificant one4 ,it may be useful here to add some information taken from ,caron's treatise concerning the influence of foreign matter on the quality of steel4 ,the principal properties of steel are those of tempering and annealing4 ,the compounds of iron with silicon and boron have not these properties4 ,they are more stable than the carbon compound1 and this latter is capable of changing its properties2 because the carbon in it either enters into combination or else is disengaged1 which determines the condition of hardness or softness of steel1 as in white and grey cast iron4 ,when slowly cooled1 steel splits up into a mixture of soft and carburetted iron2 but1 nevertheless1 the carbon does not separate from the iron4 ,if such steel be again heated1 it forms a uniform compound1 and hardens when rapidly cooled4 ,if the same steel as before be taken and heated a long time1 then1 after being slowly cooled1 it becomes much more soluble in acid1 and leaves a residue of pure carbon4 ,this shows that the combination between the carbon and iron in steel becomes destroyed when subjected to heat1 and the steel becomes iron mixed with carbon4 ,such burnt steel cannot be tempered1 but may be corrected by continued forging in a heated condition1 which has the effect of redistributing the carbon equally throughout the whole mass4 ,after the forging1 if the iron is pure and the carbon has not been burnt out1 steel is again formed1 which may be tempered4 ,if steel be repeatedly or strongly heated1 it becomes burnt through and cannot be tempered or annealed2 the carbon separates from the iron1 and this is effected more easily if the steel contains other impurities which are capable of forming stable combinations with iron1 such as silicon1 sulphur1 or phosphorus4 ,if there be much silicon1 it occupies the place of the carbon1 and then continued forging will not induce the carbon once separated to re-enter into combination4 ,such steel is easily burnt through and cannot be corrected2 when burnt through1 it is hard and cannot be annealed--this is tough steel1 an inferior kind4 ,iron which contains sulphur and phosphorus cements badly1 combines but little with carbon1 and steel of this kind is brittle1 both hot and cold4 ,iron in combination with the above-mentioned substances cannot be annealed by slow cooling1 showing that these compounds are more stable than those of carbon and iron1 and therefore they prevent the formation of the latter4 ,such metals as tin and zinc combine with iron1 but not with carbon1 and form a brittle mass which cannot be annealed and is deleterious to steel4 ,manganese and tungsten1 on the contrary1 are capable of combining with charcoal2 they do not hinder the formation of steel1 but even remove the injurious effects of other admixtures 7by transforming these admixed substances into new compounds and slags71 and are therefore ranked with the substances which act beneficially on steel2 but1 nevertheless1 the best steel1 which is capable of renewing most often its primitive qualities after burning or hot forging1 is the purest4 ,the addition of ,ni1 ,cr1 ,w1 and certain other metals to steel renders it very suitable for certain special purposes1 and is therefore frequently made use of4 ,it is worthy of attention that steel1 besides temper1 possesses many variable properties1 a review of which may be made in the classification of the sorts of steel 7#ahgh1 ,cockerell74 7#a7 ,very mild steel contains from #jje to #jbj p4c4 of carbon1 breaks with a weight of #dj to #ej kilos per square millimetre1 and has an extension of #bj to #cj p4c42 it may be welded1 like wrought iron1 but cannot be tempered2 is used in sheets for boilers1 armour plate and bridges1 nails1 rivets1 c41 as a substitute for wrought iron2 7#b7 mild steel1 from #jbj to #jce p4c4 of carbon1 resistance to tension #ej to #fj kilos1 extension #ae to #bj p4c41 not easily welded1 and tempers badly1 used for axles1 rails1 and railway tyres1 for cannons and guns1 and for parts of machines destined to resist bending and torsion2 7#c7 hard steel1 carbon #jce to #jej p4c41 breaking weight #fj to #gj kilos per square millimetre1 extension #aj to #ae p4c41 cannot be welded1 takes a temper2 used for rails1 all kinds of springs1 swords1 parts of machinery in motion subjected to friction1 spindles of looms1 hammers1 spades1 hoes1 c42 7#d7 very hard steel1 carbon #je to #jfe p4c41 tensile breaking weight #gj to #hj kilos1 extension #e to #aj p4c41 does not weld1 but tempers easily2 used for small springs1 saws1 files1 knives and similar instruments4 ,the properties of ordinary wrought iron are well known4 ,the best iron is the most tenacious--that is to say1 that which does not break up when struck with the hammer or bent1 and yet at the same time is sufficiently hard4 ,there is1 however1 a distinction between hard and soft iron4 ,generally the softest iron is the most tenacious1 and can best be welded1 drawn into wire1 sheets1 c4 ,hard1 especially tough1 iron is often characterised by its breaking when bent1 and is therefore very difficult to work1 and objects made from it are less serviceable in many respects4 ,soft iron is most adapted for making wire and sheet iron and such small objects as nails4 ,soft iron is characterised by its attaining a fibrous fracture after forging1 whilst tough iron preserves its granular structure after this operation4 ,certain sorts of iron1 although fairly soft at the ordinary temperature1 become brittle when heated and are difficult to weld4 ,these sorts are less suitable for being worked up into small objects4 ,the variety of the properties of iron depends on the impurities which it contains4 ,in general1 the iron used in the arts still contains carbon and always a certain quantity of silicon1 manganese1 sulphur1 phosphorus1 c4 ,a variety in the proportion of these component parts changes the quality of the iron4 ,in addition to this the change which soft wrought iron1 having a fibrous structure1 undergoes when subjected to repeated blows and vibrations is considerable2 it then becomes granular and brittle4 ,this to a certain degree explains the want of stability of some iron objects--such as truck axles1 which must be renewed after a certain term of service1 otherwise they become brittle4 ,it is evident that there are innumerable intermediate transitions from wrought iron to steel and cast iron4 ,at the present day the greater part of the cast iron manufactured is converted into steel1 generally cast steel 7,bessemer's and ,martin's74 ,i may add the ,urals1 ,donetz district1 and other parts of ,russia offer the greatest advantages for the development of an iron industry1 because these localities not only contain vast supplies of excellent iron ore1 but also coal1 which is necessary for smelting it4 #aa ,according to information supplied by ,a4 ,t4 ,skinder's experiments at the ,oboukoff ,steel ,works1 #adj volumes of liquid molten steel give #abh volumes of solid metal4 ,by means of a galvanic current of great intensity and dense charcoal as one electrode1 and iron as the other1 ,bernadoss welded iron and fused holes through sheet iron4 ,soft wrought iron1 like steel and soft malleable cast iron1 may be melted in ,siemens' regenerative furnaces1 and in furnaces heated with naphtha4 #aa bis ,gore 7#ahfi71 ,tait1 ,barret1 ,tchernoff1 ,osmond1 and others observed that at a temperature approaching #fjj--that is1 between dark and bright red heat--all kinds of wrought iron undergo a peculiar change called recalescence1 i4e4 a spontaneous rise of temperature4 ,if iron be considerably heated and allowed to cool1 it may be observed that at this temperature the cooling stops--that is1 latent heat is disengaged1 corresponding with a change in condition4 ,the specific heat1 electrical conductivity1 magnetic1 and other properties then also change4 ,in tempering1 the temperature of recalescence must not be reached1 and so also in annealing1 c4 ,it is evident that a change of the internal condition is here encountered1 exactly similar to the transition from a solid to a liquid1 although there is no evident physical change4 ,it is probable that attentive study would lead to the discovery of a similar change in other substances4 #ab ,the particles of steel are linked together or connected more closely than those of the other metals2 this is shown by the fact that it only breaks with a tensile strain of #ej-hj kilos per sq4 mm41 whilst wrought iron only withstands about #cj kilos1 cast iron #aj1 copper #ce1 silver #bc1 platinum #cj1 wood #h4 ,the elasticity of iron1 steel1 and other metals is expressed by the so-called coefficient of elasticity4 ,let a rod be taken whose length is ,l2 if a weight1 ,p1 be hung from the extremity of it1 it will lengthen to l4 ,the less it lengthens under other equal conditions1 the more elastic the material1 if it resumes its original length when the weight is removed4 ,it has been shown by experiment that the increase in length l1 due to elasticity1 is directly proportional to the length ,l and the weight ,p1 and inversely proportional to the section1 but changes with the material4 ,the coefficient of elasticity expresses that weight 7in kilos per sq4 mm47 under which a rod having a square section taken as #a 7we take #a sq4 mm47 acquires double the length by tension4 ,naturally in practice materials do not withstand such a lengthening1 under a certain weight they attain a limit of elasticity1 i4e4 they stretch permanently 7undergo deformation74 ,neglecting fractions 7as the elasticity of metals varies not only with the temperature1 but also with forging1 purity1 c471 the coefficient of elasticity of steel and iron is #bj1jjj1 copper and brass #aj1jjj1 silver #g1jjj1 glass #f1jjj1 lead #b1jjj1 and wood #a1bjj4 ,the chemical properties of iron have been already repeatedly mentioned in preceding chapters4 ,iron rusts in air at the ordinary temperature--that is to say1 it becomes covered with a layer of iron oxides4 ,here1 without doubt1 the moisture of the air plays a part1 because in dry air iron does not oxidise at all1 and also because1 more particularly1 ammonia is always found in iron rust2 the ammonia must arise from the action of the hydrogen of the water1 at the moment of its separation1 on the nitrogen of the air4 ,highly-polished steel does not rust nearly so readily1 but if moistened with water1 it easily becomes coated with rust4 ,as rust depends on the access of moisture1 iron may be preserved from rust by coating it with substances which prevent the moisture having access to it4 ,thus arises the practice of covering iron objects with paraffin1#ac varnish1 oil1 paints1 or enamelling it with a glassy-looking flux possessing the same coefficient of expansion as iron1 or with a dense scoria 7formed by the heat of superheated steam71 or with a compact coating of various metals4 ,wrought iron 7both as sheet iron and in other forms71 cast iron1 and steel are often coated with tin1 copper1 lead1 nickel1 and similar metals1 which prevent contact with the air4 ,these metals preserve iron very effectually from rust if they form a completely compact surface1 but in those places where the iron becomes exposed1 either accidentally or from wear1 rust appears much more quickly than on a uniform iron surface1 because1 towards these metals 7and also towards the rust71 the iron will then behave as an electro-positive pole in a galvanic couple1 and hence will attract oxygen4 ,a coating of zinc does not produce this inconvenience1 because iron is electro-negative with reference to zinc1 in consequence of which galvanised iron does not easily rust1 and even an iron boiler containing some lumps of zinc rusts less than one without zinc4#ad ,iron oxidises at a high temperature1 forming iron scale1 ,fe#c,o#d1 composed of ferrous and ferric oxides1 and1 as has been seen1 decomposes water and acids with the evolution of hydrogen4 ,it is also capable of decomposing salts and oxides of other metals1 which property is applied in the arts for the extraction of copper1 silver1 lead1 tin1 c4 ,for this reason iron is soluble in the solutions of many salts--for instance1 in cupric sulphate1 with precipitation of copper and formation of ferrous sulphate4#ae ,when iron acts on acids it always forms compounds ,fe,x#b--that is1 corresponding to the suboxide ,fe,o--and answering to magnesium compounds--and hence two atoms of hydrogen are replaced by one atom of iron4 ,strongly oxidising acids like nitric acid may transform the ferrous salt which is forming into the higher degree of oxidation or ferric salt 7corresponding with the sesquioxide1 ,fe#b,o#c71 but this is a secondary reaction4 ,iron1 although easily soluble in dilute nitric acid1 loses this property when plunged into strong fuming nitric acid2 after this operation it even loses the property of solubility in other acids until the external coating formed by the action of the strong nitric acid is mechanically removed4 ,this condition of iron is termed the passive state4 ,the passive condition of iron depends on the formation1 on its surface1 of a coating of oxide due to the iron being acted on by the lower oxides of nitrogen contained in the fuming nitric acid4#af ,strong nitric acid which does not contain these lower oxides1 does not render iron passive1 but it is only necessary to add some alcohol or other reducing agent which forms these lower oxides in the nitric acid1 and the iron will assume the passive state4 #ac ,paraffin is one of the best preservatives for iron against oxidation in the air4 ,i found this by experiments about #ahfj1 and immediately published the fact4 ,this method is now very generally applied4 #ad ,see ,chapter ,,xviii41 ,note #cd bis4 ,based on the rapid oxidation of iron and its increase in volume in the presence of water and salts of ammonium1 a packing is used for water mains and steam pipes which is tightly hammered into the socket joints4 ,this packing consists of a mixture of iron filings and a small quantity of sal-ammoniac 7and sulphur7 moistened with water2 after a certain lapse of time1 especially after the pipes have been used1 this mass swells to such an extent that it hermetically seals the joints of the pipes4 #ae ,here1 however1 a ferric salt may also be formed 7when all the iron has dissolved and the cupric salt is still in excess71 because the cupric salts are reduced by ferrous salts4 ,cast iron is also dissolved4 #af ,powdery reduced iron is passive with regard to nitric acid of a specific gravity of #acg1 but when heated the acid acts on it4 ,this passiveness disappears in the magnetic field4 ,saint-,edme attributes the passiveness of iron 7and nickel7 to the formation of nitride of iron on the surface of the metal1 because he observed that when heated in dry hydrogen ammonia is evolved by passive iron4 ,remsen observed that if a strip of iron be immersed in acid and placed in the magnetic field1 it is principally dissolved at its middle part--that is1 the acid acts more feebly at the poles4 ,according to tard 7#ahia7 strong nitric acid dissolves iron in making it passive1 although the action is a very slow one4 ,iron readily combines with non-metals--for instance1 with chlorine1 iodine1 bromine1 sulphur1 and even with phosphorus and carbon2 but on the other hand the property of combining with metals is but little developed in it--that is to say1 it does not easily form alloys4 ,mercury1 which acts on most metals1 does not act directly on iron1 and the iron amalgam1 or solution of iron in mercury1 which is used for electrical machines1 is only obtained in a particular way--namely1 with the co-operation of a sodium amalgam1 in which the iron dissolves and by means of which it is reduced from solutions of its salts4 ,when iron acts on acids it forms ferrous salts of the type ,fe,x#b1 and in the presence of air and oxidising agents they change by degrees into ferric salts of the type ,fe,x#c4 ,this faculty of passing from the ferrous to the ferric state is still further developed in ferrous hydroxide4 ,if sodium hydroxide be added to a solution of ferrous sulphate or green vitriol1 ,fe,s,o#d1ag a white precipitate of ferrous hydroxide1 ,fe,h#b,o#b1 is obtained2 but on exposure to the air1 even under water1 it turns green1 becomes grey1 and finally turns brown1 which is due to the oxidation that it undergoes4 ,ferrous hydroxide is very sparingly soluble in water2 the solution has1 however1 a distinct alkaline reaction1 which is due to its being a fairly energetic basic oxide4 ,in any case1 ferrous oxide is far more energetic than ferric oxide1 so that if ammonia be added to a solution containing a mixture of a ferrous and ferric salt1 at first ferric hydroxide only will be precipitated4 ,if barium carbonate1 ,ba,c,o#c1 be shaken up in the cold with ferrous salts1 it does not precipitate them--that is1 does not change them into ferrous carbonate2 but it completely separates all the iron from the ferric salts in the cold1 according to the equation ,fe#b;,cl#f #c;,ba,c,o#c #c;,h#b,o ,fe#b,o#c1c;,h#b,o #c;,ba,cl#b #c;,,co#b4 ,if ferrous hydroxide be boiled with a solution of potash1 the water is decomposed1 hydrogen is evolved1 and the ferrous hydroxide is oxidised4 ,the ferrous salts are in all respects similar to the salts of magnesium and zinc2 they are isomorphous with them1 but differ from them in that the ferrous hydroxide is not soluble either in aqueous potash or ammonia4 ,in the presence of an excess of ammonium salts1 however1 a certain proportion of the iron is not precipitated by alkalis and alkali carbonates1 which fact points to the formation of double ammonium salts4#ah ,the ferrous salts have a dull greenish colour1 and form solutions also of a pale green colour1 whilst the ferric salts have a brown or reddish-brown colour4 ,the ferrous salts1 being capable of oxidation1 form very active reducing agents--for instance1 under their action gold chloride1 ,au,cl#c1 deposits metallic gold1 nitric acid is transformed into lower oxides1 and the highest oxides of manganese also pass into the lower forms of oxidation4 ,all these reactions take place with especial ease in the presence of an excess of acid4 ,this depends on the fact that the ferrous oxide1 ,fe,o 7or salt71 acting as a reducing agent1 turns into ferric oxide1 ,fe#b,o#c 7or salt71 and in the ferric state it requires more acid for the formation of a normal salt than in the ferrous condition4 ,thus in the normal ferrous sulphate1 ,fe,s,o#d1 there is one equivalent of iron to one equivalent of sulphur 7in the sulphuric radicle71 but in the neutral ferric salt1 ,fe#b7,,so#d7c1 there is one equivalent of iron to one and a half of sulphur in the form of the elements of sulphuric acid4#ai #ag ,iron vitriol or green vitriol1 sulphate of iron or ferrous sulphate1 generally crystallises from solutions1 like magnesium sulphate1 with seven molecules of water1 ,fe,s,o#d1g;,h#b,o4 ,this salt is not only formed by the action of iron on sulphuric acid1 but also by the action of moisture and air on iron pyrites1 especially when previously roasted 7,fe,s#b ,o#b ,fe,s ,,so#b71 and in this condition it easily absorbs the oxygen of damp air 7,fe,s ,o#d ,fe,s,o#d74 ,green vitriol is obtained in many processes as a by-product4 ,ferrous sulphate1 like all the ferrous salts1 has a pale greenish colour hardly perceptible in solution4 ,if it be desired to preserve it without change--that is1 so as not to contain ferric compounds--it is necessary to keep it hermetically sealed4 ,this is best done by expelling the air by means of sulphurous anhydride or ether2 sulphurous anhydride1 ,,so#b1 removes oxygen from ferric compounds1 which might be formed1 and is itself changed into sulphuric acid1 and hence the oxidation of the ferrous compound does not take place in its presence4 ,unless these precautions are taken1 green vitriol turns brown1 partly changing into the ferric salt4 ,when turned brown1 it is not completely soluble in water1 because during its oxidation a certain amount of free insoluble ferric oxide is formed3 #f;,fe,s,o#d ,o#c #b;,fe#b7,,so#d7c ,fe#b,o#c4 ,in order to cleanse such mixed green vitriol from the oxide1 it is necessary to add some sulphuric acid and iron and boil the mixture2 the ferric salt is then transformed into the ferrous state3 ,fe#b7,,so#d7c ,fe #c;,fe,s,o#d4 ,green vitriol is used for the manufacture of ,nordhausen sulphuric acid 7,chapter ,,xx471 for preparing ferric oxide1 in many dye works 7for preparing the indigo vats and reducing blue indigo to white71 and in many other processes2 it is also a very good disinfectant1 and is the cheapest salt from which other compounds of iron may be obtained4 ,the other ferrous salts 7excepting the yellow prussiate1 which will be mentioned later7 are but little used1 and it is therefore unnecessary to dwell upon them4 ,we will only mention ferrous chloride1 which1 in the crystalline state1 has the composition ,fe,cl#b1d;,h#b,o4 ,it is easily prepared2 for instance1 by the action of hydrochloric acid on iron1 and in the anhydrous state by the action of hydrochloric acid gas on metallic iron at a red heat4 ,the anhydrous ferrous chloride then volatilises in the form of colourless cubic crystals4 ,ferrous oxalate 7or the double potassium salt7 acts as a powerful reducing agent1 and is frequently employed in photography 7as a developer74 #ah ,ferrous sulphate1 like magnesium sulphate1 easily forms double salts--for instance1 7,,nh#d7b,,so#d1;,fe,s,o#d1f;,h#b,o4 ,this salt does not oxidise in air so readily as green vitriol1 and is therefore used for standardising ,k,mn,o#d4 #ai ,the transformation of ferrous oxide into ferric oxide is not completely effected in air1 as then only a part of the suboxide is converted into ferric oxide4 ,under these circumstances the so-called magnetic oxide of iron is generally produced1 which contains atomic quantities of the suboxide and oxide--namely1 ,fe,o1,fe#b,o#c ,fe#c,o#d4 ,this substance1 as already mentioned1 is found in nature and in iron scale4 ,it is also formed when most ferrous and ferric salts are heated in air2 thus1 for instance1 when ferrous carbonate1 ,fe,c,o#c 7native or the precipitate given by soda in a solution of ,fe,x#b71 is heated it loses the elements of carbonic anhydride1 and magnetic oxide remains4 ,this oxide of iron is attracted by the magnet1 and is on this account called magnetic oxide1 although it does not always show magnetic properties4 ,if magnetic oxide be dissolved in any acid--for instance1 hydrochloric--which does not act as an oxidising agent1 a ferrous salt is first formed and ferric oxide remains1 which is also capable of passing into solution4 ,the best way of preparing the hydrate of the magnetic oxide is by decomposing a mixture of ferrous and ferric salts with ammonia2 it is1 however1 indispensable to pour this mixture into the ammonia1 and not vice vers1 as in that case the ferrous oxide would at first be precipitated alone1 and then the ferric oxide4 ,the compound thus formed has a bright green colour1 and when dried forms a black powder4 ,other combinations of ferrous with ferric oxide are known1 as are also compounds of ferric oxide with other bases4 ,thus1 for instance1 compounds are known containing #d molecules of ferrous oxide to #a of ferric oxide1 and also #f of ferrous to #a of ferric oxide4 ,these are also magnetic1 and are formed by heating iron in air4 ,the magnesium compound ,mg,o1,fe#b,o#c is prepared by passing gaseous hydrochloric acid over a heated mixture of magnesia and ferric oxide4 ,crystalline magnesium oxide is then formed1 and black1 shiny1 octahedral crystals of the above-mentioned composition4 ,this compound is analogous to the aluminates--for instance1 to spinel4 ,bernheim 7#ahhh7 and ,rousseau 7#ahia7 obtained many similar compounds of ferric oxide1 and their composition apparently corresponds to the hydrates 7,note #bb7 known for the oxide4 ,the most simple oxidising agent for transforming ferrous into ferric salts is chlorine in the presence of water--for instance1 #b;,fe,cl#b ,cl#b ,fe#b;,cl#f1 or1 generally speaking1 #b;,fe,o ,cl#b ,h#b,o ,fe#b,o#c #b;,h,cl4 ,when such a transformation is required it is best to add potassium chlorate and hydrochloric acid to the ferrous solution2 chlorine is formed by their mutual reaction and acts as an oxidising agent4 ,nitric acid produces a similar effect1 although more slowly4 ,ferrous salts may be completely and rapidly oxidised into ferric salts by means of chromic acid or permanganic acid1 ,h,mn,o#d1 in the presence of acids--for example1 #aj;,fe,s,o#d #b,k,mn,o#d #h;,h#b,,so#d #e;,fe#b7,,so#d7c #b,mn,s,o#d ,k#b,,so#d #h;,h#b,o4 ,this reaction is easily observed by the change of colour1 and its termination is easily seen1 because potassium permanganate forms solutions of a bright red colour1 and when added to a solution of a ferrous salt the above reaction immediately takes place in the presence of acid1 and the solution then becomes colourless1 because all the substances formed are only faintly coloured in solution4 ,directly all the ferrous compound has passed into the ferric state1 any excess of permanganate which is added communicates a red colour to the liquid 7see ,chapter ,,xxi47 ,thus when ferrous salts are acted on by oxidising agents1 they pass into the ferric form1 and under the action of reducing agents the reverse reaction occurs4 ,sulphuretted hydrogen may1 for instance1 be used for this complete transformation1 for under its influence ferric salts are reduced with separation of sulphur--for example1 ,fe#b;,cl#f ,h#b,s #b;,fe,cl#b #b;,h,cl ,s4 ,sodium thiosulphate acts in a similar way3 ,fe#b;,cl#f ,na#b,s#b,o#c ,h#b,o #b;,fe,cl#b ,na#b,,so#d #b;,h,cl ,s4 ,metallic iron or zinc1#bj in the presence1 of acids1 or sodium amalgam1 c41 acts like hydrogen1 and has also a similar reducing action1 and this furnishes the best method for reducing ferric salts to ferrous salts--for instance1 ,fe#b;,cl#f ,zn #b;,fe,cl#b ,zn,cl#b4 ,thus the transition from ferrous salts to ferric salts and vice vers is always possible4#ba #bj ,copper and cuprous salts also reduce ferric oxide to ferrous oxide1 and are themselves turned into cupric salts4 ,the essence of the reactions is expressed by the following equations3 ,fe#b,o#c ,cu#b,o #b;,fe,o #b;,cu,o2 ,fe#b,o#c ,cu #b;,fe,o ,cu,o4 ,this fact is made use of in analysing copper compounds1 the quantity of copper being ascertained by the amount of ferrous salt obtained4 ,an excess of ferric salt is required to complete the reaction4 ,here we have an example of reverse reaction2 the ferrous oxide or its salt in the presence of alkali transforms the cupric oxide into cuprous oxide and metallic copper1 as observed by ,lovel1 ,knopp1 and others4 #ba ,we will here mention the reactions by means of which it may be ascertained whether the ferrous compound has been entirely converted into a ferric compound or vice vers4 ,there are two substances which are best employed for this purpose3 potassium ferricyanide1 ,fe,k#c;,c#f,n#f1 and potassium thiocyanate1 ,,kcns4 ,the first salt gives with ferrous salts a blue precipitate of an insoluble salt1 having a composition ,fe#e;,c#ab,n#ab2 but with ferric salts it does not form any precipitate1 and only gives a brown colour1 and therefore when transforming a ferrous salt into a ferric salt1 the completion of the transformation may be detected by taking a drop of the liquid on paper or on a porcelain plate and adding a drop of the ferricyanide solution4 ,if a blue precipitate be formed1 then part of the ferrous salt still remains2 if there is none1 the transformation is complete4 ,the thiocyanate does not give any marked coloration with ferrous salts2 but with ferric salts in the most diluted state it forms a bright red soluble compound1 and therefore when transforming a ferric salt into a ferrous salt we must proceed as before1 testing a drop of the solution with thiocyanate1 when the absence of a red colour will prove the total transformation of the ferric salt into the ferrous state1 and if a red colour is apparent it shows that the transformation is not yet complete4 ,ferric oxide1 or sesquioxide of iron1 ,fe#b,o#c1 is found in nature1 and is artificially prepared in the form of a red powder by many methods4 ,thus after heating green vitriol a red oxide of iron remains1 called colcothar1 which is used as an oil paint1 principally for painting wood4 ,the same substance in the form of a very fine powder 7rouge7 is used for polishing glass1 steel1 and other objects4 ,if a mixture of ferrous sulphate with an excess of common salt be strongly heated1 crystalline ferric oxide will be formed1 having a dark violet colour1 and resembling some natural varieties of this substance4 ,when iron pyrites is heated for preparing sulphurous anhydride1 ferric oxide also remains behind2 it is used as a pigment4 ,on the addition of alkalis to a solution of ferric salts1 a brown precipitate of ferric hydroxide is formed1 which when heated 7even when boiled in water1 that is1 at about #ajj1 according to ,tomassi7 easily parts with the water1 and leaves red anhydrous ferric oxide4 ,pure ferric oxide does not show any magnetic properties1 but when heated to a white heat it loses oxygen and is converted into the magnetic oxide4 ,anhydrous ferric oxide which has been heated to a high temperature is with difficulty soluble in acids 7but it is soluble when heated in strong acids1 and also when fused with potassium hydrogen sulphate71 whilst ferric hydroxide1 at all events that which is precipitated from salts by means of alkalis1 is very readily soluble in acids4 ,the precipitated ferric hydroxide has the composition #b;,fe#b,o#cc;,h#b,o1 or ,fe#d;,h#f,o#i4 ,if this ordinary hydroxide be rendered anhydrous 7at #ajj71 at a certain moment it becomes incandescent--that is1 loses a certain quantity of heat4 ,this self-incandescence depends on internal displacement produced by the transition of the easily-soluble 7in acids7 variety into the difficultly-soluble variety1 and does not depend on the loss of water1 since the anhydrous oxide undergoes the same change4 ,in addition to this there exists a ferric hydroxide1 or hydrated oxide of iron1 which1 like the strongly-heated anhydrous iron oxide1 is difficultly soluble in acids4 ,this hydroxide on losing water1 or after the loss of water1 does not undergo such self-incandescence1 because no such state of internal displacement occurs 7loss of energy or heat7 with it as that which is peculiar to the ordinary oxide of iron4 ,the ferric hydroxide which is difficultly soluble in acids has the composition ,fe#b,o#c1;,h#b,o4 ,this hydroxide is obtained by a prolonged ebullition of water in which ferric hydroxide prepared by the oxidation of ferrous oxide is suspended1 and also sometimes by similar treatment of the ordinary hydroxide after it has been for a long time in contact with water4 ,the transition of one hydroxide to another is apparent by a change of colour2 the easily-soluble hydroxide is redder1 and the sparingly-soluble hydroxide more yellow in colour4#bb #bb ,the two ferric hydroxides are not only characterised by the above-mentioned properties1 but also by the fact that the first hydroxide forms immediately with potassium ferrocyanide1 ,k#d;,fe,c#f,n#f1 a blue colour depending on the formation of ,prussian blue1 whilst the second hydroxide does not give any reaction whatever with this salt4 ,the first hydroxide is entirely soluble in nitric1 hydrochloric1 and all other acids2 whilst the second sometimes 7not always7 forms a brick-coloured liquid1 which appears turbid and does not give the reactions peculiar to the ferric salts 7,pan de ,saint-,gilles1 ,scheurer-,kestner74 ,in addition to this1 when the smallest quantity of an alkaline salt is added to this liquid1 ferric oxide is precipitated4 ,thus a colloidal solution is formed 7hydrosol71 which is exactly similar to silica hydrosol 7,chapter ,,xvii471 according to which example the hydrosol of ferric oxide may be obtained4 ,if ordinary ferric hydroxide be dissolved in acetic acid1 a solution of the colour of red wine is obtained1 which has all the reactions characteristic of ferric salts4 ,but if this solution 7formed in the cold7 be heated to the boiling-point1 its colour is very rapidly intensified1 a smell of acetic acid becomes apparent1 and the solution then contains a new variety of ferric oxide4 ,if the boiling of the solution be continued1 acetic acid is evolved1 and the modified ferric oxide is precipitated4 ,if the evaporation of the acetic acid be prevented 7in a closed or sealed vessel71 and the liquid be heated for some time1 the whole of the ferric hydroxide then passes into the insoluble form1 and if some alkaline salt be added 7to the hydrosol formed71 the whole of the ferric oxide is then precipitated in its insoluble form4 ,this method may be applied for separating ferric oxide from solutions of its salts4 ,all phenomena observed respecting ferric oxide 7colloidal properties1 various forms1 formation of double basic salts7 demonstrate that this substance1 like silica1 alumina1 lead hydroxide1 c41 is polymerised1 that the composition is represented by 7,fe#b,o#c7n4 ,the normal salts of the composition ,fe#b,x#f or ,fe,x#c correspond with ferric oxide--for example1 the exceedingly volatile ferric chloride1 ,fe#b;,cl#f1 which is easily prepared in the anhydrous state by the action of chlorine on heated iron4#bc ,such also is the normal ferric nitrate1 ,fe#b7,,no#c7f2 it is obtained by dissolving iron in an excess of nitric acid1 taking care as far as possible to prevent any rise of temperature4#bd ,the normal salt separates from the brown solution when it is concentrated under a bell jar over sulphuric acid4 ,this salt1 ,fe#b7,,no#c7f1i;,h#b,o1 then crystallises in well-formed and perfectly colourless crystals1#be which deliquesce in air1 melt at #ce1 and are soluble in and decomposed by water4 ,the decomposition may be seen from the fact that the solution is brown and does not yield the whole of the salt again1 but gives partly basic salt4 ,the normal salt 7only stable in the presence of an excess of ,,hno#c7 is completely decomposed with great facility by heating with water1 even at #acj1 and this is made use of for removing iron 7and also certain other oxides of the form ,r#b,o#c7 from many other bases 7of the form ,,ro7 whose nitrates are far more stable4 ,the ferric salts1 ,fe,x#c1 in passing into ferrous salts1 act as oxidising agents1 as is seen from the fact that they not only liberate ,s from ,,sh#b1 but also iodine from ,,ki like many oxidising agents4#be bis #bc ,the ferric compound which is most used in practice 7for instance1 in medicine1 for cauterising1 stopping bleeding1 c4--,oleum ,martis7 is ferric chloride1 ,fe#b;,cl#f1 easily obtained by dissolving the ordinary hydrated oxide of iron in hydrochloric acid4 ,it is obtained in the anhydrous state by the action of chlorine on heated iron4 ,the experiment is carried on in a porcelain tube1 and a solid volatile substance is then formed in the shape of brilliant violet scales which very readily absorb moisture from the air1 and when heated with water decompose into crystalline ferric oxide and hydrochloric acid3 ,fe#b;,cl#f #c;,h#b,o #f;,h,cl ,fe#b,o#c4 ,ferric chloride is so volatile that the density of its vapour may be determined4 ,at #ddj it is equal to #afdj referred to hydrogen2 the formula ,fe#b;,cl#f corresponds with a density of #afbe4 ,an aqueous solution of this salt has a brown colour4 ,on evaporating and cooling this solution1 crystals separate containing #f or #ab molecules of ,h#b,o4 ,ferric chloride is not only soluble in water1 but also in alcohol 7similarly to magnesium chloride1 c47 and in ether4 ,if the latter solutions are exposed to the rays of the sun they become colourless1 and deposit ferrous chloride1 ,fe,cl#b1 chlorine being disengaged4 ,after a certain lapse of time1 the aqueous solutions of ferric chloride decompose with precipitation of a basic salt1 thus demonstrating the instability of ferric chloride1 like the other salts of ferric oxide 7,note #bb74 ,this salt is much more stable in the form of double salts1 like all the ferric salts and also the salts of many other feeble bases4 ,potassium or ammonium chloride forms with it very beautiful red crystals of a double salt1 having the composition ,fe#b;,cl#f1d,k,cl1#b;,h#b,o4 ,when a solution of this salt is evaporated it decomposes1 with separation of potassium chloride4 ,b4 ,roozeboom 7#ahib7 studied in detail 7as for ,ca,cl#b1 ,chapter ,,xiv41 ,note #ej7 the separation of different hydrates from saturated solutions of ,fe#b;,cl#f at various concentrations and temperatures2 he found that there are #d crystallohydrates with #ab1 #g1 #e1 and #d molecules of water4 ,an orange yellow only slightly hygroscopic hydrate1 ,fe#b;,cl#f1ab;,h#b,o1 is most easily and usually obtained1 which melts at #cg2 its solubility at different temperatures is represented by the curve ,,bcd in the accompanying figure1 where the point ,b corresponds to the formation1 at -#ee1 of a cryohydrate containing about ,fe#b;,cl#f #cf;,h#b,o1 the point ,c corresponds to the melting-point 7#cg7 of the hydrate ,fe#b;,cl#f1ab;,h#b,o1 and the curve ,,cd to the fall in the temperature of crystallisation with an increase in the amount of salt1 or decrease in the amount of water 7in the figure the temperatures are taken along the axis of absciss1 and the amount of n in the formula n,fe#b;,cl#f #ajj;,h#b,o along the axis of ordinates74 ,when anhydrous ,fe#b;,cl#f is added to the above hydrate 7#ab;,h#b,o71 or some of the water is evaporated from the latter1 very hygroscopic crystals of ,fe#b;,cl#f1e;,h#b,o 7,fritsche7 are formed2 they melt at #ef1 their solubility is expressed by the curve ,,hj1 which also presents a small branch at the end ,j4 ,this again gives the fall in the temperature of crystallisation with an increase in the amount of ,fe#b;,cl#f4 ,besides these curves and the solubility of the anhydrous salt expressed by the line ,,kl 7up to #ajj1 beyond which chlorine is liberated71 ,roozeboom also gives the two curves1 ,,efg and ,,jk1 corresponding to the crystallohydrates1 ,fe#b;,cl#f1g;,h#b,o 7melts at #cbe1 that is lower than any of the others7 and ,fe#b;,cl#f1d;,h#b,o 7melts at #gce71 which he discovered by a systematic research on the solutions of ferric chloride4 ,the curve ,,ab represents the separation of ice from dilute solutions of the salt4 ,illustration3 ,,fig4 #ie4--;,diagram of the solubility of ,fe#b;,cl#f4 ,the researches of the same ,dutch chemist upon the conditions of the formation of crystals from the double salt 7,,nh#d;,cl7#d;,fe#b;,cl#f1b;,h#b,o are even more perfect4 ,this salt was obtained in #ahci by ,fritsche1 and is easily formed from a strong solution of ,fe#b;,cl#f by adding sal-ammoniac1 when it separates in crimson rhombic crystals1 which1 after dissolving in water1 only deposit again on evaporation1 together with the sal-ammoniac4 ,roozeboom 7#ahib7 found that when the solution contains b molecules of ,fe#b;,cl#f1 and a molecules of ,,nh#d;,cl1 per #ajj molecules ,h#b,o1 then at #ae one of the following separations takes place3 7#a7 crystals1 ,fe#b;,cl#f1ab;,h#b,o1 when a varies between #j and #aa1 and b between #dfe and #dh1 or 7#b7 a mixture of these crystals and the double salt1 when a #acf1 and b #ddg1 or 7#c7 the double salt1 ,fe#b;,cl#f1d,,nh#d;,cl1#b;,h#b,o1 when a varies between #b and #aah1 and b between #ca and #def1 or 7#d7 a mixture of sal-ammoniac with the iron salt 7it crystallises in separate cubes1 ,retgers1 ,lehmann71 when a varies between #gg and #aji1 and b is less than #cch1 or 7#e7 sal-ammoniac1 when a #aahh4 ,and as in the double salt1 a 3 b 33 #d 3 #a it is evident that the double salt only separates out when the ratio a 3 b is less than #d 3 #a 7i4e4 when ,fe#b;,cl#f predominates74 ,the above is seen more clearly in the accompanying figure1 where a1 or the number of molecules of ,,nh#d;,cl per #ajj;,h#b,o1 is taken along the axis of absciss1 and b1 or the number of molecules of ,fe#b;,cl#f1 along the ordinates4 ,the curves ,,abcd correspond to saturation and present an iso-therm of #ae4 ,the portion ,,ab corresponds to the separation of chloride of iron 7the ascending nature of this curve shows that the solubility of ,fe#b;,cl#f is increased by the presence of ,,nh#d;,cl1 while that of ,,nh#d;,cl decreases in the presence of ,fe#b;,cl#f71 the portion ,,bc to the double salt1 and the portion ,,cd to a mixture of sal-ammoniac and ferric chloride1 while the straight line ,,of corresponds to the ratio ,fe#b;,cl#f1d,,nh#d;,cl1 or a 3 b 33 #d 3 #a4 ,the portion ,,ce shows that more double salt may be introduced into the solution without decomposition1 but then the solution deposits a mixture of sal-ammoniac and ferric chloride 7see ,chapter ,,xxiv4 ,note #i bis74 ,if there were more such well-investigated cases of solutions1 our knowledge of double salts1 solutions1 the influence of water1 equilibria1 isomorphous mixtures1 and such-like provinces of chemical relations might be considerably advanced4 ,illustration3 ,,fig4 #if4--;,diagram of the formation1 at #ae1 of the double salt ,fe#b;,cl#fd,,nh#d;,cl#b;,h#b,o or ,fe7,,nh#d7b;,cl#e;,h#b,o4 7,after ,roozeboom47 #bd ,the normal ferric salts are decomposed by heat and even by water1 forming basic salts1 which may be prepared in various ways4 ,generally ferric hydroxide is dissolved in solutions of ferric nitrate2 if it contains a double quantity of iron the basic salt is formed which contains ,fe#b,o#c 7in the form of hydroxide7 #b;,fe#b7,,no#c7f #c;,fe#b,o7,,no#c7d1 a salt of the type ,fe#b,,ox#d4 ,probably water enters into its composition4 ,with considerable quantities of ferric oxide1 insoluble basic salts are obtained containing various amounts of ferric hydroxide4 ,thus when a solution of the above-mentioned basic acid is boiled1 a precipitate is formed containing #d7;,fe#b,o#c7h1b7,n#b,o#e71c;,h#b,o1 which probably contains #b;,fe#b,o#b7,,no#c7b #b;,fe#b,o#c1c;,h#b,o4 ,if a solution of basic nitrate be sealed in a tube and then immersed in boiling water1 the colour of the solution changes just in the same way as if a solution of ferric acetate had been employed 7,note #bb74 ,the solution obtained smells strongly of nitric acid1 and on adding a drop of sulphuric or hydrochloric acid the insoluble variety of hydrated ferric oxide is precipitated4 ,normal ferric orthophosphate is soluble in sulphuric1 hydrochloric1 and nitric acids1 but insoluble in others1 such as1 for instance1 acetic acid4 ,the composition of this salt in the anhydrous state is ,fe,p,o#d1 because in orthophosphoric acid there are three atoms of hydrogen1 and iron1 in the ferric state1 replaces the three atoms of hydrogen4 ,this salt is obtained from ferric acetate1 which1 with disodium phosphate1 forms a white precipitate of ,fe,p,o#d1 containing water4 ,if a solution of ferric chloride 7yellowish-red colour7 be mixed with a solution of sodium acetate in excess1 the liquid assumes an intense brown colour which demonstrates the formation of a certain quantity of ferric acetate2 then the disodium phosphate directly forms a white gelatinous precipitate of ferric phosphate4 ,by this means the whole of the iron may be precipitated1 and the liquid which was brown then becomes colourless4 ,if this normal salt be dissolved in orthophosphoric acid1 the crystalline acid salt ,fe,h#c7,,po#d7b is formed4 ,if there be an excess of ferric oxide in the solution1 the precipitate will consist of the basic salt4 ,if ferric phosphate be dissolved in hydrochloric acid1 and ammonia be added1 a salt is precipitated on heating which1 after continued washing in water and heating 7to remove the water71 has the composition ,fe#d,p#b,o#aa--that is1 #b;,fe#b,o#c1,p#b,o#e4 ,in an aqueous condition this salt may be considered as ferric hydroxide1 ,fe#b7,,oh7#f1 in which 7,,oh7#c is replaced by the equivalent group ,,po#d4 ,whenever ammonia is added to a solution containing an excess of ferric salt and a certain amount of phosphoric acid1 a precipitate is formed containing the whole of the phosphoric acid in the mass of the ferric oxide4 ,ferric oxide is characterised as a feeble base1 and also by the fact of its forming double salts--for instance1 potassium iron alum1 which has a composition ,fe#b7,,so#d7c1,k#b,,so#d1bd;,h#b,o or ,fe,k7,,so#d7b1ab;,h#b,o4 ,it is obtained in the form of almost colourless or light rose-coloured large octahedra of the regular system by simply mixing solutions of potassium sulphate and the ferric sulphate obtained by dissolving ferric oxide in sulphuric acid4 #be ,it would seem that all normal ferric salts are colourless1 and that the brown colour which is peculiar to the solutions is really due to basic ferric salts4 ,a remarkable example of the apparent change of colour of salts is represented by the ferrous and ferric oxalates4 ,the former in a dry state has a yellow colour1 although as a rule the ferrous salts are green1 and the latter is colourless or pale green4 ,when the normal ferric salt is dissolved in water it is1 like many salts1 probably decomposed by the water into acid and basic salts1 and the latter communicates a brown colour to the solution4 ,iron alum is almost colourless1 is easily decomposed by water1 and is the best proof of our assertion4 ,the study of the phenomena peculiar to ferric nitrate might1 in my opinion1 give a very useful addition to our knowledge of the aqueous solutions of salts in general4 #be bis ,the reaction ,fe,x#c ,,ki ,fe,x#b ,,kx ,i proceeds comparatively slowly in solutions1 is not complete 7depends upon the mass71 and is reversible4 ,in this connection we may cite the following data from ,seubert and ,rohrer's 7#ahid7 comprehensive researches4 ,the investigations were conducted with solutions containing #a_/aj gram--equivalent weights of ,fe#b7,,so#d7c 7i4e4 containing #bj grams of salt per litre71 and a corresponding solution of ,,ki2 the amount of iodine liberated being determined 7after the addition of starch7 by a solution 7also #a_/aj normal7 of ,na#b,s#b,o#c 7see ,chapter ,,xx41 ,note #db74 ,the progress of the reaction was expressed by the amount of liberated iodine in percentages of the theoretical amount4 ,for instance1 the following amount of iodide of potassium was decomposed when ,fe#b7,,so#d7c #bn,,ki was taken3 n #a #b #c #f #aj #bj ,after #ae #aad #bfc #djf #gce #iaf #ifj #cj #adj #ceh #dgh #ghe #idc #igd #a hour #aij #dbg #efj #hdj #ieg #igf #aj #cbf #efj #geg #icb #ife #igf #dh #cid #fgg #hbf #icd #iff #igf ,similar results were obtained for ,fe,cl#c1 but then the amount of iodine liberated was somewhat greater4 ,similar results were also obtained by increasing the mass of ,fe,x#c per ,,ki1 and by replacing it by ,,hi 7see ,chapter ,,xxi41 ,note #bf74 ,iron forms one other oxide besides the ferric and ferrous oxides2 this contains twice as much oxygen as the former1 but is so very unstable that it can neither be obtained in the free state nor as a hydrate4 ,whenever such conditions of double decomposition occur as should allow of its separation in the free state1 it decomposes into oxygen and ferric oxide4 ,it is known in the state of salts1 and is only stable in the presence of alkalis1 and forms salts with them which have a decidedly alkaline reaction2 it is therefore a feebly acid oxide4 ,thus when small pieces of iron are heated with nitre or potassium chlorate a potassium salt of the composition ,k#b;,fe,o#d is formed1 and therefore the hydrate corresponding with this salt should have the composition ,h#b;,fe,o#d4 ,it is called ferric acid4 ,its anhydride ought to contain ,fe,o#c or ,fe#b,o#f--twice as much oxygen as ferric oxide4 ,if a solution of potassium ferrate be mixed with acid1 the free hydrate ought to be formed1 but it immediately decomposes 7#b,k#b;,fe,o#d #e;,h#b,,so#d #b,k#b,,so#d ,fe#b7,,so#d7c #e;,h#b,o ,o#c71 oxygen being evolved4 ,if a small quantity of acid be taken1 or if a solution of potassium ferrate be heated with solutions of other metallic salts1 ferric oxide is separated--for instance3 #b;,cu,s,o#d #b,k#b;,fe,o#d #b,k#b,,so#d ,o#c ,fe#b,o#c #b;,cu,o4 ,both these oxides are of course deposited in the form of hydrates4 ,this shows that not only the hydrate ,h#b;,fe,o#d1 but also the salts of the heavy metals corresponding with this higher oxide of iron1 are not formed by reactions of double decomposition4 ,the solution of potassium ferrate naturally acts as a powerful oxidising agent2 for instance1 it transforms manganous oxide into the dioxide1 sulphurous into sulphuric acid1 oxalic acid into carbonic anhydride and water1 c4#bf #bf ,if chlorine be passed through a strong solution of potassium hydroxide in which hydrated ferric oxide is suspended1 the turbid liquid acquires a dark pomegranate-red colour and contains potassium ferrate3 #aj,,kho ,fe#b,o#c #c;,cl#b #b,k#b;,fe,o#d #f,k,cl #e;,h#b,o4 ,the chlorine must not be in excess1 otherwise the salt is again decomposed1 although the mode of decomposition is unknown2 however1 ferric chloride and potassium chlorate are probably formed4 ,another way in which the above-described salt is formed is also remarkable2 a galvanic current 7from #f ,grove elements7 is passed through cast-iron and platinum electrodes into a strong solution of potassium hydroxide4 ,the cast-iron electrode is connected with the positive pole1 and the platinum electrode is surrounded by a porous earthenware cylinder4 ,oxygen would be evolved at the cast-iron electrode1 but it is used up in oxidation1 and a dark solution of potassium ferrate is therefore formed about it4 ,it is remarkable that the cast iron cannot be replaced by wrought iron4 ,iron thus combines with oxygen in three proportions3 ,,ro1 ,r#b,o#c1 and ,,ro#c4 ,it might have been expected that there would be intermediate stages ,,ro#b 7corresponding to pyrites ,fe,s#b7 and ,r#b,o#e1 but for iron these are unknown4#bf bis ,the lower oxide has a distinctly basic character1 the higher is feebly acid4 ,the only one which is stable in the free state is ferric oxide1 ,fe#b,o#c2 the suboxide1 ,fe,o1 absorbs oxygen1 and ferric anhydride1 ,fe,o#c1 evolves it4 ,it is also the same for other elements2 the character of each is determined by the relative degree of stability of the known oxides4 ,the salts ,fe,x#b correspond with the suboxide1 the salts ,fe,x#c or ,fe#b,x#f with the sesquioxide1 and ,fe,x#f represents those of ferric acid1 as its potassium salt is ,fe,o#b7,,ok7#b1 corresponding with ,k#b,,so#d1 ,k#b,mn,o#d1 ,k#b;,cr,o#d1 c4 ,iron therefore forms compounds of the types ,fe,x#b1 ,fe,x#c1 and ,fe,x#f1 but this latter1 like the type ,,nx#e1 does not appear separately1 but only when ,x represents heterogeneous elements or groups2 for instance1 for nitrogen in the form of ,,no#b7,,oh71 ,,nh#d;,cl1 c41 for iron in the form of ,fe,o#b7,,ok7#b4 ,but still the type ,fe,x#f exists1 and therefore ,fe,x#b and ,fe,x#c are compounds which1 like ammonia1 ,,nh#c1 are capable of further combinations up to ,fe,x#f2 this is also seen in the property of ferrous and ferric salts of forming compounds with water of crystallisation1 besides double and basic salts1 whose stability is determined by the quality of the elements included in the types ,fe,x#b and ,fe,x#c4bf tri ,it is therefore to be expected that there should be complex compounds derived from ferrous and ferric oxides4 ,amongst these the series of cyanogen compounds is particularly interesting2 their formation and character is not only determined by the property which iron possesses of forming complex types1 but also by the similar faculty of the cyanogen compounds1 which1 like nitriles 7,chapter ,,ix471 have clearly developed properties of polymerisation and in general of forming complex compounds4#bg #bf bis ,when ,mond and his assistants obtained the remarkable volatile compound ,ni7,,co7#d 7described later1 ,chapter ,,xxii471 it was shown subsequently by ,mond and ,quincke 7#ahia71 and also by ,berthelot1 that iron1 under certain conditions1 in a stream of carbonic oxide1 also volatilises and forms a compound like that given by nickel4 ,roscoe and ,scudder then showed that when water gas is passed through and kept under pressure 7#h atmospheres7 in iron vessels a portion of the iron volatilises from the sides of the vessel1 and that when the gas is burnt it deposits a certain amount of oxides of iron 7the same result is obtained with ordinary coal gas which contains a small amount of ,,co74 ,to obtain the volatile compound of iron with carbonic oxide1 ,mond prepared a finely divided iron by heating the oxalate in a stream of hydrogen1 and after cooling it to #hj-de he passed ,,co over the powder4 ,the iron then formed 7although very slowly7 a volatile compound containing ,fe7,,co7#e 7as though it answered to a very high type1 ,fe,x#aj71 which when cooled condenses into a liquid 7slightly coloured1 probably owing to incipient decomposition71 sp4 gr4 #adg1 which solidifies at -#ba1 boils at about #ajc1 and has a vapour density 7about #fe with respect to air7 corresponding to the above formula2 it decomposes at #ahj4 ,water and dilute acids do not act upon it1 but it decomposes under the action of light and forms a hard1 non-volatile crystalline yellow compound ,fe#b7;,,co7#g which decomposes at #hj and again forms ,fe7,,co7#e4 #bf tri ,when the molecular ,fe#b;,cl#f is produced instead of ,fe,cl#c this complication of the type also occurs4 #bg ,some light may be thrown upon the faculty of ,fe of forming various compounds with ,,cn1 by the fact that ,fe not only combines with carbon but also with nitrogen4 ,nitride of iron ,fe#b,n was obtained by ,fowler by heating finely powdered iron in a stream of ,,nh#c at the temperature of melting lead4 ,in the cyanogen compounds of iron1 two degrees might be expected3 ,fe7,,cn7#b1 corresponding with ferrous oxide1 and ,fe7,,cn7#c1 corresponding with ferric oxide4 ,there are actually1 however1 many other known compounds1 intermediate and far more complex4 ,they correspond with the double salts so easily formed by metallic cyanides4 ,the two following double salts are particularly well known1 very stable1 often used1 and easily prepared4 ,potassium ferrocyanide or yellow prussiate of potash1 a double salt of cyanide of potassium and ferrous cyanide1 has the composition ,fe,c#b,n#b1d,,kcn2 its crystals contain #c mol4 of water3 ,k#d;,fe,c#f,n#f1c;,h#b,o4 ,the other is potassium ferricyanide or red prussiate of potash4 ,it is also known as ,gmelin's salt1 and contains cyanide of potassium with ferric cyanide2 its composition is ,fe7,,cn7#c1c,,kcn or ,k#c;,fe,c#f,n#f4 ,its crystals do not contain water4 ,it is obtained from the first by the action of chlorine1 which removes one atom of the potassium4 ,a whole series of other ferrocyanic compounds correspond with these ordinary salts4 ,before treating of the preparation and properties of these two remarkable and very stable salts1 it must be observed that with ordinary reagents neither of them gives the same double decompositions as the other ferrous and ferric salts1 and they both present a series of remarkable properties4 ,thus these salts have a neutral reaction1 are unchanged by air1 dilute acids1 or water1 unlike potassium cyanide and even some of its double salts4 ,when solutions of these salts are treated with caustic alkalis1 they do not give a precipitate of ferrous or ferric hydroxides1 neither are they precipitated by sodium carbonate4 ,this led the earlier investigators to recognise special independent groupings in them4 ,the yellow prussiate was considered to contain the complex radicle ,fe,c#f,n#f combined with potassium1 namely with ,k#d1 and ,k#c was attributed to the red prussiate4 ,this was confirmed by the fact that whilst in both salts any other metal1 even hydrogen1 might be substituted for potassium1 the iron remained unchangeable1 just as nitrogen in cyanogen1 ammonium1 and nitrates does not enter into double decomposition1 being in the state of the complex radicles ,,cn1 ,,nh#d1 ,,no#b4 ,such a representation is1 however1 completely superfluous for the explanation of the peculiarities in the reactions of such compounds as double salts4 ,if a magnesium salt which can be precipitated by potassium hydroxide does not form a precipitate in the presence of ammonium chloride1 it is very clear that it is owing to the formation of a soluble double salt which is not decomposed by alkalis4 ,and there is no necessity to account for the peculiarity of reaction of a double salt by the formation of a new complex radicle4 ,in the same way also1 in the presence of an excess of tartaric acid1 cupric salts do not form a precipitate with potassium hydroxide1 because a double salt is formed4 ,these peculiarities are more easily understood in the case of cyanogen compounds than in all others1 because all cyanogen compounds1 as unsaturated compounds1 show a marked tendency to complexity4 ,this tendency is satisfied in double salts4 ,the appearance of a peculiar character in double cyanides is the more easily understood since in the case of potassium cyanide itself1 and also in hydrocyanic acid1 a great many peculiarities have been observed which are not encountered in those haloid compounds1 potassium chloride and hydrochloric acid1 with which it was usual to compare cyanogen compounds4 ,these peculiarities become more comprehensible on comparing cyanogen compounds with ammonium compounds4 ,thus in the presence of ammonia the reactions of many compounds change considerably4 ,if in addition to this it is remembered that the presence of many carbon 7organic7 compounds frequently completely disturbs the reaction of salts1 the peculiarities of certain double cyanides will appear still less strange1 because they contain carbon4 ,the fact that the presence of carbon or another element in the compound produces a change in the reactions1 may be compared to the action of oxygen1 which1 when entering into a combination1 also very materially changes the nature of reactions4 ,chlorine is not detected by silver nitrate when it is in the form of potassium chlorate1 ,k,cl,o#c1 as it is detected in potassium chloride1 ,k,cl4 ,the iron in ferrous and ferric compounds varies in its reactions4 ,in addition to the above-mentioned facts1 consideration ought to be given to the circumstance that the easy mutability of nitric acid undergoes modification in its alkali salts1 and in general the properties of a salt often differ much from those of the acid4 ,every double salt ought to be regarded as a peculiar kind of saline compound3 potassium cyanide is1 as it were1 a basic1 and ferrous cyanide an acid1 element4 ,they may be unstable in the separate state1 but form a stable double compound when combined together2 the act of combination disengages the energy of the elements1 and they1 so to speak1 saturate each other4 ,of course1 all this is not a definite explanation1 but then the supposition of a special complex radicle can even less be regarded as such4 ,potassium ferrocyanide1 ,k#d;,fe,c#f,n#f1 is very easily formed by mixing solutions of ferrous sulphate and potassium cyanide4 ,first1 a white precipitate of ferrous cyanide1 ,fe,c#b,n#b1 is formed1 which becomes blue on exposure to air1 but is soluble in an excess of potassium cyanide1 forming the ferrocyanide4 ,the same yellow prussiate is obtained on heating animal nitrogenous charcoal or animal matters--such as horn1 leather cuttings1 c4--with potassium carbonate in iron vessels1#bg bis the mass formed being afterwards boiled with water with exposure to air1 potassium cyanide first appearing1 which gives yellow prussiate4 ,the animal charcoal may be exchanged for wood charcoal1 permeated with potassium carbonate and heated in nitrogen or ammonia2 the mass thus produced is then boiled in water with ferric oxide4#bh ,in this manner it is manufactured on the large scale1 and is called 'yellow prussiate' 7'prussiate de potasse1' ,blutlaugensalz74 #bg bis ,the sulphur of the animal refuse here forms the compound ,fe,k,s#b1 which by the action of potassium cyanide yields potassium sulphide1 thiocyanate1 and ferrocyanide4 #bh ,potassium ferrocyanide may also be obtained from ,prussian blue by boiling with a solution of potassium hydroxide1 and from the ferricyanide by the action of alkalis and reducing substances 7because the red prussiate is a product of oxidation produced by the action of chlorine3 a ferric salt is reduced to a ferrous salt71 c4 ,in many works 7especially in ,germany and ,france7 yellow prussiate is prepared from the mass1 containing oxide of iron1 and employed for purifying coal gas 7,vol4 ,i41 p4 #cfa71 which generally contains cyanogen compounds4 ,about #b p4c4 of the nitrogen contained in coal is converted into cyanogen1 which forms ,prussian blue and thiocyanates in the mass used for purifying the gas4 ,on evaporation the solution yields large yellow crystals containing #c molecules of water1 which is easily expelled by heating above #ajj4 #ajj parts of water at the ordinary temperature are capable of dissolving #be parts of this salt2 its sp4 gr4 is #ahc4 ,when ignited it forms potassium cyanide and iron carbide1 ,fe,c#b 7,chapter ,,xiii41 ,note #ab74 ,oxidising substances change it into potassium ferricyanide4 ,with strong sulphuric acid it gives carbonic oxide1 and with dilute sulphuric acid1 when heated1 prussic acid is evolved according to the equation3 #b,k#d;,fe,c#f,n#f #c;,h#b,,so#d ,k#b;,fe#b;,c#f,n#f #c,k#b,,so#d #f;,,hcn2 hence in the yellow prussiate ,k#b replaces ,fe4 ,it is easy to substitute other metals for the potassium in the yellow prussiate4 ,the hydrogen salt or hydroferrocyanic acid1 ,h#d;,fe,c#f,n#f1 is obtained by mixing strong solutions of yellow prussiate and hydrochloric acid4 ,if ether be added and the air excluded1 the acid is obtained directly in the form of a white scarcely crystalline precipitate which becomes blue on exposure to air 7as ferrous cyanide does from the formation of blue compounds of ferrous and ferric cyanides1 and it is on this account used in cotton printing74 ,it is soluble in water and alcohol1 but not in ether1 has marked acid properties1 and decomposes carbonates1 which renders it easily possible to prepare ferrocyanides of the metals of the alkalis and alkaline earths2 these are readily soluble1 have a neutral reaction1 and resemble the yellow prussiate4 ,solutions of these salts form precipitates with the salts of other metals1 because the ferrocyanides of the heavy metals are insoluble4 ,here either the whole of the potassium of the yellow prussiate1 or only a part of it1 is exchanged for an equivalent quantity of the heavy metal4 ,thus1 when a cupric salt is added to a solution of yellow prussiate1 a red precipitate is obtained which still contains half the potassium of the yellow prussiate3 ,k#d;,fe,c#f,n#f ,cu,s,o#d ,k#b;,cu,fe,c#f,n#f ,k#b,,so#d4 ,but if the process be reversed 7the salt of copper being then in excess7 the whole of the potassium will be exchanged for copper1 forming a reddish-brown precipitate1 ,cu#b;,fe,c#f,n#f1i;,h#b,o4 ,this reaction and those similar to it are very sensitive and may be used for detecting metals in solution1 more especially as the colour of the precipitate very often shows a marked difference when one metal is exchanged for another4 ,zinc1 cadmium1 lead1 antimony1 tin1 silver1 cuprous and aurous salts form white precipitates2 cupric1 uranium1 titanium and molybdenum salts reddish-brown2 those of nickel1 cobalt1 and chromium1 green precipitates2 with ferrous salts1 ferrocyanide forms1 as has been already mentioned1 a white precipitate--namely1 ,fe#b;,fe,c#f,n#f1 or ,fe,c#b,n#b--which turns blue on exposure to air1 and with ferric salts a blue precipitate called ,prussian blue4 ,here the potassium is replaced by iron1 the reaction being expressed thus3 #b;,fe#b;,cl#f #c,k#d;,fe,c#f,n#f #ab,k,cl ,fe#d;,fe#c;,c#ah,n#ah1 the latter formula expressing the composition of ,prussian blue4 ,it is therefore the compound #d;,fe7,,cn7#c #c;,fe7,,cn7#b4 ,the yellow prussiate is prepared in chemical works on a large scale especially for the manufacture of this blue pigment1 which is used for dyeing cloth and other fabrics and also as one of the ordinary blue paints4 ,it is insoluble in water1 and the stuffs are therefore dyed by first soaking them in a solution of a ferric salt and then in a solution of yellow prussiate4 ,if however an excess of yellow prussiate be present complete substitution between potassium and iron does not occur1 and soluble ,prussian blue is formed2 ,k,fe#b7;,,cn7#f ,,kcn1,fe7,,cn7#b1;,fe7,,cn7#c4 ,this blue salt is colloidal1 is soluble in pure water1 but insoluble and precipitated when other salts--for instance1 potassium or sodium chloride--are present even in small quantities1 and is therefore first obtained as a precipitate4#bi #bi ,skraup obtained this salt both from potassium ferrocyanide with ferric chloride and from ferricyanide with ferrous chloride1 which evidently shows that it contains iron in both the ferric and ferrous states4 ,with ferrous chloride it forms ,prussian blue1 and with ferric chloride ,turnbull's blue4 ,prussian blue was discovered in the beginning of the last century by a ,berlin manufacturer1 ,diesbach4 ,it was then prepared1 as it sometimes is also at present1 directly from potassium cyanide obtained by heating animal charcoal with potassium carbonate4 ,the mass thus obtained is dissolved in water1 alum is added to the solution in order to saturate the free alkali1 and then a solution of green vitriol is added which has previously been sufficiently exposed to the air to contain both ferric and ferrous salts4 ,if the solution of potassium cyanide be mixed with a solution containing both salts1 ,prussian blue will be formed1 because it is a compound of ferrous cyanide1 ,fe,c#b,n#b1 and ferric cyanide1 ,fe#b;,c#f,n#f4 ,a ferric salt with potassium ferrocyanide forms a blue colour1 because ferrous cyanide is obtained from the first salt and ferric cyanide from the second4 ,during the preparation of this compound alkali must be avoided1 as otherwise the precipitate would contain oxides of iron4 ,prussian blue has not a crystalline structure2 it forms a blue mass with a copper-red metallic lustre4 ,both acids and alkalis act on it4 ,the action is at first confined to the ferric salt it contains4 ,thus alkalis form ferric oxide and ferrocyanide in solution3 #b;,fe#b;,c#f,n#f1c;,fe,c#b,n#b #ab,,kho #b7;,fe#b,o#c1c;,h#b,o7 #c,k#d;,fe,c#f,n#f4 ,various ferrocyanides may thus be prepared4 ,prussian blue is soluble in an aqueous solution of oxalic acid1 forming blue ink4 ,in air1 when exposed to the action of light1 it fades2 but in the dark again absorbs oxygen and becomes blue1 which fact is also sometimes noticed in blue cloth4 ,an excess of potassium ferrocyanide renders ,prussian blue soluble in water1 although insoluble in various saline solutions--that is1 it converts it into the soluble variety4 ,strong hydrochloric acid also dissolves ,prussian blue4 ,potassium ferricyanide1 or red prussiate of potash1 ,k#c;,fe,c#f,n#f1 is called ',gmelin's salt1' because this savant obtained it by the action of chlorine on a solution of the yellow prussiate3 ,k#d;,fe,c#f,n#f ,cl ,k#c;,fe,c#f,n#f ,k,cl4 ,the reaction is due to the ferrous salt being changed by the action of the chlorine into a ferric salt4 ,it separates from solutions in anhydrous1 well-formed prisms of a red colour1 but the solution has an olive colour2 #ajj parts of water1 at #aj1 dissolve #cg parts of the salt1 and at #ajj1 #gh parts4#cj ,the red prussiate gives a blue precipitate with ferrous salts1 called ,turnbull's blue1 very much like ,prussian blue 7and the soluble variety71 because it also contains ferrous cyanide and ferric cyanide1 although in another proportion1 being formed according to the equation3 #c;,fe,cl#b #b,k#c;,fe,c#f,n#f #f,k,cl ,fe#c;,fe#b;,c#ab,n#ab1 or #c;,fe,c#b,n#b1;,fe#b;,c#f,n#f2 in ,prussian blue we have ,fe#g;,cy#ah1 and here ,fe#e;,cy#ab4 ,a ferric salt ought to form ferric cyanide ,fe#b;,c#f,n#f1 with red prussiate1 but ferric cyanide is soluble1 and therefore no precipitate is obtained1 and the liquid only becomes brown4#ca #cj ,an excess of chlorine must not be employed in preparing this compound1 otherwise the reaction goes further4 ,it is easy to find out when the action of the chlorine on potassium ferrocyanide must cease2 it is only necessary to take a sample of the liquid and add a solution of a ferric salt to it4 ,if a precipitate of ,prussian blue is formed1 more chlorine must be added1 as there is still some undecomposed ferrocyanide1 for the ferricyanide does not give a precipitate with ferric salts4 ,potassium ferricyanide1 like the ferrocyanide1 easily exchanges its potassium for hydrogen and various metals by double decomposition4 ,with the salts of tin1 silver1 and mercury it forms yellow precipitates1 and with those of uranium1 nickel1 cobalt1 copper1 and bismuth brown precipitates4 ,the lead salt under the action of sulphuretted hydrogen forms lead sulphide and a hydrogen salt or acid1 ,h#c;,fe,c#f,n#f1 corresponding with potassium ferricyanide1 which is soluble1 crystallises in red needles1 and resembles hydroferrocyanic acid1 ,h#d;,fe,c#f,n#f4 ,under the action of reducing agents--for instance1 sulphuretted hydrogen1 copper--potassium ferricyanide is changed into ferrocyanide1 especially in the presence of alkalis1 and thus forms a rather energetic oxidising agent--capable1 for instance1 of changing manganous oxide into dioxide1 bleaching tissues1 c4 #ca ,it is important to mention a series of readily crystallisable salts formed by the action of nitric acid on potassium and other ferrocyanides and ferricyanides4 ,these salt contain the elements of nitric oxide1 and are therefore called nitro-7nitroso7 ferricyanides 7nitroprussides74 ,generally a crystalline sodium salt is obtained1 ,na#b;,fe,c#e,n#f,o1#b;,h#b,o4 ,in its composition this salt differs from the red sodium salt1 ,na#c;,fe,c#f,n#f1 by the fact that in it one molecule of sodium cyanide1 ,na,c,n1 is replaced by nitric oxide1 ,,no4 ,in order to prepare it1 potassium ferrocyanide in powder is mixed with five-sevenths of its weight of nitric acid diluted with an equal volume of water4 ,the mixture is at first left at the ordinary temperature1 and then heated on a water-bath4 ,here ferricyanide is first of all formed 7as shown by the liquid giving a precipitate with ferrous chloride71 which then disappears 7no precipitate with ferrous chloride71 and forms a green precipitate4 ,the liquid1 when cooled1 deposits crystals of nitre4 ,the liquid is then strained off and mixed with sodium carbonate1 boiled1 filtered1 and evaporated2 sodium nitrate and the salt described are deposited in crystals4 ,it separates in prisms of a red colour4 ,alkalis and salts of the alkaline earths do not give precipitates3 they are soluble1 but the salts of iron1 zinc1 copper1 and silver form precipitates where sodium is exchanged with these metals4 ,it is remarkable that the sulphides of the alkali metals give with this salt an intense bright purple coloration4 ,this series of compounds was discovered by ,gmelin and studied by ,playfair and others 7#ahdi74 ,this series to a certain extent resembles the nitro-sulphide series described by ,roussin4 ,here the primary compound consists of black crystals1 which are obtained as follows3--,solutions of potassium hydrosulphide and nitrate are mixed1 and the mixture is agitated whilst ferric chloride is added1 then boiled and filtered2 on cooling1 black crystals are deposited1 having the composition ,fe#f,s#c7,,no7#aj1;,h#b,o 7,rosenberg71 or1 according to ,demel1 ,fe,n,o#b1,,nh#b,s4 ,they have a slightly metallic lustre1 and are soluble in water1 alcohol1 and ether4 ,they absorb the latter as easily as calcium chloride absorbs water4 ,in the presence of alkalis these crystals remain unchanged1 but with acids they evolve nitric oxides4 ,there are several compounds which are capable of interchanging1 and correspond with ,roussin's salt4 ,here we enter into the series of the nitrogen compounds which have been as yet but little investigated1 and will most probably in time form most instructive material for studying the nature of that element4 ,these series of compounds are as unlike the usual saline compounds of inorganic chemistry as are organic hydrocarbons4 ,there is no necessity to describe these series in detail1 because their connection with other compounds is not yet clear1 and they have not yet any application4 ,if chlorine and sodium are representatives of independent groups of elements1 the same may also be said of iron4 ,its nearest analogues show1 besides a similarity in character1 a likeness as regards physical properties and a proximity in atomic weight4 ,iron occupies a medium position amongst its nearest analogues1 both with respect to properties and faculty of forming saline oxides1 and also as regards atomic weight4 ,on the one hand1 cobalt1 #eh1 and nickel1 #ei1 approach iron1 #ef2 they are metals of a more basic character1 they do not form stable acids or higher degrees of oxidation1 and are a transition to copper1 #fc1 and zinc1 #fe4 ,on the other hand1 manganese1 #ee1 and chromium1 #eb1 are the nearest to iron2 they form both basic and acid oxides1 and are a transition to the metals possessing acid properties4 ,in addition to having atomic weights approximately alike1 chromium1 manganese1 iron1 cobalt1 nickel1 and copper have also nearly the same specific gravity1 so that the atomic volumes and the molecules of their analogous compounds are also near to one another 7see table at the beginning of this volume74 ,besides this1 the likeness between the above-mentioned elements is also seen from the following3 ,they form suboxides1 ,,ro1 fairly energetic bases1 isomorphous with magnesia--for instance1 the salt ,,rso#d1g;,h#b,o1 akin to ,mg,s,o#d1g;,h#b,o1 and ,fe,s,o#d1g;,h#b,o1 or to sulphates containing less water2 with alkali sulphates all form double salts crystallising with #f;,h#b,o2 all are capable of forming ammonium salts1 c4 ,the lower oxides1 in the cases of nickel and cobalt1 are tolerably stable1 are not easily oxidised 7the nickel compound with more difficulty than cobalt1 a transition to copper72 with manganese1 and especially with chromium1 they are more easily oxidised than with iron and pass into higher oxides4 ,they also form oxides of the form ,r#b,o#c1 and with nickel1 cobalt1 and manganese this oxide is very unstable1 and is more easily reduced than ferric oxide2 but1 in the case of chromium1 it is very stable1 and forms the ordinary kind of salts4 ,it is isomorphous with ferric oxide1 forms alums1 is a feeble base1 c4 ,chromium1 manganese1 and iron are oxidised by alkali and oxidising agents1 forming salts like ,na#b,,so#d2 but cobalt and nickel are difficult to oxidise2 their acids are not known with any certainty1 and are1 in all probability1 still less stable than the ferrates4 ,cr1 ,mn and ,fe form compounds ,r#b;,cl#f which are like ,fe#b;,cl#f in many respects2 in ,co this faculty is weaker and in ,ni it has almost disappeared4 ,the cyanogen compounds1 especially of manganese and cobalt1 are very near akin to the corresponding ferrocyanides4 ,the oxides of nickel and cobalt are more easily reduced to metal than those of iron1 but those of manganese and chromium are not reduced so easily as iron1 and the metals themselves are not easily obtained in a pure state2 they are capable of forming varieties resembling cast iron4 ,the metals ,cr1 ,mn1 ,fe1 ,co1 and ,ni have a grey iron colour and are very difficult to melt1 but nickel and cobalt can be melted in the reverberatory furnace and are more fusible than iron1 whilst chromium is more difficult to melt than platinum 7,deville74 ,these metals decompose water1 but with greater difficulty as the atomic weight rises1 forming a transition to copper1 which does not decompose water4 ,all the compounds of these metals have various colours1 which are sometimes very bright1 especially in the higher stages of oxidation4 ,these metals of the iron group are often met with together in nature4 ,manganese nearly everywhere accompanies iron1 and iron is always an ingredient in the ores of manganese4 ,chromium is found principally as chrome ironstone--that is1 a peculiar kind of magnetic oxide in which ,fe#b,o#c is replaced by ,cr#b,o#c4 ,nickel and cobalt are as inseparable companions as iron and manganese4 ,the similarity between them even extends to such remote properties as magnetic qualities4 ,in this series of metals we find those which are the most magnetic3 iron1 cobalt1 and nickel4 ,there is even a magnetic oxide among the chromium compounds1 such being unknown in the other series4 ,nickel easily becomes passive in strong nitric acid4 ,it absorbs hydrogen in just the same way as iron4 ,in short1 in the series ,cr1 ,mn1 ,fe1 ,co1 and ,ni1 there are many points in common although there are many differences1 as will be seen still more clearly on becoming acquainted with cobalt and nickel4 ,in nature cobalt is principally found in combination with arsenic and sulphur4 ,cobalt arsenide1 or cobalt speiss1 ,co,as#b1 is found in brilliant crystals of the regular system1 principally in ,saxony4 ,cobalt glance1 ,co,as#b;,co,s#b1 resembles it very much1 and also belongs to the regular system2 it is found in ,sweden1 ,norway1 and the ,caucasus4 ,kupfernickel is a nickel ore in combination with arsenic1 but of a different composition from cobalt arsenide1 having the formula ,ni,as2 it is found in ,bohemia and ,saxony4 ,it has a copper-red colour and is rarely crystalline2 it is so called because the miners of ,saxony first mistook it for an ore of copper 7,kupfer71 but were unable to extract copper from it4 ,nickel glance1 ,ni,s#b1,ni,as#b1 corresponding with cobalt glance1 is also known4 ,nickel accompanies the ores of cobalt and cobalt those of nickel1 so that both metals are found together4 ,the ores of cobalt are worked in the ,caucasus in the ,government of ,elizavetopolsk4 ,nickel ores containing aqueous hydrated nickel silicate are found in the ,ural 7,revdansk74 ,large quantities of a similar ore are exported into ,europe from ,new ,caledonia4 ,both ores contain about #ab per cent4 ,ni4 ,garnierite1 7,,ro7#e7,si,o#b7da-a_/b;,h#b,o1 where ,r ,ni and ,mg1 predominates in the ,new ,caledonian ore4 ,large deposits of nickel have been discovered in ,canada1 where the ore 7as nickelous pyrites7 is free from arsenic4 ,cobalt is principally worked up into cobalt compounds1 but nickel is generally reduced to the metallic state1 in which it is now often used for alloys--for instance1 for coinage in many ,european ,states1 and for plating other metals1 because it does not oxidise4 ,cobalt arsenide and cobalt glance are principally used for the preparation of cobalt compounds2 they are first sorted by discarding the rocky matter1 and then roasted4 ,during this process most of the sulphur and arsenic disappears2 the arsenious anhydride volatilises with the sulphurous anhydride and the metal also oxidises4#cb ,it is a simple matter to obtain nickel and cobalt from their oxides4 ,in order to obtain the latter1 solutions of their salts are treated with sodium carbonate and the precipitated carbonates are heated2 the suboxides are thus obtained1 and these latter are reduced in a stream of hydrogen1 or even by heating with ammonium chloride4 ,they easily oxidise when in the state of powder4 ,when the chlorides of nickel and cobalt are heated in a stream of hydrogen1 the metal is deposited in brilliant scales4 ,nickel is always much more easily and quickly reduced than cobalt4 ,nickel melts more easily than cobalt1 and this even furnishes a means of testing the heating powers of a reverberatory furnace4 ,cobalt fuses at a temperature only a little lower than that at which iron does4 ,in general1 cobalt is nearer to iron than nickel1 nickel being nearer to copper4#cb bis ,both nickel and cobalt have magnetic properties like iron1 but ,co is less magnetic than ,fe1 and ,ni still less so4 ,the specific gravity of nickel reduced by hydrogen is #ia and that of cobalt #hi4 ,fused cobalt has a specific gravity of #he1 the density of ordinary nickel being almost the same4 ,nickel has a greyish silvery-white colour2 it is brilliant and very ductile1 so that the finest wire may be easily drawn from it4 ,this wire has a resistance to tension equal to iron wire4 ,the beautiful colour of nickel1 and the high polish which it is capable of receiving and retaining1 as it does not oxidise1 render it a useful metal for many purposes1 and in many ways it resembles silver4#cb tri ,it is now very common to cover other metals with a layer of nickel 7nickel plating74 ,this is done by a process of electro-plating1 using a solution of a nickel salt4 ,the colour of cobalt is dark and redder2 it is also ductile1 and has a greater tensile resistance than iron4 ,dilute acids act very slowly on nickel and cobalt2 nitric acid may be considered as the best solvent for them4 ,the solutions in every case contain salts corresponding with the ferrous salts--that is1 the salts ,co,x#b1 ,ni,x#b1 correspond with the suboxides of these metals4 ,these salts in their types are similar to the magnesium salts4 ,the salts of nickel when crystallising with water have a green colour1 and form bright green solutions1 but in the anhydrous state they most frequently have a yellow colour4 ,the salts of cobalt are generally rose-coloured1 and generally blue when in the anhydrous state4 ,their aqueous solutions are rose-coloured4 ,cobaltous chloride is easily soluble in alcohol1 and forms a solution of an intense blue colour4#cc #cb ,the residue from the roasting of cobalt ores is called zafflor1 and is often met with in commerce4 ,from this the purer compounds of cobalt may be prepared4 ,the ores of nickel are also first roasted1 and the oxides dissolved in acid1 nickelous salts being then obtained4 ,the further treatment of cobalt and nickel ores is facilitated if the arsenic can be almost entirely removed1 which may be effected by roasting the ore a second time with a small addition of nitre and sodium carbonate2 the nitre combines with the arsenic1 forming an arsenious salt1 which may be extracted with water4 ,the remaining mass is dissolved in hydrochloric acid1 mixed with a small quantity of nitric acid4 ,copper1 iron1 manganese1 nickel1 cobalt1 c41 pass into solution4 ,by passing hydrogen sulphide through the solution1 copper1 bismuth1 lead1 and arsenic are deposited as metallic sulphides2 but iron1 cobalt1 nickel1 and manganese remain in solution4 ,if an alkaline solution of bleaching powder be then added to the remaining solution1 the whole of the manganese will first be deposited in the form of dioxide1 then the cobalt as hydrated cobaltic oxide1 and finally the nickel also4 ,it is1 however1 impossible to rely on this method for effecting a complete separation1 the more so since the higher oxides of the three above-mentioned metals have all a black colour2 but1 after a few trials1 it will be easy to find how much bleaching powder is required to precipitate the manganese1 and the amount which will precipitate all the cobalt4 ,the manganese may also be separated from cobalt by precipitation from a mixture of the solutions of both metals 7in the form of the 'ous' salts7 with ammonium sulphide1 and then treating the precipitate with acetic acid or dilute hydrochloric acid1 in which manganese sulphide is easily soluble and cobalt sulphide almost insoluble4 ,further particulars relating to the separation of cobalt from nickel may be found in treatises on analytical chemistry4 ,in practice it is usual to rely on the rough method of separation founded on the fact that nickel is more easily reduced and more difficult to oxidise than cobalt4 ,the ,new ,caledonian ore is smelted with ,ca,s,o#d and ,ca,c,o#c on coke1 and a metallic regulus is obtained containing all the ,ni1 ,fe1 and ,s4 ,this is roasted with ,si,o#b1 which converts all the iron into slag1 whilst the ,ni remains combined with the ,s2 this residue on further roasting gives ,ni,o1 which is reduced by the carbon to metallic ,ni4 ,the ,canadian ore 7a pyrites containing #aa p4c4 ,ni7 is frequently treated in ,america 7after a preliminary dressing7 by smelting it with ,na#b,,so#d and charcoal2 the resultant fusible ,na#b,s then dissolves the ,cu,s and ,fe,s#b1 while the ,ni,s is obtained in a bottom layer 7,bartlett and ,thomson's process7 from which ,ni is obtained in the manner described above4 ,for manufacturing purposes somewhat impure cobalt compounds are frequently used1 which are converted into smalt4 ,this is glass containing a certain amount of cobalt oxide2 the glass acquires a bright blue colour from this addition1 so that when powdered it may be used as a blue pigment2 it is also unaltered at high temperatures1 so that it used to take the place now occupied by ,prussian blue1 ultramarine1 c4 ,at present smalt is almost exclusively used for colouring glass and china4 ,to prepare smalt1 ordinary impure cobalt ore 7zaffre7 is fused in a crucible with quartz and potassium carbonate4 ,a fused mass of cobalt glass is thus formed1 containing silica1 cobalt oxide1 and potassium oxide1 and a metallic mass remains at the bottom of the crucible1 containing almost all the other metals1 arsenic1 nickel1 copper1 silver1 c4 ,this metallic mass is called speiss1 and is used as nickel ore for the extraction of nickel4 ,smalt usually contains #gj p4c4 of silica1 #bj p4c4 of potash and soda1 and about #e to #f p4c4 of cobaltous oxide2 the remainder consisting of other metallic oxides4 #cb bis ,all we know respecting the relations of ,co and ,ni to ,fe and ,cu confirms the fact that ,co is more closely related to ,fe and ,ni to ,cu2 and as the atomic weight of ,fe #ef and of ,cu #fc1 then according to the principles of the periodic system it would be expected that the atomic weight of ,co would be about #ei-fj1 whilst that of ,ni should be greater than that of ,co but less than that of ,cu1 i4e4 about #eje-fje4 ,however1 as yet the majority of the determinations of the atomic weights of ,co and ,ni give a different result and show that a lower atomic weight is obtained for ,ni than for ,co4 ,thus ,k4 ,winkler 7#ahid7 obtained 7employing metals deposited electrolytically and determining the amount of iodine which combined with them7 ,ni #ehgb and ,co #eicg 7if ,h #a and ,i #abfec74 ,in my opinion this should not be regarded as proving that the principles of the periodic system cannot be applied in this instance1 nor as a reason for altering the position of these elements in the system 7i4e4 by placing ,ni after ,fe1 and ,co next to ,cu71 because in the first place the figures given by different chemists 7for instance1 ,zimmermann1 ,krss1 and others7 are somewhat divergent1 and in the second place the majority of the latest modes of determining the atomic weights of ,co and ,ni aim at finding what weights of these metals react with known weights of other elements without taking into account the faculty they have of absorbing hydrogen2 since this faculty is more developed in ,ni than in ,co the hydrogen 7occluded in ,ni7 should lower the atomic weight of ,ni more than that of ,co4 ,on the whole1 the question of the atomic weights of ,co and ,ni cannot yet be considered as decided1 notwithstanding the numerous researches which have been made2 still there can be no doubt that the atomic weights of these two metals are very nearly equal1 and greater than that of ,fe1 but less than that of ,cu4 ,this question is of great interest1 not only for completing our knowledge of these metals1 but also for perfecting our knowledge of the periodic system of the elements4 #cb tri ,for instance1 the alkalis may be fused in nickel vessels as well as in silver1 because they have no action upon either metal4 ,nickel1 like silver1 is not acted upon by dilute acids4 ,only nitric acid dissolves both metals well4 ,nickel is harder1 and fuses at a higher temperature than silver4 ,for castings1 a small quantity of magnesium 7#jjja part by weight7 is added to nickel to render it more homogeneous 7just as aluminium is added to steel74 ,nickel forms many valuable alloys4 ,steel containing #c p4c4 ,ni is particularly valuable1 its limit of elasticity is higher and its hardness is greater2 it is used for armour plate and other large pieces4 ,the alloys of nickel1 especially with copper and zinc 7melchior1 see later71 aluminium and silver1 although used in certain cases1 are now replaced by nickel-plated or nickel-deposited goods 7deposited by electricity from a solution of the ammonium salts74 #cc ,the change of colour is dependent in all probability on the combination with water1 or according to others on polymeric transformation4 ,it enables a solution of cobalt chloride to be used as sympathetic ink4 ,if something be written with cobalt chloride on white paper1 it will be invisible on account of the feeble colour of the solution1 and when dry nothing can be distinguished4 ,if1 however1 the paper be heated before the fire1 the rose-coloured salt will be changed into a less hydrous blue salt1 and the writing will become quite visible1 but fade away when cool4 ,the change of colour which takes place in solutions of ,co,cl#b under the influence not only of solution in water or alcohol1 but also of a change of temperature1 is a characteristic of all the halogen salts of cobalt4 ,crystalline iodide of cobalt1 ,co,i#bf;,h#b,o1 gives a dark red solution between -#bb and #bj2 above #bj the solution turns brown and passes from olive to green1 from #ce to #cbj the solution remains green4 ,according to tard the change of colour is due to the fact that at first the solution contains the hydrate ,co,i#b;,h#b,o1 and that above #ce it contains ,co,i#bd;,h#b,o4 ,these hydrates can be crystallised from the solutions2 the former at ordinary temperature and the latter on heating the solution4 ,the intermediate olive colour of the solutions corresponds to the incipient decomposition of the hexahydrated salt and its passage into ,co,i#bd;,h#b,o4 ,a solution of the hexahydrated chloride of cobalt1 ,co,cl#bf;,h#b,o1 is rose-coloured between -#bb and #be2 but the colour changes starting from #be1 and passes through all the tints between red and blue right up to #ej2 a true blue solution is only obtained at #ee and remains up to #cjj4 ,this true blue solution contains another hydrate1 ,co,cl#bb;,h#b,o4 ,the dependence between the solubility of the iodide and chloride of cobalt and the temperature is expressed by two almost straight lines corresponding to the hexa- and di-hydrates2 the passage of the one into the other hydrate being expressed by a curve4 ,the same character of phenomena is seen also in the variation of the vapour tension of solutions of chloride of cobalt with the temperature4 ,we have repeatedly seen that aqueous solutions 7for instance1 ,chapter ,,xxii41 ,note #bc for ,fe#b;,cl#f7 deposit different crystallo-hydrates at different temperatures1 and that the amount of water in the hydrate decreases as the temperature t rises1 so that it is not surprising that ,co,cl#bb;,h#b,o 7or according to ,potilitzin ,co,cl#b;,h#b,o7 should separate out above #ee and ,co,cl#bf;,h#b,o at #be and below4 ,nor is it exceptional that the colour of a salt varies according as it contains different amounts of ,h#b,o4 ,but in this instance it is characteristic that the change of colour takes place in solution in the presence of an excess of water4 ,this apparently shows that the actual solution may contain either ,co,cl#bf;,h#b,o or ,co,cl#bb;,h#b,o4 ,and as we know that a solution may contain both metaphosphoric ,,pho#c and orthophosphoric acid ,h#c,,po#d ,,hpo#c ,h#b,o1 as well as certain other anhydrides1 the question of the state of substances in solutions becomes still more complicated4 ,nickel sulphate crystallises from neutral solutions at a temperature of from #ae to #bj in rhombic crystals containing #g;,h#b,o4 ,its form approaches very closely to that of the salts of zinc and magnesium4 ,the planes of a vertical prism for magnesium salts are inclined at an angle of #ij #cj1 for zinc salts at an angle of #ia #g1 and for nickel salts at an angle of #ia #aj4 ,such is also the form of the zinc and magnesium selenates and chromates4 ,cobalt sulphate containing #g molecules of water is deposited in crystals of the monoclinic system1 like the corresponding salts of iron and manganese4 ,the angle of a vertical prism for the iron salt #hb #bj1 for cobalt #hb #bb1 and the inclination of the horizontal pinacoid to the vertical prism for the iron salt #ii #b1 and for the cobalt salt #ii #cf4 ,all the isomorphous mixtures of the salts of magnesium1 iron1 cobalt1 nickel and manganese have the same form if they contain #g mol4 ,h#b,o and iron or cobalt predominate1 whilst if there is a preponderance of magnesium1 zinc1 or nickel1 the crystals have a rhombic form like magnesium sulphate4 ,hence these sulphates are dimorphous1 but for some the one form is more stable and for others the other4 ,brooke1 ,moss1 ,mitscherlich1 ,rammelsberg1 and ,marignac have explained these relations4 ,brooke and ,mitscherlich also supposed that ,ni,s,o#d1g;,h#b,o is not only capable of assuming these forms1 but also that of the tetragonal system1 because it is deposited in this form from acid1 and especially from slightly-heated solutions 7#cj to #dj74 ,but ,marignac demonstrated that the tetragonal crystals do not contain #g1 but #f1 molecules of water1 ,ni,s,o#d1f;,h#b,o4 ,he also observed that a solution evaporated at #ej to #gj deposits monoclinic crystals1 but of a different form from ferrous sulphate1 ,fe,s,o#d1g;,h#b,o--namely1 the angle of the prism is #ga #eb1 that of the pinacoid #ie #f4 ,this salt appears to be the same with #f molecules of water as the tetragonal4 ,marignac also obtained magnesium and zinc salts with #f molecules of water by evaporating their solutions at a higher temperature1 and these salts were found to be isomorphous with the monoclinic nickel salt4 ,in addition to this it must be observed that the rhombic crystals of nickel sulphate with #g;,h#b,o become turbid under the influence of heat and light1 lose water1 and change into the tetragonal salt4 ,the monoclinic crystals in time also become turbid1 and change their structure1 so that the tetragonal form of this salt is the most stable4 ,let us also add that nickel sulphate in all its shapes forms very beautiful emerald green crystals1 which1 when heated to #bcj1 assume a dirty greenish-yellow hue and then contain one molecule of water4 ,klobb 7#ahia7 and ,langlot and ,lenoir obtained anhydrous ,co,s,o#d and ,ni,s,o#d by igniting the hydrated salt with 7,,nh#d7b,,so#d until the ammonium salt had completely volatilised and decomposed4 ,we may add that when equivalent aqueous solutions of ,ni,x#b 7green7 and ,co,x#b 7red7 are mixed together they give an almost colourless 7grey7 solution1 in which the green and red colour of the component parts disappears owing to the combination of the complementary colours4 ,a double salt ,ni,k,f#c is obtained by heating ,ni,cl#b with ,,kfhf in a platinum crucible2 ,k,co,f#c is formed in a similar manner4 ,the nickel salt occurs in fine green plates1 easily soluble in water but scarcely soluble in ethyl and methyl alcohol4 ,they decompose into green oxide of nickel and potassium fluoride when heated in a current of air4 ,the analogous salt of cobalt crystallises in crimson flakes4 ,if instead of potassium fluoride1 ,co,cl#b or ,ni,cl#b be fused with ammonium fluoride1 they also form double salts with the latter4 ,this gives the possibility of obtaining anhydrous fluorides ,ni,f#b and ,co,f#b4 ,crystalline fluoride of nickel1 obtained by heating the amorphous powder formed by decomposing the double ammonium salt in a stream of hydrofluoric acid1 occurs in beautiful green prisms1 sp4 gr4 #dfc1 which are insoluble in water1 alcohol1 and ether2 sulphuric1 hydrochloric1 and nitric acids also have no action upon them1 even when heated2 ,ni,f#b is decomposed by steam1 with the formation of black oxide1 which retains the crystalline structure of the salt4 ,fluoride of cobalt1 obtained as a rose-coloured powder by decomposing the double ammonium salt with the aid of heat in a stream of hydrofluoric acid1 fuses into a ruby-coloured mass which bears distinct signs of a crystalline structure2 sp4 gr4 #ddc4 ,the molten salt only volatilises at about #adjj1 which forms a clear distinction between ,co,f#b and the volatile ,ni,f#b4 ,hydrochloric1 sulphuric1 and nitric acids act upon ,co,f#b even in the cold1 although slowly1 while when heated the reaction proceeds rapidly 7,poulenc1 #ahib74 ,if a solution of potassium hydroxide be added to a solution of a cobalt salt1 a blue precipitate of the basic salt will be formed4 ,if a solution of a cobalt salt be heated almost to the boiling-point1 and the solution be then mixed with a boiling solution of an alkali hydroxide1 a pink precipitate of cobaltous hydroxide1 ,co,h#b,o#b1 will be formed4 ,if air be not completely excluded during the precipitation by boiling1 the precipitate will also contain brown cobaltic hydroxide formed by the further oxidation of the cobaltous oxide4#cd ,under similar circumstances nickel salts form a green precipitate of nickelous hydroxide1 the formation of which is not hindered by the presence of ammonium salts1 but in that case only requires more alkali to completely separate the nickel4 ,the nickelous oxide obtained by heating the hydroxide1 or from the carbonate or nitrate1 is a grey powder1 easily soluble in acids and easily reduced1 but the same substance may be obtained in the crystalline form as an ordinary product from the ores2 it crystallises in regular octahedra1 with a metallic lustre1 and is of a grey colour4 ,in this state the nickelous oxide almost resists the action of acids4#cd bis #cd ,hydrated suboxide of cobalt 7de ,schulten1 #ahhi7 is obtained in the following manner4 ,a solution of #aj grams of ,co,cl#bf;,h#b,o in #fj c4c4 of water is heated in a flask with #bej grams of caustic potash and a stream of coal gas is passed through the solution4 ,when heated the hydrate of the suboxide of cobalt which separates out1 dissolves in the caustic potash and forms a dark blue solution4 ,this solution is allowed to stand for #bd hours in an atmosphere of coal gas 7in order to prevent oxidation74 ,the crystalline mass which separates out has a composition ,co7,,oh7#b1 and to the naked eye appears as a violet powder1 which is seen to be crystalline under the microscope4 ,the specific gravity of this hydrate is #ceig at #ae4 ,it does not undergo change in the air2 warm acetic acid dissolves it1 but it is insoluble in warm and cold solutions of ammonia and sal-ammoniac4 #cd bis ,the following reaction may be added to those of the cobaltous and nickelous salts3 potassium cyanide forms a precipitate with cobalt salts which is soluble in an excess of the reagent and forms a green solution4 ,on heating this and adding a certain quantity of acid1 a double cobalt cyanide is formed which corresponds with potassium ferricyanide4 ,its formation is accompanied with the evolution of hydrogen1 and is founded upon the property which cobalt has of oxidising in an alkaline solution1 the development of which has been observed in such a considerable measure in the cobaltamine salts4 ,the process which goes on here may be expressed by the following equation2 ,co,c#b,n#b #d,,kcn first forms ,co,k#d;,c#f,n#f1 which salt with water1 ,h#b,o1 forms potassium hydroxide1 ,,kho1 hydrogen1 ,h1 and the salt1 ,k#c;,co,c#f,n#f4 ,here naturally the presence of the acid is indispensable in consequence of its being required to combine with the alkali4 ,from aqueous solutions this salt crystallises in transparent1 hexagonal prisms of a yellow colour1 easily soluble in water4 ,the reactions of double decomposition1 and even the formation of the corresponding acid1 are here completely the same as in the case of the ferricyanide4 ,if a nickelous salt be treated in precisely the same manner as that just described for a salt of cobalt1 decomposition will occur4 ,it is interesting to note the relation of the cobaltous and nickelous hydroxides to ammonia2 aqueous ammonia dissolves the precipitate of cobaltous and nickelous hydroxide4 ,the blue ammoniacal solution of nickel resembles the same solution of cupric oxide1 but has a somewhat reddish tint4 ,it is characterised by the fact that it dissolves silk in the same way as the ammoniacal cupric oxide dissolves cellulose4 ,ammonia likewise dissolves the precipitate of cobaltous hydroxide1 forming a brownish liquid1 which becomes darker in air and finally assumes a bright red hue1 absorbing oxygen4 ,the admixture of ammonium chloride prevents the precipitation of cobalt salts by ammonia2 when the ammonia is added1 a brown solution is obtained from which1 as in the case of the preceding solution1 potassium hydroxide does not separate the cobaltous oxide4 ,peculiar compounds are produced in this solution2 they are comparatively stable1 containing ammonia and an excess of oxygen2 they bear the name cobaltoamine and cobaltiamine salts4 ,they have been principally investigated by ,genth1 ,frmy1 ,jrgenson and others4 ,genth found that when a cobalt salt1 mixed with an excess of ammonium chloride1 is treated with ammonia and exposed to the air1 after a certain lapse of time1 on adding hydrochloric acid and boiling1 a red powder is precipitated and the remaining solution contains an orange salt4 ,the study of these compounds led to the discovery of a whole series of similar salts1 some of which correspond with particular higher degrees of oxidation of cobalt1 which are described later4#ce ,nickel does not possess this property of absorbing the oxygen of the air when in an ammoniacal solution4 ,in order to understand this distinction1 and in general the relation of nickel1 it is important to observe that cobalt more easily forms a higher degree of oxidation--namely1 sesquioxide of cobalt1 cobaltic oxide1 ,co#b,o#c--than nickel1 especially in the presence of hypochlorous acid4 ,if a solution of a cobalt salt be mixed with barium carbonate and an excess of hypochlorous acid be added1 or chlorine gas be passed through it1 then at the ordinary temperature on shaking1 the whole of the cobalt will be separated in the form of black cobaltic oxide3 #b;,co,s,o#d ,cl,h,o #b;,ba,c,o#c ,co#b,o#c #b;,ba,s,o#d ,h,cl #b;,,co#b4 ,under these circumstances nickelous oxide does not immediately form black sesquioxide1 but after a considerable space of time it also separates in the form of sesquioxide1 ,ni#b,o#c1 but always later than cobalt4 ,this is due to the relative difficulty of further oxidation of the nickelous oxide4 ,it is1 however1 possible to oxidise it2 if1 for instance1 the hydroxide ,ni,h#b,o#b be shaken in water and chlorine gas be passed through it1 then nickel chloride will be formed1 which is soluble in water1 and insoluble nickelic oxide in the form of a black precipitate3 #c,ni,h#b,o#b ,cl#b ,ni,cl#b ,ni#b,o#c1c;,h#b,o4 ,nickelic oxide may also be obtained by adding sodium hypochlorite mixed with alkali to a solution of a nickel salt4 ,nickelic and cobaltic hydrates are black4 ,nickelic oxide evolves oxygen with all acids1 and in consequence of this it is not separated as a precipitate in the presence of acids2 thus it evolves chlorine with hydrochloric acid1 exactly like manganese dioxide4 ,when nickelic oxide is dissolved in aqueous ammonia it liberates nitrogen1 and an ammoniacal solution of nickelous oxide is formed4 ,when heated1 nickelic oxide loses oxygen1 forming nickelous oxide4 ,cobaltic oxide1 ,co#b,o#c1 exhibits more stability than nickelic oxide1 and shows feeble basic properties2 thus it is dissolved in acetic acid without the evolution of oxygen4#ce bis ,but ordinary acids1 especially on heating1 evolve oxygen1 forming a solution of a cobaltous salt4 ,the presence of a cobaltic salt in a solution of a cobaltous salt may be detected by the brown colour of the solution and the black precipitate formed by the addition of alkali1 and also from the fact that such solutions evolve chlorine when heated with hydrochloric acid4 ,cobaltic oxide may not only be prepared by the above-mentioned methods1 but also by heating cobalt nitrate1 after which a steel-coloured mass remains which retains traces of nitric acid1 but when heated further to incandescence evolves oxygen1 leaving a compound of cobaltic and cobaltous oxides1 similar to magnetic ironstone4 ,cobalt 7but not nickel7 undoubtedly forms besides ,co#b,o#c a dioxide ,co,o#b4 ,this is obtained#cf when the cobaltous oxide is oxidised by iodine or peroxide of barium4#cg #ce ,the cobalt salts may be divided into at least the following classes1 which repeat themselves for ,cr1 ,ir1 ,rh 7we shall not stop to consider the latter1 particularly as they closely resemble the cobalt salts73-- 7a7 ,ammonium cobalt salts1 which are simply direct compounds of the cobaltous salts ,co,x#b with ammonia1 similar to various other compounds of the salts of silver1 copper1 and even calcium and magnesium1 with ammonia4 ,they are easily crystallised from an ammoniacal solution1 and have a pink colour4 ,thus1 for instance1 when cobaltous chloride in solution is mixed with sufficient ammonia to redissolve the precipitate first formed1 octahedral crystals are deposited which have a composition ,co,cl#b1;,h#b,o1#f,,nh#c4 ,these salts are nothing else but combinations with ammonia of crystallisation--if it may be so termed--likening them in this way to combinations with water of crystallisation4 ,this similarity is evident both from their composition and from their capability of giving off ammonia at various temperatures4 ,the most important point to observe is that all these salts contain #f molecules of ammonia to #a atom of cobalt1 and this ammonia is held in fairly stable connection4 ,water decomposes these salts4 7,nickel behaves similarly without forming other compounds corresponding to the true cobaltic47 7b7 ,the solutions of the above-mentioned salts are rendered turbid by the action of the air2 they absorb oxygen and become covered with a crust of oxycobaltamine salts4 ,the latter are sparingly soluble in aqueous ammonia1 have a brown colour1 and are characterised by the fact that with warm water they evolve oxygen1 forming salts of the following category3 ,the nitrate may be taken as an example of this kind of salt2 its composition is ,co,n#b,o#g1e,,nh#c1;,h#b,o4 ,it differs from cobaltous nitrate1 ,co7,,no#c7b1 in containing an extra atom of oxygen--that is1 it corresponds with cobalt dioxide1 ,co,o#b1 in the same way that the first salts correspond with cobaltous oxide2 they contain #e1 and not #f1 molecules of ammonia1 as if ,,nh#c had been replaced by ,o1 but we shall afterwards meet compounds containing either #e,,nh#c or #f,,nh#c to each atom of cobalt4 7c7 ,the luteocobaltic salts are thus called because they have a yellow 7luteus7 colour4 ,they are obtained from the salts of the first kind by submitting them in dilute solution to the action of the air2 in this case salts of the second kind are not formed1 because they are decomposed by an excess of water1 with the evolution of oxygen and the formation of luteocobaltic salts4 ,by the action of ammonia the salts of the fifth kind 7roseocobaltic7 are also converted into luteocobaltic salts4 ,these last-named salts generally crystallise readily1 and have a yellow colour2 they are comparatively much more stable than the preceding ones1 and even for a certain time resist the action of boiling water4 ,boiling aqueous potash liberates ammonia and precipitates hydrated cobaltic oxide1 ,co#b,o#c1c;,h#b,o1 from them4 ,this shows that the luteocobaltic salts correspond with cobaltic oxide1 ,co#b,o#c1 and those of the second kind with the dioxide4 ,when a solution of luteocobaltic sulphate1 ,co#b7,,so#d7c1ab,,nh#c1d;,h#b,o1 is treated with baryta1 barium sulphate is precipitated1 and the solution contains luteocobaltic hydroxide1 ,co7,,oh7#c1f,,nh#c1 which is soluble in water1 is powerfully alkaline1 absorbs the oxygen of the air1 and when heated is decomposed with the evolution of ammonia4 ,this compound therefore corresponds to a solution of cobaltic hydroxide in ammonia4 ,the luteocobaltic salts contain #b atoms of cobalt and #ab molecules of ammonia--that is1 #f,,nh#c to each atom of cobalt1 like the salts of the first kind4 ,the ,co,x#b salts have a metallic taste1 whilst those of luteocobalt and others have a purely saline taste1 like the salts of the alkali metals4 ,in the luteo-salts all the ,x's react 7are ionised1 as some chemists say7 as in ordinary salts--for instance1 all the ,cl#b is precipitated by a solution of ,ag,n,o#c2 all the 7,,so#d7c gives a precipitate with ,ba,x#b1 c4 ,the double salt formed with ,pt,cl#d is composed in the same manner as the potassium salt1 ,k#b,pt,cl#d #b,k,cl ,pt,cl#d1 that is1 contains 7,co,cl#c1f,,nh#c7b1c,pt,cl#d1 or the amount of chlorine in the ,pt,cl#d is double that in the alkaline salt4 ,in the rosepentamine 7e71 and rosetetramine 7f71 salts1 also all the ,x's react or are ionised1 but in the 7g7 and 7h7 salts only a portion of the ,x's react1 and they are equal to the 7e7 and 7f7 salts minus water2 this means that although the water dissolves them it is not combined with them1 as ,,pho#c differs from ,,ph#c,o#c2 phenomena of this class correspond exactly to what has been already 7,chapter ,,xxi41 ,note #g7 mentioned respecting the green and violet salts of oxide of chromium4 7d7 ,the fuscocobaltic salts4 ,an ammoniacal solution of cobalt salts acquires a brown colour in the air1 due to the formation of these salts4 ,they are also produced by the decomposition of salts of the second kind2 they crystallise badly1 and are separated from their solutions by addition of alcohol or an excess of ammonia4 ,when boiled they give up the ammonia and cobaltic oxide which they contain4 ,hydrochloric and nitric acids give a yellow precipitate with these salts1 which turns red when boiled1 forming salts of the next category4 ,the following is an example of the composition of two of the fuscocobaltic salts1 ,co#b,o7,,so#d7b1h,,nh#c1d;,h#b,o and ,co#b,o,cl#d1h,,nh#c1c;,h#b,o4 ,it is evident that the fuscocobaltic salts are ammoniacal compounds of basic cobaltic salts4 ,the normal cobaltic sulphate ought to have the composition ,co#b7,,so#d7c ,co#b,o#c1c,,so#c2 the simplest basic salts will be ,co#b,o7,,so#d7b ,co#b,o#c7b,,so#c1 and ,co#b,o#b7,,so#d7 ,co#b,o#c1,,so#c4 ,the fuscocobaltic salts correspond with the first type of basic salts4 ,they are changed 7in concentrated solutions7 into oxycobaltamine salts by absorption of one atom of oxygen1 ,co#b,o#b7,,so#d7b4 ,the whole process of oxidation will be as follows3 first of all ,co#b,x#d1 a cobaltous salt1 is in the solution 7,x a univalent haloid1 #b molecules of the salt being taken71 then ,co#b,,ox#d1 the basic cobaltic salt 7#dth series71 then ,co#b,o#b,x#d1 the salt of the dioxide 7#bnd series74 ,the series of basic salts with an acid1 #b;,,hx1 forms water and a normal salt1 ,co#b,x#f 7in #c1 #e1 #f series74 ,these salts are combined with various amounts of water and ammonia4 ,under many conditions the salts of fuscocobalt are easily transformed into salts of the next series4 ,the salts of the series that has just been described contain #d molecules of ammonia to #a atom of cobalt4 7e7 ,the roseocobaltic 7or rosepentamine71 ,co,x#b;,h#b,o1#e,,nh#c1 salts1 like the luteocobaltic1 correspond with the normal cobaltic salts1 but contain less ammonia1 and an extra molecule of water4 ,thus the sulphate is obtained from cobaltous sulphate dissolved in ammonia and left exposed to the air until transformed into a brown solution of the fuscocobaltic salt2 when this is treated with sulphuric acid a crystalline powder of the roseocobaltic salt1 ,co#b7,,so#d7c1aj,,nh#c1e;,h#b,o1 separates4 ,the formation of this salt is easily understood3 cobaltous sulphate in the presence of ammonia absorbs oxygen1 and the solution of the fuscocobaltic salt will therefore contain1 like cobaltous sulphate1 one part of sulphuric acid to every part of cobalt1 so that the whole process of formation may be expressed by the equation3 #aj,,nh#c #b;,co,s,o#d ,h#b,,so#d #d;,h#b,o ,o ,co#b7,,so#d7c1aj,,nh#c1e;,h#b,o4 ,this salt forms tetragonal crystals of a red colour1 slightly soluble in cold1 but readily soluble in warm water4 ,when the sulphate is treated with baryta1 roseocobaltic hydroxide is formed in the solution1 which absorbs the carbonic anhydride of the air4 ,it is obtained from the next series by the action of alkalis4 7f7 ,the rosetetramine cobaltic salts ,co,cl#b1b;,h#b,o1#d,,nh#c were obtained by ,jrgenson1 and belong to the type of the luteo-salts1 only with the substitution of #b,,nh#c for ,h#b,o4 ,like the luteo- and roseo-salts they give double salts with ,pt,cl#d1 similar to the alkaline double salts1 for instance 7,co#b;,h#b,o1#d,,nh#c7b7,,so#d7b;,cl#b, pt,cl#d4 ,they are darker in colour than the preceding1 but also crystallise well4 ,they are formed by dissolving ,co,c,o#c in sulphuric acid 7of a given strength71 and after ,,nh#c and carbonate of ammonium have been added1 air is passed through the solution 7for oxidation7 until the latter turns red4 ,it is then evaporated with lumps of carbonate of ammonium1 filtered from the precipitate and crystallised4 ,a salt of the composition ,co#b7;,,co#c7b7,,so#d717b;,h#b,o1#d,,nh #c7b is thus obtained1 from which the other salts may be easily prepared4 7g7 ,the purpureocobaltic salts1 ,co,x#c1e,,nh#c1 are also products of the direct oxidation of ammoniacal solutions of cobalt salts4 ,they are easily obtained by heating the roseocobaltic and luteo-salts with strong acids4 ,they are to all effects the same as the roseocobaltic salts1 only anhydrous4 ,thus1 for instance1 the purpureocobaltic chloride1 ,co#b;,cl#f1aj,,nh#c1 or ,co,cl#c1e,,nh#c1 is obtained by boiling the oxycobaltamine salts with ammonia4 ,there is the same distinction between these salts and the preceding ones as between the various compounds of cobaltous chloride with water4 ,in the purpureocobaltic only ,x#b out of the ,x#c react 7are ionised74 ,to the rosetetramine salts 7f7 there correspond the purpureotetramine salts1 ,co,x#c;,h#b,o1#d,,nh#c4 ,the corresponding chromium purpureopentamine salt1 ,cr,cl#c1e,,nh#c is obtained with particular ease 7,christensen1 #ahic74 ,dry anhydrous chromium chloride is treated with anhydrous liquid ammonia in a freezing mixture composed of liquid ,,co#b and chlorine1 and after some time the mixture is taken out of the freezing mixture1 so that the excess of ,,nh#c boils away2 the violet crystals then immediately acquire the red colour of the salt1 ,cr,cl#c1e,,nh#c1 which is formed4 ,the product is washed with water 7to extract the luteo-salt1 ,cr,cl#c1f,,nh#c71 which does not dissolve the salt1 and it is then recrystallised from a hot solution of hydrochloric acid4 7h7 ,the praseocobaltic salts1 ,co,x#c1d,,nh#c1 are green1 and form1 with respect to the rosetetramine salts 7f71 the products of ultimate dehydration 7for example1 like metaphosphoric acid with respect to orthophosphoric acid1 but in dissolving in water they give neither rosetetramine nor tetramine salts4 7,in my opinion one should expect salts with a still smaller amount of ,,nh#c1 of the blue colour proper to the low hydrated compounds of cobalt2 the green colour of the prazeo-salts already forms a step towards the blue47 ,jrgenson obtained salts for ethylene-diamine1 ,n#b;,h#d;,c#b;,h#d which replaces #b,,nh#c4 ,after being kept a long time in aqueous solution they give rosetetramine salts1 just as metaphosphoric acid gives orthophosphoric acid1 while the rosetetramine salts are converted into prazeo-salts by ,ag#b,o and ,na,h,o4 ,here only one ,x is ionised out of the ,x#c4 ,there are also basic salts of the same type2 but the best known is the chromium salt called the rhodozochromic salt1 ,cr#b7,,oh7#c;,cl#c1f,,nh#c1b;,h#b,o1 which is formed by the prolonged action of water upon the corresponding roseo-salt4 ,the cobaltamine compounds differ essentially but little from the ammoniacal compounds of other metals4 ,the only difference is that here the cobaltic oxide is obtained from the cobaltous oxide in the presence of ammonia4 ,in any case it is a simpler question than that of the double cyanides4 ,those forces in virtue of which such a considerable number of ammonia molecules are united with a molecule of a cobalt compound1 appertain naturally to the series of those slightly investigated forces which exist even in the highest degrees of combination of the majority of elements4 ,they are the same forces which lead to the formation of compounds containing water of crystallisation1 double salts1 isomorphous mixtures and complex acids 7,chapter ,,xxi41 ,note #h bis74 ,the simplest conception1 according to my opinion1 of cobalt compounds 7much more so than by assuming special complex radicles1 with ,schiff1 ,weltzien1 ,claus1 and others71 may be formed by comparing them with other ammoniacal products4 ,ammonia1 like water1 combines in various proportions with a multitude of molecules4 ,silver chloride and calcium chloride1 just like cobalt chloride1 absorb ammonia1 forming compounds which are sometimes slightly stable1 and easily dissociated1 sometimes more stable1 in exactly the same way as water combines with certain substances1 forming fairly stable compounds called hydroxides or hydrates1 or less stable compounds which are called compounds with water of crystallisation4 ,naturally the difference in the properties in both cases depends on the properties of those elements which enter into the composition of the given substance1 and on those kinds of affinity towards which chemists have not as yet turned their attention4 ,if boron fluoride1 silicon fluoride1 c41 combine with hydrofluoric acid1 if platinic chloride1 and even cadmium chloride1 combine with hydrochloric acid1 these compounds may be regarded as double salts1 because acids are salts of hydrogen4 ,but evidently water and ammonia have the same saline faculty1 more especially as they1 like haloid acids1 contain hydrogen1 and are both capable of further combination--for instance1 ammonia with hydrochloric acid4 ,hence it is simpler to compare complex ammoniacal with double salts1 hydrates1 and similar compounds1 but the ammonio-metallic salts present a most complete qualitative and quantitative resemblance to the hydrated salts of metals4 ,the composition of the latter is ,,mxnm,h#b,o1 where ,m metal1 ,x the haloid1 simple or complex1 and n and m the quantities of the haloid and so-called water of crystallisation respectively4 ,the composition of the ammoniacal salts of metals is ,,mxnm,,nh#c4 ,the water of crystallisation is held by the salt with more or less stability1 and some salts even do not retain it at all2 some part with water easily when exposed to the air1 others when heated1 and then with difficulty4 ,in the case of some metals all the salts combine with water1 whilst with others only a few1 and the water so combined may then be easily disengaged4 ,all this applies equally well to the ammoniacal salts1 and therefore the combination of ammonia may be termed the ammonia of crystallisation4 ,just as the water which is combined with a salt is held by it with different degrees of force1 so it is with ammonia4 ,in combining with #b,,nh#c1,pt,cl#b evolves #ca1jjj cals42 while ,ca,cl#b only evolves #ad1jjj cals42 and the former compound parts with its ,,nh#c 7together with ,h,cl in this case7 with more difficulty1 only above #bjj1 while the latter disengages ammonia at #ahj4 ,zn,cl#b1b,,nh#c in forming ,zn,cl#b1d,,nh#c evolves only #aa1jjj cals41 and splits up again into its components at #hj4 ,the amount of combined ammonia is as variable as the amount of water of crystallisation--for instance1 ,sn,i#dh,,nh#c1 ,cr,cl#bh,,nh#c1 ,cr,cl#cf,,nh#c1 ,cr,cl#ce,,nh#c1,pt,cl#b1d,,nh#c1 c4 are known4 ,very often ,,nh#c is replaceable by ,,oh#b and conversely4 ,a colourless1 anhydrous cupric salt--for instance1 cupric sulphate--when combined with water forms blue and green salts1 and violet when combined with ammonia4 ,if steam be passed through anhydrous copper sulphate the salt absorbs water and becomes heated2 if ammonia be substituted for the water the heating becomes much more intense1 and the salt breaks up into a fine violet powder4 ,with water ,cu,s,o#d1e;,h#b,o is formed1 and with ammonia ,cu,s,o#d1e,,nh#c1 the number of water and ammonia molecules retained by the salt being the same in each case1 and as a proof of this1 and that it is not an isolated coincidence1 the remarkable fact must be borne in mind that water and ammonia consecutively1 molecule for molecule1 are capable of supplanting each other1 and forming the compounds ,cu,s,o#d1e;,h#b,o1 ,cu,s,o#d1d;,h#b,o1,,nh#c2 ,cu,s,o#d1c;,h#b,o1#b,,nh#c2 ,cu,s,o#d1b;,h#b,o1#c,,nh#c2 ,cu,s,o#d1;,h#b,o1#d,,nh#c1 and ,cu,s,o#d1e,,nh#c4 ,the last of these compounds was obtained by ,henry ,rose1 and my experiments have shown that more ammonia than this cannot be retained4 ,by adding to a strong solution of cupric sulphate sufficient ammonia to dissolve the whole of the oxide precipitated1 and then adding alcohol1 ,berzelius obtained the compound ,cu,s,o#d1;,h#b,o1#d,,nh#c1 c4 ,the law of substitution also assists in rendering these phenomena clearer1 because a compound of ammonia with water forms ammonium hydroxide1 ,,nh#d;,,ho1 and therefore these molecules combining with one another may also interchange1 as being of equal value4 ,in general1 those salts form stable ammoniacal compounds which are capable of forming stable compounds with water of crystallisation2 and as ammonia is capable of combining with acids1 and as some of the salts formed by slightly energetic bases in their properties more closely resemble acids 7that is1 salts of hydrogen7 than those salts containing more energetic bases1 we might expect to find more stable and more easily-formed ammonio-metallic salts with metals and their oxides having weaker basic properties than with those which form energetic bases4 ,this explains why the salts of potassium1 barium1 c41 do not form ammonio-metallic salts1 whilst the salts of silver1 copper1 zinc1 c41 easily form them1 and the salts ,,rx#c still more easily and with greater stability4 ,this consideration also accounts for the great stability of the ammoniacal compounds of cupric oxide compared with those of silver oxide1 since the former is displaced by the latter4 ,it also enables us to see clearly the distinction which exists in the stability of the cobaltamine salts containing salts corresponding with cobaltous oxide1 and those corresponding with higher oxides of cobalt1 for the latter are weaker bases than cobaltous oxides4 ,the nature of the forces and quality of the phenomena occurring during the formation of the most stable substances1 and of such compounds as crystallisable compounds1 are one and the same1 although perhaps exhibited in a different degree4 ,this1 in my opinion1 may be best confirmed by examining the compounds of carbon1 because for this element the nature of the forces acting during the formation of its compounds is well known4 ,let us take as an example two unstable compounds of carbon4 ,acetic acid1 ,c#b;,h#d,o#b 7specific gravity #ajf71 with water forms the hydrate1 ,c#b;,h#d,o#b1;,h#b,o1 denser 7#ajg7 than either of the components1 but unstable and easily decomposed1 generally simply referred to as a solution4 ,such also is the crystalline compound of oxalic acid1 ,c#b;,h#b,o#d1 with water1 ,c#b;,h#b,o#d1b;,h#b,o4 ,their formation might be predicted as starting from the hydrocarbon ,c#b;,h#f1 in which1 as in any other1 the hydrogen may be exchanged for chlorine1 the water residue 7hydroxyl71 c4 ,the first substitution product with hydroxyl1 ,c#b;,h#e7;,,ho71 is stable2 it can be distilled without alteration1 resists a temperature higher than #ajj1 and then does not give off water4 ,this is ordinary alcohol4 ,the second1 ,c#b;,h#d7;,,ho7#b1 can also be distilled without change1 but can be decomposed into water and ,c#b;,h#d,o 7ethylene oxide or aldehyde72 it boils at about #aig1 whilst the first hydrate boils at #gh1 a difference of about #ajj4 ,the compound ,c#b;,h#c7;,,ho7#c will be the third product of such substitution2 it ought to boil at about #cjj1 but does not resist this temperature--it decomposes into ,h#b,o and ,c#b;,h#d,o#b1 where only one hydroxyl group remains1 and the other atom of oxygen is left in the same condition as in ethylene oxide1 ,c#b;,h#d,o4 ,there is a proof of this4 ,glycol1 ,c#b;,h#d7;,,ho7#b1 boils at #aig1 and forms water and ethylene oxide1 which boils at #ac 7aldehyde1 its isomeride1 boils at #ba72 therefore the product disengaged by the splitting up of the hydrate boils at #ahd lower than the hydrate ,c#b;,h#d7;,,ho7#b4 ,thus the hydrate ,c#b;,h#c7;,,ho7#c1 which ought to boil at about #cjj1 splits up in exactly the same way into water and the product ,c#b;,h#d,o#b1 which boils at #aag--that is1 nearly #ahc lower than the hydrate1 ,c#b;,h#c7;,,ho7#c4 ,but this hydrate splits up before distillation4 ,the above-mentioned hydrate of acetic acid is such a decomposable hydrate--that is to say1 what is called a solution4 ,still less stability may be expected from the following hydrates4 ,c#b;,h#b7;,,ho7#d also splits up into water and a hydrate 7it contains two hydroxyl groups7 called glycolic acid1 ,c#b;,h#b,o7,,ho7#b ,c#b;,h#d,o#c4 ,the next product of substitution will be ,c#b;,h7,,ho7#e2 it splits up into water1 ,h#b,o1 and glyoxylic acid1 ,c#b;,h#d,o#d 7three hydroxyl groups74 ,the last hydrate which ought to be obtained from ,c#b;,h#f1 and ought to contain ,c#b7;,,ho7#f1 is the crystalline compound of oxalic acid1 ,c#b;,h#b,o#d 7two hydroxyl groups71 and water1 #b;,h#b,o1 which has been already mentioned4 ,the hydrate ,c#b7;,,ho7#f ,c#b;,h#b,o#d1b;,h#b,o1 ought1 according to the foregoing reasoning1 to boil at about #fjj 7because the hydrate1 ,c#b;,h#d7;,,ho7#b1 boils at about #bjj1 and the substitution of #d hydroxyl groups for #d atoms of hydrogen will raise the boiling-point #djj74 ,it does not resist this temperature1 but at a much lower point splits up into water1 #b;,h#b,o1 and the hydrate ,c#b,o#b7;,,ho7#b1 which is also capable of yielding water4 ,without going into further discussion of this subject1 it may be observed that the formation of the hydrates1 or compounds with water of crystallisation1 of acetic and oxalic acids has thus received an accurate explanation1 illustrating the point we desired to prove in affirming that compounds with water of crystallisation are held together by the same forces as those which act in the formation of other complex substances1 and that the easy displaceability of the water of crystallisation is only a peculiarity of a local character1 and not a radical point of distinction4 ,all the above-mentioned hydrates1 ,c#b,x#f1 or products of their destruction1 are actually obtained by the oxidation of the first hydrate1 ,c#b;,h#c7;,,ho71 or common alcohol1 by nitric acid 7,sokoloff and others74 ,hence the forces which induce salts to combine with n,h#b,o or with ,,nh#c are undoubtedly of the same order as the forces which govern the formation of ordinary 'atomic' and saline compounds4 7,a great impediment in the study of the former was caused by the conviction which reigned in the sixties and seventies1 that 'atomic' were essentially different from 'molecular' compounds like crystallohydrates1 in which it was assumed that there was a combination of entire molecules1 as though without the participation of the atomic forces47 ,if the bond between chlorine and different metals is not equally strong1 so also the bond uniting n,h#b,o and n,,nh#c is exceeding variable2 there is nothing very surprising in this4 ,and in the fact that the combination of different amounts of ,,nh#c and ,h#b,o alters the capacity of the haloids ,x of the salts ,,rx#b for reaction 7for instance1 in the luteo-salts all the ,x#c1 while in the purpureo1 only #b out of the #c1 and in the prazeo-salts only #a of the #c ,x's reacts71 we should see in the first place a phenomenon similar to what we met with in ,cr#b;,cl#f 7,chapter ,,xxi41 ,note #g bis71 for in both instances the essence of the difference lies in the removal of water2 a molecule ,r,cl#c1f;,h#b,o or ,r,cl#c1f,,nh#c contains the halogen in a perfectly mobile 7ionised7 state1 while in the molecule ,r,cl#c1e;,h#b,o or ,r,cl#c1e,,nh#c a portion of the halogen has almost lost its faculty for reacting with ,ag,n,o#c1 just as metalepsical chlorine has lost this faculty which is fully developed in the chloranhydride4 ,until the reason of this difference be clear1 we cannot expect that ordinary points of view and generalisation can give a clear answer4 ,however1 we may assume that here the explanation lies in the nature and kind of motion of the atoms in the molecules1 although as yet it is not clear how4 ,nevertheless1 ,i think it well to call attention again 7,chapter ,i47 to the fact that the combination of water1 and hence1 also1 of any other element1 leads to most diverse consequences2 the water in the gelatinous hydrate of alumina or in the decahydrated ,glauber salt is very mobile1 and easily reacts like water in a free state2 but the same water combined with oxide of calcium1 or ,c#b;,h#d 7for instance1 in ,c#b;,h#f,o and in ,c#d;,h#aj,o71 or with ,p#b,o#e1 has become quite different1 and no longer acts like water in a free state4 ,we see the same phenomenon in many other cases--for example1 the chlorine in chlorates no longer gives a precipitate of chloride of silver with ,ag,n,o#c4 ,thus1 although the instance which is found in the difference between the roseo- and purpureo-salts deserves to be fully studied on account of its simplicity1 still it is far from being exceptional1 and we cannot expect it to be thoroughly explained unless a mass of similar instances1 which are exceedingly common among chemical compounds1 be conjointly explained4 7,among the researches which add to our knowledge respecting the complex ammoniacal compounds1 ,i think it indispensable to call the reader's attention to ,prof4 ,kournakoff's dissertation ',on complex metallic bases1' #ahic47 ,kournakoff 7#ahid7 showed that the solubility of the luteo-salt1 ,co,cl#c1f,,nh#c1 at #j #dcj 7per #ajj of water71 at #bj #gg1 that in passing into the roseo-salt1 ,co,cl#c;,h#b,o#e,,nh#c1 the solubility rises considerably1 and at #j #afd1 and at #bj about #bg1 whilst the passage into the purpureo-salt1 ,co,cl#c1e,,nh#c1 is accompanied by a great fall in the solubility1 namely1 at #j #jbc1 and at #bj about #je4 ,and as crystallohydrates with a smaller amount of water are usually more soluble than the higher crystallohydrates 7,le ,chatelier71 whilst here we find that the solubility falls 7in the purpureo-salt7 with a loss of water1 that water which is contained in the roseo-salt cannot be compared with the water of crystallisation4 ,kournakoff1 therefore1 connects the fall in solubility 7in the passage of the roseo- into the purpureo-salts7 with the accompanying loss in the reactive capacity of the chlorine4 ,in conclusion1 it may be observed that the elements of the eighth group--that is1 the analogues of iron and platinum--according to my opinion1 will yield most fruitful results when studied as to combinations with whole molecules1 as already shown by the examples of complex ammoniacal1 cyanogen1 nitro-1 and other compounds1 which are easily formed in this eighth group1 and are remarkable for their stability4 ,this faculty of the elements of the eighth group for forming the complex compounds alluded to1 is in all probability connected with the position which the eighth group occupies with regard to the others4 ,following the seventh1 which forms the type ,,rx#g1 it might be expected to contain the most complex type1 ,,rx#h4 ,this is met with in ,os,o#d4 ,the other elements of the eighth group1 however1 only form the lower types ,,rx#b1 ,,rx#c1 ,,rx#d 444 and these accordingly should be expected to aggregate themselves into the higher types1 which is accomplished in the formation of the above-mentioned complex compounds4 #ce bis ,marshall 7#ahia7 obtained cobaltic sulphate1 ,co#b7,,so#d7c1ah;,h#b,o1 by the action of an electric current upon a strong solution of ,co,s,o#d4 #cf ,the action of an alkaline hypochlorite or hypobromite upon a boiling solution of cobaltous salts1 according to ,schroederer 7#ahhi71 produces oxides1 whose composition varies between ,co#c,o#e 7,rose's compound7 and ,co#b,o#c1 and also between ,co#e,o#h and ,co#ab,o#ai4 ,if caustic potash and then bromine be added to the liquid1 only ,co#b,o#c is formed4 ,the action of alkaline hypochlorites or hypo-bromites1 or of iodine1 upon cobaltic salts1 gives a highly-coloured precipitate which has a different colour to the hydrate of the oxide ,co#b7,,oh7#f4 ,according to ,carnot the precipitate produced by the hypochlorites has a composition ,co#aj,o#af1 whilst that given by iodine in the presence of an alkali contains a larger amount of oxygen4 ,fortmann 7#ahia7 reinvestigated the composition of the higher oxygen oxide obtained by iodine in the presence of alkali1 and found that the greenish precipitate 7which disengages oxygen when heated to #ajj7 corresponds to the formula ,co,o#b4 ,the reaction must be expressed by the equation3 ,co,x#b ,i#b #d,,kho ,co,o#b #b,,kx #b,,ki #b;,h#b,o4 #cg ,prior to ,fortmann1 ,rousseau 7#ahhi7 endeavoured to solve the question as to whether ,co,o#b was able to combine with bases4 ,he succeeded in obtaining a barium compound corresponding to this oxide4 ,fifteen grams of ,ba,cl#b or ,ba,br#b are triturated with #e-f grams of oxide of barium1 and the mixture heated to redness in a closed platinum crucible2 #a gram of oxide of cobalt is then gradually added to the fused mass4 ,each addition of oxide is accompanied by a violent disengagement of oxygen4 ,after a short time1 however1 the mass fuses quietly1 and a salt settles at the bottom of the crucible1 which1 when freed from the residue1 appears as black hexagonal1 very brilliant crystals4 ,in dissolving in water this substance evolves chlorine2 its composition corresponds to the formula #b7;,co,o#b7;,ba,o4 ,if the original mass be heated for a long time 7#dj hours71 the amount of dioxide in the resultant mass decreases4 ,the author obtained a neutral salt having the composition ,co,o#b;,ba,o 7this compound ,ba,o#b;,co,o7 by breaking up the mass as it agglomerates together1 and bringing the pieces into contact with the more heated surface of the crucible4 ,this salt is formed between the somewhat narrow limits of temperature #a1jjj-a1ajj2 above and below these limits compounds richer or poorer in ,co,o#b are formed4 ,the formation of ,co,o#b by the action of ,ba,o#b1 and the easy decomposition of ,co,o#b with the evolution of oxygen1 give reason for thinking that it belongs to the class of peroxides 7like ,cr#b,o#g1 ,ca,o#b1 c472 it is not yet known whether they give peroxide of hydrogen like the true peroxides4 ,the fact that it is obtained by means of iodine 7probably through ,,hio71 and its great resemblance to ,mn,o#b1 leads rather to the supposition that ,co,o#b is a very feeble saline oxide4 ,the form ,co,o#b is repeated in the cobaltic compounds 7,note #ce71 and the existence of ,co,o#b should have long ago been recognised upon this basis4 ,nickel alloys possess qualities which render them valuable for technical purposes1 the alloy of nickel with iron being particularly remarkable4 ,this alloy is met with in nature as meteoric iron4 ,the ,pallasoffsky mass of meteoric iron1 preserved in the ,st4 ,petersburg ,academy1 fell in ,siberia in the last century2 it weighs about #ae cwt4 and contains #hh p4c4 of iron and about #aj p4c4 of nickel1 with a small admixture of other metals4 ,in the arts ,german silver is most extensively used2 it is an alloy containing nickel1 copper1 and zinc in various proportions4 ,it generally consists of about #ej parts of copper1 #be parts of zinc1 and #be parts of nickel4 ,this alloy is characterised by its white colour resembling that of silver1 and1 like this latter metal1 it does not rust1 and therefore furnishes an excellent substitute for silver in the majority of cases where it is used4 ,alloys which contain silver in addition to nickel show the properties of silver to a still greater extent4 ,alloys of nickel are used for currency1 and if rich deposits of nickel are discovered a wide field of application lies before it1 not only in a pure state 7because it is a beautiful metal and does not rust7 but also for use in alloys4 ,steel vessels 7pressed or forged out of sheet steel7 covered with nickel have such practical merits that their manufacture1 which has not long commenced1 will most probably be rapidly developed1 whilst nickel steel1 which exceeds ordinary steel in its tenacity1 has already proved its excellent qualities for many purposes 7for instance1 for armour plate74 ,until #ahij no compound of cobalt or nickel was known of sufficient volatility to determine the molecular weights of the compounds of these metals2 but in #ahij ,mr4 ,l4 ,mond1 in conducting 7together with ,langer and ,quincke7 his researches on the action of nickel upon carbonic oxide 7,chapter ,,ix41 ,note #bd bis71 observed that nickel gradually volatilises in a stream of carbonic oxide2 this only takes place at low temperatures1 and is seen by the coloration of the flame of the carbonic oxide4 ,this observation led to the discovery of a remarkable volatile compound of nickel and carbonic oxide1 having as molecular composition ,ni7,,co7#d1ch as determined by the vapour density and depression of the freezing point4 ,cobalt and many other metals do not form volatile compounds under these conditions1 but iron gives a similar product 7,note #bf bis74 ,ni7,,co7#d is prepared by taking finely divided ,ni 7obtained by reducing ,ni,o by heating it in a stream of hydrogen1 or by igniting the oxalate ,ni,c#b,o#d7ci and passing 7at a temperature below #ej1 for even at #fj decomposition may take place and an explosion7 a stream of ,,co over it2 the latter carries over the vapour of the compound1 which condenses 7in a well-cooled receiver7 into a perfectly colourless extremely mobile liquid1 boiling without decomposition at #dc1 and crystallising in needles at -#be 7,mond and ,nasini1 #ahia74 ,liquid ,ni7,,co7#d has a sp4 gr4 #acef at #j1 is insoluble in water1 dissolves in alcohol and benzene1 and burns with a very smoky flame due to the liberation of ,ni4 ,the vapour when passed through a tube heated to #ahj and above deposits a brilliant coating of metal1 and disengages ,,co4 ,if the tube be strongly heated the decomposition is accompanied by an explosion4 ,if ,ni7,,co7#d as vapour be passed through a solution of ,cu,cl#b1 it reduces the latter to metal2 it has the same action upon an ammoniacal solution of ,ag,cl1 strong nitric acid oxidises ,ni7,,co7#d1 dilute solutions of acids have no action2 if the vapour be passed through strong sulphuric acid1 ,,co is liberated1 chlorine gives ,ni,cl and ,c,o,cl#b2 no simple reactions of double decomposition are yet known for ,ni7,,co7#d1 however1 so that its connection with other carbon compounds is not clear4 ,probably the formation of this compound could be applied for extracting nickel from its ores4#dj #ch ,this compound is known as nickel tetra-carbonyl4 ,it appears to me yet premature to judge of the structure of such an extraordinary compound as ,ni7,,co7#d4 ,it has long been known that potassium combines with ,,co forming ,kn7,,co7n 7,chapter ,,ix41 ,note #ca71 but this substance is apparently saline and non-volatile1 and has as little in common with ,ni7,,co7#d as ,na#b;,h has with ,sb,h#c4 ,however1 ,berthelot observed that when ,ni,c#d,o#d is kept in air1 it oxidises and gives a colourless compound1 ,ni#c;,c#b,o#c1aj;,h#b,o1 having apparently saline properties4 ,we may add that ,schtzenberger1 on reducing ,ni,cl#b by heating it in a current of hydrogen1 observed that a nickel compound partially volatilises with the ,h,cl and gives metallic nickel when heated again4 ,the platinum compound1 ,pt,cl#b7;,,co7#c 7,chapter ,,xxiii41 ,note #aa71 offers the greatest analogy to ,ni7,,co7#d4 ,this compound was obtained as a volatile substance by ,schtzenberger by moderately heating 7to #bce7 metallic platinum in a mixture of chlorine and carbonic oxide4 ,if we designate ,,co by ,y1 and an atom of chlorine by ,x1 then taking into account that1 according to the periodic system1 ,ni is an analogue of ,pt1 a certain degree of correspondence is seen in the composition ,ni,y#d and ,pt,x#b,y#b4 ,it would be interesting to compare the reactions of the two compounds4 #ci ,according to its empirical formula oxalate of nickel also contains nickel and carbonic oxide4 #dj ,the following are the thermo-chemical data 7according to ,thomsen1 and referred to gram weights expressed by the formula1 in large calories or thousand units of heat7 for the formation of corresponding compounds of ,mn1 ,fe1 ,co1 ,ni1 and ,cu 7 ,aq signifies that the reaction proceeds in an excess of water73 ,r ,mn ,fe ,co ,ni ,cu ,r ,cl#b ,aq #abh #ajj #ie #id #fc ,r ,br#b ,aq #ajf #gh #gc #gb #da ,r ,i#b ,aq #gf #dh #dc #da #cb ,r ,o ,h#b,o #ie #fh #fc #fa #ch ,r ,o#b ,,so#b n,h#b,o #aic #afi #afc #afc #acj ,r,cl#b ,aq #af #ah #ah #ai #aa ,these examples show that for analogous reactions the amount of heat evolved in passing from ,mn to ,fe1 ,co1 ,ni1 and ,cu varies in regular sequences as the atomic weight increases4 ,a similar difference is to be found in other groups and series1 and proves that thermo-chemical phenomena are subject to the periodic law4 ,,chapter ,,xxiii ,,the ,,platinum ,,metals ,the six metals3 ruthenium1 ,ru1 rhodium1 ,rh1 palladium1 ,pd1 osmium1 ,os1 iridium1 ,ir1 and platinum1 ,pt1 are met with associated together in nature4 ,platinum always predominates over the others1 and hence they are known as the platinum metals4 ,by their chemical character their position in the periodic system is in the eighth group1 corresponding with iron1 cobalt1 and nickel4 ,the natural transition from titanium and vanadium to copper and zinc by means of the elements of the iron group is demonstrated by all the properties of these elements1 and in exactly the same manner a transition from zirconium1 niobium1 and molybdenum to silver1 cadmium1 and indium1 through ruthenium1 rhodium1 and palladium1 is in perfect accordance with fact and with the magnitude of the atomic weights1 as also is the position of osmium1 iridium1 and platinum between tantalum and tungsten on the one side1 and gold and mercury on the other4 ,in all these three cases the elements of smaller atomic weight 7chromium1 molybdenum1 and tungsten7 are able1 in their higher grades of oxidation1 to give acid oxides having the properties of distinct but feebly energetic acids 7in the lower oxides they give bases71 whilst the elements of greater atomic weight 7zinc1 cadmium1 mercury71 even in their higher grades of oxidation1 only give bases1 although with feebly developed basic properties4 ,the platinum metals present the same intermediate properties such as we have already seen in iron and the elements of the eighth group4 ,in the platinum metals the intermediate properties of feebly acid and feebly basic metals are developed with great clearness1 so that there is not one sharply-defined acid anhydride among their oxides1 although there is a great diversity in the grades of oxidation from the type ,,ro#d to ,r#b,o4 ,the feebleness of the chemical forces observed in the platinum metals is connected with the ready decomposability of their compounds1 with the small atomic volume of the metals themselves1 and with their large atomic weight4 ,the oxides of platinum1 iridium1 and osmium can scarcely be termed either basic or acid2 they are capable of combinations of both kinds1 each of which is feeble4 ,they are all intermediate oxides4 ,the atomic weights of platinum1 iridium1 and osmium are nearly #aia to #aif1 and of palladium1 rhodium1 and ruthenium1 #ajd to #ajf4 ,thus1 strictly speaking1 we have here two series of metals1 which are1 moreover1 perfectly parallel to each other2 three members in the first series1 and three members in the second--namely1 platinum presents an analogy to palladium1 iridium to rhodium1 and osmium to ruthenium4 ,as a matter of fact1 however1 the whole group of the platinum metals is characterised by a number of common properties1 both physical and chemical1 and1 moreover1 there are several points of resemblance between the members of this group and those of the iron group 7,chapter ,,xxii47 ,the atomic volumes 7,table ,,iii41 column #ah7 of the elements of this group are nearly equal and very small4 ,the iron metals have atomic volumes of nearly #g1 whilst that of the metals allied to palladium is nearly #i1 and of those adjacent to platinum 7,pt1 ,ir1 ,os7 nearly #id4 ,this comparatively small atomic volume corresponds with the great infusibility and tenacity proper to all the iron and platinum metals1 and to their small chemical energy1 which stands out very clearly in the heavy platinum metals4 ,all the platinum metals are very easily reduced by ignition and by the action of various reducing agents1 in which process oxygen1 or a haloid group1 is disengaged from their compounds and the metal left behind4 ,this is a property of the platinum metals which determines many of their reactions1 and the circumstance of their always being found in nature in a native state4 ,in ,russia in the ,urals 7discovered in #ahai7 and in ,brazil 7#agce7 platinum is obtained from alluvial deposits1 but in #ahib ,professor ,inostrantseff discovered a vein deposit of platinum in serpentine near ,tagil in the ,urals4#a ,the facility with which they are reduced is so great that their chlorides are even decomposed by gaseous hydrogen1 especially when shaken up and heated under a certain pressure4 ,hence it will be readily understood that such metals as zinc1 iron1 c41 separate them from solutions with great ease1 which fact is taken advantage of in practice and in the chemical treatment of the platinum metals4#a bis #a ,wells and ,penfield 7#ahhh7 have described a mineral sperryllite found in the ,canadian gold-bearing quartz and consisting of platinum diarsenide1 ,pt,as#b4 ,it is a noticeable fact that this mineral clearly confirms the position of platinum in the same group as iron1 because it corresponds in crystalline form 7regular octahedron7 and chemical composition with iron pyrites1 ,fe,s#b4 #a bis ,some light is thrown upon the facility with which the platinum compounds decompose by ,thomsen's data1 showing that in an excess of water 7 ,aq7 the formation from platinum1 of such a double salt as ,pt,cl#b1b,k,cl1 is accompanied by a comparatively small evolution of heat 7see ,chapter ,,xxi41 ,note #dj71 for instance1 ,pt ,cl#b #b,k,cl ,aq only evolves about #cc1jjj calories 7hence the reaction1 ,pt ,cl#b ,aq1 will evidently disengage still less1 because ,pt,cl#b #b,k,cl evolves a certain amount of heat71 whilst on the other hand1 ,fe ,cl#b ,aq gives #ajj1jjj calories1 and even the reaction with copper 7for the formation of the double salt7 evolves #fc1jjj calories4 ,all the platinum metals1 like those of the iron group1 are grey1 with a comparatively feeble metallic lustre1 and are very infusible4 ,in this respect they stand in the same order as the metals of the iron series2 nickel is more fusible and whiter than cobalt and iron1 so also palladium is whiter and more fusible than rhodium and ruthenium1 and platinum is comparatively more fusible and whiter than iridium or osmium4 ,the saline compounds of these metals are red or yellow1 like those of the majority of the metals of the iron series1 and like the latter1 the different forms of oxidation present different colours4 ,moreover1 certain complex compounds of the platinum metals1 like certain complex compounds of the iron series1 either have particular characteristic tints or else are colourless4 ,the platinum metals are found in nature associated together in alluvial deposits in a few localities1 from which they are washed1 owing to their very considerable density1 which enables a stream of water to wash away the sand and clay with which they are mixed4 ,platinum deposits are chiefly known in the ,urals1 and also in ,brazil and a few other localities4 ,the platinum ore washed from these alluvial deposits presents the appearance of more or less coarse grains1 and sometimes1 as it were1 of semi-fused nuggets4#b #b ,the largest amount of platinum is extracted in the ,urals1 about five tons annually4 ,a certain amount of gold is extracted from the washed platinum by means of mercury1 which does not dissolve the platinum metals but dissolves the gold accompanying the platinum in its ores4 ,moreover1 the ores of platinum always contain metals of the iron series associated with them4 ,the washed and mechanically sorted ore in the majority of cases contains about #gj to #hj p4c4 of platinum1 about #e to #h p4c4 of iridium1 and a somewhat smaller quantity of osmium4 ,the other platinum metals--palladium1 rhodium1 and ruthenium--occur in smaller proportions than the three above named4 ,sometimes grains of almost pure osmium-iridium1 containing only a small quantity of other metals1 are found in platinum ores4 ,this osmium-iridium may be easily separated from the other platinum metals1 owing to its being nearly insoluble in aqua regia1 by which the latter are easily dissolved4 ,there are grains of platinum which are magnetic4 ,the grains of osmium-iridium are very hard and malleable1 and are therefore used for certain purposes1 for instance1 for the tips of gold pens4 ,all the platinum metals give compounds with the halogens1 and the highest haloid type of combination for all is ,,rx#d4 ,for the majority of the platinum metals this type is exceedingly unstable2 the lower compounds corresponding to the type ,,rx#b1 which are formed by the separation of ,x#b1 are more stable4 ,in the type ,,rx#b the platinum metals form more stable salts1 which offer no little resemblance to the kindred compounds of the iron series--for example1 to nickelous chloride1 ,ni,cl#b1 cobaltous chloride1 ,co,cl#b1 c4 ,this even expresses itself in a similarity of volume 7platinous chloride1 ,pt,cl#b1 volume1 #df2 nickelous chloride1 ,ni,cl#b #ej71 although in the type ,,rx#b the true iron metals give very stable compounds1 whilst the platinum metals frequently react after the manner of suboxides1 decomposing into the metal and higher types1 #b,,rx#b ,r ,,rx#d4 ,this probably depends on the facility with which ,,rx#b decomposes into ,r and ,x#b1 when ,x#b combines with the remaining portion of ,,rx#b4 ,as in the series iron1 cobalt1 nickel1 nickel gives ,ni,o and ,ni#b,o#c1 whilst cobalt and iron give higher and varied forms of oxidation1 so also among the platinum metals1 platinum and palladium only give the forms ,,rx#b and ,,rx#d1 whilst rhodium and iridium form another and intermediate type1 ,,rx#c1 also met with in cobalt1 corresponding with the oxide1 having the composition ,r#b,o#c1 besides which they form an acid oxide1 like ferric acid1 which is also known in the form of salts1 but is in every respect unstable4 ,osmium and ruthenium1 like manganese1 form still higher oxides1 and in this respect exhibit the greatest diversity4 ,they not only give ,,rx#b1 ,,rx#c1 ,,rx#d1 and ,,rx#f1 but also a still higher form of oxidation1 ,,ro#d1 which is not met with in any other series4 ,this form is exceedingly characteristic1 owing to the fact that the oxides1 ,os,o#d and ,ru,o#d1 are volatile and have feebly acid properties4 ,in this respect they most resemble permanganic anhydride1 which is also somewhat volatile4#c #c ,in characterising the platinum metals according to their relation to the iron metals1 it is very important to add two more very remarkable points4 ,the platinum metals are capable of forming a sort of unstable compound with hydrogen2 they absorb it and only part with it when somewhat strongly heated4 ,this faculty is especially developed in platinum and palladium1 and it is very characteristic that nickel1 which exactly corresponds with platinum and palladium in the periodic system1 should exhibit the same faculty for retaining a considerable quantity of hydrogen 7,graham's and ,raoult's experiments74 ,another characteristic property of the platinum metals consists in their easily giving 7like cobalt which forms the cobaltic salts7 stable and characteristic saline compounds with ammonia1 and like ,fe and ,co1 double salts with the cyanides of the alkali metals1 especially in their lower forms of combination4 ,all the above so clearly brings the elements of the iron series in close relation to the platinum metals1 that the eighth group acquires as natural a character as can be required1 with a certain originality or individuality for each element4 ,when dissolved in aqua regia 7,pt,cl#d is formed7 and liberated from the solution by sal-ammoniac 77,,nh#d7b,pt,cl#f is formed7 and reduced by ignition 7which may be done by ,zn and other reducing agents1 direct from a solution of ,pt,cl#d7 platinum#c bis forms a powdery mass1 known as spongy platinum or platinum black4 ,if this powder of platinum be heated and pressed1 or hammered in a cylinder1 the grains aggregate or forge together1 and form a continuous1 though of course not entirely homogeneous1 mass4 ,platinum was formerly1 and is even now1 worked up in this manner4 ,the platinum money formerly used in ,russia was made in this way4 ,sainte-,claire ,deville1 in the fifties1 for the first time melted platinum in considerable quantities by employing a special furnace made in the form of a small reverberatory furnace1 and composed of two pieces of lime1 on which the heat of the oxyhydrogen flame has no action4 ,into this furnace 7shown in fig4 #cd1 ,vol4 ,i4 p4 #age7--or1 more strictly speaking1 into the cavity made in the pieces of lime--the platinum is introduced1 and two orifices are made in the lime2 through one1 the upper1 or side orifice1 is introduced an oxyhydrogen gas burner1 in which either detonating gas or a mixture of oxygen and coal-gas is burnt1 whilst the other orifice serves for the escape of the products of combustion and certain impurities which are more volatile than the platinum1 and especially the oxidised compounds of osmium1 ruthenium1 and palladium1 which are comparatively easily volatilised by heat4 ,in this manner the platinum is converted into a continuous metallic form by means of fusion1 and this method is now used for melting considerable masses of platinum#d and its alloys with iridium4 #c bis ,platinum was first obtained in the last century from ,brazil1 where it was called silver 7platinus74 ,watson in #agej characterised platinum as a separate independent metal4 ,in #ahjc ,wollaston discovered palladium and rhodium in crude platinum1 and at about the same time ,tennant distinguished iridium and osmium in it4 ,professor ,claus1 of ,kazan1 in his researches on the platinum metals 7about #ahdj7 discovered ruthenium in them1 and to him are due many important discoveries with regard to these elements1 such as the indication of the remarkable analogy between the series ,pd--,rh--,ru and ,pt--,ir--,os4 ,the treatment of platinum ore is chiefly carried on for the extraction of the platinum itself and its alloys with iridium1 because these metals offer a greater resistance to the action of chemical reagents and high temperatures than any of the other malleable and ductile metals1 and therefore the wire so often used in the laboratory and for technical purposes is made from them1 as also are various vessels used for chemical purposes in the laboratory and in works4 ,thus sulphuric acid is distilled in platinum retorts1 and many substances are fused1 ignited1 and evaporated in the laboratory in platinum crucibles and on platinum foil4 ,gold and many other substances are dissolved in dishes made of iridium-platinum1 because the alloys of platinum and iridium are but slightly attacked when subjected to the action of aqua regia4 ,the comparatively high density 7about #bae71 hardness1 ductility1 and infusibility 7it does not melt at a furnace heat1 but only in the oxyhydrogen flame or electric furnace71 as well as the fact of its resisting the action of water1 air1 and other reagents1 renders an alloy of #ij parts of platinum and #aj parts of iridium 7,deville's platinum-iridium alloy7 a most valuable material for making standard weights and measures1 such as the metre1 kilogram1 and pound1 and therefore all the newest standards of most countries are made of this alloy4 #d ,this process has altered the technical treatment of platinum to a considerable extent4 ,it has in particular facilitated the manufacture of alloys of platinum with iridium and rhodium from the pure platinum ores1 since it is sufficient to fuse the ore in order for the greater amount of the osmium to burn off1 and for the mass to fuse into a homogeneous1 malleable alloy1 which can be directly made use of4 ,there is very little ruthenium in the ores of platinum4 ,if during fusion lead be added1 it dissolves the platinum 7and other platinum metals7 owing to its being able to form a very characteristic alloy containing ,pt,pb4 ,if an alloy of the two metals be left exposed to moist air1 the excess of lead is converted into carbonate 7white lead7 in the presence of the water and carbonic acid of the air1 whilst the above platinum alloy remains unchanged4 ,the white lead may be extracted by dilute acid1 and the alloy ,pt,pb remains unaltered4 ,the other platinum metals also give similar alloys with lead4 ,the fusibility of these alloys enables the platinum metals to be separated from the gangue of the ore1 and they may afterwards be separated from the lead by subjecting the alloy to oxidation in furnaces furnished with a bone ash bed1 because the lead is then oxidised and absorbed by the bone ash1 leaving the platinum metals untouched4 ,this method of treatment was proposed by ,h4 ,sainte-,claire ,deville in the sixties1 and is also used in the analysis of these metals 7see further on74 ,to obtain pure platinum1 the ore is treated with aqua regia in which only the osmium and iridium are insoluble4 ,the solution contains the platinum metals in the form ,r,cl#d1 and in the lower forms of chlorination1 ,r,cl#c and ,r,cl#b1 because some of these metals--for instance1 palladium and rhodium--form such unstable chlorides of the type ,,rx#d that they partially decompose even when diluted with water1 and pass into the stable lower type of combination2 in addition to which the chlorine is very easily disengaged if it comes in contact with substances on which it can act4 ,in this respect platinum resists the action of heat and reducing agents better than any of its companions--that is1 it passes with greater difficulty from ,pt,cl#d to the lower compound ,pt,cl#b4 ,on this is based the method of preparation of more or less pure platinum4 ,lime or sodium hydroxide is added to the solution in aqua regia until neutralised1 or only containing a very slight excess of alkali4 ,it is best to first evaporate and slightly ignite the solution1 in order to remove the excess of acid1 and by heating it to partially convert the higher chlorides of the palladium1 c41 into the lower4 ,the addition of alkalis completes the reduction1 because the chlorine held in the compounds ,,rx#d acts on the alkali like free chlorine1 converting it into a hypochlorite4 ,thus palladium chloride1 ,pd,cl#d1 for example1 is converted into palladious chloride1 ,pd,cl#b1 by this means1 according to the equation ,pd,cl#d #b,na,h,o ,pd,cl#b ,na,cl ,na,cl,o ,h#b,o4 ,in a similar manner iridic chloride1 ,ir,cl#d1 is converted into the trichloride1 ,ir,cl#c1 by this method4 ,when this conversion takes place the platinum still remains in the form of platinic chloride1 ,pt,cl#d4 ,it is then possible to take advantage of a certain difference in the properties of the higher and lower chlorides of the platinum metals4 ,thus lime precipitates the lower chlorides of the members of the platinum metals occurring in solution without acting on the platinic chloride1 ,pt,cl#d1 and hence the addition of a large proportion of lime immediately precipitates the associated metals1 leaving the platinum itself in solution in the form of a soluble double salt1 ,pt,cl#d1;,ca,cl#b4 ,a far better and more perfect separation is effected by means of ammonium chloride1 which gives1 with platinic chloride1 an insoluble yellow precipitate1 ,pt,cl#d1b,,nh#d;,cl1 whilst it forms soluble double salts with the lower chlorides ,r,cl#b and ,r,cl#c1 so that ammonium chloride precipitates the platinum only from the solution obtained by the preceding method4 ,these methods are employed for preparing the platinum which is used for the manufacture of platinum articles1 because1 having platinum in solution as calcium platinochloride1 ,pt,ca,cl#f1 or as the insoluble ammonium platinochloride1 ,pt7,,nh#d7b;,cl#f1 the platinum compound in every case1 after drying or ignition1 loses all the chlorine from the platinic chloride and leaves finely-divided metallic platinum1 which may be converted into homogeneous metal by compression and forging1 or by fusion4#e #e ,for the ultimate purification of platinum from palladium and iridium the metals must be re-dissolved in aqua regia1 and the solution evaporated until the residue begins to evolve chlorine4 ,the residue is then re-precipitated with ammonium or potassium chloride4 ,the precipitate may still contain a certain amount of iridium1 which passes with greater difficulty from the tetrachloride1 ,ir,cl#d1 into the trichloride1 ,ir,cl#c1 but it will be quite free from palladium1 because the latter easily loses its chlorine and passes into palladious chloride1 ,pd,cl#b1 which gives an easily-soluble salt with potassium chloride4 ,the precipitate1 containing a small quantity of iridium1 is then heated with sodium carbonate in a crucible1 when the mass decomposes1 giving metallic platinum and iridium oxide4 ,if potassium chloride has been employed1 the residue after ignition is washed with water and treated with aqua regia4 ,the iridium oxide remains undissolved1 and the platinum easily passes into solution4 ,only cold and dilute aqua regia must be used4 ,the solution will then contain pure platinic chloride1 which forms the starting-point for the preparation of all platinum compounds4 ,pure platinum for accurate researches 7for instance1 for the unit of light1 according to ,violle's method7 may be obtained 7,mylius and ,foerster1 #ahib7 by ,finkener's method1 by dissolving the impure metal in aqua regia 7it should be evaporated to drive off the nitrogen compounds71 and adding ,na,cl so as to form a double sodium salt1 which is purified by crystallising with a small amount of caustic soda1 washing the crystals with a strong solution of ,na,cl1 and then dissolving them in a hot #a p4c4 solution of soda1 repeating the above and ultimately igniting the double salt1 previously dried at #abj1 in a stream of hydrogen2 platinum black and ,na,cl are then formed4 ,the three following are very sensitive tests 7to thousandths of a per cent47 for the presence of ,ir1 ,ru1 ,rh1 ,pd 7osmium is not usually present in platinum which has once been purified1 since it easily volatilises with ,cl#b and ,,co#b1 and in the first treatment of the crude platinum either passes off as ,os,o#d or remains undissolved71 ,fe1 ,cu1 ,ag1 and ,pb3 7#a7 the assay is alloyed with #aj parts of pure lead1 the alloy treated with dilute nitric acid 7to remove the greater part of the ,pb71 and dissolved in aqua regia2 the residue will consist of ,ir and ,ru2 the ,pb is precipitated from the nitric acid solution by sulphuric acid1 whilst the remaining platinum metals are reduced from the evaporated solution by formic acid1 and the resultant precipitate fused with ,,khso#d2 the ,pd and ,rh are thus converted into soluble salts1 and the former is then precipitated by ,hg,c#b,n#b4 7#b7 ,iron may be detected by the usual reagents1 if the crude platinum be dissolved in aqua regia1 and the platinum metals precipitated from the solution by formic acid4 7#c7 ,if crude platinum 7as foil or sponge7 be heated in a mixture of chlorine and carbonic oxide it volatilises 7with a certain amount of ,ir1 ,pd1 ,fe1 c47 as ,pt,cl#b1b;,,co 7,note #aa71 whilst the whole of the ,rh1 ,ag1 and ,cu it may contain remains behind4 ,among other characteristic reactions for the platinum metals1 we may mention3 7#a7 that rhodium is precipitated from the solution obtained after fusion with ,,khso#d 7in which ,pt does not dissolve7 by ,,nh#c1 acetic and formic acids2 7#b7 that dilute aqua regia dissolves precipitated ,pt1 but not ,rh2 7#c7 that if the insoluble residue of the platinum metals 7,ir1 ,ru1 ,os7 obtained1 after treating with aqua regia1 be fused with a mixture of #a part of ,,kno#c and #c parts of ,k#b;,,co#c 7in a gold crucible71 and then treated with water1 it gives a solution containing the ,ru 7and a portion of the ,ir71 but which throws it all down when saturated with chlorine and boiled2 7#d7 that if iridium be fused with a mixture of ,,kho and ,,kno#c1 it gives a soluble potassium salt1 ,ir,k#b,o#d 7the solution is blue71 which1 when saturated with chlorine1 gives ,ir,cl#d1 which is precipitated by ,,nh#d;,cl 7the precipitate is black71 forming a double salt1 leaving metallic ,ir after ignition2 7#e7 that rhodium mixed with ,na,cl and ignited in a current of chlorine gives a soluble double salt 7from which sal-ammoniac separates ,pt and ,ir71 which gives 7according to ,jrgensen7 a difficultly soluble purpureo-salt 7,chapter ,,xxii41 ,note #ce71 ,rh#b;,cl#c1e,,nh#c1 when treated with ,,nh#c2 in this form the ,rh may be easily purified and obtained in a metallic form by igniting in hydrogen2 and 7#f7 that palladium1 dissolved in aqua regia and dried 7,,nh#d;,cl throws down any ,pt71 gives soluble ,pd,cl#b1 which forms an easily crystallisable yellow salt1 ,pd,cl#b,,nh#c1 with ammonia2 this salt 7,wilm7 may be easily purified by crystallisation1 and gives metallic ,pd when ignited4 ,these reactions illustrate the method of separating the platinum metals from each other4 ,metallic platinum in a fused state has a specific gravity of #ba2 it is grey1 softer than iron but harder than copper1 exceedingly ductile1 and therefore easily drawn into wire and rolled into thin sheets1 and may be hammered into crucibles and drawn into thin tubes1 c4 ,in the state in which it is obtained by the ignition of its compounds1 it forms a spongy mass1 known as spongy platinum1 or else as powder 7platinum black74#f ,in either case it is dull grey1 and is characterised1 as we already know1 by the faculty of absorbing hydrogen and other gases4 ,platinum is not acted on by hydrochloric1 hydriodic1 nitric1 and sulphuric acids1 or a mixture of hydrofluoric and nitric acids4 ,aqua regia1 and any liquid containing chlorine or able to evolve chlorine or bromine1 dissolves platinum4 ,alkalis are decomposed by platinum at a red heat1 owing to the faculty of the platinum oxide1 ,pt,o#b1 formed to combine with alkaline bases1 inasmuch as it has a feebly-developed acid character 7see ,note #h74 ,sulphur1 phosphorus 7the phosphide1 ,pt,p#b1 is formed71 arsenic and silicon all act more or less rapidly on platinum1 under the influence of heat4 ,many of the metals form alloys with it4 ,even charcoal combines with platinum when it is ignited with it1 and therefore carbonaceous matter cannot be subjected to prolonged and powerful ignition in platinum vessels4 ,hence a platinum crucible soon becomes dull on the surface in a smoky flame4 ,platinum also forms alloys with zinc1 lead1 tin1 copper1 gold1 and silver4#g ,although mercury does not directly dissolve platinum1 still it forms a solution or amalgam with spongy platinum in the presence of sodium amalgam2 a similar amalgam is also formed by the action of sodium amalgam on a solution of platinum chloride1 and is used for physical experiments4 #f ,we have already become acquainted with the effect of finely-divided platinum on many gaseous substances4 ,it is best seen in the so-called platinum black1 which is a coal-black powder left by the action of sulphuric acid on the alloy of zinc and platinum1 or which is precipitated by metallic zinc from a dilute solution of platinum4 ,in any case1 finely-divided platinum absorbs gases more powerfully and rapidly the more finely divided and porous it is4 ,sulphurous anhydride1 hydrogen1 alcohol1 and many organic substances in the presence of such platinum are easily oxidised by the oxygen of the air1 although they do not combine with it directly4 ,the absorption of oxygen is as much as several hundred volumes per one volume of platinum1 and the oxidising power of such absorbed oxygen is taken advantage of not only in the laboratory but even in manufacturing processes4 ,asbestos or charcoal1 soaked in a solution of platinic chloride and ignited1 is very useful for this purpose1 because by this means it becomes coated with platinum black4 ,if #ej grams of ,pt,cl#d be dissolved in #fj c4c4 of water1 and #gj c4c4 of a strong 7#dj p4c47 solution of formic aldehyde added1 the mixture cooled1 and then a solution of #ej grams of ,na,h,o in #ej grams of water added1 the platinum is precipitated4 ,after washing with water the precipitate passes into solution and forms a black liquid containing soluble colloidal platinum 7,loew1 #ahij74 ,if the precipitated platinum be allowed to absorb oxygen on the filter1 the temperature rises #dj1 and a very porous platinum black is obtained which vigorously facilitates oxidation4 #g ,it is necessary to remark that platinum when alloyed with silver1 or as amalgam1 is soluble in nitric acid1 and in this respect it differs from gold1 so that it is possible1 by alloying gold with silver1 and acting on the alloy with nitric acid1 to recognise the presence of platinum in the gold1 because nitric acid does not act on gold alloyed with silver4 ,there are two kinds of platinum compounds1 ,pt,x#d and ,pt,x#b4 ,the former are produced by an excess of halogen in the cold1 and the latter by the aid of heat or by the splitting up of the former4 ,the starting-point for the platinum compounds is platinum tetrachloride1 platinic chloride1 ,pt,cl#d1 obtained by dissolving platinum in aqua regia4#g bis ,the solution crystallises in the cold1 in a desiccator1 in the form of reddish-brown deliquescent crystals which contain hydrochloric acid1 ,pt,cl#d1b;,h,cl1#f;,h#b,o1 and behave like a true acid whose salts correspond to the formula ,r#b,pt,cl#f--;ammonium platinochloride1 for example4#g tri ,the hydrochloric acid is liberated from these crystals by gently heating or evaporating the solution to dryness2 or1 better still1 after treatment with silver nitrate a reddish-brown mass remains behind1 which dissolves in water1 and forms a yellowish-red solution which on cooling deposits crystals of the composition ,pt,cl#d1h;,h#b,o4 ,the tendency of ,pt,cl#d to combine with hydrochloric acid and water--that is1 to form higher crystalline compounds--is evident in the platinum compounds1 and must be taken into account in explaining the properties of platinum and the formation of many other of its complex compounds4 ,dilute solutions of platinic chloride are yellow1 and are completely reduced by hydrogen1 sulphurous anhydride1 and many reducing agents1 which first convert the platinic chloride into the lower compound platinous chloride1 ,pt,cl#b4 ,that faculty which reveals itself in platinum tetrachloride of combining with water of crystallisation and hydrochloric acid is distinctly marked in its property1 with which we are already acquainted1 of giving precipitates with the salts of potassium1 ammonium1 rubidium1 c4 ,in general it readily forms double salts1 ,r#b,pt,cl#f ,pt,cl#d #b,r,cl1 where ,r is a univalent metal such as potassium or ,,nh#d4 ,hence the addition of a solution of potassium or ammonium chloride to a solution of platinic chloride is followed by the formation of a yellow precipitate1 which is sparingly soluble in water and almost entirely insoluble in alcohol and ether 7platinic chloride is soluble in alcohol1 potassium iridiochloride1 ,ir,k#c;,cl#f1 i4e4 a compound of ,ir,cl#c1 is soluble in water but not in alcohol74 ,it is especially remarkable in this case1 that the potassium compounds here1 as in a number of other instances1 separate in an anhydrous form1 whilst the sodium compounds1 which are soluble in water and alcohol1 form red crystals containing water4 ,the composition ,na#b,pt,cl#f1f;,h#b,o exactly corresponds with the above-mentioned hydrochloric compound4 ,the compounds with barium1 ,ba,pt,cl#f1d;,h#b,o1 strontium1 ,sr,pt,cl#f1h;,h#b,o1 calcium1 magnesium1 iron1 manganese1 and many other metals are all soluble in water4#h #g bis ,pt,cl#d is also formed by the action of a mixture of ,h,cl vapour and air1 and by the action of gaseous chlorine upon platinum4 #g tri ,pigeon 7#ahia7 obtained fine yellow crystals of ,pt,h#b;,cl#f1d;,h#b,o by adding strong sulphuric acid to a strong solution of ,pt,h#b;,cl#f1f;,h#b,o4 ,if crystals of ,h#b,pt,cl#f1f;,h#b,o be melted in vacuo 7#fj7 in the presence of anhydrous potash1 a red-brown solid hydrate is obtained containing less water and ,h,cl1 which parts with the remainder at #bjj1 leaving anhydrous ,pt,cl#d4 ,the latter does not disengage chlorine before #bbj1 and is perfectly soluble in water4 #h ,nilson 7#ahgg71 who investigated the platinochlorides of various metals subsequently to ,bonsdorff1 ,topse1 ,clve1 ,marignac1 and others1 found that univalent and bivalent metals--such as hydrogen1 potassium1 ammonium 444 beryllium1 calcium1 barium--give compounds of such a composition that there is always twice as much chlorine in the platinic chloride as in the combined metallic chloride2 for example1 ,k#b;,cl#b1,pt,cl#d2 ,be,cl#b1,pt,cl#d1h;,h#b,o1 c4 ,such trivalent metals as aluminium1 iron 7ferric71 chromium1 didymium1 cerium 7cerous7 form compounds of the type ,r,cl#c,pt,cl#d1 in which the amounts of chlorine are in the ratio #c3d4 ,only indium and yttrium give salts of a different composition--namely1 #b;,in,cl#c1e,pt,cl#d1cf;,h#b,o and #d,y,cl#c1e,pt,cl#d1ea;,h#b,o4 ,such quadrivalent metals as thorium1 tin1 zirconium give compounds of the type ,r,cl#d1,pt,cl#d1 in which the ratio of the chlorine is #a3a4 ,in this manner the valency of a metal may1 to a certain extent1 be judged from the composition of the double salts formed with platinic chloride4 ,platinic bromide1 ,pt,br#d1 and iodide1 ,pt,i#d1 are analogous to the tetrachloride1 but the iodide is decomposed still more easily than the chloride4 ,if sulphuric acid be added to platinic chloride1 and the solution evaporated1 it forms a black porous mass like charcoal1 which deliquesces in the air1 and has the composition ,pt7,,so#d7b4 ,but this1 the only oxygen salt of the type ,pt,x#d1 is exceedingly unstable4 ,this is due to the fact that platinum oxide1 the oxide of the type ,pt,o#b1 has a feeble acid character4 ,this is shown in a number of instances4 ,thus if a strong solution of platinic chloride treated with sodium carbonate be exposed to the action of light or evaporated to dryness and then washed with water1 a sodium platinate1 ,pt#c,na#b,o#g1f;,h#b,o1 remains4 ,the composition of this salt1 if we regard it in the same sense as we did the salts of silicic1 titanic1 molybdic and other acids1 will be ,pt,o7,o,na7#b1b,pt,o#b1f;,h#b,o--that is1 the same type is repeated as we saw in the crystalline compounds of platinum tetrachloride with sodium chloride1 or with hydrochloric acid--namely1 the type ,pt,x#dh,y1 where ,y is the molecule ,h#b,o1,h,cl1 c4 ,similar compounds are also obtained with other alkalis4 ,they will be platinates of the alkalis in which the platinic oxide1 ,pt,o#b1 plays the part of an acid oxide4 ,rousseau 7#ahhi7 obtained different grades of combination ,ba,o,pt,o#b1 #c7;,ba,o7#b,pt,o#b1 c41 by igniting a mixture of ,pt,cl#d and caustic baryta4 ,if such an alkaline compound of platinum be treated with acetic acid1 the alkali combines with the latter1 and a platinic hydroxide1 ,pt7,,oh7#d1 remains as a brown mass1 which loses water and oxygen when ignited1 and in so doing decomposes with a slight explosion4 ,when slightly ignited this hydroxide first loses water and gives the very unstable oxide ,pt,o#b4 ,platinic sulphide1 ,pt,s#b1 belongs to the same type2 it is precipitated by the action of sulphuretted hydrogen on a solution of platinum tetrachloride4 ,the moist precipitate is capable of attracting oxygen1 and is then converted into the sulphate above mentioned1 which is soluble in water4 ,this absorption of oxygen and conversion into sulphate is another illustration of the basic nature of ,pt,o#b1 so that it clearly exhibits both basic and acid properties4 ,the latter appear1 for instance1 in the fact that platinic sulphide1 ,pt,s#b1 gives crystalline compounds with the alkali sulphides4 ,platinous chloride1 ,pt,cl#b1 is formed when hydrogen platinochloride1 ,pt,h#b;,cl#f1 is ignited at #cjj1 or when potassium is heated at #bcj in a stream of chlorine4 ,the undecomposed tetrachloride is extracted from the residue by washing it with water1 and a greenish-grey or brown insoluble mass of the dichloride 7sp4 gr4 #ei7 is then obtained4 ,it is soluble in hydrochloric acid1 giving an acid solution of the composition ,pt,cl#b1b;,h,cl1 corresponding with the type of double salts ,pt,r#b;,cl#d4 ,although platinous chloride decomposes below #ejj1 still it is formed to a small extent at higher temperatures4 ,troost and ,hautefeuille1 and ,seelheim observed that when platinum was strongly ignited in a stream of chlorine1 the metal1 as it were1 slowly volatilised and was deposited in crystals2 a volatile chloride1 probably platinous chloride1 was evidently formed in this case1 and decomposed subsequently to its formation1 depositing crystals of platinum4 ,the properties of platinum above-described are repeated more or less distinctly1 or sometimes with certain modifications1 in the above-mentioned associates and analogues of this metal4 ,thus although palladium forms ,pd,cl#d1 this form passes into ,pd,cl#b with extreme ease4#i ,whilst rhodium and iridium in dissolving in aqua regia also form ,rh,cl#d and ,ir,cl#d1 but they pass into ,rh,cl#c and ,ir,cl#ci bis very easily when heated or when acted upon by substances capable of taking up chlorine 7even alkalis1 which form bleaching salts74 ,among the platinum metals1 ruthenium and osmium have the most acid character1 and although they give ,ru,cl#d and ,os,cl#d they are easily oxidised to ,ru,o#d1 and ,os,o#d by the action of chlorine in the presence of water2 the latter are volatile and may be distilled with the water and hydrochloric acid1 from a solution containing other platinum metals4#i tri ,thus with respect to the types of combination1 all the platinum metals1 under certain circumstances1 give compounds of the type ,,rx#d--;for instance1 ,,ro#b1 ,r,cl#d1 c4 ,but this is the highest form for only platinum and palladium4 ,the remaining platinum metals further1 like iron1 give acids of the type ,,ro#c or hydrates1 ,h#b,,ro#d ,,ro#b7;,,ho7#b 7the type of sulphuric acid72 but they1 like ferric and manganic acids1 are chiefly known in the form of salts of the composition ,k#b,,ro#d or ,k#b,r#b,o#g 7like the dichromate74 ,these salts are obtained1 like the manganates and ferrates1 by fusing the oxides1 or even the metals themselves1 with nitric1 or1 better still1 with potassium peroxide4 ,they are soluble in water1 are easily deoxidised and do not yield the acid anhydrides under the action of acids1 but break up1 either 7like the ferrate7 forming oxygen and a basic oxide 7iridium and rhodium react in this manner1 as they do not give higher forms of oxidation71 or passing into a lower and higher form of oxidation--that is1 reacting like a manganate 7or partly like nitrite or phosphite74 ,osmium and ruthenium react according to the latter form1 as they are capable of giving higher forms of oxidation1 ,os,o#d and ,ru,o#d1 and therefore their reactions of decomposition may be essentially represented by the equation3 #b,os,o#c ,os,o#b ,os,o#d4aj #i ,in comparing the characteristics of the platinum metals1 it must be observed that palladium in its form of combination ,pd,x#b gives saline compounds of considerable stability4 ,amongst them palladous chloride is formed by the direct action of chlorine or aqua regia 7not in excess or in dilute solutions7 on palladium4 ,it forms a brown solution1 which gives a black insoluble precipitate of palladous iodide1 ,pd,i#b1 with solutions of iodides 7in this respect1 as in many others1 palladium resembles mercury in the mercuric compounds ,hg,x#b74 ,with a solution of mercuric cyanide it gives a yellowish white precipitate1 palladous cyanide1 ,pd,c#b,n#b1 which is soluble in potassium cyanide1 and gives other double salts1 ,m#b,pd,c#d,n#d4 ,that portion of the platinum ore which dissolves in aqua regia and is precipitated by ammonium or potassium chloride does not contain palladium4 ,it remains in solution1 because the palladic chloride1 ,pd,cl#d1 is decomposed and the palladous chloride formed is not precipitated by ammonium chloride2 the same holds good for all the other lower chlorides of the platinum metals4 ,zinc 7and iron7 separates out all the unprecipitated platinum metals 7and also copper1 c47 from the solution4 ,the palladium is found in these platinum residues precipitated by zinc4 ,if this mixture of metals be treated with aqua regia1 all the palladium will pass into solution as palladous chloride with some platinic chloride4 ,by this treatment the main portion of the iridium1 rhodium1 c4 remains almost undissolved1 the platinum is separated from the mixture of palladous and platinic chlorides by a solution of ammonium chloride1 and the solution of palladium is precipitated by potassium iodide or mercuric cyanide4 ,wilm 7#ahha7 showed that palladium may be separated from an impure solution by saturating it with ammonia2 all the iron present is thus precipitated1 and1 after filtering1 the addition of hydrochloric acid to the filtrate gives a yellow precipitate of an ammonio-palladium compound1 ,pd,cl#b1b,,nh#c1 whilst nearly all the other metals remain in solution4 ,metallic palladium is obtained by igniting the ammonio-compound or the cyanide1 ,pd,c#b,n#b4 ,it occurs native1 although rarely1 and is a metal of a whiter colour than platinum1 sp4 gr4 #aad1 melts at about #a1ejj2 it is much more volatile than platinum1 partially oxidises on the surface when heated 7,wilm obtained spongy palladium by igniting ,pd,cl#b1b,,nh#c1 and observed that it gives ,pd,o when ignited in oxygen1 and that on further ignition this oxide forms a mixture of ,pd#b,o and ,pd71 and loses its absorbed oxygen on a further rise of temperature4 ,it does not blacken or tarnish 7does not absorb sulphur7 in the air at the ordinary temperature1 and is therefore better suited than silver for astronomical and other instruments in which fine divisions have to be engraved on a white metal1 in order that the fine lines should be clearly visible4 ,the most remarkable property of palladium1 discovered by ,graham1 consists in its capacity for absorbing a large amount of hydrogen4 ,ignited palladium absorbs as much as #idj volumes of hydrogen1 or about #jg p4c4 of its own weight1 which closely approaches to the formation of the compound ,pd#c;,h#b1 and probably indicates the formation of palladium hydride1 ,pd#b;,h4 ,this absorption also takes place at the ordinary temperature--for example1 when palladium serves as an electrode at which hydrogen is evolved4 ,in absorbing the hydrogen1 the palladium does not change in appearance1 and retains all its metallic properties1 only its volume increases by about #aj p4c4--that is1 the hydrogen pushes out and separates the atoms of the palladium from each other1 and is itself compressed to #a_/ijj of its volume4 ,this compression indicates a great force of chemical attraction1 and is accompanied by the evolution of heat 7,chapter ,,ii41 ,note #ch74 ,the absorption of #a grm4 of hydrogen by metallic palladium 7,favre7 is accompanied by the evolution of #db thousand calories 7for ,pt #bj1 for ,na #ac1 for ,k #aj thousand units of heat74 ,troost showed that the dissociation pressure of palladium hydride is inconsiderable at the ordinary temperature1 but reaches the atmospheric pressure at about #adj4 ,this subject was subsequently investigated by ,a4 ,a4 ,cracow of ,st4 ,petersburg 7#ahid71 who showed that at first the absorption of hydrogen by the palladium proceeds like solution1 according to the law of ,dalton and ,henry1 but that towards the end it proceeds like a dissociation phenomenon in definite compounds2 this forms another link between the phenomenon of solution and of the formation of definite atomic compounds4 ,cracow's observations for a temperature #ah1 showed that the electro-conductivity and tension vary until a compound ,pd#b;,h is reached1 and namely1 that the tension p rises with the volume v of hydrogen absorbed1 according to the law of ,dalton and ,henry--for instance1 for p #ba #cb #ee #gg mm4 v #ad #bj #cd #dg ,the maximum tension at #ah is #i mm4 ,at a temperature of about #adj 7in the vapour of xylene7 the maximum tension is about #gfj mm41 and when v #aj-ej vols4 the tension 7according to ,cracow's experiments7 stands at #ij-dej mm4--that is1 increases in proportion to the volume of hydrogen absorbed4 ,but from the point of view of chemical mechanics it is especially important to remark that ,moutier clearly showed1 through palladium hydride1 the similarity of the phenomena which proceed in evaporation and dissociation1 which fact ,henri ,sainte-,claire ,deville placed as a fundamental proposition in the theory of dissociation4 ,it is possible upon the basis of the second law of the theory of heat1 according to the law of the variation of the tension p of evaporation with the temperature ,t 7counted from -#bgc71 to calculate the latent heat of evaporation ,l 7see works on physics7 because #dbd,l ,t7#a_/;d - #a_/;,d7dp_/dt1 where d and ,d are the weights of cubic measures of the gas 7vapour7 and liquid4 7,thus1 for instance1 for water1 when t #ajj1 ,t #cgc1 d #jfje1 ,d #ifj1 dp_/dt #jjbg m41 #ac1eif #cfg1 ,l #ecf1 whence #dbd,l #bbg1bfd1 and the second portion of the equation #bbf1add1 which is sufficiently near1 within the limits of experimental error1 see ,chapter ,i41 ,note #aa47 ,the same equation is applicable to the dissociation of ,na#b;,h and ,k#b;,h--7,chapter ,,xii41 ,note #db7--;but it has only been verified in this respect for ,pd#b;,h1 since ,moutier1 by calculating the amount of heat ,l evolved1 for t #bj1 according to the variation of the tension 7dp_/dt7 obtained #da thousand calories1 which is very near the figure obtained experimentally by ,favre 7see ,chapter ,,xii41 ,note #dd74 ,the absorbed hydrogen is easily disengaged by ignition or decreased pressure4 ,the resultant compound does not decompose at the ordinary temperature1 but when exposed to air the metal sometimes glows spontaneously1 owing to the hydrogen burning at the expense of the atmospheric oxygen4 ,the hydrogen absorbed by palladium acts towards many solutions as a reducing agent2 in a word1 everything here points to the formation of a definite compound and at the same time of a physically-compressed gas1 and forms one of the best examples of the bond existing between chemical and physical processes1 to which we have many times drawn attention4 ,it must be again remembered that the other metals of the eighth group1 even copper1 are1 like palladium and platinum1 able to combine with hydrogen4 ,the permeability of iron and platinum tubes to hydrogen is naturally due to the formation of similar compounds1 but palladium is the most permeable4 #i bis ,rhodium is generally separated1 together with iridium1 from the residues left after the treatment of native platinum1 because the palladium is entirely separated from them1 and the ruthenium is present in them in very small traces1 whilst the osmium at any rate is easily separated1 as we shall soon see4 ,the mixture of rhodium and iridium which is left undissolved in dilute aqua regia is dissolved in chlorine water1 or by the action of chlorine on a mixture of the metals with sodium chloride4 ,in either case both metals pass into solution4 ,they may be separated by many methods4 ,in either case 7if the action be aided by heat7 the rhodium is obtained in the form of the chloride ,rh,cl#c1 and the iridium as iridious chloride1 ,ir,cl#c4 ,they both form double salts with sodium chloride which are soluble in water1 but the iridium salt is also partially soluble in alcohol1 whilst the rhodium salt is not4 ,a mixture of the chlorides1 when treated with dilute aqua regia1 gives iridic chloride1 ,ir,cl#d1 whilst the rhodium chloride1 ,rh,cl#c1 remains unaltered2 ammonium chloride then precipitates the iridium as ammonium iridiochloride1 ,ir7,,nh#d7b;,cl#f1 and on evaporating the rose-coloured filtrate the rhodium gives a crystalline salt1 ,rh7,,nh#d7c;,cl#f4 ,rhodium and its various oxides are dissolved when fused with potassium hydrogen sulphate1 and give a soluble double sulphate 7whilst iridium remains unacted on72 this fact is very characteristic for this metal1 which offers in its properties many points of resemblance with the iron metals4 ,when fused with potassium hydroxide and chlorate it is oxidised like iridium1 but it is not afterwards soluble in water1 in which respect it differs from ruthenium4 ,this is taken advantage of for separating rhodium1 ruthenium1 and iridium4 ,in any case1 rhodium under ordinary conditions always gives salts of the type ,,rx#c1 and not of any other type2 and not only halogen salts1 but also oxygen salts1 are known in this type1 which is rare among the platinum metals4 ,rhodium chloride1 ,rh,cl#c1 is known in an insoluble anhydrous and also in a soluble form 7like ,cr,x#c or salts of chromic oxides71 in which it easily gives double salts1 compounds with water of crystallisation1 and forms rose-coloured solutions4 ,in this form rhodium easily gives double salts of the two types ,rh,m#c;,cl#f and ,rh,m#b;,cl#c--;for example1 ,k#e,rh,cl#f1c;,h#b,o and ,k#b,rh,cl#e1;,h#b,o4 ,solutions of the salts 7at least1 the ammonium salt7 of the first kind give salts of the second kind when they are boiled4 ,if a strong solution of potash be added to a red solution of rhodium chloride and boiled1 a black precipitate of the hydroxide ,rh7,,oh7#c is formed2 but if the solution of potash is added little by little1 it gives a yellow precipitate containing more water4 ,this yellow hydrate of rhodium oxide gives a yellow solution when it is dissolved in acids1 which only becomes rose-coloured after being boiled4 ,it is obvious a change here takes place1 like the transmutations of the salts of chromic oxide4 ,it is also a remarkable fact that the black hydroxide1 like many other oxidised compounds of the platinoid metals1 does not dissolve in the ordinary oxygen acids1 whilst the yellow hydroxide is easily soluble and gives yellow solutions1 which deposit imperfectly crystallised salts4 ,metallic rhodium is easily obtained by igniting its oxygen and other compounds in hydrogen1 or by precipitation with zinc4 ,it resembles platinum1 and has a sp4 gr4 of #aba4 ,at the ordinary temperature it decomposes formic acid into hydrogen and carbonic anhydride1 with development of heat 7,deville74 ,with the alkali sulphites1 the salts of rhodium and iridium of the type ,,rx#c give sparingly-soluble precipitates of double sulphites of the composition ,r7,,so#c,na7#c1;,h#b,o1 by means of which these metals may be separated from solution1 and also may be separated from each other1 for a mixture of these salts when treated with strong sulphuric acid gives a soluble iridium sulphate and leaves a red insoluble double salt of rhodium and sodium4 ,it may be remarked that the oxides ,ir#b,o#c and ,rh#b,o#c are comparatively stable and are easily formed1 and that they also form different double salts 7for instance1 ,ir,cl#c1c,k,cl#c;,h#b,o1 ,rh,cl#c1b,,nh#d;,cl#d;,h#b,o1 ,rh,cl#c1c,,nh#d;,cl#a-a_/b;,h#b,o7 and compounds like the cobaltia compounds 7for instance1 luteo-salts ,rh,x#c1f,,nh#c1 roseo-salts1 ,rh,x#c;,h#b,o#e,,nh#c1 and purpureo-salts ,ir,x#c1e,,nh#c1 c47 ,iridious oxide1 ,ir#b,o#c1 is obtained by fusing iridious chloride and its compounds with sodium carbonate1 and treating the mass with water4 ,the oxide is then left as a black powder1 which1 when strongly heated1 is decomposed into iridium and oxygen2 it is easily reduced1 and is insoluble in acids1 which indicates the feeble basic character of this oxide1 in many respects resembling such oxides as cobaltic oxide1 ceric or lead dioxide1 c4 ,it does not dissolve when fused with potassium hydrogen sulphate4 ,rhodium oxide1 ,rh#b,o#c1 is a far more energetic base4 ,it dissolves when fused with potassium hydrogen sulphate4 ,from what has been said respecting the separation of platinum and rhodium it will be understood how the compounds of iridium1 which is the main associate of platinum1 are obtained4 ,in describing the treatment of osmiridium we shall again have an opportunity of learning the method of extraction of the compounds of this metal1 which has in recent times found a technical application in the form of its oxide1 ,ir#b,o#c2 this is obtained from many of the compounds of iridium by ignition with water1 is easily reduced by hydrogen1 and is insoluble in acids4 ,it is used in painting on china1 for giving a black colour4 ,iridium itself is more difficultly fusible than platinum1 and when fused it does not decompose acids or even aqua regia2 it is extremely hard1 and is not malleable2 its sp4 gr4 is #bbd4 ,in the form of powder it dissolves in aqua regia1 and is even partially oxidised when heated in air1 sets fire to hydrogen1 and1 in a word1 closely resembles platinum4 ,heated in an excess of chlorine it gives iridic chloride1 ,ir,cl#d1 but this loses chlorine at #ej2 it is1 however1 more stable in the form of double salts1 which have a characteristic black colour--for instance1 ,ir7,,nh#d7b;,cl#f--;but they give iridious chloride1 ,ir,cl#c1 when treated with sulphuric acid4 #i tri ,we have yet to become acquainted with the two remaining associates of platinum--ruthenium and osmium--whose most important property is that they are oxidised even when heated in air1 and that they are able to give volatile oxides of the form ,ru,o#d and ,os,o#d2 these have a powerful odour 7like iodine and nitrous anhydride74 ,both these higher oxides are solids2 they volatilise with great ease at #ajj2 the former is yellow and the latter white4 ,they are known as ruthenic and osmic anhydrides1 although their aqueous solutions 7they both slowly dissolve in water7 do not show an acid reaction1 and although they do not even expel carbonic anhydride from potassium carbonate1 do not give crystalline salts with bases1 and their alkaline solutions partially deposit them again when boiled 7an excess of water decomposes the salts74 ,the formul ,os,o#d and ,ru,o#d correspond with the vapour density of these oxides4 ,thus ,deville found the vapour density of osmic anhydride to be #abh 7by the formula #abge7 referred to hydrogen4 ,tennant and ,vauquelin discovered this compound1 and ,berzelius1 ,whler1 ,fritzsche1 ,struv1 ,deville1 ,claus1 ,joly1 and others helped in its investigation2 nevertheless there are still many questions concerning it which remain unsolved4 ,it should be observed that ,,ro#d is the highest known form for an oxygen compound1 and ,,rh#d is the highest known form for a compound of hydrogen2 whilst the highest forms of acid hydrates contain ,si,h#d,o#d1 ,,ph#c,o#d1 ,,sh#b,o#d1 ,cl,h,o#d--;all with four atoms of oxygen1 and therefore in this number there is apparently the limit for the simple forms of combination of hydrogen and oxygen4 ,in combination with several atoms of an element1 or several elements1 there may be more than ,o#d or ,h#d1 but a molecule never contains more than four atoms of either ,o or ,h to one atom of another element4 ,thus the simplest forms of combination of hydrogen and oxygen are exhausted by the list ,,rh#d1 ,,rh#c1 ,,rh#b1 ,,rh1 ,,ro1 ,,ro#b1 ,,ro#c1 ,,ro#d4 ,the extreme members are ,,rh#d and ,,ro#d1 and are only met with for such elements as carbon1 silicon1 osmium1 ruthenium1 which also give ,r,cl#d with chlorine4 ,in these extreme forms1 ,,rh#d and ,,ro#d1 the compounds are the least stable 7compare ,si,h#d1 ,,ph#c1 ,,sh#b1 ,cl,h1 or ,ru,o#d1 ,mo,o#c1 ,zr,o#b1 ,sr,o71 and easily give up part1 or even all1 their oxygen or hydrogen4 ,the primary source from which the compounds of ruthenium and osmium are obtained is either osmiridium 7the osmium predominates1 from ,ir,os to ,ir,os#d1 sp4 gr4 from #af to #ba71 which occurs in platinum ores 7it is distinguished from the grains of platinum by its crystalline structure1 hardness1 and insolubility in aqua regia71 or else those insoluble residues which are obtained1 as we saw above1 after treating platinum with aqua regia4 ,osmium predominates in these materials1 which sometimes contain from #cj p4c4 to #dj p4c4 of it1 and rarely more than #d p4c4 to #e p4c4 of ruthenium4 ,the process for their treatment is as follows3 they are first fused with #f parts of zinc1 and the zinc is then extracted with dilute hydrochloric acid4 ,the osmiridium thus treated is1 according to ,fritzsche and ,struv's method1 then added to a fused mixture of potassium hydroxide and chlorate in an iron crucible2 the mass as it begins to evolve oxygen acts on the metal1 and the reaction afterwards proceeds spontaneously4 ,the dark product is treated with water1 and gives a solution of osmium and ruthenium in the form of soluble salts1 ,r#b,os,o#d and ,r#b,ru,o#d1 whilst the insoluble residue contains a mixture of oxides of iridium 7and some osmium1 rhodium1 and ruthenium71 and grains of metallic iridium still unacted on4 ,according to ,frmy's method the lumps of osmiridium are straightway heated to whiteness in a porcelain tube in a stream of air or oxygen1 when the very volatile osmic anhydride is obtained directly1 and is collected in a well-cooled receiver1 whilst the ruthenium gives a crystalline sublimate of the dioxide1 ,ru,o#b1 which is1 however1 very difficultly volatile 7it volatilises together with osmic anhydride71 and therefore remains in the cooler portions of the tube2 this method does not give volatile ruthenic anhydride1 and the iridium and other metals are not oxidised or give non-volatile products4 ,this method is simple1 and at once gives dry1 pure osmic anhydride in the receiver1 and ruthenium dioxide in the sublimate4 ,the air which passes through the tube should be previously passed through sulphuric acid1 not only in order to dry it1 but also to remove the organic and reducing dust4 ,the vapour of osmic anhydride must be powerfully cooled1 and ultimately passed over caustic potash4 ,a third mode of treatment1 which is most frequently employed1 was proposed by ,whler1 and consists in slightly heating 7in order that the sodium chloride should not melt7 an intimate mixture of osmiridium and common salt in a stream of moist chlorine4 ,the metals then form compounds with chlorine and sodium chloride1 whilst the osmium forms the chloride1 ,os,cl#d1 which reacts with the moisture1 and gives osmic anhydride1 which is condensed4 ,the ruthenium in this1 as in the other processes1 does not directly give ruthenic anhydride1 but is always extracted as the soluble ruthenium salt1 ,k#b,ru,o#d1 obtained by fusion with potassium hydroxide and chlorate or nitrate4 ,when the orange-coloured ruthenate1 ,k#b,ru,o#d1 is mixed with acids1 the liberated ruthenic acid immediately decomposes into the volatile ruthenic anhydride and the insoluble ruthenic oxide3 #b,k#b,ru,o#d #d;,,hno#c ,ru,o#d ,ru,o#b1b;,h#b,o #d,,kno#c4 ,when once one of the above compounds of ruthenium or osmium is procured it is easy to obtain all the remaining compounds1 and by reduction 7by metals1 hydrogen1 formic acid1 c47 the metals themselves4 ,osmic anhydride1 ,os,o#d1 is very easily deoxidised by many methods4 ,it blackens organic substances1 owing to reduction1 and is therefore used in investigating vegetable and animal1 and especially nerve1 preparations under the microscope4 ,although osmic anhydride may be distilled in hydrogen1 still complete reduction is accomplished when a mixture of hydrogen and osmic anhydride is slightly ignited 7just before it inflames74 ,if osmium be placed in the flame it is oxidised1 and gives vapours of osmic anhydride1 which become reduced1 and the flame gives a brilliant light4 ,osmic anhydride deflagrates like nitre on red-hot charcoal2 zinc1 and even mercury and silver1 reduce osmic anhydride from its aqueous solutions into the lower oxides or metal2 such reducing agents as hydrogen sulphide1 ferrous sulphate1 or sulphurous anhydride1 alcohol1 c41 act in the same manner with great ease4 ,the lower oxides of osmium1 ruthenium1 and of the other elements of the platinum series are not volatile1 and it is noteworthy that the other elements behave differently4 ,on comparing ,,so#b1 ,,so#c2 ,as#b,o#c1 ,as#b,o#e2 ,p#b,o#c1 ,p#b,o#e2 ,,co1 ,,co#b1 c41 we observe a converse phenomenon2 the higher oxides are less volatile than the lower4 ,in the case of osmium all the oxides1 with the exception of the highest1 are non-volatile1 and it may therefore be thought that this higher form is more simply constituted than the lower4 ,it is possible that osmic oxide1 ,os,o#b1 stands in the same relation to the anhydride as ,c#b;,h#d to ,,ch#d--;i4e4 the lower oxide is perhaps ,os#b,o#d1 or is still more polymerised1 which would explain why the lower oxides1 having a greater molecular weight1 are less volatile than the higher oxides1 just as we saw in the case of the nitrogen oxides1 ,n#b,o and ,,no4 ,ruthenium and osmium1 obtained by the ignition or reduction of their compounds in the form of powder1 have a density considerably less than in the fused form1 and differ in this condition in their capacity for reaction2 they are much more difficultly fused than platinum and iridium1 although ruthenium is more fusible than osmium4 ,ruthenium in powder has a specific gravity of #he1 the fused metal of #abb2 osmium in powder has a specific gravity of #bjj1 and when semi-fused--or1 more strictly speaking1 agglomerated--in the oxyhydrogen flame1 of #bad1 and fused #bbe4 ,the powder of slightly-heated osmium oxidises very easily in the air1 and when ignited burns like tinder1 directly forming the odoriferous osmic anhydride 7hence its name1 from the ,greek word signifying odour72 ruthenium also oxidises when heated in air1 but with more difficulty1 forming the oxide ,ru,o#b4 ,the oxides of the types ,,ro1 ,r#b,o#c1 and ,,ro#b 7and their hydrates7 obtained by reduction from the higher oxides1 and also from the chlorides1 are analogous to those given by the other platinum metals1 in which respect osmium and ruthenium closely resemble them4 ,we may also remark that ruthenium has been found in the platinum deposits of ,borneo in the form of laurite1 ,ru#b,s#c1 in grey octahedra of sp4 gr4 #gj4 ,for osmium1 ,moraht and ,wischin 7#ahic7 obtained free osmic acid1 ,h#b,os,o#d1 by decomposing ,k#b,os,o#d with water1 and precipitating with alcohol in a current of hydrogen 7because in air volatile ,os,o#d is formed72 with ,h#b,s1 osmic acid gives ,os,o#c7;,,hs7#b at the ordinary temperature4 ,debray and ,joly showed that ruthenic anhydride1 ,ru,o#d1 fuses at #be1 boils at #ajj1 and evolves oxygen when dissolved in potash1 forming the salt ,k,ru,o#d 7not isomorphous with potassium permanganate74 ,joly 7#ahia71 who studied the ruthenium compounds in greater detail1 showed that the easily-formed ,k,ru,o#d gives ,ru,k,o#d,ru,o#c when ignited1 but it resembles ,k,mn,o#d in many respects4 ,in general1 ,ru has much in common with ,mn4 ,joly 7#ahhi7 also showed that if ,,kno#c be added to a solution of ,ru,cl#c containing ,h,cl1 the solution becomes hot1 and a salt1 ,ru,cl#c,,no#b,k,cl1 is formed1 which enters into double decomposition and is very stable4 ,moreover1 if ,ru,cl#c be treated with an excess of nitric acid1 it forms a salt1 ,ru,cl#c,,noh#b,o1 after being heated 7to boiling7 and the addition of ,h,cl4 ,the vapour density of ,ru,o#d1 determined by ,debray and ,joly1 corresponds to that formula4 #aj ,although palladium gives the same types of combination 7with chlorine7 as platinum1 its reduction to ,,rx#b is incomparably easier than that of platinic chloride1 and in the case of iridium it is also very easy4 ,iridic chloride1 ,ir,cl#d1 acts as an oxidising agent1 readily parts with a fourth of its chlorine to a number of substances1 readily evolves chlorine when heated1 and it is only at low temperatures that chlorine and aqua regia convert iridium into iridic chloride4 ,in disengaging chlorine iridium more often and easily gives the very stable iridious chloride1 ,ir,cl#c 7perhaps this substance is ,ir#b;,cl#f ,ir,cl#b1;,ir,cl#d1 insoluble in water1 but soluble in potassium chloride1 because it forms the double salt ,k#c;,ir,cl#f71 than the dichloride1 ,ir,cl#b4 ,this compound1 corresponding to ,ir,x#b1 is very stable1 and corresponds with the basic oxide1 ,ir#b,o#c1 resembling the oxides ,fe#b,o#c1 ,co#b,o#c4 ,to this form there correspond ammoniacal compounds similar to those given by cobaltic oxide4 ,although iridium also gives an acid in the form of the salt ,k#b;,ir#b,o#g1 it does not1 like iron 7and chromium71 form the corresponding chloride1 ,ir,cl#f4 ,in general1 in this as in the other elements1 it is impossible to predict the chlorine compounds from those of oxygen4 ,just as there is no chloride ,s,cl#f1 but only ,s,cl#b1 so also1 although ,ir,o#c exists1 ,ir,cl#f is wanting1 the only chloride being ,ir,cl#d1 and this is unstable1 like ,s,cl#b1 and easily parts with its chlorine4 ,in this respect rhodium is very much like iridium 7as platinum is like palladium74 ,for ,rh,cl#d decomposes with extreme ease1 whilst rhodium chloride1 ,rh,cl#c1 is very stable1 like many of the salts of the type ,rh,x#c1 although like the platinum elements these salts are easily reduced to metal by the action of heat and powerful reagents4 ,there is as close a resemblance between osmium and ruthenium4 ,osmium when submitted to the action of dry chlorine gives osmic chloride1 ,os,cl#d1 but the latter is converted by water 7as is osmium by moist chlorine7 into osmic anhydride1 although the greater portion is then decomposed into ,os7,,ho7#d and #d;,h,cl1 like a chloranhydride of an acid4 ,in general this acid character is more developed in osmium than in platinum and iridium4 ,having parted with chlorine1 osmic chloride1 ,os,cl#d1 gives the unstable trichloride1 ,os,cl#c1 and the stable soluble dichloride1 ,os,cl#b1 which corresponds with platinous chloride in its properties and reactions4 ,the relation of ruthenium to the halogens is of the same nature4 ,platinum and its analogues1 like iron and its analogues1 are able to form complex and comparatively stable cyanogen and ammonia compounds1 corresponding with the ferrocyanides and the ammoniacal compounds of cobalt1 which we have already considered in the preceding chapter4 ,if platinous chloride1 ,pt,cl#b 7insoluble in water71 be added by degrees to a solution of potassium cyanide1 it is completely dissolved 7like silver chloride71 and on evaporating the solution deposits rhombic prisms of potassium platinocyanide1 ,pt,k#b7;,,cn7#d1c;,h#b,o4 ,this salt1 like all those corresponding with it1 has a remarkable play of colours1 due to the phenomena of dichromism1 and even polychromism1 natural to all the platinocyanides4 ,thus it is yellow and reflects a bright blue light4 ,it is easily soluble in water1 effloresces in air1 then turns red1 and at #ajj orange1 when it loses all its water4 ,the loss of water does not destroy its stability--that is1 it still remains unchanged1 and its stability is further shown by the fact that it is formed when potassium ferrocyanide1 ,k#d;,fe7,,cn7#f1 is heated with platinum black4 ,this salt1 first obtained by ,gmelin1 shows a neutral reaction with litmus2 it is exceedingly stable under the action of air1 like potassium ferrocyanide1 which it resembles in many respects4 ,thus the platinum in it cannot be detected by reagents such as sulphuretted hydrogen2 the potassium may be replaced by other metals by the action of their salts1 so that it corresponds with a whole series of compounds1 ,r#b,pt7,,cn7#d1 and it is stable1 although the potassium cyanide and platinous salts1 of which it is composed1 individually easily undergo change4 ,when treated with oxidising agents it passes1 like the ferrocyanide1 into a higher form of combination of platinum4 ,if salts of silver be added to its solution1 it gives a heavy white precipitate of silver platinocyanide1 ,pt,ag#b7;,,cn7#d1 which when suspended in water and treated with sulphuretted hydrogen1 enters into double decomposition with the latter and forms insoluble silver sulphide1 ,ag#b,s1 and soluble hydroplatinocyanic acid1 ,h#b,pt7,,cn7#d4 ,if potassium platinocyanide be mixed with an equivalent quantity of sulphuric acid1 the hydroplatinocyanic acid liberated may be extracted by a mixture of alcohol and ether4 ,the ethereal solution1 when evaporated in a desiccator1 deposits bright red crystals of the composition ,pt,h#b7;,,cn7#d1e;,h#b,o4 ,this acid colours litmus paper1 liberates carbonic anhydride from sodium carbonate1 and saturates alkalis1 so that it presents an analogy to hydroferrocyanic acid4#aa #aa ,this acid character is explained by the influence of the platinum on the hydrogen1 and by the attachment of the cyanogen groups4 ,thus cyanuric acid1 ,h#c7;,,cn7#c,o#c1 is an energetic acid compared with cyanic acid1 ,,hcno4 ,and the formation of a compound with five molecules of water of crystallisation1 7,pt,h#b7;,,cn7#d1e;,h#b,o71 confirms the opinion that platinum is able to form compounds of still higher types than that expressed in its saline compounds1 and1 moreover1 the combination of hydroplatinocyanic acid with water does not reach the limit of the compounds which appears in ,pt,cl#d1b;,h,cl1#f;,h#b,o4 ,a whole series of platinocyanides of the common type ,pt,r#b7;,,cn7#dn,h#b,o is obtained by means of double decomposition with the potassium or hydrogen or silver salts4 ,for example1 the salts of sodium and lithium contain1 like the potassium salt1 three molecules of water4 ,the sodium salt is soluble in water and alcohol4 ,the ammonium salt has the composition ,pt7,,nh#d7b7;,,cn7#d1b;,h#b,o and gives crystals which reflect blue and rose-coloured light4 ,this ammonium salt decomposes at #cjj1 with evolution of water and ammonium cyanide1 leaving a greenish platinum dicyanide1 ,pt7,,cn7#b1 which is insoluble in water and acid but dissolves in potassium cyanide1 hydrocyanic acid1 and other cyanides4 ,the same platinous cyanide is obtained by the action of sulphuric acid on the potassium salts in the form of a reddish-brown amorphous precipitate4 ,the most characteristic of the platinocyanides are those of the alkaline earths4 ,the magnesium salt ,pt,mg7,,cn7#d1g;,h#b,o crystallises in regular prisms1 whose side faces are of a metallic green colour and terminal planes dark blue4 ,it shows a carmine-red colour along the main axis1 and dark red along the lateral axes2 it easily loses water1 7#b;,h#b,o71 at #dj1 and then turns blue 7it then contains #e;,h#b,o1 which is frequently the case with the platinocyanides74 ,its aqueous solution is colourless1 and an alcoholic solution deposits yellow crystals4 ,the remainder of the water is given off at #bcj4 ,it is obtained by saturating platinocyanic acid with magnesia1 or else by double decomposition between the barium salt and magnesium sulphate4 ,the strontium salt1 ,sr,pt7,,cn7#d1d;,h#b,o crystallises in milk-white plates having a violet and green iridescence4 ,when it effloresces in a desiccator1 its surfaces have a violet and metallic green iridescence4 ,a colourless solution of the barium salt ,pt,ba7,,cn7#d1d;,h#b,o is obtained by saturating a solution of hydroplatinocyanic acid with baryta1 or by boiling the insoluble copper platinocyanide in baryta water4 ,it crystallises in monoclinic prisms of a yellow colour1 with blue and green iridescence2 it loses half its water at #ajj1 and the whole at #aej4 ,the ethyl salt1 ,pt7,c#b;,h#e7b7;,,cn7#d1b;,h#bj1 is also very characteristic2 its crystals are isomorphous with those of the potassium salt1 and are obtained by passing hydrochloric acid into an alcoholic solution of hydroplatinocyanic acid4 ,the facility with which they crystallise1 the regularity of their forms1 and their remarkable play of colours1 renders the preparation of the platinocyanides one of the most attractive lessons of the laboratory4 ,by the action of chlorine or dilute nitric acid1 the platinocyanides are converted into salts of the composition ,pt,m#b7;,,cn7#e1 which corresponds with ,pt7,,cn7#c1b,,kcn--that is1 they express the type of a non-existent form of oxidation of platinum1 ,pt,x#c 7i4e4 oxide ,pt#b,o#c71 just as potassium ferricyanide 7,fe,cy#c1c,k,cy7 corresponds with ferric oxide1 and the ferrocyanide corresponds with the ferrous oxide4 ,the potassium salt of this series contains ,pt,k#b7;,,cn7#e1c;,h#b,o1 and forms brown regular prisms with a metallic lustre1 and is soluble in water but insoluble in alcohol4 ,alkalis re-convert this compound into the ordinary platinocyanide ,k#b,pt7,,cn7#d1 taking up the excess of cyanogen4 ,it is remarkable that the salts of the type ,pt,m#b;,cy#e contain the same amount of water of crystallisation as those of the type ,pt,m#b;,cy#d4 ,thus the salts of potassium and lithium contain three1 and the salt of magnesium seven1 molecules of water1 like the corresponding salts of the type of platinous oxide4 ,moreover1 neither platinum nor any of its associates gives any cyanogen compound corresponding with the oxide1 i4e4 having the composition ,pt,k#b;,cy#f1 just as there are no compounds higher than those which correspond to ,r,cy#cn,m,cy#c for cobalt or iron4 ,this would appear to indicate the absence of any such cyanides1 and indeed1 for no element are there yet known any poly-cyanides containing more than three equivalents of cyanogen for one equivalent of the element4 ,the phenomenon is perhaps connected with the faculty of cyanogen of giving tricyanogen polymerides1 such as cyanuric acid1 solid cyanogen chloride1 c4 ,under the action of an excess of chlorine1 a solution of ,pt,k#b7;,,cn7#d gives 7besides ,pt,k#b;,cy#e7 a product ,pt,k#b;,cy#d;,cl#b1 which evidently contains the form ,pt,x#d1 but at first the action of the chlorine 7or the electrolysis of1 or addition of dilute peroxide of hydrogen to1 a solution of ,pt,k#b;,cy#d1 acidulated with hydrochloric acid7 produces an easily soluble intermediate salt which crystallises in thin copper-red needles 7,wilm1 ,hadow1 #ahhi74 ,it only contains a small amount of chlorine1 and apparently corresponds to a compound #e,pt,k#b;,cy#d ,pt,k#b;,cy#d;,cl#b #bd;,h#b,o4 ,under the action of an excess of ammonia both these chlorine products are converted either completely or in part 7according to ,wilm ammonia does not act upon ,pt,k#b;,cy#d7 into ,pt,cy#b1b,,nh#c1 i4e4 a platino-ammonia compound 7see further on74 ,it is also necessary to pay attention to the fact that ruthenium and osmium--which1 as we know1 give higher forms of oxidation than platinum--are also able to combine with a larger proportion of potassium cyanide 7but not of cyanogen7 than platinum4 ,thus ruthenium forms a crystalline hydroruthenocyanic acid1 ,ru,h#d7;,,cn7#f1 which is soluble in water and alcohol1 and corresponds with the salts ,m#d,ru7,,cn7#f4 ,there are exactly similar osmic compounds--for example1 ,k#d,os7,,cn7#f1c;,h#b,o4 ,the latter is obtained in the form of colourless1 sparingly-soluble regular tablets on evaporating the solution obtained from a fused mixture of potassium osmiochloride1 ,k#b,os,cl#f1 and potassium cyanide4 ,these osmic and ruthenic compounds fully correspond with potassium ferrocyanide1 ,k#d;,fe7,,cn7#f1c;,h#b,o1 not only in their composition but also in their crystalline form and reactions1 which again demonstrates the close analogy between iron1 ruthenium1 and osmium1 which we have shown by giving these three elements a similar position 7in the eighth group7 in the periodic system4 ,for rhodium and iridium only salts of the same type as the ferricyanides1 ,m#c,r,cy#f1 are known1 and for palladium only of the type ,m#b,pd,cy#d1 which are analogous to the platinum salts4 ,in all these examples a constancy of the types of the double cyanides is apparent4 ,in the eighth group we have iron1 cobalt1 nickel1 copper1 and their analogues ruthenium1 rhodium1 palladium1 silver1 and also osmium1 iridium1 platinum1 gold4 ,the double cyanides of iron1 ruthenium1 osmium have the type ,k#d,r7,,cn7#f2 of cobalt1 rhodium1 iridium1 the type ,k#c,r7,,cn7#f2 of nickel1 palladium1 platinum the type ,k#b,r7,,cn7#d and ,k#b,r7,,cn7#e2 and for copper1 silver1 gold there are known ,,kr7,,cn7#b1 so that the presence of #d1 #c1 #b1 and #a atoms of potassium corresponds with the order of the elements in the periodic system4 ,those types which we have seen in the ferrocyanides and ferricyanides of iron repeat themselves in all the platinoid metals1 and this naturally leads to the conclusion that the formation of similar so-called double salts is of exactly the same nature as that of the ordinary salts4 ,if1 in expressing the union of the elements in the oxygen salts1 the existence of an aqueous residue 7hydroxyl group7 be admitted1 in which the hydrogen is replaced by a metal1 we have then only to apply this mode of expression to the double salts and the analogy will be obvious1 if only we remember that ,cl#b1 7,,cn7#b1 ,,so#d1 c41 are equivalent to ,o1 as we see in ,,ro1 ,r,cl#b1 ,,rso#d1 c4 ,they all ,x#b1 and1 therefore1 in point of fact1 wherever ,x 7 ,cl or ,,oh1 c47 can be placed1 there 7,cl#b;,h71 7,,so#d;,h71 c41 can also stand4 ,and as ,cl#b;,h ,cl ,h,cl and ,,so#d;,h ,,oh ,,so#c1 c41 it follows that molecules ,h,cl or ,,so#c1 or1 in general1 whole molecules--for instance1 ,,nh#c1 ,h#b,o1 salts1 c41 can annex themselves to a compound containing ,x4 7,this is an indirect consequence of the law of substitution which explains the origin of double salts1 ammonia compounds1 compounds with water of crystallisation1 c41 by one general method47 ,thus the double salt ,mg,s,o#d1,k#b,,so#d1 according to this reasoning1 may be considered as a substance of the same type as ,mg,cl#b1 namely1 as ,mg7,,so#d,k7#b1 and the alums as derived from ,al7,,oh77,,so#d71 namely1 as ,al7,,so#d,k77,,so#d74 ,without stopping to pursue this digression further1 we will apply these considerations to the type of the ferrocyanides and ferricyanides and their platinum analogues4 ,such a salt as ,k#b,pt,cy#d may accordingly be regarded as ,pt7,cy#b,k7#b1 like ,pt7,,oh7#b2 and such a salt as ,pt,k#b;,cy#e as ,pt,cy7,cy#b,k7#b1 the analogue of ,pt,x7,,oh7#b1 or ,al,x7,,oh7#b1 and other compounds of the type ,,rx#c4 ,potassium ferricyanide and the analogous compounds of cobalt1 iridium1 and rhodium1 belong to the same type1 with the same difference as there is between ,,rx7,,oh7#b and ,r7,,oh7#c1 since ,fe,k#c;,cy#f ,fe7,cy#b,k7#c4 ,limiting myself to these considerations1 which may partially elucidate the nature of double salts1 ,i will now pass again to the complex saline compounds known for platinum4 7,a7 ,on mixing a solution of potassium thiocyanate with a solution of potassium platinosochloride1 ,k#b,pt,cl#d1 they form a double thiocyanate1 ,pt,k#b7;,,cns7#d1 which is easily soluble in water and alcohol1 crystallises in red prisms1 and gives an orange-coloured solution1 which precipitates salts of the heavy metals4 ,the action of sulphuric acid on the lead salt of the same type gives the acid itself1 ,pt,h#b7,,scn7#d1 which corresponds with these salts4 ,the type of these compounds is evidently the same as that of the cyanides4 7,b7 ,platinous chloride1 ,pt,cl#b1 which is insoluble in water1 forms double salts with the metallic chlorides4 ,these double chlorides are soluble in water1 and capable of crystallising4 ,hence when a hydrochloric acid solution of platinous chloride is mixed with solutions of metallic salts and evaporated it forms crystalline salts of a red or yellow colour4 ,thus1 for example1 the potassium salt1 ,pt,k#b;,cl#d1 is red1 and easily soluble in water2 the sodium salt is also soluble in alcohol2 the barium salt1 ,pt,ba,cl#d1c;,h#b,o1 is soluble in water1 but the silver salt1 ,pt,ag#b;,cl#d1 is insoluble in water1 and may be used for obtaining the remaining salts by means of double decomposition with their chlorides4 7,c7 ,a remarkable example of the complex compounds of platinum was observed by ,schtzenberger 7#ahfh74 ,he showed that finely-divided platinum in the presence of chlorine and carbonic oxide at #bej-cjj gives phosgene and a volatile compound containing platinum4 ,the same substance is formed by the action of carbonic oxide on platinous chloride4 ,it decomposes with an explosion in contact with water4 ,carbon tetrachloride dissolves a portion of this substance1 and on evaporation gives crystals of #b,pt,cl#b1c;,,co1 whilst the compound ,pt,cl#b1b;,,co remains undissolved4 ,when fused and sublimed it gives yellow needles of ,pt,cl#b1;,,co1 and in the presence of an excess of carbonic oxide ,pt,cl#b1b;,,co is formed4 ,these compounds are fusible 7the first at #bej1 the second at #adb1 and the third at #aie74 ,in this case 7as in the double cyanides7 combination takes place1 because both carbonic oxide and platinous chloride are unsaturated compounds capable of further combination4 ,the carbon tetrachloride solution absorbs ,,nh#c and gives ,pt,cl#b1;,,co1#b,,nh#c1 and ,pt,cl#b1b;,,co1#b,,nh#c1 and these substances are analogous 7,foerster1 ,zeisel1 ,jrgensen7 to similar compounds containing complex amines 7for instance1 pyridine1 ,c#e;,h#e,n71 instead of ,,nh#c1 and ethylene1 c41 instead of ,,co1 so that here we have a whole series of complex platino-compounds4 ,the compound ,pt,cl#b;,,co dissolves in hydrochloric acid without change1 and the solution disengages all the carbonic oxide when ,,kcn is added to it1 which shows that those forces which bind #b molecules of ,,kcn to ,pt,cl#b can also bind the molecule ,,co1 or #b molecules of ,,co4 ,when the hydrochloric acid solution of ,pt,cl#b;,,co is mixed with a solution of sodium acetate or acetic acid1 it gives a precipitate of ,pt,o,c,o1 i4e4 the ,cl#b is replaced by oxygen 7probably because the acetate is decomposed by water74 ,this oxide1 ,pt,o,c,o1 splits up into ,pt ,,co#b at #cej4 ,pt,s,c,o is obtained by the action of sulphuretted hydrogen upon ,pt,cl#b;,,co4 ,all this leads to the conclusion that the group ,pt,c,o is able to assimilate ,x#b ,cl#b1 ,s1 ,o1 c4 7,mylius1 ,foerster1 #ahia74 ,pullinger 7#ahia71 by igniting spongy platinum at #bej1 first in a stream of chlorine1 and then in a stream of carbonic oxide1 obtained 7besides volatile products7 a non-volatile yellow substance which remained unchanged in air and disengaged chlorine and phosgene gas when ignited2 its composition was ,pt,cl#f7;,,co7#b1 which apparently proves it to be a compound of ,pt,cl#b and #b;,c,o,cl#b1 as ,pt,cl#b is able to combine with oxychlorides1 and forms somewhat stable compounds4 7,d7 ,the faculty of platinous chloride for forming stable compounds with divers substances shows itself in the formation of the compound ,pt,cl#b1,p,cl#c by the action of phosphorus pentachloride at #bej on platinum powder 7,pd reacts in a similar manner1 according to ,fink1 #ahib74 ,the product contains both phosphorus pentachloride and platinum1 whilst the presence of ,pt,cl#b is shown in the fact that the action of water produces chlorplatino-phosphorous acid1 ,pt,cl#b,p7,,oh7#c4 7,e7 ,after the cyanides1 the double salts of platinum formed by sulphurous acid are most distinguished for their stability and characteristic properties4 ,this is all the more instructive1 as sulphurous acid is only feebly energetic1 and1 moreover1 in these1 as in all its compounds1 it exhibits a dual reaction4 ,the salts of sulphurous acid1 ,r#b,,so#c1 either react as salts of a feeble bibasic acid1 where the group ,,so#c presents itself as bivalent1 and consequently equal to ,x#b1 or else they react after the manner of salts of a monobasic acid containing the same residue1 ,,rso#c1 as occurs in the salts of sulphuric acid4 ,in sulphurous acid this residue is combined with hydrogen1 ,h7,,so#c;,h71 whilst in sulphuric acid it is united with the aqueous residue 7hydroxyl71 ,,oh7,,so#c;,h74 ,these two forms of action of the sulphites appear in their reactions with the platinum salts--that is to say1 salts of both kinds are formed1 and they both correspond with the type ,pt,h#b,x#d4 ,the one series of salts contain ,pt,h#b7,,so#c7b1 and their reactions are due to the bivalent residue of sulphurous acid1 which replaces ,x#b4 ,the others1 which have the composition ,pt,r#b7,,so#c;,h7#d1 contain sulphoxyl4 ,the latter salts will evidently react like acids2 they are formed simultaneously with the salts of the first kind1 and pass into them4 ,these salts are obtained either by directly dissolving platinous oxide in water containing sulphurous acid1 or by passing sulphurous anhydride into a solution of platinous chloride in hydrochloric acid4 ,if a solution of platinous chloride or platinous oxide in sulphurous acid be saturated with sodium carbonate1 it forms a white1 sparingly soluble precipitate containing ,pt,na#b7,,so#c,na7#d1g;,h#b,o4 ,if this precipitate be dissolved in a small quantity of hydrochloric acid and left to evaporate at the ordinary temperature1 it deposits a salt of the other type1 ,pt,na#b7,,so#c7b1;,h#b,o1 in the form of a yellow powder1 which is sparingly soluble in water4 ,the potassium salt analogous to the first salt1 ,pt,k#b7,,so#c,k7#d1b;,h#b,o1 is precipitated by passing sulphurous anhydride into a solution of potassium sulphite in which platinous oxide is suspended4 ,a similar salt is known for ammonium1 and with hydrochloric acid it gives a salt of the second kind1 ,pt7,,nh#d7b7,,so#c7b1;,h#b,o4 ,if ammonio-chloride of platinum be added to an aqueous solution of sulphurous anhydride1 it is first deoxidised1 and chlorine is evolved1 forming a salt of the type ,pt,x#b2 a double decomposition then takes place with the ammonium sulphite1 and a salt of the composition ,pt7,,nh#d7b;,cl#c7,,so#c;,h7 is formed 7in a desiccator74 ,the acid character of this substance is explained by the fact that it contains the elements ,,so#c;,h--sulphoxyl1 with the hydrogen not yet displaced by a metal4 ,on saturating a solution of this acid with potassium carbonate it gives orange-coloured crystals of a potassium salt of the composition ,pt7,,nh#d7b;,cl#c7,,so#c,k74 ,here it is evident that an equivalent of chlorine in ,pt7,,nh#d7b7;,cl#d is replaced by the univalent residue of sulphurous acid4 ,among these salts1 that of the composition ,pt7,,nh#d7b7;,cl#b7,,so#c;,h7#b1;,h#b,o is very readily formed1 and crystallises in well-formed colourless crystals2 it is obtained by dissolving ammonium platinosochloride1 ,pt7,,nh#d7b;,cl#d1 in an aqueous solution of sulphurous acid4 ,the difficulty with which sulphurous anhydride and platinum are separated from these salts indicates the same basic character in these compounds as is seen in the double cyanides of platinum4 ,in their passage into a complex salt1 the metal platinum and the group ,,so#b modify their relations 7compared with those of ,pt,x#b or ,,so#b,x#b71 just as the chlorine in the salts ,k,cl,o1 ,k,cl,o#c1 and ,k,cl,o#d is modified in its relations as compared with hydrochloric acid or potassium chloride4 7,f7 ,no less characteristic are the platinonitrites formed by platinous oxide4 ,they correspond with nitrous acid1 whose salts1 ,,rno#b1 contain the univalent radicle1 ,,no#b1 which is capable of replacing chlorine1 and therefore the salts of this kind should form a common type ,pt,r#b7,,no#b7d1 and such a salt of potassium has actually been obtained by mixing a solution of potassium platinosochloride with a solution of potassium nitrite1 when the liquid becomes colourless1 especially if it be heated1 which indicates the change in the chemical distribution of the elements4 ,as the liquid decolorises it gradually deposits sparingly soluble1 colourless prisms of the potassium salt ,k#b,pt7,,no#b7d1 which does not contain any water4 ,with silver nitrate a solution of this salt gives a precipitate of silver platinonitrite1 ,pt,ag#b7,,no#b7d4 ,the silver of this salt may be replaced by other metals by means of double decomposition with metallic chlorides4 ,the sparingly soluble barium salt1 when treated with an equivalent quantity of sulphuric acid1 gives a soluble acid1 which separates1 under the receiver of an air-pump1 in red crystals2 this acid has the composition ,pt,h#b7,,no#b7d4 ,to the potassium salt1 ,k#b,pt7,,no#b7d1 there correspond 7,vzes1 #ahib7 ,k#b,pt7,,no#b7d;,br#b and ,k#b,pt7,,no#b7d;,cl#b and other compounds of the same type ,k#b,pt,x#f1 where ,x is partly replaced by ,cl or ,br and partly by 7,,no#b71 showing a transition towards the type of the double salts like the platino-ammoniacal salts4 7,the corresponding double sodium nitrite salt of cobalt is soluble in water1 while the ,k1,,nh#d and many other salts are insoluble in water1 as ,i was informed by ,prof4 ,k4 ,winkler in #ahid74 ,in all the preceding complex compounds of ,pt we see a common type ,pt,x#b1b,,mx 7i4e4 of double salts corresponding to ,pt,o7 or ,pt,m#b,x#d ,pt7,,mx#b7b1 corresponding to ,pt7,,ho7#b with the replacement of ,o by its equivalent ,x#b4 ,two other facts must also be noted4 ,in the first place these ,x's generally correspond to elements 7like chlorine7 or groups 7like ,,cn1 ,,no#b1 ,,so#c1 c471 which are capable of further combination4 ,in the second place all the compounds of the type ,pt,m#b,x#d are capable of combining with chlorine or similar elements1 and thus passing into compounds of the types ,pt,x#c or ,pt,x#d4 ,ammonia1 like potassium cyanide1 has the faculty of easily reacting with platinum dichloride1 forming compounds similar to the platinocyanide and cobaltia compounds1 which are comparatively stable4 ,but as ammonia does not contain any hydrogen easily replaceable by metals1 and as ammonia itself is able to combine with acids1 the ,pt,x#b plays1 as it were1 the part of an acid with reference to the ammonia4 ,owing to the influence of the ammonia1 the ,x#b in the resultant compound will represent the same character as it has in ammoniacal salts2 consequently1 the ammoniacal compounds produced from ,pt,x#b will be salts in which ,x will be replaceable by various other haloids1 just as the metal is replaced in the cyanogen salts2 such is the nature of the platino-ammonium compounds4 ,pt,x#b forms compounds with #b,,nh#c and with #d,,nh#c1 and so also ,pt,x#d gives 7not directly from ,pt,x#d and ammonia1 but from the compounds of ,pt,x#b by the action of chlorine1 c47 similar compounds with #b,,nh#c and with #d,,nh#c4ab #ab ,the platinum salt and ammonia1 when once combined together1 are no longer subject to their ordinary reactions but form compounds which are comparatively very stable4 ,the question at once suggests itself to all who are acquainted with these phenomena1 as to what is the relation of the elements contained in these compounds4 ,the first explanation is that these compounds are salts of ammonium in which the hydrogen is partially replaced by platinum4 ,this is the view1 with certain shades of difference1 held by many respecting the platino-ammonium compounds4 ,they were regarded in this light by ,gerhardt1 ,schiff1 ,kolbe1 ,weltzien1 and many others4 ,if we suppose the hydrogen in #b,,nh#d,x to be replaced by bivalent platinum 7as in the salts ,pt,x#b71 we shall obtain ,,nh#c ,x ,pt ,,nh#c ,x --that is1 the compound ,pt,x#b1b,,nh#c4 ,the compound with #d,,nh#c will then be represented by a further substitution of the hydrogen in ammonia by ammonium itself--i4e4 as ,,nh#b7,,nh#d,x7#b,pt or ,pt,x#b1d,,nh#c4 ,a modification of this view is found in that representation of compounds of this kind which is based on atomicity4 ,as platinum in ,pt,x#b is bivalent1 has two affinities1 and ammonia1 ,,nh#c1 is also bivalent1 because nitrogen is quinquivalent and is here only combined with ,h#c1 it is evident what bonds should be represented in ,pt,x#b1b,,nh#c and in ,pt,x#b1d,,nh#c4 ,in the former1 ,pt7,,nh#c;,cl7#b1 the nitrogen of each atom of ammonia is united by three affinities with ,h#c1 by one with platinum1 and by the fifth with chlorine4 ,the other compound is ,pt7,,nh#c4,,nh#c;,cl7#b--that is1 the ,n is united by one affinity with the other ,n1 whilst the remaining bonds are the same as in the first salt4 ,it is evident that this union or chain of ammonias has no obvious limit1 and the most essential fault of such a mode of representation is that it does not indicate at all what number of ammonias are capable of being retained by platinum4 ,moreover1 it is hardly possible to admit the bond between nitrogen and platinum in such stable compounds1 for these kinds of affinities are1 at all events1 feeble1 and cannot lead to stability1 but would rather indicate explosive and easily-decomposed compounds4 ,moreover1 it is not clear why this platinum1 which is capable of giving ,pt,x#d1 does not act with its remaining affinities when the addition of ammonia to ,pt,x#b takes place4 ,these1 and certain other considerations which indicate the imperfection of this representation of the structure of the platino-ammonium salts1 cause many chemists to incline more to the representations of ,berzelius1 ,claus1 ,gibbs1 and others1 who suppose that ,,nh#c is able to combine with substances1 to adjoin itself or pair itself with them 7this kind of combination is called ',paarung'7 without altering the fundamental capacity of a substance for further combinations4 ,thus1 in ,pt,x#b1b,,nh#c1 the ammonia is the associate of ,pt,x#b1 as is expressed by the formula ,n#b;,h#f,pt,x#b4 ,without enlarging on the exposition of the details of this doctrine1 we will only mention that it1 like the first1 does not render it possible to foresee a limit to the compounds with ammonia2 it isolates compounds of this kind into a special and artificial class2 does not show the connection between compounds of this and of other kinds1 and therefore it essentially only expresses the fact of the combination with ammonia and the modification in its ordinary reactions4 ,for these reasons we do not hold to either of these proposed representations of the ammonio-platinum compounds1 but regard them from the point of view cited above with reference to double salts and water of crystallisation--that is1 we embrace all these compounds under the representation of compounds of complex types4 ,the type of the compound ,pt,x#b1b,,nh#c is far more probably the same as that of ,pt,x#b1b,z--i4e4 as ,pt,x#d1 or1 still more accurately and truly1 it is a compound of the same type as ,pt,x#b1b,,kx or ,pt,x#b1b;,h#b,o1 c4 ,although the platinum first entered into ,pt,k#b,x#d as the type ,pt,x#b1 yet its character has changed in the same manner as the character of sulphur changes when from ,,so#b the compound ,,so#b7,,oh7#b is obtained1 or when ,k,cl,o#d1 the higher form1 is obtained from ,k,cl4 ,for us as yet there is no question as to what affinities hold ,x#b and what hold #b,,nh#c1 because this is a question which arises from the supposition of the existence of different affinities in the atoms1 which there is no reason for taking as a common phenomenon4 ,it seems to me that it is most important as a commencement to render clear the analogy in the formation of various complex compounds1 and it is this analogy of the ammonia compounds with those of water of crystallisation and double salts that forms the main object of the primary generalisation4 ,we recognise in platinum1 at all events1 not only the four affinities expressed in the compound ,pt,cl#d1 but a much larger number of them1 if only the summation of affinities is actually possible4 ,thus1 in sulphur we recognise not two but a much greater number of affinities2 it is clear that at least six affinities can act4 ,so also among the analogues of platinum3 osmic anhydride1 ,os,o#d1 ,ni7,,co7#d1 ,pt,h#b;,cl#f1 c4 indicate the existence of at least eight affinities2 whilst1 in chlorine1 judging from the compound ,k,cl,o#d ,cl,o#c7,,ok7 ,cl,x#g1 we must recognise at least seven affinities1 instead of the one which is accepted4 ,the latter mode of calculating affinities is a tribute to that period of the development of science when only the simplest hydrogen compounds were considered1 and when all complex compounds were entirely neglected 7they were placed under the class of molecular compounds74 ,this is insufficient for the present state of knowledge1 because we find that1 in complex compounds as in the most simple1 the same constant types or modes of equilibrium are repeated1 and the character of certain elements is greatly modified in the passage from the most simple into very complex compounds4 ,judging from the most complex platino-ammonium compounds ,pt,cl#d1d,,nh#c1 we should admit the possibility of the formation of compounds of the type ,pt,x#d,y#d1 where ,y#d #d,x#b #d,,nh#c1 and this shows that those forces which form such a characteristic series of double platinocyanides ,pt,k#b7;,,cn7#d1c;,h#b,o1 probably also determine the formation of the higher ammonia derivatives1 as is seen on comparing-- ,pt,cl#b ,,nh#c ,cl#b #c,,nh#c ,pt7,,cn7#b ,,kcn ,,kcn #c;,h#b,o4 ,moreover1 it is obviously much more natural to ascribe the faculty for combination with n,y to the whole of the acting elements--that is1 to ,pt,x#b or ,pt,x#d1 and not to platinum alone4 ,naturally such compounds are not produced with any ,y4 ,with certain ,x's there only combine certain ,y's4 ,the best known and most frequently-formed compounds of this kind are those with water--that is1 compounds with water of crystallisation4 ,compounds with salts are double salts2 also we know that similar compounds are also frequently formed by means of ammonia4 ,salts of zinc1 ,zn,x#b1 copper1 ,cu,x#b1 silver1 ,ag,x1 and many others give similar compounds1 but these and many other ammonio-metallic saline compounds are unstable1 and readily part with their combined ammonia1 and it is only in the elements of the platinum group and in the group of the analogues of iron1 that we observe the faculty to form stable ammonio-metallic compounds4 ,it must be remembered that the metals of the platinum and iron groups are able to form several high grades of oxidation which have an acid character1 and consequently in the lower degrees of combination there yet remain affinities capable of retaining other elements1 and they probably retain ammonia1 and hold it the more stably1 because all the properties of the platinum compounds are rather acid than basic--that is1 ,pt,xn recalls rather ,,hx or ,sn,xn or ,,cxn than ,,kx1 ,ca,x#b1 ,ba,x#b1 c41 and ammonia naturally will rather combine with an acid than with a basic substance4 ,further1 a dependence1 or certain connection of the forms of oxidation with the ammonia compounds1 is seen on comparing the following compounds3 ,pd,cl#b1b,,nh#c1;,h#b,o ,pd,cl#b1d,,nh#c1;,h#b,o ,pt,cl#b1b,,nh#c ,pt,cl#d1d,,nh#c ,rh,cl#c1e,,nh#c ,ru,cl#b1d,,nh#c1c;,h#b,o ,ir,cl#c1e,,nh#c ,os,cl#b1d,,nh#c1b;,h#b,o ,we know that platinum and palladium give compounds of lower types than iridium and rhodium1 whilst ruthenium and osmium give the highest forms of oxidation2 this shows itself in this case also4 ,we have purposely cited the same compounds with #d,,nh#c for osmium and ruthenium as we have for platinum and palladium1 and it is then seen that ,ru and ,os are capable of retaining #b;,h#b,o and #c;,h#b,o1 besides ,cl#b and ,,nh#c1 which the compounds of platinum and palladium are unable to do4 ,the same ideas which were developed in ,note #ce1 ,chapter ,,xxii4 respecting the cobaltia compounds are perfectly applicable to the present case1 i4e4 to the platinia compounds or ammonia compounds of the platinum metals1 among which ,rh and ,ir give compounds which are perfectly analogous to the cobaltia compounds4 ,iridium and rhodium1 which easily give compounds of the type ,,rx#c1 give compounds 7,claus7 of the type ,ir,x#c1e,,nh#c1 of a rose colour1 and ,rh,x#c1e,,nh#c1 of a yellow colour4 ,jrgensen1 in his researches on these compounds1 showed their entire analogy with the cobalt compounds1 as was to be expected from the periodic system4 ,if ammonia acts on a boiling solution of platinous chloride in hydrochloric acid1 it produces the green salt of ,magnus 7#ahbi71 ,pt,cl#b1b,,nh#c1 insoluble in water and hydrochloric acid4 ,but1 judging by its reactions1 this salt has twice this formula4 ,thus1 ,gros 7#ahcg71 on boiling ,magnus's salt with nitric acid1 observed that half the chlorine was replaced by the residue of nitric acid and half the platinum was disengaged3 #b,pt,cl#b7,,nh#c7b #b;,,hno#c ,pt,cl#b7,,no#c7b7,,nh#c7d #b,pt,cl#b4 ,the ,gros's salt thus obtained1 ,pt,cl#b7,,no#c7bd,,nh#c 7if ,magnus's salt belongs to the type ,pt,x#b1 then ,gros's salt belongs to the type ,pt,x#d71 is soluble in water1 and the elements of nitric acid1 but not the chlorine1 contained in it are capable of easily submitting themselves to double saline decomposition4 ,thus silver nitrate does not enter into double decomposition with the chlorine of ,gros's salt4 ,most instructive was the circumstance that ,gros1 by acting on his salt with hydrochloric acid1 succeeded in substituting the residue of nitric acid in it by chlorine1 and the chlorine thus introduced1 easily reacted with silver nitrate4 ,thus it appeared that ,gros's salt contained two varieties of chlorine--one which reacts readily1 and the other which reacts with difficulty4 ,the composition of ,gros's first salt is ,pt,cl#b7,,nh#c7d7,,no#c7b2 it may be converted into ,pt,cl#b7,,nh#c7d7,,so#d71 and in general into ,pt,cl#b7,,nh#c7d,x#b4ac #ac ,subsequently1 a whole series of such compounds was obtained with various elements in the place of the 7non-reacting7 chlorine1 and nevertheless they1 like the chlorine1 reacted with difficulty1 whilst the second portion of the ,x's introduced into such salts easily underwent reaction4 ,this formed the most important reason for the interest which the study of the composition and structure of the platino-ammonium salts subsequently presented to many chemists1 such as ,reiset1 ,blomstrand1 ,peyrone1 ,raeffski1 ,gerhardt1 ,buckton1 ,clve1 ,thomsen1 ,jrgensen1 ,kournakoff1 ,verner1 and others4 ,the salts ,pt,x#d1b,,nh#c1 discovered by ,gerhardt1 also exhibited several different properties in the two pairs of ,x's4 ,in the remaining platino-ammonium salts all the ,x's appear to react alike4 ,the quality of the ,x's1 retainable in the platino-ammonium salts1 may be considerably modified1 and they may frequently be wholly or partially replaced by hydroxyl4 ,for example1 the action of ammonia on the nitrate of ,gerhardt's base1 ,pt7,,no#c7d1b,,nh#c1 in a boiling solution1 gradually produces a yellow crystalline precipitate which is nothing else than a basic hydrate or alkali1 ,pt7,,oh7#d1b,,nh#c4 ,it is sparingly soluble in water1 but gives directly soluble salts ,pt,x#d1b,,nh#c with acids4 ,the stability of this hydroxide is such that potash does not expel ammonia from it1 even on boiling1 and it does not change below #acj4 ,similar properties are shown by the hydroxide ,pt7,,oh7#b1b,,nh#c and the oxide ,pt,o1#b,,nh#c of ,reiset's second base4 ,but the hydroxides of the compounds containing #d,,nh#c are particularly remarkable4 ,the presence of ammonia renders them soluble and energetic4 ,the brevity of this work does not permit us1 however1 to mention many interesting particulars in connection with this subject4 ,the salt of ,magnus when boiled with a solution of ammonia gives the salt 7of ,reiset's first base7 ,pt,cl#b7,,nh#c7d1 and this1 when treated with bromine1 forms the salt ,pt,cl#b;,br#b7,,nh#c7d1 which has the same composition and reactions as ,gros's salt4 ,to ,reiset's salts there corresponds a soluble1 colourless1 crystalline hydroxide1 ,pt7,,oh7#b7,,nh#c7d1 having the properties of a powerful and very energetic alkali2 it attracts carbonic anhydride from the atmosphere1 precipitates metallic salts like potash1 saturates active acids1 even sulphuric1 forming colourless 7with nitric1 carbonic1 and hydrochloric acids71 or yellow 7with sulphuric acid71 salts of the type ,pt,x#b7,,nh#c7d4ad ,the comparative stability 7for instance1 as compared with ,ag,cl and ,,nh#c7 of such compounds1 and the existence of many other compounds analogous to them1 endows them with a particular chemical interest4 ,thus ,kournakoff 7#ahhi7 obtained a series of corresponding compounds containing thiocarbamide1 ,,csn#b;,h#d1 in the place of ammonia1 ,pt,cl#b1d;,,csn#b;,h#d1 and others corresponding with ,reiset's salts4 ,hydroxylamine1 and other substances corresponding with ammonia1 also give similar compounds4 ,the common properties and composition of such compounds show their entire analogy to the cobaltia compounds 7especially for ruthenium and iridium7 and correspond to the fact that both the platinum metals and cobalt occur in the same1 eighth1 group4 #ad ,hydroxides are known corresponding with ,gros's salts1 which contain one hydroxyl group in the place of that chlorine or haloid which in ,gros's salts reacts with difficulty1 and these hydroxides do not at once show the properties of alkalis1 just as the chlorine which stands in the same place does not react distinctly2 but still1 after the prolonged action of acids1 this hydroxyl group is also replaced by acids4 ,thus1 for example1 the action of nitric acid on ,pt7,,no#c7b;,cl#b1d,,nh#c causes the non-active chlorine to react1 but in the product all the chlorine is not replaced by ,,no#c1 but only half1 and the other half is replaced by the hydroxyl group3 ,pt7,,no#c7b;,cl#b1d,,nh#c ,,hno#c ,h#b,o ,pt7,,no#c7c7,,oh71#d,,nh#c #b;,h,cl2 and this is particularly characteristic1 because here the hydroxyl group has not reacted with the acid--an evident sign of the non-alkaline character of this residue4 ,i think it may be well to call attention to the fact that the composition of the ammonio-metallosalts very often exhibits a correspondence between the amount of ,x's and the amount of ,,nh#c1 of such a nature that we find they contain either ,,xnh#c or the grouping ,x#b,,nh#c2 for example1 ,pt7,,xnh#c7b and ,pt7,x#b,,nh#c7b1 ,co7,x#b,,nh#c7c1 ,pt7,,xnh#c7d1 c4 ,judging from this1 the view of the constitution of the double cyanides of platinum given in ,note #aa finds some confirmation here1 but1 in my opinion1 all questions respecting the composition 7and structure7 of the ammoniacal1 double1 complex1 and crystallisation compounds stand connected with the solution of questions respecting the formation of compounds of various degrees of stability1 among which a theory of solutions must be included1 and therefore ,i think that the time has not yet come for a complete generalisation of the data which exist for these compounds2 and here ,i again refer the reader to ,prof4 ,kournakoff's work cited in ,chapter ,,xxii41 ,note #ce4 ,however1 we may add a few individual remarks concerning the platinia compounds4 ,to the common properties of the platino-ammonium salts1 we must add not only their stability 7feeble acids and alkalis do not decompose them1 the ammonia is not evolved by heating1 c471 but also the fact that the ordinary reactions of platinum are concealed in them to as great an extent as those of iron in the ferricyanides4 ,thus neither alkalis nor hydrogen sulphide will separate the platinum from them4 ,for example1 sulphuretted hydrogen in acting on ,gros's salts gives sulphur1 removes half the chlorine by means of its hydrogen1 and forms salts of ,reiset's first base4 ,this may be understood or explained by considering the platinum in the molecule as covered1 walled up by the ammonia1 or situated in the centre of the molecule1 and therefore inaccessible to reagents4 ,on this assumption1 however1 we should expect to find clearly-expressed ammoniacal properties1 and this is not the case4 ,thus ammonia is easily decomposed by chlorine1 whilst in acting on the platino-ammonium salts containing ,pt,x#b and #b,,nh#c or #d,,nh#c1 chlorine combines and does not destroy the ammonia2 it converts ,reiset's salts into those of ,gros and ,gerhardt4 ,thus from ,pt,x#b1b,,nh#c there is formed ,pt,x#b;,cl#b1b,,nh#c1 and from ,pt,x#b1d,,nh#c the salt of ,gros's base ,pt,x#b;,cl#b1d,,nh#c4 ,this shows that the amount of chlorine which combines is not dependent on the amount of ammonia present1 but is due to the basic properties of platinum4 ,owing to this some chemists suppose the ammonia to be inactive or passive in certain compounds4 ,it appears to me that these relations1 these modifications1 in the usual properties of ammonia and platinum are explained directly by their mutual combination4 ,sulphur1 in sulphurous anhydride1 ,,so#b1 and hydrogen sulphide1 ,,sh#b1 is naturally one and the same1 but if we only knew of it in the form of hydrogen sulphide1 then1 having obtained it in the form of sulphurous anhydride1 we should consider its properties as hidden4 ,the oxygen in magnesia1 ,mg,o1 and in nitric peroxide1 ,,no#b1 is so different that there is no resemblance4 ,arsenic no longer reacts in its compounds with hydrogen as it reacts in its compounds with chlorine1 and in their compounds with nitrogen all metals modify both their reactions and their physical properties4 ,we are accustomed to judge the metals by their saline compounds with haloid groups1 and ammonia by its compounds with acid substances1 and here1 in the platino-compounds1 if we assume the platinum to be bound to the entire mass of the ammonia--to its hydrogen and nitrogen--we shall understand that both the platinum and ammonia modify their characters4 ,far more complicated is the question why a portion of the chlorine 7and other haloid simple and complex groups7 in ,gros's salts acts in a different manner from the other portion1 and why only half of it acts in the usual way4 ,but this also is not an exclusive case4 ,the chlorine in potassium chlorate or in carbon tetrachloride does not react with the same ease with metals as the chlorine in the salts corresponding with hydrochloric acid4 ,in this case it is united to oxygen and carbon1 whilst in the platino-ammonium compounds it is united partly to platinum and partly to the platino-ammonium group4 ,many chemists1 moreover1 suppose that a part of the chlorine is united directly to the platinum and the other part to the nitrogen of the ammonia1 and thus explain the difference of the reactions2 but chlorine united to platinum reacts as well with a silver salt as the chlorine of ammonium chloride1 ,,nh#d;,cl1 or nitrosyl chloride1 ,n,o,cl1 although there is no doubt that in this case there is a union between the chlorine and nitrogen4 ,hence it is necessary to explain the absence of a facile reactive capacity in a portion of the chlorine by the conjoint influence of the platinum and ammonia on it1 whilst the other portion may be admitted as being under the influence of the platinum only1 and therefore as reacting as in other salts4 ,by admitting a certain kind of stable union in the platino-ammonium grouping1 it is possible to imagine that the chlorine does not react with its customary facility1 because access to a portion of the atoms of chlorine in this complex grouping is difficult1 and the chlorine union is not the same as we usually meet in the saline compounds of chlorine4 ,these are the grounds on which we1 in refuting the now accepted explanations of the reactions and formation of the platino-compounds1 pronounce the following opinion as to their structure4 ,in characterising the platino-ammonium compounds1 it is necessary to bear in mind that compounds which already contain ,pt,x#d do not combine directly with ,,nh#c1 and that such compounds as ,pt,x#d1d,,nh#c only proceed from ,pt,x#b1 and therefore it is natural to conclude that those affinities and forces which cause ,pt,x#b to combine with ,x#b also cause it to combine with #b,,nh#c4 ,and having the compound ,pt,x#b1b,,nh#c1 and supposing that in subsequently combining with ,cl#b it reacts with those affinities which produce the compounds of platinic chloride1 ,pt,cl#d1 with water1 potassium chloride1 potassium cyanide1 hydrochloric acid1 and the like1 we explain not only the fact of combination1 but also many of the reactions occurring in the transition of one kind of platino-ammonium salts into another4 ,thus by this means we explain the fact that 7#a7 ,pt,x#b1b,,nh#c combines with #b,,nh#c1 forming salts of ,reiset's first base2 7#b7 and the fact that this compound 7represented as follows for distinctness71 ,pt,x#b1b,,nh#c1b,,nh#c1 when heated1 or even when boiled in solution1 again passes into ,pt,x#b1b,,nh#c 7which resembles the easy disengagement of water of crystallisation1 c472 7#c7 the fact that ,pt,x#b1b,,nh#c is capable of absorbing1 under the action of the same forces1 a molecule of chlorine1 ,pt,x#b1b,,nh#c1;,cl#b1 which it then retains with energy1 because it is attracted1 not only by the platinum1 but also by the hydrogen of the ammonia2 7#d7 the fact that this chlorine held in this compound 7of ,gerhardt7 will have a position unusual in salts1 which will explain a certain 7although very feebly-marked7 difficulty of reaction2 7#e7 the fact that this does not exhaust the faculty of platinum for further combination 7we need only recall the compound ,pt,cl#d1b;,h,cl1#af;,h#b,o71 and that therefore both ,pt,x#b1b,,nh#c1;,cl#b and ,pt,x#b1b,,nh#c1b,,nh#c are still capable of combination1 whence the latter1 with chlorine1 gives ,pt,x#b1b,,nh#c1b,,nh#c1;,cl#b1 after the type of ,pt,x#d,y#d 7and perhaps higher72 7#f7 the fact that ,gros's compounds thus formed are readily reconverted into the salts of ,reiset's first base when acted on by reducing agents2 7#g7 the fact that in ,gros's salts1 ,pt,x#b1b,,nh#c7,,nh#c,x7#b1 the newly-attached chlorine or haloid will react with difficulty with salts of silver1 c41 because it is attached both to the platinum and to the ammonia1 for both of which it has an attraction2 7#h7 the fact that the faculty for further combination is not even yet exhausted in the type of ,gros's salts1 and that we actually have a compound of ,gros's chlorine salt with platinous chloride and with platinic chloride2 the salt ,pt,s,o#d1b,,nh#c1b,,nh#c1,,so#d combines further also with ,h#b,o2 7#i7 the fact that such a faculty of combination with new molecules is naturally more developed in the lower forms of combination than in the higher4 ,hence the salts of ,reiset's first base--for example1 ,pt,cl#b1b,,nh#c1b,,nh#c--;both combine with water and give precipitates 7soluble in water but not in hydrochloric acid7 of double salts with many salts of the heavy metals--for example1 with lead chloride1 cupric chloride1 and also with platinic and platinous chlorides 7,buckton's salts74 ,the latter compounds will have the composition ,pt,cl#b1b,,nh#c1b,,nh#c1,pt,cl#b--that is1 the same composition as the salts of ,reiset's second base1 but it cannot be identical with it4 ,such an interesting case does actually exist4 ,the first salt1 ,pt,cl#b1d,,nh#c1,pt,cl#b1 is green1 insoluble in water and in hydrochloric acid1 and is known as ,magnus's salt1 and the second1 ,pt,cl#b1b,,nh#c1 is ,reiset's yellow1 sparingly soluble 7in water74 ,they are polymeric1 namely1 the first contains twice the number of elements held in the second1 and at the same time they easily pass into each other4 ,if ammonia be added to a hot hydrochloric acid solution of platinous chloride1 it forms the salt ,pt,cl#b1d,,nh#c1 but in the presence of an excess of platinous chloride it gives ,magnus's salt4 ,on boiling the latter in ammonia it gives a colourless soluble salt of ,reiset's first base1 ,pt,cl#b1d,,nh#c1 and if this be boiled with water1 ammonia is disengaged1 and a salt of ,reiset's second base1 ,pt,cl#b1b,,nh#c1 is obtained4 ,a class of platino-ammonium isomerides 7obtained by ,millon and ,thomsen7 are also known4 ,buckton's salts--for example1 the copper salt--were obtained by them from the salts of ,reiset's first base1 ,pt,cl#b1d,,nh#c1 by treatment with a solution of cupric chloride1 c41 and therefore1 according to our method of expression1 ,buckton's copper salt will be ,pt,cl#b1d,,nh#c1;,cu,cl#b4 ,this salt is soluble in water1 but not in hydrochloric acid4 ,in it the ammonia must be considered as united to the platinum4 ,but if cupric chloride be dissolved in ammonia1 and a solution of platinous chloride in ammonium chloride is added to it1 a violet precipitate is obtained of the same composition as ,buckton's salt1 which1 however1 is insoluble in water1 but soluble in hydrochloric acid4 ,in this a portion1 if not all1 of the ammonia must be regarded as united to the copper1 and it must therefore be represented as ,cu,cl#b1d,,nh#c1,pt,cl#b4 ,this form is identical in composition but different in properties 7is isomeric7 with the preceding salt 7,buckton's74 ,the salt of ,magnus is intermediate between them1 ,pt,cl#b1d,,nh#c1,pt,cl#b2 it is insoluble in water and hydrochloric acid4 ,these and certain other instances of isomeric compounds in the series of the platino-ammonium salts throw a light on the nature of the compounds in question1 just as the study of the isomerides of the carbon compounds has served and still serves as the chief cause of the rapid progress of organic chemistry4 ,in conclusion1 we may add that 7according to the law of substitution7 we must necessarily expect all kinds of intermediate compounds between the platino and analogous ammonia derivatives on the one hand1 and the complex compounds of nitrous acid on the other4 ,perhaps the instance of the reaction of ammonia upon osmic anhydride1 ,os,o#d1 observed by ,fritsche1 ,frmy1 and others1 and more fully studied by ,joly 7#ahia71 belongs to this class4 ,the latter showed that when ammonia acts upon an alkaline solution of ,os,o#d the reaction proceeds according to the equation3 ,os,o#d ,,kho ,,nh#c ,os,n,k,o#c #b;,h#b,o4 ,it might be imagined that in this case the ammonia is oxidised1 probably forming the residue of nitrous acid 7,,no71 while the type ,os,o#d is deoxidised into ,os,o#b1 and a salt1 ,os,o7,,no77,,ko71 of the type ,os,x#d is formed4 ,this salt crystallises well in light yellow octahedra4 ,it corresponds to osmiamic acid1 ,os,o7,,on77,,ho71 whose anhydride ,os,o7,,no7#b1 has the composition ,os#b,n#b,o#e1 which equals #b,os ,n#b,o#e to the same extent as the above-mentioned compound ,pt,c,o#b equals ,pt ,,co#b 7see ,note #aa74 ,,chapter ,,xxiv ,,copper1 ,,silver1 ,,and ,,gold ,that degree of analogy and difference which exists between iron1 cobalt1 and nickel repeats itself in the corresponding triad ruthenium1 rhodium1 and palladium1 and also in the heavy platinum metals1 osmium1 iridium1 and platinum4 ,these nine metals form ,group ,,viii4 of the elements in the periodic system1 being the intermediate group between the even elements of the large periods and the uneven1 among which we know zinc1 cadmium1 and mercury in ,group ,,ii4 ,copper1 silver1 and gold complete#a this transition1 because their properties place them in proximity to nickel1 palladium1 and platinum on the one hand1 and to zinc1 cadmium1 and mercury on the other4 ,just as ,zn1 ,cd1 and ,hg2 ,fe1 ,ru1 and ,os2 ,co1 ,rh1 and ,ir2 ,ni1 ,pd1 and ,pt1 resemble each other in many respects1 so also do ,cu1 ,ag1 and ,au4 ,thus1 for example1 the atomic weight of copper ,cu #fc1 and in all its properties it stands between ,ni #ei and ,zn #fe4 ,but as the transition from ,group ,,viii4 to ,group ,,ii41 where zinc is situated1 cannot be otherwise than through ,group ,i41 so in copper there are certain properties of the elements of ,group ,i4 ,thus it gives a suboxide1 ,cu#b,o1 and salts1 ,cu,x1 like the elements of ,group ,i41 although at the same time it forms an oxide1 ,cu,o1 and salts ,cu,x#b1 like nickel and zinc4 ,in the state of the oxide1 ,cu,o1 and the salts1 ,cu,x#b1 copper is analogous to zinc1 judging from the insolubility of the carbonates1 phosphates1 and similar salts1 and by the isomorphism1 and other characters4#b ,in the cuprous salts there is undoubtedly a great resemblance to the silver salts--thus1 for example1 silver chloride1 ,ag,cl1 is characterised by its insolubility and capacity of combining with ammonia1 and in this respect cuprous chloride closely resembles it1 for it is also insoluble in water1 and combines with ammonia and dissolves in it1 c4 ,its composition is also ,r,cl1 the same as ,ag,cl1 ,na,cl1 ,k,cl1 c41 and silver in many compounds resembles1 and is even isomorphous with1 sodium1 so that this again justifies their being brought together4 ,silver chloride1 cuprous chloride1 and sodium chloride crystallise in the regular system4 ,besides which1 the specific heats of copper and silver require that they should have the atomic weights ascribed to them4 ,to the oxides ,cu#b,o and ,ag#b,o there are corresponding sulphides ,ag#b,s and ,cu#b,s4 ,they both occur in nature in crystals of the rhombic system1 and1 what is most important1 copper glance contains an isomorphous mixture of them both1 and retains the form of copper glance with various proportions of copper and silver1 and therefore has the composition ,r#b,s where ,r ,cu1 ,ag4 #a ,the perfectly unique position held by copper1 silver1 and gold in the periodic system of the elements1 and the degree of affinity which is found between them1 is all the more remarkable1 as nature and practice have long isolated these metals from all others by having employed them--for example1 for coinage--and determined their relative importance and value in conformity with the order 7silver between copper and gold7 of their atomic weights1 c4 #b ,cupric sulphate contains #e molecules of water1 ,cu,s,o#d1e;,h#b,o1 and the isomorphous mixtures with ,zn,s,o#d1g;,h#b,o contain either #e or #g equivalents1 according to whether copper or zinc predominates 7,vol4 ,,ii4 p4 #f74 ,if there be a large proportion of copper1 and if the mixture contain #e;,h#b,o1 the form of the isomorphous mixture 7triclinic7 will be isomorphous with cupric sulphate1 ,cu,s,o#d1e;,h#b,o1 but if a large amount of zinc 7or magnesium1 iron1 nickel1 or cobalt7 be present the form 7rhombic or monoclinic7 will be nearly the same as that of zinc sulphate1 ,zn,s,o#d1g;,h#b,o4 ,supersaturated solutions of each of these salts crystallise in that form and with that amount of water which is contained in a crystal of one or other of the salts brought in contact with the solution 7,chapter ,,xiv41 ,note #bg74 ,notwithstanding the resemblance in the atomic composition of the cuprous compounds1 ,cu,x1 and silver compounds1 ,ag,x1 with the compounds of the alkali metals ,,kx1 ,na,x1 there is a considerable degree of difference between these two series of elements4 ,this difference is clearly seen in the fact that the alkali metals belong to those elements which combine with extreme facility with oxygen1 decompose water1 and form the most alkaline bases2 whilst silver and copper are oxidised with difficulty1 form less energetic oxides1 and do not decompose water1 even at a rather high temperature4 ,moreover1 they only displace hydrogen from very few acids4 ,the difference between them is also seen in the dissimilarity of the properties of many of the corresponding compounds4 ,thus cuprous oxide1 ,cu#b,o1 and silver oxide1 ,ag#b,o1 are insoluble in water3 the cuprous and silver carbonates1 chlorides1 and sulphates are also sparingly soluble in water4 ,the oxides of silver and copper are also easily reduced to metal4 ,this difference in properties is in intimate relation with that difference in the density of the metals which exists in this case4 ,the alkali metals belong to the lightest1 and copper and silver to the heaviest1 and therefore the distance between the molecules in these metals is very dissimilar--it is greater for the former than the latter 7tables in ,chapter ,,xv474 ,from the point of view of the periodic law1 this difference between copper and silver and such elements of ,group ,i4 as potassium and rubidium1 is clearly seen from the fact that copper and silver stand in the middle of those large periods 7for example1 ,k1 ,ca1 ,sc1 ,ti1 ,v1 ,cr1 ,mn1 ,fe1 ,co1 ,ni1 ,cu1 ,zn1 ,ga1 ,ge1 ,as1 ,se1 ,br7 which start with the true metals of the alkalis--that is to say1 the analogy and difference between potassium and copper are of the same nature as that between chromium and selenium1 or vanadium and arsenic4 ,copper is one of the few metals which have long been known in a metallic form4 ,the ,greeks and ,romans imported copper chiefly from the island of ,cyprus--whence its ,latin name1 cuprum4 ,it was known to the ancients before iron1 and was used1 especially when alloyed with other metals1 for arms and domestic utensils4 ,that copper was known to the ancients will be understood from the fact that it occurs1 although rarely1 in a native state1 and is easily extracted from its other natural compounds4 ,among the latter are the oxygen compounds of copper4 ,when ignited with charcoal1 they easily give up their oxygen to it1 and yield metallic copper2 hydrogen also easily takes up the oxygen from copper oxide when heated4 ,copper occurs in a native state1 sometimes in association with other ores1 in many parts of the ,urals and in ,sweden1 and in considerable masses in ,america1 especially in the neighbourhood of the great ,american lakes2 and also in ,chili1 ,japan1 and ,china4 ,the oxygen compounds of copper are also of somewhat common occurrence in certain localities2 in this respect certain deposits of the ,urals are especially famous4 ,the geological period of the ,urals 7,permian7 is characterised by a considerable distribution of copper ores4 ,copper is met with in the form of cuprous oxide1 or suboxide of copper1 ,cu#b,o1 and is then known as red copper ore1 because it forms red masses which not unfrequently are crystallised in the regular system4 ,it is found much more rarely in the state of cupric oxide1 ,cu,o1 and is then called black copper ore4 ,the most common of the oxygenised compounds of copper are the basic carbonates corresponding with the oxides4 ,that these compounds are undoubtedly of aqueous origin is apparent1 not only from the fact that specimens are frequently found of a gradual transition from the metallic1 sulphuretted1 and oxidised copper into its various carbonates1 but also from the presence of water in their composition1 and from the laminar1 reniform structure which many of them present4 ,in this respect malachite is particularly well known2 it is used as a green paint and also for ornaments1 owing to the diversity of the shades of colour presented by the different layers of deposited malachite4 ,the composition of malachite corresponds with the basic carbonate containing one molecule of cupric carbonate to one of hydroxide3 ,cu,c,o#c1;,cu,h#b,o#b4 ,in this form the copper frequently occurs in admixture with various sedimentary rocks1 forming large strata1 which confirms the aqueous origin of these compounds4 ,there are many such localities in the ,perm and other ,governments bounding the ,urals4 ,blue carbonate of copper1 or azurite1 is also often met with in the same localities2 it contains the same ingredients as malachite1 but in a different proportion1 its composition being ,cu,h#b,o#b1b;,cu,c,o#c4 ,both these substances may be obtained artificially by the action of the alkali carbonates on solutions of cupric salts at various temperatures4 ,these native carbonates are often used for the extraction of copper1 all the more as they very readily give metallic copper1 evolving water and carbonic anhydride when ignited1 and leaving the easily-reducible cupric oxide4 ,copper is1 however1 still more often met with in the form of the sulphides4 ,the sulphides of copper generally occur in chemical combination with the sulphides of iron4#c ,these copper-sulphur compounds 7copper pyrites ,cu,fe,s#b1 variegated copper ore ,cu#c;,fe,s#c1 c47 generally occur in veins in a rock gangue4 #c ,iron pyrites1 ,fe,s#b1 very often contain a small quantity of copper sulphide 7see ,chapter ,,xxii41 ,note #b bis71 and on burning the iron pyrites for sulphurous anhydride the copper oxide remains in the residue1 from which the copper is often extracted with profit4 ,for this purpose the whole of the sulphur is not burnt off from the iron pyrites1 but a portion is left behind in the ore1 which is then slowly ignited 7roasted7 with access of air4 ,cupric sulphate is then formed1 and is extracted by water2 or what is better and more frequently done1 the residue from the roasting of the pyrites is roasted with common salt1 and the solution of cupric chloride obtained by lixiviating is precipitated with iron4 ,a far greater amount of copper is obtained from other sulphuretted ores4 ,among these copper glance1 ,cu#b,s1 is more rarely met with4 ,it has a metallic lustre1 is grey1 generally crystalline1 and is obtained in admixture with organic matter2 so that there is no doubt that its origin is due to the reducing action of the latter on solutions of cupric sulphate4 ,variegated copper ore1 which crystallises in octahedra1 not infrequently forms an admixture in copper glance2 it has a metallic lustre1 and is reddish-brown2 it has a superficial play of colours1 due to oxidation proceeding on its surface4 ,its composition is ,cu#c;,fe,s#c4 ,but the most common and widely-distributed copper ore is copper pyrites1 which crystallises in regular octahedra2 it has a metallic lustre1 a sp4 gr4 of #dj1 and yellow colour4 ,its composition is ,cu,fe,s#b4 ,it must be remarked that the sulphurous ores of copper are oxidised in the presence of water containing oxygen in solution1 and form cupric sulphate1 blue vitriol1 which is easily soluble in water4 ,if this water contains calcium carbonate1 gypsum and cupric carbonate are formed by double decomposition3 ,cu,s,o#d ,ca,c,o#c ,cu,c,o#c ,ca,s,o#d4 ,hence copper sulphide in the form of different ores must be considered as the primary product1 and the many other copper ores as secondary products1 formed by water4 ,this is confirmed by the fact that at the present time the water extracted from many copper mines contains cupric sulphate in solution4 ,from this liquid it is easy to extract cupric oxide by the action of organic matter and various impurities of water4 ,hence metallic copper is sometimes found in natural products of the modification of copper sulphide and is probably deposited by the action of organic matter present in the water4 ,the extraction of copper from its oxide ores does not present any difficulty1 because the copper1 when ignited with charcoal and melted1 is reduced from the impurities which accompany it4 ,this mode of smelting copper ores is carried on in cupola or cylindrical furnaces1 fluxes forming a slag being added to the mixture of ore and charcoal4 ,the smelted copper still contains sulphur1 iron1 and other metallic impurities1 from which it is freed by fusion in reverberatory furnaces1 with access of air to the surface of the molten metal1 as the iron and sulphur are more easily oxidised than the copper4 ,the iron then separates as oxides1 which collect in the slag4#d #d ,copper ores rich in oxygen are very rare2 the sulphur ores are of more common occurrence1 but the extraction of the copper from them is much more difficult4 ,the problem here not only consists in the removal of the sulphur1 but also in the removal of the iron combined with the sulphur and copper4 ,this is attained by a whole series of operations1 after which there still sometimes remains the extraction of the metallic silver which generally accompanies the copper1 although in but small quantity4 ,these processes commence with the roasting--i4e4 calcination--of the ore with access of air1 by which means the sulphur is converted into sulphurous anhydride4 ,it should here be remarked that iron sulphide is more easily oxidised than copper sulphide1 and therefore the greater part of the iron in the residue from roasting is no longer in the form of sulphide but of oxide of iron4 ,the roasted ore is mixed with charcoal1 and siliceous fluxes1 and smelted in a cupola furnace4 ,the iron then passes into the slag1 because its oxide gives an easily-fusible mass with the silica1 whilst the copper1 in the form of sulphide1 fuses and collects under the slag4 ,the greater part of the iron is removed from the mass by this smelting4 ,the resultant coarse metal is again roasted in order to remove the greater part of the sulphur from the copper sulphide1 and to convert the metal into oxide1 after which the mass is again smelted4 ,these processes are repeated several times1 according to the richness of the ore4 ,during these smeltings a portion of the copper is already obtained in a metallic form1 because copper sulphide gives metallic copper with the oxide 7,cu,s #b;,cu,o #c;,cu ,,so#b74 ,we will not here describe the furnaces used or the details of this process1 but the above remarks include the explanation of those chemical processes which are accomplished in the various technical operations which are made use of in the process 7for details see works on metallurgy74 ,besides the smelting of copper there also exist methods for its extraction from solutions in the wet way1 as it is called4 ,recourse is generally had to these methods for poor copper ores4 ,the copper is brought into solution1 from which it is separated by means of metallic iron or by other methods 7by the action of an electric current74 ,the sulphides are roasted in such a manner that the greater part of the copper is oxidised into cupric sulphate1 whilst at the same time the corresponding iron salts are as far as possible decomposed4 ,this process is based on the fact that the copper sulphides absorb oxygen when they are calcined in the presence of air1 forming cupric sulphate4 ,the roasted ore is treated with water1 to which acid is sometimes added1 and after lixiviation the resultant solution containing copper is treated either with metallic iron or with milk of lime1 which precipitates cupric hydroxide from the solution4 ,copper oxide ores poor in metal may be treated with dilute acids in order to obtain the copper oxides in solution1 from which the copper is then easily precipitated either by iron or as hydroxide by lime4 ,according to ,hunt and ,douglas's method1 the copper in the ore is converted by calcination into the cupric oxide1 which is brought into solution by the action of a mixture of solutions of ferrous sulphate and sodium chloride2 the oxide converts the ferrous chloride into ferric oxide1 forming copper chlorides1 according to the equation #c;,cu,o #b;,fe,cl#b ,cu,cl#b #b;,cu,cl ,fe#b,o#c4 ,the cupric chloride is soluble in water1 whilst the cuprous chloride is dissolved in the solution of sodium chloride1 and therefore all the copper passes into solution1 from which it is precipitated by iron4 ,the same ,american metallurgists give the following wet method for extracting the ,ag and ,au occurring in many copper ores1 especially in sulphurous ores3 7#a7 ,the ,cu#b,s is first converted into oxide by roasting in a calciner2 7#b7 the ,cu,o is extracted by the dilute sulphuric acid obtained in the fourth process1 the ,cu then passes into solution1 while the ,ag1 ,au and oxides of iron remain behind in the residue 7from which the noble metals may be extracted72 7#c7 a portion of the copper in solution is converted into ,cu,cl#b 7and ,ca,s,o#d precipitated7 by means of the ,ca,cl#b obtained in the fifth process2 7#d7 the mixture of solutions of ,cu,s,o#d and ,cu,cl#b is converted into the insoluble ,cu,cl 7salt of the suboxide7 by the action of the ,,so#b obtained by roasting the ore 7in the first operation71 sulphuric acid is then formed in the solution1 according to the equation3 ,cu,s,o#d ,cu,cl#b ,,so#b #b;,h#b,o #b;,h#b,,so#d #b;,cu,cl2 7#e7 the precipitated ,cu,cl is treated with lime and water1 and gives ,cu,cl#b in solution and ,cu,o in the residue2 and lastly 7#f7 the ,cu#b,o is reduced to metallic ,cu by carbon in a furnace4 ,according to ,crooke's method the impure copper regulus obtained by roasting and smelting the ore is broken up and immersed repeatedly in molten lead1 which extracts the ,ag and ,au occurring in the regulus4 ,the regulus is then heated in a reverberatory furnace to run off the lead1 and is then smelted for ,cu4 ,the copper brought into the market often contains small quantities of various impurities4 ,among these there are generally present iron1 lead1 silver1 arsenic1 and sometimes small quantities of oxides of copper4 ,as copper1 when mixed with a small amount of foreign substances1 loses its tenacity to a certain degree1 the manufacture of very thin sheet copper requires the use of ,chili copper1 which is distinguished for its great softness1 and therefore when it is desired to have pure copper1 it is best to take thin sheet copper1 like that which is used in the manufacture of cartridges4 ,but the purest copper is electrolytic copper--that is1 that which is deposited from a solution by the action of an electric current4 ,if the copper contains silver1 as is often the case1 it is used in gold refineries for the precipitation of silver from its solutions in sulphuric acid4 ,iron and zinc reduce copper salts1 but copper reduces mercury and silver salts4 ,the precipitate contains not only the silver which was previously in solution1 but also all that which was in the copper4 ,the silver solutions in sulphuric acid are obtained in the separation of silver from gold by treating their alloys with sulphuric acid1 which only dissolves the silver4 ,copper is characterised by its red colour1 which distinguishes it from all other metals4 ,pure copper is soft1 and may be beaten out by a hammer at the ordinary temperature1 and when hot may be rolled into very thin sheets4 ,extremely thin leaves of copper transmit a green light4 ,the tenacity of copper is also considerable1 and next to iron it is one of the most durable metals in this respect4 ,copper wire of #a sq4 millimetre in section only breaks under a weight of #de kilograms4 ,the specific gravity of copper is #hh1 unless it contains cavities due to the fact that molten copper absorbs oxygen from the air1 which is disengaged on cooling1 and therefore gives a porous mass whose density is much less4 ,rolled copper1 and also that which is deposited by the electric current1 has a comparatively high density4 ,copper melts at a bright red heat1 about #ajej1 although below the temperature at which many kinds of cast iron melt4 ,at a high temperature it is converted into vapour1 which communicates a green colour to the flame4 ,both native copper and that cooled from a molten state crystallise in regular octahedra4 ,copper is not oxidised in dry air at the ordinary temperature1 but when calcined it becomes coated with a layer of oxide1 and it does not burn even at the highest temperature4 ,copper1 when calcined in air1 forms either the red cuprous oxide or the black cupric oxide1 according to the temperature and quantity of air supplied4 ,in air at the ordinary temperature1 copper--as everyone knows--becomes coated with a brown layer of oxides or a green coating of basic salts1 due to the action of the damp air containing carbonic acid4 ,if this action continue for a prolonged time1 the copper is covered with a thick coating of basic carbonate1 or the so-called verdigris 7the rugo nobilis of ancient statues74 ,this is due to the fact that copper1 although scarcely capable of oxidising by itself1#e in the presence of water and acids--even very feeble acids1 like carbonic acid--absorbs oxygen from the air and forms salts1 which is a very characteristic property of it 7and of lead74#f ,copper does not decompose water1 and therefore does not disengage hydrogen from it either at the ordinary or at high temperatures4 ,nor does copper liberate hydrogen from the oxygen acids2 these act on it in two ways3 they either give up a portion of their oxygen1 forming lower grades of oxidation1 or else only react in the presence of air4 ,thus1 when nitric acid acts on copper it evolves nitric oxide1 the copper being oxidised at the expense of the nitric acid4 ,in the same way copper converts sulphuric acid into the lower grade of oxidation--into sulphurous anhydride1 ,,so#b4 ,in these cases the copper is oxidised to copper oxide1 which combines with the excess of acid taken1 and therefore forms a cupric salt1 ,cu,x#b4 ,dilute nitric acid does not act on copper at the ordinary temperature1 but when heated it reacts with great ease2 dilute sulphuric acid does not act on copper except in presence of air4 #e ,schtzenberger showed that when the basic carbonate of copper is decomposed by an electric current it gives1 besides the ordinary copper1 an allotropic form which grows on the negative platinum electrode1 if its surface be smaller than that of the positive copper electrode1 in the form of brittle crystalline growths of sp4 gr4 #ha4 ,it differs from ordinary copper by giving not nitric oxide but nitrous oxide when treated with nitric acid1 and in being very easily oxidised in air1 and coated with red shades of colour4 ,it is possible that this is copper hydride1 or copper which has occluded hydrogen4 ,spring 7#ahib7 observed that copper reduced from the oxide by hydrogen at the lowest possible temperature was pulverulent1 while that reduced from ,cu,cl#b at a somewhat high temperature appeared in bright crystals4 ,the same difference occurs with many other metals1 and is probably partly due to the volatility of the metallic chlorides4 #f ,this is taken advantage of in practice2 for instance1 by pouring dilute acids over copper turnings on revolving tables in the preparation of copper salts1 such as verdigris1 or the basic acetate #b;,c#d;,h#f;,cu,o#d1;,cu,h#b,o#b1e;,h#b ,o1 which is so much used as an oil paint 7i4e4 with boiled oil74 ,the capacity of copper for absorbing oxygen in the presence of acids is so great that it is possible by this means 7by taking1 for example1 thin copper shavings moistened with sulphuric acid7 to take up all the oxygen from a given volume of air1 and this is even employed for the analysis of air4 ,the combination of copper with oxygen is not only aided by acids but also by alkalis1 although cupric oxide does not appear to have an acid character4 ,alkalis do not act on copper except in the presence of air1 when they produce cupric oxide1 which does not appear to combine with such alkalis as caustic potash or soda4 ,but the action of ammonia is particularly distinct 7,chapter ,v41 ,note #b74 ,in the action of a solution of ammonia not only is oxygen absorbed by the copper1 but it also acts on the ammonia1 and a definite quantity of ammonia is always acted on simultaneously with the passage of the copper into solution4 ,the ammonia is then converted into nitrous acid1 according to the reaction3 ,,nh#c ,o#c ,,nho#b ,h#b,o1 and the nitrous acid thus formed passes into the state of ammonium nitrite1 ,,nh#d,,no#b4 ,in this manner three equivalents of oxygen are expended on the oxidation of the ammonia1 and six equivalents of oxygen pass over to the copper1 forming six atoms of cupric oxide4 ,the latter does not remain in the state of oxide1 but combines with the ammonia4 ,a strong solution of common salt does not act on copper1 but a dilute solution of the salt corrodes copper1 converting it into oxychloride--that is1 in the presence of air4 ,this action of salt water is evident in those cases where the bottoms of ships are coated with sheet copper4 ,from what has been said above it will be evident that copper vessels should not be employed in the preparation of food1 because this contains salts and acids which act on copper in the presence of air1 and give copper salts1 which are poisonous1 and therefore the food prepared in untinned copper vessels may be poisonous4 ,hence tinned vessels are employed for this purpose--that is1 copper vessels coated with a thin layer of tin1 on which acid and saline solutions do not act4 ,both the oxides of copper1 ,cu#b,o and ,cu,o1 are unacted on by air1 and1 as already mentioned1 they both occur in nature4#f bis ,however1 in the majority of cases copper is obtained in the form of cupric oxide and its salts--and the copper compounds used industrially generally belong to this type4 ,this is due to the fact that the cuprous compounds absorb oxygen from the air and pass into cupric compounds4 ,the cupric compounds may serve as the source for the preparation of cuprous oxide1 because many reducing agents are capable of deoxidising the oxide into the suboxide4 ,organic substances are most generally employed for this purpose1 and especially saccharine substances1 which are able1 in the presence of alkalis1 to undergo oxidation at the expense of the oxygen of the cupric oxide1 and to give acids which combine with the alkali3 #b;,cu,o - ,o ,cu#b,o4 ,in this case the deoxidation of the copper may be carried further and metallic copper obtained1 if only the reaction be aided by heat4 ,thus1 for example1 a fine powder of metallic copper may be obtained by heating an ammoniacal solution of cupric oxide with caustic potash and grape sugar4 ,but if the reducing action of the saccharine substance proceed in the presence of a sufficient quantity of alkali in solution1 and at not too high a temperature1 cuprous oxide is obtained4 ,to see this reaction clearly1 it is not sufficient to take any cupric salt1 because the alkali necessary for the reaction might precipitate cupric oxide--it is necessary to add previously some substance which will prevent this precipitation4 ,among such substances1 tartaric acid1 ,c#d;,h#f,o#f1 is one of the best4 ,in the presence of a sufficient quantity of tartaric acid1 any amount of alkali may be added to a solution of cupric salt without producing a precipitate1 because a soluble double salt of cupric oxide and alkali is then formed4 ,if glucose 7for instance1 honey or molasses7 be added to such an alkaline tartaric solution1 and the temperature be slightly raised1 it first gives a yellow precipitate 7this is cuprous hydroxide1 ,cu,h,o71 and then1 on boiling1 a red precipitate of 7anhydrous7 cuprous oxide4 ,if such a mixture be left for a long time at the ordinary temperature1 it deposits well-formed crystals of anhydrous cuprous oxide belonging to the regular system4#g #f bis ,copper1 besides the cuprous oxide1 ,cu#b,o1 and cupric oxide1 ,cu,o1 gives two known higher forms of oxidation1 but they have scarcely been investigated1 and even their composition is not well known4 ,copper dioxide 7,cu,o#b1 or ,cu,o#b1;,h#b,o1 perhaps ,cu,o,h#b,o#b7 is obtained by the action of hydrogen peroxide on cupric hydroxide1 when the green colour of the latter is changed to yellow4 ,it is very unstable1 and is decomposed even by boiling water1 with the evolution of oxygen1 whilst the action of acids gives cupric salts1 oxygen being also disengaged4 ,a still higher copper peroxide is formed by heating a mixture of caustic potash1 nitre1 and metallic copper to a red heat1 and by dissolving cupric hydroxide in solutions of the hypochlorites of the alkali metals4 ,a slight heating of the soluble salt formed is enough for it to be decomposed into oxygen and copper dioxide1 which is precipitated4 ,judging from ,frmy's researches1 the composition of the copper-potassic compound should be ,k#b;,cu,o#d4 ,perhaps this is a compound of the peroxides of potassium1 ,k#b,o#b1 and of copper1 ,cu,o#b4 #g ,colourless solutions of cuprous salts may also be obtained by the action of sulphurous or phosphorous acid and similar lower grades of oxidation on the blue solutions of the cupric salts4 ,this is very clearly and easily effected by means of sodium thiosulphate1 ,na#b,s#b,o#c1 which is oxidised in the process4 ,cuprous oxide can not only be obtained by the deoxidation of cupric oxide1 but also directly from metallic copper itself1 because the latter1 in oxidising at a red heat in air1 first gives cuprous oxide4 ,it is prepared in this manner on a large scale by heating sheet copper rolled into spirals in reverberatory furnaces4 ,care must be taken that the air is not in great excess1 and that the coating of red cuprous oxide formed does not begin to pass into the black cupric oxide4 ,if the oxidised spiral sheet is then unbent1 the brittle cuprous oxide falls away from the soft metal4 ,the suboxide obtained in this manner fuses with ease4 ,it is necessary to prevent the access of air during the fusion1 and if the mass contains cupric oxide it must be mixed with charcoal1 which reduces the latter4 ,cuprous chloride1 ,cu,cl1 corresponding with cuprous oxide 7as sodium chloride corresponds with sodium oxide71 when calcined with sodium carbonate1 gives sodium chloride and cuprous oxide1 carbonic anhydride being evolved1 because it does not combine with the cuprous oxide under these conditions4 ,the reaction can be expressed by the following equation3 #b;,cu,cl ,na#b;,,co#c ,cu#b,o #b,na,cl ,,co#b4 ,the cupric oxide itself1 when calcined with finely-divided copper1 this copper powder may be obtained by many methods--for instance1 by immersing zinc in a solution of a copper salt1 or by igniting cupric oxide in hydrogen71 gives the fusible cuprous oxide3 ,cu ,cu,o ,cu#b,o4 ,both the native and artificial cuprous oxide have a sp4 gr4 of #ef4 ,it is insoluble in water1 and is not acted on by 7dry7 air4 ,when heated with acids the suboxide forms a solution of a cupric salt and metallic copper--for example1 ,cu#b,o ,h#b,,so#d ,cu ,cu,s,o#d ,h#b,o4 ,however1 strong hydrochloric acid does not separate metallic copper on dissolving cuprous oxide1 which is due to the fact that the cuprous chloride formed is soluble in strong hydrochloric acid4 ,cuprous oxide also dissolves in a solution of ammonia1 and in the absence of air gives a colourless solution1 which turns blue in the air1 absorbing oxygen1 owing to the conversion of the cuprous oxide into cupric oxide4 ,the blue solution thus formed may be again reconverted into a colourless cuprous solution by immersing a copper strip in it1 because the metallic copper then deoxidises the cupric oxide in the solution into cuprous oxide4 ,cuprous oxide is characterised by the fact that it gives red glasses when fused with glass or with salts forming vitreous alloys4 ,glass tinted with cuprous oxide is used for ornaments4 ,the access of air must be avoided during its preparation1 because the colour then becomes green1 owing to the formation of cupric oxide1 which colours glass blue4 ,this may even be taken advantage of in testing for copper under the blow-pipe by heating the copper compound with borax in the flame of a blow-pipe2 a red glass is obtained in the reducing flame1 and a blue glass in the oxidising flame1 owing to the conversion of the cuprous into cupric oxide4 tard 7#ahhb71 by passing sulphurous anhydride into a solution of cupric acetate1 obtained a white precipitate of cuprous sulphite1 ,cu#b,,so#c1;,h#b,o1 whilst he obtained the same salt1 of a red colour1 from the double salt of sodium and copper2 but there are not any convincing proofs of isomerism in this case4 ,cupric chloride1 ,cu,cl#b1 when ignited1 gives cuprous chloride1 ,cu,cl--i4e4 the salt corresponding with suboxide of copper--and therefore cuprous chloride is always formed when copper enters into reaction with chlorine at a high temperature4 ,thus1 for example1 when copper is calcined with mercuric chloride1 it forms cuprous chloride and vapours of mercury4 ,the same substance is obtained on heating metallic copper in hydrochloric acid1 hydrogen being disengaged2 but this reaction only proceeds with finely-divided copper1 as hydrochloric acid acts very feebly on compact masses of copper1 and1 in the presence of air1 gives cupric chloride4 ,the green solution of cupric chloride is decolorised by metallic copper1 cuprous chloride being formed2 but this reaction is only accomplished with ease when the solution is very concentrated and in the presence of an excess of hydrochloric acid to dissolve the cuprous chloride4 ,the addition of water to the solution precipitates the cuprous chloride1 because it is less soluble in dilute than in strong hydrochloric acid4 ,many reducing agents which are able to take up half the oxygen from cupric oxide are able1 in the presence of hydrochloric acid1 to form cuprous chloride4 ,stannous salts1 sulphurous anhydride1 alkali sulphites1 phosphorous and hypophosphorous acids1 and many similar reducing agents1 act in this manner4 ,the usual method of preparing cuprous chloride consists in passing sulphurous anhydride into a very strong solution of cupric chloride3 #b;,cu,cl#b ,,so#b #b;,h#b,o #b;,cu,cl #b;,h,cl ,h#b,,so#d4 ,cuprous chloride forms colourless cubic crystals which are insoluble in water4 ,it is easily fusible1 and even volatile4 ,under the action of oxidising agents1 it passes into the cupric salt1 and it absorbs oxygen from moist air1 forming cupric oxychloride1 ,cu#b;,cl#b,o4 ,aqueous ammonia easily dissolves cuprous chloride as well as cuprous oxide2 the solution also turns blue on exposure to the air4 ,thus an ammoniacal solution of cuprous chloride serves as an excellent absorbent for oxygen2 but this solution absorbs not only oxygen1 but also certain other gases--for example1 carbonic oxide and acetylene4#h #h ,the solubility of cuprous chloride in ammonia is due to the formation of compounds between the ammonia and the chloride4 ,in a warm solution the compound ,,nh#c1b;,cu,cl is formed1 and at the ordinary temperature ,cu,cl1,,nh#c4 ,this salt is soluble in hydrochloric acid1 and then forms a corresponding double salt of cuprous chloride and ammonium chloride4 ,by the action of a certain excess of ammonia on a hydrochloric acid solution of cuprous chloride1 very well formed crystals1 having the composition ,cu,cl1,,nh#c1;,h#b,o1 are obtained4 ,cuprous chloride is not only soluble in ammonia and hydrochloric acid1 but it also dissolves in solutions of certain other salts--for example1 in sodium chloride1 potassium chloride1 sodium thiosulphate1 and certain others4 ,all the solutions of cuprous chloride act in many cases as very powerful deoxidising substances2 for example1 it is easy1 by means of these solutions1 to precipitate gold from its solutions in a metallic form1 according to the equation ,au,cl#c #c;,cu,cl ,au #c;,cu,cl#b4 ,among the other compounds corresponding with cuprous oxide1 cuprous iodide1 ,cu,i1 is worthy of remark4 ,it is a colourless substance which is insoluble in water and sparingly soluble in ammonia 7like silver iodide71 but capable of absorbing it1 and in this respect it resembles cuprous chloride4 ,it is remarkable from the fact that it is exceedingly easily formed from the corresponding cupric compound ,cu,i#b4 ,a solution of cupric iodide easily decomposes into iodine and cuprous iodide1 even at the ordinary temperature1 whilst cupric chloride only suffers a similar change on ignition4 ,if a solution of a cupric salt be mixed with a solution of potassium iodide the cupric iodide formed immediately decomposes into free iodine and cuprous iodide1 which separates out as a precipitate4 ,in this case the cupric salt acts in an oxidising manner1 like1 for example1 nitrous acid1 ozone1 and other substances which liberate iodine from iodides1 but with this difference1 that it only liberates half1 whilst they set free the whole of the iodine from potassium iodide3 #b,,ki ,cu,cl#b #b,k,cl ,cu,i ,i4 ,it must also be remarked that cuprous oxide1 when treated with hydrofluoric acid1 gives an insoluble cuprous fluoride1 ,cu,f4 ,cuprous cyanide is also insoluble in water1 and is obtained by the addition of hydrocyanic acid to a solution of cupric chloride saturated with sulphurous anhydride4 ,this cuprous cyanide1 like silver cyanide1 gives a double soluble salt with potassium cyanide4 ,the double cyanide of copper and potassium is tolerably stable in the air1 and enters into double decompositions with various other salts1 like those double cyanides of iron with which we are already acquainted4 ,copper hydride1 ,cu,h1 also belongs to the number of the cuprous compounds4 ,it was obtained by ,wrtz by mixing a hot 7#gj7 solution of cupric sulphate with a solution of hypophosphorous acid1 ,h#c,,po#b4 ,the addition of the reducing hypophosphorous acid must be stopped when a brown precipitate makes its appearance1 and when gas begins to be evolved4 ,the brown precipitate is the hydrated cuprous hydride4 ,when gently heated it disengages hydrogen2 it gives cuprous oxide when exposed to the air1 burns in a stream of chlorine1 and liberates hydrogen with hydrochloric acid3 ,cu,h ,h,cl ,cu,cl ,h#b4 ,zinc1 silver1 mercury1 lead1 and many other heavy metals do not form such a compound with hydrogen1 neither under these circumstances nor under the action of hydrogen at the moment of the decomposition of salts by a galvanic current4 ,the greatest resemblance is seen between cuprous hydride and the hydrogen compounds of potassium1 sodium1 ,pd1 ,ca1 and ,ba4 ,when copper is oxidised with a considerable quantity of oxygen at a high temperature1 or at the ordinary temperature in the presence of acids1 and also when it decomposes acids1 converting them into lower grades of oxidation 7for example1 when submitted to the action of nitric and sulphuric acids71 it forms cupric oxide1 ,cu,o1 or1 in the presence of acids1 cupric salts4 ,copper rust1 or that black mass which forms on the surface of copper when it is calcined1 consists of cupric oxide4 ,the coating of the oxidised copper is very easily separated from the metallic copper1 because it is brittle and very easily peels off1 when it is struck or immersed in water4 ,many copper salts 7for instance1 the nitrite and carbonate7 leave oxide of copper#h bis in the form of friable black powder1 after being ignited4 ,if the ignition be carried further1 ,cu#b,o may be formed from the ,cu,o4#h tri ,anhydrous cupric oxide is very easily dissolved in acids1 forming cupric salts1 ,cu,x#b4 ,they are analogous to the salts ,mg,x#b1 ,zn,x#b1 ,ni,x#b1 ,fe,x#b1 in many respects4 ,on adding potassium or ammonium hydroxide to a solution of a cupric salt1 it forms a gelatinous blue precipitate of the hydrated oxide of copper1 ,cu,h#b,o#b1 insoluble in water4 ,the resultant precipitate is redissolved by an excess of ammonia1 and gives a very beautiful azure blue solution1 of so intense a colour that the presence of small traces of cupric salts may be discovered by this means4#i ,an excess of potassium or sodium hydroxide does not dissolve cupric hydroxide4 ,a hot solution gives a black precipitate of the anhydrous oxide instead of the blue precipitate1 and the precipitate of the hydroxide of copper becomes granular1 and turns black when the solution is heated4 ,this is due to the fact that the blue hydroxide is exceedingly unstable1 and when slightly heated it loses the elements of water and gives the black anhydrous cupric oxide3 ,cu,h#b,o#b ,cu,o ,h#b,o4 #h bis ,the oxide of copper obtained by igniting the nitrate is frequently used for organic analyses4 ,it is hygroscopic and retains nitrogen 7#ae c4c4 per gram7 when the nitrate is heated in vacuo 7,richards and ,rogers1 #ahic74 #h tri ,oxide of copper is also capable of dissociating when heated4 ,debray and ,joannis showed that it then disengages oxygen1 whose maximum tension is constant for a given temperature1 providing that fusion does not take place 7the ,cu,o then dissolves in the molten ,cu#b,o72 that this loss of oxygen is followed by the formation of suboxide1 and that on cooling1 the oxygen is again absorbed1 forming ,cu,o4 #i ,cupric oxide and many of its salts are able to give definite1 although unstable1 compounds with ammonia4 ,this faculty already shows itself in the fact that cupric oxide1 as well as the salts of copper1 dissolves in aqueous ammonia1 and also in the fact that salts of copper absorb ammonia gas4 ,if ammonia be added to a solution of any cupric salt1 it first forms a precipitate of cupric hydroxide1 which then dissolves in an excess of ammonia4 ,the solution thus formed1 when evaporated or on the addition of alcohol1 frequently deposits crystals of salts containing both the elements of the salt of copper taken and of ammonia4 ,several such compounds are generally formed4 ,thus cupric chloride1 ,cu,cl#b1 according to ,deherain1 forms four compounds with ammonia--namely1 with one1 two1 four1 and six molecules of ammonia4 ,thus1 for example1 if ammonia gas be passed into a boiling saturated solution of cupric chloride1 on cooling1 small octahedral crystals of a blue colour separate out1 containing ,cu,cl#b1b,,nh#c1;,h#b,o4 ,at #aej this substance loses half the ammonia and all the water contained in it1 leaving the compound ,cu,cl#b1,,nh#c4 ,nitrate of copper forms the compound ,cu7,,no#c7b1b,,nh#c ,this compound remains unchanged on evaporation4 ,dry cupric sulphate absorbs ammonia gas1 and gives a compound containing five molecules of ammonia to one of sulphate 7,vol4 ,i41 p4 #beg1 and ,chapter ,,xxii41 ,note #ce74 ,if this compound is dissolved in aqueous ammonia1 on evaporation it deposits a crystalline substance containing ,cu,s,o#d1d,,nh#c1;,h#b,o4 ,at #aej this substance loses the molecule of water and one-fourth of its ammonia4 ,on ignition all these compounds part with the remaining ammonia in the form of an ammoniacal salt1 so that the residue consists of cupric oxide4 ,both the hydrated and anhydrous cupric oxide are soluble in aqueous ammonia4 ,the solution obtained by the action of aqueous ammonia and air on copper turnings 7,note #f7 is remarkable for its faculty of dissolving cellulose1 which is insoluble in water1 dilute acids1 and alkalis4 ,paper soaked in such a solution acquires the property of not rotting1 of being difficultly combustible1 and waterproof1 c4 ,it has therefore been applied1 especially in ,england1 to many practical purposes--for example1 to the construction of temporary buildings1 for covering roofs1 c4 ,the composition of the substance held in solution is ,cu7,,ho7#b1d,,nh#c4 ,if dry ammonia gas be passed over cupric oxide heated to #bfe1 a portion of the oxide of copper remains unaltered1 whilst the other portion gives copper nitride1 the oxygen of the copper oxide combining with the hydrogen and forming water4 ,the oxide of copper which remains unchanged is easily removed by washing the resultant product with aqueous ammonia4 ,copper nitride is very stable1 and is insoluble2 it has the composition ,cu#c,n 7i4e4 the copper is monatomic here as in ,cu#b,o71 and is an amorphous green powder1 which is decomposed when strongly ignited1 and gives cuprous chloride and ammonium chloride when treated with hydrochloric acid4 ,like the other nitrides1 copper nitride1 ,cu#c,n1 has scarcely been investigated4 ,granger 7#ahib71 by heating copper in the vapour of phosphorus1 obtained hexagonal prisms of ,cu#e,p1 which passed into ,cu#f,p 7previously obtained by ,abel7 when heated in nitrogen4 ,arsenic is easily absorbed by copper1 and its presence 7like ,p71 even in small quantities1 has a great influence upon the properties of copper--for instance1 pure copper wire #a sq4 mm4 in section breaks under a load of #ce kilos1 while the presence of ,o#bb p4c4 of arsenic raises the breaking load to #db kilos4 ,cupric oxide fuses at a strong heat1 and on cooling forms a heavy crystalline mass1 which is black1 opaque1 and somewhat tenacious4 ,it is a feebly energetic base1 so that not only do the oxides of the metals of the alkalis and alkaline earths displace it from its compounds1 but even such oxides as those of lead and silver precipitate it from solutions1 which is partially due to these oxides being soluble1 although but slightly so1 in water4 ,however1 cupric oxide1 and especially the hydroxide1 easily combines with even the least energetic acids1 and does not give any compounds with bases2 but1 on the other hand1 it easily forms basic salts1#i bis and in this respect outstrips magnesium and recalls the oxides of lead or mercury4 ,hence the hydroxide of copper dissolves in solutions of neutral cupric salts4 ,the cupric salts are generally blue or green1 because cupric hydroxide itself is coloured4 ,but some of the salts in the anhydrous state are colourless4#aj #i bis ,as a comparatively feeble base1 oxide of copper easily forms both basic and double salts4 ,as an instance we may mention the double salts composed of the dichloride ,cu,cl#b1b;,h#b,o and potassium chloride4 ,the double salt ,cu,k#b;,cl#d1b;,h#b,o crystallises from solutions in blue plates1 but when heated alone or with substances taking up water easily gives brown needles ,cu,k,cl#c and at the same time ,k,cl1 and this reaction is reversible at #ib as ,meyerhoffer 7#ahhi7 showed 7i4e4 above #ib the simpler double salt is formed and below #ib the more complex salt74 ,with an excess of the copper salt1 ,k,cl gives another double salt1 ,cu#b,k,cl#e1d;,h#b,o1 the transition temperature of which is #ee4 ,the instances of equilibria which are encountered in such complex relations 7see ,chapter ,,xiv41 ,note #be1 astrakhanite1 and ,chapter ,,xxii41 ,note #bc7 are embraced by the law of phases given by ,gibbs 7,transactions of the ,connecticut ,academy of ,sciences1 #ahge-ahgh1 in ,j4 ,willard ,gibbs' memoir ',on the equilibrium of heterogeneous substances3' and in a clearer and more accessible form in ,h4 ,w4 ,bakhuis ,roozeboom's papers1 ,rec4 trav4 chim41 ,vol4 ,,vi41 and in ,w4 ,meyerhoffer's memoir ,die ,phasenregel und ihre ,anwendungen1 #ahic1 to which sources we refer those desiring fuller information respecting this law74 ,gibbs calls 'bodies' substances 7simple or compound7 capable of forming homogeneous complexes 7for instance1 solutions or intercombinations7 of a varied composition2 a phase--a mechanically separable portion of such bodies or of their homogeneous complexes 7for instance1 a vapour1 liquid or precipitated solid71 perfect equilibrium--such a state of bodies and of their complexes as is characterised by a constant pressure at a constant temperature even under a change in the amount of one of the component parts 7for instance1 of a salt in a saturated solution71 while an imperfect equilibrium is such a one for which such a change corresponds with a change of pressure 7for instance1 an unsaturated solution74 ,the law of phases consists in the fact that3 n bodies only give a perfect equilibrium when n #a phases participate in that equilibrium--for example1 in the equilibrium of a salt in its saturated solution in water there are two bodies 7the salt and water7 and three phases1 namely1 the salt1 solution1 and vapour1 which can be mechanically separated from each other1 and to this equilibrium there corresponds a definite tension4 ,at the same time1 n bodies may occur in n #b phases1 but only at one definite temperature and one pressure2 a change of one of these may bring about another state 7perfect or not--equilibrium stable or unstable74 ,thus water when liquid at the ordinary temperature offers two phases 7liquid and vapour7 and is in perfect equilibrium 7as also is ice below #j71 but water1 ice1 and vapour 7three phases and only one body7 can only be in equilibrium at #j1 and at the ordinary pressure2 with a change of t there will remain either only ice and vapour or only liquid water and vapour2 whilst with a rise of pressure not only will the vapour pass into the liquid 7there again only remain two phases7 but also the temperature of the formation of ice will fall 7by about #g per #ajjj atmospheres74 ,the same laws of phases are applicable to the consideration of the formation of simple or double salts from saturated solutions and to a number of other purely chemical relations4 ,thus1 for example1 in the above-mentioned instance1 when the bodies are ,k,cl1 ,cu,cl#b1 and ,h#b,o1 perfect equilibrium 7which here has reference to the solubility7 consisting of four phases1 corresponds to the following seven cases1 considering only the phases 7above #j7 ,a ,cu,cl#b1b,k,cl1#b;,h#b,o2 ,b ,cu,cl#b,k,cl2 ,c ,cu,cl#b1b;,h#b,o1,k,cl1 solution and vapour3 7#a7 ,a ,b solution vapour2 7#b7 ,a ,c solution vapour2 7#c7 ,a ,k,cl solution vapour2 7#d7 ,a ,b ,c vapour 7it follows that ,b ,k,cl solution gives ,a72 7#e7 ,a ,c ,k,cl vapour2 7#f7 ,b ,c solution vapour2 and 7#g7 ,b ,k,cl solution vapour4 ,thus above #ib ,a gives ,b ,k,cl4 ,the law of phases by bringing complex instances of chemical reaction under simple physical schemes1 facilitates their study in detail and gives the means of seeking the simplest chemical relations dealing with solutions1 dissociation1 double decompositions and similar cases1 and therefore deserves consideration1 but a detailed exposition of this subject must be looked for in works on physical chemistry4 #aj ,the normal cupric nitrate1 ,cu,n#b,o#f1c;,h#b,o1 is obtained as a deliquescent salt of a blue colour 7soluble in water and in alcohol7 by dissolving copper or cupric oxide in nitric acid4 ,it is so easily decomposed by the action of heat that it is impossible to drive off the water of crystallisation from it before it begins to decompose4 ,during the ignition of the normal salt the cupric oxide formed enters into combination with the remaining undecomposed normal salt1 and gives a basic salt1 ,cu,n#b,o#f1b;,cu,h#b,o#b4 ,the same basic salt is obtained if a certain quantity of alkali or cupric hydroxide or carbonate be added to the solution of the normal salt1 which is even decomposed when boiled with metallic copper1 and forms the basic salt as a green powder1 which easily decomposes under the action of heat and leaves a residue of cupric oxide4 ,the basic salt1 having the composition ,cu,n#b,o#f1c;,cu,h#b,o#b1 is nearly insoluble in water4 ,the normal carbonate of copper1 ,cu,c,o#c1 occurs in nature1 although extremely rarely4 ,if solutions of cupric salts be mixed with solutions of alkali carbonates1 then1 as in the case of magnesium1 carbonic anhydride is evolved and basic salts are formed1 which vary in composition according to the temperature and conditions of the reaction4 ,by mixing cold solutions1 a voluminous blue precipitate is formed1 containing an equivalent proportion of cupric hydroxide and carbonate 7after standing or heating1 its composition is the same as malachite1 sp4 gr4 #cea3 #b;,cu,s,o#d #b,na#b;,,co#c ,h#b,o ,cu,c,o#c1;,cu,h#b,o#b #b,na#b,,so#d ,,co#b4 ,if the resultant blue precipitate be heated in the liquid1 it loses water and is transformed into a granular green mass of the composition ,cu#b;,,co#d--;i4e4 into a compound of the normal salt with anhydrous cupric oxide4 ,this salt of the oxide corresponds with orthocarbonic acid1 ,c7,,oh7#d ,,ch#d,o#d where #d;,h is replaced by #b;,cu4 ,on further boiling this salt loses a portion of the carbonic acid1 forming black cupric oxide1 so unstable is the compound of copper with carbonic anhydride4 ,another basic salt which occurs in nature1 #b;,cu,c,o#c1;,cu,h#b,o#b1 is known as azurite1 or blue carbonate of copper2 it also loses carbonic acid when boiled with water4 ,on mixing a solution of cupric sulphate with sodium sesquicarbonate no precipitate is at first obtained1 but after boiling a precipitate is formed having the composition of malachite4 ,debray obtained artificial azurite by heating cupric nitrate with chalk4 ,the commonest normal salt is blue vitriol--i4e4 the normal cupric sulphate4 ,it generally contains five molecules of water of crystallisation1 ,cu,s,o#d1e;,h#b,o4 ,it forms the product of the action of strong sulphuric acid on copper1 sulphurous anhydride being evolved4 ,the same salt is obtained in practice by carefully roasting sulphuretted ores of copper1 and also by the action of water holding oxygen in solution on them3 ,cu,s ,o#d ,cu,s,o#d4 ,this salt forms a by-product1 obtained in gold refineries1 when the silver is precipitated from the sulphuric acid solution by means of copper4 ,it is also obtained by pouring dilute sulphuric acid over sheet copper in the presence of air1 or by heating cupric oxide or carbonate in sulphuric acid4 ,the crystals of this salt belong to the triclinic system1 have a specific gravity of #bai1 are of a beautiful blue colour1 and give a solution of the same colour4 #ajj parts of water at #j dissolve #ae1 at #be #bc1 and at #ajj about #de parts of cupric sulphate1 ,cu,s,o#d4aj bis ,at #ajj this salt loses a portion of its water of crystallisation1 which it only parts with entirely at a high temperature 7#bbj7 and then gives a white powder of the anhydrous sulphate2 and the latter1 on further calcination1 loses the elements of sulphuric anhydride1 leaving cupric oxide1 like all the cupric salts4 ,the anhydrous 7colourless7 cupric sulphate is sometimes used for absorbing water2 it turns blue in the process4 ,it offers the advantage that it retains both hydrochloric acid and water1 but not carbonic anhydride4#aa ,cupric sulphate is used for steeping seed corn2 this is said to prevent the growth of certain parasites on the plants4 ,in the arts a considerable quantity of cupric sulphate is also used in the preparation of other copper salts--for instance1 of certain pigments#aa bis--and a particularly large quantity is used in the galvanoplastic process1 which consists in the deposition of copper from a solution of cupric sulphate by the action of a galvanic current1 when the metallic copper is deposited on the negative pole and takes the shape of the latter4 ,the description of the processes of galvanoplastic art introduced by ,jacobi in ,st4 ,petersburg forms a part of applied physics1 and will not be touched on here1 and we will only mention that1 although first introduced for small articles1 it is now used for such articles as type moulds 7clichs71 for maps1 prints1 c41 and also for large statues1 and for the deposition of iron1 zinc1 nickel1 gold1 silver1 c4 on other metals and materials4 ,the beginning of the application of the galvanic current to the practical extraction of metals from solutions has also been established1 especially since the dynamo-electric machines of ,gramme1 ,siemens1 and others have rendered it possible to cheaply convert the mechanical motion of the steam engine into an electric current4 ,it is to be expected that the application of the electric current1 which has long since given such important results in chemistry1 will1 in the near future1 play an important part in technical processes1 the example being shown by electric lighting4 #aj bis ,although sulphate of copper usually crystallises with #e;,h#b,o1 that is1 differently to the sulphates of ,mg1 ,fe1 and ,mn1 it is nevertheless perfectly isomorphous with them1 as is seen not only in the fact that it gives isomorphous mixtures with them1 containing a similar amount of water of crystallisation1 but also in the ease with which it forms1 like all bases analogous to ,mg,o1 double salts1 ,r#b;,cu7,,so#d7b1f;,h#b,o1 where ,r ,k1 ,rb1 ,cs1 of the monoclinic system4 ,salts of this kind1 like ,cu,cl#b1b,k,cl1#b;,h#b,o1,pt,k#b;,cy#d1 c41 present a composition ,cu,x#b if the representation of double salts given in ,chapter ,,xxiii41 ,note #aa1 be admitted1 because they1 like ,cu7,,ho7#b1 contain ,cu7,x#b,k7#b1 where ,x#b ,,so#d1 i4e4 the residue of sulphuric acid1 which combines with ,h#b1 and is therefore able to replace the ,h#b by ,x#b or ,o4 ,a detailed study of the crystalline forms of these salts1 made by ,tutton 7#ahic7 7see ,chapter ,,xiii41 ,note #a71 showed3 7#a7 that #bb investigated salts of the composition ,r#b,m7,,so#d71f;,h#b,o1 where ,r ,k1 ,rb1 ,cs1 and ,m ,mg1 ,zn1 ,cd1 ,mn1 ,fe1 ,co1 ,ni1 ,cu1 present a complete crystallographic resemblance2 7#b7 that in all respects the ,rb salts present a transition between the ,k and ,cs salts2 7#c7 that the ,cs salts form crystals most easily1 and the ,k salts the most difficultly1 and that for the ,k salts of ,cd and ,mn it was even impossible to obtain well-formed crystals2 7#d7 that notwithstanding the closeness of their angles1 the general appearance 7habit7 of the potassium compound differs very clearly from the ,cs salts1 while the ,rb salts present a distinct transition in this respect2 7#e7 that the angle of the inclination of one of the axes to the plane of the two other axes showed that in the ,k salts 7angle from #ge to #ge #ch7 the inclination is least1 in the ,cs salts 7from #gb #eb to #gc #ej7 greatest1 and in the ,rb salts 7from #gc #eg to #gd #db7 intermediate between the two2 the replacement of ,mg 444 ,cu produces but a very small change in this angle2 7#f7 that the other angles and the ratio of the axes of the crystals exhibit a similar variation2 and 7#g7 that thus the variation of the form is chiefly determined by the atomic weight of the alkaline metal4 ,as an example we cite the magnitude of the inclination of the axes of ,r#b,m7,,so#d7b1f;,h#b,o4 ,r ,k ,rb ,cs ,m ,mg #ge #ab #gd #a #gb #ed ,zn #ge #ab #gd #g #gb #ei ,cd -- #gd #g #gb #di ,mn -- #gc #c #gb #ec ,fe #ge #bh #gd #af #gc #h ,co #ge #e #gc #ei #gb #eb ,ni #ge #j #gc #eg #gb #eh ,cu #ge #cb #gd #db #gc #ej ,this shows clearly 7within the limits of possible error1 which may be as much as #cj7 the almost perfect identity of the independent crystalline forms notwithstanding the difference of the atomic weights of the diatomic elements1 ,m ,mg1 ,cu4 #aa ,in addition to what has been said 7,chapter ,i41 ,note #fe1 and ,chapter ,,xxii41 ,note #ce7 respecting the combination of ,cu,s,o#d with water and ammonia1 we may add that ,lachinoff 7#ahic7 showed that ,cu,s,o#d1e;,h#b,o loses #d-c_/d;,h#b,o at #ahj1 that ,cu,s,o#d1e,,nh#c also loses #d-c_/d,,nh#c at #cbj1 and that only #a_/d;,h#b,o and #a_/d,,nh#c remain in combination with the ,cu,s,o#d4 ,the last #a_/d;,h#b,o can only be driven off by heating to #bjj1 and the last #a_/d,,nh#c by heating to #cfj4 ,ammonia displaces water from ,cu,s,o#d1e;,h#b,o1 but water cannot displace the ammonia from ,cu,s,o#d1e,,nh#c4 ,if hydrochloric acid gas be passed over ,cu,s,o#d1e;,h#b,o at the ordinary temperature1 it first forms ,cu,s,o#d1e;,h#b,o1#c;,h,cl1 and then ,cu,s,o#d1b;,h#b,o1#b;,h,cl4 ,when air is passed over the latter compound it passes into ,cu,s,o#d;,h#b,o with a small amount of ,h,cl 7about #a_/h;,h,cl74 ,at #ajj ,cu,s,o#d1e;,h#b,o in a stream of hydrochloric acid gas gives ,cu,s,o#d1a_/d;,h#b,o1#b;,h,cl1 and then ,cu,s,o#d1a_/d;,h#b,o1,h,cl1 whilst after prolonged heating ,cu,s,o#d remains1 which rapidly passes into ,cu,s,o#d1e;,h#b,o when placed under a bell jar over water4 ,over sulphuric acid1 however1 ,cu,s,o#d1e;,h#b,o only parts with #c;,h#b,o1 and if ,cu,s,o#d1b;,h#b,o be placed over water it again forms ,cu,s,o#d1e;,h#b,o1 and so on4 #aa bis ,commercial blue vitriol generally contains ferrous sulphate4 ,the salt is purified by converting the ferrous salt into a ferric salt by heating the solution with chlorine or nitric acid4 ,the solution is then evaporated to dryness1 and the unchanged cupric sulphate extracted from the residue1 which will contain the larger portion of the ferric oxide4 ,the remainder will be separated if cupric hydroxide is added to the solution and boiled2 the cupric oxide1 ,cu,o1 then precipitates the ferric oxide1 ,fe#b,o#c1 just as it is itself precipitated by silver oxide4 ,but the solution will contain a small proportion of a basic salt of copper1 and therefore sulphuric acid must be added to the filtered solution1 and the salt allowed to crystallise4 ,acid salts are not formed1 and cupric sulphate itself has an acid reaction on litmus paper4 ,the alloys of copper with certain metals1 and especially with zinc and tin1 are easily formed by directly melting the metals together4 ,they are easily cast into moulds1 forged1 and worked like copper1 whilst they are much more durable in the air1 and are therefore frequently used in the arts4 ,even the ancients used exclusively alloys of copper1 and not pure copper1 but its alloys with tin or different kinds of bronze 7,chapter ,,xviii41 ,note #ce74 ,the alloys of copper with zinc are called brass or 'yellow metal4' ,brass contains about #cb p4c4 of zinc2 generally1 however1 it does not contain more than #fe p4c4 of copper4 ,the remainder is composed of lead and tin1 which usually occur1 although in small quantities1 in brass4 ,yellow metal contains about #dj p4c4 of zinc4#ab ,the addition of zinc to copper changes the colour of the latter to a considerable degree2 with a certain amount of zinc the colour of the copper becomes yellow1 and with a still larger proportion of zinc an alloy is formed which has a greenish tint4 ,in those alloys of zinc and copper which contain a larger amount of zinc than of copper1 the yellow colour disappears and is replaced by a greyish colour4 ,but when the amount of zinc is diminished to about #bj p4c41 the alloy is red and hard1 and is called 'tombac4' ,a contraction takes place in alloying copper with zinc1 so that the volume of the alloy is less than that of either metal individually4 ,the zinc volatilises on prolonged heating at a high temperature and the excess of metallic copper remains behind4 ,when heated in the air1 the zinc oxidises before the copper1 so that all the zinc alloyed with copper may be removed from the copper by this means4 ,an important property of brass containing about #cj p4c4 of zinc is that it is soft and malleable in the cold1 but becomes somewhat brittle when heated4 ,we may also mention that ordinary copper coins contain1 in order to render them hard1 tin1 zinc1 and iron 7,cu #ie p4c472 that it is now customary to add a small amount of phosphorus to copper and bronze1 for the same purpose2 and also that copper is added to silver and gold in coining1 c4 to render it hard2 moreover1 in ,germany1 ,switzerland1 and ,belgium1 and other countries1 a silver-white alloy 7melchior1 ,german silver1 c471 for base coinage and other purposes1 is prepared from brass and nickel 7from #aj to #bj p4c4 of nickel2 #bj to #cj p4c4 zinc3 #ej to #gj p4c4 copper71 or directly from copper and nickel1 or1 more rarely1 from an alloy containing silver1 nickel1 and copper4#ab bis #ab ,among the alloys of copper resembling brass1 delta metal1 invented by ,a4 ,dick 7,london7 is largely used 7since #ahhc74 ,it contains #ee p4c4 ,cu1 and #da p4c4 ,zn1 the remaining #d p4c4 being composed of iron 7as much as #c-a_/b p4c41 which is first alloyed with zinc71 or of cobalt1 and manganese1 and certain other metals4 ,the sp4 gr4 of delta metal is #hd4 ,it melts at #iej1 and then becomes so fluid that it fills up all the cavities in a mould and forms excellent castings4 ,it has a tensile strength of #gj kilos per sq4 mm4 7gun metal about #bj1 phosphor bronze about #cj74 ,it is very soft1 especially when heated to #fjj1 but after forging and rolling it becomes very hard2 it is more difficultly acted upon by air and water than other kinds of brass1 and preserves its golden yellow colour for any length of time1 especially if well polished4 ,it is used for making bearings1 screw propellers1 valves1 and many other articles4 ,in general the alloys of ,cu and ,zn containing about #b_/c p4c4 by weight of copper were for a long time almost exclusively made in ,sweden and ,england 7,bristol1 ,birmingham74 ,these alloys for the most part are cheaper1 harder1 and more fusible than copper alone1 and form good castings4 ,the alloys containing #de-hj p4c4 ,cu crystallise in cubes if slowly cooled 7,bi also gives crystals74 ,by washing the surface of brass with dilute sulphuric acid1 ,zn is removed and the article acquires the colour of copper4 ,the alloys approaching ,zn#b;,cu#c in their composition exhibit the greatest resistance 7under other equal conditions2 of purity1 forging1 rolling1 c47 ,the addition of #c p4c4 ,al1 or #e p4c4 ,sn1 improves the quality of brass4 ,respecting aluminium bronze see ,chapter ,,xvii4 p4 #hh4 #ab bis ,ball 7also ,kamensky71 #ahhh1 by investigating the electrical conductivity of the alloys of antimony and copper with lead1 came to the conclusion that only two definite compounds of antimony and copper exist1 whilst the other alloys are either alloys of these two together or with antimony or with copper4 ,these compounds are ,cu#b,sb and ,cu#d,sb--one corresponds with the maximum1 and the other with the minimum1 electrical resistance4 ,in general1 the resistance offered to an electrical current forms one of the methods by which the composition of definite alloys 7for example1 ,pb#b,zn#g7 is often established1 whilst the electromotive force of alloys affords 7,laurie1 #ahhh7 a still more accurate method--for instance1 several definite compounds were discovered by this method among the alloys of copper with zinc and tin2 but we will not enter into any details of this subject1 because we avoid all references to electricity1 although the reader is recommended to make himself acquainted with this branch of science1 which has many points in common with chemistry4 ,the study of alloys regarded as solid solutions should1 in my opinion1 throw much light upon the question of solutions1 which is still obscure in many aspects and in many branches of chemistry4 ,copper1 in its cuprous compounds1 is so analogous to silver1 that were there no cupric compounds1 or if silver gave stable compounds of the higher oxide1 ,ag,o1 the resemblance would be as close as that between chlorine and bromine or zinc and cadmium2 but silver compounds corresponding to ,ag,o are quite unknown4 ,although silver peroxide--which was regarded as ,ag,o1 but which ,berthelot 7#ahhj7 recognised as the sesquioxide ,ag#b,o#c--;is known1 still it does not form any true salts1 and consequently cannot be placed along with cupric oxide4 ,in distinction to copper1 silver as a metal does not oxidise under the influence of heat2 and its oxides1 ,ag#b,o and ,ag#b,o#c1 easily lose oxygen 7see ,note #h tri74 ,silver does not oxidise in air at the ordinary pressure1 and is therefore classed among the so-called noble metals4 ,it has a white colour1 which is much purer than that of any other known metal1 especially when the metal is chemically pure4 ,in the arts silver is always used alloyed1 because chemically-pure silver is so soft that it wears exceedingly easily1 whilst when fused with a small amount of copper1 it becomes very hard1 without losing its colour4#ac #ac ,there are not many soft metals2 lead1 tin1 copper1 silver1 iron1 and gold are somewhat soft1 and potassium and sodium very soft4 ,the metals of the alkaline earths are sonorous and hard1 and many other metals are even brittle1 especially bismuth and antimony4 ,but the very slight significance which these properties have in determining the fundamental chemical properties of substances 7although1 however1 of immense importance in the practical applications of metals7 is seen from the example shown by zinc1 which is hard at the ordinary temperature1 soft at #ajj1 and brittle at #bjj4 ,illustration3 ,,fig4 #ie4--;,cupel for silver assaying4 ,illustration3 ,,fig4 #if4--;,clay muffle4 ,illustration3 ,,fig4 #ig4--,portable muffle furnace4 ,as the value of silver depends exclusively on its purity1 and as there is no possibility of telling the amount of impurities alloyed with it from its external appearance1 it is customary in most countries to mark an article with the amount of pure silver it contains after an accurately-made analysis known as the assay of the silver4 ,in ,france the assay of silver shows the amount of pure silver in #a1jjj parts by weight2 in ,russia the amount of pure silver in #if parts--that is1 the assay shows the number of zolotniks 7#dbf grams7 of pure silver in one pound 7#daj grams7 of alloyed silver4 ,russian silver is generally #hd assay--that is1 contains #hd parts by weight of pure silver and #ab parts of copper and other metals4 ,french money contains #ij p4c4 7in the ,russian system this will be #hfd assay7 by weight of silver ,english coins and jewellery contain #ibe p4c4 of silver2 the silver rouble is of #hc-a_/c assay--that is1 it contains #hfh p4c4 of silver--and the smaller ,russian silver coinage is of #dh assay1 and therefore contains #ej p4c4 of silver4 ,silver ornaments and articles are usually made in ,russia of #hd and #gb assay4 ,as the alloys of silver and copper1 especially after being subjected to the action of heat1 are not so white as pure silver1 they generally undergo a process known as 'blanching' 7or 'pickling'7 after being worked up4 ,this consists in removing the copper from the surface of the article by subjecting it to a dark-red heat and then immersing it in dilute acid4 ,during the calcination the copper on the surface is oxidised1 whilst the silver remains unchanged2 the dilute acid then dissolves the copper oxides formed1 and pure silver is left on the surface4 ,the surface is dull after this treatment1 owing to the removal of a portion of the metal by the acid4 ,after being polished the article acquires the desired lustre and colour1 so as to be indistinguishable from a pure silver object4 ,in order to test a silver article1 a portion of its mass must be taken1 not from the surface1 but to a certain depth4 ,the methods of assay used in practice are very varied4 ,the commonest and most often used is that known as cupellation4 ,it is based on the difference in the oxidisability of copper1 lead1 and silver4 ,the cupel is a porous cup with thick sides1 made by compressing bone ash4 ,the porous mass of bone ash absorbs the fused oxides1 especially the lead oxide1 which is easily fusible1 but it does not absorb the unoxidised metal4 ,the latter collects into a globule under the action of a strong heat in the cupel1 and on cooling solidifies into a button1 which may then be weighed4 ,several cupels are placed in a muffle4 ,a muffle is a semi-cylindrical clay vessel1 shown in the accompanying drawing4 ,the sides of the muffle are pierced with several orifices1 which allow the access of air into it4 ,the muffle is placed in a furnace1 where it is strongly heated4 ,under the action of the air entering the muffle the copper of the silver alloy is oxidised1 but as the oxide of copper is infusible1 or1 more strictly speaking1 difficultly fusible1 a certain quantity of lead is added to the alloy2 the lead is also oxidised by the air at the high temperature of the muffle1 and gives the very fusible lead oxide4 ,the copper oxide then fuses with the lead oxide1 and is absorbed by the cupel1 whilst the silver remains as a bright white globule4 ,if the weight of the alloy taken and of the silver left on the cupel be determined1 it is possible to calculate the composition of the alloy4 ,thus the essence of cupellation consists in the separation of the oxidisable metals from silver1 which does not oxidise under the action of heat4 ,a more accurate method1 based on the precipitation of silver from its solutions in the form of silver chloride1 is described in detail in works on analytical chemistry4 ,silver occurs in nature1 both in a native state and in certain compounds4 ,native silver1 however1 is of rather rare occurrence4 ,a far greater quantity of silver occurs in combination with sulphur1 and especially in the form of silver sulphide1 ,ag#b,s1 with lead sulphide or copper sulphide1 or the ores of various other metals4 ,the largest amount of silver is extracted from the lead in which it occurs4 ,if this lead be calcined in the presence of air1 it oxidises1 and the resultant lead oxide1 ,pb,o 7'litharge' or 'silbergltte1' as it is called71 melts into a mobile liquid1 which is easily removed4 ,the silver remains in an unoxidised metallic state4#ad ,this process is called cupellation4 #ad ,in ,america1 whence the largest amount of silver is now obtained1 ores are worked containing not more than #a_/e p4c4 of silver1 whilst at #a_/b p4c4 its extraction is very profitable4 ,moreover1 the extraction of silver from ores containing not more than #jja p4c4 of this metal is sometimes profitable4 ,the majority of the lead smelted from galena contains silver1 which is extracted from it4 ,thus near ,arras1 in ,france1 an ore is worked which contains about #fe parts of lead and #jjhh part of silver in #ajj parts of ore1 which corresponds with #acf parts of silver in #ajj1jjj parts of lead4 ,at ,freiberg1 in ,saxony1 the ore used 7enriched by mechanical dressing7 contains about #ji of silver1 #afj of lead1 and #b of copper in #aj1jjj parts4 ,in every case the lead is first extracted in the manner described in ,chapter ,,xviii41 and this lead will contain all the silver4 ,not unfrequently other ores of silver are mixed with lead ores1 in order to obtain an argentiferous lead as the product4 ,the extraction of small quantities of silver from lead is facilitated by the fact 7,pattinson's process7 that molten argentiferous lead in cooling first deposits crystals of pure lead1 which fall to the bottom of the cooling vessel1 whilst the proportion of silver in the unsolidified mass increases owing to the removal of the crystals of lead4 ,the lead is enriched in this manner until it contains #a_/djj part of silver1 and is then subjected to cupellation on a larger scale4 ,according to ,park's process1 zinc is added to the molten argentiferous lead1 and the alloy of ,pb and ,zn1 which first separates out on cooling1 is collected4 ,this alloy is found to contain all the silver previously contained in the lead4 ,the addition of #je p4c4 of aluminium to the zinc 7,rossler and ,edelman7 facilitates the extraction of the ,ag from the resultant alloy besides preventing oxidation2 for1 after re-melting1 nearly all the lead easily runs off 7remains fluid71 and leaves an alloy containing about #cj p4c4 ,ag and about #gj p4c4 ,zn4 ,this alloy may be used as an anode in a solution of ,zn,cl#b1 when the ,zn is deposited on the cathode1 leaving the silver with a small amount of ,pb1 c4 behind4 ,the silver can be easily obtained pure by treating it with dilute acids and cupelling4 ,the ores of silver which contain a larger amount of it are3 silver glance1 ,ag#b,s 7sp4 gr4 #gb72 argentiferous-copper glance1 ,cu,ag,s2 horn silver or chloride of silver1 ,ag,cl2 argentiferous grey copper ore2 polybasite1 ,m#i,,rs#f 7where ,m ,ag1 ,cu1 and ,r ,sb1 ,as71 and argentiferous gold4 ,the latter is the usual form in which gold is found in alluvial deposits and ores4 ,the crystals of gold from the ,berezoffsky mines in the ,urals contain #ij to #ie of gold and #e to #i of silver1 and the ,altai gold contains #ej to #fe of gold and #cf to #ch of silver4 ,the proportion of silver in native gold varies between these limits in other localities4 ,silver ores1 which generally occur in veins1 usually contain native silver and various sulphur compounds4 ,the most famous mines in ,europe are in ,saxony 7,freiberg71 which has a yearly output of as much as #bf tons of silver1 ,hungary1 and ,bohemia 7#da tons74 ,in ,russia1 silver is extracted in the ,altai and at ,nerchinsk 7#ag tons74 ,the richest silver mines known are in ,america1 especially in ,chili 7as much as #gj tons71 ,mexico 7#bjj tons71 and more particularly in the ,western ,states of ,north ,america4 ,the richness of these mines may be judged from the fact that one mine in the ,state of ,nevada 7,comstock1 near ,washoe and the cities of ,gold ,hill and ,virginia71 which was discovered in #ahei1 gave an output of #djj tons in #ahff4 ,in place of cupellation1 chlorination may also be employed for extracting silver from its ores4 ,the method of chlorination consists in converting the silver in an ore into silver chloride4 ,this is either done by a wet or by a dry method1 roasting the ore with ,na,cl4 ,when the silver chloride is formed1 the extraction of the metal is also done by two methods4 ,the first consists in the silver chloride being reduced to metal by means of iron in rotating barrels1 with the subsequent addition of mercury which dissolves the silver1 but does not act on the other metals4 ,the mercury holding the silver in solution is distilled1 when the silver remains behind4 ,this method is called amalgamation4 ,the other method is less frequently used1 and consists in dissolving the silver chloride in sodium chloride or in sodium thiosulphate1 and then precipitating the silver from the solution4 ,the amalgamation is then carried on in rotating barrels containing the roasted ore mixed with water1 iron1 and mercury4 ,the iron reduces the silver chloride by taking up the chlorine from it4 ,the technical details of these processes are described in works on metallurgy4 ,the extraction of ,ag,cl by the wet method is carried on 7,patera's process7 by means of a solution of hyposulphite of sodium which dissolves ,ag,cl 7see ,note #bc71 or by lixiviating with a #b p4c4 solution of a double hyposulphite of ,na and ,cu 7obtained by adding ,cu,s,o#d to ,na#b,s#b,o#c74 ,the resultant solution of ,ag,cl is first treated with soda to precipitate ,pb,c,o#c1 and then with ,na#b,s1 which precipitates the ,ag and ,au4 ,the process should be carried on rapidly to prevent the precipitation of ,cu#b,s from the solution of ,cu,s,o#d and ,na#b,s#b,o#c4 ,commercial silver generally contains copper1 and1 more rarely1 other metallic impurities also4 ,chemically pure silver is obtained either by cupellation or by subjecting ordinary silver to the following treatment4 ,the silver is first dissolved in nitric acid1 which converts it and the copper into nitrates1 ,cu7,,no#c7b and ,ag,n,o#c2 hydrochloric acid is then added to the resultant solution 7green1 owing to the presence of the cupric salt71 which is considerably diluted with water in order to retain the lead chloride in solution if the silver contained lead4 ,the copper and many other metals remain in solution1 whilst the silver is precipitated as silver chloride4 ,the precipitate is allowed to settle1 and the liquid is decanted off2 the precipitate is then washed and fused with sodium carbonate4 ,a double decomposition then takes place1 sodium chloride and silver carbonate being formed2 but the latter decomposes into metallic silver1 because the silver oxide is decomposed by heat3 ,ag#b;,,co#c ,ag#b ,o ,,co#b4 ,the silver chloride may also be mixed with metallic zinc1 sulphuric acid1 and water1 and left for some time1 when the zinc removes the chlorine from the silver chloride and precipitates the silver as a powder4 ,this finely-divided silver is called 'molecular silver4'#ae #ae ,there is another practical method which is also suitable for separating the silver from the solutions obtained in photography1 and consists in precipitating the silver by oxalic acid4 ,in this case the amount of silver in the solution must be known1 and #bc grams of oxalic acid dissolved in #djj grams of water must be added for every #fj grams of silver in solution in a litre of water4 ,a precipitate of silver oxalate1 ,ag#b;,c#b,o#d1 is then obtained1 which is insoluble in water but soluble in acids4 ,hence1 if the liquid contain any free acid it must be previously freed from it by the addition of sodium carbonate4 ,the resultant precipitate of silver oxalate is dried1 mixed with an equal weight of dry sodium carbonate1 and thrown into a gently-heated crucible4 ,the separation of the silver then proceeds without an explosion1 whilst the silver oxalate if heated alone decomposes with explosion4 ,according to ,stas1 the best method for obtaining silver from its solutions is by the reduction of silver chloride dissolved in ammonia by means of an ammoniacal solution of cuprous thiosulphate2 the silver is then precipitated in a crystalline form4 ,a solution of ammonium sulphite may be used instead of the cuprous salt4 ,chemically-pure silver has an exceeding pure white colour1 and a specific gravity of #aje4 ,solid silver is lighter than the molten metal1 and therefore a piece of silver floats on the latter4 ,the fusing-point of silver is about #iej ,c41 and at the high temperature attained by the combustion of detonating gas it volatilises4#af ,by employing silver reduced from silver chloride by milk sugar and caustic potash1 and distilling it1 ,stas obtained silver purer than that obtained by any other means2 in fact1 this was perfectly pure silver4 ,the vapour of silver has a very beautiful green colour1 which is seen when a silver wire is placed in an oxyhydrogen flame4#ag #af ,silver is very malleable and ductile2 it may be beaten into leaves #jjjb mm4 in thickness4 ,silver wire may be made so fine that #a gram is drawn into a wire #b-a_/b kilometres long4 ,in this respect silver is second only to gold4 ,a wire of #b mm4 diameter breaks under a strain of #bj kilograms4 #ag ,in melting1 silver absorbs a considerable amount of oxygen1 which is disengaged on solidifying4 ,one volume of molten silver absorbs as much as #bb volumes of oxygen4 ,in solidifying1 the silver forms cavities like the craters of a volcano1 and throws off metal1 owing to the evolution of the gas2 all these phenomena recall a volcano on a miniature scale 7,dumas74 ,silver which contains a small quantity of copper or gold1 c41 does not show this property of dissolving oxygen4 ,the absorption of oxygen by molten silver is1 however1 an oxidation1 but it is at the same time a phenomenon of solution4 ,one cubic centimetre of molten silver can dissolve twenty-two cubic centimetres of oxygen1 which1 even at #j1 only weighs #jjc gram1 whilst #a cubic centimetre of silver weighs at least #aj grams1 and therefore it is impossible to suppose that the absorption of the oxygen is attended by the formation of any definite compound 7rich in oxygen7 of silver and oxygen 7about #de atoms of silver to #a of oxygen7 in any other but a dissociated form1 and this is the state in which substances in solution must be regarded 7,chapter ,i47 ,le ,chatelier showed that at #cjj and #ae atmospheres pressure silver absorbs so much oxygen that it may be regarded as having formed the compound ,ag#d,o1 or a mixture of ,ag#b and ,ag#b,o4 ,moreover1 silver oxide1 ,ag#b,o1 only decomposes at #cjj under low pressures1 whilst at pressures above #aj atmospheres there is no decomposition at #cjj but only at #djj4 ,stas showed that silver is oxidised by air in the presence of acids4 ,v4 d4 ,pfordten confirmed this1 and showed that an acidified solution of potassium permanganate rapidly dissolves silver in the presence of air4 ,it has long been known 7,whler7 that when nitrate of silver1 ,ag,n,o#c1 reacts as an oxidising agent upon citrates and tartrates1 it is able under certain conditions to give either a salt of suboxide of silver 7see ,note #ai7 or a red solution1 or to give a precipitate of metallic silver reduced at the expense of the organic substances4 ,in #ahhi ,carey ,lea1 in his researches on this class of reactions1 showed that soluble silver is here formed1 which he called allotropic silver4 ,it may be obtained by taking #bjj c4c4 of a #aj per cent4 solution of ,ag,n,o#c and quickly adding a mixture 7neutralised with ,na,h,o7 of #bjj c4c4 of a #cj per cent4 solution of ,fe,s,o#d and #bjj c4c4 of a #dj per cent4 solution of sodium citrate4 ,a lilac precipitate is obtained1 which is collected on a filter 7the precipitate becomes blue7 and washed with a solution of ,,nh#d,,no#c4 ,it then becomes soluble in pure water1 forming a red perfectly transparent solution from which the dissolved silver is precipitated on the addition of many soluble foreign bodies4 ,some of the latter--for instance1 ,,nh#d,,no#c1 alkaline sulphates1 nitrates1 and citrates--give a precipitate which redissolves in pure water1 whilst others--for instance1 ,mg,s,o#d1 ,fe,s,o#d1 ,k#b;,cr#b,o#g1 ,ag,n,o#c1 ,ba7,,no#c7b and many others--convert the precipitated silver into a new variety1 which1 although no longer soluble in water1 regains its solubility in a solution of borax and is soluble in ammonia4 ,both the soluble and insoluble silver are rapidly converted into the ordinary grey-metallic variety by sulphuric acid1 although nothing is given off in the reaction2 the same change takes place on ignition1 but in this case ,,co#b is disengaged2 the latter is formed from the organic substances which remain 7to the amount of #c per cent47 in the modified silver 7they are not removed by soaking in alcohol or water74 ,if the precipitated silver be slightly washed and laid in a smooth thin layer on paper or glass1 it is seen that the soluble variety is red when moist and a fine blue colour when dry1 whilst the insoluble variety has a blue reflex4 ,besides these1 under special conditions#ah a golden yellow variety may be obtained1 which gives a brilliant golden yellow coating on glass2 but it is easily converted into the ordinary grey-metallic state by friction or trituration4 ,there is no doubt#ah bis that there is the same relation between ordinary silver which is perfectly insoluble in water and the varieties of silver obtained by ,carey ,lea#ah tri as there is between quartz and soluble silica or between ,cu,s and ,as#b,s#b in their ordinary insoluble forms and in the state of the colloid solution of their hydrosols 7see ,chapter ,i41 ,note #eg1 and ,chapter ,,xvii41 ,note #be bis74 ,here1 however1 an important step in advance has been made in this respect1 that we are dealing with the solution of a simple body1 and moreover of a metal--i4e4 of a particularly characteristic state of matter4 ,and as boron1 gold1 and certain other simple bodies have already been obtained in a soluble 7colloid7 form1 and as numerous organic compounds 7albuminous substances1 gum1 cellulose1 starch1 c47 and inorganic substances are also known in this form1 it might be said that the colloid state 7of hydrogels and hydrosols7 can be acquired1 if not by every substance1 at all events by substances of most varied chemical character under particular conditions of formation from solutions4 ,and this being the case1 we may hope that a further study of soluble colloid compounds1 which apparently present various transitions towards emulsions1 may throw a new light upon the complex question of solutions1 which forms one of the problems of the present epoch of chemical science4 ,moreover1 we may remark that ,spring 7#ahij7 clearly proved the colloid state of soluble silver by means of dialysis as it did not pass through the membrane4 #ah ,when solutions of ,ag,n,o#c1 ,fe,s,o#d1 sodium citrate1 and ,na,h,o are mixed together in the manner described above1 they throw down a precipitate of a beautiful lilac colour2 when transferred to a filter paper the precipitate soon changes colour1 and becomes dark blue4 ,to obtain the substance as pure as possible it is washed with a #e-aj p4c4 solution of ammonium nitrate2 the liquid is decanted1 and #aej c4c4 of water poured over the precipitate4 ,it then dissolves entirely in the water4 ,a small quantity of a saturated solution of ammonium nitrate is added to the solution1 and the silver in solution again separates out as a precipitate4 ,these alternate solutions and precipitations are repeated seven or eight times1 after which the precipitate is transferred to a filter and washed with #ie p4c4 alcohol until the filtrate gives no residue on evaporation4 ,an analysis of the substance so obtained showed that it contained from #igah p4c4 to #igca p4c4 of metallic silver4 ,it remained to discover what the remaining #b-c p4c4 were composed of4 ,are they merely impurities1 or is the substance some compound of silver with oxygen or hydrogen1 or does it contain citric acid in combination which might account for its solubility8 ,the first supposition is set aside by the fact that no gases are disengaged by the precipitate of silver1 either under the action of gases or when heated4 ,the second supposition is shown to be impossible by the fact that there is no definite relation between the silver and citric acid4 ,a determination of the amount of silver in solution showed that the amount of citric acid varies greatly for one and the same amount of silver1 and there is no simple ratio between them4 ,among other methods of preparing soluble silver given by ,carey ,lea1 we may mention the method published by him in #ahia4 ,ag,n,o#c is added to a solution of dextrine in caustic soda or potash2 at first a precipitate of brown oxide of silver is thrown down1 but the brown colour then changes into a reddish chocolate1 owing to the reduction of the silver by the dextrine1 and the solution turns a deep red4 ,a few drops of this solution turn water bright red1 and give a perfectly transparent liquid4 ,the dextrine solution is prepared by dissolving #dj grams of caustic soda and the same amount of ordinary brown dextrine in two litres of water4 ,to this solution is gradually added #bh grams of ,ag,n,o#c dissolved in a small quantity of water4 ,the insoluble allotropic silver is obtained1 as was mentioned above1 from a solution of silver prepared in the manner described1 by the addition of sulphate of copper1 iron1 barium1 magnesium1 c4 ,in one experiment ,lea succeeded in obtaining the insoluble allotropic ,ag in a crystalline form4 ,the red solution1 described above1 after standing several weeks1 deposits crystals spontaneously in the form of short black needles and thin prisms1 the liquid becoming colourless4 ,this insoluble variety1 when rubbed upon paper1 has the appearance of bright shining green flakes1 which polarise light4 ,the gold variety is obtained in a different manner to the two other varieties4 ,a solution is prepared containing #bjj c4c4 of a #aj p4c4 solution of nitrate of silver1 #bjj c4c4 of a #bj p4c4 solution of ,rochelle salt1 and #hjj c4c4 of water4 ,just as in the previous case the reaction consisted in the reduction of the citrate of silver1 so in this case it consists in the reduction of the tartrate1 which here first forms a red1 and then a black precipitate of allotropic ,ag1 which1 when transferred to the filter1 appears of a beautiful bronze colour4 ,after washing and drying1 this precipitate acquires the lustre and colour peculiar to polished gold1 and this is especially remarked where the precipitate comes into contact with glass or china4 ,an analysis of the golden variety gave a percentage composition of #ihgej to #ihgdi ,ag4 ,both the insoluble varieties 7the blue and gold7 have a different specific gravity from ordinary silver4 ,whilst that of fused silver is #ajej1 and of finely-divided silver #ajfb1 the specific gravity of the blue insoluble variety is #ieh1 and of the gold variety #hea4 ,the gold variety passes into ordinary ,ag with great ease4 ,this transition may even be remarked on the filter in those places which have accidentally not been moistened with water4 ,a simple shock1 and therefore friction of one particle upon another1 is enough to convert the gold variety into normal white silver4 ,carey ,lea sent samples of the gold variety for a long distance by rail packed in three tubes1 in which the silver occupied about the quarter of their volume2 in one tube only he filled up this space with cotton-wool4 ,it was afterwards found that the shaking of the particles of ,ag had completely converted it into ordinary white silver1 and that only the tube containing the cotton-wool had preserved the golden variety intact4 ,the soluble variety of ,ag also passes into the ordinary state with great ease1 the heat of conversion being1 as ,prange showed in #ahij1 about #fj calories4 #ah bis ,the opinion of the nature of soluble silver given below was first enunciated in the ,journal of the ,russian ,chemical ,society1 ,february #a1 #ahij1 ,vol4 ,,xxii41 ,note #gc4 ,this view is1 at the present time1 generally accepted1 and this silver is frequently known as the 'colloid' variety4 ,i may add that ,carey ,lea observed the solution of ordinary molecular silver in ammonia without the access of air4 #ah tri ,it is1 however1 noteworthy that ordinary metallic lead has long been considered soluble in water1 that boron has been repeatedly obtained in a brown solution1 and that observations upon the development of certain bacteria have shown that the latter die in water which has been for some time in contact with metals4 ,this seems to indicate the passage of small quantities of metals into water 7however1 the formation of peroxide of hydrogen may be supposed to have some influence in these cases74 ,as regards the capacity of silver for chemical reactions1 it is remarkable for its small capacity for combination with oxygen and for its considerable energy of combination with sulphur1 iodine1 and certain kindred non-metals4 ,silver does not oxidise at any temperature1 and its oxide1 ,ag#b,o1 is decomposed by heat4 ,it is also a very important fact that silver is not oxidised by oxygen either in the presence of alkalis1 even at exceedingly high temperatures1 or in the presence of acids--at least1 of dilute acids--which properties render it a very important metal in chemical industry for the fusion of alkalis1 and also for many purposes in everyday life2 for instance1 for making spoons1 salt-cellars1 c4 ,ozone1 however1 oxidises it4 ,of all acids nitric acid has the greatest action on silver4 ,the reaction is accompanied by the formation of oxides of nitrogen and silver nitrate1 ,ag,n,o#c1 which dissolves in water and does not1 therefore1 hinder the further action of the acid on the metal4 ,the halogen acids1 especially hydriodic acid1 act on silver1 hydrogen being evolved2 but this action soon stops1 owing to the halogen compounds of silver being insoluble in water and only very slightly soluble in acids2 they therefore preserve the remaining mass of metal from the further action of the acid2 in consequence of this the action of the halogen acids is only distinctly seen with finely-divided silver4 ,sulphuric acid acts on silver in the same manner that it does on copper1 only it must be concentrated and at a higher temperature4 ,sulphurous anhydride1 and not hydrogen1 is then evolved1 but there is no action at the ordinary temperature1 even in the presence of air4 ,among the various salts1 sodium chloride 7in the presence of moisture1 air1 and carbonic acid7 and potassium cyanide 7in the presence of air7 act on silver more decidedly than any others1 converting it respectively into silver chloride and a double cyanide4 ,although silver does not directly combine with oxygen1 still three different grades of combination with oxygen may be obtained indirectly from the salts of silver4 ,they are all1 however1 unstable1 and decompose into oxygen and metallic silver when ignited4 ,these three oxides of silver have the following composition3 silver suboxide1 ,ag#d,o1#ai corresponding with the 7little investigated7 suboxides of the alkali metals2 silver oxide1 ,ag#b,o1 corresponding with the oxides of the alkali metals and the ordinary salts of silver1 ,ag,x2 and silver peroxide1 ,ag,o1#ai bis or1 judging from ,berthelot's researches1 ,ag#b,o#c4 ,silver oxide is obtained as a brown precipitate 7which when dried does not contain water7 by adding potassium hydroxide to a solution of a silver salt--for example1 of silver nitrate4 ,the precipitate formed seems1 however1 to be an hydroxide1 ,ag,h,o1 i4e4 ,ag,n,o#c ,,kho ,,kno#c ,ag,h,o1 and the formation of the anhydrous oxide1 #b;,ag,h,o ,ag#b,o ,h#b,o1 may be compared with the formation of the anhydrous cupric oxide by the action of potassium hydroxide on hot cupric solutions4 ,silver hydroxide decomposes into water and silver oxide1 even at low temperatures2 at least1 the hydroxide no longer exists at #fj1 but forms the anhydrous oxide1 ,ag#b,o4#ai tri ,silver oxide is almost insoluble in water2 but1 nevertheless1 it is undoubtedly a rather powerful basic oxide1 because it displaces the oxides of many metals from their soluble salts1 and saturates such acids as nitric acid1 forming with them neutral salts1 which do not act on litmus paper4#bj ,undoubtedly water dissolves a small quantity of silver oxide1 which explains the possibility of its action on solutions of salts--for example1 on solutions of cupric salts4 ,water in which silver oxide is shaken up has a distinctly alkaline reaction4 ,the oxide is distinguished by its great instability when heated1 so that it loses all its oxygen when slightly heated4 ,hydrogen reduces it at about #hj4bj bis ,the feebleness of the affinity of silver for oxygen is shown by the fact that silver oxide decomposes under the action of light1 so that it must be kept in opaque vessels4 ,the silver salts are colourless and decompose when heated1 leaving metallic silver if the elements of the acid are volatile4#bj tri ,they have a peculiar metallic taste1 and are exceedingly poisonous2 the majority of them are acted on by light1 especially in the presence of organic substances1 which are then oxidised4 ,the alkaline carbonates give a white precipitate of silver carbonate1 ,ag#b;,,co#c1 which is insoluble in water1 but soluble in ammonia and ammonium carbonate4 ,aqueous ammonia1 added to a solution of a normal silver salt1 first acts like potassium hydroxide1 but the precipitate dissolves in an excess of the reagent1 like the precipitate of cupric hydroxide4#ba ,silver oxalate and the halogen compounds of silver are insoluble in water2 hydrochloric acid and soluble chlorides give1 as already repeatedly observed1 a white precipitate of silver chloride in solutions of silver salts4 ,potassium iodide gives a yellowish precipitate of silver iodide4 ,zinc separates all the silver in a metallic form from solutions of silver salts4 ,many other metals and reducing agents--for example1 organic substances--also reduce silver from the solutions of its salts4 #ai ,silver suboxide 7,ag#d,o7 or argentous oxide is obtained from argentic citrate by heating it to #ajj in a stream of hydrogen4 ,water and argentous citrate are then formed1 and the latter1 although but slightly soluble in water1 gives a reddish-brown solution of colloid silver 7,note #ah71 and when boiled this solution becomes colourless and deposits metallic silver1 the argentic salt being again formed4 ,whler1 who discovered this oxide1 obtained it as a black precipitate by adding potassium hydroxide to the above solution of argentous citrate4 ,with hydrochloric acid the suboxide gives a brown compound1 ,ag#b;,cl4 ,since the discovery of soluble silver the above data cannot be regarded as perfectly trustworthy2 it is probable that a mixture of ,ag#b and ,ag#b,o was being dealt with1 so that the actual existence of ,ag#d,o is now doubtful1 but there can be no doubt as to the formation of a subchloride1 ,ag#b;,cl 7see ,note #be71 corresponding to the suboxide4 ,the same compound is obtained by the action of light on the higher chloride4 ,other acids do not combine with silver suboxide1 but convert it into an argentic salt and metallic silver4 ,in this respect cuprous oxide presents a certain resemblance to these suboxides4 ,but copper forms a suboxide of the composition ,cu#d,o1 which is obtained by the action of an alkaline solution of stannous oxide on cupric hydroxide1 and is decomposed by acids into cupric salts and metallic copper4 ,the problems offered by the suboxides1 as well as by the peroxides1 cannot be considered as fully solved4 #ai bis ,silver peroxide1 ,ag,o or ,ag#b,o#c1 is obtained by the decomposition of a dilute 7#aj p4c47 solution of silver nitrate by the action of a galvanic current 7,ritter74 ,on the positive pole1 where oxygen is usually evolved in the decomposition of salts1 brittle grey needles with a metallic lustre1 which occasionally attain a somewhat considerable size1 are then formed4 ,they are insoluble in water1 and decompose with the evolution of oxygen when they are dried and heated1 especially up to #aej1 and1 like lead dioxide1 barium peroxide1 c41 their action is strongly oxidising4 ,when treated with acids1 oxygen is evolved and a salt of the oxide formed4 ,silver peroxide absorbs sulphurous anhydride and forms silver sulphate4 ,hydrochloric acid evolves chlorine2 ammonia reduces the silver1 and is itself oxidised1 forming water and gaseous nitrogen4 ,analyses of the above-mentioned crystals show that they contain silver nitrate1 peroxide1 and water4 ,according to ,fisher1 they have the composition #d;,ag,o1,ag,n,o#c1;,h#b,o1 and1 according to ,berthelot1 #d;,ag#b,o#e1b;,ag,n,o#c1;,h#b,o4 #ai tri ,according to ,carey ,lea1 however1 oxide of silver still retains water even at #ajj1 and only parts with it together with the oxygen4 ,oxide of silver is used for colouring glass yellow4 #bj ,the reaction of ,pb7,,oh7#b upon ,ag,h,o in the presence of ,na,h,o leads to the formation of a compound of both oxides1 ,pb,on,ag#b,o1 from which the oxide of lead cannot be removed by alkalies 7,whler1 ,leton74 ,whler1 ,welch1 and others obtained crystalline double salts1 ,r#b;,ag,x#c1 by the action of strong solutions of ,,rx of the halogen salts of the alkaline metals upon ,ag,x1 where ,r ,cs1 ,rb1 ,k4 #bj bis ,according to ,mller1 ferric oxide is reduced by hydrogen 7see ,chapter ,,xxii41 ,note #e7 at #bie 7into what 871 cupric oxide at #adj1 ,ni#b,o#c at #aej2 nickelous oxide1 ,ni,o1 is reduced to the suboxide1 ,ni#b,o1 at #aie1 and to nickel at #bgj2 zinc oxide requires so high a temperature for its reduction that the glass tube in which ,mller conducted the experiment did not stand the heat2 antimony oxide requires a temperature of #bae for its reduction2 yellow mercuric oxide is reduced at #acj and the red oxide at #bcj2 silver oxide at #he1 and platinum oxide even at the ordinary temperature4 #bj tri ,a silica compound1 ,ag#b,o,si,o#b is obtained by fusing ,ag,n,o#c with silica2 this salt is able to decompose with the evolution of oxygen1 leaving ,ag ,si,o#b4 #ba ,if a solution of a silver salt be precipitated by sodium hydroxide1 and aqueous ammonia is added drop by drop until the precipitate is completely dissolved1 the liquid when evaporated deposits a violet mass of crystalline silver oxide4 ,if moist silver oxide be left in a strong solution of ammonia it gives a black mass1 which easily decomposes with a loud explosion1 especially when struck4 ,this black substance is called fulminating silver4 ,probably this is a compound like the other compounds of oxides with ammonia1 and in exploding the oxygen of the silver oxide forms water with the hydrogen of the ammonia1 which is naturally accompanied by the evolution of heat and formation of gaseous nitrogen1 or1 as ,raschig states1 fulminating silver contains ,n,ag#c or one of the amides 7for instance1 ,n,h,ag#b ,,nh#c ,ag#b,o - ,h#b,o74 ,fulminating silver is also formed when potassium hydroxide is added to a solution of silver nitrate in ammonia4 ,the dangerous explosions which are produced by this compound render it needful that great care be taken when salts of silver come into contact with ammonia and alkalis 7see ,chapter ,,xvi41 ,note #bf74 ,silver nitrate1 ,ag,n,o#c1 is known by the name of lunar caustic 7or lapis infernalis72 it is obtained by dissolving metallic silver in nitric acid4 ,if the silver be impure1 the resultant solution will contain a mixture of the nitrates of copper and silver4 ,if this mixture be evaporated to dryness and the residue carefully fused at an incipient red heat1 all the cupric nitrate is decomposed1 whilst the greater part of the silver nitrate remains unchanged4 ,on treating the fused mass with water the latter is dissolved1 whilst the cupric oxide remains insoluble4 ,if a certain amount of silver oxide be added to the solution containing the nitrates of silver and copper1 it displaces all the cupric oxide4 ,in this case it is of course not necessary to take pure silver oxide1 but only to pour off some of the solution and to add potassium hydroxide to one portion1 and to mix the resultant precipitate of the hydroxides1 ,cu7,,oh7#b and ,ag,o,h1 with the remaining portion4#bb ,by these methods all the copper can be easily removed and pure silver nitrate obtained 7its solution is colourless1 while the presence of ,cu renders it blue71 which may be ultimately purified by crystallisation4 ,it crystallises in colourless transparent prismatic plates1 which are not acted on by air4 ,they are anhydrous4 ,its sp4 gr4 is #dcd2 it dissolves in half its weight of water at the ordinary temperature4#bb bis ,the pure salt is not acted on by light1 but it easily acts in an oxidising manner on the majority of organic substances1 which it generally blackens4 ,this is due to the fact that the organic substance is oxidised by the silver nitrate1 which is reduced to metallic silver2 the latter is thus obtained in a finely-divided state1 which causes the black stain4 ,this peculiarity is taken advantage of for marking linen4 ,silver nitrate is for the same reason used for cauterising wounds and various growths on the body4 ,here again it acts by virtue of its oxidising capacity in destroying the organic matter1 which it oxidises1 as is seen from the separation of a coating of black metallic powdery silver from the part cauterised4#bb tri ,from the description of the preparation of silver nitrate it will have been seen that this salt1 which fuses at #bah1 does not decompose at an incipient red heat2 when cast into sticks it is usually employed for cauterising4 ,on further heating1 the fused salt undergoes decomposition1 first forming silver nitrite and then metallic silver4 ,with ammonia1 silver nitrate forms1 on evaporation of the solution1 colourless crystals containing ,ag,n,o#c1b;,,hn#c 7,marignac74 ,in general the salts of silver1 like cuprous1 cupric1 zinc1 c4 salts1 are able to give several compounds with ammonia2 for example1 silver nitrate in a dry state absorbs three molecules 7,rose74 ,the ammonia is generally easily expelled from these compounds by the action of heat4 #bb ,so that we here encounter the following phenomena3 copper displaces silver from the solutions of its salts1 and silver oxide displaces copper oxide from cupric salts4 ,guided by the conceptions enunciated in ,chapter ,,xv41 we can account for this in the following manner3 ,the atomic volume of silver #ajc1 and of copper #gb1 of silver oxide #cb1 and of copper oxide #ac4 ,a greater contraction has taken place in the formation of cupric oxide1 ,cu,o1 than in the formation of silver oxide1 ,ag#b,o1 since in the former 7#ac - #g #f7 the volume after combination with the oxygen has increased by very little1 whilst the volume of silver oxide is considerably greater than that of the metal it contains #cb - 7#b #ajc7 #aad4 ,hence silver oxide is less compact than cupric oxide1 and is therefore less stable2 but1 on the other hand1 there are greater intervals between the atoms in silver oxide than in cupric oxide1 and therefore silver oxide is able to give more stable compounds than those of copper oxide4 ,this is verified by the figures and data of their reactions4 ,it is impossible to calculate for cupric nitrate1 because this salt has not yet been obtained in an anhydrous state2 but the sulphates of both oxides are known4 ,the specific gravity of copper sulphate in an anhydrous state is #cec1 and of silver sulphate #ecf2 the molecular volume of the former is #de1 and of the latter #eh4 ,the group ,,so#c in the copper occupies1 as it were1 a volume #de - #ac #cb1 and in the silver salt a volume #eh - #cb #bf2 hence a smaller contraction has taken place in the formation of the copper salt from the oxide than in the formation of the silver salt1 and consequently the latter should be more stable than the former4 ,hence silver oxide is able to decompose the salt of copper oxide1 whilst with respect to the metals both salts have been formed with an almost identical contraction1 since #eh volumes of the silver salt contain #ba volumes of metal 7difference #cg71 and #de volumes of the copper salt contain #g volumes of copper 7difference #ch74 ,besides which1 it must be observed that copper oxide displaces iron oxide1 just as silver oxide displaces copper oxide4 ,silver1 copper1 and iron1 in the form of oxides1 displace each other in the above order1 but in the form of metals in a reverse order 7iron1 copper1 silver74 ,the cause of this order of the displacement of the oxides lies1 amongst other things1 in their composition4 ,they have the composition ,ag#b,o1 ,cu#b,o#b1 ,fe#b,o#c2 the oxide containing a less proportion of oxygen displaces that containing a larger proportion1 because the basic character diminishes with the increase of contained oxygen4 ,copper also displaces mercury from its salts4 ,it may here be remarked that ,spring 7#ahhh71 on leaving a mixture of dry mercurous chloride and copper for two hours1 observed a distinct reduction1 which belongs to the category of those phenomena which demonstrate the existence of a mobility of parts 7i4e4 atoms and molecules7 in solid substances4 #bb bis ,the reaction of #a part by weight of ,ag,n,o#c requires 7according to ,kremers7 the following amounts of water3 at #j1 #jhb part1 at #aie1 #jda part1 at #ed1 #jbj part1 at #aaj1 #jji part1 and1 according to ,tilden1 at #abe1 #jjfag part1 and at #acc1 #jjeae part4 #bb tri ,it may be remarked that the black stain produced by the reduction of metallic silver disappears under the action of a solution of mercuric chloride or of potassium cyanide1 because these salts act on finely-divided silver4 ,nitrate of silver easily forms double salts like ,ag,n,o#cb,na,n,o#c and ,ag,n,o#c,,kno#c4 ,silver nitrate under the action of water and a halogen gives nitric acid 7see ,vol4 ,i4 p4 #bhj1 formation of ,n#b,o#e71 a halogen salt of silver1 and a silver salt of an oxygen acid of the halogen4 ,thus1 for example1 a solution of chlorine in water1 when mixed with a solution of silver nitrate1 gives silver chloride and chlorate4 ,it is here evident that the reaction of the silver nitrate is identical with the reaction of the caustic alkalis1 as the nitric acid is all set free and the silver oxide only reacts in exactly the same way in which aqueous potash acts on free chlorine4 ,hence the reaction may be expressed in the following manner3 #f;,ag,n,o#c #c;,cl#b #c;,h#b,o #e;,ag,cl ,ag,cl,o#c #f,,nho#c4 ,silver nitrate1 like the nitrates of the alkalis1 does not contain any water of crystallisation4 ,moreover the other salts of silver almost always separate out without any water of crystallisation4 ,the silver salts are further characterised by the fact that they give neither basic nor acid salts1 owing to which the formation of silver salts generally forms the means of determining the true composition of acids--thus1 to any acid ,hn,x there corresponds a salt ,agn,x--for instance1 ,ag#c,,po#d 7,chapter ,,xix41 ,note #ae74 ,silver gives insoluble and exceedingly stable compounds with the halogens4 ,they are obtained by double decomposition with great facility whenever a silver salt comes in contact with halogen salts4 ,solutions of nitrate1 sulphate1 and all other kindred salts of silver give a precipitate of silver chloride or iodide in solutions of chlorides and iodides and of the halogen acids1 because the halogen salts of silver are insoluble both in water#bc and in other acids4 ,silver chloride1 ,ag,cl1 is then obtained as a white flocculent precipitate1 silver bromide forms a yellowish precipitate1 and silver iodide has a very distinct yellow colour4 ,these halogen compounds sometimes occur in nature2 they are formed by a dry method--by the action of halogen compounds on silver compounds1 especially under the influence of heat4 ,silver chloride easily fuses at #dea on cooling from a molten state2 it forms a somewhat soft horn-like mass which can be cut with a knife and is known as horn silver4 ,it volatilises at a higher temperature4 ,its ammoniacal solution1 on the evaporation of the ammonia1 deposits crystalline chloride of silver1 in octahedra4 ,bromide and iodide of silver also appear in forms of the regular system1 so that in this respect the halogen salts of silver resemble the halogen salts of the alkali metals4#bd #bc ,silver chloride is almost perfectly insoluble in water1 but is somewhat soluble in water containing sodium chloride or hydrochloric acid1 or other chlorides1 and many salts1 in solution4 ,thus at #ajj1 #ajj parts of water saturated with sodium chloride dissolve #jd part of silver chloride4 ,bromide and iodide of silver are less soluble in this respect1 as also in regard to other solvents4 ,it should be remarked that silver chloride dissolves in solutions of ammonia1 potassium cyanide1 and of sodium thiosulphate1 ,na#b,s#b,o#c4 ,silver bromide is almost perfectly analogous to the chloride1 but silver iodide is nearly insoluble in a solution of ammonia4 ,silver chloride even absorbs dry ammonia gas1 forming very unstable ammoniacal compounds4 ,when heated1 these compounds 7,vol4 ,i4 p4 #bej1 ,note #h7 evolve the ammonia1 as they also do under the action of all acids4 ,silver chloride enters into double decomposition with potassium cyanide1 forming a soluble double cyanide1 which we shall presently describe2 it also forms a soluble double salt1 ,na,ag,s#b,o#c1 with sodium thiosulphate4 ,silver chloride offers different modifications in the structure of its molecule1 as is seen in the variations in the consistency of the precipitate1 and in the differences in the action of light which partially decomposes ,ag,cl 7see ,note #be74 ,stas and ,carey ,lea investigated this subject1 which has a particular importance in photography1 because silver bromide also gives photo-salts4 ,there is still much to be discovered in this respect1 since ,abney showed that perfectly dry ,ag,cl placed in a vacuum in the dark is not in the least acted upon when subsequently exposed to light4 #bd ,silver bromide and iodide 7which occur as the minerals bromite and iodite7 resemble the chloride in many respects1 but the degree of affinity of silver for iodine is greater than that for chlorine and bromine1 although less heat is evolved 7see ,note #bh bis74 ,deville deduced this fact from a number of experiments4 ,thus silver chloride1 when treated with hydriodic acid1 evolves hydrochloric acid1 and forms silver iodide4 ,finely-divided silver easily liberates hydrogen when treated with hydriodic acid2 it produces the same decomposition with hydrochloric acid1 but in a considerably less degree and only on the surface4 ,the difference between silver chloride and iodide is especially remarkable1 since the formation of the former is attended with a greater contraction than that of the latter4 ,the volume of ,ag,cl #bf2 of chlorine #bg1 of silver #aj1 the sum #cg1 hence a contraction has ensued2 and in the formation of silver iodide an expansion takes place1 for the volume of ,ag is #aj1 of ,i #bf1 and of ,ag,i #ci instead of #cf 7density1 ,ag,cl1 #eei2 ,ag,i1 #efg74 ,the atoms of chlorine have united with the atoms of silver without moving asunder1 whilst the atoms of iodine must have moved apart in combining with the silver4 ,it is otherwise with respect to the metal2 the distance between its atoms in the metal #bb1 in silver chloride #cj1 and in silver iodide #ce2 hence its atoms have moved asunder considerably in both cases4 ,it is also very remarkable1 as ,fizeau observed1 that the density of silver iodide increases with a rise of temperature--that is1 a contraction takes place when it is heated and an expansion when it is cooled4 ,in order to explain the fact that in silver compounds the iodide is more stable than the chloride and oxide1 ,professor ,n4 ,n4 ,beketoff1 in his ',researches on the ,phenomena of ,substitutions' 7,kharkoff1 #ahfe71 proposed the following original hypothesis1 which we will give in almost the words of the author3--,in the case of aluminium1 the oxide1 ,al#b,o#c1 is more stable than the chloride1 ,al#b;,cl#f1 and the iodide1 ,al#b;,i#f4 ,in the oxide the amount of the metal is to the amount of the element combined with it as #edh 7,al #bgc7 is to #dh1 or in the ratio #aab 3 #ajj2 for the chloride the ratio is #be 3 #ajj2 for the iodide it #g 3 #ajj4 ,in the case of silver the oxide 7ratio #acej 3 #ajj7 is less stable than the chloride 7ratio #cjd 3 #ajj71 and the iodide 7ratio of the weight of metal to the weight of the halogen #he 3 #ajj7 is the most stable4 ,from these and similar examples it follows that the most stable compounds are those in which the weights of the combined substances are equal4 ,this may be partly explained by the attraction of similar molecules even after their having passed into combination with others4 ,this attraction is proportional to the product of the acting masses4 ,in silver oxide the attraction of ,ag#b for ,ag#b #baf #baf #df1fef1 and the attraction of ,ag#b for ,o #baf #af #c1def4 ,the attraction of like molecules thus counteracts the attraction of the unlike molecules4 ,the former naturally does not overcome the latter1 otherwise there would be a disruption1 but it nevertheless diminishes the stability4 ,in the case of an equality or proximity of the magnitude of the combining masses1 the attraction of the like parts will counteract the stability of the compound to the least extent--in other words1 with an inequality of the combined masses1 the molecules have an inclination to return to an elementary state1 to decompose1 which does not exist to such an extent where the combined masses are equal4 ,there is1 therefore1 a tendency for large masses to combine with large1 and for small masses to combine with small4 ,hence ,ag#b,o #b,,ki gives ,k#b,o #b;,ag,i4 ,the influence of an equality of masses on the stability is seen particularly clearly in the effect of a rise of temperature4 ,argentic1 mercuric1 auric and other oxides composed of unequal masses1 are somewhat readily decomposed by heat1 whilst the oxides of the lighter metals 7like water7 are not so easily decomposed by heat4 ,silver chloride and iodide approach the condition of equality1 and are not decomposed by heat4 ,the most stable oxides under the action of heat are those of magnesium1 calcium1 silicon1 and aluminium1 since they also approach the condition of equality4 ,for the same reason hydriodic acid decomposes with greater facility than hydrochloric acid4 ,chlorine does not act on magnesia or alumina1 but it acts on lime and silver oxide1 c4 ,this is partially explained by the fact that by considering heat as a mode of motion1 and knowing that the atomic heats of the free elements are equal1 it must be supposed that the amount of the motion of atoms 7their vis viva7 is equal1 and as it is equal to the product of the mass 7atomic weight7 into the square of the velocity1 it follows that the greater the combining weight the smaller will be the square of the velocity1 and if the combining weights be nearly equal1 then the velocities also will be nearly equal4 ,hence the greater the difference between the weights of the combined atoms the greater will be the difference between their velocities4 ,the difference between the velocities will increase with the temperature1 and therefore the temperature of decomposition will be the sooner attained the greater be the original difference--that is1 the greater the difference of the weights of the combined substances4 ,the nearer these weights are to each other1 the more analogous the motion of the unlike atoms1 and consequently1 the more stable the resultant compound4 ,the instability of cupric chloride and nitric oxide1 the absence of compounds of fluorine with oxygen1 whilst there are compounds of oxygen with chlorine1 the greater stability of the oxygen compounds of iodine than those of chlorine1 the stability of boron nitride1 and the instability of cyanogen1 and a number of similar instances1 where1 judging from the above argument1 one would expect 7owing to the closeness of the atomic weights7 a stability1 show that ,beketoff's addition to the mechanical theory of chemical phenomena is still far from sufficient for explaining the true relations of affinities4 ,nevertheless1 in his mode of explaining the relative stabilities of compounds1 we find an exceedingly interesting treatment of questions of primary importance4 ,without such efforts it would be impossible to generalise the complex data of experimental knowledge4 ,fluoride of silver1 ,ag,f1 is obtained by dissolving ,ag#b,o or ,ag#b;,,co#c in hydrofluoric acid4 ,it differs from the other halogen salts of silver in being soluble in water 7#a part of salt in #jee of water74 ,it crystallises from its solution in prisms1 ,ag,f,h#b,o 7,marignac71 or ,ag,f#b;,h#b,o 7,pfaundler71 which lose their water in vacuo4 ,gntz 7#ahia71 by electrolising a saturated solution of ,ag#b;,f1 obtained polyfluoride of silver1 ,ag#b;,f1 which is decomposed by water into ,ag,f ,ag4 ,it is also formed by the action of a strong solution of ,ag,f upon finely-divided 7precipitated7 silver4 ,silver chloride may be decomposed1 with the separation of silver oxide1 by heating it with a solution of an alkali1 and if an organic substance be added to the alkali the chloride can easily be reduced o metallic silver1 the silver oxide being reduced in the oxidation of the organic substance4 ,iron1 zinc1 and many other metals reduce silver chloride in the presence of water4 ,cuprous and mercurous chlorides and many organic substances are also able to reduce the silver from chloride of silver4 ,this shows the rather easy decomposability of the halogen compounds of silver4 ,silver iodide is much more stable in this respect than the chloride4 ,the same is also observed with respect to the action of light upon moist ,ag,cl4 ,white silver chloride soon acquires a violet colour when exposed to the action of light1 and especially under the direct action of the sun's rays4 ,after being acted upon by light it is no longer entirely soluble in ammonia1 but leaves metallic silver undissolved1 from which it might be assumed that the action of light consisted in the decomposition of the silver chloride into chlorine and metallic silver and in fact the silver chloride becomes in time darker and darker4 ,silver bromide and iodide are much more slowly acted on by light1 and1 according to certain observations1 when pure they are even quite unacted on2 at least they do not change in weight1#bd bis so that if they are acted on by light1 the change they undergo must be one of a change in the structure of their parts and not of decomposition1 as it is in silver chloride4 ,the silver chloride under the action of light changes in weight1 which indicates the formation of a volatile product1 and the deposition of metallic silver on dissolving in ammonia shows the loss of chlorine4 ,the change does actually occur under the action of light1 but the decomposition does not go as far as into chlorine and silver1 but only to the formation of a subchloride of silver1 ,ag#b;,cl1 which is of a brown colour and is easily decomposed into metallic silver and silver chloride1 ,ag#b;,cl ,ag,cl ,ag4 ,this change of the chemical composition and structure of the halogen salts of silver under the action of light forms the basis of photography1 because the halogen compounds of silver1 after having been exposed to light1 give a precipitate of finely-divided silver1 of a black colour1 when treated with reducing agents4#be #bd bis ,the changes brought about by the action of light necessitate distinguishing the photo-salts of silver4 #be ,in photography these are called 'developers4' ,the most common developers are3 solutions of ferrous sulphate1 pyrogallol1 ferrous oxalate1 hydroxylamine1 potassium sulphite1 hydroquinone 7the last acts particularly well and is very convenient to use71 c4 ,the chemical processes of photography are of great practical and theoretical interest2 but it would be impossible in this work to enter into this special branch of chemistry1 which has as yet been very little worked out from a theoretical point of view4 ,nevertheless1 we will pause to consider certain aspects of this subject which are of a purely chemical interest1 and especially the facts concerning subchloride of silver1 ,ag#b;,cl 7see ,note #ai71 and the photo-salts 7,note #bc74 ,there is no doubt that under the action of light1 ,ag,cl becomes darker in colour1 decreases in weight1 and probably forms a mixture of ,ag,cl1 ,ag#b;,cl1 and ,ag4 ,but the isolation of the subchloride has only been recently accomplished by ,gntz by means of the ,ag#b;,f1 discovered by him 7see ,note #bd74 ,many chemists 7and among them ,hodgkinson7 assumed that an oxychloride of silver was formed by the decomposition of ,ag,cl under the action of light4 ,carey ,lea's 7#ahhi7 and ,a4 ,richardson's 7#ahia7 experiments showed that the product formed does not1 however1 contain any oxygen at all1 and the change in colour produced by the action of light upon ,ag,cl is most probably due to the formation of ,ag#b;,cl4 ,this substance was isolated by ,gntz 7#ahia7 by passing ,h,cl over crystals of ,ag#b;,f4 ,he also obtained ,ag#b;,i in a similar manner by passing ,,hi1 and ,ag#b,s by passing ,h#b,s over ,ag#b;,f4 ,ag#b;,cl is best prepared by the action of phosphorus trichloride upon ,ag#b;,f4 ,at the temperature of its formation ,ag#b;,cl has an easily changeable tint1 with shades of violet red to violet black4 ,under the action of light a similar 7isomeric7 substance is obtained1 which splits up into ,ag,cl ,ag when heated4 ,with potassium cyanide ,ag#b;,cl gives ,ag ,ag,c,n ,k,cl1 whence it is possible to calculate the heat of formation of ,ag#b;,cl2 it #big1 whilst the heat of formation of ,ag,cl #bib--;i4e4 the reaction #b;,ag,cl ,ag#b;,cl ,cl corresponds to an absorption of #bhg major calories4 ,if we admit the formation of such a compound by the action of light1 it is evident that the energy of the light is consumed in the above reaction4 ,carey ,lea 7#ahib7 subjected ,ag,cl1 ,ag,br1 and ,ag,i to a pressure 7of course in the dark7 of #c1jjj atmospheres1 and to trituration with water in a mortar1 and observed a change of colour indicating incipient decomposition1 which is facilitated under the action of light by the molecular currents set up 7,lermontoff1 ,egoroff74 ,the change of colour of the halogen salts of silver under the action of light1 and their faculty of subsequently giving a visible photographic image under the action of 'developers1' must now be regarded as connected with the decomposition of ,ag,x1 leading to the formation of ,ag#b,x1 and the different tinted photo-salts must be considered as systems containing such ,ag#b,x's4 ,carey ,lea obtained photo-salts of this kind not only by the action of light but also in many other ways1 which we will enumerate to prove that they contain the products of an incomplete combination of ,ag with the halogens1 7for the salts ,ag#b,x must be regarded as such74 ,the photo-salts have been obtained 7#a7 by the imperfect chlorination of silver2 7#b7 by the incomplete decomposition of ,ag#b,o or ,ag#b;,,co#c by alternately heating and treating with a halogen acid2 7#c7 by the action of nitric acid or ,na#b,s#b,o#c upon ,ag#b;,cl2 7#d7 by mixing a solution of ,ag,n,o#c with the hydrates of ,fe,o1 ,mn,o and ,cr,o1 and precipitating by ,h,cl2 7#e7 by the action of ,h,cl upon the product obtained by the reduction of citrate of silver in hydrogen 7,note #ai71 and 7#f7 by the action of milk sugar upon ,ag,n,o#c together with soda and afterwards acidulating with ,h,cl4 ,all these reactions should lead to the formation of products of imperfect combination with the halogens and give photo-salts of a similar diversity of colour to those produced by the action of developers upon the halogen salts of silver after exposure to light4 ,the insolubility of the halogen compounds of silver forms the basis of many methods used in practical chemistry4 ,thus by means of this reaction it is possible to obtain salts of other acids from a halogen salt of a given metal1 for instance1 ,r,cl#b #b;,ag,n,o#c ,r7,,no#c7b #b;,ag,cl4 ,the formation of the halogen compounds of silver is very frequently used in the investigation of organic substances2 for example1 if any product of metalepsis containing iodine or chlorine be heated with a silver salt or silver oxide1 the silver combines with the halogen and gives a halogen salt1 whilst the elements previously combined with the silver replace the halogen4 ,for instance1 ethylene dibromide1 ,c#b;,h#d;,br#b1 is transformed into ethylene diacetate1 ,c#b;,h#d7;,c#b;,h#c,o#b7b1 and silver bromide by heating it with silver acetate1 #b;,c#b;,h#c,o#b;,ag4 ,the insolubility of the halogen compounds of silver is still more frequently taken advantage of in determining the amount of silver and halogen in a given solution4 ,if it is required1 for instance1 to determine the quantity of chlorine present in the form of a metallic chloride in a given solution1 a solution of silver nitrate is added to it so long as it gives a precipitate4 ,on shaking or stirring the liquid1 the silver chloride easily settles in the form of heavy flakes4 ,it is possible in this way to precipitate the whole of the chlorine from a solution1 without adding an excess of silver nitrate1 since it can be easily seen whether the addition of a fresh quantity of silver nitrate produces a precipitate in the clear liquid4 ,in this manner it is possible to add to a solution containing chlorine1 as much silver as is required for its entire precipitation1 and to calculate the amount of chlorine previously in solution from the amount of the solution of silver nitrate consumed1 if the quantity of silver nitrate in this solution has been previously determined4#be bis ,the atomic proportions and preliminary experiments with a pure salt--for example1 with sodium chloride--will give the amount of chlorine from the quantity of silver nitrate4 ,details of these methods will be found in works on analytical chemistry4#be tri #be bis ,in order to determine when the reaction is at an end1 a few drops of a solution of ,k#b;,cr,o#d are added to the solution of the chloride4 ,before all the chlorine is precipitated as ,ag,cl1 the precipitate 7after shaking7 is white 7since ,ag#b;,cr,o#d with #b,r,cl gives #b;,ag,cl72 but when all the chlorine is thrown down ,ag#b;,cr,o#d is formed1 which colours the precipitate reddish-brown4 ,in order to obtain accurate results the liquid should be neutral to litmus4 #be tri ,silver cyanide1 ,ag,c,n1 is closely analogous to the haloid salts of silver4 ,it is obtained1 in similar manner to silver chloride1 by the addition of potassium cyanide to silver nitrate4 ,a white precipitate is then formed1 which is almost insoluble in boiling water4 ,it is also1 like silver chloride1 insoluble in dilute acids4 ,however1 it is dissolved when heated with nitric acid1 and both hydriodic and hydrochloric acids act on it1 converting it into silver chloride and iodide4 ,alkalis1 however1 do not act on silver cyanide1 although they act on the other haloid salts of silver4 ,ammonia and solutions of the cyanides of the alkali metals dissolve silver cyanide1 as they do the chloride4 ,in the latter case double cyanides are formed--for example1 ,k,ag,c#b,n#b4 ,this salt is obtained in a crystalline state on evaporating a solution of silver cyanide in potassium cyanide4 ,it is much more stable than silver cyanide itself4 ,it has a neutral reaction1 does not change in the air1 and does not smell of hydrocyanic acid4 ,many acids1 in acting on a solution of this double salt1 precipitate the insoluble silver cyanide4 ,metallic silver dissolves in a solution of potassium cyanide in the presence of air1 with formation of the same double salt and potassium hydroxide1 and when silver chloride dissolves in potassium cyanide it forms potassium chloride1 besides the salt ,k,ag,c#b,n#b4 ,this double salt of silver is used in silver plating4 ,for this purpose potassium cyanide is added to its solution1 as otherwise silver cyanide1 and not metallic silver1 is deposited by the electric current4 ,if two electrodes--one positive 7silver7 and the other negative 7copper7--be immersed in such a solution1 silver will be deposited upon the latter1 and the silver of the positive electrode will be dissolved by the liquid1 which will thus preserve the same amount of metal in solution as it originally contained4 ,if instead of the negative electrode a copper object be taken1 well cleaned from all dirt1 the silver will be deposited in an even coating2 this1 indeed1 forms the mode of silver plating by the wet method1 which is most often used in practice4 ,a solution of one part of silver nitrate in #cj to #ej parts of water1 and mixed with a sufficient quantity of a solution of potassium cyanide to redissolve the precipitate of silver cyanide formed1 gives a dull coating of silver1 but if twice as much water be used the same mixture gives a bright coating4 ,silver plating in the wet way has now replaced to a considerable extent the old process of dry silvering1 because this process1 which consists in dissolving silver in mercury and applying the amalgam to the surface of the objects1 and then vaporising the mercury1 offers the great disadvantage of the poisonous mercury fumes4 ,besides these1 there is another method of silver plating1 based on the direct displacement of silver from its salts by other metals--for example1 by copper4 ,the copper reduces the silver from its compounds1 and the silver separated is deposited upon the copper4 ,thus a solution of silver chloride in sodium thiosulphate deposits a coating of silver upon a strip of copper immersed in it4 ,it is best for this purpose to take pure silver sulphite4 ,this is prepared by mixing a solution of silver nitrate with an excess of ammonia1 and adding a saturated solution of sodium sulphite and then alcohol1 which precipitates silver sulphite from the solution4 ,the latter and its solutions are very easily decomposed by copper4 ,metallic iron produces the same decomposition1 and iron and steel articles may be very readily silver-plated by means of the thiosulphate solution of silver chloride4 ,indeed1 copper and similar metals may even be silver-plated by means of silver chloride2 if the chloride of silver1 with a small amount of acid1 be rubbed upon the surface of the copper1 the latter becomes covered with a coating of silver1 which it has reduced4 ,silver plating is not only applicable to metallic objects1 but also to glass1 china1 c4 ,glass is silvered for various purposes--for example1 glass globes silvered internally are used for ornamentation1 and have a mirrored surface4 ,common looking-glass silvered upon one side forms a mirror which is better than the ordinary mercury mirrors1 owing to the truer colours of the image due to the whiteness of the silver4 ,for optical instruments--for example1 telescopes--concave mirrors are now made of silvered glass1 which has first been ground and polished into the required form4 ,the silvering of glass is based on the fact that silver which is reduced from certain solutions deposits itself uniformly in a perfectly homogeneous and continuous but very thin layer1 forming a bright reflecting surface4 ,certain organic substances have the property of reducing silver in this form4 ,the best known among these are certain aldehydes--for instance1 ordinary acetaldehyde1 ,c#b;,h#d,o1 which easily oxidises in the air and forms acetic acid1 ,c#b;,h#d,o#b4 ,this oxidation also easily takes place at the expense of silver oxide1 when a certain amount of ammonia is added to the mixture4 ,the oxide of silver gives up its oxygen to the aldehyde1 and the silver reduced from it is deposited in a metallic state in a uniform bright coating4 ,the same action is produced by certain saccharine substances and certain organic acids1 such as tartaric acid1 c4 ,accurate experiments1 and more especially the researches of ,stas at ,brussels1 show the proportion in which silver reacts with metallic chlorides4 ,these researches have led to the determination of the combining weights of silver1 sodium1 potassium1 chlorine1 bromine1 iodine1 and other elements1 and are distinguished for their model exactitude1 and we will therefore describe them in some detail4 ,as sodium chloride is the chloride most generally used for the precipitation of silver1 since it can most easily be obtained in a pure state1 we will here cite the quantitative observations made by ,stas for showing the co-relation between the quantities of chloride of sodium and silver which react together4 ,in order to obtain perfectly pure sodium chloride1 he took pure rock salt1 containing only a small quantity of magnesium and calcium compounds and a small amount of potassium salts4 ,this salt was dissolved in water1 and the saturated solution evaporated by boiling4 ,the sodium chloride separated out during the boiling1 and the mother liquor containing the impurities was poured off4 ,alcohol of #fe p4c4 strength and platinic chloride were added to the resultant salt1 in order to precipitate all the potassium and a certain part of the sodium salts4 ,the resultant alcoholic solution1 containing the sodium and platinum chlorides1 was then mixed with a solution of pure ammonium chloride in order to remove the platinic chloride4 ,after this precipitation1 the solution was evaporated in a platinum retort1 and then separate portions of this purified sodium chloride were collected as they crystallised4 ,the same salt was prepared from sodium sulphate1 tartrate1 nitrate1 and from the platinochloride1 in order to have sodium chloride prepared by different methods and from different sources1 and in this manner ten samples of sodium chloride thus prepared were purified and investigated in their relation to silver4 ,after being dried1 weighed quantities of all ten samples of sodium chloride were dissolved in water and mixed with a solution in nitric acid of a weighed quantity of perfectly pure silver4 ,a slightly greater quantity of silver was taken than would be required for the decomposition of the sodium chloride1 and when1 after pouring in all the silver solution1 the silver chloride had settled1 the amount of silver remaining in excess was determined by means of a solution of sodium chloride of known strength4 ,this solution of sodium chloride was added so long as it formed a precipitate4 ,in this manner ,stas determined how many parts of sodium chloride correspond to #ajj parts by weight of silver4 ,the result of ten determinations was that for the entire precipitation of #ajj parts of silver1 from #edbjfj to #edbjic parts of sodium chloride were required4 ,the difference is so inconsiderable that it has no perceptible influence on the subsequent calculations4 ,the mean of ten experiments was that #ajj parts of silver react with #edbjgh parts of sodium chloride4 ,in order to learn from this the relation between the chlorine and silver1 it was necessary to determine the quantity of chlorine contained in #edbjgh parts of sodium chloride1 or1 what is the same thing1 the quantity of chlorine which combines with #ajj parts of silver4 ,for this purpose ,stas made a series of observations on the quantity of silver chloride obtained from #ajj parts of silver4 ,four syntheses were made by him for this purpose4 ,the first synthesis consisted in the formation of silver chloride by the action of chlorine on silver at a red heat4 ,this experiment showed that #ajj parts of silver give #acbhda1 #acbhdc and #acbhdc of silver chloride4 ,the second method consisted in dissolving a given quantity of silver in nitric acid and precipitating it by means of gaseous hydrochloric acid passed over the surface of the liquid2 the resultant mass was evaporated in the dark to drive off the nitric acid and excess of hydrochloric acid1 and the remaining silver chloride was fused first in an atmosphere of hydrochloric acid gas and then in air4 ,in this process the silver chloride was not washed1 and therefore there could be no loss from solution4 ,two experiments made by this method showed that #ajj parts of silver give #acbhdi and #acbhdf parts of silver chloride4 ,a third series of determinations was also made by precipitating a solution of silver nitrate with a certain excess of gaseous hydrochloric acid4 ,the amount of silver chloride obtained was altogether #acbhdh4 ,lastly1 a fourth determination was made by precipitating dissolved silver with a solution of ammonium chloride1 when it was found that a considerable amount of silver 7#jcage7 had passed into solution in the washing2 for #ajj parts of silver there was obtained altogether #acbhdag of silver chloride4 ,thus from the mean of seven determinations it appears that #ajj parts of silver give #acbhdde parts of silver chloride--that is1 that #cbhdde parts of chlorine are able to combine with #ajj parts of silver and with that quantity of sodium which is contained in #edbjgh parts of sodium chloride4 ,these observations show that #cbhdde parts of chlorine combine with #ajj parts of silver and with #bacfcc parts of sodium4 ,from these figures expressing the relation between the combining weights of chlorine1 silver1 and sodium1 it would be possible to determine their atomic weights--that is1 the combining quantity of these elements with respect to one part by weight of hydrogen or #af parts of oxygen1 if there existed a series of similarly accurate determinations for the reactions between hydrogen or oxygen and one of these elements--chlorine1 sodium1 or silver4 ,if we determine the quantity of silver chloride which is obtained from silver chlorate1 ,ag,cl,o#c1 we shall know the relation between the combining weights of silver chloride and oxygen1 so that1 taking the quantity of oxygen as a constant magnitude1 we can learn from this reaction the combining weight of silver chloride1 and from the preceding numbers the combining weights of chlorine and silver4 ,for this purpose it was first necessary to obtain pure silver chlorate4 ,this ,stas did by acting on silver oxide or carbonate1 suspended in water1 with gaseous chlorine4#bf #bf ,the phenomenon which then takes place is described by ,stas as follows1 in a manner which is perfect in its clearness and accuracy3 if silver oxide or carbonate be suspended in water1 and an excess of water saturated with chlorine be added1 all the silver is converted into chloride1 just as is the case with oxide or carbonate of mercury1 and the water then contains1 besides the excess of chlorine1 only pure hypochlorous acid without the least trace of chloric or chlorous acid4 ,if a stream of chlorine be passed into water containing an excess of silver oxide or silver carbonate while the liquid is continually agitated1 the reaction is the same as the preceding2 silver chloride and hypochlorous acid are formed4 ,but this acid does not long remain in a free state3 it gradually acts on the silver oxide and gives silver hypochlorite1 i4e4 ,ag,cl,o4 ,if1 after some time1 the current of chlorine be stopped but the shaking continued1 the liquid loses its characteristic odour of hypochlorous acid1 while preserving its energetic decolorising property1 because the silver hypochlorite which is formed is easily soluble in water4 ,in the presence of an excess of silver oxide this salt can be kept for several days without decomposition1 but it is exceedingly unstable when no excess of silver oxide or carbonate is present4 ,so long as the solution of silver hypochlorite is shaken up with the silver oxide1 it preserves its transparency and bleaching property1 but directly it is allowed to stand1 and the silver oxide settles1 it becomes rapidly cloudy and deposits large flakes of silver chloride1 so that the black silver oxide which had settled becomes covered with the white precipitate4 ,the liquid then loses its bleaching properties and contains silver chlorate1 i4e4 ,ag,cl,o#c1 in solution1 which has a slightly alkaline reaction1 owing to the presence of a small amount of dissolved oxide4 ,in this manner the reactions which are consecutively accomplished may be expressed by the equations3 #f;,cl#b #c;,ag#b,o #c;,h#b,o #f;,ag,cl #f;,h,cl,o2 #f;,h,cl,o #c;,ag#b,o #c;,h#b,o #f;,ag,cl,o2 #f;,ag,cl,o #d;,ag,cl #b;,ag,cl,o#c4 ,hence1 ,stas gives the following method for the preparation of silver chlorate3 ,a slow current of chlorine is caused to act on oxide of silver1 suspended in water which is kept in a state of continual agitation4 ,the shaking is continued after the supply of chlorine has been stopped1 in order that the free hypochlorous acid should pass into silver hypochlorite1 and the resultant solution of the hypochlorite is drawn off from the sediment of the excess of silver oxide4 ,this solution decomposes spontaneously into silver chloride and chlorate4 ,the pure silver chlorate1 ,ag,cl,o#c1 does not change under the action of light4 ,the salt is prepared for further use by drying it in dry air at #aej4 ,it is necessary during drying to prevent the access of any organic matter2 this is done by filtering the air through cotton wool1 and passing it over a layer of red-hot copper oxide4 ,the decomposition of the silver chlorate thus obtained was accomplished by the action of a solution of sulphurous anhydride on it4 ,the salt was first fused by carefully heating it at #bdc4 ,the solution of sulphurous anhydride used was one saturated at #j4 ,sulphurous anhydride in dilute solutions is oxidised at the expense of silver chlorate1 even at low temperatures1 with great ease if the liquid be continually shaken1 sulphuric acid and silver chloride being formed3 ,ag,cl,o#c #c,,so#b #c;,h#b,o ,ag,cl #c;,h#b,,so#d4 ,after decomposition1 the resultant liquid was evaporated1 and the residue of silver chloride weighed4 ,thus the process consisted in taking a known weight of silver chlorate1 converting it into silver chloride1 and determining the weight of the latter4 ,the analysis conducted in this manner gave the following results1 which1 like the preceding1 designate the weight in a vacuum calculated from the weights obtained in air3 ,in the first experiment it appeared that #achghij grams of silver chlorate gave #ajcigie parts of silver chloride1 and in the second experiment that #beiebhg grains of chlorate gave #aidddeae grams of silver chloride1 and after fusion #aidddce grams4 ,the mean result of both experiments1 converted into percentages1 shows that #ajj parts of silver chlorate contain #gdibje of silver chloride and #bejgie parts of oxygen4 ,from this it is possible to calculate the combining weight of silver chloride1 because in the decomposition of silver chlorate there are obtained three atoms of oxygen and one molecule of silver chloride3 ,ag,cl,o#c ,ag,cl #c,o4 ,taking the weight of an atom of oxygen to be #af1 we find from the mean result that the equivalent weight of silver chloride is equal to #adccie4 ,thus if ,o #af1 ,ag,cl #adccie1 and as the preceding experiments show that silver chloride contains #cbhdde parts of chlorine per #ajj parts of silver1 the weight of the atom of silver#bf bis must be #ajgid and that of chlorine #cede4 ,the weight of the atom of sodium is determined from the fact that #bacfcc parts of sodium chloride combine with #cbhdde parts of chlorine2 consequently ,na #bcje4 ,this conclusion1 arrived at by the analysis of silver chlorate1 was verified by means of the analysis of potassium chlorate by decomposing it by heat and determining the weight of the potassium chloride formed1 and also by effecting the same decomposition by igniting the chlorate in a stream of hydrochloric acid4 ,the combining weight of potassium chloride was thus determined1 and another series of determinations confirmed the relation between chlorine1 potassium1 and silver1 in the same manner as the relation between sodium1 chlorine1 and silver was determined above4 ,consequently1 the combining weights of sodium1 chlorine1 and potassium could be deduced by combining these data with the analysis of silver chlorate and the synthesis of silver chloride4 ,the agreement between the results showed that the determinations made by the last method were perfectly correct1 and did not depend in any considerable degree on the methods which were employed in the preceding determinations1 as the combining weights of chlorine and silver obtained were the same as before4 ,there was naturally a difference1 but so small a one that it undoubtedly depended on the errors incidental to every process of weighing and experiment4 ,the atomic weight of silver was also determined by ,stas by means of the synthesis of silver sulphide and the analysis of silver sulphate4 ,the combining weight obtained by this method was #ajgibj4 ,the synthesis of silver iodide and the analysis of silver iodate gave the figure #ajgibh4 ,the synthesis of silver bromide with the analysis of silver bromate gave the figure #ajgiba4 ,the synthesis of silver chloride and the analysis of silver chlorate gave a mean result of #ajgicg4 ,hence there is no doubt that the combining weight of silver is at least as much as #ajgi--;greater than #ajgij and less than #ajgie1 and probably equal to the mean #ajgib4 ,stas determined the combining weights of many other elements in this manner1 such as lithium1 potassium1 sodium1 bromine1 chlorine1 iodine1 and also nitrogen1 for the determination of the amount of silver nitrate obtained from a given amount of silver gives directly the combining weight of nitrogen4 ,taking that of oxygen as #af1 he obtained the following combining weights for these elements3 nitrogen #adjd1 silver #ajgic1 chlorine #cedf1 bromine #giie1 iodine #abfhe1 lithium #gjb1 sodium #bcjd1 potassium #ciae4 ,these figures differ slightly from those which are usually employed in chemical investigations4 ,they must be regarded as the result of the best observations1 whilst the figures usually used in practical chemistry are only approximate--are1 so to speak1 round numbers for the atomic weights which differ so little from the exact figures 7for instance1 for ,ag #ajh instead of #ajgib1 for ,na #bc instead of #bcjd7 that in ordinary determinations and calculations the difference falls within the limits of experimental error inseparable from such determinations4 #bf bis ,the results given by ,stas' determinations have recently been recalculated and certain corrections have been introduced4 ,we give in the context the average results of van der ,plaats and ,thomsen's calculations1 as well as in ,table ,,iii4 neglecting the doubtful thousandths4 ,the exhaustive investigations conducted by ,stas on the atomic weights of the above-named elements have great significance in the solution of the problem as to whether the atomic weights of the elements can be expressed in whole numbers if the unit taken be the atomic weight of hydrogen4 ,prout1 at the beginning of this century1 stated that this was the case1 and held that the atomic weights of the elements are multiples of the atomic weight of hydrogen4 ,the subsequent determinations of ,berzelius1 ,penny1 ,marchand1 ,marignac1 ,dumas1 and more especially of ,stas1 proved this conclusion to be untenable2 since a whole series of elements proved to have fractional atomic weights--for example1 chlorine1 about #cee4 ,on account of this1 ,marignac and ,dumas stated that the atomic weights of the elements are expressed in relation to hydrogen1 either by whole numbers or by numbers with simple fractions of the magnitudes #a_/b and #a_/d4 ,but ,stas's researches refute this supposition also4 ,even between the combining weight of hydrogen and oxygen1 there is not1 so far as is yet known1 that simple relation which is required by ,prout's hypothesis1#bg i4e41 taking ,o #af1 the atomic weight of hydrogen is equal not to #a but to a greater number somewhere between #ajjb and #ajjh or mean #ajje4 ,such a conclusion arrived at by direct experiment cannot but be regarded as having greater weight than ,prout's supposition 7hypothesis7 that the atomic weights of the elements are in multiple proportion to each other1 which would give reason for surmising 7but not asserting7 a complexity of nature in the elements1 and their common origin from a single primary material1 and for expecting their mutual conversion into each other4 ,all such ideas and hopes must now1 thanks more especially to ,stas1 be placed in a region void of any experimental support whatever1 and therefore not subject to the discipline of the positive data of science4 #bg ,this hypothesis1 for the establishment or refutation of which so many researches have been made1 is exceedingly important1 and fully deserves the attention which has been given to it4 ,indeed1 if it appeared that the atomic weights of all the elements could be expressed in whole numbers with reference to hydrogen1 or if they at least proved to be commensurable with one another1 then it could be affirmed with confidence that the elements1 with all their diversity1 were formed of one material condensed or grouped in various manners into the stable1 and1 under known conditions1 undecomposable groups which we call the atoms of the elements4 ,at first it was supposed that all the elements were nothing else but condensed hydrogen1 but when it appeared that the atomic weights of the elements could not be expressed in whole numbers in relation to hydrogen1 it was still possible to imagine the existence of a certain material from which both hydrogen and all the other elements were formed4 ,if it should transpire that four atoms of this material form an atom of hydrogen1 then the atom of chlorine would present itself as consisting of #adb atoms of this substance1 the weight of whose atom would be equal to #jbe4 ,but in this case the atoms of all the elements should be expressed in whole numbers with respect to the weight of the atom of this original material4 ,let us suppose that the atomic weight of this material is equal to unity1 then all the atomic weights should be expressible in whole numbers relatively to this unit4 ,thus the atom of one element1 let us suppose1 would weigh m1 and of another n1 but1 as both m and n must be whole numbers1 it follows that the atomic weights of all the elements would be commensurable4 ,but it is sufficient to glance over the results obtained by ,stas1 and to be assured of their accuracy1 especially for silver1 in order to entirely destroy1 or at least strongly undermine1 this attractive hypothesis4 ,we must therefore refuse our assent to the doctrine of the building up from a single substance of the elements known to us4 ,this hypothesis is not supported either by any known transformation 7for one element has never been converted into another element71 or by the commensurability of the atomic weights of the elements4 ,although the hypothesis of the formation of all the elements from a single substance 7for which ,crookes has suggested the name protyle7 is most attractive in its comprehensiveness1 it can neither be denied nor accepted for want of sufficient data4 ,marignac endeavoured1 however1 to overcome ,stas's conclusions as to the incommensurability of the atomic weights by supposing that in his1 as in the determinations of all other observers1 there were unperceived errors which were quite independent of the mode of observation--for example1 silver nitrate might be supposed to be an unstable substance which changes1 under the heatings1 evaporations1 and other processes to which it is subjected in the reactions for the determination of the combining weight of silver4 ,it might be supposed1 for instance1 that silver nitrate contains some impurity which cannot be removed by any means2 it might also be supposed that a portion of the elements of the nitric acid are disengaged in the evaporation of the solution of silver nitrate 7owing to the decomposing action of water71 and in its fusion1 and that we have not to deal with normal silver nitrate1 but with a slightly basic salt1 or perhaps an excess of nitric acid which cannot be removed from the salt4 ,in this case the observed combining weight will not refer to an actually definite chemical compound1 but to some mixture for which there does not exist any perfectly exact combining relations4 ,marignac upholds this proposition by the fact that the conclusions of ,stas and other observers respecting the combining weights determined with the greatest exactitude very nearly agree with the proposition of the commensurability of the atomic weights--for example1 the combining weight of silver was shown to be equal to #ajgic1 so that it only differs by #jjh from the whole number #ajh1 which is generally accepted for silver4 ,the combining weight of iodine proved to be equal to #abfhe--that is1 it differs from #abg by #jae4 ,the combining weights of sodium1 nitrogen1 bromine1 chlorine1 and lithium are still nearer to the whole or round numbers which are generally accepted4 ,but ,marignac's proposition will hardly bear criticism4 ,indeed if we express the combining weights of the elements determined by ,stas in relation to hydrogen1 the approximation of these weights to whole numbers disappears1 because one part of hydrogen in reality does not combine with #af parts of oxygen1 but with #aeib parts1 and therefore we shall obtain1 taking ,h #a1 not the above-cited figures1 but for silver #ajgch1 for bromine #giee1 magnitudes which are still further removed from whole numbers4 ,besides which1 if ,marignac's proposition were true the combining weight of silver determined by one method--e4g4 by the analysis of silver chlorate combined with the synthesis of silver chloride--would not agree well with the combining weight determined by another method--e4g4 by means of the analysis of silver iodate and the synthesis of silver iodide4 ,if in one case a basic salt could be obtained1 in the other case an acid salt might be obtained4 ,then the analysis of the acid salt would give different results from that of the basic salt4 ,thus ,marignac's arguments cannot serve as a support for the vindication of ,prout's hypothesis4 ,in conclusion1 ,i think it will not be out of place to cite the following passage from a paper ,i read before the ,chemical ,society of ,london in #ahhi 7,appendix ,,ii471 referring to the hypothesis of the complexity of the elements recognised in chemistry1 owing to the fact that many have endeavoured to apply the periodic law to the justification of this idea 'dating from a remote antiquity1 when it was found convenient to admit the existence of many gods but only one matter4' ',when we try to explain the origin of the idea of a unique primary matter1 we easily trace that1 in the absence of deductions from experiment1 it derives its origin from the scientifically philosophical attempt at discovering some kind of unity in the immense diversity of individualities which we see around4 ,in classical times such a tendency could only be satisfied by conceptions about the immaterial world4 ,as to the material world1 our ancestors were compelled to resort to some hypothesis1 and they adopted the idea of unity in the formative material1 because they were not able to evolve the conception of any other possible unity in order to connect the multifarious relations of matter4 ,responding to the same legitimate scientific tendency1 natural science has discovered throughout the universe a unity of plan1 a unity of forces1 and a unity of matter2 and the convincing conclusions of modern science compel every one to admit these kinds of unity4 ,but while we admit unity in many things1 we none the less must also explain the individuality and the apparent diversity which we cannot fail to trace everywhere4 ,it was said of old ,give us a fulcrum and it will become easy to displace the earth4 ,so also we must say1 ,give us something that is individualised1 and the apparent diversity will be easily understood4 ,otherwise1 how could unity result in a multitude4 ',after a long and painstaking research1 natural science has discovered the individualities of the chemical elements1 and therefore it is now capable1 not only of analysing1 but also of synthesising2 it can understand and grasp generality and unity1 as well as the individualised and multifarious4 ,the general and universal1 like time and space1 like force and motion1 vary uniformly4 ,the uniform admit of interpolations1 revealing every intermediate phase2 but the multitudinous1 the individualised--such as ourselves1 or the chemical elements1 or the members of a peculiar periodic function of the elements1 or ,dalton's multiple proportions--is characterised in another way4 ,we see in it--side by side with a general connecting principle--leaps1 breaks of continuity1 points which escape from the analysis of the infinitely small--an absence of complete intermediate links4 ,chemistry has found an answer to the question as to the causes of multitudes1 and while retaining the conception of many elements1 all submitted to the discipline of a general law1 it offers an escape from the ,indian ,nirvana--the absorption in the universal--replacing it by the individualised4 ,however1 the place for individuality is so limited by the all-grasping1 all-powerful universal1 that it is merely a point of support for the understanding of multitude in unity4' ,among the platinum metals ruthenium1 rhodium1 and palladium1 by their atomic weights and properties1 approach silver1 just as iron and its analogues 7cobalt and nickel7 approach copper in all respects4 ,gold stands in exactly the same position in relation to the heavy platinum metals1 osmium1 iridium1 and platinum1 as copper and silver do to the two preceding series4 ,the atomic weight of gold is nearly equal to their atomic weights2#bh it is dense like these metals4 ,it also gives various grades of oxidation1 which are feeble1 both in a basic and an acid sense4 ,whilst near to osmium1 iridium1 and platinum1 gold at the same time is able1 like copper and silver1 to form compounds which answer to the type ,,rx--that is1 oxides of the composition ,r#b,o4 ,cuprous chloride1 ,cu,cl1 silver chloride1 ,ag,cl1 and aurous chloride1 ,au,cl1 are substances which are very much alike in their physical and chemical properties4#bh bis ,they are insoluble in water1 but dissolve in hydrochloric acid and ammonia1 in potassium cyanide1 sodium thiosulphate1 c4 ,just as copper forms a link between the iron metals and zinc1 and as silver unites the light platinum metals with cadmium1 so also gold presents a transition from the heavy platinum metals to mercury4 ,copper gives saline compounds of the types ,cu,x and ,cu,x#b1 silver of the type ,ag,x1 whilst gold1 besides compounds of the type ,au,x1 very easily and most frequently forms those of the type ,au,cl#c4 ,the compounds of this type frequently pass into those of the lower type1 just as ,pt,x#d passes into ,pt,x#b1 and the same is observable in the elements which1 in their atomic weights1 follow gold4 ,mercury gives ,hg,x#b and ,hg,x1 thallium gives ,tl,x#c and ,tl,x1 lead gives ,pb,x#d and ,pb,x#b4 ,on the other hand1 gold in a qualitative respect differs from silver and copper in the extreme ease with which all its compounds are reduced to metal by many means4 ,this is not only accomplished by many reducing agents1 but also by the action of heat4 ,thus its chlorides and oxides lose their chlorine and oxygen when heated1 and1 if the temperature be sufficiently high1 these elements are entirely expelled and metallic gold alone remains4 ,its compounds1 therefore1 act as oxidising agents4#bi #bh ,it might be expected from the periodic law and analogies with the series iron1 cobalt1 nickel1 copper1 zinc1 that the atomic weights of the elements of the series osmium1 iridium1 platinum1 gold1 mercury1 would rise in this order1 and at the time of the establishment of the periodic law 7#ahfi71 the determinations of ,berzelius1 ,rose1 and others gave the following values for the atomic weights3 ,os #bjj1 ,ir #aig1 ,pt #aih1 ,au #aif1 ,hg #bjj4 ,the fulfilment of the expectations of the periodic law was given in the first place by the fresh determinations 7,seubert1 ,dittmar1 and ,arthur7 of the atomic weight of platinum1 which proved to be nearly #aif1 if ,o #af 7as ,marignac1 ,brauner1 and others propose72 in the second place1 by the fact that ,seubert proved that the atomic weight of osmium is really less than that of platinum1 and approximately ,os #aia2 and1 in the third place1 by the fact that after the researches of ,krss1 ,thorpe1 and ,laurie there was no doubt that the atomic weight of gold is greater than that of platinum--namely1 nearly #aig4 #bh bis ,in ,chapter ,,xxii41 ,note #dj1 we gave the thermal data for certain of the compounds of copper of the type ,cu,x#b2 we will now cite certain data for the cuprous compounds of the type ,cu,x1 which present an analogy to the corresponding compounds ,ag,x and ,au,x1 some of which were investigated by ,thomsen in his classical work1 ',thermochemische ,untersuchungen' 7,vol4 iii41 #ahhc74 ,the data are given in the same manner as in the above-mentioned note3 ,r ,cu ,ag ,au ,r ,cl #cc #bi #f ,r ,br #be #bc #j ,r ,i #af #ad -#f ,r ,o #da #f -8 ,thus we see in the first place that gold1 which possesses a much smaller affinity than ,ag1 evolves far less heat than an equivalent amount of copper1 giving the same compound1 and in the second place that the combination of copper with one atom of oxygen disengages more heat than its combination with one atom of a halogen1 whilst with silver the reverse is the case4 ,this is connected with the fact that ,cu#b,o is more stable under the action of heat than ,ag#b,o4 #bi ,heavy atoms and molecules1 although they may present many points of analogy1 are more easily isolated2 thus ,c#af;,h#cb1 although1 like ,c#b;,h#d1 it combines with ,br#b1 and has a similar composition1 yet reacts with much greater difficulty than ,c#b;,h#d1 and in this it resembles gold2 the heavy atoms and molecules are1 so to say1 inert1 and already saturated by themselves4 ,gold in its higher grade of oxidation1 ,au#b,o#c1 presents feeble basic properties and weakly-developed acid properties1 so that this oxide of gold1 ,au#b,o#c1 may be referred to the class of feeble acid oxides1 like platinic oxide4 ,this is not the case in the highest known oxides of copper and silver4 ,but in the lower grade of oxidation1 aurous oxide1 ,au#b,o1 gold1 like silver and copper1 presents basic properties1 although they are not very pronounced4 ,in this respect it stands very close in its properties1 although not in its types of combination 7,au,x and ,au,x#c71 to platinum 7,pt,x#b and ,pt,x#d7 and its analogues4 ,as yet the general chemical characteristics of gold and its compounds have not been fully investigated4 ,this is partly due to the fact that very few researches have been undertaken on the compounds of this metal1 owing to its inaccessibility for working in large quantities4 ,as the atomic weight of gold is high 7,au #aig71 the preparation of its compounds requires that it should be taken in large quantities1 which forms an obstacle to its being fully studied4 ,hence the facts concerning the history of this metal are rarely distinguished by that exactitude with which many facts have been established concerning other elements more accessible1 and long known in use4 ,in nature gold occurs in the primary and chiefly in quartzose rocks1 and especially in quartz veins1 as in the ,urals 7at ,berezoffsk71 in ,australia1 and in ,california4 ,the native gold is extracted from these rocks by subjecting them to a mechanical treatment consisting of crushing and washing4#bi bis ,nature has already accomplished a similar disintegration of the hard rocky matter containing gold4#cj ,these disintegrated rocks1 washed by rain and other water1 have formed gold-bearing deposits1 which are known as alluvial gold deposits4 ,gold-bearing soil is sometimes met with on the surface and sometimes under the upper soil1 but more frequently along the banks of dried-up water-courses and running streams4 ,the sand of many rivers contains1 however1 a very small amount of gold1 which it is not profitable to work2 for example1 that of the ,alpine rivers contains #e parts of gold in #aj1jjj1jjj parts of sand4 ,the richest gold deposits are those of ,siberia1 especially in the southern parts of the ,government of ,yeniseisk1 the ,south ,urals1 ,mexico1 ,california1 ,south ,africa1 and ,australia1 and then the comparatively poorer alluvial deposits of many countries 7,hungary1 the ,alps1 and ,spain in ,europe74 ,the extraction of the gold from alluvial deposits is based on the principle of levigation2 the earth is washed1 while constantly agitated1 by a stream of water1 which carries away the lighter portion of the earth1 and leaves the coarser particles of the rock and heavier particles of the gold1 together with certain substances which accompany it1 in the washing apparatus4 ,the extraction of this washed gold only necessitates mechanical appliances1#ca and it is not therefore surprising that gold was known to savages and in the most remote period of history4 ,it sometimes occurs in crystals belonging to the regular system1 but in the majority of cases in nuggets or grains of greater or less magnitude4 ,it always contains silver 7from very small quantities up to #cj p4c41 when it is called 'electrum'7 and certain other metals1 among which lead and rhodium are sometimes found4 #bi bis ,sonstadt 7#ahgb7 showed that sea water1 besides silver1 always contains gold4 ,munster 7#ahib7 showed that the water of the ,norwegian fiords contains about #e milligrams of gold per ton 7or #e milliardths7--i4e4 a quantity deserving practical attention1 and ,i think it may be already said that1 considering the immeasurable amount of sea water1 in time means will be discovered for profitably extracting gold from sea water by bringing it into contact with substances capable of depositing gold upon their surface4 ,the first efforts might be made upon the extraction of salt from sea water1 and as the total amount of sea water may be taken as about #b1jjj1jjj1jjj1jjj1jjj1jjj tons1 it follows that it contains about #aj1jjj million tons of gold4 ,the yearly production of gold is about #bjj tons for the whole world1 of which about one quarter is extracted in ,russia4 ,it is supposed that gold is dissolved in sea water owing to the presence of iodides1 which1 under the action of animal organisms1 yield free iodine4 ,it is thought 7as ,professor ,konovaloff mentions in his work upon ',the ,industries of the ,united ,states1' #ahid7 that iodine facilitates the solution of the gold1 and the organic matter its precipitation4 ,these facts and considerations to a certain extent explain the distribution of gold in veins or rock fissures1 chiefly filled with quartz1 because there is sufficient reason for supposing that these rocks once formed the ocean bottom4 ,r4 ,dentrie1 and subsequently ,wilkinson1 showed that organic matter--for instance1 cork--and pyrites are able to precipitate gold from its solutions in that metallic form and state in which it occurs in quartz veins1 where 7especially in the deeper parts of vein deposits7 gold is frequently found on the surface of pyrites1 chiefly arsenical pyrites4 ,kazantseff 7in ,ekaterinburg1 #ahia7 even supposes1 from the distribution of the gold in these pyrites1 that it occurred in solution as a compound of sulphide of gold and sulphide of arsenic when it penetrated into the veins4 ,it is from such considerations that the origin of vein and pyritic gold is1 at the present time1 attributed to the reaction of solutions of this metal1 the remains of which are seen in the gold still present in sea water4 #cj ,however1 in recent times1 especially since about #ahgj1 when chlorine 7either as a solution of the gas or as bleaching powder7 and bromine began to be applied to the extraction of finely-divided gold from poor ores 7previously roasted in order to drive off arsenic and sulphur1 and oxidise the iron71 the extraction of gold from quartz and pyrites1 by the wet method1 increases from year to year1 and begins to equal the amount extracted from alluvial deposits4 ,since the nineties the cyanide process 7,chapter ,,xiii41 ,note #ac bis7 has taken an important place among the wet methods for extracting gold from its ores4 ,it consists in pouring a dilute solution of cyanide of potassium 7about #ejj parts of water and #a to #d parts of cyanide of potassium per #a1jjj parts of ore1 the amount of cyanide depending upon the richness of the ore7 and a mixture of it with ,na,c,n1 7see ,chapter ,,xiii41 ,note #ab7 over the crushed ore 7which need not be roasted1 whilst roasting is indispensable in the chlorination process1 as otherwise the chlorine is used up in oxidising the sulphur1 arsenic1 c47 ,the gold is dissolved very rapidly even from pyrites1 where it generally occurs on the surface in such fine and adherent particles that it either cannot be mechanically washed away1 or1 more frequently is carried away by the stream of water1 and cannot be caught by mechanical means or by the mercury used for catching the gold in the sluices4 ,chlorination had already given the possibility of extracting the finest particles of gold2 but the cyanide process enables such pyrites to be treated as could be scarcely worked by other means4 ,the treatment of the crushed ore by the ,,kcn is carried on in simple wooden vats 7coated with paraffin or tar7 with the greatest possible rapidity 7in order that the ,,kcn solution should not have time to change7 by a method of systematic lixiviation1 and is completed in #aj to #ab hours4 ,the resultant solution of gold1 containing ,au,k7,,cn7#b1 is decomposed either with freshly-made zinc filings 7but when the gold settles on the ,zn1 the cyanide solution reacts upon the ,zn with the evolution of ,h#b and formation of ,zn,h#b,o#b7 or by sodium amalgam prepared at the moment of reaction by the action of an electric current upon a solution of ,na,h,o poured into a vessel partially immersed in mercury 7the ,na,c,n is renewed continually by this means74 ,the silver in the ore passes into solution1 together with the gold1 as in amalgamation4 #ca ,but the particles of gold are sometimes so small that a large amount is lost during the washing4 ,it is then profitable to have recourse to the extraction by chlorine and ,,kcn 7,note #cj74 ,in speaking of the extraction of gold the following remarks may not be out of place3 ,in ,california advantage is taken of water supplied from high altitudes in order to have a powerful head of water1 with which the rocks are directly washed away1 thus avoiding the greater portion of the mechanical labour required for the exploitation of these deposits4 ,the last residues of gold are sometimes extracted from sand by washing them with mercury1 which dissolves the gold4 ,the sand mixed with water is caused to come into contact with mercury during the washing4 ,the mercury is then distilled4 ,many sulphurous ores1 even pyrites1 contain a small amount of gold4 ,compounds of gold with bismuth1 ,bi,au#b1 tellurium1 ,au,te#b 7calverite71 c41 have been found1 although rarely4 ,among the minerals which accompany gold1 and from which the presence of gold may be expected1 we may mention white quartz1 titanic and magnetic iron ores1 and also the following1 which are of rarer occurrence3 zircon1 topaz1 garnet1 and such like4 ,the concentrated gold washings first undergo a mechanical treatment1 and the impure gold obtained is treated for pure gold by various methods4 ,if the gold contain a considerable amount of foreign metals1 especially lead and copper1 it is sometimes cupelled1 like silver1 so that the oxidisable metals may be absorbed by the cupel in the form of oxides1 but in every case the gold is obtained together with silver1 because the latter metal also is not oxidised4 ,sometimes the gold is extracted by means of mercury1 that is1 by amalgamation 7and the mercury subsequently driven off by distillation71 or by smelting it with lead 7which is afterwards removed by oxidation7 and processes like those employed for the extraction of silver1 because gold1 like silver1 does not oxidise1 is dissolved by lead and mercury1 and is non-volatile4 ,if copper or any other metal contain gold and it be employed as an anode1 pure copper will be deposited upon the cathode1 while all the gold will remain at the anode as a slime4 ,this method often amply repays the whole cost of the process1 since it gives1 besides the gold1 a pure electrolytic copper4 ,the separation of the silver from gold is generally carried on with great precision1 as the presence of the silver in the gold does not increase its value for exchange1 and it can be substituted by other less valuable metals1 so that the extraction of the silver1 as a precious metal1 from its alloy with gold1 is a profitable operation4 ,this separation is conducted by different methods4 ,sometimes the argentiferous gold is melted in crucibles1 together with a mixture of common salt and powdered bricks4 ,the greater portion of the silver is thus converted into the chloride1 which fuses and is absorbed by the slags1 from which it may be extracted by the usual methods4 ,the silver is also extracted from gold by treating it with boiling sulphuric acid1 which does not act on the gold but dissolves the silver4 ,but if the alloy does not contain a large proportion of silver it cannot be extracted by this method or at all events the separation will be imperfect1 and therefore a fresh amount of silver is added 7by fusion7 to the gold1 in such quantity that the alloy contains twice as much silver as gold4 ,the silver which is added is preferably such as contains gold1 which is very frequently the case4 ,the alloy thus formed is poured in a thin stream into water1 by which means it is obtained in a granulated form2 it is then boiled with strong sulphuric acid1 three parts of acid being used to one part of alloy4 ,the sulphuric acid extracts all the silver without acting on the gold4 ,it is best1 however1 to pour off the first portion of the acid1 which has dissolved the silver1 and then treat the residue of still imperfectly pure gold with a fresh quantity of sulphuric acid4 ,the gold is thus obtained in the form of powder1 which is washed with water until it is quite free from silver4 ,the silver is precipitated from the solution by means of copper1 so that cupric sulphate and metallic silver are obtained4 ,this process is carried out in many countries1 as in ,russia1 at the ,government mints4 ,gold is generally used alloyed with copper2 since pure gold1 like pure silver1 is very soft1 and therefore soon worn away4 ,in assaying or determining the amount of pure gold in such an alloy it is usual to add silver to the gold in order to make up an alloy containing three parts of silver to one of gold 7this is known as quartation because the alloy contains #a_/d of gold71 and the resultant alloy is treated with nitric acid4 ,if the silver be not in excess over the gold1 it is not all dissolved by the nitric acid1 and this is the reason for the quartation4 ,the amount of pure gold 7assay7 is determined by weighing the gold which remains after this treatment4 ,english gold 7 #bb carats7 coinage is composed of an alloy containing #iaff p4c4 of gold1 but for many articles gold is frequently used containing a larger amount of foreign metals4 ,pure gold may be obtained from gold alloys by dissolving in aqua regia1 and then adding ferrous sulphate to the solution or heating it with a solution of oxalic acid4 ,these deoxidising agents reduce the gold1 but not the other metals4 ,the chlorine combined with the gold then acts like free chlorine4 ,the gold1 thus reduced1 is precipitated as an exceedingly fine brown powder4#ca bis ,it is then washed with water1 and fused with nitre or borax4 ,pure gold reflects a yellow light1 and in the form of very thin sheets 7gold leaf71 into which it can be hammered and rolled1#ca tri it transmits a bluish-green light4 ,the specific gravity of gold is about #aie1 the sp4 gr4 of gold coin is about #aga4 ,it fuses at #ajij--;at a higher temperature than silver--and can be drawn into exceedingly fine wires or hammered into thin sheets4 ,with its softness and ductility1 gold is distinguished for its tenacity1 and a gold wire two millimetres thick breaks only under a load of #fh kilograms4 ,gold vaporises even at a furnace heat1 and imparts a greenish colour to a flame passing over it in a furnace4 ,gold alloys with copper almost without changing its volume4#cb ,in its chemical aspect1 gold presents1 as is already seen from its general characteristics given above1 an example of the so-called noble metals--i4e4 it is incapable of being oxidised at any temperature1 and its oxide is decomposed when calcined4 ,only chlorine and bromine combine directly with it at the ordinary temperature1 but many other metals and non-metals combine with it at a red heat--for example1 sulphur1 phosphorus1 and arsenic4 ,mercury dissolves it with great ease4 ,it dissolves in potassium cyanide in the presence of air2 a mixture of sulphuric acid with nitric acid dissolves it with the aid of heat1 although in small quantity4 ,it is also soluble in aqua regia and in selenic acid4 ,sulphuric1 hydrochloric1 nitric1 and hydrofluoric acids and the caustic alkalis do not act on gold1 but a mixture of hydrochloric acid with such oxidising agents as evolve chlorine naturally dissolves it like aqua regia4#cb bis #ca bis ,schottlnder 7#ahic7 obtained gold in a soluble colloid form 7the solution is violet7 by the action of a mixture of solutions of cerium acetate and ,na,h,o upon a solution of ,au,cl#c4 ,the gold separates out from such a solution in exactly the same manner as ,ag does from the solution of colloid silver mentioned above4 ,there always remains a certain amount of a higher oxide of cerium1 ,ce,o#b1 in the solution--i4e4 the gold is reduced by converting the cerium into a higher grade of oxidation4 ,besides which ,krss and ,hofmann showed that sulphide of gold precipitated by the action of ,h#b,s upon a solution of ,au,k,cy#b mixed with ,h,cl easily passes into a colloid solution after being properly washed 7like ,as#b,s#c1 ,cu,s1 c41 ,chapter ,i41 ,note #eg74 #ca tri ,gold-leaf is used for gilding wood 7leather1 cardboard1 and suchlike1 upon which it is glued by means of varnish1 c471 and is about #jjjc millimetre thick4 ,it is obtained from thin sheets 7weighing at first about #a_/d grm4 to a square inch71 rolled between gold rollers1 by gradually hammering them 7in packets of a number at once7 between sheets of moist 7but not wet7 parchment1 and then1 after cutting them into four pieces1 between a specially prepared membrane1 which1 when at the right degree of moisture1 does not tear or stick together under the blows of the hammer4 #cb ,the formation of the alloys ,cu ,zn1 ,cu ,sn1 ,cu ,bi1 ,cu ,sb1 ,pb ,sb1 ,ag ,pb1 ,ag ,sn1 ,au ,zn1 ,au ,sn1 c41 is accompanied by a contraction 7and evolution of heat74 ,the formation of the alloys ,fe ,sb1 ,fe ,pb1 ,cu ,pb1 ,pb ,sn1 ,pb ,sb1 ,zn ,sb1 ,ag ,cu1 ,au ,cu1 ,au ,pb1 takes place with a certain increase in volume4 ,with regard to the alloys of gold1 it may be mentioned that gold is only slightly dissolved by mercury 7about #jjf p4c41 ,dudley1 #ahij72 the remaining portion forms a granular alloy1 whose composition has not been definitely determined4 ,aluminium 7and silicon7 also have the capacity of forming alloys with gold4 ,the presence of a small amount of aluminium lowers the melting point of gold considerably 7,roberts-,austen1 #ahib72 thus the addition of #d p4c4 of aluminium lowers it by #adbh1 the addition of #aj p4c4 ,al by #dag4 ,the latter alloy is white4 ,the alloy ,au,al#b has a characteristic purple colour1 and its melting point is #cbe above that of gold1 which shows it to be a definite compound of the two metals4 ,the melting points of alloys richer in ,al gradually fall to #ffj--that is1 below that of aluminium 7#ffe74 ,heycock and ,neville 7#ahib71 in studying the triple alloys of ,au1 ,cd1 and ,sn1 observed a tendency in the gold to give compounds with ,cd1 and by sealing a mixture of ,au and ,cd in a tube1 from which the air had been exhausted1 and heating it1 they obtained a grey crystalline brittle definite alloy ,au,cd4 #cb bis ,calderon 7#ahib71 at the request of some jewellers1 investigated the cause of a peculiar alteration sometimes found on the surface of dead-gold articles1 there appearing brownish and blackish spots1 which widen and alter their form in course of time4 ,he came to the conclusion that these spots are due to the appearance and development of peculiar micro-organisms 7,aspergillus niger and ,micrococcus cimbareus7 on the gold1 spores of which were found in abundance on the cotton-wool in which the gold articles had been kept4 ,as regards the compounds of gold1 they belong1 as was said above1 to the types ,au,x#c and ,au,x4 ,auric chloride or gold trichloride1 ,au,cl#c1 which is formed when gold is dissolved in aqua regia1 belongs to the former and higher of these types4 ,the solution of this substance in water has a yellow colour1 and it may be obtained pure by evaporating the solution in aqua regia to dryness1 but not to the point of decomposition4 ,if the evaporation proceed to the point of crystallisation1 a compound of gold chloride and hydrochloric acid1 ,au,h,cl#d1 is obtained1 like the allied compounds of platinum2 but it easily parts with the acid and leaves auric chloride1 which fuses into a red-brown liquid1 and then solidifies to a crystalline mass4 ,if dry chlorine be passed over gold in powder it forms a mixture of aurous and auric chlorides1 but the aurous chloride is also decomposed by water into gold and auric chloride4 ,auric chloride crystallises from its solutions as ,au,cl#c1b;,h#b,o1 which easily loses water1 and the dry chloride loses two-thirds of its chlorine at #ahe1 forming aurous chloride1 whilst above #cjj the latter chloride also loses its chlorine and leaves metallic gold4 ,auric chloride is the usual form in which gold occurs in solutions1 and in which its salts are used in the arts and for chemical purposes4 ,it is soluble in water1 alcohol1 and ether4 ,light has a reducing action on these solutions1 and after a time metallic gold is deposited upon the sides of vessels containing the solution4 ,hydrogen when nascent1 and even in a gaseous form1 reduces gold from this solution to a metallic state4 ,the reduction is more conveniently and usually effected by ferrous sulphate1 and in general by the action of ferrous salts4#cc #cc ,stannous chloride as a reducing agent also acts on auric chloride1 and gives a red precipitate known as purple of ,cassius4 ,this substance1 which probably contains a mixture or compound of aurous oxide and tin oxide1 is used as a red pigment for china and glass4 ,oxalic acid1 on heating1 reduces metallic gold from its salts1 and this property may be taken advantage of for separating it from its solutions4 ,the oxidation which then takes place in the presence of water may be expressed by the following equation3 #b;,au,cl#c #c;,c#b;,h#b,o#d #b;,au #f;,h,cl #f;,,co#b4 ,nearly all organic substances have a reducing action on gold1 and solutions of gold leave a violet stain on the skin4 ,auric chloride1 like platinic chloride1 is distinguished for its clearly-developed property of forming double salts4 ,these double salts1 as a rule1 belong to the type ,au,m,cl#d4 ,the compound of auric chloride with hydrochloric acid mentioned above evidently belongs to the same type4 ,the compounds #b,k,au,cl#d1e;,h#b,o1 ,na,au,cl#d1b;,h#b,o1 ,au,n,h#d;,cl#d1;,h#b,o1 ,mg7,au,cl#d7b1b;,h#b,o1 and the like are easily crystallised in well-formed crystals4 ,wells1 ,wheeler1 and ,penfield 7#ahib7 obtained ,rb,au,cl#d 7reddish yellow7 and ,cs,au,cl#d 7golden yellow71 and corresponding bromides 7dark coloured74 ,au,br#c is extremely like the chloride4 ,auric cyanide is obtained easily in the form of a double salt of potassium1 ,k,au7,,cn7#d by mixing saturated and hot solutions of potassium cyanide with auric chloride and then cooling4 ,if a solution of potassium hydroxide be added to a solution of auric chloride1 a precipitate is first formed1 which re-dissolves in an excess of the alkali4 ,on being evaporated under the receiver of an air-pump1 this solution yields yellow crystals1 which present the same composition as the double salts ,au,m,cl#d1 with the substitution of the chlorine by oxygen--that is to say1 potassium aurate1 ,au,k,o#b1 is formed in crystals containing #c;,h#b,o4 ,the solution has a distinctly alkaline reaction4 ,auric oxide1 ,au#b,o#c1 separates when this alkaline solution is boiled with an excess of sulphuric acid4 ,but it then still retains some alkali2 however1 it may be obtained in a pure state as a brown powder by dissolving in nitric acid and diluting with water4 ,the brown powder decomposes below #bej into gold and oxygen4 ,it is insoluble in water and in many acids1 but it dissolves in alkalis1 which shows the acid character of this oxide4 ,an hydroxide1 ,au7,,oh7#c may be obtained as a brown powder by adding magnesium oxide to a solution of auric chloride and treating the resultant precipitate of magnesium aurate with nitric acid4 ,this hydroxide loses water at #ajj1 and gives auric oxide4#cd #cd ,if ammonia be added to a solution of auric chloride1 it forms a yellow precipitate of the so-called fulminating gold1 which contains gold1 chlorine1 hydrogen1 nitrogen1 and oxygen1 but its formula is not known with certainty4 ,it is probably a sort of ammonio-metallic compound1 ,au#b,o#c1d,,nh#c1 or amide 7like the mercury compound74 ,this precipitate explodes at #adj1 but when left in the presence of solutions containing ammonia it loses all its chlorine and becomes non-explosive4 ,in this form the composition ,au#b,o#c1b,,nh#c1;,h#b,o is ascribed to it1 but this is uncertain4 ,auric sulphide1 ,au#b,s#c1 is obtained by the action of hydrogen sulphide on a solution of auric chloride1 and also directly by fusing sulphur with gold4 ,it has an acid character1 and therefore dissolves in sodium and ammonium sulphides4 ,the starting-point of the compounds of the type ,au,x#ce is gold monochloride or aurous chloride1 ,au,cl1 which is formed1 as mentioned above1 by heating auric chloride at #ahe4 ,aurous chloride forms a yellowish-white powder2 this1 when heated with water1 is decomposed into metallic gold and auric chloride1 which passes into solution3 #c;,au,cl ,au,cl#c #b;,au4 ,this decomposition is accelerated by the action of light4 ,hence it is obvious that the compounds corresponding with aurous oxide are comparatively unstable4 ,but this only refers to the simple compounds ,au,x2 some of the complex compounds1 on the contrary1 form the most stable compounds of gold4 ,such1 for example1 is the cyanide of gold and potassium1 ,au,k7,,cn7#b4 ,it is formed1 for instance1 when finely-divided gold dissolves in the presence of air in a solution of potassium cyanide3 #d,,kcn #b;,au ,h#b,o ,o #b,k,au7,,cn7#b #b,,kho 7this reaction also proceeds with solid pieces of gold1 although very slowly74 ,the same compound is formed in solution when many compounds of gold are mixed with potassium cyanide1 because if a higher compound of gold be taken1 it is reduced by the potassium cyanide into aurous oxide1 which dissolves in potassium cyanide and forms ,k,au7,,cn7#b4 ,this substance is soluble in water1 and gives a colourless solution1 which can be kept for a long time1 and is employed in electro-gilding--that is1 for coating other metallic objects with a layer of gold1 which is deposited if the object be connected with the negative pole of a battery and the positive pole consist of a gold plate4 ,when an electric current is passed between them1 the gold from the latter will dissolve1 whilst a coating of gold from the solution will be deposited on the object4 #ce ,many double salts of suboxide of gold belong to the type ,au,x--for instance1 the cyanide corresponding to the type ,au,k,x#b1 like ,pt,k#b,x#d1 with which we became acquainted in the last chapter4 ,we will enumerate several of the representatives of this class of compounds4 ,if auric chloride1 ,au,cl#c1 be mixed with a solution of sodium thiosulphate1 the gold passes into a colourless solution1 which deposits colourless crystals1 containing a double thiosulphate of gold and sodium1 which are easily soluble in water but are precipitated by alcohol4 ,the composition of this salt is ,na#c;,au7,s#b,o#c7b1b;,h#b,o4 ,if the sodium thiosulphate be represented as ,na,s#b,o#c,na1 the double salt in question will be ,au,na7,s#b,o#c,na7#b1b;,h#b,o1 according to the type ,au,na,x#b4 ,the solution of this colourless and easily crystallisable salt has a sweet taste1 and the gold is not separated from it either by ferrous sulphate or oxalic acid4 ,this salt1 which is known as ,fordos and ,gelis's salt1 is used in medicine and photography4 ,in general1 aurous oxide exhibits a distinct inclination to the formation of similar double salts1 as we saw also with ,pt,x#b--;for example1 it forms similar salts with sulphurous acid4 ,thus if a solution of sodium sulphite be gradually added to a solution of oxide of gold in sodium hydroxide1 the precipitate at first formed re-dissolves to a colourless solution1 which contains the double salt ,na#c;,au7,,so#c7b ,au,na7,,so#c,na7#b4 ,the solution of this salt1 when mixed with barium chloride1 first forms a precipitate of barium sulphite1 and then a red barium double salt which corresponds with the above sodium salt4 ,the oxygen compound of the type ,au,x1 aurous oxide1 ,au#b,o1 is obtained as a greenish violet powder on mixing aurous chloride with potassium chloride in the cold4 ,with hydrochloric acid this oxide gives gold and auric chloride1 and when heated it easily splits up into oxygen and metallic gold4 ,,appendix ,i ,,an ,,attempt ,,to ,,apply ,,to ,,chemistry ,,one ,,of ,,the ,,principles ,,of ,,newton',s ,,natural ,,philosophy ,,by ,,professor ,,mendel,,eff ,a ,,lecture ,,delivered ,,at ,,the ,,royal ,,institution ,,of ,,great ,,britain ,,on ,,friday1 ,,may #ca1 #ahhi ,nature1 inert to the eyes of the ancients1 has been revealed to us as full of life and activity4 ,the conviction that motion pervaded all things1 which was first realised with respect to the stellar universe1 has now extended to the unseen world of atoms4 ,no sooner had the human understanding denied to the earth a fixed position and launched it along its path in space1 than it was sought to fix immovably the sun and the stars4 ,but astronomy has demonstrated that the sun moves with unswerving regularity through the star-set universe at the rate of about #ej kilometres per second4 ,among the so-called fixed stars are now discerned manifold changes and various orders of movement4 ,light1 heat1 electricity--like sound--have been proved to be modes of motion2 to the realisation of this fact modern science is indebted for powers which have been used with such brilliant success1 and which have been expounded so clearly at this lecture table by ,faraday and by his successors4 ,as1 in the imagination of ,dante1 the invisible air became peopled with spiritual beings1 so before the eyes of earnest investigators1 and especially before those of ,clerk ,maxwell1 the invisible mass of gases became peopled with particles3 their rapid movements1 their collisions1 and impacts became so manifest that it seemed almost possible to count the impacts and determine many of the peculiarities or laws of their collisions4 ,the fact of the existence of these invisible motions may at once be made apparent by demonstrating the difference in the rate of diffusion through porous bodies of the light and rapidly moving atoms of hydrogen and the heavier and more sluggish particles of air4 ,within the masses of liquid and of solid bodies we have been forced to acknowledge the existence of persistent though limited motion of their ultimate particles1 for otherwise it would be impossible to explain1 for example1 the celebrated experiments of ,graham on diffusion through liquid and colloidal substances4 ,if there were1 in our times1 no belief in the molecular motion in solid bodies1 could the famous ,spring have hoped to attain any result by mixing carefully-dried powders of potash1 saltpetre and sodium acetate1 in order to produce1 by pressure1 a chemical reaction between these substances through the interchange of their metals1 and have derived1 for the conviction of the incredulous1 a mixture of two hygroscopic though solid salts--sodium nitrate and potassium acetate8 ,in these invisible and apparently chaotic movements1 reaching from the stars to the minutest atoms1 there reigns1 however1 a harmonious order which is commonly mistaken for complete rest1 but which is really a consequence of the conservation of that dynamic equilibrium which was first discerned by the genius of ,newton1 and which has been traced by his successors in the detailed analysis of the particular consequences of the great generalisation1 namely1 relative immovability in the midst of universal and active movement4 ,but the unseen world of chemical changes is closely analogous to the visible world of the heavenly bodies1 since our atoms form distinct portions of an invisible world1 as planets1 satellites1 and comets form distinct portions of the astronomer's universe2 our atoms may therefore be compared to the solar systems1 or to the systems of double or of single stars3 for example1 ammonia 7,,nh#c7 may be represented in the simplest manner by supposing the sun1 nitrogen1 surrounded by its planets of hydrogen2 and common salt 7,na,cl7 may be looked on as a double star formed of sodium and chlorine4 ,besides1 now that the indestructibility of the elements has been acknowledged1 chemical changes cannot otherwise be explained than as changes of motion1 and the production by chemical reactions of galvanic currents1 of light1 of heat1 of pressure1 or of steam power1 demonstrates visibly that the processes of chemical reaction are inevitably connected with enormous though unseen displacements1 originating in the movements of atoms in molecules4 ,astronomers and natural philosophers1 in studying the visible motions of the heavenly bodies and of matter on the earth1 have understood and have estimated the value of this store of energy4 ,but the chemist has had to pursue a contrary course4 ,observing in the physical and mechanical phenomena which accompany chemical reactions the quantity of energy manifested by the atoms and molecules1 he is constrained to acknowledge that within the molecules there exist atoms in motion1 endowed with an energy which1 like matter itself1 is neither being created nor capable of being destroyed4 ,therefore1 in chemistry1 we must seek dynamic equilibrium not only between the molecules1 but also in their midst among their component atoms4 ,many conditions of such equilibrium have been determined1 but much remains to be done1 and it is not uncommon1 even in these days1 to find that some chemists forget that there is the possibility of motion in the interior of molecules1 and therefore represent them as being in a condition of death-like inactivity4 ,chemical combinations take place with so much ease and rapidity1 possess so many special characteristics1 and are so numerous1 that their simplicity and order were for a long time hidden from investigators4 ,sympathy1 relationship1 all the caprices or all the fancifulness of human intercourse1 seemed to have found complete analogies in chemical combinations1 but with this difference1 that the characteristics of the material substances--such as silver1 for example1 or of any other body--remain unchanged in every subdivision from the largest masses to the smallest particles1 and consequently these characteristics must be properties of the particles4 ,but the world of heavenly luminaries appeared equally fanciful at man's first acquaintance with it1 so much so1 that the astrologers imagined a connection between the individualities of men and the conjunctions of planets4 ,thanks to the genius of ,lavoisier and of ,dalton1 man has been able1 in the unseen world of chemical combinations1 to recognise laws of the same simple order as those which ,copernicus and ,kepler proved to exist in the planetary universe4 ,man discovered1 and continues every hour to discover1 what remains unchanged in chemical evolution1 and how changes take place in combinations of the unchangeable4 ,he has learned to predict1 not only what possible combinations may take place1 but also the very existence of atoms of unknown elementary substances1 and has besides succeeded in making innumerable practical applications of his knowledge to the great advantage of his race1 and has accomplished this notwithstanding that notions of sympathy and affinity still preserve a strong vitality in science4 ,at present we cannot apply ,newton's principles to chemistry1 because the soil is only being now prepared4 ,the invisible world of chemical atoms is still waiting for the creator of chemical mechanics4 ,for him our age is collecting a mass of materials1 the inductions of well-digested facts1 and many-sided inferences similar to those which existed for ,astronomy and ,mechanics in the days of ,newton4 ,it is well also to remember that ,newton devoted much time to chemical experiments1 and while considering questions of celestial mechanics1 persistently kept in view the mutual action of those infinitely small worlds which are concerned in chemical evolutions4 ,for this reason1 and also to maintain the unity of laws1 it seems to me that we must1 in the first instance1 seek to harmonise the various phases of contemporary chemical theories with the immortal principles of the ,newtonian natural philosophy1 and so hasten the advent of true chemical mechanics4 ,let the above considerations serve as my justification for the attempt which ,i propose to make to act as a champion of the universality of the ,newtonian principles1 which ,i believe are competent to embrace every phenomenon in the universe1 from the rotation of the fixed stars to the interchanges of chemical atoms4 ,in the first place ,i consider it indispensable to bear in mind that1 up to quite recent times1 only a one-sided affinity has been recognised in chemical reactions4 ,thus1 for example1 from the circumstance that red-hot iron decomposes water with the evolution of hydrogen1 it was concluded that oxygen had a greater affinity for iron than for hydrogen4 ,but hydrogen1 in presence of red-hot iron scale1 appropriates its oxygen and forms water1 whence an exactly opposite conclusion may be formed4 ,during the last ten years a gradual1 scarcely perceptible1 but most important change has taken place in the views1 and consequently in the researches1 of chemists4 ,they have sought everywhere1 and have always found1 systems of conservation or dynamic equilibrium substantially similar to those which natural philosophers have long since discovered in the visible world1 and in virtue of which the position of the heavenly bodies in the universe is determined4 ,there where one-sided affinities only were at first detected1 not only secondary or lateral ones have been found1 but even those which are diametrically opposite2 yet among these1 dynamical equilibrium establishes itself not by excluding one or other of the forces1 but regulating them all4 ,so the chemist finds in the flame of the blast furnace1 in the formation of every salt1 and1 with especial clearness1 in double salts and in the crystallisation of solutions1 not a fight ending in the victory of one side1 as used to be supposed1 but the conjunction of forces2 the peace of dynamic equilibrium resulting from the action of many forces and affinities4 ,carbonaceous matters1 for example1 burn at the expense of the oxygen of the air1 yielding a quantity of heat1 and forming products of combustion1 in which it was thought that the affinities of the oxygen with the combustible elements were satisfied4 ,but it appeared that the heat of combustion was competent to decompose these products1 to dissociate the oxygen from the combustible elements1 and therefore to explain combustion fully it is necessary to take into account the equilibrium between opposite reactions1 between those which evolve and those which absorb heat4 ,in the same way1 in the case of the solution of common salt in water1 it is necessary to take into account1 on the one hand1 the formation of compound particles generated by the combination of salt with water1 and1 on the other1 the disintegration or scattering of the new particles formed1 as well as of these originally contained4 ,at present we find two currents of thought1 apparently antagonistic to each other1 dominating the study of solutions3 according to the one1 solution seems a mere act of building up or association2 according to the other1 it is only dissociation or disintegration4 ,the truth lies1 evidently1 between these views2 it lies1 as ,i have endeavoured to prove by my investigations into aqueous solutions1 in the dynamic equilibrium of particles tending to combine and also to fall asunder4 ,the large majority of chemical reactions which appeared to act victoriously along one line have been proved capable of acting as victoriously even along an exactly opposite line4 ,elements which utterly decline to combine directly may often be formed into comparatively stable compounds by indirect means1 as1 for example1 in the case of chlorine and carbon2 and consequently the sympathies and antipathies which it was thought to transfer from human relations to those of atoms should be laid aside until the mechanism of chemical relations is explained4 ,let us remember1 however1 that chlorine1 which does not form with carbon the chloride of carbon1 is strongly absorbed1 or1 as it were1 dissolved1 by carbon1 which leads us to suspect incipient chemical action even in an external and purely surface contact1 and involuntarily gives rise to conceptions of that unity of the forces of nature which has been so energetically insisted on by ,sir ,william ,grove and formulated in his famous paradox4 ,grove noticed that platinum1 when fused in the oxyhydrogen flame1 during which operation water is formed1 when allowed to drop into water decomposes the latter and produces the explosive oxyhydrogen mixture4 ,the explanation of this paradox1 as of many others which arose during the period of chemical renaissance1 has led1 in our time1 to the promulgation by ,henri ,sainte-,claire ,deville of the conception of dissociation and of equilibrium1 and has recalled the teaching of ,berthollet1 which1 notwithstanding its brilliant confirmation by ,heinrich ,rose and ,dr4 ,gladstone1 had not1 up to that period1 been included in received chemical views4 ,chemical equilibrium in general1 and dissociation in particular1 are now being so fully worked out in detail1 and supplied in such various ways1 that ,i do not allude to them to develop1 but only use them as examples by which to indicate the correctness of a tendency to regard chemical combinations from points of view differing from those expressed by the term hitherto appropriated to define chemical forces1 namely1 'affinity4' ,chemical equilibria1 dissociation1 the speed of chemical reactions1 thermochemistry1 spectroscopy1 and1 more than all1 the determination of the influence of masses and the search for a connection between the properties and weights of atoms and molecules--in one word1 the vast mass of the most important chemical researches of the present day--clearly indicate the near approach of the time when chemical doctrines will submit fully and completely to the doctrine which was first announced in the ,principia of ,newton4 ,in order that the application of these principles may bear fruit it is evidently insufficient to assume that statical equilibrium reigns alone in chemical systems or chemical molecules3 it is necessary to grasp the conditions of possible states of dynamical equilibria1 and to apply to them kinetic principles4 ,numerous considerations compel us to renounce the idea of statical equilibrium in molecules1 and the recent yet strongly-supported appeals to dynamic principles constitute1 in my opinion1 the foundation of the modern teaching relating to atomicity1 or the valency of the elements1 which usually forms the basis of investigations into organic or carbon compounds4 ,this teaching has led to brilliant explanations of very many chemical relations and to cases of isomerism1 or the difference in the properties of substances having the same composition4 ,it has been so fruitful in its many applications and in the foreshadowing of remote consequences1 especially respecting carbon compounds1 that it is impossible to deny its claims to be ranked as a great achievement of chemical science4 ,its practical application to the synthesis of many substances of the most complicated composition entering into the structure of organised bodies1 and to the creation of an unlimited number of carbon compounds1 among which the colours derived from coal tar stand prominently forward1 surpass the synthetical powers of ,nature itself4 ,yet this teaching1 as applied to the structure of carbon compounds1 is not on the face of it directly applicable to the investigation of other elements1 because in examining the first it is possible to assume that the atoms of carbon have always a definite and equal number of affinities1 whilst in the combinations of other elements this is evidently inadmissible4 ,thus1 for example1 an atom of carbon yields only one compound with four atoms of hydrogen and one with four atoms of chlorine in the molecule1 whilst the atoms of chlorine and hydrogen unite only in the proportions of one to one4 ,simplicity is here evident1 and forms a point of departure from which it is easy to move forward with firm and secure tread4 ,other elements are of a different nature4 ,phosphorus unites with three and with five atoms of chlorine1 and consequently the simplicity and sharpness of the application of structural conceptions are lost4 ,sulphur unites only with two atoms of hydrogen1 but with oxygen it enters into higher orders of combination4 ,the periodic relationship which exists among all the properties of the elements--such1 for example1 as their ability to enter into various combinations--and their atomic weights1 indicate that this variation in atomicity is subject to one perfectly exact and general law1 and it is only carbon and its near analogues which constitute cases of permanently preserved atomicity4 ,it is impossible to recognise as constant and fundamental properties of atoms1 powers which1 in substance1 have proved to be variable4 ,but by abandoning the idea of permanence1 and of the constant saturation of affinities--that is to say1 by acknowledging the possibility of free affinities--many retain a comprehension of the atomicity of the elements 'under given conditions2' and on this frail foundation they build up structures composed of chemical molecules1 evidently only because the conception of manifold affinities gives1 at once1 a simple statical method of estimating the composition of the most complicated molecules4 ,i shall enter neither into details1 nor into the various consequences following from these views1 nor into the disputes which have sprung up respecting them 7and relating especially to the number of isomerides possible on the assumption of free affinities71 because the foundation or origin of theories of this nature suffers from the radical defect of being in opposition to dynamics4 ,the molecule1 as even ,laurent expressed himself1 is represented as an architectural structure1 the style of which is determined by the fundamental arrangement of a few atoms1 whilst the decorative details1 which are capable of being varied by the same forces1 are formed by the elements entering into the combination4 ,it is on this account that the term 'structural' is so appropriate to the contemporary views of the above order1 and that the 'structuralists' seek to justify the tetrahedric1 plane1 or prismatic disposition of the atoms of carbon in benzene4 ,it is evident that the consideration relates to the statical position of atoms and molecules and not to their kinetic relations4 ,the atoms of the structural type are like the lifeless pieces on a chess board3 they are endowed but with the voices of living beings1 and are not those living beings themselves2 acting1 indeed1 according to laws1 yet each possessed of a store of energy which1 in the present state of our knowledge1 must be taken into account4 ,in the days of ,hay1 crystals were considered in the same statical and structural light1 but modern crystallographers1 having become more thoroughly acquainted with their physical properties and their actual formation1 have abandoned the earlier views1 and have made their doctrines dependent on dynamics4 ,the immediate object of this lecture is to show that1 starting with ,newton's third law of motion1 it is possible to preserve to chemistry all the advantages arising from structural teaching1 without being obliged to build up molecules in solid and motionless figures1 or to ascribe to atoms definite limited valencies1 directions of cohesion1 or affinities4 ,the wide extent of the subject obliges me to treat only a small portion of it1 namely of substitutions1 without specially considering combinations and decompositions1 and even then limiting myself to the simplest examples1 which1 however1 will throw open prospects embracing all the natural complexity of chemical relations4 ,for this reason1 if it should prove possible to form groups similar1 for example1 to ,h#d or ,,ch#f as the remnants of molecules ,,ch#d or ,c#b;,h#g we shall not pause to consider them1 because1 as far as we know1 they fall asunder into two parts1 ,h#b ,h#b or ,,ch#d ,h#b1 as soon as they are even temporarily formed1 and are incapable of separate existence1 and therefore can take no part in the elementary act of substitution4 ,with respect to the simplest molecules which we shall select--that is to say1 those of which the parts have no separate existence1 and therefore cannot appear in substitutions--we shall consider them according to the periodic law1 arranging them in direct dependence on the atomic weight of the elements4 ,thus1 for example1 the molecules of the simplest hydrogen compounds-- ,,hf ,h#b,o ,h#c,n ,h#d;,c hydrofluoric acid water ammonia methane correspond with elements the atomic weights of which decrease consecutively ,f #ai1 ,o #af1 ,n #ad1 ,c #ab4 ,neither the arithmetical order 7#a1 #b1 #c1 #d atoms of hydrogen7 nor the total information we possess respecting the elements will permit us to interpolate into this typical series one more additional element2 and therefore we have here1 for hydrogen compounds1 a natural base on which are built up those simple chemical combinations which we take as typical4 ,but even they are competent to unite with each other1 as we see1 for instance1 in the property which hydrofluoric acid has of forming a hydrate--that is1 of combining with water2 and a similar attribute of ammonia1 resulting in the formation of a caustic alkali1 ,,nh#c1;,h#b,o1 or ,,nh#d,,oh4 ,having made these indispensable preliminary observations1 ,i may now attack the problem itself and attempt to explain the so-called structure or rather construction1 of molecules--that is to say1 their constitution and transformations--without having recourse to the teaching of 'structuralists1' but on ,newton's dynamical principles4 ,of ,newton's three laws of motion1 only the third can be applied directly to chemical molecules when regarded as systems of atoms among which it must be supposed that there exist common influences or forces1 and resulting compounded relative motions4 ,chemical reactions of every kind are undoubtedly accomplished by changes in these internal movements1 respecting the nature of which nothing is known at present1 but the existence of which the mass of evidence collected in modern times forces us to acknowledge as forming part of the common motion of the universe1 and as a fact further established by the circumstance that chemical reactions are always characterised by changes of volume or the relations between the atoms or the molecules4 ,newton's third law1 which is applicable to every system1 declares that1 'action is also associated with reaction1 and is equal to it4' ,the brevity of conciseness of this axiom was1 however1 qualified by ,newton in a more expanded statement1 'the action of bodies one upon another are always equal1 and in opposite directions4' ,this simple fact constitutes the point of departure for explaining dynamic equilibrium--that is to say1 systems of conservancy4 ,it is capable of satisfying even the dualists1 and of explaining1 without additional assumptions1 the preservation of those chemical types which ,dumas1 ,laurent1 and ,gerhardt created unit types1 and those views of atomic combinations which the structuralists express by atomicity or the valency of the elements1 and1 in connection with them1 the various numbers of affinities4 ,in reality1 if a system of atoms or a molecule be given1 then in it1 according to the third law of ,newton1 each portion of atoms acts on the remaining portion in the same manner1 and with the same force as the second set of atoms acts on the first4 ,we infer directly from this consideration that both sets of atoms1 forming a molecule1 are not only equivalent with regard to themselves1 as they must be according to ,dalton's law1 but also that they may1 if united1 replace each other4 ,let there be a molecule containing atoms ,a ,b ,c1 it is clear that1 according to ,newton's law1 the action of ,a on ,b ,c must be equal to the action of ,b ,c on ,a1 and if the first action is directed on ,b ,c1 then the second must be directed on ,a1 and consequently then1 where ,a can exist in dynamic equilibrium1 ,b ,c may take its place and act in a like manner4 ,in the same way the action of ,c is equal to the action of ,a ,b4 ,in one word every two sets of atoms forming a molecule are equivalent to each other1 and may take each other's place in other molecules1 or1 having the power of balancing each other1 the atoms or their complements are endowed with the power of replacing each other4 ,let us call this consequence of an evident axiom 'the principle of substitution1' and let us apply it to those typical forms of hydrogen compounds which we have already discussed1 and which1 on account of their simplicity1 and regularity1 have served as starting-points of chemical argument long before the appearance of the doctrine of structure4 ,in the type of hydrofluoric acid1 ,,hf1 or in systems of double stars1 are included a multitude of the simplest molecules4 ,it will be sufficient for our purpose to recall a few3 for example1 the molecules of chlorine1 ,cl#b1 and of hydrogen1 ,h#b1 and hydrochloric acid1 ,h,cl1 which is familiar to all in aqueous solution as spirits of salt1 and which has many points of resemblance with ,,hf1 ,h,br1 ,,hi4 ,in these cases division into two parts can only be made in one way1 and therefore the principle of substitution renders it probable that exchanges between the chlorine and the hydrogen can take place1 if they are competent to unite with each other4 ,there was a time when no chemist would even admit the idea of any such action2 it was then thought that the power of combination indicated a polar difference of the molecules in combination1 and this thought set aside all idea of the substitution of one component element by another4 ,thanks to the observations and experiments of ,dumas and ,laurent fifty years ago1 such fallacies were dispelled1 and in this manner the principle of substitution was exhibited4 ,chlorine and bromine acting on many hydrogen compounds1 occupy immediately the place of their hydrogen1 and the displaced hydrogen1 with another atom of chlorine or bromine1 forms hydrochloric acid or bromide of hydrogen4 ,this takes place in all typical hydrogen compounds4 ,thus chlorine acts on this principle on gaseous hydrogen--reaction1 under the influence of light1 resulting in the formation of hydrochloric acid4 ,chlorine acting on the alkalis1 constituted similarly to water1 and even on water itself--only1 however1 under the influence of light and only partially because of the instability of ,h,cl,o--forms by this principle bleaching salts1 which are the same as the alkalis1 but with their hydrogen replaced by chlorine4 ,in ammonia and in methane1 chlorine can also replace the hydrogen4 ,from ammonia is formed in this manner the so-called chloride of nitrogen1 ,n,cl#c1 which decomposes very readily with violent explosion on account of the evolved gases1 and falls asunder as chlorine and nitrogen4 ,out of marsh gas1 or methane1 ,,ch#d1 may be obtained consecutively1 by this method1 every possible substitution1 of which chloroform1 ,c,h,cl#c1 is the best known1 and carbon tetrachloride1 ,c,cl#d1 the most instructive4 ,but by virtue of the fact that chlorine and bromine act1 in the manner shown1 on the simplest typical hydrogen compounds1 their action on the more complicated ones may be assumed to be the same4 ,this can be easily demonstrated4 ,the hydrogen of benzene1 ,c#f;,h#f1 reacts feebly under the influence of light on liquid bromine1 but ,gustavson has shown that the addition of the smallest quantity of metallic aluminium causes energetic action and the evolution of large volumes of hydrogen bromide4 ,if we pass on to the second typical hydrogen compound--that is to say1 water--its molecule1 ,,hoh1 may be split up in two ways3 either into an atom of hydrogen and a semi-molecule of hydrogen peroxide1 ,,ho1 or into oxygen1 ,o1 and two atoms of hydrogen1 ,h2 and therefore1 according to the principle of substitution1 it is evident that one atom of hydrogen can exchange with hydrogen oxide1 ,,ho1 and two atoms of hydrogen1 ,h1 with one atom of oxygen1 ,o4 ,both these forms of substitution will constitute methods of oxidation--that is to say1 of the entrance of oxygen into the compound--a reaction which is so common in nature as well as in the arts1 taking place at the expense of the oxygen of the air or by the aid of various oxidising substances or bodies which part easily with their oxygen4 ,there is no occasion to reckon up the unlimited number of cases of such oxidising reactions4 ,it is sufficient to state that in the first of these oxygen is directly transferred1 and the position1 the chemical function1 which hydrogen originally occupied1 is1 after the substitution1 occupied by the hydroxyl4 ,thus ammonia1 ,,nh#c1 yields hydroxylamine1 ,,nh#b7,,oh71 a substance which retains many of the properties of ammonia4 ,methane and a number of other hydrocarbons yield1 by substitution of the hydrogen by its oxide1 methyl alcohol1 ,,ch#c7,,oh71 and other alcohols4 ,the substitution of one atom of oxygen for two atoms of hydrogen is equally common with hydrogen compounds4 ,by this means alcoholic liquids containing ethyl alcohol1 or spirits of wine1 ,c#b;,h#e7,,oh71 are oxidised until they become vinegar1 or acetic acid1 ,c#b;,h#c,o7,,oh74 ,in the same way caustic ammonia1 or the combination of ammonia with water1 ,,nh#c1;,h#b,o1 or ,,nh#d7,,oh71 which contains a great deal of hydrogen1 by oxidation exchanges four atoms of hydrogen for two atoms of oxygen1 and becomes converted into nitric acid1 ,,no#b7,,oh74 ,this process of conversion of ammonium salts into saltpetre goes on in the fields every summer1 and with especial rapidity in tropical countries4 ,the method by which this is accomplished1 though complex1 though involving the agency of all-permeating micro-organisms1 is1 in substance1 the same as that by which alcohol is converted into acetic acid1 or glycol1 ,c#b;,h#d7,,oh7#b1 into oxalic acid1 if we view the process of oxidation in the light of the ,newtonian principles4 ,but while speaking of the application of the principle of substitution to water1 we need not multiply instances1 but must turn our attention to two special circumstances which are closely connected with the very mechanism of substitutions4 ,in the first place1 the replacement of two atoms of hydrogen by one atom of oxygen may take place in two ways1 because the hydrogen molecule is composed of two atoms1 and therefore1 under the influence of oxygen1 the molecule forming water may separate before the oxygen has time to take its place4 ,it is for this reason that we find1 during the conversion of alcohol into acetic acid1 that there is an interval during which is formed aldehyde1 ,c#b;,h#d,o1 which1 as its very name implies1 is 'alcohol dehydrogenatum1' or alcohol deprived of hydrogen4 ,hence aldehyde combined with hydrogen yields alcohol2 and united to oxygen1 acetic acid4 ,for the same reason there should be1 and there actually are1 intermediate products between ammonia and nitric acid1 ,,no#b7;,,ho71 containing either less hydrogen than ammonia1 less oxygen than nitric acid1 or less water than caustic ammonia4 ,accordingly we find1 among the products of the deoxidation of nitric acid and the oxidation of ammonia1 not only hydroxylamine1 but also nitrous oxide1 nitrous and nitric anhydrides4 ,thus1 the production of nitrous acid results from the removal of two atoms of hydrogen from caustic ammonia and the substitution of the oxygen for the hydrogen1 ,,no7,,oh72 or by the substitution1 in ammonia1 of three atoms of hydrogen by hydroxyl1 ,n7,,oh7#c1 and by the removal of water3 ,n7,,oh7#c - ,h#b,o ,,no7,,oh74 ,the peculiarities and properties of nitrous acid--as1 for instance1 its action on ammonia and its conversion1 by oxidation1 into nitric acid--are thus clearly revealed4 ,on the other hand1 in speaking of the principle of substitution as applied to water1 it is necessary to observe that hydrogen and hydroxyl1 ,h and ,,oh1 are not only competent to unite1 but also to form combinations with themselves1 and thus become ,h#b and ,h#b,o#b2 and such are hydrogen and the peroxide thereof4 ,in general1 if a molecule ,a ,b exists1 then molecules ,a ,a and ,b ,b can exist also4 ,a direct reaction of this kind does not1 however1 take place in water1 therefore undoubtedly1 at the moment of formation1 hydrogen reacts on hydrogen peroxide1 as we can show at once by experiment2 and further because hydrogen peroxide1 ,h#b,o#b1 exhibits a structure containing a molecule of hydrogen1 ,h#b1 and one of oxygen1 ,o#b1 either of which is capable of separate existence4 ,the fact1 however1 may now be taken as thoroughly established1 that1 at the moment of combustion of hydrogen or of the hydrogen compounds1 hydrogen peroxide is always formed1 and not only so1 but in all probability its formation invariably precedes the formation of water4 ,this was to be expected as a consequence of the law of ,avogadro and ,gerhardt1 which leads us to expect this sequence in the case of equal interactions of volumes of vapours and gases2 and in hydrogen peroxide we actually have such equal volumes of the elementary gases4 ,the instability of hydrogen peroxide--that is to say1 the ease with which it decomposes into water and oxygen1 even at the mere contact of porous substances--accounts for the circumstance that it does not form a permanent product of combustion1 and is not produced during the decomposition of water4 ,i may mention this additional consideration that1 with respect to hydrogen peroxide1 we may look for its effecting still further substitutions of hydrogen by means of which we may expect to obtain still more highly oxidised water compounds1 such as ,h#b,o#c and ,h#b,o#d4 ,these ,schnbein and ,bunsen have long been seeking1 and ,berthelot is investigating them at present4 ,it is probable1 however1 that the reaction will stop at the last compound1 because we find that1 in a number of cases1 the addition of four atoms of oxygen seems to form a limit4 ,thus1 ,os,o#d1 ,k,cl,o#d1 ,k,mn,o#d1 ,k#b,,so#d1 ,na#c,,po#d1 and such like1 represent the highest grades of oxidation4#a #a ,because more than four atoms of hydrogen never unite with one atom of the elements1 and because the hydrogen compounds 7e4g4 ,h,cl1 ,h#b,s1 ,h#c,p1 ,h#d,si7 always form their highest oxides with four atoms of oxygen1 and as the highest forms of oxides 7,os,o#d1 ,ru,o#d7 also contain four of oxygen1 and eight groups of the periodic system1 corresponding to the highest basic oxides ,r#b,o1 ,,ro1 ,r#b,o#c1 ,,ro#b1 ,r#b,o#e1 ,,ro#c1 ,r#b,o#g1 and ,,ro#d1 imply the above relationship1 and because of the nearest analogues among the elements--such as ,mg1 ,zn1 ,cd1 and ,hg2 or ,cr1 ,mo1 ,w1 and ,u2 or ,si1 ,ge1 ,sn1 and ,pt2 or ,f1 ,cl1 ,br1 and ,i1 and so forth--not more than four are known1 it seems to me that in these relationships there lies a deep interest and meaning with regard to chemical mechanics4 ,but because1 to my imagination1 the idea of unity of design in ,nature1 either acting in complex celestial systems or among chemical molecules1 is very attractive1 especially because the atomic teaching at once acquires its true meaning1 ,i will recall the following facts relating to the solar system4 ,there are eight major planets1 of which the four inner ones are not only separated from the four outer by asteroids1 but differ from them in many respects1 as1 for example1 in the smallness of their diameters and their greater density4 ,saturn with his ring has eight satellites1 ,jupiter and ,uranus have each four4 ,it is evident that in the solar systems also we meet with these higher numbers four and eight which appear in the combination of chemical molecules4 ,as for the last forty years1 from the times of ,berzelius1 ,dumas1 ,liebig1 ,gerhardt1 ,williamson1 ,frankland1 ,kolbe1 ,kekul1 and ,butleroff1 most theoretical generalisations have centred round organic or carbon compounds1 we will1 for the sake of brevity1 leave out the discussion of ammonia derivatives1 notwithstanding their simplicity with respect to the doctrine of substitutions2 we will dwell more especially on its application to carbon compounds1 starting from methane1 ,,ch#d1 as the simplest of the hydrocarbons1 containing in its molecule one atom of carbon4 ,according to the principles enumerated we may derive from ,,ch#d every combination of the form ,,ch#c,x1 ,,ch#b,x#b1 ,,chx#c1 and ,,cx#d1 in which ,x is an element1 or radicle1 equivalent to hydrogen--that is to say1 competent to take its place or to combine with it4 ,such are the chlorine substitutes already mentioned1 such is wood-spirit1 ,,ch#c7,,oh71 in which ,x is represented by the residue of water1 and such are numerous other carbon derivatives4 ,if we continue1 with the aid of hydroxyl1 further substitutions of the hydrogen of methane we shall obtain successively ,,ch#b7,,oh7#b1 ,,ch7,,oh7#c1 and ,c7,,oh7#d4 ,but if1 in proceeding thus1 we bear in mind that ,,ch#b7,,oh7#b contains two hydroxyls in the same form as hydrogen peroxide1 ,h#b,o#b or 7,,oh7#b1 contains them--and moreover not only in one molecule1 but together1 attached to one and the same atom of carbon--so here we must look for the same decomposition as that which we find in hydrogen peroxide1 and accompanied also by the formation of water as an independently existing molecule2 therefore ,,ch#b7,,oh7#b should yield1 as it actually does1 immediately water and the oxide of methylene1 ,,ch#b,o1 which is methane with oxygen substituted for two atoms of hydrogen4 ,exactly in the same manner out of ,,ch7,,oh7#c are formed water and formic acid1 ,,cho7,,oh71 and out of ,c7,,oh7#d is produced water and carbonic acid1 or directly carbonic anhydride1 ,,co#b1 which will therefore be nothing else than methane with the double replacement of pairs of hydrogen by oxygen4 ,as nothing leads to the supposition that the four atoms of hydrogen in methane differ one from the other1 so it does not matter by what means we obtain any one of the combinations indicated--they will be identical2 that is to say1 there will be no case of actual isomerism1 although there may easily be such cases of isomerism as have been distinguished by the term metamerism4 ,formic acid1 for example1 has two atoms of hydrogen1 one attached to the carbon left from the methane1 and the other attached to the oxygen which has entered in the form of hydroxyl1 and if one of them be replaced by some substance ,x it is evident that we shall obtain substances of the same composition1 but of different construction1 or of different orders of movement among the molecules1 and therefore endowed with other properties and reactions4 ,if ,x be methyl1 ,,ch#d--that is to say1 a group capable of replacing hydrogen because it is actually contained with hydrogen in methane itself--then by substituting this group for the original hydrogen we obtain acetic acid1 ,,cch#c,o7,,oh71 out of formic1 and by substitution of the hydrogen in its oxide or hydroxyl we obtain methyl formate1 ,,cho7,,och#c74 ,these substances differ so much from each other physically and chemically that at first sight it is hardly possible to admit that they contain the same atoms in identically the same proportions4 ,acetic acid1 for example1 boils at a higher temperature than water1 and has a higher specific gravity than it1 whilst its metameride1 methyl formate1 is lighter than water1 and boils at #cj--that is to say1 it evaporates very easily4 ,let us now turn to carbon compounds containing two atoms of carbon to the molecule1 as in acetic acid1 and proceed to evolve them from methane by the principle of substitution4 ,this principle declares at once that methane can only be split up in the four following ways3-- #a4 ,into a group ,,ch#c equivalent with ,h4 ,let us call changes of this nature methylation4 #b4 ,into a group ,,ch#b and ,h#b4 ,we will call this order of substitutions methylenation4 #c4 ,into ,,ch and ,h#c1 which commutations we will call acetylenation4 #d4 ,into ,c and ,h#d1 which may be called carbonation4 ,it is evident that hydrocarbon compounds containing two atoms of carbon can only proceed from methane1 ,,ch#d1 which contains four atoms of hydrogen by the first three methods of substitution2 carbonation would yield free carbon if it could take place directly1 and if the molecule of free carbon--which is in reality very complex1 that is to say strongly polyatomic1 as ,i have long since been proving by various means--could contain only ,c#b like the molecules ,o#b1 ,h#b1 ,n#b1 and so on4 ,by methylation we should evidently obtain from marsh gas1 ethane1 ,,ch#c;,,ch#c ,c#b;,h#f4 ,by methylenation--that is1 by substituting group ,,ch#b for ,h#b--methane forms ethylene1 ,,ch#b;,,ch#b ,c#b;,h#d4 ,by acetylenation--that is1 by substituting three atoms of hydrogen1 ,h#c1 in methane--by the remnant ,,ch1 we get acetylene1 ,,chch ,c#b;,h#b4 ,if we have applied the principles of ,newton correctly1 there should not be any other hydrocarbons containing two atoms of carbon in the molecule4 ,all these combinations have long been known1 and in each of them we can not only produce those substitutions of which an example has been given in the case of methane1 but also all the phases of other substitutions1 as we shall find from a few more instances1 by the aid of which ,i trust that ,i shall be able to show the great complexity of those derivatives which1 on the principle of substitution1 can be obtained from each hydrocarbon4 ,let us content ourselves with the case of ethane1 ,,ch#c;,,ch#c1 and the substitution of the hydrogen by hydroxyl4 ,the following are the possible changes3-- #a4 ,,ch#c;,,ch#b7,,oh73 this is nothing more than spirit of wine1 or ethyl alcohol1 ,c#b;,h#e7,,oh7 or ,c#b;,h#f,o4 #b4 ,,ch#b7,,oh7,,ch#b7,,oh73 this is the glycol of ,wrtz1 which has shed so much light on the history of alcohol4 ,its isomeride may be ,,ch#c;,,ch7,,oh7#b1 but as we have seen in the case of ,,ch7,,oh7#b1 it decomposes1 giving off water1 and forming aldehyde1 ,,ch#c;,,cho1 a substance capable of yielding alcohol by uniting with hydrogen1 and of yielding acetic acid by uniting with oxygen4 ,if glycol1 ,,ch#b7,,oh7,,ch#b7,,oh71 loses its water1 it may be seen at once that it will not now yield aldehyde1 ,,ch#c;,,cho1 but its isomeride1 ,,ch#b;,,ch#b_/,o1 the oxide of ethylene4 ,i have here indicated in a special manner the oxygen which has taken the place of two atoms of the hydrogen of ethane taken from different atoms of the carbon4 #c4 ,,ch#c;,c7,,oh7#c decomposed as ,,ch7,,oh7#c1 forming water and acetic acid1 ,,ch#c;,,co7,,oh74 ,it is evident that this acid is nothing else than formic acid1 ,,cho7,,oh71 with its hydrogen replaced by methyl4 ,without examining further the vast number of possible derivatives1 ,i will direct your attention to the circumstance that in dissolving acetic acid in water we obtain the maximum contraction and the greatest viscosity when to the molecule ,,ch#c;,,co7,,oh7 is added a molecule of water1 which is the proportion which would form the hydrate ,,ch#c;,c7,,oh7#c4 ,it is probable that the doubling of the molecule of acetic acid at temperatures approaching its boiling-point has some connection with this power of uniting with one molecule of water4 #d4 ,,ch#b7,,oh7,c7,,oh7#c is evidently an alcoholic acid1 and indeed this compound1 after losing water1 answers to glycolic acid1 ,,ch#b7,,oh7,,co7,,oh74 ,without investigating all the possible isomerides1 we will note only that the hydrate ,,ch7,,oh7#b;,,ch7,,oh7#b has the same composition as ,,ch#b7,,oh7,c7,,oh7#c1 and although corresponding to glycol1 and being a symmetrical substance1 it becomes1 on parting with its water1 the aldehyde of oxalic acid1 or the glyoxal of ,debus1 ,,chocho4 #e4 ,,ch7,,oh7#b;,c7,,oh#c71 from the tendency of all the preceding1 corresponds with glyoxylic acid1 an aldehyde acid1 ,,choco7,,oh71 because the group ,,co7,,oh71 or carboxyl1 enters into the compositions of organic acids1 and the group ,,cho defines the aldehyde function4 #f4 ,c7,,oh7#c;,c7,,oh7#c through the loss of #b;,h#b,o yields the bibasic oxalic acid ,,co7,,oh7,,co7,,oh71 which generally crystallises with #b;,h#b,o1 following thus the normal type of hydration characteristic of ethane4#b #b ,one more isomeride1 ,,ch#b;,,ch7,,oh71 is possible--that is1 secondary vinyl alcohol1 which is related to ethylene1 ,,ch#b;,,ch#b1 but derived by the principle of substitution from ,,ch#d4 ,other isomerides1 of the composition ,c#b;,h#d,o1 such1 for example1 as ,,cch#c7,,oh71 are impossible1 because it would correspond with the hydrocarbon ,,chch#c ,c#b;,h#d1 which is isomeric with ethylene1 and it cannot be derived from methane4 ,if such an isomeride existed it would be derived from ,,ch#b1 but such products are1 up to the present1 unknown4 ,in such cases the insufficiency of the points of departure of the statical structural teaching is shown4 ,it first admits constant atomicity and then rejects it1 the facts serving to establish either one or the other view2 and therefore it seems to me that we must come to the conclusion that the structural method of reasoning1 having done a service to science1 has outlived the age1 and must be regenerated1 as in their time was the teaching of the electro-chemists1 the radicalists1 and the adherents of the doctrine of types4 ,as we cannot now lean on the views above stated1 it is time to abandon the structural theory4 ,they will all be united in chemical mechanics1 and the principle of substitution must be looked on only as a preparation for the coming epoch in chemistry1 where such cases as the isomerism of fumaric and maleic acids1 when explained dynamically1 as proposed by ,le ,bel and ,van't ,hoff1 may yield points of departure4 ,thus1 by applying the principle of substitution1 we can1 in the simplest manner1 derive not only every kind of hydrocarbon compound1 such as the alcohols1 the aldehyde-alcohols1 aldehydes1 alcohol-acids1 and the acids1 but also combinations analogous to hydrated crystals which usually are disregarded4 ,but even those unsaturated substances1 of which ethylene1 ,,ch#b;,,ch#b1 and acetylene1 ,,chch1 are types1 may be evolved with equal simplicity4 ,with respect to the phenomena of isomerism1 there are many possibilities among the hydrocarbon compounds containing two atoms of carbon1 and without going into details it will be sufficient to indicate that the following formul1 though not identical1 will be isomeric substantially among themselves3--,,ch#c;,,chx#b and ,,ch#b,,xch#b,x1 although both contain ,c#b;,h#d,x#b2 or ,,ch#b;,,cx#b and ,,chxchx1 although both contain ,c#b;,h#b,x#b1 if by ,x we indicate chlorine or generally an element capable of replacing one atom of hydrogen1 or capable of uniting with it4 ,to isomerism of this kind belongs the case of aldehyde and the oxide of ethylene1 to which we have already referred1 because both have the composition ,c#b;,h#d,o4 ,what ,i have said appears to me sufficient to show that the principle of substitution adequately explains the composition1 the isomerism1 and all the diversity of combination of the hydrocarbons1 and ,i shall limit the further development of these views to preparing a complete list of every possible hydrocarbon compound containing three atoms of carbon in the molecule4 ,there are eight in all1 of which only five are known at present4#c #c ,conceding variable atomicity1 the structuralists must expect an incomparably larger number of isomerides1 and they cannot now decline to acknowledge the change of atomicity1 were it only for the examples ,hg,cl and ,hg,cl#b1 ,,co and ,,co#b1 ,p,cl#c and ,p,cl#e4 ,among those possible for ,c#c;,h#f there should be two isomerides1 propylene and trimethylene1 and they are both already known4 ,for ,c#c;,h#d there should be three isomerides3 allylene and allene are known1 but the third has not yet been discovered2 and for ,c#c;,h#b there should be two isomerides1 though neither of them is known as yet4 ,their composition and structure are easily deduced from ethane1 ethylene1 and acetylene1 by methylation1 by methylenation1 by acetylenation and by carbonation4 #a4 ,c#c;,h#h ,,ch#c;,,ch#b;,,ch#c out of ,,ch#c;,,ch#c by methylation4 ,this hydrocarbon is named propane4 #b4 ,c#c;,h#f ,,ch#c;,,chch#b out of ,,ch#c;,,ch#c by methylenation4 ,this substance is propylene4 #c4 ,c#c;,h#f ,,ch#b;,,ch#b;,,ch#b out of ,,ch#c;,,ch#c by methylenation4 ,this substance is trimethylene4 #d4 ,c#c;,h#d ,,ch#c;,,cch out of ,,ch#c;,,ch#c by acetylenation or from ,,chch by methylation4 ,this hydrocarbon is named allylene4 #e4 ,c#c;,h#d ,,chch_/,,ch#b out of ,,ch#c;,,ch#c by acetylenation1 or from ,,ch#b;,,ch#b by methylenation1 because ,,ch#b;,,ch_/,,ch ,,chch_/,,ch#b4 ,this body is as yet unknown4 #f4 ,c#c;,h#d ,,ch#b;,,cch#b out of ,,ch#b;,,ch#b by methylenation4 ,this hydrocarbon is named allene1 or iso-allylene4 #g4 ,c#c;,h#b ,,chch_/,c out of ,,ch#c;,,ch#c by symmetrical carbonation1 or out of ,,ch#b;,,ch#b by acetylenation4 ,this compound is unknown4 #h4 ,c#c;,h#b ,,cc_/,,ch#b out of ,,ch#c;,,ch#c by carbonation1 or out of ,,chch by methylenation4 ,this compound is unknown4 ,if we bear in mind that for each hydrocarbon serving as a type in the above tables there are a number of corresponding derivatives1 and that every compound obtained may1 by further methylation1 methylenation1 acetylenation1 and carbonation1 produce new hydrocarbons1 and these may be followed by a numerous suite of derivatives and an immense number of isomeric substances1 it is possible to understand the limitless number of carbon compounds1 although they all have the one substance1 methane1 for their origin4 ,the number of substances is so enormous that it is no longer a question of enlarging the possibilities of discovery1 but rather of finding some means of testing them analogous to the well-known two which for a long time have served as gauges for all carbon compounds4 ,i refer to the law of even numbers and to that of limits1 the first enunciated by ,gerhardt some forty years ago1 with respect to hydrocarbons1 namely1 that their molecules always contain an even number of atoms of hydrogen4 ,but by the method which ,i have used of deriving all the hydrocarbons from methane1 ,,ch#d1 this law may be deduced as a direct consequence of the principle of substitutions4 ,accordingly1 in methylation1 ,,ch#c takes the place of ,h1 and therefore ,,ch#b is added4 ,in methylenation the number of atoms of hydrogen remains unchanged1 and at each acetylenation it is reduced by two1 and in carbonation by four1 atoms--that is to say1 an even number of atoms of hydrogen is always added or removed4 ,and because the fundamental hydrocarbon1 methane1 ,,ch#d1 contains an even number of atoms of hydrogen1 all its derivative hydrocarbons will also contain even numbers of hydrogen1 and this constitutes the law of even numbers4 ,the principle of substitutions explains with equal simplicity the conception of the limiting compositions of hydrocarbons ,cn,h#bn #b1 which ,i derived1 in #ahfa1d in an empirical manner from accumulated materials available at that time1 and on the basis of the limits to combinations worked out by ,dr4 ,frankland for other elements4 #d ',essai d'une thorie sur les limites des combinaisons organiques1' par ,d4 ,mendeleff1 #b_/aa aot #ahfa1 ,bulletin de l',acadmie i4 d4 ,sc4 de ,st4 ,ptersbourg1 t4 v ,of all the various substitutions the highest proportion of hydrogen is yielded by methylation1 because in that operation alone does the quantity of hydrogen increase2 hence1 taking methane as a point of departure1 if we imagine methylation effected 7n - #a7 times we obtain hydrocarbon compounds containing the highest quantities of hydrogen4 ,it is evident that they will contain ,,ch#d 7n - #a7;,,ch#b1 or ,cn,h#bn #b1 because methylation leads to the addition of ,,ch#b to the compound4 ,it will thus be seen that by the principle of substitution--that is to say1 by the third law of ,newton--we are able to deduce1 in the simplest manner1 not only the individual composition1 the isomerism1 and relations of substances1 but also the general laws which govern their most complex combinations without having recourse either to statical constructions1 to the definition of atomicities1 to the exclusion of free affinities1 or to the recognition of those single1 double or treble bonds which are so indispensable to structuralists in the explanation of the composition and construction of hydrocarbon compounds4 ,and yet1 by the application of the dynamical principles of ,newton1 we can attain to that chief and fundamental object1 the comprehension of isomerism in hydrocarbon compounds1 and the forecasting of the existence of combinations as yet unknown1 by which the edifice raised by structural teaching is strengthened and supported4 ,besides--and ,i count this for a circumstance of special importance--the process which ,i advocate will make no difference in those special cases which have been already so well worked out1 such as1 for example1 the isomerism of the hydrocarbons and alcohols1 even to the extent of not interfering with the nomenclature which has been adopted1 and the structural system will retain all the glory of having worked up1 in a thoroughly scientific manner1 the store of information which ,gerhardt had accumulated about the middle of the fifties1 and the still higher glory of establishing the rational synthesis of organic substances4 ,nothing will be lost to the structural doctrine except its statical origin2 and as soon as it will embrace the dynamic principles of ,newton1 and suffer itself to be guided by them1 ,i believe that we shall attain for chemistry that unity of principle which is now wanting4 ,many an adept will be attracted to that brilliant and fascinating enterprise1 the penetration into the unseen world of the kinetic relations of atoms1 to the study of which the last twenty-five years have contributed so much labour and such high inventive faculties4 ,d',alembert found in mechanics that if inertia be taken to represent force1 dynamic equations may be applied to statical questions1 which are thereby rendered more simple and more easily understood4 ,the structural doctrine in chemistry has unconsciously followed the same course1 and therefore its terms are easily adopted2 they may retain their present forms provided that a truly dynamical--that is to say1 ,newtonian--meaning be ascribed to them4 ,before finishing my task and demonstrating the possibility of adapting structural doctrines to the dynamics of ,newton1 ,i consider it indispensable to touch on one question which naturally arises1 and which ,i have heard discussed more than once4 ,if bromine1 the atom of which is eighty times heavier than that of hydrogen1 takes the place of hydrogen1 it would seem that the whole system of dynamic equilibrium must be destroyed4 ,without entering into the minute analysis of this question1 ,i think it will be sufficient to examine it by the light of two well-known phenomena1 one of which will be found in the department of chemistry and the other in that of celestial mechanics1 and both will serve to demonstrate the existence of that unity in the plan of creation which is a consequence of the ,newtonian doctrines4 ,experiments demonstrate that when a heavy element is substituted for a light one in a chemical compound--for example1 for magnesium1 in the oxide of that metal1 an atom of mercury1 which is #h-a_/c times heavier--the chief chemical characteristics or properties are generally1 though not always1 preserved4 ,the substitution of silver for hydrogen1 than which it is #ajh times heavier1 does not affect all the properties of the substance1 though it does some4 ,therefore chemical substitutions of this kind--the substitution of light for heavy atoms--need not necessarily entail changes in the original equilibrium2 and this point is still further elucidated by the consideration that the periodic law indicates the degree of influence of an increment of weight in the atom as affecting the possible equilibria1 and also what degree of increase in the weight of the atoms reproduces some1 though not all1 of the properties of the substance4 ,this tendency to repetition--these periods--may be likened to those annual or diurnal periods with which we are so familiar on the earth4 ,days and years follow each other1 but1 as they do so1 many things change2 and in like manner chemical evolutions1 changes in the masses of the elements1 permit of much remaining undisturbed1 though many properties undergo alteration4 ,the system is maintained according to the laws of conservation in nature1 but the motions are altered in consequence of the change of parts4 ,next1 let us take an astronomical case--such1 for example1 as the earth and the moon--and let us imagine that the mass of the latter is constantly increasing4 ,the question is1 what will then occur8 ,the path of the moon in space is a wave-line similar to that which geometricians have named epicycloidal1 or the locus of a point in a circle rolling round another circle4 ,but in consequence of the influence of the moon it is evident that the path of the earth itself cannot be a geometric ellipse1 even supposing the sun to be immovably fixed2 it must be an epicycloidal curve1 though not very far removed from the true ellipse--that is to say1 it will be impressed with but faint undulations4 ,it is only the common centre of gravity of the earth and the moon which describes a true ellipse round the sun4 ,if the moon were to increase1 the relative undulations of the earth's path would increase in amplitude1 those of the moon would also change1 and when the mass of the moon had increased to an equality with that of the earth1 the path would consist of epicycloidal curves crossing each other1 and having opposite phases4 ,but a similar relation exists between the sun and the earth1 because the former is also moving in space4 ,we may apply these views to the world of atoms1 and suppose that in their movements1 when heavy ones take the place of those that are lighter1 similar changes take place1 provided that the system or the molecule is preserved throughout the change4 ,it seems probable that in the heavenly systems1 during incalculable astronomical periods1 changes have taken place and are still going on similar to those which pass rapidly before our eyes during the chemical reaction of molecules1 and the progress of molecular mechanics may--we hope will--in course of time permit us to explain those changes in the stellar world which have more than once been noticed by astronomers1 and which are now so carefully studied4 ,a coming ,newton will discover the laws of these changes4 ,those laws1 when applied to chemistry1 may exhibit peculiarities1 but these will certainly be mere variations on the grand harmonious theme which reigns in nature4 ,the discovery of the laws which produce this harmony in chemical evolution will only be possible1 it seems to me1 under the banner of ,newtonian dynamics1 which has so long waved over the domains of mechanics1 astronomy1 and physics4 ,in calling chemists to take their stand under its peaceful and catholic shadow ,i imagine that ,i am aiding in establishing that scientific union which the managers of the ,royal ,institution wish to effect1 who have shown their desire to do so by the flattering invitation which has given me--a ,russian--the opportunity of laying before the countrymen of ,newton an attempt to apply to chemistry one of his immortal principles4 ,,appendix ,,ii ,,the ,,periodic ,,law ,,of ,,the ,,chemical ,,elements ,,by ,,professor ,,mendel,,eff ,,faraday ,,lecture ,,delivered ,,before ,,the ,,fellows ,,of ,,the ,,chemical ,,society ,,in ,,the ,,theatre ,,of ,,the ,,royal ,,institution1 ,,on ,,tuesday1 ,,june #d1 #ahhi ,the high honour bestowed by the ,chemical ,society in inviting me to pay a tribute to the world-famed name of ,faraday by delivering this lecture has induced me to take for its subject the ,periodic ,law of the ,elements--this being a generalisation in chemistry which has of late attracted much attention4 ,while science is pursuing a steady onward movement1 it is convenient from time to time to cast a glance back on the route already traversed1 and especially to consider the new conceptions which aim at discovering the general meaning of the stock of facts accumulated from day to day in our laboratories4 ,owing to the possession of laboratories1 modern science now bears a new character1 quite unknown1 not only to antiquity1 but even to the preceding century4 ,bacon's and ,descartes' idea of submitting the mechanism of science simultaneously to experiment and reasoning has been fully realised in the case of chemistry1 it having become not only possible but always customary to experiment4 ,under the all-penetrating control of experiment1 a new theory1 even if crude1 is quickly strengthened1 provided it be founded on a sufficient basis2 the asperities are removed1 it is amended by degrees1 and soon loses the phantom light of a shadowy form or of one founded on mere prejudice2 it is able to lead to logical conclusions1 and to submit to experimental proof4 ,willingly or not1 in science we all must submit not to what seems to us attractive from one point of view or from another1 but to what represents an agreement between theory and experiment2 in other words1 to demonstrated generalisation and to the approved experiment4 ,is it long since many refused to accept the generalisations involved in the law of ,avogadro and ,ampre1 so widely extended by ,gerhardt8 ,we still may hear the voices of its opponents2 they enjoy perfect freedom1 but vainly will their voices rise so long as they do not use the language of demonstrated facts ,the striking observations with the spectroscope which have permitted us to analyse the chemical constitution of distant worlds1 seemed1 at first1 applicable to the task of determining the nature of the atoms themselves2 but the working out of the idea in the laboratory soon demonstrated that the characters of spectra are determined1 not directly by the atoms1 but by the molecules into which the atoms are packed2 and so it became evident that more verified facts must be collected before it will be possible to formulate new generalisations capable of taking their place beside those ordinary ones based upon the conception of simple substances and atoms4 ,but as the shade of the leaves and roots of living plants1 together with the relics of a decayed vegetation1 favour the growth of the seedling and serve to promote its luxurious development1 in like manner sound generalisations--together with the relics of those which have proved to be untenable--promote scientific productivity1 and ensure the luxurious growth of science under the influence of rays emanating from the centres of scientific energy4 ,such centres are scientific associations and societies4 ,before one of the oldest and most powerful of these ,i am about to take the liberty of passing in review the twenty years' life of a generalisation which is known under the name of the ,periodic ,law4 ,it was in ,march #ahfi that ,i ventured to lay before the then youthful ,russian ,chemical ,society the ideas upon the same subject which ,i had expressed in my just written ',principles of ,chemistry4' ,without entering into details1 ,i will give the conclusions ,i then arrived at in the very words ,i used3-- '#a4 ,the elements1 if arranged according to their atomic weights1 exhibit an evident periodicity of properties4 '#b4 ,elements which are similar as regards their chemical properties have atomic weights which are either of nearly the same value 7e4g4 platinum1 iridium1 osmium7 or which increase regularly 7e4g4 potassium1 rubidium1 csium74 '#c4 ,the arrangement of the elements1 or of groups of elements1 in the order of their atomic weights1 corresponds to their so-called valencies as well as1 to some extent1 to their distinctive chemical properties--as is apparent1 among other series1 in that of lithium1 beryllium1 barium1 carbon1 nitrogen1 oxygen1 and iron4 '#d4 ,the elements which are the most widely diffused have small atomic weights4 '#e4 ,the magnitude of the atomic weight determines the character of the element1 just as the magnitude of the molecule determines the character of a compound4 '#f4 ,we must expect the discovery of many yet unknown elements--for example1 elements analogous to aluminium and silicon1 whose atomic weight would be between #fe and #ge4 '#g4 ,the atomic weight of an element may sometimes be amended by a knowledge of those of the contiguous elements4 ,thus1 the atomic weight of tellurium must lie between #abc and #abf1 and cannot be #abh4 '#h4 ,certain characteristic properties of the elements can be foretold from their atomic weights4 ',the aim of this communication will be fully attained if ,i succeed in drawing the attention of investigators to those relations which exist between the atomic weights of dissimilar elements1 which1 so far as ,i know1 have hitherto been almost completely neglected4 ,i believe that the solution of some of the most important problems of our science lies in researches of this kind4' ,to-day1 twenty years after the above conclusions were formulated1 they may still be considered as expressing the essence of the now well-known periodic law4 ,reverting to the epoch terminating with the sixties1 it is proper to indicate three series of data without the knowledge of which the periodic law could not have been discovered1 and which rendered its appearance natural and intelligible4 ,in the first place1 it was at that time that the numerical value of atomic weights became definitely known4 ,ten years earlier such knowledge did not exist1 as may be gathered from the fact that in #ahfj chemists from all parts of the world met at ,karlsruhe in order to come to some agreement1 if not with respect to views relating to atoms1 at any rate as regards their definite representation4 ,many of those present probably remember how vain were the hopes of coming to an understanding1 and how much ground was gained at that ,congress by the followers of the unitary theory so brilliantly represented by ,cannizzaro4 ,i vividly remember the impression produced by his speeches1 which admitted of no compromise1 and seemed to advocate truth itself1 based on the conceptions of ,avogadro1 ,gerhardt1 and ,regnault1 which at that time were far from being generally recognised4 ,and though no understanding could be arrived at1 yet the objects of the meeting were attained1 for the ideas of ,cannizzaro proved1 after a few years1 to be the only ones which could stand criticism1 and which represented an atom as--'the smallest portion of an element which enters into a molecule of its compound4' ,only such real atomic weights--not conventional ones--could afford a basis for generalisation4 ,it is sufficient1 by way of example1 to indicate the following cases in which the relation is seen at once and is perfectly clear3-- ,k #ci ,rb #he ,cs #acc ,ca #dj ,sr #hg ,ba #acg whereas with the equivalents then in use-- ,k #ci ,rb #he ,cs #acc ,ca #bj ,sr #dce ,ba #fhe the consecutiveness of change in atomic weight1 which with the true values is so evident1 completely disappears4 ,secondly1 it had become evident during the period #ahfj-gj1 and even during the preceding decade1 that the relations between the atomic weights of analogous elements were governed by some general and simple laws4 ,cooke1 ,cremers1 ,gladstone1 ,gmelin1 ,lenssen1 ,pettenkofer1 and especially ,dumas1 had already established many facts bearing on that view4 ,thus ,dumas compared the following groups of analogous elements with organic radicles3-- ,diff4 ,diff4 ,diff4 ,diff4 ,mg #ab ,p #ca ,o #h #h #dd #h ,li #g ,ca #bj ,as #ge ,s #af #af #c #h #dd #c #h ,na #bc ,sr #dd ,sb #aai ,se #dj #af #c #h #b #dd #c #h ,k #ci ,ba #fh ,bi #bjg ,te #fd and pointed out some really striking relationships1 such as the following3-- ,f #ai4 ,cl #cee #ai #afe4 ,br #hj #ai #b #afe #bh4 ,i #abg #b x #ai #b #afe #b #bh4 ,a4 ,strecker1 in his work ',theorien und ,experimente zur ,bestimmung der ,atomgewichte der ,elemente' 7,braunschweig1 #ahei71 after summarising the data relating to the subject1 and pointing out the remarkable series of equivalents-- ,cr #bfb ,mn #bgf ,fe #bh ,ni #bi ,co #cj ,cu #cag ,zn #cbe remarks that3 ',it is hardly probable that all the above-mentioned relations between the atomic weights 7or equivalents7 of chemically analogous elements are merely accidental4 ,we must1 however1 leave to the future the discovery of the law of the relations which appears in these figures4'#a #a ',es ist wohl kaum anzunehmen1 dass alle im ,vorhergehenden hervorgehobenen ,beziehungen zwischen den ,atomgewichten 7oder ,aequivalenten7 in chemischen ,verhltnissen einander hnliche ,elemente bloss zufllig sind4 ,die ,auffindung der in diesen ,zahlen gesetzlichen ,beziehungen mssen wir jedoch der ,zukunft berlassen4' ,in such attempts at arrangement and in such views are to be recognised the real forerunners of the periodic law2 the ground was prepared for it between #ahfj and #ahgj1 and that it was not expressed in a determinate form before the end of the decade may1 ,i suppose1 be ascribed to the fact that only analogous elements had been compared4 ,the idea of seeking for a relation between the atomic weights of all the elements was foreign to the ideas then current1 so that neither the vis tellurique of ,de ,chancourtois1 nor the law of octaves of ,newlands1 could secure anybody's attention4 ,and yet both ,de ,chancourtois and ,newlands like ,dumas and ,strecker1 more than ,lenssen and ,pettenkofer1 had made an approach to the periodic law and had discovered its germs4 ,the solution of the problem advanced but slowly1 because the facts1 but not the law1 stood foremost in all attempts2 and the law could not awaken a general interest so long as elements1 having no apparent connection with each other1 were included in the same octave1 as for example3-- #ast octave of ,newlands ,h ,f ,cl ,co ,ni ,br ,pd ,i ,pt ,ir #gth ,ditto ,o ,s ,fe ,se ,rh ,ru ,te ,au ,os or ,th ,analogies of the above order seemed quite accidental1 and the more so as the octave contained occasionally ten elements instead of eight1 and when two such elements as ,ba and ,v1 ,co and ,ni1 or ,rh and ,ru1 occupied one place in the octave4#b ,nevertheless1 the fruit was ripening1 and ,i now see clearly that ,strecker1 ,de ,chancourtois1 and ,newlands stood foremost in the way towards the discovery of the periodic law1 and that they merely wanted the boldness necessary to place the whole question at such a height that its reflection on the facts could be clearly seen4 #b ,to judge from ,j4 ,a4 ,r4 ,newlands's work1 ,on the ,discovery of the ,periodic ,law1 ,london1 #ahhd1 p4 #adi2 ',on the ,law of ,octaves' 7from the ,chemical ,news1 #ab1 #hc1 ,august #ah1 #ahfe74 ,a third circumstance which revealed the periodicity of chemical elements was the accumulation1 by the end of the sixties1 of new information respecting the rare elements1 disclosing their many-sided relations to the other elements and to each other4 ,the researches of ,marignac on niobium1 and those of ,roscoe on vanadium1 were of special moment4 ,the striking analogies between vanadium and phosphorus on the one hand1 and between vanadium and chromium on the other1 which became so apparent in the investigations connected with that element1 naturally induced the comparison of ,v #ea with ,cr #eb1 ,nb #id with ,mo #if1 and ,ta #aib with ,w #aid2 while1 on the other hand1 ,p #ca could be compared with ,s #cb1 ,as #ge with ,se #gi1 and ,sb #abj with ,te #abe4 ,from such approximations there remained but one step to the discovery of the law of periodicity4 ,the law of periodicity was thus a direct outcome of the stock of generalisations and established facts which had accumulated by the end of the decade #ahfj-ahgj2 it is an embodiment of those data in a more or less systematic expression4 ,where1 then1 lies the secret of the special importance which has since been attached to the periodic law1 and has raised it to the position of a generalisation which has already given to chemistry unexpected aid1 and which promises to be far more fruitful in the future and to impress upon several branches of chemical research a peculiar and original stamp8 ,the remaining part of my communication will be an attempt to answer this question4 ,in the first place we have the circumstance that1 as soon as the law made its appearance1 it demanded a revision of many facts which were considered by chemists as fully established by existing experience4 ,i shall return1 later on1 briefly to this subject1 but ,i wish now to remind you that the periodic law1 by insisting on the necessity for a revision of supposed facts1 exposed itself at once to destruction in its very origin4 ,its first requirements1 however1 have been almost entirely satisfied during the last #bj years2 the supposed facts have yielded to the law1 thus proving that the law itself was a legitimate induction from the verified facts4 ,but our inductions from data have often to do with such details of a science so rich in facts1 that only generalisations which cover a wide range of important phenomena can attract general attention4 ,what were the regions touched on by the periodic law8 ,this is what we shall now consider4 ,the most important point to notice is1 that periodic functions1 used for the purpose of expressing changes which are dependent on variations of time and space1 have been long known4 ,they are familiar to the mind when we have to deal with motion in closed cycles1 or with any kind of deviation from a stable position1 such as occurs in pendulum-oscillations4 ,a like periodic function became evident in the case of the elements1 depending on the mass of the atom4 ,the primary conception of the masses of bodies1 or of the masses of atoms1 belongs to a category which the present state of science forbids us to discuss1 because as yet we have no means of dissecting or analysing the conception4 ,all that was known of functions dependent on masses derived its origin from ,galileo and ,newton1 and indicated that such functions either decrease or increase with the increase of mass1 like the attraction of celestial bodies4 ,the numerical expression of the phenomena was always found to be proportional to the mass1 and in no case was an increase of mass followed by a recurrence of properties such as is disclosed by the periodic law of the elements4 ,this constituted such a novelty in the study of the phenomena of nature that1 although it did not lift the veil which conceals the true conception of mass1 it nevertheless indicated that the explanation of that conception must be searched for in the masses of the atoms2 the more so1 as all masses are nothing but aggregations1 or additions1 of chemical atoms which would be best described as chemical individuals4 ,let me remark1 by the way1 that though the ,latin word 'individual' is merely a translation of the ,greek word 'atom1' nevertheless history and custom have drawn a sharp distinction between the two words1 and the present chemical conception of atoms is nearer to that defined by the ,latin word than by the ,greek1 although this latter also has acquired a special meaning which was unknown to the classics4 ,the periodic law has shown that our chemical individuals display a harmonic periodicity of properties dependent on their masses4 ,now natural science has long been accustomed to deal with periodicities observed in nature1 to seize them with the vice of mathematical analysis1 to submit them to the rasp of experiment4 ,and these instruments of scientific thought would surely1 long since1 have mastered the problem connected with the chemical elements1 were it not for a new feature which was brought to light by the periodic law1 and which gave a peculiar and original character to the periodic function4 ,if we mark on an axis of absciss a series of lengths proportional to angles1 and trace ordinates which are proportional to sines or other trigonometrical functions1 we get periodic curves of a harmonic character4 ,so it might seem1 at first sight1 that with the increase of atomic weights the function of the properties of the elements should also vary in the same harmonious way4 ,but in this case there is no such continuous change as in the curves just referred to1 because the periods do not contain the infinite number of points constituting a curve1 but a finite number only of such points4 ,an example will better illustrate this view4 ,the atomic weights-- ,ag #ajh ,cd #aab ,in #aac ,sn #aah ,sb #abj ,te #abe ,i #abg steadily increase1 and their increase is accompanied by a modification of many properties which constitutes the essence of the periodic law4 ,thus1 for example1 the densities of the above elements decrease steadily1 being respectively-- #aje #hf #gd #gb #fg #fd #di while their oxides contain an increasing quantity of oxygen-- ,ag#b,o ,cd#b,o#b ,in#b,o#c ,sn#b,o#d ,sb#b,o#e ,te#b,o#f ,i#b,o#g ,but to connect by a curve the summits of the ordinates expressing any of these properties would involve the rejection of ,dalton's law of multiple proportions4 ,not only are there no intermediate elements between silver1 which gives ,ag,cl1 and cadmium1 which gives ,cd,cl#b1 but1 according to the very essence of the periodic law1 there can be none2 in fact a uniform curve would be inapplicable in such a case1 as it would lead us to expect elements possessed of special properties at any point of the curve4 ,the periods of the elements have thus a character very different from those which are so simply represented by geometers4 ,they correspond to points1 to numbers1 to sudden changes of the masses1 and not to a continuous evolution4 ,in these sudden changes destitute of intermediate steps or positions1 in the absence of elements intermediate between1 say1 silver and cadmium1 or aluminium and silicon1 we must recognise a problem to which no direct application of the analysis of the infinitely small can be made4 ,therefore1 neither the trigonometrical functions proposed by ,ridberg and ,flavitzky1 nor the pendulum-oscillations suggested by ,crookes1 nor the cubical curves of the ,rev4 ,mr4 ,haughton1 which have been proposed for expressing the periodic law1 from the nature of the case1 can represent the periods of the chemical elements4 ,if geometrical analysis is to be applied to this subject1 it will require to be modified in a special manner4 ,it must find the means of representing in a special way1 not only such long periods as that comprising ,k ,ca ,sc ,ti ,v ,cr ,mn ,fe ,co ,ni ,cu ,zn ,ga ,ge ,as ,se ,br1 but short periods like the following3-- ,na ,mg ,al ,si ,p ,s ,cl4 ,in the theory of numbers only do we find problems analogous to ours1 and two attempts at expressing the atomic weights of the elements by algebraic formul seem to be deserving of attention1 although neither of them can be considered as a complete theory1 nor as promising finally to solve the problem of the periodic law4 ,the attempt of ,e4 ,j4 ,mills 7#ahhf7 does not even aspire to attain this end4 ,he considers that all atomic weights can be expressed by a logarithmic function1 #ae7n - #jicget71 in which the variables n and t are whole numbers4 ,thus1 for oxygen1 n #b1 and t #a1 whence its atomic weight is #aeid2 in the case of chlorine1 bromine1 and iodine1 n has respective values of #c1 #f1 and #i1 whilst t #g1 #f1 and #i2 in the case of potassium1 rubidium1 and csium1 n #d1 #f1 and #i1 and t #ad1 #ah1 and #bj4 ,another attempt was made in #ahhh by ,b4 ,n4 ,tchitchrin4 ,its author places the problem of the periodic law in the first rank1 but as yet he has investigated the alkali metals only4 ,tchitchrin first noticed the simple relations existing between the atomic volumes of all alkali metals2 they can be expressed1 according to his views1 by the formula ,a7#b - #jjjece;,an71 where ,a is the atomic weight1 and n is equal to #h for lithium and sodium1 to #d for potassium1 to #c for rubidium1 and to #b for csium4 ,if n remained equal to #h during the increase of ,a1 the volume would become zero at ,a #df-b_/c1 and it would reach its maximum at ,a #bc-a_/c4 ,the close approximation of the number #df-b_/c to the differences between the atomic weights of analogous elements 7such as ,cs - ,rb1 ,i - ,br1 and so on72 the close correspondence of the number #bc-a_/c to the atomic weight of sodium2 the fact of n being necessarily a whole number1 and several other aspects of the question1 induce ,tchitchrin to believe that they afford a clue to the understanding of the nature of the elements2 we must1 however1 await the full development of his theory before pronouncing judgment on it4 ,what we can at present only be certain of is this3 that attempts like the two above named must be repeated and multiplied1 because the periodic law has clearly shown that the masses of the atoms increase abruptly1 by steps1 which are clearly connected in some way with ,dalton's law of multiple proportions2 and because the periodicity of the elements finds expression in the transition from ,,rx to ,,rx#b1 ,,rx#c1 ,,rx#d1 and so on till ,,rx#h1 at which point1 the energy of the combining forces being exhausted1 the series begins anew from ,,rx to ,,rx#b1 and so on4 ,while connecting by new bonds the theory of the chemical elements with ,dalton's theory of multiple proportions1 or atomic structure of bodies1 the periodic law opened for natural philosophy a new and wide field for speculation4 ,kant said that there are in the world 'two things which never cease to call for the admiration and reverence of man3 the moral law within ourselves1 and the stellar sky above us4' ,but when we turn our thoughts towards the nature of the elements and the periodic law1 we must add a third subject1 namely1 'the nature of the elementary individuals which we discover everywhere around us4' ,without them the stellar sky itself is inconceivable2 and in the atoms we see at once their peculiar individualities1 the infinite multiplicity of the individuals1 and the submission of their seeming freedom to the general harmony of ,nature4 ,having thus indicated a new mystery of ,nature1 which does not yet yield to rational conception1 the periodic law1 together with the revelations of spectrum analysis1 have contributed to again revive an old but remarkably long-lived hope--that of discovering1 if not by experiment1 at least by a mental effort1 the primary matter--which had its genesis in the minds of the ,grecian philosophers1 and has been transmitted1 together with many other ideas of the classic period1 to the heirs of their civilisation4 ,having grown1 during the times of the alchemists up to the period when experimental proof was required1 the idea has rendered good service2 it induced those careful observations and experiments which later on called into being the works of ,scheele1 ,lavoisier1 ,priestley1 and ,cavendish4 ,it then slumbered awhile1 but was soon awakened by the attempts either to confirm or to refute the ideas of ,prout as to the multiple proportion relationship of the atomic weights of all the elements4 ,and once again the inductive or experimental method of studying ,nature gained a direct advantage from the old ,pythagorean idea3 because atomic weights were determined with an accuracy formerly unknown4 ,but again the idea could not stand the ordeal of experimental test1 yet the prejudice remains and has not been uprooted1 even by ,stas2 nay1 it has gained a new vigour1 for we see that all which is imperfectly worked out1 new and unexplained1 from the still scarcely studied rare metals to the hardly perceptible nebul1 have been used to justify it4 ,as soon as spectrum analysis appears as a new and powerful weapon of chemistry1 the idea of a primary matter is immediately attached to it4 ,from all sides we see attempts to constitute the imaginary substance helium#c the so much longed for primary matter4 ,no attention is paid to the circumstance that the helium line is only seen in the spectrum of the solar protuberances1 so that its universality in ,nature remains as problematic as the primary matter itself2 nor to the fact that the helium line is wanting amongst the ,fraunhofer lines of the solar spectrum1 and thus does not answer to the brilliant fundamental conception which gives its real force to spectrum analysis4 #c ,that is1 a substance having a wave-length equal to #jjjjehge millimetre4 ,and finally1 no notice is even taken of the indubitable fact that the brilliancies of the spectral lines of the simple substances vary under different temperatures and pressures2 so that all probabilities are in favour of the helium line simply belonging to some long since known element placed under such conditions of temperature1 pressure1 and gravity as have not yet been realised in our experiments4 ,again1 the idea that the excellent investigations of ,lockyer of the spectrum of iron can be interpreted in favour of the compound nature of that element1 evidently must have arisen from some misunderstanding4 ,the spectrum of a compound certainly does not appear as a sum of the spectra of its components2 and therefore the observations of ,lockyer can be considered precisely as a proof that iron undergoes no other changes at the temperature of the sun than those which it experiences in the voltaic arc--provided the spectrum of iron is preserved4 ,as to the shifting of some of the lines of the spectrum of iron while the other lines maintain their positions1 it can be explained1 as shown by ,m4 ,kleiber 7',journal of the ,russian ,chemical and ,physical ,society1' #ahhe1 #adg71 by the relative motion of the various strata of the sun's atmosphere1 and by ,zllner's laws of the relative brilliancies of different lines of the spectrum4 ,moreover1 it ought not to be forgotten that if iron were really proved to consist of two or more unknown elements1 we should simply have an increase in the number of our elements--not a reduction1 and still less a reduction of all of them to one single primary matter4 ,feeling that spectrum analysis will not yield a support to the ,pythagorean conception1 its modern promoters are so bent upon its being confirmed by the periodic law1 that the illustrious ,berthelot1 in his work ',les origines de l',alchimie1' #ahhe1 #cac1 has simply mixed up the fundamental idea of the law of periodicity with the ideas of ,prout1 the alchemists1 and ,democritus about primary matter4#d ,but the periodic law1 based as it is on the solid and wholesome ground of experimental research1 has been evolved independently of any conception as to the nature of the elements2 it does not in the least originate in the idea of a unique matter2 and it has no historical connection with that relic of the torments of classical thought1 and therefore it affords no more indication of the unity of matter or of the compound character of our elements1 than the law of ,avogadro1 or the law of specific heats1 or even the conclusions of spectrum analysis4 ,none of the advocates of a unique matter have ever tried to explain the law from the standpoint of ideas taken from a remote antiquity when it was found convenient to admit the existence of many gods--and of a unique matter4 #d ,he maintains 7on p4 #cji7 that the periodic law requires two new analogous elements1 having atomic weights of #dh and #fd1 occupying positions between sulphur and selenium1 although nothing of the kind results from any of the different readings of the law4 ,when we try to explain the origin of the idea of a unique primary matter1 we easily trace that in the absence of inductions from experiment it derives its origin from the scientifically philosophical attempt at discovering some kind of unity in the immense diversity of individualities which we see around4 ,in classical times such a tendency could only be satisfied by conceptions about the immaterial world4 ,as to the material world1 our ancestors were compelled to resort to some hypothesis1 and they adopted the idea of unity in the formative material1 because they were not able to evolve the conception of any other possible unity in order to connect the multifarious relations of matter4 ,responding to the same legitimate scientific tendency1 natural science has discovered throughout the universe a unity of plan1 a unity of forces1 and a unity of matter1 and the convincing conclusions of modern science compel every one to admit these kinds of unity4 ,but while we admit unity in many things1 we none the less must also explain the individuality and the apparent diversity which we cannot fail to trace everywhere4 ,it has been said of old1 ',give us a fulcrum1 and it will become easy to displace the earth4' ,so also we must say1 ',give us something that is individualised1 and the apparent diversity will be easily understood4' ,otherwise1 how could unity result in a multitude8 ,after a long and painstaking research1 natural science has discovered the individualities of the chemical elements1 and therefore it is now capable not only of analysing1 but also of synthesising2 it can understand and grasp generality and unity1 as well as the individualised and the multifarious4 ,the general and universal1 like time and space1 like force and motion1 vary uniformly2 the uniform admit of interpolations1 revealing every intermediate phase4 ,but the multitudinous1 the individualised--such as ourselves1 or the chemical elements1 or the members of a peculiar periodic function of the elements1 or ,dalton's multiple proportions--is characterised in another way3 we see in it1 side by side with a connecting general principle1 leaps1 breaks of continuity1 points which escape from the analysis of the infinitely small--an absence of complete intermediate links4 ,chemistry has found an answer to the question as to the causes of multitudes2 and while retaining the conception of many elements1 all submitted to the discipline of a general law1 it offers an escape from the ,indian ,nirvana--the absorption in the universal1 replacing it by the individualised4 ,however1 the place for individuality is so limited by the all-grasping1 all-powerful universal1 that it is merely a point of support for the understanding of multitude in unity4 ,having touched upon the metaphysical bases of the conception of a unique matter which is supposed to enter into the composition of all bodies4 ,i think it necessary to dwell upon another theory1 akin to the above conception--the theory of the compound character of the elements now admitted by some--and especially upon one particular circumstance which1 being related to the periodic law1 is considered to be an argument in favour of that hypothesis4 ,dr4 ,pelopidas1 in #ahhc1 made a communication to the ,russian ,chemical and ,physical ,society on the periodicity of the hydrocarbon radicles1 pointing out the remarkable parallelism which was to be noticed in the change of properties of hydrocarbon radicles and elements when classed in groups4 ,professor ,carnelley1 in #ahhf1 developed a similar parallelism4 ,the idea of ,m4 ,pelopidas will be easily understood if we consider the series of hydrocarbon radicles which contain1 say1 #f atoms of carbon3-- ,i4 ,,ii4 ,,iii4 ,,iv4 ,v4 ,c#f;,h#ac ,c#f;,h#ab ,c#f;,h#aa ,c#f;,h#aj ,c#f;,h#i ,,vi4 ,,vii4 ,,viii4 ,c#f;,h#h ,c#f;,h#g ,c#f;,h#f ,the first of these radicles1 like the elements of the #ast group1 combines with ,cl1 ,,oh1 and so on1 and gives the derivatives of hexyl alcohol1 ,c#f;,h#ac7,,oh72 but1 in proportion as the number of hydrogen atoms decreases1 the capacity of the radicles of combining with1 say1 the halogens increases4 ,c#f;,h#ab already combines with #b atoms of chlorine2 ,c#f;,h#aa1 with #c atoms1 and so on4 ,the last members of the series comprise the radicles of acids3 thus ,c#f;,h#h1 which belongs to the #fth group1 gives1 like sulphur1 a bibasic acid1 ,c#f;,h#h,o#b7,,oh7#b1 which is homologous with oxalic acid4 ,the parallelism can be traced still further1 because ,c#f;,h#e appears as a monovalent radicle of benzene1 and with it begins a new series of aromatic derivatives1 so analogous to the derivatives of the aliphatic series4 ,let me also mention another example from among those which have been given by ,m4 ,pelopidas4 ,starting from the alkaline radicle of monomethylammonium1 ,n7,,ch#c7;,h#c1 or ,,nch#f1 which presents many analogies with the alkaline metals of the #ast group1 he arrives1 by successively diminishing the number of the atoms of hydrogen1 at a #gth group which contains cyanogen1 ,,cn1 which has long since been compared to the halogens of the #gth group4 ,the most important consequence which1 in my opinion1 can be drawn from the above comparison is that the periodic law1 so apparent in the elements1 has a wider application than might appear at first sight2 it opens up a new vista of chemical evolutions4 ,but1 while admitting the fullest parallelism between the periodicity of the elements and that of the compound radicles1 we must not forget that in the periods of the hydrocarbon radicles we have a decrease of mass as we pass from the representatives of the first group to the next1 while in the periods of the elements the mass increases during the progression4 ,it thus becomes evident that we cannot speak of an identity of periodicity in both cases1 unless we put aside the ideas of mass and attraction1 which are the real corner-stones of the whole of natural science1 and even enter into those very conceptions of simple substances which came to light a full hundred years later than the immortal principles of ,newton4#e #e ,it is noteworthy that the year in which ,lavoisier was born 7#agdc7--the author of the idea of elements and of the indestructibility of matter--is later by exactly one century than the year in which the author of the theory of gravitation and mass was born 7#afdc ,n4,s474 ,the affiliation of the ideas of ,lavoisier and those of ,newton is beyond doubt4 ,from the foregoing1 as well as from the failures of so many attempts at finding in experiment and speculation a proof of the compound character of the elements and of the existence of primordial matter1 it is evident1 in my opinion1 that this theory must be classed among mere utopias4 ,but utopias can only be combated by freedom of opinion1 by experiment1 and by new utopias4 ,in the republic of scientific theories freedom of opinions is guaranteed4 ,it is precisely that freedom which permits me to criticise openly the widely-diffused idea as to the unity of matter in the elements4 ,experiments and attempts at confirming that idea have been so numerous that it really would be instructive to have them all collected together1 if only to serve as a warning against the repetition of old failures4 ,and now as to new utopias which may be helpful in the struggle against the old ones1 ,i do not think it quite useless to mention a phantasy of one of my students who imagined that the weight of bodies does not depend upon their mass1 but upon the character of the motion of their atoms4 ,the atoms1 according to this new utopian1 may all be homogeneous or heterogeneous1 we know not which2 we know them in motion only1 and that motion they maintain with the same persistence as the stellar bodies maintain theirs4 ,the weights of atoms differ only in consequence of their various modes and quantity of motion2 the heaviest atoms may be much simpler than the lighter ones3 thus an atom of mercury may be simpler than an atom of hydrogen--the manner in which it moves causes it to be heavier4 ,my interlocutor even suggested that the view which attributes the greater complexity to the lighter elements finds confirmation in the fact that the hydrocarbon radicles mentioned by ,pelopidas1 while becoming lighter as they lose hydrogen1 change their properties periodically in the same manner as the elements change theirs1 according as the atoms grow heavier4 ,the ,french proverb1 ,la critique est facile1 mais l'art est difficile1 however1 may well be reversed in the case of all such ideal views1 as it is much easier to formulate than to criticise them4 ,arising from the virgin soil of newly-established facts1 the knowledge relating to the elements1 to their masses1 and to the periodic changes of their properties has given a motive for the formation of utopian hypotheses1 probably because they could not be foreseen by the aid of any of the various metaphysical systems1 and exist1 like the idea of gravitation1 as an independent outcome of natural science1 requiring the acknowledgment of general laws1 when these have been established with the same degree of persistency as is indispensable for the acceptance of a thoroughly established fact4 ,two centuries have elapsed since the theory of gravitation was enunciated1 and although we do not understand its cause1 we still must regard gravitation as a fundamental conception of natural philosophy1 a conception which has enabled us to perceive much more than the metaphysicians did or could with their seeming omniscience4 ,a hundred years later the conception of the elements arose2 it made chemistry what it now is2 and yet we have advanced as little in our comprehension of simple substances since the times of ,lavoisier and ,dalton as we have in our understanding of gravitation4 ,the periodic law of the elements is only twenty years old2 it is not surprising1 therefore1 that1 knowing nothing about the causes of gravitation and mass1 or about the nature of the elements1 we do not comprehend the rationale of the periodic law4 ,it is only by collecting established laws--that is1 by working at the acquirement of truth--that we can hope gradually to lift the veil which conceals from us the causes of the mysteries of ,nature and to discover their mutual dependency4 ,like the telescope and the microscope1 laws founded on the basis of experiment are the instruments and means of enlarging our mental horizon4 ,in the remaining part of my communication ,i shall endeavour to show1 and as briefly as possible1 in how far the periodic law contributes to enlarge our range of vision4 ,before the promulgation of this law the chemical elements were mere fragmentary1 incidental facts in ,nature2 there was no special reason to expect the discovery of new elements1 and the new ones which were discovered from time to time appeared to be possessed of quite novel properties4 ,the law of periodicity first enabled us to perceive undiscovered elements at a distance which formerly was inaccessible to chemical vision2 and long ere they were discovered new elements appeared before our eyes possessed of a number of well-defined properties4 ,we now know three cases of elements whose existence and properties were foreseen by the instrumentality of the periodic law4 ,i need but mention the brilliant discovery of gallium1 which proved to correspond to eka-aluminium of the periodic law1 by ,lecoq de ,boisbaudran2 of scandium1 corresponding to ekaboron1 by ,nilson2 and of germanium1 which proved to correspond in all respects to ekasilicon1 by ,winkler4 ,when1 in #ahga1 ,i described to the ,russian ,chemical ,society the properties1 clearly defined by the periodic law1 which such elements ought to possess1 ,i never hoped that ,i should live to mention their discovery to the ,chemical ,society of ,great ,britain as a confirmation of the exactitude and the generality of the periodic law4 ,now that ,i have had the happiness of doing so1 ,i unhesitatingly say that1 although greatly enlarging our vision1 even now the periodic law needs further improvements in order that it may become a trustworthy instrument in further discoveries4#f #f ,i foresee some more new elements1 but not with the same certitude as before4 ,i shall give one example1 and yet ,i do not see it quite distinctly4 ,in the series which contains ,hg #bjd1 ,pb #bjf1 and ,bi #bjh1 we can imagine the existence 7at the place ,,vi-#aa7 of an element analogous to tellurium1 which we can describe as dvi-tellurium1 ,dt1 having an atomic weight of #bab1 and the property of forming the oxide ,dt,o#c4 ,if this element really exists1 it ought in the free state to be an easily fusible1 crystalline1 non-volatile metal of a grey colour1 having a density of about #ic1 capable of giving a dioxide1 ,dt,o#b1 equally endowed with feeble acid and basic properties4 ,this dioxide must give on active oxidation an unstable higher oxide1 ,dt,o#c1 which should resemble in its properties ,pb,o#b and ,bi#b,o#e4 ,dvi-tellurium hydride1 if it be found to exist1 will be a less stable compound than even ,h#b,te4 ,the compounds of dvi-tellurium will be easily reduced1 and it will form characteristic definite alloys with other metals4 ,i will venture to allude to some other matters which chemistry has discerned by means of its new instrument1 and which it could not have made out without a knowledge of the law of periodicity1 and ,i will confine myself to simple substances and to oxides4 ,before the periodic law was formulated the atomic weights of the elements were purely empirical numbers1 so that the magnitude of the equivalent1 and the atomicity1 or the value in substitution possessed by an atom1 could only be tested by critically examining the methods of determination1 but never directly by considering the numerical values themselves2 in short1 we were compelled to move in the dark1 to submit to the facts1 instead of being masters of them4 ,i need not recount the methods which permitted the periodic law at last to master the facts relating to atomic weights1 and ,i would merely call to mind that it compelled us to modify the valencies of indium and cerium1 and to assign to their compounds a different molecular composition4 ,determinations of the specific heats of these two metals fully confirmed the change4 ,the trivalency of yttrium1 which makes us now represent its oxide as ,y#b,o#c instead of as ,,yo1 was also foreseen 7in #ahgj7 by the periodic law1 and it has now become so probable that ,clve1 and all other subsequent investigators of the rare metals1 have not only adopted it1 but have also applied it without any new demonstration to substances so imperfectly known as those of the cerite and gadolinite group1 especially since ,hillebrand determined the specific heats of lanthanum and didymium and confirmed the expectations suggested by the periodic law4 ,but here1 especially in the case of didymium1 we meet with a series of difficulties long since foreseen through the periodic law1 but only now becoming evident1 and chiefly arising from the relative rarity and insufficient knowledge of the elements which usually accompany didymium4 ,passing to the results obtained in the case of the rare elements beryllium1 scandium1 and thorium1 it is found that these have many points of contact with the periodic law4 ,although ,avdeff long since proposed the magnesia formula to represent beryllium oxide1 yet there was so much to be said in favour of the alumina formula1 on account of the specific heat of the metals and the isomorphism of the two oxides1 that it became generally adopted and seemed to be well established4 ,the periodic law1 however1 as ,brauner repeatedly insisted 7',berichte1' #ahgh1 #hgb2 #ahha1 #ec71 was against the formula ,be#b,o#c2 it required the magnesia formula ,be,o--that is1 an atomic weight of #i--;because there was no place in the system for an element like beryllium having an atomic weight of #ace4 ,this divergence of opinion lasted for years1 and ,i often heard that the question as to the atomic weight of beryllium threatened to disturb the generality of the periodic law1 or1 at any rate1 to require some important modifications of it4 ,many forces were operating in the controversy regarding beryllium1 evidently because a much more important question was at issue than merely that involved in the discussion of the atomic weight of a relatively rare element3 and during the controversy the periodic law became better understood1 and the mutual relations of the elements became more apparent than ever before4 ,it is most remarkable that the victory of the periodic law was won by the researches of the very observers who previously had discovered a number of facts in support of the trivalency of beryllium4 ,applying the higher law of ,avogadro1 ,nilson and ,petterson have finally shown that the density of the vapour of the beryllium chloride1 ,be,cl#b1 obliges us to regard beryllium as bivalent in conformity with the periodic law4#g ,i consider the confirmation of ,avdeff's and ,brauner's view as important in the history of the periodic law as the discovery of scandium1 which1 in ,nilson's hands1 confirmed the existence of ekaboron4 #g ,let me mention another proof of the bivalency of beryllium which may have passed unnoticed1 as it was only published in the ,russian chemical literature4 ,having remarked 7in #ahhd7 that the density of such solutions of chlorides of metals1 ,m,cln1 as contain #bjj mols4 of water 7or a large and constant amount of water7 regularly increases as the molecular weight of the dissolved salt increases1 ,i proposed to one of our young chemists1 ,m4 ,burdakoff1 that he should investigate beryllium chloride4 ,if its molecule be ,be,cl#b its weight must be #hj2 and in such a case it must be heavier than the molecule of ,k,cl #gde1 and lighter than that of ,mg,cl#b1 #ic4 ,on the contrary1 if beryllium chloride is a trichloride1 ,be,cl#c #abj1 its molecule must be heavier than that of ,ca,cl#b #aaa1 and lighter than that of ,mn,cl#b #abf4 ,experiment has shown the correctness of the former formula1 the solution ,be,cl#b #bjj;,h#b,o having 7at #ae_/d7 a density of #ajach1 this being a higher density than that of the solution ,k,cl #bjj;,h#b,o 7 #ajaba71 and lower than that of ,mg,cl#b #bjj;,h#b,o 7 #ajbjc74 ,the bivalency of beryllium was thus confirmed in the case both of the dissolved and the vaporised chloride4 ,the circumstance that thorium proved to be quadrivalent1 and ,th #bcb1 in accordance with the views of ,chydenius and the requirements of the periodic law1 passed almost unnoticed1 and was accepted without opposition1 and yet both thorium and uranium are of great importance in the periodic system1 as they are its last members1 and have the highest atomic weights of all the elements4 ,the alteration of the atomic weight of uranium from ,u #abj into ,u #bdj attracted more attention1 the change having been made on account of the periodic law1 and for no other reason4 ,now that ,roscoe1 ,rammelsberg1 ,zimmermann1 and several others have admitted the various claims of the periodic law in the case of uranium1 its high atomic weight is received without objection1 and it endows that element with a special interest4 ,while thus demonstrating the necessity for modifying the atomic weights of several insufficiently known elements1 the periodic law enabled us also to detect errors in the determination of the atomic weights of several elements whose valencies and true position among other elements were already well known4 ,three such cases are especially noteworthy3 those of tellurium1 titanium and platinum4 ,berzelius had determined the atomic weight of tellurium to be #abh1 while the periodic law claimed for it an atomic weight below that of iodine1 which had been fixed by ,stas at #abfe1 and which was certainly not higher than #abg4 ,brauner then undertook the investigation1 and he has shown that the true atomic weight of tellurium is lower than that of iodine1 being near to #abe4 ,for titanium the extensive researches of ,thorpe have confirmed the atomic weight of ,ti #dh1 indicated by the law1 and already foreseen by ,rose1 but contradicted by the analyses of ,pierre and several other chemists4 ,an equally brilliant confirmation of the expectations based on the periodic law has been given in the case of the series osmium1 iridium1 platinum1 and gold4 ,at the time of the promulgation of the periodic law1 the determinations of ,berzelius1 ,rose1 and many others gave the following figures3-- ,os #bjj2 ,ir #aig2 ,pt #aih2 ,au #aif4 ,the expectations of the periodic law#h have been confirmed1 first1 by new determinations of the atomic weight of platinum 7by ,seubert1 ,dittmar1 and ,m',arthur1 which proved to be near to #aif 7taking ,o #af1 as proposed by ,marignac1 ,brauner1 and others72 secondly1 by ,seubert having proved that the atomic weight of osmium is really lower than that of platinum1 being near to #aia2 and thirdly1 by the investigations of ,krss1 ,thorpe and ,laurie1 proving that the atomic weight of gold exceeds that of platinum1 and approximates to #aig4 ,the atomic weights which were thus found to require correction were precisely those which the periodic law had indicated as affected with errors2 and it has been proved1 therefore1 that the periodic law affords a means of testing experimental results4 ,if we succeed in discovering the exact character of the periodic relationships between the increments in atomic weights of allied elements discussed by ,ridberg in #ahhe1 and again by ,bazaroff in #ahhg1 we may expect that our instrument will give us the means of still more closely controlling the experimental data relating to atomic weights4 #h ,i pointed them out in the ,liebig's ,annalen1 ,supplement ,band41 viii4 #ahga1 p4 #baa4 ,let me next call to mind that1 while disclosing the variation of chemical properties1#i the periodic law1 has also enabled us to systematically discuss many of the physical properties of elementary bodies1 and to show that these properties are also subject to the law of periodicity4 ,at the ,moscow ,congress of ,russian ,naturalists in ,august1 #ahfi1 ,i dwelt upon the relations which existed between density and the atomic weight of the elements4 ,the following year ,professor ,lothar ,meyer1 in his well-known paper1#aj studied the same subject in more detail1 and thus contributed to spread information about the periodic law4 ,later on1 ,carnelley1 ,laurie1 ,l4 ,meyer1 ,roberts-,austen1 and several others applied the periodic system to represent the order in the changes of the magnetic properties of the elements1 their melting points1 the heats of formation of their haloid compounds1 and even of such mechanical properties as the coefficient of elasticity1 the breaking stress1 c41 c4 ,these deductions1 which have received further support in the discovery of new elements endowed not only with chemical but even with physical properties1 which were foreseen by the law of periodicity1 are well known2 so ,i need not dwell upon the subject1 and may pass to the consideration of oxides4#aa #i ,thus1 in the typical small period of ,li1 ,be1 ,b1 ,c1 ,n1 ,o1 ,f1 we see at once the progression from the alkali metals to the acid non-metals1 such as are the halogens4 #aj ,liebig's ,annalen1 ,supplement ,band41 vii4 #ahgj4 #aa ,a distinct periodicity can also be discovered in the spectra of the elements4 ,thus the researches of ,hartley1 ,ciamician1 and others have disclosed1 first1 the homology of the spectra of analogous elements3 secondly1 that the alkali metals have simpler spectra than the metals of the following groups2 and thirdly1 that there is a certain likeness between the complicated spectra of manganese and iron on the one hand1 and the no less complicated spectra of chlorine and bromine on the other hand1 and their likeness corresponds to the degree of analogy between those elements which is indicated by the periodic law4 ,in indicating that the gradual increase of the power of elements of combining with oxygen is accompanied by a corresponding decrease in their power of combining with hydrogen1 the periodic law has shown that there is a limit of oxidation1 just as there is a well-known limit to the capacity of elements for combining with hydrogen4 ,a single atom of an element combines with at most four atoms of either hydrogen or oxygen2 and while ,,ch#d and ,si,h#d represent the highest hydrides1 so ,ru,o#d and ,os,o#d are the highest oxides4 ,we are thus led to recognise types of oxides1 just as we have had to recognise types of hydrides4#ab #ab ,formerly it was supposed that1 being a bivalent element1 oxygen can enter into any grouping of the atoms1 and there was no limit foreseen as to the extent to which it could further enter into combination4 ,we could not explain why bivalent sulphur1 which forms compounds such as ,o ,o _/ _/ ,s and ,s ,o1 _/ _/ ,o ,o could not also form oxides such as-- ,o--,o ,o--,o _/ _/ ,s or ,s ,o1 _/ _/ ,o--,o ,o--,o while other elements1 as1 for instance1 chlorine1 form compounds such as-- ,cl--,o--,o--,o--,o--,k ,the periodic law has demonstrated that the maximum extent to which different non-metals enter into combination with oxygen is determined by the extent to which they combine with hydrogen1 and that the sum of the number of equivalents of both must be equal to #h4 ,thus chlorine1 which combines with #a atom or #a equivalent of hydrogen1 cannot fix more than #g equivalents of oxygen1 giving ,cl#b,o#g2 while sulphur1 which fixes #b equivalents of hydrogen1 cannot combine with more than #f equivalents or #c atoms of oxygen4 ,it thus becomes evident that we cannot recognise as a fundamental property of the elements the atomic valencies deduced from their hydrides2 and that we must modify1 to a certain extent1 the theory of atomicity if we desire to raise it to the dignity of a general principle capable of affording an insight into the constitution of all compound molecules4 ,in other words1 it is only to carbon1 which is quadrivalent with regard both to oxygen and hydrogen1 that we can apply the theory of constant valency and of bond1 by means of which so many still endeavour to explain the structure of compound molecules4 ,but ,i should go too far if ,i ventured to explain in detail the conclusions which can be drawn from the above considerations4 ,still1 ,i think it necessary to dwell upon one particular fact which must be explained from the point of view of the periodic law in order to clear the way to its extension in that particular direction4 ,the higher oxides yielding salts the formation of which was foreseen by the periodic system--for instance1 in the short series beginning with sodium-- ,na#b,o1 ,mg,o1 ,al#b,o#c1 ,si,o#b1 ,p#b,o#e1 ,,so#c1 ,cl#b,o#g1 must be clearly distinguished from the higher degrees of oxidation which correspond to hydrogen peroxide and bear the true character of peroxides4 ,peroxides such as ,na#b,o#b1 ,ba,o#b1 and the like have long been known4 ,similar peroxides have also recently become known in the case of chromium1 sulphur1 titanium1 and many other elements1 and ,i have sometimes heard it said that discoveries of this kind weaken the conclusions of the periodic law in so far as it concerns the oxides4 ,i do not think so in the least1 and ,i may remark1 in the first place1 that all these peroxides are endowed with certain properties obviously common to all of them1 which distinguish them from the actual1 higher1 salt-forming oxides1 especially their easy decomposition by means of simple contact agencies2 their incapability of forming salts of the common type2 and their capability of combining with other peroxides 7like the faculty which hydrogen peroxide possesses of combining with barium peroxide1 discovered by ,schoene74 ,again1 we remark that some groups are especially characterised by their capacity of generating peroxides4 ,such is1 for instance1 the case in the sixth group1 where we find the well-known peroxides of sulphur1 chromium1 and uranium2 so that further investigation of peroxides will probably establish a new periodic function1 foreshadowing that molybdenum and tungsten will assume peroxide forms with comparative readiness4 ,to appreciate the constitution of such peroxides1 it is enough to notice that the peroxide form of sulphur 7so-called persulphuric acid7 stands in the same relation to sulphuric acid as hydrogen peroxide stands to water3-- ,h7,,oh71 or ,h#b,o1 responds to 7,,oh77,,oh71 or ,h#b,o#b1 and so also-- ,h7,,hso#d71 or ,h#b,,so#d1 responds to 7,,hso#d77;,,hso#d71 or ,h#b,s#b,o#h4 ,similar relations are seen everywhere1 and they correspond to the principle of substitutions which ,i long since endeavoured to represent as one of the chemical generalisations called into life by the periodic law4 ,so also sulphuric acid1 if considered with reference to hydroxyl1 and represented as follows3-- ,,ho7,,so#b,,oh71 has its corresponding compound in dithionic acid-- 7,,so#b,,oh77,,so#b,,oh71 or ,h#b,s#b,o#f4 ,therefore1 also1 phosphoric acid1 ,,ho7,,poh#b,o#b71 has1 in the same sense1 its corresponding compound in the subphosphoric acid of ,saltzer3-- 7,,poh#b,o#b77,,poh#b,o#b71 or ,h#d,p#b,o#f2 and we must suppose that the peroxide compound corresponding to phosphoric acid1 if it be discovered1 will have the following structure3-- 7,h#b,,po#d7b or ,h#d,p#b,o#h #b;,h#b,o #b,,po#c4ac ,so far as is known at present1 the highest form of peroxides is met with in the peroxide of uranium1 ,,uo#d1 prepared by ,fairley2#ad while ,os,o#d is the highest oxide giving salts4 ,the line of argument which is inspired by the periodic law1 so far from being weakened by the discovery of peroxides1 is thus actually strengthened1 and we must hope that a further exploration of the region under consideration will confirm the applicability to chemistry generally of the principles deduced from the periodic law4 #ac ,in this sense1 oxalic acid1 7,,cooh7#b1 also corresponds to carbonic acid1 ,,oh7,,cooh71 in the same way that dithionic acid corresponds to sulphuric acid1 and subphosphoric acid to phosphoric2 hence1 if a peroxide corresponding to carbonic acid be obtained1 it will have the structure of 7,,hco#c7b1 or ,h#b;,c#b,o#f ,h#b,o ,c#b,o#e4 ,so also lead must have a real peroxide1 ,pb#b,o#e4 #ad ,the compounds of uranium prepared by ,fairley seem to me especially instructive in understanding the peroxides4 ,by the action of hydrogen peroxide on uranium oxide1 ,,uo#c1 a peroxide of uranium1 ,,uo#d1d;,h#b,o1 is obtained 7,u #bdj7 if the solution be acid2 but if hydrogen peroxide act on uranium oxide in the presence of caustic soda1 a crystalline deposit is obtained which has the composition ,na#d,,uo#h1d;,h#b,o1 and evidently is a combination of sodium peroxide1 ,na#b,o#b1 with uranium peroxide1 ,,uo#d4 ,it is possible that the former peroxide1 ,,uo#d1d;,h#b,o1 contains the elements of hydrogen peroxide and uranium peroxide1 ,u#b,o#g1 or even ,u7,,oh7#f1;,h#b,o#b1 like the peroxide of tin recently discovered by ,spring1 which has the constitution ,sn#b,o#e1;,h#b,o#b4 ,permit me now to conclude my rapid sketch of the oxygen compounds by the observation that the periodic law is especially brought into evidence in the case of the oxides which constitute the immense majority of bodies at our disposal on the surface of the earth4 ,the oxides are evidently subject to the law1 both as regards their chemical and their physical properties1 especially if we take into account the cases of polymerism which are so obvious when comparing ,,co#b1 with ,sin,o#bn4 ,in order to prove this ,i give the densities s and the specific volumes v of the higher oxides of two short periods4 ,to render comparison easier1 the oxides are all represented as of the form ,r#b,on4 ,in the column headed ,delta the differences are given between the volume of the oxygen compound and that of the parent element1 divided by n--that is1 by the number of atoms of oxygen in the compound3--#ae s4 v4 ,delta ,na#b,o #bf #bd -#bb ,mg#b,o#b #cf #bb -#c ,al#b,o#c #dj #bf #ac ,si#b,o#d #bfe #de #eb ,p#b,o#e #bci #ei #fb ,s#b,o#f #aif #hb #hg ,k#b,o #bg #ce -#ee ,sc#b,o#c #chf #ce #j ,li#b,o#d #db #ch #e ,v#b,o#e #cdi #eb #fg ,cr#b,o#f #bgd #gc #ie #ae ,delta thus represents the average increase of volume for each atom of oxygen contained in the higher salt-forming oxide4 ,the acid oxides give1 as a rule1 a higher value of ,delta1 while in the case of the strongly alkaline oxides its value is usually negative4 ,i have nothing to add to these figures1 except that like relations appear in other periods as well4 ,the above relations were precisely those which made it possible for me to be certain that the relative density of ekasilicon oxide would be about #dg2 germanium oxide1 actually obtained by ,winkler1 proved1 in fact1 to have the relative density #dgjc4 ,the foregoing account is far from being an exhaustive one of all that has already been discovered by means of the periodic law telescope in the boundless realms of chemical evolution4 ,still less is it an exhaustive account of all that may yet be seen1 but ,i trust that the little which ,i have said will account for the philosophical interest attached in chemistry to this law4 ,although but a recent scientific generalisation1 it has already stood the test of laboratory verification1 and appears as an instrument of thought which has not yet been compelled to undergo modification2 but it needs not only new applications1 but also improvements1 further development1 and plenty of fresh energy4 ,all this will surely come1 seeing that such an assembly of men of science as the ,chemical ,society of ,great ,britain has expressed the desire to have the history of the periodic law described in a lecture dedicated to the glorious name of ,faraday4 ,,appendix ,,iii ,,argon1 ,a ,,new ,,constituent ,,of ,,the ,,atmosphere ,,written ,,by ,,professor ,,mendel,,eff ,,in ,,february #ahie ,the remarks made in ,chapter ,v41 ,note #af bis respecting the newly discovered constituent of the atmosphere are here supplemented by data 7taken from the publications of the ,royal ,society of ,london7 given by the discoverers ,lord ,rayleigh and ,professor ,ramsay in ,january #ahie1 together with observations made by ,crookes and ,olszewsky upon the same subject4 ,this gas1 which was discovered by ,rayleigh and ,ramsay in atmospheric nitrogen1 was named argon#a by them1 and upon the supposition of its being an element1 they gave it the symbol ,a4 ,but its true chemical nature is not yet fully known1 for not only has no compound of it been yet obtained1 but it has not even been brought into any reaction4 ,from all that is known about it at the present time1 we may conclude with the discoverers that argon belongs to those gases which are permanent constituents of the atmosphere1 and that it is a new element4 ,the latter statement1 however1 requires confirmation4 ,we shall presently see1 however1 that the negative chemical character of argon 7its incapacity to react with any substance71 and the small amount of it present in the atmosphere 7about #a-a_/d per cent4 by volume in the nitrogen of air1 and consequently about #a per cent4 by volume in air71 as well as the recent date of its discovery 7#ahid7 and the difficulty of its preparation1 are quite sufficient reasons for the incompleteness of the existing knowledge respecting this element4 ,but since1 so far as is yet known1 we are dealing with a normal constituent of the atmosphere#a bis1 the existing data1 notwithstanding their insufficiently definite nature1 should find a place even in such an elementary work as the present1 all the more as the names of ,rayleigh1 ,ramsay1 ,crookes and ,olszewsky1 who have worked upon argon1 are among the highest in our science1 and their researches among the most difficult4#b ,these researches1 moreover1 were directed straight to the goal1 which was only partly reached owing to the unusual properties of argon itself4 #a ,from the ,greek ,greek3 ,argon--inert4 #a bis ,in ,note #af bis1 ,chapter ,v41 ,i mentioned that1 judging from the specific gravity of argon1 it might possibly be polymerised nitrogen1 ,n#c1 bearing the same relationship to nitrogen1 ,n#b1 that ozone1 ,o#c1 bears to ordinary oxygen4 ,if this idea were confirmed1 still one would not imagine that argon was formed from the atmospheric nitrogen by those reactions by which it was obtained by ,rayleigh and ,ramsay1 but rather that it arises from the nitrogen of the atmosphere under natural conditions4 ,although this proposition is not quite destroyed by the more recent results1 still it is contradicted by the fact that the ratio of the specific heats of argon was found to be #aff1 which1 as far as is now known1 could not be the case for a gas containing #c atoms in its molecule1 since such gases 7see ,chapter ,,xiv41 ,note #g7 give the ratio approximately #ac 7for example1 ,,co#b74 ,in abstaining from further conclusions1 for they must inevitably be purely conjectural1 ,i consider it advisable to suggest that in conducting further researches upon argon it might be well to subject it to as high a temperature as possible4 ,and the possibility of nitrogen polymerising is all the more admissible from the fact that the aggregation of its atoms in the molecule is not at all unlikely1 and that polymerised nitrogen1 judging from many examples1 might be inert if the polymerisation were accompanied by the evolution of heat4 ,in the following footnotes ,i frequently return to this hypothesis1 not only because ,i have not yet met any facts definitely contradictory to it1 but also because the chief properties of argon agree with it to a certain extent4 #b ,the chief difficulty in investigating argon lies in the fact that its preparation requires the employment of a large quantity of air1 which has to be treated with a number of different reagents1 whose perfect purity 7especially that of magnesium7 will always be doubtful1 and argon has not yet been transferred to a substance in which it could be easily purified4 ,perhaps the considerable solubility of argon in water 7or in other suitable liquids1 which have not apparently yet been tried7 may give the means of doing so1 and it may be possible1 by collecting the air expelled from boiling water1 to obtain a richer source of argon than ordinary air4 ,when it became known 7,chapter ,v41 ,note #d bis7 that the nitrogen obtained from air 7by removing the oxygen1 moisture and ,,co#b1 by various reagents7 has a greater density than that obtained from the various 7oxygen1 hydrogen and metallic7 compounds of nitrogen1 it was a plausible explanation that the latter contained an admixture of hydrogen1 or of some other light gas lowering the density of the mixture4 ,but such an assumption is refuted not only by the fact that the nitrogen obtained from its various compounds 7after purification7 has always the same density 7although the supposed impurities mixed with it should vary71 but also by ,rayleigh and ,ramsay's experiment of artificially adding hydrogen to nitrogen1 and then passing the mixture over red-hot oxide of copper1 when it was found that the nitrogen regained its original density1 i4e4 that the whole of the hydrogen was removed by this treatment4 ,therefore the difference in the density of the two varieties of nitrogen had to be explained by the presence of a heavier gas in admixture with the nitrogen obtained from the atmosphere4 ,this hypothesis was confirmed by the fact that ,rayleigh and ,ramsay having obtained purified nitrogen 7by removing the ,o#b1 ,,co#b1 and ,h#b,o71 both from ordinary air and from air which had been previously subjected to atmolysis1 that is which had been passed through porous tubes 7of burnt clay1 e4g4 pipe-stem71 surrounded by a rarefied space1 and so deprived of its lighter constituents 7chiefly nitrogen71 found that the nitrogen from the air which had been subjected to atmolysis was heavier than that obtained from air which had not been so treated4 ,this experiment showed that the nitrogen of air contains an admixture of a gas which1 being heavier than nitrogen itself1#c diffuses more slowly than nitrogen through the porous material4 ,it remained1 therefore1 to separate this impurity from the nitrogen4 ,to do this ,rayleigh and ,ramsay adopted two methods1 converting the nitrogen into solid and liquid substances1 either by absorbing the nitrogen by heated magnesium 7,chapter ,v41 ,note #f1 and ,chapter ,,xiv41 ,note #ad71 with the formation of nitride of magnesium1 or else by converting it into nitric acid by the action of electric sparks or the presence of an excess of air and alkali1 as in ,cavendish's method4#c bis ,in both cases the nitrogen entered into reaction1 while the heavier gas mixed with it remained inert1 and was thus able to be isolated4 ,that is1 the argon could be separated by these means from the excess of atmospheric nitrogen accompanying it4#d ,as an illustration we will describe how argon was obtained from the atmospheric nitrogen by means of magnesium4#e ,to begin with1 it was discovered that when atmospheric nitrogen was passed through a tube containing metallic magnesium heated to redness1 its specific gravity rose to #adhh4 ,as this showed that part of the gas was absorbed by the magnesium1 a mercury gasometer filled with atmospheric nitrogen was taken1 and the gas drawn over soda-lime1 ,p#b,o#e1 heated magnesium#f and then through tubes containing red-hot copper oxide1 soda-lime and phosphoric anhydride to a second mercury gasometer4 ,every time the gas was repassed through the tubes1 it decreased in volume and increased in density4 ,after repeating this for ten days #a1ejj c4c4 of gas were reduced to #bjj cc41 and the density increased to #afa 7if that of ,h#b #a and ,n#b #ad74 ,further treatment of the remainder brought the density up to #aiji4 ,after adding a small quantity of oxygen and repassing the gas through the apparatus1 the density rose to #bjj4 ,to obtain argon by this process ,ramsay and ,rayleigh 7employing a mercury air pump and mercury gasometers7 once treated about #aej litres of atmospheric nitrogen4 ,on another occasion they treated #g1ibe c4c4 of air by the oxidation method and obtained #fe c4c4 of argon1 which corresponds to #jhb per cent4 ,the density of the argon obtained by this means was nearly #aig1 while that obtained by the magnesium method varied between #aiji and #bjch4 #c ,it might also be supposed that this heavy gas is separated by the copper when the latter absorbs the oxygen of the air2 but such a supposition is not only improbable in itself1 but does not agree with the fact that nitrogen may be obtained from air by absorbing the oxygen by various other substances in solution 7for instance1 by the lower oxides of the metals1 like ,fe,o7 besides red-hot copper1 and that the nitrogen obtained is always just as heavy4 ,besides which1 nitrogen is also set free from its oxides by copper1 and the nitrogen thus obtained is lighter4 ,therefore it is not the copper which produces the heavy gas--i4e4 argon4 #c bis ,it is worthy of note that ,cavendish obtained a small residue of gas in converting nitrogen into nitric acid2 but he paid no attention to it1 although probably he had in his hands the very argon recently discovered4 #d ,when in these experiments1 instead of atmospheric nitrogen the gas obtained from its compound was taken1 an inert residue of a heavy gas1 having the properties of argon1 was also remarked1 but its amount was very small4 ,rayleigh and ,ramsay ascribe the formation of this residue to the fact that the gas in these experiments was collected over water1 and a portion of the dissolved argon in it might have passed into the nitrogen4 ,as the authors of this supposition did not prove it by any special experiments1 it forms a weak point in their classical research4 ,if it be admitted that argon is ,n#c1 the fact of its being obtained from the nitrogen of compounds might be explained by the polymerisation of a portion of the nitrogen in the act of reaction1 although it is impossible to refute ,rayleigh and ,ramsay's hypothesis of its being evolved from the water employed in the manipulation of the gases4 ,three thousand volumes of nitrogen extracted from its compounds gave about three volumes of argon1 while thirty volumes were yielded by the same amount of atmospheric nitrogen4 #e ,the preparation of argon by the conversion of nitrogen into nitric acid is complicated by the necessity of adding a large proportion of oxygen and alkali1 of passing an electric discharge through the mixture for a long period1 and then removing the remaining oxygen4 ,all this was repeatedly done by the authors1 but this method is far more complex1 both in practice and theory1 than the preparation of argon by means of magnesium4 ,from #ajj volumes of air subjected to conversion into ,,hno#c1 #jgf volume of argon were obtained after absorbing the excess of oxygen4 #f ,in these and the following experiments the magnesium was placed in an ordinary hard glass tube1 and heated in a gas furnace to a temperature almost sufficient to soften the glass4 ,the current of gas must be very slow 7a tube containing a small quantity of sulphuric acid served as a meter71 as otherwise the heat evolved in the formation of the ,mg#c,n#b 7,chapter ,,xiv41 ,note #ad7 will melt the tube4 ,thus the first positive and very important fact respecting argon is that its specific gravity is nearly #bj--that is1 that it is #bj times heavier than hydrogen1 while nitrogen is only #ad times and oxygen #af times heavier than hydrogen4 ,this explains the difference observed by ,rayleigh between the densities of nitrogen obtained from its compounds and from the atmosphere 7,chapter ,v41 ,note #d bis74 ,at #j and #gfj mm4 a litre of the former gas weighs #abeje grm41 while a litre of the latter weighs #abegb1 or taking ,h #a1 the density of the first #aciaf1 and of the latter #aciia4 ,if the density of argon be taken as #bj1 it is contained in atmospheric nitrogen to the extent of about #abc per cent4 by volume1 whilst air contains about #jig per cent4 by volume4 ,when argon had been isolated the question naturally arose1 was it a new homogeneous substance having definite properties or was it a mixture of gases8 ,the former may now be positively asserted1 namely1 that argon is a peculiar gas previously unknown to chemistry4 ,such a conviction is in the first place established by the fact that argon has a greater number of negative properties1 a smaller capacity for reaction1 than any other simple or compound body known4 ,the most inert gas known is nitrogen1 but argon far exceeds it in this respect4 ,thus nitrogen is absorbed at a red heat by many metals1 with the formation of nitrides1 while argon1 as is seen in the mode of its preparation and by direct experiment1 does not possess this property4 ,nitrogen1 under the action of electric sparks1 combines with hydrogen in the presence of acids and with oxygen in the presence of alkalis1 while argon is unable to do so1 as is seen from the method of separation from nitrogen4 ,rayleigh and ,ramsay also proved that argon is unable to react with chlorine 7dry or moist7 either directly or under the action of an electric discharge1 or with phosphorus or sulphur1 at a red heat4 ,sodium1 potassium1 and tellurium may be distilled in an atmosphere of argon without change4 ,fused caustic soda1 incandescent soda-lime1 molten nitre1 red-hot peroxide of sodium1 and the polysulphides of calcium and sodium also do not react with argon4 ,platinum black does not absorb it1 and spongy platinum is unable to excite its reaction with oxygen or chlorine4 ,aqua regia1 bromine water1 and a mixture of hydrochloric acid and ,k,mn,o#d were also without action upon argon4 ,besides which it is evident from the method of its preparation that it is not acted upon by red-hot oxide of copper4 ,all these facts exclude any possibility of argon containing any already known body1 and prove it to be the most inert of all the gases known4 ,but besides these negative points1 the independency of argon is confirmed by four observed positive properties possessed by it1 which are3-- #a4 ,the spectrum of argon observed by ,crookes under a low pressure 7in ,geissler-,plcker tubes7 distinguishes it from other gases4#g ,it was proved by this means that the argon obtained by means of magnesium is identical with that which remains after the conversion of the atmospheric nitrogen into nitric acid4 ,like nitrogen1 argon presents two spectra produced at different potentials of the induced current1 one being orange-red1 the other steel-blue2 the latter is obtained under a higher degree of rarefaction and with a battery of ,leyden jars4 ,both the spectra of argon 7in contradistinction to those of nitrogen7 are distinguished by clearly defined lines4#h ,the red 7ordinary7 spectrum of argon has two particularly brilliant and characteristic red lines 7not far from the bright red line of lithium1 on the opposite side to the orange band7 having wave-lengths #gjefd and #fifef 7see ,vol4 ,i41 p4 #efe74 ,between these bright lines there are in addition lines with wave lengths #fjch1 #efea1 #efaj1 #eeeg1 #eaheh1 #eafe1 #dejie1 #dbjaj1 #daeie and #cidhe4 ,altogether #hj lines have been observed in this spectrum and #aai in the blue spectrum1 of which #bf are common to both spectra4#i #g ,the greatest brilliancy of the spectrum of argon is obtained at a tension of #c mm41 while for nitrogen it is about #ge mm4 7,crookes74 ,in ,chapter ,v41 ,note #af bis1 it is said that the same blue line observed in the spectrum of argon is also observed in the spectrum of nitrogen4 ,this is a mistake1 since there is no coincidence between the blue lines of the argon and nitrogen spectra4 ,however1 we may add that for nitrogen the following moderately bright lines are known of wave-lengths #ehe1 #egd1 #edd1 #eaf1 #deg1 #ddb1 #dcf1 and #dbf1 which are repeated in the spectra 7red and blue7 of argon1 judging by ,crookes' researches 7#ahie72 but it is naturally impossible to assert that there is perfect identity until some special comparative work has been done in this subject1 which is very desirable1 and more especially for the bluish-violet portion of the spectrum1 more particularly between the lines #ddb-dcf1 as these lines are distinguished by their brilliancy in both the argon and nitrogen spectra4 ,the above-mentioned supposition of argon being polymerised nitrogen 7,n#c71 formed from nitrogen 7,n#b71 with the evolution of heat1 might find some support should it be found after careful comparison that even a limited number of spectral lines coincided4 #h ,at first the spectrum of argon exhibits the nitrogen lines1 but after a certain time these lines disappear 7under the influence of the platinum1 and also of ,al and ,mg1 but with the latter the spectrum of hydrogen appears7 and leave a pure argon spectrum4 ,it does not appear clear to me whether a polymerisation here takes place or a simple absorption4 ,perhaps the elucidation of this question would prove important in the history of argon4 ,it would be desirable to know1 for instance1 whether the volume of argon changes when it is first subjected to the action of the electric discharge4 #i ,crookes supposes that argon contains a mixture of two gases1 but as he gives no reasons for this1 beyond certain peculiarities of a spectroscopic character1 we will not consider this hypothesis further4 #b4 ,according to ,rayleigh and ,ramsay the solubility of argon in water is approximately #d volumes in #ajj volumes of water at #ac4 ,thus argon is nearly #b-a_/b times more soluble than nitrogen1 and its solubility approaches that of oxygen4 ,direct experiment proves that nitrogen obtained from air from boiled water is heavier than that obtained straight from the atmosphere4 ,this again is an indirect proof of the presence of argon in air4 #c4 ,the ratio k of the two specific heats 7at a constant pressure and at a constant volume7 of argon was determined by ,rayleigh and ,ramsay by the method of the velocity of sound 7see ,chapter ,,xiv41 ,note #g and ,chapter ,,vii41 ,note #bf7 and was found to be nearly #aff1 that is greater than for those gases whose molecules contain two atoms 7for instance1 ,,co1 ,h#b1 ,n#b1 air1 c41 for which k is nearly #ad7 or those whose molecules contain three atoms 7for instance1 ,,co#b1 ,n#b,o1 c41 for which k is about #ac71 but closely approximate to the ratio of the specific heats of mercury vapour 7,kundt and ,warburg1 k #afg74 ,and as the molecule of mercury vapour contains one atom1 so it may be said that argon is a simple gaseous body whose molecule contains one atom4#aj ,a compound body should give a smaller ratio4 ,the experiments upon the liquefaction of argon1 which we shall presently describe1 speak against the supposition that argon is a mixture of two gases4 ,the importance of the results in question makes one wish that the determinations of the ratio of the specific heats 7and other physical properties7 might be confirmed with all possible accuracy4#aa ,if we admit1 as we are obliged to do for the present1 that argon is a new element1 its density shows that its atomic weight must be nearly #dj1 that is1 near to that of ,k #ci and ,ca #dj1 which does not correspond to the existing data respecting the periodicity of the properties of the elements in dependence upon their atomic weights1 for there is no reason on the basis of existing data for admitting any intermediate elements between ,cl #cee and ,k #ci1 and all the positions above potassium in the periodic system are occupied4 ,this renders it very desirable that the velocity of sound in argon should be re-determined4#ab #aj ,this portion of ,rayleigh and ,ramsay's researches deserves particular attention as1 so far1 no gaseous substance is known whose molecule contains but one atom4 ,were it not for the above determinations1 it might be thought that argon1 having a density #bj1 has a complex molecule1 and may be a compound or polymerised body1 for instance1 ,n#c or ,,nxn1 or in general ,xn2 but as the matter stands1 it can only be said that either 7#a7 argon is a new1 peculiar1 and quite unusual elementary substance1 since there is no reason for assuming it to contain two simple gases1 or 7#b7 the magnitude1 k 7the ratio of the specific heats7 does not only depend upon the number of atoms contained in the molecules1 but also upon the store of internal energy 7internal motion of the atoms in the molecule74 ,should the latter be admitted1 it would follow that the molecules of very active gaseous elements would correspond to a smaller k than those of other gases having an equal number of atoms in their molecule4 ,such a gas is chlorine1 for which k #acc 7,chapter ,,xiv41 ,note #g74 ,for gases having a small chemical energy1 on the contrary1 a larger magnitude would be expected for k4 ,i think these questions might be partially settled by determining k for ozone 7,o#c7 and sulphur 7,s#f7 7at about #ejj74 ,in other words1 ,i would suggest1 though only provisionally1 that the magnitude1 k #af1 obtained for argon might prove to agree with the hypothesis that argon is ,n#c1 formed from ,n#b with the evolution of heat or loss of energy4 ,here argon gives rise to questions of primary importance1 and it is to be hoped that further research will throw some light upon them4 ,in making these remarks1 ,i only wish to clear the road for further progress in the study of argon1 and of the questions depending on it4 ,i may also remark that if argon is ,n#c formed with the evolution of heat1 its conversion into nitrogen1 ,n#b1 and into nitride compounds 7for instance1 boron nitride or nitride of titanium7 might only take place at a very high temperature4 #aa ,without having the slightest reason for doubting the accuracy of ,rayleigh and ,ramsay's determinations1 ,i think it necessary to say that as yet 7,february #ahie7 ,i am only acquainted with the short memoir of the above chemists in the ',proceedings of the ,royal ,society1' which does not give any description of the methods employed and results obtained1 while at the end 7in the general conclusions7 the authors themselves express some doubt as to the simple nature of argon4 ,moreover1 it seems to me that 7,note #aj7 there must be a dependence of k upon the chemical energy4 ,besides which1 it is not clear what density of the gas ,rayleigh and ,ramsay took in determining k4 7,if argon be ,n#c1 its density would be near to #ba47 ,hence ,i permit myself to express some doubt as to whether the molecule of argon contains but one atom4 #ab ,if it should be found that k for argon is less than #ad1 or that k is dependent upon the chemical energy1 it would be possible to admit that the molecule of argon contains not one1 but several atoms--for instance1 either ,n#c 7then the density would be #ba1 which is near to the observed density7 or ,x#f1 if ,x stand for an element with an atomic weight near to #fg4 ,no elements are known between ,h #a and ,li #g1 but perhaps they may exist4 ,the hypothesis ,a #dj does not admit argon into the periodic system4 ,if the molecule of argon be taken as ,a#b--;i4e4 the atomic weight as ,a #bj--;argon apparently finds a place in ,group ,,viii41 between ,f #ai and ,na #bc2 but such a position could only be justified by the consideration that elements of small atomic weight belong to the category of typical elements which offer many peculiarities in their properties1 as is seen on comparing ,n with the other elements of ,group ,v41 or ,o with those of ,group ,,vi4 ,apart from this there appears to me to be little probability1 in the light of the periodic law1 in the position of an inert substance like argon in ,group ,,viii41 between such active elements as fluorine and sodium1 as the representatives of this group by their atomic weights and also by their properties show distinct transitions from the elements of the last groups of the uneven series to the elements of the first groups of the even series--for instance1 ,group ,,vi4 ,,vii4 ,,viii4 ,i4 ,,ii4 ,cr ,mn ,fe1 ,co1 ,ni ,cu ,zn ,while if we place argon in a similar manner1 ,,vi4 ,,vii4 ,,viii4 ,i4 ,,ii4 ,o #af ,f #ai ,a #bj ,na #bc ,mg #bd although from a numerical point of view there is a similar sequence to the above1 still from a chemical and physical point of view the result is quite different1 as there is no such resemblance between the properties of ,o1 ,f and ,na1 ,mg1 as between ,cr1 ,mn1 and ,cu1 ,zn4 ,i repeat that only the typical character of the elements with small atomic weights can justify the atomic weight ,a #bj1 and the placing of argon in ,group ,,viii4 amongst the typical elements2 then ,n1 ,o1 ,f1 ,a are a series of gases4 ,it appears to me simpler to assume that argon contains ,n#c1 especially as argon is present in nitrogen and accompanies it1 and1 as a matter of fact1 none of the observed properties of argon are contradictory to this hypothesis4 ,these observations were written by me in the beginning of ,february #ahie1 and on the #bith of that month ,i received a letter1 dated ,february #be1 from ,professor ,ramsay informing me that 'the periodic classification entirely corresponds to its 7argon's7 atomic weight1 and that it even gives a fresh proof of the periodic law1' judging from the researches of my ,english friends4 ,but in what these researches consisted1 and how the above agreement between the atomic weight of argon and the periodic system was arrived at1 is not referred to in the letter1 and we remain in expectation of a first publication of the work of ,lord ,rayleigh and ,professor ,ramsey4 ,for more complete information see papers read before the ,royal ,society1 ,january #ca1 #ahie1 ,february #ac1 ,march #aj1 and ,may #ba1 #ahif1 and a paper published in the ,chemical ,society's ,transactions1 #ahie1 p4 #fhd4 ,for abstracts of these and other papers on argon and helium1 and correspondence1 see ',nature1' #ahie and #ahif4 #d4 ,argon was liquefied by ,professor ,olszewsky1 who is well known for his classical researches upon liquefied gases4 ,these researches have an especial interest since they show that argon exhibits a perfect constancy in its properties in the liquid and critical states1 which almost#ac disposes of the supposition that it contains a mixture of two or more unknown gases4 ,as the first experiments showed1 argon remains a gas under a pressure of #ajj atmospheres and at a temperature of -#ij2 this indicated that its critical temperature was probably below this temperature1 as was indeed found to be the case when the temperature was lowered to -#abhfad by means of liquid ethylene4 ,at this temperature argon easily liquefies to a colourless liquid under #ch atmospheres4 ,the meniscus begins to disappear at between -#aaih and -#abaf1 mean -#aba at a pressure of #ejf atmospheres4 ,the vapour tension of liquid argon at -#abhf1 is #chj atmospheres1 at -#ahg it is one atmosphere1 and at -#ahif it solidifies to a colourless substance like ice4 ,the specific gravity of liquid argon at about -#ahg is nearly #ae1 which is far above that of other liquefied gases of very low absolute boiling point4 ,the discovery of argon is one of the most remarkable chemical acquisitions of recent times1 and we trust that ,lord ,rayleigh and ,professor ,ramsay1 who made this wonderful discovery1 will further elucidate the true nature of argon1 as this should widen the fundamental principles of chemistry1 to which the chemists of ,great ,britain have from early times made such valuable contributions4 ,it would be premature now to give any definite opinions upon so new a subject4 ,only one thing can be said2 argon is so inert that its rle in nature cannot be considerable1 notwithstanding its presence in the atmosphere4 ,but as the atmosphere itself plays such a vast part in the life of the surface of the earth1 every addition to our knowledge of its composition must directly or indirectly react upon the sum total of our knowledge of nature4 #ac ,there only remains the very remote possibility that argon consists of a mixture of two gases having very nearly the same properties4 #ad ,the following data1 given by ,olszewsky1 supplement the data given in ,chapter ,,ii41 ,note #bi1 upon liquefied gases4 7tc7 7pc7 t t#a s ,n#b -#adf #ce -#aidd -#bad #jhhe ,,co -#acie #cee -#aij -#bjg 8 ,a -#aba #ejf -#ahg -#ahif #ae ,o#b -#aahh #ejh -#ahbg 8 #aabd ,,no -#ice #gab -#aecf -#afg 8 ,,ch#d -#hah #edi -#afd -#aehh #jdae where tc is the absolute 7critical7 boiling point1 pc the pressure 7critical7 in atmospheres corresponding to it1 t the boiling point 7under a pressure of #gfj mm471 t#a the melting point1 and s the specific gravity in a liquid state at t4 ,the above shows that argon in its properties in a liquid state stands near to oxygen 7as it also does in its solubility71 but that all the temperatures relating to it 7tc1 t1 and t#a7 are higher than for nitrogen4 ,this fully answers1 not only to the higher density of argon1 but also to the hypothesis that it contains ,n#c4 ,and as the boiling point of argon differs from that of nitrogen and oxygen by less than #aj1 and its amount is small1 it is easy to understand how ,dewar 7#ahid71 who tried to separate it from liquid air and nitrogen by fractional distillation1 was unable to do so4 ,the first and last portions were identical1 and nitrogen from air showed no difference in its liquefaction from that obtained from its compounds1 or from that which had been passed through a tube containing incandescent magnesium4 ,still1 it is not quite clear why both kinds of nitrogen1 after being passed over the magnesium in ,dewar's experiments1 exhibited an almost similar alteration in their properties1 independent of the appearance of a small quantity of hydrogen in them4 ,concluding ,remarks 7,march #ca1 #ahie74--,the ',comptes rendus' of the ,paris ,academy of ,sciences of ,march #ah1 #ahie1 contains a memoir by ,berthelot upon the reaction of argon with the vapour of benzene under the action of a silent discharge4 ,in his experiments1 ,berthelot succeeded in treating #hc per cent4 of the argon taken for the purpose1 and supplied to him by ,ramsay 7#cg c4c4 in all74 ,the composition of the product could not be determined owing to the small amount obtained1 but in its outward appearance it quite resembled the product formed under similar conditions by nitrogen4 ,this observation of the famous ,french chemist to some extent supports the supposition that argon is a polymerised variety of nitrogen whose molecule contains ,n#c1 while ordinary nitrogen contains ,n#b4 ,should this supposition be eventually verified1 the interest in argon will not only not lessen1 but become greater4 ,for this1 however1 we must wait for further observations and detailed experimental data from ,rayleigh and ,ramsay4 ,the latest information obtained by me from ,london is that ,professor ,ramsay1 by treating cleveite 7containing ,pb,o1 ,,uo#c1 ,y#b,o#c1 c47 with sulphuric acid1 obtained argon1 and1 judging by the spectrum1 helium also4 ,the accumulation of similar data may1 after detailed and diversified research1 considerably increase the stock of chemical knowledge which1 constantly widening1 cannot be exhaustively treated in these ',principles of ,chemistry1' although very probably furnishing fresh proof of the 'periodicity of the elements4' 99 99 99 99 99 ,,index ,,of ,,authorities ,abasheff1 i4 #ge ,abel1 ii4 #ef1 #cbf1 #daj ,acheson1 ii4 #ajg ,adie1 ii4 #ahf ,alexeff1 i4 #ge1 #id ,alluard1 i4 #deh ,amagat1 i4 #acb1 #ace1 #adj ,amat1 ii4 #aga ,ammermller1 i4 #ejd ,ampre1 i4 #cji ,andreff1 i4 #bea ,andrews1 i4 #acf1 #bjc ,angeli1 i4 #bff ,ansdell1 i4 #dea ,arfvedson1 i4 #ege ,arrhenius1 i4 #hi1 #ib1 #chi ,aschoff1 ii4 #cac ,askenasy1 i4 #ejh ,aubel1 ii4 #de ,aubin1 i4 #bch ,avdeff1 i4 #fah2 ii4 #dhd ,avogadro1 i4 #cji ,babo1 v41 i4 #ic1 #bjj1 #bjc ,bach1 i4 #cid ,bachmetieff1 ii4 #ca ,baeyer1 v41 i4 #ejg ,bagouski1 i4 #chd ,bailey1 i4 #ddi2 ii4 #bi ,baker1 i4 #cah1 #djc ,balard1 i4 #dhj1 #did1 #die1 #eje ,ball1 ii4 #dad ,bannoff1 i4 #ejf ,barfoed1 ii4 #ec ,baroni1 i4 #cca ,barreswill1 ii4 #bhb ,baudrimont1 ii4 #ce ,baum1 i4 #aic ,baumgauer1 ii4 #bj ,baumhauer1 i4 #die ,bayer1 ii4 #gf1 #aei ,bazaroff1 i4 #dji2 ii4 #bd1 #fh1 #dhf ,becher1 i4 #ag ,becker1 i4 #af ,beckmann1 i4 #ia1 #dif2 ii4 #aef ,becquerel1 i4 #bbh2 ii4 #ig1 #bbj ,beilby1 i4 #ga ,beilstein1 i4 #cgc2 ii4 #ahh ,beketoff1 i4 #abj1 #abb1 #abd1 #adf1 #djc1 #dei1 #dff1 #ecd1 #eda1 #egd1 #egg2 ii4 #hg1 #ajb1 #bhi1 #dbi ,bender1 i4 #dgf ,benedict1 ii4 #fe ,berglund1 ii4 #bbi ,bergman1 i4 #bg1 #dce2 ii4 #ajj ,berlin1 i4 #ie ,bernouilli1 i4 #ha ,bernthsen1 ii4 #bbh ,bert1 i4 #hf1 #aec ,bertheim1 ii4 #ccg ,berthelot1 i4 #aga1 #agc1 #ahi1 #aii1 #bbi1 #bcj1 #beh1 #bfd1 #bff1 #bfg1 #bgb1 #hc1 #bhi1 #cea1 #cgb1 #cic1 #cid1 #dje1 #dae1 #dbd1 #dch1 #deg1 #dfc1 #ejb1 #ejf1 #ejg1 #eah1 #ebi1 #ecg1 #ehb2 ii4 #bc1 #eg1 #bjg1 #bji1 #bea1 #bec1 #bei1 #cde1 #cfg ,berthier1 ii4 #h ,berthollet1 i4 #bg1 #ca1 #aje1 #dcc1 #dcd1 #dei1 #dgj1 #ejb1 #fji ,berzelius1 i4 #aca1 #adh1 #aid1 #bee1 #cgi2 ii4 #h1 #ajj1 #ajb1 #adg1 #adh1 #bai1 #bha1 #cjj1 #dhe ,besson1 i4 #bhh2 ii4 #fg1 #gj1 #aje1 #agi ,beudant1 ii4 #g1 #h ,bineau1 i4 #ajj1 #bga1 #deb1 #ejd2 ii4 #bci ,binget1 i4 #ge ,blaese1 ii4 #ahh ,blagden1 i4 #ia1 #dbh ,blake1 ii4 #cj ,blitz1 ii4 #ahd ,blomstrand1 ii4 #bii ,boerwald1 ii4 #bgi ,bttger1 i4 #eie ,bogorodsky1 i4 #egd ,boilleau1 i4 #dae ,boisbaudran1 ,l4 de1 i4 #ig1 #ajb1 #egb1 #fjj2 ii4 #f1 #bf1 #ij1 #hb1 #bhd1 #dhc ,bornemann1 i4 #eji ,botkin1 ii4 #cj ,bouchardat1 ii4 #de ,boullay1 ii4 #ee ,bourdiakoff1 i4 #ehd1 #fag ,boussingault1 i4 #aca1 #aeg1 #bcc1 #bce1 #ebe1 #fae ,boyle1 i4 #abd ,brand1 ii4 #aej ,brandau1 i4 #dha ,brandes1 i4 #gb ,bravais1 i4 #bcc ,brauner1 i4 #dij1 #dia2 ii4 #bf1 #ei1 #id1 #if1 #ig1 #acd1 #add1 #aid1 #bga1 #dhc ,brewster1 i4 #efi ,brigham1 ii4 #aic ,brodie1 i4 #bab1 #cea1 #dje2 ii4 #beb ,brooke1 ii4 #ceg ,brown1 i4 #ha1 #hh ,brugellmann1 i4 #faf ,brunn1 ii4 #ahb1 #ahi ,bruyn1 i4 #bfb ,brhl1 i4 #bfc1 #ccg ,brunner1 i4 #abd1 #adf1 #bfc2 ii4 #bcj1 #cji1 #ecd ,buchner1 i4 #fae ,buckton1 ii4 #adc ,buff1 ii4 #ajc ,bunge1 i4 #bhh ,bunsen1 i4 #dc1 #fi1 #gh1 #aag1 #ahj1 #dfe1 #efh1 #ege1 #egf1 #egg2 ii4 #bg1 #bhi ,bussy1 i4 #ge1 #eid1 #fai ,butleroff1 i4 #adc ,bystrom1 i4 #ehe ,cagniard de ,latour1 i4 #ace1 #cde ,cahours1 ii4 #adc1 #agc ,cailletet1 i4 #acb1 #ach2 ii4 #de ,calderon1 i4 #eif ,callender1 i4 #acd ,calvert1 i4 #dhd2 ii4 #de ,cannizzaro1 i4 #ehd1 #ehg ,carey-,lea1 ii4 #dbj1 #dbd1 #dbe1 #dcb ,carius1 i4 #fi1 #dha ,carnelley1 i4 #dhc1 #eae1 #eee2 ii4 #bb1 #bi1 #cj1 #ca1 #fd1 #adc1 #dhf ,carnot1 ii4 #bid1 #cfa ,caron1 i4 #eie1 #fjd1 #faj2 ii4 #ccf ,carrara1 i4 #bac ,cass1 ii4 #he ,castner1 i4 #dca1 #ece1 #eda ,cavazzi1 ii4 #afj1 #agb1 #ahb ,cavendish1 i4 #aac1 #abe1 #bbh2 ii4 #dic ,chabri1 i4 #bbi ,chappuis1 i4 #ej1 #aii1 #bje1 #bfd ,chapuy1 i4 #ei ,cheltzoff1 i4 #cic1 #deg1 #ehb2 ii4 #da1 #bdg ,cherikoff1 ii4 #ajb ,chertel1 ii4 #bde ,chevillot1 ii4 #caa ,chevreul1 i4 #ecj ,chigeffsky1 ii4 #fb ,christomanos1 i4 #eaa ,chroustchoff1 i4 #cec1 #ddd2 ii4 #abb ,chydenius1 ii4 #adh1 #dhe ,ciamician1 i4 #efe1 #egc2 ii4 #dhf ,clark1 i4 #bf ,classen1 ii4 #adf ,clausius1 i4 #ha1 #ic1 #adj1 #adb1 #bab1 #cji1 #dia ,clement1 i4 #did ,clve1 ii4 #bf1 #id1 #ig1 #dhd ,cloez1 i4 #bjg1 #bdf1 #cgg ,clowes1 i4 #bdb ,collendar1 i4 #acd ,comaille1 i4 #eif ,comb1 ii4 #ha ,connell1 i4 #ejh ,coppet1 i4 #ia1 #dbh1 #fja ,corenwinder1 i4 #eja ,cornu1 i4 #efe ,courtois1 i4 #did ,cracow1 ii4 #chj ,crafts1 i4 #chj 2 ii4 #hj1 #hc ,cremers1 ii4 #ajj ,croissier1 i4 #bea ,crompton1 i4 #bdg ,crookes1 i4 #bbi1 #fag2 ii4 #bj1 #ia1 #if1 #ddj1 #dia ,crum1 ii4 #gi1 #caa ,cundall1 i4 #faa ,curtius1 i4 #beh1 #bfe ,dahl1 ii4 #ei ,dalton1 i4 #bi1 #gh1 #ha1 #aji1 #bjf1 #bga1 #cbb ,dana1 ii4 #h ,davies1 i4 #dhd ,davy1 i4 #cg1 #aad1 #aie1 #bee1 #cfd1 #dfj1 #dfc1 #dhd1 #dhi1 #did1 #ecc1 #eda1 #eid1 #fjd1 #fag ,deacon1 i4 #eii ,debray1 i4 #fji2 ii4 #de1 #abb1 #bia1 #bic1 #chd1 #che ,de ,chancourtois1 ii4 #bj1 #bf ,de ,forcrand1 ii4 #ajf1 #baa ,de ,han1 ii4 #ahi ,de ,heen1 i4 #adj ,delafontaine1 ii4 #ig1 #adh1 #aih ,de la ,rive1 i4 #aih2 ii4 #bbf ,del-,rio1 ii4 #aig ,de ,saussure1 i4 #bce1 #bdj ,de ,schulten1 ii4 #dh ,deville1 ,st4-,claire1 i4 #d1 #cf1 #aah1 #adc1 #agi1 #ahj1 #bbg1 #bci1 #bhj1 #bha1 #cja1 #cbj1 #cib1 #cic1 #cii1 #dei1 #dfg1 #dgf1 #dgg1 #ejj1 #ecd1 #eie1 #fjh1 #fji2 ii4 #dh1 #hj1 #hc1 #he1 #ajb1 #adg1 #aef1 #aih1 #bhi1 #cji1 #cba1 #ceb1 #cgc1 #cgd1 #dbi ,de ,vries1 i4 #fb1 #fd1 #dbi ,dewar1 i4 #c1 #e1 #ace1 #aci1 #afc1 #big1 #efc1 #efe1 #efi1 #ehe2 ii4 #agf1 #bbj ,dick1 ii4 #dad ,dingwall1 i4 #dhf ,ditte1 i4 #gb1 #djc1 #dcj1 #deg1 #eji1 #eci1 #fah2 ii4 #fd1 #fe1 #he1 #ahi1 #bdi ,dittmar1 i4 #ajj1 #deb2 ii4 #bdj ,divers1 i4 #bgd1 #bid2 ii4 #ed ,dixon1 i4 #aga ,dbereiner1 i4 #ade ,dokouchaeff1 i4 #cdd ,donny1 i4 #ecd ,dossios1 i4 #ejb ,draper1 i4 #dfe ,drawe1 ii4 #afa ,drebbel1 i4 #bid ,dulong1 i4 #aca1 #adh1 #dcg ,dumas1 i4 #bh1 #aca1 #adh1 #aej1 #bcc1 #cjb1 #cbj1 #cgi1 #dga1 #dgf1 #ehd1 #ehf1 #fjd2 ii4 #bb1 #cg1 #fb1 #aja1 #aef1 #dbj ,dumont1 ii4 #aig ,ebelmann1 ii4 #fe ,eder1 i4 #eff ,edron1 ii4 #ie ,edwards1 ii4 #caa ,egoreff1 i4 #efi ,eissler1 i4 #eec ,elbers1 ii4 #bba ,emich1 i4 #bhf1 #bhg ,emilianoff1 ii4 #abf ,engel1 i4 #deg2 ii4 #acj1 #acb1 #ahi1 #bjf ,engelhardt1 i4 #ecj ,etvs1 i4 #ccc ,erdmann1 i4 #aej ,ernst1 i4 #cii ,erofeff1 i4 #ceb ,esson1 ii4 #cad tard1 i4 #gb1 #eaf1 #fae2 ii4 #bhh1 #cce1 #cef ,ettinger1 i4 #ec1 #cab ,famintzin1 i4 #faa ,faraday1 i4 #acd1 #agg1 #bif1 #che1 #dfc1 #dfd ,favorsky1 i4 #cgc ,favre1 i4 #abj1 #agb1 #bfg1 #ehb2 ii4 #hc1 #bei1 #bhd1 #chj ,fick1 i4 #fb ,fisher1 ii4 #dbd ,fizeau1 ii4 #ca1 #dbi ,flavitzky1 i4 #ba 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,traub1 i4 #cab1 #faa2 ii4 #bgj ,troost1 i4 #fd1 #bgd1 #bha1 #cbj1 #dji1 #dad1 #ejj1 #ech2 ii4 #hj1 #hc1 #ajb1 #adg1 #aef1 #bed1 #cgi ,tscherbacheff1 i4 #egg ,tutton1 i4 #edc2 ii4 #afj1 #agd1 #dab ,umoff1 i4 #dbi ,unverdorben1 ii4 #bhj ,urlaub1 ii4 #cja ,valentine1 i4 #ag ,van der ,heyd1 i4 #eii ,van der ,plaats1 i4 #dif2 ii4 #dch ,van der ,waals1 i4 #hb1 #adj ,van ,deventer1 i4 #eii ,van ,helmont1 i4 #cgi ,van ,marum1 i4 #aih ,van't ,hoff1 i4 #fd1 #fe1 #cca1 #eii2 ii4 #c ,vare1 ii4 #ee ,vauquelin1 i4 #aad1 #fai2 ii4 #g ,veeren1 i4 #fab2 ii4 #de ,veley1 i4 #bgi ,verneuille1 ii4 #bbe ,vernon1 ii4 #aea ,vzes1 ii4 #cia ,viard1 ii4 #bhe ,vignon1 ii4 #abf1 #aca ,villard1 i4 #ajf1 #bif1 #big ,villiers1 ii4 #bei ,violette1 i4 #cdb1 #cde ,violle1 i4 #cja ,vogt1 i4 #faa ,volkovitch1 ii4 #bja ,voskresensky1 i4 #cde ,waage1 i4 #dci ,wachter1 i4 #ejh ,wagner1 i4 #ceg ,wahl1 ii4 #caj ,walden1 ii4 #eg ,walker1 ii4 #adc ,walmer1 i4 #egc ,walter1 ii4 #bef ,walters1 ii4 #bcd ,wanklyn1 i4 #ajj1 #eci ,warburg1 i4 #ehi2 ii4 #dif ,warder1 i4 #dej ,warren1 ii4 #ajb ,watson1 i4 #ebg2 ii4 #afi ,watts1 i4 #ebf ,weber1 i4 #bhj1 #ehc2 ii4 #hc1 #abi1 #aca1 #ahf1 #bcj1 #bcc1 #bcd1 #bdi ,weith1 i4 #ejb ,weitz1 ii4 #eg ,welch1 ii4 #dbe ,weller1 ii4 #adf ,wells1 i4 #dgg1 #ede2 ii4 #eg1 #cgj ,welsbach1 ii4 #if1 #ig ,weltzien1 i4 #bjd1 #eie ,wenzel1 i4 #aic ,weruboff 7see ,wyruboff71 ii4 #d ,weselski1 i4 #ejg ,weyl1 i4 #bee ,wheeler1 i4 #ede ,wichelhaus1 ii4 #agi ,wiedemann1 i4 #dci1 #ehh ,wilhelmj1 ii4 #cae ,willgerodt1 i4 #ejh2 ii4 #bi ,williamson1 ii4 #bfh ,wilm1 ii4 #cgf1 #chh ,winkler1 i4 #gh1 #gi1 #egg1 #eid1 #fba2 ii4 #be1 #cj1 #ff1 #ig1 #ajb1 #abd1 #abe1 #adg1 #bcd1 #bdf1 #cee1 #dhc ,wischin1 ii4 #chd ,wislicenus1 i4 #bfg1 #bid ,witt1 ii4 #c ,whler1 i4 #daj1 #fai2 ii4 #he1 #ajc1 #ajg1 #adf1 #bhe1 #bhi1 #dbj1 #dbe ,wollaston1 i4 #h ,wreden1 i4 #ejg ,wright1 ii4 #cba ,wroblewski1 i4 #gi1 #hj1 #ajf1 #aci1 #chg2 ii4 #bbf ,wlfing1 ii4 #aai ,wlner1 i4 #ia1 #egb ,wrtz1 i4 #cja1 #dgf2 ii4 #aga1 #agc1 #bac1 #bfg ,wyruboff1 ii4 #d1 #i ,young1 i4 #acd1 #acf1 #adj1 #ada1 #bdg1 #die1 #dif ,zaboudsky1 i4 #ced ,zaencheffsky1 i4 #adj ,zimmermann1 ii4 #bf1 #cjc1 #cee1 #dhe ,zinin1 i4 #bgf ,zrensen1 i4 #bhd ,zorn1 i4 #bie 99 99 99 99 99 ,,subject ,,index ,acid1 acetic sp4 gr4 of solutions of1 i4 #ei -- arsenic1 ii4 #aha -- bismuthic1 ii4 #aij -- boric1 ii4 #fd -- carbamic1 i4 #djh -- chamber1 i4 #bid -- chloric1 i4 #dhb -- chloroplatino-phosphorous1 ii4 #cij -- chlorosulphonic1 ii4 #bfh -- chlorous1 i4 #dha -- chromic1 i4 #bjh2 ii4 #bhb -- chromo-sulphuric1 ii4 #bhh -- cyanic1 i4 #dji -- cyanuric1 i4 #dji -- dithionic1 ii4 #bef -- ferric1 ii4 #cdd -- fluoboric1 ii4 #fi -- graphitic1 i4 #cea -- hydriodic1 i4 #eja1 #ejc1 #eje1 #ejf -- hydroborofluoric1 ii4 #fi -- hydrobromic1 i4 #hj1 #ejc1 #eje1 #ejf -- hydrochloric1 i4 #ddh1 #dea1 #dec -- hydrocyanic1 i4 #djf1 #daa -- hydroferrocyanic1 ii4 #cdh -- hydrofluoric1 i4 #di -- hydrofluosilic1 ii4 #ajf -- hydroplatinocyanic1 ii4 #chf -- hydrosulphurous1 ii4 #bbh -- hydroruthenocyanic1 ii4 #chh -- hypochlorous1 i4 #dgi1 #dha -- hyponitrous1 i4 #bfe1 #bid -- hypophosphoric1 ii4 #afa -- hypophosphorous1 ii4 #agb -- iodic1 i4 #ajj1 #ejh -- isethionic1 ii4 #bej -- metantimonic1 ii4 #ahh -- metaphosphoric1 ii4 #afb1 #afi -- metastannic1 ii4 #aca -- molybdic1 ii4 #bib -- nitric1 i4 #bfh1 #bgb -- ,nordhausen1 ii4 #bcc -- orthophosphoric1 ii4 #afb -- osmic1 ii4 #chd -- pentathionic1 ii4 #beg -- percarbonic1 i4 #cid -- perchloric1 i4 #dhd -- periodic1 i4 #eaj -- permanganic1 ii4 #cac -- permolybdic1 ii4 #big -- pernitric1 i4 #bfd -- persulphuric1 ii4 #bea -- pertungstic1 ii4 #big -- phosphamic1 ii4 #agi -- phosphamolybdic1 ii4 #bic -- phosphorous1 ii4 #aga -- polysilicic1 ii4 #aag -- pyrophosphoric1 ii4 #afi -- pyrosulphuric1 ii4 #bcd -- silenic1 ii4 #bgb -- silicotungstic1 ii4 #bie -- stannic1 ii4 #acj -- sulphonic1 ii4 #bdi -- sulphuric1 i4 #gf1 #gg1 #hi1 #aaa1 #bij1 #bid2 ii4 #bce1 #bch1 #bda -- telluric1 ii4 #bgb -- tetrathionic1 ii4 #beg -- thiocarbonic1 ii4 #bfc -- thiocyanic1 ii4 #bfc -- thionic1 ii4 #bee -- thiosulphuric1 ii4 #bcj -- trithionic1 ii4 #beg -- tungstic1 ii4 #bib1 #bid -- vanadic1 ii4 #aif ,acids1 i4 #ahe -- avidity of1 i4 #chi1 #ddb -- basicity of1 i4 #chg -- complex1 i4 #aig2 ii4 #bic -- fuming1 i4 #ajb -- organic1 i4 #cid1 #cif1 #dje ,acetylene1 i4 #cgb ,actinium1 ii4 #ei ,affinity1 chemical1 i4 #bf1 #chi ,air1 i4 #aca1 #bca1 #bcc ,alchemy1 i4 #ad ,alcohol1 i4 #ec1 #hh ,alkali1 metals1 i4 #eeh1 #egg -- waste1 ii4 #bjd ,alkalis1 i4 #ahf ,allotropism1 i4 #bjg ,alloys1 i4 #ecg2 ii4 #abh ,alumina1 ii4 #ge ,aluminium1 ii4 #gj1 #he -- bromide1 ii4 #hd -- bronze1 ii4 #hh -- carbide1 ii4 #hh -- chloride1 ii4 #hj1 #hc -- double chlorides1 ii4 #hd -- fluoride1 ii4 #hc -- hydroxide1 ii4 #ge -- iodide1 ii4 #he -- nitrate1 ii4 #hj -- sulphate1 ii4 #hb ,alums1 ii4 #e1 #hb1 #cdc ,alunite1 ii4 #hj ,amalgams1 ii4 #eh ,amides1 i4 #beh1 #djf ,amidogen1 i4 #beh -- hydrate1 i4 #beh ,amines1 i4 #daf ,ammonia1 i4 #bbi1 #bdf -- of crystallisation1 i4 #beg -- heat of solution of1 i4 #gd -- in air1 i4 #bdj -- liquefaction of1 i4 #bej -- salts1 i4 #bed -- soda process1 i4 #ebd -- solutions of1 i4 #hj1 #beb ,ammonium1 i4 #bed -- amalgam1 i4 #bee -- bicarbonate1 i4 #ebg -- carbamate1 i4 #djg1 #djh -- carbonate1 i4 #djg -- cobalt salts1 ii4 #cei -- dichromate1 ii4 #bgi -- molybdate1 ii4 #bib -- nitrate1 i4 #bgc1 #bgd -- nitrite1 i4 #bhd -- phosphates1 ii4 #afg -- sulphate1 ii4 #bfi -- sulphide1 ii4 #bah ,analogy of elements1 i4 #egc1 #egh ,anthracite1 i4 #cde ,antimoniuretted hydrogen1 ii4 #ahi ,antimony1 ii4 #ahf -- chlorides1 ii4 #ahi -- oxides1 ii4 #ahg1 #ahh -- sulphides1 ii4 #bba ,aqua ,regia1 i4 #dfg ,aqueous radicle1 i4 #bac ,argon1 i4 #bbf1 #bcb2 ,app4 ,,iii4 ,arsenic1 ii4 #agi -- anhydride1 ii4 #aha -- sulphides1 ii4 #bba -- tribromide1 ii4 #aha -- trichloride1 ii4 #ahj -- trifluoride1 ii4 #aha ,arsenious anhydride1 ii4 #ahd -- oxychloride1 ii4 #ahj ,arsenites1 ii4 #ahe ,arseniuretted hydrogen1 ii4 #ahb ,astrakhanite1 i4 #ei ,atmolysis1 i4 #aef ,atomic theory1 i4 #baf -- volumes1 ii4 #cc -- weights1 i4 #ba ,atoms and molecules1 i4 #cbb ,barium1 i4 #fad1 #fag -- chlorate1 i4 #dhc -- chloride1 i4 #fae -- hydroxide1 i4 #faf -- metatungstate1 ii4 #bie -- nitrate1 i4 #fae -- oxide1 i4 #faf -- peroxide1 i4 #aeg1 #afj1 #bji1 #fag -- sulphate1 i4 #fad1 #fae ,bauxite1 ii4 #gf ,benzalazine1 i4 #beh ,berthollet's doctrine1 i4 #dcc ,beryllium1 i4 #fah -- atomic weight of1 i4 #cbe1 #fah -- chloride1 i4 #ehd -- oxide1 i4 #fai ,binary theory1 i4 #aie ,bismuth1 ii4 #ahi -- nitrates1 ii4 #aib -- oxides1 ii4 #aij1 #aia ,blast furnace1 ii4 #cbd ,bleaching1 i4 #dfi -- powder1 i4 #afb1 #dgg ,boiling point1 absolute1 i4 #acj ,borates1 ii4 #fc ,borax1 ii4 #fa ,boric anhydride1 ii4 #fd ,boron1 ii4 #fj1 #ff -- chloride1 ii4 #fi -- fluoride1 ii4 #fg1 #fh -- iodide1 ii4 #gj -- nitride1 i4 #bbg2 ii4 #fg -- oxide1 ii4 #fj -- specific heat of1 i4 #ehe -- sulphide1 ii4 #fb ,bromides1 ii4 #cb ,bromine1 i4 #did ,bronze1 ii4 #abg ,butyl alcohol1 solubility of1 i4 #ge ,cadmium1 ii4 #dg -- iodide1 ii4 #dh -- oxide1 ii4 #dh -- sulphide1 ii4 #dg ,csium1 i4 #egf ,calcium1 i4 #eij1 #fjd -- carbonate1 i4 #eib1 #fjh1 #fji1 #faj -- chloride1 i4 #bcg1 #fab -- -- crystallohydrates of1 i4 #fac -- fluoride1 i4 #dia -- hypochlorite1 i4 #afb -- iodide1 i4 #fjd -- peroxide1 i4 #fjg -- phosphate1 ii4 #afg -- sulphate1 i4 #faa -- sulphide1 ii4 #bbj ,calomel1 ii4 #ed ,carbamide1 i4 #dji ,carbides1 i4 #cdi1 #cec ,carbon1 i4 #cch -- bisulphide1 ii4 #beh -- molecule of1 i4 #ced -- oxysulphide1 ii4 #bfd -- tetrachloride1 i4 #dgc ,carbonic anhydride1 i4 #cgi -- -- assimilation of by plants1 i4 #cic -- -- dissociation of1 i4 #cib1 #cic1 #cii -- -- in air1 i4 #bch1 #bdb -- -- liquid1 i4 #che -- -- solutions of1 i4 #hj1 #hf -- -- specific heat of1 i4 #cic ,carbonic oxide1 i4 #cif -- -- and nickel1 i4 #dje ,carborundum1 ii4 #ajg ,carboxyl1 i4 #cie ,carnallite1 i4 #dba1 #edd1 #efj ,catalytic phenomena1 i4 #baa ,caustic potash1 i4 #eej -- soda1 i4 #ebi ,cements1 ii4 #abb ,cerite metals1 ii4 #ic ,cerium1 ii4 #ic ,chamber crystals1 i4 #bij2 ii4 #bcj ,charcoal1 i4 #cdc ,chemical change1 rate of1 ii4 #cad -- transformations1 i4 #c ,chloranhydrides1 i4 #dfh2 ii4 #agd1 #age1 #agg ,chlorates1 i4 #dhb ,chlorides1 i4 #dee1 #dff2 ii4 #ca ,chlorine1 i4 #dfc -- compounds1 heat of formation of1 i4 #dd -- crystallohydrates of1 i4 #dfd -- oxides1 i4 #dgi -- preparation of1 i4 #dfj -- solubility of1 i4 #dfc ,chloroform1 i4 #dgc ,chlorophosphamide1 ii4 #agi ,chloryl compounds1 i4 #dgf ,chrome alum1 ii4 #bhc ,chromic acid1 i4 #bjh -- anhydride1 ii4 #bhj -- oxide1 ii4 #bhd1 #bhe ,chromium1 ii4 #bgf1 #bhi -- chlorides1 ii4 #bhe -- fluorides1 ii4 #bhj1 #bhi ,chromyl chloride1 ii4 #bha ,chryseone1 ii4 #ajh ,clay1 ii4 #gj ,coal1 i4 #cde ,cobalt1 ii4 #cec -- dioxide1 ii4 #cff -- fluoride1 ii4 #ceh ,cobaltamine salts1 ii4 #cei ,cobaltic oxide1 ii4 #cfb ,cobalto-amine1 ii4 #cei ,cobaltous hydroxide1 ii4 #ceh ,cohesion of liquids1 i4 #eb ,coke1 i4 #cde ,collodion cotton1 i4 #bge ,colloids1 i4 #fc2 ii4 #gg1 #dbc ,combination1 chemical1 i4 #c ,combining weights1 i4 #ba2 ii4 #dci ,combustion1 imperfect1 i4 #cda -- heat of1 i4 #agb1 #agf1 #cii1 #djj ,compounds1 definite and indefinite1 i4 #ca -- types of1 ii4 #aj ,compressibility of solutions1 i4 #hh ,conductivity1 electro-molecular1 i4 #chi ,contact reactions1 i4 #afc1 #bij ,copper1 ii4 #djj -- carbonate1 ii4 #daa -- complex salts of1 ii4 #dab -- nitrate1 ii4 #daa -- nitride1 ii4 #dji -- sulphate1 ii4 #dac ,corundum1 ii4 #ge ,critical points1 i4 #ada ,cryohydrates1 i4 #ii ,cryoscopic investigations of solutions1 i4 #ij1 #ccb ,crystals1 i4 #ea ,crystalline form1 ii4 #g ,crystallo-hydrates1 i4 #ajb ,crystalloids1 i4 #fc ,cupellation1 ii4 #dag ,cyanides1 i4 #djf ,cyanogen1 i4 #djf1 #dad -- chloride1 ii4 #agf ,decomposition1 chemical1 i4 #d ,deliquescence1 i4 #ajd ,delta metal1 ii4 #dad ,desiccator1 i4 #eh ,detonating gas1 i4 #aae1 #agj1 #agc ,depression of freezing point of solutions1 i4 #ij1 #ib1 #ccj ,dialysis1 i4 #fc2 ii4 #aad ,diamond1 i4 #cej1 #cec ,didymium1 ii4 #ic ,diffusion1 rate of1 i4 #fc ,dimorphism1 i4 #faj1 ii4 #agh ,disinfectants1 i4 #bde ,disodium orthophosphate1 ii4 #aff ,dissociation1 i4 #cf1 #bhb1 #fjh ,distillation1 dry1 i4 #d1 #bdg1 #cdb ,dust1 atmospheric1 i4 #bda ,efflorescence1 i4 #ajc ,ekacadmium1 ii4 #ei ,ekasilicon1 ii4 #be ,electro-chemical theory1 i4 #aie ,electric energy and thermal units1 i4 #ehb ,electrolysis1 i4 #aaf ,elements1 i4 #bj -- grouping of1 ii4 #a -- typical1 ii4 #ai ,emulsions1 i4 #ih ,energy1 chemical1 i4 #bi ,equations1 chemical1 i4 #bgh ,equivalents1 law of1 i4 #aid ,equivalent weights1 i4 #eha ,ethane1 i4 #cff ,ether1 critical points of1 i4 #ada ,ethylene1 i4 #cgj ,ethyl silicates1 i4 #ajd ,euchlorine1 i4 #dhd ,eudiometer1 i4 #afi ,expansion1 linear1 of elements1 ii4 #ca ,explosion1 rate of transmission of1 i4 #aga ,explosives1 i4 #bge1 #bgf ,felspar1 ii4 #abb ,fermentation1 i4 #bdb ,ferric chloride1 i4 #eeh2 ii4 #cdj -- hydrates1 ii4 #cci -- nitrate1 ii4 #cdj -- orthophosphate1 ii4 #cdb -- oxide1 ii4 #cci ,ferrous chloride1 ii4 #cce -- sulphate1 ii4 #cce -- -- solubility of1 i4 #gb -- sulphide1 ii4 #baj ,flame1 i4 #agg1 #agi ,fluoborates1 ii4 #fi ,fluorides1 i4 #dia1 #dic ,fluorine1 i4 #bjc1 #dhi ,fluorspar1 i4 #dia ,formula1 chemical1 i4 #aea1 #cbf ,freezing mixtures1 i4 #gf ,fuel1 calorific capacity of1 i4 #cfj ,furnace1 electrical1 i4 #ceb ,fusco-cobaltic salts1 ii4 #cfj ,gadolinite metals1 ii4 #ic ,gallium1 ii4 #hh1 #ij ,gas1 illuminating1 i4 #cfa -- producers1 i4 #cig ,gases1 absorption of1 i4 #cdh -- diffusion of1 i4 #hc -- expansion of1 i4 #acc -- liquefaction of1 i4 #acd1 #ace1 #acg -- measurement of1 i4 #gh1 #cjj -- solution of1 i4 #fh1 #gh1 #hf -- theory of1 i4 #ha1 #hc1 #adj ,germanium1 ii4 #bf1 #abd -- chloride1 ii4 #abe -- oxide1 ii4 #abe ,glass1 i4 #abc -- soluble1 ii4 #aaj ,glauber's salt1 i4 #eag ,glycols1 ii4 #aag ,gold1 ii4 #ddb -- alloys1 i4 #ddf1 #ddg -- chlorides1 ii4 #ddh1 #dej -- colloid1 ii4 #ddg -- cyanide1 ii4 #dej -- extraction of1 ii4 #ddd1 #dde -- fulminating1 ii4 #dej -- oxides1 ii4 #ddh -- refining1 ii4 #ddf ,graduators1 i4 #dbd ,graphite1 i4 #cej1 #cea ,gros' salt1 ii4 #cic ,guignet's green1 ii4 #bhe ,gunpowder1 i4 #eeg ,gypsum1 i4 #eic1 #faa ,halogens1 i4 #dde1 #dhg1 #dii ,halogen compounds1 heat of formation of1 i4 #did1 #ejb2 ii4 #cb -- -- boiling-points of1 i4 #ejb ,hausmannite1 ii4 #aj ,helium1 i4 #egj2 ii4 #dih ,hemimorphism1 ii4 #i ,homeomorphism1 ii4 #h ,homologous compounds1 i4 #ceh ,humus1 i4 #cdd ,hydrates1 i4 #aji1 #ahe ,hydrazine1 i4 #beh ,hydrides1 i4 #fba2 ii4 #bc ,hydrocarbons1 i4 #cee1 #cei ,hydrogen1 i4 #abc1 #abi1 #acj1 #adb1 #adc1 #adf -- pentasulphide1 ii4 #bag -- peroxide1 i4 #bjg1 #cab ,hydrosols1 i4 #ih ,hydroxyl1 i4 #aib1 #bac ,hydroxylamine1 i4 #bfb ,hypochlorites1 i4 #dha ,hyponitrites1 i4 #bid ,imides1 i4 #beh ,indium1 ii4 #bg1 #cg1 #hh1 #ig ,iodates1 i4 #eji ,iodides1 ii4 #cb -- of nitrogen1 i4 #ejg ,iodine1 i4 #cbj1 #cba1 #dif1 #dig1 #dih -- chlorides of1 i4 #eaa ,iodosobenzol1 i4 #ejh ,iridious oxide1 ii4 #chb ,iridium1 ii4 #chb ,iron1 i4 #ehe2 ii4 #cag1 #cbb -- and carbonic oxide1 ii4 #cde -- cast1 ii4 #cbe -- nitride1 ii4 #cdf -- ores1 ii4 #cai -- sulphate1 ii4 #cce ,isethionic acid1 ii4 #bej ,isomorphism1 i4 #bjc1 #cfh2 ii4 #a1 #d1 #h ,kaolin1 ii4 #gj ,lakes1 ii4 #gg ,lanthanum1 ii4 #ic ,laughing gas1 ii4 #big ,law of ,avogadro-,gerhardt1 i4 #cji -- -- ,berthollet1 i4 #dde -- -- ,boyle and ,mariotte1 i4 #acb -- -- combining weights1 i4 #bba -- -- ,dulong and ,petit1 i4 #ehd -- -- equivalents1 i4 #aid -- -- even numbers1 i4 #ceg -- -- ,gay ,lussac1 i4 #acc1 #cjd1 #cjg -- -- ,guldberg and ,waage1 i4 #dda -- -- ,henry and ,dalton1 i4 #gh -- -- indestructibility of matter1 i4 #f -- -- ,kirchoff1 i4 #efh -- -- limits1 i4 #ceg -- -- maximum work1 i4 #abj -- -- multiple proportions1 i4 #aji1 #bad -- -- partial pressures1 i4 #hb -- -- periodic1 ii4 #ag -- -- phases1 ii4 #daj -- -- reversed spectra1 i4 #efh -- -- specific heats1 i4 #ehd -- -- substitution1 i4 #bfj1 #cfe -- -- volumes1 i4 #cjd ,lead1 ii4 #acd -- acetate1 ii4 #acg -- carbonate1 ii4 #adj -- chloride1 ii4 #aci -- chromate1 ii4 #acf1 #bgi -- dioxide1 ii4 #adb -- nitrate1 ii4 #aci -- oxide1 ii4 #acg -- red1 ii4 #adb -- salts of1 i4 #dia -- tetrachloride1 ii4 #add -- tetrafluoride1 ii4 #add -- white1 ii4 #adj ,leucone1 ii4 #ajg ,levigation1 ii4 #gb ,light1 chemical action of1 i4 #dfe ,lime1 i4 #fje ,liquids1 boiling points of1 i4 #ace ,lithium1 i4 #egd -- carbonate1 i4 #ege ,litharge1 ii4 #acg ,litmus1 i4 #ahe ,lixiviation1 methodical1 i4 #eba ,luteocobaltic salts1 ii4 #cei ,magnus' salt1 ii4 #cib ,magnesia1 i4 #eig ,magnesium1 i4 #eij1 #eid -- carbonate1 i4 #eib1 #fjb -- chloride1 i4 #fjb -- crystallohydrates of1 i4 #fja -- double salts of1 i4 #eig -- nitride1 i4 #eie -- silicide1 ii4 #ajb -- sulphate1 i4 #fjj ,manganese1 ii4 #cjc -- nitrides1 ii4 #caj -- oxides1 ii4 #cjf1 #cjg1 #cjh1 #cac -- peroxide1 i4 #aei2 ii4 #cje -- sulphate1 ii4 #cjg ,mass1 influence of1 i4 #cb1 #dcf ,matches1 ii4 #aed ,matter1 primary1 ii4 #ddj -- transmutability of1 i4 #ad ,mercury1 ii4 #dh -- ammonia compounds1 ii4 #eg -- basic salts of1 ii4 #ed -- chlorides1 ii4 #eb1 #ec1 #ed -- compounds1 heat of formation1 ii4 #ej -- cyanide1 ii4 #ee -- fulminating1 ii4 #ef -- iodide1 ii4 #ee -- nitrates1 ii4 #ea -- nitrides1 ii4 #ef -- oxides1 ii4 #ec -- sulphate1 ii4 #eg -- sulphides1 ii4 #bba ,metalepsis1 i4 #bh1 #dga ,metalloids1 i4 #bc ,metals1 i4 #bc -- of alkaline earths1 i4 #fd1 #eij1 #eia -- of alkalis1 i4 #edc -- displacement of1 ii4 #dbg ,methane1 i4 #cfj ,moisture1 determination of1 in gases1 i4 #dj -- influence upon reaction1 i4 #djc ,molecular volumes1 ii4 #cg -- weight and boiling point1 i4 #cca -- -- -- coefficient of refraction1 i4 #ccf -- -- -- latent heat1 i4 #cbi -- -- -- specific gravity of solutions1 i4 #cce -- -- -- surface tension1 i4 #ccd ,molecules1 i4 #cai1 #cbb ,molybdates1 ii4 #bib ,molybdenum1 ii4 #bij -- anhydride1 ii4 #bia -- fluo-compounds1 ii4 #bih -- sulphides1 ii4 #big ,monophosphamide1 ii4 #agh ,monosodium orthophosphate1 ii4 #afg ,morphotropy1 ii4 #aj ,naphtha1 i4 #cgc1 #cgg ,nascent state1 i4 #cc1 #ade1 #adf ,neodymium1 ii4 #ig ,nickel1 ii4 #cec -- alloys1 ii4 #cfg -- and carbonic oxide1 ii4 #cfg -- fluoride1 ii4 #ceh -- hydroxide1 ii4 #ceh -- oxide1 ii4 #cfe -- sulphate1 i4 #ig2 ii4 #cei -- tetra-carboxyl1 ii4 #cfg ,niobium1 i4 #aii2 ii4 #aid1 #aih ,nitrates1 i4 #bgc ,nitres1 i4 #bfh1 #eee ,nitric anhydride1 i4 #bhj -- oxide1 i4 #bhf ,nitrides1 i4 #bbg1 #beh1 #fbj ,nitriles1 i4 #djf ,nitrites1 i4 #bhd ,nitro-cellulose1 i4 #bge ,nitro-compounds1 i4 #bgd ,nitrogen1 i4 #bbc1 #bbe1 #dge -- chloride1 i4 #dgf -- iodide1 i4 #ejg -- oxides of1 i4 #bfg1 #bhj1 #bhd1 #bid1 #bie -- sulphide1 ii4 #bgj ,nitro-prussides1 ii4 #cea ,nitroso-compounds1 i4 #bhh ,nitrosulphates1 ii4 #bbi ,nitrosyl chloride1 ii4 #agf ,norwegium1 ii4 #ei ,occlusion1 i4 #adc ,olefiant gas1 i4 #cgj ,organo-metallic compounds1 i4 #cef ,osmium1 ii4 #cgb1 #chb1 #chd ,osmotic pressure1 i4 #fd ,osmuridium1 ii4 #chc ,oxamide1 i4 #djf ,oxidation1 i4 #af ,oxides1 i4 #ahc2 ii4 #cf ,oxycobaltamine salts1 ii4 #cei ,oxygen1 i4 #aeb1 #aeg1 #aeh1 #afc -- compounds1 heat of formation of1 i4 #abj1 #dff ,ozone1 i4 #aih1 #bbi ,palladium1 ii4 #cfi -- hydride1 i4 #adc2 ii4 #chj ,palladous chloride1 ii4 #cgi -- iodide1 ii4 #cgi ,paracyanogen1 i4 #dad ,paramorphism1 ii4 #i ,parasulphatammon1 ii4 #bfi ,peat1 i4 #cdd ,peligot's salt1 ii4 #bha ,percentage composition1 i4 #cbf ,perchloric anhydride1 ii4 #bhb ,periodates1 i4 #eaj ,permanganic anhydride1 ii4 #cac ,permolybdates1 ii4 #big ,peroxide1 chloric1 i4 #dhd ,peroxides1 i4 #aei2 ii4 #ae1 #bc ,perstannic oxide1 ii4 #acc ,persulphates1 ii4 #bec ,petroleum1 i4 #cgc ,phenol1 solubility of1 i4 #ge ,phlogiston1 i4 #ag ,phosgene gas1 ii4 #age ,phospham1 ii4 #agh ,phosphides1 ii4 #aeg ,phosphine1 ii4 #aeh1 #afj ,phosphonium iodide1 ii4 #aei ,phosphoric anhydride1 ii4 #afa ,phosphorous anhydride1 ii4 #afj ,phosphorus1 ii4 #adi -- ammonium compounds1 ii4 #agh -- chlorides1 ii4 #agd -- fluorides1 ii4 #agc -- iodides1 i4 #eje1 #ejf2 ii4 #agb -- oxychlorides1 ii4 #age -- sulphides1 ii4 #bac -- sulphochloride1 ii4 #bac -- thermo-chemical data for1 ii4 #aec ,phosphuretted hydrogen1 ii4 #aeh1 #afj ,photography1 ii4 #dca ,photo-salts1 ii4 #dcb ,plants1 chemical reactions in1 i4 #edg -- and nitrogen1 i4 #bcj ,platinic chloride1 ii4 #cgg -- hydroxide1 ii4 #cgi ,platino-ammonium compounds1 ii4 #cia -- chlorides1 i4 #dfg2 ii4 #cgh -- cyanides1 ii4 #chf -- nitrites1 ii4 #cij -- sulphites1 ii4 #cij ,platinous chloride1 ii4 #cgi ,platinum1 ii4 #cgf -- alloys1 ii4 #cgc -- black1 ii4 #cgf -- metals1 ii4 #cfi1 #cge -- oxide1 ii4 #cgh ,poly-haloid salts1 i4 #ede ,polymerism1 i4 #bjg1 #cfg ,polysulphides1 ii4 #bag ,potassium1 i4 #edd1 #eeh -- aurate1 ii4 #ddi -- bromide1 i4 #eej -- carbonate1 i4 #edi -- chlorate1 i4 #afa1 #dhb -- chloride1 i4 #gb1 #edc -- chromate1 ii4 #bhj -- cyanide1 i4 #dab1 #eea -- dichromate1 ii4 #bgh -- ferricyanide1 ii4 #cdf -- ferrocyanide1 i4 #cdf1 #dab -- hydrosulphide1 ii4 #bai -- hydroxide1 i4 #edh -- iodide1 i4 #eej -- manganate1 ii4 #caj -- nitrate1 i4 #eec -- oxides1 i4 #eei -- permanganate1 ii4 #caa -- stannate1 ii4 #acc -- sulphate1 i4 #gb1 #edi -- sulphide1 ii4 #bai -- telluride1 ii4 #bgd ,praseocobaltic salts1 ii4 #cfa ,praseodidymium1 ii4 #ig ,proteid substances1 i4 #bbd ,prout's hypothesis1 ii4 #dci ,prussian blue1 i4 #dai2 ii4 #cdi ,purpureocobaltic salts1 ii4 #cfa ,purpureotetramine salts1 ii4 #cfa ,pyrocollodion1 i4 #bge ,pyronaphtha1 i4 #cge ,pyrosulphuryl chloride1 i4 #cba2 ii4 #bce ,reactions1 chemical1 i4 #c -- -- conditions for1 i4 #cd -- -- contact1 i4 #ci -- -- endothermal1 i4 #cj -- -- exothermal1 i4 #cj -- -- limit of1 i4 #dcg -- -- rate of1 ii4 #aeb ,recalescence1 ii4 #ccc ,reduction1 i4 #af ,refraction equivalent1 i4 #ccf ,regenerative furnaces1 i4 #cih ,reiset's salts1 ii4 #cid ,respiration1 i4 #aeb1 #aed1 #chg ,rhodium1 ii4 #cha ,rock salt1 i4 #dba ,roseocobaltic salts1 ii4 #cfj ,rosetetramine salts1 ii4 #cfa ,rubidium1 i4 #egf ,ruthenium1 ii4 #cgb1 #chb1 #chd ,sal-ammoniac1 i4 #bdh1 #cah1 #deg -- solubility of1 i4 #deh -- vapour density of1 i4 #cag ,salts1 i4 #ahg1 #dai -- acid1 i4 #aic1 #ecc -- basic1 i4 #aic1 #ecc2 ii4 #ed -- double1 i4 #eih -- electrolysis of1 i4 #aia -- heat of formation1 i4 #ahi -- melting points of1 i4 #ace -- pyro1 i4 #aic -- theory of1 i4 #aic ,saponification1 i4 #ecj ,scandium1 ii4 #id ,selenium1 ii4 #bgc -- chlorides1 ii4 #bge ,selenious anhydride1 ii4 #bga ,silica1 i4 #ajj2 ii4 #ajh -- soluble1 ii4 #aac ,silicates1 i4 #edd2 ii4 #aaf ,silicon1 ii4 #ii -- chloride1 ii4 #ajc1 #ajd -- chloroform1 ii4 #ajc -- bromide1 ii4 #ajd -- fluoride1 ii4 #aje -- hydride1 ii4 #ajb1 #ajc -- iodide1 ii4 #aje -- iodoform1 ii4 #aje ,silver1 ii4 #dah -- allotropic varieties of1 ii4 #dba -- bromide1 ii4 #dbi -- chlorate1 ii4 #dcg -- chloride1 ii4 #dbi -- cyanide1 ii4 #dcc -- fluoride1 ii4 #dcj -- fulminating1 ii4 #dbf -- hyponitrite1 i4 #bid -- iodide1 ii4 #dbi -- nitrate1 ii4 #dbf -- nitrite1 i4 #bhd -- orthophosphate1 ii4 #afd -- oxides1 ii4 #dbd -- peroxide1 ii4 #dbb -- plating1 ii4 #dcd -- soluble1 ii4 #dbj -- subchloride1 ii4 #dcb ,slags1 ii4 #cbc ,smalt1 ii4 #ced ,soaps1 i4 #eca ,soda ash1 i4 #eai -- caustic1 i4 #ebg -- manufacture of1 i4 #dei -- waste1 i4 #ebb ,soda lime1 i4 #bcg ,sodamide1 i4 #eci ,sodium1 i4 #eac1 #ecc -- alloys1 i4 #eei -- amalgams1 i4 #ecg -- bicarbonate1 i4 #ebf -- carbonate1 i4 #eai1 #ebe -- -- crystallohydrates of1 i4 #ajh -- -- manufacture of1 i4 #ebc -- -- solutions of1 i4 #ebe -- chloride1 i4 #dai -- -- double salts of1 i4 #dcj -- -- solutions of1 i4 #hh1 #ii1 #dbi -- hydride1 i4 #ecg -- hydroxide1 i4 #ebh1 #ebi -- -- solutions of1 i4 #ebi -- nitrate1 i4 #bfi -- -- solutions of1 i4 #gb -- organo compounds of1 i4 #edj -- oxides1 i4 #edj1 #eda -- phosphates1 ii4 #aff -- platinate1 ii4 #cgh -- pyrosulphate1 i4 #eah -- sesquicarbonate1 i4 #ebf -- stannate1 ii4 #acc -- subchloride1 i4 #edj -- sulphate1 i4 #eac -- -- acid salt1 i4 #eah -- -- crystallohydrates of1 i4 #eae -- -- solutions of1 i4 #gc1 #eae1 #eaf -- sulphite1 ii4 #bbf -- thiosulphate1 ii4 #bcj -- -- solutions of1 i4 #gd -- tungstate1 ii4 #bid ,soils1 i4 #cdd2 ii4 #gc ,solubility1 coefficient of1 i4 #fg1 #ga ,solutions1 i4 #ccj -- aqueous1 i4 #ei -- boiling points of1 i4 #id1 #ajj -- crystallisation of1 i4 #dbg -- colour of1 i4 #ie -- diffusion of1 i4 #fa1 #dbi -- of double salts1 i4 #eii -- formation of ice from1 i4 #ia1 #dbh -- heat of formation of1 i4 #gd1 #ge1 #gf -- of gases1 i4 #fh -- isotonic1 i4 #fd -- saturated1 i4 #fe -- specific gravity of1 i4 #dbi1 #ehd -- supersaturated1 i4 #if -- theory of1 i4 #fd1 #hi1 #ib1 #ig1 #ajf1 #bae1 #cbc1 #fjh2 ii4 #c1 #afd -- vapour tension of1 i4 #ij1 #ib -- volumes of1 i4 #hg -- ,specific heat1 i4 #ehe1 #ehf1 #ehh ,spectra absorption1 i4 #eff ,spectrum analysis1 i4 #efj1 #efa ,stannic chloride1 ii4 #acb -- fluoride1 ii4 #acb -- oxide1 ii4 #acj -- sulphide1 ii4 #acb ,stannous chloride1 ii4 #acj -- oxide1 ii4 #abi -- salts1 ii4 #abi ,steam1 vapour tension of1 i4 #ed ,steel1 ii4 #cbg1 #cbh1 #ccj ,strontium1 i4 #fae -- chloride1 i4 #fae -- hydroxide1 i4 #fae -- nitrate1 i4 #fae -- oxide1 i4 #fag ,substitution chemical1 i4 #e ,sulphamide1 ii4 #bgj ,sulphatammon1 ii4 #bfi ,sulphates1 ii4 #bdh ,sulphides1 i4 #ih2 ii4 #bac ,sulphonitrites1 ii4 #bbi ,sulphoxyl1 ii4 #bej ,sulphur1 ii4 #bjj -- chlorides of1 ii4 #bfd ,sulphuretted hydrogen1 ii4 #bjh ,sulphuric anhydride1 ii4 #bcb -- peroxide1 ii4 #bea ,sulphurous anhydride1 ii4 #bbd ,sulphuryl chloride1 ii4 #bfh ,superphosphates1 ii4 #afh ,tantalum1 ii4 #aid1 #aih ,tellurium1 ii4 #bgd -- bromide1 ii4 #bge -- chlorides1 ii4 #bge ,tellurous anhydride1 ii4 #bga ,temperature1 critical1 i4 #aca ,test papers1 i4 #ahe ,thallium1 ii4 #hh1 #ia ,thallic oxide1 ii4 #ic ,thallous hydroxide1 ii4 #ib -- oxide1 ii4 #ib ,thiocarbonates1 ii4 #bfb ,thionyl chloride1 ii4 #bfg ,thiophosgene1 ii4 #bfb ,thiophosphoryl fluoride1 ii4 #bfc ,theory1 atomic1 i4 #baf -- unitary1 i4 #aie -- vortex1 i4 #bag ,thermochemistry1 i4 #agc ,thorium1 ii4 #adh ,tin1 ii4 #abe -- alloys1 ii4 #abg ,titanium1 ii4 #add -- chloride1 ii4 #ade -- nitride1 ii4 #adf -- nitrocyanide1 ii4 #adf -- oxides1 ii4 #ade ,tripoli1 ii4 #aaj ,trisodium orthophosphate1 ii4 #aff ,tungstates1 ii4 #bib ,tungsten1 ii4 #bij -- anhydride1 ii4 #bia -- nitride1 ii4 #big -- sulphide1 ii4 #big ,turnbull's blue1 ii4 #cej ,types of combination1 ii4 #aj ,ultramarine1 ii4 #hd ,uranium1 ii4 #cj1 #big -- atomic weight of1 ii4 #bf -- dioxide1 ii4 #cja -- oxides1 ii4 #bih -- tetrachloride1 ii4 #cja ,urano-alkali compounds1 ii4 #bih ,uranyl1 ii4 #cja -- ammonium carbonate1 ii4 #cjj -- nitrate1 ii4 #cjj -- phosphate1 ii4 #cjj ,urea1 i4 #dji ,valency of elements1 i4 #djd1 #dah1 #eha ,van der ,waal's formula1 i4 #hb1 #adj ,vanadic anhydride1 ii4 #aif ,vanadium1 ii4 #aid -- oxychloride1 ii4 #aie ,vapour density1 determination of1 i4 #cja ,ventilation1 i4 #bdd ,viscosity1 i4 #cee ,volumes1 molecular1 ii4 #d -- gases1 i4 #cjj ,water1 i4 #dj -- composition of1 i4 #aad1 #aah1 #adh1 #afi1 #cje1 #ccc -- compressibility of1 i4 #ec -- of constitution1 i4 #aji -- of crystallisation1 i4 #ie1 #eaj -- dissociation of1 i4 #aah -- expansion of1 i4 #ec -- gas1 i4 #abi1 #djj1 #dja -- hard1 i4 #dg -- hygroscopic1 i4 #ef -- mineral1 i4 #de -- rain1 i4 #dc -- river1 i4 #dc -- sea1 i4 #df -- specific heat of1 i4 #eb -- -- gravity of1 i4 #ej -- spring1 i4 #dd ,wave lengths1 i4 #efd ,wood1 i4 #cci ,ytterbium1 ii4 #ic ,yttrium1 ii4 #ic ,zinc1 ii4 #ci -- ammonia-chlorides1 ii4 #da -- chloride1 ii4 #dj1 #da -- compounds1 heat of formation of1 ii4 #ea -- oxide1 ii4 #ci1 #dj -- sulphate1 ii4 #ci ,zirconium1 ii4 #adf -- chloride1 ii4 #adg -- hydroxide1 ii4 #adg -- oxide1 ii4 #adg 99 99 99 99 99 ,,printed ,,by ,,spottiswoode ,,and ,,co41 ,,new-,,street ,,square ,,london 99 99 99 99 99 ,a ,,classified ,,catalogue ,,of ,,scientific ,,works ,,published ,,by ,,messrs4 ,,longmans1 ,,green1 ,,co4 ,,london3 #ci ,,paternoster ,,row1 ,e4,c4 ,,new ,,york3 #ia #ic ,,fifth ,,avenue4 ,,bombay3 #cb ,,hornby ,,road4 ,,contents4 ,,page ,,advanced ,,science ,,manuals #cj ,,agriculture ,,and ,,gardening #bf ,,astronomy #ad ,,biology #bd ,,botany #be ,,building ,,construction #aj ,,chemistry #b ,,dynamics #f ,,electricity #aa ,,elementary ,,science ,,manuals #cj ,,engineering #ab ,,evolution #ah ,,geology #ag ,,health ,,and ,,hygiene #ag ,,heat #h ,,hydrostatics #f ,,light #h ,,london ,,science ,,class-,,books #cb ,,longmans' ,,civil ,,engineering ,,series #ac ,,machine ,,drawing ,,and ,,design #ac ,,magnetism #aa ,,manufactures #ag ,,mechanics #f ,,medicine ,,and ,,surgery #ai ,,metallurgy #ad ,,mineralogy #ad ,,natural ,,history #ah ,,navigation #ad ,,optics #h ,,photography #h ,,physics #e ,,physiography #ag ,,physiology #bd ,,proctor',s 7,r4 ,a47 ,,works #ae ,,sound #h ,,statics #f ,,steam1 ,,oil1 ,,and ,,gas ,,engines #i ,,strength ,,of ,,materials #ab ,,technology #ag ,,telegraphy #ab ,,telephone #ab ,,text-,,books ,,of ,,science #bh ,,thermodynamics #h ,,tyndall',s 7,,john7 ,,works #bg ,,workshop ,,appliances #ad 99 99 99 99 99 ,,chemistry4 ,,cornish4--,,practical ,,proofs ,,of ,,chemical ,,laws3 ,a ,course of ,experiments upon the ,combining ,proportions of the ,chemical ,elements4 ,by ,,vaughan ,,cornish1 ,m4,sc41 ,associate of the ,owens ,college1 ,manchester4 ,crown #hvo41 #bs4 ,,crookes4--,,select ,,methods ,,in ,,chemical ,,analysis1 chiefly ,inorganic4 ,by ,,william ,,crookes1 ,f4,r4,s41 etc4 ,third ,edition1 ,rewritten and ,enlarged4 ,with #fg ,woodcuts4 #hvo41 #bas4 net4 ,,cross ,,and ,,bevan4--,,cellulose3 an ,outline of the ,chemistry of the ,structural ,elements of ,plants4 ,with ,reference to their ,natural ,history and ,industrial ,uses4 ,by ,,cross and ,,bevan 7,c4 ,f4 ,cross1 ,e4 ,j4 ,bevan1 and ,c4 ,beadle74 ,with #ad ,plates4 ,crown #hvo41 #abs4 net4 ,,furneaux4--,,elementary ,,chemistry1 ,inorganic and ,organic4 ,by ,w4 ,,furneaux1 ,f4,r4,c4,s41 ,lecturer on ,chemistry1 ,london ,school ,board4 ,with #fe ,illustrations and #aee ,experiments4 ,crown #hvo41 #bs4 #f;d4 ,,hjelt4--,,principles ,,of ,,general ,,organic ,,chemistry4 ,by ,professor ,e4 ,,hjelt1 of ,helsingfors4 ,translated from the ,german by ,j4 ,,bishop ,,tingle1 ,ph4,d41 ,assistant in the ,laboratory of the ,heriot ,watt ,college1 ,edinburgh4 ,crown #hvo41 #fs4 #f;d4 ,,jago4--,works by ,w4 ,,jago1 ,f4,c4,s41 ,f4,i4,c4 ,,inorganic ,,chemistry1 ,,theoretical ,,and ,,practical4 ,with an ,introduction to the ,principles of ,chemical ,analysis1 ,inorganic and ,organic4 ,with #fc ,woodcuts and numerous ,questions and ,exercises4 ,fcp4 #hvo41 #bs4 #f;d4 ,,an ,,introduction ,,to ,,practical ,,inorganic ,,chemistry4 ,crown #hvo41 #as4 #f;d4 ,,inorganic ,,chemistry1 ,,theoretical ,,and ,,practical4 ,a ,manual for ,students in ,advanced ,classes of the ,science and ,art ,department4 ,with ,plate of ,spectra and #gh ,woodcuts4 ,crown #hvo41 #ds4 #f;d4 ,,kolbe4--,a ,,short ,,textbook ,,of ,,inorganic ,,chemistry4 ,by ,dr4 ,,hermann ,,kolbe4 ,translated and ,edited by ,t4 ,s4 ,,humpidge1 ,ph4,d4 ,with #ff ,illustrations4 ,crown #hvo41 #hs4 #f;d4 ,,mendel,,eff4--,,the ,,principles ,,of ,,chemistry4 ,by ,d4 ,,mendel,,eff1 ,professor of ,chemistry in the ,university of ,st4 ,petersburg4 ,translated by ,,george ,,kamensky1 ,a4,r4,s4,m41 of the ,imperial ,mint1 ,st4 ,petersburg1 and ,edited by ,a4 ,j4 ,,greenaway1 ,f4,i4,c41 ,sub-,editor of the ,journal of the ,chemical ,society4 ,with #ig ,illustrations4 #b vols4 #hvo41 #cfs4 ,,meyer4--,,outlines ,,of ,,theoretical ,,chemistry4 ,by ,,lothar ,,meyer1 ,professor of ,chemistry in the ,university of ,tbingen4 ,translated by ,professors ,p4 ,,phillips ,,bedson1 ,d4,sc41 and ,w4 ,,carleton ,,williams1 ,b4,sc4 #hvo41 #is4 ,,miller4--,,introduction ,,to ,,the ,,study ,,of ,,inorganic ,,chemistry4 ,by ,w4 ,,allen ,,miller1 ,m4,d41 ,,ll4,d4 ,with #ga ,woodcuts4 ,fcp4 #hvo41 #cs4 #f;d4 ,,newth4--,works by ,g4 ,s4 ,,newth1 ,f4,i4,c41 ,f4,c4,s41 ,demonstrator in the ,royal ,college of ,science1 ,london2 ,assistant ,examiner in ,chemistry1 ,science and ,art ,department4 ,,chemical ,,lecture ,,experiments1 ,,non-,,metallic ,,elements4 ,with #bcj ,diagrams4 ,crown #hvo41 #ajs4 #f;d4 ,a ,,text-,,book ,,of ,,inorganic ,,chemistry4 ,with #adf ,illustrations4 ,crown #hvo41 #fs4 #f;d4 ,,elementary ,,practical ,,chemistry3 a ,laboratory ,manual for ,use in ,organised ,science ,schools4 ,with #ajh ,illustrations and #bed ,experiments4 ,crown #hvo41 #bs4 #f;d4 ,,ostwald4--,,solutions4 ,by ,w4 ,,ostwald1 ,professor of ,chemistry in the ,university of ,leipzig4 ,being the ,fourth ,book1 with some additions1 of the ,second ,edition of ,ostwald's ',lehrbuch der allgemeinen ,chemie'4 ,translated by ,m4 ,m4 ,,pattison ,,muir1 ,fellow of ,gonville and ,caius ,college1 ,cambridge4 #hvo41 #ajs4 #f;d4 ,,payen4--,,industrial ,,chemistry4 ,a ,manual for use in ,technical ,colleges and ,schools1 based upon a ,translation of ,stohmann and ,engler's ,german ,edition of ,,payen',s ,prcis de ,chimie ,industrielle4 ,edited by ,b4 ,h4 ,,paul1 ,ph4,d4 ,with #fih ,woodcuts4 #hvo41 #dbs4 ,,reynolds4--,,experimental ,,chemistry ,,for ,,junior ,,students4 ,by ,j4 ,,emerson ,,reynolds1 ,m4,d41 ,f4,r4,s41 ,professor of ,chemistry1 ,university of ,dublin2 ,examiner in ,chemistry1 ,university of ,london4 ,fcp4 #hvo41 with numerous ,woodcuts4 ,part ,i4 ,introductory4 ,fcp4 #hvo41 #as4 #f;d4 ,part ,,ii4 ,non-,metals1 with an ,appendix on ,systematic ,testing for ,acids4 ,fcp4 #hvo41 #bs4 #f;d4 ,part ,,iii4 ,metals1 and ,allied ,bodies4 ,fcp4 #hvo41 #cs4 #f;d4 ,part ,,iv4 ,carbon ,compounds4 ,fcp4 #hvo41 #ds4 ,,shenstone4--,works by ,w4 ,a4 ,,shenstone1 ,lecturer on ,chemistry in ,clifton ,college4 ,,the ,,methods ,,of ,,glass-,,blowing4 ,for the use of ,physical and ,chemical ,students4 ,with #db ,illustrations4 ,crown #hvo41 #as4 #f;d4 ,a ,,practical ,,introduction ,,to ,,chemistry4 ,intended to give a ,practical acquaintance with the ,elementary ,facts and ,principles of ,chemistry4 ,with #be ,illustrations4 ,crown #hvo41 #bs4 ,,thorpe4--,a ,,dictionary ,,of ,,applied ,,chemistry4 ,by ,t4 ,e4 ,,thorpe1 ,b4,sc4 7,vict471 ,ph4,d41 ,f4,r4,s41 ,treas4 ,c4,s41 ,professor of ,chemistry in the ,royal ,college of ,science1 ,south ,kensington4 ,assisted by ,eminent ,contributors4 #c vols4 #hvo4 ,vols4 ,i4 and ,,ii41 #dbs4 each4 ,vol4 ,,iii41 #fcs4 ,,thorpe4--,,quantitative ,,chemical ,,analysis4 ,by ,t4 ,e4 ,,thorpe1 ,ph4,d41 ,f4,r4,s4 ,with #hh ,woodcuts4 ,fcp4 #hvo41 #ds4 #f;d4 ,,thorpe ,,and ,,muir4--,,qualitative ,,chemical ,,analysis ,,and ,,laboratory ,,practice4 ,by ,t4 ,e4 ,,thorpe1 ,ph4,d41 ,d4,sc41 ,f4,r4,s41 and ,m4 ,m4 ,,pattison ,,muir1 ,m4,a4 ,with ,plate of ,spectra and #eg ,woodcuts4 ,fcp4 #hvo41 #cs4 #f;d4 ,,tilden4--,works by ,,william ,a4 ,,tilden1 ,d4,sc4 ,london1 ,f4,r4,s41 ,professor of ,chemistry in the ,royal ,college of ,science1 ,london4 ,,introduction ,,to ,,the ,,study ,,of ,,chemical ,,philosophy4 ,the ,principles of ,theoretical and ,systematic ,chemistry4 ,with #e ,woodcuts4 ,with or without the ,,answers of ,problems4 ,fcp4 #hvo41 #ds4 #f;d4 ,,practical ,,chemistry4 ,the principles of ,qualitative ,analysis4 ,fcp4 #hvo41 #as4 #f;d4 ,,hints ,,on ,,the ,,teaching ,,of ,,elementary ,,chemistry ,,in ,,schools ,,and ,,science ,,classes4 ,with #g ,illustrations4 ,crown #hvo41 #bs4 ,,watts' ,,dictionary ,,of ,,chemistry4 ,revised and entirely ,re-written by ,h4 ,,forster ,,morley1 ,m4,a41 ,d4,sc41 ,fellow of1 and lately ,assistant-,professor of ,chemistry in ,university ,college1 ,london2 and ,m4 ,m4 ,,pattison ,,muir1 ,m4,a41 ,f4,r4,s4,e41 ,fellow1 and ,prlector in ,chemistry1 of ,gonville and ,caius ,college1 ,cambridge4 ,assisted by ,eminent ,contributors4 #d vols4 #hvo4 ,vols4 ,i4 and ,,ii41 #dbs4 each4 ,vol4 ,,iii41 #ejs4 ,vol4 ,,iv41 #fcs4 ,,whiteley4--,works by ,r4 ,,lloyd ,,whiteley1 ,f4,i4,c41 ,principal of the ,municipal ,science ,school1 ,west ,bromwich4 ,,chemical ,,calculations4 ,with ,explanatory ,notes1 ,problems and ,answers1 specially adapted for use in ,colleges and ,science ,schools4 ,with a ,preface by ,professor ,f4 ,,clowes1 ,d4,sc4 7,lond471 ,f4,i4,c4 ,crown #hvo41 #bs4 ,,organic ,,chemistry3 the ,fatty ,compounds4 ,with #de ,illustrations4 ,crown #hvo41 #cs4 #f;d4 ,,physics1 ,,etc4 ,,earl4--,,the ,,elements ,,of ,,laboratory ,,work3 a ,course of ,natural ,science4 ,by ,a4 ,g4 ,,earl1 ,m4,a41 ,f4,c4,s41 late ,scholar of ,christ's ,college1 ,cambridge4 ,with #eg ,diagrams and numerous ,exercises and ,questions4 ,crown #hvo41 #ds4 #f;d4 ,,ganot4--,works by ,,professor ,,ganot4 ,translated and ,edited by ,e4 ,,atkinson1 ,ph4,d41 ,f4,c4,s4 ,,elementary ,,treatise ,,on ,,physics1 ,experimental and ,applied4 ,with #i ,coloured ,plates and ,maps1 and #ajbh ,woodcuts1 and ,appendix of ,problems and ,examples with ,answers4 ,crown #hvo41 #aes4 ,,natural ,,philosophy ,,for ,,general ,,readers ,,and ,,young ,,persons4 ,with #g ,plates1 #fbd ,woodcuts1 and an ,appendix of ,questions4 ,crown #hvo41 #gs4 #f;d4 ,,glazebrook ,,and ,,shaw4--,,practical ,,physics4 ,by ,r4 ,t4 ,,glazebrook1 ,m4,a41 ,f4,r4,s41 and ,w4 ,n4 ,,shaw1 ,m4,a4 ,with #acd ,woodcuts4 ,fcp4 #hvo41 #gs4 #f;d4 ,,guthrie4--,,molecular ,,physics ,,and ,,sound4 ,by ,f4 ,,guthrie1 ,ph4,d4 ,with #ia ,diagrams4 ,fcp4 #hvo41 #as4 #f;d4 ,,physical ,,and ,,electrical ,,engineering ,,laboratory ,,manuals4--,vol4 #a4 ,,henderson4--,,elementary ,,physics4 ,by ,,john ,,henderson1 ,b4,sc4 7,edin471 ,a4,i4,e4,e41 ,lecturer in ,physics1 ,manchester ,municipal ,technical ,school4 ,crown #hvo41 #bs4 #f;d4 ,,helmholtz4--,,popular ,,lectures ,,on ,,scientific ,,subjects4 ,by ,,hermann ,,von ,,helmholtz4 ,translated by ,e4 ,,atkinson1 ,ph4,d41 ,f4,c4,s41 formerly ,professor of ,experimental ,science1 ,staff ,college4 ,with #fh ,illustrations4 #b vols41 crown #hvo41 #cs4 #f;d4 each4 ,,contents4--,vol4 ,i4--,the ,relation of ,natural ,science to ,science in ,general--,goethe's ,scientific ,researches--,the ,physiological ,causes of ,harmony in ,music--,ice and ,glaciers--,the ,interaction of the ,natural ,forces--,the ,recent ,progress of the ,theory of ,vision--,the ,conservation of ,force--,the ,aim and ,progress of ,physical ,science4 ,,contents4--,vol4 ,,ii4--,gustav ,magnus4 ,in ,memoriam--,the ,origin and ,significance of ,geometrical ,axioms--,the ,relation of ,optics to ,painting--,the ,origin of the ,planetary ,system--,thought in ,medicine--,academic ,freedom in ,german ,universities--,hermann ,von ,helmholtz--,an ,autobiographical ,sketch4 ,,watson4--,,elementary ,,practical ,,physics3 a ,laboratory ,manual for ,use in ,organised ,science ,schools4 ,by ,w4 ,,watson ,b4,sc4 ,demonstrator in ,physics in the ,royal ,college of ,science1 ,london2 ,assistant ,examiner in ,physics1 ,science and ,art ,department4 ,with #aai ,illustrations and #aic ,exercises4 ,crown #hvo41 #bs4 #f;d4 ,,worthington4--,a ,,first ,,course ,,of ,,physical ,,laboratory ,,practice4 ,containing #bfd ,experiments4 ,by ,a4 ,m4 ,,worthington1 ,m4,a41 ,f4,r4,s4 ,with ,illustrations4 ,crown #hvo41 #ds4 #f;d4 ,,wright4--,,elementary ,,physics4 ,by ,,mark ,r4 ,,wright1 ,professor of ,normal ,education1 ,durham ,college of ,science4 ,with #bdb ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,mechanics1 ,,dynamics1 ,,statics1 ,,hydrostatics1 ,,etc4 ,,ball4--,a ,,class-,,book ,,of ,,mechanics4 ,by ,sir ,r4 ,s4 ,,ball1 ,,ll4,d4 #hi ,diagrams4 ,fcp4 #hvo41 #as4 #f;d4 ,,geldard4--,,statics ,,and ,,dynamics4 ,by ,c4 ,,geldard1 ,m4,a41 formerly ,scholar of ,trinity ,college1 ,cambridge4 ,crown #hvo41 #es4 ,,goodeve4--,works by ,t4 ,m4 ,,goodeve1 ,m4,a41 formerly ,professor of ,mechanics at the ,normal ,school of ,science1 and the ,royal ,school of ,mines4 ,,the ,,elements ,,of ,,mechanism4 ,with #cdb ,woodcuts4 ,crown #hvo41 #fs4 ,,principles ,,of ,,mechanics4 ,with #bec ,woodcuts and numerous ,examples4 ,crown #hvo41 #fs4 ,a ,,manual ,,of ,,mechanics3 an ,elementary ,text-,book for ,students of ,applied ,mechanics4 ,with #ach ,illustrations and ,diagrams1 and #ahh ,examples taken from the ,science ,department ,examination ,papers1 with ,answers4 ,fcp4 #hvo41 #bs4 #f;d4 ,,grieve4--,,lessons ,,in ,,elementary ,,mechanics4 ,by ,w4 ,h4 ,,grieve1 ,p4,s4,a41 late ,engineer1 ,r4,n41 ,science ,demonstrator for the ,london ,school ,board1 etc4 ,stage #a4 ,with #afe ,illustrations and a large number of ,examples4 ,fcp4 #hvo41 #as4 #f;d4 ,stage #b4 ,with #abb ,illustrations4 ,fcp4 #hvo41 #as4 #f;d4 ,stage #c4 ,with #ajc ,illustrations4 ,fcp4 #hvo41 #as4 #f;d4 ,,magnus4--,works by ,,sir ,,philip ,,magnus1 ,b4,sc41 ,b4,a4 ,,lessons ,,in ,,elementary ,,mechanics4 ,introductory to the study of ,physical ,science4 ,designed for the ,use of ,schools1 and of ,candidates for the ,london ,matriculation and other ,examinations4 ,with numerous ,exercises1 ,examples1 ,examination ,questions1 and ,solutions1 etc41 from #ahgj-ahie4 ,with ,answers1 and #aca ,woodcuts4 ,fcp4 #hvo41 #cs4 #f;d4 ,key for the use of ,teachers only1 price #es4 #c-a_/b;d4 ,,hydrostatics ,,and ,,pneumatics4 ,fcp4 #hvo41 #as4 #f;d42 or1 with ,answers1 #bs4 ,the ,worked ,solutions of the ,problems1 #bs4 ,,robinson4--,,elements ,,of ,,dynamics 7,kinetics and ,statics74 ,with numerous ,exercises4 ,a ,text-book for ,junior ,students4 ,by the ,rev4 ,j4 ,l4 ,,robinson1 ,b4,a4 ,crown #hvo41 #fs4 ,,smith4--,works by ,j4 ,,hamblin ,,smith1 ,m4,a4 ,,elementary ,,statics4 ,crown #hvo41 #cs4 ,,elementary ,,hydrostatics4 ,crown #hvo41 #cs4 ,,key ,,to ,,statics ,,and ,,hydrostatics4 ,crown #hvo41 #fs4 ,,tate4--,,exercises ,,on ,,mechanics ,,and ,,natural ,,philosophy4 ,by ,,thomas ,,tate1 ,f4,r4,a4,s4 ,fcp4 #hvo41 #bs4 ,key1 #cs4 #f;d4 ,,taylor4--,works by ,j4 ,e4 ,,taylor1 ,m4,a41 ,b4,sc4 7,lond471 ,head ,master of the ,central ,higher ,grade and ,science ,school1 ,sheffield4 ,,theoretical ,,mechanics1 including ,hydrostatics and ,pneumatics4 ,with #age ,diagrams and ,illustrations1 and #ebb ,examination ,questions and ,answers4 ,crown #hvo41 #bs4 #f;d4 ,,theoretical ,,mechanics4--,,solids4 ,with #afc ,illustrations1 #abj ,worked ,examples and over #ejj ,examples from ,examination ,papers1 etc4 ,crown #hvo41 #bs4 #f;d4 ,,theoretical ,,mechanics4--,,fluids4 ,with #abb ,illustrations1 numerous ,worked ,examples1 and about #ejj ,examples from ,examination ,papers1 etc4 ,crown #hvo41 #bs4 #f;d4 ,,thornton4--,,theoretical ,,mechanics--,,solids4 ,including ,kinematics1 ,statics1 and ,kinetics4 ,by ,,arthur ,,thornton1 ,m4,a41 ,f4,r4,a4,s4 ,with #bjj ,illustrations1 #acj ,worked ,examples1 and over #ijj ,examples from ,examination ,papers1 etc4 ,crown #hvo41 #ds4 #f;d4 ,,twisden4--,works by the ,rev4 ,,john ,f4 ,,twisden1 ,m4,a4 ,,practical ,,mechanics2 an ,elementary ,introduction to their ,study4 ,with #hee ,exercises1 and #ahd ,figures and ,diagrams4 ,crown #hvo41 #ajs4 #f;d4 ,,theoretical ,,mechanics4 ,with #agb ,examples1 numerous ,exercises1 and #aed ,diagrams4 ,crown #hvo41 #hs4 #f;d4 ,,williamson4--,,introduction ,,to ,,the ,,mathematical ,,theory ,,of ,,the ,,stress ,,and ,,strain ,,of ,,elastic ,,solids4 ,by ,,benjamin ,,williamson1 ,d4,sc41 ,f4,r4,s4 ,crown #hvo41 #es4 ,,williamson ,,and ,,tarleton4--,,an ,,elementary ,,treatise ,,on ,,dynamics4 ,containing ,applications to ,thermodynamics1 with numerous ,examples4 ,by ,,benjamin ,,williamson1 ,d4,sc41 ,f4,r4,s41 and ,,francis ,a4 ,,tarleton1 ,,ll4,d4 ,crown #hvo41 #ajs4 #f;d4 ,,worthington4--,,dynamics ,,of ,,rotation3 an ,elementary introduction to ,rigid ,dynamics4 ,by ,a4 ,m4 ,,worthington1 ,m4,a41 ,f4,r4,s4 ,crown #hvo41 #cs4 #f;d4 ,,optics ,,and ,,photography4 ,,abney4--,a ,,treatise ,,on ,,photography4 ,by ,captain ,w4 ,,de ,,wiveleslie ,,abney1 ,f4,r4,s41 ,director for ,science in the ,science and ,art ,department4 ,with #aae ,woodcuts4 ,fcp4 #hvo41 #cs4 #f;d4 ,,glazebrook4--,,physical ,,optics4 ,by ,r4 ,t4 ,,glazebrook1 ,m4,a41 ,f4,r4,s41 ,fellow and ,lecturer of ,trinity ,college1 ,demonstrator of ,physics at the ,cavendish ,laboratory1 ,cambridge4 ,with #ahc ,woodcuts of ,apparatus1 etc4 ,fcp4 #hvo41 #fs4 ,,wright4--,,optical ,,projection3 a ,treatise on the ,use of the ,lantern in ,exhibition and ,scientific ,demonstration4 ,by ,,lewis ,,wright1 ,author of ',light3 a ,course of ,experimental ,optics'4 ,with #bcb ,illustrations4 ,crown #hvo41 #fs4 ,,sound1 ,,light1 ,,heat1 ,,and ,,thermodynamics4 ,,alexander4--,,treatise ,,on ,,thermodynamics4 ,by ,,peter ,,alexander1 ,m4,a4 ,crown #hvo41 #es4 ,,cumming4--,,heat4 ,for the ,use of ,schools and ,students4 ,by ,,linn,,us ,,cumming1 ,m4,a4 ,with numerous ,illustrations4 ,crown #hvo41 #ds4 #f;d4 ,,day4--,,numerical ,,examples ,,in ,,heat4 ,by ,r4 ,e4 ,,day1 ,m4,a4 ,fcp4 #hvo41 #cs4 #f;d4 ,,emtage4--,,light4 ,by ,w4 ,t4 ,a4 ,,emtage1 ,m4,a4 ,with #bcb ,illustrations4 ,crown #hvo41 #fs4 ,,helmholtz4--,,on ,,the ,,sensations ,,of ,,tone ,,as ,a ,,physiological ,,basis ,,for ,,the ,,theory ,,of ,,music4 ,by ,,hermann ,,von ,,helmholtz4 ,royal #hvo41 #bhs4 ,,madan4--,,an ,,elementary ,,text-,,book ,,on ,,heat4 ,for the ,use of ,schools4 ,by ,h4 ,g4 ,,madan1 ,m4,a41 ,f4,c4,s41 ,fellow of ,queen's ,college1 ,oxford2 late ,assistant ,master at ,eton ,college4 ,crown #hvo41 #is4 ,,maxwell4--,,theory ,,of ,,heat4 ,by ,j4 ,,clerk ,,maxwell1 ,m4,a41 ,f4,r4,,ss41 ,l4 and ,e4 ,with ,corrections and ,additions by ,lord ,,rayleigh4 ,with #ch ,illustrations4 ,fcp4 #hvo41 #ds4 #f;d4 ,,smith4--,,the ,,study ,,of ,,heat4 ,by ,j4 ,,hamblin ,,smith1 ,m4,a41 of ,gonville and ,caius ,college1 ,cambridge4 ,crown #hvo41 #cs4 ,,tyndall4--,works by ,,john ,,tyndall1 ,d4,c4,l41 ,f4,r4,s4 ,see p4 #bg4 ,,wormell4--,a ,,class-,,book ,,of ,,thermodynamics4 ,by ,,richard ,,wormell1 ,b4,sc41 ,m4,a4 ,fcp4 #hvo41 #as4 #f;d4 ,,wright4--,works by ,,mark ,r4 ,,wright1 ,hon4 ,inter4 ,b4,sc41 ,london4 ,,sound1 ,,light1 ,,and ,,heat4 ,with #afj ,diagrams and ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,advanced ,,heat4 ,with #acf ,diagrams and numerous ,examples and ,examination ,papers4 ,crown #hvo41 #ds4 #f;d4 ,,steam1 ,,oil1 ,,and ,,gas ,,engines4 ,,bale4--,a ,,handbook ,,for ,,steam ,,users2 being ,rules for ,engine ,drivers and ,boiler ,attendants1 with ,notes on ,steam ,engine and ,boiler ,management and ,steam ,boiler ,explosions4 ,by ,m4 ,,powis ,,bale1 ,m4,i4,m4,e41 ,a1,m4,i4,c4,e4 ,fcp4 #hvo41 #bs4 #f;d4 ,,bolton4--,,motive ,,powers ,,and ,,their ,,practical ,,selection4 ,by ,,reginald ,,bolton1 ,associate ,member of the ,institution of ,civil ,engineers1 etc4 ,crown #hvo41 #fs4 #f;d4 net4 ,,clerk4--,,the ,,gas ,,and ,,oil ,,engine4 ,by ,,dugald ,,clerk1 ,associate ,member of the ,institution of ,civil ,engineers1 ,fellow of the ,chemical ,society1 ,member of the ,royal ,institution1 ,fellow of the ,institute of ,patent ,agents4 ,with #bbh ,illustrations and ,diagrams4 #hvo41 #aes4 ,,holmes4--,,the ,,steam ,,engine4 ,by ,,george ,c4 ,v4 ,,holmes1 ,whitworth ,scholar1 ,secretary of the ,institution of ,naval ,architects4 ,with #bab ,woodcuts4 ,fcp4 #hvo41 #fs4 ,,norris4--,a ,,practical ,,treatise ,,on ,,the ',,otto' ,,cycle ,,gas ,,engine4 ,by ,,william ,,norris1 ,m4,i4,mech4,e4 ,with #bjg ,illustrations4 #hvo41 #ajs4 #f;d4 ,,ripper4--,,steam4 ,by ,,william ,,ripper1 ,member of the ,institution of ,mechanical ,engineers2 ,professor of ,mechanical ,engineering in the ,sheffield ,technical ,school4 ,with #adb ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,sennett4--,,the ,,marine ,,steam ,,engine4 ,a ,treatise for the ,use of ,engineering ,students and ,officers of the ,royal ,navy4 ,by ,,richard ,,sennett1 ,r4,n41 late ,engineer-in-,chief of the ,royal ,navy4 ,with #bfa ,illustrations4 #hvo41 #bas4 ,,stromeyer4--,,marine ,,boiler ,,management ,,and ,,construction4 ,being a ,treatise on ,boiler ,troubles and ,repairs1 ,corrosion1 ,fuels1 and ,heat1 on the proporties of ,iron and ,steel1 on ,boiler ,mechanics1 ,workshop ,practices1 and ,boiler ,design4 ,by ,c4 ,e4 ,,stromeyer1 ,graduate of the ,royal ,technical ,college at ,aix-la-,chapelle1 ,member of the ,institute of ,naval ,architects1 etc4 #hvo41 #ahs4 net4 ,,building ,,construction4 ,,advanced ,,building ,,construction4 ,by the ,author of ',rivington's' ,notes on ,building ,construction'4 ,with #che ,illustrations4 ,crown #hvo41 #ds4 #f;d4 ,,burrell4--,,building ,,construction4 ,by ,,edward ,j4 ,,burrell1 ,second ,master of the ,people's ,palace ,technical ,school1 ,london4 ,with #cjc ,working ,drawings4 ,crown #hvo41 #bs4 #f;d4 ,,seddon4--,,builder',s ,,work ,,and ,,the ,,building ,,trades4 ,by ,col4 ,h4 ,c4 ,,seddon1 ,r4,e41 ,superintending ,engineer1 ,h4,m4's ,dockyard1 ,portsmouth2 ,examiner in ,building ,construction1 ,science and ,art ,department1 ,south ,kensington2 with numerous ,illustrations4 ,medium #hvo41 #afs4 ,,rivington',s ,,course ,,of ,,building ,,construction4 ,,notes ,,on ,,building ,,construction4 ,arranged to meet the requirements of the syllabus of the ,science and ,art ,department of the ,committee of ,council on ,education1 ,south ,kensington4 ,medium #hvo4 ,part ,i4 ,first ,stage1 or ,elementary ,course4 ,with #eeb ,woodcuts1 #ajs4 #f;d4 ,part ,,ii4 ,commencement of ,second ,stage1 or ,advanced ,course4 ,with #dgi ,woodcuts1 #ajs4 #f;d4 ,part ,,iii4 ,materials4 ,advanced ,course1 and ,course for ,honours4 ,with #ahh ,woodcuts1 #bas4 ,part ,,iv4 ,calculations for ,building ,structures4 ,course for ,honours4 ,with #eig ,woodcuts1 #aes4 ,,electricity ,,and ,,magnetism4 ,,cumming4--,,electricity ,,treated ,,experimentally4 ,for the ,use of ,schools and ,students4 ,by ,,linn,,us ,,cumming1 ,m4,a41 ,assistant ,master in ,rugby ,school4 ,with #bdb ,illustrations4 ,crown #hvo41 #ds4 #f;d4 ,,day4--,,exercises ,,in ,,electrical ,,and ,,magnetic ,,measurements1 with ,answers4 ,by ,r4 ,e4 ,,day4 #abmo41 #cs4 #f;d4 ,,du ,,bois4--,,the ,,magnetic ,,circuit ,,in ,,theory ,,and ,,practice4 ,by ,dr4 ,h4 ,,du ,,bois1 ,privatdocent in the ,university of ,berlin4 ,translated by ,e4 ,,atkinson1 ,ph4,d41 formerly ,professor of ,experimental ,science in the ,staff ,college1 ,sandhurst4 ,with #id ,illustrations4 #hvo41 #abs4 net4 ,,gore4--,,the ,,art ,,of ,,electro-,,metallurgy1 including all known ,processes of ,electro-,deposition4 ,by ,g4 ,,gore1 ,,ll4,d41 ,f4,r4,s4 ,with #ef ,woodcuts4 ,fcp4 #hvo41 #fs4 ,,jenkin4--,,electricity ,,and ,,magnetism4 ,by ,,fleeming ,,jenkin1 ,f4,r4,s4,s41 ,l4 and ,e41 ,m4,i4,c4,e4 ,with #agg ,illustrations4 ,fcp4 #hvo41 #cs4 #f;d4 ,,joubert4--,,elementary ,,treatise ,,on ,,electricity ,,and ,,magnetism4 ,founded on ,,joubert',s ',trait lmentaire d'lectricit'4 ,by ,g4 ,c4 ,,foster1 ,f4,r4,s41 ,quain ,professor of ,physics in ,university ,college1 ,london2 and ,e4 ,,atkinson1 ,ph4,d41 formerly ,professor of ,experimental ,science in the ,staff ,college1 ,sandhurst4 ,with #cha ,illustrations4 ,crown #hvo41 #gs4 #f;d4 ,,larden4--,,electricity ,,for ,,public ,,schools ,,and ,,colleges4 ,by ,w4 ,,larden1 ,m4,a4 ,with #bae ,illustrations1 and a ,series of ,examination ,papers1 with ,answers4 ,crown #hvo41 #fs4 ,,merrifield4--,,magnetism ,,and ,,deviation ,,of ,,the ,,compass4 ,for the ,use of ,students in ,navigation and ,science ,schools4 ,by ,,john ,,merrifield1 ,l4,l4,d41 ,f4,r4,a4,s41 #ahmo41 #bs4 #f;d4 ,,poyser4--,works by ,a4 ,w4 ,,poyser1 ,m4,a41 ,grammar ,school1 ,wisbeck4 ,,magnetism ,,and ,,electricity4 ,with #bce ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,advanced ,,electricity ,,and ,,magnetism4 ,with #cag ,illustrations4 ,crown #hvo41 #ds4 #f;d4 ,,slingo ,,and ,,brooker4--,works by ,w4 ,,slingo and ,a4 ,,brooker4 ,,electrical ,,engineering ,,for ,,electric ,,light ,,artisans ,,and ,,students4 ,with #cdf ,illustrations4 ,crown #hvo41 #abs4 ,,problems ,,and ,,solutions ,,in ,,elementary ,,electricity ,,and ,,magnetism4 ,embracing a ,complete ,set of ,answers to the ,south ,kensington ,papers for the years #ahhe-ahid1 and a ,series of ,original ,questions4 ,with #fg ,original ,illustrations4 ,crown #hvo41 #bs4 ,,tyndall4--,works by ,,john ,,tyndall1 ,d4,c4,l41 ,f4,r4,s4 ,see p4 #bg4 ,,telegraphy ,,and ,,the ,,telephone4 ,,bennett4--,,the ,,telephone ,,systems ,,of ,,continental ,,europe4 ,by ,a4 ,r4 ,,bennett1 ,member of the ,institute of ,electrical ,engineers2 late ,general ,manager in ,scotland of the ,national ,telephone ,company1 and ,general ,manager and ,electrician of the ,mutual and ,new ,telephone ,companies4 ,with #afi ,illustrations4 ,crown #hvo41 #aes4 ,,culley4--,a ,,handbook ,,of ,,practical ,,telegraphy4 ,by ,r4 ,s4 ,,culley1 ,m4,i4,c4,e41 late ,engineer-in-,chief of ,telegraphs to the ,post ,office4 ,with #ace ,woodcuts and #ag ,plates4 #hvo41 #afs4 ,,preece ,,and ,,sivewright4--,,telegraphy4 ,by ,w4 ,h4 ,,preece1 ,c4,b41 ,f4,r4,s41 ,v4,p4,inst41 ,c4,e41 etc41 ,engineer-in-,chief and ,electrician ,post ,office ,telegraphs2 and ,sir ,j4 ,,sivewright1 ,k4,c4,m4,g41 ,general ,manager1 ,south ,african ,telegraphs4 ,with #beh ,woodcuts4 ,fcp4 #hvo41 #fs4 ,,engineering1 ,,strength ,,of ,,materials1 ,,etc4 ,,anderson4--,,the ,,strength ,,of ,,materials ,,and ,,structures3 the ,strength of ,materials as depending on their ,quality and as ascertained by ,testing ,apparatus4 ,by ,sir ,j4 ,,anderson1 ,c4,e41 ,,ll4,d41 ,f4,r4,s4,e4 ,with #ff ,woodcuts4 ,fcp4 #hvo41 #cs4 #f;d4 ,,barry4--,,railway ,,appliances3 a ,description of ,details of ,railway ,construction subsequent to the completion of the ,earthworks and ,structures4 ,by ,,john ,,wolfe ,,barry1 ,c4,b41 ,m4,i4,c4,e4 ,with #bah ,woodcuts4 ,fcp4 #hvo41 #ds4 #f;d4 ,,smith4--,,graphics1 or the ,art of ,calculation by ,drawing ,lines1 applied especially to ,mechanical ,engineering4 ,by ,,robert ,h4 ,,smith1 ,professor of ,engineering1 ,mason ,college1 ,birmingham4 ,part ,i4 ,with separate ,atlas of #bi ,plates containing #ig ,diagrams4 #hvo41 #aes4 ,,stoney4--,,the ,,theory ,,of ,,the ,,stresses ,,on ,,girders ,,and ,,similar ,,structures4 ,with ,practical ,observations on the ,strength and other ,properties of ,materials4 ,by ,,bindon ,b4 ,,stoney1 ,,ll4,d41 ,f4,r4,s41 ,m4,i4,c4,e4 ,with #e ,plates and #adc ,illustrations in the ,text4 ,royal #hvo41 #cfs4 ,,unwin4--,works by ,,william ,,cawthorne ,,unwin1 ,f4,r4,s41 ,b4,s4,c4 ,,the ,,testing ,,of ,,materials ,,of ,,construction4 ,embracing the description of ,testing ,machinery and ,apparatus ,auxiliary to ,mechanical ,testing1 and an ,account of the most ,important ,researches on the ,strength of ,materials4 ,with #ada ,woodcuts and #e ,folding-out ,plates4 #hvo41 #bas4 ,,on ,,the ,,development ,,and ,,transmission ,,of ,,power ,,from ,,central ,,stations3 being the ,howard ,lectures delivered at the ,society of ,arts in #ahic4 ,with #ha ,diagrams4 #hvo41 #ajs4 net4 ,,warren4--,,engineering ,,construction ,,in ,,iron1 ,,steel1 ,,and ,,timber4 ,by ,,william ,,henry ,,warren1 ,challis ,professor of ,civil and ,mechanical ,engineering1 ,university of ,sydney4 ,with #ac ,folding ,plates1 and #cge ,diagrams4 ,royal #hvo41 #afs4 net4 ,,machine ,,drawing ,,and ,,design4 ,,low ,,and ,,bevis4--,a ,,manual ,,of ,,machine ,,drawing ,,and ,,design4 ,by ,,david ,,allan ,,low 7,whitworth ,scholar71 ,m4,i4,mech4,e41 ,head ,master of the ,technical ,school1 ,people's ,palace1 ,london2 and ,,alfred ,,william ,,bevis 7,whitworth ,scholar71 ,m4,i4,mech4,e41 ,director of ,manual ,training to the ,birmingham ,school ,board4 ,with over #gjj ,illustrations4 #hvo41 #gs4 #f;d4 ,,low4--,works by ,,david ,,allan ,,low1 ,head ,master of the ,technical ,school1 ,people's ,palace1 ,london4 ,,improved ,,drawing ,,scales4 #d;d4 in case4 ,,an ,,introduction ,,to ,,machine ,,drawing ,,and ,,design4 ,with #ig ,illustrations and ,diagrams4 ,crown #hvo41 #bs4 ,,unwin4--,,the ,,elements ,,of ,,machine ,,design4 ,by ,w4 ,,cawthorne ,,unwin1 ,f4,r4,s41 ,professor of ,engineering at the ,central ,institute of the ,city and ,guilds of ,london ,institute4 ,part ,i4 ,general ,principles1 ,fastenings1 and ,transmissive ,machinery4 ,with #cjd ,diagrams1 etc4 ,crown #hvo41 #fs4 ,part ,,ii4 ,chiefly on ,engine ,details4 ,with #agd ,woodcuts4 ,crown #hvo41 #ds4 #f;d4 ,,longmans' ,,civil ,,engineering ,,series4 ,edited by the ,author of ',notes on ,building ,construction'4 ,,tidal ,,rivers3 their 7#a7 ,hydraulics1 7#b7 ,improvement1 7#c7 ,navigation4 ,by ,w4 ,h4 ,,wheeler1 ,m4,inst4,c4,e41 author of ',the ,drainage of ,fens and ,low ,lands by ,gravitation and ,steam ,power'4 ,with #ge ,illustrations4 ,medium #hvo41 #afs4 net4 ,,notes ,,on ,,docks ,,and ,,dock ,,construction4 ,by ,c4 ,,colson1 ,m4,inst4,c4,e41 ,assistant ,director of ,works1 ,admiralty4 ,with #cfe ,illustrations4 ,medium #hvo41 #bas4 net4 ,,principles ,,and ,,practice ,,of ,,harbour ,,construction4 ,by ,,william ,,shield1 ,f4,r4,s4,e41 ,m4,inst4,c4,e41 and ,executive ,engineer1 ,national ,harbour of ,refuge1 ,peterhead1 ,n4,b4 ,with #ig ,illustrations4 ,medium #hvo41 #aes4 net4 ,,calculations ,,for ,,engineering ,,structures4 ,by ,t4 ,,claxton ,,fidler1 ,m4,i4,c4,e41 ,professor of ,engineering in the ,university of ,dundee2 ,author of ',a ,practical ,treatise on ,bridge ,construction'4 ,in preparation4 ,a ,,course ,,of ,,civil ,,engineering4 ,by ,l4 ,f4 ,,vernon-,,harcourt1 ,m4,inst4,c4,e41 ,professor of ,civil ,engineering at ,university ,college1 ,london4 ,in preparation4 ,,railway ,,construction4 ,by ,w4 ,h4 ,,mills1 ,m4,i4,c4,e41 ,engineer-in-,chief1 ,great ,northern ,railway1 ,ireland4 ,in preparation4 ,,workshop ,,appliances1 ,,etc4 ,,northcott4--,,lathes ,,and ,,turning1 ,simple1 ,mechanical and ,ornamental4 ,by ,w4 ,h4 ,,northcott4 ,with #cch ,illustrations4 #hvo41 #ahs4 ,,shelley4--,,workshop ,,appliances1 including ,descriptions of some of the ,gauging and ,measuring ,instruments1 ,hand-cutting ,tools1 ,lathes1 ,drilling1 ,plaining1 and other ,machine ,tools used by ,engineers4 ,by ,c4 ,p4 ,b4 ,,shelley1 ,m4,i4,c4,e4 ,with an additional ,chapter on ,milling by ,r4 ,r4 ,,lister4 ,with #cbc ,woodcuts4 ,fcp4 #hvo41 #es4 ,,mineralogy1 ,,metallurgy1 ,,etc4 ,,bauerman4--,works by ,,hilary ,,bauerman1 ,f4,g4,s4 ,,systematic ,,mineralogy4 ,with #cgc ,woodcuts and ,diagrams4 ,fcp4 #hvo41 #fs4 ,,descriptive ,,mineralogy4 ,with #bcf ,woodcuts and ,diagrams4 ,fcp4 #hvo41 #fs4 ,,bloxam ,,and ,,huntington4--,,metals3 their ,properties and ,treatment4 ,by ,c4 ,l4 ,,bloxam and ,a4 ,k4 ,,huntington1 ,professors in ,king's ,college1 ,london4 ,with #acj ,woodcuts4 ,fcp4 #hvo41 #es4 ,,gore4--,,the ,,art ,,of ,,electro-,,metallurgy1 including all known ,processes of ,electro-,deposition4 ,by ,g4 ,,gore1 ,,ll4,d41 ,f4,r4,s4 ,with #ef ,woodcuts4 ,fcp4 #hvo41 #fs4 ,,mitchell4--,a ,,manual ,,of ,,practical ,,assaying4 ,by ,,john ,,mitchell1 ,f4,c4,s4 ,revised1 with the ,recent ,discoveries incorporated4 ,by ,w4 ,,crookes1 ,f4,r4,s4 ,with #bja ,illustrations4 #hvo41 #cas4 #f;d4 ,,rhead4--,,metallurgy4 ,an ,elementary ,text-,book4 ,by ,e4 ,c4 ,,rhead1 ,lecturer on ,metallurgy at the ,municipal ,technical ,school1 ,manchester4 ,with #id ,illustrations4 ,crown #hvo41 #cs4 #f;d4 ,,rutley4--,,the ,,study ,,of ,,rocks3 an ,elementary ,text-book of ,petrology4 ,by ,f4 ,,rutley1 ,f4,g4,s4 ,with #f ,plates and #hh ,woodcuts4 ,fcp4 #hvo41 #ds4 #f;d4 ,,astronomy1 ,,navigation1 ,,etc4 ,,abbott4--,,elementary ,,theory ,,of ,,the ,,tides3 the ,fundamental ,theorems ,demonstrated without ,mathematics and the ,influence on the ,length of the ,day ,discussed4 ,by ,t4 ,k4 ,,abbott1 ,b4,d41 ,fellow and ,tutor1 ,trinity ,college1 ,dublin4 ,crown #hvo41 #bs4 ,,ball4--,works by ,sir ,,robert ,s4 ,,ball1 ,,ll4,d41 ,f4,r4,s4 ,,elements ,,of ,,astronomy4 ,with #acj ,figures and ,diagrams4 ,fcp4 #hvo41 #fs4 #f;d4 ,a ,,class-,,book ,,of ,,astronomy4 ,with #da ,diagrams4 ,fcp4 #hvo41 #as4 #f;d4 ,,brinkley4--,,astronomy4 ,by ,f4 ,,brinkley1 formerly ,astronomer ,royal for ,ireland4 ,re-edited and ,revised by ,j4 ,w4 ,,stubbs1 ,d4,d41 and ,f4 ,,br,,nnow1 ,ph4,d4 ,with #di ,diagrams4 ,crown #hvo41 #fs4 ,,clerke4--,,the ,,system ,,of ,,the ,,stars4 ,by ,,agnes ,m4 ,,clerke4 ,with #f ,plates1 and numerous ,illustrations4 #hvo41 #bas4 ,,goodwin4--,,azimuth ,,tables ,,for ,,the ,,higher ,,declinations4 7,limits of ,declination #bd to #cj1 both inclusive47 ,between the ,parallels of ,latitude #j and #fj4 ,with ,examples of the ,use of the ,tables in ,english and ,french4 ,by ,h4 ,b4 ,,goodwin1 ,naval ,instructor1 ,royal ,navy4 ,royal #hvo41 #gs4 #f;d4 ,,herschel4--,,outlines ,,of ,,astronomy4--,by ,sir ,,john ,f4 ,w4 ,,herschel1 ,bart41 ,k4,h41 etc4 ,with #i ,plates1 and numerous ,diagrams4 #hvo41 #abs4 ,,lowell4--,,mars4 ,by ,,percival ,,lowell1 ,fellow ,american ,academy1 ,member ,royal ,asiatic ,society1 ,great ,britain and ,ireland1 etc4 ,with #bd ,plates4 #hvo41 #abs4 #f;d4 ,,martin4--,,navigation ,,and ,,nautical ,,astronomy4 ,compiled by ,staff ,commander ,w4 ,r4 ,,martin1 ,r4,n4 ,royal #hvo41 #ahs4 ,,merrifield4--,a ,,treatise ,,on ,,navigation4 ,for the ,use of ,students4 ,by ,j4 ,,merrifield1 ,,ll4,d41 ,f4,r4,a4,s41 ,f4,m4,s4 ,with ,charts and ,diagrams4 ,crown #hvo41 #es4 ,,parker4--,,elements ,,of ,,astronomy4 ,with ,numerous ,examples and ,examination ,papers4 ,by ,,george ,w4 ,,parker1 ,m4,a41 of ,trinity ,college1 ,dublin4 ,with #hd ,diagrams4 #hvo41 #es4 net4 ,,webb4--,,celestial ,,objects ,,for ,,common ,,telescopes4 ,by the ,rev4 ,t4 ,w4 ,,webb1 ,m4,a41 ,f4,r4,a4,s4 ,fifth ,edition1 ,revised and greatly ,enlarged by the ,rev4 ,t4 ,e4 ,,espin1 ,m4,a41 ,f4,r4,a4,s4 7,two ,volumes47 ,vol4 ,i41 with ,portrait and a ,reminiscence of the ,author1 #b ,plates1 and numerous ,illustrations4 ,crown #hvo41 #fs4 ,vol4 ,,ii41 with numerous ,illustrations4 ,crown #hvo41 #fs4 #f;d4 ,,works ,,by ,,richard ,a4 ,,proctor4 ,,old ,,and ,,new ,,astronomy4 ,with #ba ,plates and #dgb ,illustrations in the ,text4 #dto41 #bas4 ,,myths ,,and ,,marvels ,,of ,,astronomy4 ,crown #hvo41 #cs4 #f;d4 ,,the ,,moon3 ,her ,motions1 ,aspect1 ,scenery1 and ,physical ,condition4 ,with many ,plates and ,charts1 ,wood ,engravings1 and #b ,lunar ,photographs4 ,crown #hvo41 #es4 ,,the ,,universe ,,of ,,stars3 ,researches into1 and ,new ,views respecting the ,constitution of the ,heavens4 ,with #bb ,charts 7#d ,coloured71 and #bb ,diagrams4 #hvo41 #ajs4 #f;d4 ,,other ,,worlds ,,than ,,ours3 the ,plurality of ,worlds ,studied ,under the ,light of ,recent ,scientific ,researches4 ,with #ad ,illustrations2 ,map1 ,charts1 etc4 ,crown #hvo41 #cs4 #f;d4 ,,the ,,orbs ,,around ,,us2 ,essays on the ,moon and ,planets1 ,meteors and ,comets1 the ,sun and ,coloured ,pairs of ,suns4 ,crown #hvo41 #cs4 #f;d4 ,,light ,,science ,,for ,,leisure ,,hours3 ,familiar ,essays on ,scientific ,subjects4 ,natural ,phenomena1 etc4 #c vols41 crown #hvo41 #es4 each4 ,,the ,,expanse ,,of ,,heaven3 ,essays on the ,wonders of the ,firmament4 ,crown #hvo41 #cs4 #f;d4 ,,other ,,suns ,,than ,,ours3 a ,series of ,essays on ,suns--,old1 ,young1 and ,dead4 ,with other ,science ,gleanings4 ,two ,essays on ,whist1 and ,correspondence with ,sir ,john ,herschel4 ,with #i ,star-,maps and ,diagrams4 ,crown #hvo41 #cs4 #f;d4 ,,half-,,hours ,,with ,,the ,,telescope3 a ,popular ,guide to the ,use of the ,telescope as a means of ,amusement and ,instruction4 ,with #g ,plates4 ,fcp4 #hvo41 #bs4 #f;d4 ,,new ,,star ,,atlas ,,for ,,the ,,library1 the ,school1 and the ,observatory1 in ,twelve ,circular ,maps 7with ,two ,index-,plates74 ,with an ,introduction on the ,study of the ,stars4 ,illustrated by #i ,diagrams4 ,crown #hvo41 #es4 ,,the ,,southern ,,skies3 a ,plain and ,easy ,guide to the ,constellations of the ,southern ,hemisphere4 ,showing in #ab ,maps the position of the principal ,star-,groups night after night throughout the year4 ,with an ,introduction and a separate ,explanation of each ,map4 ,true for every ,year4 #dto41 #es4 ,,half-,,hours ,,with ,,the ,,stars3 a ,plain and ,easy ,guide to the ,knowledge of the ,constellations4 ,showing in #ab ,maps the position of the principal ,star-,groups night after night throughout the year4 ,with ,introduction and a separate ,explanation of each ,map4 ,true for every ,year4 #dto41 #cs4 #f;d4 ,,larger ,,star ,,atlas ,,for ,,observers ,,and ,,students4 ,in ,twelve ,circular ,maps1 showing #fjjj ,stars1 #aejj ,double ,stars1 ,nebul1 etc4 ,with #b ,index-,plates4 ,folio1 #aes4 ,,the ,,stars ,,in ,,their ,,seasons3 an ,easy ,guide to a ,knowledge of the ,star-,groups4 ,in #ab ,large ,maps4 ,imperial #hvo41 #es4 ,,rough ,,ways ,,made ,,smooth4 ,familiar ,essays on ,scientific ,subjects4 ,crown #hvo41 #cs4 #f;d4 ,,pleasant ,,ways ,,in ,,science4 ,crown #hvo41 #cs4 #f;d4 ,,nature ,,studies4 ,by ,r4 ,a4 ,,proctor1 ,,grant ,,allen1 ,a4 ,,wilson1 ,t4 ,,foster1 and ,e4 ,,clodd4 ,crown #hvo41 #cs4 #f;d4 ,,leisure ,,readings4 ,by ,r4 ,a4 ,,proctor1 ,e4 ,,clodd1 ,a4 ,,wilson1 ,t4 ,,foster1 and ,a4 ,c4 ,,ranyard4 ,crown #hvo41 #cs4 #f;d4 ,,manufactures1 ,,technology1 ,,etc4 ,,bell4--,,jacquard ,,weaving ,,and ,,designing4 ,by ,f4 ,t4 ,,bell1 ,medallist in ,honours and ,certificated ,teacher in ',linen ,manufacturing' and in ',weaving and ,pattern ,designing1' ,city and ,guilds of ,london ,institute4 ,with #aii ,diagrams4 #hvo41 #abs4 net4 ,,cross ,,and ,,bevan4--,,cellulose3 an ,outline of the ,chemistry of the ,structural ,elements of ,plants4 ,with ,reference to their ,natural ,history and ,industrial ,uses4 ,by ,,cross and ,,bevan 7,c4 ,f4 ,cross1 ,e4 ,j4 ,bevan1 and ,c4 ,beadle74 ,with #ad ,plates4 ,crown #hvo41 #abs4 net4 ,,taylor4--,,cotton ,,weaving ,,and ,,designing4 ,by ,,john ,t4 ,,taylor4 ,with #cgc ,diagrams4 ,crown #hvo41 #gs4 #f;d4 net4 ,,lupton4--,,mining4 ,an ,elementary ,treatise on the ,getting of ,minerals4 ,by ,,arnold ,,lupton1 ,m4,i4,c4,e41 ,f4,g4,s41 etc4 ,with #eif ,diagrams and ,illustrations4 ,crown #hvo41 #is4 net4 ,,watts4--,,an ,,introductory ,,manual ,,for ,,sugar ,,growers4 ,by ,,francis ,,watts1 ,f4,c4,s41 ,f4,i4,c4 ,with #bj ,illustrations4 ,crown #hvo41 #fs4 ,,physiography ,,and ,,geology4 ,,bird4--,works by ,,charles ,,bird1 ,b4,a4 ,,elementary ,,geology4 ,with ,geological ,map of the ,british ,isles1 and #bdg ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,advanced ,,geology4 ,a ,manual for ,students in ,advanced ,classes and for ,general ,readers4 ,with over #cjj ,illustrations1 a ,geological ,map of the ,british ,isles 7coloured71 and a set of ,questions for ,examination4 ,crown #hvo41 #gs4 #f;d4 ,,green4--,,physical ,,geology ,,for ,,students ,,and ,,general ,,readers4 ,with ,illustrations4 ,by ,a4 ,h4 ,,green1 ,m4,a41 ,f4,g4,s4 #hvo41 #bas4 ,,thornton4--,works by ,j4 ,,thornton1 ,m4,a4 ,,elementary ,,physiography3 an ,introduction to the ,study of ,nature4 ,with #ab ,maps and #bdg ,illustrations4 ,with ,appendix on ,astronomical ,instruments and ,measurements4 ,crown #hvo41 #bs4 #f;d4 ,,advanced ,,physiography4 ,with #f ,maps and #ahj ,illustrations4 ,crown #hvo41 #ds4 #f;d4 ,,health ,,and ,,hygiene4 ,,bray4--,,physiology ,,and ,,the ,,laws ,,of ,,health1 in1 ,easy ,lessons for ,schools4 ,by ,mrs4 ,,charles ,,bray4 ,fcp4 #hvo41 #as4 ,,brodribb4--,,manual ,,of ,,health ,,and ,,temperance4 ,by ,t4 ,,brodribb1 ,m4,a4 ,with ,extracts from ,gough's ',temperance ,orations'4 ,revised and ,edited by the ,rev4 ,w4 ,,ruthven ,,pym1 ,m4,a41 ,member of the ,sheffield ,school ,board4 ,crown #hvo41 #as4 #f;d4 ,,buckton4--,,health ,,in ,,the ,,house2 ,twenty-five ,lectures on ,elementary ,physiology4 ,by ,mrs4 ,c4 ,m4 ,,buckton4 ,with #da ,woodcuts and ,diagrams4 ,crown #hvo41 #bs4 ,,corfield4--,,the ,,laws ,,of ,,health4 ,by ,w4 ,h4 ,,corfield1 ,m4,a41 ,m4,d4 ,fcp4 #hvo41 #as4 #f;d4 ,,frankland4--,,micro-,,organisms ,,in ,,water1 ,,their ,,significance1 ,,identification1 ,,and ,,removal4 ,together with an ,account of the ,bacteriological ,methods ,involved in their ,investigation4 ,specially ,designed for the ,use of those connected with the ,sanitary ,aspects of ,water ,supply4 ,by ,professor ,,percy ,,frankland1 ,ph4,d41 ,b4,sc4 7,lond471 ,f4,r4,s41 ,fellow of the ,chemical ,society2 and ,mrs4 ,,percy ,,frankland4 ,with #b ,plates and numerous ,diagrams4 #hvo41 #afs4 net4 ,,notter ,,and ,,firth4--,,hygiene4 ,by ,j4 ,l4 ,,notter1 ,m4,a41 ,m4,d41 and ,r4 ,h4 ,,firth1 ,f4,r4,c4,s4 ,with #ie ,illustrations4 ,crown #hvo41 #cs4 #f;d4 ,,poore4--,,essays ,,on ,,rural ,,hygiene4 ,by ,,george ,,vivian ,,poore1 ,m4,d4 ,crown #hvo41 #fs4 #f;d4 ,,wilson4--,a ,,manual ,,of ,,health-,,science3 adapted for use in ,schools and ,colleges1 and suited to the requirements of ,students preparing for the ,examinations in ,hygiene of the ,science and ,art ,department1 etc4 ,by ,,andrew ,,wilson1 ,f4,r4,s4,e41 ,f4,l4,s41 etc4 ,with #gd ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,natural ,,history1 ,,evolution1 ,,etc4 ,,clodd4--,works by ,,edward ,,clodd4 ,,the ,,story ,,of ,,creation3 ,a ,plain ,account of ,evolution4 ,with #gg ,illustrations4 ,crown #hvo41 #cs4 #f;d4 ,a ,,primer ,,of ,,evolution3 being a ,popular ,abridged ,edition of ',the ,story of ,creation'4 ,with ,illustrations4 ,fcp4 #hvo41 #as4 #f;d4 ,,furneaux4--,works by ,,william ,s4 ,,furneaux4 ,,the ,,outdoor ,,world2 or1 ,the ,young ,collector's ,handbook4 ,with #ah ,plates1 #af of which are coloured1 and #edi ,illustrations in the ,text4 ,crown #hvo41 #gs4 #f;d4 ,,butterflies ,,and ,,moths 7,british74 ,with #ab ,coloured ,plates and #bda ,illustrations in the ,text4 #abs4 #f;d4 ,,life ,,in ,,ponds ,,and ,,streams4 ,with #h ,coloured ,plates and #caa ,illustrations in the ,text4 ,crown #hvo41 #abs4 #f;d4 ,,hudson4--,,british ,,birds4 ,by ,w4 ,h4 ,,hudson1 ,c4,m4,z4,s4 ,with #h ,coloured ,plates from ,original ,drawings by ,a4 ,,thorburn1 and #h ,plates and #ajj ,figures in black and white from ,original ,drawings by ,c4 ,e4 ,,lodge1 and #c ,illustrations from ,photographs by ,r4 ,b4 ,,lodge4 ,crown #hvo41 #abs4 #f;d4 ,,romanes4--,works by ,,george ,,john ,,romanes1 ,,ll4,d41 ,f4,r4,s4 ,,darwin1 ,,and ,,after ,,darwin3 an ,exposition of the ,darwinian ,theory1 and a ,discussion on ,post-,darwinian ,questions4 ,part ,i4 ,,the ,,darwinian ,,theory4 ,with ,portrait of ,darwin and #abe ,illustrations4 ,crown #hvo41 #ajs4 #f;d4 ,part ,,ii4 ,,post-,,darwinian ,,questions3 ,heredity and ,utility4 ,with ,portrait of the ,author and #e ,illustrations4 ,crown #hvo41 #ajs4 #f;d4 ,,an ,,examination ,,of ,,weismannism4 ,crown #hvo41 #fs4 ,,medicine ,,and ,,surgery4 ,,ashby ,,and ,,wright4--,,the ,,diseases ,,of ,,children1 ,,medical ,,and ,,surgical4 ,by ,,henry ,,ashby1 ,m4,d41 ,lond41 ,f4,r4,c4,p41 and ,g4 ,a4 ,,wright1 ,b4,a41 ,m4,b41 ,oxon41 ,f4,r4,c4,s41 ,eng4 ,with #aib ,illustrations4 #hvo41 #bes4 ,,bennett4--,works by ,,william ,h4 ,,bennett1 ,f4,r4,c4,s41 ,surgeon to ,st4 ,george's ,hospital4 ,,clinical ,,lectures ,,on ,,varicose ,,veins ,,of ,,the ,,lower ,,extremities4 ,with #c ,plates4 #hvo41 #fs4 ,,on ,,varicocele2 ,a ,,practical ,,treatise4 ,with #d ,tables and a ,diagram4 #hvo41 #es4 ,,clinical ,,lectures ,,on ,,abdominal ,,hernia3 chiefly in relation to ,treatment1 including the ,radical ,cure4 ,with #ab ,diagrams in the ,text4 #hvo41 #hs4 #f;d4 ,,clarke4--,,post-,,mortem ,,examinations ,,in ,,medico-,,legal ,,and ,,ordinary ,,cases4 ,with ,special ,chapters on the ,legal ,aspects of ,post-,mortems1 and on ,certificates of ,death4 ,by ,j4 ,,jackson ,,clarke1 ,m4,b4 7,lond471 ,f4,r4,c4,s4 ,fcp4 #hvo41 #bs4 #f;d4 ,,coats4--,a ,,manual ,,of ,,pathology4 ,by ,,joseph ,,coats1 ,m4,d41 ,professor of ,pathology in the ,university of ,glasgow4 ,third ,edition4 ,revised throughout4 ,with #ejg ,illustrations4 #hvo41 #cas4 #f;d4 ,,cooke4--,works by ,,thomas ,,cooke1 ,f4,r4,c4,s4 ,eng41 ,b4,a41 ,b4,sc41 ,m4,d41 ,paris4 ,,tablets ,,of ,,anatomy4 ,being a ,synopsis of ,demonstrations given in the ,westminster ,hospital ,medical ,school in the years #ahga-ge4 ,tenth ,thousand1 being a selection of the ,tablets believed to be most useful to ,students generally4 ,post #dto41 #ajs4 #f;d4 ,,aphorisms ,,in ,,applied ,,anatomy ,,and ,,operative ,,surgery4 ,including #ajj ,typical viva voce ,questions on ,surface ,marking1 etc4 ,crown #hvo41 #cs4 #f;d4 ,,dissection ,,guides4 ,aiming at ,extending and ,facilitating such ,practical work in ,anatomy as will be specially useful in connection with an ordinary ,hospital ,curriculum4 #hvo41 #ajs4 #f;d4 ,,dickinson4--,works by ,w4 ,,howship ,,dickinson1 ,m4,d4 ,cantab41 ,f4,r4,c4,p4 ,,on ,,renal ,,and ,,urinary ,,affections4 ,complete in ,three ,parts1 #hvo41 with #ab ,plates and #abb ,woodcuts4 ,price #c #ds4 #f;d4 cloth4 asterism ,the ,parts can also be had separately1 each complete in itself1 as follows3-- ,part ,i4 ,diabetes1 #ajs4 #f;d4 sewed1 #abs4 cloth4 ,part ,,ii4 ,albuminuria1 #a sewed1 #a #as4 cloth4 ,part ,,iii4 ,miscellaneous ,affections of the ,kidneys and ,urine1 #a #ajs4 sewed1 #a #aas4 #f;d4 cloth4 ,,the ,,tongue ,,as ,,an ,,indication ,,of ,,disease2 being the ,lumleian ,lectures delivered at the ,royal ,college of ,physicians in ,march1 #ahhh4 #hvo41 #gs4 #f;d4 ,,the ,,harveian ,,oration ,,on ,,harvey ,,in ,,ancient ,,and ,,modern ,,medicine4 ,crown #hvo41 #bs4 #f;d4 ,,occasional ,,papers ,,on ,,medical ,,subjects1 #ahee-ahif4 #hvo41 #abs4 ,,erichsen4--,,the ,,science ,,and ,,art ,,of ,,surgery2 a ,treatise on ,surgical ,injuries1 ,diseases1 and ,operations4 ,tenth ,edition4 ,revised by the late ,,marcus ,,beck1 ,m4,s41 and ,m4,b4 7,lond471 ,f4,r4,c4,s41 and by ,,raymond ,,johnson1 ,m4,b4 and ,b4,s4 7,lond471 ,f4,r4,c4,s4 ,illustrated by nearly #ajjj ,engravings on ,wood4 #b vols41 royal #hvo41 #bhs4 ,,garrod4--,works by ,,sir ,,alfred ,,baring ,,garrod1 ,m4,d41 ,f4,r4,s41 etc4 ,a ,,treatise ,,on ,,gout ,,and ,,rheumatic ,,gout 7,,rheumatoid ,,arthritis74 ,with #f ,plates1 comprising #ba ,figures 7#ad ,coloured71 and #bg ,illustrations engraved on ,wood4 #hvo41 #bas4 ,,the ,,essentials ,,of ,,materia ,,medica ,,and ,,therapeutics4 ,revised and ,edited1 under the supervision of the ,author1 by ,,nestor ,,tirard1 ,m4,d41 ,lond41 ,f4,r4,c4,p41 ,professor of ,materia ,medica and ,therapeutics in ,king's ,college1 ,london1 etc4 ,crown #hvo41 #abs4 #f;d4 ,,gray4--,,anatomy1 ,,descriptive ,,and ,,surgical4 ,by ,,henry ,,gray1 ,f4,r4,s41 late ,lecturer on ,anatomy at ,st4 ,george's ,hospital4 ,the ,thirteenth ,edition1 re-edited by ,t4 ,,pickering ,,pick1 ,surgeon to ,st4 ,george's ,hospital2 ,member of the ,court of ,examiners1 ,royal ,college of ,surgeons of ,england4 ,with #fcf large ,woodcut ,illustrations1 a large proportion of which are coloured1 the ,arteries being coloured red1 the ,veins blue1 and the ,nerves yellow4 ,the attachments of the muscles to the bones1 in the section on ,osteology1 are also shown in coloured outline4 ,royal #hvo41 #cfs4 ,,halliburton4--,works by ,w4 ,d4 ,,halliburton1 ,m4,d41 ,f4,r4,s41 ,m4,r4,c4,p4 ,a ,,text-,,book ,,of ,,chemical ,,physiology ,,and ,,pathology4 ,with #ajd ,illustrations4 #hvo4 #bhs4 ,,essentials ,,of ,,chemical ,,physiology4 ,second ,edition4 #hvo41 #es4 ,,lang4--,,the ,,methodical ,,examination ,,of ,,the ,,eye4 ,being ,part ,i4 of a ,guide to the ,practice of ,ophthalmology for ,students and ,practitioners4 ,by ,,william ,,lang1 ,f4,r4,c4,s41 ,eng41 ,surgeon to the ,royal ,london ,ophthalmic ,hospital1 ,moorfields1 etc4 ,with #ae ,illustrations4 ,crown #hvo41 #cs4 #f;d4 ,,liveing4--,works by ,,robert ,,liveing1 ,m4,a4 and ,m4,d4 ,cantab41 ,f4,r4,c4,p41 ,lond41 etc41 ,physician to the ,department for ,diseases of the ,skin at the ,middlesex ,hospital1 etc4 ,,handbook ,,on ,,diseases ,,of ,,the ,,skin4 ,with especial reference to ,diagnosis and ,treatment4 ,fcap4 #hvo41 #es4 ,,elephantiasis ,,gr,,corum1 ,,or ,,true ,,leprosy2 ,being the ,goulstonian ,lectures for #ahgc4 ,cr4 #hvo41 #ds4 #f;d4 ,,longmore4--,works by ,surgeon-,general ,sir ,t4 ,,longmore 7,retired71 ,c4,b41 ,f4,r4,c4,s4 ,,the ,,illustrated ,,optical ,,manual2 ,,or1 ,,handbook ,,of ,,instructions ,,for ,,the ,,guidance ,,of ,,surgeons ,,in ,,testing ,,quality ,,and ,,range ,,of ,,vision1 ,,and ,,in ,,distinguishing ,,and ,,dealing ,,with ,,optical ,,defects ,,in ,,general4 ,illustrated by #gd ,drawings and ,diagrams by ,inspector-,general ,dr4 ,,macdonald1 ,r4,n41 ,f4,r4,s41 ,c4,b4 #hvo41 #ads4 ,,gunshot ,,injuries4 ,their ,history1 ,characteristic ,features1 ,complications1 and ,general ,treatment2 with ,statistics concerning them as they have been met with in ,warfare4 ,with #gh ,illustrations4 #hvo41 #cas4 #f;d4 ,,luff4--,,text-,,book ,,of ,,forensic ,,medicine ,,and ,,toxicology4 ,by ,,arthur ,p4 ,,luff1 ,m4,d41 ,b4,sc4 7,lond471 ,physician in ,charge of ,out-,patients and ,lecturer on ,medical ,jurisprudence and ,toxicology in ,st4 ,mary's ,hospital2 ,examiner in ,forensic ,medicine in the ,university of ,london2 ,external ,examiner in ,forensic ,medicine in the ,victoria ,university2 ,official ,analyst to the ,home ,office4 ,with numerous ,illustrations4 #b vols41 crown #hvo41 #bds4 ,,newman4--,,on ,,the ,,diseases ,,of ,,the ,,kidney ,,amenable ,,to ,,surgical ,,treatment4 ,lectures to ,practitioners4 ,by ,,david ,,newman1 ,m4,d41 ,surgeon to the ,western ,infirmary ,out-,door ,department2 ,pathologist and ,lecturer on ,pathology at the ,glasgow ,royal ,infirmary2 ,examiner in ,pathology in the ,university of ,glasgow2 ,vice-,president ,glasgow ,pathological and ,clinical ,society4 #hvo41 #afs4 ,,owen4--,a ,,manual ,,of ,,anatomy ,,for ,,senior ,,students4 ,by ,,edmund ,,owen1 ,m4,b41 ,f4,r4,s4,c41 ,senior ,surgeon to the ,hospital for ,sick ,children1 ,great ,ormond ,street1 ,surgeon to ,st4 ,mary's ,hospital1 ,london1 and co-,lecturer on ,surgery1 late ,lecturer on ,anatomy in its ,medical ,school4 ,with #baj ,illustrations4 ,crown #hvo41 #abs4 #f;d4 ,,poole4--,,cookery ,,for ,,the ,,diabetic4 ,by ,w4 ,h4 and ,mrs4 ,,poole4 ,with ,preface by ,dr4 ,,pavy4 ,fcap4 #hvo41 #bs4 #f;d4 ,,quain4--,a ,,dictionary ,,of ,,medicine2 ,including ,general ,pathology1 ,general ,therapeutics1 ,hygiene1 and the ,diseases of ,women and ,children4 ,by ,various ,writers4 ,edited by ,,richard ,,quain1 ,bart41 ,m4,d4 ,lond41 ,,ll4,d4 ,edin41 7,hon47 ,f4,r4,s41 ,physician ,extraordinary to ,h4,m4 the ,queen1 ,president of the ,general ,medical ,council1 ,member of the ,senate of the ,university of ,london1 etc4 ,assisted by ,,frederick ,,thomas ,,roberts1 ,m4,d4 ,lond41 ,b4,sc41 ,fellow of the ,royal ,college of ,physicians1 ,fellow of ,university ,college1 ,professor of ,materia ,medica and ,therapeutics1 ,university ,college1 c42 and ,j4 ,,mitchell ,,bruce1 ,m4,a4 ,abdn41 ,m4,d4 ,lond41 ,fellow of the ,royal ,college of ,physicians of ,london1 ,physician and ,lecturer on the ,principles and ,practice of ,medicine1 ,charing ,cross ,hospital1 c4 ,new ,edition1 ,revised throughout and ,enlarged4 ,in #b ,vols41 medium #hvo41 cloth1 red edges1 price #djs4 net4 ,,quain4--,,quain',s 7,,jones7 ,,elements ,,of ,,anatomy4 ,the ,tenth ,edition4 ,edited by ,,edward ,,albert ,,sch,,fer1 ,f4,r4,s41 ,professor of ,physiology and ,histology in ,university ,college1 ,london2 and ,,george ,,dancer ,,thane1 ,professor of ,anatomy in ,university ,college1 ,london4 ,in #c ,vols4 asterism ,the several parts of this work form ,,complete ,,text-,,books ,,of ,,their ,,respective ,,subjects4 ,they can be obtained separately as follows3-- ,,vol4 ,i41 ,,part ,i4 ,,embryology4 ,by ,e4 ,a4 ,,sch,,fer1 ,f4,r4,s4 ,with #bjj ,illustrations4 ,royal #hvo41 #is4 ,,vol4 ,i41 ,,part ,,ii4 ,,general ,,anatomy ,,or ,,histology4 ,by ,e4 ,a4 ,,sch,,fer1 ,f4,r4,s4 ,with #bia ,illustrations4 ,royal #hvo41 #abs4 #f;d4 ,,vol4 ,,ii41 ,,part ,i4 ,,osteology4 ,by ,g4 ,d4 ,,thane4 ,with #afh ,illustrations4 ,royal #hvo41 #is4 ,,vol4 ,,ii41 ,,part ,,ii4 ,,arthrology--,,myology--,,angeiology4 ,by ,g4 ,d4 ,,thane4 ,with #bee ,illustrations4 ,royal #hvo41 #ahs4 ,,vol4 ,,iii41 ,,part ,i4 ,,the ,,spinal ,,cord ,,and ,,brain4 ,by ,e4 ,a4 ,,sch,,fer1 ,f4,r4,s4 ,with #aci ,illustrations4 ,royal #hvo41 #abs4 #f;d4 ,,vol4 ,,iii41 ,,part ,,ii4 ,,the ,,nerves4 ,by ,g4 ,d4 ,,thane4 ,with #ajb ,illustrations4 ,royal #hvo41 #is4 ,,vol4 ,,iii41 ,,part ,,iii4 ,,the ,,organs ,,of ,,the ,,senses4 ,by ,e4 ,a4 ,,sch,,fer1 ,f4,r4,s4 ,with #agh ,illustrations4 ,royal #hvo41 #is4 ,,vol4 ,,iii41 ,,part ,,iv4 ,,splanchnology4 ,by ,e4 ,a4 ,,sch,,fer1 ,f4,r4,s41 and ,,johnson ,,symington1 ,m4,d4 ,with #ccg ,illustrations4 ,royal #hvo41 #afs4 ,,appendix4 ,,superficial ,,and ,,surgical ,,anatomy4 ,by ,professor ,g4 ,d4 ,,thane and ,professor ,r4 ,j4 ,,godlee1 ,m4,s4 ,with #bi ,illustrations4 ,royal #hvo41 #fs4 #f;d4 ,,sch,,fer4--,,the ,,essentials ,,of ,,histology4 ,descriptive and ,practical4 ,for the ,use of ,students4 ,by ,e4 ,a4 ,,sch,,fer1 ,f4,r4,s41 ,jodrell ,professor of ,physiology in ,university ,college1 ,london2 ,editor of the ,histological ,portion of ,quain's ',anatomy'4 ,illustrated by more than #cjj ,figures1 many of which are new4 #hvo41 #gs4 #f;d4 7,interleaved1 #ajs47 ,,schenk4--,,manual ,,of ,,bacteriology4 ,for ,practitioners and ,students4 ,with especial reference to ,practical ,methods4 ,by ,dr4 ,s4 ,l4 ,,schenk1 ,professor 7,extraordinary7 in the ,university of ,vienna4 ,translated from the ,german1 with an ,appendix1 by ,w4 ,r4 ,,dawson1 ,b4,a41 ,m4,d41 ,univ4 ,dub42 late ,university ,travelling ,prizeman in ,medicine4 ,with #ajj ,illustrations1 some of which are coloured4 #hvo41 #ajs4 net4 ,,smale ,,and ,,colyer4 ,,diseases ,,and ,,injuries ,,of ,,the ,,teeth1 including ,pathology and ,treatment3 a ,manual of ,practical ,dentistry for ,students and ,practitioners4 ,by ,,morton ,,smale ,m4,r4,c4,s41 ,l4,s4,a41 ,l4,d4,s41 ,dental ,surgeon to ,st4 ,mary's ,hospital1 ,dean of the ,school1 ,dental ,hospital of ,london1 etc42 and ,j4 ,f4 ,,colyer1 ,l4,r4,c4,p41 ,m4,r4,c4,s41 ,l4,d4,s41 ,assistant ,dental ,surgeon to ,charing ,cross ,hospital1 and ,assistant ,dental ,surgeon to the ,dental ,hospital of ,london4 ,with #ccd ,illustrations4 ,large ,crown #hvo41 #aes4 ,,smith 7,h4 ,f474 ,,the ,,handbook ,,for ,,midwives4 ,by ,,henry ,,fly ,,smith1 ,b4,a41 ,m4,b4 ,oxon41 ,m4,r4,c4,s4 ,with #da ,woodcuts4 ,crown #hvo41 price #es4 ,,steel4--,works by ,,john ,,henry ,,steel1 ,f4,r4,c4,v4,s41 ,f4,z4,s41 ,a4,v4,d4 ,a ,,treatise ,,on ,,the ,,diseases ,,of ,,the ,,dog2 being a ,manual of ,canine ,pathology4 ,especially adapted for the use of ,veterinary ,practitioners and ,students4 #hh ,illustrations4 #hvo41 #ajs4 #f;d4 ,a ,,treatise ,,on ,,the ,,diseases ,,of ,,the ,,ox2 being a ,manual of ,bovine ,pathology4 ,especially adapted for the use of ,veterinary ,practitioners and ,students4 #b ,plates and #aag ,woodcuts4 #hvo41 #aes4 ,a ,,treatise ,,on ,,the ,,diseases ,,of ,,the ,,sheep2 being a ,manual of ,ovine ,pathology for the use of ,veterinary ,practitioners and ,students4 ,with ,coloured ,plate and #ii ,woodcuts4 #hvo41 #abs4 ,,outlines ,,of ,,equine ,,anatomy2 a ,manual for the use of ,veterinary ,students in the ,dissecting ,room4 ,crown #hvo41 #gs4 #f;d4 ',,stonehenge4'--,,the ,,dog ,,in ,,health ,,and ,,disease4 ,by ',,stonehenge'4 ,with #hd ,wood ,engravings4 ,square ,crown #hvo41 #gs4 #f;d4 ,,waller4--,,an ,,introduction ,,to ,,human ,,physiology4 ,by ,,augustus ,d4 ,,waller1 ,m4,d41 ,lecturer on ,physiology at ,st4 ,mary's ,hospital ,medical ,school1 ,london2 late ,external ,examiner at the ,victorian ,university4 ,second ,edition1 ,revised4 ,with #cje ,illustrations4 #hvo41 #ahs4 ,,weichselbaum4--,,the ,,elements ,,of ,,pathological ,,histology4 ,with ,special ,reference to ,practical ,methods4 ,by ,dr4 ,,anton ,,weichselbaum1 ,professor of ,pathology in the ,university of ,vienna4 ,translated by ,w4 ,r4 ,,dawson1 ,m4,d4 7,dub471 ,demonstrator of ,pathology in the ,royal ,college of ,surgeons1 ,ireland1 late ,medical ,travelling ,prizeman of ,dublin ,university1 c4 ,with #bba ,figures1 partly in ,colours1 a ,cromo-lithographic ,plate1 and #g ,photographic ,plates4 ,royal #hvo41 #bas4 net4 ,,wilks ,,and ,,moxon4--,,lectures ,,on ,,pathological ,,anatomy4 ,by ,,samuel ,,wilks1 ,m4,d41 ,f4,r4,s41 ,consulting ,physician to1 and formerly ,lecturer on ,medicine and ,pathology at ,guy's ,hospital1 and the late ,,walter ,,moxon1 ,m4,d41 ,f4,r4,c4,p41 ,physician to1 and some time ,lecturer on ,pathology at ,guy's ,hospital4 ,third ,edition1 thoroughly ,revised4 ,by ,,samuel ,,wilks1 ,m4,d41 ,,ll4,d41 ,f4,r4,s4 #hvo41 #ahs4 ,,youatt4--,works by ,,william ,,youatt4 ,,the ,,horse4 ,revised and ,enlarged by ,w4 ,,watson1 ,m4,r4,c4,v4,s4 ,with #eb ,woodcuts4 #hvo41 #gs4 #f;d4 ,,the ,,dog4 ,revised and ,enlarged4 ,with #cc ,woodcuts4 #hvo41 #fs4 ,,physiology1 ,,biology1 ,,etc4 ,,ashby4--,,notes ,,on ,,physiology1 for the ,use of ,students ,preparing for ,examination4 ,by ,,henry ,,ashby1 ,m4,d4 ,with #ada ,illustrations4 ,fcp4 #hvo41 #es4 ,,barnett4--,,the ,,making ,,of ,,the ,,body3 a ,children's ,book on ,anatomy and ,physiology1 for ,school and ,home ,use4 ,by ,mrs4 ,s4 ,a4 ,,barnett4 ,with #aac ,illustrations4 ,crown #hvo41 #as4 #i;d4 ,,bidgood4--,a ,,course ,,of ,,practical ,,elementary ,,biology4 ,by ,,john ,,bidgood1 ,b4,sc41 ,f4,l4,s4 ,with #bbf ,illustrations4 ,crown #hvo41 #ds4 #f;d4 ,,bray4--,,physiology ,,and ,,the ,,laws ,,of ,,health1 in ,easy ,lessons for ,schools4 ,by ,mrs4 ,,charles ,,bray4 ,fcp4 #hvo41 #as4 ,,frankland4--,,micro-,,organisms ,,in ,,water4 ,together with an ,account of the ,bacteriological ,methods involved in their ,investigation4 ,specially designed for the use of those connected with the ,sanitary ,aspects of ,water-,supply4 ,by ,,percy ,,frankland1 ,ph4,d41 ,b4,sc4 7,lond471 ,f4,r4,s41 and ,mrs4 ,,percy ,,frankland4 ,with #b ,plates and ,numerous ,diagrams4 #hvo41 #afs4 net4 ,,furneaux4--,,human ,,physiology4 ,by ,w4 ,,furneaux1 ,f4,r4,g4,s4 ,with #bah ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,hudson ,,and ,,gosse4--,,the ,,rotifera1 or ',,wheel-,,animalcules'4 ,by ,c4 ,t4 ,,hudson1 ,,ll4,d41 and ,p4 ,h4 ,,gosse1 ,f4,r4,s4 ,with #cj ,coloured and #d ,uncoloured ,plates4 ,in #f ,parts4 #dto41 #ajs4 #f;d4 each2 ,supplement #abs4 #f;d4 ,complete in #b vols41 with ,supplement1 #dto41 #d #ds4 ,,macalister4--,works by ,,alexander ,,macalister1 ,m4,d4 ,,zoology ,,and ,,morphology ,,of ,,vertebrata4 #hvo41 #ajs4 #f;d4 ,,zoology ,,of ,,the ,,invertebrate ,,animals4 ,with #ei ,diagrams4 ,fcp4 #hvo41 #as4 #f;d4 ,,zoology ,,of ,,the ,,vertebrate ,,animals4 ,with #gg ,diagrams4 ,fcp4 #hvo41 #as4 #f;d4 ,,morgan4--,,animal ,,biology3 an ,elementary ,text-,book4 ,by ,c4 ,,lloyd ,,morgan4 ,with numerous ,illustrations4 ,crown #hvo41 #hs4 #f;d4 ,,schenk4--,,manual ,,of ,,bacteriology1 for ,practitioners and ,students1 with ,especial ,reference to ,practical ,methods4 ,by ,dr4 ,s4 ,l4 ,,schenk4 ,with #ajj ,illustrations1 some of which are ,coloured4 #hvo41 #ajs4 net4 ,,thornton4--,,human ,,physiology4 ,by ,,john ,,thornton1 ,m4,a4 ,with #bfg ,illustrations1 some ,coloured4 ,crown #hvo41 #fs4 ,,botany4 ,,aitken4--,,elementary ,,text-,,book ,,of ,,botany4 ,for the use of ,schools4 ,by ,,edith ,,aitken1 late ,scholar of ,girton ,college4 ,with over #djj ,diagrams4 ,crown #hvo41 #ds4 #f;d4 ,,bennett ,,and ,,murray4--,,handbook ,,of ,,cryptogamic ,,botany4 ,by ,,alfred ,w4 ,,bennett1 ,m4,a41 ,b4,sc41 ,f4,l4,s41 ,lecturer on ,botany at ,st4 ,thomas's ,hospital2 and ,,george ,,murray1 ,f4,l4,s41 ,keeper of ,botany1 ,british ,museum4 ,with #cgh ,illustrations4 #hvo41 #afs4 ,,cross ,,and ,,bevan4--,,cellulose3 an ,outline of the ,chemistry of the ,structural ,elements of ,plants4 ,with ,reference to their ,natural ,history and ,industrial ,uses4 ,by ,,cross and ,,bevan 7,c4 ,f4 ,cross1 ,e4 ,j4 ,bevan1 and ,c4 ,beadle74 ,with #ad ,plates4 ,crown #hvo41 #abs4 net4 ,,edmonds4--,works by ,,henry ,,edmonds1 ,b4,sc41 ,london4 ,,elementary ,,botany1 ,theoretical and ,practical4 ,with #cai ,diagrams and ,woodcuts4 ,crown #hvo41 #bs4 #f;d4 ,,botany ,,for ,,beginners4 ,with #he ,illustrations4 ,fcp4 #hvo41 #as4 #f;d4 ,,kitchener4--,a ,,year',s ,,botany4 ,adapted to ,home and ,school ,use4 ,with ,illustrations by the ,author4 ,by ,,frances ,,anna ,,kitchener4 ,crown #hvo41 #es4 ,,lindley ,,and ,,moore4--,,the ,,treasury ,,of ,,botany2 or1 ,popular ,dictionary of the ,vegetable ,kingdom3 with which is incorporated a ,glossary of ,botanical ,terms4 ,edited by ,j4 ,,lindley1 ,m4,d41 ,f4,r4,s41 and ,t4 ,,moore1 ,f4,l4,s4 ,with #bj ,steel ,plates and numerous ,woodcuts4 ,two parts1 fcp4 #hvo41 #abs4 ,mc,n,a,b4--,,class-,,book ,,of ,,botany4 ,by ,w4 ,r4 ,,mcnab4 ,,morphology ,,and ,,physiology4 ,with #db ,diagrams4 ,fcp4 #hvo41 #as4 #f;d4 ,,classification ,,of ,,plants4 ,with #aah ,diagrams4 ,fcp4 #hvo41 #as4 #f;d4 ,,thom ,,and ,,bennett4--,,structural ,,and ,,physiological ,,botany4 ,by ,dr4 ,,otto ,,wilhelm ,,thom and by ,,alfred ,w4 ,,bennett1 ,m4,a41 ,b4,sc41 ,f4,l4,s4 ,with ,coloured ,map and #fjj ,woodcuts4 ,fcp4 #hvo41 #fs4 ,,watts4--,a ,,school ,,flora4 ,for the use of ,elementary ,botanical ,classes4 ,by ,w4 ,,marshall ,,watts1 ,d4,sc4 ,lond4 ,crown #hvo41 #bs4 #f;d4 ,,agriculture ,,and ,,gardening4 ,,addyman4--,,agricultural ,,analysis4 ,a ,manual of ,quantitative ,analysis for ,students of ,agriculture4 ,by ,,frank ,t4 ,,addyman1 ,b4,sc4 7,lond471 ,f4,i4,c41 ,lecturer on ,agricultural ,chemistry1 ,university ,college1 ,nottingham1 etc4 ,with #di ,illustrations4 ,crown #hvo41 #es4 net4 ,,coleman ,,and ,,addyman4--,,practical ,,agricultural ,,chemistry4 ,for ,elementary ,students1 adapted for use in ,agricultural ,classes and ,colleges4 ,by ,j4 ,,bernard ,,coleman1 ,a4,r4,c4,sc41 ,f4,i4,c41 and ,,frank ,t4 ,,addyman1 ,b4,sc4 7,lond471 ,f4,i4,c4 ,with #bd ,illustrations4 ,crown #hvo41 #as4 #f;d4 net4 ,,loudon4--,,encyclop,,dia ,,of ,,agriculture2 the ,laying-out1 ,improvement1 and ,management of ,landed ,property2 the ,cultivation and ,economy of the ,productions of ,agriculture4 ,by ,j4 ,c4 ,,loudon1 ,f4,l4,s4 ,with #aajj ,woodcuts4 #hvo41 #bas4 ,,sorauer4--,a ,,popular ,,treatise ,,on ,,the ,,physiology ,,of ,,plants4 ,for the use of ,gardeners1 or for ,students of ,horticulture and of ,agriculture4 ,by ,dr4 ,,paul ,,sorauer4 ,translated by ,f4 ,e4 ,,weiss1 ,b4,sc41 ,f4,l4,s4 ,with #cc ,illustrations4 #hvo41 #is4 net4 ,,webb4--,works by ,,henry ,j4 ,,webb1 ,ph4,d41 ,b4,sc4 7,lond471 late ,principal of the ,agricultural ,college1 ,aspatria4 ,,elementary ,,agriculture4 ,a ,text-,book specially adapted to the requirements of the ,science and ,art ,department1 the ,junior ,examination of the ,royal ,agricultural ,society1 and other ,elementary ,examinations4 ,with #cd ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,agriculture4 ,a ,manual for ,advanced ,science ,students4 ,with #ajj ,illustrations4 ,crown #hvo41 #gs4 #f;d4 net4 ,,works ,,by ,,john ,,tyndall1 ,d4,c4,l41 ,,ll4,d41 ,f4,r4,s4 ,,fragments ,,of ,,science3 a ,series of ,detached ,essays1 ,addresses1 and ,reviews4 #b vols4 ,crown #hvo41 #afs4 ,vol4 ,i4--,the ,constitution of ,nature--,radiation--,on ,radiant ,heat in ,relation to the ,colour and ,chemical ,constitution of ,bodies--,new ,chemical ,reactions produced by ,light--,on ,dust and ,disease--,voyage to ,algeria to observe the ,eclipse--,niagara--,the ,parallel ,roads of ,glen ,roy--,alpine ,sculpture--,recent ,experiments on ,fog-,signals--,on the ,study of ,physics--,on ,crystalline and ,slaty ,cleavage--,on ,paramagnetic and ,diamagnetic ,forces--,physical ,basis of ,solar ,chemistry--,elementary ,magnetism--,on ,force--,contributions to ,molecular ,physics--,life and ,letters of ,,faraday--,the ,copley ,medallist of #ahgj--,the ,copley ,medallist of #ahga--;,death by ,lightning--,science and the ,spirits4 ,vol4 ,,ii4--,reflections on ,prayer and ,natural ,law--,miracles and ,special ,providences--,on ,prayer as a ,form of ,physical ,energy--,vitality--,matter and ,force--,scientific ,materialism--,an ,address to ,students--,scientific ,use of the ,imagination--,the ,belfast ,address--,apology for the ,belfast ,address--,the ,rev4 ,,james ,,martineau and the ,belfast ,address--,fermentation1 and its ,bearings on ,surgery and ,medicine--,spontaneous ,generation--,science and ,man--,professor ,,virchow and ,evolution--,the ,electric ,light4 ,,new ,,fragments4 ,crown #hvo41 #ajs4 #f;d4 ,,contents4--,the ,sabbath--,goethe's ',farbenlehre'--,atoms1 ,molecules1 and ,ether ,waves--,count ,rumford--,louis ,pasteur1 his ,life and ,labours--,the ,rainbow and its ,congeners--,address delivered at the ,birkbeck ,institution on ,october #bb1 #ahhd--,thomas ,young--,life in the ,alps--,about ,common ,water--,personal ,recollections of ,thomas ,carlyle--,on ,unveiling the ,statue of ,thomas ,carlyle--,on the ,origin1 ,propagation1 and ,prevention of ,phthisis--,old ,alpine ,jottings--,a ,morning on ,alp ,lusgen4 ,,lectures ,,on ,,sound4 ,with ,frontispiece of ,fog-,syren1 and #bjc other ,woodcuts and ,diagrams in the ,text4 ,crown #hvo41 #ajs4 #f;d4 ,,heat1 ,a ,,mode ,,of ,,motion4 ,with #abe ,woodcuts and ,diagrams4 ,crown #hvo41 #abs4 ,,lectures ,,on ,,light ,,delivered ,,in ,,the ,,united ,,states ,,in #ahgb ,,and #ahgc4 ,with ,portrait1 ,lithographic ,plate1 and #ei ,diagrams4 ,crown #hvo41 #es4 ,,essays ,,on ,,the ,,floating ,,matter ,,of ,,the ,,air ,,in ,,relation ,,to ,,putrefaction ,,and ,,infection4 ,with #bd ,woodcuts4 ,crown #hvo41 #gs4 #f;d4 ,,researches ,,on ,,diamagnetism ,,and ,,magnecrystallic ,,action2 including the ,question of ,diamagnetic ,polarity4 ,crown #hvo41 #abs4 ,,notes ,,of ,a ,,course ,,of ,,nine ,,lectures ,,on ,,light1 delivered at the ,royal ,institution of ,great ,britain1 #ahfi4 ,crown #hvo41 #as4 #f;d4 ,,notes ,,of ,a ,,course ,,of ,,seven ,,lectures ,,on ,,electrical ,,phenomena ,,and ,,theories1 delivered at the ,royal ,institution of ,great ,britain1 #ahgj4 ,crown #hvo41 #as4 #f;d4 ,,lessons ,,in ,,electricity ,,at ,,the ,,royal ,,institution #ahge-ahgf4 ,with #eh ,woodcuts and ,diagrams4 ,crown #hvo41 #bs4 #f;d4 ,,the ,,glaciers ,,of ,,the ,,alps3 being a ,narrative of ,excursions and ,ascents4 ,an ,account of the ,origin and ,phenomena of ,glaciers1 and an ,exposition of the ,physical ,principles to which they are related4 ,with numerous ,illustrations4 ,crown #hvo41 #fs4 #f;d4 net4 ,,faraday ,,as ,a ,,discoverer4 ,crown #hvo41 #cs4 #f;d4 ,,text-,,books ,,of ,,science4 ,,photography4 ,by ,captain ,w4 ,,de ,,wiveleslie ,,abney1 ,c4,b41 ,f4,r4,s41 ,director for ,science in the ,science and ,art ,department4 ,with #aee ,woodcuts4 ,price #cs4 #f;d4 ,,the ,,strength ,,of ,,materials ,,and ,,structures3 the ,strength of ,materials as depending on their quality and as ascertained by ,testing ,apparatus2 the ,strength of ,structures1 as depending on their form and arrangement1 and on the materials of which they are composed4 ,by ,sir ,j4 ,,anderson1 ,c4,e41 etc4 ,with #ff ,woodcuts4 ,price #cs4 #f;d4 ,,railway ,,appliances4 ,a ,description of ,details of ,railway ,construction subsequent to the completion of ,earthworks and ,structures1 including a short ,notice of ,railway ,rolling ,stock4 ,by ,,john ,,wolfe ,,barry1 ,c4,b41 ,m4,i4,c4,e4 ,with #bah ,woodcuts4 ,price #ds4 #f;d4 ,,introduction ,,to ,,the ,,study ,,of ,,inorganic ,,chemistry4 ,by ,,william ,,allen ,,miller1 ,m4,d41 ,,ll4,d41 ,f4,r4,s4 ,with #gb ,woodcuts4 ,price #cs4 #f;d4 ,,quantitative ,,chemical ,,analysis4 ,by ,t4 ,e4 ,,thorpe1 ,f4,r4,s41 ,ph4,d41 ,professor of ,chemistry in the ,royal ,college of ,science1 ,london4 ,with #hh ,woodcuts4 ,price #ds4 #f;d4 ,,qualitative ,,chemical ,,analysis ,,and ,,laboratory ,,practice4 ,by ,t4 ,e4 ,,thorpe1 ,ph4,d41 ,d4,sc41 ,f4,r4,s41 ,principal ,chemist of the ,government ,laboratories1 ,london1 and ,m4 ,m4 ,,pattison ,,muir1 ,m4,a4 ,with ,plate of ,spectra and #eg ,woodcuts4 ,price #cs4 #f;d4 ,,introduction ,,to ,,the ,,study ,,of ,,chemical ,,philosophy4 ,the ,principles of ,theoretical and ,systematic ,chemistry4 ,by ,,william ,a4 ,,tilden1 ,d4,sc41 ,london1 ,f4,r4,s41 ,professor of ,chemistry at the ,royal ,college of ,science4 ,with #e ,woodcuts4 ,with or without ,answers to ,problems4 ,price #ds4 #f;d4 ,,elements ,,of ,,astronomy4 ,by ,sir ,r4 ,s4 ,,ball1 ,,ll4,d41 ,f4,r4,s41 ,lowndean ,professor of ,astronomy in the ,university of ,cambridge4 ,with #acj ,woodcuts4 ,price #fs4 #f;d4 ,,systematic ,,mineralogy4 ,by ,,hilary ,,bauerman1 ,f4,g4,s41 ,associate of the ,royal ,school of ,mines4 ,with #cgc ,woodcuts4 ,price #fs4 ,,descriptive ,,mineralogy4 ,by ,,hilary ,,bauerman1 ,f4,g4,s41 etc4 ,with #bcf ,woodcuts4 ,price #fs4 ,,metals1 ,,their ,,properties ,,and ,,treatment4 ,by ,c4 ,l4 ,,bloxam and ,a4 ,k4 ,,huntington1 ,professors in ,king's ,college1 ,london4 ,with #acj ,woodcuts4 ,price #es4 ,,physical ,,optics4 ,by ,r4 ,t4 ,,glazebrook1 ,m4,a41 ,f4,r4,s41 ,fellow and ,lecturer of ,trinity ,college1 and ,demonstrator of ,physics at the ,cavendish ,laboratory1 ,cambridge4 ,with #ahc ,woodcuts4 ,price #fs4 ,,practical ,,physics4 ,by ,r4 ,t4 ,,glazebrook1 ,m4,a41 ,f4,r4,s41 and ,w4 ,n4 ,,shaw1 ,m4,a4 ,with #acd ,woodcuts4 ,price #gs4 #f;d4 ,,preliminary ,,survey4 ,by ,,theodore ,,graham ,,gribble1 ,civil ,engineer4 ,including ,elementary ,astronomy1 ,route ,surveying1 ,tacheometry1 ,curveranging1 ,graphic ,mensuration1 ,estimates1 ,hydrography1 and ,instruments4 ,with #acj ,illustrations1 ,quantity ,diagrams1 and a ,manual of the ,slide-,rule4 ,price #f,s4 ,,algebra ,,and ,,trigonometry4 ,by ,,william ,,nathaniel ,,griffin1 ,b4,d4 ,price #cs4 #f;d4 ,notes on1 with ,solutions of the more difficult ,questions4 ,price #cs4 #f;d4 ,,the ,,steam ,,engine4 ,by ,,george ,c4 ,v4 ,,holmes 7,whitworth ,scholar71 ,secretary of the ,institution of ,naval ,architects4 ,with #bab ,woodcuts4 ,price #fs4 ,,electricity ,,and ,,magnetism4 ,by ,,fleeming ,,jenkin1 ,f4,r4,,ss41 ,l4 ,e41 late ,professor of ,engineering in the ,university of ,edinburgh4 ,with #agg ,woodcuts4 ,price #cs4 #f;d4 ,,the ,,art ,,of ,,electro-,,metallurgy1 including all known ,processes of ,electro-,deposition4 ,by ,g4 ,,gore1 ,,ll4,d41 ,f4,r4,s4 ,with #ef ,woodcuts4 ,price #fs4 ,,telegraphy4 ,by ,w4 ,h4 ,,preece1 ,c4,b41 ,f4,r4,s41 ,v4,p4,inst41 ,c4,e41 ,engineer-in-,chief1 and ,electrician1 ,post ,office ,telegraphs1 and ,sir ,j4 ,,sivewright1 ,m4,a41 ,k4,c4,m4,g4 ,with #beh ,woodcuts4 ,price #fs4 ,,theory ,,of ,,heat4 ,by ,j4 ,,clerk ,,maxwell1 ,m4,a41 ,,ll4,d41 ,edin41 ,f4,r4,,ss41 ,l4 ,e4 ,new ,edition4 ,with ,corrections and ,additions by ,,lord ,,rayleigh1 ,sec4 ,r4 ,s4 ,with #ch ,woodcuts4 ,price #ds4 #f;d4 ,,technical ,,arithmetic ,,and ,,mensuration4 ,by ,,charles ,w4 ,,merrifield1 ,f4,r4,s4 ,price #cs4 #f;d4 ,key1 by the ,rev4 ,,john ,,hunter1 ,m4,a4 ,price #cs4 #f;d4 ,,the ,,study ,,of ,,rocks1 an ,elementary ,text-,book of ,petrology4 ,by ,,frank ,,rutley1 ,f4,g4,s41 of ,her ,majesty's ,geological ,survey4 ,with #f ,plates and #hh ,woodcuts4 ,price #ds4 #f;d4 ,,workshop ,,appliances1 including ,descriptions of some of the ,gauging and ,measuring ,instruments--,hand-,cutting ,tools1 ,lathes1 ,drilling1 ,planing1 and other ,machine ,tools used by ,engineers4 ,by ,c4 ,p4 ,b4 ,,shelley1 ,m4,i4,c4,e4 ,with an additional ,chapter on ,milling4 ,by ,r4 ,r4 ,,lister4 ,with #cbc ,woodcuts4 ,price #es4 ,,elements ,,of ,,machine ,,design4 ,by ,w4 ,,cawthorne ,,unwin1 ,f4,r4,s41 ,b4,sc41 ,m4,i4,c4,e4 ,,part ,i4 ,general ,principles1 ,fastenings1 and ,transmissive ,machinery4 ,with #cjd ,woodcuts4 ,price #fs4 ,,part ,,ii4 ,chiefly on ,engine ,details4 ,with #agd ,woodcuts4 ,price #ds4 #f;d4 ,,structural ,,and ,,physiological ,,botany4 ,by ,dr4 ,,otto ,,wilhelm ,,thom1 ,rector of the ,high ,school1 ,cologne1 and ,a4 ,w4 ,,bennett1 ,m4,a41 ,b4,sc41 ,f4,l4,s4 ,with #fjj ,woodcuts and a coloured ,map4 ,price #fs4 ,,plane ,,and ,,solid ,,geometry4 ,by ,h4 ,w4 ,,watson1 ,m4,a41 formerly ,fellow of ,trinity ,college1 ,cambridge4 ,price #cs4 #f;d4 ,,advanced ,,science ,,manuals4 asterism ,written specially to meet the requirements of the ,,advanced ,,stage of ,science ,subjects as laid down in the ,syllabus of the ,directory of the ,,science ,,and ,,art ,,department1 ,,south ,,kensington4 ,,building ,,construction4 ,by the ,author of ',rivington's ,notes on ,building ,construction'4 ,with #che ,illustrations and an ,appendix of ,examination ,questions4 ,crown #hvo41 #ds4 #f;d4 ,,theoretical ,,mechanics4 ,solids1 including ,kinematics1 ,statics1 and ,kinetics4 ,by ,a4 ,,thornton1 ,m4,a41 ,f4,r4,a4,s41 ,with #bbj ,illustrations1 #acj ,worked ,examples1 and over #ijj ,examples from ,examination ,papers1 etc4 ,crown #hvo41 #ds4 #f;d4 ,,heat4 ,by ,,mark ,r4 ,,wright1 ,hon4 ,inter4 ,b4,sc4 ,lond4 ,with #acf ,illustrations and numerous ,examples and ,examination ,papers4 ,crown #hvo41 #ds4 #f;d4 ,,light4 ,by ,w4 ,j4 ,a4 ,,emtage1 ,m4,a4 ,with #bcb ,illustrations4 ,cr4 #hvo41 #fs4 ,,magnetism ,,and ,,electricity4 ,by ,,arthur ,,william ,,poyser1 ,m4,a4 ,with #cag ,illustrations4 ,crown #hvo41 #ds4 #f;d4 ,,inorganic ,,chemistry1 ,,theoretical ,,and ,,practical4 ,a ,manual for ,students in ,advanced ,classes of the ,science and art ,department4 ,by ,,william ,,jago1 ,f4,c4,s41 ,f4,i4,c4 ,with ,plate of ,spectra and #gh ,woodcuts4 ,crown #hvo41 #ds4 #f;d4 ,,geology3 a ,manual for ,students in ,advanced ,classes and for ,general ,readers4 ,by ,,charles ,,bird1 ,b4,a4 7,lond471 ,f4,g4,s4 ,with over #cjj ,illustrations1 a ,geological ,map of the ,british ,isles 7coloured71 and a set of ,questions for ,examination4 ,crown #hvo41 #gs4 #f;d4 ,,human ,,physiology3 a ,manual for ,students in advanced ,classes of the ,science and ,art ,department4 ,by ,,john ,,thornton1 ,m4,a4 ,with #bfh ,illustrations1 some of which are ,coloured1 and a set of ,questions for ,examination4 ,crown #hvo41 #fs4 ,,physiography4 ,by ,,john ,,thornton1 ,m4,a4 ,with #f ,maps1 #ahj ,illustrations1 and ,coloured ,plate of ,spectra4 ,crown #hvo41 #ds4 #f;d4 ,,agriculture4 ,by ,dr4 ,,henry ,j4 ,,webb1 ,ph4,d41 ,b4,sc4 ,with #ajj ,illustrations4 ,crown #hvo41 #gs4 #f;d4 net4 ,,elementary ,,science ,,manuals4 ,,practical1 ,,plane1 ,,and ,,solid ,,geometry1 including ,graphic ,arithmetic4 ,by ,i4 ,h4 ,,morris4 ,fully ,illustrated with ,drawings prepared specially for the book4 ,crown #hvo41 #bs4 #f;d4 ,,geometrical ,,drawing ,,for ,,art ,,students4 ,embracing ,plane ,geometry and its ,applications1 the ,use of ,scales1 and the ,plans and ,elevations of ,solids1 as required in ,section ,i4 of ,science ,subject ,i4 ,by ,i4 ,h4 ,,morris4 ,crown #hvo41 #as4 #f;d4 ,,text-,,book ,,on ,,practical1 ,,solid1 ,,or ,,descriptive ,,geometry4 ,by ,,david ,,allan ,,low 7,whitworth ,scholar74 ,part ,i4 ,crown #hvo41 #bs4 ,part ,,ii4 ,crown #hvo41 #cs4 ,,an ,,introduction ,,to ,,machine ,,drawing ,,and ,,design4 ,by ,,david ,,allan ,,low 7,whitworth ,scholar74 ,with #ig ,illustrations and ,diagrams4 ,crown #hvo41 #bs4 ,,building ,,construction4 ,by ,,edward ,j4 ,,burrell1 ,second ,master of the ,technical ,school of the ,people's ,palace1 ,mile ,end4 ,with #cjh ,illustrations and ,working ,drawings4 ,crown #hvo41 #bs4 #f;d4 ,,an ,,elementary ,,course ,,of ,,mathematics4 ,containing ,arithmetic2 ,euclid 7,book ,i41 with ,deductions and ,exercises72 and ,algebra4 ,crown #hvo41 #bs4 #f;d4 ,,theoretical ,,mechanics4 ,including ,hydrostatics and ,pneumatics4 ,by ,j4 ,e4 ,,taylor1 ,m4,a41 ,b4,sc4 ,with numerous ,examples and ,answers1 and #age ,diagrams4 ,crown #hvo41 #bs4 #f;d4 ,,theoretical ,,mechanics--,,solids4 ,by ,j4 ,e4 ,,taylor1 ,m4,a41 ,b4,sc4 ,with #afc ,illustrations1 #abj ,worked ,examples1 and over #ejj ,examples from ,examination ,papers1 etc4 ,crown #hvo41 #bs4 #f;d4 ,,theoretical ,,mechanics--,,fluids4 ,by ,j4 ,e4 ,,taylor1 ,m4,a41 ,b4,sc4 ,with #abb ,illustrations1 numerous ,worked ,examples1 and about #ejj ,examples from ,examination ,papers1 etc4 ,crown #hvo41 #bs4 #f;d4 ,a ,,manual ,,of ,,mechanics3 an ,elementary ,text-,book for ,students of ,applied ,mechanics4 ,with #ach ,illustrations and ,diagrams1 and #ahh ,examples taken from the ,science ,department ,examination ,papers1 with ,answers4 ,by ,t4 ,m4 ,,goodeve1 ,m4,a4 ,fcp4 #hvo41 #bs4 ,,sound1 ,,light1 ,,and ,,heat4 ,by ,,mark4 ,r4 ,,wright1 ,hon4 ,inter4 ,b4,sc41 ,london4 ,with ,examples1 ,examination ,papers1 and #afe ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,physics4 ,alternative ,course4 ,by ,,mark ,r4 ,,wright1 ,hon4 ,inter4 ,b4,sc41 ,london4 ,with ,examples1 ,examination ,papers1 and #bdb ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,elementary ,,practical ,,chemistry3 a ,laboratory ,manual for ,use in ,organised ,science ,schools4 ,by ,g4 ,s4 ,,newth1 ,f4,i4,c41 ,f4,c4,s41 ,demonstrator in the ,royal ,college of ,science1 ,london2 ,assistant ,examiner in ,chemistry1 ,science and ,art ,department4 ,with #ajh ,illustrations and #bed ,experiments4 ,crown #hvo4 ,price #bs4 #f;d4 ,,elementary ,,practical ,,physics3 a ,laboratory ,manual for ,use in ,organised ,science ,schools4 ,by ,w4 ,,watson1 ,b4,sc4 ,demonstrator in ,physics in the ,royal ,college of ,science1 ,london2 ,assistant ,examiner in ,physics1 ,science and ,art ,department4 ,with #aai ,illustrations and #aic ,exercises4 ,crown #hvo4 ,price #bs4 #f;d4 ,,magnetism ,,and ,,electricity4 ,by ,a4 ,w4 ,,poyser1 ,m4,a4 ,with ,examination ,papers and #bce ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,problems ,,and ,,solutions ,,in ,,elementary ,,electricity ,,and ,,magnetism4 ,embracing a ,complete ,set of ,answers to the ,south ,kensington ,papers for the ,years #ahhe-ahid1 and a ,series of ,original ,questions4 ,by ,w4 ,,slingo and ,a4 ,,brooker4 ,with #fg ,illustrations4 ,crown #hvo41 #bs4 ,,inorganic ,,chemistry1 ,,theoretical ,,and ,,practical4 ,with an ,introduction to the ,principles of ,chemical ,analysis4 ,by ,,william ,,jago1 ,f4,c4,s41 ,f4,i4,c4 ,with #fc ,woodcuts and numerous ,questions and ,exercises4 ,fcp4 #hvo41 #bs4 #f;d4 ,,an ,,introduction ,,to ,,practical ,,inorganic ,,chemistry4 ,by ,,william ,,jago1 ,f4,c4,s41 ,f4,i4,c4 ,with ,illustrations4 ,crown #hvo41 #as4 #f;d4 ,,practical ,,chemistry3 the ,principles of ,qualitative ,analysis4 ,by ,,william ,a4 ,,tilden1 ,d4,sc4 ,with ,illustrations4 ,fcp4 #hvo41 #as4 #f;d4 ,,elementary ,,chemistry1 ,inorganic and ,organic4 ,by ,,william ,s4 ,,furneaux4 ,with ,examination ,questions1 and #fe ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,organic ,,chemistry3 the ,fatty ,compounds4 ,by ,r4 ,,lloyd ,,whiteley1 ,f4,i4,c41 ,f4,c4,s4 ,with #de ,illustrations4 ,crown #hvo41 #cs4 #f;d4 ,,elementary ,,geology4 ,by ,,charles ,,bird1 ,b4,a41 ,f4,g4,s4 ,with ,coloured ,geological ,map of the ,british ,islands1 and #bdg ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,human ,,physiology4 ,by ,,william ,s4 ,,furneaux4 ,with #bah ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,biology4 ,by ,,john ,,bidgood1 ,b4,sc4 ,with #bbf ,illustrations4 ,crown #hvo41 #ds4 #f;d4 ,,elementary ,,botany1 ,,theoretical ,,and ,,practical4 ,by ,,henry ,,edmonds1 ,b4,sc41 ,london4 ,with #cai ,woodcuts4 ,crown #hvo41 #bs4 #f;d4 ,,metallurgy4 ,by ,e4 ,l4 ,,rhead1 ,lecturer on ,metallurgy at the ,municipal ,technical ,school1 ,manchester4 ,with #id ,illustrations4 ,crown #hvo41 #cs4 #f;d4 ,,steam4 ,by ,,william ,,ripper1 ,member of the ,institution of ,mechanical ,engineers1 ,professor of ,mechanical ,engineering in the ,sheffield ,technical ,school4 ,with #adb ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,elementary ,,physiography4 ,by ,,john ,,thornton1 ,m4,a4 ,with #ab ,maps and #bdg ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,agriculture4 ,by ,,henry ,j4 ,,webb1 ,ph4,d41 ,b4,sc4 7,lond474 ,late ,principal of the ,agricultural ,college1 ,aspatria4 ,with #cd ,illustrations4 ,crown #hvo41 #bs4 #f;d4 ,,hygiene4 ,by ,j4 ,l4 ,,notter1 ,m4,a41 ,m4,d41 ,fellow and ,member of ,council of the ,sanitary ,institute of ,great ,britain1 ,examiner in ,hygiene1 ,science and ,art ,department2 ,examiner in ,public ,health in the ,university of ,cambridge and in the ,victoria ,university1 ,manchester2 and ,r4 ,h4 ,,firth1 ,f4,r4,c4,s41 ,assistant ,professor of ,hygiene1 in the ,army ,medical ,school1 ,netley4 ,with #ie ,illustrations4 ,crown #hvo41 #cs4 #f;d4 ,,the ,,london ,,science ,,class-,,books4 ,edited by ,g4 ,,carey ,,foster1 ,f4,r4,s41 and by ,sir ,,philip ,,magnus1 ,b4,sc41 ,b4,a41 of the ,city and ,guilds of ,london ,institute4 ,,astronomy4 ,by ,sir ,,robert ,,stawell ,,ball1 ,,ll4,d41 ,f4,r4,s4 #da ,diagrams4 #as4 #f;d4 ,,mechanics4 ,by ,,sir ,,robert ,,stawell ,,ball1 ,,ll4,d41 ,f4,r4,s4 #hi ,diagrams4 #as4 #f;d4 ,,the ,,laws ,,of ,,health4 ,by ,w4 ,h4 ,,corfield1 ,m4,a41 ,m4,d41 ,f4,r4,c4,p4 ,with #bb ,illustrations4 #as4 #f;d4 ,,molecular ,,physics ,,and ,,sound4 ,by ,,fred4 ,,guthrie1 ,f4,r4,s4 #ia ,diagrams4 #as4 #f;d4 ,,geometry1 ,,congruent ,,figures4 ,by ,o4 ,,henrici1 ,ph4,d41 ,f4,r4,s4 ,with #ada ,diagrams4 #as4 #f;d4 ,,zoology ,,of ,,the ,,invertebrate ,,animals4 ,by ,,alexander ,,macalister1 ,m4,d4 ,with #ei ,diagrams4 #as4 #f;d4 ,,zoology ,,of ,,the ,,vertebrate ,,animals4 ,by ,,alexander ,,macalister1 ,m4,d4 ,with #gg ,diagrams4 #as4 #f;d4 ,,hydrostatics ,,and ,,pneumatics4 ,by ,sir ,,philip ,,magnus1 ,b4,sc41 ,b4,a4 #gi ,diagrams4 #as4 #f;d4 7,to be had also with ,answers1 #bs474 ,the ,worked ,solutions of the ,problems4 #bs4 ,,botany4 ,outlines of the ,classification of ,plants4 ,by ,w4 ,r4 ,,mcnab1 ,m4,d4 ,with #aah ,diagrams4 #as4 #f;d4 ,,botany4 ,outlines of ,morphology and ,physiology4 ,by ,w4 ,r4 ,,mcnab1 ,m4,d4 ,with #db ,diagrams4 #as4 #f;d4 ,,thermodynamics4 ,by ,,richard ,,wormell1 ,m4,a41 ,d4,sc4 #da ,diagrams4 #as4 #f;d4 99 99 99 99 99 ,transcriber's ,notes ,the half-title has been deleted4 ,spelling and punctuation of the original text were taken over and obvious errors have been corrected silently4 ,inconsistant hyphenation was kept as it is4 ,table ,,iii has been split in three parts4 ,text in italics has been marked with underscores 7text74 ,the ligature oe has been marked as oe4 ,the asterism sign has been marked as asterism4 ,the #croot sign has been marked as #croot4 ,the sign has been used as a superscript4