- ,i - !i*5v-;.- 
 
 Hi 
 
FOUNDATIONS OF 
 CHEMISTRY 
 
 BY 
 
 ARTHUR A. BLANCHARD, PH.D. 
 
 ASSOCIATE PROFESSOR OF INORGANIC CHEMISTRY AT THE 
 MASSACHUSETTS INSTITUTE OF TECHNOLOGY 
 
 AND 
 
 FRANK B. WADE, B.S. 
 
 HEAD OF THE DEPARTMENT OF CHEMISTRY AT THE 
 8HORTRIDGE HIGH SCHOOL, INDIANAPOLIS, INDIANA 
 
 AMERICAN BOOK COMPANY 
 
 NEW YORK CINCINNATI CHICAGO 
 
COPYKIGHT, 1914, 
 
 BY A. A. BLANCHARD 
 AND FRANK B. WADE. 
 
 COPYRIGHT, 1914, IN GBEVT BRITAIN. 
 
 BLANCHARD AND WADE, FOUND. OF CHBM. 
 W. P. I 
 
PREFACE 
 
 FORMERLY, the study of the classics occupied a very 
 prominent position in educational training, and many of 
 the ablest men of our times owe their efficiency largely 
 to the excellence of the mental discipline thus acquired. 
 The essential mental training can, however, be furnished 
 in the study of subjects that possess vital interest and 
 present-day usefulness, provided these subjects are as 
 well taught as were the classics. 
 
 A tendency is now evident in secondary school educa- 
 tion to depart from the study of the classics and to substi- 
 tute therefor a multitude of vocational and informational 
 subjects. It is extremely likely that this type of study 
 will not only fail to prove as practically useful as its 
 advocates hope, but that it will fail to impart that sturdy 
 independence of thinking that ability to apply what 
 has previously been gained which is so essential to 
 success in all walks of life, and which can be imparted 
 in large measure by a thorough study of the underlying 
 principles of science in their applications to well-selected 
 cases. 
 
 With the ideal in mind of teaching the scientific method 
 of thought while considering the facts and principles of 
 chemistry, the authors have striven to write a book the 
 intelligent study of which will develop both the power 
 of the pupil to think originally and his appreciation of 
 the relation between the subject matter of chemistry and 
 his daily life. 
 
 In illustrating the principles of chemistry, very many 
 important industrial processes and applications to daily 
 
 3 
 
 302077 
 
4 PREFACE 
 
 lilV have beea chosen, but the greatest effort has been 
 made to keep the idea uppermost that the principles con- 
 cerned are of universal application, whereas the individual 
 processes are transient and of relatively less importance 
 to the general student of chemistry. 
 
 In the development of the subject, the plan has been 
 to proceed from simple and well-known facts to others 
 less familiar. The consideration of chemical theory is 
 deferred to later chapters so that a good basis of fact 
 may have accumulated before the theory arising from the 
 facts is considered. 
 
 The problems at the end of the chapters are graded in 
 difficulty and some are designed to tax the thinking powers 
 of the brightest students, for it is true that a course in 
 science to be of greatest value must inspire the pupil to 
 think. The instructor may find it wise in some cases to 
 select from the list of questions those which best meet the 
 needs of his own students. 
 
 In the opinion of the authors, the first twenty-four 
 chapters include as much ground as can be thoroughly 
 covered by the average high school pupil in a year. The 
 subject matter of the remaining chapters is, on the whole, 
 more difficult, and a more advanced method of treatment 
 has been used in order that more mature classes may con- 
 tinue to receive mental stimulus from the work. 
 
 In conclusion, the authors find it a pleasant duty to 
 acknowledge encouragement and assistance received from 
 many of their friends. 
 
 The chapters relating to food chemistry have been read 
 by Professor A. G. Woodman and the chapters on the 
 carbon compounds by Professor F. J. Moore, both of the 
 Massachusetts Institute of Technology, and both of these 
 gentlemen have offered many helpful suggestions. The 
 
PREFACE 5 
 
 chapter on Metallurgy has been written in collaboration 
 with Professor Carle R. Hayward, of the Department 
 of Mining and Metallurgy of the Massachusetts Institute 
 of Technology. The entire manuscript has been read by 
 Professors J. W. Phelan and Edward Mueller, of the 
 Massachusetts Institute of Technology. 
 
 Mr. Charles J. Pieper, of the University High School, 
 Chicago, Miss Ellinor Garber, Mr. Mont K. Baird, and 
 Mr. E. Vernon Hahn, of the Shortridge High School, 
 Indianapolis, have made many valuable suggestions. Pho- 
 tographs for illustrations have been furnished by : The 
 Solvay Process Company, W. B. Scaife and Sons Com- 
 pany, The Carborundum Company, The Goldschmidt 
 Thermit Company, the Loomis-Pettibone Company, and 
 The American Museum of Natural History. 
 
TABLE OF CONTENTS 
 
 CHAPTER PAGE 
 
 I. CHEMICAL AND PHYSICAL CHANGES .... 9 
 
 II. MIXTURES AND PURE CHEMICAL SUBSTANCES . . 15 
 
 III. ELEMENTS AND COMPOUNDS . . . . .20 
 
 IV. COMBUSTION ' "* '*'.' 25 
 
 V. OXYGEN .38 
 
 VI. THE OXIDES OF CARBON . . .. . . .50 
 
 VII. THE ATMOSPHERE AND NITROGEN .... 67 
 
 VIII. THE GAS LAWS ........ 79 
 
 IX. WATER . .91 
 
 X. THE COMPOSITION OF WATER 100 
 
 XL HYDROGEN . . . . . ... .111 
 
 XII. THE ATOMIC THEORY . . . . . . .121 
 
 XIII. HYDROGEN CHLORIDE . 129 
 
 XIV. AVOGADRO'S THEORY . 141 
 
 XV. ATOMIC AND MOLECULAR WEIGHTS; SYMBOLS AND 
 
 FORMULAS 147 
 
 XVI. CHLORINE . . ... . . . . 164 
 
 XVII. SODIUM . . . . " . . . . . .177 
 
 XVIII. CALCIUM . . . . . . . . .192 
 
 XIX. ACIDS, BASES, AND SALTS; NEUTRALIZATION . . 207 
 
 XX. NOMENCLATURE OF ACIDS, BASES, AND SALTS . 220 
 
 XXL METALS . ... ... . . . . 225 
 
 XXII. METALLURGY T . . . . . . .239 
 
 XXIII. COMPOUNDS OF CARBON 264 
 
 XXIV. COMPOUNDS OF CARBON (continued) .... 282 
 
 6 
 
TABLE OF CONTENTS 
 
 CHAPTER 
 
 XXV. 
 XXVI. 
 XXVII. 
 
 THE IONIC THEORY 
 ELECTROLYSIS 
 ELECTROMOTIVE SERIES . . . . . 
 
 PAGE 
 
 . 299 
 . 311 
 327 
 
 XXVIII. 
 XXIX. 
 XXX. 
 XXXI. 
 XXXII. 
 
 HYDROGEN EQUIVALENTS AND VALENCE 
 SULPHUR AND ITS COMPOUNDS 
 NITROGEN AND ITS COMPOUNDS 
 THE HALOGENS; THE PERIODIC SYSTEM 
 REVERSIBLE REACTIONS AND EQUILIBRIUM . 
 
 . 333 
 . 342 
 . 358 
 . 377 
 . 392 
 
 MATIONS 413 
 
 APPENDIX : 
 
 TABLE OF PRESSURE OF WATER VAPOR . . . 425 
 METHOD OF CORRECTING GAS VOLUMES FOR THE PRES- 
 SURE OF WATER VAPOR 425 
 
 SOME PROPERTIES OF COMMON ELEMENTS . . . 427 
 
 DENSITIES OF GASES 428 
 
 SOME PROPERTIES OF COMPOUNDS 429 
 
 SOLUBILITY, TABLE AND RULES 430 
 
 IMPORTANT TEMPERATURES 431 
 
 COMPOSITION OF ALLOYS 432 
 
 COMPOSITION OF THE EARTH'S CRUST .... 433 
 
 LOGARITHMS 434, 435 
 
 METRIC SYSTEM OF WEIGHTS AND MEASURES . . 436 
 
 METRIC EQUIVALENTS 436 
 
 PERIODIC ARRANGEMENT OF THE ELEMENTS. Facing in- 
 side back cover. 
 
 INTERNATIONAL ATOMIC WEIGHT TABLE FOR 1914. In- 
 side back cover. 
 
 INDEX , 437 
 
FOUNDATIONS OF CHEMISTRY 
 
 CHAPTER I 
 
 CHEMICAL AND PHYSICAL CHANGES 
 
 CHEMISTRY is the science which deals with the substances 
 which go to make up our earth and everything in the earth, 
 sea, atmosphere, rocks, plants, and animals. Chemistry 
 is little interested in the size or shape of bodies of matter, 
 its concern is with the substances of which the bodies are 
 composed. For example, a large irregular ledge of marble 
 is marble, and is to the chemist the same substance as the 
 marble of the most beautifully chiseled statue. To a sculptor 
 or an architect the size and form of a marble block are of 
 supreme importance ; but to the chemist it is the substance 
 that is of importance. To a zoologist the difference between 
 two kinds of animals, for example between a rabbit and an 
 elephant, is most marked ; to a chemist, on the other hand, 
 the differences are of small importance, since both creatures 
 are built up of practically the same chemical substances, and 
 the life of both is dependent on the same kind of chemical 
 processes. 
 
 Substances are continually undergoing change, as when 
 coal burns or wood decays or the food of animals is digested ; 
 and all such changes of substances come within the scope of 
 chemistry. Mere changes in size and form, as when a block 
 of marble is chiseled or a band of rubber is stretched, have 
 no place in the study of chemistry, because there is no change 
 of substance. 
 
 9 
 
10 : ' CBBMtCX&teffi PHYSICAL CHANGES 
 
 1. A 'Typical Cher&ical Substance: Charcoal. Let us 
 examine a familiar substance, charcoal. Because ordinary 
 wood charcoal contains impurities, it is better for us to con- 
 sider a very pure form of charcoal, which may easily be made 
 by charring sugar. 
 
 Charcoal is black, porous, light in weight, brittle, and easily 
 crushed to a powder. These are some of the physical prop- 
 erties of charcoal and they are inherent in charcoal. It is 
 by observing these properties that we are enabled to dis- 
 tinguish it from other substances ; for example, from marble. 
 
 When charcoal burns, it undergoes a great change and 
 thereby loses all of these physical properties. The fact that 
 it can burn when in contact with air constitutes one of the 
 chemical properties of charcoal. 
 
 2. A Typical Chemical Change. Let us place a layer of 
 sugar charcoal upon a grate so that air may have free access 
 to it, and heat the lower part of the layer until it begins to 
 glow ; in other words, let us set fire to it. As we continue 
 to observe the charcoal after removing the source of heat, 
 we note that it does not become cool again, but that the heat 
 persists, and even grows stronger, and the glow spreads 
 throughout the whole layer. We note that the bulk of the 
 charcoal is diminishing, and at length we find that it has 
 entirely disappeared. When ordinary wood charcoal is 
 burned, a small quantity of white ashes is left, otherwise its 
 behavior is exactly the same. 
 
 What now is the real nature of this change? Has the 
 charcoal been destroyed ? We can certainly no longer see 
 it or feel it, but this does not necessarily mean that it has 
 ceased to exist as matter. Many well-known forms of matter 
 are imperceptible so far as our most-used means of observa- 
 tion go. For example, when we look through a pane of very 
 
A TYPICAL CHEMICAL CHANGE 11 
 
 clear glass or a layer of very clear water, we can hardly detect 
 these materials in our line of vision. We live at the bottom 
 of a sea of air, of the presence of which we have abundant 
 evidence in the wind and in such facts as our ability to use 
 it to inflate automobile tires. Moreover, it has been found 
 by scientific men to be an invariable rule of nature that 
 matter is never destroyed. This rule is known as the law 
 of the conservation of matter. Matter may change its form, but 
 its quantity, which is measured by its weight, never increases or 
 decreases. 
 
 If we accept the experience of scientific men as proof of 
 the correctness of this law, we must conclude that the char- 
 coal has not ceased to exist, but has merely changed to or 
 become part of a substance which, like air, is invisible. In 
 point of fact this conclusion is correct. The substance pro- 
 duced by burning the charcoal has many properties by 
 which its presence may be ascertained. One of its most 
 characteristic properties is that it is absorbed by limewater, 
 and thereby at once renders the latter milky in appearance. 
 This is a property not possessed by air or by charcoal. If 
 this product of burning charcoal is collected and weighed, 
 it is found to weigh three and a half times as much as the 
 original charcoal. 
 
 Assuming again the correctness of the law of the conser- 
 vation of matter, which states also that the quantity of 
 matter does not increase, we must conclude that this gas 
 that is formed cannot be composed alone of the same matter 
 as the charcoal, but that something must have been added 
 to that substance. This added substance must have come 
 from the air. It is in fact what we call oxygen, and the 
 new substance formed by its action with the charcoal is 
 called carbon dioxide. 
 
12 CHEMICAL AND PHYSICAL CHANGES 
 
 That something from the air is essential in the production 
 of the new substance is all the more strikingly shown if the 
 charcoal is heated out of contact with the air ; as, for ex- 
 ample, in a vacuum, that is, in a closed vessel out of which 
 the air has been pumped. When the charcoal is again allowed 
 to cool after this heating, it recovers its original appearance 
 and is found to have neither lost nor gained in weight. 
 
 Let us sum up the facts already stated concerning the 
 behavior of charcoal and air. When charcoal burns in air, 
 the charcoal ceases to exist as charcoal, but it and some- 
 thing from the air form a new substance, which has proper- 
 ties different from those of either of the original substances. 
 Accompanying this change in the kind of substance, a large 
 amount of heat is developed. 
 
 3. Characteristics of a Chemical Change. In the example 
 which we have been considering we have illustrated some of 
 the important characteristics of chemical changes, and we 
 should now be able to recognize a case of chemical change by 
 observing these characteristics. The substances present in 
 the beginning lose their properties and are changed into new 
 substances with radically different properties. In general, heat 
 effects accompany chemical changes and these effects are usually 
 wry marked when the change takes place rapidly. The heat 
 may be less intense, however, than in the case of the burning 
 charcoal. Some chemical changes absorb heat rather than 
 give it off. 
 
 4. Examples of Chemical Change. All other cases of 
 burning are examples of chemical change; for in all such 
 cases whatever the fuel that is burnt new substances 
 with new properties are formed and the old substances 
 disappear. Moreover the change is accompanied by the 
 active giving forth of heat. The explosion of gunpowder 
 
PHYSICAL CHANGE 13 
 
 and of dynamite (see frontispiece) are also instances of 
 chemical change. 
 
 The rusting of iron, the souring of milk, the decaying 
 of wood, and the digestion of food in the body may be men- 
 tioned as other familiar cases of chemical change. In these 
 latter cases the rate of change is slower than in burning and 
 the heat effects are not so apparent. Nevertheless, it is 
 true that the animal body is kept warm by the chemical 
 changes which the food undergoes. 
 
 5. Physical Change. We observe changes of some of the 
 properties when a block of marble is broken into fragments, 
 or a steel spring is compressed, or the filament of an incan- 
 descent electric lamp is heated to white heat by the current, 
 or gold is melted, or water is vaporized over a fire or is frozen 
 on a cold day. But the steel spring returns to its original 
 shape when it is released; on turning off the current, the 
 incandescent filament again grows cold and black ; on cool- 
 ing, the melted gold resolidifies and the water vapor con- 
 denses to liquid water; and, on returning to the original 
 temperature, the ice again turns to water. The fragments 
 of the shattered block of marble, it is true, do not reunite 
 into one solid piece, but this is not essential, because each 
 of the fragments is recognized at once as marble, since it 
 possesses the properties of marble and- differs only in size 
 and shape from the original block. 
 
 Such changes involve no change in the chemical nature of 
 the substances and they are known as physical changes. 
 
 In our study of chemistry we shall have frequent occasion 
 to distinguish between chemical and physical changes, and 
 in most cases it is a very simple matter to make the distinc- 
 tion. There are, however, cases on the border line concern- 
 ing which even scientists fail to agree. 
 
14 CHEMICAL AND PHYSICAL CHANGES 
 
 SUMMARY 
 
 Chemistry is the science which deals with substances and the changes 
 which substances undergo and are capable of undergoing. 
 
 A chemical change takes place when a substance, or substances, 
 undergoes a change into a new substance, or substances, with 
 widely different properties. Chemical changes usually involve 
 the production of or the absorption of a large amount of heat. 
 The burning of charcoal is one of the best known and most 
 typical of chemical changes. 
 
 Conservation of Matter: The amount of matter in the universe is 
 constant; matter is not created or destroyed. This statement 
 is known as the law of the conservation of matter. 
 
 Physical changes are those in which bodies of substance are changed 
 in any way without being altered in their chemical nature. 
 
 Questions 
 
 1. How are different chemical substances distinguished ? 
 
 2. State three ways in which chemical changes differ from phys- 
 ical changes. 
 
 3. Give five examples of physical change. 
 
 4. Give five examples of chemical change. State what distin- 
 guishes each of these as a chemical rather than a physical change. 
 
 6. Mention three instances of chemical change in which the heat 
 effect is so intense as to cause emission of light. 
 
 6. Mention three instances in which the heat effect is easily 
 noticeable, but still not intense enough to produce a glow. 
 
 7. Mention three instances in which the heat effect is so slight 
 that it is unnoticeable. 
 
 8. We may accept it as a reasonable supposition that just as 
 much heat would be produced by the complete decay of a piece of 
 wood as if the wood were to be burned. How do you explain the 
 fact that the heat is very intense in only one of these cases ? 
 
 9. Name the products of "burning coal in a furnace. Is the 
 chemical reaction carried on to obtain these new substances ? 
 
 10. When a mason slakes lime to make mortar, is he interested 
 in the heat produced? 
 
CHAPTER II 
 
 MIXTURES AND CHEMICAL SUBSTANCES 
 
 6. Mixtures. Many, in fact most, of the bodies of matter 
 familiar to us in everyday life are mixtures. Salt water, for 
 example, is a mixture containing water and salt. A glass of 
 salt water appears as clear as ordinary pure water, and it is 
 impossible to see any separation into individual grains of 
 salt or drops of water. Yet we know that we can make 
 salt water by dissolving salt in water. 
 
 Granite, which is a well-known building stone, is also a 
 mixture, usually of three substances, quartz, feldspar, 
 and mica; but in granite the separate particles of these 
 substances are large enough to be easily seen. 
 
 Ordinary garden soil is a very complex mixture, containing 
 sand, particles of decaying leaves, water, and various salts 
 such as potassium nitrate, potassium carbonate, and calcium 
 phosphate. The ingredients of the soil are so thoroughly 
 mixed that they cannot be identified with the naked eye. 
 
 Many of the materials which are brought to the practical 
 chemist for " analysis " are very complicated mixtures, and 
 the work of the chemist frequently consists in finding out 
 what substances are present in the mixtures and usually 
 also what quantity of each substance. This he is able to 
 do because he has been trained to know pure substances by 
 their properties and has learned to use systematic methods 
 of separating these substances. 
 
 B. AND W. CHEM, 2 15 
 
10 MIXTURES AND CHEMICAL SUBSTANCES 
 
 7. Chemical Substances. Any kind of matter which is 
 not a mixture is a chemical substance. Salt, sugar, sulphur, 
 and carbon (charcoal) are examples of chemical substances, 
 and none of these can be produced like salt water or garden 
 soil by the mere putting together of different ingredients. 
 
 A chemical substance is uniform throughout its mass. 
 Thus if we break a piece of any one of the above-mentioned 
 substances into countless small pieces and examine each of 
 these pieces by any means at our disposal, we find that each 
 of the minute particles has just the same properties, except 
 those of size and shape, as all the other pieces or as the un- 
 broken lump. 
 
 But mere uniformity throughout the mass of a body of 
 matter does not necessarily show that it is a single substance, 
 for some mixtures, like salt water, are as uniform as the 
 substances, salt, sugar, sulphur, and charcoal. Yet we know 
 that we can prepare salt water by mixing ; we find further- 
 more that we are able to separate salt water, as well as 
 other mixtures, by rather simple processes, a few of which 
 are outlined in the next section. 
 
 8. Methods of separating mixtures into their components 
 are based on some physical property by which the compo- 
 nents differ markedly from each other. Thus a component 
 may be attracted to a magnet and the other components 
 not; a component may be very volatile or very soluble 
 or very heavy. Methods of separation are as varied as 
 physical properties are varied, but we shall describe only a 
 few practical methods of separating some typical mixtures. 
 
 A block of granite might be crushed, and then with the 
 aid of a magnifying glass and delicate forceps the separate 
 particles of quartz, feldspar, and mica might be picked out 
 and laid in separate piles. This method, which may be 
 
MECHANICAL SEPARATION 
 
 17 
 
 called simple mechanical separation, would, however, prove 
 very wearisome. 
 
 Salt water is a mixture of so intimate a character that the 
 most powerful microscope fails to show any separate particles 
 of salt and of water, yet this mixture may be separated by 
 distilling. The salt water is placed in a flask and boiled ; 
 the water changes into a vapor, steam, which passes off and 
 may be led through 
 a condenser, that is, 
 a pipe surrounded by 
 a cooling bath. Here 
 the steam condenses 
 to water which drips 
 from the lower end 
 of the condenser tube 
 (see Fig. 1). The 
 salt, which is not 
 volatile, is left behind 
 in the flask as a mass 
 
 FIG. 1. Distilling Apparatus. A, flask in 
 which liquid is boiled. B, trap to catch spray 
 from boiling liquid and prevent any non- 
 volatile matter passing over with the vapor. 
 C, condenser. D, receiver. E, cooling water 
 
 of crystals. This 
 method of distillation 
 has a very wide prac- e " ters u from *? .f / erflow - <*> 
 
 through which liquid returns to flask. 
 
 tical use for separat- 
 ing mixtures of volatile and non-volatile substances, or even 
 for separating substances of different degrees of volatility. 
 
 A mixture of sugar and sand can be separated if it is 
 stirred up with water; the sugar dissolves in the water, 
 while the sand remains unchanged. By pouring off the solu- 
 tion of sugar from the sand one accomplishes the separation. 
 The solution may be made to give up its sugar if the water 
 is evaporated away, just as the salt water gave up its salt 
 on distillation. Here separation is accomplished by taking 
 
18 MIXTURES AND CHEMICAL SUBSTANCES 
 
 advantage of differences in solubility. Such separations are 
 carried out on an enormous scale in practical work. 
 
 A mixture of light and heavy particles, as, for example, 
 a mixture of powdered sulphur and iron filings, may be 
 separated by taking advantage of differences in density. 
 Neither of these substances dissolves in water; but if the 
 mixture is stirred vigorously with a large amount of water, 
 the whole becomes suspended in the liquid. If the liquid 
 is then left a moment at rest, the particles of iron, being heavy, 
 settle rapidly to the bottom, while the lighter particles of 
 sulphur remain suspended for a longer time. Then if the 
 upper part of the liquid is poured off at the right moment, 
 most of the suspended sulphur is carried with it, whereas 
 the iron is left behind. If this process be carried out with 
 sufficient care, the sulphur can be completely separated 
 from the iron. 
 
 This type of separation is frequently made use of in indus- 
 trial and mining operations that are carried out on a large 
 scale. Most interesting perhaps is the separation of gold 
 dust from gold-bearing sand. 
 
 9. Chemical Substances that can be separated. As 
 already said above, a chemical substance is a material which 
 cannot be prepared by the mere mixing of different ingredi- 
 ents, nor can it be separated by non-chemical means into 
 different kinds of matter. Now the great majority of chemi- 
 cal substances, for example salt and sugar, can be separated 
 chemically into two or more different substances, but the 
 chemical means that must be employed to do this are very 
 unlike the methods described under the last heading. To 
 break down a chemical substance into different substances 
 generally involves the expenditure of a large amount of 
 energy, perhaps in the form of intense heat, perhaps in the 
 
SUMMARY AND QUESTIONS 19 
 
 form of an electric current, and perhaps as chemical energy 
 through interaction with some other chemical substance. 
 
 Furthermore, when a pure substance is separated chemi- 
 cally, the new substances are totally different in their proper- 
 ties from the original substance; whereas when a mixture 
 is separated, each of the components still possesses the same 
 properties which it showed in the mixture. 
 
 SUMMARY 
 
 A mixture is composed of two or more chemical substances. A 
 coarse-grained mixture may be laboriously separated into its 
 components by sorting out the particles by hand. More in- 
 timate mixtures may be separated by taking advantage of 
 differences in the physical properties of the components, as, 
 for example, differences in volatility, solubility, or density. 
 
 A pure chemical substance consists of a single kind of matter. If 
 a pure substance is capable of being separated chemically 
 into different substances, it is only by a process totally dif- 
 ferent from the methods of physical separation of mixtures; 
 moreover the separation yields totally new substances with 
 altogether new properties. 
 
 Questions 
 
 1. Look up in the dictionary the words matter, substance, mixture, 
 body, object, and decide which of the meanings applies in chemistry. 
 
 2. Distinguish between the popular meaning of the word sub- 
 stance and the scientific meaning. of the term pure substance. 
 
 3. Make use of the terms substance, mixture, body, and object in 
 classifying the following: rain water, sea water, the Atlantic 
 Ocean, Lake Superior, the block of ice that the ice man just de- 
 livered, sugar, maple sugar, hash, a mince pie, the marble statue 
 in front of the city library, the ledge of marble on the mountain, 
 iron, the old cannon in the museum. 
 
 4. How could the property of magnetism be used to separate a 
 mixture of iron filings and powdered sulphur? 
 
 6. How could salt be separated from sand? 
 
CHAPTER III 
 ELEMENTS AND COMPOUNDS 
 
 10. Elements. Of the substances of which we have 
 spoken in the previous chapter, some namely, sulphur, 
 charcoal, and iron cannot be separated into other than 
 just the single substances by any means known to us, either 
 by physical or by chemical processes. Such substances are 
 known as elements ; and up to the present day about eighty 
 of these elementary substances have been discovered (see 
 table inside the back cover). 
 
 The elements may combine chemically with other ele- 
 ments and thereby form totally different substances, but 
 the elements can always be separated again undiminished 
 in weight from the compounds. For example, if one kilo- 
 gram of charcoal burns, although the charcoal disappears, 
 there is still one kilogram of carbon in the carbon dioxide 
 which is formed. (Carbon is the name of the element of 
 which the substance charcoal consists. The element is 
 always carbon, whatever the form or state of chemical com- 
 bination; charcoal is a form of the uncombined element.) 
 The carbon dioxide which escapes into the air is taken up 
 mostly by trees and plants, where the element undergoes 
 further chemical change, and thus this kilogram of carbon 
 may eventually become part of the wood of trees. The 
 wood may be charred again, and thus some at least of the 
 original charcoal will return again to the form of charcoal. 
 
 20 
 
CHEMICAL COMPOUNDS 21 
 
 Whatever the final form of the one kilogram of carbon, it 
 still exists somewhere unchanged in weight. 
 
 We are perhaps not warranted in claiming with certainty 
 that the elements are absolutely the simplest forms of matter. 
 All that the chemist means to imply, when he calls a sub- 
 stance an element, is that it is something which human skill 
 has been unable to resolve into two or more different sub- 
 stances. 1 In the past men have regarded as elements many 
 substances which have since been shown to be separable. 
 
 One of the early attempts to classify substances was that 
 of the ancient Greek philosophers, under the leadership of 
 Aristotle, who divided all substances into four supposed 
 elements, earth, air, fire, and water. This division was 
 based on fanciful speculation instead of scientific knowledge ; 
 but within recent times, even within a few decades, what 
 have been supposed to be elements have in a few instances 
 been found to be really mixtures of two or more elements. 
 
 11. Chemical Compounds. The number of chemical sub- 
 stances which the chemist has discovered is almost countless. 
 A few of them, as we have seen, are elements, but the great 
 majority are compounds of two or more elements. Salt 
 and sugar are chemical compounds, so also are water, baking 
 soda, washing soda, and alum. 
 
 It must not be thought, however, that these compounds 
 are any the less chemical substances than the elements car- 
 
 1 Recent discoveries in connection with the study of radio- 
 active elements such as radium have tended to show that some 
 of the elements, perhaps all, are constantly undergoing changes, 
 some being produced while others are being disintegrated. It may 
 be that the agencies which have produced the elements are still at 
 work. Even with the most rapidly changing element, however, 
 any increase or decrease in quantity is so small that it is almost or 
 quite beyond the range of detection with the chemical balance. 
 
22 ELEMENTS AND COMPOUNDS 
 
 bon, sulphur, and iron, for compounds have just as charac- 
 teristic properties as have the elements themselves, and these 
 properties are lost altogether whenever the compounds are 
 separated into their elements. 
 
 Another important characteristic of chemical compounds 
 is that they always contain exactly the same proportion by 
 weight of their constituent elements. This statement is known 
 as the law of definite proportions. Mixtures, on the other 
 hand, may contain variable proportions of their ingredients. 
 We shall find in succeeding chapters that a knowledge of the 
 definite proportions in which elements are united in com- 
 pounds is a matter of the utmost importance in the develop- 
 ment of chemical science. 
 
 12. Mixtures and Compounds. Let us try to make clear 
 the difference between physical mixtures and chemical com- 
 pounds by comparing the effect of merely mixing two chemi- 
 cal substances on the one hand and causing them to com- 
 bine chemically on the other hand. 
 
 Mixing may be accomplished by merely shaking or stirring 
 substances together if they are first very finely divided. 
 
 13. Mixture of Iron and Sulphur. A mixture which 
 can readily be made in the laboratory is one of iron and 
 sulphur. If the very finest powdered sulphur and an irn- 
 palpably fine iron dust are thoroughly stirred together, 
 a mixture is obtained which appears like a uniform gray 
 powder ; to discover any unevenness in its texture it is 
 necessary to employ a powerful microscope. Still this 
 mixture may be separated into sulphur and iron by the 
 method described on page 18. Another convenient method 
 by which it can be separated is to treat it with carbon 
 disulphide, a liquid in which sulphur dissolves much as salt 
 dissolves in water. The iron is left undissolved and may 
 
COMPOUND OF IRON AND SULPHUR 23 
 
 be separated by pouring off the liquid, and the sulphur 
 may be obtained from the solution by allowing the carbon 
 disulphide to evaporate. 
 
 14. Compound of Iron and Sulphur. Now let us fill 
 a test tube with some of this intimate mixture of sulphur 
 and iron, and heat the mixture in one spot until it begins 
 to glow. On removing the test tube from the flame the 
 glow does not subside, but spreads to every part of the 
 mixture, giving forth light and heat and thus furnishing 
 abundant evidence that a vigorous change is taking place. 
 After the whole mass has thus entered into this reaction 
 and has afterward been allowed to cool, it is found that there 
 remains a hard cake. If proper proportions of iron and of 
 sulphur were used this cake may now be pulverized and stirred 
 up with water, and we shall not find any lighter particles of 
 sulphur which float off nor any heavier particles of iron 
 which settle. Neither will it be possible to dissolve put 
 sulphur by means of carbon . disulphicje and leave iron 
 behind. 
 
 Here, again, a chemical reaction has occurred with the 
 appearance of a good deal of heat and light energy. A new 
 substance totally unlike either of the original substances has 
 been formed, and this cannot now be separated into the 
 two original substances by any of the comparatively simple 
 methods by which mixtures of the latter substances were 
 separated. 
 
 The study of chemistry is vitally concerned with chemical 
 compounds, but it is concerned to a much smaller extent 
 with mixtures. For in mixtures there is no real associa- 
 tion of the component substances and a study of the prop- 
 erties of the mixture is only a study of the properties of 
 the separate substances. But in compounds, on the other 
 
24 ELEMENTS AND COMPOUNDS 
 
 hand, the characteristics of the constituent substances are 
 lost and the compounds themselves are distinctive chemical 
 individuals with distinctive properties of their own. 
 
 SUMMARY 
 
 An element is a substance which cannot be resolved into different 
 
 chemical substances by any agency under human control. 
 
 All the matter of which our earth is composed is made up of 
 
 about eighty elements. 
 Chemical compounds are pure substances which can be separated 
 
 by chemical means into two or more elementary substances. 
 
 Chemical compounds are characterized by a definite ratio by 
 
 weight of their constituent elements. 
 
 Questions 
 
 1. Define element ; compound. 
 
 2. Name five common elements. 
 
 3. Name five common compounds. 
 
 4. In the light of our present knowledge of the elements, can we 
 ever hope to be able to convert lead into gold? 
 
 5. What is true of the proportions of the constituents of a com- 
 pound that is not true of the components of a mixture? 
 
 
CHAPTER IV 
 COMBUSTION 
 
 THE chemical phenomenon most familiar in everyday 
 life, in fact so familiar that the average person hardly 
 realizes that it has any connection with chemistry, is ordinary 
 burning or combustion. Combustion is, however, not only 
 the most common, but also one of the most important, of 
 chemical reactions, since it is the energy liberated in this 
 reaction which furnishes the human race with most of its 
 heat, light, and power. 
 
 15. Historic Views as to the Nature of Combustion. Com- 
 mon as is the phenomenon of fire, it is, until understood, 
 most mysterious. Fire was regarded by the ancients as one 
 of the gifts of the gods. By the Greek philosophers it was 
 regarded as one of the four elements of which the world is 
 composed. At a later period it was regarded as consisting 
 in the escape of a volatile substance called phlogiston, which 
 was supposed to be contained in all substances capable of 
 burning. It was only during the last of the eighteenth cen- 
 tury and in the beginning of the nineteenth that the true 
 chemical nature of combustion gradually came to be appre- 
 ciated. This was scarcely more than a century ago, and 
 since combustion is one of the most important of chemical 
 phenomena and since an explanation of its nature first led 
 to an understanding of other chemical phenomena, it is 
 plain that chemistry is still a comparatively young science. 
 
 25 
 
26 COMBUSTION 
 
 16. Modern Theory of Combustion. Combustion con- 
 sists of a chemical uniting of the combustible substance with 
 oxygen, a substance which is one of the components of the 
 air; the product of this union is in many cases a gaseous 
 substance, but in all cases, whether the combustion product 
 be a solid, a liquid, or a gas, its weight is exactly equal to 
 the weight of the substance burned plus the weight of the 
 oxygen consumed. 
 
 17. Growth of Modern Theory of Combustion. Let us 
 outline a few of the important facts regarding combustion 
 and recount some of the important steps by which the modern 
 view of the nature of combustion was developed. 
 
 Wood, coal, and charcoal, if kindled, that is if heated suffi- 
 ciently so that active combustion begins, will burn, and 
 what we call fire is observed. Flames which are hot and 
 luminous arise and then seem to vanish into the air. 
 
 Combustion is not limited, however, to those cases where 
 substances burn vigorously with a flame. Even the earlier 
 chemists who upheld the phlogiston theory realized that the 
 burning of wood and the rusting of iron were phenomena of a 
 similar nature. Their mistake lay in thinking that in each 
 case there was an escape of phlogiston. When iron rusted, 
 they thought that phlogiston escaped, and that the rust 
 left, or the calx, as it was then termed, was iron which had 
 lost the phlogiston which belonged to it. We now know 
 that iron rust is produced by the slow combining of iron 
 with oxygen, and that the weight of the rust, or oxide, is 
 exactly equal to the sum of the weights of the iron and the 
 oxygen consumed. 
 
 Much iron oxide is found in the earth as a brown or black 
 ore, and to obtain the metal this ore is heated in a furnace 
 with charcoal or coke which removes the oxygen from the 
 
OXIDATION 27 
 
 oxide and leaves uncombined iron. This process for obtain- 
 ing iron from its ore is a very ancient one, and was well 
 known to the phlogistic chemists, but they imagined that 
 charcoal was pure phlogiston and that it combined with the 
 calx (iron oxide) to produce the metal, which they regarded 
 as the compound of the calx and phlogiston. They failed to 
 appreciate and correctly interpret the fact that the calx 
 weighed more than the metal. 
 
 18. Use of the Balance. When, however, the balance 
 came into general use as a necessary instrument in the study 
 of chemistry and the fact that metal oxides weigh more than 
 the metals from which they are formed became better under- 
 stood, the old phlogistic idea of combustion gave way in 
 favor of the modern theory of oxidation. 
 
 19. Oxidation of Metals. Iron is not the only metal 
 which on exposure to the atmosphere becomes coated with 
 a dull non-metallic layer. In fact, most of the better-known 
 metals, with the exception of the precious metals, gold, silver, 
 and platinum, are soon tarnished or corroded to a greater 
 or less degree, depending on their chemical activity and on 
 whether the coating first formed is permeable or impermeable 
 to the gases of the air. 
 
 Lead, copper, and zinc, for example, when freshly polished, 
 display bright metallic surfaces; but after exposure to the 
 air, as when they are used for gutters or for trimmings on 
 roofs, lead becomes covered with a gray and lusterless coat- 
 ing, copper with a green coating, and zinc with a dull 
 whitish coating. If instead of being exposed to the weather 
 these metals are heated in contact with the air, a more rapid 
 change occurs. Lead, if it is kept above its melting tem- 
 perature and stirred so as to have a fresh surface con- 
 tinually exposed, changes in a fairly short time to a dull yellow 
 
28 
 
 COMBUSTION 
 
 powder. Copper when heated to redness becomes covered 
 with a black or reddish crust which can be scraped off as a 
 brittle scale. Zinc if heated to a high temperature catches 
 fire and burns with an intense bluish white light and a fine 
 white powdery substance (zinc white) is formed. In all 
 these cases it was found, when the balance was used, that 
 the product of the combustion was heavier than the original 
 
 metal ; furthermore 
 it was observed that 
 when a metal had 
 once been heated or 
 charcoal burned in a 
 quantity of air con- 
 fined in a closed 
 vessel, the residual 
 air had no further 
 power to cause cor- 
 rosion or burning. 
 It thus became ap- 
 parent that in com- 
 bustion some com- 
 ponent must betaken 
 from the air to com- 
 bine with the com- 
 bustible substance. 
 
 20. The Products 
 of Combustion of a 
 Candle. It can be 
 shown by the balance 
 that there is an in- 
 crease in weight, not 
 only when metals 
 
 FIG. 2. For showing that the Products of Com- 
 bustion of a Candle weigh more than the Candle Itself. 
 The candle is placed on one pan of the balance 
 and above it is suspended a glass cylinder filled 
 with sticks of sodium hydroxide. Weights are 
 then placed on the other pan to exactly counter- 
 balance the candle and absorption cylinder. 
 The candle is now lighted, the gases from the 
 flame pass through the funnel into the absorp- 
 tion tube ; the pan with the candle soon sinks, 
 showing that it is growing heavier. To keep it 
 in balance more weights must continually be 
 added to the other pan as long as the candle 
 burns. 
 
DISCOVERY OF OXYGEN 29 
 
 corrode to form solid oxides, but also in those cases in 
 which substances burn to form gaseous products. Thus, 
 for example, a balance may be arranged with a candle 
 on one pan and suspended above it a lamp chimney con- 
 taining sticks of sodium hydroxide to absorb the products 
 of combustion (Fig. 2), and the whole may be exactly 
 counterpoised by placing weights on the other pan. 
 So long as the candle remains unlighted, the pans remain 
 balanced and neither rises or falls. When the candle is 
 lighted and begins to waste away, one would expect the pan 
 holding it to rise because of a decrease in weight. What is 
 actually seen is that that pan sinks. The gaseous combus- 
 tion products of the candle have been caught by the sodium 
 hydroxide and these are thus shown to weigh more than the 
 candle alone. 
 
 21. Discovery of Oxygen by Priestley, 1774. The dis- 
 covery of pure oxygen by Priestley paved the way for recog- 
 nizing the true nature of combustion, although Priestley 
 himself was unable to fit together the facts and deduce the 
 true solution. 
 
 Mercury, on account of its remarkable properties, was 
 always a favorite substance for experimentation with the 
 early chemists. It had been known that if this metal was 
 maintained at a temperature just below its boiling point 
 (considerably below a red heat) it slowly changed into a 
 bright red powder the calx of the phlogistic chemists. 
 Priestley put some of the red powder in the top of a glass 
 tube filled with mercury and placed it with its closed end 
 up and its lower end sealed by being dipped in a vessel of 
 mercury. By focusing the sun's rays by means of a burn- 
 ing glass upon the red powder at the top of the tube, he found 
 that a gas was formed which forced down the mercury and 
 
30 COMBUSTION 
 
 filled some little space. On placing a lighted candle in this 
 gas, he found that it burned with a remarkably brilliant 
 flame far more brilliant than when it burned in ordinary 
 air. He was much mystified by this behavior, and he de- 
 scribed the gas as having all the properties of ordinary air 
 only in much greater perfection. He called it dephlogisti- 
 cated air and regarded it only as very pure ordinary air. 
 
 22. Lavoisier's Explanation of Combustion. It remained 
 for the French chemist Lavoisier to clearly recognize and 
 state the true nature of combustion. He connected Priestley's 
 discovery with the fact that an increase rather than a 
 decrease in weight takes place when substances burn, and 
 with the fact that during the burning the air not only loses 
 in volume, but also loses its power to support combustion. 
 
 Lavoisier's crucial experiment was to heat mercury within 
 an inclosed vessel of air. He found that the volume of the 
 air contracted by about one fifth, while at the same time 
 a red powder formed on the surface of the mercury; the 
 residual air had no power to support combustion. After- 
 wards, on heating this red compound of mercury, a gas was 
 given off whose volume was one fifth that of the original air. 
 This gas alone supported combustion with great vigor, and 
 when mixed with the residual four fifths of the original air, 
 restored to it the property of supporting combustion in the 
 ordinary manner. 
 
 23. Combustion in the Light of our Present Knowledge. 
 The atmosphere consists chiefly of a mixture of two gases, 
 about one fifth part by volume is oxygen, the supporter of 
 combustion; about four fifths is nitrogen, an inert gas 
 which plays no part in combustion except that it dilutes the 
 oxygen and decreases the intensity of its action. 
 
 When substances burn in the air, they combine chemically 
 
OXIDES OF CARBON 31 
 
 with the oxygen to form oxides, while the nitrogen is left 
 unchanged. An oxide is a chemical compound of an element 
 with oxygen and nearly all of the elements are capable of 
 forming oxides. 
 
 24. Oxides of Carbon. Charcoal, which is nearly pure 
 carbon, burns vigorously when it has a plentiful supply of 
 air and forms carbon dioxide, an invisible gas. If all or 
 nearly all of the oxygen of the air is used up in this way, 
 the latter can no longer support combustion ; neither is air 
 that is so deprived of its oxygen able to support human or 
 animal life. Carbon dioxide is not actively poisonous, but 
 the absence of oxygen results in suffocation. 
 
 If the charcoal is burned with a restricted supply of air, 
 then a part or even the whole of the product of combustion 
 consists of carbon monoxide, another oxide of carbon which 
 contains a lesser proportion of oxygen. This substance is 
 also a gas, but it is extremely poisonous when breathed by 
 human beings or animals. It is due to the formation of 
 this gas that charcoal fires in unventilated rooms have been 
 responsible for many deaths. 
 
 25. Combustion of Wood. Wood is a compound contain- 
 ing carbon, hydrogen, and oxygen. When it burns the 
 chemical reaction is not unlike that of burning charcoal. 
 The existing form of chemical combination of the wood is 
 broken down by the heat of the fire, and the carbon and 
 hydrogen combine with oxygen from the air in addition to 
 that which comes from the wood itself and form carbon 
 dioxide, and oxide of hydrogen (water vapor), respectively. 
 
 When wood decays, it undergoes a chemical change not 
 essentially different from that of burning except in rapidity. 
 The heat of the reaction is not produced fast enough to 
 cause flame or even to make the wood feel warm to the 
 
 B. AND W. CHEM. 3 
 
32 COMBUSTION 
 
 touch, but still the products of the reaction contain carbon 
 dioxide and water. 
 
 26. Slow Combustion of Foods in our Bodies. The source 
 of the body warmth and muscular energy of men and ani- 
 mals lies in a chemical reaction similar to that of the burn- 
 ing or the decay of wood. The burning of wood is a violent 
 reaction and produces intense local heat ; the combustion of 
 foodstuffs in animals, on the other hand, takes place slowly, 
 like the decay of wood, and produces only the degree of 
 warmth necessary to keep the animal in health. A furnace 
 fire is fed with coal or wood. The fire in a man's body is fed 
 with the foods that contain sugar, starch, or fat. Sugar, 
 starch, and fat have a chemical composition somewhat 
 similar to that of wood ; that is, they are composed of car- 
 bon, hydrogen, and oxygen. In the digestive organs they 
 are made soluble and pass into the blood and are taken by 
 the blood into all the tissues of the body. In the tissues, to 
 which the blood also brings oxygen, taken from the air that 
 is breathed into the lungs, there takes place the most mar- 
 velously regulated combustion. This combustion, like the 
 active burning of wood in the air, results in the formation 
 of carbon dioxide and water, and both of these products are 
 exhaled with every breath from the lungs. To demonstrate 
 that water vapor is present in the air from the lungs, one 
 has only to breathe against a cold window pane, when the 
 glass becomes clouded with condensed droplets of water ; 
 and to show the presence of carbon dioxide, one need only 
 blow the breath through a glass tube into a tumbler of lime- 
 water, which is immediately rendered white and cloudy. 
 
 When we exercise violently, our breath comes much 
 faster. This is because the waste or combustion of bodily 
 tissue is much more rapid during exercise and more oxygen 
 
SMOKE PREVENTION 33 
 
 has to be supplied from the lungs to consume it. Also it 
 is necessary for the lungs to work more rapidly in order to 
 remove the greater amount of carbon dioxide which is 
 produced. 
 
 27. Forced Draft. A similar case of the need of an in- 
 creased supply of oxygen when more rapid combustion is 
 desired, is seen in the use of the blacksmith's bellows. In 
 order to hasten his fire, the blacksmith pumps air rapidly 
 through the fire by means of the bellows, thus supplying 
 more oxygen and hence burning more fuel in a given time 
 and producing a hotter fire. 
 
 A battleship uses a forced draft, that is, it pumps air 
 rapidly through the fires, when attempting to attain a high 
 speed. The principle is, of course, the same as that in- 
 volved in the blacksmith's fire ; a limited amount of air can 
 burn only a limited amount of coal and thereby produce 
 only a limited amount of heat. By supplying more air, 
 more coal can be burned and more heat obtained. 
 
 28. Smoke and Smoke Prevention. It is not an easy 
 matter to regulate the proper supply of fuel and air in the 
 fires of manufacturing establishments, or, for that matter, 
 in other fires, and as a consequence our manufacturing cities 
 are to-day burdened with the smoke nuisance. The ob- 
 noxious black smoke which issues from the chimneys consists 
 in the main of unburned fuel material, for the most part in 
 the solid condition, but so finely divided that it floats for a 
 long time in the air just as fine dust will do. 
 
 There is, however, no good excuse, now, for allowing the 
 smoke nuisance to continue. Modern smoke-preventing 
 devices are designed in the first place to regulate the supply 
 of both the air and the fuel so that neither an excess of fuel 
 shall be wasted as smoke nor too great an excess of air shall 
 
34 
 
 COMBUSTION 
 
 enter to cool off the fire and diminish its efficiency. This 
 regulation is usually accomplished by means of some form 
 of automatic stoker which can be made to supply the fuel 
 as rapidly or as slowly as desired, while the air supply is 
 controlled by a blower. In the second place, it is necessary 
 that the smoke which does form shall be burned before it 
 can pass into the cooler flues and become chilled to a tem- 
 perature below its burning point. This is accomplished by 
 admitting some fresh air into the chamber above the fire 
 and allowing this, mixed with the hot gases and smoke, to 
 pass through a considerable distance over the white-hot 
 fire bed between it and the arch of very hot fire brick which 
 forms the top of the furnace. In this way the smoke, 
 together with sufficient air, is kept at a temperature above 
 
 FIG. 3. Smoke Nuisance and Smoke Prevention. Automatic stoker and large- 
 combustion chamber used in furnace whose chimney shows no smoke. 
 
 its kindling point until it is completely burned. Such smoke 
 consumers are now largely used, and allow the burning of 
 even the cheapest grades of soft coal in the powdered form 
 
SMOKE PREVENTION 
 
 35 
 
 without an objectionable amount of smoke issuing from the 
 chimney. The saving due to the economy of fuel, in many 
 cases, more than offsets the cost of the smoke prevention 
 devices. 
 
 S i r * 
 
 WATfK LfVCL -^ A 
 
 : --t , _^ ^ f ^^ t _=. _~~** _- 7 jFZ-fr^r"E^ 
 
 FIG. 4. Boiler and Furnace with Chain Grate Stoker. 
 
 A. Coal chute. 
 
 B. Chain grate. 
 
 C. Air inlet. M. 
 
 D. Damper. N. 
 
 E. Flames. O-P. 
 
 F. Course of heated gases. 
 
 G-H. Baffle walls. Q. 
 
 J. Bridge wall. 
 K-L. Zig-zag passage in bridge 
 
 wall for delivering heated 
 air to fire. 
 Water in drum. 
 Water inlet. 
 Outlet and inlet for water 
 
 circulation. 
 Water tubes. 
 R. Blow-off pipe. 
 S. Steam outlet. 
 
36 COMBUSTION 
 
 SUMMARY 
 
 The discovery of oxygen by Priestley in 1774 was the first step 
 towards understanding the nature of combustion. Some- 
 what later Lavoisier developed the present explanation by 
 connecting Priestley's discovery with the fact, shown with the 
 chemical balance, that an increase in weight always occurs 
 during combustion. 
 
 Combustion is the most frequently observed as well as the most 
 important of chemical changes. Combustion consists in the 
 uniting of oxygen, the active component of the air, with the 
 combustible substance. In rapid combustion great heat is 
 developed and incandescence, or flame, is observed. 
 
 Slow combustion, as the rusting of iron, or the decay of wood, is 
 chemically the same sort of a process as rapid combustion, 
 but the heat produced has time to escape so that no incan- 
 descence, or flame, is to be seen. Food is the fuel for the 
 bodies of men and animals, and by a process of slow combus- 
 tion it furnishes animal warmth and muscular energy. 
 
 Oxides. Most metals give solid oxides as combustion products. 
 Carbon gives two different oxides : with a plentiful supply 
 of air, carbon dioxide, a comparatively harmless gas ; with a 
 restricted supply of air, carbon monoxide, a most poisonous 
 gas. 
 
 Fuels contain carbon as their most important constituent, and 
 besides carbon they usually contain hydrogen. Their ma- 
 terial combustion products are principally gases and are of 
 no value. They are burned for heat, light, and power, which 
 are essential for the welfare of the human race. 
 
 Smoke consumption. As ordinarily burned, much fuel is wasted 
 as smoke, but by the use of suitable devices this waste may 
 be prevented and the nuisance of smoke avoided. 
 
 Questions 
 
 1. How might one prove that something from the air is con- 
 cerned in combustion? 
 
 2. Why does the rusting of iron continue until all the iron is 
 rusted, whereas the tarnishing of copper, zinc, and lead is on the 
 surface only? 
 
QUESTIONS 37 
 
 3. Why, then, is it necessary to paint iron bridges, although it 
 is not necessary to paint copper-covered roofs ? 
 
 4. Explain the danger from charcoal fires in closed rooms. 
 Why is there not the same danger from a burning gas jet? 
 
 5. Give some evidence to prove that combustion takes place in 
 the animal body. 
 
 6. Discuss from a common viewpoint the rapid breathing of a 
 person running and the use of a blacksmith's bellows. 
 
 7. What is smoke? Why is it an economy to prevent it? 
 
 8. When burning dry leaves, if one rakes a lot of new leaves 
 all at once on top of the fire a very dense smoke is formed. Explain 
 why it is that when the flame finally works up through the new 
 leaves and bursts out through the top, the smoke all seems to 
 vanish. 
 
 9. Explain why in unprogressive manufacturing establishments 
 black smoke belches from the chimney when the stoker opens the 
 furnace door and shovels a quantity of soft coal on the fire. How 
 might the stoker by care lessen the amount of smoke? How would 
 you design and run a furnace to prevent smoke? 
 
 10. What does the fact that a pile of barnyard manure steams 
 in winter indicate is taking place within the pile? 
 
 11. Why does a camper get down and blow his fire when it gets 
 low? 
 
 12. Why does water extinguish a fire? 
 
CHAPTER V 
 
 OXYGEN 
 
 IN the last chapter it has been seen that the atmosphere 
 contains a chemically active substance which is called 
 oxygen; and that when any one of a number of metals is 
 heated in the air, this oxygen combines with the metal to 
 form an oxide. It was by heating one of these oxides, namely 
 oxide of mercury, that pure oxygen was discovered by 
 Priestley. 
 
 29. Abundance. Oxygen is now known to be the most 
 abundant of all the elements, for it is estimated that about 
 one half of the whole earth, as far as we know it, is composed 
 of oxygen. Uncombined oxygen comprises about one fifth 
 of the air. Eight ninths by weight of water is oxygen, which 
 is in combination with hydrogen. The great bulk of the 
 solid crust of the earth is composed of compounds of oxygen ; 
 thus quartz rock and ordinary sand, which is quartz in a 
 fine state of subdivision, are oxide of silicon, containing 53 
 per cent of oxygen; limestone consists of two oxides in 
 combination, calcium oxide and carbon dioxide, 48 per cent 
 by weight of the limestone being oxygen. 
 
 30. Preparation by heating Oxides. The method of 
 Pjiestley for the preparation of oxygen is still used as a 
 convenient laboratory method for showing that oxygen can 
 be generated from an oxide; it is never used, however, to 
 pi/epare any large quantity of oxygen, because mercury and 
 its compounds are too costly. 
 
 38 
 
PREPARATION OF OXYGEN 
 
 39 
 
 Many less expensive oxides will evolve oxygen when 
 heated sufficiently, but in most cases the amount of heat 
 required is so great that the process is too costly or too 
 inconvenient on that account. 
 
 31. Preparation from Potassium Chlorate. For the 
 preparation of oxygen on the small scale in the laboratory, 
 recourse is had to potassium chlorate, which contains about 
 40 per cent by weight of oxygen and gives it all off when 
 heated. The potassium chlorate is mixed with its own bulk 
 of powdered manganese dioxide, and the mixture is placed 
 in a test tube (Fig. 5) . 
 The latter is provided 
 with a delivery tube 
 leading to a water 
 trough, and on gently 
 heating the test tube 
 oxygen gas is evolved 
 and can be collected 
 in test tubes or in 
 wide-mouthed gas 
 bottles which have 
 been previously filled with water and inverted in the trough. 
 
 The manganese dioxide and the potassium chlorate both 
 contain oxygen, and either alone will give up oxygen upon 
 being strongly heated. The potassium chlorate, however, 
 requires to be heated to considerably above its melting 
 point (334 C.) before giving up its oxygen rapidly, and the 
 manganese dioxide when alone yields oxygen only when 
 heated to a red heat. If, however, the two substances are 
 mixed together and heated, oxygen begins to come off at a 
 temperature in the neighborhood of 200 C. Hence the 
 mixture is invariably used. 
 
 FIG. 5. Preparation of Oxygen. Potassium 
 chlorate mixed with manganese dioxide is 
 heated and the gas is collected over water. 
 
40 OXYGEN 
 
 32. Catalysis. If the separate substances are carefully 
 weighed before they are heated and the products left after 
 the decomposition are separated and also weighed, it is 
 found that exactly as much manganese dioxide remains as 
 was taken at the start, while in place of the potassium 
 chlorate, a new substance, potassium chloride, is left. The 
 latter contains no oxygen, and it is clear therefore that all 
 of the oxygen has come from the decomposition of the potas- 
 sium chlorate. The manganese dioxide has suffered no ap- 
 parent change, but has, by its mere presence, helped the 
 other substance to undergo a change very much more 
 smoothly and quickly than it could have done alone. Cases 
 like this we shall find are very frequent in chemistry and 
 they are known as cases of catalysis. The catalytic agent 
 (in this case the manganese dioxide) does not cause the re- 
 action, it merely makes it easier for it to take place. No 
 more does lubricating oil cause a wheel with a rusted bearing 
 to turn, it simply makes it easier for it to turn. 
 
 33. Preparation from Liquid Air. The most inexpensive 
 source of oxygen is obviously the air, and comparatively 
 recently a method of cheaply separating it from the air has 
 been perfected. By the Linde process, the air is first liquefied 
 by high compression and intense cold, and the liquefied 
 air within the apparatus is then allowed to boil, whereby 
 nitrogen, which is the more volatile component of the air, 
 passes off, leaving fairly pure oxygen. The latter is then 
 allowed to vaporize and is pumped under high pressure into 
 steel cylinders, in which it is transported and sold. 
 
 34. Properties of Oxygen. When oxygen prepared by 
 one of the above methods is examined, it is found to be a 
 colorless, odorless, tasteless gas and one which will cause a 
 glowing splinter to burst into a vigorous flame, but will not 
 
PROPERTIES OF OXYGEN 
 
 41 
 
 itself burn. These properties can be discovered without the 
 use of any elaborate apparatus and without any great 
 degree of skill in observation. If we were to obtain a gas 
 
 FIG. 6. Linde Apparatus for making Liquid Air. A, air inlet. B, com- 
 pressing pump. C, cooling coil where the heat developed by the compres- 
 sion of the air is withdrawn. Coil is surrounded by running cold water. 
 D, inner pipe of the liquefying coil ; here the compressed air is cooled to a 
 very low temperature. E, outer pipe of liquefying coil ; here the expanding 
 air cools the compressed air in DD. F, expansion chamber and reservoir 
 for liquid air. The air emerging from the valve at lower end of D expands 
 suddenly and produces great cold. Part of the air is thus liquefied and 
 drops into the reservoir while the rest passes through E and cools the 
 compressed air in D to the liquefaction point. 
 
 from some unknown source and find that it possessed the 
 properties mentioned, it would be natural to assume that it 
 was oxygen. There is at least one other gas, however, 
 and there might be more, which shows approximately the 
 
42 OXYGEN 
 
 properties mentioned, and it might be possible for us to 
 obtain this gas and mistake it for oxygen. Hence in order 
 to distinguish oxygen with certainty from all other sub- 
 stances, we must define its properties more completely and 
 more exactly. 
 
 Properties such as the specific gravity, the degree of 
 solubility in water, and the temperature of liquefaction and 
 of solidification can be accurately measured and stated in 
 exact numerical terms. It is extremely improbable we 
 can even say impossible that a substance can have all 
 the easily observed properties of oxygen, noted earlier, and 
 give exactly the same quantitative values for the last-named 
 properties, and still be any other substance than oxygen. 
 Of course, if the substance were further studied and foiind to 
 differ from oxygen in any single particular, it could not be 
 oxygen ; but it is our experience with nature that when two 
 substances are exactly alike in several of their properties 
 they will be found to be alike in all of their properties. 
 
 35. Density. Oxygen is a little heavier than air, its 
 specific gravity referred to air being 1.105, that is, one liter 
 of oxygen weighs 1.105 times as much as one liter of air at 
 the same temperature and under the same pressure. Ex- 
 pressed in other terms, one liter of oxygen at C. and 
 under 760 millimeters pressure (that is under standard con- 
 ditions) weighs 1.43 grams; that is, 1000 cubic centimeters 
 of oxygen weigh about the same as one and one half cubic 
 centimeters of water. 
 
 36. Solubility. Oxygen is slightly soluble in water. At 
 ordinary temperature and pressure about three volumes of 
 oxygen dissolve in one hundred volumes of water. Thus 
 oxygen is available to fishes, for it can pass from solution in 
 water into the blood of the fishes through the delicate mem- 
 
LIQUID OXYGEN 43 
 
 branes of the gills, the gills serving fishes in the way that 
 the lungs serve human beings. 
 
 As is the case with all other gases, oxygen is more soluble 
 in cold water than in warm water. It is a frequently ob- 
 served fact that when a glass of freshly drawn cold water 
 is allowed to stand in a warm room little bubbles form and 
 cling to the side of the glass. These bubbles are composed in 
 part of oxygen. Besides being essential to the life of fishes, the 
 oxygen dissolved in w r ater plays a large part in purifying 
 natural waters from sewage and other contamination. Many 
 of the harmful substances contained in sewage combine with 
 oxygen and are thus converted into harmless compounds. 
 
 37. Liquid and Solid Oxygen. We are familiar with 
 oxygen only as a gas, but to the scientist with the requisite 
 apparatus, liquid and solid oxygen are familiar forms, just 
 as ice is to the everyday man a familiar form of water. If 
 oxygen gas is kept in a vessel at the ordinary pressure and 
 cooled sufficiently, it will condense to a liquid when the tem- 
 perature of 182.5 C. is reached. This same temperature, 
 182.5 C., is also the boiling point, because if liquid oxygen 
 is allowed to stand in an open vessel it boils at this tempera- 
 ture, that is, bubbles of gas form within the body of the 
 liquid, rise to the surface, and escape. In the same way 
 water boils at 100 C. 
 
 The liquid oxygen has a blue color, it is somewhat heavier 
 than water, its specific gravity being l.lS, and it shows the 
 surprising property of being magnetic. 
 
 On cooling liquid oxygen still further, it changes to a solid 
 at about 200 C. in the same way that water changes to 
 ice at C. 
 
 38. Chemical Properties. The most marked chemical 
 property of oxygen is its great combining activity. Com- 
 
44 OXYGEN 
 
 pounds of it with every other element, except fluorine and 
 certain inert gases of the atmosphere, are known. More- 
 over, it will combine with most of the elements directly, par- 
 ticularly when heated with them. This was seen in Chapter 
 IV to be the case with many metallic elements, and it is 
 likewise true of many non-metallic elements such as phos- 
 phorus, sulphur, and carbon. 
 
 39. Oxides. The product formed by the union of oxygen 
 with another element is called an oxide. It is a custom 
 among chemists in naming compounds consisting of only 
 two elements to use the name of the more metallic element 
 in full and the root of the name of the more non-metallic 
 element together with the termination ide. Thus sulphur 
 and oxygen form sulphur oxide ; iron and oxygen form iron 
 oxide. 
 
 40. Combustion in Pure Oxygen. Fuels when once 
 kindled react vigorously with the oxygen of the air giving 
 heat and light; many metals when wet rust or corrode 
 slowly, which is in the main a combining with oxygen. The 
 power to support active combustion is much stronger with 
 pure oxygen than with air. For example, a lump of charcoal 
 with a barely glowing spark flames up brilliantly when 
 thrust into a jar of pure oxygen. Burning bits of sulphur or 
 phosphorus burn far more vigorously in pure oxygen. Even 
 a piece of iron wire, if a glowing bit of wood is attached to 
 its end, will burn vigorously and throw off a beautiful 
 shower of sparks, when lowered into pure oxygen. 
 
 41. Kindling Point. At ordinary temperatures, most 
 combustible materials do not burn, not even in pure 
 oxygen. If they are dry, most materials can be preserved 
 almost indefinitely in oxygen without a perceptible amount 
 of chemical union. Thus dry, cold oxygen is pretty nearly 
 
KINDLING POINT 45 
 
 an inert substance chemically. It is probably not ab- 
 solutely inert, however, for there is perhaps a slow com- 
 bustion always taking place, even although not enough 
 change may occur in one hundred or one thousand years 
 to be noticeable. 
 
 Now it is a general rule that chemical reactions take place 
 faster the higher the temperature. Let us apply this rule, 
 for example, to a piece of dry wood which at ordinary tem- 
 perature does not combine perceptibly with the oxygen of 
 the air ; if the wood is placed in a cooking oven, it combines 
 without doubt far more rapidly, but the reaction is still too 
 slow to produce more heat on its own account than can easily 
 escape. Placed in hotter and hotter places, the wood reacts 
 more and more rapidly, until at length a point is reached 
 at which the heat is produced more rapidly by the reaction 
 than it can escape from the vicinity of the wood. At this 
 point the wood bursts into flame, for since the heat cannot 
 all escape it must raise the temperature about the wood still 
 higher and this higher temperature must produce a more 
 rapid reaction which must in turn raise the temperature still 
 higher. 
 
 The kindling temperature is that temperature at which a slow 
 combustion changes abruptly to a rapid one and a correspond- 
 ing sudden rise in temperature occurs. 
 
 The kindling temperature of different substances is very 
 different. Thus yellow phosphorus catches fire when exposed 
 to air even at the ordinary room temperature, sulphur has to 
 be heated moderately, whereas charcoal must be raised to a 
 red heat before it will burn. 
 
 42. We can now appreciate why an iron wire burns bril- 
 liantly in pure oxygen, but not at all in air. The kindling 
 temperature of iron is high. When once it is reached in pure 
 
46 OXYGEN 
 
 oxygen, the heat of the chemical action is enough to maintain 
 the temperature above this point. But in air there are four 
 volumes of inert nitrogen to each volume of oxygen, and the 
 nitrogen as well as the oxygen has to be raised to the kindling 
 temperature of the iron if the iron is to continue to burn. 
 In addition to this the oxygen is impeded by the nitrogen 
 in reaching the surface of the iron. 
 
 In extinguishing a fire with water, the main function of 
 the water is to cool the burning objects to below the kindling 
 temperature. 
 
 43. Spontaneous Combustion. In some cases of slow 
 oxidation the amount of heat given off, although not enough 
 to cause the kindling of the substance concerned when it is 
 freely exposed to the air, is yet sufficient to set fire to it, if in a 
 situation from which it is difficult for heat to escape. Oily 
 rags sometimes cause fires in this way, if thrown into corners. 
 Some kinds of oil oxidize quite perceptibly even at ordinary 
 temperatures. When the rags are packed together so that 
 the heat produced by this slow combustion cannot escape, 
 the temperature rises until the mass breaks into flame. This 
 type of action is called spontaneous combustion, and it is a 
 very frequent cause of factory fires. 
 
 44. Slow Combustion. Dry oxygen is almost inert at 
 ordinary temperatures, but dissolved in water it is capable 
 of reacting slowly, as is shown by the rusting of moist iron. 
 In the human body the oxygen dissolved in the blood com- 
 bines with the elements of the food, giving the warmth and 
 energy necessary to the human being. This is a wonderfully 
 regulated slow combustion, for in normal health it is never 
 allowed to carry the temperature much above the normal 
 body temperature of 37 C. nor to let it get much below that 
 mark in cold weather. 
 
DECAY OF WOOD 47 
 
 45. Decay of Wood. Dissolved oxygen is also responsible 
 for the decaying of wood, which is also a case of slow combus- 
 tion. We often see perfectly sound timbers in houses over a 
 century old where the rain has been carefully kept out, but 
 the same timbers thrown out on the moist ground are rotted 
 through in a year or two. Moisture, however, is not all that 
 aids in the decay of the wood ; an important part is played 
 by bacteria, microscopic living organisms, which in the 
 chemistry of their life processes bring about the oxidation 
 of the wood in much the same way as animals bring 
 about the oxidation of their food. Wood that is to be used 
 in wet places, as for example, piles for buildings, is pre- 
 served by being saturated with creosote or other material 
 poisonous to bacteria. 
 
 Dry wood does not decay because the bacteria can live 
 only when wet or at least moist. Painting preserves wood 
 because it excludes both moisture and oxygen. 
 
 46. The spoiling of food is similar to the decay of wood 
 in that it is due to chemical changes which are promoted by 
 bacteria, although many of these changes consist only of the 
 partial decomposition of the complex compounds of which 
 food consists, and do not involve any action of the oxygen 
 of the air. Thus the souring of milk is due to a decomposi- 
 tion of milk sugar into lactic acid under the influence of a 
 certain kind of bacteria. The fruit sugar of apples decom- 
 poses into carbon dioxide^and alcohol under the influence of 
 yeast cells when sweet cider ferments. When cider or wine 
 turn to vinegar it is due to the oxidation of alcohol to acetic 
 acid through the agency of the acetic bacteria. This change 
 is an oxidation and it can only progress when the cider or 
 wine is exposed to the air. The well known "mother of 
 vinegar " which is often seen in vinegar bottles consists of a 
 
 B. AND W. CHEM. 4 
 
48 OXYGEN 
 
 cohering mass of the acetic bacteria. When meats and 
 fish spoil the products are very poisonous and this kind of 
 spoiling may take place in the absence of oxygen. 
 
 Anything which will kill bacterial life will stop the spoil- 
 ing of food. Thus to make milk keep longer without sour- 
 ing, we heat it. In canning fruit or meat, the material is 
 heated as high as the boiling temperature of water in order 
 to kill bacteria. In the packing houses, the cans after sealing 
 are invariably heated again to assure the destruction of all 
 bacterial life. 
 
 SUMMARY 
 
 Oxygen is prepared in bulk, most cheaply by methods by which 
 it is extracted from the air, but for the laboratory the most 
 convenient method is to heat potassium chlorate, to which 
 some manganese dioxide has been added. 
 
 Properties of Oxygen. Oxygen can generally be recognized by its 
 easily observed properties. It is a colorless, odorless gas, 
 slightly soluble in water. The most marked chemical char- 
 acteristic of oxygen is its great power to combine with other 
 elements. Oxygen under standard conditions weighs 1.43 
 grams per liter. 
 
 The kindling temperature is the lowest temperature at which slow 
 combustion changes to rapid combustion. The kindling 
 point is different for different substances. Above the kindling 
 temperature, oxygen combines violently with many substances. 
 
 Slow combustion consists in the union of a substance with oxygen, 
 below its kindling temperature, as in the rusting of iron, the 
 decaying of wood, and the spoiling of food. The latter two 
 actions are promoted by bacterial life. 
 
 Spontaneous combustion results when, during slow combustion, 
 heat accumulates until the kindling temperature is reached, 
 then the substance takes fire. 
 
 Questions 
 
 1. What is the most prominent chemical property of oxygen? 
 
 2. Why do metals, such as copper, lead, and zinc, which oxidize 
 
QUESTIONS 49 
 
 , l 
 
 quickly when hot, wear as well as they do when exposed to the air 
 on roofs ? 
 
 3. Why does not gold corrode? 
 
 4. What would be the effect of using pure oxygen in the black- 
 smith's bellows? 
 
 5. Give reasons why it is fortunate that the atmosphere does 
 not consist entirely of oxygen. 
 
 6. In view of the combustibility of wood, why is it that the fire 
 danger in wooden buildings is so slight? 
 
 7. Under what conditions do fires sometimes start without the 
 application of a flame? 
 
 8. Would oxygen be a useful gas with which to fill balloons? 
 Explain. 
 
 9. How do fish breathe? What would be the effect of putting 
 goldfish in distilled water? Why would freshly distilled water lack 
 oxygen? 
 
 10. Explain why a fallen tree in the forest disappears after a 
 period of years. 
 
 11. It is unsafe to drink water from a river that has been freshly 
 contaminated with sewage. How is oxygen responsible for making 
 the water safe to drink after it has run for miles over rapids in a 
 river ? 
 
 12. How does (a) canning, (b) smoking, (c) salting, (d) refrigerat- 
 ing, (e) drying, and (/) preserving in sirup, prevent in food products 
 the kind of slow oxidation called decay? 
 
CHAPTER VI 
 THE OXIDES OF CARBON 
 
 IN the preceding chapters it has been seen that when the 
 element carbon burns, it unites with oxygen of the air to 
 form a gaseous product which is always carbon dioxide when 
 sufficient air can come in contact with the burning object, 
 although carbon monoxide may result with insufficient air. 
 
 47. Enormous Production of Carbon Dioxide. Enormous 
 quantities of charcoal, coke, coal, and wood, fuels which 
 consist largely or wholly of carbon, are being burned all the 
 time. Added to this artificial combustion, we have an even 
 greater production of carbon dioxide by the slow combustion 
 of food in human beings and animals and of wood and dead 
 leaves in the process of decay. It has, in fact, been estimated 
 that 97 per cent of the carbon dioxide turned into the air 
 is the product of decay. 
 
 48. Utilization of Carbon Dioxide by Plants. In view of 
 the great amount of carbon dioxide produced, it would seem 
 as if the air must become filled with this gas. Still it is a 
 fact that pure air in the country never contains more than 
 three or four one hundredths of 1 per cent of it. How can 
 it be that such large quantities of this gas are all the time 
 being put into the air and yet the amount present never 
 increases ? It must be because carbon dioxide is being con- 
 tinually withdrawn from the air. The study of the life of 
 green plants has shown that it is they that perform this 
 
 60 
 
LIMESTONE 51 
 
 service; they require carbon dioxide for their development, 
 and their green leaves take in the carbon dioxide from the 
 air. But this is not all. The lungs of animals withdraw 
 oxygen from the air and give back carbon dioxide ; the green 
 leaves of plants withdraw the carbon dioxide and after ap- 
 propriating the carbon in their chemical life processes, give 
 back the oxygen. Thus there is a continuous interchange 
 between animals and plants, each utilizing what is a waste 
 product from the other, and with these two agencies at work 
 the quantity of carbon dioxide in the air never varies much 
 from the mean of 0.04 per cent. 
 
 49. Source of Pure Carbon Dioxide. In our laboratory 
 study of carbon dioxide our first task is to collect some of 
 this gas pure. One might first think to do this by collecting 
 the gaseous combustion products of charcoal, but it would 
 prove difficult to get the gas in this way unmixed with nitro- 
 gen and unconsumed air. Our best source of carbon dioxide 
 has been found to be limestone, a rock that is very abundant 
 in the earth. 
 
 50. Limestone. In past geologic ages, plants have been 
 absorbing carbon dioxide from the air, just as at present. 
 Certain low orders of sea animals also have been utilizing 
 carbon dioxide in the formation of their shells, in which it 
 becomes combined and held in the form of calcium carbonate. 
 Coral, for example, and the shells of oysters and clams con- 
 sist largely of calcium carbonate. Masses of these and simi- 
 lar shells which accumulated in past ages, have been deeply 
 covered by deposits of earth. They have since been trans- 
 formed gradually, through the agency of great pressure and 
 heat, into compact masses of limestone. 
 
 A very pure variety of limestone is marble, and in the 
 laboratory we shall use marble as the source of carbon dioxide. 
 
52 
 
 THE OXIDES OF CARBON 
 
 FIG. 7. Test for Carbon Dioxide. A clear 
 drop of limewater suspended on a stirring rod 
 is rendered milky if lowered into a vessel con- 
 taining carbon dioxide. Notice that the stopper 
 of the limewater bottle is held between the 
 third and fourth ringers at the back of the right 
 hand instead of being laid on the desk top 
 where it may be contaminated before being 
 replaced in bottle. 
 
 It is only necessary 
 to treat this sub- 
 stance with a dilute 
 acid when carbon 
 dioxide is liberated, 
 while the product 
 formed from the cal- 
 cium and the acid 
 remains behind. 
 
 51. Means of rec- 
 ognizing Carbon 
 Dioxide. If a pinch 
 of powdered marble 
 is placed in a test tube 
 and covered with a 
 few cubic centi- 
 meters of dilute acid, 
 hydrochloric acid, 
 for example, a 
 vigorous efferves- 
 cence 1 takes place 
 and continues until 
 either the marble or 
 the acid is all used 
 up. 
 
 If a lighted taper 
 is inserted into the 
 
 test tube while the effervescence is taking place, the flame is 
 
 1 Effervescence consists in the rapid evolution of bubbles of a 
 gas and in this respect it has somewhat the appearance of boiling 1 . 
 It is, however, an entirely different phenomenon from boiling, since 
 in boiling the vapor that rises is always the same substance as the 
 liquid from which it comes. 
 
CARBON DIOXIDE 53 
 
 extinguished. This accords with our knowledge that carbon 
 dioxide is a non-supporter of combustion. If a stirring rod 
 is dipped into a bottle of clear limewater and then with- 
 drawn so that a clear drop hangs from its lower end, and if 
 this is then lowered into the test tube, it immediately 
 becomes clouded or milky in appearance. This test has 
 already been mentioned and is one of the most distinctive 
 tests for carbon dioxide. 
 
 If the last two tests are made repeatedly in inverted and 
 upright test tubes in which carbon dioxide has been gener- 
 ated, it will be found that all evidence of the gas disappears 
 in a moment from an inverted test tube, whereas it persists 
 for some time in an upright test tube. This shows that 
 carbon dioxide must be heavier than air. 
 
 The three properties of carbon dioxide enumerated in the 
 last few paragraphs, namely its power to extinguish flame, 
 its ability to render limewater milky, and its being heavier 
 than air, are all properties which can be recognized with 
 great ease and it is these properties for which we first look 
 when we wish to find out whether a given gas is or is not 
 carbon dioxide. If we find the gas to possess these three 
 properties, we are reasonably certain that it is carbon dioxide. 
 
 Of course to render identification of this gas absolutely 
 certain, its properties must be observed with much greater 
 exactness and to accomplish this it is necessary to prepare 
 some considerable quantity of the gas 'and to collect it 
 unmixed with air. 
 
 52. Carbon Dioxide Generator. Place several lumps of 
 marble in the bottom of a bottle or flask (see Fig. 8) fitted 
 with a two-holed rubber stopper. Through one hole is 
 inserted a thistle tube which reaches quite to the bottom of 
 the generating flask, where it is sealed air- or gas-tight when 
 
54 
 
 THE OXIDES OF CARBON 
 
 a little liquid is poured into the flask. Through the other 
 hole of the stopper passes a delivery tube and this tube is 
 prolonged so that it reaches below the surface of the water 
 in the trough where are placed inverted bottles filled with 
 water ready for collecting the gas. 
 
 It will be recollected that this method of displacing water 
 from inverted bottles immersed in a trough of water was 
 
 also used for collect- 
 ing oxygen. This is 
 in fact the usual 
 method of collecting 
 gases, and may be 
 used for any gas that 
 is not very soluble in 
 water. 
 
 Now with the gen- 
 erator and connec- 
 Cracked tions all arranged a 
 Enough little water is poured 
 
 FIG. 8. Carbon Dioxide Generator, 
 marble is placed in generator flask, 
 water is added to close the lower end of the 
 thistle tube. Then hydrochloric acid is added 
 a little at a time to obtain a moderate flow of 
 the gas. 
 
 into the thistle tube 
 until its lower end 
 within the generator 
 
 is submerged and thus sealed so that no gas can escape 
 this way. Then concentrated hydrochloric acid is added, 
 a few drops at a time, until a fairly brisk effervescence 
 takes place in the flask. 
 
 The first gas to issue from the delivery tube should be 
 rejected because it is mixed with the air that was originally 
 in the generator, but after considerable gas has escaped, the 
 air will all have been swept from the generator and pure 
 carbon dioxide can be collected by sliding the in verted bottles 
 of water over the end of the delivery tube. 
 
CARBON DIOXIDE 
 
 55 
 
 PROPERTIES OF CARBON DIOXIDE 
 
 53. Specific Gravity. Accurate experiments have shown 
 that carbon dioxide weighs 1.529 times as much as air, in 
 other words that its specific gravity is 1.529. It is not 
 necessary or even desirable for every student of chemistry to 
 repeat the somewhat 
 
 elaborate experiment 
 necessary to prove 
 the correctness of this 
 exact figure, which 
 has been obtained by 
 skillful and reliable 
 experimenters. 
 
 A striking experi- 
 ment for showing the 
 greater density of car- 
 bon dioxide is illus- 
 trated in Fig. 9. Sev- 
 eral lighted candles 
 are placed in an in- 
 clined trough ; then 
 carbon dioxide, pre- 
 viously collected in 
 a large cylinder, is 
 poured into the top of the trough. It is shown by the 
 candles becoming successively extinguished that the carbon 
 dioxide flows down hill through the trough. 
 
 54. Solubility in Water. Carbon dioxide is not very solu- 
 ble in water, as has been shown by the fact that it has been 
 collected in bottles inverted over water. It could be shown, 
 however, that some of the gas dissolved in the water through 
 
 FIG. 9. Carbon Dioxide flowing down hill. 
 
56 THE OXIDES OF CARBON 
 
 which it bubbled. Close the mouth of one of the bottles of 
 carbon dioxide inverted in the collecting trough by placing 
 the palm of the hand under it, transfer the bottle to another 
 trough containing fresh cold water. On letting the bottle 
 stand in this trough a few hours, it is found that the water 
 level within the bottle rises very considerably, showing that 
 some of the gas has disappeared and the water risen to take 
 its place. The only way in which the gas can disappear is 
 by dissolving in the water. 
 
 At ordinary temperature and with the gas under the pres- 
 sure of the atmosphere, a volume of water is capable of dis- 
 solving about its own volume of carbon dioxide gas. Under 
 less pressure, less, and under greater pressure, more, gas can 
 be dissolved. Plain soda water, more correctly called car- 
 bonated water, obtained at a soda fountain or dispensed 
 in siphon bottles, is simply a solution of carbon dioxide in 
 water. The carbon dioxide is forced under a high pressure 
 into bottles or metal tanks of water, and under the high pres- 
 sure a correspondingly large amount dissolves. When the 
 carbonated water is drawn into a glass, the pressure is re- 
 lieved, and we see most of the carbon dioxide escaping in the 
 bubbles which rapidly rise. 
 
 55. Liquid Carbon Dioxide. Dry carbon dioxide gas 
 may be liquefied by compression at the ordinary room tem- 
 perature. At 20 C. a pressure of 861 pounds per square 
 inch or, in other words, a pressure 59 times as great as that 
 of the atmosphere, is required. Of course very strong con- 
 tainers are necessary to withstand this pressure, and it is 
 customary to compress the gas into steel cylinders in which 
 it is put on the market. Compression always produces heat, 
 and unless the compressing apparatus and the receiving 
 cylinder are surrounded by cold running water to carry away 
 
SOLID CARBON DIOXIDE 57 
 
 the heat, the temperature will rise and liquefaction will be 
 impossible. 
 
 56. Solid Carbon Dioxide. If the cylinder of liquid 
 carbon dioxide is placed with the valve at the bottom and 
 the valve is opened, some of the liquid will be forced out. 
 But here we make the surprising observation that we do not 
 obtain any liquid at all outside of the pressure cylinder, but 
 we do get a solid substance which looks like snow. A good 
 way to obtain this snow is to tie securely a stout, coarse bag 
 over the escape pipe of the cylinder and open the valve for 
 a few minutes. Considerable frost can be seen on the out- 
 side of the bag and the hissing of escaping gas is heard. On 
 closing the valve and opening the bag, several handfuls of 
 carbon dioxide snow are found. 
 
 On compressing carbon dioxide gas to a liquid, we just 
 said that a large amount of heat is produced that has to be 
 removed with cold water. Now on letting liquid carbon 
 dioxide escape from the cylinder, an equal amount of heat 
 must be supplied from somewhere if the liquid is to be changed 
 back to a gas. Enough heat is not at once available from the 
 liquid and its immediate surroundings, but what there is, is 
 taken, and some of the liquid is thereby changed to gas. 
 This withdrawal of heat produces great cold and it is thus 
 that the remaining carbon dioxide is frozen. The tem- 
 perature of the snow is as low as 60 C. It could serve thus 
 as an excellent refrigerating agent for temperatures below 
 that of the ordinary ice-salt mixture. 
 
 This carbon dioxide snow is a fascinating substance to 
 handle. Holding a little lump in the palm of the hand, it 
 may be seen to evaporate. A lump thrown into a dish of 
 water causes the water to freeze. Mercury poured upon it 
 at once becomes solid. In handling it, however, one must 
 
58 THE OXIDES OF CARBON 
 
 avoid pressing it against the flesh, else it causes frostbite, 
 the effects of which are quite similar to those of burning. 
 
 57. Chemical Properties of Carbon Dioxide. We have 
 already seen that carbon dioxide is absorbed by limewater 
 and produces in it a white turbidity, also that it dissolves 
 to some extent in water. 
 
 We know that a glass of plain soda water, that is, the 
 carbonated water without the addition of fruit sirups, 
 tastes somewhat sour. Carbon dioxide, in fact, forms a 
 weak acid with the water in which it dissolves. We shall 
 learn more later about acids, but it is true that all acids are 
 sour in taste. Another general property of acids is that they 
 cause the color of a vegetable dyestuff called litmus to change 
 from blue to red. When a piece of paper colored blue with 
 litmus is dipped into water containing dissolved carbon 
 dioxide, the color is changed to a rather pale red. 
 
 Another property ofjicids is that they react with the oxide^ 
 of metals to form salts. Now limewater is obtained by allow- 
 ing lime, which is oxide of calcium, to react with water. 
 The product of the reaction is slightly^ soluble in water and 
 the clear solution is known as limewater. Carbon dioxide 
 reacting with the limewater gives calcium carbonate, a white 
 insoluble salt which produces the milky appearance which 
 we have described as a distinctive test for carbon dioxide. 
 
 USES OF CARBON DIOXIDE 
 
 58. Fire Extinguishers. The experiment of extinguish- 
 ing the burning candles suggests one of the important uses 
 of carbon dioxide, namely, as a fire extinguisher. The so- 
 called automatic fire extinguishers are a familiar sight in 
 the corridors of public buildings and in railway cars. The 
 most useful form consists merely of a device for manufactur- 
 
FIRE EXTINGUISHERS 
 
 59 
 
 ing, when the occasion may suddenly demand it, a large 
 amount of carbon dioxide which will charge the water in the 
 extinguisher and at the same time create 
 a pressure to force the charged water 
 through the nozzle so that it can be di- 
 rected at the fire. The carbonated water, 
 on being relieved from the great pressure 
 and moreover warmed on striking the fire, 
 gives up a large amount of the carbon 
 dioxide, which it can no longer hold in 
 solution. The gas, being heavier than 
 air, tends to spread over the fire and 
 exclude the air. The water thrown by 
 the extinguisher also helps to put out the 
 fire by cooling the fuel below its kindling 
 point, but the efficiency of one of these 
 so-called chemical fire extinguishers is 
 greater than if only the same amount of 
 water were thrown. 
 
 The extinguisher is usually constructed 
 as shown in the diagram (see Fig. 11). 
 The metal tank is filled with water nearly to the top 
 (the level of the water is seen at A) and a proper quantity 
 of some carbonate, usually sodium bicarbonate, or com- 
 mon baking soda, is added and allowed to dissolve in 
 the water. Marble would be too slow 'in its action, but 
 the soluble carbonate being infinitely more finely divided 
 when in the dissolved state than the most finely ground 
 marble dust, is much more rapidly acted upon. The 
 amount to add would be determined by the capacity and 
 strength of the tank. Directions always accompany the 
 chemical extinguishers and state how much sodium bicar- 
 
 FIG. 10. Chemical 
 Fire Extinguisher. 
 
60 
 
 THE OXIDES OF CARBON 
 
 bonate and sulphuric acid to use. In the top of the tank is 
 a support for a bottle of concentrated sulphuric acid. This 
 support (B) is made of some metal little 
 likely to corrode in a damp place. The 
 stopper of the sulphuric acid bottle (C) 
 is of lead and fits loosely. The hose 
 through which the contents of the tank 
 are to be discharged is attached to what 
 is the top of the tank when the latter 
 is not in use. When occasion arises to 
 use the extinguisher, it is taken to the 
 scene of the fire and at once inverted. 
 The sulphuric acid is thus emptied out 
 into the solution of sodium bicarbonate, 
 and rapid evolution of carbon dioxide 
 begins. The pressure rises and the so- 
 lution is expelled forcibly through the 
 hose which leads from what is now the 
 bottom of the tank. If the hose were 
 not at the bottom (when in action), of 
 course only gas would escape. 
 59. Soda Water. The use of carbon dioxide dissolved 
 in water in the production of effervescing drinks has already 
 been referred to in the paragraph on the solubility of carbon 
 dioxide. The original soda water was prepared by mixing' 
 baking soda (sodium bicarbonate) in solution with some 
 fruit acid. Carbon dioxide was produced as is the case 
 when any acid acts on any carbonate, and the water was thus 
 charged with the gas. But carbon dioxide is only one of the 
 products of the action of sodium bicarbonate with an acid. 
 The other product is a salt, the sodium salt of the fruit acid. 
 This salt is not harmful, but it does not add to the attrac- 
 
 FIG. 11. Section of 
 Fire Extinguisher. 
 
RAISING OF BREAD AND CAKE 61 
 
 tiveness of the beverage. To-day soda water is universally 
 made by charging pure water in strong metal tanks with 
 pure carbon dioxide gas. Thus the modern soda water really 
 contains no soda at all. 
 
 60. Raising of Bread and Cake. In making bread and 
 cake it is essential that the product shall be light and porous, 
 for otherwise it would be neither appetizing to eat nor easy 
 to digest. Lightness is obtained through the agency of 
 carbon dioxide, which is generated throughout the mass of 
 the dough, either by the action of yeast or of baking powder, 
 so that the Plough becomes filled with a multitude of little 
 bubbles. These bubbles " raise " the bread. 
 
 Yeast consists of a vast number of little plant cells, which 
 grow and multiply very rapidly when put in the moist dough, 
 and in the process of their growth cause a chemical change 
 in the starch of the flour and in the sugars present in 
 the dough. The final products of this change are chiefly 
 alcohol and carbon dioxide. The amount of alcohol is so 
 small that it is quite unnoticeable ; but the carbon dioxide, 
 being a gas, has a large volume in proportion to its weight 
 and thus it causes the expansion of the bread. 
 
 Baking powder is made by mixing sodium bicarbonate 
 with some dry powdered acid substance, as for example 
 cream of tartar. So long as the baking powder remains dry 
 no action occurs ; but when it is moistened, the acid reacts 
 with the carbonate and produces carbon dioxide gas. 
 
 The baking powder should^therefore be first well mixed 
 with the flour so that gas will be released equally in every 
 part of the mass and the mixing of the flour with the watery 
 materials (milk, water, or eggs) should take place just before 
 the material is to go into the oven so as to avoid the loss of gas. 
 
 Baking soda, which is sodium bicarbonate, is frequently 
 
62 THE OXIDES OF CARBON 
 
 used with sour milk to bring about the raising of homemade 
 products such as griddle cakes or gingerbread. In this case, 
 carbon dioxide is released from the sodium bicarbonate by 
 the action of lactic acid in the sour milk. Frequently the 
 housewife takes too much, or perhaps too little, soda for the 
 amount of acid in the sour milk. The resulting product 
 may then taste strongly either of the excess of soda or of acid. 
 In making baking powder, the manufacturers are careful to 
 properly proportion the two ingredients so that no excess of 
 either shall be left unchanged at the end of the reaction. 
 
 61. Commercial Methods of making Carbon Dioxide. 
 Sulphuric acid is cheaper than hydrochloric acid, and it 
 is therefore used in the commercial manufacture in preference 
 to the more expensive acid which is most often used in the 
 laboratory. With the strong effervescence, a spray carrying 
 considerable sulphuric acid is thrown up, and therefore the 
 gas must be passed through a washing vessel containing pure 
 water and best also strained through some porous material 
 before being charged into the siphons of carbonated water 
 or liquefied into steel cylinders. 
 
 Carbon dioxide is the chief gaseous product from the fer- 
 mentation of grain, and large quantities of this gas are 
 produced in distilleries and breweries. Of late years the 
 practice has grown not to allow this gas to go to waste, but 
 to collect it and compress it in steel cylinders, so that 
 to-day a large part of the carbon dioxide in use is obtained 
 in this way. 
 
 CARBON MONOXIDE 
 
 62. Formation. In connection with our study of combus- 
 tion (page 31) it was said that if carbon is burned in an in- 
 sufficient supply of oxygen, a gas called carbon monoxide is 
 
CARBON MONOXIDE 63 
 
 produced. The most favorable conditions for the formation of 
 carbon monoxide exist in a deep coal or charcoal fire to which 
 air is admitted only at the bottom. The air at the bottom 
 doubtless burns some of the carbon to carbon dioxide. The 
 heat of the reaction brings the layer of fuel above to incan- 
 descence, and any carbon dioxide starting to pass up through 
 this layer of white-hot carbon reacts with it and thus becomes 
 changed back to carbon monoxide. 
 
 63. Properties of Carbon Monoxide. Physical Properties. 
 Carbon monoxide is colorless and odorless. It is lighter 
 than carbon dioxide, being a trifle less heavy than air, whereas 
 carbon dioxide, as we have seen, is about one and one half 
 times as heavy as air. It is very slightly soluble in water. 
 
 Chemical Properties. Carbon monoxide, unlike carbon 
 dioxide, does not react withrwater to form an acid. Its most 
 striking and useful property is its ability to take on more 
 oxygen when burning, thus forming carbon dioxide. Carbon 
 monoxide is excessively poisonous to breathe, even when 
 largely diluted with air. Hence the danger from leaky fur- 
 naces and from leaking water gas (see below). 
 
 64. Uses of Carbon Monoxide. Large amounts of carbon 
 monoxide, usually mixed with other fuel gases, are prepared 
 and used as artificial gas for -heating and lighting. For 
 lighting, other gases must be present as carbon monoxide 
 itself burns with a non-luminous flame. Water gas, which 
 is a variety of illuminating gas used ver^ largely in cities, 
 and producer gas which is much employed as a fuel gas, both 
 contain very high proportions of carbon monoxide. 
 
 65. Combining Proportions. Carbon dioxide and carbon 
 monoxide are both composed of exactly the same elements, 
 yet the two gases have very different properties, as different 
 in fact as two gases composed of totally different elements. 
 
 B. AND W. CHEM. 5 
 
64 THE OXIDES OF CARBON 
 
 The difference is to be accounted for only on the ground of 
 the difference in the proportion of the two elements com- 
 bined. 
 
 In carbon monoxide one gram of carbon is combined with 
 1.333 grams of oxygen. In carbon dioxide one gram of 
 carbon is combined with 2.666 grams of oxygen. The re- 
 markably simple relation is at once perceived that for a 
 given amount of carbon (one gram in each of the above cases) 
 the second gas contains exactly twice as much oxygen as the 
 first gas. Hence the name di-oxide, the prefix di coming 
 from the Greek and meaning two. In distinction, the prefix 
 mono means one. 
 
 66. Law of Multiple Proportions. Besides carbon and 
 oxygen there are many pairs of elements which combine in 
 more than one proportion. We have found the very remark- 
 able fact that the two combining ratios of carbon and oxygen 
 bear the simple relation to each other of two to one. Now it 
 has been found that in all cases of more than a single combin- 
 ing ratio, the relations are of the same simple nature. A gen- 
 eral statement of this fact is known as the Law of Multiple 
 Proportions. 
 
 We shall see later that this law, together with the law of 
 definite proportions, at which we have already hinted 
 (page 22), are of the greatest significance, since they point the 
 way to our present conception of the nature of matter, 
 namely, to the theory of atoms. 
 
 SUMMARY 
 
 Carbon Dioxide in Nature. The amount of carbon dioxide being 
 continually turned into the atmosphere by fires, the exhala- 
 tions of animals, and decay is enormous, yet the amount present 
 does not increase. 
 
QUESTIONS 65 
 
 Green plants absorb carbon dioxide, using the carbon and re- 
 turning oxygen to the air. 
 
 Large amounts of limestone, a rock which contains carbon dioxide 
 united with the oxide of calcium, are found in nature. Some 
 mountain ranges are composed mainly of this one kind of 
 rock. Marble is a pure form of limestone. It readily gives 
 up pure carbon dioxide when it is treated with an acid. 
 
 Properties of Carbon Dioxide. Carbon dioxide is colorless, odor- 
 less, and has a slight acid taste, is somewhat soluble in cold 
 water, and becomes very soluble under high pressure. It is 
 about one and one half times as heavy as air, it may be lique- 
 fied by pressure at ordinary temperature, and it may be frozen 
 by the cold produced by the vaporization of the liquid. 
 Carbon dioxide neither burns nor supports combustion. It reacts 
 feebly with water to form a weak acid. With limewater it 
 reacts to form a white precipitate of calcium carbonate, and 
 this reaction is a distinctive test for the presence of carbon 
 dioxide. 
 
 An important use of carbon dioxide is in the chemical fire ex- 
 tinguisher. Dissolved in water under pressure, it is an essen- 
 tial constituent of carbonated beverages. When produced 
 chemically by the action of yeast or baking powder through- 
 out a mass of dough, it serves in raising bread and cake. 
 
 Carbon monoxide is obtained when carbon burns with insufficient 
 oxygen. It contains the same elements as carbon dioxide, 
 but it has very different properties. For the same weight of 
 carbon, carbon dioxide contains just twice as much oxygen 
 as does carbon monoxide. A relation of this kind holds for 
 many other sets of compounds besides the oxides of carbon, 
 and it finds general expression in the law of multiple propor- 
 tions. 
 
 Questions 
 
 1. Enumerate several of the ways in which carbon dioxide is 
 being continually turned into the atmosphere. 
 
 2. Explain how the quantity of carbon dioxide in the atmosphere 
 is regulated by natural processes so that it is nearly constant. 
 
 3. A fragment of building stone when dropped into a test tube 
 
66 THE OXIDES OF CARBON 
 
 containing acid effervesces and the gas given off clouds limewater. 
 What probably is the stone? 
 
 4. Upon what three properties of carbon dioxide does its use in 
 fire extinguishers depend ? 
 
 5. How could one tell whether a gas that would not support 
 combustion was carbon dioxide or nitrogen? 
 
 6. Why is it dangerous to health to have leaks in the fire pot 
 of a hot-air furnace? 
 
 7. If the water of a mineral spring effervesces strongly on 
 reaching the surface, what gas would you suspect and how would 
 you prove the point? 
 
 8. Why is it customary to lower a lighted candle into a well 
 before sending a man down to make repairs? 
 
 9. Explain two different methods of " raising " bread. 
 
 10. What is one of the principal fuel constituents of " water 
 gas"? 
 
CHAPTER VII 
 
 THE ATMOSPHERE AND NITROGEN 
 
 67. Approximate Composition of Air. We have already 
 seen that about one fifth of the air consists of oxygen, 
 the supporter of combustion, and that after that one fifth 
 is used up the residual gas is inert. The residual gas con- 
 sists mainly of the element nitrogen. 
 
 68. Nitrogen from the Air. If we wish to obtain fairly 
 pure nitrogen from air, it is only necessary to exhaust the 
 oxygen by causing it to combine with some substance with 
 which it gives a solid 
 
 oxide, for example, 
 with iron, copper, or 
 better, phosphorus. 
 Charcoal would not 
 serve the purpose, 
 because its combus- 
 tion yields a gas 
 which would remain 
 admixed with the 
 nitrogen. 
 
 A jarful of nitro- 
 gen is prepared most 
 readily as 
 
 ,, FIG. 12. Exhaustion of Oxygen. Oxygen re- 
 
 lOllOWS : moved from air under a bell jar by means of 
 
 Place a piece of phos- burning phosphorus. 
 
 phorus on a porcelain crucible cover which rests on a cork 
 floating on the surface of a large panful of water. Set 
 
 67 
 
68 THE ATMOSPHERE AND NITROGEN 
 
 fire to the phosphorus and quickly cover it with a large 
 glass bell jar (see Fig. 12) so that the air within the jar is 
 sealed from the outer air by means of the water. At first 
 the heat of combustion may cause so much expansion 
 that a few bubbles of air will be forced out from under 
 the sides of the jar. A very dense white smoke is formed 
 but this should not be mistaken for a gas. It consists simply 
 of very fine solid particles of oxide of phosphorus and after 
 a sufficient time it settles out completely and leaves a 
 perfectly clear gas. As the gaseous residue cools, the 
 water is observed to rise a considerable distance in the bell 
 jar, indicating, of course, that there is now less gas than 
 formerly. 
 
 If enough phosphorus was taken at the outset in the above 
 experiment, it is now observed that some of it remains un- 
 burned; if any other burning material is now introduced 
 into the residual gas, it is extinguished, showing that the gas 
 is a non-supporter of combustion. When we first found that 
 combustible substances burn better in pure oxygen than in 
 air, we at once assumed that, mixed with the oxygen of the 
 air, there was another gas which was a non-supporter of 
 combustion. We have now shown that this assumption is 
 correct. 
 
 69. Preparation of Pure Nitrogen. The nitrogen ob- 
 tained by removing oxygen from air has small quantities of 
 other gases mixed with it, since the phosphorus removes 
 only the oxygen. Pure nitrogen is usually prepared by 
 heating a concentrated solution of ammonium chloride and 
 sodium nitrite. The gas is collected in bottles by water 
 displacement. 
 
 70. Properties of Nitrogen. On testing the gas in the 
 bottles, it is found that it neither burns nor supports com- 
 
AIR A MIXTURE 69 
 
 bustion. In this respect it resembles carbon dioxide, but it 
 differs from that gas in that it does not cloud limewater. 
 Nit^gen is a little lighter than air, having a density, at 
 standard conditions, of 1.25 grams per liter. Nitrogen is 
 only half as soluble in water as oxygen is. 100 volumes of 
 water under usual conditions, dissolve about 1.6 volumes 
 of nitrogen. 
 
 71. Air a Mixture. The difference in solubility of the 
 two chief components of the air furnishes a strong reason for 
 believing that air is a mixture and not a chemical compound 
 of oxygen and nitrogen. If water which has been standing 
 in contact with the air is boiled and the dissolved air thereby 
 expelled is caught and analyzed, it is found to contain 34 
 per cent of oxygen, whereas atmospheric air contains but 21 
 per cent. If air were a chemical compound, it would be 
 dissolved as a whole and afterwards on removal from the 
 solution its composition would not be changed. 
 
 We shall see in a later chapter that there are several dis- 
 tinct compounds of oxygen and nitrogen, the properties of 
 which are radically different from each other and from either 
 of the uncombined elements. On the other hand, air shows 
 the properties of both oxygen and nitrogen, only modified 
 to the extent to which these components are diluted with 
 one another. Thus in this respect also air shows the char- 
 acteristics of a mixture. 
 
 Furthermore, oxygen and nitrogen can be mixed and 
 the mixture at once shows the properties of air, although no 
 evidence of chemical reaction, such as evolution of heat, 
 is to be observed. The mixture indeed can be made in pro- 
 portions other than those existing in air and yet the proper- 
 ties are not essentially different. If air were a chemical 
 compound, its composition would be unalterable. 
 
70 THE ATMOSPHERE AND NITROGEN 
 
 72. Inertness of Free Nitrogen and Importance of Com- 
 bined Nitrogen. The above described simple experiments 
 with the bottle of nitrogen have shown that nitrogen is a 
 very inert gas. Nitrogen can, however, enter into chemical 
 combination, and many important compounds, including 
 ammonia and nitric acid, are formed from it. Nitrogen is an 
 essential constituent of all living organisms; indeed human 
 food is judged largely according to the percentage of 
 chemically combined nitrogen which it contains ; and 
 soils and fertilizers are of value as plant foods largely in 
 proportion to the amount of chemically combined nitro- 
 gen which they contain. In spite of the great importance 
 of nitrogen in the chemistry of living things, the atmos- 
 pheric nitrogen plays almost no direct part in the nutri- 
 tion of animals and plants. This fact further emphasizes 
 the inert nature of this element when it is in the uncom- 
 bined state. Of the air that men and animals breathe, it 
 is only the oxygen that is utilized ; the nitrogen is entirely 
 exhaled again. 
 
 73. Nitrogenous Foods. All the nitrogen for our nutri- 
 tion enters our bodies as combined nitrogen in our food. 
 Meat and fish foods, milk and cheese, beans and peas and 
 mushrooms, contain a considerable proportion of combined 
 nitrogen ; most grains and vegetables contain less. The 
 gluten of wheat, which comprises some twelve to fifteen per 
 cent of the weight of the whole wheat, is a nitrogen-containing 
 food, and it is largely due to the quantity of gluten that 
 wheat is so highly prized as a food. 
 
 Just as animals are compelled to take the nitrogen that 
 they need in the combined form, so plants obtain theirs from 
 the soil in the form of soluble nitrogen compounds which are 
 taken up with the water of the soil through their roots. It 
 
FIXATION OF NITROGEN 71 
 
 is on account of the nitrogen which it contains that slaughter- 
 house refuse is valuable for fertilizer. 
 
 74. Fixation of Nitrogen by means of Legumes. There 
 are a few plants, namely, those of the legume family, of which 
 beans, peas, and clover are members, which are able through 
 the agency of colonies of bacteria which live on their roots, 
 to obtain a certain amount of atmospheric nitrogen by caus- 
 ing it to enter chemical combination. It is on this account 
 that when a field is exhausted of its nitrogenous material 
 by long cultivation, the farmer plants it with clover to re- 
 store its fertility. 
 
 75. Artificial Methods of Causing Nitrogen to Combine. 
 We have seen that the natural means of " fixing nitrogen," 
 as it is called, that is, of causing the inert gas of the air 
 to enter chemical combination, in which state it is avail- 
 able for nutrition, are very limited. Within recent years 
 artificial means have been developed, and now the fixation 
 of nitrogen directly from the air, for use as a fertilizer, is 
 becoming an industry of importance. Indeed, this industry 
 promises to increase to a very great extent. 
 
 One of the most important of the artificial methods de- 
 pends on a fact discovered by Cavendish as long ago as the 
 latter part of the eighteenth century. He passed electric 
 sparks through a confined volume of air and found that the 
 " air " would then dissolve in small amount in water to form an 
 acid (nitric acid). Under the influence of the electric spark 
 nitrogen arid oxygen combine to form nitric oxide. This 
 oxide of nitrogen is a chemical compound; it is no longer a 
 mixture of oxygen and nitrogen, but an entirely new sub- 
 stance with entirely new properties. The important new 
 property from the standpoint of this process is that it unites 
 readily with water and more oxygen to form nitric acid. 
 
72 THE ATMOSPHERE AND NITROGEN 
 
 For use as a fertilizer the acid is treated with limestone 
 whereby calcium nitrate is obtained. . 
 
 A large amount of electrical energy is expended in effecting 
 this chemical combination of nitrogen, and it is therefore only 
 near great waterfalls, where power is abundant, that this 
 process has a chance of success. Niagara Falls being in a 
 thickly settled district where the demand for power is great, 
 the price is not as low as one might expect from the magni- 
 tude of the supply. Norway possesses great waterfalls where 
 electric power is developed so cheaply that the manufacture 
 of nitric acid and nitrates from the air is proving a distinct 
 commercial success. 
 
 76. Carbon Dioxide and Water Vapor in Air. Oxygen 
 and nitrogen constitute the main bulk of the atmosphere, 
 and they are perhaps the most important constituents of 
 the air ; but there are two other constituents which are of 
 exceedingly great importance, namely, carbon dioxide, which 
 is only present to the extent of three or four volumes in 10,000 
 volumes of air, and water vapor, which is present in variable 
 amount according to atmospheric conditions, but rarely 
 exceeds 2 per cent of the whole. 
 
 77. Argon. In addition to these gases, there is still 
 another, whose presence was not even suspected until 1894. 
 It is of no practical importance, but it is of very great interest 
 on account of the fact that it constitutes nearly 1 per cent of 
 the air and yet it remained so long undiscovered. 
 
 If the residual part of the air from which oxygen has been 
 extracted is subjected to the action of magnesium and the 
 electric spark, the nitrogen combines to form magnesium 
 nitride. When this is done there is always left a small 
 amount of gas, amounting to about 1 per cent of the air 
 taken at first. This fact was observed by Cavendish, who 
 
ARGON 73 
 
 noticed that whenever he attempted to remove all the oxygen 
 and nitrogen from a confined volume of air, a small bubble 
 of gas always remained. Cavendish observed this fact, but 
 paid little attention to it, probably thinking that the gas 
 remaining was some nitrogen which had not been completely 
 removed. Indeed, this residual gas shows the same general 
 property of inertness as nitrogen. It thus escaped serious 
 attention until 1894. In that year Lord Rayleigh, an English 
 physicist, made accurate measurements of the density of 
 nitrogen and other gases. He observed that the result 
 with nitrogen obtained from air was different from that with 
 nitrogen obtained by decomposing a chemical compound of 
 nitrogen. The fact was then recalled that a residue was 
 always left when the nitrogen residue of air was sparked 
 with magnesium, and Rayleigh concluded that there must 
 be another, previously unsuspected, gas in the air. Ray- 
 leigh was not a chemist and did not feel competent to 
 carry the study of the problem further; he therefore en- 
 listed the aid of the noted chemist, Sir William Ramsay, 
 who after extensive study confirmed the discovery of 
 another constituent of the air, and declared further that this 
 gas was a new element. It was named argon, meaning inert. 
 
 Argon constitutes about 1 per cent by volume of the air. 
 Besides argon, Ramsay discovered four other new gases, 
 helium, neon, krypton, and xenon which, however, are present 
 in the air in exceedingly minute quantities. 
 
 The most remarkable property of argon, as well as of the 
 four other more recently discovered gases, is that of absolute 
 chemical inertness. These gases can be made to combine 
 with no other element, and this accounts for their being so 
 long undiscovered and mistaken for a slight residue of in- 
 active nitrogen. Physically, argon is not very different 
 
74 THE ATMOSPHERE AND NITROGEN 
 
 from nitrogen. It is colorless, odorless, and tasteless; it is 
 heavier than nitrogen, which fact, as we have seen, led to its 
 discovery ; its boiling point is higher than that of nitrogen 
 and lower than that of oxygen. 
 
 ACCURATE DETERMINATION OF THE VOLUME PER CENT OF 
 OXYGEN IN AIR 
 
 78. In order that an accurate knowledge of the composi- 
 tion of the air may be obtained, a much more careful method 
 of removing the oxygen must be employed than that de- 
 scribed in the first part of this chapter. There, it will be re- 
 membered, it was difficult to prevent the escape of some of 
 the confined gas in consequence of the expansive effect of the 
 heat of the burning phosphorus. 
 
 To carry out an analysis of the air, it is necessary to start 
 with an accurately measured quantity, to remove all of the 
 oxygen w r hile care is taken to lose none of the nitrogen, and, 
 finally, to measure the volume of the residual gas. The final 
 volume is, of course, the sum of the volumes of the nitrogen 
 and argon. The quantity of carbon dioxide only yf -$ of 1 
 per cent of the whole is so small as to be negligible. The 
 water vapor in the air may also be neglected if the volumes 
 measured are all uniformly confined over water. 
 
 Let us now follow out step by step the course of an actual 
 analysis of air such as we might perform in the chemical 
 laboratory. 
 
 A narrow cylindrical glass tube which holds 100 c.c. and 
 which is graduated to tenths of a cubic centimeter is used to 
 contain and to measure the air. The cylinder is inverted 
 and its open end is sunk beneath the surface of a deep 
 body of water in a tall glass jar. A definite volume of 
 air is thus confined in the measuring tube. If a few 
 
VOLUME PER CENT OF OXYGEN IN AIR 
 
 75 
 
 cubic centimeters of water are poured into the cylinder 
 before inverting it, the air volume will not reach to the 
 lower end of the tube, but its boundary will come where 
 it can be seen behind the graduations. The tube is now 
 raised or lowered until the water levels inside and outside 
 are the same. There is thus no 
 pressure on the gas due to dif- 
 ference in water level. If there 
 were any such difference, it 
 would have to be taken into ac- 
 count; therefore it is simpler to 
 bring the levels both to the 
 same point and thus avoid the 
 complication. The volume is 
 noted as 95.9 c.c. At the same 
 time the atmospheric pressure 
 is noted as 778 mm. of mer- 
 cury, and the temperature as 
 21 C. The necessity for the 
 latter readings will appear a 
 little later. Now that the defi- 
 nite amount of air is measured, 
 we proceed to remove the 
 oxygen by inserting from under- 
 neath a piece of yellow phos- F '- 
 phorus attached to a bent piece 
 of slender wire (Fig. 13). This wet phosphorus does not take 
 fire in the tube, but it does combine slowly with oxygen and 
 if time enough is allowed, it removes the oxygen as com- 
 pletely as if it had flamed up in rapid combustion. It is 
 therefore necessary to leave the whole apparatus over night. 
 The next morning it is extremely probable that the oxygen has 
 
76 
 
 THE ATMOSPHERE AND NITROGEN 
 
 been completely exhausted. The remaining lump of phos- 
 phorus is removed and the readings taken as before. They 
 are : volume, 77.2 c.c. ; pressure, 756 
 mm. ; and temperature, 18 C. To 
 prove, now, that no oxygen is left in 
 the tube, a fresh piece of phosphorus, 
 which will act more vigorously than 
 the old piece, should be inserted and 
 allowed to stand an hour or two. 
 This is then removed and the volume 
 is again read and found to be 77.2 c.c. 
 This reading, being the same as 
 the second, shows that no oxygen has 
 been absorbed by the second piece 
 of phosphorus. The thermometer and 
 barometer are again read and found 
 to be 18 degrees and 756 mm., re- 
 spectively, not having changed since 
 the previous reading. (If they had 
 changed a little, it might have caused 
 some slight change in the volume of the 
 gas not due to further absorption of 
 oxygen.) 
 
 Since we are compelled to leave the 
 experiment over night, a complication 
 arises which would not bother us if 
 all the readings could be taken at 
 about the same time. The volume of 
 any gas changes with changes of 
 temperature and pressure. Now the 
 temperature of the gas we are interested in will probably not 
 be the same the next day as at the time when the experi- 
 
 FIG. 14. Barometer. 
 The pressure of the at- 
 mosphere on the sur- 
 face of the mercury in 
 the cup counterbalances 
 the weight of the column 
 of mercury in the tube. 
 The height of the top of 
 the mercury surface in 
 the tube above the free 
 surface in the cup thus 
 measures the pressure of 
 the atmosphere. The 
 scale and measuring de- 
 vice is not shown in the 
 figure. 
 
SUMMARY 77 
 
 merit was started; neither will the pressure of the atmos- 
 phere upon the water in the deep jar (and hence on our air 
 which is confined above the water) be the same the follow- 
 ing day. Hence the necessity of noting the temperature 
 and pressure at the time of each reading of volume. The 
 temperature may be found by hanging a thermometer in 
 the water, if the latter has been drawn long enough to come 
 to the temperature of the room. The pressure of the air is 
 found by reading the barometer (see Fig. 14). 
 
 In making our calculations, of the composition of the air, 
 it will not do to subtract the 77.2 c.c. from the 95.9 c.c. and 
 claim that 18.7 c.c. of oxygen were removed, for the tempera- 
 ture and the pressure both changed between the readings. 
 We must first learn what effect change in temperature and in 
 pressure have upon the volume of a gas and then correct the 
 observed volumes for these changes. The next chapter is 
 devoted to the effect of conditions on the volume of gases. 
 
 SUMMARY 
 
 Components of Air. The air is a physical mixture of several gases, 
 of which about one fifth by volume is oxygen and nearly all 
 of the other four fifths is nitrogen. 
 
 About one per cent of the air consists of argon, an absolutely inert 
 gas. Besides argon, there are four other similarly inert gases 
 in very minute amounts. 
 Air contains a small amount of carbon dioxide, but this small 
 
 component is of very great importance. * 
 
 Water vapor is present in the air in varying proportions, but 
 rarely exceeding two per cent. Its presence is of great im- 
 portance. 
 
 Nitrogen an Important Plant Food. Nitrogen is very inert chemi- 
 cally and can be made to combine with other elements only 
 with difficulty. All plant and animal life requires nitrogen 
 for its nutrition, but, with the exception of plants of the 
 
78 THE ATMOSPHERE AND NITROGEN 
 
 legume family, which get nitrogen from the air by the aid of 
 colonies of bacteria growing on their roots, all plant and animal 
 life is compelled to use nitrogen that is already in the com- 
 bined state. Combined nitrogen is, therefore, an essential 
 constituent of fertilizers. Meats and fish, cheese and milk, 
 beans and peas, and to some extent grains and vegetables, 
 supply us with the necessary nitrogen in our foods. Artifi- 
 cial methods of causing the atmospheric nitrogen to combine 
 are assuming commercial importance in connection with the 
 manufacture of nitrogenous fertilizers. 
 
 Questions 
 
 1. Why is air considered a mixture rather than a definite 
 chemical compound ? Give facts which show this, other than those 
 mentioned in Section 71. 
 
 2. Name in the order of their abundance the gases present in 
 the air. 
 
 3. Discuss the relative importance of these gases. 
 
 4. Explain why the fixation of nitrogen is difficult, but of great 
 importance. 
 
 5. Describe processes by which atmospheric nitrogen is in nature 
 brought into a state of combination. 
 
 6. Describe artificial methods of accomplishing the same thing. 
 
 7. Give three methods by which oxygen can be removed from 
 the air. 
 
 8. Why would it be advantageous from the standpoint of 
 economy of heat to use pure oxygen rather than air in burning coal 
 under boilers? Why is pure oxygen not thus used at present? 
 
 9. When meat is excessively high priced, what substitutes 
 which would furnish nearly or quite as much available nitrogen 
 might be used as food ? 
 
 10. Why do farmers plant clover or alfalfa on fields which have 
 become exhausted from frequent raising of wheat? 
 
CHAPTER VIII 
 
 THE GAS LAWS 
 
 79. It is a familiar fact that air and other gases expand 
 when heated and contract when cooled. The expansion of 
 the air over the torrid zone and the resulting trade winds is 
 an example familiar from the study of geog- 
 raphy. A similar phenomenon on a small 
 
 scale is observed in the rise of hot air over a 
 radiator. 
 
 The expansion and contraction of air may 
 be readily demonstrated if a flask is closed 
 with a one-holed rubber stopper and through 
 the latter is passed a narrow glass tube in the 
 middle of which a short column of colored 
 liquid is caught so as to indicate the boundary 
 of the definite volume of confined air. The air 
 expands even with the slight warmth imparted 
 by holding the hands against the sides of the 
 flask, and the thread of liquid is seen to move 
 up in the tube. On the other hand, the vol- FIG. 15. Gas 
 ume of air contracts if the flask is cooled, and Volumes change 
 
 with Temperature. 
 
 the thread of liquid can be seen to move 
 
 downward. Exactly the same behavior is observed if the 
 
 flask is filled with any other gas in place of air. 
 
 80. Measurement of Temperature; Centigrade Scale. 
 In all scientific work, temperature is measured by a scale 
 known as the centigrade scale. This scale possesses two 
 
 B. AND W. C'HEM. 6 79 
 
80 THE GAS LAWS 
 
 fixed points which are very easy to duplicate; namely, the 
 temperature of melting ice and the temperature of the steam 
 from water boiling under a pressure equal to the average 
 atmospheric pressure at sea level. The first point is called 
 zero degrees and the second point is called 100 degrees; 
 and the interval between these two points is divided into 
 100 parts (hence the name centigrade, from the Latin, indi- 
 cating that the scale is graduated into one hundred parts). 
 By extending spacings of equal lengths below degrees and 
 above 100 degrees, the centigrade thermometer is made to 
 read over all ranges of temperature. 
 
 81. When it is wished to express the quantity of a gas in 
 terms of its volume, it is clearly necessary to state the tem- 
 perature of the gas at the time the volume was measured. 
 One liter of a gas at 100 C. would have a different weight 
 from one liter of the same gas at C. 
 
 If gases were not so difficult to weigh, we might perhaps 
 always express the quantity of a gas by weight; but on 
 account of the extreme lightness of gases, it is difficult to 
 weigh them accurately. It is, however, very easy to meas- 
 ure the volume of a gas. 
 
 It has been found that for all gases the change in volume 
 for change in temperature is regular, namely, for an in- 
 crease of 1 C. the increase in volume is equal to %j% of the 
 volume at C., or for a decrease of 1 of temperature, 
 the decrease is likewise 2 TIT f the volume at C. This 
 uniformity in the rate of change was first noted by Charles, 
 in 1787, and his name is now given to the law which connects 
 the change of volume with the change of temperature. 
 
 82. Absolute Zero. Before we take up the study of the 
 application of Charles' law, it will be necessary to consider 
 briefly the matter of absolute temperatures, since the modern 
 
THE ABSOLUTE SCALE OF TEMPERATURE 
 
 81 
 
 treatment of Charles' law makes use of 
 the absolute scale of temperature. Let 
 Figure 16 represent a vessel filled with 
 a gas at C. Suppose the piston with 
 which the top is closed to be gas-tight 
 and to slip up and down without fric- 
 tion. If, now, the gas is cooled by 
 1 C., the volume, according to the rule 
 just stated, will decrease ^y^, and the 
 piston will sink to a position shown by 
 the first dotted line. If it is again 
 cooled by 1 C., that is to - 2, the 
 volume will again be diminished by an 
 amount equal to ^yj of its volume at 
 C., and the piston will sink to the 
 second dotted line. It can readily be 
 seen that when the temperature has 
 been decreased to 273 degrees below 
 zero, the volume will have decreased 
 to zero if the same regularity in -be- 
 havior has continued. This value, 
 273 degrees centigrade, has a great 
 theoretical importance and it is what is 
 known as the absolute zero of tem- 
 perature. 
 
 83. The absolute scale of tempera- 
 ture is graduated in degrees which are 
 equal to those on the centigrade ther- 
 mometer, but the zero point is 273 
 degrees lower than that of the centi- 
 grade scale. This being the case, it is 
 necessary, whenever we wish to convert 
 
 11 
 
 o*c 
 
 t- -5'C 
 HO'C 
 
 - -20C 
 
 -273'C 
 
 FIG. 16. Showing 
 Change of Volume of Gas 
 with Changing Tempera- 
 ture. The volumes 
 marked off on the lower 
 part of the cylinder 
 show the behavior of 
 the idealy perfect gas. 
 Of course no actual gas 
 conforms perfectly to 
 this ideal at very low 
 temperatures although 
 helium comes fairly 
 near to it. 
 
82 
 
 THE GAS LAWS 
 
 -too* 
 
 -373- - 
 
 a centigrade reading into absolute, to add 273 degrees to 
 the centigrade reading. The adding must be algebraic in 
 
 order to take account 
 properly of any minus read- 
 ings. For example, to 
 change 20 centigrade to 
 absolute, 20 + 273 = 293. 
 Hence 20 C. equals 293 
 absolute. Again, to change 
 - 20 C. to absolute : - 20 
 + 273 = 253 absolute. 
 That is, if the absolute 
 zero is 273 degrees below 
 the centigrade zero, and 
 if the temperature 20 C. 
 is 20 degrees below the 
 centigrade zero, then 
 - 20 C. is 253 degrees 
 above the absolute zero. 
 
 84. Charles' Law. Now 
 if any volume of gas say, 
 for the sake of convenience, 
 273 c.c. were taken at 
 C., which equals 273 
 absolute, and cooled, say 
 10, to 263 absolute, then, according to the rule previously 
 mentioned, it would shrink by ffls f its volume at zero, or 
 in this case by ^VV of the 273 c.c. which we chose for con- 
 venience to take. Hence the new volume would be 
 273 c.c. - (^ of 273 c.c.) 
 = 273 c.c. - 10 c.c. 
 = 263 c.c. 
 
 -275. _JLO'__ 
 FAHRENHEIT CENTIGRADE ABSOLUTE 
 
 FIG. 17. Comparison of Different Ther- 
 mometric Scales. 
 
CORRECTION OF GAS VOLUMES 83 
 
 It will be noticed that the new volume in this case numeri- 
 cally equals the new temperature on the absolute scale. If 
 some volume other than 273 c.c. had been taken, the new 
 volume would not have equaled the new temperature numeri- 
 cally, but a simple proportion would have existed between 
 the two temperatures and the two volumes ; hence a simple 
 statement of the law of the effect of temperature on gas 
 volumes, in terms of the absolute temperature, is as follows : 
 
 // the pressure upon a gas remains constant, the volume varies 
 in direct proportion to the absolute temperature. 
 
 The law in this form will be found simpler to use in calculat- 
 ing corrections of gas volumes than in the form which states 
 that the change in volume per one degree change in tempera- 
 ture is 2T3- f the volume at centigrade. 
 
 85. Example of a Calculation based on Charles' Law. 
 In the experiment to determine the per cent of oxygen in air 
 (Chapter VII, p. 74), there were 95.9 c.c. of air in the gas 
 measuring tube at the start. The next day, after the phos- 
 phorus had taken out the oxygen, there were 77.2 c.c. of 
 residual gas. The temperature at the time the first reading 
 was taken was 21 C. The next day, when the volume was 
 read, the temperature was 18 C. To make a fair comparison 
 between the two volumes they must either be brought to the 
 same temperature, or, what is more easily done, be calculated 
 to the same temperature by the use of^Charles' law. Let 
 us change the first volume to the volume it would occupy at 
 the temperature of the final reading. We will first change 
 the centigrade readings to absolute : 21 + 273 = 294 ; 
 18 + 273 = 291. " The problem then becomes : the volume 
 of the gas is 95.9 c.c. at 294 absolute. What will be the 
 volume at 291 absolute? " According to Charles' law the 
 volume varies directly as the absolute temperature, that is, 
 
84 THE GA$ LAWS 
 
 the two volumes and the two temperatures are in simple 
 proportion. 
 
 Then 95.9 = 294 
 
 x 291 
 
 where x stands for the new volume. Multiplying the means 
 and the extremes of the proportion, we have : 
 
 294 x = 95.9 X 291 = 27907 
 
 whence x = - 94.9 
 
 which is the number of cubic centimeters in the new volume. 
 
 We now might subtract the 77.2 c.c. of residual gas from 
 the 94.9 c.c. to find how much oxygen had been removed, 
 provided only that the pressure on the gas had remained 
 constant over night, but the pressure did not remain constant. 
 We shall, therefore, need to consider how changes of pressure 
 affect the volume of a gas. 
 
 86. Effect of Pressure on Volume ; Boyle's Law. It is a 
 fact well known to all who have used a bicycle pump that air 
 decreases in volume under increased pressure, and that it 
 increases in volume if the pressure is diminished. It has 
 been found by accurate measurements that if the temperature 
 is kept constant, the volume of a definite quantity of gas varies in 
 inverse proportion to the pressure. This rule holds for all 
 gases, and it is known as Boyle's law. 1 
 
 Illustration of Boyle's law : If the pressure upon one liter 
 of gas in a cylinder with an air-tight piston is doubled, the 
 volume decreases to one half liter. If, on the other hand, 
 
 1 For accurate work at extremely high pressures, this law does 
 not hold strictly true ; neither does the law of Charles hold strictly 
 true under all conditions; nevertheless, for all ordinary purposes 
 these two laws may be regarded as correct. 
 
CORRECTION OF GAS VOLUMES 85 
 
 the pressure is lowered to one half its initial amount, the 
 volume increases to two liters. 
 
 87. To return, now, to the calculations of our experiment 
 on the volume composition of air, we found on page 84 that 
 the 95.9 c.c. of air with which we started would have had a 
 volume of 94.9 c.c. at the temperature of the final measure- 
 ment ; but we did not take into account the change of pres- 
 sure. That we must do. The pressure as read on the 
 barometer on the first day was 778 mm. and on the second day 
 it was 756 mm. It is therefore necessary to correct the 94.9 
 c.c. for the change of pressure from 778 mm. to 756 mm. in 
 order to find what volume the air originally taken would 
 have had, if it had been measured under the same conditions 
 as the residual gas. The calculation is as follows : 
 
 94.9 = 756 
 x 778 
 
 whence, multiplying means and extremes: 
 756 x = 94.9 X 778 = 73832 
 and x = 73832/756 = 97.7 
 
 Therefore the new volume is 97.7 c.c. 
 
 We have now calculated our initial air volume to the same 
 conditions) 1 as those of the residue, and we can subtract the 
 volume of residue from that of air to find the volume of 
 oxygen removed by the phosphorus. 
 
 97.7 - 77.2 = 20.5 
 
 1 In all of these measurements the gases are measured over water 
 and hence are saturated with water vapor. The amount of water 
 vapor present is nearly the same in every case if the measurements 
 are all made at about room temperature, and hence the errors due 
 to neglecting it very nearly compensate each other. (See footnote 
 on page 86.) 
 
86 THE GAS LAWS 
 
 Thus 20.5 c.c. of oxygen have been removed. Next to find 
 the volume per cent of oxygen divide 20.5 by 97.7. The 
 quotient is 0.210 and thus 21.0 per cent by volume of the air 
 is shown to be oxygen. This result is of approximate accu- 
 racy and a result obtained by this method should not vary 
 by more than 0.2 of one per cent from the true value. 
 
 88. Standard Conditions. We most frequently use 
 Charles' and Boyle's laws for the purpose of changing from 
 ordinary conditions of temperature and pressure to C. and 
 760 mm. These are called standard temperature and standard . 
 pressure and together are often spoken of as standard condi- 
 tions. 1 
 
 The standard temperature is chosen and agreed upon by all 
 scientific workers as C. because this is the temperature of 
 melting ice and is the most easily and accurately obtainable 
 temperature. 
 
 The standard pressure is taken as 760 mm. of mercury 
 because that is found to be the average pressure of the 
 atmosphere at sea level. 
 
 89. Calculations to Standard Conditions. The weight 
 per liter of all gases at standard conditions has been very 
 carefully determined; and in most cases, when we wish to 
 know the weight of any gas that we may collect, we measure 
 its volume, take its temperature and pressure and calculate 
 
 1 The weight of a gas at standard conditions always refers to dry 
 gas. If the gas is collected over water at room temperature and 
 atmospheric pressure, it will occupy between two and three per cent 
 more volume than if it were collected dry. In connection with the 
 study of this chapter, the student is recommended to ignore the 
 possible presence of water vapor. 
 
 For those who have time to study the matter or the necessity 
 for so doing, the method for correcting for the presence of water 
 vapor is outlined on page 426, in the Appendix. 
 
CALCULATIONS TO STANDARD CONDITIONS 87 
 
 what volume it would have at standard conditions and then 
 calculate its weight by comparing its volume with the unit 
 volume (the liter) whose weight is known. The method of 
 calculating to standard conditions is precisely similar to that 
 for calculating to any other conditions. The volume varies 
 directly with the absolute temperature and inversely with the 
 pressure. 1 
 
 For example let the observed volume be 45.0 c.c., the 
 temperature, as read, be 20 C., and the pressure be 740 mm. 
 The gas may be supposed to be dry in this case. If it were 
 wet, a further correction would be necessary in accurate work, 
 as the water vapor has a pressure of its own which has to be 
 taken into account. We wish to find the volume at C. and 
 760 mm. The steps in the calculation are (correcting first 
 for the temperature change) : 
 
 45.0 = 273 + 20 = 293 
 x 273 + 273 
 
 then, multiplying means and extremes, we have 
 
 293 x = 45 X 273 
 whence, dividing through by 293, we have 
 
 _ 45 X 273 
 293 
 
 We might perform the indicated operations and thus 
 find the numerical value of x, which would be the new 
 volume after the temperature change ; but we do not care to 
 know that, but rather the volume after both temperature and 
 
 45 X 273 
 pressure have changed. We can therefore let 
 
 1 See previous footnote. 
 
88 THE GAS LAWS 
 
 stand for the present volume and correct it further for pres- 
 sure as follows : 45 x 273 
 
 293 760 
 
 x 740 
 
 Multiplying means and extremes, we have 
 
 76Q x = 45 X 273 X 740 
 
 293 
 
 and dividing through by 760, we have 
 = 45 X 273 X 740 
 
 293 X 760 
 
 The problem is now in form for numerical solution. The 
 use of logarithms or of the slide rule will be of great assistance 
 in performing the indicated operations at this point. 1 If the 
 pupils are not acquainted with logarithms or the slide rule, 
 the longer arithmetical method will have to be followed. 
 
 Performing the indicated operation, x = 40.8; thus we 
 see that the volume would be 40.8 c.c. at standard conditions. 
 Throughout this chapter it has been assumed that the 
 levels of the liquid over which the gas has been collected are 
 alike inside and outside the gas measuring tubes. In case 
 this is not true, a further correction must be applied to the 
 calculation or else the levels must be made alike. In most 
 cases, the latter is the easier thing to do. 
 
 SUMMARY 
 
 Charles' Law: If the pressure remains constant, the volume of 
 any gas varies directly as the absolute temperature. In other 
 words, the first volume is to the final volume as the first tem- 
 perature is to the final temperature, or 
 
 first volume _ first temperature 
 final volume final temperature 
 
 1 For table of logarithms, see Appendix. 
 
QUESTIONS 89 
 
 whence, final volume = first volume x ^ nal tem P erature 
 
 first temperature 
 
 Boyle's Law: If the temperature remains constant, the volume of 
 any gas varies inversely as the pressure. In other words, 
 the first volume is to the final volume as the final pressure is 
 to the first pressure, or 
 
 first volume _ final pressure 
 final volume first pressure 
 
 whence, final volume = first volume x fi r pressure 
 
 final pressure 
 
 Combined Laws: When both the temperature and pressure are 
 varied at the same time, the combined laws may be expressed 
 as follows : 
 
 final volume = first volume X ^temperature x first pressure 
 
 first temperature final pressure 
 
 Questions 
 
 What will be the final volume if 25 c.c. of gas at 20 C. is 
 30 C. at constant pressure? j*/tA-4-4-<c-^ 
 
 2. If 50.0 c.c. of gas at 30 C. is^coolgdJo 20 C.? 
 
 3. If 45.0 c.c. of gas at 24 C. is cooled to C.? 
 
 4. If 50.0 c.c. of gas at - 10 C. is warmed to C.? 
 
 5. If 100.0 c.c. of gas at C. is heated to 546 absolute? 
 
 6. The temperature remaining constant, calculate the final 
 volume if the pressure on 200 c.c. of gas at 740 mm. is changed to 
 760 mm. 
 
 7. If the pressure on 100.0 c.c. of gas at 780 mm. is changed to 
 760 mm. 
 
 8. If the pressure on 40.1 c.c. of gas at 740 mm. is changed to 
 780 mm. 
 
 9. If the pressure on 20 c.c. of gas at 780 mm. is changed to 
 740 mm. 
 
 10. What will be the final volume if 100 c.c. of gas at 760 mm. 
 are compressed under 1520 mm. pressure? 
 
90 THE GAS LAWS 
 
 11. A given amount of gas measures 100 c.c. at 20 C. and 740 
 mm. What will be the volume under standard conditions, that is, 
 at C. and 760 mm.? 
 
 12. Correct the volume of 50 c.c. of gas at 30 C. and 745 mm. 
 to standard conditions. 
 
 13. Correct the volume of 55 c.c. of gas at 10 C. and 780 mm. 
 to standard conditions. 
 
 14. A given amount of gas measures 55 c.c. at 10 C. and 780 
 mm. What is its volume at 10 C. and 740 mm.? 
 
 15. A certain volume of gas at C. and 760 mm. has its tem- 
 perature raised until its volume is doubled, and then the pressure 
 raised until its volume is brought back to the original value. What 
 are the final conditions of temperature and pressure? 
 
CHAPTER IX 
 
 WATER 
 
 90. Properties of Water. Water is universally known as a 
 colorless, odorless, tasteless, mobile liquid. There are a 
 great many liquids besides water, however, and many of 
 them are colorless, many are odorless, and some are tasteless. 
 So it appears that even so common a substance as water 
 might -be confused with some other substance unless its 
 properties were accurately known. The statement that has 
 already been made applies well here : that the properties of a 
 substance are absolutely constant. Hence, once knowing 
 accurately the properties of water, we may be certain that 
 any liquid that has exactly the same properties is also water, 
 but that any liquid that shows any properties different from 
 those of water is not water. 
 
 It would take a good many pages to describe fully all of the 
 properties of water, and we may content ourselves with a 
 few of the most striking ones which are most useful in dis- 
 tinguishing it from other substances. 
 
 Water is a liquid at ordinary temperatures. At a cer- 
 tain definite temperature, C., it solidifies to a form that 
 we know as ice ; at 100 C., at the ordinary atmospheric 
 pressure, it boils, whereby it is converted into a gas that fills 
 many times the volume (in round numbers 1700 times) 
 that is occupied by the water as a liquid. This gas is known 
 as steam ; it is colorless and transparent, but if it escapes into 
 the cold air, it condenses into droplets of liquid water which 
 produce a cloud or mist. 
 
 91 
 
92 WATER 
 
 91. Water as a Solvent. Water has the power of dis- 
 solving many substances ; for example, a substance like sugar 
 when put into water goes into the water and mixes uniformly 
 with it, thereby becoming a part of the liquid, which is now 
 a solution of sugar in water. This power of water to dis- 
 solve other substances renders it useful for cleaning purposes. 
 It is also of supreme importance in connection with the diges- 
 tion and assimilation of food in the body. Most chemical 
 changes in the practical work of the manufacturing chemist, 
 as well as most of those that we meet with in the laboratory, 
 take place in water solution. Hence the solvent power of 
 water is of great importance. 
 
 Limit of Solubility. On testing the power of water to dis- 
 solve different substances, it is found that there is a definite 
 limit to the amount of a substance that a given amount of 
 water will dissolve at a given temperature. This limit is 
 different for each different substance. For example, 100 
 grams of water at 25 C. will dissolve 37 grams of saltpeter 
 (potassium nitrate), 35 grams of common salt, and only 5 
 grams of boric acid. There is a wide range of solubility 
 among the many different substances that will dissolve in 
 water. 
 
 Change in Solubility with Change in Temperature. In 
 general, the higher the temperature the greater the solubility 
 of solid substances in water. Thus 100 grams of water at 
 100 C. will dissolve 246 grams of saltpeter, 40 grams of salt, 
 and 27 grams of boric acid. It will be noted that common 
 salt gains but little in its solubility at 100 C. over that at 
 25 C. A few substances, among them calcium hydroxide 
 (slaked lime), become less soluble as the temperature increases. 
 
 92. Water in Chemical Life Processes. Its power to dis- 
 solve other substances makes water essential in the chemistry 
 
ATMOSPHERIC MOISTURE 93 
 
 of the life processes of plants and animals. Food in the 
 course of digestion is transformed into soluble compounds 
 wAich pass in solution through the membranes of the di- 
 gestive tract into the blood, and by the blood are carried to 
 the various parts of the body, where they undergo further 
 reaction in the formation of muscular tissue, bone, and other 
 tissues. 
 
 Water plays an equally important part in plant life. 
 Nitrogen-containing substances and mineral substances neces- 
 sary for plant nutrition are in solution in the water in the soil 
 and are sucked up by the roots of plants. Plants, to be sure, 
 draw a considerable part of their nutrition from the carbon 
 dioxide of the atmosphere. This reacts with water in the 
 cells of the green leaves and forms sugar-like substances which 
 are conveyed in the sap to the growing parts of the plant. 
 Thus water is absolutely essential to all the chemical processes 
 taking place in animals and plants 
 
 93. Irrigation. Some of the deserts in our great West 
 which were formerly absolutely barren of any useful vegeta- 
 tion are now, through irrigation, among the most fertile lands 
 of the country. The necessary food materials were in the soil, 
 but lacked the solvent power of water to make them available 
 for plant life. 
 
 94. Atmospheric Moisture, Humidity, and Precipitation. 
 The greater part of the cultivated land depends upon the 
 rain for its moisture. Even when the land is irrigated, the 
 water comes from rivers which are supplied by the rain and 
 snow that fall on the mountains. So the ability of the atmos- 
 phere to contain water vapor is essential to the existence of 
 life. 
 
 It is a well-known fact that wet clothes are hung out to 
 dry. The water evaporates and becomes a part of the air. 
 
94 WATER 
 
 Likewise the water of the ocean evaporates and the moisture 
 is carried by the wind over the land. Now the amount of 
 water which can evaporate into a given space depends only 
 on the temperature and varies very greatly with change in 
 temperature. At C. one cubic meter (about 1.3 cubic 
 yards) of space can take up nearly 5 grams of water vapor ; 
 at 20 C. or approximately room temperature, 17 grams, at 
 30 C. or warm summer temperature, 30 grams ; at 40 C. or 
 excessively warm summer temperature, 52 grams. 
 
 Relative humidity is a term used in reporting atmos- 
 pheric conditions. When the air contains the maximum 
 possible water vapor at the given temperature, it is saturated 
 and its relative humidity is 100 per cent. With lesser 
 amounts of moisture, it is unsaturated and its humidity is 
 expressed in per cent of the saturation value for that tem- 
 perature. 
 
 Precipitation occurs when the air becomes supersaturated 
 with moisture. This can occur when nearly saturated warm air 
 becomes cooled. Its capacity for water vapor is much lower 
 at the lower temperature and so what will only saturate at the 
 higher temperature will more than saturate the air at the 
 lower temperature. Therefore the excess above the satura- 
 tion point precipitates as mist or rain. Water vapor is entirely 
 invisible. For example, the average schoolroom contains 
 one kilogram or about two pounds of water as invisible 
 vapor. Likewise, the air on a perfectly clear day may 
 contain large amounts of water vapor. If the air currents 
 become cooled, mist and clouds are formed. Mist consists 
 of a vast number of very small globules of liquid water, 
 which are so small that they remain suspended in the atmos- 
 phere. If these mist globules become larger, they fall to the 
 earth as rain. 
 
DRINKING WATER 95 
 
 95. Relative Humidity and Human Comfort. The water 
 vapor is a very important constituent of the air when con- 
 sidered from the standpoint of human comfort. When the 
 relative humidity is high, human beings become very uncom- 
 fortable because the perspiration fails to evaporate promptly 
 from the surface of the body. Now the evaporation of per- 
 spiration is one of the most important means of regulating the 
 body temperature, heat being taken up when the moisture 
 evaporates. Hence, when the relative humidity is high, peo- 
 ple are usually very uncomfortable. High relative humid- 
 ity is more oppressive than a high temperature accompanied 
 by a relatively dry atmosphere. The oppressive character 
 of the air in schoolrooms, crowded halls, or other public 
 gathering places is largely due to the high relative humidity 
 caused by the evaporation of perspiration and by the water 
 vapor exhaled with the air from the lungs. 
 
 96. Drinking Water. Those who have always lived in 
 cities and have had an abundant supply of clear, pure water 
 whenever they chose to turn the faucet, find it hard to realize 
 what a serious matter the problem of water supply is. Water 
 that is to be used for drinking must be pure from a sani- 
 tary standpoint, that is, it must contain nothing that can 
 cause sickness. Bacteria, microscopic living organisms, 
 which cause certain diseases, notably typhoid fever, are 
 likely to be present in water as a result of pollution by 
 sewage. . 
 
 A few bacteria taken into the system in a glass of even 
 badly polluted water are not in themselves harmful, but the 
 danger lies in the fact that they find in the human intestines a 
 favorable place to multiply. So, if a few disease germs get 
 into the system, they may within a short time have increased 
 until there are countless numbers of them. Usually the hu- 
 
 B. AND W. CHEM. 7 
 
96 WATER 
 
 man system is strong enough to destroy the disease germs 
 before they gain the ascendency. But when the system is 
 weakened through abuse, or overwork, or lack of exercise, it 
 falls an easy prey to disease bacteria. 
 
 The best safeguard against disease is to keep the body in 
 healthy condition, but still one will not willingly subject it to 
 infection by disease germs. Hence those in charge of city 
 water supplies must be continually on the alert to keep them 
 free from infection. The appearance is not a criterion of the 
 safety of water. The clearest looking water may contain 
 millions of typhoid bacilli, whereas, often, yellow and even 
 muddy water may be quite safe. It requires chemical and 
 bacteriological tests to prove the danger or safety of water, 
 and in city supplies the city chemists and bacteriologists 
 must be depended upon to see to this. In country places, 
 where each house has its own well or spring, the safety of the 
 water should be determined from time to time by analysis. 
 Samples of water are usually tested free of charge at the 
 laboratories of the state board of health. This testing is 
 particularly necessary when the well is near the closet or barn- 
 yard, but distance from apparent source of infection cannot 
 always be taken as assurance of safety. 
 
 97. The purification of water for sanitary purposes 
 consists in the main in destroying or removing bacteria. 
 Filtration will accomplish the removal if the pores of the 
 filter are small enough. The ordinary filter which screws on 
 the faucet is entirely valueless for this purpose. The type 
 of filter which is made of unglazed porcelain is effective in 
 removing bacteria, but its pores are so small that the water 
 filters very slowly. 
 
 Sand filters are used in purifying large city supplies but the 
 safety of these filters is due in part to the action of beneficent 
 
PURIFICATION OF WATER 97 
 
 bacteria which abound in the filter and destroy the harmful 
 organisms. 
 
 Chemical destruction of bacteria is a great safeguard. 
 When water is stored for a long period in reservoirs, the 
 bacteria are destroyed through the oxidizing action of the 
 air. More rapid destruction may be accomplished through 
 the use of chlorine or bleaching powder, and recently the use 
 of ozone, a particularly active modification of oxygen (see 
 Chapter XV, p. 159) has come into favor, particularly in 
 European cities. 
 
 Sterilization by Boiling. In country places which have to 
 depend on polluted wells and in cases of epidemic in cities 
 when the public health authorities cannot control the situa- 
 tion, danger of infection is obviated by boiling the water for 
 at least five minutes, since none of the disease-producing 
 organisms are capable of withstanding the boiling tempera- 
 ture for that length of time. 
 
 98. Chemically Pure Water. Water that is pure from a 
 sanitary standpoint may contain considerable quantities of 
 dissolved mineral matter. Indeed, water with a small 
 mineral content is probably more desirable for drinking than 
 absolutely pure water. 
 
 Natural waters may be purified of their mineral content by 
 means of distillation (see page 17). Rain water has been 
 subjected to a natural process of distillation and is free from 
 mineral matter except as it drags down smoke and dust from 
 the atmosphere. 
 
 99. Water for industrial purposes, as, for example, for use in 
 laundries or for feeding steam boilers, should contain as small 
 a mineral content as possible (see Hard Water, page 201). 
 It is, of course, impossible from the standpoint of expense to 
 distil all the water needed in industrial operations, and it is 
 
98 WATER 
 
 therefore very necessary to obtain a natural supply as free as 
 possible from dissolved minerals. 
 
 SUMMARY 
 
 Water is a colorless, odorless, tasteless, mobile liquid which freezes 
 at C. and boils at 100 C. One volume of liquid water 
 gives about 1700 volumes of steam. 
 
 Water is a solvent for a great many substances. Each substance 
 has its own definite limit of solubility. In general solid sub- 
 stances are more soluble the higher the temperature. The 
 solvent power of water makes it very useful for cleansing pur- 
 poses and essential in the life processes of plants and animals. 
 
 Water vapor in the atmosphere is the source of rain and of all natural 
 fresh water. Precipitation occurs when the atmosphere is 
 left more than saturated with water vapor as a result of 
 cooling. 
 
 In arid regions, the conveyance of water from a distance permits 
 the raising of abundant crops. 
 
 Relative humidity is expressed in per cent of the moisture neces- 
 sary for saturation at the given temperature. 
 Human comfort depends largely on the degree of relative hu- 
 midity. 
 
 Drinking water is often rendered dangerous by the presence of 
 disease-producing bacteria, so that wells and other water 
 supplies should be tested. 
 
 Impure water may be rendered safe by proper filtration or by 
 sterilization. Water may be sterilized by boiling it for at 
 least five minutes or by the addition of chemical substances 
 such as chlorine or ozone. 
 Water may be freed of mineral matter by distillation. 
 
 Questions 
 
 1. How could you make sure that a certain colorless liquid was 
 water ? 
 
 2. On a cold day, with no tendency for ice to melt, how could 
 you distinguish ice from rock crystal? 
 
QUESTIONS 99 
 
 3. Cite some experiments by which you can prove that the air 
 of the schoolroom contains water vapor. 
 
 4. Why is it necessary, from a chemical standpoint, for us to 
 drink water ? 
 
 5. Some of our western deserts are very fertile when irrigated. 
 Would they be equally fertile to-day if they had been subjected to 
 rainfall for the past century? 
 
 6. Explain the cause of the dew found on the grass in the 
 morning. 
 
 7. Why are people so uncomfortable in humid weather ? 
 
 8. State and explain the necessary precautions to be taken in 
 connection with the source of your drinking water. 
 
 9. How are municipal water supplies safeguarded? 
 
 10. Why do not the same standards of purity apply to water 
 for drinking and for industrial purposes? 
 
 11. Supposing the fresh water supply had given out, how might 
 drinking water be obtained in mid-ocean on a steamship? 
 
CHAPTER X 
 
 COMPOSITION OF WATER 
 
 IN preceding chapters we have seen that although air was 
 regarded by the ancients as one of the elements, it consists in 
 reality of two different gases, oxygen and nitrogen, not to 
 mention small quantities of several other gases. Water 
 was regarded by the ancients as another of the elements, 
 but we are to show that it is in reality a compound of two 
 elements, oxygen and hydrogen ; for it can, by suitable means, 
 be decomposed into these two elements. 
 
 100. Decomposition of Water by Hot Iron. For ex- 
 ample, by boiling water and leading the steam through a 
 tube containing red-hot iron filings, we find that the vapor 
 which escapes from the farther end of the tube does not 
 entirely condense again to the liquid water, as it would if 
 no chemical change had taken place, but that a part of it 
 remains permanently as a gas, Fig. 18. This gas does not 
 dissolve in water; it is colorless and odorless; it burns 
 readily but it does not itself support combustion ; in short, 
 it is an entirely new substance, different in its properties from 
 either the iron or the water used in obtaining it. It is 
 hydrogen. This gas cannot have come from the iron, for 
 in all our experience with iron no other substance has ever 
 been obtained from it, that is, iron is an element. The gas 
 must, then, have come from the only other possible source ; 
 that is, from the water. 
 
 100 
 
DECOMPOSITION OF WATER* 3t 'HOT IRON 
 
 101 
 
 If we examine the substance remaining in the tube, we 
 find, in place of the iron, a black substance which is brittle, 
 rather than malleable like iron. This substance is oxide of 
 
 iron. 
 
 The water, therefore, must have had in it not only hydrogen, 
 but also something which united with the element iron to 
 
 FIG. 18. Decomposition of Steam by Hot Iron. 
 
 form the iron oxide. Upon studying the properties of this 
 iron oxide more completely, we find it to be the same sub- 
 stance that was obtained when iron was burned in pure 
 oxygen (see page 44). As the same elements are required 
 to produce the same chemical substance in every case, we 
 thus have made certain that there must be some oxygen in 
 this new substance formed from iron and water. Since 
 iron is an element, the oxygen must have come from the 
 
102 COMPOSITION OF WATER 
 
 water, and water must therefore contain oxygen as well as 
 hydrogen. 
 
 101. Decomposition of Water by Sodium. Many other 
 metals when hot can decompose water vapor. Hydro- 
 gen is liberated because the metal attaches the oxygen to 
 itself in each case and thus leaves nothing to hold the hydro- 
 gen in combination. Some metals are sufficiently active 
 towards water to decompose it even when cold; but such 
 metals are never found free in nature, as they would long 
 ago have been acted upon by natural waters. These very 
 active metals can be prepared by decomposing such of their 
 compounds as are readily available, and this is most often 
 accomplished by the aid of the electric current. One of 
 these metals is sodium, which is prepared in considerable 
 quantities by decomposing sodium hydroxide by means of 
 the electric current. 
 
 If a piece of sodium, which is lighter than water, is thrown 
 upon water, a lively action begins at once ; a gas is evolved, 
 and the bit of sodium darts round and round the dish, due 
 to the reaction from the pressure of the issuing gas. The 
 sodium melts from the heat evolved by the chemical reaction 
 and then forms a round ball which speedily grows less and 
 less in size and then disappears. If the reaction is carried 
 out under an inverted cylinder full of water, the gas evolved 
 rises to the top of the cylinder. 1 The gas can then be ex- 
 amined and its properties determined. It proves to be 
 hydrogen. Thus sodium can accomplish, in the cold, 
 what iron could only accomplish when the temperature 
 was raised; namely, the displacement of hydrogen from 
 water. 
 
 1 This experiment should be performed only by the instructor, as 
 an explosion may result if not carefully handled. 
 
ELECTROLYSIS OF WATER 103 
 
 102. Further Displacement of Hydrogen. If, now, the 
 solution remaining after the action of sodium on water is 
 evaporated to dry ness, thus removing all water not acted 
 upon by the sodium, the product is found to be a white solid 
 which has all the properties of the substance known as 
 sodium hydroxide. On powdering this product and mixing 
 it with an equal bulk of powdered zinc and heating the 
 mixture gently in a dry test tube, a quantity of gas is evolved 
 which on testing proves to be hydrogen. Now both sodium 
 and zinc are known to be elements and therefore do not con- 
 tain hydrogen. The hydrogen, then, since it cannot have 
 come from either of the metals employed, must have come 
 originally from the water. Thus we have twice obtained 
 hydrogen, which was originally a component of the same water, 
 and we can assert that the hydrogen of water exists in two 
 portions, one of which is more easily displaced than the 
 other. An accurate comparison of the amounts of hydrogen 
 set free by the sodium and by the zinc, respectively, has 
 shown that they are equal. 
 
 103. Electrolysis of Water; Volume Composition. Our 
 next step in the study of water will be to study the effect of 
 passing an electric current through it. An electric current 
 passes through pure water with great difficulty, but if a little 
 sulphuric acid is added to the water, the current then passes 
 freely. The exact nature of the action of the sulphuric acid 
 in allowing the current to flow more freely will not be ex- 
 plained here, but it may be stated that there is just the same 
 amount of acid present after the passage of a large amount 
 of current as there was at first. In this experiment, then, 
 we shall add a little sulphuric acid to the water as a matter 
 of convenience ; but in studying the changes that occur, we 
 shall leave the acid entirely out of account, for as just stated 
 
104 
 
 COMPOSITION OF WATER 
 
 the acid itself is not permanently altered. The electrolysis of 
 water can best be carried out in an apparatus devised by 
 Hofmann and known as Hofmann's electrolytic apparatus. 
 It consists of three tubes connecting at the bottom, as shown 
 in Fig. 19. Two of the tubes are in the same plane, the 
 third is in the rear and is provided 
 with a bulb at the top to act as a 
 reservoir for the acidulated water. 
 In the lower part of the front tubes 
 are placed small pieces of sheet 
 platinum which are supported by 
 platinum wires connected respec- 
 tively with the two poles of an elec- 
 tric battery. These metal 'terminals 
 are known as electrodes and it is at 
 the surface of these electrodes that 
 the chemical changes brought about 
 by the electric current take place. 
 The tops of the two front tubes 
 are provided with glass stopcocks 
 through which any gases that collect 
 may be removed for examination. 
 
 On filling the apparatus with the 
 acidulated water and allowing the 
 electric current to pass, bubbles of 
 gas at once appear at each of the 
 
 electrodes and continue to rise so long as the current is 
 passing. It is soon evident that more gas collects at the 
 negative electrode (that is, the one connected with the nega- 
 tive electrical conductor) than at the positive electrode, 
 and when carefully measured under like conditions of 
 temperature and pressure, it is found that the volume of 
 
 FIG. 19. Electrolysis of 
 Water. 
 
SYNTHESIS OF WATER 105 
 
 gas collected at the negative electrode is exactly twice that 
 collected at the positive. On withdrawing some of the gas 
 that occupies the larger volume and testing it, we find that 
 it will burn, but will not support combustion ; it is colorless 
 and odorless, and insoluble in water. It has, in fact, the 
 characteristic properties of hydrogen. The other gas, that 
 from around the positive electrode, is colorless and odorless, 
 it will not burn, but it does support combustion ; it shows 
 the characteristic properties of oxygen. 
 
 104. Synthesis of Water. After showing thus that water 
 can be decomposed into two volumes of hydrogen gas and 
 one volume of oxygen gas, the thought naturally arises : if 
 this is all that water consists of, it should be possible to form 
 water from these two gases when they are taken in the pro- 
 portion of two volumes of the former to one volume of the 
 latter. And, as a matter of fact, this can be done with 
 perfect ease for there is great chemical attraction between 
 hydrogen and oxygen (it is this attraction for each other that 
 has to be overcome when water is decomposed by the electric 
 current or other means) . To form water, it is only necessary 
 to bring hydrogen and oxygen into the presence of each other 
 and to start chemical combination by means of a spark or a 
 small flame. For example, hydrogen gas issuing from a jet 
 may be lighted just as ordinary illuminating gas is lighted. 
 The hydrogen burns, however, with a colorless flame. 
 That water is really a product of this reaction may be 
 proved by holding a piece of cold glass over the flame and 
 noting the moisture that condenses. 
 
 105. By means of the apparatus shown in Fig. 20, it 
 can be readily shown that two volumes of hydrogen and 
 one volume of oxygen actually do combine to form water. 
 The inner tube is filled to mark 1 with oxygen and then to 
 
106 
 
 COMPOSITION OF WATER 
 
 mark 3 with hydrogen, precaution being taken by raising or 
 lowering the apparatus that the top of the mercury column 
 in the tube is always at the same 
 height above the free surface of 
 mercury in the reservoir M. After 
 causing combination to take place by 
 jumping a spark between the term- 
 inals of the electrical conductors, 
 E E, we see the mercury almost 
 immediately rise until it reaches 
 the top of the tube, if the experi- 
 ment is carried out at the ordinary 
 temperature. 
 
 When however the experiment is 
 performed while steam is being passed 
 through the outer jacket, thus keep- 
 ing the temperature constantly at 
 100 C., the mercury level rises only 
 to the mark 2 (the same precaution 
 being observed of adjusting the ap- 
 paratus until the top of the mercury 
 is at the same height above the level 
 in the reservoir). 
 
 We have thus shown that at a 
 temperature where water will remain 
 a gas, two volumes of hydrogen com- 
 bine with one volume of oxygen to 
 produce two volumes of water vapor. 
 106. Law of Definite Combining 
 FIG. 20. -combining Pro- Proportions Illustrated. These gases 
 portions by Volume of Hydrogen W JU no t combine in any other pro- 
 portions than those stated. If, for 
 
 \M 
 
 
WEIGHT COMPOSITION OF WATER 107 
 
 example, one volume of oxygen is mixed with three volumes 
 of hydrogen, two volumes of the latter combine as before 
 to produce water, while one volume is left uncombined and 
 will remain as a permanent gas even if the tube is cold and 
 the water vapor condenses to liquid water. Similarly, if 
 two volumes of oxygen are mixed with two volumes of 
 hydrogen, it is found, after the explosion, that one volume 
 of oxygen is left uncombined. These facts illustrate again 
 the law of definite proportions. 
 
 Such simple and exact relations as are thus observed in 
 the combining volumes of these gases would never exist by 
 mere chance. There must be some underlying explanation 
 for it and we shall try in a forthcoming chapter to develop 
 such an explanation. 
 
 107. Weight Composition of Water. Very exact measure- 
 ments of the weights of these gases have shown that one 
 liter of oxygen at C. and 760 mm. pressure weighs 
 l I 42/_^g., while one liter of hydrogen weighs 0.08996 g. 
 Since, as we have seen, two volumes of hydrogen com- 
 bine with one of oxygen, it follows that 1.429 g. of 
 oxygen combine with 0.17992 g. of hydrogen. These 
 weights are in the porportion of 7.94 to 1.00; in other words, 
 7.94 parts by weight of oxygen combine with one part by 
 weight of hydrogen to produce 8.94 parts by weight of water. 
 The combining weight of oxygen is, then, 7.94, if that of 
 hydrogen is considered as one. 
 
 We shall find in every case in which two elements com- 
 bine, as do hydrogen and oxygen in this case, to form a 
 definite chemical compound such as water, that there is a 
 certain definite ratio between the weights of the two ele- 
 ments that enter the combination. Although these ratios are 
 always absolutely the same for the same combination, they 
 
108 COMPOSITION OF WATER 
 
 are not as a rule simple whole numbers. Contrasted 
 with this, the ratios of the volumes of gaseous substances 
 which combine are not only absolutely definite, but they 
 are in the proportion of simple whole numbers. We shall 
 seek for explanations of these interesting facts in a future 
 chapter. 
 
 108. Hydrogen peroxide is a compound that, like water, 
 contains only the elements hydrogen and oxygen, but here 
 we find that 15.88 parts by weight of oxygen instead of 7.94 
 parts are combined with one part of hydrogen. 
 
 The common pharmaceutical preparation which is some- 
 times sold under the correct name of hydrogen peroxide and 
 sometimes under trade names suggesting the double amount 
 of oxygen, is a mixture of about 3 parts of hydrogen peroxide 
 with 97 parts of water. It is used in cleansing wounds since 
 it has a destructive action on the germs that cause blood 
 poisoning, while it is not injurious to the flesh. 
 
 Pure hydrogen peroxide is a sirupy liquid one and one half 
 times as heavy as water. It blisters the skin and will set fire 
 to finely divided cotton. The pure substance is dangerous to 
 handle, since it will explode violently on rather slight prov- 
 ocation. The explosion is due to a sudden decomposition 
 into water and oxygen. In solution in water it is not danger- 
 ous, but it decomposes with ease, giving off oxygen and only 
 water remaining. If a pinch of some powdered substance, 
 sand, or, still better, manganese dioxide, is dropped into a 
 3 per cent hydrogen peroxide solution in a test tube, a vigor- 
 ous effervescence begins at once and the escaping gas will 
 cause a glowing splinter to burst into flame. The powder 
 can be shown not to have changed chemically, thus it acts 
 only catalytically in hastening the natural decomposition of 
 the hydrogen peroxide. 
 
SUMMARY 109 
 
 SUMMARY 
 
 Water is not an element as the ancients believed. It is composed 
 of the elements hydrogen and oxygen. It may be decomposed 
 by iron at a high temperature or by a very active metal such 
 as sodium at the ordinary temperature. Hydrogen gas is 
 evolved in these cases and a residue containing oxygen and 
 the metal is left. 
 
 Volumetric Composition: Decomposition of water by the electric 
 current and synthesis of water from its elements show that 
 two volumes of hydrogen and one volume of oxygen enter 
 into its composition. When the temperature is high enough 
 to keep the water in the gaseous form, the two volumes of 
 hydrogen and one volume of oxygen yield two volumes of 
 water vapor. 
 
 The proportion by weight in which the elements combine in water 
 are 7.94 parts of oxygen and 1.00 part of hydrogen. This 
 relation is as definite but not as simple as the volume relation. 
 
 Hydrogen peroxide is another compound of hydrogen and oxygen, 
 and for a given Weight of hydrogen it contains exactly twice 
 as much oxygen as does water. 
 
 Questions 
 
 1. How do you know that the ancients were wrong when they 
 said that water is an element? 
 
 2. Which would give a sharper explosion a mixture of oxygen 
 and hydrogen in which the two gases were present in equal volumes, 
 or one containing two volumes of hydrogen to one of oxygen? 
 Why? 
 
 3. Which weighs more one liter of oxygen or two liters of 
 hydrogen? How much more? 
 
 4. Thirty cubic centimeters of hydrogen and 30 c.c. of oxygen 
 are collected over mercury in a measuring tube at 20 C. After 
 exploding the mixture, what will be the volume at 20 C. if the 
 pressure is kept the same ? 
 
 6. If 30 c.c. of hydrogen and 30 c.c. of oxygen are collected in a 
 measuring tube at 100 C. and the tube is kept at this temperature, 
 by surrounding it with a steam jacket, what will be the total 
 
110 COMPOSITION OF WATER 
 
 volume of gases present after exploding the mixture, if the pressure 
 is kept the same ? What are the gases ? What is the volume of 
 each? 
 
 6. An evacuated heavy glass tube is filled at room temperature 
 with oxygen until the pressure is 76 cm. and then hydrogen is 
 forced in until the pressure has risen to 228 cm. The mixture 
 is then exploded by a spark. What will be the condition in the 
 tube after it has cooled to the original temperature? 
 
 7. If the same evacuated tube is kept at 100 C. and filled with 
 oxygen to 10 cm. pressure and with hydrogen to 50 cm. pressure, 
 what will be the pressure after the explosion if the temperature is 
 still 100 C. ? if the tube is cooled to C. ? (Neglect pressure of 
 water vapor at C.) 
 
 8. A certain substance yields equal volumes of hydrogen and 
 chlorine gases on decomposition. Find weight per liter of each of 
 these gases in the Appendix (page 428) and calculate the weight 
 composition of the substance. 
 
 9. Would a water chemist in " analyzing " a sample of water 
 decompose the water as described in this chapter? Would he be 
 at all interested in a real analysis of water in such a case? Why? 
 
 10. In the practical uses of water does the water usually become 
 decomposed? 
 
 11. Explain how hydrogen peroxide and water illustrate the law 
 of multiple proportions. What other illustration of this law have 
 we already encountered? 
 
 12. Explain the action caused by dropping manganese dioxide 
 into 3 per cent hydrogen peroxide. 
 
 13. How does hydrogen peroxide destroy germs? 
 
 14. Explain why pure hydrogen peroxide will blister the skin 
 and set fire to cotton. 
 
CHAPTER XI 
 HYDROGEN 
 
 HYDROGEN, as has been seen in the last chapter, is one of 
 the constituents of water, and when liberated from its com- 
 bination with oxygen in that compound it assumes the form 
 of a gas. 
 
 109. Discovery of Hydrogen. Hydrogen was discovered 
 in 1766 by Cavendish, who was the first to make clear its 
 elementary character, but it had been obtained prior to 
 Cavendish's discovery by Paracelsus and perhaps by others 
 while working with active metals and sulphuric acid. It 
 was not called hydrogen by Cavendish, but by Lavoisier 
 who named it from Greek words meaning the water former, 
 because when it is burned in air or oxygen, water is formed. 
 
 110. Hydrogen in Water. Water is in fact the most 
 abundant substance of which hydrogen is a constituent. 
 In water, as we have learned in the last chapter, hydrogen 
 and oxygen are held together by some force, so that, instead 
 of having a mixture of two gases, we have the liquid water, 
 a substance which has different properties from either 
 hydrogen or oxygen. By overcoming the force that holds 
 its constituents together it should be possible to separate 
 water again into its elements. As already seen in the last 
 chapter, water can be decomposed into its elements by 
 means of the energy of the electric current; and hydrogen 
 may be set free from water by means of some metals, as 
 
 B. AND W. CHEM. 8 111 
 
112 
 
 HYDROGEN 
 
 sodium or iron, which possess a greater chemical energy and 
 therefore a greater attraction for the oxygen. 
 
 111. Hydrogen from Acids. When hydrogen is to be 
 made in the laboratory, water is not chosen as its source, but 
 rather an acid such as sulphuric acid or hydrochloric acid. 
 An acid always contains hydrogen, although not all sub- 
 stances that contain hydrogen are acids. In an acid the 
 hydrogen is in such a peculiar state of combination that if 
 the acid is dissolved in water and the solution treated with 
 the metal zinc, or iron, or any one of a considerable number 
 of active metals, the hydrogen is displaced by the metal, 
 escaping as a gas, while the metal assumes the place in the 
 acid which was vacated by the hydrogen. 
 
 112. Hydrogen Generator. The simplest form of labora- 
 tory generator consists of a bottle or flask (Fig. 21) with 
 
 FIG. 21. Hydrogen Generator. 
 
 a two-holed stopper through one hole of which a thistle 
 tube enters, reaching the bottom of the bottle, and thus 
 serving not only for the entrance of fresh acid but also as a 
 
% PROPERTIES OF HYDROGEN 113 
 
 trap to prevent the escape of the hydrogen. The hydrogen 
 passes through a delivery tube which is led through the 
 other hole in the stopper. This tube should just barely pass 
 through the stopper and not be pushed down into the liquid, 
 as there would then be no escape for the hydrogen. The 
 delivery tube leads the gas into a trough or pan of water in 
 which several test tubes or wide-mouth gas bottles have 
 been inverted after having been filled with water. When 
 zinc (preferably in a coarsely granular form, to expose a 
 large surface) has been placed in the generating bottle and 
 covered with water to seal the thistle tube and dilute sul- 
 phuric acid is poured in through the tube, a lively effer- 
 vescence begins. Since the bottle was filled with air at the 
 outset, the gas which first issues from the delivery tube will 
 be a mixture and should be rejected because it is explosive 
 and because it does not have the same properties as pure 
 hydrogen. After a few minutes the air will all have been 
 displaced, and then one of the bottles in the trough may be 
 held over the end of the delivery tube and some hydrogen 
 collected. 
 
 113. Properties. Hydrogen burns with a very hot but 
 almost colorless flame. It does not support combustion 
 when a lighted match is thrust into it. It is colorless and 
 odorless when pure (although when prepared as usual from 
 impure materials, other substances may be present in it 
 which have odor of their own). 
 
 114. Lightness. Hydrogen is the lightest gas known, 
 one liter of it weighing only 0.09 g., that is, less than nrthnr 
 as much as the same volume of water. In virtue of its 
 lightness, it is used to fill balloons, for it is less than one 
 fourteenth as heavy as the air which it displaces. For 
 every liter of hydrogen in the balloon, the lifting power is 
 
114 
 
 HYDROGEN 
 
 equal to the difference in weight between a liter of air and 
 a liter of hydrogen, or, 1.29 0.09 = 1.20 grams. 
 
 115. Diffusibility. Hydrogen is the most diffusible of all 
 gases, that is to say, it passes most readily through small 
 openings or through porous material. It is well known 
 
 that toy balloons, which are 
 filled usually with illuminating 
 .gas containing a considerable 
 amount of hydrogen, soon lose 
 their lifting power. This is 
 very largely due to the diffusion 
 of hydrogen through the rubber 
 skin of the balloon. 
 
 The effect of diffusion may 
 be prettily shown if a large jar 
 of hydrogen is placed over an 
 unglazed earthen cylinder filled 
 with air and mounted as shown 
 in Fig. 22. Hydrogen diffusing 
 into the porous cylinder faster 
 than air, which is more slug- 
 gish, can diffuse out, a greater 
 pressure is created within the 
 
 FIG. 22. Diffusion of Hydrogen 
 H, bell jar filled with hydrogen. 
 A, unglazed earthen cylinder 
 
 sealed to vertical tube dipping in cylinder, and this pressure is 
 
 conveyed through the tube 
 
 reaching down and dipping into the beaker of water. Thus 
 bubbles of gas are seen to rise in the beaker almost im- 
 mediately after the jar of hydrogen is placed over the 
 porous cylinder. If after considerable hydrogen has diffused 
 into the cylinder the jar is removed, the hydrogen inside 
 the porous vessel will diffuse out into the air faster than 
 the air can get in and there will be less pressure inside 
 
DETONATING GAS 115 
 
 than out so that the water in the beaker will be forced by 
 the outside air pressure up into the inner cylinder. 
 
 116. Liquefaction and Solidification. Besides being the 
 most diffusible of all gases, hydrogen is, with one exception, 
 the most difficult gas to liquefy and solidify. It has long 
 been known that by great cold and pressure air could be 
 condensed to a liquid, although it is only comparatively 
 recently that the liquefaction of air on a commercial scale 
 has been possible. But it was not until 1898 that hydrogen 
 was first liquefied. Dewar, an English scientist, accom- 
 plished this. Under ordinary atmospheric pressure it 
 liquefies at about 252 C., or only 21 above the abso- 
 lute zero. If it is highly compressed, the gas liquefies more 
 easily, that is to say, at a higher temperature, but above the 
 temperature of 241 C. or 32 absolute, which is known 
 as its critical temperature, it cannot be liquefied at all. It is 
 thus evident why, for so long a time, hydrogen resisted all 
 efforts to bring it into the liquid form. Pressure alone was 
 not sufficient ; a very low temperature was necessary, and 
 many attempts were made before this was finally attained. 
 Liquid hydrogen freezes at 257 C. or 16 absolute. 
 
 Both the liquid and the solid are colorless. 
 
 117. Detonating Gas. A mixture of two volumes of 
 hydrogen and one volume of oxygen (the ratio by volume in 
 which they combine to form water) is known as detonating 
 gas because it detonates or explodes 'so violently when 
 ignited by a spark or kindled in any other way. If soap 
 bubbles are blown with this mixture and lighted as they 
 float away, they explode with a deafening report. This ex- 
 plosion is due to the great heat liberated when the hydrogen 
 combines with oxygen. This heat expands the resulting 
 gaseous product (steam) so suddenly and to such an extent 
 
116 HYDROGEN 
 
 that a violent blow is struck against the surrounding air, 
 thus producing the loud noise. Mixtures of hydrogen and 
 oxygen in other proportions than 2 to 1 are also more or 
 less explosive, as are also mixtures of hydrogen with air. 
 Mixtures of illuminating gas (which usually contain consider- 
 able hydrogen) with air are similarly explosive, hence the 
 need for great caution in regard to using an open flame in 
 the vicinity of a gas leak. 
 
 118. Oxyhydrogen Flame. The great heat of combus- 
 tion of hydrogen is utilized for obtaining very high tempera- 
 tures by means of the oxyhydrogen blowpipe, a device in 
 which hydrogen and oxygen are led into a small mixing 
 chamber from which they issue into the flame (Fig. 23). 
 
 FIG. 23. Oxyhydrogen Blowpipe. 
 
 The operation of the blowpipe is as follows : first the hydro- 
 gen cock is opened and the gas is lighted and burns with the 
 oxygen of the air. Then the oxygen cock is gradually opened, 
 introducing oxygen into the interior of the flame. The 
 flame grows sharp and pointed and the inside blue cone re- 
 treats more and more with increasing supply of oxygen until 
 it is very short and barely reaches beyond the orifice. The 
 two gases are then issuing in the correct combining propor- 
 tions and the most intense heat can be obtained for they 
 are already mixed and ready to combine as they leave the 
 orifice. It frequently happens, if the flame is not skillfully 
 manipulated, that it strikes back into the mixing chamber 
 
OXYHYDROGEN FLAME 117 
 
 and produces a sharp report from the explosion there. The 
 mixing chamber is made so small, however, that if the 
 flame accidentally strikes back, it will not produce a trouble- 
 some explosion. 
 
 119. With the oxy hydrogen flame, a temperature of 
 about 2500 C. can be obtained, which is sufficient to melt 
 such ordinarily infusible substances as platinum, quartz, 
 and aluminium oxide. The limit to the temperature which 
 can be obtained is set by the point at which water vapor 
 itself will decompose, for when water vapor is heated to 
 2500 C. a large part of it is decomposed into hydrogen and 
 oxygen gases, by which process it absorbs heat instead of 
 evolving it. In just the same way, mercuric oxide is de- 
 composed by heat into mercury and oxygen, only this occurs 
 at a much lower temperature. 
 
 120. There are many practical applications of the oxy- 
 hydrogen flame in cases where a very high temperature is 
 needed. One of the most interesting of these is in melting 
 aluminium oxide in making artificial rubies and sapphires. 
 These stones are composed of aluminium oxide with slight 
 admixtures of other oxides. Aluminium oxide can only be 
 melted at temperatures above 2000 C. It is a common 
 enough substance and in its ordinary form is of very small 
 value; but by melting it in the oxyhydrogen flame, clear, 
 transparent, finely colored stones can be made that are 
 equal in beauty to the natural gems. 
 
 121. With air hydrogen gives a very hot flame, but not 
 so hot as with pure oxygen, because four volumes of cold 
 nitrogen are mixed with every volume of oxygen that enters 
 the flame, and a considerable part of the heat of combustion 
 must be used to bring this nitrogen up to the temperature 
 of the flame. 
 
118 HYDROGEN 
 
 122. Hydrogen Burns in Chlorine. Not only does hydro- 
 gen combine with oxygen but also with other elements, 
 notably chlorine, which is to be studied a little later. If a 
 jet of burning hydrogen is inserted into a jar of chlorine 
 gas, it continues to burn, but now combines with the chlorine 
 instead of with oxygen, forming hydrogen chloride instead 
 of hydrogen oxide (water). By making a mixture of one 
 volume of hydrogen and one volume of chlorine, an explosive 
 mixture is obtained which resembles in its violence the 
 oxygen-hydrogen mixture. 
 
 123. Reducing Action. On account of its great affinity 
 for oxygen and for chlorine, hydrogen can, in many cases, 
 take these elements away from the metallic elements with 
 which they are frequently combined, thus leaving the metallic 
 element uncombined. Thus if black copper oxide is placed 
 in a glass tube through which hydrogen is being passed and 
 if the tube is heated, the black oxide of copper changes, 
 and in its place we see red metallic copper while at the same 
 time drops of water condense in the cooler part of the tube, 
 showing that the oxygen of the oxide united with the hydro- 
 gen to form water. This type of chemical action in which 
 oxygen, or an element similar to oxygen, is taken away from 
 its combination with a metal is called reduction. The 
 copper oxide is reduced to the metallic condition by the heated 
 hydrogen. 
 
 124. Gaseous Fuels. The great heat of combustion of 
 hydrogen makes it valuable for fuel purposes. It is, how- 
 ever, too costly in the pure state to use for any except very 
 special purposes where comparatively small quantities are 
 needed. 
 
 Many kinds of artificial gas such as those used for illu- 
 minating purposes contain large amounts of hydrogen either 
 
SUMMARY 119 
 
 in the free state or combined with carbon or both free and 
 combined. These mixtures make splendid fuel, as they give 
 great heat without making smoke or leaving ashes, the 
 products of combustion being invisible gases. 
 
 Whenever it can be obtained, illuminating gas is used 
 rather than pure hydrogen for filling balloons, as, being in 
 most cases about one half hydrogen, it is fairly light and is 
 much cheaper. 
 
 SUMMARY 
 
 In decomposing water, energy is required to overcome the 
 attraction between oxygen and hydrogen. This energy is 
 supplied by the electric current or by the greater chemical 
 energy of some metal such as sodium, which is more active 
 than hydrogen. 
 
 Hydrogen may be more easily obtained from acids than from 
 water. Any active metal such as zinc will displace the hydro- 
 gen of an acid. 
 
 Properties of Hydrogen: Hydrogen is the lightest and most 
 diffusible gas known. It is with one exception the most 
 difficult gas to liquefy. Free hydrogen has a strong tendency 
 to combine with oxygen, and the heat produced by the com- 
 bination gives the very high temperature of the oxyhydrogen 
 flame. 
 
 Hydrogen is a reducing agent, since it can withdraw oxygen from 
 its combination with many of the metals in their oxides. 
 Hydrogen forms compounds also with other non-metals than 
 oxygen, notably with chlorine. 
 
 Questions 
 
 1. What chemical property of hydrogen was responsible for its 
 name? 
 
 2. What has to be overcome to separate the hydrogen from the 
 oxygen in water? Mention two different methods for accom- 
 plishing this. 
 
120 HYDROGEN 
 
 3. How is it that sodium can decompose water when there is 
 so strong a force holding the hydrogen and the oxygen together? 
 
 4. From what source is hydrogen released more readily than 
 from water? 
 
 5. How could you distinguish hydrogen from other colorless, 
 odorless gases, such as oxygen, or nitrogen? 
 
 6. What property of hydrogen accounts for the constant loss 
 of gas from a hydrogen balloon? 
 
 7. Why is the flame of hydrogen burning in the air less hot 
 than that obtained when hydrogen burns in oxygen? 
 
 8. What practical use is made of impure hydrogen? 
 
 9. Why is illuminating gas so much used for filling balloons? 
 
 10. Why do not gas stoves create a smoke nuisance? 
 
 11. Under what conditions does a gas flame smoke? Explain 
 why. 
 
 12. How might metallic iron be obtained from ordinary iron 
 rust? 
 
 13. Some clean, dry iron filings which weigh 5.1300 g. are 
 heated in a current of steam and afterward are found to have in- 
 creased in weight to 5.8446 g. What weight of hydrogen has been 
 liberated and what volume would it occupy under standard con- 
 ditions ? 
 
 14. Eleven and two tenths liters of hydrogen measured under 
 standard conditions are passed through a heated tube containing 
 dry copper oxide. What weight of water could be condensed be- 
 yond the heated tube? 
 
CHAPTER XII 
 
 THE ATOMIC THEORY 
 
 WE have learned that when chemical substances combine 
 to form definite new substances, they do so in perfectly 
 definite proportions. For example, in a case already dwelt 
 upon at some length, one part by weight of hydrogen com- 
 bines with 7.94 parts by weight of oxygen, no more, no less, 
 to form 8.94 parts of water. Almost countless illustrations 
 of similar definite combining proportions might be cited. 
 
 This definiteness of the combining proportions is a very 
 important characteristic of chemical compounds, and it is 
 one that is often used to distinguish compounds from phys- 
 ical mixtures. Thus, as we have seen, one of the reasons 
 why we believe air to be merely a mixture of oxygen and 
 nitrogen is that it can contain these two elements in varying 
 proportions. 
 
 125. Law of Definite Proportions. It is repeatedly found 
 in the study of nature that a certain striking regularity 
 exists among a great number of otherwise more or less dif- 
 ferent phenomena. When this regularity is reduced to 
 words, and the statement so made is found always to be true, 
 this statement becomes known as a law. The law of defi- 
 nite proportions would read thus : Whenever two or more 
 elements are combined with each other in a definite chemical 
 compound, the weights of the elements in that compound are 
 to each other always in the same definite numerical ratio. 
 
 121 
 
122 THE ATOMIC THEORY 
 
 126. Hypothesis and Theory. When such a law exists, 
 it cannot be accidental; there must be some underlying 
 cause for it. Scientific men are impelled to speculate upon 
 the nature of things beyond what can actually be seen and 
 felt, and thus, if possible, to reach a better understanding of 
 the workings of nature. Any suggestion as to the under- 
 lying causes of natural phenomena is known as an hypothesis. 
 When an hypothesis has been found to fit a large number of 
 cases, and thus to be of very general importance, it becomes 
 known as a theory. 
 
 127. Atomic Theory of Dalton. In an attempt to explain 
 the nature of matter, the atomic hypothesis in a crude form 
 was brought forward by the very ancient philosophers, 
 prominent among whom was Democritus (about 400 B.C.). 
 When, with the increase in the knowledge of chemical facts, 
 the law of definite proportions became recognized (late in the 
 eighteenth century), it was found that the atomic hypothesis 
 furnished for this law a beautiful explanation. The law of 
 multiple proportions, which was discovered a little later, 
 could likewise be explained by the atomic hypothesis. Thus 
 this hypothesis rose to the dignity of a theory and is known 
 as the Atomic Theory. This theory is closely associated 
 with the name of Dalton, and is often spoken of as Dalton 's 
 atomic theory because it was Dalton who was the first to 
 clearly see the application of the hypothesis to the laws of 
 definite and multiple proportions. 
 
 As has already been said, a crude form of the atomic hy- 
 pothesis was advanced many centuries ago by the old Greek 
 philosophers. They observed that any body of matter 
 could be divided into pieces, each piece could be divided 
 into smaller pieces, each of these smaller pieces could be 
 divided, and so on until the pieces were smaller than could 
 
ANALOGY OF ATOMIC THEORY 123 
 
 be distinguished with the eye. They could not see any limit 
 to the divisibility, and yet they could not conceive of the 
 subdivision going on without limit. They therefore imagined 
 the existence of atoms, very small indivisible particles of 
 which all matter was composed. 1 Bodies of matter were 
 simply aggregates of atoms, and the aggregates could be 
 divided until the single atoms were reached, but no further. 
 
 When at a much later day it became recognized that there 
 were a number of entirely distinct elements of which the 
 earth was composed, the idea of atoms became more specific, 
 for it was thought that the atoms of any one element must 
 all be alike but that the atoms of different elements must 
 be different . 
 
 The final form was given to the atomic theory by Dalton, 
 who made it plain, that, when elements unite to form a 
 compound, it must really be the atoms which unite in pairs 
 or in simple groups. They must therefore be regarded as 
 having some sort of attraction for each other. Dalton es- 
 pecially emphasized, as a vital part of his theory, that all 
 the atoms of a given element are exactly alike in weight as 
 well as in all of their other properties, but that atoms of 
 different elements differ in weight and in many of their other 
 properties. 
 
 128. Analogy of Atomic Theory. Red beans and green 
 peas could be put into the same pail and shaken together 
 and a mixture thus obtained that would "have a mottled ap- 
 pearance, some of the small bodies being red and others green. 
 There might be more beans or there might be more peas 
 without essentially changing the mottled appearance of the 
 mixture. Now let us suppose a case that would be analogous 
 to a case of chemical combination. 
 
 1 The word atom comes from the Greek, and means indivisible. 
 
124 THE ATOMIC THEORY 
 
 Suppose that each bean had a latent power to attach to 
 itself just one pea, no more and no less. Suppose, further, 
 that this power was very strong and that at a given signal 
 it might be brought into operation. When the signal was 
 given, the mixture of beans and peas would be thrown into 
 violent agitation, the individual particles would be pulled 
 to and fro in the effort to attach themselves to their partners. 
 Finally the mass would come to rest again, and if at the out- 
 set there had been exactly the same number of peas as beans, 
 we should have now only pairs composed of one bean and one 
 pea each, and no unattached beans or peas would be left. 
 If at the start there had been more beans than peas, there 
 would now be some single beans left unattached ; if at the 
 start there had been more peas, there would now be single peas. 
 
 The foregoing is a fair analogy to what is supposed to take 
 place, according to Dalton's atomic theory, when two ele- 
 ments, for example hydrogen and oxygen, unite. These two 
 gases may be mixed in any proportion whatever so long as 
 no signal is given for them to enter into chemical combination. 
 Only a mixture is produced like that of the beans and peas. 
 This mixture appears uniform because we are incapable 
 of distinguishing particles so small as the atoms, but if 
 our vision were more powerful, there would doubtless be 
 some such mottled appearance as that of the beans and peas. 
 Now when the signal for the two elements to combine is 
 given, for example when an electric spark is passed through 
 the mixture, the agitation caused is so violent that we see 
 the effect of an explosion. After the explosion there is an 
 entirely different substance, as we know; its smallest par- 
 ticles cannot be atoms, because they contain both hydrogen 
 and oxygen. The smallest particles of the compound are 
 called molecules. 
 
MULTIPLE PROPORTIONS 125 
 
 We learned in Chapter X that water contains two parts of 
 hydrogen because one part can be set free before and more 
 easily than the other. Perhaps, then, in the molecule of 
 water there are two atoms of hydrogen to one atom of oxygen. 
 If we consider the red bean to represent the oxygen atom and 
 the pea the hydrogen atom, our new molecule may be pic- 
 tured as consisting of a bean with two peas instead of one 
 attached to it. 
 
 129. Analogy Applies to Multiple Proportions. In our 
 analogy with beans and peas let us make a still further sup- 
 position. After every bean has found one pea to which to 
 attach itself, suppose that it still has some attractive power 
 for a second pea, although considerably less than for the first. 
 If there were enough more peas in the mixture, each bean 
 might acquire two peas and a new kind of grouping would 
 be in evidence in which one bean would be attached to two 
 peas. The fact that almost the exact counterpart of this 
 analogy is frequently met in chemistry furnishes us our 
 strongest reason for believing in the essential truth of the 
 atomic theory. 
 
 The law of multiple proportions is illustrated by the two 
 oxides of carbon which were discussed in Chapter VI. The 
 Law of Multiple Proportions may be stated as follows : 
 
 When two elements are able to form more than one definite 
 compound, if such weights of each of the compounds are taken 
 that they contain the same weight of the first element, then the 
 weights of the second element in the different compounds are 
 to each other in the ratio of small whole numbers. 
 
 To return to our analogy, let us consider the two different 
 kinds of groups of beans and peas. In each group we had 
 one bean, but in the second group we had two peas instead 
 of one as in the first group. The number of peas in the two 
 
126 THE ATOMIC THEORY 
 
 groups are in the ratio of small whole numbers, namely as 
 one is to two. In carboa monoxide let us suppose that the 
 smallest particle of the compound, that is, the molecule, 
 contains just one atom of carbon and one atom of oxygen. 
 Then for carbon dioxide, which we know contains twice as 
 much oxygen to a given amount of carbon, we should have 
 two atoms of oxygen combined with each atom of carbon. 
 
 ^-^ ^^^ ^_^ ^^^ x*^s ^ e can i ma g me the 
 
 f H Ik ( jfl Ik j molecule as looking 
 
 ^-^^^r^^/ somewhat as the ar- 
 
 FIG. 24.-A co^eption^of ;he structure rangement of beans 
 
 and peas. In the 
 
 diagram (Fig. 24) each white sphere is meant to represent an 
 atom of oxygen and each black sphere an atom of carbon. 
 
 130. Value of Atomic Theory. If no one had ever con- 
 ceived of the atomic theory, it seems as if it would be im- 
 possible for us to give any plausible explanation of the re- 
 markable fact that elements combine in definite and in 
 multiple proportions. It must never be lost sight of, how- 
 ever, that the atomic theory is only an attempt at an ex- 
 planation. We cannot see the atoms, and we shall probably 
 never be able to verify by direct observation the correctness 
 of the atomic theory. The value of the atomic theory is 
 that it does explain satisfactorily the facts regarding chemical 
 combination, and thus explaining, it serves as a framework 
 for building the structure of our knowledge of chemical 
 facts. 
 
 It may be stated that there is a great deal more evidence 
 in support of the atomic theory than that given here. To 
 understand this evidence requires a knowledge of mathe- 
 matics and of physical science; nevertheless the atomic 
 theory has been so strengthened thereby that we can as 
 
MOLECULES 127 
 
 nearly accept the existence of atoms for an absolute certainty 
 as anything which it is impossible to see by direct observation. 
 
 131. Possible Complexity of Atoms. It was formerly 
 supposed that the atoms were very small, hard, elastic 
 spheres which were absolutely indivisible. Recent dis- 
 coveries have tended to show that the atoms are really very 
 complex, but if this is true, it nevertheless remains a fact 
 that we are unable by any agency under human control to 
 break apart the atoms into smaller particles or to build up 
 atoms from smaller particles. So far as the chemist is con- 
 cerned the idea of atoms as indivisible particles may be taken 
 without reservation. 
 
 132. Molecules. It is practically a certainty that matter 
 consists of atoms and that there are as many different kinds 
 as there are elements (i.e. about eighty), and that the atoms 
 of any given element are all exactly alike in weight and in 
 all of their properties. When elements combine to form 
 compounds, it is then really the atoms which unite to form 
 atom groups and these groups are the smallest particles, 
 that is, the molecules of the compounds. 
 
 So far we have not shown any way in which to tell how 
 many of the atoms of each element enter into the formation 
 of the molecule. We have, however, spoken of the wonder- 
 ful simplicity shown in the combining volumes of gases, and 
 in a later chapter we shall show that much light is thrown 
 upon this problem by a study of these combining volumes. 
 
 SUMMARY 
 
 Law of Definite Proportions. When two or more elements are 
 combined with each other in a definite chemical compound, 
 the weights of the elements in that compound are to each 
 other, always, in the same definite numerical ratio. 
 
 B. AND W. CHEM. 9 
 
128 THE ATOMIC THEORY 
 
 Law of Multiple Proportions. When two elements are able to form 
 more than one definite compound, if such weights of each of 
 the compounds are taken that they contain exactly the same 
 amount by weight of the first element, then the weights of 
 the second element in the different compounds are to each 
 other in the ratio of simple whole numbers. 
 
 A natural law is a statement of a general truth which is capable of 
 being proved by direct observation. 
 
 An hypothesis is a suggestion advanced to explain any truth of nature. 
 
 A theory is an hypothesis which has been thoroughly tested and 
 found to explain a great number of facts. A theory cannot 
 become a law because it is incapable of proof by direct ob- 
 servation. 
 
 According to the atomic theory, matter is made up of infinitely 
 small particles called atoms. The atoms of each of the ele- 
 ments are alike, but different from those of the other elements. 
 It is the atoms themselves which are concerned in the forma- 
 tion of chemical compounds, for different atoms attract and 
 hold each other in small definite groups which are called mole- 
 cules and which are the smallest possible particles of the com- 
 pound. Thus the atomic theory explains the law of definite 
 proportions and the law of multiple proportions. Although 
 the atomic theory can hardly be proved by direct observation, 
 it is abundantly proved by deduction. It is of the greatest 
 service in chemistry, for it furnishes a framework for building 
 the structure of our knowledge of chemical fact. 
 
 Questions 
 
 1. On what two groups of facts was Dalton's atomic theory 
 based? 
 
 2. How does an hypothesis differ from a theory? 
 
 3. Was the idea of an atomic structure of matter original with 
 Dalton? 
 
 4. Use the atomic theory to explain what happens when charcoal 
 burns. 
 
 5. Discuss water and hydrogen peroxide from the viewpoint of 
 the atomic theory. 
 
 6. Of what use is the atomic theory ? 
 
CHAPTER XIII 
 
 HYDROGEN CHLORIDE 
 
 A METHOD of preparing hydrogen chloride was touched 
 upon in the chapter on hydrogen when the ability of hydro- 
 gen to burn in chlorine was described. Hydrogen chloride 
 is to demand our attention in the present chapter. 
 
 133. Formation and Recognition of Hydrogen Chloride. 
 For its study in the laboratory, hydrogen chloride can be 
 prepared more easily by another method than the one al- 
 ready mentioned. If a pinch of sodium chloride, that is 
 common salt, is placed in a test tube and covered with a few 
 drops of concentrated sulphuric acid, and perhaps warmed 
 a little, a colorless gas is evolved which has a sharp and very 
 choking odor. On blowing the breath across the mouth of 
 the tube, a white cloud is formed; and on bringing near 
 the mouth of the tube a piece of filter paper wet with am- 
 monia water, a very dense white smoke appears. These 
 properties are very characteristic of hydrogen chloride gas 
 and serve admirably as a means of recognizing it. 
 
 134. Hydrogen Chloride Generator. * When larger quan- 
 tities of hydrogen chloride are to be prepared in the labora- 
 tory, a somewhat more elaborate apparatus than the simple 
 test tube must be used. Some coarse rock salt is placed in the 
 bottom of a large flask, provided with a two-holed rubber 
 stopper. Through one hole passes a thistle tube which 
 reaches to the bottom of the flask; through the other hole 
 
 129 
 
130 
 
 HYDROGEN CHLORIDE 
 
 passes a short elbow tube for leading away the gas (see Fig. 
 25). To start the evolution of gas, concentrated sulphuric 
 acid is poured through the thistle tube until it stands high 
 enough in the flask to seal the lower end of the tube. .In 
 order to maintain a vigorous evolution of gas, the flask is 
 
 warmed rather cau- 
 tiously with a Bunsen 
 flame, when it be- 
 comes necessary. 
 
 Hydrogen chloride 
 cannot be collected 
 over water because 
 of its great solubility. 
 Dry collecting bottles 
 are therefore set up- 
 right and the gas 
 is led downward 
 through the delivery 
 tube to the bottom 
 of the bottle. The 
 hydrogen chloride is 
 heavier than air, and 
 as it rises and fills 
 the bottle it lifts the 
 air and forces it out. 
 Of course the hydro- 
 gen chloride mixes quite rapidly with the air by diffusion ; 
 still if the gas is supplied rapidly and the top of the bottle 
 loosely covered with a glass plate, the gas can be collected 
 nearly pure. 
 
 135. Great Solubility. An interesting experiment show- 
 ing the great solubility of hydrogen chloride is to close the 
 
 FIG. 25. Hydrogen Chloride Generator. 
 
GREAT SOLUBILITY 
 
 131 
 
 neck of a large bottle of the dry gas with a one-holed rubber 
 stopper through which passes a short straight glass tube 
 (Fig. 26). Now, on inverting the bottle and thrusting its 
 neck into water, a fountain soon begins to play from the 
 narrow end of the glass tube and this continues until the 
 bottle is practically full of water. Hydrogen chloride is so 
 very soluble that as soon as a little water enters the bottle 
 a nearly complete 
 vacuum is created. 
 The pressure of the 
 air outside is now 
 no longer counter- 
 balanced by the pres- 
 sure of a gas inside 
 the bottle, and water 
 is forced with some 
 violence through the 
 nozzle of the tube. 
 
 Hydrogen chloride 
 is one of the most 
 soluble of gases ; one 
 cubic centimeter of 
 water at ordinary 
 temperature will dissolve 450 cubic centimeters of the gas. 
 This amount of gas weighs 0.8 gram, and thus one gram of 
 water will dissolve 0.8 gram of hydrogen chloride to form 
 1.8 grams of solution. 
 
 The volume of this solution is 1.5 cubic centimeters and 
 thus the dissolving of the 450 cubic centimeters of the gas 
 in 1 cubic centimeter of water increases the volume of the 
 latter by only one half of a cubic centimeter. 
 
 It was stated in a preceding paragraph that hydrogen 
 
 FIG. 26. Fountain Experiment showing Great 
 Solubility of Hydrogen Chloride. 
 
132 HYDROGEN CHLORIDE 
 
 chloride was a colorless gas, and yet it was also stated that 
 a white cloud is seen when the breath is blown across the 
 mouth of a test tube from which the gas is issuing. The 
 white cloud, however, does not consist alone of hydrogen 
 chloride, and furthermore, it is not a gas at all but it consists 
 of a vast number of little liquid droplets which are condensed 
 from the moisture in the breath together with the hydrogen 
 chloride. These droplets consist, then, of a solution of 
 hydrogen chloride, and their formation results from the great 
 solubility of the gas. 
 
 It is still strictly true that hydrogen chloride gas is color- 
 less and invisible. It only becomes visible as a result of 
 condensation with moisture, but such condensation usually 
 occurs when the gas escapes into the air, for the air always 
 contains some water vapor. Thus a little cloud is almost 
 always seen above the mouth of the bottle of concentrated 
 hydrochloric acid when the stopper is removed. 
 
 136. Hydrochloric Acid. Hydrogen chloride, when dis- 
 solved in water, is most commonly known as muriatic acid 
 or as hydrochloric acid, for when in solution it possesses 
 the properties of a strong acid. In the form of the dry gas, 
 it possesses no acid properties. Muriatic acid is the com- 
 mercial term, while hydrochloric acid is the scientific name 
 for the solution. 
 
 It is already known from the chapter on hydrogen that 
 acids contain hydrogen which can be driven out by zinc and 
 some other metals. Two other very characteristic proper- 
 ties of acids are their sour taste and their ability to change 
 the color of litmus from blue to red. Litmus is a vegetable 
 dyestuff which is very sensitive to acids and alkalies, it being 
 turned red by acids and blue by alkalies. Usually strips of 
 paper are colored with the dye, and a strip of paper thus 
 
USES OF HYDROCHLORIC ACID 133 
 
 colored blue will immediately change to red when dipped in 
 acid. 
 
 When hydrochloric acid is treated with pieces of zinc, a 
 vigorous evolution of hydrogen takes place. Hydrochloric 
 acid turns blue litmus to red and it tastes excessively sour. 
 In fact, concentrated hydrochloric acid is very corrosive and 
 totally unsafe to taste; one part of this acid diluted with 
 one hundred parts of water gives a solution which will change 
 litmus to red and which is sour although quite safe to taste. 
 
 137. Method of Manufacture. From a practical point 
 of view, the dry hydrogen chloride is of little importance, 
 but in solution as hydrochloric acid it finds extended use. 
 The method of its manufacture on a large scale is not different 
 in principle from that of the laboratory preparation. Com- 
 mon salt is treated in large cast-iron pans with concentrated 
 sulphuric acid. The pans are heated by a fire built under- 
 neath. When the reaction is one half completed, the charge 
 in the pans is raked upon hearths of fire brick where it is 
 heated much hotter and the reaction is carried to an end. 
 The gas is led off through flues and brought in contact with 
 water so that it is entirely dissolved. The saturated solu- 
 tion that is thus obtained contains about 40 per cent by weight 
 of hydrogen chloride and is known as concentrated hydro- 
 chloric acid. 
 
 138. Uses of Hydrochloric Acid. Considerable quantities 
 of hydrochloric acid are manufactured for use in the indus- 
 trial arts. Most of this is sold in the somewhat impure 
 condition known as muriatic acid. Some, however, is further 
 purified and sold as C.P. (meaning chemically pure) hydro- 
 chloric acid. The acid is usually shipped in large glass 
 carboys packed in wooden boxes with some sort of packing 
 material to prevent breakage. Such carboys are to be seen 
 
134 HYDROGEN CHLORIDE 
 
 at many manufacturing plants. The acid is used by tinmen 
 and plumbers for cleaning metal surfaces to be soldered. 
 Hydrochloric acid is also used in preparing chlorides of the 
 metals, in preparing chlorine and hydrogen in the laboratory, 
 in making aqua regia, and in analytical work both in schools 
 and colleges and in practical analytical laboratories. The 
 use of this acid is not nearly so extensive as that of sulphuric 
 acid, which is much cheaper arid serves equally well many of 
 the purposes for which an acid is required. Likewise when 
 a compound containing chlorine is required, it is customary 
 to use sodium chloride on account of its cheapness, rather 
 than the more expensive hydrochloric acid. 
 
 139. Nature of the Reaction in the Generator. Concen- 
 trated sulphuric acid is composed of hydrogen, sulphur, and 
 oxygen. It may be called hydrogen sulphate, as we shall 
 see later, just as hydrochloric acid is called hydrogen chloride. 
 Sodium chloride, as the name implies, is a compound of sodium 
 and chlorine. When sulphuric acid and sodium chloride 
 interact, the hydrogen of the former and the chlorine of the 
 latter combine to form hydrogen chloride, which in virtue of 
 the fact that it is a gas, escapes readily from the mixture and 
 is thus obtained in the pure condition. The sodium of the 
 sodium chloride and the sulphur and oxygen of the sulphuric 
 acid are still to be accounted for. They combine to form 
 another new substance, sodium sulphate. The residue left 
 in the generator after the evolution of hydrogen chloride 
 according to the laboratory process, is a solid substance. 
 As ordinarily left, it will doubtless contain either some unused 
 sodium chloride or sulphuric acid, but by a process of puri- 
 fication, pure sodium sulphate can be separated from it. 
 This substance is another go?? and has many similarities to 
 common salt in its appearance and in other of its properties. 
 
COMPOSITION 135 
 
 140. Composition. We already know from the first- 
 mentioned method of formation in which hydrogen is burned 
 in chlorine, that hydrogen chloride is composed of hydrogen 
 and chlorine and solely of these two elements. The scien- 
 tific men of earlier days who helped to bring our science of 
 chemistry to its present standing, did not possess as much 
 knowledge as we. They discovered the substance we call 
 hydrogen chloride by treating salt with sulphuric acid, and 
 they called it muriatic acid, meaning the acid obtained 
 from sea salt. It was found that zinc acting on the acid 
 solution set free hydrogen. It was believed that zinc was 
 an element and did not contain hydrogen ; and it was known 
 that zinc acting on water alone did not liberate hydrogen. 
 Hence it was Ibelieved that the hydrogen came from the 
 muriatic acid. What was apparently another constituent 
 of the muriatic acid was obtained by treating it with a black 
 substance which we know as manganese dioxide. A greenish- 
 yellow, ill-smelling gas was obtained which was called 
 chlorine on account of its color (Moros, meaning green). 
 Manganese dioxide was known to give off oxygen when 
 strongly heated. Now possibly on reacting with muriatic 
 acid, the manganese dioxide gave up some oxygen to com- 
 bine with the hydrogen of the acid and form water, thus 
 leaving the residue of the muriatic acid uncombined and 
 free to escape as the evil-smelling, greenish-yellow gas, 
 chlorine. 
 
 The next step in establishing the composition of muriatic 
 acid was to see if it could be made from hydrogen and chlorine. 
 This was, of course, found to be possible, and when, with fur- 
 ther study, it was decided that chlorine as well as hydrogen 
 was an element, the chemical nature of muriatic acid was 
 definitely settled. 
 
136 
 
 HYDROGEN CHLORIDE 
 
 141. Combining Ratio by Volume. When concentrated 
 hydrochloric acid is electrolyzed, it is found that hydrogen is 
 evolved at the negative electrode and chlorine at the positive. 
 When water was electrolyzed, we found that two volumes of 
 hydrogen and one volume of oxygen were obtained. We 
 
 FIG. 27. Electrolysis of Hydrochloric Acid. E : electrolytic cell; SS : three- 
 way stopcocks which may be turned so that the gases run to waste until 
 solution in cell E has become saturated with chlorine ; when the gases are 
 being evolved at a uniform rate, the stopcocks are turned and the gases 
 collected in the measuring tubes C and H. These tubes are filled with a 
 saturated salt solution which dissolves but little chlorine. 
 
 find in the case of hydrochloric acid that we obtain equal 
 volumes of hydrogen and chlorine. In order to show this 
 fact satisfactorily, the experiment must be performed in a 
 specially designed apparatus such as that shown in Fig. 27. 
 Chlorine is somewhat soluble in water and slightly so in 
 hydrochloric acid, and if the experiment is carried out in the 
 
COMBINING RATIO BY VOLUME 
 
 137 
 
 ordinary Hofmann electrolysis apparatus (see page 104), so 
 much chlorine is dissolved that a true measure of its volume 
 is not obtained. 
 
 Although we obtain equal volumes of hydrogen and 
 chlorine from the hydrochloric acid, we cannot be absolutely 
 sure that these gases have come from the hydrogen chloride 
 and not from the water. If we could now show that equal 
 volumes of hydrogen and chlorine combine with each other, 
 
 FIG. 28. Collecting Electrolytic Hydrogen and Chlorine. E : electrolytic cell ; 
 A : explosion tube ; T : tower packed with lime and glass wool to absorb 
 waste chlorine. 
 
 our proof would be complete. To this end we can obtain 
 a mixture of equal volumes of hydrogen and chlorine and 
 then we pass the mixture through a delivery tube into the 
 explosion tube shown in Fig. 28. When all the air is 
 driven out and the tube is filled with the mixture at atmos- 
 pheric pressure, the stopcocks at both ends are closed. The 
 explosion of tKis mixture can be brought about even more 
 easily than that of the oxygen-hydrogen mixture. Exposure 
 to direct sunlight or to a magnesium flashlight such as is 
 used in photography is all that is necessary. Of course the 
 
138 HYDROGEN CHLORIDE 
 
 explosion tube should be strong, and furthermore a shield 
 should always be kept between the tube and the observer. 
 
 If, as we suspect, the gases combine in the ratio of one to 
 one by volume, there should now be no gas in the tube except 
 hydrogen chloride. To find the volume of the product, 
 one end of the tube may be placed under concentrated sul- 
 phuric acid (in which hydrogen chloride is not soluble) and 
 the stopcock opened. We find that the liquid does not rise 
 in the tube nor do bubbles escape through the acid. Hence 
 the volume of the hydrogen chloride at atmospheric pressure 
 is just equal to the sum of the volumes of the hydrogen and 
 chlorine. To finally prove that the gaseous product is hy- 
 drogen chloride, we dip the end of the tube into water and 
 find that the water rises until the entire tube is filled. 
 
 These experiments prove that one volume of hydrogen com- 
 bines with one volume of chlorine to form two volumes of hydro- 
 gen chloride gas. 
 
 It was found (p. 103) that hydrogen is combined in two 
 different portions in water, for one portion can be displaced 
 by sodium ; and from sodium hydroxide, the new substance 
 formed, still another portion of hydrogen can be obtained 
 by treating this product with zinc. 
 
 In hydrogen chloride, on the other hand, hydrogen is com- 
 bined all in the same portion, so far as we can tell, for if 
 sodium reacts with hydrogen chloride, sodium chloride is 
 formed and hydrogen is liberated, but the sodium chloride 
 is incapable of giving off any more hydrogen. 
 
 142. Hydrogen Chloride and the Atomic Theory. Viewed 
 in the light of the atomic theory, it is obvious that every 
 molecule of hydrogen chloride must contain hydrogen and 
 chlorine atoms. The simplest arrangement that we can 
 imagine for the molecule of the compound is that it contains 
 
SUMMARY 139 
 
 only two atoms, one of hydrogen and one of chlorine. All 
 the facts that we have so far described are in accord with 
 this view, and unless further facts are brought forward to 
 combat it, we shall adhere to this view and write the formula 
 of hydrogen chloride as HC1. 
 
 The combining ratio by weight of hydrogen chloride is 
 1 part of hydrogen to 35.2 parts of chlorine. As with hy- 
 drogen and oxygen, the ratio by weight is perfectly definite, 
 although not in simple whole numbers as the volume ratio. 
 If it is true that hydrogen and chlorine combine atom for 
 atom, it follows that the atom of chlorine weighs 35.2 times 
 as much as the atom of hydrogen. 
 
 SUMMARY 
 
 Hydrogen chloride is prepared by the action of concentrated sul- 
 phuric acid on sodium chloride. 
 
 Properties of Hydrogen Chloride. Hydrogen chloride is a colorless 
 gas with an extremely irritating odor. It forms a cloud with 
 moist air and a dense white smoke with ammonia. It is 
 extremely soluble in water and is heavier than air. 
 In solution in water it is a strong acid and is called muriatic or 
 hydrochloric acid ; in this solution it shows the characteristics 
 of acids in that it reacts with zinc, evolving hydrogen; it 
 tastes sour and it colors blue litmus red. 
 
 Composition of Hydrogen Chloride. Hydrogen chloride contains 
 only hydrogen and chlorine. One volume of hydrogen will 
 combine with one volume of chlorine to yield two volumes of 
 hydrogen chloride. 
 
 By weight, hydrogen chloride contains 35.2 parts of chlorine to 
 one part of hydrogen. The weight relation is definite, al- 
 though not so simple as the volume relation. 
 It seems probable that hydrogen and chlorine combine in the ratio 
 . of atom for atom. The atom of chlorine weighs, then, 35.2 
 times as much as the atom of hydrogen and the formula of 
 the compound may be written HC1. 
 
140 HYDROGEN CHLORIDE 
 
 Questions 
 
 1. How is hydrochloric acid made? 
 
 2. What elements does hydrogen chloride contain and how may 
 it be shown by experiment ? 
 
 3. What is the volume relation of the constituents of hydrogen 
 chloride? By what experiments can it be shown? 
 
 4. What are the properties of dry hydrogen chloride? 
 
 5. How do the properties of hydrochloric acid in solution differ 
 from those of the dry gas? 
 
 6. What are the uses of hydrochloric acid? 
 
 7. Chlorine is allowed to enter a 100 c.c. evacuated tube until 
 the pressure rises to 20 cm. ; then hydrogen is admitted until the 
 total pressure is 76 cm. After exploding the gas mixture what 
 will be the total pressure of the gases when they have returned to 
 the initial temperature ? 
 
 8. If one end of the tube from above question is opened under 
 water and the water allowed to rise as far as it will, what volume of 
 gas at 76 cm. pressure will be left? 
 
 9. How does muriatic acid serve a useful purpose in soldering 
 metals? 
 
 10. Why is less hydrochloric than sulphuric acid used in the arts ? 
 
CHAPTER XIV 
 
 AVOGADRO'S THEORY 
 
 WE have seen in the chapter on the atomic theory that all 
 matter is composed of atoms of which there are as many 
 different kinds as there are different elements. Since com- 
 pounds contain more than one element, their smallest par- 
 ticles must contain more than a single atom. The smallest 
 possible particles of a compound are called molecules. 
 
 The atomic theory is almost a necessary consequence of 
 the law of definite proportions. This law holds for all com- 
 binations whether the combining substances be solid, liquid, 
 or gaseous. But when the substances are gaseous, a still 
 simpler law holds. We have, for example, seen that two 
 volumes of hydrogen combine with one volume of oxygen 
 to form water and one volume of hydrogen with one volume 
 of chlorine to form hydrogen chloride. 
 
 143. Gay Lussac's Law of Combining Volumes. The 
 fact that gases combine according to simple volume relations 
 was discovered by a French scientist, Gay Lussac, and first 
 published by him in 1808. The Law of Combining Volumes 
 which is known as Gay Lussac's law, may be stated as 
 follows : 
 
 Whenever gaseous substances combine, the volumes involved 
 are to each other in the ratio of small whole numbers: further- 
 more, if the product formed is also a gas, its volume is to the 
 other volumes also in the ratio of small whole numbers. 
 
 144. Avogadro's Hypothesis. In order to account for 
 these simple relations and also to account for the uniform 
 
 141 
 
142 AVOGADRO'S THEORY 
 
 behavior of all gases under changes of temperature and pres- 
 sure (Boyle's and Charles' laws) Avogadro, an Italian phys- 
 icist, in 1811 proposed the hypothesis that equal volumes of 
 all gases under like conditions of pressure and temperature 
 contain the same number of molecules. 
 
 This hypothesis, however, proves inadequate if one makes 
 the perfectly natural assumption that the molecules of the 
 elementary gases such as hydrogen, oxygen, and chlorine 
 consist of single atoms. Avogadro pointed out, as a neces- 
 sary part of his hypothesis, that the molecules of the com- 
 mon elementary gases, oxygen, hydrogen, chlorine, etc., 
 must contain two atoms each. 
 
 145. Applications of Avogadro's Hypothesis. We know 
 that one volume of hydrogen combines with one volume of 
 chlorine to form two volumes of hydrogen chloride. To 
 give a clear picture of this, let us use the following diagram, 
 in which each of the squares represents one volume of the gas : 
 
 1,000,000 
 Molecules 
 
 
 1,000,000 
 Molecules 
 
 
 
 2,0 
 Mol 
 
 X),( 
 eci 
 
 DO 
 
 lies 
 
 1 volume 
 hydrogen 
 
 1 volume 
 chlorine 
 
 2 volumes 
 hydrogen chloride 
 
 Let us assume that the one volume of hydrogen contains one 
 million molecules of the substance. 1 The equal volume of 
 chlorine would then contain, according to Avogadro's hy- 
 pothesis, one million molecules of chlorine. The two vol- 
 umes of the gaseous product must then contain two million 
 
 x We say one million merely to have some definite number to 
 work with ; in point of fact the real number of molecules in a liter 
 of hydrogen under standard conditions has been estimated to be 
 38,000,000,000,000,000,000,000. 
 
CHEMICAL SYMBOLS 
 
 143 
 
 molecules of hydrogen chloride. Now each molecule of 
 hydrogen chloride must contain at least one atom of hydro- 
 gen, therefore there must have been at least two million 
 atoms of hydrogen in the original one million molecules. 
 Similarly there must have been two million atoms of chlorine 
 in the original one million molecules of chlorine. Therefore 
 the molecules of these elementary gases contain at least two 
 atoms each, as Avogadro pointed out as a necessary conclu- 
 sion from his hypothesis. 
 
 146. Chemical Symbols. It is customary in chemical 
 notation to use symbols, and the elements are represented 
 by single letters, or at most by two letters each, usually 
 the first letter of the name of the element is used. Thus H 
 stands for hydrogen and Cl for chlorine. Furthermore, the 
 letter H may be understood to mean one atom of hydrogen 
 and the symbol H 2 to mean a group of two atoms, or a mole- 
 cule, of hydrogen. Using these symbols, we may represent 
 the statement that one molecule of hydrogen combines with 
 one molecule of chlorine to give two molecules of hydrogen 
 chloride as follows : 
 
 H 2 + C1 2 ->2HC1. 
 
 Again, we know that two volumes of hydrogen combine 
 with one volume of oxygen to give two volumes of water 
 vapor. This fact may also be expressed in terms of the 
 hypothesis as follows : 
 
 2,000,000 molecules 1,000,000 molecules- 2,000,000 molecules 
 
 
 
 
 + 
 
 c 
 
 
 > 
 
 
 
 
 two volumes 
 of hydrogen 
 
 ne volume 
 of oxygen 
 
 two volumes of 
 water vapor 
 
 or, reduced to simplest terms, 
 
 B. AND W. CHEM. 
 
 10 
 
144 AVOGADRO'S THEORY 
 
 147. Scope of Avogadro's Theory. As we have already 
 said in connection with the atomic theory, we must not 
 allow ourselves to accept theory unreservedly as we do 
 facts that are proven by the direct evidence of our senses. 
 A theory is merely a deduction which we draw from facts 
 with the aid of our imagination. Avogadro's theory belongs 
 in the same category with the atomic theory, and the actual 
 molecules, like the actual atoms, are too small to be seen or 
 directly counted, as we could count peas in a pan of peas. 
 We can thus scarcely hope to prove Avogadro's theory by the 
 direct evidence of our senses. Yet, like the atomic theory, 
 Avogadro's theory rests to-day on a great deal more evidence 
 than that which we have given. This evidence is of so con- 
 vincing a character that the theory does not fall far short of 
 being a proven fact. Indeed, many choose to call it Avogadro's 
 Law, thus signifying their belief in its absolute correctness. 
 
 148. l The fact that all gases behave alike under changing 
 pressure and temperature (Boyle's and Charles' laws, 
 Chapter VIII) had caused much speculation among scien- 
 tific men, and it was in fact largely through the effort to 
 explain these laws that Avogadro advanced his hypothesis. 
 The necessary consequence of this hypothesis that the mole- 
 cules of the elementary gases must contain two atoms ap- 
 peared so improbable to the scientific men of that time that 
 the hypothesis did not find favor until many years later. 
 Although the physicists were ready to admit that equal 
 volumes of gases under like condition must contain the same 
 number of particles, neither they nor the chemists were 
 clear as to what the particles were and the chemists were not 
 
 1 The remainder of this chapter may be omitted at the discretion 
 of the teacher, since the understanding of later chapters does not 
 depend on it. 
 
BOYLE'S LAW EXPLAINED 145 
 
 then ready to admit that molecules of elementary gases 
 could contain two atoms of the same kind. 
 
 149. Molecules of Gases must be widely Separated. 
 When we take into consideration that water expands 1700 
 times when it is converted into steam, and that liquid air 
 and other liquefied gases expand in similar degree when they 
 change to gases, it becomes apparent that if matter really 
 does consist of individual particles, or molecules, there 
 must be spaces between the molecules which are very large 
 compared with the size of the molecules themselves. 
 
 150. Nature of Heat. If the particles of a gas are so 
 widely separated (i.e. when compared with their size), what 
 can it be that keeps them apart ? We know that heat causes 
 the expansion of gases. Can it be, then, that heat is a sort 
 of subtle fluid which flows in between the particles of a gas 
 and thus keeps them separated? The idea does not appear 
 absurd, but it has been decided by physicists to be incorrect. 
 Heat is believed to be nothing but the energy of motion of 
 the particles of a substance, moving in every direction, back 
 and forth, within the limits set by other particles with which 
 they are continually coming into collision. 
 
 151. Boyle's Law Explained. Gases can exert enormous 
 pressures when they are confined, as is shown by steam in a 
 steam engine. It is unsafe to confine liquid air in closed 
 vessels, because, on changing to a gas, jt develops such an 
 enormous pressure as to burst any ordinary steel cylinder. 
 The pressure is caused by the impact of the molecules of gas 
 as they repeatedly strike and rebound from the walls of the 
 confining vessel. The explanation of Boyle's law can now be 
 seen : when the volume of a gas is decreased, the number of 
 molecules in each unit of volume is correspondingly increased, 
 and therefore the frequency of the impacts on each unit of 
 
146 AVOGADRO'S THEORY 
 
 surface is increased. Since the impacts constitute the pres- 
 sure, the pressure must increase as the volume is decreased. 
 152. Charles' Law Explained. Heat, as already stated, 
 is nothing more or less than the energy of motion of the par- 
 ticles of a substance. The intensity of heat is measured by 
 the temperature. Hence the intensity of the energy of the 
 moving molecules must be measured by the temperature. 
 The explanation of Charles' law may now be seen. The 
 intensity of the motion of gas molecules is proportional to 
 the absolute temperature, and thus the pressure of the gas 
 is proportional to the absolute temperature. At the absolute 
 zero, the gas would no longer have any pressure, because its 
 particles would no longer be in motion. The actual vol- 
 ume of gas particles being not more than about one one- 
 thousandth of the volume that the gas ordinarily occupies, 
 it is evident that the volume would decrease to very nearly 
 zero at the absolute zero of temperature. 
 
 SUMMARY 
 
 Gay Lussac's Law. The fact that the ratio of the volumes of re- 
 acting gases to each other as well as the ratio of either of these 
 volumes to the volume of the gaseous product may always be 
 expressed by small whole numbers was announced by Gay 
 Lussac in 1808. 
 
 Avogadro's Theory. Avogadro, an Italian physicist, in 1811 
 proposed the hypothesis that equal volumes of all gases under 
 like conditions contain equal numbers of molecules. This hy- 
 pothesis was not well received at first, but today it is ac- 
 cepted as a satisfactory theory if not indeed as a law. 
 
 Applications of Avogadro' s Hypothesis. As a necessary deduction 
 from Avogadro's hypothesis, the molecules of the common 
 elementary gases must contain at least two atoms each. 
 The hypothesis also furnishes a reasonable explanation for the 
 Law of Boyle and the Law of Charles. 
 
 Heat is believed to consist of the kinetic energy of moving molecules. 
 
CHAPTER XV 
 
 ATOMIC AND MOLECULAR WEIGHTS 
 
 153. Absolute Weights of the Atoms. The actual weight 
 of the atoms is so exceedingly small that to give it in figures 
 conveys but little meaning to one's intelligence. For ex- 
 ample, it has been estimated that one atom of hydrogen 
 weighs 0.000,000,000,000,000,000,000,0012 gram. For prac- 
 tical purposes, such a figure can have very little importance ; 
 furthermore, it cannot be estimated with any great degree of 
 accuracy. But the relative weights of the atoms can be deter- 
 mined with a high degree of accuracy, and are of great im- 
 portance, as we shall show in this chapter. 
 
 154. Relative Weights of the Atoms. When different 
 elements combine, the atomic theory tells us that it is really 
 the atoms which combine, and furthermore, that they com- 
 bine in some very simple numerical proportion. What we 
 observe is that tangible amounts of the different elements 
 disappear in the formation of the compound ; but the weights 
 which combine must be in the same proportion or some simple 
 multiple of the same proportion as the weights of the actual 
 atoms. 
 
 Now we know, for example, that 35.2 grams of chlorine 
 combine with 1.000 gram of hydrogen, and furthermore, we 
 have decided from the volume composition of hydrogen 
 chloride in connection with Avogadro's theory, that hydrogen 
 and chlorine combine atom for atom. Hence the actual 
 
 147 
 
148 ATOMIC AND MOLECULAR WEIGHTS 
 
 atom of chlorine must weigh 35.2 times as much as the 
 actual atom of hydrogen. 
 
 Again, we know that 7.94 grams of oxygen combine with 
 1.000 gram of hydrogen, in the formation of water, and we 
 are convinced that each atom of oxygen combines with two 
 atoms of hydrogen. Hence the atom of oxygen weighs 7.94 
 times as much as two atoms of hydrogen, or 15.88 times as 
 much as a single hydrogen atom. From a comparison of these 
 figures, it follows that the weights of the atoms of oxygen 
 and chlorine are to each other in the ratio of 15.88 to 
 35.2. 
 
 155. Standard of Atomic Weights. It is perfectly clear 
 that w r e need some measure by which to express atomic 
 weights, just as the pound is a measure for expressing quan- 
 tities of sugar and flour. We have seen that to give the 
 weights of the single atoms in grams is inconvenient, as well 
 as uncertain. But why not take the weight of the atom of 
 some element as the standard measure? Although we do 
 not know this accurately in terms of the measure we use for 
 ordinary objects, we do know accurately its ratio to the 
 weight of the other atoms, and this is all that is needed. 
 The weight of the lightest atom, that is of the hydrogen atom, 
 is the most logical unit to choose, because when the weights 
 of other atoms are expressed in terms of the weight of the 
 hydrogen atom, the numbers are all larger than one. Thus 
 if the atomic weight of hydrogen is 1.000, the atomic weight 
 of oxygen becomes 15.88 and that of chlorine 35.2. 
 
 The hydrogen standard for atomic weights was formerly 
 used very generally, but at present a slight modification of 
 this standard has been adopted by almost all chemists. 
 Oxygen is now made exactly 16.00 instead of being taken as 
 15.88, and the other atomic weights are made to correspond. 
 
ATOMIC WEIGHT DETERMINATIONS 149 
 
 This brings the figure for hydrogen to 1.008 and that for 
 chlorine to 35.45. 
 
 The standard O = 16.00 is used instead of H = 1.000 
 because nearly all of the elements combine with oxygen and 
 because most of the oxides can be weighed with great ac- 
 curacy. Many of the elements do not combine at all with 
 hydrogen, and in the case of those that do the hydrogen com- 
 pounds are difficult to weigh. Thus it is apparent that 
 oxygen is a far more practical standard for comparison. 
 
 156. Atomic Weight Determinations. To illustrate the 
 general mode of procedure in determining atomic weights, 
 let us imagine that we wish to determine the atomic weight 
 of copper. We weigh a definite piece of pure copper; let 
 us suppose that it weighs 1.0000 gram. Since, as we have just 
 seen, oxygen is the element most used for comparison, we 
 will seek to find what weight of oxygen is capable of combining 
 with the copper. To do this we convert the copper into 
 copper oxide. We must take the greatest precaution that 
 every bit of the metal is changed and also that no particle 
 of the metal or its compound is lost during the process. 
 Then we weigh the copper oxide, subtract the weight of the 
 copper which was used, and thus find the weight of oxygen 
 which was combined with the copper. The entries which we 
 would make in our notebooks and our calculations would 
 appear as follows : 
 
 Weight of copper .'.... 1.0000 
 
 Weight of copper oxide 1.2517 
 
 Calculations 
 
 Weight of oxygen = difference 0.2517 
 
 r^ i , copper 1.0000 r^o 
 Combining ratio - - = - - = 3.973 
 oxygen 0.2517 
 
150 ATOMIC AND MOLECULAR WEIGHTS 
 
 Atomic weight (assuming that the oxide is CuO) = 
 3.973 X 16.00 = 63.57. 
 
 Thus if we can assume that copper and oxygen are com- 
 bined with each other in the proportion of atom for atom, we 
 have found the atomic weight of copper to be 63.57. The 
 most careful study of the compound has made it reasonably 
 certain that this oxide contains copper and oxygen atoms 
 in equal numbers and 63.57 is therefore accepted as the 
 atomic weight of copper. 
 
 157. Molecular Weights. It is true of molecules as well 
 as of single atoms that the actual weight is too small and too 
 inaccurately known to be used for any practical purpose. 
 But since molecules are made up of definite numbers of atoms, 
 and we know accurately the weight of each of the atoms in 
 terms of the weight of the oxygen atom taken as 16.00, - 
 we can also express the weights of the molecules in terms of 
 the same standard. Thus the molecular weight of oxygen, 
 which has the formula O 2 , is 2 X 16.00 = 32.00, and the 
 molecular weight of hydrogen chloride, HC1, is 1.008 + 35.45 
 = 36.46. 
 
 158. Gram-Molecular Weights; Moles. Atomic and 
 molecular weights are in themselves hardly more than ab- 
 stract numbers. Thus when we say that 32.00 is the mo- 
 lecular weight of oxygen, we have only expressed a number 
 which does not indicate any tangible amount of the sub- 
 stance. But if we say 32.00 grams of oxygen, we have speci- 
 fied a definite amount. Likewise,' 2.016 grams of hydrogen 
 is a definite amount of that substance. The molecular 
 weight in grams of a substance is the molecular weight num- 
 ber taken in grams, and this quantity is so much used by 
 chemists that the rather long expression has been shortened 
 to the single word mole. 
 
MOLAL VOLUME 
 
 151 
 
 The molecule is the smallest actual particle of a substance, 
 whereas the mole is a quantity of the substance which con- 
 tains an inconceivably great number of molecules. Yet a 
 mole of oxygen contains the same number of molecules as a 
 mole of hydrogen, or of any other substance, however in- 
 conceivably great that number may be with respect to our 
 ordinary powers of perception. The molecule of oxygen 
 weighs 16 times (in round numbers) as much as the molecule 
 of hydrogen; likewise two molecules of oxygen weigh 16 
 times as much as two molecules of hydrogen, and so with 
 any greater number ; thus the mole of oxygen, which contains 
 something like 850,000,000,000,000,000,000,000 actual mole- 
 cules, weighs 16 times as much as the mole of hydrogen which 
 contains the same number of actual molecules of hydrogen. 
 
 Molal Volume. The volume of a mole of oxygen is also 
 a quantity which is of importance. One liter of oxygen 
 measured under standard conditions (see Chapter VIII) is 
 known to weigh 1.4296 grams. Hence one mole, or 32.00 
 
 32.00 . r , 
 
 grams, must occupy = 22.4 liters. 
 
 1.4.29o 
 
 This volume is known as the gram-molecular volume, or 
 simply as the molal volume, and it applies not only to oxygen 
 but to all gases, because, according to Avogadro's principle, 
 the same volume always contains the same number of mole- 
 cules of a gas, whatever the gas, if the temperature and the 
 pressure are the same. 
 
 32.00 grams, or one 
 mole of oxygen. 
 
 71 grams, or one 
 mole of chlorine. 
 
 2.015 grams, or one 
 mole of hydrogen. 
 
152 ATOMIC AND MOLECULAR WEIGHTS 
 
 Thus the weight of 22.4 liters of any other gas is the molal 
 weight of that gas, and when it is desired to find what is 
 the molecular weight of a new gas, it is only necessary to 
 find by measurement what is the weight of 22.4 liters, since 
 the molecular and molal weights are numerically the same. 
 
 159. Molecular Weight determined by Weight of Molal 
 Volume. Of course the amount of gas actually weighed 
 need not be exactly 22.4 liters. For example, 100 c.c. of 
 chlorine under standard conditions is found to weigh 
 0.3170 gram. The mole of chlorine would then weigh 
 
 - - X 22,400 = 71.0 grams. Hence the molecular weight 
 
 J-UU 
 of chlorine is 71.0. 
 
 160. Use of Weight of Molal Volume in finding a Formula. 
 We have already decided to write the formula of water as 
 H 2 O. If we are correct in this, the molecular weight of water 
 should be 18 and we should be able to test the correctness of 
 this figure by finding the weight of the molal volume. Under 
 standard conditions the molal volume of any gas is 22.4 
 liters, but water is not a gas under standard conditions. 
 We may, however, calculate the molal volume for conditions 
 under which water is a gas, and any temperature above 100 C. , 
 if the pressure is 760 mm., would meet these requirements. 
 Let us choose the temperature 273 C., which is 546 on the 
 absolute scale and therefore has on this scale exactly twice the 
 value of the standard temperature of 273 absolute. The 
 molal volume of oxygen under these conditions is given by 
 the calculation : 
 
 volume (760 mm. and 273 C.) = 22.4 X X = 44.8 liters. 
 
 i \y\) / o 
 
 That is, it is just twice the molal volume under standard 
 conditions. We have now only to find the weight of water 
 
MOLECULES OF COMMON ELEMENTARY GASES 153 
 
 vapor which will occupy 44.8 liters at 273 C. and 760 mm. 
 This weight proves to be 18 grams, and thus we establish 
 the molecular weight of water as 18 and further confirm 
 the formula as H 2 O. 
 
 44.8 liters 
 
 of Oxygen at 
 
 273C.and 760 ram. 
 
 44.8 liters 
 
 of Water Vapor 
 
 at 273C.and 760 mm. 
 
 32 grams, or one mole of oxygen. 18 grams, or one mole of water vapor. 
 
 161. Reason for Believing that Molecules of Common 
 Elementary Gases do not contain more than Two Atoms. It 
 was shown in the chapter on Avogadro's Theory that the 
 molecules of hydrogen as well as of chlorine, oxygen, and the 
 common elementary gases must contain at least two atoms 
 each. We have tacitly assumed that they do not contain 
 more than two atoms, and we will now show that this assump- 
 tion is almost certainly correct. The proof depends on a 
 comparison of the molal volume of the elementary gas with 
 that of a large number of its gaseous compounds. 
 
 One molal volume of hydrogen weighs 2 grams (in round 
 numbers), and hence the molecular weight is 2. It seems 
 extremely probable that among all the compounds of hydro- 
 gen there are at least some in which only a single atom enters 
 into the composition of the molecule. But a very great 
 number of gaseous compounds of hydrogen have been studied, 
 and none has been found in which a volume of 22.4 liters 
 contains less than 1 gram of hydrogen. Our confidence thus 
 becomes very great that the atomic weight of hydrogen is not 
 less than one half of the molecular weight, or, in other words, 
 that the molecule does not contain more than two atoms. 
 
154 ATOMIC AND MOLECULAR WEIGHTS 
 
 162. Quantitative Significance of Chemical Symbols. 
 Although chemical symbols serve a valuable purpose in 
 abbreviating chemical names and thus save much time in 
 chemical notation, this is not by any means their only use- 
 fulness. They serve also to indicate the weights of the ele- 
 ments in question. 
 
 Thus the formula of water, H 2 O, indicates that two atoms 
 of hydrogen are combined with one atom of oxygen in the 
 molecule of the substance. It indicates, furthermore, that 
 2X1 parts by weight of hydrogen are united with 16 parts 
 by weight of oxygen. Since the approved scientific unit of 
 weight is the gram, the parts by weight in the formula may 
 be taken in grams. Then H 2 O signifies 2 grams of hydrogen 
 and 16 grams of oxygen in combination, and the whole formula 
 stands for 2 + 16 = 18 grams, or one mole, of the compound. 
 
 163. Formulas contain Condensed Information. We have 
 devoted a good deal of attention in foregoing chapters to 
 the methods by which the composition of water has been 
 found and its molecular constitution deduced. Practically 
 all of the information so obtained is condensed in the formula 
 H 2 O. The formulas of other substances have been obtained 
 by equally painstaking and laborious processes, but we have 
 not the time, nor is it desirable for us, to go through all the 
 steps for obtaining every formula that we shall use. These 
 formulas have been derived through the labor of competent 
 scientific men, and their labor would have been in vain if it 
 were still necessary for every one who uses the formulas to 
 verify them step by step. The only way in which scientific 
 knowledge can advance is for each student to learn how to 
 grasp the knowledge that has already been obtained, so that 
 he can use this knowledge as a starting point in seeking to 
 discover new truth. 
 
INTERPRETATION OF FORMULAS 155 
 
 Formulas condense and systematize vast funds of chemical 
 knowledge, so that when we learn to readily interpret 
 formulas we have at our command information which has 
 taken years of effort to obtain. 
 
 164. Interpretation of Formulas. To understand the 
 meaning of formulas, it is only necessary for us to remember 
 that each symbol signifies one atomic weight of the particular 
 element, and that each subscript means that the atomic 
 weight of the element which the subscript follows must be 
 taken that number of times. For example, the formula of 
 sulphuric acid, H 2 SO4, means that in this substance the three 
 elements hydrogen, sulphur, and oxygen are present. Further 
 it means that sulphuric acid contains two atomic weights of 
 hydrogen, one of sulphur, and four of oxygen. Since the 
 atomic weight of hydrogen is 1, that of sulphur is 32, and 
 that of oxygen 16, it follows that sulphuric acid contains 2 
 parts by weight of hydrogen to 32 of sulphur and 64 of oxygen, 
 making in all 98 parts by weight. If as is usually the custom, 
 these parts by weight are to be taken in grams, the whole 
 formula denotes 98 grams of sulphuric acid. In working 
 with formulas after this manner, it is often convenient to 
 write the numbers standing for the weights of the respective 
 elements below the symbols, as follows: 
 
 H 2 S O 4 
 (2X1) + 32 + (4X16). 
 
 The atomic weights are understood in this fashion whenever 
 chemical formulas are written, but ordinarily they are not 
 thus expressed ; the values for all of the elements are to be 
 found in the table of atomic weights, a copy of which is 
 printed inside the back cover of this book. The pupil will 
 
156 ATOMIC AND MOLECULAR WEIGHTS 
 
 find occasion to use the atomic weights of a few of the 
 commonest elements so frequently that he will hardly fail to 
 memorize them. A table of the most important elements 
 is printed on page 340. 
 
 165. Equations. When chemical reactions take place, 
 the initial substances disappear but none of the elements 
 are destroyed ; they are unchanged in quantity and remain 
 as constituents of the new substances which appear. If the 
 formulas of all the substances involved are known, as well 
 as the weight of each, it is possible to write the story of the 
 reaction in an equation. 
 
 The formulas of each of the initial substances are placed 
 on the left-hand side of the equation. Each formula is taken 
 as many times as there are formula weights. In the same way 
 the formulas of the substances formed, taken the appropriate 
 number of times, are placed on the right-hand side of the 
 equation. A number placed before the formula of a sub- 
 stance means that the whole formula, not merely a single 
 symbol, is to be multiplied by the number. 
 
 166. Example of an Equation. Let us, as an illustration, 
 see how the reaction which occurs when common salt is 
 treated with sulphuric acid at a high temperature may be 
 expressed by means of an equation. It is known that 98 
 grams of sulphuric acid react with 117 grams of sodium 
 chloride. Since the formula weights of these two substances 
 are 98 and 58.5, respectively, the formula of the latter must 
 be taken twice if that of the former is taken once. The 
 products formed are hydrogen chloride and sodium sulphate, 
 in fact 73 grams of the former and 142 grams of the latter, 
 and these amounts are equal to two formula weights of the 
 hydrogen chloride and to one formula weight of the sodium 
 sulphate. We may now write the equation as follows : 
 
CHEMICAL CALCULATIONS 157 
 
 H 2 SO 2 + 2 NaCl-^2 HC1 + Na 2 SO 4 
 
 98 2(58.5) 2(36.5) 142 
 
 As in mathematical equations, the two sides of chemical 
 equations are exactly equal ; the laws of the conservation 
 of matter and of the elements tell us that none of the elements 
 can have increased or decreased in amount during the reac- 
 tion. Nevertheless, it is not very customary to use the 
 equality sign in chemical equations. Most chemical reactions 
 are, to some extent at least, reversible ; that is, they may pro- 
 ceed forward or backward according to varying conditions. 
 Instead of the equality sign, then, an arrow is more often 
 used so as to indicate the prevalent direction of the reaction. 
 
 167. Practical Bearing of Atomic and Molecular Weights. 
 The accurate knowledge of molecular and atomic weights is 
 not a matter merely of theoretical interest, but it is one of 
 immense practical importance ; for, with the aid of it, chemi- 
 cal manufacturers can calculate the quantities of the dif- 
 ferent chemicals which they must take in their work. 
 
 For example, suppose a manufacturer of carbonated water, 
 who is forced to prepare his own carbon dioxide, has 150 kilos 
 of cracked marble (calcium carbonate) from which to manu- 
 facture carbon dioxide gas for charging the wate^r (see 
 page 60) . He must find out how much sulphuric acid must 
 be taken to react with the marble. He knows the chemical 
 formulas of all the substances ; he first writes the equation 
 for the chemical reaction ; he looks up in the table the 
 atomic weights of the elements and adds them to give the 
 formula weights of calcium carbonate and sulphuric acid : 
 
 CaC0 3 + H 2 S0 4 = CaSO 4 +CO 2 +H 2 O 
 
 40+12+(3X16) (2 XI) +32+ (4X16) 
 
 100 98 
 
158 ATOMIC AND MOLECULAR WEIGHTS 
 
 So the quantities of calcium carbonate and sulphuric 
 acid, since one formula weight of each is involved in the re- 
 action, are in the ratio of 100 to 98. If a greater amount of 
 one is taken, the amount of the other must be correspondingly 
 greater. Therefore, to find the amount of sulphuric acid 
 required in the above case, we make the proportion : 
 
 100 = 98 
 150 x 
 
 Solving : x = 147. Thus, 147 kilos of sulphuric acid are 
 required to react with 150 kilos of calcium carbonate. 
 
 The weight of carbon dioxide to be obtained in the same 
 reaction can be calculated in a similar fashion : 
 
 CO 2 = 12 + (2 X 16) = 44 
 
 Each formula weight of calcium carbonate gives one mole 
 of carbon dioxide. Therefore : 
 
 100^44 
 150 x 
 
 Solving : x = 66. Thus, 66 kilos of carbon dioxide are 
 obtained. 
 
 The manufacturer might like to know what volume this 
 carbon dioxide would occupy as a gas; he might wish to 
 state in his advertisements how many volumes of gas were 
 compressed into each volume of liquid. Each formula 
 weight in grams of calcium carbonate gives one mole of car- 
 bon dioxide, which under standard conditions occupies 22.4 
 liters. Each formula weight in kilograms gives 1000 X 22.4 
 = 22,400 liters. Therefore, 
 
 100 = 22400 
 150 x 
 
OZONE 159 
 
 Solving : x = 33,600. Thus, 33,600 liters of carbon diox- 
 ide gas under standard conditions would be obtained. 
 
 If it were of interest to the manufacturer to calculate the 
 weight of calcium sulphate which he could obtain, that could 
 be done by a similar process, but ordinarily it is not necessary 
 to know this quantity, for the calcium sulphate is a worthless 
 product and is thrown away. 
 
 The foregoing illustrations should have made clear how ex- 
 tremely important is the knowledge of molecular and atomic 
 weights for the purposes of chemical calculations. It would 
 be advisable for the pupil at this point to practice with a 
 number of similar calculations. He will find several problems 
 at the end of this chapter. He should also make up problems 
 for himself based on the substances discussed in the earlier 
 chapters. 
 
 168. Ozone. When oxygen is subjected to the action of 
 electrical oscillations obtained from a powerful induction 
 coil (see Fig. 29), it is found to suffer a slight diminution 
 
 /- TTn foit on outer tube ^Oc/ter Taf>e 
 
 |H,;iii<iiiiiiMHmmHJM^^ 71/be 
 
 ^ v,,,,,,,,,,,,,,:,,,,,:,,,,,,:,,,,,,:,,,,,^^^ OX^S) Of -4/A /rtfa 
 
 r/n fo/7 on /nner tube^ 
 
 D/scngrge- O^on/^ec/ Oxygen or Air 
 
 FIG. 29. Ozonizing Apparatus. Air or Oxygen is passed slowly through the 
 space between two concentric glass tubes. Electrical oscillations (but no 
 actual passage of current) are being caused in this space, for the tinfoil con- 
 ductor inside the inner glass tube and that outside the outer glass tube are 
 connected with the terminals of an induction coil. 
 
 in volume and to acquire a strong irritating odor and a num- 
 ber of other properties not possessed by ordinary oxygen. 
 For example, it will quickly darken a lustrous surface of silver 
 or mercury, due to formation of a film of oxide. It will 
 
 B. AND W. CHEM. 11 
 
160 
 
 ATOMIC AND MOLECULAR WEIGHTS 
 
 bleach the color from litmus, and it will turn to a deep blue 
 some starch emulsion to which a little potassium iodide has 
 been added. 
 
 The new substance which causes these effects is called 
 ozone, but it is composed only of oxygen. If the gas is 
 heated to 300 C. or above, it loses all its remarkable prop- 
 erties; the ozone has been converted back into ordinary 
 oxygen. At best only a rather small proportion of the 
 oxygen (about 7 per cent) can be converted into ozone by 
 means of electrical oscillations, but if the gas coming from the 
 ozonizing tube is passed through a tube cooled with liquid 
 oxygen, the ozone is condensed to an intensely blue liquid. 
 
 By allowing this liquid to boil ( 119 C.) nearly pure 
 ozone is obtained as a blue gas, but this rapidly changes 
 until only a small per cent of ozone is left if it is allowed to rise 
 to the room temperature. Measurements of the weight per 
 liter of this gas at a very low temperature before it has had 
 a chance to change to any extent into ordinary oxygen, show 
 that the weight of the molal volume is 48 grams. What is 
 the significance of this in the light of Avogadro's theory? 
 
 Simply that one molecule of ozone weighs =1.5 times as 
 
 o2 
 
 much as a molecule of oxygen. Since we believe the oxygen 
 molecule to contain two atoms of oxygen, we must con- 
 clude that the ozone molecule contains three atoms of 
 oxygen and write the formula of ozone O 3 . 
 
 The volume change when ozone decomposes to ordinary 
 oxygen is as follows : 
 
 two volumes ozone 
 
 three volumes oxygen 
 
OZONE 161 
 
 Ozone is formed in small amounts in many different ways. 
 Electric sparks through the air produce ozone, and its odor 
 is always noticeable near the brushes of electrical machines. 
 When an electric current is passed through dilute sulphuric 
 acid, the oxygen escaping from the positive pole contains 
 ozone. 
 
 Ozone is a far more vigorous oxidizer than ordinary oxygen, 
 as shown by its action on silver and mercury. The pure 
 ozone, either as the liquid or the gas, is explosive. These 
 facts all show that it possesses more energy than ordinary 
 oxygen. When it is prepared from oxygen, energy must be 
 supplied electrically or otherwise. 
 
 Ozone is also formed in the presence of a number of sub- 
 stances, notably yellow phosphorus and resins, which are 
 capable of undergoing a noticeable slow oxidation at or- 
 dinary temperatures. If a stick of freshly scraped yellow 
 phosphorus is placed in the bottom of a glass jar and left 
 half covered with water, the odor of ozone in the jar soon 
 becomes very strong, and a piece of paper moistened with 
 starch emulsion containing potassium iodide is turned blue. 
 At the same time the phosphorus becomes covered with a 
 dull whitish coating, because of oxidation. The energy 
 yielded by the oxidation of the phosphorus must be used in 
 the change of some of the surplus oxygen to ozone. 
 
 The air in pine and spruce forests is^ regarded as being 
 especially invigorating, and this property is possibly due in 
 part to traces of ozone formed in connection with the slow 
 oxidation of the resins on the trees. 
 
 Ozone, like hydrogen peroxide, is a germicidal agent. It 
 has been used with marked success in purifying water sup- 
 plies. A little of it introduced into the air of crowded school- 
 rooms and public halls probably has a good effect. 
 
162 ATOMIC AND MOLECULAR WEIGHTS 
 
 SUMMARY 
 
 Atomic Weights. The absolute weights of the atoms are too small 
 to be of any practical importance. The relative weights of 
 the atoms of the different elements, on the other hand, are of 
 the greatest importance and can be determined with a high 
 degree of accuracy. 
 
 These atomic weights are based on the standard of the oxygen 
 atom, which is taken as exactly 16. By this means the hy- 
 drogen atom, which is the lightest atom, becomes approxi- 
 mately, although not exactly, one. 
 
 The atomic weight of an element is most often found by making a 
 very accurate quantitative analysis of a simple oxygen com- 
 pound of the element. 
 
 Molecular weights are based on the same standard as atomic weights. 
 The gram-molecular weight of a substance is its molecular 
 weight taken in grams ; for brevity this quantity is called a 
 mole. 
 
 Molal Volume. The volume of one mole of any gas at standard 
 conditions is 22.4 liters. This volume is known as the gram- 
 molecular volume or the molal volume. 
 
 To find the molecular weight of any substance that can be vapor- 
 ized it is only necessary to find the weight of 22.4 liters under 
 standard conditions, or of the molal volume calculated to the 
 conditions of the gas if the substance does not vaporize under 
 standard conditions. 
 
 The chemical symbol of an element signifies the atomic weight in 
 grams of the element. 
 
 The formula of a substance signifies the formula weight in grams of 
 the substance. Formulas contain much information in re- 
 gard to the quantitative composition of the substances which 
 they represent. 
 
 Equations tell in abbreviated form not only the different substances 
 but the weights of the substances which take part in chem- 
 ical reactions. 
 
 Ozone is an extremely active modification of oxygen. Its formula 
 isO 3 . 
 
QUESTIONS 163 
 
 Questions 
 
 1. What weights of each of the following elements are repre- 
 sented by the following symbols: O, H, Cl, Na, and Fe? 
 
 2. What weights of each of the following substances are indi- 
 cated by the formulas H 2 0, HC1, NH 3 , N 2 , and H 2 S0 4 ? 
 
 3. Forty grams of sodium hydroxide are dissolved in water and 
 neutralized with hydrochloric acid, according to the equation, 
 NaOH +HC1 ->- NaCl +H 2 O. Neglecting the accompanying water, 
 how many grams of hydrochloric acid are necessary? 
 
 4. What volume of hydrogen chloride gas under standard con- 
 ditions is necessary to furnish the hydrochloric acid needed in 
 Questions? 
 
 5. What weight of sodium chloride would be obtained if the 
 solution from Question 3 were evaporated to dryness? 
 
 6. Calculate the weight of barium sulphate which would be 
 formed if 100 grams of barium chloride were treated according to 
 the reaction, BaCl 2 -f H 2 S0 4 -^BaS0 4 + 2 HC1. 
 
 7. What volume of carbon dioxide under standard conditions 
 would be given off if 100 grams of sodium bicarbonate, NaHC0 3 , 
 entered into the reaction, NaHC0 3 '+ HC1^C0 2 + H 2 + NaCl? 
 
 8. If 100 c.c. of ozonized oxygen is passed through a red-hot tube 
 and then cooled to the first temperature, it is found to measure 102 c.c. 
 What per cent by volume of the gas was ozone ? 
 
 9. If one gram of liquid ozone were to evaporate, what volume 
 would it occupy under standard conditions if none of it became 
 changed to ordinary oxygen ? 
 
 10. What volume would it occupy after 92 per cent was changed 
 to oxygen? 
 
 11. How many cubic centimeters will 100 c.c. of air contract if it is 
 subjected to electrical oscillations in an ozonizing tube until 3 per 
 cent of the oxygen has been converted into ozone (21 per cent by 
 volume of air is oxygen) ? 
 
 12. Refer to statements as to composition of hydrogen peroxide 
 on page 108 and decide what is the formula of the substance. 
 
 13. In what respects are hydrogen peroxide and ozone similar in 
 their properties ? 
 
CHAPTER XVI 
 
 CHLORINE 
 
 IT was stated in Chapter XIII that chlorine is obtained 
 from hydrochloric acid by oxidizing away the hydrogen of 
 the latter by means of manganese dioxide. Using now the 
 knowledge of chemical abbreviations gained in the last 
 chapter, we can express this reaction by means of the 
 equation : 
 
 4 HC1 + MnO 2 -^MnCl 2 + 2 H 2 O + C1 2 . 
 
 This equation shows that water is formed by the union of the 
 hydrogen and oxygen, manganese chloride is formed, and 
 half of the chlorine from the hydrochloric acid is set free. 
 
 169. Source of Chlorine. The source of hydrochloric 
 acid, and in fact of most of the chlorine of commerce as well 
 as most of the chlorine compounds, is common salt. Sodium 
 chloride is present in the water of the ocean to the extent of 
 about 2.65 per cent. It is also found in vast deposits in many 
 parts of the earth where formerly there have existed salt 
 lakes, or bays, the water of which has evaporated, leaving 
 solid salt. 
 
 In the course of ages these deposits have frequently be- 
 come covered with earth and buried deeply beneath the sur- 
 face. Such salt beds may be worked by mining, or, more 
 often, by sinking pipes through which water may be intro- 
 duced to the deposit. When the water becomes saturated 
 
 164 
 
DEACON'S PROCESS 
 
 165 
 
 with salt, it is pumped up again and evaporated to obtain 
 the dry salt. There is a great advantage in evaporating this 
 concentrated brine, which contains nearly 40 per cent of salt, 
 instead of sea water, which contains less than 3 per cent. 
 
 FIG. 30. Vats for Evaporating Brine in Salt Industry. 
 
 Consequently, sea water is not much used as a source of salt 
 except in very warm and sunny climates. 
 
 170. Deacon's Process. On the large scale, instead of 
 using the oxygen of manganese dioxide to oxidize the hydro- 
 gen of hydrogen chloride, an ingenious method of using the 
 oxygen of the air was devised by Deacon in 1868. Although 
 the free oxygen of the air will not oxidize hydrogen chloride 
 under ordinary conditions, it will do so when the conditions 
 are made right. A careful study, by methods which we shall 
 not attempt to discuss fully, has proved that oxygen has a 
 greater chemical attraction for hydrogen than chlorine has, 
 and thus it is only to be expected that oxygen should be able 
 to withdraw hydrogen from its combination with chlorine. 
 
166 CHLORINE 
 
 Under ordinary conditions this attraction is not apparent, 
 any more than the attraction between oxygen and charcoal 
 in the cold. 
 
 When, however, hydrogen chloride gas and air are mixed 
 and drawn through heated tubes containing copper chloride, 
 a reaction takes place and chlorine is liberated freely : 
 
 O 2 + 4HC1->2H 2 O + 2C1 2 . 
 
 The copper chloride is not changed by this reaction ; it acts 
 therefore merely as a catalyzer, just as does the manganese 
 dioxide in the preparation of oxygen from potassium chlorate 
 (see page 40). In order that the copper chloride shall work 
 efficiently, a large surface of it must be exposed to the mixture 
 of gases. This is accomplished by saturating sopie porous 
 material, such as pumice stone, with a solution of the copper 
 salt and then drying it. This method of obtaining chlorine 
 from hydrogen chloride is known as Deacon's process. 
 
 171. Electrolysis of Brine. At the present day a large 
 part of the chlorine of commerce is made by the electrolysis 
 of common salt solution. The chlorine is given off at the 
 positive pole; at the negative pole sodium hydroxide is 
 formed, while hydrogen gas escapes. 
 
 When dry sodium chloride melted by intense heat is 
 electrolyzed, chlorine and sodium are obtained. The attrac- 
 tion which holds sodium and chlorine in combination is over- 
 come by means of the electric current. Since we know that 
 sodium reacts rapidly with water, 
 
 2 Na + 2 H 2 O->2 NaOH + H 2 , 
 
 the formation of sodium hydroxide at the negative pole when 
 the water solution is electrolyzed is easily understood. 
 Thus by the electrolytic process another valuable product 
 
167 
 
 is obtained besides the chlorine. Such a product other than 
 the chief one sought is known as a by-product. Many com- 
 mercial processes of to-day yield large profits from their 
 by-products, and often thereby the price of the principal 
 product is materially lessened. 
 
 172. Laboratory Preparation of Chlorine. To prepare 
 chlorine in the laboratory for the purpose of studying its 
 properties, the older method of oxidizing hydrochloric acid 
 with manganese dioxide is suitable. Manganese dioxide 
 in small lumps is placed in a generator flask like that used 
 in preparing hydrogen chloride (see Fig. 25). Enough 
 hydrochloric acid is poured in through the thistle tube to 
 seal the latter and cover the manganese dioxide. A reaction 
 begins at once, but to yield a free supply of chlorine the flask 
 may be cautiously warmed with a Bunsen flame. 
 
 Chlorine gas cannot well be collected over water, as it 
 dissolves to some extent in the latter. It may be led through 
 a delivery tube to the bottom of a bottle. When the bottle 
 is filled with the greenish-yellow gas, a glass plate is placed 
 over the top to prevent the gas from diffusing out. 
 
 All work with chlorine should be done under a hood with 
 a strong draft, so that none of this offensive gas which escapes 
 from the generator and from the bottles may get out into the 
 laboratory. 
 
 173. Physical Properties. Chlorine is a gas of a pale 
 yellowish-green color. It has an offensive and suffocating 
 odor. When inhaled, even in minute quantities mixed with 
 air, it is very irritating to the mucous membranes ; when at 
 all concentrated, it is most dangerous to inhale. One volume 
 of water dissolves a little more than two volumes of chlorine ; 
 the solution is yellow and smells strongly of chlorine. Chlo- 
 rine is about two and one half times as heavy as air. The dry 
 
168 CHLORINE 
 
 gas is much more easily liquefied than air; at atmospheric 
 pressure it is liquid at 34 C. ; at ordinary temperature it 
 is liquefied by higher pressure, seven atmospheres sufficing 
 at 20 C. 
 
 174. Chemical Properties. Chlorine does not burn in the 
 air, neither is it a supporter of the combustion of ordinary 
 fuel materials. A lighted taper thrust into a bottle of chlo- 
 rine is extinguished. Nevertheless, chlorine can, like oxygen, 
 combine with almost all of the other elements, and, with 
 some of them, with considerable violence. For example, 
 if a little powdered antimony is dropped into a jar of chlorine, 
 a brilliant shower of sparks is instantly produced. 
 
 175. Chlorine and Metals. Likewise, iron, zinc, and cop- 
 per, if very finely powdered so that a large surface is pre- 
 sented for the chemical action, ignite spontaneously in chlo- 
 rine. The combustion of these, as well as of other metals in 
 chlorine, yields the chlorides of the metals. Thus, sodium 
 chloride is formed when sodium is burned in chlorine, whereby 
 our conclusion already made that common salt is composed 
 of chlorine and sodium receives further confirmation. 
 
 176. Chlorine and Hydrogen. Chlorine has a strong 
 tendency to combine with hydrogen. As already stated 
 (page 118), a jet of hydrogen burns in a jar of chlorine ; like- 
 wise, a jet of chlorine will burn in a jar of hydrogen. An 
 explosive mixture is formed by chlorine and hydrogen, just 
 as detonating gas (see page 115) is formed by oxygen and 
 hydrogen, and this mixture is naturally most explosive when 
 it contains the two gases in the proportion in which they 
 combine, that is, volume for volume. 
 
 Such a mixture is made to explode even more easily than 
 the oxygen-hydrogen mixture. To illustrate this let us fill 
 a thin glass bulb in a shaded comer of the laboratory with a 
 
CHLORINE 169 
 
 mixture of equal volumes of chlorine and hydrogen. Then, 
 for protection, support a pane of thick plate glass between 
 the bulb and the observer and bring the whole into the direct 
 rays of the sun. A deafening explosion occurs immediately. 
 The light from a magnesium flashlight powder is also suffi- 
 cient to explode the mixture. 
 
 This experiment does not necessarily show that chlorine is 
 stronger than oxygen in its chemical affinity for hydrogen, 
 for we have already stated (page 165) that the exact contrary is 
 the case ; the fact that the attraction of the oxygen is really 
 greater is shown in that the oxygen-hydrogen mixture ex- 
 plodes with more violence and develops more heat thereby. 
 Starting an explosion is something like pulling the trigger of 
 a rifle ; the pull necessary to release the hammer gives little 
 indication as to the power of the rifle. 
 
 The affinity of chlorine for hydrogen is further shown in 
 the behavior of turpentine, which is a compound consisting 
 of only hydrogen and carbon. If a piece of filter paper is 
 wet with hot turpentine and then lowered into a jar of 
 chlorine, a flash followed by the escape of dense black 
 smoke occurs. The chlorine has combined with the hydro- 
 gen of the turpentine and left the carbon uncombined to 
 appear as the black smoke : 
 
 C 10 Hi 6 + 8 C1 2 -> 16 HC1 + 10 C. 
 
 That hydrogen chloride has also been formed is indicated 
 in that a strip of litmus paper is turned red when it is mois- 
 tened and then lowered into the jar. 
 
 177. Chlorine and Carbon. The last experiment would 
 also indicate that chlorine does not unite directly with carbon, 
 which is much in line with the fact that ordinary fuels do not 
 burn in chlorine. Carbon does, to be sure, form compounds 
 
170 CHLORINE 
 
 with chlorine, of which the most important is carbon tetrachlo- 
 ride, CC1 4 , a liquid substance that is well known and exten- 
 sively used as a solvent and as a fire extinguisher. These 
 compounds are not made, however, by direct synthesis from 
 the two elements. 
 
 178. Chlorine Water. For many purposes chlorine reacts 
 more satisfactorily in water solution than in the form of the 
 dry gas. Such a solution is known as chlorine water. It 
 reacts with the precious metals which are not affected by 
 ordinary acids. Thus a piece of gold leaf is at once dissolved 
 by chlorine water. The chlorine combines directly with 
 the gold, forming chloride of gold, and the latter is soluble in 
 water. 
 
 179. Aqua Regia. Chlorine may be liberated from hydro- 
 chloric acid by oxidation with nitric acid. A mixture of 
 three volumes of concentrated hydrochloric acid and one 
 volume of concentrated nitric acid is in the correct proportion, 
 and such a mixture is known as aqua regia (literally, kingly 
 water) because it continually liberates chlorine, which causes 
 the precious metals to form soluble chlorides and thus appear 
 to dissolve. Aqua regia is used by jewelers and chemists 
 when gold and platinum are to be converted into soluble 
 compounds. 
 
 180. Bleaching. The most important use of free chlorine 
 is in bleaching linen and cotton fabrics. The natural fibers 
 when woven into cloth present a pale yellow or greenish- 
 brown tinge, and this is destroyed by the bleaching, leaving 
 the goods pure white. 
 
 Chlorine water itself is unstable, as is shown by the fact 
 that it loses its yellow color in a few hours or, at most, 
 days. It is, however, this very instability which gives it 
 its power to bleach. 
 
HYPOCHLOROUS ACID 171 
 
 When chlorine is dissolved in water, a small portion of it 
 interacts to form hydrochloric and hypochlorous acids : 
 
 H 2 O + C1 2 ^HCH-HC10. 
 
 When a small amount of these products is formed, the re- 
 action ordinarily stops, because whenever any considerable 
 amounts of these products are brought together, they react 
 to form chlorine and water. Thus in the above equation 
 arrows are made to point in both directions because the re- 
 action may go either way, according to conditions. What we 
 call chlorine water thus contains hydrochloric acid and 
 hypochlorous acid in addition to the chlorine and water. 
 
 181. Instability of Hypochlorous Acid. Hypochlorous 
 acid is a most unstable substance, and it gives up its oxygen 
 to oxidizable substances with extreme ease. In fact, in the 
 sunlight, it breaks down rather rapidly of itself : 
 
 2 HC1O - 2 HC1 + O 2 . 
 
 Thus, if we invert a test tube of chlorine water in a beaker of 
 the same solution and allow the whole to stand in the sun- 
 light, we find in an hour or so that the yellow color of the 
 chlorine has gone and that in the test tube a few bubbles of a 
 gas, which proves to be oxygen, have collected. As fast as the 
 hypochlorous acid is taken out of the way through the de- 
 composing agency of the sunlight, the reaction of the chlorine 
 with the water progresses further, since the tendency to op- 
 pose this reaction is now removed. Thus all the chlorine 
 ultimately disappears. 
 
 The total change effected by the succeeding reactions sums 
 up as follows : 
 
 2 C1 2 + 2 H 2 -* 2 HC1O + 2 HC1 
 2 HC1O -* 2 HC1 + Q 2 
 
 2 C1 2 + 2 H 2 Q -> 4 HC1 + O ? 
 
172 CHLORINE 
 
 or expressed in words, chlorine has displaced the oxygen 
 from water. This is the direct opposite of what takes place 
 in the Deacon process, but it is to be noted that this reaction 
 takes place in water solution, whereas the Deacon process 
 was carried out with the dry gases. Such a difference of 
 conditions oftentimes occasions an entire change in the 
 direction of a reaction. 
 
 182. Theory of Bleaching. Dry chlorine gas is incapable 
 of bleaching dry fabrics, as is easily shown by suspending a 
 piece of colored calico in a bottle of dry chlorine. Wet the 
 cloth, however, and lower it again into the chlorine and it is 
 very soon decolorized. Most dyestuffs, both the coal-tar 
 dyes, which are principally used in coloring cotton goods, and 
 the yellow and brown coloring matter of the natural fibers, 
 are very complex compounds containing carbon and hydro- 
 gen and often nitrogen and oxygen. Very slight changes in 
 their make-up, such as the addition of a little oxygen, often 
 completely change the color, and most often remove it al- 
 together. It is generally supposed that bleaching really 
 consists in adding oxygen to the dyestuff molecule. The 
 instability of hypochlorous acid furnishes what is practically 
 atomic oxygen ready to add directly to the dyestuff: 
 
 HC1O + dyestuff -> HC1 + dyestuff oxide. 
 
 183. Bleaching Powder. Chlorine gas itself is most dis- 
 agreeable and dangerous to handle and is difficult to trans- 
 port and store. For bleaching purposes, it has therefore 
 been customary to absorb the chlorine in calcium hydroxide, 
 with which it reacts to form what is known as bleaching 
 powder ; 
 
 Ca(OH) 2 + C1 2 -> Ca< + H 2 0. 
 
BLEACHING POWDER 
 
 173 
 
 This substance is a dry powder ; it can be kept indefinitely 
 without decomposition, and can be handled and transported 
 without danger. 
 
 When it is to be used for bleaching, it is stirred up to a very 
 thin paste with water and placed in vats, through which 
 the goods are run over mechanical rollers (Fig. 31). The 
 bleaching powder itself is rather ineffective when compared 
 with hypochlorous acid, but it readily gives hypochlorous 
 acid when treated with sulphuric acid : 
 
 H 2 S0 4 -> CaS0 4 + HC1 + HC1O. 
 
 It is not advisable, however, to mix the bleaching powder 
 and the sulphuric acid all at once. The roll of cloth after 
 
 S 
 
 C 
 
 w 
 
 w 
 
 FIG. 31. Bleaching. A, unbleached goods on roll; BB, vats of bleach 
 liquid; SS, vats of dilute sulphuric acid; C, vat of sodium sulphite; 
 WW, water for washing cloth; H, steam heated roll; F, roll for the 
 bleached goods. 
 
 passing through the bleach vat is next passed through a vat 
 containing very dilute sulphuric acid. Thus the hypochlo- 
 rous acid is produced only within the fibers of the cloth where 
 it will be effective. 
 
 In the diagram, the roll of goods is represented as being 
 passed alternately through two bleach vats and two sulphuric 
 
1 74 CHLQRINE 
 
 acid vats, then through a bath of sodium sulphite to destroy 
 any hypochlorous acid which would otherwise rot the goods, 
 then through a washing bath of water, and lastly over steam- 
 heated cylinders -to dry and iron the cloth. 
 
 Bleaching powder is also known as chloride of lime, and 
 under this name it is extensively sold in small cans for use as 
 a deodorizer and disinfectant. It has an intense and to most 
 people disagreeable odor which to some extent resembles 
 that of chlorine. The odor is really that of hypochlorous 
 acid, a little of which exists even in the unacidified bleaching 
 powder. Its deodorizing power comes from the same cause 
 as its bleaching power, namely, the readiness with which it 
 gives off oxygen to oxidizable material. Noxious matter is, 
 for the most part, readily oxidizable, and by oxidation is 
 converted into harmless substances. As a disinfectant, 
 bleaching powder kills disease germs. 
 
 184. Liquid Chlorine. At present much chlorine is con- 
 densed to the liquid condition and stored and shipped in 
 strong steel cylinders instead of being absorbed by slaked 
 lime. Such chlorine is very convenient for use by skilled 
 workmen, but the bleaching powder is safer. In some 
 towns, liquid chlorine, bought in ton lots, is being used 
 to render the municipal water supply safe for drinking 
 purposes. 
 
 185. Comparison of Oxygen and Chlorine. In its gen- 
 eral chemical nature, chlorine is extremely like oxygen. It 
 is a characteristic non-metal and unites with all the metals, 
 forming chlorides, just as oxygen forms oxides. In the 
 chlorides and oxides, chlorine and oxygen are mutually in- 
 terchangeable ; one atom of oxygen, however, is equivalent 
 to two atoms of chlorine. Under most conditions, the 
 chemical affinity of oxygen is somewhat greater than that 
 
SUMMARY 175 
 
 of chlorine, and oxygen can drive chlorine out of its com- 
 pounds more easily than chlorine can displace oxygen. In 
 its power to combine with carbon, oxygen stands consider- 
 ably ahead of chlorine, but, on the other hand, chlorine ex- 
 cels oxygen in its ability to form compounds with the pre- 
 cious metals. 
 
 SUMMARY 
 
 The chief source of chlorine and all chlorine compounds is common 
 salt, which is the most abundant material containing chlorine. 
 
 Free chlorine is obtained by oxidizing the hydrochloric acid ob- 
 tained from salt. The hydrogen forms water with oxygen, 
 while the chlorine is left uncombined. 
 
 But by far the greatest part of the chlorine used commercially 
 is obtained by electrolyzing common salt solution. By this 
 process, sodium hydroxide is obtained as a by-product. 
 
 Properties of Chlorine. Chlorine is a greenish-yellow gas, heavier 
 than air, and somewhat soluble in water. It is irritating 
 to the breathing passages and is dangerous if inhaled in 
 quantity. 
 
 Chemically, chlorine is a very active non-metallic element, resem- 
 bling oxygen in this respect. It forms compounds with almost 
 all of the other elements. Towards hydrogen, carbon, and 
 the majority of the elements, it is somewhat less active than 
 oxygen; towards the precious metals, however, it is more 
 active. 
 
 The principal use of chlorine is based on its indirect bleaching of 
 organic coloring matter. This property depends upon the 
 release of oxygen from water by the action of chlorine, this 
 released oxygen being in a condition to enter into reaction 
 far more easily than atmospheric oxygen. 
 
 For practical bleaching purposes, chlorine itself is not much used, 
 but rather bleaching powder, which is obtained by allowing 
 chlorine to react with calcium hydroxide. Some chlorine, 
 however, is compressed to the liquid condition in strong 
 steel cylinders, for transportation and use. 
 
 B. AND W. CHEM. 12 
 
176 CHLORINE 
 
 Questions 
 
 1. What compound occurring in nature is the chief source of 
 chlorine? Describe two totally different methods by which free 
 chlorine may be obtained from it. 
 
 2. In obtaining salt on the large scale, why is brine from salt 
 wells used rather than sea water? 
 
 3. What becomes of the sodium of the salt in each of the methods 
 by which chlorine is obtained? 
 
 4. How could you identify chlorine without making use of the 
 properties of odor or color? 
 
 5. Give three reasons for considering oxygen a somewhat more 
 active non-metallic element than chlorine. 
 
 6. What uses has chlorine, in a practical way? 
 
 7. Give reasons for thinking that the bleaching of organic color- 
 ing matter is a process of oxidation. 
 
 8. What weight of manganese dioxide must be used to liberate 
 chlorine from 100 kilograms of 36.5 per cent hydrochloric acid ac- 
 cording to the reaction 4 HC1 + Mn0 2 -> MnCl 2 + 2 H 2 + C1 2 ? 
 
 9. What weight of chlorine will be obtained in Question 8? 
 
 10. What volume will the chlorine obtained in Question 9 oc- 
 cupy under standard conditions? 
 
 11. If we start with the 100 kilograms of 36.5 per cent hydro- 
 chloric acid used in Question 8, and could use sulphuric acid and 
 manganese dioxide, what is the maximum amount of free chlorine 
 that could be obtained? Write the equation and compute the 
 amounts of sulphuric acid and manganese dioxide that would be 
 required. 
 
 12. How would you treat bleaching powder in order to obtain 
 chlorine gas? Give equations. 
 
CHAPTER XVII 
 
 SODIUM 
 
 IN the preceding chapter, we have discussed chlorine, a 
 non-metal which is one of the constituents of common salt. 
 The other constituent of salt is sodium, a metallic element. 
 Sodium is a different sort of metal from iron, zinc, copper, 
 and those metals that are used in everyday life. 
 
 In the first place, we never see sodium in everyday life 
 because it is such a chemically active substance that it can- 
 not be kept in contact with the atmosphere. A little piece 
 of sodium left uncovered in a dish immediately loses its 
 bright metallic appearance and turns dull, shortly a white 
 crust forms which continually swells up with little bubbles, 
 until at last the whole lump seems to liquefy. This change 
 is due to the reaction of sodium with the water vapor of the 
 atmosphere. We have already seen (Chapter X) that sodium 
 reacts rapidly with cold water, displacing hydrogen from the 
 latter. 
 
 186. Preparation of Sodium. When, melted sodium 
 chloride is decomposed by electrolysis, sodium is set free 
 at the negative pole, at the opposite pole from that at which 
 the chlorine is liberated. But it is a difficult matter to keep 
 sodium chloride at a high enough temperature to melt it 
 and thus enable the electrolysis to take place. Solid salt 
 is a non-conductor of electricity and thus cannot be elec- 
 trolyzed. 
 
 177 
 
178 SODIUM 
 
 In the actual preparation of sodium by electrolysis, sodium 
 hydroxide, NaOH, commonly called caustic soda, is used, 
 because this melts at a fairly low temperature. When this 
 is electrolyzed, oxygen is evolved at the positive pole and 
 sodium and hydrogen are both formed at the negative pole. 
 The hydrogen escapes, and the sodium which is molten at 
 the temperature of the bath, is drawn off and allowed to 
 solidify in appropriate molds. The sticks of sodium so 
 prepared are preserved under kerosene or similar oil to pro- 
 tect them from the atmosphere. 
 
 187. Physical Properties. Sodium has a silver-white 
 color and a metallic luster. In its possession of this metallic 
 luster and in its ability to conduct electricity, it resembles 
 all other metals. In other respects it has quite different 
 physical properties from those that the everyday man as- 
 sociates with metals. Thus it is very soft; it can be cut 
 with a knife almost as easily as cheese ; it is so light that it 
 floats on water, and it melts below the temperature at which 
 water boils. 
 
 188. Chemical Properties. Chemically, sodium differs 
 from the common metals in its extremely great activity. 
 As we have seen, it rapidly decomposes cold water, liberating 
 hydrogen. It burns intensely in air, forming sodium peroxide. 
 It does not, however, ignite spontaneously, because it be- 
 comes covered with a thin coating of oxide which protects 
 the metal underneath. We have already seen that sodium 
 combines with chlorine as well as with oxygen ; in fact, sodium 
 has a very strong tendency to unite with all the non-metallic 
 elements. 
 
 Being itself far more active than most of the other metals, 
 sodium is capable of displacing the latter from their com- 
 pounds just as it displaces hydrogen from water. For 
 
SODIUM CHLORIDE 
 
 179 
 
 example, metallic aluminium is formed when aluminium 
 chloride and metallic sodium are heated together. The so- 
 dium takes the chlorine away from the aluminium, whereby 
 sodium chloride is formed. Likewise, sodium can remove 
 the oxygen from the oxide of any less active metal. 
 
 COMPOUNDS OF SODIUM 
 
 189. Sodium Chloride, or Common Salt, NaCl. Besides 
 being the chief source of chlorine, common salt is also the 
 chief source of sodium. Salt also is as useful a substance 
 as it is abundant. The human blood contains 0.8 per cent 
 of sodium chloride. 
 
 Although necessary in small amount in the food, too 
 much salt is harmful and even dangerously poisonous. Ship- 
 wrecked sailors perish of thirst 
 because they cannot drink salt 
 water. Salt in any quantity 
 is also harmful to the lower 
 organisms that cause putre- 
 faction and decay. Hence the 
 use of salt as a preservative for 
 meats, for fish, for hides, etc. 
 
 Salt is easily soluble in cold 
 water, but, unlike most sub- 
 stances, it is but slightly more 
 soluble in hot water. When 
 the water of the solution is 
 evaporated, the salt crystallizes 
 in cubical crystals. These 
 
 FIG. 32. Hopper-shaped Salt Crystals. 
 
 crystals when perfect are true 
 
 cubes, but it is seldom that the faces are evenly developed. 
 
 We frequently find the salt growing in hopper-shaped crys- 
 
180 SODIUM 
 
 tals. Figure 32 shows the formation of an idealized hopper 
 crystal. 
 
 190. Sodium Bicarbonate, or Baking Soda, NaHCO 3 . 
 This substance has been mentioned in the chapter on carbon 
 dioxide (pages 59 and 61) as the material which is used to 
 supply that gas in fire extinguishers and in baking powder. 
 The sodium which sodium bicarbonate contains is derived 
 from sodium chloride ; the carbon dioxide may be obtained 
 by heating limestone (see page 51, also see next chapter). 
 
 The process of manufacturing sodium bicarbonate is 
 carried out as follows : A saturated solution of sodium chlo- 
 ride containing about 36 grams of sodium chloride to 100 
 grams of water is first prepared. This is saturated with 
 ammonia and then carbon dioxide is passed into it. Sodium 
 bicarbonate, which is sparingly soluble, thereupon precipi- 
 tates out in the solid form, and after it is drained, washed, 
 and dried, it is ready to be marketed. 
 
 The reactions occurring in this process are of interest. 
 First, ammonia unites with water to form ammonium hy- 
 
 Ammonium hydroxide is a base, and bases are exactly op- 
 posed in chemical nature to acids. 
 
 Next, carbon dioxide dissolves and reacts with water to 
 form the weak carbonic acid. It is characteristic of bases 
 and acids that they mutually neutralize each other and 
 thereby form a salt and water. Thus the carbonic acid is 
 neutralized by the ammonium hydroxide : 
 
 H(HC0 3 ) + (NH 4 )OH->(NH 4 )(HC0 3 ) + H 2 O 
 
 and the salt ammonium bicarbonate is formed. 
 
 Now this salt and sodium chloride are both fairly soluble 
 
SODIUM BICARBONATE 181 
 
 in water. Any two salts in solution are capable of inter- 
 changing their component parts, or radicals. These two may 
 interchange in this way, whereby ammonium chloride and 
 sodium bicarbonate are formed. If both of these new salts 
 were as soluble as the former, no change would be seen by an 
 observer, but in fact the sodium bicarbonate is only sparingly 
 soluble and hence it precipitates out as a powdery solid. 
 
 (NH 4 )(HCO 3 ) + NaCl-^Na(HCOa) | + (NH 4 )C1. 
 
 The arrow pointing downward signifies that the substance 
 precipitates. 
 
 This process is called the Solvay process, and it is carried 
 on extensively at Syracuse, New York, where an abundant 
 supply of concentrated brine is supplied by salt wells. The 
 amount of salt drawn from the wells amounts to several 
 hundred tons, daily. 
 
 In order for this process to be possible from a commercial 
 standpoint, it is necessary to work up the ammonium chlo- 
 ride left in the solution so that all of the ammonia may be 
 recovered from it and used over again in the process. 
 
 Sodium bicarbonate is easily decomposed by heat and 
 it gives off some carbon dioxide if thrown into boiling 
 water. It is completely decomposed by acids so that a 
 large amount of carbon dioxide is evolved. On this prop- 
 erty depends the use in baking powders and fire extinguish- 
 ers. When decomposed by the acid, it in turn neutralizes 
 the acid. Thus sodium bicarbonate is a good deal used to 
 neutralize acids where it is essential not to use any substance 
 which on its own part is corrosive. For example, it is used 
 to relieve burns on the flesh, as an eyewash when the eyes 
 are inflamed and develop an acidity, and internally as a 
 corrective for sour stomach. 
 
SODIUM CARBONATE 183 
 
 191. Baking Powder. The majority of baking powders 
 contain sodium bicarbonate, together with some mildly acid 
 solid substance such as cream of tartar, or calcium acid 
 phosphate, or alum. On wetting the mixture immediate 
 reaction results, whereby a large volume of carbon dioxide is 
 released. If the powder has been previously well blended 
 with the flour the carbon dioxide is scattered throughout 
 the loaf and leavens it. Some other harmless product always 
 remains in the dough. In the case of a cream of tartar pow- 
 der, potassium sodium tartrate (Rochelle salt) is the product, 
 as is shown by the following equation for the reaction 
 between cream of tartar and bicarbonate of soda. 
 
 NaHC0 3 + KH(C 4 H 4 6 ) -^KNa(C 4 H 4 O 6 ) + CO 2 + H 2 O. 
 
 Cream of tartar Rochelle salt 
 
 192. Sodium Carbonate, or Washing Soda, Na 2 CO 3 . A 
 
 large quantity of the sodium bicarbonate manufactured by 
 the Solvay process is used as such, but a far greater quantity 
 is converted into sodium carbonate, Na 2 COs. On heating, 
 the bicarbonate decomposes into the carbonate while water 
 vapor and carbon dioxide are evolved. 
 
 2 NaHC0 3 -+ NaaCOs + H 2 O f + CO 2 f 
 
 The arrows pointing upward indicate that the substances 
 escape as gases. The carbon dioxide thus freed is returned 
 into the Solvay process for the conversion of more sodium 
 chloride into bicarbonate. 
 
 Sodium carbonate is also called washing soda because this 
 name describes one of its important household uses. 
 
 Sodium carbonate acts as a mild alkali, one indication of 
 this being that it colors litmus blue in distinction to acids, 
 which color it red. The use of sodium carbonate for cleans- 
 ing purposes depends on its alkaline character, for alkalies 
 
184 SODIUM 
 
 possess the power of loosening grease and dirt and thus allow- 
 ing of their removal with water. Sodium carbonate is suffi- 
 ciently alkaline for the purpose and yet not so alkaline as 
 to injure seriously the flesh or fabrics or woodwork. Caustic 
 soda, on the other hand, is too powerful an alkali to use in 
 cleaning, for besides removing dirt, it attacks the flesh 
 strongly and it disintegrates woolen fabrics and wood. 
 
 The alkaline character of sodium carbonate is further 
 exhibited in its power to neutralize acids. Except for very 
 delicate neutralizations, it is used for this purpose more 
 extensively than sodium bicarbonate. Its action is similar 
 to that of the latter, in that a neutral salt, water, and carbon 
 dioxide are formed. 
 
 NajCOs + H 2 SO 4 ->- Na 2 SO 4 + H 2 O + CO 2 . 
 
 But it will be noticed on comparing the reactions that only 
 one half as much carbon dioxide escapes for the same amount 
 of acid neutralized. 
 
 Sodium carbonate has a multitude of industrial uses which 
 for the most part depend on its alkalinity and its ability to 
 neutralize acids. Enormous quantities also are used to 
 manufacture sodium hydroxide or caustic soda, in the manu- 
 facture of soap, and in the manufacture of glass. 
 
 193. Soda Crystals, Na 2 CO 3 -io H 2 O. Much of the 
 sodium carbonate of commerce is put on the market as a dry 
 powder of the formula Na 2 CO 3 . But another large part is 
 sold as so-called soda crystals which consist in fact of trans- 
 parent crystals which contain ten molecules of water in addi- 
 tion to the sodium carbonate proper, as is indicated in the 
 above formula. 
 
 When a solution of sodium carbonate in water is allowed 
 to crystallize at a low temperature, the solid that separates 
 
SODIUM HYDROXIDE, OR CAUSTIC SODA 185 
 
 contains ten moles of water for each formula weight of sodium 
 carbonate. This is regarded as a true chemical compound, 
 for it always contains sodium carbonate and water in exactly 
 the same proportions. Furthermore, the crystals are totally 
 different in structure from anhydrous sodium carbonate 
 (that is, Na 2 CO 3 without water) or from ice (that is, crystal- 
 lized water). The chemical affinity binding the water and 
 the sodium carbonate together is, however, much weaker than 
 that which holds the hydrogen and oxygen together in water, 
 or the sodium, carbon, and oxygen in the sodium carbonate. 
 That the water is bound very loosely to the salt in the 
 crystals is shown by the fact that it can all be driven off with 
 very gentle heating, thus leaving the salt anhydrous. In 
 fact, this decomposition takes place slowly even at ordinary 
 temperatures, and the crystals crumble to a white powder 
 consisting of the more or less dehydrated substance. 
 
 194. Crystal Hydrates and Efflorescence. When crystals 
 of this type decompose spontaneously in this way, they are 
 said to effloresce (literally to bloom) because the powder 
 frequently resembles masses of snowy blossoms. 
 
 Water held in combination with a salt in crystal form is 
 known as water of crystallization. Such salts are called crystal 
 hydrates. A great many salts besides sodium carbonate 
 possess the power of thus taking on water of crystallization. 
 
 195. Sodium Hydroxide, or Caustic Soda, NaOH. This 
 substance is obtained in the solution when metallic sodium 
 reacts with water and displaces one half of the Iwdrogen. 
 It is made commercially by the electrolysis of sodium chloride 
 solution. Probably the largest part of the sodium hydroxide 
 used is made by causticizing sodium carbonate. 
 
 In the last-mentioned method, the source of the sodium is 
 sodium carbonate and that of the hydroxide radical is cal- 
 
186 SODIUM 
 
 cium hydroxide (see next chapter). The success of this 
 method depends on the fact that the unwished-for con- 
 stituents, that is, the carbonate radical and the calcium, form 
 together a very insoluble substance, calcium carbonate, 
 which precipitates, and thus can be separated from the sodium 
 hydroxide remaining in solution : 
 
 Na 2 C0 3 + Ca(OH) 2 -> CaCO 3 | + 2 NaOH. 
 
 To carry out the process, a solution of sodium carbonate is 
 thoroughly mixed with calcium hydroxide. The precipitate 
 is allowed to settle and the clear liquor containing the sodium 
 hydroxide is drawn off. This liquor is boiled in iron pots 
 until all the water is driven off, when pure sodium hydroxide 
 is left as a melted substance. This is then poured off into 
 molds or into large iron drums, in which it solidifies. 
 
 Sodium hydroxide is a white solid substance which is 
 extremely soluble in water. It melts very easily at a tem- 
 perature below a visible red heat. It has a great attraction 
 for water, as is shown by the experiment of leaving a small 
 lump of sodium hydroxide exposed to the air. The surface 
 of the lump almost immediately becomes moist and soon the 
 whole lump appears to liquefy. The sodium hydroxide 
 dissolves in the water which it absorbs from the atmos- 
 phere. Moist sodium hydroxide also absorbs carbon dioxide 
 with great avidity and thereby forms sodium carbonate. 
 
 2 NaOH + CO 2 ->Na 2 CO 3 + H 2 O. 
 
 Thus if a lump of sodium hydroxide is left exposed for a long 
 time to the air, it is ultimately all changed to carbonate be- 
 cause the air contains a minute amount of carbon dioxide - 
 much less, however, than it does of water vapor. 
 
 In Chapter IV, the experiment of absorbing the products 
 
SODIUM NITRATE 187 
 
 of burning a candle by means of sticks of caustic soda 
 placed in a lamp chimney was described. It is now obvious 
 that this absorption takes place because the combustion 
 products consist entirely of water vapor and carbon dioxide. 
 Great quantities of sodium hydroxide are used in the 
 industries wherever a very strong alkali is required ; especially 
 is it used in soap making, in petroleum refining, and in 
 preparing coal-tar products. 
 
 196. Sodium peroxide, Na 2 O 2 , is made by burning metallic 
 sodium in the air. It is itself a powerful oxidizing agent, for 
 it contains twice as much oxygen as the ordinary oxide, 
 Na 2 O, and the extra oxygen is given up with ease to oxidizable 
 substances. Sodium peroxide yields hydrogen peroxide 
 when it is treated with an acid. 
 
 Na 2 O 2 + H 2 SO 4 ->Na 2 SO 4 + H 2 O 2 . 
 
 Hydrogen peroxide is useful as an oxidizing agent in general 
 and particularly as an antiseptic and as a bleaching agent 
 for silk and wool. 
 
 A convenient method for preparing oxygen in the labo- 
 ratory is to treat sodium peroxide with water. Probably 
 hydrogen peroxide is first formed and then decomposed into 
 water and oxygen by the high temperature resulting from 
 the heat of the reaction. 
 
 197. Sodium Nitrate, NaNO 3 Chili Saltpeter. This 
 compound of sodium is found in immense deposits in Chili 
 in South America. It is a valuable fertilizer furnishing 
 nitrogen in a soluble form, and hence readily available for 
 plant food. Sodium nitrate is also the raw material from 
 which most of the nitric acid of commerce is made. 
 
 198. Flame Test for Sodium. Sodium is remarkable for 
 the intense pure yellow light which the vapor of the metal 
 
188 
 
 SODIUM 
 
 FIG. 34. Packing Sodium Nitrate in Chili. 
 
 or of its compounds imparts to a flame. When a clean plati- 
 num wire is held in the colorless flame of a Bunsen burner, no 
 effect is noticed. If the wire is dipped into a solution of so- 
 dium chloride or any sodium compound and then held in the 
 flame, the latter is colored intensely yellow. The minutest 
 trace of sodium causes this coloration, and so this flame test is 
 valuable as a means of detecting the presence of this element. 
 
 199. Potassium is an element which is extremely like 
 sodium. In fact, all that we have said about sodium would 
 apply almost equally well for potassium. Potassium is 
 even a little more active than sodium ; it decomposes water 
 with even more violence. 
 
 200. Natural Occurrence of Sodium and Potassium. All 
 of the simple compounds of both sodium and potassium are 
 easily soluble in water. Hence sodium chloride is found in 
 
GLASS 
 
 189 
 
 such abundance in sea water. The rain washes it from the 
 land into the sea. Sea water contains potassium salts also 
 but in much smaller amount. Many rocks contain both 
 sodium and potassium. For example, the minerals feldspar 
 and mica contain either one or both of these metals in the 
 form of double sili- 
 cates with alumin- 
 ium. As the rocks 
 slowly disintegrate 
 under the action of 
 the frost, the rain, 
 and the carbon 
 dioxide of the air, 
 the potassium and 
 sodium become 
 
 FIG. 35. Results of Using Potassium Salts as 
 Fertilizer. A, fertilized with 200 Ib. Muriate of 
 Potash per acre ; yield per acre, 73.4 bushels. 
 B, without fertilizer ; yield per acre, 32.1 bushels. 
 These experiments were conducted side by side on 
 soil containing otherwise sufficient plant food. 
 
 washed out as solu- 
 ble carbonates. On percolating through the soil these salts 
 become changed before long into nitrates or chlorides of the 
 metals. Potassium salts are essential to the growth of 
 plants, and much of the potassium thus washed from the dis- 
 integrated rocks is taken from the soil by the roots of plants. 
 On the other hand, the greater part of the sodium is washed 
 on into the ocean. 
 
 201. Glass. Sodium and potassium are essential con- 
 stituents of glass, which is a double silicate of either sodium or 
 potassium on the one hand and of calcium Or lead on the other 
 hand. Common window glass, for example, is a sodium 
 and calcium silicate of approximately the composition, 
 
 Glass is comparatively easy to melt as compared with most 
 natural silicates, and when it cools, it remains transparent 
 
190 SODIUM 
 
 while it hardens. Like feldspar, mica, and other natural 
 silicates, glass is almost insoluble in water, but it must be 
 remembered that glass, too, like them, is a complex com- 
 pound, whereas all of the simple compounds of both sodium 
 and potassium are comparatively very soluble. 
 
 SUMMARY 
 
 Common salt is composed of chlorine and sodium, the former a 
 non-metal, the latter a metal. 
 
 Metallic sodium is obtained by the electrolysis of sodium chloride, 
 or better, by electrolysis of sodium hydroxide. 
 
 Properties of Sodium. Sodium differs from the more common 
 metals in that it is far more active. It unites with all non- 
 metals. It displaces hydrogen from water and metals from 
 their compounds. Sodium is very soft ; it is light in weight, 
 and it melts below the boiling point of water. It possesses, 
 however, metallic luster and conductance for electricity, 
 which are properties that belong to all metals. 
 
 Important compounds of sodium are: sodium chloride, NaCl, a 
 neutral salt ; sodium bicarbonate, NaHCO 8 , a compound which 
 finds use in neutralizing acids and in the production of carbon 
 dioxide; sodium carbonate, Na 2 C0 3 , a salt which is mildly 
 alkaline and used as a washing powder ; sodium hydroxide, 
 NaOH, which is very strongly alkaline; sodium peroxide, 
 Na 2 2 , which is a strong oxidizing agent and a source of 
 hydrogen peroxide; and sodium nitrate, NaN0 3 , a valuable 
 fertilizer and source of nitric acid. Baking powders usually 
 contain sodium bicarbonate, together with some mildly acid 
 solid substance such as cream of tartar. 
 
 Potassium is a metallic element extremely like sodium in properties. 
 It is more active than sodium. 
 
 All simple compounds of sodium and potassium are easily soluble 
 in water. These elements, however, are essential constitu- 
 ents of glass and of minerals like feldspar and mica, which 
 are practically insoluble, but in many years the slow weather- 
 ing of rocks does wash out the salts of sodium and potassium. 
 
QUESTIONS 191 
 
 Questions 
 
 1. Why is common salt rather than some other naturally oc- 
 curring compound used to prepare sodium compounds? 
 
 2. Explain the use of baking soda in connection with sour milk 
 in raising dough. 
 
 3. Which would be more economical to buy, washing soda 
 that had stood in an open barrel for a month, or freshly opened 
 washing soda ? Why ? 
 
 4. Why are soda crystals regarded as a compound rather than 
 as a mixture of sodium carbonate and water? 
 
 5. How could you make caustic soda, using washing soda as 
 the source of the sodium? 
 
 6. How is metallic sodium protected from the action of the air? 
 
 7. What changes are seen when a bit of sodium is left for a long 
 time exposed to the air ? Give equations for chemical changes and 
 explain the physical changes involved. 
 
 8. In a hollow in a large rock near the ocean, some small cube- 
 shaped crystals were found. What substance had probably crys- 
 tallized there ? 
 
 9. What substance studied in this chapter might be used to 
 dry gases ? 
 
 10. Why is sodium carbonate used to scrub dirty floors? Why is 
 sodium hydroxide not used instead ? 
 
 11. Why is sodium bicarbonate to be preferred to sodium car- 
 bonate for use in fire extinguishers ? 
 
 12. What weight of metallic aluminium could be prepared by 
 using 1 kilogram of sodium according to the reaction: 
 
 3 Na + AlCl 3 ->3 NaCl + Al? 
 
 13. Glass is made by melting together sodium carbonate, lime- 
 stone, CaCO 3 , and pure sand, Si02, the reaction being approximately 
 
 Na 2 C0 3 + CaC0 3 + 6 Si0 2 -> Na 2 - CaO 6 Si0 2 + 2 CO 2 . 
 What weights of materials would be taken to make 1000 kilograms 
 of glass? 
 
 14. How many cubic meters of carbon dioxide would escape from 
 the melting pot in Question 13 ? 
 
 B. AND W. CHEM. 13 
 
CHAPTER XVIII 
 
 CALCIUM 
 
 SODIUM and potassium in the uncombined or metallic 
 state are unfamiliar in everyday life, but in their compounds 
 these elements are abundant and necessary to the welfare of 
 mankind. Calcium is a metal that is like sodium and potas- 
 sium in these respects as well as in many others. It is never 
 found uncombined in nature, and in the metallic form it is 
 not much more than a laboratory curiosity. 
 
 Calcium salts are found in sea water in very small quantity ; 
 they are found, too, in appreciable although small quantities 
 in spring and river waters, especially those that are known as 
 hard waters. Calcium is an even more abundant constit- 
 uent of the rocks of the earth's surface than sodium or potas- 
 sium. Limestone and marble, which are both calcium car- 
 bonate, CaCO 3 , gypsum, which is hydrated calcium sulphate, 
 CaSO 4 2 H 2 O, and phosphate rock, which is mainly calcium 
 phosphate, Ca 3 (PO 4 ) 2 are our most important natural com- 
 pounds of calcium. 
 
 202. Preparation of Calcium. Metallic calcium can be 
 obtained in much the same manner as metallic sodium. The 
 electric current is passed through molten calcium chloride, 
 which melts more easily than sodium chloride, and the metal 
 is set free at the negative pole while the chlorine as usual is 
 liberated at the positive pole. 
 
 203. Physical Properties. Metallic calcium is silver- 
 white, and like all metals it has a metallic luster and conducts 
 
 192 
 
CALCIUM CHLORIDE 193 
 
 electricity. It is harder, heavier, and tougher than sodium. 
 It is about as hard as zinc ; it is about one and one half times 
 as heavy as water and thus it is light in comparison with iron, 
 zinc, or copper; it is somewhat malleable and extremely 
 tough. 
 
 204. Chemical Properties. Calcium is less active than 
 sodium or potassium, but it is still an extremely active metal. 
 This accounts for its never being found free in nature. Cal- 
 cium is not much attacked by dry air at the ordinary tem- 
 perature ; in moist air, however, it is attacked quite rapidly. 
 When heated, it catches fire and burns with intense heat, 
 forming, in the main, the oxide CaO, but there is always a 
 little nitride formed as well. When heated in pure nitrogen, 
 calcium forms the nitride very readily. This nitride, how- 
 ever, will catch fire when heated in air and burn to the oxide. 
 
 Calcium reacts with cold water and liberates hydrogen : 
 
 Ca + 2 HOH-^Ca(OH) 2 + H 2 . 
 
 This reaction is far less violent than the similar action of 
 sodium, which, of course, is to be expected if calcium is a less 
 active metal than sodium. Furthermore, calcium hydroxide 
 is rather insoluble and is inclined to adhere to the metal 
 surface, thus impeding the reaction with the water. Like 
 sodium, calcium combines with all the non-metallic elements, 
 but with considerably less violence in each case. 
 
 COMPOUNDS OF CALCIUM 
 
 205. Calcium Chloride, CaCl 2 , is an extremely soluble 
 substance. It is left in solution in the carbon dioxide gen- 
 erator in which hydrochloric acid acts on calcium carbonate. 
 Calcium chloride is not found extensively in nature. A 
 very small amount is found in sea water ; but large quantities 
 
194 CALCIUM 
 
 of it are obtained in chemical factories as by-products, just 
 as it is left as a by-product in the generation of carbon dioxide. 
 One of the chief uses of calcium chloride is in non-freezing 
 solutions. It is, as stated, extremely soluble in water and a 
 concentrated solution of it freezes at a temperature far below 
 the freezing point of pure water. Hence calcium chloride 
 solution is much used as a liquid to circulate in the cooling 
 pipes of refrigerating plants. 
 
 206. Deliquescence. Calcium chloride is not only very 
 soluble in water but it has a strong attraction for water. To 
 illustrate this point, leave a few small lumps of calcium chic- 
 ride exposed to the air on a watch glass. Soon the lumps are 
 seen to be growing moist, and before long they have liquefied 
 
 FIG. 36. Calcium Chloride Drying Tube. 
 
 altogether. They have absorbed water vapor from the air 
 and dissolved in the water so condensed. Such action is 
 called deliquescence. This property suggests an important 
 laboratory use for calcium chloride, namely, to dry gases. 
 Some of this substance in granulated form (A) is placed in 
 the center of a wide tube (drying tube) between two plugs of 
 cotton (B) to keep it in place (Fig. 36). The gas to be dried, 
 for example the hydrogen generated by the action of zinc 
 on hydrochloric acid solution, and consequently nearly sat- 
 urated with water vapor, is passed through this tube of 
 calcium chloride and emerges practically free of water 
 vapor. 
 
CALCIUM CARBONATE 
 
 195 
 
 207. Calcium Carbonate, CaCO 3 . This substance is 
 found in nature in rocks of widely differing appearance. 
 Iceland spar is the 
 purest form. This 
 is crystalline and as 
 transparent as glass. 
 
 Marble is a very 
 pure form, and it is 
 beautifully white in 
 consequence of its 
 being composed of 
 a mass of tiny crys- 
 tals cemented to- 
 gether. The mass 
 of crystals presents 
 a dazzling white 
 appearance for the 
 same reason that snow does, snow consisting of a lot of tiny 
 ice crystals. A compact block of ice is colorless and trans- 
 parent like Iceland spar. 
 
 Limestone is the most abundant, although the least at- 
 tractive, form of calcium carbonate. It shows less marked 
 crystalline structure than marble, and it is usually of a dirty 
 gray color. 
 
 The origin of limestone from the shells of sea animals of a 
 previous age has been discussed under the subject of carbon 
 dioxide. Limestone serves as the chief source of calcium 
 compounds as well as an important source of carbon dioxide, 
 for when it is heated, oxide of calcium is left as a solid, while 
 the carbon dioxide escapes : 
 
 FIG. 37. Iceland Spar, 
 
 CO 2 \. 
 
196 CALCIUM 
 
 208. Calcium Oxide, or Quicklime, CaO. The decomposi- 
 tion of calcium carbonate by heat may be shown on a small 
 scale if a little powdered marble is heated in a crucible in 
 a Bunsen flame. That carbon dioxide is given off may be 
 shown by introducing a drop of limewater suspended on a 
 glass rod into the crucible. This is at once clouded and much 
 more strongly than it would be by the gases coming from the 
 flame alone. It is clouded but slowly when held in the same 
 way in an empty crucible which is heated over a similar flame. 
 
 The residue is still a powder, but it no longer shows the 
 glint of the crystal grains of the marble ; it has a uniformly 
 dull appearance. That it is different chemically from the 
 original marble may be shown by barely wetting it with a 
 few drops of water. If one observes carefully, it is noticed 
 that considerable heat is produced. The effect may be better 
 observed if a large lump of quicklime, that is, the commercial 
 calcium oxide obtained by heating limestone in kilns, is dipped 
 into water and then taken out. The lime is porous, and 
 soaks up a good deal of water. Soon it is noticed that the 
 lump is growing warm and a little later clouds of steam 
 issue and the lump cracks and expands and finally falls 
 to a fluffy white powder. 
 
 If some of this powder, or the powder left in the crucible, 
 is wet with a little more water and placed on a piece of lit- 
 mus paper, it colors the latter blue. This shows that the 
 substance is alkaline. Now marble does not interact at all 
 with water, and it has not the property of turning litmus blue. 
 
 The burning of limestone to make quicklime is an enor- 
 mous industry, and rows of lime kilns are a familiar sight in 
 the regions of limestone quarries. Large lumps of limestone 
 are packed in the kilns, where they are heated for a number 
 of hours either by being mixed with the burning fuel or, 
 
CALCIUM HYDROXIDE, OR SLAKED LIME 
 
 197 
 
 limestone 
 
 better, by being subjected to the heat of the hot gases from 
 the fire. The product is 
 the quicklime of com- 
 merce. It is usually 
 packed in barrels for 
 shipment, but it is very 
 important that the bar- 
 rels be kept dry. If the 
 lime gets wet, not only 
 is its usefulness impaired 
 but there is grave danger 
 of fire, for the reaction 
 with water may develop 
 heat enough to set the 
 wood of the barrel on fire. 
 Calcium oxide is very 
 infusible, and thus lime 
 finds a use in making 
 crucibles and in lining 
 furnaces for very high tern- 
 perature work. Its use 1> F ': 38 'T* "?. ?" ,. Tho t TCrtic , a ' 
 
 shait is packed with broken limestone. At 
 in the SO-called limelight regular intervals, the charge is replenished 
 
 is particularly interesting. with fresh ^stone at the top, as the 
 
 quicklime is taken out from the bottom. 
 
 Here the flame of an oxy- 
 
 hydrogen blowpipe is directed upon a block of lime which be- 
 comes intensely hot without melting and thus emits a brilliant 
 white light. 
 
 209. Calcium Hydroxide, or Slaked Lime, Ca(OH) 2 . The 
 reaction of quicklime with water, 
 
 CaO + H 2 0->Ca(OH) 2 , 
 yields calcium hydroxide, which is ordinarily known as slaked 
 
198 CALCIUM 
 
 lime. Calcium hydroxide is slightly soluble in water, and 
 as we have seen, the solution colors litmus blue, showing 
 that it is alkaline. When slaked lime is stirred with water 
 a saturated solution of calcium hydroxide is obtained, and 
 if then the undissolved substance is allowed to settle, the 
 clear solution may be siphoned off. This is known as lime- 
 water. Limewater is very useful on account of its mild 
 alkalinity, and it is frequently mixed with the food of infants 
 and invalids to counteract a sour or acid condition of the 
 stomach. The use of lime water in testing for carbon dioxide 
 has already been mentioned. 
 
 When slaked lime is agitated with water, only a little of 
 the calcium hydroxide actually dissolves; the rest, which 
 is very light and flocculent, becomes suspended in the liquid. 
 Such a suspension is known as milk of lime because it has 
 the appearance of milk. Common whitewash is nothing 
 more than milk of lime. 
 
 Slaked lime finds, perhaps, its largest application in'making 
 mortar and plaster. Lime is mixed with enough water to 
 slake it and leave it as a thin paste. Sand is then put in to 
 give it body, and often hair is added in order to sustain the 
 weight of the plaster until it hardens. After the plastic 
 mass has been put in place with a trowel, it soon sets or 
 hardens and makes a permanent part of the masonry or of 
 the plastering of houses. The setting is due first to the 
 drying out of the surplus water of the mixture, but the 
 permanent setting is largely caused by a chemical reaction 
 with the carbon dioxide of the air, 
 
 Ca(OH) 2 + CO 2 ->CaCO 3 + H 2 O, 
 
 by which calcium carbonate is formed. Thus the plaster 
 finally becomes chemically the same substance as the lime- 
 
CALCIUM BICARBONATE 199 
 
 stone from which it was originally derived. In consequence 
 of the small amount of carbon dioxide in the air and the 
 slowness with which it can penetrate the mass of the plaster, 
 the change from calcium hydroxide to calcium carbonate is 
 almost never complete, the internal portions of the plaster 
 remaining unchanged for many years. The water that is 
 liberated during the setting of plaster is largely responsible 
 for the dampness of the air in new buildings. Sometimes 
 the setting of plaster is hastened by burning wood in stoves 
 in new houses ; the heat serves to help circulate the air and 
 thus to more rapidly dry out the plaster, and the carbon 
 dioxide from the fire, if allowed to escape into the air of the 
 building, hastens the change of the slaked lime into calcium 
 carbonate. 
 
 210. Water-slaked and Air-slaked Lime. Unless lime is 
 preserved in hermetically sealed containers, a thing which 
 it is practically impossible to do, lime must be used before it 
 has stood too long because it is all the time deteriorating 
 through action with the components of the air. In the first 
 place, it reacts with the water vapor and slowly forms cal- 
 cium hydroxide ; then the calcium hydroxide reacts with the 
 carbon dioxide and ultimately changes to calcium carbonate. 
 Lime which has thus been kept too long has become air 
 slaked. It then refuses to slake properly with water ; that 
 is, it fails to heat up strongly and fall to the powdery calcium 
 hydroxide that we know as water-slaked lime. 
 
 211. Calcium Bicarbonate. A very interesting experi- 
 ment which shows an important property of calcium bicar- 
 bonate is to blow the breath from the lungs through a glass 
 tube into a test tube of lime water. As already seen (page 
 52), a turbidity is quickly produced, due to a precipitate of 
 calcium carbonate formed from the carbon dioxide of the 
 
200 
 
 CALCIUM 
 
 breath and the calcium hydroxide of the limewater. But 
 on persistently blowing the breath into the limewater, a 
 surprising thing occurs; the turbidity disappears and we 
 again obtain a clear solution. 
 
 This result is due to the formation of calcium bicarbonate, 
 Ca(HCO 3 ) 2 , a substance which is more soluble than calcium 
 carbonate. After the calcium carbonate has all precipitated, 
 the excess of carbon dioxide forms a weak solution of carbonic 
 acid, and this reacts with the calcium carbonate : 
 
 H 2 CO 3 + CaCO 3 ->Ca(HC0 3 ) 2 . 
 
 An effect that is often seen on the marble shelves of soda 
 fountains may be accounted for in the same way ; namely, 
 
 where the carbon- 
 ated water drips 
 upon the marble a 
 hollow is in time 
 eaten away, due to 
 the solvent action of 
 the carbonic acid 
 and the formation 
 of calcium bicar- 
 bonate. 
 
 A similar phe- 
 nomenon occurs in 
 limestone regions in 
 the earth. Water 
 which percolates 
 through the surface 
 soil in wooded re- 
 gions becomes nearly 
 
 FlG. 39. Stalactites and Stalagmites in Mammoth 
 
 Cave saturated with car- 
 
HARD WATER 201 
 
 bon dioxide from the decaying vegetation; and when it 
 flows through limestone, it slowly dissolves away the rock. 
 Thus in the course of ages immense caverns are sometimes 
 hollowed out. The famous Mammoth Cave of Kentucky 
 is supposed to have been formed in this way. 
 
 212. Calcium Sulphate. This salt of calcium occurs in 
 nature in the hydrated form as the mineral gypsum, CaSO 4 - 
 2 H 2 O. Alabaster, which is used for fine vases and other 
 ornamental purposes, is one of the natural forms of hydrated 
 calcium sulphate. Calcium sulphate is also present in hard 
 waters and in sea water, although it is but sparingly soluble. 
 Plaster of Paris is made by partially dehydrating gypsum. 
 
 2 CaSO 4 2 H 2 O -> 3 H 2 O f + (CaSO 4 ) 2 H 2 O. 
 
 The reverse reaction takes place when the plaster is mixed 
 with water and " setting " of the plaster results. The set- 
 ting of cement, although much more complicated chemically 
 than the setting of plaster of Paris, consists in the main in a 
 similar addition of water to the finely powdered anhydrous 
 material. 
 
 213. Hard Water. Water which contains calcium bi- 
 carbonate, or calcium sulphate, or in fact any soluble salt of 
 calcium or magnesium, is said to be hard. Such water does 
 not readily yield lather with soap, and if it is used in steam 
 boilers, a deposit of mineral matter known as boiler scale is 
 formed inside of the tubes to the great injury of the boilers. 
 
 214. Softening Hard Water. There are a good many 
 kinds of soap, but for the purpose of discussing its action 
 with hard water, we may regard soap as consisting of 
 sodium stearate, NaCi 8 H 35 O 2 . Now sodium stearate is 
 soluble in water, but calcium and magnesium stearates 
 are not soluble. Therefore when soap is used with hard 
 
202 
 
 CALCIUM 
 
 water a precipitate of calcium or magnesium stearate is 
 thrown down : 
 
 2 NaCi 8 H 35 O 2 + Ca(HCO 3 ) 2 -* Ca(Ci 8 H 35 2 ) 2 | + 2 NaHC0 3 . 
 
 Any one who has tried to wash his hands with hard water 
 and soap knows of the dirty sediment which collects in the 
 wash basin. 
 
 Of course the amount of calcium and magnesium com- 
 pounds in hard water is limited, and enough soap can be 
 taken to react with all the hardness. After this, any addi- 
 
 FlG. 40. Settling Tanks, Water Softening Process. 
 
 tional soap forms lather freely. In laundries where a great 
 deal of water is used, it would become a matter of consider- 
 able expense to depend upon soap to soften the water in this 
 way. 
 
 It becomes necessary, therefore, to soften hard waters 
 before they can be used in laundries or in steam boilers. If, 
 as is very often the case, the hardness is caused by calcium 
 bicarbonate alone, the method of softening is comparatively 
 
VALENCE 203 
 
 simple. Calcium bicarbonate is very unstable, and is en- 
 tirely broken up at the boiling temperature of water : 
 Ca(HCO 3 ) 2 ->CaCO 3 1 + H 2 O + CO 2 f. So if the water is 
 first heated, all of the calcium will be thrown down as in- 
 soluble calcium carbonate, and the water, which is now soft, 
 may be used in the laundries or pumped into steam boilers. 
 Hardness caused by calcium bicarbonate is known as tem- 
 porary hardness because it can be so easily overcome by 
 heating. 
 
 Permanent hardness can be remedied by adding chemical 
 reagents which will precipitate the calcium and magnesium 
 compounds. For example, if the hardness is caused by cal- 
 cium sulphate, the addition of sodium carbonate will pre- 
 cipitate calcium carbonate, and leave the soluble but harm- 
 less sodium sulphate in solution : 
 
 CaSO 4 f Na 2 CO, -> CaCO 3 1 + Na 2 SO 4 . 
 
 This method is largely used in practice. 
 
 Either type of hardness can be removed by distillation, 
 the involatile mineral substances remaining behind when 
 the water evaporates. This last method, however, is too 
 costly for extensive use, and is only employed when limited 
 amounts of very pure water are necessary. 
 
 215. Valence. The pupil has doubtless wondered why 
 the formula of sodium chloride is written NaCl and that of 
 calcium chloride CaCl 2 ; that of water *H 2 O and that of 
 hydrogen chloride HC1. Formulas, as we learned in Chapter 
 XV, are used not only to designate substances, but to show 
 their composition. The above formulas tell us, then, that 
 one atom of sodium is combined with a single atom of chlo- 
 rine, whereas one atom of calcium is combined with two atoms 
 of chlorine ; that an atom of oxygen is combined with two 
 
204 CALCIUM 
 
 atoms of hydrogen, whereas an atom of chlorine is combined 
 with but a single atom of hydrogen. 
 
 Clearly the number of atoms of another element that one 
 atom of a given element holds in combination is a very im- 
 portant property ; this property has been given the name of 
 valence. The valence of hydrogen in its compounds has been 
 chosen as one for a standard of valence. The valence of 
 chlorine in hydrogen chloride is one because one atom of 
 chlorine is combined with a single atom of hydrogen. The 
 valence of oxygen in water is two because the atom of oxygen 
 is combined with two atoms of hydrogen. The valence of 
 sodium in sodium chloride is one because one atom of sodium 
 is combined with the same amount of chlorine that can 
 combine with one atom of hydrogen. The valence of cal- 
 cium in calcium chloride is two because an atom of calcium 
 is combined with the same number of atoms of chlorine that 
 can combine with two atoms of hydrogen. 
 
 It is to be noted that valence is concerned solely with the 
 number of atoms that an atom of a given element holds in 
 combination. It has nothing whatever to do with whether 
 the other elements are held tenaciously or feebly. 
 
 SUMMARY 
 
 Calcium resembles sodium and potassium in many respects. It is 
 never found in nature as the uncombined metal, but its com- 
 pounds are very abundant and useful to mankind. The metal 
 may be obtained by electrolyzing melted calcium chloride. 
 
 Properties of Calcium. Calcium is a very active metallic element, 
 but it is less active than sodium or potassium. It combines 
 with vigor with all non-metals. It displaces hydrogen from 
 water, although not as vigorously as sodium or potassium. 
 Metallic calcium is about as hard as zinc. It is heavier than 
 sodium, but lighter than most metals. It possesses metallic 
 luster and conducts electricity. 
 
QUESTIONS 205 
 
 Important compounds of calcium are calcium carbonate, CaCOs, of 
 which some of the rock of the earth's surface consists ; cal- 
 cium oxide or quicklime, CaO, which is obtained by strongly 
 heating calcium carbonate; calcium hydroxide or slaked 
 lime, Ca(OH) 2 , which is obtained by the action of calcium 
 oxide with water. 
 
 Quicklime is used for making slaked lime in the preparation of 
 mortar and plaster. The permanent hardening of these 
 materials depends upon their combining with the carbon di- 
 oxide in the air, thus forming calcium carbonate. 
 
 Calcium carbonate reacts with carbonic acid to form calcium bi- 
 carbonate, which is somewhat soluble. In nature, water con- 
 taining carbonic acid slowly dissolves limestone rock and forms 
 caverns. 
 
 Calcium sulphate in a hydrated form occurs in nature as gypsum. 
 Plaster of Paris is" made by partially dehydrating gypsum. 
 
 Hard Waters. Water containing calcium bicarbonate or other 
 soluble calcium or magnesium salts is known as hard water, 
 and it cannot be satisfactorily used in laundries or in steam 
 boilers. Temporary hardness, which is caused by calcium 
 bicarbonate alone, may be remedied by pre-heating. Per- 
 manent hardness can be relieved by chemical treatment or by 
 distillation. 
 
 The valence of an element is a property which depends on the num- 
 ber of atoms of another element which its own atom may hold 
 in combination. The valence of calcium in its compounds is 
 two. 
 
 Questions 
 
 1. Why cannot metallic calcium exist free in nature? 
 
 2. What occurs when marble is strongly heated? 
 
 3. How may lime water be prepared, starting with marble? 
 
 4. Why does a wood fire in a new house aid the setting of the 
 plaster? 
 
 6. Explain the chemistry of limestone cave formation. 
 
 6. Can you offer an explanation of the formation of stalactites 
 (consult a dictionary, if you are not familiar with the meaning of the 
 word) in a limestone cave ? 
 
206 CALCIUM 
 
 7. How might one soften a little hard water in order to obtain 
 a good lather with soap ? 
 
 8. What would be a good way to keep metallic calcium from 
 oxidizing ? 
 
 9. Mention two ways in which sea water might be softened for 
 use in the boilers of a battleship. Which method would give the 
 better drinking water? 
 
 10. What marked difference of behavior on exposure to air might 
 be used to tell whether a certain white solid was sodium carbonate 
 or calcium chloride? 
 
 11. A crystal of gypsum (from which plaster of Paris is made) 
 was heated moderately in a dry test tube. The upper walls of the 
 tube became covered with moisture. The gypsum was dry when 
 first heated. Explain. 
 
 12. What weight of water would be necessary to slake one kilo- 
 gram of quicklime? 
 
 13. What volume of carbon dioxide must be v absorbed by one 
 kilogram of quicklime before it is completely air-slaked? What 
 will be the final weight of the air-slaked lime? 
 
 14. Some hard water contains 0.5 gram of calcium sulphate per 
 liter. How much sodium carbonate should be added to 1000 liters 
 of the water to soften it according to the reaction : 
 
 CaS0 4 + NasCOs-^CaCOa.H- Na 2 S0 4 ? 
 
 15. If the same water were used for washing, what weight of 
 soap would be used up by each liter of the water before a lather 
 could be produced? (See Sec. 214, and use an equation similar 
 to that there given.) 
 
 16. Starting on the basis of the valence of hydrogen as one, what 
 is the valence of each of the elements in the following compounds : 1 
 
 HC1, HBr, H 2 S, NH 3 , CH 4 ; 
 
 H 2 0, CaO, Sn0 2 , S0 3 , OsO 4 , Fe 2 3 , N 2 5 , Mn 2 7 ; 
 
 HC1, AgCl, CuCl 2 , FeCl 2 , FeCl 3 , SnCl 2 , SnCl 4 , PC1 3 , PC1 5 . 
 
 H 2 O, CaO, CaS, Ca 3 N 2 . 
 
CHAPTER XIX 
 
 ACIDS AND BASES; NEUTRALIZATION 
 
 216. Properties of Acids. We have, up to this point, 
 spoken of a few acids ; namely, hydrochloric acid, sulphuric 
 acid, and the very weak acid, carbonic acid, which is obtained 
 when carbon dioxide dissolves in water. These acids, as 
 well as other acids, have a good many properties in common, 
 those properties that we have learned being, first, a sour 
 taste, which is very strong with hydrochloric and sulphuric 
 acids and much weaker with carbonic acid ; second, ability 
 
 , to change the vegetable coloring matter litmus from blue 
 
 > to red; and third, ability to give off hydrogen gas when 
 
 allowed to react with zinc, magnesium, or certain other active 
 
 metals. Carbonic acid is weaker than the other acids, and 
 
 J one ordinarily fails to perceive any escape of hydrogen gas 
 
 on treating this acid with zinc or magnesium. 
 
 217. Characteristic Component of Acids. The one con- 
 stituent which is possessed by all acids is hydrogen, but it is 
 hydrogen in a peculiar condition of combination, because 
 this hydrogen is more or less easily displaced by metals. 
 Water, alcohol, sugar, and petroleum all contain hydrogen, 
 but these substances are not acids, for their hydrogen is not 
 easily displaced by metals like zinc and iron, neither do these 
 substances taste sour nor do they affect the color of litmus. 
 The nature of this peculiar state in which hydrogen exists in 
 acids will be taken up in a later chapter, and now we shall 
 
 B. AND W. CHEM. 14 207 
 
208 ACIDS AND BASES; NEUTRALIZATION 
 
 describe the manner in which a certain large class of acids 
 the so-called oxygen acids, or oxy-acids is formed. 
 
 218. Oxy-acids; Carbon Dioxide and Carbonic Acid. 
 As we have seen, carbon burns in air or oxygen to form 
 carbon dioxide, CO 2 , and the carbon dioxide dissolves to 
 some extent in water, forming the weak acid, carbonic acid. 
 It is believed that carbonic acid is a definite chemical com- 
 pound formed from a molecule each of carbon dioxide and 
 water: CO 2 + H 2 O -^ H 2 CO 3 , 
 
 but this compound, H 2 CO 3 , is so feebly joined together 
 or to use the technical expression, it is so unstable that 
 it can only exist when dissolved in a comparatively large 
 amount of water. As we know, when the pressure is re- 
 leased by removing the cork from a bottle of carbonated 
 water, bubbles of a gas, which is carbon dioxide, commence 
 to escape. The compound, carbonic acid, is breaking down, 
 
 and the reaction TT ^^ ^ TT /^ /^/^ 
 .H 2 ClJ 3 > rl 2 (J -f- l_,U 2 
 
 is taking place ; that is, the reaction of formation is proceed- 
 ing in the reverse direction. 
 
 219. Sulphur Dioxide and Sulphurous Acid. When 
 sulphur burns, a very choking gas is formed, which is sulphur 
 dioxide, SO 2 . This gas dissolves in water much more easily 
 than carbon dioxide, and a more strongly acid solution is 
 produced. The definite compound, sulphurous acid, H 2 SO 3 , 
 is supposed to be formed 
 
 S0 2 + H 2 O->H 2 SO 3 
 
 and to exist in the solution, but, like carbonic acid, it is 
 unstable and readily breaks down again 
 
SULPHUR TRIOXIDE AND SULPHURIC ACID 209 
 
 except when it is dissolved in a large amount of water. 
 Under ordinary pressure and at 20 C. one volume of water 
 will dissolve nearly 40 volumes of sulphur dioxide. The 
 solution so formed is far more strongly acid than that of 
 carbon dioxide, and it smells strongly of sulphur dioxide on 
 account of the continuous slow escape of that gas. 
 
 220. Sulphur Trioxide and Sulphuric Acid. There is an- 
 other oxide of sulphur, sulphur trioxide, SO 3 , which can be 
 prepared if sulphur dioxide is allowed to combine with more 
 oxygen under the right conditions. These conditions will 
 be more fully discussed in the chapter on sulphur. Sulphur 
 trioxide is extremely soluble in water, in fact, this hardly 
 expresses it; the sulphur trioxide has a great chemical 
 affinity for water, as is evidenced by the large amount of 
 heat developed when the two substances come in contact. 
 Indeed, the greatest caution must be exercised in adding 
 sulphur trioxide to water if one would avoid a dangerously 
 violent reaction. 
 
 In this case, there is no doubt of the existence of the definite 
 compound H 2 SO 4 ; for unlike carbonic and sulphurous acids, 
 it can be prepared pure. At a low temperature it can be 
 obtained as a crystalline solid, but at ordinary temperatures 
 it is a thick, oily liquid. It can be proved by chemical anal- 
 ysis to have the composition corresponding to the formula, 
 H 2 SO 4 . The pure substance does not show very marked 
 acid properties, but it mixes freely with water and its fairly 
 dilute solution is very strongly acid. 
 
 221. Phosphorus Pentoxide and Phosphoric Acid. When 
 phosphorus burns with plenty of air, the oxide formed has the 
 composition P 2 O 5 . This oxide combines with the water as 
 
210 ACIDS AND BASES; NEUTRALIZATION 
 
 vigorously as does sulphur trioxide. It forms with the water 
 several clearly defined compounds, but the most important 
 one is the common phosphoric acid, H 3 PO4. 
 
 P 2 O5 + 3H 2 O->2H 3 PO 4 . 
 
 This compound can be prepared pure as a crystalline solid 
 which melts at 37 C. (about the body temperature) to a 
 sirupy liquid. Like pure sulphuric acid, this pure substance 
 has no marked acid properties, but it mixes easily with water, 
 and the dilute solution is distinctly acidic, about as 
 strongly acidic as the solution of sulphurous acid. 
 
 222. Non-metals are Acid-forming Elements. We have 
 now seen that the oxides of three different elements, carbon, 
 sulphur, and phosphorus, can combine with hydrogen oxide, 
 or water, to form compounds, 
 
 CO 2 + H 2 O-> H 2 CO 3 
 
 50 2 + H 2 0-> H 2 SO 3 
 
 50 3 + H 2 0-> H 2 S0 4 
 
 3H 2 O->2H 3 PO 4 
 
 and that these compounds, when dissolved in or mixed with 
 large additional amounts of water, show acid properties. 
 
 The three elements just mentioned are non-metals. It 
 is one of the important chemical properties of non-metallic 
 elements that their oxides are acid-forming. Non-metallic 
 elements possess distinct physical as well as distinct chemical 
 properties ; for they are poor conductors of heat and elec- 
 tricity, and they do not usually possess a metallic luster. 
 Metals can be easily distinguished by their peculiar metallic 
 luster and by the ease with which they conduct heat and 
 electricity. 
 
 The non-metallic oxides from which acids can be formed 
 
BASE-FORMING ELEMENTS 211 
 
 by combination with water are known as acid anhydrides, 
 the term anhydride being derived from Greek words meaning 
 without water. 
 
 As we know, hydrogen is essential in the make-up of an 
 acid. The anhydride contains no hydrogen, but the water 
 does, although in water this hydrogen is so closely bound 
 to the oxygen that it is not readily displaced by metals like 
 zinc or magnesium, nor does the hydrogen of water exhibit 
 the other characteristics of acids, such as the sour taste and 
 the power to redden litmus. When the acid anhydride is 
 added to water, it seems to partially appropriate the oxygen 
 of the water, leaving the hydrogen less closely bound. So 
 the hydrogen becomes displaceable by metals, and at the same 
 time it develops the properties of sour taste and effect on 
 litmus. It is for this reason that in the formula of an acid 
 the hydrogen is written by itself, and the group containing 
 the acid anhydride plus the oxygen from the water is all 
 written together : H 2 SO 4 instead of H 2 O SO 3 . 
 
 223. Metals are Base-forming Elements. All elements 
 belong to one of two classes, either to the metals or the non- 
 metals. There is, however, no sharp boundary between 
 these classes, but rather, there is a gradual transition, and 
 some of the elements in between might at one time be classed 
 as metals and at another as non-metals. We know that the 
 physical properties of metals are very characteristic; the 
 chemical properties are equally so. One *of the most im- 
 portant of the chemical properties is the behavior of the 
 oxides of the metals ; for these, instead of forming acids like 
 thet)xi3es oHhelibn-metals, when they combine with water, 
 produce bases, which are the exact opposites of acids. 
 
 224. Sodium Oxide and Sodium Hydroxide. When 
 sodium burns with a plentiful supply of air, sodium peroxide, 
 
212 ACIDS AND BASES; NEUTRALIZATION 
 
 Na 2 O 2 , is formed. This substance has already been men- 
 tioned as a source of hydrogen peroxide and of oxygen. But 
 in the present connection we are more interested in sodium 
 oxide, 1 Na 2 O, which can be prepared by burning sodium with 
 a limited amount of oxygen. This oxide of sodium reacts 
 very vigorously with water, producing great heat, just as 
 sulphur trioxide and water produce great heat ; and a distinct 
 new substance sodium hydroxide is formed : 
 
 Na 2 O + H 2 0-*2NaOH. 
 
 Sodium hydroxide is a solid white substance. It will dis- 
 solve in less than its own weight of water. Its solution 
 possesses properties which are almost the exact opposite of 
 the properties of acid solutions. It has an alkaline instead 
 of a sour taste ; in experimenting to find out what this taste 
 is, only very dilute solutions should be used, not more 
 than one part by weight of sodium hydroxide to 1000 parts 
 of water; it turns red litmus blue, and it has the power of 
 neutralizing acids. 
 
 These alkaline properties are characteristic not only of 
 a sodium hydroxide solution, but of the solution of any 
 soluble base. A base is obtained when a metallic oxide 
 combines with water, and sodium hydroxide is one of the 
 strongest bases. 
 
 225. Neutralization. When a solution of sodium hydroxide 
 is added little by little to a solution of any acid, let us say 
 sulphuric acid, so as to have a concrete example, it is 
 found that the acid properties grow less and less marked 
 until at a certain point they disappear altogether ; addition 
 
 1 This is sometimes called sodium monoxide when it is wished to 
 distinguish it from the peroxide. Otherwise, sodium oxide always 
 means this oxide. 
 
CALCIUM OXIDE AND CALCIUM HYDROXIDE 213 
 
 of any further sodium hydroxide imparts the characteristics 
 of a base to the whole solution. At the exact point at which 
 the acid properties have disappeared and the basic properties 
 have not begun to appear the solution is neutral, just as pure 
 water is neutral. The process of just destroying acid prop- 
 erties by the careful addition of a base is known as neu- 
 tralization; likewise the reverse process, that of exactly 
 removing all basic properties by carefully adding an acid, 
 is neutralization. 
 
 In the above process of neutralization exactly two moles 
 of sodium hydroxide must be added to destroy the acid 
 properties of each mole of sulphuric acid, or, in other words, 
 one molecule of sodium hydroxide for each acid hydrogen 
 in a molecule of sulphuric acid. If the neutralized solution 
 is evaporated, it is found that after all the water is driven 
 off a solid white substance is left, which is sodium sulphate. 
 The reaction of neutralization may be formulated : 
 
 2 NaOH + H 2 S0 4 -> 2 H 2 O + Na 2 SO 4 . 
 
 226. Calcium Oxide and Calcium Hydroxide. The metal 
 calcium yields calcium oxide on burning. Calcium oxide is 
 the very common substance that is known as quicklime, and 
 it is, of course, usually obtained by a cheaper method than 
 that of burning the rather expensive metallic calcium. 
 Treated with water, calcium oxide shows characteristics 
 similar to those of sodium oxide ; for a gceat deal of heat is 
 produced and a base is formed, according to the reaction : 
 
 CaO + H 2 O->Ca(OH) 2 . 
 
 As we have seen in the preceding chapter, the saturated 
 solution of calcium hydroxide, which is known as limewater, 
 possesses the same alkaline properties as sodium hydroxide 
 solution, but to a smaller degree, because calcium hydroxide 
 
214 ACIDS AND BASES; NEUTRALIZATION 
 
 is so insoluble that the solution contains a comparatively 
 small amount of the base. 
 
 227. Other Basic Oxides and Bases. Oxides of other 
 metals can yield bases; as, for example, magnesium oxide, 
 MgO + H 2 O -> Mg(OH) 2 ; zinc oxide, ZnO -f H 2 O -> 
 Zn(OH) 2 ; silver oxide, Ag 2 O + H 2 O -> 2 AgOH ; but these 
 last-mentioned bases are much weaker in their basic prop- 
 erties than sodium or calcium hydroxide. All of these 
 bases are capable of neutralizing acids as shown in the 
 following reactions : 
 
 Ca(OH) 2 + H 2 S0 4 -^CaS0 4 + 2 H 2 O 
 Mg(OH) 2 + H 2 S0 4 ->MgS0 4 + 2 H 2 O 
 Zn(OH) 2 + H 2 SO 4 ->ZnSO 4 + 2 H 2 O 
 2 AgOH + H 2 SO 4 -> Ag 2 S0 4 + 2 H 2 O 
 
 228. Characteristic Component of Bases. It has already 
 been seen that the displaceable hydrogen of acids is the com- 
 ponent responsible for the acid characteristics. When this 
 component is removed during neutralization, the acid 
 properties disappear. It is evident from the above reactions 
 that bases likewise have a certain component which must 
 be responsible for the basic properties, and this component 
 is the OH, or hydroxyl group. As the non-metallic oxide is 
 known as an acid anhydride, so the metallic oxide from which 
 a base is formed by combination with water is known as a 
 basic anhydride. It is evident that the hydroxyl group can- 
 not have come wholly from the basic anhydride. It appears 
 as if the basic anhydride had attached to itself a molecule 
 of water, CaO + H 2 O > CaO H 2 O and that this compound 
 had rearranged itself so that its hydrogen and oxygen formed 
 two hydroxyl groups 
 
 CaO + H 2 O -+ CaO - H 2 O -+ Ca(OH) 2 . 
 
PRODUCTS OF NEUTRALIZATION 215 
 
 229. Formation of Water in Neutralization. In the process 
 of neutralization it is the hydrogen of acids and the hydroxyl 
 of bases which mutually destroy each other's properties. 
 They simply combine to form water 
 
 in which, as we know, neither basic nor acidic properties 
 are manifest. It would appear as if in water these com- 
 ponents were very closely bound together, whereas the hy- 
 drogen of acids and the hydroxyl of bases are less closely 
 joined to the rest of the molecule and are thus free to mani- 
 fest their specific properties. 
 
 230. Formation of Salts during Neutralization. The for- 
 mation of water during neutralization accounts for two of 
 the original components of the acid and base. The other 
 components, that is, the metal of the base and the radical 
 of the acid, constitute a salt which in many cases remains 
 dissolved in the solution ; in other cases in which the par- 
 ticular salt is insoluble it separates out at once as a solid 
 precipitate. In any case, solid salt may be made to separate 
 out if the water both the original solvent water and the 
 water produced in the neutralization is evaporated off 
 by heat. The immediate and invariable product of every 
 neutralization is water, but besides this there is always a salt 
 which is different for every different acid and base. A salt 
 may be defined as a substance which is composed of the metal 
 of some base and the radical of some acid. Different salts 
 differ, of course, in many respects among themselves, but 
 we shall find that salts, as a class, have a good many prop- 
 erties in common. 
 
 231. Acids containing no Oxygen. We have just seen 
 that acids and bases may be formed by the union of non- 
 
216 ACIDS AND BASES; NEUTRALIZATION 
 
 metallic oxides and metallic oxides, respectively, with water. 
 But there are acids and bases other than those formed in 
 this way. We have seen that the essential component of an 
 acid is displaceable hydrogen, and the essential component of 
 a base is a loosely attached hydroxyl group. Hydrogen 
 chloride, a compound already familiar to us, contains only 
 hydrogen and chlorine, yet when it is dissolved in water, 
 its hydrogen assumes the easily displaceable condition that 
 is characteristic of an acid. Hydrochloric acid is one of the 
 strongest acids. It neutralizes bases in just the same manner 
 as all other acids ; for example, it reacts with sodium hy- 
 droxide, giving water and sodium chloride : 
 
 HC1 + NaOH^H 2 O + NaCl. 
 
 232. Acid Radicals. When the neutralization reactions 
 of the oxy-acids are compared with that of hydrochloric acid, 
 
 H 2 CO 3 + 2 NaOH -> 2 H 2 O + Na 2 CO 3 
 H 2 SO 3 + 2 NaOH -> 2 H 2 O + Na 2 SO 3 
 H 2 S0 4 + 2 NaOH -> 2 H 2 O + Na 2 SO 4 
 H 3 PO 4 + 3 NaOH -^ 3 H 2 O + Na 3 PO 4 
 
 it becomes obvious that the groups CO 3 , SO 3 , SO 4 , and PO 4 
 function in the same manner as the single atom Cl ; that is 
 to say, these groups remain intact while the hydrogen is 
 removed and the metallic element takes its place. The 
 term radical is used to denote this part of an acid which 
 remains unchanged when the acid is neutralized, and the 
 radical may consist of a single element only ; as, for example, 
 chlorine, or of several elements. Salts, of course, contain 
 the same radicals as the acids from which the salts are 
 derived. 
 
METALLIC RADICALS 217 
 
 233. Ammonium Hydroxide. We have not yet discussed 
 ammonia; ammonia water, however, is something familiar 
 to every one. It is used in the household for cleansing 
 purposes because it is a mild alkali. Ammonia itself is a 
 gas containing only hydrogen and nitrogen, and its formula 
 is NH 3 . It is thus in no respect a metal oxide, yet it dis- 
 solves freely in water and gives a solution that shows the 
 characteristics of a base. This indicates that in some way 
 the water has been altered so that loosely bound hydroxyl 
 groups now exist. The NH 3 molecules may be supposed 
 to have each appropriated one of the H atoms of a water 
 molecule to form the group NH 4 , which is known as the 
 ammonium group, or radical, whereby the OH of water is 
 left in the loosely bound condition : 
 
 NH 3 + HOH -+ (NH 3 H)OH -> NH 4 OH. 
 
 234. Metallic Radicals. Ammonium hydroxide can be 
 used to neutralize an acid, 
 
 NH 4 OH + HC1 -> H 2 O + NH 4 C1 
 
 and it is found that the ammonium group remains intact 
 during the process and that it enters into the composition 
 of the salt, ammonium chloride. A group like this, which 
 plays the same part in a base or salt as the atoms of single 
 metallic elements, is likewise known as a radical, a metallic 
 radical, in this case. 
 
 Every one knows that ammonia water is not nearly 
 so caustic an alkali as sodium hydroxide. Ammonium 
 hydroxide is, as a matter of fact, a much weaker base. The 
 cause of greater or less strength among the different bases 
 and acids has not yet been suggested, but it is to be dis- 
 cussed in Chapter XXV. 
 
218 ACIDS AND BASES; NEUTRALIZATION 
 
 SUMMARY 
 
 Acids contain hydrogen and a radical consisting of a non-metal or 
 of non-metallic elements. When the acid is dissolved in 
 water, tlje attachment between the hydrogen and the radical 
 is apparently weakened, so that the hydrogen is displaceable 
 by metals, and is free enough to manifest its characteristics 
 of sour taste, power to redden litmus, and ability to combine 
 with the hydroxyl of bases, thereby neutralizing the latter. 
 
 The oxides of the non-metallic elements form acids when combined 
 with water. 
 
 Bases contain the hydroxyl group, OH, and a metallic element or 
 radical. When a base is dissolved in water, the hydroxyl 
 group becomes active, in the same manner as the hydrogen of 
 acids. It then displays its characteristics of alkaline taste, 
 power to turn litmus blue, and ability to neutralize acids. 
 
 The oxides of the metallic elements form bases when combined with 
 water. 
 
 When an acid and base neutralize each other, the hydrogen of the 
 one and the hydroxyl of the other combine to form water and 
 thus disappear as active components, while the metal or 
 metallic radical of the base and the non-metallic radical of the 
 acid together yield a salt. 
 
 Questions 
 
 1. Cream of tartar has a sour taste. This taste is due to the 
 presence of what component in the cream of tartar ? 
 
 2. To the presence of what group of elements would you attrib- 
 ute the alkaline taste of limewater (calcium hydroxide solution)? 
 
 3. What becomes of the components which are responsible for 
 the sour taste and the alkaline taste, respectively, when an acid 
 is neutralized by a base? 
 
 4. What is a salt? What acid and what base yield common 
 salt by neutralization? 
 
 6. How could you make sodium sulphate from (a) sodium 
 hydroxide? (6) sodium chloride? (c) sodium carbonate? Give 
 equations. 
 
QUESTIONS 219 
 
 6. If one has spilled sulphuric acid on his garment, why does 
 he use ammonia water to prevent a hole being eaten? Why not 
 use sodium hydroxide? 
 
 7. Why does limewater correct sour stomach? 
 
 8. What weight of (a) hydrochloric acid, (6) sulphuric acid, 
 should be taken to neutralize 40 grams of sodium hydroxide ? 
 
 9. What volume of carbon dioxide (standard conditions) 
 should be passed into a solution of 40 grams of sodium hydroxide 
 to form sodium carbonate 2 NaOH + C0 2 -> Na 2 C0 3 + H 2 ? 
 
 10. Ammonium salts are obtained from the liquors condensed 
 in gas works by distilling off ammonia and passing it into acid. 
 What volume of ammonia gas (standard conditions) can be caught 
 in one kilogram of sulphuric acid? 
 
 11. What volume of potassium hydroxide solution containing 
 100 grams KOH per liter will just neutralize 100 c.c. of hydrochloric 
 acid containing 200 grams HC1 per liter? 
 
 12. Cite several examples in which an acid is made by treating 
 the oxide of a non-metal with water ; in which a base is made by 
 treating the oxide of a metal with water. 
 
 
 
CHAPTER XX 
 NOMENCLATURE. 
 
 SEVERAL acids, bases, and salts have been discussed in the 
 last chapter, and names have been used for them which are 
 probably not as yet fully understood by the pupil. It seems 
 best, therefore, to pause at this point and explain the system 
 of naming which is in use generally by chemists. 
 
 235. As has already been explained, when a substance 
 consists of but two elements, its name includes the names, 
 or at least the roots of the names, of each element, the more 
 metallic element being taken first, and the suffix ide is added 
 to the name of the second element. The suffix ide has this 
 significance; namely, it indicates a compound consisting 
 usually of only two elements : 
 
 HC1 hydrogen chloride 
 
 NaCl sodium chloride 
 
 H 2 O hydrogen oxide 
 
 Na 2 O sodium oxide 
 
 H 2 S hydrogen sulphide 
 
 Na 2 S sodium sulphide. 
 
 236. It frequently happens that two elements form more 
 than one compound with each other (see law of Multiple 
 Proportions). One method of distinguishing the different 
 compounds in such a series is by using the Greek or Latin 
 prefixes before the name of the non-metal in order to indicate 
 the number of atoms of this element. 
 
 220 
 
NOMENCLATURE 221 
 
 CO carbon monoxide 
 
 CO2 carbon dioxide 
 
 SOs sulphur trioxide 
 
 CCLj carbon tetrachloride 
 
 PCls phosphorus pentachloride. 
 
 237. When a compound of two elements is an acid and 
 it is wished to indicate this fact, the word acid is added to 
 the name, and the names of the two elements are contracted 
 into a single word which is now used as an adjective with the 
 common English adjective ending ic instead of ide. 
 
 HC1 hydrochloric acid 
 H 2 S hydrosulphuric acid 
 HBr hydrobromic acid. 
 
 On passing from the simpler acids containing only two 
 elements to the more complicated oxy-acids which contain 
 three elements, the naming becomes simpler instead of more 
 complicated. It must be remembered that the oxy-acids 
 were the first acids to be discovered ; indeed, it was thought 
 formerly that oxygen was the essential acid-producing con- 
 stituent of acids. It is only comparatively recently that 
 hydrogen has become recognized as the true acid-producing 
 constituent. Acids were thus originally named, in accordance 
 with this erroneous conception, after the non-metal whose 
 oxide gave the acid when it united with water. For example, 
 carbonic acid was the acid derived from the 'oxide of carbon. 
 This nomenclature has proved perfectly satisfactory and has 
 been retained. 
 
 The suffix ic- is the common termination for the names of 
 acids. Some of the non-metals have more than one oxide 
 and, corresponding to the different oxides, yield more than 
 one acid. In such cases the suffix ic is retained for the 
 
222 
 
 NOMENCLATURE 
 
 commonest, or the most important, of these acids. For an 
 acid containing less oxygen, the suffix ous is used (eras is 
 another common English adjective ending). 
 
 Thus, the most important acid from sulphur is sulphuric 
 acid, derived from sulphur trioxide. From sulphur dioxide 
 an acid with less oxygen is obtained which is called sul- 
 phuTous acid. The acid which contains hydrogen and sul- 
 phur alone is distinguished from these oxy-acids in that the 
 prefix hydro is used. 
 
 OXIDE 
 
 FORMULA OF ACID 
 
 NAME OP ACID 
 
 
 H 2 S 
 
 Hydro sulphuric acid 
 
 
 S0 2 
 
 H 2 S0 3 
 
 Sulphurous acid 
 
 S0 3 
 
 H 3 S0 4 
 
 Sulphuric acid 
 
 P 2 3 
 
 H 3 P0 3 
 
 Phosphorous acid 
 
 P 2 5 
 
 H 3 P0 4 
 
 Phosphoric acid 
 
 238. Some elements, notably chlorine, yield more than 
 two acids. In such cases the prefix per is used to denote 
 a greater oxygen content than that of the plain ic acid, and 
 the prefix hypo to denote a lower oxygen content than that 
 of the plain oiis acid. To illustrate this point, the chlorine 
 acids, including the acid with no oxygen, are given in the 
 following table : 
 
 OXIDE 
 
 FORMULA OF ACID 
 
 NAME OF ACID 
 
 
 HC1 
 
 hydro chloric acid 
 
 
 C1 2 O 
 
 HC10 
 
 hypo chlorous acid 
 
 C1 2 3 
 
 HC10 2 
 
 chlorows acid 
 
 C1 2 5 
 
 HC10 3 
 
 chloric acid 
 
 C1 2 7 
 
 HC1O 4 
 
 perchloric acid 
 
 
NOMENCLATURE 
 
 223 
 
 239. Bases always consist of a metallic element combined 
 with hydroxyl. In naming bases, the name of the metal 
 is first given, and this is followed by the word hydroxide. 
 
 NaOH sodium hydroxide 
 
 KOH potassium hydroxide 
 
 Zn(OH) 2 zinc hydroxide. 
 
 The termination ide usually signifies that a compound con- 
 taining only two elements is indicated. Still its use in this 
 case is justified on the ground that the OH group behaves 
 quite like a single atom. 
 
 240. Salts may be derived by the neutralization of bases 
 and acids and are named in accordance. Salts containing 
 but two elements are named according to the ru!e already 
 given for compounds of only two elements. Salts of oxy- 
 acids are named after the acids, except that the ending ic 
 is changed to ate and the ending ous is changed to ite. The 
 prefixes hypo and per are retained in the names of the oxy- 
 salts, but the prefix hydro is not retained in the names of 
 the salts derived from the hydro-acids. 
 
 FORMULA 
 OF ACID 
 
 NAME OP ACID 
 
 FORMULA OF 
 SODIUM SALT 
 
 NAME OF SALT 
 
 HC1 
 
 hydrochloric acid 
 
 NaCl 
 
 sodium chloride 
 
 HC10 
 
 hypochlorous acid 
 
 NaCIO 
 
 sodium hypochlorite 
 
 HC10 2 
 
 chlorous acid 
 
 NaC10 2 
 
 sodium chlorite 
 
 HC10 3 
 
 chloric acid 
 
 NaC10 3 
 
 sodium chlorate 
 
 HC10 4 
 
 perchloric acid 
 
 . NaC10 4 
 
 sodium perchlorate 
 
 H 2 S 
 
 hydrosulphuric acid 
 
 Na 2 S 
 
 sodium sulphide 
 
 H 2 S0 3 
 
 sulphurous acid 
 
 Na 2 S0 3 
 
 sodium sulphite 
 
 H 2 S0 4 
 
 sulphuric acid 
 
 Na 2 S0 4 
 
 sodium sulphate 
 
 HN0 2 
 
 nitrous acid 
 
 NaNO 2 
 
 sodium nitrite 
 
 HN0 3 
 
 nitric acid 
 
 NaNO 3 
 
 sodium nitrate 
 
 B. AND W. CHEM. 15 
 
224 NOMENCLATURE 
 
 Questions 
 
 1. Name the compound whose formula is KI. 
 
 2. Name the acid from which KI is derived. 
 
 3. What acid yields iodates on neutralization? 
 
 4. What acid yields per chlorates? 
 
 6. Name the sodium salt of phosphorous acid. 
 
 6. Name the potassium salt of hypochlorous acid. 
 
 7. What acid yields hypochlorites ? 
 
 8. Name salts derived from silicic acid. 
 
 9. Name compounds having the following formulas: NaBr, 
 HBr, KBrO, Ca(Br0 3 ) 2 , KI0 4 , H 2 S, K 2 S, CaS0 3 , KN0 2 , Zn(N0 3 ) 2 . 
 
 10. Give the formulas of potassium chloride, potassium sulphide, 
 potassium sulphite, ammonium sulphate, potassium perchlorate. 
 

 CHAPTER XXI 
 
 THE METALS 
 
 IT has already been seen that it is impossible to deal with 
 the chemistry of the non-metals without describing the com- 
 pounds that they form with the metals. We have already 
 acquired some knowledge of the metals sodium and calcium 
 and a fragmentary knowledge of some of the other metals ; 
 to make this knowledge more systematic, we shall devote 
 this chapter to the study of the metals and the following 
 chapter to the methods of winning the metals from the rocks 
 and earths in which they are found in nature. 
 
 241. Physical Properties of Metals. A metal can be 
 almost unerringly recognized even at a glance by its peculiar 
 luster, the so-called metallic luster. It is very difficult 
 to describe metallic luster, but it is something that would 
 never be confused with the luster of non-metallic substances 
 such as glass, or sulphur crystals. 
 
 Besides having metallic luster, all metals have a high 
 degree of conductivity for heat and electricity. 1 
 
 Many of the common metals are strong, or hard, or ductile, 
 or tenaceous, or malleable, or heavy, or 'difficult to melt, 
 but none of these properties are distinctive of the metals, 
 
 1 It is true that graphite (carbon) and some of the sulphides 
 and oxides of the heavy metals, for example, magnetic oxide 
 of iron, possess metallic luster and conduct electricity. They thus 
 possess the distinctive physical properties of the uncombined metals, 
 but this does not impair the correctness of the above statement 
 that all metals have these properties. 
 
 225 
 
226 THE METALS 
 
 as are the metallic luster and the conductivity for heat and 
 electricity. For example, iron is strong, hard, and difficult 
 to melt, but lead is weak, soft, and easily melted. Gold 
 and copper are ductile and malleable, but chromium, man- 
 ganese, and bismuth are so brittle that they can be broken 
 into fragments with a hammer. Platinum will barely melt 
 in the oxy-hydrogen blowpipe, while sodium will melt below 
 the temperature of boiling water, and mercury melts at a 
 temperature 40C. below the melting point of ice. Gold, 
 lead, and mercury are very heavy ; aluminium and magnesium 
 are light, and sodium is so light, that it floats on water. 
 
 To sum up the physical characteristics of metals: the 
 metallic luster and the conductivity for heat and electricity 
 are properties possessed by the metals without exception. 
 Numerous other properties are associated in the popular 
 mind with metals, but they are not invariable and distinctive 
 properties of metals. 
 
 242. Chemical Properties of Metals. In chemical prop- 
 erties the metals are as different from the non-metals as in 
 physical properties. One of the most striking chemical 
 characteristics of the metals has already been mentioned in 
 Chapter XIX; namely, that the oxides of the metals are 
 base-forming in distinction to the oxides of the non-metals, 
 which are acid-forming. 
 
 Acids and bases are opposed to each other in their chemical 
 nature, as we may conclude from their ability to neutralize 
 each other. In a similar way, the metals and the non- 
 metals themselves are opposed to each other in their chemical 
 nature, for they are capable of changing, or neutralizing, 
 each other's properties when they combine. We are familiar, 
 for example, with the striking properties of sodium and the 
 striking properties of chlorine; when these elements com- 
 
HYDROGEN AS A METAL 227 
 
 bine, these striking properties disappear and we have ordinary 
 common salt, which does not have the metallic luster and 
 the conductance for electricity of sodium nor the evil odor 
 and the yellowish color of chlorine. 
 
 243. Hydrogen as a Metal. The element hydrogen does 
 not possess the physical characteristics of metals, but in 
 chemical properties it shows a strong resemblance to the 
 metals. It combines with non-metals, forming such com- 
 pounds as hydrogen chloride and water, but it does not show 
 any marked tendency to form compounds with the metals. 
 Furthermore, hydrogen is interchangeable with the metals 
 in nearly all of their compounds. For example, on treating 
 an acid such as hydrogen chloride with zinc or iron, the 
 metals displace hydrogen according to the equations : 
 
 2HC1 + Fe-*FeCl 2 + H 2 . 
 
 Zinc chloride and iron chloride, then, may be regarded as 
 hydrochloric acid in which zinc or iron has been substituted 
 for hydrogen. When copper chloride is heated in hydrogen 
 gas, uncombined copper and hydrogen chloride are obtained : 
 
 Hydrogen chloride may be regarded as copper chloride in 
 which hydrogen has been substituted for copper. 
 
 It is thus seen that metals, including hydrogen, all have 
 the same kind of combining power. So, if one metal forms 
 a chloride, then all of the metals including hydrogen should 
 do the same. It is in fact true that all of the metallic 
 elements form distinct chlorides. Nearly all likewise form 
 oxides. 
 
 Not only are metals interchangeable with hydrogen in 
 
228 THE METALS 
 
 the simple compounds hydrogen chloride and water, but 
 also in the oxy-acids such as sulphuric, phosphoric, and 
 carbonic acids, in which hydrogen is in combination with 
 radicals instead of with single elements. In fact, sulphates, 
 phosphates, and carbonates of all the most active metals 
 are well known. Whole mountain ranges, for example, are 
 composed of calcium carbonate and magnesium carbonate, 
 and deposits of calcium sulphate and calcium phosphate, 
 of iron carbonate, copper carbonate, zinc carbonate, and 
 lead carbonate are often found in the earth. 
 
 244. Electrical Nature of Chemical Attraction. It is 
 clear from what has already been said that it is oppositeness 
 in chemical nature that makes it possible for two elements 
 to form compounds. We know that when an electric current 
 is passed through water, the latter is decomposed into 
 hydrogen and oxygen; likewise hydrochloric acid is de- 
 composed into hydrogen and chlorine. The hydrogen is 
 liberated in each case at the negative electrode, and since it 
 is known that unlike electric charges attract each other, 
 whereas like charges repel, it must be that the hydrogen in 
 the compound is electrically positive in order to be attracted 
 to the negative electrode. According to the same reasoning, 
 since the oxygen and chlorine are liberated at the positive 
 electrode, these must be electrically negative as they exist 
 in their compounds. Like hydrogen, the metals must all be 
 electro-positive in their compounds ; for they are always set 
 free at the negative electrode when the current is passed 
 through solutions of any of their salts. 
 
 We are certain that in many compounds the attractive 
 force holding the elements together is in some way dependent 
 on their electrical condition. It may be that this is true of 
 all chemical compounds, although this would be too sweeping 
 
ALLOYS 229 
 
 a statement to make unconditionally in the light of our 
 present knowledge. 
 
 At all events this statement may be made without reser- 
 vation : that in compounds of metals and non-metals the 
 metals are electro-positive in nature and the non-metals are 
 electro-negative. 
 
 245. Compounds of Non-Metals with Non-Metals. It 
 is true that non-metals often form compounds among them- 
 selves ; as, for example, in the oxides of carbon, sulphur, and 
 phosphorus. There must be some difference in nature to 
 make the chemical union possible, and if this difference is 
 electrical, it must be that the carbon, sulphur, and phos- 
 phorus are forced to play the electro-positive role in these 
 compounds because the oxygen has so much greater ability 
 to play the electro-negative role. It is true, however, as 
 a general rule that the compounds of the non-metals among 
 themselves are feebler (that is, much more easily broken 
 apart) than the compounds of the non-metals with the 
 metals. 
 
 246. Compounds of Metals with Metals ; Alloys. Metals 
 show even less tendency to form compounds among them- 
 selves than do the non-metals. When different metals are 
 melted and poured together, alloys are obtained : brass is 
 an alloy of copper and zinc ; bronze an alloy of copper and 
 tin ; solder an alloy of tin and lead. These alloys are not def- 
 inite compounds of the metals, but are in the main mixtures, 
 much like the mixture that we obtain by pouring alcohol 
 and water together. The molten metals mix, and when the 
 mixture cools, it solidifies to a metallic mass which has 
 metallic luster and conducts electricity as do both of its 
 component metals. 
 
 The most recent study of alloys has indeed proved that 
 
230 THE METALS 
 
 they sometimes contain minute crystals of certain definite 
 compounds embedded in the mass of the metal. These 
 crystals can sometimes be observed with a microscope on 
 a polished surface of the alloy that has been carefully etched 
 with acid. At best, however, the power of metals to combine 
 chemically with other metals is very limited. 
 
 247. Classification of the Metals. Now that we have 
 shown in a general way how metals are different from non- 
 metals, let us divide them into groups or classes according 
 to their properties. They might be classed according to 
 their base-forming properties or according to their behavior 
 with acids, or according to their physical properties. We 
 shall group them into three main classes ; namely, the alkali 
 metals, the earth-forming metals, and the heavy metals. 
 This grouping is in the main based on the physical property 
 of weight, although the chemical properties also follow this 
 grouping to a great extent. 
 
 248. The alkali metals are those from which the caustic 
 alkalies are obtained. We have already considered the two 
 of most frequent occurrence ; namely, sodium and potassium, 
 which yield the bases, sodium hydroxide and potassium 
 hydroxide respectively. These bases are extremely soluble 
 and their concentrated solutions are caustic or corrosive to 
 the flesh or to any animal or vegetable tissues. The terms 
 alkali and base are somewhat interchangeable. A base, as 
 seen in Chapter XIX, is a substance that contains an hydroxyl 
 group and can neutralize an acid. An alkali is a substance 
 that dissolves freely in water and then shows to a marked 
 degree the characteristics of soluble bases. For example, 
 an alkali turns red litmus blue, it has an alkaline taste, it is 
 useful in cleansing or removing grease and dirt. 
 
 As already seen, metallic sodium and potassium are light 
 
THE ALKALI METALS 231 
 
 in weight, they will float on water ; they are soft and can 
 be cut with a knife almost as easily as cheese; they melt 
 below the boiling point of water. These metals conduct 
 electricity and show a bright metallic luster on freshly 
 exposed surfaces. Exposed to the air, the surfaces soon 
 grow dull on account of the formation of a layer of oxide 
 or hydroxide on the surface. 
 
 Sodium and potassium both react violently when thrown 
 on cold water. They float around, giving a rapid evolution 
 of hydrogen, and, especially with potassium, the heat of the 
 reaction is so intense as to set fire to the hydrogen. The 
 reaction yields the hydroxides : 
 
 K +H 2 0->KOH + H. 
 
 Sodium and potassium combine violently with oxygen and 
 chlorine when heated in these gases. The alkali metals are, 
 in fact, the most active of the metallic elements. The 
 oxides react energetically with water and give the hydroxides. 
 For example, sodium oxide reacts as follows : 
 
 Na 2 + H 2 0-*2NaOH. 
 
 It has already been mentioned that when sodium burns 
 in a plentiful supply of air, a higher oxide a so-called 
 peroxide is formed. Potassium also forms a peroxide, 
 K 2 O4. When either of these peroxides is treated with water, 
 the ordinary hydroxide is obtained just as from the mon- 
 oxide, and the excess of oxygen escapes as oxygen gas : 
 
 2 K 2 4 + 2 H 2 0-M KOH + 3 O 2 . 
 
 Since the alkali metals are the most energetic of the 
 metallic elements and show so great a tendency to react 
 
232 THE METALS 
 
 with the abundant substances, water and oxygen, it is not 
 strange that these metals are never found uncombined in 
 nature. Nearly all the salts of the alkali metals are very 
 soluble in water. 
 
 The most generally useful and important compounds of 
 the alkali metals are the hydroxides and the carbonates. 
 The hydroxides constitute the caustic alkalies, the carbonates 
 are mild alkalies. We might expect that the carbonates 
 would be neutral and not alkaline, because they are salts 
 and may be obtained by neutralizing a base with an acid : 
 
 2 NaOH +' H 2 CO 3 -> 2 H 2 O + Na 2 CO 3 . 
 
 But it must not be lost sight of that sodium hydroxide is an 
 extremely strong base, whereas carbonic acid is a very weak 
 acid. This fact permits the neutralization to reverse itself 
 to a certain extent when water has access to salts of this 
 type and hence a little of the base is present in the solution 
 (see Hydrolysis, p. 405). 
 
 249. Ammonium. The ammonium group, or radical 
 (NH 4 ), as we have already seen in Chapter XIX, acts chemi- 
 cally very much like a metal. Its compounds are almost 
 without exception soluble, as are those of the alkali metals, 
 and like them, its hydroxide is very soluble in water and 
 is a pronounced base (or alkali). Hence the hypothetical 
 metal ammonium is classed among the alkali metals. 
 
 250. The Earth-forming Metals. Our next class of 
 metals, the earth-forming metals, is, as the name implies, 
 a group whose compounds form a large part of the earthy 
 matter of which the surface of our earth is made. The 
 most important metals in this class are magnesium, calcium, 
 barium, and aluminium. 
 
 In physical properties these metals are much harder and 
 

 THE EARTH-FORMING METALS 233 
 
 more tenacious than the alkali metals, although they fall 
 a good deal below iron in these respects. They are light in 
 weight as compared with the heavy metals iron, copper, and 
 zinc, but they are heavier than the alkali metals. One of 
 the very valuable properties of aluminium is its lightness, 
 for it approaches iron in strength and yet it is of far less 
 weight. These metals all have fairly high melting points. 
 
 The earth-forming metals are like the alkali metals in 
 that they could by no possibility remain long uncombined 
 in the earth, and as we should expect, they are always found 
 in a state of combination. 
 
 Of the metals mentioned in this class calcium and barium 
 are most like the alkali metals, for they react with cold water 
 and liberate hydrogen : 
 
 Ca + H 2 O->Ca(OH) 2 + H 2 , 
 Ba -f H 2 O->Ba(OH) 2 + H 2 . 
 
 Likewise, their oxides react energetically with water to form 
 hydroxides : 
 
 H 2 0->Ca(OH) 2 , 
 
 H 2 O-^Ba(OH) 2 . 
 
 The hydroxides are not so soluble as the hydroxides of the 
 alkali metals and are not so strongly basic. Calcium and 
 barium are often called alkaline earth metals to show that 
 they are intermediate between alkali metals and the more 
 strictly earth metals. 
 
 Magnesium and aluminium do not react appreciably 
 with cold water. Their hydroxides are bases and react 
 with acids to form salts; magnesium hydroxide is almost 
 insoluble, and aluminium hydroxide is still less soluble and 
 withal a very weak base. Although these bases are insoluble 
 
234 THE METALS 
 
 in water, they dissolve easily in dilute acid solutions because 
 their salts, which are soluble, are formed. 
 
 All of the earth-forming metals react vigorously with acids 
 with displacement of hydrogen and formation of the cor- 
 responding salt: 
 
 2 Al + 6 HC1 ->2 A1C1 3 + 3 H 2 , 
 Mg + H 2 S0 4 -*MgS0 4 + H 2 . 
 
 These metals are thus shown to be more active than hydrogen, 
 as is also shown by the fact that it is impossible to reduce 
 their oxides by heating them in hydrogen. 
 
 Magnesium and barium, like calcium, are found frequently 
 in nature as the carbonates. 
 
 Aluminium is the most abundant of the metallic elements 
 in the earth's crust. It occurs as silicate in clay and in most 
 of the rocks of the earth's crust. Metallic aluminium is 
 obtained almost solely by the electrolysis of the hydrated 
 oxide which is found in the earth in fair abundance as the 
 mineral bauxite. 
 
 251. The Heavy Metals. The remaining metals that 
 we have to consider we shall group together under the title 
 of the heavy metals. The most important ones of this 
 group are copper, silver, gold, mercury, platinum, zinc, tin, 
 lead, chromium, manganese, iron, and nickel, and it may be 
 seen that this list includes all, except aluminium, of the 
 metals that are familiar in our everyday life. 
 
 As the name implies, these metals are all of high specific 
 gravity. They possess to a high degree the characteristic 
 physical properties of metals ; that is, metallic luster and con- 
 ductivity for heat and electricity. Most of them have great 
 strength and considerable hardness, which make them useful 
 for structural purposes and for making machines and utensils. 
 
THE HEAVY METALS 235 
 
 In chemical properties the metallic character is not so 
 strongly marked in this group as in the other two groups. 
 The heavy metals form hydroxides which are capable of 
 neutralizing acids and forming salts, for example : 
 
 Zn(OH) 2 + H 2 S0 4 -*2 H 2 O + ZnSO 4 . 
 
 But the hydroxides are hardly to be called alkalies ; they are 
 only very weak bases. Most of these bases are very insoluble 
 in water, and only one or two of them are strong enough to 
 barely impart to litmus the blue color that is the characteristic 
 effect of bases. 
 
 As a class, the heavy metals are far less active chemically 
 than the alkali or the earth-forming metals. They do not 
 react to any great extent with dry air or with pure water, 
 and this freedom from attack is one of the 
 properties that makes them useful metals. Manganese 
 
 252. Varying Activity of the Heavy Metals. chromium 
 The heavy metals may be graded according i ron 
 to their chemical activity, and in this respect Nickel 
 they fall in the order indicated in the accom- Tin 
 panying list. 
 
 All the metals standing above hydrogen in 
 this list are more active than hydrogen and Mercury 
 can displace that element from acids. Zinc Silver 
 acts vigorously with dilute sulphuric or hydro- Platinum 
 chloric acid, and hydrogen gas is evolved. Gold 
 Iron acts somewhat less vigorously. Tin and Relative Activ- 
 
 ' ity of Metals 
 
 lead displace hydrogen, only very slowly. 
 Metals below hydrogen are less active and will not displace 
 hydrogen at all from acids. For example, if a clean piece 
 of copper is placed in dilute sulphuric or hydrochloric acid, 
 no reaction occurs. (It is true that copper reacts freely 
 
236 THE METALS 
 
 with nitric acid and a gas is given off, but this gas is not 
 hydrogen.) 
 
 The metals higher in the list are not only more active in 
 displacing hydrogen, but they are also more active in com- 
 bining with non-metals ; for example, the oxygen of the air. 
 Bright polished surfaces of iron, zinc, and lead do not remain 
 bright long when exposed to the air, particularly if the air is 
 moist. Copper also tarnishes when exposed to the weather. 
 When the film of oxide first formed on the surface of a metal 
 is impervious, further action of the weather is stopped; 
 whereas if the film is porous, as is the case with iron rust, 
 the corrosion may continue until the metal is all eaten 
 away. 
 
 Silver, platinum, and gold, which are known as precious 
 metals on account of their value, are so inactive that they 
 completely withstand the action of the weather. 
 
 Both copper and silver coins darken when carried in the 
 pocket, and silver spoons grow black when they are used in 
 eating eggs. This blackening is caused by sulphur com- 
 pounds which are present in small amounts in the perspira- 
 tion and in eggs. Copper and silver show a peculiarly strong 
 inclination to form compounds with sulphur, and these sul- 
 phides are very black, so that they are very conspicuous 
 on the metallic surface. 
 
 Platinum and gold are almost perfectly resistant to cor- 
 rosion or to attack of any kind. Not only are they un- 
 attacked by the ordinary acids, but they are not even acted 
 on by the oxidizing acid, nitric acid, which reacts readily 
 with copper, silver, and mercury. As was seen under the 
 topic " aqua regia," gold and platinum are, however, attacked 
 by a mixture of hydrochloric and nitric acids. Gold and 
 platinum chlorides are formed by the action, and these com- 
 

 SUMMARY 237 
 
 pounds being soluble, the metals appear to dissolve in the 
 aqua regia. 
 
 253. Occurrence in Nature. According to their activity, 
 we can predict with some certainty which of the heavy metals 
 will be found combined and which uncombined in the earth. 
 The metals above hydrogen are not found uncombined, 
 except that metallic iron is sometimes found in meteorites. 
 These metals are often found in large deposits as oxides, sul- 
 phides, and carbonates. 
 
 The metals below hydrogen are all found at times un- 
 combined in nature. Copper is more frequently found as 
 the oxide or sulphide. Silver and mercury are found often 
 as sulphide and often in the uncombined state. Gold and 
 platinum are usually found in the uncombined state. 
 
 SUMMARY 
 
 The metals form a class of elements as distinguished from the non- 
 metals. 
 
 The principal physical characteristics by which metals differ from 
 non-metals are that they possess metallic luster and con- 
 ductivity for heat and electricity. 
 
 Chemically, metals are base formers and non-metals are acid 
 formers. 
 
 Classes of metals: We have grouped the metals into three main 
 classes ; namely, the alkali metals, the earth-forming metals, 
 and the heavy metals. 
 
 The alkali metals are extremely active chemically and their hydrox- 
 ides are very strong bases, the so-called caustic alkalies. 
 
 The earth-forming metals are also very active, but they do not 
 furnish such strong bases. Many of their compounds are 
 insoluble in water and earthy in their nature ; a large part 
 of the earth's crust is composed of these compounds. 
 
 The heavy metals are heavy in weight and inactive chemically in 
 comparison with the other two classes. The heavy metals 
 may be divided into two groups according to their activity : 
 
238 THE METALS 
 
 those standing above hydrogen in this respect and those 
 standing below. The former are found combined, the latter 
 are frequently found free in nature. 
 
 Questions 
 
 1. How can you tell a metal from a non-metal? 
 
 2. Why is hydrogen regarded as a metal in its chemical relations ? 
 
 3. Can metals unite chemically with metals ? What are alloys ? 
 
 4. Can non-metals unite with non-metals? Give illustrations. 
 6. What was the basis of the classification of the metals into 
 
 three groups in this chapter? 
 
 6. What are the principal chemical characteristics of the alkali 
 metals ? 
 
 7. What hypothetical metal is classed with the alkali metals? 
 
 8. How do the metals of the earth-forming group differ from 
 those of the alkali group in general physical properties? 
 
 9. Into what group would the precious metals naturally fall? 
 
 10. Which of the metals would you expect to find uncombined 
 in nature ? 
 
 11. Which class of metals can best be used for structural work? 
 Why? 
 
 12. Which of the heavy metals can best be used for jewelry? 
 
 13. Why is zinc, which is a more active metal than iron, superior 
 to iron for use on roofs ? 
 
 14. Why is the sheet iron used in the canning industry always 
 coated with tin? (Food products often contain weak acids.) Is 
 tin a perfect metal for the purpose ? 
 
 15. How is the iron of bridges and other structures guarded from 
 corrosion? 
 
CHAPTER XXII 
 
 METALLURGY 
 
 254. Minerals and Ores. It has been seen in the preced- 
 ing chapter that the metallic elements, except sometimes 
 copper, mercury, and the precious metals, silver, platinum, 
 and gold, are found in nature combined with non-metals. 
 Such compounds, and indeed all pure substances occurring 
 in rocks, are known as minerals. 
 
 Sometimes large deposits of pure mineral are found, but 
 more often the valuable mineral is found in veins and pockets 
 in other rock, or disseminated through it, and it is impossible 
 to treat the mineral in the metallurgical process without 
 treating also large amounts of worthless rock. 
 
 Such a mixture of rock and mineral or native metal is 
 called an ore when the cost of mining and extracting the 
 metal from it is less than the value of the metal obtained. 
 
 Thus a rock which contains as little as a gram of gold per 
 ton may be considered an ore, if it occurs in a large deposit 
 and in a locality where it can be cheaply handled. Few rocks 
 contain so small an amount of iron as this and many of the 
 common rocks contain several per cent of iron ; to be of use 
 as an iron ore the rock must consist almost exclusively of 
 the iron mineral. 
 
 In the table on the next page are given the names and 
 chemical formulas of the most important minerals of the 
 commoner metals. 
 
 B. AND W. CHEM. 16 239 
 
240 
 
 METALLURGY 
 
 METAL 
 
 MINERAL 
 
 FORMULA OF MINEAL 
 
 Iron 
 
 Hematite 
 Magnetite 
 Siderite 
 Limonite 
 
 Fe 2 3 
 Fe 3 4 
 FeC0 3 
 Fe 2 3 3 H 2 
 
 Copper 
 
 Native Copper 
 Chalcopyrite 
 Cuprite 
 Chalcocite 
 
 Cu 
 CuFeS 2 
 Cu 2 
 Cu 2 S 
 
 Lead 
 
 Galena 
 
 PbS 
 
 Tin 
 
 Cassiterite or Tinstone 
 
 Sn0 2 
 
 Zinc 
 
 Zinc Blende 
 Zincite 
 Calamine 
 
 ZnS 
 ZnO 
 Zn 2 SiO 4 
 
 Mercury 
 
 Cinnabar 
 
 HgS 
 
 Silver 
 
 Native Silver 
 Argentite or Silver Glance 
 Cerargyrite or Horn Silver 
 Proustite or Ruby Silver 
 
 Ag 
 Ag 2 S 
 AgCl 
 3 Ag 2 S As 2 S 3 
 
 Gold 
 
 Native Gold 
 Calaverite 
 
 Au 
 AuTe 2 
 
 Platinum 
 
 Native Platinum 
 
 Pt 
 
 Aluminium 
 
 Bauxite 
 
 Al 2 0a 2 H 2 
 
 Nickel 
 
 Millerite 
 
 NiS 
 
 Antimony 
 
 Stibnite 
 
 Sb 2 S 3 
 
 IRON 
 
 255. Iron is the most important of all the metals. Its 
 cheap production and the development of different grades 
 such as cast iron, wrought iron, and steel, varying in hard- 
 
IRON 
 
 241 
 
 ness and strength, have made possible the enormous growth 
 of railroads, the development of building construction, and 
 the expansion of industrial operations within recent years. 
 
 Although iron is found abundantly in nature as sulphide 
 and silicate and to some extent as carbonate, only a very 
 small amount of the 
 iron produced comes 
 from these sources. 
 The principal ores are 
 the oxides, which fre- 
 quently occur in ex- 
 tensive deposits and 
 can be mined cheaply 
 on a large scale. The 
 metallurgical treat- 
 ment of the oxide 
 ores is also compara- 
 tively simple, for the 
 oxygen is readily re- 
 moved when the ore is heated with some form of carbon. 
 Charcoal is used in a few places for this purpose, but coke 
 is more commonly used. To make iron as cheaply as is 
 to-day demanded, operations must be carried out on a large 
 scale so that all possible economies may be introduced. 
 
 256. Blast Furnace. The reduction of the iron ore is 
 carried out in a blast furnace (Figure 42). Blast furnaces 
 are often built as high as 100 feet; they consist of a steel 
 shell lined with fire brick. Since the ore, the coke, and other 
 materials which must sometimes be mixed with the ore are 
 put into the furnace from the top, it is necessary to provide 
 some form of hoisting apparatus. 
 
 The rock which is associated with the iron oxide in the ore 
 
 FIG. 41. Hematite. 
 
242 
 
 METALLURGY 
 
 4ffllL.ro/fc*. 
 
 &.../ron Ore. 
 O....Ltme Stone. 
 4 
 
 fie/ ted /r on. 
 ..... Drops of 
 
 D. . ..Lower ftopjoer. 
 E.. -tower Be//. 
 
 . 42. Blast Furnace. 
 

 BLAST FURNACE 243 
 
 does not melt easily, and it is necessary to add something 
 which will unite with it and form more fusible compounds. 
 (Notice that the blast furnace has no grate at the bottom for 
 shaking out the ashes, only two holes through which liquids 
 may be withdrawn.) Anything which will thus form a fusible 
 mixture with the worthless rock is called a flux. The rock 
 is usually composed mostly of silicon dioxide with consider- 
 able aluminium oxide, and other oxides are united with part 
 of the silicon dioxide in the form of silicates. Aluminium 
 silicate forms the principal part of ordinary clay. The silicon 
 dioxide which is not combined with the other oxides is nothing 
 but common quartz. This is an acidic oxide and, as we 
 would suppose from our study of acids and bases, a proper 
 flux for it is a basic oxide. Limestone is always used for 
 this purpose in the iron blast furnace. The calcium carbon- 
 ate, of which it is composed, is changed by the heat into 
 calcium oxide (lime), which unites with the quartz and other 
 oxides in the charge and forms a fusible silicate. When the 
 latter flows from the furnace and cools slowly in the air, it 
 looks much like pumice stone ; when it cools rapidly, it looks 
 like glass. Indeed it is not unlike glass in character. It is 
 known as the slag. 
 
 The coke serves a double purpose, first to reduce the iron 
 oxide, and second to act as a fuel and melt both the reduced 
 iron and the slag. A small part of the carbon of the coke is 
 dissolved in the molten iron. Heated air is blown under a 
 high pressure through the pipes, known as the tuyeres, 
 entering near the base of the furnace. The coke meeting 
 this air blast is burned to carbon dioxide, but this gas 
 passes up through the heated coke and is reduced to carbon 
 monoxide, 
 
 CO 2 +C->2CO. 
 
244 METALLURGY 
 
 The carbon monoxide passing through the hot iron oxide 
 in the middle part of the furnace reduces it, 
 
 Fe 2 O 3 + 3 CO 2 Fe + 3 CO 2 . 
 
 This reaction, however, is a reversible one, as indicated by 
 the double arrow, and it only proceeds in the desired direc- 
 tion towards the right so long as an abundance of carbon 
 monoxide compared with the amount of carbon dioxide is 
 present. Consequently, the escaping gases have a large con- 
 tent of carbon monoxide; the amount usually exceeds 20 
 per cent by volume of the total gas and it possesses about 
 one half the heating value of the coke used in the furnace. 
 The blast furnace gas is burned outside of the furnace to 
 heat boilers, and to preheat the air blown into the furnace. 
 It is also used in gas explosion engines to furnish power. 
 
 The ore and limestone are mixed and fed with alternate 
 layers of coke into the top of the furnace. The charge 
 gradually sinks through the shaft and undergoes various 
 changes as it approaches the point where the air enters, 
 which is the hottest part of the furnace. In the upper part 
 it is merely heated and dried ; in the central part most of the 
 reduction takes place, but the heat is not intense enough to 
 melt the iron. As the charge descends into the narrower 
 part of the furnace it becomes very hot and the iron alloys 
 with some of the carbon. Now pure iron melts only at 1520 
 C., a temperature which is hardly reached in any part of the 
 furnace ; but iron alloyed with a few per cent of carbon melts 
 as low as 1125 C. The molten iron sinks into the crucible 
 at the bottom of the furnace. The flux arid foreign rock 
 melt together as slag, which floats on the molten iron and 
 protects it from the oxidizing influence of the blast. 
 
 At the bottom of the crucible is the metal tap through 
 
BESSEMER PROCESS 245 
 
 which the molten iron is withdrawn about every six hours. 
 At other times the tap is kept closed. Above this is the slag 
 tap through which the molten slag is withdrawn every two 
 hours. The iron may be either cast into molds, forming 
 what is called pig iron, or it may be converted into steel as 
 described below. The slag is sometimes thrown away and 
 sometimes used for making cement. 
 
 257. Cast Iron. The direct product of the blast furnace is 
 not pure iron. It contains 3 to 4 per cent of carbon, some- 
 times as much as 3 per cent of silicon from a reduction of 
 some of the silicon dioxide and manganese, phosphorus, and 
 sulphur, if the ore contained these elements. This impure 
 iron melts easily and is useful in making castings, but it is 
 brittle and lacks strength. 
 
 Nevertheless it is able to resist crushing and it is largely 
 used in making supporting columns to sustain great weights 
 in buildings. It is also used for engine bases and supporting 
 structures for heavy machinery. Since it expands at the 
 moment of solidifying, it is forced into every corner of the 
 mold and very sharply defined castings are thus obtained. 
 On account of its cheapness and the facility with which it 
 is made into castings enormous quantities are used where 
 brittleness is not too objectionable a feature. 
 
 MANUFACTURE OF STEEL 
 
 The carbon in excess of 2 per cent together with the 
 silicon and some of the other impurities in pig iron make it 
 brittle and weak and unsuitable for many purposes. These 
 impurities, which are due to the reducing action in the blast 
 furnace, can be removed by an oxidizing process. 
 
 258. Bessemer Process. This method, which takes its 
 name from the inventor, is carried out in the so-called Besse- 
 
246 
 
 METALLURGY 
 
 mer converter, Figure 43. The converter, which may hold 
 as much as 20 tons of metal, is a steel shell lined with silicious 
 material; but when the metal contains much phosphorus 
 or sulphur it is necessary to make the lining of burnt dolomite 
 (limestone containing magnesium carbonate in addition to 
 calcium carbonate). When the silicious lining is used, the 
 
 method is called the 
 acid process; and 
 when the dolomite 
 lining is used, the 
 method is called the 
 basic process. 
 
 The converter is 
 partly filled with 
 molten iron from the 
 blast furnace, and 
 air under high pres- 
 sure is forced into the 
 hollow place in the 
 bottom, from which it 
 passes through small 
 perforations into the 
 molten metal. The 
 
 impurities are more easily oxidized by the air than is the iron. 
 The silicon and manganese oxides formed (and magnesium 
 phosphate in the basic process) float as molten slag on the 
 surface of the metal, and the carbon passes off as monoxide 
 gas. The heat produced in burning these impurities is 
 sufficient to keep the charge in a fluid condition. The 
 disappearance of the carbon flame indicates that the oxida- 
 tion is completed. It is impossible to stop the process when 
 the carbon is reduced to just the desired per cent, so it is 
 
 FIG. 43. Bessemer Converter. 
 
OPEN HEARTH PROCESS 
 
 247 
 
 customary to burn oft all the carbon and then add the nec- 
 essary amount in the form of an alloy of iron, manganese, 
 and carbon. The manganese improves the quality of the 
 product. 
 
 After the iron has been recarburized, the converter is tipped, 
 and the contents, which are now in the form of steel, are 
 poured into large ladles from which the ingot molds are filled. 
 
 259. Open Hearth Process. This is carried on in a fur- 
 nace such as is shown in Figure 44. Some of these furnaces 
 will hold 75 tons or more of charge. The hearths are lined 
 
 FIG. 44. Open Hearth Furnace. Gas (A) and air (B) after passing over hot 
 bricks enter the furnace together. The iron (C) rests upon the hearth lin- 
 ing (D). The hot gaseous products heat the bricks in E and F which are 
 later made the inlets in order to preheat the entering gas and air. 
 
 with the same materials used for converter linings. They 
 are heated by burning gas above the charge ; both the gas and 
 the air which is necessary to burn it are previously heated by 
 passing over hot bricks below the furnace, thus increasing 
 the furnace temperature. 
 
248 
 
 METALLURGY 
 
 The material used for making steel in these furnaces is a 
 mixture of pig iron, scrap iron or steel, and oxide iron ore. 
 
 FIG. 45. Open Hearth Furnaces. Pouring Ingots. 
 
 The scrap dilutes the impurities in the pig iron, but most 
 of the impurities are removed by oxidation, due partly to 
 the oxygen in th air and partly to the oxygen of the iron 
 oxide. When a sample shows that the impurities are suffi- 
 
SPECIAL STEELS 249 
 
 ciently removed, the charge is withdrawn into ladles, car- 
 burized if necessary in the same manner as in the Besse- 
 mer process, and then cast into ingots. Since it is impossible 
 to take samples during the treatment in the Bessemer con- 
 verter, the process cannot be so well regulated as the open 
 hearth process, where frequent samples may be taken and a 
 definite product obtained. For this reason, open hearth 
 steel is usually considered more reliable than Bessemer 
 steel. 
 
 260. Uses of Mild Steel. Steel containing less than 0.3 
 per cent of carbon is known as mild steel. Most of the steel 
 produced by the Bessemer and open hearth processes is of 
 this kind, and it is used in tremendous quantities for railroad 
 rails, for structural work in buildings and bridges, for wire 
 fences, for telegraph wires, and for rolling into sheet metal. 
 The sheet metal may be used uncoated for many purposes. 
 For so called tin cans it is coated with tin to protect it from 
 oxidation and from the action of the food products which may 
 be put up in the cans. Sheet iron or steel is coated with zinc 
 (galvanized), especially when it must resist the corrosive ac- 
 tion of a damp atmosphere. Sheet iron for house furnaces in 
 damp cellars and for roofing purposes is always galvanized. 
 
 Great strength and toughness combined with a consider- 
 able degree of hardness characterize mild steel and give it its 
 great usefulness. 
 
 261. Special Steels. Steels may contain amounts of car- 
 bon between and 1.5 per cent. In general, the higher the 
 carbon, the harder the steel, but the heat treatment (temper- 
 ing, annealing, etc.) has a great effect in determining the hard- 
 ness. 
 
 High carbon steel for tools, watch springs, razor blades, 
 and the like requires special treatment arid is made on a 
 
250 
 
 METALLURGY 
 
 much smaller scale and by a more expensive process than 
 common steel. 
 
 Of the other elements than carbon added to give special 
 properties may be mentioned chromium, which gives a very 
 hard steel used in making burglar-proof safes, and nickel, 
 which gives a tough steel used for the armor plate of warships. 
 
 WROUGHT IRON 
 
 262. The process by which most of the wrought iron is 
 made is called the puddling process. The furnace used re- 
 sembles slightly the open hearth steel furnace, but it has a 
 fire box at one end where coal, oil, or gas is burned and the 
 flame passes over the charge to the flue at the other end. 
 
 FlG. 46. Reverberatory Furnace. 
 
 This type of furnace is called a reverberatory furnace because 
 the roof is so constructed as to deflect or reverberate the heat 
 of the flame down on the charge. Modifications of it are used 
 in various other metallurgical processes. 
 
 The hearth of the puddling furnace is lined with blocks of 
 oxide iron ore. The pig iron is usually charged in the solid 
 
WROUGHT IRON 251 
 
 form and melted in the furnace. The oxygen of the lining and 
 of the atmosphere unites with the impurities in the charge, 
 the carbon passes off as carbon monoxide, and the other 
 oxides combine to form slag. The iron, which is now nearly 
 pure, has a much higher melting point than the original pig 
 iron and instead of being liquid is in a pasty condition. The 
 men in charge of the furnace, with tools made for the purpose, 
 now stir the charge, mixing slag and iron together and then 
 divide it into several balls which can be removed from the 
 furnace with tongs suspended from a traveling pulley. 
 These balls are passed through machines which squeeze 
 out most of the slag and finally roll the iron out into the rods 
 and bars of commerce. 
 
 263. Uses of Wrought Iron and Very Low Carbon Steel. 
 Pure iron, unlike the impure material, corrodes but slowly. 
 It is rather soft, being easily scratched with a knife, highly 
 ductile and malleable, but still it has a fair degree of tenacity. 
 It is very useful where great toughness combined with con- 
 siderable strength is required. 
 
 Wrought iron is almost pure iron. It softens sufficiently 
 for welding below 1000 C. although it does not melt below 
 1500 C. In this it is very different from cast iron, which does 
 not soften before it melts. Wrought iron is therefore suitable 
 for forging it is the metal used by the blacksmith and 
 the slight admixture of slag that it contains gives it a fibrous 
 structure which seems to increase rather than detract from 
 its usefulness for forging. Wrought iron probably resists 
 corrosion better than any other form of iron and this property 
 seems to be due to its freedom from carbon. 
 
 Wrought iron, however, is more costly than mild steel and in 
 recent years a steel unusually low in carbon, sometimes called 
 " ingot iron," has been prepared in large amounts and is 
 
252 METALLURGY 
 
 coming into use for wire fences and many other objects which 
 must have a high resistance to corrosion when exposed to 
 the weather. It is a fact of common knowledge that some 
 wire fences resist corrosion for years, whereas others are 
 badly corroded in a few months. The difference can almost 
 always be traced to the quality of the iron. 
 
 COPPER 
 
 264. Native copper is found abundantly in the Lake Su- 
 perior mines in northern Michigan. It is also found in some 
 
 other places, but not 
 in workable quanti- 
 ties. The rock in 
 which the native cop- 
 per is imbedded is 
 crushed, and the cop- 
 per particles are sep- 
 arated from the rock 
 
 FIG. 47. Native Copper. 
 
 by a washing process 
 
 which is based on the higher specific gravity of the copper. 
 The metal is then melted and cast into ingots. 
 
 Copper is found in nature principally as the sulphide, and 
 it is usually associated with iron sulphide and other sulphides. 
 The upper layers of great copper deposits are often found to 
 consist of the oxide and the carbonate, but as the mines are 
 deepened the ore always changes to sulphide. The oxygen 
 and carbon dioxide in the air, assisted by percolating waters, 
 acting for thousands of years, have worked down to some 
 depth and slowly oxidized the original sulphide. 
 
 Copper is obtained from the sulphide ores in two steps. 
 The first step is to eliminate all of the waste rock and part 
 of the iron and sulphur, thus producing copper matte, a 
 
COPPER 
 
 253 
 
 FIG. 48. Chalcopyrite. 
 
 mixture o^ the sulphides of copper and iron. This may con- 
 tain varying amounts of copper up to 80 per cent, but usually 
 between 20 and 40 per 
 cent. The next step 
 is to oxidize all the re- 
 maining iron and sul- 
 phur, leaving metallic 
 copper. 
 
 The first step may 
 be performed either in 
 a reverberatory fur- 
 nace or in a blast 
 furnace. The latter 
 resembles the iron 
 blast furnace, but is 
 much smaller. The second step is to treat the molten 
 matte in a converter similar to the Bessemer steel converter, 
 except that instead of being admitted at the bottom the 
 air is blown in at one side a short distance above the 
 bottom. The oxygen of the air unites with the sulphur 
 and the iron; the sulphur dioxide passes off and the iron 
 oxide unites with the silicious lining of the converter, or with 
 silicious material thrown into the matte, and forms slag. 
 When the impurities are oxidized as far as possible, the slag 
 is poured off and the copper cast into cakes for refining. 
 
 Oxide ores may be reduced directly to 'metallic copper in 
 the blast furnace. 
 
 265. Refining of Copper. The copper obtained from the 
 furnaces invariably contains other metals, including gold and 
 silver. The most important use of copper is as a conductor 
 of electricity. Even small amounts of such good conductors 
 as gold and silver alloyed with copper impair its conductivity ; 
 
254 
 
 METALLURGY 
 
 and other elements, notably arsenic, impair the conductivity 
 to a still greater degree. 
 
 Crude copper may be refined either in a reverberatory fur- 
 nace or by an electrolytic method. The former is an oxidiz- 
 ing process which slags most of the impurities and is used 
 when the arsenic and precious metals are low; the latter 
 are not as easily oxidized as the copper itself. The electro- 
 lytic method removes practically all of the impurities ; and 
 since the gold and silver can be saved, it is always used 
 when there is a sufficient quantity of these metals present to 
 warrant the extra expense of the process. The main opera- 
 tions are as follows : 
 
 The copper is cast in plates about two inches thick and 
 four feet square which are hung alternately as positive elec- 
 trodes in a bath con- 
 taining copper sul- 
 phate and sulphuric 
 acid. Alternating in 
 the bath with these 
 plates are thin plates 
 of pure copper, all 
 connected with the 
 negative conductor of 
 the electric circuit. 
 In Figure 49 we have 
 shown five negative 
 and four positive 
 plates. In one of the large refining works, they put twenty- 
 three negative and twenty-two positive plates in one tank. 
 One building has sixteen hundred of these tanks in opera- 
 tion. The current in passing dissolves copper from the 
 positive electrode, takes it through the solution, and deposits 
 
 FIG. 49. Electrolytic Refining of Copper. 
 
LEAD 
 
 255 
 
 it upon the negative plates. The impurities either do not 
 dissolve at all or else they pass into solution and remain in 
 the solution. The insoluble impurities, among which are all 
 the gold and silver, simply drop to the bottom of the tank as 
 the electrode is eaten away. The mud from the bottom is 
 worked up for gold and silver and yields a valuable profit. 
 
 266. Uses of Copper. Copper is ductile, tough, and resist- 
 ant to corrosion, and it has the highest electrical conductivity 
 of any metal except silver. It is used to a very large ex- 
 tent in electrical work, for telephone, electric light, and 
 trolley wires, and for the coils of all electrical machines. 
 
 Its resistance to corrosion makes it a useful metal for ex- 
 posed corners and edges of roofs, for water conductors, and 
 cooking utensils. 
 
 Copper is an important component of many useful alloys, 
 notably brass and bronze. Brass usually contains about 
 two thirds copper and one third zinc. 
 
 LEAD 
 
 267. By far the commonest ore of lead is galena, or lead 
 sulphide. It is a 
 
 beautifully lustrous 
 gray crystalline sub- 
 stance, and it is often 
 found crystallized in 
 almost perfect cubes. 
 
 The metallurgical 
 treatment of lead sul- 
 phide is similar in 
 principle to that of 
 copper sulphide. One 
 method is to roast it ~FIG. 50. Galena. 
 
 B. AND W. CHEM. 17 
 
256 METALLURGY 
 
 in a reverberatory furnace so as to burn the sulphur and 
 leave uncombined lead. The process is not carried out, 
 however, in a single operation. It is usually roasted first 
 with free access of air whereby only a part of the ore is oxi- 
 dized. Part of the lead sulphide so attacked is changed to 
 lead sulphate and the other part to lead oxide and sulphur 
 dioxide. 
 
 PbS + 2 O 2 -> PbS0 4 , 
 2 PbS + 3 O 2 -> 2 PbO + 2 SO 2 . 
 
 The air is then cut off and the temperature is raised, whereby 
 the unchanged lead sulphide reacts with the lead sulphate 
 and lead oxide, yielding metallic lead and sulphur dioxide. 
 
 PbSO 4 + PbS -> 2 Pb + 2 SO 2 , 
 2 PbO + PbS -> 3 Pb + SO 2 . 
 
 Another method is to treat the ore with coke and fluxes 
 in a blast furnace. The products of this furnace are slag, 
 lead matte, and metallic lead. 
 
 The crude lead obtained by either of the above methods 
 may carry considerable amounts of silver and gold, in which 
 case it is refined by special processes designed to save these 
 metals. The amount of silver obtained in this way is of 
 great importance. 
 
 268. Uses of Lead. Lead, owing to its high degree of 
 resistance to the action of water and of some acids, is used 
 for water pipes, coverings of wire cables in conduits, tanks 
 and containers for various liquids, and for the chambers in 
 which sulphuric acid is made. 
 
 Lead salts are extremely poisonous, and the use of lead for 
 conveying drinking water is open to objection. Although 
 no harmful amount is dissolved by hard water, nevertheless 
 
ZINC 257 
 
 soft water, particularly rain water, dissolves sufficient lead 
 oxide from the pipes to cause serious danger. 
 
 Lead melts very easily ; alloyed with tin it makes solder. 
 
 With antimony lead forms the alloy called type metal. 
 
 The great density of lead early led to its use in bullets and 
 shot. 
 
 Large amounts are also made into white lead, a basic car- 
 bonate of approximately the composition Pb(OH) 2 2 PbCO 3 , 
 which is used in paints. 
 
 ZINC 
 
 269. The most important ore of zinc is zinc sulphide. 
 This is roasted, whereby it is changed to oxide. 
 
 2 ZnS + 3 O 2 -> 2 ZnO + 2 SO 2 . 
 
 The sulphur dioxide given off is commonly utilized to make 
 sulphuric acid, as indeed is also sometimes done at lead and 
 copper smelters. The zinc oxide is mixed with crushed 
 coal and heated in retorts. 
 
 ZnO + C -> Zn + CO. 
 
 Zinc is a volatile metal when compared with copper, lead, and 
 iron. Zinc vapor consequently passes from the retort to- 
 gether with the carbon monoxide. It is condensed to liquid 
 zinc, which is run into molds to solidify. 
 
 Some ores which are not suitable for the production of 
 metallic zinc are heated on a grate with coal, and the gases 
 after cooling are filtered through cloth. The zinc is thus re- 
 covered as zinc oxide, a white powder, which has a ready 
 sale to paint and rubber manufacturers. 
 
 270. Uses of Zinc. Zinc is one of the most active of the 
 heavy metals, as is evidenced by the vigor with which it 
 
258 METALLURGY 
 
 displaces hydrogen from acids. Hence arises its use in 
 battery cells such as are used for ringing electric bells. It is 
 the zinc rod or plate in such cells which is eaten away. 
 
 In view of the great chemical activity of zinc it may seem 
 strange that it is so little attacked by the weather, and that 
 it is used to galvanize iron and thus to protect the less active 
 metal. The secret of its resistance to corrosion is that it 
 quickly becomes coated with a thin impervious layer of oxide, 
 which excludes air and dampness from the metal beneath. 
 
 MERCURY 
 
 271. The sulphide ore of mercury is roasted in furnaces 
 with access of air. The sulphur burns to sulphur dioxide, 
 and the mercury, which is but an inactive metal, is left 
 uncombined. It distills with the heat, and mercury vapor 
 passes with the gases into a condensing chamber from which 
 the liquid mercury is obtained. 
 
 SILVER 
 
 272. A large part of the world's supply of silver, as already 
 noted, is obtained as a by-product from the production of 
 lead and copper. 
 
 Apart from some native silver, the important ores which 
 are worked for silver alone are the sulphide, arseno-sulphide, 
 and the chloride. Many different processes are employed 
 for treating silver ores ; the one to be described is perhaps 
 typical. 
 
 The crushed rock containing sulphide ore is mixed with 
 common salt and roasted, whereby the silver sulphide is 
 changed to chloride. Silver chloride is insoluble in water 
 but is soluble in a dilute solution of sodium thiosulphate. 
 
 
GOLD 
 
 259 
 
 
 The roasted sulphide ore, or the chloride ore direct, is treated 
 with sodium thiosulphate solution and the liquid is then 
 run into tanks and the silver precipitated as sulphide by 
 adding sodium sulphide. The insoluble silver sulphide is 
 recovered by filtering, and silver is obtained from this by 
 burning off the sulphur. 
 
 The cyanide process as described under gold is also exten- 
 sively used for silver ores. 
 
 GOLD 
 
 273. Gold is usually found in the uncombined condition, 
 but in exceedingly small particles disseminated throughout 
 masses of rock. Most 
 of the gold can be 
 recovered by finely 
 crushing the ore in 
 stamping machines 
 and washing it with 
 water through a shal- 
 . low trough, the wide 
 flat bottom of which 
 consists of a copper 
 plate coated with mercury. When the gold comes in con- 
 tact with the mercury, it amalgamates with it, while the 
 waste material passes on. The plates are scraped periodi- 
 cally and the gold is recovered from the amalgam by distill- 
 ing off the mercury. 
 
 Some ores can be more successfully treated by a chemical 
 method. The one most used is the cyanide process, in which 
 the finely crushed ore is treated with a solution of potassium 
 
 I cyanide which, together with oxygen of the air, reacts with 
 the gold, producing a soluble compound. The solution is run 
 
 FIG. 51. Native Gold. 
 
260 METALLURGY 
 
 into tanks filled with zinc shavings. It has already been 
 noted that zinc is a more active metal than gold. Here again 
 this fact is shown, for the zinc passes into the solution, forcing 
 the gold to precipitate as free metal. This finely divided 
 gold is then melted and cast into bars. 
 
 ALUMINIUM 
 
 274. Aluminium oxide cannot be reduced to metallic alu- 
 minium by means of carbon in a blast furnace because of the 
 very great chemical activity of the element. Aluminium 
 oxide will react with carbon at a very high temperature, but 
 aluminium carbide and not the uncombined metal is ob- 
 tained. 
 
 Formerly aluminium was obtained by treating aluminium 
 chloride with sodium, 
 
 3 Na + Aids -> 3 Nad + Al, 
 
 but this method is now entirely superseded by the electrolytic 
 method. 
 
 Aluminium oxide can be melted only at a very high 
 temperature, but cryolite, a mineral of the formula 
 
 _____ 3 NaF A1F 3 , melts 
 
 very easily, and, fur- 
 thermore, will dis- 
 solve aluminium 
 oxide much as water 
 will dissolve common 
 salt. In the elec- 
 
 FIG. 52. Electrolytic Production of Aluminium. 
 
 trolytic process cry- 
 olite is melted in iron vats lined with carbon, aluminium 
 oxide is added, and carbon electrodes are introduced. The 
 current enters through the carbon electrodes and passes out 
 
ALUMINIUM 261 
 
 through the iron vats. The resistance to the passage of 
 the current causes heating sufficient to keep the charge 
 melted. Oxygen is liberated at the carbon electrode and 
 either escapes or burns the carbon to carbon monoxide. 
 The aluminium is liberated at the surface of the carbon 
 lining and sinks in the melted condition to the bottom of 
 the bath, where it is occasionally tapped off. The process 
 is continuous and fresh aluminium oxide is added as fast 
 as that in the bath is decomposed. The cryolite suffers no 
 change. 
 
 The chief ore of aluminium is bauxite, a rather impure 
 aluminium oxide containing water. For the best grade of 
 metal, this ore must be purified chemically so that only pure 
 aluminium oxide shall be introduced into the electrolytic 
 bath. 
 
 275. Uses of Aluminium. Aluminium is the lightest of 
 the metals which are strong enough and resistant enough 
 to corrosion to be useful for objects to stand wear and 
 weather. The resistance to corrosion does not arise, however, 
 from its chemical inactivity, but rather from the fact that it 
 coats itself with a very impervious film of oxide. The truth 
 of this statement is shown by an interesting experiment. 
 If a piece of aluminium is carefully cleaned with hydrochloric 
 acid and a little mercury is rubbed on the surface, it amalga- 
 mates. Soon a white fluffy powder, aluminium oxide, is seen 
 to form over the amalgamated surface and* to increase quite 
 rapidly in bulk. Before long the aluminium has entirely 
 disappeared, a little globule of mercury is left, and a heap of 
 the fluffy powder. On the surface of the amalgam the 
 aluminium oxidizes as well as on the surface of the pure metal, 
 but the oxide does not adhere to the liquid surface ; it floats 
 off and therefore the oxidation continues. 
 
262 METALLURGY 
 
 Aluminium is not as cheap as steel, and its use is confined 
 mostly to articles in which lightness is a prime essential, 
 such as parts of automobiles and flying machines. Alumin- 
 ium serves excellently for cooking utensils. It is a very good 
 conductor of heat and electricity and it is sometimes used in 
 place of copper for electric conductors. 
 
 SUMMARY 
 
 Metals in Nature : All metals except the chemically inactive ones, 
 such as copper, silver, gold, and platinum, are found in nature 
 always in combination with non-metals, most often with 
 oxygen and sulphur. Gold and platinum are almost always, 
 and silver and copper are sometimes, found uncombined. 
 
 Metals from Ores : Oxygen can be removed from combination with 
 most of the heavy metals by means of carbon, for the heavy 
 metals are, in the main, not very active chemically. 
 
 The sulphides can be converted into oxides by roasting, whereby 
 sulphur dioxide escapes. 
 
 Oxides of the very active metals like aluminium, sodium, potas- 
 sium, magnesium, and calcium cannot be reduced with carbon 
 and obtained as uncombined metals. Recourse is usually had 
 in these cases to electrolysis of their fusible compounds. 
 
 Questions 
 
 1. Suggest a method to obtain metallic tin from tinstone. 
 
 2. What metals can be obtained from their oxide ores by re- 
 duction with carbon ? What ones cannot ? 
 
 3. What method is available for separating the metal when 
 the oxide cannot be reduced with carbon? 
 
 4. How might mercury be obtained from mercuric oxide with- 
 out using carbon ? 
 
 6. Explain how aluminium oxide is brought into the liquid 
 condition previous to the separation of the metal by electrolysis. 
 
 6. How are gold and silver extracted from the crude copper 
 from the smelter? 
 
QUESTIONS 263 
 
 7. When refuse rock from copper mines is heaped up and kept 
 moist, any copper sulphide present oxidizes slowly to copper sul- 
 phate, which is soluble. How might metallic copper be obtained 
 from the solution draining from the bottom of the heap ? 
 
 8. Calculate the per cent of iron in each of the four minerals, 
 Fe 2 3 , Fe 3 4 , FeC0 3 , and Fe 2 3 3 H 2 O. 
 
 9. What weight of carbon would be necessary to reduce (a) 1000 
 kilograms of cuprous oxide, Cu 2 0, (6) 1000 kilograms of cupric 
 oxide, CuO, assuming the carbon is all changed to carbon dioxide 
 in the process and neglecting the amount of fuel which must be 
 burned to supply heat. 
 
 10. What weight of carbon is needed to reduce 1000 kilograms 
 of zinc oxide? The carbon is oxidized only to carbon monoxide. 
 
CHAPTER XXIII 
 
 COMPOUNDS OF CARBON 
 
 WE have already become familiar with some of the prop- 
 erties and some of the compounds of carbon. We have 
 seen that carbon enters into a continuous cycle of changes 
 between living and inorganic matter. Fuels, wood, coal, 
 charcoal, which are without exception the product of 
 present or past organic life burn, and the carbon in them 
 yields the gas carbon dioxide. Plants take carbon dioxide 
 from the air through the surfaces of their green leaves and 
 with the aid of the energy obtained from sunlight convert 
 it into the most complex and varied compounds containing 
 sometimes oxygen and hydrogen and sometimes nitrogen in 
 addition. These compounds in time always yield carbon 
 dioxide back again to the air, for they are either burned 
 directly as fuel, or they are eaten by animals and burned 
 slowly in the animal tissues, or they decay, which is also a 
 process of slow combustion. 
 
 In the present chapter we shall deal mainly with carbon 
 as it exists in substances which are not closely related to 
 living things. In Chapter XXIV, a brief view will be 
 given of a few of the more important of the compounds 
 of carbon, which are formed like starch and sugar directly 
 in life processes, or are at least derived from compounds so 
 formed. 
 
 264 
 
AMORPHOUS CARBON 265 
 
 UNCOMBINED CARBON 
 
 There are three different forms in which uncombined carbon 
 exists, namely, amorphous carbon, which, as the name im- 
 plies, is without definite form or shape, and two different 
 crystalline forms, graphite and diamond. 
 
 276. Amorphous carbon is without crystalline structure 
 and in that sense it is without form. Masses of it may, of 
 course, exist in any shape, but there is no evidence within 
 the mass of any tendency to a definite structure. Amorphous 
 carbon is obtained when organic matter is decomposed by 
 great heat. The carbon is left as a charred mass, while the 
 other elements of the compound are driven off as volatile 
 matter. Charcoal, coke, lampblack, and gas carbon are 
 well-known varieties of amorphous carbon. 
 
 Charcoal is obtained by heating wood in the absence of 
 air ; a number of volatile products, including water, wood 
 alcohol, acetic acid, acetone, and tar, are driven off, and with 
 these products escape all of the hydrogen and oxygen as well 
 as a portion of the carbon of the wood, while charcoal is left 
 as a non- volatile residue. Charcoal is nearly pure carbon, 
 except that it still contains the mineral matter of the wood. 
 All ordinary kinds of charcoal, therefore, leave a little mineral 
 ash when they are burned. 
 
 Coke is obtained from soft coal in much the same manner 
 as charcoal is obtained from wood. The 'volatile products 
 driven off are mainly illuminating gas, coal tar, and ammonia. 
 
 Lampblack is familiar to all who have seen a smoking 
 kerosene lamp. It is manufactured by allowing petroleum 
 oil or natural gas to burn with an insufficient supply of air. 
 The heat of the flame decomposes the compound ; the hydro- 
 gen burns and maintains the flame, while a large part of the 
 
266 COMPOUNDS OF CARBON 
 
 carbon remains in extremely small particles as soot or lamp- 
 black. This adheres to a cooled surface which continually 
 revolves just above the flame. A scraper bears upon another 
 part of the revolving surface and scrapes off the lampblack 
 into an appropriate receptacle. Lampblack is much used as 
 a pigment in paints and especially in printer's ink. 
 
 Gas carbon is formed in the retorts in which soft coal is 
 destructively distilled in the manufacture of illuminating 
 gas. It is formed where the gas comes in contact with the 
 white-hot top and sides of the retort and is there decomposed. 
 Being formed at a higher temperature, it is harder and more 
 compact than lampblack. It is largely used in the manu- 
 facture of electric-light carbons. 
 
 277. Coal. Coal is not pure carbon, but it consists very 
 largely of carbon. It is a product of the decomposition of 
 trees and plants which grew in a long-past geologic age. By 
 floods or other natural agencies, the luxuriant vegetation of 
 the so-called carboniferous period of the earth's history be- 
 came covered with deep layers of earth in some localities 
 before it had a chance to fully decay. Deep down beneath 
 the earth's surface, heat and pressure have in the course of 
 centuries changed the original organic material into coal. 
 Coal still contains some of the hydrogen, oxygen, and nitro- 
 gen of the original organic matter ; soft or bituminous coal 
 contains a considerable amount ; hard or anthracite coal 
 contains much less. 
 
 278. Graphite. We have seen above that the residue 
 obtained by artificially heating coal in coking ovens is coke, 
 one of the varieties of amorphous carbon. The final product 
 of a similar process in nature is graphite. Where coal has 
 been very deeply buried and consequently subjected to more 
 of the earth's interior heat, as well as enormous pressure, the 
 
GRAPHITE 267 
 
 decomposition has been more complete. The result of this 
 decomposition when carried to its final stage is graphite. 
 
 Graphite is found in nature crystallized in soft hexagonal 
 plates or prisms. Its specific gravity is 2.25 ; it is consider- 
 ably more dense than amorphous carbon. It is exceedingly 
 soft and offers but little friction when rubbed ; on account of 
 this property, it is much used as a lubricant. It is black and 
 opaque and it conducts electricity. It is much used in elec- 
 trical work on account of its conductance and its low coeffi- 
 cient of friction. 
 
 The most familiar use of graphite is in " lead " pencils, 
 for which purpose it is mixed with clay to give the desired 
 degree of hardness and then molded into the " leads." 
 
 Graphite is very resistant to heat, so that it is an excellent 
 material for making crucibles, electrodes, and linings in fur- 
 naces in which high temperatures are employed. It is ex- 
 tremely hard to make graphite burn. The harder an anthra- 
 cite coal, the more difficulty there is in getting it to burn, 
 and when the coal is graphitic in nature, it scarcely burns at 
 all in a furnace. 
 
 In pure oxygen, a complete combustion of graphite can be 
 effected, and the only product of the combustion is carbon 
 dioxide. It is thus made certain that graphite is composed 
 only of carbon. 
 
 Graphite is now made artificially in an electric-furnace 
 process in which an enormous current is Sent through a fur- 
 nace packed with anthracite coal. The current produces 
 the temperature of the electric arc; the coal is completely 
 decomposed and all the ordinarily volatile matter and even 
 the mineral matter, which in an ordinary furnace is involatile, 
 are expelled as vapor. Carbon alone is left as a residue, and 
 this is changed into the form of graphite. 
 
268 
 
 COMPOUNDS OF CARBON 
 
 279. Diamond is the most beautiful and the rarest as well 
 as, perhaps, the most interesting form of carbon. It is just 
 as much pure carbon as are graphite and amorphous carbon, 
 as can be proved by burning it in oxygen ; it gives only car- 
 bon dioxide, and a given weight of diamond gives exactly 
 the same amount of carbon dioxide as the same weight of 
 either of the other forms of carbon. 
 
 One would never suspect from their physical properties 
 that diamond and graphite are both composed entirely of 
 the same element, for no two substances 
 could be more dissimilar. Diamond is 
 the hardest substance known, whereas 
 graphite is one of the softest of solid sub- 
 stances. Diamond is colorless, transpar- 
 ent, and a non-conductor of electricity, 
 whereas graphite is black, opaque, and a 
 conductor of electricity. The diamond is 
 insoluble in all known liquids under ordi- 
 nary conditions of temperature and pres- 
 sure. Diamond crystallizes in the regular 
 system, usually in octahedra, whereas 
 graphite crystallizes in hexagonal plates. 
 Diamond has a specific gravity of 3.51, and it is thus by far 
 the densest form of carbon. When it is intensely heated in 
 the absence of air, it swells and becomes black graphite, but 
 when heated intensely in oxygen, the diamond burns com- 
 pletely, producing only a gaseous product. 
 
 The differences between diamond, graphite, and amorphous 
 carbon are believed to be due to the same causes as the dif- 
 ference between ozone and ordinary oxygen, that is, to a 
 difference in the number of atoms in the molecule and possibly, 
 also, to the way in which the atoms are linked together. 
 
 FIG. 53. Diamond. 
 
 (Natural Crystal.) 
 
DIAMONDS 269 
 
 It was discovered by Moissan, the French chemist, that 
 diamonds of microscopic size can be made artificially by al- 
 lowing carbon to crystallize from solution in a molten material 
 kept under great pressure. Carbon dissolves to a consider- 
 able extent in molten iron. If a mass of molten iron satu- 
 rated with carbon is suddenly chilled, the outer layers 
 solidify, while the inner portion remains liquid. The latter 
 afterwards solidifies more slowly, and since iron containing 
 much carbon expands on solidifying, it exerts a great pressure 
 against the already solid exterior of the mass. The dissolved 
 carbon crystallizing out under this great pressure assumes 
 the form of diamond. Under ordinary pressure, the carbon 
 separates as graphite. By dissolving away the iron with 
 acid, one can obtain the tiny diamond crystals, but all that 
 have ever been made in this way are too small to be of value. 
 There is geological evidence that the natural diamonds 
 of South Africa have crystallized from solution in molten 
 rock subjected to enormous pressure. 
 
 280. Uses of Diamonds. Aside from its beauty when cut 
 as a gem, diamond is of use in the industrial arts on account 
 of its great hardness. The poorer stones that cannot be made 
 
 into gems are set in solder 
 on the edges of great saws 
 that are used for stone 
 cutting ; similarly, they 
 are set 'at the bottom of 
 tubular drills that are used 
 
 FIG. 54. -Diamond. (Cut Gem.) " for making deep borings in 
 
 rock. Diamonds are used 
 in the jeweled bearings of delicate instruments of precision. 
 Wires of exact dimensions are made by drawing the metal 
 through perforations in thin plates of diamond. 
 
270 COMPOUNDS OF CARBON 
 
 CARBON AND OXYGEN 
 
 We have already seen in Chapter IV that carbon burns in 
 a plentiful supply of oxygen to form carbon dioxide, but with 
 a restricted supply it forms carbon monoxide. 
 
 281. Carbon dioxide is the anhydride of carbonic acid, 
 H 2 CO 3 , a comparatively weak acid, but still one that is ca- 
 pable of forming salts with all strong bases. A vast amount 
 of carbon dioxide is thus held in the mineral world in com- 
 bination with various bases. Calcium carbonate is the 
 most plentiful of the carbonates. Limestone, marble, and 
 shells of marine animals are natural forms of this substance. 
 Magnesium carbonate is also very abundant ; carbonates of 
 iron, lead, and copper are abundant and constitute valuable 
 ores of these metals. 
 
 282. Carbon monoxide is not acidic in nature, as is the 
 dioxide ; it therefore does not combine with bases, and we 
 never find it fixed as a component of any of the solid matter 
 of the earth's crust. Its most striking properties are its 
 poisonous character and its combustibility. 
 
 The escape of carbon monoxide into living rooms, either 
 from charcoal fires, from faulty furnaces, or from illuminating 
 gas cocks, is a source of grave danger. 
 
 Carbon monoxide is so combustible and yields so much 
 heat in burning that in spite of its poisonous character great 
 quantities of it are made and used admixed with other gases 
 as fuel. Pure carbon monoxide burns with a pale blue 
 flame and yields carbon dioxide. 
 
 283. Water gas is essentially a mixture of equal volumes of 
 carbon monoxide and hydrogen. It is made by blowing steam 
 through incandescent carbon with which it reacts according 
 to the equation : c ^ CQ ^ 
 
WATER GAS 
 
 271 
 
 In the process of making water gas for lighting in large 
 cities, coke or anthracite coal is placed in large vertical cylin- 
 drical furnaces (generators) and kindled at the bottom. Air 
 is blown in until the fire has heated the whole mass to incan- 
 descence. Then the air is cut off and steam is blown in and 
 
 FIG. 55. Manufacture of Water Gas. 
 
 the water gas is produced. When the furnace has become 
 partly cooled by this last process, the gas formation ceases, 
 and the mass must be again heated by blowing in air. 
 
 Since hydrogen and carbon monoxide both burn with nearly 
 colorless flames, water gas cannot be used by itself for illumi- 
 nating purposes. Illuminants are usually added to it by 
 " cracking " petroleum oil. The gas is led through a chamber 
 (the carburetor) containing a checkerwork of white-hot fire 
 brick over which petroleum oil drops. The heat decomposes 
 the oil vapor as it passes through the superheater and per- 
 manent gases of high illuminating power are thereby formed. 
 
 284. Producer Gas. When air enters from the bottom of 
 a deep anthracite coal or coke fire, carbon dioxide is, without 
 
 B. AND W. CHEM. 18 
 
272 
 
 COMPOUNDS OF CARBON 
 
 doubt, formed in the lower layer. As this gas rises, however, 
 it passes through other layers of white-hot carbon and is 
 thereby reduced to carbon monoxide. 
 
 C0 2 +C->2CO. 
 
 The long, pale blue flames seen rising from an anthracite 
 fire, in an ordinary house furnace, are due to the burning 
 carbon monoxide. 
 
 The heat developed, when carbon monoxide burns to car- 
 bon dioxide, is more than twice as great as that set free when 
 carbon burns to carbon monoxide. It is obvious, then, that 
 to obtain anything like the full heating value of the coal, 
 
 FIG. 56. Manufacture of Producer Gas. 
 
 enough air must be admitted through the upper door of the 
 furnace to completely burn the carbon monoxide. 
 
 Gas that is formed in a manner similar to this is used ex- 
 tensively in metallurgy and other industries, and is known 
 
COAL GAS 273 
 
 as producer gas. Air is drawn through a very deep coal 
 fire in the generator. The resulting gas mixture contains 
 all the nitrogen of the air, but all of the oxygen has com- 
 bined with carbon to form carbon monoxide. The gas is 
 conducted through pipes to the furnaces where it is to be 
 burned as fuel. By the process as so far outlined, it is ap- 
 parent that the heat developed by the addition of the first 
 unit of oxygen to the carbon would be wasted. By moist- 
 ening the in-going air as it passes through the economizer or 
 by introducing a carefully regulated quantity of steam into 
 the furnace, together with the air, this heat is largely 
 utilized in producing water gas. The addition of this water 
 gas to the producer gas, of course, considerably increases the 
 fuel value of the latter. 
 
 285. Coal gas is made by the destructive distillation of 
 soft coal. The coal is placed in fire-clay retorts or in ovens 
 and heated to a white heat. The chemical compounds exist- 
 ing in the coal are mostly broken down and simpler substances 
 are formed. Coke is left behind while a great variety of vol- 
 atile substances, containing some of the carbon of the coal and 
 all of the hydrogen, are driven off. After purification from 
 tar, ammonia, sulphur compounds, etc., the gas is ready for 
 delivery to the pipes of the city lighting system. This 
 purification consists mainly in condensing all substances 
 which, if not thus removed, would later condense when cooled 
 in the gas mains, thus tending to clog them. It also serves 
 to remove certain valuable by-products, principally coal tar 
 and ammonia. The process in addition largely removes 
 hydrogen-sulphide gas, the presence of which in the illumi- 
 nating gas is objectionable, because on burning it produces 
 sulphur-dioxide gas, which is harmful to people and to plants, 
 especially when formed in poorly ventilated houses. The 
 
274 
 
 COMPOUNDS OF CARBON 
 
 condensation of the less volatile materials, such as tar, takes 
 place in a series of condensers and scrubbers. The condensers 
 may be either air or water cooled. In the scrubbers the gases 
 are subjected to the cooling and dissolving action of water 
 which is sprayed over a grid or lattice-like arrangement 
 of wooden strips in a rectangular tower. The gases are 
 thoroughly washed by contact with the large extent of wet 
 surface. Thus much tar and ammonia are removed from the 
 
 FIG. 57. Manufacture of Coal Gas. 
 
 crude gas. Rotary scrubbers are also sometimes used in 
 which the crude gas is churned with water to remove tar 
 and ammonia and other objectionable materials. 
 
 The removal of the hydrogen sulphide is effected by 
 means of iron rust, in the following fashion : iron turnings 
 (to give great surface) are mixed with wood shavings (to 
 keep the mass porous) , and the mixture is then moistened and 
 the iron allowed to rust. Large flat boxes (the purifiers) 
 are packed with the mixture and sealed tightly by water 
 seals. The gas is then led through the mass, when the 
 hydrogen sulphide reacts with the hydrated iron oxide, iron 
 
LUMINOSITY OF FLAME 275 
 
 sulphide and water resulting. Thus the sulphur compound 
 is removed from the gas. When the iron rust is spent, the 
 mass is removed from the box and exposed to the action 
 of the air, whereby the iron sulphide is oxidized and iron 
 oxide is again obtained. The mixture can thus be used re- 
 peatedly until too full of the resulting uncombined sulphur 
 for efficient results. Coal gas contains on an average nearly 
 50 per cent of hydrogen by volume, a considerable amount 
 of methane, CH 4 , and smaller amounts of ethylene, C 2 H 4 , 
 acetylene, C 2 H 2 , and many other compounds of carbon and 
 hydrogen. 
 
 286. Luminosity of Flame. As a rule, hot gases are not 
 of themselves luminous. Consequently, a flame which con- 
 tains nothing but heated gases, as, for example, the hydrogen 
 flame or the carbon monoxide flame, does not give off light. 
 
 On the other hand, the flame of burning ethylene, C 2 H 4 , is 
 brilliantly luminous. The light comes from solid particles 
 of carbon raised to incandescence by the heat of the flame. 
 On entering the hot zone, the gas is decomposed by the heat 
 into hydrogen and free carbon. The hydrogen burns first 
 with the limited supply of air that reaches the interior of the 
 flame, while the minute particles of solid carbon remain sus- 
 pended in the current of gas and give the light. As the white- 
 hot carbon reaches the exterior of the flame, it comes in con- 
 tact with oxygen and it too burns. 
 
 It is easy to prove that solid carbon exists in the interior 
 of a luminous flame, for if a piece of cold porcelain is thrust 
 into the flame, it becomes coated with soot (lampblack). The 
 glowing particles of carbon are cooled by contact with the 
 porcelain to below their kindling temperature before they 
 get a chance to burn. (See Lampblack, Sec. 276.) 
 
 Ethylene is one of the typical illuminants of both water 
 
276 COMPOUNDS OF CARBON 
 
 and coal gas. It is obtained in water gas by the cracking 
 of petroleum oil, whereas in coal gas it results naturally 
 in small quantities from the decomposition of the coal. 
 Another and more powerful illuminant that is present to some 
 extent in water and coal gas is acetylene, C 2 H 2 . The higher 
 proportion of carbon which it contains is responsible in part 
 for its high illuminating power. When pure acetylene is 
 burned, it gives an extremely brilliant light. 
 
 287. Welsbach Mantles. One of the greatest inventions 
 in the field of gas lighting is the Welsbach mantle. It is 
 this mantle that is raised to incandescence by the heat of the 
 flame rather than solid particles of carbon resulting from the 
 decomposition of the gas itself. Where Welsbach mantles 
 are used, it is a matter of indifference whether gas is rich in 
 illuminants or not. Water gas can then be used without 
 being enriched with " cracked " petroleum. The Welsbach 
 mantles are composed of the oxides of two rare metals, tho- 
 rium and cerium. 
 
 CARBIDES 
 
 288. Carbides. It has already been seen that the typi- 
 cally non-metallic elements, oxygen, chlorine, and sulphur, 
 form compounds with the metals, that is, oxides, chlorides, 
 and sulphides, respectively. Carbon is less distinctly a 
 non-metal than the elements mentioned. It does not unite 
 energetically with metallic elements, and the carbides when 
 they are obtained are not as well-defined compounds as the 
 oxides, chlorides, and sulphides. The carbides of iron, silicon, 
 and calcium are worthy of mention on account of their im- 
 portance in the industrial arts. 
 
 289. Iron Carbide. Molten iron is capable of dissolving 
 a good deal of carbon in much the same manner as water 
 
CARBIDES 
 
 277 
 
 dissolves sugar. When the molten mass is allowed to cool 
 very slowly, the carbon separates from its solution in the 
 iron and appears partly as flakes of graphite and partly as 
 microscopic crystals of a definite carbide of iron, Fe 3 C. These 
 flakes of graphite and crystals of iron carbide do not get a 
 chance to settle out or to float off, but they remain suspended 
 throughout the mass of metal to the etched surface of which 
 they give a mottled appearance under the microscope. 
 
 If the melted iron is cooled very rapidly, none of the carbon 
 has a chance to separate out, but it still remains in solution 
 in the now solid iron (solid solution), and in consequence of 
 the presence of carbon in this state the metal is extremely 
 hard as well as brittle. The extreme hardness and brittle- 
 ness may be removed to any desired extent by cautious 
 reheating, the so-called tempering process. During the 
 tempering process more or less of the carbon passes from the 
 solid solution into the microscopic crystals of iron carbide. 
 
 Iron carbide has never been prepared pure in large masses ; 
 it is only known in the form of the infinitesimally small crys- 
 tals embedded in masses of iron. It is, nevertheless, a sub- 
 stance of great im- 
 portance in view of 
 its pronounced effect 
 upon the properties 
 of iron and steel. 
 
 290. Silicon Car- 
 bide, SiC. This 
 compound of carbon 
 is of considerable 
 practical importance 
 on account of its ex- 
 treme hardness, 
 
 FIG. 58. Making Carborundum in an Electric 
 Furnace. 
 
 
278 
 
 COMPOUNDS OF CARBON 
 
 which renders it of great value as a grinding material. 
 It is known in the trade as carborundum. Grinding wheels, 
 sharpening stones, etc., are made from powdered car- 
 borundum which is mixed with a binding material and 
 molded into shape. Carborundum is made by heating 
 quartz sand (SiO 2 ) with coke in an electric furnace. Part 
 of the carbon withdraws oxygen from the silicon dioxide, 
 while at the same time another part of the carbon unites with 
 the silicon : 
 
 SiO 2 + 3 C -> SiC + 2 CO. 
 
 The carborundum is vaporized in the hottest part of the elec- 
 tric furnace, close to the coke core, and it crystallizes from 
 
 the state of vapor 
 in the cooler regions 
 around the core. 
 The crystals are flat 
 and thin and often- 
 times are beautifully 
 iridescent. They 
 usually appear 
 opaque because they 
 contain traces of 
 graphite, but the 
 pure substance is 
 colorless and transparent. Carborundum is a very hard sub- 
 stance, harder than any precious stone except the diamond. 
 A crystal of carborundum will scratch glass with the greatest 
 ease, but carborundum itself is easily scratched by the 
 diamond. 
 
 291. Calcium Carbide is another important carbon com- 
 pound, which, like carborundum, is made in the electric fur- 
 
 FIG. 59. Section of Carborundum Furnace. 
 
COMPOUNDS WITH NON-METALS 279 
 
 nace. The raw materials are lime and coke, which react 
 according to the equation : 
 
 CaO + 3 C ->- CaC 2 + CO. 
 
 The calcium carbide thus formed is a hard, dark gray solid. 
 The greatest value of calcium carbide depends upon the fact 
 that it reacts with water to form acetylene gas : 
 
 CaC 2 + 2 H 2 O^Ca(OH) 2 + C 2 H 2 . 
 
 COMPOUNDS WITH NON-METALS 
 
 292. In the carbides, carbon plays the part of a non- 
 metallic or electro-negative element. When, however, 
 carbon combines with the more active non-metallic elements, 
 it becomes forced to take up the electro-positive role itself 
 and thus we have carbon oxide as well as carbon sulphide and 
 carbon chloride. 
 
 293. Carbon disulphide, CS 2 , is made by the direct union 
 of carbon and sulphur vapor at a high temperature. It is 
 a colorless volatile liquid which is much used as a solvent 
 in rubber cements. It also dissolves fats, waxes, iodine, 
 sulphur, and many other substances which do not dissolve 
 in water. Hence its greatest use is as a solvent. It is also 
 used to exterminate insect pests which infest grain, and to 
 kill ants. It should be used with caution for these purposes, 
 for inhaling its vapor is injurious and may even prove fatal. 
 
 294. Carbon tetrachloride, CCL,, is a colorless liquid which, 
 like carbon disulphide, finds its principal use as a solvent. 
 It has an advantage over the latter in that it is non-inflam- 
 mable, and it is not so volatile. It is usually made by 
 treating carbon disulphide with chlorine, 
 
 CS 2 + 3 C1 2 -> CC1 4 + S 2 C1 2 , 
 
280 COMPOUNDS OF CARBON 
 
 and distilling it off from the resulting mixture. Large 
 quantities are now sold under various fanciful names as 
 a cleansing fluid for removing grease spots. Being non- 
 inflammable, it is safer than benzine and gasoline. Other 
 large amounts are sold for use in fire extinguishers. These 
 are especially efficient in putting out gasoline fires. The 
 vapor of carbon tetrachloride is not only non-inflammable, 
 but it is also very heavy and hangs over the fire and 
 smothers it. 
 
 SUMMARY 
 
 Free carbon exists in three forms: (1) amorphous carbon (coke, 
 charcoal, lampblack, gas carbon, coal) ; (2) graphite ; 
 (3) diamond. Amorphous carbon is without definite form. 
 Graphite forms hexagonal crystals. Diamond crystallizes in 
 the regular system. Graphite is one of the softest solid sub- 
 stances. Diamond is the hardest substance known. Graph- 
 ite, diamond, and amorphous carbon all burn in oxygen 
 and yield only carbon dioxide. The differences between 
 amorphous carbon, graphite, and diamond are believed to be 
 due to a difference in molecular structure. 
 
 Carbon dioxide is the product of the free combustion of carbon ; it is 
 stored in vast quantities in nature in the form of carbonates. 
 
 Carbon monoxide is a valuable fuel. It is largely present in water 
 gas and in producer gas. 
 
 Water gas is made by blowing steam through white-hot coke. 
 
 Producer gas is made by blowing air through a deep bed of hot coal 
 or coke. 
 
 Coal gas is made by the destructive distillation of soft coal in retorts. 
 
 The luminosity of flames is due to the presence in them of heated 
 solid particles, usually of carbon. 
 
 Carbides : Carbon is not a very active non-metal, hence the carbides 
 of the metals are not as easily formed as the oxides, chlorides, 
 and sulphides. 
 
 Iron carbide is exceedingly important because of the effect of its 
 presence upon the properties of iron and steel. 
 

 QUESTIONS 281 
 
 Silicon carbide (carborundum) is a very useful artificial abrasive. 
 Calcium carbide is important as a source of acetylene. 
 Carbon disulphide and carbon tetrachloride are compounds of carbon 
 with non-metals. Their chief value is due to their solvent 
 
 powers. 
 
 Questions 
 
 
 1. What is the most valuable form of carbon? What is the 
 most useful form ? 
 
 2. Of what substance are the " leads " of lead pencils made? 
 How is the hardness of pencils varied? 
 
 3. Why is graphite used on bicycle chains? 
 
 4. How may diamonds be made artificially? 
 6. How is graphite made artificially? 
 
 6. Why does not pure water gas give a luminous flame? How 
 may it be made to do so ? 
 
 7. Explain the function of the " generator," the " carburetor" 
 and the " superheater " in the production of water gas as shown in 
 Fig. 55. Explain the operation of the valves. 
 
 8. How is producer gas made? Explain the diagram, Fig. 56. 
 What is the service performed by the economizer? What is the 
 object of allowing water to trickle into the economizer ? 
 
 9. How is coal gas made? Explain the diagram, Fig. 57. 
 
 10. Which would give the hotter flame, producer gas or water 
 gas? Why? 
 
 11. How is carborundum made? 
 
 12. How is calcium carbide made? 
 
 13. What are the principal uses of carbon tetrachloride? What 
 advantage has it over carbon disulphide? 
 
CHAPTER XXIV 
 
 COMPOUNDS OF CARBON (Continued) 
 
 295. Organic Chemistry. The compounds of carbon arc 
 studied under a special division of chemistry known as or- 
 ganic chemistry; the original significance of the name was 
 that these compounds were produced by the life processes 
 of plants or animals, that is, of living organisms. Some 
 compounds, it is true, which were considered organic were 
 formed by the partial decomposition of compounds produced 
 by living organisms rather than formed directly by the or- 
 ganisms themselves. 
 
 As examples of the type of substances formed directly in 
 living organisms, we have starch and sugar. Starch is 
 formed in potatoes, in grains, and in many other kinds of 
 plants. Sugar is formed in the sugar cane, the sugar maple, 
 and the sugar beet. Acetic acid, methyl alcohol, and acetone 
 are examples of organic substances produced indirectly from 
 others which were formed by living organisms. These three 
 substances result when wood is destructively distilled. Ben- 
 zene, carbolic acid, naphthalene, and methane are organic 
 substances obtained by the destructive distillation of soft 
 coal (coal being the product of the partial decomposition 
 of woody material which grew in some past geologic age). 
 As examples of organic substances 'produced by the growth of 
 animals, we have the various protein substances such as egg 
 albumin (the white of egg is mainly albumin and water) and 
 gelatin (which is extracted from bones and hides by boiling). 
 
 282 
 
ORGANIC CHEMISTRY 283 
 
 Formerly it was supposed that the mysterious agency of 
 life was essential to the formation of organic compounds, 
 but one by one the organic compounds have been synthesized 
 in the laboratory until now all but the most complicated can 
 be built up by strictly inorganic agencies from their elements, 
 these elements being carbon and usually hydrogen, with oxy- 
 gen and nitrogen often, and sulphur, phosphorus, and iron 
 sometimes, in addition. 
 
 Thus there is really no hard and fast line between organic 
 and inorganic chemistry. The compounds of carbon are so 
 numerous and the chemistry of these compounds so compli- 
 cated that it is more convenient to separate this field 
 of chemistry from the inorganic field for the purpose of 
 study. 
 
 As was suggested above, it was once thought that organic 
 compounds could be produced only by the agency of vital 
 force. To-day it is recognized that chemical reactions, which 
 are in every way analogous to the reactions which take 
 place in laboratory test tubes, take place within animal and 
 plant tissues and that the life and growth of the organisms 
 depend on the chemical changes rather than that the chemi- 
 cal changes depend on the vital force. 
 
 In our study of inorganic chemistry, we have observed 
 that compounds are always possible between metals and non- 
 metals, or, in other words, between electro-positive and elec- 
 tro-negative elements. Now carbon is neither a distinct 
 metal nor a distinct non-metal, and in its ability to form com- 
 pounds it shows itself markedly different from other elements. 
 Its valence in its compounds is four, and the most striking 
 feature about its combining relations is that it is apparently 
 a matter of indifference whether these four valences are ex- 
 erted in holding positive or negative elements or whether 
 
284 COMPOUNDS OF CARBON 
 
 they are divided, part holding positive and the rest holding 
 negative elements. Moreover, carbon possesses a peculiar 
 ability to use a part of its valences in uniting with other 
 carbon, while at the same time the rest of its valences are 
 exerted in holding other elements. On this account, a vastly 
 increased number of compounds of carbon is possible. 
 
 Among the possible compounds, thousands of actual ones 
 are known, and in this brief chapter on organic compounds a 
 few only of the more interesting of the carbon compounds can 
 be considered. Compounds consisting only of carbon and 
 hydrogen (called hydrocarbons) form a large and important 
 group. 
 
 METHANE AND THE PARAFFIN SERIES 
 
 296. Methane, marsh gas, CH 4 , is the simplest member 
 of an extended series of organic compounds. The gas which 
 arises when one pokes a stick into the mud beneath the pools 
 of water in marshes consists mainly of this substance. In 
 addition to being formed in the mud of marshes, methane is 
 also frequently present in coal mines, resulting from the 
 decomposition of coal, and its presence is the cause of many 
 serious explosions. The coal miners call it fire damp. It is 
 also a very important constituent of the illuminating gas 
 that is obtained by the destructive distillation of coal, and 
 large amounts of it are present in natural gas. 
 
 Carbon tetrachloride is of interest in its relation to 
 methane. In methane the carbon atom has attached to it 
 four positive hydrogen atoms, whereas in carbon tetrachlo- 
 ride the place of the hydrogen is taken by four electro-nega- 
 tive chlorine atoms. 
 
 Compounds with the formulas, CH 3 C1, CH 2 C1 2 , and CHC1 3 , 
 are also known. The last is the well-known substance chloro- 
 
THE PARAFFIN SERIES 285 
 
 form. In these compounds carbon is united with both posi- 
 tive and negative elements. Not only is it possible to re- 
 place one or all of the hydrogen atoms of methane with 
 chlorine, but also with other atoms or groups of atoms. 
 
 297. The Paraffin Series. A compound is known, which 
 may be regarded as methane in which one hydrogen atom has 
 been replaced by the group CH 3 . This new compound is 
 called ethane. Here, carbon may be considered as united with 
 itself as well as with an electro-positive element, hydrogen. 
 
 H H H 
 
 I I I 
 H C H H C C H 
 
 I ! 
 
 H H H 
 
 Methane Ethane 
 
 Ethane, like methane, is found in illuminating gas made 
 by the destructive distillation of soft coal. 
 
 By displacing an atom of hydrogen from ethane by means 
 of the CH 3 group, a new compound known as propane results. 
 
 H H H 
 
 I I I 
 H C C C H 
 
 I I I 
 H H H 
 
 Propane 
 
 By replacing an atom of hydrogen of propane by a 
 group, butane is obtained. 
 
 H H H H 
 
 I I I I 
 H C C C C H 
 
 III! 
 
 H H H H 
 
 Butane 
 
286 COMPOUNDS OF CARBON 
 
 Butane is one of the more volatile components of petroleum. 
 Petroleum, which is a crude, offensive oil drawn from the 
 earth in various localities, is in the main a mixture of many 
 hydrocarbon compounds belonging to the series whose first few 
 members have just been mentioned. In this series with the 
 introduction of each new CH2 group, the molecular weight, 
 of course, increases, and it is interesting to note that the 
 boiling points of the successive substances increase in a some- 
 what regular fashion. Other properties, such as specific 
 gravity, for example, also vary with varying molecular weight. 
 The higher the molecular weight, the denser the substance 
 becomes. 
 
 298. Distillation of Petroleum. In separating the great 
 mixture of hydrocarbons, known as crude petroleum, advan- 
 tage is taken of the variation in boiling points, and by distill- 
 ing off fractions of the whole into separate containers, the 
 crude mixture is separated into portions of varying volatility, 
 the most volatile portions being first to come off. Petro- 
 leum contains so many different members of the paraffin 
 series, and the molecular weights and hence the boiling points 
 are so near to each other, that it is not practically possible by 
 distillation to obtain one of the pure substances entirely by 
 itself. 
 
 The first fractions containing several of the more vol- 
 atile members of the paraffin series are condensed and 
 sold under the trade names of cymogene and rhigolene. 
 These are very volatile liquids, and they are sometimes used 
 to chill portions of the body surface to deaden sensation dur- 
 ing minor surgical operations. The rapid evaporation of the 
 very volatile liquid takes up the heat of the part sprayed 
 with it, thus chilling the flesh and causing it to become 
 numb. The later and less volatile fractions -from petro- 
 
UNSATURATED HYDROCARBONS 287 
 
 leum are called successively gasoline, naphtha, benzine (not 
 benzene) and kerosene. 
 
 After the kerosene is distilled off, there remains still a 
 mixture of many of the higher hydrocarbons of the 
 paraffin series from which heavier oils are distilled. When 
 these oils are chilled, flakes of paraffin separate. This is 
 removed by filter pressing and the oil is used for lubri- 
 cants. The viscous substance known as vaseline is ob- 
 tained from the residue left when the crude oil is distilled 
 in a vacuum. 
 
 The last volatile fractions of the petroleum come off only 
 when the bottom of the still has risen to a red heat; and 
 the residue then left in the still is coke in a form which is 
 highly valued for making electric light carbons. 
 
 All of these substances obtained from petroleum are very 
 resistant to attack by chemicals except at high tempera- 
 tures. Hence the origin of the name of the series, paraffin, 
 suggesting lack of affinity. 
 
 UNSATURATED HYDROCARBONS 
 
 299. A number of other natural series of hydrocarbons are 
 known, the ethylene series in which the first member is 
 ethylene, C 2 H 4 , and the acetylene series in which acetylene, 
 C 2 H 2 , is the first member, being among the more important. 
 The relation between molecular weights and properties which 
 was noted in the paraffin series is found also in the other 
 series of hydrocarbons. 
 
 In ethylene and acetylene it is believed that carbon still 
 possesses its universal valence of four, but in order to main- 
 tain this belief, it becomes necessary to suppose that more than 
 a single valence of one carbon atom is employed in holding 
 
 B. AND W. CHEM. 19 
 
288 COMPOUNDS OF CARBON 
 
 an adjacent carbon atom. Thus ethylene is supposed to 
 possess a double bond jj\ /H 
 
 >C=C/ 
 W X H 
 
 and acetylene a triple bond 
 
 H C = C H 
 
 The justification of the term unsaturated in describing com- 
 pounds of this character lies in the fact that they are literally 
 unsaturated. For example, ethylene, when mixed with 
 hydrogen and passed through a heated tube containing a 
 suitable catalyzer, takes up additional hydrogen easily and 
 is changed into ethane, a saturated compound 
 
 ri2vy = (_yii2 i -H-2 ^ .tiaO - Oils 
 
 or, treated with chlorine, ethylene readily changes into di- 
 chlor-ethane. 
 
 H H Ck Cl 
 
 C=C + C1 2 ->- l 
 W X H H/ \H 
 
 As already indicated in the preceding chapter, ethylene 
 is an important constituent of illuminating gas, and acetylene 
 finds extensive use as an illuminant, as in automobile head- 
 lights. 
 
 CARBOHYDRATES 
 
 300. There is another great class of carbon compounds, 
 known as carbohydrates, in which hydrogen and oxygen in 
 precisely the right proportion to form water are united with 
 carbon. Starch, sugars, gums, and cellulose are carbohy- 
 drates. The formulas of a few of the many carbohydrates 
 are as follows : 
 
 Starch Grape sugar Cane sugar Cellulose 
 

 SUGARS 289 
 
 It is seen that starch and cellulose have the same formula 
 with the exception of the subscripts ra and n. These sub- 
 scripts m and n signify some definite but unknown numbers, 
 probably large and probably different. 
 
 301. Sugars. Sugars are found in nature in the sap of 
 plants and the juices of fruits. The sugars are built in the 
 leaves of plants by the interaction of the carbon dioxide of 
 the air and the water of the sap under the influence of sun- 
 light and the chlorophyll, or green coloring matter of the 
 leaves. The energy of the sunlight is consumed in splitting 
 up the carbon dioxide so that oxygen is returned to the air, 
 while the carbon and water unite, forming carbohydrates. 
 
 The sugars, which are soluble in water, are conveyed by the 
 sap to all parts of the plant and are converted into starch, 
 or cellulose, or other sugars by the chemical addition or 
 subtraction of water as the needs of the plant may require. 
 
 Cane sugar is the variety of sugar found in the sap of the 
 sugar cane, the sugar beet, and the maple tree. 
 
 Grape sugar is found in grapes and other fruits. It is less 
 sweet than cane sugar. Starch can be converted artificially 
 into grape sugar by boiling with dilute acids, this treatment 
 promoting the addition of water according to the equation 
 
 (C 6 Hi O 5 ) n + n H 2 O -> n C 6 Hi 2 O 6 
 
 Starch Grape sugar 
 
 Enormous quantities of corn starch are thus treated in mak- 
 ing commercial glucose, a product which consists mainly of 
 grape sugar and dextrin (see below) , the latter being an inter- 
 mediate product between starch and grape sugar. Commer- 
 cial glucose is ordinarily a thick sirupy product and is often 
 sold for table use under the name of corn sirup. Evapo- 
 rated to dryness, it yields solid " grape sugar." 
 
290 COMPOUNDS OF CARBON 
 
 302. Starch is insoluble in water and it is the form in which 
 carbohydrates are stored up by plants for their future use as 
 foods. It is thus found especially in bulbs, tubers, and seeds, 
 where it is accumulated for the nutrition of the young 
 plants. 
 
 Potatoes are composed almost wholly of starch and water. 
 Wheat, rice, barley, corn, and, in fact, all grains are composed 
 largely of starch. Consequently, the food value to man as 
 well as to the plants themselves, of all kinds of grains, tubers, 
 bulbs, etc., is largely due to their content of starch. 
 
 Starch before it is assimilated in the human body is con- 
 verted back to soluble sugars by the action of the digestive 
 juices. 
 
 Starch is always found in plants in the form of small com- 
 pact granules, and it is usually possible to determine the 
 source of any particular starch by a microscopic examina- 
 tion of the starch granules. 
 
 Dextrin, which is the adhesive substance with which the 
 backs of postage stamps are coated, is an intermediate prod- 
 uct between starch and sugar, and it is obtained by heating 
 starch. Dextrin is formed to some extent in baking bread, 
 and it is present in the browned crust. 
 
 303. Cellulose is the chemical substance of which the 
 fibrous and woody part of plants is composed. It is not 
 used as food by man (except in small quantities in the tender 
 green leaves of lettuce, spinach, etc.), but it finds enormous 
 use in the textile industries and in paper making. Cotton, 
 linen, and wood fiber, for example, are almost pure cellulose. 
 
 Wood consists of bundles of cellulose fibers cemented 
 together with resinous or gummy material. Although old 
 linen rags furnish the cellulose fiber for some of the strongest 
 grades of paper, the principal source of the cellulose is wood. 
 
 

 ALCOHOLS 291 
 
 The fibers are sometimes torn apart mechanically for the 
 cheapest paper, but usually wood chips are treated chemically 
 to dissolve out the binding material and thus leave the pure 
 cellulose as a loose mass of fibers. 
 
 The paper used in the laboratory for making filters is 
 practically pure cellulose. Other grades of paper are likely 
 to be filled with mineral matter to give weight, or with glue 
 or casein to give a hard, smooth finish. 
 
 ALCOHOLS 
 
 304. Alcohol, C 2 H 5 OH, is prepared by the action of yeast, 
 a microscopic plant cell, upon grape sugar, or other type of 
 sugar. These little plants consume a great deal of sugar 
 in their life process, and they increase in numbers with as- 
 tonishing rapidity when placed in a favorable medium. The 
 reaction brought about by the yeast plants is approximately 
 expressed by the equation 
 
 C 6 Hi 2 O 6 -+ 2 CO 2 + 2 C 2 H 5 OH. 
 
 Heat is evolved in this reaction, and carbon dioxide is formed 
 as well as alcohol. Since most of the sugar thus fermented 
 in the commercial preparation of alcohol is derived from the 
 starch of grains, this kind of alcohol is known as grain alco- 
 hol, to distinguish it from other alcohols. 
 
 When, in the fermentation of the grain, the alcohol reaches 
 a concentration of 10 to 12 per cent, the action becomes 
 very slow and almost ceases. By fractional distillation, 
 the alcohol is now separated from the water and the solid 
 residue, so that a 95 per cent alcohol is obtained in the dis- 
 tillate. 
 
 The distillation of alcohol is an important industry, since 
 alcohol finds many uses in the arts, as a fuel, as a solvent, 
 
292 COMPOUNDS OF CARBON 
 
 and in many other ways. Large quantities of it are con- 
 sumed in a more or less diluted condition in spirituous and 
 fermented liquors. 
 
 From the standpoint of chemistry as well as from that of 
 economics, the use of alcohol in beverages is wasteful. In 
 fermenting the sugars much energy is lost as heat, and much 
 labor that might be used productively is required to care for 
 the process. The distillation, also, requires much heat, 
 energy, and labor, and the products are stored for long 
 periods, thus keeping much capital idle. 
 
 From the physiological standpoint alcohol is a powerful 
 poison. Although it has been shown by scientists that 
 alcohol is burned in the body and furnishes heat and energy 
 like the carbohydrates, nevertheless alcohol has very harmful 
 effects upon the nervous system and through that upon 
 the processes of assimilation of food. Pure alcohol is a 
 deadly poison; somewhat diluted, as in whiskey, rum, and 
 brandy, it is very harmful; and more highly diluted, as in 
 fermented beverages, it is injurious and its use is not advisable 
 
 305. Denatured Alcohol. On account of the far-reaching 
 evil effects of the use of alcohol as a beverage governments 
 have frequently placed heavy internal revenue taxes upon 
 the traffic in alcohol, thus limiting its use and at the same 
 time raising revenue for governmental expenses. 
 
 The resulting high price of alcohol has in times past limited 
 its use as a fuel and as a solvent in the arts and industries. 
 Recently the United States government has permitted 
 the sale without tax of alcohol which has been " denatured," 
 as it is called, by the addition of certain other substances. 
 The object of this addition is to render the alcohol unfit 
 for use as a beverage without in any way harming it for 
 industrial purposes. Various substances, among them pyri- 
 
ORGANIC ACIDS 293 
 
 dine, may b'e used to denature alcohol. A substance with 
 an evil odor is usually employed so as to render the mix- 
 ture offensive to drink. 
 
 306. Wood Alcohol, CH 3 OH, is obtained by the destruc- 
 tive distillation of wood. Wood alcohol is very similar to 
 grain alcohol in its properties and these two alcohols can 
 be used almost interchangeably for fuel and solvent pur- 
 poses. It should never be used as a constituent of beverages, 
 because, although its poisonous properties are of the same 
 general character as those of grain alcohol, it is a so much 
 more violent poison that its use is likely to prove imme- 
 diately fatal. The vapor even is dangerous if inhaled in 
 quantity, and its action upon the eyes is likely to cause 
 blindness. 
 
 ORGANIC ACIDS 
 
 307. Organic acids are found in many fruits, notably 
 citric acid in the lemon, orange, and other citrus fruits, malic 
 acid in the apple, and the acid salt of tartaric acid (cream 
 of tartar) in grapes. In addition to these natural fruit acids 
 there are a great many acids which are formed by the partial 
 oxidation of organic substances like the alcohols and sugars. 
 Organic acids are, as a rule, very weak as compared with the 
 mineral acids, hydrochloric, nitric, and sulphuric. Like the 
 carbohydrates, they are oxidizable in the body ; hence their 
 desirability in foods to which they impart a mild and 
 pleasing sour taste. 
 
 308. Acetic acid, H(C 2 H 3 O 2 ), perhaps ranks first in im- 
 portance among the organic acids. It is the acid of vine- 
 gar. Cider is the product of the alcoholic fermentation of 
 apple juice. By allowing cider or other fermented liquor 
 of similar alcohol content to undergo a different sort of 
 
294 COMPOUNDS OF CARBON 
 
 fermentation under the influence of certain bacteria, in the 
 presence of air, an oxidation of the alcohol to acetic acid 
 takes place. 
 
 H H HO 
 
 I I II 
 
 H C C O H + O 2 -^ H C C O H + H 2 O. 
 
 i I 
 
 H H H 
 
 Alcohol Acetic acid 
 
 For industrial uses, acetic acid is made by the destructive 
 distillation of wood. The cellulose is not completely decom- 
 posed by the heat, but it is broken down into a great variety 
 of volatile organic substances, which distill off, and charcoal, 
 which remains in the retort. Wood alcohol, as already men- 
 tioned, is one important product of the distillation ; acetic 
 acid is another. 
 
 It should be noted that although practically all organic 
 compounds contain hydrogen, not all are acids. Even in 
 acetic acid, only one of the hydrogens functions as acid 
 hydrogen. Hence in the formula, H(C 2 H 3 O 2 ), a single hy- 
 drogen is placed alone, whereas the other three are placed 
 with the acid radical (C 2 H 3 O 2 ). 
 
 FATS 
 
 309. Fats are compounds of carbon, hydrogen, and oxygen, 
 and they may be regarded as a product of the union of cer- 
 tain higher alcohols with certain higher acids, called fatty 
 acids, much as salts are the product of the union of bases 
 and acids. Instead of acting instantly with acids, as do 
 bases, the alcohols react very slowly. 
 
 Stearin is the principal fat in tallow and is represented 
 by the formula C 3 H 5 (Ci 8 H 3 5O 2 ) 3 . It is derived from glycerol, 
 
SOAPS 295 
 
 C 3 H 5 (OII) 3 , an alcohol with three hydroxyl groups, and 
 stearic acid, H(Ci 8 H 35 O2). Three molecules of stearic acid 
 are necessary to unite with glycerol according to the equation 
 
 C 3 H 5 (OH) 3 + 3 H(C 18 H 35 2 ) -> C 3 H 5 (C 18 H 35 O 2 ) 3 + 3 H 2 O. 
 
 Glycerol Stearic acid Stearin 
 
 The equation is similar to that of a neutralization reaction, 
 but it should be remembered that the glycerol is not per- 
 ceptibly a base and such a reaction can be carried out only 
 with difficulty in the laboratory. Fats are formed mainly 
 in the slow chemical processes taking place in animal and 
 plant tissues. 
 
 The reaction represented by the reverse of the above 
 equation can take place rather easily, and fats on standing 
 often become rancid, due in large part to the separation in 
 this manner of the free fatty acid. This action is known as 
 hydrolysis. 
 
 Fats are valuable foods; they yield nearly two and one 
 quarter times as much heat when oxidized in the body as 
 carbohydrates or proteins. They are thus splendid food for 
 cold weather or cold climates, but they are somewhat difficult 
 of digestion. Broadly speaking, all fats and oils obtained 
 from animals and plants, including butter, lard, olive oil, 
 cottonseed oil, and castor oil, are similar chemically to 
 stearin. 
 
 310. Soaps are made by the action of strong mineral 
 bases upon fats. For example, when sodium hydroxide 
 acts upon stearin, glycerol is separated from the fat and 
 sodium stearate, a salt of the organic acid, is formed. 
 
 3 NaOH + C 3 H 5 (C 18 H 35 O 2 ) 3 -> C 3 H 5 (OH) 3 + 3 Na(C 18 H 35 O 2 ) . 
 
 Stearin Glycerol Soap 
 
 Sodium stearate is a typical soap. 
 
296 COMPOUNDS OF CARBON 
 
 PROTEINS 
 
 311. The albumin of the white of eggs is one of a number 
 of carbon compounds which may be classed together under 
 the name of proteins. The proteins contain carbon, hydro- 
 gen, oxygen, and nitrogen always, and they may contain 
 small amounts of other elements, as phosphorus, sulphur, and 
 iron. To this class of carbon compounds belong the tissue- 
 building foods such as are found in greatest abundance in 
 meat, milk, eggs, cheese, the gluten of wheat, beans, and peas. 
 It was said in Chapter VII (while discussing the fixation of 
 atmospheric nitrogen) that legumes were able, by the aid 
 of bacteria living on their roots, to cause the free nitrogen 
 of the air to combine with other elements to form nitrogenous 
 compounds. These compounds become stored up as pro- 
 teins principally in the seeds of the leguminous plants. The 
 animal foods meat, milk, eggs, and cheese contain pro- 
 teins derived from the plant food eaten by the animals. 
 Animals possess the power to make over many protein sub- 
 stances into other proteins which are better adapted to the 
 needs of the particular organism, but animals do not them- 
 selves seem to be able to put together the elementary sub- 
 stances to form the proteins. 
 
 SUMMARY 
 
 Many of the compounds of carbon, which it was formerly supposed 
 could only be formed in living organisms, can to-day be pre- 
 pared in the laboratory. 
 
 The valence of carbon is four. These valences may be exercised in 
 holding electro-positive or electro-negative elements or part of 
 both at the same time. Some of the carbon valences may 
 also hold other carbon atoms. Many thousands of different 
 compounds of carbon are known. 
 
 Methane is the first member of a series of hydrocarbons called the 
 paraffin series. Ethane, propane, and butane are the next three 
 
SUMMARY 297 
 
 members of this series. Methane is one of the products 
 formed when organic substances decompose without a free sup- 
 ply of air. It is found in coal mines, and the gas from marshes 
 is mainly methane. Natural gas also contains methane. 
 
 Carbon tetrachloride is a useful solvent. Its composition shows 
 that it may be regarded as a derivative of methane. In it the 
 carbon is united to an electro-negative element. 
 
 The paraffin series illustrates the remarkable relation between 
 molecular weights and properties in an homologous series. 
 
 Petroleum oil consists mainly of various members of the paraffin 
 series. It may be roughly separated by fractional distilla- 
 tion into the various commercial products of petroleum. 
 
 Ethylene and acetylene are the first members of two unsaturated 
 series of hydrocarbons. 
 
 Carbohydrates are a very important class of carbon compounds. 
 Many of our most valuable foods are carbohydrates, as, for 
 example, sugar and starch. Dextrin and cellulose also are 
 carbohydrates. 
 
 Alcohol is another carbon compound of considerable use in the arts. 
 It is also used in many beverages, but such use is both uneco- 
 nomical and unwise from the standpoint of health. Wood 
 alcohol is chemically similar to grain alcohol. It is far more 
 poisonous. 
 
 Organic acids are found in many fruits. They are far weaker than 
 the mineral acids H 2 S04, HC1, and HNOs. Some organic 
 acids are derived from the oxidation of alcohols or sugars by 
 fermentation. Acetic acid, the acid of vinegar, is the princi- 
 pal one of these. Acetic acid is also obtained by the destruc- 
 tive distillation of wood. 
 
 Fats are valuable foods. They are formed from alcohols and 
 organic acids. They may hydrolyze, whereby the fatty acid 
 is set free. Soap is the sodium salt of some of the fatty acids 
 of common fats. Glycerol is a by-product of the soap in- 
 dustry. 
 
 The proteins are organic compounds containing nitrogen, and they 
 are valuable foods. Plants form proteins directly from the 
 simpler substances, but animals only remake proteins from 
 other proteins obtained from plants. 
 
298 COMPOUNDS OF CARBON 
 
 Questions 
 
 1. Why is organic chemistry usually studied apart from inor- 
 ganic chemistry? 
 
 2. Is there any real difference between the two branches of 
 chemistry ? 
 
 3. What peculiarity in combining ability distinguishes carbon 
 from other elements ? 
 
 4. What has this peculiarity to do with the existence of a vast 
 number of organic compounds? 
 
 5. Any member of the paraffin series may be represented, by 
 the general formula C n H( 2n + 2). What, then, is the formula of /that 
 member of the series which has 18 carbon atoms? 10 carbon 
 atoms? 5 carbon atoms? 
 
 6. How is gasoline obtained from crude petroleum? 
 
 7. What peculiarity of composition distinguishes the carbohy- 
 drates? 
 
 8. What is grape sugar commonly called ? 
 
 9. What weight of alcohol might be obtained by the complete 
 transformation of 100 grams of glucose ? (See equation on page 291 .) 
 
 10. Why is the use of alcohol as a beverage uneconomical, aside 
 from its harmful effect ? 
 
CHAPTER XXV 
 
 THE IONIC THEORY 
 
 312. Electrical Conditions of Acid Hydrogen. It was 
 shown in Chapter XIX that the characteristic properties of 
 acids must be attributed to the presence in them of hydro- 
 gen which is in a different state of combination from ordi- 
 nary combined hydrogen and which has been designated as 
 dizolaceable or acid hydrogen. 
 
 The acid properties of the hydrogen in acids are not mani- 
 fest when the acid is pure and dry, but are developed when 
 the acid is dissolved in water. It is now generally believed 
 that the solvent in some way separates the molecules of acid 
 into two components, of which one is the hydrogen atom (or 
 atoms in acids like H 2 SO4 and H 3 PO 4 ) and the other is the acid 
 radical. Furthermore, it is believed that the hydrogen atom 
 so separated is charged with positive electricity and the acid 
 radical is charged with negative electricity. These electri- 
 cally charged components of the acid are known as ions. 
 According to this supposition, the hydrogen ion is a compo- 
 nent of every acid solution, and it is the one which produces 
 the acid properties. 
 
 313. Electrostatic Attraction and Repulsion. It is a well- 
 known fact that when the hair is combed on a cold, dry day 
 the hair stands on end as if the separate hairs repelled each 
 other, but that the hairs are all attracted to the comb. The 
 friction of the comb on hair leaves the latter charged with 
 
 299 
 
300 THE IONIC THEORY 
 
 positive electricity and the former with negative electricity. 
 / This simple experiment illustrates a general law of electricity, 
 y^ that like charges repel and unlike charges attract each other. 
 The electricity that is available in the laboratory for chemi- 
 cal work is generated either chemically in electro-chemical 
 cells, or mechanically by dynamos in which coils of wire are 
 rotated in magnetic fields, but scarcely ever by friction. 
 
 314. Electricity is something very intangible. We do 
 not feel like calling it a substance, for it does not seem to have 
 weight. It probably pervades all ordinary substances, and 
 yet its presence is commonly unnoticed. We are not ordi- 
 narily conscious on a windless day that we are living at the 
 bottom of a sea of air which presses heavily upon us and every- 
 thing around us. But we become conscious of the presence 
 of the air when it is in motion, as when the wind blows, or 
 when it is compressed as in an automobile tire, or when it is 
 rarefied, as in an electric light bulb, which collapses with a loud 
 report when it is broken. In these respects, electricity is 
 not very unlike air. Friction may be supposed to act in a 
 measure like an air pump and to withdraw electricity from 
 one object and compress it into another. If positive elec- 
 tricity is at a higher pressure in the hair than in the surround- 
 ings, it makes itself obvious, and we see the hair stand on end 
 as a result. Similarly, if negative electricity is at a higher 
 pressure on the rubber comb than in surrounding objects, it 
 again makes that fact obvious by its ability to attract the 
 positively electrified hair. Air can be forced by a pump 
 through a pipe and at the end of the pipe be made to do work, 
 as in running a compressed air drill. Likewise, electricity 
 may be forced by an electric pump, that is, a dynamo, 
 or an electro-chemical cell, to flow through a circuit and 
 to do work as in running a motor or in decomposing a 
 
NON-CONDUCTORS 
 
 301 
 
 chemical compound like sodium chloride into its constituent 
 elements. 
 
 315. Metallic Conduction. It is a matter of common 
 knowledge that metals are invariably used to conduct elec- 
 tric currents, and that non-metallic substances, such as glass, 
 rubber, and sulphur, are used as insulators. Electricity 
 passes with great ease through metals, in fact, its flow through 
 metals can be likened to the flow of water through pipes. 
 So far as we can detect, 
 
 the metal suffers no more 
 alteration by the passage 
 of the current than the 
 pipe suffers by the pas- 
 sage of water. 
 
 316. Non-Conductors. 
 Substances other than 
 metals ordinarily offer 
 great resistance to the 
 passage of electricity, 
 arid on this account are 
 termed non-conductors. 
 Non-metallic substances 
 include not only the 
 non-metallic elements 
 themselves, but also com- 
 pounds, even compounds 
 
 Containing metals. For FIG. 60. Apparatus for showing Electrical 
 i j 11 i Conductivity. The brilliancy with which the 
 
 example, sodium chloride lamp glows is a measure of the conduct i v it y 
 
 possesses none of the f ^ ne substance placed between the elec- 
 . . trodes. 
 
 characteristics ot metals 
 
 and when it is dry it does not conduct electricity. Water 
 
 is another distinctly non-metallic substance and, like the 
 
302 THE IONIC THEORY 
 
 other substances in its class, it is when pure an almost com- 
 plete non-conductor of electricity. 
 
 317. Electrolytic Conduction. We now come to a most 
 remarkable series of phenomena. Water as stated does not 
 conduct electricity when pure, no more does dry sodium 
 chloride ; but dissolve sodium chloride in water, and a solu- 
 tion is obtained which conducts the current readily. 
 
 This may be strikingly shown if an electric circuit is ar- 
 ranged as shown in Fig. 60. Connections are made at 
 the points marked + and with the two wires of the 110- 
 volt direct-current incandescent lighting system. Alternat- 
 ing current will serve equally well. Between these two con- 
 nections there are inserted in the circuit an incandescent 
 lamp and a gap between two platinum wires (electrodes). 
 These wires are suspended from binding clamps, parallel and 
 near to each other, but not touching. The circuit as now 
 arranged passes through the incandescent lamp but is broken 
 by the gap between the platinum electrodes. If these are 
 connected by a piece of metal, the circuit is completed and 
 the lamp glows with its full brilliancy. If a piece of non- 
 conducting substance is held so as to touch both electrodes, 
 no current passes and the lamp does not glow. 
 
 On holding a dry lump of common salt so that it touches 
 both platinum electrodes, the lamp does not glow and the salt 
 is thus shown to be a non-conductor. On raising a small 
 vessel filled with distilled water from underneath so that both 
 electrodes dip in the liquid, no light is seen in the lamp, and 
 water is also shown to be a non-conductor. If, nt>w, a little 
 of the salt is dissolved in the water and the conductivity of 
 the solution is tested in the same way, the lamp is seen to 
 glow brilliantly, and the solution of sodium chloride is proved 
 to be a good conductor. 
 
 
ELECTROLYTIC CONDUCTION . 303 
 
 
 318. Not only does a solution of sodium chloride conduct 
 
 strongly, but solutions of all salts conduct in about the same 
 degree. Hydrochloric and sulphuric acids, which we have 
 spoken of as strong acids, likewise cause the lamp to glow 
 brightly when their solutions are placed between the plati- 
 num wires ; phosphoric and acetic acids, which are known to 
 be weaker acids, cause the lamp to glow with a dull red, show- 
 ing that these acids conduct, but to a much smaller extent 
 than the strong acids ; carbonic acid, which we know as a 
 very weak acid, does not conduct sufficiently to cause the 
 lamp to glow, but still it does conduct to some extent, as could 
 be shown with a more delicate instrument for measuring the 
 passage of the electric current. Solutions of the strong 
 bases, sodium hydroxide and potassium hydroxide, give a 
 brilliant glow to the lamp, showing that they conduct the 
 current to about the same degree as solutions of salts and 
 of strong acids. A solution of the weak base ammonium 
 hydroxide gives a dull red glow to the filament, and thus 
 conducts to about the same extent as the weaker acids. 
 
 319. Non-Electrolytes. Solutions of some substances, for 
 example sugar and alcohol, do not conduct any better than 
 pure water. Such substances are called non-electrolytes, in 
 distinction to electrolytes which do conduct when dissolved. 
 
 320. Character of Electrolytic Conduction. All dry, solid 
 salts are like dry sodium chloride in that they do not conduct 
 electricity. Pure acids and pure bases when entirely free 
 from water are also non-conductors. All become conduc- 
 tors when they are dissolved in water, but the manner in 
 which the conduction takes place differs strikingly from the 
 manner in which it takes place in metals. In metals, abso- 
 lutely no permanent change takes place in the conductor, 
 but in solutions the passage of the current is accompanied 
 
 B. AND W. CHEM. 20 
 
304 THE IONIC THEORY 
 
 by a decomposition of either the dissolved substance or the 
 water. The passage of electricity through a solution to- 
 gether with the accompanying decomposition is known as 
 electrolysis, a term which we have already used a few times. 
 
 321. The Ionic Theory. It was in the effort to explain the 
 remarkable facts concerning electrolytic conduction that the 
 theory of ions was developed. The theory in its present 
 form was proposed by Arrhenius, a Swedish physicist, in 
 1887, and was called by him the electrolytic dissociation theory; 
 it is now more commonly known as the ionic theory. 
 
 According to the ionic theory, when a salt or acid, or 
 base is dissolved in water, its molecules become disso- 
 ciated, or separated, into two components called ions. These 
 ions are heavily charged with positive and negative electricity, 
 respectively. The process of ionization may be represented 
 by an equation in the same manner as an ordinary chemical 
 reaction, for example the ionization of sodium chloride takes 
 
 place as follows : 
 
 NaCl -+ Na + + Cl". 
 
 The electric charges are represented by the symbols"*" 
 and". 
 
 322. Pairing of Ions. The ions are separated by the action 
 of the water so that they are free to move about in the solution 
 to some extent independent of each other ; but, of course, the 
 attraction between the unlike charges of electricity is so great 
 that a positive ion cannot be drawn away from the immediate 
 neighborhood of its accompanying negative ion unless there is 
 another negative ion near which will attract it, while at the 
 same time there is another positive ion near to attract the 
 now unbalanced negative ion. This amounts to saying that 
 every positive ion must at all times be paired off with a nega- 
 tive ion, but that the attachment of the ions in the pair is not 
 
DEGREE OF IONIZATION 305 
 
 / so firm as to prevent a continual interchange of partners, so 
 
 ) to speak. 
 
 L- 323. Reactivity of Ionized Substances. In non-ionized 
 substances, we may suppose, if we like, that the two com- 
 ponents still possess the electric charges, but that, without 
 the action of water to separate the components, they remain 
 so firmly bound together in ihe molecule that this interchange 
 of partners is not possible.^ 
 
 It is a well-known fact that dry, solid substances are inac- 
 tive when cold. For example, baking powder, which is a 
 mixture of a dry powdered acid substance with dry sodium 
 bicarbonate, remains without action indefinitely so long as it 
 is kept dry. W T hen it is moistened, on the other hand, it 
 reacts immediately. The acid substance dissolving in the 
 water gives H + ions and the sodium bicarbonate gives HCOs" 
 ions. These ions enter immediately into reaction, leaving 
 their former partners and pairing with each other, whereby 
 they form carbonic acid and so produce the effervescence : 
 
 H + + HC0 3 - -> H 2 CO 3 -t H 2 + C0 2 f. 
 
 324. Electrolytic Conduction. When an electric current 
 passes through a solution, it does not pass in a continuous 
 stream, as water through a pipe, but it travels only upon the 
 ions, which act as carriers. Each ion bears a definite load 
 of electricity, the positive ion a load of .positive electricity 
 which it carries through the solution to the negative electrode, 
 and the negative ion a load of negative electricity which it 
 carries to the positive electrode. 
 
 325. Degree of lonization. Some substances in solution 
 conduct electricity strongly. It seems fair to assume that 
 these substances have yielded a large number of carriers, that 
 is, of ions. As a matter of fact, there are good reasons for 
 
 
306 THE IONIC THEORY 
 
 believing that salts and strong acids and strong bases do yield 
 a large number of ions when dissolved ; the great majority 
 of the molecules are dissociated. On the other hand, only a 
 small proportion of the molecules in the weak acids and bases 
 are split up into ions ; the rest of the molecules remain un- 
 dissociated and incapable of taking part in the conduction of 
 electricity. Thus in a solution of acetic acid, which we have 
 said is a weak acid, it is estimated that about one molecule 
 in every one hundred is dissociated, whereas the other ninety- 
 nine molecules are intact. We attribute acid properties 
 to the presence of hydrogen ions, and it may be seen that 
 according to the theory the weakness of the acid character 
 of acetic acid and the feebleness of its conductance arise from 
 the same cause, namely, from a disinclination or inability 
 of its molecules to break apart into ions. 
 
 326. Value of Ionic Theory. When Arrhenius originated 
 the ionic theory, he was led to his conclusions, not only by the 
 phenomena of conduction and by the similarity of properties 
 of all acids and of all bases, but also by a number of other 
 striking properties of conducting solutions. It is beyond the 
 scope of this book to give all of the reasons for adopting the 
 ionic theory ; but it may be said that it is believed to-day by 
 most chemists that the ionic theory gives a reasonably correct 
 picture of the conditions in solutions that conduct electricity. 
 Without this theory it would be difficult to account for 
 electrolytic conduction or for the fact that all acids have the 
 same acid properties and all bases have the same basic prop- 
 erties. We make use of the ionic theory because it is a great 
 aid in helping us to understand chemical principles and to 
 systematize our knowledge of the chemistry of solutions. 
 
 327. Neutralization According to Ionic Theory. One of 
 the greatest services of the ionic theory is that it has given us 
 
NEUTRALIZATION ACCORDING TO IONIC THEORY 307 
 
 a far clearer understanding of neutralization reactions. We 
 have said that the neutralization of an acid and a base results 
 in the formation of water and a salt with a disappearance of 
 the characteristic properties of acid and base. According 
 to the ionic theory an acid when in solution consists of a hy- 
 drogen ion and a radical ion and a base consists of a metal 
 ion and an hydroxyl ion. Thus hydrochloric acid is 
 
 H + + Gl- 
 and sodium hydroxide is 
 
 Na + + OH-. 
 
 Pure water does not conduct electricity and therefore does not 
 contain ions but only molecules of H^O (or HOH). " Now on 
 bringing acid and base together, H + ions and OH~ ions come 
 into contact. They are components of water, but water 
 cannot exist in ionized form ; in other words, these compo- 
 nents cannot continue to exist separately when in presence of 
 each other, they combine to form undissociated water mole- 
 cules, H+ + QH - ^ (HQH) or H2 Q 
 
 Sodium chloride, on the other hand, we know to exist in solu- 
 tion in the form of ions. Hence the Cl~ ion of the acid and 
 the Na + ion of the base do not suffer any change during the 
 neutralization but simply remain in the neutralized solution. 
 The complete neutralization reaction would thus appear as 
 follows : 
 
 H + + Cr + Na + + OH- -+ HOH + Na + + CT. 
 
 The resulting solution is identical with one that would be ob- 
 tained by dissolving solid sodium chloride in water, hence we 
 are perfectly correct in speaking of it as a sodium chloride 
 solution. If this solution is evaporated, water escapes as 
 water vapor and the Na + ions and Cl~ ions, no longer being 
 
308 THE IONIC THEORY 
 
 held apart by the water, join to form molecules of sodium 
 chloride. When the water is all evaporated, nothing is left 
 but solid sodium chloride. 
 
 It is thus true that water and a salt are the products of 
 neutralization, but it must be borne in mind that undisso- 
 ciated water is always formed, whereas undissociated salt is 
 usually not formed unless the water is first driven off. 
 
 SUMMARY 
 
 Metallic Conductance : All metals conduct electricity without 
 suffering perceptible changes. 
 
 Non- Conductors : Dry non-metallic substances, including com- 
 pounds of metals, do not conduct electricity. 
 
 Electrolytic Conductance : Pure water is a non-conductor of elec- 
 tricity. Dry acids, bases, and salts also are non-conductors. 
 But water solutions of acids, bases, and salts conduct. Elec- 
 trolytic conduction, however, is different from metallic conduc- 
 tion in that solutions of acids, bases, and salts undergo chemical 
 change during the passage of an electric current. 
 
 The ionic theory assumes that when an acid, base, or salt is dissolved 
 in water, its molecules become separated into two components 
 called ions. Furthermore, the ions are heavily charged with 
 positive and negative electricity, respectively. 
 
 Attraction and Repulsion : Bodies bearing like electric charges repel 
 
 each other, whereas bodies with unlike charges attract. 
 Thus positively charged ions in solution attract and hold an elec- 
 trically equivalent number of negatively charged ions. The 
 ions are free to move past each other and they are all the time 
 exchanging partners, but it is not possible for ions of one kind 
 to exist in solution except when balanced by ions of opposite 
 charge in their immediate vicinity. 
 
 Ions convey the electric current which passes through a solution. 
 
 Hydrogen ions are responsible for the properties of acids. 
 
 Hydroxyl ions are responsible for the properties of bases. 
 
 Salts, strong acids, and strong bases conduct strongly and are highly 
 ionized when dissolved in water. 
 
QUESTIONS 309 
 
 Weak acids and weak bases contain proportionately fewer ions than 
 strong acids and bases. Thus the conductance for electricity 
 and the acid and basic properties are weaker. 
 
 Substances enter readily into reaction when in the ionized condi- 
 tion, because their components are separated and thus free to 
 exchange partners. When un-ionized, the components are 
 rigidly bound together and substances do not readily enter into 
 reaction. 
 
 Neutralization according to the ionic theory consists in the pairing 
 of positive hydrogen ions of the acid with negative hydroxyl 
 ions of the base to form undissociated water. The negative 
 radical ions of the acid and the positive metal ions of the base 
 remain in the solution as a dissociated salt. The undissociated 
 dry salt is obtained by evaporating off the water. 
 
 Questions 
 
 1. In what important respect is acid hydrogen different from 
 ordinary hydrogen? To what is this difference attributed? 
 
 2. What component of all bases causes litmus to become blue? 
 of all acids causes litmus to become red ? 
 
 3. Why do solutions of acids, bases, and salts conduct the electric 
 current, whereas the dry substances are non-conductors? 
 
 4. Explain in terms of the ionic theory why carbonic acid is so 
 much weaker than sulphuric acid. 
 
 5. What argument can you advance in favor of the truth of the 
 ionic theory, other than those drawn from the conductivity of solu- 
 tions of electrolytes? 
 
 6. Formulate in terms of the ionic theory what takes place during 
 the neutralization of 
 
 KOH and HC1 Ca(OH) 2 'and H 2 S0 4 
 
 NaOH and H 2 S0 4 NH 4 OH and H 2 S0 4 
 
 KOH and H 2 SO 4 NH 4 OH and HC1 
 
 Ca(OH) 2 and HC1 KOH and HN0 3 
 
 7. Remembering that silver chloride is insoluble, write ionized 
 equations for the following cases 
 
 AgN0 3 + HC1 -^ ? 
 Ag 2 S0 4 + KCi -> ? 
 
310 THE IONIC THEORY 
 
 8. Remembering that barium sulphate is insoluble, write ionized 
 equations for the following cases 
 
 BaCl 2 + Na 2 S0 4 -> ? 
 Ba(OH) 2 +H 2 S0 4 -? 
 
 9. Remembering that all sodium, potassium, and ammonium salts 
 are soluble, write ionized equations for the following cases 
 
 NaOH + HNO 3 -+ ? 
 
 NH 4 C1 + NaN0 3 -> ? 
 
 KN0 3 + NaCl - ? 
 
 NH 4 C1 + NaOH -> ? 
 
 NH 4 OH + HC1 -> ? 
 
 
CHAPTER XXVI 
 
 ELECTROLYSIS 
 
 328. Electrolysis of Hydrochloric Acid. When a solution 
 of hydrochloric acid is electrolyzed, hydrogen gas is given off 
 at the negative pole and chlorine gas at the positive pole 
 (Chapter XIII). The poles, or electrodes, should consist of 
 strips of platinum, 
 because platinum is 
 attacked but little by 
 either the acid or the 
 chlorine. The elec- 
 trodes are immersed 
 at opposite sides of 
 the solution and they 
 are connected by 
 metal wires with the 
 electric cell or the 
 dynamo (Fig. 61). 
 Thus one electrode is kept constantly charged with posi- 
 tive electricity and the other with negative electricity. 
 Since chlorine is given off at the positive pole, the chlorine 
 must first have been attracted through the solution to 
 the surface of the pole, and since it is attracted to a positively 
 charged body, it must itself be negatively charged. By the 
 same reasoning, since hydrogen is given off at the negative 
 electrode, the hydrogen in the solution must be positively 
 charged. 
 
 311 
 
 FIG. 61. Electrolysis of Hydrochloric Acid. 
 
312 ELECTROLYSIS 
 
 v 
 
 329. Discharge of Ions. It is, of course, obvious that 
 ordinary hydrogen gas and chlorine gas are not electrically 
 charged. Before their escape from the surface of the elec- 
 trodes, the hydrogen and chlorine ions, respectively, must 
 have surrendered their electric charges, 
 
 + 
 
 Cl" 
 
 The electric charges thus given up to the electrodes neutralize 
 the opposite charges which are being continually supplied 
 from the dynamo. 
 
 330. Ions as Carriers. The ions which come up to the 
 electrodes during the electrolysis and give up their charges 
 are bringing a steady supply, or current, of electricity. They 
 may be likened to a line of laborers each with a wheelbarrow 
 load of gravel. Each laborer comes up in turn, discharges 
 his load of gravel in the desired place, and steps aside with his 
 wheelbarrow. In the same way a file of H + ions moves 
 towards the negative electrode. As each ion reaches the 
 electrode, it discharges its load of electricity and retires to 
 form hydrogen gas (by doubling up with the next hydrogen 
 atom released). A file of Cl~ ions moves at the same time in 
 the opposite direction, and each ion in turn gives up its charge 
 at the positive electrode and retires to form ordinary chlorine 
 gas (by pairing with the next atom of chlorine). 
 
 Let us picture the process by means of diagrams. Let 
 a white circle O represent a hydrogen atom and a circle with 
 
 a + sign O represent a hydrogen ion. Let a black circle 
 represent a chlorine atom and a chlorine ion. At the out- 
 set let us represent six of each kind of ions in the solution be- 
 
IONS AS CARRIERS 
 
 313 
 
 tween the electrodes instead of the countless number which 
 is actually present (Fig. 62). After the current has passed 
 for some time, a certain number of ions let us say two of 
 each kind has been discharged. The two H + ions nearest 
 the negative electrode have moved up to it and discharged. 
 
 
 
 o 
 
 o 
 
 
 
 o 
 
 o 
 
 FIG. 62. Ions in Solution before Current has passed between Electrodes. 
 
 This leaves unbalanced the two Cl~ ions which were originally 
 paired with the two H + ions. It is impossible for them to 
 remain long unbalanced. They are repelled by the nega- 
 tively charged electrode and they move away from it, but in 
 moving away they repel the four Cl~ ions in front of them. 
 At the same time they attract the hydrogen ions farther down 
 the line and these move up to balance them. At the other 
 electrode a similar process has taken place ; two chlorine 
 ions have discharged and left two hydrogen ions unbalanced. 
 The latter are repelled and move away, following the other 
 hydrogen ions. At this point in the electrolysis we have 
 
 I 
 
 + 
 
 O 
 
 o 
 
 + 
 
 o 
 
 + 
 
 o 
 
 8 
 
 FIG. 63. Showing Condition of Solution from Fig. 62, after Current has passed for 
 
 a Time. 
 
 positive and negative ions balanced against each other 
 throughout the solution just as at the outset, but there are 
 only four pairs now instead of six as at first (Fig. 63) ; 
 
314 ELECTROLYSIS 
 
 and accumulated on the poles we have a molecule of hydrogen 
 and a molecule of chlorine, respectively. 
 
 If the electrolysis were continued long enough, all the ions 
 would be withdrawn from the solution and nothing but pure 
 water would be left. In such a case, of course, the current 
 would stop flowing, for there would be nothing left to conduct 
 it ; for pure water is a non-conductor. 
 
 331. Atomic Structure of Electricity; Electrons. It has 
 probably occurred to the reader to wonder what determines 
 just how much electricity each ion carries. Evidently the 
 positive charge of the hydrogen ion is just equal and opposite 
 to the negative charge of the chlorine ion ; and it is almost 
 equally evident that every hydrogen ion always has just the 
 same amount of positive electricity and every chlorine ion 
 has just the same amount of negative electricity. One might 
 well wonder if electricity does not have an atomic structure 
 just like ordinary matter and if the charge on the hydrogen 
 ion is not really a single atom of positive electricity and the 
 charge on the chlorine ion a single atom of negative electricity. 
 That this is really so seems extremely probable in the light 
 of our present knowledge, and we shall from now on speak of 
 the electric atoms as confidently as we speak of the atoms of 
 the material elements. We shall call these smallest divisions 
 of electricity electrons and we shall distinguish positive and 
 negative electrons and give them the symbols and . 
 
 Recent study of electric discharges in vacuum tubes, and 
 work with the wonderful element radium have thrown a 
 great deal of light on the subject of electrons. The negative 
 electrons have actually been discovered, unassociated with 
 ordinary matter, in the discharge from the negative electrode 
 in vacuum tubes. Positive electrons have never been found 
 except in association with atoms of the ordinary elements. 
 
ELECTROLYSIS OF SULPHURIC ACID 315 
 
 It may be that only what we call the negative electrons have 
 a real existence and that what we call positive electrons are 
 merely atoms of ordinary matter deprived of negative elec- 
 trons which belong there. We shall find it convenient to speak 
 of both positive and negative electrons as well as of positive 
 and negative electricity as if both existed, and we shall not 
 concern ourselves with the question as to whether there are 
 really two kinds or only one kind of electricity. 
 
 332. Electrolysis of Sulphuric Acid. Sulphuric acid con- 
 tains hydrogen and a sulphate radical. Since the acid gives 
 H + ions when it dissociates, the sulphate radical must form 
 the negative ions : 
 
 When this acid is electrolyzed, it might be expected that 
 SO 4 ions would travel towards the positive electrode and 
 H + ions towards the negative electrode. As a matter of fact, 
 hydrogen is given off at the negative electrode, but at the other 
 electrode oxygen is set free instead of the SO 4 radical. 
 
 The electrolysis of most substances is a more complicated 
 phenomenon than that of hydrochloric acid, in which the ions 
 that carry the current simply discharge and the respective 
 elements escape in the uncombined condition. The SO 4 
 ion of sulphuric acid is actually the carrier of the negative 
 electricity, but the uncharged SO 4 radical is incapable of 
 existence alone. W 7 hen it parts with its 'electricity it would 
 either itself have to break down into other substances or it 
 would react with the solvent water. The latter is probably 
 what happens and it is thus the oxygen of the water that 
 escapes. 
 
 S0 4 + H 2 -> H 2 S0 4 + O 
 
 2 > O 2 (molecule of oxygen gas which escapes) . 
 
316 
 
 ELECTROLYSIS 
 
 The sulphuric acid thus formed in this secondary reaction of 
 course dissociates immediately into ions under the influence 
 of the water. jj^ _^ 2 H + + SOT ~. 
 
 333. It will be remembered that in decomposing water 
 by the electric current (page 103), sulphuric acid was added 
 in order to make the solution conduct. It was then stated 
 that the sulphuric acid suffered no change but that only the 
 water was decomposed, and it is now seen why the statement 
 was justified. It is really the ions of sulphuric acid that carry 
 
 the current, but for every molecule 
 of sulphuric acid that is drawn 
 apart another molecule is generated 
 by the secondary reaction at the 
 positive electrode, and the amount 
 of sulphuric acid in the whole solu- 
 tion suffers no change. 
 
 334. If what has just been said 
 is true, there must, however, be 
 an accumulation of sulphuric acid 
 around the positive electrode and 
 a depletion around the negative 
 electrode, for the SO4 ions are 
 drawn away from the latter and the 
 H + ions are discharged there. We 
 ought to be able to show this ac- 
 FIG. 64. Electrolysis of Sui- cumulation and depletion in order 
 
 phuricAcid. Arranged to prove , . ,. 
 
 the passage of sulphate ions to justify our arguments. 
 
 In the apparatus shown in Fig. 61 
 the solution around the electrodes 
 would be continually in circulation and on this account 
 no accumulation of sulphuric acid would last long enough 
 
 away from the electrode 
 and towards the + electrode. 
 
SECONDARY REACTION AT ELECTRODES 
 
 317 
 
 to be demonstrated. It is necessary to modify the apparatus 
 somewhat and to arrange glass cups around the electrodes 
 to prevent circulation of the liquid (Fig. 64). Where the 
 sulphuric acid accumulates, the cup 
 must be open at the top and closed 
 at the bottom because the more con- 
 centrated a solution the heavier it is. 
 Where the sulphuric acid is depleted, 
 the cup must have an opening at the 
 bottom for the passage of the current 
 and the top must rise above the sur- 
 face of the liquid because the acid of 
 diminished concentration is lighter 
 than the original acid. 
 
 If after the current has passed for 
 some time through a dilute solution 
 of sulphuric acid in this apparatus, 
 portions of the solution are removed 
 with a pipette (Fig. 65) from the two 
 cups and analyzed, it is actually found 
 that the one from the cup around the negative electrode 
 contains less sulphuric acid and that from the cup around 
 the positive electrode more sulphuric acid than at the start. 
 
 335. Secondary Reaction at Electrodes. As already 
 stated, it is not always true that the products which appear 
 at the electrodes as a result of electrolysis are formed directly 
 from the ions that carry the current through the solution. 
 These products arise quite as often from secondary reactions 
 which the discharged ions enter into either among themselves 
 or with water. It is hence not possible to say from an ob- 
 servation of the products liberated at the poles what are the 
 ions in the solution. In the electrolysis of sodium hydroxide 
 
 FIG. 65. Pipette. 
 
318 ELECTROLYSIS 
 
 and sodium sulphate, for example, the products liberated are 
 hydrogen and oxygen. These gases are evolved in the pro- 
 portion of two volumes of the former to one of the latter, 
 just as in the electrolysis of dilute sulphuric acid. We have 
 thus a typical acid, a typical base, and a typical salt all of 
 which yield as the final products of their electrolysis only 
 the two constituents of pure water. Yet these substances 
 cannot all have the same ions. 
 
 336. Electrolysis of Sodium Hydroxide. It has already 
 been stated that the ions of sodium hydroxide are Na + and 
 OH~ and it must be these that carry the current. At the 
 negative electrode we may imagine the Na + ion to be dis- 
 charged, Na+ -* Na + 
 
 and the sodium atom to react with water, 
 
 2 Na + 2 HOH -^ 2 NaOH + H 2 . 
 
 At the positive electrode, we may imagine that the OH~ ions 
 discharge, 
 
 and that the hydroxyl groups so formed react together to 
 give water and oxygen gas : 
 
 4 OH -> 2 H 2 O + O 2 . 
 
 We have taken for granted that hydrogen is only the sec- 
 ondary product of the electrolysis and that it results from the 
 reaction of the water on the sodium which is first set free. 
 If it were possible to electrolyze sodium hydroxide without 
 using water as a solvent, it might be possible to obtain metal- 
 lic sodium instead of hydrogen at the negative electrode. 
 Dry, solid sodium hydroxide does not conduct electricity; 
 but if heated strongly it melts, and the liquid sodium hydrox- 
 ide is an excellent electrolytic conductor. Metallic sodium 
 
ELECTROLYSIS OF SODIUM SULPHATE 319 
 
 is then obtained as a deposit at the negative electrode, and 
 this is one of the methods by which metallic sodium is manu- 
 factured on a commercial scale. 
 
 337. Electrolysis of Sodium Sulphate. Sodium sulphate 
 is the salt obtained by neutralizing sodium hydroxide with 
 sulphuric acid, and its solution contains the same metal ion 
 as the base and the same radical ion as the acid. Thus on 
 electrolyzing a sodium sulphate solution, since the negative 
 ion is the same, the same change occurs at the positive pole 
 as when sulphuric acid is electrolyzed, namely, the ion dis- 
 charges and the sulphate radical reacts with water, 
 
 2 S0 4 + 2 H 2 -> 2 H 2 SO 4 + O 2 . 
 
 At the negative electrode the same change occurs as when 
 sodium hydroxide is electrolyzed, namely, the sodium ion 
 discharges and the metal atom then reacts with water, 
 2 Na + 2 HOH->2 NaOH + H 2 . 
 
 Sodium sulphate is a neutral salt and its solution does not 
 change the~color of either red or blue litmus. If the solution 
 is electrolyzed, however, in an apparatus similar to that 
 shown in Fig. 64, in which both electrodes are surrounded by 
 cups, a piece of litmus placed in the cup around the positive 
 pole will immediately turn red, showing that an acid is formed, 
 and the piece of litmus in the other cup will immediately turn 
 blue, showing that a base is produced. By glancing back to 
 the equations for the secondary reactions, one sets that in 
 accounting for the formation of the hydrogen and oxygen, it 
 was necessary to allow also for the formation of sodium hy- 
 droxide and sulphuric acid at the respective electrodes. The 
 formation of base and acid at the two poles agrees, therefore, 
 with our interpretation of the secondary reactions and in- 
 creases our confidence in the correctness of our deductions. 
 
 B. AND W. CHEM. 21 
 
320 ELECTROLYSIS 
 
 If the reactions are studied a little further, it will be seen 
 that since two atoms of hydrogen are liberated for each atom 
 of oxygen, two molecules of sodium hydroxide should be 
 formed at the one pole for each molecule of sulphuric acid 
 at the other. These are equivalent quantities, and should 
 just neutralize each other. Now if to test this deduction the 
 whole solution is thoroughly mixed after the electrolysis has 
 been stopped, it is found that the solution becomes again per- 
 fectly neutral and will not change either red or blue litmus. 
 Thus there are in fact exactly equivalent quantities of acid 
 and base produced by the electrolysis of the salt. 
 
 338. Electrolysis of Sodium Chloride. One of the im- 
 portant commercial methods of manufacturing sodium hy- 
 droxide is by the electrolysis of sodium chloride, the most 
 abundant and least expensive compound of sodium. The 
 sodium hydroxide is obtained at the negative electrode, and 
 chlorine, which is an even more valuable product, is obtained 
 at the other electrode (see Chlorine, Chapter XVI). 
 
 Sodium is one of the most active of all metals and it is be- 
 cause of this that sodium does not appear as one of the prod- 
 ucts when solutions of sodium salts are electrolyzed. No 
 more do we obtain potassium or calcium when solutions of 
 their salts are electrolyzed ; we obtain, instead, the bases 
 potassium hydroxide and calcium hydroxide, just as we ob- 
 tained sodium hydroxide by the electrolysis of a sodium 
 salt. 
 
 339. Electrolysis of Copper Sulphate. When, however, a 
 salt of a metal which does not decompose water is electrolyzed, 
 the metal itself ought to be obtained. For example, if the 
 current is passed through a solution of copper sulphate, 
 CuSO 4 , between platinum electrodes, a reddish metallic de- 
 posit of copper begins at once to appear on the negative pole, 
 
ELECTROPLATING OF COPPER 321 
 
 while at the other pole oxygen escapes. The copper ions 
 simply surrender their charges to the electrode, 
 
 Cu ++ -> Cu + 2 
 
 and the unelectrified atoms stick there and soon build up a 
 coherent layer of the metal. At the other electrode, the ions 
 which come up to discharge are the same as with sulphuric 
 acid or sodium sulphate, and so long as the electrodes are of 
 the unattackable metal platinum, the reaction is the same as 
 already described under the electrolysis of these substances. 
 
 340. The electroplating of copper is an art of very great 
 importance. The object to be covered is made the negative 
 electrode in a bath of a copper salt, frequently copper sul- 
 phate ; for the other electrode a thick plate of copper is used 
 instead of platinum or other unattackable metal. Now, 
 when the current passes, Cu ++ ions discharge at one electrode 
 and this would, after a while, deplete the bath of copper ex- 
 cept that the metal of the other electrode dissolves and main- 
 tains the supply. The SC>4 ions are attracted to the posi- 
 tive electrode as usual, but instead of having to give up their 
 charges, they become electrically balanced by new copper 
 ions which are formed from the metal of the electrode and the 
 positive electricity. 
 
 Cu + 2 -> Cu ++ . 
 
 Thus electroplating consists merely in transferring copper 
 in the form of ions through a solution from a thick mass of 
 the metal to the object to be plated. (Compare Electrolytic 
 Refining of Copper, page 254.) 
 
 341. Multiple Proportions among Ionic Charges. Of the 
 several ions mentioned in this and the preceding chapter, it 
 is noticed that some are represented as carrying single charges 
 of electricity, or single electrons, whereas others are repre- 
 
322 ELECTROLYSIS 
 
 sented as having exactly twice as much electricity, that is, 
 two electrons each. Following is a table giving some of the 
 very common ions and showing the number and character of 
 the charges on each : , 
 
 Hydrogen . \ . . . H+ Chloride . . . . Cl~ 
 
 Sodium . . , Na + Nitrate .... N0 3 ~ 
 
 Potassium . . . . K + Bromide .... Br~ 
 
 Ammonium .... NH 4 + 
 
 Silver Ag+ 
 
 Calcium Ca++ Sulphate . . . . S0 4 ~ 
 
 Copper Cu ++ Carbonate . . . C0s~ " 
 
 Barium Ba ++ 
 
 Zinc ...... Zn++ 
 
 Magnesium .... Mg ++ 
 
 Aluminium .... A1+++ Phosphate . . . P0 4 ~- 
 
 The fact that the amount of electricity on an ion is always 
 some whole multiple of the unit amount that resides on the 
 H + ion or the Cl~ ion was originally the reason for wanting 
 to ascribe an atomic structure to electricity. If electricity 
 were continuous in nature and not atomic, it would be hard 
 to see why some ions should bear exactly the unit charge, 
 some exactly twice, and some exactly three times the unit 
 charge, but none should ever bear fractional amounts. As 
 already stated, page 314, the idea of the atomic, or electronic, 
 structure of electricity is now firmly established. 
 
 342. Faraday's Law. It was observed as long ago as early 
 in the nineteenth century that when chemical decompositions 
 were caused by the passage of the current, there was a 
 simple relation between the amounts of different substances 
 decomposed by the same quantity of electricity. The rela- 
 tion was first clearly recognized by Faraday, and the law 
 which expresses this relation is known as Faraday's law. 
 
FARADAY'S LAW 
 
 323 
 
 We may state the law as follows : The passage of the same 
 amount of electricity causes the liberation of equivalent amounts 
 of different substances at the electrodes. We have already seen 
 that two volumes of hydrogen are liberated at one electrode 
 while one volume of oxygen is set free at the other. These 
 are equivalent quantities, for they are the amounts which 
 combine with each other to form water. We have also seen 
 that equivalent amounts of acid and base are formed at the 
 electrodes when a salt solution is electrolyzed. 
 
 343. When an electric current flows in a given circuit, 
 it is true that the quantity which passes in any one part of 
 the circuit is exactly the same as that which passes any other 
 part of the circuit. Let us. construct a circuit with several 
 electrolytic cells as shown in Fig. 66, the first cell having 
 silver electrodes in silver nitrate solution, the second copper 
 electrodes in copper sulphate solution, the third platinum 
 electrodes in sulphuric acid, and the fourth platinum elec- 
 trodes in sodium sulphate solution. 
 
 FIG. 66. Electrolytic Cells in Series. 
 
 Let us now allow an amount of electricity to pass which 
 is sufficient to carry 108 grams of silver from the positive 
 electrode into the solution and to deposit 108 grams of silver 
 on the negative pole of the first cell, and let us observe what 
 
324 ELECTROLYSIS 
 
 corresponding changes take place in other parts of the cir- 
 cuit. 108 is the atomic weight number of silver and 108 
 grams is the gram-atomic weight. 
 
 In the second cell, we find that 31.8 grams of copper are 
 dissolved from the positive electrode and that an equal 
 amount is deposited on the negative electrode. The atomic 
 weight of copper is 63.6; hence 31.8 grams is one half an 
 atomic weight in grams. This amount of copper, then, is 
 equivalent to 108 grams or a whole atomic weight in grams 
 of silver, electrically as well as chemically. Chemically, an 
 atom of copper is equivalent to two atoms of silver, for it has 
 twice the capacity for holding atoms of non-metallic elements 
 in combination. This is shown, for example, by comparison 
 of the oxides and chlorides : 
 
 CuO CuCl 2 
 
 A g2 AgCl 
 
 In the third cell of the series, 5.6 liters of oxygen gas (meas- 
 ured under standard conditions) are liberated at the positive 
 electrode and 11.2 liters of hydrogen gas at the negative 
 electrode. These quantities are equivalent to the amounts of 
 silver and copper deposited in the first two cells, for a simple 
 calculation will show that 11.2 liters of hydrogen weigh 
 1 gram and thus equal one gram-atomic weight of that ele- 
 ment, and that 5.6 liters of oxygen weigh 8 grams and thus 
 equal one half gram-atomic weight of the latter element. 
 
 In the fourth cell of the series, a chemical analysis of the 
 solution in the cup around the negative electrode would 
 show that 40 grams or one mole of sodium hydroxide is pro- 
 duced, and an analysis of the solution at the other electrode 
 would show that 49 grams or one half mole of sulphuric acid 
 is produced. These amounts are equivalent to each other 
 
SUMMARY 325 
 
 and to the amounts of silver, copper, hydrogen, and oxygen 
 involved in the other cells. 
 
 344. The foregoing illustrations have shown the wide appli- 
 cation of Faraday's law. Every year the application of 
 electricity in chemical manufactures is growing more and 
 more extensive. From a knowledge of Faraday's law and 
 the electrochemical equivalent, it is possible to figure just 
 how much electric current will be required to carry out any 
 desired electrochemical process, and the practical electro- 
 chemist makes constant use of this law in his calculations. 
 
 SUMMARY 
 
 Electrolytic conduction is always accompanied by a chemical decom- 
 position. In the simplest case of electrolysis, the ions of the 
 dissolved substance discharge and the two constituents ap- 
 pear at the electrodes. Thus the electrolysis of hydrochloric 
 acid gives hydrogen and chlorine, respectively. 
 
 Secondary Reactions: In many cases, the discharged ions yield 
 chemically active elements or radicals which enter into a 
 secondary reaction with the solution so that the products 
 actually liberated do not correspond with the ions that take 
 part in the conduction through the liquid. 
 
 Electroplating : In the electrolysis of the salts of the less active metals, 
 the metals themselves are deposited, or plated, on the negative 
 electrode. In this wise the extensive art of electroplating is 
 carried out. To avoid depletion of the metal in the solution, 
 the positive electrode is made of a heavy mass of the metal to 
 be plated, and the metal then dissolves from this electrode as 
 fast as it is deposited upon the other. 
 
 Faraday's Law: The passage of the same amount of electricity 
 causes the liberation of chemically equivalent amounts of dif- 
 ferent substances at the electrodes. The electricity required 
 to set free one gram-atomic weight of any element whose ions 
 carry a single electron, will set free one half gram-atomic 
 weight of any element, or radical, whose ions carry two elec- 
 trons. 
 
326 ELECTROLYSIS 
 
 Questions 
 
 1. How does electrolytic conduction differ from that in a metallic 
 conductor ? 
 
 2. What becomes of the charges which the ions carry up to the 
 electrodes ? 
 
 3. What would happen if a dilute solution of H 2 S0 4 were to be 
 electrolyzed for a long time ? 
 
 4. What becomes of the sulphate radical when H 2 S0 4 is electro- 
 lyzed? 
 
 6. What becomes of the metallic sodium which one might expect 
 to get at the negative electrode when sodium hydroxide solution 
 is electrolyzed? 
 
 6. What facts prove that there is a greater concentration of sul- 
 phate ions around the positive electrode than anywhere else in the 
 solution during the electrolysis of H 2 S0 4 ? 
 
 7. How does it happen that the acid formed around the positive 
 electrode during the electrolysis of sodium sulphate solution exactly 
 neutralizes the base formed around the negative electrode? 
 
 8. What sort of metals would be obtained in the metallic state on 
 the negative electrode during the electrolysis of their salts ? 
 
 9. Show how practical use is made of the above type of 
 electrolysis. 
 
 10. Try to devise a means of measuring electricity based upon 
 what you have just learned about Faraday's law. 
 
 11. What weight of silver would be deposited from AgN0 3 
 solution by the same current that deposits 6.36 grams of copper from 
 Cu(N0 3 ) 2 solution? 
 
 12. A certain amount of electric current liberates 27.1 kilograms 
 of aluminium from the solution of aluminium oxide in fused cryolite 
 (page 260). How much copper would the same current deposit on 
 the negative electrode in copper refining (page 254) ? 
 
CHAPTER XXVII 
 
 THE ELECTROMOTIVE SERIES 
 
 345. Displacement of Hydrogen by Metals. It has al- 
 ready been seen in the chapters on the Ionic Theory and on 
 Electrolysis that the peculiar properties of acid hydrogen are 
 in all probability due to the latter being in an ionized condi- 
 tion and carrying positive electric charges. 
 
 When an active metal, such as aluminium, magnesium, or 
 sodium, reacts with an acid and sets free hydrogen gas, a 
 salt of the metal is formed in the solution and we know that 
 this salt is ionized ; we also know that the hydrogen as gas 
 is no longer ionized, for it is not possessed of any free electric 
 charge. The metal must then have taken the electric charges 
 away from the hydrogen ions, and the hydrogen atoms with- 
 out the charges have combined to form the molecules, H 2 , 
 of ordinary hydrogen. Thus the displacement of hydrogen 
 by metallic sodium may be represented as follows : 
 
 Na + H + Cr -+ Na + Cr + H. 
 
 In order to obtain molecular hydrogen, this equation must 
 be taken twice so as to give two atoms. Since the chlorine 
 ion remains unchanged, it may be omitted from both sides 
 in writing the equation and thus we have 
 
 2 Na + 2 H + -> H 2 + 2 Na+ . 
 
 The metal on acquiring the positive charges from the hydro- 
 gen passes into the form of ions and as such no longer exists 
 
 327 
 
328 THE ELECTROMOTIVE SERIES 
 
 as a compact metallic mass, but forms a component of the 
 solution, whereas the hydrogen on passing out of the ionic 
 condition ceases to be a component of the solution. 
 
 346. Displacement of One Metal by Another. Not only 
 can an active metal displace hydrogen from the solution of an 
 acid, but it can displace metals less active than itself from the 
 solutions of their salts. For example, when a knife blade is 
 dipped into a solution of copper sulphate, a copper-colored 
 coating is at once deposited on the blade. The coating is 
 copper, and at the same time that it is being thrown down, 
 iron from the knife blade is passing into solution. It is true 
 that the passage of iron into the solution cannot be seen as 
 can the depositing of the metallic copper, but we can easily 
 convince ourselves that it takes place ; for if after a little while 
 the solution is tested chemically, it is found to contain iron 
 ions. Iron displaces hydrogen from sulphuric acid and in 
 just the same way that it displaces the copper from copper 
 sulphate, except that free un-ionized copper forms a compact 
 metallic mass rather than a gas. The atoms of iron of course 
 acquire electric charges and pass into the solution as ions, 
 while simultaneously the copper ions lose their charges and 
 are deposited as metallic copper : 
 
 Fe + Cu ++ SO 4 --->Fe ++ S<V + Cu, 
 or, since the sulphate ion is unchanged, 
 
 Fe + Cu ++ -> Fe ++ + Cu. 
 
 A number of active metals besides iron can displace copper 
 and hydrogen from solutions. Among them are the ex- 
 tremely active metals sodium and potassium, which react 
 with great violence, the active metals magnesium, aluminium, 
 and zinc, which react rapidly, and the moderately active 
 metals such as tin and lead, which react rather slowly. Not 
 
ELECTROMOTIVE SERIES 
 
 329 
 
 only do these metals displace hydrogen and copper, but they 
 displace the precious metals, silver, gold, and platinum, from 
 solutions of their salts. In fact, copper itself displaces the 
 metals silver, gold, and platinum. 
 
 If a little piece of clean copper is placed in some silver nitrate 
 solution in a test tube, a moss-like deposit begins at once to 
 form over the surface of the metal. The deposit is metallic 
 silver, and it appears mossy because it is built up of tiny 
 branching crystals instead of forming a smooth uniform layer. 
 At the same time the solution acquires a blue color which is 
 due to the blue copper ions that are formed. 
 
 Cu + 2 Ag + -* Cu ++ + 2 Ag. 
 
 Copper ions always possess the same blue color whatever the 
 negative ions that balance them. Thus dilute solutions of 
 copper nitrate, copper sulphate, and copper chloride all pos- 
 sess exactly the same color. 
 
 347. Electromotive Series. All metals 
 seem to possess a tendency to pass into the 
 form of ions when in contact with water or 
 with a solution. The magnitude of this tend- 
 ency is enormous with metals like sodium 
 and potassium ; it is less, although large, with 
 magnesium, aluminium, and zinc; it is small 
 with iron, tin, and lead ; and, finally, it is 
 very small with the precious metals. 'The 
 metals can all be arranged, as in the table, in 
 the order in which they possess this tendency, 
 and the series so obtained is known as the 
 electromotive series. 
 
 348. Hydrogen is given a position in this 
 series because it is like the metals in that it 
 
 Potassium 
 
 Sodium 
 
 Calcium 
 
 Magnesium 
 
 Aluminium 
 
 Zinc 
 
 Iron 
 
 Nickel 
 
 Tin 
 
 Lead 
 
 Hydrogen 
 
 Copper 
 
 Mercury 
 
 Silver 
 
 Platinum 
 
 Gold 
 
 Electromotive 
 Series. 
 
330 THE ELECTROMOTIVE SERIES 
 
 forms simple, positive ions. Any metal in this series can 
 drive any metal standing below it from the ionic into the 
 metallic condition, whereas its own ions can be driven out 
 of solution by any metal standing above it. Thus all 
 the metals standing above hydrogen cause the evolution 
 of hydrogen gas, when placed in an acid solution, but the 
 metals copper, silver, mercury, gold, and platinum, which 
 stand below, do not displace hydrogen. 
 
 349. Sodium reacts violently even with pure water and 
 liberates hydrogen. Water itself ionizes to an infinitesimal 
 extent, although so little that this point has been ignored 
 in all our previous discussions. Sodium is so very active 
 that it reacts even with the few hydrogen ions in water 
 and drives them out. This quantity would be altogether 
 too small to be perceptible, except that, with these ions 
 removed, the water dissociates further so as to keep up 
 its normal infinitesimal supply of ions. The sodium con- 
 tinues to react with these few ions, and new ones are 
 continually formed in their place, so that in the end the 
 sodium has all reacted and liberated an equivalent amount 
 of hydrogen from the water which at the outset was prac- 
 tically un-ionized. 
 
 350. The farther above hydrogen a metal stands in the elec- 
 tromotive series, the greater is its tendency to pass into the 
 form of ions, and consequently the more rapidly should it be 
 able to displace hydrogen. By testing all of the metals with 
 an acid, for example dilute hydrochloric acid, one finds that 
 the metals towards the top of the list cause a violent evolu- 
 tion of hydrogen ; that those lower down react less vigorously ; 
 that tin and lead, which stand only just above hydrogen, dis- 
 place hydrogen, but so slowly that it might escape observa- 
 tion unless carefully looked for; and that all of the metals 
 
SUMMARY 331 
 
 below hydrogen in the list cause no evolution at all of hydro- 
 gen gas. 
 
 351. Electrochemical Equivalents. In the chapter on 
 Electrolysis, it was found to be a law that the passage of the 
 same amount of electricity causes the liberation of equivalent 
 amounts of different substances at the electrodes. The law, 
 which we know as Faraday's law, applies equally well to the 
 displacement of one metal by another metal, and in reality 
 the latter sort of displacement is just as much an electrolytic 
 action as if the current entered by one electrode and left by 
 another electrode. Here the same piece of metal serves as 
 both electrodes in short electric circuits. At some points 
 on the surface, its own atoms are passing into the solution 
 as ions and taking positive charges with them, while at other 
 points, the ions of hydrogen or other metal are depositing 
 out of the solution and returning just as much positive 
 electricity to the piece of metal as was given off at the first 
 mentioned points. Hence the quantities of the different 
 metals involved in these displacements are chemically equiv- 
 alent quantities. 
 
 SUMMARY 
 
 Electromotive Series : All metals, in which classification hydrogen 
 is included, have the ability, under proper conditions, to pass 
 back and forth between the forms of ordinary massive metals, 
 and positively electrified ions in solutions of the metal salts 
 or of acids. The metals are arranged in a series in the order 
 of their tendency to pass into the ionic form. This is known 
 as the Electromotive Series. 
 
 Metals standing above hydrogen in the electromotive series set free 
 hydrogen from acids ; those standing below hydrogen cannot 
 set hydrogen free. 
 
 As a general rule, a metal can drive any metal standing below it 
 in the electromotive series from the ionic into the metallic 
 
332 THE ELECTROMOTIVE SERIES 
 
 form. The amounts of the metals involved in such displace- 
 ments are always equivalent. 
 
 Questions 
 
 1. Explain the difference between copper in the metallic condi- 
 tion and in solution using the ionic theory in your explanation. 
 
 2. Write, in ionic form, the equation for the displacement of copper 
 by iron. Assume that the copper was present as dissolved copper 
 sulphate. 
 
 3. Between what two members of the electromotive series should 
 we draw a line to separate those metals which can displace hydrogen 
 from acid solution from those that cannot f 
 
 4. Why should hydrogen be included in a list of metals? 
 
 5. How is it possible that the active metals displace hydrogen 
 from water? 
 
 6. According to Faraday's law as applied to the displacement 
 of one metal by another what weight of metallic copper would 
 be displaced by 56 grams of iron? By 65 grams of zinc? By 24 
 grams of magnesium? By 27 grams of aluminium ? 
 
 7. Write in ionic form equations for the following : 
 
 (a) Zn + HC1 (6) Zn + CuCl 2 (c) Zn + AgNO 3 
 
 (d) Al + Hg(N0 3 ) 2 (e) Fe + AuCl 3 (/) Cu + ZnCl 2 
 
 (g) Cu + HC1 (h) Cu + HgN0 3 (i) Cu + Hg(NO 3 ) 2 
 
 0') Cu + PtCU (*) Ag + AuCl 3 (/) Ag + PtCl 4 
 
CHAPTER XXVIII 
 HYDROGEN EQUIVALENTS AND VALENCE 
 
 352. It is of the utmost importance in chemistry to know 
 what amounts of different elements can mutually displace 
 each other or combine with one another. If these amounts 
 are always referred to the same standard, they are known 
 as equivalent weights, and for the standard of reference, one 
 gram atomic weight, that is practically one gram of hydro- 
 gen, is used. 
 
 The hydrogen equivalent of any metal is that weight of the 
 metal which is required to displace one gram of hydrogen, or, 
 in the case of a metal standing below hydrogen in the elec- 
 tromotive series, it is that weight of the metal which will be 
 deposited by the same quantity of electricity as will set free one 
 gram of hydrogen. 
 
 353. Experimental Determination of Hydrogen Equiva- 
 lents. Let us consider in some detail the actual steps we 
 would follow to determine the hydrogen equivalents of the 
 three common metals, aluminium, magnesium, and sodium; 
 and then let us study the results and see how they compare 
 with the atomic weights of these metals. 
 
 To find the weight of aluminium which will displace 
 one gram of hydrogen from an acid, we take a little piece of 
 pure aluminium wire and weigh it accurately. It weighs 
 0.0388 gram in a specific case that we are considering. The 
 wire is placed in the bottom of a good-sized beaker and over 
 it is placed an inverted funnel to direct the hydrogen gas 
 
 333 
 
334 
 
 HYDROGEN EQUIVALENTS AND VALENCE 
 
 into the collecting vessel (Fig. 67). The beaker is now 
 
 filled with water until the stem of the funnel is covered. 
 
 To measure the hydrogen gas, we take a 100 c.c. measuring 
 tube such as that used for determining the 
 volume per cent of oxygen in air (page 74) . 
 This tube is filled completely with hydro- 
 chloric acid, the thumb is placed over the 
 mouth of the tube, and the latter is then 
 inverted over the stem of the funnel in 
 the beaker. When the thumb is removed, 
 the heavier acid sinks through the water 
 to the bottom of the beaker where it 
 comes in contact with the aluminium and 
 reacts with it. The hydrogen evolved 
 rises through the stem of the funnel and 
 into the measuring 'tube. When all the 
 aluminium has reacted, the tube is some- 
 what more than one half filled with hy- 
 drogen, the volume of which is now to 
 be accurately measured. The thumb is 
 FIG 67 Deter- a g am placed over the mouth of the tube, 
 
 mining the Hydrogen and without allowing any gas to escape or 
 
 Equivalent of a Metal. &{jt t() ^^ ^ tube j g transferred to a 
 
 deep vessel of water where its height is so adjusted that the 
 water level inside the tube is the same as that outside. 
 The volume is then read off from the markings on the tube 
 and at the same time the temperature and the barometric 
 pressure are noted. The data thus obtained are : 
 
 Weight of aluminium 0.0384 g. 
 
 Measured volume of hydrogen .... 53.4 c.c. 
 
 Temperature 20 C. 
 
 Barometric pressure 740 mm. 
 
EXPERIMENTAL DETERMINATION 335 
 
 We know that one liter of hydrogen under standard con- 
 ditions weighs 0.09 gram, but before we can calculate 
 the weight of the gas obtained, we must find its volume under 
 standard conditions. 
 
 Applying the correction for temperature: 
 
 53.4 c.c. at 20 = 53.4 X = 49.8 c.c. at 
 and for pressure : 
 
 m. = 49.8 
 
 760 
 
 74-0 
 49.8 c.c. at 740 mm. = 49.8 X - = 48.5 c.c. at 760 mm. 1 
 
 This volume weighs : 
 
 X 0.09 = 0.00427 gram. 
 1000 
 
 We have now found that 0.0384 gram of aluminium dis- 
 places 0.00427 gram of hydrogen. Therefore x grams of 
 aluminium will displace 1 gram of hydrogen. 
 
 0.0384 = 0.00427 
 
 x 1 
 
 0.0384 
 
 and the hydrogen equivalent of aluminium is 9. 
 
 Experiments carried out with magnesium and sodium 2 
 after the manner just described for aluminium show that 12 
 grams of magnesium are required to displace 1 gram of hydro- 
 gen and that 23 grams of sodium are required to displace 
 1 gram of hydrogen. The hydrogen equivalent of magne- 
 sium is therefore 12, and that of sodium is 23. 
 
 354. The atomic weights of these three elements are, 
 
 1 This is only approximate, since water vapor is neglected. 
 
 2 Sodium is so active that the method must be modified in some 
 of its details. 
 
 B. AND W. CHEM. - 22 
 
336 HYDROGEN EQUIVALENTS AND VALENCE 
 
 aluminium 27, magnesium 24, and sodium 23. So it is seen 
 that the hydrogen equivalent and the atomic weight are iden- 
 tical in the case of sodium ; that the hydrogen equivalent of 
 magnesium is one half the atomic weight ; and that the hy- 
 drogen equivalent of aluminium is one third of the atomic 
 weight. From this it follows that one atomic weight of 
 sodium can displace a single atomic weight of hydrogen ; 
 that one atomic weight of magnesium can displace two atomic 
 weights of hydrogen ; and that one atomic weight of alumin- 
 ium can displace three atomic weights of hydrogen. 
 
 355. Valence. The number which expresses how many 
 atomic weights of hydrogen are displaced by one atomic weight 
 of an element is the valence of that element (see section 215). 
 
 Thus, since one atomic weight of aluminium can take the 
 place of three atomic weights of hydrogen when this metal 
 reacts with an acid, 
 
 Al +3HC1->A1C1 8 + 3H, 
 
 the valence of aluminium is three. Similarly the valence 
 of magnesium is two, and that of sodium is one. 
 
 356. It has already been seen that hydrogen is more like 
 the metals than the non-metals in its chemical properties. 
 It forms positive ions like the metals, never negative ions 
 as do the non-metals. Its shows little ability to form com- 
 pounds with the metals, to which it is similar in nature; 
 but it does form compounds with the non-metals, to which 
 it is dissimilar. 
 
 Hydrogen can take the place of, or be displaced by, metals, 
 and the valence of a metal is measured by the amount of 
 hydrogen to which it is equivalent. But the valence of a 
 non-metallic element cannot be measured by the number of 
 atomic weights of hydrogen that one atomic weight can 
 
VALENCE 337 
 
 displace, because hydrogen and the non-metals, being oppo- 
 site in their chemical nature, are not mutually interchange- 
 able. But non-metals can combine with hydrogen, and their 
 valence is measured by the number of atomic weights of hy- 
 drogen which one atomic weight of the element will hold 
 in chemical combination. 
 
 The weight of chlorine which combines with 1 gram of 
 hydrogen to form hydrogen chloride is 35.5 grams, and since 
 this quantity is the gram-atomic weight of chlorine, it 
 follows that chlorine combines with hydrogen, atomic 
 weight for atomic weight, therefore the valence of chlorine 
 is one. 
 
 The weight of oxygen which combines with 1 gram of 
 hydrogen to form water is 8 grams. Since this is one half 
 the gram-atomic weight of oxygen, it follows that one whole 
 atomic weight of oxygen can combine with two atomic 
 weights of hydrogen; therefore the valence of oxygen is 
 two. 
 
 The weight of sulphur which combines with 1 gram of 
 hydrogen is 16 grams. The atomic weight of sulphur is 32 ; 
 hence 16 grams is one half of a gram-atomic weight. One 
 whole atomic weight of sulphur combines with two atomic 
 weights of hydrogen and the valence of sulphur is two. 
 
 357. When it is desired to know the valence of any ele- 
 ment, it is only necessary to find the composition of its simple 
 compounds. The knowledge of the composition of all the 
 compounds that have been thoroughly studied is already 
 at hand, and this knowledge is expressed in the chemical 
 formulas of the compounds. Hence to find the valence 
 of an element, we refer to the formulas of its simple com- 
 pounds. 
 
 The formula of hydrogen chloride, HC1, tells us that chlo- 
 
338 HYDROGEN EQUIVALENTS AND VALENCE 
 
 rine combines atomic weight for atomic weight, or atom for 
 atom, with hydrogen and that the valence of chlorine is one. 
 The formulas of water and hydrogen sulphide are H 2 O and 
 H 2 S, respectively, and the valence of oxygen, as well as of 
 sulphur, is therefore two. 
 
 358. In compounds containing no hydrogen, comparison 
 must be made with the known valence of one of the elements 
 of the compound. In the compound potassium chloride, 
 whose formula is KC1, the valence of chlorine is known to be 
 one, because chlorine has already been compared directly 
 with hydrogen as stated above. Then since potassium com- 
 bines with chlorine in the proportion of atom for atom, the 
 valence of potassium must also be one. That this method 
 of comparison is justified, may be shown from the hydro- 
 gen equivalent of potassium. It requires 39 grams of 
 potassium, or one gram-atomic weight, to displace 1 gram 
 of hydrogen. 
 
 The valence of magnesium is seen to be two by an inspec- 
 tion of the formula of magnesium chloride, MgCl 2 ; and the 
 valence of aluminium to be three from the formula Aids. 
 
 359. Valence in Compounds Containing More than Two 
 Elements. When three or more elements are present in a 
 compound, the problem of finding the valence of each ele- 
 ment becomes more complicated. More must be known 
 about the mutual relations of the elements in the compound 
 than is shown in the formula. Indeed, very different opin- 
 ions are held to-day by the foremost chemists as to the real 
 valence of some of the elements in complex compounds ; and, 
 such being the case, we shall not attempt here to go into the 
 question. We shall satisfy ourselves with applying our ideas 
 of valence to the compounds containing two elements only, 
 and within these limits we shall find the conception of valence 
 

 VARIABLE VALENCE 339 
 
 to be of the greatest service in understanding chemical com- 
 binations. 
 
 360. Variable Valence. Many of the elements show 
 different valences according to different conditions under 
 which they combine with other elements. For example, 
 sulphur may combine with either two or three atomic weights 
 of oxygen per atomic weight of sulphur (see page 350). The 
 valence of sulphur in sulphur dioxide, SO 2 , is four because the 
 sulphur combines with two oxygens each of which has a va- 
 lence of two against hydrogen. In sulphur trioxide, SOs, the 
 valence of sulphur is six. 
 
 Many other cases of change of valence are known and 
 in the table on page 340 is found a list of the commoner ele- 
 ments with their valences ; in many instances it is seen that 
 two or more valences are given opposite a single element. 
 
 361. The valence which an element shows toward hydro- 
 gen is very often different from the valence of the same ele- 
 ment towards oxygen. Thus sulphur, which we have just 
 seen has the valence of four or six towards oxygen, shows the 
 valence of two against hydrogen in hydrogen sulphide, H 2 S. 
 A considerable degree of regularity in the valence of elements 
 of different families as well as in the differences in the valences 
 displayed towards hydrogen and oxygen, is shown in the 
 periodic arrangement of the elements on the page facing the 
 inside back cover. 
 
 362. As already hinted, the conception of valence and a 
 knowledge of valence numbers is an invaluable aid in de- 
 veloping our knowledge of chemistry. For example, if we 
 know the combining habits and the valence numbers of all 
 the elements, we can predict with certainty how any two 
 elements will combine in a compound of which we have no 
 other knowledge. 
 
340 
 
 HYDROGEN EQUIVALENTS AND VALENCE 
 
 
 TABLE OF THE COMMONER ELEMENTS, THEIR SYMBOLS, VALENCES, 
 AND APPROXIMATE ATOMIC WEIGHTS 
 
 NAME 
 
 SYMBOL 
 
 ATOMIC 
 
 WEIGHT 
 
 VALENCE 
 
 Towards 
 Hydrogen or 
 Metals 
 
 Towards Oxygen 
 or Chlorine 
 
 Aluminium 
 
 Al 
 
 27 
 
 
 
 III 
 
 Antimony 
 
 Sb 
 
 120 
 
 III 
 
 III, V 
 
 Argon 
 
 A 
 
 40 
 
 
 
 
 
 Arsenic 
 
 As 
 
 75 
 
 III 
 
 III, V 
 
 Barium 
 
 Ba 
 
 137 
 
 
 
 II 
 
 Bismuth 
 
 Bi 
 
 208 
 
 
 
 III 
 
 Boron 
 
 B 
 
 11 
 
 
 
 III 
 
 Bromine 
 
 Br 
 
 80 
 
 I 
 
 I, III, V, VII 
 
 Cadmium 
 
 Cd 
 
 112 
 
 
 
 II 
 
 Calcium 
 
 Ca 
 
 40 
 
 
 
 11 
 
 Carbon 
 
 C 
 
 12 
 
 IV 
 
 IV 
 
 Chlorine 
 
 Cl 
 
 35.5 
 
 I 
 
 I, III, V, VII 
 
 Copper 
 
 Cu 
 
 63.6 
 
 - 
 
 I, II 
 
 Fluorine 
 
 F 
 
 19 
 
 1 
 
 
 
 Gold 
 
 Au 
 
 197 
 
 
 
 I, III 
 
 Helium 
 
 He 
 
 4 
 
 
 
 
 
 Hydrogen 
 
 H 
 
 1 
 
 
 
 I 
 
 Iodine 
 
 I 
 
 127 
 
 I 
 
 I, III, V, VII 
 
 Iron 
 
 Fe 
 
 56 
 
 
 
 II, III 
 
 Lead 
 
 Pb 
 
 207 
 
 
 
 II, IV 
 
 Lithium 
 
 Li 
 
 7 
 
 
 
 1 
 
 Magnesium 
 Manganese 
 
 Mg 
 Mn 
 
 24.3 
 55 
 
 
 
 11 
 
 11, III, IV, VI, VII 
 
 Mercury 
 
 Hg 
 
 200 
 
 
 
 1,11 
 
 Nickel 
 
 Ni 
 
 58.7 
 
 
 
 II, III 
 
 Nitrogen 
 
 N 
 
 14 
 
 III 
 
 III, V 
 
 Oxygen 
 
 
 
 16 
 
 II 
 
 
 
 Phosphorus 
 
 P 
 
 31 
 
 III 
 
 Ill, V 
 
 Platinum 
 
 Pt 
 
 195 
 
 
 
 II, IV 
 
 Potassium 
 
 K 
 
 39 
 
 
 
 I 
 
 Silicon 
 
 Si 
 
 28.3 
 
 IV 
 
 IV 
 
 Silver 
 
 Ag 
 
 108 
 
 
 
 I 
 
 Sodium 
 
 Na 
 
 23 
 
 
 
 I 
 
 Strontium 
 
 Sr 
 
 88 
 
 
 
 II 
 
 Sulphur 
 
 S 
 
 32 
 
 II 
 
 IV, VI 
 
 Tin 
 
 Sn 
 
 119 
 
 
 
 II, IV 
 
 Zinc 
 
 Zn 
 
 65.4 
 
 
 
 11 
 
QUESTIONS 341 
 
 SUMMARY 
 
 The hydrogen equivalent is that weight of a metal that is inter- 
 changeable with 1 gram of hydrogen. This amount of the 
 metal is equivalent both electrically and chemically to one 
 gram-atomic weight of hydrogen. 
 
 The valence of a metal is the number of gram-atomic weights of 
 hydrogen which are equivalent to one gram-atomic weight of 
 the metal. 
 
 The valence of a non-metal is the number of gram-atomic weights 
 of hydrogen which one gram-atomic weight of the non-metal 
 holds in combination. 
 
 In compounds that contain no hydrogen, the valence of the elements 
 is derived from comparison with compounds that do contain 
 hydrogen. 
 
 The valence of an element in a simple compound is usually apparent 
 from an inspection of the formula of the compound. The 
 conception of valence is often difficult to apply to compounds 
 that contain more than two elements. 
 
 Variable Valences : The same element frequently displays different 
 valences under different conditions. The valence of an ele- 
 ment towards hydrogen is often different from th$ valence 
 towards oxygen. 
 
 The conception of valence is of great value in developing our knowl- 
 edge of chemistry. 
 
 Questions 
 
 1. Define " hydrogen equivalent." 
 
 2. Explain how the weight of the hydrogen displaced by a known 
 weight of a metal may be found without actually weighing the gas. 
 
 3. Calculate the hydrogen equivalent of cadmium from the follow- 
 ing data : 0.1 12 g. of cadmium released 24.4 c.c. of hydrogen at 20 
 C. and 740 mm. (1 liter H 2 at standard conditions = .09 g.) 
 
 4. The atomic weight of cadmium is 112. Using the hydrogen 
 equivalent calculated in Question 3, find the valence of cadmium. 
 
 5. Calculate what weight of zinc (atomic weight, 65 hydrogen 
 equivalent, 32.5) would be convenient to use in a hydrogen equiv- 
 alent determination the gas measuring tube having a volume 
 of 100 c.c. 
 
CHAPTER XXIX 
 
 SULPHUR 
 
 363. Familiar Forms and Uses of Sulphur. Sulphur is 
 familiar to us in the uncombined state as a brittle, yellow, 
 non-metallic substance. We can buy it at a drug store in 
 the form of a yellow powder or of coarse lumps or sticks. 
 Powdered sulphur is used as an ingredient of various salves 
 on account of its germicidal properties and it is often given 
 internally for the purpose of " purifying the blood." A 
 familiar old-fashioned remedy for the blood, that very 
 likely has a good deal of virtue, is a mixture of sulphur and 
 molasses. Sulphur is boiled with lime and water to make 
 " lime sulphur " spray for killing insect pests that destroy 
 our fruit trees. Sticks of sulphur, or prepared sulphur 
 candles, are burned in rooms after sickness in order to de- 
 stroy lingering disease germs. Sulphur is likewise burned 
 in clothes closets in order to kill moths. The suffocating 
 fumes of burning sulphur, which are composed of sulphur 
 dioxide, are familiar, and in view of their offensiveness, it is 
 not surprising that they are powerful in destroying pests. 
 Sulphur is used in large quantities to " vulcanize " rubber. 
 
 Sulphur under ordinary conditions is a crystalline solid. 
 The masses which we more usually see are opaque because 
 they are composed of a great number of very small crystals 
 overlapping and interlacing. It is well known that if the 
 clearest specimen of transparent glass is pulverized, the 
 powdered mass thus obtained presents the opaque appear- 
 
 342 
 
SULPHUR 
 
 343 
 
 ance of snow. Thus with the mass of small sulphur crystals, 
 each one of which by itself is transparent. 
 
 When sulphur crystallizes under the right conditions, 
 that is, when the crystallization takes place very slowly, as 
 for example in fissures 
 in the earth, clear 
 transparent crystals 
 of considerable size 
 are formed. These 
 crystals are very 
 beautiful ; they are 
 bounded by smooth 
 lustrous surfaces 
 which lie in certain 
 
 definite planes with 
 reference to imaginary 
 
 FIG. 68. Rhombic Sulphur Crystals, clinging to 
 
 axes of the cr\ T Stals. a fragment of rock broken from the interior of a 
 cavity in the earth. 
 
 Some idea of their 
 
 shape and appearance may be obtained from Fig. 68. It is 
 easy to obtain very small crystals of this kind in the labora- 
 tory, and they are just as perfect in shape as the large ones. 
 It is only necessary to dissolve some sulphur in carbon 
 disulphide, a liquid in which it is very soluble, and to leave 
 the solution in a watch glass for a little time while the 
 carbon disulphide evaporates. A number of the small crys- 
 tals are left in the watch glass when the liquid has gone. 
 These crystals belong to a certain system of crystals known 
 as the rhombic system, and they are therefore spoken of as 
 rhombic sulphur crystals. 
 
 364. Allotropic Forms of Sulphur. It is well known that 
 uncombined carbon can exist in different forms, as char- 
 coal, graphite, and diamond (Chapter XXIII). Charcoal is 
 
344 
 
 SULPHUR 
 
 amorphous, that is, without definite shape, whereas the other 
 two forms are crystalline as they occur in nature. Sulphur 
 likewise is known in three different forms, although these 
 forms do not differ so extremely from one another as do 
 graphite and diamond. The rhombic crystals which have 
 just been described are the most frequent of the three forms. 
 
 Another crystal- 
 line variety of 
 sulphur can be ob- 
 tained if a mass of 
 melted sulphur is 
 allowed to cool 
 and solidify slowly. 
 These crystals ap- 
 pear in the shape of 
 long needles, which 
 belong to the so- 
 called monoclinic system, and are known as monoclinic 
 sulphur. They can be obtained in the laboratory if sulphur 
 is melted in a clay crucible and is then left undisturbed to 
 cool. When a thin solid crust has just formed over the 
 surface, if a hole is broken and the still liquid sulphur un- 
 derneath is poured out, a loose mass of needle-like crys- 
 tals is found to fill the interior of the crucible. An idea of 
 their appearance can be obtained from Fig. 69. 
 
 Another form of sulphur, the so-called amorphous form, 
 is obtained when melted sulphur, which has been heated to 
 about 250 C., is suddenly chilled as when it is poured into 
 water. At first this cooled sulphur is of a consistency much 
 like soft rubber, but on standing it gradually stiffens and 
 becomes brittle like ordinary sulphur. 
 The common form of sulphur melts at 114.5 C. to a pale 
 
 FIG. 69. Monoclinic Sulphur Crystals. 
 
 
OCCURRENCE OF SULPHUR 
 
 345 
 
 yellow, mobile liquid. Liquid sulphur has one very sur- 
 prising property, namely, when heated to a higher tempera- 
 ture, instead of growing even more mobile, as do liquid 
 substances generally, it becomes viscous. At the same time 
 it turns dark in color. At about 250 C. it is so viscous that 
 the vessel containing it may be inverted without its running 
 out. Above 250 C. it again grows less viscous and at 448 C. 
 it boils and is converted into a pale yellowish-brown vapor. 
 365. Occurrence of Sulphur. Sulphur occurs in nature as 
 uncombined sulphur; as sulphides of the heavy metals, es- 
 pecially of iron, copper, lead, and zinc; and as sulphates, 
 calcium sulphate (gypsum is CaSO 4 2 H 2 O), barium sul- 
 phate, and lead sulphate. 
 
 FIG. 70. A Block of Louisiana Sulphur. The molten sulphur is pumped 
 from the wells into huge wooden bins. The solid block in the picture is 48 
 feet high. The boards have been removed from the front face of the bin 
 but have been left at the end. The sulphur is broken from the front of the 
 block with blasting powder and is loaded on to freight cars for shipment. 
 
346 SULPHUR 
 
 Uncombined sulphur is found in many parts of the earth, 
 notably in Sicily, in volcanic regions where it is deposited 
 from the volcanic gases in fissures in the rocks. It is also 
 found in some places where its formation does not seem to 
 be due to volcanic action, notably in Louisiana. 
 
 In Sicily sulphur is extracted from the rocks by melting, 
 the heat usually being obtained by the crude method of 
 burning a part of the sulphur itself. In Louisiana, where 
 the deposits are deep beneath the surface, a novel method has 
 been invented for extracting the sulphur. Pipes are driven 
 to the sulphur-bearing stratum and superheated water is 
 forced down. The sulphur is thus melted ; it sinks to the 
 bottom of the well and is pumped to the surface by means 
 of compressed air and run into huge wooden bins, where it 
 is allowed to solidify. 
 
 SULPHIDES AND HYDROGEN SULPHIDE 
 
 366. Sulphides. In its chemical properties, sulphur is 
 in many respects like the typical non-metals, oxygen and 
 chlorine, that we have already studied. It combines with 
 metallic elements including hydrogen forming sulphides 
 just as oxygen and chlorine form oxides or chlorides. For 
 example, when iron or copper or zinc filings are mixed with 
 powdered sulphur and heated in a test tube over a Bunsen 
 burner, a reaction soon begins, and if the tube is then re- 
 moved from the flame the reaction continues under the in- 
 fluence of the heat which it, itself, develops, and the incan- 
 descence spreads through every part of the mixture. The 
 substance that remains is neither sulphur, nor the metal, 
 but is the sulphide of the metal. 
 
 Sulphur also combines directly with hydrogen but not 
 
HYDROGEN SULPHIDE 347 
 
 as energetically as with the metals. If sulphur is placed 
 in a hard glass tube and a current of hydrogen is passed over 
 the sulphur while the tube is heated with a Bunsen flame, 
 a little hydrogen sulphide is formed, but the reaction is not 
 energetic and continues to take place only so long as external 
 heat is being supplied. 
 
 367. Hydrogen sulphide, H 2 S, is a gas which has a very 
 offensive odor, the odor of rotten eggs. It is frequently 
 formed in the decomposition of organic matter containing 
 sulphur, and thus its odor is apparent not only in eggs, but 
 in sewage. When the mud of mud flats near where sewage 
 is discharged is disturbed with a stick, the bubbles of gas 
 which rise have a strong odor of hydrogen sulphide. 
 
 This gas is extremely poisonous to inhale. Breathing the 
 undiluted gas will render a man unconscious almost in- 
 stantly, and it will prove fatal unless he is immediately 
 removed to the open air and restoratives are employed. 
 Breathing very dilute hydrogen sulphide, as it is often pres- 
 ent in the air of the laboratory, is offensive and may make 
 one feel rather sick, but it is not especially dangerous. 
 
 The so-called sulphur water of sulphur springs is really 
 water charged with hydrogen sulphide issuing from the in- 
 terior of the earth. A small amount of hydrogen sulphide 
 taken into the stomach in this way is not injurious and is 
 in some cases perhaps even beneficial. 
 
 368. Laboratory Method of Preparing Hydrogen Sulphide. 
 In the laboratory, hydrogen sulphide is made by allowing 
 an acid to react with iron sulphide. 
 
 FeS + 2 HC1 -^ FeCl 2 + H 2 S. 
 
 The desired product, being a gas, escapes as fast as it is 
 formed and can be led as desired through delivery tubes. 
 
348 SULPHUR 
 
 369. Hydrogen Sulphide as a Precipitant. One of the 
 most important uses of hydrogen sulphide is as a precipitant. 
 If the gas is bubbled into the solution of a salt of copper, 
 silver, mercury, lead, tin, or of any one of several other 
 of the heavy metals, the sulphide of the metal is precipitated. 
 Hydrogen sulphide is only slightly dissociated into ions, 
 H2S ^> H + + H + + S~ ~~, but since the sulphides of the 
 heavy metals are extremely insoluble, even the few sulphide 
 ions from the hydrogen sulphide cannot remain in presence 
 of the metal ions. Therefore metal sulphide precipitates, 
 but as the sulphide ions are thus taken out of the solution, 
 more hydrogen sulphide is able to dissociate and this con- 
 tinues until there are no more metal ions left to remove 
 further sulphide ions. 
 
 By the formation or non-formation of a precipitate when 
 hydrogen sulphide is passed into a solution, it is possible to 
 tell whether salts of the heavy metals are present, and further- 
 more the color of the precipitate gives an indication as to what 
 metal is present. Thus the sulphides of silver, lead, mercury, 
 bismuth, and tin in the divalent condition precipitate from 
 an acidified solution either black or very dark brown; the 
 sulphides of cadmium, arsenic, and tin in the tetravalent 
 condition, yellow; the sulphide of antimony, orange red. 
 The sulphide of zinc precipitates white from a very weakly 
 acid or an alkaline solution, but not from a strongly acid one ; 
 and from an ammoniacal but not from an acid solution, the 
 sulphides of iron, nickel, and cobalt precipitate black and the 
 sulphide of manganese, flesh-colored. 
 
 370. Hydrosulphuric Acid. A solution of hydrogen sul- 
 phide is faintly acid, sufficiently so to barely turn blue 
 litmus to red. This indicates a small content of hydrogen 
 ions and corresponds to the low degree of dissociation re- 
 
OXIDES OF SULPHUR 349 
 
 f erred to in the foregoing paragraph. If it is wished to lay 
 emphasis on the fact that hydrogen sulphide is an acid, 
 it is spoken of as hydrosulphuric acid (see page 221). 
 It is almost never used for its acid properties, however, and 
 hence we rarely see it mentioned by this name. 
 
 On the other hand, hydrogen chloride is a strong acid 
 when it is dissolved in water, that is, its solution contains 
 a large proportion of hydrogen ions. Its acid properties 
 are the foremost in importance and we find it most commonly 
 called hydrochloric acid. 
 
 OXIDES OF SULPHUR 
 
 371. Sulphur Dioxide and Sulphurous Acid. It is well 
 known that sulphur burns readily in the air and forms a very 
 choking gas. This gas is sulphur dioxide, SO2. To pre- 
 pare sulphur dioxide free from nitrogen and excess of air, the 
 usual laboratory method is to heat together concentrated sul- 
 phuric acid and copper turnings. Sulphuric acid contains 
 the oxide SO 3 in combination with water. The trioxide is 
 reduced by copper to sulphur dioxide, which escapes as the 
 gas desired. The copper is at the same time oxidized to 
 copper oxide, and the copper oxide being a basic oxide re- 
 acts with surplus sulphuric acid to form the salt copper 
 sulphate : 
 
 H 2 S0 4 -> H 2 + SO 3 
 S0 3 + Cu -+ CuO + SO 2 1 
 CuO + H 2 SO 4 - H 2 O + CuSO 4 
 Cu + 2 H 2 SO 4 -* 2 H 2 O -f CuSO 4 + SO 2 f 
 
 Sulphur dioxide is somewhat soluble in water and the 
 solution is acid. It is supposed that a definite compound, 
 sulphurous acid, is formed : H 2 O + SO 2 -> H 2 SO3, but this 
 
350 SULPHUR 
 
 compound is so unstable that it is impossible to separate it 
 out in the pure state from the water in which it is dissolved. 
 The main reason for believing in the existence of this definite 
 acid is that salts of the acid can be prepared. For example, 
 the acid solution can be neutralized by adding sodium hy- 
 droxide ; then, on evaporation of the neutral solution, a solid 
 substance is left which on analysis is shown to have a com- 
 position corresponding to the formula Na 2 SO 3 . This salt 
 is sodium sulphite, and its relation to sulphurous acid is 
 apparent from the mode of its formation : 
 
 H 2 SO 3 + 2 NaOH -> 2 H 2 O + Na 2 SO 3 . 
 
 372. Sulphur Trioxide and Sulphuric Acid. Although 
 sulphur dioxide is the invariable product obtained when sul- 
 phur burns, it is not the only oxide of sulphur. Sulphur tri- 
 oxide, SO 3 , is of still greater importance because of the fact 
 that with water it gives sulphuric acid : 
 
 SO 3 + H 2 O -> H 2 SO 4 . 
 
 Sulphur trioxide is obtained by allowing sulphur dioxide to 
 combine with more oxygen : 
 
 2 SO 2 + O 2 -> 2 SO 3 . 
 
 There is a good deal of chemical affinity between the sulphur 
 dioxide and the oxygen and there is no difficulty in keeping 
 them combined (as sulphur trioxide) if once they can be in- 
 duced to unite. But the reaction by which they combine 
 is sluggish, and very little sulphur trioxide can be obtained 
 by merely bringing the two gases together, even if they are 
 heated. 
 
 373. Manufacture of Sulphuric Acid. Since sulphuric 
 acid is one of the most extensively used of chemicals, its 
 
SULPHURIC ACID BY CONTACT PROCESS 351 
 
 manufacture is of the greatest importance. There are two 
 widely used processes for this. In both processes, the first 
 step is the same, namely, burning sulphur to sulphur dioxide. 
 Instead of free sulphur, iron pyrite, a sulphide of iron that is 
 high in sulphur content, is often burned. 
 
 4 FeS 2 + 11 O 2 - 8 SO 2 + 2 Fe 2 O 3 . 
 
 At zinc smelters, zinc sulphide ore must be roasted to convert 
 it to zinc oxide : 
 
 2 ZnS + 3 O 2 -> 2 SO 2 + 2 ZnO. 
 
 Sulphuric acid plants are usually set up in such places so as 
 to utilize the sulphur dioxide. 
 
 It is in the next step in the manufacture, namely, the con- 
 version of sulphur dioxide to sulphur trioxide that the chief 
 difficulty lies. The difficulty is overcome by the use of a 
 catalyzer, which, as we have already seen, is a substance which 
 does not undergo any permanent alteration itself, but by its 
 mere presence causes an ordinarily sluggish reaction to be- 
 come rapid. The difference between the two processes lies 
 mainly in the different catalytic agents used. 
 
 374. Contact Process. In the so-called contact process, 
 the catalytic substance is platinum. The action takes place 
 at the surface of the metal ; therefore, to present as large a 
 surface as possible with a small quantity of this very ex- 
 pensive metal, the latter is spread out over asbestos fibers. 
 The asbestos is dipped into a water solution of platinum 
 chloride, it is dried and then ignited (heated strongly). The 
 platinum chloride is decomposed and the metal is left in an 
 extremely fine state of subdivision on the surface of the 
 fibers. Tubes are now packed with this platinized asbestos, 
 
 B. AND W. CHEM. 23 
 
352 SULPHUR 
 
 and when these tubes are kept at a temperature of 400 C. 
 and a mixture of sulphur dioxide and air is passed through 
 them, the formation of sulphur trioxide takes place with great 
 readiness. 
 
 To obtain sulphuric acid, it is only necessary to mix the 
 sulphur trioxide with water (see equation on page 350). 
 Although this would seem to be a very simple operation, it 
 does, as a matter of fact, offer a good deal of difficulty, for 
 the reaction produces great heat ; and since sulphur trioxide 
 is very volatile, a fearful smoke is produced if the mixing is 
 not carried out with the greatest caution. In practice, the 
 sulphur trioxide is not added directly to water but rather to 
 a fairly concentrated sulphuric acid, as for example the acid 
 that is obtained from the chamber process. 
 
 375. Chamber Process. In this process, oxides of nitro- 
 gen are used as the catalytic agent. There are a number of 
 different oxides of nitrogen, among them being NO and NO 2 . 
 Sulphur dioxide takes oxygen readily from the higher oxide, 
 NO 2 , but the lower oxide NO thus formed takes oxygen at 
 once from the air to form NO 2 again. The NO 2 again gives 
 oxygen to sulphur dioxide and is immediately regenerated 
 by taking on more oxygen from the air, and thus a very small 
 amount of oxide of nitrogen by repeating the action a great 
 many times can " carry " oxygen to a large amount of sul- 
 phur dioxide, whereas sulphur dioxide by itself is incapable 
 of combining to any extent with the oxygen. 
 
 In practice, the sulphur dioxide from the sulphur or pyrite 
 burners, together with an excess of air, is conveyed through 
 a tower (see diagram, Fig. 71) which serves partly to cool 
 the gases and partly to charge them with oxides of nitrogen. 
 They are then allowed to pass through large lead chambers 
 (sometimes as large as 100 X 40 X 20 feet) where they be- 
 
SULPHURIC ACID BY CHAMBER PROCESS 
 
 353 
 
 come thoroughly mixed and where the oxide of nitrogen gets 
 a full opportunity to carry oxygen to the sulphur dioxide. 
 To aid in this process as well as to furnish the water necessary 
 to convert the sulphur trioxide into sulphuric acid, steam or 
 water in a fine spray is blown into the lead chambers. The 
 liquid sulphuric acid collects on the bottom of the chamber 
 and from there is siphoned off. 
 
 From the last of the series of chambers, there is little left 
 to pass out as gas except the nitrogen of the air used for the 
 oxidations, and the oxides of nitrogen. These oxides of 
 
 * Shows Course of Su/fur D/oxidanc/ Air 
 - Oxides ofWtrogrn 
 
 Tower Ac/d 
 
 FIG. 71. Chamber Process for the Manufacture of Sulphuric Acid. 
 (From Thorp's Outlines of Industrial Chemistry.) 
 
 nitrogen are poisonous and very offensive, and it would not 
 be permitted to throw them out into the atmosphere even if 
 the manufacturers were willing to waste them. The es- 
 caping gas, therefore, is allowed to pass up through a tower 
 filled with tiles over which concentrated sulphuric acid is 
 trickling down. This concentrated acid absorbs the oxides 
 of nitrogen while the uncombined nitrogen passes out from 
 the top. The concentrated acid containing the oxides of 
 nitrogen is pumped to the top of the first-mentioned tower, 
 where by dilution with water it is made to give up its oxides 
 
354 SULPHUR 
 
 of nitrogen, which are thus reintroduced into the process to 
 serve again as oxygen carriers. 
 
 Under perfectly ideal conditions, a limited amount of 
 nitrogen oxide should serve forever in this process. Prac- 
 tically, a little is continually being lost ; this is made up by 
 introducing into the gases from the sulphur burners a little 
 vaporized nitric acid which decomposes and is reduced as 
 
 folloWS : _ TTxrrA 
 
 2 HNO 3 -> H 2 O + N 2 O 5 
 N 2 O 5 + 3 SO 2 -> 2 NO + 3 SO 3 
 
 and then the nitrogen oxide continues to act as oxygen 
 carrier. The nitric acid used is generated by allowing 
 sulphuric acid to react with sodium nitrate (Chili saltpeter) 
 placed in a small pot in the flue between the burners and the 
 first tower. 
 
 2 NaNO 3 + H 2 S0 4 -> Na 2 SO 4 + 2 HNO 3 . 
 
 376. Properties of Sulphur Trioxide and Sulphuric Acid. 
 
 Sulphur trioxide is unlike sulphur dioxide in that it is not 
 a gas. It exists in two modifications, one of which is liquid 
 at ordinary temperature, the other of which is a fibrous 
 white crystalline solid. Both of these forms are very vola- 
 tile and if left open to the atmosphere evolve dense white 
 fog due to combining with the water vapor in the air to 
 form sulphuric acid which, condensing to minute droplets 
 of liquid, gives the fog. Sulphur trioxide has a great af- 
 finity for water, and if a fragment is thrown upon water 
 it gives a violent hissing sound like the quenching of red- 
 hot iron, owing to the heat released by the reaction. 
 
 377. Pure sulphuric acid, H 2 SO 4 , is a heavy, oily liquid 
 of specific gravity 1.84. Unlike the sulphur trioxide, from 
 which it is obtained, it is not at all volatile at ordinary tern- 
 
SUMMARY 355 
 
 perature. It mixes with water in all proportions and much 
 heat is developed by the admixture. Indeed, sulphuric 
 acid has a good deal of affinity for water. For example, if 
 air or any other gas is slowly bubbled through concentrated 
 sulphuric acid, it is practically freed from water vapor. This 
 is a convenient method for drying gases. Again, if wood or 
 sugar are placed in contact with concentrated sulphuric 
 acid, they are rapidly charred ; the hydrogen and oxygen 
 of the wood or sugar have been removed in the form of water, 
 while the carbon is left and gives the charred appearance. 
 
 When it is diluted with a considerable amount of water, 
 sulphuric acid is a very strong acid, that is to say, it is 
 largely dissociated into ions : 
 
 In virtue of its hydrogen ions, it shows to a marked degree 
 all the typical properties of acids. For example, all metals 
 standing above hydrogen in the electromotive series react 
 with sulphuric acid solution ; hydrogen is set free and a sul- 
 phate of the metal is left. The sulphates of most of the 
 metals are soluble, so the observed effect of treating a metal 
 with sulphuric acid is that the metal dissolves and hydrogen 
 gas escapes in bubbles. 
 
 Sulphuric acid neutralizes bases and basic oxides; sul- 
 phates are thereby formed, but there is no effervescence, be- 
 cause the hydroxyl of the base, or the oxygen of the basic 
 oxide, is present to combine with the hydrogen of the acid 
 and retain it in the form of water. 
 
 SUMMARY 
 
 Sulphur is a typical non-metal. It combines directly with metals 
 
 and with hydrogen to form sulphides. 
 Sulphur combines with oxygen to form oxides. These oxides are 
 
356 
 
 SULPHUR 
 
 acid-forming, which fact is in accord with the non-metallic 
 
 character of the element sulphur. 
 Sulphur dioxide when dissolved in water gives sulphurous acid, H 2 S0 3 , 
 
 a weak and very unstable acid. Neutralization of this acid 
 
 gives a sulphite of the metallic element of the base. 
 Sulphur trioxide when dissolved in water gives sulphuric acid, 
 
 H 2 S0 4 , a strong and stable acid. Neutralization of this acid 
 
 gives a sulphate. 
 
 Much information concerning the relationships among the most 
 important of the compounds of sulphur is shown in the following 
 table : 
 
 SIMPLE 
 COMPOUND 
 
 VALENCE 
 
 OP SULPHUB 
 
 ACID 
 
 STRENGTH 
 OP ACID 
 
 FORMULA OF 
 SODIUM SALT 
 
 H 2 S 
 
 S 
 S0 2 
 S0 3 
 
 -2 
 
 
 + 4 
 + 6 
 
 H 2 S 
 
 Very weak 
 
 Na 2 S 
 
 H 2 S0 3 
 
 H2S04 
 
 Weak 
 Strong 
 
 Na 2 SO 3 
 Na 2 S0 4 
 
 Questions 
 
 1. In which of the two great subdivisions of the elements does 
 sulphur belong? 
 
 2. The oxides of sulphur yield what type of substance on union 
 with water ? 
 
 3. Of what practical use is sulphur? 
 
 4. What is meant by the popular expression sulphur water, re- 
 ferring to spring water of a certain type ? 
 
 5. Which of the three elements oxygen, chlorine, and sulphur 
 would you regard as the weakest non-metallic element, and why ? 
 
 6. Explain briefly how the difficulty in getting S0 2 to unite 
 with oxygen is overcome in (a) the contact process, (6) the chamber 
 process of making sulphuric acid. 
 
 7. How could you tell by mere inspection whether the acid in 
 a bottle was concentrated HC1 or concentrated H 2 S0 4 ? 
 
 8. In order to appreciate the vast extent of the use of sulphuric 
 acid, try to find in the reference books the value of the acid manu- 
 
QUESTIONS 357 
 
 factured in the United States in one year. See, also, if you can 
 think of any manufactured article which has not had sulphuric 
 acid used either directly in its manufacture or indirectly in the mak- 
 ing of the things used in making the article in question. 
 
 9. Compare sulphur with oxygen as to its existing in two or more 
 forms. 
 
 10. If a bottle contained sulphuric acid, what effect would it have 
 upon a splinter of wood clipped into it ? 
 
 11. What weight of sulphuric acid could be obtained from 1000 
 kilograms of iron pyrite, FeS 2 , if all of the sulphur of the pyrite were 
 utilized ? 
 
 12. What volume would the sulphur dioxide (figured under stand- 
 ard conditions) obtained as the direct product of burning the 1000 
 kilograms of pyrite occupy? 
 
 13. What property of sulphuric acid makes is useful for drying 
 gases ? 
 
 14. Why would you not advise trying to dry ammonia gas by 
 bubbling it through sulphuric acid ? 
 
CHAPTER XXX 
 COMPOUNDS OF NITROGEN 
 
 WE have already learned in connection with our study of 
 the atmosphere (Chapter VII) that nitrogen, although it com- 
 prises four fifths of the air, is ordinarily an inert element. 
 Only under special conditions does atmospheric nitrogen 
 enter into combination with other elements. When, how- 
 ever, it is once in combination, it enters into further chemical 
 change with great readiness and it is largely on this account 
 that combined nitrogen is of such importance in the chemistry 
 of animal and plant life as well as of explosives. 
 
 COMPOUNDS WITH METALS AND WITH HYDROGEN 
 
 378. Nitrides. With the very active metals, especially 
 calcium and magnesium, free nitrogen unites with consider- 
 able ease to form the nitrides CasN 2 and Mg 3 N 2 . This ac- 
 tivity, however, plays no part in the economy of nature, first, 
 because calcium and magnesium are too active to be found 
 uncombined, and second, because the ever present oxygen 
 in the air would have the stronger claim upon their com- 
 bining powers if the metals were ever free to act with the 
 atmosphere. 
 
 379. Ammonia. It has already been seen that, chemically, 
 hydrogen is classed with the metals. The nitride of hydro- 
 gen, or as it is commonly called, ammonia, NH 3 , is one of the 
 very important compounds of nitrogen. 
 
 358 
 
AMMONIA 359 
 
 Ammonia can be made from the nitride of calcium or mag- 
 nesium by treating it with water : 
 
 Ca 3 N 2 + 6 H 2 -> 3 Ca(OH) 2 + 2 NH 3 . 
 
 Ammonia can also be made to a slight extent by the direct 
 combination of hydrogen and nitrogen under the influence of 
 the electric spark or of certain catalyzers. If a mixture 
 of three volumes of hydrogen and one volume of nitrogen is 
 subjected to a spark discharge, about 2 per cent of the mix- 
 ture combines. That the tendency to combine is extremely 
 small is further shown by the fact that if ammonia gas is sub- 
 jected to the same spark discharge, all but about 2 per cent 
 of it becomes decomposed into the free elements. 
 
 The actual source of all the ammonia of commerce is the 
 so-called gas liquor obtained from gas works. Coal is the 
 fossil remains of former vegetation and still contains some of 
 the combined nitrogen that originally existed in the plants. 
 When, in the process of gas manufacture, the coal is sub- 
 jected to destructive distillation, a large part of the nitrogen 
 passes off as ammonia. In the process of purification, the 
 gas is passed through water ; and since ammonia is very solu- 
 ble in water, the gas liquor retains it and becomes the princi- 
 pal source of this compound. The ammonia of the crude gas 
 liquor is expelled by heat and absorbed in sulphuric acid, 
 forming ammonium sulphate. Crude ammonium sulphate 
 is much used as a fertilizer on account of its nitrogen content. 
 It is also used as a starting point in the manufacture of pure 
 ammonia and pure ammonium salts. It is mixed with cal- 
 cium hydroxide, whereby the weaker base is set free : 
 
 (NH 4 ) 2 S0 4 + Ca(OH) 2 -> CaSO 4 + 2 NH 4 OH. 
 
 On heating this mixture, ammonia gas passes off, and after 
 proper purification, it is absorbed in water to form ammonia 
 
360 COMPOUNDS OF NITROGEN 
 
 water, or after drying it is liquefied by compression in steel 
 cylinders for use in refrigerating plants, or it is absorbed in 
 hydrochloric acid to form ammonium chloride (sal am- 
 moniac). 
 
 380. Laboratory Preparation of Ammonia. For prepar- 
 ing ammonia in the laboratory, an ammonium salt, usually 
 ammonium chloride, is mixed with a strong base, calcium 
 or sodium hydroxide, and the mixture is heated. Owing to 
 its great solubility, the gas cannot be collected over water. 
 It can be caught over mercury, or for simple experiments it 
 may be run into dry bottles held mouth downward. 
 
 381. Properties of Ammonia. Ammonia is a colorless 
 gas of an extremely penetrating but not disagreeable odor. 
 It is dangerous if inhaled in quantity, but diluted with much 
 air it is harmless. 
 
 Ammonia is very soluble in water; at 20 C. and atmos- 
 pheric pressure, one volume of water dissolves 710 volumes of 
 ammonia. The great solubility can be strikingly shown by 
 the same fountain experiment (page 131) that was given to 
 show the extreme solubility of hydrogen chloride. The solu- 
 tion of ammonia is mildly alkaline, due to the formation of 
 ammonium hydroxide, which is a comparatively weak base ; 
 
 NH 3 + H 2 O -> NH4OH 
 
 (See Chapter XIX.) It is on account of its alkaline char- 
 acter that ammonia is useful for cleaning purposes. 
 
 Dry ammonia gas is easily liquefied. At 20 C., a pressure 
 of 8.4 atmospheres is sufficient to cause its condensation. 
 At atmospheric pressure, a temperature of 34 C. will cause 
 it to liquefy. 
 
 382. Refrigeration. Liquid ammonia is much used in ice 
 machines (see Fig. 72). By means of the engine and pump, 
 the gas is compressed and liquefied. The heat produced by 
 
REFRIGERATION 
 
 361 
 
 the compression is removed by passing the ammonia through 
 condenser pipes over which cold water is flowing. The 
 liquid ammonia is now allowed to issue through a small ori- 
 fice of the expansion valve, into a coil of larger pipe. Heat 
 
 ^ water for Condenser 
 
 A JL A JL A A A A J. J* J A -A A 
 
 A I ,1 
 
 pi 
 
 Dl 
 
 Expansion Coil 
 
 Expansion Valve- 
 
 Compressor. Drine Tank.- 
 
 FIG. 72. Ammonia Refrigerating Plant. 
 
 is necessary to cause the liquid to vaporize just as it is neces- 
 sary to convert water into steam. This liquid ammonia has 
 already been deprived of much of the heat it originally pos- 
 sessed as a gas. In order to vaporize, then, it has to with- 
 draw what heat it can get from its surroundings and hence the 
 
362 COMPOUNDS OF NITROGEN 
 
 latter are cooled to a very low degree. The expansion pipes 
 are surrounded by a non-freezing brine such as a concentrated 
 solution of calcium chloride (see page 194) . This liquid serves 
 as a bath in which to immerse vessels containing the water 
 that is to be converted to ice. Or the liquid itself may be 
 circulated through pipes in the refrigerating plant. As fast 
 as the ammonia vaporizes in the expansion pipes, it is with- 
 drawn by means of the pump and is forced again through the 
 same cycle of operations. 
 
 383. Ammonium Salts. Like other bases, ammonium 
 hydroxide is capable of neutralizing acids, as, for example, 
 
 NH 4 OH + HC1 -+ NH 4 C1 + H 2 O, 
 
 and thus we have a series of ammonium salts including the 
 chloride, the sulphate, the nitrate, the carbonate, etc. 
 
 Ammonium chloride, NH 4 C1, is commonly known as sal 
 ammoniac, and its solution is much used in bell-ringing 
 electric batteries. 
 
 Ammonium carbonate is used in smelling salts. Lumps 
 of the solid salt are covered with alcohol and a little aromatic 
 oil such as oil of lavender is added. The salt is unstable and 
 is continually decomposing into ammonia and carbon dioxide. 
 Thus the smelling salts possess a powerful odor of ammonia. 
 
 Ammonium nitrate is used in considerable quantities in 
 explosives. It leaves no solid products, as does the potas- 
 sium nitrate used in gunpowder ; it is serviceable as one of 
 the ingredients of some kinds of blasting powder. 
 
 COMPOUNDS WITH OXYGEN 
 
 384. A number of compounds of nitrogen and oxygen are 
 known, nevertheless it is a matter of great difficulty to make 
 the two elements combine directly. Ordinarily, they remain 
 
OXIDES OF NITROGEN 
 
 363 
 
 mixed together in the air without the least trace of interac- 
 tion, but at the high temperature that accompanies the pas- 
 sage of an electric spark they combine to a slight extent. 
 Thus a small amount of nitrogen oxide is formed during 
 thunderstorms in the paths of the lightning flashes. With 
 the rain water it is converted to nitric acid and contributes 
 thus a small share toward fertilizing the soil. 
 
 An artificial method of making nitric acid from the air l>v 
 means of electric sparks has already been referred to in sc<> 
 tion 75. The success of this process depends largely on being 
 able to withdraw the nitric oxide quickly from the influence of 
 the spark discharge before it can again be decomposed into 
 its elements. 
 
 385. There are five distinct oxides of nitrogen; their 
 composition and some of their properties are shown in the 
 following table : 
 
 NAME 
 
 FORMULA 
 
 PROPERTIES 
 
 Nitrous Oxide 
 
 N 2 
 
 Colorless gas 
 
 Nitric Oxide 
 
 NO 
 
 Colorless gas ; unites spon- 
 
 
 
 taneously with oxygen to 
 
 
 
 form the red gas N0 2 . 
 
 Nitrogen Trioxide 
 
 N 2 3 
 
 Very unstable, anhydride of 
 
 
 
 nitrous acid, HNO 2 . 
 
 Nitrogen Tetroxide 
 
 N0 2 (or N 2 4 ) 
 
 Brownish red gas ; dissolved 
 
 
 
 in water gives a mixture of 
 
 
 
 nitrous and nitric acids. 
 
 Nitrogen Pentoxide 
 
 N 2 5 
 
 White unstable solid, anhy- 
 
 
 
 dride of nitric acid. 
 
 386. Nitrous Oxide, N 2 O, may be prepared by heating 
 ammonium nitrate which decomposes according to the 
 reaction NH 4 NO 3 -* N 2 O + 2 HA 
 
364 COMPOUNDS OF NITROGEN 
 
 This gas is much used by dentists and surgeons to produce 
 anaesthesia for short operations. Nitrous oxide is a colorless 
 gas, it is somewhat soluble in water, and it has a sweetish 
 taste. It causes a glowing splinter of wood to burst into 
 flame and it supports the combustion of sulphur, phos- 
 phorus, and other combustibles with much the same vigor 
 as does pure oxygen ; but the animal body is unable to obtain 
 oxygen from it and so it does not sustain life. It is usual to 
 mix it with air when producing anaesthesia so as not entirely 
 to deprive the patient of oxygen. 
 
 387. Nitric Oxide, NO. For laboratory study, this gas 
 
 is made by the action of copper on nitric acid. The nitric 
 
 acid is reduced, that is, it has oxygen taken away from it 
 
 by the copper : 2 HN Q 3 -> H 2 O + 2 NO + 3 O (1) 
 
 3 O + 3 Cu -+ 3 CuO 
 
 The copper is thereby oxidized to copper oxide, a basic oxide. 
 We do not see any appearance of this oxide, however, because 
 as fast as it is formed it reacts with the surplus nitric acid to 
 form the salt, copper nitrate : 
 
 3 CuO + 6 HNO 3 -> 3 Cu(NO 2 ) 2 + 3 H 2 O. (2) 
 
 Reactions (1) and (2) occur simultaneously and are dependent 
 on each other ; if their equations are added, the equation for 
 the entire change becomes : 
 
 3 Cu + 8 HNO 3 -> 3 Cu(NO 3 ) 2 + 4 H 2 O + 2 NO. 
 
 Nitric oxide is a colorless gas and is but slightly soluble 
 in water, with which it does not react. It does not support 
 ordinary combustion, but phosphorus which has been pre- 
 viously kindled will continue to burn in nitric oxide. 
 
 Its most remarkable property is that it combines spon- 
 taneously with oxygen in the cold, thereby producing nitro- 
 
NITROGEN TETROXIDE 365 
 
 gen tetroxide, a deep brownish red gas of a suffocating odor. 
 When, for example, colorless nitric oxide emerges from a 
 delivery tube into the open air, it changes as if by magic 
 into the deep red vapor of nitrogen tetroxide. 
 
 388. Nitrogen Tetroxide, NO 2 , is, as stated, a deep red gas 
 at ordinary temperature. Its odor is suffocating and not 
 altogether dissimilar to that of chlorine. On heating, its 
 color becomes deeper red ; on cooling, its color becomes paler 
 until the gas condenses to a pale yellow liquid. This liquid 
 boils at 22 C. and gives the characteristic reddish fumes. 
 At 12 C. it freezes to an almost colorless solid. 
 
 The changes of color are believed to be due to a change in 
 the size of the molecule. The red gas is believed to consist 
 of molecules of NO 2 . At 144C., the vapor density corre- 
 sponds to the molecular weight 46 of NO 2 . At lower tem- 
 peratures the density is higher, indicating a mixture of NO 2 
 and N 2 C>4 molecules. The liquid is supposed to consist 
 entirely of N 2 O 4 . 
 
 Nitrogen tetroxide is a powerful oxidizing agent, support- 
 ing the combustion of most of the ordinarily combustible 
 substances. It dissolves in water and at the same time reacts 
 with it to form a mixture of nitrous and nitric acids : 
 
 2 N0 2 + H 2 -> HN0 2 + HNO 3 . 
 
 If the water is warm, the unstable nitrous acid decomposes 
 as follows : 
 
 3 HNO 2 -> H 2 O + 2 NO + HNO 3 . 
 
 The escaping NO can form further NO 2 when it comes in 
 contact with the air. These reactions play an important 
 part in the process of making nitric acid from the air, for the 
 nitric oxide first formed in the path of the electric spark re- 
 
366 COMPOUNDS OF NITROGEN 
 
 acts with oxygen to form nitrogen tetroxide and the latter 
 reacts with water. 
 
 389. Nitric Acid, HNO 3 , is the most important compound 
 of nitrogen. The great bulk of it is made from crude sodium 
 nitrate, NaNOg, which is found in extensive deposits in 
 Chili, South America, and is hence known as Chili saltpeter. 
 The origin of the deposit will be spoken of in a later part of 
 this chapter. Although this deposit is of great magnitude, 
 it is, nevertheless, being used so extensively that it cannot 
 last for a great many years longer, and eventually the world 
 must look to other sources for its nitrate supply, very prob- 
 ably to the electrical method of " fixing " the atmospheric 
 nitrogen. 
 
 In the manufacture of nitric acid, Chili saltpeter is treated 
 with concentrated sulphuric acid and the mixture is heated. 
 Nitric acid, being volatile, distils off, while sodium acid sul- 
 phate is left in the retort : 
 
 NaN0 3 + H 2 SO 4 -> NaHSO 4 + HNO 3 . 
 
 The vapor of the nitric acid is passed through air-cooled 
 earthenware or glass vessels in which it condenses to a liquid. 
 
 390. Properties of Nitric Acid. Nitric acid, when pure, 
 is a colorless liquid of specific gravity 1.5, but it readily de- 
 composes to some extent, especially if warmed or exposed to 
 the light. Some nitrogen tetroxide is formed, and this colors 
 the liquid yellow or even reddish, and red fumes of it are fre- 
 quently observed above the liquid in the bottle. Commercial 
 nitric acid has a specific gravity of 1 .42 and contains only 60 
 to 70 per cent of HNO 3 , the rest being water. 
 
 One of the most marked properties of nitric acid is its effect 
 on organic matter. It attacks the skin, turning it bright 
 yellow, and when concentrated, it makes severe and deep 
 
PROPERTIES OF NITRIC ACID 367 
 
 burns. Fabrics are at once destroyed if concentrated nitric 
 acid is spilled on them. An ignited piece of charcoal will 
 continue to burn when thrust below the surface of concen- 
 trated nitric acid. 
 
 Nitric acid is a strong acid in the same sense that hydro- 
 chloric and sulphuric acids are strong, that is, it is very 
 highly ionized in its dilute solution and thus furnishes an 
 abundance of hydrogen ions. It has, however, other im- 
 portant properties besides those caused by the hydrogen ions ; 
 for example, nitric acid readily attacks copper, silver, and mer- 
 cury, metals which stand below hydrogen in the electromotive 
 series and which are unacted upon by hydrochloric acid 
 or dilute sulphuric acid. No hydrogen, however, is liberated 
 by the action of nitric acid on these metals ; a gas is evolved 
 which is colorless in the bubbles which rise through the liquid 
 but turns red when the bubbles burst and the gas comes in 
 contact with the air. This gas obviously is nitric oxide. 
 The reaction of copper with nitric acid has already been 
 explained in section 387. Nitric acid, coming as it does from 
 the anhydride N 2 O 5 , contains an abundant supply of oxygen 
 and is able to release a large part of it very readily. Thus 
 it oxidizes metals. It is most often reduced thereby to 
 nitric oxide: NI Q, _* 2 NO + 3 O. 
 
 After oxidizing the metal, nitric acid begins to display its 
 acid function in that it neutralizes the basic oxide, forming 
 water and a salt (nitrate) of the metal. In just the same 
 way, hydrochloric and dilute sulphuric acids react with the 
 oxides of the metals copper, silver, and mercury and form the 
 corresponding chlorides and sulphates, although the latter 
 acids have no action at all on the uncombined metals. 
 
 When metals standing above hydrogen in the electro- 
 
 B. AND W. CHEM. 24 
 
368 COMPOUNDS OF NITROGEN 
 
 motive series react with nitric acid, there is no reason why 
 hydrogen should not be displaced. Usually, however, it 
 does not escape as such, for nitric acid, being an oxidizing 
 agent, catches the hydrogen in the moment of its formation, 
 when it is particularly active, and oxidizes it to water. A 
 very active metal like magnesium can sometimes, when the 
 acid is dilute, produce hydrogen so copiously that some of 
 it escapes the oxidizing action of the nitric acid and is evolved 
 as hydrogen gas. 
 
 Hydrogen is able to react with nitric acid only when it is 
 in the particularly active condition at the moment of its for- 
 mation at the surface of the metal. A stream of hydrogen 
 formed in a separate generator may be passed freely into 
 nitric acid without the least reaction taking place. Thus 
 whatever hydrogen can get fairly formed and escape from the 
 surface of the magnesium before it is oxidized will be evolved 
 with the other reaction products. 
 
 It has already been seen under the preparation of sulphur 
 dioxide that hot concentrated sulphuric acid can react as an 
 oxidizing agent upon copper and that the reduction product 
 of the sulphuric acid is sulphur dioxide in the same way that 
 the reduction product of nitric acid is nitric oxide. Sulphur 
 is a more active element than nitrogen ; in consequence, its 
 oxides are more stable, and the oxides, or the acids derived 
 from them, are more difficult to reduce. Cold or dilute sul- 
 phuric acid thus is without action on copper, whereas nitric 
 acid reacts when it is both cold and dilute. 
 
 391. Reduction of Nitric Acid to Ammonia. The usual 
 reduction product of nitric acid is nitric oxide, NO. If we 
 should imagine the reduction to be carried further, we might 
 expect to obtain free nitrogen. If, however, the reduction 
 gets as far as this, it seldom stops here, but goes a step further. 
 
REDUCTION OF NITRIC ACID TO AMMONIA 369 
 
 It may be wondered how this is possible, how anything not 
 possessed can be taken away ! Electrically speaking, we have 
 already seen that addition of positive is equivalent to the 
 taking away of n gative, and vice versa. The same is true chem- 
 ically, and the addition of positive hydrogen is considered 
 reduction as much as the taking away of negative oxygen. 
 
 Now when nitric acid is treated with magnesium or zinc 
 or any metal standing high in the electromotive series, there 
 is aways the possibility of the setting free of hydrogen. 
 This hydrogen is especially active at the moment of its for- 
 mation ; and if it finds free nitrogen at the moment of its lib- 
 eration by the reduction of nitric oxide, it combines with it 
 to form ammonia. 
 
 Let us consider the actual experiment of treating zinc 
 turnings with cold dilute nitric acid. The reaction is not so 
 violent as with more concentrated acid, and little or no red 
 fumes of nitrogen dioxide can be seen escaping. We suspect 
 ammonia is formed, but we cannot see it or perceive its odor. 
 In fact, if we reflect a moment we should not expect to find 
 free ammonia, for ammonia is basic ; it forms ammonium hy- 
 droxide with some of the water present and that in turn reacts 
 with the surplus nitric acid to form ammonium nitrate. 
 With this idea in mind, we can start to show the existence of 
 the ammonia in combination. It is only necessary to add to 
 the solution a stronger base which will liberate the weaker 
 base from its salt : 
 
 Na + OH" + NH 4 + NO 3 - -> Na + NOT \ + (NH 4 OH). 
 Then, especially on warming the solution, ammonium hy- 
 droxide breaks up into ammonia and water : 
 
 NH 4 OH -^ NH 3 f + H 2 0, 
 and the odor of the escaping ammonia gas is evident. 
 
370 COMPOUNDS OF NITROGEN 
 
 The reduction of nitric acid by copper was compared with 
 the similar reduction of sulphuric acid. It is also true of 
 sulphuric acid that it can be reduced to a stage further than 
 the lower oxide or even than free sulphur. When fairly con- 
 centrated, warm sulphuric acid is treated with zinc or mag- 
 nesium, a considerable amount of hydrogen sulphide is ob- 
 tained among the other gases that escape. The active 
 hydrogen liberated by the metal adds itself to the sulphur. 
 
 392. Explosive Compounds of Nitrogen. It has already 
 been stated that nitric acid is a strong oxidizing agent 
 because it is unstable and gives up its oxygen readily. It is 
 also true of nitrogen compounds in general that they are un- 
 stable. Many of the compounds of nitrogen are so unstable 
 that they are explosive, that is to say, when they start to de- 
 compose they do so with violence. 
 
 393. Gunpowder is a mixture of potassium nitrate with 
 powdered charcoal and sulphur. Potassium nitrate, like 
 nitric acid, gives up oxygen readily, and with carbon present 
 to unite with the oxygen, the reaction, if once started, be- 
 comes violent within an instant. Nitrogen gas and carbon 
 dioxide, with possibly some carbon monoxide, are gaseous prod- 
 ucts of the reaction ; and the sudden production of a large 
 quantity of these gases added to the expansive effect of the 
 great heat of the reaction accounts for the power of the ex- 
 plosion. 
 
 394. Cellulose Nitrate ; Guncotton. Most of the modern 
 high explosives are made by the carefully regulated action of 
 nitric acid on some of the organic compounds of carbon. 
 Guncotton is one of these and it is made by the action of a 
 mixture of concentrated nitric and sulphuric acids on pure 
 cotton fiber, which is almost pure cellulose (CeHioOs)^ 
 
 2 CeH lo 5 + 6 HN0 3 -> C 12 H 14 4 (N0 3 )6 + 6 H 2 O. 
 
NITROGLYCERIN 371 
 
 As seen in the equation, water is one of the products of the 
 reaction; the function of the sulphuric acid is to appro- 
 priate this water, which would otherwise accumulate and 
 check the reaction. 
 
 When guncotton explodes, a rearrangement of the atoms 
 takes place so that the simpler and much stabler molecules 
 CO, CO 2 , H 2 O, and N 2 are formed. All of the products are 
 gases and hence no smoke is produced. Guncotton is the 
 basis of modern smokeless powder. 
 
 Guncotton is fairly safe to handle, for it is stable enough 
 to withstand considerable heat and shock without exploding. 
 It is customarily fired by means of a detonating cap of mer- 
 curic fulminate (Hg(ONC)2 also a nitrogen compound). 
 The shock of the explosion of the cap detonates, or explodes, 
 the guncotton. If not detonated but simply ignited with a 
 match in the open, guncotton burns rapidly but usually 
 without trace of explosion. 
 
 Lower nitrates of cellulose are made by using less con- 
 centrated nitric acid ; they are far less explosive than the 
 hexanitrate and find use in making collodion, celluloid, and 
 artificial silk. Articles made from them are extremely in- 
 flammable. 
 
 395. Nitroglycerin, C 3 H 5 (NO 3 )3, is made by treating 
 glycerin (glycerol) in the same way as cellulose is treated in 
 making guncotton. Nitroglycerin is far more dangerous to 
 handle because it explodes with very slight provocation. 
 Dynamite is made by impregnating diatomaceous earth or 
 other porous material with nitroglycerin. It is far safer to 
 handle than the clear nitroglycerin, and it gives nearly as 
 powerful an explosion. 
 
 396. Fixation of Nitrogen by Aid of Bacteria. It was 
 stated in Chapter VII that much atmospheric nitrogen is 
 
372 COMPOUNDS OF NITROGEN 
 
 continually finding its way into the combined form through 
 the agency of the life processes of certain bacteria which live 
 on the roots of plants belonging to the legume family (peas, 
 beans, lentils, alfalfa, and clover belong to this family). 
 The plants assimilate the nitrogen thus combined and con- 
 vert it into the complex compounds with carbon, hydrogen, 
 and oxygen which go to make up the protoplasm of the plant 
 cells, the chlorophyll or green coloring matter, etc. The 
 seeds usually are especially rich in nitrogenous substances. 
 Peas and beans thus make valuable food material for men and 
 animals. 
 
 The total amount of nitrogen combined by all of the arti- 
 ficial means as well as by the lightning discharges in thunder 
 storms is entirely insignificant in comparison with that fixed 
 by bacterial action. 
 
 By plowing under a crop of clover, or other legume, nitrog- 
 enous matter can be introduced into the soil, where it be- 
 comes finally converted into nitrates. The latter change is 
 accomplished through the oxidizing agency of the air in the 
 presence of the alkaline material of the soil and with the aid 
 of the various bacteria of decay. Nitrogen in the form of 
 nitrates is available for the nutrition of other kinds of plants, 
 such as wheat and oats, which cannot take nitrogen from the 
 air. Unless some such method of getting nitrogenous matter 
 into the soil is adopted, grain and other crops will not thrive 
 after a few years without artificial fertilizers containing nitro- 
 gen, such as animal manure or Chili saltpeter (sodium 
 nitrate) . 
 
 Farmers generally understand the necessity of keeping 
 up the nitrogen content of the soil, and they frequently plant 
 clover, alfalfa, or other legumes, since this method is cheaper 
 than buying expensive sodium nitrate. 
 
THE NITROGEN CYCLE IN NATURE 373 
 
 397. Origin of Saltpeter Beds. The origin of the Chili 
 saltpeter deposits is not known, but it is generally agreed that 
 the nitrogen is of organic origin, either animal or vegetable. 
 When organic material decays, as in the damp soil of cattle 
 yards, some of the nitrogen is oxidized to nitric acid, which 
 gives nitrates with the alkaline material in the soil ; if the 
 surface of the soil is dry, a whitish crust made up of small 
 crystals of potassium nitrate (saltpeter) often forms. In 
 some localities, notably in India, the soil near the villages 
 where, due to imperfect sewage disposal, much nitrogenous 
 matter decomposes, is extracted with water every few years 
 and the nitrates, chiefly calcium and potassium nitrates, are 
 obtained by evaporation. 
 
 The Chili saltpeter without doubt arose through the 
 oxidation of vast deposits of nitrogenous organic matter. 
 The soil in that region must have abounded in soda rather 
 than potash or lime. The peculiar formation of the plateau 
 and the absence of rain accounts for the retention of the 
 deposit. 
 
 398. The Nitrogen Cycle in Nature. When nitrogenous 
 compounds of either plant or animal origin decay under usual 
 conditions, the carbon is oxidized to carbon dioxide and the 
 hydrogen to water ; the nitrogen appears at first in the form 
 of ammonia but this is oxidized partly to free nitrogen which 
 escapes as gas and partly to nitrate. We have thus a com- 
 plete cycle through which nitrogen passes from the free state 
 in the air, through the combined state in the legume, from 
 the legume to other states of combination in plant and animal 
 matter, and finally through decay back again to the atmos- 
 phere. If the legume is eaten by animals the nitrogen is 
 changed into the various nitrogenous substances of the animal 
 body ; the decay of either the legumes or of the animal matter 
 
374 
 
 COMPOUNDS OF NITROGEN 
 
 yields in part free nitrogen and in part nitrates, which in the 
 soil serve to nourish other vegetation, which in turn nourishes 
 
 animals, or else de- 
 cays and forms ni- 
 trates again or yields 
 back free nitrogen to 
 the air. 
 
 In this respect, ni- 
 trogen resembles car- 
 bon, which was 
 shown in Chapter VI 
 to go through a cycle 
 of changes in which 
 plants and animals 
 and the carbon di- 
 oxide of the air play 
 a part. 
 
 The amount of 
 
 FIG. 73. Nitrogen Cycle. 
 
 nitrogen involved in these changes is smaller than the amount 
 of carbon involved in the carbon cycle. Nevertheless, the 
 same sort of equilibrium is maintained. The relative 
 amounts of combined nitrogen and of uncombined atmos- 
 pheric nitrogen remain constant because the amount enter- 
 ing combination is just equalled by the amount which is all 
 the time being returned to the atmosphere. 
 
 SUMMARY 
 
 Free nitrogen is very inactive, but in combination, nitrogen enters 
 freely into reactions and its compounds are of great impor- 
 tance. 
 
 Nitrides and Ammonia. Nitrogen combines with the very active 
 metals to form nitrides. The nitride of hydrogen is known as 
 ammonia. It unites with water to form ammonium hydroxide, 
 
QUESTIONS 375 
 
 a rather weak base. Nitrides other than ammonia are of little 
 practical importance. Ammonia is obtained as a by-product 
 from gas works. 
 
 Oxides. Oxygen forms five distinct compounds with nitrogen. 
 Nitrogen pentoxide, N 2 0s, is the anhydride of nitric acid. 
 
 Nitric acid is the most important derivative of the oxygen com- 
 pounds. It is a strong acid and also a strong oxidizing agent. 
 When it oxidizes other substances, it is, according to condi- 
 tions, itself reduced to N0 2 , NO, N 2 , or even in extreme cases 
 to NH 3 . Nitric acid is obtained principally by treating Chili 
 saltpeter, NaN0 3 , with sulphuric acid. 
 
 Explosives. Oxygen compounds of nitrogen and their derivatives 
 are very unstable and form the basis of all the common ex- 
 plosives. 
 
 A natural cycle of changes is undergone by nitrogen in much the 
 same manner as by carbon. The decay of nitrogenous mate- 
 rial returns to the atmosphere an amount of nitrogen just 
 equalled by that entering combination chiefly under the in- 
 fluence of leguminous plants. 
 
 Questions 
 
 1. When powdered magnesium is heated in a crucible with 
 loosely fitting lid and water is added to the residue. after cooling, 
 some ammonia is set free, as can be told by the odor. Account for 
 the formation of the ammonia. 
 
 2. Explain the use of anhydrous ammonia in making artificial ice. 
 
 3. A flask is filled with a colorless gas, but when the stopper is 
 taken out the gas in the neck of the flask turns brown. What is the 
 gas? 
 
 4. How does the action of nitric acid on copper differ from the 
 action of hydrochloric acid on zinc? 
 
 5. Write the reaction of nitric acid with silver, remembering that 
 the formula of silver oxide is Ag 2 0. 
 
 6. Show by equations how ammonium nitrate can be one of the 
 products of the action of nitric acid on zinc. What gaseous reduc- 
 tion products may escape at the same time that the ammonium, 
 nitrate is being formed ? 
 
376 COMPOUNDS OF NITROGEN 
 
 7. Why do farmers sometimes plant clover only to plow it under 
 without harvesting the crop ? 
 
 8. What weight of calcium hydroxide is necessary to react with 
 100 grams of ammonium sulphate in the preparation of ammonia ? 
 
 9. What volume would the ammonia gas occupy under standard 
 conditions ? 
 
 10. What weight of 28 per cent ammonia solution would be ob- 
 tained ? 
 
 11. What volume would this solution occupy if its specific gravity 
 is 0.90? 
 
 12. What weight of 70 per cent HNOs should be taken to just 
 dissolve 190.8 grams of copper ? 
 
 3 Cu + 8 HN0 3 -* 3 Cu(N0 3 ) 2 + 2 NO + 4 H 2 0. 
 
 13. At standard conditions, what volume of NO gas would be 
 evolved in question 12? 
 
 14. With what volume of air (20 per cent oxygen) should this 
 nitric oxide be mixed in order to change it all to N0 2 ? 
 
 15. Formulate as well as you are able the reactions for the ex- 
 plosion of ordinary gunpowder and of smokeless powder. Explain 
 why the former produces smoke and the latter does not. 
 
 16. Heat is evolved when N 2 decomposes into nitrogen and oxy- 
 gen. Consider this fact and explain why N 2 should support com- 
 bustion practically as well as pure oxygen. 
 
CHAPTER XXXI 
 
 THE HALOGEN FAMILY; THE PERIODIC SYSTEM 
 
 399. Natural Families of the Elements. With the eighty 
 or more elements which are known to exist, it would be strange 
 if there were not resemblances between some and dissimilari- 
 ties between others. A comparison of all the elements has 
 shown that what would thus be expected is amply fulfilled 
 by the facts, for the elements seem to arrange themselves 
 naturally into families, and the elements within a family 
 show to a marked degree certain traits which are character- 
 istic of that family. One of these families, the so-called 
 halogen family, forms the subject matter for this chapter. 
 
 The best-known element of this family is chlorine. The 
 other elements are fluorine, bromine, and iodine. All four 
 elements form salts which are extremely alike in character. 
 Thus the sodium salts of fluorine, bromine, and iodine are 
 very similar to common salt, which is the sodium salt of 
 chlorine, and hence the name halogen, which comes from 
 the Greek and means salt-former. 
 
 It is recalled that chlorine is a gas with "a very disagreeable 
 odor, that it unites readily with metallic elements and forms 
 salts. Fluorine, bromine, and iodine also are all possessed 
 of a most disagreeable odor. They all combine easily with 
 metals and give salts which strongly resemble the chlorides. 
 Whenever the chloride of a metal is colorless, the fluoride, 
 bromide, and iodide of that metal are apt to be also colorless. 
 
 377 
 
378 THE HALOGEN FAMILY; THE PERIODIC SYSTEM 
 
 Most of these salts are soluble in water. The hydrogen com- 
 pounds are all soluble in water and form acids, namely hydro- 
 fluoric acid, hydrochloric acid, hydrobromic acid, and hy- 
 driodic acid. All four elements possess the same valence in 
 their compounds with metals and with hydrogen, namely, 
 the valence one. Hence they can mutually replace each other, 
 atom for atom, in their compounds without materially alter- 
 ing the nature of the compound. Thus the symbols of the 
 acids are: HF HQ HRr ffl 
 
 and of the sodium salts are : 
 
 NaF NaCl NaBr Nal 
 
 FLUORINE 
 
 400. Uncombined fluorine is a gas like chlorine. It 
 possesses a similar color and odor, the color being a paler 
 yellow, whereas the odor is even more offensive. Fluorine 
 is a more active element than chlorine; it is in fact the 
 most energetic non-metallic element known. It reacts spon- 
 taneously with all of the ordinary substances of which the 
 vessels used in preparing and collecting gases are made, and 
 for this reason it defied for a long time all attempts to ob- 
 tain it in the uncombined condition. 
 
 It reacts vigorously with water, setting oxygen free and 
 forming hydrofluoric acid. It combines spontaneously and 
 with intense energy with most of the elements, including 
 sulphur, phosphorus, and the metals. Gold and platinum 
 vessels resist it to a sufficient extent so that they may be 
 used as containers in preparing it. 
 
 Fluorine has a strong action on glass. It attacks organic 
 compounds, such as wood, rubber, paraffin, and oil, with 
 violence, so that they are often inflamed. Fluorine enters 
 
FLUORINE 379 
 
 into chemical combination with the silicon of the glass and 
 with the hydrogen of the organic substances. 
 
 401. Preparation. Fluorine being the most active non- 
 metallic element, there can be no other element which can 
 displace it from its compounds, after the manner in which 
 the more active oxygen of oxidizing agents can displace the 
 less active chlorine from hydrochloric acid : 
 
 O + 2 HC1 -* H 2 O + C1 2 . 
 
 Our only recourse, then, is to drag fluorine apart from the 
 element with which it is in combination by means of the 
 electric current. 
 
 Moissan, a noted French chemist, succeeded in 1886 in ob- 
 taining uncombined fluorine by passing an electric current 
 through a solution of potassium fluoride in dry liquid hydro- 
 gen fluoride contained in a platinum U-tube. Hydrogen was 
 evolved at the negative electrode, fluorine at the positive 
 electrode. The fluorine was passed through platinum tubes 
 and was caught in platinum vessels by displacement of air. 
 It is perhaps needless to say that the preparation of fluorine 
 has not often been repeated. 
 
 402. Occurrence. Fluorine is found in nature as a con- 
 stituent of certain minerals, the most important of which 
 is fluorspar (CaF 2 ). Unfortunately, the .phosphate rock, 
 CasCPO^, which is used in making fertilizer, often contains 
 some calcium fluoride ; the hydrofluoric acid evolved when 
 the rock is treated with sulphuric acid is a menace to the 
 health of the workmen. 
 
 403. Hydrofluoric acid. The most important compound 
 of fluorine is hydrogen fluoride, or hydrofluoric acid, HF. 
 This is prepared much after the manner of hydrochloric acid : 
 Fluorspar is treated with concentrated sulphuric acid in lead 
 
380 THE HALOGEN FAMILY; THE PERIODIC SYSTEM 
 
 retorts. On distillation, the gaseous hydrogen fluoride 
 passes off, and this is passed into water in lead bottles, where 
 a solution of hydrofluoric acid is obtained. This acid is put 
 on the market in bottles of gutta percha or wax because glass 
 is attacked by it. 
 
 Hydrofluoric acid does not attack rubber, wax and paraf- 
 fin as does uncombined fluorine, because the element is al- 
 ready in combination with hydrogen in the acid ; but hydro- 
 fluoric acid does attack glass. It reacts with the silicon 
 dioxide, which is one of the principal components of glass : 
 
 4 HF + SiO 2 -> SiF 4 + 2 H 2 O. 
 
 Silicon tetrafluoride, SiF 4 , is a gaseous substance and es- 
 capes from the sphere of action. 
 
 One of the most important uses of hydrofluoric acid is for 
 etching glass. The aqueous acid dissolves away the glass 
 and leaves a smooth hollowed surface, but gaseous hydrogen 
 fluoride, although it acts chemically in much the same way, 
 leaves a roughened surface which has the appearance of 
 ground glass. The object to be etched is coated with wax and 
 the design is drawn in the wax, making bare the glass in the 
 desired places. Then the whole is exposed to hydrogen 
 fluoride gas and the design is etched. The graduations on 
 our glass measuring vessels are usually marked in this manner. 
 
 Hydrofluoric acid is extremely poisonous; its vapor is 
 dangerous to breathe, and even small drops of the solution 
 cause painful ulcerated sores on the flesh. 
 
 BROMINE 
 
 404. Uncombined Bromine is a dark red liquid which 
 freezes at - 7C. and boils at 63 C. It is about three times 
 as heavy as water. It evaporates very easily at ordinary tern- 
 
BROMINE 381 
 
 perature, and when a bottle is partly filled with liquid bro- 
 mine, the upper part is always filled with red bromine vapor. 
 The odor of bromine is similar to that of chlorine and it is 
 fully as offensive, in fact, its name is derived from the Greek 
 word meaning stench. 
 
 The chemical reactions of bromine are much the same as 
 those of chlorine, except that they are generally less vigorous. 
 If powdered antimony is thrown into a jar of bromine vapor, 
 it does not flame up spontaneously as it does when thrown 
 into chlorine. If, however, the antimony is dropped into a 
 little liquid bromine in a test tube, it shows a vigorous reac- 
 tion. 
 
 If a mixture of hydrogen and bromine vapor is passed 
 through a heated tube, the elements combine quietly and 
 form hydrogen bromine, but there is no explosion as when a 
 mixture of hydrogen and chlorine reacts (see page 169). 
 
 405. Occurrence and Preparation. Wherever chlorine 
 occurs in nature, bromine almost invariably appears, but 
 only in extremely small amounts. Thus in the brine from 
 salt wells there is usually a small amount of bromine. 
 After these brines have been evaporated and all the salt pos- 
 sible has been crystallized out, the " mother liquor " still 
 contains all the bromine as sodium bromide (or magnesium 
 bromide) . The bromine is then liberated from this compound, 
 much as chlorine is liberated from common salt, namely, by 
 the addition of sulphuric acid and an oxidizing agent : 
 
 H 2 SO 4 + 2 NaBr -> Na 2 SO 4 + 2 HBr 
 2 HBr + O -> H 2 O + Br 2 . 
 
 The bromine is distilled off and condensed as the dark red 
 liquid of commerce. 
 
 It has been said that chlorine is a more active element 
 
382 THE HALOGEN FAMILY; THE PERIODIC SYSTEM 
 
 than bromine. Once in combination, it is more difficult to 
 get it out of combination. It is, therefore, quite as one 
 would expect, that when a bromide is treated with chlorine 
 the bromine is forced out of combination while the chlorine 
 enters in its place : 
 
 C1 2 + 2 NaBr -+ 2 NaCl + Br 2 . 
 
 Use is often made of this fact in the manufacture of bromine. 
 Chlorine gas is blown into the hot colorless sodium bromide 
 liquor, where it is absorbed, while the red vapors of bromine 
 emerge and are blown along to the condensing tubes. 
 
 406. Hydrobromic acid. Hydrogen bromide is a sub- 
 stance most strikingly like hydrogen chloride in all its prop- 
 erties. It is a colorless gas of an irritating odor. It is ex- 
 tremely soluble in water and in aqueous solution is known 
 as hydrobromic acid, an acid which is fully equal in strength 
 to hydrochloric acid. 
 
 407. Uses of Bromine and of Bromides. Bromine is of 
 more practical use than fluorine, although it is not nearly so 
 much used as chlorine, whose compounds are more abundant. 
 Most of the uses of free bromine depend on its being an oxi- 
 dizing agent, but a somewhat less vigorous one than chlorine. 
 It finds use in the preparation of many of the coal tar dyes. 
 
 Some of the bromides are used as sedatives in medicine. 
 Silver bromide is the light-sensitive substance of most photo- 
 graphic plates and films and of much of the photographic 
 paper. Silver bromide, like the chloride and iodide, is ex- 
 tremely insoluble in water. 
 
 IODINE 
 
 408. Uncombined Iodine is a dark, blue-black solid sub- 
 stance which is usually formed in thin platelike crystals. 
 
IODINE 383 
 
 It is so dark colored that it appears opaque when seen in a 
 mass, but in thin plates it is found to be as transparent as an 
 equally deep colored piece of glass. Like bromine, iodine 
 is very volatile, and if a small grain of it is warmed in a test 
 tube, the tube becomes filled with the most beautiful violet 
 vapor of iodine. 
 
 Iodine is a noteworthy substance on account of its great 
 volatility ; when it is warmed in an open dish, as for example 
 on a watch glass, it all passes directly from the solid state to 
 the vapor state without first melting. If, however, a consid- 
 erable amount of iodine is heated in a narrow-necked flask, 
 it melts at 114 C. and the liquid iodine boils at 184 C. 
 
 The chemical reactions of iodine are very similar to those 
 of chlorine and bromine, except that they are much less 
 vigorous than the latter. Iodine can without difficulty be 
 made to combine with the more active of the metals, but the 
 combination is not attended with evidence of a violent re- 
 action as is the case with chlorine and to a lesser extent with 
 bromine. 
 
 409. Uses of Iodine. Iodine dissolved in alcohol or in a 
 solution of potassium iodide finds extensive use in medicine. 
 Concentrated, it is used as a counter irritant, being 
 painted on the skin over a bruise or other injury to bring the 
 blood more abundantly to the surface and hence relieve the 
 congestion beneath. In a more diluted condition iodine 
 solutions make a valuable antiseptic wash-for wounds. The 
 iodides are also used in medicine. 
 
 Hydrogen and iodine can be made to combine to a slight 
 extent when a mixture of the two is passed through a heated 
 tube, but the combination is far less complete than that of 
 hydrogen and bromine. Hydrogen iodide is a colorless gas 
 like hydrogen chloride and hydrogen bromide; like them, 
 
 B. AND W. CHEM. 25 
 
384 THE HALOGEN FAMILY; THE PERIODIC SYSTEM 
 
 also, it is very soluble in water and its solution is a strong 
 acid, hydriodic acid. 
 
 410. Occurrence and Preparation. Although it is a well- 
 known and a frequently used element, iodine is not at all 
 abundant in nature. It is found in extremely minute 
 amounts in the ashes of seaweeds and in Chili saltpeter. 
 It is obtained from the mother liquor when the latter is crys- 
 tallized, much as bromine is obtained from the mother liquor 
 when common salt is crystallized (see page 381). The 
 quantity of iodine in the earth is about as many times less 
 than that of bromine as that of bromine is less than that of 
 chlorine. 
 
 411. Displacement by other Halogens. Iodine is the 
 least active of the halogens ; it shows the least energy when 
 it enters into combination with metallic elements, it is corre- 
 spondingly the most easy to separate from its compounds. 
 Both chlorine and bromine (and, of course, fluorine) are able 
 to displace it from its compounds, 
 
 C1 2 + 2 KI -> I 2 + 2 KC1, 
 Br 2 + 2 KI -> I 2 + 2 KBr. 
 
 Thus if a little chlorine is bubbled into a colorless solution 
 of potassium iodide, the iodine is displaced according to the 
 foregoing equation, the liquid becomes dark colored in conse- 
 quence, and flakes of solid iodine are precipitated out when 
 enough has been set free to more than saturate the solution. 
 If the above equations are written in ionic form : 
 
 C1 2 + 2 K + + 2 I" -> I 2 + 2 K + + 2 CT, 
 
 it is seen that the metal ion is unchanged and may be can- 
 celled from the equation : 
 
 ci 2 + 2 1- -> 2 cr + 1 2 . 
 
PERIODIC CLASSIFICATION OF THE ELEMENTS 385 
 
 The reaction appears thus to be merely a matter of the more 
 active negative element withdrawing electric charges from 
 the less active element. 
 
 Iodine has a very characteristic property of giving, with 
 starch, an intense blue color. When so small an amount 
 of iodine is set free in solution that its own color is scarcely 
 perceptible, if a little cooked starch paste is added, a marked 
 blue color may be seen. 
 
 Combined iodine does not give this test. A colorless 
 mixture of potassium iodide and starch can therefore be pre- 
 pared ; and strips of paper soaked in this mixture and dried 
 are useful in testing for chlorine and bromine. 
 
 THE PERIODIC CLASSIFICATION OF THE ELEMENTS 
 
 412. In the living world, scientists have found that ani- 
 mals and plants can be classified into families. For example, 
 the domestic cat, the wild cat, the leopard, the tiger, and the 
 lion are placed in one family because they all possess certain 
 family characteristics in their physiological structure and 
 their habits of life. On the other hand, the horse, the donkey, 
 and the zebra are placed in another family because they have 
 family characteristics markedly different from those of the 
 cat family. 
 
 A similar sort of classification can be applied in the in- 
 organic world, and even the elements themselves fall into 
 natural groups or families of which the halogen family is a 
 striking example. The Russian chemist, Mendelejeff, first 
 clearly perceived and showed that all the elements could be 
 arranged according to a definite system, which we know 
 as the periodic system. 
 
 He arranged all of the elements in a regular order, starting 
 
386 THE HALOGEN FAMILY; THE PERIODIC SYSTEM 
 
 with the one of lowest atomic weight and proceeding 
 in the order of increase of atomic weight, and he thus 
 showed that certain special properties recur at fairly regu- 
 lar intervals. The elements in which these properties 
 recur are the ones which, like the halogens, fall into the 
 same family. 
 
 The lightest known element upon this earth is hydrogen, 
 to which we give, arbitrarily, the atomic weighj; of one. This 
 element seems to stand rather by itself, but the next eight 
 elements, with their atomic weights, are shown in the follow- 
 ing table : 
 
 HELIUM 
 
 LITHIUM 
 
 BERYL- 
 
 BORON 
 
 CARBON 
 
 NITROGEN 
 
 OXYGEN 
 
 FLUORINE 
 
 (4) 
 
 (7) 
 
 LIUM (9) 
 
 (11) 
 
 (12) 
 
 (14) 
 
 (16) 
 
 (19) 
 
 
 1 00 
 
 1* 
 
 
 
 "3 
 
 1 
 
 a 
 
 i 
 
 1 a 
 
 ^| 
 
 Jj 
 
 .S 
 
 i 
 
 
 g 
 
 8 
 
 
 1 S l 
 
 3 
 
 c3 
 
 2 
 
 P 
 
 O 
 
 
 
 
 3 1 
 
 
 s 
 
 | 
 
 
 
 oT 
 
 o3 
 
 3 * 
 
 S o 
 
 .2 
 
 ' 
 
 O 
 
 9 
 
 Si 
 
 +1 
 
 SH O 
 
 
 ^ W)^ 
 
 ^ 1^ 
 
 C^) 
 
 H Q^ 
 
 S 
 
 S 
 
 1? 
 
 o> 
 
 V* n * rH 
 
 -*-^. oC tJD 
 
 r-j .^H 
 
 ^ "fr 
 
 o 
 
 ^_j 
 
 
 ^a 
 
 33s 
 
 a 12 
 
 SI 
 
 igl 
 
 1 1 
 
 
 H 
 
 
 Li 2 
 
 BeO 
 
 B 2 3 
 
 C0 2 
 
 N 2 5 
 
 
 
 
 
 
 
 H 4 C 
 
 H 3 N 
 
 H 2 
 
 HF 
 
 It is seen from the few properties enumerated in the table 
 that these elements are very unlike each other in their 
 physical properties and in the kind of compounds that 
 they form. Next to helium, the absolutely inert gas, comes 
 the very active metallic element lithium. The next element 
 is a metal, but not as active a one as lithium. The next is 
 not a metal, although it is not a pronounced non-metal. With 
 each successive element, the non-metallic properties grow 
 
PERIODIC CLASSIFICATION OF THE ELEMENTS 387 
 
 more marked, until in fluorine we find the most active of all 
 the non-metallic elements. 
 
 The next element beyond fluorine is neon, but we do not 
 place this to the right of fluorine, but rather we begin a new 
 series, and place neon beneath helium, for, like the latter, it 
 also is an absolutely inert gas. Next comes sodium, which is a 
 sister element to lithium and therefore fits naturally into the 
 position below the latter. 
 
 The complete series of the .eight elements following fluorine 
 is shown in the next table, and an inspection shows at once 
 a marked similarity in every case between the elements 
 
 NEON 
 
 SODIUM 
 
 MAGNE- 
 
 ALUMIN- 
 
 SILICON 
 
 PHOSPHO- 
 
 SULPHUR 
 
 CHLORINE 
 
 (20) 
 
 (23) 
 
 SIUM (24) 
 
 IUM (27) 
 
 (28) 
 
 RUS (31) 
 
 (32) 
 
 (35.5) 
 
 
 
 +a 
 
 ^ 
 
 02 
 
 02 
 
 02 
 
 
 
 i 
 
 
 o3 
 
 o3 
 
 -a 
 
 +5 
 
 "33' 
 
 
 i) 
 
 o 
 
 ^ 
 
 i 
 
 ^ 
 
 a 
 
 a 
 
 ^ 
 
 g 
 
 i 
 
 a 
 
 a 
 
 a 
 
 l-s 
 
 3 
 
 1 
 
 '| 
 
 
 13 
 
 o3 
 
 "3 
 
 1 
 
 a 
 
 a ^ 
 
 o3 
 
 02 
 
 ! 
 
 O 
 ^ ;>> 
 
 !i 
 
 !i 
 
 ii 
 
 I 
 
 s' 
 
 & 
 
 |1 
 
 a| 
 
 i i a 
 
 il 
 
 $% 
 
 iyg 
 
 'O HJ 
 
 O} o3 
 
 ii 
 
 CC 03 
 
 w 1 
 
 
 Na 2 
 
 MgO 
 
 A1 2 3 
 
 Si0 2 
 H 4 Si 
 
 P 2 5 
 H,P 
 
 S0 3 
 H 2 S 
 
 C1 2 7 
 HC1 
 
 that occupy the corresponding places. Sulphur corresponds 
 to oxygen in position, and we have already learned that sul- 
 phur and oxygen are interchangeable atom for atom in the 
 sulphides and oxides. Chlorine corresponds to fluorine, and 
 we have already discovered their strong family resemblance 
 in the first part of this chapter. 
 
 The next element to chlorine is argon, another inert gas 
 which falls naturally into the position below neon ; next is 
 
388 THE HALOGEN FAMILY; THE PERIODIC SYSTEM 
 
 potassium, an alkali metal which falls naturally below magne- 
 sium. As we go on in this next series, however, we find that 
 the seventh and eighth elements, chromium and manganese, 
 respectively, are heavy metals and do not correspond in prop- 
 erties with oxygen and sulphur, fluorine and chlorine, respec- 
 tively. In fact, we now have to go through a series of 
 eighteen, instead of eight, elements before we come to bromine, 
 the next member of the halogen family. The periods, after 
 the first two, lengthen out to eighteen instead of eight ele- 
 ments ; and the fourth as well as the third period contains this 
 number of members (if we are willing to take one for granted 
 which has not yet been discovered, but which we feel sure 
 must exist and probably will some day be found), and the 
 eighteenth element beyond bromine is iodine, another of the 
 halogen family. 
 
 This brief discussion of the periodic system shows that 
 there must be some regular law according to which the ele- 
 ments have been formed perhaps are still being infinitely 
 slowly formed. So far we have taken up the study of about 
 twenty only of the most common of the elements, and it is 
 therefore impossible to discuss in detail all of the wonderful 
 analogies brought to light in the periodic system. 
 
 A complete table of the periodic classification is given on 
 the opposite page, and it is possible to tell a great deal about 
 the properties of any element, of which we have no other 
 previous knowledge, simply by observing the position it oc- 
 cupies in the table. It will strongly resemble the other ele- 
 ments in its family and particularly those lying nearest to it. 
 
 Thus we can conclude that krypton and xenon, Kr and 
 Xe, which appear in column 0, are inert elements like argon, 
 and thus are capable of forming no compounds whatever. 
 Rubidium and caesium, Rb and Cs, in Family A, Group I, 
 
PERIODIC CLASSIFICATION OF THE ELEMENTS 389 
 
 _* 
 
 Qo 
 
 l 
 
 a 
 
 si 
 
 N , 
 
 82 
 
 P 
 
390 THE HALOGEN FAMILY; THE PERIODIC SYSTEM 
 
 are very active alkali metals like sodium and potassium. 
 Strontium, barium, and radium, Sr, Ba, and Ra of Family A, 
 Group II, are active alkaline earth metals like calcium. 
 Selenium and tellurium, Se and Te, of Family B, Group VI, 
 are non-metals resembling sulphur. 
 
 The periodic classification has been of very great use in 
 inspiring and directing search after new elements. It is also 
 very useful because of the means which it affords of enabling 
 us to remember the properties of the elements by groups. 
 Thus if one knows well the general properties of the halogen 
 family, he has to remember but little more in order to be quite 
 familiar with the properties of each member of that family. 
 
 SUMMARY 
 
 The halogen family of the elements includes fluorine, chlorine, bro- 
 mine, and iodine which show marked resemblances to each 
 other in their physical and chemical properties and constitute 
 a natural family of the elements. 
 
 Fluorine is the most active of the halogens, in fact, of all the non- 
 metallic elements. Hence it cannot be displaced from its 
 compounds by any other non-metallic element. It can be 
 prepared only by electrolysis. 
 
 Hydrofluoric acid resembles hydrochloric acid in its properties. 
 It is prepared from calcium fluoride in the same manner as 
 hydrochloric acid is made from sodium chloride. Its most 
 remarkable property is its ability to attack glass and it finds 
 use in etching glass. 
 
 Bromine resembles chlorine but is denser (being liquid at ordinary 
 temperatures), darker, and less active. Chlorine displaces it 
 from its compounds. 
 
 Hydrobromic acid, like hydrofluoric, resembles hydrochloric acid. 
 
 Iodine is solid at ordinary temperatures but readily volatilizes if 
 warmed. It resembles the other members of the family, but 
 it is the least active and can be displaced from its compounds 
 by any one of the others. 
 
QUESTIONS 391 
 
 Hydriodic acid resembles hydrochloric acid, but it is less stable. 
 
 Periodic Classification. With increasing atomic weights of the ele- 
 ments, the properties undergo regular cycles of changes. 
 Given properties recur periodically at the same point in each 
 cycle. The credit belongs to Mendelejeff for arranging the 
 elements according to the periodic classification in which the 
 members of a given family occupy similar positions in the 
 succeeding periods. 
 
 Questions 
 
 1. In what respects do the elements of the halogen family re- 
 semble each other most strongly ? 
 
 2. Explain the principal use of hydrofluoric acid. 
 
 3. Compare the behavior of each of the halogens with hydrogen. 
 
 4. How would you test a material to see if it contained free 
 iodine? combined iodine? 
 
 6. How would you test a sweet potato for presence of starch? 
 
 6. Explain the test given by the potassium iodide-starch paper 
 for free chlorine or bromine. 
 
 7. How might a study of the periodic table of the elements show 
 what elements, not yet discovered, may sometime be found in the 
 earth? Could the properties of such elements be foretold? 
 
 8. What weight of iodine is contained in 1000 grams of potas- 
 sium iodide ? 
 
 9. What weight of chlorine is necessary to just displace the iodine 
 from 1000 grams of potassium iodide? 
 
 10. What volume of chlorine (standard conditions) corresponds 
 to the weight taken in Question 9? 
 
 11. How large a flask may be filled with pure bromine vapor at 
 atmospheric pressure if 5 c.c. of liquid bromine, sp. grav. = 3.19, is 
 poured into the flask which is then immersed in boiling water? 
 
 12. Write equations for the following cases : (a) CaF 2 + H 2 S0 4 
 (hot concentrated) ; (6) Mn0 2 + HBr (see chapter on chlorine) ; 
 
 (c) Cu + Br 2 ; (d) CuO + HBr. 
 
 13. Write ionized equations for the following : 
 
 (a) KI + C1 2 ; (6) KBr + AgN0 3 ; (c) CuBr 2 + C1 2 ; 
 
 (d) HI + Zn ; (e) HBr + NaOH ; (/) HBr + CuO. 
 
CHAPTER XXXII 
 
 REVERSIBLE CHEMICAL REACTIONS; CHEMICAL 
 EQUILIBRIUM 
 
 413. Reversible Reactions. It has probably not escaped 
 the attention of the thoughtful reader that many of the chem- 
 ical reactions studied in the foregoing chapters can under 
 certain conditions be made to reverse themselves, that is to 
 say, the products of the ordinary reaction may be made to 
 interact with each other to give back again the substances 
 originally started with. Reactions which are thus capable 
 of proceeding in opposite directions under different conditions 
 are known as reversible reactions. 
 
 414. Reversal effected by Varying the Temperature. 
 When mercury is heated moderately in the presence of oxygen 
 or air, it combines with oxygen, and the red oxide is formed : 
 
 2 Hg + 2 -+ 2 HgO. 
 
 When, however, as in the course of the preparation of oxygen 
 (page 29), mercuric oxide is more strongly heated, it decom- 
 poses into mercury and oxygen : 
 
 2 HgO -> 2 Hg + 2 . 
 
 If it is desired to draw attention to the reversibility of a 
 reaction, the equation is written with a double arrow, one 
 pointing in each direction : 
 
 2 HgO ^> 2 Hg + O 2 . 
 
 It is often the custom to make one arrow heavier to indicate 
 the direction of the prevailing reaction. 
 
 392 
 
REVERSAL EFFECTED BY TEMPERATURE 393 
 
 Such reactions as the one just mentioned, in which the 
 direction may be changed by change of temperature, are very 
 frequent. 
 
 It may seem a little perplexing that moderate heat appears 
 to be necessary to induce mercury and oxygen to combine, 
 although a more intense heat causes decomposition. As a 
 matter of fact, the lower the temperature the greater is the 
 tendency of mercuric oxide to form in comparison to its 
 tendency to decompose. All reactions take place more 
 rapidly when hot, more slowly when cold, and the particular 
 reaction of the formation of mercuric oxide takes place so 
 slowly at room temperature that it is not perceptible. 
 
 Heat is a form of energy which works most often in opposi- 
 tion to chemical affinity. The affinity between mercury and 
 oxygen is not extremely great, mercury being one of the 
 least active metals, and only a rather moderate degree 
 of temperature is necessary to overcome this affinity and de- 
 compose the compound. This temperature is only a little 
 higher than the temperature necessary to make the reaction of 
 formation perceptible, and thus we explain the fact that mer- 
 cury and oxygen are apparently indifferent to each other at 
 room temperature, that they unite at a slightly elevated 
 temperature, but that they break apart again at a still higher 
 temperature. 
 
 What has been said of mercuric oxide is true of almost 
 every chemical compound. Take, for example, water : At 
 ordinary temperatures, hydrogen and oxygen gases do not 
 react perceptibly when mixed together. Raise the tempera- 
 ture, however, to a point where the reaction commences to 
 be appreciable, and a very violent explosion ensues. The 
 water vapor formed is ordinarily a very stable compound, 
 but raise it to 2000 C. (a temperature higher than that of 
 
394 REVERSIBLE CHEMICAL REACTIONS 
 
 the hottest part of the Bunsen flame) and it is decomposed 
 to a slight degree into hydrogen and oxygen ; raise the water 
 vapor to 3000 C. and it is entirely decomposed. 
 
 Very few compounds exist that cannot be decomposed into 
 their elements by a sufficiently high degree of heat. Cal- 
 cium and oxygen have a tremendous affinity for each other, 
 and calcium oxide can withstand the temperature of the 
 oxyhydrogen flame (about 2500 C.) without decomposition. 
 In the sun, however, where the temperature is estimated to be 
 about 6000 C., calcium oxide does not appear to exist, for the 
 spectroscope shows us the presence of uncombined calcium 
 vapor. 
 
 415. Reversal caused by Change of Concentration. It is 
 possible to change the direction of chemical reactions, not only 
 by altering the temperature, but by varying the concentration 
 of one or more of the reacting substances. The effect of con- 
 centration is well illustrated by a process which was much 
 used in the commercial preparation of oxygen before the 
 liquid air method was perfected, and which is based on the re- 
 versibility of the reaction between barium oxide and oxygen 
 on the one hand, and barium peroxide on the other hand : 
 
 2 BaO + O 2 ; 2 Baft. 
 
 Although it is true that barium oxide will take on oxygen 
 from the air at a moderate red heat, whereas barium peroxide 
 will decompose into barium oxide and oxygen at a white heat 
 and the direction may thus be reversed by changing the tem- 
 perature, it was found in practice to be more economical to 
 maintain a constant temperature at 700 C. and to effect the 
 change by altering the concentration of the oxygen in the 
 tubes containing the solid oxide. 
 
 According to this process, air is first forced under high 
 
CHEMICAL EQUILIBRIUM 395 
 
 pressure into the tubes and the concentration of oxygen is 
 thus increased, thereby causing the oxygen to combine with 
 barium oxide and form the peroxide. The nitrogen which is 
 left is allowed to escape through a valve at the further end 
 of the tubes, and fresh air is continually pumped into the 
 tubes. When all of the barium oxide is changed to barium 
 peroxide, the pumps are reversed so as to produce a vacuum 
 in the tubes. The concentration of the oxygen is thus re- 
 duced and the barium peroxide begins to decompose and con- 
 tinues to give off oxygen until only the original barium oxide 
 is left. The oxygen thus pumped out is forced under pres- 
 sure into the steel cylinders in which it is marketed, and the 
 barium oxide left in the tubes is ready to be again carried 
 through the same cycle of operations. 
 
 416. Chemical Equilibrium. Barium peroxide has a tend- 
 ency to decompose at 700 C. and we can actually observe 
 that it gives off oxygen at this temperature into a vacuum 
 or into a space containing very little oxygen. A theory of 
 reversible reactions and of chemical equilibrium has been 
 worked out ; and in the light of this theory, we believe that 
 at 700 C barium peroxide decomposes and gives off oxygen 
 just as rapidly into a space already filled with oxygen as into a 
 vacuum. Only we cannot observe it under these conditions, 
 for the reverse reaction, that is, the formation of barium per- 
 oxide, is now progressing more rapidly than its decomposition. 
 
 When no oxygen is present, this reverse reaction cannot 
 take place, and we observe only the decomposition of the 
 peroxide. When oxygen is present, it reacts with the barium 
 oxide and with a rapidity that depends on its concentration. 
 So if there is but little oxygen in the chambers with the barium 
 oxide, the rapidity of the combination is not great. The 
 decomposition of the barium peroxide is progressing all the 
 
396 REVERSIBLE CHEMICAL REACTIONS 
 
 time, but the recombination (which we regard as altogether 
 another reaction) is inappreciable. So when the exhaust 
 pumps are working and the amount of oxygen is being kept 
 low, we observe only the decomposition of the barium perox- 
 ide, which is then the predominating reaction. 
 
 If the amount of oxygen in the chambers is increased, 
 the rapidity of the recombination is increased. When a 
 point is reached at which the rapidity of recombination is 
 equal to the rapidity of decomposition, the two opposed reac- 
 tions balance each other, because the sum of their effects is 
 zero. No change, therefore, can be observed to take place, 
 although we believe that the two opposite reactions are really 
 taking place. 
 
 If the amount of oxygen in the chambers is increased 
 still further, the reaction of combination begins to outdis- 
 tance that of decomposition, and the amount of barium per- 
 oxide increases. This is the condition that prevails in the 
 process when air is pumped under high pressure into the 
 chambers in order to build up the barium peroxide. 
 
 The point at which the rate of the opposed reactions is 
 equal and at which there is therefore no apparent change is 
 known as the point of equilibrium. Such an equilibrium point 
 exists for every reversible reaction, and if a system is left to 
 itself either one reaction or the other will predominate until 
 the equilibrium point is reached, after which the two reactions 
 will continue to mutually undo the effects of each other. 
 
 417. Another Reversible Reaction and its Equilibrium 
 Point. Let us consider one more example of an easily revers- 
 ible reaction and let us also consider the conditions which lead 
 to a state of equilibrium when the rate of the forward reac- 
 tion is just equaled by the rate with which the products of 
 this reaction interact to form again the original substances. 
 
EQUILIBRIUM OF A REVERSIBLE REACTION 397 
 
 It will be recalled that one of the practical methods of pre- 
 paring hydrogen gas is to pass superheated steam through 
 a tube containing iron turnings kept at a high temperature. 
 The oxide of iron, Fe 3 O4, is formed and hydrogen is left un- 
 combined. 
 
 The hydrogen passes out of the further end of the tube to- 
 gether with a large amount of undecomposed steam. The 
 latter condenses to liquid water when it is cooled, whereas 
 the hydrogen passes along for use. 
 
 It is^, well-known fact that iron oxide may be reduced to 
 metallic iron if it is heated in a tube through which hydro- 
 gen is being passed : 
 
 Fe 3 (V+ 4 H 2 -> 3 Fe + 4 H 2 O. 
 
 The water vapor so formed is swept along by the current of 
 hydrogen and drops of liquid water may be seen to condense 
 beyond in the cool part of the tube. 
 
 The two reactions just discussed are the exact reverse of 
 each other. In the first of them, an abundant supply of 
 steam is kept continually in contact with the iron. This nat- 
 urally tends to react, but the product of this reaction, the hy- 
 drogen, is not allowed to remain to reduce the iron oxide again, 
 but is swept along out of the way by the excess of the steam. 
 
 In the second of the reactions, the reverse is true. Hy- 
 drogen is supplied abundantly and has every opportunity to 
 react with the iron oxide. The water vapor formed is given 
 no chance to oxidize back any of the reduced iron, for it is 
 swept along out of the way by the excess of hydrogen. 
 
 In neither of these cases is there any chance given to at- 
 tain an equilibrium, for one of the reaction products is in each 
 case removed as fast as it is formed. 
 
398 REVERSIBLE CHEMICAL REACTIONS 
 
 If, however, iron filings are heated in a sealed bulb with 
 some water vapor, the hydrogen formed remains in the field 
 of action and it begins at once to reduce the oxide. As the 
 amount of hydrogen increases, the rate at which it reduces the 
 iron oxide increases, and finally a point is reached at which 
 the rate of reduction is just equal to the rate of oxidation 
 of iron. This is the equilibrium point for the reversible 
 
 reaction: 3 Fe + 4 H 2 O ^ Fe 3 O 4 + 4 H 2 . 
 
 If, on the other hand, we start with iron oxide and pure hy- 
 drogen in the bulb, the right-to-left reaction begins at once, 
 but as the water vapor accumulates, the rate of the left-to- 
 right reaction increases until equilibrium is reached from this 
 side. 
 
 The point of equilibrium for this, or any, reaction is ex- 
 actly the same from whichever side it is approached. 
 
 418. The Mass Law. The primary cause of all reactions 
 is chemical affinity, that is, the mysterious force of attrac- 
 tion which holds compounds together ; but, as we have just 
 seen, the direction of a reaction and its point of equilibrium 
 are strongly influenced by two other factors, namely, tempera- 
 ture and concentration of the reacting substances and re- 
 action products. 
 
 At a constant temperature, the course of many reactions 
 can thus be determined by fixing the concentration of the sub- 
 stances involved. The term " mass " is used a great deal in 
 this connection instead of the term concentration, and the 
 principle just stated is known as the mass law. It is a law of 
 the most far-reaching importance and to-day no efficient 
 chemist undertakes to carry through a chemical process 
 without studying it fully from the viewpoint of the mass 
 law. 
 
FORMATION OF PRECIPITATES 399 
 
 Some of the applications of the mass law in complex mix- 
 tures become very involved, but in its essence, the law is as 
 simple as the law of mass plays on a football field, that the 
 side which gets the most men and the strongest men into the 
 action succeeds in pushing the ball towards the opponents' 
 goal. 
 
 419. Formation of Precipitates. When solutions of two 
 salts are mixed together, there is oftentimes very little evi- 
 dence of reaction. For example, if a solution of potassium 
 chloride is poured into a solution of sodium nitrate, both 
 salts are ionized : 
 
 KC1 ^ K + + Cr ; NaN0 3 ^ Na + + NOT. 
 
 A glance at these formulas shows that reactions to form two 
 new salts, 
 
 K + + NOT -> KNO 3 ; Na + + Cl~ -> NaCl, 
 
 are possible, but these are both reversible reactions and the 
 two new salts have a strong tendency to remain in the ionized 
 condition (see page 307). Consequently, there is but very 
 little reaction. If, however, it were possible to remove one 
 of these new salts from the sphere of action as fast as it 
 formed, it could no longer enter the reverse reaction and we 
 should find the forward action prevailing. 
 
 When a salt is insoluble and falls out of the solution in the 
 form of a precipitate, it is effectively removed from the sphere 
 of action. Thus when potassium chloride and silver nitrate 
 solutions are mixed, the reaction, 
 
 Ag + + Cr -> AgCl, 
 
 becomes possible because silver chloride is extremely in- 
 soluble ; as fast as it is formed, it drops from the solution 
 
 B. AND W. CHEM. 26 
 
400 REVERSIBLE CHEMICAL REACTIONS 
 
 as a white precipitate. There being practically no silver 
 chloride left in the solution to dissociate again into the ions, 
 the reaction in this direction is lacking and consequently 
 the reaction in the direction of the formation of the salt be- 
 comes complete. 
 
 The foregoing is but one illustration of the general rule : 
 When ionized substances are mixed in solution, a reaction will 
 take place if any one of the possible products is insoluble. The 
 reaction ivill run the more nearly to completion the more insol- 
 uble the new compound is. 
 
 420. Formation of Volatile Products. In the preparation 
 of hydrochloric acid (page 129), concentrated sulphuric acid 
 is allowed to react with solid sodium chloride and the reac- 
 
 tlon 2 NaCl + H 2 S0 4 -> Xa 2 SO 4 + 2 HClf 
 
 takes place. Now the only reason that the reverse reaction 
 does not take place is that hydrogen chloride is a gas and is 
 not soluble in the concentrated sulphuric acid. It therefore 
 escapes from the sphere of action, and the reaction which re- 
 sults in its formation proceeds to completion. 
 
 It is also a general rule that whenever any product of a possi- 
 ble reaction is volatile and can escape from the sphere of action, 
 that reaction will take place. 
 
 That the direction of the above reaction is dependent 
 on the conditions which favor the escape of hydrogen chlo- 
 ride can be proved by observing the effect of altering the con- 
 ditions. Hydrogen chloride we know to be extremely soluble 
 in water ; therefore if it is formed by a reaction carried out 
 in a water solution, it will not escape from the sphere of ac- 
 tion. When sulphuric acid is added to a solution of sodium 
 chloride, no effect is noticed because the reaction comes to a 
 standstill almost immediately. It may even be shown that 
 
UNDISSOCIATED SUBSTANCES 401 
 
 the reaction can be forced in the opposite direction when the 
 reaction products are brought together in high concentration, 
 for if hydrogen chloride gas is passed into a nearly saturated 
 solution of sodium sulphate, a heavy precipitate of sodium 
 chloride is thrown down, 
 
 2 HC1 + Na 2 SO 4 -> 2 NaCl| + H 2 SO 4 . 
 
 421. Formation of Undissociated Substances. We have 
 already learned that the neutralization of an acid and a base 
 consists in the formation of un-ionized water from the hydro- 
 gen ions of the acid and the hydroxyl ions of the base. It 
 is a general rule that whenever different ionized substances 
 are brought together in solution, if any possible new combina- 
 tion of ions can yield a substance whose ability to ionize is 
 small, that substance will form. 
 
 The neutralization of a strong acid with a strong base is 
 a non-reversible reaction. For example, take the neutraliza- 
 tion of hydrochloric acid by sodium hydroxide. Both of 
 these substances exist mainly in the form of ions in dilute 
 solutions. When they are mixed, the H + and OH~ ions unite 
 completely in the formation of undissociated water : 
 
 H + Cr + Na + OH" -> H 2 O + Na + CT. 
 
 There is no tendency to make this reaction reverse, for the 
 only possible undissociated compound on either side of the 
 equation is water. 
 
 422. Neutralization of Weak Acids and Weak Bases. 
 Acetic acid is a good example of a weak acid, since in a mod- 
 erately dilute solution, it is only about one per cent ionized, 
 that is to say, one in every one hundred molecules is separated 
 into ions, H(C 2 H 3 O 2 ) ^ H + + (C 2 H 3 O 2 )-, whereas the other 
 ninety-nine are intact. Ammonium hydroxide is a base of 
 almost the same degree of ionization as acetic acid. 
 
402 REVERSIBLE CHEMICAL REACTIONS 
 
 Both this acid and this base display a slight electrical con- 
 ductivity, but only slight, for they cause the incandescent 
 filament to glow just visibly when they are tested separately 
 in the conductivity apparatus described on page 301. But 
 if the acid and base solutions just tested for conductivity 
 are poured together and the mixed solution is tested, it causes 
 the incandescent filament to glow with its full brilliancy, 
 thus showing a conductivity about equal to that of any fully 
 ionized salt. By merely mixing two solutions of weak con- 
 ductivity, we obtain one which conducts strongly. 
 
 But this apparent magic is easily explained according to 
 our knowledge of the equilibrium conditions of reversible 
 reactions. In the acetic acid solution, the few ions are in 
 equilibrium with the undissociated molecules according to 
 the reversible reaction 
 
 H(C 2 H 3 2 ) H + + (C 2 H 3 2 ) + , 
 
 and a like condition holds in the solution of ammonium 
 hydroxide, 
 
 
 4+ + OR- . 
 
 But when we mix the solutions, more H + and OH~ ions are 
 brought together than can exist in equilibrium with water 
 in the reversible reaction 
 
 H + + OH- ^ H 2 0. 
 
 Consequently, these ions disappear because they unite to 
 form water. But this destroys the equilibrium which existed 
 between the undissociated acid and its ions and between the 
 undissociated base and its ions. The acid and base dissociate 
 further to produce more Ii + and OH~ ions, respectively, in an 
 attempt to reestablish equilibrium, but equilibrium cannot 
 be established because the H + and OH~ ions are continuously 
 
A WEAK ACID AND A WEAK BASE 403 
 
 removed in the formation of water as fast as they are formed 
 by the ionization of the acid and base. 
 
 If equivalent amounts of the weak acid and weak base are 
 taken at the outset, they neutralize each other almost as 
 completely as do strong acids and bases, but the reaction is 
 more complicated. In addition to the formation of water 
 from the H + and OH~ ions, the progressive ionization of the 
 acid and base takes place. The negative ion of the acid 
 and the positive ion of the base thus formed remain as ions 
 in the solution as the highly ionized salt and it is these 
 new ions that account for the very great increase in conduc- 
 tivity. The whole course of the reaction may perhaps best 
 be shown by the following scheme : 
 
 H(C 2 H 3 2 ) ^ H + + (C 2 H 3 2 )- 
 NH 4 OH ^ OH' + NIV 
 
 I 
 H 2 O 
 
 NEUTRALIZATION OF A WEAK ACID AND A WEAK BASE 
 
 The two reactions written horizontally are ordinarily reversible 
 and by themselves tend far more strongly to run towards the left. 
 When, however, certain of their products are almost completely 
 withdrawn as fast as they are formed, as by the formation of water 
 in the vertically written reaction, the horizontal reactions are able 
 to run nearly to completion towards the right. The other products 
 formed in the horizontal reactions accumulate in the solution and 
 form the ionized and highly conducting salt, NH 4 + (C 2 H 3 2 )~. 
 
 423. Incompleteness of the Neutralization of Very Weak 
 Acids and Bases. When an acid or base is very weak, that is, 
 much weaker than acetic acid or ammonium hydroxide, its neu- 
 tralization is less complete but otherwise takes place in the 
 same manner. It dissociates progressively as fast as its dis- 
 sociation product, the H + or the OH~ ion, as the case may be, 
 
404 REVERSIBLE CHEMICAL REACTIONS 
 
 is removed through the formation of water. Although water 
 on the one side is the least dissociated of all the substances 
 concerned in the reaction, yet the acid or base on the other 
 side is very little dissociated. According to the rule above 
 stated that reactions tend to run in the direction in which 
 they will form un-ionized substances, we have two tendencies 
 pulling in opposite directions. Water being the least disso- 
 ciated, the whole reaction tends more strongly in the direc- 
 tion of neutralization. 
 
 Carbonic acid is a very weak acid. As its formula shows, 
 its molecules contain two acid hydrogens. One of these 
 hydrogens is given off far more easily than the other, but 
 the first one dissociates less easily than the hydrogen of acetic 
 acid. About one tenth of one per cent of the molecules of 
 H 2 CO 3 ionize into H + and HCO 3 ~ ions. When treated with 
 one mole of sodium hydroxide, carbonic acid reacts almost 
 completely in the direction of the arrows in the diagrammatic 
 scheme ^ H+ + HCQr 
 
 + Na + 
 
 I 
 H 2 
 
 REACTION OF CARBONIC ACID WITH ONE MOLE OF SODIUM 
 HYDROXIDE 
 
 Neutralization is practically complete. Negative bicarbonate 
 ions, HC0 3 ~, accumulate and, balanced by Na + ions, form the ionized 
 salt sodium bicarbonate, Na + HC0 3 ~. 
 
 The ion HCO 3 ~ itself acts asan acid, HCO 3 ~ ^ H + +CO 3 , 
 although to a far less degree than the original H 2 CO 3 ; and 
 if a second mole of sodium hydroxide is added, the reaction 
 represented in the following scheme takes place, although it 
 does not progress to completion : 
 
HYDROLYSIS 405 
 
 Na + HC0 3 - ^ Na + + H + + CO 
 
 Na + 
 
 H 2 O 
 
 REVERSIBLE REACTION OF SODIUM BICARBONATE WITH 
 SODIUM HYDROXIDE 
 
 Neutralization is only partial with an acid so weak as HC0 3 ~. 
 To indicate this fact, the arrows are made to point in both directions. 
 
 424. Hydrolysis. Hydrolysis is the exact reverse of 
 neutralization. When an acid and a base are brought to- 
 gether, neutralization takes place to a greater or less extent, 
 water and a dissociated salt being formed ; but when a pure 
 salt is treated with water, hydrolysis takes place to some ex- 
 tent if either the acid or the base, or if both, are very weak. 
 
 Na + + Na + + CQT' 
 H 2 O ^ OH~ + H + 
 
 It 
 HCOs~ 
 
 HYDROLYSIS OF SODIUM CARBONATE 
 
 Water ionizes to a very small extent into H+ and OH~ ions. The 
 H + ions are continuously removed by the COs ions to form HCO 3 ~ 
 and so the water is allowed to ionize continuously. The OH~ ions 
 accumulate and impart the alkaline character to the solution. Be- 
 fore the hydrolysis has progressed far, it is brought to a standstill 
 by the opposed reaction of neutralization, as indicated by the re- 
 versed arrows. 
 
 Thus, for example, if we bring together sodium carbonate and 
 water, we observe hydrolysis, for the resulting solution is 
 found to be alkaline to the taste and to turn red litmus blue. 
 On the other hand, a salt of a strong acid and a strong 
 base, for example sodium chloride, is neither alkaline nor 
 acid. Sodium carbonate dissociates at once in water, 
 
406 REVERSIBLE CHEMICAL REACTIONS 
 
 Na 2 CO 3 -> 2 Na + -f CO 3 ~ ", but the CO 3 ion cannot exist 
 by the side of even the few H + ions coming from water 
 without reacting to form HCO 3 ~. Removal of even a part 
 of the few ions which water normally yields allows water 
 to ionize further, and since the new H + ions combine further 
 with CCV" " ions, the reaction of hydrolysis progresses in 
 this manner until it is overcome by the opposing reaction 
 of neutralization. 
 
 425. Alkalinity of Salts of Very Weak Acids. Many salts 
 of weak acids and strong bases are of great service on account 
 of their mildly alkaline reaction. Sodium carbonate is com- 
 monly known as washing soda and its usefulness in cleansing 
 is determined by its mild alkalinity. Hydroxyl ions have the 
 property of causing grease and dirt to emulsify, that is, to 
 separate into innumerable little globules, so that they are 
 readily floated off with water. 
 
 Soap is a sodium or potassium salt of the weak organic 
 acids which are constituents of fats. Hydrolysis of soap 
 plays an important part in the cleaning action, although it 
 is true that soap is a much more effective cleaning agent 
 than solutions of sodium hydroxide or of sodium carbonate 
 of an equal degree of alkalinity. 
 
 Borax is the sodium salt of the weak boric acid, and borax 
 is often used to give a mildly alkaline reaction. 
 
 426. Acidity of Salts of Very Weak Bases. Salts of very 
 weak bases and strong acids show acid characteristics when 
 dissolved in water. For example, aluminium sulphate, 
 A1 2 (804)3, is the salt of the weak base A1(OH) 3 and the strong 
 acid H 2 SO 4 . Its hydrolysis produces equivalent amounts of 
 the weak and inactive base and the strong and active acid 
 
 A1 2 (SO 4 ) 3 + 6 H 2 O ^ 2 A1(OH) 3 + 3 H 2 SO 4 . 
 
EXTENT OF HYDROLYSIS 407 
 
 Hence the solution turns blue litmus red. Alum, which 
 contains aluminium sulphate, is sometimes used in baking 
 powder on account of its slightly acid character. 
 
 The hydroxides of the heavy metals are all very weak 
 bases. Hence the salts are inclined to hydrolyze. Thus 
 solutions of such salts as ferric chloride, FeCl 3 ; ferric sul- 
 phate, Fe 2 (SO 4 ) 3 ; ferric nitrate, Fe(NO 3 ) 3 ; tin chloride, 
 SnCl 2 ; mercuric nitrate, Hg(NO 3 ) 2 , all possess an acid char- 
 acter and are able to turn blue litmus red. 
 
 427. Extent of Hydrolysis. The hydrolysis of a salt 
 always produces equivalent quantities of acid and base. Hy- 
 drolysis cannot occur at all if the acid and base are both 
 moderately strong, but if one is weak, its weakness deter- 
 mines the degree of hydrolysis. Since the weak one is un- 
 dissociated, it is itself inactive and the other imparts its acid 
 or alkaline character to the whole solution. 
 
 If the acid and base are both very weak, the hydrolysis is 
 all the more complete. For example, aluminium sulphide 
 is the salt of the weak base A1(OH) 3 , and the weak acid H 2 S. 
 It can be made in the dry way by heating together aluminium 
 and sulphur, 2 Al + 3 S -+ A1 2 S 3 . 
 
 When it is treated with water, hydrolysis takes place, 
 A1 2 S 3 +6 H 2 O -+ 3 H 2 S + 2 A1(OH) 3 , 
 
 with a vigorous effervescence due to the escape of hydrogen 
 sulphide and the formation of a flocculent insoluble residue 
 of aluminium hydroxide. Hydrolysis is' complete in this case, 
 but no marked alkaline or acid effect is noted because both 
 the acid and the base are very weak. 
 
 The useful hydrolyzable salts are all composed of either 
 a weak acid and a strong base or of a strong acid and a weak 
 base. The extent of the hydrolysis is rarely larger than a 
 
408 REVERSIBLE CHEMICAL REACTIONS 
 
 few per cent of the salt, although it varies, of course, ac- 
 cording to the weakness of the acid or base. For example, a 
 solution of sodium carbonate is of about the same degree of 
 alkalinity as a solution of ammonium hydroxide of equivalent 
 concentration, and we have already found that ammonium 
 hydroxide is only about one per cent ionized. 
 
 428. Uses of Hydrolyzable Salts. When it is desired to 
 produce for practical purposes a solution of mild alkalinity 
 or acidity, the use of hydrolyzable salts has very great ad- 
 vantages over the use of very small amounts of strong bases 
 or acids. For example, suppose the housewife were to use 
 sodium hydroxide to scrub the kitchen floor. Knowing little 
 of chemistry, she might take too much, and the skin would be 
 taken from her hands and the floor surface would be injured. 
 Washing soda gives only a very small per cent of sodium 
 hydroxide, and she cannot take enough to give more than the 
 desirable mild alkalinity. 
 
 Suppose, however, that she was careful to take just the 
 small amount of sodium hydroxide necessary to give the 
 proper alkalinity. A little acid on the floor, as for example 
 from crushed fruit or spilled vinegar, would quickly neutralize 
 the small amount of base and destroy the alkalinity. On the 
 other hand, if she used washing soda, the acid would be neu- 
 tralized, but more of the salt would at once hydrolyzeto main- 
 tain the alkalinity. 
 
 A similar condition governs the use of acid substances in 
 baking powder. Sulphuric acid would be out of the question, 
 but alum, which hydrolyzes to give a little sulphuric acid, is 
 useful. As fast as the sulphuric acid so formed is used up in 
 reacting with the sodium bicarbonate of the baking powder, 
 the alum hydrolyzes further until finally it has yielded its 
 entire store of sulphuric acid. 
 
HYDROLYZABLE SALTS 409 
 
 Another important use of a hydrolyzable salt is in the 
 settling of muddy water for municipal use. Sedimenta- 
 tion alone would be too slow a process, although it would 
 help greatly. Aluminium sulphate is therefore added to 
 the muddy water, whereupon hydrolysis results, yielding a 
 precipitate of gelatinous aluminium hydroxide and sulphuric 
 acid. The gelatinous aluminium hydroxide in settling car- 
 ries down most of the suspended material with it, leaving 
 clear water. The sulphuric acid which also results reacts 
 with calcium bicarbonate (present in most water supplies) 
 and forms calcium sulphate, which is harmless, and carbonic 
 acid, which decomposes into water and carbon dioxide. 
 
 429. Importance in Living Organisms. The delicate 
 regulation of acid or alkaline qualities that is possible with 
 hydrolyzable salts is not only made use of practically in the 
 household and in the chemical factory, but it occurs exten- 
 sively in nature. It is essential to the life processes that 
 the blood of men and animals and the juices of plants be 
 maintained at the exact degree of alkalinity or acidity re- 
 quired by the organism, and the regulation is "usually effected 
 by the presence of hydrolyzable salts. The human blood 
 is maintained at almost the exact neutral point by means 
 of a mixture of several hydrolyzable salts, important among 
 which is sodium phosphate. If the blood varies appreciably 
 to either side of this point, death will almost immediately 
 ensue. These salts constitute a reservoir of neutrality. 
 Suppose they were not present and that 4 a person took lemon 
 juice (citric acid) into his stomach. This would pass into 
 the blood and rapidly increase its acidity and cause death. 
 But with sodium phosphate present, the citric acid is neutral- 
 ized by the base progressively set free by hydrolysis. If 
 considerable alkali is taken into the stomach, the blood does 
 
410 
 
 REVERSIBLE CHEMICAL REACTIONS 
 
 not become alkaline, but its neutrality is maintained by a 
 similar process. 
 
 430. In the following tables, some of the important hydro- 
 lyzable salts are summarized : 
 
 SALT 
 
 FORMULA 
 OF SALT 
 
 WEAK ACID 
 
 STRONG 
 BASE 
 
 REACTION OF 
 SALT SOLUTION 
 
 Washing Soda 
 
 Na 2 CO 3 
 
 HCO S - 
 
 NaOH 
 
 Distinctly al- 
 
 
 
 
 
 kaline 
 
 Baking Soda 
 
 NaHCO 3 
 
 H 2 COs 
 
 NaOH 
 
 Barely alka- 
 
 
 
 
 
 line 
 
 Borax 
 
 Na 2 B 4 O 7 
 
 H 2 B 4 07 
 
 NaOH 
 
 Mildly alka- 
 
 
 
 
 
 line 
 
 Soap 
 
 Na(Ci 8 H 35 O 2 )i 
 
 H(Ci ? H36O 2 ) 
 
 NaOH 
 
 Mildly alka- 
 
 
 
 
 
 line 
 
 ( 
 
 Na 3 P04 
 
 HPO 4 
 
 NaOH 
 
 Strongly alka- 
 
 Sodium Phos-l 
 
 
 
 
 line 
 
 phate 
 
 Na 2 HPO 4 
 
 H 2 PO 4 - 
 
 NaOH 
 
 Mildly alkaline 
 
 I 
 
 NaH 2 PO 4 
 
 H(H 2 PO 4 ) 
 
 NaOH 2 
 
 Mildly acid 
 
 SALT 
 
 oF R S M A U LT A STRONG ACID 
 
 WEAK 
 BASE 
 
 REACTION OF 
 SALT SOLUTION 
 
 Alum 
 
 K 2 SO 4 A1 2 (SO 4 ) 3 
 
 H 2 S0 4 
 
 Al(OH), 
 
 Mildly acid 
 
 
 24H 2 O 
 
 
 
 
 Aluminium sul- 
 
 
 
 
 
 phate 
 
 A1 2 (SO 4 ) 3 
 
 H 2 SO 4 
 
 Al(OH)i 
 
 Mildly acid 
 
 Sal Ammoniac 
 
 NH 4 C1 
 
 HC1 
 
 NH 4 OH 
 
 Neutral to litmus 
 
 Ferric Chloride 
 
 FeCh 
 
 HC1 
 
 Fe(OH) 3 
 
 Acid 
 
 Gold Chloride 
 
 AuCl 3 
 
 HC1 
 
 Au(OH) 3 
 
 Strongly acid 
 
 SUMMARY 
 
 Many chemical reactions are practically complete under ordinary 
 conditions, that is, they proceed entirely in one direction until 
 either one (or all) of the reacting substances is used up. 
 
 Chemical affinity is the force which causes substances to combine. 
 This force cannot be altered by changing exterior conditions, 
 
 1 This is the formula of sodium stearate, which is one of the many 
 similar salts which constitute soaps. 
 
 2 Insufficient to neutralize acid. 
 
SUMMARY 411 
 
 but the exterior conditions may produce forces which can 
 overcome this chemical affinity. Thus reactions can often 
 be made to run in the opposite direction by the application 
 of intense heat or of an electric current. 
 
 Effect of Mass. A number of reactions are capable of reversal even 
 under ordinary conditions. Such reactions are governed 
 largely by the mass of the reacting substances. Increase in the 
 mass of the reacting materials causes the reaction to proceed 
 farther. Increase in the mass of the products of the reaction 
 causes the change to proceed in the reverse direction. 
 
 Chemical Equilibrium. A reversible reaction seeks to reach a state 
 of chemical equilibrium which is a condition of apparent rest. 
 The substances on one side of the reaction equation exist in the 
 presence of the substances on the other side. Although at 
 ( the point of equilibrium there is no apparent change taking 
 place, still it is believed that both of the opposed reactions are 
 taking place, only with equal velocities so that the total of 
 the resulting change is zero. 
 
 Removal of Products of Reaction. If a substance involved in a re- 
 versible reaction is continually removed so that the reaction 
 cannot reach a condition of equilibrium, the reaction may 
 thus be made complete in this direction. 
 
 Substances may be removed from the sphere of action by precipi- 
 tation or by volatilization. Un-ionized substances are practi- 
 cally inactive so that when they are formed the effect is as if 
 they were withdrawn from the sphere of action. Hence the 
 general rule : Whenever a reaction in solution is possible which 
 can produce a precipitate, a volatile product, or an undis- 
 sociated substance, that reaction will take place. 
 
 Neutralization and Hydrolysis. Neutralization is a reaction in 
 which the undissociated substance, water, is formed. Hy- 
 drolysis is the exact reverse of neutralization. Hydrolysis 
 can take place by the action of water with the salt of a very 
 weak acid or a very weak base. 
 
 Some of the hydrolyzable salts are of very great usefulness on 
 account of the mild degree of akalinity or acidity of their 
 solutions. 
 
412 REVERSIBLE CHEMICAL REACTIONS 
 
 Questions 
 
 1. Give several reactions that you have already studied which 
 are capable of being reversed. 
 
 2. Tell of one means by which reactions are made to reverse 
 themselves. 
 
 3. What is meant by the term equilibrium? 
 
 4. Give three methods of causing a reaction that is reversible 
 in its nature to proceed to completion in one direction. 
 
 5. What is meant by hydrolysis ? 
 
 6. Why does sodium carbonate, which is salt, have an alkaline 
 reaction in water solution ? 
 
 7. Name three substances the principal uses of which depend 
 upon their ability to hydrolyze. 
 
 8. Apply the idea of equilibrium to the reversible reaction 
 NaCl ^ Na + + Cl~, in a solution of common salt. How would 
 this equilibrium be affected (a) by adding a solution of silver nitrate, 
 (6) by evaporating off the water? 
 
 9. Does guncotton exist in a state of chemical equilibrium? 
 What would you do to make guncotton come to a state of equilib- 
 rium ? What is the reaction and is it a reversible one ? 
 
CHAPTER XXXIII 
 CHEMICAL REACTIONS AND ENERGY TRANSFORMATIONS 
 
 IN the first chapter of this book it was stated that one of 
 the most noticeable characteristics of chemical changes is the 
 evolution of heat and often of light. Not all changes, it is 
 true, develop as much heat as the oxidation of charcoal ; in 
 fact, some reactions absorb heat ; it is, however, true with- 
 out exception that all reactions are accompanied by some 
 kind of an energy change. 
 
 431. Different Forms of Energy. Energy manifests 
 itself in many forms, of which heat is only one. The heat 
 produced by a coal fire can be made to run a steam engine in 
 which a part of the heat is transformed into mechanical en- 
 ergy. This in turn can be made to rotate the coils of a dy- 
 namo and produce electric energy. The later can be turned 
 back again into mechanical energy by means of an electric 
 motor, or it may be converted into heat in an electric stove, 
 or into heat and light in an incandescent lamp, or into chemi- 
 cal energy by being made to decompose some chemical com- 
 pound. 
 
 432. Chemical Energy. When an electric current is forced 
 to pass through acidulated water, the latter is decomposed 
 into hydrogen and oxygen. The energy possessed by these 
 two elements is thereby increased by an amount equal to the 
 electric energy expended in decomposing the water. 
 
 It is true that hydrogen and oxygen remain quiescent 
 at ordinary temperature for an indefinitely long time. This 
 
 413 
 
414 ENERGY TRANSFORMATIONS 
 
 energy may be compared to the' energy of water in a reservoir 
 in a high mountain valley. The water is quiescent so long as 
 it remains in the reservoir; but if the gate is opened which 
 allows it to flow downhill to a water wheel, its stored-up 
 energy can do mechanical work. In a similar way, hydrogen 
 and oxygen when uncombined possess stored-up energy 
 which may be set free by starting them in reaction with a tiny 
 flame or a spark. If a mixture of the two is exploded, the 
 expansion can be made to do mechanical work, or if the gases 
 are slowly fed to each other and burned, the heat of their 
 union can be used in heating a steam boiler. 
 
 433. Exothermic Reactions. A reaction which, like the 
 combination of oxygen and hydrogen, gives off heat as it pro- 
 ceeds, is known as an exothermic reaction (meaning to give 
 off heat). In general, all reactions which proceed of them- 
 selves when once started are exothermic, and the amount of 
 heat or other form of energy given off is a measure of the 
 tendency which the reaction had to take place. 
 
 It is fortunate that strongly exothermic reactions such 
 as the burning of coal and wood do not commence sponta- 
 neously. The energy stored up in wood and coal, except for 
 slow decay, which can be likened to the leakage of energy, 
 stays stored up waiting for the hand of man to call it into use- 
 ful action by the application of the kindling flame. 
 
 Most chemical reactions that are carried out in the labora- 
 tory are exothermic, although many yield so little heat or 
 yield it so slowly under the conditions of the experiment 
 that its escape is scarcely noticeable. For example, when 
 substances in solution enter into reaction, the heat produced 
 cannot be expected to produce incandescence ; the water 
 may be warmed in some cases so that it boils vigorously, but 
 more often it will be warmed only a few degrees. 
 
ALUMINOTHERMY 
 
 415 
 
 When pure, dry substances react and the heat of the 
 reaction all goes to warming a limited amount of solid or 
 molten material, the temperature may rise very greatly. 
 Thus a mixture of zinc filings and powdered sulphur rises to 
 incandescence when a reaction is started. 
 
 434. Aluminothermy. A very high temperature can 
 be obtained by the reaction of granulated aluminium with 
 iron oxide : 
 
 2M+ 
 
 + g 
 
 The mixture of iron oxide and aluminium is placed in a refrac- 
 
 tory crucible and a little fuse powder is placed on top. The 
 
 fuse powder when 
 
 ignited produces an 
 
 intense local heat 
 
 and this starts the 
 
 reaction of the main 
 
 mixture. A refer- 
 
 ence to the potential 
 
 series of the metals 
 
 (page 329) shows 
 
 that aluminium 
 
 stands high in the 
 
 series and therefore 
 
 that it must be a FlG ' 74> pre P arin 6 Molds about Rail Joints for 
 
 welding with Thermit. 
 
 very active metal. 
 
 It takes oxygen away from the iron oxide, and the heat of 
 formation of the aluminium oxide so far exceeds the heat 
 necessary to decompose the iron oxide that a large excess is 
 left to heat the residual iron and the aluminium oxide. 
 This heat is all confined within the crucible, for no gaseous 
 products are formed to carry away part of it. The iron 
 and aluminium oxide are thus not only melted, but are raised 
 
 B. AND W. CHEM. - 27 
 
416 
 
 ENERGY TRANSFORMATIONS 
 
 to a temperature about 3000 C. approaching that of 
 the electric arc. 
 
 This process represents the highest temperature which can 
 be obtained for industrial purposes by means of a chemical 
 
 reaction. A mixture 
 of iron oxide and 
 aluminium is a com- 
 mercial product and 
 is sold under the 
 name of Thermit. 
 One of the impor- 
 tant applications of 
 Thermit is in the 
 welding together of 
 iron and steel parts 
 as, for example, the 
 parts of a broken 
 propeller shaft of a 
 steam vessel and the 
 rails of the car track. The crucible is so arranged that the 
 molten iron which sinks to the bottom can be tapped off 
 and run into a mold placed around the joint to be welded. 
 The iron is so hot that it melts the surfaces of the broken 
 ends, which thus become welded to a perfectly solid joint. 
 In making welds in large pieces, it is a common practice to 
 preheat the pieces to be welded with a blast flame. This 
 prevents conduction and loss of so much of the heat con- 
 tained in the welding steel which comes from the crucibles 
 and so insures a more perfect weld. 
 
 435. Familiar Exothermic Processes. The most exten- 
 sive industrial chemical reaction is the combustion of fuel 
 for the production of heat, light, and power, and in this case 
 
 FIG. 75. Crucibles containing Thermit in Place 
 over Molds. The rubber hose shown delivers a 
 blast for the preheating process. 
 
EXOTHERMIC AND ENDOTHERMIC COMPOUNDS 417 
 
 the energy set free is all that is sought from the reaction ; 
 the material products are of no value, and the residues, such 
 as ashes and smoke, are a source of annoyance and expense. 
 
 Most of the chemical reactions in which it is the material 
 products that are sought are also of the exothermic type. 
 For example, in the manufacture of sulphuric acid, the 
 oxidation of the sulphur yields heat at both stages (Chapter 
 XXIX) and the union of sulphur trioxide with water also 
 yields heat. 
 
 The reactions that take place in animal bodies are also 
 exothermic and serve to warm and move the body, while the 
 material products of the reaction are waste and have to be 
 eliminated. The food, which is the fuel with which the body 
 is fed, is not all burned at once, but a large part of it is slightly 
 altered chemically without much loss of energy and stored 
 up as muscular tissue and fat. In this form it remains tem- 
 porarily, but finally it suffers combustion like the rest of the 
 material assimilated by the body. 
 
 436. Exothermic and Endothermic Compounds. If heat 
 or other form of energy is evolved by the reaction in which a 
 compound is formed by the combination of its constituents, 
 the compound is said to be exothermic. Exothermic com- 
 pounds, such as water, zinc sulphide, aluminium oxide, are 
 stable, that is to say, they never decompose of themselves and 
 can only be decomposed by the expenditure of energy in some 
 form, such as electrical or chemical. 
 
 When heat or other form of energy is absorbed in the forma- 
 tion of a compound from its constituents, that compound is 
 said to be endothermic (meaning heat is absorbed). Nitro- 
 glycerine is an example of an endothermic compound. In 
 general, such compounds are not stable and they tend to 
 decompose, thereby giving off energy ; in fact many of them 
 
418 ENERGY TRANSFORMATIONS 
 
 decompose explosively when the reaction gathers sufficient 
 headway. The energy given off when nitro-glycerine decom- 
 poses is used in blasting, the blasting material dynamite 
 is infusorial earth or other porous substance impregnated 
 with nitroglycerine. 
 
 437. Photosynthesis. We see on every hand examples 
 of exothermic chemical change, the burning of fuels, the decay 
 of wood, the consumption of foods, and the majority of the 
 thousands of chemical reactions employed in the manufactur- 
 ing industries. In all of these changes, chemical energy is 
 converted into heat. The thought naturally arises, will not 
 all of the chemical energy become exhausted, or, in other 
 words, will not all of the materials which can react exother- 
 mically become used up ? It will be recalled, however, from 
 the chapters on carbon and particularly from the section on 
 the carbon cycle in nature, that all fuels and foods contain 
 carbon as one of their chief constituents. The carbon dioxide 
 formed by the combustion of these materials does not remain 
 long in the atmosphere, but reacts with water in the green 
 leaves of plants, whereby sugars are built up and oxygen is 
 released again to the atmosphere. The sugar so formed may 
 be changed in the plant into starch, cellulose, or other sugars, 
 and ultimately the wood may be converted into coal, so the 
 sugar formed in the green leaves is the parent substance of all 
 foods and fuels. The combustion of sugar, or any food or 
 fuel, to form carbon dioxide and water is a strongly exothermic 
 reaction. Consequently, carbon dioxide and water cannot of 
 themselves, nor even with the aid of catalyzers, react 
 to form sugar and oxygen. Energy must be applied to compel 
 this change, and this energy is supplied by sunlight. The 
 chlorophyll of the green leaves does not cause this chemical 
 change, but its function is to direct the action of the light 
 
THE CARBON CYCLE 419 
 
 energy, just as the function of a harness is to make the power 
 of a horse available, or the function of a water wheel and dy- 
 namo is to convert the energy of falling water into usable 
 electric energy. 
 
 Thus the energy of the sun is the great source of the chemi- 
 cal energy stored up in foods and fuels. The building up 
 process is called photosynthesis, meaning the putting to- 
 gether through the agency of light. 
 
 438. Energy Changes and the Carbon Cycle. From what 
 has just been said, it is seen that not all of the sun's energy 
 goes at once to simply warm the surface of the earth. Some 
 of it first traverses a circular path, entering, so to speak, into 
 single revolutions of the carbon cycle. On the one side of 
 the cycle, the green plants, by using water and carbon dioxide 
 as materials, and sunlight as energy, are storing up chemical 
 energy by means of endo thermic reactions. On the other 
 side, man is supplying his needs, both external and internal, 
 and all animals, and also bacteria and fungous plants, which 
 live upon other plants or upon animal tissues, all these 
 are bringing about exothermic reactions by which chemical 
 energy is released, ultimately becoming heat, and the simpler 
 substances, water and carbon dioxide, are once more formed 
 as a result of the combustion or decay that takes place. 
 
 The material elements of the cycle are ready to go through 
 another revolution, but the energy necessary to carry on the 
 cycle must again be obtained from the sunlight. The form 
 in which energy is given off at the end of each cycle cannot be 
 again utilized by the green plants. 
 
 It is a law of physical science that no energy can be lost, 
 and this is as fundamental as is the law that matter cannot 
 be destroyed. All forms of energy tend, however, to change 
 into heat. Heat energy, where there are differences in tern- 
 
420 ENERGY TRANSFORMATIONS 
 
 perature (intensity), can be partly converted into other forms, 
 as for example by the steam engine, but uniformly distributed 
 heat cannot be converted into useful forms of energy. Thus 
 large bodies of water contain enormous quantities of uni- 
 formly distributed heat, but this form of energy cannot be 
 made to propel vessels. The earth is all the time losing en- 
 ergy by the radiation of heat into space, and this loss is prob- 
 ably a trifle greater than the gain from the energy received 
 from the sun. 
 
 439. Artificial Preparation of Endothermic Substances. 
 As already stated, reactions naturally tend to proceed in the 
 direction in which energy is evolved, and outside of photo- 
 synthesis, comparatively few endothermic processes are ob- 
 served in nature. Yet it is possible by bringing forces into 
 play in the right manner to cause artificially the formation 
 of endothermic substances, and man's ingenuity has devised 
 many ways in which to manufacture useful compounds of 
 this type. 
 
 Nitric oxide, NO, is strongly endothermic. When it is 
 made from atmospheric oxygen and nitrogen by the electrical 
 method (page 71), its energy is derived from the heat of the 
 electric spark. Nitric oxide is of importance mainly from the 
 fact that nitric acid can be made from it. Nitric oxide com- 
 bines with oxygen and water by an exothermic process one 
 which therefore takes place without further application of 
 energy to form nitric acid. 
 
 Nitroglycerin. From nitric acid are derived practically 
 all of the explosive substances in commercial use. Typical 
 of these explosives is nitroglycerin, which is made from nitric 
 acid and glycerol, according to the following reaction : 
 
 C 8 H 6 (OH) 3 + 3 HN0 3 -^ C 3 H 5 (N0 3 )3 + 3 H 2 O. 
 
ENDOTHERMIC COMPOUNDS 421 
 
 One of the products of this reaction is the highly exothermic 
 substance water, and the energy liberated by its formation is 
 in large part added to the energy already possessed by the 
 nitric acid and the glycerol in building up the energy con- 
 tent of the nitroglycerin. Furthermore, concentrated sul- 
 phuric acid must be added to the reaction mixture (see 
 manufacture of guncotton, page 370) in order to carry 
 forward the reaction. Water and sulphuric acid mix with 
 the evolution of heat, and, although we do not write any 
 definite chemical equation for this combination, still it is ob- 
 viously a strong exothermic process. Its energy is likewise 
 available for the building up of the energy of the nitro- 
 glycerin. 
 
 Calcium carbide is an endothermic compound, and it is 
 formed in the electric furnace according to the reaction : 
 
 CaO + 3 C -> CO + CaC 2 . 
 
 The formation of carbon monoxide is exothermic, and the 
 energy thus liberated, as well as that of the intense heat of the 
 furnace, is available to add to the energy already possessed by 
 the calcium and carbon. 
 
 Acetylene is made by the action of water on calcium car- 
 
 CaC 2 + 2 H 2 -> Ca(OH) 2 + C 2 H 2 . 
 
 Calcium hydroxide is an exothermic substance and its forma- 
 tion aids in the formation of the highly endothermic acetylene. 
 Acetylene is so highly endothermic that "it is dangerously ex- 
 plosive even when unmixed with air. It can ordinarily be 
 handled and burned with a fair degree of safety; but when 
 once its decomposition is violently started, it continues with 
 great violence. The great amount of heat liberated by its 
 decomposition causes a sudden and violent expansion and it is 
 
422 ENERGY TRANSFORMATIONS 
 
 this that does the damage. One reads occasionally of serious 
 explosions occurring in acetylene factories. 
 
 The endothermic character of acetylene adds to its value 
 as a fuel, for not only is the heat of formation of carbon 
 dioxide and water yielded by its combustion, but added to this 
 is its own very considerable heat of decomposition. The 
 acetylene flame is, therefore, much hotter than the ordinary 
 gas flame and on that account, as well as because it contains 
 more luminous carbon particles (see page 275), it is far more 
 luminous. The oxyacetylene flame is much used in place 
 of the oxyhydrogen flame (see page 116) on account of the 
 superior degree of heat it produces. 
 
 Ozone is a more active form of oxygen because it is pos- 
 sessed of a higher energy content. In the reaction by which 
 it is formed from ordinary oxygen, 3 O 2 > 2 O 3 , energy is 
 absorbed from the electric impulses which constitute the so- 
 called silent electrical discharge. 
 
 The formation of hydrogen peroxide from water and oxygen 
 involves the acquisition of energy and it is this energy which 
 accounts for the activity of hydrogen peroxide. Dilute 
 solutions of hydrogen peroxide are not dangerous but the pure 
 substance is highly explosive. 
 
 440. Theory of Explosions. Whether an explosion takes 
 place from the union of two substances, as, for example, 
 hydrogen and oxygen, or from the decomposition of a sub- 
 stance like nitroglycerin or acetylene, the theory is the same. 
 The explosive reaction is an exothermic one. So long as the 
 temperature is low and no shock is given, the reaction does not 
 acquire any headway ; but when it once commences to a con- 
 siderable extent, its own progress furnishes heat which raises 
 the temperature. The rise in temperature promotes the 
 speed of the reaction itself ; thus more heat is furnished and 
 
THE STORAGE BATTERY 423 
 
 so on, and in an inconceivably short space of time the reaction 
 is finished. 
 
 Some substances explode more easily than others; nitro- 
 glycerin goes off with extreme ease and is one of the most 
 dangerous explosives to handle. Guncotton is far safer, 
 and, in fact, it can usually be burned in the open air without 
 exploding. Yet, when it is exploded by detonation, its power 
 is not much inferior to that of nitroglycerin. Acetylene can be 
 burned with safety as an illuminant, yet when it is detonated, 
 it is an explosive of a good deal of power. 
 
 441. The Storage Battery is an arrangement of electro- 
 chemical cells in which electrical energy can be converted 
 into chemical energy by causing an endothermic reaction to 
 take place. When charged, the battery is ready to give back 
 all the energy it received. The chemical reaction takes 
 place in the reverse direction, and in so doing it causes an 
 amount of electricity, equal in amount and opposite in direc- 
 tion to the charging current, to flow. The reversible reaction 
 which takes place in the usual type of lead storage battery is 
 
 2 PbSO 4 + 2 H 2 O ^ Pb + PbO 2 + 2 H 2 SO 4 . 
 The reversible reaction in the Edison storage battery is 
 substantially as follows : 
 
 Fe(OH) 2 + 2 Ni(OH) 2 ^ Fe + Ni 2 O 3 + 3 H 2 O. 
 
 SUMMARY 
 
 Exothermic reactions are accompanied by an evolution of energy 
 so that the energy content of the product, or products, is less 
 than that of the reacting substances. The energy released 
 is most commonly in the form of heat, but it may be in some 
 other form, as, for example, electrical energy or light. Most 
 reactions that take place in nature and the majority of those 
 that are carried out in the laboratory and in manufacturing 
 processes are of the exothermic type. 
 
424 ENERGY TRANSFORMATIONS 
 
 Endothermic reactions are those in which the energy content of the 
 products is greater than that of the reacting substances. Very 
 important endothermic reactions take place in the green 
 leaves of plants and some of the energy of sunlight is thereby 
 converted into stored-up chemical energy. The material 
 products which are stored up in the plants are carbohydrates, 
 and the process is called photosynthesis. 
 
 The chemical energy continually being stored up by plants 
 in forming carbohydrates and oxygen from carbon dioxide and 
 water is continually being used up in satisfying the wants of 
 men and animals, and in very large amount being wasted by 
 decay and useless fires. 
 
 Exothermic compounds are stable, whereas endothermic com- 
 pounds are unstable and many of them are explosive. 
 
 Endothermic compounds are made artificially, sometimes by uti- 
 lizing electric energy, sometimes heat energy, and sometimes 
 the energy liberated in the formation of exothermic compounds. 
 
 Questions 
 
 1. Cite several exothermic reactions which are carried out solely 
 for the heat produced and in which the material products are 
 merely waste. 
 
 2. Cite exothermic processes which yield energy as an electric 
 current. 
 
 3. How do chemical processes store up the sun's energy? 
 
 4. Name several explosives in which the power is developed by 
 the decomposition of an endothermic substance. 
 
 5. Describe explosive mixtures in which the power is developed 
 through the formation of an exothermic compound. 
 
 6. To which of the sciences does the study of energy naturally 
 belong? Why is it impossible to study any one science, such as 
 chemistry, without overlapping into the other sciences? 
 
 7. Why is a knowledge of chemistry fundamental in the under- 
 standing of the sciences of physiology and geology? 
 
APPENDIX 
 
 I. PRESSURE OF SATURATED WATER VAPOR 
 
 Temperatures in degrees centigrade. Pressures in millimeters of 
 
 mercury 
 
 TEMP. 
 
 PKESS. 
 
 TEMP. 
 
 PRESS. 
 
 TEMP. 
 
 PRESS. 
 
 
 
 4.6 
 
 11 
 
 9.8 
 
 22 
 
 19.7 
 
 1 
 
 4.9 
 
 12 
 
 10.5 
 
 23 
 
 20.9 
 
 2 
 
 5.3 
 
 13 
 
 11.2 
 
 24 
 
 22.2 
 
 3 
 
 5.7 
 
 14 
 
 11.9 
 
 25 
 
 23.6 
 
 4 
 
 6.1 
 
 15 
 
 12.7 
 
 26 
 
 25.0 
 
 5 
 
 6.5 
 
 16 
 
 13.5 
 
 27 
 
 26.5 
 
 6 
 
 7.0 
 
 17 
 
 14.4 
 
 28 
 
 28.1 
 
 7 
 
 7.5 
 
 18 
 
 15.4 
 
 . 29 
 
 29.8 
 
 8 
 
 8.0 
 
 19 
 
 16.4 
 
 30 
 
 31.6 
 
 9 
 
 8.6 
 
 20 
 
 17.4 
 
 50 
 
 92.0 
 
 10 
 
 9.2 
 
 21 
 
 18.5 
 
 100 
 
 760.0 
 
 II. CORRECTION OF GAS VOLUMES FOR AQUEOUS 
 
 VAPOR 
 
 When a gas is saturated with water vapor, the volume 
 which it would occupy dry may be calculated with the aid of 
 the above table and the following two rules. 
 
 In a mixture of two or more gases each gas exerts its own 
 pressure independently of all the other gases present, and the 
 total pressure is equal to the sum of tlie pressures which each 
 one would exert if it were the only gas filling the space. 
 
 The amount of water which is able to evaporate into a defi- 
 nite space depends solely on the temperature and is independent 
 of the quantity and kind of other gas which already fills the 
 space. 
 
 425 
 
426 APPENDIX 
 
 If a little water is admitted to an evacuated vessel and the 
 temperature is 20 C., the water evaporates until the pressure 
 of its vapor is 17.4 mm. (see foregoing table). If the vessel 
 is already filled with dry air at 760 mm. before the water is 
 admitted, or forced in, the water evaporates just the 
 same until its pressure has reached 17.4 mm. A barometer 
 placed in the vessel would now show a pressure of 760 + 17.4 
 mm., provided the vessel were kept closed and its pressure 
 were not allowed to equalize itself with that of the outside 
 atmosphere. 
 
 Suppose we were measuring the volume of a gas by confin- 
 ing it over water at 20 C. and 760 mm. The gas is saturated 
 with water vapor, the pressure of which at 20 C. is 17.4 mm. 
 Since the total pressure is only 760 mm. and the gas itself 
 is only one of the two gases which constitute the mixture, 
 the pressure of the gas itself can be but 760 17.4 = 742.6 
 mm. 
 
 In the problem on page 87 it was found that 45 c.c. of dry 
 gas at 20 C. and 740 mm. would have a volume of 40.8 c.c. 
 under standard conditions. Let us now calculate what would 
 be its volume under standard conditions, if the gas had been 
 saturated with water vapor when its volume was measured : 
 
 pressure of gas + pressure of water vapor = 740 mm. 
 pressure of gas = 740 pressure of water vapor 
 = 740 - 17.4 = 722.6 mm. 
 
 v stand, temp. press, of gas 
 
 vol. (standard) = vol. (meas.) X - ^ X - 
 
 temp, ot gas stand, press. 
 
 273 , 722.6 
 = 45X ^3 
 
 = 39.9 c.c. 
 
APPENDIX 
 
 427 
 
 This volume is 0.9 c.c. less than the volume calculated for 
 the dry gas, and we thus see that at 20 C. saturating a gas 
 with water vapor increases its volume by 2 per cent when 
 the total pressure is not allowed to increase. 
 
 Therefore in making accurate measurements the presence 
 of water vapor should not be neglected when calculating gas 
 volumes to standard conditions. 
 
 On the other hand, when a number of gas volumes are 
 being measured over water all at about room temperature 
 and it is necessary only to make a comparison of the different 
 volumes, it is unnecessary to take the water vapor into ac- 
 count, because it is present in every case in almost the same 
 proportion. 
 
 In correcting to the same conditions the volumes measured 
 in determining the volume per cent of oxygen in air (page 85) 
 the presence of water vapor was neglected. The pupil is 
 advised to recalculate this problem, correcting all volumes 
 to standard conditions (dry) and convince himself that the 
 same per cent by volume of oxygen is found. 
 
 III. SOME PROPERTIES OF COMMON ELEMENTS 
 
 ELEMENT 
 
 SPECIFIC 
 GRAVITY 
 
 MELTING POINT 
 
 BOILING POINT 
 
 
 2 7 
 
 fi^7 P 
 
 
 Calcium .... 
 
 1.58 
 
 C Q 
 
 800 
 104.^ 
 
 
 
 Gold 
 
 19.3 
 
 1065 
 
 9^7 
 
 OCOO p 
 
 Iron 
 
 78 
 
 1550 
 
 
 Lead 
 Mercury .... 
 
 11.4 
 13.6 
 
 01 K 
 
 327 
 -39.4 
 
 i 77f) 
 
 357 
 
 Potassium .... 
 Silver 
 
 .87 
 105 
 
 62.5 
 955 
 
 720 
 
 
 
 
 
428 
 
 APPENDIX 
 
 III. SOME PROPERTIES OF COMMON ELEMENTS 
 
 Continued. 
 
 ELEMENT 
 
 SPECIFIC 
 GRAVITY 
 
 MELTING POINT 
 
 BOILING POINT 
 
 Sodium . . . . 
 Tin 
 
 .97 
 
 7 3 
 
 95.6 
 233 
 
 742 
 
 Tunsrsten 
 
 1Q 1 
 
 flhnvp ^000 
 
 
 Zinc 
 Bromine .... 
 ( diamond 
 Carbon -} graphite 
 ( amorphous 
 
 7.2 
 
 3.2 (liquid) 
 3.51 
 2.25 
 1.70 
 
 420 
 
 7 
 
 ^3500? 
 
 i no 
 
 918 
 
 59 
 
 00 K 
 
 
 
 L\JA 
 914 
 
 oo.O 
 1 Qfi 
 
 Oxygen .... 
 Phosphorus (yellow) 
 Iodine . 
 
 1.82 
 4 95 
 
 -227 
 44.2 
 114 
 
 - 181 
 269 
 184 
 
 *W | [1-SiO 
 
 2.06 
 1.96 
 
 114.5 
 119 
 
 |449 
 
 IV. WEIGHT OF ONE LITER OF VARIOUS GASES 
 UNDER STANDARD CONDITIONS 
 
 GAS 
 
 FORMULA 
 
 WEIGHT 
 
 Air 
 
 
 1 29 grams 
 
 Ammonia 
 
 NH 3 
 
 76 
 
 Argon 
 
 A 
 
 1 79 
 
 Carbon dioxide 
 Carbon monoxide 
 Chlorine . 
 
 C0 2 
 CO 
 
 Clo 
 
 1.98 
 
 I'll t oV 
 
 Fluorine 
 Helium 
 Hydrogen 
 
 F 2 
 He 
 H 2 
 
 1.70 
 0.18 
 09 
 
 Hydrogen chloride 
 Hydrogen sulphide 
 Methane 
 
 HC1 
 H 2 S 
 CH 4 
 
 1.61' 
 1.54 
 072 
 
 Nitrogen 
 
 N 2 
 
 1 25 
 
 Nitric oxide 
 Oxygen 
 Steam (hypothetical) .... 
 Sulphur dioxide 
 
 NO 
 
 0, 
 H 2 
 
 S0 2 
 
 1.34 
 1.43 
 0.81 
 2.86 
 
APPENDIX 429 
 
 V. SOME PROPERTIES OF COMPOUNDS 
 
 NAME 
 
 FORMULA 
 
 SPECIFIC 
 GRAVITY 
 
 STATE 
 
 MELT- 
 ING 
 POINT 
 
 BOILING 
 POINT 
 
 Acetic acid (glacial) 
 
 H(C 2 H 3 2 ) 
 
 1.055 
 
 liquid above 
 
 17.5 C. 
 
 119.0 C. 
 
 
 
 
 17.5 C. 
 
 
 
 Acetone 
 
 C 3 H 6 
 
 0.79 
 
 liquid 
 
 
 
 56.3 
 
 Alcohol (grain) 
 
 C 2 H 6 OH 
 
 0.79 
 
 liquid 
 
 -130 
 
 78.4 
 
 Alcohol (grain) 
 
 
 
 
 
 
 95% constant boil- 
 
 
 
 
 
 
 ing mixture 
 
 C 2 H 5 OH Aq 
 
 0.80 
 
 liquid 
 
 
 
 78.15 
 
 Alcohol (wood) 
 
 CH 3 OH 
 
 0.79 
 
 liquid 
 
 -97.8 
 
 66 
 
 Ammonia 
 
 NH 3 
 
 ( 8.5(H 2 =1) 1 
 \0.73(HjO=l)J 
 
 /gaseousl 
 \ liquid / 
 
 -75.5 
 
 -33.5 
 
 Ammonium 
 
 ( NH 4 OH } 
 
 
 
 
 
 hydroxide 
 
 I NH 3 in \ 0.90 
 
 solution 
 
 
 
 
 
 (28% NHs) 
 
 ( solution J 
 
 
 
 
 
 Carbon dioxide 
 
 C0 2 
 
 /22.0 \ 
 \ 0.72J 
 
 /gaseousl 
 1 liquid J 
 
 
 
 -79 
 
 Carbon tetrachloride 
 
 ecu 
 
 1.59 
 
 liquid 
 
 
 
 77 
 
 Chloroform 
 
 CHCls 
 
 1.52 
 
 liquid 
 
 -63.2 
 
 61.2 
 
 Ether 
 
 (C 2 H 5 ) 2 
 
 .73 
 
 volatile 
 liquid 
 
 -117 
 
 35 
 
 Hydrochloric acid 
 
 
 
 
 
 
 (concentrated ; 40%, 
 
 
 
 
 
 
 HCI) 
 
 HCI Aq 
 
 1.20 
 
 solution 
 
 
 
 
 
 Hydrochloric acid 
 
 
 
 
 
 
 (constant boiling 
 
 
 
 
 
 
 point mixture; 
 
 
 
 
 
 
 20.2% HCI) 
 
 HCI Aq 
 
 1.10 
 
 solution 
 
 
 
 110 
 
 Hydrogen chloride 
 
 HCI 
 
 (18.21 
 1 0.8/ 
 
 /gaseousl 
 1 liquid / 
 
 -116 
 
 -80 
 
 Hydrogen peroxide 
 
 H 2 2 
 
 1.45 
 
 i- -i 
 liquid 
 
 
 
 
 
 Hydrogen sulphide 
 
 H 2 S 
 
 /17.0 \ 
 I -86 
 
 /gaseousl 
 \ liquid } 
 
 -82.9 
 
 -61.8 
 
 Nitric acid (pure) 
 
 HNOs 
 
 1.52 
 
 liquid 
 
 -47 
 
 86 
 
 Nitric acid 
 
 
 
 
 
 
 (constant boiling 
 
 
 
 
 
 
 point mixture 
 
 
 
 
 
 
 (68% HNOs)) 
 
 HNOs Aq 
 
 1.42 
 
 Solution 
 
 
 
 120.5 
 
 Petroleum products 
 
 Various hy- 
 
 
 
 
 
 (a) Petroleum ether 
 
 drocarbons, 
 
 0.635 to 0.660 
 
 mixed liquid 
 
 
 
 40 to 70 
 
 (6) Gasoline 
 
 chiefly of the 
 
 0.660 to 0.667 
 
 mixed liquid 
 
 
 
 70 to 80 
 
 (c) Benzine 
 
 marsh gas 
 
 0.667 to 0.707 
 
 mixedliquid 
 
 
 
 80 to 100 
 
 (d) Kerosene 
 Grade I 
 Grade II 
 Grade III 
 
 series. The 
 mean molec- 
 ular weight 
 increases 
 
 0.753 to 0.864 
 
 J 
 
 mixed liquid 
 
 
 
 150 to 200 
 200 to 250 
 250 to 300 
 
 
 with increase 
 
 
 
 
 
 
 in the boiling 
 
 
 
 
 
 
 point. 
 
 
 
 
 
 Phosphoric acid 
 
 H 3 PO 4 
 
 1-88 
 
 solid below 
 
 40.5 
 
 
 
 (ortho) 
 
 
 
 40.5 C. 
 
 
 
 Sulphur dioxide 
 
 S0 2 
 
 /32 } 
 
 /gaseousl 
 i liquid / 
 
 -76.1 
 
 -8 
 
 Sulphuric acid (98% 
 
 H 2 S0 4 
 
 
 
 
 
 H 2 S0 4 ) 
 
 i H 2 O 
 
 1.84 
 
 liquid 
 
 below 
 
 383 
 
 Sulphuric acid (mono- 
 
 
 
 
 
 
 hydrate) 
 
 H 2 SO 4 H 2 O 
 
 1.79 
 
 liquid 
 
 8 
 
 . 
 
 Sulphur trioxide 
 
 80s 
 
 f 1.901 
 
 11.97/ 
 
 /liquid! 
 \ solid / 
 
 14.8 
 
 46 
 50 
 
430 
 
 APPENDIX 
 
 VI. SOLUBILITIES OF SOME BASES AND SALTS 
 
 Grams of Substance Soluble in 100 cc. of Water at 18 C. 
 
 
 K 
 
 Na 
 
 Ag 
 
 Ba 
 
 Ca 
 
 Mg 
 
 Zn 
 
 Pb 
 
 Cl 
 
 33 
 
 36 
 
 0.0 3 16 
 
 37 
 
 73 
 
 56 
 
 204 
 
 1.5 
 
 Br 
 
 66 
 
 89 
 
 o.oa 
 
 104 
 
 143 
 
 103 
 
 478 
 
 0.60 
 
 I 
 
 137 
 
 178 
 
 0.0*3 
 
 201 
 
 200 
 
 148 
 
 419 
 
 0.08 
 
 N0 3 
 
 30 
 
 84 
 
 213 
 
 8.7 
 
 122 
 
 74 
 
 118 
 
 52 
 
 C1O 3 
 
 6.6 
 
 97 
 
 12 
 
 35 
 
 179 
 
 126 
 
 184 
 
 151 
 
 SO, 
 
 11 
 
 36 
 
 0.55 
 
 0.0.23 
 
 0.20 
 
 35 
 
 53 
 
 0.004 
 
 C0 3 
 
 108 
 
 19 
 
 0.003 
 
 0.0023 
 
 0.0013 
 
 0.1 
 
 0.004 ? 
 
 0.0*1 
 
 OH 
 
 149 
 
 11C 
 
 0.01 
 
 3.7 
 
 0.17 
 
 0.001 
 
 0.0 3 5 
 
 0.01 
 
 VII. GENERAL RULES OF SOLUBILITY 
 
 In addition to the above exact figures for the solubility of a few 
 substances, the following approximate rules are of value : 
 
 1. All salts of the alkali metals (Na, K, NH 4 ) are soluble. 
 
 2. All bromides are soluble except those of Ag, Hg, Pb. 
 
 3. All carbonates are insoluble except those of the alkali metals. 
 
 4. All chlorates are soluble. 
 
 5. All chlorides are soluble except those of Ag, Pb, and Hg (ous) . 
 
 6. All hydroxides are insoluble except those of the alkali metals 
 (Na, K, NH 4 ), Ba, and Sr. 
 
 7. All nitrates are soluble. 
 
 8. The oxides of the heavy metals are insoluble and do not re- 
 act with water. The oxides of the alkali metals, Ca, and Ba react 
 vigorously with water to form the hydroxides. 
 
 9. All phosphates are insoluble except those of the alkali metals. 
 
 10. All silicates are insoluble except those of the alkali metals. 
 Glass and rocks, such as feldspar and mica, are insoluble, although 
 they contain silicates of the alkali metals mixed with other 
 silicates. 
 
 11. All sulphates are soluble except those of Ba, Ca, Sr, and Pb. 
 
APPENDIX 
 
 431 
 
 VIII. IMPORTANT TEMPERATURES 
 
 2. 
 3. 
 
 Zero absolute ... - 2 
 Boiling point of helium 
 Melting point of hydrogen 
 
 73 C. 
 
 268.5 
 
 260 
 
 22. 
 23. 
 
 24. 
 
 Dull red heat .... 
 Melting point of alumin- 
 ium 
 Melting point of com- 
 
 650 
 660 
 
 4. 
 
 Boiling point of hydrogen 
 
 252.6 
 
 25 
 
 mon salt .... 
 Red heat 
 
 792 
 800 
 
 5. 
 
 Melting point of nitrogen 
 
 214 
 
 26. 
 
 97 
 
 Bright red heat . . . 
 
 1000 
 
 1 nfi4. 
 
 6. 
 
 Boiling point of nitrogen 
 
 194 
 
 28. 
 29. 
 
 Melting point of copper 
 Yellow heat 
 
 1090 
 1200 
 
 7. 
 
 Boiling point of oxygen 
 
 
 30 
 
 White heat 
 
 1350 
 
 
 _ 
 
 182.5 
 
 
 
 
 8. 
 
 Freezing point of grain al- 
 cohol .... 
 
 130 
 
 31. 
 
 Temperature of glass 
 furnace . . . . ; 
 
 1375 
 
 9. 
 
 Freezing point of mercury 
 
 - 39 5 
 
 32. 
 33. 
 
 Melting point of iron . 
 Melting point of plati- 
 
 1520 
 
 
 
 
 
 num 
 
 1750 
 
 10. 
 11. 
 
 Freezing point of water 
 Average room tempera- 
 
 
 
 34. 
 
 Melting point of corun- 
 dum 
 
 2000 
 
 
 ture 
 
 20 
 
 
 
 
 12. 
 13. 
 14. 
 
 Normal temperature of 
 the body 
 
 Melting point of Wood's 
 metal 
 
 Boiling point of grain al- 
 cohol .... 
 
 37 
 60 
 785 
 
 35. 
 36. 
 37. 
 
 00 
 
 Melting point of irid- 
 ium 
 Temperature of oxyhy- 
 drogen flame . . . 
 Melting point of os- 
 mium 
 
 2300 
 2500 
 2500 
 
 15. 
 
 Boiling point of water . . 
 
 100 
 
 
 acetylene flame . . 
 above 
 
 2700 
 
 16. 
 
 Melting point of rhombic 
 sulphur . 
 
 114 5 
 
 39. 
 
 Melting point of tung- 
 
 
 17. 
 18. 
 19. 
 20. 
 
 Melting point of tin . . 
 Melting point of lead . . 
 Melting point of zinc . . 
 Boiling point of sulphur . 
 
 232 
 327 
 419 
 445 
 
 40. 
 41. 
 
 sten 
 Temperature of alu- 
 mino-thermy . . . 
 Temperature of electric 
 arc 
 
 3000 
 3500 
 4000 
 
 21. 
 
 Incipient red heat . . . 
 
 550 
 
 42. 
 
 Temperature of sun . . 
 
 6000 
 
 B. AND W. CHEM. 28 
 
432 
 
 APPENDIX 
 
 IX. COMPOSITION OF ALLOYS 
 
 TYPE OP ALLOY 
 
 NAME 
 
 APPROXIMATE COMPOSITION 
 IN PARTS PER 100 
 
 Copper Alloys 
 
 Brass 
 
 Cu (67-80) ; Zn (20-33) ; Pb \ 
 
 
 Bronze 
 
 Cu 84; Pb 1; Sn 5; Zn 10 
 
 
 Aluminium bronze 
 
 Cu (90-95) ; Al (5-10) 
 
 
 Manganese bronze 
 
 Cu 70 ; Mn 30 
 
 
 Gun metal 
 
 Cu 90 ; Sn 10 
 
 
 Bell metal 
 
 Cu 75 ; Sn 25 
 
 
 Dutch metal 
 
 Cu 80 ; Zn 20 
 
 
 Copper coins 
 
 Cu 95 ; Sn 4 ; Zn 1 
 
 
 5-cent piece 
 
 Cu 75 ; Ni 25 
 
 
 German silver 
 
 Cu (55-60) ; Zn 20 ; Ni (20-25) 
 
 Iron Alloys 
 
 Steel 
 
 Fe (99-99.75); C (0.25-1) 
 
 
 Nickel steel 
 
 Fe94; C 1 ; Ni 5 
 
 
 Chrome steel 
 
 Fe (94^-96*) , C (1-1*) ; 
 
 
 
 Cr (2J-4) 
 
 
 Tungsten steel 
 
 Fe94; C 1; W 5 
 
 
 Manganese steel 
 
 Fe91; C 1; Mn 8 
 
 
 Molybdenum steel 
 
 Fe (89-94) ; C 1 ; Mo (5-10) 
 
 Lead-Tin Alloys 
 
 Solder 
 
 Pb (33-66) ; Sn (33-66) 
 
 
 Pewter 
 
 Sn 75 ; Pb 25 
 
 
 Shot metal 
 
 Pb99; As 1 
 
 
 Type metal 
 
 Pb 75 ; Sb 20 ; Sn 5 
 
 
 Britannia metal 
 
 Sn 85 ; Sb 10 ; Cu 5 
 
 Silver Alloys 
 
 Sterling silver 
 
 Ag92.5; Cu7.5 
 
 
 Coin silver 
 
 Ag 90 ; Cu 10 
 
 Gold Alloys 
 
 U.S. gold coinage 21. 6k 
 
 Au 90 ; Cu 10 
 
 
 18 k gold 
 
 Au 75 ; Cu 25 
 
 
 14 k gold 
 
 Au58.3; Cu 41.7 
 
 
 10 k gold 
 
 Au41.6; Cu 58.4 
 
 Fusible Alloys 
 
 Wood's metal 
 
 Bi 50 ; Pb 25 ; Cd 12.5 ; Sn 12.5 
 
 
 (melts at 60.5 C.) 
 
 
 
 Rose's metal 
 
 Bi 82 ; Pb 9 ; Sn 9 
 
 
 (melts at 94 C.) 
 
 
 Miscellaneous 
 
 Babbitt's antifriction 
 
 
 Alloys 
 
 metal 
 
 Zn 69 ; Sn 19 ; Pb 5 ; As 4 ; Sb 3 
 
APPENDIX 
 
 433 
 
 X. COMPOSITION OF TERRESTRIAL MATTER TO A 
 DEPTH OF 10 MILES 
 
 
 SOLID CRUST 
 OF EARTH, 
 
 93 PER CENT 
 
 OCEANS, 
 
 7 PER CENT 
 
 AVERAGE, 
 INCLUDING 
 ATMOSPHERE 
 
 Oxygen 
 Silicon .' 
 Aluminium 
 Iron . 
 
 47.17 
 28.00 
 
 7.84 
 4.44 
 
 85.79 
 
 49.85 
 26.03 
 7.28 
 4.12 
 
 Calcium . ... . 
 
 3.42 
 
 .05 
 
 3.18 
 
 Magnesium 
 
 2 27 
 
 .14 
 
 2.11 
 
 Sodium 
 Potassium 
 Hydrogen 
 Titanium 
 
 2.43 
 2.49 
 .23 
 44 
 
 1.14 
 .04 
 10.67 
 
 2.33 
 2.33 
 .97 
 41 
 
 
 19 
 
 002 
 
 19 
 
 Chlorine 
 
 .06 
 
 2.07 
 008 
 
 .20 
 
 Phosphorus 
 Sulphur 
 Barium 
 Manganese 
 Strontium 
 Nitrogen 
 
 .11 
 .11 
 .09 
 .08 
 .03 
 
 ' .09 ' 
 
 .10 
 .10 
 .09 
 .08 
 .03 
 03 
 
 Fluorine 
 
 10 
 
 
 10 
 
 All other elements 
 
 .50 
 
 
 .47 
 
 
 
 
 
 
 100.00 
 
 100.00 
 
 100.00 
 
 The average density of the solid crust to a 10-mile depth is 2.6. The 
 mean density of the ocean is 1.027. The average density of the whole earth 
 is somewhat over 5. The average content of dissolved salts in ocean water 
 is 3.5 per cent. 
 
 COMPOSITION OF OCEANIC SALTS 
 
 Sodium chloride, NaCl 77.76 
 
 Magnesium chloride, MgCU 10.88 
 
 Magnesium sulphate, MgSCh 4.74 
 
 Calcium sulphate, CaSC>4 ..." 3.60 
 
 Potassium sulphate, K2SO4 2.46 
 
 Magnesium bromide, MgBr2 22 
 
 Calcium carbonate, CaCOs .34 
 
 100.00 
 
 The above figures were calculated by F. W. Clarke and published in 1911 
 in Bulletin 491 of The United States Geological Survey entitled The Data of 
 Geochemistry. 
 
XL Logarithms 
 
 Nat. 
 Number 
 
 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 '7 
 
 8 
 
 9 
 
 PROPORTIONAL 
 
 PARTS 
 
 
 10 
 11 
 12 
 13 
 14 
 
 15 
 16 
 17 
 18 
 19 
 
 0000 
 0414 
 0792 
 1139 
 1461 
 
 1761 
 2041 
 2304 
 2553 
 
 2788 
 
 0043 
 0453 
 0828 
 1173 
 1492 
 
 1790 
 2068 
 2330 
 2577 
 2810 
 
 0086 
 0492 
 0864 
 1206 
 1523 
 
 1818 
 2095 
 2355 
 2601 
 2833 
 
 0128 
 0531 
 0899 
 1239 
 1553 
 
 1847 
 2122 
 2380 
 2625 
 2856 
 
 0170 
 0569 
 0934 
 1271 
 1584 
 
 1875 
 2148 
 2405 
 2648 
 2878 
 
 0212 
 0607 
 0969 
 1303 
 1614 
 
 1903 
 2175 
 2430 
 2672 
 2900 
 
 0253 
 0645 
 1004 
 1335 
 1644 
 
 1931 
 2201 
 2455 
 2695 
 2923 
 
 0294 
 0682 
 1038 
 1367 
 1673 
 
 1959 
 2227 
 2480 
 2718 
 2945 
 
 0334 0374 
 07190755 
 1072 1106 
 1399 1430 
 1703 1732 
 
 1987 2014 
 2253 2279 
 2504 2529 
 2742 2765 
 2967 2989 
 
 4 8 12; 17 21 25 29 33 37 
 4 8 ll! 15 19 23 26 30 34 
 3 710 141721 242831 
 3 610131619232629 
 369 121518212427 
 
 3 6 8 111417 202225 
 3 5 8 111316 182124 
 2 5 7 101215 172022 
 2 5 7 91214 161921 
 247 91113161820 
 
 20 
 21 
 22 
 23 
 24 
 
 25 
 26 
 27 
 
 28 
 29 
 
 3010 
 3222 
 3424 
 3617 
 3802 
 
 3979 
 4150 
 4314 
 4472 
 4624 
 
 3032 
 3243 
 3444 
 3636 
 3820 
 
 3997 
 4166 
 4330 
 4487 
 4639 
 
 4786 
 4928 
 5065 
 5198 
 5328 
 
 5453 
 5575 
 5694 
 5809 
 5922 
 
 3054 
 3263 
 3464 
 3655 
 3838 
 
 4014 
 4183 
 4346 
 4502 
 4654 
 
 4800 
 4942 
 5079 
 5211 
 5340 
 
 5465 
 5587 
 5705 
 5821 
 5933 
 
 6042 
 6149 
 6253 
 6355 
 6454 
 
 6551 
 6646 
 6739 
 6830 
 6920 
 
 3075 
 3284 
 3483 
 3674 
 3856 
 
 4031 
 4200 
 4362 
 4518 
 4669 
 
 4814 
 4955 
 5092 
 5224 
 5353 
 
 5478 
 5599 
 5717 
 5832 
 5944 
 
 3096 
 3304 
 3502 
 3692 
 3874 
 
 4048 
 4216 
 4378 
 4533 
 4683 
 
 4829 
 4969 
 5105 
 5237 
 5366 
 
 5490 
 5611 
 5729 
 5843 
 5955 
 
 3118 
 3324 
 3522 
 3711 
 3892 
 
 4065 
 4232 
 4393 
 4548 
 4698 
 
 3139 
 3345 
 3541 
 3729 
 3909 
 
 4082 
 4249 
 4409 
 4564 
 4713 
 
 4857 
 4997 
 5132 
 5263 
 5391 
 
 5514 
 5635 
 5752 
 
 5866 
 5977 
 
 3160 
 3365 
 3560 
 3747 
 3927 
 
 4099 
 4265 
 4425 
 4579 
 
 4728 
 
 4871 
 5011 
 5145 
 5276 
 5403 
 
 5527 
 5647 
 5763 
 
 5877 
 5988 
 
 3181 
 3385 
 3579 
 3766 
 3945 
 
 4116 
 4281 
 4440 
 4594 
 4742 
 
 4886 
 5024 
 5159 
 5289 
 5416 
 
 5539 
 5658 
 5775 
 
 5888 
 5999 
 
 3201 
 3404 
 3598 
 3784 
 3962 
 
 4133 
 4298 
 4456 
 4609 
 4757 
 
 246 
 246 
 246 
 246 
 245 
 
 235 
 235 
 235 
 235 
 1 3 4 
 
 81113 
 81012 
 
 81012 
 7 911 
 7 911 
 
 7 910 
 7 810 
 689 
 689 
 679 
 
 151719 
 14 16 18 
 141517 
 131517 
 121416 
 
 121415 
 111315 
 111314 
 111214 
 10 12 13 
 
 30 
 31 
 32 
 33 
 34 
 
 35 
 36 
 37 
 38 
 39 
 
 4771 
 4914 
 5051 
 5185 
 5315 
 
 5441 
 5563 
 5682 
 5798 
 5911 
 
 4843 
 4983 
 5119 
 5250 
 5378 
 
 5502 
 5623 
 5740 
 5855 
 5966 
 
 4900 
 5038 
 5172 
 5302 
 
 5428 
 
 5551 
 5670 
 
 5786 
 5899 
 6010 
 
 134 
 1 3 4 
 1 3 4 
 1 3 4 
 134 
 
 1 2 4 
 124 
 1 2 3 
 1 2 3 
 1 2 3 
 
 679 
 678 
 578 
 568 
 568 
 
 567 
 567 
 567 
 567 
 457 
 
 101113 
 1011 12 
 911 12 
 91012 
 91011 
 
 91011 
 81011 
 8 910 
 8 910 
 8 910 
 
 40 
 41 
 42 
 43 
 44 
 
 45 
 46 
 47 
 
 48 
 49 
 
 6021 
 6128 
 6232 
 6335 
 6435 
 
 6532 
 6628 
 6721 
 6812 
 6902 
 
 6031 
 6138 
 6243 
 6345 
 6444 
 
 6542 
 6637 
 6730 
 6821 
 6911 
 
 6053 
 6160 
 6263 
 6365 
 6464 
 
 6561 
 6656 
 6749 
 6839 
 6928 
 
 7016 
 7101 
 7185 
 7267 
 7348 
 
 6064 
 6170 
 6274 
 6375 
 6474 
 
 6571 
 6665 
 6758 
 6848 
 6937 
 
 7024 
 7110 
 7193 
 7275 
 7356 
 
 6075 
 6180 
 6284 
 6385 
 6484 
 
 6580 
 6675 
 6767 
 6857 
 6946 
 
 7033 
 
 7118 
 7202 
 7284 
 7364 
 
 6085 
 6191 
 6294 
 6395 
 6493 
 
 6590 
 6684 
 6776 
 6866 
 6955 
 
 6096 
 6201 
 6304 
 6405 
 6503 
 
 6599 
 6693 
 6785 
 6875 
 6964 
 
 6107 
 6212 
 6314 
 6415 
 6513 
 
 6609 
 6702 
 6794 
 6884 
 6972 
 
 6117 
 6222 
 6325 
 6425 
 6522 
 
 6618 
 6712 
 6803 
 6893 
 6981 
 
 1 2 3 
 1 2 3 
 1 2 3 
 123 
 1 2 3 
 
 1 2 3 
 1 2 3 
 1 2 3 
 123 
 123 
 
 456 
 456 
 456 
 456 
 456 
 
 456 
 456 
 455 
 445 
 445 
 
 8 910 
 
 789 
 789 
 789 
 789 
 
 789 
 
 778 
 678 
 678 
 678 
 
 50 
 51 
 52 
 53 
 54 
 
 6990 
 7076 
 7160 
 7243 
 7324 
 
 6998 
 7084 
 7168 
 7251 
 7332 
 
 7007 
 7093 
 7177 
 7259 
 7340 
 
 7042 
 7126 
 7210 
 7292 
 7372 
 
 70507059 
 71357143 
 72187226 
 7300 7308 
 73807388 
 
 7067 
 7152 
 7235 
 7316 
 7396 
 
 1 2 3 
 123 
 122 
 122 
 1 2 2 
 
 345 
 345 
 345 
 345 
 345 
 
 678 
 678 
 677 
 667 
 667 
 
 
 
 
 | 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 123 
 
 456 
 
 789 
 
 PROPORTIONAL 
 
 PARTS 
 
 434 
 
XL Logarithms 
 
 Nat. 
 Number 
 
 
 
 I 
 
 2 
 
 3 
 
 7427 
 7505 
 7582 
 7657 
 7731 
 
 7803 
 7875 
 7945 
 8014 
 8082 
 
 4 
 
 5 
 
 7443 
 7520 
 7597 
 7672 
 
 7745 
 
 7818 
 7889 
 7959 
 8028 
 8096 
 
 8162 
 8228 
 8293 
 8357 
 8420 
 
 8482 
 8543 
 8603 
 8663 
 
 8722 
 
 6 
 
 7 
 
 8 
 
 7466 
 7543 
 7619 
 7694 
 7767 
 
 7839 
 7910 
 7980 
 8048 
 8116 
 
 8182 
 8248 
 8312 
 8376 
 8439 
 
 8500 
 8561 
 8621 
 8681 
 8739 
 
 9 
 
 PROPORTIONAL PARTS 
 
 1 2 34 5 6 
 
 789 
 
 55 
 56 
 57 
 
 58 
 59 
 
 60 
 61 
 62 
 63 
 64 
 
 7404 
 7482 
 7559 
 7634 
 7709 
 
 7782 
 7853 
 7924 
 7993 
 8062 
 
 7412 7419 
 7490 7497 
 7566 7574 
 7642 7649 
 7716 7723 
 
 77897796 
 7860:7868 
 7931 7938 
 80008007 
 8069 8075 
 
 7435 
 7513 
 
 7589 
 7664 
 
 7738 
 
 7810 
 7882 
 7952 
 8021 
 8089 
 
 7451 
 
 7528 
 7604 
 7679 
 7752 
 
 7825 
 7896 
 7966 
 8035 
 8102 
 
 8169 
 8235 
 8299 
 8363 
 8426 
 
 8488 
 8549 
 8609 
 8669 
 
 8727 
 
 7459 
 7536 
 7612 
 7686 
 7760 
 
 7832 
 7903 
 7973 
 8041 
 8109 
 
 8176 
 8241 
 8306 
 8370 
 8432 
 
 8494 
 8555 
 8615 
 8675 
 8733 
 
 7474 
 7551 
 7627 
 7701 
 7774 
 
 7846 
 7917 
 7987 
 8055 
 8122 
 
 2 2 
 2 2 
 2 2 
 1 2 
 1 2 
 
 1 2 
 1 2 
 1 2 
 1 2 
 1 2 
 
 345 
 
 345 
 345 
 344 
 344 
 
 344 
 344 
 334 
 334 
 334 
 
 6 7 
 6 7 
 6 7 
 6 7 
 6 7 
 
 6 6 
 6 6 
 566 
 556 
 556 
 
 65 
 66 
 67 
 68 
 69 
 
 70 
 71 
 73 
 73 
 74 
 
 8129 
 8195 
 8261 
 8325 
 8388 
 
 8451 
 8513 
 8573 
 8633 
 8692 
 
 8136 
 8202 
 8267 
 8331 
 8395 
 
 8457 
 8519 
 8579 
 8639 
 8698 
 
 81428149 
 82098215 
 8274 8280 
 8338 8344 
 8401 8407 
 
 8463 8470 
 85258531 
 8585 8591 
 8645 8651 
 8704 8710 
 
 8156 
 8222 
 8287 
 8351 
 8414 
 
 8476 
 8537 
 8597 
 8657 
 8716 
 
 8189 
 8254 
 8319 
 8382 
 8445 
 
 8506 
 8567 
 8627 
 8686 
 8745 
 
 1 1 2 
 112 
 1 2 
 1 2 
 1 2 
 
 1 2 
 1 2 
 1 2 
 1 2 
 1 2 
 
 334 
 334 
 334 
 334 
 234 
 
 234 
 234 
 234 
 234 
 234 
 
 556 
 556 
 556 
 456 
 456 
 
 456 
 455 
 455 
 455 
 455 
 
 75 
 
 76 
 77 
 
 78 
 79 
 
 80 
 
 81 
 83 
 83 
 
 84 
 
 8751 
 8808 
 8865 
 8921 
 8976 
 
 9031 
 9085 
 9138 
 9191 
 9243 
 
 8756 8762 8768 
 8814:88208825 
 8871 8876 8882 
 8927 89328938 
 898289878993 
 
 9036 9042 9047 
 909090969101 
 9143'9149 9154 
 9196 9201 9206 
 9248^253 9258 
 
 8774 
 8831 
 8887 
 8943 
 8998 
 
 9053 
 9106 
 9159 
 9212 
 9263 
 
 8779 
 8837 
 8893 
 8949 
 9004 
 
 9058 
 9112 
 9165 
 9217 
 9269 
 
 8785 
 8842 
 8899 
 8954 
 9009 
 
 9063 
 9117 
 9170 
 9222 
 9274 
 
 8791 
 8848 
 8904 
 8960 
 9015 
 
 9069 
 9122 
 9175 
 9227 
 9279 
 
 8797 
 8854 
 8910 
 8965 
 9020 
 
 9074 
 9128 
 9180 
 9232 
 9284 
 
 8802 
 8859 
 8915 
 8971 
 9025 
 
 9079 
 9133 
 9186 
 9238 
 9289 
 
 1 2 
 1 2 
 1 2 
 1 2 
 1 2 
 
 1 2 
 1 2 
 1 2 
 1 2 
 1 2 
 
 233 
 233 
 233 
 233 
 233 
 
 233 
 233 
 233 
 233 
 233 
 
 455 
 455 
 445 
 445 
 445 
 
 445 
 445 
 445 
 445 
 445 
 
 85 
 86 
 87 
 88 
 89 
 
 90 
 91 
 93 
 93 
 94 
 
 9294 
 9345 
 9395 
 9445 
 9494 
 
 9542 
 9590 
 9638 
 9685 
 9731 
 
 9299 
 9350 
 9400 
 9450 
 9499 
 
 9547 
 9595 
 9643 
 9689 
 9736 
 
 9304 
 9355 
 9405 
 9455 
 9504 
 
 9552 
 9600 
 9647 
 9694 
 9741 
 
 9309 
 9360 
 9410 
 9460 
 9509 
 
 9557 
 9605 
 9652 
 9699 
 9745 
 
 9315 ! 9320 
 93659370 
 9415 9420 
 9465 9469 
 95139518 
 
 95629566 
 9609 9614 
 9657 9661 
 9703 9708 
 9750 9754 
 
 9325 
 9375 
 9425 
 9474 
 9523 
 
 9571 
 9619 
 9666 
 9713 
 9759 
 
 9805 
 9850 
 9894 
 9939 
 9983 
 
 9330 
 9380 
 9430 
 9479 
 9528 
 
 9576 
 9624 
 9671 
 9717 
 9763 
 
 9335 
 9385 
 9435 
 9484 
 9533 
 
 9581 
 9628 
 9675 
 9722 
 9768 
 
 9340 
 9390 
 9440 
 9489 
 9538 
 
 9586 
 8633 
 9680 
 9727 
 9773 
 
 1 2 
 1 2 
 1 
 1 
 1 
 
 1 
 1 
 1 
 1 
 1 
 
 233 
 
 233 
 223 
 223 
 223 
 
 223 
 223 
 223 
 223 
 223 
 
 445 
 
 445 
 344 
 344 
 344 
 
 344 
 344 
 344 
 344 
 344 
 
 95 
 96 
 97 
 98 
 99 
 
 9777 
 9823 
 9868 
 9912 
 9956 
 
 9782 
 9827 
 9872 
 9917 
 9961 
 
 9786 
 9832 
 9877 
 9921 
 9965 
 
 9791 
 9836 
 9881 
 9926 
 9969 
 
 9795 
 9841 
 9886 
 9930 
 9974 
 
 9800 
 9845 
 9890 
 9934 
 9978 
 
 9809 
 9854 
 9899 
 9943 
 9987 
 
 9814 
 9859 
 9903 
 9948 
 9991 
 
 9818 
 9863 
 9908 
 9952 
 9996 
 
 1 
 1 
 1 
 1 
 1 
 
 223 
 
 223 
 223 
 223 
 223 
 
 344 
 344 
 344 
 344 
 334 
 
 
 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 123 
 
 456 
 
 789 
 
 PROPORTIONAL PARTS 
 
 435 
 
436 APPENDIX 
 
 XII. METRIC SYSTEM 
 
 The standard unit of the Metric System is the meter. 
 It is a unit of length. Its multiples and submultiples are 
 obtained decimally 
 
 10 millimeters (mm.) = 1 centimeter (cm.) 
 10 cm. = 1 decimeter (dm.) 
 
 10 dm. = 1 meter (m.) 
 
 The unit of volume in the metric system is the liter. It 
 is the cubic decimeter. Like the meter it is divided decimally. 
 
 1000 cu. cm. (c.c.)l 
 
 , . \ = 1 liter 
 
 or 1 cu. decimeter J 
 
 The unit of weight is the gram. It is the weight of 1 c.c. 
 of water at 4 C. It is divided decimally. 
 
 10 milligrams (mg.) = 1 centigram (eg.) 
 
 10 eg. = 1 decigram (dg.) 
 
 10 dg. = 1 gram (g.) 
 
 1000 g. = 1 kilogram (kg.) 
 
 XIII. TABLE OF EQUIVALENTS 
 
 Showing relation between some frequently used metric 
 measures and their English equivalents. 
 
 1 meter = 39.37 inches 
 1 centimeter = .3937 inch 
 
 1 inch = 2.54 centimeters 
 
 1 liter = 1.0567 quarts 
 1 cubic centimeter = .061 cubic inch 
 
 1 gram = 15.43 grains 
 1 kilogram = 2.2046 Ib. 
 1 ounce = 28.35 grams 
 
INDEX 
 
 Absolute temperature, 81. 
 Absolute zero, 80. 
 Acetic acid, 293. 
 Acetone, from wood, 265. 
 Acetylene, 276, 279, 287. 
 Acid, acetic, 293. 
 
 anhydrides, 211. 
 
 carbonic, 208. 
 
 forming elements, 210. 
 
 hydrobromic, 382. 
 
 hydrochloric, 132. 
 
 hydrogen, 211. 
 
 hypochlorous, 171. 
 
 nitric, 366. 
 
 muriatic, 132. 
 
 phosphoric, 209. 
 
 radicals, 216. 
 
 sulphuric, 209. 
 \ sulphurous, 208. 
 
 Acids, characteristic component, 207. 
 
 fatty, 294, 295. 
 
 nomenclature, 220-223. 
 
 organic, 293. 
 
 properties of, 207. 
 Air, composition, 67, 72. 
 
 determination of oxygen in, 74-77. 
 
 liquid, 40. 
 
 mixture, 69. 
 
 questions on, 78. 
 
 summary, 77. 
 Alabaster, 201. 
 Alcohol, 291. 
 
 denatured, 292. 
 
 wood, 293. 
 
 Alkali metals, 230. - 
 Alkaline, 212. 
 Alkaline earth metals, 233. 
 Alloys, 229. 
 
 brass, 229, 255. 
 
 bronze, 229. 
 
 composition of, Table, 432. 
 
 Alloys, solder, 229, 257. 
 
 type metal, 257. 
 Aluminium, 232-234. 
 
 metallurgy, 260. 
 
 ore, 240, 261. 
 
 uses, 261. 
 
 Aluminothermy, 415. 
 Aluminum, see Aluminium. 
 Amalgamation process, gold, 259. 
 Ammonia, 358. 
 
 commercial, 359. 
 
 preparation, 360. 
 
 properties, 360. 
 
 refrigeration, 360. 
 
 water, 217, 360. 
 Ammonium carbonate, 362. 
 
 chloride, 362. 
 
 hydroxide, 217. 
 
 nitrate, 362. 
 
 radical, 217, 232. 
 
 salts, 362. 
 Amorphous carbon, 265. 
 
 sulphur, 344. 
 Anhydride, acid, 211. 
 
 basic, 214. 
 Appendix, 425-436. 
 Aqua regia, 170, 236. 
 Aqueous pressure, 425. 
 Argon, in air, 72. 
 Artificial diamond, 269. 
 Artificial fertilizers, 372. 
 Artificial gems, 117. 
 Artificial graphite, 267. 
 Artificial silk, 371. 
 Atmosphere, 67. 
 
 Atomic and molecular weights 
 (Chap. XV), 147. 
 
 questions, 163. 
 
 summary, 162. 
 Atomic theory (Chap. XII), 121. 
 
 questions, 128. 
 
 437 
 
438 
 
 INDEX 
 
 Atomic theory, summary, 127. 
 
 value, 126. 
 Atomic weights, determination, 149. 
 
 practical use, 157. 
 
 standard, 148. 
 
 Table, common elements, 340. 
 
 Table, International. Inside back 
 
 cover. 
 Atoms, absolute weight, 147. 
 
 possible complexity, 127. 
 
 relations to electrons, 314. 
 
 relative weight. 147. 
 Avogadro's Theory (Chapter XIV), 
 141. 
 
 applications, 142. 
 
 scope, 144. 
 
 summary, 146. 
 
 Bacteria, and decay, 47. 
 
 cause oxidation, 294. 
 
 chemical destruction, 97. 
 
 in drinking water, 95. 
 
 nitrogen fixing, 371. 
 Baking powder, 183. 
 Baking soda, 180. 
 Balloons, hydrogen, 113. 
 
 illuminating gas, 119. 
 
 lifting power of, 113. 
 Barium, 232, 233. 
 Barometer, 76. 
 Base, 211, 212. 
 Bases, 214. 
 
 characteristic component, 214. 
 
 nomenclature, 223. 
 Basic oxides, 214. 
 Battery, the storage, 423. 
 Bauxite, 234, 261. 
 Benzine, 287. 
 Bessemer steel, 245. 
 Bicarbonate of soda, 180. 
 Blast furnace, 241. 
 
 diagram, 242. 
 Bleaching, chlorine, 172. 
 
 powder, 172-174. 
 
 theory, 172. 
 
 Blowpipe, oxy hydrogen, 116. 
 Borax, 406. 
 Boyle's law, 84. 
 
 explained, 145. 
 
 Bread and cake, raising, 61, 62. 
 Bromides, 382. 
 Bromine, 380. 
 
 Burning, see Combustion. 
 Butane, 285. 
 
 Calcium, 192, 232, 233. 
 
 bicarbonate, 199. 
 
 carbide, 278, 421. 
 
 carbonate, 195. 
 
 chloride, 193. 
 
 drying gases, 194. 
 
 fluoride, 379. 
 
 hydroxide, 197, 213. 
 
 oxide, 196, 213. 
 
 questions, 205. 
 
 sulphate, 201. 
 
 summary, 204. 
 Calculations, chemical, 157. 
 Candle, products of combustion, 28. 
 Cane sugar, 289. 
 Carbides, calcium, 278. 
 
 iron, 276. 
 
 silicon, 277. 
 Carbohydrates, 288. 
 Carbon, amorphous, 265. 
 
 crystalline, 267. 
 
 diamond, 268. 
 
 oxides, 31, 50. 
 Carbonates, 270. 
 Carbonate, calcium, 195. 
 Carbonate, sodium, 180-185. 
 Carbon cycle, 419. 
 Carbon dioxide, 50. 
 
 chemical properties, 58. 
 
 commercial production, 62. 
 
 enormous production, 50. 
 
 from burning charcoal, 11. 
 
 from limestone, 51. 
 
 generator, 53. 
 
 heat of formation, 272. 
 
 in air, 72. 
 
 liquid, 56. 
 
 physical properties, 55. 
 
 properties, 53-58. 
 
 questions, 65. 
 
 solid, 57. 
 
 summary, 64. 
 
 test, 52. 
 
 uses, 58-61. 
 
 utilization by plants, 50. 
 Carbon disulphide, 279. 
 Carbon monoxide, 62, 272. 
 
 blast furnace, 244. 
 
 combining proportions, 63. 
 
INDEX 
 
 439 
 
 Carbon monoxide, formation, 62. 
 
 poisonous, 270. 
 
 properties, 63. 
 
 uses, 63. 
 
 Carbon tetrachloride, 279. 
 Carborundum, 277. 
 
 furnace, 278. 
 Cast iron, 245. 
 Catalysis, 40. 
 Caustic, 230. 
 Caustic soda, 185. 
 Celluloid, 371. 
 Cellulose, 290. 
 
 nitrate, 370. 
 Cement, 201. 
 Cerium, 276. 
 
 Chamber process, sulphuric acid, 352. 
 Charcoal, 265. 
 
 reducing agent, 241. 
 Charles' law, 80, 82, 83. 
 
 example of calculation, 83. 
 
 explained, 146. 
 
 modern expression, 83. 
 Chemical affinity, 398. 
 Chemical and physical changes, 
 
 questions, 14. 
 
 summary, 14. 
 Chemical attraction, 228. 
 Chemical change, 9. 
 
 a typical, 10. 
 
 definition, 12. 
 
 examples, 12. 
 Chemical compounds, 21. 
 Chemical energy, 413. 
 Chemical formulas, 155. 
 Chemical substances, 15. 
 Chemistry, definition, 9. 
 
 organic, 282. 
 Chili saltpeter, 366, 372. 
 
 origin, 373. 
 Chloride of lime, 174. 
 Chlorine, action on metals, 168. 
 
 and carbon, 169. 
 
 and hydrogen, 168. 
 
 and oxygen, 174. 
 
 bleaching, 173. 
 
 chemical properties, 168. 
 
 commercial preparation, 166. 
 
 laboratory preparation, 167. 
 
 liquid, 174. 
 
 physical properties, 167. 
 
 questions, 176. 
 
 Chlorine, source of, 164. 
 
 summary, 175. 
 
 water, 170. 
 Chloroform, 284. 
 Chlorophyll, 289, 372. 
 Chromium, 234. 
 Cleaning, 230. 
 Coal, 266. 
 
 hard, 266. 
 
 soft, 266. 
 Coal gas, 273. 
 Coal tar, 273. 
 Coke, 265. 
 
 from petroleum, 287. 
 
 in blast furnace, 241, 242. 
 Collodion, 371. 
 Combustion, historic views, 25. 
 
 in pure oxygen, 44. 
 
 Lavoisier's experiment, 30. 
 
 modern theory, 26, 30. 
 
 questions, 36. 
 
 slow, 46, 264. 
 
 spontaneous, 46. 
 
 summary, 36. 
 Common salt, 179. 
 Compound, formation of a typical, 
 
 23. 
 Compounds, chemical, 21. 
 
 questions, 24. 
 
 summary, 24. 
 
 Conduction, electrolytic, 302, 303, 
 304. 
 
 metallic, 301. 
 
 Conservation of matter, law of, 11. 
 Contact process, sulphuric acid, 351. 
 Converter, Bessemer, 246. 
 Cooking soda, see Baking soda. 
 Copper, 234, 235, 236, 237, 252. 
 
 native, 252. 
 
 ores, 240, 252. 
 
 oxide, 236, 237, 240. 
 
 plating, 321. 
 
 refining, 253. 
 
 smelting, 253. 
 
 sulphate, 320, 321. 
 
 sulphide, 236, 237, 252. 
 
 uses, 255. 
 
 Cream of tartar, 183. 
 Cryolite, 260. 
 Crystal hydrates, 185. 
 Cyanide process, gold, 259. 
 Cymogene, 286. 
 
440 
 
 INDEX 
 
 Deacon's process for chlorine, 165. 
 Decay, of wood, 31, 47. 
 Definite proportions, law, 22. 
 
 illustrated, 106. 
 
 stated, 121. 
 Deliquescence, 194. 
 Dextrin, 290. 
 Diamond, 268. 
 
 artificial, 269. 
 
 uses, 269. 
 
 Displacement, of hydrogen by metals 
 328. 
 
 of iodine by other halogens, 384. 
 
 of one metal by another, 328. 
 Distillation, 17. 
 
 for soft water, 203. 
 
 of alcohol, 291. 
 
 of coal, 273. 
 
 of petroleum, 286. 
 
 of wood, 293. 
 Draft, forced, 33. 
 Drinking water, 95. 
 Dynamite, 371, 418. 
 
 Earth, composition, 453. 
 
 Earth forming metals, 230, 232. 
 
 Effervescence, 52, 305. 
 
 Efflorescence, 185. 
 
 Electricity, atomic structure, 314, 
 
 322. 
 
 Electrochemical equivalents, 331. 
 Electrolysis (Chap. XXVI), 311. 
 
 copper sulphate, 320. 
 
 hydrochloric acid, 311. 
 
 questions, 326. 
 
 sodium chloride, 320. 
 
 sodium hydroxide, 318. 
 
 sodium sulphate, 319. 
 
 sulphuric acid, 315. 
 
 summary, 325. 
 
 water, 103. 
 Electrolytic conduction, 302, 305. 
 
 character, 303. 
 
 dissociation, 304. 
 
 Electromotive series (Chap. XXVII), 
 327. 
 
 questions, 332. 
 
 summary, 331. 
 Electrons, 314. 
 
 Electroplating of copper, 321. 
 Electrostatic, attraction and repul- 
 sion, 299 r 
 
 Elements, 20. 
 
 of the Greek philosophers, 25. 
 
 periodic classification, 385. 
 
 periodic table, 389. 
 
 possible complexity, 21. 
 
 proportion in earth's crust, 433. 
 
 questions, 24. 
 
 summary, 24. 
 
 table of properties, 427. , 
 Endothermic reactions, 417. 
 Endothermic substances, artificial, 
 
 420. 
 Energy changes and the carbon 
 
 cycle, 419. 
 
 Energy, chemical, 413. 
 Energy, different forms, 413. 
 Equations, 156. 
 
 example, 156. 
 
 ionic, 304, 
 Equilibrium (Chap. XXXII), 392. 
 
 questions, 412. 
 
 summary, 410. 
 
 chemical, 395. 
 Equivalents, electrochemical, 331. 
 
 hydrogen, 333. 
 
 metric, tables, 436. 
 Ethane, 285, 288. 
 Ethylene, 287, 288. 
 Exothermic compounds, 417. 
 Exothermic familiar reactions, 416. 
 Exothermic reactions, 414. 
 Explosions, theory of, 422. 
 
 Faraday's law, 322. 
 Fats, 294. 
 
 as foods, 295. 
 Fermentation, acetic, 293-294. 
 
 alcoholic, 291. 
 
 Fertilizer, 72, 187, 372, 379. 
 Filtration, to purify water, 96. 
 Fire, 25. 
 
 extinguishers, 58, 59, 60, 280. 
 Flame, color, 187. 
 
 luminosity, 275. 
 
 oxyhydrogen, 116, 117. 
 Fluorine, 378. 
 Flux, in blast furnace, 242. 
 Food, canning, 48. 
 
 nitrogenous, 70, 372. 
 
 spoiling, 47. 
 
 Foods, slow combustion in body, 32. 
 Formula, how to find, 152. 
 
INDEX 
 
 441 
 
 Formulas, condensed information, 
 154. 
 
 of some compounds, 429. 
 
 interpretation of, 155. 
 Formula weights, 157. 
 Fuels, gaseous, 118. 
 Furnace, blast, 241-244. 
 
 open hearth, 247. 
 
 reverberatory, 250. 
 
 Galena, 240, 255. 
 Galvanized iron, 249, 258. 
 Gas, acetylene, 276, 279, 287. 
 
 artificial, 118, 271, 273, 275, 
 276. 
 
 carbon, 266. 
 
 coal, 273. 
 
 density, 428. 
 
 detonating, 115. 
 
 illuminating, 271, 275, 276. 
 
 producer, 271. 
 
 volumes, and water vapor, 426. 
 
 water, 270. 
 
 Gases, separation of molecules, 145. 
 Gas laws (Chap. VIII), 79. 
 
 questions, 89-90. 
 
 summary, 88-89. 
 Gasoline, 287. 
 Gay Lussac's law of combining 
 
 volumes, 141. 
 Gems, artificial rubies, 117. 
 
 artificial sapphires, 117. 
 
 diamond, 268. 
 Generator, carbon dioxide, 53. 
 
 hydrogen, 112. 
 
 hydrogen chloride, 129. 
 
 producer gas, 272. 
 
 water gas, 271. 
 Glass, 189. 
 Glucose, 289. 
 Gluten, 296. 
 Glycerine, see Glycerol. 
 Glycerol, 295. 
 Gold, inactivity, 236. 
 
 in aqua regia, 236. 
 
 metallurgy, 259. 
 
 occurrence, 237, 259. 
 
 ore, 240, 259. 
 
 resistance to corrosion, 236. 
 Gram-atomic weights, 337. 
 Gram-molecular volumo, 151. 
 Gram-molecular weights, 150. 
 
 Grape sugar, 289. 
 Graphite, 266. 
 
 artificial, 267. 
 Guncotton, 370. 
 Gunpowder, 370. 
 
 smokeless, 371. 
 Gypsum, 192, 201. 
 
 Halogen family (Chap. XXXI), 377. 
 
 questions, 391. 
 
 summary, 390. 
 Hardness, permanent, of water, 203. 
 
 temporary, of water, 203. 
 Hard water, 201. 
 
 softening, 201. 
 Heat, and chemical reaction, 413-422. 
 
 nature of, 145. 
 Helium, 73. 
 Hematite, 240. 
 Hofmann, apparatus, 104. 
 Humidity, 93. 
 
 and human comfort, 95. 
 
 relative, 94. 
 Hydriodic acid, 384. 
 Hydrobromic acid, 382. 
 Hydrocarbons, 284. 
 
 unsaturated, 287. 
 Hydrochloric acid, 132. 
 
 uses, 133. 
 
 see Hydrogen chloride. 
 
 manufacture, 133. 
 Hydrofluoric acid, 379. 
 
 use, 380. 
 Hydrogen (Chapter XI), 111. 
 
 acid, or displaceable, 211, 299. 
 
 a measure of valence, 204, 336. 
 
 as a metal, 227. 
 
 burns in chlorine, 118. 
 
 discovery, 111. 
 
 displacement by metals, 327. 
 
 equivalents, 333. 
 
 from acjds, 112. 
 
 generator, 112. 
 
 in water, 100, 101, 111. 
 
 liquefaction, 115. 
 
 properties, 113. 
 
 rapid diffusion of, 114. 
 
 reducing action of, 118. 
 
 summary and questions, 119. 
 
 two parts in water, 103. 
 Hydrogen chloride (Chapter XIII), 
 129. 
 
442 
 
 INDEX 
 
 Hydrogen chloride, composition, 135 
 
 formula, 139. 
 
 great solubility, 131. 
 
 questions, 140. 
 
 synthesis of, 137. 
 
 summary, 139. 
 
 volume composition, 136. 
 
 weight composition, 139. 
 Hydrogen equivalents (Chap. 
 XXVIII), 333. 
 
 questions, 341. 
 
 summary 341. 
 Hydrogen peroxide, 108, 422. 
 
 preparation, 187, 422. 
 
 uses, 187. 
 Hydrogen sulphide, 347. 
 
 as a precipitant, 348. 
 
 preparation, 347. 
 Hydrolysis, 232, 405. 
 Hydrolyzable salts, uses of, 408. 
 Hydrosulphuric acid, 348. 
 Hydroxide, ammonium, 217. 
 
 calcium, 213. 
 
 sodium, 211. 
 Hydroxides, 223, 232. 
 Hydroxyl, 223. 
 Hydroxyl ion, 307. 
 Hypochlorous acid, 171. 
 
 instability, 171. 
 Hypothesis, vs. theory, 122. 
 
 Avogadro's, 141. 
 
 Iceland spar, 195. 
 Ice making, 361. 
 Illuminants, 271, 275, 276, 288. 
 Illuminating gas, acetylene, 276. 
 
 coal, 273. 
 
 water, 270. 
 Ingots, copper, 252. 
 
 iron, 249, 251. 
 Inorganic matter, 264. 
 Iodine, 382. 
 
 displacement, 384. 
 
 uses, 383. 
 Ionic theory (Chap. XXV), 299. 
 
 equations, 304. 
 
 questions, 309. 
 
 summary, 308. 
 
 theory, statement of, 304. 
 
 value, 306. 
 
 lonization, degree, 305. 
 Ionized substances, reactivity, 305. 
 
 Ions, as carriers, 312. 
 
 discharge, 312. 
 
 pairing, 304. 
 Iron, 234, 235, 236, 237. 
 
 carbide, 276. 
 
 cast, 245. 
 uses, 248. 
 
 galvanized, 249. 
 
 ingot, 251, 252. 
 
 metallurgy, 240-245. 
 
 ores, 240. 
 
 wrought, 250. 
 
 uses, 251. 
 Irrigation, 93. 
 
 Kerosene, 287. 
 Kindling point, 44. 
 
 definition, 45. 
 Krypton, 73. 
 
 Lampblack, 265. 
 
 Lavoisier and combustion, 30. 
 
 Law, 121. 
 
 Boyle, 84, 145. 
 
 Charles, 82, 83, 146. 
 
 conservation of matter, 11. 
 
 definite proportions, 22, 64, 107, 
 121. 
 
 Faraday, 322. 
 
 Gay Lussac, 141. 
 
 mass, 398. 
 
 multiple proportions, 64, 125. 
 Lead, 234, 236. 
 
 ores, 240, 255. 
 
 poisoning, 256. 
 
 refining, 256. 
 
 smelting, 255. 
 
 uses, 256. 
 
 Light and chemical energy, 418. 
 Light, chemical reaction, 137. 
 Lime, 196. 
 
 air slaked, 199. 
 
 calcium oxide, 196. 
 
 kiln, 196, 197. 
 
 milk of, 198. 
 
 uses, 197-198. 
 Lime, slaked, 197, 199. 
 
 uses, 198. 
 Limestone, 195. 
 
 caves, 200. 
 Limewater, 198. 
 Linde apparatus, 41. 
 Liquid air, 41. 
 
INDEX 
 
 443 
 
 Liquors, alcoholic, 292. 
 Litmus, with acids, 211. 
 
 with bases, 212. 
 Logarithms, 434, 435. 
 Lubricating oil, 287. 
 Luminosity of flames, 275. 
 
 Magnesium, 232, 233, 234. 
 Mammoth cave, 200, 201. 
 Manganese, heavy metals, 234. 
 Marble, 195. 
 Marsh gas, 284. 
 Mass law, 398. 
 Matte, copper, 252. 
 
 lead, 256. 
 Melting points, elements, 427, 431. 
 
 compounds, 429, 431. 
 Mercury, 234. 
 
 metallurgy, 258. 
 
 occurrence, 237. 
 
 ore, 240, 258. 
 
 oxide, 38. 
 
 Metallic conductor, 301. 
 Metallic radicals, 217. 
 Metals (Chapter XXI), 225. 
 
 alkali, 230. 
 
 alkaline earth, 233. 
 
 as base formers, 211. 
 
 chemical properties, 226. 
 
 classification, 230. 
 
 compounds with other metals, 229. 
 
 earth-forming, 232. 
 
 heavy, 234. 
 
 oxidation of, 27. 
 
 physical properties, 225. 
 
 tarnishing, 236. 
 
 varying activity, 235. 
 Methane, 284. 
 
 Methyl alcohol, see Wood alcohol. 
 Metric system, 436. 
 
 equivalents, 436. 
 Milk of lime, 198. 
 Minerals, 239. 
 
 table of important, 240. 
 Mixtures (Chap. II), 15. 
 
 and compounds, 22. 
 
 methods of separating, 16. 
 
 iron and sulphur, 22. 
 
 questions and summary, 19. 
 Moisture, atmospheric, 93. 
 Molal volume, 151. 
 
 finding formulae, 152. 
 
 Molecular weights, 150. 
 
 how determined, 152. 
 
 practical use, 157. 
 Molecules, 127. 
 
 elementary gases, 142, 153. 
 Moles, 150, 152. 
 
 Monoclinic sulphur crystals, 344. 
 Mortar, 198. 
 
 Multiple proportions, among ionic 
 charges, 321. 
 
 law of, 64. 
 
 law stated, 125. 
 Muriatic acid, see Hydrochloric acid. 
 
 Naphtha, 287. 
 
 Natural families of elements, 377. 
 
 Neon, 73. 
 
 Neutralization, 212. 
 
 according to ionic theory, 306. 
 
 formation of water, 215. 
 
 weak acids and weak bases, 401. 
 Nickel, the heavy metals, 234. 
 Nitrate, cellulose, 370. 
 
 sodium, 187, 366, 372, 373. 
 Nitric acid, 366. 
 
 properties, 366. 
 
 reduction, 368. 
 Nitric oxide, 364, 420. 
 Nitrides, 358. 
 
 Nitrogen and compounds (Chap. 
 XXX), 358. 
 
 questions, 375. 
 
 summary, 374. 
 Nitrogen, artificial fixation, 71. 
 
 explosive compounds, 370. 
 
 fixation of by bacteria, 371. 
 
 fixation of by legumes, 71. 
 
 from air, 67. 
 
 inertness of free, 70. 
 
 properties, 68, 69. 
 
 pure, preparation, 68. 
 
 tetroxide, 365. 
 
 Nitrogen cycle in nature, 373. 
 Nitroglycerin, 371, 420. 
 Nitrous oxide, 363. 
 Nomenclature (Chap. XX), 220. 
 
 bases, 223. 
 
 binary acids, 221. 
 
 binary compounds, 220. 
 
 oxy-acids, 221. 
 
 questions, 224. 
 
 salts, 223. 
 
444 
 
 INDEX 
 
 Non-conductors, electricity, 301. 
 Non-electrolytes, 303. 
 Non-ionized substances, 305. 
 Non-metals, acid formers, 210. 
 compounds with non-metals, 229. 
 
 Oil, crude, 286. 
 
 kerosene, 287. 
 
 Oil of vitriol, see Sulphuric acid. 
 Oils, vegetable, 295. 
 Open hearth furnace, 247. 
 Ore, aluminium, 240, 260. 
 
 antimony, 240. 
 
 copper, 240, 252. 
 
 gold, 240, 259. 
 
 iron, 240, 241. 
 
 lead, 240, 255. 
 
 mercury, 240, 258. 
 
 nickel, 240. 
 
 platinum, native, 240. 
 
 silver, 240, 258. 
 
 tin, 240. 
 
 zinc, 240, 257. 
 Ores, 239. 
 
 Organic chemistry, 282. 
 Oxidation, 27, 31, 32, 44, 46, 47. 
 Oxides, naming, 44. 
 Oxygen (Chapter V), 38. 
 
 chemical properties, 43, 44. 
 
 discovery, 29. 
 
 liquid and solid, 43. 
 
 physical properties, 40, 41, 42. 
 
 preparation, 38, 39, 40. 
 
 preparation from sodium peroxide, 
 187. 
 
 questions, 48. 
 
 unites with charcoal, 11. 
 
 summary, 48. 
 
 Oxyhydrogen blowpipe, 116. 
 Ozone, 159, 422. 
 
 properties of, 160. 
 
 use in purifying water, 161. 
 
 Paraffin, 287. 
 
 series, 285. 
 Periodic classification, 385. 
 
 table, 389 and facing inside back 
 
 cover. 
 
 Petroleum, distillation, 286. 
 Phlogiston, 26. 
 Phosphoric acid, 210. 
 Phosphorus, action in air, 67. 
 
 determination of oxygen in air, 74. 
 
 peritoxide, 209. 
 Photosynthesis, 418. 
 Physical change, examples, 13. 
 
 questions and summary, 14. 
 Plants, and carbon cycle, 419. 
 
 legumes, 71. 
 Plaster, 198. 
 Plaster of Paris, 201. 
 Platinum, 236. 
 
 occurrence, 237. 
 
 resistance to corrosion, 236. 
 Potassium, 188. 
 
 natural occurrence, 188. 
 
 properties, 230. 
 Potassium peroxide, 231. 
 Potassium salts, fertilizer, 189. 
 Powder, gun, 370. 
 
 smokeless, 371. 
 Precious metals, 236. 
 Precipitates, 399. 
 Precipitation, moisture, 94. 
 
 with hydrogen sulphide, 348. 
 Pressure, standard, 86. 
 
 water vapor, table, 425. 
 Priestley, discovery of oxygen, 29. 
 Printer's ink, 266. 
 
 Problems or questions, 14, 19, 24, 36, 
 48, 65, 78, 89, 98, 109, 119, 128, 
 140, 163, 176, 191, 205, 218, 224, 
 238, 262, 281, 298, 309, 326, 332, 
 341, 356, 375, 391, 412, 424. 
 Producer gas, 271. 
 Propane, 285. 
 Protein, 296. 
 Puddling, 250. 
 Purification, water, 96. 
 
 Questions and problems, 14, 19, 24. 
 36, 48, 65, 78, 89, 98, 109, 119, 
 128, 140, 163, 176, 191, 205, 218, 
 224, 238, 262, 281, 298, 309, 326, 
 332, 341, 356, 375, 391, 412, 424, 
 
 Quicklime, 196. 
 
 Radicals, acid, 216. 
 
 metallic, 217. 
 Ramsay, 73. 
 Rare gases, in air, 73. 
 Rayleigh, 73. 
 Reduction, by copper, 364. 
 
 by hydrogen, 118. 
 
INDEX 
 
 445 
 
 Reduction of iron ore, 243. 
 
 of nitric acid, 368. 
 Refining, copper, 253. 
 Refrigeration, 360. 
 Relative humidity, 94. 
 Reverberatory furnace, 250. 
 Reversible reactions (Chap. XXXII), 
 392. 
 
 by concentration, 394. 
 
 by heat, 392. 
 
 equilibrium point, 395, 396. 
 
 questions, 412. 
 
 summary, 410. 
 Rhigolene, 286. 
 Rochelle salt, 183. 
 Rubies, artificial, 117. 
 Rum, 292. 
 Rust, iron, 236. 
 
 Salt, common, 179. 
 
 as a preservative, 179. 
 Saltpeter, Chili, 187, 372. 
 
 source, 373. 
 
 Salts, from neutralization, 215. 
 Sapphire, artificial, 117. 
 Secondary reactions at electrodes, 
 
 317. 
 
 Silicon, carbide, 277. 
 Silver, 234, 237. 
 
 blackening of, 236. 
 
 metallurgy, 258. 
 
 occurrence, 237. 
 
 ores, 240, 258. 
 Slag, blast furnace, 242. 
 Slaked lime, 197. 
 Smelling salts, 362. 
 Smokeless powder, 371. 
 Smoke preventer, 33. 
 Soap and hard water, 201. 
 Soaps, 295, 406. 
 Soda, baking, 180. 
 
 washing, 183. 
 Soda water, 60. 
 Sodium (Chap. XVII), 177. 
 
 chemical properties, 178, 231. 
 
 flame test, 187. 
 
 metallic, 177, 230. 
 
 physical properties, 178, 230. 
 
 preparation, 177. 
 
 questions, 191. 
 
 summary, 190. 
 Sodium bicarbonate, 180. 
 
 Sodium bicarbonate, Solvay process, 
 181. 
 
 uses, 181. 
 Sodium carbonate, 183. 
 
 uses, 183. 
 
 Sodium chloride, 179. 
 Sodium hydroxide, 185, 211. 
 
 properties and uses, 186. 
 Sodium nitrate, 187, 366, 372, 373. 
 Sodium oxide, 211. 
 Sodium peroxide, 187, 211, 231. 
 Sodium stearate, 295. 
 Solubilities, table, 430. 
 
 rules of, 430. 
 Solubility and temperature, 92. 
 
 limit, 92. 
 
 Solvay process, 181. 
 Soot, 266, 275. 
 Slag, blast furnace, 243, 245. 
 
 copper, 253. 
 Slow combustion, 264. 
 Specific gravity, of elements, 427, 
 428. 
 
 of compounds, 429. 
 Standard conditions, 86. 
 
 calculation, 86. 
 Starch, 290. 
 
 Stearic acid, 295. 
 
 Stearin, 294. 
 Steel, Bessemer, 245. 
 
 low carbon, uses, 251. 
 
 mild, 249. 
 
 open hearth, 247. 
 
 special, 249. 
 Sterilization, 97. 
 Stoker, chain grate, 35. 
 Storage battery, the, 423. 
 Substance, a typical chemical, 10. 
 Substances, chemical, 16. 
 
 complexity, 18. 
 
 questions and summary, 19. 
 Sugars, 289. 
 
 Sulphide, hydrogen, 347. 
 Sulphides, 346. 
 Sulphur, 342. 
 
 allotropic forms, 343. 
 
 occurrence, 345. 
 
 uses, 342. 
 
 Sulphur and Compounds (Chap. 
 XXIX), 342. 
 
 questions, 356. 
 
 summary, 355. 
 
446 
 
 INDEX 
 
 Sulphur dioxide, 208, 349. 
 Sulphur oxides, 349. 
 Sulphur trioxide, 209, 350. 
 Sulphuric acid, 350. 
 
 chamber process, 352. 
 
 contact process, 351. 
 
 properties, 354. 
 
 Sunlight in photosynthesis, 418. 
 Symbols, chemical, 143. 
 
 of elements, Table, 340 and inside 
 back cover 
 
 quantitative significance, 154. 
 
 Table, atomic weight and valence of 
 common elements, 340. 
 
 atomic weight, complete, inside 
 back cover. 
 
 chemical symbols, 340 and inside 
 back cover. 
 
 composition of alloys, 432. 
 earth's crust, 433. 
 
 density of gases, 428. 
 
 electromotive series, 329. 
 
 important temperatures, 431. 
 
 logarithms, 434, 435. 
 
 metric and equivalents, 436. 
 
 oxides of nitrogen, 363. 
 
 periodic arrangement, 389 and 
 facing inside back cover. 
 
 pressure saturated water vapor, 
 425. 
 
 properties of common elements, 
 427, 428. 
 
 properties of compounds, 429. 
 
 solubilities of bases and salts, 430. 
 
 sulphur compounds, 356. 
 
 valence of elements, 340. 
 Tar, from coal, 273, 274. 
 
 from wood, 265. 
 Temperature, absolute, 81. 
 
 rate chemical change, 45. 
 Theory, atomic, 122. 
 
 Avogadro's, 141. 
 
 electrolytic dissociation, 304. 
 
 ionic, 304. 
 Thermit, 416. 
 Thermometer, absolute, 81. 
 
 centigrade, 79, 80. 
 Thorium, Welsbach mantle, 276. 
 Tin, 234, 235. 
 Tuyeres, 242. 
 
 Valence, 203, 336. 
 
 of elements, 340. 
 
 summary, 341. 
 
 variable, 339. 
 Vaseline, 287. 
 
 Washing soda, 183, 184. 
 Water (Chap. IX), 91. 
 
 a solvent, 92. 
 
 chemically pure, 97. 
 
 composition (Chap. X), 100. 
 
 decomposition, by electricity, 103. 
 by hot iron, 100. . 
 
 by sodium, 102. 
 
 drinking, 95. 
 
 electrolysis, 103. 
 
 gas, 270. 
 
 hard, 201. 
 
 industrial purposes, 97. 
 
 in life processes, 92. 
 
 properties, 91. 
 
 purification, 96. 
 
 sterilization, 97. 
 
 summary and questions, 98. 
 
 summary of composition, 109. 
 
 synthesis, 105. 
 Water, volume composition, 103, 106. 
 
 weight composition, 107. 
 Water vapor, in air, 72. 
 
 pressure in gases, 425. 
 Weight per liter of gases, 428. 
 Welsbach, mantles, 276. 
 Whiskey, 292. 
 White lead, 257. 
 Whitewash, 198. 
 Wood alcohol, 293. 
 Wood, combustion of, 31. 
 Wrought iron, 250, 251. 
 
 Xenon, 73. 
 
 Yeast, action on fruit sugar, 47. 
 alcohol production, 291. 
 raising bread, 61. 
 
 Zero, absolute, 80. 
 
 centigrade, 80. 
 Zinc, 257. 
 
 battery cells, 258. 
 
 galvanizing, 258. 
 
 ores, 240, 257. 
 
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 Antimony Sb 120.2 
 
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 Neodymium .... 
 Neon 
 
 Mo 96.0 
 Nd 144.3 
 Ne 20.2 
 Ni 58.68 
 Nt 222.4 
 N 14.01 
 Os 190.9 
 O 16.00 
 Pd 106.7 
 P 31.04 
 Pt 195.2 
 K 39.10 
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 \rsenic As 74.96 
 
 Nickel 
 
 Barium . . Ba 137.37 
 
 Niton (radium emanation) 
 Nitrogen 
 
 Beryllium .... Be 9.1 ; 
 Bismuth . Bi 208.0 
 
 Osmium . . ... 
 
 Boron B 11.0 
 
 jQxygen 
 
 Bromine . Br 79.92 
 
 Palladium 
 
 Cadmium . . . . Cd 112.40 
 
 Phosphorus .... 
 Platinum 
 
 Csesium Cs 132.81 
 
 Calcium Ca 40.07 
 
 Potassium 
 
 
 
 Cerium fc 
 Chlorin ! 
 
 Chromi 
 
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 Erbium |# 
 Europii 
 Fluorin 
 Gadolin - 
 Gallium 
 German 
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 Helium 
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 Iodine I 126.92 
 Iridium Ir 193.1 
 Iron Fe 55.84' 
 
 Tin 
 Titanium .... 
 
 Sn 119.0 
 Ti 48.1 
 W 184.0 
 U 238.5 
 V 51.0 
 Xe 130.2 
 
 Yb 172.0 
 Yt 89.0 
 Zn 65.37 
 Zr 90.6 
 
 Tungsten 
 
 Krypton . Kr 82.92 
 
 Uranium 
 
 Lanthanum .... La 139.0 
 Lead Pb 207 10 
 
 Vanadium 
 Xenon . . 
 
 Lithium Li 6.94 
 
 Ytterbium (Neoyttcr- 
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 Lutecium Lu 174 
 
 Magnesium . . . . Mg 24.32 
 Manganese .. . .... . Mn 54.93 
 Mercury . . . .- . Hg 200.6 
 
 Yttrium 
 
 Zinc 
 
 Zirconium . .