GIFT OF Pacific Coast Journal of* BIOLOGY LIBRARY i* APPLIED CHEMISTRY APPLIED CHEMISTRY AN ELEMENTARY TEXT BOOK FOR SECONDARY SCHOOLS BY FREDUS N. PETERS, PH.D. Instructor in Chemistry in Central High School, Kansas City, Mo., for twenty-three years; More Recently Vice-Principal; Author of "Chemistry for Nurses," etc. ILLUSTRATED ST LOUIS C. V. MOSBY COMPANY 1922 ap3i B10LOGY R D GIFT PACIFIC 00 AST JOURNAL} OF NUBS1NG TO H/QcJrtE DEPT COPYRIGHT, 1922, BY THE C. V. MOSBY COMPANV. (All rights reserved) Printed in U. S. A. Press of C. V. Mosby Company St. Louis o the hundreds of young men and women, students of mine in the past, whom it has been my privilege to know and to love ; especially to my own son, Fredus Nelson, Junior, who in his early childhood, playing at chemistry among the bottles and apparatus of my laboratory, found his chief delight and who now in his early manhood gives promise of at- taining to heights in this realm of science of which his father only dreamed, this little book is affection- ately dedicated by the author. 743629 PREFACE The author is not very sure but that the preface of any book is a useless page. It is doubtful whether a sufficient number ever read this personal letter of the author to pay him for the writing or the publisher for printing it. Yet every writer by force of custom feels compelled to address his readers by a foreword. Like Livy, in his preface to his History of the Roman People, I do not know whether I am doing a work worth while in putting another text of elementary chemistry be- fore the public ; and even if I knew, modesty would forbid that I speak very strongly. Permit me to say that to me it has never seemed neces- sary for a high school chemistry to present a mere skeleton of the most interesting of sciences when that skeleton may just as easily be clothed with wonderful symmetry and charming beauty. On the contrary, it has always seemed that a text for secondary schools may and ought to be a readable book just as well as one merely surfeited with facts. No dinner menu is complete which offers nothing but lean meat and vegetables. It may thus contain all that is essential, but far from all that is desired. Entrees and desserts round out the repast and give a sense of satisfac- tion not otherwise possible. Such is the attempt of this text, to present the chemical facts of every-day life in a readable form and by so doing make them interesting. If this cannot be done, for most students the book is a failure. To the teacher let me say that my long experience com- pels me to believe that very few classes, in a school year of nine or ten months, are able to complete a text of this size. 11 12 PREFACE Some portions must be omitted. No one in a table d'hote dinner is expected to order everything on the bill of fare. Let him use judgment and discretion, the teacher likewise. Almost a quarter of a century has elapsed since I began my work in Central High School in Kansas City, one of the great high schools of the Middle West. I should not be true to my own better self did I fail to acknowledge my debt of gratitude to the hundreds of students whom I have had in that time. In this particular work I wish to thank especially Mr. J. U. Young, now head of the department of Chemistry of Central High School, Kansas City, for his many valuable suggestions and also Mr. G. W. Davis, of the Northeast High School, Kansas City. I am also under obligations to Mr. G. H. Wilkinson of the Physics Depart- ment of Jefferson High School, Los Angeles, Cal., who has been of material assistance in reading the manuscript ; to Mr. F. N. Peters, Jr., of the Department of Chemistry of the University of Missouri, for suggestions in methods of presentation of certain gas laws, to Mr. V. W. Peters, of Los Angeles, Cal., for drawings from which many of the illustrations were made ; to the Goldschmidt Thermit Co., of New York City, for illustrations of thermit welding, to the Permutit Water Softener Co., of New York, as well as to two or three publishing houses who have extended courtesies in the way of illustrations. F. N. P. Los Angeles, California. CONTENTS CHAPTER I A STUDY OF MATTER 21 CHAPTER II WATER AND HYDROGEN PEROXIDE 34 CHAPTER III OXYGEN AND OZONE 51 CHAPTER IV HYDROGEN 63 CHAPTER V THE ATMOSPHERE 72 CHAPTER VI GASES AND SOME GAS LAWS 84 CHAPTER VII SYMBOLS AND FORMULAS , . . ... 106 CHAPTER VIII SOME CHEMICAL PROBLEMS 112 CHAPTER IX THE HALOGENS 119 CHAPTER X ACIDS AND BASES 136 CHAPTER XI NITROGEN AND COMPOUNDS ..... 145 13 14 CONTENTS CHAPTER XII CARBON 159 CHAPTER XIII VALENCE 173 CHAPTER XIV ILLUMINATING AND FUKL GASES 183 CHAPTER XV FLAME 189 CHAPTER XVI METHODS OF LIGHTING 197 CHAPTER XVII SOME ORGANIC COMPOUNDS 203 CHAPTER XVIII ETHEREAL SALTS, OILS, FATS, SUGARS 212 CHAPTER XIX FOODS AND THEIR BODY VALUES 224 CHAPTER XX SOLUTION AND IONIZATION 233 CHAPTER XXI SULPHUR AND COMPOUNDS 249 CHAPTER XXII PERIODIC CLASSIFICATION OF ELEMENTS 265 CHAPTER XXIII THE NITROGEN FAMILY 274 CONTENTS 15 CHAPTER XXIV COMPOUNDS OF SILICON 294 CHAPTER XXV THE ALKALI METALS 305 CHAPTER XXVI SOME LEAVENING AGENTS 327 CHAPTER XXVII THE CALCIUM FAMILY 336 CHAPTER XXVIII HARD WATERS METHODS OF SOFTENING 346 CHAPTER XXIX CLEANING AND POLISHING 353 CHAPTER XXX THE COPPER GROUP 362 CHAPTER XXXI THE MAGNESIUM- FAMILY 379 CHAPTER XXXII THE ALUMINUM FAMILY 392 CHAPTER XXXIII THE LEAD FAMILY 402 CHAPTER XXXIV THE CHROMIUM FAMILY 411 CHAPTER XXXV MANGANESE AND COMPOUNDS 416 16 CONTENTS CHAPTER XXXVI THE IRON GROUP 419 CHAPTER XXXVII THE PLATINUM AND PALLADIUM GROUPS 434 REFERENCE TABLES AND GLOSSARY REFERENCE TABLES AND GLOSSARY 437 ILLUSTRATIONS FIG. PAGE 1. Abundance of certain elements 20 2. Showing the "north" end of a magnetic needle being at- tracted by the "south'' end of another 28 3. Wire showing the anode and the cathode 29 4. Electrolysis or Hoffmann apparatus 37 5. Composition of water by weight 39 (5. Manometer used in testing gas pressure 42 7. Diagrammatic view of city water plant 46 8. Roosevelt Dam, which is very similar to the one at Sweet- water . 47 9. Showing relative abundance of oxygen in nature ... 52 10. Preparation of oxygen 53 11. Preparing oxygen from sodium peroxide 54 12. Boiling water in paper cup 57 13. Machine for making ozone 59 14. Electromotive series of metals and bar magnet with iron filings attached 65 15. Preparing hydrogen from water by means of sodium . . 60 16. Preparation of hydrogen from acids 67 37. Oxyhydrogen blowpipe . 68 18. Lavoisier, beheaded in French Revolution, the Father of Modern Chemistry 70 19. Nodules in which the nitrogen-fixing bacteria live on the roots of a bean 77 ?0. Dewar bulbs. The thermos bottle is merely different in shape o . . . . 81 21. Comparison of thermometers 85 22. Aneroid barometer 88 23. Illustrating pressure of water vapor 91 24. Contraction of volume on mixing two liquids .... 94 25. Dalton, who proposed the atomic theory of matter ... 98 26. A simple eudiometer connected to induction coil . . . 101 27. Preparation of chlorine in the laboratory 121 28. Manufacture of chlorine 122 29. Effect of sunlight on chlorine water 124 I 17 18 ILLUSTRATIONS TIG. PAGE 150. Apparatus for purifying iodine by sublimation .... 132 .'51. Method of determining approximately the proportion of nitrogen in the air 140 32. Manufacture of ice 149 33. Preparation of nitric acid 152 34. Some forms of smokeless powder 15(5 35. Burning of a diamond 1(51 3(5, Moissan's electric furnace . 162 37. Oil derricks, a familiar sight in oil-producing sections . 1C5 38. Formation of carbon monoxide in a furnace 169 39. Pouring carbon dioxide upon burning candles in a trough 172 40. Babcock fire extinguisher 174 41. Acetylene burner 184 42. "Burning" air ..." 191 43. Match suspended within burning gas jet 192 44. Burning gas drawn from center of candle flame .... 193 45. Determination of flash point of an oil 198 46. Starch granules 221 47. Foods rich in iron 231 48. Foods rich in phosphorus . 232 49. lonization of a solution of common salt, and proof of same 242 50. Method of obtaining sulphur in Louisiana 250 51. Sulphur crystals 251 52. Chamber process for sulphuric acid 261 53. Manufacture of phosphorus 276 54. Preparation of phosphine 279 55. Marsh 's test for arsenic 283 50. A scene in one of the petrified forests in Arizona . . . 295 57. Mold for making glass tumblers 300 58. Mold for blowing glass bottles 301 59. Making window glass 302 60. Preparation of sodium by the Oastner process .... 307 01. Preparation of salt in San Francisco Bay, by evaporation of sea water 310 62. Scale in iron pipes, from an actual cnse 347 63. Making an electrotype 367 64. Hydraulic mining 375 65. Manufacture of aluminum 394 66. Thermit crucible, sectional view 395 ILLUSTRATIONS 19 FIG. PAGE 67. A thermit crucible ready for use in mending a broken casting- 396 68. A thermit crucible in operation, mending a broken casting 397 69. A battery " grid" 408 70. A blast furnace for preparing cast iron 421 71. A blast furnace, showing the molds for the "pigs" in the sand 423 72. The Bessemer converter 425 APPLIED CHEMISTRY CHAPTER I A STUDY OF MATTER Outline Introduction Former Method of Reasoning Present Methods of Scientific Investigation Old Theories of Matter (a) Composition of (&) Transmutation Present Ideas Elements Compounds (a) Definition of (6) Chemical Union (c) Method of Naming (d) Explanation of Chemical Union Chemical Changes Kinds and Illustrations Mixtures 1. Introduction. Nearly every normal child is born an interrogation point. Almost as soon as he can form sentences be begins asking "why;" and many a Christ- mas, toy has served best by its sacrifice upon the altar of childish investigation in the effort to learn what makes the noise, or why the wheels go around. The his- tory of the child is largely the history of the human race. Were the spirit of inquiry not crushed out in childhood, grown to youth and maturity, all would still find the greatest pleasure in studying the phenomena of nature. Some few survive the rebuffs and repressions of child- 21 22 APPLIED CHEMISTRY hood and to them nature ever speaks in loving and fascinating words. Others must have this instinct of investigation revived in their hearts if they find pleas- ure in axijyi seienc^v ; Chemistry , as 1 0,1? e, branch of learning probably enters more 1 largely l mfed th&i affairs ,bf ordinary everyday life than any other. Without it, not only would most of the great engineering achievements of the world, such as the construction of great bridges and transcontinental railways, and the Panama Canal; not only would the au- tomobile and the airplane and all other modern means of rapid transportation be unknown, but the many little things of life would be mysterious and unintelligible. Cookery is a science dependent in many ways upon chemistry ; pure foods and drinks can be kept so only by a knowledge of chemistry; healthful air and sani- tary conditions in the home must be secured by a knowl- edge of chemistry on the part of some one. Careful investigation shows that a knowledge of chemistry must be had for scientific progress in almost every line of human activity. This little book, therefore, will seek to be helpful in furnishing such chemical information as shall be needed in the affairs of the home and in giving added interest to everyday life ; such, that these affairs may be administered the more wisely and that nature may speak the more intelligibly; such that those who read may not only add to their own pleasures but contribute to the welfare and happiness of all who may come under their influence. 2. Source of Scientific Knowledge. There was a time in the world's history when scientific knowledge was thought possible of attainment by reasoning alone. Aris- totle, it is said, maintained that a vessel filled with ashes or sand would hold as much water as if there were nq A STUDY OF MATTER 23 ashes or sand in it. He never made the experiment to prove or disprove the truth of his statement and such was the strength of his influence, and such the method of reasoning- of the times and long after, that centuries passed before anyone sought to question by experiment the truth of his statement. 3. Present Methods. In this age of the world every statement of scientific fact or supposed fact is sub- mitted to the most rigid and searching examination; not only is reason applied, but every possible .method of testing experimentally the truth of the statement is used. To illustrate: Some years ago one of England's greatest chemists announced in a paper read before a scientific gathering that he had succeeded in making a certain amount of lithium from copper by the use of radium. The next morning's sun had hardly risen be- fore many of his hearers were preparing to repeat his experiment, not for the sake of the experiment, but to prove or disprove his claims. So, in the present age of the world, every theory of every scientist, no matter how noted he may be, or however plausible his theory may seem, must be subjected to the test of practical ex- periment before it can be accepted as a scientific fact. 4. Some Abandoned Theories. As a result of the manner of thought of centuries ago, many theories were accepted as sufficiently plausible which long since have been abandoned. When a vessel of water is left exposed to the air or placed upon some source of heat, the water disappears. Centuries ago it was believed that water upon the addition of heat is changed into air ; further, that the air upon the removal of the heat again be- comes water. This was based upon a very superficial observation, first the disappearance of the water as stated, and second, its appearance upon the surface of 24 APPLIED CHEMISTRY any cold object brought into a warm room, as upon the outside of a tumbler of ice water. But no careful experiments were ever made to prove or disprove the theory. It was also believed that when water is boiled, a portion of it is converted into an earthy substance. True, upon the inside of the tea-kettle in the kitchen a hard, brittle crust gradually forms, but this is simply mineral matter which has been previously dissolved in the water. Pure water never leaves any such residue. But the old philosophers never made the experiment with pure water, as they might have done, to prove the truth of their position. 5. Transmutation, At the time chemistry had its birth, philosophers believed thoroughly in the possi- bility of the transmutation of one substance into an- other. Just as they maintained that water could be changed into earth and air, and air into water, so they believed one metal could be transmuted into another. They had observed some things that to them seemed sufficient evidence. Often, in their copper mines they had noticed that the iron tools left standing for some time in the water, which seeped in, became reddish in color and looked as if the iron were changing to cop- per. This may be seen by putting a bright nail or knife blade into a solution of blue vitriol for a minute or two. A deposit of copper really forms upon the iron, but it may be shown experimentally that the two meta^ are simply being exchanged for one another and that the iron is not changing into copper. They knew also a process for making brass by fusing copper with an ore of zinc which they called cadmeia. They recognized there were vast differences between brass and gold, yet never did they doubt that it was entirely pos- A STUDY OF MATTER 25 sible to change iron into copper and this into gold ; in fact they strongly believed in the possibility of trans- muting any metal into any other if they could but learn the method. 6. Matter. Matter is anything which occupies space, and may be visible or otherwise. Thus, air is matter just as much as is water or wood or iron. What the real composition of matter is has long been one of the great questions of man. There have possibly always been those who believed that there is but one kind of matter in all the world, and that everything we knoAV is simply a modified form of this one kind. On the basis of such a theory it was not hard to believe in the transmutation of the metals. Others claimed there were four primary substances, earth, air, fire, and water, and that these in a way could be changed from the one into the other. 7. Present Theory. Robert Boyle, sometimes called the Father of Physics and Chemistry, who was born in 1626, advanced the theory that there is a large number of kinds of matter, how many no one knows. To these primary forms he gave the name of elements, and the truth of his view has long been accepted by most of the scientific world. According to this idea, an ele- ment is a substance that cannot be divided into two or more kinds of matter. Thus gold is believed to contain only .gold and copper nothing but copper. At present there are known 83 elements, the greater portion of which exist in comparatively small quantities, and most of which have been discovered since the beginning of the nineteenth century. Of these, eleven are gases, two are liquids, and the others solids. Some of the rarer may on more careful study be found not to be elements, while others as yet unknown will probably be 26 APPLIED CHEMISTRY discovered. It is estimated that two elements, oxygen and silicon, constitute about 75 per cent of all the mat- ter of the earth and seven others nearly all the re- maining 25 per cent. Clark gives this table: Per cent Oxygen 49.98 Silicon 25.30 Aluminum 7.26 Iron 5.08 Calcium 3.51 Magnesium 2.50 Sodium 2.28 Potassium 2.23 Hydrogen 0.94 The same facts are shown more graphically in Fig. 1. Oxygen 50 % SUicon 257. Fig. 1. Abundance of certain elements. 8. Compounds. A compound is a substance contain- ing two or more elements chemically united and in- variably in the same proportion by weight. The most familiar of all compounds is water, which consists of two elements, hydrogen and oxygen, always in the pro- portion of 1 to 8. Common salt is another compound containing the two elements, sodium and chlorine, al- ways united in the proportion approximately of 46 to 71. 9. Chemical Union Defined. In defining a compound in the preceding paragraph the expression, chemically united, was used. If two substances are mixed, the re- sulting product will partake of the nature of each in- gredient. Two white substances will give a white pro- duct, a red and white will give a pink, a white and black A STUDY OF MATTER 27 a gray. But if two substances differing from each other unite chemically the product formed may not partake of the properties of either even to the slightest extent, and will be essentially different. To illustrate: Hydrogen and oxygen are both colorless gases, the former inflam- mable ; the latter essential for life and ordinary combus- tion. When the two unite chemically, at ordinary tem- peratures, the resulting product is a liquid, which is not only not inflammable but will even extinguish fire and cannot be inhaled. Sodium, in common salt, is a soft metal, silvery white in color, which upon the moistened hand or in the mouth would catch fire and produce most serious burns. Chlorine, the other ingredient, is a heavy yellow gas, terribly destructive of life if inhaled and used with frightful results in the late great war. When these two unite chemically each loses its properties, and the two produce an entirely new substance, not only not harmful, in ordinary quantities, but even regarded as an essential in the animal economy. Likewise, two white substances, uniting chemically, may produce a brilliant red, as do potassium iodide and mercuric chloride; two gases may form a solid, as will ammonia and hydrogen chloride ; two liquids a solid. Many of these in great variety will be taken up from time to time and need not be emphasized here. 10. General Plan of Naming Compounds. A few gen- eral statements as to IIOAV compounds are named will be helpful at this time. In the early days of chemistry no plan was followed in naming the various substances prepared. As a result, peculiar and fantastic names of very familiar things have come down to us. At the present time so vast is the number of compounds known hundreds of thousands that some very definite and systematic method is necessary, In most cases as soon 28 APPLIED CHEMISTRY as a chemist hears the name of a compound, he knows its composition even though it may be one not familiar to him. Common salt is chemically known as sodium chlo- ride, and one knows immediately that it consists of so- dium and chlorine ; if the name ends in ide the compound contains only the elements mentioned, which, except in a few cases, are but two in number. Thus, mercuric chloride contains mercury and chlorine; potassium io- dide, potassium and iodine. If the name of the com- pound ends injite, with few exceptions which need not be mentioned here, the compound contains oxygen, in ad- dition to the other elements named. Thus, sodium chlo- Fig. 2. Showing the "north" end of a magnetic needle being attracted by the "south" end of another. rate contains sodium, chlorine and oxygen; potassium sulphate, potassium, sulphur and oxygen. 11. What Elements will Unite? Not every element will unite with every other element. If two magnets, either bar or horseshoe, be placed together, end to end, there will be no attraction if the two ends marked - are brought together or likewise if the two marked + ; but if an end marked -{- be brought up to one with the opposite sign they adhere strongly. This is always true. Everyone is familiar with the ordinary compass, often spoken of as th.e mariner's compass. If the end of the A STUDY OF MATTER 29 needle which points north be approached by the north end of a similar magnetic needle, the one free to move will swing away; if the opposite end be approached they will attract each other. (See Fig. 2.) From these facts a simple law has been formulated: "Like poles repel and unlike poles attract each other. ' ' If the ends of two wires connected with an electric battery be dipped in a solution through which the current can pass in a U-shaped tube as shown in Fig. 3, the wire upon which the current enters is spoken of as the anode, from a Greek word meaning the road in and the wire upon which the current passes out is called the cathode, or the road out. Often the Fig. 3. The wire marked + is the anode and the other is the cathode. anode is called the positive and the cathode the negative electrode. Now if the solution used be one of common salt, sodium chloride, it will be found that the sodium al- ways collects at the cathode and the chlorine at the anode. For this reason, applying the law stated above, sodium is regarded as a positive element and chlorine as a negative. In general, in all similar compounds the metal collects at the cathode and the other element at the anode. Hence, all such consist of a positive and a negative element or group of elements. In naming such compounds the positive is always given first. Thus, sodium chloride contains a positive element, sodium, and a negative ele- 30 APPLIED CHEMISTRY ment, chlorine. Copper sulphate contains copper, a posi- tive element and a negative group, consisting of sulphur and oxygen. It would seem then from these statements that chemical union is a kind of electrical attraction. 12. Chemical Changes, Kinds. There are several kinds of chemical changes; in all cases the identity and the characteristics of the substances involved are lost or destroyed. This has been illustrated in the case of hydro- gen and oxygen uniting to form water and of sodium and chlorine, to form common salt. Such as these are very simple and are known as "Additive Reactions/' an expres- sion which indicates that the two substances have been added or joined together and have formed a single sub- stance. Another similar and very familiar case is that o flashlight powders used in photography. The essential in- gredient, that which produces the intensely white light, is magnesium, a steel-gray metal which has been pow- dered. In burning, it simply combines with oxygen, pro- ducing a white compound known as magnesium oxide, often called magnesia, used in cleaning felt hats, kid gloves, as a dressing for white shoes and for similar well- known purposes. 13. Simple Decomposition. Another kind of chemical change equally simple as the preceding is known as "Simple Decomposition." In such changes the process is the reverse of the additive. A single compound by heat or some other force is decomposed into its component ele- ments. To illustrate by a familiar example, mercuric ox- ide, a compound whose name indicates its composition, if heated strongly is decomposed into mercury, which col- lects upon the sides of the vessel in which it is heated, and oxygen, which is invisible, but which may be detected by holding a pine splinter with a spark upon the end above in the outgoing current of gas. The splinter will A STUDY OP MATTER 31 burst into a flame. Likewise, if a current of electricity be passed through water acidulated to render it a conduc- tor, it will decompose the liquid into the two gases of which it is composed. 14. Metathesis, or Double Decomposition. By far the greater number of chemical changes are not as simple as the two kinds already mentioned. More frequently two, and sometimes more than two, substances unite or react with each other, in which case both substances are decomposed and two or more new ones are produced, by a rearrangement of the elements contained in the com- pounds. Such a change is spoken of as "Metathesis" or "Double Decomposition." It may be illustrated by add- ing a few cubic centimeters of a solution of potassium io- dide to one of mercuric chloride in a test tube. Two new substances are formed, both entirely different from the original, one of them now a brilliant red color and not sol- uble in water. Numerous illustrations of this kind of change will be had from time to time. Really, metathesis is but a combination of the other two kinds of change in which both or all of the substances used are decomposed and the products combined in a new way. 15. Mixtures. A mixture differs from a compound in that the composing substances do not unite with each other as in additive reactions; neither is there any rearrang- ing of the elements into new groupings. Further, as a rule, no definite amounts of the two substances are used, or at least are not necessary. The particles of one inter- mingle with those of the other, but each retains all its own properties. White sand may be mixed with com- mon salt, but neither has lost its distinguishing properties. A little placed on the tongue will possess a salty taste and at the same time will have the gritty feeling of the sand. Moreover, one may readily be separated from the other 32 APPLIED CHEMISTRY by adding water, stirring and after a few minutes decant- ing or filtering. A common case given by nearly all books is that of fine iron filings and flowers of sulphur. Mixed together, the result is a greenish-gray powder, but neither has lost its distinguishing properties, and as in the case of the salt and sand they may be readily separated. With patience most of the iron filings may be successfully separated from the sulphur by a good magnet. An easier and more satisfactory method is to add carbon disulphide which upon shaking will dissolve the sulphur as water will salt. The dissolved sulphur may then be poured off through a filter paper; if the filings are washed with another portion of the carbon disulphide all the sulphur may be removed. By evaporating the liquid the sulphur may be recovered with all the properties it possessed be- fore. If, however, the intimate mixture be heated for some time strongly in a test tube, the resulting mass will be black instead of greenish, will not be attracted by the magnet as the filings were, and the sulphur cannot be re- moved by solution. Chemical union has taken place and we now have a compound of iron and sulphur, called iron sulphide. Exercises for Review 1. Do you believe Aristotle's statement about the globe of sand? Give reason for your answer. 2. At the present time how is scientific truth obtained? Can reason aid at all in the discovery of Nature's laws? Explain. 3. What was the old idea regarding the relation of water to air? What facts had they to cause such a belief? 4. What is meant by transmutation? What led the ancient phil- osophers to believe in such a thing? Do you believe it possible? Why? 5. What is matter? How many kinds can you find in this book? In this room? Give two old theories about the composition of matter. A STUDY OF MATTER 33 6. What was Boyle's idea of matter? What is the present idea? Is this necessarily the true idea? Explain. 7. Define an element. How many are known? How many are liquids? Solids? How many constitute nearly the whole of the earth? What two are the most abundant? 8. What is a compound? Name two and give composition. Ex- plain what is meant by chemical union. Illustrate. 9. What is the general plan of naming compounds? Give the signification of the endings ide and ate. Give illustrations. 10. Into what two classes are elements divided? Will copper and silver unite to form a compound? Give reason for your answer. 11. How can one learn experimentally whether an element be- longs to one class or the other? Give meaning of the terms anode and cathode. What synonyms are sometimes used? 12. Name three kinds of chemical changes. Give illustration of each. Show how the third may be regarded as a combination of the other two. 13. How does a mixture differ from a compound? Name two mixtures and give some easy way of separating them. CHAPTER II WATER AND HYDROGEN PEROXIDE Outline Forms of Appearance Characteristics of Pure Water Water in the Human Body and Foods Necessity of Water to the Body Proof of Composition () By Electrolysis (&) By Weight Law of Definite Proportions Water of Combination Hydrates Efflorescence Deliquescence Domestic Water Supplies City Water Supplies Hydrogen Peroxide Law of Multiple Proportions 1. Its Familiarity. Water is at once the most famil- iar of all natural substances and one of the most inter- esting. It appears in a very large variety of forms, all more or less familiar: in partially condensed vapor as fog ; in the feathery cirrus cloud ; the billowy cumulus, the beautiful summer cloud ; the stormy and threatening nimbus. In the solid form as snow, hail, ice, glaciers and icebergs. 2. Characteristics of Water. Pure water is tasteless, odorless and colorless, except in great depths as lakes and seas, when it appears blue or bluish green. It is often said that distilled water tastes flat, but this is be- cause we are accustomed to drinking water somewhat impure. Just as beans or potatoes or other vegetables served without salt would taste flat so does water with- 34 WATER AND HYDROGEN PEROXIDE 35 out the usual impurities. Pure water when evaporated leaves no residue, hence would form no incrustation on the inside of kettles or boilers. 3. Water in the Human Body. Not only does water appear in such variety of form and such quantities in nature, but it constitutes a very large proportion of the animal body. Only about 40 per cent of the human body is solid matter, while in the lower animals the percentage of water is much higher. Our foods are also high in water content. Even butter and flour, which we often think of as dry, contain as much as 12 to 14 per cent of water for the former, and 10 to 11 for the latter. The following table will give an idea as to many of the com- mon food products: TABLE Per cent Beans, dry , 12.60 Beans, string 89.00 Bread, yeast 36.12-37.70 Cabbage 91.50 Carrots 88.20 Cauliflower . 92.30 Celery 94.50 Cheese 34.38-38.60 Com, dry 13.12 Eggs 73.67 Flour, wheat 10.11 Meat, lean beef 67.00-70.00 Meat, lean pork 60.00 Meat, veal 73.30 Mutton 50.20 Oat Meal 12.37 Peas, dry 12.62 Peas, green 79.93 Potatoes, sweet 75.00 Potatoes, white 66.10-80.60 Rice 13.11 Turnips 89.60 Watermelons . ..92.40 36 APPLIED CHEMISTRY 4. Value of Water to Animals and Plants. Nothing need be said about the value of water in the household. Life itself is impossible without it, to say nothing of the comfort it brings. Digestion is merely a process by which solid foods are made soluble that they may be carried through the blood to all parts of the body. As water is the most nearly universal solvent it enters largely into the process of digestion. Assimilation of food is impossible in the absence of water; and not only is this true, but most of the waste matter of the body is carried away dissolved in water or mixed with it in large amounts. On account of its high specific heat, that is, a given amount of water contains more heat energy than the same weight of any other liquid at the same temperature, it is regarded as the best means of warming houses in severe weather. It is this very fact that tempers the winters in the Great Lake regions and along the oceans, and renders the climate of countries washed by the Gulf Stream and Japan Current far warmer than other countries in the same latitude not thus favored. In the human body, the blood, largely water, in constant circulation, tends to keep the body of perfectly uniform temperature. In summer, the body is cooled by the rapid evaporation of the water in the blood through the pores of the skin; thus, summer and winter, the water in the body serves to keep a uniform temperature throughout. To maintain the supply thus needed, an ordinary per- son requires from two to three pints of water per day, in summer more than in cold weather. Plants, likewise, must have water to enable them to absorb the necessary substances of food value from the soil, as also, to make the cellulose, starch and sugar, which they store up in their stems, seeds and fruits. WATER AND HYDROGEN PEROXIDE 37 5. Composition of Water. By volume, water is com- posed of hydrogen, two parts, and oxygen, one part. This is usually shown experimentally by the Hoffman apparatus (Fig. 4). K is a reservoir into which the water is poured in filling the apparatus. It is neces- sary to use water slightly acidulated with some acid, as sulphuric, since pure water is not a conductor of elec- tricity. In filling the side tubes, B, B, the stop-cocks are carefully opened, one at a time, and the water allowed to flow in until it barely reaches the stop-cock level. Fig. 4. Electrolysis or Hoffmann apparatus. Not much more should be put into R than will fill the three tubes, for a small amount of water makes a large quantity of gas and this forces the excess back into the reservoir, hence room must be left to receive it. Plat- inum strips, A, A, serve as electrodes and are connected with the source of current by means of wires sealed in glass tubes passed through the corks, C, C. When every- thing is ready the current is turned on ; bubbles imme- diately begin to rise from both electrodes, much faster from the cathode than the anode. After a few moments 38 APPLIED CHEMISTRY the quantity of gas in each tube may be read from the graduations etched 011 the tubes, B, B. It will be found that the quantity of one gas is always double that of the other. To know that the smaller volume is oxygen, hold a splinter with a spark on the end over the tip of the tube and carefully open the stopcock. The pressure of the water in R will force the gas out and ignite the splinter. This characteristic test for oxygen has been mentioned in the preceding chapter. The usual method of testing hydrogen is by lighting it. A burning match or better, a small candle, brought to the tip of the tube containing the larger quantity of gas, will ignite it when the stop cock is cautiously opened. The flame at first will be invisible, or until the glass becomes red-hot; but a piece of paper held to it will be instantly ignited, thus showing the presence of a flame. 6. Explanation of the Experiment. Students fre- quently ask why the hydrogen goes to the cathode or negative electrode, and the oxygen to the anode. This will be readily understood if it is remembered what was said in the preceding chapter about compounds con- sisting of a positive and a negative element or group. Since oxygen belongs to what we call the negative group, it would necessarily be attracted to the anode : while hydrogen, being positive, would be attracted to the negative electrode. 7. Proof of Composition by Weight. Since gases are very light substances it is necessary to obtain their weights indirectly in this experiment. In Fig. 5 hy- drogen is obtained from any suitable generator, K, which for convenience may well be a Kipp apparatus. In order that the gas may be perfectly dry it is allowed to bubble slowly through a wash bottle, containing concentrated sulphuric acid, which is an excellent dry- WATER AND HYDROGEN PEROXIDE 39 ing agent in that it absorbs water readily. The tube, T, macb of hard glass, contains copper oxide, preferably in what is known as the wire form. Before connecting, this tube with contents is carefully weighed. In the U-tube calcium chloride in small lumps is placed, the tube and contents carefully weighed and connected to the combustion tube as shown. The hydrogen is then turned on, the heat applied, gently at first, until the glass is well warmed, and the operation continued until the contents of C have become red like bright copper. The heat is then turned off, the hydrogen allowed to flow until the tube is cooled enough to handle comfort- Fig. 5. Composition of water by weight. ably when both T and U with contents are again carefully weighed. What has happened is as follows: Hydrogen has the power of taking oxygen away from many oxides when heated strongly. It does so in this case and leaves in the combustion tube mostly pure copper. The loss of weight in this tube, therefore, is the weight of the oxygen used. The hydrogen and oxygen at the tem- perature present combine to form water, which in the condition of vapor passes over and is absorbed by the calcium chloride in tube U. The gain here, therefore, is the weight of the water produced. Subtracting the weight of the oxygen used from that of the water formed 40 APPLIED CHEMISTRY gives the weight of the hydrogen. Allowing for experi- mental errors which are always possible, it will be found that the average of a large number of experiments car- ried out thus is always 8 parts of oxygen to 1 of hy- drogen. A typical case with data obtained by actual experiment is given below: Copper oxide and tube before heating 37.23 grams Weight of same, after heating 29.87 Loss, which is oxygen 7.36 Calcium chloride and tube, before heating. . . .25.18 Weight of same, after heating 33.46 Gain, which is the water 8.28 Subtracting the oxygen from weight of water 0.92 Ratio of oxygen, 7.36, to hydrogen, .92, is 8 to 1 8. Law of Definite Proportions. It was stated in the preceding chapter that a compound is a substance con- taining two or more elements united in a fixed and defi- nite proportion by weight. The above experiment il- lustrates the definition and at the same itime shows proof. Out of this truth, which applies to all compounds, grows the "Law of Definite Proportions," which is usually stated thus: When two or more elements unite chemically to form a compound they always do so in the same fixed and definite proportion ~by weight. Why they must necessarily do this will be taken up at another time in Chapter VI. 9. Hydrates Water of Combination. All have seen various substances in crystalline form, such as rock candy, alum, blue vitriol, or such natural compounds as iron pyrite, silica, called rock crystal, and galena. Crys- tals of artificial compounds are usually prepared by dis- solving the substance in water and allowing the water to evaporate. When this occurs, very often a consider- able portion of the water combines with the dissolved WATER AND HYDROGEN PEROXIDE 41 solid instead of passing off into the air. Sometimes the water thus combined weighs even more than the solid itself. The water thus taken up is called water of com- bination or sometimes water of crystallization, and the compound thus formed is called a hydrate. Familiar ex- amples of hydrates are blue vitriol, Epsom salts, alum, sal soda, and green vitriol. TABLE SHOWING A FEW HYDRATES AND AMOUNT OF WATER Alum, common. .45.57 per cent Blue Vitriol 36.14 Borax 47.12 Epsom salts 51.22 per cent Green Vitriol 45.32 Sal Soda 62.93 10. Efflorescence. Hydrates may be regarded as true compounds, for they differ greatly in their physical properties from the anhydrous compound. Thus, ordi- nary hydrated copper sulphate is deep blue in color, and occurs in. more or less regularly-shaped triclinic crys- tals. Anhydrous copper sulphate is white in color and when crystalline, which is not common, is in slender needle-like crystals. However, this combination is rather an unstable one. By heat, usually the water of the hy- drate may be removed without affecting the composi- tion of the remaining portion of the compound at all. Even at ordinary room temperatures in many cases con- siderable portions or all of the w^ater of combination spontaneously passes off into the air. The extent of this loss depends upon the humidity of the air, the tem- perature and the specific rate of the particular compound itself. This may be seen in an interesting little experi- ment. A manometer as shown in Fig. 6 is attached to a side-neck test tube. A bent glass tube may serve as a manometer if no other is at hand. A rubber cork 42 APPLIED CHEMISTRY is fitted snugly into the test tube filled about half full of mercury. The bent tube also contains mercury at the same level in both arms. A crystal of some hydrate, such as sodium sulphate is put upon the mercury in the test tube and the cork carefully inserted again so as not to disturb the level of the mercury in the bent tube, M. Even at the room temperature water will escape from the crystal, producing pressure upon the mercury in the manometer, moving it up the longer arm, until there is Fig. 6. Manometer, used in testing gas pressure. equilibrium. At this point no more water escapes from the hydrate on account of the pressure exerted upon it. Now, if the temperature be raised a few degrees, more water will be expelled and the mercury will rise in the outer arm still higher, until the added pressure again equals the vapor pressure of the water in the crystal. Upon cooling the equilibrium is again disturbed and through the pressure of the mercury the hydrate will ab- sorb water vapor until there is again equal pressure within and without the hydrate. In the open air, as the pres- sure is not increased by the escape of the water, the loss WATER AND HYDROGEN PEROXIDE 43 continues until no more can be driven off at that tem- perature. A considerable number of hydrates are able to part with all their water at ordinary room tempera- ture and usual atmospheric conditions. Such hydrates are said to be efflorescent. Efflorescence may be denned as the property which some hydrates possess of giving off to the air their water of combination and of crumb- ling to a powder. The word, literally translated, means becoming flowers or flour, that is, a fine powder. When efflorescence occurs, the crystalline structure of the sub- stance is destroyed and usually a powder results. Such hydrates as sal soda, often called washing soda, ferrous sulphate, and Glauber's salt, or sodium sulphate, are ex- cellent examples of efflorescent hydrates. 11. Deliquescence. Deliquescence may be defined as the property some substances have of attracting mois- ture from the air in such quantities as to be dissolved in it. The word means becoming liquid. Two such sub- stances have been mentioned already, used in the experi- ment for the determination of the composition of water by weight, sulphuric acid and calcium chloride. They have frequent applications in the chemical laboratory for drying gases. As calcium chloride is a by-product of cer- tain industries and very cheap, it has been tried by the United States government experimentally as a preventive of dust on roadways, instead of frequent sprinkling. Ob- viously it could not be used thus where there is much rain in the summer season, since, on account of its great solubility, it would be quickly washed away. Other good examples of deliquescent substances are caustic soda, of- ten called lye, and caustic potash. A hygroscopic sub- stance is one that will in damp weather absorb moisture from the air in sufficient quantities to become moist but not to liquefy. For example, common salt in our homes 44 APPLIED CHEMISTRY often becomes damp in rainy weather but it never lique- fies, hence is hygroscopic rather than deliquescent. Keally, however, in this case the condition is due to the presence of a small quantity of a deliquescent substance, such as magnesium chloride, and not to the salt itself be- ing hygroscopic. 12. Domestic Water Supplies. Water is the most nearly universal solvent known. Glass, rocks and min- erals of all sorts, which ordinarily are thought of as in- soluble in water, when left for long periods in contact with water, do dissolve appreciably. This is the source of all mineral and hard waters. Organic impurities likewise and substances of all sorts are dissolved by water, so that especially in towns and cities, but in reality everywhere, the domestic supply of water must be carefully guarded. Cisterns, springs and wells in large towns and cities are never safe, and frequently not in smaller places. Sewage and seepage from cess pools make their way through the soil to all such sources of water and cause serious contamination. The water may be perfectly clear and tasteless, yet abso- lutely unfit to drink. Only chemical and bacteriologic tests can show and in case of doubt these should be applied. 13. Rivers as a Source of Supply. Probably more of the large American cities obtain their water supplies from rivers than from any other source. It would seem at first thought that such would be open to the greatest objection, because of the fact that they are the common means used by cities in disposing of their sewage, and are accessible to contamination in various ways. For- tunately, however, nature has a method of destroying such impurities. Exposure to the air in a flowing stream, especially if the bed be rocky so as to cause an WATER AND HYDROGEN PEROXIDE 45 agitation of the water and to bring all portions of it to the surface, soon results in the destruction of most organic impurities. The city of Los Angeles obtains its water supply from the Owens River, bringing it over two hundred miles. When it enters the upper end of the San Fernando valley it dashes rapidly down in an open viaduct over a very rocky artificial bed, such that the water is churned into a foam, thoroughly impreg- nating it with air. A very noted case was brought to the attention of the public a feAv years ago when St. Louis brought suit in the courts against Chicago on the grounds that the latter city was contaminating the water supply of the former by conveying vast quantities of sewage through the Illinois River into the Mississippi not far above the intake of the St. Louis supply. Nu- merous analyses of the water were made, but bacteri- ologic and chemical tests failed to sustain St. Louis in her claims. Nevertheless, pathologic bacteria are able to withstand long exposure of this character and daily tests of city water must be made. If the water be muddy, as it may be more or less all the time, and very much so at certain seasons, further purification is nec- essary. Briefly stated, the steps are about as follows: The river water is pumped into huge basins or reservoirs, where a stream of lime water and another of a solution of alum or some other coagulant, are allowed to enter through pipes. These two solutions in meeting produce a coagulum or gelatinous precipitate which in settling carries practically all the mud with it. Naturally, as most of the bacteria present are attached to mud particles, they are carried down also. At intervals this accumulated deposit is washed back into the river. In very large cities, such treatment is usually supplemented by nitration ba- sins from which the water passes out through thick layers 46 APPLIED CHEMISTRY of sand and gravel as is shown in Fig. 7. Finally, before the water begins its journey to the mains of the city, either liquid chlorine or a solution of bleaching powder in small quantities is introduced for the purpose of destroy- ing any pathologic bacteria which may remain. 14. Lakes as a Source of Supply. Many cities obtain their supply from lakes either natural or artificial. In such cases, unless the lake be large such as those upon which Chicago, Cleveland and other northern cities are located, another serious problem is confronted. A cer- Fig. 7. Diagrammatic view of city water plant. B, the settling basin; F, the filter, in the bottom of which are layers of sand and gravel, indicated by the letters 5* and G. tain kind of algae, a species of plant to which the com- mon green scum seen upon stagnant ponds belongs, grows in the water and late in summer produces spores which upon bursting liberate a very offensive odor, so that the water cannot be used for drinking or cooking. It has been found that the presence of a minute quantity of some copper compound, as blue vitriol, will prevent the growth of such algae. Accordingly, a burlap sack, filled with blue vitriol crystals, is suspended from a WATER AND HYDROGEN PEROXIDE 47 boat and is rowed back and forth across the lake in ev- ery direction for hours or days, until the copper com- pound is dissolved. The amount of blue vitriol present is so small as to have no appreciable effect upon the human system, but is destructive to the algae. By some it is thought that the copper enters into combination with the albumin of the alga3 and settles to the bottom. If this be the explanation, then there is none left in the Fig. 8. Roosevelt Dam, which is very similar to the one at Sweetwater. water. There are several cities of the southern states which have had to adopt this plan; but one of the most noted is that of Sweetwater Dam a few miles from National City and San Diego in southern California. It. is a huge reservoir in a mountain valley, formed by a concrete dam and holds fit its capacity several billion gallons of water. See Fig. 8, a typical dam for such water systems. 48 APPLIED CHEMISTRY HYDROGEN PEROXIDE 15. Composition. In composition, hydrogen peroxide, or dioxide, as it is often called, closely resembles water. Instead of having eight parts of oxygen to one of hy- drogen, as is the case with water, it has sixteen of oxy- gen to one of hydrogen. This added amount, however, is held very loosely, much as is true of the water contained by many hydrates. As a result, therefore, it is escaping at all times, unless in tightly corked bottles, which should be kept in a cool place. Even then the oxygen es- capes until sufficient pressure is attained in the bottle to produce equilibrium between the vapor tending to escape from combination and that of the air above. This explains why the cork comes out with a "pop" when it has not been previously removed for some time. Hy- drogen peroxide is put on the market in the form of a weak solution, usually about 3 per cent, not only under the name of hydrogen dioxide but also as dioxygen. 16. Uses. The value of dioxygen as an antiseptic de- pends upon the oxygen being continually liberated. Just as flowing water is purified by the oxygen of the air, so bacteria in wounds and diseased portions of the body are destroyed by this more concentrated or more active oxygen. It will be observed that when this additional amount of oxygen is removed from the dioxide, only water remains, which cannot cause irritation. Hence, hydrogen peroxide is probably the safest as well as one of the most efficient germicides for general use. It is also a good bleaching agent and is employed successfully for silks, wool, ivory, feathers and hair, animal prod- ucts which would be seriously injured by more power- ful agents such as chlorine. WATER AND HYDROGEN PEROXIDE 40 17. Method of Testing. The usual method of testing a solution of hydrogen peroxide is by adding a few drops of it to some starch mucilage or very thin paste to which has previously been added a very small quantity of potassium iodide solution. A deep blue solution re- sults. Another sensitive test is to add some potassium dichromate solution to one of hydrogen peroxide acid- ulated slightly with sulphuric acid. A deep blue color forms which lasts but a moment. It is not known what this blue substance is, because its temporary character prevents any examination of it. If some ether be added before putting the peroxide into the dichromate the deep blue compound is more permanent; by shaking, the ether layer may be made to take up most of the color, so that the test is thus intensified. 18. Law of Multiple Proportions. It has been seen that the composition of water is oxygen, eight parts, hydrogen one ; hydrogen peroxide, oxygen, sixteen, hy- drogen one. Thus two elements, uniting in different proportions, form two different compounds. In doing so, for a certain fixed amount of hydrogen the oxygen is twice as much in one case as the other, that is, it varies in a simple ratio. This has been found to be generally true and in chemical union for a fixed amount of one element, the other will always unite in some simple ratio as 1:2, 1:3, and the like. Dalton for- mulated this in what is known as the "Law of Multiple Proportions." Briefly stated it is, When two or more substances unite in different proportions to produce two or more different compounds, for a fixed amount of one, the varying quantities of the oilier will always bear some simple ratio to each other. Later, reasons will bo seen why this must necessarily bo so, as was the case in the law of definite proportions. 50 APPLIED CHEMISTRY Exercises for Review 1. Name six different forms in which water occurs. 2. Give the characteristics of pure water. Why does it taste "flat"? 3. Give some idea as to the amount of water in the human body; also in many of our food products. 4. Explain how water aids in digestion and assimilation; also how it aids in warming the body and equalizing temperature in summer. 5. Describe the experiment showing analytic proof for composi- tion of water. Explain why the oxygen collects at the anode. 6. Outline the experiment for proof of composition of water by \v eight. 7. State the "Law of Definite Proportions." Illustrate. 8. What jt a hydrate? Water of combination? Give examples of hydrates. 9. Define efflorescence. What is the cause of it? What is a manometer? Give some experiment using a manometer and its purpose. 10. Define deliquescence. Name four deliquescent compounds. What use? 11. What is a hygroscopic substance? Why does salt become damp in wet weather? 12. How do cisterns and wells become contaminated? Why are rivers apt to be purer than cisterns in a city? How are river waters clarified? 13. What often occurs in small lakes used for water supply? How treated? 14. Compare water and hydrogen peroxide. Give uses of latter. 15. Give method of testing hydrogen peroxide. 16. State "Law of Multiple Proportions." Illustrate. CHAPTER III OXYGEN AND OZONE Outline Abundance of Oxygen in Nature Preparation in Laboratory Catalysis Characteristics () Physical (fc) Chemical Uses of Oxygen () Respiration (6) Combustion (<") Medical and Others Oxidation, Combustion, Explosion Ozone, its Relation to Oxygen Preparation of Ozone (rt) In Laboratory (&) For Commerce Characteristics (rt) Physical (/;) Chemical Uses 1. Abundance of Oxygen. Oxygen constitutes about 50 per cent of all terrestrial matter. Of water it is eight-ninths by weight ; of the rocky crust of the earth, such as limestone, sand, sandstone, it is practically 50 per cent; of the air about 23 per cent by weight; of the human body about two-thirds. Thus it is by far the most abundant of all the elements. Fig. 9 gives approx- imately the relative amount of oxygen and the seven other elements which constitute the greater part of the material of the earth. 2. Preparation. As far as known, Scheele, a Swedish chemist, first prepared oxygen about 1773, using man- ~A 52 APPLIED CHEMISTRY ganese dioxide and sulphuric acid. However, he did not publish any account of his experiments for several years, and in the meantime Joseph Priestley, an English chemist, had in August, 1774, prepared and studied oxygen, making it by heating red mercuric oxide. It is interesting to know that he used as his source of heat a large lens or burning glass to concentrate the sun's rays and instead of the modern test tube he had a sawed- off gun barrel. Both of the above methods are still sometimes used, but there are much better ways. The most common method for obtaining oxygen in the labo- ratory is by heating potassium chlorate, mixed with manganese dioxide. The first named compound fur- nishes all the oxygen, although both contain it, but Oxygen 50% Silicon 25% Fig. 9. Showing relative abundance of oxygen in nature. much less heat and time are needed if the mixture is used. By putting equal amounts of potassium chlorate into each of two test tubes and adding to one a small quantity of manganese dioxide, it is interesting to note that the mixture will give the oxygen test at the mouth of the tube in from one-sixth to one-fourth the time that is required for the other. Chemical tests show that the manganese dioxide is unchanged and may easily be recov- ered from the remaining mixture and used again. The ac- tion of any substance in thus hastening a chemical change is called catalysis, and the agent itself a catalyst or a catalytic agent. Many such cases will be observed from time to time in our study of chemical reactions. For exam- ple, it has been stated that hydrogen peroxide is a very unstable compound and owes its value to the fact of giving OXYGEN AND OZONE 53 off oxygen so readily. The addition of powdered metals or of charcoal, even in weak solutions, causes rapid decom- position of the peroxide. In a polished platinum dish a concentrated solution shows little evolution of oxygen, even at temperatures considerably above that of the or- dinary room ; but if the dish be roughened or scratched the decomposition becomes rapid. In all these cases, the powdered metals, the charcoal and the roughened plat- inum serve as catalytic agents in hastening the decom- position. Fig. 10. Preparation of oxygen. The laboratory method of setting up the apparatus and of collecting the gas is shown in Fig. 10. The method is called collecting over water, and all gases not soluble in water may be collected in this manner. One precaution must be rigidly observed and that is, to remove the deliv- ery tube from the water before taking the heat away from the generator. A third method often used when only small quantities are wanted is by allowing water to drop slowly upon sodium peroxide, a compound sold under the 54 APPLIED CHEMISTRY name of "oxone." It gives off oxygen on the addition of water just as does hydrogen peroxide spontaneously. 3. Characteristics of Oxygen. Physical. Oxygen is an odorless gas, slightly heavier than air, and in small quantities, is colorless. When liquefied, as it may be at 182 C. below zero, it is of a distinctly blue color. It is possible that what we speak of as the blue sky may be the color, at least in part, of the great depth of oxygen. It is soluble in water ; at 20 C., to the extent of 3 c.c. in 100, and in ice water about 4 c.c. in 100. In the liquid form Fig. 11. Preparing oxygen from sodium peroxide. it is distinctly magnetic, as is shown by a suspended test tube of it being strongly attracted by a magnet. It may be solidified by surrounding with liquid hydrogen and is then a pale blue solid. Chemical Characteristics. The most important chemi- cal property of oxygen is the vigor with which it com- bines with a large number of other elements, forming oxides. Charcoal, heated to redness, and lowered into a bottle of oxygen, glows brightly and if made from soft wood, it bursts into sparks. Phosphorus, ignited, in OXYGEN AND OZONE 55 a deflagrating' spoon, in oxygen burns with dazzling brightness, while iron in the form of wire or a watch spring burns with a beautiful shower of sparks. Sulphur and zinc both burn much brighter than in the air. All of these are additive reactions in which oxygen has com- bined with another element forming an oxide. Usually upon the sides of the bottle, in which the watch spring is burned, will be seen a reddish deposit of iron oxide, like rust, but most of the iron has been converted into what is called magnetic oxide and has dropped to the bottom of the bottle in the molten condition. The charcoal, being largely carbon, has produced carbon dioxide, and so on. Many of the oxides, like the one formed from sulphur, when dissolved in water give an acid test, and this fact gave oxygen its name, from the Greek words meaning acid former. 4. Uses. First of all should be mentioned its need in respiration. Aquatic animals breathe the small quantity of free oxygen dissolved in water, while land animals use the more concentrated form found in the air. Next to its value in respiration is its use in combustion. Or- dinary fire is impossible without oxygen ; and without fire man must have remained little more than a savage. II? could hardly have passed the advancement of the stone age; the reduction of metals from their ores; the making of steel tools; the locomotive, the steamship, the automobile, the airplane, all would have remained for- ever beyond him. Besides these two great uses there are many minor ones. The oxygen helmet is often used by firemen to enter places impossible otherwise ; by div- ers in exploring sunken vessels and for other under- sea work ; by rescuers after explosions in mines. The pulmotor is now a common appliance in the hospital, for inducing artificial respiration at critical times, such 56 APPLIED CHEMISTRY as cases of asphyxiation, drowning, electric shock, and in crises of some diseases. 5. Oxidation. The uniting of oxygen with any sub- stance is called oxidation, although, in the broadest sense, to the chemist the term means much more than this. The action may be slow, or so rapid as to be ac- companied by the generation of much heat. If suffi- ciently rapid to cause noticeable heat and light it is called combustion, but we shall see that combustion often takes place between substances when neither one is oxy- gen. Some substances, for example, oily waste or rags, absorb oxygen from the air: oxidation begins, and often sufficient heat is produced to ignite the rags. This is spontaneous combustion. It is never safe, therefore, to leave waste saturated with oils, especially drying oils like linseed, exposed long to the air. The manufacturers of the familiar cedar mop and others of like character, who use some kind of oil upon the cotton thread, provide a metal box to enclose the mop when not in use. At al- most every coal mine, the dump is seen to be on fire. Cer- tain iron compounds, when wet by rains and exposed to the air, begin to oxidize ; the temperature rises and even- tually is sufficiently high to ignite the small quantities of coal thrown out with the waste material. The fires in coal bins on shipboard probably often occur in the same way. A simple experiment illustrating spontaneous combustion may be made by dissolving a piece of yellow phosphorus the size of a pea in a cubic centimeter of car- bon disulphide and pouring the solution on a filter paper resting upon a ring stand. As soon as the carbon disul- phide has evaporated, which will be in a few seconds, ox- idation begins, followed very quickly by the ignition of the phosphorus. An instantaneous or nearly instantane- ous combustion is called an explosion. In all cases the to- OXYGEN AND OZONE 57 tal amount of heat produced is the same : in slow oxida- tions it is dissipated as fast as formed; in explosions, the whole generated in an instant of time, causes enormous expansion of all gases produced and, as a result, tre- mendous pressures and often frightful results. 6. Kindling Temperature. The point at which com- bustion begins is called the kindling temperature. For phosphorus this is very low ; for iron very high, with a great variety in between these two. A bit of yellow Fig. 12. Boiling water in paper cup. phosphorus exposed to the air soon reaches its kindling temperature ; a pile of shavings needs but the heat of a burning match ; while anthracite coal must be fur- nished much kindling before it will burn. A little ex- periment giving some idea of the kindling point of pa- per, not essentially different from that of shavings, may be made by boiling water in an ordinary sanitary paper drinking cup, as shown in Fig. 12. In a few minutes the 58 APPLIED CHEMISTRY water will boil vigorously, but as the temperature of the paper is not greatly above that of the boiling water it does not catch fire. Ozone 7. What Is Ozone? Ozone is an unusual form of ox- ygen, always produced when an electric discharge takes place in oxygen or in the air. It is noticeable about the open arc in stereopticon work, in wireless telegraphy, and all similar places. The word ozone is from the Greek, meaning to smell and was given this gas because of its peculiar odor. It is often spoken of as an allotropic form of oxygen, which means another form. Many sub- stances appear in two or more distinct forms almost as different from each other as if they were not related at all; usually the rarer one, or more, are spoken of as the allotropes of the other, or the allotropic forms. 8. Preparation of Ozone. To secure sufficient ozone for a test, a stick of freshly scraped phosphorus partly submerged in water in a bottle is generally used. For the test, a strip of white paper dipped in some starch mucilage, to which has been added a very little of a solution of potassium iodide, is suspended in the bottle. In a short time the paper turns blue. The ozone has united with the potassium, has set the iodine free, and this has formed a solution with the starch which has a blue color. It is believed that ozone is also produced by other slow oxidations. It is probable, that, being a form of oxygen, ozone is always produced in the prep- aration of oxygen by any method. However, as we shall see later, ozone is a very unstable body, and if much heat is needed or produced in the method used for pre- paring oxygen, most of the ozone will be decomposed al- OXYGEN AND OZONE 59 most immediately into ordinary oxygen. By the meth- ods already suggested for the preparation of oxygen, by heating mercuric oxide or potassium chlorate, practi- cally 110 ozone is obtained. But if a method is used in- volving the application of no heat and in which no high temperature is reached through the chemical action, ap- preciable amounts of ozone ought to be present. Such a method may be tried by adding a few drops of strong sulphuric acid to a solution of potassium permanganate Fig. 13. Machine for making ozone. in water. The bubbles of oxygen may be seen coming up through the solution and the odor of ozone may be readily distinguished, often being sufficiently strong to irritate the throat. For commercial purposes ozone is now prepared by means of apparatus illustrated in Fig. 13. The current from an induction coil spreads over the tin foil coating on the outside of the outer tube through which a stream of oxygen or air is slowly flowing, as indi- 60 APPLIED CHEMISTRY cated by the two arrows at E and D. The electricity by brush discharge passes across to the tin foil coating on the inner surface of the other tube and out over the return wire. Thus, by a silent discharge of the current, little heat is generated and a very appreciable quantity of ozone is present in the escaping current of air. 9. Characteristics. Physical. As already mentioned, ozone has a peculiar odor and is irritating to the throat and bronchial tubes, if present in considerable quantities. It is blue in color. It is much more soluble in water than oxygen; at 12 C. 100 c.c. of water will dissolve about 50 of ozone, while even at zero only 4 c.c. of oxygen would be dissolved by the same volume of water. Ozone is also very soluble in turpentine and this method is sometimes used to isolate it from other gases. Having a density one and a half that of oxygen indicates that three volumes of oxygen have been condensed to form two of the allotropic form. It liquefies at -119 C. If a current of ozone mixed with air be passed through a tube surrounded by liquid oxygen, the ozone is readily liquefied, while most "of the oxygen will escape as a gas. Liquid ozone is deep blue in color and not transparent like liquid oxygen. 10. Chemical Characteristics. The most important chemical property of ozone is its strong oxidizing power; it is also very unstable. Mercury and silver both remain untarnished in pure air, but in ozone they are quickly darkened. It attacks many other substances much more actively than does ordinary oxygen. 11. Uses. Ozonized air, prepared as described in a preceding section, is now used in many photoplay houses of our cities as a means of vitalizing or purifying the air. Theoretically, it would seem to be an excellent plan, but in real practice there seems to be much doubt OXYGEN AND OZONE Cl on the part of some as to its efficiency. In some large flour mills, the wheat, after scrubbing, is passed still damp through ozonizers for destroying any traces of smut or mildew not removed by previous processes of milling. In some cities of Europe, ozone is used as is liquid chlorine in this country for purifying the water supplies. It is claimed that a gram of ozone, which if pure would be only about a half liter, or one pint, is sufficient to destroy as many as 30,000 bacteria per cubic centimeter in 1,000 liters, or 250 gallons. As there are 1,000 cubic centimeters in a liter, this would mean that a half liter of ozone or an equivalent mixed with air bubbled slowly through 250 gallons of water, would be sufficient to destroy thirty billion bacteria. Exercises for Review 1. What part of the earth's crust does oxygen form? Give its proportions in several familiar things. 2. What two men first prepared oxygen? What did they use? 3. What is the usual method in the laboratory? Define cataly- sis. Name some other instance of catalytic action. 4. Give its chief physical and chemical characteristics. How did it; receive the name oxygen? What other names was it known by in an early day? 5. Name the most important uses of oxygen. Give five minor uses. 6. Define oxidation, combustion, explosion. How can you ac- count for spontaneous combustion? Give some case where caution must be exercised about the home. 7. What is meant by the kindling temperature of a substance? Name one substance with very low r kindling point: one with very high. 8. Has water a kindling temperature? Give reason for your answer. 9. What is ozone? Origin of its name? What is an allotrope? G2 APPLIED CHEMISTRY 10. Give two ways of preparing ozone and method of testing its presence. 11. How is ozone prepared on a large scale? 12. Compare ozone with oxygen. 13. Give three uses of ozone. 14. "When a bellows is used to cause a fire to burn faster, is the action catalytic? Explain. CHAPTER IV HYDROGEN Outline History of Hydrogen Occurrence Preparation () From Water (b) From Acids (c) From Oils Characteristics of Hydrogen () Physical (Z>) Chemical Practical Uses The Phlogiston Theory of Combustion 1. History. It is presumed that Paracelsus, the great physician-chemist in the sixteenth century, discovered hydrogen, for he carried out experiments that involved the preparation of it. But he records no facts regard- ing it and may have overlooked it entirely. In 1766, Cavendish, an English chemist, prepared hj'drogen and recognized it as a new substance but did not consider it an element. He called it inflammable air. Later when it was discovered that in burning, it produces water, it was given its present name which is from the Greek, meaning waicr producer. 2. Occurrence. It lias been stated that hydrogen ranks ninth in abundance among the elements. In many ways, however, it is an important element. It consti- tutes as previously seen, one-ninth of the weight of water; it is an important constituent of nearly all or- ganic matter such as oils and fats, sugars, starches and the like; also of all acids, many of which are already 63 64 APPLIED CHEMISTRY familiar to the student. For example, acetic acid in vinegar, citric in lemons and grape fruit, oxalic in rhu- barb as well as several others, are well known. In the laboratory the most common acids are hydrochloric, sul- phuric and nitric. 3. Preparation from Water. The preparation of hy- drogen by the electrolysis of water has already been described. With the ordinary laboratory apparatus it is a slow process, but the gas obtained is very pure and sometimes this fact overbalances the lack of rapidity. Hydrogen may also be prepared from water by treating with some metal, as sodium or potassium. It may seem strange that a metal could do this. It has been seen al- ready that hydrogen belongs among the electropositive elements. It must be stated, however, that some ele- ments are much more positive in their behavior than others. Without attempting to be very exact, the ele- ments may be arranged and compared to the parts of a bar magnet, as illustrated in Fig. 14. If the magnet is laid down upon a sheet of paper upon which iron filings have been sprinkled, most of the filings will be at- tracted to the ends which are called the poles of the magnet, with the quantity rapidly diminishing toward the center. In a similar way the elements may be arranged in the order of their electropositive charac- ter, and those the better known to the student are thus shown in Fig. 14. It will thus be seen that hydrogen is well down the list. Naturally, therefore, such elements as pcttassium and sodium would be presumed to have the power of taking a negative element away from hydrogen and setting it free. Experiment shows that potassium does this violently, such that even on cold water the hydro- gen set free is ignited almost instantly and unless the piece of potassium is very small even it will burst into HYDROGEN G5 pieces from the heat generated. Sodium, though much less active, decomposes water rapidly, but unless the water is warm the hydrogen is not ignited. With mag- nesium the water must be hot for even moderate re- sults. In using sodium, since the metal melts almost K Na Ca M Al Zn Fe Sn Pb H Cu Au Fig. 14. Electromotive series ot metals and bar magnet with iron filings attached. instantly when it touches the water, because of the heat generated by the chemical action, a gauze spoon is employed as shown in Fig. 15. The sodium is enclosed in this, inserted under the mouth of the test tube or bottle, which is filled with water and inverted over a 66 APPLIED CHEMISTRY trough of water, whereupon the gas rises and fills the bottle. It is a method somewhat expensive, but the gas obtained is pure. 4. Obtaining Hydrogen from Acids. As hydrogen may be expelled from water so it may be from acids, in a similar way and for the same reason. A very con- siderable number of metals might be used. Sodium and potassium would do, but their action is dangerously violent; hence, it should not be attempted. It is custo- mary to use some metal much farther down the electro- motive series, whereby the action is much slower. In the laboratory zinc is most often used either with hy- Fig. 15. Preparing hydrogen from water by means of sodium. drochloric or sulphuric acid diluted. Iron is cheaper and is used when large amounts are desired, but the gas is not so pure as when zinc is employed. The metal in mossy form, is put into the generating flask and barely covered with water. When the receiving bottles are ready in the trough, the acid is added through the thistle tube a little at a time until action begins. The thistle tube must dip below the surface of the water in the flask (Fig. 16). 5. Preparation of Hydrogen from Oils. It is possible by heat alone to obtain hydrogen from such oils as kero- sene and similar oils, prepared from crude petroleum HYDROGEN 67 by distillation. But the gas thus obtained is only about 50 per cent hydrogen, the remainder being a variety. Yet for some purposes even this is sufficiently pure and is exceedingly cheap. 6. Characteristics of Hydrogen, Physical. Hydrogen 'is an odorless, colorless gas, the lightest known. It is only about one-fourteenth as heavy as air, so that something over 11 liters are necessary to weigh 1 gram. It is a fairly good conductor of heat, which cannot be said of any other gas. It may be liquefied at a tem- perature of about -252 C. in which condition it is color- less. At -256 C. it becomes a solid. One of the most Fig. 16. Preparation of hydrogen from acids. interesting of its physical properties is its ability of be ing absorbed by certain metals with the evolution of heat. This may be shown by the platinum sponge held over a jet of escaping hydrogen. In a very few seconds the sponge becomes red-hot and the hydrogen is ig- nited. It may likewise be shown by lowering the sponge into a bottle of hydrogen and oxygen mixed in about the proportions of 2 to 1. The sponge quickly becomes red and the gases explode violently. There is no danger, however, if a wide mouthed bottle is used. This property is often called occlusion. Palladium has 68 APPLIED CHEMISTRY more remarkable powers for absorbing hydrogen than has platinum, in that it will take up nearly seven hun- dred times its own volume of the gas. Hydrogen read- ily passes through unglazed porcelain and cracks in bot- tles which would not leak water, and a cork made of plas- ter of paris is so porous as to offer little obstruction to the escape of the gas. For the same reason, toy balloons soon lose their buoyancy. 7. Chemical Characteristics. Hydrogen burns with a very pale blue flame with intense heat. If the delivery tube be glass, it is soon heated to redness, when the flame becomes visible, because of the constituents of the glass giving a yellow color. One gram of hydrogen in burning will produce more than four times as many Fig. 17. Oxyhydrogen blowpipe. heat units as the same weight of anthracite coal. Water is the sole product of combustion. 8. Practical Uses. One valuable use is in the oxyfe^j- drogen blowpipe or torch as it is often called. It is il- lustrated in Fig. 17. The hydrogen enters through one pipe and the oxygen by the other, and near the point where ignited they are thoroughly mixed. The stop- cocks are so opened by the operator as to furnish twice as much hydrogen as oxygen. Intense heat is thus ob- tained, ranging in temperature from 2,000 to 2,500 C., at which platinum and other refractory metals are read- ily melted. If this flame be allowed to impinge upon a stick of lime, it gives a dazzling white light, called the calcium ,or Drummond light. Up to the introduction of HYDROGEN G9 the electric arc, this was the best and commonly used light for stereopticons and stage effects. Another use for hy- drogen is in filling' balloons. Especially during* the world war was this extensive for dirigibles and for observation balloons. For some purposes natural gas may be used and has often been in flight contests, but it is eight times as heavy as hydrogen, hence does not compare in efficiency. However, its loss through diffusion would be much slower. For short flights, such as those seen at amusement parks and the like, the balloons are usually filled by heating kerosene or naphtha, as suggested in a preceding section. As this is often done by spraying the oil upon a bed of hot coals, there is usually some small amount of air present and some imperfect combustion resulting in the forma- tion of some smoke. For this reason, when the aeronaut leaps from the car in the parachute, a puff of smoke is often seen emerging from the capsized balloon. 9. An Old Theory of Combustion. Combustion is now well understood, but during the last quarter of the eighteenth century it was a matter of constant study and of much dispute. With the exception of Lavoisier, who lost his life at the time of the French Revolution, practically all the chemists of that day accepted the theory that a substance called phlogiston was contained in every combustible substance, and that it escaped as the substance was burned. The great French chemist never accepted this theory ; and finally by the use of the balance, which up to that time chemists had not employed to any great extent, he succeeded in showing the fallacy of the phlogistic theory. It is now known that when a metal or any substance is burned, if all the products of combustion are saved and weighed, the total is greater than the weight of the original substance. Lavoisier called attention to this fact, and argued that if something 70 APPLIED CHEMISTRY escaped, the resulting oxides, or calces, as they were called in that day, ought to weigh less. The upholders of the theory replied that, since phlogiston is an exceed- ingly light substance, it has a buoyant effect upon what- ever contains it, and therefore, the more there is the Fig. 18. Lavoisier, beheaded in French Revolution, was the Father of Modern Chemistry. lighter the object. When hydrogen was discovered and its extreme lightness noted, as well as its great combusti- bility, many of the phlogistonists believed they had dis- covered phlogiston and regarded it as upholding their HYDROGEN 71 theory. But, in the light of what the balance continu- ally showed, they were finally obliged to acknowledge the fallacy of their position and that Lavoisier was correct. Exercises for Review 1. Give a brief account of the discovery of hydrogen. How did it come to receive its present name? 2. Name some very common substances containing hydrogen. How does it rank among the elements in total amount? 3. Give two ways of obtaining hydrogen from water. What can be said about the value of these methods? 4. What do you understand by the electromotive series of met- als? Where does hydrogen come in this series? 5. How may hydrogen be obtained from acids? What metals are best? Why? What acids are generally used? Would nitric do? 6. How may hydrogen be obtained from kerosene or gasoline? What is true of the purity of the gas thus obtained? 7. Give the chief characteristics of hydrogen. Explain what is meant by occlusion. Give two experiments to illustrate. 8. Give three important uses of hydrogen. What is the Drum- mond light? 9. Give briefly the phlogiston theory of combustion. What was the most absurd thing about this theory? Who finally overthrew it? CHAPTER V THE ATMOSPHERE Outline Early ideas of the Air Composition of Air Proportions Proof that Air is Mixture Diffusion of Gases Ventilation Purposes of the Constituents (a) The Oxygen (&) Nitrogen (c) Carbon Dioxide (d~) Water A 7 apor Humidity and Health Liquid Air Argon and Helium 1. Early Ideas of the Air. Even before the begin- ning of the Christian era the air was an object of in- terest among philosophers. For centuries thereafter, however, little advancement was made in the knowledge concerning it, for the reason that no experimental study of it was attempted. In the latter part of the eighteenth century when the phlogiston theory was at its height a very considerable number of gases was discovered and the air itself received a very careful study in its rela- tion to combustion. Even thus, until near the end of the century, all the gases known were regarded as modifications of atmospheric air and were named ac- cordingly. Thus, Cavendish called hydrogen inflamma- ble air; Scheele called oxygen fire air; Priestley named it depklogisticated air; Black, the discoverer of carbon dioxide called it fixed air; nitrogen was known as azote 72 THE ATMOSPHERE To or phlogisticated air and so on. As we have seen it was Lavoisier who overturned the prevalent ideas and sug- gested suitable names for some of the gases of recent dis- covery. 2. Components of the Air. In what is often spoken of as pure air there are always found nitrogen, oxygen, argon, carbon dioxide and water vapor, besides minute quantities of a few very rare elements. Sometimes the first three of these are regarded as the atmosphere proper, for the reason that the}" vary little; but when the evident purposes of the air are considered, the other two are essentials, and in the following study will be regarded as constituents. For years the air was believed to contain the two main gases in the form of a com- pound. At that time, the presence of argon was not known and the apparent unvarying proportion of oxygen and nitrogen led chemists to believe they were in com- bination. 3. Proportions of These Constituents. By volume the oxygen in the air constitutes about 21 per cent; the ni- trogen, 78 per cent ; the argon, a little less than 1 per cent 0.94 and the carbon dioxide, about .03 per cent, with the water vapor decidedly variable. If the air were of the same density throughout, it would extend above the surface about five miles. Then if the various con- stituents were arranged in layers about the earth, in accordance with their respective densities, there would be nearest the ground a layer of water about 5 inches d?ep; above that, one of argon, about 250 feet deep; then carbon dioxide, 12 or 13 feet; above that, oxygen one mile, and lastly the nitrogen, four miles. 4. Proof That Air Is a Mixture. There is very strong and convincing evidence now that air is a mixture. When pure distilled water is exposed to the air, al- 74 APPLIED CHEMISTRY though the amount of nitrogen is about four times that of the oxygen, the oxygen absorbed is nearly double that of the nitrogen. If the air were a compound, the absorption of the two gases would necessarily be in the proportion in which they entered into the compound. Again, air is now readily liquefied. When this hap- pens the carbon dioxide and the water vapor solidify and precipitate out. A vessel of liquid air left standing shows, when about four-fifths of it has boiled away, that the residue is nearly pure oxygen. This would be possible only if. the air were a mixture and the boiling point of nitrogen lower than that of oxygen. Alcohol in boiling gives off vapor of the same composition as the liquid and so does every liquid compound. Air, therefore, cannot be a compound. Again, every com- pound consists of two or more elements in unvarying proportions. In the air the oxygen may vary as much as three-fourths of 1 per cent. Not only these, but other proofs make it sure that the air is a mixture and not a compound. By weight the constituents are Nitrogen 75.46 per cent Oxygen 23.18 " Argon 1.29 ' ' Carbon Dioxide 03 to .04 " Water Vapor Variable Other rare Gases. . .Very small amounts 5. Diffusion of Gases, If in a tall cylinder nearly filled with water, colored blue with litmus, a few cu- bic centimeters of sulphuric acid be introduced be- low the water by means of a pipette, in two or three days the heavy acid will have moved upward through the entire mass of water. This will be known by the litmus solution turning red, as it does in the pres- THE ATMOSPHERE 75 ence of any acid. Likewise any gas tends to occupy all the space afforded it. If a cylinder of ammo- nia be inverted over one of hydrogen chloride, al- though the lighter gas is above one more than twice as heavy, in a very few minutes the two will be evenly distributed throughout the entire space, as can be seen by the action which takes place. This shows that the particles of a gaseous body are apparently moving in all directions all the time regardless of their density. This explains largely why the air is always a practically uniform mixture. Equilibrium is constantly being de- stroyed by various processes of nature and otherwise, but diffusion, as this movement is called, aided by wind currents, keeps the composition practically constant. 6. Value of Each Constituent. It has been stated in a preceding chapter that oxygen is necessary for respi- ration. When taken into the lungs it enters into a loose combination with the hemoglobin and is by the circu- lation taken throughout the body. Meeting the carbon in the various tissues, carbon dioxide is formed and by the oxidation heat is produced. Thus the body is warmed. In aquatic animals where the only oxygen attainable is the small amount dissolved in the water, the quantity of carbon consumed in the tissues is small, and thus little heat is produced. Such animals are "cold blooded"; naturally, therefore, the food required to sustain life is small in proportion. A good comparison may be had by noting the amount of food consumed by a canary bird and a gold fish of about the same weight. The human body of average size consumes daily about 750 grams or 26 ounces of oxygen. This is the equivalent of the entire amount of oxygen con- tained in over 2,600 liters of air. From this is produced carbon dioxide to the amount of about 2.2 pounds or 76 APPLIED CHEMISTRY 1,000 grams. When the air leaves the lungs at each respiration only about 16 per cent of oxygen remains instead of the original 23 per cent, while the carbon dioxide in the exhaled breath is present to the extent of about 4.4 per cent or more than 100 times as much as is contained in ordinary air. 7. Ventilation. It is apparent from the above how im- portant good ventilation becomes. This importance is emphasized when it is remembered that while the first respiration of a given volume of air removes over one- fourth of the oxygen, the second inhalation of the same volume of air only takes about the same proportion of what remains. Thus the body in obtaining impoverished air is not receiving anything like the amount needed. Lack of proper ventilation is most apt to be found in school rooms or other places where people congregate in considerable numbers, as photoplay houses, theaters, and the like. Health boards in many cities require that means shall be provided for furnishing 30 cubic feet of fresh air per minute per individual. In the ordinary home where the family is small there is no special pro- vision needed, for even in cold weather when doors and windows are closed there is sufficient leakage to fur- nish an abundance of fresh air. It is only in poor tenement houses and basements used as homes, where large families are often found, that the lack of ventila- tion is apparent in the home. 8. Value of the Nitrogen. To the human body, nitro- gen, as it exists in the air in a free state, seems to serve no other purpose than to dilute the oxygen. A fish out of water dies, partly probably because of the very rich, atmosphere it is compelled to breathe. In the same way the human body, as at present constituted, could prob- ably not inhale pure oxygen continuously without un- THE ATMOSPHERE 77 due stimulation and serious results. In the combined form nitrogen enters into the muscular part of the body and only through the use of nitrogenous foods can its waste be repaired. Neither animals nor plants, as a general rule, can obtain nitrogen directly from the air, at least in sufficient quantities to meet their necessities. Animals secure it mainly through lean meats or legu- minous foods such as beans, peas and the clovers. Most plants in continuously cultivated fields obtain their Fig. 19. Nodules in which the nitrogen-fixing bacteria live on the roots of a bean. (From Warren Klements of Agriculture.) needed supply through fertilizers, which are largely ob- tained from the waste eliminated by the animal economy. So it will be seen there is an endless cycle existing here in which animals and plants each supplement the needs of the other. It should be stated, however, that there is one class of plants which, fortunately, is able through the aid of bacteria to obtain the nitrogen needed di- rectly from the air. These are the legumes, and agricul- 78 APPLIED CHEMISTRY turists at present are employing this means extensively in restoring the needed nitrogen to the soils. The accom- panying figure shows the nodules upon the roots of a bean plant, formed by the nitrogen fixing bacteria. (Fig. 19.) 9. Carbon Dioxide. It will be learned later that car- bon dioxide is an inert gas as far as the human system is concerned, in that it is devoid of toxic effects. It is true, however, that a considerable quantity of it in the air usually indicates the presence of other substances deleterious to health. This is especially true if the air be impoverished by frequent respiration and therefore abounding in the waste materials thrown off from the body. It is this condition mainly that proper ventilation seeks to avoid. Health experiments carried out in such places as breweries, where considerable amounts of car- bon dioxide are continually escaping into the air, shoAV that, other conditions not being unfavorable, headache and drowsiness, usually apparent in poorly ventilated rooms, do not occur and no unfavorable results follow. To plants, carbon dioxide is as essential as oxygen to animals. The leaves, corresponding to the lungs of the body, absorb the carbon dioxide and under the influence of sunlight are able to decompose it. In the plant labor- atory the carbon is combined with the water obtained from the soil and cellulose results to build the woody structure of the plant or tree. Another arrangement by another plant produces starch or sugar and a great variety of other well-known substances. But they all come primarily from the carbon dioxide obtained from the air through the leaves and must have the heat and light of the sun for the process. It is seen, therefore, as in the case of the nitrogen, that there is an endless cycle in the transference of carbon from the animal to THE ATMOSPHERE 79 the vegetable world and back again, and that the ex- istence of either without the other would in all proba- bilit3 r not be of long endurance. 10. The Water Vapor. It has been stated that the water vapor in the air varies greatly. The amount that can be held is dependent upon the temperature. At C. a cubic meter, which is something more than a cubic yard, is able to hold only 4.87 grams of water: at 10 C. it can hold 9.92 grams; at 20, which is but little cooler than ordinary room temperature, 17.16 grams. For health, from two-thirds to three-fourths of the amount specified at room temperature is regarded as best; more than this, if the temperature be high, is op- pressive. The reason is that the human body regulates its temperature by the evaporation of Avater through the pores of the skin. A single gram of water for its evaporation requires something like 550 calories of heat; an ounce of water, which is about 28 grams, in being evaporated from the surface of the human body, would reduce the temperature of the entire body of 150 pounds weight about .5 of a degree. Anything therefore, which prevents or retards evaporation prevents the cooling of the body. When the humidity is high, as it often is in summer in the Atlantic, Gulf and Mississippi Valley states, the air surrounding the body is already nearly saturated Avith moisture. This greatly retards evapora- tion, and interferes with the regulation of the body temperature. 11. Moisture and Health. The public has been more or less well informed as to the importance of fresh air; but the humidity of the air in the home in winter has not been greatly considered. As stated already, air at C. or 32 F. can hold only 4.87 grams of water vapor. Usually there is present not one-half this amount. This 80 APPLIED CHEMISTRY air is taken into our homes, warmed to 20 or 21 C. or about 70 F., without the addition of any appreciable amount of water. The result is a condition decidedly adverse to health. Unduly dry nasal passages, irritated throat and bronchi, susceptibility to colds, chapped hands and skin and other evils follow. The question of humidity is now carefully considered by architects in the construction of large school buildings and the mois- ture content of the air is kept reasonably uniform by artificial means. In the homes like provision should be made. As it is not provided by the usual methods of construction and heating, the individual must do this himself. In rooms heated by radiators, either steam or hot water, a towel suspended from a rack, fastened behind the radiator and dipping in a pan of water sit- ting on the floor, will be out of sight and will furnish ample moisture. With hot air furnaces the problem is more difficult. It may be partially met by putting shal- low pans of water beneath each register where such are located in the floor. When not, each case with its pos- sibilities must be taken up by itself. It is a problem the student should interest himself in for the benefit of everyone in the home. 12. Liquid Air. For some years air has been lique- fied in commercial quantities. The principle underly- ing is that ordinary gases expanding from great pres- sure into a more or less perfect vacuum are cooled. In the apparatus used, this cooled, expanded air is com- pelled to pass out around the pipe through which the compressed air is entering. Thus at each impulse of the pump, cooler and cooler portions of air are forced out around the incoming supply, until eventually the point of liquefaction is reached. It is a colorless liquid, like water, and usually consists of 50 per cent or more THE ATMOSPHERE 81 of oxygen instead of 23 per cent as in the atmosphere. The reason is that the boiling point of nitrogen is 194 C. below zero, while that of oxygen is ll 1 /^ degrees higher. Thus from the constant loss of the nitrogen through evaporation the proportion of oxygen continu- ally increases the longer the vessel stands. Liquid air is kept and shipped in what are called Dewar bulbs, shown in Fig. 20. They are the original of what the public knows as thermos bottles, being double-walled flasks with a vacuum between and the walls coated with silver. 13. Argon and Helium. It has long been known that nitrogen prepared from the air is heavier than samples made from various nitrogen compounds. This led to Fig. 20. Dewar bulbs. The thermos bottle is merely different in shape. the suspicion that there was some heavier gas mixed with it. Even as early as the latter part of the eighteenth century, Cavendish, the discoverer of hydrogen, was convinced that atmospheric nitrogen contained another gas and attempted to prove it experimentally. In elim- inating the nitrogen he had as a residual gas only a small bubble which he concluded to disregard. He prob- ably used too small quantities of air, for Ramsey, in 3894, by practically the same experiment succeeded in obtaining sufficient quantity of the argon to prove it was the same gas he had obtained by another method of separating it from nitrogen. It is an inert gas and 82 APPLIED CHEMISTRY received the name "argon" from a Greek word, meaning lazy or inactive. No compounds of argon are known. 14. Helium. The word is derived from the Greek for sun, and the name was given to this element because be- fore it was known upon the earth a line in the orange band of the solar spectrum was observed which belonged to some undiscovered element. Later, it was discovered in certain spring waters ; it may be -obtained from cer- tain minerals, compounds of uranium and thorium and is found in minute quantities in the air. It is a gas which is harder to liquefy than is hydrogen, having a boiling point of -268.5 C. It is only twice as heavy as hydro- gen and unlike hydrogen is not combustible. It forms no known compounds. It is admirably adapted for filling balloons and dirigibles, and during the latter part of the war the United States was making great efforts at dis- covering some method of preparing it in commercial quan- tities. Not until too late was such a method devised. It is still a secret of the war department. Exercises for Review 1. Name some of the gases discovered during the latter part of the eighteenth century and the names applied to them. Why were they given such names? 2. Name the five components of the air. Give their proportions by volume and by weight. In what condition are they, free or com- bined? 3. Give three or four proofs that the air is a mixture. 4. What is meant by diffusion of gases? What effect does dif- fusion have on the homogeneity of the air? 5. What is the use of oxygen to the human body? Why are most aquatic animals cold bJooded? Why is the whale not? Explain how the body is warmed. 6. How much oxygen is removed from the air at each respira- tion? How many cubic feet per minute are needed for an indi- vidual? THE ATMOSPHERE 83 7. Of what use is the nitrogen of the air to the body? How arc the muscles repaired? Describe the nitrogen cycle. 8. How are legumes different from most other plants? What gives them this power? 9. What do considerable quantities of carbon dioxide in a room indicate? Is it deleterious to health? 10. Describe the carbon cycle between plants and animals. What use do plants make of carbon? Of what use to animals? 11. What governs the amount of moisture the air can hold? What is meant by saturated air? How much more moisture can air at ordinary room temperature hold than at zero? 12. Why is a humid atmosphere oppressive in summer? 13. What effect does an excessively dry atmosphere have upon the body? 14. Give some methods of increasing the humidity in the home in winter. 15. Give the principle underlying the liquefaction of air. What is a Dewar bulb? 16. Describe liquid air. 17. How did argon come to be discovered? Who was first to at- tempt its discovery? Who finally discovered it? 18. How did helium receive its name? Where is it found upon the earth? Of what special value will it be in large amounts? CHAPTER VI GASES AND SOME GAS LAWS Outline States of Matter Charles' Law and Absolute Zero Applications of the Law Boyle's Law Correction for Changes in Temperature and Pressure Aqueous Tension Deductions from these Gas Laws () The Molecular Theory (&) Molecular Motion (c) Gas Pressures The Atomic Theory The Corpuscular Theory Atomic and Molecular Weights Avogadro 's Hypothesis Atomic Structure of Molecules Determination of Molecular Weights Gram Molecular Weight 1. States of Matter. We are familiar with water in three conditions: solid ice; liquid water; gas, as steam. It has been stated in preceding chapters that oxygen, hydrogen and other gases may also exist in these three states. There are two forces present in ev- ery body: cohesion, an attractive force, tending to hold its particles together, and heat, a repellant force, tend- ing to expand it, or to separate its particles. Hence, when heat is applied, first the body expands, then if capable of doing so, it melts, and on the continued addition of heat the liquid vaporizes with very great expansion. Removal of the heat reverses the process. In gases, therefore, the repellant force is in the ascendancy ; in S4 GASES AND SOME GAS LAWS 85 solids, the cohesive force. Solids and liquids upon being heated expand very irregularly ; but gases are practi- cally constant and their behavior is described by cer- tain clearly defined laws. 2. Charles' Law. Experiment shows that any gas if heated from C. to 1 above, expands 1/273 of its vol- ume at zero. Thus, if at the beginning there were 273 c.c., at 1 C. there would be 274 c.c. ; at 10 C. 283 c.c. ; at 100, 373 c.c. Likewise, if cooled below zero, at 373 -H Boilinj Point [-459- ( Freezing Pi. o- I Fig. 21. Comparison of thermometers. - 10 C., there would be 263 c.c. at 100 below, 173 c.c. Theoretically, therefore, if a gas were cooled 273 below zero its volume would have decreased to zero. But all gases become liquids before reaching this temperature; oxygen at -182.5, hydrogen at -252.6, helium at -268.5 and thereafter the contraction is very slight for each degree. The point, 273 below zero is known as absolute zero. While it does not mean the elimination of the substance, for that is unthinkable, it may be assumed 86 APPLIED CHEMISTRY to mean the temperature at which there is no longer any heat in the body. In the liquefaction of helium, that point has been very nearly reached. It must be seen then that the volume of a gas varies as the absolute temperature. Charles' law states this fact thus: The volume of a gas, pressure remaining constant, increases or decreases directly as the absolute temperature. The absolute thermometer is not a manufactured article, but its degrees are the same as on the Centigrade scale, and it must be used in all problems involving Charles ' law ; hence Fig. 21 is given to make the method clear. Thus the boiling point of water would be 373 absolute and of melting ice 273 absolute. 3. Value of Charles' Law. Gases for the sake of con- venience are measured in volumes, but as they change greatly under varying conditions some standard must be adopted. For temperature this is the freezing point of water zero Centigrade. However, as in actual work gases are seldom obtained at this temperature, their volume must be calculated from the measured volume. Knowing that they increase 1/273 for every degree raised above zero, this is not difficult. Putting Charles' law into a proportion we have V : V ::T : T' In which V is the original volume and V the new vol- ume, while T is the original temperature, absolute, and T' the new temperature absolute. In the form of an equation this reads, VT' = V'T from which either volume or temperature may be calcu- lated, knowing the other factors. To make the process clear, suppose we have in the laboratory a bottle hold- GASES AND SOME GAS LAWS 87 ing 800 c.c. of oxygen, with the temperature 15 C. and without any change in pressure the temperature was raised to 22. It is desired to know the new volume. Changing 15 C. and 22 C. to absolute temperatures, we have 273 + 15 = 288 and 273 + 22 == 295. Substi- tuting we have 800x295=V'x288 800 x 295 288 from which the value of V, or the volume at 22 will be known. 4. Boyle's Law. It was formerly believed that liquids and solids could not be compressed; it is known now, however, that they may be, but as is true in variation of temperature they obey no law. Gases, on the other hand, are practically constant, a fact which was dis- covered by Robert Boyle and formulated by him in this law: The volume of any gas, provided the temperature remains constant, varies inversely as the pressure. In- versely means that if the pressure be increased the volume is diminished correspondingly and if the pressure be de- creased the volume increases in the same ratio. Put into mathematical form it is stated thus : V : V : : P' : P in which V and V have the same signification as stated under Charles' law and P and P' are the original and new pressures respectively. In the form of an equation the proportion becomes which leads to another statement of the law, thus: The product of the volume of any gas multiplied by its pres- sure, alivays assuming that the temperature is constant, is a constant quantity. To illustrate, suppose we have 88 APPLIED CHEMISTRY 200 c.c. of oxygen in a bottle at 15 pounds' pressure to the square inch. The product of the volume and pres- sure, VxP, or 200x15, is 3,000. If the pressure be doubled, according to Boyle's law, the volume now would be 100. The product of V by P', or 100 x 30 is 3,000, the same as before. Hence the statement that the vol- ume of any gas multiplied by its pressure is always equal Fig. 22. Aneroid barometer. to its volume at any other time multiplied by the pressure at that time; in other words, the product is a constant quantity. 5. Pressures, How Stated. In most practical prob- lems involving Boyle's law the changes are those of at- mospheric pressure only. The amount of such pressure is obtained by the use of the barometer, which for the GASES AND SOME GAS LAWS 89 sake of convenience is read in units of length and not weight. In the aneroid barometer, shown in Fig. 22, the figures on the dial indicate inches, while the smaller divisions are millimeters of which practically 760 equal 30 inches. In the mercurial barometer at sea level, the pressure of the air supports a column of mercury 30 inches in height or, in other words, the weight of 30 inches of mercury. But as the iveiylit of 28 inches of mercury would have the same mathematical relation to the ivcight of 30 inches of mercury as 28 inches to 30 inches, and as length can be read immediately from the barometer, in all problems it is customary to use linear units, and those of the metric system ; that is, millimeters or centimeters. To illustrate: Suppose the barometer reads 750 mm. and we have in a bottle standing over mercury 500 c.c. of gas, and wish to know the volume at standard pressure, which means pressure at sea level, or 760 mm. pressure. Substituting in the formula, VP == V'P', we have 500 x 750 = V x 760 500 x 750 ~~ in which V will be the true volume at one atmosphere's pressure. 6. Corrections for Pressure and Temperature. In practical work often both pressure and temperature have changed during the time of an experiment. In such cases calculation must be made to correct both. This may be done in two steps, by finding the volume resulting from one change, either pressure or tempera- ture, and then using this in the other equation. In fact beginners may find all such problems easier if solved by analysis instead of by use of formula given. At any 90 APPLIED CHEMISTRY rate the method has the advantage of appealing to the reasoning powers at every step and on that account is good. It must be evident that increased pressure would cause decreased volume. Hence the original volume must be multiplied by a fraction greater or less than one as the change in pressure would cause increase or decrease in volume. Thus, if we have 500 volumes of gas at 760 mm. pressure and wish to know what it would be at 780, we must ask ourselves, whether the volume is increased or decreased. As the pressure is greater, the volume would be less: hence the original 500 cubic centi- meters must be multiplied by 760/780 which will give a result less than 500. In the same way Charles' Law may be applied. Increase in temperature causes increase in volume. Thus, remembering that absolute temperatures are always used, suppose we have 500 c.c. of gas at zero Centigrade and wish to know its volume at 20 degrees above: we must first change Centigrade readings into Absolute. In this case they would be respectively 273 and 293. As the volume is increased the 500 c.c. must be multiplied by the fraction 293/273 which will give a value greater than 500. In case both temperature and pressure change, the result obtained in one of the above operations must be used as the original volume for the next. It is somewhat simpler, however, to use a combined for- mula, VPT' = V'P'T, in which the letters mean as previously stated. To il- lustrate its use : Suppose we have 500 c.c. of hydrogen over a trough of mercury at a temperature of 21 C. with the barometer reading 740 mm. It is desired to know the volume at standard conditions, that is zero Centigrade and 760 mm. pressure. Substituting in the formula VPT' = V'P'T, we have GASES AND SOME GAS LAWS 91 500 x 740 x (273' + 0) = V x 760 x (273 + 21) 500 x 740 x 273 In a similar or any other 760 x 294 The value of V will be the true volume. way we might find the value of T' or P' factor provided the others were known. 7. Correction for Water Vapor. In the laboratory gases are usually collected over water and hence con- tain some vapor. To learn their true volume at standard conditions, correction must be made for this. It has been found that at any given temperature the vapor, passing off from an enclosed vessel of water, will exert a definite pressure, always the same for that particular tempera- AIR PRESSURE Fig. 23. Illustrating pressure of water vapor. ture. In Fig. 23', suppose we have a volume of gas with the water at the same level inside and without the bot- tle. Obviously the pressure within and without must be the same. On the outside the pressure is due to the weight of the air resting upon the water. Inside, the pressure results mainly from the gas enclosed!, buit partly from the vapor mixed with the gas. To know the real pressure of the gas, that of the vapor, which is spoken of as aqueous tension, must be subtracted from the total pressure. To illustrate : Suppose the gas in the bottle measures 900 c.c. and the barometer reads 750 mm., and the thermometer, 20 C. The aqueous tension at 20 92 APPLIED CHEMISTRY is about 17 mm. ; hence, the pressure which the gas within the bottle is exerting is 750 minus 17 or 733 mm. Then, if it were required to find the true volume at standard pressure, the following substitution would be made in the formula, VP == V'P' 900 x (750 -17) = Y'x760 The following table gives the aqueous tension for a short range of ordinary room temperatures. Temperature Aq. Tension Temperature Aq. Tension 16 C. 17 18 19 20 13.54 mm. 14.42 15.36 16.35 17.39 21 C. 22 23 24 25 18.49 mm. 19.66 20.88 22.18 23.55 8. Application of these Laws. The gas in most cities is furnished by some company which is required by or- dinance to maintain a certain pressure, say 6 or 8 inches, water pressure. If instead of doing this the company allow the pressure to drop to 4 or 2 inches or any lower pressure than that specified, it is, according to Boyle's law, furnishing the consumer an expanded gas ; therefore, while the meter registers the larger amount the consum- er only has the value contained in the real volume. It should be stated, however, that as the 6 or 8 inches re- quired is necessarily the pressure in addition to one at- mosphere or 30 water feet, a drop of 4 inches is not rel- atively large. Nevertheless, consumers should be fur- nished gas by the number of heat units contained and not by volume. The aeronaut must observe these gas laws in filling his balloon. Too great initial pressure, when he has ascended into a rarer atmosphere, and bright sunlight, may result in such increased pressure through expansion from the heat of the sun as to burst the balloon. On the other hand, too low initial pressure, GASES AND SOME GAS LAWS 03 when night comes, with the great drop of temperature in the upper air may cause such contraction of volume that the buoyancy of the balloon will 110 longer support the attendant weight. 9. Some Deductions. Cooling or heating a given vol- ume of gas does not change its weight. Compressing, or the reverse, likewise, has no effect upon the weight; therefore, obviously by any of these changes we have not affected the real quantity of the gas. At sea level, the pressure of the air per square inch of surface is about 15 pounds. Now it is possible by modern appliances to obtain pressures approximating 150,000 pounds to the square inch. To some gases, such pressures as these may be applied and they are still gases unless the tempera- ture is also greatly decreased: according to Boyle's law the volume has been decreased to one ten-thousandth part of what it was originally. In other words, the par- ticles constituting the gas have been moved closer to- gether, so that now they are only one ten-thousandth part as far from each other as they were at the begin- ning. Under moderate pressures, as we have seen, all gases behave alike ; hence, there can be only one deduc- tion and that is that all gases are composed of particles not touching each other ; really, of particles at relatively great distances from each other. As all liquids may likewise be compressed, though but slightly and irreg- ularly, their particles also must not be contiguous. This may be shown to be true by a simple experiment. If a liter cylinder be half filled with alcohol and then a like amount of water cautiously introduced beneath the alcohol by means of a pipette, at first there will be 1,000 c.c. of the two unmixed liquids (Fig. 24). Now, if by a stirring rod they are thoroughly mixed, the volume will be found to have decreased about 10 per cent. Like- 94 APPLIED CHEMISTRY wise, considerable quantities of various solids like salt, or sugar or alum may be dissolved in a given volume of water without increasing the volume to any great ex- tent. It is like pouring a pint of sand upon a quart of coarse shot. By adding the sand cautiously with fre- quent shaking, the sand may be largely introduced into the bottle of shot. About 500 liters of hydrogen chlo- ride gas may be passed into a liter of ice water with comparatively little increase in volume, and of ammonia, Before mixing A-fic Fig. 24. Contraction of volume on mixing two liquids. more than 1,000 may be thus introduced. Experiments with solids many years ago showed that they were po- rous. Metal globes filled with water were subjected to pressure and were flattened. The liquid was forced through the metal and, appearing as drops upon the out- side, showed that there were spaces between the particles of the solid through which the water particles could pass. Another experiment made some years ago in Lon- don proves not only the same thing, but that the par- GASES AND SOME GAS LAWS 95 tides of a solid are even free to move about from one place to another. Some cylinders of lead were placed upon sheets of gold and allowed to remain thus for four years. Analyses were then made of the lower end of the lead cylinders and the gold was found to have pene- trated them to a distance of 8 mm. 10. Molecular Theory, The foregoing and many other experiments have led scientists to believe as conclusive that matter is not continuous, but made up of minute particles not touching each other. To these they have given the name of molecules. They are the smallest divi- sion of matter possible without destroying the identity of the substance. Thus a molecule of water or of salt, would possess all the essential characteristics of the larger mass of water or salt. In solids these molecules are close together; in liquids farther apart, and in gases at rela- tively very great distances. To illustrate: In a gas un- der ordinary room conditions, the individual molecules are relatively farther apart than is the moon from the earth, when diameters are considered. The diameter of the earth is about 8,000 miles, so that the distance of the moon is only about 30 times the diameter of the earth. Many gases may be compressed thirtyfold and still remain gases, showing that their molecules are still far apart. A gas which may be compressed by ten thousand atmos- pheres would have its molecules brought ten thousand times nearer together than they were ; ten thousand times the diameter of the earth would approach in distance that of the sun. from the earth. This gives some idea of the real distance of the molecules from each other. A bottle full of hydrogen, as we say, is really a bottle with com- paratively few particles of the gas at relatively great distances from each other. It is difficult for the human mind to form any conception of the infinitesimal size of 96 APPLIED CHEMISTRY a molecule. Someone has said that if a buckshot were mag- nified to the size of the earth and the composing mole- cules likewise were magnified, they would then be some- thing like the size of the buckshot. Lord Kelvin, the great English scientist, has shown that in solids, the dis- tance from the center of one molecule to the center of the next is not less than one five-hundred-millionth of an inch. So if they were actually touching, their diameters would be one five-hundred-millionth of an inch. If their distances apart equal the diameter of the molecule, then their diameters would be one half as great or one billionth of an inch. To count the number possible of lying upon a line 1 inch long, at the rate of one per second, would require nearly 39 years of 360 days each, ten hours per day. Automobiles, equal in number, with a wheel-base of 120 inches spaced 10 feet apart would form a proces- sion reaching a little more than seventy-five times around the earth. 11. Molecules Not at Rest. At several times in pre- ceding chapters it has been necessary to refer to the fact that the particles of gases or liquids are not at rest. The experiment of Roberts-Austin of the gold leaf under the lead cylinders shows the same for solids. Molecules are not like dust particles in the air. These soon settle when the existing cause is removed, but not so with mole- cules. According to Boyle's law, when the pressure is removed from gases, they tend to expand indefinitely, so that a pint of any gas opened into a vacuum, no mat- ter how large, would be quickly distributed throughout the entire space. The passage of a gas throughout the space occupied by another or of one liquid through an- other has been spoken of as diffusion, and can be ex- plained only on the assumption that molecules possess the inherent power of motion and that they are continuously GASES AND SOME GAS LAWS 97 in motion. This is known as the kinetic theory of gases. 12. Gas Pressure, Result of This Motion. By methods not necessary to be discussed here, it has been learned that the average velocity with which these gas molecules are moving is very considerable. With the lightest gases such as hydrogen, it is several miles per second. Naturally, therefore, the numerous successive impacts upon the wall of any containing vessel must produce a pressure. Such is the cause of the pressure exerted by any gas upon the inside of the containing vessel and is simply its resistance to being compressed. It is not the same as the air pressure upon a surface at any par- ticular altitude, for that is merely the weight of the column of air supported at that point. In discussing hydrates in Chapter II, it will be remembered that a manometer tube was mentioned as being used to show the pressure of the water vapor at different tempera- tures. It is simply the impacts of the molecules of va- por upon the surface of the mercury that push it up into the bent tube. Similarly, when we pump air into an automobile tire and the pressure gauge registers an increase from 40 to 80 pounds, we have simply doubled the quantity of air in the tire so that the number of im- pacts per second has been doubled. 13. The Atomic Theory. John Dalton, a scientist who died in 1844, showed conclusively that while the as- sumption of the molecular structure of matter satisfies most of the needs of physical phenomena, it does not explain many things in chemistry. He proposed what is now known as the atomic theory. The most important features of this theory are, first, that molecules are cap- able of division into still smaller particles, which he called atoms. The word means not able to be divided, and up to comparatively recent years the atom has been 98 APPLIED CHEMISTRY regarded as the smallest possible division of matter. It is usually defined as the smallest particle of matter capable of entering into a chemical reaction. Second, it is as- Fig. 25. Dalton, who proposed the atomic theory of matter. sumed by this theory that the atoms of each particular element have a definite and fixed weight. Hence, when they enter into combination, one or more of these defi- nite weights must be used. Third, the weight of an atom GASES AND SOME GAS LAWS 99 of each clement is different from that of every other element; fourth, chemical action takes place between atoms and not between larger masses. Accordingly, to use a somewhat unscientific illustration, matter is tied up by nature in small packages or bundles, and when these are used together in chemical reactions it becomes neces- sary to use one, two or more of the packages. 14. The Corpuscular Theory. As stated just above, the word atom means unable to be divided. Recently, however, it has been found that certain substances, ra- dium for example, are able to give off particles with a velocity nearly the same as that of light and with a mass about one-thousandth part that of the hydrogen atom. These particles are called electrons or corpuscles, and are found to carry a negative charge of electricity. Further, electrons, no matter what their origin, all seem to be of the same mass. Prof. J. J. Thompson suggests that just as the molecules of a gas are at great distances from each other, so are these electrons in the atom, and he com- pares them to a thousand dots (.) scattered throughout a church building. The work of Thompson and of other experimenters seems to admit of no doubt as to the truth of the theory, yet it in no way lessens the value or de- stroys the probability of the truth of the atomic theory. Chemical action is between or among atoms, and the ex- istence of electrons simply aids in explaining many phe- nomena observed which otherwise is not possible. 15. Atomic Weights. It was stated above that Dai- ton's atomic theory assumes that the atoms of each ele- ment have a particular and definite weight. Naturally, it will be understood that to weigh anything so small as an atom is impossible. Hence, atomic weights are merely relative weights. As hydrogen is the lightest of all sub- stances, it would be presumed that its atom would be 100 APPLIED CHEMISTRY used as a standard for measuring others. This was at first done and the term microcrith was applied to the unit. On this basis the weight of the oxygen atom is approxi- mately 16, more accurately, 15.998. It was found, fur- ther, that if the hydrogen atom was assumed to have a weight of one microcrith, the atomic weights of a large number of other elements differ considerably from whole numbers. On the other hand, if oxygen is assumed as weighing exactly 16 microcriths, which will give hydro- gen a weight of 1.008, a very considerable number of the other elements will have atomic weights of either whole numbers or closely approaching these. On account of the advantage which this affords in accurate chemical calcu- lations, it is regarded as preferable. Tables of atomic weights are, therefore, usually given on the basis of the oxygen atom having a mass of 16 microcriths. To define atomic weight, therefore, we would say that it is the weight in microcriths of an atom of any element as compared with the oxygen atom whose mass is 16 microcriths, or with hydrogen, 1.008 microcriths. Thus when we say sulphur has an atomic weight of 32, we mean in the form of va- por it is twice as heavy as oxygen or nearly 32 times as heavy as hydrogen. (See page 441.) 16. Molecular Weights. The molecular weight of a substance is the sum of the weights of all the atoms found in a molecule of that particular substance. It will be shown later that a molecule of water contains two atoms of hydrogen and 1 of oxygen. Adding the weights of two atoms of hydrogen and 1 of oxygen, gives for water a molecule weight of 18. Thus, knowing the composition of the molecule of any substance, we may determine its molecular weight. 17. Avogadro's Hypothesis. The great Italian phys- icist in 1811 formulated the hypothesis which bears GASES AND SOME GAS LAWS 101 his name. It is, Equal volumes of all gases under the same pressure and temperature, contain the same number ,of molecules. To illustrate, this simply; ^atoS/that L*] f fc.c. of hydrogen contain a thousand ,moh;cnle,'v on/J, qi' w oxygen, or any other gas would contain the gaftjje., : No absolute ex : perimental proof of its truth has been furnished, but similar changes of volume for all gases under varying temperatures and pressure, as well as many other ob- Fig. 26. A simple eudiometer connected to induction coil, marked I. served facts, are strong presumptive evidences of its truth. 18. Numbers of Atoms in a Molecule. Assuming the truth of the hypothesis just given, it is possible to as- certain the number of atoms in a molecule of the various gaseous elements or of those which may be vaporized. For example, it has been found that water consists of two volumes of hydrogen to one of oxygen. If the con- verse of the experiment described in Chapter II be car- 102 APPLIED CHEMISTRY ried out with an apparatus called a eudiometer, shown in Fig. 26, and correction be made for temperature, this fact? is .Obsertedi ;/ \ ?? " JtJ$rogei\ exploded with 1 of oxygen produce 2 vol- knifes of sic-Kin;, or-- Cutting it more concretely, 20 c.c. hydrogen with 10 c.c. oxygen produce 20 c.c. steam. The experiment shows that the 30 c.c. of mixed gases when combined yield only 20 c.c. of the vapor, there being a condensation of one-third. Applying Avoga- dro's hypothesis, supposing there are 20 thousand mole- cules in the 20 c.c. of hydrogen, and substituting we should have 20 thousand mol. hydrogen with 10 thousand mol. O. produce 20 thousand mol. steam ; or, 2 mol. hydrogen + 1 mol. oxygen give 2 mol. steam. Now it must be admitted as true that each molecule of steam contains some oxygen ; hence, as there are 2 mole- cules of steam produced for every molecule of oxygen, the oxygen molecule must have been divided into two parts. Using the same apparatus and substituting chlo- rine for oxygen, but using equal volumes of each gas, the experiment may be repeated, with these results: 20 c.c. hydrogen + 20 c.c. chlorine give 40 c.c. hydrogen chloride. Here it will be noticed that although chemical change has taken place the volume has not changed, the new substance having the same as the combined volume of the mixed gases. Applying Avogadro's hypothesis as before, 2 mol. hydrogen 4- 2 mol. chlorine give 4 mol. hydrogen chloride. Now since the number of hydrogen chloride molecules is double that of the hydrogen molecules, each one of GASES AND SOME GAS LAWS 103 the latter must have been broken into at least two portions. Likewise has the ehlorine molecule. Since no cases have ever been observed in which the molecules of these gases are broken into more than two parts, it is assumed that a smaller division is impossible chemically and these particles are atoms. With the exception of ozone, which has been stated as being a peculiar form of oxygen, with three atoms to the molecule, all the common ele- mentary gases, like hydrogen and chlorine, have two atoms to the molecule and are said to be diatomic. Argon, helium, and the other rare gases, belonging to the same family, are monatomic. Mercury and some other metals are likewise monatomic, while phosphorus and arsenic are tetratomic. 19. Gay-Lussac's Law. In all the experiments out- lined just above where one gas combined with another, it will be noticed that the volumes always bore some simple relation to each other. When weights are con- sidered, this is often not true. For example, in common salt by weight chlorine unites with sodium in the pro- portion of about 35.5 to 23. In volumes it will be seen that exactly two of hydrogen combine with one of oxy- gen to form water ; one of hydrogen combines with one of chlorine to produce hydrogen chloride, and three of hy- drogen with one of nitrogen to form ammonia. This has been discovered to be a general truth and has been form- ulated in what is known as Gay-Lussac's law. It is usu- ally stated thus: The volumes of gases when uniting with each other chemically and of the gaseous products formed ~by the union may always l)C expressed in small whole numbers. This law will be further illustrated in the fol- lowing chapter in some problems of combustion. 20. Determination of Molecular Weights. It has been found by experiment that a liter of hydrogen weighs 104 APPLIED CHEMISTRY .0898 grams, and one of oxygen 1.429; or, in larger amounts, 22.4 liters of hydrogen weigh 2 grams and the same volume of oxygen, 32 grams. According to Avogadro's hypothesis, since there are the same num- ber of molecules of each gas in the 22.4 liters, the rela- tive weight of the two must be the relative weight of the two molecules. It may be said, in fact, that 22.4 liters of any gas will always weigh approximately as many grams as there are microcriths in the molecular weight of that gas. It has been stated above that hydrogen and oxygen are both diatomic gases ; hence, since their atomic weights are 1 to 16 respectively, their molecular weights would be 2 and 32 respectively which correspond to the weights in grams given above for 22.4 liters. Likewise, the molecular weight of carbon monoxide is 28, and 22.4 liters weigh approximately 28 grams. This fact may be used to determine the molecular weight of various gases. For example, 22.4 liters of carbon dioxide weigh approx- imately 44 grams; hence, the molecular weight of this gas would be 44. 21. Gram Molecular Weight. The molecular weight of any substance, stated in grams, is called its gram mo- lecular weight. Thus the molecular weight of water is 18; of cane sugar, 342; hence, 18 grams and 342 grams would be Respectively gram molecular weights of these two substances. Sometimes such a weight is spoken of as a mol or a molar weight. If a gram molecular weight of various gases be measured under standard temperature and pressure, allowing for slight variations which admit of explanation, the volume is always approximately 22.4 liters. Thus, Hydrogen, 2 grams occupy 22.4 liters Oxygen, 32 grams occupy 22.4 liters Nitrogen, 28 grams occupy 22.4 liters Carbon Dioxide, 44 grams occupy 22.4 liters GASES AND SOME GAS LAWS 105 Conversely, therefore, if we determine the weight of 22.4 liters of any gas we have a means of knowing approxi- mately its molecular weight. This method often serves in checking up other methods of finding molecular weights and in this way is of great value. Exercises for Review 1. Name the throe states of matter and the two forces which govern them. 2. State Charles' law. Illustrate. What is the absolute zero point? How did it come to be adopted? 3. State Boyle's law. What is meant by standard pressure and temperature? 4. What is the formula for correcting volumes when both tem- perature and pressure change? 5. What is meant by aqueous tension? Would it be used when a gas is collected over mercury? Explain. 6. What can be said about the contiguity of matter? Why must this conclusion be reached? 7. Give some experimental proof that matter is not continuous. 8. W r hat is the molecular theory? A molecule? Give some idea of the size of a molecule ; of the distance they are apart in gases. 9. What proofs can you offer that molecules are not at rest? 10. What gives the pressure on the inside of a tire on a motor car? If you double the quantity of air already in a tire what ef- fect upon the pressure? Why? 11. Give the four main assumptions of the atomic theory. What is an atom? 12. What is an electron? What can you say of its mass? Does this theory destroy the truth of the atomic? Why? 13. What is meant by the atomic weight of an element? Illus- trate. What is a microcrith? 14. State Avogadro's hypothesis. Of what use is it? 15. What is a monatomic molecule? A diatomic? Name some. 16. Give one method of determining experimentally the molecu- lar weight of a gas. CHAPTER VII SYMBOLS AND FORMULAS Outline The Origin of Symbols Present Use of Symbols Formulas (a) Empirical (fr) Structural Eadicals Equations 1. Origin of Symbols. The use of symbols began with the alchemists who sought thereby to render unintelli- gible the notation of their attempts at making gold from the baser elements. Modern chemists have found it necessary in mathematical calculations and in vari- ous other ways to use short methods of representing chemical compounds and the reactions taking place. Moreover, chemical symbols as now used are intelligible to all chemists the world over, so that out of a plan adopted to keep secret the work done has come a uni- versal language read by all chemists. 2. What Are Symbols? A symbol is a letter or letters used to represent a single atom of an element. Usually it is the initial letter, but as this is the same for a number of elements, the initial letter is often followed by some other distinctive one of the word. It must be noted that the initial letter is always capitalized, while the second, if another be used, is not. Thus C is the symbol for carbon; Ca for calcium; Cd for cadmium; Co for cobalt. Several of the elements receive their symbols from the Latin or some other foreign language; thus, K is for 106 SYMBOLS AND FORMULAS 107 potassium, Kalium; Na for sodium, Natrium; Ag, silver, Argent-inn; Hg for Mercury, Hydrargyrum. 3. Formulas. A formula is a combination of symbols representing a molecule of a substance, usually that of a compound. In its broadest sense it may represent the molecule of an element. Thus, HC1 is the formula for hydrogen chloride, while HH, usually written H 2 is the formula for a molecule of hydrogen. To represent the formula of a compound naturally the number of atoms of each element contained must be shown. If there be more than one of any of them, that fact is indicated by a small figure written at the right and slightly below the symbol to be multiplied. Thus, water is H 2 0, showing two atoms of hydrogen to one of oxygen per molecule : likewise sulphuric acid has the formula, H 2 S0 4 ; sugar, C 1 oH, 2 11 . Sometimes a certain group or combination of symbols will be contained more than once in the com- pound ; in such cases the group is usually enclosed in parentheses and the number of times it is contained ex- pressed by a subfigure. Thus, aluminum carbonate is A1 2 (C0 3 ) 3 in which the group C0 3 occurs three times. It might be written C 3 9 , but for reasons which will ap- pear later the method first given is usually followed. If it is desired to represent more than a molecule of a sub- stance, the proper figure is placed before the formula as a coefficient. Thus, 5K 2 CO 3 indicates five molecules of potassium carbonate and the coefficient multiplies each symbol in the formula. That is, in SK^COo there are not only ten atoms of potassium, but five of carbon and fifteen of oxygen. Sal soda has the formula, Na 2 C0 3 . 10H 2 0. Written thus it is typical of the method used for all hy- drates. The number of molecules of water entering into the compound is indicated by the coefficient of the water. Written thus, that the compound is a hydrate, is indicated 108 APPLIED CHEMISTRY at once, as is also the fact that the combination is some- what of a molecular or loose one. 4. Structural Formulas. Often it is very desirable to show how the atoms are arranged in the molecule. Especially is this true in the case of many compounds of carbon, in which two or more may have the same per- centage composition and same molecular weight, but very different properties. Thus, C 2 H 6 is the empirical formula for more than one compound in which there are two atoms of carbon, six of hydrogen and one of oxygen per molecule, but the formula shows nothing more. Ob- viously, if written C 2 H 5 OH or (CH 3 ) 2 O, the molecular weights are the same, but the first indicates an alcohol and the second an ether. To the chemist, written thus, they indicate the manner of arrangement of the atoms in the molecule. This is shown more fully thus ; H H H-C-C-0-H, ethyl alcohol. H H H H H-C-0-C-H, methyl ether. H H Such formulas as these are called structural or some- times graphic, and in very complex compounds are of the greatest help in understanding the relations existing. 5. Radicals. In many compounds certain groups of elements will be found, which behave as if they were single elements. Thus in sulphuric acid and in all the sulphates there occurs the group, - S0 4 . This constitutes the negative portion of the compound and in case of electrolysis appears at the positive electrode. It can- SYMBOLS AND FORMULAS 109 not be separated out or isolated, and in the electrolytic apparatus it immediately combines with the anode if that be possible; if not, it combines with hydrogen from the water present and forms a molecule of sulphuric acid. Looking at the formulas, K 2 S0 4 , CuS0 4 , A1 2 (S0 4 ) 3 , K 2 A1,(S0 4 ) 4 , we see the same combination of elements. All such groups are called radicals. Ordi- narily the term indicates a group of atoms forming a part of a compound but unable to exist alone. There is only one common electropositive radical, ammonium, NII 4 - ; it is found in all ammonium compounds. Thus am- monium chloride, NH 4 C1, ammonium sulphate (NH 4 ) 2 S0 4 . The other more common radicals are - N0 3 seen in nitric acid and all nitrates, - C0 3 in the carbonates, - P0 4 in phosphates, - C10 3 in chlorates, - HO in hydroxides. 6. Equations. Chemical changes or reactions have been classified as being mainly of three kinds. It is customary among chemists to show what takes place in a chemical change by an equation. The left hand side contains the formulas of the substances used and the right hand side, the products formed, with the sign > between, which is read yields or produces. Going back to the experiment of heating mercuric oxide, we find that, Mercuric oxide, heated, yields oxygen and mercury. For the sake of brevity this is written, HgO (heated) -> Hg + or better, 2HgO(heated) -* 2TTg + 2 . It was stated in the preceding chapter that the oxygen molecule contains two atoms. It is known that all sub- stances exist as aggregations of molecules and not of atoms. The second equation just above shows the oxy- 110 APPLIED CHEMISTRY gen in the molecular form as it would exist after 'it has been liberated from the compound, hence is the better form. Again, water electrolyzed, gives hydrogen, two parts and oxygen, one. More briefly, but indicating the same thing, 2H 2 -> 2H 2 + 2 Equations are not something merely abstract as equations in algebra, or merely theoretical. Every equation must be verified by actual experiment, otherwise it has no value. For example, we prepared hydrogen by allowing sodium to react with water. Algebraically we might write the equation, 2Na + H 2 0-Na 2 + H 2 or 2Na + 2H 2 -* 2NaHO + H 2 . Only by experiment can we know which is correct. The first of the two equations shows sodium oxide formed ; the second, sodium hydroxide. Which is correct ? Chem- ical tests show that, performed as the experiment was, sodium hydroxide is present; hence, the equation must be written to show that fact. We prepared oxygen by heating potassium chlorate, KC10 3 . Theoretically, all or part of the oxygen might be displaced by heating the com- pound, just as was the case when sodium reacted, as above, with water in producing hydrogen. Testing the residue shows that potassium chloride is present, and our equation must be written to indicate the fact, thus, 2KC10 3 -> 2KC1 + 30 2 . In like manner all equations are determined by experi- ment and merely state in brief form what was learned thereby. SYMBOLS AND FORMULAS 111 Exercises for Review 1. What was the origin of symbols? Give the purpose of a sym- bol now. 2. Define a symbol. 3. Of what do symbols consist and how written? Illustrate. 4. Give several derived from the Latin or Greek. 5. What is a formula and what does it represent in its broad- est sense? 6. What effect has a coefficient before a formula? Illustrate. How is it different from the coefficient as used in algebra? 7. What is a structural formula? Of what advantage? 8. What is a radical? Give five. How are they different from compounds? 9. What is the purpose of an equation? What do they show? 10. Which is the better form, and why : 2K + 2H 2 O - H 2 + 2KHO, or, K + II 2 O -> H + KHO? 11. How do chemists know whether an equation is correct? 12. Is this equation true: CiiSO 4 + 2KHO - Cu(HO) 2 + K 2 SO 4 ? How can you find out? CHAPTER VIII SOME CHEMICAL PROBLEMS Outline- Practical Value of the Equation Problems in Manufacturing Industries Percentage Composition of Compounds Problems in Combustion Liter Weights of Gases Determination of Formulas 1. Value of Equations, Almost every manufacturing industry involves more or less chemistry. In baking powders, of the three ingredients most often used, two of them must be exactly proportioned, otherwise the food in which they are used will be valueless. The chemical change occurring when such chemicals are put together is first determined by experiment in the labora- tory; this is then expressed by an equation, and from this without repeating the experiment the quantities needed may be calculated by any one at any time. To illustrate with a case somewhat simpler than that of baking powder, we have learned that 2KC10 3 - 2KC1 + 30 2 . This equation shows that two molecular weights of po- tassium chlorate produce three molecular weights of oxygen. Calculating these weights from the table of atomic weights given on p. 441, we find that 245 parts of potassium chlorate yield 96 of oxygen. Suppose a man- ufacturer needs to know how much oxygen he can obtain from 1,000 grams of potassium chlorate. Knowing from 112 SOME CHEMICAL PROBLEMS 113 the equation that 245 grams of the chlorate will produce 96 of oxygen 1,000 will produce x grams, or 245 : 96 : : 1,000 : x, from which x may be easily calculated. Or, putting it in another form, the oxygen obtained is seen to be 96/245 of the weight of the chlorate used. The oxygen obtained, therefore, would be 96/245 of 1,000 ^ 96X1 > QQ 245 Manufacturers of oxygen for use in the oxyhydrogeii blowpipe or for other purposes furnish it in gaseous form, which might sometimes be given in volume and not weight as above. Knowing the weight of a liter of oxy- gen, 1.43 gram, which may be obtained by multiplying the weight of a liter of hydrogen by the density of oxy- gen, if we divide the weight obtained above by the weight of a liter of oxygen we shall have the volume. It may also be obtained another way, which is often easier. It has already been stated that a gram molecular weight of oxy- gen as of any other gas is 22.4 liters. By looking at the equation, 2KC10 3 ->2KC1 + 30 2 , we see that two molecular weights of potassium chlorate produce three molecular weights of oxygen. But 3 gram molecular weights of oxygen would be, in volume, three times 22.4 liters. That is, 245 grams of potassium chlo- rate would produce 3 x 22.4 liters of oxygen, or 67.2 liters. Hence, 1,000 grams of potassium chlorate would yield Tli is would be the volume under standard conditions of 114 APPLIED CHEMISTRY temperature and pressure. If the gas is to be delivered under five atmospheres' pressure, according to Boyle's law, five volumes of the uncompressed gas must be pre- pared for every one of that to be delivered. 2. To Find Percentage Composition. Knowing the formula, the method is very simple. Suppose it is de- sired to know the amount of water contained in Epsom salt, MgS0 4 .7H 2 0. Ascertaining the atomic weights from the table, p. 441, we have 24 + 32 + 64 +(7x18) =246. The weight of the seven molecules of water is 126. It is, therefore, 126/246 of the whole compound, or 51.2 per cent. 3. Some Combustion Problems. Ordinary combustion has been defined as rapid oxidation. It is often desir- able to know the character and quantity of products formed as well as the amount of air needed for per- fect combustion. Natural gas consists mainly of what is known as marsh gas, CH 4 . When it burns the follow- ing equation illustrates the change taking place, CH 4 + 20 2 ->C0 2 + 2H 2 0. This shows that one volume of marsh gas requires two volumes of oxygen and produces one of carbon dioxide and two of vapor. Applying Avogadro's hypothesis, any problems involving volumes may be read off at once from the equation. Suppose 1,000 cubic feet of marsh gas are burned; from the equation we can see that twice as much oxygen would be needed and there would be produced the same volume of carbon dioxide and twice the volume of water vapor. As air is only about one- fifth oxygen, to burn this volume of gas would require SOME CHEMICAL PROBLEMS 115 10,000 cubic feet of air. Acetylene is a gas producing great heat when properly burned and often used in blow pipe work for welding, 2C 2 H 2 + 50 2 -> 4C0 2 + 2H 2 0. The equation indicates that two volumes of acetylene re- quire five of oxygen and yield four of carbon dioxide and two of vapor. From this it is seen at once that 1,000 cubic feet of the gas would need two and a half times as much oxygen or 2,500 cubic feet, and would produce 2,000 cubic feet of carbon dioxide and 1,000 of vapor. When rooms are warmed by an open gas heater or by an oil stove, by which the necessary oxygen is taken directly from the room and the products left in the room, it is seen how rapidly the air is being vitiated. The water pro- duced in such cases is often sufficient to loosen the paper upon the walls, and even the parts of furniture glued together. It must be remembered that the air being used is more than five times the volume of the oxygen shown in the equation. 4. To Find the Weight of a Liter of Any Gas. It is not necessary for the student to commit to memory many figures. But the weight of a liter of hydrogen should be remembered, for by means of it the weight of a liter of other gases may readily be calculated. It is nec- essary first to determine the vapor density of the gas, that is, its density compared to hydrogen. Obviously, from Avogadro's hypothesis, if we divide the molecular weight of any gas by the molecular weight of hydrogen, we shall have the density of the gas compared to hydro- gen. The molecular weight of hydrogen is 2, hence divid- ing the molecular weight of any gas by 2 gives its vapor density. Then, knowing the weight of a liter of hydrogen, if we multiply this by the density we shall have the 116 APPLIED CHEMISTRY weight of a liter of the gas in question. To illustrate: Take carbon dioxide, C0 2 . It has a molecular weight of 44 ; its vapor density would, therefore, be 22 : multiply- ing the weight of a liter of hydrogen, .0898, by 22 gives 1.9756 as the weight of a liter of carbon dioxide. 5. Determination of Formulas. Knowing by experi- ment the percentage composition of a substance, and the atomic weights of the elements contained, it is possi- ble to determine the empirical formula. Thus, wood al- cohol contains 31 l / 2 per cent of carbon, 12% per cent of hydrogen and 50 per cent of oxygen. Dividing these percentages by the atomic weight of each element, on the assumption that they are microcriths of weight and not percentages, we have 37 ' 5 =3.125 ^==12.5 4?- ==3.125. 12 1 16 Had the figures representing per cents really been mi- crocriths, as assumed, the quotients would have been the number of atoms of each element in the formula. While the assumption is not true, the mathematical re- lation obtained is true, that is, for every 3.125 atomic weights of carbon there would be 12.5 atomic weights of hydrogen and 3.125 of oxygen. If we divide through by the smallest of these weights we shall remove the fractional amounts and obtain as a result, carbon, 1; hydrogen, 4 and oxygen, 1. The formula, therefore, would be CH 4 0. To know whether this is correct the vapor density of the alcohol must be determined. Sup- pose by experiment this is found to be 16. We know from a previous statement that the molecular weight is double the density, hence the molecular weight of this compound would be 32. By adding the atomic weights represented in the formula obtained, CH 4 0, SOME CHEMICAL PROBLEMS 117 we obtain 32, which agrees with the weight obtained by experiment ; hence is correct. Take another case. Anal- ysis of sulphuric acid shows it to contain hydrogen, 2.04 per cent; sulphur, 32.65; oxygen, 65.30. Dividing these figures by the respective atomic weights we have as the quotients, 2.04, 1.02 and 4.08, which give the relative number of atomic weights contained in the molecule. Dividing \)y the smallest quotient, we have as a result, 2, 1, 4 respectively, giving for the formula H.,S0 4 . Again, acetylene has a percentage composition of carbon, 92.31, and hydrogen, 7.69 per cent. Dividing by the atomic weights we have as the quotients, 7.7 and 7.69. Dividing these results \)y 7.69 we have 1 and 1 respectively, which gives as the empirical formula for acetylene, GIL Is this correct? By experiment in the laboratory a liter of acetylene is found to weight 1.167 grams. As a liter of hydrogen weighs .0898 grams, acetylene is found to be thirteen times as heavy. The molecular weight, therefore, must be 2 x 13, or 26. If CII were the formula, its molec- ular weight would be only 13 ; hence, the empirical for- mula we obtained by calculation is just half the correct one ; in other words, it must be doubled, so that it becomes. C 2 H 2 . Exercises for Review 1. Determine the weight of oxygen obtainable from 980 grams of potassium chlorate. What volume would the oxygen have? 2. How much potassium chlorate would be needed to prepare 500 liters of oxygen if under five atmospheres' pressure? 3. What weight of hydrogen may be had from 260 grams of zinc by allowing it to react with sulphuric acid? Suppose hydro- chloric acid were used, what would be the weight of hydrogen? 4. What weight of sulphuric acid would be needed to react with 100, grams of magnesium in preparing hydrogen? What would be the volume of the hydrogen obtained? 5. Calculate the per cent of sulphur in sulphuric acid. Also the per cent of oxygen. 118 APPLIED CHEMISTRY 6. What is the percentage of water in sal soda; formula, Na 2 C0 3 10H 2 0? 7. The gas ethylene has the formula, C 2 H 4 . If 1,000 liters of it are burned, what volume of carbon dioxide is produced and what of water vapor? 8. Find the weight of a liter of oxygen; of carbon monoxide, CO; of ozone; of nitrogen monoxide, N 2 O; of arsenic vapor. 9. The percentage composition of a certain alcohol is carbon, 52.17, hydrogen, 13.04, and oxygen 34.78. Find the empirical formula. 10. If the vapor density of nitric oxide is 15, is its formula NO or N 2 O 2 ? CHAPTER IX THE HALOGENS Outline Relation of the Halogens to Each Other Chlorine, its History (a) Preparation in Laboratory (ft) Commercial Methods (c) Physical Characteristics (d) Chemical Characteristics (e) Uses Hydrogen Chloride Characteristics Hydrochloric Acid (a) Preparation (6) Characteristics (c) Uses Hydrofluoric Acid Uses Bromine (a) Occurrence (&) Preparation (c) Characteristics (d) Uses Iodine (a) Occurrence (6) Preparation (c) Characteristics (d) Uses 1. General View. There are four elements in the halo- gen group fluorine, chlorine, bromine and iodine. They are called halogens, a word meaning salt producers, be- cause they all produce many compounds resembling com- mon salt; and from the similarity of their physical char- acteristics and their chemical behavior, must be re- garded as belonging to a single group of elements. Their 119 120 APPLIED CHEMISTRY densities compared to hydrogen are in the order given above, with atomic weights, respectively of, approxi- mately, 19, 35.5, 80 and 127. Their chemical activity is in the inverse order of their densities, that of iodine being the least. All have an irritating odor, although that of iodine is rather feeble when compared with the others. The two lightest are gases; bromine is a liquid, the only liquid element except mercury, and iodine is a solid. 2. Discovery of Chlorine. It will be remembered that in 1773 Scheele prepared oxygen by heating manganese dioxide with sulphuric acid. The following year he ob- tained chlorine by treating manganese dioxide with hydrochloric acid, although he had no idea he had dis- covered a new element. Knowing that it was possible to obtain oxygen from manganese dioxide, he believed he had simply caused a union between the hydrochloric acid and the oxygen of the dioxide. And, in accordance with the phlogistic ideas of combustion, he named the gas dephlogisticated marine acid air. At that time oxy- gen was often called dephlogisticated air; hence, the name in modern chemical terms would be oxidized hydro- chloric acid gas, for marine acid was then what we now call hydrochloric. More than a quarter of a century passed away and chlorine was still unknown as an element until Sir Humphrey Davy gave it a careful study and so pronounced it. 3. Preparation of Chlorine. The usual laboratory method of preparing chlorine is the same as used by Scheele. (Fig. 27.) The accompanying figure shows one form of apparatus and the method of collecting. Being a gas much heavier than air it may be collected by downward displacement. As it is considerably soluble in water, the plan used in the case of hydrogen and oxygen is not satis- THE HALOGENS 121 factory, but may be employed if the water has a consid- erable amount of common salt dissolved in it. The man- ganese dioxide is placed in the flask, and when the col- lecting bottles are all ready the hydrochloric acid is added through the thistle tube and gentle heat applied as needed. 4. Commercial Methods. As chlorine is used so ex- tensively in various ways, several processes of obtaining it cheaply have been devised. Since common salt is Fig. 27. Preparation of chlorine in the laboratory. abundant and not expensive, one of the plans widely adopted is that of separating its constituents, sodium and chlorine, by electrolysis. There are many difficul- ties in the way of carrying out the method successfully, but one type of machine is shown in Fig. 28. In the cen- ter compartment the bundle of carbon rods serves as the cathode, while a heavy carbon rod enters each of the two outer compartments, giving a double anode. The cathode dips into pure water, the anodes into sat- 122 APPLIED CHEMISTRY urated salt solution; a thin layer of mercury covers the bottom of the apparatus and fills two grooves into which the partitions dip, shown by the heavily shaded portion in the figure. Chlorine being an electronegative element is liberated at the anodes and is drawn off, dried, and compressed in tanks or drums. The sodium, electropositive, is repelled by the anodes, moves toward the cathode, meets the mercury and is dissolved by it. In the figure, E is an eccentric which rocks the tank continually. In this way the mercury containing the sodium is brought into contact with the water, where- E FA Fig. 28. Manufacture of chlorine. upon the sodium reacts with the water forming sodium hydroxide. The two reactions are 2NaCl -> C1 2 + 2Na, 2Na + 2H 2 -> H 2 + 2NaHO. 5. Physical Characteristics of Chlorine. Chlorine is a .greenish-yellow gas, about two and a half times as heavy as air, and of very irritating odor. It may be liquefied at 33.6 C. at atmospheric pressure and in this condition is a limpid, golden yellow fluid. It may be kept thus sealed hermetically in strong glass tubes. At about -102 C. it becomes a pale yellow solid, which upon further cooling changes to a pure white substance resembling snow. Upon melting it assumes the same THE HALOGENS 123 yellow color again. It is soluble in water about two volumes to one. 6. Chemical Characteristics. Chlorine is an exceed- ingly active element, possibly even more so than oxygen. Nearly all the metals, especially in a finely divided form or in thin sheets, ignite spontaneously in chlorine. So- dium must be heated before combustion takes place, but when this is done the action is vigorous with the formation of common salt. Turpentine, near its boil- ing point, on a strip of blotting paper, when lowered into .a jar of chlorine, catches fire almost instantly, produc- ing an immense quantity of black smoke. Yellow phos- phorus in a deflagrating spoon in chlorine begins to burn almost immediately, and a jet of hydrogen, lighted in the air, continues to burn as well or better than before. From these experiments it is evident that combustion means more than the union of a substance with oxygen. Any two substances, combining with such rapidity as to produce heat and light, undergo combustion. Chlorine attacks the throat and bronchial tubes, causing great suffering for which there is no good antidote. A satu- rated solution of chlorine in water, if surrounded by ice, deposits yellow crystals of chlorine hydrate, having the composition C1.4H 2 0. A mixture of equal parts of hy- drogen and chlorine, if exposed to bright sunlight, ex- plodes with violence. The light from a burning magne- sium ribbon will bring about the same results. A solu- tion of chlorine in water, exposed to strong light, decom- poses, forming hydrochloric acid and setting free the oxy- gen. This is shown by a simple experiment illustrated by Fig. 29. The test tube is filled with chlorine water and inverted over an evaporating dish partly filled with the same solution. In a short time, bubbles of gas may be seen rising to the top of the tube; when the action has 124 APPLIED CHEMISTRY ceased the color will all have disappeared from the water. Chemical tests show that the gas is oxygen and that at the close the water contains hydrochloric acid. The final result is shown by the equation, 2H 2 + 2C1 2 - O 2 + 4HCL 7. Uses of Chlorine. Chlorine is used extensively for bleaching, especially cottons and linens. The cloth is drawn slowly through successive vats of bleaching pow- der solution and dilute hydrochloric acid. Thus the chlorine is set free and oxidizes the coloring matter. Much of the paper pulp used is bleached in the same way, and in the Middle West most of the large flour Fig. 29. Effect of sunlight on chlorine water. mills employ liquid chlorine to bleach their products, to enable them to compete with other flours which by nature need no such bleaching. Practically all steam laundries now use chlorine to whiten the cotton and linen goods in order to please a critical public. Such frequent use of chlorine upon the fibers of the cloth greatly weakens them and hastens the end of their usefulness. Chlorine is frequently employed as a disinfectant; its use for the destruction of pathologic germs in city wa- ters has already been mentioned. Bleaching powder, a compound formed by the interaction of chlorine with lime is valuable in the sick-room; a small amount in a THE HALOGENS 125 saucer, moistened with water, slowly gives off chlorine to the air. The quantity is so small as to be unnoticea- ble except close at hand, yet by diffusion throughout the room brings very valuable results. Chlorine is also used in the extraction of gold from its ores : for this purpose, bleaching powder, treated with hydrochloric acid is frequently employed, but in places remote from railway or other good means of transportation liquid chlorine put up in steel cylinders is used. Chlorine was the first of the poisonous gases used in the late war. Steel cylinders filled with the gas liquefied by great pressure were opened with nozzles towards the Allies with the wind blowing in that direction. Carried down hill by its own weight and aided by the wind the huge greenish-yellow billows caused the greatest suffering and thousands of deaths. Later the gas mask was de- vised to protect the wearer against such attacks. In the American mask all the air taken into the lungs was compelled to pass through a specially absorptive kind of charcoal made from the shells of nuts, or of charcoal mixed with an antichlor, a substance which combines with the chlorine. One of the best substances of this nature is what is known by photographers under the name of hypo or sodium thiosulphate. 8. Hydrogen Chloride. This compound has been known to chemists several hundred years, under the names, spirit of salt and marine acid air. It was so named because prepared from common salt, at that time derived mostly from the Mediterranean Sea. 9. Physical Characteristics of Hydrogen Chloride. It is a colorless gas of very irritating odor, and considera- bly heavier than air. It is very soluble in water ; a liter of water at C. will absorb between 500 and 600 liters 126 APPLIED CHEMISTRY of the gas. In other words, 600 liters are about the same as 600 quarts or three 50-gallon barrels, so that one quart of ice water will absorb about three barrels of hydrogen chloride. Blowing across the top of a tube or flask in which the gas is being evolved always shows heavy white fumes ; this is because the moisture of the breath is absorbed and condensed by the gas. When a jet of hydrogen burns in a bottle of damp chlorine, or turpentine upon the blotting paper as previously de- scribed, a white cloud always appears, from the condensa- tion of the moisture by the hydrogen chloride formed. H 2 + C1 2 -> 2HC1 C 10 H 16 + 8C1 2 ->16HC1 + 10C. These two equations represent the burning of hydrogen and of turpentine respectively in an atmosphere of chlo- rine. A liter of the hydrogen chloride weighs 1.64 grams. At -83.7 C. it becomes a colorless liquid and at -110 a solid. The liquid has no effect upon dry metals such as zinc and others, readily acted upon by the solution of the gas. 10. Hydrochloric Acid. When hydrogen chloride gas is allowed to pass into water the solution formed is called hydrochloric acid. The ordinary commercial va- riety, yellow in color, due to the presence of small quan- tities of iron chloride, is sold under the name, muriatic acid. It was formerly a by-product obtained in the man- ufacture of sodium carbonate, the first step of which in- volves the treatment of common salt with sulphuric acid. At temperatures such as those obtained in the laboratory with the bunsen burner, the following reaction takes place, NaCl + H 2 S0 4 -> HCl + NaHS0 4 . In the factories a much higher temperature is used with THE HALOGENS 127 double the quantity of salt which results in a different reaction, thus, 2NaCl + H 2 S0 4 -> 2HCl + Na 2 S0 4 . The gas thus obtained is conducted into towers filled with coke or some similar material, which is kept moist by wa- ter trickling over it. Owing to its great solubility the gas is all absorbed and when concentrated the solution is the acid of commerce. 11. Characteristics of Hydrochloric Acid. When pure it is a colorless solution. If a weak solution be boiled it becomes more and more concentrated until it reaches about 20 per cent of hydrogen chloride ; one stronger than this, if heated, gives off the gas faster than the water until it reaches a strength of about 20 per cent, when it remains constant. Ordinary concen- trated hydrochloric acid contains about 36 per cent of hydrogen chloride and is strongly acid. Litmus paper is turned red as are various other vegetable colors or dyes; by such metals as magnesium, iron, zinc it is readily decomposed with the evolution of hydrogen. Thus, Zn + 2HCl -> H 2 + ZnCl 2 , Mg + 2HC1 -> H 2 + MgCl 2 . This is very different from the action of the liquid hy- drogen chloride. The two are not different in appearance, but the latter, as previously stated, does not affect dry metals; neither is it a conductor of electricity, whereas the acid is. 12. Uses. A century ago hydrogen chloride was a waste product of the Leblanc process of making soda crystals. Being heavier than air it settled doAvn from the lofty towers built to carry it away, destroying veg- etable life and corroding tools and everything of a me- 128 APPLIED CHEMISTRY tallic character. When conducted into streams it killed the fish and other aquatic animals, so that eventually most stringent laws were enacted against all such manu- facturers. Finally, by the aid of chemical research, valuable uses were suggested for it, and now it ranks among the most valuable of the acids. Every laboratory uses it abundantly; almost every manufacturing in- dustry employs it to a greater or less extent. In the stom- ach it is believed to be an essential of digestion. The fact that bones, very imperfectly masticated, are readily digested by various carnivorous animals is explained by the excessive amount of hydrochloric acid found in their stomach, which dissolves the mineral matter from the bones and leaves them about as soft as so much gelatine. Hydrochloric acid is used mixed with nitric acid, three parts of the former to one of the latter, in what is called aqua regia. The words mean royal water and were so employed for the reason that formerly this was the only known solvent for gold, the king of metals. The solution is effected by the chlorine which is set free thus, 3HC1 + HN0 3 - 2H 2 + 2C1 + NOC1. 13. Hydrofluoric Acid. The preparation of hydrogen fluoride is similar to that of the corresponding com- pound of chlorine. The cheapest natural compound of fluorine is calcium fluoride, known as fluor spar, CaF 2 . This is mixed with sulphuric acid and heated in a plati- num retort. A colorless, irritating gas distils over, which is caught in water. This solution is the hydro- fluoric acid of commerce. It is put on the market usu- ally in ceresine or wax bottles. At ordinary tempera- tures the gas is believed to have the formula H 2 F 2 . Above 30 C. it begins to decompose and at a little be- THE HALOGENS 129 low 90 the density of the vapor indicates a molecular weight of 20 which is that for the formula HP. Its chief use is for etching glass. The article to be etched is covered with paraffin, the design is cut in the wax so as to expose the glass, and the hydrofluoric acid is dropped on. In a very few minutes the etching is done. Graduations upon scientific instruments and apparatus such as barometers, burettes, pipettes and the like, are thus made. The following equations show the chemical reactions in preparing the hydrogen fluoride and the glass etching, CaF 2 + H 2 S0 4 -* H 2 F 2 + CaS0 4 , CaSi0 3 Na 2 Si0 3 + 6H 2 F 2 -> 2NaF + CaF 2 + 2SiF 4 + 6H 2 0. The silicon fluoride is a gas and escapes, while the cal- cium and sodium fluorides are solids which are washed away in cleaning the glass. Porcelain and chinaware, in being prepared for hand decoration, are often treated with hydrofluoric acid to remove the glazed surface and thus cause the gold or other decoration to adhere the better. Bromine 14. Where Found. Bromine in potassium and mag- nesium bromide occurs in nature associated with com- mon salt. Being more soluble than salt, these com- pounds do not crystallize out as readily; hence, they are usually found in the upper layers of salt beds. Our supply is largely obtained as a by-product of the salt works of Ohio, Kentucky and Michigan. 15. Preparation. The method is very similar to that for the preparation of chlorine. It will be remembered that in the laboratory chlorine is made by treating manganese dioxide with hydrochloric acid. Hydrobro- 130 APPLIED CHEMISTRY mic acid is not an article of commerce, because of its instability; hence, it must be prepared as needed. If magnesium bromide or any other bromide is treated with sulphuric acid, hydrogen bromide may be obtained, thus, MgBr 2 + H 2 S0 4 -> 2HBr + MgS0 4 . It has many properties similar to hydrogen chloride in that it is a colorless gas, has a very irritating odor, and is very soluble in water. For the last reason it con- denses moisture in the air or from the breath readily. Passed into distilled water, hydrobromic acid is formed, but it very soon begins to decompose and in a few days no acid at all remains. In preparing bromine, if man- ganese dioxide is added to the mixture of magnesium bromide and sulphuric acid, we have conditions similar to those in the preparation of chlorine. First the hy- drogen bromide is formed, then this oxidized by the manganese dioxide with the formation of free bromine. It is then distilled out and condensed under water. The following equation shows the final reaction, MgBr 2 + Mn0 2 + 2H 2 S0 4 - MgS0 4 + MnS0 4 + 2H 2 + Br, 16. Physical Characteristics. Bromine is a dark red- dish-brown liquid, the only liquid nonmetallic element. It is a little more than three times as heavy as water in which it is not greatly soluble about 3 c.c. in one hun- dred. It is a very volatile liquid ; hence, if a bottle of it is left open it soon passes off into the air. It boils at 59 C. and solidifies at - 7.3, in slender, needle-like crystals. Its vapors are exceedingly irritating to the throat and bronchi, and upon the skin the liquid pro- duces serious and painful burns; therefore, the utmost care must be exercised in handling it. 17. Chemical Characteristics. Many of the character- istics of chlorine are observable in bromine, but in a THE HALOGENS 131 less marked degree. A jet of hydrogen burns in a bot- tle of bromine vapor producing white fumes due to the hydrogen bromide formed. A mixture of the two gases, however, is not explosive, but a platinum sponge greatly hastens the union as was the case with the chlorine and hydrogen mixture. A piece of yellow phosphorus, placed in bromine vapor, does not usually ignite, but a slow combination takes place, with the formation of phos- phorous tribromide. If a small drop of liquid bromine be allowed to fall upon a piece of yellow phosphorus, the action is immediate. The chemical union is so vi- olent that the phosphorus is ignited, bursts into frag- ments, and burns vigorously. Small pieces of antimony dropped upon bromine in a test tube become red-hot almost instantly, float around upon the liquid, and fin- ally disappear. The chemical reaction is 2Sb + 3Br 2 -* 2SbBi%. With many other metals the action is equally violent. 18. Uses. Bromine is used to some extent in the lab- oratory in analytical work, but more largely in the manufacture of aniline dyes. The compounds, potassium and magnesium bromide, are used in medicine, mainly as sedatives. Iodine 19. Occurrence. Like chlorine and bromine, iodine in the form of compounds occurs in sea water. From this it is separated by certain seaweeds, especially kelp, and stored up in the form of rather complicated com- pounds. In many places along the Pacific Coast, nota- bly, in the neighborhood of San Diego, vast quantities of kelp are found, so that ocean vessels are unable to make their way through. In the form of compounds, sodium iodide and iodate, iodine occurs in the saltpeter 132 APPLIED CHEMISTRY beds of Chile as bromine does in the salt beds of the United States. 20. Preparation. Formerly most of the iodine of commerce was obtained from seaweeds. They were cau- tiously burned so as not to vaporize the iodine present, and the ashes were treated as in the preparation of bro- mine, that is with manganese dioxide and sulphuric acid. The equation is similar : 2KI + 3H 2 S0 4 + Mn0 2 -> MnS0 4 + 2KHS0 4 + 2H 2 + 1 2 The iodine distils out and is condensed. It is purified by vaporizing again in specially constructed furnaces, shown Fig. 30. Apparatus for purifying iodine by sublimation. in Fig. 30. In recent years probably more of the iodine supply has come from the deposits in Chile; although during the late war in the manufacture of potassium and other compounds from kelp much iodine 'was ob- tained as a by-product. 21. Physical Characteristics. Iodine is a lustrous,, nearly black solid. It crystallizes in thin plates, which even at room temperature are volatile, as may be seen if the crystals are placed in a white dish. Upon warm- ing gently it vaporizes without melting. The process is called sublimation and is used for purifying iodine and THE HALOGENS 133 other substances which pass directly from the solid to the gaseous condition upon heating. It corresponds to the distillation of liquids. For medical purposes iodine is sublimed more than once as is indicated by the labels upon the bottles marked, resublimed. Iodine has an odor resembling dilute chlorine. It is very slightly soluble in water, barely sufficient to color the solution. However, in a solution of potassium iodide in water iodine is very solu- ble, giving a dark brown color. The same is true of al- cohol and ether solutions, in both of which liquids it is very soluble. Carbon disulphide is also an excellent sol- vent and gives a beautiful violet solution; starch muci- lage is turned deep blue, a reaction which serves as the test both for iodine and starch, as may be needed. The quantity of iodine should be small, just sufficient to give the solution a pale yellow color ; otherwise, the starch will turn so dark it will appear black. To the eye weak solutions of iodine appear not unlike those of bromine. They may be distinguished by adding 1 or 2 c.c. of carbon disulphide to the solution of iodine or bromine and shak- ing well. As the carbon disulphide is a much better sol- vent than the water, the bromine or iodine will be col- lected in the small quantity of the heavy carbon disulphide at the bottom of the test tube. The bromine will give a golden brown and the iodine a purple color. 22. Chemical Characteristics. These resemble those of chlorine, but are much feebler. A crystal of iodine laid upon a thin slice of phosphorus reacts vigorously so that the phosphorus catches fire and burns, while considerable of the iodine is vaporized. Iodine is read- ily displaced from soluble compounds by both chlorine and bromine, but much more easily by the former. Thus, 2KI + Cl, -* 2KC1 + 1, 134 APPLIED CHEMISTRY Even a single bubble of chlorine causes a brown dis- coloration of the liquid. A very interesting fact about iodine is its behavior at high temperatures. In a pre- ceding section in this chapter the atomic weight of io- dine was mentioned as about 127. Its molecular w r eight is found to be 254, which shows that like chlorine and bromine it is diatomic. When heated above 700 C. the vapor becomes lighter and lighter, much more so than agrees with Charles' law, until at 1,700 it is just half what it was at 700. This indicates that the molecules have been broken into two parts and that the gas is now monatomic. The same is true of bromine vapor, but to a considerably less extent. It must be noted further that as the temperature is lowered the lighter molecules recombine to form the diatomic molecules; at the same time a very considerable amount of heat is evolved, just as when steam is cooled it gives off the heat previously consumed in producing it. The following equation il- lustrates what is happening, I 2 * 21. The double arrow sign used is read, gives reversMy. Such changes are called dissociation, a term which means the process of decomposing a substance and reforming it under varying conditions. It is probable that at all temperatures, between 700 and 1700, the action is pro- ceeding in both directions, that is, some of the diatomic molecules are being decomposed and others are being re- formed by the union of two monatomics. 23'. Uses. Iodine is used mainly in medicinal prepa- rations. The tincture, the best known, an alcoholic so- lution, is used as a counter-irritant in sprains, bruises and swellings; as a germicide in preventing the spread of erysipelas and other similar diseases ; as an antiseptic in surgical operations and wounds in place of hydrogen THE HALOGENS 135 peroxide. It is more powerful, more penetrating and more lasting, than the peroxide, but at the same time much more severe, causes much more irritation, and in unskilled hands is much less safe. lodoform, CHI 3 , is a pale-yellow solid; has a peculiar odor, disagreeable to most individuals; is strongly germicidal, and often used by physicians as an antiseptic in contagious diseases, lodothyrin, an extract obtained from the thyroid gland of sheep is sometimes used in cases of underdevelop- ment of the same gland in the human body. Exercises for Review 1. Name the halogens and state why so called. 2. Who discovered chlorine? What was the discoverer's idea regarding it? What was the old name? Who proved it was an element? 3. Give usual method of preparing and collecting chlorine. 4. Describe one commercial method of obtaining chlorine. 5. Give the physical characteristics of chlorine. 6. Give the chemical characteristics. 7. Name the important uses of chlorine. 8. How is hydrogen chloride prepared? Give its character- istics. 9. How is hydrochloric acid prepared? What is muriatic acid? 10. Give the characteristics of hydrochloric acid. 11. What can you say of the history of it? Name some uses. 12. What is aqua regia? Why so called? 13. Give the uses of hydrofluoric acid. How is it kept for use? 14. What can you say of the occurrence of bromine? 15. How is bromine prepared for commerce? Compare method with that of chlorine. 16. Describe bromine. What danger in handling it? 17. What is the chief use of bromine? 18. Where is iodine found? How prepared? 19. Give the principal characteristics of iodine physical and chemical. 20. What is sublimation? How is it different from distilla- tion? 21. Give uses of iodine and iodine compounds. CHAPTER X ACIDS AND BASES Outline- Oxides, Basic and Acidic Acids Bases .Nomenclature of Compounds (a) Acids (6) Bases Neutralization Salts (a) Normal or Neutral (ft) Acid (c) Basic (d) Nomenclature (e) Binary 1. Oxides. An oxide is a compound consisting of only two elements one of which is oxygen. Since oxygen combines with all the elements except fluorine and the argon group, we should expect there would be a very large number. Already we have met with several. Mer- curic oxide has been used in preparing oxygen ; man- ganese dioxide as a catalyst in making oxygen and in the preparation of chlorine, bromine and iodine. When- ever we have burned a metal in oxygen or the air, as for example iron or magnesium, we obtained an oxide. Likewise, when phosphorus and sulphur were burned in oxygen or in the air their oxides were produced. 2. Two Classes of Oxides. If oxides, such as will re- act with water, are put with water, some will be found to give a sour taste, and will turn litmus paper red, while others thus treated, have a soapy taste and turn reddened litmus paper blue. When Lavoisier gave the 136 ACIDS AND BASES 137 name, oxygen, meaning acid former to the gas, he did not recognize the fact that a chemical change takes place be- tween certain oxides and water, but considered the oxides themselves as acids. Such oxides as react with water to form acids are called acidic oxides, or anhydrides, and those that form hydroxides with the water are called basic oxides. Typical of the former class are those obtained when sulphur and phosphorus were burned in oxygen. With water they react thus, S0 2 + H 2 O ^H 2 SO 3 , P 2 Q 3 + H 2 -> 2HP0 3 . The most familiar basic oxide is lime. When treated with water vigorous chemical action results accompanied by great heat. The equation is CaO + H 2 -> Ca(HO) 2 Similar reactions are those of sodium and potassium ox- ides with water, Na 2 + H 2 - 2NaHO, ' K 2 + H 2 - 2KHO. A careful study of the various oxides shows that, gener- ally speaking, those of the metals react with water more or less rapidly to produce bases, while those of the non- metalic elements are anhydrides, or acid-forming oxides. 3. Acids, It has been said elsewhere that all acids contain hydrogen. Most of them also contain oxygen. If all were formed by the union of an oxide with water, all would necessarily contain oxygen. A few, such as the acids of the halogens, hydrofluoric and others, are solutions of certain compounds and are not formed by the interaction of some oxide with water. In all of them, however, the hydrogen forms the positive part of the compound, while the other element together with 138 APPLIED CHEMISTRY the oxygen when present, constitutes the negative part. It is the hydrogen in a peculiar condition which will be discussed later that causes all acids to turn litmus red. 4. Bases. Theoretically, at least, all bases may be formed by the interaction of a metallic oxide and water ; naturally therefore, all must contain a metal, hydro- gen and oxygen, since the action is an additive one. They are all called hydroxides, a term which indicates that they contain hydrogen and oxygen. There is no ex- ception to this. One base is known, however, which con- tains no metal, ammonium hydroxide, NH 4 HO, but the chemical group, NH 4 shows many of the characteristics of a metal. The soluble bases are called alkalies; they are potassium hydroxide, sodium hydroxide, ammonium hydroxide, and those of barium, strontium and calcium. The blue litmus test which they give is due to the hydroxyl group, HO, which they all contain, and which is the only thing common to all. 5. Nomenclature. Little need be said about how bases are named. They are all called hydroxides with the name of the metal prefixed, thus: Cu(HO) 2 is called cop- per hydroxide and A1(HO) 3 is aluminum hydroxide. In a preceding chapter the gas, HC1, has been spoken of as hydrogen chloride. This is for the reason that when per- fectly free from water it shows no acid properties. Like- wise, we should expect a compound with the formula H 2 S0 4 to be called hydrogen sulphate ; H 2 C0 3 , hydrogen carbonate; HNO 3 , hydrogen nitrate. They are all acids as the formulas indicate and this plan would be in accord- ance with what has been said in Chapter I. Attempts have been made to adopt such a nomenclature, but as sev- eral of the familiar acids were discovered and in common use before there was any system in the naming of com- ACIDS AND BASES 139 pounds, such efforts have met with failure. Accordingly, in the oxygen acids the electronegative element suggests the name. Thus, in the three given above, sulphur, car- bon and nitrogen have given the respective names. This is true, generally. However, there are many cases in which there are two or more acids formed from the same three elements. Thus sulphur has H 2 S0 4 Sulphuric, H 2 S0 8 Sulphurous, H 2 S0 2 Hyposulphurous, and chlorine forms HC10 4 Perchloric, HC10 3 Chloric, HC10 2 Chlorous, HC10 Hypochlorous. In such case the quantity of the oxygen determines the ending of the name. It is usually true that the most com- mon acid in any group has a name ending in ic; then, the one with a smaller amount of oxygen next to this is given the same name with the ending changed to ous. If there be others, the prefixes hypo, meaning under, and per, meaning beyond or above, are used. This is seen in the four chlorine acids given above. In the case of the acids containing no oxygen the prefix hydro is used in all cases, thus, H 2 F 2 Hydrofluoric, HC1 Hydrochloric, HBr Hydrobromic, HI Hydriodic H 2 S Hydrosulphuric. 6. Neutralization. If a base and an acid are brought together in suitable proportions, chemical ac- tion takes place, in which both are destroyed and new 140 APPLIED CHEMISTRY compounds are formed. The process is called neutraliza- tion, for the reason that when the two are exactly propor- tioned the compound resulting affects neither red nor blue litmus paper. The following equations illustrate a few cases, Ca(HO) 2 + H 2 S0 4 - CaS0 4 + 2H 2 0, KHO + HC1 -^KC1 + H 2 0, Ba(HO) 2 + 2HCl -> BaCl 2 + 2H 2 0, NaHO + HN0 3 - NaN0 3 + H 2 0, 2NaHO + H 2 C0 3 -> Na 2 C0 3 + 2H 2 0. It will be noticed in all these cases that one of the pro- ducts is water. The other is a compound which is not a base since it does not contain hydroxyl; it is not an acid since it has no positive hydrogen. It is a new compound. All such, produced by the union of a base and an acid, or by a similar process, are called salts. This name was given for the reason that a very large number of them resemble common salt and may be formed the same way. 7. Classes of Salts. All those shown in the equations just above are called neutral or normal salts, because the hydrogen has all been removed from the acid and the hydroxyl from the base, so that generally speaking they should affect neither red nor blue litmus. However, such proportions of the acid or base might be used as to leave some hydrogen from the acid or some hydroxyl from the base not thus neutralized. For example, H 2 S0 4 + NaHO -> NaHS0 4 + H 2 0, H 3 P0 4 + NaHO - NaH 2 P0 4 + H 2 0, H 8 P0 4 + 2NaHO - Na 2 HP0 4 + 2H 2 0, H 3 P0 4 + 3NaHO - Na 3 P0 4 + 3H 2 0. In three of the above equations some of the hydrogen re- mains in the salt obtained and should give the test. In fact, frequently in such salts the sour taste of the acid is ACIDS AND BASES 141 still very noticeable and blue litmus is quickly reddened. All such are called acid salts: they are very common. Obviously such an acid as hydrochloric could not form an acid salt. It must be observed further, that not all salts containing hydrogen are acid salts. Thus, NH 4 HO + HN0 3 -* NH 4 N0 3 + H 2 O, NaHO + HC 2 H 3 2 -* NaC 2 H 3 2 + H 2 0. Both the salts formed in these equations contain hydro- gen, yet both are neutral salts. In both cases all the positive hydrogen has been removed from the acid. In the first one, the hydrogen remaining in the salt was ob- tained from the base, and belongs to the group, NH 4 . In the second, only the hydrogen atom written by itself is positive: the other three are combined in the group C 2 H 3 2 which is a radical and the hydrogen is not free to act alone. On the other hand, there might be more hydroxyl groups present in the base used than the hydro- gen in the acid could remove in the formation of water. Thus, 2Cu(HO) 2 + H 2 C0 3 - 2H 2 + Cu 2 (HO) 2 CO 3 . Usually this is written CuC0 3 .Cu(HO) 2 . Such salts are not as common as the acid salts, but they do appear and are formed in various ways. They are called basic salts. The above is called basic copper carbonate. 8. Nomenclature of Salts. The common salts offer no difficulties to the student in their nomenclature. Thus, KBr Potassium bromide ZnCl 2 Zinc chloride K 2 S Potassium sulphide CuS0 4 Copper sulphate NaN0 3 Sodium nitrate CaC0 3 Calcium carbonate, 142 APPLIED CHEMISTRY KC10 3 Potassium chlorate, Na 3 P0 4 Sodium phosphate, KI0 3 Potassium iodate, KBr0 3 Potassium bromate. Compounds with two elements have names ending in ide; while the others end in ate unless formed from an acid whose ending is ous when the salt has a name end- ing in ite. The difficulty is with the compounds formed from the same three elements used in different propor- tions. Thus, Na 2 S0 4 Sodium sulphate, formed from H 2 S0 4 sulphuric acid, Na 2 S0 3 Sodium sulphite, formed from H 2 S0 3 sulphur- ous acid, Na 2 S0 2 Sodium hyposulphite, formed from H 2 S0 2 , hy- posulphurous acid, and KC10 4 Potassium perchlorate from HC1 4 perchloric acid, KC1O 3 Potassium chlorate from HC10 3 chloric acid, KC10 2 Potassium chlorite, from HC10 2 chlorous acid, KC1O Potassium hypochlorite, from HC10 hypochlo- rous acid. Only memorizing the formulas of the acids in the series, and the fact that oxygen acids ending in ic give salts end- ing in ate; and ending in ous, salts ending in ite can suf- fice. However, most of these are not of sufficient import- ance in warranting the beginner in making the attempt. Again, the acid salts offer some trouble, thus, K 2 S0 4 is potassium sulphate, KHS0 4 is acid potassium sulphate or potassium hydro- gen sulphate. As there can be only one acid potassium sulphate no confusion results from the use of either term. ACIDS AND BASES 143 But tribasic acids, like phosphoric, H 3 P0 4 , yield two acid salts, thus, K 3 P0 4 Potassium phosphate, K 2 HP0 4 Dipotassium phosphate, KII 2 P0 4 Monopotassium phosphate. As the last two are both acid salts they could not be read acid potassium phosphate, for either might be meant. It is customary, therefore, to follow the plan suggested, in which the amount of the base used is indicated by the prefix di or mono. The fact that one hydrogen remains from the acid in the salt is implied by the prefix di, for the reason that the acid originally contained three hydro- gen atoms and only two have been replaced. Likewise, mono implies that two atoms of hydrogen remain in the salt. 9. Binary Salts. Compounds of two elements are called binaries. Such are all salts made from the binary or no-oxygen acids. Their nomenclature offers no diffi- culty except in cases of two or more formed from the same two elements. When such is the case, the endings, ous and ic are used just as has been said in the acid end- ings. The one ending in ous always indicates the one full of or having the greater relative amount of the posi- tive part of the compound. Thus, Hg 2 Mercurous oxide, HgO Mercuric oxide, FeCl 2 Ferrous chloride, FeCl 3 Ferric Chloride, HgCl 2 Mercuric chloride, Hg 2 Cl 2 Mercurous chloride, Sn0 2 Stannic oxide, SnO Stannous oxide. Oftentimes prefixes are used which may lessen the dif- 144 APPLIED CHEMISTRY ficulty. Thus, manganese cfo'oxide indicates the amount of the oxygen ; again old forms, now obsolete, are some- times used which are often obscure. Thus, Fe 2 3 is sometimes called iron sesquioxide, instead of ferric oxide. The prefix means a ratio of two to three and was applied to such compounds as the one just given. Proto and sub, meaning the first and under are also used applied to the lowest of the compounds in a series. Exercises for Review 1. What is an oxide? Name two classes, define each and give examples. 2. What can you give for the composition of acids? What two tests do they give? 3. Give the composition of bases? What tests do they give? 4. What is an alkali? Name five. 5. How are bases named? Acids? 6. Give names of HC1O 3 , HIO 3 , HBr, HBr0 3 , H 2 SO 4 , H 3 PO 4 , Ba(HO),, Ca(HO) 2 NaHO. 7. What is meant by neutralization? Write an equation illus- trating. 8. Complete the following equations: HCl + Ba(HO) 2 , CaO + H 2 SO 4 -^ , ZnO + H,SO 4 -> , Zn + H 2 SO 4 ->. 9. How many salts were obtained in the above equations? Were any formed without the use of a base? Why was this? .10. What is a salt? Name three kinds. Define each and give examples. 11. Which of the following are acid salts: KNO 3 , KHSO 4 , CuSO 4 , AgNO 3 , K,HPO 4 , KH 2 PO 4 , K,PO 4 , CaH 2 (CO 3 ) 2 ? 12. Give names of all formulas in question 11. 13. What is a binary compound? Illustrate. 14. Give names of FeO, Fe,O 3J FeCl 3 , Fe01 2 , CuS, Cu 2 S, H 2 O, H 2 2 , Hg 2 0, HgO. CHAPTER XI NITROGEN AND COMPOUNDS Outline Nitrogen (a) Occurrence (fc) Preparation from the Air (c) Preparation from Chemicals (d) Characteristics Ammonia (a) Occurrence (b) Commercial Supply (c) Uses Oxides of Nitrogen Nitric Acid (tt) Preparation (b) Characteristics (c) Uses Explosives (a) 'Gunpowder (6) Nitroglycerine (c) Dynamite (e?) Nitrocellulose (e) Smokeless Powders (/) Picrates (0) T.N.T. Other Products (a) Collodion (b) Celluloid (c) Fiber Silk 1. Occurrence of Nitrogen. In another chapter it has been seen that nitrogen constitutes about four-fifths of the air. It is found in many compounds in nature, es- pecially the nitrates of sodium and potassium. The former occurs in large quantities in Chile, whence it is 145 146 APPLIED CHEMISTRY exported to all parts of the world. Nitrogen is an im- portant constituent of such food products as lean meat, eggs, beans and peas, and is found to some extent in grains, wood, coals and like substances. Some varieties of coal contain in the neighborhood of 2 per cent. 2. Preparation. By removing the other constituents of the air, nitrogen may be obtained comparatively pure except for the admixture of the argon. This is generally done by the use of phosphorus or by passing a stream of air over heated copper turnings. The proportion of nitrogen in the air may be shown somewhat approxi- Fig. 31. Method of determining approximately the proportion of nitrogen in the air. mately by apparatus shown in Fig. 31. A graduated cylinder is inverted qver a deflagrating spoon with handle bent as shown. Into the spoon is put a piece of yellow phosphorus the size of a small bean; then the whole is placed over a trough of water and the cylinder clamped so that the water level inside and out is at the zero mark. The phosphorus will slowly combine with the oxygen and at the end of two or three days the water level will have become stationary except for at- mospheric changes of pressure and temperature. The NITROGEN AND COMPOUNDS 147 volume of the residual nitrogen and argon may then be read off. From compounds nitrogen is generally pre- pared by gently heating a solution of ammonium chlo- ride and sodium nitrite. The following equations illus- trate the changes taking place, NH 4 Cl + NaN0 2 - NaCl + NH 4 N0 2 , NH 4 N0 2 - N 2 + 2H 2 0. 3. Characteristics of Nitrogen. Nitrogen is a color- less gas, slightly lighter than air, may be liquefied at -194 C. and solidified at -214 C. It is much less solu- ble in water than oxygen. Chemically, it is a very in- active element; it will not burn or combine with many of the elements directly. Passed over strongly heated magnesium or calcium it will form a nitride with them. It was by passing nitrogen over heated magnesium that argon was discovered, since it will not combine with magnesium. By means of a powerful electric dis- charge through a mixture of oxygen and nitrogen, chem- ical union takes place between these two elements with the formation of one or more oxides of nitrogen. Like- wise a mixture of hydrogen and nitrogen, three parts to one, by means of the electric spark is slowly changed into ammonia. The uses of nitrogen have been dis- cussed in the chapter on the atmosphere. 4. Occurrence of Ammonia. Because of the fact that certain waste products of the animal economy, as well as other nitrogenous bodies in their decomposition, pro- duce ammonia in appreciable quantities, it has long been familiar to scientists. For many years it was sold in solution under the name "spirits of hartshorn" be- cause of the fact that it was formerly obtained by the distillation of the horns of deer and cattle. 5. Commercial Supply. Some varieties of ordinary soft coal contain nitrogen in appreciable quantities, in 148 APPLIED CHEMISTRY the form of compounds. When such coals are heated the nitrogenous bodies are decomposed and the nitrogen comes off as ammonia, NH 3 , mixed with a great variety of other gases. On account of its high solubility it may be largely separated from the others by passing through towers or cylinders containing coke or something simi- lar, kept moist by dripping water. This very impure solution, called gas liquor is drawn off, lime is added and the mixture is boiled. The ammonia distils out and is passed into either hydrochloric or sulphuric acid, when the chloride or sulphate of ammonia is formed, NH 3 + HC1 -> NH 4 C1, 2NH 3 + H 2 S0 4 - (NH 4 ) 2 S0 4 . By treating a solution of either of these salts with lime and passing the gas into distilled water, pure ammonium hydroxide or aqua ammonia is obtained, (NH 4 ) 2 S0 4 + CaO-- CaS0 4 + 2NH 3 + H 2 0, NH 3 + H 2 -> NH 4 HO. 6. Characteristics of Ammonia. Ammonia is a color- less gas, with very pungent odor. It is exceedingly sol- uble in water so that about 1,200 liters will dissolve in 1 liter of water at C. Putting it into other words, one quart of ice water will absorb nearly six barrels of am- monia gas. It may be liquefied at -38.5 C. and solidified at -77 C. The strong ammonia water of commerce con- tains about 35 per cent of the gas with a specific gravity of 0.88. At ordinary temperatures, except under pres- sure, water will hold only about 28 per cent of ammonia, and at 100 the ammonia is entirely expelled. 7. Uses of Ammonia. Its principal use is in the liquid form for refrigeration purposes. From a container the liquid is allowed to pass through a needle valve into pipes surrounded by a solution of salt, of such strength NITROGEN AND COMPOUNDS 149 that its freezing point is much lower than that of pure water. A pump is constantly withdrawing the gasified ammonia, thus maintaining a partial vacuum, so that a rapid evaporation of the ammonia is secured. The rapidity of the evaporation causes a lowering of the temperature of the pipes and the surrounding brine, which is kept circulating by a special brine pump. For cold storage purposes this brine is forced through pipes to any place desired: in this way meats, fruits, but- Fig. 32. Manufacture of ice. ter, eggs, and all other perishable food products may be kept near the freezing point for long periods. For pro- tection against moths, furs and woolen clothing are often stored thus in the summer. Temperatures low enough to freeze meats may easily be secured; fishing vessels, gone on long trips, often return after months with their cargo of fish frozen solid. Markets, floral shops, and various other places employ these methods of preserving 150 APPLIED CHEMISTRY their goods; everyone has seen the brine pipes, heavily coated with frost, which furnilsh the cold for such pur- poses. For the manufacture of ice, galvanized iron boxes filled with pure water are lowered into the brine tank. In from sixty to seventy-two hours the water has become solid, whereupon the container with the ice is lifted from the brine ; a stream of warm water is run over it for a moment to loosen the ice, when it slips out and slides down into the storage room. Fig. 32 shows the main steps in the process. When the ammonia is withdrawn from the pipes it is again compressed and in summer time is cooled by streams of running water, whereby it again becomes a liquid. It is said that to make 3 pounds of ice requires about 1 pound of ammo- nia, but as the liquid is used over and over again the process is very cheap. In the household, ammonia is of- ten used in a dilute solution for softening water and for similar purposes. In commerce it finds extensive use in the manufacture of cooking soda and of sodium carbonate. The process will be described elsewhere in the text. 8. The Oxides. There are five oxides of nitrogen known. They are: Nitrous oxide, Nitrogen monoxide, N 2 0, Nitric oxide, Nitrogen dioxide, NO, sometimes written NA, Nitrous anhydride, Nitrogen trioxide, N 2 3 , Nitrogen peroxide, Nitrogen tetroxide, N0 2 , also writ- ten, N 2 4 , Nitric anhydride, Nitrogen pentoxide, N 2 5 . About the only facts of interest regarding the third and fifth in the series are that they are the anhydrides of acids, thus, N 2 3 + H 2 -> 2HN0 2 , Nitrous acid, N 2 5 + H 2 -* 2HN0 3 , Nitric acid. NITROGEN AND COMPOUNDS 151 Nitric oxide is mentioned for the reason that almost in- variably when nitric acid is added to a metal, it is pro- duced. However, it is never seen unless precautions are taken to collect it over water, because of the fact that as soon as exposed to the air it combines spontaneously with oxygen and forms the tetroxide. Thus, 3Cu + 8HN0 8 -> 2NO + 4H 2 + 3Cu(NO s ) 2 ; 2NO + 0, -> 2X0,. The peroxide is a heavy, reddish-brown gas resembling bromine vapor, with very irritating odor. It is very sol- uble in water with which it reacts, thus, 2N0 2 + H 2 -> HN0 3 + HN0 2 . 9. Nitrous Oxide. Nitrous oxide may be prepared by cautiously heating ammonium nitrate, thus, NH 4 N0 3 -^ N 2 + 2H 2 0. As it is somewhat soluble in cold water it must be col- lected over warm water. It is a colorless gas, with a very faint pleasant odor. In it various substances will burn when ignited almost as well as in oxygen and a spark on a pine splinter will burst into flame. It becomes a liquid at about -90 C. and a solid at -102 C. If in- haled it produces insensibility and mixed with oxygen it is frequently used as an anesthetic for minor surgical operations such as the extraction of teeth. It is some- times called laughing gas, because of its intoxicating ef- fects upon some individuals. 10. Nitric Acid. It is said that occasionally, after un- usually violent electrical storms accompanied by little rain, traces of nitric acid have been found in the water which has fallen. As nitric acid is an oxyacid it should be able to be formed in this manner. 11. Commercial Preparation. In the laboratory and commercially up to very recent times nitric acid has 152 APPLIED CHEMISTRY always been prepared by treating sodium nitrate with sulphuric acid, thus, NaN0 3 + H 2 S0 4 -> NaHS0 4 + HN0 3 . The laboratory form of apparatus is shown in the illus- tration. No corks, either rubber or otherwise, may be used as they are rapidly attacked by the fumes. From the fact that during the war, trade with Chile was largely interrupted so that adequate supplies of sodium nitrate could not be obtained, other methods had to be adopted. Consequently, preparation from the air dur- ing the last years of the war was carried on extensively. At points where electricity of high voltage could be ob- Fig. 33. Preparation of nitric acid. tained cheaply from water power, by electric discharge through a slowly moving current of air, certain oxides of nitrogen are obtained. These are passed into water with the formation of nitrous and nitric acid, H 2 + N 2 3 -> 2HN0 2 , 2N0 2 + H 2 - HN0 2 + HN0 3 , N 2 5 + H 2 -> 2HN0 3 . As nitrous acid readily takes up more oxygen and be- comes nitric, the ultimate product is nitric. It is prob- NITROGEN AND COMPOUNDS 153 able that this method in some form will eventually dis- place the older one of obtaining nitric acid from salt- peter. 12. Characteristics of Nitric Acid. When pure, ni- tric acid is a colorless liquid, but exposed to bright sun- light, or heated, decomposition takes place with the formation of sufficient peroxide to color the liquid more or less brown. It boils at 86 C. and solidifies at -47 C. The concentrated acid of commerce contains 68 per cent nitric acid, with a specific gravity of 1.42. Upon the hands or clothing it produces a yellowish-brown stain, which cannot be removed by ammonia as can those of hydrochloric acid. It is a strong oxidizing agent, for reasons shown by the equation, 2HN0 3 - H 2 + 2N0 2 + 0. Prom the fact that it thus readily yields free oxygen it reacts differently with metals from that of other acids thus far mentioned. Instead of giving up hydrogen as do hydrochloric and sulphuric, when put with a metal, as iron or zinc, it converts the metal into an oxide. Then, this oxide often dissolves in other portions of the acid present and forms a nitrate. For example, copper reacts with nitric acid forming copper nitrate, Cu(N0 3 ) 2 and nitric oxide and water but no hydrogen. The changes which may be presumed to take place may be represented thus, 3Cu + 2HNO., - 3CuO + H 2 + 2NO, 3CuO + 6HN0 3 -* 3Cu(N0 3 ) 2 + 3H 2 0. Adding the two equations together we have the result as obtained by the actual experiment, 3Cu + 8HN0 3 -> 3Cu(N0 3 ) 2 + 4H 2 + 2NO. 13. Uses, One of the most important uses of nitric acid is in the manufacture of explosives. Gunpowder, 154 APPLIED CHEMISTRY while not made from nitric acid, contains potassium or sodium nitrate, both of which are salts of nitric acid. The other constituents are sulphur and charcoal, but the nitrate forms 75 per cent of the whole. Being a mix- ture, an appreciable length of time is required for the combustion to proceed throughout the entire mass; hence, gunpowder is a low power explosive. Among those of high power, glyceryl nitrate, commonly called nitroglycerine, is one of the longest known. It is pre- pared by treating glycerine with fuming nitric acid. The reaction, C 3 H 5 (HO) 3 + 3HN0 3 - C 3 H 5 (.NO a ) 8 + 3H 2 0, shows that for every molecular weight of nitroglycerine produced there are three of water formed. In a short time this would so dilute the nitric acid that chemical action would cease, or become exceedingly slow. It be- comes necessary, therefore, to remove it. This is done by introducing continuously with the nitric acid fuming sulphuric, which as we have seen is a great absorbent of water. In this way the process becomes continuous. Ni- troglycerine is a heavy, oily liquid, and for this reason not convenient to handle or transport. Much of it is therefore made into dynamite or giant powder and other explosives. By mixing with it sawdust or kieselguhr, a silicious earth of tubular structure, both of which have high absorbtive powers for nitroglycerine, dynamite is prepared. It is commonly sold under the name of giant powder with percentages of nitroglycerine ranging from 25 to 75. It is used in the form of sticks or in coarse granules. Such explosives as these are fired by a detona- tor, such as mercuric fulminate, Hg(CNO) 2 , commonly called fulminating mercury. This compound is decom- posed by a sharp blow, giving a spark and heat sufficient NITROGEN AND COMPOUNDS 155 to begin the decomposition of the main explosive. All explosives contain combustible material and within them- selves oxygen sufficient or nearly so to burn completely. In two nitroglycerine molecules, 2C 3 H 5 (N0 3 ) 3 , there are 6 atoms of carbon and 10 of hydrogen. The hydrogen requires 5 atomic weights of oxygen for its combustion and the carbon 12. By looking at the formula it will be seen that the oxygen is a little more than sufficient, as the nitrogen is set free and passes off in this condition. It is apparent, therefore, that the liquid or solid, except- ing the inert material used, is entirely converted into gases of very great volume, which through the heat gen- erated are enormously expanded ; coming almost instan- taneously the pressures are tremendous and the results terrific. 14. Nitrocellulose. This is commonly called guncot- ton. Cellulose, of which filter paper or cotton is largely composed, has the formula, (C 6 H 10 O r ,) n - Into this mole- cule we may introduce nitrate groups as in the case of the glycerine and by the same method. Water is a by- product and must be removed as before. In this case any number of nitrate groups may be substituted, from three to six, the hexanitrate being much more explosive than the compounds with fewer nitrate groups. The following equation shows the reaction, 2C G H 1(1 5 + 6HN0 3 -> C 12 H 14 4 (N0 3 ) + 6H 2 0. The products of the explosion are the same as before. Guncotton is safe to handle if kept damp and in this condition it is uniformly transported on shipboard or elsewhere. Even when damp it may be exploded by the use of a detonator or electric spark with a small amount of dry to start the process. It is used in mining harbors or other places against attack as well as for other simi- 156 APPLIED CHEMISTRY lar purposes. The ternitrate, being much less explo- sive, when dissolved in a mixture of alcohol and ether, is sold under the name collodion. It is a viscous, quick- drying liquid, used in photography, and as new skin, so- called, in medicine. For the latter purpose a small per cent of Venice turpentine and castor oil is added to ren- der it more flexible and less liable to crack when dried upon the skin. If a solution of camphor in alcohol is used as a solvent for the guncotton, celluloid is obtained, the uses of which are familiar. Fiber silk is another product closely related. The guncotton, by one method, is dissolved as in making collodion: when it has reached Fig. 34. Some forms of smokeless powder. a thick, viscous stage it is forced through tiny openings like those in the spinneret of the spider or silk worm. These threads dry instantly upon coming into the air, are wound on bobbins and made into cloth as if real silk. The explosive nitrate groups must be removed and this is done by treatment with an alkali or with calcium sul- phide. The luster is not greatly different from that of real silk, but the fibers are more brittle and the wearing qualities as a result inferior. 15. Smokeless Powders. Two varieties are sold under the names, cordite and ~ballistite. The former is a mixture NITROGEN AND COMPOUNDS 157 of nitroglycerine and guncotton with a little vaseline added. Ballistite is a mixture of the same two ex- plosives to which is added a small amount of diphen- ylamine, which reduces the explosive character. Other varieties are simply the hexanitrate cellulose dissolved and molded into various shapes, some of which are shown in Fig. 34. 16. Picric Acid and T. N. T. Picric acid with the formula, C G H 2 (N0 2 ) 3 OH, is obtained from phenol, com- monly known as carbolic acid, C H 5 OII, in which have been substituted three nitro groups for three of the hy- drogen atoms. This will be seen by examining the two formulas. It is a very explosive substance and from it a very considerable number of high explosives have been prepared. An intimate mixture of red lead, Pb 3 4 , with about an equal volume of picric acid makes a powerful explosive which may be fired by heat alone. During the war a great deal was heard about the explosive, T.N.T. and its terrific power. Toluol is a compound closely re- lated to phenol, with the formula, C G H-CH 3 . The group, CH 3 , has taken the place of hydroxyl, HO, in the phenol. T.N.T. is trinitrotoluol, with the formula, C G H 2 (N0 2 ) 3 - CH 3 , which will be observed is toluol with three hydrogen atoms replaced by nitro groups. When exploded the pro- ducts are not essentially different from those already de- scribed elsewhere. Exercises for Review 1. State where nitrogen occurs in nature. What food products contain it? 2. How is nitrogen obtained from the air? How from chemicals? 3. Describe nitrogen. How was argon discovered? 4. How do you account for the presence of ammonia in the air? 5. What is spirits of hartshorn? 6. State how ammonia is prepared for commerce. Write the equations. 158 APPLIED CHEMISTRY 7. Describe ammonia. 8. Give important uses of ammonia. 9. Name the oxides of nitrogen and give formulas. 10. How is nitrous oxide prepared? Chief use? 11. How is nitric acid prepared? Equation. 12. Explain how nitric acid is made synthetically. What led to this? 13. Give chief properties of nitric acid. Why is it an oxidizing agent ? 14. Give important uses of nitric acid. 15. How is nitroglycerine made? Dynamite? When exploded, what forms? 16. What is nitrocellulose? Collodion? Celluloid? Fiber silk? 17. Name two smokeless powders. State how made. 18. What is T.N.TJ CHAPTER XII CARBON Outline Occurrence in Nature Allotropic Forms of Carbon Characteristics of Carbon Diamonds (a) Origin (fc) Uses Graphite, Compared with the Diamond Uses Coals, How Produced in Nature Varieties Petroleum (a) Origin (&) Kinds (c) Products obtained by Distillation Natural Gas Charcoal (a) Kinds (fe) Uses Lampblack Coke Gas Carbon Carbon Monoxide (a) Formation (&) Characteristics Carbon Dioxide (a) Preparation (fc) Characteristics (c) Uses Other Carbon Compounds 1. Occurrence of Carbon. The relative amount of carbon in nature is not large. It will be remembered that it is not among the eight most abundant elements 159 160 APPLIED CHEMISTRY which constitute almost the entire amount of the matter composing the earth. However, in the form of com- pounds it is familiar in a very great variety. In fact, so numerous are they that they constitute an entirely separate branch of chemistry, called organic, for the reason that years ago they were supposed to be produced by organized or life forces alone. The muscles of the body consist largely of proteins, composed mainly of car- bon, hydrogen, oxygen and nitrogen. The stems of plants and trunks of trees are largely cellulose, containing car- bon, hydrogen and oxygen. The mineral world furnishes the corals, limestone, marble, calcite, dog tooth spar, and many other carbon compounds. It is some form of car- bon that constitutes the fuel of the world ; carbon com- pounds in the form of starches, sugars and fats furnish heat and energy for the human body, while protein foods, similar compounds of carbon containing nitrogen, are nec- essary to rebuild the wasted muscles. Carbon thus be- comes a very interesting and a very important element. 2. Forms of Carbon. The only pure form of carbon is the diamond. Graphite, however, although in appear- ance it is entirely different, is nearly pure ; closely re- lated are anthracite coal and the artificial forms, coke, charcoal, gas carbon and lampblack. Other varieties of coal contain less free carbon and more bituminous compounds of carbon, hydrogen and nitrogen. Graphite may be considered a crystallized, allotropic form of the diamond, and lampblack an amorphous or uncrystallized allotrope. 3. Some General Characteristics. The physical prop- erties of carbon are so entirely different in the three allotropic forms that they must be considered sepa- /\ rately. The crystallized varieties will burn only at very high temperatures and in an atmosphere of oxygen; the CARBON 161 amorphous forms, especially the more impure, burn readily in the air without the addition of great heat. At high temperatures carbon combines with various elements to form carbides. It is a strong reducing agent also at red heat, that is it has the power of removing oxygen from its combination with metals. This equa- tion will illustrate, ZnO + C -* Zn + CO. 4. Proofs for Composition of Diamond. If heated in the absence of air to a dull-red temperature the diamond expands considerably, becomes lighter, and turns dark in color. If put into a tube, as shown in Fig. 35, with the air replaced by oxygen, and heated to bright red- ness, the diamond disappears and leaves only an at- x - - diamond Fig, 35. Burning of a diamond. mosphere of carbon dioxide. A piece of graphite treated in the same way gives like results. 5. Origin of Diamonds. Some believe that diamonds are of meteoric origin and not native to the earth, but of this there is little evidence. Undoubtedly they were formed under great pressure and a temperature suffi- ciently high to render the carbon more or less plas- tic, so that crystallization took place upon cooling. The great Kimberly mines of South Africa have been thought to be the crater of an extinct volcano, and some mines discovered in other places seem to be the same. The artificial diamonds made by Moissan some years ago point to the same theory as probably true. lie mixed fine iron filings and charcoal made from sugar together, 162 APPLIED CHEMISTRY put them into an electric furnace made from a block of lime, shown in Fig. 36, and by the electric arc melted the iron. It is well-known that molten iron will dissolve small amounts of carbon. So at this stage, Moissan plunged the mass into cold water, whereupon the iron solidified upon the outside, and by its contraction pro- duced great pressure upon the interior. Thus the dis- solved carbon crystallized under sufficient pressure to give it the density of the diamond, which is considerably above that of graphite. When cool the mass was broken up and the iron dissolved in nitric acid, leaving the diamonds unaffected. They possessed the hardness and Fig. 36. Moissan's electric furnace. other characteristics of native diamonds, but were dark in color due to the presence of some .uncrystallized par- ticles of carbon. The experiment was of scientific in- terest, because of the fact indicated that if a source of heat sufficient to melt carbon is ever found artificial dia- monds will become a possibility. 6. Uses of Diamonds. Until it was discovered that diamonds could be cut and polished by their own dust, they never came into use as ornaments. Imperfect and discolored diamonds are used in various ways, because of their hardness; for example, in the bearings of fine CARBON 163 watches, delicate balances, for cutting glass, polishing other stones, on tips of drills, and other similar ways. 7. Graphite. Next to the diamond graphite is the most nearly pure form of carbon. It occurs in nature, but not in sufficient quantities to meet the demands of commerce. Compared with the diamond it has a density of only 2.3, diamond being 3.5 ; it is a good conductor of electricity, the diamond poor; graphite occurs in six- sided plates, the diamond in regular octahedrons; graph- ite is a soft, greasy-feeling, black solid, the diamond the hardest mineral known, being 10 in the scale, and color- less. Since graphite is unaffected by the air it is used to give a finished coating to shot and the grains of both black and giant powder. It is an ingredient of most stove polishes, for the same reason. It is used in cru- cibles for melting very refractory substances and to give conductivity to wax plates in making electrotypes. Mixed with oil it is frequently used as a lubricant for bearings of heavy machinery. The most familiar of its many uses is in the so-called ''lead pencil." This con- sists of a mixture of graphite and clay, proportioned in such a way as to give varying degrees of hardness from very soft to very hard. The clay and graphite mixed are moistened with water, made into a soft plia- ble mass and by pressure forced through small openings in metal plates. When dried these "leads" are ready for insertion in the wooden coverings familiar to all. 8. Coals. Natural coals are believed to be the meta- morphosed remains of the forests of another day. Grow- ing at a time possibly when there was more carbon dioxide in the air than now, in a climate warm and moist, the forests undoubtedly surpassed in luxuriance and density anything known upon the earth at the present day. Swept down by some great catastrophe of nature 164 APPLIED CHEMISTRY these forests were buried sufficiently deep to protect them from decay through access of the air and at the same time to subject them to heat and pressure. Under vary- ing conditions of these two factors, a great variety of coals was formed, ranging from lignite, brown in color, soft, and often showing the original woody structure, to anthracite, hard, clean and lustrous. Intermediate between these are bituminous coals of great variety, rich in oily products, which burn with a yellow, smoky flame, and semianthracite with most of the bitumen ex- pelled, which burns with but little smoke and but slightly yellow flame. Cannel coal is very rich in oily matter, not suitable for furnaces, but excellent for grate fires on account of the freedom with which it burns and the abundant yellow flames it gives. Peat is a modern va- riety of coal consisting largely of roots only partly changed, with the admixture of considerable earthy mat- ter. 9. Petroleum. From 30 to 40 per cent of some coals is an oily product. This may be easily expelled by heat. Undoubtedly anthracite and semianthracite coals were produced by the greater heat to which they have been subjected, which resulted in the volatilization of the oily matter. When this took place ages ago, if the heat was not so great as to decompose the bitumen in the soft coal ; it was expelled and found its way into layers of sand or other places where it is obtained to- day as rock oil or petroleum. Occasionally it is under so great a pressure that when opened up it shoots far above the surface in a "gusher. ' ' More often it must be pumped from the well. Fig 37 shows a number of oil derricks with the customary pumps. 10. By-products of Petroleum. Petroleum is a black or brownish oil of varying density and viscosity, com- CARBON 165 posed of a great variety of carbon compounds. When dark in color it is because of particles of free carbon contained. There are two general classes of these oils: paraffin-base and asphalt -base. These names are given for the reason that in the former the thick, less volatile portion of the oil is paraffin, while in the latter it is as- phaltum. The paraffin oils are regarded as the more de- sirable, for the reason that they give on distillation a higher percentage of refined products. The asphalt oils are regarded by some as of animal origin, instead of veg- Fig. 37. Oil derricks, a familiar sight in oil-producing sections. etable, but produced in the same way. When petroleum is heated in retorts, the low boiling oils distill over first. The process is spoken of as fractional distillation, because of the fact that certain portions or fractions coming over at a given temperature are separated from other fractions obtained at a different temperature. Below 150 C. the fraction distilling out is called gasoline; 150 to 300, ker- osene; then successive fractions of heavy burning oil, par- affin oil, lubricating oil, vaseline, and paraffin. After the 166 APPLIED CHEMISTRY volatile products are all off from the paraffin oils a con- siderable quantity of petroleum coke remains, light and porous, which forms a very excellent fuel. These various fractions may be still further subdivided if desired. Gas- oline may, by taking the portions coming off at smaller intervals, be fractionated into petroleum ether, rhigoline, 'benzine, naphtha and gasoline. In fact, it is said that some of the refining companies make over one hundred products in distilling paraffin-base oils. At present the demand made by motor cars and other machines using gas engines is mostly for gasoline. Unfortunately, the percentage of this in crude oil is not high. Of late years the great problem has been to devise some way of convert- ing the heavier portions of the oils into the lighter. This is called " cracking" and various plans have been sug- gested, some of which are fairly successful. Thus a very considerable amount of gasoline, although not present originally in the oil, may be obtained from most good varieties of petroleum. 11. Natural Gas. If sawdust or powdered soft coal is put into a test tube and heated, not merely is there an oily substance, having the odor of tar, driven off, but gaseous products as well, which are combustible. So, in the earth when the buried forests were being subjected to heat, these gaseous products were expelled. Probably vast quantities escaped and were lost; other portions were caught beneath impervious layers of rock and furnish the natural gas of today. Some of it may be due to the chemical action of water upon carbides that were formed, but this will be considered at another time. 12. Charcoal. Formerly charcoal was made in the characteristic wasteful American way. Great piles of wood were covered w r ith earth and sod with several CARBON 1 67 openings at the bottom to allow the entrance of air. The wood was then set on fire and the lower portions in burning- expelled the volatile products from the upper portion, forming charcoal. At the present time, with our rapidly disappearing forests, the wood in suitable lengths is put into iron retorts and heated from beneath by means of coal. By this plan not only is a cheaper fuel used, but various valuable by-products, such as wood alcohol, acetone and acetic acid are saved, with a value probably as great as that of the charcoal itself. There is great demand also for boneblack, a charcoal made from bones. During the last year of the war there was ur- gent need also for all the nut charcoal obtainable. This is made from cocoanut shells, and all other nuts, even from the pits of the peach, apricot and other similar fruits. This variety of charcoal is by far the most ab- sorptive of any and was used in making gas masks. 13. Uses for Charcoal. Besides the special temporary use of nut charcoal just mentioned, it has some use at all times in research chemical laboratories in absorbing and separating small quantities of rare gases such as those found in the air belonging to the argon group. Boneblack of all the charcoals is probably the most ex- tensively used. Its chief value is in refining sugar. The syrup, brown in color, is passed through charcoal filters whereby the color is removed. A special form of bone- black, known as ivory ~black, made from the horns and tusks of animals, is used considerably as a black paint. Wood charcoal is sometimes used as a fuel in open fires; als:o in filters for cisterns in suburban and country homes. If so used it should be removed at intervals, and heated to redness to destroy any organic matter collected within the pores. By doing this it is again fit for service. For water in a cistern already contaminated a bag of char- 168 APPLIED CHEMISTRY coal suspended in the water for a few days is sometimes helpful. 14. Lamp Black. This is a finely divided form of car- bon obtained by burning in a limited supply of air some oil or gas containing carbon and hydrogen. The hydro- gen burns, but most of the carbon is deposited as a soot. It is the best black paint known when ground in oil. It is also the main ingredient of printers' ink. 15. Coke. Coke is made by heating coal in iron re- torts, as described for making charcoal, or in specially constructed ovens. When prepared in retorts the vola- tile products are saved and utilized as will be described later: from ovens the volatile gases are often allowed to escape thus involving great financial loss, as fully one-fourth the fuel value is contained in the volatile portions. Coke is a dark, or steel-gray, porous solid, which burns with intense heat. It is used in iron and other smelters because of its fuel and reducing values. 16. Gas Carbon. On the interior of retorts used in making coke a fine-grained form of carbon is slowly deposited. At intervals this is removed, molded into sticks and plates, and used in arc lights, battery plates and similar other electrical work. 17. Carbon Monoxide. Carbon forms two oxides, the monoxide, CO, and the dioxide, C0 2 . The latter is al- ways produced in the combustion of carbon when the supply of oxygen is plentiful ; when insufficient the for- mer is the result. Little thought is usually given to the lower oxide, but on account of its poisonous properties it demands a very careful study. It may find access to the home in various ways. Most modern houses are heated by hot-air furnaces, usually made of cast iron. Fig. 38 shows the construction. The air enters freely through the ash-pit and in the lower portions of the CARBON 169 firebox carbon dioxide is produced. As this passes up through the layers of red-hot carbon, where there is no air, carbon monoxide is formed, thus, CO, + C -> 2CO. Then as the monoxide flows into the space above the fire it again meets oxygen entering through the drafts and about, the door. Hence, it burns and forms carbon dioxide again, thus, 2CO + 0,, -> 2C(X. Fig. 38. Formation of carbon monoxide in a furnace. The flickering blue flames of burning carbon monoxide may plainly be seen in a furnace into which no coal has been thrown for some time. Likewise, most of the time it may be seen in base burners which use hard coal. Under conditions, as just described, no carbon monoxide remains and the products of combustion are carried out through the flue to the air. There are times, however, when this is not true. At night, in banking the fire so that it will keep well till morning, usually con- 170 APPLIED CHEMISTRY siderable coal is put into the firebox. Now, when the carbon monoxide formed in the interior of the fire reaches the open space, it has been cooled by the layer of coal on top to such an extent that it does not burn. It is then occluded or absorbed by the hot iron of the furnace as is hydrogen by platinum or palladium. Quickly it passes through to the air space about the fur- nace and is carried by the ascending currents into the living rooms above. The same thing occurs with base burners when the coal is shaken down in considerable quantities from the reservoir above. Gas heaters, when improperly regulated, as may be known by the flame being yellow, often produce carbon monoxide, and to- bacco smoke always contains a considerable quantity of the poisonous gas. In lighting with gas, if the man- tle is being blackened by a deposit of soot, carbon mon- oxide is invariably being formed; a cook stove, burning with a yellow flame, is not receiving sufficient air for perfect combustion, and in all probability is producing some carbon monoxide. The burned gases from a motor car or other similar gas engine, especially if the engine is running "idle," contain considerable quantities of carbon monoxide. 18. Characteristics of Carbon Monoxide. It is a col- orless gas, of nearly the same density as air. It has a peculiar, somewhat disagreeable but very faint odor. It may be liquefied at -190 C. It burns with a pale blue flame, producing carbon dioxide. From this fact, that it is able to take up more oxygen, it is a reducing agent and often serves thus in the separation of metals from their oxides. This is notably the case with iron, shown by the equation, Fe 2 3 + 3CO - 2Fe + 3C0 2 . CARBON 171 Carbon monoxide is very poisonous. When inhaled it forms a compound with the hemoglobin which prevents the carrying of oxygen to the tissues. Thus even in moderate amounts, it causes serious results, asphyxiation and death. Most fatalities reported from asphyxiation by the exhaust from motor cars in a closed garage are due to the poisonous effects of carbon monoxide. Years ago, in the warmer countries of Europe, open charcoal fires were the common method of heating the homes, and many cases of death, accidental or otherwise, are on record due to putting considerable charcoal on top of the fire and retiring. Knowing the poisonous charac- ter of the gas no one should sleep in a room warmed by a furnace with the register left open, and even thus, the windows should be raised. In the case of other sources of the gas, as already mentioned, steps should be taken at once to remove the cause. Following ex- plosions in coal mines, quantities of carbon monoxide exist, called by the miners " after damp" or "black damp." Usually it is the cause of the greater number of fatalities. 19. Carbon Dioxide. This gas has already been men- tioned as a constituent of the air. It results from the decomposition of organic matter, from combustion and from respiration. All of these sources furnish very con- siderable amounts, but the proportion of three or four parts per ten thousand of air remains practically con- stant, due to the action of plant life. 20. Preparation. Carbon dioxide in the laboratory or for commercial purposes is usually obtained by the re- action of some carbonate, as limestone or marble, with an acid, generally h} r drochloric. The equation is CaC0 3 + 2HCl -* C0 2 + H 2 + CaCl 2 . 172 APPLIED CHEMISTRY It may be collected either by downward displacement or over water; for commerce it is compressed in steel cylinders. 21. Characteristics. Carbon dioxide is a colorless, odorless gas with a density about once and a half that of the air. This may be shown by pouring the gas from a wide-mouthed liter bottle into the upper end of a trough in which are some short burning candles as shown in Pig. 39. The gas cannot be seen, but one candle after another is extinguished as the carbon di- oxide flows down. A liter bottle is usually sufficient to make the experiment three times in succession. The gas Fig. 39. Pouring carbon dioxide upon burning candles in a trough. is soluble in water, about volume for volume at ordi- nary temperatures. At -79 C. it may be liquefied; if the liquid be allowed to escape rapidly, the lowering of temperature caused by the evaporation converts a con- siderable amount of the liquid into a white solid, resem- bling snow, which vaporizes without melting, just as io- dine crystals do. Mixed with ether, solid carbon dioxide is often used as a freezing mixture ; with it mercury may be easily solidified and many other interesting ex- periments performed. Carbon dioxide will not burn and is so stable that with very few exceptions it cannot CARBON 173 be decomposed by a burning metal. Magnesium rib- bon, ignited and thrust into a bottle of the gas, con- tinues to burn with the formation of magnesium oxide and free carbon. Both products, being solids, may be seen upon the sides of the bottle. The equation illus- trating the action is 2Mg + C0 2 -> C + 2MgO. When dissolved in water some portion of the gas reacts chemically, forming a weak and unstable acid, thus, C0 2 + H 2 i=* H 2 C0 3 . Under pressure, carbon dioxide obeys Henry's law, that the amount of gas dissolved by a liquid is proportional to the pressure. That is, at five atmospheres' pressure a liter of water would dissolve five times as much gas as at one atmosphere. 22. Uses. The purpose of the small amount of carbon dioxide in the air has already been mentioned. Soda water, so called, is familiar to all. It is water charged with the gas under two or three atmospheres' pressure; as soon as this is relieved the gas begins to escape with the familiar effervescence. Most soft drinks in bottled form are thus carbonated. Carbon dioxide, liquefied in tiny steel capsules, called "sparklets," may be had from the supply houses. They are to be used for the carbon - ation of water either at home or in camp; for this a specially designed apparatus is necessary, which allows the escape of the gas into the bottle of water by piercing the cap with a stiff needle. Two sizes are made, suffi- cient for the carbonation of a pint or a quart of water. The chemical fire extinguisher, seen often in the hall- ways of public buildings, and larger sizes upon fire trucks, makes use of carbon dioxide. Fig. 40 gives a sectional view. Water is put into the vessel, made of 174 APPLIED CHEMISTRY copper or brass, up to the shoulder ; in this a pound or a pound and a half of baking soda is dissolved. In the tank near the top supported in a wire frame is a bottle partially filled with sulphuric acid. The stopper of this bottle fits very loosely so that it readily drops out if in- verted. For use the whole apparatus is turned upside down; the acid flows out into the soda solution, and reacting with the bicarbonate generates carbon dioxide Fig. 40. Babcock fire extinguisher. rapidly: the pressure thus obtained throws the water charged with gas upon the fire. The reaction is shown by the equation, NaHC0 3 + H 2 S0 4 -> C0 2 + H 2 + NaHS0 4 . The effect of carbon dioxide may be illustrated by a lit- tle experiment upon the lecture table. A small evap- CARBON 175 orating dish partly filled with gasoline is ignited; it may be instantly extinguished by pouring carbon di- oxide from a wide mouthed liter bottle. Usually a liter of gas is sufficient to repeat the experiment, twice. 23. The Test for Carbon Dioxide. On account of its density carbon dioxide often collects in old, long-unused wells and shafts. Although it is not poisonous, one may drown in it as quickly as in water. It is necessary, therefore, to test the air before entering places where it may have accumulated. This may be done by lower- ing a lantern : if it continues to burn well, the air is safe to breathe. In the laboratory carbon dioxide is tested by bubbling it into lime water, with which it forms a milky white precipitate. If the operation be long continued the precipitate redissolves, thus, Ca(HO) 2 + C0 2 -> CaC0 3 + H 2 0. The white precipitate is calcium carbonate CaC0 3 + H 2 + C0 2 - CaH 2 (C0 3 ) 2 . The product formed by the continued action is acid cal- cium carbonate which is soluble in water, hence the ex- planation of the disappearance of the precipitate. 24. Other Carbon Compounds. Carbon tetrachloride, as the name would indicate, has the formula, CC1 4 . It is a slightly yellow, oily liquid, heavier than water, not in- flammable, an excellent solvent for oils and grease, and at present not very expensive. It may, therefore, be used instead of gasoline with perfect safety for cleaning garments. "Carbona," a largely advertised cleaning compound, is mostly carbon tetrachloride. While it contains some benzine there is not sufficient quantity to render the mixture inflammable. "Pyrene," a well- known fire extinguisher, frequently carried by motor car owners in small cylinders, is largely carbon tetra- 176 APPLIED CHEMISTRY chloride. It is readily vaporized, and as the gas is heavy and not inflammable it extinguishes the fire by shutting off the oxygen supply. Silicon carbide, SiC, made by fusing in an electric furnace a mixture of sand and coke with common salt, is a crystalline solid of a dark gray or purple color. The reaction is shown thus, Si0 2 + 30 - 2CO + SiC. The compound is said to be even a shade harder than the diamond and is used extensively under the name, carborundum, as an abrasive. It is made into whetstones, wheels, and a great variety of other forms for cutting and polishing. Another very valuable carbide is made by fus- ing in an electric furnace a mixture of lime and coke, thus, CaO + 3C - CaC 2 + CO. It is known as calcium carbide and is used extensively as mentioned elsewhere for the preparation of acetylene. Exercises for Review 1. What can you say of the importance and total quantity of carbon in nature? Name some of the many forms in which it oc- curs, as compounds. 2. Classify the forms of carbon. 3. Give proof that the diamond is carbon. 4. Give an account of Moissan's experiment in making diamonds. 5. Give the chief characteristics and practical uses of the dia- mond. 6. Compare graphite with diamond. Give several important uses. 7. Classify the coals. What is their origin? Why so different? 8. What is the origin of petroleum? Name two kinds. Why so called? 9. What is fractional distillation? What use is -made of it? What is meant by "cracking" an oil? 10. Name some of the valuable products obtained from petro- leum. 11. What is the probable origin of natural gas? 12. How is charcoal made and what by-products are obtained? CARBON 177 !.'>. Name several varieties of charcoal and give uses of each. 14. What is ivory black? Lamp black? Uses of each? 1-"). How is coke prepared? Its chief uses? l(i. What is the source of gas carbon? What uses has it? 17. Name several ways in which carbon monoxide may find its way into the home. Give the details of one case. 15. Describe carbon monoxide. Its effects upon the blood. 1!>. Give the sources of carbon dioxide in the air. 20. How is carbon dioxide made for commerce? Equation. 21. Give chief properties of carbon dioxide. 22. Name some important uses for carbon dioxide. 2'>. Describe the chemical fire extinguisher. Give the chemical reaction. 24. Give two tests for carbon dioxide. 25. What valuable uses has carbon tctrachloride? Name some commercial forms in which it appears. 2(5. Name two carbides, state how made and uses of them. CHAPTER XIII VALENCE Outline- Meaning of Valence Degrees of Valence Valence of Eadicals Variation of Valence Saturated and Unsaturated Compounds Valence in Ternary Compounds 1. Meaning of Term. As used in chemistry the term valence means the power an atom has of combining with one atomic weight of hydrogen or its equivalent. Thus, in hydrogen chloride, one atomic weight of chlorine combines with one of hydrogen. As the hydrogen atom serves as the unit, chlorine must have a valence of one; likewise, do bromine, fluorine and iodine. Radicals, not being com- pounds but groups serving like atoms, as parts of a com- pound, likewise have valence. Thus, chloric acid, HC1O 3 , shows that the group -C10 3 has a valence of one ; so, also, ammonium, NH 4 -, in ammonium chloride; -N0 3 in ni- tric acid; -HO in sodium hydroxide and several others. As the metals are electropositive and do not form any familiar compounds with hydrogen, their valence must be determined by examining some such compound as their chlorides. Thus, common salt, NaCl, shows that so- dium has a valence of one ; KC1, that potassium has a val- ence of one. All atoms or groups having a valence of one are said to be univalent or are sometimes called monads. 2. Valence Greater than One. If we examine the for- mula for the water molecule, we see that oxygen has combined with two atoms of hydrogen, hence oxygen is 178 VALENCE 179 said to have a valence of two. Similarly, magnesium as seen in magnesium oxide, MgO, copper in copper oxide, CuO, calcium in lime, CaO, all have a valence of two and are called bivalent or diads. Aluminum and iron as shown by the formulas, A1G1 3 and FeCl 3 , are trivalent or triads; while carbon, as seen in carbon dioxide or car- bon tetrachloride, and silicon in silicon dioxide, Si0 2 , are tetrads or quadrivalent. Phosphorus as seen in the com- pounds P 2 5 and arsenic in As 2 5 are pentads. 3. Radicals of Valence Higher than One. In sul- phuric acid, H 2 S0 4 , sodium carbonate, Na 2 C0 3 , and po- tassium chromate, K 2 Cr0 4 , are seen radicals combining with two univalent atoms; hence, -SO 4 , -Cr0 4 and -C0 3 must be bivalent. Likewise, -P0 4 and -B0 3 , seen in the phosphoric and boric acids, H 3 P0 4 and IT 3 B0 3 , are tri- valent ; while -Si0 4 found in orthosilicic acid, II 4 Si0 4 , is quadrivalent. 4. Variation in Valence. Nitrogen and phosphorus are spoken of above as being quinquivalent. Their ox- ides indicate this. But they also form the hydrogen compounds, ammonia, NH 3 , and phosphine, PH 3 , in which a valence of three is indicated. In another chap- ter, copper is seen to form two compounds, as also mer- cury, CuO and Cu 2 0, HgCl 2 and Hg 2 Cl 2 , indicating sometimes a valence of one, sometimes of two. Many other cases might be cited, notably carbon in carbon monoxide and the dioxide, also marsh gas, CH 4 , and ethylene, C 2 H 4 . In the case of the carbon atom the va- lence is universally regarded as four and such compounds as ethylene, C 2 H 4 , acetylene, C 2 H 2 , and the monoxide are said to be unsaturated. By this is meant that the carbon atom in such compounds has not combined with all that it is capable of holding. There is abundant evidence that this is true. We have seen already in the case of the 180 APPLIED CHEMISTRY carbon monoxide that it readily combines with another atom of oxygen forming the dioxide; also, -that inhaled it completes the saturation by combining with the hemoglo- bin of the blood ; likewise, it readily unites with two atoms of chlorine to form phosgene, COC1 2 . Other very re- markable and interesting proofs for the carbon com- pounds are abundant. One of these is the passage of the gas through a solution of bromine in water or through a quantity of bromine beneath a layer of water to prevent its escape into the air. Marsh gas, CH 4 , if carbon has a valence of four, would be a saturated compound. When it is slowly bubbled through bromine, no matter how long continued, the escaping gas has all the properties of marsh gas and the bromine remains unchanged. On the other hand, if ethylene, C 2 H 4 , be used in the same way, the bubbles in passing through seem to become smaller as if they were being absorbed, and after an hour or two, the red color of the bromine has entirely disappeared, and in its place is a colorless, oily liquid, of pleasant odor, without the slightest resemblance to bromine. An analy- sis of this liquid shows that it contains two atomic weights of bromine per molecule, as would be represented by the formula, C 2 H 4 Br 2 . If written graphically, which shows the structure or arrangement, marsh gas is H H H I I I H-O-H, ethylene, -C-C-, and the bromine compound, H H H H H I I Br-C-C-Br. These formulas show that in marsh gas, the H H carbon atom has all its bonds saturated with hydrogen: that in ethylene there are two not so used and it is to VALENCE 181 these that the bromine lias been attached. A very large number of other similar experiments have been made, all of which seem to show the truth of the position taken. Likewise, in the case of most of the seeming variations in valence, one or more of the compounds are unsaturated ones. Thus nitrogen in ammonia, NH 3 , seems to have a valence of three ; but ammonia readily forms additional compounds, as when it is brought into contact with hydro- chloric acid, thus, NH 3 + HC1 - NH 4 C1. In the last compound the nitrogen atom is combined with five univalent atoms. Likewise, ammonia combines addi- tively with nitric acid, NH 3 + HN0 3 -> NH 4 N0 3 , in which compound the nitrogen atom is combined with four univalent atoms and one univalent group. Mercury in mercurous chloride, Hg 2 Cl 2 has apparently a valence of one, while in mercuric chloride, HgCL, it is evidently two. In all probability the mercury atom always has a valence of two, and any compounds not indicating such are unsat- urated. It is well known that mercurous salts readily take up more of an electronegative element or group and become mercuric compounds. Thus, many other cases might be considered but for the present these seem sufficient. 5. Ternary Compounds. Sometimes it becomes de- sirable to determine the valence of an element in a com- pound, knowing the formula. In binary compounds, if the valence of one of the elements is known, the other is evident at a glance. In ternary compounds this is not true. However, if it is known that the valence of the oxygen atoms is equivalent to the added valences of the other atoms present, it becomes easy. To illus- 182 APPLIED CHEMISTRY trate, sulphuric acid has the formula, H 2 S0 4 . It is de- sired to know the valence of the sulphur atom in the compound. There are four oxygen atoms whose total valence is 8; the two hydrogen atoms have a valence of 2 ; hence, 2 + S = 8, from whicli sulphur must be 6. In potassium dichromate, K 2 Cr 2 7 , the equation, 2 + 2Cr = 14, indicates the several valences, from which chro- mium is found to be six. Exercises for Review 1. Define and illustrate valence. 2. Name some elements with a valence of one; some radicals with the same valence. 3. Name some elements with valence of two; also some radicals. 4. What names are given to elements with valence of one, two, three, etc.? 5. What is meant by an unsaturated compound? Name two. 6. Give some experimental proof that ethylene is unsaturated, 7. What facts indicate that carbon monoxide is unsaturated? 8. What is a structural or graphic formula? What advantage has it? 9. Wliat evidence is there that ammonia is unsaturated? 10. Find the valence of chromium in K,CrO 4 ; nitrogen in HNO 3 ; manganese in KMnO 4 ; iron in Fe 2 O 3 ; phosphorus in P 2 O 5 ; phos- ph-orus in H 3 PO 4 . CHAPTER XIV ILLUMINATING AND FUEL GASES Outline- Natural Gas Acetylene Pintsch Gas Blau Gas Coal Gas Water Gas 1. Natural Gas. This has already been mentioned and its supposed origin. Another theory has been sug- gested by some which may possibly account for at least a part of the natural supply. Two carbides have been mentioned in the preceding chapter. One of them re- acts with water, as will be seen, to form a combustible gas. Another, aluminum carbide, does likewise. It is thought that at some time in the past this carbide has been formed in the earth and that water coming in contact with it reacts forming marsh gas, which is the main constituent of natural gas. The reaction with water is here shown, A1 4 C 3 + 12H 2 - 3CH 4 + 2Al 2 (HO) a . . 2. Acetylene. For commercial purposes, acetylene is always prepared by the reaction of water upon calcium carbide, thus, CaC 2 + 2H 2 -> C 2 H 2 + Ca(HO) 2 . Owing to the high percentage of carbon in the gas, it cannot be used in an ordinary burner, for the insuffi- cient amount of air supplied results in a very smoky flame. A special tip, shown in Fig. 41, is designed so 183 184 APPLIED CHEMISTRY as to draw in the air by two minute jets of gas directed toward each other. Burned thus, a brilliant white light is obtained with only about one-fifth the quantity of gas consumed as in other common burners. It is thus used extensively in motor cycles : for this purpose it is con- tained in the familiar "Prestolite" tank. At first, at- tempts w r ere made to use acetylene in liquefied form, but it was found under such pressures to be readily explosive and many accidents occurred. It is very solu- ble in acetone, a liquid of pleasing odor obtained in the destructive distillation of wood in making charcoal. The prestolite tank applies this principle : large quan- Fig. 41. Acetylene burner. tities of acetylene under several atmospheres pressure are dissolved in the acetone in the tank and in this form it is perfectly safe. On use the gas escapes, but the acetone remains and may be recharged. For cooking purposes special plans must be had for furnishing in- creased quantities of air, otherwise the cooking vessels become heavily coated with soot. At the present time acetylene is used extensively in country churches and suburban homes both for lighting and cooking. There are several types of generators, but the most satisfac- tory is one in which the carbide in coarse grains drops slowly into a considerable quantity of water. The gas ILLUMINATING AND FUEL GASKS 185 is piped throughout the house in the usual way and burned in tips like the one described above. The most valuable use of acetylene at the present time is for welding and similar work where great heat is required. The gas is used in a torch such as was described for oxy- hydrogen work, and when properly adjusted burns with a pale blue, intensely hot flame. Even when air in- stead of oxygen is used, furnished with a foot bellows, iron wire, such as is used in baling hay, may be burned rapidly in the air with a beautiful and dazzling shower of sparks. In welding, the broken object is heated, the crack made somewhat larger; then a rod of steel is melted in the oxyacetylene flame and the molten steel allowed to flow down into the crack. Welding thus properly done is said to make the object as strong as at the beginning. 3. Pintsch Gas. This gas received its name from an Englishman who first prepared it for the purpose of lighting the stage coaches of that day. At the present time it is used practically nowhere outside railway coaches, where it is seen in clusters, usually enclosed in glass globes at the ceiling. It is prepared from some oil, often naphtha, by heating sufficiently high to decom- pose it into gases which will not liquefy again upon cooling. As it is thus made from a refined oil, the re- sulting gas needs little purification, other than the re- moval of a little tar and water. It is carried, heavily com- pressed, in cylinders under the railway coaches. Unlike most similar gases, the compression does not greatly re- duce its illuminating powers. 4. Blau Gas. At the present time a similar gas, called Blau gas, is being manufactured from a less refined oil than the pintsch uses. It is purified and compressed, whereupon some of the constituents become liquid. 186 APPLIED CHEMISTRY These are removed and the gas is then stored in steel cylinders under high pressure. In the oxyhydrogen blowpipe it gives intense heat ; it is also used in subur- ban homes for cooking and lighting purposes as other gases are in the city. For such use two tanks of the compressed gas are placed in a container outside the building and attached to the piping of the house. When one is exhausted it is sent to the factory for refilling and the other put in service. 5. Coal Gas. Most cities in sections where bitumi- nous coals are to be had, use large quantities of coal gas. It is prepared by heating the soft coal in iron retorts as already mentioned for making coke. The resulting gaseous mixture, very impure, must be puri- fied before being suitable for use. By cooling, first the tar is removed and flows into a tank or well fitted to re- ceive it. The gas next passes through, usually, two "towers," filled with lumps of coke or something equiv- alent, kept moist by water trickling over it. Here the ammonia is removed. The gas next passes through three or four purifiers, containing lime or ferric oxide, which remove other compounds like sulphur dioxide, hydrogen sulphide and carbon dioxide, all acidic in character and either not combustible or very undesir- able in an illuminating gas. Finally, the gas is metered and passed into a storage tank from which it is piped to all parts of the city. Remembering that coke and gas carbon are both obtained in the retorts it will be seen that there are four by-products of the manufacture of coal gas. Besides the two just named, are the tar and ammonia. Tar is a black, viscous, ill-smelling liquid consisting of a mixture of a great variety of compounds and black because of the presence of some free carbon. From it are made several colorless liquids, such as ILLUMINATING AND FUEL GASES 187 aniline and toluol. These form the basis of an indefi- nite number of other compounds of the very greatest value: photographic developers, such as hydroquinon; many medicines, like aspirin; all the great variety of beautiful aniline dyes; phenol or carbolic acid and its many derivatives; picric acid and the explosives from it; the explosives from toluol, and hundreds of others. A ton of coal will make about ten thousand cubic feet of gas containing one-fourth to one-third the fuel value of the original coal. The gas consists of hydro- gen and marsh gas, over 40 per cent of each, with carbon monoxide, and ethylene as the greater part of the bal- ance. Small proportions of some higher hydrocarbons are usually present. 6. Water Gas. This receives its name from the fact that steam is used in its preparation. Often both coal and water gas are manufactured simultaneously in the same building. The coke obtained as a by-product in the coal gas department is withdrawn red-hot from the retorts into small steel cars in which it is carried quickly to another part of the building. Here it is dumped through a trap door into a vertical, cylindrical retort on the floor below. A blast of air is turned on the hot coke to raise its temperature, and then live steam is passed through it, when the following reaction takes place, H 2 + C -> H 2 + CO. At the end of about three minutes the temperature is too low to effect the decomposition of the steam, which then, automatically, is cut off and the air again turned on. Thus, in three minute periods, mechanically, all day the steam and air are turned on alternately, with results as shown by the equation. Both the constitu- ents thus obtained are combustible, but a gas richer in 188 APPLIED CHEMISTRY carbon is more desirable. Hence, it is passed through another retort containing a lattice work of fire brick heated to redness by a gaseous fuel. Into this cham- ber is sprayed an oil obtained from petroleum, which is decomposed as was described in making pintsch gas. These products are mixed with the two already obtained from the steam and coke, such that the final result is not essentially different from coal gas. The percentage of carbon monoxide is higher, hence the gas is more poisonous. In factories making both coal and water gas the large storage tank receives both usually in something like the proportion of 3 of water to two of coal gas. In other cities where cheap supplies of soft coal are not available, as in California, a gas is prepared from crude petroleum, not essentially different from the coal gas, and of excellent quality. Exercises for Review 1. Give a chemical theory for the formation of natural gas. Of what does natural gas consist? 2. How is acetylene made? Write the equation. Describe the tip necessary for burning it successfully. 3. Describe the prestolite system of lighting. 4. Why not use liquefied acetylene for lighting? 5. Give some important uses of acetylene. 6. How is pintsch gas made? Where is it used? 7. How is blau gas made? For what used? 8. Describe the process of making coal gas. Name the impuri- ties removed in its manufacture ; also the by-products obtained. 9. How is the ammonia recovered and purified? 10. What are some of the products obtained from tar? 11. What are gas carbon and coke used for? 12. Describe the preparation of water gas. Why is it so called? 13. How is the composition of water gas different from that of coal gas? 14. Write the equation showing the effect of the hot coke on the steam. 15. What is meant by "live" steam? CHAPTER XV FLAME Outline Definition of Flame Chemical Reaction in a Flame Structure of Flames The Bunsen Burner Applications in the Home The Oxyhydrogen Blowpipe The Blast Lamp 1. What is a Flame? Briefly stated, a flame is usu- ally said to be a burning gas. It is the phenomenon which accompanies the rapid union of two gases, produc- ing heat and usually light also. At first thought this might not seem to be always true. In the case of a burning gas jet there could be no question about it. The gas, being heated to the kindling temperature, begins to combine with the oxygen of the air; this chemical union is productive of heat and a temperature above that nec- essary for the kindling of the gas is constantly maintained. With a candle it is equally true. The wick is filled with wax. When a burning match is applied to it, first the wax is melted, then it begins to vaporize and the gas thus formed is ignited. Thereafter, the heat of the chemical union is such as to vaporize continuously the paraffin with a steady flow of gas. By quickly blowing out the flame of the candle, the paraffin vapors may be seen floating upward and may easily be ignited with- out touching the wick. When this is done the flame rapidly passes down the stream of gas to the wick. Ex- actly the same thing is true of the kerosene or alcohol lamp. Likewise, when wood is burning the heat of 189 190 APPLIED CHEMISTRY combustion decomposes the cellulose and other com- pounds present, converting much of them into gaseous form. These escape in tiny streams here and there and combining with the oxygen produce flames. It is the same with soft coal. The oil contained, by means of the kindling used, is first partially volatilized; later, by the heat of combustion not only does volatilization continue but also decomposition of the vapors into hydrocarbon gases, all of which are combustible. Charcoal, coke and anthracite coal contain little or no volatile matter; hence, they burn without flame. It is true that often light blue lambent flames may be seen above the surface of such fires, but these are due to the carbon monoxide, produced in the interior of the burning mass through the interaction of the carbon dioxide and red-hot carbon. This has been explained elsewhere. It must be con- cluded, therefore, that whenever there is flame, there is a gas present. 2. The Chemical Action. Combustion is sometimes spoken of as the rapid union of oxygen and some other substance. This is a narrow view. A flame may accom- pany the union of a variety of substances, and in each particular case, one of the substances is as essential as the other. For example, an ignited jet of hydrogen, thrust into a bottle of chlorine, continues to burn as vig- orously as in the air. Likewise, if an inverted bottle of hydrogen be ignited at the mouth and a jet of chlorine be introduced through the flame into the bottle, the chlorine will be seen to burn. In this case combustion is the rapid union of the hydrogen and chlorine, and it makes little difference which is introduced into the other; one is just as essential as the other. In the same way a stream of air, or oxygen, passed through the flame into the bottle of hydrogen continues to burn just as well as the jet of FLAME 191 hydrogen does in the air. This is illustrated by a com- mon, simple experiment. The smaller tube in Fig. 42, marked ' ' gas, ' ' is attached to the gas supply. The larger, short tube is open to the air. When the gas has been flow- ing sufficiently long to expel all the air a small flame brought to the upper end of the "air" tube will apparently ignite the air current and it will continue to burn. Here the combustion is the union of the gas and oxygen and the flame occurs at the place where this union is going on. Fig. 42. "Burning" air. 3. Structure of a Flame. The ordinary flame of which that given by a candle is typical consists of three portions, or concentric cones. A few simple experiments readily enable one to determine the condition of each of these portions. A pine splint held across the flame of a large candle, or more conveniently, a small Bunsen burner flame, will be scorched in two places, at the points where it intersects with the circumference of the flame. If a sheet of paper be pressed down upon a small Bunsen flame, or better, if the burner be inverted and held close to the paper lying on the table, it will be scorched in a circle, agreeing with the circumfer- ence of the flame. These would indicate that the burn- 192 APPLIED CHEMISTRY ing- portion of the flame is at the outer edge. To show this more strongly, a match may be thrust through the outer zone and held until the wood begins to burn at the circumference of the flame without the more com- bustible material of the head of the match being ignited at all. This may be varied by turning off the gas and suspending a match in the burner by means of a pin thrust through the wood a half inch or so from the head. If now the gas is turned on and ignited at some dis- tance above the tip, it will burn as usual while the match remains unaffected at the center. These experiments I Fig. 43. Match suspended within burning gas jet. show that there is no heat in this innermost cone; lastly, a small tube inserted into this section and held at an an- gle, may be lit at the upper end. This shows that this portion contains unburned gas. The same experiments may be carried out with a large candle. (See Fig. 44.) Inspection of a Bunsen flame Avith the openings near the bottom closed or of the candle flame shows that the middle cone is yellow. Around this is an outer blue cone, very thin at the base, much larger in the upper part. A cold dish held against the yellow portion is FLAME 193 soon covered with soot which we know is a deposit of carbon. It is the myriads of carbon particles floating in this zone and heated to incandescence, that is to a temperature at which they will glow, which give the light. It may be concluded then that this middle cone consists of gas undergoing combustion but not com- pleted and contains much incandescent carbon. The outer cone gives little or no light. In the daytime it looks much smaller than it really is. A pine splint ap- Fig. 44. Burning gas drawn from center of candle flame. proached slowly from above or from the side ignites long before it touches any visible flame. This is evi- dently the hot portion and is the zone of complete or perfect combustion: In it the carbon is burned to carbon dioxide and the hydrogen to vapor. Obviously, if heat is, desired as in softening a glass rod, it will be secured in the upper, nearly invisible, blue portion of the flame. If reducing action is wanted, since red-hot carbon has 194 APPLIED CHEMISTRY such power, it will be had in the yellow cone. A penny held in the tip of the flame becomes black from a coating of copper oxide ; held in the yellow portion it becomes bright again because the hot carbon removes the oxygen from the film of oxide. 4. The Bunsen Burner. There are several types of this burner found in laboratories. In all of them the gas enters through a very small opening somewhere near the bottom, and all have some arrangement for introducing considerable air somewhere near where the gas enters, so that the two become mixed before leav- ing the tube. The result is that if properly adjusted there are only two portions to such a flame. The lu- minous part has disappeared, while the outer cone is much enlarged. There is thus obtained a hotter flame than is possible otherwise. By opening and closing the air vents at the bottom it will be seen that the flame is much shorter when the air is on than otherwise; hence all the heat of the combustion is concentrated within a shorter portion than when the air is not entering. Some- times, in such burners, if the gas pressure is low, the burner "strikes back" and continues to burn near the base. In this case the rate of combustion or speed of propagation of the flame has been more rapid than the flow of gas, and the flame is passed down the pipe to the point of exit of the gas. Owing to the lack of air needed for perfect combustion, acetylene and other offensive gases are often produced in such cases and the difficulty should be speedily remedied. Usually by turn- ing off the gas and lessening the air supply the burner may be relit successfully. 5. Applications in the Home. Every gas stove used for cooking and, as a rule, for heating as well, employs the principle of the Bunsen burner. There is some de- FLAME 195 vice for admitting a supply of air and mixing it with the gas before it reaches the burner where it is to be consumed. If properly adjusted, the flame will be blue and relatively hot. A yellow flame indicates that not sufficient air is being provided ; hence results will be slow and unsatisfactory. Sometimes the burners on a stove, especially the oven, may strike back and burn at the point of admixture of the gas and air. This is espe- cially apt to occur after the oven has been burning for some time and the pipes have become hot, The cause is the same as in the case of the Bunsen burner. The rem- edy is to turn off the gas, decrease the air supply and relight. With poor gas pressure there is sometimes no remedy except to allow the pipes to cool. 6. The Oxyhydrogen Blowpipe. This burner has been described elsewhere, under hydrogen. If the flame ob- tained by this torch or with acetylene be examined, it will be seen to consist of only two portions a very small inner cone and a nearly invisible outer one. The gases used are so proportioned and so thoroughly mixed before they issue from the tip that the combustion is perfect throughout nearly the entire mass. Further, it will be seen that the flame is relatively a small one. The result is a flame of very great intensity. 7. The Blast Lamp. The construction of the blast lamp is not essentially different from that of the oxy- hydrogen torch. The inner pipe is attached either to a foot bellows or to a tank of compressed air, while the outer connects with the gas supply. Before the air is turned on, the gas burns with a- large, flickering, yellow flame, with low temperature. With the air, the flame decreases greatly in size, loses its yellow portion, be- comes blue and almost invisible, and has a high tern- 196 APPLIED CHEMISTRY perature. The admixture of the air in the tube enables the entire amount of the gas to be consumed within a small space, so that the heat is all concentrated therein. Exercises for Eeview 1. What is a flame? Show that what you say is true of the can- dle and of a kerosene lamp. 2. Give some experimental proof that a stream of gas is being formed in the candle wick. 3. What is the explanation of the flame above a hard coal fire? 4. Explain combustion in a broad sense. Show how air may be "burned." 5. Of how many portions does an ordinary flame consist? 6. Give some simple experiments to show something as to the character of the innermost part of a flame. 7. What does the middle cone contain? What proof can you give? 8. What is the character of the outer cone? How do you think it would appear different at night from in the daytime? 9. What is meant by incandescence? 10. Describe the Bunsen burner as found on your desk. 11. What effect does the construction of the Bunsen burner have on the structure and character of the flame? 12. Why is the flame shorter when the air is on -at the bottom? 13. Explain why a burner strikes back and give the remedy. 14. What applications of the Bunsen burner are found in most city homes? 15. What is the trouble when a gas flame on a cook stove burns yellow? How can it be remedied? 16. Explain why the oxyhydrogen flame is so intense in heat. 17. Describe the construction of the blast lamp. Why is the flame so large before the air is turned on? CHAPTER XVI METHODS OF LIGHTING Outline Primitive Methods of Lighting Kerosene Lamps Gas Illumination Incandescent Electric Lights The Wclsbach System Tungsten Electric Lamps The Lime Light Arc Lights 1. Primitive Methods of Lighting. When man first began to use artificial light is not known. Probably in some localities, at first it was the pine knot full of resin ; in others, a bowl of oil into which was dipped a twisted rag or something Avhich served as a wick. Miners, even now, often carry upon their caps a lamp containing a thick oil with a wick enclosed in a tube. Such lights are necessarily poor, more or less unsteady, and produc- tive of smoke. The candle was an improvement upon the old, open oil lamp. At first, tallow was used and later the oil of the sperm whale. Sometimes, even now, for hard candles, tallow is treated with an acid to pre- cipitate the stearic acid from the stearin and this is melted and molded into shape. Those most commonly used, however, are made of paraffin, obtained from pe- troleum. The light obtained is due, as explained in a preceding chapter, to the presence of the incandescent carbon particles in the flame. 2. The Kerosene Lamp. A decided advancement was made in lighting when the kerosene lamp was invented. The principle is not different from that of the candle. 197 198 APPLIED CHEMISTRY By capillarity the oil is drawn up through the wick and burned at the top. The chimney is the source of the increased light. By means of the perforations in the support for the chimney at the bottom a draft is se- cured so that the combustion is more rapid, the carbon particles in the incandescent zone reach a higher tem- perature and, therefore, give more light. Moreover, the flame is a steady one and produces less smoke. In ear- lier years there was frequently more or less gasoline Fig. 45. Determination of flash point of an oil. mixed with the kerosene, for at that time there was no demand for the lighter oil. As a result, explosions were not uncommon. This led to legislation requiring all merchantable kerosene to be inspected and possess a certain " flash point." This means the temperature at which the vapor arising from it will ignite. It may be shown fairly well by a very simple method, as seen in Fig. 45. A thermometer is supported on a stand at such a height as to dip within some gasoline or kerosene in a beaker. A piece of cardboard with an opening METHODS OF LIGHTING 199 cut on one side covers the beaker. The oil is then slowly and cautiously heated with a small flame. At intervals, a small wax taper, lighted, is brought to the opening in the cardboard. The temperature at which the vapor arising catches fire or " flashes" through the space above the oil is called the flash point. At the present time, since gasoline is the valuable product obtained from pe- troleum, kerosene is always free from the more volatile oil and explosions are almost unknown. 3. Gas Illumination. The next step in artificial light- ing was by means of gas, at first made from soft coal. For its combustion a burner was used closed at the top by a little cap made of fire clay or some similar non- combustible material, with a narrow slit for the escape of the gas. When ignited a thin, fan-shaped flame was the result. The light produced was the result of the incandescent carbon particles as in other cases already studied. 4. Electric Lights. The next improvement in light- ing systems was that of the incandescent electric bulb. It had long been known that a wire of high resistance carrying an electric current would become luminous. Attempts were made with platinum and other metals in electric lamps, but none of them gave sufficient light to be of value. Finally, after years of experimenting with all sorts of vegetable fibers, one from a special bamboo was obtained sufficiently strong to be used in a lamp. Later, these carbon filaments were obtained by carbon- izing threads made from a viscous solution of cellulose, much as fiber silk is now. The air was pumped out of the bulb, so as to prevent the rapid disintegration or combustion of the carbon thread. In such lamps, it will be seen that the light, as in all other cases already mentioned, is obtained by incandescent carbon. Natu- 200 APPLIED CHEMISTRY rally, they were called incandescent lights. The con- venience of turning on or off such lamps was great, and the candle power was higher, but the quality of the light otherwise was not essentially different from the gas-light. 5. The Welsbach Mantle. Two things led to the in- vention of the gas mantle. One was the discovery of natural gas, and the desire to use it for illuminating purposes. As it is low in carbon content, when burned in the old-fashioned slit-top burner, it gives very little light, not sufficient to be of value. The other reason was the greater convenience offered by electricity with the resulting strong competition, threatening to dis- place gas entirely. At such a time the mantle was in- vented by a man named Welsbach. It is made by spray- ing upon a little hood made from long fiber mercerized cotton, a mixture of thorium and cerium nitrates, 99 parts to 1. The burner upon which it is used is almost identically that invented by Bunsen. For use the, man- tle is hung over the burner and ignited. The cotton burns off, while the two nitrates by the heat are con- verted into oxides. Now, when the gas is ignited, the burner gives a short, hot flame which heats the two ox- ides into incandescence just as the oxyhydrogen flame does the stick of lime, which is calcium oxide. At the temperature obtained, the oxides give a beautiful, white light, six or eight times as strong as the old style tip. Natural gas can be used in this burner as well as arti- ficial. The quality of the light is greatly superior to that of the incandescent carbon electric, and not essen- tially different in candle power. 6. Acetylene. This gas has been mentioned elsewhere although it is used more for illumination than for cook- ing purposes. It must be burned in a special tip and cannot be used with the Welsbach mantle. It gives a METHODS OF LIGHTING 201 beautiful white light, but as the gas must be manufac- tured in the place where it is be used, it is not adapted to the wants of a city. Its field must always be the suburban or country home. 7. The Tungsten Lamp. The quality of the light af- forded by the Welsbach gas system stimulated the elec- tric companies to discover some filament which would give a white light comparable with gas. Several sub- stances other than carbon have been tried, but at the present time tungsten is regarded as the most desira- ble. When first adopted such lamps were very fragile, owing to the brittleness of the filament, and gained slowly in favor. They have been perfected now, how- ever, so that they are practically as durable as the car- bon filaments. They give a brilliant white light, and consume much less current for the saine candle power than the old style lamp. An improved form of the tungsten lamp now has the bulb filled with nitrogen instead of the usual vacuum. They are more durable and at the same time give a better light, Without acci- dent a tungsten lamp should give about 1,000 hours of actual service. 8. The Calcium or Lime Light. This has been men- tioned elsewhere as the Drummond light. The principle is not different from that seen in all other cases and is due to the incandescence of a solid. In this case it is the stick of lime, calcium oxide, upon which an intensely hot flame is allowed to strike. Its brilliance rivals that of the electric arc. Its use has been mentioned else- where. 9. Arc Lights. In arc lights two sticks of gas carbon are used which in service are separated from each other by a short distance. An electric current of high voltage, in spanning the gap, does so not in a straight line, but curved like the arc of a circle. The positive carbon 202 APPLIED CHEMISTRY is worn away and the particles, white hot, are carried across the gap and in part deposited upon the negative carbon. It is these white-hot particles which produce the dazzling light. At first the two carbons were used in large globes entirely exposed to the air. As a result they were burned away rapidly, so that a great deal of time was needed in replacing them, in addition to the ex- pense of the carbons themselves. At the present time they are enclosed in small globes. . These are not air- tight, but through combustion they are soon filled with carbon dioxide so that the subsequent disintegration is slow. Arc lights are used mainly for lighting of streets, and spot lights for stage effects. Exercises for Review 1. Name some of the different kinds of candles made. How is light produced in a candle? 2. Explain why the kerosene lamp gives better light than the candle. Why were they explosive at first? 3. What is meant by the flash point of an oil? How may it be obtained approximately? 4. Describe the tip used in the original gas lamp. What pro- duces the light in such a flame? 5. Describe the incandescent carbon lamp. How are the car- bon filaments made now? How originally obtained? 6. What objection to the carbon electric? What advantage has it over 'gas? 7. Describe the Welsbach mantle and burner. What are its ad- vantages? 8. What kind of a tip is used with acetylene? Where are acety- lene lights seen frequently? To what kind of lighting is it essen- tially suited? 9. How is the tungsten lamp different from the old carbon? What objection was there to them at first? 10. In working about a tungsten lamp, as in dusting or cleaning, what can be done to render them still less liable to break? 11. How is the calcium light obtained? For what is it used? 12. Why are arc lights so named? Where used? What produces the light? Where are the carbons obtained whi^h are used in the arc light? CHAPTER XVII SOME ORGANIC COMPOUNDS Outline Hydrocarbons (a) Methane (&) Gasoline and Kerosene (c) Derivatives of Methane The Alcohols () AA^ood Alcohol (&) Grain Alcohol Organic Acids (a) Formic (b) Acetic Aldehydes Formalin Ethers 1. Hydrocarbons. It has been stated elsewhere that the study of carbon compounds constitutes a separate branch of chemistry, known as "Organic Chemistry." The compounds were originally so named because, as far as observed, they were produced only by organized life forces. This is known IIOAV not to be true. From their very great practical value in everyday life with some of these compounds it is important that the student should become familiarized. Among the simplest of such compounds are the hydrocarbons, which contain as the name indicates only carbon and hydrogen. In a pre- ceding chapter marsh gas has been mentioned, as have also gasoline, kerosene and various other oils derived from petroleum. All these are really paraffins and belong to 203 204 APPLIED CHEMISTRY a regular series in which over sixty have been prepared. The first six are here given, Methane, CH 4 , Ethane, C 2 H (; , Propane, C 3 H 8 , Butane, C 4 H 10 , Pentane, C 5 H 12 , Hexane, C H 14 . The subsequent members of the series receive their names from the Greek numerals as the last two given above, the first part of the name indicating the number of carbon atoms. Examination of the formulas shows that the dif- ference between any two successive members is CH 2 ; hence, it becomes a simple matter to write formulas for the entire series. Further it will be observed that the hydrogen is always twice the carbon plus two. The gen- eral formula for any paraffin, therefore, is C n H 2n + 2 in which n represents the number of the carbon atoms. Of the more than sixty paraffins known, the first five are gases, then follow a very considerable number of liquids, and above these are the solids with which all are familiar in the white wax of commerce. 2. Methane. This is commonly known as marsh gas, because of the fact that it is produced in swamps and stagnant creek beds where decomposition of leaves and other organic matter is taking place. It occurs in coal mines, and is known by the miners as fire damp, the word damp being their name for gas. It is so called be- cause of its dangerous, explosive character. It is this gas which causes practicallly all the explosions in coal mines. As in such cases the combustion is more or less imperfect from the limited supply of air, much carbon monoxide usually exists in the mine following the explo- SOME ORGANIC COMPOUNDS 205 sion. This has been mentioned before as the fatal black damp. It has been mentioned, also, that methane is the chief constituent of natural gas, is more than 40 per cent of coal gas, as well as a very considerable part of water gas. It is colorless, has a density only eight times that of hydrogen or little more than half that of the air, is odorless, and burns with an almost invisible blue flame. On account of its having no odor its presence in mines cannot be detected by the senses. For protection against it, more than a century ago, Sir Humphrey Davy in- vented a safety lamp which consists really of very little more than a chimney of fine wire gauze, surrounding the flame, like the chimney on a lantern. All it does is to prevent the gas on the outside from becoming heated to its kindling temperature. This will be understood if a wire gauze be held above a burning Bunsen flame. Ap- parently, it is possible by means of the gauze to push the flame down. Really, however, what it does is to conduct the heat away from the gas and dissipate it so that the gas in passing through is cooled below its kindling point. That this is so may be shown by bringing a flame to the current of the gas above the gauze. It is quickly ignited and goes on burning. 3. Gasoline and Kerosene. Gasoline consists mainly of the sixth, seventh and eighth of the paraffin series, hence is a mixture. Benzine and the other light oils mentioned as belonging to the gasoline fraction obtained from petroleum below 150 C. may be separated from each other by taking smaller fractions. To illustrate, a sample of gasoline may begin to boil at about 75 C.: the petroleum ether comes off first and because it has a very low boiling point it is soon all distilled over. The receiving flask will then be removed and another at- tached for the next fraction. Kerosene consists of the 206 APPLIED CHEMISTRY eight paraffins just above the gasoline series. Having seen the close relation of the various oils to each other in the paraffin series, it is less difficult to understand how by "cracking" it might be possible to convert the higher members into the lower, since a single molecule of the heavy oils might make two or more of the lighter ones. 4. Derivatives of Methane. A derivative as the term is used here is a compound obtained by substituting an atom or atoms of some element or some radical group' for one or more of the hydrogen atoms in the com- pound. One of the most simple as well as familiar de- rivatives of methane is chloroform, CHC1 3 , obtained in- directly by substituting three atoms of chlorine for three of the hydrogen in methane. lodoform, men- tioned elsewhere, is a corresponding derivative with the formula, CHL. Carbon tetrachloride, mentioned as a good fire extinguisher, is also a derivative in which all the hydrogen in methane has been replaced by chlorine. Chloroform is a colorless, oily liquid of rather pleasant odor and not inflammable. Its use as an anesthetic is familiar. It has the advantage over ether that it may be used near an open flame without danger. 5. The Alcohols, There are two, familiar to all, methyl, or wood alcohol, and ethyl or grain alcohol. They are derivatives of the first two paraffins: thus, CH 4 - CH 3 OH, and C 2 H 6 -> C 2 H 5 OH, in both of which a hy- droxyl group has been substituted for a hydrogen atom. Each of the paraffins has a corresponding alcohol, the higher ones in the series being white crystalline solids. Wood alcohol is obtained by the destructive distillation of wood in making charcoal. It is a colorless liquid, if pure, has a somewhat unpleasant odor, is very poison- ous, inflammable and an excellent solvent for many SOME ORGANIC COMPOUNDS 207 things. Because of this last property it has many uses as in making shellac, and similar preparations. How- ever, denatured alcohol, being much cheaper, is fast tak- ing the place of the wood alcohol in many cases. It is grain alcohol, adulterated by the addition of about 10 per cent of methyl or wood alcohol or some other liquid to render it more or less disagreeable in odor, and unfit for medicines, extracts or as a beverage. Adulterated, as mentioned, it is often called methylated spirits. The United States government has specified at least eight formu- las for denaturing alcohol to meet the various demands of manufacturers. It now has very extensive uses. It is one of the most commonly employed substances to prevent the freezing of the water in radiators of motor cars and trucks. Ethyl alcohol is made from grains. These are kept damp and warm for several days till sprouted. During this time a ferment called diastase, present in the seed and provided by nature to convert the insoluble starch present into soluble form, so that the embryo plant and rootlets can use it, has changed the starch into a form of sugar. At the proper stage, learned by experience, the grain is heated to stop the process; it is then ground, yeast is added and fermentation begins whereby the sugar into which the starch was converted changes into alcohol and carbon dioxide. Thus, C fi II 12 (; - 2C 2 H 5 OH + 2C0 2 . When the fermentation is completed the alcohol is dis- tilled out and put upon the market about 95 per cent strength. If absolute alcohol is desired it may be ob- tained by treating the commercial variety with lime or anhydrous copper sulphate and distilling carefully. Grain alcohol is a colorless liquid, of pleasant odor, boil- 208 APPLIED CHEMISTRY ing point of 78 C., and almost as poisonous as methyl. It is used in preparing many medicines as a solvent or preservative, in extracts for domestic or other purposes, and in a great variety of other ways. 6. Organic Acids. From each of the alcohols, by oxi- dation, an acid may be derived. Thus, if two of the hy- drogens in an alcohol are removed and an oxygen atom substituted for them, an acid is obtained. Methyl al- cohol thus gives formic acid, HCOOH. The equations for the first two are CH 3 OH + 2 - HCOOH + H 2 0, C 2 H B OH + 2 - CH 3 COOH + H 2 0. Like the paraffins and the alcohols, the acids differ by CH 2 , so that the entire series is easily written. These two acids might be given thus, H 2 C0 2 and H 4 C 2 2 ; but they are usually presented, as above, to indicate the structure of the molecule, and this is decidedly pref- erable. The empirical formula, H 4 C 2 2 , tells nothing but the number of atomic weights of each element pres- ent, from which may be calculated the percentage com- position : the graphic formula indicates that three hy- drogen atoms are attached to one carbon atom, and that the two oxygen atoms are attached to the other carbon but not in the same manner, and that the remain- ing hydrogen atom is attached to the second oxygen. It is more fully shown thus, H H-C-C-0-H. I H The first acid has little commercial value. It is secreted by some ants and received its name from the Latin word SOME ORGANIC COMPOUNDS 209 for ant, forma. It is also secreted by the stinger gland of such insects as the wasp, bee, and the hornet, when ex- cited. The pure acid is a colorless liquid, and upon the skin causes intense pain and produces blisters. It is this acid injected hypodermically, that causes the pain when stung by any of the above insects. Acetic acid is widely used in a diluted form, 2 to 5 per cent, as vinegar. Orig- inally, it was obtained largely from apple cider through, first alcoholic fermentation, when the cider became hard, and then subsequent oxidation by means of another spe- cies of bacterium. At the present time the demands are too great to be met in this way. Some is obtained in the distillation of wood in making charcoal ; some in the fer- mentation of fruit juices other than that of the apple; but most comes from the glucose prepared from corn starch. A solution of the glucose is passed slowly through tanks or barrels filled with shavings, previously inoculated with the bacterium, Mycoderma aceti, familiarly known as "mother of vinegar." The process is rapid and the vinegar obtained is free from the many organic impuri- ties of the old-time product, especially the decayed pulp of the apple. It also does not contain the vinegar eel, a tiny white worm, which frequently may be seen in count- less numbers in cider vinegar if examined carefully. Pure acetic acid is a colorless liquid, which becomes solid at 16.7 C. It is often called glacial acetic for this reason. 7. Aldehydes. From each alcohol in the series a cor- responding aldehyde may be obtained. This is done by carrying the oxidation only far enough to remove two atoms of hydrogen without introducing anything in their place. This leaves them unsaturated compounds ; hence, they are reducing agents. The only one of im- portance is formaldehyde, which is prepared from methyl 210 APPLIED CHEMISTRY alcohol. All the aldehydes obtain their names from the corresponding acid, hence, the name in this case. The preparation from methyl alcohol is shown by the equa- tion, 2CH 3 OH + 2 -> 2HCOH + 2H 2 0. Formic aldehyde is a gas which liquefies at -21 C. For use it is dissolved in water and is put on the market under the name of formalin, a 40 per cent solution. From this the gas is constantly escaping, irritating in odor, affecting both the nostrils and eyes. It is strongly germi- cidal and is used extensively for disinfecting purposes. This is easily done by pouring the solution upon lime with which the water present reacts giving sufficient heat to expel the gas rapidly. Since it is a hardener of tis- sues and cheaper than alcohol it is used extensively in preserving various zoological and botanical specimens. 8. The Ethers. Corresponding to each alcohol is an ether. From ethyl alcohol is obtained the only impor- tant one, ethyl ether. Its formula is (C 2 H 5 ) 2 0, which indicates that it is an oxide of the ethyl group. It is a colorless liquid, of sweet pleasant odor, with a boiling point below the temperature of the human body, 34.9 C. It is very inflammable, and an excellent solvent of iodine, as also of oils and fats. Inhaled it produces anesthesia. It is regarded as a safer anesthetic than chloroform, but cannot be used near an open flame. Exercises for Review 1. What is a hydrocarbon 1 ? Name six with formulas. What is an organic compound? What is a paraffin? 2. How many paraffins are known? What is their physical con- dition? 3. Give two other names for methane. How does it receive these? SOME ORGANIC COMPOUNDS 211 4. Describe the safety lamp and explain how it works. 5. Of what does gasoline consist? Into what several oils may it be separated? What is this process called? 6. Name two halogen derivatives of methane and use of each. 7. Name two alcohols with formulas. To what class of com- pounds do they belong? 8. What is denatured alcohol? Give some uses for it. 9. What is methylated spirits? What is a ferment? 10. How is grain alcohol made? Give uses. 11. Name two important organic acids. From what are they derived? 12. Where does each of these occur in Nature? 13. How is the commercial supply of vinegar obtained? 14. What is the common aldehyde? Its trade name? Uses for it? 15. Give formula for common ether. Of what use is it? Com- pare with chloroform. CHAPTER XVIII ETHEREAL SALTS, OILS, FATS, SUGARS Outline- Esters or Ethereal Salts Glycerol Esters of Glycerine Oleomargarine Compound Lards Molecular Structure of Fats The Olenns Hydrogenation of Oils The Carbohydrates (a) Monosaccharides (5) Disaccharides (c) Polysaccharides 1. Esters. It will be remembered that a base is a hy- droxide. By examining the formulas of the alcohols it will be seen that they are hydroxides. They are organic bases and, combined with organic acids, they produce what are called ethereal salts or esters. The first term is used for the reason that many of them have pleasant odors somewhat resembling ether. The word, ester t is coined from the other two and has no meaning. Several of these ethereal salts are familiar in the form of arti- ficial flavors and extracts, such as banana, pineapple, and the like. They may be had of the grocers and are found at soda fountains in some of the syrups used. Thus, artificial pineapple is ethyl butyrate, an ester of grain alcohol and butyric acid. It is the latter that gives the strong, disagreeable taste to rancid butter ; apple is amyl valerate, and pear, isoamyl acetate. The ester formed by the union of ethyl alcohol and acetic acid has a pleasant 212 ETHEREAL SALTS, OILS, FATS, SUGARS 213 fruity odor and is easily made in the laboratory. It is sometimes used as a test for the presence of alcohol in a substance. 2. Glycerol. This compound is commonly known as glycerine. Its formula, C 3 H 5 (OH) 3 , shows that it is an organic base with three hydroxyl groups; it is, there- fore, an alcohol. It is obtained as a by-product of the soap industry. In home-made soaps it is not separated out and in some special varieties of factory-made, such as the transparent soaps. But the great demand for glycerine in the manufacture of explosives as described elsewhere and the fact that it adds little to the value of the soap for general purposes, has led to its careful separation. Glycerine is a sweet syrupy liquid, nearly colorless if pure and very soluble in water. It derives its name from the Greek word for sweet on account of its taste. Because of the fact that it is hygroscopic, when the price will permit, it is sometimes used in small quan- tities by bakers in cakes to prevent their drying out so rapidly. It is also used in toilet and other pharmaceuti- cal preparations, but the greater proportion goes to the explosive factories. 3. Esters of Glycerine. It is the salts of glycerine that chiefly interest us, for they are the common fats and oils used as foods. The four most common are Glyceryl butyrate, Butyrin, C 3 H 5 (C 3 H 7 COO) S , Glyceryl palmitate, Palmitin, G 3 H 5 (C 15 H 31 COO) 3 , Glyceryl oleate, Olein, C 3 H 5 (C 17 H 33 COO) 3 , Glyceryl stearate, Stearin, C 3 H-(C 17 H 35 COO).,. All the common fats and oils are mixtures of three or all four of these. Butter contains all four ; when free from water the butyrin is about 8 per cent of the whole. It is this ester that gives the characteristic pleasant odor 214 APPLIED CHEMISTRY and taste to butter. Ordinarily, there is in butter about 12 to 14 per cent of water, with some casein from the milk. Olive oil is about 75 per cent olein. Of the four fats mentioned, olein has the lowest melting point, being a liquid at ordinary temperatures, and stearin has the highest. Any fat, therefore, with a high proportion of olein will melt easily and may be liquid at all ordinary temperatures; thus, cotton-seed oil and "mazola," an oil made from corn as a by-product in the manufacture of starch and glucose, are high in olein. Common lard is about 60 per cent olein and melts easily, while beef fat is high in stearin. It w T ill be seen, therefore, that the vari- ous edible fats, whether from beef, pork, mutton, or of vegetable origin, are very similar in character. If the formulas given above are examined, this fact is even greatly emphasized. 4. Oleomargarine. The demand for butter is far greater than the supply. This has led to the preparation of artificial butters, most of which are called oleomar- garines. These are made by the mixture of animal and vegetable oils, which are much cheaper than butter. One formula, used by one of the large packing houses, is given below, Neutral lard, 75 pounds Cottonseed oil, 175 pounds Oleo oil, 675 pounds Peanut oil, 75 pounds These are put into 60 gallons of milk from which the cream has been separated and churned. The purpose of this is to add something of the flavor of real butter and possibly some of the casein of the milk. The fats are removed from the milk, and 150 pounds of real but- ter and 125 pounds of salt are added and the whole ETHEREAL SALTS, OILS, FATS, SUGARS 215 thoroughly worked together. This gives a total weight of solids of 1,275 pounds. In the churning and subse- quent working of the mixture considerable water, even as much as 12 per cent is taken up, so that there is finally a total weight of between 1,400 and 1,500 pounds. In this variety it will be seen the butter is approximately 10 per cent of the whole. In another formula used, the real butter mixed with the other fats may run as high as 25 per cent, but it is understood that this par- ticular brand is not put on the general market but sold entirely to special customers. Many brands contain no butter at all. At the present time oleos in which cocoa- nut oil enters to a very considerable extent are being manufactured by nearly all the large packing compa- nies. The advantage claimed for these butters is that co- coanut oil contains about 5 per cent of butyrin ; hence, they much more nearly approach real butter in com- position and taste than do those with a higher percent- age of animal oils. For years after their introduction into the United States there was great objection made to them by the butter producers and much adverse legis- lation resulted. They may not be colored, although all creamery butter and cheese are ; moreover, oleos, must pay an excise tax, which somewhat increases their cost to the general public. Nevertheless, these artificial but- ters are clean, wholesome articles of food, nutritious, and to all purposes, of practically the same food value as the real article. There is only one objection and that is the low melting point ; thus in warm weather oleo- margarine is more difficult to keep as hard as is desira- ble. In spite of adverse legislation and the prejudice existing, their consumption has increased wonderfully in the last five years. Some idea of this may be obtained from the government reports concerning the importa- 216 APPLIED CHEMISTRY tion of cocoanut and other vegetable oils. The follow- ing table gives the amounts for the years 1914 and 1918, the last available at this time. Oil 1914 1918 Peanut Oil Soy Bean Oil Cocoanut Oil 1,000,000 gals. 16,000,000 Ibs. 74,000,000 '* Over 8,000,000 gals. 337,000,000 Ibs. 259,000,000 " 5. Artificial Lards. As the high price of butter and the inadequate supplies have led to the substitution of oleos, so has it been in the case of lard. The demand is vastly greater than the supply and today a consider- able number of so-called "compound lards" are found on the market. Such are "Suetene," "Cottolene," "White Cloud," "Snowdrift," and numbers of others. As the names of some indicate, many of them contain more or less of cotton-seed oil. But as this runs high in olein it is liquid at ordinary temperatures. The public is accustomed, however, to a solid fat for short- ening and for various other food purposes; hence, it is slow to accept a liquid, however equally good it might be. Efforts were made, therefore, to overcome this difficulty, and these 'have been eminently successful as will be shown later in this chapter. 6. Structural Composition of Fats. With the excep- tion of olein the fats mentioned in this chapter may be regarded as derivatives of the paraffins. Thus, butane, C 4 H 10 , is the fourth in the paraffin series. The acid de- rived from it, butyric, would have the formula, C 3 H 7 COOH. Combining this acid with the base, glyce- rol, as shown by the equation, C 3 H 5 (HO) 3 + 3C 3 H 7 COOH -> 3H 2 + C 3 H 5 (C 3 H 7 COO) 3 we have butyrin. As the paraffins are all saturated com- pounds, so are the glyceryl salts derived from them. To ETHEREAL SALTS, OILS, FATS, SUGARS 217 illustrate: Methane, ethane and butane are respectively represented by the structural formulas, PI H H H H H II I II I I I I H-C-H H-C-O-H H-C-C-C-C-H, and butyric "I II I I I I H H H HH HH HH HO acid by H-C-C-C-C-0-H. I I I HH H In all these it is seen that every carbon atom is fully saturated; so are the esters as may be seen in the fol- lowing formula for butyrin. To the glyceryl radical, (C 3 H 5 ) three carbon chains are attached, but only one is written for the sake of convenience, HH HO H-C-C-C-C-0-(C,H,) =. I I I H II H 7. The Olefins. There is another class of hydrocar- bons to which attention must be directed in order that the preparation of compound lards may be understood. These are the olefins, many in number, of which the first few of the series are given. Ethylene, C 2 H 4 , Propylene, C 8 H , Butylene, C 4 H 8 , Amylene, C 5 H 10 , also called Pentylene, Hexylene, C H 12 . It will be observed that they are given names derived from those of the paraffins, with the ending changed. There is no olefin corresponding to methane. These com- pounds may also form acids and alcohols as in the case 218 APPLIED CHEMISTRY of the paraffins. The important distinction to be noticed at this time is that these are unsaturated compounds. A proof of this was given in the case of ethylene on p. HH I I 180. Structurally, this would be represented thus, -C-C-, I I HH which shows two of the carbon atoms with one free bond. In the same way the acids and the esters derived from them would be unsaturated. Therefore, olein, belonging in this group, is an unsaturated compound. If the for- mulas for stearin and olein be compared, it will be ob- served that they differ only by two atoms of hydrogen, yet one is a hard white solid, and the other a liquid at ordinary temperatures. Without attempting to write the entire carbon chain, they may be compared thus, HHHO Chain of Carbon-C-C-C-C-0-(C 3 H 5 ) = 2 Carbon Chains, I I I HHH H HO Chain of Carbon-C-C-C-c'-0-(C 3 H 5 ) =2 Carbon Chains. I I I H H The first of these is stearin, the second, olein. 8. Hydrogenation of Oils. If the above statements are true it would seem that if it were possible to cause the unsaturated carbon atom in olein to take up two additional atoms of hydrogen, the olein should be changed into stearin with a corresponding change in melting point. This has been found possible and the process is called hydroyenation. A current of hydrogen introduced into any of these oils has no effect, but if a ETHEREAL SALTS, OILS, FATS, SUGARS 219 catalytic agent be used, more often nickel in this case, the unsaturated olein takes up the additional hydrogen and at room temperature becomes a white solid. The process has the greatest commercial value. "Crisco, " as well as the various compound lards mentioned, are vegeta- ble oils, thus hydrogenated, or they are mixtures of the same with animal fats. Wesson oil is cotton-seed oil pre- pared by a certain process for cooking purposes. All the edible vegetable oils such as those made from corn, pea- nuts, cotton seed, soy beans, cocoanuts, arc now being hydrogenated and made into pure white solid fats. They are all wholesome, probably even more so than those of animal origin, because not subject to disease and equally valuable as energy and heat producers. 9. The Carbohydrates. The organic compounds con- sidered thus far in this chapter have all been hydrocar- bons and derivatives from them. There is another very important class known as the carbohydrates, which as the name indicates contain carbon, hydrogen and oxygen. The hydrogen and oxygen with scarcely any exception are in the proportion of 2 to 1. Three of the most com- mon, which are typical of the three classes are Glucose, C G H 12 6 , a monosaccharide, Cane Sugar, C^H^O^, a disaccharide, Starch, (C 6 H 10 5 )n, a polysaccharide. The prefixes mono-, di- and poly- refer to the number of aldehyde or ketone groups which the various compounds in these three classes contain. One aldehyde, HCOII, has been studied, but the ketones are not of sufficient im- portance to demand our attention here. The group -COII is contained in all aldehydes; glucose has one of these groups, cane sugar two, and starch several or many. Glu- cose is one of several sugars with the same empirical for- 220 APPLIED CHEMISTRY mula, found in nature in various fruits. It is manufac- tured extensively from corn starch. The oil is first re- moved from the corn; in water under the action of di- lute sulphuric acid, the starch takes up two additional atoms of hydrogen and one of oxygen for each saccharide group, thus, The sulphuric acid used is merely catalytic and is re- moved by adding lime or some similar substance which converts it into an insoluble compound, so that it settles out. The glucose is then concentrated and put on the mar- ket mostly in the form of a syrup under a variety of trade names. One of the most advertised is "Karo," which may be had in a dark variety, the natural color, and a light variety, which has been bleached by sulphur dioxide. Glucose, while only about three-fifths as sweet as cane sugar, is a wholesome article of food notwith- standing a popular prejudice against it. This has come through a misunderstanding regarding the sulphuric acid used in the inversion of the starch. The bleached or color- less syrups may sometim.es contain a trace of the gas used in the process of bleaching, but this objection cannot be offered to the dark syrups. Much of the candy on the market contains more or less glucose. Probably the only objection that can be offered is that it absorbs moisture from the air more readily than that made from cane sugar, and thus in damp weather tends to become "sticky." Glucose, as a food, is more readily assimilated than cane sugar; in fact, the latter, before assimilation, must be changed by the digestive fluids into the monosac- charide variety. 10. The Disaccharides. Cane and beet sugar are the two most abundant of this class and have the same com- position. Their source is well known and need not be ETHEREAL SALTS, OILS, FATS, SUGARS 221 discussed here. Milk sugar, obtained as a by-product from the whey in cheese factories, differs from the two already mentioned in that it contains a molecule of com- bined water, thus, C^H^On.ILO. Milk becomes sour through the changing of this sugar into lactic acid just as acetic acid is produced in cider through the fermen- tation of the fruit sugar contained in the apple. The lactic acid produced thus converts the casein, originally present in the soluble form, into the insoluble variety, va Fig. 46. Starch granules. The shape of the granules is different in the various starch-containing foods, so that under the microscope the variety may he readily recognized. so that the milk becomes "curdled." The same thing occurs in the stomach through the action upon the casein of the hydrochloric acid always normally present. 11. Starches. A large number of plants produce starch. The most familiar to us are the grains, such as wheat and corn, and the potato. All have the same formula, but under the microscope, their granules are very different in shape (Fig. 46). The number of sac- charide groups contained in the molecule is not known 222 APPLIED CHEMISTRY as is indicated by the formula. Cellulose is represented by the same empirical formula, but probably the value of n is different from what it is with the starches. It would seem possible, judging from the formulas of starch and cellulose, to convert such waste products as sawdust, which is largely cellulose, into a monosaccha- ride, as starch is made into glucose. No method, how- ever, has ever been devised which is cheap enough, al- though experimentally it is entirely possible. When dry starch is heated to 250 C. it is converted into a product called dextrin; when made into a paste, it is used instead of mucilage extensively, especially upon envelopes, stamps, and for similar purposes. It is also employed largely in sizing paper, weighting cloth, paper for cardboard, and for sizing walls preparatory to paper- ing. Paper is made from wood, straw, and various other articles which consist largely of cellulose. Another organic compound in the wood, known as liguin, is first removed by treatment with sodium hydroxide or some other chemi- cal reagent, and the remaining cellulose washed thoroughly with water. The pulp is then rolled into sheets and dried. Filter paper is nearly pure cellulose. Exercises for Review 1. What is an ester? How did it receive the name? Name three. 2. What is glycerol? Formula? Where obtained? 3. Name four esters of glycerine. 4. Of what does butter consist? What is mazola? 5. What is oleomargarine? What advantages do the cocoanut oleos have? 6. What is a compound lard? Name some on the market. 7. Write the structural formula of butyric acid to show it is a saturated compound. 8. Name four olefins. How are they different from the paraf- fins? ETHEREAL SALTS, OILS, FATS, SUGARS 223 9. How docs olein differ from stearin? 10. What is meant by hydrogenation? What effect does it have on an oil? Can stearin be hydrogenated ? Why? 11. What is a carbohydrate? Name three classes with example of each. 12. What is "karo"? How made? 13. Name three disaccharides. What is the origin of lactic acid in milk? 14. How is cellulose different from starch? 15. How is dextrin, made? Uses? 16. Of what does paper consist mainly? CHAPTER XIX FOODS AND THEIR BODY VALUES Outline Classes of Foods Carbohydrates (a) Sugars (7?) Starches (c) Cellulose Oils and Fats Proteins Minerals 1. Kinds of Foods. The various foods used may be classified as carbohydrates, oils and fats, and proteins, to which some add inorganic or mineral foods which may be made to include water. 2. Carbohydrates. The carbohydrates most commonly used as foods are the various sugars, starch and cellu- lose. When sucrose, a general term for either cane or beet sugar, is boiled in the presence of an acid, it is slowly changed into glucose and fructose, both mono- saccharides, called in this case, invert sugars. The proc- ess is called inversion. As the invert sugar obtained is not as sweet as the cane sugar used, in stewing any acid fruit for table use it is better not to add the sugar till the fruit is about done. By this plan less inversion takes place and less sugar is required to render the fruit pal- atable. Not only do acids have the catalytic action of inverting sugar, but certain enzymes as well. In our foods before sucrose is assimilated by the body it is con- verted into invert sugar by the enzymes of the diges- tive fluids.. The sugars and starches serve mainly as 224 FOODS AND THEIR BODY VALUES 225 fuel and energy producers. Since they contain suffi- cient oxygen to convert the hydrogen present into wa- ter, it is the carbon content alone that determines the relative fuel value of a carbohydrate. In the body it combines with oxygen obtained through the lungs and heat results, just as if so much carbon in the form of coal were burned in a stove. Starchy foods are obtained mainly from the various grains, wheat, corn, rice, rye, oats and barley; also from the potato, tapioca, arroAvroot and sago. Bananas con- tain about 22 per cent of carbohydrates, much of which before the fruit is fully ripe is in the form of starch. When starchy foods are toasted, a portion of the starch is converted into dextrin, as is the outer portion of the crust of bread in baking. It is sweeter than starch, more soluble and more easily digested. All starchy foods, before digestion can take place, must be hydro- lyzed or converted into invert sugar: this is partly ac- complished in mastication through the action of the enzymes in the saliva. The equation shows the change, which is altogether catalytic, Used in the body carbohydrates serve two purposes, giving energy for muscular exertion and warming of the body. When assimilated into the circulatory sys- tem they meet the oxygen and chemical union takes place, accompanied by heat. Any excess may be stored up in the muscles and liver in the form of an animal starch called glycogen. This may be used whenever an insufficient amount is furnished by the daily food. Cellulose is found in many of our foods and is a car- bohydrate as seen in the preceding chapter, but it is not an energy producer, for the reason that it is not 226 APPLIED CHEMISTRY digestible. It is the enclosing wall of starch granules; it is abundant in the stems of plants. As maturity is reached in many vegetable foods, the quantity of cellu- lose increases. This is seen in asparagus, string beans, turnips, beets, celery and various others. It is what is spoken of as crude fiber in grains; the outside cover- ing of wheat, corn, unpolished rice and other cereals. It is not capable of inversion by any of the enzymes of the body and for that reason, as stated above, is indi- gestible. Nevertheless, it plays a far more important part in digestion and the bodily health than most of us realize. It serves as a stimulant to the secretion of the fluids necessary for digestion and excretion and aids in increasing peristaltic action; in other words, it is a body-regulator food. Domestic animals such as the horse and cow use large amounts of what is called " roughness" or hay, much of which is cellulose. Fed on concentrated foods entirely they lose appetite and quickly become a prey for all sorts of diseases. In all probability a large proportion of the bodily ills of man- kind may be traced directly to the use of foods too much refined and lacking in crude fiber or cellulose. Herein lies the health value of graham and bran breads and whole wheat foods and others of similar character. Pectin is another vegetable carbohydrate found in the juices of many fruits and in the inner portion of the peeling of the orange and other citrus fruits. It is the principle involved in the making of jellies. It is coagulated by acids and also by sugar. In boiling fruit juice the water is removed and the pectin concentrated. The point is finally reached where coagulation takes place upon cooling. This is determined by the house- wife by frequently testing small portions in a dish. For years numerous attempts were made to prepare FOODS AND THEIR BODY VALUES 227 jellies from the cheaper grades of oranges regarded as unsalable by the packing houses, but all without suc- cess. Finally, it was found that in the orange the pectin is contained in the white portion of the peeling and not in the juice. Therefore when this portion is used with the juice of the fruit the operation is successful ; and orange jelly and marmalade are now common arti- cles of commerce. 3. Oils and Fats. These foods are also heat and en- ergy producing. One pound of this class is about the equivalent of 2% pounds of carbohydrates. This is because the amount of oxygen contained is much less in proportion in the fats and oils. They produce heat and energy in the same manner as the carbohydrates. In good assimilation any excess of such foods is stored up as glycogen in the liver, or as adipose tissue in various parts of the body, presumably to be used in cases of forced abstinence or as other needs might come. 4. Protein Foods. Proteins are primarily muscle builders and not energy producing. It is true they may serve as body fuel, but as nitrogen is not oxidizable, they are poor in this respect and should never be used with this idea in view. The body contains about 18 per cent of proteins. Whenever work is done, or muscular exercise of any kind- is taken, some of the cells of the tissues are torn down and must be replaced. Plants have the power of building their own protein from the carbon dioxide inhaled from the air together with the nitrogen and water absorbed from the soil. Some few, the leg- umes, through the aid of bacteria, may even obtain the needed nitrogen from the air. But no animal has such pow r er. It must use, for replacing wasted muscular tis- sue, protein already formed ; this may be either of ani- mal or vegetable origin. Such foods as eggs, lean meat, 228 APPLIED CHEMISTRY milk, cheese, beans, peas and other legumes are rich in protein. Several grains also furnish considerable pro- tein if the whole of the grain is used. As protein serves mainly to restore wasted muscular tissue, the amount needed depends upon the amount of bodily exercise taken. In general, it may be said that not over 3 ounces, 80 grams, per day, are necessary, often much less. Those with sedentary employment require but little, while those engaged in manual labor need much. Too little regard is paid to this fact, with serious results to the bodily health. When carbohydrates are oxidized in the body, carbon dioxide and water are the sole prod- ucts and these are eliminated largely through the lungs. Proteins, being nitrogenous foods, are converted into urea, (NH 2 ) 2 CO, and this is eliminated through the perspiratory glands and by the kidneys. In case of ex- TABLE OF FOOD VALUES OF CERTAIN NUTS From Farmer's Bulletin, No. 332- NUT WASTE % WATER PRO- TEIN PAT CARBO- HYDRATE FUEL VALUE PER POUND CALORIES Pecans 50 3.4 12.1 70.7 12.2 3325 Hickory Walnut 62 59 3.7 3.4 15.4 18.2 67.4 60.7 11.4 16.0 3240 3100 Cocoanuts 35 13.0 6.6 56.2 22.6 2825 Peanuts 27 7.4 29.8 43.5 17.1 2625 Chocolate 5.9 12.9 48.7 30.3 2770 Cocoa 4.6 21.6 28.9 37.7 2255 SOME DRIED FRUITS FRUIT WASTE % WATER PRO- TEIN FAT CARBO- HYDRATE CALORIES Dates Raisins Figs Prunes Apples 10 10 15 15.4 14.6 18.8 22.3 28.1 2.1 2.6 4.3 2.1 1.6 2.8 3.3 0.3 2.2 78.4 76.1 74.2 73.3 66.1 1575 1560 1435 1370 1320 FOODS AND THEIR BODY VALUES 229 SOME FRESH FRUIT FRUIT WASTE % WATER PRO- TEIN FAT CARBO- HYDRATE CALORIES Banana 35 75.3 1.3 0.6 22.0 450 Grapes 25 77.4 1.3 1.6 19.2 435 Plums 5 78.4 1.0 20.1 380 Cherries 5 80.9 1.0 0.8 16.7 355 Pears 10 84.4 0.6 0.5 ' 14.1 285 Apples 25 84.6 0.4 0.5 14.2 285 Orange 27 86.9 0.8 0.2 11.6 235 Peach 18 89.4 0.7 0.1 9.4 185 FOOD VALUES OF CEREAL PRODUCTS NAME WATER % PRO- TEIN FAT CARBO- HYDRATE CALORIES Crackers 5.9 9.8 9.1 73.1 1875 Rolled Oats 7.7 16.7 7.3 66.2 1800 Shredded Wheat 8.1 10.5 1.4 77.9 1660 Graham Flour 11.3 13.3 2.2 71.4 1630 Macaroni 10.3 13.4 0.9 74.1 1625 Hominy 11.8 8.3 0.6 79.0 1610 White Flour 12.8 10.8 1.1 74.8 1610 Rice 12.3 8.0 0.3 79.0 1590 White Bread 35.0 9.1 1.6 53.3 1200 Graham Flour 35.7 8.9 1.8 52.1 1180 FOOD CONTENT OF CERTAIN VEGETABLES NAME WATER % PRO- TEIN FAT CARBO- HYDRATE CALORIES Sweet Potato 20 1.8 0.7 27.4 560 Irish Potato 20 2.2 0.1 18.4 380 Parsnips 20 1.6 0.5 13.5 295 Onions 10 1.6 0.3 9.9 220 Beets 20 1.6 0.1 9.7 210 Carrots 20 1.1 0.4 9.3 205 Turnips 30 1.3 0.2 8.1 180 Cabbage 15 1.6 0.3 5.6 145 Cauliflower 1.8 0.5 4.7 140 Spinach 2.1 0.3 3.2 110 Celery 20 1.1 0.1 3.3 85 Cucumber 15 0.8 0.2 3.1 80 Green Peas 45 7.0 0.5 16.9 455 String Beans n 2.3 0.3 7.4 190 Squash 50 1.4 0.5 9.0 210 Tomatoes 10 0.9 0.4 3.9 105 230 APPLIED CHEMISTRY cess, uric acid forms and tends to accumulate in the muscles and about the joints and causes rheumatism. Those in sedentary employments, therefore, should use little meat or other nitrogenous foods. Nitrogenous foods in decomposing often produce what are called amines. These are substitution products of ammonia, one of which is NH 2 CH 3 , methyl amine. Some of these are very poisonous and are called ptomains. In tables showing content of protein in various food products, the amount is often given in terms of nitrogen. As on an average the nitrogen in a protein is 16 per cent, to determine the amount of protein contained the nitro- gen must be multiplied by 6.25. The preceding tables show the food content and the fuel or calorific value of a large number of common articles of diet : 5. Mineral Foods. In all foods used there are small quantities of mineral matter or ash. These come from the soils and are taken up by the growing plant. While the amounts are small, certain portions seem necessary for health. The blood owes its color to the presence of iron compounds, and certain foods especially are rela- tively rich in these. Such are eggs, milk, peas, beans, figs, dates, raisins, wheat, rye, barley, and spinach. Cal- cium and phosphorus, usually combined as a phosphate, are especially needed in youth, but more or less at all times. The dry bone is over 50 per cent calcium phos- phate, while other portions of the body also contain smaller amounts. This must, therefore, be supplied. Such foods as milk, eggs, cheese, whole wheat, nuts and beans are rich in phosphorus. White flours are made by milling off the outer portions of the grain; hence, the cellulose and the mineral portions are lost as foods with serious consequences to the bodily health. In the body are also found sodium, potassium, magne- FOODS AND THEIR BODY VALUES 231 slum, chlorine and sulphur. More than sufficient so- dium and chlorine are supplied in the common salt used. Sulphur is contained in such foods as eggs, and often in other protein foods. Magnesium and potassium are found in various nuts, cocoa, beans, peas, prunes, Fig. 47. Foods rich in iron. (From Greer's Textbook of Cooking.) a, Peas; b, figs; c, wheat; d, lentils; c, spinach; /, dates; g, eggs; h, rye; i, beef; j, beans; k, raisins; I, lima beans. figs, raisins, oats and rye. The following tables give the quantity of mineral matter contained in a number of common articles of diet. The value of water in the human economy has been discussed elsewhere. FOODS RICH IN IKON The following contain .003 per cent or more Beans, dry Lean beef Whole barley Dates Peas, dry Whole rye Fggs Eaisins Whole wheat Figs, dried Spinach FOODS RICH IN PHOSPHORUS The following contain .9 per cent or more B'eans, dry Cocoa Peas, dry Cheese Eggs, the yolk Whole wheat Chocolate Peanuts 232 APPLIED CHEMISTRY Fig. 48. Foods rich in phosphorus. (From Greer's Textbook of Cook- ing.) a, Peas; b, chocolate; c, beans; d, peanuts; e, whole wheat; /, cheese; g, cocoa; h, yolk of egg. Figs. 47 and 48 show graphically what is given in the tables. (From Greer's Textbook of Cooking.) Exercises for Review 1. Name the four classes of foods. 2. What is meant by inversion? Why should the sugar be added after the fruit has about finished cooking? 3. Why is cellulose not digestible? Of what value is it to the body? What is meant by crude fiber? 4. What is pectin? Of what practical value is it in the house- hold? Where is it found in most fruits? Any exception? 5. What is the use of carbohydrate foods in the body? Why is a fat of greater fuel value than a sugar? 6. Explain how the heat is produced in the body. How are the products of combustion in the body eliminated? 7. Of what do protein foods consist? Name some typical ones. 8. What value has a protein food to the body? How much of this kind of food is needed per day? 9. Into what is protein food converted when it has been used in the body? How is it removed? 10. In case of excess of protein foods what is apt to follow? How remove this condition? 11. Name the more common mineral foods. From what may the three most important be obtained? 12. What do most "tonics" contain? What is the supposed purpose? CHAPTER XX SOLUTION AND IONIZATION Outline- Meaning and Kinds of Solution Concentration of Solutions Characteristics of Solutions (a) Change in Freezing Point (&) Eise in Boiling Point (c) Difference in Density Law of Variation Noted Exceptions Cause of Variation Conductivity of Solutions Dissociation (a) By Heat (&) By Solution lonization and Ions Ions and Valence Ions and Chemical Action 1. Definition of Solution. As generally defined a so- lution is a homogeneous mixture of two or more sub- stances. Usually we think of it as a solid in a liquid, for such are the more common. The solvent is the sub- stance of greater amount, while the solute is the other. Thus, if a few grams of salt be dissolved in a liter of water, the salt is the solute and the water is the solvent. There are several kinds of solutions besides that of a solid in a liquid. For example, air is a solution, in which the nitrogen is the solvent. Soda water is a solution of a gas, carbon dioxide, in water; a silver dollar is a solution of 10 parts of copper in 90 of silver. However, as solutions of solids in liquids are by far the most common, it is with them that this chapter deals. 233 234 APPLIED CHEMISTRY 2. Solution Concentration. The properties of solu- tions differ from those of the solvent. For the sake of comparisons it is necessary to agree upon some stand- ard when speaking of the strength of a solution. If a gram molecular weight of any substance be dissolved in a liquid so as to make one liter of the mixture, the solution is said to have a concentration of one, and is marked C . If a liter of a solution contains 2 gram molecular weights of the solute, its concentration is two, marked C 2 . Obviously, a gram molecular weight of sugar would contain the same number of molecules as a gram molecular weight of salt, although the former would con- tain 342 grams and the latter only 58.46 grams. So in all solutions with a concentration of one there would be the same number of molecules of the solute. 3. Characteristics of Solutions. As there is always a diminution of volume when two substances are mixed homogeneously, the specific gravity of the solution is always greater than that of the solvent. Again, the freezing point is always lower than that of the solvent, and the boiling point is higher, or, as it is usually ex- pressed, the vapor pressure is lowered. A little thought will make all three statements apparent. As a small handful of salt may be dissolved in a quart of water with- out greatly increasing the volume, evidently the water per cubic centimeter is heavier than before the salt was added. Heat is merely a form of molecular energy; when a body is warmed its molecules are made to move faster; when cooled their motion becomes slower. There- fore, since there are more molecules in a given volume of a solution than in the same volume of the solvent, it would take more heat energy to set them in motion or, on the other hand, to stop them than if dealing with the pure solvent. In other words, speaking of cold as if it were SOLUTION AND IONIZATION 235 a force, it would require a greater degree of cold to "slow down" the larger number of molecules in the solu- tion than it would the fewer number in the solvent, that is it is harder to freeze salt water than pure. Likewise, in bringing a solution to the boiling point, there would be more molecules to which there must be imparted a certain velocity before boiling begins, so the temperature would be higher before the boiling is reached. From the fact that a liquid begins to boil when the pressure of the vapor passing off from it equals or is slightly in excess of the atmospheric pressure above it, we usually say the vapor pressure is lowered instead of saying the boiling point is raised, but both expressions mean the same thing. 4. Concentration and Freezing Point Lowering. Since all solutions with a concentration of one contain the same number of molecules of the solute per liter, it would seem from the kinetic viewpoint that the freez- ing point of all solutions, no matter what the solute, would be lowered the same for the same solvent. That is, if pure water freezes at C. and a solution- contain- ing a gram molecule of sugar per liter freezes at -1.8 C., we should expect a solution of alcohol containing a gram molecule per liter also to freeze at 1.8 below zero. Likewise we should expect such solutions with a concentration of two, that is with 2 gram molecules of the solute per liter, to freeze at -3.6. If such experi- ments are made, using any of the soluble organic com- pounds mentioned in the preceding chapters, our ex- pectations are realized. These facts, then, are stated in this conclusion, that the lowering of the freezing point of a solution is directly proportional to the con- centration. Briefly it is expressed thus, L oc C, in which L means lowering of freezing point and C the 236 APPLIED CHEMISTRY concentration, and the sign, oc ? varies as. Experiments made upon the lowering of the vapor pressure of such solutions, show like results, so that the same formula may be applied to both cases. In tabular form below are shown some of the solutions comnionly used with results upon the freezing point : TABLE OF FREEZING POINT LOWERING SUBSTANCE CONCENTRA- TION FREEZING POINT GRAMS PER LITER Alcohol C = l -1.8 46 Glucose C = l -1.8 186 Cane Sugar = 1 -1.8 342 Glycerine = 1 -1.8 92 Alcohol C = 2 -3.6 92 Glucose C 2 -3.6 360 Cane Sugar C = 2 -3.6 684 Glycerine C = 2 -3.6 184 Alcohol C = 3 -5.4 138 The results given above have disregarded slight varia- tions due to experimental errors or otherwise easily accounted for; they show conclusively Avhat was pre- viously stated that the lowering of the freezing point de- pends upon the concentration. 5. Exceptions to the Above. It will be noticed that all the substances given in the table are organic com- pounds. We should expect the same results, however, with the inorganic compounds, such as common salt, sulphuric acid, potassium chloride, and others familiar to us. When such are tried, using a concentration of one, the same as before, so as to introduce the same number of molecules per liter, the results do not agree at all. In some cases the freezing point is lowered nearly twice as much, in others nearly three times, and still others nearly four times as much as expected. SOLUTION AND IONIZATION 237 6. Cause of This Irregularity. It lias 'been observed that chemical reactions between substances perfectly dry are practically nil. Pure dry hydrogen chloride does not react with zinc. It has been said elsewhere, Chapter I, that compounds, inorganic, are composed of an elec- tropositive and an electronegative portion and that each gives a separate test. In the absence of all water such tests cannot be made. With the organic compounds this is not true. They are not composed of a positive and a negative part and tests with them are tests upon the sub- stance as a whole. It seems then that when an inorganic compound is dissolved in water, in some way the posi- tive and negative portions are separated from each other so that each may be tested. Further, it was no- ticed that such compounds as common salt, potassium chloride, hydrochloric acid, Ammonium chloride and many others, which were possible of separation into only tw r o particles, one positive and one negative, always gave a lowering of freezing point almost double that of the organic compounds when concentration of one was used. Further, such compounds as calcium chloride, CaCl 2 , barium chloride, BaCl 2 , sulphuric acid, H 2 S0 4 , calcium hydroxide, Ca(HO) 2 and many others capable of breaking up into three portions, two positive and one negative or one positive and two negative, in concen- trations of one gave a lowering of freezing point nearly three times what the organic compounds did with the same concentration. Again, aluminum chloride, A1C1 3 , phosphoric acid, H 3 P0 4 , capable of breaking up into four parts, gave a lowering of the freezing point almost four times that given by the organic compounds in so- lutions of the same strength. From conclusions already reached in the case of the organic compounds, namely, that the lowering is proportional to the concentration, 238 APPLIED CHEMISTRY it came to be believed from the above observations that in water the inorganic compounds are broken up into parts and exist there not as molecules but as parts of molecules. If this be true, a solution of potassium chlo- ride, for example, would have as many particles to be "slowed down" in their movement as if the concentration were two; that is, the freezing point should be lowered 3.6. Likewise, such substances as sulphuric acid, or cal- cium chloride in solution would contain as many parti- cles as of the organic compounds with a concentration of three, and should give a lowering of 5.4. 7. Variation from Regular Lowering. In all these cases, however, the lowering falls short of the theoretic amount, as shown by the following table: LOWERING OF FREEZING POINTS Substance Concentration Degrees Lowered Cane Sugar 1 1.8 Grain Alcohol 1 1.8 Sodium Chloride 1 3.5 Calcium Chloride 1 5.1 Aluminum Chloride 1 6.8 Thus it will be seen that the greater the number of pos- sible particles into which the compound may be broken the greater the variation from the theoretic value. Ac- cording to the kinetic theory, not only are the mole- cules of a body in motion, but the atoms likewise in the molecule. Some years ago it was shown by the great Dutch chemist, van't Hoff that in dilute solutions the molecules of the solute are at such distances from each other that they obey all the gas laws. In these cases, therefore, the parts into which the molecules are broken would be moving in all directions, and in all probability SOLUTION AND IONIZATION 239 would collide more or less frequently. For example, if potassium chloride is broken up into potassium and chlorine particles, in their movement the potassium and chlorine would more or less frequently collide and thus a molecule of the salt would be reformed. Among bil- lions of particles with a rapid motion these collisions would be frequent, so that there Avould always be, ex- cept in cases of very great dilution, a very apprecia- ble number of the molecules not broken up. Therefore, the number of particles in the solution, to be "slowed down," would never be quite double the number of the molecules, and, hence, the freezing point would not be lowered fully twice as much as in the case of the organic compounds. The same way with the calcium chloride, alu- minum chloride and others : there being more particles per degree of concentration, since each molecule may break up into three or four parts, collisions would be more frequent, more molecules would exist intact, and the lowering would vary further from three or four times the theo- retic amount. 8. Conductivity. It was long ago observed that such substances as sugar, and the organic bodies are not con- ductors of electricity, either by themselves or dissolved in water. It has also been seen that pure water is not a conductor. Inorganic compounds, which have been found to give very irregular results in lowering of freez- ing point, are not conductors when in the solid form, but dissolved in water are almost universally good conduc- tors. Such substances are spoken of as electrolytes, while those which will not conduct a current when dis- solved in water are called nonclectrolytes. From the above observations and further, that when solutions of the inor- ganic compounds are electrolyzed the metal always ap- pears at the cathode and the nonmetal at the anode, it 240 APPLIED CHEMISTRY was thought possible that the positive particles might be the means of conducting the current through the solution and of giving it up to the negative electrode. Further- more it was concluded that organic compounds are not conductors, because in water they are not broken up into particles so as to make it possible for one portion to be attracted toward the negative electrode. 9. Dissociation. It has been seen in a very consid- erable number of cases that at different temperatures substances may exist with molecules of differing com- position. Thus, nitrogen peroxide, at a temperature of about 23 C., has a molecular weight of 92, while at about 135 it is only 46, and at temperatures between these two it varies, being lower as the temperature is raised. As the molecular weight of 92 would correspond to the formula, N 2 4 , and 46 to that of N0 2 , there can be only one explanation and that is that heat decom- poses nitrogen tetroxide, and at a certain point this decomposition is complete, whereas at temperatures lower than this there are always present molecules of the greater density mixed with the lighter ones. This is shown by the equation, N 2 4 * 2N0 2 , which means that the process is reversible and, what is more, is probably occurring at all times. When the temperature is lowered the reverse action is more rapid than the direct till a certain definite proportion is reached when equilibrium obtains. Such a reaction as this is called dissociation. Defined, dissociation is the decomposi- tion of a substance and the reforming of the same by the union of the products, when the decomposing cause is re- moved. Likewise, ammonium chloride, heated, decom- poses into ammonia and hydrogen chloride, but when the SOLUTION AND IONIZATION 241 two gases are carried away from the source of heat they recombine to form ammonium chloride. Thus, NH 4 C1 * NII 3 + HC1. Again, iodine vapor, below 700 C. shows a density of about 127 compared to hydrogen or a molecular weight of 254, which indicates I 2 for the formula. Above 700 C. the density rapidly decreases and at about 1,700 it is only half what it was at 700. The same thing has occurred as in the case of the nitrogen peroxide and may be repre- sented thus, I 2 ?=> 21. Many others might be given. Such cases are spoken of as dissociation by heat. 10. Dissociation by Solution. As heat may be the means of dissociating substances, so it is believed liquids may be. When this occurs it is called dissociation ~by so- lution, or ionization. Because of the fact that dissocia- tion by solution permits of conductivity and the electroly- sis of the substance dissolved, it is often called electrolytic dissociation, but it must be remembered that electricity has nothing to do with the dissociation. Further, since in dissociation by this means the particles formed are able to be attracted to the electrodes of an electric cir- cuit", they are believed to be electrically charged; hence, an equation representing the results of the dissociation of potassium chloride in water would be thus, KC1 ? K + Cl, and of zinc sulphate, ZnS0 4 <= Zn + S0 4 . These electrically charged particles, whether atoms or groups of atoms, are called ions, from a Greek word 242 APPLIED CHEMISTRY meaning to travel. They were so named because of the fact of their constant movement from place to place, lonization would be, therefore, the dissociation of a sub- stance into ions. 11. Kind of Ions. Ions are either positive or negative according to whether they are attracted to the cathode or the anode in an electrolyte. As already indicated, hydro- gen, ammonium and the metals may form positive ions, called cations or cathions, because they are attracted by the cathode : the nonmetals, hydroxyl, and many oxygen radicals, like -S0 4 , form negative ions, called anions, at- tracted to the anode. Ions are also spoken of as simple Fig. 49. lonization of a solution of common salt, and proof of same. and complex. A simple ion consists of a single atom, elec- trically charged, while a complex ion contains more than one atom, that is an electrically charged radical, like -HO. It must be remembered that ions are not atoms. A solu- tion of potassium chloride abounds in chlorine ions, but it possesses none of the properties of free chlorine no color, no odor, no bleaching properties. The electric charge upon it, like an efficient rain coat not only pre- vents its "solution" in water, as it were, but also from doing the other things free chlorine would do. A very simple experiment shows the movement of the ions toward the electrodes in a solution. If salt water, colored with SOLUTION AND IONIZATION 243 litmus cubes, be put into the U-tube, as shown in Fig. 49, and the terminals of a battery be inserted, in a very short time the blue color at the anode will disappear. The chlorine ions have been attracted to this arm, and, coming* in contact with the positively charged carbon or platinum electrode, have lost the charge they held by having it neutralized. Now, they have become atoms of free chlorine. Immediately, they begin to bleach the litmus solution and decompose the water. Likewise, the odor of fre? chlorine becomes apparent as well as the color, if the process is continued long. If the salt water had been colored by a red litmus solution the anode arm would have been bleached as before while at the cathode the solution would have turned blue. The sodium ions move toward the cathode ; on meeting it they give up their positive charge to the electrode, become atoms of sodium, and immediately begin to decompose the water there. Thus, 2Na + H 2 - II, + 2NaIIO. The hydrogen escapes in bubbles as can easily be seen, and the hydroxyl ions of the sodium hydroxide change the red litmus to blue. This, as has been stated elsewhere, is characteristic of all soluble hydroxides. Phenolphthalein is a coal tar product, which by soluble hydroxides is turned a beautiful violet-red color. In the above exper- iment, if a few drops of an alcoholic solution of phenol- phthalein be added to the salt solution instead of coloring with litmus, the solution at the cathode quickly turns pink, when the current is passed, showing the formation of a hydroxide just as before. 12. Ions and Valence. It will be noticed that the + hydrogen ion was written above H while that of zinc + + was Zn. It will be found that the electric charge 244 APPLIED CHEMISTRY upon an ion is the same as the valence. In making hydrogen, experimentally, it was found that one atomic weight of sodium displaces one atomic weight of hydro- gen from water and that one of zinc displaces two of hydrogen from acids. From this it would be seen that the valence of sodium is one and that of zinc is two. The ions, therefore, would carry single and double + + -f charges, respectively, Na, Zn. 13. Chemical Action Ionic. It has been seen that a piece of zinc dropped into pure dry hydrogen chloride liquefied, shows no chemical action, but if water be added it becomes vigorous immediately. Likewise, zinc in concentrated sulphuric acid in making hydrogen gives very indifferent results. Ferrous sulphide in concen- trated sulphuric acid shows almost no chemical action at all. In both of the last cases the addition of water brings vigorous results. It is believed from these and a very large number of other experiments, all indicating the same thing, that chemical action takes place between ions. In terms of the kinetic theory the presence of the water results in the ionization of the compounds, and the ions, moving through the solution in all directions, meet each other and form new combinations. Thus, If these two solutions are poured together collisions between the potassium and silver ions are impossible, because being with like charge, as they approached each other repulsion would take place ; likewise, the chloride ion and nitrate ion. But collisions between potassium ions and nitrate ions, also between chloride and silver ions could occur and would, as well as those indicated SOLUTION AND IONIZATION 245 by the equations. But silver chloride is an insoluble compound, and hence could not ionize; therefore, as fast as silver chloride formed it would separate out from the solution. Ultimately, all the silver and chloride ions would have collided and been removed, at which time there would be solid silver chloride which would be in the form of a precipitate, potassium ions and nitrate ions, with some molecular potassium nitrate. 14. Other Types of Reactions. In the case just given one of the products is in the form of a precipitate and is thus removed from the sphere of action. The same is true if one of the products is a gas. Thus, if lime water is added to a solution of ammonium chloride, these steps would result, NH 4 C1 ? NH 4 + Cl, Ca(HO) 2 i= Ca + HO + HO, NH 4 + HO ^ NIIJIO, Ca + Cl + Cl ^ CaCL. Now if the solution is warmed as is done in preparing ammonia, the following results, NH 4 HO - NH 3 + H,0. Ammonia, being a gas, is constantly escaping, so that the ammonium hydroxide is being removed all the time. Therefore, the ammonium ions are being removed and the final result is calcium chloride in water ionized as shown by the equation, Ca + Cl + Cl<=CaCl 2 . This is typical of all cases in which one product is a gas. There are many others in which all the products are 246 APPLIED CHEMISTRY soluble in water. Thus, when potassium nitrate and sodium chloride are mixed in solution, KN0 3 2H 2 + 2S0 2 . If a cold dish be held against the flame, a deposit of sul- phur is formed. This shows that by the heat present the escaping hydrogen sulphide is dissociated to a greater or less extent, thus, 2H 2 S * 2H 2 + S 2 . It is a very poisonous gas, producing dizziness, uncon- sciousness, and ultimately death. However, as at least SULPHUR AND COMPOUNDS 255 1/2 of 1 per cent is necessary for fatal results, and as very much smaller proportions than this are distinctly notice- able on account of its very strong odor, serious results very rarely occur. It is said that very dilute chlorine, obtained by adding' hydrochloric acid to bleaching pow- der solution, is the best antidote. It must be remembered, however, that chlorine is more poisonous than hydrogen sulphide ; hence, when used as an antidote, great care must be exercised. Like carbon and carbon monoxide, hydrogen sulphide is a reducing agent. Hence, when bubbled through strong sulphuric acid, partial reduction of the acid results with the formation of sulphur dioxide, thus, H 2 S0 4 + H 2 S - S + S0 2 + 2H 2 0. Hydrogen sulphide, therefore, cannot be dried by this method. Brought into contact with sulphur dioxide, a similar reduction takes place with the precipitation of free sulphur, thus, 2H 2 S-f S0 2 - 2H 2 + 3S. This probably accounts in part at least for the deposits of sulphur in volcanic regions, as both the sulphide and oxide are produced by the action of heat upon compounds present in the earth. Dissolved in natural water, artesian or spring, hydro- gen sulphide is supposed to have therapeutic value, but this is very doubtful. In the laboratory, however, it is indispensable. It serves as the means of separating a large number of the metals into groups as the starting point of most chemical analyses. 8. Sulphur Dioxide. There are two oxides, sulphur dioxide and trioxide, but the former is the more com- mon. It is produced when either sulphur or hydrogen sulphide is burned in the air. In the laboratory it is 256 APPLIED CHEMISTRY generally prepared by treating copper turnings or bits of charcoal with concentrated sulphuric acid, heated cautiously but somewhat strongly. It might be sup- posed at first thought that copper added to sulphuric acid would cause an evolution of hydrogen as zinc did. It will be found, however, by referring to Fig. 14 on p. 65 that copper is less strongly electropositive than is hydrogen, hence could not displace the latter from an acid. Moreover, we have seen that concentrated sul- phuric as used in this case gives but few hydrogen ions, and as chemical changes are usually between ions, a re- action similar to that between zinc and dilute sulphuric acid could not be expected here. Thus with zinc we had Zn + H 2 SO 4 - H 2 + ZnS0 4 . Concentrated sulphuric acid, when heated, is an oxidiz- ing agent, that is, it gives Up a part of its oxygen; in other words, in the present case the copper serves as a reducing agent in its reaction with sulphuric acid. It is not possible to prove that a certan chemical reac- tion takes place by steps, still it is entirely possible that in this case as in many others, such is true. On the above supposition, the first step in the reaction would be shown by the equation, Cu + H 2 S0 4 -> CuO + H 2 + S0 2 . Then, secondly, CuO + H 2 S0 4 -> CuS0 4 + H 2 0. Adding the two equations gives the final result as it is known to be, Cu + 2H 2 S0 4 -> CuS0 4 + 2H 2 + S0 2 . 9. Characteristics of Sulphur Dioxide. Sulphur diox- ide is a colorless gas with a very suffocating odor. It is one of the easiest gases to liquefy; this may be ac- complished in any laboratory by surrounding a spiral SULPHUR AND COMPOUNDS 257 tube connected with the sulphur dioxide generator with a freezing mixture of ice and salt. The liquid may be kept sealed hermetically in glass tubes, as the pressure at ordinary temperatures is only about three and a half atmospheres. The liquid if pure is nearly colorless, like water, and boils at -8 C. The gas is soluble in water to the extent of about fifty volumes in one and forms the unstable sulphurous acid, H 2 S0 3 , It has a density compared to hydrogen of 32, hence is nearly two and a half times as heavy as air. Being an unsaturated compound, since the valence of sulphur is six, it has the power of taking up another atomic weight of oxygen for each molecule, and thus forms sulphur tri- oxide. 10. Uses of Sulphur Dioxide. Until comparatively re- cent years sulphur dioxide was used for disinfecting public buildings and homes in case of contagious dis- eases. The gas was secured by burning sulphur "can- dles" in the various rooms or where the ventilating fans would carry it to all parts of the building. As formalde- hyde is much more effective and more easily obtained it is largely supplanting sulphur dioxide for fumigating purposes. It is used extensively for bleaching various food products, as, for example, glucose syrups, already mentioned ; also, for freshly cut fruits in drying. The fruit is peeled, cored and sliced, by machine at a single operation, and the slices spread upon trays over a fur- nace in an evaporator. A teaspoonful of sulphur is put into a cup on top of the furnace each time a double tray of fruit is inserted. The sulphur burns, forming sulphur dioxide, and the gas flows up over the fruit. No brown discoloration occurs as would be the case in pure 258 APPLIED CHEMISTRY air, and in a very few minutes the fruit is dry upon the surface after which it remains perfectly white. In many localities in the West, fruits, especially peaches and apricots, are dried in the sun. To prevent attack by ants and other insects, the fruit after being cut is taken to a "sulphuring" room where it is exposed to sulphur dioxide fumes for a time. Sufficient is absorbed to protect the fruit in drying ; however, at the tempera- ture present, as the water evaporates, the sulphur diox- ide, except in minute traces, also disappears, so that no harmful results follow. The bleaching of English wal- nuts and almonds, possibly of some other nuts in Califor- nia, is a common practice. Lying upon the ground in the "hulls" as they may for some days before being gathered, the white shells become stained or mildewed, so that when finally shelled and dried they are of vary- ing shades of brown and gray. When taken to the packing houses, after being assorted into sizes, they are passed through a solution of bleaching powder to which dilute hydrochloric acid has been added, then carried by elevators to a "sulphuring" room, where they are exposed for some time to the fumes of sulphur dioxide. The result is a product with shells of a uniformly creamy-white color. They are thus rendered pleasing in appearance without detracting from the wholesome character of the nuts. Liquefied sulphur dioxide is now an article of com- merce and is used extensively for bleaching woolens, straws and silks. Naturally, these articles are all of varying shades of yellow and woven thus are unattrac- tive in appearance. Chlorine is destructive of all such and cannot be used. Sometimes hydrogen peroxide is employed, but it is not so satisfactory as sulphur di- oxide. What the chemical action is when bleaching is SULPHUR AND COMPOUNDS 259 done with this gas is uncertain. The other two bleaching agents already studied undoubtedly act by oxidation. As sulphur dioxide is an unsaturated compound it would presumably act by reduction of the colored compounds in the fabric to colorless. All such articles, on exposure to air and sunlight, again become yellow, caused possi- bly by their again taking up oxygen and returning to their first condition. Iceless refrigerators kept cold by the evaporation of liquid sulphur dioxide are now being installed in many homes. The principle is the same as already explained in the manufacture of ice. 11. Sulphur Trioxide. This oxide has little interest outside the fact that it is the anhydride of sulphuric acid. It will be taken up in connection with the prepara- tion of that acid. 12. Sulphurous Acid. As already stated this acid is formed when sulphur dioxide is passed into w r ater. It is unstable and of little importance. 13. Sulphuric Acid. Under the name, oil of vitriol, sulphuric acid has been known for centuries. It was formerly made, somewhat impure, by distilling ferrous sulphate, called green vitriol, which gave the name to the acid. At the present time two methods are used in its manufacture, the chamber and the contact process. The former is the older method, but the latter, where it may be applied is the cheaper. Both employ sulphur dioxide as the starting point. 14. The Chamber Process. By this method the sul- phur dioxide needed is usually obtained by roasting iron pyrite, FeS 2 , which reacts with the oxygen of the air thus, 4FeS 2 hll0 2 -> 8S0 2 + 2Fe 2 3 - The gas is passed into large chambers where it meets 260 APPLIED CHEMISTRY nitric acid vapors prepared by the action of sulphuric acid upon sodium nitrate, thus, 2NaN0 3 + H 2 S0 4 - 2HN0 3 + Na 2 S0 4 . The nitric acid and the sulphur dioxide react, with the formation of sulphur trioxide and one or more nitrogen oxides, 2HN0 3 + 3S0 2 -> 3S0 3 + H 2 + 2NO. Steam and currents of air are also introduced by which the sulphur trioxide forms sulphuric acid and the nitric oxide becomes peroxide, thus, H 2 + S0 3 - H 2 S0 4 , 2NO + 2 -> 2N0 2 . Only small quantities of nitric acid are needed, since it serves merely as a catalytic agent to transfer the oxy- gen from the air to the sulphur dioxide. However, as four-fifths of the air is nitrogen which has no use in this process, in removing it special plans must be adopted to prevent loss of the nitrogen oxides also. The es- caping gases are made to pass up through what is called the Gay-L/ussac tower, little more than a chimney with a lattice work of brick or tile, over which sulphuric acid slowly trickles. This acid has the power of com- bining with the nitrogen oxide present but not with the nitrogen, and forms what is called nitre acid or nitrosyl sulphuric acid. Thus, little of the nitric oxide is lost. The nitrosyl sulphuric is then pumped up to the top of another chimney known as the Glover tower and trickling down there meets the steam and fresh supplies of sulphur dioxide. The steam decomposes the niter acid forming sulphuric and sets free the nitric oxide which again com- bines with the oxygen of the air; hence the process be- comes continuous. The chambers where the acid is pro- SULPHUR AND COMPOUNDS 261 duced are lined with lead, since it is not attacked by di- lute sulphuric. When it reaches a strength at which it begins to react with the lead, it is removed and further concentrated in stills made of cast iron or platinum. (See Fig. 52.) 15. The Contact Process. This process uses platinum as the catalytic agent. It is found that sulphur dioxide and air, mixed and passed through a heated tube, do not react to any appreciable extent. If finely divided HUer Pot S Pyritet Burners Fig. 52. Chamber process for sulphuric acid. The escaping gases pass up the Gay-Lussac tower where they meet the streams of sulphuric acid. This combines with the nitrogen oxide present, forming the niter acid, so called. This is pumped to the top of the Glover tower, where, descending, it meets the steam, which decomposes it. The nitrogen oxide then begins its work all over again. platinum be present, however, the union is rapid. In preparing the catalyzer, asbestos is dipped into a solu- tion of platinum chloride and heated. The chlorine is expelled and the finely divided platinum is left adher- ing to the surface of the asbestos. When this is heated and the mixed air and sulphur dioxide passed through it, sulphur trioxide is formed, which though a solid, is vaporized by the heat present and passes out of the 262 APPLIED CHEMISTRY catalyzer into a receiver containing moderately dilute sulphuric acid, such as is obtained by the chamber proc- ess. This continues till the liquid becomes a white crystalline solid, known as fuming sulphuric acid, with the formula, H 2 S 2 7 , or H 2 S0 4 .S0 3 . This indicates it is sulphuric acid saturated with the anhydride, sulphur trioxide. It might be supposed that the sulphur triox- ide obtained by the contact process would be passed directly into water, rather than into dilute sulphuric acid. The reason that this is not done is that the reac- tion is so violent that the heat produced volatilizes con- siderable portions of the trioxide with much loss. 16. Characteristics of Sulphuric Acid. When pure, sulphuric acid is a colorless, oily liquid, with a specific gravity of 1.84. It boils at 330 C., but considerable portions are broken up into sulphur trioxide and water, thus, H 2 S0 4 * S0 3 + H 2 0. Sulphuric acid is strongly hygroscopic and exposed to the air rapidly increases in volume with corresponding dilution. When water is added, great heat is produced; hence, it is never safe to pour water into the concen- trated acid. The reverse order should always be fol- lowed. As already seen, this strong attraction for water is made use of in drying gases. When a pine splinter is dipped into concentrated sulphuric acid, it is charred, as is also a lump of sugar. From the former, being largely cellulose, C G H 10 5 the acid removes the hydrogen and oxygen as if it were water, leaving the carbon be- hind. The same is true of the sugar. In the diluted form sulphuric acid is largely ionized, hence is a good conductor of electricity, and with any metal more pos- itive than hydrogen readily reacts, giving off the hydro- gen. In concentrated form there are very few ions pres- SULPHUR AND COMPOUNDS 263 ent; it is then a very poor conductor and with such metals as zinc and iron its reaction is very slight. 17. Uses. This is the most extensively employed of all acids. It is used in the preparation of all other acids ; the method for hydrochloric and nitric AVC have already seen. It is used in the manufacture of explosives such as nitroglycerine and guncotton, for the preparation of fertilizers from native phosphate rocks, in refining oils derived from petroleum and in the preparation of coal tar dyes. 18. Thiosulphuric Acid. This acid has never been prepared but its salts are well known. It has the for- mula, H 2 S 2 0.5, which will be seen to be sulphuric with one of the atoms of oxygen replaced by one of sulphur. The first part of the word, thio, is from the Greek word for sulphur, and is given to this acid to indicate the fact of the substitution of the sulphur for the oxygen. One salt of this acid, sodium thiosulphate, is very important. It is sold under the name "hypo," formerly erroneously called hyposulphite of soda. It is used extensively in photography in "fixing" plates and prints so that they will not be further acted upon by the light. It is also used as an antichlor in the bleaching of textile fabrics to remove the last traces of the chlorine, so as to prevent its attacking the cloth. The fact that it was used during the later part of the war in gas masks has been mentioned elsewhere. Exercises for Review 1. Name three localities where sulphur is found very abundantly. In what condition is it and how situated? 2. Give the method of obtaining the supply used in the United States. P>. Name four varieties of sulphur and state how each may be obtained. 264 APPLIED CHEMISTRY 4. Give some important differences between the two crystalline varieties. 5. Give the chief physical characteristics of sulphur. How does the amorphous differ from the yellow? 6. What is an allotrope? What other substances have we met with in allotropic forms? 7. Give the chief chemical characteristics of sulphur. 8. Give some very important uses of sulphur. What is vulcan- ite? Uses. 9. Where is hydrogen sulphide found in nature? Give some of its properties. 10. Write the equation showing the combustion of hydrogen sul- phide. Why cannot it be dried by sulphuric acid as many gases are? 11. What is meant by reduction? When hydrogen sulphide and sulphur dioxide are mixed, which is reduced, which is oxidized? Is it possible to reduce one substance without oxidizing another. 12. Name the oxides of sulphur and give their formulas. 13. How is sulphur dioxide prepared in the laboratory? How for fumigating? Why is hydrogen not obtained from the sul- phuric acid by copper? 14. Give the chief properties of sulphur dioxide. 15. Name the most important uses of sulphur dioxide. 16. Name two other bleaching agents previously studied. For \hat are they used to bleach? 17. Give the names of two processes for making sulphuric acid. How did it come to be called "oil of vitriol"? 18. Describe briefly the chamber process and write the equations. 19. Describe briefly the contact process. What is the catalytic agent in each process? 20. Describe the sulphuric acid and give some important uses. 21. Why does a lump of sugar in concentrated sulphuric acid turn black? 22. What is the action of sulphuric acid in making nitrocellu- lose? 23. For what is hypo used? What is its chemical name? CHAPTER XXII PERIODIC CLASSIFICATION OF ELEMENTS Outline Comparison of Metals and Nonmetals Atomic Weight and Chemical Characteristics The Periodic Table Valence in the Table Relation of the Properties to Position in Table Group Characteristics Numerical Relations Characteristics of Compounds as Related to Position 1. Classification of the Elements. Heretofore we have spoken of the elements as metals and nonmetals. Most of the common metals are of considerable density and lustrous; but sodium and potassium are both so light as to float on water, yet are decidedly metallic in char- acteristics. Arsenic has a bright, metallic luster, yet can hardly be called a true metal. We have spoken of the metals as forming electropositive ions and the non- metals, electronegative: in a general way this is true, yet many of the metals are found in complex electronegative ions. Aluminum and tin are both metals, yet well known salts exist in which with oxygen these metals constitute the negative ion. Likewise some nonmetals may form positive ions. The metals have been spoken of as form- ing basic oxides and the nonmetals as anhydrides. Gen- erally speaking, this is true. However, zinc hydroxide, Zn(HO) 2 , and aluminum hydroxide, A1(HO) 3 , are both soluble in sodium hydroxide, which indicates that the two bases must have ionized as if they were acids, thus, 265 266 APPLIED CHEMISTRY H 2 Zn0 2 * HH + Zn0 2 , H 3 A10 3 ^ HHH + A10 3 . This must be true for the salts formed are Na 2 Zn0 2 and Na 3 A10 3 , sodium zincate and sodium aluminate. It is seen, therefore, that there are many exceptions to the general statements regarding the two divisions of ele- ments hitherto used, such that this method of classifi- cation is far from satisfactory. 2. Classification by Atomic Weights. For long years there have been chemists who believed that the charac- teristics of an element bore some close relation to and are dependent upon its atomic weight. Various attempts were made to show this, but too many facts were un- known for any marked success. It remained for a great Russian chemist who died in 1907, to prepare what is known as the "Periodic Table" and to present the "Periodic System" in such a way as to cause its ac- ceptance by chemists at large. Starting with the idea that the properties of an element are a function of the atomic weight, Mendeleeff arranged the elements in the order of their atomic weights, beginning with the light- est, but omitting hydrogen. In this way he had lithium, glucinum, boron, carbon, nitrogen, oxygen, fluorine, sodium, magnesium, aluminum, silicon, phosphorus, sul- phur, chlorine, potassium, calcium, and so on. By in- specting this arrangement he discovered that leaving lithium, there is no other element similar to it until sodium is reached in the eighth space beyond, and then potassium another octave beyond the sodium. Starting with fluorine, no other element is met similar to it until chlorine is reached, the eighth beyond. Observing this fact in many instances, he next attempted to arrange the elements known to him into octaves, putting like elements PERIODIC CLASSIFICATION OF ELEMENTS 267 under each other. To make the elements known at that time agree with his theory, he was compelled to leave many spaces in the table he prepared blank. But in doing so he predicted these spaces would be filled in the years to come ; what is more, he even foretold the general prop- erties these unknown elements would possess, their ap- proximate atomic weights, and, in some instances, actually suggested names for them. Most of his predictions have since that time been fulfilled, although the names he sug- gested have not been accepted. The latest form of the ta- ble, with some omissions as noted, as well as of some" very rare elements whose position as yet is not deter- mined, is given on page 268. Only a very brief study of the table is possible at this time, but some knowledge of it is necessary and will be found very helpful to the student. Let it be remembered that the basis of arrangement is the atomic weights of the elements. 3. Valence in the Table. The vertical divisions in the table are called Groups and the horizontal divisions, Pe- riods. By looking at the top of each group, beginning with lithium, it will be seen that the valence increases from one up to seven. This is true for each period, with few exceptions which will be noticed. It is based upon the oxides which the elements form. For example, taking the second period, the respective oxides have the formu- las, Na 2 0, MgO, A1 2 3 , SiO 2 , P 2 5 , S0 3 , CL0 7 . The next period, if the oxides are taken, shows the same va- lence, and so on through the table. If the hydrogen com- pounds are considered after the carbon group is passed, in which the valence is four, the apparent value decreases by one at each group. Thus, we have the formulas for the four compounds, marsh gas, ammonia, water and hy- drogen chloride, H 4 C, H 8 N, H 2 ? HC1. The following 268 APPLIED CHEMISTRY LO oq^ 01 ' w a, - s, w |s? 2, SONSIVA PnO JO d ^l 1 l^l cTaf (M rt -M fc aT QJiLVallJjVb ill T iq ^pM 9 = 3QN31VA (M ^ i H 00 00 CO 2 = ^2 cT o S ^ ID" . S ..JO oaivanjvs ji Tt< rH 10 oT <^ o T ^ 3 9 nvA 0) 02 o CO "1 M ^JH l rH ^1 t- \X"^ 3 *'% co TJH TjJ (O S 'is - j 525 w 05 a C U2 " S 2 S saNnojptoo ON >0 "S bC-2 = 30N31VA o rtl (M OS as CO o CO rH (M jsl^l aT aT CO s-T r- r. ^5 ^ M M ^ 55 g PERIODIC CLASSIFICATION OF ELEMENTS 269 periods show like valence with the hydrogen compounds. When M'endeleeff first prepared the table no element of the first column had been discovered and he made no plans for any such group. But strange to say, and won- derfully strengthening the probable truth underlying his plan, when the argon group was discovered one by one, with a slight exception to be noted, they all fitted into the general plan and no changes had to be made. Singu- larly, too, their valence is zero, that is they have no power of combining with other elements and as far as discovered form no compounds whatever. The slight exception to be noted is that argon as thus far prepared is slightly heavier than potassium, whereas it should be lighter. The probable explanation is that the argon thus far obtained is not pure but contains small quantities of one or more of the heavier gases belonging to the same group. It will be remembered that for years this was found true of the nitrogen obtained from the air ; and the fact of its un- seeming density when thus prepared led to the discovery of argon. One other exception which might be mentioned here is that iodine is slightly lighter than tellurium, whereas the reverse should be true. It is generally be- lieved that the weight of the iodine will sometimes be found to be slightly incorrect. Constant efforts are be- ing made to ascertain whether this may not be true. 4. Position of the Elements and Properties. It will be found that as we go from left to right in the table, omitting always the argon group, the elements become less and less electropositive and passing the carbon group, become more and more negative. Thus, sodium is very strongly positive while chlorine is equally strongly negative. Sodium forms a very strong base, chlorine a very strong acid. Taking the right hand end of the table it will be found, as we go down the 270 APPLIED CHEMISTRY group, that with the increasing weight the elements become less and less acidic in properties and begin to have some of the physical properties of the metals. Thus, in the halogen group, iodine is solid in form and has a luster, closely resembling that of most metals. In the nitrogen family the lightest one is a gas, phosphorus is a waxy solid, arsenic a brittle solid, but lustrous, antimony decidedly metallic in appearance but with some chemical properties of an acidic element, while bis- muth, the heaviest, is a metal both in appearance and behavior. Hence, instead of dividing the table into positive and negative elements by a vertical line near the center, it must be done by an irregular, or zigzag diagonal, starting at the left of boron, leaving it above and aluminum below the line, and so on through, leaving iodine above. Divided in this way the elements above the line generally speaking are electronegative or acid forming elements, while those below are positive or base forming elements. However, it must be further noted, that the elements near the irregular diagonal usually partake of a dual character and form both acids and bases, though weak ones. Thus aluminum, arsenic, an- timony, tin and others less familiar to the student all serve both as acid- and base-forming elements at dif- ferent times. 5. Group Characteristics. Taking any particular group for study it is found that all the members possess the same general characteristics and form similar com- pounds. We have thus noticed two members of the sodium group. Both are silvery white metals, light enough to float on water, decompose it readily even in the cold, are strongly caustic and form strong hydrox- ides. Taking the chlorine group, it is found that they resemble each other equally strongly. SQ ^ it is foun4 PERIODIC CLASSIFICATION OF ELEMENTS 271 largely true throughout. Most strikingly is this ob- served in the chemical behavior and in the compounds formed. Thus, the sodium group forms no ordinary compounds of hydrogen for the reason that they are all strongly positive as is hydrogen also, but they do form oxides of the type, Na 2 0. The halogens form acids after the type, HC1. The sulphur group forms com- pounds with hydrogen seen in the formulas, H 2 0, H 2 S, H 2 Se, H 2 Te and with the oxides whose formulas are S0 3 , Se0 3 , Te0 3 . The nitrogen family forms hydrogen com- pounds shown in the formulas, NH 3 , PH 3 , AsH 3 , SbH 3 and oxide compounds in N 2 5 , P 2 5 , As 2 5 , Sb 2 r> , Bi 2 5 . Hence, having learned the characteristics and com- pounds of one member of a group, we may know, in a measure that the same things are true of other members of the same group. 6. Numerical Relations. It was stated that Mende- leeff predicted with approximate accuracy the atomic weights of the unknown elements. By observation it will be seen that the atomic weight of any element is roughly speaking the arithmetic mean of those of the two adjacent elements. To illustrate: Sodium, weight 23, is one-half the sum of 7 and 39, the weights of lithium and potassium; scandium, weight 44, is half the weight of calcium and titanium, 40 and 48. Thus it is all through the table, although not always as exact as in these two cases ; but the variation is not great. 7. Characteristics of Compounds Formed. In a gen- eral way the character of the compounds may be known someAvhat from the position of the elements forming them. Thus, nearby elements, possessing similar char- acteristics would not be expected to unite to form com- pounds at all. In the case of the metals, most of the unions formed are not true compounds. With the non- 272 APPLIED CHEMISTRY metals, such as nitrogen and oxygen, nitrogen and chlo- rine, and others, when such do form compounds it is usu- ally through indirect processes by which the two ele- ments are left together and such compounds are very un- stable. The oxides of nitrogen already studied, are all more or less unstable; further, it has been noted that practically all the explosives are compounds of nitro- gen and oxygen and owe their explosive properties to the instability of such compounds. Chlorine and oxygen form oxides, indirectly, but they are dangerously explo- sive, as are also those of nitrogen and chlorine. On the other hand, elements distantly located in the table form very stable compounds. Thus, sodium and chlorine, or calcium and fluorine, unite readily and directly and form relatively very stable compounds. Such are a few of the more important facts regarding the periodic table. From this time forward the various elements studied will be taken up in accordance with the "Periodic System" or arrangement, as shown in the table. Exercises for Review 1. What two divisions of the elements have been used thus far? Give some of the general characteristics of each division. 2. What objection is offered to this as a scientific method of classification? 3. What is the basis of arrangement in Mendeleeff 's table? How did he come to discover the recurrence of properties? 4. What arrangement was made of the elements after the recur- rence of properties was observed? 5. What is a group in the table? A period? 6. State what is observed regarding valence in the table, using both the oxygen and the hydrogen compounds. What is the valence of the argon family? What is meant by that statement? 7. State what is observed in passing from left to right in a period. 8. What is true in each group at the right side of the table as the \veight increases? PERIODIC CLASSIFICATION OF ELEMENTS 273 9. Where does the dividing line come in the table? Give the general characteristics of the elements on either side of the line. 10. What may be said of the elements close to the diagonal on either side? Illustrate. 11. What is true of the general characteristics of the elements ir. any particular group? Illustrate by taking some family as that of sulphur or chlorine. 12. What numerical relation exists among the elements? Take the entire first period and show this. 13. What would be the approximate weight of the unknown ele- ment belonging in the space below cesium, in the sodium family? At the right of radium? At the right of molybdenum? 14. What is generally true of compounds formed from elements near each other in the table? Illustrate. 15. What is true of compounds formed from distantly placed elements? Illustrate. 16. Why should arsenic be expected to have both basic and acidic properties? Which would be the more pronounced? 17. Would you expect to find zinc with any acidic tendencies? If so, how would they compare with those of aluminum? 18. Noting the fact that hydrogen and bromine are close to the diagonal, what would you expect to be true of the stability of hy- drogen bromide as compared with hydrogen chloride? What of hydrogen iodide? What does our work in bromine show? 19. Ought chlorine to displace bromine from a compound or the reverse? How about chlorine and iodine? CHAPTER XXIII THE NITROGEN FAMILY Outline Members of the Group Phosphorus (n) Occurrence (fe) Preparation (c) Forms of (tZ) Characteristics ( e) Uses Poisons Matches (/) Hydrogen Compound (g) Oxides (7i) Phosphates (i) Fertilizers Arsenic (a) Occurrence (1)} Characteristics (c) Uses ((7) Arsine (e} Tests for (/) Oxides of (g} Antidote for Poisoning (ft) Pigments Antimony (a) Characteristics (ft) Uses (c) Stibine (d) The Sulphide (e) Tartar Emetic P.ismuth (a) Characteristics (&) Uses (c) The Nitrates Tabular Comparison of Compounds 274 THE NITROGEN FAMILY 275 1. Members of the Family. Nitrogen, the lightest, has already been studied in connection with the atmos- phere. The other members are phosphorus, arsenic, an- timony and bismuth. These four are all solids, and the last three, while not strikingly alike in some of their physical properties when untarnished, closely resemble each other in their bright metallic luster and crystal- line appearance ; but it is in the compounds formed and the chemical behavior in which they agree most closely. 2. Phosphorus. Phosphorus was discovered as long ago as 1669. About a century later, 1771, Scheele pre- pared it from bone-ash, a plan which has been followed nearly ever since. The word phosphorus means liglit- licarer, and was given to the element because of the fact that it glows in the dark when exposed to the air. In the form of a phosphate rock, calcium phosphate, it oc- curs abundantly in some of the Southern States, es- pecially Florida, South Carolina and Tennessee. It is found in small quantities in the nerve centers and muscles of the body, but more largely in the bones, of which, as calcium phosphate, it constitutes about three-fifths in weight. In the average human body it is said that there are about 3 pounds of phosphorus, nine-tenths of which is in the bones and most of the remainder in the muscles. 3. Preparation of Phosphorus. Up to recent years the bones of cattle, obtained from the packing houses, from which the gelatine and oil had been extracted, were charred to form bone charcoal. When this was no longer valuable for refining sugar, it was burned to a white ash in the air and from this calcium phosphate the phosphorus was distilled. At the present time, native phosphate rock, supposedly the fossil remains of birds, is mainly employed. With the crushed rock are mixed sand and coke or charcoal, the mixture is fed into an 276 APPLIED CHEMISTRY electric furnace by a worm drive below the hopper, as shown in Fig. 53. When strongly heated the carbon re- moves a portion of the oxygen, while the sand forms a slag with the calcium and is drawn off at the bottom. The phosphorus, thus set free, distils out in the form of vapor, is condensed under water, and molded into small sticks. 4. Forms of Phosphorus. Similar to several other ele- ments already studied, especially, oxygen, carbon and sulphur, phosphorus occurs in two distinct varieties. Fig. 53. Manufacture of phosphorus. Prepared, as described above, it is known as yellow phosphorus; if this be heated to a temperature of 250 C. out of contact with the air red phosphorus is obtained. 5. Physical Characteristics. Yellow phosphorus, when freshly prepared or when first opened from a "tin" container which has excluded all light, is of a very pale- amber color, so nearly colorless, that it is sometimes called white phosphorus. It is of waxy appearance when cut. On exposure to light it deepens in color, owing to the formation of a coating of the red variety. The yellow is soluble in carbon disulphide, and taken internally is THE NITROGEN FAMILY 277 very poisonous. The vapors, continually inhaled, are also poisonous, and produce a disease of the jaw bones, known locally as "phossy jaw," which may be relieved only by surgical operation and generally is incurable. The molecular weight of phosphorus vapor is 128, which indicates four atoms to the molecule, formula P 4 . Red phosphorus is a dark reddish-brown powder, not soluble in carbon disulphide. It is not poisonous and need not be kept in water as must the yellow. If vaporized at a temperaure of 300 it changes to the yellow variety ; that is, the vapor from both the red and yellow varieties is the same and upon being condensed forms the unstable va- riety. 6. Chemical Properties. YelloAv phosphorus, exposed to air, glows in the dark ; in contact with chlorine it catches fire instantly; with liquid bromine, and after a few seconds with iodine, it does the same. If ignited, both varieties burn in oxygen with great brilliance. It is singular, however, that in a jar of oxygen, phosphorus does not glow at ordinary temperatures. If a solution of phosphorus in carbon disulphide be put upon two strips of blotting paper and inserted, one into a bottle of oxygen and the other into one of air, the latter will ignite as soon as the solvent has evaporated. The other remains unaffected unless the bottle be opened to the air when ignition takes place only after from one to three minutes have elapsed. 7. Uses. Yellow phosphorus in small quantities is used in poisons for rats, mice and similar vermin. Most of it, however, is employed in the manufacture of matches. The original sulphur match was made by dip- ping pine splints into molten sulphur, and then adding a mixture of phosphorus in glue. Friction exposed the phosphorus and ignited it, whereupon, the sulphur, of 278 APPLIED CHEMISTRY low kindling point, caught fire and in turn the pine splint. Such matches, while, vastly better than none or those that had preceded them, burn slowly and form considerable sulphur dioxide. On this account they fell into disfavor. To increase the speed of combustion some oxidizing material, like potassium chlorate or ni- trate was added; instead of sulphur, the splints were dipped into melted paraffin for kindling. This gave a rapid match and a serviceable one, but dangerous. The mixture upon the head was too easily ignited; many fires were caused by the ordinary friction incident to their transportation. Moreover, owing to the amount of yellow phosphorus in their composition, not only were the workmen in the factories constantly subjected to the fumes, but children were often poisoned by them. These facts led to adverse legislation and in many states such matches were forbidden; then came matches of the "Birdseye" type, which contained phosphorus only in the tip of the head and which could not be ignited by friction on the sides. These did away with most of the fires, but not with the poisonous properties. Fi- nally, the United States government by levying a direct tax of 2 cents per hundred matches legislated them out of existence. At present, ordinary matches are made by dipping the splints into melted paraffin for kindling, then into a mixture of some compound of phosphorus and some oxidizing material, as potassium chlorate, with dex- trin or glue as the adhesive. The friction produced by "striking" the match is sufficient to decompose the phos- phorus compound, ignite the phosphorus and then the kindling. The phosphorus compound used is not poi- sonous. 8. Safety Matches. In this variety of match red phos- phorus and antimony trisulphide mixed together are put THE NITROGEN FAMILY 279 upon the box by means of a little glue : upon the splint is the paraffin for kindling, and antimony trisulphide with some oxidizing compound. Friction upon the pre- pared surface of the box vaporizes a small portion of the red phosphorus, the vapor is ignited and sets fire to the combustible material upon the splint. Such matches may be ignited upon other surfaces, not thus prepared, but a long stroke, with much friction is needed to produce sufficient heat to ignite the antimony compound which is combustible. Fig. 54. Preparation of phosphine. 9. Phosphine. This compound is a gas made by the reaction of a solution of either sodium or potassium hy- droxide upon yelloAv phosphorus. It is of interest be- cause of the fact that as thus obtained it ignites spon- taneously on exposure to the air. The following equa- tion shows the chemical reaction, P 4 + 3NaHO + 3H 2 - 3NaHP0 2 + PH 3 . The reaction takes place at the boiling temperature, only slowly at room temperatures; the spontaneous ig- 280 APPLIED CHEMISTRY nition is said to be due to the presence of a minute quan- tity of a liquid hydrogen phosphide, P 2 H 4 . If the gas be collected over water and allowed to stand thus for several hours, the liquid, P 2 H 4 , is dissolved and the gas does not ignite spontaneously. Apparatus such as was used for making hydrogen, may be used, except that the thistle tube should have substituted for it a piece of ordinary glass tubing bent at the upper end as shown in Fig. 54. This must reach to the bot- tom of the flask. Before applying heat the air must be removed; this is most easily done by attaching the gas supply to the bent tube and running the gas through for two or three minutes. The same should be repeated at the close of the experiment, otherwise as the air en- ters to take the place left by the contracting gas as it cools, it will cause an explosion. As the bubbles of phos- phine come to the surface of the water in the trough they ignite spontaneously and in still air rings of white "smoke" float upward. The gas has no practical uses. 10. The Oxides. Phosphorus forms two common ox- ides, the trioxide and pentoxide, P 2 3 , and P 2 5 , both produced by burning of phosphorus in the air. When the supply is plentiful, the higher oxide is obtained; when limited, the trioxide. They are both white solids and are the anhydrides of acids. Thus, P 2 3 + 3H 2 0-2H 8 P0 8 , P 2 5 + H 2 - 2HP0 3 . The latter is very vigorous in chemical action such that when the oxide is dropped into water a hissing sound like that of a hot iron touching the water is heard. The acid produced is known as meta- or glacial phosphoric .acid and corresponds to nitric acid, HN0 3 . If the pen- THE NITROGEN FAMILY 281 toxide is put into boiling 1 hot water the reaction is dif- ferent, thus, 3H 2 + PA -> 2H 3 P0 4 . This is known as orthophosphoric acid. Upon heating, it loses water and changes into the metaphosphoric. 11. Phosphates. Salts of orthophosphoric acid are called phosphates. The most common are those of so- dium, potassium and calcium. These are found in most soils in sufficient quantities for plant growth, but suc- cessive cropping, especially by various grains such as wheat or corn, remove them to such an extent that they must be replaced by fertilizers. The human body re- quires phosphates for the bones, muscles and nerve cen- ters. This is obtained mainly through the cereal foods, although eggs, beans and peas also contain it. 12. Fertilizers. The three things most needed for plants to insure vigorous growth and production of fruit or seed are nitrogen, phosphorus and potash. Means of procuring the nitrogen have already been studied. Two important sources of phosphates are the native rock already mentioned and bone products from the packing houses. Neither of these compounds is soluble in water and hence unavailable for plant food. However, if treated with sulphuric acid, they are converted into an acid phosphate, CaII 4 (P0 4 ),, which is soluble in water and therefore suitable as a fertilizer. The reaction is shown thus, Ca 3 (P0 4 ), + 2H 2 S0 4 - 2CaS0 4 + CaH 4 (P0 4 ) 2 Phosphorus-bearing iron ores are also a source of a con- siderable amount of the same acid phosphate, commercially known as the "superphosphate." It is said that in soils containing much humus the acids formed by the decom- position of the organic matter slowly convert native 282 APPLIED CHEMISTRY phosphate into the superphosphate and thus make it available. 13. Arsenic. This element, third in density in the ni- trogen family, occurs in nature in arsenical iron pyrite (FeAs)S; also as realgar and orpiment, both sulphides of arsenic. The . first named is the usual source of the commercial supply. 14. Characteristics. Arsenic as obtained from the py- rite is of a dark gray color, and as usually seen, not lustrous. Upon heating in an open dish the dull coat- ing disappears, leaving the element in its natural lus- trous, steel-gray color. It vaporizes upon heating without melting, at a temperature of 180 C. The molecular weight of the vapor is 300 which is four times the atomic weight. This shows that the formula for the molecule, like that of phosphorus, is As 4 . Powdered arsenic sifted into a jar of chlorine ignites spontaneously and burns as it falls; on bromine, it combines likewise with vigor. In the air it burns with a purplish white light and forms heavy white fumes of the trioxide, As 2 3 . 15. Uses. There are few uses for the element. In the manufacture of shot from lead about 1 per cent of arsenic is added. The main reason for this is that the mixture of lead and arsenic is when molten much more limpid or mobile than pure lead. As a result, in pour- ing, the liquid is broken up the more easily and the shot are much more perfect. They are at the same time a shade harder than they would be otherwise. As the melting point of the mixture is lower than that of lead alone, solidification does not take place so rapidly, which gives the shot more time in assuming perfect spherical form. 16. Arsine. As nitrogen and phosphorus form hydro- gen compounds so does arsenic, with a formula corre- THE NITROGEN FAMILY 283 spending to that of ammonia and phosphine. It is visu- ally prepared by adding 1 to a hydrogen generator a so- lution of arsenic. It is usually not collected, but burned as generated. The equations show the chemical reac- tions taking place, Zn + ILS0 4 -> ZnS0 4 + 2II, AsCl 3 + 611 -> AsH 3 In the equation it may be noticed that the hydrogen was not written IL, as has been done in previous cases, when it has been collected in the molecular condition. In Fig. 55. Marsh's test for arsenic. the present instance it reacts with the arsenic as fast as it is set free from the acid and is said to be in the nascent condition. The term means being set free. In such condition it is much more active than in the molec- ular form. Some chemists offer a different explanation for the greater activity but the term is commonly used and should be understood. The arsine obtained thus always contains an admixture of hydrogen, but this does not in- terfere with the study of it. 17. Characteristics. Arsine is a colorless gas with a somewhat offensive and nauseating odor. It may be 284 APPLIED CHEMISTRY liquefied at -40 C. It is exceedingly poisonous, so that small quantities inhaled may result fatally. It is easily decomposed by heat as shown by the equation, 4AsH 3 -H> As 4 + 6H 2 . This is easily shown experimentally. If a hard glass tube is attached to the arsine generator and a Bunsen flame is placed beneath the tube, the arsine is decom- posed; and at a short distance beyond the heated portion a black ring of the arsenic appears, while the hydrogen escapes from the tube and may be burned. The plan is simplified oftentimes, as shown in Fig. 55, by holding a cold dish against a small arsine flame. Brownish black spots with metallic luster appear upon the dish. The explanation is the same as before; the vapor of ar- senic obtained by the dissociation of the arsine is con- densed in solid form upon the cold dish. This is usually spoken of as Marsh's test for arsenic, and is exceedingly delicate. The merest traces may be detected in this manner. The reaction when the arsine is burning freely in the air is, 2AsH 3 + 30 2 - 3H 2 + As 2 3 . The white fumes appearing are the trioxide of arsenic. When a cold dish is held in the flame, this equation shows what is happening, 4AsH 3 + 30 2 - 6H 2 + As 4 . The hydrogen continues to burn, but the arsenic vapors are condensed in solid form. In making this test precau- tion must be taken not to light the escaping gas until all the air is removed from the flask. A serious explosion is apt to result if this is not done. 18. The Oxides. There are two oxides of arsenic, the trioxide, As 2 3 , and the pentoxide, As 2 5 . The first is THE NITROGEN FAMILY 285 much the more common. In commerce it is sold under three other names : arsenious acid, a misnomer, for it is merely the anhydride of arsenious acid, "white arsenic," and "arsenic." 19. Characteristics of the Trioxide. Usually it is ob- tained as a white powder, although occasionally as a colorless, glass-like solid. Like iodine, carbon dioxide snow, and elementary arsenic it vaporizes without melt- ing. It is slightly soluble in water and forms the corre- sponding acid, thus, As 2 3 + 3H 2 -> 2H 3 As0 3 . Taken internally it is a poison, but because of the fact that it is not very soluble it acts slowly. It is used very commonly as a poison for vermin and in large quantities in spraying apple trees to destroy coddling moth. For this purpose it is usually combined with lead acetate to form lead arsenite. This compound is the most desirable because on account of insolubility it is not washed away readily by rains and for the same rea- son does not "burn" the foliage. Arsenic trioxide is used to some extent in preserving skins in taxidermy and to a limited degree in medicine, especially Fowler's solution, a solution of the trioxide in potassium hy- droxide. 20. Antidotes for Arsenic Poisoning. The antidote most generally recommended for arsenic poisoning is freshly prepared ferric hydroxide. It is quickly made by putting together ferric chloride solution and ammo- nia water, taking care that the ammonia be not present in great excess. A heavy, brownish, flocculent precip- itate of ferric hydroxide is formed and this, filtered out, is used in a glass of water. The ferric hydroxide combines with the arsenic forming an insoluble com- 286 APPLIED CHEMISTRY pound which as a result cannot be absorbed by the sys- tem. An emetic or stomach pump should follow the antidote. Another sometimes used, which is easier to obtain but slower in action, is magnesium oxide, com- monly sold as magnesia. Its chemical action is the same as the ferric hydroxide. 21. Paris Green. This is rather a complicated com- pound as shown by the formula, Cu(C 2 H 3 2 ) 2 + CuHAsOg. It will be seen that it consists of copper ace- tate and acid copper arsenite, combined. Scheele's green is acid copper arsenite, CuHAs0 3 . Both com- pounds are bright green pigments and formerly were used extensively in coloring wall papers. Through the probable action of the decomposing paste upon the ar- senic compound, volatile compounds were produced which are very poisonous and serious results often fol- lowed. Coal tar dyes have now entirely supplanted these pigments for wall papers. Paris green is abundantly used in spraying or dusting potato plants to kill the Col- orado beetle. For small patches the powder mixed with flour or air-slaked lime is dusted upon the plants when wet with dew by means of a " shaker," homemade from a baking powder or similar can, by perforating the top with numerous holes. On a large scale the Paris green is usually mixed in water and sprayed on by pumps. 22. Characteristics of Antimony. In the nitrogen family antimony follows arsenic in density with an atomic weight of 120.2. It is a highly-crystallized, lust- rous, steel-white metal. Like arsenic it is very brittle, but does not tarnish as readily in the air. It has a melting point of about 445 and upon solidifying it ex- pands greatly. It combines readily with chlorine and bromine, and heated in the air, burns to antimony triox- ide. THE NITROGEN FAMILY 287 23. Uses of. In the form of antimony black, a very finely powdered or precipitated antimony, it is often used upon plaster casts to give them a metallic appearance. Its chief use is in alloys. By an alloy is meant an intimate mixture of two or more metals, melted together. They are generally really solutions, although some few are known which seem to partake somewhat of the nature of a compound. The more important alloys of antimony are brittania,. pewter, babbitt, stereotype and type metal. The first two are alloys of copper, tin and antimony and are used mainly because they do not tarnish greatly in the air. Babbitt is used for bearings in machinery, as for example those of the crank shaft in motor cars, to reduce friction. Type metal consists of antimony, tin and lead and is of the utmost importance. The antimony causes the expansion of the type metal when it solidifies and thus gives sharp outlines to all the finest details. Made of lead alone, which contracts upon cooling, type would give prints entirely illegible. The purpose of anti- mony in stereotypes is the same. 24. Stibine. Antimony forms the hydride, SbII 3 , cor- responding to those of the members of this family al- ready studied. It may be prepared as was arsine. It may be liquefied at -18 C. It is even more easily dis- sociated by heat than is arsine and gives the same spots upon a porcelain dish as does the arsenic, although they are black rather than brown, more soft and velvety in appearance. If heat be applied, since arsenic is vola- tile, spots made by arsine will disappear, while the anti- mony will not. Further, a solution of bleaching powder will dissolve the arsenic spots and leave the antimony unaffected. 25. Antimony Trichloride, SbCl 3 . This compound may be made by dissolving antimony in aqua regia. 288 APPLIED CHEMISTRY It is sometimes called butter of antimony, because of the fact if not concentrated to the point of crystallization, it is an oily, yellow liquid, resembling melted butter. In the solid form it is white and crystalline. If water is added, partial solution takes place with the precipitation of a white compound having the formula, SbOCl, anti- mony oxychloride. The reaction is SbCl s + H 2 ? SbOCl + 2HC1. By cautiously adding hydrochloric acid and stirring, the reaction is entirely reversed ; upon adding more water the white precipitate again appears. It is an interesting case because it is one of the few in which reversibility is easily seen. 26. Antimony Trisulphide, Sb,S 3 . Found in nature this compound is steel-gray, about the color of lead. Prepared in the laboratory by passing a current of hy- drogen sulphide through a solution of some antimony compound, it is a beautiful orange colored precipitate which turns dark if melted. It is used extensively in the preparation of matches as previously stated. 27. Tartar Emetic, KSbOC 4 H 4 6 . From the formula this compound is seen to be basic antimony potassium tartrate. It is one of the few basic salts we have seen. It is a white solid and unlike the chloride is completely soluble in water. It is used somewhat in medicine as an emetic, but like all antimony compounds is very poison- ous. 28. Characteristics of Bismuth. Bismuth resembles antimony in general appearance in that it is highly crys- talline in structure, but its color is darker and of a pur- plish or golden luster. It is very brittle, much heavier than antimony with an atomic weight of 208. It melts at about 270 C. With chlorine and bromine its behavior THE NITROGEN FAMILY 289 is about the same as that of antimony. Upon solidify- ing the metal expands greatly. 29. Uses. While it is eminently suited for type metal on account of its expansibility, being much more ex- pensive, it is rarely thus used, except in delicate stereo- types. One of its most important uses is in making alloys of low fusing point. Some of them are very re- markable in this respect. Thus : ALLOY BISMUTH LEAD TIN CADMIUM MELT. PT. Wood's Metal Rose 's Metal 4 parts (270) 82 parts 2 (825) 9 parts 1 (232) 9 parts 1 (820) none 60.5C. 94C. It will be seen that both these alloys melt below the temperature of boiling water, one of them much below. Thus, spoons cast of the former, if placed in a cup of hot tea or coffee would be melted and drop to the bottom. They are interesting illustrations of the fact brought out that solutions have their freezing point lowered. In these alloys bismuth may be regarded as the solvent with a freezing point of 270 C. for freezing point and melting point are the same. When the other metals are dissolved in this, the freezing point is lowered, in one case to 94 and" in the other to about 60 C. This low melting property of bismuth alloys enables it to be em- ployed in a variety of interesting ways. Most city or- dinances require that the lanterns for moving picture shows be enclosed in a metal or fire-proof booth. The openings are provided with shutters held open by a chain one link of which is made of an easily fusible al- loy. In case of the film taking fire this link is easily melted, the shutter closes automatically and the fire is kept within the booth. Metal fire doors, between dif- ferent apartments in large manufacturing establish- ments, are often held open during the day by fusible 290 APPLIED CHEMISTRY metal devices. In case of fire, the metal melts and the door is closed by the ordinary air spring attached. Au- tomatic sprinkling systems in large department and wholesale houses employ the same principle. Plugs in the pipes occur at intervals; if fire occurs they are melted and the water is turned on automatically. Steam boilers are likewise often provided with fusible plugs, such as to melt out and allow the escape of the steam before the danger point is reached. 30. Compounds. Not many of these are of sufficient importance to need attention here. The nitrate, Bi(N0 3 ) 3 , is a white crystalline solid, prepared by treat- ing bismuth with nitric acid. The reaction is thus shown, Bi + 4HN0 3 - Bi(NO s ) 3 + 2H 2 + NO. When water is added a white precipitate forms of the basic or oxynitrate, Bi(NO s ) 3 + H 2 *= BiON0 3 + 2HN0 3 . Tested with litmus paper the solution is found to be acidic as is true also when antimony chloride is dis- solved in water. The reaction is also equally reversible, as may be shown by the cautious addition of nitric acid. This white precipitate is sold under the name "subni- trate" of bismuth and is used frequently in medicine, as a cosmetic and for stomach trouble. Bismuth forms no compound corresponding to those of arsine and stib- ine. 31. Comparison of the Members of the Family. Ni- trogen and phosphorus in their outward appearance at ordinary temperatures differ greatly from the other three. Nevertheless, nitrogen at low temperatures is a white solid and phosphorus nearly so. In their chem- ical behavior they are very similar in most respects. As THE NITROGEN FAMILY 291 stated elsewhere, as the elements in a group increase in weight, the tendency, seen best in the oxides, is to be- come basic or metallic in character. Thus the oxides of nitrogen and phosphorus are strongly acidic; of ar- senic, the trioxide has a double character, being both basic and acidic. It reacts with hydrochloric acid to form arsenious chloride, and with sodium hydrox- ide to form sodium arsenite. The pentoxide, As 2 5 , is acidic as might be expected with its higher percentage of oxygen. In the case of antimony, the trioxide is also of dual character, but more strongly basic than acidic, while the pentoxide is still acidic. With bismuth the trioxide is basic only. As further showing this same fact, nitrogen and phosphorus form no salts with these as the positive ions ; arsenic forms but few, not very sta- ble, antimony and bismuth many, especially the bismuth. The following table compares the several members in regard to other compounds not already named: TABLE FOR COMPARISON NITROGEN N = 14 PHOSPHOR- US P = 31 ARSENIC As = 75 ANTIMONY Sb = 120 BISMUTH Bi 208 Hydrogen Compound Ammonia NH 3 Phosphine PH 3 Arsine AslL Stibine SbH 3 None Oxides N.,(X NA PA PA AsA AsA SbA SbA BiA BiA Chlorides NC1 3 PC1 3 AsCl 3 (?) SbCl 3 BiCl 3 Oxychlorides NOC1 POCl SbOCl BiOCl Acids HN0 3 HPOg H 3 P0 4 H 3 AsO 4 H 3 Sb0 4 .None i Exercises for Review 1. Name the members of the nitrogen group. 2. From what has phosphorus been mostly prepared? What in very late years? Give a brief outline of the process. 292 APPLIED CHEMISTRY 3. Name the forms of phosphorus. Compare them with sulphur. What other elements studied have been seen in allotropic forms? 4. Give the characteristics of yellow phosphorus and compare with it the red. 5. Which is the poisonous variety? What disease do the vapors produce? What remedy is there for it? 6. What is the chief use of phosphorus? Give another use. 7. Give the various steps in the evolution of the common match as we have it to-day. 8. Describe the safety match and state how different from the ordinary. 9. How is phosphine made ? What is the chief point of interest regarding it? What use has it? 10. Name the oxides of phosphorus and give formulas. How prepared? 11. Name two or three acids of phosphorus and state how they may be obtained from the oxides. 12. What phosphates occur in nature? Of what use are they? How are they produced artificially for fertilizers? 13. Give the chief characteristics of arsenic. 14. Explain the purpose of the one use of arsenic. 15. How is arsinc made? How can you show that it is readily decomposed by heat? 16. What is a nascent gas? How different from the molecular form ? 17. Describe Marsh's test in full. 18. Name the oxides of arsenic and give formulas. 19. Describe the trioxide and give uses. What is the antidote for arsenic poisoning? Why may so much time be taken in pre- paring the antidote? 20. AVhat two pigments of arsenic are common 1 ? What former use had they? Why no longer used this way? Chief use now? 21. Give characteristics of antimony and compare with arsenic. 22. What is antimony black? Use of it? 23. Name the most important alloys of antimony and give some use of each? What is an alloy? 24. Give composition of type metal and state wherein is its chief value. 25. How is stibine made? How can its spot be distinguished from that made by arsine? THE NITROGEN FAMILY 293 26. What is butter of antimony? How made? Why so called? When water is added to it, what results? Write the equation. 27. What do you call an equation like the above? How can you prove that it is reversible? 28. How is antimony trisulphide formed in laboratory? Of what practical use is it? 29. Give use of tartar emetic. 30. Describe bismuth and compare with antimony. 31. Give chief uses of bismuth. 32. Name two very fusible alloys of bismuth. Why do they have such a low melting point? 33. Name two compounds of bismuth and state how prepared. 34. Write the equation showing the reaction of water with the nitrate. 35. What kind of an equation is this? How can you show ex- perimentally that it is reversible? 36. Give a general comparison of the members of the group. 37. Show how they become less acidic as they increase in weight. 38. Compare the various oxides of the group in chemical behavior. CHAPTER XXIV COMPOUNDS OF SILICON Outline- Natural Compounds Silica (a) Variety of (6) Characteristics (c) Uses Artificial Compounds (a) Water Glass (&) Crown Glass (c) Bohemian Glass (d) Flint Glass Manufacture of Glass Articles Annealing Glass 1. Occurrence of Silicon. Silicon belongs to the car- bon group. The latter element has already been stud- ied. Two metals, tin and lead, also belong to this group. They all have a valence of four. Next to oxygen, silicon is the most abundant of all the elements and constitutes something more than 25 per cent of the earth's crust. It is never found free as is carbon. In the combined form, sand, Si0 2 , is a very abundant mineral. Sandstone is the same with some cementing material holding the particles together. Crystallized, this same compound often occurs as hexagonal prisms; when transparent it is then called rock crystal. When delicately colored it is known as rose quartz, amethyst, milky, and smoky quartz, according to the nature of the coloring. Opals, agate, chalcedony, jasper, flint and onyx are other well- known varieties. Much of the agate is petrified wood; as the cells of the woody structure have been broken down in the process of very slow decomposition the sil- 294 COMPOUNDS OF SILICON 295 ica has replaced them. The different colors are due to different compounds dissolved in the silica when it was deposited. The most noted of these petrified forests is near Adamana in Arizona. Here trunks of trees of all sizes, for the most part broken squarely across, are found in great numbers, covering many square miles in area. Many of the rocks constituting the crust of the earth are compounds of silicon. Such are kaolin, Fig. 56. A scene in one of the petrified forests in Arizona. feldspar, and the clays resulting from the decomposition of the latter. Mica, which has the property of splitting into thin sheets, commonly used in stoves and often re- ferred to erroneously as isinglass, is a silicate. Granite is ordinarily a mixture of quartz, feldspar and mica. Pumice stone is a porous lava, used as an abrasive and in some washing powders, as "Dutch Cleanser." In- fusorial earth, spoken of in connection with the manu- facture of dynamite, is a porous, siliceous rock formed 296 APPLIED CHEMISTRY from the shells of microscopic animals. Fig. 56 is a view of a portion of the petrified forests of Arizona. 2. Characteristics of Silica. If pure, silica is color- less. It ranks seventh in the scale of hardness, in which the diamond is tenth. It is not soluble in any acid ex- cept hydrofluoric, but is somewhat readily so in alkalies. Some of the hot springs in Yellowstone Park contain very considerable quantities of dissolved silica, so that articles left where the spray may fall upon them, or if dipped into the water repeatedly become covered with a silicious coating. Its melting point is so high that- only the electric arc or the oxyhydrogen lamp is suffi- cient to fuse it. 3. Uses of Some Forms of Silica. The uses of sand for "building purposes in mortar and cement are well known. For such work a coarse sand, with grains more or less rough, and not well polished, makes a much stronger wall or foundation. All glass requires sand for its manufacture ; sand papers of all degrees of fine- ness are made for polishing and smoothing wood sur- faces. Pure sand is now being made into crucibles and various other chemical apparatus, preferable in many ways to glass. As its coefficient of expansion is very low, it is much less liable to be broken by sudden great changes in temperature. The finer grained infusorial earths are used as abrasives for polishing metals, while sandstone is made into whetstones and grindstones for sharpening tools. The tinted varieties of quartz men- tioned are often cut and mounted in cheaper jewelry, where, owing to their hardness, they are very service- able. Lenses for optical instruments and spectacles are sometimes made from pure quartz. 4. Silicic Acid. Silicon dioxide, Si0 2 , is an acidic oxide as would be indicated by the fact that it combines COMPOUNDS OF SILICON 297 so readily with alkalies. Theoretically, it is the anhy- dride of silicic acid, but as it is neither soluble in water nor reacts with it, silicic acid is not obtainable by di- rect means. Orthosilicic acid has the formula H 4 Si0 4 , but when precipitated from a silicate it loses a molecule of water and becomes H,Si0 3 . Many salts of these two acids are known. 5. Water Glass. When silica is fused with sodium carbonate, the following reaction takes place, Si(X + Na 2 C0 3 -> Na 2 Si0 3 + C0 2 . This sodium salt of silicic acid is generally used in the liquid form, or solution, somewhat resembling glycerine in appearance. If all water is removed, a transparent, colorless solid remains, closely resembling glass. In the viscous solution it is often called "water glass." At the present time very large quantities of it are used. It is probably the best preservative of eggs. For this pur- pose, a mixture of one part water glass and nine parts of water are put into a jar of suitable size. Into this are put the eggs from day to day, the fresher the better. It is well not to make up a very great quantity of the solution at one time, although there should be sufficient to keep the eggs covered. Any egg which floats in the solution should be discarded as it is already stale and may be the cause of spoiling others. Eggs decompose because of bacteria, which pass through the shell along with the air as it takes the place of the moisture which is being constantly evaporated. The water glass fills and closes the pores of the shell and thus prevents this inter- change. Eggs may be thus kept for months and are always far preferable to storage eggs even of less age. The jar and contents must be stored where the contents will not freeze, although a warm room is not desirable. 298 APPLIED CHEMISTRY It may be remembered that the solution will have a freezing point much lower than that of water; hence it will stand a considerable degree of cold. It is well to know that such eggs cannot be boiled without the shells cracking, as a rule. This is because at the boiling point the air contained would be greatly expanded ; because it cannot pass through the pores of the shells, it bursts them. After standing for some months a white gelati- nous mass will be found collecting in the bottom of the jar. This is silicic acid, and is formed as indicated by the equation, Na 2 Si0 3 + 2H 2 -> H 2 Si0 3 + 2NaHO. It has been said that water does not ionize and for that reason is not a conductor of electricity. It does, how- ever, ionize to a very slight extent, so that there are al- ways a few hydrogen and a few hydroxyl ions present in the water. Thus, H 2 * H + HO. Sodium silicate, being a salt, is largely ionized, thus, Na 2 Si0 3 ? Na,Na, +~Si0 3 . Therefore, the hydrogen ions colliding with the silicate ions would form silicic acid, and as this is not appreciably soluble in water, it soon begins to separate out as a precipi- tate. This continues slowly and at the end of some months even an inch or more of white, gelatinous silicic acid may be found at the bottom of the jar. At the same time the hydroxyl ions meeting the sodium ions form sodium hy- droxide, but this being very soluble remains largely in the form of ions in the solution. This may be shown by testing with red litmus paper; it is also noticeable in its effect upon the hands, giving the skin a slippery feel- COMPOUNDS OF SILICON 299 ing as alkalies all do. Such chemical action as this be- tween a salt and water is called hydrolysis, from two Greek words, meaning decomposition ~by water. Various other cases of hydrolysis will be studied later. In reality the action of water upon antimony and bismuth salts, ob- served in the preceding chapter, is an instance of hy- drolysis. Water glass is also used as a cheap cementing mate- rial, in many cases taking the place of glue. This is seen in the manufacture of paper boxes, trunks, and valises. 6. Crown Glass. When lime, sodium carbonate and silica are fused together, a double silicate of calcium and sodium is formed which is called crown glass. Un- less very pure sand is used there will be small quantities of iron present, which will give the product a green color. It may be largely removed by the addition of some oxi- dizing material like manganese dioxide; but any slight excess of this compound imparts an amethyst color to the glass. Crown glass has a relatively low melting point ; hence, it may easily be softened in the Bunsen burner. It is also more readily attacked by alkalies than some other varieties. However, on account of its cheapness it is used for all ordinary bottles, for common window glass, and most of the test tubes and glass tubing used in the chemical laboratory. 7. Bohemian Glass. When potassium carbonate is fused with sand and lime a variety known as Bohemian glass is obtained. It is harder than crown glass, more transparent, less readily attacked by chemical reagents and has a much higher melting point. It is commonly spoken of in the laboratory as "hard glass." It is used for the better chemical glassware beakers, flasks, and all sorts of other apparatus. The better grades of tumblers APPLIED CHEMISTRY and other glassware in the home are also made from Bo- hemian glass. 8. Flint Glass. When sand, lead oxide and silica are fused together, a variety called flint glass is obtained. In the purest form it is sometimes called paste, and from it are made the imitation or paste diamonds. Flint glass is almost perfectly transparent, is very soft so that it is easily scratched, and has high refractive power. Most op- tical lenses are made from it on account of the ease with which it is cut, its brilliancy and high refractive power. It is the last property that gives the play of colors seen in the imitation diamonds, almost equal to the genuine; but the softness of the glass soon causes a loss of this power. It is also used in the manufacture of cut glass found in the home. 9. Manufacture of Glass Articles. Tumblers and sim- ilar articles of household use are molded. A sufficient amount of molten glass is -put into a heated mold the size Fig. 57. Mold for making glass tumblers. and shape of a tumbler. As shown in Fig 57, a rod de- scends, mechanically, bearing a solid but smaller tumbler. This squeezes the molten glass into the space COMPOUNDS OF SILICON 301 between the two and in a second of time the glass is done. Bottles are made by blowing. A suitable amount of molten glass is taken from the furnace upon the end of a blowpipe. (See Fig. 58.) This is placed within a mold, and by lung power or compressed air the glass is blown until it issues from the top of the mold in the form of a Fig. 58. Mold for blowing glass bottles. The blow-pipe with molten glass is shown hanging within the opened mold. large bubble and bursts. Immediately, the bottle with its ragged top in placed in another machine which, while the glass is still soft, turns it round and round until the neck and top are perfectly smooth. Ordinary win- dow glass is first blown into long cylinders. These are cut lengthwise and flattened out while still hot, just as a 302 APPLIED CHEMISTRY roll of paper might be with a pair of scissors. (See Fig. 59.) Heavy plate glass is made by pouring a ladle of mol- ten glass upon a table and immediately rolling until it covers the top of the table and has attained a uniform thickness. It is then polished by revolving discs with water and pumice or some similar abrasive. The color of Fig. 59. Making window glass. It is first blown into form of a cylinder. This is cut open, flattened out and annealed. glass articles is secured by the introduction of small quan- tities of some other compound. It has already been stated that manganese gives an amethyst color; cobalt gives a beautiful, deep blue; copper a lighter or greenish blue; chromium a clear, beautiful green; calcium fluoride a translucent white; iron, pale green, yellow or brown, COMPOUNDS OF SILICON 303 according to the kind of iron salt introduced; gold and some copper compounds give a red color. A glass rod kept soft lay heat may be drawn out into thread and wound like silk fibers upon a large wheel or bobbin. From this it may be woven into various articles such as ribbons, bows for neckwear and even into cloth. Thus used it has the sheen of satin, but naturally it is not very durable. 10. Annealing Glass. All glass articles when first made are very brittle. Annealing consists in cooling them so very slowly that the molecules are enabled to move into relatively stable positions. This is done by putting the articles into a very long oven, one end of which is extremely hot. They are then very slowly moved mechanically toward the cooler end and after several days are ready for packing and shipping. Exercises for Review 1. What can you say of the abundance of silicon compounds in nature ? 2. Name several varieties of quartz. 3. Name several other minerals consisting of silica, some of \\hich are prized for their beauty. 4. What is petrified wood? How formed? 5. Give the characteristics of quartz. 6. Mention some uses for some of the natural forms of silica. 7. What kind of an oxide is silica? What acid is formed theo- retically from it? 8. How is water glass made? In what form is it used? 9. Give method of preserving eggs with water glass. 10. Why do preserved eggs crack when boiled? 11. What is meant by hydrolysis? Illustrate by means of so- dium silicate. 12. Name two cases of hydrolysis in a preceding chapter. 13. How is crown glass made? Give some common uses for it. Why is it green in color? How may this be removed? 304 APPLIED CHEMISTRY 14. From what is Bohemian glass made? Give its differences from crown. 15. What laboratory uses have these two kinds of glass, and why ? 16. From what is flint glass made? Give its most important uses. Why so used? What use has it in our homes? 17. Give the common method of making tumblers. How are bot- tles made? Plate glass? Window glass? 18. What is meant by annealing? How is it done? What is really accomplished by annealing? CHAPTER XXV THE ALKALI METALS Outline Comparison of the Members Sodium (a) Occurrence (fc) Method of Preparing (c) Characteristics (fZ) Uses Compounds () Sodium Chloride (ft) Sodium Bicarbonate (c) Sodium Carbonate (d) Sodium Hydroxide (e) Soap (/) Borax (/7) Hydrolysis of Compounds Potassium (a} Occurrence (1} Characteristics Compounds (a) Potassium Carbonate (6) Potassium Hydroxide (c) Potass'um Nitrate (d) Potassium Chlorate (e~) Other Compounds 1. General Comparison. This group includes the most strongly positive metals, as the halogen group does the most strongly negative. They occupy a position at the left end of the periodic table while the halogens are at the extreme right. The two important members are sodium and potassium; the other three, lithium, caesium and rubidium, are much less common. More or less vigorously they all decompose water, forming strong 305 306 , APPLIED CHEMISTRY bases or alkalies, for which reason they are commonly called the alkali metals. . 2. Occurrence of Sodium. Common salt is one of the most familiar of all substances. It occurs in small quantities in nearly all soils; it is present in the dust particles floating in the air; it is the sodium in this compound which colors a flame yellow when a room is being swept. A clean platinum wire, drawn through the fingers, in a Bunsen flame will give the characteristic yellow coloration. It is found in the blood to the extent of 0.8 per cent. About seven-tenths of the solid matter found in sea water, or nearly 3 per cent by weight, is common salt, and amounts to the astonishing sum of over 35,000 billion tons. Some one has calculated that on the basis of an average depth of 1,000 feet, the common salt in the various oceans would occupy a bulk of 3,500,000 cubic miles and that if this were separated out and piled up it would make a mountain range rivaling in height and length some of our great western chains. In some of the Middle-West States, notably, Kansas, deposits of nearly pure salt are known, 300 feet in thickness, cov- ering vast areas. Likewise, New. York, Ohio and Mich- igan have extensive deposits and these three states to- gether with Kansas furnish about nine-tenths of all the salt made in the United States. California, Utah, West Virginia, Pennsylvania, Louisiana, Texas and Oklahoma also produce considerable amounts. In California one or more lakes covering an area of from 30 to 50 square miles are known, saturated with salt: a crust 6 to 8 inches in thickness of nearly pure salt covers the surface over which in the dry season anyone may walk with safety. These lakes glisten in the sun like one in our northern climates, frozen over and covered with snow. Chile saltpeter, NaN0 3 , is another abundant natural THE ALKALI METALS 307 compound but not so widely distributed as common salt. It is found mostly in the desert areas of Chile, covering about 450 square miles or about the size of a single county in some of the Middle-West states. The deposits are from 25 to 50 per cent sodium nitrate and something like 5 feet in thickness, while the quantity is consider- able it is far from unlimited. Other natural compounds of sodium are known, but they are unimportant. 3. Preparation of Sodium. Sir Humphrey Davy, in 1807, first prepared the metal by the electrolysis of so- dium hydroxide. At the present time the same method is used, improved, and known as the Castner process. Fig. 60 gives an idea of the apparatus. The sodium hy- Fig. 60. Preparation of sodium, by the Castner process. droxide is melted in a vessel, marked V, usually made of cast iron ; to this is attached the cathode in the form of a bundle of carbon rods. The anode, marked W, is a vessel, similar to V, inverted over and dipping into the melted caustic soda. In the center, the vessel, P, which reaches down below the upper end of the carbon rods is the receiver for the sodium and is closed at the bottom by a coarse wire gauze. The current causes the sodium and hydrogen, both positive, to collect upon the carbon rods, from which they rise to the top within the vessel, P. The hydrogen escapes and the sodium when cooled is removed and molded into sticks. The 308 APPLIED CHEMISTRY oxygen collects upon the vessel, W, which is the anode, from which it may be drawn off or allowed to bubble out and escape. 4. Characteristics. Sodium is a silvery-white metal, at ordinary temperatures soft and pliable. It reacts vigorously with water and must be kept under naphtha or some hydrocarbon oil free from oxygen. Exposed to the air it rapidly attracts the moisture, with which it reacts and forms sodium hydroxide. This in turn ab- sorbs the carbon dioxide and forms sodium carbonate, so that ultimately the metal when exposed to the air becomes a white, brittle mass. On a vessel of water at room temperature a piece of sodium rolls about, grad- ually diminishing in size, until it finally disappears. On warm or hot water the heat generated is sufficient to ignite the hydrogen evolved and volatilize small portions of the sodium which color the flame yellow. On wet blotting paper, a small bit of sodium, not able to roll around, soon becomes hot enough to melt, at a tempera- ture but little below the boiling point of water, 96 C. It is then a silvery globule like mercury ; if dropped upon the floor at this point it breaks into numerous smaller globules Avhich burn with the usual yellow flame as they roll off in all directions. The irritating white fumes which arise as the metal thus burns are sodium peroxide, Na 2 2 . Sodium is soluble in mercury, and if present in sufficient quantity forms a solid amalgam, an alloy of which one constituent is mercury. This readily decomposes water, but less rapidly than sodium alone. The fact is made use of in the electrolytic process of making chlorine described on p. 122. Sodium may be converted into vapor at about 750 C. The density of the vapor shows it to be monatomic. When heated sodium combines readily with both oxygen and chlorine ; the oxy- THE ALKALI METALS 300 gen compound thus obtained is the peroxide, spoken of elsewhere as "oxone" used in preparing oxygen. 5. Uses. Sodium lias no commercial uses. In drying some organic compounds and in some other laboratory work it is of value. The preparation of artificial rubber, still in the experimental stage, employs sodium in one step of the process. 6. Compounds. The occurrence of sodium chloride in nature has already been mentioned. It is obtained from these sources in two or three ways. A very consid- erable amount is mined as any other mineral. Since more or less insoluble foreign matter usually accompan- ies this rock salt as it is called, it is largely used for stock, or crushed to coarse grains for making freezing mixtures for refrigeration and for keeping ices and creams. At Salt Lake, Utah, the water, already satu- rated, is pumped into basins and evaporated by the heat of the sun. The product is somewhat impure but suita- ble for refrigeration and for packing purposes. At San Francisco the A\ 7 ater is pumped likewise into basins and evaporated. Most of the salt used upon the table and in food products is obtained from salt wells. These are drilled down to reach the layer of salt, water is run in and allowed to remain until saturated. It is then pumped out and after any insoluble matter has settled out, it is evaporated and crystallized. 7. Characteristics of Salt. Salt obtained from wells is comparatively pure. Usually it contains a very small percentage of magnesium chloride which, being deli- quescent, causes the whole mass to become damp in wet weather. If a stream of hydrogen chloride be passed through a saturated solution of salt, pure sodium chlo- ride will separate out in fine crystals. As the mag- nesium chloride contained is usually less than 1/2 of 310 APPLIED CHEMISTRY 1 per cent and most of the samples of salt upon the mar- ket assay from 97 to 99 per cent in purity, it is not nec- essary, except for some chemical purposes, to purify the commercial supply. At the present time several brands of table salt may be obtained which do not cake in damp weather. They have not been freed from the mag- nesium chloride, but have had some finely powdered sub- stance like starch or cooking soda or prepared chalk in very small amounts intimately mixed with the salt, us* Fig. 61. Preparation of salt in San Francisco Bay, by evaporation of sea water. so that the individual grains are protected from the air by a thin coating of the powder. It will probably be found, if the label upon the container is read, that the adulterant used will be stated. As the substance thus employed is harmless and always in very small propor- tions, it cannot be said to be especially objectionable. Upon the lower organisms salt is altogether destructive. Such is the explanation of its preservative qualities. Sprinkled upon such soft bodied animals as snails and THE ALKALI METALS oil slugs, which in some parts of our country grow to great size, salt seems to extract the moisture from the body. It shrinks rapidly in size, and the animal soon dies. In large amounts it is harmful to the human body, and in some countries has been frequently used as a means of suicide. In small quantities it is regarded not only as not harmful but even necessary for the body, to provide the hydrochlo- ric acid needed in digestion. Undoubtedly, however, nearly everyone uses much more than necessary, so that it must be eliminated by the skin in the perspiration and through other excretory organs. 8. Uses. It is said that about 11 pounds per capita of refined salt is used every year in the United States in the seasoning of foods. Much more is employed in the pres- ervation of meats and meat products. Altogether, sta- tistics show that the total quantity used every year in various ways amounts to 30,000,000 barrels, more than a barrel for every family of four individuals. Besides these uses, so familiar to all, salt forms the starting point in the manufacture of several very important compounds which will be studied later. 9. Sodium Bicarbonate. This compound, chemically known as acid sodium carbonate with formula NaHCOo,, is common cooking soda. The word 'bicarbonate means twice carbonated, and was so given because the compound was formerly prepared by passing a stream of carbon di- oxide into a solution of sodium carbonate, whereupon the bicarbonate, being much less soluble, crystallized out. Thus it was obtained by carbonating sodium carbonate. The equation shows the reaction, C0 2 + Na 2 CO, + H 2 - 2NaHC0 3 . At the present time the commercial supply is made by what is known as the Solvay process. A saturated solu- 312 APPLIED CHEMISTRY tion of salt is treated with ammonia and carbon dioxide when three reactions take place, thus, NH 3 + H 2 - NH 4 HO, NH 4 HO + C0 2 -> NH 4 HC0 3 , NaCl + NH 4 HC0 3 -> NaHC0 3 + NH 4 C1. A 1 . the acid carbonate is not very soluble in water it crys- tallizes, after which it is removed, dried and pulverized, usually, for the commercial supply. The ammonium chlo- ride solution is saved, treated with lime and heated, whereupon the ammonia is recovered to be used again in the first step of the process. It will be seen, there- fore, that the manufacture is very cheap, 2NH 4 C1 + CaO -> CaCl 2 + 2NH 3 + H 2 0. 10. Sodium Carbonate. The greater portion of the acid carbonate made by the Solvay process is converted into the normal carbonate by heating, thus, 2NaHC0 3 - Na 2 C0 3 + H 2 + C0 2 . The carbon dioxide thus obtained is used in the first step of the process described above for making sodium bicarbonate, which still further cheapens the process. Another method, known as the Leblanc process, was used for many years. This consisted in the conversion of common salt into sodium sulphate by strongly heat- ing with sulphuric acid during which reaction hydrogen chloride was evolved. (See p. 126.) By further treat- ment of the sodium sulphate thus obtained with coke and limestone the sulphate was converted into a carbonate which was separated from the mixture by dissolving in water. The process is much more complicated and expensive than the Solvay and would now be abandoned were it not for the by-product obtained, hydrochloric acid. By the Solvay process anhydrous sodium carbonate THE ALKALI METALS 313 is obtained; by the Leblanc, the hydrate, Na,CO, . 10H,0. This is known as sal soda or washing soda. It is strongly ^ efflorescent and when exposed to the air rapidly loses nine of the water molecules contained. Heat is necessary to remove the remainder. Sodium carbonate is a neutral salt, yet, dissolved in water, it gives an alkaline reaction with litmus. This is explained in the same way as in the case of the water glass, p. 298. The sodium carbonate in water is largely ionized, thus, Na 2 C0 3 <=>Na, Na + C0 3 . Water forms some few ions, H 2 ?= H +HO. The hydrogen ions reacting with the carbonate ions pro- duce carbonic acid. This, however, is an exceedingly weak acid, and, as is true of all weak acids, is very slightly ionized, hence exists almost entirely in the molecular form. The hydroxide ions reacting with the sodium form sodium hydroxide, which being a very strong base is largely ionized. Thus a very considerable amount of hy- droxide ion is always present in such a solution. As the alkali reaction is due to the presence of hydroxide ions a solution of sodium carbonate always turns litmus paper blue. 11. Further Study of Hydrolysis. As stated above the alkaline reaction of sodium' carbonate is due to hy- drolysis. It is of such importance as to merit further study. Common salt dissolved in water shows no litmus reaction. The reason may be seen by writing the ionic reactions, NaCl * Na + Cl 314 APPLIED CHEMISTRY When the ions present react, two new products form, NaHO and HCL As one is a strong base and the other a strong acid they give relatively equal quantities of hydrogen and hydroxide ion and hence neutralize each other so that there is no litmus reaction. If sodium sulphate be used, like results are obtained, Na 2 S0 4 ^Na, Na + S0 4 , H 2 <= H + HO. The new products are sulphuric acid and sodium hy- droxide, both strong. Again the hydrogen ions and hy- droxide ions practically neutralize each other and there is no litmus reaction. This is true of all salts formed by the union of a strong base and a strong acid. It is usually stated thus: Salts formed by the union of a strong base uniting with a strong acid are not hydrolyzed appre- ciably in water. Salts like sodium carbonate and sodium silicate are the result of the union of a strong base and a weak acid and give alkaline reaction. Conversely, salts formed from a weak base and a strong acid give an acid reaction. This will be evident if the ionic equations are written, FeCl 3 ? Fe*+Cl, Cl, Cl, H 2 0?H-HO. The new products formed are hydrochloric acid and ferric hydroxide. The acid is very strong, while the base is weak; obviously, therefore, the litmus reaction will be acid in character. CuS0 4 * Cu + S0 4 . H 2 * H + HO. In the above solution the base formed will be copper hy- THE ALKALI METALS 315 droxide which is weak and the acid sulphuric which is strong. Again the litmus reaction will be acid. All such salts behave in a similar manner. This case is usually expressed thus: Salts formed by the union of a weak base rvith a strong acid, or conversely, by the union of a strong base with a weak acid are partially hydrolyzed. They give an acid or alkaline reaction according as the acid or the base is the strong factor. There is a third class of salts formed by the union of a weak base with a weak acid. Such are ferric carbonate and aluminum sulphide. lonically written, ferric car- bonate gives Fe 2 (C0 3 ) 3 ?Fe, Fe + CO 3 + C0 3 + C0 3 , The ferric ions collide with the hydroxide ions and give ferric hydroxide ; likewise, the hydrogen and carbonate ions form carbonic acid. Both compounds are ionized very slightly. The result is the molecules accumulate ; the solution becomes saturated with carbonic acid and at once it begins to decompose with the escape of carbon dioxide, thus, H 2 C0 3 - H 2 + C0 2 . Thus the carbonate ions are constantly forming mole- cules of carbonic acid and this is being destroyed by the escape of the carbon dioxide, so that it is removed from the sphere of action. Likewise, the ferric hydroxide, not being appreciably soluble in water, begins to form a pre- cipitate and it also is removed from the sphere of reac- tion. The ultimate result is that practically all the car- bon dioxide escapes and the ferric ions have formed fer- ric hydroxide which alone remains as a precipitate. In other words, ferric carbonate in water has been converted entirely into ferric hydroxide, that is completely decom- 316 APPLIED CHEMISTRY posed. The conclusion is usually stated thus: Com- pounds formed by the union of a weak base with a weak acid in water are completely hydrolyzed. The action of one class of baking powders depends upon this very fact and will be taken up at another time. 12. Uses of Sodium Carbonate. Its chief use is for the manufacture of other compounds. With silica it is used in making two varieties of glass; it is also used in preparing sodium hydroxide, a very important com- pound to be studied later. It is used extensively in soft- ening water and is the chief constituent of most wash- ing powders. In addition, these may contain powdered caustic soda, borax, pumice stone, soap powder, sodium peroxide, and possibly sometimes some other substances. Scouring powders usually contain pumice; if put into a glass of water and stirred the other ingredients will dissolve leaving the pumice as a gray deposit. " Dutch Cleanser" is a washing powder of this kind. They are excellent in their way, but should not be used on highly polished surfaces such as silverware and the like. 13. Sodium Hydroxide. This compound, NaHO, is commonly called caustic soda. In an impure form it is frequently sold at groceries under the name of "lye." Much of it is prepared from sodium carbonate by treat- ing it with slaked lime thus, Ca(HO) 2 + Na 2 C0 3 - CaC0 3 + 2NaHO. The calcium carbonate is not soluble in water, hence forms a precipitate from which the caustic may be drained off. A considerable amount of sodium hydrox- ide is also made electrolytically as described under chlorine. Made thus it is much more apt to be pure than by the other process; in fact, commercial caustic THE ALKALI METALS 317 soda made from sodium carbonate often contains as much as 25 per cent of the latter compound or other im- purities. For most of its uses such impurities, however, are not especially objectionable. To obtain pure caus- tic soda from this commercial variety it is dissolved in alcohol, filtered and the solvent evaporated. The im- purities do not dissolve in the alcohol, hence are left behind in the filtration. 14. Characteristics of Sodium Hydroxide. It is a white solid : the pure caustic is usually sold in the form of small sticks although it may be had in a powder. The commercial variety is usually powdered. It is exceed- ingly caustic when moist, and is very deliquescent. Ex- posed to the air it rapidly dissolves in the moisture present, takes up carbon dioxide, and ultimately, as stated in the case of sodium, forms solid sodium car- bonate. 15. Uses. As already stated caustic soda is a constit- uent of many washing powders. It is used in the manu- facture of paper pulp, in decomposing the woody fiber; also in many other manufacturing processes. Probably its most extensive use is in the manufacture of soap. 16. Soap. Soap is a salt which in water gives an alkaline reaction because of hydrolysis. It is prepared by treating some fat or oil with caustic soda. The reac- tion is shown by the following equation, 3\alIO -I- C a TT 3 (C 17 II 3rj COO) 3 - 3NaC 17 H,,COO + C 3 II 5 (HO) 3 . Stearin has been used here as typical of the other fats. It will be noted that glycerine is the by-product. On a large scale, soaps are generally made from the waste fats, or those of animals condemned by inspectors at 318 APPLIED CHEMISTRY the packing houses as unfit for food, and from other similar sources; also from some of the cheaper oils. The yellow rosin soaps usually contain considerable rosin substituted for a portion of the fat. The chemical proc- ess in the making of soap is called saponification. Chem- ical reaction with organic compounds is nearly always slow, for the reason that they are not ionized. Hence, three or four days of constant -boiling are necessary for the completion of the process. At the end of this time, salt is added, which causes a more perfect separation of the salt and glycerine. The salt water with the glycerine is drawn off beneath the soap layer, evaporated until of such concentration that the salt will crystallize out, after which the glycerine is concentrated in "vacuum pans" under partial air pressure. If potassium hydroxide is used instead of sodium, a soft soap is obtained in which the glycerine remains dissolved. In small quantities it is prepared for use in pharmacy, from pure fats or oils, especially linseed. Formerly, practically all the soap used by those living in the country was home-made. The ashes obtained during the winter months were put into hoppers and kept dry. In the spring lime was added and the mix- ture leached with water, added in small quantities at a time. These reactions took place, CaO + H 2 -> Ca(HO) 2 , Ca(HO) 2 + K 2 CO a -> CaCO 3 + 2KHO. The water, which slowly trickled from the hopper, con- tained the potassium hydroxide and was called lye. It was then boiled in large iron kettles with any waste fats that had accumulated during the winter. If hard soap was desired, when saponification was complete, salt was added and the whole allowed to cool. The soap floated on the spent lye and when cold could be lifted off and cut THE ALKALI METALS 319 into cakes. Made thus it is always brown in color and usually contains more or less free alkali. Since soap is a salt made by the union of a strong base and a weak acid, in water owing to hydrolysis, it will give an alkaline reaction even if there be no free alkali contained. To determine whether the sample be devoid of free alkali, some of it must be dissolved in alcohol which does not cause hydrolysis. A strong alkaline test in such a solu- tion indicates free alkali in the soap. Floating soaps are produced partly by forcing minute bubbles of air into the soap before -it is made into cakes and partly by the removal of much of the water present. They are more durable than soaps containing much water, although possibly a little slower in producing a "suds" or lather. Transparent, glycerine soaps are made by dissolving ordinary soap in alcohol and filtering out. the insoluble residue ; the alcohol is recovered by distillation. Such soaps are expensive because of the added labor in prepar- ing them and also from the fact that they dissolve rapidly in water and hence do not last well. Many soaps contain fillers, that is substances like sodium carbonate or water glass worked in by "crutchers. " These consist of a large endless screw like an augur fitting somewhat loosely within a large upright cylinder. The warm, pasty soap is run into these, the filler added and the screw started. In the course of several hours the whole is thoroughly mixed. Some of these fillers, especially sodium carbonate, are not particularly objectionable, but the value of the water glass is doubtful. All of them cheapen the cost of the soap to the manufacturer. From the crutchers the soap is run into large molds holding several hundred pounds, where it hardens. It is removed from these, al- lowed to dry several weeks, is then cut into bars, pressed 320 APPLIED CHEMISTRY into cakes by machinery, wrapped and packed almost en- tirely without the touch of a human hand. 17. Sodium Nitrate, NaN0 3 . This compound is known commercially as Chile saltpeter, and has been mentioned elsewhere. It is a white, crystalline solid, used for the manufacture of gunpowder, nitric acid and extensively as a fertilizer. 18. Borax. Chemically, borax is sodium tetraborate, Na 2 B 4 7 . 10H 2 0. Our supply is obtained principally from the deposits of calcium borate in California. This natural compound is treated with sodium carbonate with the following reaction, CaB 4 7 + Na 2 C0 3 -> CaCO s + Na 2 B 4 7 . The mixture is treated with hot water which dissolves out the borax, but not the calcium carbonate. When crystallizing the salt takes up ten molecules of water. It is a white solid, somewhat efflorescent, giving an alka- line reaction in water due to partial hydrolysis. It is used in many washing powders, but is more expensive than sal soda. Small quantities are used in the chemi- cal laboratory in testing for various metals. When fused in a loop on the end of a platinum wire, it loses its water of combination and forms a perfectly transparent glass ; now, if this is dipped into a solution of certain met- als and again fused, or if a minute portion of certain ox- ides be fused with it, it forms beautifully colored "beads" which are distinctive. For example, cobalt gives a deep blue ; nickel a brown ; chromium a bright emerald green ; manganese, amethyst. It is commonly used in hard soldering as a flux. There is always a film of oxide more or less thin upon the surface of nearly every metal. If solder is poured upon such a surface it will not adhere because it does not really come in contact with the THE ALKALI METALS 321 metal. When borax is applied, it melts, at the tem- perature necessary for doing the work, dissolves the thin film of oxide, and leaves a perfectly clean metal to which the solder strongly adheres. 19. Occurrence of Potassium. The third member of the sodium group in point of density is potassium with an atomic weight of 39. It is found in several natural compounds, but much less abundantly than sodium. The most common is potassium chloride, mixed usually with magnesium chloride. Most salt lakes contain small quantities of both potassium and magnesium chloride. The presence of magnesium chloride in table salt has already been mentioned. As these two chlorides are much more soluble in water than common salt, they will remain in solution until most of the sodium chloride has already crystallized out, Thus, in the famous Stass- furt deposits of Germany, the lower portions, many hundreds of feet in thickness, are common salt, while the upper layers contain much potassium and magne- sium chloride. Probably the same will be found true when the Great Salt Lake in Utah and other similar lakes in this country have finally become dry. At pres- ent, the portion separating out is largely sodium chlo- ride, while the water still contains the greater part of the magnesium and potassium compounds. Potassium ni- trate is also found in nature, but not in such quantities as the sodium nitrate beds of Chile. 20. Preparation of Potassium. Potassium was first prepared by Davy by the same method he used for making sodium, and in the same year. Later, for many years the commercial supply was obtained by heating potassium hydroxide with carbon. Now, however, it is made electrolytically by a process similar to that of sodium. 322 APPLIED CHEMISTRY 21. Characteristics of. Potassium is a silvery-white metal, lighter than water, with a melting point of about 63. Small quantities of the metal volatilized in the Bunsen flame give a violet color. This generally serves as the test for potassium salts, just as the yellow flame does for sodium. The vapor of potassium is green in color. The density of the vapor shows that it is monat- omic. It reacts vigorously with water even if cold, with the evolution of sufficient heat to ignite the hydro- gen set free. Sufficient of the metal is always at the same time volatilized to color the flame decidedly vio- let. The following equation shows the reaction, 2K + 2II 2 -> H 2 + 2KHO. Exposed to the air reactions similar to those in the case of the sodium occur with the ultimate formation of potassium carbonate. It must, therefore, like sodium, be preserved in some oil like naphtha which contains no oxygen. Outside the chemical laboratory potassium has little use. 22. Potassium Carbonate, K 2 C0 8 . Years ago consid- erable quantities of this salt were obtained from wood ashes. From their treatment in large iron pots, the salt extracted by the water came to be known as pot- ashes, and later as potash, from which the name of the metal was derived. Since the disappearance of many of the original great forests ? this source has become neg- ligible. At the present time, sugar beets furnish a very considerable amount. The sap is boiled down in vacuum pans to the point at which the crystallizablc sugar will separate out ; the portion which will not crystallize is known as molasses and is separated from the sugar by centrifugal machines. The molasses is fermented with yeast and made into alcohol. From the residue the potas- THE ALKALI METALS 323 slum carbonate is obtained. Another source of consider- able potassium carbonate is the wool of sheep. An oily substance called siiint which sometimes equals the weight of the clean wool itself is secreted by the glands of the skin. This is removed from the wool by hot water ; from it potassium carbonate and a valuable oil are obtained. Some potassium carbonate is also prepared from potassium chloride, as sodium carbonate is made from the chloride. Potassium carbonate is a white crystalline salt, which is very deliquescent. Commercially, it is known as pearl ash. As already stated, it is used in making Bohemian and flint glass. From it also potassium hydroxide is pre- pared. 23. Potassium Hydroxide, KHO. This is made by processes exactly similar to those for making sodium hydroxide, thus, K 2 C0 3 + Ca(HO) 2 - 2KHO + CaC0 3 . The calcium carbonate is an insoluble compound and the hydroxide may be decanted or filtered off. It may also be prepared electrolytically from potassium chloride as is caustic soda. Commercially it is known as caustic potash. It is a white solid, extremely deliquescent, and caustic, similar in all respects to caustic soda. It is used chiefly in making soft soap ; a special variety prepared for the drug trade is made by combining the caustic potash with linseed oil. This is used in making certain salves and other pharmaceutic preparations. 24. Potassium Nitrate, KNO : ,. This compound occurs in limited quantities in the soil in certain parts of Per- sia and India. It is supposed to be formed through the action of bacteria upon animal refuse. Considerable amounts are made from Chile saltpeter by treating that salt with potassium chloride. Potassium nitrate is a 324 APPLIED CHEMISTRY white crystalline salt, not greatly different from com- mon salt in taste. Commercially, it is known as salt- peter. It is used to some extent in curing meats but mainly for making gunpowder. The composition is not materially different from that given when sodium nitrate is used, 75 per cent of the mixture being saltpeter. Sulphur and charcoal with a little moisture make up the balance. When exploded, the gases formed are mostly nitrogen and one or both of the oxides of carbon. The smoke produced when fired in a gun is a mixture of two or more solid compounds, mainly potassium sulphide and potassium carbonate. Partly because of the smoke and partly because less powerful, ordinary black powder is being largely supplanted by smokeless powders which have been mentioned on p. 156. 25. Potassium Chlorate, KC10 3 . This salt is a white crystalline solid. It melts easily in the Bunsen burner and decomposes, forming potassium chloride. All the oxygen is evolved, thus, 2KC10 3 - 2KC1 + 30 2 . In the presence of manganese dioxide, which serves as a catalytic agent, when heated the decomposition is rapid. Potassium chlorate is used in the preparation of oxygen, in making fireworks, and in matches, as already described. It has a mild, cooling taste, and is sometimes used to allay irritation of the throat and coughing. 26. Other Compounds. Potassium bromide and iodide are white compounds which crystallize in cubes consid- erably larger than those of common salt. They are both very soluble in water, and are both used to some extent in medicine. The former is a sedative and the latter an alterative. Potassium bromide is also used in pho- tography as a means of preparing the silver bromide THE ALKALI METALS 325 upon the plates and films. Potassium cyanide, KCN, is a white compound, very deliquescent, with a peculiar, unpleasant odor. It is one of the most violent poisons known. Its chief use is in silver and gold plating and as a means of extracting gold from its ores by what is known as the cyanide process. Exercises for Review 1. Name the metals of the sodium group. By what other name are they known? Why s:> called? 2. Give in some detail the occurrence of common salt upon the earth. 3. Who discovered sodium? How is it prepared now? 4. Describe sodium. How is it preserved? Why? 5. What is an amalgam? What use is made of sodium amalgam? 6. Give methods of preparing common salt for the market. 7. Give the chief properties of common salt. 8. What causes table salt to become damp? How is this pre- vented in some samples? 9. Give uses for common salt. State amount used per capita. 10. W T hat is sodium bicarbonate? How did it receive the name? How is it prepared now? 11. How is sodium carbonate made? Give steps in the Leblanc process and write the equations, omitting the coke from your last equation. 12. Give some important uses for sodium carbonate. 13. What is sal soda? Why does it give an alkaline reaction in water ? 14. What is hydrolysis? State what kind of a litmus reaction a solution of each of the following will give : sodium nitrate, potas- sium sulphate, copper chloride, potassium carbonate, aluminum sul- phate, potassium chloride, ammonium nitrate. 15. Describe the reason for each case of the above. 16. Describe caustic soda and give uses. 17. How is soap made? What by-product is obtained? How is it separated? 18. How can you determine whether a soap contains free alkali? Why will all soaps dissolved in water give an alkali test? 326 APPLIED CHEMISTRY 19. Give the chemical names for borax, caustic soda, Chili salt- peter, pearl ash, baking soda, sal soda, caustic potash, saltpeter. 20. Give some uses for borax. Explain what it does as a flux in soldering. 21. Describe potassium and compare with sodium. 22. What is the origin of the word potassium? Give three sources of potassium carbonate. What uses has it? 23. What is saltpeter used for? Wliat is produced when gun- powder is exploded? 24. Why are smokeless powders supplanting ordinary black powder? 25. Describe potassium chlorate and give uses. What is its pur- pose in a match head? 26. What use has potassium cyanide? 27. Give formulas for sal soda, anhydrous sodium carbonate, po- tassium chlorate, borax, caustic soda, pearl ash. 28. Complete the following equations and state \\liat they indi- cate: Na 2 CO 3 + Ca(HO) 2 - , KC1O 3 heated - , Na + H 2 -> , H 2 SO 4 -i- NajCl -> , NaHCO 3 (heated) -> , K 2 C0 8 + H 2 - . Note. In completing these equations, the student may use any quantity needed. CHAPTER XXVI SOME LEAVENING AGENTS Outline Chemical Agents () Baking Soda (&) Baking Powders (c) Comparative Healthfulness Yeast as a Leavening Agent Salt-rising Bread Aerated Bread Beaten Biscuits 1. Baking Soda. The most common chemical reagent used in leavening bread is sodium bicarbonate, sold as soda or bakiny soda. It has been in use for years. The flour with the soda well-mixed is "wet up" with sour milk or buttermilk both of which contain lactic acid. The acid reacting with the soda, forms carbon dioxide as shown by the following equation, NaHC0 3 + HC 3 II,O 3 -* C0 2 + H 2 + NaC 3 H 5 3 - The carbon dioxide, formed throughout the dough, when greatly expanded by the heat of the oven, tends to escape. In most flours there is a considerable amount of a com- pound called "gluten" through which the gas cannot readily pass : in its effort, however, the dough is raised and the bread is made light and porous. This gluten may be obtained for examination by tying a spoonful of flour in a thin cloth and washing for sometime in. cold water. The starch granules will pass through the cloth and disappear in the water. A sticky, gummy mass, which is mainly gluten, will be left behind. It is a nitrog- enous compound and is the muscle building part of the flour. 327 328 APPLIED CHEMISTRY There is one difficulty in the way of successful use of soda as a leavening agent. It has been explained else- where, that it is the lactose, or milk sugar, that by fer- mentation produces the lactic acid in sour milk. When the milk first begins to taste sour the quantity of acid present is not large, but continually increases until all the lactose has been changed. It is impossible to know without chemical test how much soda is needed to neutral- ize the acid present. Hence, too little may result in a sour and heavy bread, or too much may produce a dis- colored, alkaline-tasting bread. In very warm weather the decomposition of milk is rapid ; as it is an excellent medium of growth for all kinds of bacteria other prod- ucts besides lactic acid form, which may result in an unwholesome bread. 2. Baking Powders. The uncertainty of the results to be expected from the use of soda with sour milk led to the preparation of baking powders. There are a great variety of them at present, but the underlying principle in all of them is the same. This is the formation of carbon dioxide from soda by the use of an acid salt or its equivalent. They all, therefore, contain sodium bicarbonate. In addition, one class, known as the tar- trate powders, uses potassium acid tartrate, commercially called "cream of tartar." A second class, the phosphate powders, uses acid calcium phosphate; a third, usually called alum powders, uses aluminum sulphate. Besides these three classes there are many mixed powders, which usually contain mixtures of the second and third. In all cases starch or flour is added to the other ingredients to prevent chemical action taking place through exposure to the moisture of the air. The principle is the same as that employed in preventing common salt from becoming damp in wet weather. SOME LEAVENING AGENTS 329 3. The Chemical Action. In the tartrate powders the reaction is shown by the equation, NaIIC0 3 + KHC 4 H 4 (i - KNaC 4 H 4 G + H 2 + C0 2 . It Avill be seen that the residue left in the baked prod- uct is potassium sodium tartrate, known as Rochelle salt. When phosphate powders are used the following reaction takes place, 4XaHCO, + CaH 4 (P0 4 ), - CaNa 4 (P0 4 ) 2 + 4H 2 + 4C0 2 . As will be seen, in this case a phosphate of sodium and calcium is left in the bread or cake, a compound not greatly different from the phosphate contained in the bones. With the alum powders the reaction is somewhat more complicated. Aluminum sulphate is not an acid salt and its action depends upon the complete hydrolysis of the aluminum carbonate and the instability of the carbonic acid formed. This will be made clearer by observing the equations below, Al 2 (SOJ 3 + 6NaHC0 3 -> 3Na 2 S0 4 + A1 2 (C0 3 ) 3 + 3H 2 + 3C0 2 . This shows the results of the interaction of the two salts when brought together by the milk or water used in the dough. But it will be remembered that salts formed from weak acids with weak bases are completely hydrolyzed in water. Aluminum carbonate is such a compound. Hence, immediately a second reaction be- gins, thus, A1 2 (C0 3 ) 3 + 6HOH -> A1 2 (HO) 6 + 3C0 2 + 3H 2 0. It will be seen from the equations that the carbon di- oxide is evolved in two successive steps. In most of the alum powders, the soda is in such proportion as to furnish only about two-thirds as much available carbon dioxide as that given by the other powders; but to offset 330 APPLIED CHEMISTRY this, the manufacturers claim that the evolution of the gas, in stages and not all at once, more than compen- sates for the smaller amount produced, in that the loss is much less in making up and handling the dough. It will be noticed that the two products which remain in the bread in this case are sodium sulphate and aluminum hydroxide. It must be remembered that baking powders are not used with sour milk, for the acid salt or the alum takes the place of the lactic acid and the different ingredients are so proportioned that at the close of the operation there shall be no excess of either. One or more well-known brands of baking powders incor- porate with the other ingredients a small quantity of egg albumin. The claim of the manufacturers is that this in- creases the viscosity of the liquids used in making up the dough so that as a result the carbon dioxide will be retained the better. Carried out as an experiment in a test tube with water to bring about the reaction and no flour present, this is found to be true. But in the biscuit, itself, the claim is a very doubtful one. Sugges- tions have been made to use hydrochloric acid with soda as a leavening agent. Its reaction is NaHC0 3 + HCl - Nad + H 2 + C0 2 . It shows that only common salt is left in the bread. The objection to this is that the hydrochloric acid is a liquid and therefore cannot be mixed with the soda before- hand. Each separate portion would have to be meas- ured out at the time of using, so that the inconvenience might outweigh other considerations. The salt formed in a given quantity of bread is only about half what is ordinarily mixed with the flour; hence no objection could be offered in that respect. Scores of actual ex- periments with muffins, biscuits, every variety of cake and doughnuts, have been carried out by the author's SOME LEAVENING AGENTS 331 students using 1 soda and hydrochloric acid, with uni- formly successful results. 4. Healthfulness of Baking Powders. Owing to the intense rivalry among the manufacturers themselves, the public has taken more or less interest in the comparative healthfulness of the various baking powders on the market. A general idea prevails that the tartrate pow- ders are the most wholesome ; this has come through un- limited advertising by the manufacturers of that class of powders. Food experts of the United States who have given special attention to the effects of adulterations and preservatives in foods unite in saying that all bak- ing powders leave in the bread one or more substances classed as drugs, and since no efforts have ever been made to ascertain the effects in small quantities of these sub- stances upon the human system, no one can say what the result is upon health. Inasmuch as the quantity con- sumed by any individual is not great, it is probable that the effects upon health are so small as to be negligible in the case of any of the powders. Moreover, other kinds of bread in which baking powders are not used seem to be gaining in use and popularity in America; hence, the discussion may well be left until it has been settled by actual experiment. 5. Yeast Bread. A very considerable amount of the bread used at the present time, especially in cities, is what is commonly called "light bread" or that in which yeast is the leavening agent. Yeast is a microscopic plant which grows rapidly in a mixture of flour and water, if kept warm. As the growth proceeds, the sugar added and the starch which is changed into invert sujrar as explained elsewhere, p. 220, are transformed into alcohol and carbon dioxide thus, C (; H 12 (; - 2aiI 5 OH + 2CO,. 332 APPLIED CHEMISTRY The equation showing the inversion of the starch is C 6 H 10 5 + H 2 -*C 6 H 12 6 - When the dough has risen to a certain extent it is kneaded back; this breaks up the bubbles of gas into a very large number of small ones and gives a loaf of much more uniform texture. When heated in the oven the alcohol is expelled, since its boiling point is only 78. The carbon dioxide is expanded so as to raise the dough and the yeast plants are killed. From the fact that large bakeries can control and maintain uniform conditions of temperature in their establish- ments, and more than this, can secure uniform quality of flour by blending if necessary, their product is fast supplanting that made in the home. It has been said before that it is the gluten that serves to hold the gas in the dough until the baking is completed. Naturally, therefore, a flour deficient in this respect will not rise well; one with too much will produce bread too light, with large pores. For this reason, up to within recent years, it was difficult for the housewife with different flours to make a uniformly satisfactory loaf, yet with no fault on her part. At present, all large flour mills have the wheat they intend buying tested as to per- centage of gluten as well as in other respects. The flours they make are likewise tested. Thus with the composition known, a flour low in gluten may be mixed with one having a high percentage and both will be made right. At the present time, the output of flour is much more uniform than some years ago. This has resulted in large baking concerns themselves putting out a much more uniform product than was possible formerly. Since carbon dioxide in yeast bread is ob- tained through the decomposition of the starch, it will SOME LEAVENING AGENTS 333 be seen that there must be considerable loss in weight. In baking, including the Avater, which escapes, this is fully 15 or 20 per cent. It was estimated by Liebig, a German chemist, some years ago, that the alcohol pro- duced in this way amounted in the German empire to twelve million gallons annually, and that the flour thus passing off into the air in gaseous form was sufficient for the bread required by an army of 30,000 men. Formerly the housewife was dependent largely upon her own efforts for a continued supply of yeast. A piece of dough was saved each time and put away in a cool place until time for the next baking. Sometimes this was mixed with corn meal and dried, in which case it was good for several weeks or even longer. Later dry yeast was made an article of commerce and sold under the trade name of "Yeast Foam." At the present time "compressed yeast" which is a fresh and not a dried yeast has largely supplanted the dry form because of its very much more rapid growth when put into "sponge." Large bakeries use a yeast in a semi-liquid condition closely resembling thin batter. 6. Salt Rising Bread. This special variety is made by mixing up a sponge of corn meal, and milk with some salt added, and allowing it to stand for some hours. Thereafter the procedure is not essentially different from that of ordinary bread. It is supposed that a special variety of yeast spore which grows rapidly in the corn meal mixture and which finds entrance from the air is the cause of the leavening and of the pecu- liar taste as well. Some few years ago this "wild yeast" was isolated by a graduate student at Kansas University, and salt rising bread may now be made with as much assurance of uniform results as with or- dinary yeast. 334 APPLIED CHEMISTRY 7. Aerated Bread. On account of the loss in weight in light bread as explained above, efforts have been made to force carbon dioxide into the dough mechani- cally, without the use of any yeast at all. This is done by putting the materials into large cylinders and pump- ing in carbon dioxide until a considerable pressure is reached. It is then kneaded mechanically by rotating the cylinders. After some time the dough is forced out, cut into suitable sizes and baked. The gas absorbed, having the pressure removed and the temperature greatly raised, expands in accordance with both Boyle's and Charles' laws and makes the product porous and light. The bread thus obtained is sweet and wholesome, but lacks the "yeasty" taste; it is more inclined to be dry than ordinary bread and has not been received well by the public. 8. Beaten Biscuits. These were probably the original aerated bread. No leavening agent is used, but by con- tinued kneading and "beating" more or less air is worked into the dough, which expands upon baking. Such biscuits are never as light as those made from soda or baking powder, but they retain all the relative, wholesome taste of the flour, with nothing objectionable or questionable added. The amount of time needed to make them is fast causing them to be an unknown ar- ticle of food. Exercises for Review 1. Explain the action of soda in making biscuits. Write the equation. 2. What prevents a gas escaping rapidly from 'dough? How may a sample be obtained for examination? 3. What difficulty is there in obtaining uniform results with soda ? 4. Name the three classes of baking powders and give compo- sition. What is the purpose of each ingredient in the baking powders ? SOME LEAVENING AGENTS 335 5. What is left in the bread in the case of each baking powder? 6. Why can biscuit made from a baking powder never shoAv an alkaline reaction? 7. Give advantages and disadvantages of using hydrochloric acid with soda as a leavening agent. 8. What may be said of the relative healthfulness of the various baking powders? 9. What is yeast? How does it leaven bread? Why were light breads in former years of such varying quality? Why more uni- form now? 10. What can be said of the loss in making yeast bread? 11. What is aerated bread? How is the gas introduced into the dough? What advantages has it? Why has it not become popular? 12. How are beaten biscuits made? What disadvantage regard- ing them? CHAPTER XXVII THE CALCIUM FAMILY Outline- Members of the Group Occurrence of Calcium Properties of Calcium Lime (a) Manufacture (&) Uses Plaster of Paris Cements (a) Natural and Portland (6) Concrete Work Chalk Calcium Chloride Strontium and Barium 1. Metals of the Group. The metals belonging to this group are calcium, strontium, barium and radium, rang- ing in atomic weights from 40 to 226. The first three react with cold water and form hydroxides, which are strongly alkaline although not very soluble. They are often called the alkaline earth metals. 2. Occurrence of Calcium. Rocks containing calcium compounds are among the most abundant of the earth's crust. Limestone and the semicrystalline variety, mar- ble, are both calcium carbonate as are also corals and shells. Limestone is produced by the cementing together of shells and similar material ground up by the action of the waves. Fossil remains of crinoid stems and brachiopods are commonly seen in ordinary limestone. The famous coquina rock, from which the old Spanish fort at St. Augustine in Florida was built, is made en- 336 THE CALCIUM FAMILY 337 tirely of coarse fragments of shells, firmly cemented to- gether. Marble is usually more free from silica and other impurities than common limestone. It has been subjected to intense heat at some time in the earth's history such that it was softened and upon cooling became more or less crystalline in structure. Chalk beds are composed of the remains of the shells of microscopic animals, known as globigerina. In some parts of the ocean at the present time globigerina ooze is being deposited where chalk beds of a future day may be found. Calcium carbonate also occurs in crystals, often of considerable size, in the shape of flat rhombohedrons and sometimes in six-sided crystals, known as "dog-tooth spar." It is sometimes mistaken for quartz, but need not be, for its hardness is only three in the scale while that of quartz is seven. Gypsum, calcium sulphate, is also widely distributed. One very pure variety, known as alabastine, is often beauti- fully colored and is used for vases and similar wares. The native phosphate of calcium as well as feldspars con- taining calcium have been mentioned elsewhere. 3. Description of Calcium. It has not been many years since calcium became an article of commerce, but it was first prepared more than a century ago by Sir Humphrey Davy, by methods similar to those he used for sodium and potassium. It is now made by electro- lyzing melted calcium chloride, much as sodium is by the Castner process. It is a silvery white metal, resem- bling sodium, but much harder. It may be cut and worked much as lead may be. It reacts readily with water Avith the evolution of hydrogen; when heated it combines rapidly with chlorine, bromine and oxygen. 4. Lime, CaO. This compound is made by calcining limestone in kilns. The native rock is heated strongly 338 APPLIED CHEMISTRY with coke or wood for several clays during which the carbon dioxide is expelled, thus, CaC0 3 - CaO + C0 2 . The better lime kilns are arranged so that the process is continuous. Limestone is fed in from above, while the finished product may be removed at the bottom. It is then shipped in barrels or loose to points where needed. Exposed to the air lime absorbs moisture and carbon dioxide and crumbles to a fine powder. Ulti- mately it becomes a carbonate again, so that the above reaction might be written CaC0 3 ? CaO + C0 2 . It reacts with water vigorously with the evolution of much heat. Use is made of this fact by balloonists as a means of securing heat at high altitudes without the use of fire. In case of considerable quantities of lime in contact with wood or other combustible material, the temperature reached, on the addition of water, is often sufficient to cause combustion. An illustration of this was seen at the time of the flood of the Kansas River at Kansas City in 1903, when many box cars loaded with lime were partially submerged in the freight yards. All of them took fire and burned to the surface of the water. 5. Uses of Lime. One of the most important uses is for making mortar in building foundations for houses, brick work, stone walls, and the like. For large build- ings, cement is used because of its greater strength, but it will be seen later that cement contains a considerable percentage of lime. Mortar is made by mixing sand with slaked lime. When exposed to the air, as in the foundation of a building:, chemical reaction with the carbon dioxide of the air takes place, the water is evap- THE CALCIUM FAMILY 339 orated, and ultimately, if properly made, the mortar becomes a silicious limestone. Thus, Ca(HO) 2 + C0 2 -> CaC0 3 + ILO. As the carbon dioxide in the air is limited in amount, the action is slow and probably continues for months or even longer. Moisture aids in the absorption. Slaked lime is often used to remove the hair from hides ; boiled with sulphur it is used as a spray to prevent fungous destruction of peaches, plums, grapes and possibly other fruits, Molded into round sticks it is used in the cal- cium light, already mentioned on p. 68. It is also valuable as a whitewash for basements, board walls, trees and as a cheap disinfectant. Dilute solutions of the hydroxide are called lime water and are used in various ways in medicine. Milk of lime, which is water containing considerable calcium hydroxide in suspen- sion is used with alum in settling the mud from river water for city supplies, also as a means of softening water, which will be explained later. 6. Plaster of Paris. tty calcining gypsum at such a temperature as to remove a portion of the water of combination, plaster of Paris is obtained. The reaction is CaS0 4 .2H 2 - CaS0 4 .H 2 + H 2 0. As put on the market it is a white powder. Its most re- markable property is that of being able to take up water and change back rapidly into the hydrated form again. This property is called "setting." If the quan- tity of water is not too great it takes place in a very short space of time. Examination with a magnifying glass shows the formation of a crystalline structure. In preparing plaster of Paris, if the calcining is con- tinued sufficiently long to expel all the combined water, the product is called "burnt plaster" and has very little 340 APPLIED CHEMISTRY value, for it takes up water again very slowly. Plaster of Paris is used in the finishing coat in plastering houses, for making plaster casts and statuary, in dental and other surgery, for interior raised decorations in large halls, panel work, as a filler for paper pulp, for school crayons, and in numerous other ways. When used in statuary, to prevent injury in washing, since calcium sul- phate is somewhat soluble in water, the surface is usually treated with a solution of paraffin in naphtha or some similar volatile oil. Gypsum is often called "land plaster" and is frequently used as a corrective of alka- linity in soils. 7. Cements. This class of complex substances may be divided into natural and portland cements. They all contain more or less lime, usually some magnesia, MgO, with silica, and aluminum oxide as the main ingredients. The first two of these are usually found together in what is called magnesium limestone; the others are ob- tained from shale, a hydrated aluminum silicate. When a quarry of rock contains all of these in such proportions as are more or less suited for the manufacture, the cement made therefrom is called a natural cement. However when the limestone is obtained from one quarry and the other rock from another, it is called a portland cement. This last name was given in England for the reason that when used the finished product resembled closely a spe- cial building stone known as Portland rock. Natural ce- ments, as a rule, are comparatively high in the lime con- tent. As this sets by the absorption of carbon dioxide from the air, such cements harden slowly. In preparing portland cement the separate portions are weighed in such amounts as have been found by experience to be best, are then calcined, mixed and ground to a fine pow- der. In the calcining two changes take place : the carbon THE CALCIUM FAMILY 341 dioxide is expelled from the limestone and a part of the water from the hydrated shale. These steps, in a sim- ple way, may be illustrated thus, CaMg(C0 3 ), -* CaO + MgO + 2C0 2 , Al 4 (Si0 4 ) a iiH 2 -> Al 4 (SiOJ 3 mH 2 + xH 2 0. As plaster of Paris sets quickly through the hydration of the molecules, so any cement with the partially dehy- drated silicate in excess will also. Since this is true of all portland cements, they harden rapidly even in the presence of much moisture and are for this reason often called hydraulic cements. For work in very cold weather cements with very high content of silicate are sometimes used; hence, they set before they have time to freeze. On the other hand, natural cements cannot be used under any such conditions or where much moisture will be pres- ent, as in piers for bridges, sewers, and similar places, for they set too slowly. Likewise, they cannot be used in large buildings, for the weight to which they are subjected before thoroughly hardened is sufficient to crush them. Concrete is made by mixing cement, sand and crushed rock, often called "grits," in the proportion of 1, 3, and 5. Water is added and the whole rotated in a mechanical mixer till relatively homogeneous. This is then poured into position and allowed to harden. Thus are made roadways, sidewalks, foundations, bridge piers, and a vast number of other things. Much of the building in cities now is of reenforced concrete. This is made by putting iron rods into position and pouring the concrete mixture over and about them. For roadways, woven wire fencing is sometimes used. Floors of fireproof buildings and roofs, supported temporarily by false woodwork are thus made. The reenforcement enables the concrete to withstand any sudden shocks or great strain. The great 342 APPLIED CHEMISTRY earthquake and fire resulting in San Francisco in the spring of 1906 gave great impetus to this method of build- ing. It was found that the reenforced, fireproof con- struction was able to stand with relatively little damage even such terrible forces of destruction. During the last year of the Great War reenforced concrete was even used for a number of medium-sized ocean going vessels. Its uses are being extended more and more every year, since lumber is becoming more scarce. In 1915, government bulletins showed that there was an output in the United States of 90,000,000 barrels of cement, with great in- creases each year over the preceding. During the war this fell off some, because little building was done, but only temporarily. 8. Prepared Chalk. Native chalk, it has been said, is formed from the minute shells of sea animals cemented together. It may be prepared artificially by treating a solution of some calcium compound with sodium car- bonate in solution, thus, CaCl 2 + Na 2 C0 3 - CaC0 3 + 2NaCl. The carbonate is a white precipitate; it is filtered out, washed, and molded into the desired shape or used as a powder. Properly made it is a perfectly smooth powder, entirely free from any gritty feeling. It is used in tooth powders and pastes, as well as in a variety of other ways in pharmacy. 9. Calcium Chloride, CaCl 2 , This compound is a white solid obtained as a by-product in the Solvay proc- ess of making sodium carbonate and in some other manufactures. For example, 2NH 4 Cl + CaO -> 2NH 3 + H 2 + CaCl 2 . By evaporation of the solution thus obtained, the salt crystallizes out as a decahydrate, CaCl 2 + 10H 2 0, which THE CALCIUM FAMILY 343 is very soluble in water and hence very deliquescent. If heated strongly the hydrate loses all its water and becomes a dry, porous solid. It is this form which is most desirable for drying gases in the laboratory. A few cannot be dried this way, as they form molecular com- pounds resembling hydrates. For example, ammonia unites with the calcium chloride, eight molecules for one and forms a compound with the formula, CaCl 2 + 8XII 3 . The crystalline variety is used in the brine tanks of many refrigerating plants instead of common salt. It is said to attack the metal pipes and boxes less than the sodium chloride does. Since a solution of cal- cium chloride may be made that will not freeze except at very low temperatures it has the advantage of being able to be transmitted considerable distances in re- frigeration systems and still possess such a degree of cold as may be necessary. Since the supply of calcium chloride is greater than the demand, attempts have been made to find other uses for it. For preventing dust on roadways its use has been mentioned on p. 143. In many localities asphaltic petroleum is used. This prevents erosion by heavy rains, as well as by winds and heavy traffic. The calcium chloride cannot prevent dam- age by rains on account of its great solubility. 10. Other Members of the Group. Strontium and ba- rium occur in native compounds corresponding to those of calcium, the sulphate and carbonate. Barium sul- phate, especially that made artificially, is used in many ways for adding weight. Paper pulp intended for card- board and white paints often contain it as a filler, or adulterant. The nitrates are both used in making fireworks and colored fires. Fusees, used upon railways to give warn- ing of the nearness of another train, contain mixtures of strontium nitrate, shellac or sulphur and potassium chlo- 344 APPLIED CHEMISTRY rate. The strontium compound gives the red color, the chlorate furnishes oxygen for rapid combustion, and the remaining portion is the fuel. Barium nitrate used in the same way gives a green fire. These were formerly used extensively for stage effects and still are where the electric spot light is not available. If to be burned indoors, shellac and not sulphur should be used on ac- count of the fumes produced. Strontium hydroxide, Sr(HO) 2 , is used in the refining of cane sugar. It causes the separation of portions of sugar from the molasses after the main crystallization has taken place which would not otherwise be obtained. Barium forms both a monoxide, BaO, and a dioxide, Ba0 2 . The latter is of interest in that it may be used for the manufacture of hydrogen peroxide, thus, Ba0 2 + H 2 S0 4 -> BaS0 4 + H 2 2 . Barium hydroxide, Ba(HO) 2 , is often used in the labora- tory as a reagent instead of lime water. Exercises for Review 1. Name the metals of the calcium group. By what other name are they known? 2. Give some of the familiar natural compounds of calcium. What is coquina? Marble? Chalk? Alabastine? 3. How may calcite be distinguished from quartz when the crys- tals resemble? 4. How is calcium prepared? Describe the metal. 5. How is lime made? Equation? 6. Give the characteristics of lime. 7. Give important uses of lime. How does mortar harden? Show by an equation. 8. How is plaster of Paris made? What is its most remarkable property? 9. Give uses of plaster of Paris. What is land plaster? 10. Name the two classes of cements and state how each is obtained. THP: CALCIUM FAMILY 345 11. What advantage has portland over the other? Can you think of any reason why the natural might be preferred? 12. What is concrete? How does it harden? What is reenforced concrete ? 13. How is prepared chalk made? Give uses. 14. What is the source of the calcium chloride of commerce? What two varieties? Explain the difference between them. 15. Give some valuable uses for calcium chloride. 16. Give some uses for the nitrates of strontium and barium. Why are they so used? 17. Name some other compounds of barium and strontium that are of some use. 18. Complete these equations, using amounts needed, Ba(HO) 2 SrC0 3 + HN0 3 -> , Sr(N0 3 ) 2 -t-NH,HO CHAPTER XXVIII HARD WATERS METHODS OF SOFTENING Outline Kinds of Hard Waters Effects of Hard Waters Treatment for Hardness (a) In the Home (6) For Commercial Enterprises Effects of Coagulants upon City Supplies Hardness as Belated to Soap Method of Estimating Hardness 1. Kinds of Hardness. Any water containing mineral matter in solution which will cause a precipitate with a soap solution is said to be hard. The soap solution must be perfectly clear: when added, the formation even of a slight cloudy appearance shows that the water is distinctly hard. More often hardness is caused by the presence of calcium or magnesium salts, but occasionally by iron. When the hardness is such that boiling will re- move it, it is said to be temporary; otherwise it is perma- nent hardness. This does not mean, however, that there is no possible way of removing it. Both kinds of hardness may be present and often are. Temporary hardness is caused by the presence in the water of the acid carbonate of calcium or magnesium, often called the bicarbonate, CaH 2 (C0 3 ) 2 . When boiled, decomposition takes place, with the formation of the normal carbonate. This being insoluble in water precipitates out, thus, CaC0 3 .H 2 C0 3 - CaC0 3 + C0 2 + H 2 O. It is the compound, CaC0 3 , which collects upon the inside of teakettles as a rough deposit, also in the hot water coils 346 HARD WATERS METHODS OF SOFTENING 347 in furnaces and water heaters, and in all steam boilers which use hard water. It is one of the greatest annoy- ances with which the engineer has to deal as well as one of great expense. All sorts of "water softeners" have been put upon the market under various names, many of them worthless. Fig. 62 shows two actual cases of sections of pipe taken from two manufacturing plants, which show that the "boiler scale" as it is called had nearly closed the pipes. It is said that a layer 14 inch in thickness lessens the heating effect by half, or in other Fig. 62. Scale in iron pipes, from an actual case. words it is the equivalent of an iron pipe 5 inches in thickness. In the cases shown in Fig. 62 the scale was about % i ncn thick. Under such conditions, in gas heaters or furnace coils, in the home, the water in the tank is warmed very slowly, while the iron of the pipe is being rather rapidly burned away. Finally, it becomes so thin that under the water pressure it bursts, and must be renewed. Permanent hardness is caused usually by the presence of sulphates of calcium or magnesium, although the chlo- ride, especially of magnesium, may be the cause. As these 348 APPLIED CHEMISTRY compounds are not decomposed at the temperature of boiling water, they remain in solution. 2. Removal of Temporary Hardness. Since temporary hardness is caused by the presence of an acid salt, it would seem that naturally an alkali would remove it. For laundry and bath purposes at home, dilute ammonia water is thus often employed. The reaction is shown by the equation, CaC0 3 .H 2 C0 3 + 2NH 4 HO -> CaC0 3 + (NH 4 ) 2 C0 3 . As the calcium carbonate is not soluble in water it set- tles to the bottom and leaves the water soft. The am- monium carbonate, unless present in large quantities has little effect upon the soap, hence is not objection- able. If much water is to be treated, this method is too expensive. Therefore, steam laundries, many of which use from 50,000 to 100,000 gallons of water per day, and other similar establishments, must employ a cheaper alkali. The cheapest known is lime water, and this is used. Daily analysis of the water is made so as to know exactly the amount of hardness present. This be- ing known, into large settling tanks, holding sufficient for a day's run, milk of lime is added sufficient to com- bine with the acid carbonate and convert it into the normal salt. This reaction takes place, CaC0 3 .H 2 C0 3 + Ca(HO) 2 -> 2CaC0 3 + 2H 2 0. The precipitated carbonate settles to the bottom and is then drawn off to the sewers. Lime water cannot be employed in the home because the quantity of water used is relatively small and any excess of the reagent would leave the water as bad or worse than before. Many cities, with river water more or less muddy, use milk of lime as already mentioned on p. 45 in removing the turbidity. Not only does it accomplish this, but to HARD WATERS METHODS OF SOFTENING 349 prevent any excess, even minute, of the alum or whatever is employed as a coagulant, a very slight excess of lime is used. This reacts, as shown above, with the precipi- tation at least of a portion of the temporary hardness. In such treatment of water, however, for turbidity, the permanent hardness is always increased as the equation will show, Al 2 (S0 4 ) 3 + 3Ca(HO) 2 -> 3CaS0 4 + A1 2 (HO) . The aluminum hydroxide is the gelatinous coagulum which drags down the mud, but the calcium sulphate is soluble to a degree and in this way adds to the perma- nent hardness as stated. 3. Removal of Permanent Hardness. For removal of this in large plants the water is treated w r ith the requi- site amount of sodium carbonate in solution. This reac- tion then takes place, CaS0 4 + Na 2 C0 3 -> CaC0 3 + Na 2 S0 4 . The sodium carbonate is added at the same time as the milk of lime previously mentioned. The precipitate, it will be noticed, is the same as in the other case; both will settle together and be removed at the same time. Sodium sulphate in this case remains in the water, but in small quantities causes no appreciably bad results. In large amounts any sodium salt would cause the pre- cipitation of the soap when added, from ionic reasons. This was found true when hydrogen chloride was passed into a solution of common salt to produce pure sodium chloride. (See p. 309.) The Permutit System. This is sometimes called the zeolite process, and is protected by rigid patents. The water containing the calcium or magnesium compounds is made to flow through cylinders containing an artificial sodium compound known as zeolite. In the process the 350 APPLIED CHEMISTRY magnesium and calcium in the hard water are removed by interchange with the sodium in the zeolite. It is said the water is rendered perfectly soft. In the case of very hard waters, however, considerable amounts of sodium salts are introduced into the softened water. As this is objectionable, the water must be further treated with lime as described already. 4. Effects of Hardness upon Soap. Without the soft- ening of the water used in large plants, the cost of the soap item would be enormous. No work can be done by soap as long as the water is hard, for it reacts with the compounds of calcium present thus, CaS0 4 + 2NaC 17 II 3 .,COO -> Na 2 S0 4 + Ca(C 17 H 35 COO) 2 . The equation shows by the interaction that a calcium stearate is formed, a species of soap, which is insoluble in water, and floats. It forms the disagre?able, greasy- feeling scum upon such waters and adhering to the sides of the bath tub. In laundry work it sticks to the clothing and under the hot iron it melts like wax and is thus spread out upon the garment as a dark gray or dirty looking spot. So with hard water, aside from the expense, high quality work in a laundry is impossible. When the soap has combined with all the calcium salts present in the water then it can begin to form emulsions for the removal of the foreign matter from the clothing, but not before. In all cities using hard water the soap bill is a constant tax upon the people. In Glasgow, Scotland, a few years ago, a change was made from the hard water supply which had been used for years to one much softer. In the first year the saving in soap bills was estimated' at $200,000. In the home, therefore, if the water is appreciably hard, small quantities of sal soda with very little ammonia water should be used both as a means of economy and for better results. Borax, as a water softener, when delicate HARD WATERS METHODS OF SOFTENING 351 garments are to be laundered or for washing the hair, is regarded as preferable to sal soda. Its reaction upon the hard water is not essentially different from that of the soda, except that the calcium is changed into a boratc instead of a carbonate, thus, Na 2 B 4 0- + CaS0 4 - CaB 4 O 7 + Na 2 SO 4 . 5. Degree of Hardness. Hardness in water is esti- mated in degrees. Thus, water which contains 1 grain, or about % 5 of a gram, in a gallon, of calcium carbonate or its equivalent of any other calcium salt is said to have one degree of hardness. This is about the equivalent of one part of calcium carbonate in 50,000 or 60,000 of water. For every hundred gallons of water with one de- gree of hardness, between 2 and 21/2 ounces of soap must be used simply to remove the hardness before doing any cleansing. Not only is this much soap wasted, but the greasy precipitate gathers upon the clothing as men- tioned. For a family of four it is estimated that about 16 pounds of soap would be required in a year to soften the water alone. Hardness sometimes reaches as high as ten or even twenty degrees in which case the soap used is no small item, when the laundry work is done at home. If treated with sodium carbonate, a little over !/ 2 ounce is sufficient to remove one degree of hardness from 100 gallons of water; 5 or 6 pounds would be sufficient for laundry and bath purposes for a whole year. With ten degrees of hardness 50 to 60 pounds would be needed. Since a pound of sal soda is very cheap it becomes a matter of great economy to soften the water thus be- fore adding the soap. Exercises for Review 1. What is meant by hard water? What two kinds are there? Explain the difference? . 352 APPLIED CHEMISTRY 2. Can water be both temporarily and permanently hard? Ex- plain. 3. What produces temporary hardness? Permanent? 4. What is boiler scale? Show by an equation how it forms. 5. How may temporary hardness be removed at home? On a large scale how is it done? 6. What is the effect upon city waters of removing the mud by a coagulant? 7. How do laundries soften the water for their w T ork? Show by equations how they remove both kinds of hardness. 8. What is meant by one degree of hardness? How high may water run? 9. State effect of great hardness upon cost of living. 10. What is the effect of hardness upon soap? What unpleasant results follow the use of soap in hard water? 11. Complete these equations: CaH 2 (CO 3 ) 2 + soap -> , CaSO 4 (heated) -> , CaS0 4 + NH 4 HO - , CaS0 4 + Ca(HO) 2 - , CaH 2 (C0 3 ) 2 + NH 4 HO -> , In which of these five equations is the water softened and in which not? CHAPTER XXIX CLEANING AND POLISHING Outline- Necessity for Cleanliness Solutions and Emulsions Cleansing by Soap Chemistry of Dry Cleaning Sinks and Waste Pipes Cleaning Metal Wares (a) Silverware (&) Copper and Brass (c) Aluminum Vessels ( 3AgN0 3 + NO + 2H 2 0. Silver nitrate crystallizes in thin, flat plates, rhombic in 370 APPLIED CHEMISTRY shape, colorless and transparent. Commercially, it is sold for medical purposes in small round sticks under the name "lunar caustic." These usually contain a small percentage of silver chloride. It has caustic prop- erties and is used for this reason in cauterizing wounds, such as dog bites, and others presumably infected. In solution it is sometimes used for sore throat and other- wise as an antiseptic. Exposed to light, especially in contact with organic matter, it turns dark. On this account it is a constituent of many indelible inks used in laundry marking; also of most hair dyes, and as the source of the silver compounds used in photography. 12. Silver Chloride, AgCl. If a solution of common salt be added to one of silver nitrate, silver chloride is produced, thus, AgN0 3 + NaCl - AgCl + NaN0 3 . It is a curdy white precipitate, especially if shaken vig- orously ; it rapidly turns dark when exposed to sunlight. It is very soluble in ammonium hydroxide, forming a complex silver salt resembling the hydrates. Thus, AgCl + 2NH 4 HO - AgC1.2NH 3 + 2H 2 0. Silver chloride is used extensively in preparing one class of photographic papers which will be studied later. 13. Silver Bromide, AgBr. This compound is made by adding to a solution of silver nitrate one of potassium or ammonium bromide, thus, AgN0 3 + NH 4 Br -> AgBr + NH 4 N0 3 . It is a very pale-yellow precipitate, much less soluble in ammonium hydroxide than is the chloride. It is much more sensitive to light. For this reason it is employed in photography for very rapid work both on plates and films, as well as for papers and enlargements. THE COPPER GROUP 371 14. Photography. Most everyone is interested more or less in photography, yet but few do much more than "press the button." In sensitizing plates and films a solution of silver nitrate and one of ammonium or po- tassium bromide are added to one of gelatine, whereupon the reaction shown above takes place. The emulsion is kept warm until the silver bromide -has formed a fine precipitate throughout the entire mass, after which it is allowed to solidify. The mass is then cut into shreds and treated with cold water to dissolve out the ammo- nium nitrate w r hich was formed as a by-product. It is then dried, melted and allowed to flow over the plate, forming a thin film. Most photographic papers used by amateurs are made in a similar way and contain the silver bromide in a thin film upon the paper. On ex- posure to light, plates and papers, containing silver bro- mide in the film, show no results. The plate is put into a solution of some reducing agent, more often now a coal tar product such as metol or hydroquinon, together with an alkaline salt such as sodium carbonate. The re- ducing agent acts upon the silver salt, decomposes it and sets the silver free. This occurs much more rapidly where the light has already 'begun the process. The operation is called developing the plate. Naturally, such portions of the landscape, or object being photographed, as reflect considerable light will affect the silver bromide the most, and upon developing will have the silver reduced most rapidly, hence will become dark. For this reason, since white objects appear upon the plate as black after development, it is spoken of as a negative. If the plate be allowed to remain in the developer indefinitely finally all the silver is reduced and the plate becomes black all over. To prevent this, at the proper time, known usually by the image beginning to appear upon the reverse side of 372 APPLIED CHEMISTRY the plate, it is removed from the developer, rinsed and put quickly into a solution of sodium thiosulphate, called "hypo." This is an excellent solvent for silver chloride and bromide, so that any portions of these salts left un- reduced by the developer are dissolved out and thus the reduction and darkening of the plate is stopped. This is called fixing the plate. The process is complete when on being held up to the light no white appears anywhere and the plate is more or less transparent. Developing is done under red light. Students of physics know that sunlight consists of three kinds of rays light, heat and chemical rays. In a study of the spectrum it has been found that most of the heat rays are at the red end and most of the chemic at the violet end of the spectrum. Therefore, light passed through red glass or other red objects has most of the chemic rays filtered out. Hence, the sensitized plate is not affected by such light. 15. Printing-Out Papers. There are two kinds of pa- pers used in photography in making the prints. Print- ing-out papers have a film containing silver chloride which is not nearly as sensitive to light as silver bromide. They are placed in a printing frame under the negative and ex- posed directly to good sunlight. The image prints out slowly and can be seen as it appears. When the proper degree of intensity has been reached it is fixed and toned. The fixing is with hypo as already described. The toning is done with gold or platinum compounds in which small portions of these metals take the place of an equivalent amount of silver and give a richer and softer print. The 1 i proof ' ' which the photographer furnishes is on printing- out paper and has not been fixed or toned. Hence, it is not permanent, and exposed to light soon darkens all over. 16. Developing- Papers. Developing papers, such as velox, argo, and many others now largely advertised, THE COPPER GROUP 373 contain silver bromide in the film of gelatine. They are intended to be printed by artificial light and if used in daylight it must be very much subdued and the exposure of the briefest possible time. No image appears upon ex- posure, but it must be brought out as with plates and films by developing. This fact gives to such papers the name developing papers. With ordinary electric light an ex- posure of from ten to thirty seconds, depending upon the negative, soon learned by a little practice, is usually suffi- cient. The developing is in the usual way, but a stronger solution is used and the image must come up quickly and sharply; if it does not, the paper becomes stained and the picture ruined. It is quickly transferred to the fixing bath and after a few minutes to a tray of water where it must be washed thoroughly. 17. Blue Prints. Blue prints, used somewhat for landscape work, but mostly by architects and engineers, are not made from silver compounds, but from iron. However, they will be considered at this time. A good grade of paper in a room with subdued light is brushed over with a solution of ferric ammonium citrate. This gives to the paper on the one side a pale-yellow color. For use it is exposed under a negative or architectural drawing to direct sunlight, siiice it is not very sensitive. When the proper exposure has been made, which may be known by a sort of bluish-bronze appearance, the paper is removed from the frame, and submerged in water. Wherever the sunlight has been able to pass through the negative or draAving it has reduced the ferric citrate to a ferrous salt, blue in color and not soluble in w r ater. The water, therefore, washes out the unchanged yellow ferric citrate and leaves the blue in the paper. Hence, in an architectural drawing since the original lines are in black, in the print they will be white upon a blue background. 374 APPLIED CHEMISTRY Blue print paper may easily be prepared by the student for his own use in the laboratory. Blue prints are so simple and so easily prepared that many attempts have been made to change them into sepia or black by the application of some reagent. Most formulas, however, in the hands of the amateur give rather indifferent and unsatisfactory results. 18. Occurrence of Gold. As a rule gold occurs free in nature; in Colorado, however, it is sometimes found in combination with tellurium as gold telluride. Originally, probably, the grains or nuggets were scattered through veins of quartz found in cracks in the earth's crust. How- ever, as erosion took place, the disintegrated particles of rock and gold have been carried down till now they are found in river beds and alluvial deposits in many places. 19. Mining of Gold. The early history of every gold field is largely the same. The prospector recovers the coarser particles of gold by "panning" or "cradling." This consists in washing out by a rocking motion, usually in a stream of water, the sand and lighter particles. From the heavier particles remaining in the cradle will be obtained, by hand, the grains and nuggets of gold. When the field becomes" proved as a valuable producer, capital comes in with dredging or hydraulic mining. In the latter, streams of water, brought from distances up in the mountains under tremendous pressure, are directed against the hillsides and other gold bearing deposits, which are thus disintegrated and washed down. The whole is made to flow through troughs or flumes over fre- quently recurring pockets of mercury or over copper plates amalgamated with mercury. In this way, the gold particles are caught by the mercury and at intervals the mercury is distilled and recovered for use again. In California large quantities of gold have been recovered in THE COPPER GROUP 375 this way; but from the fact that the great volume of water used has resulted in washing down over good agri- cultural lands immense quantities of sand and gravel, much litigation has resulted in recent years with the aban- doning of such methods in many places. (Fig. 64.) Dredging is usually employed for working deposits along river beds. For the purpose, a boat of considerable size is constructed upon the land to be dredged near some river or water supply. A pond is dug large enough to contain the boat and the water turned in to fill it. A steam or Fig. 64. Hydraulic mining. (From Cook's "A Practical Chemistry.") motor shovel, such as is used for extensive excavation work, is erected at one end of the boat. This scoops out the gravel in front of the vessel, swings it around upon the deck and dumps it where streams of water provided by pumps wash it off at the stern over amalgamated cop- per plates. The gold is caught by the mercury as already explained. Thus the pond is constantly being filled in the rear and dug out in front of the boat. Large tracts of alluvial deposits are worked in this way with very profit a- 376 APPLIED CHEMISTRY ble results. One of the best known sections in the Califor- nia fields is that at Oroville. "Quartz vein mining" is the term applied to that used when tunnels are run or shafts sunk to follow the veins of gold-bearing quartz. In such cases, as the rock is brought to the surface it is sorted by hand and the portions containing little or no gold are carried by small cars to the dump and constitute the "tailings." The quartz containing the gold is crushed and the gold recovered either by the chlorination or the cyanide process. In the former, the quartz rock is roasted, which serves to bring the gold to the surface or if it be in the form of the telluride, to volatilize the tellu- rium and leave the gold free. It is then dissolved by liquid chlorine or by treatment with bleaching powder mixed with hydrochloric acid. From the solution of gold chlo- ride thus obtained the metal is recovered by precipitating with ferrous sulphate or oxalic acid. If the cyanide proc- ess is used, roasting is not necessary. The gold is dissolved in a solution of potassium cyanide and precipitated from this by zinc. In many places stamp mills are now used. They consist of steel cylinders of considerable size and weight held upright by supports. They are continually lifted by machinery and dropped automatically upon the quartz, which is slowly fed upon the platform or table. The continued ' ' stamping ' ' crushes the rock into fine par- ticles; a stream of water washes it over amalgamated plates and it is recovered as in the case of dredging. 20. Characteristics of Gold. Gold is a soft, yellow metal with a specific gravity of 19 and melting point about 1,060 C.- It is thus between that of silver and cop- per. It is the most malleable of all metals and in the form of gold leaf is beaten so thin that it is said 1,500 sheets together are no thicker than an ordinary sheet of writing paper. Gold is the least active chemically of THE COPPER GROUP 377 the more familiar metals. It is not attacked by oxy- gen or tarnished by hydrogen sulphide in the air as is silver. It is soluble in aqua regia in which it forms gold chloride, AuCl 3 . It is also soluble in potassium cyanide by which a complex potassium auric cyanide is produced, KCN.Au(CN) 3 . Nothing need be said re- garding the uses of gold. When pure it is spoken of as twenty-four carats fine. Ordinary jewelry is not over fourteen carats and may even run as low as ten without being objectionable. Gold plating, or gilding, uses a cyanide solution and the process is similar to that al- ready described for copper and silver. American gold coins are 90 per cent gold and 10 per cent copper. Exercises for Review 1. Name the metals of the copper group and state their position in the periodic table. What is meant by a long period in the table? 2. What is a noble metal? 3. Describe the deposits of copper in the north; in the west. Name some important ores and give composition. 4. Give the characteristics of copper. 5. Name the most important uses of copper and state why so used in each case. 6. Name three alloys of copper and give composition. 7. Give formula for blue vitriol and state how made. 8. Explain how an electrotype is made. What advantage is there in an electrotype? Give uses for them. What is electrolytic copper? How made? 9. Name some other compounds of copper with formulas. 10. What is the source of most of our silver? 11. Give chief characteristics of silver. 12. Name some familiar uses for silver. How are mirrors made? 13. How is silver nitrate made? What is its commercial name? 14. Give characteristics of silver nitrate. Also its chief uses and state the principle underlying each use. 15. How is silver chloride made? Use? 16. How is silver bromide made? What use has it? 17. How are photographic plates and films made? 378 APPLIED CHEMISTRY 18. What is a negative? Why so called? 19. Explain the process of developing a plate. 20. Name two kinds of photographic papers. What is the dif- ference between them in action and composition? 21. Give process of making a print on each kind of paper. 22. In what does fixing a negative consist? What reagent is used for doing this? 23. What is the sensitizing agent in blue print papers? What happens when they are exposed to the light? What does the wa- ter do? 24. What can you say of the occurrence of gold? 25. What is meant by panning? By hydraulic mining? 26. Describe dredge boat mining. How is the gold recovered? What becomes of the mercury? 27. Of what does the chlorination process consist? 28. Give the chief characteristics of gold. 29. What are the two best solvents of gold? 30. How is an article gold plated? 31. What is meant by gold eighteen carats fine? 32. What is the carat of the five dollar gold coin? CHAPTER XXXI THE MAGNESIUM FAMILY Outline Members of the Group Magnesium () Natural compounds (&) Characteristics of (c) Uses (d) The Oxide (c} Other Compounds Zinc (a) Ores of (6) Reduction (c) Characteristics of Zinc (d) Uses (e) Zinc Sulphate (/) Zinc Chloride (g) Zinc Oxide Mercury (a) Occurrence (&) Characteristics (c) Uses (d} Mercuric Oxide (e) The Chlorides (/) Vermilion 1. General Comparison. Besides magnesium, beryl- lium, also known as glucinum, zinc, cadmium and mer- cury belong to this group. Beryllium is the lightest with an atomic weight of 9.1 and mercury the heaviest with a weight of 200. They all form compounds with a valence of two, and with the exception of mercury form no other series. Magnesium in some of its reac- tions resembles calcium and in analytic separations is often classed in that group. 379 380 APPLIED CHEMISTRY 2. Natural Compounds of Magnesium. Besides the sulphate found in sea water and in springs, known as Epsom salt, magnesium chloride, MgCl 2 , is found asso- ciated with common salt, and the double carbonate of magnesium and calcium, known as dolomite, occurs with limestone. Magnesium also is found in several natural silicates of more or less complex composition. One of the best known of these is meerschaum. It is a soft, white mineral used in making pipes for which it is prized because of the brown colors it assumes. Much more valuable than this is asbestos, a greenish, anhy- drous silicate. This mineral has a silken luster and is fibrous, so that by mechanical process it may be worked into a loose mass. In this form it has numerous uses. Mixed with magnesium oxide it is employed as an insulating ma- terial for steam pipes to prevent loss of heat by radia- tion; railway locomotives are thus jacketed; it is used for insulation against fire in many ways ; for large stage drop curtains; in stoves; about furnaces and furnace pipes; in gaskets for steam pipe fittings; brake linings for motor cars; as a cement for expensive stucco work; imitation tile and shingle roofing and in scores of other ways. 3. Characteristics of Magnesium. Magnesium is pre- pared much as is calcium, that is, by the electrolysis of the double salt of magnesium and potassium, KC1. MgCl 2 . It is a grayish white metal, with a specific gravity of 1.75. In the air it reacts slowly with oxygen by which a thin coating upon the surface is formed. When heated it burns vigorously with a brilliant white light. It is one of very few elements which combines directly with nitrogen. When burned in the air an ap- preciable amount of the product formed is magnesium THE MAGNESIUM FAMILY nitride, Mg 3 N,. Magnesium does not react with cold water, but will set free hydrogen from boiling hot water. It is high in the electromotive series of metals and rap- idly decomposes even dilute acids with evolution of hy- drogen. It is brittle, but when heated somewhat it may be drawn into wires ; flattened, this is spoken of as mag- nesium ribbon. It is also sold in the form of powder. 4. Uses of Magnesium. The powdered magnesium is used extensively for flashlight work in photography. For this purpose, sometimes it is blown into the flame of a specially constructed alcohol lamp; again it is mixed with potassium chlorate, which causes a very rapid com- bustion of the whole mass. The same mixture is used in fireworks to give the intensely white lights in the vari- colored bombs. Flashlight powders must be regarded as explosives and handled with great care. Magnalium is an alloy of magnesium and aluminum, light and tena- cious in properties, at present being made for use in air ships and for similar work where a light metal is needed. 5. Magnesium Oxide, MgO. This is sold under the name of magnesia. It is a fine, white powder, made by calcining magnesium carbonate, as lime is prepared from limestone. The reaction is the same, MgC0 3 -> MgO + C0 2 . It is an excellent insulating material against loss of heat. Hence, as stated elsewhere, it is mixed with as- bestos, about four parts to one, as a covering for steam pipes and all similar places where loss of heat is to be prevented. Our great railway locomotives, in cold weath- er, would never be able to make sufficient steam to pull a loaded train were it not for the heavy jacketing of the boilers with magnesia. Likewise, in refrigeration systems, the pipes which transmit the brine from the 382 APPLIED CHEMISTRY source to points of use are protected against access of outside heat. For a similar reason, and because it is infusible, it is used in lining electric furnaces and for making crucibles where great heat is to be employed. 6. Other Compounds. Magnesium sulphate, sold un- der the name of Epsom salt, is a light crystalline solid, with the formula MgS0 4 .7H 2 0. It is somewhat efflo- rescent. The use of the salt in medicine as a purgative is well known. It is also sometimes used in weighting cotton goods. Magnesium carbonate as prepared in the laboratory is a basic salt, having the formula MgC0 3 . Mg(HO) 2 . This is because of the hydrolysis which takes place. It is a fine, white powder often used in tooth pastes and in metal polishes. The chloride, MgCl 2 , has been mentioned as a deliquescent salt, found in sea water, causing the dampness often observed in table salt. 7. Occurrence of Zinc. The greater portion of the supply of zinc in the United States is obtained from the Joplin district, which includes not only southwest Missouri, but southeast Kansas and northeast Oklahoma. It occurs in this section as a sulphide, ZnS, known locally by the name of "jack" but scientifically as sphalerite or zinc blende. In some parts of the district it is mixed 'with a lead ore, galena, also a sulphide. In several of the Western States, for example, Colorado and Mon- tana, zinc occurs mixed with copper and silver ores, usually as a sulphide ; in some of the Eastern States it occurs as franldinite, ZnO.Fe 2 3 . 8. Reduction of Zinc Ores. Several of the metals thus far studied, notably the silver group, are either found free or may be reduced by heat alone. Some of the copper ores, because of their complexity and mixture of other metals, require special treatment, but even THE MAGNESIUM FAMILY 383 many of these may be reduced by heat alone. Most of the other metals studied thus far are reduced electro- lytically. Zinc introduces a third type, those which re- quire the aid of some reducing agent, such as carbon. The process will be considered very briefly. As carbon, even when heated, does not combine readily with sul- phur, it becomes necessar}^ to convert the zinc ores into an oxide. This is done by a process known technically as "roasting." The term means heating strongly with a plentiful supply of air. By this process the sulphur and zinc both are converted into oxides, thus, 2ZnS + 30 2 - 2S0 2 + 2ZiiO. The zinc oxide is next mixed with coke, heated strongly in cylindrical retorts made of fire clay. The zinc dis- tils out in the form of vapor and is condensed. 9. Characteristics of Zinc. Zinc is a bluish-white metal with a melting point of about 420 C., and boiling point of 950 C. It will be seen that a temperature suffi- cient to melt silver will vaporize zinc. "Spelter," as the product from the zinc smelters is called, is brittle ; but if heated, at a temperature between 125 and 150 C., it becomes malleable. Rolled into sheets at this temperature its malleability becomes permanent. It is a poor conductor of heat and electricity. It is only slightly attacked by the air, for the basic carbonate w^hich forms upon the surface is closely adhering and protects the metal almost as if painted. AVater is not decomposed by zinc, but dilute acids are readily, with the evolution of hydrogen. This is especially true of commercial zinc which is somewhat impure. Molten zinc mixes readily with silver, copper, tin and antimony, but not with lead or bismuth. Melted with lead it will float as ether upon water with only a small quantity of each dissolved in the other. This fact is employed 384 APPLIED in separating silver from lead when obtained from ar- gentiferous lead ores. 10. Uses. Because of its nonconductivity it is often used for lining refrigerators and beneath or behind stoves to protect the floors or walls. Its most extensive use, probably, is for "galvanizing" iron. This is not done electrolytically as the name might imply, but by dipping the heated iron, previously well cleaned, into molten zinc. Upon withdrawing the iron a coating of zinc adheres. Practically all iron wire fencing is now made in this way. Galvanized sheet iron is used for gutters, downspouts, cornice work, granaries, wind mills, feed and watering troughs, as well as for countless smaller articles. Dry cells consist of a container made of zinc which serves as the positive plate, a carbon rod at the center as the negative, and a packing, in part, of sal ammoniac or some other salt which reacts with the zinc. Many valuable alloys of zinc are familiar. Brass and German silver have already been mentioned. Some "white" metals, from which various articles of plated silverware are made, are an alloy of copper and zinc in which the proportion of zinc is high, to such an extent that the color of the copper is not apparent at all. 11. Zinc Sulphate, ZnS0 4 .7H 2 0. Commercially this compound is known under the name of white vitriol. It contains the same quantity of combined water per mole- cule as magnesium sulphate. It may be prepared by treating zinc with dilute sulphuric acid or from the native blende in a similar manner. Like magnesium sulphate it is efflorescent. It is used somewhat as a mordant and to some extent as an antiseptic in medicine. A mordant is a reagent which has the power of fixing a dye in the fibers of a cloth so that it is not easily removed by water. THE MAGNESIUM FAMILY 385 12. Zinc Chloride, ZnCl 2 . This is a white compound which may be prepared by treating zinc with dilute hydrochloric acid in slight excess and boiling to dry- ness. It is very deliquescent and in solution gives an acid reaction owing to partial hydrolysis. For this rea- son it is commonly used in soldering as a flux to give a clean surface. The free hydrochloric acid in the solu- tion dissolves the film of oxide always present, so that the melted solder may come into direct contact with the metal. Melted zinc chloride has the remarkable property of be- ing able to dissolve cellulose ; by dipping sheets of paper into the liquid, parchment is made. 13. Zinc Oxide, ZnO. As usually obtained, zinc oxide is a faintly yellow compound. Perfectly pure it is white when cold, but distinctly yellow when hot. It is a valua- ble by-product of many smelters, being obtained by the roasting of ores containing a very small percentage of zinc. The oxide is vaporized and carried over with the sulphur dioxide and other gases and is condensed in large, cool chambers upon coarse sacking. Afterward it is purified by continued heating below its point of vaporization. It is used extensively in the manufacture of paints and enamels. Ground in oil the former is sold under the trade name of "zinc white." Small quantities of the oxide, carefully purified, are used in pharmacy for making salves and other applications for skin diseases. Its action is probably largely antiseptic. It is also used in dentistry in making temporary fill- ings for teeth, especially for children. For this purpose it is mixed with glacial phosphoric acid (p. 280) to form a soft mass which is placed in the prepared cavity. It very soon hardens much as does plaster of Paris, form- ing an oxyphosphate of zinc. This oxide is of interest, for the reason that it possesses a dual character, serv- 386 APPLIED CHEMISTRY ing sometimes as if basic and again as if acidic. In the hydrated form, Zn(HO) 2 , it readily dissolves in dilute acids, forming zinc salts, in which zinc is the posi- tive ion. On the other hand, it will dissolve, though somewhat less readily, in strong bases, such as sodium hydroxide. It then forms salts called "zincates" in which zinc is found in the negative ion. Thus, 2HCl + Zn(HO) 2 - ZnCl 2 + 2H 2 0, 2NaHO + Zn(HO) 2 - Na 2 ZnO 2 + 2H 2 0. In these cases the zinc hydroxide evidently has ionized as follows, n(HO) 2 5 H 2 Zn0 2 * Zn + (HO) (HO) + H,H + Zn6 2 . Therefore, although zinc hydroxide is but slightly solu- ble in water, such portions as do dissolve are evidently ionized in both ways in fixed definite amounts. From the location of zinc in the periodic table, not far from the diagonal, such behavior might be expected. 14. Occurrence of Mercury. Mercury has been- known at least since 300 B.C. when it was prepared by Theo- phrastus, who gave it the name meaning liquid silver. Its symbol is derived from the Greek word, hydrargyrum. It is found in comparatively small quantities and in few places in the world. In America the mines in central California are the most productive. In Europe, Spain and Austria produce the greater part. In all cases the sulphide, HgS, known as cinnabar, with some inter- mingled free mercury, is the ore found. From this the mercury is obtained by distillation. 15. Characteristics of Mercury. Mercury is the only metal, liquid at ordinary temperatures. It becomes a solid at about -39 C. and boils about 360. In the solid form mercury is somewhat malleable and to a consid- erable extent resembles lead. It dissolves or alloys THE MAGNESIUM FAMILY 387 readily with many of the other metals, especially gold, silver, copper, tin and zinc. Such alloys are called amal- gams. They may be obtained by putting the finely di- vided metals into mercury, or a surface amalgamation may be had by dipping the clean metal into a solution of some salt of mercury. A bit of clean gold dropped upon mercury will sink and dissolve as a lump of sugar in a cup of hot water. Again, a clean penny in a solu- tion of mercuric nitrate soon takes on a coating of mer- cury which upon slight rubbing has the appearance of burnished silver. In the latter case an amount of cop- per has dissolved equivalent to the mercury deposited, that is, one atomic weight of copper has been dissolved for each atomic weight of mercury deposited. Mercury is not tarnished by the air, nor does it set free hydrogen from acids It decomposes nitric acid and boiling sul- phuric with the usual results in such cases. The two equations following indicate the reactions, 3Hg + 8HN0 3 -> 3Hg(N0 3 ) 2 + 4H 2 + 2NO, Hg + 2H 2 S0 4 - HgS0 4 + 2H 2 + S0 2 . 16. Uses of Mercury. The use of mercury for amalga- mating copper plates and otherwise in obtaining gold has been described. (See p. 374.) It is used in thermometers and to some extent in barometers, although the aneroid is taking the place of the mercurial barometer in many places. The advantages of mercury in thermometers are that it has a high and uniform rate of expansion through a lone: range of temperature and is of high boiling point. Alcohol thermometers are valuable for use below the freezing point of mercury. Zinc plates in galvanic batteries are commonly amalgamated to prevent local circuits with rapid wasting of the metal. In dentistry amalgam fillings, consisting of silver and tin with sufficient mercury to form a soft pliable mass, 388 APPLIED CHEMISTRY are commonly used except for front teeth. This amal- gam has the property of setting rapidly and of retaining its color, while dental amalgams containing cadmium, a metal formerly used considerably, turn dark and be- come unsightly. 17. Mercuric Oxide, HgO. This is a heavy solid, crys- talline or amorphous, yellow, orange or red in color, according to the method by which it is obtained. The yellow is obtained by treating a warm solution of mer- curic chloride or of some other mercuric salt with sodium or potassium hydroxide solution, in slight excess. The hydroxide, formed at first, quickly decomposes into mer- curic oxide and water, thus, , HgCl 2 + 2KHO - Hg(HO) 2 + 2KC1-* HgO + H 2 + 2KC1. It is regarded as the same chemically as the orange or red variety but in a finer state of division, since by trituration the red variety changes to yellow. It is used somewhat in medicine in the form of salves, mainly on account of its antiseptic properties. 18. Mercurous Chloride or Calomel, Hg 2 Cl 2 . This is a finely divided white powder used in medicine. It is easily prepared in the laboratory by treating a solution of mercurous nitrate with a solution of common salt or hydrochloric acid, thus, Hg 2 (N0 3 ) 2 + 2NaCl - Hg 2 Cl 2 + 2NaN0 3 . As it is insoluble in water it is easily separated by filtra- tion. On a large scale it is made by mixing common salt, mercury and mercuric sulphate intimately and dis- tilling. The calomel passes over as a vapor and is con- densed. It is apt to contain small quantities of the mer- curic chloride and should be freed from it by washing. Like all salts of mercury, calomel is poisonous and all the excretory organs are thereby stimulated by its pres- THE MAGNESIUM FAMILY 389 ence. Being an unsaturated compound it tends to take up an additional negative ion and form the mercuric salt. Therein lies the danger of its use in medicine, that of causing mercurial poisoning with consequent saliva- tion. With the hydrochloric acid present in the stomach or in the presence of acid foods, the mercurous molecule begins to change into the mercuric chloride which is much more soluble. Its action then upon the system is rapid, and before it is eliminated the salivary glands may be affected, followed by the well-known soreness of gums and teeth. Such instances are not common now, for physi- cians, knowing the danger, administer the calomel mixed with common soda. This neutralizes the acid in the stom- ach and prevents the calomel changing to the soluble form. Even as given now, however, acid foods should not be used at the same time. 19. Mercuric Chloride, HgCl,. This is commonly known as corrosive sublimate. It is prepared by sub- limating a mixture of common salt and mercuric sul- phate. It is highly poisonous. The white of eggs is regarded as the best antidote, with which the mercuric salt forms an insoluble mass. Owing to its poisonous properties it is an excellent antiseptic and is frequently used for sterilizing surgical instruments and upon band- ages for wounds. Applied in this way it is not poison- ous. To prevent "scab," a disease which causes a rough surface upon potatoes, a dilute solution of corrosive sublimate is sometimes used in which the seed potatoes are immersed a short time before planting. 20. Mercuric Sulphide, HgS. The artificial sulphide is sold under the name vermilion. It is a brilliant red pow- der, used as a pigment. Prepared in the laboratory by adding hydrogen sulphide to a solution of some mercuric salt it is a black powder. The reaction is HgCl, + H,S -* HgS + 2HC1. 390 APPLIED CHEMISTRY If this black precipitate is sublimed, it changes to the red variety. Exercises for Review 1. Name the metals of the magnesium group. Where are they located in the table? What is their valence? 2. Give the important natural compounds of magnesium. What are the chief uses for asbestos? 3. Give the characteristics of magnesium. In what two forms does it occur? 4. What are the principal uses of magnesium? State why so used. o. What is magnesia? What are its chief uses? 6. Give formulas and uses for the sulphate and carbonate of magnesium. 7. Name the important ores of zinc. Where is it mostly ob- tained in the United States? 8. How is zinc blende reduced? Name two other methods of re- duction and some metal obtained each way. 9. Give the most important characteristics of zinc. 10. What is galvanized iron? Its important uses? 11. How is zinc sulphate obtained? Its commercial name? What other vitriols have been studied? 12. What is a mordant? 13. Give method of making zinc chloride. Name some impor- tant use. 14. What is the source of the commercial supply of zinc oxide? What is its chief use? 15. From what are the temporary fillings for teeth made? 16. Chemically, what point of interest attaches to zinc oxide? .17. Why will zinc oxide dissolve both in acids and bases? 18. What is the only ore of mercury? Where found? 19. Give the important properties of mercury. What is an amalgam? How may amalgams be made? Name some uses for them. 20. Give some valuable uses for mercury. 21. How may yellow mercuric oxide be obtained? What other varieties occur? Wherein are they different? 22. What is calomel? What danger attaches to its use as a medicine? THE MAGNESIUM FAMILY 391 2a. What is corrosive sublimate? Why so called? What uses lias it? 21. How may vermilion be made? Of what use is it? 125. Complete these equations and state what process is repre- sented, Mg + O 2 -> , MgCO 3 (heated) , ZnO + C -> , Zn + HC1 - , ZnO + HC1 -> , HgS + <>,-, Hg a (NO 3 ) 2 + NaCl > , HgSO 4 + NaCl + Hg -* , HgSO 4 + NaCl -^ , . In the above equations the student must supply coeffi- cients as needed for proper quantity of each reagent. CHAPTER XXXII THE ALUMINUM FAMILY Outline- Members of the Group Compounds of Boron Aluminum (a) Occurrence in Nature (b) Precious Stones (c) Manufacture of Aluminum (d) Characteristics (e) Uses . (/) Alloys (g) Alums (7i) Aluminum Hydroxide 1. Members of the Group. Aluminum is the only im- portant metal of the family. Boron is a member and the lightest with an atomic weight of only 11. It forms two compounds of some importance, borax and boric acid. The former has been studied under the sodium compounds. Boric acid is a white, crystalline solid, mildly antiseptic, and frequently used in solution as an eye wash. 2. Abundance of Aluminum. By referring to Fig. 9 on p. 52 it will be seen that aluminum constitutes about 8 per cent of all the matter of the earth, and ranks next to silicon in abundance. It is a constituent of all clays and of the feldspar rocks from which clays are derived by decomposition. Mica, a rock which easily splits into thin leaves used in stoves and for insulation in various ways, is a silicate of aluminum and potassium. Kaolin, Fuller's earth, garnets, sapphires, emeralds, rubies, are all aluminum compounds. 392 THE ALUMINUM FAMILY 393 Corundum, an impure oxide of aluminum, ranks next to the diamond in the scale of hardness. Emery is of the same composition and is familiar to all. It is used in various forms as an abrasive: emery powder, grind- stones, and emery wheels, whetstones, emery paper and emery cloth. Kaolin is a pure white clay used in making porcelain ware and the various grades of china. Ful- ler's earth is a similar compound used in absorbing the coloring matter from vegetable oils such as that made from cotton seed. It also has various other uses. 3. The Precious Stones. To the mineralogist, rubies, sapphires and emeralds are all sapphires. They are crys- tallized aluminum oxide, ALC^, and differ from emery in that it is uncrystallized and less pure. Their color is due to small quantities of another metallic oxide. At the present time great quantities of these jewels are being manufactured even more perfect than the natural stones and with all their characteristics. The white sapphire, which resembles the diamond somewhat though less bril- liant, is of the same composition as the other sapphires, but uncolored. These stones are sometimes spoken of as synthetic. For some years, it is said, over nine mil- lion carats of rubies and about half as many sapphires have been made annually. The garnet is more complex in composition than the above stones being an orthosilicate of aluminum and calcium, Ca. 5 Al.,(Si0 4 ) 3 . 4. Preparation of Aluminum. At the present time alu- minum is made by the electrolysis of bauxite, a hydrated oxide of aluminum. The principle is the same as used for sodium, calcium and several other metals already studied. Bauxite, however, does not melt easily, neither does it dissolve in water. The problem, therefore, is to secure it in liquid form so that it may become a conductor. An- other compound of aluminum known as cryolite, a word 394 APPLIED CHEMISTRY which means ice stone, and given to this mineral because of its low melting point, is put into an electric furnace and melted. Powdered bauxite is added and dissolves read- ily. It will be seen that the cryolite is simply a solvent or, as it is technically called, a flux. When the current is passed the bauxite decomposes and the aluminum collects at the cathode. Fig. 65 illustrates the process. Fresh quantities of bauxite are added from time to time as needed, the aluminum is drawn off occasionally and the process is continuous. The heat generated by the re- sistance to the current keeps the cryolite melted. The manufacture of aluminum is carried on where cheap Fig. 65. Manufacture of aluminum. electric power may be had, especially at Niagara Falls. Up to the present time no commercial method has been devised for extracting aluminum from such complicated compounds as clays. Such a process would be eminently desirable. 5. Characteristics of Aluminum. Aluminum is a white metal, of low specific gravity, being only 2.6 times as heavy as water. It is an excellent conductor both of heat and electricity. As a given weight of aluminum will make a wire of much greater cross section than the same weight of copper, it is even better than copper as a conductor. In tensile strength it is not greatly dif- ferent from copper and most other common metals, ex- THE ALUMINUM FAMILY 395 cept steel, but it has a tendency to crystallize and un- protected wires to become somewhat brittle. Its melting point is about 700 0. At ordinary temperatures it does not react appreciably with oxygen and does not tarnish greatly in the air. It is ductile and malleable and easily made into thin foil. While it is below magnesium in the electromotive series of metals, it is strongly positive. It decomposes concentrated hydrochloric acid vigor- ously, with the evolution of hydrogen. With nitric acid the action is practically nil; with sulphuric acid there is Fig. 66. Thermit crucible, sectional view. practically no action at room temperature, but when heated to boiling the metal is oxidized and sulphur di- oxide evolved as is usual in such cases. Strong alkaline solutions attack aluminum readily and form a class of salts called aluminates, corresponding to the zincates, mentioned previously. 6. Uses.- On account of its electric conductivity it is used in some localities as feed wires for trolley systems. In the home it makes an ideal cooking vessel. Its con- ductivity is about the equal of copper, so that all por- tions of the vessel become heated alike and food prod- ucts which burn easily are much less readilv scorched 396 APPLIED CHEMISTRY than in ordinary granite ware or tinware. Further, it is not attacked by weak acids such as those found in any fruits used as food. Moreover, it is light, does not tarnish readily, and is easily cleaned. Anything alkaline Fig. 67. A thermit crucible ready for use in mending a broken casting. (By courtesy of the Goldschmidt Thermit Co.) in character cannot be cooked in aluminum vessels but none of our food is alkaline. In the finely powdered form aluminum is mixed with linseed oil and used as a paint for metallic objects to which it adheres well. Its use in this way is seen in many of the penny-weighing THE ALUMINUM FAMILY 397 machines, mail boxes, steam and hot water radiators, and other familiar objects. Very considerable quanti- ties of powdered aluminum are used in a patented arti- cle called "thermit." This consists of ferric oxide and Fig. 68. A thermit crucible in operation, mending a broken casting. (Hy courtesy of the Goldschmidt Thermit Co.) aluminum intimately mixed; for use it is put into a cru- cible of suitable size, conical in shape, as shown in Fig. 66, and a small amount of powdered magnesium placed on top as kindling. When eve^thing is ready the mag- nesium is lighted. The heat thus obtained is sufficient 398 APPLIED CHEMISTRY to start the chemical action between the aluminum and ferric oxide, Fe 2 3 . Once begun it is self continuous from the heat liberated'. In a short time the aluminum has become aluminum oxide and the iron is free, in a mol- t?n condition with a temperature over 1,500. In fact, it is said that a temperature of 3,000 is often reached in" the process. By substituting the oxides of other metals, such as chromium or vanadium or manganese, it is possible to obtain these rare metals in a pure condition. The process is used for welding almost everything of any size, made of iron or steel. Thus are mended broken drive wheels for locomotives, propeller shafts for great engines, rails in street railway systems, and the like. It is frequently used on shipboard for repairs not easily made otherwise. The aluminum oxide obtained as a by- product, is often used for the manufacture of synthetic rubies and sapphires already mentioned and as an abra- sive. Another extensive use for aluminum is in the man- ufacture of steel. There is a tendency for molten steel, made as much of it is, to retain oxygen or other gases within the mass. This is probably due to the viscosity. When such ingots of steel are made into rails these "air holes" form weak places and probably are occasionally the cause of railway accidents. On account of the ten- dency of aluminum to combine with oxygen readily at high temperatures, a certain amount of the metal is added to the steel: the aluminum combines with the oxy- gen, forms a kind of slag and rises to the top. 7. Alloys. Aluminum forms several alloys of value. Magnalium, containing about 2 per cent of magnesium, has already been mentioned. (See p. 381.) Aluminum bronze is prepared in two varieties, one with a very small percentage of copper, which is even whiter than pure aluminum and resembles silver . closely except in THE ALUMINUM FAMILY 399 density. It is used extensively in novelty articles and occasionally in such kitchen utensils as teapots. The other variety, with copper as high as 90 per cent, some- what resembles gold in color and is frequently used in making Avatch cases as well as a great variety of novelty articles. 8. Alums. An alum is a double sulphate of a univalent and a trivalent metal. There are many of them, but the most common is potassium aluminum sulphate, K 2 S0 4 .A1 2 (S0 4 ) 3 .24H 2 0. Almost as common is ammo- nium alum in which ammonium has taken the place of the potassium in common alum. Sodium being univalent, en- ters into the composition of several alums; chromium and trivalent iron, likewise, may take the place of alu- minum in common alum. They are all hydrates and con- tain the same amount of water; they are all also iso- morphous, that is, they all crystallize in the same shape. "Burnt" alum is obtained by heating alum to expel the water of combination. It is a mild caustic and is some- times used medicinally in that way, especially for ulcer- ations of the mouth. 9. Uses of Alum. Mention has already been made that alum is used as a coagulant in purifying muddy waters for city supplies. More often, not alum, but aluminum sulphate is used, although it is generally referred to as alum. Its reaction with the milk of lime is 3Ca(HO) 2 + A1 2 (S0 4 ) 5 - A1,(HO) 6 + 3CaS0 4 . Likewise, alum has been spoken of as an ingredient of baking powders. More often, here also, aluminum sul- phate is used instead of real alum. It is supplied the baking powder factories under the trade name of C.T.S. meaning "cream tartar substitute." The chemical action has already been noted on page 329. 10. Aluminum Hydroxide, Al,(HO) (i . This is easily 400 APPLIED CHEMISTRY prepared in the laboratory by treating a solution of alum with ammonium or sodium hydroxide, taking care not to use the latter reagent in excess. Sodium carbon- ate may be substituted for the alkali. It is a white gelatinous precipitate, in many ways a very interesting compound chemically. Like zinc hydroxide, it ionizes both as a base and as an acid, thus. -H-+ A1(HO) 3 ^A1+ (HO), (HO), (HO), H 8 A10 a *= H, H, H + Al"<5 8 . As a result aluminum hydroxide is very soluble not only in acids, with which it forms aluminum salts with alu- minum as the positive ion, but is also soluble in bases, with which it forms aluminates, in which the negative ion is -A1O 3 . To illustrate, A1(HO) 3 + 3HC1 -> A1C1 3 + 3H 2 O, H 8 A10 3 + 3NaHO - Na 3 A10 3 + 3H 2 0. Its position in the table, near the acid forming elements, would lead us to expect such behavior. On account of its gelatinous character not only has it the power of clarifying muddy waters, but also of remov- ing colors from solutions. Thus, if an alum solution, deeply colored with some dye, such as carmine, has a little alkali added to precipitate the aluminum as hydrox- ide, in settling, the aluminum hydroxide will carry with it practically all the coloring matter. Such precipitates dried and ground in oil are sold as tube paints for artists under the name of lakes, of crimson and other brilliant colors. It is the same principle that makes it a good mor- dant. Precipitated within the fibers of the cloth it holds or fixes the color. Canvas for tents and other fabrics are sometimes waterproofed by this compound. Treated first with aluminum chloride or some similar compound THE ALUMINUM FAMILY 401 the cloth is heated by steam which hydrolyzes the alu- minum compound, forming aluminum hydroxide within fibers of the cloth. Upon drying it becomes waterproof. Some papers are sized by aluminum hydroxide. To the pulp aluminum sulphate and rosin soap are added ; through hydrolysis aluminum hydroxide is precipitated in the pulp. When dry it is run between hot rollers. This melts the rosin and gives a surface to the paper while the aluminum hydroxide fills the pores, so that ink is not taken up readily. Exercises for Keview 1. Name the members of the aluminum family and give location in the table. 2. State Avhat is true of the abundance of aluminum. Name some familiar natural compounds. 3. What is emery? The ruby? Kaolin? A synthetic stone? 4. Describe the preparation of aluminum. What is a flux? 5. Give the characteristics of aluminum. 6. Why is aluminum suited for cooking vessels? What advan- tage has it over copper? 7. Describe the use of thermit. 8. Name some alloys of aluminum and give uses. 9. What is an alum? Name two. What is burnt alum? 10. What is the meaning of the term isomorphous? 11. Why is aluminum hydroxide soluble in both acids and bases? What other hydroxide has been seen to have the same property? 12. How are painters' lakes made? 13. What is meant by sizing paper? 14. Complete the following equations, Al,(S0 4 ) 3 + KHO - , A1,(HO) 6 + H 2 S0 4 - , A1,(HO) B (heated) -> , A1 2 O 3 (electrolysed) , Fe 2 O 3 + Al , Al h O 2 -^ . Note. The student will use the amounts as needed in the above equations. CHAPTER XXXIII THE LEAD FAMILY Outline Members of the Group Tin () Occurrence (b) Characteristics (c) Uses (d) Alloys (e) Compounds Lead (a) Occurrence (b) Characteristics (c) Uses (of) Alloys (e] Compounds (a) The Oxides (b) Lead Acetate (c) White Lead (d) Chrome Yellow Storage Batteries 1. Metals of the Group. The only common metals be- longing to this group are tin and lead, the former with an atomic weight of 119 and the latter, 207.1. Their position in the table should show a valence of four and their higher oxides indicate this. 2. Occurrence of Tin. The oldest tin mines of the world are those of Cornwall, England. It is said that the ancient Phoenicians obtained their supplies from this source. These mines now at great depth and ex- tending out under the ocean are still in operation but produce scarcely 10 per cent of the world's output of the present time. Most of that used comes from the 402 THE LEAD FAMILY 403 East Indies where it is found as tin oxide, Sn(X, called cassiterite. It is the same ore as that from the English mines. 3. Characteristics. Tin is a white metal with a melt- ing point of 232 C. It is soft, very malleable and has a specific gravity of 7.3. It is crystalline in structure, but much less so than antimony or bismuth. Like phos- phorus, sulphur and some other elements already stud- ied, tin also occurs in an allotropic form not often seen. Kept continuously below 20 C. it sometimes changes to a gray powder, expanding to such an extent that its specific gravity is only 5.8. Tin is not tarnished in the air or attacked by any of the organic acids. It decom- poses hydrochloric acid with the evolution of hydrogen, also concentrated nitric, with the formation of nitrogen peroxide. Hot sulphuric acid gives off with tin sulphur dioxide, as is usual in such cases. 4. Uses of Tin. Because of its permanence in the air tin is used extensively in protecting iron in what is called "tin plate." It is made in a manner similar to that used for galvanizing iron. Clean, heated sheets of steel are dipped into molten tin and upon removal a coating adheres. However, as iron is more electroposi- tive than tin, if the coating is scratched so as to expose the iron the corrosion is then rapid. The reverse is true with galvanized iron. Of tin plate are made the so-called "tin cans" used so extensively in preserving various food products. During the year 1919 more than six bil- lion tin cans were used in the United States in the various canned-food industries. In the infancy of food preservation in this manner, each canner made in his own establishment by hand labor the cans needed. A good workman could not produce over 150 per day; now by machine they are turned out at the rate of about 404 APPLIED CHEMISTRY one per second. Heavy tin plate is used for roofing and gutters. Some years ago cooking vessels of tin plate were common, but they have been largely replaced by granite ware, which is more serviceable, and more recently by aluminum. Copper cooking vessels used in large eating houses, such as the Harvey system, are tinned on the inside to prevent attack by organic acids. This has to be done somewhat frequently, but the proc- ess is simple. The vessel is thoroughly cleaned as if for soldering, is heated to the melting point of tin and then the powdered metal rubbed on the surface to which it adheres. The flux used in cleaning the copper, usu- ally ammonium chloride, prevents oxidation when the ves- sel is heated. Common brass pins usually have a thin coating of tin to prevent their tarnishing in the air. 5. Alloys. Many valuable alloys of tin are used in the arts. Bronze is composed of copper and tin, some- times with zinc added; brittania and pewter have al- ready been mentioned, as have certain fusible alloys. (See p. 289.) Soft solder contains tin and lead in equal proportions. Tin is also an important component of the most common dental amalgams. 6. Compounds. Tin forms both stannous and stannic salts, represented by the chlorides, SnCl 2 and SnCl 4 . The stannous chloride is an unsaturated compound and therefore a reducing agent. Added to a solution of mercuric chloride, first a white precipitate of calomel is obtained; upon warming or adding more stannous chloride a gray or black precipitate is formed consisting of finely divided mercury or a mixture of it with mer- curous chloride. These two equations represent the re- actions occurring, THE LEAD FAMILY 405 2HgCl a + SnCL - SnCl 4 + IIg 2 CL, Hg 2 Cl 2 -f SnCl 2 -> SnCl 4 + 2Hg. The experiment serves as a test for mercuric compounds, or reversed, for a stannous salt. On account of this reducing- power of stannous chloride it is used with "old chloride in toning printing out papers as already described. There are two oxides of tin, stannous, SnO, and stan- nic, Sn0 2 . The latter is the compound found native. It may be obtained by treating tin with concentrated nitric acid and heating the white powder obtained. It is white when cold, but distinctly yellow when hot. Stannic acid, which is a white gelatinous compound, is used extensively in weighting silk goods. The chlo- rides are used somewhat as mordants. 7. Occurrence of Lead. Galena, PbS, is the only im- portant ore of lead. It is a lustrous, dark gray mineral crystallizing in cubes, with cubical lines of cleavage. It is associated with many of the zinc deposits in south- west Missouri and with silver and other metals in many of the Western States. 8. Characteristics of Lead. Lead is a dark gray metal with a specific gravity of 11.38; it is soft and malleable but of little tenacity. It tarnishes somewhat readily in the air, but the coating adheres firmly and serves to protect the metal from further oxidation. The melt- ing point is 325 C. Being just above hydrogen in the elec- tromotive series it has little power of replacing that element in acids. With nitric acid it reacts as do most of the metals to form nitric oxide, thus, 3Pb + 8HNO., -* 3Pb(N(X) 2 + 4H 2 + 2NO. Sulphuric acid, boiling hot and much concentrated pro- duces sulphur dioxide, thus, 406 APPLIED CHEMISTRY Pb + 2H 2 S0 4 -> PbS0 4 + 2H 2 + S0 2 . Acetic acid, though a weak organic acid, reacts slowly with lead, forming the acetate. Lead salts are all poi- sonous and are difficult of elimination from the system, hence are what are called accumulative poisons. 10. Uses. Lead is used largely for making pipe. Mol- ten lead near the point of solidification is forced by hy- draulic pressure through annular openings. It is used as waste pipes in plumbing, and for protecting over- head and underground electric cables. In sheet form lead is used to line the rooms where chamber sulphuric acid is manufactured, also for sinks in chemical laborato- ries and other places where acids are used. Many of its alloys are valuable. Common solder has been men- tioned as has also type metal, containing lead, antimony and tin. It will also be recalled that shot is an alloy of lead and arsenic. Alloyed with antimony it is used extensively in making storage batteries. 11. The Oxides. Three oxides of lead are common, the monoxide, PbO, often called litharge; lead dioxide, PbO 2 ; and minium, Pb 3 4 , often called red lead. The first is of light brown color, the second dark brown and the third red. All are in the form of powders. Litharge is a by-product of the silver refineries and is used largely in the manufacture of flint glass. (See p. 300.) Red lead is used in making gas-tight joints in plumbing, also as a red paint for metals. The dioxide is used in storage batteries. 12. Lead Acetate, Pb(C 2 H,0 2 ) 2 .3H 2 0. Commercially this is known as sugar of lead because of its sweet taste. It is easiest made by treating lead monoxide with acetic acid, thus, 2HC 2 H 3 2 - H 2 + Pb(C 2 H 3 2 ) 2 . THE LEAD FAMILY 407 It is a white crystalline salt, readily soluble in water. It is often used in solution as an external application in cases of "ivy poisoning." 13. White Lead. Chemically, white lead is basic lead carbonate, Pb(HO) 2 .2PbC0 3 . It is the most commonly used white paint. It was formerly made entirely by what was known as the "old Dutch process" which re- quired several weeks for its completion. It consisted in the exposure of "buckles" or short strips of sheet lead to the fumes of strong vinegar or acetic acid, and the introduction of carbon dioxide. This gas was ob- tained from tan bark which was used to cover the pots containing the lead and acid. The heat needed was obtained by the decomposition of refuse from stables with which the pile of pots was covered. At the pres- ent time most of the commercial supply is manufac- tured by a more rapid process. By means of compressed air with an apparatus on the order of an atomizer, the molten lead is made into a fine dust. This is treated with acetic acid, and owing to the finely divided condi- tion of the lead, the process is completed in a few days. Carbon dioxide is then introduced or sodium carbonate added, which produces the basic carbonate. It is dried and ground in linseed oil. White lead as a paint has one disadvantage in sections where much soft coal is used. Considerable quantities of hydrogen sulphide are pro- duced. This gas reacts with the lead compounds form- ing the sulphide, PbS, which is black. The paint as a result becomes grayish in color. The following equation will illustrate the interchange, Zinc white, the other common white paint, when thus treated does not change in color, for the reason that 408 APPLIED CHEMISTRY zinc sulphide is a pure white compound, ZnO + H 2 S > H 2 + ZnS. 14. Lead Chromate, PbCr0 4 . Commercially known as chrome yellow, lead chromate is probably the best yellow pigment to be had. It is prepared by treating lead ace- tate in solution with potassium chromate or dichromate. Lead chromate is insoluble in water, hence forms a pre- cipitate. It is filtered out, washed, and dried. For use it is ground in oil. 15. Other Compounds. The chloride, PbCl 2 , nitrate, Pb(N0 3 ) 2 , and sulphate, PbS0 4 , are three well-known compounds, but they have few practical uses and need Fig. 69. A battery "grid." not be considered here. Lead iodide, dissolved in boil- ing water and allowed to cool, crystallizes out again in beautiful golden scales. 16. Storage Batteries. In this day of motor cars a study of lead would hardly be complete without some- thing about storage batteries. Each cell of a storage battery consists of a number of lead plates or "grids" separated from each other by thin sheets of wood. One set of these grids is connected to the positive post or pole and the other alternating set to the negative post. The wood serves to keep them from touching each other yet does not prevent the passage of the ions from one plate to another. These grids are not solid sheets of THE LEAD FAMILY 409 lead but mere skeletons like the registers over hot-air furnace pipes as shown in Fig. 69. One set is packed tightly with lead dioxide or with red lead or both mixed: the other set with finely divided lead. They are then placed in a container with dilute sulphuric acid as the electrolyte. In charging the battery a current is led in from a dynamo during which time the lead dioxide is the anode. To this the sulphate ions will be attracted, which in combining with the lead oxide will give up their negative charge and convert a portion of the oxide into sulphate. The hydrogen ions of the sulphuric acid will move to the cathode, and, giving up their charge, the hydrogen escapes, leaving the lead plate positively charged. Two to three days are needed in bringing the battery up to the desired strength. When put into serv- ice, what was the negative pole or cathode now be- comes the positive pole. The reverse process now takes place; the lead is slowly converted into sulphate as it loses its positive charge and the sulphated oxide at the other pole is slowly reduced to oxide again by the hy- drogen ions which move in that direction. Exercises for Review 1. Name the metals of the lead group. Look up the table and see if any other elements belong in the same family. 2. What can you say of the occurrence of tin? What is the name of the only ore? 3. Describe tin. Under what conditions may the amorphous va- riety form ? 4. What is tin plate? Give some of the uses for tin plate. 5. Give some other uses for tin. Name its more important alloys. 6. What two classes of compounds does tin form? Why is stan- nous chloride a reducing agent? 7. Name the oxides of tin and give formulas. 8. What is the chief ore of lead? Where found in the United States? 410 APPLIED CHEMISTRY 9. Describe lead. Where is it in the electromotive series? What does this tell one about the reaction of a metal with an acid? 10. Give the more important uses of lead. 11. How is lead pipe used? How made? 12. Name three oxides of lead and give formulas. 13. How is sugar of lead made? Write equation. 14. What is white lead? How formerly made? How made at present? 15. What is chrome yellow? What is its use? 16. Describe the construction of a storage battery. 17. What is an electrolyte? What is the electrolyte in a stor- age battery? 18. Why do instructions in regard to care of storage batteries tell one not to bring a lighted match near? 19. If the water in the battery did not evaporate at all, would it still be necessary to add distilled water occasionally? Explain your answer. 20. Complete the following equations using amounts as may be needed, PbCl 2 + H,S0 4 - , Pb(NO,) 2 + KI , Pb + H 2 SQ 4 -> , PbCL, + K.CrO, -> , PbO + HN0 3 -> , Pb + HNO 3 - , PbS + 2 - . CHAPTER XXXIV THE CHROMIUM FAMILY Outline Members of the Group Chromium (a) Preparation (&) Characteristics (c) Uses (d) Compounds (a) Chromates (b) Bichromates (c) Chromic Salts Tungsten Uranium 1. Members of the Group. To this group belong chromium, molybdenum, tungsten and uranium, all of them rather unfamiliar elements. Their higher oxides all show a valence of six as would be expected from their position in the table. Chromium has an atomic weight of 52, molybdenum, of 96 ; tungsten, 184 ; ura- nium, 238.5. 2. Preparation of Chromium. The easiest method of obtaining chromium is by the thermit process in which chromic oxide is substituted for the ferric oxide. This has been described on p. 397. 3. Characteristics of Chromium. Chromium is a metal of very high melting point, steel-gray in color and very hard. It does not tarnish readily in the air. With warm hydrochloric acid it reacts with the evolution of hydrogen. 4. Uses. The chief use of chromium is in making an alloy with steel which is called chrome steel. It pos- 411 412 APPLIED CHEMISTRY sesses unusual hardness and resistance to stress. It is used in parts of machinery as motor cars and trucks where great strength is required. 5. Classes of Compounds. Chromium forms several series of compounds of interest to the chemist. The oxide, Cr0 3 , is acidic, the anhydride of chromic acid, corresponding to sulphuric acid. With the metals it forms a number of salts called chromates. One of the most common of these is potassium chromate, K 2 O0 4 , a crystalline salt of lemon-yellow color. Prom the chro- mates by treatment with an acid, another set of salts is obtained, called the dichromates, of which potassium dichromate, K 2 Cr 2 7 , is the most common. Its formula might be written, K 2 O0 4 .O0 3 . Another oxide of chro- mium gives a series of salts in which chromium is the positive ion. Thus chromic oxide, Cr 2 3 , is a basic oxide with the corresponding hydroxide, Cr 2 (HO) G , also writ- ten Cr(HO) 3 . Theoretically it is formed thus, Cr 2 3 + 3H 2 ->2Cr(HO) 8 . If to this acids are added we obtain the corresponding salts. Chromic compounds are mostly green or violet; in fact, the word chromium is from the Greek for color, given because so many of the compounds of this metal are highly colored. The following equation shows, the preparation of the sulphate, 2Cr(HO) 3 + 3H 2 S0 4 - Cr 2 (S0 4 ) 3 + 6H 2 0. 6. Conversion of One Class to Another. Very readily these compounds may be changed from one class into another. Since the dichromates contain an anhydride, seen when potassium dichromate is written, K 2 Cr0 4 . Cr0 3 , they may be regarded as acid salts. The addition of an alkali, therefore, should neutralize the anhydride and make a normal salt of it. In other words, it should THE CHROMIUM FAMILY 413 become a eliminate. This actually happens as shown by the following equation, K 2 Cr0 4 .CrO, f 2K1IO -> 2K,CrO 4 + II,<>. At the same time the color should change, as it does, from orange to lemon-yellow. On the other hand, the addition of an acid to the chromate converts it into the dichromate, thus, 2K 2 Cr0 4 + H 2 S0 4 - K,S0 4 + H 2 + K 2 (Y0 4 .Cr0 3 . Chromates or dichromates treated with hydrochloric acid and, especially if a reducing agent be present, are changed into green salts with chromium as the positive ion, thus, K 2 Cr 2 7 + 14HC1 -> 2CrCl 3 + 7H 2 + 2KC1 + 3C1 2 2K 2 Cr0 4 + 3ILS + 10HC1 -> 2CrCl 3 + 8H 2 -f 4KC1 + 3S. On the other hand, compounds containing chromium as a positive ion may be changed to chromates by heating with an alkali. Oxygen is taken up from the air, thus, 4Cr(HO), + 8XaIIO + 30 2 - 4Na 2 Cr0 4 + 10H 2 0. 7. Chromic Compounds. Most of the chromic com- pounds are green in color; however, chromic alum, K 2 Cr 2 (S0 4 ) 4 , is violet. Chromic oxide, Cr 2 ;i , is a green powder. It is used as a pigment, in coloring glass a deep green and in artificial emeralds. Chromic chloride, CrCl,.6H 2 O, may be prepared by treating chromium hy- droxide with hydrochloric acid. It is of a bright green color. Chromium sulphate, Cr 2 (SO 4 ),.l OILO, is of a reddish-violet color, made by treating the hydroxide with sulphuric acid. 8. Insoluble Chromates. Potassium chromate already named is readily soluble in water. If to this is added a 414 APPLIED CHEMISTRY solution of lead acetate an insoluble compound of lead chromate precipitates out, thus, K 2 Cr0 4 + Pb(C 2 H 3 2 ) 2 -> PbO0 4 + 2KC 2 H 3 2 . It has been mentioned already as a bright yellow pig- ment. Chrome red is a basic lead chromate with the composition, PbO.PbO0 4 ; it is of bright red color. Sil- ver chromate, Ag 2 Cr0 4 , of deep red color and barium chromate, BaCr0 4 , a pale yellow, are both insoluble compounds. 9. Tungsten. The symbol for this element is W. De- posits of tungsten are said to exist in both South Da- kota and Colorado, but most of our supply is imported. It is of interest mainly because of the fact that the filament of most electric light bulbs is now made from it. Such lamps give a much whiter and more brilliant light than the old carbon ones. For the same candle power tungsten lamps consume much less current and hence are much less expensive. When first introduced they were very fragile and required most careful han- dling, hence were not received favorably by the public. That objection has now been removed and their life is practically the same as that of the carbon lamp, that is about 1,000 light hours. 10. Uranium. Uranium has the highest atomic weight of all the elements, 238.5. It is also remarkable in that, contrary to our general ideas of elementary matter, it has the property of disintegrating and forming other elements. Thus, one of the products of uranium is ra- dium, and from radium by a similar decomposition, he- lium is obtained. So, uranium forces us to the conclu- sion that at least some elements are capable of self dis- integration. THE CHROMIUM FAMILY 415 Exercises for Review 1. Name the elements of the chromium group, and give symbols. 2. What is the simplest method of obtaining pure chromium? >. Give chief properties of chromium. 4. For what is chromium used? 5. Name three classes of chromium compounds and give one ex- ample of each. G. Name two oxides of chromium with formulas. Which one is acidic? Of what acid is it the anhydride? 7. Why will an alkali change a dichromate into a chromate? Illustrate. S. Show how chromates may be changed into dichromates. 9. How may chromates or dichromates be changed into chromic- salts? 10. Name three chromic salts and give formulas. 11. Name four insoluble chromates and give formulas; also uses, if any. 12. What use has tungsten? Why are such lamps desirable? 13. What is the most remarkable property of uranium? 14. Complete the following equations, using amounts needed to balance, Cr(HO) 3 + HC1 , Cr(HO) 3 + H.SO, -> , Cr 2 3 + H 2 S0 4 ~ -* , CrO 3 + H,O -> , Cr,O., + H 2 O -> , K,CrO 4 + AgNO 3 , K,CrO 4 + BaCl 2 -> , PbCl 2 + K 2 CrO 4 -> . 15. In Section 6, remembering that reduction consists in lower- ing the valence of an element and oxidation is the reverse, raising Ihe valence, has chromium been oxidized or reduced in the last three equations given? 16. In the first two equations in Section 6, has chromium been oxidized or reduced? Give reason for vour answer. CHAPTER XXXV MANGANESE AND COMPOUNDS Outline Manganese Relation to Other Elements in the Table Characteristics Compounds (a) The Oxides (&) Manganic Compounds (c) Manganates (d) Permanganates 1. Position in Periodic Table. Manganese is found in the same column in the table as the halogen group, but at the left hand side of the space. The correspond- ing positions in the long periods that follow manganese, by looking at the table are seen to be vacant. So at present this element is all alone. 2. Characteristics. In some respects manganese re- sembles iron. It occurs in nature as a dioxide, Mn0 2 , called pyrolusite, always mixed with iron. It is a gray- ish metal, with the power of reacting with dilute acids and evolving hydrogen. It forms an alloy with iron and is tarnished when exposed to the air. Its chief use is in making manganese steel, by alloying it with iron. 3. The Oxides. Manganese forms five oxides most of which are of no great importance. The lowest is MnO, which is a basic oxide; as they increase in amount of oxygen, as might be expected, they become more acidic until the highest is reached, Mn 2 7 , which is strongly acidic. The dioxide is the most familiar to the student because he has used it on several occasions. The hep r 416 MANGANESE AND COMPOUNDS 417 toxide shows the metal to have the combining power or valence of seven as would be expected from its posi- tion in the table. We have used the dioxide catalyti- cally in making oxygen, and as an oxidizing agent in the preparation of bromine and chlorine. It is a basic oxide and unites readily with acids to form manganous salts. 4. Manganous Salts. Manganese forms both mangan- ous and manganic salts just as chromium does, but the manganous are the more common. They may be ob- tained from manganese dioxide by treatment with an acid. Thus manganese dioxide with hydrochloric acid gives the chloride, Mn0 2 + 4HC1 -> MnCl 2 + 2H 2 + C1 2 . On evaporation the solution gives a pink crystalline hy- drate, with the formula, MnCl 2 .4H 2 0. The sulphate may be obtained by treating the dioxide with sulphuric acid, thus, 2Mn0 2 + 2H 2 S0 4 -> 2MnS0 4 + 2H 2 + 2 . It is also a pink hydrate, but the quantity of water varies at different temperatures. At ordinary condi- tions the formula is MnS0 4 .5H 2 0. Manganous salts or the dioxide, fused with borax, impart an amethyst color to the bead. 5. Manganates and Permanganates. Manganese forms a series of salts known as manganates, of which potassium manganate, K 2 Mn0 4 , is one of the more com- mon. The permanganate, KMn0 4 , is a much more im- portant compound. It is a purple solid with greenish luster, and crystallizes in small rhombic prisms. In solution it gives a deep purple color. It has frequent use in the chemical laboratory in estimating the quantity 418 APPLIED CHEMISTRY of iron and in various other ways. It is sometimes used in cisterns for oxidizing the organic impurities present. Exercises for Review 1. Give the location of manganese in ths table. 2. How does the element occur in nature! 3. Give the chief properties of manganese. 4. What is the chief use of manganese? 5. How many oxides of manganese are there? Name two and state whether basic or acidic. 6. Describe the appearance of manganese dioxide. What uses has it? 7. How may manganous chloride be made? Describe it. 8. Describe potassium permanganate. Give its uses. 9. Complete these equations, using such amounts as are neces- sary, MnO 2 + HBr , MnO, + HC1 -> , Mn 2 O 7 + H 2 O -^ , Mn(HO) 2 + H,SO 4 - , MnCl 2 + KHO -> , MnSO 4 + Ca(HO), - . 10. In the following equations, what- substances have been re- duced and what oxidized? MnO 2 + 4HC1 -> MnCl 2 + 2H 2 O + CL,, 2KMnO 4 + 8ILSO. I- 10FeSO 4 -> 5Fc s (O 4 ) 3 + K 2 SO 4 + 2MnSO 4 4 CHAPTER XXXVI THE IRON GROUP Outline Members of the Group Iron () Occurrence (6) Reduction of (c) The Blast Furnace (d) Wrought Iron (e) Steel () Cementation Process (&) Bessemer Process (c) Open Hearth Process (d) Characteristics (e) Method of Tempering (/) Varieties of General Characteristics of Iron Compounds () Ferrous Sulphate (ft) Ferric Chloride Oxidation and Reduction of Salts Pigments Nickel (rt) Characteristics (5) Uses (c) Compounds Cobalt (fl) Characteristics (ft) Compounds 1. Members of the Group. Iron, nickel and cobalt are usually associated, but not as a periodic group. They have atomic weights close together and do not form a vertical column in the table. Two of them are elements of importance, iron being intrinsically the most valuable of all metals. 419 420 APPLIED CHEMISTRY 2. Occurrence of Iron. There are several ores of iron used in the preparation of the metal. Of these, hematite, Fe 2 3 , is the most important. It is a dark colored mineral, reddish-brown to black, which drawn across a piece of unglazed porcelain gives a dull red streak. It is this fact that gave the name to the ore, the word hematite being from the Greek meaning blood. Limonite, which is a hydrated oxide, Fe 2 3 .3H 2 O, gives a yellow streak, and received its name from the Latin word for lemon. In some sections, the magnetic oxide, Fe 3 4 , is found. The carbonate, FeC0 3 , called siderite, and the disulphide, FeS 2 , commonly known as "fool's gold" should also be mentioned. Iron never occurs free upon the earth except in very minute quantities. Meteo- rites have been discovered containing from 92 to 97 per cent of iron and the remainder nickel. Lieutenant Peary, some years ago, in one of his Arctic trips discovered through the aid of his Esquimos two large meteorites, one of which weighed in the neighborhood of 100 tons, the largest ever found. Later, he brought this one back to the Brooklyn Navy Yards. In the form of compounds, iron is found everywhere. It is. the most common coloring agent in rocks and soils, and exists in many food prod- ucts and in the blood. 3. Reduction of Iron. It will be remembered that zinc is. reduced from its chief ore by means of coke, after the preliminary roasting has converted the sulphide into an oxide. Since most of the iron ores are already oxides, this - preliminary treatment is not necessary. Coke is used to furnish the heat and the carbon for the reduction. 4. The Blast Furnace. The ordinary blast furnace varies from 20 to 25 feet in diameter and from 75 to 90 feet in height, It is made of fire brick and strength- THE IRON GROUP 421 ened 011 the outside by heavy boiler plate iron. The top of the furnace is so constructed that it is practically air- tight, and any gases formed within must pass off through a pipe near the top shown in Fig. 70. How- ever, as the process is a continuous one, additions of Fig. 70. A blast furnace for preparing cast iron. 422 APPLIED CHEMISTRY material are made repeatedly through a hopper which opens mechanically when a load is dumped upon it and then closes again when the material has fallen into the furnace. Near the bottom is an opening for drawing off the molten iron, which is kept closed by means of clay until needed. At some distance above is an open- ing for the exit of the slag. As the quantity is usually large, this is open most of the time with a steady outflow of the molten material. Above this, entering from the sides, are the blast pipes, often called tuyeres, through which the air is forced into the furnace. This is needed to give the intense heat required. The furnace is tapped usually every twelve hours and the molten iron run off into trenches and side trenches in the ground. These short trenches are called "pigs" and the iron formed in them "pig iron." Sometimes the molten iron is run into steel molds bolted upon an endless chain, which moves slowly forward as each is filled from a large cauldron. (See Fig. 71 for illustration of method of molding pig iron.) 5. The Charge. The materials used in the "charge" put into the furnace are usually iron ore, coke and lime- stone. Most ores when brought from the mine contain more or less silica. In the furnace the limestone with the silica forms a species of glass, called slag. It floats above the molten metal and protects it from the oxidizing action of the blasts of air. When the ore contains lime- stone as a gangue, instead of silica, some silicious material is added to serve as the flux. 6. The Chemical Action. Owing to the large amount of air introduced through the tuyeres, at the bottom of the furnace carbon dioxide is produced. (See p. 169.) As this flows upward it meets red-hot carbon and is changed to carbon monoxide, thus, THE IRON GROUP CO., + C - 2CO. 423 This being an unsaturated gas removes the oxygen from the iron ore and the free iron thus produced flows to the bottom of the furnace. The gas, which escapes at the top, contains much carbon monoxide as well as other combustible gases. This is used to heat the air forced 71. A blast furnace, showing the molds for the "pigs" in the sand, 424 APPLIED CHEMISTRY in and to run the fans for the air pressure. The iron thus obtained is known as cast iron. It contains a high percentage of carbon, sometimes as much as 3 or 4 per cent as well as silica and other impurities. It is coarse grained, brittle, hard, and has a melting point relatively low, about 1250 C. 7. Wrought Iron. Wrought iron is made by heating the cast iron in a reverberatory furnace with ferric oxide. The purpose of the oxide is to furnish oxygen for union with the carbon in the iron, by which carbon monoxide is formed. These are sometimes called pud- dling furnaces, because the molten pig iron is " puddled" or stirred so as to facilitate the action. When the mass has become stiff and very difficult to stir, it is known that the carbon is burned out. Pure iron melts with much more difficulty than impure, and the temperature of these furnaces is only sufficient to keep the impure form in a molten condition. It is the same principle, seen often before, in which a solution will remain liquid while the solvent will solidify. At this stage the iron, called "bloom," is removed from the furnace, and beaten with trip hammers, which forces out the silica and any slag remaining. Such is now wrought iron. It is malleable and may be welded; it is fine grained, somewhat more dense than cast iron, melts at about 1,500 C. and contains only about 0.1 to 0.2 per cent of carbon. It should not contain much phosphorus or sulphur. Wrought iron is made into sheets, and is used in chains, wire, and in many other ways where a cheap, malleable metal is de- sired. 8. Steel. The oldest method of making steel was by the cementation process. Bars of wrought iron were im- bedded in powdered charcoal and heated strongly for a number of days. The iron slowly absorbed small portions THE IRON GROUP 425 of the carbon and was changed thereby into steel. How- ever, it was far from satisfactory, for the reason that the carbon was not taken up uniformly. Some portions would contain so much as to be more or less brittle, while others would not contain enough. Cast steel was first made by melting cementation steel and molding it into a bar so as to give uniform composition. This greatly improved the produce previously obtained. The process is entirely too slow for modern demands; for years, until recently, most of the steel used has been made by the Bessemer process Fig. 72. The Bessemer converter. (Fig. 72). This process uses a movable furnace, called a converter, made of boiler-plate iron and lined with a silicious earth called ganister, which is infusible. The compressed air passes up through a supporting post, through the horizontal trunnion, and down the pipe into the tuyere box or air chamber, then into the body of the converter. For use it is filled half or two-thirds with molten cast iron and the air is turned on. No heat is ap- plied ; the interaction of the oxygen of the air with the car- bon and other impurities in the iron is sufficient not only to keep the metal molten, but even raise the temperature. 426 APPLIED CHEMISTRY At first luminous flames and great showers of sparks shoot from the mouth of the converter, but as the carbon is burned out the action becomes more quiet until finally it practically ceases altogether. If the product obtained at this stage were hammered, it would form wrought iron. For steel a definite amount of spiegel iron is added. This is an iron-manganese alloy which may have as high as 20 per cent of manganese, but usually only a small pro- portion. It contains also a fixed amount of carbon so that any required proportion of carbon may be thus put back into the iron to form the steel. The blast of air is continued just long enough to mix the spiegel thoroughly with the other when the whole is poured out and cast into ingots. It will be seen that the process consists in burning out all the carbon and then restoring whatever may be desired for a particular variety of steel. This method works successfully unless phosphorus be present in the cast iron. The Bessemer converter will not remove phosphorus, and its presence makes steel brittle. To re- move it, a converter lined with lime is used. Phosphorus, being an acidic element, unites with the lime, a basic oxide, forming the superphosphate of calcium, mentioned on p. 281 as a valuable fertilizer. This modified plan is called the basic lining or the Thomas-Gilchrist process. 9. Open Hearth Steel. In the last few years much steel has been made by what is known as the open hearth or Siemens-Martin process. The cast iron, whose carbon content is known by chemical analysis, is mixed with a definite amount of hematite, ferric oxide, or some other iron ore, and heated in an open furnace with a gaseous fuel, for about ten hours. The materials are so propor- tioned as to leave a definite amount of carbon in the steel. The gas used for fuel is heated before being burned and the THE IRON GROUP 427 charge is tested from time to time to know when the proc- ess is complete. 10. Characteristics of Steel. Steel is between wrought and cast iron in content of carbon. The amount varies from 0.5 to 1.5 per cent. Its most remarkable property is its ability to be tempered, that is, to be so treated as to hold a cutting edge. It also has wonderful tensile strength. Wires of lead, copper and steel, of equal diam- eter, show that steel will withstand twice what copper will and forty times what lead will. This is one of the chief reasons for the great use of steel in the arts. 11. Tempering Steel. If a piece of steel is heated to redness and then cooled sloAvly it is soft and malleable like wrought iron ; but if so heated and cooled suddenly it is hard and brittle. Now if it be heated again to a much lower temperature, ranging from 225 to 325 C., it assumes degrees of hardness and brittleness be- tween these two conditions and is suitable for cutting instruments. At the lower temperature, such keen- edged instruments as razors and instruments employed in surgery are made; at the higher, saws and similar tools. The explanation of this, put as simply as possible, is as fol- lows. At the temperature first used a considerable amount of iron carbide is formed which makes the steel brittle. If the bar is cooled suddenly the carbide remains in the steel; if cooled slowly the carbide de- composes and leaves less of it in the steel. At the sec- ond heating, if only a low temperature is used, not so much time is given in cooling for the iron carbide to be decomposed ; hence, a considerable amount remains and the steel is harder and takes a keener edge, but is more brittle. When heated to a higher temperature more time is given for the carbide to be decomposed ; hence, the steel is left softer, less brittle and better 428 APPLIED CHEMISTRY suited for rough tools, but not capable of so keen an edge. 12. Kinds of Steel. By mixing in the converter one or more of some of the rarer metals, alloys of great value may be obtained. As they consist mainly of steel they are spoken of as such. Chrome steel contains a small percentage of chromium or sometimes both chro- mium and vanadium. It is a steel of special strength and is used in parts of machinery where great strain may come, as in the axles and frames of motor cars. Nickel steel may contain as much as 4 per cent of nickel and is especially desirable as armor for war vessels. It has great strength, is very tenacious, hard to pierce with projectiles, and resistant to sea water. A manganese steel gives a variety used for making burglar proof safes of very great hardness. 13. General Characteristics of Iron. The most im- portant physical properties have been given in describ- ing the different varieties of iron. It is well up in the electromotive series of metals and readily displaces hy- drogen from dilute acids. Very concentrated nitric acid products a singular condition known as the passive state in which it will not react with dilute acids with the evo- lution of hydrogen. Chromium is affected in a similar manner. Hammering will restore its former properties; In oxygen, iron when heated burns readily with a beauti- ful shower of sparks, and forms mainly the magnetic oxide, Fe 3 O 4 . Superheated steam, directed upon iron, gives it a blue color due to the formation of a closely-ad- hering, protecting film of this same oxide. In the air, in the presence of moisture, ferric oxide, Fe 2 3 , is formed; this being nonadhering, the metal becomes entirely cor- roded. THE IRON GROUP 429 14. Compounds of Iron. Iron forms two classes of compounds, ferrous and ferric. The former are mostly green in color, the latter brown. Ferrous compounds are unsaturated and, as a rule, tend to become oxidized to the ferric. Ferrous sulphate, FeS0 4 .7H 2 0, is commonly known by the name of green vitriol, or copperas. It is an efflorescent hydrate, but as it loses its water, it also be- comes oxidized from the air and forms a basic ferric sulphate. Therefore, unlike effloresced blue vitriol, the addition of water does not re-form the ferrous sulphate. It is used in various wa} T s. Common black ink is a mix- ture of ferrous sulphate and tannic acid, which on ex- posure changes into a black ferric salt. To give it more body some mucilage is usually added and often some dye as well. Ferrous chloride, FeCl 2 , may be made by dis- solving iron in dilute Iwdrochloric acid. It is a very un- stable salt and rapidly oxidizes to a ferric. Ferrous hydroxide, Fe(HO) 2 may be prepared by adding, to any soluble ferrous salt, a solution of some alkali. If pure it is white in color, but as usually obtained is greenish, changing rapidly to brown as it is oxidized by the air. The double salt, ferrous ammonium sulphate, (NH 4 ) 2 S0 4 .FeS0 4 .6H 2 0, is the most stable of the ferrous salts. It is pale green in color, crystalline in structure and soluble in water. For experimental work in the lab- oratory it is far the best for use. 15. Ferric Compounds. Ferric chloride, FeCl 8 .GH,O, is a very deliquescent, brown solid. It is employed in most pharmaceutic preparations of iron. Mention has been made of its use in preparing the best antidote for arsenic. Ferric sulphate, Fe 2 (SO 4 ). { , may be made by the oxidation of ferrous sulphate with nitric acid or bro- mine or with some other oxidizing agent. Ferric hy- 430 APPLIED CHEMISTRY droxide, Fe(HO) 3 , may be prepared by treating ferric chloride with ammonium hydroxide or any other solu- ble hydroxide. It is a gelatinous, brownish colored precipitate. Heated, it loses water and becomes ferric oxide, Fe 2 3 . 16. Oxidation and Reduction of Iron Compounds. As stated above, ferrous salts may be readily changed to ferric by oxidation. If a solution of ferrous sulphate acidulated with sulphuric acid has nitric acid added and is then heated, it is changed into ferric sulphate, thus, 2FeS0 4 + H 2 S0 4 + 2HN0 3 -> Fe 2 (S0 4 ) 3 + 2H 2 + 2N0 2 . Potassium permanganate is used to oxidize ferrous salts to ferric in the same way. As it is of a deep violet, a coloration of the iron solution is seen as soon as the oxi- dation is completed. A permanganate solution, there- fore, of known strength, may be used to determine the amount of iron present, by noting the number of cubic centimeters needed to oxidize a certain amount of the ferrous solution. The equation is 2KMn0 4 + 8H 2 SO .+ 10FeS0 4 -> 5Fe 2 (S0 4 ) 3 + K 2 S0 4 + 2MnS0 4 + 8H 2 0. Conversely, ferric salts may be reduced to ferrous. This is easily done by nascent hydrogen, thus, 2FeCl 3 + 2H -* 2FeCl 2 + 2HC1. The hydrogen may be obtained by putting pieces of zinc into the ferric solution and adding a dilute acid as hydrochloric. In a similar way hydrogen sulphide re- duces iron salts in the presence of an acid, thus, 2FeCl 3 + H 2 S -* 2FeCl 2 + 2HC1 + S. The sulphur is precipitated. 17. Other Iron Compounds. There are a few com- pounds in which iron forms a part of the negative ion. Such are potassium ferrocyanide, K 4 Fe(CN) 6 , and ferri- THE IRON GROUP 43.1 cyanide, K 3 Fe(CN) fl . These were formerly regarded as double salts as their present names indicate. Potassium ferrous cyanide was regarded as Pe(CN) 2 .4KCN and the other as Fe(CN) s .3KCN. If really double salts, as last written, the former would in solution contain fer- rous ions, and the latter ferric ions. Chemical tests show this is not true. Mixed with ferric or ferrous salts, they give compounds, one of which is known as Prussian blue, Fe 4 [Fe(CN) 6 ] 3 , which was formerly used frequently in- stead of indigo as a cheap bluing in laundry work. Both of the cyanide compounds have use in the laboratory in making delicate tests for the presence of iron. 18. Some Pigments. Rouge is the commercial name for a form of ferric oxide used in polishing. It is made from ferrous sulphate which is obtained in cleaning iron for the purpose of galvanizing. Venetian Red and other cheap red pigments, used for painting roofs and out- buildings, are largely ferric oxide mixed with more or less clay. Yellow oclire is a hydrated form of the same compound and corresponds to limonite, already men- tioned. It is used sometimes for priming woodwork and as a cheap paint. Raw and burnt sienna and raw and burnt umber are other well-known pigments of similar composition, two of them obtained, as the names indicate by strongly heating the oxide. 19. Nickel, its Characteristics. Nickel is a hard white metal which tarnishes very slowly in the air. It is sus- ceptible of a high polish. It is little attacked either by dilute hydrochloric or sulphuric acid. It is exten- sively used in plating iron. The method is the same as described in the case of the other metals, except a dif- ferent solution of nickel is used. The double sulphate of nickel and ammonium, (NH 4 ).>S0 4 .NiS0 4 .(>II,(), gives a plating which adheres best. It is a greenish col- ored salt, soluble in water. Nickel is also used in coin- 432 APPLIED CHEMISTRY age, alloyed with copper in the familiar five-cent piece; in the powdered form it is used somewhat in wireless telegraphy and in the familiar alloy, German silver. Its use in making nickel steel has been mentioned as well as its catalytic action in the hydrogenation of oils. 20. Compounds of Nickel. Nickel forms two series of compounds, nickelous and nickelic. The former are the more common. They are mostly green in color; however, fused in the borax bead, they give a brown coloration, which is distinctive. The most important salt is the double sulphate already mentioned as of use in plating. 21. Characteristics of Cobalt. Cobalt is a hard, white metal resembling nickel. It has no uses. It forms two classes of compounds, cobaltous and cobaltic. The for- mer are the more common and the more important. They are deep pink or reddish in color. Fused in a borax bead, even in minute quantity, they give a beautiful blue color, which serves to identify the metal. 22. Uses of Cobalt Compounds. Some very valuable pigments are made from cobalt compounds. Smalt, a kind of glass, made by fusing some cobalt compound as the oxide, with sand and potassium nitrate, is of a deep blue color. It is powdered and mixed in the paste used on the outside of iron vessels in the manufacture of ' ' granite ware. ' ' When these are heated strongly in ovens the coating melts and gives the familiar blue ware in common use. It is also ground in oil and used as a paint for chinaware. Several cobalt salts become blue in color when they lose their water of combination. Based upon this fact is the "cobalt barometer" occasionally seen. It consists of a strip of unsized paper or cloth moistened with cobaltous solution. If the air is very dry the paper turns blue; if damp, red. Sympathetic inks, containing some cobalt compound, depend upon the same property. THE IRON GROUP 433 When used upon paper the pink color is scarcely visible; if warmed, the water of combination is removed and the compound turns blue. It then may be plainly read. In damp air it will again become invisible. Exercises for Review 1. Name the metals usually associated with iron. Why do they not form a periodic group ? 2. Mention the chief ores of iron and give composition. 3. How could you recognize a piece of hematite? Of limonite? 4. Describe the construction of the blast furnace. 5. Of what does the charge put into a blast furnace consist? What is the purpose of each? 6. Describe the chemical action which takes place in the blast furnace. 7. How is wrought iron made? W T hat are some of its uses? 8. Describe the cementation process of making steel. Why was cast steel used? 9. Describe the Bessemer converter and state the principle un- derlying its use. 10. What is the Thomas-Gilchrist process of making steel? 11. Describe the open hearth process. 12. How is steel tempered? Explain the principle underlying. 13. Name some different kinds of steel and state for what adapted. 14. Give the chemical properties of iron. What is meant by the passive state? 15. What is green vitriol? How made? Uses? Name some other ferrous compound. 16. Name one ferric salt and tell how to prepare ferric hydrox- ide from it. What use has the hydroxide? 17. How can ferrous sulphate be changed to ferric? Ferric chloride to ferrous? What is oxidation in the broad sense? 18. Name some common iron pigments and give uses for them. Of what do they consist? 19. Give the chief characteristics of nickel and uses. 20. How is nickel plating done? 21. Name one important compound of cobalt and give important use for it. 22. What is a sympathetic ink? Explain how one made from cobalt compounds works. CHAPTER XXXVII THE PLATINUM AND PALLADIUM GROUPS Outline Members of the Group Occurrence Platinum (a) Characteristics (6) Uses Osmium Iridium Palladium 1. Members of the Group. Osmium, iridium and plat- inum are associated as are iron, nickel and cobalt, but do not constitute a periodic group, for their weights run consecutively and not as octaves. Osmium has an atomic weight of 191, iridium, 193, and platinum, 194.8. 2. Occurrence. These metals are found as grains or small nuggets in alluvial deposits, much as is gold, but in very limited quantities. California produces about all there is obtained in the United States. Nearly the entire world's supply comes from the Ural Mountains in eastern Russia. The three metals are nearly always found mixed together, with platinum the more abundant. They are separated by difficult chemical processes which would not be of interest to the student. 3. Characteristics of Platinum. Platinum is the most important metal of the group. It is steel-white in color, very hard> not attacked by acids, but is soluble in aqua regia, or nascent chlorine. It is exceedingly malleable and ductile, and when heated may be welded like wrought iron. At red heat it easily forms alloys with 434 PLATINUM AND PALLADIUM GROUPS 435 metals of low melting point, such as lead and antimony and will also combine with carbon, phosphorus and sil- ica. The alloys mentioned have low melting points; hence, the greatest care must be exercised not to heat any such metals in platinum ware. If it is done, the alloy is readily formed, and then melts out leaving a hole in the platinum vessel. Silica and phosphorus ren- der platinum brittle, so may likewise cause serious in- jury. If pure, platinum has a high melting point of about 1,700 C. When finely divided it has great power of occluding or absorbing hydrogen. It frequently pos- sesses the power of catalysis. This has already been seen in several instances. It may likewise be shown by hold- ing a spiral of platinum wire in the neck of a flask of strong ammonium hydroxide, slightly warmed. If the wire is heated before being thrust into the neck of the flask at some point where the ammonia and air are mixed, the wire will become red hot and so continue as long as the current of ammonia is escaping. The wire may even be withdrawn from the flask and reinserted when it will again heat up as before. 4. Uses of Platinum. On account of its high melting point and resistance to attack by acids, platinum is em- ployed extensively in the laboratory in the form of cru- cibles, wire and foil. In late years, unfortunately for science, it has been used very largely in jewelry. Cata- lytically, it is used in making sulphuric acid by the contact process (p. 261) as well as in other manufactur- ing processes. In dentistry platinum wire is used as " posts" in fastening artificial teeth to the plate. It is also used in electric lamps as the connection between the inside filament and the outside copper wire. This is for the reason that platinum has practically the same rate of expansion when heated as glass: any metal used 436 APPLIED CHEMISTRY thus which expands more than glass when heated by the current would crack the lamp. 5. The Other Metals of the Group. Osmium is re- markable for its high melting point, being over 2,000 C. Iridium is harder than platinum and is sometimes alloyed with the latter for the purpose of securing a metal with extreme resistance to acids. It is also some- times used on the tips of fountain pens. Palladium is of special interest because of its remarkable power of absorbing hydrogen and other gases. When heated it will occlude about seven hundred times its own volume of hydrogen. It does not belong with the platinum met- als, but is the most important metal of another special group, much lighter in weight. Exercises for Review 1. Name the metals of the platinum group and give atomic weights. 2. Why can these three not be regarded as forming a periodic group? 3. What can you say of the occurrence of the metals of this group ? 4. Give the important characteristics of platinum. 5. What precaution must be taken regarding heating low-melt- itig metals in a platinum vessel? 6. What other substances also injure platinum seriously? 7. In what way have you seen platinum used in chemical experi- ments? Why is it used frequently in the chemical laboratory? 8. Name some other valuable uses for platinum in the arts. 9. Why should platinum not be used for jewelry? 10. Give some one point of interest about osmium, iridium and palladium. Give some use for iridium. 11. Where does palladium belong in the table? What other metals are associated with it? TABLES FOR REFERENCE AND GLOSSARY 438 APPLIED CHEMISTRY Solubilities of Common Compounds It may be desirable to know at times whether a com- pound is soluble in water. A few general rules may be helpful and are given below. (a) All salts of the sodium group, including those of ammonium are soluble, with the exception of two or three very uncommon ones. (b) All bromides are soluble except those of lead, mercury, and silver. (c) All carbonates of the sodium group, including ammonium, are soluble; all others are insoluble. (d) All chlorates are soluble. (e) All chlorides are soluble except lead chloride, mer- curous chloride, and silver chloride. (f) T.he hydroxides of the sodium group, ammonium, and the calcium group are soluble, calcium only moder- ately so, while all others are insoluble. (g) All nitrates are soluble. (h) The oxides of the sodium and calcium group are chemically soluble in water, that is, they react to form a new compound, the hydroxide. All other oxides are insoluble in water. (i) Phosphates are insoluble except those of the al- kali metals and ammonium. (j) Silicates are insoluble except those of the alka- lies and ammonium. Even then if mixed with silicates of heavier metals they are insoluble. (k) The sulphates of barium, calcium, lead and stron- tium are insoluble ; others are soluble. TABLES FOR REFERENCE 439 Some Interesting Temperatures Absolute zero -273 C Hydrogen melts -200 Hydrogen boils -252.6 Nitrogen melts -21-4 Nitrogen boils -194 Oxygen boils -182.5 Alcohol freezes -130 Mercury freezes - 39.5 Water freezes Room temperature 21 Ether boils 34.6 Human body 37 Wood's Metal melts 60 Alcohol boils 78.5 Water boils 100 Sulphur melts (rhomb) 114.5 Tin melts 232 Lead melts 327 Mercury boils 357 Zinc melts 419 Dull red heat 650 Aluminum melts 6(50 Bright red heat 1,000 (Jold melts ' 1,064 White heat 1,350 Iron melts 1,520 Platinum melts 1,750 Corundum melts 2,000 (about) Oxyhydrogen flame 2,500 Oxyacetylene flame 2,700 Tungsten melts 3,000 Thermit gives 3,500 (about) Electric arc 4,000 (about) 440 APPLIED CHEMISTRY Tables of Weights and Measures WEIGHTS 10 milligrams (mg.) = 1 centigram (eg.) 10 centigrams = 1 decigram (dg.) 10 decigrams = 1 gram (g.) 1,000 grams = 1 kilogram (kg.) ENGLISH EQUIVALENTS 1 kilogram 2.2046 pounds 28.35 grams =1 ounce 1 gram = 15.43 grains 500 grams = 1.1023 pounds The unit of weight in the Metric System is the gram. VOLUMES 1,000 cubic centimeters (c.c.) 1 liter 1 cubic decimeter (c.d.) = 1 liter 1 liter (1.) =1.056 liquid quarts The unit in the Metric System is the liter. LENGTH 10 millimeters (mm.) = 1 centimeter (cm.) 10 centimeters = 1 .decimeter (dm.) 10 decimeters = 1 meter (m.) ENGLISH EQUIVALENTS 1 centimeter = 0.3937 inches 2.54 centimeters =. 1.0 inch 1 meter = 39.37 inches THERMOMETER EQUIVALENTS For scientific work the centigrade thermometer is always used and readings given in scientific books are always centigrade unless otherwise specified. Freezing water is C. and boiling point is 100 C. Centigrade is 32 Fahrenheit and 273 Absolute 100 " " 212 " " 373 " One degree Centigrade % of a degree Fahrenheit One degree Fahrenheit =% of a degree Centigrade One degree Centigrade = One degree Absolute To convert centigrade degrees into Fahrenheit, multiply by % and add 32, algebraically. This means that if the centigrade read- ing is below zero, it would have the minus sign and one would be TABLES FOR REFERENCE 441 substracted from the other. To convert Fahrenheit readings into centigrade multiply by % after substracting 32 from the Fahrenheit reading. LIST OF ELEMENTS, THEIR SYMBOLS AND ATOMIC WEIGHTS. (Cb=16.) (The more important elements are printed in heavy type.) NAME OF ELEMENT SYM- BOL ATOMIC WEIGHT NAME OF ELEMENT SYM- BOL ATOMIC WEIGHT Aluminum Antimony Argon. . Al Sb A 27.1 120.2 39.88 Molybdenum. . Neodymium . . . Neon Mo Nd Ne 96.0 144.3 20.2 Arsenic As 7496 Nickel . . . . Ni 58.68 Barium Ba 137 37 Niton Nt 222 4 Bismuth Boron Bi B 208.0 110 Nitrogen Osmium .... N Os 14.01 190 9 Bromine .... Br 79 92 Oxvsen o 16 00 Cadmium Cd 112 4 Palladium Pd 106 7 Caesium Cs 132 81 Phosphorus. . . . p 31.04 Calcium Ca 40.07 Platinum Pt 195.2 Carbon c 12 00 Potassium K 39.1 Cerium Ce 140.25 Praseodymium Pr 140.6 Chlorine Cl 35 46 Radium Ra 2264 Chromium Cr 52 Rhodium Eh 102.9 Cobalt Co 58.97 Rubidium Rb 85.45 Columbium. . . . Cb Cu 93.5 63.57 Ruthenium. Samarium .... Ru Sa 101.7 150.4 Dysprosium Dv 162 5 Scandium Ss 44.1 Erbium Er 167.7 Selenium S