,,an ,,elementary ,,study ,,of ,,chemistry ,,by ,,william ,mc,p,h,e,r,s,o,n1 ,,ph4,d4 ,,professor ,,of ,,chemistry1 ,,ohio ,,state ,,university ,,and ,,william ,,edwards ,,henderson1 ,,ph4,d4 ,,associate ,,professor ,,of ,,chemistry1 ,,ohio ,,state ,,university ,,revised ,,edition ,,ginn ,,company ,,boston 99 ,,new ,,york 99 ,,chicago 99 ,,london ,,copyright1 #aije1 #aijf1 ,,by ,,william ,,mcpherson ,,and ,,william ,e4 ,,henderson ,,all ,,rights ,,reserved ,the ,athenum ,press ,,ginn ,,company 99 ,,proprietors 99 ,,boston 99 ,u4,s4,a4 ,transcriber's note3 ,for ,text3 ,a word surrounded by a cedilla such as this signifies that the word is bolded in the text4 ,a word surrounded by underscores like this signifies the word is italics in the text4 ,the italic and bold markup for single italized letters 7such as variables in equations7 and foreign abbreviations are deleted for easier reading4 ,for numbers and equations3 ,parentheses have been added to clarify fractions4 ,underscores before bracketed numbers in equations denote a subscript4 ,superscripts are designated with a caret and brackets1 e4g4 #aa4ac is #aa4a to the third power4 ,appendix ,a and ,b have been moved to the end of the book4 ,minor typos have been corrected4 ,,preface ,in offering this book to teachers of elementary chemistry the authors lay no claim to any great originality4 ,it has been their aim to prepare a text-book constructed along lines which have become recognized as best suited to an elementary treatment of the subject4 ,at the same time they have made a consistent effort to make the text clear in outline1 simple in style and language1 conservatively modern in point of view1 and thoroughly teachable4 ,the question as to what shall be included in an elementary text on chemistry is perhaps the most perplexing one which an author must answer4 ,while an enthusiastic chemist with a broad understanding of the science is very apt to go beyond the capacity of the elementary student1 the authors of this text1 after an experience of many years1 cannot help believing that the tendency has been rather in the other direction4 ,in many texts no mention at all is made of fundamental laws of chemical action because their complete presentation is quite beyond the comprehension of the student1 whereas in many cases it is possible to present the essential features of these laws in a way that will be of real assistance in the understanding of the science4 ,for example1 it is a difficult matter to deduce the law of mass action in any very simple way2 yet the elementary student can readily comprehend that reactions are reversible1 and that the point of equilibrium depends upon1 rather simple conditions4 ,the authors believe that it is worth while to present such principles in even an elementary and partial manner because they are of great assistance to the general student1 and because they make a foundation upon which the student who continues his studies to more advanced courses can securely build4 ,the authors have no apologies to make for the extent to which they have made use of the theory of electrolytic dissociation4 ,it is inevitable that in any rapidly developing science there will be differences of opinion in regard to the value of certain theories4 ,there can be no question1 however1 that the outline of the theory of dissociation here presented is in accord with the views of the very great majority of the chemists of the present time4 ,moreover1 its introduction to the extent to which the authors have presented it simplifies rather than increases the difficulties with which the development of the principles of the science is attended4 ,the oxygen standard for atomic weights has been adopted throughout the text4 ,the ,international ,committee1 to which is assigned the duty of yearly reporting a revised list of the atomic weights of the elements1 has adopted this standard for their report1 and there is no longer any authority for the older hydrogen standard4 ,the authors do not believe that the adoption of the oxygen standard introduces any real difficulties in making perfectly clear the methods by which atomic weights are calculated4 ,the problems appended to the various chapters have been chosen with a view not only of fixing the principles developed in the text in the mind of the student1 but also of enabling him to answer such questions as arise in his laboratory work4 ,they are1 therefore1 more or less practical in character4 ,it is not necessary that all of them should be solved1 though with few exceptions the lists are not long4 ,the answers to the questions are not directly given in the text as a rule1 but can be inferred from the statements made4 ,they therefore require independent thought on the part of the student4 ,with very few exceptions only such experiments are included in the text as cannot be easily carried out by the student4 ,it is expected that these will be performed by the teacher at the lecture table4 ,directions for laboratory work by the student are published in a separate volume4 ,while the authors believe that the most important function of the elementary text is to develop the principles of the science1 they recognize the importance of some discussion of the practical application of these principles to our everyday life4 ,considerable space is therefore devoted to this phase of chemistry4 ,the teacher should supplement this discussion whenever possible by having the class visit different factories where chemical processes are employed4 ,although this text is now for the first time offered to teachers of elementary chemistry1 it has nevertheless been used by a number of teachers during the past three years4 ,the present edition has been largely rewritten in the light of the criticisms offered1 and we desire to express our thanks to the many teachers who have helped us in this respect1 especially to ,dr4 ,william ,lloyd ,evans of this laboratory1 a teacher of wide experience1 for his continued interest and helpfulness4 ,we also very cordially solicit correspondence with teachers who may find difficulties or inaccuracies in the text4 ,the authors wish to make acknowledgments for the photographs and engravings of eminent chemists from which the cuts included in the text were taken2 to ,messrs4 ,elliott and ,fry1 ,london1 ,england1 for that of ,ramsay2 to ,the ,macmillan ,company for those of ,davy and ,dalton1 taken from the ,century ,science ,series2 to the ,l4 ,e4 ,knott ,apparatus ,company1 ,boston1 for that of ,bunsen4 ,,the ,,authors ,,ohio ,,state ,,university ,,columbus1 ,,ohio ,,contents ,,chapter ,,page ,i4 ,,introduction #a ,,ii4 ,,oxygen #ac ,,iii4 ,,hydrogen #bh ,,iv4 ,,water ,,and ,,hydrogen ,,dioxide #dj ,v4 ,,the ,,atomic ,,theory #ei ,,vi4 ,,chemical ,,equations ,,and ,,calculations #fh ,,vii4 ,,nitrogen ,,and ,,the ,,rare ,,elements ,,in ,,the ,,atmosphere #gh ,,viii4 ,,the ,,atmosphere #hc ,,ix4 ,,solutions #id ,x4 ,,acids1 ,,bases1 ,,and ,,salts2 ,,neutralization #ajf ,,xi4 ,,valence #aaf ,,xii4 ,,compounds ,,of ,,nitrogen #abb ,,xiii4 ,,reversible ,,reactions ,,and ,,chemical ,,equilibrium #acg ,,xiv4 ,,sulphur ,,and ,,its ,,compounds #adc ,,xv4 ,,periodic ,,law #afe ,,xvi4 ,,the ,,chlorine ,,family #agd ,,xvii4 ,,carbon ,,and ,,some ,,of ,,its ,,simpler ,,compounds #aif ,,xviii4 ,,flames1--,,illuminants #bac ,,xix4 ,,molecular ,,weights1 ,,atomic ,,weights1 ,,formulas #bbc ,,xx4 ,,the ,,phosphorus ,,family #bch ,,xxi4 ,,silicon1 ,,titanium1 ,,boron #beg ,,xxii4 ,,the ,,metals #bfg ,,xxiii4 ,,the ,,alkali ,,metals #bgd ,,xxiv4 ,,the ,,alkaline-,,earth ,,family #cjj ,,xxv4 ,,the ,,magnesium ,,family #caf ,,xxvi4 ,,the ,,aluminium ,,family #cbg ,,xxvii4 ,,the ,,iron ,,family #cch ,,xxviii4 ,,copper1 ,,mercury1 ,,and ,,silver #cef ,,xxix4 ,,tin ,,and ,,lead #cgj ,,xxx4 ,,manganese ,,and ,,chromium #cgi ,,xxxi4 ,,gold ,,and ,,the ,,platinum ,,family #cij ,,xxxii4 ,,some ,,simple ,,organic ,,compounds #cig ,,index #dba ,,appendix ,a ,facing back cover ,,appendix ,b ,inside back cover ,,list ,,of ,,full-,,page ,,illustrations ,,page ,,antoine ,,laurent ,,lavoisier ,frontispiece ,,joseph ,,priestley #ad ,,john ,,dalton #fj ,,william ,,ramsay #hb ,,dmitri ,,ivanovitch ,,mendel,,eff #aff ,,henri ,,moissan #agf ,,sir ,,humphry ,,davy #bgf ,,robert ,,wilhelm ,,bunsen #bih ,,an ,,elementary ,,study ,,of ,,chemistry ,,chapter ,i ,,introduction ,the natural sciences4 ,before we advance very far in the study of nature1 it becomes evident that the one large study must be divided into a number of more limited ones for the convenience of the investigator as well as of the student4 ,these more limited studies are called the natural sciences4 ,since the study of nature is divided in this way for mere convenience1 and not because there is any division in nature itself1 it often happens that the different sciences are very intimately related1 and a thorough knowledge of any one of them involves a considerable acquaintance with several others4 ,thus the botanist must know something about animals as well as about plants2 the student of human physiology must know something about physics as well as about the parts of the body4 ,intimate relation of chemistry and physics4 ,physics and chemistry are two sciences related in this close way1 and it is not easy to make a precise distinction between them4 ,in a general way it may be said that they are both concerned with inanimate matter rather than with living1 and more particularly with the changes which such matter may be made to undergo4 ,these changes must be considered more closely before a definition of the two sciences can be given4 ,physical changes4 ,one class of changes is not accompanied by an alteration in the composition of matter4 ,when a lump of coal is broken the pieces do not differ from the original lump save in size4 ,a rod of iron may be broken into pieces2 it may be magnetized2 it may be heated until it glows2 it may be melted4 ,in none of these changes has the composition of the iron been affected4 ,the pieces of iron1 the magnetized iron1 the glowing iron1 the melted iron1 are just as truly iron as was the original rod4 ,sugar may be dissolved in water1 but neither the sugar nor the water is changed in composition4 ,the resulting liquid has the sweet taste of sugar2 moreover the water may be evaporated by heating and the sugar recovered unchanged4 ,such changes are called physical changes4 ,,definition3 ,physical changes are those which do not involve a change in the composition of the matter4 ,chemical changes4 ,matter may undergo other changes in which its composition is altered4 ,when a lump of coal is burned ashes and invisible gases are formed which are entirely different in composition and properties from the original coal4 ,a rod of iron when exposed to moist air is gradually changed into rust1 which is entirely different from the original iron4 ,when sugar is heated a black substance is formed which is neither sweet nor soluble in water4 ,such changes are evidently quite different from the physical changes just described1 for in them new substances are formed in place of the ones undergoing change4 ,changes of this kind are called chemical changes4 ,,definition3 ,chemical changes are those which involve a change in the composition of the matter4 ,how to distinguish between physical and chemical changes4 ,it is not always easy to tell to which class a given change belongs1 and many cases will require careful thought on the part of the student4 ,the test question in all cases is1 ,has the composition of the substance been changed8 ,usually this can be answered by a study of the properties of the substance before and after the change1 since a change in composition is attended by a change in properties4 ,in some cases1 however1 only a trained observer can decide the question4 ,changes in physical state4 ,one class of physical changes should be noted with especial care1 since it is likely to prove misleading4 ,it is a familiar fact that ice is changed into water1 and water into steam1 by heating4 ,here we have three different substances1--the solid ice1 the liquid water1 and the gaseous steam1--the properties of which differ widely4 ,the chemist can readily show1 however1 that these three bodies have exactly the same composition1 being composed of the same substances in the same proportion4 ,hence the change from one of these substances into another is a physical change4 ,many other substances may1 under suitable conditions1 be changed from solids into liquids1 or from liquids into gases1 without change in composition4 ,thus butter and wax will melt when heated2 alcohol and gasoline will evaporate when exposed to the air4 ,the three states--solid1 liquid1 and gas--are called the three physical states of matter4 ,physical and chemical properties4 ,many properties of a substance can be noted without causing the substance to undergo chemical change1 and are therefore called its physical properties4 ,among these are its physical state1 color1 odor1 taste1 size1 shape1 weight4 ,other properties are only discovered when the substance undergoes chemical change4 ,these are called its chemical properties4 ,thus we find that coal burns in air1 gunpowder explodes when ignited1 milk sours when exposed to air4 ,definition of physics and chemistry4 ,it is now possible to make a general distinction between physics and chemistry4 ,,definition3 ,physics is the science which deals with those changes in matter which do not involve a change in composition4 ,,definition3 ,chemistry is the science which deals with those changes in matter which do involve a change in composition4 ,two factors in all changes4 ,in all the changes which matter can undergo1 whether physical or chemical1 two factors must be taken into account1 namely1 energy and matter4 ,energy4 ,it is a familiar fact that certain bodies have the power to do work4 ,thus water falling from a height upon a water wheel turns the wheel and in this way does the work of the mills4 ,magnetized iron attracts iron to itself and the motion of the iron as it moves towards the magnet can be made to do work4 ,when coal is burned it causes the engine to move and transports the loaded cars from place to place4 ,when a body has this power to do work it is said to possess energy4 ,law of conservation of energy4 ,careful experiments have shown that when one body parts with its energy the energy is not destroyed but is transferred to another body or system of bodies4 ,just as energy cannot be destroyed1 neither can it be created4 ,if one body gains a certain amount of energy1 some other body has lost an equivalent amount4 ,these facts are summed up in the law of conservation of energy which may be stated thus3 ,while energy can be changed from one form into another1 it cannot be created or destroyed4 ,transformations of energy4 ,although energy can neither be created nor destroyed1 it is evident that it may assume many different forms4 ,thus the falling water may turn the electric generator and produce a current of electricity4 ,the energy lost by the falling water is thus transformed into the energy of the electric current4 ,this in turn may be changed into the energy of motion1 as when the current is used for propelling the cars1 or into the energy of heat and light1 as when it is used for heating and lighting the cars4 ,again1 the energy of coal may be converted into energy of heat and subsequently of motion1 as when it is used as a fuel in steam engines4 ,since the energy possessed by coal only becomes available when the coal is made to undergo a chemical change1 it is sometimes called chemical energy4 ,it is this form of energy in which we are especially interested in the study of chemistry4 ,matter4 ,matter may be defined as that which occupies space and possesses weight4 ,like energy1 matter may be changed oftentimes from one form into another2 and since in these transformations all the other physical properties of a substance save weight are likely to change1 the inquiry arises1 ,does the weight also change8 ,much careful experimenting has shown that it does not4 ,the weight of the products formed in any change in matter always equals the weight of the substances undergoing change4 ,law of conservation of matter4 ,the important truth just stated is frequently referred to as the law of conservation of matter1 and this law may be briefly stated thus3 ,matter can neither be created nor destroyed1 though it can be changed from one form into another4 ,classification of matter4 ,at first sight there appears to be no limit to the varieties of matter of which the world is made4 ,for convenience in study we may classify all these varieties under three heads1 namely1 mechanical mixtures1 chemical compounds1 and elements4 ,illustration3 ,fig4 #a ,mechanical mixtures4 ,if equal bulks of common salt and iron filings are thoroughly mixed together1 a product is obtained which1 judging by its appearance1 is a new substance4 ,if it is examined more closely1 however1 it will be seen to be merely a mixture of the salt and iron1 each of which substances retains its own peculiar properties4 ,the mixture tastes just like salt2 the iron particles can be seen and their gritty character detected4 ,a magnet rubbed in the mixture draws out the iron just as if the salt were not there4 ,on the other hand1 the salt can be separated from the iron quite easily4 ,thus1 if several grams of the mixture are placed in a test tube1 and the tube half filled with water and thoroughly shaken1 the salt dissolves in the water4 ,the iron particles can then be filtered from the liquid by pouring the entire mixture upon a piece of filter paper folded so as to fit into the interior of a funnel 7,fig4 #a74 ,the paper retains the solid but allows the clear liquid1 known as the filtrate1 to drain through4 ,the iron particles left upon the filter paper will be found to be identical with the original iron4 ,the salt can be recovered from the filtrate by evaporation of the water4 ,to accomplish this the filtrate is poured into a small evaporating dish and gently heated 7,fig4 #b7 until the water has disappeared1 or evaporated4 ,the solid left in the dish is identical in every way with the original salt4 ,both the iron and the salt have thus been recovered in their original condition4 ,it is evident that no new substance has been formed by rubbing the salt and iron together4 ,the product is called a mechanical mixture4 ,such mixtures are very common in nature1 almost all minerals1 sands1 and soils being examples of this class of substances4 ,it is at once apparent that there is no law regulating the composition of a mechanical mixture1 and no two mixtures are likely to have exactly the same composition4 ,the ingredients of a mechanical mixture can usually be separated by mechanical means1 such as sifting1 sorting1 magnetic attraction1 or by dissolving one constituent and leaving the other unchanged4 ,illustration3 ,fig4 #b ,,definition3 ,a mechanical mixture is one in which the constituents retain their original properties1 no chemical action having taken place when they were brought together4 ,chemical compounds4 ,if iron filings and powdered sulphur are thoroughly ground together in a mortar1 a yellowish-green substance results4 ,it might easily be taken to be a new body2 but as in the case of the iron and salt1 the ingredients can readily be separated4 ,a magnet draws out the iron4 ,water does not dissolve the sulphur1 but other liquids do1 as1 for example1 the liquid called carbon disulphide4 ,when the mixture is treated with carbon disulphide the iron is left unchanged1 and the sulphur can be obtained again1 after filtering off the iron1 by evaporating the liquid4 ,the substance is1 therefore1 a mechanical mixture4 ,if now a new portion of the mixture is placed in a dry test tube and carefully heated in the flame of a ,bunsen burner1 as shown in ,fig4 #c1 a striking change takes place4 ,the mixture begins to glow at some point1 the glow rapidly extending throughout the whole mass4 ,if the test tube is now broken and the product examined1 it will be found to be a hard1 black1 brittle substance1 in no way recalling the iron or the sulphur4 ,the magnet no longer attracts it2 carbon disulphide will not dissolve sulphur from it4 ,it is a new substance with new properties1 resulting from the chemical union of iron and sulphur1 and is called iron sulphide4 ,such substances are called chemical compounds1 and differ from mechanical mixtures in that the substances producing them lose their own characteristic properties4 ,we shall see later that the two also differ in that the composition of a chemical compound never varies4 ,illustration3 ,fig4 #c ,,definition3 ,a chemical compound is a substance the constituents of which have lost their own characteristic properties1 and which cannot be separated save by a chemical change4 ,elements4 ,it has been seen that iron sulphide is composed of two entirely different substances1--iron and sulphur4 ,the question arises1 ,do these substances in turn contain other substances1 that is1 are they also chemical compounds8 ,chemists have tried in a great many ways to decompose them1 but all their efforts have failed4 ,substances which have resisted all efforts to decompose them into other substances are called elements4 ,it is not always easy to prove that a given substance is really an element4 ,some way as yet untried may be successful in decomposing it into other simpler forms of matter1 and the supposed element will then prove to be a compound4 ,water1 lime1 and many other familiar compounds were at one time thought to be elements4 ,,definition3 ,an element is a substance which cannot be separated into simpler substances by any known means4 ,kinds of matter4 ,while matter has been grouped in three classes for the purpose of study1 it will be apparent that there are really but two distinct kinds of matter1 namely1 compounds and elements4 ,a mechanical mixture is not a third distinct kind of matter1 but is made up of varying quantities of either compounds or elements or both4 ,alchemy4 ,in olden times it was thought that some way could be found to change one element into another1 and a great many efforts were made to accomplish this transformation4 ,most of these efforts were directed toward changing the commoner metals into gold1 and many fanciful ways for doing this were described4 ,the chemists of that time were called alchemists1 and the art which they practiced was called alchemy4 ,the alchemists gradually became convinced that the only way common metals could be changed into gold was by the wonderful power of a magic substance which they called the philosopher's stone1 which would accomplish this transformation by its mere touch and would in addition give perpetual youth to its fortunate possessor4 ,no one has ever found such a stone1 and no one has succeeded in changing one metal into another4 ,number of elements4 ,the number of substances now considered to be elements is not large--about eighty in all4 ,many of these are rare1 and very few of them make any large fraction of the materials in the earth's crust4 ,clarke gives the following estimate of the composition of the earth's crust3 ,oxygen #dg4j ,calcium #c4e ,silicon #bg4i ,magnesium #b4e ,aluminium #h4a ,sodium #b4g ,iron #d4g ,potassium #b4d ,other elements #a4b ,a complete list of the elements is given in the ,appendix4 ,in this list the more common of the elements are marked with an asterisk4 ,it is not necessary to study more than a third of the total number of elements to gain a very good knowledge of chemistry4 ,physical state of the elements4 ,about ten of the elements are gases at ordinary temperatures4 ,two--mercury and bromine--are liquids4 ,the others are all solids1 though their melting points vary through wide limits1 from csium which melts at #bf to elements which do not melt save in the intense heat of the electric furnace4 ,occurrence of the elements4 ,comparatively few of the elements occur as uncombined substances in nature1 most of them being found in the form of chemical compounds4 ,when an element does occur by itself1 as is the case with gold1 we say that it occurs in the free state or native2 when it is combined with other substances in the form of compounds1 we say that it occurs in the combined state1 or in combination4 ,in the latter case there is usually little about the compound to suggest that the element is present in it2 for we have seen that elements lose their own peculiar properties when they enter into combination with other elements4 ,it would never be suspected1 for example1 that the reddish1 earthy-looking iron ore contains iron4 ,names of elements4 ,the names given to the elements have been selected in a great many different ways4 7#a7 ,some names are very old and their original meaning is obscure4 ,such names are iron1 gold1 and copper4 7#b7 ,many names indicate some striking physical property of the element4 ,the name bromine1 for example1 is derived from a ,greek word meaning a stench1 referring to the extremely unpleasant odor of the substance4 ,the name iodine comes from a word meaning violet1 alluding to the beautiful color of iodine vapor4 7#c7 ,some names indicate prominent chemical properties of the elements4 ,thus1 nitrogen means the producer of niter1 nitrogen being a constituent of niter or saltpeter4 ,hydrogen means water former1 signifying its presence in water4 ,argon means lazy or inert1 the element being so named because of its inactivity4 7#d7 ,other elements are named from countries or localities1 as germanium and scandium4 ,symbols4 ,in indicating the elements found in compounds it is inconvenient to use such long names1 and hence chemists have adopted a system of abbreviations4 ,these abbreviations are known as symbols1 each element having a distinctive symbol4 7#a7 ,sometimes the initial letter of the name will suffice to indicate the element4 ,thus ,i stands for iodine1 ,c for carbon4 7#b7 ,usually it is necessary to add some other characteristic letter to the symbol1 since several names may begin with the same letter4 ,thus ,c stands for carbon1 ,cl for chlorine1 ,cd for cadmium1 ,ce for cerium1 ,cb for columbium4 7#c7 ,sometimes the symbol is an abbreviation of the old ,latin name4 ,in this way ,fe 7ferrum7 indicates iron1 ,cu 7cuprum71 copper1 ,au 7aurum71 gold4 ,the symbols are included in the list of elements given in the ,appendix4 ,they will become familiar through constant use4 ,chemical affinity the cause of chemical combination4 ,the agency which causes substances to combine and which holds them together when combined is called chemical affinity4 ,the experiments described in this chapter1 however1 show that heat is often necessary to bring about chemical action4 ,the distinction between the cause producing chemical action and the circumstances favoring it must be clearly made4 ,chemical affinity is always the cause of chemical union4 ,many agencies may make it possible for chemical affinity to act by overcoming circumstances which stand in its way4 ,among these agencies are heat1 light1 and electricity4 ,as a rule1 solution also promotes action between two substances4 ,sometimes these agencies may overcome chemical attraction and so occasion the decomposition of a compound4 ,,exercises #a4 ,to what class of changes do the following belong8 7a7 ,the melting of ice2 7b7 the souring of milk2 7c7 the burning of a candle2 7d7 the explosion of gunpowder2 7e7 the corrosion of metals4 ,what test question must be applied in each of the above cases8 #b4 ,give two additional examples 7a7 of chemical changes2 7b7 of physical changes4 #c4 ,is a chemical change always accompanied by a physical change8 ,is a physical change always accompanied by a chemical change8 #d4 ,give two or more characteristics of a chemical change4 #e4 7a7 ,when a given weight of water freezes1 does it absorb or evolve heat8 7b7 ,when the resulting ice melts1 is the total heat change the same or different from that of freezing8 #f4 ,give three examples of each of the following3 7a7 mechanical mixtures2 7b7 chemical compounds2 7c7 elements4 #g4 ,give the derivation of the names of the following elements3 thorium1 gallium1 selenium1 uranium4 7,consult dictionary47 #h4 ,give examples of chemical changes which are produced through the agency of heat2 of light2 of electricity4 ,,chapter ,,ii ,,oxygen ,history4 ,the discovery of oxygen is generally attributed to the ,english chemist ,priestley1 who in #aggd obtained the element by heating a compound of mercury and oxygen1 known as red oxide of mercury4 ,it is probable1 however1 that the ,swedish chemist ,scheele had previously obtained it1 although an account of his experiments was not published until #aggg4 ,the name oxygen signifies acid former4 ,it was given to the element by the ,french chemist ,lavoisier1 since he believed that all acids owe their characteristic properties to the presence of oxygen4 ,this view we now know to be incorrect4 ,occurrence4 ,oxygen is by far the most abundant of all the elements4 ,it occurs both in the free and in the combined state4 ,in the free state it occurs in the air1 #ajj volumes of dry air containing about #ba volumes of oxygen4 ,in the combined state it forms eight ninths of water and nearly one half of the rocks composing the earth's crust4 ,it is also an important constituent of the compounds which compose plant and animal tissues2 for example1 about #ff by weight of the human body is oxygen4 ,preparation4 ,although oxygen occurs in the free state in the atmosphere1 its separation from the nitrogen and other gases with which it is mixed is such a difficult matter that in the laboratory it has been found more convenient to prepare it from its compounds4 ,the most important of the laboratory methods are the following3 #a4 ,preparation from water4 ,water is a compound1 consisting of #aa4ah hydrogen and #hh4hb oxygen4 ,it is easily separated into these constituents by passing an electric current through it under suitable conditions4 ,the process will be described in the chapter on water4 ,while this method of preparation is a simple one1 it is not economical4 #b4 ,preparation from mercuric oxide4 ,this method is of interest1 since it is the one which led to the discovery of oxygen4 ,the oxide1 which consists of #g4d oxygen and #ib4f mercury1 is placed in a small1 glass test tube and heated4 ,the compound is in this way decomposed into mercury which collects on the sides of the glass tube1 forming a silvery mirror1 and oxygen which1 being a gas1 escapes from the tube4 ,the presence of the oxygen is shown by lighting the end of a splint1 extinguishing the flame and bringing the glowing coal into the mouth of the tube4 ,the oxygen causes the glowing coal to burst into a flame4 ,in a similar way oxygen may be obtained from its compounds with some of the other elements4 ,thus manganese dioxide1 a black compound of manganese and oxygen1 when heated to about #gjj1 loses one third of its oxygen1 while barium dioxide1 when heated1 loses one half of its oxygen4 #c4 ,preparation from potassium chlorate 7usual laboratory method74 ,potassium chlorate is a white solid which consists of #ca4i potassium1 #bh4i chlorine1 and #ci4b oxygen4 ,when heated it undergoes a series of changes in which all the oxygen is finally set free1 leaving a compound of potassium and chlorine called potassium chloride4 ,the change may be represented as follows3 _/potassium 7potassium _/ potassium 7potassium chlorine oxygen chlorate7 chlorine _/ chloride7 oxygen _/ ,illustration3 ,,joseph ,,priestley 7,english7 7#agcc-ahjd7 ,school-teacher1 theologian1 philosopher1 scientist2 friend of ,benjamin ,franklin2 discoverer of oxygen2 defender of the phlogiston theory2 the first to use mercury in a pneumatic trough1 by which means he first isolated in gaseous form hydrochloric acid1 sulphur dioxide1 and ammonia ,the evolution of the oxygen begins at about #djj4 ,it has been found1 however1 that if the potassium chlorate is mixed with about one fourth its weight of manganese dioxide1 the oxygen is given off at a much lower temperature4 ,just how the manganese dioxide brings about this result is not definitely known4 ,the amount of oxygen obtained from a given weight of potassium chlorate is exactly the same whether the manganese dioxide is present or not4 ,so far as can be detected the manganese dioxide undergoes no change4 ,illustration3 ,fig4 #d ,directions for preparing oxygen4 ,the manner of preparing oxygen from potassium chlorate is illustrated in the accompanying diagram 7,fig4 #d74 ,a mixture consisting of one part of manganese dioxide and four parts of potassium chlorate is placed in the flask ,a and gently heated4 ,the oxygen is evolved and escapes through the tube ,b4 ,it is collected by bringing over the end of the tube the mouth of a bottle completely filled with water and inverted in a vessel of water1 as shown in the figure4 ,the gas rises in the bottle and displaces the water4 ,in the preparation of large quantities of oxygen1 a copper retort 7,fig4 #e7 is often substituted for the glass flask4 ,illustration3 ,fig4 #e ,in the preparation of oxygen from potassium chlorate and manganese dioxide1 the materials used must be pure1 otherwise a violent explosion may occur4 ,the purity of the materials is tested by heating a small amount of the mixture in a test tube4 ,the collection of gases4 ,the method used for collecting oxygen illustrates the general method used for collecting such gases as are insoluble in water or nearly so4 ,the vessel ,c 7,fig4 #d71 containing the water in which the bottles are inverted1 is called a pneumatic trough4 ,commercial methods of preparation4 ,oxygen can now be purchased stored under great pressure in strong steel cylinders 7,fig4 #f74 ,it is prepared either by heating a mixture of potassium chlorate and manganese dioxide1 or by separating it from the nitrogen and other gases with which it is mixed in the atmosphere4 ,the methods employed for effecting this separation will be described in subsequent chapters4 ,illustration3 ,fig4 #f ,physical properties4 ,oxygen is a colorless1 odorless1 tasteless gas1 slightly heavier than air4 ,one liter of it1 measured at a temperature of #j and under a pressure of one atmosphere1 weighs #a4dbhe g41 while under similar conditions one liter of air weighs #a4bibc g4 ,it is but slightly soluble in water4 ,oxygen1 like other gases1 may be liquefied by applying very great pressure to the highly cooled gas4 ,when the pressure is removed the liquid oxygen passes again into the gaseous state1 since its boiling point under ordinary atmospheric pressure is -#ahb4e4 ,chemical properties4 ,at ordinary temperatures oxygen is not very active chemically4 ,most substances are either not at all affected by it1 or the action is so slow as to escape notice4 ,at higher temperatures1 however1 it is very active1 and unites directly with most of the elements4 ,this activity may be shown by heating various substances until just ignited and then bringing them into vessels of the gas1 when they will burn with great brilliancy4 ,thus a glowing splint introduced into a jar of oxygen bursts into flame4 ,sulphur burns in the air with a very weak flame and feeble light2 in oxygen1 however1 the flame is increased in size and brightness4 ,substances which readily burn in air1 such as phosphorus1 burn in oxygen with dazzling brilliancy4 ,even substances which burn in air with great difficulty1 such as iron1 readily burn in oxygen4 ,the burning of a substance in oxygen is due to the rapid combination of the substance or of the elements composing it with the oxygen4 ,thus1 when sulphur burns both the oxygen and sulphur disappear as such and there is formed a compound of the two1 which is an invisible gas1 having the characteristic odor of burning sulphur4 ,similarly1 phosphorus on burning forms a white solid compound of phosphorus and oxygen1 while iron forms a reddish-black compound of iron and oxygen4 ,oxidation4 ,the term oxidation is applied to the chemical change which takes place when a substance1 or one of its constituent parts1 combines with oxygen4 ,this process may take place rapidly1 as in the burning of phosphorus1 or slowly1 as in the oxidation 7or rusting7 of iron when exposed to the air4 ,it is always accompanied by the liberation of heat4 ,the amount of heat liberated by the oxidation of a definite weight of any given substance is always the same1 being entirely independent of the rapidity of the process4 ,if the oxidation takes place slowly1 the heat is generated so slowly that it is difficult to detect it4 ,if the oxidation takes place rapidly1 however1 the heat is generated in such a short interval of time that the substance may become white hot or burst into a flame4 ,combustion2 kindling temperature4 ,when oxidation takes place so rapidly that the heat generated is sufficient to cause the substance to glow or burst into a flame the process is called combustion4 ,in order that any substance may undergo combustion1 it is necessary that it should be heated to a certain temperature1 known as the kindling temperature4 ,this temperature varies widely for different bodies1 but is always definite for the same body4 ,thus the kindling temperature of phosphorus is far lower than that of iron1 but is definite for each4 ,when any portion of a substance is heated until it begins to burn the combustion will continue without the further application of heat1 provided the heat generated by the process is sufficient to bring other parts of the substance to the kindling temperature4 ,on the other hand1 if the heat generated is not sufficient to maintain the kindling temperature1 combustion ceases4 ,oxides4 ,the compounds formed by the oxidation of any element are called oxides4 ,thus in the combustion of sulphur1 phosphorus1 and iron1 the compounds formed are called respectively oxide of sulphur1 oxide of phosphorus1 and oxide of iron4 ,in general1 then1 an oxide is a compound of oxygen with another element4 ,a great many substances of this class are known2 in fact1 the oxides of all the common elements have been prepared1 with the exception of those of fluorine and bromine4 ,some of these are familiar compounds4 ,water1 for example1 is an oxide of hydrogen1 and lime an oxide of the metal calcium4 ,products of combustion4 ,the particular oxides formed by the combustion of any substance are called products of combustion of that substance4 ,thus oxide of sulphur is the product of the combustion of sulphur2 oxide of iron is the product of the combustion of iron4 ,it is evident that the products of the combustion of any substance must weigh more than the original substance1 the increase in weight corresponding to the amount of oxygen taken up in the act of combustion4 ,for example1 when iron burns the oxide of iron formed weighs more than the original iron4 ,in some cases the products of combustion are invisible gases1 so that the substance undergoing combustion is apparently destroyed4 ,thus1 when a candle burns it is consumed1 and so far as the eye can judge nothing is formed during combustion4 ,that invisible gases are formed1 however1 and that the weight of these is greater than the weight of the candle may be shown by the following experiment4 ,illustration3 ,fig4 #g ,a lamp chimney is filled with sticks of the compound known as sodium hydroxide 7caustic soda71 and suspended from the beam of the balance1 as shown in ,fig4 #g4 ,a piece of candle is placed on the balance pan so that the wick comes just below the chimney1 and the balance is brought to a level by adding weights to the other pan4 ,the candle is then lighted4 ,the products formed pass up through the chimney and are absorbed by the sodium hydroxide4 ,although the candle burns away1 the pan upon which it rests slowly sinks1 showing that the combustion is attended by an increase in weight4 ,combustion in air and in oxygen4 ,combustion in air and in oxygen differs only in rapidity1 the products formed being exactly the same4 ,that the process should take place less rapidly in the former is readily understood1 for the air is only about one fifth oxygen1 the remaining four fifths being inert gases4 ,not only is less oxygen available1 but much of the heat is absorbed in raising the temperature of the inert gases surrounding the substance undergoing combustion1 and the temperature reached in the combustion is therefore less4 ,phlogiston theory of combustion4 ,the ,french chemist ,lavoisier 7#agdc-agid71 who gave to oxygen its name was the first to show that combustion is due to union with oxygen4 ,previous to his time combustion was supposed to be due to the presence of a substance or principle called phlogiston4 ,one substance was thought to be more combustible than another because it contained more phlogiston4 ,coal1 for example1 was thought to be very rich in phlogiston4 ,the ashes left after combustion would not burn because all the phlogiston had escaped4 ,if the phlogiston could be restored in any way1 the substance would then become combustible again4 ,although this view seems absurd to us in the light of our present knowledge1 it formerly had general acceptance4 ,the discovery of oxygen led ,lavoisier to investigate the subject1 and through his experiments he arrived at the true explanation of combustion4 ,the discovery of oxygen together with the part it plays in combustion is generally regarded as the most important discovery in the history of chemistry4 ,it marked the dawn of a new period in the growth of the science4 ,combustion in the broad sense4 ,according to the definition given above1 the presence of oxygen is necessary for combustion4 ,the term is sometimes used1 however1 in a broader sense to designate any chemical change attended by the evolution of heat and light4 ,thus iron and sulphur1 or hydrogen and chlorine under certain conditions1 will combine so rapidly that light is evolved1 and the action is called a combustion4 ,whenever combustion takes place in the air1 however1 the process is one of oxidation4 ,spontaneous combustion4 ,the temperature reached in a given chemical action1 such as oxidation1 depends upon the rate at which the reaction takes place4 ,this rate is usually increased by raising the temperature of the substances taking part in the action4 ,when a slow oxidation takes place under such conditions that the heat generated is not lost by being conducted away1 the temperature of the substance undergoing oxidation is raised1 and this in turn hastens the rate of oxidation4 ,the rise in temperature may continue in this way until the kindling temperature of the substance is reached1 when combustion begins4 ,combustion occurring in this way is called spontaneous combustion4 ,certain oils1 such as the linseed oil used in paints1 slowly undergo oxidation at ordinary temperatures1 and not infrequently the origin of fires has been traced to the spontaneous combustion of oily rags4 ,the spontaneous combustion of hay has been known to set barns on fire4 ,heaps of coal have been found to be on fire when spontaneous combustion offered the only possible explanation4 ,importance of oxygen4 #a4 ,oxygen is essential to life4 ,among living organisms only certain minute forms of plant life can exist without it4 ,in the process of respiration the air is taken into the lungs where a certain amount of oxygen is absorbed by the blood4 ,it is then carried to all parts of the body1 oxidizing the worn-out tissues and changing them into substances which may readily be eliminated from the body4 ,the heat generated by this oxidation is the source of the heat of the body4 ,the small amount of oxygen which water dissolves from the air supports all the varied forms of aquatic animals4 #b4 ,oxygen is also essential to decay4 ,the process of decay is really a kind of oxidation1 but it will only take place in the presence of certain minute forms of life known as bacteria4 ,just how these assist in the oxidation is not known4 ,by this process the dead products of animal and vegetable life which collect on the surface of the earth are slowly oxidized and so converted into harmless substances4 ,in this way oxygen acts as a great purifying agent4 #c4 ,oxygen is also used in the treatment of certain diseases in which the patient is unable to inhale sufficient air to supply the necessary amount of oxygen4 ,,ozone ,preparation4 ,when electric sparks are passed through oxygen or air a small percentage of the oxygen is converted into a substance called ozone1 which differs greatly from oxygen in its properties4 ,the same change can also be brought about by certain chemical processes4 ,thus1 if some pieces of phosphorus are placed in a bottle and partially covered with water1 the presence of ozone may soon be detected in the air contained in the bottle4 ,the conversion of oxygen into ozone is attended by a change in volume1 #c volumes of oxygen forming #b volumes of ozone4 ,if the resulting ozone is heated to about #cjj1 the reverse change takes place1 the #b volumes of ozone being changed back into #c volumes of oxygen4 ,it is possible that traces of ozone exist in the atmosphere1 although its presence there has not been definitely proved1 the tests formerly used for its detection having been shown to be unreliable4 ,properties4 ,as commonly prepared1 ozone is mixed with a large excess of oxygen4 ,it is possible1 however1 to separate the ozone and thus obtain it in pure form4 ,the gas so obtained has the characteristic odor noticed about electrical machines when in operation4 ,by subjecting it to great pressure and a low temperature1 the gas condenses to a bluish liquid1 boiling at -#aai4 ,when unmixed with other gases ozone is very explosive1 changing back into oxygen with the liberation of heat4 ,its chemical properties are similar to those of oxygen except that it is far more active4 ,air or oxygen containing a small amount of ozone is now used in place of oxygen in certain manufacturing processes4 ,the difference between oxygen and ozone4 ,experiments show that in changing oxygen into ozone no other kind of matter is either added to the oxygen or withdrawn from it4 ,the question arises then1 ,how can we account for the difference in their properties8 ,it must be remembered that in all changes we have to take into account energy as well as matter4 ,by changing the amount of energy in a substance we change its properties4 ,that oxygen and ozone contain different amounts of energy may be shown in a number of ways2 for example1 by the fact that the conversion of ozone into oxygen is attended by the liberation of heat4 ,the passage of the electric sparks through oxygen has in some way changed the energy content of the element and thus it has acquired new properties4 ,oxygen and ozone must1 therefore1 be regarded as identical so far as the kind of matter of which they are composed is concerned4 ,their different properties are due to their different energy contents4 ,allotropic states or forms of matter4 ,other elements besides oxygen may exist in more than one form4 ,these different forms of the same element are called allotropic states or forms of the element4 ,these forms differ not only in physical properties but also in their energy contents4 ,elements often exist in a variety of forms which look quite different4 ,these differences may be due to accidental causes1 such as the size or shape of the particles or the way in which the element was prepared4 ,only such forms1 however1 as have different energy contents are properly called allotropic forms4 ,,measurement ,,of ,,gas ,,volumes ,standard conditions4 ,it is a well-known fact that the volume occupied by a definite weight of any gas can be altered by changing the temperature of the gas or the pressure to which it is subjected4 ,in measuring the volume of gases it is therefore necessary1 for the sake of accuracy1 to adopt some standard conditions of temperature and pressure4 ,the conditions agreed upon are 7#a7 a temperature of #j1 and 7#b7 a pressure equal to the average pressure exerted by the atmosphere at the sea level1 that is1 #ajcc4c g4 per square centimeter4 ,these conditions of temperature and pressure are known as the standard conditions1 and when the volume of a gas is given it is understood that the measurement was made under these conditions1 unless it is expressly stated otherwise4 ,for example1 the weight of a liter of oxygen has been given as #a4dbhe g4 ,this means that one liter of oxygen1 measured at a temperature of #j and under a pressure of #ajcc4c g4 per square centimeter1 weighs #a4dbhe g4 ,the conditions which prevail in the laboratory are never the standard conditions4 ,it becomes necessary1 therefore1 to find a way to calculate the volume which a gas will occupy under standard conditions from the volume which it occupies under any other conditions4 ,this may be done in accordance with the following laws4 ,law of ,charles4 ,this law expresses the effect which a change in the temperature of a gas has upon its volume4 ,it may be stated as follows3 ,for every degree the temperature of a gas rises above zero the volume of the gas is increased by #a_/bgc of the volume which it occupies at zero2 likewise for every degree the temperature of the gas falls below zero the volume of the gas is decreased by #a_/bgc of the volume which it occupies at zero1 provided in both cases that the pressure to which the gas is subjected remains constant4 ,if ,v represents the volume of gas at #j1 then the volume at #a will be ,v #a_/bgc ,v2 at #b it will be ,v #b_/bgc ,v2 or1 in general1 the volume v1 at the temperature t1 will be expressed by the formula 7#a7 v ,v t_/#bgc ,v1 or 7#b7 v ,v7#a 7t_/#bgc774 ,since #a_/bgc #j4jjcff1 the formula may be written 7#c7 v ,v7#a #j4jjcfft74 ,since the value of ,v 7volume under standard conditions7 is the one usually sought1 it is convenient to transpose the equation to the following form3 7#d7 ,v v_/7#a #j4jjcfft74 ,the following problem will serve as an illustration of the application of this equation4 ,the volume of a gas at #bj is #gej cc42 find the volume it will occupy at #j1 the pressure remaining constant4 ,in this case1 v #gej cc4 and t #bj4 ,by substituting these values1 equation 7#d7 becomes ,v #gej_/7a #j4jjcff #bj7 #fih4i cc4 ,law of ,boyle4 ,this law expresses the relation between the volume occupied by a gas and the pressure to which it is subjected4 ,it may be stated as follows3 ,the volume of a gas is inversely proportional to the pressure under which it is measured1 provided the temperature of the gas remains constant4 ,if ,v represents the volume when subjected to a pressure ,p and v represents its volume when the pressure is changed to p1 then1 in accordance with the above law1 ,v 3 v 33 p 3 ,p1 or ,,vp vp4 ,in other words1 for a given weight of a gas the product of the numbers representing its volume and the pressure to which it is subjected is a constant4 ,since the pressure of the atmosphere at any point is indicated by the barometric reading1 it is convenient in the solution of the problems to substitute the latter for the pressure measured in grams per square centimeter4 ,the average reading of the barometer at the sea level is #gfj mm41 which corresponds to a pressure of #ajcc4c g4 per square centimeter4 ,the following problem will serve as an illustration of the application of ,boyle's law4 ,a gas occupies a volume of #ejj cc4 in a laboratory where the barometric reading is #gdj mm4 ,what volume would it occupy if the atmospheric pressure changed so that the reading became #gej mm48 ,substituting the values in the equation ,,vp vp1 we have #ejj #gdj v #gej1 or v #dic4c cc4 ,variations in the volume of a gas due to changes both in temperature and pressure4 ,inasmuch as corrections must be made as a rule for both temperature and pressure1 it is convenient to combine the equations given above for the corrections for each1 so that the two corrections may be made in one operation4 ,the following equation is thus obtained3 7#e7 ,vs vp_/7#gfj7a #j4jjcfft771 in which ,vs represents the volume of a gas under standard conditions and v1 p1 and t the volume1 pressure1 and temperature respectively at which the gas was actually measured4 ,the following problem will serve to illustrate the application of this equation4 ,a gas having a temperature of #bj occupies a volume of #ejj cc4 when subjected to a pressure indicated by a barometric reading of #gdj mm4 ,what volume would this gas occupy under standard conditions8 ,in this problem v #ejj1 p #gdj1 and t #bj4 ,substituting these values in the above equation1 we get ,vs 7#ejj #gdj7_/7gfj 7#a #j4jjcff #bj77 #dec4f cc4 ,illustration3 ,fig4 #h ,variations in the volume of a gas due to the pressure of aqueous vapor4 ,in many cases gases are collected over water1 as explained under the preparation of oxygen4 ,in such cases there is present in the gas a certain amount of water vapor4 ,this vapor exerts a definite pressure1 which acts in opposition to the atmospheric pressure and which therefore must be subtracted from the latter in determining the effective pressure upon the gas4 ,thus1 suppose we wish to determine the pressure to which the gas in tube ,a 7,fig4 #h7 is subjected4 ,the tube is raised or lowered until the level of the water inside and outside the tube is the same4 ,the atmosphere presses down upon the surface of the water 7as indicated by the arrows71 thus forcing the water upward within the tube with a pressure equal to the atmospheric pressure4 ,the full force of this upward pressure1 however1 is not spent in compressing the gas within the tube1 for since it is collected over water it contains a certain amount of water vapor4 ,this water vapor exerts a pressure 7as indicated by the arrow within the tube7 in opposition to the upward pressure4 ,it is plain1 therefore1 that the effective pressure upon the gas is equal to the atmospheric pressure less the pressure exerted by the aqueous vapor4 ,the pressure exerted by the aqueous vapor increases with the temperature4 ,the figures representing the extent of this pressure 7often called the tension of aqueous vapor7 are given in the ,appendix4 ,they express the pressure or tension in millimeters of mercury1 just as the atmospheric pressure is expressed in millimeters of mercury4 ,representing the pressure of the aqueous vapor by a1 formula 7#e7 becomes 7#f7 ,vs v7p - a7_/7#gfj7a #j4jjcfft774 ,the following problem will serve to illustrate the method of applying the correction for the pressure of the aqueous vapor4 ,the volume of a gas measured over water in a laboratory where the temperature is #bj and the barometric reading is #gdj mm4 is #ejj cc4 ,what volume would this occupy under standard conditions8 ,the pressure exerted by the aqueous vapor at #bj 7see table in ,appendix7 is equal to the pressure exerted by a column of mercury #ag4d mm4 in height4 ,substituting the values of v1 t1 p1 and a in formula 7#f71 we have 7#f7 ,vs #ejj7gdj - #ag4d7_/7gfj7a #j4jjcff #bj77 #ddb4i cc4 ,adjustment of tubes before reading gas volumes4 ,in measuring the volumes of gases collected in graduated tubes or other receivers1 over a liquid as illustrated in ,fig4 #h1 the reading should be taken after raising or lowering the tube containing the gas until the level of the liquid inside and outside the tube is the same2 for it is only under these conditions that the upward pressure within the tube is the same as the atmospheric pressure4 ,,exercises #a4 ,what is the meaning of the following words8 phlogiston1 ozone1 phosphorus4 7,consult dictionary47 #b4 ,can combustion take place without the emission of light8 #c4 ,is the evolution of light always produced by combustion8 #d4 7a7 ,what weight of oxygen can be obtained from #ajj g4 of water8 7b7 ,what volume would this occupy under standard conditions8 #e4 7a7 ,what weight of oxygen can be obtained from #ejj;g4 of mercuric oxide8 7b7 ,what volume would this occupy under standard conditions8 #f4 ,what weight of each of the following compounds is necessary to prepare #ej l4 of oxygen8 7a7 water2 7b7 mercuric oxide2 7c7 potassium chlorate4 #g4 ,reduce the following volumes to #j1 the pressure remaining constant3 7a7 #aej cc4 at #aj2 7b7 #hdj cc4 at #bgc4 #h4 ,a certain volume of gas is measured when the temperature is #bj4 ,at what temperature will its volume be doubled8 #i4 ,reduce the following volumes to standard conditions of pressure1 the temperature remaining constant3 7a7 #bjj cc4 at #gdj mm42 7b7 #ejj l4 at #chj mm4 #aj4 ,what is the weight of #a l4 of oxygen when the pressure is #gej mm4 and the temperature #j8 #aa4 ,reduce the following volumes to standard conditions of temperature and pressure3 7a7 #cdj cc4 at #ab and #gec mm2 7b7 #ejj cc4 at #ae and #gdj mm4 #ab4 ,what weight of potassium chlorate is necessary to prepare #bej l4 of oxygen at #bj and #gej mm48 #ac4 ,assuming the cost of potassium chlorate and mercuric oxide to be respectively #j4ej and #a4ej per kilogram1 calculate the cost of materials necessary for the preparation of #ej l4 of oxygen from each of the above compounds4 #ad4 #ajj g4 of potassium chlorate and #be g4 of manganese dioxide were heated in the preparation of oxygen4 ,what products were left in the flask1 and how much of each was present8 ,,chapter ,,iii ,,hydrogen ,historical4 ,the element hydrogen was first clearly recognized as a distinct substance by the ,english investigator ,cavendish1 who in #agff obtained it in a pure state1 and showed it to be different from the other inflammable airs or gases which had long been known4 ,lavoisier gave it the name hydrogen1 signifying water former1 since it had been found to be a constituent of water4 ,occurrence4 ,in the free state hydrogen is found in the atmosphere1 but only in traces4 ,in the combined state it is widely distributed1 being a constituent of water as well as of all living organisms1 and the products derived from them1 such as starch and sugar4 ,about #aj of the human body is hydrogen4 ,combined with carbon1 it forms the substances which constitute petroleum and natural gas4 ,it is an interesting fact that while hydrogen in the free state occurs only in traces on the earth1 it occurs in enormous quantities in the gaseous matter surrounding the sun and certain other stars4 ,preparation from water4 ,hydrogen can be prepared from water by several methods1 the most important of which are the following4 #a4 ,by the electric current4 ,as has been indicated in the preparation of oxygen1 water is easily separated into its constituents1 hydrogen and oxygen1 by passing an electric current through it under certain conditions4 #b4 ,by the action of certain metals4 ,when brought into contact with certain metals under appropriate conditions1 water gives up a portion or the whole of its hydrogen1 its place being taken by the metal4 ,in the case of a few of the metals this change occurs at ordinary temperatures4 ,thus1 if a bit of sodium is thrown on water1 an action is seen to take place at once1 sufficient heat being generated to melt the sodium1 which runs about on the surface of the water4 ,the change which takes place consists in the displacement of one half of the hydrogen of the water by the sodium1 and may be represented as follows3 hydrogen sodium sodium hydrogen 7water7 hydrogen 7sodium hydroxide7 hydrogen oxygen oxygen ,the sodium hydroxide formed is a white solid which remains dissolved in the undecomposed water1 and may be obtained by evaporating the solution to dryness4 ,the hydrogen is evolved as a gas and may be collected by suitable apparatus4 ,other metals1 such as magnesium and iron1 decompose water rapidly1 but only at higher temperatures4 ,when steam is passed over hot iron1 for example1 the iron combines with the oxygen of the steam1 thus displacing the hydrogen4 ,experiments show that the change may be represented as follows3 hydrogen iron hydrogen 7water7 iron 7iron oxide7 hydrogen oxygen oxygen hydrogen ,the iron oxide formed is a reddish-black compound1 identical with that obtained by the combustion of iron in oxygen4 ,directions for preparing hydrogen by the action of steam on iron4 ,the apparatus used in the preparation of hydrogen from iron and steam is shown in ,fig4 #i4 ,a porcelain or iron tube ,b1 about #ej cm4 in length and #b cm4 or #c cm4 in diameter1 is partially filled with fine iron wire or tacks and connected as shown in the figure4 ,the tube ,b is heated1 slowly at first1 until the iron is red-hot4 ,steam is then conducted through the tube by boiling the water in the flask ,a4 ,the hot iron combines with the oxygen in the steam1 setting free the hydrogen1 which is collected over water4 ,the gas which first passes over is mixed with the air previously contained in the flask and tube1 and is allowed to escape1 since a mixture of hydrogen with oxygen or air explodes violently when brought in contact with a flame4 ,it is evident that the flask ,a must be disconnected from the tube before the heat is withdrawn4 ,that the gas obtained is different from air and oxygen may be shown by holding a bottle of it mouth downward and bringing a lighted splint into it4 ,the hydrogen is ignited and burns with an almost colorless flame4 ,illustration ,fig4 #i ,preparation from acids 7usual laboratory method74 ,while hydrogen can be prepared from water1 either by the action of the electric current or by the action of certain metals1 these methods are not economical and are therefore but little used4 ,in the laboratory hydrogen is generally prepared from compounds known as acids1 all of which contain hydrogen4 ,when acids are brought in contact with certain metals1 the metals dissolve and set free the hydrogen of the acid4 ,although this reaction is a quite general one1 it has been found most convenient in preparing hydrogen by this method to use either zinc or iron as the metal and either hydrochloric or sulphuric acid as the acid4 ,hydrochloric acid is a compound consisting of #b4gg hydrogen and #ig4bc chlorine1 while sulphuric acid consists of #b4je hydrogen1 #cb4gj sulphur1 and #fe4be oxygen4 ,the changes which take place in the preparation of hydrogen from zinc and sulphuric acid 7diluted with water7 may be represented as follows3 hydrogen 7sulphuric zinc 7zinc zinc sulphur acid7 sulphur sulphate7 hydrogen oxygen oxygen ,in other words1 the zinc has taken the place of the hydrogen in sulphuric acid4 ,the resulting compound contains zinc1 sulphur1 and oxygen1 and is known as zinc sulphate4 ,this remains dissolved in the water present in the acid4 ,it may be obtained in the form of a white solid by evaporating the liquid left after the metal has passed into solution4 ,when zinc and hydrochloric acid are used the following changes take place3 hydrogen 7hydrochloric zinc 7zinc zinc chlorine acid7 chlorine chloride7 hydrogen ,when iron is used the changes which take place are exactly similar to those just given for zinc4 ,illustration ,fig4 #aj4 ,directions for preparing hydrogen from acids4 ,the preparation of hydrogen from acids is carried out in the laboratory as follows3 ,the metal is placed in a flask or wide-mouthed bottle ,a 7,fig4 #aj7 and the acid is added slowly through the funnel tube ,b4 ,the metal dissolves in the acid1 while the hydrogen which is liberated escapes through the exit tube ,c and is collected over water4 ,it is evident that the hydrogen which passes over first is mixed with the air from the bottle ,a4 ,hence care must be taken not to bring a flame near the exit tube1 since1 as has been stated previously1 such a mixture explodes with great violence when brought in contact with a flame4 ,precautions4 ,both sulphuric acid and zinc1 if impure1 are likely to contain small amounts of arsenic4 ,such materials should not be used in preparing hydrogen1 since the arsenic present combines with a portion of the hydrogen to form a very poisonous gas known as arsine4 ,on the other hand1 chemically pure sulphuric acid1 i4e4 sulphuric acid that is entirely free from impurities1 will not act upon chemically pure zinc4 ,the reaction may be started1 however1 by the addition of a few drops of a solution of copper sulphate or platinum tetrachloride4 ,physical properties4 ,hydrogen is similar to oxygen in that it is a colorless1 tasteless1 odorless gas4 ,it is characterized by its extreme lightness1 being the lightest of all known substances4 ,one liter of the gas weighs only #j4jhihd g4 ,on comparing this weight with that of an equal volume of oxygen1 viz41 #a4dbhe g41 the latter is found to be #ae4hh times as heavy as hydrogen4 ,similarly1 air is found to be #ad4ch times as heavy as hydrogen4 ,soap bubbles blown with hydrogen rapidly rise in the air4 ,on account of its lightness it is possible to pour it upward from one bottle into another4 ,thus1 if the bottle ,a 7,fig4 #aa7 is filled with hydrogen1 placed mouth downward by the side of bottle ,b1 filled with air1 and is then gradually inverted under ,b as indicated in the figure1 the hydrogen will flow upward into bottle ,b1 displacing the air4 ,its presence in bottle ,b may then be shown by bringing a lighted splint to the mouth of the bottle1 when the hydrogen will be ignited by the flame4 ,it is evident1 from this experiment1 that in order to retain the gas in an open bottle the bottle must be placed mouth downward4 ,illustration ,fig4 #aa ,hydrogen is far more difficult to liquefy than any other gas1 with the exception of helium1 a rare element recently found to exist in the atmosphere4 ,the ,english scientist ,dewar1 however1 in #ahih succeeded not only in obtaining hydrogen in liquid state but also as a solid4 ,liquid hydrogen is colorless and has a density of only #j4jg4 ,its boiling point under atmospheric pressure is -#beb4 ,under diminished pressure the temperature has been reduced to -#bfb4 ,the solubility of hydrogen in water is very slight1 being still less than that of oxygen4 ,pure hydrogen produces no injurious results when inhaled4 ,of course one could not live in an atmosphere of the gas1 since oxygen is essential to respiration4 ,chemical properties4 ,at ordinary temperatures hydrogen is not an active element4 ,a mixture of hydrogen and chlorine1 however1 will combine with explosive violence at ordinary temperature if exposed to the sunlight4 ,the union can be brought about also by heating4 ,the product formed in either case is hydrochloric acid4 ,under suitable conditions hydrogen combines with nitrogen to form ammonia1 and with sulphur to form the foul-smelling gas1 hydrogen sulphide4 ,the affinity of hydrogen for oxygen is so great that a mixture of hydrogen and oxygen or hydrogen and air explodes with great violence when heated to the kindling temperature 7about #fab74 ,nevertheless under proper conditions hydrogen may be made to burn quietly in either oxygen or air4 ,the resulting hydrogen flame is almost colorless and is very hot4 ,the combustion of the hydrogen is1 of course1 due to its union with oxygen4 ,the product of the combustion is therefore a compound of hydrogen and oxygen4 ,that this compound is water may be shown easily by experiment4 ,illustration ,fig4 #ab ,directions for burning hydrogen in air4 ,the combustion of hydrogen in air may be carried out safely as follows3 ,the hydrogen is generated in the bottle ,a 7,fig4 #ab71 is dried by conducting it through the tube ,x1 filled with some substance 7generally calcium chloride7 which has a great attraction for moisture1 and escapes through the tube ,t1 the end of which is drawn out to a jet4 ,the hydrogen first liberated mixes with the air contained in the generator4 ,if a flame is brought near the jet before this mixture has all escaped1 a violent and very dangerous explosion results1 since the entire apparatus is filled with the explosive mixture4 ,on the other hand1 if the flame is not applied until all the air has been expelled1 the hydrogen is ignited and burns quietly1 since only the small amount of it which escapes from the jet can come in contact with the oxygen of the air at any one time4 ,by holding a cold1 dry bell jar or bottle over the flame1 in the manner shown in the figure1 the steam formed by the combustion of the hydrogen is condensed1 the water collecting in drops on the sides of the jar4 ,precautions4 ,in order to avoid danger it is absolutely necessary to prove that the hydrogen is free from air before igniting it4 ,this can be done by testing small amounts of the escaping gas4 ,a convenient and safe method of doing this is to fill a test tube with the gas by inverting it over the jet4 ,the hydrogen1 on account of its lightness1 collects in the tube1 displacing the air4 ,after holding it over the jet for a few moments in order that it may be filled with the gas1 the tube is gently brought1 mouth downward1 to the flame of a burner placed not nearer than an arm's length from the jet4 ,if the hydrogen is mixed with air a slight explosion occurs1 but if pure it burns quietly in the tube4 ,the operation is repeated until the gas burns quietly1 when the tube is quickly brought back over the jet for an instant1 whereby the escaping hydrogen is ignited by the flame in the tube4 ,illustration4 ,fig4 #ac ,a mixture of hydrogen and oxygen is explosive4 ,that a mixture of hydrogen and air is explosive may be shown safely as follows3 ,a cork through which passes a short glass tube about #a cm4 in diameter is fitted air-tight into the tubule of a bell jar of #b l4 or #c l4 capacity4 7,a thick glass bottle with bottom removed may be used47 ,the tube is closed with a small rubber stopper and the bell jar filled with hydrogen1 the gas being collected over water4 ,when entirely filled with the gas the jar is removed from the water and supported by blocks of wood in order to leave the bottom of the jar open1 as shown in ,fig4 #ac4 ,the stopper is now removed from the tube in the cork1 and the hydrogen1 which on account of its lightness escapes from the tube1 is at once lighted4 ,as the hydrogen escapes1 the air flows in at the bottom of the jar and mixes with the remaining portion of the hydrogen1 so that a mixture of the two soon forms1 and a loud explosion results4 ,the explosion is not dangerous1 since the bottom of the jar is open1 thus leaving room for the expansion of the hot gas4 ,since air is only one fifth oxygen1 the remainder being inert gases1 it may readily be inferred that a mixture of hydrogen with pure oxygen would be far more explosive than a mixture of hydrogen with air4 ,such mixtures should not be made except in small quantities and by experienced workers4 ,hydrogen does not support combustion4 ,while hydrogen is readily combustible1 it is not a supporter of combustion4 ,in other words1 substances will not burn in it4 ,this may be shown by bringing a lighted candle supported by a stiff wire into a bottle or cylinder of the pure gas1 as shown in ,fig4 #ad4 ,the hydrogen is ignited by the flame of the candle and burns at the mouth of the bottle1 where it comes in contact with the oxygen in the air4 ,when the candle is thrust up into the gas1 its flame is extinguished on account of the absence of oxygen4 ,if slowly withdrawn1 the candle is relighted as it passes through the layer of burning hydrogen4 ,illustration3 ,fig4 #ad ,illustration3 ,fig4 #ae ,reduction4 ,on account of its great affinity for oxygen1 hydrogen has the power of abstracting it from many of its compounds4 ,thus1 if a stream of hydrogen1 dried by passing through the tube ,b 7,fig4 #ae71 filled with calcium chloride1 is conducted through the tube ,c containing some copper oxide1 heated to a moderate temperature1 the hydrogen abstracts the oxygen from the copper oxide4 ,the change may be represented as follows3 hydrogen copper hydrogen oxygen7copper oxide7 oxygen 7water7 copper ,the water formed collects in the cold portions of the tube ,c near its end4 ,in this experiment the copper oxide is said to undergo reduction4 ,reduction may therefore be defined as the process of withdrawing oxygen from a compound4 ,relation of reduction to oxidation4 ,at the same time that the copper oxide is reduced it is clear that the hydrogen is oxidized1 for it combines with the oxygen given up by the copper oxide4 ,the two processes are therefore very closely related1 and it usually happens that when one substance is oxidized some other substance is reduced4 ,that substance which gives up its oxygen is called an oxidizing agent1 while the substance which unites with the oxygen is called a reducing agent4 ,the oxyhydrogen blowpipe4 ,this is a form of apparatus used for burning hydrogen in pure oxygen4 ,as has been previously stated1 the flame produced by the combustion of hydrogen in the air is very hot4 ,it is evident that if pure oxygen is substituted for air1 the temperature reached will be much higher1 since there are no inert gases to absorb the heat4 ,the oxyhydrogen blowpipe1 used to effect this combination1 consists of a small tube placed within a larger one1 as shown in ,fig4 #af4 ,illustration3 ,fig4 #af ,the hydrogen1 stored under pressure1 generally in steel cylinders1 is first passed through the outer tube and ignited at the open end of the tube4 ,the oxygen from a similar cylinder is then conducted through the inner tube1 and mixes with the hydrogen at the end of the tube4 ,in order to produce the maximum heat1 the hydrogen and oxygen must be admitted to the blowpipe in the exact proportion in which they combine1 viz41 #b volumes of hydrogen to #a of oxygen1 or by weight1 #a part of hydrogen to #g4id parts of oxygen4 ,the intensity of the heat may be shown by bringing into the flame pieces of metal such as iron wire or zinc4 ,these burn with great brilliancy4 ,even platinum1 having a melting point of #aggi1 may be melted by the heat of the flame4 ,while the oxyhydrogen flame is intensely hot1 it is almost non-luminous4 ,if directed against some infusible substance like ordinary lime 7calcium oxide71 the heat is so intense that the lime becomes incandescent and glows with a brilliant light4 ,this is sometimes used as a source of light1 under the name of ,drummond or lime light4 ,illustration3 ,fig4 #ag ,the blast lamp4 ,a similar form of apparatus is commonly used in the laboratory as a source of heat under the name blast lamp 7,fig4 #ag74 ,this differs from the oxyhydrogen blowpipe only in the size of the tubes4 ,in place of the hydrogen and oxygen the more accessible coal gas and air are respectively used4 ,the former is composed largely of a mixture of free hydrogen and gaseous compounds of carbon and hydrogen4 ,while the temperature of the flame is not so high as that of the oxyhydrogen blowpipe1 it nevertheless suffices for most chemical operations carried out in the laboratory4 ,uses of hydrogen4 ,on account of its cost1 hydrogen is but little used for commercial purposes4 ,it is sometimes used as a material for the inflation of balloons1 but usually the much cheaper coal gas is substituted for it4 ,even hot air is often used when the duration of ascension is very short4 ,it has been used also as a source of heat and light in the oxyhydrogen blowpipe4 ,where the electric current is available1 however1 this form of apparatus has been displaced almost entirely by the electric light and electric furnace1 which are much more economical and more powerful sources of light and heat4 ,,exercises #a4 ,will a definite weight of iron decompose an unlimited weight of steam8 #b4 ,why is oxygen passed through the inner tube of the oxyhydrogen blowpipe rather than the outer8 #c4 ,in ,fig4 #ad1 will the flame remain at the mouth of the tube8 #d4 ,from ,fig4 #ae1 suggest a way for determining experimentally the quantity of water formed in the reaction4 #e4 ,distinguish clearly between the following terms3 oxidation1 reduction1 combustion1 and kindling temperature4 #f4 ,is oxidation always accompanied by reduction8 #g4 ,what is the source of heat in the lime light8 ,what is the exact use of lime in this instrument8 #h4 ,in ,fig4 #ab1 why is it necessary to dry the hydrogen by means of the calcium chloride in the tube ,x8 #i4 ,at what pressure would the weight of #a l4 of hydrogen be equal to that of oxygen under standard conditions8 #aj4 7a7 ,what weight of hydrogen can be obtained from #aej g4 of sulphuric acid8 7b7 ,what volume would this occupy under standard conditions8 7c7 ,the density of sulphuric acid is #a4hd4 ,what volume would the #aej g4 of the acid occupy8 #aa4 ,how many liters of hydrogen can be obtained from #ej cc4 of sulphuric acid having a density of #a4hd8 #ab4 ,suppose you wish to fill five liter bottles with hydrogen1 the gas to be collected over water in your laboratory1 how many cubic centimeters of sulphuric acid would be required8 ,,chapter ,,iv ,,compounds ,,of ,,hydrogen ,,and ,,oxygen2 ,,water ,,and ,,hydrogen ,,dioxide ,,water ,historical4 ,water was long regarded as an element4 ,in #agha ,cavendish showed that it is formed by the union of hydrogen and oxygen4 ,being a believer in the phlogiston theory1 however1 he failed to interpret his results correctly4 ,a few years later ,lavoisier repeated ,cavendish's experiments and showed that water must be regarded as a compound of hydrogen and oxygen4 ,general methods employed for the determination of the composition of a compound4 ,the composition of a compound may be determined by either of two general processes these are known as analysis and synthesis4 #a4 ,analysis is the process of decomposing a compound into its constituents and determining what these constituents are4 ,the analysis is qualitative when it results in merely determining what elements compose the compound2 it is quantitative when the exact percentage of each constituent is determined4 ,qualitative analysis must therefore precede quantitative analysis1 for it must be known what elements1 are in a compound before a method can be devised for determining exactly how much of each is present4 #b4 ,synthesis is the process of forming a compound from its constituent parts4 ,it is therefore the reverse of analysis4 ,like analysis1 it may be either qualitative or quantitative4 ,application of these methods to the determination of the composition of water4 ,the determination of the composition of water is a matter of great interest not only because of the importance of the compound but also because the methods employed illustrate the general methods of analysis and synthesis4 ,methods based on analysis4 ,the methods based on analysis may be either qualitative or quantitative in character4 ,illustration3 ,fig4 #ah #a4 ,qualitative analysis4 ,as was stated in the study of oxygen1 water may be separated into its component parts by means of the electric current4 ,the form of apparatus ordinarily used for effecting this analysis is shown in ,fig4 #ah4 ,a platinum wire1 to the end of which is attached a small piece of platinum foil 7about #ae mm4 by #be mm471 is fused through each of the tubes ,b and ,d1 as shown in the figure4 ,the stopcocks at the ends of these tubes are opened and water1 to which has been added about one tenth of its volume of sulphuric acid1 is poured into the tube ,a until the side tubes ,b and ,d are completely filled4 ,the stopcocks are then closed4 ,the platinum wires extending into the tubes ,b and ,d are now connected with the wires leading from two or three dichromate cells joined in series4 ,the pieces of platinum foil within the tubes thus become the electrodes1 and the current flows from one to the other through the acidulated water4 ,as soon as the current passes1 bubbles of gas rise from each of the electrodes and collect in the upper part of the tubes4 ,the gas rising from the negative electrode is found to be hydrogen1 while that from the positive electrode is oxygen4 ,it will be seen that the volume of the hydrogen is approximately double that of the oxygen4 ,oxygen is more soluble in water than hydrogen1 and a very little of it is also lost by being converted into ozone and other substances4 ,it has been found that when the necessary corrections are made for the error due to these facts1 the volume of the hydrogen is exactly double that of the oxygen4 ,fig4 #ai illustrates a simpler form of apparatus1 which may be used in place of that shown in ,fig4 #ah4 ,a glass or porcelain dish is partially filled with water to which has been added the proper amount of acid4 ,two tubes filled with the same liquid are inverted over the electrodes4 ,the gases resulting from the decomposition of the water collect in the tubes4 ,illustration3 ,fig4 #ai #b4 ,quantitative analysis4 ,the analysis just described is purely qualitative and simply shows that water contains hydrogen and oxygen4 ,it does not prove the absence of other elements2 indeed it does not prove that the hydrogen and oxygen are present in the proportion in which they are liberated by the electric current4 ,the method may be made quantitative1 however1 by weighing the water decomposed and also the hydrogen and oxygen obtained in its decomposition4 ,if the combined weights of the hydrogen and oxygen exactly equal the weight of the water decomposed1 then it would be proved that the water consists of hydrogen and oxygen in the proportion in which they are liberated by the electric current4 ,this experiment is difficult to carry out1 however1 so that the more accurate methods based on synthesis are used4 ,methods based on synthesis4 ,two steps are necessary to ascertain the exact composition of water by synthesis3 7#a7 to show by qualitative synthesis that water is formed by the union of oxygen with hydrogen2 7#b7 to determine by quantitative synthesis in what proportion the two elements unite to form water4 ,the fact that water is formed by the combination of oxygen with hydrogen was proved in the preceding chapter4 ,the quantitative synthesis may be made as follows3 ,illustration3 ,fig4 #bj ,the combination of the two gases is brought about in a tube called a eudiometer4 ,this is a graduated tube about #fj cm4 long and #b cm4 wide1 closed at one end 7,fig4 #bj74 ,near the closed end two platinum wires are fused through the glass1 the ends of the wires within the tube being separated by a space of #b mm or #c mm4 ,the tube is entirely filled with mercury and inverted in a vessel of the same liquid4 ,pure hydrogen is passed into the tube until it is about one fourth filled4 ,the volume of the gas is then read off on the scale and reduced to standard conditions4 ,approximately an equal volume of pure oxygen is then introduced and the volume again read off and reduced to standard conditions4 ,this gives the total volume of the two gases4 ,from this the volume of the oxygen introduced may be determined by subtracting from it the volume of the hydrogen4 ,the combination of the two gases is now brought about by connecting the two platinum wires with an induction coil and passing a spark from one wire to the other4 ,immediately a slight explosion occurs4 ,the mercury in the tube is at first depressed because of the expansion of the gases due to the heat generated1 but at once rebounds1 taking the place of the gases which have combined to form water4 ,the volume of the water in the liquid state is so small that it may be disregarded in the calculations4 ,in order that the temperature of the residual gas and the mercury may become uniform1 the apparatus is allowed to stand for a few minutes4 ,the volume of the gas is then read off and reduced to standard conditions1 so that it may be compared with the volumes of the hydrogen and oxygen originally taken4 ,the residual gas is then tested in order to ascertain whether it is hydrogen or oxygen1 experiments having proved that it is never a mixture of the two4 ,from the information thus obtained the composition of the water may be calculated4 ,thus1 suppose the readings were as follows3 ,volume of hydrogen taken #bj4c cc4 ,volume of hydrogen and oxygen #ch4g ,volume of oxygen #ah4d ,volume of gas left after combination has taken place 7oxygen7 #h4c ,the #bj4c cc4 of hydrogen have combined with #ah4d cc4 minus #h4c cc4 7or #aj4a cc47 of oxygen2 or approximately #b volumes of hydrogen have combined with #a of oxygen4 ,since oxygen is #ae4hh times as heavy as hydrogen1 the proportion by weight in which the two gases combine is #a part of hydrogen to #g4id of oxygen4 ,precaution4 ,if the two gases are introduced into the eudiometer in the exact proportions in which they combine1 after the combination has taken place the liquid will rise and completely fill the tube4 ,under these conditions1 however1 the tube is very likely to be broken by the sudden upward rush of the liquid4 ,hence in performing the experiment care is taken to introduce an excess of one of the gases4 ,a more convenient form of eudiometer4 ,a form of eudiometer 7,fig4 #ba7 different from that shown on page #dc is sometimes used to avoid the calculations necessary in reducing the volumes of the gases to the same conditions of temperature and pressure in order to make comparisons4 ,with this apparatus it is possible to take the readings of the volumes under the same conditions of temperature and pressure1 and thus compare them directly4 ,the apparatus 7,fig4 #ba7 is filled with mercury and the gases introduced into the tube ,a4 ,the experiment is carried out as in the preceding one1 except that before taking the reading of the gas volumes1 mercury is either added to the tube ,b or withdrawn from it by means of the stopcock ,c1 until it stands at exactly the same height in both tubes4 ,the gas inclosed in tube ,a is then under atmospheric pressure2 and since but a few minutes are required for performing the experiment1 the conditions of temperature and pressure may be regarded as constant4 ,hence the volumes of the hydrogen and oxygen and of the residual gas may be read off from the tube and directly compared4 ,illustration3 ,fig4 #ba ,method used by ,berzelius and ,dumas4 ,the method used by these investigators enables us to determine directly the proportion by weight in which the hydrogen and oxygen combine4 ,fig4 #bb illustrates the apparatus used in making this determination4 ,b is a glass tube containing copper oxide4 ,c and ,d are glass tubes filled with calcium chloride1 a substance which has great affinity for water4 ,the tubes ,b and ,c1 including their contents1 are carefully weighed1 and the apparatus connected as shown in the figure4 ,a slow current of pure hydrogen is then passed through ,a1 and that part of the tube ,b which contains copper oxide is carefully heated4 ,the hydrogen combines with the oxygen present in the copper oxide to form water1 which is absorbed by the calcium chloride in tube ,c4 ,the calcium chloride in tube ,d prevents any moisture entering tube ,c from the air4 ,the operation is continued until an appreciable amount of water has been formed4 ,the tubes ,b and ,c are then weighed once more4 ,the loss of weight in the tube ,b will exactly equal the weight of oxygen taken up from the copper oxide in the formation of the water4 ,the gain in weight in the tube ,c will exactly equal the weight of the water formed4 ,the difference in these weights will of course equal the weight of the hydrogen present in the water formed4 ,illustration3 ,fig4 #bb ,dumas' results4 ,the above method for the determination of the composition of water was first used by ,berzelius in #ahbj4 ,the work was repeated in #ahdc by ,dumas1 the average of whose results is as follows3 ,weight of water formed #bcf4cf g4 ,oxygen given up by the copper oxide #baj4jd ------ ,weight of hydrogen present in water #bf4cb ,according to this experiment the ratio of hydrogen to oxygen in water is therefore #bf4cb to #baj4jd1 or as l to #g4ih ,morley's results4 ,the ,american chemist ,morley has recently determined the composition of water1 extreme precautions being taken to use pure materials and to eliminate all sources of error4 ,the hydrogen and oxygen which combined1 as well as the water formed1 were all accurately weighed4 ,according to ,morley's results1 #a part of hydrogen by weight combines with #g4id parts of oxygen to form water4 ,comparison of results obtained4 ,from the above discussions it is easy to see that it is by experiment alone that the composition of a compound can be determined4 ,different methods may lead to slightly different results4 ,the more accurate the method chosen and the greater the skill with which the experiment is carried out1 the more accurate will be the results4 ,it is generally conceded by chemists that the results obtained by ,morley in reference to the composition of water are the most accurate ones4 ,in accordance with these results1 then1 water must be regarded as a compound containing hydrogen and oxygen in the proportion of #a part by weight of hydrogen to #g4id parts by weight of oxygen4 ,relation between the volume of aqueous vapor and the volumes of the hydrogen and oxygen which combine to form it4 ,when the quantitative synthesis of water is carried out in the eudiometer as described above1 the water vapor formed by the union of the hydrogen and oxygen at once condenses4 ,the volume of the resulting liquid is so small that it may be disregarded in making the calculations4 ,if1 however1 the experiment is carried out at a temperature of #ajj or above1 the water-vapor formed is not condensed and it thus becomes possible to compare the volume of the vapor with the volumes of hydrogen and oxygen which combined to form it4 ,this can be accomplished by surrounding the arm ,a of the eudiometer 7,fig4 #bc7 with the tube ,b through which is passed the vapor obtained by boiling some liquid which has a boiling point above #ajj4 ,in this way it has been proved that #b volumes of hydrogen and #a volume of oxygen combine to form exactly #b volumes of water vapor1 the volumes all being measured under the same conditions of temperature and pressure4 ,it will be noted that the relation between these volumes may be expressed by whole numbers4 ,the significance of this very important fact will be discussed in a subsequent chapter4 ,illustration3 ,fig4 #bc ,occurrence of water4 ,water not only covers about three fourths of the surface of the earth1 and is present in the atmosphere in the form of moisture1 but it is also a common constituent of the soil and rocks and of almost every form of animal and vegetable organism4 ,the human body is nearly #gj water4 ,this is derived not only from the water which we drink but also from the food which we eat1 most of which contains a large percentage of water4 ,thus potatoes contain about #gh of water1 milk #he1 beef over #ej1 apples #hd1 tomatoes #id4 ,impurities in water4 ,chemically pure water contains only hydrogen and oxygen4 ,such a water never occurs in nature1 however1 for being a good solvent1 it takes up certain substances from the rocks and soil with which it comes in contact4 ,when such waters are evaporated these substances are deposited in the form of a residue4 ,even rain water1 which is the purest form occurring in nature1 contains dust particles and gases dissolved from the atmosphere4 ,the foreign matter in water is of two kinds1 namely1 mineral1 such as common salt and limestone1 and organic1 that is the products of animal and vegetable life4 ,mineral matter in water4 ,the amount and nature of the mineral matter present in different waters vary greatly1 depending on the character of the rocks and soil with which the waters come in contact4 ,the more common of the substances present are common salt and compounds of calcium1 magnesium1 and iron4 ,one liter of the average river water contains about #age mg4 of mineral matter4 ,water from deep wells naturally contains more mineral matter than river water1 generally two or three times as much1 while sea water contains as much as #ce1jjj mg4 to the liter4 ,effect of impurities on health4 ,the mineral matter in water does not1 save in very exceptional cases1 render the water injurious to the human system4 ,in fact the presence of a certain amount of such matter is advantageous1 supplying the mineral constituents necessary for the formation of the solid tissues of the body4 ,the presence of organic matter1 on the other hand1 must always be regarded with suspicion4 ,this organic matter may consist not only of the products of animal and vegetable life but also of certain microscopic forms of living organisms which are likely to accompany such products4 ,contagious diseases are known to be due to the presence in the body of minute living organisms or germs4 ,each disease is caused by its own particular kind of germ4 ,through sewage these germs may find their way from persons afflicted with disease into the water supply1 and it is principally through the drinking water that certain of these diseases1 especially typhoid fever1 are spread4 ,it becomes of great importance1 therefore1 to be able to detect such matter when present in drinking water as well as to devise methods whereby it can be removed or at least rendered harmless4 ,analysis of water4 ,the mineral analysis of a water is1 as the name suggests1 simply the determination of the mineral matter present4 ,sanitary analysis1 on the other hand1 is the determination of the organic matter present4 ,the physical properties of a water give no conclusive evidence as to its purity1 since a water may be unfit for drinking purposes and yet be perfectly clear and odorless4 ,neither can any reliance be placed on the simple methods often given for testing the purity of water4 ,only the trained chemist can carry out such methods of analysis as can be relied upon4 ,illustration3 ,fig4 #bd ,purification of water4 ,three general methods are used for the purification of water1 namely1 distillation1 filtration1 and boiling4 #a4 ,distillation4 ,the most effective way of purifying natural waters is by the process of distillation4 ,this consists in boiling the water and condensing the steam4 ,fig4 #bd illustrates the process of distillation1 as commonly conducted in the laboratory4 ,ordinary water is poured into the flask ,a and boiled4 ,the steam is conducted through the condenser ,b1 which consists essentially of a narrow glass tube sealed within a larger one1 the space between the two being filled with cold water1 which is admitted at ,c and escapes at ,d4 ,the inner tube is thus kept cool and the steam in passing through it is condensed4 ,the water formed by the condensation of the steam collects in the receiver ,e and is known as distilled water4 ,such water is practically pure1 since the impurities are nonvolatile and remain in the flask ,a4 ,commercial distillation4 ,in preparing distilled water on a large scale1 the steam is generated in a boiler or other metal container and condensed by passing it through a pipe made of metal1 generally tin4 ,this pipe is wound into a spiral and is surrounded by a current of cold water4 ,distilled water is used by the chemist in almost all of his work4 ,it is also used in the manufacture of artificial ice and for drinking water4 ,fractional distillation4 ,in preparing distilled water1 it is evident that if the natural water contains some substance which is volatile its vapor will pass over and be condensed with the steam1 so that the distillate will not be pure water4 ,even such mixtures1 however1 may generally be separated by repeated distillation4 ,thus1 if a mixture of water 7boiling point #ajj7 and alcohol 7boiling point #gh7 is distilled1 the alcohol1 having the lower boiling point1 tends to distill first1 followed by the water4 ,the separation of the two is not perfect1 however1 but may be made nearly so by repeated distillations4 ,the process of separating a mixture of volatile substances by distillation is known as fractional distillation4 #b4 ,filtration4 ,the process of distillation practically removes all nonvolatile foreign matter1 mineral as well as organic4 ,in purifying water for drinking purposes1 however1 it is only necessary to eliminate the latter or to render it harmless4 ,this is ordinarily done either by filtration or boiling4 ,in filtration the water is passed through some medium which will retain the organic matter4 ,ordinary charcoal is a porous substance and will condense within its pores the organic matter in water if brought in contact with it4 ,it is therefore well adapted to the construction of filters4 ,such filters to be effective must be kept clean1 since it is evident that the charcoal is useless after its pores are filled4 ,a more effective type of filter is the ,chamberlain-,pasteur filter4 ,in this the water is forced through a porous cylindrical cup1 the pores being so minute as to strain out the organic matter4 ,city filtration beds4 ,for purifying the water supply of cities1 large filtration beds are prepared from sand and gravel1 and the water is allowed to filter through these4 ,some of the impurities are strained out by the filter1 while others are decomposed by the action of certain kinds of bacteria present in the sand4 ,fig4 #be shows a cross section of a portion of the filter used in purifying the water supply of ,philadelphia4 ,the water filters through the sand and gravel and passes into the porous pipe ,a1 from which it is pumped into the city mains4 ,the filters are covered to prevent the water from freezing in cold weather4 ,illustration3 ,fig4 #be #c4 ,boiling4 ,a simpler and equally efficient method for purifying water for drinking purposes consists in boiling the water4 ,it is the germs in water that render it dangerous to health4 ,these germs are living forms of matter4 ,if the water is boiled1 the germs are killed and the water rendered safe4 ,while these germs are destroyed by heat1 cold has little effect upon them4 ,thus ,dewar1 in working with liquid hydrogen1 exposed some of these minute forms of life to the temperature of boiling hydrogen 7-#beb7 without killing them4 ,self-purification of water4 ,it has long been known that water contaminated with organic matter tends to purify itself when exposed to the air4 ,this is due to the fact that the water takes up a small amount of oxygen from the air1 which gradually oxidizes the organic matter present in the water4 ,while water is undoubtedly purified in this way1 the method cannot be relied upon to purify a contaminated water so as to render it safe for drinking purposes4 ,physical properties4 ,pure water is an odorless and tasteless liquid1 colorless in thin layers1 but having a bluish tinge when observed through a considerable thickness4 ,it solidifies at #j and boils at #ajj under the normal pressure of one atmosphere4 ,if the pressure is increased1 the boiling point is raised4 ,when water is cooled it steadily contracts until the temperature of #d is reached3 it then expands4 ,water is remarkable for its ability to dissolve other substances1 and is the best solvent known4 ,solutions of solids in water are more frequently employed in chemical work than are the solid substances1 for chemical action between substances goes on more readily when they are in solution than it does when they are in the solid state4 ,chemical properties4 ,water is a very stable substance1 or1 in other words1 it does not undergo decomposition readily4 ,to decompose it into its elements by heat alone requires a very high temperature2 at #bejj1 for example1 only about #e of the entire amount is decomposed4 ,though very stable towards heat1 water can be decomposed in other ways1 as by the action of the electrical current or by certain metals4 ,heat of formation and heat of decomposition are equal4 ,the fact that a very high temperature is necessary to decompose water into hydrogen and oxygen is in accord with the fact that a great deal of heat is evolved by the union of hydrogen and oxygen2 for it has been proved that the heat necessary to decompose a compound into its elements 7heat of decomposition7 is equal to the heat evolved in the formation of a compound from its elements 7heat of formation74 ,water of crystallization4 ,when a solid is dissolved in water and the resulting solution is allowed to evaporate1 the solid separates out1 often in the form of crystals4 ,it has been found that the crystals of many compounds1 although perfectly dry1 give up a definite amount of water when heated1 the substance at the same time losing its crystalline form4 ,such water is called water of crystallization4 ,this varies in amount with different compounds1 but is perfectly definite for the same compound4 ,thus1 if a perfectly dry crystal of copper sulphate is strongly heated in a tube1 water is evolved and condenses on the sides of the tube1 the crystal crumbling to a light powder4 ,the weight of the water evolved is always equal to exactly #cf4jg of the weight of copper sulphate crystals heated4 ,the water must therefore be in chemical combination with the substance composing the crystal2 for if simply mixed with it or adhering to it1 not only would the substance appear moist but the amount present would undoubtedly vary4 ,the combination1 however1 must be a very weak one1 since the water is often expelled by even a gentle heat4 ,indeed1 in some cases the water is given up on simple exposure to air4 ,such compounds are said to be efflorescent4 ,thus a crystal of sodium sulphate 7,glauber's salt7 on exposure to air crumbles to a fine powder1 owing to the escape of its water of crystallization4 ,other substances have just the opposite property3 they absorb moisture when exposed to the air4 ,for example1 if a bit of dry calcium chloride is placed in moist air1 in the course of a few hours it will have absorbed sufficient moisture to dissolve it4 ,such substances are said to be deliquescent4 ,a deliquescent body serves as a good drying or desiccating agent4 ,we have already employed calcium chloride as an agent for absorbing the moisture from hydrogen4 ,many substances1 as for example quartz1 form crystals which contain no water of crystallization4 ,mechanically inclosed water4 ,water of crystallization must be carefully distinguished from water which is mechanically inclosed in a crystal and which can be removed by powdering the crystal and drying4 ,thus1 when crystals of common salt are heated1 the water inclosed in the crystal is changed into steam and bursts the crystal with a crackling sound4 ,such crystals are said to decrepitate4 ,that this water is not combined is proved by the fact that the amount present varies and that it has all the properties of water4 ,uses of water4 ,the importance of water in its relation to life and commerce is too well known to require comment4 ,its importance to the chemist has also been pointed out4 ,it remains to call attention to the fact that it is used as a standard in many physical measurements4 ,thus #j and #ajj on the centigrade scale are respectively the freezing and the boiling points of water under normal pressure4 ,the weight of #a cc4 of water at its point of greatest density is the unit of weight in the metric system1 namely1 the gram4 ,it is also taken as the unit for the determination of the density of liquids and solids as well as for the measurement of amounts of heat4 ,,hydrogen ,,dioxide ,composition4 ,as has been shown1 #a part by weight of hydrogen combines with #g4id parts by weight of oxygen to form water4 ,it is possible1 however1 to obtain a second compound of hydrogen and oxygen differing from water in composition in that #a part by weight of hydrogen is combined with #b #g4id1 or #ae4hh parts1 of oxygen4 ,this compound is called hydrogen dioxide or hydrogen peroxide1 the prefixes di- and per- signifying that it contains more oxygen than hydrogen oxide1 which is the chemical name for water4 ,preparation4 ,hydrogen dioxide cannot be prepared cheaply by the direct union of hydrogen and oxygen1 and indirect methods must therefore be used4 ,it is commonly prepared by the action of a solution of sulphuric acid on barium dioxide4 ,the change which takes place may be indicated as follows3 sulphuric acid barium dioxide barium sulphate hydrogen dioxide -------------- -------------- --------------- ---------------- hydrogen barium barium hydrogen sulphur oxygen sulphur oxygen oxygen oxygen ,in other words1 the barium and hydrogen in the two compounds exchange places4 ,by this method a dilute solution of the dioxide in water is obtained4 ,it is possible to separate the dioxide from the water by fractional distillation4 ,this is attended with great difficulties1 however1 since the pure dioxide is explosive4 ,the distillation is carried on under diminished pressure so as to lower the boiling points as much as possible2 otherwise the high temperature would decompose the dioxide4 ,properties4 ,pure hydrogen dioxide is a colorless sirupy liquid having a density of #a4di4 ,its most characteristic property is the ease with which it decomposes into water and oxygen4 ,one part by weight of hydrogen is capable of holding firmly only #g4id parts of oxygen4 ,the additional #g4id parts of oxygen present in hydrogen dioxide are therefore easily evolved1 the compound breaking down into water and oxygen4 ,this decomposition is attended by the generation of considerable heat4 ,in dilute solution hydrogen dioxide is fairly stable1 although such a solution should be kept in a dark1 cool place1 since both heat and light aid in the decomposition of the dioxide4 ,uses4 ,solutions of hydrogen dioxide are used largely as oxidizing agents4 ,the solution sold by druggists contains #c of the dioxide and is used in medicine as an antiseptic4 ,its use as an antiseptic depends upon its oxidizing properties4 ,,exercises #a4 ,why does the chemist use distilled water in making solutions1 rather than filtered water8 #b4 ,how could you determine the total amount of solid matter dissolved in a sample of water8 #c4 ,how could you determine whether a given sample of water is distilled water8 #d4 ,how could the presence of air dissolved in water be detected8 #e4 ,how could the amount of water in a food such as bread or potato be determined8 #f4 ,would ice frozen from impure water necessarily be free from disease germs8 #g4 ,suppose that the maximum density of water were at #j in place of #d2 what effect would this have on the formation of ice on bodies of water8 #h4 ,is it possible for a substance to contain both mechanically inclosed water and water of crystallization8 #i4 ,if steam is heated to #bjjj and again cooled1 has any chemical change taken place in the steam8 #aj4 ,why is cold water passed into ,c instead of ,d 7,fig4 #bd78 #aa4 ,mention at least two advantages that a metal condenser has over a glass condenser4 #ab4 ,draw a diagram of the apparatus used in your laboratory for supplying distilled water4 #ac4 #bj cc4 of hydrogen and #g cc4 of oxygen are placed in a eudiometer and the mixture exploded4 7a7 ,how many cubic centimeters of aqueous vapor are formed8 7b7 ,what gas and how much of it remains in excess8 #ad4 7a7 ,what weight of water can be formed by the combustion of #ajj ,l of hydrogen1 measured under standard conditions8 7b7,what volume of oxygen would be required in 7a78 7c7,what weight of potassium chlorate is necessary to prepare this amount of oxygen8 #ae4 ,what weight of oxygen is present in #a kg4 of the ordinary hydrogen dioxide solution8 ,in the decomposition of this weight of the dioxide into water and oxygen1 what volume of oxygen 7measured under standard conditions7 is evolved8 ,,chapter ,v ,,the ,,atomic ,,theory ,three fundamental laws of matter4 ,before we can gain any very definite idea in regard to the structure of matter1 and the way in which different kinds of substances act chemically upon each other1 it is necessary to have clearly in view three fundamental laws of matter4 ,these laws have been established by experiment1 and any conception which may be formed concerning matter must therefore be in harmony with them4 ,the laws are as follows3 ,law of conservation of matter4 ,this law has already been touched upon in the introductory chapter1 and needs no further discussion4 ,it will be recalled that it may be stated thus3 ,matter can neither be created nor destroyed1 though it can be changed from one form into another4 ,law of definite composition4 ,in the earlier days of chemistry there was much discussion as to whether the composition of a given compound is always precisely the same or whether it is subject to some variation4 ,two ,frenchmen1 ,berthollet and ,proust1 were the leaders in this discussion1 and a great deal of most useful experimenting was done to decide the question4 ,their experiments1 as well as all succeeding ones1 have shown that the composition of a pure chemical compound is always exactly the same4 ,water obtained by melting pure ice1 condensing steam1 burning hydrogen in oxygen1 has always #aa4ah hydrogen and #hh4hb oxygen in it4 ,red oxide of mercury1 from whatever source it is obtained1 contains #ib4f mercury and #g4d oxygen4 ,this truth is known as the law of definite composition1 and may be stated thus3 ,the composition of a chemical compound never varies4 ,law of multiple proportion4 ,it has already been noted1 however1 that hydrogen and oxygen combine in two different ratios to form water and hydrogen dioxide respectively4 ,it will be observed that this fact does not contradict the law of definite composition1 for entirely different substances are formed4 ,these compounds differ from each other in composition1 but the composition of each one is always constant4 ,this ability of two elements to unite in more than one ratio is very frequently observed4 ,carbon and oxygen combine in two different ratios2 nitrogen and oxygen combine to form as many as five distinct compounds1 each with its own precise composition4 ,in the first decade of the last century ,john ,dalton1 an ,english school-teacher and philosopher1 endeavored to find some rule which holds between the ratios in which two given substances combine4 ,his studies brought to light a very simple relation1 which the following examples will make clear4 ,in water the hydrogen and oxygen are combined in the ratio of #a part by weight of hydrogen to #g4id parts by weight of oxygen4 ,in hydrogen dioxide the #a part by weight of hydrogen is combined with #ae4hh parts by weight of oxygen4 ,the ratio between the amounts of oxygen which combine with the same amount of hydrogen to form water and hydrogen dioxide respectively is therefore #g4id3 #ae4hh1 or #a3 #b4 ,illustration3 ,,john ,,dalton 7,english7 7#agff-ahdd7 ,developed the atomic theory2 made many studies on the properties and the composition of gases4 ,his book entitled ,a ,new ,system of ,chemical ,philosophy had a large influence on the development of chemistry ,similarly1 the element iron combines with oxygen to form two oxides1 one of which is black and the other red4 ,by analysis it has been shown that the former contains #a part by weight of iron combined with #j4bhf parts by weight of oxygen1 while the latter contains #a part by weight of iron combined with #j4dbi parts by weight of oxygen4 ,here again we find that the amounts of oxygen which combine with the same fixed amount of iron to form the two compounds are in the ratio of small whole numbers1 viz41 #b3c4 ,many other examples of this simple relation might be given1 since it has been found to hold true in all cases where more than one compound is1 formed from the same elements4 ,dalton's law of multiple proportion states these facts as follows3 ,when any two elements1 ,a and ,b1 combine to form more than one compound1 the amounts of ,b which unite with any fixed amount of ,a bear the ratio of small whole numbers to each other4 ,hypothesis necessary to explain the laws of matter4 ,these three generalizations are called laws1 because they express in concise language truths which are found by careful experiment to hold good in all cases4 ,they do not offer any explanation of the facts1 but merely state them4 ,the human mind1 however1 does not rest content with the mere bare facts1 but seeks ever to learn the explanation of the facts4 ,a suggestion which is offered to explain such a set of facts is called an hypothesis4 ,the suggestion which ,dalton offered to explain the three laws of matter1 called the atomic hypothesis1 was prompted by his view of the constitution of matter1 and it involves three distinct assumptions in regard to the nature of matter and chemical action4 ,dalton could not prove these assumptions to be true1 but he saw that if they were true the laws of matter become very easy to understand4 ,dalton's atomic hypothesis4 ,the three assumptions which ,dalton made in regard to the nature of matter1 and which together constitute the atomic hypothesis1 are these3 #a4 ,all elements are made up of minute1 independent particles which ,dalton designated as atoms4 #b4 ,all atoms of the same element have equal masses2 those of different elements have different masses2 in any change to which an atom is subjected its mass does not change4 #c4 ,when two or more elements unite to form a compound1 the action consists in the union of a definite small number of atoms of each element to form a small particle of the compound4 ,the smallest particles of a given compound are therefore exactly alike in the number and kinds of atoms which they contain1 and larger masses of the substances are simply aggregations of these least particles4 ,molecules and atoms4 ,dalton applied the name atom not only to the minute particles of the elements but also to the least particles of compounds4 ,later ,avogadro1 an ,italian scientist1 pointed out the fact that the two are different1 since the smallest particle of an element is a unit1 while that of a compound must have at least two units in it4 ,he suggested the name molecule for the least particle of a compound which can exist1 retaining the name atom for the smallest particle of an element4 ,in accordance with this distinction1 we may define the atom and the molecule as follows3 ,an atom is the smallest particle of an element which can exist4 ,a molecule is the smallest particle of a compound which can exist4 ,it will be shown in a subsequent chapter that sometimes two or more atoms of the same element unite with each other to form molecules of the element4 ,while the term atom1 therefore1 is applicable only to elements1 the term molecule is applicable both to elements and compounds4 ,the atomic hypothesis and the laws of matter4 ,supposing the atomic hypothesis to be true1 let us now see if it is in harmony with the laws of matter4 #a4 ,the atomic hypothesis and the law of conservation of matter4 ,it is evident that if the atoms never change their masses in any change which they undergo1 the total quantity of matter can never change and the law of conservation of matter must follow4 #b4 ,the atomic hypothesis and the law of definite composition4 ,according to the third supposition1 when iron combines with sulphur the union is between definite numbers of the two kinds of atoms4 ,in the simplest case one atom of the one element combines with one atom of the other4 ,if the sulphur and the iron atoms never change their respective masses when they unite to form a molecule of iron sulphide1 all iron sulphide molecules will have equal amounts of iron in them and also of sulphur4 ,consequently any mass made up of iron sulphide molecules will have the same fraction of iron by weight as do the individual iron sulphide molecules4 ,iron sulphide1 from whatever source1 will have the same composition1 which is in accordance with the law of definite composition4 #c4 ,the atomic hypothesis and the law of multiple proportion4 ,but this simplest case may not always be the only one4 ,under other conditions one atom of iron might combine with two of sulphur to form a molecule of a second compound4 ,in such a case the one atom of iron would be in combination with twice the mass of sulphur that is in the first compound1 since the sulphur atoms all have equal masses4 ,what is true for one molecule will be true for any number of them2 consequently when such quantities of these two compounds are selected as are found to contain the same amount of iron1 the one will contain twice as much sulphur as the other4 ,the combination between the atoms may of course take place in other simple ratios4 ,for example1 two atoms of one element might combine with three or with five of the other4 ,in all such cases it is clear that the law of multiple proportion must hold true4 ,for on selecting such numbers of the two kinds of molecules as have the same number of the one kind of atoms1 the numbers of the other kind of atoms will stand in some simple ratio to each other1 and their weights will therefore stand in the same simple ratio4 ,testing the hypothesis4 ,efforts have been made to find compounds which do not conform to these laws1 but all such attempts have resulted in failure4 ,if such compounds should be found1 the laws would be no longer true1 and the hypothesis of ,dalton would cease to possess value4 ,when an hypothesis has been tested in every way in which experiment can test it1 and is still found to be in harmony with the facts in the case1 it is termed a theory4 ,we now speak of the atomic theory rather than of the atomic hypothesis4 ,value of a theory4 ,the value of a theory is twofold4 ,it aids in the clear understanding of the laws of nature because it gives an intelligent idea as to why these laws should be in operation4 ,a theory also leads to discoveries4 ,it usually happens that in testing a theory much valuable work is done1 and many new facts are discovered4 ,almost any theory in explaining given laws will involve a number of consequences apart from the laws it seeks to explain4 ,experiment will soon show whether these facts are as the theory predicts they will be4 ,thus ,dalton's atomic theory predicted many properties of gases which experiment has since verified4 ,atomic weights4 ,it would be of great advantage in the study of chemistry if we could determine the weights of the different kinds of atoms4 ,it is evident that this cannot be done directly4 ,they are so small that they cannot be seen even with a most powerful microscope4 ,it is calculated that it would take #bjj1jjj1jjj hydrogen atoms placed side by side to make a row one centimeter long4 ,no balance can weigh such minute objects4 ,it is possible1 however1 to determine their relative weights1--that is1 how much heavier one is than another4 ,these relative weights of the atoms are spoken of as the atomic weights of the elements4 ,if elements were able to combine in only one way1--one atom of one with one atom of another1--the problem of determining the atomic weights would be very simple4 ,we should merely have to take some one convenient element as a standard1 and find by experiment how much of each other element would combine with a fixed weight of it4 ,the ratios thus found would be the same ratios as those between the atoms of the elements1 and thus we should have their relative atomic weights4 ,the law of multiple proportion calls attention to the fact that the atoms combine in other ratios than #a3 #a1 and there is no direct way of telling which one1 if any1 of the several compounds in a given case is the one consisting of a single atom of each element4 ,if some way were to be found of telling how much heavier the entire molecule of a compound is than the atom chosen as a standard1--that is1 of determining the molecular weights of compounds1--the problem could be solved1 though its solution would not be an entirely simple matter4 ,there are ways of determining the molecular weights of compounds1 and there are other experiments which throw light directly upon the relative weights of the atoms4 ,these methods cannot be described until the facts upon which they rest have been studied4 ,it will be sufficient for the present to assume that these methods are trustworthy4 ,standard for atomic weights4 ,since the atomic weights are merely relative to some one element chosen as a standard1 it is evident that any one of the elements may serve as this standard and that any convenient value may be assigned to its atom4 ,at one time oxygen was taken as this standard1 with the value #ajj1 and the atomic weights of the other elements were expressed in terms of this standard4 ,it would seem more rational to take the element of smallest atomic weight as the standard and give it unit value2 accordingly hydrogen was taken as the standard with an atomic weight of #a4 ,very recently1 however1 this unit has been replaced by oxygen1 with an atomic weight of #af4 ,why oxygen is chosen as the standard for atomic weights4 ,in the determination of the atomic weight of an element it is necessary to find the weight of the element which combines with a definite weight of another element1 preferably the element chosen as the standard4 ,since oxygen combines with the elements far more readily than does hydrogen to form definite compounds1 it is far better adapted for the standard element1 and has accordingly replaced hydrogen as the standard4 ,any definite value might be given to the weight of the oxygen atom4 ,in assigning a value to it1 however1 it is convenient to choose a whole number1 and as small a number as possible without making the atomic weight of any other element less than unity4 ,for these reasons the number #af has been chosen as the atomic weight of oxygen4 ,this makes the atomic weight of hydrogen equal to #a4jjh1 so that there is but little difference between taking oxygen as #af and hydrogen as #a for the unit4 ,the atomic weights of the elements are given in the ,appendix4 ,,exercises #a4 ,two compounds were found to have the following compositions3 7a7 oxygen #fi4ec1 nitrogen #cj4dg2 7b7 oxygen #ec4bg1 nitrogen #df4gc4 ,show that the law of multiple proportion holds in this case4 #b4 ,two compounds were found to have the following compositions3 7a7 oxygen #dc4fd1 phosphorus #ef4cf2 7b7 oxygen #ef4ce1 phosphorus #dc4fe4 ,show that the law of multiple proportion holds in this case4 #c4 ,why did ,dalton assume that all the atoms of a given element have the same weight8 ,,chapter ,,vi ,,chemical ,,equations ,,and ,,calculations ,formulas4 ,since the molecule of any chemical compound consists of a definite number of atoms1 and this number never changes without destroying the identity of the compound1 it is very convenient to represent the composition of a compound by indicating the composition of its molecules4 ,this can be done very easily by using the symbols of the atoms to indicate the number and the kind of the atoms which constitute the molecule4 ,hg,o will in this way represent mercuric oxide1 a molecule of which has been found to contain #a atom each of mercury and oxygen4 ,h#b,o will represent water1 the molecules of which consist of #a atom of oxygen and #b of hydrogen1 the subscript figure indicating the number of the atoms of the element whose symbol precedes it4 ,h#b,,so#d will stand for sulphuric acid1 the molecules of which contain #b atoms of hydrogen1 #a of sulphur1 and #d of oxygen4 ,the combination of symbols which represents the molecule of a substance is called its formula4 ,equations4 ,when a given substance undergoes a chemical change it is possible to represent this change by the use of such symbols and formulas4 ,in a former chapter it was shown that mercuric oxide decomposes when heated to form mercury and oxygen4 ,this may be expressed very briefly in the form of the equation 7#a7 ,hg,o ,hg ,o4 ,when water is electrolyzed two new substances1 hydrogen and oxygen1 are formed from it4 ,this statement in the form of an equation is 7#b7 ,h#b,o #b;,h ,o4 ,the coefficient before the symbol for hydrogen indicates that a single molecule of water yields two atoms of hydrogen on decomposition4 ,in like manner the combination of sulphur with iron is expressed by the equation 7#c7 ,fe ,s ,fe,s4 ,the decomposition of potassium chlorate by heat takes place as represented by the equation 7#d7 ,k,cl,o#c ,k,cl #c,o4 ,reading of equations4 ,since equations are simply a kind of shorthand way of indicating chemical changes which occur under certain conditions1 in reading an equation the full statement for which it stands should be given4 ,equation 7#a7 should be read1 ,mercuric oxide when heated gives mercury and oxygen2 equation 7#b7 is equivalent to the statement1 ,when electrolyzed1 water produces hydrogen and oxygen2 equation 7#c71 ,when heated together iron and sulphur unite to form iron sulphide2 equation 7#d71 ,potassium chlorate when heated yields potassium chloride and oxygen4 ,knowledge required for writing equations4 ,in order to write such equations correctly1 a considerable amount of exact knowledge is required4 ,thus1 in equation 7#a7 the fact that red oxide of mercury has the composition represented by the formula ,hg,o1 that it is decomposed by heat1 that in this decomposition mercury and oxygen are formed and no other products1--all these facts must be ascertained by exact experiment before the equation can be written4 ,an equation expressing these facts will then have much value4 ,having obtained an equation describing the conduct of mercuric oxide on being heated1 it will not do to assume that other oxides will behave in like manner4 ,iron oxide 7,fe,o7 resembles mercuric oxide in many respects1 but it undergoes no change at all when heated4 ,manganese dioxide1 the black substance used in the preparation of oxygen1 has the formula ,mn,o#b4 ,when this substance is heated oxygen is set free1 but the metal manganese is not liberated2 instead1 a different oxide of manganese containing less oxygen is produced4 ,the equation representing the reaction is #c,mn,o#b ,mn#c,o#d #b,o4 ,classes of reactions4 ,when a chemical change takes place in a substance the substance is said to undergo a reaction4 ,although a great many different reactions will be met in the study of chemistry1 they may all be grouped under the following heads4 #a4 ,addition4 ,this is the simplest kind of chemical action4 ,it consists in the union of two or more substances to produce a new substance4 ,the combination of iron with sulphur is an example3 ,fe ,s ,fe,s4 #b4 ,decomposition4 ,this is the reverse of addition1 the substance undergoing reaction being parted into its constituents4 ,the decomposition of mercuric oxide is an example3 ,hg,o ,hg ,o4 #c4 ,substitution4 ,it is sometimes possible for an element in the free state to act upon a compound in such a way that it takes the place of one of the elements of the compound1 liberating it in turn4 ,in the study of the element hydrogen it was pointed out that hydrogen is most conveniently prepared by the action of sulphuric or hydrochloric acid upon zinc4 ,when sulphuric acid is used a substance called zinc sulphate1 having the composition represented by the formula ,zn,s,o#d1 is formed together with hydrogen4 ,the equation is ,zn ,h#b,,so#d ,zn,s,o#d #b;,h4 ,when hydrochloric acid is used zinc chloride and hydrogen are the products of reaction3 ,zn #b;,h,cl ,zn,cl#b #b;,h4 ,when iron is used in place of zinc the equation is ,fe ,h#b,,so#d ,fe,s,o#d #b;,h4 ,these reactions are quite similar1 as is apparent from an examination of the equations4 ,in each case #a atom of the metal replaces #b atoms of hydrogen in the acid1 and the hydrogen escapes as a gas4 ,when an element in the free state1 such as the zinc in the equations just given1 takes the place of some one element in a compound1 setting it free from chemical combination1 the act is called substitution4 ,other reactions illustrating substitution are the action of sodium on water1 ,na ,h#b,o ,na,o,h ,h2 and the action of heated iron upon water1 #c;,fe #d;,h#b,o ,fe#c,o#d #h;,h4 #d4 ,double decomposition4 ,when barium dioxide 7,ba,o#b7 is treated with sulphuric acid two compounds are formed1 namely1 hydrogen dioxide 7,h#b,o#b7 and barium sulphate 7,ba,s,o#d74 ,the equation is ,ba,o#b ,h#b,,so#d ,ba,s,o#d ,h#b,o#b4 ,in this reaction it will be seen that the two elements barium and hydrogen simply exchange places4 ,such a reaction is called a double decomposition4 ,we shall meet with many examples of this kind of chemical reactions4 ,chemical equations are quantitative4 ,the use of symbols and formulas in expressing chemical changes has another great advantage4 ,thus1 according to the equation ,h#b,o #b;,h ,o1 #a molecule of water is decomposed into #b atoms of hydrogen and #a atom of oxygen4 ,but1 as we have seen1 the relative weights of the atoms are known1 that of hydrogen being #a4jjh1 while that of oxygen is #af4 ,the molecule of water1 being composed of #b atoms of hydrogen and #a atom of oxygen1 must therefore weigh relatively #b4jaf #af1 or #ah4jaf4 ,the amount of hydrogen in this molecule must be #b4jaf_/ah4jaf1 or #aa4ah of the whole1 while the amount of oxygen must be #af_/ah4jah1 or #hh4hb of the whole4 ,now1 since any definite quantity of water is simply the sum of a great many molecules of water1 it is plain that the fractions representing the relative amounts of hydrogen and oxygen present in a molecule must likewise express the relative amounts of hydrogen and oxygen present in any quantity of water4 ,thus1 for example1 in #bj g4 of water there are #b4jaf_/ah4jaf #bj1 or #b4bch g4 of hydrogen1 and #af_/ah4jaf #bj1 or #ag4gfb g4 of oxygen4 ,these results in reference to the composition of water of course agree exactly with the facts obtained by the experiments described in the chapter on water1 for it is because of those experiments that the values #a4jjh and #af are given to hydrogen and oxygen respectively4 ,it is often easier to make calculations of this kind in the form of a proportion rather than by fractions4 ,since the molecule of water and the two atoms of hydrogen which it contains have the ratio by weight of #ah4jaf3 #b4jaf1 any mass of water has the same ratio between its total weight and the weight of the hydrogen in it4 ,hence1 to find the number of grams 7x7 of hydrogen in #bj g4 of water1 we have the proportion #ah4jaf 3 #b4jaf 33 #bj g4 3 x 7grams of hydrogen74 ,solving for x1 we get #b4bch for the number of grams of hydrogen4 ,similarly1 to find the amount 7x7 of oxygen present in the #bj g4 of water1 we have the proportion #ah4jaf 3 #af 33 #bj 3 x from which we find that x #ag4gfb g4 ,again1 suppose we wish to find what weight of oxygen can be obtained from #ae g4 of mercuric oxide4 ,the equation representing the decomposition of mercuric oxide is ,hg,o ,hg ,o4 ,the relative weights of the mercury and oxygen atoms are respectively #bjj and #af4 ,the relative weight of the mercuric oxide molecule must therefore be the sum of these1 or #baf4 ,the molecule of mercuric oxide and the atom of oxygen which it contains have the ratio #baf3 #af4 ,this same ratio must therefore hold between the weight of any given quantity of mercuric oxide and that of the oxygen which it contains4 ,hence1 to find the weight of oxygen in #ae g4 of mercuric oxide1 we have the proportion #baf 3 #af 33 #ae 3 x 7grams of oxygen74 ,on the other hand1 suppose we wish to prepare1 say1 #bj g4 of oxygen4 ,the problem is to find out what weight of mercuric oxide will yield #bj g4 of oxygen4 ,the following proportion evidently holds #baf 3 #af 33 x 7grams of mercuric oxide7 3 #bj2 from which we get x #bgj4 ,in the preparation of hydrogen by the action of sulphuric acid upon zinc1 according to the equation1 ,zn ,h#b,,so#d ,zn,s,o#d #b ,h1 suppose that #ej g4 of zinc are available2 let it be required to calculate the weight of hydrogen which can be obtained4 ,it will be seen that #a atom of zinc will liberate #b atoms of hydrogen4 ,the ratio by weight of a zinc to an hydrogen atom is #fe4d3 #a4jjh2 of #a zinc atom to #b hydrogen atoms1 #fe4d3 #b4jaf4 ,zinc and hydrogen will be related in this reaction in this same ratio1 however many atoms of zinc are concerned4 ,consequently in the proportion #fe4d 3 #b4jaf 33 #ej 3 x1 x will be the weight of hydrogen set free by #ej g4 of zinc4 ,the weight of zinc sulphate produced at the same time can be found from the proportion #fe4d 3 #afa4df 33 #ej 3 x2 where #afa4df is the molecular weight of the zinc sulphate1 and x the weight of zinc sulphate formed4 ,in like manner1 the weight of sulphuric acid used up can be calculated from the proportion #fe4d 3 #ih4jgf 33 #ej 3 x4 ,these simple calculations are possible because the symbols and formulas in the equations represent the relative weights of the substances concerned in a chemical reaction4 ,when once the relative weights of the atoms have been determined1 and it has been agreed to allow the symbols to stand for these relative weights1 an equation or formula making use of the symbols becomes a statement of a definite numerical fact1 and calculations can be based on it4 ,chemical equations not algebraic4 ,although chemical equations are quantitative1 it must be clearly understood that they are not algebraic4 ,a glance at the equations #g #d #aa1 #h #e #i #d will show at once that they are true4 ,the equations ,hg,o ,hg ,o1 ,fe,o ,fe ,o are equally true in an algebraic sense1 but experiment shows that only the first is true chemically1 for iron oxide 7,fe,o7 cannot be directly decomposed into iron and oxygen4 ,only such equations as have been found by careful experiment to express a real chemical transformation1 true both for the kinds of substances as well as for the weights1 have any value4 ,chemical formulas and equations1 therefore1 are a concise way of representing qualitatively and quantitatively facts which have been found by experiment to be true in reference to the composition of substances and the changes which they undergo4 ,formulas representing water of crystallization4 ,an examination of substances containing water of crystallization has shown that in every case the water is present in such proportion by weight as can readily be represented by a formula4 ,for example1 copper sulphate 7,cu,s,o#d7 and water combine in the ratio of #a molecule of the sulphate to #e of water2 calcium sulphate 7,ca,s,o#d7 and water combine in the ratio #a3 #b to form gypsum4 ,these facts are expressed by writing the formulas for the two substances with a period between them4 ,thus the formula for crystallized copper sulphate is ,cu,s,o#de;,h#b,o2 that of gypsum is ,ca,s,o#db;,h#b,o4 ,heat of reaction4 ,attention has frequently been directed to the fact that chemical changes are usually accompanied by heat changes4 ,in general it has been found that in every chemical action heat is either absorbed or given off4 ,by adopting a suitable unit for the measurement of heat1 the heat change during a chemical reaction can be expressed in the equation for the reaction4 ,heat cannot be measured by the use of a thermometer alone1 since the thermometer measures the intensity of heat1 not its quantity4 ,the easiest way to measure a quantity of heat is to note how warm it will make a definite amount of a given substance chosen as a standard4 ,water has been chosen as the standard1 and the unit of heat is called a calorie4 ,a calorie is defined as the amount of heat required to raise the temperature of one gram of water one degree4 ,by means of this unit it is easy to indicate the heat changes in a given chemical reaction4 ,the equation #b;,h ,o ,h#b,o #fh1cjj cal4 means that when #b4jaf g4 of hydrogen combine with #af g4 of oxygen1 #ah4jaf g4 of water are formed and #fh1cjj cal4 are set free4 ,c #b,s ,,cs#b - #ai1jjj cal4 means that an expenditure of #ai1jjj cal4 is required to cause #ab g4 of carbon to unite with #fd4ab g4 of sulphur to form #gf4ab g4 of carbon disulphide4 ,in these equations it will be noted that the symbols stand for as many grams of the substance as there are units in the weights of the atoms represented by the symbols4 ,this is always understood to be the case in equations where the heat of reaction is given4 ,conditions of a chemical action are not indicated by equations4 ,equations do not tell the conditions under which a reaction will take place4 ,the equation ,hg,o ,hg ,o does not tell us that it is necessary to keep the mercuric oxide at a high temperature in order that the decomposition may go on4 ,the equation ,zn #b;,h,cl ,zn,cl#b #b;,h in no way indicates the fact that the hydrochloric acid must be dissolved in water before it will act upon the zinc4 ,from the equation ,h ,cl ,h,cl it would not be suspected that the two gases hydrogen and chlorine will unite instantly in the sunlight1 but will stand mixed in the dark a long time without change4 ,it will therefore be necessary to pay much attention to the details of the conditions under which a given reaction occurs1 as well as to the expression of the reaction in the form of an equation4 ,,exercises #a4 ,calculate the percentage composition of the following substances3 7a7 mercuric oxide2 7b7 potassium chlorate2 7c7 hydrochloric acid2 7d7 sulphuric acid4 ,compare the results obtained with the compositions as given in ,chapters ,,ii and ,,iii4 #b4 ,determine the percentage of copper1 sulphur1 oxygen1 and water in copper sulphate crystals4 ,what weight of water can be obtained from #aej g4 of this substance8 #c4 ,what weight of zinc can be dissolved in #aj g4 of sulphuric acid8 ,how much zinc sulphate will be formed8 #d4 ,how many liters of hydrogen measured under standard conditions can be obtained from the action of #h g4 of iron on #aj g4 of sulphuric acid8 ,how much iron sulphate 7,fe,s,o#d7 will be formed8 #e4 #aj g4 of zinc were used in the preparation of hydrogen2 what weight of iron will be required to prepare an equal volume8 #f4 ,how many grams of barium dioxide will be required to prepare #a kg4 of common hydrogen dioxide solution8 ,what weight of barium sulphate will be formed at the same time8 #g4 ,what weight of the compound ,mn#c,o#d will be formed by strongly heating #be g4 of manganese dioxide8 ,what volume of oxygen will be given off at the same time1 measured under standard conditions8 #h4 7a7 ,what is the weight of #ajj l4 of hydrogen measured in a laboratory in which the temperature is #bj and pressure #gej mm48 7b7 ,what weight of sulphuric acid is necessary to prepare this amount of hydrogen8 7c7 ,the density of sulphuric acid is #a4hd4 ,express the acid required in 7b7 in cubic centimeters4 #i4 ,what weight of potassium chlorate is necessary to furnish sufficient oxygen to fill four #bjj cc4 bottles in your laboratory 7the gas to be collected over water78 ,,chapter ,,vii ,,nitrogen ,,and ,,the ,,rare ,,elements3 ,,argon1 ,,helium1 ,,neon1 ,,krypton1 ,,xenon ,historical4 ,nitrogen was discovered by the ,english chemist ,rutherford in #aggb4 ,a little later ,scheele showed it to be a constituent of air1 and ,lavoisier gave it the name azote1 signifying that it would not support life4 ,the name nitrogen was afterwards given it because of its presence in saltpeter or niter4 ,the term azote and symbol ,az are still retained by the ,french chemists4 ,occurrence4 ,air is composed principally of oxygen and nitrogen in the free state1 about #gh parts by volume out of every #ajj parts being nitrogen4 ,nitrogen also occurs in nature in the form of potassium nitrate 7,,kno#c7--;commonly called saltpeter or niter--as well as in sodium nitrate 7,na,n,o#c74 ,nitrogen is also an essential constituent of all living organisms2 for example1 the human body contains about #b4d of nitrogen4 ,preparation from air4 ,nitrogen can be prepared from air by the action of some substance which will combine with the oxygen1 leaving the nitrogen free4 ,such a substance must be chosen1 however1 as will combine with the oxygen to form a product which is not a gas1 and which can be readily separated from the nitrogen4 ,the substances most commonly used for this purpose are phosphorus and copper4 #a4 ,by the action of phosphorus4 ,the method used for the preparation of nitrogen by the action of phosphorus is as follows3 ,the phosphorus is placed in a little porcelain dish1 supported on a cork and floated on water 7,fig4 #bf74 ,it is then ignited by contact with a hot wire1 and immediately a bell jar or bottle is brought over it so as to confine a portion of the air4 ,the phosphorus combines with the oxygen to form an oxide of phosphorus1 known as phosphorus pentoxide4 ,this is a white solid which floats about in the bell jar1 but in a short time it is all absorbed by the water1 leaving the nitrogen4 ,the withdrawal of the oxygen is indicated by the rising of the water in the bell jar4 ,illustration3 ,fig4 #bf #b4 ,by the action of copper4 ,the oxygen present in the air may also be removed by passing air slowly through a heated tube containing copper4 ,the copper combines with the oxygen to form copper oxide1 which is a solid4 ,the nitrogen passes on and may be collected over water4 ,nitrogen obtained from air is not pure4 ,inasmuch as air1 in addition to oxygen and nitrogen1 contains small amounts of other gases1 and since the phosphorus as well as the copper removes only the oxygen1 it is evident that the nitrogen obtained by these methods is never quite pure4 ,about #a of the product is composed of other gases1 from which it is very difficult to separate the nitrogen4 ,the impure nitrogen so obtained may1 however1 be used for a study of most of the properties of nitrogen1 since these are not materially affected by the presence of the other gases4 ,preparation from compounds of nitrogen4 ,pure nitrogen may be obtained from certain compounds of the element4 ,thus1 if heat is applied to the compound ammonium nitrite 7,,nh#d,,no#b71 the change represented in the following equation takes place3 ,,nh#d,,no#b #b;,h#b,o #b,n4 ,physical properties4 ,nitrogen is similar to oxygen and hydrogen in that it is a colorless1 odorless1 and tasteless gas4 ,one liter of nitrogen weighs #a4beja g4 ,it is almost insoluble in water4 ,it can be obtained in the form of a colorless liquid having a boiling point of -#aie at ordinary pressure4 ,at -#bad it solidifies4 ,chemical properties4 ,nitrogen is characterized by its inertness4 ,it is neither combustible nor a supporter of combustion4 ,at ordinary temperatures it will not combine directly with any of the elements except under rare conditions4 ,at higher temperatures it combines with magnesium1 lithium1 titanium1 and a number of other elements4 ,the compounds formed are called nitrides1 just as compounds of an element with oxygen are called oxides4 ,when it is mixed with oxygen and subjected to the action of electric sparks1 the two gases slowly combine forming oxides of nitrogen4 ,a mixture of nitrogen and hydrogen when treated similarly forms ammonia1 a gaseous compound of nitrogen and hydrogen4 ,since we are constantly inhaling nitrogen1 it is evident that it is not poisonous4 ,nevertheless life would be impossible in an atmosphere of pure nitrogen on account of the exclusion of the necessary oxygen4 ,argon1 helium1 neon1 krypton1 xenon4 ,these are all rare elements occurring in the air in very small quantities4 ,argon1 discovered in #ahid1 was the first one obtained4 ,lord ,rayleigh1 an ,english scientist1 while engaged in determining the exact weights of various gases1 observed that the nitrogen obtained from the air is slightly heavier than pure nitrogen obtained from its compounds4 ,after repeating his experiments many times1 always with the same results1 ,rayleigh finally concluded that the nitrogen which he had obtained from the air was not pure1 but was mixed with a small amount of some unknown gas1 the density of which is greater than that of nitrogen4 ,acting on this assumption1 ,rayleigh1 together with the ,english chemist ,ramsay1 attempted to separate the nitrogen from the unknown gas4 ,knowing that nitrogen would combine with magnesium1 they passed the nitrogen obtained from the air and freed from all known substances through tubes containing magnesium heated to the necessary temperature4 ,after repeating this operation1 they finally succeeded in obtaining from the atmospheric nitrogen a small volume of gas which would not combine with magnesium and hence could not be nitrogen4 ,this proved to be a new element1 to which they gave the name argon4 ,as predicted1 this new element was found to be heavier than nitrogen1 its density as compared with hydrogen as a standard being approximately #bj1 that of nitrogen being only #ad4 ,about #a of the atmospheric nitrogen proved to be argon4 ,the new element is characterized by having no affinity for other elements4 ,even under the most favorable conditions it has not been made to combine with any other element4 ,on this account it was given the name argon1 signifying lazy or idle4 ,like nitrogen1 it is colorless1 odorless1 and tasteless4 ,it has been liquefied and solidified4 ,its boiling point is -#ahg4 ,helium was first found in the gases expelled from certain minerals by heating4 ,through the agency of the spectroscope it had been known to exist in the sun long before its presence on the earth had been demonstrated1--a fact suggested by the name helium1 signifying the sun4 ,its existence in traces in the atmosphere has also been proven4 ,it was first liquefied by ,onnes in ,july1 #aijh4 ,its boiling point1 namely -#bfi1 is the lowest temperature yet reached4 ,the remaining elements of this group--neon1 krypton1 and xenon--have been obtained from liquid air4 ,when liquid air is allowed to boil1 the constituents which are the most difficult to liquefy1 and which therefore have the lowest boiling points1 vaporize first1 followed by the others in the order of their boiling points4 ,it is possible in this way to make at least a partial separation of the air into its constituents1 and ,ramsay thus succeeded in obtaining from liquid air not only the known constituents1 including argon and helium1 but also the new elements1 neon1 krypton1 and xenon4 ,these elements1 as well as helium1 all proved to be similar to argon in that they are without chemical activity1 apparently forming no compounds whatever4 ,the percentages present in the air are very small4 ,the names1 neon1 krypton1 xenon1 signify respectively1 new1 hidden1 stranger4 ,,exercises #a4 ,how could you distinguish between oxygen1 hydrogen1 and nitrogen8 #b4 ,calculate the relative weights of nitrogen and oxygen2 of nitrogen and hydrogen4 #c4 ,in the preparation of nitrogen from the air1 how would hydrogen do as a substance for the removal of the oxygen8 #d4 ,what weight of nitrogen can be obtained from #aj l4 of air measured under the conditions of temperature and pressure which prevail in your laboratory8 #e4 ,how many grams of ammonium nitrite are necessary in the preparation of #bj l4 of nitrogen measured over water under the conditions of temperature and pressure which prevail in your laboratory8 #f4 ,if #aj l4 of air1 measured under standard conditions1 is passed over #ajj g4 of hot copper1 how much will the copper gain in weight8 ,illustration3 ,,william ,,ramsay 7,scotch7 7#ahee-7 ,has made many studies in the physical properties of substances2 discovered helium2 together with ,lord ,rayleigh and others he discovered argon1 krypton1 xenon1 and neon2 has contributed largely to the knowledge of radio-active substances1 showing that radium gradually gives rise to helium2 professor at ,university ,college1 ,london ,,chapter ,,viii ,,the ,,atmosphere ,atmosphere and air4 ,the term atmosphere is applied to the gaseous envelope surrounding the earth4 ,the term air is generally applied to a limited portion of this envelope1 although the two words are often used interchangeably4 ,many references have already been made to the composition and properties of the atmosphere4 ,these statements must now be collected and discussed somewhat more in detail4 ,air formerly regarded as an element4 ,like water1 air was at first regarded as elementary in character4 ,near the close of the eighteenth century ,scheele1 ,priestley1 and ,lavoisier showed by their experiments that it is a mixture of at least two gases1--those which we now call oxygen and nitrogen4 ,by burning substances in an inclosed volume of air and noting the contraction in volume due to the removal of the oxygen1 they were able to determine with some accuracy the relative volumes of oxygen and nitrogen present in the air4 ,the constituents of the atmosphere4 ,the constituents of the atmosphere may be divided into two general groups3 those which are essential to life and those which are not essential4 #a4 ,constituents essential to life4 ,in addition to oxygen and nitrogen at least two other substances1 namely1 carbon dioxide and water vapor1 must be present in the atmosphere in order that life may exist4 ,the former of these is a gaseous compound of carbon and oxygen having the formula ,,co#b4 ,its properties will be discussed in detail in the chapter on the compounds of carbon4 ,its presence in the air may be shown by causing the air to bubble through a solution of calcium hydroxide 7,ca7,,oh7#b71 commonly called lime water4 ,the carbon dioxide combines with the calcium hydroxide in accordance with the following equation3 ,ca7,,oh7#b ,,co#b ,ca,c,o#c ,h#b,o4 ,the resulting calcium carbonate 7,ca,c,o#c7 is insoluble in water and separates in the form of a white powder1 which causes the solution to appear milky4 ,the presence of water vapor is readily shown by its condensation on cold objects as well as by the fact that a bit of calcium chloride when exposed to the air becomes moist1 and may even dissolve in the water absorbed from the air4 #b4 ,constituents not essential to life4 ,in addition to the essential constituents1 the air contains small percentages of various other gases1 the presence of which so far as is known is not essential to life4 ,this list includes the rare elements1 argon1 helium1 neon1 krypton1 and xenon2 also hydrogen1 ammonia1 hydrogen dioxide1 and probably ozone4 ,certain minute forms of life 7germs7 are also present1 the decay of organic matter being due to their presence4 ,function of each of the essential constituents4 7#a7 ,the oxygen directly supports life through respiration4 7#b7 ,the nitrogen1 on account of its inactivity1 serves to dilute the oxygen1 and while contrary to the older views1 it is possible that life might continue to exist in the absence of the atmospheric nitrogen1 yet the conditions of life would be entirely changed4 ,moreover1 nitrogen is an essential constituent of all animal and plant life4 ,it was formerly supposed that neither animals nor plants could assimilate the free nitrogen1 but it has been shown recently that the plants of at least one natural order1 the ,leguminos1 to which belong the beans1 peas1 and clover1 have the power of directly assimilating the free nitrogen from the atmosphere4 ,this is accomplished through the agency of groups of bacteria1 which form colonies in little tubercles on the roots of the plants4 ,these bacteria probably assist in the absorption of nitrogen by changing the free nitrogen into compounds which can be assimilated by the plant4 ,fig4 #bg shows the tubercles on the roots of a variety of bean4 7#c7 ,the presence of water vapor in the air is necessary to prevent excessive evaporation from both plants and animals4 7#d7 ,carbon dioxide is an essential plant food4 ,illustration3 ,fig4 #bg ,the quantitative analysis of air4 ,a number of different methods have been devised for the determination of the percentages of the constituents present in the atmosphere4 ,among these are the following4 #a4 ,determination of oxygen4 7#a7 ,the oxygen is withdrawn from a measured volume of air inclosed in a tube1 by means of phosphorus4 ,to make the determination1 a graduated tube is filled with water and inverted in a vessel of water4 ,air is introduced into the tube until it is partially filled with the gas4 ,the volume of the inclosed air is carefully noted and reduced to standard conditions4 ,a small piece of phosphorus is attached to a wire and brought within the tube as shown in ,fig4 #bh4 ,after a few hours the oxygen in the inclosed air will have combined with the phosphorus1 the water rising to take its place4 ,the phosphorus is removed and the volume is again noted and reduced to standard conditions4 ,the contraction in the volume of the air is equal to the volume of oxygen absorbed4 ,illustration3 ,fig4 #bh 7#b7 ,the oxygen may also be estimated by passing a measured volume of air through a tube containing copper heated to a high temperature4 ,the oxygen in the air combines with the copper to form copper oxide 7,cu,o74 ,hence the increase in the weight of the copper equals the weight of the oxygen in the volume of air taken4 7#c7 ,a more accurate method is the following4 ,a eudiometer tube is filled with mercury and inverted in a vessel of the same liquid4 ,a convenient amount of air is then introduced into the tube and its volume accurately noted4 ,there is then introduced more than sufficient hydrogen to combine with the oxygen present in the inclosed air1 and the volume is again accurately noted4 ,the mixture is then exploded by an electric spark1 and the volume is once more taken4 ,by subtracting this volume from the total volume of the air and hydrogen there is obtained the contraction in volume due to the union of the oxygen and hydrogen4 ,the volume occupied by the water formed by the union of the two gases is so small that it may be disregarded in the calculation4 ,since oxygen and hydrogen combine in the ratio #a3 #b by volume1 it is evident that the contraction in volume due to the combination is equal to the volume occupied by the oxygen in the air contained in the tube1 plus twice this volume of hydrogen4 ,in other words1 one third of the total contraction is equal to the volume occupied by the oxygen in the inclosed air4 ,the following example will make this clear3 ,volume of air in tube #ej4j cc4 ,volume after introducing hydrogen #hj4j ,volume after combination of oxygen and hydrogen #dh4e ,contraction in volume due to combination 7#hj cc4-#dh4e cc47 #ca4e ,volume of oxygen in #ej cc4 of air 7#a_/c of #ca4e7 #aj4e ,all these methods agree in showing that #ajj volumes of dry air contain approximately #ba volumes of oxygen4 #b4 ,determination of nitrogen4 ,if the gas left after the removal of oxygen from a portion of air is passed over heated magnesium1 the nitrogen is withdrawn1 argon and the other rare elements being left4 ,it may thus be shown that of the #gi volumes of gas left after the removal of the oxygen from #ajj volumes of air1 approximately #gh are nitrogen and #j4ic argon4 ,the other elements are present in such small quantities that they may be neglected4 #c4 ,determination of carbon dioxide4 ,the percentage of carbon dioxide in any given volume of air may be determined by passing the air over calcium hydroxide or some other compound which will combine with the carbon dioxide4 ,the increase in the weight of the hydroxide equals the weight of the carbon dioxide absorbed4 ,the amount present in the open normal air is from #c to #d parts by volume in #aj1jjj volumes of air1 or about #j4jd4 #d4 ,determination of water vapor4 ,the water vapor present in a given volume of air may be determined by passing the air over calcium chloride 7or some other compound which has a strong affinity for water71 and noting the increase in the weight of the chloride4 ,the amount present varies not only with the locality1 but there is a wide variation from day to day in the same locality because of the winds and changes in temperature4 ,processes affecting the composition of the air4 ,the most important of these processes are the following4 #a4 ,respiration4 ,in the process of respiration some of the oxygen in the inhaled air is absorbed by the blood and carried to all parts of the body1 where it combines with the carbon of the worn-out tissues4 ,the products of oxidation are carried back to the lungs and exhaled in the form of carbon dioxide4 ,the amount exhaled by an adult averages about #bj l4 per hour4 ,hence in a poorly ventilated room occupied by a number of people the amount of carbon dioxide rapidly increases4 ,while this gas is not poisonous unless present in large amounts1 nevertheless air containing more than #ae parts in #aj1jjj is not fit for respiration4 #b4 ,combustion4 ,all of the ordinary forms of fuel contain large percentages of carbon4 ,on burning1 this carbon combines with oxygen in the air1 forming carbon dioxide4 ,combustion and respiration1 therefore1 tend to diminish the amount of oxygen in the air and to increase the amount of carbon dioxide4 #c4 ,action of plants4 ,plants have the power1 when in the sunlight1 of absorbing carbon dioxide from the air1 retaining the carbon and returning at least a portion of the oxygen to the air4 ,it will be observed that these changes are just the opposite of those brought about by the processes of respiration and combustion4 ,poisonous effect of exhaled air4 ,the differences in the percentages of oxygen1 carbon dioxide1 and moisture present in inhaled air and exhaled air are shown in the following analyses4 ,,inhaled ,,air ,,exhaled ,,air ,oxygen #ba4jj #af4jj ,carbon dioxide #j4jd #d4ch ,moisture variable saturated ,the foul odor of respired air is due to the presence of a certain amount of organic matter4 ,it is possible that this organic matter rather than the carbon dioxide is responsible for the injurious effects which follow the respiration of impure air4 ,the extent of such organic impurities present may be judged1 however1 by the amount of carbon dioxide present1 since the two are exhaled together4 ,the cycle of carbon in nature4 ,under the influence of sunlight1 the carbon dioxide absorbed from the air by plants reacts with water and small amounts of other substances absorbed from the soil to form complex compounds of carbon which constitute the essential part of the plant tissue4 ,this reaction is attended by the evolution of oxygen1 which is restored to the air4 ,the compounds resulting from these changes are much richer in their energy content than are the substances from which they are formed2 hence a certain amount of energy must have been absorbed in their formation4 ,the source of this energy is the sun's rays4 ,if the plant is burned1 the changes which took place in the formation of the compounds present are largely reversed4 ,the carbon and hydrogen present combine with oxygen taken from the air to form carbon dioxide and water1 while the energy absorbed from the sun's rays is liberated in the form of energy of heat4 ,if1 on the other hand1 the plant is used as food1 the compounds present are used in building up the tissues of the body4 ,when this tissue breaks down1 the changes which it undergoes are very similar to those which take place when the plant is burned4 ,the carbon and hydrogen combine with the inhaled oxygen to form carbon dioxide and water1 which are exhaled4 ,the energy possessed by the complex substances is liberated partly in the form of energy of heat1 which maintains the heat of the body1 and partly in the various forms of muscular energy4 ,the carbon originally absorbed from the air by the plant in the form of carbon dioxide is thus restored to the air and is ready to repeat the cycle of changes4 ,the composition of the air is constant4 ,notwithstanding the changes constantly taking place which tend to alter the composition of the air1 the results of a great many analyses of air collected in the open fields show that the percentages of oxygen and nitrogen as well as of carbon dioxide are very nearly constant4 ,indeed1 so constant are the percentages of oxygen and nitrogen that the question has arisen1 whether these two elements are not combined in the air1 forming a definite chemical compound4 ,that the two are not combined but are simply mixed together can be shown in a number of ways1 among which are the following4 #a4 ,when air dissolves in water it has been found that the ratio of oxygen to nitrogen in the dissolved air is no longer #ba3 #gh1 but more nearly #ce3 #fe4 ,if it were a chemical compound1 the ratio of oxygen to nitrogen would not be changed by solution in water4 #b4 ,a chemical compound in the form of a liquid has a definite boiling point4 ,water1 for example1 boils at #ajj4 ,moreover the steam which is thus formed has the same composition as the water4 ,the boiling point of liquid air1 on the other hand1 gradually rises as the liquid boils1 the nitrogen escaping first followed by the oxygen4 ,if the two were combined1 they would pass off together in the ratio in which they are found in the air4 ,why the air has a constant composition4 ,if air is a mixture and changes are constantly taking place which tend to modify its composition1 how1 then1 do we account for the constancy of composition which the analyses reveal8 ,this is explained by several facts4 7#a7 ,the changes which are caused by the processes of combustion and respiration1 on the one hand1 and the action of plants1 on the other1 tend to equalize each other4 7#b7 ,the winds keep the air in constant motion and so prevent local changes4 7#c7 ,the volume of the air is so vast and the changes which occur are so small compared with the total amount of air that they cannot be readily detected4 7#d7 ,finally it must be noted that only air collected in the open fields shows this constancy in composition4 ,the air in a poorly ventilated room occupied by a number of people rapidly changes in composition4 ,the properties of the air4 ,inasmuch as air is composed principally of a mixture of oxygen and nitrogen1 which elements have already been discussed1 its properties may be inferred largely from those of the two gases4 ,one liter weighs #a4bibc g4 ,it is thus #ad4ch times as heavy as hydrogen4 ,at the sea level it exerts an average pressure sufficient to sustain a column of mercury #gfj mm4 in height4 ,this is taken as the standard pressure in determining the volumes of gases as well as the boiling points of liquids4 ,water may be made to boil at any temperature between #j and considerably above #ajj by simply varying the pressure4 ,it is only when the pressure upon it is equal to the normal pressure of the atmosphere at the sea level1 as indicated by a barometric reading of #gfj mm41 that it boils at #ajj4 ,preparation of liquid air4 ,attention has been called to the fact that both oxygen and nitrogen can be obtained in the liquid state by strongly cooling the gases and applying great pressure to them4 ,since air is largely a mixture of these two gases1 it can be liquefied by the same methods4 ,the methods for liquefying air have been simplified greatly in that the low temperature required is obtained by allowing a portion of the compressed air to expand4 ,the expansion of a gas is always attended by the absorption of heat4 ,in liquefying air the apparatus is so constructed that the heat absorbed is withdrawn from air already under great pressure4 ,this process is continued until the temperature is lowered to the point of liquefaction4 ,illustration3 ,fig4 #bi ,the ,dewar bulb4 ,it is not possible to preserve air in the liquid state in a closed vessel1 on account of the enormous pressure exerted by it in its tendency to pass into the gaseous state4 ,it may however be preserved for some hours or even days before it will completely evaporate1 by simply placing it in an open vessel surrounded by a nonconducting material4 ,the most efficient vessel for this purpose is the ,dewar bulb shown in ,fig4 #bi4 ,the air is withdrawn from the space between the two walls1 thus making it nonconducting4 ,properties and uses of liquid air4 ,when first prepared1 liquid air is cloudy because of the presence of particles of solid carbon dioxide4 ,these may be filtered off1 leaving a liquid of slightly bluish color4 ,it begins to boil at about -#aij1 the nitrogen passing off first1 gradually followed by the oxygen1 the last portions being nearly pure oxygen4 ,to a certain extent oxygen is now prepared in this way for commercial purposes4 ,the extremely low temperature of liquid air may be inferred from the fact that mercury when cooled by it is frozen to a mass so hard that it may be used for driving nails4 ,liquid air is used in the preparation of oxygen and as a cooling agent in the study of the properties of matter at low temperatures4 ,it has thus been found that elements at extremely low temperatures largely lose their chemical activity4 ,,exercises #a4 ,when oxygen and nitrogen are mixed in the proportion in which they exist in the atmosphere1 heat is neither evolved nor absorbed by the process4 ,what important point does this suggest8 #b4 ,what essential constituent of the air is found in larger amount in manufacturing districts than in the open country8 #c4 ,can you suggest any reason why the growth of clover in a field improves the soil8 #d4 ,why are the inner walls of a ,dewar bulb sometimes coated with a film of silver8 #e4 ,to what is the blue color of liquid air due8 ,does this color increase in intensity on standing8 #f4 ,when ice is placed in a vessel containing liquid air1 the latter boils violently4 ,explain4 #g4 ,taking the volumes of the oxygen and nitrogen in #ajj volumes of air as #ba and #gh respectively1 calculate the percentages of these elements present by weight4 #h4 ,would combustion be more intense in liquid air than in the gaseous substance8 #i4 ,a tube containing calcium chloride was found to weigh #cj4abic g4 ,a volume of air which weighed #ae4bacd g4 was passed through1 after which the weight of the tube was found to be #cj4cdje g4 ,what was the percentage amount of moisture present in the air8 #aj4 #aj l4 of air measured at #bj and #gdj mm4 passed through lime water caused the precipitation of #j4jajb g4 of ,ca,c,o#c4 ,find the number of volumes of carbon dioxide in #aj1jjj volumes of the air4 ,,chapter ,,ix ,,solutions ,definitions4 ,when a substance disappears in a liquid in such a way as to thoroughly mix with it and to be lost to sight as an individual body1 the resulting liquid is called a solution4 ,the liquid in which the substance dissolves is called the solvent1 while the dissolved substance is called the solute4 ,classes of solutions4 ,matter in any one of its physical states may dissolve in a liquid1 so that we may have solutions of gases1 of liquids1 and of solids4 ,solutions of liquids in liquids are not often mentioned in the following pages1 but the other two classes will become very familiar in the course of our study1 and deserve special attention4 ,,solution ,,of ,,gases ,,in ,,liquids ,illustration3 ,fig4 #cj ,it has already been stated that oxygen1 hydrogen1 and nitrogen are slightly soluble in water4 ,accurate study has led to the conclusion that all gases are soluble to some extent not only in water but in many other liquids4 ,the amount of a gas which will dissolve in a liquid depends upon a number of conditions1 and these can best be understood by supposing a vessel ,b 7,fig4 #cj71 to be filled with the gas and inverted over the liquid4 ,under these circumstances the gas cannot escape or become mixed with another gas4 ,circumstances affecting the solubility of gases4 ,a number of circumstances affect the solubility of a gas in a liquid4 #a4 ,nature of the gas4 ,other conditions being equal1 each gas has its own peculiar solubility1 just as it has its own special taste or odor4 ,the solubility of gases varies between wide limits1 as will be seen from the following table1 but as a rule a given volume of a liquid will not dissolve more than two or three times its own volume of a gas4 ,solubility of ,gases in ,water #a l4 of water at #gfj mm4 pressure and at #j will dissolve3 ,ammonia #aadh4jj l4 ,hydrochloric acid #ejc4jj ,sulphur dioxide #gi4gi ,carbon dioxide #a4hj ,oxygen #da4ad cc4 ,hydrogen #ba4ae ,nitrogen #bj4jc ,in the case of very soluble gases1 such as the first three in the table1 it is probable that chemical combination between the liquid and the gas takes place4 #b4 ,nature of the liquid4 ,the character of the liquid has much influence upon the solubility of a gas4 ,water1 alcohol1 and ether have each its own peculiar solvent power4 ,from the solubility of a gas in water1 no prediction can be made as to its solubility in other liquids4 #c4 ,influence of pressure4 ,it has been found that the weight of gas which dissolves in a given case is proportional to the pressure exerted upon the gas4 ,if the pressure is doubled1 the weight of gas going into solution is doubled2 if the pressure is diminished to one half of its original value1 half of the dissolved gas will escape4 ,under high pressure1 large quantities of gas can be dissolved in a liquid1 and when the pressure is removed the gas escapes1 causing the liquid to foam or effervesce4 #d4 ,influence of temperature4 ,in general1 the lower the temperature of the liquid1 the larger the quantity of gas which it can dissolve4 #ajjj volumes of water at #j will dissolve #da4ad volumes of oxygen2 at #ej1 #ah4cg volumes2 at #ajj none at all4 ,while most gases can be expelled from a liquid by boiling the solution1 some cannot4 ,for example1 it is not possible to expel hydrochloric acid gas completely from its solution by boiling4 ,,solution ,,of ,,solids ,,in ,,liquids ,this is the most familiar class of solutions1 since in the laboratory substances are much more frequently used in the form of solutions than in the solid state4 ,circumstances affecting the solubility of a solid4 ,the solubility of a solid in a liquid depends upon several factors4 #a4 ,nature of the solid4 ,other conditions being the same1 solids vary greatly in their solubility in liquids4 ,this is illustrated in the following table3 ,table of ,solubility of ,solids at #ah #ajj cc4 of water will dissolve3 ,calcium chloride #ga4j g4 ,sodium chloride #ce4i ,potassium nitrate #bi4a ,copper sulphate #ba4d ,calcium sulphate #j4bjg ,no solids are absolutely insoluble1 but the amount dissolved may be so small as to be of no significance for most purposes4 ,thus barium sulphate1 one of the most insoluble of common substances1 dissolves in water to the extent of #a part in #djj1jjj4 #b4 ,nature of the solvent4 ,liquids vary much in their power to dissolve solids4 ,some are said to be good solvents1 since they dissolve a great variety of substances and considerable quantities of them4 ,others have small solvent power1 dissolving few substances1 and those to a slight extent only4 ,broadly speaking1 water is the most general solvent1 and alcohol is perhaps second in solvent power4 #c4 ,temperature4 ,the weight of a solid which a given liquid can dissolve varies with the temperature4 ,usually it increases rapidly as the temperature rises1 so that the boiling liquid dissolves several times the weight which the cold liquid will dissolve4 ,in some instances1 as in the case of common salt dissolved in water1 the temperature has little influence upon the solubility1 and a few solids are more soluble in cold water than in hot4 ,the following examples will serve as illustrations3 ,table of ,solubility at #j and at #ajj #ajj cc4 of water will dissolve3 ,at #j ,at #ajj ,calcium chloride #di4f g4 #aee4j g4 ,sodium chloride #ce4g #ci4h ,potassium nitrate #ac4c #bdg4j ,copper sulphate #ae4e #gc4e ,calcium sulphate #j4bje #j4bag ,calcium hydroxide #j4agc #j4jgi ,saturated solutions4 ,a liquid will not dissolve an unlimited quantity of a solid4 ,on adding the solid to the liquid in small portions at a time1 it will be found that a point is reached at which the liquid will not dissolve more of the solid at that temperature4 ,the solid and the solution remain in contact with each other unchanged4 ,this condition may be described by saying that they are in equilibrium with each other4 ,a solution is said to be saturated when it remains unchanged in concentration in contact with some of the solid4 ,the weight of the solid which will completely saturate a definite volume of a liquid at a given temperature is called the solubility of the substance at that temperature4 ,supersaturated solutions4 ,when a solution1 saturated at a given temperature1 is allowed to cool it sometimes happens that no solid crystallizes out4 ,this is very likely to occur when the vessel used is perfectly smooth and the solution is not disturbed in any way4 ,such a solution is said to be supersaturated4 ,that this condition is unstable can be shown by adding a crystal of the solid to the solution4 ,all of the solid in excess of the quantity required to saturate the solution at this temperature will at once crystallize out1 leaving the solution saturated4 ,supersaturation may also be overcome in many cases by vigorously shaking or stirring the solution4 ,general physical properties of solutions4 ,a few general statements may be made in reference to the physical properties of solutions4 #a4 ,distribution of the solid in the liquid4 ,a solid1 when dissolved1 tends to distribute itself uniformly through the liquid1 so that every part of the solution has the same concentration4 ,the process goes on very slowly unless hastened by stirring or shaking the solution4 ,thus1 if a few crystals of a highly colored substance such as copper sulphate are placed in the bottom of a tall vessel full of water1 it will take weeks for the solution to become uniformly colored4 #b4 ,boiling points of solutions4 ,the boiling point of a liquid is raised by the presence of a substance dissolved in it4 ,in general the extent to which the boiling point of a solvent is raised by a given substance is proportional to the concentration of the solution1 that is1 to the weight of the substance dissolved in a definite weight of the solvent4 #c4 ,freezing points of solutions4 ,a solution freezes at a lower temperature than the pure solvent4 ,the lowering of the freezing point obeys the same law which holds for the raising of the boiling point3 the extent of lowering is proportional to the weight of dissolved substance1 that is1 to the concentration of the solution4 ,electrolysis of solutions4 ,pure water does not appreciably conduct the electric current4 ,if1 however1 certain substances such as common salt are dissolved in the water1 the resulting solutions are found to be conductors of electricity4 ,such solutions are called electrolytes4 ,when the current passes through an electrolyte some chemical change always takes place4 ,this change is called electrolysis4 ,illustration3 ,fig4 #ca ,the general method used in the electrolysis of a solution is illustrated in ,fig4 #ca4 ,the vessel ,d contains the electrolyte4 ,two plates or rods1 ,a and ,b1 made of suitable material1 are connected with the wires from a battery 7or dynamo7 and dipped into the electrolyte1 as shown in the figure4 ,these plates or rods are called electrodes4 ,the electrode connected with the zinc plate of the battery is the negative electrode or cathode1 while that connected with the carbon plate is the positive electrode or anode4 ,theory of electrolytic dissociation4 ,the facts which have just been described in connection with solutions1 together with many others1 have led chemists to adopt a theory of solutions called the theory of electrolytic dissociation4 ,the main assumptions in this theory are the following4 #a4 ,formation of ions4 ,many compounds when dissolved in water undergo an important change4 ,a portion of their molecules fall apart1 or dissociate1 into two or more parts1 called ions4 ,thus sodium nitrate 7,na,n,o#c7 dissociates into the ions ,na and ,,no#c2 sodium chloride1 into the ions ,na and ,cl4 ,these ions are free to move about in the solution independently of each other like independent molecules1 and for this reason were given the name ion1 which signifies a wanderer4 #b4 ,the electrical charge of ions4 ,each ion carries a heavy electrical charge1 and in this respect differs from an atom or molecule4 ,it is evident that the sodium in the form of an ion must differ in some important way from ordinary sodium1 for sodium ions1 formed from sodium nitrate1 give no visible evidence of their presence in water1 whereas metallic sodium at once decomposes the water4 ,the electrical charge1 therefore1 greatly modifies the usual chemical properties of the element4 #c4 ,the positive charges equal the negative charges4 ,the ions formed by the dissociation of any molecule are of two kinds4 ,one kind is charged with positive electricity and the other with negative electricity2 moreover the sum of all the positive charges is always equal to the sum of all the negative charges4 ,the solution as a whole is therefore electrically neutral4 ,if we represent dissociation by the usual chemical equations1 with the electrical charges indicated by and - signs following the symbols1 the dissociation of sodium chloride molecules is represented thus3 ,na,cl -- ,na1 ,cl-4 ,the positive charge on each sodium ion exactly equals the negative charge on each chlorine ion4 ,sodium sulphate dissociates1 as shown in the equation ,na#b,,so#d -- #b,na1 ,,so#d--4 ,here the positive charge on the two sodium ions equals the double negative charge on the ,,so#d ion4 #d4 ,not all compounds dissociate4 ,only those compounds dissociate whose solutions form electrolytes4 ,thus salt dissociates when dissolved in water1 the resulting solution being an electrolyte4 ,sugar1 on the other hand1 does not dissociate and its solution is not a conductor of the electric current4 #e4 ,extent of dissociation differs in different liquids4 ,while compounds most readily undergo dissociation in water1 yet dissociation often occurs to a limited extent when solution takes place in liquids other than water4 ,in the discussion of solutions it will be understood that the solvent is water unless otherwise noted4 ,the theory of electrolytic dissociation and the properties of solutions4 ,in order to be of value1 this theory must give a reasonable explanation of the properties of solutions4 ,let us now see if the theory is in harmony with certain of these properties4 ,the theory of electrolytic dissociation and the boiling and freezing points of solutions4 ,we have seen that the boiling point of a solution of a substance is raised in proportion to the concentration of the dissolved substance4 ,this is but another way of saying that the change in the boiling point of the solution is proportional to the number of molecules of the dissolved substance present in the solution4 ,it has been found1 however1 that in the case of electrolytes the boiling point is raised more than it should be to conform to this law4 ,if the solute dissociates into ions1 the reason for this becomes clear4 ,each ion has the same effect on the boiling point as a molecule1 and since their number is greater than the number of molecules from which they were formed1 the effect on the boiling point is abnormally great4 ,in a similar way1 the theory furnishes an explanation of the abnormal lowering of the freezing point of electrolytes4 ,the theory of electrolytic dissociation and electrolysis4 ,the changes taking place during electrolysis harmonize very completely with the theory of dissociation4 ,this will become clear from a study of the following examples4 ,illustration3 ,fig4 #cb #a4 ,electrolysis of sodium chloride4 ,fig4 #cb represents a vessel in which the electrolyte is a solution of sodium chloride 7,na,cl74 ,according to the dissociation theory the molecules of sodium chloride dissociate into the ions ,na and ,cl-4 ,the ,na ions are attracted to the cathode owing to its large negative charge4 ,on coming into contact with the cathode1 the ,na ions give up their positive charge and are then ordinary sodium atoms4 ,they immediately decompose the water according to the equation ,na ,h#b,o ,na,o,h ,h1 and hydrogen is evolved about the cathode4 ,the chlorine ions on being discharged at the anode in similar manner may either be given off as chlorine gas1 or may attack the water1 as represented in the equation #b;,cl ,h#b,o #b;,h,cl ,o4 #b4 ,electrolysis of water4 ,the reason for the addition of sulphuric acid to water in the preparation of oxygen and hydrogen by electrolysis will now be clear4 ,water itself is not an electrolyte to an appreciable extent2 that is1 it does not form enough ions to carry a current4 ,sulphuric acid dissolved in water is an electrolyte1 and dissociates into the ions #b ,h and ,,so#d--4 ,in the process of electrolysis of the solution1 the hydrogen ions travel to the cathode1 and on being discharged escape as hydrogen gas4 ,the ,,so#d ions1 when discharged at the anode1 act upon water1 setting free oxygen and once more forming sulphuric acid3 ,,so#d ,h#b,o ,h#b,,so#d ,o4 ,the sulphuric acid can again dissociate and the process repeat itself as long as any water is left4 ,hence the hydrogen and oxygen set free in the electrolysis of water really come directly from the acid but indirectly from the water4 #c4 ,electrolysis of sodium sulphate4 ,in a similar way1 sodium sulphate 7,na#b,,so#d71 when in solution1 gives the ions #b ,na and ,,so#d--4 ,on being discharged1 the sodium atoms decompose water about the cathode1 as in the case of sodium chloride1 while the ,,so#d ions when discharged at the anode decompose the water1 as represented in the equation ,,so#d ,h#b,o ,h#b,,so#d ,o ,illustration3 ,fig4 #cc ,that new substances are formed at the cathode and anode may be shown in the following way4 ,a ,u-tube1 such as is represented in ,fig4 #cc1 is partially filled with a solution of sodium sulphate1 and the liquid in one arm is colored with red litmus1 that in the other with blue litmus4 ,an electrode placed in the red solution is made to serve as cathode1 while one in the blue solution is made the anode4 ,on allowing the current to pass1 the blue solution turns red1 while the red solution turns blue4 ,these are exactly the changes which would take place if sodium hydroxide and sulphuric acid were to be set free at the electrodes1 as required by the theory4 ,the properties of electrolytes depend upon the ions present4 ,when a substance capable of dissociating into ions is dissolved in water1 the properties of the solution will depend upon two factors3 7#a7 the ions formed from the substance2 7#b7 the undissociated molecules4 ,since the ions are usually more active chemically than the molecules1 most of the chemical properties of an electrolyte are due to the ions rather than to the molecules4 ,the solutions of any two substances which give the same ion will have certain properties in common4 ,thus all solutions containing the copper ion 7,cu7 are blue1 unless the color is modified by the presence of ions or molecules having some other color4 ,,exercises #a4 ,distinguish clearly between the following terms3 electrolysis1 electrolyte1 electrolytic dissociation1 ions1 solute1 solvent1 solution1 saturated solution1 and supersaturated solution4 #b4 ,why does the water from some natural springs effervesce8 #c4 7a7 ,why does not the water of the ocean freeze8 7b7 ,why will ice and salt produce a lower temperature than ice alone8 #d4 ,why does shaking or stirring make a solid dissolve more rapidly in a liquid8 #e4 ,by experiment it was found that a certain volume of water was saturated at #ajj with #aad g4 of potassium nitrate4 ,on cooling to #j a portion of the substance crystallized4 7a7 ,how many grams of the substance remained in solution8 7b7 ,what was the strength of the solution at #ah8 7c7 ,how much water had been used in the experiment8 #f4 7a7 #aj g4 of common salt were dissolved in water and the solution evaporated to dryness2 what weight of solid was left8 7b7 #aj g4 of zinc were dissolved in hydrochloric acid and the solution evaporated to dryness2 what weight of solid was left8 #g4 ,account for the fact that sugar sometimes deposits from molasses1 even when no evaporation has taken place4 #h4 7a7 ,from the standpoint of the theory of electrolytic dissociation1 write the simple equation for a dilute solution of copper sulphate 7,cu,s,o#d72 this solution is blue4 7b7 ,in the same manner1 write one for sodium sulphate2 this solution is colorless4 7c7 ,how would you account for the color of the copper sulphate solution8 #i4 7a7 ,as in the preceding exercise1 write a simple equation for a dilute solution of copper chloride 7,cu,cl#b72 this solution is blue4 7b7 ,in the same manner1 write one for sodium chloride2 this solution is colorless4 ,to what is the blue color due8 #aj4 ,what component is present in concentrated sulphuric acid that is almost wanting in very dilute sulphuric acid8 #aa4 ,why will vegetables cook faster when boiled in strong salt water than when boiled in pure water8 #ab4 ,how do you explain the foaming of soda water8 ,,chapter ,x ,,acids1 ,,bases1 ,,and ,,salts2 ,,neutralization ,acids1 bases1 and salts4 ,the three classes of compounds known respectively as acids1 bases1 and salts include the great majority of the compounds with which we shall have to deal4 ,it is important1 therefore1 for us to consider each of these classes in a systematic way4 ,the individual members belonging to each class will be discussed in detail in the appropriate places1 but a few representatives of each class will be described in this chapter with special reference to the common properties in accordance with which they are classified4 ,the familiar acids4 ,hydrochloric acid is a gas composed of hydrogen and chlorine1 and has the formula ,h,cl4 ,the substance is very soluble in water1 and it is this solution which is usually called hydrochloric acid4 ,nitric acid is a liquid composed of hydrogen1 nitrogen1 and oxygen1 having the formula ,,hno#c4 ,as sold commercially it is mixed with about #cb of water4 ,sulphuric acid1 whose composition is represented by the formula ,h#b,,so#d1 is an oily liquid nearly twice as heavy as water1 and is commonly called oil of vitriol4 ,characteristics of acids4 7#a7 ,all acids contain hydrogen4 7#b7 ,when dissolved in water the molecules of the acid dissociate into two kinds of ions4 ,one of these is always hydrogen and is the cation 771 while the other consists of the remainder of the molecule and is the anion 7-74 7#c7 ,the solution tastes sour4 7#d7 ,it has the power to change the color of certain substances called indicators4 ,thus blue litmus is changed to red1 and yellow methyl orange is changed to red4 ,since all acids produce hydrogen cations1 while the anions of each are different1 the properties which all acids have in common when in solution1 such as taste and action on indicators1 must be attributed to the hydrogen ions4 ,,definition3 ,an acid is a substance which produces hydrogen ions when dissolved in water or other dissociating liquids4 ,undissociated acids4 ,when acids are perfectly free from water1 or are dissolved in liquids like benzene which do not have the power of dissociating them into ions1 they should have no real acid properties4 ,this is found to be the case4 ,under these circumstances they do not affect the color of indicators or have any of the properties characteristic of acids4 ,the familiar bases4 ,the bases most used in the laboratory are sodium hydroxide 7,na,o,h71 potassium hydroxide 7,,koh71 and calcium hydroxide 7,ca7,,oh7#b74 ,these are white solids1 soluble in water1 the latter sparingly so4 ,some bases are very difficultly soluble in water4 ,the very soluble ones with most pronounced basic properties are sometimes called the alkalis4 ,characteristics of bases4 7#a7 ,all bases contain hydrogen and oxygen4 7#b7 ,when dissolved in water the molecules of the base dissociate into two kinds of ions4 ,one of these is always composed of oxygen and hydrogen and is the anion4 ,it has the formula ,,oh and is called the hydroxyl ion4 ,the remainder of the molecule1 which usually consists of a single atom1 is the cation4 7#c7 ,the solution of a base has a soapy feel and a brackish taste4 7#d7 ,it reverses the color change produced in indicators by acids1 turning red litmus blue1 and red methyl orange yellow4 ,since all bases produce hydroxyl anions1 while the cations of each are different1 the properties which all bases have in common when in solution must be due to the hydroxyl ions4 ,,definition3 ,a base is a substance which produces hydroxyl ions when dissolved in water or other dissociating liquids4 ,undissociated bases4 ,bases1 in the absence of water or when dissolved in liquids which do not dissociate them1 should have none of the properties characteristic of this class of substances4 ,this has been found to be the case4 ,for example1 they have no effect upon indicators under these circumstances4 ,neutralization4 ,when an acid and a base are brought together in solution in proper proportion1 the characteristic properties of each disappear4 ,the solution tastes neither sour nor brackish2 it has no effect upon indicators4 ,there can therefore be neither hydrogen nor hydroxyl ions present in the solution4 ,a study of reactions of this kind has shown that the hydrogen ions of the acid combine with the hydroxyl ions of the base to form molecules of water1 water being a substance which is not appreciably dissociated into ions4 ,this action of an acid on a base is called neutralization4 ,the following equations express the neutralization of the three acids by three bases1 water being formed in each case4 ,na1 ,,oh- ,h1 ,cl- ,na1 ,cl- ,h#b,o4 ,k1 ,,oh- ,h1 ,,no#c- ,k1 ,,no#c- ,h#b,o4 ,ca1 7,,oh7#b-- ,h#b1 ,,so#d-- ,ca1 ,,so#d-- #b;,h#b,o4 ,,definition3 ,neutralization consists in the union of the hydrogen ion of an acid with the hydroxyl ion of a base to form water4 ,salts4 ,it will be noticed that in neutralization the anion of the acid and the cation of the base are not changed4 ,if1 however1 the water is expelled by evaporation1 these two ions slowly unite1 and when the water becomes saturated with the substance so produced1 it separates in the form of a solid called a salt4 ,,definition3 ,a salt is a substance formed by the union of the anion of an acid with the cation of a base4 ,characteristics of salts4 7#a7 ,from the definition of a salt it will be seen that there is no element or group of elements which characterize salts4 7#b7 ,salts as a class have no peculiar taste4 7#c7 ,in the absence of all other substances they are without action on indicators4 7#d7 ,when dissolved in water they form two kinds of ions4 ,heat of neutralization4 ,if neutralization is due to the union of hydrogen ions with hydroxyl ions1 and nothing more1 it follows that when a given weight of water is formed in neutralization1 the heat set free should always be the same1 no matter from what acid and base the two kinds of ions have been supplied4 ,careful experiments have shown that this is the case1 provided no other reactions take place at the same time4 ,when #ah;g4 of water are formed in neutralization1 #ac1gjj cal4 of heat are set free4 ,this is represented in the equations ,na1 ,,oh- ,h1 ,cl- ,na1 ,cl- ,h#b,o #ac1gjj cal4 ,k1 ,,oh- ,h1 ,,no#c- ,k1 ,,no#c- ,h#b,o #ac1gjj cal4 ,ca1 7,,oh7#b-- ,h#b1 ,,so#d-- ,ca1 ,,so#d-- #b;,h#b,o #b #ac1gjj cal4 ,neutralization a quantitative act4 ,since neutralization is a definite chemical act1 each acid will require a perfectly definite weight of each base for its neutralization4 ,for example1 a given weight of sulphuric acid will always require a definite weight of sodium hydroxide1 in accordance with the equation ,h#b1 ,,so#d #b,na1 ,,oh ,na#b1 ,,so#d #b;,h#b,o4 ,determination of the ratio in neutralization4 ,the quantities of acid and base required in neutralization may be determined in the following way4 ,dilute solutions of the two substances are prepared1 the sulphuric acid being placed in one of the burettes 7,fig4 #cd7 and the sodium hydroxide in the other4 ,the levels of the two liquids are then brought to the zero marks of the burettes by means of the stopcocks4 ,a measured volume of the acid is drawn off into a beaker1 a few drops of litmus solution added1 and the sodium hydroxide is run in drop by drop until the red litmus just turns blue4 ,the volume of the sodium hydroxide consumed is then noted4 ,if the concentrations of the two solutions are known1 it is easy to calculate what weight of sodium hydroxide is required to neutralize a given weight of sulphuric acid4 ,by evaporating the neutralized solution to dryness1 the weight of the sodium sulphate formed can be determined directly4 ,experiment shows that the weights are always in accordance with the equation in the preceding paragraph4 ,illustration3 ,fig4 #cd ,extent of dissociation4 ,the question will naturally arise1 ,when an acid1 base1 or salt dissolves in water1 do all the molecules dissociate into ions1 or only a part of them8 ,the experiments by which this question can be answered cannot be described here4 ,it has been found1 however1 that only a fraction of the molecules dissociate4 ,the percentage which will dissociate in a given case depends upon several conditions1 the chief of which are3 7#a7 ,the concentration of the solution4 ,in concentrated solutions only a very small percentage of dissociation occurs4 ,as the solution is diluted the percentage increases1 and in very dilute solutions it may be very large1 though it is never complete in any ordinary solution4 7#b7 ,the nature of the dissolved compound4 ,at equal concentrations substances differ much among themselves in the percentage of dissociation4 ,the great majority of salts are about equally dissociated4 ,acids and bases1 on the contrary1 show great differences4 ,some are freely dissociated1 while others are dissociated to but a slight extent4 ,strength of acids and bases4 ,since acid and basic properties are due to hydrogen and hydroxyl ions respectively1 the acid or base which will produce the greatest percentage of these ions at a given concentration must be regarded as the strongest representative of its class4 ,the acids and bases described in the foregoing paragraphs are all quite strong4 ,in #aj solutions they are dissociated to about #ej1 and this is also approximately the extent to which most salts are dissociated at this same concentration4 ,partial neutralization4 #a4 ,basic salts4 ,the chemical action between an acid and a base is not always as complete as has been represented in the foregoing paragraphs4 ,for example1 if the base magnesium hydroxide 7,mg7,,oh7#b7 and hydrochloric acid 7,h,cl7 are brought together in the ratio of an equal number of molecules of each1 there will be only half enough hydrogen ions for the hydroxyl ions present4 ,mg1 7,,oh7#b ,h1 ,cl ,mg1 ,,oh1 ,cl ,h#b,o4 ,magnesium1 hydroxyl1 and chlorine ions are left at the close of the reaction1 and under the proper conditions unite to form molecules of the compound ,mg7,,oh7,cl4 ,this compound1 when dissolved1 can form hydroxyl ions and therefore possesses basic properties2 it can also form the ions of a salt 7,mg and ,cl71 and has properties characteristic of salts4 ,substances of this kind are called basic salts4 ,,definition3 ,a basic salt is a substance which can give the ions both of a base and of a salt when dissolved in water4 #b4 ,acid salts4 ,in a similar way1 when sulphuric acid and sodium hydroxide are brought together in the ratio of equal numbers of the molecules of each1 it is possible to have a reaction expressed by the equation ,na1 ,,oh ,h#b1 ,,so#d ,na1 ,h1 ,,so#d ,h#b,o4 ,the ions remaining after all the hydroxyl ions have been used up are those of an acid 7,h7 and those of a salt 7,na and ,,so#d74 ,these unite to form the substance ,na,h,s,o#d1 and as the solution becomes saturated with this substance through evaporation1 it separates in the form of crystals4 ,in solution this substance can give hydrogen ions1 and therefore possesses acid properties2 it can also give the ions characteristic of a salt4 ,it is therefore called an acid salt4 ,,definition3 ,an acid salt is one which can give the ions of an acid and of a salt when in solution4 #c4 ,normal salts4 ,salts which are the products of complete neutralization1 such as ,na#b,,so#d1 and which in solution can give neither hydrogen nor hydroxyl ions1 but only the ions of a salt1 are called normal salts to distinguish them from acid and basic salts4 ,methods of expressing reactions between compounds in solution4 ,chemical equations representing reactions between substances in solution may represent the details of the reaction1 or they may simply indicate the final products formed4 ,in the latter case the formation of ions is not indicated4 ,thus1 if we wish to call attention to the details of the reaction between sodium hydroxide and hydrochloric acid in solution1 the equation is written as follows3 ,na1 ,,oh- ,h1 ,cl- ,na1 ,cl- ,h#b,o4 ,on the other hand1 if we wish simply to represent the final products formed1 the following is used4 ,na,o,h ,h,cl ,na,cl ,h#b,o4 ,both of these methods will therefore be used3 ,radicals4 ,it has been emphasized that the hydroxyl group 7,,oh7 always forms the anion of a base1 while the group ,,no#c forms the anion of nitric acid and sodium nitrate2 the group ,,so#d1 the anion of sulphuric acid and calcium sulphate4 ,a group of elements which in this way constitutes a part of a molecule1 acting as a unit in a chemical change1 or forming ions in solution1 is called a radical4 ,some of these radicals have been given special names1 the names signifying the elements present in the radical4 ,thus we have the hydroxyl radical 7,,oh7 and the nitrate radical 7,,no#c74 ,,definition3 ,a radical is a group of elements forming part of a molecule1 and acting as a unit in chemical reactions4 ,names of acids1 bases1 and salts4 ,since acids1 bases1 and salts are so intimately related to each other1 it is very advantageous to give names to the three classes in accordance with some fixed system4 ,the system universally adopted is as follows3 ,naming of bases4 ,all bases are called hydroxides4 ,they are distinguished from each other by prefixing the name of the element which is in combination with the hydroxyl group4 ,examples3 sodium hydroxide 7,na,o,h72 calcium hydroxide 7,ca7,,oh7#b72 copper hydroxide 7,cu7,,oh7#b74 ,naming of acids4 ,the method of naming acids depends upon whether the acid consists of two elements or three4 #a4 ,binary acids4 ,acids containing only one element in addition to hydrogen are called binary acids4 ,they are given names consisting of the prefix hydro-1 the name of the second element present1 and the termination -ic4 ,examples3 hydrochloric acid 7,h,cl72 hydrosulphuric acid 7,h#b,s74 #b4 ,ternary acids4 ,in addition to the two elements present in binary acids1 the great majority of acids also contain oxygen4 ,they therefore consist of three elements and are called ternary acids4 ,it usually happens that the same three elements can unite in different proportions to make several different acids4 ,the most familiar one of these is given a name ending in the suffix -ic1 while the one with less oxygen is given a similar name1 but ending in the suffix -ous4 ,examples3 nitric acid 7,,hno#c72 nitrous acid 7,,hno#b74 ,in cases where more than two acids are known1 use is made of prefixes in addition to the two suffixes -ic and -ous4 ,thus the prefix per- signifies an acid still richer in oxygen2 the prefix hypo- signifies one with less oxygen4 ,naming of salts4 ,a salt derived from a binary acid is given a name consisting of the names of the two elements composing it1 with the termination -ide4 ,example3 sodium chloride 7,na,cl74 ,all other binary compounds are named in the same way4 ,a salt of a ternary acid is named in accordance with the acid from which it is derived4 ,a ternary acid with the termination -ic gives a salt with the name ending in -ate1 while an acid with termination -ous gives a salt with the name ending in -ite4 ,the following table will make the application of these principles clear3 ,,acids ,,symbol ,,salts ,,symbol ,hydrochloric ,h,cl ,sodium chloride ,na,cl ,hypochlorous ,h,cl,o ,sodium hypochlorite ,na,cl,o ,chlorous ,h,cl,o#b ,sodium chlorite ,na,cl,o#b ,chloric ,h,cl,o#c ,sodium chlorate ,na,cl,o#c ,perchloric ,h,cl,o#d ,sodium perchlorate ,na,cl,o#d ,,exercises #a4 #be cc4 of a solution containing #dj g4 of sodium hydroxide per liter was found to neutralize #be cc4 of a solution of hydrochloric acid4 ,what was the strength of the acid solution8 #b4 ,after neutralizing a solution of sodium hydroxide with nitric acid1 there remained after evaporation #ajj g4 of sodium nitrate4 ,how much of each substance had been used8 #c4 ,a solution contains #ah g4 of hydrochloric acid per #ajj cc4 ,it required #be cc4 of this solution to neutralize #cj cc4 of a solution of sodium hydroxide4 ,what was the strength of the sodium hydroxide solution in parts per hundred8 #d4 ,when perfectly dry sulphuric acid is treated with perfectly dry sodium hydroxide1 no chemical change takes place4 ,explain4 #e4 ,when cold1 concentrated sulphuric acid is added to zinc1 no change takes place4 ,recall the action of dilute sulphuric acid on the same metal4 ,how do you account for the difference8 #f4 ,a solution of hydrochloric acid in benzene does not conduct the electric current4 ,when this solution is treated with zinc1 will hydrogen be evolved8 ,explain4 #g4 7a7 ,write equation for preparation of hydrogen from zinc and dilute sulphuric acid4 7b7 ,rewrite the same equation from the standpoint of the theory of electrolytic dissociation1 7c7 ,subtract the common ,,so#d ion from both members of the equation1 7d7 ,from the resulting equation1 explain in what the preparation of hydrogen consists when examined from the standpoint of this theory4 #h4 ,in the same manner as in the preceding exercise1 explain in what the action of sodium on water to give hydrogen consists4 ,,chapter ,,xi ,,valence ,definition of valence4 ,a study of the formulas of various binary compounds shows that the elements differ between themselves in the number of atoms of other elements which they are able to hold in combination4 ,this is illustrated in the formulas ,h,cl1 ,h#b,o1 ,h#c,n1 ,h#d;,c4 7hydrochloric acid7 7water7 7ammonia7 7marsh gas7 ,it will be noticed that while one atom of chlorine combines with one atom of hydrogen1 an atom of oxygen combines with two1 an atom of nitrogen with three1 one of carbon with four4 ,the number which expresses this combining ratio between atoms is a definite property of each element and is called its valence4 ,,definition3 ,the valence of an element is that property which determines the number of the atoms of another element which its atom can hold in combination4 ,valence a numerical property4 ,valence is therefore merely a numerical relation and does not convey any information in regard to the intensity of the affinity between atoms4 ,judging by the heat liberated in their union1 oxygen has a far stronger affinity for hydrogen than does nitrogen1 but an atom of oxygen can combine with two atoms only of hydrogen1 while an atom of nitrogen can combine with three4 ,measure of valence4 ,in expressing the valence of an element we must select some standard for comparison1 just as in the measurement of any other numerical quantity4 ,it has been found that an atom of hydrogen is never able to hold in combination more than one atom of any other element4 ,hydrogen is therefore taken as the standard1 and other elements are compared with it in determining their valence4 ,a number of other elements are like hydrogen in being able to combine with at most one atom of other elements1 and such elements are called univalent4 ,among these are chlorine1 iodine1 and sodium4 ,elements such as oxygen1 calcium1 and zinc1 which can combine with two atoms of hydrogen or other univalent elements1 are said to be divalent4 ,similarly1 we have trivalent1 tetravalent1 pentavalent elements4 ,none have a valence of more than #h4 ,indirect measure of valence4 ,many elements1 especially among the metals1 do not readily form compounds with hydrogen1 and their valence is not easy to determine by direct comparison with the standard element4 ,these elements1 however1 combine with other univalent elements1 such as chlorine1 and their valence can be determined from the compounds so formed4 ,variable valence4 ,many elements are able to exert different valences under differing circumstances4 ,thus we have the compounds ,cu#b,o and ,cu,o1 ,,co and ,,co#b1 ,fe,cl#b and ,fe,cl#c4 ,it is not always possible to assign a fixed valence to an element4 ,nevertheless each element tends to exert some normal valence1 and the compounds in which it has a valence different from this are apt to be unstable and easily changed into compounds in which the valence of the element is normal4 ,the valences of the various elements will become familiar as the elements are studied in detail4 ,valence and combining ratios4 ,when elements combine to form compounds1 the ratio in which they combine will be determined by their valences4 ,in those compounds which consist of two elements directly combined1 the union is between such numbers of the two atoms as have equal valences4 ,elements of the same valence will therefore combine atom for atom4 ,designating the valence of the atoms by ,roman numerals placed above their symbols1 we have the formulas ,,ii ,,ii ,,ii ,,iii ,,iii ,,iv ,,iv ,h,cl1 ,zn,o1 ,,bn1 ,c,si4 ,a divalent element1 on the other hand1 will combine with two atoms of a univalent element4 ,thus we have ,,ii ,,ii ,,ii ,,ii ,zn,cl#b and ,h#b,o 7the numerals above each symbol representing the sum of the valences of the atoms of the element present74 ,a trivalent atom will combine with three atoms of a univalent element1 as in the compound ,,iii ,,iii ,h#c,n4 ,if a trivalent element combines with a divalent element1 the union will be between two atoms of the trivalent element and three of the divalent element1 since these numbers are the smallest which have equal valences4 ,thus the oxide of the trivalent metal aluminium has the formula ,al#b,o#c4 ,finally one atom of a tetravalent element such as carbon will combine with four atoms of a univalent element1 as in the compound ,,ch#d1 or with two atoms of a divalent element1 as in the compound ,,co#b4 ,we have no knowledge as to why elements differ in their combining power1 and there is no way to determine their valences save by experiment4 ,valence and the structure of compounds4 ,compounds will be met from time to time which are apparent exceptions to the general statements just made in regard to valence4 ,thus1 from the formula for hydrogen dioxide 7,h#b,o#b71 it might be supposed that the oxygen is univalent2 yet it is certainly divalent in water 7,h#b,o74 ,that it may also be divalent in ,h#b,o#b may be made clear as follows3 ,the unit valence of each element may be represented graphically by a line attached to its symbol4 ,univalent hydrogen and divalent oxygen will then have the symbols ,h- and -,o-4 ,when atoms combine1 each unit valence of one atom combines with a unit valence of another atom4 ,thus the composition of water may be expressed by the formula ,h-,o-,h1 which is meant to show that each of the unit valences of oxygen is satisfied with the unit valence of a single hydrogen atom4 ,the chemical conduct of hydrogen dioxide leads to the conclusion that the two oxygen atoms of its molecule are in direct combination with each other1 and in addition each is in combination with a hydrogen atom4 ,this may be expressed by the formula ,h-,o-,o-,h4 ,the oxygen in the compound is therefore divalent1 just as it is in water4 ,it will thus be seen that the structure of a compound must be known before the valences of the atoms making up the compound can be definitely decided upon4 ,such formulas as ,h-,o-,h and ,h-,o-,o-,h are known as structural formulas1 because they are intended to show what is known in regard to the arrangement of the atoms in the molecules4 ,valence and the replacing power of atoms4 ,just as elements having the same valence combine with each other atom for atom1 so if they replace each other in a chemical reaction they will do so in the same ratio4 ,this is seen in the following equations1 in which a univalent hydrogen atom is replaced by a univalent sodium atom3 ,na,o,h ,h,cl ,na,cl ,h#b,o4 #b,na,o,h ,h#b,,so#d ,na#b,,so#d #b;,h#b,o4 ,na ,h#b,o ,na,o,h ,h4 ,similarly1 one atom of divalent calcium will replace two atoms of univalent hydrogen or one of divalent zinc3 ,ca7,,oh7#b #b ,h,cl ,ca,cl#b #b;,h#b,o4 ,ca,cl#b ,zn,s,o#d ,ca,s,o#d ,zn,cl#b4 ,in like manner1 one atom of a trivalent element will replace three of a univalent element1 or two atoms will replace three atoms of a divalent element4 ,valence and its applications to formulas of salts4 ,while the true nature of valence is not understood and many questions connected with the subject remain unanswered1 yet many of the main facts are of much help to the student4 ,thus the formula of a salt1 differs from that of the acid from which it is derived in that the hydrogen of the acid has been replaced by a metal4 ,if1 then1 it is known that a given metal forms a normal salt with a certain acid1 the formula of the salt can at once be determined if the valence of the metal is known4 ,since sodium is univalent1 the sodium salts of the acids ,h,cl and ,h#b,,so#d will be respectively ,na,cl and ,na#b,,so#d4 ,one atom of divalent zinc will replace #b hydrogen atoms1 so that the corresponding zinc salts will be ,zn,cl#b and ,zn,s,o#d4 ,the formula for aluminium sulphate is somewhat more difficult to determine4 ,aluminium is trivalent1 and the simplest ratio in which the aluminium atom can replace the hydrogen in sulphuric acid is #b atoms of aluminium 7#f valences7 to #c molecules of sulphuric acid 7#f hydrogen atoms74 ,the formula of the sulphate will then be ,al#b7,,so#d7c4 ,valence and its application to equation writing4 ,it will be readily seen that a knowledge of valence is also of very great assistance in writing the equations for reactions of double decomposition4 ,thus1 in the general reaction between an acid and a base1 the essential action is between the univalent hydrogen ion and the univalent hydroxyl ion4 ,the base and the acid must always be taken in such proportions as to secure an equal number of each of these ions4 ,thus1 in the reaction between ferric hydroxide 7,fe7,,oh7#c7 and sulphuric acid 7,h#b,,so#d71 it will be necessary to take #b molecules of the former and #c of the latter in order to have an equal number of the two ions1 namely1 #f4 ,the equation will then be #b;,fe7,,oh7#c #c;,h#b,,so#d ,fe#b7,,so#d7c #f;,h#b,o4 ,under certain conditions the salts ,al#b7,,so#d7c and ,ca,cl#b undergo double decomposition1 the two metals1 aluminium and calcium1 exchanging places4 ,the simplest ratio of exchange in this case is #b atoms of aluminium 7#f valences7 and #c atoms of calcium 7#f valences74 ,the reaction will therefore take place between #a molecule of ,al#b7,,so#d7c and #c of ,ca,cl#b1 and the equation is as follows3 ,al#b7,,so#d7c #c ,ca,cl#b #c;,ca,s,o#d #b;,al,cl#c4 ,,exercises #a4 ,sodium1 calcium1 and aluminium have valences of #a1 #b1 and #c respectively2 write the formulas of their chlorides1 sulphates1 and phosphates 7phosphoric acid ,h#c,,po#d71 on the supposition that they form salts having the normal composition4 #b4 ,iron forms one series of salts in which it has a valence of #b1 and another series in which it has a valence of #c2 write the formulas for the two chlorides of iron1 also for the two sulphates1 on the supposition that these have the normal composition4 #c4 ,write the equation representing the neutralization of each of the following bases by each of the acids whose formulas are given3 ,na,o,h ,h,cl ,ba7,,oh7#b ,h#b,,so#d ,al7,,oh7#c ,h#c,,po#d #d4 ,silver acts as a univalent element and calcium as a divalent element in the formation of their respective nitrates and chlorides4 7a7 ,write the formula for silver nitrate2 for calcium chloride4 7b7 ,when solutions of these two salts are mixed1 the two metals1 silver and calcium1 exchange places2 write the equation for the reaction4 #e4 ,antimony acts as a trivalent element in the formation of a chloride4 7a7 ,what is the formula for antimony chloride8 7b7 ,when hydrosulphuric acid 7,h#b,s7 is passed into a solution of this chloride the hydrogen and antimony exchange places2 write the equation for the reaction4 #f4 ,lead has a valence of #b and iron of #c in the compounds known respectively as lead nitrate and ferric sulphate4 7a7 ,write the formulas for these two compounds4 7b7 ,when their solutions are mixed the two metals exchange places2 write the equation for the reaction4 ,,chapter ,,xii ,,compounds ,,of ,,nitrogen ,occurrence4 ,as has been stated in a former chapter1 nitrogen constitutes a large fraction of the atmosphere4 ,the compounds of nitrogen1 however1 cannot readily be obtained from this source1 since at any ordinary temperature nitrogen is able to combine directly with very few of the elements4 ,in certain forms of combination nitrogen occurs in the soil from which it is taken up by plants and built into complex substances composed chiefly of carbon1 hydrogen1 oxygen1 and nitrogen4 ,animals feeding on these plants assimilate the nitrogenous matter1 so that this element is an essential constituent of both plants and animals4 ,decomposition of organic matter by bacteria4 ,when living matter dies and undergoes decay complicated chemical reactions take place1 one result of which is that the nitrogen of the organic matter is set free either as the element nitrogen1 or in the form of simple compounds1 such as ammonia 7,,nh#c7 or oxides of nitrogen4 ,experiment has shown that all such processes of decay are due to the action of different kinds of bacteria1 each particular kind effecting a different change4 ,decomposition of organic matter by heat4 ,when organic matter is strongly heated decomposition into simpler substances takes place in much the same way as in the case of bacterial decomposition4 ,coal is a complex substance of vegetable origin1 consisting largely of carbon1 but also containing hydrogen1 oxygen1 and nitrogen4 ,when this is heated in a closed vessel so that air is excluded1 about one seventh of the nitrogen is converted into ammonia1 and this is the chief source from which ammonia and its compounds are obtained4 ,,compounds ,,of ,,nitrogen ,,with ,,hydrogen ,ammonia 7,,nh#c74 ,several compounds consisting exclusively of nitrogen and hydrogen are known1 but only one1 ammonia1 need be considered here4 ,preparation of ammonia4 ,ammonia is prepared in the laboratory by a different method from the one which is used commercially4 #a4 ,laboratory method4 ,in the laboratory ammonia is prepared from ammonium chloride1 a compound having the formula ,,nh#d;,cl1 and obtained in the manufacture of coal gas4 ,as will be shown later in the chapter1 the group ,,nh#d in this compound acts as a univalent radical and is known as ammonium4 ,when ammonium chloride is warmed with sodium hydroxide1 the ammonium and sodium change places1 the reaction being expressed in the following equation4 ,,nh#d;,cl ,na,o,h ,na,cl ,,nh#d,,oh4 ,the ammonium hydroxide 7,,nh#d,,oh7 so formed is unstable and breaks down into water and ammonia4 ,,nh#d,,oh ,,nh#c ,h#b,o4 ,calcium hydroxide 7,ca7,,oh7#b7 is frequently used in place of the more expensive sodium hydroxide1 the equations being #b,,nh#d;,cl ,ca7,,oh7#b ,ca,cl#b #b,,nh#d,,oh1 #b,,nh#d,,oh #b;,h#b,o #b,,nh#c4 ,in the preparation1 the ammonium chloride and calcium hydroxide are mixed together and placed in a flask arranged as shown in ,fig4 #ce4 ,the mixture is gently warmed1 when ammonia is evolved as a gas and is collected by displacement of air4 ,illustration3 ,fig4 #ce #b4 ,commercial method4 ,nearly all the ammonia of commerce comes from the gasworks4 ,ordinary illuminating gas is made by distilling coal1 as will be explained later1 and among the products of this distillation a solution of ammonia in water is obtained4 ,this solution1 known as gas liquor1 contains not only ammonia but other soluble substances4 ,most of these combine chemically with lime1 while ammonia does not2 if then lime is added to the gas liquor and the liquor is heated1 the ammonia is driven out from the mixture4 ,it may be dissolved again in pure1 cold water1 forming aqua ammonia1 or the ammonia water of commerce4 ,preparation from hydrogen and nitrogen4 ,when electric sparks are passed for some time through a mixture of hydrogen and nitrogen1 a small percentage of the two elements in the mixture is changed into ammonia4 ,the action soon ceases1 however1 for the reason that ammonia is decomposed by the electric discharge4 ,the reaction expressed in the equation ,n #c;,h ,,nh#c can therefore go in either direction depending upon the relative quantities of the substances present4 ,this recalls the similar change from oxygen into ozone1 which soon ceases because the ozone is in turn decomposed into oxygen4 ,physical properties4 ,under ordinary conditions ammonia is a gas whose density is #j4ei4 ,it is therefore little more than half as heavy as air4 ,it is easily condensed into a colorless liquid1 and can now be purchased in liquid form in steel cylinders4 ,the gas is colorless and has a strong1 suffocating odor4 ,it is extremely soluble in water1 #a l4 of water at #j and #gfj mm4 pressure dissolving #aadh l4 of the gas4 ,in dissolving this large volume of gas the water expands considerably1 so that the density of the solution is less than that of water1 the strongest solutions having a density of #j4hh4 ,chemical properties4 ,ammonia will not support combustion1 nor will it burn under ordinary conditions4 ,in an atmosphere of oxygen it burns with a feeble1 yellowish flame4 ,when quite dry it is not a very active substance1 but when moist it combines with a great many substances1 particularly with acids4 ,uses4 ,it has been stated that ammonia can be condensed to a liquid by the application of pressure4 ,if the pressure is removed from the liquid so obtained1 it rapidly passes again into the gaseous state and in so doing absorbs a large amount of heat4 ,advantage is taken of this fact in the preparation of artificial ice4 ,large quantities of ammonia are also used in the preparation of ammonium compounds4 ,the manufacture of artificial ice4 ,fig4 #cf illustrates the method of preparing artificial ice4 ,the ammonia gas is liquefied in the pipes ,x by means of the pump ,y4 ,the heat generated is absorbed by water flowing over the pipes4 ,the pipes lead into a large brine tank1 a cross section of which is shown in the figure4 ,into the brine 7concentrated solution of common salt7 contained in this tank are dipped the vessels ,a1 ,b1 ,c1 filled with pure water4 ,the pressure is removed from the liquid ammonia as it passes into the pipes immersed in the brine1 and the heat absorbed by the rapid evaporation of the liquid lowers the temperature of the brine below zero4 ,the water in ,a1 ,b1 ,c is thereby frozen into cakes of ice4 ,the gaseous ammonia resulting from the evaporation of the liquid ammonia is again condensed1 so that the process is continuous4 ,illustration ,fig4 #cf ,ammonium hydroxide 7,,nh#d,,oh74 ,the solution of ammonia in water is found to have strong basic properties and therefore contains hydroxyl ions4 ,it turns red litmus blue2 it has a soapy feel2 it neutralizes acids1 forming salts with them4 ,it seems probable1 therefore1 that when ammonia dissolves in water it combines chemically with it according to the equation ,,nh#c ,h#b,o ,,nh#d,,oh1 and that it is the substance ,,nh#d,,oh1 called ammonium hydroxide1 which has the basic properties1 dissociating into the ions ,,nh#d and ,,oh4 ,ammonium hydroxide has never been obtained in a pure state4 ,at every attempt to isolate it the substance breaks up into water and ammonia1-- ,,nh#d,,oh ,,nh#c ,h#b,o4 ,the ammonium radical4 ,the radical ,,nh#d plays the part of a metal in many chemical reactions and is called ammonium4 ,the ending -ium is given to the name to indicate the metallic properties of the substance1 since the names of the metals in general have that ending4 ,the salts formed by the action of the base ammonium hydroxide on acids are called ammonium salts4 ,thus1 with hydrochloric acid1 ammonium chloride is formed in accordance with the equation ,,nh#d,,oh ,h,cl ,,nh#d;,cl ,h#b,o4 ,similarly1 with nitric acid1 ammonium nitrate 7,,nh#d,,no#c7 is formed1 and with sulphuric acid1 ammonium sulphate 77,,nh#d7b,s#jd74 ,it will be noticed that in the neutralization of ammonium hydroxide by acids the group ,,nh#d replaces one hydrogen atom of the acid1 just as sodium does4 ,the group therefore acts as a univalent metal4 ,combination of nitrogen with hydrogen by volume4 ,under suitable conditions ammonia can be decomposed into nitrogen and hydrogen by passing electric sparks through the gas4 ,accurate measurement has shown that when ammonia is decomposed1 two volumes of the gas yield one volume of nitrogen and three volumes of hydrogen4 ,consequently1 if the two elements were to combine directly1 one volume of nitrogen would combine with three volumes of hydrogen to form two volumes of ammonia4 ,here1 as in the formation of steam from hydrogen and oxygen1 small whole numbers serve to indicate the relation between the volumes of combining gases and that of the gaseous product4 ,,compounds ,,of ,,nitrogen ,,with ,,oxygen ,,and ,,hydrogen ,in addition to ammonium hydroxide1 nitrogen forms several compounds with hydrogen and oxygen1 of which nitric acid 7,,hno#c7 and nitrous acid 7,,hno#b7 are the most familiar4 ,nitric acid 7,,hno#c74 ,nitric acid is not found to any extent in nature1 but some of its salts1 especially sodium nitrate 7,na,n,o#c7 and potassium nitrate 7,,kno#c7 are found in large quantities4 ,from these salts nitric acid can be obtained4 ,illustration ,fig4 #cg ,preparation of nitric acid4 ,when sodium nitrate is treated with concentrated cold sulphuric acid1 no chemical action seems to take place4 ,if1 however1 the mixture is heated in a retort1 nitric acid is given off as a vapor and may be easily condensed to a liquid by passing the vapor into a tube surrounded by cold water1 as shown in ,fig4 #cg4 ,an examination of the liquid left in the retort shows that it contains sodium acid sulphate 7,na,h,s,o#d71 so that the reaction may be represented by the equation ,na,n,o#c ,h#b,,so#d ,na,h,s,o#d ,,hno#c4 ,if a smaller quantity of sulphuric acid is taken and the mixture is heated to a high temperature1 normal sodium sulphate is formed3 #b,na,n,o#c ,h#b,,so#d ,na#b,,so#d #b;,,hno#c4 ,in this case1 however1 the higher temperature required decomposes a part of the nitric acid4 ,the commercial preparation of nitric acid4 ,fig4 #ch illustrates a form of apparatus used in the preparation of nitric acid on a large scale4 ,sodium nitrate and sulphuric acid are heated in the iron retort ,a4 ,the resulting acid vapors pass in the direction indicated by the arrows1 and are condensed in the glass tubes ,b1 which are covered with cloth kept cool by streams of water4 ,these tubes are inclined so that the liquid resulting from the condensation of the vapors runs back into ,c and is drawn off into large vessels 7,d74 ,illustration ,fig4 #ch ,physical properties of nitric acid4 ,pure nitric acid is a colorless liquid1 which boils at about #hf and has a density of #a4ef4 ,the concentrated acid of commerce contains about #fh of the acid1 the remainder being water4 ,such a mixture has a density of #a4d4 ,the concentrated acid fumes somewhat in moist air1 and has a sharp choking odor4 ,chemical properties4 ,the most important chemical properties of nitric acid are the following4 #a4 ,acid properties4 ,as the name indicates1 this substance is an acid1 and has all the properties of that class of substances4 ,it changes blue litmus red and has a sour taste in dilute solutions4 ,it forms hydrogen ions in solution and neutralizes bases forming salts4 ,it also acts upon the oxides of most metals1 forming a salt and water4 ,it is one of the strongest acids4 #b4 ,decomposition on heating4 ,when boiled1 or exposed for some time to sunlight1 it suffers a partial decomposition according to the equation #b;,,hno#c ,h#b,o #b,,no#b ,o4 ,the substance ,,no#b1 called nitrogen peroxide1 is a brownish gas1 which is readily soluble in water and in nitric acid4 ,it therefore dissolves in the undecomposed acid1 and imparts a yellowish or reddish color to it4 ,concentrated nitric acid highly charged with this substance is called fuming nitric acid4 #c4 ,oxidizing action4 ,according to its formula1 nitric acid contains a large percentage of oxygen1 and the reaction just mentioned shows that the compound is not a very stable one1 easily undergoing decomposition4 ,these properties should make it a good oxidizing agent1 and we find that this is the case4 ,under ordinary circumstances1 when acting as an oxidizing agent1 it is decomposed according to the equation #b;,,hno#c ,h#b,o #b,,no #c,o4 ,the oxygen is taken up by the substance oxidized1 and not set free1 as is indicated in the equation4 ,thus1 if carbon is oxidized by nitric acid1 the oxygen combines with carbon1 forming carbon dioxide 7,,co#b73 ,c #b,o ,,co#b4 #d4 ,action on metals4 ,we have seen that when an acid acts upon a metal hydrogen is set free4 ,accordingly1 when nitric acid acts upon a metal1 such as copper1 we should expect the reaction to take place which is expressed in the equation ,cu #b;,,hno#c ,cu7,,no#c7b #b;,h4 ,this reaction does take place1 but the hydrogen set free is immediately oxidized to water by another portion of the nitric acid according to the equation ,,hno#c #c;,h #b;,h#b,o ,,no4 ,as these two equations are written1 two atoms of hydrogen are given off in the first equation1 while three are used up in the second4 ,in order that the hydrogen may be equal in the two equations1 we must multiply the first by #c and the second by #b4 ,we shall then have #c;,cu #f;,,hno#c #c;,cu7,,no#c7b #f;,h1 #b;,,hno#c #f;,h #d;,h#b,o #b,,no4 ,the two equations may now be combined into one by adding the quantities on each side of the equality sign1 canceling the hydrogen which is given off in the one reaction and used up in the other4 ,we shall then have the equation #c;,cu #h;,,hno#c #c;,cu7,,no#c7b #b,,no #d;,h#b,o4 ,a number of other reactions may take place when nitric acid acts upon metals1 resulting in the formation of other oxides of nitrogen1 free nitrogen1 or even ammonia4 ,the reaction just given is1 however1 the usual one4 ,importance of steps in a reaction4 ,this complete equation has the advantage of making it possible to calculate very easily the proportions in which the various substances enter into the reaction or are formed in it4 ,it is unsatisfactory in that it does not give full information about the way in which the reaction takes place4 ,for example1 it does not suggest that hydrogen is at first formed1 and subsequently transformed into water4 ,it is always much more important to remember the steps in a chemical reaction than to remember the equation expressing the complete action2 for if these steps in the reaction are understood1 the complete equation is easily obtained in the manner just described4 ,salts of nitric acid1--nitrates4 ,the salts of nitric acid are called nitrates4 ,many of these salts will be described in the study of the metals4 ,they are all soluble in water1 and when heated to a high temperature undergo decomposition4 ,in a few cases a nitrate on being heated evolves oxygen1 forming a nitrite3 ,na,n,o#c ,na,n,o#b ,o4 ,in other cases the decomposition goes further1 and the metal is left as oxide3 ,cu7,,no#c7b ,cu,o #b,,no#b ,o4 ,nitrous acid 7,,hno#b74 ,it is an easy matter to obtain sodium nitrite 7,na,n,o#b71 as the reaction given on the previous page indicates4 ,instead of merely heating the nitrate1 it is better to heat it together with a mild reducing agent1 such as lead1 when the reaction takes place which is expressed by the equation ,na,n,o#c ,pb ,pb,o ,na,n,o#b4 ,when sodium nitrite is treated with an acid1 such as sulphuric acid1 it is decomposed and nitrous acid is set free3 ,na,n,o#b ,h#b,,so#d ,na,h,s,o#d ,,hno#b4 ,the acid is very unstable1 however1 and decomposes readily into water and nitrogen trioxide 7,n#b,o#c73 #b;,,hno#b ,h#b,o ,n#b,o#c4 ,dilute solutions of the acid1 however1 can be obtained4 ,,compounds ,,of ,,nitrogen ,,with ,,oxygen ,nitrogen combines with oxygen to form five different oxides4 ,the formulas and names of these are as follows3 ,n#b,o nitrous oxide4 ,,no nitric oxide4 ,,no#b nitrogen peroxide4 ,n#b,o#c nitrogen trioxide1 or nitrous anhydride4 ,n#b,o#e nitrogen pentoxide1 or nitric anhydride4 ,these will now be briefly discussed4 ,nitrous oxide 7laughing gas7 7,n#b,o74 ,ammonium nitrate1 like all nitrates1 undergoes decomposition when heated2 and owing to the fact that it contains no metal1 but does contain both oxygen and hydrogen1 the reaction is a peculiar one4 ,it is represented by the equation ,,nh#d,,no#c #b;,h#b,o ,n#b,o4 ,the oxide of nitrogen so formed is called nitrous oxide or laughing gas4 ,it is a colorless gas having a slight odor4 ,it is somewhat soluble in water1 and in solution has a slightly sweetish taste4 ,it is easily converted into a liquid and can be purchased in this form4 ,when inhaled it produces a kind of hysteria 7hence the name laughing gas71 and even unconsciousness and insensibility to pain if taken in large amounts4 ,it has long been used as an ansthetic for minor surgical operations1 such as those of dentistry1 but owing to its unpleasant after effects it is not so much in use now as formerly4 ,chemically1 nitrous oxide is remarkable for the fact that it is a very energetic oxidizing agent4 ,substances such as carbon1 sulphur1 iron1 and phosphorus burn in it almost as brilliantly as in oxygen1 forming oxides and setting free nitrogen4 ,evidently the oxygen in nitrous oxide cannot be held in very firm combination by the nitrogen4 ,illustration ,fig4 #ci ,nitric oxide 7,,no74 ,we have seen that when nitric acid acts upon metals1 such as copper1 the reaction represented by the following equation takes place3 #c;,cu #h;,,hno#c #c;,cu7,,no#c7c #b,,no #d;,h#b,o4 ,nitric oxide is most conveniently prepared in this way4 ,the metal is placed in the flask ,a 7,fig4 #ci7 and the acid added slowly through the funnel tube ,b4 ,the gas escapes through ,c and is collected over water4 ,pure nitric oxide is a colorless gas1 slightly heavier than air1 and is practically insoluble in water4 ,it is a difficult gas to liquefy4 ,unlike nitrous oxide1 nitric oxide does not part with its oxygen easily1 and burning substances introduced into this gas are usually extinguished4 ,a few substances like phosphorus1 which have a very strong affinity for oxygen and which are burning energetically in the air1 will continue to burn in an atmosphere of nitric oxide4 ,in this case the nitric oxide loses all of its oxygen and the nitrogen is set free as gas4 ,action of nitric oxide with oxygen4 ,when nitric oxide comes into contact with oxygen or with the air1 it at once combines with the oxygen even at ordinary temperatures1 forming a reddish-yellow gas of the formula ,,no#b1 which is called nitrogen peroxide4 ,this action is not energetic enough to produce a flame1 though considerable heat is set free4 ,nitrogen peroxide 7,,no#b74 ,this gas1 as we have just seen1 is formed by allowing nitric oxide to come into contact with oxygen4 ,it can also be made by heating certain nitrates1 such as lead nitrate3 ,pb7,,no#c7b ,pb,o #b,,no#b ,o4 ,it is a reddish-yellow gas of unpleasant odor1 which is quite poisonous when inhaled4 ,it is heavier than air and is easily condensed to a liquid4 ,it dissolves in water1 but this solution is not a mere physical solution2 the nitrogen peroxide is decomposed1 forming a mixture of nitric and nitrous acids3 #b,,no#b ,h#b,o ,,hno#b ,,hno#c4 ,nitrogen peroxide will not combine with more oxygen2 it will1 however1 give up a part of its oxygen to burning substances1 acting as an oxidizing agent3 ,,no#b ,,no ,o4 ,acid anhydrides4 ,the oxides ,n#b,o#c 7nitrogen trioxide7 and ,n#b,o#e 7nitrogen pentoxide7 are rarely prepared and need not be separately described4 ,they bear a very interesting relation to the acids of nitrogen4 ,when dissolved in water they combine with the water1 forming acids3 ,n#b,o#c ,h#b,o #b;,,hno#b1 ,n#b,o#e ,h#b,o #b;,,hno#c4 ,on the other hand1 nitrous acid very easily decomposes1 yielding water and nitrogen trioxide1 and by suitable means nitric acid likewise may be decomposed into water and nitrogen pentoxide3 #b;,,hno#b ,h#b,o ,n#b,o#c1 #b;,,hno#c ,h#b,o ,n#b,o#e4 ,in view of the close relation between these oxides and the corresponding acids1 they are called anhydrides of the acids1 ,n#b,o#c being nitrous anhydride and ,n#b,o#e nitric anhydride4 ,,definition3 ,any oxide which will combine with water to form an acid1 or which together with water is formed by the decomposition of an acid1 is called an anhydride of that acid4 ,,exercises #a4 ,perfectly dry ammonia does not affect litmus paper4 ,explain4 #b4 ,can ammonia be dried by passing the gas through concentrated sulphuric acid8 ,explain4 #c4 ,ammonium hydroxide is a weak base1 i4e4 it is not highly dissociated4 ,when it is neutralized by strong acids the heat of reaction is less than when strong bases are so neutralized4 ,suggest some possible cause for this4 #d4 ,why is brine used in the manufacture of artificial ice8 #e4 ,discuss the energy changes which take place in the manufacture of artificial ice4 #f4 ,what weight of ammonium chloride is necessary to furnish enough ammonia to saturate #a l4 of water at #j and #gfj mm48 #g4 ,what weight of sodium nitrate is necessary to prepare #ajj cc4 of commercial nitric acid8 ,what weight of potassium nitrate is necessary to furnish the same weight of acid8 #h4 #ajj l4 of nitrogen peroxide were dissolved in water and neutralized with sodium hydroxide4 ,what substances were formed and how much of each87#a l4 nitrogen peroxide weighs #b4je grams47 #i4 ,how many liters of nitrous oxide1 measured under standard conditions1 can be prepared from #aj g4 of ammonium nitrate8 #aj4 ,what weight of copper is necessary to prepare #ej l4 of nitric oxide under standard conditions8 #aa4 7a7 ,calculate the percentage composition of the oxides of nitrogen4 7b7 ,what important law does this series of substances illustrate8 #ab4 ,write the equations representing the reactions between ammonium hydroxide1 and sulphuric acid and nitric acid respectively1 in accordance with the theory of electrolytic dissociation4 #ac4 ,in the same way1 write the equations representing the reactions between nitric acid and each of the following bases3 ,na,o,h1 ,,koh1 ,,nh#d,,oh1 ,ca7,,oh7#b4 ,,chapter ,,xiii ,,reversible ,,reactions ,,and ,,chemical ,,equilibrium ,reversible reactions4 ,the reactions so far considered have been represented as continuing1 when once started1 until one or the other substance taking part in the reaction has been used up4 ,in some reactions this is not the case4 ,for example1 we have seen that when steam is passed over hot iron the reaction is represented by the equation #c;,fe #d;,h#b,o ,fe#c,o#d #h;,h4 ,on the other hand1 when hydrogen is passed over hot iron oxide the reverse reaction takes place3 ,fe#c,o#d #h;,h #c;,fe #d;,h#b,o4 ,the reaction can therefore go in either direction1 depending upon the conditions of the experiment4 ,such a reaction is called a reversible reaction4 ,it is represented by an equation with double arrows in place of the equality sign1 thus3 #c;,fe #d;,h#b,o -- ,fe#c,o#d #h;,h4 ,in a similar way1 the equation ,n #c;,h -- ,,nh#c expresses the fact that under some conditions nitrogen may unite with hydrogen to form ammonia1 while under other conditions ammonia decomposes into nitrogen and hydrogen4 ,the conversion of oxygen into ozone is also reversible and may be represented thus3 oxygen -- ozone4 ,chemical equilibrium4 ,reversible reactions do not usually go on to completion in one direction unless the conditions under which the reaction takes place are very carefully chosen4 ,thus1 if iron and steam are confined in a heated tube1 the steam acts upon the iron1 producing iron oxide and hydrogen4 ,but these substances in turn act upon each other to form iron and steam once more4 ,when these two opposite reactions go on at such rates that the weight of the iron changed into iron oxide is just balanced by the weight of the iron oxide changed into iron1 there will be no further change in the relative weights of the four substances present in the tube4 ,the reaction is then said to have reached an equilibrium4 ,factors which determine the point of equilibrium4 ,there are two factors which have a great deal of influence in determining the point at which a given reaction will reach equilibrium4 #a4 ,influence of the chemical nature of the substances4 ,if two reversible reactions of the same general kind are selected1 it has been found that the point of equilibrium is different in the two cases4 ,for example1 in the reactions represented by the equations #c;,fe #d;,h#b,o -- ,fe#c,o#d #h;,h1 ,zn ,h#b,o -- ,zn,o #b;,h1 the equilibrium will be reached when very different quantities of the iron and zinc have been changed into oxides4 ,the individual chemical properties of the iron and zinc have therefore marked influence upon the point at which equilibrium will be reached4 #b4 ,influence of relative mass4 ,if the tube in which the reaction #c;,fe #d;,h#b,o -- ,fe#c,o#d #h;,h has come to an equilibrium is opened and more steam is admitted1 an additional quantity of the iron will be changed into iron oxide4 ,if more hydrogen is admitted1 some of the oxide will be reduced to metal4 ,the point of equilibrium is therefore dependent upon the relative masses of the substances taking part in the reaction4 ,when one of the substances is a solid1 however1 its mass has little influence1 since it is only the extent of its surface which can affect the reaction4 ,conditions under which reversible reactions are complete4 ,if1 when the equilibrium between iron and steam has been reached1 the tube is opened and a current of steam is passed in1 the hydrogen is swept away as fast as it is formed4 ,the opposing reaction of hydrogen upon iron oxide must therefore cease1 and the action of steam on the iron will go on until all of the iron has been transformed into iron oxide4 ,on the other hand1 if a current of hydrogen is admitted into the tube1 the steam will be swept away by the hydrogen1 and all of the iron oxide will be reduced to iron4 ,a reversible reaction can therefore be completed in either direction when one of the products of the reaction is removed as fast as it is formed4 ,equilibrium in solution4 ,when reactions take place in solution in water the same general principles hold good4 ,the matter is not so simple1 however1 as in the case just described1 owing to the fact that many of the reactions in solution are due to the presence of ions4 ,the substances most commonly employed in solution are acids1 bases1 or salts1 and all of these undergo dissociation4 ,any equilibrium which may be reached in solutions of these substances must take place between the various ions formed1 on the one hand1 and the undissociated molecules1 on the other4 ,thus1 when nitric acid is dissolved in water1 equilibrium is reached in accordance with the equation ,h ,,no#c- -- ,,hno#c4 ,conditions under which reversible reactions in solution are complete4 ,the equilibrium between substances in solution may be disturbed and the reaction caused to go on in one direction to completion in either of three ways4 #a4 ,a gas may be formed which escapes from the solution4 ,when sodium nitrate and sulphuric acid are brought together in solution all four ions1 ,na1 ,,no#c-1 ,h1 ,,so#d--1 are formed4 ,these ions are free to rearrange themselves in various combinations4 ,for example1 the ,h and the ,,no#c- ions will reach the equilibrium ,h ,,no#c- -- ,,hno#c4 ,if the experiment is performed with very little water present1 as is the case in the preparation of nitric acid1 the equilibrium will be reached when most of the ,h and the ,,no#c- ions have combined to form undissociated ,,hno#c4 ,finally1 if the mixture is now heated above the boiling point of nitric acid1 the acid distills away as fast as it is formed4 ,more and more ,h and ,,no#c- ions will then combine1 and the process will continue until one or the other of them has all been removed from the solution4 ,the substance remaining is sodium acid sulphate 7,na,h,s,o#d71 and the reaction can therefore be expressed by the equation ,na,n,o#c ,h#b,,so#d ,na,h,s,o#d ,,hno#c4 #b4 ,an insoluble solid may be formed4 ,when hydrochloric acid 7,h,cl7 and silver nitrate 7,ag,n,o#c7 are brought together in solution the following ions will be present3 ,h1 ,cl-1 ,ag1 ,,no#c-4 ,the ions ,ag and ,cl- will then set up the equilibrium ,ag ,cl- -- ,ag,cl4 ,but silver chloride 7,ag,cl7 is almost completely insoluble in water1 and as soon as a very little of it has formed the solution becomes supersaturated1 and the excess of the salt precipitates4 ,more silver and chlorine ions then unite1 and this continues until practically all of the silver or the chlorine ions have been removed from the solution4 ,we then say that the following reaction is complete3 ,ag,n,o#c ,h,cl ,ag,cl ,,hno#c4 #c4 ,two different ions may form undissociated molecules4 ,in the neutralization of sodium hydroxide by hydrochloric acid the ions ,h and ,,oh- come to the equilibrium ,h ,,oh- -- ,h#b,o4 ,but since water is almost entirely undissociated1 equilibrium can only be reached when there are very few hydroxyl or hydrogen ions present4 ,consequently the two ions keep uniting until one or the other of them is practically removed from the solution4 ,when this occurs the neutralization expressed in the following equation is complete3 ,na,o,h ,h,cl ,h#b,o ,na,cl4 ,preparation of acids4 ,the principle of reversible reactions finds practical application in the preparation of most of the common acids4 ,an acid is usually prepared by treating the most common of its salts with some other acid of high boiling point4 ,the mixture is then heated until the lower boiling acid desired distills out4 ,owing to its high boiling point 7#cch71 sulphuric acid is usually employed for this purpose1 most other acids boiling below that temperature4 ,,exercises #a4 ,what would take place when solutions of silver nitrate and sodium chloride are brought together8 ,what other chlorides would act in the same way8 #b4 ,is the reaction expressed by the equation ,,nh#c ,h#b,o ,,nh#d,,oh reversible8 ,if so1 state the conditions under which it will go in each direction4 #c4 ,is the reaction expressed by the equation #b;,h ,o ,h#b,o reversible8 ,if so1 state the conditions under which it will go in each direction4 #d4 ,suggest a method for the preparation of hydrochloric acid4 ,,chapter ,,xiv ,,sulphur ,,and ,,its ,,compounds ,occurrence4 ,the element sulphur has been known from the earliest times1 since it is widely distributed in nature and occurs in large quantities in the uncombined form1 especially in the neighborhood of volcanoes4 ,sicily has long been famous for its sulphur mines1 and smaller deposits are found in ,italy1 ,iceland1 ,mexico1 and especially in ,louisiana1 where it is mined extensively4 ,in combination1 sulphur occurs abundantly in the form of sulphides and sulphates4 ,in smaller amounts it is found in a great variety of minerals1 and it is a constituent of many animal and vegetable substances4 ,extraction of sulphur4 ,sulphur is prepared from the native substance1 the separation of crude sulphur from the rock and earthy materials with which it is mixed being a very simple process4 ,the ore from the mines is merely heated until the sulphur melts and drains away from the earthy impurities4 ,the crude sulphur obtained in this way is distilled in a retort-shaped vessel made of iron1 the exit tube of which opens into a cooling chamber of brickwork4 ,when the sulphur vapor first enters the cooling chamber it condenses as a fine crystalline powder called flowers of sulphur4 ,as the condensing chamber becomes warm1 the sulphur collects as a liquid in it1 and is drawn off into cylindrical molds1 the product being called roll sulphur or brimstone4 ,physical properties4 ,roll sulphur is a pale yellow1 crystalline solid1 without marked taste and with but a faint odor4 ,it is insoluble in water1 but is freely soluble in a few liquids1 notably in carbon disulphide4 ,roll sulphur melts at #aad4h4 ,just above the melting point it forms a rather thin1 straw-colored liquid4 ,as the temperature is raised1 this liquid turns darker in color and becomes thicker1 until at about #bce it is almost black and is so thick that the vessel containing it can be inverted without danger of the liquid running out4 ,at higher temperatures it becomes thin once more1 and boils at #ddh1 forming a yellowish vapor4 ,on cooling the same changes take place in reverse order4 ,varieties of sulphur4 ,sulphur is known in two general forms1 crystalline and amorphous4 ,each of these forms exists in definite modifications4 ,crystalline sulphur4 ,sulphur occurs in two crystalline forms1 namely1 rhombic sulphur and monoclinic sulphur4 #a4 ,rhombic sulphur4 ,when sulphur crystallizes from its solution in carbon disulphide it separates in crystals which have the same color and melting point as roll sulphur1 and are rhombic in shape4 ,roll sulphur is made up of minute rhombic crystals4 #b4 ,monoclinic sulphur4 ,when melted sulphur is allowed to cool until a part of the liquid has solidified1 and the remaining liquid is then poured off1 it is found that the solid sulphur remaining in the vessel has assumed the form of fine needle-shaped crystals4 ,these differ much in appearance from the rhombic crystals obtained by crystallizing sulphur from its solution in carbon disulphide4 ,the needle-shaped form is called monoclinic sulphur4 ,the two varieties differ also in density and in melting point1 the monoclinic sulphur melting at #abj4 ,monoclinic and rhombic sulphur remain unchanged in contact with each other at #if4 ,above this temperature the rhombic changes into monoclinic2 at lower temperatures the monoclinic changes into rhombic4 ,the temperature #if is therefore called the transition point of sulphur4 ,heat is set free when monoclinic sulphur changes into rhombic4 ,amorphous sulphur4 ,two varieties of amorphous sulphur can be readily obtained4 ,these are white sulphur and plastic sulphur4 #a4 ,white sulphur4 ,flowers of sulphur1 the preparation of which has been described1 consists of a mixture of rhombic crystals and amorphous particles4 ,when treated with carbon disulphide1 the crystals dissolve1 leaving the amorphous particles as a white residue4 #b4 ,plastic sulphur4 ,when boiling sulphur is poured into cold water it assumes a gummy1 doughlike form1 which is quite elastic4 ,this can be seen in a very striking manner by distilling sulphur from a small1 short-necked retort1 such as is represented in ,fig4 #dj1 and allowing the liquid to run directly into water4 ,in a few days it becomes quite brittle and passes over into ordinary rhombic sulphur4 ,illustration ,fig4 #dj ,chemical properties of sulphur4 ,when sulphur is heated to its kindling temperature in oxygen or in the air it burns with a pale blue flame1 forming sulphur dioxide 7,,so#b74 ,small quantities of sulphur trioxide 7,,so#c7 may also be formed in the combustion of sulphur4 ,most metals when heated with sulphur combine directly with it1 forming metallic sulphides4 ,in some cases the action is so energetic that the mass becomes incandescent1 as has been seen in the case of iron uniting with sulphur4 ,this property recalls the action of oxygen upon metals1 and in general the metals which combine readily with oxygen are apt to combine quite readily with sulphur4 ,uses of sulphur4 ,large quantities of sulphur are used as a germicide in vineyards1 also in the manufacture of gunpowder1 matches1 vulcanized rubber1 and sulphuric acid4 ,,compounds ,,of ,,sulphur ,,with ,,hydrogen ,hydrosulphuric acid 7,h#b,s74 ,this substance is a gas having the composition expressed by the formula ,h#b,s and is commonly called hydrogen sulphide4 ,it is found in the vapors issuing from volcanoes1 and in solution in the so-called sulphur waters of many springs4 ,it is formed when organic matter containing sulphur undergoes decay1 just as ammonia is formed under similar circumstances from nitrogenous matter4 ,preparation4 ,hydrosulphuric acid is prepared in the laboratory by treating a sulphide with an acid4 ,iron sulphide 7,fe,s7 is usually employed3 ,fe,s #b;,h,cl ,fe,cl#b ,h#b,s4 ,a convenient apparatus is shown in ,fig4 #da4 ,a few lumps of iron sulphide are placed in the bottle ,a1 and dilute acid is added in small quantities at a time through the funnel tube ,b1 the gas escaping through the tube ,c4 ,illustration3 ,fig4 #da ,explanation of the reaction4 ,iron sulphide is a salt of hydrosulphuric acid1 and this reaction is therefore similar to the one which takes place when sulphuric acid acts upon a nitrate4 ,in both cases a salt and an acid are brought together1 and there is a tendency for the reaction to go on until a state of equilibrium is reached4 ,this equilibrium is constantly disturbed by the escape of the gaseous acid set free1 so that the reaction goes on until all of the original salt has been decomposed4 ,the two reactions differ in that the first one is complete at ordinary temperatures1 while in the case of sulphuric acid acting upon sodium nitrate1 the reacting substances must be heated so as to secure a temperature at which nitric acid is a gas4 ,physical properties4 ,hydrosulphuric acid is a colorless gas1 having a weak1 disagreeable taste and an exceedingly offensive odor4 ,it is rather sparingly soluble in water at ordinary temperatures1 about three volumes dissolving in one of water4 ,in boiling water it is not soluble at all4 ,in pure form it acts as a violent poison1 and even when diluted largely with air produces headache1 dizziness1 and nausea4 ,it is a little heavier than air1 having a density of #a4ah4 ,chemical properties4 ,the most important chemical properties of hydrosulphuric acid are the following3 #a4 ,acid properties4 ,hydrosulphuric acid is a weak acid4 ,in solution in water it turns blue litmus red and neutralizes bases1 forming salts called sulphides4 #b4 ,action on oxygen4 ,the elements composing hydrosulphuric acid have each a strong affinity for oxygen1 and are not held together very firmly4 ,consequently the gas burns readily in oxygen or the air1 according to the equation ,h#b,s #c,o ,h#b,o ,,so#b4 ,when there is not enough oxygen for both the sulphur and the hydrogen1 the latter element combines with the oxygen and the sulphur is set free3 ,h#b,s ,o ,h#b,o ,s4 #c4 ,reducing action4 ,owing to the ease with which hydrosulphuric acid decomposes and the strong affinity of both sulphur and hydrogen for oxygen1 the substance is a strong reducing agent1 taking oxygen away from many substances which contain it4 #d4 ,action on metals4 ,hydrosulphuric acid acts towards metals in a way very similar to water4 ,thus1 when it is passed over heated iron in a tube1 the reaction is represented by the equation #c;,fe #d;,h#b,s ,fe#c,s#d #h;,h4 ,water in the form of steam1 under similar circumstances1 acts according to the equation #c;,fe #d;,h#b,o ,fe#c,o#d #h;,h4 ,salts of hydrosulphuric acid1--sulphides4 ,the salts of hydrosulphuric acid1 called sulphides1 form an important class of salts4 ,many of them are found abundantly in nature1 and some of them are important ores4 ,they will be frequently mentioned in connection with the metals4 ,most of the sulphides are insoluble in water1 and some of them are insoluble in acids4 ,consequently1 when hydrosulphuric acid is passed into a solution of a salt1 it often happens that a sulphide is precipitated4 ,with copper chloride the equation is ,cu,cl#b ,h#b,s ,cu,s #b;,h,cl4 ,because of the fact that some metals are precipitated in this way as sulphides while others are not1 hydrosulphuric acid is extensively used in the separation of the metals in the laboratory4 ,explanation of the reaction4 ,when hydrosulphuric acid and copper chloride are brought together in solution1 both copper and sulphur ions are present1 and these will come to an equilibrium1 as represented in the equation ,cu ,s- -- ,cu,s4 ,since copper sulphide is almost insoluble in water1 as soon as a very small quantity has formed the solution becomes supersaturated1 and the excess keeps precipitating until nearly all the copper or sulphur ions have been removed from the solution4 ,with some other ions1 such as iron1 the sulphide formed does not saturate the solution1 and no precipitate results4 ,,oxides ,,of ,,sulphur ,sulphur forms two well-known compounds with oxygen3 sulphur dioxide 7,,so#b71 sometimes called sulphurous anhydride2 and sulphur trioxide 7,,so#c71 frequently called sulphuric anhydride4 ,sulphur dioxide 7,,so#b74 ,sulphur dioxide occurs in nature in the gases issuing from volcanoes1 and in solution in the water of many springs4 ,it is likely to be found wherever sulphur compounds are undergoing oxidation4 ,preparation4 ,three general ways may be mentioned for the preparation of sulphur dioxide3 #a4 ,by the combustion of sulphur4 ,sulphur dioxide is readily formed by the combustion of sulphur in oxygen or the air3 ,s #b,o ,,so#b4 ,it is also formed when substances containing sulphur are burned3 ,zn,s #c,o ,zn,o ,,so#b4 #b4 ,by the reduction of sulphuric acid4 ,when concentrated sulphuric acid is heated with certain metals1 such as copper1 part of the acid is changed into copper sulphate1 and part is reduced to sulphurous acid4 ,the latter then decomposes into sulphur dioxide and water1 the complete equation being ,cu #b;,h#b,,so#d ,cu,s,o#d ,,so#b #b;,h#b,o4 #c4 ,by the action of an acid on a sulphite4 ,sulphites are salts of sulphurous acid 7,h#b,,so#c74 ,when a sulphite is treated with an acid1 sulphurous acid is set free1 and being very unstable1 decomposes into water and sulphur dioxide4 ,these reactions are expressed in the equations ,na#b,,so#c #b;,h,cl #b,na,cl ,h#b,,so#c1 ,h#b,,so#c ,h#b,o ,,so#b4 ,explanation of the reaction4 ,in this case we have two reversible reactions depending on each other4 ,in the first reaction1 7#a7 ,na#b,,so#c #b;,h,cl -- #b,na,cl ,h#b,,so#c1 we should expect an equilibrium to result1 for none of the four substances in the equation are insoluble or volatile when water is present to hold them in solution4 ,but the quantity of the ,h#b,,so#c is constantly diminishing1 owing to the fact that it decomposes1 as represented in the equation 7#b7 ,h#b,,so#c -- ,h#b,o ,,so#b1 and the sulphur dioxide1 being a gas1 escapes4 ,no equilibrium can therefore result1 since the quantity of the sulphurous acid is constantly being diminished because of the escape of sulphur dioxide4 ,physical properties4 ,sulphur dioxide is a colorless gas1 which at ordinary temperatures is #b4b times as heavy as air4 ,it has a peculiar1 irritating odor4 ,the gas is very soluble in water1 one volume of water dissolving eighty of the gas under standard conditions4 ,it is easily condensed to a colorless liquid1 and can be purchased in this condition stored in strong bottles1 such as the one represented in ,fig4 #db4 ,illustration3 ,fig4 #db ,chemical properties4 ,sulphur dioxide has a marked tendency to combine with other substances1 and is therefore an active substance chemically4 ,it combines with oxygen gas1 but not very easily4 ,it can1 however1 take oxygen away from some other substances1 and is therefore a good reducing agent4 ,its most marked chemical property is its ability to combine with water to form sulphurous acid 7,h#b,,so#c74 ,sulphurous acid 7,h#b,,so#c74 ,when sulphur dioxide dissolves in water it combines chemically with it to form sulphurous acid1 an unstable substance having the formula ,h#c,,so#c4 ,it is impossible to prepare this acid in pure form1 as it breaks down very easily into water and sulphur dioxide4 ,the reaction is therefore reversible1 and is expressed by the equation ,h#b,o ,,so#b -- ,h#b,,so#c4 ,solutions of the acid in water have a number of interesting properties4 #a4 ,acid properties4 ,the solution has all the properties typical of an acid4 ,when neutralized by bases1 sulphurous acid yields a series of salts called sulphites4 #b4 ,reducing properties4 ,solutions of sulphurous acid act as good reducing agents4 ,this is due to the fact that sulphurous acid has the power of taking up oxygen from the air1 or from substances rich in oxygen1 and is changed by this reaction into sulphuric acid3 ,h#b,,so#c ,o ,h#b,,so#d1 ,h#b,,so#c ,h#b,o#b ,h#b,s#jd ,h#b,o4 #c4 ,bleaching properties4 ,sulphurous acid has strong bleaching properties1 acting upon many colored substances in such a way as to destroy their color4 ,it is on this account used to bleach paper1 straw goods1 and even such foods as canned corn4 #d4 ,antiseptic properties4 ,sulphurous acid has marked antiseptic properties1 and on this account has the power of arresting fermentation4 ,it is therefore used as a preservative4 ,salts of sulphurous acid1--sulphites4 ,the sulphites1 like sulphurous acid1 have the power of taking up oxygen very readily1 and are good reducing agents4 ,on account of this tendency1 commercial sulphites are often contaminated with sulphates4 ,a great deal of sodium sulphite is used in the bleaching industry1 and as a reagent for softening paper pulp4 ,sulphur trioxide 7,,so#c74 ,when sulphur dioxide and oxygen are heated together at a rather high temperature1 a small amount of sulphur trioxide 7,,so#c7 is formed1 but the reaction is slow and incomplete4 ,if1 however1 the heating takes place in the presence of very fine platinum dust1 the reaction is rapid and nearly complete4 ,illustration3 ,fig4 #dc ,experimental preparation of sulphur trioxide4 ,the experiment can be performed by the use of the apparatus shown in ,fig4 #dc1 the fine platinum being secured by moistening asbestos fiber with a solution of platinum chloride and igniting it in a flame4 ,the fiber1 covered with fine platinum1 is placed in a tube of hard glass1 which is then heated with a burner to about #cej1 while sulphur dioxide and air are passed into the tube4 ,union takes place at once1 and the strongly fuming sulphur trioxide escapes from the jet at the end of the tube1 and may be condensed by surrounding the receiving tube with a freezing mixture4 ,properties of sulphur trioxide4 ,sulphur trioxide is a colorless liquid1 which solidifies at about #ae and boils at #df4 ,a trace of moisture causes it to solidify into a mass of silky white crystals1 somewhat resembling asbestos fiber in appearance4 ,in contact with the air it fumes strongly1 and when thrown upon water it dissolves with a hissing sound and the liberation of a great deal of heat4 ,the product of this reaction is sulphuric acid1 so that sulphur trioxide is the anhydride of that acid3 ,,so#c ,h#b,o ,h#b,,so#d4 ,catalysis4 ,it has been found that many chemical reactions1 such as the union of sulphur dioxide with oxygen1 are much influenced by the presence of substances which do not themselves seem to take a part in the reaction1 and are left apparently unchanged after it has ceased4 ,these reactions go on very slowly under ordinary circumstances1 but are greatly hastened by the presence of the foreign substance4 ,substances which hasten very slow reactions in this way are said to act as catalytic agents or catalyzers1 and the action is called catalysis4 ,just how the action is brought about is not well understood4 ,,definition3 ,a catalyzer is a substance which changes the velocity of a reaction1 but does not change its products4 ,examples of ,catalysis4 ,we have already had several instances of such action4 ,oxygen and hydrogen combine with each other at ordinary temperatures in the presence of platinum powder1 while if no catalytic agent is present they do not combine in appreciable quantities until a rather high temperature is reached4 ,potassium chlorate1 when heated with manganese dioxide1 gives up its oxygen at a much lower temperature than when heated alone4 ,hydrogen dioxide decomposes very rapidly when powdered manganese dioxide is sifted into its concentrated solution4 ,on the other hand1 the catalytic agent sometimes retards chemical action4 ,for example1 a solution of hydrogen dioxide decomposes more slowly when it contains a little phosphoric acid than when perfectly pure4 ,for this reason commercial hydrogen dioxide always contains phosphoric acid4 ,many reactions are brought about by the catalytic action of traces of water4 ,for example1 phosphorus will not burn in oxygen in the absence of all moisture4 ,hydrochloric acid will not unite with ammonia if the reagents are perfectly dry4 ,it is probable that many of the chemical transformations in physiological processes1 such as digestion1 are assisted by certain substances acting as catalytic agents4 ,the principle of catalysis is therefore very important4 ,sulphuric acid 7oil of vitriol7 7,h#b,,so#d74 ,sulphuric acid is one of the most important of all manufactured chemicals4 ,not only is it one of the most common reagents in the laboratory1 but enormous quantities of it are used in many of the industries1 especially in the refining of petroleum1 the manufacture of nitroglycerin1 sodium carbonate1 and fertilizers4 ,manufacture of sulphuric acid4 #a4 ,contact process4 ,the reactions taking place in this process are represented by the following equations3 ,,so#b ,o ,,so#c1 ,,so#c ,h#b,o ,h#b,,so#d4 ,to bring about the first of these reactions rapidly1 a catalyzer is employed1 and the process is carried out in the following way3 ,large iron tubes are packed with some porous material1 such as calcium and magnesium sulphates1 which contains a suitable catalytic substance scattered through it4 ,the catalyzers most used are platinum powder1 vanadium oxide1 and iron oxide4 ,purified sulphur dioxide and air are passed through the tubes1 which are kept at a temperature of about #cej4 ,sulphur trioxide is formed1 and as it issues from the tube it is absorbed in water or dilute sulphuric acid4 ,the process is continued until all the water in the absorbing vessel has been changed into sulphuric acid1 so that a very concentrated acid is made in this way4 ,an excess of the trioxide may dissolve in the strong sulphuric acid1 forming what is known as fuming sulphuric acid4 #b4 ,chamber process4 ,the method of manufacture exclusively employed until recent years1 and still in very extensive use1 is much more complicated4 ,the reactions are quite involved1 but the conversion of water1 sulphur dioxide1 and oxygen into sulphuric acid is accomplished by the catalytic action of oxides of nitrogen4 ,the reactions are brought about in large lead-lined chambers1 into which oxides of nitrogen1 sulphur dioxide1 steam1 and air are introduced in suitable proportions4 ,reactions of the chamber process4 ,in a very general way1 the various reactions which take place in the lead chambers may be expressed in two equations4 ,in the first reaction sulphur dioxide1 nitrogen peroxide1 steam1 and oxygen unite1 as shown in the equation 7#a7 #b,,so#b #b,,no#b ,h#b,o ,o #b,,so#b 7,,oh7 7,,no#b74 ,the product formed in this reaction is called nitrosulphuric acid or chamber crystals4 ,it actually separates on the walls of the chambers when the process is not working properly4 ,under normal conditions1 it is decomposed as fast as it is formed by the action of excess of steam1 as shown in the equation 7#b7 #b,,so#b 7,,oh7 7,,no#b7 ,h#b,o ,o #b;,h#b,,so#d #b,,no#b4 ,the nitrogen dioxide formed in this reaction can now enter into combination with a new quantity of sulphur dioxide1 steam1 and oxygen1 and the series of reactions go on indefinitely4 ,many other reactions occur1 but these two illustrate the principle of the process4 ,the relation between sulphuric acid and nitrosulphuric acid can be seen by comparing their structural formulas3 ,o -,,oh ,o -,,oh ,s ,s ,o -,,oh ,o -,,no#b ,the latter may be regarded as derived from the former by the substitution of the nitro group 7,,no#b7 for the hydroxyl group 7,,oh74 ,illustration3 ,fig4 #dd ,the sulphuric acid plant4 ,fig4 #dd illustrates the simpler parts of a plant used in the manufacture of sulphuric acid by the chamber process4 ,sulphur or some sulphide1 as ,fe,s#b1 is burned in furnace ,a4 ,the resulting sulphur dioxide1 together with air and some nitrogen peroxide1 are conducted into the large chambers1 the capacity of each chamber being about #ge1jjj cu4 ft4 ,steam is also admitted into these chambers at different points4 ,these compounds react to form sulphuric acid1 according to the equations given above4 ,the nitrogen left after the withdrawal of the oxygen from the admitted air escapes through the ,gay-,lussac tower ,x4 ,in order to prevent the escape of the oxides of nitrogen regenerated in the reaction1 the tower is filled with lumps of coke1 over which trickles concentrated sulphuric acid admitted from ,y4 ,the nitrogen peroxide dissolves in the acid and the resulting solution collects in ,h4 ,this is pumped into ,e1 where it is mixed with dilute acid and allowed to trickle down through the chamber ,d 7,glover tower71 which is filled with some acid-resisting rock4 ,here the nitrogen peroxide is expelled from the solution by the action of the hot gases entering from ,a1 and together with them enters the first chamber again4 ,the acid from which the nitrogen peroxide is expelled collects in ,f4 ,theoretically1 a small amount of nitrogen peroxide would suffice to prepare an unlimited amount of sulphuric acid2 practically1 some of it escapes1 and this is replaced by small amounts admitted at ,b4 ,the sulphuric acid so formed1 together with the excess of condensed steam1 collect upon the floor of the chambers in the form of a liquid containing from #fb to #gj of sulphuric acid4 ,the product is called chamber acid and is quite impure2 but for many purposes1 such as the manufacture of fertilizers1 it needs no further treatment4 ,it can be concentrated by boiling it in vessels made of iron or platinum1 which resist the action of the acid1 nearly all the water boiling off4 ,pure concentrated acid can be made best by the contact process1 while the chamber process is cheaper for the dilute impure acid4 ,physical properties4 ,sulphuric acid is a colorless1 oily liquid1 nearly twice as heavy as water4 ,the ordinary concentrated acid contains about #b of water1 has a density of #a4hd1 and boils at #cch4 ,it is sometimes called oil of vitriol1 since it was formerly made by distilling a substance called green vitriol4 ,chemical properties4 ,sulphuric acid possesses chemical properties which make it one of the most important of chemical substances4 #a4 ,action as an acid4 ,in dilute solution sulphuric acid acts as any other acid1 forming salts with oxides and hydroxides4 #b4 ,action as an oxidizing agent4 ,sulphuric acid contains a large percentage of oxygen and is1 like nitric acid1 a very good oxidizing agent4 ,when the concentrated acid is heated with sulphur1 carbon1 and many other substances1 oxidation takes place1 the sulphuric acid decomposing according to the equation ,h#b,,so#d ,h#b,,so#c ,o4 #c4 ,action on metals4 ,in dilute solution sulphuric acid acts upon many metals1 such as zinc1 forming a sulphate and liberating hydrogen4 ,when the concentrated acid is employed the hydrogen set free is oxidized by a new portion of the acid1 with the liberation of sulphur dioxide4 ,with copper the reactions are expressed by the equations 7#a7 ,cu ,h#b,,so#d ,cu,s,o#d #b;,h1 7#b7 ,h#b,,so#d #b;,h ,h#b,,so#c ,h#b,o1 7#c7 ,h#b,,so#c ,h#b,o ,,so#b4 ,by combining these equations the following one is obtained3 ,cu #b;,h#b,,so#d ,cu,s,o#d ,,so#b #b;,h#b,o4 #d4 ,action on salts4 ,we have repeatedly seen that an acid of high boiling point heated with the salt of some acid of lower boiling point will drive out the low boiling acid4 ,the boiling point of sulphuric acid 7#cch7 is higher than that of almost any common acid2 hence it is used largely in the preparation of other acids4 #e4 ,action on water4 ,concentrated sulphuric acid has a very great affinity for water1 and is therefore an effective dehydrating agent4 ,gases which have no chemical action upon sulphuric acid can be freed from water vapor by bubbling them through the strong acid4 ,when the acid is diluted with water much heat is set free1 and care must be taken to keep the liquid thoroughly stirred during the mixing1 and to pour the acid into the water1--never the reverse4 ,not only can sulphuric acid absorb water1 but it will often withdraw the elements hydrogen and oxygen from a compound containing them1 decomposing the compound1 and combining with the water so formed4 ,for this reason most organic substances1 such as sugar1 wood1 cotton1 and woolen fiber1 and even flesh1 all of which contain much oxygen and hydrogen in addition to carbon1 are charred or burned by the action of the concentrated acid4 ,salts of sulphuric acid1--sulphates4 ,the sulphates form a very important class of salts1 and many of them have commercial uses4 ,copperas 7iron sulphate71 blue vitriol 7copper sulphate71 and ,epsom salt 7magnesium sulphate7 serve as examples4 ,many sulphates are important minerals1 prominent among these being gypsum 7calcium sulphate7 and barytes 7barium sulphate74 ,thiosulphuric acid 7,h#b,s#b,o#c72 ,thiosulphates4 ,many other acids of sulphur containing oxygen are known1 but none of them are of great importance4 ,most of them cannot be prepared in a pure state1 and are known only through their salts4 ,the most important of these is thiosulphuric acid4 ,when sodium sulphite is boiled with sulphur the two substances combine1 forming a salt which has the composition represented in the formula ,na#b,s#b,o#c3 ,na#b,,so#c ,s ,na#b,s#b,o#c4 ,the substance is called sodium thiosulphate1 and is a salt of the easily decomposed acid ,h#b,s#b,o#c1 called thiosulphuric acid4 ,this reaction is quite similar to the action of oxygen upon sulphites3 ,na#b,,so#c ,o ,na#b,,so#d4 ,more commonly the salt is called sodium hyposulphite1 or merely hypo4 ,it is a white solid and is extensively used in photography1 in the bleaching industry1 and as a disinfectant4 ,monobasic and dibasic acids4 ,such acids as hydrochloric and nitric acids1 which have only one replaceable hydrogen atom in the molecule1 or in other words yield one hydrogen ion in solution1 are called monobasic acids4 ,acids yielding two hydrogen ions in solution are called dibasic acids4 ,similarly1 we may have tribasic and tetrabasic acids4 ,the three acids of sulphur are dibasic acids4 ,it is therefore possible for each of them to form both normal and acid salts4 ,the acid salts can be made in two ways3 the acid may be treated with only half enough base to neutralize it1-- ,na,o,h ,h#b,,so#d ,na,h,s,o#d ,h#b,o2 or a normal salt may be treated with the free acid1-- ,na#b,,so#d ,h#b,,so#d #b,na,h,s,o#d4 ,acid sulphites and sulphides may be made in the same ways4 ,carbon disulphide 7,,cs#b74 ,when sulphur vapor is passed over highly heated carbon the two elements combine1 forming carbon disulphide 7,,cs#b71 just as oxygen and carbon unite to form carbon dioxide 7,,co#b74 ,the substance is a heavy1 colorless liquid1 possessing1 when pure1 a pleasant ethereal odor4 ,on standing for some time1 especially when exposed to sunlight1 it undergoes a slight decomposition and acquires a most disagreeable1 rancid odor4 ,it has the property of dissolving many substances1 such as gums1 resins1 and waxes1 which are insoluble in most liquids1 and it is extensively used as a solvent for such substances4 ,it is also used as an insecticide4 ,it boils at a low temperature 7#df71 and its vapor is very inflammable1 burning in the air to form carbon dioxide and sulphur dioxide1 according to the equation ,,cs#b #f,o ,,co#b #b,,so#b4 ,illustration3 ,fig4 #de ,commercial preparation of carbon disulphide4 ,in the preparation of carbon disulphide an electrical furnace is employed1 such as is represented in ,fig4 #de4 ,the furnace is packed with carbon ,c1 and this is fed in through the hoppers ,b1 as fast as that which is present in the hearth of the furnace is used up4 ,sulphur is introduced at ,a1 and at the lower ends of the tubes it is melted by the heat of the furnace and flows into the hearth as a liquid4 ,an electrical current is passed through the carbon and melted sulphur from the electrodes ,e1 heating the charge4 ,the vapors of carbon disulphide pass up through the furnace and escape at ,d1 from which they pass to a suitable condensing apparatus4 ,comparison of sulphur and oxygen4 ,a comparison of the formulas and the chemical properties of corresponding compounds of oxygen and sulphur brings to light many striking similarities4 ,the conduct of hydrosulphuric acid and water toward many substances has been seen to be very similar2 the oxides and sulphides of the metals have analogous formulas and undergo many parallel reactions4 ,carbon dioxide and disulphide are prepared in similar ways and undergo many analogous reactions4 ,it is clear1 therefore1 that these two elements are far more closely related to each other than to any of the other elements so far studied4 ,selenium and tellurium4 ,these two very uncommon elements are still more closely related to sulphur than is oxygen4 ,they occur in comparatively small quantities and are usually found associated with sulphur and sulphides1 either as the free elements or more commonly in combination with metals4 ,they form compounds with hydrogen of the formulas ,h#b,se and ,h#b,te2 these bodies are gases with properties very similar to those of ,h#b,s4 ,they also form oxides and oxygen acids which resemble the corresponding sulphur compounds4 ,the elements even have allotropic forms corresponding very closely to those of sulphur4 ,tellurium is sometimes found in combination with gold and copper1 and occasions some difficulties in the refining of these metals4 ,the elements have very few practical applications4 ,crystallography4 ,in order to understand the difference between the two kinds of sulphur crystals1 it is necessary to know something about crystals in general and the forms which they may assume4 ,an examination of a large number of crystals has shown that although they may differ much in geometric form1 they can all be considered as modifications of a few simple plans4 ,the best way to understand the relation of one crystal to another is to look upon every crystal as having its faces and angles arranged in definite fashion about certain imaginary lines drawn through the crystal4 ,these lines are called axes1 and bear much the same relation to a crystal as do the axis and parallels of latitude and longitude to the earth and a geographical study of it4 ,all crystals can be referred to one of six simple plans or systems1 which have their axes as shown in the following drawings4 ,the names and characteristics of these systems are as follows3 #a4 ,isometric or regular system 7,fig4 #df74 ,three equal axes1 all at right angles4 ,illustration3 ,fig4 #df #b4 ,tetragonal system 7,fig4 #dg74 ,two equal axes and one of different length1 all at right angles to each other4 ,illustration3 ,fig4 #dg #c4 ,orthorhombic system 7,fig4 #dh74 ,three unequal axes1 all at right angles to each other4 ,illustration3 ,fig4 #dh #d4 ,monoclinic system 7,fig4 #di74 ,two axes at right angles1 and a third at right angles to one of these1 but inclined to the other4 ,illustration3 ,fig4 #di #e4 ,triclinic system 7,fig4 #ej74 ,three axes1 all inclined to each other4 ,illustration3 ,fig4 #ej #f4 ,hexagonal system 7,fig4 #ea74 ,three equal axes in the same plane intersecting at angles of #fj1 and a fourth at right angles to all of these4 ,illustration3 ,fig4 #ea ,every crystal can be imagined to have its faces and angles arranged in a definite way around one of these systems of axes4 ,a cube1 for instance1 is referred to ,plan #a1 an axis ending in the center of each face2 while in a regular octohedron an axis ends in each solid angle4 ,these forms are shown in ,fig4 #df4 ,it will be seen that both of these figures belong to the same system1 though they are very different in appearance4 ,in the same way1 many geometric forms may be derived from each of the systems1 and the light lines about the axes in the drawings show two of the simplest forms of each of the systems4 ,in general a given substance always crystallizes in the same system1 and two corresponding faces of each crystal of it always make the same angle with each other4 ,a few substances1 of which sulphur is an example1 crystallize in two different systems1 and the crystals differ in such physical properties as melting point and density4 ,such substances are said to be dimorphous4 ,,exercises #a4 7a7 ,would the same amount of heat be generated by the combustion of #a g4 of each of the allotropic modifications of sulphur8 7b7 ,would the same amount of sulphur dioxide be formed in each case8 #b4 ,is the equation for the preparation of hydrosulphuric acid a reversible one8 ,as ordinarily carried out1 does the reaction complete itself8 #c4 ,suppose that hydrosulphuric acid were a liquid1 would it be necessary to modify the method of preparation8 #d4 ,can sulphuric acid be used to dry hydrosulphuric acid8 ,give reason for answer4 #e4 ,does dry hydrosulphuric acid react with litmus paper8 ,state reason for answer4 #f4 ,how many grams of iron sulphide are necessary to prepare #ajj l4 of hydrosulphuric acid when the laboratory conditions are #ag and #gdj mm4 pressure8 #g4 ,suppose that the hydrogen in #a l4 of hydrosulphuric acid were liberated2 what volume would it occupy1 the gases being measured under the same conditions8 #h4 ,write the equations representing the reaction between hydrosulphuric acid and sodium hydroxide and ammonium hydroxide respectively4 #i4 ,show that the preparation of sulphur dioxide from a sulphite is similar in principle to the preparation of hydrogen sulphide4 #aj4 7a7 ,does dry sulphur dioxide react with litmus paper8 7b7 ,how can it be shown that a solution of sulphur dioxide in water acts like an acid8 #aa4 7a7 ,calculate the percentage composition of sulphurous anhydride and sulphuric anhydride4 7b7 ,show how these two substances are in harmony with the law of multiple proportion4 #ab4 ,how many pounds of sulphur would be necessary in the preparation of #ajj lb4 of #ih sulphuric acid8 #ac4 ,what weight of sulphur dioxide is necessary in the preparation of #a kg4 of sodium sulphite8 #ad4 ,what weight of copper sulphate crystals can be obtained by dissolving #a kg4 of copper in sulphuric acid and crystallizing the product from water8 #ae4 ,write the names and formulas of the oxides and oxygen acids of selenium and tellurium4 #af4 ,in the commercial preparation of carbon disulphide1 what is the function of the electric current8 #ag4 ,if the ,gay-,lussac tower were omitted from the sulphuric acid factory1 what effect would this have on the cost of production of sulphuric acid8 ,,chapter ,,xv ,,periodic ,,law ,a number of the elements have now been studied somewhat closely4 ,the first three of these1 oxygen1 hydrogen1 and nitrogen1 while having some physical properties in common with each other1 have almost no point of similarity as regards their chemical conduct4 ,on the other hand1 oxygen and sulphur1 while quite different physically1 have much in common in their chemical properties4 ,about eighty elements are now known4 ,if all of these should have properties as diverse as do oxygen1 hydrogen1 and nitrogen1 the study of chemistry would plainly be a very difficult and complicated one4 ,if1 however1 the elements can be classified in groups1 the members of which have very similar properties1 the study will be very much simplified4 ,earlier classification of the elements4 ,even at an early period efforts were made to discover some natural principle in accordance with which the elements could be classified4 ,two of these classifications may be mentioned here4 #a4 ,classification into metals and non-metals4 ,the classification into metals and non-metals most naturally suggested itself4 ,this grouping was based largely on physical properties1 the metals being heavy1 lustrous1 malleable1 ductile1 and good conductors of heat and electricity4 ,elements possessing these properties are usually base-forming in character1 and the ability to form bases came to be regarded as a characteristic property of the metals4 ,the non-metals possessed physical properties which were the reverse of those of the metals1 and were acid-forming in character4 ,not much was gained by this classification1 and it was very imperfect4 ,some metals1 such as potassium1 are very light2 some non-metals1 such as iodine1 have a high luster2 some elements can form either an acid or a base4 #b4 ,classification into triad families4 ,in #ahbe ,dbereiner observed that an interesting relation exists between the atomic weights of chemically similar elements4 ,to illustrate1 lithium1 sodium1 and potassium resemble each other very closely1 and the atomic weight of sodium is almost exactly an arithmetical mean between those of the other two3 7#g4jc #ci4ae7_/b #bc4ji4 ,in many chemical and physical properties sodium is midway between the other two4 ,a number of triad families were found1 but among eighty elements1 whose atomic weights range all the way from #a to #bdj1 such agreements might be mere chance4 ,moreover many elements did not appear to belong to such families4 ,periodic division4 ,in #ahfi the ,russian chemist ,mendeleff devised an arrangement of the elements based on their atomic weights1 which has proved to be of great service in the comparative study of the elements4 ,a few months later the ,german1 ,lothar ,meyer1 independently suggested the same ideas4 ,this arrangement brought to light a great generalization1 now known as the periodic law4 ,an exact statement of the law will be given after the method of arranging the elements has been described4 ,illustration3 ,,dmitri ,,ivanovitch ,,mendel,,eff 7,russian7 7#ahcd-aijg7 ,author of the periodic law2 made many investigations on the physical constants of elements and compounds2 wrote an important book entitled ,principles of ,chemistry2 university professor and government official ,arrangement of the periodic table4 ,the arrangement suggested by ,mendeleff1 modified somewhat by more recent investigations1 is as follows3 ,beginning with lithium1 which has an atomic weight of #g1 the elements are arranged in a horizontal row in the order of their atomic weights1 thus3 ,li 7#g4jc71 ,be 7#i4a71 ,b 7#aa71 ,c 7#ab71 ,n 7#ad4jd71 ,o 7#af71 ,f 7#ai74 ,these seven elements all differ markedly from each other4 ,the eighth element1 sodium1 is very similar to lithium4 ,it is placed just under lithium1 and a new row follows3 ,na7#bc4je71 ,mg 7#bd4cf71 ,al 7#bg4a71 ,si 7#bh4d71 ,p 7#ca71 ,s 7#cb4jf71 ,cl7#ce4de74 ,when the fifteenth element1 potassium1 is reached1 it is placed under sodium1 to which it is very similar1 and serves to begin a third row3 ,k 7#ci4ae71 ,ca 7#dj4a71 ,sc 7#dd4a17 ,ti 7#dh4a71 ,v 7#ea4b71 ,cr 7#eb4a71 ,mn7#ee74 ,not only is there a strong similarity between lithium1 sodium1 and potassium1 which have been placed in a vertical row because of this resemblance1 but the elements in the other vertical rows exhibit much of the same kind of similarity among themselves1 and evidently form little natural groups4 ,the three elements following manganese1 namely1 iron1 nickel1 and cobalt1 have atomic weights near together1 and are very similar chemically4 ,they do not strongly resemble any of the elements so far considered1 and are accordingly placed in a group by themselves1 following manganese4 ,a new row is begun with copper1 which somewhat resembles the elements of the first vertical column4 ,following the fifth and seventh rows are groups of three closely related elements1 so that the completed arrangement has the appearance represented in the table on page #afh4 ,,the ,,periodic ,,arrangement ,,of ,,the ,,elements ---------------------------------------- ----------------------- ,periods ,,group ,,group ,,group ,,group ,,group #j ,i ,,ii ,,iii ,,iv ,a ,b,a ,b,a ,b,a ,b,a ,b ---------------------------------------- ----------------------- #a ,h#a4jjh #b ,he#d ,li#g4jc ,be#i4a ,b#aa ,c#ab ---------------------------------------- ----------------------- #c ,ne#bj,na#bc4je ,mg#bd4cf ,,al#bg4a ,si#bh4d ---------------------------------------- ----------------------- #d ,a#ci4i ,k#ci4ae ,ca#dj4a ,sc#dd4a ,ti#dh4a ---------------------------------------- ----------------------- #e ,cu#fc4f ,zn#fe4d ,ga#gj ,ge#gb4e ---------------------------------------- ----------------------- #f ,kr#ha4h ,rb#he4e ,sr#hg4f ,y#hi ,zr#ij4f ---------------------------------------- ----------------------- #g ,ag#ajg4ic ,cd#aab4d ,in#aae ,sn#aai ---------------------------------------- ----------------------- #h ,x#abh ,cs#acb4i ,ba#acg4d ,la#ach4i ,ce,yb99 #adj4be-agc ---------------------------------------- ----------------------- #i ,au#aig4b ,hg#bjj ,tl#bjd4a ,pb#bjf4i ,bi#bjh4e ---------------------------------------- ----------------------- #aj ,ra#bbe ,th#bcb4e ---------------------------------------- ----------------------- ,r#b,o ,,ro ,r#b,o#c ,,ro#b ,,rh ,,rh#b ,,rh#c ,,rh#d ---------------------------------------- ----------------------- part #b ---------------------------------------- ------------ ,periods ,,group ,,group ,,group ,,group ,v ,,vi ,,vii ,,viii ,a ,b,a ,b,a ,b ---------------------------------------- ------------ #a #b ,n#ad4jd ,o#af ,f#ai ---------------------------------------- ------------ #c ,p#ca ,s#cb4jf ,cl#ce4de ---------------------------------------- ------------ #d ,v#ea4b ,cr#eb4a ,mn#ee ,fe#ee4i ,ni#eh4g ,co#ei ---------------------------------------- ------------ #e ,as#ge ,se#gi4b ,br#gi4if ---------------------------------------- ------------ #f ,cb#id ,mo#if ,ru#aja4g ,rh#ajc ,pd#ajf4e ---------------------------------------- ------------ #g ,sb#abj4b ,te#abg4f ,i#abf4ig ---------------------------------------- ------------ #h ,ta#ahc ,w#ahd ,os#aia ,ir#aic ,pt#aid4h ---------------------------------------- ------------ #i ---------------------------------------- ------------ #aj ,u#bch4e ---------------------------------------- ------------ ,r#b,o#e ,,ro#c ,r#b,o#g ,,ro#d ,,rh#c ,,rh#b ,,rh ---------------------------------------- ------------ 99 ,this includes a number of elements whose atomic weights lie between #adj and #agc1 but which have not been accurately studied1 and so their proper arrangement is uncertain4 ,place of the atmospheric elements4 ,when argon was discovered it was seen at once that there was no place in the table for an element of atomic weight approximately #dj4 ,when the other inactive elements were found1 however1 it became apparent that they form a group just preceding ,group #a4 ,they are accordingly arranged in this way in ,group #j 7see table on opposite page74 ,a study of this table brings to light certain very striking facts4 ,properties of elements vary with atomic weights4 ,there is evidently a close relation between the properties of an element and its atomic weight4 ,lithium1 at the beginning of the first group1 is a very strong base-forming element1 with pronounced metallic properties4 ,beryllium1 following lithium1 is less strongly base-forming1 while boron has some base-forming and some acid-forming properties4 ,in carbon all base-forming properties have disappeared1 and the acid-forming properties are more marked than in boron4 ,these become still more emphasized as we pass through nitrogen and oxygen1 until on reaching fluorine we have one of the strongest acid-forming elements4 ,the properties of these seven elements therefore vary regularly with their atomic weights1 or1 in mathematical language1 are regular functions of them4 ,periodic law4 ,the properties of the first seven elements vary continuously--that is steadily--away from base-forming and toward acid-forming properties4 ,if lithium had the smallest atomic weight of any of the elements1 and fluorine the greatest1 so that in passing from one to the other we had included all the elements1 we could say that the properties of elements are continuous functions of their atomic weights4 ,but fluorine is an element of small atomic weight1 and the one following it1 sodium1 breaks the regular order1 for in it reappear all the characteristic properties of lithium4 ,magnesium1 following sodium1 bears much the same relation to beryllium that sodium does to lithium1 and the properties of the elements in the second row vary much as they do in the first row until potassium is reached1 when another repetition begins4 ,the properties of the elements do not vary continuously1 therefore1 with atomic weights1 but at regular intervals there is a repetition1 or period4 ,this generalization is known as the periodic law1 and may be stated thus3 ,the properties of elements are periodic functions of their atomic weights4 ,the two families in a group4 ,while all the elements in a given vertical column bear a general resemblance to each other1 it has been noticed that those belonging to periods having even numbers are very strikingly similar to each other4 ,they are placed at the left side of the group columns4 ,in like manner1 the elements belonging to the odd periods are very similar and are arranged at the right side of the group columns4 ,thus calcium1 strontium1 and barium are very much alike2 so1 too1 are magnesium1 zinc1 and cadmium4 ,the resemblance between calcium and magnesium1 or strontium and zinc1 is much less marked4 ,this method of arrangement therefore divides each group into two families1 each containing four or five members1 between which there is a great similarity4 ,family resemblances4 ,let us now inquire more closely in what respects the elements of a family resemble each other4 #a4 ,valence4 ,in general the valence of the elements in a family is the same1 and the formulas of their compounds are therefore similar4 ,if we know that the formula of sodium chloride is ,na,cl1 it is pretty certain that the formula of potassium chloride will be ,k,cl--not ,k,cl#b or ,k,cl#c4 ,the general formulas ,r#b,o1 ,,ro1 etc41 placed below the columns show the formulas of the oxides of the elements in the column provided they form oxides4 ,in like manner the formulas ,,rh1 ,,rh#b1 etc41 show the composition of the compounds formed with hydrogen or chlorine4 #b4 ,chemical properties4 ,the chemical properties of the members of a family are quite similar4 ,if one member is a metal1 the others usually are2 if one is a non-metal1 so1 too1 are the others4 ,the families in the first two columns consist of metals1 while the elements found in the last two columns form acids4 ,there is in addition a certain regularity in properties of the elements in each family4 ,if the element at the head of the family is a strong acid-forming element1 this property is likely to diminish gradually1 as we pass to the members of the family with higher atomic weights4 ,thus phosphorus is strongly acid-forming1 arsenic less so1 antimony still less so1 while bismuth has almost no acid-forming properties4 ,we shall meet with many illustrations of this fact4 #c4 ,physical properties4 ,in the same way1 the physical properties of the members of a family are in general somewhat similar1 and show a regular gradation as we pass from element to element in the family4 ,thus the densities of the members of the magnesium family are ,mg #a4ge1 ,zn #g4jj1 ,cd #h4fg1 ,hg #ac4f4 ,their melting points are ,mg #gej1 ,zn #dbj1 ,cd #cbj1 ,hg -#ci4e4 ,value of the periodic law4 ,the periodic law has proved of much value in the development of the science of chemistry4 #a4 ,it simplifies study4 ,it is at once evident that such regularities very much simplify the study of chemistry4 ,a thorough study of one element of a family makes the study of the other members a much easier task1 since so many of the properties and chemical reactions of the elements are similar4 ,thus1 having studied the element sulphur in some detail1 it is not necessary to study selenium and tellurium so closely1 for most of their properties can be predicted from the relation which they sustain to sulphur4 #b4 ,it predicts new elements4 ,when the periodic law was first formulated there were a number of vacant places in the table which evidently belonged to elements at that time unknown4 ,from their position in the table1 ,mendeleff predicted with great precision the properties of the elements which he felt sure would one day be discovered to fill these places4 ,three of them1 scandium1 germanium1 and gallium1 were found within fifteen years1 and their properties agreed in a remarkable way with the predictions of ,mendeleff4 ,there are still some vacant places in the table1 especially among the heavier elements4 #c4 ,it corrects errors4 ,the physical constants of many of the elements did not at first agree with those demanded by the periodic law1 and a further study of many such cases showed that errors had been made4 ,the law has therefore done much service in indicating probable error4 ,imperfections of the law4 ,there still remain a good many features which must be regarded as imperfections in the law4 ,most conspicuous is the fact that the element hydrogen has no place in the table4 ,in some of the groups elements appear in one of the families1 while all of their properties show that they belong in the other4 ,thus sodium belongs with lithium and not with copper2 fluorine belongs with chlorine and not with manganese4 ,there are two instances where the elements must be transposed in order to make them fit into their proper group4 ,according to their atomic weights1 tellurium should follow iodine1 and argon should follow potassium4 ,their properties show in each case that this order must be reversed4 ,the table separates some elements altogether which1 in many respects have closely agreeing properties4 ,iron1 chromium1 and manganese are all in different groups1 although they are similar in many respects4 ,the system is therefore to be regarded as but a partial and imperfect expression of some very important and fundamental relation between the substances which we know as elements1 the exact nature of this relation being as yet not completely clear to us4 ,,exercises #a4 ,suppose that an element were discovered that filled the blank in ,group ,o1 ,period #e2 what properties would it probably have8 #b4 ,suppose that an element were discovered that filled the blank in ,group ,,vi1 ,period #i1 family ,b2 what properties would it have8 #c4 ,sulphur and oxygen both belong in ,group ,,vi1 although in different families2 in what respects are the two similar8 ,,chapter ,,xvi ,,the ,,chlorine ,,family ,,atomic ,,melting ,,boiling ,,color ,,and ,,state ,,weight ,,point ,,point ,fluorine 7,f7 #ai4jj -#bbc -#ahg ,pale yellowish gas4 ,chlorine 7,cl7 #ce4de -#ajb -#cc4f ,greenish-yellow gas4 ,bromine 7,br7 #gi4if -#g #ei ,red liquid4 ,iodine 7,i7 #abf4ig #ajg #age ,purplish-black solid4 ,the family4 ,the four elements named in the above table form a strongly marked family of elements and illustrate very clearly the way in which the members of a family in a periodic group resemble each other1 as well as the character of the differences which we may expect to find between the individual members4 #a4 ,occurrence4 ,these elements do not occur in nature in the free state4 ,the compounds of the last three elements of the family are found extensively in sea water1 and on this account the name halogens1 signifying producers of sea salt1 is sometimes applied to the family4 #b4 ,properties4 ,as will be seen by reference to the table1 the melting points and boiling points of the elements of the family increase with their atomic weights4 ,a somewhat similar gradation is noted in their color and state4 ,one atom of each of the elements combines with one atom of hydrogen to form acids1 which are gases very soluble in water4 ,the affinity of the elements for hydrogen is in the inverse order of their atomic weights1 fluorine having the strongest affinity and iodine the weakest4 ,only chlorine and iodine form oxides1 and those of the former element are very unstable4 ,the elements of the group are univalent in their compounds with hydrogen and the metals4 ,,fluorine ,occurrence4 ,the element fluorine occurs in nature most abundantly as the mineral fluorspar 7,ca,f#b71 as cryolite 7,na#c;,al,f#f71 and in the complex mineral apatite 7#c ,ca#c7,,po#d7b;,ca,f#b74 ,preparation4 ,all attempts to isolate the element resulted in failure until recent years4 ,methods similar to those which succeed in the preparation of the other elements of the family cannot be used2 for as soon as the fluorine is liberated it combines with the materials of which the apparatus is made or with the hydrogen of the water which is always present4 ,the preparation of fluorine was finally accomplished by the ,french chemist ,moissan by the electrolysis of hydrofluoric acid4 ,perfectly dry hydrofluoric acid 7,,hf7 was condensed to a liquid and placed in a ,u-shaped tube made of platinum 7or copper71 which was furnished with electrodes and delivery tubes1 as shown in ,fig4 #eb4 ,this liquid is not an electrolyte1 but becomes such when potassium fluoride is dissolved in it4 ,when this solution was electrolyzed hydrogen was set free at the cathode and fluorine at the anode4 ,illustration3 ,fig4 #eb ,properties4 ,fluorine is a gas of slightly yellowish color1 and can be condensed to a liquid boiling at -#ahg under atmospheric pressure4 ,it solidifies at -#bbc4 ,it is extremely active chemically1 being the most active of all the elements at ordinary temperatures4 ,it combines with all the common elements save oxygen1 very often with incandescence and the liberation of much heat4 ,it has a strong affinity for hydrogen and is able to withdraw it from its compounds with other elements4 ,because of its great activity it is extremely poisonous4 ,fluorine does not form any oxides1 neither does it form any oxygen acids1 in which respects it differs from the other members of the family4 ,hydrofluoric acid 7,,hf74 ,hydrofluoric acid is readily obtained from fluorspar by the action of concentrated sulphuric acid4 ,the equation is ,ca,f#b ,h#b,,so#d ,ca,s,o#d #b;,,hf4 ,in its physical properties it resembles the binary acids of the other elements of this family1 being1 however1 more easily condensed to a liquid4 ,the anhydrous acid boils at #ai and can therefore be prepared at ordinary pressures4 ,it is soluble in all proportions in water1 and a concentrated solution--about #ej--;is prepared for the market4 ,its fumes are exceedingly irritating to the respiratory organs1 and several chemists have lost their lives by accidentally breathing them4 ,illustration3 ,,henri ,,moissan 7,french7 7#ahec-aijg7 ,famous for his work with the electric furnace at high temperatures2 prepared artificial diamonds1 together with many new binary compounds such as carbides1 silicides1 borides1 and nitrides2 isolated fluorine and studied its properties and its compounds very thoroughly ,chemical properties4 ,hydrofluoric acid1 like other strong acids1 readily acts on bases and metallic oxides and forms the corresponding fluorides4 ,it also dissolves certain metals such as silver and copper4 ,it acts very vigorously upon organic matter1 a single drop of the concentrated acid making a sore on the skin which is very painful and slow in healing4 ,its most characteristic property is its action upon silicon dioxide 7,si,o#b71 with which it forms water and the gas silicon tetrafluoride 7,si,f#d71 as shown in the equation ,si,o#b #d;,,hf ,si,f#d #b;,h#b,o4 ,glass consists of certain compounds of silicon1 which are likewise acted on by the acid so that it cannot be kept in glass bottles4 ,it is preserved in flasks made of wax or gutta-percha4 ,etching4 ,advantage is taken of this reaction in etching designs upon glass4 ,the glass vessel is painted over with a protective paint upon which the acid will not act1 the parts which it is desired to make opaque being left unprotected4 ,a mixture of fluorspar and sulphuric acid is then painted over the vessel and after a few minutes the vessel is washed clean4 ,wherever the hydrofluoric acid comes in contact with the glass it acts upon it1 destroying its luster and making it opaque1 so that the exposed design will be etched upon the clear glass4 ,frosted glass globes are often made in this way4 ,the etching may also be effected by covering the glass with a thin layer of paraffin1 cutting the design through the wax and then exposing the glass to the fumes of the acid4 ,salts of hydrofluoric acid1--fluorides4 ,a number of the fluorides are known1 but only one of them1 calcium fluoride 7,ca,f#b71 is of importance4 ,this is the well-known mineral fluorspar4 ,,chlorine ,historical4 ,while studying the action of hydrochloric acid upon the mineral pyrolusite1 in #aggd1 ,scheele obtained a yellowish1 gaseous substance to which he gave a name in keeping with the phlogiston theory then current4 ,later it was supposed to be a compound containing oxygen4 ,in #ahaj1 however1 the ,english chemist ,sir ,humphry ,davy proved it to be an element and named it chlorine4 ,occurrence4 ,chlorine does not occur free in nature1 but its compounds are widely distributed4 ,for the most part it occurs in combination with the metals in the form of chlorides1 those of sodium1 potassium1 and magnesium being most abundant4 ,nearly all salt water contains these substances1 particularly sodium chloride1 and very large salt beds consisting of chlorides are found in many parts of the world4 ,preparation4 ,two general methods of preparing chlorine may be mentioned1 namely1 the laboratory method and the electrolytic method4 #a4 ,laboratory method4 ,in the laboratory chlorine is made by warming the mineral pyrolusite 7manganese dioxide1 ,mn,o#b7 with concentrated hydrochloric acid4 ,the first reaction1 which seems to be similar to the action of acids upon oxides in general1 is expressed in the equation ,mn,o#b #d;,h,cl ,mn,cl#d #b;,h#b,o4 ,the manganese compound so formed is very unstable1 however1 and breaks clown according to the equation ,mn,cl#d ,mn,cl#b #b;,cl4 ,instead of using hydrochloric acid in the preparation of chlorine it will serve just as well to use a mixture of sodium chloride and sulphuric acid1 since these two react to form hydrochloric acid4 ,the following equations will then express the changes3 7#a7 #b,na,cl ,h#b,,so#d ,na#b,,so#d #b;,h,cl4 7#b7 ,mn,o#b #d ,h,cl ,mn,cl#b #b;,cl #b;,h#b,o4 7#c7 ,mn,cl#b ,h#b,,so#d ,mn,s,o#d #b;,h,cl4 ,combining these equations1 the following equation expressing the complete reaction is obtained3 #b,na,cl ,mn,o#b #b;,h#b,,so#d ,mn,s,o#d ,na#b,,so#d #b;,h#b,o #b;,cl4 ,since the hydrochloric acid liberated in the third equation is free to act upon manganese dioxide1 it will be seen that all of the chlorine originally present in the sodium chloride is set free4 ,the manganese dioxide and the hydrochloric acid are brought together in a flask1 as represented in ,fig4 #ec1 and a gentle heat is applied4 ,the rate of evolution of the gas is regulated by the amount of heat applied1 and the gas is collected by displacement of air4 ,as the equations show1 only half of the chlorine present in the hydrochloric acid is liberated4 ,illustration3 ,fig4 #ec #b4 ,electrolytic method4 ,under the discussion of electrolysis 7p4 #ajb7 it was shown that when a solution of sodium chloride is electrolyzed chlorine is evolved at the anode1 while the sodium set free at the cathode reacts with the water to form hydrogen1 which is evolved1 and sodium hydroxide1 which remains in solution4 ,a great deal of the chlorine required in the chemical industries is now made in this way in connection with the manufacture of sodium hydroxide4 ,physical properties4 ,chlorine is a greenish-yellow gas1 which has a peculiar suffocating odor and produces a very violent effect upon the throat and lungs4 ,even when inhaled in small quantities it often produces all the symptoms of a hard cold1 and in larger quantities may have serious and even fatal action4 ,it is quite heavy 7density #b4de7 and can therefore be collected by displacement of air4 ,one volume of water under ordinary conditions dissolves about three volumes of chlorine4 ,the gas is readily liquefied1 a pressure of six atmospheres serving to liquefy it at #j4 ,it forms a yellowish liquid which solidifies at -#ajb4 ,chemical properties4 ,at ordinary temperatures chlorine is far more active chemically than any of the elements we have so far considered1 with the exception of fluorine2 indeed1 it is one of the most active of all elements4 #a4 ,action on metals4 ,a great many metals combine directly with chlorine1 especially when hot4 ,a strip of copper foil heated in a burner flame and then dropped into chlorine burns with incandescence4 ,sodium burns brilliantly when heated strongly in slightly moist chlorine4 ,gold and silver are quickly tarnished by the gas4 #b4 ,action on non-metals4 ,chlorine has likewise a strong affinity for many of the non-metals4 ,thus phosphorus burns in a current of the gas1 while antimony and arsenic in the form of a fine powder at once burst into flame when dropped into jars of the gas4 ,the products formed in all cases where chlorine combines with another element are called chlorides4 #c4 ,action on hydrogen4 ,chlorine has a strong affinity for hydrogen1 uniting with it to form hydrochloric acid4 ,a jet of hydrogen burning in the air continues to burn when introduced into a jar of chlorine1 giving a somewhat luminous flame4 ,a mixture of the two gases explodes violently when a spark is passed through it or when it is exposed to bright sunlight4 ,in the latter case it is the light and not the heat which starts the action4 #d4 ,action on substances containing hydrogen4 ,not only will chlorine combine directly with free hydrogen but it will often abstract the element from its compounds4 ,thus1 when chlorine is passed into a solution containing hydrosulphuric acid1 sulphur is precipitated and ,hydrochloric acid formed4 ,the reaction is shown by the following equation3 ,h#b,s #b;,cl #b;,h,cl ,s4 ,with ammonia the action is similar3 ,,nh#c #c;,cl #c;,h,cl ,n4 ,the same tendency is very strikingly seen in the action of chlorine upon turpentine4 ,the latter substance is largely made up of compounds having the composition represented by the formula ,c#aj;,h#af4 ,when a strip of paper moistened with warm turpentine is placed in a jar of chlorine dense fumes of hydrochloric acid appear and a black deposit of carbon is formed4 ,even water1 which is a very stable compound1 can be decomposed by chlorine1 the oxygen being liberated4 ,this may be shown in the following way3 ,illustration3 ,fig4 #ed ,if a long tube of rather large diameter is filled with a strong solution of chlorine in water and inverted in a vessel of the same solution1 as shown in ,fig4 #ed1 and the apparatus is placed in bright sunlight1 very soon bubbles of a gas will be observed to rise through the solution and collect in the tube4 ,an examination of this gas will show that it is oxygen4 ,it is liberated from water in accordance with the following equation3 ,h#b,o #b;,cl #b;,h,cl ,o4 #e4 ,action on color substances1--bleaching action4 ,if strips of brightly colored cloth or some highly colored flowers are placed in quite dry chlorine1 no marked change in color is noticed as a rule4 ,if1 however1 the cloth and flowers are first moistened1 the color rapidly disappears1 that is1 the objects are bleached4 ,evidently the moisture as well as the chlorine is concerned in the action1 and a study of the case shows that the chlorine has combined with the hydrogen of the water4 ,the oxygen set free oxidizes the color substance1 converting it into a colorless compound4 ,it is evident from this explanation that chlorine will only bleach those substances which are changed into colorless compounds by oxidation4 #f4 ,action as a disinfectant4 ,chlorine has also marked germicidal properties1 and the free element1 as well as compounds from which it is easily liberated1 are used as disinfectants4 ,nascent state4 ,it will be noticed that oxygen when set free from water by chlorine is able to do what ordinary oxygen cannot do1 for both the cloth and the flowers are unchanged in the air which contains oxygen4 ,it is generally true that the activity of an element is greatest at the instant of liberation from its compounds4 ,to express this fact elements at the instant of liberation are said to be in the nascent state4 ,it is nascent oxygen which does the bleaching4 ,hydrochloric acid 7muriatic acid7 7,h,cl74 ,the preparation of hydrochloric acid may be discussed under two general heads3 #a4 ,laboratory preparation4 ,the product formed by the burning of hydrogen in chlorine is the gas hydrochloric acid4 ,this substance is much more easily obtained1 however1 by treating common salt 7sodium chloride7 with sulphuric acid4 ,the following equation shows the reaction3 #b,na,cl ,h#b,,so#d ,na#b,,so#d #b;,h,cl4 ,the dry salt is placed in a flask furnished with a funnel tube and an exit tube1 the sulphuric acid is added1 and the flask gently warmed4 ,the hydrochloric acid gas is rapidly given off and can be collected by displacement of air4 ,the same apparatus can be used as was employed in the preparation of chlorine 7,fig4 #ec74 ,when a solution of salt is treated with sulphuric acid there is no very marked action4 ,the hydrochloric acid formed is very soluble in water1 and so does not escape from the solution2 hence a state of equilibrium is soon reached between the four substances represented in the equation4 ,when concentrated sulphuric acid1 in which hydrochloric acid is not soluble1 is poured upon dry salt the reaction is complete4 #b4 ,commercial preparation4 ,commercially1 hydrochloric acid is prepared in connection with the manufacture of sodium sulphate1 the reaction being the same as that just given4 ,the reaction is carried out in a furnace1 and the hydrochloric acid as it escapes in the form of gas is passed into water in which it dissolves1 the solution forming the hydrochloric acid of commerce4 ,when the materials are pure a colorless solution is obtained4 ,the most concentrated solution has a density of #a4b and contains #dj ,h,cl4 ,the commercial acid1 often called muriatic acid1 is usually colored yellow by impurities4 ,composition of hydrochloric acid4 ,when a solution of hydrochloric acid is electrolyzed in an apparatus similar to the one in which water was electrolyzed 7,fig4 #ah71 chlorine collects at the anode and hydrogen at the cathode4 ,at first the chlorine dissolves in the water1 but soon the water in the one tube becomes saturated with it1 and if the stopcocks are left open until this is the case1 and are then closed1 it will be seen that the two gases are set free in equal volumes4 ,when measured volumes of the two gases are caused to unite it is found that one volume of hydrogen combines with one of chlorine4 ,other experiments show that the volume of hydrochloric acid formed is just equal to the sum of the volumes of hydrogen and chlorine4 ,therefore one volume of hydrogen combines with one volume of chlorine to form two volumes of hydrochloric acid gas4 ,since chlorine is #ce4ah times as heavy as hydrogen1 it follows that one part of hydrogen by weight combines with #ce4ah parts of chlorine to form #cf4ah parts of hydrochloric acid4 ,physical properties4 ,hydrochloric acid is a colorless gas which has an irritating effect when inhaled1 and possesses a sour1 biting taste1 but no marked odor4 ,it is heavier than air 7density #a4bf7 and is very soluble in water4 ,under standard conditions #a volume of water dissolves about #ejj volumes of the gas4 ,on warming such a solution the gas escapes1 until at the boiling point the solution contains about #bj by weight of ,h,cl4 ,further boiling will not drive out any more acid1 but the solution will distill with unchanged concentration4 ,a more dilute solution than this will lose water on boiling until it has reached the same concentration1 #bj1 and will then distill unchanged4 ,under high pressure the gas can be liquefied1 #bh atmospheres being required at #j4 ,under these conditions it forms a colorless liquid which is not very active chemically4 ,it boils at -#hj and solidifies at -#aac4 ,the solution of the gas in water is used almost entirely in the place of the gas itself1 since it is not only far more convenient but also more active4 ,chemical properties4 ,the most important chemical properties of hydrochloric acid are the following3 #a4 ,action as an acid4 ,in aqueous solution hydrochloric acid has very strong acid properties2 indeed1 it is one of the strongest acids4 ,it acts upon oxides and hydroxides1 converting them into salts3 ,na,o,h ,h,cl ,na,cl ,h#b,o1 ,cu,o #b;,h,cl ,cu,cl#b ,h#b,o4 ,it acts upon many metals1 forming chlorides and liberating hydrogen3 ,zn #b;,h,cl ,zn,cl#b #b;,h1 ,al #c;,h,cl ,al,cl#c #c;,h4 ,unlike nitric and sulphuric acids it has no oxidizing action1 so that when it acts on metals hydrogen is always given off4 #b4 ,relation to combustion4 ,hydrochloric acid gas is not readily decomposed1 and is therefore neither combustible nor a supporter of combustion4 #c4 ,action on oxidizing agents4 ,although hydrochloric acid is incombustible1 it can be oxidized under some circumstances1 in which case the hydrogen combines with oxygen1 while the chlorine is set free4 ,thus1 when a solution of hydrochloric acid acts upon manganese dioxide part of the chlorine is set free3 ,mn,o#b #d;,h,cl ,mn,cl#b #b;,h#b,o #b;,cl4 ,aqua regia4 ,it has been seen that when nitric acid acts as an oxidizing agent it usually decomposes1 as represented in the equation #b;,,hno#c ,h#b,o #b,,no #c,o4 ,the oxygen so set free may act on hydrochloric acid3 #f;,h,cl #c,o #c;,h#b,o #f;,cl4 ,the complete equation therefore is #b;,,hno#c #f;,h,cl #d;,h#b,o #b,,no #f;,cl4 ,when concentrated nitric and hydrochloric acids are mixed this reaction goes on slowly1 chlorine and some other substances not represented in the equation being formed4 ,the mixture is known as aqua regia and is commonly prepared by adding one volume of nitric acid to three volumes of hydrochloric acid4 ,it acts more powerfully upon metals and other substances than either of the acids separately1 and owes its strength not to acid properties but to the action of the nascent chlorine which it liberates4 ,consequently1 when it acts upon metals such as gold it converts them into chlorides1 and the reaction can be represented by such equations as ,au #c;,cl ,au,cl#c4 ,salts of hydrochloric acid1--chlorides4 ,the chlorides of all the metals are known and many of them are very important compounds4 ,some of them are found in nature1 and all can be prepared by the general method of preparing salts4 ,silver chloride1 lead chloride1 and mercurous chloride are insoluble in water and acids1 and can be prepared by adding hydrochloric acid to solutions of compounds of the respective elements4 ,while the chlorides have formulas similar to the fluorides1 their properties are often quite different4 ,this is seen in the solubility of the salts4 ,those metals whose chlorides are insoluble form soluble fluorides1 while many of the metals which form soluble chlorides form insoluble fluorides4 ,compounds of chlorine with oxygen and hydrogen4 ,chlorine combines with oxygen and hydrogen to form four different acids4 ,they are all quite unstable1 and most of them cannot be prepared in pure form2 their salts can easily be made1 however1 and some of them will be met with in the study of the metals4 ,the formulas and names of these acids are as follows3 ,h,cl,o hypochlorous acid4 ,h,cl,o#b chlorous acid4 ,h,cl,o#c chloric acid4 ,h,cl,o#d perchloric acid4 ,oxides of chlorine4 ,two oxides are known1 having the formulas ,cl#b,o and ,cl,o#b4 ,they decompose very easily and are good oxidizing agents4 ,,bromine ,historical4 ,bromine was discovered in #ahbf by the ,french chemist ,ballard1 who isolated it from sea salt4 ,he named it bromine 7stench7 because of its unbearable fumes4 ,occurrence4 ,bromine occurs almost entirely in the form of bromides1 especially as sodium bromide and magnesium bromide1 which are found in many salt springs and salt deposits4 ,the ,stassfurt deposits in ,germany and the salt waters of ,ohio and ,michigan are especially rich in bromides4 ,preparation of bromine4 ,the laboratory method of preparing bromine is essentially different from the commercial method4 ,illustration ,fig4 #ee #a4 ,laboratory method4 ,as in the case of chlorine1 bromine can be prepared by the action of hydrobromic acid 7,h,br7 on manganese dioxide4 ,since hydrobromic acid is not an article of commerce1 a mixture of sulphuric acid and a bromide is commonly substituted for it4 ,the materials are placed in a retort arranged as shown in ,fig4 #ee4 ,the end of the retort just touches the surface of the water in the test tube4 ,on heating1 the bromine distills over and is collected in the cold receiver4 ,the equation is #b,na,br #b;,h#b,,so#d ,mn,o#b ,na#b,,so#d ,mn,s,o#d #b;,h#b,o #b;,br4 #b4 ,commercial method4 ,bromine is prepared commercially from the waters of salt wells which are especially rich in bromides4 ,on passing a current of electricity through such waters the bromine is first liberated4 ,any chlorine liberated1 however1 will assist in the reaction1 since free chlorine decomposes bromides1 as shown in the equation ,na,br ,cl ,na,cl ,br4 ,when the water containing the bromine is heated1 the liberated bromine distills over into the receiver4 ,physical properties4 ,bromine is a dark red liquid about three times as heavy as water4 ,its vapor has a very offensive odor and is most irritating to the eyes and throat4 ,the liquid boils at #ei and solidifies at -#g2 but even at ordinary temperatures it evaporates rapidly1 forming a reddish-brown gas very similar to nitrogen peroxide in appearance4 ,bromine is somewhat soluble in water1 #ajj volumes of water under ordinary conditions dissolving #a volume of the liquid4 ,it is readily soluble in carbon disulphide1 forming a yellow solution4 ,chemical properties and uses4 ,in chemical action bromine is very similar to chlorine4 ,it combines directly with many of the same elements with which chlorine unites1 but with less energy4 ,it combines with hydrogen and takes away the latter element from some of its compounds1 but not so readily as does chlorine4 ,its bleaching properties are also less marked4 ,bromine finds many uses in the manufacture of organic drugs and dyestuffs and in the preparation of bromides4 ,hydrobromic acid 7,h,br74 ,when sulphuric acid acts upon a bromide hydrobromic acid is set free3 #b,na,br ,h#b,,so#d ,na#b,,so#d #b;,h,br4 ,at the same time some bromine is set free1 as may be seen from the red fumes which appear1 and from the odor4 ,the explanation of this is found in the fact that hydrobromic acid is much less stable than hydrochloric acid1 and is therefore more easily oxidized4 ,concentrated sulphuric acid is a good oxidizing agent1 and oxidizes a part of the hydrobromic acid1 liberating bromine3 ,h#b,,so#d #b;,h,br #b;,h#b,o ,,so#b #b;,br4 ,preparation of pure hydrobromic acid4 ,a convenient way to make pure hydrobromic acid is by the action of bromine upon moist red phosphorus4 ,this can be done with the apparatus shown in ,fig4 #ef4 ,bromine is put into the dropping funnel ,a1 and red phosphorus1 together with enough water to cover it1 is placed in the flask ,b4 ,by means of the stopcock the bromine is allowed to flow drop by drop into the flask1 the reaction taking place without the application of heat4 ,the equations are 7#a7 ,p #c;,br ,p,br#c1 7#b7 ,p,br#c #c;,h#b,o ,p7,,oh7#c #c;,h,br4 ,illustration ,fig4 #ef ,the ,u-tube ,c contains glass beads which have been moistened with water and rubbed in red phosphorus4 ,any bromine escaping action in the flask acts upon the phosphorus in the ,u-tube4 ,the hydrobromic acid is collected in the same way as hydrochloric acid4 ,properties4 ,hydrobromic acid very strikingly resembles hydrochloric acid in physical and chemical properties4 ,it is a colorless1 strongly fuming gas1 heavier than hydrochloric acid and1 like it1 is very soluble in water4 ,under standard conditions #a volume of water dissolves #faj volumes of the gas4 ,chemically1 the chief point in which it differs from hydrochloric acid is in the fact that it is much more easily oxidized1 so that bromine is more readily set free from it than chlorine is from hydrochloric acid4 ,salts of hydrobromic acid1--bromides4 ,the bromides are very similar to the chlorides in their properties4 ,chlorine acts upon both bromides and free hydrobromic acid1 liberating bromine from them3 ,k,br ,cl ,k,cl ,br1 ,h,br ,cl ,h,cl ,br4 ,silver bromide is extensively used in photography1 and the bromides of sodium and potassium are used as drugs4 ,oxygen compounds4 ,no oxides of bromine are surely known1 and bromine does not form so many oxygen acids as chlorine does4 ,salts of hypobromous acid 7,h,br,o7 and bromic acid 7,h,br,o#c7 are known4 ,,iodine ,historical4 ,iodine was discovered in #ahab by ,courtois in the ashes of certain sea plants4 ,its presence was revealed by its beautiful violet vapor1 and this suggested the name iodine 7from the ,greek for violet appearance74 ,occurrence4 ,in the combined state iodine occurs in very small quantities in sea water1 from which it is absorbed by certain sea plants1 so that it is found in their ashes4 ,it occurs along with bromine in salt springs and beds1 and is also found in ,chili saltpeter4 ,preparation4 ,iodine may be prepared in a number of ways1 the principal methods being the following3 #a4 ,laboratory method4 ,iodine can readily be prepared in the laboratory from an iodide by the method used in preparing bromine1 except that sodium iodide is substituted for sodium bromide4 ,it can also be made by passing chlorine into a solution of an iodide4 ,illustration3 ,fig4 #eg #b4 ,commercial method4 ,commercially iodine was formerly prepared from seaweed 7kelp71 but is now obtained almost entirely from the deposits of ,chili saltpeter4 ,the crude saltpeter is dissolved in water and the solution evaporated until the saltpeter crystallizes4 ,the remaining liquors1 known as the mother liquors1 contain sodium iodate 7,na,i,o#c71 in which form the iodine is present in the saltpeter4 ,the chemical reaction by which the iodine is liberated from this compound is a complicated one1 depending on the fact that sulphurous acid acts upon iodic acid1 setting iodine free4 ,this reaction is shown as follows3 #b;,,hio#c #e;,h#b,,so#c #e;,h#b,,so#d ,h#b,o #b;,i4 ,purification of iodine4 ,iodine can be purified very conveniently in the following way4 ,the crude iodine is placed in an evaporating dish ,e 7,fig4 #eg71 and the dish is set upon the sand bath ,s4 ,the iodine is covered with the inverted funnel ,f1 and the sand bath is gently heated with a ,bunsen burner4 ,as the dish becomes warm the iodine rapidly evaporates and condenses again on the cold surface of the funnel in shining crystals4 ,this process1 in which a solid is converted into a vapor and is again condensed into a solid without passing through the liquid state1 is called sublimation4 ,physical properties4 ,iodine is a purplish-black1 shining1 heavy solid which crystallizes in brilliant plates4 ,even at ordinary temperatures it gives off a beautiful violet vapor1 which increases in amount as heat is applied4 ,it melts at #ajg and boils at #age4 ,it is slightly soluble in water1 but readily dissolves in alcohol1 forming a brown solution 7tincture of iodine71 and in carbon disulphide1 forming a violet solution4 ,the element has a strong1 unpleasant odor1 though by no means as irritating as that of chlorine and bromine4 ,chemical properties4 ,chemically iodine is quite similar to chlorine and bromine1 but is still less active than bromine4 ,it combines directly with many elements at ordinary temperatures4 ,at elevated temperatures it combines with hydrogen1 but the reaction is reversible and the compound formed is quite easily decomposed4 ,both chlorine and bromine displace it from its salts3 ,,ki ,br ,k,br ,i1 ,,ki ,cl ,k,cl ,i4 ,when even minute traces of iodine are added to thin starch paste a very intense blue color develops1 and this reaction forms a delicate test for iodine4 ,iodine is extensively used in medicine1 especially in the form of a tincture4 ,it is also largely used in the preparation of dyes and organic drugs1 iodoform1 a substance used as an antiseptic1 has the formula ,,chi#c4 ,hydriodic acid 7,,hi74 ,this acid cannot be prepared in pure condition by the action of sulphuric acid upon an iodide1 since the hydriodic acid set free is oxidized by the sulphuric acid just as in the case of hydrobromic acid1 but to a much greater extent4 ,it can be prepared in exactly the same way as hydrobromic acid1 iodine being substituted for bromine4 ,it can also be prepared by passing hydrosulphuric acid into water in which iodine is suspended4 ,the equation is ,h#b,s #b;,i #b;,,hi ,s4 ,the hydriodic acid formed in this way dissolves in the water4 ,properties and uses4 ,hydriodic acid resembles the corresponding acids of chlorine and bromine in physical properties1 being a strongly fuming1 colorless gas1 readily soluble in water4 ,under standard conditions #a volume of water dissolves about #dfj volumes of the gas4 ,it is1 however1 more unstable than either hydrochloric or hydrobromic acids1 and on exposure to the air it gradually decomposes in accordance with the equation #b;,,hi ,o ,h#b,o #b;,i4 ,owing to the slight affinity between iodine and hydrogen the acid easily gives up its hydrogen and is therefore a strong reducing agent4 ,this is seen in its action on sulphuric acid4 ,the salts of hydriodic acid1 the iodides1 are1 in general1 similar to the chlorides and bromides4 ,potassium iodide 7,,ki7 is the most familiar of the iodides and is largely used in medicine4 ,oxygen compounds4 ,iodine has a much greater affinity for oxygen than has either chlorine or bromine4 ,when heated with nitric acid it forms a stable oxide 7,i#b,o#e74 ,salts of iodic acid 7,,hio#c7 and periodic acid 7,,hio#d7 are easily prepared1 and the free acids are much more stable than the corresponding acids of the other members of this family4 ,,gay-,,lussac',s ,,law ,,of ,,volumes ,in the discussion of the composition of hydrochloric acid it was stated that one volume of hydrogen combines with one volume of chlorine to form two volumes of hydrochloric acid4 ,with bromine and iodine similar combining ratios hold good4 ,these facts recall the simple volume relations already noted in the study of the composition of steam and ammonia4 ,these relations may be represented graphically in the following way3 --- ---- ------ ------ ,h ,cl ,h ,cl ,h ,cl --- ---- ------ ------ --- --- --- -------- -------- ,h ,h ,o ,h#b,o ,h#b,o --- --- --- -------- -------- --- --- --- --- -------- -------- ,h ,h ,h ,n ,,nh#c ,,nh#c --- --- --- --- -------- -------- ,in the early part of the past century ,gay-,lussac1 a distinguished ,french chemist1 studied the volume relations of many combining gases1 and concluded that similar relations always hold4 ,his observations are summed up in the following law3 ,when two gases combine chemically there is always a simple ratio between their volumes1 and between the volume of either one of them and that of the product1 provided it is a gas4 ,by a simple ratio is meant of course the ratio of small whole numbers1 as #a 3 #b1 #b 3 #c4 ,,exercises #a4 ,how do we account for the fact that liquid hydrofluoric acid is not an electrolyte8 #b4 ,why does sulphuric acid liberate hydrofluoric acid from its salts8 #c4 ,in the preparation of chlorine1 what advantages are there in treating manganese dioxide with a mixture of sodium chloride and sulphuric acid rather than with hydrochloric acid8 #d4 ,why must chlorine water be kept in the dark8 #e4 ,what is the derivation of the word nascent8 #f4 ,what substances studied are used as bleaching agents8 ,to what is the bleaching action due in each case8 #g4 ,what substances studied are used as disinfecting agents8 #h4 ,what is meant by the statement that hydrochloric acid is one of the strongest acids8 #i4 ,what is the meaning of the phrase aqua regia8 #aj4 ,cl#b,o is the anhydride of what acid8 #aa4 ,a solution of hydriodic acid on standing turns brown4 ,how is this accounted for8 #ab4 ,how can bromine vapor and nitrogen peroxide be distinguished from each other8 #ac4 ,write the equations for the reaction taking place when hydriodic acid is prepared from iodine1 phosphorus1 and water4 #ad4 ,from their behavior toward sulphuric acid1 to what class of agents do hydrobromic and hydriodic acids belong8 #ae4 ,give the derivation of the names of the elements of the chlorine family4 #af4 ,write the names and formulas for the binary acids of the group in the order of the stability of the acids4 #ag4 ,what is formed when a metal dissolves in each of the following8 nitric acid2 dilute sulphuric acid2 concentrated sulphuric acid2 hydrochloric acid2 aqua regia4 #ah4 ,how could you distinguish between a chloride1 a bromide1 and an iodide8 #ai4 ,what weight of sodium chloride is necessary to prepare sufficient hydrochloric acid to saturate #a l4 of water under standard conditions8 #bj4 ,on decomposition #ajj l4 of hydrochloric acid would yield how many liters of hydrogen and chlorine respectively1 the gases being measured under the same conditions8 ,are your results in accord with the experimental facts8 ,,chapter ,,xvii ,,carbon ,,and ,,some ,,of ,,its ,,simpler ,,compounds ,the family4 ,carbon stands at the head of a family of elements in the fourth group in the periodic table4 ,the resemblances between the elements of this family1 while quite marked1 are not so striking as in the case of the elements of the chlorine family4 ,with the exception of carbon1 these elements are comparatively rare1 and need not be taken up in detail in this chapter4 ,titanium will be referred to again in connection with silicon which it very closely resembles4 ,occurrence4 ,carbon is found in nature in the uncombined state in several forms4 ,the diamond is practically pure carbon1 while graphite and coal are largely carbon1 but contain small amounts of other substances4 ,its natural compounds are exceedingly numerous and occur as gases1 liquids1 and solids4 ,carbon dioxide is its most familiar gaseous compound4 ,natural gas and petroleum are largely compounds of carbon with hydrogen4 ,the carbonates1 especially calcium carbonate1 constitute great strata of rocks1 and are found in almost every locality4 ,all living organisms1 both plant and animal1 contain a large percentage of this element1 and the number of its compounds which go to make up all the vast variety of animate nature is almost limitless4 ,over one hundred thousand definite compounds containing carbon have been prepared4 ,in the free state carbon occurs in three allotropic forms1 two of which are crystalline and one amorphous4 ,crystalline carbon4 ,crystalline carbon occurs in two forms1--diamond and graphite4 #a4 ,diamond4 ,diamonds are found in considerable quantities in several localities1 especially in ,south ,africa1 the ,east ,indies1 and ,brazil4 ,the crystals belong to the regular system1 but the natural stones do not show this very clearly4 ,when found they are usually covered with a rough coating which is removed in the process of cutting4 ,diamond cutting is carried on most extensively in ,holland4 ,the density of the diamond is #c4e1 and1 though brittle1 it is one of the hardest of substances4 ,black diamonds1 as well as broken and imperfect stones which are valueless as gems1 are used for grinding hard substances4 ,few chemical reagents have any action on the diamond1 but when heated in oxygen or the air it blackens and burns1 forming carbon dioxide4 ,lavoisier first showed that carbon dioxide is formed by the combustion of the diamond2 and ,sir ,humphry ,davy in #ahad showed that this is the only product of combustion1 and that the diamond is pure carbon4 ,the diamond as a gem4 ,the pure diamond is perfectly transparent and colorless1 but many are tinted a variety of colors by traces of foreign substances4 ,usually the colorless ones are the most highly prized1 although in some instances the color adds to the value2 thus the famous ,hope diamond is a beautiful blue4 ,light passing through a diamond is very much refracted1 and to this fact the stone owes its brilliancy and sparkle4 ,artificial preparation of diamonds4 ,many attempts have been made to produce diamonds artificially1 but for a long time these always ended in failure1 graphite and not diamonds being the product obtained4 ,the ,french chemist ,moissan1 in his extended study of chemistry at high temperatures1 finally succeeded 7#ahic7 in making some small ones4 ,he accomplished this by dissolving carbon in boiling iron and plunging the crucible containing the mixture into water1 as shown in ,fig4 #eh4 ,under these conditions the carbon crystallized in the iron in the form of the diamond4 ,the diamonds were then obtained by dissolving away the iron in hydrochloric acid4 ,illustration3 ,fig4 #eh #b4 ,graphite4 ,this form of carbon is found in large quantities1 especially in ,ceylon1 ,siberia1 and in some localities of the ,united ,states and ,canada4 ,it is a shining black substance1 very soft and greasy to the touch4 ,its density is about #b4ae4 ,it varies somewhat in properties according to the locality in which it is found1 and is more easily attacked by reagents than is the diamond4 ,it is also manufactured by heating carbon with a small amount of iron 7#c7 in an electric furnace4 ,it is used in the manufacture of lead pencils and crucibles1 as a lubricant1 and as a protective covering for iron in the form of a polish or a paint4 ,amorphous carbon4 ,although there are many varieties of amorphous carbon known1 they are not true allotropic modifications4 ,they differ merely in their degree of purity1 their fineness of division1 and in their mode of preparation4 ,these substances are of the greatest importance1 owing to their many uses in the arts and industries4 ,as they occur in nature1 or are made artificially1 they are nearly all impure carbon1 the impurity depending on the particular substance in question4 #a4 ,pure carbon4 ,pure amorphous carbon is best prepared by charring sugar4 ,this is a substance consisting of carbon1 hydrogen1 and oxygen1 the latter two elements being present in the ratio of one oxygen atom to two of hydrogen4 ,when sugar is strongly heated the oxygen and hydrogen are driven off in the form of water and pure carbon is left behind4 ,prepared in this way it is a soft1 lustrous1 very bulky1 black powder4 #b4 ,coal and coke4 ,coals of various kinds were probably formed from vast accumulations of vegetable matter in former ages1 which became covered over with earthy material and were thus protected from rapid decay4 ,under various natural agencies the organic matter was slowly changed into coal4 ,in anthracite these changes have gone the farthest1 and this variety of coal is nearly pure carbon4 ,soft or bituminous coals contain considerable organic matter besides carbon and mineral substances4 ,when heated strongly out of contact with air the organic matter is decomposed and the resulting volatile matter is driven off in the form of gases and vapors1 and only the mineral matter and carbon remain behind4 ,the gaseous product is chiefly illuminating gas and the solid residue is coke4 ,some of the coke is found as a dense cake on the sides and roof of the retort4 ,this is called retort carbon and is quite pure4 #c4 ,charcoal4 ,this is prepared from wood in the same way that coke is made from coal4 ,when the process is carried on in retorts the products expelled by the heat are saved4 ,among these are many valuable substances such as wood alcohol and acetic acid4 ,where timber is abundant the process is carried out in a wasteful way1 by merely covering piles of wood with sod and setting the wood on fire4 ,some wood burns and the heat from this decomposes the wood not burned1 forming charcoal from it4 ,the charcoal1 of course1 contains the mineral part of the wood from which it is formed4 #d4 ,bone black4 ,this is sometimes called animal charcoal1 and is made by charring bones and animal refuse4 ,the organic part of the materials is thus decomposed and carbon is left in a very finely divided state1 scattered through the mineral part which consists largely of calcium phosphate4 ,for some uses this mineral part is removed by treatment with hydrochloric acid and prolonged washing4 #e4 ,lampblack4 ,lampblack and soot are products of imperfect combustion of oil and coal1 and are deposited from a smoky flame on a cold surface4 ,the carbon in this form is very finely divided and usually contains various oily materials4 ,properties4 ,while the various forms of carbon differ in many properties1 especially in color and hardness1 yet they are all odorless1 tasteless solids1 insoluble in water and characterized by their stability towards heat4 ,only in the intense heat of the electric arc does carbon volatilize1 passing directly from the solid state into a vapor4 ,owing to this fact the inside surface of an incandescent light bulb after being used for some time becomes coated with a dark film of carbon4 ,it is not acted on at ordinary temperatures by most reagents1 but at a higher temperature it combines directly with many of the elements1 forming compounds called carbides4 ,when heated in the presence of sufficient oxygen it burns1 forming carbon dioxide4 ,uses of carbon4 ,the chief use of amorphous carbon is for fuel to furnish heat and power for all the uses of civilization4 ,an enormous quantity of carbon in the form of the purer coals1 coke1 and charcoal is used as a reducing agent in the manufacture of the various metals1 especially in the metallurgy of iron4 ,most of the metals are found in nature as oxides1 or in forms which can readily be converted into oxides4 ,when these oxides are heated with carbon the oxygen is abstracted1 leaving the metal4 ,retort carbon and coke are used to make electric light carbons and battery plates1 while lampblack is used for indelible inks1 printer's ink1 and black varnishes4 ,bone black and charcoal have the property of absorbing large volumes of certain gases1 as well as smaller amounts of organic matter2 hence they are used in filters to remove noxious gases and objectionable colors and odors from water4 ,bone black is used extensively in the sugar refineries to remove coloring matter from the impure sugars4 ,chemistry of carbon compounds4 ,carbon is remarkable for the very large number of compounds which it forms with the other elements1 especially with oxygen and hydrogen4 ,compounds containing carbon are more numerous than all others put together1 and the chemistry of these substances presents peculiarities not met with in the study of other substances4 ,for these reasons the systematic study of carbon compounds1 or of organic chemistry as it is usually called1 must be deferred until the student has gained some knowledge of the chemistry of other elements4 ,an acquaintance with a few of the most familiar carbon compounds is1 however1 essential for the understanding of the general principles of chemistry4 ,compounds of carbon with hydrogen1--the hydrocarbons4 ,carbon unites with hydrogen to form a very large number of compounds called hydrocarbons4 ,petroleum and natural gas are essentially mixtures of a great variety of these hydrocarbons4 ,many others are found in living plants1 and still others are produced by the decay of organic matter in the absence of air4 ,only two of them1 methane and acetylene1 will be discussed here4 ,methane 7marsh gas7 7,,ch#d74 ,this is one of the most important of these hydrocarbons1 and constitutes about nine tenths of natural gas4 ,as its name suggests1 it is formed in marshes by the decay of vegetable matter under water1 and bubbles of the gas are often seen to rise when the dead leaves on the bottom of pools are stirred4 ,it also collects in mines1 and1 when mixed with air1 is called fire damp by the miners because of its great inflammability1 damp being an old name for a gas4 ,it is formed when organic matter1 such as coal or wood1 is heated in closed vessels1 and is therefore a principal constituent of coal gas4 ,preparation4 ,methane is prepared in the laboratory by heating sodium or calcium acetate with soda-lime4 ,equal weights of fused sodium acetate and soda-lime are thoroughly dried1 then mixed and placed in a good-sized1 hard-glass test tube fitted with a one-holed stopper and delivery tube4 ,the mixture is gradually heated1 and when the air has been displaced from the tube the gas is collected in bottles by displacement of water4 ,soda-lime is a mixture of sodium and calcium hydroxides4 ,regarding it as sodium hydroxide alone1 the equation is ,na,c#b;,h#c,o#b ,na,o,h ,na#b;,,co#c ,,ch#d4 ,properties4 ,methane is a colorless1 odorless gas whose density is #j4ee4 ,it is difficult to liquefy1 boiling at -#aee under standard pressure1 and is almost insoluble in water4 ,it burns with a pale blue flame1 liberating much heat1 and when mixed with oxygen is very explosive4 ,davy's safety lamp4 ,in #ahae ,sir ,humphry ,davy invented a lamp for the use of miners1 to prevent the dreadful mine explosions then common1 due to methane mixed with air4 ,the invention consisted in surrounding the upper part of the common miner's lamp with a mantle of wire gauze and the lower part with glass 7,fig4 #ei74 ,it has been seen that two gases will not combine until raised to their kindling temperature1 and if while combining they are cooled below this point1 the combination ceases4 ,a flame will not pass through a wire gauze because the metal1 being a good conductor of heat1 takes away so much heat from the flame that the gases are cooled below the kindling temperature4 ,when a lamp so protected is brought into an explosive mixture the gases inside the wire mantle burn in a series of little explosions1 giving warning to the miner that the air is unsafe4 ,illustration3 ,fig4 #ei ,acetylene 7,c#b;,h#b74 ,this is a colorless gas usually having a disagreeable odor due to impurities4 ,it is now made in large quantities from calcium carbide 7,ca,c#b74 ,this substance is formed when coal and lime are heated together in an electric furnace4 ,when treated with water the carbide is decomposed1 yielding acetylene3 ,ca,c#b #b;,h#b,o ,c#b;,h#b ,ca7,,oh7#b4 ,under ordinary conditions the gas burns with a very smoky flame2 in burners constructed so as to secure a large amount of oxygen it burns with a very brilliant white light1 and hence is used as an illuminant4 ,laboratory preparation4 ,the gas can be prepared readily in a generator such as is shown in ,fig4 #fj4 ,the inner tube contains fragments of calcium carbide1 while the outer one is filled with water4 ,as long as the stopcock is closed the water cannot rise in the inner tube4 ,when the stopcock is open the water rises1 and1 coming into contact with the carbide in the inner tube1 generates acetylene4 ,this escapes through the stopcock1 and after the air has been expelled may be lighted as it issues from the burner4 ,illustration3 ,fig4 #fj ,carbon forms two oxides1 namely1 carbon dioxide 7,,co#b7 and carbon monoxide 7,,co74 ,carbon dioxide 7,,co#b74 ,carbon dioxide is present in the air to the extent of about #c parts in #aj1jjj1 and this apparently small amount is of fundamental importance in nature4 ,in some localities it escapes from the earth in great quantities1 and many spring waters carry large amounts of it in solution4 ,when these highly charged spring waters reach the surface of the earth1 and the pressure on them is removed1 the carbon dioxide escapes with effervescence4 ,it is a product of the oxidation of all organic matter1 and is therefore formed in fires as well as in the process of decay4 ,it is thrown off from the lungs of all animals in respiration1 and is a product of many fermentation processes such as vinegar making and brewing4 ,combined with metallic oxides it forms vast deposits of carbonates in nature4 ,preparation4 ,in the laboratory carbon dioxide is always prepared by the action of an acid upon a carbonate1 usually calcium carbonate1 the apparatus shown in ,fig4 #ci serving the purpose very well4 ,this reaction might be expected to produce carbonic acid1 thus3 ,ca,c,o#c #b;,h,cl ,ca,cl#b ,h#b;,,co#c4 ,carbonic acid is very unstable1 however1 and decomposes into its anhydride1 ,,co#b1 and water1 thus3 ,h#b;,,co#c ,h#b,o ,,co#b4 ,the complete reaction is represented by the equation ,ca,c,o#c #b;,h,cl ,ca,cl#b ,,co#b ,h#b,o4 ,physical properties4 ,carbon dioxide is a colorless1 practically odorless gas whose density is #a4e4 ,its weight may be inferred from the fact that it can be siphoned1 or poured like water1 from one vessel downward into another4 ,at #ae and under ordinary pressure it dissolves in its own volume of water and imparts a somewhat biting1 pungent taste to it4 ,it is easily condensed1 and is now prepared commercially in this form by pumping the gas into steel cylinders 7see ,fig4 #f7 which are kept cold during the process4 ,when the liquid is permitted to escape into the air part of it instantly evaporates1 and in so doing absorbs so much heat that another portion is solidified1 the solid form strikingly resembling snow in appearance4 ,this snow is very cold and mercury can easily be frozen with it4 ,solid carbon dioxide4 ,cylinders of liquid carbon dioxide are inexpensive1 and should be available in every school4 ,to demonstrate the properties of solid carbon dioxide1 the cylinder should be placed across the table and supported in such a way that the stopcock end is several inches lower than the other end4 ,a loose bag is made by holding the corners of a handkerchief around the neck of the stopcock1 and the cock is then turned on so that the gas rushes out in large quantities4 ,very quickly a considerable quantity of the snow collects in the handkerchief4 ,to freeze mercury1 press a piece of filter paper into a small evaporating dish and pour the mercury upon it4 ,coil a flat spiral upon the end of a wire1 and dip the spiral into the mercury4 ,place a quantity of solid carbon dioxide upon the mercury and pour #aj cc4-#ae cc4 of ether over it4 ,in a minute or two the mercury will solidify and may be removed from the dish by the wire serving as a handle4 ,the filter paper is to prevent the mercury from sticking to the dish2 the ether dissolves the solid carbon dioxide and promotes its rapid conversion into gas4 ,chemical properties4 ,carbon dioxide is incombustible1 since it is1 like water1 a product of combustion4 ,it does not support combustion1 as does nitrogen peroxide1 because the oxygen in it is held in very firm chemical union with the carbon4 ,very strong reducing agents1 such as highly heated carbon1 can take away half of its oxygen3 ,,co#b ,c #b;,,co4 ,uses4 ,the relation of carbon dioxide to plant life has been discussed in a previous chapter4 ,water highly charged with carbon dioxide is used for making soda water and similar beverages4 ,since it is a non-supporter of combustion and can be generated readily1 carbon dioxide is also used as a fire extinguisher4 ,some of the portable fire extinguishers are simply devices for generating large amounts of the gas4 ,it is not necessary that all the oxygen should be kept away from the fire in order to smother it4 ,a burning candle is extinguished in air which contains only #b4e of carbon dioxide4 ,carbonic acid 7,h#b;,,co#c74 ,like most of the oxides of the non-metallic elements1 carbon dioxide is an acid anhydride4 ,it combines with water to form an acid of the formula ,h#b;,,co#c1 called carbonic acid3 ,h#b,o ,,co#b ,h#b;,,co#c4 ,the acid is1 however1 very unstable and cannot be isolated4 ,only a very small amount of it is actually formed when carbon dioxide is passed into water1 as is evident from the small solubility of the gas4 ,if1 however1 a base is present in the water1 salts of carbonic acid are formed1 and these are quite stable3 #b,na,o,h ,h#b,o ,,co#b ,na#b;,,co#c #b;,h#b,o4 ,action of carbon dioxide on bases4 ,this conduct is explained by the principles of reversible reactions4 ,the equation ,h#b,o ,,co#b -- ,h#b;,,co#c is a reversible equation1 and the extent to which the reaction progresses depends upon the relative concentrations of each of the three factors in it4 ,equilibrium is ordinarily reached when very little ,h#b;,,co#c is formed4 ,if a base is present in the water to combine with the ,h#b;,,co#c as fast as it is formed1 all of the ,,co#b is converted into ,h#b;,,co#c1 and thence into a carbonate4 ,salts of carbonic acid1--carbonates4 ,the carbonates form a very important class of salts4 ,they are found in large quantities in nature1 and are often used in chemical processes4 ,only the carbonates of sodium1 potassium1 and ammonium are soluble1 and these can be made by the action of carbon dioxide on solutions of the bases1 as has just been explained4 ,the insoluble carbonates are formed as precipitates when soluble salts are treated with a solution of a soluble carbonate4 ,thus the insoluble calcium carbonate can be made by bringing together solutions of calcium chloride and sodium carbonate3 ,ca,cl#b ,na#b;,,co#c ,ca,c,o#c #b,na,cl4 ,most of the carbonates are decomposed by heat1 yielding an oxide of the metal and carbon dioxide4 ,thus lime 7calcium oxide7 is made by strongly heating calcium carbonate3 ,ca,c,o#c ,ca,o ,,co#b4 ,acid carbonates4 ,like all acids containing two acid hydrogen atoms1 carbonic acid can form both normal and acid salts4 ,the acid carbonates are made by treating a normal carbonate with an excess of carbonic acid4 ,with few exceptions they are very unstable1 heat decomposing them even when in solution4 ,action of carbon dioxide on calcium hydroxide4 ,if carbon dioxide is passed into clear lime water1 calcium carbonate is at first precipitated3 ,h#b,o ,,co#b ,h#b;,,co#c1 ,ca7,,oh7#b ,h#b;,,co#c ,ca,c,o#c #b;,h#b,o4 ,advantage is taken of this reaction in testing for the presence of carbon dioxide1 as already explained in the chapter on the atmosphere4 ,if the current of carbon dioxide is continued1 the precipitate soon dissolves1 because the excess of carbonic acid forms calcium acid carbonate which is soluble3 ,ca,c,o#c ,h#b;,,co#c ,ca7,,hco#c7b4 ,if now the solution is heated1 the acid carbonate is decomposed and calcium carbonate once more precipitated3 ,ca7,,hco#c7b ,ca,c,o#c ,h#b;,,co#c4 ,carbon monoxide 7,,co74 ,carbon monoxide can be made in a number of ways1 the most important of which are the three following3 #a4 ,by the partial oxidation of carbon4 ,if a slow current of air is conducted over highly heated carbon1 the monoxide is formed1 thus3 ,c ,o ,,co ,it is therefore often formed in stoves when the air draught is insufficient4 ,water gas1 which contains large amounts of carbon monoxide1 is made by partially oxidizing carbon with steam3 ,c ,h#b,o ,,co #b;,h4 #b4 ,by the partial reduction of carbon dioxide4 ,when carbon dioxide is conducted over highly heated carbon it is reduced to carbon monoxide by the excess of carbon3 ,,co#b ,c #b;,,co4 ,when coal is burning in a stove or grate carbon dioxide is at first formed in the free supply of air1 but as the hot gas rises through the glowing coal it is reduced to carbon monoxide4 ,when the carbon monoxide reaches the free air above the coal it takes up oxygen to form carbon dioxide1 burning with the blue flame so familiar above a bed of coals1 especially in the case of hard coals4 #c4 ,by the decomposition of oxalic acid4 ,in the laboratory carbon monoxide is usually prepared by the action of concentrated sulphuric acid upon oxalic acid4 ,the latter substance has the formula ,c#b;,h#b,o#d4 ,the sulphuric acid1 owing to its affinity for water1 decomposes the oxalic acid1 as represented in the equation ,c#b;,h#b,o#d 7,h#b,,so#d7 7,h#b,,so#d7 ,h#b,o ,,co#b ,,co4 ,properties4 ,carbon monoxide is a light1 colorless1 almost odorless gas1 very difficult to liquefy4 ,chemically it is very active1 combining directly with a great many substances4 ,it has a great affinity for oxygen and is therefore combustible and a good reducing agent4 ,thus1 if carbon monoxide is passed over hot copper oxide1 the copper is reduced to the metallic state3 ,cu,o ,,co ,cu ,,co#b4 ,when inhaled it combines with the red coloring matter of the blood and in this way prevents the absorption of oxygen1 so that even a small quantity of the gas may prove fatal4 ,illustration3 ,fig4 #fa ,the reducing power of carbon monoxide4 ,fig4 #fa illustrates a method of showing the reducing power of carbon monoxide4 ,the gas is generated by gently heating #g or #h g4 of oxalic acid with #be cc4 of concentrated sulphuric acid in a #bjj cc4 flask ,a4 ,the bottle ,b contains a solution of sodium hydroxide1 which removes the carbon dioxide formed along with the monoxide4 ,c contains a solution of calcium hydroxide to show that the carbon dioxide is completely removed4 ,e is a hard-glass tube containing #a or #b g4 of copper oxide1 which is heated by a burner4 ,the black copper oxide is reduced to reddish metallic copper by the carbon monoxide1 which is thereby changed to carbon dioxide4 ,the presence of the carbon dioxide is shown by the precipitate in the calcium hydroxide solution in ,d4 ,any unchanged carbon monoxide is collected over water in ,f4 ,carbon disulphide 7,,cs#b74 ,just as carbon combines with oxygen to form carbon dioxide1 so it combines with sulphur to form carbon disulphide 7,,cs#b74 ,this compound has been described in the chapter on sulphur4 ,hydrocyanic acid 7prussic acid77,,hcn74 ,under the proper conditions carbon unites with nitrogen and hydrogen to form the acid ,,hcn1 called hydrocyanic acid4 ,it is a weak1 volatile acid1 and is therefore easily prepared by treating its salts with sulphuric acid3 ,,kcn ,h#b,,so#d ,,khso#d ,,hcn4 ,it is most familiar as a gas1 though it condenses to a colorless liquid boiling at #bf4 ,it has a peculiar odor1 suggesting bitter almonds1 and is extremely poisonous either when inhaled or when taken into the stomach4 ,a single drop may cause death4 ,it dissolves readily in water1 its solution being commonly called prussic acid4 ,the salts of hydrocyanic acid are called cyanides1 the cyanides of sodium and potassium being the best known4 ,these are white solids and are extremely poisonous4 ,solutions of potassium cyanide are alkaline4 ,a solution of potassium cyanide turns red litmus blue1 and must therefore contain hydroxyl ions4 ,the presence of these ions is accounted for in the following way4 ,although water is so little dissociated into its ions ,h and ,,oh- that for most purposes we may neglect the dissociation1 it is nevertheless measurably dissociated4 ,hydrocyanic acid is one of the weakest of acids1 and dissociates to an extremely slight extent4 ,when a cyanide such as potassium cyanide dissolves it freely dissociates1 and the ,,cn- ions must come to an equilibrium with the ,h ions derived from the water3 ,h ,,cn- -- ,,hcn4 ,the result of this equilibrium is that quite a number of ,h ions from the water are converted into undissociated ,,hcn molecules4 ,but for every ,h ion so removed an ,,oh- ion remains free1 and this will give the solution alkaline properties4 ,,exercises #a4 ,how can you prove that the composition of the different allotropic forms of carbon is the same8 #b4 ,are lampblack and bone black allotropic forms of carbon8 ,will equal amounts of heat be liberated in the combustion of #a g4 of each8 #c4 ,how could you judge of the relative purity of different forms of carbon8 #d4 ,apart from its color1 why should carbon be useful in the preparation of inks and paints8 #e4 ,could asbestos fibers be used to replace the wire in a safety lamp8 #f4 ,why do most acids decompose carbonates8 #g4 ,what effect would doubling the pressure have upon the solubility of carbon dioxide in water8 #h4 ,what compound would be formed by passing carbon dioxide into a solution of ammonium hydroxide8 ,write the equation4 #i4 ,write equations for the preparation of ,k#b;,,co#c2 of ,ba,c,o#c2 of ,mg,c,o#c4 #aj4 ,in what respects are carbonic and sulphurous acids similar8 #aa4 ,give three reasons why the reaction which takes place when a solution of calcium acid carbonate is heated1 completes itself4 #ab4 ,how could you distinguish between carbonates and sulphites8 #ac4 ,how could you distinguish between oxygen1 hydrogen1 nitrogen1 nitrous oxide1 and carbon dioxide8 #ad4 ,could a solution of sodium hydroxide be substituted for the solution of calcium hydroxide in testing for carbon dioxide8 #ae4 ,what weight of sodium hydroxide is necessary to neutralize the carbonic acid formed by the action of hydrochloric acid on #ajj g4 of calcium carbonate8 #af4 ,what weight of calcium carbonate would be necessary to prepare sufficient carbon dioxide to saturate #aj l4 of water at #ae and under ordinary pressure8 #ag4 ,on the supposition that calcium carbide costs #ab cents a kilogram1 what would be the cost of an amount sufficient to generate #ajj l4 of acetylene measured at #bj and #gdj mm48 #ah4 ,how would the volume of a definite amount of carbon monoxide compare with the volume of carbon dioxide formed by its combustion1 the measurements being made under the same conditions8 ,,chapter ,,xviii ,,flames1--,,illuminants ,conditions necessary for flames4 ,it has been seen that when two substances unite chemically1 with the production of light and heat1 the act of union is called combustion4 ,when one of the substances undergoing combustion remains solid at the temperature occasioned by the combustion1 light may be given off1 but there is no flame4 ,thus iron wire burning in oxygen throws off a shower of sparks and is brilliantly incandescent1 but no flame is seen4 ,when1 however1 both of the substances are gases or vapors at the temperature reached in the combustion1 the act of union is accompanied by a flame4 ,flames from burning liquids or solids4 ,many substances which are liquids or solids at ordinary temperatures burn with a flame because the heat of combustion vaporizes them slowly1 and the flame is due to the union of this vapor with the gas supporting the combustion4 ,supporter of combustion4 ,that gas which surrounds the flame and constitutes the atmosphere in which the combustion occurs is said to support the combustion4 ,the other gas which issues into this atmosphere is said to be the combustible gas4 ,thus1 in the ordinary combustion of coal gas in the air the coal gas is said to be combustible1 while the air is regarded as the supporter of combustion4 ,these terms are entirely relative1 however1 for a jet of air issuing into an atmosphere of coal gas will burn when ignited1 the coal gas supporting the combustion4 ,ordinarily1 when we say that a gas is combustible we mean that it is combustible in an atmosphere of air4 ,illustration3 ,fig4 #fb ,either gas may be the supporter of combustion4 ,that the terms combustible and supporter of combustion are merely relative may be shown in the following way3 ,a lamp chimney ,a is fitted with a cork and glass tubes1 as shown in ,fig4 #fb4 ,the tube ,c should have a diameter of from #ab to #ae mm4 ,a thin sheet of asbestos in which is cut a circular opening about #b cm4 in diameter is placed over the top of the chimney4 ,the opening in the asbestos is closed with the palm of the hand1 and gas is admitted to the chimney through the tube ,b4 ,the air in the chimney is soon expelled through the tube ,c1 and the gas itself is then lighted at the lower end of this tube4 ,the hand is now removed from the opening in the asbestos1 when the flame at the end of the tube at once rises and appears at the end within the chimney1 as shown in the figure4 ,the excess of coal gas now escapes from the opening in the asbestos and may be lighted4 ,the flame at the top of the asbestos board is due to the combustion of coal gas in air1 while the flame within the chimney is due to the combustion of air in coal gas1 the air being drawn up through the tube by the escaping gas4 ,appearance of flames4 ,the flame caused by the union of hydrogen and oxygen is almost colorless and invisible4 ,chlorine and hydrogen combine with a pale violet flame1 carbon monoxide burns in oxygen with a blue flame1 while ammonia burns with a deep yellow flame4 ,the color and appearance of flames are therefore often quite characteristic of the particular combustion which occasions them4 ,structure of flames4 ,when the gas undergoing combustion issues from a round opening into an atmosphere of the gas supporting combustion1 as is the case with the burning ,bunsen burner 7,fig4 #fc71 the flame is generally conical in outline4 ,it consists of several distinct cones1 one within the other1 the boundary between them being marked by differences of color or luminosity4 ,in the simplest flame1 of which hydrogen burning in oxygen is a good example1 these cones are two in number1--an inner one1 formed by unburned gas1 and an outer one1 usually more or less luminous1 consisting of the combining gases4 ,this outer one is in turn surrounded by a third envelope of the products of combustion2 this envelope is sometimes invisible1 as in the present case1 but is sometimes faintly luminous4 ,the lower part of the inner cone of the flame is quite cool and consists of unburned gas4 ,toward the top of the inner cone the gas has become heated to a high temperature by the burning envelope surrounding it4 ,on reaching the supporter of combustion on the outside it is far above its kindling temperature1 and combustion follows with the evolution of much heat4 ,the region of combustion just outside the inner cone is therefore the hottest part of the flame4 ,illustration3 ,fig4 #fc ,oxidizing and reducing flames4 ,since the tip of the outside cone consists of very hot products of combustion mixed with oxygen from the air1 a substance capable of oxidation placed in this part of the flame becomes very hot and is easily oxidized4 ,the oxygen with which it combines comes1 of course1 from the atmosphere1 and not from the products of combustion4 ,this outer tip of the flame is called the oxidizing flame4 ,at the tip of the inner cone the conditions are quite different4 ,this region consists of a highly heated combustible gas1 which has not yet reached a supply of oxygen4 ,if a substance rich in oxygen1 such as a metallic oxide1 is placed in this region of the flame1 the heated gases combine with its oxygen and the substance is reduced4 ,this part of the flame is called the reducing flame4 ,these flames are used in testing certain substances1 especially minerals4 ,for this purpose they are produced by blowing into a small luminous ,bunsen flame from one side through a blowpipe4 ,this is a tube of the shape shown in ,fig4 #fd4 ,the flame is directed in any desired way and has the oxidizing and reducing regions very clearly marked 7,fig4 #fe74 ,it is non-luminous from the same causes which render the open ,bunsen burner flame non-luminous1 the gases from the lungs serving to furnish oxygen and to dilute the combustible gas4 ,illustration3 ,fig4 #fd ,illustration3 ,fig4 #fe ,luminosity of flames4 ,the luminosity of flames is due to a number of distinct causes1 and may therefore be increased or diminished in several ways4 #a4 ,presence of solid matter4 ,the most obvious of these causes is the presence in the flame of incandescent solid matter4 ,thus chalk dust sifted into a non-luminous flame renders it luminous4 ,when hydrocarbons form a part of the combustible gas1 as they do in nearly all illuminating gases and oils1 some carbon is usually set free in the process of combustion4 ,this is made very hot by the flame and becomes incandescent1 giving out light4 ,in a well-regulated flame it is afterward burned up1 but when the supply of oxygen is insufficient it escapes from the flame as lampblack or soot4 ,that it is temporarily present in a well-burning luminous flame may be demonstrated by holding a cold object1 such as a small evaporating dish1 in the flame for a few seconds4 ,this cold object cools the carbon below its kindling temperature1 and it is deposited on the object as soot4 #b4 ,pressure4 ,a second factor in the luminosity of flames is the pressure under which the gases are burning4 ,under increased pressure there is more matter in a given volume of a gas1 and the chemical action is more energetic than when the gases are rarefied4 ,consequently there is more heat and light4 ,a candle burning on a high mountain gives less light than when it burns at the sea level4 ,if the gas is diluted with a non-combustible gas1 the effect is the same as if it is rarefied1 for under these conditions there is less combustible gas in a given volume4 #c4 ,temperature4 ,the luminosity also depends upon the temperature attained in the combustion4 ,in general the hotter the flame the greater the luminosity2 hence cooling the gases before combustion diminishes the luminosity of the flame they will make1 because it diminishes the temperature attained in the combustion4 ,thus the luminosity of the ,bunsen flame is largely diminished by the air drawn up with the gas4 ,this is due in part to the fact that the burning gas is diluted and cooled by the air drawn in4 ,the oxygen thus introduced into the flame also causes the combustion of the hot particles of carbon which would otherwise tend to make the flame luminous4 ,illuminating and fuel gases4 ,a number of mixtures of combustible gases1 consisting largely of carbon compounds and hydrogen1 find extensive use for the production of light and heat4 ,the three chief varieties are coal gas1 water gas1 and natural gas4 ,the use of acetylene gas has already been referred to4 ,coal gas4 ,coal gas is made by heating bituminous coal in large retorts out of contact with the air4 ,soft or bituminous coal contains1 in addition to large amounts of carbon1 considerable quantities of compounds of hydrogen1 oxygen1 nitrogen1 and sulphur4 ,when distilled the nitrogen is liberated partly in the form of ammonia and cyanides and partly as free nitrogen gas2 the sulphur is converted into hydrogen sulphide1 carbon disulphide1 and oxides of sulphur2 the oxygen into water and oxides of carbon4 ,the remaining hydrogen is set free partly as hydrogen and partly in combination with carbon in the form of hydrocarbons4 ,the most important of these is methane1 with smaller quantities of many others1 some of which are liquids or solids at ordinary temperatures4 ,the great bulk of the carbon remains behind as coke and retort carbon4 ,the manufacture of coal gas4 ,in the manufacture of coal gas it is necessary to separate from the volatile constituents formed by the heating of the coal all those substances which are either solid or liquid at ordinary temperature1 since these would clog the gas pipes4 ,certain gaseous constituents1 such as hydrogen sulphide and ammonia1 must also be removed4 ,the method used to accomplish this is shown in ,fig4 #ff4 ,the coal is heated in air-tight retorts illustrated by ,a4 ,the volatile products escape through the pipe ,x and bubble into the tarry liquid in the large pipe ,b1 known as the hydraulic main1 which runs at right angles to the retorts4 ,here is deposited the greater portion of the solid and liquid products1 forming a tarry mass known as coal tar4 ,much of the ammonia also remains dissolved in this liquid4 ,the partially purified gas then passes into the pipes ,c1 which serve to cool it and further remove the solid and liquid matter4 ,the gas then passes into ,d1 which is filled with coke over which a jet of water is sprayed4 ,the water still further cools the gas and at the same time partially removes such gaseous products as hydrogen sulphide and ammonia1 which are soluble in water4 ,in ,e the gas passes over some material such as lime1 which removes the last portions of the sulphur compounds as well as much of the carbon dioxide present4 ,from ,e the gas passes into the large gas holder ,f1 from which it is distributed through pipes to the places where it is burned4 ,illustration3 ,fig4 #ff ,one ton of good gas coal yields approximately #aj1jjj cu4 ft4 of gas1 #adjj lb4 of coke1 #abj lb4 of tar1 and #bj gal4 of ammoniacal liquor4 ,not only is the ammonia obtained in the manufacture of the gas of great importance1 but the coal tar also serves as the source of many very useful substances1 as will be explained in ,chapter ,,xxxii4 ,water gas4 ,water gas is essentially a mixture of carbon monoxide and hydrogen4 ,it is made by passing steam over very hot anthracite coal1 when the reaction shown in the following equation takes place3 ,c ,h#b,o ,,co #b;,h4 ,when required merely to produce heat the gas is at once ready for use4 ,when made for illuminating purposes it must be enriched1 that is1 illuminants must be added1 since both carbon monoxide and hydrogen burn with non-luminous flames4 ,this is accomplished by passing it into heaters containing highly heated petroleum oils4 ,the gas takes up hydrocarbon gases formed in the decomposition of the petroleum oils1 which make it burn with a luminous flame4 ,water gas is very effective as a fuel1 since both carbon monoxide and hydrogen burn with very hot flames4 ,it has little odor and is very poisonous4 ,its use is therefore attended with some risk1 since leaks in pipes are very likely to escape notice4 ,natural gas4 ,this substance1 so abundant in many localities1 varies much in composition1 but is composed principally of methane4 ,when used for lighting purposes it is usually burned in a burner resembling an open ,bunsen1 the illumination being furnished by an incandescent mantle4 ,this is the case in the familiar ,welsbach burner4 ,contrary to statements frequently made1 natural gas contains no free hydrogen4 ,,table ,,showing ,,composition ,,of ,,gases ,,pennsylvania ,,coal ,,water ,,enriched ,,natural ,,gas ,,gas ,,water ,,gas ,,gas ---------------------------------------- ----------------------- ,hydrogen #da4c #eb4hh #cj4jj ,methane #ij4fd #dc4f #b4af #bd4jj ,illuminants #c4i #ab4je ,carbon monoxide #f4d #cf4hj #bi4jj ,carbon dioxide #j4cj #b4j #c4dg #j4cj ,nitrogen #i4jf #a4b #d4fi #b4ej ,oxygen #j4c #a4ej ,hydrocarbon vapors #a4e #a4ej ,these are analyses of actual samples1 and may be taken as about the average for the various kinds of gases4 ,any one of these may vary considerably4 ,the nitrogen and oxygen in most cases is due to a slight admixture of air which is difficult to exclude entirely in the manufacture and handling of gases4 ,fuels4 ,a variety of substances are used as fuels1 the most important of them being wood1 coal1 and the various gases mentioned above4 ,wood consists mainly of compounds of carbon1 hydrogen1 and oxygen4 ,the composition of coal and the fuel gases has been given4 ,since these fuels are composed principally of carbon and hydrogen or their compounds1 the chief products of combustion are carbon dioxide and water4 ,the practice of heating rooms with portable gas or oil stoves with no provision for removing the products of combustion is to be condemned1 since the carbon dioxide is generated in sufficient quantities to render the air unfit for breathing4 ,rooms so heated also become very damp from the large amount of water vapor formed in the combustion1 and which in cold weather condenses on the window glass1 causing the glass to sweat4 ,both coal and wood contain a certain amount of mineral substances which constitute the ashes4 ,the electric furnace4 ,in recent years electric furnaces have come into wide use in operations requiring a very high temperature4 ,temperatures as high as #cejj can be easily reached1 whereas the hottest oxyhydrogen flame is not much above #bjjj4 ,these furnaces are constructed on one of two general principles4 ,illustration3 ,fig4 #fg #a4 ,arc furnaces4 ,in the one type the source of heat is an electric arc formed between carbon electrodes separated a little from each other1 as shown in ,fig4 #fg4 ,the substance to be heated is placed in a vessel1 usually a graphite crucible1 just below the arc4 ,the electrodes and crucible are surrounded by materials which fuse with great difficulty1 such as magnesium oxide1 the walls of the furnace being so shaped as to reflect the heat downwards upon the contents of the crucible4 ,illustration3 ,fig4 #fh #b4 ,resistance furnaces4 ,in the other type of furnace the heat is generated by the resistance offered to the current in its passage through the furnace4 ,in its simplest form it may be represented by ,fig4 #fh4 ,the furnace is merely a rectangular box built up of loose bricks4 ,the electrodes ,e1 each consisting of a bundle of carbon rods1 are introduced through the sides of the furnace4 ,the materials to be heated1 ,c1 are filled into the furnace up to the electrodes1 and a layer of broken coke is arranged so as to extend from one electrode to the other4 ,more of the charge is then placed on top of the coke4 ,in passing through the broken coke the electrical current encounters great resistance4 ,this generates great heat1 and the charge surrounding the coke is brought to a very high temperature4 ,the advantage of this type of furnace is that the temperature can be regulated to any desired intensity4 ,,exercises #a4 ,why does charcoal usually burn with no flame8 ,how do you account for the flame sometimes observed when it burns8 #b4 ,how do you account for the fact that a candle burns with a flame8 #c4 ,what two properties must the mantle used in the ,welsbach lamp possess8 #d4 7a7 ,in what respects does the use of the ,welsbach mantle resemble that of lime in the calcium light8 7b7 ,if the mantle were made of carbon1 would it serve the same purpose8 #e4 ,would anthracite coal be suitable for the manufacture of coal gas8 #f4 ,how could you prove the formation of carbon dioxide and water in the combustion of illuminating gases8 #g4 ,suggest a probable way in which natural gas has been formed4 #h4 ,coal frequently contains a sulphide of iron4 7a7 ,what two sulphur compounds are likely to be formed when gas is made from such coal8 7b7 ,suggest some suitable method for the removal of these compounds4 #i4 ,why does the use of the bellows on the blacksmith's forge cause a more intense heat8 #aj4 ,what volume of oxygen is necessary to burn #ajj l4 of marsh gas and what volume of carbon dioxide would be formed1 all of the gases being measured under standard conditions8 #aa4 ,suppose a cubic meter of ,pennsylvania natural gas1 measured under standard conditions1 were to be burned4 ,how much water by weight would result8 ,,chapter ,,xix ,,molecular ,,weights1 ,,atomic ,,weights1 ,,formulas ,introduction4 ,in the chapter on ,the ,atomic ,theory1 it was shown that if it were true that two elements uniting to form a compound always combined in the ratio of one atom of one element to one atom of the other element1 it would be a very easy matter to decide upon figures which would represent the relative weights of the different atoms4 ,it would only be necessary to select some one element as a standard and determine the weight of every element which combines with a definite weight 7say #a g47 of the standard element4 ,the figures so obtained would evidently represent the relative weights of the atoms4 ,but the law of multiple proportion at once reminds us that two elements may unite in several proportions2 and there is no simple way to determine the number of atoms present in the molecule of any compound4 ,consequently the problem of deciding upon the relative atomic weights is not an easy one4 ,to the solution of this problem we must now turn4 ,dalton's method of determining atomic weights4 ,when ,dalton first advanced the atomic theory he attempted to solve this problem by very simple methods4 ,he thought that when only one compound of two elements is known it is reasonable to suppose that it contains one atom of each element4 ,he therefore gave the formula ,,ho to water1 and ,,hn to ammonia4 ,when more than two compounds were known he assumed that the most familiar or the most stable one had the simple formula4 ,he then determined the atomic weight as explained above4 ,the results he obtained were contradictory and very far from satisfactory1 and it was soon seen that some other method1 resting on much more scientific grounds1 must be found to decide what compounds1 if any1 have a single atom of each element present4 ,determination of atomic weights4 ,three distinct steps are involved in the determination of the atomic weight of an element3 7#a7 determination of the equivalent1 7#b7 determination of molecular weights of its compounds1 and 7#c7 deduction of the exact atomic weight from the equivalent and molecular weights4 #a4 ,determination of the equivalent4 ,by the equivalent of an element is meant the weight of the element which will combine with a fixed weight of some other element chosen as a standard4 ,it has already been explained that oxygen has been selected as the standard element for atomic weights1 with a weight of #af4 ,this same standard will serve very well as a standard for equivalents4 ,the equivalent of an element is the weight of the element which will combine with #af g4 of oxygen4 ,thus #af g4 of oxygen combines with #af4jc g4 of sulphur1 #fe4d g4 of zinc1 #bae4hf g4 of silver1 #gj4i g4 of chlorine4 ,these figures1 therefore1 represent the equivalent weights of these elements4 ,relation of atomic weights to equivalents4 ,according to the atomic theory combination always takes place between whole numbers of atoms4 ,thus one atom unites with one other1 or with two or three2 or two atoms may unite with three1 or three with five1 and so on4 ,when oxygen combines with zinc the combination must be between definite numbers of the two kinds of atoms4 ,experiment shows that these two elements combine in the ratio of #af g4 of oxygen to #fe4d g4 of zinc4 ,if one atom of oxygen combines with one atom of zinc1 then this ratio must be the ratio between the weights of the two atoms4 ,if one atom of oxygen combines with two atoms of zinc1 then the ratio between the weights of the two atoms will be #af3 #cb4g4 ,if two atoms of oxygen combine with one atom of zinc1 the ratio by weight between the two atoms will be #h3 #fe4d4 ,it is evident1 therefore1 that the real atomic weight of an element must be some multiple or submultiple of the equivalent2 in other words1 the equivalent multiplied by #a_/b1 #a1 #b1 or #c will give the atomic weight4 ,combining weights4 ,a very interesting relation holds good between the equivalents of the various elements4 ,we have just seen that the figures #af4jc1 #fe4d1 #bae4hf1 and #gj4i are the equivalents respectively of sulphur1 zinc1 silver1 and chlorine4 ,these same figures represent the ratios by weight in which these elements combine among themselves4 ,thus #bae4hf g4 of silver combine with #gj4i g4 of chlorine and with #b #af4jc g4 of sulphur4 #fe4d g4 of zinc combine with #gj4i g4 of chlorine and #b #af4jc g4 of sulphur4 ,by taking the equivalent or some multiple of it a value can be obtained for each element which will represent its combining value1 and for this reason is called its combining weight4 ,it is important to notice that the fact that a combining weight can be obtained for each element is not a part of a theory1 but is the direct result of experiment4 ,elements with more than one equivalent4 ,it will be remembered that oxygen combines with hydrogen in two ratios4 ,in one case #af g4 of oxygen combine with #b4jaf g4 of hydrogen to form water2 in the other #af g4 of oxygen combine with #a4jjh g4 of hydrogen to form hydrogen dioxide4 ,the equivalents of hydrogen are therefore #b4jaf and #a4jjh4 ,barium combines with oxygen in two proportions3 in barium oxide the proportion is #af g4 of oxygen to #acg4d g4 of barium2 in barium dioxide the proportion is #af g4 of oxygen to #fh4g g4 of barium4 ,in each case one equivalent is a simple multiple of the other1 so the fact that there may be two equivalents does not add to the uncertainty4 ,all we knew before was that the true atomic weight is some multiple of the equivalent4 #b4 ,the determination of molecular weights4 ,to decide the question as to which multiple of the equivalent correctly represents the atomic weight of an element1 it has been found necessary to devise a method of determining the molecular weights of compounds containing the element in question4 ,since the molecular weight of a compound is merely the sum of the weights of all the atoms present in it1 it would seem to be impossible to determine the molecular weight of a compound without first knowing the atomic weights of the constituent atoms1 and how many atoms of each element are present in the molecule4 ,but certain facts have been discovered which suggest a way in which this can be done4 ,avogadro's hypothesis4 ,we have seen that the laws of ,boyle1 ,charles1 and ,gay-,lussac apply to all gases irrespective of their chemical character4 ,this would lead to the inference that the structure of gases must be quite simple1 and that it is much the same in all gases4 ,in #ahaa ,avogadro1 an ,italian physicist1 suggested that if we assume all gases under the same conditions of temperature and pressure to have the same number of molecules in a given volume1 we shall have a probable explanation of the simplicity of the gas laws4 ,it is difficult to prove the truth of this hypothesis by a simple experiment1 but there are so many facts known which are in complete harmony with this suggestion that there is little doubt that it expresses the truth4 ,avogadro's hypothesis may be stated thus3 ,equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules4 ,avogadro's hypothesis and molecular weights4 ,assuming that ,avogadro's hypothesis is correct1 we have a very simple means for deciding upon the relative weights of molecules2 for if equal volumes of two gases contain the same number of molecules1 the weights of the two volumes must be in the same ratio as the weights of the individual molecules which they contain4 ,if we adopt some one gas as a standard1 we can express the weights of all other gases as compared with this one1 and the same figures will express the relative weights of the molecules of which the gases are composed4 ,oxygen as the standard4 ,it is important that the same standard should be adopted for the determination of molecular weights as has been decided upon for atomic weights and equivalents1 so that the three values may be in harmony with each other4 ,accordingly it is best to adopt oxygen as the standard element with which to compare the molecular weights of other gases1 being careful to keep the oxygen atom equal to #af4 ,the oxygen molecule contains two atoms4 ,one point must not be overlooked1 however4 ,we desire to have our unit1 the oxygen atom1 equal to #af4 ,the method of comparing the weights of gases just suggested compares the molecules of the gases with the molecule of oxygen4 ,is the molecule and the atom of oxygen the same thing8 ,this question is answered by the following considerations4 ,we have seen that when steam is formed by the union of oxygen and hydrogen1 two volumes of hydrogen combine with one volume of oxygen to form two volumes of steam4 ,let us suppose that the one volume of oxygen contains #ajj molecules2 then the two volumes of steam must1 according to ,avogadro's hypothesis1 contain #bjj molecules4 ,but each of these #bjj molecules must contain at least one atom of oxygen1 or #bjj in all1 and these #bjj atoms came from #ajj molecules of oxygen4 ,it follows that each molecule of oxygen must contain at least two atoms of oxygen4 ,evidently this reasoning merely shows that there are at least two atoms in the oxygen molecule4 ,there may be more than that1 but as there is no evidence to this effect1 we assume that the molecule contains two atoms only4 ,it is evident that if we wish to retain the value #af for the atom of oxygen we must take twice this value1 or #cb1 for the value of the oxygen molecule1 when using it as a standard for molecular weights4 ,determination of the molecular weights of gases from their weights compared with oxygen4 ,assuming the molecular weight of oxygen to be #cb1 ,avogadro's hypothesis gives us a ready means for determining the molecular weight of any other gas1 for all that is required is to know its weight compared with that of an equal volume of oxygen4 ,for example1 #a l4 of chlorine is found by experiment to weigh #b4baf times as much as #a l4 of oxygen4 ,the molecular weight of chlorine must therefore be #b4baf #cb1 or #gj4ia4 ,if1 instead of comparing the relative weights of #a l4 of the two gases1 we select such a volume of oxygen as will weigh #cb g41 or the weight in grams corresponding to the molecular weight of the gas1 the calculation is much simplified4 ,it has been found that #cb g4 of oxygen1 under standard conditions1 measure #bb4d l4 ,this same volume of hydrogen weighs #b4jai g42 of chlorine #gj4i g42 of hydrochloric acid #cf4deh g4 ,the weights of these equal volumes must be proportional to their molecular weights1 and since the weight of the oxygen is the same as the value of its molecular weight1 so too will the weights of the #bb4d l4 of the other gases be equal to the value of their molecular weights4 ,as a summary we can then make the following statement3 ,the molecular weight of any gas may be determined by calculating the weight of #bb4d l4 of the gas1 measured under standard conditions4 ,determination of molecular weights from density of gases4 ,in an actual experiment it is easier to determine the density of a gas than the weight of a definite volume of it4 ,the density of a gas is usually defined as its weight compared with that of an equal volume of air4 ,having determined the density of a gas1 its weight compared with oxygen may be determined by multiplying its density by the ratio between the weights of air and oxygen4 ,this ratio is #j4ijdf4 ,to compare it with our standard for atomic weights we must further multiply it by #cb1 since the standard is #a_/cb the weight of oxygen molecules4 ,the steps then are these3 #a4 ,determine the density of the gas 7its weight compared with air74 #b4 ,multiply by #j4ijdf to make the comparison with oxygen molecules4 #c4 ,multiply by #cb to make the comparison with the unit for atomic weights4 ,we have1 then1 the formula3 molecular weight density #j4ijdf #cb2 or1 still more briefly1 ,m4 ,d4 #bh4i4 ,the value found by this method for the determination of molecular weights will of course agree with those found by calculating the weight of #bb4d l4 of the gas1 since both methods depend on the same principles4 ,illustration3 ,fig4 #fi ,determination of densities of gases4 ,the relative weights of equal volumes of two gases can be easily determined4 ,the following is one of the methods used4 ,a small flask1 such as is shown in ,fig4 #fi1 is filled with one of the gases1 and after the temperature and pressure have been noted the flask is sealed up and weighed4 ,the tip of the sealed end is then broken off1 the flask filled with the second gas1 and its weight determined4 ,if the weight of the empty flask is subtracted from these two weighings1 the relative weights of the gases is readily found4 #c4 ,deduction of atomic weights from molecular weights and equivalents4 ,we have now seen how the equivalent of an element and the molecular weight of compounds containing the element can be obtained4 ,let us see how it is possible to decide which multiple of the equivalent really is the true atomic weight4 ,as an example1 let us suppose that the equivalent of nitrogen has been found to be #g4jb and that it is desired to obtain its atomic weight4 ,the next step is to obtain the molecular weights of a large number of compounds containing nitrogen4 ,the following will serve3 ,,approximate ,,percentage ,,of ,,part ,,of ,,density ,,by ,,molecular ,,nitrogen ,,by ,,molecular ,,experiment ,,weight ,,experiment ,,weight ,,due 7,d4 #bh4i7 ,,to ,,nitrogen ---------------------------------------- --------------------------------- ,nitrogen gas #j4ifga #bg4ie #ajj4jj #bg4ie ,nitrous oxide #a4ebg #dd4ac #fc4gj #bg4aa ,nitric oxide #a4jchd #cj4jj #df4gd #ad4jb ,nitrogen peroxide #a4ehj #de4ff #cj4di #ac4ij ,ammonia #j4eia #ag4je #hb4bh #ad4jc ,nitric acid #b4ahj #fc4jf #bb4bg #ad4jc ,hydrocyanic acid #j4icj #bf4hg #ea4ij #ac4id ,method of calculation4 ,the densities of the various gases in the first column of this table are determined by experiment1 and are fairly accurate but not entirely so4 ,by multiplying these densities by #bh4i the molecular weights of the compounds as given in the second column are obtained4 ,by chemical analysis it is possible to determine the percentage composition of these substances1 and the percentages of nitrogen in them as determined by analysis are given in the third column4 ,if each of these molecular weights is multiplied in turn by the percentage of nitrogen in the compound1 the product will be the weight of the nitrogen in the molecular weight of the compound4 ,this will be the sum of the weights of the nitrogen atoms in the molecule4 ,these values are given in the fourth column in the table4 ,if a large number of compounds containing nitrogen are studied in this way1 it is probable that there will be included in the list at least one substance whose molecule contains a single nitrogen atom4 ,in this case the number in the fourth column will be the approximate atomic weight of nitrogen4 ,on comparing the values for nitrogen in the table it will be seen that a number which is approximately #ad is the smallest1 and that the others are multiples of this4 ,these compounds of higher value1 therefore1 contain more than one nitrogen atom in the molecule4 ,accurate determination of atomic weights4 ,molecular weights cannot be determined very accurately1 and consequently the part in them due to nitrogen is a little uncertain1 as will be seen in the table4 ,all we can tell by this method is that the true weight is very near #ad4 ,the equivalent can however be determined very accurately1 and we have seen that it is some multiple or submultiple of the true atomic weight4 ,since molecular-weight determinations have shown that in the case of nitrogen the atomic weight is near #ad1 and we have found the equivalent to be #g4jb1 it is evident that the true atomic weight is twice the equivalent1 or #g4jb #b #ad4jd4 ,summary4 ,these1 then1 are the steps necessary to establish the atomic weight of an element4 #a4 ,determine the equivalent accurately by analysis4 #b4 ,determine the molecular weight of a large number of compounds of the element1 and by analysis the part of the molecular weight due to the element4 ,the smallest number so obtained will be approximately the atomic weight4 #c4 ,multiply the equivalent by the small whole number 7usually #a1 #b1 or #c71 which will make a number very close to the approximate atomic weight4 ,the figure so obtained will be the true atomic weight4 ,molecular weights of the elements4 ,it will be noticed that the molecular weight of nitrogen obtained by multiplying its density by #bh4i is #bh4jh4 ,yet the atomic weight of nitrogen as deduced from a study of its gaseous compounds is #ad4jd4 ,the simplest explanation that can be given for this is that the gaseous nitrogen is made up of molecules1 each of which contains two atoms4 ,in this respect it resembles oxygen2 for we have seen that an entirely different line of reasoning leads us to believe that the molecule of oxygen contains two atoms4 ,when we wish to indicate molecules of these gases the symbols ,n#b and ,o#b should be used4 ,when we desire to merely show the weights taking part in a reaction this is not necessary4 ,the vapor densities of many of the elements show that1 like oxygen and nitrogen1 their molecules consist of two atoms4 ,in other cases1 particularly among the metals1 the molecule and the atom are identical4 ,still other elements have four atoms in their molecules4 ,while oxygen contains two atoms in its molecules1 a study of ozone has led to the conclusion that it has three4 ,the formation of ozone from oxygen can therefore be represented by the equation #c,o#b #b,o#c4 ,other methods of determining molecular weights4 ,it will be noticed that ,avogadro's law gives us a method by which we can determine the relative weights of the molecules of two gases because it enables us to tell when we are dealing with an equal number of the two kinds of molecules4 ,if by any other means we can get this information1 we can make use of the knowledge so gained to determine the molecular weights of the two substances4 ,raoult's laws4 ,two laws have been discovered which give us just such information4 ,they are known as ,raoult's laws1 and can be stated as follows3 #a4 ,when weights of substances which are proportional to their molecular weights are dissolved in the same weight of solvent1 the rise of the boiling point is the same in each case4 #b4 ,when weights of substances which are proportional to their molecular weights are dissolved in the same weight of solvent1 the lowering of the freezing point is the same in each case4 ,by taking advantage of these laws it is possible to determine when two solutions contain the same number of molecules of two dissolved substances1 and consequently the relative molecular weights of the two substances4 ,law of ,dulong and ,petit4 ,in #ahai ,dulong and ,petit discovered a very interesting relation between the atomic weight of an element and its specific heat1 which holds true for elements in the solid state4 ,if equal weights of two solids1 say1 lead and silver1 are heated through the same range of temperature1 as from #aj to #bj1 it is found that very different amounts of heat are required4 ,the amount of heat required to change the temperature of a solid or a liquid by a definite amount compared with the amount required to change the temperature of an equal weight of water by the same amount is called its specific heat4 ,dulong and ,petit discovered the following law3 ,the specific heat of an element in the solid form multiplied by its atomic weight is approximately equal to the constant #f4be4 ,that is1 at4 wt4 sp4 ht4 #f4be4 ,consequently1 #f4be at4 wt4 -------- sp4 ht4 ,this law is not very accurate1 but it is often possible by means of it to decide upon what multiple of the equivalent is the real atomic weight4 ,thus the specific heat of iron is found by experiment to be #j4aab1 and its equivalent is #bg4ie4 #f4be #j4aab #ee4h4 ,we see1 therefore1 that the atomic weight is twice the equivalent1 or #ee4i4 ,how formulas are determined4 ,it will be well in connection with molecular weights to consider how the formula of a compound is decided upon1 for the two subjects are very closely associated4 ,some examples will make clear the method followed4 ,the molecular weight of a substance containing hydrogen and chlorine was #cf4d4 ,by analysis #cf4d parts of the substance was found to contain #a part of hydrogen and #ce4d parts of chlorine4 ,as these are the simple atomic weights of the two elements1 the formula of the compound must be ,h,cl4 ,a substance consisting of oxygen and hydrogen was found to have a molecular weight of #cd4 ,analysis showed that in #cd parts of the substance there were #b parts of hydrogen and #cb parts of oxygen4 ,dividing these figures by the atomic weights of the two elements1 we get #b #a #b for ,h2 #cb #af #b for ,o4 ,the formula is therefore ,h#b,o#b4 ,a substance containing #b4jd ,h1 #cb4f ,s1 and #fe4c ,o was found to have a molecular weight of #ih4 ,in these #ih parts of the substance there are #ih #b4jd #b parts of ,h1 #ih #cb4f #cb parts of ,s1 and #ih #fe4c #fd parts of ,o4 ,if the molecule weighs #ih1 the hydrogen atoms present must together weigh #b1 the sulphur atoms #cb1 and the oxygen atoms #fd4 ,dividing these figures by the respective atomic weights of the three elements1 we have1 for ,h1 #b #a #b atoms2 for ,s1 #cb #cb #a atom2 for ,o1 #fd #af #d atoms4 ,hence the formula is ,h#b,,so#d4 ,we have1 then1 this general procedure3 ,find the percentage composition of the substance and also its molecular weight4 ,multiply the molecular weight successively by the percentage of each element present1 to find the amount of the element in the molecular weight of the compound4 ,the figures so obtained will be the respective parts of the molecular weight due to the several atoms4 ,divide by the atomic weights of the respective elements1 and the quotient will be the number of atoms present4 ,avogadro's hypothesis and chemical calculations4 ,this law simplifies many chemical calculations4 #a4 ,application to volume relations in gaseous reactions4 ,since equal volumes of gases contain an equal number of molecules1 it follows that when an equal number of gaseous molecules of two or more gases take part in a reaction1 the reaction will involve equal volumes of the gases4 ,in the equation ,c#b;,h#b,o#d ,h#b,o ,,co#b ,,co1 since #a molecule of each of the gases ,,co#b and ,,co is set free from each molecule of oxalic acid1 the two substances must always be set free in equal volumes4 ,acetylene burns in accordance with the equation #b;,c#b;,h#b #e,o#b #d;,,co#b #b;,h#b,o4 ,hence #b volumes of acetylene will react with #e volumes of oxygen to form #d volumes of carbon dioxide and #b volumes of steam4 ,that the volume relations may be correct a gaseous element must be given its molecular formula4 ,thus oxygen must be written ,o#b and not #b,o4 #b4 ,application to weights of gases4 ,it will be recalled that the molecular weight of a gas is determined by ascertaining the weight of #bb4d l4 of the gas4 ,this weight in grams is called the gram-molecular weight of a gas4 ,if the molecular weight of any gas is known1 the weight of a liter of the gas under standard conditions may be determined by dividing its gram-molecular weight by #bb4d4 ,thus the gram-molecular weight of a hydrochloric acid gas is #cf4deh4 ,a liter of the gas will therefore weigh #cf4deh #bb4d #a4fbg g4 ,,exercises #a4 ,from the following data calculate the atomic weight of sulphur4 ,the equivalent1 as obtained by an analysis of sulphur dioxide1 is #af4jc4 ,the densities and compositions of a number of compounds containing sulphur are as follows3 ,,name ,,density ,,composition ,,by ,,percentage ,hydrosulphuric acid #a4agia ,s #id4aa ,h #e4hi ,sulphur dioxide #b4bbb ,s #ej4je ,o #di4ie ,sulphur trioxide #b4gd ,s #dj4je ,o #ei4ie ,sulphur chloride #d4gj ,s #dg4dh ,cl #eb4eb ,sulphuryl chloride #d4fd ,s #bc4ge ,cl #eb4ec ,o #bc4gj ,carbon disulphide #b4fh ,s #hd4bd ,c #ae4gf #b4 ,calculate the formulas for compounds of the following compositions3 ,,molecular ,,weight 7#a7 ,s #ci4jg ,o #eh4di ,h #b4dd #ha4j 7#b7 ,ca #bi4dj ,s #bc4ef ,o #dg4jd #acf4b 7#c7 ,k #ch4fg ,n #ac4hh ,o #dg4de #aja4b #c4 ,the molecular weight of ammonia is #ag4jf2 of sulphur dioxide is #fd4jf2 of chlorine is #gj4i4 ,from the molecular weight calculate the weight of #a l4 of each of these gases4 ,compare your results with the table on the back cover of the book4 #d4 ,from the molecular weight of the same gases calculate the density of each1 referred to air as a standard4 #e4 ,a mixture of #ej cc4 of carbon monoxide and #ej cc4 of oxygen was exploded in a eudiometer1 7a7 ,what gases remained in the tube after the explosion8 7b7 ,what was the volume of each8 #f4 ,in what proportion must acetylene and oxygen be mixed to produce the greatest explosion8 #g4 ,solve ,problem #ah1 ,chapter ,,xvii1 without using molecular weights4 ,compare your results4 #h4 ,solve ,problem #aj1 ,chapter ,,xviii1 without using molecular weights4 ,compare your results4 #i4 ,the specific heat of aluminium is #j4bad2 of lead is #j4jca4 ,from these specific heats calculate the atomic weights of each of the elements4 ,,chapter ,,xx ,,the ,,phosphorus ,,family ,,atomic ,,melting ,,symbol ,,weight ,,density ,,point ---------------------------------------- ------ ,phosphorus ,p #ca4j #a4h #dc4c ,arsenic ,as #ge4j #e4gc --- ,antimony ,sb #abj4b #f4g #dcb ,bismuth ,bi #bjh4e #i4h #bgj ,the family4 ,the elements constituting this family belong in the same group with nitrogen and therefore resemble it in a general way4 ,they exhibit a regular gradation of physical properties1 as is shown in the above table4 ,the same general gradation is also found in their chemical properties1 phosphorus being an acid-forming element1 while bismuth is essentially a metal4 ,the other two elements are intermediate in properties4 ,compounds4 ,in general the elements of the family form compounds having similar composition1 as is shown in the following table3 ,,ph#c ,p,cl#c ,p,cl#e ,p#b,o#c ,p#b,o#e ,as,h#c ,as,cl#c ,as,cl#e ,as#b,o#c ,as#b,o#e ,sb,h#c ,sb,cl#c ,sb,cl#e ,sb#b,o#c ,sb#b,o#e 4444 ,bi,cl#c ,bi,cl#e ,bi#b,o#c ,bi#b,o#e ,in the case of phosphorus1 arsenic1 and antimony the oxides are acid anhydrides4 ,salts of at least four acids of each of these three elements are known1 the free acid in some instances being unstable4 ,the relation of these acids to the corresponding anhydrides may be illustrated as follows1 phosphorus being taken as an example3 ,p#b,o#c #c;,h#b,o #b;,h#c,,po#c 7phosphorous acid74 ,p#b,o#e #c;,h#b,o #b;,h#c,,po#d 7phosphoric acid74 ,p#b,o#e #b;,h#b,o ,h#d,p#b,o#g 7pyrophosphoric acid74 ,p#b,o#e ,h#b,o #b;,,hpo#c 7metaphosphoric acid74 ,,phosphorus ,history4 ,the element phosphorus was discovered by the alchemist ,brand1 of ,hamburg1 in #affi1 while searching for the philosopher's stone4 ,owing to its peculiar properties and the secrecy which was maintained about its preparation1 it remained a very rare and costly substance until the demand for it in the manufacture of matches brought about its production on a large scale4 ,occurrence4 ,owing to its great chemical activity phosphorus never occurs free in nature4 ,in the form of phosphates it is very abundant and widely distributed4 ,phosphorite and sombrerite are mineral forms of calcium phosphate1 while apatite consists of calcium phosphate together with calcium fluoride or chloride4 ,these minerals form very large deposits and are extensively mined for use as fertilizers4 ,calcium phosphate is a constituent of all fertile soil1 having been supplied to the soil by the disintegration of rocks containing it4 ,it is the chief mineral constituent of bones of animals1 and bone ash is therefore nearly pure calcium phosphate4 ,preparation4 ,phosphorus is now manufactured from bone ash or a pure mineral phosphate by heating the phosphate with sand and carbon in an electric furnace4 ,the materials are fed in at ,m 7,fig4 #gj7 by the feed screw ,f4 ,the phosphorus vapor escapes at ,p and is condensed under water1 while the calcium silicate is tapped off as a liquid at ,s4 ,the phosphorus obtained in this way is quite impure1 and is purified by distillation4 ,illustration3 ,fig4 #gj ,explanation of the reaction4 ,to understand the reaction which occurs1 it must be remembered that a volatile acid anhydride is expelled from its salts when heated with an anhydride which is not volatile4 ,thus1 when sodium carbonate and silicon dioxide are heated together the following reaction takes place3 ,na#b;,,co#c ,si,o#b ,na#b,si,o#c ,,co#b4 ,silicon dioxide is a less volatile anhydride than phosphoric anhydride 7,p#b,o#e71 and when strongly heated with a phosphate the phosphoric anhydride is driven out1 thus3 ,ca#c7,,po#d7b #c,si,o#b #c;,ca,si,o#c ,p#b,o#e4 ,if carbon is added before the heat is applied1 the ,p#b,o#e is reduced to phosphorus at the same time1 according to the equation ,p#b,o#e #e;,c #b,p #e;,,co4 ,physical properties4 ,the purified phosphorus is a pale yellowish1 translucent1 waxy solid which melts at #dc4c and boils at #bfi4 ,it can therefore be cast into any convenient form under warm water1 and is usually sold in the market in the form of sticks4 ,it is quite soft and can be easily cut with a knife1 but this must always be done while the element is covered with water1 since it is extremely inflammable1 and the friction of the knife blade is almost sure to set it on fire if cut in the air4 ,it is not soluble in water1 but is freely soluble in some other liquids1 notably in carbon disulphide4 ,its density is #a4h4 ,chemical properties4 ,exposed to the air phosphorus slowly combines with oxygen1 and in so doing emits a pale light1 or phosphorescence1 which can be seen only in a dark place4 ,the heat of the room may easily raise the temperature to the kindling point of phosphorus1 when it burns with a sputtering flame1 giving off dense fumes of oxide of phosphorus4 ,it burns with dazzling brilliancy in oxygen1 and combines directly with many other elements1 especially with sulphur and the halogens4 ,on account of its great affinity for oxygen it is always preserved under water4 ,phosphorus is very poisonous1 from #j4b to #j4c gram being a fatal dose4 ,ground up with flour and water or similar substances1 it is often used as a poison for rats and other vermin4 ,precaution4 ,the heat of the body is sufficient to raise phosphorus above its kindling temperature1 and for this reason it should always be handled with forceps and never with the bare fingers4 ,burns occasioned by it are very painful and slow in healing4 ,red phosphorus4 ,on standing1 yellow phosphorus gradually undergoes a remarkable change1 being converted into a dark red powder which has a density of #b4a4 ,it no longer takes fire easily1 neither does it dissolve in carbon disulphide4 ,it is not poisonous and1 in fact1 seems to be an entirely different substance4 ,the velocity of this change increases with rise in temperature1 and the red phosphorus is therefore prepared by heating the yellow just below the boiling point 7#bej-cjj74 ,when distilled and quickly condensed the red form changes back to the yellow4 ,this is in accordance with the general rule that when a substance capable of existing in several allotropic forms is condensed from a gas or crystallized from the liquid state1 the more unstable variety forms first1 and this then passes into the more stable forms4 ,matches4 ,the chief use of phosphorus is in the manufacture of matches4 ,common matches are made by first dipping the match sticks into some inflammable substance1 such as melted paraffin1 and afterward into a paste consisting of 7#a7 phosphorus1 7#b7 some oxidizing substance1 such as manganese dioxide or potassium chlorate1 and 7#c7 a binding material1 usually some kind of glue4 ,on friction the phosphorus is ignited1 the combustion being sustained by the oxidizing agent and communicated to the wood by the burning paraffin4 ,in sulphur matches the paraffin is replaced by sulphur4 ,in safety matches red phosphorus1 an oxidizing agent1 and some gritty material such as emery is placed on the side of the box1 while the match tip is provided as before with an oxidizing agent and an easily oxidized substance1 usually antimony sulphide4 ,the match cannot be ignited easily by friction1 save on the prepared surface4 ,compounds of phosphorus with hydrogen4 ,phosphorus forms several compounds with hydrogen1 the best known of which is phosphine 7,,ph#c7 analogous to ammonia 7,,nh#c74 ,preparation of phosphine4 ,phosphine is usually made by heating phosphorus with a strong solution of potassium hydroxide1 the reaction being a complicated one4 ,illustration3 ,fig4 #ga ,the experiment can be conveniently made in the apparatus shown in ,fig4 #ga4 ,a strong solution of potassium hydroxide together with several small bits of phosphorus are placed in the flask ,a1 and a current of coal gas is passed into the flask through the tube ,b until all the air has been displaced4 ,the gas is then turned off and the flask is heated4 ,phosphine is formed in small quantities and escapes through the delivery tube1 the exit of which is just covered by the water in the vessel ,c4 ,each bubble of the gas as it escapes into the air takes fire1 and the product of combustion 7,p#b,o#e7 forms beautiful small rings1 which float unbroken for a considerable time in quiet air4 ,the pure phosphine does not take fire spontaneously4 ,when prepared as directed above1 impurities are present which impart this property4 ,properties4 ,phosphine is a gas of unpleasant odor and is exceedingly poisonous4 ,like ammonia it forms salts with the halogen acids4 ,thus we have phosphonium chloride 7,,ph#d;,cl7 analogous to ammonium chloride 7,,nh#d;,cl74 ,the phosphonium salts are of but little importance4 ,oxides of phosphorus4 ,phosphorus forms two well-known oxides1--the trioxide 7,p#b,o#c7 and the pentoxide 7,p#b,o#e71 sometimes called phosphoric anhydride4 ,when phosphorus burns in an insufficient supply of air the product is partially the trioxide2 in oxygen or an excess of air the pentoxide is formed4 ,the pentoxide is much the better known of the two4 ,it is a snow-white1 voluminous powder whose most marked property is its great attraction for water4 ,it has no chemical action upon most gases1 so that they can be very thoroughly dried by allowing them to pass through properly arranged vessels containing phosphorus pentoxide4 ,acids of phosphorus4 ,the important acids of phosphorus are the following3 ,h#c,,po#c phosphorous acid4 ,h#c,,po#d phosphoric acid4 ,h#d,p#b,o#g pyrophosphoric acid4 ,,hpo#c metaphosphoric acid4 ,these may be regarded as combinations of the oxides of phosphorus with water according to the equations given in the discussion of the characteristics of the family4 #a4 ,phosphorous acid 7,h#c,,po#c74 ,neither the acid nor its salts are at all frequently met with in chemical operations4 ,it can be easily obtained1 however1 in the form of transparent crystals when phosphorus trichloride is treated with water and the resulting solution is evaporated3 ,p,cl#c #c;,h#b,o ,h#c,,po#c #c;,h,cl4 ,its most interesting property is its tendency to take up oxygen and pass over into phosphoric acid4 #b4 ,orthophosphoric acid 7phosphoric acid7 7,h#c,,po#d74 ,this acid can be obtained by dissolving phosphorus pentoxide in boiling water1 as represented in the equation ,p#b,o#e #c;,h#b,o #b;,h#c,,po#d4 ,it is usually made by treating calcium phosphate with concentrated sulphuric acid4 ,the calcium sulphate produced in the reaction is nearly insoluble1 and can be filtered off1 leaving the phosphoric acid in solution4 ,very pure acid is made by oxidizing phosphorus with nitric acid4 ,it forms large colorless crystals which are exceedingly soluble in water4 ,being a tribasic acid1 it forms acid as well as normal salts4 ,thus the following compounds of sodium are known3 ,na,h#b,,po#d monosodium hydrogen phosphate4 ,na#b;,,hpo#d disodium hydrogen phosphate4 ,na#c,,po#d normal sodium phosphate4 ,these salts are sometimes called respectively primary1 secondary1 and tertiary phosphates4 ,they may be prepared by bringing together phosphoric acid and appropriate quantities of sodium hydroxide4 ,phosphoric acid also forms mixed salts1 that is1 salts containing two different metals4 ,the most familiar compound of this kind is microcosmic salt1 which has the formula ,na7,,nh#d7;,,hpo#d4 ,orthophosphates4 ,the orthophosphates form an important class of salts4 ,the normal salts are nearly all insoluble and many of them occur in nature4 ,the secondary phosphates are as a rule insoluble1 while most of the primary salts are soluble4 #c4 ,pyrophosphoric acid 7,h#d,p#b,o#g74 ,on heating orthophosphoric acid to about #bbe pyrophosphoric acid is formed in accordance with the following equation3 #b;,h#c,,po#d ,h#d,p#b,o#g ,h#b,o4 ,it is a white crystalline solid4 ,its salts can be prepared by heating a secondary phosphate3 #b,na#b;,,hpo#d ,na#d,p#b,o#g ,h#b,o4 #d4 ,metaphosphoric acid 7glacial phosphoric acid7 7,,hpo#c74 ,this acid is formed when orthophosphoric acid is heated above #djj3 ,h#c,,po#d ,,hpo#c ,h#b,o4 ,it is also formed when phosphorus pentoxide is treated with cold water3 ,p#b,o#e ,h#b,o #b;,,hpo#c4 ,it is a white crystalline solid1 and is so stable towards heat that it can be fused and even volatilized without decomposition4 ,on cooling from the fused state it forms a glassy solid1 and on this account is often called glacial phosphoric acid4 ,it possesses the property of dissolving small quantities of metallic oxides1 with the formation of compounds which1 in the case of certain metals1 have characteristic colors4 ,it is therefore used in the detection of these metals4 ,while the secondary phosphates1 on heating1 give salts of pyrophosphoric acid1 the primary phosphates yield salts of metaphosphoric acid4 ,the equations representing these reactions are as follows3 #b,na#b;,,hpo#d ,na#d,p#c,o#g ,h#b,o1 ,na,h#b,,po#d ,na,p,o#c ,h#b,o4 ,fertilizers4 ,when crops are produced year after year on the same field certain constituents of the soil essential to plant growth are removed1 and the soil becomes impoverished and unproductive4 ,to make the land once more fertile these constituents must be replaced4 ,the calcium phosphate of the mineral deposits or of bone ash serves well as a material for restoring phosphorus to soils exhausted of that essential element2 but a more soluble substance1 which the plants can more readily assimilate1 is desirable4 ,it is better1 therefore1 to convert the insoluble calcium phosphate into the soluble primary phosphate before it is applied as fertilizer4 ,it will be seen by reference to the formulas for the orthophosphates 7see page #bdd7 that in a primary phosphate only one hydrogen atom of phosphoric acid is replaced by a metal4 ,since the calcium atom always replaces two hydrogen atoms1 it might be thought that there could be no primary calcium phosphate2 but if the calcium atom replaces one hydrogen atom from each of two molecules of phosphoric acid1 the salt ,ca7,h#b,,po#d7b will result1 and this is a primary phosphate4 ,it can be made by treatment of the normal phosphate with the necessary amount of sulphuric acid1 calcium sulphate being formed at the same time1 thus3 ,ca#c7,,po#d7b #b;,h#b,,so#d ,ca7,h#b,,po#d7b #b;,ca,s,o#d4 ,the resulting mixture is a powder1 which is sold as a fertilizer under the name of superphosphate of lime4 ,,arsenic ,occurrence4 ,arsenic occurs in considerable quantities in nature as the native element1 as the sulphides realgar 7,as#b,s#b7 and orpiment 7,as#b,s#c71 as oxide 7,as#b,o#c71 and as a constituent of many metallic sulphides1 such as arsenopyrite 7,fe,as,s74 ,preparation4 ,the element is prepared by purifying the native arsenic1 or by heating the arsenopyrite in iron tubes1 out of contact with air1 when the reaction expressed by the following equation occurs3 ,fe,as,s ,fe,s ,as4 ,the arsenic1 being volatile1 condenses in chambers connected with the heated tubes4 ,it is also made from the oxide by reduction with carbon3 #b;,as#b,o#c #c;,c #d;,as #c;,,co#b4 ,properties4 ,arsenic is a steel-gray1 metallic-looking substance of density #e4gc4 ,though resembling metals in appearance1 it is quite brittle1 being easily powdered in a mortar4 ,when strongly heated it sublimes1 that is1 it passes into a vapor without melting1 and condenses again to a crystalline solid when the vapor is cooled4 ,like phosphorus it can be obtained in several allotropic forms4 ,it alloys readily with some of the metals1 and finds its chief use as an alloy with lead1 which is used for making shot1 the alloy being harder than pure lead4 ,when heated on charcoal with the blowpipe it is converted into an oxide which volatilizes1 leaving the charcoal unstained by any oxide coating4 ,it burns readily in chlorine gas1 forming arsenic trichloride1-- ,as #c;,cl ,as,cl#c4 ,unlike most of its compounds1 the element itself is not poisonous4 ,arsine 7,as,h#c74 ,when any compound containing arsenic is brought into the presence of nascent hydrogen1 arsine 7,as,h#c71 corresponding to phosphine and ammonia1 is formed4 ,the reaction when oxide of arsenic is so treated is ,as#b,o#c #ab;,h #b;,as,h#c #c;,h#b,o4 ,arsine is a gas with a peculiar garlic-like odor1 and is intensely poisonous4 ,a single bubble of pure gas has been known to prove fatal4 ,it is an unstable compound1 decomposing into its elements when heated to a moderate temperature4 ,it is combustible1 burning with a pale bluish-white flame to form arsenic trioxide and water when air is in excess3 #b;,as,h#c #f,o ,as#b,o#c #c;,h#b,o4 ,when the supply of air is deficient water and metallic arsenic are formed3 #b;,as,h#c #c,o #c;,h#b,o #b;,as4 ,these reactions make the detection of even minute quantities of arsenic a very easy problem4 ,illustration3 ,fig4 #gb ,marsh's test for arsenic4 ,the method devised by ,marsh for detecting arsenic is most frequently used1 the apparatus being shown in ,fig4 #gb4 ,hydrogen is generated in the flask ,a by the action of dilute sulphuric acid on zinc1 is dried by passing over calcium chloride in the tube ,b1 and after passing through the hard-glass tube ,c is ignited at the jet ,d4 ,if a substance containing arsenic is now introduced into the generator ,a1 the arsenic is converted into arsine by the action of the nascent hydrogen1 and passes to the jet along with the hydrogen4 ,if the tube ,c is strongly heated at some point near the middle1 the arsine is decomposed while passing this point and the arsenic is deposited just beyond the heated point in the form of a shining1 brownish-black mirror4 ,if the tube is not heated1 the arsine burns along with the hydrogen at the jet4 ,under these conditions a small porcelain dish crowded down into the flame is blackened by a spot of metallic arsenic1 for the arsine is decomposed by the heat of the flame1 and the arsenic1 cooled below its kindling temperature by the cold porcelain1 deposits upon it as a black spot4 ,antimony conducts itself in the same way as arsenic1 but the antimony deposit is more sooty in appearance4 ,the two can also be distinguished by the fact that sodium hypochlorite 7,na,cl,o7 dissolves the arsenic deposit1 but not that formed by antimony4 ,oxides of arsenic4 ,arsenic forms two oxides1 ,as#b,o#c and ,as#b,o#e1 corresponding to those of phosphorus4 ,of these arsenious oxide1 or arsenic trioxide 7,as#b,o#c71 is much better known1 and is the substance usually called white arsenic1 or merely arsenic4 ,it is found as a mineral1 but is usually obtained as a by-product in burning pyrite in the sulphuric-acid industry4 ,the pyrite has a small amount of arsenopyrite in it1 and when this is burned arsenious oxide is formed as a vapor together with sulphur dioxide3 #b;,fe,as,s #aj,o ,fe#b,o#c ,as#b,o#c #b,,so#b4 ,the arsenious oxide is condensed in appropriate chambers4 ,it is a rather heavy substance1 obtained either as a crystalline powder or as large1 vitreous lumps1 resembling lumps of porcelain in appearance4 ,it is very poisonous1 from #j4b to #j4c g4 being a fatal dose4 ,it is frequently given as a poison1 since it is nearly tasteless and does not act very rapidly4 ,this slow action is due to the fact that it is not very soluble1 and hence is absorbed slowly by the system4 ,arsenious oxide is also used as a chemical reagent in glass making and in the dye industry4 ,acids of arsenic4 ,like the corresponding oxides of phosphorus1 the oxides of arsenic are acid anhydrides4 ,in solution they combine with bases to form salts1 corresponding to the salts of the acids of phosphorus4 ,thus we have salts of the following acids3 ,h#c;,as,o#c arsenious acid4 ,h#c;,as,o#d orthoarsenic acid4 ,h#d;,as#b,o#c pyroarsenic acid4 ,h,as,o#c metarsenic acid4 ,several other acids of arsenic are also known4 ,not all of these can be obtained as free acids1 since they tend to lose water and form the oxides4 ,thus1 instead of obtaining arsenious acid 7,h#c;,as,o#c71 the oxide ,as#b,o#c is obtained3 #b;,h#c;,as,o#c ,as#b,o#c #c;,h#b,o4 ,salts of all the acids are known1 however1 and some of them have commercial value4 ,most of them are insoluble1 and some of the copper salts1 which are green1 are used as pigments4 ,paris green1 which has a complicated formula1 is a well-known insecticide4 ,antidote for arsenical poisoning4 ,the most efficient antidote for arsenic poisoning is ferric hydroxide4 ,it is prepared as needed1 according to the equation ,fe#b7,,so#d7c #c,mg7,,oh7#b #b;,fe7,,oh7#c #c,mg,s,o#d4 ,sulphides of arsenic4 ,when hydrogen sulphide is passed into an acidified solution containing an arsenic compound the arsenic is precipitated as a bright yellow sulphide1 thus3 #b;,h#c;,as,o#c #c;,h#b,s ,as#b,s#c #f;,h#b,o1 #b;,h#c;,as,o#d #e;,h#b,s ,as#b,s#e #h;,h#b,o4 ,in this respect arsenic resembles the metallic elements1 many of which produce sulphides under similar conditions4 ,the sulphides of arsenic1 both those produced artificially and those found in nature1 are used as yellow pigments4 ,,antimony ,occurrence4 ,antimony occurs in nature chiefly as the sulphide 7,sb#b,s#c71 called stibnite1 though it is also found as oxide and as a constituent of many complex minerals4 ,preparation4 ,antimony is prepared from the sulphide in a very simple manner4 ,the sulphide is melted with scrap iron in a furnace1 when the iron combines with the sulphur to form a slag1 or liquid layer of melted iron sulphide1 while the heavier liquid1 antimony1 settles to the bottom and is drawn off from time to time4 ,the reaction involved is represented by the equation ,sb#b,s#c #c;,fe #b,sb #c;,fe,s4 ,physical properties4 ,antimony is a bluish-white1 metallic-looking substance whose density is #f4g4 ,it is highly crystalline1 hard1 and very brittle4 ,it has a rather low melting point 7#dcb7 and expands very noticeably on solidifying4 ,chemical properties4 ,in chemical properties antimony resembles arsenic in many particulars4 ,it forms the oxides ,sb#b,o#c and ,sb#b,o#e1 and in addition ,sb#b,o#d4 ,it combines with the halogen elements with great energy1 burning brilliantly in chlorine to form antimony trichloride 7,sb,cl#c74 ,when heated on charcoal with the blowpipe it is oxidized and forms a coating of antimony oxide on the charcoal which has a characteristic bluish-white color4 ,stibine 7,sb,h#c74 ,the gas stibine 7,sb,h#c7 is formed under conditions which are very similar to those which produce arsine1 and it closely resembles the latter compound1 though it is still less stable4 ,it is very poisonous4 ,acids of antimony4 ,the oxides ,sb#b,o#c and ,sb#b,o#e are weak acid anhydrides and are capable of forming two series of acids corresponding in formulas to the acids of phosphorus and arsenic4 ,they are much weaker1 however1 and are of little practical importance4 ,sulphides of antimony4 ,antimony resembles arsenic in that hydrogen sulphide precipitates it as a sulphide when conducted into an acidified solution containing an antimony compound3 #b,sb,cl#c #c;,h#b,s ,sb#b,s#c #f;,h,cl1 #b,sb,cl#e #e;,h#b,s ,sb#b,s#e #aj;,h,cl4 ,the two sulphides of antimony are called the trisulphide and the pentasulphide respectively4 ,when prepared in this way they are orange-colored substances1 though the mineral stibnite is black4 ,metallic properties of antimony4 ,the physical properties of the element are those of a metal1 and the fact that its sulphide is precipitated by hydrogen sulphide shows that it acts like a metal in a chemical way4 ,many other reactions show that antimony has more of the properties of a metal than of a non-metal4 ,the compound ,sb7,,oh7#c1 corresponding to arsenious acid1 while able to act as a weak acid is also able to act as a weak base with strong acids4 ,for example1 when treated with concentrated hydrochloric acid antimony chloride is formed3 ,sb7,,oh7#c #c;,h,cl ,sb,cl#c #c;,h#b,o4 ,a number of elements act in this same way1 their hydroxides under some conditions being weak acids and under others weak bases4 ,,alloys ,some metals when melted together thoroughly intermix1 and on cooling form a homogeneous1 metallic-appearing substance called an alloy4 ,not all metals will mix in this way1 and in some cases definite chemical compounds are formed and separate out as the mixture solidifies1 thus destroying the uniform quality of the alloy4 ,in general the melting point of the alloy is below the average of the melting points of its constituents1 and it is often lower than any one of them4 ,antimony forms alloys with many of the metals1 and its chief commercial use is for such purposes4 ,it imparts to its alloys high density1 rather low melting point1 and the property of expanding on solidification4 ,such an alloy is especially useful in type founding1 where fine lines are to be reproduced on a cast4 ,type metal consists of antimony1 lead1 and tin4 ,babbitt metal1 used for journal bearings in machinery1 contains the same metals in a different proportion together with a small percentage of copper4 ,,bismuth ,occurrence4 ,bismuth is usually found in the uncombined form in nature4 ,it also occurs as oxide and sulphide4 ,most of the bismuth of commerce comes from ,saxony1 and from ,mexico and ,colorado1 but it is not an abundant element4 ,preparation4 ,it is prepared by merely heating the ore containing the native bismuth and allowing the melted metal to run out into suitable vessels4 ,other ores are converted into oxides and reduced by heating with carbon4 ,physical properties4 ,bismuth is a heavy1 crystalline1 brittle metal nearly the color of silver1 but with a slightly rosy tint which distinguishes it from other metals4 ,it melts at a low temperature 7#bgj7 and has a density of #i4h4 ,it is not acted upon by the air at ordinary temperatures4 ,chemical properties4 ,when heated with the blowpipe on charcoal1 bismuth gives a coating of the oxide ,bi#b,o#c4 ,this has a yellowish-brown color which easily distinguishes it from the oxides formed by other metals4 ,it combines very readily with the halogen elements1 powdered bismuth burning readily in chlorine4 ,it is not very easily acted upon by hydrochloric acid1 but nitric and sulphuric acids act upon it in the same way that they do upon copper4 ,uses4 ,bismuth finds its chief use as a constituent of alloys1 particularly in those of low melting point4 ,some of these melt in hot water4 ,for example1 ,wood's metal1 consisting of bismuth1 lead1 tin1 and cadmium1 melts at #fj4e4 ,compounds of bismuth4 ,unlike the other elements of this group1 bismuth has almost no acid properties4 ,its chief oxide1 ,bi#b,o#c1 is basic in its properties4 ,it dissolves in strong acids and forms salts of bismuth3 ,bi#b,o#c #f;,h,cl #b;,bi,cl#c #c;,h#b,o1 ,bi#b,o#c #f;,,hno#c #b;,bi7,,no#c7c #c;,h#b,o4 ,the nitrate and chloride of bismuth can be obtained as well-formed colorless crystals4 ,when treated with water the salts are decomposed in the manner explained in the following paragraph4 ,,hydrolysis ,many salts such as those of antimony and bismuth form solutions which are somewhat acid in reaction1 and must therefore contain hydrogen ions4 ,this is accounted for by the same principle suggested to explain the fact that solutions of potassium cyanide are alkaline in reaction 7p4 #baj74 ,water forms an appreciable number of hydrogen and hydroxyl ions1 and very weak bases such as bismuth hydroxide are dissociated to but a very slight extent4 ,when ,bi ions from bismuth chloride1 which dissociates very readily1 are brought in contact with the ,,oh- ions from water1 the two come to the equilibrium expressed in the equation ,bi #c,,oh- -- ,bi7,,oh7#c4 ,for every hydroxyl ion removed from the solution in this way a hydrogen ion is left free1 and the solution becomes acid in reaction4 ,reactions of this kind and that described under potassium cyanide are called hydrolysis4 ,,definition3 ,hydrolysis is the action of water upon a salt to form an acid and a base1 one of which is very slightly dissociated4 ,conditions favoring hydrolysis4 ,while hydrolysis is primarily due to the slight extent to which either the acid or the base formed is dissociated1 several other factors have an influence upon the extent to which it will take place4 #a4 ,influence of mass4 ,since hydrolysis is a reversible reaction1 the relative masses of the reacting substances influence the point at which equilibrium will be reached4 ,in the equilibrium ,bi,cl#c #c;,h#b,o -- ,bi7,,oh7#c #c;,h,cl the addition of more water will result in the formation of more bismuth hydroxide and hydrochloric acid4 ,the addition of more hydrochloric acid will convert some of the bismuth hydroxide into bismuth chloride4 #b4 ,formation of insoluble substances4 ,when one of the products of hydrolysis is nearly insoluble in water the solution will become saturated with it as soon as a very little has been formed4 ,all in excess of this will precipitate1 and the reaction will go on until the acid set free increases sufficiently to bring about an equilibrium4 ,thus a considerable amount of bismuth and antimony hydroxides are precipitated when water is added to the chlorides of these elements4 ,the greater the dilution the more hydroxide precipitates4 ,the addition of hydrochloric acid in considerable quantity will1 however1 redissolve the precipitate4 ,partial hydrolysis4 ,in many cases the hydrolysis of a salt is only partial1 resulting in the formation of basic salts instead of the free base4 ,most of these basic salts are insoluble in water1 which accounts for their ready formation4 ,thus bismuth chloride may hydrolyze by successive steps1 as shown in the equations ,bi,cl#c ,h#b,o ,bi7,,oh7,cl#b ,h,cl1 ,bi,cl#c #b;,h#b,o ,bi7,,oh7#b;,cl #b;,h,cl1 ,bi,cl#c #c;,h#b,o ,bi7,,oh7#c #c;,h,cl4 ,the basic salt so formed may also lose water1 as shown in the equation ,bi7,,oh7#b;,cl ,bi,o,cl ,h#b,o4 ,the salt represented in the last equation is sometimes called bismuth oxychloride1 or bismuthyl chloride4 ,the corresponding nitrate1 ,bi,o,n,o#c1 is largely used in medicine under the name of subnitrate of bismuth4 ,in these two compounds the group of atoms1 ,bi,o1 acts as a univalent metallic radical and is called bismuthyl4 ,similar basic salts are formed by the hydrolysis of antimony salts4 ,,exercises #a4 ,name all the elements so far studied which possess allotropic forms4 #b4 ,what compounds would you expect phosphorus to form with bromine and iodine8 ,write the equations showing the action of water on these compounds4 #c4 ,in the preparation of phosphine1 why is coal gas passed into the flask8 ,what other gases would serve the same purpose8 #d4 ,give the formula for the salt which phosphine forms with hydriodic acid4 ,give the name of the compound4 #e4 ,could phosphoric acid be substituted for sulphuric acid in the preparation of the common acids8 #f4 ,write the equations for the preparation of the three sodium salts of orthophosphoric acid4 #g4 ,why does a solution of disodium hydrogen phosphate react alkaline8 #h4 ,on the supposition that bone ash is pure calcium phosphate1 what weight of it would be required in the preparation of #a kg4 of phosphorus8 #i4 ,if arsenopyrite is heated in a current of air1 what products are formed8 #aj4 7a7 ,write equations for the complete combustion of hydrosulphuric acid1 methane1 and arsine4 7b7 ,in what respects are the reactions similar8 #aa4 ,write the equations for all the reactions involved in ,marsh's test for arsenic4 #ab4 ,write the names and formulas for the acids of antimony4 #ac4 ,write the equations showing the hydrolysis of antimony trichloride2 of bismuth nitrate4 #ad4 ,in what respects does nitrogen resemble the members of the phosphorus family8 ,,chapter ,,xxi ,,silicon1 ,,titanium1 ,,boron ,,symbol ,,atomic ,,density ,,chlorides ,,oxides ,,weight ,silicon ,si #bh4d #b4ce ,si,cl#d ,si,o#b ,titanium ,ti #dh4a #c4e ,ti,cl#d ,ti,o#b ,boron ,b #aa4j #b4de ,b,cl#c ,b#b,o#c ,general4 ,each of the three elements1 silicon1 titanium1 and boron1 belongs to a separate periodic family1 but they occur near together in the periodic grouping and are very similar in both physical and chemical properties4 ,since the other elements in their families are either so rare that they cannot be studied in detail1 or are best understood in connection with other elements1 it is convenient to consider these three together at this point4 ,the three elements are very difficult to obtain in the free state1 owing to their strong attraction for other elements4 ,they can be prepared by the action of aluminium or magnesium on their oxides and in impure state by reduction with carbon in an electric furnace4 ,they are very hard and melt only at the highest temperatures4 ,at ordinary temperatures they are not attacked by oxygen1 but when strongly heated they burn with great brilliancy4 ,silicon and boron are not attacked by acids under ordinary conditions2 titanium is easily dissolved by them4 ,,silicon ,occurrence4 ,next to oxygen silicon is the most abundant element4 ,it does not occur free in nature1 but its compounds are very abundant and of the greatest importance4 ,it occurs almost entirely in combination with oxygen as silicon dioxide 7,si,o#b71 often called silica1 or with oxygen and various metals in the form of salts of silicic acids1 or silicates4 ,these compounds form a large fraction of the earth's crust4 ,most plants absorb small amounts of silica from the soil1 and it is also found in minute quantities in animal organisms4 ,preparation4 ,the element is most easily prepared by reducing pure powdered quartz with magnesium powder3 ,si,o#b #b,mg #b,mg,o ,si4 ,properties4 ,as would be expected from its place in the periodic table1 silicon resembles carbon in many respects4 ,it can be obtained in several allotropic forms1 corresponding to those of carbon4 ,the crystallized form is very hard1 and is inactive toward reagents4 ,the amorphous variety has1 in general1 properties more similar to charcoal4 ,compounds of silicon with hydrogen and the halogens4 ,silicon hydride 7,si,h#d7 corresponds in formula to methane 7,,ch#d71 but its properties are more like those of phosphine 7,,ph#c74 ,it is a very inflammable gas of disagreeable odor1 and1 as ordinarily prepared1 takes fire spontaneously on account of the presence of impurities4 ,silicon combines with the elements of the chlorine family to form such compounds as ,si,cl#d and ,si,f#d4 ,of these silicon fluoride is the most familiar and interesting4 ,as stated in the discussion of fluorine1 it is formed when hydrofluoric acid acts upon silicon dioxide or a silicate4 ,with silica the reaction is thus expressed3 ,si,o#b #d;,,hf ,si,f#d #b;,h#b,o4 ,it is a very volatile1 invisible1 poisonous gas4 ,in contact with water it is partially decomposed1 as shown in the equation ,si,f#d #d;,h#b,o #d;,,hf ,si7,,oh7#d4 ,the hydrofluoric acid so formed combines with an additional amount of silicon fluoride1 forming the complex fluosilicic acid 7,h#b,si,f#f71 thus3 #b;,,hf ,si,f#d ,h#b,si,f#f4 ,silicides4 ,as the name indicates1 silicides are binary compounds consisting of silicon and some other element4 ,they are very stable at high temperatures1 and are usually made by heating the appropriate substances in an electric furnace4 ,the most important one is carborundum1 which is a silicide of carbon of the formula ,c,si4 ,it is made by heating coke and sand1 which is a form of silicon dioxide1 in an electric furnace1 the process being extensively carried on at ,niagara ,falls4 ,the following equation represents the reaction ,si,o#b #c;,c ,c,si #b;,,co4 ,the substance so prepared consists of beautiful purplish-black crystals1 which are very hard4 ,carborundum is used as an abrasive1 that is1 as a material for grinding and polishing very hard substances4 ,ferrosilicon is a silicide of iron alloyed with an excess of iron1 which finds extensive use in the manufacture of certain kinds of steel4 ,manufacture of carborundum4 ,the mixture of materials is heated in a large resistance furnace for about thirty-six hours4 ,after the reaction is completed there is left a core of graphite ,g4 ,surrounding this core is a layer of crystallized carborundum ,c1 about #af in4 thick4 ,outside this is a shell of amorphous carborundum ,a4 ,the remaining materials ,m are unchanged and are used for a new charge4 ,illustration3 ,fig4 #gc ,silicon dioxide 7silica7 7,si,o#b74 ,this substance is found in a great variety of forms in nature1 both in the amorphous and in the crystalline condition4 ,in the form of quartz it is found in beautifully formed six-sided prisms1 sometimes of great size4 ,when pure it is perfectly transparent and colorless4 ,some colored varieties are given special names1 as amethyst 7violet71 rose quartz 7pale pink71 smoky or milky quartz 7colored and opaque74 ,other varieties of silicon dioxide1 some of which also contain water1 are chalcedony1 onyx1 jasper1 opal1 agate1 and flint4 ,sand and sandstone are largely silicon dioxide4 ,properties4 ,as obtained by chemical processes silicon dioxide is an amorphous white powder4 ,in the crystallized state it is very hard and has a density of #b4f4 ,it is insoluble in water and in most chemical reagents1 and requires the hottest oxyhydrogen flame for fusion4 ,acids1 excepting hydrofluoric acid1 have little action on it1 and it requires the most energetic reducing agents to deprive it of oxygen4 ,it is the anhydride of an acid1 and consequently it dissolves in fused alkalis to form silicates4 ,being nonvolatile1 it will drive out most other anhydrides when heated to a high temperature with their salts1 especially when the silicates so formed are fusible4 ,the following equations illustrate this property3 ,na#b;,,co#c ,si,o#b ,na#b,si,o#c ,,co#b1 ,na#b,,so#d ,si,o#b ,na#b,si,o#c ,,so#c4 ,silicic acids4 ,silicon forms two simple acids1 orthosilicic acid 7,h#d,si,o#d7 and metasilicic acid 7,h#b,si,o#c74 ,orthosilicic acid is formed as a jelly-like mass when orthosilicates are treated with strong acids such as hydrochloric4 ,on attempting to dry this acid it loses water1 passing into metasilicic or common silicic acid3 ,h#d,si,o#d ,h#b,si,o#c ,h#b,o4 ,metasilicic acid when heated breaks up into silica and water1 thus3 ,h#b,si,o#c ,h#b,o ,si,o#b4 ,salts of silicic acids1--silicates4 ,a number of salts of the orthosilicic and metasilicic acids occur in nature4 ,thus mica 7,k,al,si,o#d7 is a salt of orthosilicic acid4 ,polysilicic acids4 ,silicon has the power to form a great many complex acids which may be regarded as derived from the union of several molecules of the orthosilicic acid1 with the loss of water4 ,thus we have #c;,h#d,si,o#d ,h#d,si#c,o#h #d;,h#b,o4 ,these acids cannot be prepared in the pure state1 but their salts form many of the crystalline rocks in nature4 ,feldspar1 for example1 has the formula ,k,al,si#c,o#h1 and is a mixed salt of the acid ,h#d,si#c,o#h1 whose formation is represented in the equation above4 ,kaolin has the formula ,al#b,si#b,o#gb;,h#b,o4 ,many other examples will be met in the study of the metals4 ,glass4 ,when sodium and calcium silicates1 together with silicon dioxide1 are heated to a very high temperature1 the mixture slowly fuses to a transparent liquid1 which on cooling passes into the solid called glass4 ,instead of starting with sodium and calcium silicates it is more convenient and economical to heat sodium carbonate 7or sulphate7 and lime with an excess of clean sand1 the silicates being formed during the heating3 ,na#b;,,co#c ,si,o#b ,na#b,si,o#c ,,co#b1 ,ca,o ,si,o#b ,ca,si,o#c4 ,illustration3 ,fig4 #gd ,the mixture is heated below the fusing point for some time1 so that the escaping carbon dioxide may not spatter the hot liquid2 the heat is then increased and the mixture kept in a state of fusion until all gases formed in the reaction have escaped4 ,molding and blowing of glass4 ,the way in which the melted mixture is handled in the glass factory depends upon the character of the article to be made4 ,many articles1 such as bottles1 are made by blowing the plastic glass into hollow molds of the desired shape4 ,the mold is first opened1 as shown in ,fig4 #gd4 ,a lump of plastic glass ,a on the hollow rod ,b is lowered into the mold1 which is then closed by the handles ,c4 ,by blowing into the tube the glass is blown into the shape of the mold4 ,the mold is then opened and the bottle lifted out4 ,the neck of the bottle must be cut off at the proper place and the sharp edges rounded off in a flame4 ,other objects1 such as lamp chimneys1 are made by getting a lump of plastic glass on the end of a hollow iron rod and blowing it into the desired shape without the help of a mold1 great skill being required in the manipulation of the glass4 ,window glass is made by blowing large hollow cylinders about #f ft4 long and #a-a_/b ft4 in diameter4 ,these are cut longitudinally1 and are then placed in an oven and heated until they soften1 when they are flattened out into plates 7,fig4 #ge74 ,plate glass is cast into flat slabs1 which are then ground and polished to perfectly plane surfaces4 ,varieties of glass4 ,the ingredients mentioned above make a soft1 easily fusible glass4 ,if potassium carbonate is substituted for the sodium carbonate1 the glass is much harder and less easily fused2 increasing the amount of sand has somewhat the same effect4 ,potassium glass is largely used in making chemical glassware1 since it resists the action of reagents better than the softer sodium glass4 ,if lead oxide is substituted for the whole or a part of the lime1 the glass is very soft1 but has a high index of refraction and is valuable for making optical instruments and artificial jewels4 ,illustration3 ,fig4 #ge ,coloring of glass4 ,various substances fused along with the glass mixture give characteristic colors4 ,the amber color of common bottles is due to iron compounds in the glass2 in other cases iron colors the glass green4 ,cobalt compounds color it deep blue2 those of manganese give it an amethyst tint and uranium compounds impart a peculiar yellowish green color4 ,since iron is nearly always present in the ingredients1 glass is usually slightly yellow4 ,this color can be removed by adding the proper amount of manganese dioxide1 for the amethyst color of manganese and the yellow of iron together produce white light4 ,nature of glass4 ,glass is not a definite chemical compound and its composition varies between wide limits4 ,fused glass is really a solution of various silicates1 such as those of calcium and lead1 in fused sodium or potassium silicate4 ,a certain amount of silicon dioxide is also present4 ,this solution is then allowed to solidify under such conditions of cooling that the dissolved substances do not separate from the solvent4 ,the compounds which are used to color the glass are sometimes converted into silicates1 which then dissolve in the glass1 giving it a uniform color4 ,in other cases1 as in the milky glasses which resemble porcelain in appearance1 the color or opaqueness is due to the finely divided color material evenly distributed throughout the glass1 but not dissolved in it4 ,milky glass is made by mixing calcium fluoride1 tin oxide1 or some other insoluble substance in the melted glass4 ,copper or gold in metallic form scattered through glass gives it shades of red4 ,,titanium ,titanium is a very widely distributed element in nature1 being found in almost all soils1 in many rocks1 and even in plant and animal tissues4 ,it is not very abundant in any one locality1 and it possesses little commercial value save in connection with the iron industry4 ,its most common ore is rutile 7,ti,o#b71 which resembles silica in many respects4 ,in both physical and chemical properties titanium resembles silicon1 though it is somewhat more metallic in character4 ,this resemblance is most marked in the acids of titanium4 ,it not only forms metatitanic and orthotitanic acids but a great variety of polytitanic acids as well4 ,,boron ,occurrence4 ,boron is never found free in nature4 ,it occurs as boric acid 7,h#c;,,bo#c71 and in salts of polyboric acids1 which usually have very complicated formulas4 ,preparation and properties4 ,boron can be prepared from its oxide by reduction with magnesium1 exactly as in the case of silicon4 ,it resembles silicon very strikingly in its properties4 ,it occurs in several allotropic forms1 is very hard when crystallized1 and is rather inactive toward reagents4 ,it forms a hydride1 ,,bh#c1 and combines directly with the elements of the chlorine family4 ,boron fluoride 7,,bf#c7 is very similar to silicon fluoride in its mode of formation and chemical properties4 ,boric oxide 7,b#b,o#c74 ,boron forms one well-known oxide1 ,b#b,o#c1 called boric anhydride4 ,it is formed as a glassy mass by heating boric acid to a high temperature4 ,it absorbs water very readily1 uniting with it to form boric acid again3 ,b#b,o#c #c;,h#b,o #b;,h#c;,,bo#c4 ,in this respect it differs from silicon dioxide1 which will not combine directly with water4 ,boric acid 7,h#c;,,bo#c74 ,this is found in nature in considerable quantities and forms one of the chief sources of boron compounds4 ,it is found dissolved in the water of hot springs in some localities1 particularly in ,italy4 ,being volatile with steam1 the vapor which escapes from these springs has some boric acid in it4 ,it is easily obtained from these sources by condensation and evaporation1 the necessary heat being supplied by other hot springs4 ,boric acid crystallizes in pearly flakes1 which are greasy to the touch4 ,in the laboratory it is easily prepared by treating a strong1 hot solution of borax with sulphuric acid4 ,boric acid being sparingly soluble in water crystallizes out on cooling3 ,na#b;,b#d,o#g #e;,h#b,o ,h#b,,so#d ,na#b,,so#d #d;,h#c;,,bo#c4 ,the substance is a mild antiseptic1 and on this account is often used in medicine and as a preservative for canned foods and milk4 ,metaboric and polyboric acids4 ,when boric acid is gently heated it is converted into metaboric acid 7,,hbo#b73 ,h#c;,,bo#c ,,hbo#b ,h#b,o4 ,on heating metaboric acid to a somewhat higher temperature tetraboric acid 7,h#b;,b#d,o#g7 is formed3 #d;,,hbo#b ,h#b;,b#d,o#g ,h#b,o4 ,many other complex acids of boron are known4 ,borax4 ,borax is the sodium salt of tetraboric acid1 having the formula ,na#b;,b#d,o#gaj ,h#b,o4 ,it is found in some arid countries1 as southern ,california and ,tibet1 but is now made commercially from the mineral colemanite1 which is the calcium salt of a complex boric acid4 ,when this is treated with a solution of sodium carbonate1 calcium carbonate is precipitated and borax crystallizes from the solution4 ,when heated borax at first swells up greatly1 owing to the expulsion of the water of crystallization1 and then melts to a clear glass4 ,this glass has the property of easily dissolving many metallic oxides1 and on this account borax is used as a flux in soldering1 for the purpose of removing from the metallic surfaces to be soldered the film of oxide with which they are likely to be covered4 ,these oxides often give a characteristic color to the clear borax glass1 and borax beads are therefore often used in testing for the presence of metals1 instead of the metaphosphoric acid bead already described4 ,the reason that metallic oxides dissolve in borax is that borax contains an excess of acid anhydride1 as can be more easily seen if its formula is written #b,na,b,o#b ,b#b,o#c4 ,the metallic oxide combines with this excess of acid anhydride1 forming a mixed salt of metaboric acid4 ,borax is extensively used as a constituent of enamels and glazes for both metal ware and pottery4 ,it is also used as a flux in soldering and brazing1 and in domestic ways it serves as a mild alkali1 as a preservative for meats1 and in a great variety of less important applications4 ,,exercises #a4 ,account for the fact that a solution of borax in water is alkaline4 #b4 ,what weight of water of crystallization does #a kg4 of borax contain8 #c4 ,when a concentrated solution of borax acts on silver nitrate a borate of silver is formed4 ,if the solution of borax is dilute1 however1 an hydroxide of silver forms4 ,account for this difference in behavior4 ,,chapter ,,xxii ,,the ,,metals ,the metals4 ,the elements which remain to be considered are known collectively as the metals4 ,they are also called the base-forming elements1 since their hydroxides are bases4 ,a metal may therefore be defined as an element whose hydroxide is a base4 ,when a base dissolves in water the hydroxyl groups form the anions1 while the metallic element forms the cations4 ,from this standpoint a metal can be defined as an element capable of forming simple cations in solution4 ,the distinction between a metal and a non-metal is not a very sharp one1 since the hydroxides of a number of elements act as bases under some conditions and as acids under others4 ,we have seen that antimony is an element of this kind4 ,occurrence of metals in nature4 ,a few of the metals are found in nature in the free state4 ,among these are gold1 platinum1 and frequently copper4 ,they are usually found combined with other elements in the form of oxides or salts of various acids4 ,silicates1 carbonates1 sulphides1 and sulphates are the most abundant salts4 ,all inorganic substances occurring in nature1 whether they contain a metal or not1 are called minerals4 ,those minerals from which a useful substance can be extracted are called ores of the substance4 ,these two terms are most frequently used in connection with the metals4 ,extraction of metals1--metallurgy4 ,the process of extracting a metal from its ores is called the metallurgy of the metal4 ,the metallurgy of each metal presents peculiarities of its own1 but there are several methods of general application which are very frequently employed4 #a4 ,reduction of an oxide with carbon4 ,many of the metals occur in nature in the form of oxides4 ,when these oxides are heated to a high temperature with carbon the oxygen combines with it and the metal is set free4 ,iron1 for example1 occurs largely in the form of the oxide ,fe#b,o#c4 ,when this is heated with carbon the reaction expressed in the following equation takes place3 ,fe#b,o#c #c ,c #b ,fe #c ,,co4 ,many ores other than oxides may be changed into oxides which can then be reduced by carbon4 ,the conversion of such ores into oxides is generally accomplished by heating1 and this process is called roasting4 ,many carbonates and hydroxides decompose directly into the oxide on heating4 ,sulphides1 on the other hand1 must be heated in a current of air1 the oxygen of the air entering into the reaction4 ,the following equations will serve to illustrate these changes in the case of the ores of iron3 ,fe,c,o#c ,fe,o ,,co#b1 #b;,fe7,,oh7#c ,fe#b,o#c #c;,h#b,o1 #b;,fe,s#b #aa,o ,fe#b,o#c #d,,so#b4 #b4 ,reduction of an oxide with aluminium4 ,not all oxides1 however1 can be reduced by carbon4 ,in such cases aluminium may be used4 ,thus chromium may be obtained in accordance with the following equation3 ,cr#b,o#c #b ,al #b ,cr ,al#b,o#c4 ,this method is a comparatively new one1 having been brought into use by the ,german chemist ,goldschmidt2 hence it is sometimes called the ,goldschmidt method4 #c4 ,electrolysis4 ,in recent years increasing use is being made of the electric current in the preparation of metals4 ,in some cases the separation of the metal from its compounds is accomplished by passing the current through a solution of a suitable salt of the metal1 the metal usually being deposited upon the cathode4 ,in other cases the current is passed through a fused salt of the metal1 the chloride being best adapted to this purpose4 ,electro-chemical industries4 ,most of the electro-chemical industries of the country are carried on where water power is abundant1 since this furnishes the cheapest means for the generation of electrical energy4 ,niagara ,falls is the most important locality in this country for such industries1 and many different electro-chemical products are manufactured there4 ,some industries depend upon electrolytic processes1 while in others the electrical energy is used merely as a source of heat in electric furnaces4 ,preparation of compounds of the metals4 ,since the compounds of the metals are so numerous and varied in character1 there are many ways of preparing them4 ,in many cases the properties of the substance to be prepared1 or the material available for its preparation1 suggest a rather unusual way4 ,there are1 however1 a number of general principles which are constantly applied in the preparation of the compounds of the metals1 and a clear understanding of them will save much time and effort in remembering the details in any given case4 ,the most important of these general methods for the preparation of compounds are the following3 #a4 ,by direct union of two elements4 ,this is usually accomplished by heating the two elements together4 ,thus the sulphides1 chlorides1 and oxides of a metal can generally be obtained in this way4 ,the following equations serve as examples of this method3 ,fe ,s ,fe,s1 ,mg ,o ,mg,o1 ,cu #b;,cl ,cu,cl#b4 #b4 ,by the decomposition of a compound4 ,this decomposition may be brought about either by heat alone or by the combined action of heat and a reducing agent4 ,thus when the nitrate of a metal is heated the oxide of the metal is usually obtained4 ,copper nitrate1 for example1 decomposes as follows3 ,cu7,,no#c7b ,cu,o #b,,no#b ,o4 ,similarly the carbonates of the metals yield oxides1 thus3 ,ca,c,o#c ,ca,o ,,co#b4 ,most of the hydroxides form an oxide and water when heated3 #b;,al7,,oh7#c ,al#b,o#c #c;,h#b,o4 ,when heated with carbon1 sulphates are reduced to sulphides1 thus3 ,ba,s,o#d #b;,c ,ba,s #b;,,co#b4 #c4 ,methods based on equilibrium in solution4 ,in the preparation of compounds the first requisite is that the reactions chosen shall be of such a kind as will go on to completion4 ,in the chapter on chemical equilibrium it was shown that reactions in solution may become complete in either of three ways3 7#a7 a gas may be formed which escapes from solution2 7#b7 an insoluble solid may be formed which precipitates2 7#c7 two different ions may combine to form undissociated molecules4 ,by the judicious selection of materials these principles may be applied to the preparation of a great variety of compounds1 and illustrations of such methods will very frequently be found in the subsequent pages4 #d4 ,by fusion methods4 ,it sometimes happens that substances which are insoluble in water and in acids1 and which cannot therefore be brought into double decomposition in the usual way1 are soluble in other liquids1 and when dissolved in them can be decomposed and converted into other desired compounds4 ,thus barium sulphate is not soluble in water1 and sulphuric acid1 being less volatile than most other acids1 cannot easily be driven out from this salt ,when brought into contact with melted sodium carbonate1 however1 it dissolves in it1 and since barium carbonate is insoluble in melted sodium carbonate1 double decomposition takes place3 ,na#b;,,co#c ,ba,s,o#d ,ba,c,o#c ,na#b,,so#d4 ,on dissolving the cooled mixture in water the sodium sulphate formed in the reaction1 together with any excess of sodium carbonate which may be present1 dissolves4 ,the barium carbonate can then be filtered off and converted into any desired salt by the processes already described4 #e4 ,by the action of metals on salts of other metals4 ,when a strip of zinc is placed in a solution of a copper salt the copper is precipitated and an equivalent quantity of zinc passes into solution3 ,zn ,cu,s,o#d ,cu ,zn,s,o#d4 ,in like manner copper will precipitate silver from its salts3 ,cu ,ag#b,,so#d #b;,ag ,cu,s,o#d4 ,it is possible to tabulate the metals in such a way that any one of them in the table will precipitate any one following it from its salts4 ,the following is a list of some of the commoner metals arranged in this way3 ,zinc ,iron ,tin ,lead ,copper ,bismuth ,mercury ,silver ,gold ,according to this table copper will precipitate bismuth1 mercury1 silver1 or gold from their salts1 and will in turn be precipitated by zinc1 iron1 tin1 or lead4 ,advantage is taken of this principle in the purification of some of the metals1 and occasionally in the preparation of metals and their compounds4 ,important insoluble compounds4 ,since precipitates play so important a part in the reactions which substances undergo1 as well as in the preparation of many chemical compounds1 it is important to know what substances are insoluble4 ,knowing this1 we can in many cases predict reactions under certain conditions1 and are assisted in devising ways to prepare desired compounds4 ,while there is no general rule which will enable one to foretell the solubility of any given compound1 nevertheless a few general statements can be made which will be of much assistance4 #a4 ,hydroxides4 ,all hydroxides are insoluble save those of ammonium1 sodium1 potassium1 calcium1 barium1 and strontium4 #b4 ,nitrates4 ,all nitrates are soluble in water4 #c4 ,chlorides4 ,all chlorides are soluble save silver and mercurous chlorides4 7,lead chloride is but slightly soluble47 #d4 ,sulphates4 ,all sulphates are soluble save those of barium1 strontium1 and lead4 7,sulphates of silver and calcium are only moderately soluble47 #e4 ,sulphides4 ,all sulphides are insoluble save those of ammonium1 sodium1 and potassium4 ,the sulphides of calcium1 barium1 strontium1 and magnesium are insoluble in water1 but are changed by hydrolysis into acid sulphides which are soluble4 ,on this account they cannot be prepared by precipitation4 #f4 ,carbonates1 phosphates1 and silicates4 ,all normal carbonates1 phosphates1 and silicates are insoluble save those of ammonium1 sodium and potassium4 ,,exercises #a4 ,write equations representing four different ways for preparing ,cu7,,no#c7b4 #b4 ,write equations representing six different ways for preparing ,zn,s,o#d4 #c4 ,write equations for two reactions to illustrate each of the three ways in which reactions in solutions may become complete4 #d4 ,give one or more methods for preparing each of the following compounds3 ,ca,cl#b1 ,pb,cl#b1 ,ba,s,o#d1 ,ca,c,o#c1 7,,nh#d7b,s1 ,ag#b,s1 ,pb,o1 ,cu7,,oh7#b 7for solubilities1 see last paragraph of chapter74 ,state in each case the general principle involved in the method of preparation chosen4 ,,chapter ,,xxiii ,,the ,,alkali ,,metals ,,symbol ,,atomic ,,density ,,melting ,,first ,,prepared ,,weight ,,point ,lithium ,li #g4jc #j4ei #ahf4 ,davy #ahbj ,sodium ,na #bc4je #j4ig #ig4f #ahjg ,potassium ,k #ci4ae #j4hg #fb4e #ahjg ,rubidium ,rb #he4e #a4eb #ch4e ,bunsen #ahfa ,csium ,cs #acb4i #a4hh #bf4e #ahfj ,the family4 ,the metals listed in the above table constitute the even family in ,group ,i in the periodic arrangement of the elements1 and therefore form a natural family4 ,the name alkali metals is commonly applied to the family for the reason that the hydroxides of the most familiar members of the family1 namely sodium and potassium1 have long been called alkalis4 #a4 ,occurrence4 ,while none of these metals occur free in nature1 their compounds are very widely distributed1 being especially abundant in sea and mineral waters1 in salt beds1 and in many rocks4 ,only sodium and potassium occur in abundance1 the others being rarely found in any considerable quantity4 #b4 ,preparation4 ,the metals are most conveniently prepared by the electrolysis of their fused hydroxides or chlorides1 though it is possible to prepare them by reducing their oxides or carbonates with carbon4 #c4 ,properties4 ,they are soft1 light metals1 having low melting points and small densities1 as is indicated in the table4 ,their melting points vary inversely with their atomic weights1 while their densities 7sodium excepted7 vary directly with these4 ,the pure metals have a silvery luster but tarnish at once when exposed to the air1 owing to the formation of a film of oxide upon the surface of the metal4 ,they are therefore preserved in some liquid1 such as coal oil1 which contains no oxygen4 ,because of their strong affinity for oxygen they decompose water with great ease1 forming hydroxides and liberating hydrogen in accordance with the equation ,m ,h#b,o ,,moh ,h1 where ,m stands for any one of these metals4 ,these hydroxides are white solids2 they are readily soluble in water and possess very strong basic properties4 ,these bases are nearly equal in strength1 that is1 they all dissociate in water to about the same extent4 #d4 ,compounds4 ,the alkali metals almost always act as univalent elements in the formation of compounds1 the composition of which can be represented by such formulas as ,,mh1 ,m,cl1 ,,mno#c1 ,m#b,,so#d1 ,m#c,,po#d4 ,these compounds1 when dissolved in water1 dissociate in such a way as to form simple1 univalent metallic ions which are colorless4 ,with the exception of lithium these metals form very few insoluble compounds1 so that it is not often that precipitates containing them are obtained4 ,only sodium and potassium will be studied in detail1 since the other metals of the family are of relatively small importance4 ,the compounds of sodium and potassium are so similar in properties that they can be used interchangeably for most purposes4 ,other things being equal1 the sodium compounds are prepared in preference to those of potassium1 since they are cheaper4 ,when a given sodium compound is deliquescent1 or is so soluble that it is difficult to purify1 the corresponding potassium compound is prepared in its stead1 provided its properties are more desirable in these respects4 ,,sodium ,occurrence in nature4 ,large deposits of sodium chloride have been found in various parts of the world1 and the water of the ocean and of many lakes and springs contains notable quantities of it4 ,the element also occurs as a constituent of many rocks and is therefore present in the soil formed by their disintegration4 ,the mineral cryolite 7,na#c;,al,f#f7 is an important substance1 and the nitrate1 carbonate1 and borate also occur in nature4 ,preparation4 ,in #ahjg ,sir ,humphry ,davy succeeded in preparing very small quantities of metallic sodium by the electrolysis of the fused hydroxide4 ,on account of the cost of electrical energy it was for many years found more economical to prepare it by reducing the carbonate with carbon in accordance with the following equation3 ,na#b;,,co#c #b;,c #b,na #c;,,co4 ,the cost of generating the electric current has been diminished to such an extent1 however1 that it is now more economical to prepare sodium by ,davy's original method1 namely1 by the electrolysis of the fused hydroxide or chloride4 ,when the chloride is used the process is difficult to manage1 owing to the higher temperature required to keep the electrolyte fused1 and because of the corroding action of the fused chloride upon the containing vessel4 ,illustration3 ,,sir ,,humphry ,,davy 7,english7 7#aggh-ahbi7 ,isolated sodium1 lithium1 potassium1 barium1 strontium1 and calcium by means of electrolysis2 demonstrated the elementary nature of chlorine2 invented the safety lamp2 discovered the stupefying effects of nitrous oxide ,technical preparation4 ,the sodium hydroxide is melted in a cylindrical iron vessel 7,fig4 #gf7 through the bottom of which rises the cathode ,k4 ,the anodes ,a1 several in number1 are suspended around the cathode from above4 ,a cylindrical vessel ,c floats in the fused alkali directly over the cathode1 and under this cap the sodium and hydrogen liberated at the cathode collect4 ,the hydrogen escapes by lifting the cover1 and the sodium1 protected from the air by the hydrogen1 is skimmed or drained off from time to time4 ,oxygen is set free upon the anode and escapes into the air through the openings ,o without coming into contact with the sodium or hydrogen4 ,this process is carried on extensively at ,niagara ,falls4 ,illustration3 ,fig4 #gf ,properties4 ,sodium is a silver-white metal about as heavy as water1 and so soft that it can be molded easily by the fingers or pressed into wire4 ,it is very active chemically1 combining with most of the non-metallic elements1 such as oxygen and chlorine1 with great energy4 ,it will often withdraw these elements from combination with other elements1 and is thus able to decompose water and the oxides and chlorides of many metals4 ,sodium peroxide 7,na,o74 ,since sodium is a univalent element we should expect it to form an oxide of the formula ,na#b,o4 ,while such an oxide can be prepared1 the peroxide 7,na,o7 is much better known4 ,it is a yellowish-white powder made by burning sodium in air4 ,its chief use is as an oxidizing agent4 ,when heated with oxidizable substances it gives up a part of its oxygen1 as shown in the equation #b,na,o ,na#b,o ,o4 ,water decomposes it in accordance with the equation #b,na,o #b;,h#b,o #b,na,o,h ,h#b,o#b4 ,acids act readily upon it1 forming a sodium salt and hydrogen peroxide3 #b,na,o #b;,h,cl #b,na,cl ,h#b,o#b4 ,in these last two reactions the hydrogen dioxide formed may decompose into water and oxygen if the temperature is allowed to rise3 ,h#b,o#b ,h#b,o ,o4 ,peroxides4 ,it will be remembered that barium dioxide 7,ba,o#b7 yields hydrogen dioxide when treated with acids1 and that manganese dioxide gives up oxygen when heated with sulphuric acid4 ,oxides which yield either hydrogen dioxide or oxygen when treated with water or an acid are called peroxides4 ,sodium hydroxide 7caustic soda7 7,na,o,h74 #a4 ,preparation4 ,sodium hydroxide is prepared commercially by several processes4 7a7 ,in the older process1 still in extensive use1 sodium carbonate is treated with calcium hydroxide suspended in water4 ,calcium carbonate is precipitated according to the equation ,na#b;,,co#c ,ca7,,oh7#b ,ca,c,o#c #b,na,o,h4 ,the dilute solution of sodium hydroxide1 filtered from the calcium carbonate1 is evaporated to a paste and is then poured into molds to solidify4 ,it is sold in the form of slender sticks4 7b7 ,the newer methods depend upon the electrolysis of sodium chloride4 ,in the ,castner process a solution of salt is electrolyzed1 the reaction being expressed as follows3 ,na,cl ,h#b,o ,na,o,h ,h ,cl4 ,the chlorine escapes as a gas1 and by an ingenious mechanical device the sodium hydroxide is prevented from mixing with the salt in the solution4 ,in the ,acker process the electrolyte is fused sodium chloride4 ,the chlorine is evolved as a gas at the anode1 while the sodium alloys with the melted lead which forms the cathode4 ,when this alloy is treated with water the following reaction takes place3 ,na ,h#b,o ,na,o,h ,h4 ,illustration3 ,fig4 #gg ,technical process4 ,a sketch of an ,acker furnace is represented in ,fig4 #gg4 ,the furnace is an irregularly shaped cast-iron box1 divided into three compartments1 ,a1 ,b1 and ,c4 ,compartment ,a is lined with magnesia brick4 ,compartments ,b and ,c are filled with melted lead1 which also covers the bottom of ,a to a depth of about an inch4 ,above this layer in ,a is fused salt1 into which dip carbon anodes ,d4 ,the metallic box and melted lead is the cathode4 ,when the furnace is in operation chlorine is evolved at the anodes1 and is drawn away through a pipe 7not represented7 to the bleaching-powder chambers4 ,sodium is set free at the surface of the melted lead in ,a1 and at once alloys with it4 ,through the pipe ,e a powerful jet of steam is driven through the lead in ,b upwards into the narrow tube ,f4 ,this forces the lead alloy up through the tube and over into the chamber ,g4 ,in this process the steam is decomposed by the sodium in the alloy1 forming melted sodium hydroxide and hydrogen4 ,the melted lead and sodium hydroxide separate into two layers in ,g1 and the sodium hydroxide1 being on top1 overflows into tanks from which it is drawn off and packed in metallic drums4 ,the lead is returned to the other compartments of the furnace by a pipe leading from ,h to ,i4 ,compartment ,c serves merely as a reservoir for excess of melted lead4 #b4 ,properties4 ,sodium hydroxide is a white1 crystalline1 brittle substance which rapidly absorbs water and carbon dioxide from the air4 ,as the name 7caustic soda7 indicates1 it is a very corrosive substance1 having a disintegrating action on most animal and vegetable tissues4 ,it is a strong base4 ,it is used in a great many chemical industries1 and under the name of lye is employed to a small extent as a cleansing agent for household purposes4 ,sodium chloride 7common salt7 7,na,cl74 #a4 ,preparation4 ,sodium chloride1 or common salt1 is very widely distributed in nature4 ,thick strata1 evidently deposited at one time by the evaporation of salt water1 are found in many places4 ,in the ,united ,states the most important localities for salt are ,new ,york1 ,michigan1 ,ohio1 and ,kansas4 ,sometimes the salt is mined1 especially if it is in the pure form called rock salt4 ,more frequently a strong brine is pumped from deep wells sunk into the salt deposit1 and is then evaporated in large pans until the salt crystallizes out4 ,the crystals are in the form of small cubes and contain no water of crystallization2 some water is1 however1 held in cavities in the crystals and causes the salt to decrepitate when heated4 #b4 ,uses4 ,since salt is so abundant in nature it forms the starting point in the preparation of all compounds containing either sodium or chlorine4 ,this includes many substances of the highest importance to civilization1 such as soap1 glass1 hydrochloric acid1 soda1 and bleaching powder4 ,enormous quantities of salt are therefore produced each year4 ,small quantities are essential to the life of man and animals4 ,pure salt does not absorb moisture2 the fact that ordinary salt becomes moist in air is not due to a property of the salt1 but to impurities commonly occurring in it1 especially calcium and magnesium chlorides4 ,sodium sulphate 7,glauber's salt7 7,na#b,,so#daj;,h#b,o74 ,this salt is prepared by the action of sulphuric acid upon sodium chloride1 hydrochloric acid being formed at the same time3 #b,na,cl ,h#b,,so#d ,na#b,,so#d #b;,h,cl4 ,some sodium sulphate is prepared by the reaction represented in the equation ,mg,s,o#d #b,na,cl ,na#b,,so#d ,mg,cl#b4 ,the magnesium sulphate required for this reaction is obtained in large quantities in the manufacture of potassium chloride1 and being of little value for any other purpose is used in this way4 ,the reaction depends upon the fact that sodium sulphate is the least soluble of any of the four factors in the equation1 and therefore crystallizes out when hot1 saturated solutions of magnesium sulphate and sodium chloride are mixed together and the resulting mixture cooled4 ,sodium sulphate forms large efflorescent crystals4 ,the salt is extensively used in the manufacture of sodium carbonate and glass4 ,small quantities are used in medicine4 ,sodium sulphite 7,na#b,,so#cg;,h#b,o74 ,sodium sulphite is prepared by the action of sulphur dioxide upon solutions of sodium hydroxide1 the reaction being analogous to the action of carbon dioxide upon sodium hydroxide4 ,like the carbonate1 the sulphite is readily decomposed by acids3 ,na#b,,so#c #b;,h,cl #b,na,cl ,h#b,o ,,so#b4 ,because of this reaction sodium sulphite is used as a convenient source of sulphur dioxide4 ,it is also used as a disinfectant and a preservative4 ,sodium thiosulphate 7hyposulphite of soda or hypo7 7,na#b,s#b,o#ce;,h#b,o74 ,this salt1 commonly called sodium hyposulphite1 or merely hypo1 is made by boiling a solution of sodium sulphite with sulphur3 ,na#b,,so#c ,s ,na#b,s#b,o#c4 ,it is used in photography and in the bleaching industry1 to absorb the excess of chlorine which is left upon the bleached fabrics4 ,thio compounds4 ,the prefix thio means sulphur4 ,it is used to designate substances which may be regarded as derived from oxygen compounds by replacing the whole or a part of their oxygen with sulphur4 ,the thiosulphates may be regarded as sulphates in which one atom of oxygen has been replaced by an atom of sulphur4 ,this may be seen by comparing the formula ,na#b,,so#d 7sodium sulphate7 with the formula ,na#b,s#b,o#c 7sodium thiosulphate74 ,sodium carbonate 7sal soda77,na#b;,,co#caj;,h#b,o74 ,there are two different methods now employed in the manufacture of this important substance4 #a4 ,le ,blanc process4 ,this older process involves several distinct reactions1 as shown in the following equations4 7a7 ,sodium chloride is first converted into sodium sulphate3 #b,na,cl ,h#b,,so#d ,na#b,,so#d #b;,h,cl4 7b7 ,the sodium sulphate is next reduced to sulphide by heating it with carbon3 ,na#b,,so#d #b;,c ,na#b,s #b;,,co#b4 7c7 ,the sodium sulphide is then heated with calcium carbonate1 when double decomposition takes place3 ,na#b,s ,ca,c,o#c ,ca,s ,na#b;,,co#c4 ,technical preparation of sodium carbonate4 ,in a manufacturing plant the last two reactions take place in one process4 ,sodium sulphate1 coal1 and powdered limestone are heated together to a rather high temperature4 ,the coal reduces the sulphate to sulphide1 which in turn reacts upon the calcium carbonate4 ,some limestone is decomposed by the heat1 forming calcium oxide4 ,when treated with water the calcium oxide is changed into hydroxide1 and this prevents the water from decomposing the insoluble calcium sulphide4 ,the crude product of the process is a hard black cake called black ash4 ,on digesting this mass with water the sodium carbonate passes into solution4 ,the pure carbonate is obtained by evaporation of this solution1 crystallizing from it in crystals of the formula ,na#b;,,co#caj;,h#b,o4 ,since over #fj of this salt is water1 the crystals are sometimes heated until it is driven off4 ,the product is called calcined soda1 and is1 of course1 more valuable than the crystallized salt4 #b4 ,solvay process4 ,this more modern process depends upon the reactions represented in the equations ,na,cl ,,nh#d;,,hco#c ,na,h,c,o#c ,,nh#d;,cl1 #b,na,h,c,o#c ,na#b;,,co#c ,h#b,o ,,co#b4 ,the reason the first reaction takes place is that sodium hydrogen carbonate is sparingly soluble in water1 while the other compounds are freely soluble4 ,when strong solutions of sodium chloride and of ammonium hydrogen carbonate are brought together the sparingly soluble sodium hydrogen carbonate is precipitated4 ,this is converted into the normal carbonate by heating1 the reaction being represented in the second equation4 ,technical preparation4 ,in the ,solvay process a very concentrated solution of salt is first saturated with ammonia gas1 and a current of carbon dioxide is then conducted into the solution4 ,in this way ammonium hydrogen carbonate is formed3 ,,nh#c ,h#b,o ,,co#b ,,nh#d;,,hco#c4 ,this enters into double decomposition with the salt1 as shown in the first equation under the ,solvay process4 ,after the sodium hydrogen carbonate has been precipitated the mother liquors containing ammonium chloride are treated with lime3 #b,,nh#d;,cl ,ca,o ,ca,cl#b #b ,,nh#c ,h#b,o4 ,the lime is obtained by burning limestone3 ,ca,c,o#c ,ca,o ,,co#b4 ,the ammonia and carbon dioxide evolved in the latter two reactions are used in the preparation of an additional quantity of ammonium hydrogen carbonate4 ,it will thus be seen that there is no loss of ammonia4 ,the only materials permanently used up are calcium carbonate and salt1 while the only waste product is calcium chloride4 ,historical4 ,in former times sodium carbonate was made by burning seaweeds and extracting the carbonate from their ash4 ,on this account the salt was called soda ash1 and the name is still in common use4 ,during the ,french ,revolution this supply was cut off1 and in behalf of the ,french government ,le ,blanc made a study of methods of preparing the carbonate directly from salt4 ,as a result he devised the method which bears his name1 and which was used exclusively for many years4 ,it has been replaced to a large extent by the ,solvay process1 which has the advantage that the materials used are inexpensive1 and that the ammonium hydrogen carbonate used can be regenerated from the products formed in the process4 ,much expense is also saved in fuel1 and the sodium hydrogen carbonate1 which is the first product of the process1 has itself many commercial uses4 ,the ,le ,blanc process is still used1 however1 since the hydrochloric acid generated is of value4 ,by-products4 ,the substances obtained in a given process1 aside from the main product1 are called the by-products4 ,the success of many processes depends upon the value of the by-products formed4 ,thus hydrochloric acid1 a by-product in the ,le ,blanc process1 is valuable enough to make the process pay1 even though sodium carbonate can be made cheaper in other ways4 ,properties of sodium carbonate4 ,sodium carbonate forms large crystals of the formula ,na#b;,,co#c #aj ,h#b,o4 ,it has a mild alkaline reaction and is used for laundry purposes under the name of washing soda4 ,mere mention of the fact that it is used in the manufacture of glass1 soap1 and many chemical reagents will indicate its importance in the industries4 ,it is one of the few soluble carbonates4 ,sodium hydrogen carbonate 7bicarbonate of soda7 7,na,h,c,o#c74 ,this salt1 commonly called bicarbonate of soda1 or baking soda1 is made by the ,solvay process1 as explained above1 or by passing carbon dioxide into strong solutions of sodium carbonate3 ,na#b;,,co#c ,h#b,o ,,co#b #b,na,h,c,o#c4 ,the bicarbonate1 being sparingly soluble1 crystallizes out4 ,a mixture of the bicarbonate with some substance 7the compound known as cream of tartar is generally used7 which slowly reacts with it1 liberating carbon dioxide1 is used largely in baking4 ,the carbon dioxide generated forces its way through the dough1 thus making it porous and light4 ,sodium nitrate 7,chili saltpeter7 7,na,n,o#c74 ,this substance is found in nature in arid regions in a number of places1 where it has been formed apparently by the decay of organic substances in the presence of air and sodium salts4 ,the largest deposits are in ,chili1 and most of the nitrate of commerce comes from that country4 ,smaller deposits occur in ,california and ,nevada4 ,the commercial salt is prepared by dissolving the crude nitrate in water1 allowing the insoluble earthy materials to settle1 and evaporating the clear solution so obtained to crystallization4 ,the soluble impurities remain for the most part in the mother liquors4 ,since this salt is the only nitrate found extensively in nature1 it is the material from which other nitrates as well as nitric acid are prepared4 ,it is used in enormous quantities in the manufacture of sulphuric acid and potassium nitrate1 and as a fertilizer4 ,sodium phosphate 7,na#b;,,hpo#dab;,h#b,o74 ,since phosphoric acid has three replaceable hydrogen atoms1 three sodium phosphates are possible1--two acid salts and one normal4 ,all three can be made without difficulty1 but disodium phosphate is the only one which is largely used1 and is the salt which is commonly called sodium phosphate4 ,it is made by the action of phosphoric acid on sodium carbonate3 ,na#b;,,co#c ,h#c,,po#d ,na#b;,,hpo#d ,,co#b ,h#b,o4 ,it is interesting as being one of the few phosphates which are soluble in water1 and is the salt commonly used when a soluble phosphate is needed4 ,normal sodium phosphate 7,na#c,,po#d74 ,although this is a normal salt its solution has a strongly alkaline reaction4 ,this is due to the fact that the salt hydrolyzes in solution into sodium hydroxide and disodium phosphate1 as represented in the equation ,na#c,,po#d ,h#b,o ,na#b;,,hpo#d ,na,o,h4 ,sodium hydroxide is strongly alkaline1 while disodium phosphate is nearly neutral in reaction4 ,the solution as a whole is therefore alkaline4 ,the salt is prepared by adding a large excess of sodium hydroxide to a solution of disodium phosphate and evaporating to crystallization4 ,the excess of the sodium hydroxide reverses the reaction of hydrolysis and the normal salt crystallizes out4 ,sodium tetraborate 7borax7 7,na#b;,b#d,o#gaj;,h#b,o74 ,the properties of this important compound have been discussed under the head of boron4 ,,potassium ,occurrence in nature4 ,potassium is a constituent of many common rocks and minerals1 and is therefore a rather abundant element1 though not so abundant as sodium4 ,feldspar1 which occurs both by itself and as a constituent of granite1 contains considerable potassium4 ,the element is a constituent of all clay and of mica and also occurs in very large deposits at ,stassfurt1 ,germany1 in the form of the chloride and sulphate1 associated with compounds of sodium and magnesium4 ,in small quantities it is found as nitrate and in many other forms4 ,the natural decomposition of rocks containing potassium gives rise to various compounds of the element in all fertile soils4 ,its soluble compounds are absorbed by growing plants and built up into complex vegetable substances2 when these are burned the potassium remains in the ash in the form of the carbonate4 ,crude carbonate obtained from wood ashes was formerly the chief source of potassium compounds2 they are now mostly prepared from the salts of the ,stassfurt deposits4 ,stassfurt salts4 ,these salts form very extensive deposits in middle and north ,germany1 the most noted locality for working them being at ,stassfurt4 ,the deposits are very thick and rest upon an enormous layer of common salt4 ,they are in the form of a series of strata1 each consisting largely of a single mineral salt4 ,a cross section of these deposits is shown in ,fig4 #gh4 ,while these strata are salts from a chemical standpoint1 they are as solid and hard as many kinds of stone1 and are mined as stone or coal would be4 ,since the strata differ in general appearance1 each can be mined separately1 and the various minerals can be worked up by methods adapted to each particular case4 ,the chief minerals of commercial importance in these deposits are the following3 ,sylvine ,k,cl4 ,anhydrite ,ca,s,o#d4 ,carnallite ,k,cl,mg,cl#bf;,h#b,o4 ,kainite ,k#b,,so#d,mg,s,o#d,mg,cl#bf;,h#b,o4 ,polyhalite ,k#b,,so#d,mg,s,o#db;,ca,s,o#db;,h#b,o4 ,kieserite ,mg,s,o#d;,h#b,o4 ,schnite ,k#b,,so#d,mg,s,o#df;,h#b,o4 ,preparation and properties4 ,the metal is prepared by the same method used in the preparation of sodium4 ,in most respects it is very similar to sodium1 the chief difference being that it is even more energetic in its action upon other substances4 ,the freshly cut1 bright surface instantly becomes dim through oxidation by the air4 ,it decomposes water very vigorously1 the heat of reaction being sufficient to ignite the hydrogen evolved4 ,it is somewhat lighter than sodium and is preserved under gasoline4 ,illustration3 ,fig4 #gh ,potassium hydroxide 7caustic potash7 7,,koh74 ,potassium hydroxide is prepared by methods exactly similar to those used in the preparation of sodium hydroxide1 which compound it closely resembles in both physical and chemical properties4 ,it is not used to any very great extent1 being replaced by the cheaper sodium hydroxide4 ,action of the halogen elements on potassium hydroxide4 ,when any one of the three halogen elements--chlorine1 bromine1 and iodine--is added to a solution of potassium hydroxide a reaction takes place1 the nature of which depends upon the conditions of the experiment4 ,thus1 when chlorine is passed into a cold dilute solution of potassium hydroxide the reaction expressed by the following equation takes place3 7#a7 #b,,koh #b;,cl ,k,cl ,k,cl,o ,h#b,o4 ,if the solution of hydroxide is concentrated and hot1 on the other hand1 the potassium hypochlorite formed according to equation 7#a7 breaks down as fast as formed3 7#b7 #c,k,cl,o ,k,cl,o#c #b,k,cl4 ,equation 7#a71 after being multiplied by #c1 may be combined with equation 7#b71 giving the following3 7#c7 #f,,koh #f;,cl #e,k,cl ,k,cl,o#c #c;,h#b,o4 ,this represents in a single equation the action of chlorine on hot1 concentrated solutions of potassium hydroxide4 ,by means of these reactions one can prepare potassium chloride1 potassium hypochlorite1 and potassium chlorate4 ,by substituting bromine or iodine for chlorine the corresponding compounds of these elements are obtained4 ,some of these compounds can be obtained in cheaper ways4 ,if the halogen element is added to a solution of sodium hydroxide or calcium hydroxide1 the reaction which takes place is exactly similar to that which takes place with potassium hydroxide4 ,it is possible1 therefore1 to prepare in this way the sodium and calcium compounds corresponding to the potassium compounds given above4 ,potassium chloride 7,k,cl74 ,this salt occurs in nature in sea water1 in the mineral sylvine1 and1 combined with magnesium chloride1 as carnallite 7,k,cl,mg,cl#bf;,h#b,o74 ,it is prepared from carnallite by saturating boiling water with the mineral and allowing the solution to cool4 ,the mineral decomposes while in solution1 and the potassium chloride crystallizes out on cooling1 while the very soluble magnesium chloride remains in solution4 ,the salt is very similar to sodium chloride both in physical and chemical properties4 ,it is used in the preparation of nearly all other potassium salts1 and1 together with potassium sulphate1 is used as a fertilizer4 ,potassium bromide 7,k,br74 ,when bromine is added to a hot concentrated solution of potassium hydroxide there is formed a mixture of potassium bromide and potassium bromate in accordance with the reactions already discussed4 ,there is no special use for the bromate1 so the solution is evaporated to dryness1 and the residue1 consisting of a mixture of the bromate and bromide1 is strongly heated4 ,this changes the bromate to bromide1 as follows3 ,k,br,o#c ,k,br #c,o4 ,the bromide is then crystallized from water1 forming large colorless crystals4 ,it is used in medicine and in photography4 ,potassium iodide 7,,ki74 ,potassium iodide may be made by exactly the same method as has just been described for the bromide1 substituting iodine for bromine4 ,it is more frequently made as follows4 ,iron filings are treated with iodine1 forming the compound ,fe#c;,i#h2 on boiling this substance with potassium carbonate the reaction represented in the following equation occurs3 ,fe#c;,i#h #d,k#b;,,co#c ,fe#c,o#d #h,,ki #d;,,co#b4 ,potassium iodide finds its chief use in medicine4 ,potassium chlorate 7,k,cl,o#c74 ,this salt1 as has just been explained1 can be made by the action of chlorine on strong potassium hydroxide solutions4 ,the chief use of potassium chlorate is as an oxidizing agent in the manufacture of matches1 fireworks1 and explosives2 it is also used in the preparation of oxygen and in medicine4 ,commercial preparation4 ,by referring to the reaction between chlorine and hot concentrated solutions of potassium hydroxide1 it will be seen that only one molecule of potassium chlorate is formed from six molecules of potassium hydroxide4 ,partly because of this poor yield and partly because the potassium hydroxide is rather expensive1 this process is not an economical one for the preparation of potassium chlorate4 ,the commercial method is the following4 ,chlorine is passed into hot solutions of calcium hydroxide1 a compound which is very cheap4 ,the resulting calcium chloride and chlorate are both very soluble4 ,to the solution of these salts potassium chloride is added1 and as the solution cools the sparingly soluble potassium chlorate crystallizes out3 ,ca7,cl,o#c7b #b,k,cl #b,k,cl,o#c ,ca,cl#b4 ,electro-chemical processes are also used4 ,potassium nitrate 7saltpeter7 7,,kno#c74 ,this salt was formerly made by allowing animal refuse to decompose in the open air in the presence of wood ashes or earthy materials containing potassium4 ,under these conditions the nitrogen in the organic matter is in part converted into potassium nitrate1 which was obtained by extracting the mass with water and evaporating to crystallization4 ,this crude and slow process is now almost entirely replaced by a manufacturing process in which the potassium salt is made from ,chili saltpeter3 ,na,n,o#c ,k,cl ,na,cl ,,kno#c4 ,this process has been made possible by the discovery of the ,chili niter beds and the potassium chloride of the ,stassfurt deposits4 ,the reaction depends for its success upon the apparently insignificant fact that sodium chloride is almost equally soluble in cold and hot water4 ,all four factors in the equation are rather soluble in cold water1 but in hot water sodium chloride is far less soluble than the other three4 ,when hot saturated solutions of sodium nitrate and potassium chloride are brought together1 sodium chloride precipitates and can be filtered off1 leaving potassium nitrate in solution1 together with some sodium chloride4 ,on cooling1 potassium nitrate crystallizes out1 leaving small amounts of the other salts in solution4 ,potassium nitrate is a colorless salt which forms very large crystals4 ,it is stable in the air1 and when heated is a good oxidizing agent1 giving up oxygen quite readily4 ,its chief use is in the manufacture of gunpowder4 ,gunpowder4 ,the object sought for in the preparation of gunpowder is to secure a solid substance which will remain unchanged under ordinary conditions1 but which will explode readily when ignited1 evolving a large volume of gas4 ,when a mixture of carbon and potassium nitrate is ignited a great deal of gas is formed1 as will be seen from the equation #b,,kno#c #c;,c ,,co#b ,,co ,n#b ,k#b;,,co#c4 ,by adding sulphur to the mixture the volume of gas formed in the explosion is considerably increased3 #b,,kno#c #c;,c ,s #c;,,co#b ,n#b ,k#b,s4 ,gunpowder is simply a mechanical mixture of these three substances in the proportion required for the above reaction4 ,while the equation represents the principal reaction1 other reactions also take place4 ,the gases formed in the explosion1 when measured under standard conditions1 occupy about two hundred and eighty times the volume of the original powder4 ,potassium sulphide 7,k#b,s7 is a solid substance1 and it is largely due to it that gunpowder gives off smoke and soot when it explodes4 ,smokeless powder consists of organic substances which1 on explosion1 give only colorless gases1 and hence produce no smoke4 ,sodium nitrate is cheaper than potassium nitrate1 but it is not adapted to the manufacture of the best grades of powder1 since it is somewhat deliquescent and does not give up its oxygen so readily as does potassium nitrate4 ,it is used1 however1 in the cheaper grades of powder1 such as are employed for blasting4 ,potassium cyanide 7,,kcn74 ,when animal matter containing nitrogen is heated with iron and potassium carbonate1 complicated changes occur which result in the formation of a substance commonly called yellow prussiate of potash1 which has the formula ,k#d;,fe,c#f,n#f4 ,when this substance is heated with potassium1 potassium cyanide is formed3 ,k#d;,fe,c#f,n#f #b ,k #f,,kcn ,fe4 ,since sodium is much cheaper than potassium it is often used in place of it3 ,k#d;,fe,c#f,n#f #b,na #d,,kcn #b,na,c,n ,fe4 ,the mixture of cyanides so resulting serves most of the purposes of the pure salt4 ,it is used very extensively in several metallurgical processes1 particularly in the extraction of gold4 ,potassium cyanide is a white solid characterized by its poisonous properties1 and must be used with extreme caution4 ,potassium carbonate 7potash7 7,k#b;,,co#c74 ,this compound occurs in wood ashes in small quantities4 ,it cannot be prepared by the ,solvay process1 since the acid carbonate is quite soluble in water1 but is made by the ,le ,blanc process4 ,its chief use is in the manufacture of other potassium salts4 ,other salts of potassium4 ,among the other salts of potassium frequently met with are the sulphate 7,k#b,,so#d71 the acid carbonate 7,,khco#c71 the acid sulphate 7,,khso#d71 and the acid sulphite 7,,khso#c74 ,these are all white solids4 ,,lithium1 ,,rubidium1 ,c,,sium ,of the three remaining elements of the family--lithium1 rubidium1 and csium--lithium is by far the most common1 the other two being very rare4 ,lithium chloride and carbonate are not infrequently found in natural mineral waters1 and as these substances are supposed to increase the medicinal value of the water1 they are very often added to artificial mineral waters in small quantities4 ,,compounds ,,of ,,ammonium ,general4 ,as explained in a previous chapter1 when ammonia is passed into water the two compounds combine to form the base ,,nh#d,,oh1 known as ammonium hydroxide4 ,when this base is neutralized with acids there are formed the corresponding salts1 known as the ammonium salts4 ,since the ammonium group is univalent1 ammonium salts resemble those of the alkali metals in formulas2 they also resemble the latter salts very much in their chemical properties1 and may be conveniently described in connection with them4 ,among the ammonium salts the chloride1 sulphate1 carbonate1 and sulphide are the most familiar4 ,ammonium chloride 7sal ammoniac7 7,,nh#d;,cl74 ,this substance is obtained by neutralizing ammonium hydroxide with hydrochloric acid4 ,it is a colorless substance crystallizing in fine needles1 and1 like most ammonium salts1 is very soluble in water4 ,when placed in a tube and heated strongly it decomposes into hydrochloric acid and ammonia4 ,when these gases reach a cooler portion of the tube they at once recombine1 and the resulting ammonium chloride is deposited on the sides of the tube4 ,in this way the salt can be separated from nonvolatile impurities4 ,ammonium chloride is sometimes used in preparation of ammonia2 it is also used in making dry batteries and in the laboratory as a chemical reagent4 ,ammonium sulphate 77,,nh#d7b,,so#d74 ,this salt resembles the chloride very closely1 and1 being cheaper1 is used in place of it when possible4 ,it is used in large quantity as a fertilizer1 the nitrogen which it contains being a very valuable food for plants4 ,ammonium carbonate 77,,nh#d7b;,,co#c74 ,this salt1 as well as the acid carbonate 7,,nh#d;,,hco#c71 is used as a chemical reagent4 ,they are colorless solids1 freely soluble in water4 ,the normal carbonate is made by heating ammonium chloride with powdered limestone 7calcium carbonate71 the ammonium carbonate being obtained as a sublimate in compact hard masses3 #b,,nh#d;,cl ,ca,c,o#c 7,,nh#d7b;,,co#c ,ca,cl#b4 ,the salt always smells of ammonia1 since it slowly decomposes1 as shown in the equation 7,,nh#d7b;,,co#c ,,nh#d;,,hco#c ,,nh#c4 ,the acid carbonate1 or bicarbonate1 is prepared by saturating a solution of ammonium hydroxide with carbon dioxide3 ,,nh#d,,oh ,,co#b ,,nh#d;,,hco#c4 ,it is a well-crystallized stable substance4 ,ammonium sulphide 77,,nh#d7b,s74 ,ammonium sulphide is prepared by the action of hydrosulphuric acid upon ammonium hydroxide3 #b,,nh#d,,oh ,h#b,s 7,,nh#d7b,s #b;,h#b,o4 ,if the action is allowed to continue until no more hydrosulphuric acid is absorbed1 the product is the acid sulphide1 sometimes called the hydrosulphide3 ,,nh#d,,oh ,h#b,s ,,nh#d;,,hs ,h#b,o4 ,if equal amounts of ammonium hydroxide and ammonium acid sulphide are brought together1 the normal sulphide is formed3 ,,nh#d,,oh ,,nh#d;,,hs 7,,nh#d7b,s ,h#b,o ,it has been obtained in the solid state1 but only with great difficulty4 ,as used in the laboratory it is always in the form of a solution4 ,it is much used in the process of chemical analysis because it is a soluble sulphide and easily prepared4 ,on exposure to the air ammonium sulphide slowly decomposes1 being converted into ammonia1 water1 and sulphur3 7,,nh#d7b,s ,o #b,,nh#c ,h#b,o ,s4 ,as fast as the sulphur is liberated it combines with the unchanged sulphide to form several different ammonium sulphides in which there are from two to five sulphur atoms in the molecule1 thus3 7,,nh#d7b,s#b1 7,,nh#d7b,s#c1 7,,nh#d7b,s#e4 ,these sulphides in turn decompose by further action of oxygen1 so that the final products of the reaction are those given in the equation4 ,a solution of these compounds is yellow and is sometimes called yellow ammonium sulphide4 ,,flame ,,reaction--,,spectroscope ,when compounds of either sodium or potassium are brought into the non-luminous flame of a ,bunsen burner the flame becomes colored4 ,sodium compounds color it intensely yellow1 while those of potassium color it pale violet4 ,when only one of these elements is present it is easy to identify it by this simple test1 but when both are present the intense color of the sodium flame entirely conceals the pale tint characteristic of potassium compounds4 ,it is possible to detect the potassium flame in such cases1 however1 in the following way4 ,when light is allowed to shine through a very small hole or slit in some kind of a screen1 such as a piece of metal1 upon a triangular prism of glass1 the light is bent or refracted out of its course instead of passing straight through the glass4 ,it thus comes out of the prism at some angle to the line at which it entered4 ,yellow light is bent more than red1 and violet more than yellow4 ,when light made up of the yellow of sodium and the violet of potassium shines through a slit upon such a prism1 the yellow and the violet lights come out at somewhat different angles1 and so two colored lines of light--a yellow line and a violet line--are seen on looking into the prism in the proper direction4 ,the instrument used for separating the rays of light in this way is called a spectroscope 7,fig4 #gi74 ,the material to be tested is placed on a platinum wire and held in the colorless ,bunsen flame4 ,the resulting light passes through the slit in the end of tube ,b1 and then through ,b to the prism4 ,the resulting lines of light are seen by looking into the tube ,a1 which contains a magnifying lens4 ,most elements give more than one image of the slit1 each having a different color1 and the series of colored lines due to an element is called its spectrum4 ,illustration3 ,fig4 #gi ,the spectra of the known elements have been carefully studied1 and any element which imparts a characteristic color to a flame1 or has a spectrum of its own1 can be identified even when other elements are present4 ,through the spectroscopic examination of certain minerals a number of elements have been discovered by the observation of lines which did not belong to any known element4 ,a study of the substance then brought to light the new element4 ,rubidium and csium were discovered in this way1 rubidium having bright red lines and csium a very intense blue line4 ,lithium colors the flame deep red1 and has a bright red line in its spectrum4 ,,exercises #a4 ,what is an alkali8 ,can a metal itself be an alkali8 #b4 ,write equations showing how the following changes may be brought about1 giving the general principle involved in each change3 ,na,cl -- ,na#b,,so#c1 ,na#b,,so#c -- ,na,cl1 ,na,cl -- ,na,br1 ,na#b,,so#d -- ,na,n,o#c1 ,na,n,o#c -- ,na,h,c,o#c4 #c4 ,what carbonates are soluble8 #d4 ,state the conditions under which the reaction represented by the following equation can be made to go in either direction3 ,na#b;,,co#c ,h#b,o ,,co#b -- #b ,na,h,c,o#c4 #e4 ,account for the fact that solutions of sodium carbonate and potassium carbonate are alkaline4 #f4 ,what non-metallic element is obtained from the deposits of ,chili saltpeter8 #g4 ,supposing concentrated hydrochloric acid 7den4 #a4b7 to be worth six cents a pound1 what is the value of the acid generated in the preparation of #a ton of sodium carbonate by the ,le ,blanc process8 #h4 ,what weight of sodium carbonate crystals will #a kg4 of the anhydrous salt yield8 #i4 ,write equations for the preparation of potassium hydroxide by three different methods4 #aj4 ,what would take place if a bit of potassium hydroxide were left exposed to the air8 #aa4 ,write the equations for the reactions between sodium hydroxide and bromine2 between potassium hydroxide and iodine4 #ab4 ,write equations for the preparation of potassium sulphate2 of potassium acid carbonate4 #ac4 ,what weight of carnallite would be necessary in the preparation of #a ton of potassium carbonate8 #ad4 ,write the equations showing how ammonium chloride1 ammonium sulphate1 ammonium carbonate1 and ammonium nitrate may be prepared from ammonium hydroxide4 #ae4 ,write an equation to represent the reaction involved in the preparation of ammonia from ammonium chloride4 #af4 ,what substances already studied are prepared from the following compounds8 ammonium chloride2 ammonium nitrate2 ammonium nitrite2 sodium nitrate2 sodium chloride4 #ag4 ,how could you prove that the water in crystals of common salt is not water of crystallization8 #ah4 ,how could you distinguish between potassium chloride and potassium iodide8 between sodium chloride and ammonium chloride8 between sodium nitrate and potassium nitrate8 ,illustration3 ,,robert ,,wilhelm ,,bunsen 7,german7 7#ahaa-ahii7 ,invented many lecture-room and laboratory appliances 7,bunsen burner72 invented the spectroscope and with it discovered rubidium and csium2 greatly perfected methods of electrolysis1 inventing a new battery2 made many investigations among metallic and organic substances ,,chapter ,,xxiv ,,the ,,alkaline-,,earth ,,family ,,milligrams ,,sol- ,,uble ,,in #a ,l4 ,,of ,,water ,,at #ah ,,symbol ,,atomic ,,density ,,carbonate ,,weight ,,decomposes ,,sulphate ,,hydrox- ,,ide ,calcium ,ca #dj4a #a4ed #bjgj4jj #afgj4 ,at dull red heat ,strontium ,sr #hg4f #b4ej #agj4jj #gdfj4 ,at white heat ,barium ,ba #acg4d #c4ge #b4bi #cfcjj4 ,scarcely at all ,the family4 ,the alkaline-earth family consists of the very abundant element calcium and the much rarer elements strontium and barium4 ,they are called the alkaline-earth metals because their properties are between those of the alkali metals and the earth metals4 ,the earth metals will be discussed in a later chapter4 ,the family is also frequently called the calcium family4 #a4 ,occurrence4 ,these elements do not occur free in nature4 ,their most abundant compounds are the carbonates and sulphates2 calcium also occurs in large quantities as the phosphate and silicate4 #b4 ,preparation4 ,the metals were first prepared by ,davy in #ahjh by electrolysis4 ,this method has again come into use in recent years4 ,strontium and barium have as yet been obtained only in small quantities and in the impure state1 and many of their physical properties1 such as their densities and melting points1 are therefore imperfectly known4 #c4 ,properties4 ,the three metals resemble each other very closely4 ,they are silvery-white in color and are about as hard as lead4 ,their densities increase with their atomic weights1 as is shown in the table on opposite page4 ,like the alkali metals they have a strong affinity for oxygen1 tarnishing in the air through oxidation4 ,they decompose water at ordinary temperatures1 forming hydroxides and liberating hydrogen4 ,when ignited in the air they burn with brilliancy1 forming oxides of the general formula ,,mo4 ,these oxides readily combine with water1 according to the equation ,,mo ,h#b,o ,m7,,oh7#b4 ,each of the elements has a characteristic spectrum1 and the presence of the metals can easily be detected by the spectroscope4 #d4 ,compounds4 ,the elements are divalent in almost all of their compounds1 and these compounds in solution give simple1 divalent1 colorless ions4 ,the corresponding salts of the three elements are very similar to each other and show a regular variation in properties in passing from calcium to strontium and from strontium to barium4 ,this is seen in the solubility of the sulphate and hydroxide1 and in the ease of decomposition of the carbonates1 as given in the table4 ,unlike the alkali metals1 their normal carbonates and phosphates are insoluble in water4 ,,calcium ,occurrence4 ,the compounds of calcium are very abundant in nature1 so that the total amount of calcium in the earth's crust is very large4 ,a great many different compounds containing the clement are known1 the most important of which are the following3 ,calcite 7marble7 ,ca,c,o#c4 ,phosphorite ,ca#c7,,po#d7b4 ,fluorspar ,ca,f#b4 ,wollastonite ,ca,si,o#c4 ,gypsum ,ca,s,o#db;,h#b,o4 ,anhydrite ,ca,s,o#d4 ,preparation4 ,calcium is now prepared by the electrolysis of the melted chloride1 the metal depositing in solid condition on the cathode4 ,it is a gray metal1 considerably heavier and harder than sodium4 ,it acts upon water1 forming calcium hydroxide and hydrogen1 but the action does not evolve sufficient heat to melt the metal4 ,it promises to become a useful substance1 though no commercial applications for it have as yet been found4 ,calcium oxide 7lime1 quicklime7 7,ca,o74 ,lime is prepared by strongly heating calcium carbonate 7limestone7 in large furnaces called kilns3 ,ca,c,o#c ,ca,o ,,co#b4 ,when pure1 lime is a white amorphous substance4 ,heated intensely1 as in the oxyhydrogen flame1 it gives a brilliant light called the lime light4 ,although it is a very difficultly fusible substance1 yet in the electric furnace it can be made to melt and even boil4 ,water acts upon lime with the evolution of a great deal of heat1--hence the name quicklime1 or live lime1--the process being called slaking4 ,the equation is ,ca,o ,h#b,o ,ca7,,oh7#b4 ,lime readily absorbs moisture from the air1 and is used to dry moist gases1 especially ammonia1 which cannot be dried by the usual desiccating agents4 ,it also absorbs carbon dioxide1 forming the carbonate ,ca,o ,,co#b ,ca,c,o#c4 ,lime exposed to air is therefore gradually converted into hydroxide and carbonate1 and will no longer slake with water4 ,it is then said to be air-slaked4 ,limekilns4 ,the older kiln1 still in common use1 consists of a large cylindrical stack in which the limestone is loosely packed4 ,a fire is built at the base of the stack1 and when the burning is complete it is allowed to die out and the lime is removed from the kiln4 ,the newer kilns are constructed as shown in ,fig4 #hj4 ,a number of fire boxes are built around the lower part of the kiln1 one of which is shown at ,b4 ,the fire is built on the grate ,f and the hot products of combustion are drawn up through the stack1 decomposing the limestone4 ,the kiln is charged at ,c1 and sometimes fuel is added with the limestone to cause combustion throughout the contents of the kiln4 ,the burned lime is raked out through openings in the bottom of the stack1 one of which is shown at ,d4 ,the advantage of this kind of a kiln over the older form is that the process is continuous1 limestone being charged in at the top as fast as the lime is removed at the bottom4 ,illustration3 ,fig4 #hj ,calcium hydroxide 7slaked lime7 7,ca7,,oh7#b74 ,pure calcium hydroxide is a light white powder4 ,it is sparingly soluble in water1 forming a solution called limewater1 which is often used in medicine as a mild alkali4 ,chemically1 calcium hydroxide is a moderately strong base1 though not so strong as sodium hydroxide4 ,owing to its cheapness it is much used in the industries whenever an alkali is desired4 ,a number of its uses have already been mentioned4 ,it is used in the preparation of ammonia1 bleaching powder1 and potassium hydroxide4 ,it is also used to remove carbon dioxide and sulphur compounds from coal gas1 to remove the hair from hides in the tanneries 7this recalls the caustic or corrosive properties of sodium hydroxide71 and for making mortar4 ,mortar is a mixture of calcium hydroxide and sand4 ,when it is exposed to the air or spread upon porous materials moisture is removed from it partly by absorption in the porous materials and partly by evaporation1 and the mortar becomes firm1 or sets4 ,at the same time carbon dioxide is slowly absorbed from the air1 forming hard calcium carbonate3 ,ca7,,oh7#b ,,co#b ,ca,c,o#c ,h#b,o4 ,by this combined action the mortar becomes very hard and adheres firmly to the surface upon which it is spread4 ,the sand serves to give body to the mortar and makes it porous1 so that the change into carbonate can take place throughout the mass4 ,it also prevents too much shrinkage4 ,cement4 ,when limestone to which clay and sand have been added in certain proportions is burned until it is partly fused 7some natural marl is already of about the right composition71 and the clinker so produced is ground to powder1 the product is called cement4 ,when this material is moistened it sets to a hard stone-like mass which retains its hardness even when exposed to the continued action of water4 ,it can be used for under-water work1 such as bridge piers1 where mortar would quickly soften4 ,several varieties of cement are made1 the best known of which is ,portland cement4 ,growing importance of cement4 ,cement is rapidly coming into use for a great variety of purposes4 ,it is often used in place of mortar in the construction of brick buildings4 ,mixed with crushed stone and sand it forms concrete which is used in foundation work4 ,it is also used in making artificial stone1 terra-cotta trimmings for buildings1 artificial stone walks and floors1 and the like4 ,it is being used more and more for making many articles which were formerly made of wood or stone1 and the entire walls of buildings are sometimes made of cement blocks or of concrete4 ,calcium carbonate 7,ca,c,o#c74 ,this substance is found in a great many natural forms to which various names have been given4 ,they may be classified under three heads3 #a4 ,amorphous carbonate4 ,this includes those forms which are not markedly crystalline4 ,limestone is the most familiar of these and is a grayish rock usually found in hard stratified masses4 ,whole mountain ranges are sometimes made up of this material4 ,it is always impure1 usually containing magnesium carbonate1 clay1 silica1 iron and aluminium compounds1 and frequently fossil remains4 ,marl is a mixture of limestone and clay4 ,pearls1 chalk1 coral1 and shells are largely calcium carbonate4 #b4 ,hexagonal carbonate4 ,calcium carbonate crystallizes in the form of rhomb-shaped crystals which belong to the hexagonal system4 ,when very pure and transparent the substance is called ,iceland spar4 ,calcite is a similar form1 but somewhat opaque or clouded4 ,mexican onyx is a massive variety1 streaked or banded with colors due to impurities4 ,marble when pure is made up of minute calcite crystals4 ,stalactites and stalagmites are icicle-like forms sometimes found in caves4 #c4 ,rhombic carbonate4 ,calcium carbonate sometimes crystallizes in needle-shaped crystals belonging to the rhombic system4 ,this is the unstable form and tends to go over into the other variety4 ,aragonite is the most familiar example of this form4 ,preparation and uses of calcium carbonate4 ,in the laboratory pure calcium carbonate can be prepared by treating a soluble calcium salt with a soluble carbonate3 ,na#b;,,co#c ,ca,cl#b ,ca,c,o#c #b,na,cl4 ,when prepared in this way it is a soft white powder often called precipitated chalk1 and is much used as a polishing powder4 ,it is insoluble in water1 but dissolves in water saturated with carbon dioxide1 owing to the formation of the acid calcium carbonate which is slightly soluble3 ,ca,c,o#c ,h#b;,,co#c ,ca7,,hco#c7b4 ,the natural varieties of calcium carbonate find many uses1 such as in the preparation of lime and carbon dioxide2 in metallurgical operations1 especially in the blast furnaces2 in the manufacture of soda1 glass1 and crayon 7which1 in addition to chalk1 usually contains clay and calcium sulphate72 for building stone and ballast for roads4 ,calcium chloride 7,ca,cl#b74 ,this salt occurs in considerable quantity in sea water4 ,it is obtained as a by-product in many technical processes1 as in the ,solvay soda process4 ,when crystallized from its saturated solutions it forms colorless needles of the composition ,ca,cl#bf;,h#b,o4 ,by evaporating a solution to dryness and heating to a moderate temperature calcium chloride is obtained anhydrous as a white porous mass4 ,in this condition it absorbs water with great energy and is a valuable drying agent4 ,bleaching powder 7,ca,o,cl#b74 ,when chlorine acts upon a solution of calcium hydroxide the reaction is similar to that which occurs between chlorine and potassium hydroxide3 #b ,ca7,,oh7#b #d ,cl ,ca,cl#b ,ca7,cl,o7#b #b ,h#b,o4 ,if1 however1 chlorine is conducted over calcium hydroxide in the form of a dry powder1 it is absorbed and a substance is formed which appears to have the composition represented in the formula ,ca,o,cl#b4 ,this substance is called bleaching powder1 or hypochlorite of lime4 ,it is probably the calcium salt of both hydrochloric and hypochlorous acids1 so that its structure is represented by the formula _/,cl,o ,ca ,cl4 ,in solution this substance acts exactly like a mixture of calcium chloride 7,ca,cl#b7 and calcium hypochlorite 7,ca7,cl,o7#b71 since it dissociates to form the ions ,ca1 ,cl-1 and ,cl,o-4 ,bleaching powder undergoes a number of reactions which make it an important substance4 #a4 ,when treated with an acid it evolves chlorine3 _/,cl,o ,ca ,h#b,,so#d ,ca,s,o#d ,h,cl ,h,cl,o1 ,cl ,h,cl ,h,cl,o ,h#b,o #b;,cl4 ,this reaction can be employed in the preparation of chlorine1 or the nascent chlorine may be used as a bleaching agent4 #b4 ,it is slowly decomposed by the carbon dioxide of the air1 yielding calcium carbonate and chlorine3 ,ca,o,cl#b ,,co#b ,ca,c,o#c #b;,cl4 ,owing to this slow action the substance is a good disinfectant4 #c4 ,when its solution is boiled the substance breaks down into calcium chloride and chlorate3 #f;,ca,o,cl#b #e;,ca,cl#b ,ca7,cl,o#c7b4 ,this reaction is used in the preparation of potassium chlorate4 ,calcium fluoride 7fluorspar7 7,ca,f#b74 ,fluorspar has already been mentioned as the chief natural compound of fluorine4 ,it is found in large quantities in a number of localities1 and is often crystallized in perfect cubes of a light green or amethyst color4 ,it can be melted easily in a furnace1 and is sometimes used in the fused condition in metallurgical operations to protect a metal from the action of the air during its reduction4 ,it is used as the chief source of fluorine compounds1 especially hydrofluoric acid4 ,calcium sulphate 7gypsum7 7,ca,s,o#db;,h#b,o74 ,this abundant substance occurs in very perfectly formed crystals or in massive deposits4 ,it is often found in solution in natural waters and in the sea water4 ,salts deposited from sea water are therefore likely to contain this substance 7see ,stassfurt salts74 ,it is very sparingly soluble in water1 and is thrown down as a fine white precipitate when any considerable amounts of a calcium salt and a soluble sulphate 7or sulphuric acid7 are brought together in solution4 ,its chief use is in the manufacture of plaster of ,paris and of hollow tiles for fireproof walls4 ,such material is called gypsite4 ,it is also used as a fertilizer4 ,calcium sulphate1 like the carbonate1 occurs in many forms in nature4 ,gypsum is a name given to all common varieties4 ,granular or massive specimens are called alabaster1 while all those which are well crystallized are called selenite4 ,satin spar is still another variety often seen in mineral collections4 ,plaster of ,paris4 ,when gypsum is heated to about #aae it loses a portion of its water of crystallization in accordance with the equation #b7;,ca,s,o#db;,h#b,o7 #b;,ca,s,o#d;,h#b,o #b;,h#b,o4 ,the product is a fine white powder called plaster of ,paris4 ,on being moistened it again takes up this water1 and in so doing first forms a plastic mass1 which soon becomes very firm and hard and regains its crystalline structure4 ,these properties make it very valuable as a material for forming casts and stucco work1 for cementing glass to metals1 and for other similar purposes4 ,if overheated so that all water is driven off1 the process of taking up water is so slow that the material is worthless4 ,such material is said to be dead burned4 ,plaster of ,paris is very extensively used as the finishing coat for plastered walls4 ,hard water4 ,waters containing compounds of calcium and magnesium in solution are called hard waters because they feel harsh to the touch4 ,the hardness of water may be of two kinds1--7#a7 temporary hardness and 7#b7 permanent hardness4 #a4 ,temporary hardness4 ,we have seen that when water charged with carbon dioxide comes in contact with limestone a certain amount of the latter dissolves1 owing to the formation of the soluble acid carbonate of calcium4 ,the hardness of such waters is said to be temporary1 since it may be removed by boiling4 ,the heat changes the acid carbonate into the insoluble normal carbonate which then precipitates1 rendering the water soft3 ,ca7,,hco#c7b ,ca,c,o#c ,h#b,o ,,co#b4 ,such waters may also be softened by the addition of sufficient lime or calcium hydroxide to convert the acid carbonate of calcium into the normal carbonate4 ,the equation representing the reaction is ,ca7,,hco#c7b ,ca7,,oh7#b #b;,ca,c,o#c #b;,h#b,o4 #b4 ,permanent hardness4 ,the hardness of water may also be due to the presence of calcium and magnesium sulphates or chlorides4 ,boiling the water does not affect these salts2 hence such waters are said to have permanent hardness4 ,they may be softened1 however1 by the addition of sodium carbonate1 which precipitates the calcium and magnesium as insoluble carbonates3 ,ca,s,o#d ,na#b;,,co#c ,ca,c,o#c ,na#b,,so#d4 ,this process is sometimes called breaking the water4 ,commercial methods for softening water4 ,the average water of a city supply contains not only the acid carbonates of calcium and magnesium but also the sulphates and chlorides of these metals1 together with other salts in smaller quantities4 ,such waters are softened on a commercial scale by the addition of the proper quantities of calcium hydroxide and sodium carbonate4 ,the calcium hydroxide is added first to precipitate all the acid carbonates4 ,after a short time the sodium carbonate is added to precipitate the other soluble salts of calcium and magnesium1 together with any excess of calcium hydroxide which may have been added4 ,the quantity of calcium hydroxide and sodium carbonate required is calculated from a chemical analysis of the water4 ,it will be noticed that the water softened in this way will contain sodium sulphate and chloride1 but the presence of these salts is not objectionable4 ,calcium carbide 7,ca,c#b74 ,this substance is made by heating well-dried coke and lime in an electrical furnace4 ,the equation is ,ca,o #c;,c ,ca,c#b ,,co4 ,the pure carbide is a colorless1 transparent1 crystalline substance4 ,in contact with water it is decomposed with the evolution of pure acetylene gas1 having a pleasant ethereal odor4 ,the commercial article is a dull gray porous substance which contains many impurities4 ,the acetylene prepared from this substance has a very characteristic odor due to impurities1 the chief of these being phosphine4 ,it is used in considerable quantities as a source of acetylene gas for illuminating purposes4 ,technical preparation4 ,fig4 #ha represents a recent type of a carbide furnace4 ,the base of the furnace is provided with a large block of carbon ,a1 which serves as one of the electrodes4 ,the other electrodes ,b1 several in number1 are arranged horizontally at some distance above this4 ,a mixture of coal and lime is fed into the furnace through the trap top ,c1 and in the lower part of the furnace this mixture becomes intensely heated1 forming liquid carbide4 ,this is drawn off through the taphole ,d4 ,the carbon monoxide formed in the reaction escapes through the pipes ,e and is led back into the furnace4 ,the pipes ,f supply air1 so that the monoxide burns as it renters the furnace and assists in heating the charge4 ,the carbon dioxide so formed1 together with the nitrogen entering as air1 escape at ,g4 ,an alternating current is used4 ,illustration3 ,fig4 #ha ,calcium phosphate 7,ca#c7,,po#d7b74 ,this important substance occurs abundantly in nature as a constituent of apatite 7#c;,ca#c7,,po#d7b;,ca,f#b71 in phosphate rock1 and as the chief mineral constituent of bones4 ,bone ash is therefore nearly pure calcium phosphate4 ,it is a white powder1 insoluble in water1 although it readily dissolves in acids1 being decomposed by them and converted into soluble acid phosphates1 as explained in connection with the acids of phosphorus4 ,,strontium ,occurrence4 ,strontium occurs sparingly in nature1 usually as strontianite 7,sr,c,o#c7 and as celestite 7,sr,s,o#d74 ,both minerals form beautiful colorless crystals1 though celestite is sometimes colored a faint blue4 ,only a few of the compounds of strontium have any commercial applications4 ,strontium hydroxide 7,sr7,,oh7#bh;,h#b,o74 ,the method of preparation of strontium hydroxide is analogous to that of calcium hydroxide4 ,the substance has the property of forming an insoluble compound with sugar1 which can easily be separated again into its constituents4 ,it is therefore sometimes used in the sugar refineries to extract sugar from impure mother liquors from which the sugar will not crystallize4 ,strontium nitrate 7,sr7,,no#c7bd;,h#b,o74 ,this salt is prepared by treating the native carbonate with nitric acid4 ,when ignited with combustible materials it imparts a brilliant crimson color to the flame1 and because of this property it is used in the manufacture of red lights4 ,,barium ,barium is somewhat more abundant than strontium1 occurring in nature largely as barytes1 or heavy spar 7,ba,s,o#d71 and witherite 7,ba,c,o#c74 ,like strontium1 it closely resembles calcium both in the properties of the metal and in the compounds which it forms4 ,oxides of barium4 ,barium oxide 7,ba,o7 can be obtained by strongly heating the nitrate3 ,ba7,,no#c7b ,ba,o #b,,no#b ,o4 ,heated to a low red heat in the air1 the oxide combines with oxygen1 forming the peroxide 7,ba,o#b74 ,if the temperature is raised still higher1 or the pressure is reduced1 oxygen is given off and the oxide is once more formed4 ,the reaction ,ba,o#b -- ,ba,o ,o is reversible and has been used as a means of separating oxygen from the air4 ,treated with acids1 barium peroxide yields hydrogen peroxide3 ,ba,o#b #b;,h,cl ,ba,cl#b ,h#b,o#b4 ,barium chloride 7,ba,cl#bb;,h#b,o74 ,barium chloride is a white well-crystallized substance which is easily prepared from the native carbonate4 ,it is largely used in the laboratory as a reagent to detect the presence of sulphuric acid or soluble sulphates4 ,barium sulphate 7barytes7 7,ba,s,o#d74 ,barium sulphate occurs in nature in the form of heavy white crystals4 ,it is precipitated as a crystalline powder when a barium salt is added to a solution of a sulphate or sulphuric acid3 ,ba,cl#b ,h#b,,so#d ,ba,s,o#d #b;,h,cl4 ,this precipitate is used1 as are also the finely ground native sulphate and carbonate1 as a pigment in paints4 ,on account of its low cost it is sometimes used as an adulterant of white lead1 which is also a heavy white substance4 ,barium compounds color the flame green1 and the nitrate 7,ba7,,no#c7b7 is used in the manufacture of green lights4 ,soluble barium compounds are poisonous4 ,,radium ,historical4 ,in #ahif the ,french scientist ,becquerel observed that the mineral pitchblende possesses certain remarkable properties4 ,it affects photographic plates even in complete darkness1 and discharges a gold-leaf electroscope when brought close to it4 ,in #ahih ,madam ,curie made a careful study of pitchblende to see if these properties belong to it or to some unknown substance contained in it4 ,she succeeded in extracting from it a very small quantity of a substance containing a new element which she named radium4 ,in #aiaj ,madam ,curie succeeded in obtaining radium itself by the electrolysis of radium chloride4 ,it is a silver-white metal melting at about #gjj4 ,it blackens in the air1 forming a nitride1 and decomposes water4 ,its atomic weight is about #bbf4e4 ,properties4 ,compounds of radium affect a photographic plate or electroscope even through layers of paper or sheets of metal4 ,they also bring about chemical changes in substances placed near them4 ,investigation of these strange properties has suggested that the radium atoms are unstable and undergo a decomposition4 ,as a result of this decomposition very minute bodies1 to which the name corpuscles has been given1 are projected from the radium atom with exceedingly great velocity4 ,it is to these corpuscles that the strange properties of radium are due4 ,it seems probable that the gas helium is in some way formed during the decomposition of radium4 ,two or three other elements1 particularly uranium and thorium1 have been found to possess many of the properties of radium in smaller degree4 ,radium and the atomic theory4 ,if these views in regard to radium should prove to be well founded1 it will be necessary to modify in some respects the conception of the atom as developed in a former chapter4 ,the atom would have to be regarded as a compound unit made up of several parts4 ,in a few cases1 as in radium and uranium1 it would appear that this unit is unstable and undergoes transformation into more stable combinations4 ,this modification would not1 in any essential way1 be at variance with the atomic theory as propounded by ,dalton4 ,,exercises #a4 ,what properties have the alkaline-earth metals in common with the alkali metals8 ,in what respects do they differ8 #b4 ,write the equation for the reaction between calcium carbide and water4 #c4 ,for what is calcium chlorate used8 #d4 ,could limestone be completely decomposed if heated in a closed vessel8 #e4 ,caves often occur in limestone4 ,account for their formation4 #f4 ,what is the significance of the term fluorspar8 7,consult dictionary47 #g4 ,could calcium chloride be used in place of barium chloride in testing for sulphates8 #h4 ,what weight of water is necessary to slake the lime obtained from #a ton of pure calcium carbonate8 #i4 ,what weight of gypsum is necessary in the preparation of #a ton of plaster of ,paris8 #aj4 ,write equations to represent the reactions involved in the preparation of strontium hydroxide and strontium nitrate from strontianite4 #aa4 ,write equations to represent the reactions involved in the preparation of barium chloride from heavy spar4 #ab4 ,could barium hydroxide be used in place of calcium hydroxide in testing for carbon dioxide8 ,,chapter ,,xxv ,,the ,,magnesium ,,family ,,symbol ,,atomic ,,density ,,melting ,,boiling ,,oxide ,,weight ,,point ,,point ---------------------------------------- ----------------------------------- ,magnesium ,mg #bd4cf #a4ge #gej #ibj ,mg,o ,zinc ,zn #fe4d #g4jj #dbj #iej ,zn,o ,cadmium ,cd #aab4d #h4fg #cbj #ggh ,cd,o ,the family4 ,in the magnesium family are included the four elements3 magnesium1 zinc1 cadmium1 and mercury4 ,between the first three of these metals there is a close family resemblance1 such as has been traced between the members of the two preceding families4 ,mercury in some respects is more similar to copper and will be studied in connection with that metal4 #a4 ,properties4 ,when heated to a high temperature in the air each of these metals combines with oxygen to form an oxide of the general formula ,,mo1 in which ,m represents the metal4 ,magnesium decomposes boiling water slowly1 while zinc and cadmium have but little action on it4 #b4 ,compounds4 ,the members of this group are divalent in nearly all their compounds1 so that the formulas of their salts resemble those of the alkaline-earth metals4 ,like the alkaline-earth metals1 their carbonates and phosphates are insoluble in water4 ,their sulphates1 however1 are readily soluble4 ,unlike both the alkali and alkaline-earth metals1 their hydroxides are nearly insoluble in water4 ,most of their compounds dissociate in such a way as to give a simple1 colorless1 metallic ion4 ,,magnesium ,occurrence4 ,magnesium is a very abundant element in nature1 ranking a little below calcium in this respect4 ,like calcium1 it is a constituent of many rocks and also occurs in the form of soluble salts4 ,preparation4 ,the metal magnesium1 like most metals whose oxides are difficult to reduce with carbon1 was formerly prepared by heating the anhydrous chloride with sodium3 ,mg,cl#b #b,na #b,na,cl ,mg4 ,it is now made by electrolysis1 but instead of using as the electrolyte the melted anhydrous chloride1 which is difficult to obtain1 the natural mineral carnallite is used4 ,this is melted in an iron pot which also serves as the cathode in the electrolysis4 ,a rod of carbon dipping into the melted salt serves as the anode4 ,the apparatus is very similar to the one employed in the preparation of sodium4 ,properties4 ,magnesium is a rather tough silvery-white metal of small density4 ,air does not act rapidly upon it1 but a thin film of oxide forms upon its surface1 dimming its bright luster4 ,the common acids dissolve it with the formation of the corresponding salts4 ,it can be ignited readily and in burning liberates much heat and gives a brilliant white light4 ,this light is very rich in the rays which affect photographic plates1 and the metal in the form of fine powder is extensively used in the production of flash lights and for white lights in pyrotechnic displays4 ,magnesium oxide 7magnesia7 7,mg,o74 ,magnesium oxide1 sometimes called magnesia or magnesia usta1 resembles lime in many respects4 ,it is much more easily formed than lime and can be made in the same way1--by igniting the carbonate4 ,it is a white powder1 very soft and light1 and is unchanged by heat even at very high temperatures4 ,for this reason it is used in the manufacture of crucibles1 for lining furnaces1 and for other purposes where a refractory substance is needed4 ,it combines with water to form magnesium hydroxide1 but much more slowly and with the production of much less heat than in the case of calcium oxide4 ,magnesium hydroxide 7,mg7,,oh7#b74 ,the hydroxide formed in this way is very slightly soluble in water1 but enough dissolves to give the water an alkaline reaction4 ,magnesium hydroxide is therefore a fairly strong base4 ,it is an amorphous white substance4 ,neither magnesia nor magnesium salts have a very marked effect upon the system2 and for this reason magnesia is a very suitable antidote for poisoning by strong acids1 since any excess introduced into the system will have no injurious effect4 ,magnesium cement4 ,a paste of magnesium hydroxide and water slowly absorbs carbon dioxide from the air and becomes very hard4 ,the hardness of the product is increased by the presence of a considerable amount of magnesium chloride in the paste4 ,the hydroxide1 with or without the chloride1 is used in the preparation of cements for some purposes4 ,magnesium carbonate 7,mg,c,o#c74 ,magnesium carbonate is a very abundant mineral4 ,it occurs in a number of localities as magnesite1 which is usually amorphous1 but sometimes forms pure crystals resembling calcite4 ,more commonly it is found associated with calcium carbonate4 ,the mineral dolomite has the composition ,ca,c,o#c,mg,c,o#c4 ,limestone containing smaller amounts of magnesium carbonate is known as dolomitic limestone4 ,dolomite is one of the most common rocks1 forming whole mountain masses4 ,it is harder and less readily attacked by acids than limestone4 ,it is valuable as a building stone and as ballast for roadbeds and foundations4 ,like calcium carbonate1 magnesium carbonate is insoluble in water1 though easily dissolved by acids4 ,basic carbonate of magnesium4 ,we should expect to find magnesium carbonate precipitated when a soluble magnesium salt and a soluble carbonate are brought together3 ,na#b;,,co#c ,mg,cl#b ,mg,c,o#c #b,na,cl4 ,instead of this1 some carbon dioxide escapes and the product is found to be a basic carbonate4 ,the most common basic carbonate of magnesium has the formula #d,mg,c,o#c,mg7,,oh7#b1 and is sometimes called magnesia alba4 ,this compound is formed by the partial hydrolysis of the normal carbonate at first precipitated3 #e,mg,c,o#c #b;,h#b,o #d,mg,c,o#c,mg7,,oh7#b ,h#b;,,co#c4 ,magnesium chloride 7,mg,cl#bf;,h#b,o74 ,magnesium chloride is found in many natural waters and in many salt deposits 7see ,stassfurt salts74 ,it is obtained as a by-product in the manufacture of potassium chloride from carnallite4 ,as there is no very important use for it1 large quantities annually go to waste4 ,when heated to drive off the water of crystallization the chloride is decomposed as shown in the equation ,mg,cl#bf;,h#b,o ,mg,o #b;,h,cl #e;,h#b,o4 ,owing to the abundance of magnesium chloride1 this reaction is being used to some extent in the preparation of both magnesium oxide and hydrochloric acid4 ,boiler scale4 ,when water which contains certain salts in solution is evaporated in steam boilers1 a hard insoluble material called scale deposits in the boiler4 ,the formation of this scale may be due to several distinct causes4 #a4 ,to the deposit of calcium sulphate4 ,this salt1 while sparingly soluble in cold water1 is almost completely insoluble in superheated water4 ,consequently it is precipitated when water containing it is heated in a boiler4 #b4 ,to decomposition of acid carbonates4 ,as we have seen1 calcium and magnesium acid carbonates are decomposed on heating1 forming insoluble normal carbonates3 ,ca7,,hco#c7b ,ca,c,o#c ,h#b,o ,,co#b4 #c4 ,to hydrolysis of magnesium salts4 ,magnesium chloride1 and to some extent magnesium sulphate1 undergo hydrolysis when superheated in solution1 and the magnesium hydroxide1 being sparingly soluble1 precipitates3 ,mg,cl#b #b;,h#b,o -- ,mg7,,oh7#b #b;,h,cl4 ,this scale adheres tightly to the boiler in compact layers and1 being a non-conductor of heat1 causes much waste of fuel4 ,it is very difficult to remove1 owing to its hardness and resistance to reagents4 ,thick scale sometimes cracks1 and the water coming in contact with the overheated iron occasions an explosion4 ,moreover1 the acids set free in the hydrolysis of the magnesium salts attack the iron tubes and rapidly corrode them4 ,these causes combine to make the formation of scale a matter which occasions much trouble in cases where hard water is used in steam boilers4 ,water containing such salts should be softened1 therefore1 before being used in boilers4 ,magnesium sulphate 7,epsom salt7 7,mg,s,o#dg;,h#b,o74 ,like the chloride1 magnesium sulphate is found rather commonly in springs and in salt deposits4 ,a very large deposit of the almost pure salt has been found in ,wyoming4 ,its name was given to it because of its abundant occurrence in the waters of the ,epsom springs in ,england4 ,magnesium sulphate has many uses in the industries4 ,it is used to a small extent in the preparation of sodium and potassium sulphates1 as a coating for cotton cloth1 in the dye industry1 in tanning1 and in the manufacture of paints and laundry soaps4 ,to some extent it is used in medicine4 ,magnesium silicates4 ,many silicates containing magnesium are known and some of them are important substances4 ,serpentine1 asbestos1 talc1 and meerschaum are examples of such substances4 ,,zinc ,occurrence4 ,zinc never occurs free in nature4 ,its compounds have been found in many different countries1 but it is not a constituent of common rocks and minerals1 and its occurrence is rather local and confined to definite deposits or pockets4 ,it occurs chiefly in the following ores3 ,sphalerite 7zinc blende7 ,zn,s4 ,zincite ,zn,o4 ,smithsonite ,zn,c,o#c4 ,willemite ,zn#b,si,o#d4 ,franklinite ,zn,o,fe#b,o#c4 ,one fourth of the world's output of zinc comes from the ,united ,states1 ,missouri being the largest producer4 ,metallurgy4 ,the ores employed in the preparation of zinc are chiefly the sulphide1 oxide1 and carbonate4 ,they are first roasted in the air1 by which process they are changed into oxide3 ,zn,c,o#c ,zn,o ,,co#b1 ,zn,s #c,o ,zn,o ,,so#b4 ,the oxide is then mixed with coal dust1 and the mixture is heated in earthenware muffles or retorts1 natural gas being used as fuel in many cases4 ,the oxide is reduced by this means to the metallic state1 and the zinc1 being volatile at the high temperature reached1 distills and is collected in suitable receivers4 ,at first the zinc collects in the form of fine powder1 called zinc dust or flowers of zinc1 recalling the formation under similar conditions of flowers of sulphur4 ,later1 when the whole apparatus has become warm1 the zinc condenses to a liquid in the receiver1 from which it is drawn off into molds4 ,commercial zinc often contains a number of impurities1 especially carbon1 arsenic1 and iron4 ,physical properties4 ,pure zinc is a rather heavy bluish-white metal with a high luster4 ,it melts at about #dbj1 and if heated much above this temperature in the air takes fire and burns with a very bright bluish flame4 ,it boils at about #iej and can therefore be purified by distillation4 ,many of the physical properties of zinc are much influenced by the temperature and previous treatment of the metal4 ,when cast into ingots from the liquid state it becomes at ordinary temperatures quite hard1 brittle1 and highly crystalline4 ,at #aej it is malleable and can be rolled into thin sheets2 at higher temperatures it again becomes very brittle4 ,when once rolled into sheets it retains its softness and malleability at ordinary temperatures4 ,when melted and poured into water it forms thin brittle flakes1 and in this condition is called granulated or mossy zinc4 ,chemical properties4 ,zinc is tarnished superficially by moist air1 but beyond this is not affected by it4 ,it does not decompose even boiling water4 ,when the metal is quite pure1 sulphuric and hydrochloric acids have scarcely any action upon it2 when1 however1 it contains small amounts of other metals such as magnesium or arsenic1 or when it is merely in contact with metallic platinum1 brisk action takes place and hydrogen is evolved4 ,for this reason1 when pure zinc is used in the preparation of hydrogen a few drops of platinum chloride are often added to the solution to assist the chemical action4 ,nitric acid dissolves the metal readily1 with the formation of zinc nitrate and various reduction products of nitric acid4 ,the strong alkalis act upon zinc and liberate hydrogen3 ,zn #b,,koh ,zn7,,ok7#b #b;,h4 ,the product of this reaction1 potassium zincate1 is a salt of zinc hydroxide1 which is thus seen to have acid properties1 though it usually acts as a base4 ,uses of zinc4 ,the metal has many familiar uses4 ,rolled into sheets1 it is used as a lining for vessels which are to contain water4 ,as a thin film upon the surface of iron 7galvanized iron7 it protects the iron from rust4 ,iron is usually galvanized by dipping it into a bath of melted zinc1 but electrical methods are also employed4 ,zinc plates are used in many forms of electrical batteries4 ,in the laboratory zinc is used in the preparation of hydrogen1 and in the form of zinc dust as a reducing agent4 ,one of the largest uses of zinc is in the manufacture of alloys4 ,brass1 an alloy of zinc and copper1 is the most important of these2 ,german silver1 consisting of copper1 zinc1 and nickel1 has many uses2 various bronzes1 coin metals1 and bearing metals also contain zinc4 ,its ability to alloy with silver finds application in the separation of silver from lead 7see silver74 ,compounds of zinc4 ,in general1 the compounds of zinc are similar in formula and appearance to those of magnesium1 but in other properties they often differ markedly4 ,a number of them have value in commercial ways4 ,zinc oxide 7zinc white7 7,zn,o74 ,zinc oxide occurs in impure form in nature1 being colored red by manganese and iron compounds4 ,it can be prepared just like magnesium oxide1 but is more often made by burning the metal4 ,zinc oxide is a pure white powder which becomes yellow on heating and regains its white color when cold4 ,it is much used as a white pigment in paints1 under the name of zinc white1 and has the advantage over white lead in that it is not changed in color by sulphur compounds1 while lead turns black4 ,it is also used in the manufacture of rubber goods4 ,commercial preparation of zinc oxide4 ,commercially it is often made from franklinite in the following way4 ,the franklinite is mixed with coal and heated to a high temperature in a furnace1 by which process the zinc is set free and converted into vapor4 ,as the vapor leaves the furnace through a conduit it meets a current of air and takes fire in it1 forming zinc oxide4 ,the oxide passes on and is filtered from the air through canvas bags1 which allow the air to pass but retain the oxide4 ,it is thus made by burning the metal1 though the metal is not actually isolated in the process4 ,soluble salts4 ,the soluble salts of zinc can be made by dissolving the metal or the oxide in the appropriate acid4 ,they are all somewhat poisonous4 ,the sulphate and chloride are the most familiar4 ,zinc sulphate 7white vitriol7 7,zn,s,o#dg;,h#b,o74 ,this salt is readily crystallized from strong solutions in transparent colorless crystals4 ,it is prepared commercially by careful roasting of the sulphide3 ,zn,s #d,o ,zn,s,o#d4 ,zinc chloride 7,zn,cl#b;,h#b,o74 ,when a solution of zinc chloride is slowly evaporated a salt of the composition ,zn,cl#b;,h#b,o crystallizes out4 ,if the water is completely expelled by heat and the residue distilled1 the anhydrous chloride is obtained and may be cast into sticks or broken into lumps4 ,in this distillation1 just as in heating magnesium chloride1 some of the chloride is decomposed3 ,zn,cl#b;,h#b,o ,zn,o #b;,h,cl4 ,the anhydrous chloride has a great affinity for water1 and is used as a dehydrating agent4 ,it is also a germicide1 and wood which is to be exposed to conditions which favor decay1 as1 for example1 railroad ties1 is often soaked in solutions of this salt4 ,insoluble compounds4 ,the insoluble compounds of zinc can be prepared by precipitation4 ,the most important are the sulphide1 carbonate1 and hydroxide4 ,zinc sulphide 7,zn,s74 ,this substance occurs as the mineral sphalerite1 and is one of the most valued ores of zinc4 ,very large deposits occur in southwestern ,missouri4 ,the natural mineral is found in large crystals or masses1 resembling resin in color and luster4 ,when prepared by precipitation the sulphide is white4 ,,cadmium ,the element4 ,this element occurs in small quantities in some zinc ores4 ,in the course of the metallurgy of zinc the cadmium compounds undergo chemical changes quite similar to those of the zinc compounds1 and the cadmium distills along with the zinc4 ,being more volatile1 it comes over with the first of the zinc and is prepared from the first portions of the distillate by special methods of purification4 ,the element very closely resembles zinc in most respects4 ,some of its alloys are characterized by having low melting points4 ,compounds of cadmium4 ,among the compounds of cadmium may be mentioned the chloride 7,cd,cl#bb;,h#b,o71 the sulphate 7#c;,cd,s,o#dh;,h#b,o71 and the nitrate 7,cd7,,no#c7bd;,h#b,o74 ,these are white solids soluble in water4 ,the sulphide 7,cd,s7 is a bright yellow substance which is insoluble in water and in dilute acids4 ,it is valuable as a pigment in fine paints4 ,,exercises #a4 ,what properties have the metals of the magnesium family in common with the alkali metals2 with the alkaline-earth metals8 #b4 ,compare the action of the metals of the magnesium group on water with that of the other metals studied4 #c4 ,what metals already studied are prepared by electrolysis8 #d4 ,write the equations representing the reactions between magnesium and hydrochloric acid2 between magnesium and dilute sulphuric acid4 #e4 ,what property of magnesium was taken advantage of in the isolation of argon8 #f4 ,with phosphoric acid magnesium forms salts similar to those of calcium4 ,write the names and formulas of the corresponding magnesium salts4 #g4 ,how could you distinguish between magnesium chloride and magnesium sulphate8 between ,glauber's salts and ,epsom salts8 #h4 ,what weight of carnallite is necessary in the preparation of #ejj g4 of magnesium8 #i4 ,account for the fact that paints made of zinc oxide are not colored by hydrosulphuric acid4 #aj4 ,what hydroxide studied1 other than zinc hydroxide1 has both acid and basic properties8 #aa4 ,write equations showing how the following compounds of zinc may be obtained from metallic zinc3 the oxide1 chloride1 nitrate1 carbonate1 sulphate1 sulphide1 hydroxide4 ,,chapter ,,xxvi ,,the ,,aluminium ,,family ,the family4 ,the element aluminium is the most abundant member of the group of elements known as the aluminium family2 indeed1 the other members of the family--gallium1 indium1 and thallium--are of such rare occurrence that they need not be separately described4 ,the elements of the family are ordinarily trivalent1 so that the formulas for their compounds differ from those of the elements so far studied4 ,their hydroxides are practically insoluble in water and are very weak bases2 indeed1 the bases are so weak that their salts are often hydrolyzed into free base and free acid in solution4 ,the salts formed from these bases usually contain water of crystallization1 which cannot be driven off without decomposing them more or less4 ,the trivalent metals1 which in addition to aluminium include also iron and chromium1 are sometimes called the earth metals4 ,the name refers to the earthy appearance of the oxides of these metals1 and to the fact that many earths1 soils1 and rocks are composed in part of these substances4 ,,aluminium ,occurrence4 ,aluminium never occurs in the free state in nature1 owing to its great affinity for oxygen4 ,in combined form1 as oxides1 silicates1 and a few other salts1 it is both abundant and widely distributed1 being an essential constituent of all soils and of most rocks excepting limestone and sandstone4 ,cryolite 7,na#c;,al,f#f71 found in ,greenland1 and bauxite1 which is an aluminium hydroxide usually mixed with some iron hydroxide1 are important minerals4 ,it is estimated that aluminium composes about #h of the earth's crust4 ,in the industries the metal is called aluminum1 but its chemical name is aluminium4 ,illustration3 ,fig4 #hb ,preparation4 ,aluminium was first prepared by ,whler1 in #ahbg1 by heating anhydrous aluminium chloride with potassium3 ,al,cl#c #c,k #c,k,cl ,al4 ,this method was tried after it was found impossible to reduce the oxide of aluminium with carbon4 ,the metal possessed such interesting properties and promised to be so useful that many efforts were made to devise a cheap way of preparing it4 ,the method which has proved most successful consists in the electrolysis of the oxide dissolved in melted cryolite4 ,metallurgy4 ,an iron box ,a 7,fig4 #hb7 about eight feet long and six feet wide is connected with a powerful generator in such a way as to serve as the cathode upon which the aluminium is deposited4 ,three or four rows of carbon rods ,b dip into the box and serve as the anodes4 ,the box is partially filled with cryolite and the current is turned on1 generating enough heat to melt the cryolite4 ,aluminium oxide is then added1 and under the influence of the electric current it decomposes into aluminium and oxygen4 ,the temperature is maintained above the melting point of aluminium1 and the liquid metal1 being heavier than cryolite1 sinks to the bottom of the vessel1 from which it is tapped off from time to time through the tap hole ,c4 ,the oxygen in part escapes as gas1 and in part combines with the carbon of the anode1 the combustion being very brilliant4 ,the process is carried on at ,niagara ,falls4 ,the largest expense in the process1 apart from the cost of electrical energy1 is the preparation of aluminium oxide free from other oxides1 for most of the oxide found in nature is too impure to serve without refining4 ,bauxite is the principal ore used as a source of the aluminium because it is converted into pure oxide without great difficulty4 ,since common clay is a silicate of aluminium and is everywhere abundant1 it might be expected that this would be utilized in the preparation of aluminium4 ,it is1 however1 very difficult to extract the aluminium from a silicate1 and no practical method has been found which will accomplish this4 ,physical properties4 ,aluminium is a tin-white metal which melts at #fdj and is very light1 having a density of #b4fh4 ,it is stiff and strong1 and with frequent annealing can be rolled into thin foil4 ,it is a good conductor of heat and electricity1 though not so good as copper for a given cross section of wire4 ,chemical properties4 ,aluminium is not perceptibly acted on by boiling water1 and moist air merely dims its luster4 ,further action is prevented in each case by the formation of an extremely thin film of oxide upon the surface of the metal4 ,it combines directly with chlorine1 and when heated in oxygen burns with great energy and the liberation of much heat4 ,it is therefore a good reducing agent4 ,hydrochloric acid acts upon it1 forming aluminium chloride3 nitric acid and dilute sulphuric acid have almost no action on it1 but hot1 concentrated sulphuric acid acts upon it in the same way as upon copper3 #b;,al #f;,h#b,,so#d ,al#b7,,so#d7c #f;,h#b,o #c,,so#b4 ,alkalis readily attack the metal1 liberating hydrogen1 as in the case of zinc3 ,al #c,,koh ,al7,,ok7#c #c;,h4 ,salt solutions1 such as sea water1 corrode the metal rapidly4 ,it alloys readily with other metals4 ,uses of aluminium4 ,these properties suggest many uses for the metal4 ,its lightness1 strength1 and permanence make it well adapted for many construction purposes4 ,these same properties have led to its extensive use in the manufacture of cooking utensils4 ,the fact that it is easily corroded by salt solutions is1 however1 a disadvantage4 ,owing to its small resistance to electrical currents1 it is replacing copper to some extent in electrical construction1 especially for trolley and power wires4 ,some of its alloys have very valuable properties1 and a considerable part of the aluminium manufactured is used for this purpose4 ,aluminium bronze1 consisting of about #ij copper and #aj aluminium1 has a pure golden color1 is strong and malleable1 is easily cast1 and is permanent in the air4 ,considerable amounts of aluminium steel are also made4 ,goldschmidt reduction process4 ,aluminium is frequently employed as a powerful reducing agent1 many metallic oxides which resist reduction by carbon being readily reduced by it4 ,the aluminium in the form of a fine powder is mixed with the metallic oxide1 together with some substance such as fluorspar to act as a flux4 ,the mixture is ignited1 and the aluminium unites with the oxygen of the metallic oxide1 liberating the metal4 ,this collects in a fused condition under the flux4 ,an enormous quantity of heat is liberated in this reaction1 and a temperature as high as #cejj can be reached4 ,the heat of the reaction is turned to practical account in welding car rails1 steel castings1 and in similar operations where an intense local heat is required4 ,a mixture of aluminium with various metallic oxides1 ready prepared for such purposes1 is sold under the name of thermite4 ,illustration3 ,fig4 #hc ,preparation of chromium by the ,goldschmidt method4 ,a mixture of chromium oxide and aluminium powder is placed in a ,hessian crucible 7,a1 ,fig4 #hc71 and on top of it is placed a small heap ,b of a mixture of sodium peroxide and aluminium1 into which is stuck a piece of magnesium ribbon ,c4 ,powdered fluorspar ,d is placed around the sodium peroxide1 after which the crucible is set on a pan of sand and the magnesium ribbon ignited4 ,when the flame reaches the sodium peroxide mixture combustion of the aluminium begins with almost explosive violence1 so that great care must be taken in the experiment4 ,the heat of this combustion starts the reaction in the chromium oxide mixture1 and the oxide is reduced to metallic chromium4 ,when the crucible has cooled a button of chromium will be found in the bottom4 ,aluminium oxide 7,al#b,o#c74 ,this substance occurs in several forms in nature4 ,the relatively pure crystals are called corundum1 while emery is a variety colored dark gray or black1 usually with iron compounds4 ,in transparent crystals1 tinted different colors by traces of impurities1 it forms such precious stones as the sapphire1 oriental ruby1 topaz1 and amethyst4 ,all these varieties are very hard1 falling little short of the diamond in this respect4 ,chemically pure aluminium oxide can be made by igniting the hydroxide1 when it forms an amorphous white powder3 #b;,al7,,oh7#c ,al#b,o#c #c;,h#b,o4 ,the natural varieties1 corundum and emery1 are used for cutting and grinding purposes2 the purest forms1 together with the artificially prepared oxide1 are largely used in the preparation of aluminium4 ,aluminium hydroxide 7,al7,,oh7#c74 ,the hydroxide occurs in nature as the mineral hydrargyllite1 and in a partially dehydrated form called bauxite4 ,it can be prepared by adding ammonium hydroxide to any soluble aluminium salt1 forming a semi-transparent precipitate which is insoluble in water but very hard to filter4 ,it dissolves in most acids to form soluble salts1 and in the strong bases to form aluminates1 as indicated in the equations ,al7,,oh7#c #c;,h,cl ,al,cl#c #c;,h#b,o1 ,al7,,oh7#c #c,na,o,h ,al7,o,na7#c #c;,h#b,o4 ,it may act1 therefore1 either as a weak base or as a weak acid1 its action depending upon the character of the substances with which it is in contact4 ,when heated gently the hydroxide loses part of its hydrogen and oxygen according to the equation ,al7,,oh7#c ,al,o,,oh ,h#b,o4 ,this substance1 the formula of which is frequently written ,h,al,o#b1 is a more pronounced acid than is the hydroxide1 and its salts are frequently formed when aluminium compounds are fused with alkalis4 ,the magnesium salt ,mg7,al,o#b7b is called spinel1 and many other of its salts1 called aluminates1 are found in nature4 ,when heated strongly the hydroxide is changed into oxide1 which will not again take up water on being moistened4 ,mordants and dyeing4 ,aluminium hydroxide has the peculiar property of combining with many soluble coloring materials and forming insoluble products with them4 ,on this account it is often used as a filter to remove objectionable colors from water4 ,this property also leads to its wide use in the dye industry4 ,many dyes will not adhere to natural fibers such as cotton and wool1 that is1 will not dye fast4 ,if1 however1 the cloth to be dyed is soaked in a solution of aluminium compounds and then treated with ammonia1 the aluminium salts which have soaked into the fiber will be converted into the hydroxide1 which1 being insoluble1 remains in the body of it4 ,if the fiber is now dipped into a solution of the dye1 the aluminium hydroxide combines with the color material and fastens1 or fixes1 it upon the fiber4 ,a substance which serves this purpose is called a mordant1 and aluminium salts1 particularly the acetate1 are used in this way4 ,aluminium chloride 7,al,cl#cf ,h#b,o74 ,this substance is prepared by dissolving the hydroxide in hydrochloric acid and evaporating to crystallization4 ,when heated it is converted into the oxide1 resembling magnesium in this respect3 #b7;,al,cl#cf ,h#b,o7 ,al#b,o#c #f;,h,cl #i;,h#b,o4 ,the anhydrous chloride1 which has some important uses1 is made by heating aluminium turnings in a current of chlorine4 ,alums4 ,aluminium sulphate can be prepared by the action of sulphuric acid upon aluminium hydroxide4 ,it has the property of combining with the sulphates of the alkali metals to form compounds called alums4 ,thus1 with potassium sulphate the reaction is expressed by the equation ,k#b,,so#d ,al#b7,,so#d7c #bd;,h#b,o #b7,k,al7,,so#d7bab;,h#b,o74 ,under similar conditions ammonium sulphate yields ammonium alum3 7,,nh#d7b,,so#d ,al#b7,,so#d7c #bd;,h#b,o #b7,,nh#d;,al7,,so#d7bab;,h#b,o74 ,other trivalent sulphates besides aluminium sulphate can form similar compounds with the alkali sulphates1 and these compounds are also called alums1 though they contain no aluminium4 ,they all crystallize in octahedra and contain twelve molecules of water of crystallization4 ,the alums most frequently prepared are the following3 ,potassium alum ,k,al7,,so#d7bab;,h#b,o4 ,ammonium alum ,,nh#d;,al7,,so#d7bab;,h#b,o4 ,ammonium iron alum ,,nh#d;,fe7,,so#d7bab;,h#b,o4 ,potassium chrome alum ,k,cr7,,so#d7bab;,h#b,o4 ,an alum may therefore be regarded as a compound derived from two molecules of sulphuric acid1 in which one hydrogen atom has been displaced by the univalent alkali atom1 and the other three hydrogen atoms by an atom of one of the trivalent metals1 such as aluminium1 iron1 or chromium4 ,very large1 well-formed crystals of an alum can be prepared by suspending a small crystal by a thread in a saturated solution of the alum1 as shown in ,fig4 #hd4 ,the small crystal slowly grows and assumes a very perfect form4 ,illustration3 ,fig4 #hd ,other salts of aluminium4 ,while aluminium hydroxide forms fairly stable salts with strong acids1 it is such a weak base that its salts with weak acids are readily hydrolyzed4 ,thus1 when an aluminium salt and a soluble carbonate are brought together in solution we should expect to have aluminium carbonate precipitated according to the equation #c,na#b;,,co#c #b;,al,cl#c ,al#b7;,,co#c7c #f,na,cl4 ,but if it is formed at all1 it instantly begins to hydrolyze1 the products of the hydrolysis being aluminium hydroxide and carbonic acid1 ,al#b7;,,co#c7c #f;,h#b,o #b;,al7,,oh7#c #c;,h#b;,,co#c4 ,similarly a soluble sulphide1 instead of precipitating aluminium sulphide 7,al#b,s#c71 precipitates aluminium hydroxide2 for hydrogen sulphide is such a weak acid that the aluminium sulphide at first formed hydrolyzes at once1 forming aluminium hydroxide and hydrogen sulphide3 #c,na#b,s #b;,al,cl#c #f;,h#b,o #b;,al7,,oh7#c #f,na,cl #c;,h#b,s4 ,alum baking powders4 ,it is because of the hydrolysis of aluminium carbonate that alum is used as a constituent of some baking powders4 ,the alum baking powders consist of a mixture of alum and sodium hydrogen carbonate4 ,when water is added the two compounds react together1 forming aluminium carbonate1 which hydrolyzes into aluminium hydroxide and carbonic acid4 ,the carbon dioxide from the latter escapes through the dough and in so doing raises it into a porous condition1 which is the end sought in the use of a baking powder4 ,aluminium silicates4 ,one of the most common constituents of rocks is feldspar 7,k,al,si#c,o#h71 a mixed salt of potassium and aluminium with the polysilicic acid 7,h#d,si#c,o#h74 ,under the influence of moisture1 carbon dioxide1 and changes of temperature this substance is constantly being broken down into soluble potassium compounds and hydrated aluminium silicate4 ,this compound has the formula ,al#b,si#b,o#gb;,h#b,o4 ,in relatively pure condition it is called kaolin2 in the impure state1 mixed with sand and other substances1 it forms common clay4 ,mica is another very abundant mineral1 having varying composition1 but being essentially of the formula ,k,al,si,o#d4 ,serpentine1 talc1 asbestos1 and meerschaum are important complex silicates of aluminium and magnesium1 and granite is a mechanical mixture of quartz1 feldspar1 and mica4 ,ceramic industries4 ,many articles of greatest practical importance1 ranging from the roughest brick and tile to the finest porcelain and chinaware1 are made from some form of kaolin1 or clay4 ,no very precise classification of such ware can be made1 as the products vary greatly in properties1 depending upon the materials used and the treatment during manufacture4 ,porcelain is made from the purest kaolin1 to which must be added some less pure1 plastic kaolin1 since the pure substance is not sufficiently plastic4 ,there is also added some more fusible substance1 such as feldspar1 gypsum1 or lime1 together with some pure quartz4 ,the constituents must be ground very fine1 and when thoroughly mixed and moistened must make a plastic mass which can be molded into any desired form4 ,the article molded from such materials is then burned4 ,in this process the article is slowly heated to a point at which it begins to soften and almost fuse1 and then it is allowed to cool slowly4 ,at this stage1 a very thin vessel will be translucent and have an almost glassy fracture2 if1 however1 it is somewhat thicker1 or has not been heated quite so high1 it will still be porous1 and partly on this account and partly to improve its appearance it is usually glazed4 ,glazing is accomplished by spreading upon the object a thin layer of a more fusible mixture of the same materials as compose the body of the object itself1 and again heating until the glaze melts to a transparent glassy coating upon the surface of the vessel4 ,in some cases fusible mixtures of quite different composition from that used in fashioning the vessel may be used as a glaze4 ,oxides of lead1 zinc1 and barium are often used in this way4 ,when less carefully selected materials are used1 or quite thick vessels are made1 various grades of stoneware are produced4 ,the inferior grades are glazed by throwing a quantity of common salt into the kiln towards the end of the first firing4 ,in the form of vapor the salt attacks the surface of the baked ware and forms an easily fusible sodium silicate upon it1 which constitutes a glaze4 ,vitrified bricks1 made from clay or ground shale1 are burned until the materials begin to fuse superficially1 forming their own glaze4 ,other forms of brick and tile are not glazed at all1 but are left porous4 ,the red color of ordinary brick and earthenware is due to an oxide of iron formed in the burning process4 ,the decorations upon china are sometimes painted upon the baked ware and then glazed over1 and sometimes painted upon the glaze and burned in by a third firing4 ,care must be taken to use such pigments as are not affected by a high heat and do not react chemically with the constituents of the baked ware or the glaze4 ,,exercises #a4 ,what metals and compounds studied are prepared by electrolysis8 #b4 ,write the equation for the reaction between aluminium and hydrochloric acid2 between aluminium and sulphuric acid 7in two steps74 #c4 ,what hydroxides other than aluminium hydroxide have both acid and basic properties8 #d4 ,write equations showing the methods used for preparing aluminium hydroxide and sulphate4 #e4 ,write the general formula of an alum1 representing an atom of an alkali metal by ,x and an atom of a trivalent metal by ,y4 #f4 ,what is meant by the term polysilicic acid1 as used in the discussion of aluminium silicates8 #g4 ,compare the properties of the hydroxides of the different groups of metals so far studied4 #h4 ,in what respects does aluminium oxide differ from calcium oxide in properties8 #i4 ,supposing bauxite to be #ij aluminium hydroxide1 what weight of it is necessary for the preparation of #ajj kg4 of aluminium8 ,,chapter ,,xxvii ,,the ,,iron ,,family ,,approximate ,,symbol ,,atomic ,,density ,,melting ,,oxides ,,weight ,,point ,iron ,fe #ee4i #g4ic #ahjj ,fe,o1 ,fe#b,o#c ,cobalt ,co #ei4j #h4ee #ahjj ,co,o1 ,co#b,o#c ,nickel ,ni #eh4g #h4i #afjj ,ni,o1 ,ni#b,o#c ,the family4 ,the elements iron1 cobalt1 and nickel form a group in the eighth column of the periodic table4 ,the atomic weights of the three are very close together1 and there is not the same gradual gradation in the properties of the three elements that is noticed in the families in which the atomic weights differ considerably in magnitude4 ,the elements are very similar in properties1 the similarity being so great in the case of nickel and cobalt that it is difficult to separate them by chemical analysis4 ,the elements occur in nature chiefly as oxides and sulphides1 though they have been found in very small quantities in the native state1 usually in meteorites4 ,their sulphides1 carbonates1 and phosphates are insoluble in water1 the other common salts being soluble4 ,their salts are usually highly colored1 those of iron being yellow or light green as a rule1 those of nickel darker green1 while cobalt salts are usually rose colored4 ,the metals are obtained by reducing the oxides with carbon4 ,,iron ,occurrence4 ,the element iron has long been known1 since its ores are very abundant and it is not difficult to prepare the metal from them in fairly pure condition4 ,it occurs in nature in many forms of combination1--in large deposits as oxides1 sulphides1 and carbonates1 and in smaller quantities in a great variety of minerals4 ,indeed1 very few rocks or soils are free from small amounts of iron1 and it is assimilated by plants and animals playing an important part in life processes4 ,metallurgy4 ,it will be convenient to treat of the metallurgy of iron under two heads1--,materials ,used and ,process4 ,materials used4 ,four distinct materials are used in the metallurgy of iron3 #a4 ,iron ore4 ,the ores most frequently used in the metallurgy of iron are the following3 ,hematite ,fe#b,o#c4 ,magnetite ,fe#c,o#d4 ,siderite ,fe,c,o#c4 ,limonite #b;,fe#b,o#bc;,h#b,o4 ,these ores always contain impurities1 such as silica1 sulphides1 and earthy materials4 ,all ores1 with the exception of the oxides1 are first roasted to expel any water and carbon dioxide present and to convert any sulphide into oxide4 #b4 ,carbon4 ,carbon in some form is necessary both as a fuel and as a reducing agent4 ,in former times wood charcoal was used to supply the carbon1 but now anthracite coal or coke is almost universally used4 #c4 ,hot air4 ,to maintain the high temperature required for the reduction of iron a very active combustion of fuel is necessary4 ,this is secured by forcing a strong blast of hot air into the lower part of the furnace during the reduction process4 #d4 ,flux4 7a7 ,purpose of the flux4 ,all the materials which enter the furnace must leave it again either in the form of gases or as liquids4 ,the iron is drawn off as the liquid metal after its reduction4 ,to secure the removal of the earthy matter charged into the furnace along with the ore1 materials are added to the charge which will1 at the high temperature of the furnace1 combine with the impurities in the ore1 forming a liquid4 ,the material added for this purpose is called the flux2 the liquid produced from the flux and the ore is called slag4 7b7 ,function of the slag4 ,while the main purpose of adding flux to the charge is to remove from the furnace in the form of liquid slag the impurities originally present in the ore1 the slag thus produced serves several other functions4 ,it keeps the contents of the furnace in a state of fusion1 thus preventing clogging1 and makes it possible for the small globules of iron to run together with greater ease into one large liquid mass4 7c7 ,character of the slag4 ,the slag is really a kind of readily fusible glass1 being essentially a calcium-aluminium silicate4 ,the ore usually contains silica and some aluminium compounds1 so that limestone 7which also contains some silica and aluminium7 is added to furnish the calcium required for the slag4 ,if the ore and the limestone do not contain a sufficient amount of silica and aluminium for the formation of the slag1 these ingredients are added in the form of sand and feldspar4 ,in the formation of slag from these materials the ore is freed from the silica and aluminium which it contained4 ,illustration3 ,fig4 #he ,process4 ,the reduction of iron is carried out in large towers called blast furnaces4 ,the blast furnace 7,fig4 #he7 is usually about #hj ft4 high and #bj ft4 in internal diameter at its widest part1 narrowing somewhat both toward the top and toward the bottom4 ,the walls are built of steel and lined with fire-brick4 ,the base is provided with a number of pipes ,t1 called tuyers1 through which hot air can be forced into the furnace4 ,the tuyers are supplied from a large pipe ,s1 which circles the furnace as a girdle4 ,the base has also an opening ,m1 through which the liquid metal can be drawn off from time to time1 and a second opening ,p1 somewhat above the first1 through which the excess of slag overflows4 ,the top is closed by a movable trap ,c and ,c1 called the cone1 and through this the materials to be used are introduced4 ,the gases produced by the combustion of the fuel and the reduction of the ore1 together with the nitrogen of the air forced in through the tuyers1 escape through pipes ,d1 called downcomer pipes1 which leave the furnace near the top4 ,these gases are very hot and contain combustible substances1 principally carbon monoxide2 they are therefore utilized as fuel for the engines and also to heat the blast admitted through the tuyers4 ,the lower part of the furnace is often furnished with a water jacket4 ,this consists of a series of pipes ,w built into the walls1 through which water can be circulated to reduce their temperature4 ,charges consisting of coke 7or anthracite coal71 ore1 and flux in proper proportions are introduced into the furnace at intervals through the trap top4 ,the coke burns fiercely in the hot-air blast1 giving an intense heat and forming carbon monoxide4 ,the ore1 working down in the furnace as the coke burns1 becomes very hot1 and by the combined reducing action of the carbon and carbon monoxide is finally reduced to metal and collects as a liquid in the bottom of the furnace1 the slag floating on the molten iron4 ,after a considerable amount of the iron has collected the slag is drawn off through the opening ,p4 ,the molten iron is then drawn off into large ladles and taken to the converters for the manufacture of steel1 or it is run out into sand molds1 forming the bars or ingots called pigs4 ,the process is a continuous one1 and when once started it is kept in operation for months or even years without interruption4 ,it seems probable that the first product of combustion of the carbon1 at the point where the tuyers enter the furnace1 is carbon dioxide4 ,this is at once reduced to carbon monoxide by the intensely heated carbon present1 so that no carbon dioxide can be found at that point4 ,for practical purposes1 therefore1 we may consider that carbon monoxide is the first product of combustion4 ,varieties of iron4 ,the iron of commerce is never pure1 but contains varying amounts of other elements1 such as carbon1 silicon1 phosphorus1 sulphur1 and manganese4 ,these elements may either be alloyed with the iron or may be combined with it in the form of definite chemical compounds4 ,in some instances1 as in the case of graphite1 the mixture may be merely mechanical4 ,the properties of iron are very much modified by the presence of these elements and by the form of the combination between them and the iron2 the way in which the metal is treated during its preparation has also a marked influence on its properties4 ,owing to these facts many kinds of iron are recognized in commerce1 the chief varieties being cast iron1 wrought iron1 and steel4 ,cast iron4 ,the product of the blast furnace1 prepared as just described1 is called cast iron4 ,it varies considerably in composition1 usually containing from #ij to #ie iron1 the remainder being largely carbon and silicon with smaller amounts of phosphorus and sulphur4 ,when the melted metal from the blast furnace is allowed to cool rapidly most of the carbon remains in chemical combination with the iron1 and the product is called white cast iron4 ,if the cooling goes on slowly1 the carbon partially separates as flakes of graphite which remain scattered through the metal4 ,this product is softer and darker in color and is called gray cast iron4 ,properties of cast iron4 ,cast iron is hard1 brittle1 and rather easily melted 7melting point about #aajj74 ,it cannot be welded or forged into shape1 but is easily cast in sand molds4 ,it is strong and rigid but not elastic4 ,it is used for making castings and in the manufacture of other kinds of iron4 ,cast iron1 which contains the metal manganese up to the extent of #bj1 together with about #c carbon1 is called spiegel iron2 when more than this amount of manganese is present the product is called ferromanganese4 ,the ferromanganese may contain as much as #hj manganese4 ,these varieties of cast iron are much used in the manufacture of steel4 ,wrought iron4 ,wrought iron is made by burning out from cast iron most of the carbon1 silicon1 phosphorus1 and sulphur which it contains4 ,the process is called puddling1 and is carried out in a furnace constructed as represented in ,fig4 #hf4 ,the floor of the furnace ,f is somewhat concave and is made of iron covered with a layer of iron oxide4 ,a long flame produced by burning fuel upon the grate ,g is directed downward upon the materials placed upon the floor1 and the draught is maintained by the stack ,s4 ,a is the ash box and ,t a trap to catch the solid particles carried into the stack by the draught4 ,upon the floor of the furnace is placed the charge of cast iron1 together with a small amount of material to make a slag4 ,the iron is soon melted by the flame directed upon it1 and the sulphur1 phosphorus1 and silicon are oxidized by the iron oxide1 forming oxides which are anhydrides of acids4 ,these combine with the flux1 which is basic in character1 or with the iron oxide1 to form a slag4 ,the carbon is also oxidized and escapes as carbon dioxide4 ,as the iron is freed from other elements it becomes pasty1 owing to the higher melting point of the purer iron1 and in this condition forms small lumps which are raked together into a larger one4 ,the large lump is then removed from the furnace and rolled or hammered into bars1 the slag2 being squeezed out in this process4 ,the product has a stranded or fibrous structure4 ,the product of a puddling furnace is called wrought iron4 ,illustration3 ,fig4 #hf ,properties of wrought iron4 ,wrought iron is nearly pure iron1 usually containing about #j4c of other substances1 chiefly carbon4 ,it is tough1 malleable1 and fibrous in structure4 ,it is easily bent and is not elastic1 so it will not sustain pressure as well as cast iron4 ,it can be drawn out into wire of great tensile strength1 and can also be rolled into thin sheets 7sheet iron74 ,it melts at a high temperature 7about #afjj7 and is therefore forged into shape rather than cast4 ,if melted1 it would lose its fibrous structure and be changed into a low carbon steel4 ,steel4 ,steel1 like wrought iron1 is made by burning out from cast iron a part of the carbon1 silicon1 phosphorus1 and sulphur which it contains2 but the process is carried out in a very different way1 and usually1 though not always1 more carbon is found in steel than in wrought iron4 ,a number of processes are in use1 but nearly all the steel of commerce is made by one of the two following methods4 ,illustration3 ,fig4 #hg #a4 ,bessemer process4 ,this process1 invented about #ahfj1 is by far the most important4 ,it is carried out in great egg-shaped crucibles called converters 7,fig4 #hg71 each one of which will hold as much as #ae tons of steel4 ,the converter is built of steel and lined with silica4 ,it is mounted on trunnions ,t1 so that it can be tipped over on its side for filling and emptying4 ,one of the trunnions is hollow and a pipe ,p connects it with an air chamber ,a1 which forms a false bottom to the converter4 ,the true bottom is perforated1 so that air can be forced in by an air blast admitted through the trunnion and the air chamber4 ,white-hot1 liquid cast iron from a blast furnace is run into the converter through its open necklike top ,o1 the converter being tipped over to receive it2 the air blast is then turned on and the converter rotated to a nearly vertical position4 ,the elements in the iron are rapidly oxidized1 the silicon first and then the carbon4 ,the heat liberated in the oxidation1 largely due to the combustion of silicon1 keeps the iron in a molten condition4 ,when the carbon is practically all burned out cast iron or spiegel iron1 containing a known percentage of carbon1 is added and allowed to mix thoroughly with the fluid4 ,the steel is then run into molds1 and the ingots so formed are hammered or rolled into rails or other forms4 ,by this process any desired percentage of carbon can be added to the steel4 ,low carbon steel1 which does not differ much from wrought iron in composition1 is now made in this way and is replacing the more expensive wrought iron for many purposes4 ,the basic lining process4 ,when the cast iron contains phosphorus and sulphur in appreciable quantities1 the lining of the converter is made of dolomite4 ,the silicon and carbon burn1 followed by the phosphorus and sulphur1 and the anhydrides of acids so formed combine with the basic oxides of the lining1 forming a slag4 ,this is known as the basic lining process4 #b4 ,open-hearth process4 ,in this process a furnace very similar to a puddling furnace is used1 but it is lined with silica or dolomite instead of iron oxide4 ,a charge consisting in part of old scrap iron of any kind and in part of cast iron is melted in the furnace by a gas flame4 ,the silicon and carbon are slowly burned away1 and when a test shows that the desired percentage of carbon is present the steel is run out of the furnace4 ,steel may therefore be defined as the product of the ,bessemer or open-hearth processes4 ,properties of steel4 ,bessemer and open-hearth steel usually contain only a few tenths of a per cent of carbon1 less than #j4a silicon1 and a very much smaller quantity of phosphorus and sulphur4 ,any considerable amount of the latter elements makes the steel brittle1 the sulphur affecting it when hot1 and the phosphorus when cold4 ,this kind of steel is used for structural purposes1 for rails1 and for nearly all large steel articles4 ,it is hard1 malleable1 ductile1 and melts at a lower temperature than wrought iron4 ,it can be forged into shape1 rolled into sheets1 or cast in molds4 ,relation of the three varieties of iron4 ,it will be seen that wrought iron is usually very nearly pure iron1 while steel contains an appreciable amount of alloy material1 chiefly carbon1 and cast iron still more of the same substances4 ,it is impossible1 however1 to assign a given sample of iron to one of these three classes on the basis of its chemical composition alone4 ,a low carbon steel1 for example1 may contain less carbon than a given sample of wrought iron4 ,the real distinction between the three is the process by which they are made4 ,the product of the blast furnace is cast iron2 that of the puddling furnace is wrought iron2 that of the ,bessemer and open-hearth methods is steel4 ,tool steel4 ,steel designed for use in the manufacture of edged tools and similar articles should be relatively free from silicon and phosphorus1 but should contain from #j4e to #a4e carbon4 ,the percentage of carbon should be regulated by the exact use to which the steel is to be put4 ,steel of this character is usually made in small lots from either ,bessemer or open-hearth steel in the following way4 ,a charge of melted steel is placed in a large crucible and the calculated quantity of pure carbon is added4 ,the carbon dissolves in the steel1 and when the solution is complete the metal is poured out of the crucible4 ,this is sometimes called crucible steel4 ,tempering of steel4 ,steel containing from #j4e to #a4e carbon is characterized by the property of taking temper4 ,when the hot steel is suddenly cooled by plunging it into water or oil it becomes very hard and brittle4 ,on carefully reheating this hard form it gradually becomes less brittle and softer1 so that by regulating the temperature to which steel is reheated in tempering almost any condition of temper demanded for a given purpose1 such as for making springs or cutting tools1 can be obtained4 ,steel alloys4 ,it has been found that small quantities of a number of different elements when alloyed with steel very much improve its quality for certain purposes1 each element having a somewhat different effect4 ,among the elements most used in this connection are manganese1 silicon1 chromium1 nickel1 tungsten1 and molybdenum4 ,the usual method for adding these elements to the steel is to first prepare a very rich alloy of iron with the element to be added1 and then add enough of this alloy to a large quantity of the steel to bring it to the desired composition4 ,a rich alloy of iron with manganese or silicon can be prepared directly in a blast furnace1 and is called ferromanganese or ferrosilicon4 ,similar alloys of iron with the other elements mentioned are made in an electric furnace by reducing the mixed oxides with carbon4 ,pure iron4 ,perfectly pure iron is rarely prepared and is not adapted to commercial uses4 ,it can be made by reducing pure oxide of iron in a current of hydrogen at a high temperature4 ,prepared in this way it forms a black powder2 when melted it forms a tin-white metal which is less fusible and more malleable than wrought iron4 ,it is easily acted upon by moist air4 ,compounds of iron4 ,iron differs from the metals so far studied in that it is able to form two series of compounds in which the iron has two different valences4 ,in the one series the iron is divalent and forms compounds which in formulas and many chemical properties are similar to the corresponding zinc compounds4 ,it can also act as a trivalent metal1 and in this condition forms salts similar to those of aluminium4 ,those compounds in which the iron is divalent are known as ferrous compounds1 while those in which it is trivalent are known as ferric4 ,oxides of iron4 ,iron forms several oxides4 ,ferrous oxide 7,fe,o7 is not found in nature1 but can be prepared artificially in the form of a black powder which easily takes up oxygen1 forming ferric oxide3 #b;,fe,o ,o ,fe#b,o#c4 ,ferric oxide is the most abundant ore of iron and occurs in great deposits1 especially in the ,lake ,superior region4 ,it is found in many mineral varieties which vary in density and color1 the most abundant being hematite1 which ranges in color from red to nearly black4 ,when prepared by chemical processes it forms a red powder which is used as a paint pigment 7,venetian red7 and as a polishing powder 7rouge74 ,magnetite has the formula ,fe#c,o#d and is a combination of ,fe,o and ,fe#b,o#c4 ,it is a very valuable ore1 but is less abundant than hematite4 ,it is sometimes called magnetic oxide of iron1 or lodestone1 since it is a natural magnet4 ,ferrous salts4 ,these salts are obtained by dissolving iron in the appropriate acid1 or1 when insoluble1 by precipitation4 ,they are usually light green in color and crystallize well4 ,in chemical reactions they are quite similar to the salts of magnesium and zinc1 but differ from them in one important respect1 namely1 that they are easily changed into compounds in which the metal is trivalent4 ,thus ferrous chloride treated with chlorine or aqua regia is changed into ferric chloride3 ,fe,cl#b ,cl ,fe,cl#c4 ,ferrous hydroxide exposed to moist air is rapidly changed into ferric hydroxide3 #b;,fe7,,oh7#b ,h#b,o ,o #b;,fe7,,oh7#c4 ,ferrous sulphate 7copperas1 green vitriol7 7,fe,s,o#dg;,h#b,o74 ,ferrous sulphate is the most familiar ferrous compound4 ,it is prepared commercially as a by-product in the steel-plate mills4 ,steel plates are cleaned by the action of dilute sulphuric acid upon them1 and in the process some of the iron dissolves4 ,the liquors are concentrated and the green vitriol separates from them4 ,ferrous sulphide 7,fe,s74 ,ferrous sulphide is sometimes found in nature as a golden-yellow crystalline mineral4 ,it is formed as a black precipitate when a soluble sulphide and an iron salt are brought together in solution3 ,fe,s,o#d ,na#b,s ,fe,s ,na#b,,so#d4 ,it can also be made as a heavy dark-brown solid by fusing together the requisite quantities of sulphur and iron4 ,it is obtained as a by-product in the metallurgy of lead3 ,pb,s ,fe ,fe,s ,pb4 ,it is used in the laboratory in the preparation of hydrosulphuric acid3 ,fe,s #b;,h,cl ,fe,cl#b ,h#b,s4 ,iron disulphide 7pyrites7 7,fe,s#b74 ,this substance bears the same relation to ferrous sulphide that hydrogen dioxide does to water4 ,it occurs abundantly in nature in the form of brass-yellow cubical crystals and in compact masses4 ,sometimes the name fool's gold is applied to it from its superficial resemblance to the precious metal4 ,it is used in very large quantities as a source of sulphur dioxide in the manufacture of sulphuric acid1 since it burns readily in the air1 forming ferric oxide and sulphur dioxide3 #b;,fe,s#b #aa,o ,fe#b,o#c #d,,so#b4 ,ferrous carbonate 7,fe,c,o#c74 ,this compound occurs in nature as siderite1 and is a valuable ore4 ,it will dissolve to some extent in water containing carbon dioxide1 just as will calcium carbonate1 and waters containing it are called chalybeate waters4 ,these chalybeate waters are supposed to possess certain medicinal virtues and form an important class of mineral waters4 ,ferric salts4 ,ferric salts are usually obtained by treating an acidified solution of a ferrous salt with an oxidizing agent3 #b;,fe,cl#b #b;,h,cl ,o #b;,fe,cl#c ,h#b,o1 #b;,fe,s,o#d ,h#b,,so#d ,o ,fe#b7,,so#d7c ,h#b,o4 ,they are usually yellow or violet in color1 are quite soluble1 and as a rule do not crystallize well4 ,heated with water in the absence of free acid1 they hydrolyze even more readily than the salts of aluminium4 ,the most familiar ferric salts are the chloride and the sulphate4 ,ferric chloride 7,fe,cl#c74 ,this salt can be obtained most conveniently by dissolving iron in hydrochloric acid and then passing chlorine into the solution3 ,fe #b;,h,cl ,fe,cl#b #b;,h1 ,fe,cl#b ,cl ,fe,cl#c4 ,when the pure salt is heated with water it is partly hydrolyzed3 ,fe,cl#c #c ,h#b,o -- ,fe7,,oh7#c #c;,h,cl4 ,this is a reversible reaction1 however1 and hydrolysis can therefore be prevented by first adding a considerable amount of the soluble product of the reaction1 namely1 hydrochloric acid4 ,ferric sulphate 7,fe#b7,,so#d7c74 ,this compound can be made by treating an acid solution of green vitriol with an oxidizing agent4 ,it is difficult to crystallize and hard to obtain in pure condition4 ,when an alkali sulphate in proper quantity is added to ferric sulphate in solution an iron alum is formed1 and is easily obtained in large crystals4 ,the best known iron alums have the formulas ,k,fe7,,so#d7bab;,h#b,o and ,,nh#d;,fe7,,so#d7bab;,h#b,o4 ,they are commonly used when a pure ferric salt is required4 ,ferric hydroxide 7,fe7,,oh7#c74 ,when solutions of ferric salts are treated with ammonium hydroxide1 ferric hydroxide is formed as a rusty-red precipitate1 insoluble in water4 ,iron cyanides4 ,a large number of complex cyanides containing iron are known1 the most important being potassium ferrocyanide1 or yellow prussiate of potash 7,k#d;,fe,c#f,n#f71 and potassium ferricyanide1 or red prussiate of potash 7,k#c;,fe,c#f,n#f74 ,these compounds are the potassium salts of the complex acids of the formulas ,h#d;,fe,c#f,n#f and ,h#c;,fe,c#f,n#f4 ,oxidation of ferrous salts4 ,it has just been seen that when a ferrous salt is treated with an oxidizing agent in the presence of a free acid a ferric salt is formed3 #b;,fe,s,o#d ,h#b,,so#d ,o ,fe#b7,,so#d7c ,h#b,o4 ,in this reaction oxygen is used up1 and the valence of the iron is changed from #b to #c4 ,the same equation may be written #b;,fe1 #b,,so#d-- #b;,h1 ,,so#d-- ,o #b;,fe1 #c,,so#d-- ,h#b,o4 ,hydrogen ions have been oxidized to water1 while the charge of each iron ion has been increased from #b to #c4 ,in a similar way the conversion of ferrous chloride into ferric chloride may be written ,fe1 #b;,cl- ,cl ,fe1 #c;,cl-4 ,here again the valence of the iron and the charge on the iron ion has been increased from #b to #c1 though no oxygen has entered into the reaction4 ,as a rule1 however1 changes of this kind are brought about by the use of an oxidizing agent1 and are called oxidations4 ,the term oxidation is applied to all reactions in which the valence of the metal of a compound is increased1 or1 in other words1 to all reactions in which the charge of a cation is increased4 ,reduction of ferric salts4 ,the changes which take place when a ferric salt is converted into a ferrous salt are the reverse of the ones just described4 ,this is seen in the equation ,fe,cl#c ,h ,fe,cl#b ,h,cl ,in this reaction the valence of the iron has been changed from #c to #b4 ,the same equation may be written ,fe1 #c;,cl- ,h ,fe1 ,h #c;,cl- ,it will be seen that the charge of the iron ions has been diminished from #c to #b4 ,since these changes are the reverse of the oxidation changes just considered1 they are called reduction reactions4 ,the term reduction is applied to all processes in which the valence of the metal of a compound is diminished1 or1 in other words1 to all processes in which the charge on the cations is diminished4 ,,nickel ,,and ,,cobalt ,these elements occur sparingly in nature1 usually combined with arsenic or with arsenic and sulphur4 ,both elements have been found in the free state in meteorites4 ,like iron they form two series of compounds1 but the salts corresponding to the ferrous salts are the most common1 the ones corresponding to the ferric salts being difficult to obtain4 ,thus we have the chlorides ,ni,cl#bf;,h#b,o and ,co,cl#bf;,h#b,o2 the sulphates ,ni,s,o#dg;,h#b,o and ,co,s,o#dg;,h#b,o2 the nitrates ,ni7,,no#c7bf;,h#b,o and ,co7,,no#c7bf;,h#b,o4 ,nickel is largely used as an alloy with other metals4 ,alloyed with copper it forms coin metal from which five-cent pieces are made1 with copper and zinc it forms ,german silver1 and when added to steel in small quantities nickel steel is formed which is much superior to common steel for certain purposes4 ,when deposited by electrolysis upon the surface of other metals such as iron1 it forms a covering which will take a high polish and protects the metal from rust1 nickel not being acted upon by moist air4 ,salts of nickel are usually green4 ,compounds of cobalt fused with glass give it an intensely blue color4 ,in powdered form such glass is sometimes used as a pigment called smalt4 ,cobalt salts1 which contain water of crystallization1 are usually cherry red in color2 when dehydrated they become blue4 ,,exercises #a4 ,in the manufacture of cast iron1 why is the air heated before being forced into the furnace8 #b4 ,write the equations showing how each of the following compounds of iron could be obtained from the metal itself3 ferrous chloride1 ferrous hydroxide1 ferrous sulphate1 ferrous sulphide1 ferrous carbonate1 ferric chloride1 ferric sulphate1 ferric hydroxide4 #c4 ,account for the fact that a solution of sodium carbonate1 when added to a solution of a ferric salt1 precipitates an hydroxide and not a carbonate4 #d4 ,calculate the percentage of iron in each of the common iron ores4 #e4 ,one ton of steel prepared by the ,bessemer process is found by analysis to contain #j4b carbon4 ,what is the minimum weight of carbon which must be added in order that the steel may be made to take a temper8 ,,chapter ,,xxviii ,,copper1 ,,mercury1 ,,and ,,silver ,,formulas ,,of ,,oxides ,,symbol ,,atomic ,,density ,,melting ,,weight ,,point ous ic ,copper ,cu #fc4f #h4hi #ajhd ,cu#b,o ,cu,o ,mercury ,hg #bjj4jj #ac4eif -#ci4e ,hg#b,o ,hg,o ,silver ,ag #ajg4ic #aj4e #ifj ,ag#b,o ,ag,o ,the family4 ,by referring to the periodic arrangement of the elements 7page #afh71 it will be seen that mercury is not included in the same family with copper and silver4 ,since the metallurgy of the three elements is so similar1 however1 and since they resemble each other so closely in chemical properties1 it is convenient to class them together for study4 #a4 ,occurrence4 ,the three elements occur in nature to some extent in the free state1 but are usually found as sulphides4 ,their ores are easy to reduce4 #b4 ,properties4 ,they are heavy metals of high luster and are especially good conductors of heat and electricity4 ,they are not very active chemically4 ,neither hydrochloric nor dilute sulphuric acid has any appreciable action upon them4 ,concentrated sulphuric acid attacks all three1 forming metallic sulphates and evolving sulphur dioxide1 while nitric acid1 both dilute and concentrated1 converts them into nitrates with the evolution of oxides of nitrogen4 #c4 ,two series of salts4 ,copper and mercury form oxides of the types ,m#b,o and ,,mo1 as well as two series of salts4 ,in one series the metals are univalent and the salts have formulas like those of the sodium salts4 ,they are called cuprous and mercurous salts4 ,in the other series the metals are divalent and resemble magnesium salts in formulas4 ,these are called cupric and mercuric salts4 ,silver forms only one series of salts1 being always a univalent metal4 ,,copper ,occurrence4 ,the element copper has been used for various purposes since the earliest days of history4 ,it is often found in the metallic state in nature1 large masses of it occurring pure in the ,lake ,superior region and in other places to a smaller extent4 ,the most valuable ores are the following3 ,cuprite ,cu#b,o4 ,chalcocite ,cu#b,s4 ,chalcopyrite ,cu,fe,s#b4 ,bornite ,cu#c;,fe,s#c4 ,malachite ,cu,c,o#c;,cu7,,oh7#b4 ,azurite #b;,cu,c,o#c;,cu7,,oh7#b4 ,metallurgy of copper4 ,ores containing little or no sulphur are easy to reduce4 ,they are first crushed and the earthy impurities washed away4 ,the concentrated ore is then mixed with carbon and heated in a furnace1 metallic copper resulting from the reduction of the copper oxide by the hot carbon4 ,metallurgy of sulphide ores4 ,much of the copper of commerce is made from chalcopyrite and bornite1 and these ores are more difficult to work4 ,they are first roasted in the air1 by which treatment much of the sulphur is burned to sulphur dioxide4 ,the roasted ore is then melted in a small blast furnace or in an open one like a puddling furnace4 ,in melting1 part of the iron combines with silica to form a slag of iron silicate4 ,the product1 called crude matte1 contains about #ej copper together with sulphur and iron4 ,further purification is commonly carried on by a process very similar to the ,bessemer process for steel4 ,the converter is lined with silica1 and a charge of matte from the melting furnace1 together with sand1 is introduced1 and air is blown into the mass4 ,by this means the sulphur is practically all burned out by the air1 and the remaining iron combines with silica and goes off as slag4 ,the copper is poured out of the converter and molded into anode plates for refining4 ,refining of copper4 ,impure copper is purified by electrolysis4 ,a large plate of it1 serving as an anode1 is suspended in a tank facing a thin plate of pure copper1 which is the cathode4 ,the tank is filled with a solution of copper sulphate and sulphuric acid to serve as the electrolyte4 ,a current from a dynamo passes from the anode to the cathode1 and the copper1 dissolving from the anode1 is deposited upon the cathode in pure form1 while the impurities collect on the bottom of the tank4 ,electrolytic copper is one of the purest of commercial metals and is very nearly pure copper4 ,recovery of gold and silver4 ,gold and silver are often present in small quantities in copper ores1 and in electrolytic refining these metals collect in the muddy deposit on the bottom of the tank4 ,the mud is carefully worked over from time to time and the precious metals extracted from it4 ,a surprising amount of gold and silver is obtained in this way4 ,properties of copper4 ,copper is a rather heavy metal of density #h4i1 and has a characteristic reddish color4 ,it is rather soft and is very malleable1 ductile1 and flexible1 yet tough and strong2 it melts at #ajhd4 ,as a conductor of heat and electrical energy it is second only to silver4 ,hydrochloric acid1 dilute sulphuric acid1 and fused alkalis are almost without action upon it2 nitric acid and hot1 concentrated sulphuric acid1 however1 readily dissolve it4 ,in moist air it slowly becomes covered with a thin layer of green basic carbonate2 heated in the air it is easily oxidized to black copper oxide 7,cu,o74 ,uses4 ,copper is extensively used for electrical purposes1 for roofs and cornices1 for sheathing the bottom of ships1 and for making alloys4 ,in the following table the composition of some of these alloys is indicated3 ,,composition ,,of ,,alloys ,,of ,,copper ,,in ,,percentages ,aluminium bronze copper 7#ij to #ig71 aluminium 7#c to #aj74 ,brass copper 7#fc to #gc71 zinc 7#bg to #cg74 ,bronze copper 7#gj to #ie71 zinc 7#a to #be71 tin 7#a to #ah74 ,german silver copper 7#ef to #fj71 zinc 7#bj71 nickel 7#bj to #be74 ,gold coin copper 7#aj71 gold 7#ij74 ,gun metal copper 7#ij71 tin 7#aj74 ,nickel coin copper 7#ge71 nickel 7#be7 ,silver coin copper 7#aj71 silver 7#ij74 ,electrotyping4 ,matter is often printed from electrotype plates which are prepared as follows4 ,the matter is set up in type and wax is firmly pressed down upon the face of it until a clear impression is obtained4 ,the impressed side of the wax is coated with graphite and the impression is made the cathode in an electrolytic cell containing a copper salt in solution4 ,when connected with a current the copper is deposited as a thin sheet upon the letters in wax1 and when detached is a perfect copy of the type1 the under part of the letters being hollow4 ,the sheet is strengthened by pouring on the under surface a suitable amount of molten metal 7commercial lead is used74 ,the sheet so strengthened is then used in printing4 ,two series of copper compounds4 ,copper1 like iron1 forms two series of compounds3 in the cuprous compounds it is univalent2 in the cupric it is divalent4 ,the cupric salts are much the more common of the two1 since the cuprous salts pass readily into cupric by oxidation4 ,cuprous compounds4 ,the most important cuprous compound is the oxide 7,cu#b,o71 which occurs in nature as ruby copper or cuprite4 ,it is a bright red substance and can easily be prepared by heating copper to a high temperature in a limited supply of air4 ,it is used for imparting a ruby color to glass4 ,by treating cuprous oxide with different acids a number of cuprous salts can be made4 ,many of these are insoluble in water1 the chloride 7,cu,cl7 being the best known4 ,when suspended in dilute hydrochloric acid it is changed into cupric chloride1 the oxygen taking part in the reaction being absorbed from the air3 #b;,cu,cl #b;,h,cl ,o #b;,cu,cl#b ,h#b,o4 ,cupric compounds4 ,cupric salts are easily made by dissolving cupric oxide in acids1 or1 when insoluble1 by precipitation4 ,most of them are blue or green in color1 and the soluble ones crystallize well4 ,since they are so much more familiar than the cuprous salts1 they are frequently called merely copper salts4 ,cupric oxide 7,cu,o74 ,this is a black insoluble substance obtained by heating copper in excess of air1 or by igniting the hydroxide or nitrate4 ,it is used as an oxidizing agent4 ,cupric hydroxide 7,cu7,,oh7#b74 ,the hydroxide prepared by treating a solution of a copper salt with sodium hydroxide is a light blue insoluble substance which easily loses water and changes into the oxide4 ,heat applied to the liquid containing the hydroxide suspended in it serves to bring about the reaction represented by the equation ,cu7,,oh7#b ,cu,o ,h#b,o4 ,cupric sulphate 7blue vitriol7 7,cu,s,o#de;,h#b,o74 ,this substance1 called blue vitriol or bluestone1 is obtained as a by-product in a number of processes and is produced in very large quantities4 ,it forms large blue crystals1 which lose water when heated and crumble to a white powder4 ,the salt finds many uses1 especially in electrotyping and in making electrical batteries4 ,cupric sulphide 7,cu,s74 ,the insoluble black sulphide 7,cu,s7 is easily prepared by the action of hydrosulphuric acid upon a solution of a copper salt3 ,cu,s,o#d ,h#b,s ,cu,s ,h#b,,so#d4 ,it is insoluble in water and dilute acids4 ,,mercury ,occurrence4 ,mercury occurs in nature chiefly as the sulphide 7,hg,s7 called cinnabar1 and in globules of metal inclosed in the cinnabar4 ,the mercury mines of ,spain have long been famous1 ,california being the next largest producer4 ,metallurgy4 ,mercury is a volatile metal which has but little affinity for oxygen4 ,sulphur1 on the other hand1 readily combines with oxygen4 ,these facts make the metallurgy of mercury very simple4 ,the crushed ore1 mixed with a small amount of carbon to reduce any oxide or sulphate that might be formed1 is roasted in a current of air4 ,the sulphur burns to sulphur dioxide1 while the mercury is converted into vapor and is condensed in a series of condensing vessels4 ,the metal is purified by distillation4 ,properties4 ,mercury is a heavy silvery liquid with a density of #ac4eif4 ,it boils at #ceg and solidifies at -#ci4e4 ,small quantities of many metals dissolve in it1 forming liquid alloys1 while with larger quantities it forms solid alloys4 ,the alloys of mercury are called amalgams4 ,toward acids mercury conducts itself very much like copper2 it is easily attacked by nitric and hot1 concentrated sulphuric acids1 while cold sulphuric and hydrochloric acids have no effect on it4 ,uses4 ,mercury is extensively used in the construction of scientific instruments1 such as the thermometer and barometer1 and as a liquid over which to collect gases which are soluble in water4 ,the readiness with which it alloys with silver and gold makes it very useful in the extraction of these elements4 ,compounds of mercury4 ,like copper1 mercury forms two series of compounds3 the mercurous1 of which mercurous chloride 7,hg,cl7 is an example2 and the mercuric1 represented by mercuric chloride 7,hg,cl#b74 ,mercuric oxide 7,hg,o74 ,mercuric oxide can be obtained either as a brick-red or as a yellow substance4 ,when mercuric nitrate is heated carefully the red modification is formed in accordance with the equation ,hg7,,no#c7b ,hg,o #b,,no#b ,o4 ,the yellow modification is prepared by adding a solution of a mercuric salt to a solution of sodium or potassium hydroxide3 ,hg7,,no#c7b #b,na,o,h #b,na,n,o#c ,hg7,,oh7#b1 ,hg7,,oh7#b ,hg,o ,h#b,o4 ,when heated the oxide darkens until it becomes almost black2 at a higher temperature it decomposes into mercury and oxygen4 ,it was by this reaction that oxygen was discovered4 ,mercurous chloride 7calomel7 7,hg,cl74 ,being insoluble1 mercurous chloride is precipitated as a white solid when a soluble chloride is added to a solution of mercurous nitrate3 ,hg,n,o#c ,na,cl ,hg,cl ,na,n,o#c4 ,commercially it is manufactured by heating a mixture of mercuric chloride and mercury4 ,when exposed to the light it slowly changes into mercuric chloride and mercury3 #b;,hg,cl ,hg,cl#b ,hg4 ,it is therefore protected from the light by the use of colored bottles4 ,it is used in medicine4 ,most mercurous salts are insoluble in water1 the principal soluble one being the nitrate1 which is made by the action of cold1 dilute nitric acid on mercury4 ,mercuric chloride 7corrosive sublimate7 7,hg,cl#b74 ,this substance can be made by dissolving mercuric oxide in hydrochloric acid4 ,on a commercial scale it is made by subliming a mixture of common salt and mercuric sulphate3 #b,na,cl ,hg,s,o#d ,hg,cl#b ,na#b,,so#d4 ,the mercuric chloride1 being readily volatile1 vaporizes and is condensed again in cool vessels4 ,like mercurous chloride it is a white solid1 but differs from it in that it is soluble in water4 ,it is extremely poisonous and in dilute solutions is used as an antiseptic in dressing wounds4 ,mercuric sulphide 7,hg,s74 ,as cinnabar this substance forms the chief native compound of mercury1 occurring in red crystalline masses4 ,by passing hydrosulphuric acid into a solution of a mercuric salt it is precipitated as a black powder1 insoluble in water and acids4 ,by other means it can be prepared as a brilliant red powder known as vermilion1 which is used as a pigment in fine paints4 ,the iodides of mercury4 ,if a solution of potassium iodide is added to solutions of a mercurous and a mercuric salt respectively1 the corresponding iodides are precipitated4 ,mercuric iodide is the more important of the two1 and as prepared above is a red powder which changes to yellow on heating to #aej4 ,the yellow form on cooling changes back again to the red form1 or may be made to do so by rubbing it with a knife blade or some other hard object4 ,,silver ,occurrence4 ,silver is found in small quantities in the uncombined state2 usually1 however1 it occurs in combination with sulphur1 either as the sulphide 7,ag#b,s7 or as a small constituent of other sulphides1 especially those of lead and copper4 ,it is also found alloyed with gold4 ,metallurgy4 ,parkes's process4 ,silver is usually smelted in connection with lead4 ,the ores are worked over together1 as described under lead1 and the lead and silver obtained as an alloy1 the silver being present in small quantity4 ,the alloy is melted and metallic zinc is stirred in4 ,zinc will alloy with silver but not with lead1 and it is found that the silver leaves the lead and1 in the form of an alloy with zinc1 forms as a crust upon the lead and is skimmed off4 ,this crust1 which1 of course1 contains lead adhering to it1 is partially melted and the most of the lead drained off4 ,the zinc is removed by distillation1 and the residue is melted on an open hearth in a current of air2 by this means the zinc and lead remaining with the silver are changed into oxides and the silver remains behind unaltered4 ,amalgamation process4 ,in some localities the old amalgamation process is used4 ,the silver ore is treated with common salt and ferrous compounds1 which process converts the silver first into chloride and then into metallic silver4 ,mercury is then added and thoroughly mixed with the mass1 forming an amalgam with the silver4 ,after some days the earthy materials are washed away and the heavier amalgam is recovered4 ,the mercury is distilled off and the silver left in impure form4 ,refining silver4 ,the silver obtained by either of the above processes may still contain copper1 gold1 and iron1 and is refined by parting with sulphuric acid4 ,the metal is heated with strong sulphuric acid which dissolves the silver1 copper1 and iron present1 but not the gold4 ,in the solution of silver sulphate so obtained copper plates are suspended1 upon which the pure silver precipitates1 the copper going into solution as sulphate1 as shown in the equation ,ag#b,,so#d ,cu #b;,ag ,cu,s,o#d4 ,the solution obtained as a by-product in this process furnishes most of the blue vitriol of commerce4 ,silver is also refined by electrolytic methods similar to those used in refining copper4 ,properties of silver4 ,silver is a heavy1 rather soft1 white metal1 very ductile and malleable and capable of taking a high polish4 ,it surpasses all other metals as a conductor of heat and electricity1 but is too costly to find extensive use for such purposes4 ,it melts at a little lower temperature than copper 7#ifa74 ,it alloys readily with other heavy metals1 and when it is to be used for coinage a small amount of copper--from #h to #aj--;is nearly always melted with it to give it hardness4 ,it is not acted upon by water or air1 but is quickly tarnished when in contact with sulphur compounds1 turning quite black in time4 ,hydrochloric acid and fused alkalis do not act upon it1 but nitric acid and hot1 concentrated sulphuric acid dissolve it with ease4 ,illustration3 ,fig4 #hh ,electroplating4 ,since silver is not acted upon by water or air1 and has a pleasing appearance1 it is used to coat various articles made of cheaper metals4 ,such articles are said to be silver plated4 ,the process by which this is done is called electroplating4 ,it is carried on as follows3 ,the object to be plated 7such as a spoon7 is attached to a wire and dipped into a solution of a silver salt4 ,electrical connection is made in such a way that the article to be plated serves as the cathode1 while the anode is made up of one or more plates of silver 7,fig4 #hh1 ,a74 ,when a current is passed through the electrolyte silver dissolves from the anode plate and deposits on the cathode in the form of a closely adhering layer4 ,by making the proper change in the electrolyte and anode plate objects may be plated with gold and other metals4 ,compounds of silver4 ,silver forms two oxides but only one series of salts1 namely1 the one which corresponds to the mercurous and cuprous series4 ,silver nitrate 7lunar caustic7 7,ag,n,o#c74 ,this salt is easily prepared by dissolving silver in nitric acid and evaporating the resulting solution4 ,it crystallizes in flat plates1 and when heated carefully can be melted without decomposition4 ,when cast into sticks it is called lunar caustic1 for it has a very corrosive action on flesh1 and is sometimes used in surgery to burn away abnormal growths4 ,the alchemists designated the metals by the names of the heavenly bodies4 ,the moon 7luna7 was the symbol for silver2 hence the name lunar caustic4 ,silver sulphide 7,ag#b,s74 ,this occurs in nature and constitutes one of the principal ores of silver4 ,it can be obtained in the form of a black solid by passing hydrosulphuric acid through a solution of silver nitrate4 ,compounds of silver with the halogens4 ,the chloride1 bromide1 and iodide of silver are insoluble in water and acids1 and are therefore precipitated by bringing together a soluble halogen salt with silver nitrate3 ,ag,n,o#c ,k,cl ,ag,cl ,,kno#c4 ,they are remarkable for the fact that they are very sensitive to the action of light1 undergoing a change of color and chemical composition when exposed to sunlight1 especially if in contact with organic matter such as gelatin4 ,photography4 ,the art of photography is based on the fact that the halogen compounds of silver are affected by the light1 particularly in the presence of organic matter4 ,from a chemical standpoint the processes involved may be described under two heads3 7#a7 the preparation of the negative2 7#b7 the preparation of the print4 #a4 ,preparation of the negative4 ,the plate used in the preparation of the negative is made by spreading a thin layer of gelatin1 in which silver bromide is suspended 7silver iodide is sometimes added also71 over a glass plate or celluloid film and allowing it to dry4 ,when the plate so prepared is placed in a camera and the image of some object is focused upon it1 the silver salt undergoes a change which is proportional at each point to the intensity of the light falling upon it4 ,in this way an image of the object photographed is produced upon the plate1 which is1 however1 invisible and is therefore called latent4 ,it can be made visible by the process of developing4 ,to develop the image the exposed plate is immersed in a solution of some reducing agent called the developer4 ,the developer reduces that portion of the silver salt which has been affected by the light1 depositing it in the form of black metallic silver which closely adheres to the plate4 ,the unaffected silver salt1 upon which the developer has no action1 must now be removed from the plate4 ,this is done by immersing the plate in a solution of sodium thiosulphate 7hypo74 ,after the silver salt has been dissolved off1 the plate is washed with water and dried4 ,the plate so prepared is called the negative because it is a picture of the object photographed1 with the lights exactly reversed4 ,this is called fixing the negative4 #b4 ,preparation of the print4 ,the print is made from paper which is prepared in the same way as the negative plate4 ,the negative is placed upon this paper and exposed to the light in such a way that the light must pass through the negative before striking the paper4 ,if the paper is coated with silver chloride1 a visible image is produced1 in which case a developer is not needed4 ,the proofs are made in this way4 ,in order to make them permanent the unchanged silver chloride must be dissolved off with sodium thiosulphate4 ,the print is then toned by dipping it into a solution of gold or platinum salts4 ,the silver on the print passes into solution1 while the gold or platinum takes its place4 ,these metals give a characteristic color or tone to the print1 the gold making it reddish brown1 while the platinum gives it a steel-gray tone4 ,if a silver bromide paper is used in making the print1 a latent image is produced which must be developed as in the case of the negative itself4 ,the silver bromide is much more sensitive than the chloride1 so that the printing can be done in artificial light4 ,since the darkest places on the negative cut off the most light1 it is evident that the lights of the print will be the reverse of those of the negative1 and will therefore correspond to those of the object photographed4 ,the print is therefore called the positive4 ,,exercises #a4 ,account for the fact that copper has been used for so long a time4 #b4 ,write equations for the action of concentrated sulphuric and nitric acids upon the metals of this family4 #c4 ,how would you account for the fact that normal copper sulphate is slightly acid to litmus8 #d4 ,contrast the action of heat on cupric nitrate and mercuric nitrate4 #e4 ,state reasons why mercury is adapted for use in thermometers and barometers4 #f4 ,how could you distinguish between mercurous chloride and mercuric chloride8 #g4 ,write equations for the preparation of mercuric and mercurous iodides4 #h4 ,how would you account for the fact that solutions of the different salts of a metal usually have the same color8 #i4 ,crude silver usually contains iron and lead4 ,what would become of these metals in refining by parting with sulphuric acid8 #aj4 ,in the amalgamation process for extracting silver1 how does ferrous chloride convert silver chloride into silver8 ,write equation4 ,why is the silver sulphide first changed into silver chloride8 #aa4 ,what impurities would you expect to find in the copper sulphate prepared from the refining of silver8 #ab4 ,how could you prepare pure silver chloride from a silver coin8 #ac4 ,mercuric nitrate and silver nitrate are both white solids soluble in water4 ,how could you distinguish between them8 #ad4 ,account for the fact that sulphur waters turn a silver coin black2 also for the fact that a silver spoon is blackened by foods 7eggs1 for example7 containing sulphur4 #ae4 ,when a solution of silver nitrate is added to a solution of potassium chlorate no precipitate forms4 ,how do you account for the fact that a precipitate of silver chloride is not formed8 ,,chapter ,,xxix ,,tin ,,and ,,lead ,,symbol ,,atomic ,,density ,,melting ,,common ,,oxides ,,weight ,,point ,tin ,sn #aai4j #g4ce #bce ,sn,o ,sn,o#b ,lead ,pb #bjf4i #aa4ch #cbg ,pb,o ,pb#c,o#d ,pb,o#b ,the family4 ,tin and lead1 together with silicon and germanium1 form a family in ,group ,,iv of the periodic table4 ,silicon has been discussed along with the non-metals1 while germanium1 on account of its rarity1 needs only to be mentioned4 ,the other family of ,group ,,iv includes carbon1 already described1 and a number of rare elements4 ,,tin ,occurrence4 ,tin is found in nature chiefly as the oxide 7,sn,o#b71 called cassiterite or tinstone4 ,the most famous mines are those of ,cornwall in ,england1 and of the ,malay ,peninsula and ,east ,india ,islands2 in small amounts tinstone is found in many other localities4 ,metallurgy4 ,the metallurgy of tin is very simple4 ,the ore1 separated as far as possible from earthy materials1 is mixed with carbon and heated in a furnace1 the reduction taking place readily4 ,the equation is ,sn,o#b ,c ,sn ,,co#b4 ,the metal is often purified by carefully heating it until it is partly melted2 the pure tin melts first and can be drained away from the impurities4 ,properties4 ,pure tin1 called block tin1 is a soft white metal with a silver-like appearance and luster2 it melts readily 7#bce7 and is somewhat lighter than copper1 having a density of #g4c4 ,it is quite malleable and can be rolled out into very thin sheets1 forming tin foil2 most tin foil1 however1 contains a good deal of lead4 ,under ordinary conditions it is quite unchanged by air or moisture1 but at a high temperature it burns in air1 forming the oxide ,sn,o#b4 ,dilute acids have no effect upon it1 but concentrated acids attack it readily4 ,concentrated hydrochloric acid changes it into the chloride ,sn #b;,h,cl ,sn,cl#b #b;,h4 ,with sulphuric acid tin sulphate and sulphur dioxide are formed3 ,sn #b;,h#b,,so#d ,sn,s,o#d ,,so#b #b;,h#b,o ,concentrated nitric acid oxidizes it1 forming a white insoluble compound of the formula ,h#b,sn,o#c1 called metastannic acid3 #c,sn #d;,,hno#c ,h#b,o #c;,h#b,sn,o#c #d,,no4 ,uses of tin4 ,a great deal of tin is made into tin plate by dipping thin steel sheets into the melted metal4 ,owing to the way in which tin resists the action of air and dilute acids1 tin plate is used in many ways1 such as in roofing1 and in the manufacture of tin cans1 cooking vessels1 and similar articles4 ,many useful alloys contain tin1 some of which have been mentioned in connection with copper4 ,when tin is alloyed with other metals of low melting point1 soft1 easily melted alloys are formed which are used for friction bearings in machinery2 tin1 antimony1 lead1 and bismuth are the chief constituents of these alloys4 ,pewter and soft solder are alloys of tin and lead4 ,compounds of tin4 ,tin forms two series of compounds3 the stannous1 in which the tin is divalent1 illustrated in the compounds ,sn,o1 ,sn,s1 ,sn,cl#b2 the stannic1 in which it is tetravalent as shown in the compounds ,sn,o#b1 ,sn,s#b4 ,there is also an acid1 ,h#b,sn,o#c1 called stannic acid1 which forms a series of salts called stannates4 ,while this acid has the same composition as metastannic acid1 the two are quite different in their chemical properties4 ,this difference is probably due to the different arrangement of the atoms in the molecules of the two substances4 ,only a few compounds of tin need be mentioned4 ,stannic oxide 7,sn,o#b74 ,stannic oxide is of interest1 since it is the chief compound of tin found in nature4 ,it is sometimes found in good-sized crystals1 but as prepared in the laboratory is a white powder4 ,when fused with potassium hydroxide it forms potassium stannate1 acting very much like silicon dioxide3 ,sn,o#b #b,,koh ,k#b,sn,o#c ,h#b,o4 ,chlorides of tin4 ,stannous chloride is prepared by dissolving tin in concentrated hydrochloric acid and evaporating the solution to crystallization4 ,the crystals which are obtained have the composition ,sn,cl#bb;,h#b,o1 and are known as tin crystals4 ,by treating a solution of stannous chloride with aqua regia1 stannic chloride is formed3 ,sn,cl#b #b;,cl ,sn,cl#d4 ,the salt which crystallizes from such a solution has the composition ,sn,cl#de;,h#b,o1 and is known commercially as oxymuriate of tin4 ,if metallic tin is heated in a current of dry chlorine1 the anhydrous chloride 7,sn,cl#d7 is obtained as a heavy colorless liquid which fumes strongly on exposure to air4 ,the ease with which stannous chloride takes up chlorine to form stannic chloride makes it a good reducing agent in many reactions1 changing the higher chlorides of metals to lower ones4 ,thus mercuric chloride is changed into mercurous chloride3 ,sn,cl#b #b;,hg,cl#b ,sn,cl#d #b;,hg,cl4 ,if the stannous chloride is in excess1 the reaction may go further1 producing metallic mercury3 ,sn,cl#b #b;,hg,cl ,sn,cl#d #b;,hg4 ,ferric chloride is in like manner reduced to ferrous chloride3 ,sn,cl#c #b;,fe,cl#c ,sn,cl#d #b;,fe,cl#b4 ,the chlorides of tin1 as well as the alkali stannates1 are much used as mordants in dyeing processes4 ,the hydroxides of tin and free stannic acid1 which are easily liberated from these compounds1 possess in very marked degree the power of fixing dyes upon fibers1 as explained under aluminium4 ,,lead ,occurrence4 ,lead is found in nature chiefly as the sulphide 7,pb,s71 called galena2 to a much smaller extent it occurs as carbonate1 sulphate1 chromate1 and in a few other forms4 ,practically all the lead of commerce is made from galena1 two general methods of metallurgy being in use4 ,metallurgy4 #a4 ,the sulphide is melted with scrap iron1 when iron sulphide and metallic lead are formed2 the liquid lead1 being the heavier1 sinks to the bottom of the vessel and can be drawn off3 ,pb,s ,fe ,pb ,fe,s4 #b4 ,the sulphide is roasted in the air until a part of it has been changed into oxide and sulphate4 ,the air is then shut off and the heating continued1 the reactions indicated in the following equations taking place3 #b,pb,o ,pb,s #c,pb ,,so#b1 ,pb,s,o#d ,pb,s #b,pb #b,,so#b4 ,the lead so prepared usually contains small amounts of silver1 arsenic1 antimony1 copper1 and other metals4 ,the silver is removed by ,parkes's method1 as described under silver1 and the other metals in various ways4 ,the lead of commerce is one of the purest commercial metals1 containing as a rule only a few tenths per cent of impurities4 ,properties4 ,lead is a heavy metal 7den4 #aa4cc7 which has a brilliant silvery luster on a freshly cut surface1 but which soon tarnishes to a dull blue-gray color4 ,it is soft1 easily fused 7melting at #cbg71 and quite malleable1 but has little toughness or strength4 ,it is not acted upon to any great extent by the oxygen of the air under ordinary conditions1 but is changed into oxide at a high temperature4 ,with the exception of hydrochloric and sulphuric acids1 most acids1 even very weak ones1 act upon it1 forming soluble lead salts4 ,hot1 concentrated hydrochloric and sulphuric acids also attack it to a slight extent4 ,uses4 ,lead is employed in the manufacture of lead pipes and in large storage batteries4 ,in the form of sheet lead it is used in lining the chambers of sulphuric acid works and in the preparation of paint pigments4 ,some alloys of lead1 such as solder and pewter 7lead and tin71 shot 7lead and arsenic71 and soft bearing metals1 are widely used4 ,type metal consists of lead1 antimony1 and sometimes tin4 ,compounds of lead form several important pigments4 ,compounds of lead4 ,in nearly all its compounds lead has a valence of #b1 but a few corresponding to stannic compounds have a valence of #d4 ,lead oxides4 ,lead forms a number of oxides1 the most important of which are litharge1 red lead or minium1 and lead peroxide4 #a4 ,litharge 7,pb,o74 ,this oxide forms when lead is oxidized at a rather low temperature1 and is obtained as a by-product in silver refining4 ,it is a pale yellow powder1 and has a number of commercial uses4 ,it is easily soluble in nitric acid3 ,pb,o #b;,,hno#c ,pb7,,no#c7b ,h#b,o4 #b4 ,red lead1 or minium 7,pb#c,o#d74 ,minium is prepared by heating lead 7or litharge7 to a high temperature in the air4 ,it is a heavy powder of a beautiful red color1 and is much used as a pigment4 #c4 ,lead peroxide 7,pb,o#b74 ,this is left as a residue when minium is heated with nitric acid3 ,pb#c,o#d #d;,,hno#c #b,pb7,,no#c7b ,pb,o#b #b;,h#b,o4 ,it is a brown powder which easily gives up a part of its oxygen and1 like manganese dioxide and barium dioxide1 is a good oxidizing agent4 ,soluble salts of lead4 ,the soluble salts of lead can be made by dissolving 7,pb7,c#b;,h#c,o#b7bc;,h#b,o71 litharge in acids4 ,lead acetate called sugar of lead1 and lead nitrate 7,pb7,,no#c7b7 are the most familiar examples4 ,they are while crystalline solids and are poisonous in character4 ,insoluble salts of lead2 lead carbonate4 ,while the normal carbonate of lead 7,pb,c,o#c7 is found to some extent1 in nature and can be prepared in the laboratory1 basic carbonates of varying composition are much more easy to obtain4 ,one of the simplest of these has the composition #b,pb,c,o#c,pb7,,oh7#b4 ,a mixture of such carbonates is called white lead4 ,this is prepared on a large scale as a paint pigment and as a body for paints which are to be colored with other substances4 ,white lead4 ,white lead is an amorphous white substance which1 when mixed with oil1 has great covering power1 that is1 it spreads out in an even waxy film1 free from streaks and lumps1 and covers the entire surface upon which it is spread4 ,its disadvantage as a pigment lies in the fact that it gradually blackens when exposed to sulphur compounds1 which are often present in the air1 forming black lead sulphide 7,pb,s74 ,technical preparation of white lead4 ,different methods are used in the preparation of white lead1 but the old one known as the ,dutch process is still the principal one employed4 ,in this process1 earthenware pots about ten inches high and of the shape shown in ,fig4 #hi are used4 ,in the bottom ,a is placed a #c solution of acetic acid 7vinegar answers the purpose very well74 ,the space above this is filled with thin1 perforated1 circular pieces of lead1 supported by the flange ,b of the pot4 ,these pots are placed close together on a bed of tan bark on the floor of a room known as the corroding room4 ,they are covered over with boards1 upon which tan bark is placed1 and another row of pots is placed on this4 ,in this way the room is filled4 ,the white lead is formed by the fumes of the acetic acid1 together with the carbon dioxide set free in the fermentation of the tan bark acting on the lead4 ,about three months are required to complete the process4 ,illustration #a3 ,fig4 #hi ,lead sulphide 7,pb,s74 ,in nature this compound occurs in highly crystalline condition1 the crystals having much the same luster as pure lead4 ,it is readily prepared in the laboratory as a black precipitate1 by the action of hydrosulphuric acid upon soluble lead salts3 ,pb7,,no#c7b ,h#b,s ,pb,s #b;,,hno#c4 ,it is insoluble both in water and in dilute acids4 ,other insoluble salts4 ,lead chromate 7,pb,cr,o#d7 is a yellow substance produced by the action of a soluble lead salt upon a soluble chromate1 thus3 ,k#b;,cr,o#d ,pb7,,no#c7b ,pb,cr,o#d #b ,,kno#c4 ,it is used as a yellow pigment4 ,lead sulphate 7,pb,s,o#d7 is a white substance sometimes found in nature and easily prepared by precipitation4 ,lead chloride 7,pb,cl#b7 is likewise a white substance nearly insoluble in cold water1 but readily soluble in boiling water4 ,thorium and cerium4 ,these elements are found in a few rare minerals1 especially in the monazite sand of the ,carolinas and ,brazil4 ,the oxides of these elements are used in the preparation of the ,welsbach mantles for gas lights1 because of the intense light given out when a mixture of the oxides is heated4 ,these mantles contain the oxides of cerium and thorium in the ratio of about #a of the former to #ii of the latter4 ,compounds of thorium1 like those of radium1 are found to possess radio-activity1 but in a less degree4 ,,exercises #a4 ,how could you detect lead if present in tin foil8 #b4 ,stannous chloride reduces gold chloride 7,au,cl#c7 to gold4 ,give equation4 #c4 ,what are the products of hydrolysis when stannic chloride is used as a mordant8 #d4 ,how could you detect arsenic1 antimony1 or copper in lead8 #e4 ,why is lead so extensively used for making water pipes8 #f4 ,what sulphates other than lead are insoluble8 #g4 ,could lead nitrate be used in place of barium chloride in testing for sulphates8 #h4 ,how much lead peroxide could be obtained from #a kg4 of minium8 #i4 ,the purity of white lead is usually determined by observing the volume of carbon dioxide given off when it is treated with an acid4 ,what acid should be used8 ,on the supposition that it has the formula #b,pb,c,o#c,pb7,,oh7#b1 how nearly pure was a sample if #a g4 gave #cj cc4 of carbon dioxide at #bj and #gej mm48 #aj4 ,silicon belongs in the same family with tin and lead4 ,in what respects are these elements similar8 #aa4 ,what weight of tin could be obtained by the reduction of #a ton of cassiterite8 #ab4 ,what reaction would you expect to take place when lead peroxide is treated with hydrochloric acid8 #ac4 ,white lead is often adulterated with barytes4 ,suggest a method for detecting it1 if present1 in a given example of white lead4 ,,chapter ,,xxx ,,manganese ,,and ,,chromium ,,symbol ,,atomic ,,density ,,melting ,,formulas ,,of ,,acids ,,weight ,,point ,manganese ,mn #ee4j #h4ja #aijj ,h#b,mn,o#d and ,h,mn,o#d ,chromium ,cr #eb4a #g4c #cjjj ,h#b;,cr,o#d and ,h#b;,cr#b,o#g ,general4 ,manganese and chromium1 while belonging to different families1 have so many features in common in their chemical conduct that they may be studied together with advantage4 ,they differ from most of the elements so far studied in that they can act either as acid-forming or base-forming elements4 ,as base-forming elements each of the metals forms two series of salts4 ,in the one series1 designated by the suffix ous1 the metal is divalent2 in the other series1 designated by the suffix ic1 the metal is trivalent4 ,only the manganous and the chromic salts1 however1 are of importance4 ,the acids in which these elements play the part of a non-metal are unstable1 but their salts are usually stable1 and some of them are important compounds4 ,,manganese ,occurrence4 ,manganese is found in nature chiefly as the dioxide ,mn,o#b1 called pyrolusite4 ,in smaller amounts it occurs as the oxides ,mn#b,o#c and ,mn#c,o#d1 and as the carbonate ,mn,c,o#c4 ,some iron ores also contain manganese4 ,preparation and properties4 ,the element is difficult to prepare in pure condition and has no commercial applications4 ,it can be prepared1 however1 by reducing the oxide with aluminium powder or by the use of the electric furnace1 with carbon as the reducing agent4 ,the metal somewhat resembles iron in appearance1 but is harder1 less fusible1 and more readily acted upon by air and moisture4 ,acids readily dissolve it1 forming manganous salts4 ,oxides of manganese4 ,the following oxides of manganese are known3 ,mn,o1 ,mn#b,o#c1 ,mn#c,o#d1 ,mn,o#b1 and ,mn#b,o#g4 ,only one of these1 the dioxide1 needs special mention4 ,manganese dioxide 7pyrolusite7 7,mn,o#b74 ,this substance is the most abundant manganese compound found in nature1 and is the ore from which all other compounds of manganese are made4 ,it is a hard1 brittle1 black substance which is valuable as an oxidizing agent4 ,it will be recalled that it is used in the preparation of chlorine and oxygen1 in decolorizing glass which contains iron1 and in the manufacture of ferromanganese4 ,compounds containing manganese as a base-forming element4 ,as has been stated previously1 manganese forms two series of salts4 ,the most important of these salts1 all of which belong to the manganous series1 are the following3 ,manganous chloride ,mn,cl#bd;,h#b,o4 ,manganous sulphide ,mn,s4 ,manganous sulphate ,mn,s,o#dd;,h#b,o4 ,manganous carbonate ,mn,c,o#c4 ,manganous hydroxide ,mn7,,oh7#b4 ,the chloride and sulphate may be prepared by heating the dioxide with hydrochloric and sulphuric acids respectively3 ,mn,o#b #d;,h,cl ,mn,cl#b #b;,h#b,o #b;,cl1 ,mn,o#b ,h#b,,so#d ,mn,s,o#d ,h#b,o ,o4 ,the sulphide1 carbonate1 and hydroxide1 being insoluble1 may be prepared from a solution of the chloride or sulphate by precipitation with the appropriate reagents4 ,most of the manganous salts are rose colored4 ,they not only have formulas similar to the ferrous salts1 but resemble them in many of their chemical properties4 ,compounds containing manganese as an acid-forming element4 ,manganese forms two unstable acids1 namely1 manganic acid and permanganic acid4 ,while these acids are of little interest1 some of their salts1 especially the permanganates1 are important compounds4 ,manganic acid and manganates4 ,when manganese dioxide is fused with an alkali and an oxidizing agent a green compound is formed4 ,the equation1 when caustic potash is used1 is as follows3 ,mn,o#b #b,,koh ,o ,k#b,mn,o#d ,h#b,o4 ,the green compound 7,k#b,mn,o#d7 is called potassium manganate1 and is a salt of the unstable manganic acid 7,h#b,mn,o#d74 ,the manganates are all very unstable4 ,permanganic acid and the permanganates4 ,when carbon dioxide is passed through a solution of a manganate a part of the manganese is changed into manganese dioxide1 while the remainder forms a salt of the unstable acid ,h,mn,o#d1 called permanganic acid4 ,the equation is #c,k#b,mn,o#d #b;,,co#b ,mn,o#b #b,k,mn,o#d #b,k#b;,,co#c4 ,potassium permanganate 7,k,mn,o#d7 crystallizes in purple-black needles and is very soluble in water1 forming an intensely purple solution4 ,all other permanganates1 as well as permanganic acid itself1 give solutions of the same color4 ,oxidizing properties of the permanganates4 ,the permanganates are remarkable for their strong oxidizing properties4 ,when used as an oxidizing agent the permanganate is itself reduced1 the exact character of the products formed from it depending upon whether the oxidation takes place 7#a7 in an alkaline or neutral solution1 or 7#b7 in an acid solution4 #a4 ,oxidation in alkaline or neutral solution4 ,when the solution is either alkaline or neutral the potassium and the manganese of the permanganate are both converted into hydroxides1 as shown in the equation #b,k,mn,o#d #e;,h#b,o #b,mn7,,oh7#d #b,,koh #c,o4 #b4 ,oxidation in acid solution4 ,when free acid such as sulphuric is present1 the potassium and the manganese are both changed into salts of the acid3 #b,k,mn,o#d #c;,h#b,,so#d ,k#b,,so#d #b,mn,s,o#d #c;,h#b,o #e,o4 ,under ordinary conditions1 however1 neither one of these reactions takes place except in the presence of a third substance which is capable of oxidation4 ,the oxygen is not given off in the free state1 as the equations show1 but is used up in effecting oxidation4 ,potassium permanganate is particularly valuable as an oxidizing agent not only because it acts readily either in acid or in alkaline solution1 but also because the reaction takes place so easily that often it is not even necessary to heat the solution to secure action4 ,the substance finds many uses in the laboratory1 especially in analytical work4 ,it is also used as an antiseptic as well as a disinfectant4 ,,chromium ,occurrence4 ,the ore from which all chromium compounds are made is chromite1 or chrome iron ore 7,fe,cr#b,o#d74 ,this is found most abundantly in ,new ,caledonia and ,turkey4 ,the element also occurs in small quantities in many other minerals1 especially in crocoisite 7,pb,cr,o#d71 in which mineral it was first discovered4 ,preparation4 ,chromium1 like manganese1 is very hard to reduce from its ores1 owing to its great affinity for oxygen4 ,it can1 however1 be made by the same methods which have proved successful with manganese4 ,considerable quantities of an alloy of chromium with iron1 called ferrochromium1 are now produced for the steel industry4 ,properties4 ,chromium is a very hard metal of about the same density as iron4 ,it is one of the most infusible of the metals1 requiring a temperature little short of #cjjj for fusion4 ,at ordinary temperatures air has little action on it2 at higher temperatures1 however1 it burns brilliantly4 ,nitric acid has no action on it1 but hydrochloric and dilute sulphuric acids dissolve it1 liberating hydrogen4 ,compounds containing chromium as a base-forming element4 ,while chromium forms two series of salts1 chromous salts are difficult to prepare and are of little importance4 ,the most important of the chromic series are the following3 ,chromic hydroxide ,cr7,,oh7#c4 ,chromic chloride ,cr,cl#cf;,h#b,o4 ,chromic sulphate ,cr#b7,,so#d7c4 ,chrome alums ,chromic hydroxide 7,cr7,,oh7#c74 ,this substance1 being insoluble1 can be obtained by precipitating a solution of the chloride or sulphate with a soluble hydroxide4 ,it is a greenish substance which1 like aluminium hydroxide1 dissolves in alkalis1 forming soluble salts4 ,dehydration of chromium hydroxide4 ,when heated gently chromic hydroxide loses a part of its oxygen and hydrogen1 forming the substance ,cr,o,,oh1 which1 like the corresponding aluminium compound1 has more pronounced acid properties than the hydroxide4 ,it forms a series of salts very similar to the spinels2 chromite is the ferrous salt of this acid1 having the formula ,fe7,cr,o#b7b4 ,when heated to a higher temperature chromic hydroxide is completely dehydrated1 forming the trioxide ,cr#b,o#c4 ,this resembles the corresponding oxides of aluminium and iron in many respects4 ,it is a bright green powder1 and when ignited strongly becomes almost insoluble in acids1 as is also the case with aluminium oxide4 ,chromic sulphate 7,cr#b7,,so#d7c74 ,this compound is a violet-colored solid which dissolves in water1 forming a solution of the same color4 ,this solution1 however1 turns green on heating1 owing to the formation of basic salts4 ,chromic sulphate1 like ferric and aluminium sulphates1 unites with the sulphates of the alkali metals to form alums1 of which the best known are potassium chrome alum 7,k,cr7,,so#d7bab;,h#b,o7 and ammonium chrome alum 7,,nh#d;,cr7,,so#d7bab;,h#b,o74 ,these form beautiful dark purple crystals and have some practical uses in the tanning industry and in photography4 ,a number of the salts of chromium are also used in the dyeing industry1 for they hydrolyze like aluminium salts and the hydroxide forms a good mordant4 ,hydrolysis of chromium salts4 ,when ammonium sulphide is added to a solution of a chromium salt1 such as the sulphate1 chromium hydroxide precipitates instead of the sulphide4 ,this is due to the fact that chromic sulphide1 like aluminium sulphide1 hydrolyzes in the presence of water1 forming chromic hydroxide and hydrosulphuric acid4 ,similarly1 a soluble carbonate precipitates a basic carbonate of chromium4 ,compounds containing chromium as an acid-forming element4 ,like manganese1 chromium forms two unstable acids1 namely1 chromic acid and dichromic acid4 ,their salts1 the chromates and dichromates1 are important compounds4 ,chromates4 ,when a chromium compound is fused with an alkali and an oxidizing agent a chromate is produced4 ,when potassium hydroxide is used as the alkali the equation is #b;,cr7,,oh7#c #d,,koh #c,o #b,k#b;,cr,o#d #e;,h#b,o4 ,this reaction recalls the formation of a manganate under similar conditions4 ,properties of chromates4 ,the chromates are salts of the unstable chromic acid 7,h#b;,cr,o#d71 and as a rule are yellow in color4 ,lead chromate 7,pb,cr,o#d7 is the well-known pigment chrome yellow4 ,most of the chromates are insoluble and can therefore be prepared by precipitation4 ,thus1 when a solution of potassium chromate is added to solutions of lead nitrate and barium nitrate respectively1 the reactions expressed by the following equations occur3 ,pb7,,no#c7b ,k#b;,cr,o#d ,pb,cr,o#d #b,,kno#c1 ,ba7,,no#c7b ,k#b;,cr,o#d ,ba,cr,o#d #b,,kno#c4 ,the chromates of lead and barium separate as yellow precipitates4 ,the presence of either of these two metals can be detected by taking advantage of these reactions4 ,dichromates4 ,when potassium chromate is treated with an acid the potassium salt of the unstable dichromic acid 7,h#b;,cr#b,o#g7 is formed3 #b,k#b;,cr,o#d ,h#b,,so#d ,k#b;,cr#b,o#g ,k#b,,so#d ,h#b,o4 ,the relation between the chromates and dichromates is the same as that between the phosphates and the pyrophosphates4 ,potassium dichromate might therefore be called potassium pyrochromate4 ,potassium dichromate 7,k#b;,cr#b,o#g74 ,this is the best known dichromate1 and is the most familiar chromium compound4 ,it forms large crystals of a brilliant red color1 and is rather sparingly soluble in water4 ,when treated with potassium hydroxide it is converted into the chromate ,k#b;,cr#b,o#g #b,,koh #b,k#b;,cr,o#d ,h#b,o4 ,when added to a solution of lead or barium salt the corresponding chromates 7not dichromates7 are precipitated4 ,with barium nitrate the equation is #b;,ba7,,no#c7b ,k#b;,cr#b,o#g ,h#b,o #b;,ba,cr,o#d #b,,kno#c #b;,,hno#c4 ,potassium dichromate finds use in many industries as an oxidizing agent1 especially in the preparation of organic substances1 such as the dye alizarin1 and in the construction of several varieties of electric batteries4 ,sodium chromates4 ,the reason why the potassium salt rather than the sodium compound is used is that sodium chromate and dichromate are so soluble that it is hard to prepare them pure4 ,this difficulty is being overcome now1 and the sodium compounds are replacing the corresponding potassium salts4 ,this is of advantage1 since a sodium salt is cheaper than a potassium salt1 so far as raw materials go4 ,oxidizing action of chromates and dichromates4 ,when a dilute solution of a chromate or dichromate is acidified with an acid1 such as sulphuric acid1 no reaction apparently takes place4 ,however1 if there is present a third substance capable of oxidation1 the chromium compound gives up a portion of its oxygen to this substance4 ,since the chromate changes into a dichromate in the presence of an acid1 it will be sufficient to study the action of the dichromates alone4 ,the reaction takes place in two steps4 ,thus1 when a solution of ferrous sulphate is added to a solution of potassium dichromate acidified with sulphuric acid1 the reaction is expressed by the following equations3 7#a7 ,k#b;,cr#b,o#g #d;,h#b,,so#d ,k#b,,so#d ,cr#b7,,so#d7c #d;,h#b,o #c,o1 7#b7 #f;,fe,s,o#d #c;,h#b,,so#d #c,o #c;,fe#b7,,so#d7c #c;,h#b,o4 ,the dichromate decomposes in very much the same way as a permanganate does1 the potassium and chromium being both changed into salts in which they play the part of metals1 while part of the oxygen of the dichromate is liberated4 ,by combining equations 7#a7 and 7#b71 the following is obtained3 ,k#b;,cr#b,o#g #g;,h#b,,so#d #f;,fe,s,o#d ,k#b,,so#d ,cr#b7,,so#d7c #c;,fe#b7,,so#d7c #g;,h#bj4 ,this reaction is often employed in the estimation of iron in iron ores4 ,potassium chrome alum4 ,it will be noticed that the oxidizing action of potassium dichromate leaves potassium sulphate and chromium sulphate as the products of the reaction4 ,on evaporating the solution these substances crystallize out as potassium chrome alum1 which substance is produced as a by-product in the industries using potassium dichromate for oxidizing purposes4 ,chromic anhydride 7,cr,o#c74 ,when concentrated sulphuric acid is added to a strong solution of potassium dichromate1 and the liquid allowed to stand1 deep red needle-shaped crystals appear which have the formula ,cr,o#c4,this oxide of chromium is called chromic anhydride1 since it combines readily with water to form chromic acid3 ,cr,o#c ,h#b,o ,h#b;,cr,o#d4 ,it is therefore analogous to sulphur trioxide which forms sulphuric acid in a similar way3 ,,so#c ,h#b,o ,h#b,,so#d4 ,chromic anhydride is a very strong oxidizing agent1 giving up oxygen and forming chromic oxide3 #b;,cr,o#c ,cr#b,o#c #c,o4 ,rare elements of the family4 ,molybdenum1 tungsten1 and uranium are three rather rare elements belonging in the same family with chromium1 and form many compounds which are similar in formulas to the corresponding compounds of chromium4 ,they can play the part of metals and also form acids resembling chromic acid in formula4 ,thus we have molybdic acid 7,h#b,mo,o#d71 the ammonium salt of which is 7,,nh#d7b,mo,o#d4 ,this salt has the property of combining with phosphoric acid to form a very complex substance which is insoluble in nitric acid4 ,on this account molybdic acid is often used in the estimation of the phosphoric acid present in a substance4 ,like chromium1 the metals are difficult to prepare in pure condition4 ,alloys with iron can be prepared by reducing the mixed oxides with carbon in an electric furnace2 these alloys are used to some extent in preparing special kinds of steel4 ,,exercises #a4 ,how does pyrolusite effect the decolorizing of glass containing iron8 #b4 ,write the equations for the preparation of manganous chloride1 carbonate1 and hydroxide4 #c4 ,write the equations representing the reactions which take place when ferrous sulphate is oxidized to ferric sulphate by potassium permanganate in the presence of sulphuric acid4 #d4 ,in the presence of sulphuric acid1 oxalic acid is oxidized by potassium permanganate according to the equation ,c#b;,h#b,o#d ,o #b;,,co#b ,h#b,o4 ,write the complete equation4 #e4 #aj g4 of iron were dissolved in sulphuric acid and oxidized to ferric sulphate by potassium permanganate4 ,what weight of the permanganate was required8 #f4 ,what weight of ferrochromium containing #dj chromium must be added to a ton of steel to produce an alloy containing #a of chromium8 #g4 ,write the equation representing the action of ammonium sulphide upon chromium sulphate4 #h4 ,potassium chromate oxidizes hydrochloric acid1 forming chlorine4 ,write the complete equation4 #i4 ,give the action of sulphuric acid on potassium dichromate 7a7 in the presence of a large amount of water2 7b7 in the presence of a small amount of water4 ,,chapter ,,xxxi ,,gold ,,and ,,the ,,platinum ,,family ,,atomic ,,highest ,,highest ,,melting ,,symbol ,,weight ,,density ,,oxide ,,chloride ,,point ,ruthenium ,ru #aja4g #ab4bf ,ru,o#d ,ru,cl#d ,electric arc ,rhodium ,rh #ajc4 #ab4a ,rh,o#b ,rh,cl#b ,electric arc ,palladium ,pd #ajf4e #aa4h ,pd,o#b ,pd,cl#d #aejj ,iridium ,ir #aic4 #bb4db ,ir,o#b ,ir,cl#d #aiej ,osmium ,os #aia4 #bb4dg ,os,o#d ,os,cl#d ,electric arc ,platinum ,pt #aid4h #ba4ej ,pt,o#b ,pt,cl#d #aggi ,gold ,au #aig4b #ai4cj ,au#b,o#c ,au,cl#c #ajfd ,the family4 ,following iron1 nickel1 and cobalt in the eighth column of the periodic table are two groups of three elements each4 ,the metals of the first of these groups--ruthenium1 rhodium1 and palladium--have atomic weights near #ajj and densities near #ab4 ,the metals of the other group--iridium1 osmium1 and platinum--have atomic weights near #bjj and densities near #ba4 ,these six rare elements have very similar physical properties and resemble each other chemically not only in the type of compounds which they form but also in the great variety of them4 ,they occur closely associated in nature1 usually as alloys of platinum in the form of irregular metallic grains in sand and gravel4 ,platinum is by far the most abundant of the six4 ,although the periodic classification assigns gold to the silver-copper group1 its physical as well as many of its chemical properties much more closely resemble those of the platinum metals1 and it can he conveniently considered along with them4 ,the four elements gold1 platinum1 osmium1 and iridium are the heaviest substances known1 being about twice as heavy as lead4 ,,platinum ,occurrence4 ,about #ij of the platinum of commerce comes from ,russia1 small amounts being produced in ,california1 ,brazil1 and ,australia4 ,preparation4 ,native platinum is usually alloyed with gold and the platinum metals4 ,to separate the platinum the alloy is dissolved in aqua regia1 which converts the platinum into chloroplatinic acid 7,h#b,pt,cl#f74 ,ammonium chloride is then added1 which precipitates the platinum as insoluble ammonium chloroplatinate3 ,h#b,pt,cl#f #b,,nh#d;,cl 7,,nh#d7b,pt,cl#f #b;,h,cl4 ,some iridium is also precipitated as a similar compound4 ,on ignition the double chloride is decomposed1 leaving the platinum as a spongy metallic mass1 which is melted in an electric furnace and rolled or hammered into the desired shape4 ,physical properties4 ,platinum is a grayish-white metal of high luster1 and is very malleable and ductile4 ,it melts in the oxyhydrogen blowpipe and in the electric furnace2 it is harder than gold and is a good conductor of electricity4 ,in finely divided form it has the ability to absorb or occlude gases1 especially oxygen and hydrogen4 ,these gases1 when occluded1 are in a very active condition resembling the nascent state1 and can combine with each other at ordinary temperatures4 ,a jet of hydrogen or coal gas directed upon spongy platinum is at once ignited4 ,platinum as a catalytic agent4 ,platinum is remarkable for its property of acting as a catalytic agent in a large number of chemical reactions1 and mention has been made of this use of the metal in connection with the manufacture of sulphuric acid4 ,when desired for this purpose some porous or fibrous substance1 such as asbestos1 is soaked in a solution of platinic chloride and then ignited4 ,the platinum compound is decomposed and the platinum deposited in very finely divided form4 ,asbestos prepared in this way is called platinized asbestos4 ,the catalytic action seems to be in part connected with the property of absorbing gases and rendering them nascent4 ,some other metals possess this same power1 notably palladium1 which is remarkable for its ability to absorb hydrogen4 ,chemical properties4 ,platinum is a very inactive element chemically1 and is not attacked by any of the common acids4 ,aqua regia slowly dissolves it1 forming platinic chloride 7,pt,cl#d71 which in turn unites with the hydrochloric acid present in the aqua regia1 forming the compound chloroplatinic acid 7,h#b,pt,cl#f74 ,platinum is attacked by fused alkalis4 ,it combines at higher temperatures with carbon and phosphorus and alloys with many metals4 ,it is readily attacked by chlorine but not by oxidizing agents4 ,applications4 ,platinum is very valuable as a material for the manufacture of chemical utensils which are required to stand a high temperature or the action of strong reagents4 ,platinum crucibles1 dishes1 forceps1 electrodes1 and similar articles are indispensable in the chemical laboratory4 ,in the industries it is used for such purposes as the manufacture of pans for evaporating sulphuric acid1 wires for sealing through incandescent light bulbs1 and for making a great variety of instruments4 ,unfortunately the supply of the metal is very limited1 and the cost is steadily advancing1 so that it is now more valuable than gold4 ,compounds4 ,platinum forms two series of salts of which platinous chloride 7,pt,cl#b7 and platinic chloride 7,pt,cl#d7 are examples4 ,platinates are also known4 ,while a great variety of compounds of platinum have been made1 the substance is chiefly employed in the metallic state4 ,platinic chloride 7,pt,cl#d74 ,platinic chloride is an orange-colored1 soluble compound made by heating chloroplatinic acid in a current of chlorine4 ,if hydrochloric acid is added to a solution of the substance1 the two combine1 forming chloroplatinic acid 7,h#b,pt,cl#f73 #b;,h,cl ,pt,cl#d ,h#b,pt,cl#f4 ,the potassium and ammonium salts of this acid are nearly insoluble in water and alcohol4 ,the acid is therefore used as a reagent to precipitate potassium in analytical work4 ,with potassium chloride the equation is #b,k,cl ,h#b,pt,cl#f ,k#b,pt,cl#f #b;,h,cl4 ,other metals of the family4 ,the other members of the family have few applications4 ,iridium is used in the form of a platinum alloy1 since the alloy is much harder than pure platinum and is even less fusible4 ,this alloy is sometimes used to point gold pens4 ,osmium tetroxide 7,os,o#d7 is a very volatile liquid and is used under the name of osmic acid as a stain for sections in microscopy4 ,,gold ,occurrence4 ,gold has been found in many localities1 the most famous being ,south ,africa1 ,australia1 ,russia1 and the ,united ,states4 ,in this country it is found in ,alaska and in nearly half of the states of the union1 notably in ,california1 ,colorado1 and ,nevada4 ,it is usually found in the native condition1 frequently alloyed with silver2 in combination it is sometimes found as telluride 7,au,te#b71 and in a few other compounds4 ,mining4 ,native gold occurs in the form of small grains or larger nuggets in the sands of old rivers1 or imbedded in quartz veins in rocks4 ,in the first case it is obtained in crude form by placer mining4 ,the sand containing the gold is shaken or stirred in troughs of running waters called sluices4 ,this sweeps away the sand but allows the heavier gold to sink to the bottom of the sluice4 ,sometimes the sand containing the gold is washed away from its natural location into the sluices by powerful streams of water delivered under pressure from pipes4 ,this is called hydraulic mining4 ,in vein mining the gold-bearing quartz is mined from the veins1 stamped into fine powder in stamping mills1 and the gold extracted by one of the processes to be described4 ,extraction4 #a4 ,amalgamation process4 ,in the amalgamation process the powder containing the gold is washed over a series of copper plates whose surfaces have been amalgamated with mercury4 ,the gold sticks to the mercury or alloys with it1 and after a time the gold and mercury are scraped off and the mixture is distilled4 ,the mercury distills off and the gold is left in the retort ready for refining4 #b4 ,chlorination process4 ,when gold occurs along with metallic sulphides it is often extracted by chlorination4 ,the ore is first roasted1 and is then moistened and treated with chlorine4 ,this dissolves the gold but not the metallic oxides3 ,au #c;,cl ,au,cl#c4 ,the gold chloride1 being soluble1 is extracted from the mixture with water1 and the gold is precipitated from the solution1 usually by adding ferrous sulphate3 ,au,cl#c #c;,fe,s,o#d ,au ,fe,cl#c ,fe#b7,,so#d7c4 #c4 ,cyanide process4 ,this process depends upon the fact that gold is soluble in a solution of potassium cyanide in the presence of the oxygen of the air4 ,the powder from the stamping mills is treated with a very dilute potassium cyanide solution which extracts the gold3 #b;,au #d,,kcn ,h#b,o ,o #b,,koh #b,k,au7,,cn7#b4 ,from this solution the gold can be obtained by electrolysis or by precipitation with metallic zinc3 #b,k,au7,,cn7#b ,zn ,k#b,zn7,,cn7#d #b;,au4 ,refining of gold4 ,gold is refined by three general methods3 #a4 ,electrolysis4 ,when gold is dissolved in a solution of potassium cyanide1 and the solution electrolyzed1 the gold is deposited in very pure condition on the cathode4 #b4 ,cupellation4 ,when the gold is alloyed with easily oxidizable metals1 such as copper or lead1 it may be refined by cupellation4 ,the alloy is fused with an oxidizing flame on a shallow hearth made of bone ash1 which substance has the property of absorbing metallic oxides but not the gold4 ,any silver which may be present remains alloyed with the gold4 #c4 ,parting with sulphuric acid4 ,gold may be separated from silver1 as well as from many other metals1 by heating the alloy with concentrated sulphuric acid4 ,this dissolves the silver1 while the gold is not attacked4 ,physical properties4 ,gold is a very heavy bright yellow metal1 exceedingly malleable and ductile1 and a good conductor of electricity4 ,it is quite soft and is usually alloyed with copper or silver to give it the hardness required for most practical uses4 ,the degree of fineness is expressed in terms of carats1 pure gold being twenty-four carats2 the gold used for jewelry is usually eighteen carats1 eighteen parts being gold and six parts copper or silver4 ,gold coinage is #ij gold and #aj copper4 ,chemical properties4 ,gold is not attacked by any one of the common acids2 aqua regia easily dissolves it1 forming gold chloride 7,au,cl#c71 which in turn combines with hydrochloric acid to form chlorauric acid 7,h,au,cl#d74 ,fused alkalis also attack it4 ,most oxidizing agents are without action upon it1 and in general it is not an active element4 ,compounds4 ,the compounds of gold1 though numerous and varied in character1 are of comparatively little importance and need not be described in detail4 ,the element forms two series of salts in which it acts as a metal3 in the aurous series the gold is univalent1 the chloride having the formula ,au,cl2 in the auric series it is trivalent1 auric chloride having the formula ,au,cl#c4 ,gold also acts as an acid-forming element1 forming such compounds as potassium aurate 7,k,au,o#b74 ,its compounds are very easily decomposed1 however1 metallic gold separating from them4 ,,exercises #a4 ,from the method of preparation of platinum1 what metal is likely to be alloyed with it8 #b4 ,the platinum chloride of the laboratory is made by dissolving platinum in aqua regia4 ,what is the compound8 #c4 ,how would you expect potassium aurate and platinate to be formed8 ,what precautions would this suggest in the use of platinum vessels8 #d4 ,why must gold ores be roasted in the chlorination process8 ,,chapter ,,xxxii ,,some ,,simple ,,organic ,,compounds ,division of chemistry into organic and inorganic4 ,chemistry is usually divided into two great divisions1--organic and inorganic4 ,the original significance of these terms was entirely different from the meaning which they have at the present time4 #a4 ,original significance4 ,the division into organic and inorganic was originally made because it was believed that those substances which constitute the essential parts of living organisms were built up under the influence of the life force of the organism4 ,such substances1 therefore1 should be regarded as different from those compounds prepared in the laboratory or formed from the inorganic or mineral constituents of the earth4 ,in accordance with this view organic chemistry included those substances formed by living organisms4 ,inorganic chemistry1 on the other hand1 included all substances formed from the mineral portions of the earth4 ,in #ahbh the ,german chemist ,whler prepared urea1 a typical organic compound1 from inorganic materials4 ,the synthesis of other so-called organic compounds followed1 and at present it is known that the same chemical laws apply to all substances whether formed in the living organism or prepared in the laboratory from inorganic constituents4 ,the terms organic and inorganic have therefore lost their original significance4 #b4 ,present significance4 ,the great majority of the compounds found in living organisms contain carbon1 and the term organic chemistry1 as used at present1 includes not only these compounds but all compounds of carbon4 ,organic chemistry has become1 therefore1 the chemistry of the compounds of carbon1 all other substances being treated under the head of inorganic chemistry4 ,this separation of the compounds of carbon into a group by themselves is made almost necessary by their great number1 over one hundred thousand having been recorded4 ,for convenience some of the simpler carbon compounds1 such as the oxides and the carbonates1 are usually discussed in inorganic chemistry4 ,the grouping of compounds in classes4 ,the study of organic chemistry is much simplified by the fact that the large number of bodies included in this field may be grouped in classes of similar compounds4 ,it thus becomes possible to study the properties of each class as a whole1 in much the same way as we study a group of elements4 ,the most important of these classes are the hydrocarbons1 the alcohols1 the aldehydes1 the acids1 the ethereal salts1 the ethers1 the ketones1 the organic bases1 and the carbohydrates4 ,a few members of each of these classes will now be discussed briefly4 ,,the ,,hydrocarbons ,carbon and hydrogen combine to form a large number of compounds4 ,these compounds are known collectively as the hydrocarbons4 ,they may be divided into a number of groups or series1 each being named from its first member4 ,some of the groups are as follows3 ,,methane ,,series ,,ch#d methane ,c#b;,h#f ethane ,c#c;,h#h propane ,c#d;,h#aj butane ,c#e;,h#ab pentane ,c#f;,h#ad hexane ,c#g;,h#af heptane ,c#h;,h#ah octane ,,ethylene ,,series ,c#b;,h#d ethylene ,c#c;,h#f propylene ,c#d;,h#h butylene ,,benzene ,,series ,c#f;,h#f benzene ,c#g;,h#h toluene ,c#h;,h#aj xylene ,,acetylene ,,series ,c#b;,h#b acetylene ,c#c;,h#d allylene ,only the lower members 7that is1 those which contain a small number of carbon atoms7 of the above groups are given4 ,the methane series is the most extensive1 all of the compounds up to ,c#bd;,h#ej being known4 ,it will be noticed that the successive members of each of the above series differ by the group of atoms 7,,ch#b74 ,such a series is called an homologous series4 ,in general1 it may be stated that the members of an homologous series show a regular gradation in most physical properties and are similar in chemical properties4 ,thus in the methane group the first four members are gases at ordinary temperatures2 those containing from five to sixteen carbon atoms are liquids1 the boiling points of which increase with the number of carbon atoms present4 ,those containing more than sixteen carbon atoms are solids4 ,sources of the hydrocarbons4 ,there are two chief sources of the hydrocarbons1 namely1 7#a7 crude petroleum and 7#b7 coal tar4 #a4 ,crude petroleum4 ,this is a liquid pumped from wells driven into the earth in certain localities4 ,pennsylvania1 ,ohio1 ,kansas1 ,california1 and ,texas are the chief oil-producing regions in the ,united ,states4 ,the crude petroleum consists largely of liquid hydrocarbons in which are dissolved both gaseous and solid hydrocarbons4 ,before being used it must be refined4 ,in this process the petroleum is run into large iron stills and subjected to fractional distillation4 ,the various hydrocarbons distill over in the general order of their boiling points4 ,the distillates which collect between certain limits of temperature are kept separate and serve for different uses2 they are further purified1 generally by washing with sulphuric acid1 then with an alkali1 and finally with water4 ,among the products obtained from crude petroleum in this way are the naphthas1 including benzine and gasoline1 kerosene or coal oil1 lubricating oils1 vaseline1 and paraffin4 ,none of these products are definite chemical compounds1 but each consists of a mixture of hydrocarbons1 the boiling points of which lie within certain limits4 #b4 ,coal tar4 ,this product is obtained in the manufacture of coal gas1 as already explained4 ,it is a complex mixture and is refined by the same general method used in refining crude petroleum4 ,the principal hydrocarbons obtained from the coal tar are benzene1 toluene1 naphthalene1 and anthracene4 ,in addition to the hydrocarbons1 coal tar contains many other compounds1 such as carbolic acid and aniline4 ,properties of the hydrocarbons4 ,the lower members of the first two series of hydrocarbons mentioned are all gases2 the succeeding members are liquids4 ,in some series1 as the methane series1 the higher members are solids4 ,the preparation and properties of methane and acetylene have been discussed in a previous chapter4 ,ethylene is present in small quantities in coal gas and may be obtained in the laboratory by treating alcohol 7,c#b;,h#f,o7 with sulphuric acid3 ,c#b;,h#f,o ,c#b;,h#d ,h#b,o4 ,benzene1 the first member of the benzene series1 is a liquid boiling at #hj4 ,the hydrocarbons serve as the materials from which a large number of compounds can be prepared2 indeed1 it has been proposed to call organic chemistry the chemistry of the hydrocarbon derivatives4 ,substitution products of the hydrocarbons4 ,as a rule1 at least a part of the hydrogen in any hydrocarbon can be displaced by an equivalent amount of certain elements or groups of elements4 ,thus the compounds ,,ch#c;,cl1 ,,ch#b;,cl#b1 ,c,h,cl#c1 ,c,cl#d can be obtained from methane by treatment with chlorine4 ,such compounds are called substitution products4 ,chloroform 7,c,h,cl#c74 ,this can be made by treating methane with chlorine1 as just indicated1 although a much easier method consists in treating alcohol or acetone 7which see7 with bleaching powder4 ,chloroform is a heavy liquid having a pleasant odor and a sweetish taste4 ,it is largely used as a solvent and as an ansthetic in surgery4 ,iodoform 7,,chi#c74 ,this is a yellow crystalline solid obtained by treating alcohol with iodine and an alkali4 ,it has a characteristic odor and is used as an antiseptic4 ,,alcohols ,when such a compound as ,,ch#c;,cl is treated with silver hydroxide the reaction expressed by the following equation takes place3 ,,ch#c;,cl ,ag,o,h ,,ch#c,,oh ,ag,cl4 ,similarly ,c#b;,h#e;,cl will give ,c#b;,h#e,,oh and ,ag,cl4 ,the compounds ,,ch#c,,oh and ,c#b;,h#e,,oh so obtained belong to the class of substances known as alcohols4 ,from their formulas it will be seen that they may be regarded as derived from hydrocarbons by substituting the hydroxyl group 7,,oh7 for hydrogen4 ,thus the alcohol ,,ch#c,,oh may be regarded as derived from methane 7,,ch#d7 by substituting the group ,,oh for one atom of hydrogen4 ,a great many alcohols are known1 and1 like the hydrocarbons1 they may be grouped into series4 ,the relation between the first three members of the methane series and the corresponding alcohols is shown in the following table3 ,,ch#d 7methane7 ,,ch#c,,oh 7methyl alcohol74 ,c#b;,h#f 7ethane7 ,c#b;,h#e,,oh 7ethyl alcohol74 ,c#c;,h#h 7propane7 ,c#c;,h#g,,oh 7propyl alcohol74 ,methyl alcohol 7wood alcohol7 7,,ch#c,,oh74 ,when wood is placed in an air-tight retort and heated1 a number of compounds are evolved1 the most important of which are the three liquids1 methyl alcohol1 acetic acid1 and acetone4 ,methyl alcohol is obtained entirely from this source1 and on this account is commonly called wood alcohol4 ,it is a colorless liquid which has a density of #j4gi and boils at #fg4 ,it burns with an almost colorless flame and is sometimes used for heating purposes1 in place of the more expensive ethyl alcohol4 ,it is a good solvent for organic substances and is used especially as a solvent in the manufacture of varnishes4 ,it is very poisonous4 ,ethyl alcohol 7common alcohol7 7,c#b;,h#e,,oh74 #a4 ,preparation4 ,this compound may be prepared from glucose 7,c#f;,h#ab,o#f71 a sugar easily obtained from starch4 ,if some baker's yeast is added to a solution of glucose and the temperature is maintained at about #cj1 bubbles of gas are soon evolved1 showing that a change is taking place4 ,the yeast contains a large number of minute organized bodies1 which are really forms of plant life4 ,the plant grows in the glucose solution1 and in so doing secretes a substance known as zymase1 which breaks down the glucose in accordance with the following equation3 ,c#f;,h#ab,o#f #b;,c#b;,h#e,,oh #b;,,co#b4 ,laboratory preparation of alcohol4 ,the formation of alcohol and carbon dioxide from glucose may be shown as follows3 ,about #ajj g4 of glucose are dissolved in a liter of water in flask ,a 7,fig4 #ij74 ,this flask is connected with the bottle ,b1 which is partially filled with limewater4 ,the tube ,c contains solid sodium hydroxide4 ,a little baker's yeast is now added to the solution in flask ,a1 and the apparatus is connected1 as shown in the figure4 ,if the temperature is maintained at about #cj1 the reaction soon begins4 ,the bubbles of gas escape through the limewater in ,b4 ,a precipitate of calcium carbonate soon forms in the limewater1 showing the presence of carbon dioxide4 ,the sodium hydroxide in tube ,c prevents the carbon dioxide in the air from acting on the limewater4 ,the alcohol remains in the flask ,a and may be separated by fractional distillation4 ,illustration3 ,fig4 #ij #b4 ,properties4 ,ethyl alcohol is a colorless liquid with a pleasant odor4 ,it has a density of #j4gh and boils at #gh4 ,it resembles methyl alcohol in its general properties4 ,it is sometimes used as a source of heat1 since its flame is very hot and does not deposit carbon1 as the flame from oil does4 ,when taken into the system in small quantities it causes intoxication2 in larger quantities it acts as a poison4 ,the intoxicating properties of such liquors as beer1 wine1 and whisky are due to the alcohol present4 ,beer contains from #b to #e of alcohol1 wine from #e to #bj1 and whisky about #ej4 ,the ordinary alcohol of the druggist contains #id of alcohol and #f of water4 ,when this is boiled with lime and then distilled nearly all the water is removed1 the distillate being called absolute alcohol4 ,commercial preparation of alcohol4 ,alcohol is prepared commercially from starch obtained from corn or potatoes4 ,the starch is first converted into a sugar known as maltose1 by the action of malt1 a substance prepared by moistening barley with water1 allowing it to germinate1 and then drying it4 ,there is present in the malt a substance known as diastase1 which has the property of changing starch into maltose4 ,this sugar1 like glucose1 breaks down into alcohol and carbon dioxide in the presence of yeast4 ,the resulting alcohol is separated by fractional distillation4 ,denatured alcohol4 ,the #id alcohol is prepared at present at a cost of about #ce cents per gallon1 which is about half the cost of the preparation of methyl alcohol4 ,the government1 however1 imposes a tax on all ethyl alcohol which amounts to #b4jh per gallon on the #id product4 ,this increases its cost to such an extent that it is not economical to use it for many purposes for which it is adapted1 such as a solvent in the preparation of paints and varnishes and as a material for the preparation of many important organic compounds4 ,by an act of ,congress in #aijf1 the tax was removed from denatured alcohol1 that is alcohol mixed with some substance which renders it unfit for the purposes of a beverage but will not impair its use for manufacturing purposes4 ,some of the ,european countries have similar laws4 ,the substances ordinarily used to denature alcohol are wood alcohol and pyridine1 the latter compound having a very offensive odor4 ,fermentation4 ,the reaction which takes place in the preparation of ethyl alcohol belongs to the class of changes known under the general name of fermentation4 ,thus we say that the yeast causes the glucose to ferment1 and the process is known as alcoholic fermentation4 ,there are many kinds of fermentations1 and each is thought to be due to the presence of a definite substance known as an enzyme1 which acts by catalysis4 ,in many cases1 as in alcoholic fermentation1 the change is brought about by the action of minute forms of life4 ,these probably secrete the enzymes which cause the fermentation to take place4 ,thus the yeast plant is supposed to bring about alcoholic fermentation by secreting the enzyme known as zymase4 ,glycerin 7,c#c;,h#e7,,oh7#c74 ,this compound may be regarded as derived from propane 7,c#c;,h#h7 by displacing three atoms of hydrogen by three hydroxyl groups1 and must therefore be regarded as an alcohol4 ,it is formed in the manufacture of soaps1 as will be explained later4 ,it is an oily1 colorless liquid having a sweetish taste4 ,it is used in medicine and in the manufacture of the explosives nitroglycerin and dynamite4 ,,aldehydes ,when alcohols are treated with certain oxidizing agents two hydrogen atoms are removed from each molecule of the alcohol4 ,the resulting compounds are known as aldehydes4 ,the relation of the aldehydes derived from methyl and ethyl alcohol to the alcohols themselves may be shown as follows3 ,alcohols ,,ch#c,,oh ,corresponding aldehydes ,,ch#b,o ,c#b;,h#e,,oh ,c#b;,h#d,o ,the first of these 7,,ch#b,o7 is a gas known as formaldehyde4 ,its aqueous solution is largely used as an antiseptic and disinfectant under the name of formalin4 ,acetaldehyde 7,c#b;,h#d,o7 is a liquid boiling at #ba4 ,,acids ,like the other classes of organic compounds1 the organic acids may be arranged in homologous series4 ,one of the most important of these series is the fatty-acid series1 the name having been given to it because the derivatives of certain of its members are constituents of the fats4 ,some of the most important members of the series are given in the following table4 ,they are all monobasic1 and this fact is expressed in the formulas by separating the replaceable hydrogen atom from the rest of the molecule3 ,h,,cho#b formic acid1 a liquid boiling at #ajj4 ,h,c#b;,h#c,o acetic acid1 a liquid boiling at #aah4 ,h,c#c;,h#e,o#b propionic acid1 a liquid boiling at #adj4 ,h,c#d;,h#g,o#b butyric acid1 a liquid boiling at #afc4 ,h,c#af;,h#ca,o#b palmitic acid1 a solid melting at #fb4 ,h,c#ah;,h#ce,o#b stearic acid1 a solid melting at #fi4 ,formic acid 7,h,,cho#b74 ,the name formic is derived from the ,latin formica1 signifying ant4 ,this name was given to the acid because it was formerly obtained from a certain kind of ants4 ,it is a colorless liquid and occurs in many plants such as the stinging nettles4 ,the inflammation caused by the sting of the bee is due to formic acid4 ,acetic acid 7,h,c#b;,h#c,o#b74 ,acetic acid is the acid present in vinegar1 the sour taste being due to it4 ,it can be prepared by either of the following methods4 #a4 ,acetic fermentation4 ,this consists in the change of alcohol into acetic acid through the agency of a minute organism commonly called mother of vinegar4 ,the change is represented by the following equation3 ,c#b;,h#e,,oh #b,o ,,hc#b;,h#c,o#b ,h#b,o4 ,the various kinds of vinegars are all made by this process4 ,in the manufacture of cider vinegar the sugar present in the cider first undergoes alcoholic fermentation2 the resulting alcohol then undergoes acetic fermentation4 ,the amount of acetic acid present in vinegars varies from #c to #f4 #b4 ,from the distillation of wood4 ,the liquid obtained by heating wood in the absence of air contains a large amount of acetic acid1 and this can be separated readily in a pure state4 ,this is the most economical method for the preparation of the concentrated acid4 ,acetic acid is a colorless liquid and has a strong pungent odor4 ,many of its salts are well-known compounds4 ,lead acetate 7,pb7,c#b;,h#c,o#b7b7 is the ordinary sugar of lead4 ,sodium acetate 7,na,c#b;,h#c,o#b7 is a white solid largely used in making chemical analyses4 ,copper acetate 7,cu7,c#b;,h#c,o#b7b7 is a blue solid4 ,when copper is acted upon by acetic acid in the presence of air a green basic acetate of copper is formed4 ,this is commonly known as verdigris4 ,all acetates are soluble in water4 ,butyric acid 7,h,c#d;,h#g,o#b74 ,derivatives of butyric acid are present in butter and impart to it its characteristic flavor4 ,palmitic and stearic acids4 ,ordinary fats consist principally of derivatives of palmitic and stearic acids4 ,when the fats are heated with sodium hydroxide the sodium salts of these acids are formed4 ,if hydrochloric acid is added to a solution of the sodium salts1 the free palmitic and stearic acids are precipitated4 ,they are white solids1 insoluble in water4 ,stearic acid is often used in making candles4 ,acids belonging to other series4 ,in addition to members of the fatty-acid series1 mention may be made of the following well-known acids4 ,oxalic acid 7,h#b;,c#b,o#d74 ,this is a white solid which occurs in nature in many plants1 such as the sorrels4 ,its ammonium salt 77,,nh#d7b;,c#b,o#d7 is used as a reagent for the detection of calcium4 ,when added to a solution of a calcium compound the white1 insoluble calcium oxalate 7,ca,c#b,o#d7 precipitates4 ,tartaric acid 7,h#b;,c#d;,h#d,o#f74 ,this compound occurs either in a free state or in the form of its salts in many fruits4 ,the potassium acid salt 7,,khc#d;,h#d,o#f7 occurs in the juice of grapes4 ,when the juice ferments in the manufacture of wine1 this salt1 being insoluble in alcohol1 separates out on the sides of the cask and in this form is known as argol4 ,this is more or less colored by the coloring matter of the grape4 ,when purified it forms a white solid and is sold under the name of cream of tartar4 ,the following are also well-known salts of tartaric acid3 potassium sodium tartrate 7,rochelle salt7 7,k,na,c#d;,h#d,o#f71 potassium antimonyl tartrate 7tartar emetic7 7,k,sb,o,c#d;,h#d,o#f74 ,cream of tartar baking powders4 ,the so-called cream of tartar baking powders consist of a mixture of cream of tartar1 bicarbonate of soda1 and some starch or flour4 ,when water is added to this mixture the cream of tartar slowly acts upon the soda present liberating carbon dioxide in accordance with the following equation3 ,,khc#d;,h#d,o#f ,na,h,c,o#c ,k,na,c#d;,h#d,o#f ,h#b,o ,,co#b4 ,the carbon dioxide evolved escapes through the dough1 thus making it light and porous4 ,citric acid 7,h#c;,c#f;,h#e,o#g74 ,this acid occurs in many fruits1 especially in lemons4 ,it is a white solid1 soluble in water1 and is often used as a substitute for lemons in making lemonade4 ,lactic acid 7,h,c#c;,h#e,o#c74 ,this is a liquid which is formed in the souring of milk4 ,oleic acid 7,h,c#ah;,h#cc,o#b74 ,the derivatives of this acid constitute the principal part of many oils and liquid fats4 ,the acid itself is an oily liquid4 ,,ethereal ,,salts ,when acids are brought in contact with alcohols under certain conditions a reaction takes place similar to that which takes place between acids and bases4 ,the following equations will serve as illustrations3 ,,koh ,,hno#c ,,kno#c ,h#b,o1 ,,ch#c,,oh ,,hno#c ,,ch#c,,no#c ,h#b,o4 ,the resulting compounds of which methyl nitrate 7,,ch#c,,no#c7 may be taken as the type belong to the class known as ethereal salts1 the name having been given them because some of them possess pleasant ethereal odors4 ,it will be seen that the ethereal salts differ from ordinary salts in that they contain a hydrocarbon radical1 such as ,,ch#c1 ,c#b;,h#e1 ,c#c;,h#e1 in place of a metal4 ,the nitrates of glycerin 7nitroglycerin74 ,nitric acid reacts with glycerin in the same way that it reacts with a base containing three hydroxyl groups such as ,fe7,,oh7#c3 ,fe7,,oh7#c #c;,,hno#c ,fe7,,no#c7c #c;,h#b,o1 ,c#c;,h#e7,,oh7#c #c;,,hno#c ,c#c;,h#e7,,no#c7c #c;,h#b,o4 ,the resulting nitrate 7,c#c;,h#e7,,no#c7c7 is the main constituent of nitroglycerin1 a slightly yellowish oil characterized by its explosive properties4 ,dynamite consists of porous earth which has absorbed nitroglycerin1 and its strength depends on the amount present4 ,it is used much more largely than nitroglycerin itself1 since it does not explode so readily by concussion and hence can be transported with safety4 ,the fats4 ,these are largely mixtures of the ethereal salts known respectively as olein1 palmitin1 and stearin4 ,these salts may be regarded as derived from oleic1 palmitic1 and stearic acids respectively1 by replacing the hydrogen of the acid with the glycerin radical ,c#c;,h#e4 ,since this radical is trivalent and oleic1 palmitic1 and stearic acids contain only one replaceable hydrogen atom to the molecule1 it is evident that three molecules of each acid must enter into each molecule of the ethereal salt4 ,the formulas for the acids and the ethereal salts derived from each are as follows3 ,,hc#ah;,h#cc,o#b 7oleic acid7 ,c#h;,h#f7;,c#ah;,h#cc,o#b7c1 7olein7 ,,hc#af;,h#ca,o#b 7palmitic acid7 ,c#c;,h#e7;,c#af;,h#cajb7c 7palmitin7 ,,hc#ah;,h#ce,o#b 7stearic acid7 ,c#c;,h#e7;,c#ah;,h#ce,o#b7c 7stearin7 ,olein is a liquid and is the main constituent of liquid fats4 ,palmitin and stearin are solids4 ,butter fat and oleomargarine4 ,butter fat consists principally of olein1 palmitin1 and stearin4 ,the flavor of the fat is due to the presence of a small amount of butyrin1 which is an ethereal salt of butyric acid4 ,oleomargarine differs from butter mainly in the fact that a smaller amount of butyrin is present4 ,it is made from the fats obtained from cattle and hogs4 ,this fat is churned up with milk1 or a small amount of butter is added1 in order to furnish sufficient butyrin to impart the butter flavor4 ,saponification4 ,when an ethereal salt is heated with an alkali a reaction expressed by the following equation takes place3 ,c#b;,h#e,,no#c ,,koh ,c#b;,h#e,,oh ,,kno#c4 ,this process is known as saponification1 since it is the one which takes place in the manufacture of soaps4 ,the ordinary soaps are made by heating fats with a solution of sodium hydroxide4 ,the reactions involved may be illustrated by the following equation representing the reaction between palmitin and sodium hydroxide3 ,c#c;,h#e7;,c#af;,h#ca,o#b7c #c ,na,o,h #c ,na,c#af;,h#ca,o#b ,c#c;,h#e7,,oh7#c4 ,in accordance with this equation the ethereal salts in the fats are converted into glycerin and the sodium salts of the corresponding acids4 ,the sodium salts are separated and constitute the soaps4 ,these salts are soluble in water4 ,when added to water containing calcium salts the insoluble calcium palmitate and stearate are precipitated4 ,magnesium salts act in a similar way4 ,it is because of these facts that soap is used up by hard waters4 ,,ethers ,when ethyl alcohol is heated to #adj with sulphuric acid the reaction expressed by the following equation takes place3 #b;,c#b;,h#e,,oh 7,c#b;,h#e7b,o ,h#b,o4 ,the resulting compound1 7,c#b;,h#e7b,o1 is ordinary ether and is the most important member of the class of compounds called ethers4 ,ordinarily ether is a light1 very inflammable liquid boiling at #ce4 ,it is used as a solvent for organic substances and as an ansthetic in surgical operations4 ,,ketones ,the most common member of this group is acetone 7,c#c;,h#f,o71 a colorless liquid obtained when wood is heated in the absence of air4 ,it is used in the preparation of other organic compounds1 especially chloroform4 ,,organic ,,bases ,this group includes a number of compounds1 all of which contain nitrogen as well as carbon4 ,they are characterized by combining directly with acids to form salts1 and in this respect they resemble ammonia4 ,they may1 indeed1 be regarded as derived from ammonia by displacing a part or all of the hydrogen present in ammonia by hydrocarbon radicals4 ,among the simplest of these compounds may be mentioned methylamine 7,,ch#c,,nh#b7 and ethylamine 7,c#b;,h#e,,nh#b74 ,these two compounds are gases and are formed in the distillation of wood and bones4 ,pyridine 7,c#e;,h#f,n7 and quinoline 7,c#i;,h#g,n7 are liquids present in small amounts in coal tar1 and also in the liquid obtained by the distillation of bones4 ,most of the compounds now classified under the general name of alkaloids 7which see7 also belong to this group4 ,,carbohydrates ,the term carbohydrate is applied to a class of compounds which includes the sugars1 starch1 and allied bodies ,these compounds contain carbon1 hydrogen1 and oxygen the last two elements generally being present in the proportion in which they combine to form water4 ,the most important members of this class are the following3 ,cane sugar ,c#ab;,h#bb,o#aa4 ,milk sugar ,c#ab;,h#bb,o#aa4 ,dextrose ,c#f;,h#ab,o#f4 ,levulose ,c#f;,h#ab,o#f4 ,cellulose ,c#f;,h#aj,o#e4 ,starch ,c#f;,h#ajje4 ,cane sugar 7,c#ab;,h#bb,o#aa74 ,this is the well-known substance commonly called sugar4 ,it occurs in many plants especially in the sugar cane and sugar beet4 ,it was formerly obtained almost entirely from the sugar cane1 but at present the greatest amount of it comes from the sugar beet4 ,the juice from the cane or beet contains the sugar in solution along with many impurities4 ,these impurities are removed1 and the resulting solution is then evaporated until the sugar crystallizes out4 ,the evaporation is conducted in closed vessels from which the air is partially exhausted4 ,in this way the boiling point of the solution is lowered and the charring of the sugar is prevented4 ,it is impossible to remove all the sugar from the solution4 ,in preparing sugar from sugar cane the liquors left after separating as much of it as possible from the juice of the cane constitute ordinary molasses4 ,maple sugar is made by the evaporation of the sap obtained from a species of the maple tree4 ,its sweetness is due to the presence of cane sugar1 other products present in the maple sap imparting the distinctive flavor4 ,when a solution of cane sugar is heated with hydrochloric or other dilute mineral acid1 two compounds1 dextrose and levulose1 are formed in accordance with the following equation3 ,c#ab;,h#bb,o#aa ,h#b,o ,c#f;,h#ab,o#f ,c#f;,h#ab,o#f4 ,this same change is brought about by the action of an enzyme present in the yeast plant4 ,when yeast is added to a solution of cane sugar fermentation is set up4 ,the cane sugar1 however1 does not ferment directly3 the enzyme in the yeast first transforms the sugar into dextrose and levulose1 and these sugars then undergo alcoholic fermentation4 ,when heated to #afj cane sugar melts2 if the temperature is increased to about #bae1 a partial decomposition takes place and a brown substance known as caramel forms4 ,this is used largely as a coloring matter4 ,milk sugar 7,c#ab;,h#bb,o#aa74 ,this sugar is present in the milk of all mammals4 ,the average composition of cow's milk is as follows3 ,water #hg4ag ,casein 7nitrogenous matter7 #c4ef ,butter fat #c4fd ,milk sugar #d4hh ,mineral matter #j4ge ,when rennin1 an enzyme obtained from the stomach of calves1 is added to milk1 the casein separates and is used in the manufacture of cheese4 ,the remaining liquid contains the milk sugar which separates on evaporation2 it resembles cane sugar in appearance but is not so sweet or soluble4 ,the souring of milk is due to the fact that the milk sugar present undergoes lactic fermentation in accordance with the equation ,c#ab;,h#bb,o#aa ,h#b,o #d;,c#c;,h#f,o#c4 ,the lactic acid formed causes the separation of the casein1 thus giving the well-known appearance of sour milk4 ,isomeric compounds4 ,it will be observed that cane sugar and milk sugar have the same formulas4 ,their difference in properties is due to the different arrangement of the atoms in the molecule4 ,such compounds are said to be isomeric4 ,dextrose and levulose are also isomeric4 ,dextrose 7grape sugar1 glucose7 7,c#f;,h#ab,o#f74 ,this sugar is present in many fruits and is commonly called grape sugar because of its presence in grape juice4 ,it can be obtained by heating cane sugar with dilute acids1 as explained above2 also by heating starch with dilute acids1 the change being as follows3 ,c#f;,h#ajfe ,h#b,o ,c#f;,h#ab,o#f4 ,pure dextrose is a white crystalline solid1 readily soluble in water1 and is not so sweet as cane sugar4 ,in the presence of yeast it undergoes alcoholic fermentation4 ,it is prepared from starch in large quantities1 and being less expensive than cane sugar1 is used as a substitute for it in the manufacture of jellies1 jams1 molasses1 candy1 and other sweets4 ,the product commonly sold under the name of glucose contains about #de of dextrose4 ,levulose 7fruit sugar77,c#f;,h#ab,o#f74 ,this sugar is a white solid which occurs along with dextrose in fruits and honey4 ,it undergoes alcoholic fermentation in the presence of yeast4 ,cellulose 7,c#f;,h#aj,o#e74 ,this forms the basis of all woody fibers4 ,cotton and linen are nearly pure cellulose4 ,it is insoluble in water1 alcohol1 and dilute acids4 ,sulphuric acid slowly converts it into dextrose4 ,nitric acid forms nitrates similar to nitroglycerin in composition and explosive properties4 ,these nitrates are variously known as nitrocellulose1 pyroxylin1 and gun cotton4 ,when exploded they yield only colorless gases2 hence they are used especially in the manufacture of smokeless gunpowder4 ,collodion is a solution of nitrocellulose in a mixture of alcohol and ether4 ,celluloid is a mixture of nitrocellulose and camphor4 ,paper consists mainly of cellulose1 the finer grades being made from linen and cotton rags1 and the cheaper grades from straw and wood4 ,starch 7,c#f;,h#aj,o#e74 ,this is by far the most abundant carbohydrate found in nature1 being present especially in seeds and tubers4 ,in the ,united ,states it is obtained chiefly from corn1 nearly #hj of which is starch4 ,in ,europe it is obtained principally from the potato4 ,it consists of minute granules and is practically insoluble in cold water4 ,these granules differ somewhat in appearance1 according to the source of the starch1 so that it is often possible to determine from what plant the starch was obtained4 ,when heated with water the granules burst and the starch partially dissolves4 ,dilute acids1 as well as certain enzymes1 convert it into dextrose or similar sugars4 ,when seeds germinate the starch present is converted into soluble sugars1 which are used as food for the growing plant4 ,chemical changes in bread making4 ,the average composition of wheat flour is as follows3 ,water4 #ac4h ,protein 7nitrogenous matter7 #g4i ,fats #a4d ,starch #gf4d ,mineral matter #j4e ,in making bread the flour is mixed with water and yeast1 and the resulting dough set aside in a warm place for a few hours4 ,the yeast first converts a portion of the starch into dextrose or a similar sugar1 which then undergoes alcoholic fermentation4 ,the carbon dioxide formed escapes through the dough1 making it light and porous4 ,the yeast plant thrives best at about #cj2 hence the necessity for having the dough in a warm place4 ,if the temperature rises above #ej1 the vitality of the yeast is destroyed and fermentation ceases4 ,in baking the bread1 the heat expels the alcohol and also expands the bubbles of carbon dioxide caught in the dough1 thus increasing its lightness4 ,,some ,,derivatives ,,of ,,benzene ,attention has been called to the complex nature of coal tar4 ,among the compounds present are the hydrocarbons1 benzene1 toluene1 naphthalene1 and anthracene4 ,these compounds are not only useful in themselves but serve for the preparation of many other important compounds known under the general name of coal-tar products4 ,nitrobenzene 7oil of myrbane7 7,c#f;,h#e,,no#b74 ,when benzene is treated with nitric acid a reaction takes place which is expressed by the following equation3 ,c#f;,h#f ,,hno#c ,c#f;,h#e,,no#b ,h#b,o4 ,the product ,c#f;,h#e,,no#b is called nitrobenzene4 ,it is a slightly yellowish poisonous liquid1 with a characteristic odor4 ,its main use is in the manufacture of aniline4 ,aniline 7,c#f;,h#e,,nh#b74 ,when nitrobenzene is heated with iron and hydrochloric acid the hydrogen evolved by the action of the iron upon the acid reduces the nitrobenzene in accordance with the following equation3 ,c#f;,h#e,,no#b #f;,h ,c#f;,h#e,,nh#b #b;,h#b,o4 ,the resulting compound is known as aniline1 a liquid boiling at #ahb4 ,when first prepared it is colorless1 but darkens on standing4 ,large quantities of it are used in the manufacture of the aniline or coal-tar dyes1 which include many important compounds4 ,carbolic acid 7,c#f;,h#e,,oh74 ,this compound1 sometimes known as phenol1 occurs in coal tar1 and is also prepared from benzene4 ,it forms colorless crystals which are very soluble in water4 ,it is strongly corrosive and very poisonous4 ,naphthalene and anthracene4 ,these are hydrocarbons occurring along with benzene in coal tar4 ,they are white solids1 insoluble in water4 ,the well-known moth balls are made of naphthalene4 ,large quantities of naphthalene are used in the preparation of indigo1 a dye formerly obtained from the indigo plant1 but now largely prepared by laboratory methods4 ,similarly anthracene is used in the preparation of the dye alizarin1 which was formerly obtained from the madder root4 ,,the ,,alkaloids ,this term is applied to a group of compounds found in many plants and trees4 ,they all contain nitrogen1 and most of them are characterized by their power to combine with acids to form salts4 ,this property is indicated by the name alkaloids1 which signifies alkali-like4 ,the salts are soluble in water1 and on this account are more largely used than the free alkaloids1 which are insoluble in water4 ,many of the alkaloids are used in medicine1 some of the more important ones being given below4 ,quinine4 ,this alkaloid occurs along with a number of others in the bark of certain trees which grow in districts in ,south ,america and also in ,java and other tropical islands4 ,it is a white solid1 and its sulphate is used in medicine in the treatment of fevers4 ,morphine4 ,when incisions are made in the unripe capsules of one of the varieties of the poppy plant1 a milky juice exudes which soon thickens4 ,this is removed and partially dried4 ,the resulting substance is the ordinary opium which contains a number of alkaloids1 the principal one being morphine4 ,this alkaloid is a white solid and is of great service in medicine4 ,among the other alkaloids may be mentioned the following3 ,nicotine1 a very poisonous liquid1 the salts of which occur in the leaves of the tobacco plant2 cocaine1 a crystalline solid present in coca leaves and used in medicine as a local ansthetic2 atropine1 a solid present in the berry of the deadly nightshade1 and used in the treatment of diseases of the eye2 strychnine1 a white1 intensely poisonous solid present in the seeds of the members of the ,strychnos family4 ,,index ,acetaldehyde #dje ,acetic acid #djf ,acetone #daa ,acetylene #bjc series #cii ,acids #ajf binary #aac characteristics #ajf definition #ajg dibasic #aei familiar #ajf monobasic #aei nomenclature #aac organic #dje preparation #ada strength #aaa ternary #aac undissociated #ajg ,acker furnace1 #bgi ,agate #bfj ,air #hc a mechanical mixture #hi carbon dioxide in #hg changes in composition #hg liquid #ia nitrogen in #hg oxygen in #he poisonous effects of exhaled #hh properties #ij quantitative analysis of #he regarded as an element #hc standard for density #bbi water vapor in #hg ,alabaster #cjh ,alchemists #i ,alchemy #i ,alcohol1 common #djb denatured #djd ethyl #djb methyl #djb wood #djb ,alcohols #dja ,aldehydes #dje ,alizarin #dah ,alkali #ajg1 #bgd family #bgd ,alkaline-earth family #cjj ,alkaloids #dah ,allotropic forms #bb ,alloys #beb ,alum #ccc ammonium #ccd ammonium chrome #chd ammonium iron #ceb baking powders #cce potassium #ccc potassium chrome #chd potassium iron #ceb ,aluminates #ccb ,aluminium #cbg bronze #ccj1 #cei chloride #ccc family #cbg hydroxide #ccb metallurgy #cbh occurrence #cbg oxide #cca preparation #cbh properties #cbi silicates #cce uses #ccj ,amalgam #cfb ,amethyst #bfj1 #cca ,ammonia #abc composition #abg preparation #abc properties #abd uses #abe ,ammonium #abf acid carbonate #bie carbonate #bie chloride #bid compounds #bid ,ammonium hydrosulphide #bif hydroxide #abf molybdate #chh oxalate #djg sulphate #bie sulphide #bie sulphide1 yellow #bif ,analysis #dj ,anhydride #ace carbonic #bjf chromic #chg nitric #ace nitrous #ace phosphoric #bdc sulphuric #aec ,anhydrite #bhh ,aniline #dag ,anion #ajf ,anode #ii ,anthracene #dah ,antimony #bej acids #bea alloys #bec chloride #beb metallic properties #beb occurrence #bea oxides #bea preparation #bea properties #bea sulphides #bea ,apatite #age1 #bci1 #caa ,aqua ammonia #abd ,aqua regia #ahe ,aqueous tension #be ,argon #hj ,arsenic #bdf acids #bej antidote #bej ,marsh's test #bdh occurrence #bdf oxides #bdi preparation #bdf properties #bdg sulphides #bej white #bdi ,arsenopyrites #bdf ,arsine #bdg ,asbestos #cba1 #ccf ,atmosphere #hc constituents #hc function of constituents #hd ,atomic hypothesis #fa theory #ei and laws of matter #fc and radium #cad weights1 #fe accurate determination #bca and general properties #afg and specific heats #bcc calculation of #bca ,dalton's method #bbc direct determination #bcc from molecular weights #bcj relation to equivalent #bbd standard for #ff steps in determining #bbd ,atoms #fb size #fe ,atropine #dai ,aurates #cif ,avogadro's hypothesis #bbf and chemical calculations #bce and molecular weights #bbg ,azote #gh ,azurite #ceg ,babbitt metal #bec ,bacteria #he decomposition of organic matter by #abb nitrifying #he ,baking powders #bhe1 #djh alum #cce soda #bhe ,barium #cab chloride #cac nitrate #cac oxides #cab sulphate #cac ,barytes #cab ,bases #ajg characteristics #ajg definition #ajh familiar #ajg nomenclature #aac organic #dab strength #aac undissociated #ajh ,basic lining process #cdf ,bauxite #ccb ,beer #djd ,benzene #dag derivatives #dag series #cii ,benzine #djj ,bessemer process #cde ,bismuth #bec basic salts #bee chloride #bec nitrate #bec occurrence #bec oxides #bed preparation #bec salts1 hydrolysis of #bed subnitrate #bef uses #bec ,bismuthyl chloride #bef ,blast furnace #cda lamp #ch ,bleaching powder #cjf ,bleaching by chlorine #aha by sulphurous acid #aeb ,boiler scale #cbj ,bone ash #caa ,bone black #bjj ,borax #bfe bead #bff ,bornite #ceg ,boron #beg1 #bfd acids #bfe fluoride #bfd hydride #bfd occurrence #bfd oxides #bfd preparation #bfd properties #bfd ,brass #cbc ,bread making #daf ,bromides #aij ,bromine #ahg occurrence #ahg oxygen compounds #aij preparation #ahg properties #ahh ,bronze #cei aluminium #ccj1 #cei ,butter fat #daj ,butyric acid #djg ,by-product #bhd ,cadmium #cbe compounds #cbf ,csium #bid ,calamine #cba ,calcite #cje ,calcium #cja carbide #bjc1 #caj carbonate #cje chloride #cjf fluoride #cjh hydroxide #cjc occurrence #cja oxide #cjb phosphate #bdf1 #caa preparation #cjb sulphate #cjh ,calomel #cfc ,calorie #gf ,caramel #dad ,carbohydrates #dac ,carbolic acid #dag ,carbon #aif allotropic forms #aif amorphous #aih compounds #aif crystalline forms #aig cycle in nature #hh dioxide #bjd and bases #bjf and plant life #hh in air #hg occurrence #bjd preparation #bjd properties #bjd solid #bjd disulphide #afj1 #baj family #aif hydrogen compounds #bja monoxide #bjh occurrence #aif oxides #bjc properties #bjj pure #aih retort #aii uses #bjj ,carbonates #bjg acid #bjg ,carbonic acid #bjf ,carborundum #bei ,carnallite #bhh ,casein #dad ,cassiterite #cgj ,catalysis #aec ,catalyzers #aec ,cathode #ii ,cation #ajf ,caustic potash #bhh soda #bgh ,celestite #cab ,celluloid #dae ,cellulose #dae ,cement #cjd ,ceramic industries #ccf ,cerium #cgg ,chalcedony #bfj ,chalcocite #ceg ,chalcopyrite #ceg ,chalk #cje ,chamber acid #aeg ,changes1 physical and chemical #b ,charcoal #aii ,chemical affinity #ab changes #b compounds #g equilibrium #abh properties #c ,chemistry1 definition #d ,chili saltpeter #aia1 #bhe ,chinaware #ccf ,chloric acid #ahg ,chlorides #ahf ,chlorine #agg bleaching action #aha chemical properties #ahj family #agd historical #agg occurrence #agh oxides #ahg oxygen acids #ahg preparation #agh properties #agi ,chloroform #dja ,chloroplatinic acid #cic ,chlorous acid #ahg ,chromates #che ,chrome alum #chd ,chromic acid #chh anhydride #chg chloride #chc hydroxide #chc sulphate #chd sulphide #chd ,chromite #chc ,chromium #chc a base-forming element #chc an acid-forming element #che occurrence #chc ,cinnabar #cfc ,citric acid #djh ,clay #ccf ,coal #aii gas #bag products #djj tar #bah ,cobalt #ced compounds #ced ,cocaine #dai ,coke #aii ,collodion #dae ,colemanite #bfe ,combining weights #bbe ,combustion #ag broad sense #bj in air #ai phlogiston theory #ai products #ah spontaneous #bj supporters #bac ,compounds1 chemical #g isomeric #dad of metals1 preparation #bfe structure of #aah ,conservation of energy #d of matter #e ,contact process #aed ,converter1 ,bessemer #cde ,copper #ceg acetate #djg alloys of #cei family #cef hydroxide #cfj metallurgy #ceg occurrence #ceg ores #ceg oxide #cfj properties #ceh refining #ceh sulphate #cfa sulphide #cfa uses #cei ,copperas #cej ,coral #cje ,corrosive sublimate #cfc ,corundum #cca ,cream of tartar #djh ,crocoisite #chc ,cryolite #age1 #cbh ,crystallization #ih water of #ed1 #ge ,crystallography #afa ,crystals #afa axes of #afa systems #afb ,cupric compounds #cfj ,cuprite #cfj ,cuprous compounds #cfj chloride #cfj oxide #cfj ,cyanides #baj solutions are alkaline #baj ,dalton's atomic hypothesis #fa ,decay #ba ,decomposition of organic matter #abb ,decrepitation #ee ,deliquescence #ee ,density of gases #bcj ,desiccating agents #ee ,developers #cfg ,dewar bulb #ia ,dextrose #dad ,diamond #aig ,dichromates #che ,dichromic acid #che ,dimorphous substances #afc ,dissociation #ii and boiling point #aja and freezing point #aja equations of #aab extent of #aac ,distillation #ej ,dogtooth spar #cjf ,dolomite #cai ,double decomposition #ga ,drummond light #ch ,dyeing #ccc ,dynamite #dji ,earth metals #cbg ,efflorescence #ed ,electric furnace #bba ,electro-chemical industries #bfi ,electrode #ii ,electrolysis #ii of sodium chloride #ajb of sodium sulphate #ajc of water #da1 #ajb ,electrolytes #ii ,electrolytic dissociation #ii ,electroplating #cff ,electrotyping #cei ,elements1 definition #h atomic weights #bcb earlier classification #afe names #aa natural groups #afe number of #i occurrence #aj periodic division #aff physical state #aj symbols of #aa ,emery #cca ,energy #d and plant life #hi chemical #e conservation of #d transformation of #e ,enzyme #dje ,epsom salts #cbj ,equations #fh are quantitative #gb knowledge requisite for #fi not algebraic #gd reading of #fi ,equilibrium #ach chemical #ach in solution #aci point of #ach ,equivalent #bbd determination of #bbd elements with more than one #bbe relation to atomic weight #bbd ,etching #agg ,ether #daa ,ethereal salts #dji ,ethers #daa ,ethylamine #dab ,ethylene series #cii ,eudiometer #dc ,evaporation #aa ,families in periodic groups #agj triads #afe ,family resemblances #agj ,fats #dji ,fatty acid series #dje ,feldspar #bfa1 #cce ,fermentation #djd acetic #djf alcoholic #djd1 #dje lactic #dad ,ferric chloride #ceb hydroxide #ceb salts #cea reduction #cec sulphate #ceb ,ferrochromium1 #chc ,ferromanganese #cdc ,ferrosilicon #bei ,ferrous carbonate #cea salts #cej oxidation of #cec sulphate #cej sulphide #cej ,fertilizers #bde ,filtration #f1 #ea beds #eb ,fire damp #bjb ,flames #bac appearance #bad blowpipe #baf ,bunsen #bad conditions for #bac hydrogen #cd luminosity #baf oxidizing #bad oxyhydrogen #cg reactions #bif reducing #bad structure #bad ,flash lights #cag ,flint #bfj ,fluorides #agg ,fluorine #age ,fluorspar #age1 #cjh ,fluosilicic acid #bei ,flux #cdj ,fool's gold #cea ,formaldehyde #dje ,formalin #dje ,formic acid #djf ,formulas #fh how determined #bcd structural #aai ,fractional distillation #ea ,franklinite #cba ,fuels #bbj ,furnace1 arc #bba electric #bba resistance #bba ,fusion methods #bga ,galena #cgc ,gallium #cbg ,galvanized iron #cbc ,gas1 collection of #ae coal #bag fuel #bag illuminating #bag measurement of #bc natural #bai purification of #bah water #bai ,gases1 table #bbj ,gasoline #djj ,german silver #cbc1 #cei ,germanium #cgj ,germs1 effect of cold on #ec in air #hd in water #eb ,glass #bfb coloring of #bfc etching of #agg molding of #bfc nature of #bfc varieties #bfc ,glauber's salt #bha ,glazing #ccf ,glucose #dad ,glycerin #dje nitrates of #dji ,gold #cic alloys #cif chloride #cif coin #cei extraction of #cid in copper #ceh mining #cid occurrence #cic properties #cif refining of #cie telluride #cid ,goldschmidt method #bfi1 #ccj ,gram-molecular weight #bcf ,granite #ccf ,graphite #aih ,gun cotton #dae metal #cei powder #bib ,gypsite #cjh ,gypsum #cjh ,halogens #agd ,hard water #cji ,heat of reaction #ge ,helium #hj1 #cad ,hematite #cci1 #cdi ,homologous series #cih ,hydriodic acid #aic ,hydrobromic acid #ahi ,hydrocarbons #bja1 #cih properties #djj series #cih substitution products #dja ,hydrochloric acid #ahb composition #ahc oxidation of #ahe preparation #ahb properties #ahd salts #ahf ,hydrocyanic acid #baj ,hydrofluoric acid #agf etching by #agg salts of #agg ,hydrogen #bh dioxide #ef explosive with oxygen #ce occurrence #bh preparation from acids #cj preparation from water #bh properties #cb standard for atomic weights #ff standard for molecular weights #bbg sulphide #adf uses #ch ,hydrolysis #bed conditions affecting #bee partial #bee ,hydrosulphuric acid #adf ,hydroxyl radical #aab ,hypochlorous acid #ahg ,hypothesis #fa ,avogadro's #bbf ,dalton's #fa ,ice manufacture #abe ,iceland spar #cje ,indigo #dah ,indium #cbg ,insoluble compounds #bgb ,iodic acid #aid ,iodides #aic ,iodine #aij oxygen compounds #aic preparation #aia properties #aib tincture #aib ,iodoform #aib1 #dja ,ions #ajj and electrolytes #ajd ,iridium #cic ,iron #cci alum #ceb cast #cdc compounds #cdi cyanides #ceb disulphide #cea family #cch metallurgy #cci occurrence #cci ores #cci oxides #cdi pure #cdh varieties #cdb1 #cdg wrought #cdc ,jasper #bfj ,kainite #bhh ,kaolin #bfa1 #cce ,kerosene #djj ,ketones #daa ,kieserite #bhh ,kindling temperature #ag ,krypton #hj ,lactic acid #djh ,lampblack #bjj ,laughing gas #acb ,law1 definition #fa of ,boyle #bd of ,charles #bc of combining volumes #aid of conservation of energy #d of conservation of matter #e1 #ei of definite composition #ei of ,dulong and ,petit #bcc of ,gay-,lussac #aid of multiple proportion #fj of ,raoult #bcc periodic #afi ,lead #cgc acetate #cge1 #djg alloys #cge basic carbonate #cgf carbonate #cgf chloride #cgg chromate #cgg insoluble compounds #cgf metallurgy #cgc nitrate #cge occurrence #cgc oxides #cge peroxide #cge properties #cgd red #cge soluble salts #cge sugar of #cge sulphate #cgg sulphide #cgg white #cgf ,le ,blanc soda process #bhb ,levulose #dae ,lime #cjb air-slaked #cjc hypochlorite #cjg kilns #cjc slaked #cjc ,lime light #ch ,limestone #cje ,limewater #cjc ,limonite #cci ,litharge #cge ,lithium #bid ,luminosity of flames #baf ,lunar caustic #cff ,magnesia #cah alba #cai usta #cah ,magnesite #cah ,magnesium #cag basic carbonate #cai carbonate #cah cement #cah chloride #cai family #caf hydroxide #cah oxide #cah silicates #cba sulphate #cbj ,magnetite #cci1 #cdi ,malachite #ceg ,manganates #cha ,manganese #cgi a base-forming element #chj an acid-forming element #cha in glass #bfc occurrence #cgi oxides #chj ,manganic acid #cha ,manganous salts #chj ,marble #cje ,marl #cje ,marsh gas #bjb ,matches #bdb ,matte #ceh ,matter1 classification #f conservation #e definition #e kinds #i ,measurement of gases #bc ,mechanical mixtures #f ,meerschaum #cba1 #ccf ,mercuric chloride #cfc iodide #cfd oxide #ad1 #cfb sulphide #cfc ,mercurous chloride #cfc ,mercury #cfa iodides #cfd metallurgy #cfa occurrence #cfa oxides #cfb uses #cfb ,metaboric acid #bfe ,metallurgy #bfh ,metals #afe1 #bfg action on salts #bga definition #bfg extraction #bfh occurrence #bfg preparation of compounds #bfi reduction from ores #bfh ,metaphosphoric acid #bde ,metarsenic acid #bej ,metasilicic acid #bfa ,metastannic acid #cga ,methane #bjb1 #cii ,methylamine #dab ,mexican onyx #cje ,mica #bfa1 #ccf ,microcosmic salt #bdd ,milk #dad ,minerals #bfg ,minium #cge ,mixed salts #bdd ,molasses #dac ,molecular weights #bbf boiling-point method #bcc compared with oxygen #bbh determination #bbf freezing-point method #bcc oxygen standard #bbg of elements #bcb vapor-density method #bbi ,molecule #fb ,molybdenum #chh ,molybdic acid #chh ,monazite sand #cgg ,mordants #ccc ,morphine #dah ,mortar #cjd ,moth balls #dah ,muriatic acid #ahb ,naphthalene #dah ,naphthas #djj ,nascent state #ahb ,natural gas #bai sciences #a ,neon #hj ,neutralization #ajh a definite act #aji definition #aji heat of #aji partial #aaa ,niagara ,falls #bfi1 #cbi ,nickel #ced coin #cei compounds #ced plating #ced ,nicotine #dai ,nitrates #aca ,nitric acid1 #abh action on metals #acj decomposition #abi oxidizing action #acj preparation #abh1 #adj properties #abi salts #aca ,nitric oxide #acc ,nitrites #acb ,nitrobenzene #dag ,nitrocellulose #dae ,nitrogen #gh compounds #abb in air #hg occurrence #gh1 #abb oxides #acb preparation #gh properties #hj ,nitroglycerin #dji ,nitrosulphuric acid #aee ,nitrous acid #acb oxide #acb ,non-metals #afe ,oil of myrbane #dag of vitriol #aed ,oleic acid #djh ,olein #dji ,oleomargarine #daj ,onyx #bfj ,opal #bfj ,open-hearth process #cdf ,opium #dah ,ores #bfg ,organic bases #dab chemistry #bja1 #cig matter1 decomposition #abb ,orpiment #bdf ,orthoarsenic acid #bej ,orthophosphates #bdd ,orthophosphoric acid #bdd ,orthosilicic acid #bfa ,osmic acid #cic ,osmium #cic tetroxide #cic ,oxalic acid #djg ,oxidation #ag1 #cec definition #ah ,oxidizing agent #cg ,oxygen #ac and ozone #bb commercial preparation #af history #ac importance #ba in air estimation1 #he in air function1 #hd occurrence #ac preparation #ac properties #af standard for atomic weights #ff two atoms in molecule #bbg ,oxyhydrogen blowpipe #cg ,ozone #ba1 #acg ,palladium #cij ,palmitic acid #djg ,palmitin #dji ,paraffin #djj ,paris green #bej ,parkes's method for silver #cfd ,pearls #cje ,perchloric acid #ahg ,periodic acid #aid ,periodic division #aff groups #afg law #afi law1 imperfections #agb law1 value #aga table #afh table1 arrangement #aff ,permanent hardness #caj ,permanganates #cha ,permanganic acid #cha ,peroxides #bgh ,petroleum #cii ,pewter #cgb ,phenol #dag ,philosopher's stone #i ,phlogiston #ai ,phosphates #bde ,phosphine #bdb ,phosphonium compounds #bdc ,phosphoric acid #bdd ,phosphorite #bci ,phosphorous acid #bdd ,phosphorus #bci acids #bdc family #bch hydrogen compounds #bdb occurrence #bci oxides #bdc preparation #bci properties #bdj red #bda yellow #bdj ,photography #cfg ,physical changes #b properties #c properties and periodic groups #aga state #c ,physics #a1 #d ,pitchblende #cad ,plaster of ,paris #cjh ,platinic chloride #cic ,platinized asbestos #cia ,platinous chloride #cic ,platinum #cia a catalytic agent #aeb1 #cib ,pneumatic trough #af ,polyboric acid #bfe ,polyhalite #bhh ,polysilicic acids #bfa ,porcelain #ccf ,portland cement #cjd ,potash #bic ,potassium #bhg acid carbonate #bid acid sulphate #bid acid sulphite #bid alum1 aluminium #ccd alum1 chrome #chd alum1 iron #ceb and plant life #bhg aurate #cif bromide #bij carbonate #bic chlorate #bia chloride #bij chromate #che cyanide #bic dichromate #chf ferricyanide #ceb ferrocyanide #ceb hydroxide #bhh hydroxide1 action of halogens #bhi hypochlorite #bhi iodide #bij manganate #cha nitrate #bia occurrence #bhg permanganate #cha preparation #bhh sulphate #bid ,precipitated chalk #cjf ,precipitation #adj ,properties1 chemical #c physical #c ,prussic acid #baj ,puddling #cdc furnace #cdd ,pyridine #dab ,pyrites #cea ,pyrolusite #chj ,pyrophosphoric acid #bde ,quantitative equations #gb ,quartz #bfj ,quicklime #cjb ,quinine #dah ,quinoline #dab ,radical #aab ,radium #cac ,reaction1 classes #gj addition #gj completed #aci heat of #ge of decomposition #gj of double decomposition #ga of substitution #gj reversible #acg steps in #aca ,realgar #bdf ,red lead #cge phosphorus #bda ,reducing agent #cg ,reduction #cf1 #ced ,rennin #dad ,resemblances1 family #agj ,respiration #hg ,rhodium #cij ,rochelle salts #djh ,rouge #cdi ,rubidium #bid ,ruby #cca ,ruthenium #cij ,rutile #bfd ,safety lamp #bjb ,sal ammoniac #bid soda #bhb ,salt #bhj ,saltpeter #bia ,chili #bhe ,salts1 #aji acid1 #aab ,salts basic #aaa binary #aad characteristics #aji definition #aji insoluble #bgb mixed #bdd nomenclature #aac normal #aab preparation by precipitation #bgj ,sand #bfj ,sandstone #bfj ,saponification #daj ,sapphire #cca ,satinspar #cjh ,scale #cbj ,schnite #bhh ,selenite #cjh ,selenium #afa ,serpentine #cbj1 #ccf ,shot #bdg1 #cge ,siderite #cci ,silica #bfj ,silicates #bfa ,silicic acids #bfa ,silicides #bei ,silicon #beh acids #bfa dioxide #bfj fluoride #beh hydride #beh ,silver #cfd amalgamation process #cfd bromide #cfg chloride #cfg coin #cei ,german #cei in copper ores #ceh iodide #cfg metallurgy #cfd nitrate #cff oxide #cff parting of #cfe refining #cfe sulphide #cff ,slag #cdj ,smalt #cee ,smithsonite #cba ,smokeless powder #bic ,soaps #daj ,soda ash #bhd ,soda lime #bjb ,sodium #bgf acetate #djg bicarbonate #bhe carbonate #bhb carbonate1 historical #bhd chloride #bhj chromates #chf hydrogen carbonate #bhe hydroxide #bgh hyposulphite #bhb iodate #aia nitrate #bhe occurrence #bgf peroxide #bgg phosphates #bhf preparation #bgf properties #bgg sulphate #bha sulphite #bha tetraborate #bhg thiosulphate #bhb ,solder #cgb1 #cge ,solubility of gases #ie of solids #if ,solution #id and chemical action #ec boiling point #ih classes #id distribution of solids in #ih electrolysis of #ii freezing point #ii of gases in liquids #id of solids in liquids #if properties #ih saturated #ig supersaturated #ih ,solvay soda process #bhc ,sombrerite #bci ,spectroscope #bif ,sphalerite #cbe ,spiegel iron #cdc ,spinel #ccb ,spontaneous combustion #bj ,stalactites #cje ,stalagmites #cje ,standard conditions #bc ,stannates #cgb ,stannic acid #cgb chloride #cgb oxide #cgb ,stannous chloride #cgb ,starch #dae ,stassfurt salts #bhg ,stearic acid #djg ,stearin #dji ,steel #cde alloys #cdh properties #cdg tempering of #cdh tool #cdg ,stibine #bea ,stibnite #bej ,stoneware #ccf ,strontianite #cab ,strontium #cab hydroxide #cab nitrate #cab ,structural formulas #aai ,structure of compounds #aai ,strychnine #dai ,substitution #gj ,sugars #dab cane #dab fruit #dae grape #dad milk #dad ,sulphates #aei ,sulphides #adh ,sulphites #aeb action of acids on #aej ,sulphur #adc allotropic forms #add chemical properties #ade comparison with oxygen #afa dioxide #adi preparation #adi properties #aej extraction #adc flowers of #adc occurrence #adc oxides #adi physical properties #add trioxide #aeb uses #adf varieties #add ,sulphuric acid #aed action as an acid #aeg action on metals #aeg action on organic matter #aeh action on salts #aeh action on water #aeh fuming #aee manufacture #aed oxidizing action #aeg plant #aef properties #aeg salts #aei ,sulphuric anhydride #aec ,sulphurous acid #aea ,superphosphate of lime #bdf ,sylvine #bhh ,symbols #aa ,synthesis #dj ,table1 alkali metals #bgd alkaline-earth metals #cjj alloys of copper #cei aqueous tension ,appendix ,b atomic weights ,appendix ,a chlorine family #agd composition of earth's crust #aj composition of fuel gases #bbj constants of elements ,appendix ,b copper family #cef elements ,appendix ,a gold and platinum metals #cij hydrocarbons #cii magnesium family #caf manganese and chromium #cgi periodic arrangement #afh phosphorus family #bch silicon family #beg solubility of gases in water #ie solubility of salts #if solubility of salts at different temperatures #ig tin and lead #cgj weights of gases ,appendix ,b ,talc #cba1 #ccf ,tartar emetic #djh ,tartaric acid #djh ,tellurium #afa ,temporary hardness #cji ,ternary acids #aac salts #aad ,tetraboric acid #bfe ,thallium #cbg ,theory1 atomic #fa definition #fd value of #fd ,thermite #cca ,thio compounds #bhb ,thiosulphates #aei ,thiosulphuric acid #aei ,thorium #cgg ,tin #cgj block #cga compounds #cgb crystals #cgb family #cgj foil #cga metallurgy #cgj plate #cga properties #cga uses #cga ,titanium #beg1 #bfd ,topaz #cca ,triad families #aff ,tungsten #chh ,type metal #bec1 #cge ,uranium #chh ,valence #aaf a numerical property #aaf and combining ratios #aah and equations #abj and formulas #abj and periodic groups #afb and structure #aah definition #aaf indirectly determined #aag measure of #aag variable #aag ,vaseline #djj ,venetian red #cdi ,verdigris #djg ,vermilion #cfc ,vinegar #djf ,vitriol1 blue #cfa green #cej oil of #aed white #cbd ,volume and aqueous tension #be and pressure #bd and temperature #bc of combining gases #aid ,water #dj a compound #dj and disease #di catalytic action of #aed chalybeate #cea chemical properties #ec composition #dg composition by volume #dd composition by weight #dg dissociation of #baj distillation of #ej electrolysis of #da1 #ajc filtration of #ea gas #bai hard #cji historical #dj impurities in #dh in air #hg mineral #di occurrence #dh of crystallization #ed1 #ge physical properties #ec purification of #ej qualitative analysis #da quantitative analysis #db river #di sanitary analysis #ej self-purification #ec softening of #caj standard substance #ee synthesis #dc uses of #ee ,weights1 atomic #fe ,welsbach mantles #bai1 #cgg ,whisky #djd ,wine #djd ,witherite #cab ,wood alcohol #djb distillation #djb ,wood's metal #bed ,xenon #hj ,yeast #djc ,zinc #cba alloys of #cbc blende #cba chloride #cbe flowers of #cbb metallurgy #cba occurrence #cba oxide #cbd sulphate #cbd sulphide #cbe white #cbd ,zymase1 #djc ,,announcements ,,an ,,elementary ,,study ,,of ,,chemistry ,by ,,william ,mc,p,h,e,r,s,o,n1 ,professor of ,chemistry in ,ohio ,state ,university1 and ,,william ,e4 ,,henderson1 ,associate ,professor of ,chemistry in ,ohio ,state ,university4 #abmo4 ,cloth4 #dcd pages4 ,illustrated4 ,list price1 #a4be2 mailing price1 #a4dj ,this book is the outgrowth of many years of experience in the teaching of elementary chemistry4 ,in its preparation the authors have steadfastly kept in mind the limitations of the student to whom chemistry is a new science4 ,they have endeavored to present the subject in a clear1 well-graded way1 passing in a natural and logical manner from principles which are readily understood to those which are more difficult to grasp4 ,the language is simple and as free as possible from unusual and technical phrases4 ,those which are unavoidable are carefully defined4 ,the outline is made very plain1 and the paragraphing is designed to be of real assistance to the student in his reading4 ,the book is in no way radical1 either in the subject-matter selected or in the method of treatment4 ,at the same time it is in thorough harmony with the most recent developments in chemistry1 both in respect to theory and discovery4 ,great care has been taken in the theoretical portions to make the treatment simple and well within the reach of the ability of an elementary student4 ,the most recent discoveries have been touched upon where they come within the scope of an elementary text4 ,especial attention has been given to the practical applications of chemistry1 and to the description of the manufacturing processes in use at the present time4 ,,exercises ,,in ,,chemistry4 ,by ,,william ,mc,p,h,e,r,s,o,n and ,,william ,e4 ,,henderson4 7,in press47 ,,ginn ,,company ,,publishers ,a ,,first ,,course ,,in ,,physics ,by ,,robert ,a4 ,,millikan1 ,associate ,professor of ,physics1 and ,,henry ,g4 ,,gale1 ,assistant ,professor of ,physics in ,the ,university of ,chicago #abmo1 cloth1 #dhh pages1 illustrated1 #a4be ,a ,,laboratory ,,course ,,in ,,physics ,,for ,,secondary ,,schools ,by ,,robert ,a4 ,,millikan and ,,henry ,g4 ,,gale #abmo1 flexible cloth1 #acd pages1 illustrated1 #dj cents ,this one-year course in physics has grown out of the experience of the authors in developing the work in physics at the ,school of ,education of ,the ,university of ,chicago1 and in dealing with the physics instruction in affiliated high schools and academies4 ,the book is a simple1 objective presentation of the subject as opposed to a formal and mathematical one4 ,it is intended for the third-year high-school pupils and is therefore adapted in style and method of treatment to the needs of students between the ages of fifteen and eighteen4 ,it especially emphasizes the historical and practical aspects of the subject and connects the study very intimately with facts of daily observation and experience4 ,the authors have made a careful distinction between the class of experiments which are essentially laboratory problems and those which belong more properly to the classroom and the lecture table4 ,the former are grouped into a ,laboratory ,manual which is designed for use in connection with the text4 ,the two books are not1 however1 organically connected1 each being complete in itself4 ,all the experiments included in the work have been carefully chosen with reference to their usefulness as effective classroom demonstrations4 ,,ginn ,,and ,,company ,,publishers ,,appendix ,a ,,list ,,of ,,the ,,elements1 ,,their ,,symbols1 ,,and ,,atomic ,,weights ,the more important elements are marked with an asterisk ,o #af 99,antimony ,sb #abj4b 99,argon ,a #ci4i 99,arsenic ,as #ge4j 99,barium ,ba #acg4d ,beryllium ,be #i4a 99,bismuth ,bi #bjh4e 99,boron ,b #aa4j 99,bromine ,br #gi4if 99,cadmium ,cd #aab4d ,csium ,cs #acb4i 99,calcium ,ca #dj4a 99,carbon ,c #ab4jj ,cerium ,ce #adj4be 99,chlorine ,cl #ce4de 99,chromium ,cr #eb4a 99,cobalt ,co #ei4j ,columbium ,cb #id4j 99,copper ,cu #fc4f ,erbium ,er #aff4j 99,fluorine ,f #ai4j ,gadolinium ,gd #aef4j ,gallium ,ga #gj4j ,germanium ,ge #gb4e 99,gold ,au #aig4b ,helium ,he #d4j 99,hydrogen ,h #a4jjh ,indium ,in #aae4j 99,iodine ,i #abf4ig ,iridium ,ir #aic4j 99,iron ,fe #ee4i ,krypton ,kr #ha4h ,lanthanum ,la #ach4i 99,lead ,pb #bjf4i ,lithium ,li #g4jc 99,magnesium ,mg #bd4cf 99,manganese ,mn #ee4j 99,mercury ,hg #bjj4j ,molybdenum ,mo #if4j ,neodymium ,nd #adc4f ,neon ,ne #bj4j 99,nickel ,ni #eh4g 99,nitrogen ,n #ad4jd ,osmium ,os #aia4j 99,oxygen ,o #af4jj ,palladium ,pd #ajf4e 99,phosphorus ,p #ca4j 99,platinum ,pt #aid4h 99,potassium ,k #ci4ae ,praseodymium ,pr #adj4e ,radium ,ra #bbe4j ,rhodium ,rh #ajc4j ,rubidium ,rb #he4e ,ruthenium ,ru #aja4g ,samarium ,sm #aej4c ,scandium ,sc #dd4a ,selenium ,se #gi4b 99,silicon ,si #bh4d 99,silver ,ag #ajg4ic 99,sodium ,na #bc4je 99,strontium ,sr #hg4f 99,sulphur ,s #cb4jf ,tantalum ,ta #ahc4j ,tellurium ,te #abg4f ,terbium ,tb #afj4j ,thallium ,tl #bjd4a ,thorium ,th #bcb4e ,thulium ,tm #aga4j 99,tin ,sn #aai4j ,titanium ,ti #dh4a ,tungsten ,w #ahd4j ,uranium ,u #bch4e ,vanadium ,v #ea4b ,xenon ,xe #abh4j ,ytterbium ,yb #agc4j ,yttrium ,yt #hi4j 99,zinc ,zn #fe4d ,zirconium ,zr #ij4f ,,appendix ,b ,tension of ,aqueous ,vapor expressed in ,millimeters of ,mercury ,,temperature ,,pressure #af #ac4e #ag #ad4d #ah #ae4c #ai #af4c #bj #ag4d #ba #ah4e #bb #ai4f #bc #bj4i #bd #bb4b #be #bc4e ,weight of #a ,liter of ,various ,gases measured under ,standard ,conditions ,acetylene #a4afad ,air #a4bibc ,ammonia #j4gfag ,carbon dioxide #a4ifda ,carbon monoxide #a4bdii ,chlorine #c4afej ,hydrocyanic acid #a4bjcf ,hydrochloric acid #a4fbge ,hydrogen #j4jhihd ,hydrosulphuric acid #a4ebaa ,methane #j4gaeg ,nitric oxide #a4cdaj ,nitrogen #a4beja ,nitrous oxide #a4ifgg ,oxygen #a4dbhe ,sulphur dioxide #b4heif ,densities and ,melting ,points of ,some ,common ,elements ,,density ,,melting ,,point ,aluminium #b4fh #fdj ,antimony #f4gj #dcb ,arsenic #e4gc -- ,barium #c4ge -- ,bismuth #i4hj #bgj ,boron #b4de -- ,cadmium #h4fg #cbj ,csium #a4hh #bf4e ,calcium #a4ed -- ,carbon1 ,diamond #c4ej -- ,graphite #b4ae -- ,charcoal #a4hj -- ,chromium #g4cj #cjjj ,cobalt #h4ee #ahjj ,copper #h4hi #ajhd ,gold #ai4cj #ajfd ,iridium #bb4db #aiej ,iron #g4ic #ahjj ,lead #aa4ch #cbg ,lithium #j4ei #ahf ,magnesium #a4ge #gej ,manganese #h4ja #aijj ,mercury #ac4eif -#ci4e ,nickel #h4i #afjj ,osmium #bb4dg -- ,palladium #aa4hj #aejj ,phosphorus #a4hj #de ,platinum #ba4ej #aggi ,potassium #j4hg #fb4e ,rhodium #ab4aj -- ,rubidium #a4eb #ch4e ,ruthenium #ab4bf -- ,silicon #b4ce -- ,silver #aj4e #ifj ,sodium #j4ig #ig4f ,strontium #b4ej -- ,sulphur #b4jj #aad4h ,tin #g4ce #bce ,titanium #c4ej -- ,zinc #g4jj #dbj