,transcriber's ,note3 ,boldface text is indicated by bars and ,italic text by underscores4 ,subscripts are shown as normal numbers3 ,h#b,o4 ,a ,,history ,,of ,,the ,,sciences ,astronomy1 by ,prof4 ,,george ,,forbes1 ,f4,r4,s4 ,chemistry1 #b volumes1 by ,sir ,,edward ,,thorpe1 ,c4,b41 ,d ,sc41 ,f4,r4,s41 etc4 7,director of ,government ,laboratories7 ,old ,testament ,criticism1 by ,prof4 ,,archibald ,,duff 7,prof4 of ,hebrew and ,old ,testament ,theology in the ,united ,college1 ,bradford7 ,in ,active ,preparation-- ,new ,testament ,criticism1 by ,f4 ,c4 ,,conybeare1 ,m4,a4 7,late ,fellow and ,prlector of ,univ4 ,coll41 ,oxford7 ,geology1 by ,h4 ,b4 ,,woodward1 ,f4,r4,s41 ,f4,g4,s4 7,assistant ,director of ,geological ,survey7 ,geography1 by ,dr4 ,,scott ,,keltie1 ,f4,r4,g4,s41 ,f4,s4,a4 ,g4 ,p4 ,,putnam',s ,,sons ,new ,york ,london ,illustration3 ,,justus ,,von ,,liebig ,a ,,history ,,of ,,the ,,sciences ,,history ,,of ,,chemistry ,,by ,,sir ,,edward ,,thorpe ,c4,b41 ,,ll4,d41 ,f4,r4,s4 ,,author ,,of 8,,essays ,,in ,,historical ,,chemistry10 8,,humphry ,,davy3 ,,poet ,,and ,,philosopher10 8,,joseph ,,priestley10 ,,etc41 ,,etc4 ,,two ,,volumes ,,ii4 ,from #ahej to #aiaj ,,with ,,illustrations ,g4 ,p4 ,,putnam',s ,,sons ,,new ,,york ,,and ,,london ,the ,knickerbocker ,press #aiaj ,,copyright1 #aiaj ,,by ,g4 ,p4 ,,putnam',s ,,sons ,this series is published in ,london by ,,the ,,rationalist ,,press ,,association1 ,,limited ,the ,knickerbocker ,press1 ,new ,york ,,publishers' ,,note ,a ,history of the ,sciences has been planned to present for the information of the general public a historic record of the great divisions of science4 ,each volume is the work of a writer who is accepted as an authority on his own subject-matter4 ,the books are not to be considered as primers1 but present thoroughly digested information on the relations borne by each great division of science to the changes in human ideas and to the intellectual development of mankind4 ,the monographs explain how the principal scientific discoveries have been arrived at and the names of the workers to whom such discoveries are due4 ,the books will comprise each about #bjj pages4 ,each volume will contain from #ab to #af illustrations1 including portraits of the discoverers and explanatory views and diagrams4 ,each volume contains also a concise but comprehensive bibliography of the subject-matter4 ,the following volumes will be issued during the course of the autumn of #aiji4 ,the ,history of ,astronomy4 ,by ,,george ,,forbes1 ,m4,a41 ,f4,r4,s41 ,m4 ,inst4 ,c4,e42 author of ,the ,transit of ,venus1 etc4 ,the ,history of ,chemistry3 ,vol4 ,i4 circa #bjjj ,b4,c4 to #ahej ,a4,d4 ,vol4 ,,ii4 #ahej ,a4,d4 to date4 ,by ,,sir ,,edward ,,thorpe1 ,c4,b41 ,,ll4,d41 ,f4,r4,s41 ,director of the ,government ,laboratories1 ,london2 ,professor-elect and ,director of the ,chemical ,laboratories of the ,imperial ,college of ,science and ,technology2 author of ,a ,dictionary of ,applied ,chemistry4 ,to be followed by3 ,the ,history of ,geography4 ,by ,dr4 ,,john ,,scott ,,keltie1 ,f4,r4,g4,s41 ,f4,s4,s41 ,f4,s4,a41 ,hon4 ,mem4 ,geographical ,societies of ,paris1 ,berlin1 ,rome1 ,brussels1 ,amsterdam1 ,geneva1 etc42 author of ,report on ,geographical ,education1 ,applied ,geography4 ,the ,history of ,geology4 ,by ,,horace ,b4 ,,woodward1 ,f4,r4,s41 ,f4,g4,s41 ,assistant ,director of ,geological ,survey of ,england and ,wales2 author of ,the ,geology of ,england and ,wales1 etc4 ,the ,history of ,anthropology4 ,by ,a4 ,c4 ,,haddon1 ,m4,a41 ,sc4,d41 ,f4,r4,s41 ,lecturer in ,ethnology1 ,cambridge and ,london2 author of ,study of ,man1 ,magic and ,fetishism1 etc4 ,the ,history of ,old ,testament ,criticism4 ,by ,,archibald ,,duff1 ,professor of ,hebrew and ,old ,testament ,theology in the ,united ,college1 ,bradford2 author of ,theology and ,ethics of the ,hebrews1 ,modern ,old ,testament ,theology1 etc4 ,the ,history of ,new ,testament ,criticism4 ,by ,f4 ,c4 ,,conybeare1 ,m4,a41 late ,fellow and ,praelector of ,univ4 ,coll41 ,oxford2 ,fellow of the ,british ,academy2 ,doctor of ,theology1 honoris causa1 of ,giessen2 ,officer d',academie2 author of ,old ,armenian ,texts of ,revelation1 etc4 ,further volumes are in plan on the following subjects3 ,mathematics and ,mechanics4 ,molecular ,physics1 ,heat1 ,life1 and ,electricity4 ,human ,physiology1 ,embryology1 and ,heredity4 ,acoustics1 ,harmonics1 and the ,physiology of ,hearing1 together with ,optics ,chromatics1 and ,physiology of ,seeing4 ,psychology1 ,analytic1 ,comparative1 and ,experimental4 ,sociology and ,economics4 ,ethics4 ,comparative ,philology4 ,criticism1 ,historical ,research1 and ,legends4 ,comparative ,mythology and the ,science of ,religions4 ,the ,criticism of ,ecclesiastical ,institutions4 ,culture1 ,moral and ,intellectual1 as ,reflected in ,imaginative ,literature and in the ,fine ,arts4 ,logic4 ,philosophy4 ,education4 ,,contents ,,chapter ,i ,,page ,,state ,,of ,,chemistry ,,in ,,the ,,middle ,,of ,,the ,,nineteenth ,,century #a ,introductory4 ,some ,founders of ,modern ,chemistry3 ,liebig1 ,whler1 ,dumas4 ,rapid ,extension of ,organic ,chemistry after #ahej3 ,laurent and ,gerhardt1 ,hofmann4 ,development of theory in ,organic ,chemistry4 ,other representative men of the middle period of the ,nineteenth ,century3 ,graham1 ,williamson1 ,bunsen4 ,modern ,chemistry in relation to the ,atomic ,theory4 ,,chapter ,,ii ,,the ,,chemical ,,elements ,,discovered ,,since #ahej #bf ,nomenclature and ,classification of ,elements4 ,numerical relationships4 ,modes of discovery4 ,the ,spectroscope4 ,csium1 rubidium1 thallium1 indium1 gallium1 scandium1 germanium4 ,the rare earth elements4 ,industrial applications of rare elements4 ,,chapter ,,iii ,,the ,,inactive ,,elements3 ,,radium ,,and ,,radio-,,activity #dc ,argon1 helium1 krypton1 neon1 and xenon4 ,radium4 ,disintegration theory of ,rutherford and ,soddy4 ,actinium and polonium4 ,the emanations4 ,,chapter ,,iv ,,atoms ,,and ,,molecules3 ,,atomic ,,weights ,,and ,,equivalents #fa ,hypothesis of ,avogadro4 ,stanislao ,cannizzaro4 ,determination of molecular weights4 ,applicability of law of ,dulong and ,petit4 ,relations of molecular weight to osmotic pressures4 ,determination of atomic weights4 ,hypothesis of ,prout1 ,dumas1 ,stas1 ,lord ,rayleigh1 ,leduc1 ,morley1 ,guye1 ,theodore ,richards4 ,validity of law of conservation of mass3 ,landolt4 ,,chapter ,v ,,the ,,molecular ,,theory ,,of ,,gases #gi ,interdependence of the gaseous laws4 ,kinetic theory of gases3 ,bernoulli1 ,waterston1 ,clausius1 ,maxwell1 ,boltzmann1 ,schmidt1 ,graham4 ,gaseous diffusion4 ,van der ,waals's equation4 ,ratio of specific heats3 ,kundt and ,warburg4 ,liquefaction of gases4 ,critical temperatures and pressures3 ,andrews1 ,pictet and ,cailletet1 ,wroblewski1 ,olszewki1 ,dewar1 ,kammerlingh ,onnes4 ,liquefaction of air on the large scale4 ,research at low temperatures4 ,,chapter ,,vi ,,the ,,periodic ,,law #aja ,prout1 ,thomson1 ,dbereiner1 ,newlands1 ,de ,chancourtois4 ,statement of the ,periodic ,law by ,mendeleff and ,lothar ,meyer4 ,its importance as a system of classification4 ,,chapter ,,vii ,,valency #aab ,origin of conception of ,valency3 ,williamson1 ,gerhardt1 ,frankland1 ,couper1 ,kekul4 ,tetravalency of carbon and linkage of atoms4 ,rational and constitutional formul4 ,dynamical theories of valency4 ,,chapter ,,viii ,,the ,,chemistry ,,of ,,aromatic ,,compounds #aai ,peculiarities of aromatic compounds4 ,kekul's benzene theory4 ,its applications4 ,the essential oils4 ,terpenes4 ,camphor4 ,synthesis of perfumes4 ,alkaloids4 ,,chapter ,,ix ,,stereo-,,isomerism3 ,,stereo-,,chemistry #ach ,opticity3 ,biot1 ,mitscherlich1 ,pasteur1 ,wislicenus1 ,van 't ,hoff1 ,le ,bel4 ,asymmetry4 ,racemisation4 ,multirotation4 ,geometrical isomerism4 ,geometrical inversion4 ,stereo-isomerism among nitrogen1 sulphur1 selenium1 tin1 and silicon compounds4 ,tautomerism4 ,steric hindrance4 ,,chapter ,x ,,organic ,,synthesis3 ,,condensation3 ,,synthesis ,,of ,,vital ,,products #aeb ,use of specific condensing reagents4 ,carbon suboxide4 ,artificial preparation of naturally occurring substances4 ,synthetic medicines4 ,the ptomaines4 ,artificial alizarin4 ,indigo4 ,the sugars and proteins3 ,emil ,fischer4 ,the doctrine of 8vital force40 ,,chapter ,,xi ,,on ,,the ,,development ,,of ,,physical ,,chemistry ,,since #ahej #aga ,molecular volumes of liquids4 ,nature of solution4 ,van 't ,hoff's application of the gas laws to phenomena of solution4 ,osmosis and osmotic pressure4 ,traube4 ,pfeffer4 ,semi-permeable membranes4 ,measurement of osmotic pressure4 ,arrhenius4 ,doctrine of ionisation4 ,its applicability to the explanation of chemical phenomena4 ,thermo-chemistry4 ,mass action4 ,nature of reversible reactions4 ,thermal and ,electrolytic dissociation4 ,relation between chemical nature and opticity1 magnetic rotation and viscosity4 ,theory of phases4 ,catalysis4 ,enzyme action4 ,relations between valency and volume4 ,photochemistry4 ,,bibliography #ahg ,,index #aia ,,illustrations ,,page ,,justus ,,von ,,liebig ,frontispiece ,,jean ,,baptiste ,,andr ,,dumas #i ,,thomas ,,graham #ac ,from a painting by ,g4 ,f4 ,watts1 ,r4,a41 in the possession of the ,royal ,society ,,alexander ,,william ,,williamson #ae ,,bunsen1 ,,kirchhoff1 ,,and ,,roscoe #ai ,,sir ,,william ,,ramsay #dh ,,marie ,,curie 7ne ,,sklodowska7 #ef ,,stanislao ,,cannizzaro #fe ,,sir ,,james ,,dewar #ih ,,dmitri ,,ivanowitsch ,,mendel,,eff #aaj ,,august ,,kekul ,,von ,,stradonitz #abf ,,jacobus ,,henricus ,,van ',t ,,hoff #adb ,,emil ,,fischer #aff ,,svante ,,august ,,arrhenius #ahj ,,history ,,of ,,chemistry ,,chapter ,i ,,state ,,of ,,chemistry ,,in ,,the ,,middle ,,of ,,the ,,nineteenth ,,century ,in the preceding volume an attempt was made to outline the significant features in the development of chemistry1 as an art and as a science1 from the earliest times down to about the middle of the last century4 ,since that time chemistry has progressed at a rate and to an extent unparalleled at any period of its history4 ,not only have the number and variety of chemical products--inorganic and organic--been enormously increased1 but the study of their modes of origin1 properties1 and relations has greatly extended our means of gaining an insight into the internal structure and constitution of bodies4 ,this extraordinary development has carried the science beyond the limits of its own special field of inquiry1 and has influenced every department of natural knowledge4 ,concurrently there has been a no less striking extension of its applications to the prosperity and material welfare of mankind4 ,with the death of ,davy the era of brilliant discovery in chemistry1 wrote ,edward ,turner1 appeared for the moment to have terminated4 ,although the number of workers in the science steadily increased1 the output of chemical literature in ,england actually diminished for some years2 and1 as regards inorganic chemistry1 few first-rate discoveries were made during the two decades prior to #ahej4 ,chemists seemed to be of ,turner's opinion that the time had arrived for reviewing their stock of information1 and for submitting the principal facts and fundamental doctrines to the severest scrutiny4 ,their activity was employed not so much in searching for new compounds or new elements as in examining those already discovered4 ,the foundations of the atomic theory were being securely laid4 ,the ratios in which the elements of known compounds are united were being more exactly ascertained4 ,the efforts of workers1 ,graham excepted1 seemed to be spent more on points of detail1 on the filling-in of little gaps in the chemical structure1 as it then existed1 than in attempts at new developments4 ,for a time--during the early 'thirties--chemists struggled with the claims of rival methods of notation1 and it was only gradually that the system of ,berzelius gained general acceptance4 ,at none of the ,british universities was there anything in the nature of practical tuition in chemistry4 ,thomson1 at ,glasgow1 occasionally permitted a student to work under him1 but no systematic instruction was ever attempted4 ,the first impulses came from ,graham in #ahcg1 when he took charge of the chemical teaching at the ,university of ,london1 and when1 in #ahda1 he assisted to create the ,chemical ,society of ,london4 ,four years later the ,royal ,college of ,chemistry in ,london was founded and placed under the direction of ,august ,wilhelm ,hofmann--one of the most distinguished pupils of ,liebig4 ,under his inspiration the study of practical chemistry made extraordinary progress1 and discovery succeeded discovery in rapid succession4 ,in bringing ,hofmann to ,england we had1 in fact1 imported something of the spirit and power of his master1 ,liebig4 ,among the pupils and co-workers of ,hofmann were ,warren de la ,rue1 ,abel1 ,nicholson1 ,mansfield1 ,medlock1 ,crookes1 ,church1 ,griess1 ,martius1 ,sell1 ,divers1 and ,perkin4 ,whilst at ,giessen he had begun the study of the organic bases in coal-tar with a view more especially of establishing the identity of ,fritzsche's anilin with the benzidam of ,zinin and the krystallin of ,unverdorben4 ,hofmann continued to cultivate with unremitting zeal the field thus entered4 ,with ,muspratt he discovered paratoluidine and nitraniline2 with ,cahours allyl alcohol4 ,his pupil ,mansfield worked out1 at the cost of his life1 the methods for the technical extraction of benzene and toluene from coal-tar1 and thereby made the coal-tar colour-industry possible4 ,it was in attempting to synthesise quinine by the oxidation of aniline that ,perkin1 then an assistant at the college1 obtained1 in #ahef1 aniline purple1 or mauve1 as it came to be called by the ,french1 the first of the so-called coal-tar colouring matters4 ,in #ahei this was followed by the discovery of magenta1 or fuchsine1 by ,verquin4 ,for its manufacture ,medlock1 one of ,hofmann's pupils1 in #ahfj devised a process by which for a time it was almost exclusively made4 ,hofmann studied the products thus obtained1 and showed that they were derivatives of a base he called rosaniline2 and he demonstrated that the colouring matters were only produced through the concurrent presence of aniline and toluidine4 ,he also proved that the base of the dye1 known as aniline blue1 was triphenylrosaniline4 ,as the result of these inquiries he obtained the violet or purple colouring matters known by his name4 ,lastly1 all his classical work on the amines1 ammonium compounds1 and the analogous phosphorus derivatives was done at the ,royal ,college of ,chemistry4 ,prior to the establishment by ,liebig1 in #ahbf1 of the ,giessen laboratory1 the state of chemistry in ,germany was not much1 if at all1 better than with us4 ,the creation of the ,giessen school initiated a movement which has culminated in the pre-eminent position which ,germany now occupies in the chemical world4 ,students from every civilised country came to study and to work under its leader1 and to carry away with them the influence of his example1 the inspiration of his genius1 and the stimulating power of his enthusiasm4 ,justus von ,liebig1 was born at ,darmstadt on ,may #ab1 #ahjc1 and after graduating at ,erlangen1 where he worked on the fulminates1 he repaired to ,paris and entered the laboratory of ,gay ,lussac1 with whom he continued his inquiries4 ,returning to ,germany1 he was appointed ,professor of ,chemistry at ,giessen in #ahbf1 and began those remarkable series of scientific contributions upon which the superstructure of organic chemistry largely rests4 ,he investigated the cyanates1 cyanides1 ferrocyanides1 thiocyanates1 and their derivatives4 ,in conjunction with ,whler he discovered the group of the benzoic compounds and created the radical theory4 ,with ,whler also he investigated uric acid and its derivatives4 ,he discovered hippuric acid1 fulminuric acid1 chloral1 chloroform1 aldehyde1 thialdine1 benzil1 and elucidated the constitution of the organic acids and the amides4 ,he greatly improved the methods of organic analysis1 and was thereby enabled to determine the empirical formul of a number of carbon compounds of which the composition was imperfectly known4 ,he practically laid the foundations of modern agricultural chemistry1 and to his teaching is due the establishment of an important branch of technology--the manufacture of chemical fertilisers4 ,he worked on physiological chemistry1 especially on the elaboration of fat1 on the nature of blood1 bile1 and on the juice of flesh4 ,he studied the processes of fermentation1 and of the decay of organised matter4 ,he was a most prolific writer4 ,the ,royal ,society's ,catalogue of ,scientific ,papers enumerates no fewer than #cag contributions from his pen4 ,he was the founder of the ,annalen der ,chemie1 which is now associated with his name1 and of the ,jahresbericht2 he published an ,encyclopdia of ,pure and ,applied ,chemistry and a ,handbook of ,organic ,chemistry4 ,his ,familiar ,letters on ,chemistry was translated into every modern language1 and exercised a powerful influence in developing popular appreciation of the value and utility of science4 ,liebig left ,giessen in #aheb to become ,professor of ,chemistry at the ,university of ,munich and ,president of the ,academy of ,sciences4 ,he died at ,munich on ,april #ah1 #ahgd4 ,with the name of ,liebig that of ,whler is indissolubly connected4 ,although the greater part of their work was not published in conjunction1 what they did together exercised a profound influence on the development of chemical theory4 ,friedrich ,whler was born at ,eschersheim1 near ,frankfort1 on ,july #ca1 #ahjj4 ,after studying at ,marburg1 where he discovered1 independently of ,davy1 cyanogen iodide1 and worked on mercuric thiocyanate1 he went to ,heidelberg and investigated cyanic acid and its compounds1 under the direction of ,gmelin4 ,in #ahbc he worked with ,berzelius at ,stockholm1 where he prepared some new tungsten compounds and practised mineral analysis4 ,in #ahbe he became a teacher of chemistry in the ,berlin ,trade ,school4 ,here he succeeded for the first time in preparing the metal aluminium and in effecting the synthesis of urea--one of the first organic compounds to be prepared from inorganic materials4 ,jointly with ,liebig he worked upon mellitic and cyanic and cyanuric acids4 ,in #ahcb ,whler1 now appointed to the ,polytechnic at ,cassel1 began with ,liebig their memorable investigation on bitter-almond oil4 ,in #ahcf he was called to the ,chair of ,chemistry in the ,university of ,gttingen1 and with ,liebig attacked the constitution of uric acid and its derivatives--the last great investigation the friends did in common4 ,whler subsequently devoted himself mainly to inorganic chemistry4 ,he isolated crystalline boron1 and prepared its nitrides1 discovered the spontaneously inflammable silicon hydride1 titanium nitride1 and analysed great numbers of minerals and meteorites and compounds of the rarer metals4 ,he made ,gttingen famous as a school of chemistry4 ,at the time of the one and twentieth year of his connection with the ,university it was found that upwards of #hjjj students had listened to his lectures or worked in his laboratory4 ,he died on ,september #bc1 #ahhb4 ,in ,france1 ,dumas exercised a no less powerful influence4 ,if ,liebig could reckon among his pupils ,redtenbacher1 ,bromeis1 ,varrentrapp1 ,gregory1 ,playfair1 ,williamson1 ,gilbert1 ,brodie1 ,anderson1 ,gladstone1 ,hofmann1 ,will1 and ,fresenius2 ,dumas could point to ,boullay1 ,piria1 ,stas1 ,melsens1 ,wurtz1 and ,leblanc--all of whom did yeoman service in developing the rapidly expanding branch of organic chemistry4 ,illustration3 ,,jean ,,baptiste ,,andr ,,dumas ,jean ,baptiste ,andr ,dumas was born on ,july #ad1 #ahjj1 at ,alais1 where he was apprenticed to an apothecary4 ,in his sixteenth year he went to ,geneva and entered the pharmaceutical laboratory of ,le ,royer4 ,without1 apparently1 having received any systematic instruction in chemistry1 he commenced the work of investigation4 ,with ,coindet he established the therapeutic value of iodine in the treatment of gotre2 with ,prevost he attempted to isolate the active principle of digitalis1 and studied the chemical changes in the development of the chick in the egg4 ,in his twenty-fourth year ,dumas went to ,paris and became ,rptiteur de ,chimie at the cole ,polytechnique4 ,he joined ,audouin and ,brongniart in founding the ,annales des ,sciences ,naturelles1 and began his great work on ,chemistry ,applied to the ,arts1 of which the first volume appeared in #ahbh4 ,at about this time he devised his method of determining vapour densities1 and published the results of a number of estimations made by means of it4 ,with ,boullay he began an inquiry on the compound ethers1 out of which grew the etherin theory1 which served as a stepping-stone to the theory of compound radicals--subsequently elaborated by ,liebig and ,whler4 ,dumas discovered the nature of oxamide and of ethyl oxamate1 isolated methyl alcohol1 and established the generic connection of groups of similarly constituted organic substances1 or1 in a word1 the doctrine of homology4 ,his work on the metaleptic action of chlorine upon organic substances eventually effected the overthrow of the electro-chemical theory of ,berzelius and led to the theory of types1 which1 in the hands of ,williamson1 ,laurent1 ,gerhardt1 and ,odling1 was of great service in explaining the analogies and relationships of whole groups of organic compounds4 ,he worked in every field of chemistry4 ,he invented many analytical processes1 established the gravimetric composition of water and of air1 and revised the atomic weights of the greater number of the elements then known4 ,dumas exercised great influence in scientific and academic circles in ,france4 ,he was an admirable speaker1 and had rare literary gifts4 ,on the creation of the ,empire he was made a ,senator1 and was elected a member of the ,municipal ,council of ,paris1 of which he became president in #ahei4 ,he died on ,april #aa1 #ahhd4 ,it was largely through the influence of these master-minds that chemistry took a new departure4 ,prior to their time organic chemistry hardly existed as a branch of science3 organic products1 as a rule1 were interesting only to the pharmacist mainly by reason of their technical or medicinal importance4 ,but by the middle of the nineteenth century the richness of this hitherto untilled field became manifest1 and scores of workers hastened to sow and to reap in it4 ,the most striking feature1 indeed1 of the history of chemistry during the past sixty years has been the extraordinary expansion of the organic section of the science4 ,the chemical literature relating to the compounds of carbon now exceeds in volume that devoted to all the rest of the elements4 ,in the middle of the nineteenth century chemists began to concern themselves with the systematisation of the results of the study of organic compounds1 and something like a theory of organic chemistry gradually took shape4 ,from this period we may date the attempts at expressing the internal nature1 constitution1 and relations of substances which1 step by step1 have culminated in our present representations of the structure and spatial arrangement of molecules4 ,in #ahej the dualistic conceptions of ,berzelius ceased to influence the doctrines of organic chemistry4 ,the enunciation by ,dumas of the principle of substitution1 and its logical outcome in the nucleus theory and in the theory of types1 had not only effected the overthrow of dualism1 but was undermining the position of the radical theory of ,liebig and ,whler4 ,the teaching of ,gerhardt and ,laurent had spread over ,europe1 and was influencing those younger chemists who1 while renouncing dualism1 were not wholly satisfied with a belief in compound radicals4 ,williamson's discovery1 in #ahej1 of the true nature of ether and of its relation to alcohol1 and his subsequent preparation of mixed ethers1 served not only to reconcile conflicting interpretations of the process of etherification1 but also to reconcile the theory of types with that of radicals4 ,lastly1 his method of representing the constitution of the ethers and their mode of origin gave a powerful stimulus to the use of type-formul in expressing the nature and relations of organic compounds4 ,illustration3 ,,thomas ,,graham4 ,from a painting by ,g4 ,f4 ,watts1 ,r4,a41 in the possession of the ,royal ,society4 ,other representative men of the middle period of the nineteenth century1 in addition to ,williamson1 were ,graham and ,bunsen4 ,the three men were investigators of very different type1 and their work had little in common4 ,but each was identified with discoveries of a fundamental character1 constituting turning-points in the history of chemical progress1 valuable either as regards their bearing on chemical doctrine or as regards their influence on operative chemistry4 ,thomas ,graham was born in ,glasgow on ,december #ba1 #ahje1 and1 after studying under ,thomas ,thomson at the ,university of that city1 attended the lectures of ,hope and ,leslie in ,edinburgh4 ,in #ahcj he succeeded ,ure as teacher of chemistry at ,anderson's ,college in ,glasgow1 and in #ahcg was called to the ,chair of ,chemistry in the newly-founded ,university of ,london1 in succession to ,edward ,turner4 ,in #ahed he was made ,master of the ,mint4 ,he died in ,london on ,september #af1 #ahfi4 ,graham's work was mainly devoted to that section of the science now known as physical chemistry4 ,his contributions to pure chemistry are few in number4 ,by far the most important is his discovery of metaphosphoric acid and its relations to the other modifications of phosphoric acid4 ,ortho- or ordinary phosphoric acid was known to ,boyle2 pyrophosphoric acid was discovered by ,clark4 ,graham's work is noteworthy as first definitely indicating the inherent property of the acids to combine with variable but definite amounts of basic substances by successive replacement of hydroxyl groups--the property we now term basicity1 and was of fundamental importance in regard to its bearing on the constitution of acids and salts4 ,graham's fame chiefly rests upon his discovery of the law of gaseous diffusion 7#ahbi-ahca71 upon his work on the diffusion of liquids1 and upon his recognition of the condensed form of hydrogen he termed hydrogenium4 ,questions involving the conception of molecular mobility1 indeed1 constituted the main feature of his inquiries4 ,we owe to him1 among others1 the terms crystalloid1 colloid1 dialysis1 atmolysis1 occlusion--all of which have taken a permanent place in the terminology of science4 ,illustration3 ,,alexander ,,william ,,williamson4 ,alexander ,william ,williamson was born at ,wandsworth1 ,london1 on ,may #a1 #ahbd4 ,his father1 a ,scotchman and a fellow-clerk of ,james ,mill 7the father of ,john ,stuart ,mill7 in the ,east ,india ,house1 took an active share in the foundation1 in #ahbf1 of the ,university of ,london1 subsequently known as ,university ,college4 ,in #ahdj the younger ,williamson entered the ,university of ,heidelberg with the intention of studying medicine2 but1 under the influence of ,leopold ,gmelin1 he turned to chemistry4 ,in #ahdd he went to ,giessen1 to work under ,liebig1 and there made his first contributions to chemical science--viz41 on the decomposition of oxides and salts by chlorine2 on ozone2 and on the blue compounds of cyanogen and iron4 ,after graduating at ,giessen he went1 in #ahdf1 to ,paris1 where he came under the influence of ,comte1 with whom he studied mathematics4 ,in #ahej1 at ,graham's solicitation1 he was appointed to the ,chair of ,practical ,chemistry at ,university ,college1 vacant by the death of ,fownes4 ,he at once embarked upon those researches which constitute his main contribution to science4 ,in the attempt to build up the homologous series of the aliphatic alcohols from ordinary alcohol he succeeded in demonstrating the real nature of ether and its genetic relation to alcohol1 and in explaining the process of etherification4 ,the memoirs 7#ahej-eb7 in which he embodied the facts had an immediate influence on the development of chemical theory4 ,his explanation of the process of etherification familiarised chemists with the idea of the essentially dynamical nature of chemical change4 ,he imported the conception of molecular mobility not only into the explanation of such metathetical reactions as the formation of the ethers1 but into the interpretation of the phenomena of chemical change in general4 ,in these papers1 as also in one on the constitution of salts1 published in #ahea1 he attempted to systematise the representation of the constitution and relations of oxidised substances--organic and inorganic--by showing how they may be regarded as built up upon the type of water considered as ,h ,o1 ,h in which the hydrogen atoms are replaced1 wholly or in part1 by other chemically equivalent atoms4 ,this idea was immediately adopted by ,gerhardt1 was further elaborated by ,odling and ,kekul1 and was eventually developed into a theory of chemistry4 ,williamson continued to direct the laboratory of ,university ,college until #ahhg1 when he retired to the country4 ,he died at ,hindhead on ,may #f1 #aijd4 ,robert ,wilhelm ,bunsen was born at ,gttingen on ,march #ca1 #ahaa1 and after studying chemistry under ,stromeyer1 the discoverer of cadmium1 went to ,paris and worked with ,gay ,lussac4 ,in #ahcf he succeeded ,whler as teacher of chemistry in the ,polytechnic ,school of ,cassel1 and in #ahdb became ,professor of ,chemistry in the ,university of ,marburg4 ,in #aheb he was called to ,heidelberg1 and occupied the ,chair of ,chemistry there until his retirement in #ahhi4 ,he died at ,heidelberg on ,august #af1 #ahii4 ,illustration3 ,,bunsen1 ,,kirchhoff1 ,,and ,,roscoe4 ,bunsen first distinguished himself by his classical work on the cacodyl compounds1 obtained as the result of an inquiry into the nature of the so-called 8fuming liquor of ,cadet10 an evil-smelling1 highly poisonous1 inflammable liquid formed by heating arsenious oxide with an alkaline acetate4 ,the investigation 7#ahcg-ahde7 is noteworthy1 not only for the skill it exhibits in dealing with a difficult and highly dangerous manipulative problem1 but also for the remarkable nature of its results and on account of their influence on contemporary chemical theory4 ,the research1 in the words of ,berzelius1 was the foundation-stone of the theory of compound radicals4 ,the name cacodyl or kakodyl was suggested by ,berzelius in allusion to the nauseous smell of the compounds of the new radical arsinedimethyl1 ,as 7,,ch#c7b1 as it was subsequently termed by ,kolbe4 ,bunsen greatly improved the methods of gasometric analysis2 these he applied1 in conjunction with ,playfair1 to an examination of the gaseous products of the blast furnace in the manufacture of iron1 and thereby demonstrated the enormous waste of energy occasioned by allowing the gases to escape unused into the air1 as was then the universal practice4 ,this inquiry effected a revolution in the manufacture of iron as important1 indeed1 as that due to the introduction of the hot blast4 ,bunsen devised methods for determining the solubility of gases in liquids1 for ascertaining the specific gravity of gases1 their rates of diffusion1 and of combination or inflammation4 ,in #ahda he invented the carbon-zinc battery1 and applied it to the electrolytic production of metals1 notably of magnesium1 the properties of which he first accurately described4 ,in #ahdd he contrived the grease-spot photo-meter1 which was long in general use for ascertaining the photometric value of illuminating gas4 ,his methods of ascertaining the specific heats of solids and liquids were simple1 ingenious1 and accurate4 ,in #ahee-ahfc he carried out1 in conjunction with ,roscoe1 a long series of investigations on the chemical action of light4 ,in #ahei1 in association with ,kirchhoff1 he devised the first methods of spectrum analysis1 and explained the origin and significance of the ,fraunhofer lines in the solar spectrum1 thus laying the foundations of solar and stellar chemistry4 ,the application of the spectroscope to analytical chemistry almost immediately resulted in his discovery of csium and rubidium4 ,bunsen worked on problems of chemical geology1 and made a long series of analyses of volcanic products4 ,with ,schischkoff1 he examined1 in #aheg1 the products of fired gunpowder4 ,he effected many improvements in analytical chemistry2 devised the iodiometric method of volumetric analysis1 and systematised the processes of water analysis4 ,lastly1 he invented the gas-burner--a piece of apparatus with which his name is inseparably associated1 and which has been of inestimable service to operative chemistry and in the arts4 ,bunsen was no theorist1 and purely speculative questions had little or no interest for him4 ,at the same time he was a great teacher1 and made the chemical school of ,heidelberg no less famous than the schools of ,giessen and ,gttingen4 99 99 99 99 99 ,the mass of material relating to the development of chemistry which has been accumulated during the past sixty years is so vast that it would be hopeless to attempt to survey it in detail within the limits of such a work as this4 ,nor1 indeed1 is this required in a history of this character4 ,those who desire information concerning the origin and sequence of the facts which collectively make up the superstructure of modern chemistry must be referred to the encyclopdias or larger treatises--or1 preferably1 to the numerous monographs1 dealing with special sections1 which the volume and complexity of the matter to be dealt with seem to render increasingly necessary4 ,all we can do here is to attempt to show what has been the main outcome of this sixty years of incessant effort to elucidate the mysteries of chemical phenomena and to ascertain the nature of the conditions which control1 modify1 or determine them4 ,all this effort is ultimately directed to the solution of the fundamental problem of the constitution of matter4 ,the most significant result of this endeavour has been the elaboration and consolidation of the doctrine of chemical atoms1 not necessarily of atoms in the limited ,daltonian sense1 but of atoms considered as associations of particles1 or corpuscles--that is1 of entities which may be divisible1 but which1 in the main1 are not divided in the vast number of the transformations in which they are concerned4 ,this modification of the original conception of ,dalton has been thought by some to destroy the basis upon which his theory really rests4 ,there is no necessity for such an assumption4 ,so pronounced an atomist as ,graham1 as far back as #ahfc1 in a suggestive paper entitled ,speculative ,ideas on the ,constitution of ,matter1 enlarged the conception of the ,daltonian atom in precisely the sense which recent experimental work appears to require4 ,the present position1 too1 as it affects chemists1 was equally well stated by ,kekul1 in #ahfg1 in the following terms3 ,the question whether atoms exist or not has but little significance from a chemical point2 its discussion belongs rather to metaphysics4 ,in chemistry we have only to decide whether the assumption of atoms is an hypothesis adapted to the explanation of chemical phenomena4 ,more especially have we to consider the question whether a further development of the atomic hypothesis promises to advance our knowledge of the mechanism of chemical phenomena4 ,i have no hesitation in saying that1 from a philosophical point of view1 ,i do not believe in the actual existence of atoms1 taking the word in its literal signification of indivisible particles of matter2 ,i rather expect that we shall some day find for what we now call atoms a mathematico-mechanical explanation which will render an account of atomic weight1 of atomicity1 and of numerous other properties of the so-called atoms4 ,as a chemist1 however1 ,i regard the assumption of atoms not only as advisable1 but as absolutely necessary1 in chemistry4 ,i will even go further1 and declare my belief that chemical atoms exist1 provided the term be understood to denote those particles of matter which undergo no further division in chemical metamorphoses4 ,should the progress of science lead to a theory of the constitution of chemical atoms--important as such a knowledge might be for the general philosophy of matter--it would make but little alteration in chemistry itself4 ,the chemical atoms will always remain the chemical unit2 and for the specially chemical considerations we may always start from the constitution of atoms1 and avail ourselves of the simplified expression thus obtained--that is to say1 of the atomic hypothesis4 ,we may1 in fact1 adopt the view of ,dumas and of ,faraday--that1 whether matter be atomic or not1 thus much is certain3 that1 granting it to be atomic1 it would appear as it now does4#a #a ,the ,study of ,chemical ,composition1 by ,ida ,freund 7,cambridge ,university ,press71 #aijd4 ,the greater part of that which follows will be devoted1 therefore1 to an exposition of certain of the great advances in knowledge--many of them of primary importance--which have been made during the last fifty or sixty years and which have served to strengthen this extended conception of the atomic theory1 and to establish its position as an article of the scientific faith of the twentieth century4 ,,chapter ,,ii ,,the ,,chemical ,,elements ,,discovered ,,since #ahej ,in #ahej the number of substances generally recognised as chemical elements1 in the sense in which that term was first employed by ,boyle1 was sixty-two4 ,two members--viz41 the pelopium of ,rose and the ilmenium of ,hermann--were1 however1 subsequently shown to be identical with metals already known4 ,at the present time 7#aiaj7 the number of the chemical elements definitely recognised as such is eighty-two4 ,in #ahej1 as now1 they were broadly classified as metals and non-metals1 although it was felt then1 no less strongly than now1 that no very clear line of demarcation was traceable between the two groups4 ,sixty years ago the elements usually styled non-metals were thirteen in number2 to-day the number is nineteen--the increase being due to the inclusion of arsenic and the discovery of the so-called inactive elements1 helium1 argon1 krypton1 neon1 and xenon4 ,in #ahej there were forty-seven elements definitely classed as metals2 in #aiaj the number is sixty-three4 ,at all periods in the history of chemistry as a science the general tendency has been to name substances1 whenever possible1 in accordance with the theoretical conceptions of the time1 and hence it has happened that the same body at successive periods has had very dissimilar names4 ,but in naming the substances we term elements1 theoretical conceptions are not usually applicable4 ,oxygen1 it is true1 derives its name from such a conception2 and1 etymologically1 the name connotes an error4 ,hydrogen1 too1 has no more right to be called the water former than oxygen4 ,davy1 who invented the term chlorine1 advocated that the chemical elements should be named from some distinguishing peculiarity1 either of origin or of physical property4 ,in the main this principle has been adopted especially in later years although there are numerous instances of names derived from pure arbitrary sources4 ,it is largely for the reason that the names of the elements are1 with rare exceptions1 unconnected with theories that they have remained unchanged1 whereas names of compounds1 which are far more frequently dependent upon speculative ideas1 have constantly been altered in order to comply with the prevailing hypotheses of the period4 ,at the same time it is not always clear that the etymology of certain of the elements is well ascertained4 ,it has been recently shown1 for example that the commonly accepted origin of the word 8antimony0 from antimoine1 based on the alleged experiences of medival ecclesiastics has no valid foundation4 ,the word is1 in reality1 derived from the ,arabic alhmoud3 this became latinised to althimodium and eventually to antimonium4 ,by the middle of the nineteenth century the system of symbolical notation suggested by ,berzelius was everywhere current2 and1 stripped largely of its dualistic associations1 this system still remains the most generally convenient method of expressing the composition1 analogies1 and numerical relations of substances4 ,during the middle of the last century philosophic chemists1 although subscribing1 with hardly an exception1 to the doctrine of definite combining proportions1 were by no means agreed as to the sufficiency of ,dalton's explanation of the experimental laws of chemical combination2 and the hypothesis of atoms in the ,daltonian sense was not universally accepted4 ,to some the atomic theory of ,dalton1 which assumed that the combining proportion was identical with the relative weight of the atom1 was unnecessary as an explanation of the laws of combination4 ,or at most it was only one out of a variety of molecular conditions in which matter might exist4 ,consequently some chemists were in the habit of drawing a distinction between chemical atoms and physical atoms4 ,the chemical atom was identical with the ,daltonian atom but this was by no means the same as the physical atom of ,democritus or ,leucippus4 ,the view in #ahej1 in fact1 was not very dissimilar from that to which recent experimental inquiry has led4 ,but it can hardly be said that the doubts were dependent upon valid experimental evidence2 they arose rather from the erroneous interpretation of imperfectly ascertained facts--upon the supposed inconsistencies of the law of ,gay ,lussac with the hypotheses of ,avogadro and ,ampre4 ,as soon as the facts were clearly perceived and the inconsistencies reconciled we heard less of the supposed distinction between the chemical and the physical atom4 ,it is only within quite recent time1 and as the result of entirely new lines of inquiry1 that the distinction has been revived4 ,in the early part of the last century attempts were made by ,berzelius to classify the chemical elements according to their electro-chemical relations1 and by ,thomson according as they were 8supporters0 or 8non-supporters of combustion40 ,it was soon perceived that ,thomson's system had no philosophical basis1 and it quickly fell into disuse4 ,after the discovery of isomorphism1 an endeavour was made by ,graham to arrange the simple bodies in accordance with their natural relations1 and even before #ahej the various elements were grouped by him very much as now4 ,this scheme of classification1 somewhat modified by considerations of valency1 and occasionally corrected by more accurate information concerning true analogies 7as when vanadium was transferred by ,roscoe to the nitrogen group71 was in general use for practically a quarter of a century--in fact1 until it was superseded by the gradual adoption of ,mendeleff's arrangement based on periodicity4 ,there can1 however1 be little doubt that this attempt by ,graham at a natural classification paved the way along which ,newlands and eventually ,mendeleff were led to devise our present rational system of grouping the chemical elements4 ,the numerical relationships existing among the equivalents and atomic weights of the elements of certain of these groups1 pointed out by ,dumas1 ,pettenkofer1 ,odling1 ,gladstone1 and others1 gave rise to much speculation4 ,the values of the gradational differences1 of course1 depended upon whether equivalents or atomic weights were employed2 but the immediate point is that1 whichever basis was adopted1 definite numerical relations were to be perceived4 ,thus1 in the case of the group of the halogens1 it was pointed out that the individual members are connected together as follows3 ,fluorine4 ,chlorine4 ,bromine4 ,iodine4 #ai #ce4e #hj #abg a a d a #b;d d #b;a #b;d #b;d where a #ai2 d #af4e2 d #bh4 ,thus1 too1 in the case of the nitrogen group3 ,nitrogen4 ,phosphorus4 ,arsenic4 ,antimony4 ,bismuth4 #ad #ca #ge #aai #bjg a a d a d d a d #b;d a d #d;d where a #ad2 d #ag2 d #dd4 99 99 99 99 99 ,on the basis of these and similar numerical relationships it was surmised that1 just as the successive members of a group of homologous organic radicals are formed by increments of ,,ch#b1 so the substances in the several groups of the elements may be produced by successive additions of some form of matter common to them all4 ,this has its counterpart1 somewhat modified1 in the modern hypothesis of the disintegration of the elements4 ,dumas conceived the elements in any particular group to be built up by successive accretions of particular forms of matter2 ,rutherford and ,soddy suppose them to be derived by the successive elimination of matter from some unstable parent substance4 ,since #ahej the existence of at least twenty-two new elements may be said to have been established4 ,of course1 many more than this number have been announced1 more or less tentatively2 but subsequent investigation has either not confirmed their existence1 or has definitely disproved it4 ,the names1 symbols1 and atomic weights of the twenty-two1 arranged in alphabetical order1 are as follows3 ,argon ,a #ci4i ,csium ,cs #acb4h ,dysprosium ,dy #afb4e ,europium ,eu #aeb4j ,gadolinium ,gd #aeg4c ,gallium ,ga #fi4i ,germanium ,ge #gb4e ,helium ,he #d4j ,indium ,in #aad4h ,krypton ,kr #hc4j ,lutecium ,lu #agd4j ,neodymium ,nd #add4c ,neon ,ne #bj4j ,praseodymium ,pr #adj4f ,radium ,ra #bbf4d ,rubidium ,rb #he4d ,samarium ,sa #aej4d ,scandium ,sc #dd4a ,thallium ,tl #bjd4j ,thulium ,tm #afh4e ,xenon ,xe #acj4g ,ytterbium ,yb #agb4j 7,neoytterbium7 ,the additions have been due1 to some extent1 to the refinement of processes of analysis already in use1 but more especially to the employment of new analytical methods2 or1 lastly1 to the application of a generalisation concerning the mutual relations of the elements which has served to indicate not only the existence of new and specific members of families of elements already known1 but to point out the probable mode of their occurrence4#b #b ,the substances which appear to be formed by the disintegration of uranium1 radium1 thorium--the so-called radio-active elements--such as ionium1 actinium1 polonium1 and the various emanations to which they give rise1 are not here enumerated4 ,they are dealt with in ,chapter ,,iii4 ,although the existence of the element fluorine was surmised as far back as #agga1 when ,scheele first recognised that the product of the action of oil of vitriol upon fluor-spar contained a hitherto unknown substance1 it was not until #ahhf that this substance was definitely isolated by ,moissan by the electrolysis of the acid potassium fluoride in solution in hydrogen fluoride4 ,cerium tetrafluoride1 ,ce,f#d1 and lead tetrafluoride1 ,pb,f#d1 when heated1 were observed by ,brauner to evolve a gas having a smell resembling that of hypochlorous acid1 which was probably free fluorine4 ,certain violet-coloured varieties of fluor-spar1 when powdered1 emit a peculiar smell1 which has been attributed to free fluorine4 ,gore observed that anhydrous hydrogen fluoride would not conduct electricity--a fact confirmed by ,moissan4 ,moissan found1 however1 that on adding potassium fluoride to the liquid it readily suffered electrolysis with the liberation of free fluorine as a light greenish yellow gas with a pungent1 irritating smell resembling that of hypochlorous acid4 ,it has a vapour density corresponding with an atomic weight #ai4 ,by the application of cold and pressure it may be liquefied4 ,at still lower temperatures it may be frozen to a white solid4 ,fluorine is characterised by an extraordinary chemical activity1 and combines1 even at ordinary temperatures1 with a large number of substances4 ,sulphur1 phosphorus1 arsenic1 antimony1 boron1 iodine1 and silicon inflame or become incandescent in contact with it4 ,it combines with hydrogen with explosive violence1 even in the dark and at the lowest temperature4 ,it unites also with the metals1 occasionally with incandescence1 and decomposes water with liberation of oxygen4 ,the application1 by ,bunsen1 of the spectroscope to chemical analysis almost immediately resulted in his discovery1 in #ahfj1 of csium1 and1 in #ahfa1 of rubidium4 ,csium was first detected in the mineral water of ,drkheim in the ,palatinate and in the mineral petalite1 by the two blue lines it forms in the spectrum1 whence its name from the ,latin csius1 used to designate the blue of the clear sky4 ,rubidium was found in a lepidolite by means of a number of lines in different parts of the spectrum not previously observed1 two being especially remarkable in the outermost region of the visible red portion--whence the name of the element from the ,latin rubidus1 used to designate the darkest red colour4 ,the new metals were found to have the closest analogies to potassium1 with which they usually occur associated in nature4 ,rubidium is found in a number of lepidolites1 leucite1 spodumene1 triphylite1 mica1 and orthoclase1 and in the ,stassfurt carnallite2 in sea-water and in many mineral waters4 ,it occurs also in the ashes of many plants such as those of beetroot1 tobacco1 tea1 coffee1 etc4 ,it is doubtful if it is a normal constituent of plant food1 attempts to introduce it in place of potash having failed4 ,it is not improbable that these elements would have remained unknown except for spectrum analysis4 ,at all events1 one of them--csium--was missed in #ahdf by ,plattner1 in the course of the analysis of the mineral pollucite1 in which it occurs to the extent of one third of its weight4 ,after the discovery of csium by ,bunsen1 this mineral was again analysed by ,pisani1 when it was found that the alkali which ,plattner had mistaken for potassium was in reality csium4 ,csium is found to a very small extent in many mineral waters1 in a variety of minerals1 and in the ashes of plants4 ,in #ahfa ,sir ,william ,crookes made known the existence of a new element which he called thallium4 ,he found it in a seleniferous deposit obtained from an oil of vitriol factory in the ,harz4 ,it was characterised by giving a bright green line in the spectroscope--whence its name from 1 a green or budding twig4 ,the discovery was confirmed in the following year by ,lamy4 ,thallium1 in its general chemical relations1 has many analogies to the metals of the alkalis although in the metallic state it has the closest resemblance to lead4 ,it occurs in many varieties of pyrites1 in a few minerals1 such as crookesite1 lorandite1 zinc-blende and copper pyrites1 etc41 and in certain mineral waters4 ,in #ahfc ,reich and ,richter1 by means of the spectroscope1 detected the presence of a new element in the zinc-blende of ,freiberg4 ,the observation that it afforded two indigo-blue lines in the spark-spectrum led them to give it the name indium4 ,it has since been found in numerous blendes1 in various zinc and tungsten ores1 and in many iron ores4 ,it is a silver-white1 ductile1 and malleable metal1 melting at #agd1 and burning when heated with a violet flame4 ,it is related in chemical characters to aluminium and zinc4 ,its true place in the natural scheme of classification of the elements was indicated by ,mendeleff4 ,in #ahge ,lecoq de ,boisbaudran discovered a new element in the zinc-blende of ,pierrefitte in the ,pyrenees1 also by means of spectrum analysis4 ,the spark-spectrum of its salts affords two characteristic violet lines quite different in position from those given by indium4 ,to the new element its discoverer gave the name of gallium4 ,it has been found in very small amounts in other blendes1 but is still one of the rarest of the chemical elements4 ,it is a bluish-white1 hard1 and slightly malleable metal fusing at a temperature not much higher than that of a hot summer day4 ,its existence and main properties1 as well as its more significant chemical relationships1 were predicted by ,mendeleff in #ahfi from considerations based upon his periodic law4 7,see ante47 ,in the same year ,mendeleff also predicted the existence of a new element belonging to the group of which boron is the first member1 which he provisionally termed eka-boron1 and described its main properties4 ,mendeleff's prediction was verified in #ahgi by ,nilson's discovery of the element scandium4 ,scandium occurs associated with yttrium1 ytterbium1 etc41 in many ,swedish minerals1 such as euxenite1 gadolinite1 yttrotitanite1 etc4 ,the metal itself has not been isolated1 but the properties of its compounds correspond closely with those of the corresponding ekaboron compounds1 as predicted by ,mendeleff4 ,a further illustration of the value of the principle of periodicity1 as developed by ,mendeleff1 in indicating the existence of new elements1 is seen in the discovery of germanium4 ,in #ahhe ,weisbach discovered a new ,freiberg silver mineral1 to which he gave the name argyrodite4 ,this on analysis by ,winkler was found to contain a new element to the extent of about seven per cent4 with properties identical with those predicted by ,mendeleff for a missing element in the fourth group of the periodic series1 consisting of silicon1 tin1 and lead1 and which he had provisionally termed eka-silicon4 ,argyrodite1 in fact1 is a double sulphide of silver and germanium1 #b;,ag#b,s4,ge,s#b4 ,germanium is a greyish-white1 lustrous metal of sp4gr4 #e4e41 melting at about #ijj1 and resembling silicon and tin in its general chemical relations4 ,dysprosium1 europium1 gadolinium1 lutecium1 neodymium1 praseodymium1 samarium1 thulium1 and ytterbium 7neoytterbium7 belong1 like scandium1 to the group of the so-called rare earth metals4 ,these substances have been detected in a great variety of minerals1 many of which are extremely rare4 ,the elements most frequently occur in nature associated with yttrium1 cerium1 thorium1 and zirconium4 ,dysprosium was first detected1 in #ahhf1 by ,lecoq de ,boisbaudran in the so-called erbium earth of ,mosander1 in which ,cleve had previously 7#ahhj7 announced the existence of two other elements1 holmium and thulium4 ,there is some reason to believe that the holmium of ,cleve is identical with dysprosium4 ,ytterbium was discovered by ,marignac1 in #ahgh1 in the mineral gadolinite4 ,in #aijf ,auer von ,welsbach announced that ,marignac's ytterbia was a mixture1 which was confirmed in the following year by ,urbain1 who separated it into two elements1 which he named neoytterbium and lutecium4 ,europium was discovered by ,demaray in #aija4 ,all these earths are met with in small quantities associated with yttria in gadolinite1 euxenite1 samarskite1 xenotime1 cerite1 orthite1 and other similar minerals4 ,their compounds1 or such of them as have been described1 resemble the corresponding compounds of yttria4 ,they are recognised by differences in their spectroscopic behaviour4 ,gadolinium was detected1 independently1 in #ahhf1 by ,marignac and ,lecoq de ,boisbaudran in the terbium earth of ,mosander4 ,what was long known as didymium 7 a twin7 was discovered by ,mosander in #ahda4 ,it owes its name to its close chemical relationship to1 and almost constant association with1 lanthanum--both elements occurring in many minerals1 more particularly in cerite1 allanite1 and monazite4 ,in #ahhe ,auer von ,welsbach announced that the didymium of ,mosander was1 in reality1 a mixture of two elements which could be separated by the systematic fractional crystallisation of the double ammonium nitrates2 to these elements he gave the names praseodymium 71 leek-green7 and neodymium 71 new74 ,neodymium salts are rose-coloured1 whereas those of praseodymium are green1 and the elements are further characterised by differences in their absorption and spark-spectra4 ,when mixed1 the substances give the spectrum originally considered to be characteristic of didymium4 ,samarium was discovered in #ahgi by ,lecoq de ,boisbaudran in samarskite4 ,its salts are yellow1 and afford in solution characteristic absorption bands4 ,it is not improbable that many of the minerals from which the so-called rare earths are obtained contain elements hitherto unrecognised1 and it is possible that certain of the substances now assumed to be elements may1 like didymium1 turn out to be mixtures4 ,in fact1 additional elements have from time to time been announced1 as for example1 the decipium of ,delafontaine 7#ahgh7 and the monium or victorium of ,crookes 7#ahii71 pronounced by ,urbain to be identical with gadolinium3 their individuality cannot as yet be said to be established4 ,didymium itself was stated by ,krss and ,nilson 7#ahhh7 to be even more complicated than the work of ,auer von ,welsbach would seem to indicate1 and to contain no fewer than eight elementary substances4 ,as yet1 however1 no confirmation of this surmise has been obtained4 ,the chemistry of the rare earths has of late years been greatly extended owing to the employment of certain of the members of the group in the manufacture of the 8mantles0 used in gas-lighting1 and which consist substantially of thoria1 mixed with about one per cent4 of ceria4 ,large quantities of monazite1 thorianite1 thorite1 cerite1 and other minerals1 are now worked up for the sake of the thoria and ceria they contain1 and considerable amounts of residual products1 consisting largely of other members of the family1 are now available for investigation4 ,it is reasonably certain1 therefore1 that our knowledge of this section of inorganic chemistry will be largely augmented in the immediate future4 ,indeed1 the application of thoria to the construction of gas-mantles may be said to have removed that substance from the category of the rare elements4 ,no sooner was it discovered that it was capable of useful application than unexpected sources of supply were found4 ,the same result has followed in other cases4 ,one of the most significant developments of modern chemistry is seen in the efforts which are constantly being made to turn the so-called rare elements to useful account2 and when they are found to be technically valuable it is generally observed that hitherto unknown sources of supply are soon available4 ,cerium salts have been found to be useful in the colouring of glass and porcelain1 as mordants in dyeing1 in photography1 and in medicine4 ,zirconium has been used in incandescent electric lighting1 and thallium has been employed in the manufacture of highly refractive optical glass4 ,titanium1 molybdenum1 and vanadium are used in the manufacture of steel of high tensile strength4 ,tantalum and tungsten are employed in the construction of filaments in incandescent electric lighting4 ,tantalum1 indeed1 has been found to occur in considerable quantities1 and to be more largely distributed than was hitherto supposed4 ,alloys of tungsten and aluminium are used in automobile construction1 and alloys of tungsten1 aluminium1 and copper in the manufacture of propeller blades4 ,tungsten steel is used in armour plates1 and to stiffen the springs of cars2 in the manufacture of piano-wire1 and to increase the permanency of magnets4 ,even the rarer metals of the platinum group are finding many important applications4 ,osmium-iridium is used for the bearings of compasses1 for the tips of gold pens1 and in the construction of standard weights4 ,osmium and ruthenium enter into the composition of filaments for electric lighting4 ,the extraordinary influence of light on the electric conductivity of selenium has been made use of in the transmission of photographs by telegraph and telephone wires1 and for measuring the light intensity of the ,rntgen rays in clinical work4 ,,chapter ,,iii ,,the ,,inactive ,,elements3 ,,radium ,,and ,,radio-,,activity ,argon1 helium1 krypton1 neon1 and xenon belong to the group of the so-called inactive elements1 and constitute what are known as the rare gases of the atmosphere4 ,the existence of these bodies is of great theoretical value and few discoveries of recent times have exacted more interest and curiosity4 ,twenty years ago it was generally assumed that practically all that was to be known concerning the composition of atmospheric air had been ascertained4 ,priestley and ,cavendish had recognised that it was mainly composed of oxygen and nitrogen1 and ,cavendish had definitely stated that these gases are present in practically constant proportion1 independent of season1 climate1 or locality4 ,thnard1 ,saussure1 and others1 had determined the limits of variation in the amount of carbon dioxide4 ,bunsen and ,regnault had established that the quantities of oxygen and nitrogen are subject to slight alteration1 the extent of which could be readily determined by the exact eudiometric processes they had devised4 ,lastly1 it was proved beyond a doubt that the gases of the atmosphere are simply mechanically mixed1 and can be separated by a variety of physical methods4 ,in fact1 of no single subject could it be more confidently assumed that finality of knowledge had apparently been reached4 ,in #ahib1 in the course of a series of determinations of the densities of the common gases1 ,lord ,rayleigh found that the density of nitrogen obtained from the air was slightly greater than the density of that gas prepared by the decomposition of ammonia and of nitric acid1 the difference in weight being about #a part in #bjj--;an amount far greater than could be accounted for by errors of weighing4 ,various suppositions were made in explanation of the discrepancy2 but these1 when tested1 were found not to account for the facts4 ,by heating the atmospheric nitrogen with metallic magnesium1 whereby the greater portion of the gas is absorbed to form the nitride1 ,sir ,william ,ramsay found that the density of the residual gas was still further increased1 which rendered it probable that the relatively high density of atmospheric nitrogen as compared with that derived from ammonia1 and1 as ,lord ,rayleigh found1 from other sources also1 was due to the presence of a gaseous substance in the air of considerably greater density than nitrogen or oxygen4 ,lord ,rayleigh also subjected atmospheric nitrogen mixed with oxygen to the electric discharge over a solution of caustic soda1 in a manner similar to that already employed by ,cavendish1 and found also that the residual gas was considerably increased in density4 ,at the ,oxford meeting of the ,british ,association in ,august1 #ahid1 the two investigators were in a position to announce that the discrepancy was actually due to the presence of a hitherto unknown gaseous constituent of atmospheric air1 considerably more soluble in water than nitrogen1 and to which1 on account of its chemical inertness1 the name of argon 71 idle7 was given4 ,by a special apparatus devised by ,lord ,rayleigh1 in which a mixture of air and oxygen is submitted to an electric flame produced by a powerful1 rapidly alternating current1 considerable quantities of argon were separated from the air4 ,it has also been found that by the use of metallic calcium or a mixture of magnesium and lime1 the atmospheric nitrogen is absorbed at a lower temperature1 and more rapidly than by magnesium alone4 ,argon has been found to exist in the gases from springs and mineral waters1 notably in those of ,bath1 ,cauterets1 ,wildbad1 and ,harrogate4 ,it has also been found in a meteorite1 in the gas occluded in rock-salt1 and in the minerals malacone1 uraninite1 brggerite1 etc4 ,no animal or vegetable substance appears to contain it4 ,it is present in atmospheric air to the extent of about one per cent4 by volume4 ,it is a colourless gas of an atomic weight of #ci4i3 one litre of it at the standard temperature and pressure weighs #a4ghae grams4 ,experiments made by the method of ,kundt and ,warburg--i4e41 by determining the ratio of the specific heats at constant pressure and constant volume by the velocity of sound in the gas--prove that argon1 like mercury gas1 is monatomic4 ,this of itself indicates that argon is an element1 since a monatomic compound is a contradiction in terms4 ,the calculations from the experimental data presuppose that argon obeys the laws of ,boyle and ,dalton1 which was found on trial to be the case4 ,by the application of cold and pressure argon can be liquefied4 ,the liquid boils at -#ahf4a and freezes at -#ahg4i4 ,the spectrum of the gas is exceedingly complicated1 consisting of a great number of lines extending throughout the visible portion and far into the extreme red and ultra-violet4 ,the colour of the light emitted on sparking the gas changes with increase of temperature from a brilliant red to a bright blue--depending on the intensity of the discharge4 ,all attempts to induce argon to enter into combination with other substances have failed4 ,the methods of its preparation show that it does not combine with oxygen1 although ,troost and ,ouvrard state that it unites with magnesium vapour4 ,it forms no compounds with hydrogen1 chlorine1 phosphorus1 sulphur1 sodium1 tellurium1 etc4 ,even fluorine1 probably the most generally active of the chemical elements1 shows no tendency to unite with it4 ,in #ahhh ,dr4 ,hillebrand1 of the ,u4,s4 ,geological ,survey1 in examining a form of uraninite known as cleveite1 so named from the late ,professor ,cleve1 found that on treatment with dilute sulphuric acid it gave off considerable quantities of a gas which was assumed to consist only of nitrogen1 as it gave the spectroscopic reactions of that element4 ,to test whether this gas contained argon1 ,ramsay1 in #ahie1 further examined it spectroscopically4 ,after sparking it with oxygen in the presence of caustic soda solution1 in the way already described1 it gave no indications of argon4 ,the main characteristic of its spectrum was a bright yellow line1 known as ,d#c1 not coincident with that afforded by sodium1 but identical in position with a line detected in the chromosphere during the solar eclipse of #ahfh1 which line1 on examination by ,frankland and ,lockyer1 could not be ascribed to any known element4 ,for this supposed new element the name helium1 from 1 the sun1 had been suggested4 ,this was the first occasion on which an element observed originally only in the sun was found to occur also on the earth4 ,the presence of the new element in the gas from cleveite was subsequently confirmed by ,langlet working in ,cleve's laboratory4 ,illustration3 ,,sir ,,william ,,ramsay4 ,helium is a monatomic gas having the atomic weight #d4 ,it is less soluble in water than argon4 ,like argon1 it shows no tendency to enter into chemical union with any other substance4 ,it has been found in many minerals1 particularly in those containing uranium and the so-called rare earth metals4 ,it also occurs among the gases issuing from certain mineral springs1 such as those of ,bath and at ,cauterets in the ,pyrenees1 and also at ,adano near ,padua4 ,the spectrum of helium contains1 in addition to the characteristic yellow line--by which its presence had been recognised not only in the solar chromosphere1 but also in certain of the fixed stars--two lines in the red1 and lines in the green1 blue1 and violet4 ,the character of the light emitted by the spark-discharge is modified by the intensity of the discharge in a manner similar to that of argon4 ,it has been shown by ,collie that its spectrum is altered by the presence of mercury vapour4 ,it is the least refractive of all the gases4 ,helium was liquefied by ,kammerlingh ,onnes in #aijh4 ,it forms a colourless liquid of sp4 gr4 #j4aed1 boiling at -#bfh4e2 that is1 #d4e above the absolute zero of temperature4 ,its critical temperature is about #e absolute1 and its critical pressure above #b atmospheres4 ,the methods now in use for obtaining liquid air1 referred to in a subsequent chapter1 enable large quantities of that material to be obtained readily2 and it was in investigating spectroscopically the residues left after volatilising a quantity of liquid air that ,ramsay and ,travers1 in #ahih1 detected the existence of two new monatomic gaseous constituents of the air which they named respectively krypton 71 hidden7 and neon 71 new71 the former heavier and the latter lighter than argon4 ,by fractional distillation of the argon1 simultaneously procured1 a gas was obtained which in the spectroscope showed the characteristic lines of helium--previously recognised in atmospheric argon by ,kayser and ,friedlnder--together with a complicated spectrum consisting of a number of lines in the red1 orange1 and yellow due to the new element neon4 ,on cooling this mixture to -#beb by means of liquid hydrogen1 the neon solidified1 while the helium remained gaseous and could thus be separated4 ,krypton was obtained from the residues left on the evaporation of a large quantity of liquid air4 ,mixed with the krypton was a third gaseous constituent of air1 to which the name xenon 71 the stranger7 was given4 ,the boiling-point of krypton at atmospheric pressure was found to be -#aeb1 and its melting-point -#afi2 the boiling-point of xenon was -#aji and its melting-point -#adj4 ,their critical temperatures were respectively -#fb4e and #ad4g4 ,hence xenon could be liquefied by pressure a very little below the mean temperature of the air4 ,neon boils at -#bdc and freezes at -#bec4 ,they form colourless liquids freezing to ice-like solids4 ,all of them1 with the exception of argon1 which is present to the extent of about #a part in #ajg parts of air1 are contained in extremely small amounts in the atmosphere1 approximately in the following proportions3 ,helium #a part in #bde1cjj parts by volume4 ,neon #a 0 0 #hj1hjj 0 0 ,krypton #a 0 0 #bj millions 0 0 ,xenon #a 0 0 #agj 0 0 0 ,many tons of liquefied air have since been systematically fractionated1 but no other gas than those above named has been obtained4 ,julius ,thomsen1 of ,copenhagen1 in a paper published in #ahie1 entitled ,on the ,probability of the ,existence of a ,group of ,inactive ,elements1 pointed out1 in relation to ,mendeleff's ,law of ,periodicity 7see ante71 that in periodic functions the change from negative to positive value1 or the reverse1 can take place only by a passage through zero or through infinity2 in the first case the change is gradual1 and in the second case it is sudden4 ,the first case corresponds with the gradual change in electrical character with rising atomic weight in the separate series of the periodic system1 and the second case corresponds with a passage from one series to the next4 ,it therefore appears that the passage from one series to the next in the periodic system should take place through an element which is electrically indifferent4 ,the valency of such an element would be zero1 and therefore in this respect also it would represent a transitional stage in the passage from the univalent electronegative elements of the seventh to the univalent electropositive elements of the first group4 ,this indicates the possible existence of a group of inactive elements with the atomic weights #d1 #bj1 #cf1 #hd1 #acb--numbers corresponding fairly closely with the atomic weights respectively of helium1 neon1 argon1 krypton1 and xenon4 99 99 99 99 99 ,no discovery of recent years has created more widespread interest than that of the radio-active elements4 ,in #ahif ,henri ,becquerel found that uranium salts emitted an invisible radiation which had the power of affecting a photographic plate1 even though not directly exposed to it1 exactly in the same way as the ,rntgen or ,x-rays4 ,since that time a number of substances have been shown to possess a similar property4 ,such substances are said to be radio-active4 ,the radiation emitted by them is not uniform in character4 ,it has been found to be of three distinct types1 known respectively as the 1 1 and radiations4 ,the rays consist of positively electrified particles moving with a velocity equal to about a fifteenth of that of light4 ,these rays have little penetrative power1 and are capable of being deflected by a magnet4 ,the rays consist of negatively electrified particles of a mass not greater than one thousandth of that of the hydrogen atom1 and they move with a velocity approximating to that of light4 ,the rays have a greater penetrative power than the rays1 and are even more readily deflected by a magnet4 ,the rays are analogous to1 if not identical with1 the ,x or ,rntgen rays2 they move with the velocity of light1 have a high penetrative power1 but are not affected by the magnet4 ,all three forms of radiation render gases electrically conductive1 excite luminescence or fluorescence in certain substances1 change the colour of glass1 convert oxygen into ozone and yellow phosphorus into red phosphorus1 and act upon photographic plates4 ,according to the disintegration theory of ,rutherford and ,soddy1 the radio-active elements are forms of matter undergoing changes resulting in the formation of new forms possessing chemical and physical properties differing from those of the parent substance1 these changes being accompanied by the production of sensible heat1 or some other manifestation of energy1 due to the process of transformation of the changing atoms4 ,the rate of change is found to be different for each radio-active element1 but to be constant for the same element irrespective of its particular form of combination4 ,the relative radio-activity of the various chemical combinations of a given radio-active element is directly proportional to the quantity of the element contained in them4 ,the process of disintegration may be carried through a number of intermediate products until a stable form is produced4 ,uranium1 in which the phenomenon of radio-activity was first perceived1 is supposed to give rise to no fewer than seventeen different forms of matter1 including radium1 actinium1 and polonium4 ,thorium1 another radio-active element1 is supposed to disintegrate into eight different forms of matter4 ,uranium disintegrates with extreme slowness2 it is calculated that in a year not more than one ten-billionth part of the uranium is transformed4 ,the first disintegration product is termed uranium x4 ,if a quantity of dehydrated uranium nitrate be treated with ordinary ether1 a slight residue is obtained which is found to contain uranium x4 ,it emits and rays1 and is relatively rapidly transformed into other substances4 ,ordinary uranium1 freed from uranium x1 only emits rays4 ,uranium salts can be freed from uranium x by repeated crystallisation1 uranium x remaining in the mother liquors4 ,illustration3 ,,marie ,,curie 7ne ,,sklodowska74 ,the existence of radium was first made known by ,mme4 ,curie in #ahih4 ,in examining certain uranium minerals and uranium products1 ,mme4 ,curie observed that their radio-activity was apparently greater than that corresponding with the amount of uranium contained in them1 and she was led to surmise that this might be due to the presence of some constituent more strongly radio-active than uranium4 ,this supposition proved to be well founded1 and she eventually succeeded in isolating a new element termed radium1 forming compounds with characters and relationships akin to those of barium4 ,the richest source of radium at present known consists of certain residues occurring at ,joachimsthal1 in ,bohemia1 left after the extraction of uranium from pitch-blende1 in which radium occurs to the extent of #j4b gram per ton4 ,these residues are mainly sulphates of lead and calcium1 mixed with a great variety of other metallic compounds4 ,to obtain the radium the mixture is heated with concentrated caustic soda solution1 the residue washed with water and treated with hydrochloric acid which dissolves the greater portion of the material4 ,nearly the whole of the radium is left in the insoluble portion4 ,this1 after washing with water1 is boiled with a solution of sodium carbonate so as to transform the alkali-earths into carbonates4 ,these are converted into chlorides or bromides from which1 by repeated crystallisation1 barium chloride or bromide is obtained1 containing the greater portion of the radium as a halide salt4 ,the radium and barium salts are then separated by fractional crystallisation1 the radium salts being slightly less soluble in water and alcohol1 and in solutions containing the halogen acid1 than the barium salt4 ,pure radium chloride 7,ra,cl#b7 is a white crystalline salt1 resembling barium chloride1 with which it appears to be isomorphous4 ,radium1 like barium1 forms an insoluble carbonate and sulphate1 but a soluble nitrate and bromide4 ,the bromide is much less stable than the chloride2 on standing it evolves bromine and becomes basic4 ,radium has as yet been obtained in such small quantities that very few of its compounds have been prepared4 ,the rays from radium salts burn the skin1 and are found to be useful in the destruction of rodent ulcers2 they appear to act upon proteids1 destroy bacteria1 bleach chlorophyll1 and affect the germinative power of seeds4 ,a pure and freshly-prepared salt of radium seems to emit only rays1 but it soon forms disintegration products1 and then gives out1 in addition1 the and rays4 ,in the process of disintegration the salts emit heat corresponding to about #ge gram calories per hour for each gram of radium present2 their temperature is thus uniformly higher than that of their environment4 ,one product of the change probably connected with the emission of the rays1 is the gas helium4 ,radium has an atomic weight of #bbf4e4 ,it is regarded as a product of the disintegration of uranium1 the atomic weight of which is #bch4e4 ,it is believed to have been formed through an intermediate product known as ionium1 a radio-active element discovered by ,boltwood in the mineral carnolite4 ,the atomic weight of ionium is surmised to be about #bcj4 ,radium itself is supposed to form at least eight disintegration products1 the first of which is the so-called emanation1 discovered by ,dorn in #aijj1 an inactive gas with an atomic weight of about #ahj1 giving a bright line spectrum1 decomposing into helium1 liberating oxygen and hydrogen from water1 and capable of being condensed to a liquid and solidified at a low temperature4 ,ramsay and ,gray have determined its physical constants4 ,the liquid is phosphorescent and shines with a colour depending on the nature of the glass of the vessel which contains it4 ,the solid is also phosphorescent1 the colour varying with the temperature4 ,it gives out only rays and in its disintegration1 like radium1 evolves heat4 ,its position in the ,periodic ,table is probably above that of xenon4 ,other products are known as radio-lead and polonium4 ,the latter substance was identified by ,m4 and ,mme4 ,curie in #ahih1 and was the first of the strongly radio-active substances to be recognised4 ,in the periodic system it seems to follow bismuth and to be a member of ,group ,,vi41 with a possible atomic weight of #baj4 ,its spectroscopic characters have recently been examined by ,mme4 ,curie and ,debierne1 who have shown that in its decay it evolves helium4 ,the rate of disintegration of radium is relatively slow2 it has been calculated that the time required for half of any given quantity of radium to change completely into other products is about #bjjj years4 ,rutherford has calculated that in #bf1jjj years a kilogram of radium would be reduced to one milligram of active substance1 the remainder having passed into degradation products4 ,in #ahii ,debierne announced the existence of another radio-active element contained in uranium minerals1 which he termed actinium4 ,this is probably a disintegration product of uranium and identical with the emanium of ,giesel4 ,it occurs associated with the rare earths which can be separated from the pitch-blende residues1 and is eventually found in the lanthanum salts4 ,nothing is known as to its atomic weight or its chemical relationships4 ,it undergoes change1 and forms1 apparently1 a gaseous emanation which rapidly disintegrates and can be condensed to a liquid at a low temperature4 ,four other successive products have been identified by the character of the radiation they emit1 their degradation constants1 and the time required for one half of any given quantity to disintegrate into other forms of matter4 ,thorium was shown to contain a radio-active element by ,mme4 ,curie and ,schmidt1 independently1 in #ahih4 ,whether thorium is itself active is doubtful4 ,the rate of disintegration of radio-thorium is probably greater than that of uranium4 ,it1 too1 seems to form a gaseous emanation which can be condensed at the temperature of liquid air and appears to be an inert gas of high molecular weight with the characteristics of the argon family4 ,the type of radiation emitted by the several products has been observed1 and their constants of change and half-value periods calculated2 but little or nothing is known at present concerning their atomic weights1 spectroscopic or chemical characters4 ,,chapter ,,iv ,,atoms ,,and ,,molecules3 ,,atomic ,,weights ,,and ,,equivalents ,it has already been pointed out that the discovery by ,gay ,lussac1 and independently by ,dalton1 that gases combine in simple proportions by volume1 and that the volume of the gaseous product1 measured under comparable conditions of temperature and pressure1 stand in simple relation to the volumes of the constituents1 seemed to most of ,dalton's contemporaries1 but not to ,dalton himself1 to afford strong evidence of the validity of his explanation of the essential nature of chemical combination4 ,it appeared obvious from the facts that there must exist some simple relation between the densities1 or specific gravities1 of the elementary gases and their atomic weights4 ,when1 however1 the principle underlying ,gay ,lussac's law was extended so as to include gases in general--both simple and compound--difficulties were met with which were only satisfactorily cleared away during the latter half of the nineteenth century4 ,the first rational attempt to explain the facts observed by ,dalton and ,gay ,lussac1 concerning the volumetric relations of gases1 was made in #ahac by ,amedeo ,avogadro by the assumption that a given volume of all gases--simple or compound--contains the same number of integral molecules2 hence the relative weights of these volumes represent the relative weights of the molecules4 ,according to ,avogadro1 in the case of the simple gases the integral molecules are composed of a certain number of elementary molecules of the same kind1 whereas the integral molecules of compound gases and vapours are made up of elementary molecules of different kinds4 ,the elementary molecule of ,avogadro is now termed the atom2 his integral molecule we call simply a molecule4 ,similar conceptions were published independently by ,ampre in #ahad4 ,it follows from the doctrine of ,avogadro and ,ampre that1 as the number of integral molecules is the same in equal volumes of all gases1 these molecules must be equidistant from each other1 their mutual distances depending upon pressure and temperature4 ,this at once serves to explain the laws of ,boyle and ,dalton that gases1 no matter what their chemical nature1 behave identically1 as regards change of volume1 when compressed by pressure or expanded by heat4 ,the true significance of the hypotheses of ,avogadro and ,ampre was long obscured1 first on account of their imperfect appreciation by the great leaders of chemical thought during the first half of the nineteenth century--,berzelius1 ,gay ,lussac1 ,wollaston1 and ,gmelin--and1 secondly1 on account of the almost universal practice of deducing atomic weights from purely chemical considerations of equivalence4 ,at the same time1 it must be admitted that the recognition of the value of these hypotheses was still further retarded by the seeming anomalies which resulted from a more extended knowledge of the vapour densities of elements and compounds4 ,thus the vapour densities of mercury1 sulphur1 phosphorus1 and arsenic1 as ascertained by ,dumas and ,mitscherlich1 were plainly inconsistent with chemical analogies and the law of ,dulong and ,petit4 ,so1 too1 what appeared to be the vapour densities of sal-ammoniac1 phosphorus pentachloride1 sulphuric acid1 calomel1 and of other substances that might be mentioned1 were not in accordance with the values demanded by other well-ascertained facts4 ,by the middle of the nineteenth century the hypothesis of ,avogadro was practically forgotten and the law of volumes ignored4 ,the atomic weights of the elements1 and the system of notation universally employed in ,england and ,germany1 were based wholly upon equivalents4 ,the anomalies thus created were clearly pointed out by ,gerhardt1 and subsequently by ,laurent who showed how a consistent and harmonious explanation of the facts could be reached by regarding as true equivalents equal volumes--for example1 of steam1 ammonia1 hydrogen chloride1 carbon dioxide1 marsh gas1 etc42 by assuming1 in other words1 that equal numbers of the molecules of these various substances are contained in equal volumes of the gases1 as contended by ,avogadro and ,ampre4 ,the simplicity and consistency of the new notation gradually won for it the adhesion of chemists4 ,this adhesion was facilitated by the memorable researches of ,williamson on etherification1 of ,gerhardt on the anhydrides1 and by the work of ,frankland on the radicals2 and it reached its logical conclusion when ,cannizzaro--on the basis of ,avogadro's hypothesis--discussed1 in #aheh1 the true atomic weights of the metallic elements as distinguished from their equivalent values4 ,in certain of its aspects the new table of atomic weights drawn up by ,cannizzaro resembled that originally proposed by ,berzelius2 but the numbers adopted by the ,swedish chemist were founded on no uniform or rational basis1 and were frequently inconsistent4 ,illustration3 ,,stanislao ,,cannizzaro4 ,our present tables of atomic weight bring1 therefore1 the values for the several elements into harmony with the doctrine of ,avogadro and ,ampre1 with the law of ,dulong and ,petit1 and with the facts of isomorphism4 ,the values are1 in fact1 in unison with all the criteria which serve to indicate the atomic weights of the elements4 ,as a result1 our present system of notation1 which is1 of course1 based upon these atomic weights1 assigns formul to compounds which indicate their true relative molecular weights and simplify the accurate expression of their relationships and chemical transformations4 ,one by one the instances of anomalous vapour density1 which were so many stumbling blocks to the universal acceptance of a system based upon the law of gaseous volumes1 have been shown to be not only not inconsistent with it1 but actually so many corroborative proofs4 ,thus1 in the case of ammonium chloride1 the observed vapour density of which was found to be practically half its calculated value1 it has been proved that the vapour of this salt1 when heated to the temperature at which the observations were made1 is mainly resolved into molecules of ammonia and hydrogen chloride1 which together occupy double the space of the ammonium chloride molecule4 ,phosphorus pentachloride vapour1 on being sufficiently heated1 is similarly more or less resolved into phosphorus trichloride and chlorine4 ,moreover1 it has been found1 by a more accurate study of the action of heat upon the vapour of ammonium chloride and of phosphorus pentachloride1 that within certain narrow limits of temperature these substances can actually exist as such in the gaseous state1 and that the density of their vapours does actually conform to that demanded by theory4 ,moreover1 phosphorus pentafluoride1 the analogue of the pentachloride1 is gaseous at ordinary temperatures1 and has a normal density4 ,it may be heated to a high temperature without showing any sign of decomposition4 ,limitations of space will not allow of a fuller explanation of the apparent anomalies already alluded to4 ,they have each in turn been experimentally attacked and satisfactorily explained4 ,no valid exception is now known to the universal applicability of the principle4 ,to-day the chemical history of a substance1 whether elementary or compound1 if vaporisable1 is not complete until its vapour density is known1 since a knowledge of this constant affords the most certain means of establishing the relative weight of its molecule4 ,accordingly many chemists have endeavoured to simplify and render more convenient the modes of determining vapour densities4 ,thanks to the efforts of ,hofmann and ,victor ,meyer1 the processes associated with the names of ,dumas1 ,gay ,lussac1 ,deville1 and ,troost1 which have furnished us with valuable information in the past1 have now given way to comparatively simple and rapid methods1 which1 although not necessarily more accurate1 furnish the required information with less expenditure of time and trouble2 that is to say1 they serve to indicate which of two1 or more1 presumed molecular weights is correct1 and so enable us to establish the molecular formula of the substance4 ,the chemical formula of a substance is a condensed expression of a number of facts connected with its history4 ,thus the expression ,h#b,o--the chemical formula for water--indicates that the substance is composed of hydrogen and oxygen1 in the proportion1 using round numbers1 of #b parts by weight of hydrogen and #af parts by weight of oxygen2 or1 in other words1 of #b atoms of hydrogen1 each weighing #a1 and #a atom of oxygen weighing #af4 ,the formula1 moreover1 connotes the fact that when the gases combine #b volumes of hydrogen unite with #a volume of oxygen to form #b volumes of water-vapour 7steam74 ,so1 too1 the formula ,h,cl--which represents hydrogen chloride--means that the substance is a compound of #a atom of hydrogen weighing #a united with #a atom of chlorine weighing #ce4e2 it also denotes the fact that in the act of union #a volume of hydrogen combines with #a volume of chlorine to form #b volumes of hydrogen chloride4 ,lastly1 the formula ,,nh#c signifies that the molecule of ammonia is composed of #a atom of nitrogen weighing #ad1 and #c atoms of hydrogen1 each weighing #a2 it further indicates that when ammonia gas is resolved into its constituents1 as it can be when sufficiently heated1 #b volumes of ammonia gas are increased to #d volumes of a mixture made up of #a volume of nitrogen and #c volumes of hydrogen4 ,in short1 all the formul are what are called two-volume formul2 that is1 the relative molecular weights of the substances occupy the same volume as two relative parts by weight of hydrogen4 ,hence their vapour densities--referred to hydrogen as unity--are the halves respectively of their molecular weights4 ,steam is #i times1 hydrogen chloride #ah4be times1 and ammonia #h4e times heavier than hydrogen1 when measured under identical conditions of temperature and pressure4 ,the quantities expressed by the formul ,h#b1 ,h#b,o1 ,h,cl1 ,,nh#c1 occupy the same volume4 ,this is equally true of the quantities expressed by ,o#b1 ,n#b1 ,cl#b1 etc4 ,these expressions signify that the molecules of the elements of hydrogen1 oxygen1 nitrogen1 and chlorine consist each of #b atoms of the respective substances3 the molecule of water consists of #c atoms--#b of hydrogen and #a of oxygen2 the molecule of hydrogen chloride of #b atoms--#a of hydrogen and #a of chlorine2 whereas the molecule of ammonia contains #d atoms--#a atom of nitrogen and #c atoms of hydrogen4 ,certain of the elementary bodies are1 as already stated1 capable of existing in different allotropic states4 ,thus there is a modification of oxygen known as ozone4 ,this substance has long been recognised as being formed from air under the influence of the electric discharge4 ,it was the subject of study by ,schnbein as far back as #ahci2 but that it was a condensed form of oxygen and not a peroxide of hydrogen--as was at one time surmised--was first established by ,andrews and ,tait4 ,the degree of its condensation was definitely ascertained by ,soret by observing its rate of diffusion1 from which1 on the basis of ,graham's law1 its density could be inferred4 ,it was found to be #a times that of ordinary oxygen4 ,hence1 if the molecule of oxygen consists of #b atoms1 that of ozone consists of #c atoms4 ,the chemical symbol of ozone is1 therefore1 ,o#c4 ,it has been found also that the molecule of sulphur1 in the state of solution1 contains eight atoms4 ,this complex molecule in the gaseous state gradually breaks down as the temperature is increased1 and at temperatures above #hej contains1 like its analogue oxygen1 only two atoms4 ,the molecules of phosphorus and arsenic1 in the gaseous state1 are each found to consist of four atoms4 ,on the other hand1 the molecules of mercury1 zinc1 and cadmium each consist of only one atom4 ,as will be shown later1 ,kundt and ,warburg established1 in #ahge1 the fact that mercury vapour is a monatomic gas1 by determining the rate at which sound is propagated through it4 ,in the same way it was shown that helium1 argon1 and its congeners are also1 as already stated1 monatomic gases4 ,the applicability of the law of ,dulong and ,petit to the determination of atomic weights has been frequently exemplified during the last sixty years2 and a number of these constants have been rectified by its means--e4g41 of thallium1 uranium1 glucinum1 indium1 etc4 ,the anomalies presented by the cases of elements of low atomic weight--e4g41 carbon1 boron1 silicon--have been further inquired into2 and it has been shown by ,weber1 and independently by ,dewar1 that in the case of these substances the specific heat rapidly increases with the temperature1 and approximates at high temperatures to a value required by the law of ,dulong and ,petit4 ,within recent years other methods of ascertaining molecular weights have been put at the disposal of chemists4 ,these methods are especially valuable in the case of bodies which cannot be volatilised4 ,they depend upon the influence of the substance 7#a7 upon the freezing-point and 7#b7 upon the boiling-point of a solvent4 ,it has long been known that a substance in solution affects the freezing-point of the solvent1 and in the great majority of cases depresses it4 ,sir ,charles ,blagden1 as far back as #aghh1 showed that in aqueous solutions of inorganic salts the depression was proportional to the amount dissolved4 ,it was subsequently found by ,coppet that1 in a number of solutions of similar salts where these were present in the ratio of their molecular weights1 the solutions froze at practically the same temperature3 the molecular depressions of the freezing-points differ from group to group but are nearly equal in groups of similar compounds4 ,raoult further observed that1 when certain quantities of the same substance are successively dissolved in a solvent on which it exerts no chemical action1 there is a progressive lowering of the point of solidification of the solution1 and this depression is proportional to the weight of the substance dissolved in a constant weight of the solvent4 ,in the case of a large number of solvents the depressions of the freezing-point1 calculated for amounts proportional to the molecular weights of the dissolved substance1 were nearly constant4 ,raoult pointed out that these relations between the molecular weights and the lowering in the freezing-point may be employed to determine the molecular weight of a soluble substance4 ,the molecular weight m is found from the expression m ,k_/,a1 where ,a is the quotient obtained by dividing the observed depression in the freezing-point of the solvent by the percentage content of the solution1 and ,k 7the molecular depression7 is a constant dependent on the solvent4 ,thus in the case of phosphorous oxide it was found that #j4fgfj gram added to #bj4fih grams of benzene--in which the oxide is soluble without change--lowered the freezing-point of the #c4af per cent4 benzene solution by #j4fh4 ,since the value of ,k for benzene is #di1 we have 7#c4af #di7_/j4fh #bbg1 which serves to indicate that ,p#d,o#f is the true molecular formula for phosphorous oxide4 ,this result is confirmed by vapour-density observations4 ,the effect of adding a substance to a solvent is to diminish the vapour pressure of the liquid4 ,hence1 since the boiling-point of a liquid is that temperature at which the vapour pressure is equal to the atmospheric pressure1 the effect of adding the soluble substance is to raise the boiling-point1 since a higher temperature is required in order that the pressure of the vapour shall equal that of the atmosphere4 ,it has been proved that equal volumes of solutions in the same solvent which have the same boiling-point contain an equal number of molecules of the dissolved substance4 ,the equation for the molecular increment of the boiling-point for a solvent is d #j4jb,t_/w1 in which d is the increment of the boiling-point caused by the solution of one gram-molecule of a substance in #ajj grams of the solvent1 ,t the absolute boiling-point of the solvent1 and w the heat of vaporisation of the solvent for one gram4 ,the molecular rise of the boiling-point is therefore independent of the nature of the dissolved substance4 ,the molecular weight of the substance m is obtained from the formula m pd_/1 in which p the percentage weight of the dissolved substance1 d the molecular increment in boiling-point 7#j4jb,t_/w71 the observed rise in boiling-point4 ,if the latent heat of vaporisation of the liquid is unknown1 the value of d may be obtained by preliminary experiments with a substance of known molecular weight2 in this case d m_/p4 ,the calculation of the molecular weight m may also be made by the formula m ,k7s_/,l7 #ajj1 in which is the rise in boiling-point1 s the weight of dissolved substance1 ,l the weight of solvent1 and ,k the molecular boiling-point increment4 ,convenient forms of apparatus for using these methods have been devised by ,beckmann1 and are now in general use4 99 99 99 99 99 ,from the time of ,berzelius1 each successive generation of chemists has striven to better the example of that master of determinative chemistry in the effort to obtain accurate values for the atomic weights of the elements4 ,among the immediate successors of ,berzelius in this work should be mentioned ,turner1 ,penny1 ,dumas1 and ,marignac4 ,dumas in #ahei published the results of an extensive revision of the atomic weights of the elements4 ,on this he based the far-reaching generalisation that1 in the language of ,prout1 8the combining or atomic weights of bodies bear certain simple relations to one another1 frequently by multiple1 and consequently that many of them must necessarily be multiples of some one unit40 ,dumas further agreed with ,prout that 8there seems to be no reason why bodies still lower in the scale than hydrogen 7similarly1 however1 related to one another1 as well as to those above hydrogen7 may not exist1 of which other bodies may be multiples1 without being actually multiples of the intermediate hydrogen40 ,the ,belgian chemist1 ,stas1 who had been associated with ,dumas in a classical determination of the atomic weight of carbon1 set himself to determine1 with the highest degree of precision then possible1 the atomic weights of about a dozen of the elements1 with a view of ascertaining 7#a7 whether an atomic weight is a definite and constant quantity1 or whether1 as suggested by ,marignac1 and subsequently by ,crookes1 an atomic weight represents 8a mean value around which the actual weights of the atoms vary within certain narrow limits02 7#b7 whether1 if the atomic weights of the elements are respectively definite and invariable1 the numbers are commensurable as alleged by ,prout and ,dumas2 and 7#c7 if it should turn out that the numbers are severally fixed and commensurable1 whether this necessarily indicates that the elements are built up of a primordial matter1 the of the ancients1 referred to by ,prout in #ahaf4 ,stas devoted many years to the solution of these questions1 working on a scale and with an accuracy and manipulative skill previously unapproached4 ,the main results of his labour appeared in #ahfe4 ,he concluded 7#a7 that the atomic weights of the elements are absolutely constant values1 and are not affected by the nature of the compounds in which they occur1 or the physical conditions of their existence2 7#b7 that the numbers so obtained are not commensurable3 to quote his own words3 8,on doit considrer la loi de ,prout comme une pure illusion40 ,hence the elements must1 on the basis of ,stas's experimental evidence1 be regarded as 8individualits part10 as he expressed it--each a primordial and unalterable substance4 ,the appearance of this monumental work1 which will ever remain one of the classics of chemistry1 created a great impression4 ,its effect persists to this day4 ,it constituted a model and furnished a standard which each successive worker has striven to emulate1 with the result that atomic weights to-day are among the best ascertained of physical constants4 ,space will not permit of any detailed account of the work done in connection with atomic weights during the forty-five years which have elapsed since the publication of ,stas's memoirs2 and the reader who desires fuller information must be referred to the special treatises on the subject1 such as the ,constants of ,nature of ,f4 ,w4 ,clarke1 or the monographs of ,meyer and ,seubert1 ,becker1 ,sebelien1 and ,van der ,plaats4 ,reference1 however1 must be made to the determinations by ,lord ,rayleigh1 ,leduc1 ,morley1 ,noyes1 ,guye1 ,dixon1 and ,edgar of values which1 like those of oxygen1 hydrogen1 nitrogen1 silver1 and the halogens1 are largely made use of as fiduciary values in atomic-weight work4 ,lastly1 it should be mentioned1 the re-determination of the atomic weights of the elements with the highest attainable precision and by the most refined and most modern methods has for some years past been a special feature of the work of the ,harvard ,laboratory1 under the direction of ,theodore ,richards2 and some of the most trustworthy and best established values we possess have been ascertained by him and his pupils4 ,atomic weights are of such fundamental importance that the various nations interested in the pursuit of chemistry have consented to the establishment of an ,international ,committee1 which will take cognisance of the work done from time to time in this department of operative chemistry1 examine and assess its value1 and draw up an annual report on the subject4 ,despite the accumulated testimony of this work in relation to the validity of the law of the conservation of mass1 the sufficiency of the evidence has now and again been impugned4 ,this aspect of the matter has within recent years been directly investigated by ,landolt2 and as the result of a painstaking series of experiments1 in which every recognised source of error was removed or allowed for1 it would appear that there is absolutely no ground for the belief that there is any dissipation of mass in the course of1 or as the result of1 a chemical change4 ,,chapter ,v ,,the ,,molecular ,,theory ,,of ,,gases ,the more obvious physical phenomena of gases were1 of course1 well known by the middle of the nineteenth century2 and the so-called gaseous laws--the laws of ,boyle1 ,dalton1 and ,gay ,lussac--were universally accepted by chemists and physicists at that time as fundamental4 ,that the first two laws were only approximations to truth in a mathematical sense was also well known2 and the experimental labours of ,regnault and ,magnus had not only established limits within which they were inexact1 but had1 to some extent1 indicated the cause of their departure from the ideal condition4 ,the hypothesis of ,avogadro1 as already stated1 was practically ignored at this period1 or at least its value was unappreciated until the time of ,gerhardt and ,laurent1 and more particularly ,cannizzaro1 who in #aheh pointed out its real meaning and made it the keystone in the edifice of modern chemistry4 ,one of the most significant achievements of the last half-century has been the demonstration that these gaseous laws are interdependent4 ,their further study1 and in particular the study of their variation from exact mathematical expression1 has led to a conception of the real nature of a gas which not only comprehends and knits together these laws1 but affords a rational explanation of them4 ,if the laws of ,boyle and ,dalton concerning the relations between pressure1 temperature1 and gaseous volume are1 and must be from the very nature of the case1 only approximations1 it follows that the same is equally true of the laws of ,gay ,lussac and ,avogadro1 since these are dependent on the others4 ,the definite experimental proof that gases do not actually combine in the precise ratios demanded by the law of ,gay ,lussac has been forthcoming only during the last twenty years4 ,it has been found that1 instead of oxygen and hydrogen combining in the exact ratio of one volume of oxygen to two volumes of hydrogen to form water1 as stated by ,gay ,lussac1 one volume of oxygen combines with1 according to ,scott1 #b4jjbde vols42 according to ,leduc1 #b4jjbd vols42 according to ,morley1 #b4jjbfh vols4 of hydrogen4 ,what is true of the volume-ratios in which oxygen and hydrogen are actually found to combine1 under ordinary conditions1 is no doubt equally true of analogous instances1 such as the union of hydrogen and chlorine to form hydrogen chloride4 ,it follows also that the extent of the variation from the mathematical expression of ,gay ,lussac's law must get smaller and smaller as the combining gases approach the condition of the ideal gas--as they do1 for example1 under very low pressures4 ,the precise degree of departure from ,gay ,lussac's law is therefore in a sense accidental1 and is dependent upon the conditions under which combination takes place4 ,the more exact study of the physical phenomena of gases1 and in particular the clearer recognition of the causes which determine the extent of their departure from the ideal gaseous laws1 have afforded valuable assistance in ascertaining the atomic weights of certain elements independently of chemical considerations4 ,the processes of physical measurement have been so refined within recent years that physical methods of arriving at molecular--and1 inferentially1 at atomic--weights1 in the case of all elements and compounds which can be brought into a condition approaching that of the ideal gas1 are to be preferred to the gravimetric methods of analysis or synthesis as affording the most probable values of the true atomic weights of the elements4 ,the work of ,lord ,rayleigh1 ,leduc1 and of ,guye and his pupils on the densities of the gases has furnished us with a series of values for the atomic weights of a number of the elements which1 in point of accuracy1 are as superior to the values of ,stas as the values of ,stas were superior to those of his predecessors4 ,daniel ,berthelot pointed out in #ahih that the true molecular weight of a gas can be deduced from its density and its observed variations from ,boyle's law under atmospheric pressure and at very low pressures4 ,incidentally1 the study of gaseous phenomena has served to place the theory of atoms upon a far more stable foundation than it occupied half a century ago4 ,how halting was the adhesion which even some of the most eminent chemists then gave to this theory was well exemplified by the remarkable lecture given before the ,chemical ,society of ,london in #ahfi1 in which ,williamson--one of the most sturdy champions of ,dalton's doctrine--set forth its true value4 ,that a gas may be looked upon as an association of particles--hard elastic spheres--moving backwards and forwards in right lines with great velocity1 and possessing in the aggregate a very small proportion of the space through which they travel1 was first conceived by ,daniel ,bernoulli in #agch4 ,by means of this hypothesis he explained the direct proportionality between the density and pressure of a gas4 ,if the gas consists of moving particles1 and the pressure which it exerts on the sides of the containing vessel is due to the impacts of these particles1 it is obvious that by halving the original volume of the containing space we halve the space through which the particles travel1 and therefore double the number of their impacts in a given time2 in other words1 by compressing the gas to half its initial volume we double the pressure it exerts1 which is nothing else than the law of ,boyle4 ,this conception of the nature of a gas is known as the kinetic theory of gases2 it was further developed by ,waterston in #ahde1 still more fully by ,clausius in #aheg1 and was subsequently placed in its present position by ,maxwell and ,boltzmann4 ,that gases actually do move1 and at rates depending on their specific nature1 was rendered probable--apart from this explanation of ,boyle's law--by many phenomena observed by chemists and physicists in the eighteenth and early part of the nineteenth century4 ,it was known from the observations of ,leslie in #ahjd that specifically light gases moved or diffused faster than heavy gases4 ,attempts to determine these rates were made by ,schmidt in #ahbj1 and by ,graham in #ahdf1 both of whom found that the rate of movement of a gas was independent of its chemical nature1 and was determined solely by its mass3 gases move at rates inversely proportional to the square roots of their densities4 ,the following table given by ,graham shows the experimentally ascertained relative rates for a number of gases compared with the rates demanded by the 8law of gaseous diffusion40 ,column one gives the name of the gas2 column two1 the observed rate of diffusion2 and column three1 the square root of the density of the gas 7air #a73 ,gas4 ,time of diffusion4 density4 ,air #a #a ,hydrogen #j4bgf #j4bfc ,marsh gas #j4gec #j4gde ,ethylene #j4ihg #j4ihe ,nitrogen #j4ihf #j4ihf ,oxygen #a4jec #a4jea ,carbon dioxide #a4bjc #a4bcg ,nitrogen and ethylene are1 chemically1 totally dissimilar gases1 but they have the same density and hence the same rate of movement4 ,as ,graham showed1 it is possible to separate more or less completely a mixture of gases1 if the constituents are of different densities1 by taking advantage of their different rates of movement4 ,such an atmolytic method was employed by ,rayleigh and ,ramsay to prove that atmospheric nitrogen contained argon4 ,the fact that all gaseous substances1 however different their chemical nature1 conform in the main to certain simple 8laws0 indicates the probability that their mechanical structure is similar and comparatively simple4 ,the so-called gaseous 8laws0--the laws of ,boyle1 ,dalton1 ,gay ,lussac1 ,avogadro1 and ,graham--are to-day explained on the assumption that a gas consists of an aggregation of molecules1 moving incessantly in straight lines and with great rapidity4 ,the rate of movement of the particles is variable by reason of their mutual encounters2 at the same instant some are moving rapidly1 others more slowly4 ,as already explained1 to this ceaseless movement of the molecules is to be ascribed the pressure they exert2 the pressure which a gas exerts on any containing surface is the aggregate effect of the impact of its molecules4 ,the law of ,boyle states that the product of the volume ,v and pressure ,p of a given mass of gas is invariable so long as the temperature is unchanged3 ,,pv constant4 ,it was found by ,regnault1 ,magnus1 ,natterer1 and ,amagat that all gases1 with the exception of hydrogen1 show a departure from ,boyle's law in the sense that ,,pv is less than theory demands4 ,in the case of hydrogen ,,pv is greater than theory4 ,this exception1 however1 is only apparent4 ,every gas1 if maintained above a certain temperature1 shows1 after a certain pressure has been reached1 a deviation in the same sense as that exhibited by hydrogen4 ,the deviations from ,boyle's law are probably due to two causes3 7#a7 to the effect of cohesion among the molecules1 whereby the volume1 and hence ,,pv1 is less than theory requires2 7#b7 the molecules are not mathematical points--they have a certain volume2 hence1 with increasing pressure1 ,,pv is greater than theory demands4 ,the effect of the molecule having a certain magnitude will be clear from the following figure3 ,let ,m be a molecule moving backwards and forwards within a certain space1 a b3 ,m a b ,assume1 now1 we halve the containing space3 ,m a b ,it will be seen that ,m1 since its volume is unchanged1 will have less than half the original distance to travel or1 in other words1 it will strike the boundaries of the containing space more than twice as frequently in the same interval of time as before2 hence ,p1 and therefore ,,pv1 becomes greater than ,boyle's law demands4 ,it will be noticed1 then1 that the two causes tending to bring about deviations from ,boyle's law act in contrary directions4 ,in the greater number of gases the effect due to cohesion at ordinary pressure is greater than the effect due to the actual space occupied by the molecules4 ,in the case of hydrogen at ordinary temperature the contrary is the case2 if1 however1 hydrogen is strongly cooled1 it shows variations similar to those exhibited by other gases at ordinary temperatures4 ,by heating these gases the effect due to cohesion--to the mutual attraction of the molecules--becomes less and less2 in such circumstances these gases show departures from theory in the same sense that hydrogen does at ordinary temperatures4 ,the effect of mutual attraction among the molecules is to make the volume of the gas less than the theoretical value2 the cohesive force may therefore be regarded as equal in effect to a certain additional pressure2 that is1 7,p ,a7 ,v constant1 in which ,a is the measure of the force of cohesion4 ,a1 of course1 must have relation to the number of molecules mutually attracted3 ,a is proportional to the square of the number of the molecules4 ,but the number of the molecules in the unit volume is proportional to the density of the gas1 and in a given mass of gas the density is inversely proportional to the volume4 ,hence ,a is inversely proportional to the square of the volume--,a a_/,v#b1 hence 7,p a_/,v#b7 ,v constant4 ,now let us trace the effect of the second cause of variation from the mathematical exactitude of ,boyle's law4 ,the fact that the molecules are not mathematical points means that ,v in the foregoing expression is not identical with the space in which the molecules move4 ,that space is ,v - b1 in which b is the measure of the aggregate volume of the molecules4 ,hence the true expression becomes 7,p a_/,v#b7 7,v - b7 constant4 ,the law of ,dalton 7,charles7 also receives its simplest explanation by the kinetic theory of gases2 and1 moreover1 the departures from the mathematical truth of the statement follow as a necessary consequence of the facts that the molecules have sensible magnitudes and are mutually attracted4 ,we can measure the effect of heat upon a gas in two ways4 ,we can either keep the pressure of the gas constant1 and measure the increase in volume2 or we can prevent the gas from expanding1 and measure the elastic force or pressure it exerts4 ,if the law of ,dalton were mathematically true1 it would follow that1 if the volume of the gas were maintained constant during the heating1 its pressure would increase in the same proportion as the volume would have increased if the gas had been allowed to expand1 but maintained at a constant pressure4 ,in other words1 the expansion-coefficient and the pressure-coefficient should be the same4 ,experiment shows1 however1 that they are not identical4 ,the following table gives the results of a number of measurements by ,regnault3 ,expansion ,pressure 7,pressure 7,volume ,constant74 ,constant74 ,hydrogen 4#jjcffa 4#jjcffg ,air 4#jjcfgj 4#jjcffe ,carbon dioxide 4#jjcgaj 4#jjcfhh ,sulphur dioxide 4#jjcijc 4#jjchde ,variations in the same sense have since been observed by ,jolly and ,chappuis4 ,with the exception of hydrogen1 and probably also helium1 all the gases show greater values for the coefficient of expansion than for the coefficient of pressure1 and the differences are greater the greater the coefficient of expansion of the gas4 ,since1 as we have already stated1 the law of ,boyle is directly related to the law of ,dalton1 both being dependent on molecular movements1 the same course of reasoning used to account for the variations in the case of ,boyle's law applies equally to the case of ,dalton's law4 ,the 8law0 of ,avogadro follows also as a necessary consequence of this explanation of the laws of gaseous pressure and temperature4 ,if all gases show approximately the same increase in pressure when heated under constant volume1 and if the increased pressure is due only to the increased energy with which the molecules strike the sides of the containing vessel1 it follows that all gases must contain the same number of molecules in unit volume4 ,but as1 from the very nature of the case1 the laws of ,boyle and ,dalton cannot be mathematically true1 it follows that the laws of ,avogadro and ,gay ,lussac must be only approximations in the same sense4 ,the law of ,graham1 connecting the rate of diffusion of a gas with its density1 follows also as a necessary consequence of this explanation of the laws of ,boyle1 ,dalton1 ,gay ,lussac1 and ,avogadro4 ,if the number of molecules in the unit volume of any gas1 whatever be its nature and whatever be their mass1 is approximately the same1 it follows that the mean velocity of the molecules must be variable2 their mean velocities must be in the inverse ratio of the square roots of their densities4 ,the mean velocity with which the molecules of a gas move can be calculated if we know the pressure it exerts1 the weight of a definite volume1 and the value of the acceleration due to gravity4 ,the square of this velocity in metres per second of time at #j;,c4 is given by the expression ,u #cpg_/q in which p pressure per square metre #aj1ccc kilograms2 g the gravitation constant #i4ha2 q weight of a cubic metre of the gas at #j;,c4 and one atmosphere of pressure4 ,for hydrogen we have ,u #c #aj1ccc #i4ha_/j4jhii whence ,u #ahdb metres per second2 for oxygen we have ,u #c #aj1ccc #i4ha_/a4dcj1 whence ,u #dfa4 ,these numbers accord with those demanded by ,graham's law4 ,the density of ,h being taken as #a1 that of oxygen is #af and #af #d2 the numbers #ahdb and #dfa are in the ratio of #d to #a4 ,the amount of heat required to raise the temperature of the unit mass of a gas through a definite interval depends1 as ,laplace first pointed out1 upon whether the gas is allowed to expand or not2 in other words1 the specific heat of a gas varies as the heating is at constant volume or at constant pressure4 ,if1 having raised the temperature of the unit mass1 and so expanded it1 we then compress it until it occupies its initial volume1 a further rise of temperature takes place without any external heat having been applied4 ,this rise of temperature is1 in fact1 due to the liberation of the amount of heat required merely to expand the gas without increasing its temperature4 ,the quantity of heat needed to raise the temperature of a gas through a definite interval is therefore greater when it is allowed to expand than when its volume is kept constant2 in other words1 the specific heat at constant pressure is greater than the specific heat at constant volume4 ,the ratio of the two specific heats can be calculated3 on the assumption that the energy imparted to the molecules simply accelerates their mean rectilinear velocity1 and that no energy is absorbed in doing internal work among them1 it is found that1 when the gas is permitted to expand1 the amount of heat required is #a4fg times greater than that needed when its volume is kept constant4 ,this ratio has been experimentally determined for a number of gases4 ,for oxygen under normal conditions it is #a4djh1 for hydrogen #a4dad1 for carbon dioxide #a4bfd1 for methane #a4bfi--;all numbers notably below the value #a4fg4 ,the direct experimental determination of this ratio by thermometric measurements is a matter of some difficulty4 ,it was1 however1 demonstrated by ,dulong that it can be ascertained with comparative ease from observations on the velocity of sound in the gas--the velocity being probably a direct function of this ratio4 ,as carried out experimentally1 the method consists in sending a sound-wave through the gas contained in a glass tube along the horizontal length of which is strewn a quantity of a light powder such as the spores of lycopodium or finely divided silica4 ,the glass tube is fitted at one end with a glass rod2 by rubbing this a series of longitudinal vibrations is set up and communicated to the gas whereby the light powder is thrown up into little heaps along the tube1 the distance between the heaps being equal to half a wave length4 ,by comparative measurements with air and the gas under examination1 data are obtained from which the ratio of the specific heats can be deduced4 ,by experiments conducted on this principle ,kundt and ,warburg found that mercury vapour gave numbers agreeing with the theoretical ratio #a4fg4 ,now1 its vapour density shows that mercury vapour is a monatomic gas2 it actually fulfils the conditions prescribed for a gas which theory indicates should give the value #a4fg4 ,all the energy imparted to its molecules on heating simply accelerates their translational velocity4 ,on the other hand1 all the gases above named as giving values below #a4fg are diatomic gases2 in their case the energy imparted to them is employed partly in augmenting the translational velocity of the molecules1 and partly in bringing about internal changes within them4 ,by experiments made in like manner ,ramsay and ,travers succeeded in showing that the inert gases of the atmosphere are monatomic4 ,no attempt can be made here to explain the various methods by which it has been sought to obtain an estimate of the absolute size of gaseous molecules or to determine their number in a definite volume4 ,by observations on their viscosity1 rates of diffusion1 conductivity for heat1 variations from the law of ,boyle1 dielectric constants1 electric charges1 etc41 ,maxwell1 ,o4 ,e4 ,meyer1 ,loschmidt1 ,lothar ,meyer1 ,van der ,waals1 ,mossotti1 ,planck1 ,sir ,j4 ,j4 ,thomson1 and others1 have arrived at estimates of the magnitude and number of molecules in a gas4 ,these estimates necessarily vary with the hypotheses made in deducing them4 ,it would serve no useful purpose to give the results1 since the figures convey no impression to the mind of the minuteness of molecules1 or even as to the extraordinary number of them in1 say1 so small a volume as one cubic centimetre4 ,as an example1 it has been calculated that there are about #fdj trillions of hydrogen molecules in one milligram of the gas4#c #c ,o4 ,e4 ,meyer1 ,the ,kinetic ,theory of ,gases1 #ahii4 99 99 99 99 99 ,in the preceding volume a short account has been given of the history of the early attempts to effect the liquefaction of the gases4 ,these resulted in their division into the two classes of liquefiable and permanent gases4 ,one of the most notable achievements of the latter half of the last century was to sweep away this arbitrary distinction4 ,the fundamental condition needed to effect the liquefaction of a gas1 although surmised by ,faraday1 was first clearly indicated by ,andrews about #ahfc4 ,he showed that1 in order to liquefy a gas1 its temperature must be lowered to a point peculiar to each gas1 when1 on the application of sufficient pressure1 it will become a liquid4 ,thus1 in the case of gaseous carbon dioxide1 ,andrews found that1 if its temperature were maintained above #ca ,c41 no amount of pressure would cause it to liquefy2 if the temperature were lowered just below this point--termed the critical point--a pressure of #ge atmospheres would effect its liquefaction4 ,on the other hand1 if the temperature of the liquid carbon dioxide be slowly raised to about #ca1 the surface of demarcation between the liquid and the gas becomes gradually fainter and eventually disappears4 ,carbon dioxide may thus be made to pass from the state of liquid to that of gas without any sudden alteration of volume4 ,if a given volume of the gas1 say at #ej1 be exposed to gradually increasing pressure1 say up to #aej atmospheres1 the volume is gradually diminished with the increment of pressure1 but no sudden contraction indicating liquefaction occurs4 ,if the gas under the high pressure be allowed to cool down to the ordinary temperature1 no sudden contraction is observed to follow4 ,the carbon dioxide1 at the outset a gas1 in the end becomes a liquid by a gradual and continuous transition1 unaccompanied by any abrupt change of volume4 ,these observations show that what we style the liquid and gaseous states are simply separated manifestations of the same condition of matter4 ,there is a definite temperature for every gaseous substance at which it ceases to be liquefiable under pressure2 and the reason that ,faraday failed to liquefy certain gases was that he was unable1 with the means at his command1 to lower their temperatures sufficiently and so reach their critical points2 hence the enormous pressures which he and other investigators applied were unavailing4 ,these facts were definitely made known by ,andrews in #ahfi1 were theoretically developed by ,van der ,waals in #ahgc1 and practically applied to the liquefaction of oxygen in #ahgg1 independently and almost simultaneously1 by ,pictet1 of ,geneva1 and ,cailletet1 of ,chtillon-sur-,seine4 ,pictet exposed oxygen1 under great pressure1 to the cold produced by the rapid evaporation of liquid carbon dioxide2 ,cailletet brought about the same result by suddenly diminishing the tension of the strongly compressed oxygen1 the rapid expansion of the gas effecting the reduction of its temperature below the critical point4 ,other workers took up the subject1 notably ,wroblewski and ,olszewki in ,poland1 ,dewar in ,england1 and ,kammerlingh ,onnes in ,holland2 and the liquefaction of all the gases has now been accomplished4 ,the following table shows the absolute boiling-7,b4,p47 and melting-points 7,m4,p471 critical points 7,c4,p471 and pressures 7,c4,press471 together with the density 7,d7 at their boiling-points of a number of liquefied gases3 ,c4 ,b4 ,p4 ,m4 ,p4 ,c4 ,p4 ,press4 ,d4 degrees degrees degrees m4 ,helium #d4e ---- ---- ---- #j4ae ,hydrogen #bj #ae #ce #aa4f #j4jf ,oxygen #ij4e below #ej #aed #dd #a4aca ,nitrogen #gg4e #fj #abd #bj4i #j4gia ,methane #ajh4c ---- #aia #db4d #j4daf ,ethylene #afi4e #ajd #bhb #dd #j4ega ,fluorine #ahf #dj ---- ---- #a4aa ,chlorine #bci4f ---- ---- ---- #a4ejg ,ammonia #bcd4e #aig4e #djd #he4i ---- ,neon #cj4dj ---- below #fe ---- ---- ,argon #hf4ij ---- #aee4f #dj4b #a4bab ,krypton #aba4cc ---- #baj4e #da4b #b4aee ,xenon #afc4i ---- #bhg4h #dc4e #c4eb ,the principle of the ,cailletet method of effecting the liquefaction of oxygen had been theoretically and experimentally studied by ,joule and ,lord ,kelvin many years previously4 ,it was extended by ,siemens and has been applied by ,linde and ,hampson to the construction of machinery for the production of liquid air on a large scale1 without the use of any intermediate refrigerant4 ,it is now readily possible to procure considerable quantities of liquid air1 and even of liquid hydrogen4 ,by the evaporation of liquid hydrogen temperatures approaching the absolute zero--that is1 #bgc ,c4 below the melting-point of ice--can now be reached4 ,incidentally there has been developed a special field of inquiry relating to the behaviour of substances at low temperatures4 ,illustration3 ,,sir ,,james ,,dewar4 ,the pioneers in this field have been ,dewar in ,england and ,kammerlingh ,onnes in ,holland4 ,research at low temperatures1 indeed1 has been the main feature of the work of the ,royal ,institution of ,great ,britain during the last twenty years4 ,it has included observations at temperatures approaching the absolute zero1 on the electrical resistivity of metals and alloys1 on the behaviour of so-called insulators1 on changes in the cohesive force of metals1 on the dielectric constants of frozen electrolytes1 on the influence of cold on magnetisation and on magnetic permeability1 and on the optical behaviour of bodies1 on vital phenomena at low temperatures1 and on the influence of cold on chemical change4 ,dewar has succeeded in liquefying and solidifying large quantities of hydrogen1 and has studied its properties at low temperatures4 ,liquid hydrogen is transparent and colourless4 ,it is a non-conductor of electricity1 and gives no absorption spectrum4 ,it freezes into an ice-like solid1 devoid of metallic properties4 ,dewar has made use of the property possessed by charcoal of occluding gases1 especially at low temperatures1 in the production of high vacua1 and in the separation of gases2 and he has also determined the molecular heat of absorption by charcoal of various gases4 ,he has employed liquid air1 liquid nitrogen1 and liquid hydrogen as calorimetric agents1 and has determined by means of them the heat capacities of a number of substances at very low temperatures4 ,lastly1 his ingenious contrivance of silvered vacuum protected vessels1 now introduced into commerce under the name of 8,thermos flasks10 has greatly facilitated the manipulation of liquefied gases for experimental purposes4 ,,chapter ,,vi ,,the ,,periodic ,,law ,in an anonymous essay 8,on the ,relation between the ,specific ,gravities of ,bodies in their ,gaseous ,state and the ,weights of their ,atoms10 published in ,thomson's ,annals of ,philosophy in #ahae1 the attempt was made to indicate certain consequences which seem to follow from ,dalton's law of gaseous volumes1 as generalised by ,gay ,lussac4 ,the author of this essay was subsequently discovered to be a medical student named ,william ,prout1 noteworthy as having been one of the first to point out the suggestiveness of the numerical relationships which occur among the atomic weights of the elements4 ,this paper is usually assumed to contain the statement that the atomic weights of the elements are multiples of that of hydrogen4 ,as a fact1 however1 this hypothesis is nowhere explicitly stated in the paper4 ,the inference was practically due to ,thomson1 who strove to support it by experimental proof of so weak a character as to draw forth the remark of ,berzelius that much of it appeared to have been made at the writing-desk4 ,nevertheless1 the occurrence of such numerical relationships continued1 as already stated1 to excite speculation4 ,dbereiner1 in #ahbi1 pointed out that in certain groups of correlated elements1 consisting each of three members1 the middle member had an atomic weight practically identical with the arithmetic mean of the atomic weights of the others2 and similar observations were made by ,gmelin1 ,dumas1 ,gladstone1 and ,strecker4 ,an approach to the recognition of the general law underlying these facts was made by ,newlands in ,england1 and independently by ,de ,chancourtois in ,france1 who were the first to indicate that the properties of the elements are related to their atomic weights4 ,this conception was developed by the ,russian chemist1 ,mendeleff4 ,in ,mendeleff's arrangement1 first published in #ahfi1 the elements are so grouped that their properties are periodic functions of their atomic weights4 ,the general statement of what is now known as the ,periodic ,law may be put in this form3 ,if the elements are arranged in order of increasing atomic weight1 the properties of these elements vary from member to member of the series1 but return more or less nearly to the same value at certain fixed points in the series4 ,this is observed to occur in the atomic value1 or valency1 of the several members2 also in their specific volumes1 melting-points1 ductility1 hardness1 volatility1 crystalline form1 thermal expansion1 refraction equivalents1 and conductivities for heat and electricity1 in their magnetic properties and electro-chemical behaviour1 and in their heats of chemical combination1 etc4 ,the first chemist of note to grasp the significance of ,mendeleff's generalisation was ,lothar ,meyer1 who1 dealing at the outset with one of the characteristic properties of the elements--viz41 their specific or atomic volumes 7that is1 the values obtained by dividing their specific gravities into their respective atomic weights7--greatly developed the principle of periodicity1 representing it graphically in a most striking and suggestive manner1 leading up to a classification almost identical with that of ,mendeleff4 ,since the date of its promulgation the scheme of classification of the elements in accordance with the principle of periodicity has experienced certain minor modifications necessitated by fuller knowledge2 but in its essential features it remains very much in the form devised by ,mendeleff4 ,the discovery of the so-called inert and radio-active elements required that their relations to the periodic law should be defined4 ,their inclusion raises no fundamental difficulty4 ,indeed1 the generalisation seems to adapt itself to the far-reaching considerations which spring from modern views of the nature of the atom1 its electro-chemical relationships1 and the orderly arrangement of the corpuscles of which it may be composed4 ,in the #aije edition of the ,english translation of his famous ,principles of ,chemistry1 ,mendeleff has given a table which may be said to embody his final views concerning the systematic classification of the elements4 ,this is reproduced on p4 #aje4 ,in this table he postulates the existence of two hypothetical elements1 x and y1 the former of which he regards as identical with the physical ether2 while the latter is an analogue of helium1 possibly identical with the 8coronium0 of the solar coronal atmosphere1 with a molecular weight of about #j4d4 ,the striking feature of ,mendeleff's generalisation is its universality4 ,in this respect it differs from all previous attempts at natural classifications of the elements2 these were limited and partial1 and therefore unsatisfactory4 ,nevertheless1 it is easy to trace in them fundamental conceptions upon which ,mendeleff built4 ,mendeleff1 in fact1 gave a great extension to ideas with which the chemical world of half a century ago was more or less familiar2 and doubtless it was this circumstance1 combined with the remarkable boldness and comprehensiveness of this extension1 followed almost immediately by a most striking series of confirmations of his own previsions1 as logical consequences of his generalisation1 that secured for it attention1 and ultimately universal adoption4 ---------------------------------------- ---------------- ,series4,zero group4 ,group ,i4 ,group ,,ii4 ,group ,,iii4 ---------------------------------------- ---------------- #j x ---- ---- ---- #a y ,hydrogen4 ,h #a4jjh ---- ---- #b ,helium4 ,lithium4 ,beryllium4 ,boron4 ,he #d4j ,li #g4jc ,be #i4a ,b #aa4j #c ,neon4 ,sodium4 ,magnesium4 ,aluminium4 ,ne #ai4i ,na #bc4je ,mg #bd4a ,al #bg4j #d ,argon4 ,potassium4 ,calcium4 ,scandium4 ,ar #ch ,k #ci4a ,ca #dj4a ,sc #dd4a #e ---- ,copper4 ,zinc4 ,gallium4 ,cu #fc4f ,zn #fe4d ,ga #gj4j #f ,krypton4 ,rubidium4 ,strontium4 ,yttrium4 ,kr#ha4h ,rb #he4d ,sr #hg4f ,y #hi4j #g ---- ,silver4 ,cadmium4 ,indium4 ,ag #ajg4i ,cd #aab4d ,in #aad4j #h ,xenon4 ,csium4 ,barium4 ,lanthanum4 ,xe #abh ,cs #acb4b ,ba #acg4d ,la #aci #i ---- ---- ---- ---- #aj ---- ---- ---- ,ytterbium4 ,yb #agc #aa ---- ,gold4 ,mercury4 ,thallium4 ,au #aig4b ,hg #bjj4j ,tl #bjd4a #ab ---- ---- ,radium4 ---- ,rd #bbd ---------------------------------------- ---------------- ---------------------------------------- ---------------- ,series4 ,group ,,iv4 ,group ,v4 ,group ,,vi4 ,group ,,vii4 ---------------------------------------- ---------------- #j ---- ---- ---- ---- #a ---- ---- ---- ---- #b ,carbon4 ,nitrogen4 ,oxygen4 ,fluorine4 ,c #ab4j ,n #ad4jd ,o #af4j ,f #ai4j #c ,silicon4 ,phosphorus4 ,sulphur4 ,chlorine4 ,si #bh4d ,p #ca4j ,s #cb4jf ,cl #ce4de #d ,titanium4 ,vanadium4 ,chromium4 ,manganese4 ,ti #dh4a ,v #ea4d ,cr #eb4a ,mn #ee4j #e ,germanium4 ,arsenic4 ,selenium4 ,bromine4 ,ge #gb4c ,as #ge4j ,se #gi4j ,br #gi4ie #f ,zirconium4 ,niobium4 ,molybdenum4 ---- ,zr #ij4f ,nb #id4j ,mo #if4j #g ,tin4 ,antimony4 ,tellurium4 ,iodine4 ,sn #aai4j ,sb #abj4j ,te #abg ,i #abg #h ,cerium4 ---- ---- ---- ,ce #adj #i ---- ---- ---- ---- #aj ---- ,tantalum4 ,tungsten4 ---- ,ta #ahc4j ,w #ahd #aa ,lead4 ,bismuth4 ---- ---- ,pb #bjf4i ,bi #bjh #ab ,thorium4 ---- ,uranium4 ---- ,th #bcb ,u #bci ---------------------------------------- ---------------- ----------------------- ,series4 ,group ,,viii4 ----------------------- #j -- #a -- #b -- #c -- ,iron4 ,fe #ee4i #d ,cobalt4 ,co #ei ,nickel4 ,ni #ei7;,cu7 #e -- ,ruthenium4 ,ru #aja4g #f ,rhodium4 ,rh #ajc4j ,palladium4 ,pd #ajf4e7;,ag7 #g -- #h -- #i -- ,osmium4 ,os #aia #aj ,iridium4 ,ir #aic ,platinum4 ,pt #aid4i7;,au7 #aa -- #ab -- ------------------------ ,the periodic law1 in the words of its author1 is the 8direct outcome of the stock of generalisations of established facts which had been accumulated by the end of the decade #ahfj-ahgj40 ,it is founded wholly on experiment1 and is as much the embodiment of fact as are the laws of chemical combination4 ,it was based upon the adoption of the definite numerical values of the atomic weights1 as indicated by ,cannizzaro1 as a consequence of the hypothesis of ,avogadro1 and upon the assumption that the relations between the atomic weights of analogous elements must be governed by a general law4 ,the application of the periodic law immediately led to the re-determination of certain atomic weights and to the correction of their assumed atomic values4 ,at the time of its enunciation the determination of the valency of an element was purely empirical1 with no apparent necessary relation to that of other elements4 ,we find now that the valency is a matter of a priori knowledge1 just as much as any other property of the element4 ,the amended values for the atomic weight and valency of a number of elements thus demanded by the law have been confirmed by all the experimental criteria employed by chemists4 ,the generalisation further indicated the existence of new elements2 it pointed out their probable sources1 and foretold their properties4 ,instances of this power of divination in the law are to be seen1 as already mentioned1 in the discovery of gallium by ,lecoq de ,boisbaudran1 of scandium by ,nilson1 and of germanium by ,winkler1 the existence and main properties of which were severally foretold by ,mendeleff in #ahga4 ,the promulgation of the law was heralded as a proof of the validity of the conception of a primordial matter4 ,it was held that it can find a rational explanation only in the idea of unity in the formative material4 ,but its author would not admit that his generalisation had any relation to the ,pythagorean hypothesis3 ,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 elements4 ,it does not in the least originate in the idea of an unique matter1 and it has no historical connection with that relic of the torments of classical thought2 and therefore it affords no more indication of the unity of matter or of the compound nature of the elements than do the laws of ,avogadro1 and ,gerhardt1 or the law of specific heats1 or even the conclusions of spectrum analysis4 ,none of the advocates of a unique matter has ever tried to explain the law from the standpoint of ideas taken from a remote antiquity1 when it was found convenient to admit the existence of many gods--and of a unique matter4 ,the reader who desires a fuller exposition of the principles of the periodic law must be referred to special treatises on the subject1 or to the larger manuals on general chemistry4 ,it must1 however1 be stated that1 while many facts discovered since the original promulgation of the principle and since its development by ,lothar ,meyer1 ,carnelley1 ,thomsen1 and others1 are consistent with the law1 other facts1 some of which were known before #ahgj1 are apparently out of harmony with it1 or at all events await a fuller interpretation4 ,for example1 tellurium is not in its proper place in the scheme if its atomic weight1 #abg4e1 has been correctly ascertained4 ,cobalt 7#eh4ig7 and nickel 7#eh4fh7 have atomic weights so closely accordant that their properties and those of their corresponding compounds should be very similar1 and1 in fact1 almost identical2 but such is not the case4 ,indeed1 it has been said1 no prevision of the periodic law would have led to the discovery of nickel4 ,similar considerations apply to manganese1 chromium1 and iron2 the atomic weights of these elements are less widely different than the differences in their properties and the divergence in their chemical relationships would seem to require4 ,the relative positions of argon and potassium are also not consistent with the law4 ,there are difficulties1 too1 connected with what we know at present concerning the atomic weights of the so-called rare earth metals4 ,in spite1 however1 of these seeming anomalies1 it can hardly be doubted that the periodic law is as much the expression of a natural law as is the law of gravitation2 although it is possible1 and indeed probable1 that1 as we now define it1 it is only the first approximation to the truth1 and that1 as our knowledge becomes more precise1 ,mendeleff's classification1 in its present form1 will require modification and extension1 just as ,mendeleff's own scheme may be said to be a modification and extension of the attempts at the rational classification of the chemical elements made by his predecessors4 ,illustration3 ,,dmitri ,,ivanowitsch ,,mendel,,eff4 ,dmitri ,ivanowitsch ,mendeleff1 with whose name this fruitful generalisation is indissolubly connected1 was born ,february #g1 #ahcd 7,n4,s471 at ,tobolsk1 in ,siberia1 and was the fourteenth and youngest child of ,ivan ,mendeleff1 the ,director of the gymnasium at that place4 ,soon after the birth of ,dmitri his father became blind1 and the family were practically dependent upon the mother1 ,maria ,dmitrievna ,mendeleeva1 who established a glass works near ,tobolsk1 on the profits of which she brought up and educated her large family4 ,at the age of fifteen ,mendeleff was taken by his mother to ,st4 ,petersburg1 and began the study of natural science at the ,physico-,mathematical ,faculty of the ,institute4 ,after serving as a science master at ,simferopol in the ,crimea and at ,odessa1 in #ahef he became a privat-docent in the ,university2 then1 following a short period of study in ,france and ,germany1 he returned to ,st4 ,petersburg1 and in #ahff he was made ,professor of ,general ,chemistry in the ,university4 ,his reputation mainly rests upon his contributions to chemical philosophy and physical chemistry1 notably on specific volumes1 on critical temperatures1 on the thermal expansion of liquids1 on the nature of solutions1 on the elasticity of gases1 and the origin and nature of petroleum4 ,he died on ,january #ca1 #aijg4 ,,chapter ,,vii ,,valency ,chemical formul1 from the time of ,berzelius onwards1 have been regarded as rational expressions--that is1 they serve to represent the relations and analogies of the substance they are employed to designate1 and indicate in the simplest and at the same time the most comprehensive manner the chemical changes in which the substances take part4 ,in the words of ,gerhardt1 those formul are 8the best that make evident the greatest number of such relations and analogies10 and that serve to express the greatest number of the chemical changes in which they are concerned4 ,in such concrete expressions of chemical change it was frequently observed that a definite group of some or all of the constituent elements of the substance hung together1 as it were1 and passed1 apparently unchanged1 into the products of its transformation4 ,these groups were not necessarily radicals in the sense in which ,liebig and ,whler used the term2 to ,gerhardt and to ,kekul they were simply residues1 remaining unattacked in a chemical metamorphosis1 and passing as such into the products of the change4 ,they might or might not be capable of isolation as definite entities4 ,thus1 for example1 we may represent the composition of the following sulphur compounds so as to show that they all contain the group ,,so#b1 or sulphuryl3 ,,so#b;,cl ,,so#b;,cl ,cl ,,oh ,sulphuryl chloride4 ,chlorosulphonic acid4 ,,so#b,,no#b ,,so#b,,no#b ,,so#b,,oh ,cl ,,oh ,,oh ,sulphuryl nitryl ,leaden chamber ,sulphuric chloride4 crystals4 acid4 ,these formul serve to show how the several substances are mutually related1 and that they may be derived from one another by the substitution of atoms of chlorine for hydroxyl 7,,oh71 or nitryl 7,,no#b71 or vice versa4 ,it was pointed out in #ahea by ,williamson1 and subsequently by ,gerhardt1 that these groups are characterised by differences in their power of combining with or replacing atoms of hydrogen1 or of groups or elements which1 like chlorine1 are chemically equivalent to hydrogen4 ,such a radical or residue as ethyl 7,c#b;,h#e7 is chemically equivalent to one atom of hydrogen1 as is shown when we compare the formula for ether1 as established by ,williamson1 with that of ordinary alcohol3 ,c#b;,h#e,o ,c#b;,h#e,o ,h ,c#b;,h#e ,alcohol4 ,ether4 ,sulphuryl1 ,,so#b1 is chemically equivalento two atoms of hydrogen2 phosphoryl1 ,,po1 as suggested by ,odling1 to three atoms of hydrogen4 ,gerhardt therefore proposed to designate these and similar groups as monatomic1 diatomic1 triatomic1 according to their respective hydrogen-replacing power4 ,this conception of the definite atom-fixing or replacing power of groups or compound radicals was extended by ,frankland1 in #aheb1 so as to include the simple radical--that is1 the elements4 ,in the memoir in which he announced the existence of the organometallic compounds he pointed out that the elements may be classified according to their combining power1 or1 as he expressed it1 according as 8their affinities are best satisfied40 ,this idea was independently developed by ,couper and ,kekul in #aheh2 it is from that period that the definite introduction of the conception of atomicity1 atomic-value1 or valency1 into chemical doctrine may be said to date4 ,the memoir in ,liebig's ,annalen der ,chemie und ,pharmacie1 in which ,kekul announced his views1 deals particularly with the tetravalency of carbon and the doctrine of linking of atoms in terms of their valency4 ,as formulated by ,kekul and as subsequently developed in his famous text-book1 this doctrine exercised an immediate effect on the progress of the chemistry of carbon compounds4 ,like every fruitful hypothesis1 it stimulated inquiry1 and brought out analogies2 and the more it was applied the more apparent became its suggestiveness and utility4 ,the scope of chemical formul was greatly extended4 ,rational formul grew into dissected or constitutional formul2 and on the system of constitutional formul have been grafted successive attempts to elucidate the manner in which the constituents of a molecule are grouped and held together4 ,it is interesting to note that the proximate effect of the theory of chemical structure which grew out of ,kekul's doctrine was to assimilate what was sound in the seemingly antagonistic theories of types and radicals4 ,as a mode of exposition1 ,kekul used models to illustrate the manner in which the affinity-values of compounds are satisfied2 these were not intended to represent the actual spatial distribution of the atoms in a molecule1 but they nevertheless familiarised the mind with the idea first clearly recognised by ,wollaston and ,berzelius that this is the ultimate aim of chemistry4 ,it was probably their use1 either actually or by visualisation1 that led ,kekul in #ahfe to his theory of the constitution of benzene1 as developed in his paper on the constitution of the aromatic compounds--a theory no less fruitful in its consequences than that of the tetravalency of carbon and of the linkage of atoms4 ,such models1 too1 in the hands of ,van 't ,hoff1 subsequently served to elucidate the connection between optical characters and crystalline form1 and to explain the isomerism of certain organic substances4 ,kekul was of opinion that the valency1 or affinity-value1 of an element was a definite and invariable quantity--a fundamental property of the atom as immutable as its atomic weight4 ,many facts appear to show that such is not the case4 ,thus phosphorus and nitrogen are sometimes trivalent and at other times pentavalent2 tin1 in certain of its compounds1 is divalent2 in others1 tetravalent4 ,sulphur may be a dyad1 a tetrad1 or a hexad4 ,it will be seen that the valency of these particular elements varies by two units3 this was at one time held to be a natural law1 and the various elements were divided by ,frankland into the two main groups of 7#a7 perissads1 or elements of odd atomic value1 and 7#b7 artiads1 or elements of even atomic value4 ,experience has demonstrated that a rigid classification on this basis is not possible4 ,many instances are known of elements not only varying in valency by two units1 but even by one unit4 ,thus nitrogen1 which is usually a perissad1 is apparently an artiad in nitric oxide and in gaseous nitrogen peroxide4 ,roscoe has shown that uranium and tungsten1 originally regarded as artiads1 form pentachlorides4 ,to what the difference in the affinity-value of an element is due1 and why different elements should manifest different values1 is at present unknown4 ,valency1 like other properties1 appears to be a periodic function of atomic weight2 from the behaviour of such analogous compounds as phosphorus pentafluoride1 phosphorus pentachloride1 phosphorus pentabromide1 it seems1 too1 to be related to the weights of the atoms in combination4 ,further1 it would appear that the mutual affinities of substances vary with temperature--i4e41 with the energy imparted to their molecules2 numerous instances appear to indicate that the atom-fixing power of an element decreases when it is strongly heated--that is1 when the internal energy imparted to its combinations exceeds a certain limiting value4 ,van 't ,hoff has attempted a mechanical explanation of valency depending on the shape of the atoms1 as affected by variation in their vibratory motions resulting from differences of temperature4 ,helmholtz suggested that the different charges of electricity associated with the atoms may determine their affinity-values--that1 for example1 a monad carries a single charge1 a dyad two1 a triad three charges4 ,many considerations go to show that the affinity-value of an element is not capable of definite numerical expression in the sense which the doctrine of valency as generally understood implies1 and that the variations are not of the per saltum character assumed by saying that the affinity-value is sometimes #a1 sometimes #b1 at other times #c1 and so on4 ,when we have apparently satisfied the accepted atomic value of an element by allocating to it what we regard as the necessary complement of atoms of other bodies1 it is frequently evident that the capacity for combination of the whole molecule is not satisfied4 ,many apparently saturated molecules have the power of combining with other equally saturated molecules4 ,sulphur trioxide 7,,so#c7 and barium monoxide 7,ba,o7 would appear each to have their affinity-values satisfied2 nevertheless they combine with great readiness to form barium sulphate1 ,ba,s,o#d4 ,,chapter ,,viii ,,the ,,chemistry ,,of ,,aromatic ,,compounds ,the suggestions of ,couper and ,kekul that an explanation of the properties of chemical compounds should be sought in the nature and mutual affinities of their constituent elements rather than of their radicals were not wholly accepted at the time they were first made4 ,speculative ideas have to justify themselves by facts4 ,the value of an hypothesis depends upon its usefulness and expediency1 and on its power of indicating the lines of future inquiry4 ,how far it is inductively sound and deductively useful is a matter for individual judgment4 ,consequently the tendency to pass from purely rational and constitutional formul to formul which sought to symbolise the inner structure--the very skeleton1 as it were--of a molecule1 was resisted for a time1 and by no one more strongly than by ,kolbe4 ,kolbe's attitude to the new doctrine may be said to have had its justification in his own work4 ,his remarkable prediction1 based on considerations which had nothing in common with ,kekul's doctrine1 of the existence of the secondary and tertiary alcohols1 so soon to be confirmed by ,friedel's discovery of secondary propyl alcohol1 and by ,butlerow's isolation of tertiary butyl alcohol1 served to retard the general adoption of ,kekul's views by showing that apparently they were no more fruitful in suggestiveness than those they were intended to supplant4 ,but it was exactly in their suggestiveness with regard to the development of isomerism that structural formul based upon valency were gradually found to be most useful4 ,it was perceived that it was now possible not only to foretell the existence of isomers1 but to determine their number1 and to some extent to forecast their properties and modes of decomposition4 ,cayley1 for example1 calculated the number of possible isomers of the hydrocarbons of the generic formula ,cn,h#bn#b up to ,c#f;,h#ad all those that theory predicted have been discovered4 ,in no single case have more been obtained than the number indicated by theory4 ,the accumulated weight of this and similar testimony ultimately established the doctrine of chemical structure on a firm basis4 ,this conception received a great extension as the result of ,kekul's application of his ideas to the explanation of the chemical constitution of the group of substances of vegetable origin--consisting of essential oils1 balsams1 resins1 and their products1 which1 on account of their characteristic odours1 were collectively known to the older chemists as the aromatic compounds4 ,some of these1 like oil of bitter almonds1 gum benzoin1 coumarin1 oil of wintergreen1 oil of anise1 oil of cinnamon1 oil of cumin1 balsam of tolu1 phenol1 and certain of their derivatives1 such as benzene1 aniline1 salicylic acid1 cinnamic acid1 toluene1 cymene1 had already been investigated with important theoretical results2 but as a class they had received far less attention than the derivatives of the great group of homologous radicals of which methyl is the initial member4 ,of course it was part of the doctrine of ,liebig--the discoverer of benzoyl--that the aromatic compounds also contained specific radicals2 but the relation of these compounds to those we now call aliphatic 7fatty7 compounds was not understood1 although certain analogies were recognised4 ,in #ahff ,kekul drew attention to the following significant peculiarities of the aromatic compounds3 7#a7 ,all aromatic compounds1 even the simplest1 are comparatively richer in carbon than the corresponding class of fatty 7aliphatic7 compounds2 7#b7 among the aromatic substances1 as among fatty compounds1 numerous homologous compounds exist2 7#c7 the simplest aromatic substances contain at least six atoms of carbon2 7#d7 all decomposition products of aromatic substances show a certain family resemblance2 the main product of the decomposition contains at least six atoms of carbon--e4g41 benzene ,c#f;,h#f1 phenol ,c#f;,h#f,o1 etc41 which would seem to indicate that all aromatic substances contain a nucleus or atomic grouping containing six carbon atoms4 ,within this nucleus the carbon atoms are in closer connection or denser combination1 from which it follows that all aromatic compounds are comparatively rich in carbon4 ,more carbon atoms can then be added to this nucleus according to the same laws that govern the fatty compounds4 ,in this way the existence of homologous compounds may be explained4 ,on the assumption that carbon is tetravalent and that its valency is constant1 ,kekul showed how1 by linking together six carbon atoms by alternate single and double bonds1 six affinity units may be left free4 ,if we assume that six carbon atoms are attached to one another according to this law of symmetry1 we obtain a group which1 regarded as an open chain1 contains eight unsaturated units of affinity3 ----,c,c----,c,c----,c,c---- ,by making the further assumption that the two carbon atoms at the ends of the chain are linked together by one unit of affinity each1 a closed chain 7a symmetrical ring7 is obtained which now contains six unsaturated units of affinity3 -------------- ,c,c----,c,c----,c,c ,from this closed chain all the substances usually designated as 8aromatic compounds0 are derived4 ,in these a common nucleus may be assumed3 it is the closed chain ,c#f;,a#f1 where ,a denotes an unsaturated affinity4 ,the six affinities of this nucleus may be satisfied by six monovalent elements4 ,they may also1 wholly or in part1 be satisfied by one affinity of polyvalent elements1 the latter necessarily bringing with them other atoms into the compound1 thus producing one or more side chains1 which in their turn may be lengthened by the addition of other atoms4 ,if each of the free units is satisfied by an atom of hydrogen1 we obtain benzene1 which1 as ,kekul demonstrated1 becomes the centre round which the great group of aromatic compounds might be said to revolve4 ,benzene was discovered by ,faraday in #ahbe among the volatile liquids condensed from the oil-gas made by the ,portable ,gas ,company4 ,it had already played a notable part in the development of chemical theory in connection with the discovery of isomerism4 ,it was now to play a far more important rle3 to become1 in fact1 the progenitor of a great family of substances1 not only of theoretical value1 but of great economic importance4 ,the limits of this work preclude any attempt to trace in detail the development of the conception with which ,kekul enriched science1 or to dilate upon the great extension of benzenoid or cyclic chemistry which has resulted from it during the past forty years4 ,it has been said that ,kekul's memoir on the benzene theory is the most brilliant piece of scientific prediction to be found in the whole range of organic chemistry4 ,of course1 on its promulgation it had to run the gauntlet of criticism2 and an army of eager1 active workers was soon engaged in testing its sufficiency and in developing the rich province which it first made known4 ,as the facts multiplied1 other statical formul were suggested by ,dewar1 ,ladenburg1 and ,claus1 but they have not proved more adequate to explain the facts as these have become better understood4 ,observations which seemed to contradict ,kekul's theory1 or which seemed to be imperfectly explained by it1 have1 in the light of fuller knowledge1 been shown to be in harmony with it2 and such additional proofs of agreement have thereby served to strengthen its position4 ,its capacity for development is1 indeed1 as in the case of every other hypothesis of the first rank1 one of its cardinal qualities4 ,it adequately explains the constitution of great numbers of derivatives whose analogies and relations1 apart from it1 would have remained obscure and in many cases unintelligible4 ,the symmetrical distribution of the carbon and hydrogen atoms in the benzene molecule1 assumed by ,kekul on indirect grounds1 has been established by the independent investigations of ,ladenburg and others1 and its ring structure has been demonstrated by ,baeyer and ,perkin4 ,purely physical evidence1 based upon its thermo-chemical and optical characters can be adduced in its support4 ,determinations of the molecular volume and magnetic rotation of its compounds further serve to substantiate it4 ,illustration3 ,,august ,,kekul ,,von ,,stradonitz4 ,friedrich ,august ,kekul was born at ,darmstadt on ,september #g1 #ahbi4 ,after passing through the gymnasium of his native town1 he entered1 in #ahdg1 the ,university of ,giessen1 with the intention of becoming an architect4 ,attracted by ,liebig's teaching1 he turned to chemistry1 and worked with ,will on amyl sulphuric acid and its salts4 ,in #ahea he went to ,paris1 heard ,dumas's lectures1 and formed a friendship with ,gerhardt1 whose ,trait de ,chimie ,organique largely moulded his views4 ,he became an assistant to ,von ,planta1 occupying himself with the chemistry of the alkaloids4 ,subsequently he came to ,london1 worked under ,stenhouse1 and made the acquaintance of ,williamson1 then in the full vigour of his scientific activity4 ,here he discovered thioacetic acid4 ,it was at this time1 also1 that his ideas with regard to structural chemistry began to take shape4 ,returning to ,germany1 he attached himself to the ,university of ,heidelberg as a privat-docent1 and had for a pupil ,baeyer1 who took up the study of the organo-arsenic compounds4 ,in #aheh he published his memorable paper 8,on the ,constitution and ,metamorphoses of ,chemical ,compounds and on the ,chemical ,nature of ,carbon10 in which he developed his views on the linking of atoms1 out of which has grown our system of constitutional formul4 ,the immediate result of this celebrated memoir was a call to the chemical chair of the ,university of ,ghent1 where ,kekul had among other students ,baeyer1 ,hbner1 ,krner1 ,ladenburg1 ,linnemann1 and ,dewar4 ,here he remained nine years1 and here he published his classical ,lehrbuch der ,organischen ,chemie4 ,the years he spent in ,ghent were the most productive time of his career1 and it was there that he developed his benzene theory--a conception as fruitful as that of his doctrine of atom-linking4 ,in #ahfg ,kekul was called to ,bonn to take charge of the newly erected laboratory which ,hofmann had designed4 ,although he continued to work1 mostly in collaboration with his pupils1 among whom may be named ,anschtz1 ,bernthsen1 ,thorpe1 ,carnelley1 ,claisen1 ,dittmar1 ,franchimont1 ,van 't ,hoff1 ,japp1 ,schultz1 ,wallach1 and ,zincke1 his health after #ahgf began to fail4 ,he died on ,july #ac1 #ahif4 99 99 99 99 99 ,of course no statical formula can be the ultimate representation of the constitution of benzene4 ,however convenient and suggestive such a formula may be1 it can be only a transitional phase in its complete chemical and physical history4 ,kekul was early conscious of this fact1 and suggested a dynamical hypothesis based upon a mechanical conception of valency4 ,this he imagined might represent the number of contacts with other atoms which a vibrating atom experienced in the unit of time4 ,two atoms of tetravalent carbon1 each linked by one combining unit1 will experience four oscillations1 striking each other and three other atoms in the unit of time1 while the monovalent hydrogen atom makes only one oscillation4 ,the doubly linked carbon will collide with its neighbouring atom twice1 and also with two other atoms within the same period4 ,the assumption that the carbon atom has a more rapid motion than the hydrogen atom is1 however1 not warranted by the kinetic theory4 ,other dynamic formul have been proposed by ,knorr and by ,collie4 ,collie and ,baly have further suggested that the absorption bands of benzene observed in the ultra violet of its spectrum point to synchronous oscillations of its molecule1 due to dynamic changes in the making and breaking of the links between the several pairs of the carbon atoms1 setting up vibrations in the benzene ring comparable with those of an elastic ring in the act of expanding and contracting4 99 99 99 99 99 ,the large group of the essential oils1 containing hydrocarbons similar to oil of turpentine1 and classed under the generic term of terpenes1 might1 from their origin and mode of occurrence1 be expected to be allied in constitution to the aromatic compounds2 and such is found to be the case4 ,the terpenes are isomeric hydrocarbons of the formula ,c#aj;,h#af4 ,they are found sometimes singly1 at other times mixed1 in a great variety of plants1 associated with sesquiterpenes ,c#ae;,h#bd1 and oxygenated substances1 such as camphor1 borneol1 menthol1 etc41 some of which have long been known and valued for their medicinal properties and technical applications4 ,the elucidation of their constitution has taxed the skill of many workers during the past thirty years2 but1 thanks to the labours of ,wallach1 ,baeyer1 ,perkin1 ,tiemann1 ,bredt1 ,komppa1 and others1 an insight has been gained into their nature and analogies4 ,they are apparently all cyclic compounds with certain attributes which connect them with hydrocarbons of the aliphatic series4 ,pinene1 the characteristic constituent of oil of turpentine1 obtained by distilling the resinous exudations of many species of pines1 exists in two modifications1 distinguished by differences in optical activity1 known respectively as australene1 found in ,american1 ,russian1 and ,swedish turpentine1 and terebenthene1 found mainly in ,french turpentine4 ,it would seem from their empirical formul1 as well as from their association in nature1 that the terpenes and camphor1 which ,dumas first showed to have the composition ,c#aj;,h#af,o1 should be closely allied in constitution1 and that it ought to be readily possible to effect their mutual transformation4 ,the constitution of camphor was long one of the standing problems of organic chemistry1 and dozens of formul have been suggested at various times during the last twenty years in explanation of its structure4 ,that it contained a benzene nucleus seemed to be proved by the ease with which it yielded toluene1 cymene1 and other benzene homologues4 ,the first real insight into its structure was gained when ,bredt ascertained the constitution of camphoronic acid1 ,c#f;,h#aa 7,,co#b;,h7#d--;a product1 together with camphoric acid1 of the oxidation of camphor--which he found broke up into trimethylsuccinic acid and isobutyric acid1 and the structure of which was established by ,perkin and ,j4 ,f4 ,thorpe4 ,the result of the ,japanese monopoly has been to greatly enhance the price of natural camphor2 during the last ten years it has practically trebled4 ,this has naturally stimulated endeavours to prepare this substance by synthetical means4 ,artificial camphor is now made from pinene by transforming the hydrocarbon into bornyl chloride by the action of hydrochloric acid4 ,from this camphene is prepared2 by treatment with glacial acetic acid it forms isobornyl acetate4 ,on hydrolysis this is transformed into isoborneol1 which by oxidation yields camphor1 differing from the naturally occurring variety only in the fact that it is optically inactive4 ,all so-called aromatic compounds are not necessarily cyclic systems1 for it has been recognised within the past few years that some of the most valuable natural perfumes1 such as that of the rose1 lavender1 and orange blossom1 lemon-grass1 geranium1 ylang-ylang1 neroli1 etc41 owe their characteristic aroma to the presence of terpenes and camphors1 which are not strictly benzenoid or cyclic compounds1 but 8ruptured rings0 behaving like open-chain or aliphatic substances4 ,to judge from past experience1 it may confidently be stated that1 now the constitution of these substances is understood1 their synthetical preparation on an industrial scale is practicable4 ,the discovery by ,cahours in #ahdd that oil of wintergreen is substantially methyl salicylate led to its artificial production from synthetically prepared salicylic acid4 ,sir ,william ,perkin in #ahfh effected the synthesis of coumarin1 the aromatic principle in woodruff and hay4 ,fittig and ,mielck in #ahfi synthesised heliotropin1 and in #ahga ,tiemann and ,haarmann obtained vanillin1 the characteristic aromatic body in the vanilla pod1 by synthetic means1 and established its manufacture on a commercial scale4 ,the chemical nature of the characteristic odoriferous substances in oil of cumin1 anise1 rue1 cinnamon1 heliotrope1 jasmine1 violet1 parsley1 etc41 has now been established and some of them are made industrially4 ,the artificial essence of violets known as ionone1 prepared by ,tiemann in #ahic1 and now made commercially1 is similar but not identical in structure with the true perfume--irone4 ,what is known as artificial musk is a trinitro-butyl toluol4 ,artificial orange-flower oil is a methyl ester of anthranilic acid4 ,in ,vol4 ,i4 a short account has been given of the early history of the large and important group of vegetable products known as the alkaloids4 ,many of these have long been valued on account of their powerful physiological action4 ,as they all contain nitrogen and are generally basic1 they were regarded by ,berzelius1 and subsequently by ,liebig and ,hofmann1 as akin to ammonia in constitution1 and were classed as amines4 ,the first experimental evidence of their nature was obtained by ,gerhardt1 who found that1 when strychnine and certain of the alkaloids belonging to the quinine group are treated with potash1 an oil was obtained which he termed quinoline1 and which was recognised by ,hofmann as identical with a substance obtained in #ahcd from coal-tar by ,runge1 and at that time known as leucol4 ,by other modes of treatment certain alkaloids--e4g41 nicotine and conine--are found to yield pyridine1 a basic substance found by ,anderson1 in #ahdf1 in the ftid liquor obtained by distilling bones1 and since found in coal-tar4 ,others of them--e4g41 papaverine1 narcotine1 etc4--yield isoquinoline1 an oil also discovered in coal-tar1 by ,hoogewerff1 and ,van ,dorp1 in #ahhe4 ,these three substances--quinoline1 isoquinoline1 and pyridine--constitute so many nuclei in the constitution of a large number of alkaloids4 ,pyridine resembles benzene in being a cyclic compound1 consisting of five carbon atoms and one nitrogen atom4 ,quinoline stands to pyridine in much the same relation that naphthalene stands to benzene4 ,it can be obtained synthetically1 as first shown by ,koenigs and ,skraup1 and subsequently by ,doebner and ,von ,miller1 from benzene derivatives4 ,isoquinoline1 isomeric with quinoline1 differs from that substance in the position of the nitrogen atom4 ,it1 too1 has been synthetically prepared from benzene derivatives in a number of ways4 ,among the naturally occurring pyridine alkaloids may be named piperine1 found in black pepper1 and conine1 the poisonous principle of hemlock 7conium maculatum74 ,the latter alkaloid was prepared synthetically by ,ladenburg in #ahhf2 as first obtained it differed from the naturally occurring product1 which is dextro-rotatory1 in being optically inactive4 ,ladenburg surmised that the synthetic preparation stood to the naturally occurring compound in the same relation that racemic acid stood to tartaric acid1 and that1 by treatment in the manner employed by ,pasteur1 the racemic modification of conine might be separated into its dextro- and lvo-constituents4 ,this was found to be the case2 but the separated dextro component was now found to be distinctly more optically active than the pure1 natural variety4 ,it was1 in fact1 an isomeric modification--iso-conine4 ,by heating this to #cjj it was transformed into ordinary conine1 identical in all respects with the natural alkaloid4 ,ladenburg has also effected the synthesis of piperine by condensing piperidine and piperinic acid4 ,nicotine1 the alkaloid of tobacco1 was discovered by ,posselt and ,reimann in #ahbh4 ,its constitution was first ascertained by ,pinner1 and it was synthetically obtained by ,am ,pictet1 in #aijd1 as an inactive substance1 capable of being resolved by the crystallisation of its tartrates into a dextro- and lvo-modification1 the latter of which was identical with that found in the tobacco leaf4 ,atropine and hyoscyamine--the poisonous principles of belladonna and henbane--are isomeric alkaloids1 the former of which is optically inactive1 and the latter is lvo-rotatory4 ,atropine is1 in fact1 the racemic modification4 ,the constitution of both alkaloids is known1 and their synthesis is now possible4 ,the successive steps may be thus indicated3 #a4 ,synthesis of glycerin 7,faraday1 ,kolbe1 ,melsens1 ,boerhave1 ,friedel1 and ,silva74 #b4 ,glycerin to glutaric acid 7,berthelot and ,de ,luca1 ,cahours and ,hofmann1 ,erlenmeyer1 ,lermantoff1 and ,markownikoff74 #c4 ,glutaric acid to suberone 7,brown and ,walker1 ,boussingault74 #d4 ,suberone to tropidine 7,willsttter74 #e4 ,tropidine to tropine 7,willsttter1 ,ladenburg74 #f4 ,synthesis of tropic acid 7,berthelot1 ,fittig and ,tollens1 ,friedel1 ,ladenburg1 and ,rgheimer74 #g4 ,tropine and tropic acid3 atropine 7,ladenburg74 ,the alkaloid cocane1 contained in the leaves of erythroxylon coca and now employed as a local ansthetic1 was discovered by ,niemann in #ahfj4 ,it has been shown to be closely related to atropine in constitution1 and has now been synthetically prepared in the dextro-modification4 ,the alkaloids papaverine1 narcotine1 narcene1 contained in opium1 are derivatives of isoquinoline1 as also is berberine1 found in the common barberry 7berberis vulgaris74 ,papaverine1 which occurs in opium to the extent of about one per cent41 was first isolated by ,merck in #ahdh4 ,its constitution has been established by ,goldschmidt4 ,narcotine is1 next to morphine1 the most abundant constituent of opium4 ,the study of the products of its hydrolysis and oxidation--viz41 opianic acid and cotarnine1 both of which substances have long been known--has indicated its probable structure4 ,narcene is closely allied to narcotine1 and can1 indeed1 be obtained from it by combining the latter alkaloid with methyl iodide and treating the compound with caustic potash4 ,the constitution of berberine1 which is one of the few coloured vegeto-alkaloids known1 has been worked out by ,perkin4 ,as yet nothing definite is known concerning the structure of the most important and largest constituent of opium--viz41 morphine2 or of its congeners codene and thebaine4 ,grimaux1 however1 in #ahha converted morphine into codene by treatment with methyl iodide and potash2 hence the two alkaloids stand in a relation somewhat similar to that in which narcene stands to narcotine4 ,there is very little doubt that the three alkaloids are very closely related1 and that a knowledge of the constitution of one of them would immediately elucidate the structure of the others4 ,they are probably phenanthrene derivatives4 ,quinine and cinchonine1 the most important of the cinchona alkaloids1 are quinoline compounds1 and are closely related in constitution4 ,but the many attempts to unravel their structure have yielded no definite results up to the present4 ,,chapter ,,ix ,,stereo-,,isomerism3 ,,stereo-,,chemistry ,the first gropings in the search for light on the inner structure of molecular groupings may be said to date from ,biot's work on polarisation4 ,in #ahae ,biot1 a pupil of ,malus1 made the remarkable discovery that a number of naturally occurring organic compounds--e4g41 sugar1 tartaric acid1 oil of turpentine1 camphor1 etc41 are optically active--that is1 rotate the plane of polarisation in one direction or the other4 ,the property had previously been observed in quartz1 and was assumed to be connected with the crystalline character of that substance4 ,biot1 however1 pointed out that the case of oil of turpentine which is a liquid1 and the cases of the other substances when in solution1 showed that crystalline character had no necessary connection with the phenomenon1 but that it must be dependent upon the internal or molecular arrangement of the optically active substance4 ,in #ahdd ,mitscherlich1 who first demonstrated the relation between atomic constitution and crystalline form1 drew attention to the fact that the salts of the isomeric modifications of tartaric acid1 studied by ,berzelius1 although possessing the same chemical composition1 the same crystalline form1 with the same angles1 the same double refraction1 and therefore the same angles between their optical axes1 nevertheless behave quite differently as regards their optical activity1 solutions of the tartrates rotating the plane of polarisation1 whereas those of the racemates are inactive4 ,in #ahdh this remarkable circumstance engaged the attention of ,louis ,pasteur1 a young man who had just completed his course at the cole ,normale in ,paris1 and was acting as assistant to ,balard1 the discoverer of the element bromine4 ,pasteur1 on examining the crystals of the two forms of tartaric acid1 and of some of their salts1 detected the presence1 on some of them1 of certain facets--so-called hemihedral faces--which had hitherto been unrecognised1 but were similar to facets which ,hay had observed on quartz4 ,hay had1 in fact1 divided quartz crystals into two classes--right-handed and left-handed1 depending upon the side on which these facets occurred4 ,the forms were1 as it is termed1 enantiomorphous4 ,biot1 moreover1 found that some quartz crystals1 cut parallel to the axis1 turned the plane of polarisation to the right1 whereas others turned it to the left2 and ,herschel suggested that the phenomena were probably connected1 and such was found to be the case4 ,mindful of ,herschel's observation1 ,pasteur found that the crystals of certain of the optically active tartrates showed hemihedral faces1 whereas those of the corresponding racemates showed no trace of them4 ,on recrystallising the racemates1 however1 it was noticed that two sets of crystals were formed--enantiomorphic forms--the first set of crystals having hemihedral forms on the right-hand side1 and the second set on the left-hand side4 ,the forms1 in fact1 were so related that one appeared1 as if it were the image1 as seen in a mirror1 of the other4 ,when solutions of these crystals were examined1 one set was found to rotate to the right1 the other to an equal degree to the left4 ,the dextro-rotatory salt yielded ordinary tartaric acid2 the corresponding lvo-rotatory acid was a hitherto unknown modification3 the two together1 in equal proportions1 constituted racemic acid4 ,in #ahfc ,wislicenus published a remarkable memoir on the synthesis of lactic acid4 ,the acid in sour milk was discovered by ,scheele in #aghj4 ,in #ahjg ,berzelius discovered a similar acid1 called sarcolactic acid1 in muscle juice2 this was erroneously pronounced by ,liebig to be identical with that of sour milk4 ,other forms of lactic acid were made known1 the structural character of which was not to be explained by current hypotheses4 ,wislicenus concluded that their differences could be due only to different arrangements of their atoms in space4 ,in #ahgd the conception of atomic grouping received a remarkable development by the publication of two memoirs--one by ,van 't ,hoff1 and the other by ,le ,bel--which served to connect molecular structure with optical activity4 ,confining their attention to carbon compounds1 they inferred that all optically active substances contained at least one multivalent atom1 united to other atoms or groups1 so as to form in space an unsymmetrical arrangement4 ,van 't ,hoff regarded the carbon atom as occupying the centre of a tetrahedron1 to the summits of which its valencies were directed4 ,if different groupings are attached to these summits1 the structure is asymmetrical1 and is optically active4 ,the two forms of lactic acid1 for example1 may be represented by the following space formul3 ,illustration ,it will be seen from an inspection of the figures that the one is the image-form of the other1 and1 no matter how they are turned1 they are not superposable2 they are right- and left-handed1 or1 as it is termed1 enantiomorphs4 ,there is no fundamental distinction between the hypothesis of ,van 't ,hoff and ,le ,bel as to the effect of asymmetry on optical behaviour4 ,le ,bel regards the effect of asymmetry simply as a necessary consequence of the presence of four dissimilar groupings1 and as independent of valency and the geometrical form of the molecule4 ,illustration3 ,,jacobus ,,henricus ,,van ',t ,,hoff4 ,it was surmised by ,pasteur that every liquid or solid in solution showing optical activity1 if crystallisable1 would be found to manifest hemihedral faces2 but this has not been generally established4 ,further1 it does not always happen that an optically active substance in solution is so when solid4 ,lastly1 optical activity may be latent even in asymmetric carbon compounds if dextro- or lvo-modifications are present in equal proportions1 as in racemic acid4 ,such compounds are1 in fact1 termed 8racemic10 or racemoids2 and they may be separated occasionally by crystallisation1 as in ,pasteur's method with the tartrates2 or as shown by him by the action of the racemoid upon another optically active substance2 or1 lastly1 by taking advantage of the specific action 7specific assimilation7 of organisms--,pasteur's so-called biochemical method4 ,it is a physiological fact of great interest that the behaviour of enantiomorphs towards the animal organism is frequently markedly different4 ,lvo-tartaric acid administered to guinea-pigs is found to be twice as poisonous as the dextro-acid2 dextro-asparagine possesses a sweet taste1 but lvo-asparagine is tasteless2 lvo-nicotine is more poisonous than the dextro-alkaloid4 ,the ferments known as enzymes are also found to possess the power of selection1 behaving differently towards the different optically active modifications of the same substance4 ,it is frequently observed that an optically active substance may be rendered inactive by the conversion of half the substance into its enantiomorph4 ,this operation was first performed by ,pasteur1 and may be brought about by heating the substance1 either alone or with water1 under pressure4 ,indeed1 it is occasionally observed to take place at the ordinary temperature 7autoracemisation74 ,by the action of various reagents the derivatives of an optically active substance are found not unfrequently to change the direction of their optical activity4 ,indeed1 by such means one enantiomorph may be changed into another4 ,thus lvo-menthol may be converted into the dextro-modification by treatment with sulphuric acid4 ,the rotatory power of a substance is frequently modified by the character of its solvent1 and varies with the temperature and concentration of the solution4 ,landolt and ,oudemans found that the specific rotation of dilute solutions of tartrates and of salts of the active alkaloids was independent of the nature of the base and acid respectively present--a fact which finds its explanation in the theory of electrolytic dissociation4 ,it has been known for some years past that the specific rotation of solutions of certain sugars changes with time1 being sometimes less and sometimes more than the initial amount4 ,this phenomenon is now known as multirotation1 or mutarotation4 ,it seems to be connected with an alteration in the configuration of the molecules4 ,there is a special case of stereo-isomerism1 differing from that of optical isomerism and of structural isomerism 7with which we have hitherto been alone concerned71 which was predicted by ,van 't ,hoff in his remarkable work ,la ,chimie dans l',espace1 published in #ahgg--noteworthy as being the first serious attempt to grapple with the problem of spatial molecular grouping1 foreshadowed by ,wollaston1 ,berzelius1 and1 indeed1 all the early philosophic thinkers who accepted the atomic theory4 ,the special form of stereo-isomerism now referred to1 which has been more particularly investigated by ,wislicenus1 is distinguished as geometrical isomerism2 not1 perhaps1 a sufficiently descriptive term1 since1 comprehensively1 all forms of isomerism are really cases of geometrical isomerism4 ,instances of it are to be met with among the isomeric acids existing as glycerides in certain fats1 in cinnamic acid1 in stilbene and its derivatives1 etc4 ,it was first observed in maleic and fumaric acids--isomeric acids of the empirical formula ,c#b;,h#b 7,,cooh7#b1 obtained by the distillation of malic acid1 the characteristic acid met with in the apple and other fruits and in certain other vegetal products4 ,these acids may be represented by the following space formul3 ,,cooh----,c----,h ,,cooh----,c----,h ,,cooh----,c----,h ,h----,c----,,cooh ,maleic acid4 ,fumaric acid4 which show no asymmetry1 and hence no possibility of optical activity or enantiomorphous modifications4 ,in the case of maleic acid it will be seen that the same groups 7,,cooh or ,h7 are represented on the same side of the molecule--in other words1 they are placed symmetrically in a plane--whereas in fumaric acid they are placed diagonally or are axially symmetrical4 ,isomers of the first case are classified as malenoid or cis-forms1 while those of the latter are termed fumaroid or trans-forms4 ,substances of the character referred to are1 as a rule1 mutually convertible with more or less ease2 they are susceptible of what is called geometrical inversion4 ,thus fumaric acid may be readily converted into maleic acid by heating2 maleic chloride is gradually transformed into fumaric chloride at ordinary temperatures4 ,sunlight1 or a particular solvent1 or the presence of some substance which acts as a catalyst1 may effect the inversion4 ,cis and trans isomerism is also met with among cyclic compounds2 it occurs among the terpenes2 and certain alkaloids1 as1 for example1 cocane1 exhibit it4 ,although the doctrine of stereo-chemistry was first enunciated in the case of carbon1 and was1 indeed1 for a time solely confined to compounds in which carbon was the nucleal element1 there is no a priori reason why the phenomenon should be so restricted4 ,van 't ,hoff1 in fact1 in #ahgh1 discussed the question in relation to nitrogen compounds4 ,stereo-isomeric nitrogen derivatives were first obtained by ,victor ,meyer and his pupils1 and the stereo-chemistry of nitrogen has since proved to be a very fruitful field of investigation1 notably in the hands of ,goldschmidt1 ,beckmann1 ,hantzsch and ,werner1 ,le ,bel1 ,ladenburg1 ,bamberger1 ,kipping1 ,h4 ,o4 ,jones1 ,pope1 and others4 ,the stereo-chemistry of nitrogen differs from that of carbon1 inasmuch as variation of valency plays a far more important part in the case of nitrogen than it has hitherto been observed to do in that of carbon2 the spatial representation of the trivalent nitrogen atom differs from that of the pentavalent atom4 ,le ,bel1 in #ahia1 succeeded in obtaining an optically active nitrogen enantiomorph by the application of ,pasteur's biochemical method4 ,optically active compounds have since been prepared by ,pope and ,peachey and ,h4 ,o4 ,jones4 ,pope and ,peachey have also prepared optically active compounds of sulphur1 selenium1 and tin2 and ,kipping has obtained an asymmetric compound of silicon4 ,in #ahfc ,geuther1 and1 independently1 ,frankland and ,duppa1 made known the existence of aceto-acetic ester4 ,by ,geuther this compound was termed ethyl-di-acetic acid-- ,,ch#c4;,c7,,oh73 ,,chcooc#b;,h#e by ,frankland and ,duppa it was considered to be acetone-carboxylic acid-- ,,ch#c4;,,co4,,ch#b4;,,cooc#b;,h#e4 ,the essential difference in these formul1 as the two names respectively indicate1 is that the first implies that the ester has an acidic or hydroxylic character1 proved by its forming characteristic salts2 the other that it contains the group ,,co1 proved by its yielding acetone and the usual reactions of the ketones4 ,the attempt to settle the constitution of this substance gave rise to much controversy1 and1 as it was found to be very reactive1 led to a great amount of conflicting experimental work4 ,the ultimate result was to show that both formul are correct3 at the time of reaction the ester is sometimes hydroxylic1 at other times ketonic1 or1 adopting the terminology of ,brhl1 it sometimes shows the enol form1 at other times the keto form4 ,other substances were subsequently found to behave in the same way4 ,in #ahhe the question was discussed by ,laar1 who suggested the term tautomerism 71 the same2 1 a part7 to denote the fact that one and the same substance could have structural formul varying with conditions of reaction and depending upon the migrations of certain of its atoms within the molecule4 ,during the last twenty years a large number of examples of the kind have been discovered4 ,they are found to occur1 not only among aliphatic substances1 but in cyclic and heterocyclic compounds4 ,we now know that such intermolecular changes may occur by the migration of any of the elements or groups present in the molecule4 ,thus1 to confine ourselves to simple and well-known examples1 the transformation of sodium phenyl carbonate into sodium salicylate1 discovered by ,kolbe1 is due to the wandering of an atom of hydrogen from the benzene residue to oxygen1 thus3 ,,oh _/ ,c#f;,h#e4,o4,c,o,o,na,c#f;,h#d ,c,o,o,na4 ,the conversion of the nitriles into the cyanides by heating is due to the transference of the alkyl radical from the nitrogen atom to the carbon-- ,r4,,nc,,nc4,r4 ,alkyl groups may also be transferred from oxygen to nitrogen2 a radical may detach itself from a carbon atom and wander to a nitrogen atom2 radicals in cyclic compounds may be transferred from the side chains to the nucleus1 etc4 ,the phenomenon1 in fact1 is now so general that grave doubts have been thrown upon the uniform value of deducing the structural formula of a substance from the study of its decomposition products1 or from the nature of its derivatives1 owing to the readiness with which tautomerism may occur4 ,the change may be brought about by variation of temperature1 by the reagent itself1 by the action of a solvent or the presence of a catalyst--that is1 of a substance which apparently plays no part in the metamorphosis4 ,hence the value of specific reagents as clues to constitution is considerably weakened1 since the results may be equivocal4 ,fortunately1 the great extension1 within recent years1 of the application of physical methods has considerably strengthened our means of gaining an insight into molecular structure2 and the investigations of ,brhl on refraction and dispersion1 of ,perkin on magnetic rotation1 of ,hantzsch on electrical conductivity1 of ,lowry on solubility1 of ,lowry and ,e4 ,f4 ,armstrong on optical activity1 of ,knorr and ,findlay on melting-points1 and1 lastly1 of ,hartley1 ,dobbie1 ,lauder1 ,baly1 and ,desch on absorption spectra1 have collectively afforded valuable information on the mechanism of isomeric change based upon dynamical considerations4 ,space will not permit of a more extended treatment of the subject of stereo-chemistry2 and certain matters relating to it1 as1 for example1 the phenomena classed under the term steric hindrance1 must be left unnoticed4 ,this term has reference to the hindrance which certain groups1 or the particular distribution in space of certain atoms1 exert on the progress or extent of a reaction1 as1 for example1 of hydrolysis or esterification1 etc4 ,the influence of special groupings in retarding chemical change is apparently well established1 but no comprehensive theory of the subject is yet possible4 ,until such a theory is forthcoming a dynamical theory of stereo-chemistry is incomplete4 ,,chapter ,x ,,organic ,,synthesis3 ,,condensation3 ,,the ,,synthesis ,,of ,,vital ,,products ,in its widest sense1 the term 8synthesis10 as used in organic chemistry1 means the building-up of carbon compounds1 either from their constituent elements or from groups of differently constituted molecules4 ,at one period this term was confined to cases in which the organic compound was prepared from inorganic materials1 or from combinations which themselves could be formed from their elements2 but latterly it has lost1 in large measure1 this restricted signification4 ,at the same time1 the attempt has been made to indicate by special terms certain classes of synthetical reactions4 ,thus the special case of the formation of an organic compound by the union of two or1 it may be1 more molecular groupings is now frequently spoken of as condensation4 ,organic chemistry has been largely developed by the discovery from time to time of special reagents and special types of reactions which have shown themselves to be capable of extensive application4 ,such1 for example1 was ,frankland's discovery1 in #aheb1 of zinc-ethyl--the first of the organo-metallic compounds1 and the type of a series of substances of great theoretical importance1 and of great practical value by reason of their reactive powers4 ,they led to the synthesis of the paraffins1 the secondary and tertiary alcohols1 and ketones4 ,a few years later ,wurtz introduced the use of metallic sodium as a condensing agent1 and showed thereby how the hydrocarbon butane could be produced from ethyl iodide3 #b;,c#b;,h#e;,i ,na#b ,c#d;,h#aj #b,na,i4 ,use was made of the same agent by ,fittig1 in #ahfc1 in effecting the synthesis of the homologues of benzene by the action of an alkyl iodide upon bromobenzene3 ,c#f;,h#e;,br ,,ch#c;,i ,na#b ,c#f;,h#e4;,,ch#c ,na,i ,na,br4 ,in like manner ,kekul1 in #ahff1 obtained benzoic acid by the action of carbon dioxide upon bromobenzene3 ,c#f;,h#e;,br ,,co#b ,na#b ,c#f;,h#e;,c,o,o,na ,na,br4 ,the readiness with which magnesium can now be obtained1 mainly as the result of ,sonstadt's efforts to develop its metallurgy1 has led to its application1 at the suggestion of ,barbier1 in #ahii1 in place of zinc4 ,the particular form of magnesium compound now employed as a reagent was prepared by ,grignard in #aijj1 and is known by his name4 ,it is obtained by bringing an ethereal solution of an alkyl iodide or bromide into contact with magnesium1 when the metal is dissolved1 forming1 in the case of methyl iodide1 ,mg,c,h#c;,i47,c#b;,h#e7b,o4 ,grignard's reagent has shown itself to be extraordinarily reactive1 and a great number of condensations--of hydrocarbons1 alcohols1 aldehydes1 acids1 ketones1 amides1 and additive compounds--have been effected by means of it4 ,other condensing reagents of value are aceto-acetic ester1 sodium amalgam1 sodamide1 sodium ethoxide1 dimethyl sulphate1 zinc chloride1 aluminium chloride1 fused caustic potash1 hydrogen chloride1 phenyl-hydrazine1 hydrogen peroxide in presence of a ferrous salt 7,fenton's reagent71 ammonia1 and various amines4 ,the application of these reagents has led to the discovery of a variety of new compounds1 the mode of origin of which has served to elucidate their constitution4 ,the great majority of organic syntheses1 especially when they start by the use of inorganic materials1 consist in passing from simple to complex molecular groupings by condensation processes4 ,an interesting example of the reverse process is seen in the production of carbon suboxide1 or carbon carbonyl1 ,c#c,o#b1 obtained from various malonyl compounds1 but most conveniently prepared by the action of phosphoric oxide on malonic acid under diminished pressure1 or by treating an ethereal solution of dibromomalonyl chloride with zinc3 ,,cooh ,,co _/ _/_/ 7#a7 ,,ch#b #b;,h#b,o ,c ,,cooh ,,co ,,co _/_/ 7#b7 ,c,br#b7;,c,o,cl47#b ,zn#b ,zn,cl#b ,zn,br#b ,c ,,co ,carbon suboxide is a colourless1 extremely mobile1 refractive1 poisonous liquid1 of sp4 gr4 #a4aa1 with a strong and peculiar smell4 ,it boils at #g1 and freezes at -#ajg4 ,it is stable only at low temperatures2 at ordinary temperatures it polymerises to a red solid1 which dissolves in water1 forming a solution of the colour of eosin4 ,the change is almost instantaneous at #ajj4 ,carbon suboxide is inflammable1 burning with a blue but smoky flame3 ,c#c,o#b #b,o#b #c;,,co#b4 ,its low boiling-point and the high value of its molecular refraction and dispersion1 its general resemblance to the metallic carbonyls and ketones1 etc41 indicate that this remarkable oxide of carbon is1 in all probability1 the anhydride of malonic acid4 ,indeed1 by the action of water upon it1 it is reconverted into malonic acid4 ,in point of principle1 and viewed as chemical operations1 the synthesis of vital products is in nowise different from the synthesis of any other group of organic compounds2 and the special interest1 and even astonishment1 at one time created by the artificial preparation of such products has largely died away4 ,the synthetical production of some of the substances formerly known only to be formed by vital action1 either in the animal or the plant1 has already been incidentally referred to4 ,but it may be convenient to treat the subject of the artificial production of this group of bodies rather more comprehensively and as a sub-section of this chapter on organic synthesis1 since their formation by such means constitutes a phase in the development of chemistry1 and has undoubtedly exercised a profound influence on scientific thought and on philosophical and even theological doctrine4 ,during the past fifty or sixty years the chemist has been enabled to form the active principles or characteristic products of many plants and animals4 ,he has built up substances which were formerly regarded as capable of being made only by the very process of living4 ,he has prepared compounds which were at one time considered as only producible by changes in organised matter after death4 ,since the date of ,whler's epoch-making discovery1 already referred to#d urea has been synthetically prepared by many reactions1 notably by ,regnault and ,natanson by the action of ammonia on carbonyl chloride1 and by ,basarow and ,dexter from ammonium carbamate4 ,both these substances can be formed directly or indirectly from their elements4 ,it may also be obtained by the hydrolysis of lead cyanate3 ,pb7,,cno7#b #b;,h#b,o ,pb,c,o#c ,,co7,,nh#b7b4 #d ,vol4 ,i41 p4 #afc4 ,the successive steps in its production from inorganic materials by this method are3 ,k ,c ,n ,,kcn ,,kcno ,pb7,,cno7#b ,,co7,,nh#b7b4 ,associated with urea as products of metabolism are uric acid1 xanthine1 and sarcine4 ,urea was first artificially transformed into uric acid by ,horbaczewski1 and its synthesis was effected by ,behrend and ,roosen4 ,closely related in chemical composition to these substances are theobromine and caffeine1 the characteristic principles respectively of cocoa 7the fruit of theobroma cacao72 and of coffee1 tea1 mat 7the leaves of ilex paraguayensis72 8guarana10 obtained from the seeds of the ,south ,american plant paullinia sorbilis1 and the kola-nut of ,central ,africa4 ,strecker1 in #ahfj1 showed how theobromine may be converted into caffeine2 and ,emil ,fischer1 by similar means1 transformed xanthine into theobromine4 ,since that time xanthine itself has been prepared artificially4 ,caffeine can now be built up from its elements by a series of transformations effected by a succession of chemists1 as follows3 #a4 ,carbon and oxygen give carbonic oxide4--,priestley1 ,cruickshank4 #b4 ,carbonic oxide and chlorine give carbonyl chloride4--,j4 ,davy4 #c4 ,carbonyl chloride and ammonia give urea4--,natanson4 #d4 ,urea gives uric acid4--,horbaczewski2 ,behrend and ,roosen4 #e4 ,uric acid gives xanthine4--,e4 ,fischer4 #f4 ,xanthine gives theobromine4--,strecker4 #g4 ,theobromine gives caffeine4--,e4 ,fischer4 ,synthetic theobromine is now made on the large scale1 and introduced as a soda compound1 in combination with sodium acetate1 into medicine as a diuretic under the name of agurin4 ,synthetic caffeine is also prepared on a manufacturing scale from uric acid through the medium of the methylxanthines4 ,the close relationship of xanthine to uric acid is of great physiological significance1 since there is little doubt that the xanthine bases are the most important sources of uric acid within the organism4 ,in this connection reference may be made to the large number of synthetic organic products which have been introduced into medicine during the past few years4 ,the investigation of the constitution of the alkaloids has served to show in many cases to what particular molecular grouping the physiological action of the drug is mainly due1 and this has led to the production of substances containing these groups1 but not necessarily existing as natural products4 ,among these may be mentioned antipyrin1 a derivative of the pyrazol group1 discovered by ,knorr in #ahhc1 and of which upwards of #ag1jjj kilos1 of the approximate value of #ce1jjj1 were produced in #ahii4 ,this substance is a phenyl-dimethyl-pyrazolone4 ,acetanilide ,c#f;,h#e,,nh4,,coch#c1 an aniline derivative1 was discovered by ,gerhardt in #ahec4 ,phenacetin is a derivative of para-aminophenol3 ,,oc#b;,h#e _/ ,c#f;,h#d ,,nh4,,coch#c4 ,an extraordinary number of synthetical soporifics have been introduced at various times during recent years--e4g41 chloral hydrate1 veronal1 sulphonal1 trional and tetronal1 etc4 ,the three last-named substances are closely related1 as the following formul indicate3 ,,ch#c ,,ch#c ,c7,,so#b;,c#b;,h#e7b ,c7,,so#b;,c#b;,h#e7b _/ _/ ,,ch#c ,c#b;,h#e ,sulphonal4 ,trional4 ,c#b;,h#e ,c7,,so#b;,c#b;,h#e7b _/ ,c#b;,h#e ,tetronal4 ,sulphonal is prepared by the oxidation of a substance obtained by the combination of acetone and ethylmercaptan4 ,veronal is an ethyl compound of barbituric acid1 obtained by the condensation of urea and diethyl malonyl chloride3 ,,nh4,,co _/ ,,co ,c7,c#b;,h#e7b _/ ,,nh4,,co ,veronal4 ,attempts have been made to connect the physiological working of local ansthetics with particular constitutional groupings1 as1 for example1 in cocane2 and these have led to the introduction of such substances as the orthoforms1 nirvanine1 stovane1 alyhine1 novocane1 and adrenaline into medicine4 ,adrenaline1 used in conjunction with cocane1 has proved itself a most valuable agent in producing what is called lumbal ansthesia1 whereby large sections of the lower half of the body may be rendered completely insensitive to pain4 ,the study of the putrefactive changes of albuminous substances of animal origin1 induced by the activity of micro-organisms1 has revealed the existence of a number of basic nitrogenous compounds1 some of which are highly poisonous4 ,these were classed by ,selmi under the generic name of ptomaines 71 a corpse74 ,brieger found that the typhoid bacillus yielded a poisonous substance--typhotoxine1 and that the bacillus of tetanus forms a highly toxic basic body1 tetanine4 ,all the ptomaines1 however1 are not poisonous4 ,some of them1 like choline 71 bile7--originally discovered by ,strecker in bile1 in the brain1 in yolk of egg1 and now found to be among the products of the putrefaction of meat and fish--have been known for some time past4 ,choline was first synthetically prepared by ,wurtz4 ,neurine 71 nerve71 a derivative of brain substance1 is related to choline1 and is readily transformed into it1 but differs from it in being very poisonous4 ,it has been synthesised by ,hofmann and by ,baeyer4 ,another of the so-called corpse-alkaloids--cadaverine--has been synthetically formed by ,ladenburg4 ,schmiedeberg and ,kopp isolated the poisonous principle of the fungus agaricus muscarius1 which they named muscarine4 ,it occurs with choline1 from which it can be readily obtained1 among the products of the putrefaction of flesh1 as well as in many fungi4 ,the synthesis of the alkaloids conine1 atropine1 cocane1 piperine1 and nicotine has been already referred to#e as also that of vanillin1 the aromatic principle of the dried fermented pods of certain orchids2 coumarin1 the odoriferous principle of woodruff and of the tonka bean2 of salicylic acid1 oil of wintergreen1 oil of mustard1 bitter-almond oil1 and camphor4 ,acetic1 succinic1 tartaric1 and citric acids have also been artificially obtained1 and may1 indeed1 be built up from their elements4 #e ,p4 #acc4 ,no synthesis of recent years created more widespread interest than that of alizarin1 first effected by ,graebe and ,liebermann in #ahfh4 ,its successful commercial manufacture by ,sir ,william ,perkin in this country and by ,caro in ,germany created nothing less than a revolution in one of our leading industries1 and completely destroyed a staple trade of ,france1 ,holland1 ,italy1 and ,turkey4 ,to procure alizarin1 anthraquinone is treated with sulphuric acid1 and the product is fused with alkali and potassium chlorate4 ,the remarkable industrial results attending the synthetical formation of this madder-product naturally led to attempts to procure other important vegetable dye-stuffs artificially1 notably indigo4 ,the synthetical production of indigo has been accomplished by the joint labours of many chemists1 notably ,baeyer1 ,heumann1 and ,heymann1 and the substance is now prepared on an industrial scale4 ,the starting-point is naphthalene1 obtained from coal-tar4 ,this is converted into phthalic acid1 which is then transformed into phthalimide4 ,the last-named substance is converted into anthranilic acid1 which1 on treatment with monochloracetic acid1 is changed into phenylglycin-ortho-carbonic acid4 ,on melting this with caustic potash it yields indoxyl acid1 which is transformed into indoxyl1 and thence into indigo4 ,another method is to treat the sodium salt of phenylglycin with sodamide1 whereby indoxyl is at once obtained1 and this by condensation yields indigo blue3 ,c#f;,h#e4,,nh4,,ch#b4;,c,o,o,na ,na4,,nh#b ,sodium salt of ,sodamide4 phenylglycin4 ,,co _/ ,c#f;,h#d ,,ch#b _/ ,,nh ,indoxyl4 ,,co ,,co _/ _/ ,c#f;,h#d ,c3,c ,c#f;,h#d _/ _/ ,,nh ,,nh ,indigo blue4 ,phenylglycin is obtained by the action of monochloracetic acid on aniline1 which in its turn is obtained through nitrobenzene from benzene4 ,since benzene can be synthetically prepared by the condensation of acetylene1 which can be obtained by the direct union of carbon and hydrogen at a high temperature1 it is theoretically possible to build up indigo blue from inorganic materials4 ,synthetical indigo blue was placed on the market in #ahig with an almost immediate effect on the production and price of the natural variety1 and to-day the output of ,bengal indigo has fallen by more than fifty per cent4 ,in #aijb the amount of the natural product was probably not greater than three million kilos1 whereas in the same year the production of synthetic indigo was upwards of five million kilos4 ,before the introduction of the artificial variety the price of pure indigo blue ranged from sixteen to twenty shillings per kilo2 by the end of #aije it had fallen to seven or eight shillings4 ,mention should be made also of thio-indigo red and the thionaphthene derivatives1 some of which promise to be important colouring matters4 ,in recent years the so-called sulphur colouring matters have acquired considerable importance4 ,space will not permit of any fuller treatment of the development of the manufacture of the artificial organic colouring matters4 ,this industry had its beginnings in ,england1 but it is now mainly carried on in ,germany4 ,its importance may be gleaned from the fact that the value of the production at the present time amounts to not less than #ab1ejj1jjj per annum1 two thirds of the output being exported4 ,it demands the services of battalions of skilled chemists1 and gives employment to many thousands of artisans4 ,some of the most notable achievements of modern synthetical chemistry are to be found in the work of ,emil ,fischer on the sugars and the proteins4 ,although the sugars have from the earliest times been reckoned among the most characteristic products of plant life1 and have long been used as food and as sources of alcohol1 comparatively little was known until lately of their real nature and mutual relations1 in spite of numerous attempts to elucidate their constitution4 ,much of the mystery surrounding their chemical history has now been dispelled4 ,not only has the molecular structure of the more important naturally occurring sugars been unravelled1 but a large number of hitherto unknown members of the various groups of the great family to which they belong have been prepared4 ,the first insight into the constitution of these bodies may be said to date from the researches of ,kiliani1 made about a quarter of a century ago4 ,in #ahhg ,fischer effected the synthesis of a form of fructose 7fruit sugar71 and immediately afterwards of ordinary dextro-glucose 7grape sugar7 and its enantiomorph lvo-glucose1 and the two optically active forms of natural fruit sugar4 ,since that time such sugars as arabinose1 xylose1 fucose1 mannose1 sorbose1 cane-sugar1 maltose1 lactose1 etc41 and the sugars existing as glucosides1 have been examined1 their stereo-chemical relations defined1 and synthetic methods of production devised4 ,incidentally1 their behaviour towards enzymes has been studied1 and the remarkable selective action of these ferments on the various groups1 due apparently to differences of configuration1 has been established1 with the result that much light has been thrown on the mechanism of enzyme action and on the general theory of fermentation4 ,illustration3 ,,emil ,,fischer4 ,the study of the proteins by ,fischer constitutes a new chapter in bio-chemistry4 ,although long recognised as among the most important of vital products1 from the circumstance that they enter into the composition of animal tissues and secretions and are essential constituents of protoplasm1 the proteins are among the worst defined substances known to the chemist4 ,they are difficult to separate1 as they closely resemble one another1 and afford no certain indications of individuality4 ,very few of them have been obtained in a form in which their identity could be established4 ,oxyhmoglobin was isolated some years ago1 but the proteins of serum albumin and of egg albumin have only recently been obtained in definite crystalline shape4 ,all the proteins--even the simplest of them--are of great complexity1 and possess apparently very high molecular weights4 ,hmoglobin1 for example1 appears to have approximately the formula ,c#aeh;,h#abc,n#aie,o#bah;,fe,s#c1 with a minimum molecular weight of #af1fjj4 ,indeed1 there is experimental evidence to show that it is even considerably higher than this4 ,the main clues to the nature of these substances have been gained by the systematic study of their hydrolysis1 induced by reagents1 or by the action of enzymes1 whereby they are found to break down into proteoses1 peptones1 and a great variety of amino acids1 some of which have been synthesised4 ,among the proteins of simplest constitution are the protamines1 found in the spermatozoa of fish4 ,they are basic substances1 especially rich in nitrogen1 forming salts with platinum chloride and certain metallic oxides4 ,the best investigated member of the group is salmine1 obtained from the testicle of the salmon4 ,the products of its hydrolysis have been fairly well ascertained1 and their quantitative relation is such that the substance must have at least a molecular weight of #bjde1 corresponding to the formula ,c#ha;,h#aee,n#de,o#ah4 ,many of the albumins and globulins--coagulable proteins contained in the animal tissues--have been isolated in a more or less definite form1 and some of them have been found to yield substances akin to carbohydrates4 ,thyreoglobulin1 the globulin of the thyroid gland1 has been found to contain iodine1 apparently as a normal constituent of a body which can be isolated as a definite proximate principle4 ,the presence of this element is possibly connected with the curative value of the globulin in crtinism4 ,a considerable amount of work on the vegetable albumins has also been done of late years2 and some of them1 as edestin from hemp seed and zein from maize1 have been obtained in definite form4 ,the limits of this work preclude a more detailed account of one of the most interesting but at the same time one of the most obscure departments of chemistry4 ,the field has hitherto been tilled in a somewhat intermittent and partial manner4 ,now that it has been entered by chemists of experience and resourcefulness1 armed with modern methods of cultivation1 it will doubtless soon yield a rich harvest of facts1 valuable alike to the physiologist and the physician4 ,there can be no reasonable doubt that the chemical processes of organic life are essentially similar to those of the laboratory4 ,the doctrine that a special 8vital force0 is concerned in the production of vital products receives no support from the teaching of modern science1 and is1 indeed1 contradicted by it4 ,at the same time1 it must be admitted that we know very little as yet of the real agencies at work in the elaboration and mutations of chemical products in the living organism4 ,because we have effected the putting together of such a product by purely laboratory processes--it may be1 indeed1 by a variety of different and dissimilar processes--it by no means follows that any one of them is identical with that actually occurring in nature4 ,the building up of materials in the plant by the agency of light1 for example1 has not yet been imitated in the laboratory4 ,many plant products are produced by the action of unorganised ferments--so-called enzymes--none of which the chemist has succeeded in creating4 ,processes akin to condensation undoubtedly occur in the living organism2 but the means by which they are effected are1 in all probability1 very different from anything known to the chemist at present4 ,many laboratory condensations are only accomplished at relatively high temperatures or under considerable pressure--or1 in other words1 under totally different conditions from those which obtain in the organism4 ,,chapter ,,xi ,,on ,,the ,,development ,,of ,,physical ,,chemistry ,,since #ahej ,chemistry and physics are each complementary to the other3 that region of inquiry in which they mutually overlap is known as physical chemistry4 ,its beginnings are practically contemporaneous with those of chemistry itself4 ,its main development has occurred1 however1 during the last twenty-five years4 ,certain of its leading features have been referred to already in connection with the establishment of the fundamental principles of chemistry1 the explanation of the so-called gaseous laws1 the constitution of gases1 the relations of their volumes to heat and pressure1 and the conditions affecting their transition to the liquid state4 ,as regards the molecular volumes of gases it has been shown that simple relations are obtained when quantities represented by their respective molecular weights are compared under identical conditions of temperature and pressure--that is1 under circumstances in which equal numbers of molecules form the basis of comparison4 ,the investigation of the molecular volumes of liquids is complicated by the uncertainty as to what constitutes in their case a valid condition of comparison4 ,kopp's assumption that a comparable condition was the temperature at which the vapour pressures of the liquids are equal to the mean atmospheric pressure was justified by the fact that the boiling-points of liquids are approximately two thirds of their respective critical temperatures4 ,his conclusions have been confirmed and extended by ,lossen1 ,thorpe1 and ,schiff4 ,it has been shown that the molecular volume of a liquid--that is1 the product of its relative density at the boiling-point into its molecular weight--is in the main an additive function modified by constitutive influences4 ,definite values have thus been obtained for a number of the elements from a comparison of homologous or similarly constituted compounds2 and in certain cases these are found to be practically identical with the values of the elements in the uncombined state4 ,considerable light has been gained during the last two decades concerning the nature of solution4 ,in its most comprehensive sense solution means the homogeneous mixture of two or more substances3 thus the gases which exert no chemical action on each other are mutually soluble2 gases1 liquids1 and solids may be soluble in liquids2 and1 lastly1 solids maybe soluble in solids1 forming what are known as solid solutions4 ,the mutual solubility of gases was studied by ,dalton who enunciated the law of partial pressures1 which states that the total pressure of a mixture of gases is the sum of the pressures exerted by the individual components4 ,this1 like all the so-called gaseous laws1 is necessarily not strictly accurate under ordinary conditions1 but approximates to truth in proportion as the gases are rarefied4 ,van 't ,hoff pointed out that the true partial pressures of the components of a gaseous mixture might be experimentally ascertained by the use of a membrane capable of effecting their separation1 and on this principle ,ramsay measured the partial pressures of a mixture of hydrogen and nitrogen contained in a palladium vessel connected with a manometer4 ,the palladium1 at a sufficiently high temperature1 is permeable to hydrogen to the exclusion of the nitrogen4 ,the conditions affecting the solubility of gases in liquids were experimentally studied by ,dalton and ,henry1 and what is known as ,henry's law implies that the volume of a gas dissolved by a definite volume of a liquid is independent of the pressure2 or1 in other words1 the density 7concentration7 of the gas in solution is proportional to that in the space above the liquid4 ,gases are dissolved by liquids in very different amounts1 but nothing definite is known as yet concerning the relation between the nature of the gas and its solubility1 although certain broad generalisations are possible4 ,thus neutral gases--e4g41 hydrogen and nitrogen--are sparingly soluble1 whereas gases which show acidic or basic properties1 such as the hydrogen halides1 etc41 ammonia1 etc41 are freely soluble4 ,easily liquefiable gases are also comparatively soluble as noted by ,graham4 ,comparatively little is known definitely concerning the conditions of solubility of liquids in liquids4 ,some liquids are wholly1 others partially miscible2 and temperature and pressure appear to affect the proportions in which the components form a homogeneous mixture4 ,as regards the solubility of solids in liquids1 our knowledge is more extensive1 and a considerable body of literature exists on the subject1 chiefly concerning solubility of solids in water4 ,the solubility of a solid depends on the temperature of the solvent1 and1 as a rule1 increases with the temperature until a certain amount of the solid has been dissolved1 when the solution is said to be saturated4 ,if the clear saturated solution be slowly cooled1 say1 to a particular temperature1 it is frequently observed that more of the solid remains in solution than is normal to that temperature2 such a solution is said to be supersaturated4 ,on adding some of the solid to the supersaturated solution the excess of the solute is precipitated4 ,in certain cases of solubility of substances in water1 increase of temperature appears to diminish the amount dissolved4 ,in nearly all such cases the difference in solubility is due to differences in the hydration of the solute4 ,the phenomena of solid solutions have been less perfectly investigated1 but the facts appear to show that such solutions in general tend to obey the laws regulating the solution of liquids in liquids4 ,alloys may be looked upon as solid solutions2 and ,roberts-,austen has shown that metals are capable of intradiffusion1 like liquids and gases respectively4 ,the general question of solution was greatly developed in #ahhe by ,van 't ,hoff1 by specially considering the case of dilute solutions4 ,the gaseous laws are capable of their simplest expression when the gases are rarefied to such an extent that their molecules exert no sensible mutual influence4 ,the case of dilute solutions is analogous4 ,if the solute is present only in very small amount1 the mutual influence of its molecules is practically negligible4 ,under such conditions it obeys the laws hitherto supposed to be applicable only to matter in the gaseous state4 ,it may be desirable to explain how this fundamental fact was recognised4 ,it has long been known to the physiologist that certain membranes are semi-permeable--that is1 they allow of the passage of certain liquids1 and of substances in solution1 to the exclusion of others4 ,this phenomenon is termed osmosis1 and is of great biological significance4 ,it was first studied by plant-physiologists1 notably by ,traube and ,pfeffer4 ,many such semi-permeable membranes can be formed artificially1 but the most generally convenient is found to be one consisting of copper ferrocyanide deposited on the walls of a porous vessel4 ,if a vessel so prepared be filled with a solution of sugar1 and be then placed in water1 the water is found to pass through the membrane1 but the membrane is impermeable to the sugar4 ,in consequence pressure1 termed osmotic pressure1 is found to occur within the pot1 and may be measured by suitable means4 ,these osmotic pressures may at times be very large3 thus a #a per cent4 solution of sugar may exert a pressure of half an atmosphere1 and in the case of a solution of potassium nitrate of the same concentration it may amount to a couple of atmospheres4 ,pfeffer determined the relation of the osmotic pressures to the concentration of solutions of these substances1 measuring the pressures in centimetres of mercury by a manometer attached to the closed porous vessel4 ,his results in the case of sugar were as follows3 ,percentage ,pressure in cm4 strength 7,c74 of mercury 7,p74 ,p_/,c4 #a #ec4e #ec4e #b #aja4f #ej4h #d #bjh4b #eb4a #f #cjg4e #ea4c ,it will be seen from these numbers that the ratio ,p_/,c is practically constant--that is1 the osmotic pressure varies directly as the concentration4 ,it was further found that the osmotic pressure exerted by a solution of uniform strength increases with the temperature4 ,the importance1 of these observations in relation to the general theory of solution was first recognised by ,van 't ,hoff4 ,osmotic pressure was regarded by him as analogous to gaseous pressure4 ,since ,p_/,c is constant for any one substance1 and since for a definite weight of the solute the concentration is inversely as the volume of the solution1 we obtain an equation analogous to the statement of ,boyle's law1 ,,pv constant4 ,van 't ,hoff also found that the osmotic pressure is proportional to the absolute temperature1 like the gaseous pressure4 ,from these results1 in conjunction with ,avogadro's hypothesis1 it follows that the osmotic pressure exerted by any substance in solution is the same as it would exert if present as gas in the same volume as that occupied by the solution1 provided that the solution is so dilute that the volume occupied by the solute is negligible in comparison with that occupied by the solvent4 ,another important consequence is that solutes1 when present in the ratio of their molecular weights in equal volumes of the same solvent1 exert the same osmotic pressure4 ,such solutions are said to be isomotic or isotonic4 ,it can be proved by thermodynamical reasoning that depression of the vapour pressure and freezing-point of a solution is proportional to its osmotic pressure4 ,the significance of this relation in connection with the determination of the molecular weight of a soluble substance has already been referred to4#f #f ,see pp4 #gj-gc4 ,determinations of molecular freezing-point depressions by ,raoult and others showed that certain substances exerted only about half the osmotic pressure calculated from their known formul1 whereas others have abnormally high osmotic pressures4 ,the explanation of the discrepancies in the latter case was given in #ahhg by ,arrhenius1 who pointed out that only those solutions which have abnormally high osmotic pressures are electrically conductive4 ,this pregnant observation proved to be very fruitful in suggestiveness2 and the connection between conductivity and ,van 't ,hoff's theory of solution was developed by ,arrhenius into the doctrine of electrolytic dissociation or ionisation--one of the most important consequences of ,faraday's electrolytic laws1 the work of ,hittorf1 and the kinetic conceptions of ,williamson and ,clausius to which the last quarter of a century has given rise4 ,arrhenius showed that not only were free ions present in an electrically conductive solution before electrolysis1 as maintained by ,clausius1 but that the proportion of molecules dissociated into ions could be calculated from measurements of electrical conductivity1 as well as from measurements of osmotic pressure4 ,both methods give concordant results--a strong confirmation of the validity of the theory4 ,in a solution of common salt1 containing a gramme equivalent of that substance in a litre1 ,arrhenius calculated that only about three tenths of the salt exists as ,na,cl1 the remaining seven tenths being resolved into independent ions of chlorine 7chloridion7 and sodium 7sodion73 ,na,cl,na ,cl1 each moving freely in all directions1 like gaseous molecules4 ,on passing the current1 electrodes placed in the solution exert a directive action on the free ions1 these alone being concerned in determining the conductivity1 the un-ionised molecules or the solvent itself exercising no influence4 ,methods of determining the migration velocity of the ions have been worked out by ,hittorf1 ,kohlrausch1 ,lodge1 and others4 ,illustration3 ,,svante ,,august ,,arrhenius4 ,the theory of ionisation affords a satisfactory explanation of many chemical phenomena4 ,it accounts for the characteristic properties of acids1 and explains why different acids have varying 8strengths0 and why a 8weak0 acid has the same 8strength0 as the 8strong0 acid at high equivalent dilutions3 in each case the acid is nearly completely ionised--in other words1 the 8strength0 of an acid depends on the concentration of its hydrogen ions4 ,so1 too1 the 8strength0 of a base is related to the number of its hydroxyl ions4 ,aqueous ammonia is relatively a 8weak0 base--its solution contains few hydroxyl ions4 ,on the other hand1 caustic potash is a 8strong0 base--its solution1 on moderate dilution1 is almost completely ionised3 ,,koh ,k ,,oh1 the positive ion being represented by one or more dots1 and the negative ion by one or more dashes4 ,the theory accounts1 too1 for many phenomena in analytical chemistry--such as why magnesia is precipitated by ammonia only in the absence of ammonium chloride1 and why sulphuretted hydrogen throws down zinc sulphide in the absence of hydrochloric acid4 ,it also serves to explain many thermo-chemical facts observed by ,hess1 ,thomsen1 and others1 such as the fact that the heat of neutralisation of the 8strong0 acids and bases is independent of their nature1 and has the uniform value of #ac1gjj calories1 in agreement with the value1 as calculated by ,van 't ,hoff1 for the reaction ,h ,,oh ,h#b,o1 deduced from ,kohlrausch's measurements of the conductivity of water at varying temperatures4 ,certain phenomena relative to the effect of concentration 7mass action7 in determining chemical change--many of which have been studied by ,ostwald and his pupils1 as1 for example1 why two dilute solutions can be mixed together without thermal disturbance2 numerous hydrolytic actions2 the alkalinity and acidity of salts on solution2 the behaviour of the 8indicators0 in analysis2 such phenomena as the precipitability of common salt in aqueous solution by hydrogen chloride2 the influence of an excess of a precipitant2 the varying behaviour of reagents2 the varying colour of salt solutions2 the reason why water is formed in so many reactions2 why a potential difference occurs at the surface of two electrolytic solutions1 etc4--phenomena for the most part otherwise unintelligible1 are all capable of explanation by means of it4 ,although1 in the above statement1 we have been mainly concerned with aqueous solutions1 it should be said that the theory of ionisation is applicable to other solvents1 organic and inorganic4 ,moreover1 it should be added1 the theory has not been universally accepted as accounting for all the phenomena of solution4 ,many substances form definite hydrates which can be isolated1 and it is a moot point whether such hydrates are capable of existing in aqueous solution1 as contended by ,mendeleff1 ,pickering1 ,kahlenberg1 ,armstrong1 and others4 ,such hydrates are1 however1 unstable compounds1 affected by temperature changes1 and dissociable on dilution in accordance with the law of concentration 7mass action74 ,further1 there is evidence1 largely based on the work of ,kohlrausch1 ,h4 ,c4 ,jones1 and ,lowry1 to show that the ions in aqueous solutions of electrolytes are themselves hydrated4 ,limitations of space preclude further attempts to deal with the development of physical chemistry during the last half-century1 and many important matters must remain practically unnoticed4 ,the subject of thermo-chemistry is mainly the creation of the last half-century1 elaborated by the labours of ,hess1 ,andrews1 ,thomsen1 ,favre and ,silbermann1 and ,berthelot4 ,the work of ,wenzel and ,berthollet on the influence of molecular concentration on chemical change has been greatly extended by ,berthelot1 ,guldberg and ,waage1 ,julius ,thomsen1 ,van 't ,hoff1 ,harcourt and ,esson1 and ,le ,chatelier2 and the theory of mass action and the nature of reversible processes are now capable of definite expression1 and can be proved independently by thermo-dynamical and kinetic reasoning4 ,the phenomena of catalysis and the action of enzymes and of fermentation in general have received attention from many investigators4 ,the phenomena of gaseous transpiration have been studied by ,graham1 ,maxwell1 and ,o4 ,e4 ,meyer4 ,thermal dissociation has been experimentally observed by ,deville1 ,troost1 and others1 and mathematically investigated by ,willard ,gibbs and ,van der ,waals2 and its analogy to electrolytic dissociation has been established4 ,the nature of gaseous explosions has been investigated by ,berthelot1 ,le ,chatelier1 ,abel1 and ,dixon4 ,important work has been done by ,gladstone1 ,lorentz1 ,landolt1 ,nasini1 ,brhl1 and others1 on the connection between the nature and constitution of substances and their optical characters4 ,similar work has been done by ,sir ,william ,perkin as regards their magnetic rotation1 and by ,thorpe and ,rodger with reference to their viscosity4 ,the theory of phases1 originating with ,gibbs and developed by ,van der ,waals and ,roozeboom1 has been greatly extended4 ,sir ,j4 ,j4 ,thomson and ,sir ,j4 ,larmor have elaborated an electrical theory of the atom4 ,barlow and ,pope have traced the relation between valency and volume1 and the accurate measurements of ,groth and of ,tutton have extended our knowledge of the crystallographic relations of correlated substances4 ,lastly1 the whole subject of photo-chemistry1 although originating with the observations of ,ingenhousz1 ,scheele1 and ,senebier1 may be said to have been studied only within our own time1 notably by ,bunsen and ,roscoe1 ,pringsheim1 ,pfeffer1 ,vogel1 and ,abney4 ,,bibliography ,,relating ,,to ,,the ,,period ,,covered ,,by ,,vol ,,ii4 ,alembic ,club1 ,publications of the4 ,w4 ,clay1 ,edinburgh4 ,arrhenius1 ,svante4 ,theories of ,chemistry4 ,translated by ,t4 ,slater ,price4 ,longmans1 #aijg4 ,beilstein's ,handbuch der ,organischen ,chemie4 ,nine vols4 ,leopold ,voss1 ,hamburg1 #aija-aijf4 ,bischoff's ,materialen der ,stereochemie4 ,vieweg and ,son1 ,brunswick1 #aijd4 ,bischoff and ,walden's ,handbuch der ,stereochemie4 ,h4 ,beckhold1 ,frankfort-on-the-,main1 #ahid4 ,cain1 ,j4 ,c41 and ,thorpe1 ,j4 ,f4 ,synthetic ,dyestuffs and ,intermediate ,products4 ,griffin and ,co41 #aije4 ,chemical ,society's ,annual ,reports4 ,gurney and ,jackson4 ,chemical ,society4 ,memorial ,lectures1 #ahic-aijj4 ,gurney and ,jackson1 #aija4 ,cohen1 ,julius ,b4 ,organic ,chemistry4 ,edward ,arnold1 #aijg4 ,curie1 ,marie4 ,radio-,active ,substances4 8,chemical ,news10 ,london1 #aijc4 ,findlay1 ,a4 ,the ,phase ,rule4 ,longmans1 #aijd4 ,fischer1 ,emil4 ,die ,aminosuren1 ,polypeptide und ,proteine4 ,julius ,springer1 ,berlin1 #aijf4 ,fischer1 ,emil4 ,untersuchungen in der ,puringruppe4 ,julius ,springer1 ,berlin1 #aijg4 ,fischer1 ,emil4 ,untersuchungen ber ,kohlenhydrate und ,fermente4 ,julius ,springer1 ,berlin1 #aiji4 ,freund1 ,ida4 ,study of ,chemical ,composition4 ,cambridge ,university ,press1 #aijd4 ,garrett1 ,a4 ,e4 ,the ,periodic ,law4 ,kegan ,paul1 #aiji4 ,ladenburg1 ,albert4 ,development of ,chemistry since the ,time of ,lavoisier4 ,translated by ,leonard ,dobbin4 ,alembic ,club1 ,edinburgh1 #aijj4 ,landolt1 ,h4 ,optical ,activity and ,chemical ,composition4 ,translated by ,j4 ,mc,crae4 ,whittaker1 #aijj4 ,laurent1 ,a4 ,chemical ,method4 ,translated by ,w4 ,odling4 ,cavendish ,society's ,publications1 ,london1 #ahee4 ,mann1 ,gustav4 ,chemistry of the ,proteids4 ,macmillan1 #aijf4 ,maxwell1 ,clerk4 ,theory of ,heat4 ,with corrections and additions by ,lord ,rayleigh4 ,longmans4 ,meldola1 ,raphael4 ,chemical ,synthesis of ,vital ,products4 ,edward ,arnold1 #aijd4 ,mendeleff1 ,d4 ,principles of ,chemistry4 ,translated by ,kamensky and ,greenaway4 ,longmans4 ,meyer1 ,lothar4 ,outlines of ,theoretical ,chemistry4 ,translated by ,bedson and ,williams4 ,longmans1 #ahib4 ,meyer1 ,lothar4 ,modern ,theories of ,chemistry4 ,translated by ,bedson and ,williams4 ,longmans1 #ahhh4 ,meyer and ,jacobson's ,lehrbuch der ,organischen ,chemie4 ,veit and ,co41 ,leipzig4 ,meyer1 ,o4 ,e4 ,the ,kinetic ,theory of ,gases4 ,translated by ,r4 ,e4 ,baynes4 ,longmans1 #ahii4 ,muir1 ,m4 ,m4 ,pattison4 ,history of ,chemical ,theories and ,laws4 ,john ,wiley and ,sons1 ,new ,york1 #aijg4 ,nernst1 ,walter4 ,theoretical ,chemistry4 ,translated by ,c4 ,s4 ,palmer4 ,macmillan1 #ahie4 ,ostwald's ,klassiker der ,exakten ,wissenschaften4 ,pictet1 ,am4 ,vegetable ,alkaloids4 ,translated by ,h4 ,c4 ,biddle4 ,john ,wiley and ,sons1 ,new ,york1 #aijd4 ,richter's ,lexikon der ,kohlenstoff ,verbindungen4 ,leopold ,voss1 ,hamburg and ,leipzig4 ,roscoe and ,schorlemmer1 ,treatise on ,chemistry4 ,macmillan4 ,rutherford1 ,e4 ,radio-,activity4 ,cambridge ,university ,press1 #aijd4 ,schorlemmer1 ,carl4 ,rise and ,development of ,organic ,chemistry4 ,edited by ,arthur ,smithells4 ,macmillan4 ,schryver1 ,s4 ,b4 ,chemistry of the ,albumens4 ,murray1 #aijf4 ,soddy1 ,f4 ,radio-,activity4 ,the ,electrician ,printing and ,publishing ,co41 ,london1 #aijd4 ,stas4 ,recherches sur les ,rapports rciproques des ,poids ,atomique1 #ahfj-ahfe4 ,stewart1 ,a4 ,w4 ,recent ,advances in ,organic ,chemistry4 ,longmans1 #aijh4 ,stewart1 ,a4 ,w4 ,stereo ,chemistry4 ,longmans1 #aijg4 ,thorpe1 ,t4 ,e4 ,dictionary of ,applied ,chemistry4 ,three vols4 ,longmans4 ,thorpe1 ,t4 ,e4 ,essays in ,historical ,chemistry4 ,macmillan1 #aijb4 ,travers1 ,morris ,w4 ,study of ,gases4 ,macmillan1 #aija4 ,van 't ,hoff1 ,j4 ,h4 ,arrangement of ,atoms in ,space4 ,translated by ,a4 ,eiloart4 ,longmans1 #ahih4 ,walker1 ,j4 ,introduction to ,physical ,chemistry4 ,macmillan4 ,wurtz1 ,ad4 ,the ,atomic ,theory4 ,translated by ,e4 ,cleminshaw4 ,kegan ,paul4 ,,index ,abel1 #ahd ,abney1 #ahe ,absolute zero1 #ig ,acetanilide1 #aei ,aceto-acetic ester1 #adh ,actinium1 #ei ,adrenaline1 #afj ,agurin1 #aeh ,alizarin1 #afb ,alkaloids1 #acb ,allyl alcohol1 #d ,alyhine1 #afj ,ammonium chloride1 dissociation of1 #ff ,ampre1 #fb ,anderson1 #acc ,andrews1 #gj1 #ie1 #ahc ,aniline blue1 #d ,aniline purple1 #d ,antimony1 origin of name1 #bh ,antipyrin1 #aei ,argon1 #dc1 #de1 #df ,argyrodite1 #cg ,armstrong1 ,e4 ,f41 #aea ,armstrong1 ,h4 ,e41 #ahc ,aromatic compounds1 #aba1 #abc ,arrhenius1 #agi1 #ahj ,arsine-dimethyl1 #bj ,artiads1 #aaf ,asymmetry1 #ada ,atmolysis1 #hd ,atomic value1 #aad ,atomic weight1 determination of1 #ge ,atomicity1 #aad ,atropine1 #ace1 #afb its synthesis #ace ,australene1 #acj ,autoracemisation1 #add ,avogadro1 #fb his hypothesis1 #fc ,baeyer1 #abe1 #abi1 #afa1 #afc ,balard1 #aci ,baly1 #abi1 #aea ,bamberger1 #adg ,barbier1 #aed ,barlow1 #ahd ,basarow1 #aeg ,basicity1 #af ,becquerel1 ,henri1 #eb ,behrend1 #aeg ,benzene1 #abc its constitution1 #abc et seq41 #abh ,benzidam1 #c ,berberine1 #acf ,bernoulli1 ,daniel1 #hb ,berthelot1 ,daniel1 #hb1 #ahc1 #ahd ,berthollet1 #ahc ,berzelius1 #fc ,biot1 #ach ,bitter almond oil1 #g ,blagden1 ,sir ,charles1 #gb ,boisbaudran1 ,lecoq de1 #cf1 #ch1 #ci ,boltzmann1 #hc ,bone oil1 #acc ,boron1 specific heat of1 #ga ,boyle's law1 #hd-hg ,brauner1 #cc ,bredt1 #abi1 #acj ,brieger1 #afa ,brhl1 #adi1 #aea ,bunsen1 ,robert ,w41 #ah1 #cd1 #dc1 #ahe ,bunsen burner1 #bb ,cacodyl1 #bj ,cadaverine1 #afa ,csium1 #ba1 #cd ,caffeine1 #aeg ,cahours1 #d1 #acb ,cailletet1 #if ,camphene1 #aca ,camphor1 #acj1 #aca1 #afb ,cannizzaro1 ,stanislao1 #fd1 #gi ,carbon1 atomic weight of1 #ge specific heat of1 #ga tetravalency of1 #aae ,carbon carbonyl1 #aee ,carbon suboxide1 #aee ,carnelley1 #ajh ,carnolite1 #eh ,cavendish1 #dc1 #de ,cayley1 #abj de ,chancourtois1 #ajb ,chloral hydrate1 #aei ,choline1 #afa ,cinchonine1 #acg ,clausius1 #hc1 #agi ,cleve1 #ch1 #dg ,cleveite1 #dg ,cocane1 #acf1 #afb ,codeine1 #acg ,coindet1 #h ,collie1 #di1 #abh ,condensation1 #aeb ,conine1 #afb ,conservation of mass1 law of1 #gh ,coumarin1 #acb1 #afb ,critical point1 #id ,critical pressure1 #ie ,crookes1 ,sir ,william1 #ce1 #dj1 #ge ,curie1 ,marie1 #ee ,cyanic acid1 #g ,cyanuric acid1 #g ,debierne1 #ei ,decipium1 #dj ,delafontaine1 #di ,demaray1 #cj ,desch1 #aea ,deville1 #ahd ,dewar1 #ga1 #if1 #abg ,dexter1 #aeg ,didymium1 #dj ,digitalis1 #aj ,disintegration theory1 #ed ,dixon1 #ahd ,dobbie1 #aea ,doebner1 #acd ,dumas1 ,jean ,b4 ,a41 #h1 #i1 #cj1 #ca1 #fc1 #ge1 #ajb1 #acj ,duppa1 #adh ,dysprosium1 #ch ,edestin1 #afi ,electrolysis1 #agi ,elements1 nomenclature of1 #bg ,emanation from ,radium1 #eh ,emanium1 #fj ,enantiomorphism1 #adj ,enzymes1 #add ,ether1 discovery of its constitution1 #ab1 #ag ,etherin theory1 #aj ,europium1 #ci ,favre1 #ahc ,fenton's reagent1 #aed ,findlay1 #aea ,fischer1 ,emil1 #aeh1 #afe1 et seq4 ,fittig1 #aec ,fluorine1 #cc1 #cd ,formul1 chemical1 significance of1 #fh ,frankland1 #aad1 #aaf1 #adh ,fuchsine1 #d ,fumaric acid1 #adf ,gadolinium1 #ci ,gallium1 #cf1 #ajg ,gases1 kinetic theory of1 #hc law of diffusion of1 #hd1 #hi liquefaction of1 #id molecular theory of1 #gi ,gas-mantles1 #dj ,gay ,lussac1 #fc1 #hj ,geometrical isomerism1 #adf1 #adg ,gerhardt1 #gi1 #aac ,germanium1 #cg1 #ajg ,geuther1 #adh ,gibbs1 ,willard1 #ahd ,giesel1 #fj ,gladstone1 #cj1 #ajb1 #ahd ,gmelin1 #g1 #fc1 #ajb ,gore1 #cc ,graebe1 #afb ,graham1 ,thomas1 #b1 #ad1 #bc1 #bi1 #hc ,grignard's reagent1 #aed ,groth1 #ahd ,guldberg1 #ahc ,guye1 #ha ,haarmann1 #acb ,hmoglobin1 #afh ,hantzsch1 #adg ,hartley1 #aea ,hay1 #aci ,heliotropin1 #acb ,helium1 #dc1 #dg1 #di ,helmholtz1 #aag ,henry's law1 #agc ,hermann1 #bf ,herschel1 #adj ,hess1 #aha1 #ahc ,heumann1 #afc ,heymann1 #afc ,hillebrand1 #dg ,hittorf1 #agi ,hofmann1 ,august ,w41 #c1 #fg1 #acc1 #afa ,holmium1 #ch ,hoogewerff1 #acc ,horbaczewski1 #aeg ,hbner1 #abg ,hydrogenium1 #af ,hyoscyamine1 #ace ,ilmenium1 #bf ,indigo1 #afb1 #afd ,indigo blue1 #afc ,indium1 #cf ,ingenhousz1 #ahe ,ionisation1 #agh ,ionium1 #eh ,ionone1 #acb ,irone1 #acb ,isoborneol1 #aca ,isoconine1 #acd ,isoquinoline1 #acc ,isotonic solutions1 #agh ,jones1 ,h4 ,c41 #ahc ,jones1 ,h4 ,o41 #adg ,kahlenberg1 #ahc ,kammerlingh ,onnes1 #di1 #ig ,kekul1 ,friedrich ,august1 #bc1 #aac1 #aad1 #aba1 #abc1 #abe1 #aec ,kiliani1 #afe ,kipping1 #adg ,kirchhoff1 #ba ,knorr1 #abh1 #aea1 #aei ,koenigs1 #acc ,kohlrausch1 #ahb1 #ahc ,komppa1 #abi ,kopp1 #agb ,krner1 #abg ,krss1 #dj ,krypton1 #dc1 #ej ,krystallin1 #c ,kundt1 #df ,laar1 #adi ,lactic acid1 spatial representation of1 #ada ,ladenburg1 #abg1 #acd1 #adg1 #afa ,lamy1 #ce ,landolt1 #gh1 #ahd ,langlet1 #di ,larmor1 ,sir ,j41 #ahd ,lauder1 #aea ,laurent1 #gi ,le ,bel1 #adc1 #adg1 #adh ,leduc1 #hj1 #ha ,le ,royer1 #h ,leucol1 #acc ,liebermann1 #afb ,liebig1 ,justus von1 #e ,linnemann1 #abg ,liquid diffusion1 #af ,liquids1 molecular volumes of1 #agb ,lossen1 #agb ,lowry1 #aea1 #ahc ,low temperature research1 #ig1 #ci ,lutecium1 #hi ,magenta1 #d ,magnus1 #gi ,maleic acid1 #adf ,mansfield1 #c ,marignac1 #ci1 #ge ,mauve1 #d ,maxwell1 #hc ,medlock1 #c ,mellitic acid1 #g ,membranes1 semi-permeable1 #agf ,mendeleff1 #cj1 #ajb1 #aji1 #ahc ,mercury forms a monatomic gas1 #ga1 #ib ,metaphosphoric acid1 #ad ,meyer ,lothar1 #ajc ,meyer1 ,victor1 #fg1 #adg ,mitscherlich1 #fc1 #ach ,moissan1 #cc ,molecule1 integral1 #fb ,molecules1 their number1 #ic their size1 #ic ,monium1 #dj ,morley1 #hj ,morphine1 #acg ,mosander1 #ci ,multirotation1 #ade ,muscarine1 #afa ,muspratt1 #d ,mutarotation1 #ade ,naphthalene1 #afc ,narcene1 #acf ,narcotine1 #acf ,nasini1 #ahd ,natanson1 #aeg ,neodymium1 #ci ,neon1 #dc1 #ej ,neoytterbium1 #ch ,neurine1 #afa ,newlands1 #ajb ,nicotine1 #ace1 #afb ,nilson1 #cg1 #dj1 #ajg ,nirvanine1 #afj ,nitrogen compounds1 stereo-isomerism of1 #adg ,novocane1 #afj ,odling1 #cj1 #aad ,oil of wintergreen1 #afb ,olszewki1 #if ,opianic acid1 #acf ,organic synthesis1 #aeb ,orthoforms1 #afj ,osmotic pressure1 #agf ,ostwald1 #ahb ,oxyhmoglobin1 #afg ,ozone1 #gj its symbol1 #gj ,papaverine1 #acf ,partial pressure1 law of1 #agc ,pasteur1 #aci ,peachey1 #adh ,pelopium1 #bf ,penny1 #ge ,periodic law1 #aja ,perissads1 #aaf ,perkin1 ,sir ,william1 #c1 #abi1 #aca1 #acb1 #afb ,pettenkofer1 #cj ,pfeffer1 #agf1 #ahe ,phenacetin1 #aei ,phenylglycin1 #afc ,phosphorous oxide1 molecular weight of1 #gc ,phosphorus pentachloride1 #ff ,phosphorus pentafluoride1 #fg ,phthalic acid1 #afc ,pickering1 #ahc ,pictet1 #if1 #ace ,pinene1 #acj1 #aca ,pinner1 #ace ,piperine1 #acd1 #afb ,plattner1 #ce ,playfair1 #bj ,pollucite1 #ce ,pope1 #adg1 #ahd ,posselt1 #ace ,praseodymium1 #ch ,pringsheim1 #ahe ,protamines1 #afh ,proteins1 #afe ,prout's law1 an illusion1 #gf ,ptomaines1 #afa ,pyridine1 #acc ,quinine1 #acg ,quinoline1 #acc ,racemic acid1 #adj ,racemism1 #adc ,radio-thorium1 #fj ,radium1 atomic weight of1 #eh discovery of1 #ee disintegration of1 #eh emanation1 #eh extraction of1 #ee ,radium chloride1 #eg ,ramsay1 ,sir ,william1 #dd1 #dg1 #agc ,raoult1 #gb1 #agh ,rayleigh1 ,lord1 #dd1 #ha ,regnault1 #dc1 #gi1 #hh1 #aeg ,reich1 #cf ,reimann1 #ace ,richards1 ,theodore1 #gg ,richter1 #cf ,rodger1 #ahd ,roosen1 #aeg ,roozeboom1 #ahd ,rosaniline1 #d ,roscoe1 #ba1 #cj1 #aag1 #ahe ,rose1 #bf ,rotatory power1 #add ,rubidium1 #ba1 #cd ,runge1 #acc ,rutherford1 #ei ,salicylic acid1 #afb ,salmine1 #afh ,samarium1 #dj ,sarcine1 #aeg ,sarcolactic acid1 #adj ,saturated solutions1 #agd ,saussure1 #dc ,scandium1 #cg1 #ajg ,scheele1 #cc1 #adj1 #ahe ,schiff1 #agb ,schischkoff1 #ba ,schmidt1 #hc ,schmiedeberg1 #afa ,scott1 #hj ,selmi1 #afa ,senebier1 #ahe ,sesquiterpenes1 #abi ,silbermann1 #ahc ,silicon1 specific heat of1 #ga ,skraup1 #acc ,solute1 #age influence of1 on boiling-point1 #ga on freezing-point1 #ga on vapour pressure1 #gc ,sonstadt1 #aec ,soret1 #gj ,spectrum analysis1 #ba ,stas1 #ge ,steric hindrance1 #aea ,stovane1 #afj ,strecker1 #ajb1 #aeh1 #afa ,sugars1 #afe ,sulphonal1 #aei ,supersaturated solutions1 #agd ,tait1 #gj ,tautomerism1 #adi ,terebenthene1 #acj ,terpenes1 #abi ,tetanine1 #afa ,tetronal1 #aei ,thallium1 #ce ,thebaine1 #acg ,thnard1 #dc ,theobromine1 #aeg ,thioacetic acid1 #abg ,thomsen1 ,julius1 #ea1 #ajh1 #ahc ,thomson1 ,sir ,j4 ,j41 #ahd ,thomson1 ,thomas1 #c ,thorium1 #fj ,thorpe1 #agb1 #ahd ,thulium1 #ch ,thyreoglobulin1 #afi ,tiemann1 #abi1 #acb ,traube1 #agf ,travers1 #ej ,trional1 #aei ,triphenylrosaniline1 #d ,troost1 #ahd ,turner1 ,edward1 #b1 #ad1 #ge ,turpentine1 oil of1 #abi ,tutton1 #ahd ,type theory1 #ah ,typhotoxine1 #afa ,unverdorben1 #c ,uranium1 #ed ,uranium x1 #ed ,urbain1 #dj ,urea1 synthesis of1 #aeg1 #aeh ,uric acid1 #aeh ,valency1 #aab ,vanadium1 #cj ,van der ,waals1 #ie1 #ahd ,van ,dorp1 #acc ,vanillin1 #acb1 #afb ,van 't ,hoff1 #aag1 #ada1 #ade1 #adg1 #agc1 #agg ,veronal1 #aei ,verquin1 #d ,victorium1 #dj 8,vital force0 doctrine1 #afi ,vogel1 #ahe ,von ,miller1 #acd ,waage1 #ahc ,wallach1 #abi ,warburg1 #df ,waterston1 #hc ,weber1 #ga ,weisbach1 #cg ,welsbach1 ,auer von1 #ch ,werner1 #adg ,williamson1 ,alexander ,w41 #ad1 #af1 #aac ,winkler1 #ajg ,wintergreen1 oil of1 #acb ,wislicenus1 #adj ,whler1 ,friedrich1 #e1 #g ,wollaston1 #fc ,wroblewski1 #if ,wurtz1 #aec ,xanthine1 #aeg ,xenon1 #dc1 #ea ,zein1 #afi ,zinin1 #c ,a ,history of the ,sciences ,hitherto there have been few1 if any1 really popular works touching the historical growth of the various great branches of knowledge4 ,the ordinary primer leaves unexploited the deep human interest which belongs to the sciences as contributing to progress and civilization1 and calling into play the faculties of many of the finest minds4 ,something more attractive is wanted4 ,the above need in literature has now been met4 ,each volume in ,the ,history of ,sciences is written by an expert in the given subject1 and by one who has studied the history as well as the conclusions of his own branch of science4 ,the monographs deal briefly with the myths or fallacies which preceded the development of the given science1 or include biographical data of the great discoverers4 ,consideration is given to the social and political conditions and to the attitudes of rulers and statesmen in furthering or in hindering the progress of the given science4 ,the volumes record the important practical application of the given science to the arts and life of civilized mankind1 and also contain a carefully-edited bibliography of the subject4 ,each volume contains from twelve to sixteen carefully-prepared illustrations1 including portraits of celebrated discoverers1 many from originals not hitherto reproduced1 and explanatory views and diagrams4 ,the series as planned should cover in outline the whole sphere of human knowledge4 ,science is to be viewed as a product of human endeavor and mental discipline1 rather than taken in its purely objective reference to facts4 ,the essential purpose has been to present as far as practicable the historical origins of important discoveries1 also to indicate the practical utility of the sciences to human life4 ,g4 ,p4 ,putnam's ,sons ,new ,york ,london ,a ,history of the ,sciences ,each volume is adequately illustrated1 attractively printed1 and substantially bound4 #afmo4 ,each1 net1 #ge cents4 ,by mail1 #he cents4 #ab illustrations ,history of ,astronomy ,by ,george ,forbes1 ,m4,a41 ,f4,r4,s41 ,m4,inst4 ,c4,e4 ,formerly ,professor of ,natural ,philosophy1 ,anderson's ,college1 ,glasgow ,i thank you for the copy of ,forbes's ,history of ,astronomy received4 ,i have run it over1 and think it very good indeed4 ,the plan seems excellent1 and ,i would say the same of your general plan of a series of brief histories of the various branches of science4 ,the time appears to be ripe for such a series1 and if all the contributions are as good as ,prof4 ,forbes's1 the book will deserve a wide circulation1 and will prove very useful to a large class of readers4--,extract from a letter received from ,garrett ,p4 ,serviss1 ,b4 ,s4 ,history of ,chemistry ,by ,sir ,edward ,thorpe1 ,c4,b41 ,,ll4,d41 ,f4,r4,s4 ,author of 8,essays in ,historical ,chemistry10 8,humphry ,davy3 ,poet and ,philosopher10 8,joseph ,priestley10 etc4 #ab illustrations4 ,two vols4 ,vol4 ,i--circa #bjjj ,b4,c4 to #ahej ,a4,d4 ,vol4 ,,ii--#ahej ,a4,d4 to date ,the author traces the evolution of intellectual thought in the progress of chemical investigation1 recognizing the various points of view of the different ages1 giving due credit even to the ancients4 ,it has been necessary to curtail many parts of the ,history1 to lay before the reader in unlimited space enough about each age to illustrate its tone and spirit1 the ideals of the workers1 the gradual addition of new points of view and of new means of investigation4 ,the ,history of ,old ,testament ,criticism ,by ,archibald ,duff ,professor of ,hebrew and ,old ,testament ,theology in the ,united ,college1 ,bradford ,the author sets forth the critical views of the ,hebrews concerning their own literature1 the early ,christian treatment of the ,old ,testament1 criticism by the ,jewish rabbis1 and criticism from ,spinoza to ,astruc1 and from ,astruc until the present4 ,in ,preparation ,the ,history of ,geography4 ,by ,dr4 ,,john ,,scott ,,keltie1 ,f4,r4,g4,s41 ,f4,s4,a41 ,hon4 ,mem4 ,geographical ,societies of ,paris1 ,berlin1 ,rome1 ,brussels1 ,amsterdam1 ,geneva1 etc4 ,the ,history of ,geology4 ,by ,,horace ,b4 ,,woodward1 ,f4,r4,s41 ,f4,g4,s41 ,assistant ,director of ,geological ,survey of ,england and ,wales4 ,the ,history of ,anthropology4 ,by ,a4 ,c4 ,,haddon1 ,m4,a41 ,sc4,d41 ,f4,r4,s41 ,lecturer in ,ethnology1 ,cambridge and ,london4 ,the ,history of ,new ,testament ,criticism4 ,by ,f4 ,c4 ,,conybeare1 ,m4,a41 late ,fellow and ,praelector of ,univ4 ,coll41 ,oxford2 ,fellow of the ,british ,academy2 ,doctor of ,theology1 honoris causa1 of ,giessen2 ,officer d',academie4 ,further volumes are in plan on the following subjects3 ,mathematics and ,mechanics--,molecular ,physics1 ,heat1 ,light1 and ,electricity--,human ,physiology1 ,embryology1 and ,heredity--,acoustics1 ,harmonics1 and the ,physiology of ,hearing1 together with ,optics1 ,chromatics1 and ,physiology of ,seeing--,psychology1 ,analytic1 ,comparative1 and ,experimental--,sociology and ,economics--,ethics--,comparative ,philology--,criticism1 ,historical ,research1 and ,legends--,comparative ,mythology and the ,science of ,religions--,the ,criticism of ,ecclesiastical ,institutions--,culture1 ,moral and ,intellectual1 as ,reflected in ,imaginative ,literature and in the ,fine ,arts--,logic--,philosophy--,education4 ,new ,york ,g4 ,p4 ,putnam's ,sons ,london ,transcriber's ,notes ,punctuation and spelling were made consistent when a predominant preference was found in this book2 otherwise they were not changed4 ,simple typographical errors were corrected2 occasional unbalanced quotation marks retained4 ,ambiguous hyphens at the ends of lines were retained2 occurrences of inconsistent hyphenation have not been changed4 ,index not checked for proper alphabetization or correct page references4 ,the table on page #aje has been split into three parts to keep it narrow4