GIFT OF 
 
 PROF. W.B. RISING 
 
APPLETONS' 
 SCIENCE TEXT-BOOKS. 
 
 CHEMISTRY. 
 
SPKOTKA OF VARIOUS SOimcKS OK LIGHT. 
 
 The Sun,.2.Tfi& 
 
 9 . Calcium 
 
 ye. . . 
 lQ.Sfjwn.tiu.ms. H-Barium. 12 
 
 6. Caesium,. 
 
 . 8 Th 
 
THE 
 
 ELEMENTS OF CHEMISTRY. 
 
 BY 
 F. W. CLARKE, 
 
 CHEMIST OF THE UNITED STATES GEOLOGICAL SURVEY. 
 
 NEW YORK: 
 
 D. APPLETON AND COMPANY, 
 
 I, 3, AND 5 BOND STREET. 
 
 1884. 
 
o 
 
 COPYRIGHT, 1884, 
 BY D. APPLETON AND COMPANY. 
 
 
PREFACE. 
 
 IN preparing this little treatise the author has 
 had several objects in view. First, he has sought 
 to write a text-book which should be available for 
 use with elementary classes, and in which the diffi- 
 culties of chemical science should be encountered 
 progressively, rather than at the beginning. Sec- 
 ondly, he has considered the needs of those stu- 
 dents who, while anxious to learn, are unable to 
 secure the aid of a teacher, and who, therefore, are 
 obliged to study by themselves. For the latter, es- 
 pecially, are the foot-note references to other works 
 on chemistry ; and only such works have been cited 
 as are to be found on the shelves of nearly every 
 well-equipped public library. He has also borne 
 steadily in mind the fact that in most schools there 
 are two classes of students : those who study chem- 
 istry merely as part of a general education, without 
 thought of going further ; and those who are likely 
 in time to take a more advanced course of chemi- 
 cal training. For the former class the book is suffi- 
 
 237513 
 
vi PREFACE. 
 
 ciently full, particularly with regard to the every- 
 day applications of chemistry ; for the second class 
 it is intended to serve as a legitimate scientific basis 
 for subsequent higher study. 
 
 The value of a school text-book, other things 
 being equal, depends much upon the use made of it 
 by the teacher. In his hands it may become an 
 instrument for developing thought, or merely a 
 device for drilling the memory. This is especially 
 true of text-books upon -chemistry. To use them 
 properly it must always be remembered that chem- 
 istry is essentially a disciplinary study as much 
 so as language or mathematics; and the constant 
 effort of the teacher should be to train the pupil 
 in the accurate observation of phenomena, and 
 the ability to draw correct conclusions from what 
 he sees. Good discipline in scientific methods of 
 thought must always be kept in view ; and this 
 discipline can be best attained by simultaneous drill 
 in the facts of science as observed in the lecture- 
 room or laboratory, and in the philosophy of sci- 
 ence which is reared upon them. In this book 
 the effort has been made to present, as a rule, 
 experimental evidence first and theoretical discus- 
 sions afterward ; and a glance at the chapters upon 
 atomic weights, formulae, and valency, will fairly 
 illustrate the manner in which this purpose has 
 been carried out. 
 
 Nearly all the experiments cited in this volume 
 
PREFACE. vii 
 
 are of the simplest character. The greater num- 
 ber of them can be easily performed by the pupil 
 himself, with no more complicated apparatus than 
 can be improvised from such common materials as 
 are everywhere at hand. The chemicals, with few 
 exceptions, are inexpensive, and within the reach of 
 every school ; and, although a good laboratory is 
 desirable, it is not necessary to the attainment of 
 really substantial results. Every experiment should 
 be studied, not as an amusement, but for what it 
 signifies ; and, if there are not means for perform- 
 ing it just as it is described, other means may be 
 readily devised. The student who constructs his 
 own apparatus understands its meaning much bet- 
 ter than if he had bought a far more elegant outfit 
 of some dealer. 
 
 The questions and exercises at the end of the 
 book are not meant to be exhaustive. They are 
 merely hints to aid both teacher and pupil in their 
 work. The problems, in particular, are only tenta- 
 tive ; some classes will need many more than are 
 given, and the teacher must devise such as will be 
 best suited to circumstances. 
 
 The author's acknowledgments are due to Miss 
 Caroline A. Lord, of Cincinnati, for efficient serv- 
 ice in the preparation of a considerable number of 
 the illustrations. 
 
 WASHINGTON, April, 1884. 
 
I 
 
TABLE OF CONTENTS. 
 
 PART I. INORGANIC CHEMISTRY. 
 
 CHAP. PAGE 
 
 I. INTRODUCTION . / . . , r . . i 
 
 II. THE CONSTITUTION OF MATTER. , ., , . . 8 
 
 III. HYDROGEN . . . . . , '"".". . . 14 
 
 IV. OXYGEN 24 
 
 V. WATER 32 
 
 VI. NITROGEN AND THE ATMOSPHERE . . . .49 
 
 VII. AMMONIA AND THE OXIDES OF NITROGEN . . 55 
 
 VIII. ATOMIC WEIGHTS AND CHEMICAL FORMULAE . . 66 
 
 IX. CARBON . . ' 74 
 
 X. CARBON (continued) 90 
 
 XI. COMBINATION BY VOLUME 99 
 
 XII. VALENCY 105 
 
 XIII. THE CHLORINE GROUP in 
 
 XIV. THE CHLORINE GROUP (continued) . . . .122 
 XV. SULPHUR . . .132 
 
 XVI. SULPHUR (continued) 141 
 
 XVII. PHOSPHORUS 151 
 
 XVIII. ARSENIC, BORON, AND SILICON 159 
 
 XIX. INTRODUCTORY TO THE METALS . . . .172 
 XX. THE METALS OF THE ALKALIES . . . .183 
 
 XXI. SILVER AND THALLIUM 196 
 
 XXII. CALCIUM, STRONTIUM, AND BARIUM .... 205 
 
 XXIII. SPECTRUM ANALYSIS 213 
 
 XXIV. GLUCINUM, MAGNESIUM, ZINC, CADMIUM, AND MER- 
 
 CURY 222 
 
 XXV. THE ALUMINUM GROUP 232 
 
TABLE OF CONTENTS. 
 
 CHAP. PAGE 
 
 XXVI. THE TETRAD METALS 239 
 
 XXVII. THE ANTIMONY GROUP .246 
 
 XXVIII. THE CHROMIUM GROUP. 253 
 
 XXIX. MANGANESE AND IRON. 262 
 
 XXX. NICKEL, COBALT, AND COPPER 273 
 
 XXXI. GOLD, AND THE PLATINUM GROUP .... 280 
 
 PART II. ORGANIC CHEMISTRY. 
 
 XXXII. PRELIMINARY OUTLINE 285 
 
 XXXIII. CYANOGEN AND CARBONYL COMPOUNDS . . . 291 
 
 XXXIV. THE METHANE SERIES . . . . . .296 
 
 XXXV. THE FATTY ACIDS 303 
 
 XXXVI. THE OLEFINES 310 
 
 XXXVII. GLYCERIN AND THE FATS 316 
 
 XXXVIII. THE CARBOHYDRATES 322 
 
 XXXIX. THE BENZENE DERIVATIVES 329 
 
 XL. THE TERPENE, CAMPHORS, ALKALOIDS, AND GLU- 
 
 COSIDES 338 
 
 XLI. ANIMAL CHEMISTRY, FERMENTATION . . . 344 
 
 APPENDIX I. COMPARATIVE TABLE OF ENGLISH AND METRIC 
 
 MEASURES, THERMOMETRIC RULES , .351 
 APPENDIX II. QUESTIONS AND EXERCISES 353 
 
PART I. 
 
 INORGANIC CHEMISTRY. 
 
 CHAPTER I. 
 
 INTROD UCTION. 
 
 WHEN we closely observe, the occurrences of 
 Nature, we soon see that two great classes of 
 changes are constantly taking place. First, there 
 are the changes which do not affect the essential 
 character of things : like the motion of a body from 
 one spot to another, and the variations between heat 
 and cold, sound and silence, light and darkness, and 
 so on. Secondly, there are the changes which sub- 
 stances undergo in their innermost structure : like 
 the transformation of wood into charcoal, of the con- 
 stituents of soil and air into the stems and leaves 
 of plants, and a multitude of other similar altera- 
 tions of different degrees of complexity. Changes 
 of the first class are called physical changes, while 
 the others are known as chemical; and it is with 
 the latter that the science of chemistry has to do. 
 
 For example, a piece of iron may be converted 
 into a magnet and afterward deprived of its mag- 
 netic power, thus acquiring and losing a certain 
 new property without ceasing to be metallic iron. 
 These changes, which do not affect the nature of 
 
the metal as a metal, are physical ; and so also are 
 those involved in raising a piece of the iron to a red 
 heat, or in rendering it fluid by melting. But if the 
 iron be placed in a shallow pool of water, so as to 
 be partly covered and partly exposed to the air, it 
 will be slowly transformed into a brownish-red sub- 
 stance called rust, and here the alteration is chem- 
 ical. The iron has ceased to exist as iron, and has 
 become changed into something quite different. 
 Again, water may be frozen into ice, or converted 
 by heat into steam ; thus showing its capacity to 
 exist in several different conditions, without ceasing 
 to be the same substance. These changes, there- 
 fore, are physical. , But, by chemical means, the 
 water may be decomposed into two gases oxygen 
 and hydrogen each of which differs widely in its 
 properties from water, and neither of which with- 
 out the other can reproduce water. This trans- 
 formation of water into something else is a chemical 
 transformation. 
 
 The following experiments will serve to illus- 
 trate chemical changes: 
 
 EXPERIMENT i. Rub together in a mortar a 
 small quantity of copper -filings with half their 
 weight of sulphur. No matter how thoroughly you 
 mix them, you can still, with a magnify ing-glass, 
 discern the separate particles of the two substances. 
 Now insert the mixture in a glass tube sealed at the 
 lower end, and heat gently over a flame. Presently 
 the sulphur will melt, and shortly afterward the 
 entire mass will become incandescent. Upon cool- 
 ing, it will be found that both copper and sulphur 
 have disappeared, and in their place is a grayish 
 substance, in which the most powerful microscope 
 
INTRODUCTION. 3 
 
 can detect no particle of either of the original 
 bodies. The copper and sulphur have united to 
 form a new substance, known as copper sulphide ; 
 
 FIG. i. Union by Heat. 
 
 and thus the experiment serves to illustrate chemical 
 combination. It also teaches the difference between 
 chemical combination and mere mechanical mixture. 
 Instead of copper, iron may be used in this experi- 
 ment, and then iron sulphide will be formed. Be- 
 fore heating, the metal may be separated from the 
 sulphur by means of a magnet ; but after union has 
 taken place the iron can not be thus withdrawn. 
 
 EXPERIMENT 2. Place in a dry test-tube a lit- 
 tle red mercuric oxide, and heat cautiously over a 
 flame. Soon globules of metallic mercury or quick- 
 silver will be seen in the bottom of the tube, or con- 
 densed upon its cooler sides. In the tube there will 
 also be a quantity of oxygen gas, which may be 
 recognized by the fact that a kindled match will 
 burn more brilliantly in it than in the outer air. 
 
4 INORGANIC CHEMISTRY. 
 
 The original red substance has been divided into 
 two substances, a gas and a metal ; so that here we 
 have an instance of chemical decomposition.* 
 
 EXPERIMENT 3. Rub together in a mortar a lit- 
 tle potassium iodide and a little mercuric chloride. 
 Presently, in place of the two white substances, a 
 scarlet powder will appear. This chemical change 
 is more complicated than either of the foregoing 
 cases, and is an instance of double decomposition. 
 Here two compounds exchange their constituents, 
 each decomposing the other, new compounds at the 
 same time being formed. This phase of action will 
 be considered more fully in another chapter. 
 
 In several ways these experiments are instructive. 
 They show, for example, how wonderfully a chem- 
 ical change affects the physical properties of things, 
 the properties of a compound being often widely 
 different from those of the substances which have 
 united to produce it. Under proper conditions, 
 black, tasteless, odorless charcoal may be made to 
 unite with yellow, tasteless, odorless sulphur; the 
 product of the union of these two solids being a 
 volatile, colorless, transparent liquid, with a nau- 
 seous odor and burning taste. A more complete 
 transformation can hardly be imagined. f 
 
 It will be observed that in two of the foregoing 
 
 * Copper formate is even better than mercuric oxide for strikingly 
 illustrating decomposition. When heated in a tube the brilliant blue 
 crystals evolve gas copiously, and pure metallic copper remains behind. 
 The substance may be prepared by dissolving copper oxide in warm 
 formic acid, and aHowing the solution to crystallize. Unfortunately, 
 the materials are not readily available in all school laboratories. 
 
 f At this point the teacher will do well to show the class, side by 
 side, a fragment of charcoal, a bit of sulphur, and a bottle of carbon 
 disulphide. 
 
INTRODUCTION. 5 
 
 experiments heat is applied: in one case as a de- 
 composing agent, in the other as a means of caus- 
 ing union. Another experiment will bear advanta- 
 geously upon these. 
 
 EXPERIMENT 4. Pulverize, in a perfectly clean 
 mortar, a little potassium chlorate. Transfer it to a 
 sheet of paper, and mix carefully with it, without 
 rubbing, an equal quantity of powdered sugar. Place 
 the mixture where no harm can be done, and drop 
 upon it, from a glass rod, a single drop of strong 
 sulphuric acid. The mass will immediately catch 
 fire, burning with almost explosive violence, and 
 with a peculiar rose-colored flame. Here, then, we 
 have a chemical change which produces a great 
 amount of heat. 
 
 We now see that heat plays a very important 
 part in chemical changes ; and, as we go on, we 
 shall find that other agencies, such as light, elec- 
 tricity, etc., are also often involved. In order, 
 then, that a chemical change may be completely 
 understood, three things have to be studied, as 
 follows : 
 
 First, the properties of the substances entering 
 into the change. Secondly, the physical phenomena 
 occurring during the change. Thirdly, the prop- 
 erties of the substances which result from the 
 change. 
 
 In such investigations one principle, which un- 
 derlies all science, must be steadily kept in view. 
 In no case is anything, either matter or force, ever 
 created or destroyed. By matter is meant any- 
 thing which occupies space and possesses weight : 
 like iron, wood, water, or air. By force is under- 
 stood any agency capable of producing motion, or 
 
6 INORGANIC CHEMISTRY. 
 
 of altering the direction of a moving body ; * and such 
 things as heat, light, electricity, mechanical power, 
 etc., are called forces. When two bodies act upon 
 each other chemically, they do so under the influence 
 of a peculiar force, known variously as chemical 
 affinity, chemical attraction, or, more briefly, chem- 
 ism. When two substances unite, it is this force 
 which brings them together ; when they are separat- 
 ed, this force has to be overcome. In consequence, 
 every chemical change involves some transformation 
 of force, but none is ever created or destroyed. So 
 also with the matter changed : however complicated 
 its alteration may be, no particle is ever lost, no new 
 particle ever appears. When a candle is burned, a 
 series of chemical changes takes place. Heat is de- 
 veloped by chemical action, and a certain amount of 
 matter seems to disappear. But, if all the products 
 of combustion, solid or gaseous, be collected and accu- 
 rately weighed, it will be found that nothing has real- 
 ly vanished. The matter of the candle and of the air 
 in which it burned have acted upon each other chem- 
 ically, and new substances have been formed ; but 
 neither destruction nor creation of matter was possi- 
 ble. It is with the transformations of matter, its combi- 
 nations and decompositions, that the chemist has to deal. 
 In the light of the foregoing pages we may now 
 frame an intelligible definition, as follows : Chemistry 
 is the science which investigates the composition of sub- 
 stances, together with the combinations and decomposi- 
 tions resulting from their action upon one another under 
 the influence of chemical force.\ 
 
 * For more exhaustive definitions, the works on mechanics and 
 physics may be consulted. 
 
 f The essential features of this definition may be expressed in a 
 
INTRODUCTION. j 
 
 At the beginning of any study the question of 
 utility is apt to arise. With chemistry the answer 
 to this question is twofold : First, its value as an 
 educational instrument, as a means of mental dis- 
 cipline, is very great. Secondly, its material advan- 
 tages are enormous. The discoveries of chemists 
 are now applied to practical use in agriculture, in 
 medicine, and in every great manufacturing indus- 
 try. By the help of chemistry many substances 
 which were formerly wasted are now rendered use- 
 ful. For example, from coal-tar the most brilliant 
 dyes are made. Our dwellings are now lighted 
 with chemically refined oil and candles, or by chem- 
 ically made gas ; and these are kindled with matches 
 which chemistry has given us in place of the old 
 flint and steel. Our clothing is bleached or dyed 
 by chemical means ; metals are extracted from their 
 ores by chemical processes ; soap, glass, porcelain, 
 paints, varnishes, etc., have all become better and 
 cheaper than before the chemist studied them. Bar- 
 ren soil is now rendered fruitful by chemical fer- 
 tilizers ; wood is preserved from decay by chemical 
 applications ; diseases are checked by chemical dis- 
 infectants ; and a multitude of chemical preparations 
 aid the physician in alleviating pain. 
 
 variety of other ways. The pupil will find it a useful exercise to ar- 
 range other definitions, so as to see the subject from several different 
 points of view. 
 
CHAPTER II. 
 
 THE CONSTITUTION OF MATTER. 
 
 IN order to determine the composition of any 
 substance, the chemist may resort to two distinct 
 methods, analysis and synthesis. By analysis, a body 
 is separated into its component parts, which are then 
 identified. By synthesis these parts may be artifi- 
 cially combined, so as to produce the substance 
 under investigation. For example, the composition 
 of water may be ascertained by dividing it into its 
 two constituents, oxygen and hydrogen ; or it may 
 be determined by causing these gases to unite, and 
 proving that by their union water is actually formed. 
 Each method re-enforces the other, and strengthens 
 the final conclusion. 
 
 In Nature the chemist recognizes an almost limit- 
 less number of different substances, the composition 
 of which he tries to discover by either or both of 
 the above methods. Besides, he has to deal with 
 vast numbers of artificial bodies ; of which so many 
 are theoretically possible that infinity would barely 
 suffice to express them. In the analysis of all these 
 substances, however, he finds the same component 
 parts continually repeated in various modes of un- 
 ion ; and he finally arrives at bodies so simple that 
 they can not be analyzed further. These simple 
 
THE CONSTITUTION OF MATTER. 
 
 9 
 
 substances, of which at present some seventy are 
 known, he terms elements. All other substances, 
 which are formed by the chemical union of elements 
 with each other, and which are consequently sepa- 
 rable into elements by analysis, he calls compounds. 
 Thus, the oxygen and hydrogen previously referred 
 to are elements, for by no means within the chem- 
 ist's control can they be decomposed into simpler 
 bodies ; while the water formed by their union is 
 a compound, and is said to be composed of these 
 elements. The following table contains a list of all 
 the elements now known. The use of the " sym- 
 bols" and the meaning of the "atomic weights" 
 will be explained further on. New elements are 
 occasionally discovered, usually as constituents of 
 very rare minerals. 
 
 Table I. Elements, Symbols, and Atomic Weights. 
 
 NAME. 
 
 Symbol. 
 
 Atomic 
 weight. 
 
 NAME. 
 
 Symbol. 
 
 Atomic 
 weight. 
 
 Aluminum 
 
 Al. 
 
 27. 
 
 Erbium 
 
 Er. 
 
 1 66. 
 
 Antimony 
 
 Sb. 
 
 120. 
 
 FLUORINE 
 
 F. 
 
 19. 
 
 ARSENIC 
 
 As. 
 
 75. 
 
 Gallium 
 
 Ga. 
 
 69. 
 
 jBarium 
 
 Ba. 
 
 I?7. 
 
 Glucinum 
 
 Gl. 
 
 9- 
 
 Bismuth 
 
 Bi 
 
 ->o8 
 
 Gold. 
 
 Au. 
 
 196.5 
 
 BORON 
 
 B. 
 
 1 1. 
 
 v HYDROGEN . . . 
 
 H. 
 
 i. 
 
 ^BROMINE 
 
 Br. 
 
 80. 
 
 Indium 
 
 In. 
 
 113.6 
 
 Cadmium 
 
 Cd 
 
 112. 
 
 V !ODINE 
 
 I. 
 
 127. 
 
 CcCsium 
 
 Cs. 
 
 J-2 J. 
 
 Iridium 
 
 Ir. 
 
 193. 
 
 Calcium 
 
 Ca 
 
 ' 4.O 
 
 Iron 
 
 Fe. 
 
 f 
 
 56. 
 
 "CARBON 
 
 C. 
 
 12. 
 
 Lanthanum .... 
 
 La. 
 
 138.2 
 
 CERIUM 
 
 Ce 
 
 T/1T 
 
 Lead 
 
 Pb. 
 
 207. 
 
 ^CHLORINE 
 
 Cl 
 
 2C C 
 
 Lithium 
 
 Li. 
 
 7. 
 
 Chromium 
 
 Cr. 
 
 C2. 
 
 Magnesium .... 
 
 Mg. 
 
 24. 
 
 Cobalt 
 
 Co. 
 
 CQ 
 
 Manganese .... 
 
 Mn. 
 
 cc. 
 
 Columbium 
 
 Cb 
 
 QA 
 
 Mercury 
 
 HP- 
 
 2OO. 
 
 Conner . . 
 
 Cu. 
 
 5a 
 
 Molybdenum . . 
 
 Mo. 
 
 96. 
 
 X *? . 
 
 Decipium 
 
 Dp. 
 
 > 3 
 
 Nickel 
 
 Ni. 
 
 58. 
 
 Didvmium . . 
 
 DL 
 
 14.2.1 
 
 ^NITROGEN . . 
 
 N. 
 
 14.. 
 
10 
 
 INORGANIC CHEMISTRY. 
 
 NAME. 
 
 Symbol. 
 
 Atomic 
 weight. 
 
 NAME. 
 
 Symbol. 
 
 Atomic 
 weight. 
 
 Osmium . 
 
 Os. 
 0. 
 Pd. 
 P. 
 Pt. 
 K. 
 Rh. 
 Rb. 
 Ru. 
 Sm. 
 Sc. 
 Se. 
 Si. 
 Ag. 
 Na. 
 Sr. 
 
 199.? 
 
 1 6. 
 106. 
 
 31- 
 195. 
 
 39- 
 104. 
 
 85.5 
 104. 
 150. 
 
 44. 
 
 79- 
 28. 
 108. 
 
 5 
 
 \i>ULPHUR 
 
 S. 
 Ta. 
 Te. 
 Tb. 
 Tl. 
 Th. 
 Tm. 
 Sn. 
 Ti. 
 W. 
 U. 
 V. 
 Yt. 
 Yb. 
 Zn. 
 Zr. 
 
 32. 
 IS2.6 
 126. ? 
 ? 
 204. 
 
 23 |- 
 
 118. 
 48. 
 184. 
 
 239- 
 
 ^ 
 
 173- 
 65. 
 90. 
 
 OXYGEN. 
 
 Tantalum . 
 
 Palladium 
 
 TELLURIUM... 
 Terbium 
 
 ^PHOSPHORUS... 
 Platinum. 
 
 Thallium 
 
 Potassium 
 
 Thorium 
 
 Rhodium . 
 
 Thulium 
 
 Rubidium , . 
 
 Tin 
 
 Ruthenium 
 
 Titanium 
 Tungsten 
 
 Samarium .. 
 
 Scandium 
 
 Uranium 
 
 SELENIUM 
 
 Vanadium . 
 
 SILICON . 
 
 Yttrium 
 
 
 Ytterbium 
 
 Sodium . 
 
 Zinc 
 
 Strontium 
 
 Zirconium 
 
 
 
 Of these elements by far the greater number are 
 metallic ; like gold, iron, zinc, etc. A smaller num- 
 ber, given in the table in small capitals, are called 
 non-metallic ; and of these carbon, oxygen, and sul- 
 phur are good examples. In the subsequent chap- 
 ters the latter class of elements will be studied first. 
 Between the metals and the non-metals, however, 
 no sharp distinctions can be drawn; arsenic, for 
 example, may be fairly put in either class; the 
 division, therefore, is mainly one of convenience, 
 and is not fundamentally important. 
 
 In order that we may be able to account for 
 many of the properties of matter, we must study 
 its physical constitution still more closely. Take, 
 for example, a piece of iron : when it is heated, it 
 expands, and occupies more space than before ; 
 when cooled, it contracts and becomes smaller ; al- 
 though in both cases the weight remains the same. 
 
THE CONSTITUTION OF MATTER. u 
 
 Weight, therefore, may be regarded a constant 
 property of matter, while volume or bulk is vari- 
 able. This variability in volume is most easily ac- 
 counted for upon the supposition that matter, as we 
 ordinarily recognize it, is made up of minute, sepa- 
 rate particles, which may be driven farther apart or 
 crowded closer together by various means. These 
 particles the physicist terms molecules, and they are 
 considered to be by all mechanical means indivisi- 
 ble. Every kind of matter is built up of its own 
 characteristic kind of molecules ; these are exactly 
 alike, although different from the molecules of every 
 other substance, and they are separated by larger or 
 smaller spaces. They are furthermore supposed to 
 be in more or less rapid motion ; and upon this sup- 
 position the mathematical theories of heat and elec- 
 tricity are very largely based. Of course, molecules 
 are exceedingly small so small that we may never 
 be able to see or handle them experimentally. There 
 are, however, abundant reasons for asserting their 
 existence ; and it is even possible to calculate from 
 physical data something approximate concerning 
 their size. Evidence can be drawn from several 
 sources showing that about five hundred millions of 
 hydrogen-molecules, placed in a row, would only 
 form a line an inch long ; or, in other words, there 
 are about two hundred millions to the linear centi- 
 metre.* 
 
 But, although molecules are mechanically indi- 
 visible, by chemical means we can divide them into 
 smaller particles still. For example, a drop of water 
 
 * For fuller details, consult Tait's " Recent Advances in Physical 
 Science," chapters xii and xiii ; also Cooke's " New Chemistry," pp. 
 27-36. 
 
12 INORGANIC CHEMISTRY. 
 
 may be divided and subdivided until the molecules 
 of water are reached ; and each of these will still 
 possess all the properties of water. But water is a 
 compound of two elements, oxygen and hydrogen ; 
 and therefore every one of its molecules may be 
 decomposed into these two substances. The smaller 
 portions of oxygen and hydrogen thus recognized 
 are called atoms. The molecule of any chemical 
 compound, then, is a cluster of atoms ; and it is only 
 between atoms that the force of chemical attraction 
 comes into play. In future chapters some of the 
 properties of atoms will be considered. For pres- 
 ent purposes the following definitions will be found 
 useful : 
 
 A mass of matter is any portion of matter 
 which can be recognized by the senses. Every 
 mass is an aggregation of molecules. Masses at- 
 tract each other by the force of gravitation. The 
 science of mechanics deals with masses and their 
 motions. 
 
 A molecule is the smallest particle of any sub- 
 stance which can exist in the free state, and in 
 which the characteristic properties of the sub- 
 stance are retained. It is also the smallest por- 
 tion of matter which can take part in any phy- 
 sical change. The science of molecular physics 
 (including heat, light, and electricity) deals large- 
 ly with molecules and their motions. Nearly all 
 molecules are clusters of atoms; but, for a very 
 few substances, the molecule and the atom are the 
 same. 
 
 An atom is the smallest quantity of any substance 
 which can enter into chemical union, or take part 
 in any chemical change. Chemistry may be defined 
 
THE CONSTITUTION OF MATTER. ^ 
 
 as the science which treats of atoms and their at- 
 tractions for each other.* 
 
 * This definition may be considered as a supplement to the one 
 given in the preceding chapter. The subject of atoms and molecules 
 may be read up to advantage in Cooke's " New Chemistry," Wurtz's 
 " Atomic Theory," Cooke's " Chemical Philosophy," or Remsen's 
 " Theoretical Chemistry." 
 
CHAPTER III. 
 
 HYDROGEN. 
 
 IN the preceding chapters reference has been 
 made to the fact that water is composed of hydro- 
 gen and oxygen. We may now study hydrogen, 
 oxygen, and water separately and in detail. 
 
 Hydrogen, although it had been obtained and 
 partly examined by several earlier investigators, 
 was first accurately studied by Cavendish in 1766. 
 In 1781 he made the additional discovery that water 
 is the only product of its combustion ; and, on ac- 
 count of this fact, Lavoisier gave it its present name, 
 which signifies " water-producer." It may be easily 
 obtained from water as follows : 
 
 EXPERIMENT 5. Wrap a bit of sodium as large 
 as a pea in some wire-gauze, and hold it by a handle 
 of stout wire under the mouth of an inverted test- 
 tube filled with water in a pneumatic trough. In- 
 stead of the latter piece of apparatus, a common, 
 deep earthenware dish full of water may be used. 
 The test-tube should be filled with water completely ; 
 then, by closing its mouth with the thumb, it may 
 be inverted and placed easily in position. The so- 
 dium will at once be attacked by the water, bubbles 
 of gas will be evolved and rise into the tube, and soon 
 the latter will be full. Again close the mouth of 
 
HYDROGEN. 
 
 the tube with the thumb, and bring it mouth upper- 
 most. Now, upon removing the thumb, and in- 
 stantly applying a match, the gas in the tube will 
 
 FIG. 2. Preparation of Hydrogen with Sodium. 
 
 ignite, and burn with a pale, bluish flame. The gas 
 is hydrogen. Since the bit of sodium may produce 
 a slight explosion, it is prudent in this experiment 
 to wear stout gloves. 
 
 In the foregoing experiment the sodium with- 
 draws oxygen from the water, setting hydrogen 
 free. When steam is passed through a gun-barrel 
 or piece of gas-pipe filled with iron-filings and heated 
 to redness, a similar change takes place ; the oxygen 
 of the steam being retained by the iron, so that only 
 hydrogen escapes at the farther end of the appa- 
 ratus. But, for preparing hydrogen in quantity, the 
 subjoined method is the most convenient : 
 
 EXPERIMENT 6. Place a quantity of granulated 
 zinc (prepared by pouring melted zinc from a height 
 of three or four feet into cold water) in a gas deliv- 
 ery-flask (Fig. 3), and cover it with dilute hydro- 
 chloric acid. Iron-filings may be used instead of 
 zinc, and sulphuric acid in place of hydrochloric.* 
 
 * Some druggists and dealers in chemicals still retain for this acid 
 the nearly obsolete name of muriatic acid. 
 2 
 
i6 
 
 INORGANIC CHEMISTRY. 
 
 In either case hydrogen will be copiously evolved ; 
 and it may be collected over water in a number of 
 small, wide-mouthed bottles. The first portions of 
 gas should be allowed to escape, since they will be 
 
 FIG. 3. Preparation of Hydrogen. 
 
 contaminated with the air which originally filled 
 the apparatus. By applying a flame to the mouth 
 of one of the little bottles, the inflammability of hy- 
 drogen may again be recognized. 
 
 Hydrogen, when perfectly pure, is a colorless, 
 tasteless, odorless gas. As ordinarily prepared, how- 
 ever, it is apt to be disagreeably scented by impuri- 
 ties derived from the materials used in its manufac- 
 ture. It is found in Nature, in the free state, among 
 the gases exhaled by certain volcanoes ; and it is 
 also contained in many meteoric irons. Not only 
 iron, but several other metals also, notably palla- 
 dium, have the property of absorbing (or occluding) 
 
HYDROGEN. 17 
 
 considerable quantities of hydrogen. Since metals 
 containing occluded hydrogen exhibit in some de- 
 gree the properties of alloys, it has been suggested 
 that hydrogen ought to be classed as a metal also ; 
 and some chemical reasons, which will be cited 
 further on, tend to support this view. Hydrogen 
 exists in enormous quantities in the atmosphere of 
 the sun, and in most of the other self-luminous 
 heavenly bodies, its presence there being revealed 
 to us by the spectroscope. It is an important con- 
 stituent of coal-gas ; and in the combined state we 
 find it not only in water, but in nearly all animal 
 and vegetable substances, in petroleum, and in a 
 great many artificial products. 
 
 We have already seen that hydrogen is inflam- 
 mable, and that its flame is but feebly luminous. It 
 is, however, exceedingly hot, as the following ex- 
 periment will show : 
 
 FIG. 4. Combustion of Hydrogen. 
 
 EXPERIMENT 7. Generate hydrogen as in Ex- 
 periment 6 ; only, instead of collecting it over water, 
 
1 8 INORGANIC CHEMISTRY. 
 
 allow it to issue into the air through a long glass 
 tube drawn out to a fine jet at the end. Allow the 
 gas to escape for some time, until all the air origi- 
 nally contained in the flask has been expelled ; then 
 light the jet of gas and observe the character of the 
 flame. Now insert in the flame a little fine coil of 
 platinum wire. It will at once become brilliantly 
 white-hot If the gas is kindled while air remains in 
 the flask, a violent explosion will ensue. By holding 
 a cold test-tube inverted over the hydrogen-flame, 
 the formation of drops of water as a product of com- 
 bustion may be observed. 
 
 Hydrogen is incapable of supporting respira- 
 tion ; hence, small animals immersed in it soon die. 
 The pure gas may, however, be inhaled to a limited 
 extent without danger. When the lungs are filled 
 with it, even the gruffest voice becomes curiously 
 shrill and hollow. 
 
 Hydrogen is the lightest of all known substances. 
 Hence its use in the filling of balloons, although for 
 this purpose coal-gas is now more generally em- 
 ployed. 
 
 EXPERIMENT 8. Collect the hydrogen from a 
 generating-flask in a large bladder, and, when the 
 latter is full, tie it tightly around the neck with 
 string. An inexpensive toy-balloon is thus made. 
 
 EXPERIMENT 9. Fill a small india-rubber gas- 
 bag with hydrogen, and attach a clay tobacco-pipe 
 to its nozzle by a bit of rubber tube. The pipe 
 may now be used for blowing soap-bubbles, which 
 are filled with hydrogen by a gentle pressure on 
 the bag. The bubbles rise at once to the ceil- 
 ing, on account of their remarkable lightness. 
 By touching each bubble with a candle-flame, the 
 
HYDROGEN. 
 
 inflammability of hydrogen may be further illus- 
 trated. 
 
 EXPERIMENT 10. Hydrogen may be poured 
 from one bottle into another, but it must be poured 
 upward. One of the small 
 bottles filled in Experiment 
 6 will do for this experi- 
 ment. When the gas has 
 been transferred, it may be 
 recognized in the second 
 bottle by its inflammability. 
 (See Fig. 5.) 
 
 The weight of one litre 
 (or cubic decimetre) of hy- 
 drogen, measured at the 
 temperature of o centi- 
 grade, and under a baro- 
 metric pressure of 760 mil- 
 limetres, is only 0.0896 gramme.* This weight is 
 called a crith, and is an important unit of weight 
 in all gas calculations. In the subjoined table it is 
 compared with the weight of equal bulks of air, 
 water, and platinum the latter being the heaviest 
 substance known. 
 
 One cubic decimetre of hydrogen weighs 0.0896 gramme. 
 " air " 1.2932 
 
 " water " 1000.0000 grammes. 
 <4 " platinum " 21500.0000 " 
 
 Hence, air is 14.43 times, water a little over 11,000 
 times, and platinum about 240,000 times heavier than 
 hydrogen. 
 
 In many chemical calculations the volume occu- 
 
 * Tables of metric weights and measures, and of the different ther- 
 mometric scales, may be found in the Appendix. 
 
 FIG. 5. Pouring Hydro- 
 gen up. 
 
20 INORGANIC CHEMISTRY. 
 
 pied by a given quantity of gas is a very important 
 factor. Since the volume of a gas depends upon 
 conditions of temperature and pressure, we must 
 take these agencies into account, and, for conven- 
 ience, we must first establish some definite standards 
 of comparison. The normal, or standard, tempera- 
 ture is assumed to be o centigrade, or 32 Fahren- 
 heit. The normal atmospheric pressure is indicated 
 by the barometer when the mercurial column is 
 exactly 760 millimetres high. Volumes of gases, 
 then, are always to be compared at o centigrade, 
 and under 760 millimetres pressure ; and, whenever 
 they have been measured under other conditions, it 
 is customary to reduce them to these standards. 
 
 The law governing the expansion of gases by 
 heat is very simple. For present purposes it may 
 be stated thus : All gases expand equally for equal rises 
 of temperature. Although this is only approximately 
 true, its variations from absolute accuracy need not 
 be considered in ordinary calculations. The errors 
 introduced are so small that they may be safely 
 ignored ; just as in measuring the width of a room a 
 thousandth of an inch more or less counts for nothing. 
 For each degree centigrade, a gas, measured origi- 
 nally at o, will expand -^ of its bulk ; thus : 
 
 273 volumes of air at o become 
 
 274 at i, 
 275 
 
 276 
 
 273 + t 
 
 272 
 
 271 ' " 2, etc. 
 
 If this rule were absolutely true, then, at 273 be- 
 low zero, the volume of a gas would become nothing, 
 
HYDROGEN. 21 
 
 and matter would absolutely vanish. Accordingly, 
 273 below the centigrade zero is called the absolute 
 zero of temperature. Of course, this value has no ex- 
 perimental meaning, since it can never be reached : 
 but it has some mathematical importance. Gases 
 cease to be gases, and condense to liquids or solids, 
 long before reaching so low a temperature. 
 
 Suppose, now, we have two volumes (two litres, 
 or two cubic feet, or whatever units you please) of 
 hydrogen at o, and wish to calculate what its bulk 
 would be if heated up to 25. The formula is as 
 follows : 
 
 273 : 273 + 25 :: 2 : x. 
 
 Conversely, if we measure two volumes at 25, and 
 wish to reduce it to o : 
 
 273 + 25 : 273 :: 2 : x. 
 
 Again, let us take twelve volumes of gas at 37, and 
 wish to determine its volume after cooling to 23 : 
 
 273 + 37 : 273 + 23 :: 12 : x. 
 
 In some cases we have to deal with volumes of 
 gases below o. Then, instead of adding, we sub- 
 tract the given number of degrees from the stand- 
 ard volume, 273. In short, we always express the 
 volume of a gas at o by 273, assume an increase or 
 decrease, as the case may be, for each~degree of 
 difference from o, and then, by a simple propor- 
 tion, the reduction to o may be easily made.* 
 
 The changes in the volume of a gas due to va- 
 
 * Most of the problems which arise in chemical calculations are 
 most clearly and logically stated in the form of simple proportions. 
 Every pupil should, therefore, become accustomed to this method of 
 computing. 
 
22 INORGANIC CHEMISTRY. 
 
 nations in pressure are governed by a very simple 
 law, as follows : The volume of a gas is inversely pro- 
 portional to the pressure. This is termed the law of 
 Boyle and Marriotte, having been independently dis- 
 covered by these two investigators. If we double 
 the pressure under which a gas is kept, we halve its 
 volume ; if we halve the pressure, we double the 
 volume, and so on. This relation is conveniently 
 expressed by the formula P, : P : : V : V x ; in which 
 V represents the volume under the pressure P, and 
 Vj the volume under the altered pressure P,. For 
 example, suppose we have measured ten volumes of 
 hydrogen when the barometer stood at 771 milli- 
 metres, and we wish to calculate what it would be- 
 come at 760 millimetres : 
 
 760 : 771 :: 10 : x. 
 
 Here we see that, under the lower pressure, the gas 
 has expanded slightly. Conversely, if ten volumes 
 have been measured at 760 millimetres, they will 
 become less than ten at 771 millimetres, thus: 
 
 771 : 760 :: 10 : x. 
 
 The law governing pressures is, like that relating 
 to temperatures, only a very close approximation to 
 the truth. Its variations from accuracy can, how- 
 ever, only be detected by the most refined experi- 
 ments.* 
 
 By intense cold and great pressure all gases are 
 condensible to liquids, and even into the solid state. 
 For hydrogen, this was first experimentally accom- 
 
 * The experimental evidence for these laws may be read up in a 
 volume upon physics. A good theoretical discussion of them may be 
 found in the third chapter of Cooke's " Chemical Philosophy," new 
 edition. 
 
HYDROGEN. 23 
 
 plished by MM. Cailletet and Pictet (working inde- 
 pendently of each other) at the close of the year 
 1877. By Pictet it was cooled to 140 centigrade 
 under a pressure of 650 atmospheres. (The press- 
 ure exerted by the air in maintaining a barometric 
 column of mercury at the height of 760 millimetres 
 is called one atmosphere.) Under these conditions 
 hydrogen became visible as a steel-blue liquid, a 
 portion of which solidified as it issued from the ap- 
 paratus, and fell to the ground in grains. These 
 emitted a shrill, metallic sound as they struck the 
 floor, thus emphasizing the idea that hydrogen is 
 really a metal. Many metals can be converted into 
 gases at high temperatures ; mercury becomes gase- 
 ous at 350 centigrade, and is liquid under ordinary 
 circumstances. The gaseous nature of hydrogen, 
 therefore, has nothing to do with the question 
 whether it is metallic or non-metallic. The chemi- 
 cal significance of these terms will appear in later 
 chapters. 
 
CHAPTER IV. 
 
 OXYGEN. 
 
 OXYGEN, which was discovered by Priestley in 
 1774, and a little later, but independently, by Scheele, 
 is the most abundant of all the elements. Uncom- 
 bined, but mixed with nitrogen, it constitutes one 
 fifth of the atmosphere ; combined, it forms eight 
 ninths of the material composing water, and about 
 one half the weight of all the rocks. It is also a 
 very important constituent of animal and vegetable 
 matter. 
 
 Oxygen was originally prepared by heating mer- 
 curic oxide (see Experiment 2), mercury being left 
 behind, while the oxygen was given off. This meth- 
 od, however, is inconvenient, and is now replaced 
 in ordinary practice by the following cheaper pro- 
 cess: 
 
 EXPERIMENT 11. Take a stout test-tube, or, 
 better, a piece of glass combustion-tubing sealed at 
 one end, and close its mouth with a perforated cork, 
 through which is inserted a delivery-tube, also of 
 glass. Mix thoroughly upon a sheet of paper equal 
 weights of potassium chlorate and manganese diox- 
 ide, taking care that both are perfectly pure and 
 dry. Fill the test-tube one third full with this mix- 
 ture, and heat carefully over a spirit-lamp or a 
 
OXYGEN. 25 
 
 Bunsen gas-burner. Oxygen will be given off co- 
 piously, and may be collected either in a rubber 
 gas-bag, or in several bottles over water in the 
 pneumatic trough. (Fig. 6.) When oxygen is to 
 be prepared in large quantities, a copper or iron 
 retort is used instead of a glass tube. For safety, 
 several precautions ought to be observed. First, it 
 is well to heat the manganese dioxide to redness in 
 an iron dish before using it, in order to burn out 
 
 FIG. 6. Preparation of Oxygen. 
 
 any deleterious impurities. Were particles of or- 
 ganic matter or charcoal to be present, a dangerous 
 explosion might ensue. Secondly, the upper por- 
 tions of the mixture in the tube should be heated 
 first, and later the lower portions. Thirdly, the 
 heat should be so regulated that the oxygen will be 
 given off in a steady, tranquil stream ; not in sudden 
 gusts, explosively. 
 
 In this experiment the potassium chlorate, which 
 consists of potassium, chlorine, and oxygen chemi- 
 
26 INORGANIC CHEMISTRY. 
 
 cally combined, is decomposed ; the oxygen being 
 set free, while potassium chloride, a compound of 
 potassium and chlorine, remains behind. The man- 
 ganese dioxide undergoes no change, but in some 
 way it facilitates the decomposition of the chlorate. 
 This kind of action, in which a body assists a chemi- 
 cal process without being itself altered, is often met 
 with, and is termed catalytic action. Some cases of 
 catalysis are easily explained, but this particular case 
 awaits an explanation. Several other processes for 
 preparing oxygen are somewhat in use, and one or 
 two of them will be hereafter referred to. 
 
 Oxygen is a colorless, tasteless, odorless gas, six- 
 teen times heavier than hydrogen. By cooling to 
 a temperature of 140 centigrade, under a press- 
 ure of 320 atmospheres, it has been condensed to a 
 colorless liquid. It unites with all the other ele- 
 ments, except fluorine, and its compounds with 
 them are called oxides. For example, with zinc it 
 forms zinc oxide ; with copper, copper oxide, etc. 
 Water, in chemical nomenclature, can be called 
 hydrogen oxide. The names of chemical com- 
 pounds are intended to express, more or less per- 
 fectly, their composition. When oxygen unites with 
 other substances, the process is termed oxidation. 
 
 The most characteristic property of oxygen is its 
 power of sustaining combustion. In nearly all cases 
 combustion is merely oxidation accompanied by the 
 development of heat and light. When oxygen is ex- 
 cluded from a burning body, the fire goes out. In 
 the air, we have one fifth of oxygen diluted with 
 four fifths of nitrogen, the latter element being inert 
 and exerting no direct influence upon combustion 
 whatever. Naturally, combustion takes place much 
 
OXYGEN. 
 
 more vividly in pure oxygen than in diluted oxygen 
 (or air), as the following easy experiments will show : 
 
 EXPERIMENT 12. Blow out a lighted candle, 
 leaving a glowing spark at the end of the wick. 
 Lower the candle into a bottle or jar of oxygen, and 
 the wick will relight, burning far more brightly than 
 before. 
 
 EXPERIMENT 13. Charcoal burns in the air with- 
 out flame, with only a dull-red glow. Plunge a bit 
 of ignited charcoal into a jar of oxygen, and it will 
 burn brilliantly. 
 
 EXPERIMENT 14. Kindle a bit of sulphur in a 
 deflagrating spoon, and note the insignificant flame. 
 Now lower it into pure oxygen, and the combus- 
 tion will become exceedingly vivid (Fig. 7). 
 
 EXPERIMENT 15. 
 Repeat the last experi- 
 ment, using a much 
 larger jar of oxygen, 
 and burning phosphor- 
 us instead of sulphur. 
 The combustion will be 
 so dazzlingly brilliant 
 that the experiment has 
 sometimes been fanci- 
 fully called "the phos- 
 phoric sun." 
 
 EXPERIMENT 16. 
 Some substances which 
 do not ordinarily burn 
 
 in air burn easily in pure oxygen. For example, 
 fasten a bit of steel watch-spring to a stout wire, and 
 dip the end of it in melted sulphur. Kindle the 
 latter and immerse the spring in oxygen. Present- 
 
 Flo. 7. Combustion in Oxygen. 
 
28 INORGANIC CHEMISTRY. 
 
 ly the steel itself will ignite, burning brilliantly and 
 sending forth a shower of sparks. It will be well 
 to cover the bottom of the oxygen-jar with sand, 
 to catch any particles of melted metal which may 
 fall. 
 
 Oxygen is also essential to respiration. Exclude 
 it from the lungs, and death follows, as in cases of 
 drowning, when the lungs become filled with water. 
 Inclose a small animal in a limited volume of air, 
 and it lives only until the supply of oxygen con- 
 tained in it is exhausted. In pure oxygen it will 
 live much longer, but the vital processes will go 
 on too violently and rapidly, and death will result.* 
 Even the fishes need oxygen, and they secure it 
 through their gills from the air which is dissolved 
 in the water. In a shallow pool insufficiently sup- 
 plied with air a fish will soon die. 
 
 Oxygen is administered by physicians to a cer- 
 tain extent as a remedy in cases of impeded breath- 
 ing. A croupy or asthmatic patient, for instance, 
 can not get enough air for proper respiration ; but 
 upon breathing a little pure oxygen he will experi- 
 ence great relief. When the lungs are filled with 
 oxygen instead of air, it is possible to " hold the 
 breath " much longer than ordinarily a fact which 
 might be used by divers. Oxygen is now made for 
 sale in most of our large cities. It is used chiefly in 
 the calcium-light (see next chapter), and is stored up 
 under compression in strong iron cylinders. 
 
 The fact that oxygen dissolves somewhat in wa- 
 ter, as hinted in a preceding paragraph, is one of 
 vast importance in the economy of Nature. In the 
 
 * In the chapter upon carbon the phenomena of combustion and 
 respiration will be treated more fully. 
 
OXYGEN. 
 
 2 9 
 
 falling of the rain, the agitation of the waves, and the 
 flowing of streams, water is being constantly charged 
 with fresh supplies of air. The oxygen thus ab- 
 sorbed at once attacks the decaying animal and 
 vegetable matter which is continually flowing into 
 rivers, lakes, and oceans, and by a process of slow 
 combustion literally burns it up. Thus oxygen be- 
 comes a great disinfectant, transforming noxious 
 substances into simpler and harmless compounds, 
 and keeping the waters of our planet always sweet 
 and clean. In a similar way it oxidizes injurious 
 vapors in the air, and is effective in the removal of 
 all kinds of corruption from the face of the earth. 
 All decay involves the phenomenon of oxidation. 
 
 Many elements, and possibly all of them, are ca- 
 pable of existing in more than one modification. 
 For example, carbon exists as charcoal, as graphite 
 or " black-lead," and as diamond ; and similar prop- 
 erties are strikingly displayed by phosphorus and 
 sulphur. This phenomenon is called allotropy, and 
 charcoal, grapm'te, and diamond are termed allotropic 
 modifications of carbon. 
 
 When an electrical machine is rapidly worked, 
 or when a series of electrical sparks are passed 
 through air, a peculiar odor, something like that 
 of burning sulphur, soon becomes noticeable. This 
 odor is due to the formation of an allotropic modi- 
 fication of oxygen, to which the name of ozone has 
 been given. 
 
 EXPERIMENT 17. Suspend a freshly-scraped 
 stick of phosphorus in a jar containing a little wa- 
 ter, so that it shall be partly immersed. It will 
 slowly oxidize ; and soon the air in the jar will ac- 
 quire the peculiar odor of ozone. 
 
30 INORGANIC CHEMISTRY. 
 
 Ozone has properties quite unlike those of ordi- 
 nary oxygen. It not only has a characteristic suffo- 
 cating odor, but it exhibits a remarkable chemical 
 activity, attacking and tarnishing metals like silver 
 and mercury, which common oxygen does not affect 
 at all. It bleaches many vegetable colors, like indi- 
 go, deodorizes putrefying animal matter, and cor- 
 rodes such substances as cork, India-rubber, etc. A 
 common test for it is paper soaked in a solution of 
 potassium iodide and starch. Moist slips of such 
 paper, exposed to the action of ozone, turn blue ; 
 because the ozone liberates iodine from the potas- 
 sium iodide, and iodine forms a blue compound with 
 starch. 
 
 In ordinary experiments only a very small por- 
 tion of any mass of oxygen can be transformed into 
 ozone. The transformation is, however, attended 
 by a shrinkage in the volume of the oxygen, so that 
 ozone is really oxygen in a more concentrated state. 
 Three volumes of oxygen would yield, if wholly 
 converted into ozone, only two volumes of the lat- 
 ter ; whence it is easy to see that, bulk for bulk, 
 ozone is half as heavy again as oxygen. The full 
 significance of this fact will appear in a later chap- 
 ter. Quite recently, ozone has been liquefied by 
 the application of cold and pressure. Liquid ozone 
 has a deep indigo-blue color, and is less volatile than 
 liquefied oxygen. 
 
 Ozone is continually being produced in nature, 
 both by the electric discharges which take place 
 during thunder-storms, and by the many phenomena 
 of slow oxidation which may be observed in the 
 vegetable kingdom. It undoubtedly plays an im- 
 portant part in the world as a natural disinfectant, 
 
OXYGEN. 3I 
 
 but upon this point much remains to be discovered. 
 At one time a third variety of oxygen, named anto- 
 zone, was supposed to exist ; but the evidence in 
 favor of it is now generally considered unsatisfac- 
 tory. 
 
CHAPTER V. 
 
 WATER. 
 
 ALTHOUGH oxygen and hydrogen gases may 
 be mixed together in any proportions, they unite 
 chemically to form only two real compounds, both 
 of which at ordinary temperatures are liquids. One 
 contains exactly twice as much oxygen as the other, 
 and on this account the names hydrogen monoxide 
 and hydrogen dioxide are respectively applied to 
 them. In chemical nomenclature numeral prefixes 
 have to be frequently employed. 
 
 When oxygen and hydrogen combine directly, 
 that is, without the intervention of other substances, 
 only hydrogen monoxide or water is produced. 
 The dioxide is prepared by indirect, roundabout 
 processes. 
 
 The formation of water from oxygen and hydro- 
 gen may be brought about either by the passage of 
 an electric spark through the mixed gases, or by 
 the agency of heat. Whenever hydrogen or any 
 compound of hydrogen is burned, water is pro- 
 duced ; as was partly demonstrated in Experiment 
 7. All ordinary illuminating materials, such as coal- 
 gas, oils, candles, etc., contain hydrogen ; and if a 
 piece of cold porcelain be held for a moment over 
 their flames, the deposition of dew will show that 
 water is actually formed. 
 
WATER. 33 
 
 Under ordinary circumstances the combustion 
 of hydrogen takes place quietly ; but if it be burned 
 in pure oxygen some extraordinary phenomena may 
 be observed. 
 
 EXPERIMENT 18. Fill an India-rubber gas-bag 
 with a mixture of two parts by volume of hydrogen 
 and one part of oxygen. Then, as in Experiment 9, 
 attach a clay pipe to the bag and use the gaseous mix- 
 ture for blowing soap-bubbles. Each bubble, when 
 touched with a lighted candle, will explode with a 
 violent report. If a heap of bubbles be blown in a 
 common tin basin and ignited, the explosion will be 
 deafening. Before applying a flame to any of the 
 bubbles the stop-cock of the bag should be closed 
 and the bag itself removed. Serious accidents 
 have happened from the ignition of large mixtures 
 of oxygen and hydrogen. Even coal-gas and com- 
 mon air will give a powerfully explosive mixture, 
 fully as dangerous as gunpowder. This is shown 
 by the terrible explosions which sometimes occur 
 when a light is carelessly carried into a room in 
 which gas has been escaping. 
 
 This experiment shows us that the formation of 
 water from its elements is attended by a remark- 
 able development of force or energy. This force 
 may be best measured in the form of heat : and it is 
 found that more heat is produced in this chemical 
 change than in any other chemical change what- 
 ever. The usual unit of heat is the quantity of heat 
 needed to raise the temperature of one gramme of 
 water from o to i C. ; and in the combustion of 
 one gramme of hydrogen 34,462 such units of heat 
 are set free. A gramme of charcoal, burning, yields 
 only 8,080 heat-units a figure in striking contrast 
 
34 INORGANIC CHEMISTRY. 
 
 with the foregoing. When hydrogen burns in ordi- 
 nary air, just as much heat is developed as if the 
 combustion took place in pure oxygen ; but the 
 temperature of the flame is lower partly because 
 the heat is generated more slowly, and partly be- 
 cause much of it is expended in warming the ni- 
 trogen with which the oxygen of the atmosphere 
 is diluted. By using pure oxygen instead of air, an 
 enormously high temperature may be attained and 
 utilized. 
 
 Although mixtures of oxygen and hydrogen ex- 
 plode violently when ignited, the two gases may be 
 made to burn together quietly by mingling them 
 just at the moment of combustion. This is done in 
 the compound (or oxyhydrogen) blow-pipe invented 
 by Dr. Hare. In this apparatus (Fig. 8) the oxygen 
 
 FIG. 8. Oxyhydrogen Blow-pipe. 
 
 and hydrogen are contained in two separate bags 
 or cylinders. They are mixed just at the tip of 
 the burner (Fig. 9), which consists of two tubes, 
 one within the other. Through the central or inner 
 tube oxygen is allowed to flow, while the outer tube 
 connects with the hydrogen-reservoir. The hydro- 
 gen is first turned on and kindled, then the oxygen 
 
WA TER. 
 
 35 
 
 is admitted ; the flow of both gases being carefully 
 regulated by stop-cocks, and by pressure on the 
 bags. The flame, although almost non-luminous, is 
 intensely hot; and many substances which were 
 
 FIG. 9. Oxyhydrogen Blow-pipe Tip. 
 
 once deemed infusible melt in it easily. Platinum, 
 for example, melts like wax before the compound 
 blow-pipe, although in the hottest furnace it only 
 softens. In the metallurgy of platinum this fact 
 is carefully utilized. Some metals, like silver, are 
 vaporized by the heat of the oxy hydrogen jet, 
 while others burn in it brilliantly. A steel file, for 
 instance, is easily consumed, sending forth a mag- 
 ficent shower of sparks as it burns. 
 
 When any substance capable of resisting the 
 excessively high temperature is inserted in the 
 oxyhydrogen flame, it becomes intensely luminous. 
 This fact is applied in the calcium or Drummond 
 light, now extensively used in stereopticon exhibi- 
 tions and for theatrical effects. This light con- 
 sists simply of a small cylinder of common lime, 
 upon which the flame of a compound blow-pipe 
 is allowed to play. It rivals the electric light in in- 
 tensity. 
 
 Up to this point we have been considering only 
 the qualitative composition of water, and the phe- 
 nomena attending its formation. We now need to 
 enter upon quantitative discussions, both as to the 
 
36 INORGANIC CHEMISTRY. 
 
 volumes and the weights of the oxygen and hydro- 
 gen which unite. 
 
 Whenever a current of electricity is passed 
 through a liquid capable of conducting it, that 
 liquid, if compound, will be decomposed. This 
 method of decomposition is known as electrolysis. 
 Pure water is not' a conductor of electricity, but by 
 adding to it a few drops of sulphuric acid it be- 
 comes one, and is then capable of electrolytic analy- 
 sis. 
 
 EXPERIMENT 19. Fill and invert two test-tubes 
 in a vessel of water slightly acidulated with sulphu- 
 ric acid. Now bring under their mouths the two 
 terminal wires of a small galvanic battery, best of a 
 couple of Grove, Bunsen, or Daniell cells (Fig. 10). 
 
 FIG. 10. Electrolysis of Water. 
 
 Bubbles of gas will slowly form (more rapidly with 
 a more powerful battery) and rise into the test-tubes, 
 
WA TER. 
 
 37 
 
 displacing the water which they at first contained. 
 Allow this action to continue until enough gas has 
 accumulated for convenient examination, and notice 
 that one tube contains just twice as much as the 
 other. By applying a match to the more volumi- 
 nous gas it may be identified as hydrogen ; while by 
 plunging an ignited splinter of wood into the con- 
 tents of the other tube oxygen may at once be recog- 
 nized. By analysis, therefore, water yields two vol- 
 umes of hydrogen to one of oxygen. In this experi- 
 ment the battery-wires, as far as they dip into the 
 acidulated liquid, should terminate in slips of plati- 
 num. 
 
 The foregoing method of analysis is not rigidly 
 exact, for the reason that traces of the gases evolved, 
 and rather more of the oxygen than of the hy- 
 drogen, remain dissolved in the water. Synthetic 
 methods, though more difficult, are better. 
 
 When an electric spark, either from an electri- 
 cal machine, a Leyden-jar, or an induction-coil, is 
 passed through a mixture of hydrogen and oxygen, 
 the two gases unite with an explosion. For quanti- 
 tative purposes this experiment is usually performed 
 in a graduated glass tube, called a eudiometer, and 
 the spark is transmitted between two platinum wires 
 which are melted into the glass at the closed upper 
 end (Fig. n). In such a tube the gases can be ac- 
 curately measured ; and it is found that when just 
 two volumes of hydrogen and one of oxygen are 
 taken, the union is complete. If the mixture of 
 gases contains more than two thirds hydrogen or 
 more than one third oxygen, the excess of either 
 element simply serves to dilute the rest, and re- 
 mains unaltered after the explosion. The oxygen 
 
38 INORGANIC CHEMISTRY. 
 
 and hydrogen under these circumstances combine 
 only in the proportions above indicated.* 
 
 FIG. ii. Eudiometer. 
 
 In experiments upon the union of gases by vol- 
 ume an important question always arises namely, 
 Is the volume of the product the same as that of the 
 original mixture, or does condensation occur ? Sup- 
 pose, for example, that two litres of hydrogen com- 
 bine with one litre of oxygen, and that we measure 
 the volume of the resulting water in the form of 
 steam. We shall find that, if we compare the steam 
 with the component gases at identical temperatures 
 and under the same pressure, only two litres of 
 steam have been formed. In other words, the three 
 original volumes of elementary gases have con- 
 densed to two volumes during union. When we 
 
 * For class-room illustration this experiment may be roughly per- 
 formed with improvised apparatus, as far as demonstrating the effect 
 of an electric spark is concerned. Accurate work is hardly possible 
 under such circumstances. 
 
WATER, 
 
 39 
 
 come to consider this fact in its relations to other 
 facts further on, we shall see that it has a very 
 important bearing upon the theories of chemistry. 
 For the present we may use it to determine the 
 weight of steam as compared with that of hydro- 
 gen. One volume of oxygen weighs sixteen times 
 as much as an equal volume of hydrogen. Hence 
 the three volumes of elementary gases which unite 
 to form water must weigh i-)-i-f-i6r= 18 times as 
 much as one volume of hydrogen. But this is also 
 the weight of two volumes of steam, so that one 
 volume of steam must weigh half as much, and be 
 nine times heavier than hydrogen. Furthermore, 
 these figures give us the composition of water by 
 weight. The one volume of oxygen must be just 
 eight times as heavy as the two volumes of hydro- 
 gen, and accordingly water consists of one part by 
 weight of the latter element to eight parts of the 
 former. This ratio of one to eight is more com- 
 monly written two to sixteen, for reasons which will 
 appear in a later chapter. 
 
 The different phenomena and substances with 
 which chemistry has to deal are so intimately con- 
 nected one with another, that it is always desirable 
 to verify important facts by several distinct lines of 
 investigation. Since the composition of water is a 
 matter of very great importance, we can not rest 
 content with the volumetric analysis and synthesis 
 given above, much as they confirm each other, but 
 we must make use of other modes of demonstration 
 also. For the composition of water by weight we 
 have so far only an indirect estimation ; and for ad- 
 ditional proof an actual synthesis by weight must 
 be resorted to. This is best accomplished with the 
 
40 INORGANIC CHEMISTRY. 
 
 aid of copper oxide, a substance containing a defi- 
 nite quantity of oxygen in a condition very available 
 for our purposes. 
 
 EXPERIMENT 20. Place a quantity of dry cop- 
 per oxide in a tube of hard glass, and connect the 
 latter, held horizontally, with the exit-tube of a flask 
 in which hydrogen is being generated. When the 
 apparatus is full of hydrogen, so that an explosion 
 
 
 FIG. 12. Synthesis of Water. 
 
 due to admixed air may be no longer feared, heat 
 the copper oxide carefully to near redness (Fig. 12). 
 As the hydrogen streams over it, oxygen will be 
 withdrawn and water will be formed ; which, as 
 steam, will issue from the farther end of the tube. 
 When the operation is complete, all of the black ox- 
 ide will have been reduced to pure, bright, metallic 
 copper. 
 
 This experiment, with some delicate refinements, 
 
WATER. 4I 
 
 gives us the means for accurately ascertaining the 
 weight-composition of water. We have only to 
 weigh the copper oxide before the experiment, and 
 afterward to weigh the remaining metallic copper 
 and the water which has been formed, and all the 
 necessary data are at our disposal. The difference 
 between the weights of the copper oxide and the 
 copper is plainly the weight of the oxygen in the 
 water produced. This weight, subtracted from that 
 of the water, gives us, of course, the weight of the 
 hydrogen. By this method, water is found to con- 
 tain, by weight 
 
 88.89 per cent of oxygen, 
 1 1. 1 1 " " hydrogen. 
 
 loo.oo total. 
 
 These figures give us, in strict accordance with 
 those calculated from the volumes of the two gases, 
 the ratio of one to eight, or two to sixteen,* between 
 the weights of oxygen and hydrogen in water. 
 Water, then, contains, by volume, two of hydrogen 
 to one of oxygen, these three volumes being con- 
 densed by union into two. By weight it contains 
 two parts of hydrogen and sixteen of oxygen fig- 
 ures which we shall have occasion to use repeatedly 
 hereafter. 
 
 Water, or hydrogen monoxide, is a transparent, 
 tasteless, odorless liquid. In small quantities it ap- 
 pears colorless also, but in thick layers it is found 
 to have a decided blue tint. Its physical properties 
 are of the highest importance, inasmuch as they 
 
 * The ratio actually deduced from all the best experiments is 
 2 : 15.9633. The latter figure is so nearly 16 that 16 may fairly be 
 used in ordinary calculations. 
 
42 INORGANIC CHEMISTRY. 
 
 furnish some of the most convenient standards with 
 which to compare those of other substances. Our 
 thermometric scales, for example, depend upon the 
 boiling of water and the melting of ice ; the boiling- 
 point being taken as one standard of temperature 
 and the melting-point as another. In the centi- 
 grade scale, which alone is used in this book, the 
 temperature at which ice melts or water freezes is 
 arbitrarily put at zero, while the boiling-point is 
 given the value of 100. The interval between is 
 divided into one hundred equal parts, and similar 
 degrees are marked off for temperatures above or 
 below the two standards. The Fahrenheit scale, 
 which is the one in common use, assumes 32 for 
 the freezing-point of water and 212 for the boiling- 
 point, dividing the space between into one hundred 
 and eighty degrees. 
 
 When boiled, water yields a larger volume of 
 vapor than any other known liquid. One litre of 
 water, measured at o C., converted into steam 
 at 100, will give 1,696 litres of the latter. Hence 
 the common expression that " a cubic inch of water 
 yields a cubic foot of steam " is approximately true. 
 But few other liquids out of the hundreds known 
 give even one third as great a volume of vapor. 
 
 Upon cooling, water again behaves remarkably. 
 It contracts regularly until the temperature of 4 is 
 reached, at which degree it attains its maximum 
 density. Cooled still further, it expands, and at o 
 it solidifies into ice, undergoing another more sud- 
 den expansion. It is this expansive force which 
 breaks bottles and pitchers in which water is al- 
 lowed to freeze, and which gives to frost its great 
 power in disintegrating rocks. Because of the ex- 
 
WATER. 
 
 43 
 
 pansion, ice is lighter than water and floats upon it ; 
 were it to sink, fresh surfaces of liquid would be ex- 
 posed to freezing during winter, until our lakes and 
 rivers were frozen solid. Such masses of ice could 
 not be melted by the summer's heat, fish-life would 
 become impossible, and the temperate zones would 
 in time be almost frigid. When the vapor of wa- 
 ter is suddenly chilled, snow is formed, and every 
 flake exhibits a regular crystalline structure. Each 
 
 FIG. 13. Snowflake Crystals. 
 
 snow-crystal is a symmetrical, six-pointed star, one 
 varying from another only in minor particulars 
 (Fig. 13). Form is as distinct a property of sub- 
 stances as color, taste, or smell ; and every solid 
 has its own characteristic shape, in which, if left to 
 themselves, its molecules become arranged in ac- 
 cordance with rigid mathematical laws. 
 
44 INORGANIC CHEMISTRY. 
 
 As regards weight, water is again an important 
 standard. In the metric system the unit of weight 
 is the gramme ; and this is denned as the weight of 
 a cubic centimetre of water measured at its tem- 
 perature of maximum density. A cubic decimetre 
 of water, or a litre, weighs just a thousand grammes, 
 or one kilogramme. The most exact weights and 
 measures, therefore, depend for their accuracy upon 
 a precise knowledge of some of the properties of 
 water. 
 
 In dealing with solids and liquids, specific grav- 
 ity or density is always referred to water as the unit 
 of comparison. If a body is twice as heavy as water, 
 bulk for bulk, its specific gravity is said to be two ; 
 if five times heavier, it is expressed by five, and so 
 on. The specific gravity of a gas or vapor is now 
 generally referred to hydrogen as unity, although 
 in some works air is still retained as the standard.* 
 
 As a solvent, water far exceeds every other liquid 
 known. Certain liquids, like alcohol or chloroform, 
 will dissolve some substances which water can not 
 attack, but in the long run water leads them all. 
 As a general rule, with comparatively few excep- 
 tions, solids dissolve more easily in hot water than 
 in cold. Gases, on the other hand, are more solu- 
 ble in cold water. Some substances, like sugar, dis- 
 solve easily and in large quantity in water ; others, 
 as for example gypsum, dissolve but sparingly ; but 
 for each one there is a limit beyond which solu- 
 bility can not go. These facts may advantageously 
 
 * Some of this material belongs more properly in a work on physics, 
 so that fuller discussion is impracticable here. Such physical data as 
 have chemical importance will be introduced here and there through- 
 out this volume. 
 
IV A TER. 
 
 45 
 
 be verified by the student with self-devised experi- 
 ments upon salt, sugar, alum, and such other soluble 
 bodies as may happen to be most readily available. 
 The phenomenon of solution is one which has not 
 yet been fully explained ; it is probably due to a very 
 weak kind of chemical attraction between the solv- 
 ent liquid and the substance dissolved. 
 
 Because of its great solvent properties, natural 
 water is never strictly pure. Rain-water contains 
 gaseous impurities, and even traces of solid matter 
 dissolved in it ; while river, spring, well, and lake 
 waters absorb a variety of substances from the soil. 
 Evaporate any ordinary drinking-water to dryness 
 on a slip of clean, bright platinum-foil, and you will 
 obtain visible traces of a solid residue. In sea-water, 
 salt lakes, and mineral springs, saline substances are 
 present in large quantities. Effervescent waters, 
 like those of the Saratoga springs, are also heavily 
 charged with a well-known gas, carbon dioxide or 
 carbonic acid. Waters nearly free from solid ingre- 
 dients are called soft waters. Waters containing 
 much lime in solution are called hard. Perfectly 
 pure water is so tasteless as to seem flat and un- 
 drinkable. Only after it has been aerated by expos- 
 ure to the air does it become palatable. 
 
 Water may be readily freed from suspended 
 sediments either by settling in large tanks or by fil- 
 tration. On the large scale it is best filtered by 
 allowing it to percolate through layers of charcoal 
 and sand, but in the laboratory filters of paper are 
 commonly used. A circular sheet of unsized paper 
 is doubled, and then folded again at right angles to 
 the crease first made. By lifting one of the folds 
 away from the other three, a hollow cone of paper 
 
4 6 
 
 INORGANIC CHEMISTRY. 
 
 is obtained which will fit snugly to the sides of a 
 glass funnel. When water containing sediment is 
 poured through this arrangement, the suspended 
 solids are retained by the paper, and the liquid is 
 transmitted clear (Fig. 14). 
 
 In order to obtain water free from dissolved im- 
 purities, resort must be had to distillation. This 
 
 FIG. 14. Filtration. 
 
 process consists simply in boiling the water away, 
 and then condensing and collecting it from the 
 steam. Distillatory apparatus may be made after a 
 great variety of patterns, according to the exact use 
 
WATER. 
 
 47 
 
 to which it is to be applied. For school purposes, 
 a glass retort will suffice, arranged as shown in Fig. 
 
 FIG. 15. Distillation. 
 
 15. The retort, mounted on a convenient stand, is 
 half filled with water and heated by a lamp placed 
 below. To diminish the danger of breaking, the 
 bottom of the retort should be separated from the 
 direct flame by a sheet of fine wire-gauze. ^ The neck 
 of the retort dips into a flask called a receiver, which, 
 together with the neck, is kept cold by the applica- 
 tion of wet cloths. When the water in the retort is 
 boiled, the steam passes over to be condensed in the 
 receiver.* From gaseous impurities water may be 
 freed by simple boiling. 
 
 Water is capable of entering into chemical union 
 with many other substances. A great number of 
 crystalline salts contain definite quantities of it, in a 
 
 * The author purposely describes the apparatus in its very simplest 
 form. Schools having more elaborate appliances will of course use 
 them. 
 
48 INORGANIC CHEMISTRY. 
 
 condition known as water of crystallization. Heat a 
 crystal of alum in a glass tube, and it will give off 
 water, which may be recognized by its condensing 
 in drops on the cooler parts of the tube above. Sul- 
 phate of copper (blue vitriol) owes its brilliant blue 
 color to water of crystallization. Upon carefully 
 heating one of the blue crystals it will become white ; 
 and after standing a while it will regain its color by 
 absorption of water from the atmosphere. Many 
 substances have this power of absorbing water from 
 the air. A bit of calcium chloride, left in an open 
 vessel for a few days, will become wet, and in time 
 will even liquefy, so much water is taken up. This 
 phenomenon is called deliquescence. When a body 
 loses water spontaneously it is said to effloresce. 
 Many minerals contain water of crystallization, and 
 water is an essential and important constituent of 
 all animals and vegetables. 
 
 The second compound of hydrogen and oxygen, 
 hydrogen dioxide,* is a very interesting substance, 
 but hardly important enough for extended descrip- 
 tion here. It is a liquid nearly half as heavy again 
 as water, and it actively bleaches vegetable colors. 
 As a powerful oxidizer it behaves very much like 
 ozone. 
 
 * Sometimes called peroxide of hydrogen. 
 
CHAPTER VI. 
 
 NITROGEN AND THE ATMOSPHERE. 
 
 NITROGEN, which was discovered by Rutherford 
 in 1772, occurs abundantly in the atmosphere, and 
 also as an important constituent of animal and vege- 
 table matter. It is furthermore contained in very 
 many artificial substances ; as, for example, nitric 
 acid, ammonia, saltpeter, nitroglycerine, and so on. 
 In the air it is found to be mixed with oxygen ; and it 
 is most readily isolated by simply withdrawing the 
 latter element from it. 
 
 EXPERIMENT 21. Place a bit of carefully dried 
 phosphorus, as big as a pea, upon a piece of flat 
 cork, and float it in a large earthen dish half full 
 of water. Kindle the phosphorus, and then cover 
 it with a capacious glass jar or bell-glass, whichever 
 happens to be most convenient (Fig. 16). In burn- 
 ing, the phosphorus is of course only uniting with 
 the oxygen of the air ; and white clouds of a solid 
 oxide of phosphorus are formed. These dissolve 
 in the water of the dish, and at last the gas remain- 
 ing in the jar will be approximately pure nitrogen. 
 This may be allowed to stand for further examina- 
 tion. In order to protect the cork from burning 
 with the phosphorus, the latter may rest directly 
 upon a layer of either plaster-of-paris or lime, which 
 will serve as a non-conductor of heat. 
 
INORGANIC CHEMISTRY. 
 
 Nitrogen may also be prepared by a sort of re- 
 versal of Experiment 20. In that experiment, cop- 
 per oxide was heated in 
 a stream of hydrogen ; 
 water being formed, 
 and metallic copper re- 
 maining behind. Now, 
 by heating the copper 
 to redness and pass- 
 ing over it a slow but 
 steady current of air, 
 copper oxide will be 
 
 FIG. i6.-Prqparatiohof Nitrogen, reproduced, and only 
 
 nitrogen will issue from 
 
 the farther end of the tube. There, by means of a 
 delivery-tube, made to dip under water, it may be 
 collected in jars and further investigated. There 
 are several other processes for the preparation of 
 nitrogen, but they need no description here.* 
 
 In the free state nitrogen is one of the least inter- 
 esting of the elements. It is a colorless gas, four- 
 teen times heavier than hydrogen, and having nei- 
 ther taste nor odor. It is incapable of supporting 
 either life or combustion : a lighted candle plunged 
 in it is extinguished ; an animal immersed in it 
 immediately dies. Its occurrence in the air, how- 
 ever, shows that it is not poisonous ; it kills, not 
 by any deleterious action, but simply because it 
 lacks the power of keeping up the vital processes ; 
 when it fills the lungs, the necessary oxygen is ex- 
 cluded. 
 
 Nitrogen combines directly with only a very few 
 
 * In short courses of study the experimental preparation of nitrogen 
 may be omitted altogether. 
 
NITROGEN AND THE ATMOSPHERE. 51 
 
 of the other elements, such as boron, silicon, and the 
 rare metals titanium and tungsten. Its important 
 compounds with oxygen, hydrogen, and so on, are 
 all formed by indirect processes, and, as a general 
 rule, are very easily decomposed. Nearly all of 
 the explosive substances practically in use are com- 
 pounds of nitrogen, and their explosiveness is a 
 consequence of this ready decomposibility. Gun- 
 powder, gun-cotton, nitroglycerine, dynamite, and 
 fulminating powder, are all cases in point. 
 
 The composition of air, which may be approxi- 
 mately put at one fifth oxygen with four fifths nitro- 
 gen, is more precisely given in the following per- 
 centages : 
 
 
 By weight. 
 
 By volume. 
 
 Oxvsrcn . 
 
 2^.0 
 
 20.8 
 
 Nitrogen 
 
 77.O 
 
 70-2 
 
 
 
 
 
 100.0 
 
 1 00.0 
 
 In a rough way the composition by volume may 
 be verified in a class-experiment, as follows : 
 
 EXPERIMENT 22. Invert a large test-tube, or, 
 better, a graduated tube closed at one end, in a 
 dish containing mercury (Fig. 17). Now melt under 
 warm water a little phosphorus, and take up a drop 
 of it upon the end of a stout wire. When it solidi- 
 fies, pass the small pellet thus formed under the sur- 
 face of the mercury and up into the tube. Leave it 
 in position for several hours, or longer if need be. 
 The phosphorus will slowly oxidize, and the mer- 
 cury will gradually rise in the tube until but four 
 fifths of the original air remains. A lighted match 
 
52 INORGANIC CHEMISTRY. 
 
 plunged into this remaining gas will be extinguished, 
 showing it to be nitrogen. 
 
 FIG. 17. Analysis of Air. 
 
 Air is only a mixture not a chemical compound. 
 This will appear more clearly after we study the 
 true oxides of nitrogen in the next chapter. Still, 
 
NITROGEN AND THE ATMOSPHERE. 
 
 53 
 
 some considerations bearing upon this point may 
 well be offered here. If we artificially mix oxygen 
 and nitrogen gases in the proper proportions, the 
 mixture will have all the characteristic properties 
 of air, and yet none of the usual phenomena which 
 attend chemical union will be manifest. Further- 
 more, although air is practically constant in its 
 composition, whether taken from the tops of mount- 
 ains or the depths of valleys, from near the Equator 
 or in the Arctic zone, it does exhibit slight varia- 
 tions which can be detected by refined analyses. 
 Some remarkable experiments by Professor Morley 
 illustrate this fact. It has been supposed by some 
 meteorologists that the sudden periods of severe 
 weather popularly known as " cold snaps " are due 
 to the vertical descent of intensely cold air from 
 very great elevations. Now, oxygen is heavier than 
 nitrogen in the ratio of sixteen to fourteen, and is 
 consequently more powerfully affected by gravita- 
 tion. There is, therefore, in spite of the ease with 
 which gases diffuse into each other, becoming more 
 and more perfectly mixed, a slight tendency to a 
 concentration of the heavier oxygen near the earth's 
 surface, and a corresponding excess of nitrogen at 
 very great heights above. If, now, a " cold snap " 
 is caused by a sudden descent of air from an exceed- 
 ingly high level, the air during it should be slightly 
 poorer in oxygen than at other times. This, by a 
 long series of daily analyses of air, Professor Mor- 
 ley finds to be the fact ; although the differences are 
 so small as to be comparatively unimportant. 
 
 In speaking of air we always mean the gaseous 
 mixture above described, which is 14.43 times as 
 heavy as hydrogen. In the atmosphere around us, 
 
54 INORGANIC CHEMISTRY. 
 
 however, several other substances occur, but in 
 widely varying proportions. First, the vapor of 
 water is always present, and plays an important 
 part in determining the character of a climate. 
 Secondly, carbon dioxide is invariably to be found, 
 in quantities ranging from three to seven volumes 
 in ten thousand volumes of air. The average 
 amount in the open country is about four volumes ; 
 at sea the proportion is less, and near large towns 
 it is greater. Any quantity over seven volumes 
 is decidedly injurious to health. Small as these 
 proportions are, the total quantity of carbon dioxide 
 in the atmosphere is enormous ; and, as we shall 
 see when we come to study carbon, its influence in 
 connection with the growth of plants is extremely 
 important. Thirdly, ammonia in minute traces is a 
 regular constituent of the atmosphere. This, fre- 
 quently combined with nitric acid, is brought down 
 to the earth by snow and rain, and serves to supply 
 plants with a considerable part of their nitrogen. 
 All of these ingredients of the atmosphere, and 
 probably also ozone, are essential, and necessary in 
 the economy of nature. With them various acci- 
 dental impurities are frequently found, products of 
 putrefaction, of combustion, and so on. 
 
CHAPTER VII. 
 
 AMMONIA AND THE OXIDES OF NITROGEN. 
 
 THE compounds formed by the union of nitro- 
 gen with hydrogen and oxygen are extremely im- 
 portant and interesting, both from a practical and 
 from a theoretical point of view. 
 
 With hydrogen alone, nitrogen combines in only 
 a single proportion ; the compound being the well- 
 known substance, ammonia. We have already seen 
 that this body occurs in minute quantities in the 
 atmosphere ; it is also found in rain and river wa- 
 ters, and in all fertile soils. It is continually pro- 
 duced in nature by the decomposition of animal 
 matter, and it may be prepared artificially by dis- 
 tilling refuse scraps of horn, hoofs, bones, or hair. 
 In the manufacture of illuminating-gas it is devel- 
 oped from the nitrogen contained in the coal, and it 
 is retained by the water through which the gas is 
 passed on its way to the gas-holders. The ammo- 
 niacal solution thus obtained is now the chief com- 
 mercial source of ammonia. It is first mixed with 
 sulphuric acid, forming a substance known as am- 
 monium sulphate, which is used to some extent 
 as a fertilizer. This compound, heated with lime, 
 evolves ammonia copiously. 
 
 EXPERIMENT 23. Rub together in a mortar a 
 
56 INORGANIC CHEMISTRY. 
 
 fragment of " sal ammoniac " (ammonium chloride), 
 a bit of lime, and a few drops of water. Ammonia 
 will be set free and may be recognized by its smell. 
 All compounds of ammonia behave in the same 
 way ; so that trituration with lime affords a ready 
 means of testing for the substance. 
 
 EXPERIMENT 24. Pulverize two parts by weight 
 of ammonium chloride and one part of quicklime. 
 Mix, and transfer the mixture to a stout glass flask 
 provided with a delivery-tube (Fig. 18). Upon 
 heating, ammonia will be freely given off, and it 
 
 FIG. 18. Preparation of Ammonia. 
 
 can be collected in test-tubes or small bottles in- 
 verted over mercury. The usual pneumatic trough 
 or water-pan can not be used in this case, because 
 of the solubility of ammonia in water. 
 
 Ammonia, thus prepared, is a colorless gas of a 
 peculiar, characteristic, very pungent odor. Under 
 ordinary circumstances it is neither combustible nor 
 
AMMONIA AND THE OXIDES OF NITROGEN. 57 
 
 a supporter of combustion ; but, mixed with a large 
 quantity of oxygen, it may be made to burn with a 
 yellow flame. By weight it is composed of four- 
 teen parts of nitrogen united with three of hydro- 
 gen ; or, by bulk, one volume of the former gas to 
 three of the latter. These four volumes condense 
 to two in the compound, the ammonia formed being 
 eight and one half times heavier than hydrogen. 
 These figures carry weighty significance, which will 
 appear in the next chapter. 
 
 Ammonia is extremely soluble in water, particu- 
 larly when the latter is cold. At the temperature 
 of o Q, one cubic centimetre of water will absorb 
 1,148 c. c. of the gas ; while at 15 only 783 c. c. will 
 be taken up. This solubility may be illustrated by 
 introducing a few drops of water into one of the 
 tubes filled with ammonia during Experiment 24, 
 and left in position over mercury. The water will 
 absorb the gas almost instantaneously, and the mer- 
 cury will suddenly rise to take its place in the tube. 
 
 The aqueous solution of ammonia is the common 
 aqua ammonia, ammonia-water, or spirits of harts- 
 horn of the shops. The last name reminds us that 
 ammonia was at one time prepared from the horns 
 of deer. Ammonia-water is used to some extent in 
 medicine, and has many important applications in 
 chemical manufactures. It varies much in strength, 
 but it always has the characteristic odor of the 
 gas, and is strongly alkaline. It. is also caustic; 
 and, when strong, readily blisters the skin. When 
 boiled, it gives off its gaseous ammonia. The latter, 
 by cold and great pressure, is easily condensed to a 
 colorless liquid, which, when the pressure is re- 
 leased, rapidly evaporates, producing intense cold. 
 
58 INORGANIC CHEMISTRY. 
 
 This fact is applied in Carre's machine for making 
 artificial ice.* All ice-machines depend upon the 
 principle that a liquid, in evaporating, absorbs heat 
 from surrounding objects. Liquefied gases evapo- 
 rate suddenly, and therefore absorb heat suddenly. 
 
 With oxygen, nitrogen unites in five different 
 proportions ; and two of its oxides combine further 
 with water to form two well-known acids. Since 
 nitric acid is the most convenient starting-point for 
 the preparation of all these other compounds, it 
 may properly be the next substance to engage our 
 attention. 
 
 EXPERIMENT 25. Arrange a retort and receiver 
 as in Fig. 15. Put a weighed quantity of saltpeter 
 (potassium nitrate) in the retort, pour over it an 
 equal weight of strong sulphuric acid, and heat. 
 Nitric acid will distil over ; and at last a white solid, 
 'potassium hydrogen sulphate, will remain behind. 
 
 In the commercial manufacture of nitric acid 
 sodium nitrate is used instead of saltpeter, being 
 cheaper. But any nitrate, distilled with sulphuric 
 acid, will yield nitric acid in the same way. - Ni- 
 trates are simply the compounds formed by nitric 
 acid with the various metals and bases, and all have 
 names similar to those mentioned above. Sulphu- 
 ric acid is stronger than nitric acid, and displaces 
 it from its compounds, forming sulphates instead. 
 Such names as silver nitrate, lead nitrate, copper 
 sulphate, and zinc sulphate, are good examples of 
 this kind of nomenclature. Similarly, carbonic acid 
 forms carbonates ; boric acid, borates ; phosphoric 
 acid, phosphates ; acetic acid, acetates, and so on. 
 
 * See " Roscoe and Schorlemmer's Chemistry," vol. i, p. 3^3 I or 
 " Deschanel's Physics," pp. 329-330. 
 
AMMONIA AND THE OXIDES OF NITROGEN. 59 
 
 Nitric acid, when pure, is a colorless liquid of 
 specific gravity 1.52. Commonly it is somewhat 
 yellow, from the presence, as an impurity, of one 
 of the oxides of nitrogen. It has a suffocating odor, 
 an intensely sour taste, and is exceedingly corrosive. 
 It attacks all ordinary metals except gold and plat- 
 inum ; and, indeed, dissolves most of them. Hence 
 the early chemists gave it the name of aquafortis, or 
 " strong water." Applied to the skin, it produces 
 yellow stains, which wear off only after several 
 days ; and, if strong, it causes corrosion as painful 
 as a burn. Physicians use it somewhat as a caustic ; 
 it is employed in etching copper plates for engrav- 
 ings; and it has important applications in refining 
 the precious metals, in making nitroglycerine, gun- 
 cotton, the aniline dyes, and so on. The following 
 experiments with nitric acid will be found instruc- 
 tive: 
 
 EXPERIMENT 26. Cover a piece of bright sheet 
 copper with a thin coating of wax. Scratch a de- 
 sign through the wax with a sharp needle. Now 
 pour over the sheet a little nitric acid, previously 
 diluted with an equal bulk of water, and after a few 
 minutes wash it off again. Upon cleaning off the 
 wax the design will be found to be etched into the 
 copper. 
 
 EXPERIMENT 27. Cover a bit of lead in a glass 
 or porcelain dish with nitric acid diluted as before. 
 Reddish fumes will be given off, and the metal will 
 dissolve. If the solution be allowed to stand for a 
 while, or if it be boiled down somewhat, it will de- 
 posit white crystals of lead nitrate.* These can be 
 
 * This experiment may be varied by using other metals than lead 
 and getting other nitrates. Any common metal will do, except tin or 
 
60 INORGANIC CHEMISTRY. 
 
 used, if time permits, in a repetition of Experiment 
 25 for the preparation of nitric acid. 
 
 EXPERIMENT 28. Pour dilute nitric acid over a 
 few clippings of quill, bits of white feather, or fibres 
 of white silk. They will be stained permanently 
 yellow. 
 
 EXPERIMENT 29. Put a fragment of any nitrate 
 into a test-tube, and dissolve it in the smallest pos- 
 sible quantity of water. Add to the solution, cau- 
 tiously, an equal bulk of strong sulphuric acid, and 
 allow the mixture, which has become hot, to cool. 
 In another test-tube dissolve with water a crystal of 
 sulphate of iron. Pour this solution, very slowly, 
 into the first test-tube, holding the latter slantwise, 
 so that the two fluids will form two separate layers, 
 without mixing. At the boundary between these 
 layers a brown ring will appear. This is the test 
 by means of which nitric acid and nitrates are ordi- 
 narily detected. 
 
 In speaking of ammonia it was described as be- 
 ing strongly alkaline. Inasmuch as the terms acid 
 and alkaline will be frequently used in this book, the 
 distinction between them may well be illustrated 
 here. 
 
 EXPERIMENT 30. Into one test-tube of water 
 pour a few drops of nitric acid, and into another a 
 little ammonia. Into the one containing the acid 
 dip a slip of blue litmus-paper.* It will become 
 red ; and if it be now inserted into the ammonia the 
 
 antimony. These, instead of dissolving, are converted into white, in- 
 soluble oxides. 
 
 * Litmus is a coloring matter obtained from certain lichens. The 
 juice of the common red cabbage may be used as a substitute for it ; 
 being turned green by alkalies and regaining its tint with acids. 
 
AMMONIA AND THE OXIDES OF NITROGEN. 6 1 
 
 blue color will be restored. Blue litmus, then, is 
 reddened by an acid, and reddened litmus is turned 
 blue by an alkali. An alkali is in its chemical prop- 
 erties the opposite of an acid ; and in litmus-paper 
 we have a convenient means of recognizing either 
 class of substances. 
 
 Any substance which unites with an acid is 
 termed a base. The compounds formed are known 
 as salts, and, in general, have no effect upon litmus- 
 paper. Strictly speaking, the alkalies are simply 
 the stronger soluble bases, of which soda, potash, 
 and ammonia* are the best examples. Lime is also 
 strongly alkaline.* 
 
 EXPERIMENT 31. Put a slip of litmus-paper in a 
 porcelain or glass dish containing ammonia, and add 
 nitric acid cautiously, stirring meanwhile, until the 
 paper is just faintly reddened. Now add a drop 
 of ammonia, then a drop of acid, and so on, until 
 the acid and alkali exactly neutralize one another. 
 Evaporate the liquid, and white crystals will form 
 which are neither acid nor alkaline. They consti- 
 tute a salt, ammonium nitrate, which may be re- 
 served for use in a future experiment. 
 
 The other nitrogen acid previously referred to 
 is unimportant. It contains less oxygen than nitric 
 acid, and is named nitrous acid. The terminations 
 ous and ic are used in chemical nomenclature to in- 
 dicate lower and higher degrees of combination 
 respectively. The salts of nitrous acid are called 
 nitrites. So, also, we have sulphurous and sulphu- 
 ric acids, the one forming sulphites and the other 
 
 * The true significance of the terms acid, alkali, base, and salt will 
 be developed in subsequent chapters. Exhaustive definitions would be 
 inappropriate here. 
 
62 INORGANIC CHEMISTRY. 
 
 sulphates. The names of salts derived from ous 
 acids end in ite, those from ic acids in ate. 
 
 One of the fundamental principles of chemistry 
 is the law of definite proportions. This law asserts 
 that any given chemical compound always contains pre- 
 cisely the same elements in exactly the same proportions. 
 No variation is possible. When, however, two ele- 
 ments unite to form more than one distinct com- 
 pound, the law of multiple proportions comes into 
 play. This law is best illustrated by the five oxides 
 of nitrogen, which are composed by volume as fol- 
 lows : 
 
 Nitrogen monoxide contains 2 vols. nitrogen with I vol. oxygen, 
 
 dioxide " " " " " 2 " 
 
 trioxide " " " " " 3 " 
 
 tetroxide " " " " " 4 " 
 
 pentoxide " " " " " 5 " 
 
 We find a similar regularity in their composition 
 by weight : 
 
 Nitrogen monoxide contains 28 parts of nitrogen to 16 of oxygen. 
 
 dioxide " " " " " 32 " 
 
 trioxide " " " " " 48 " 
 
 tetroxide " " " " " 64 " 
 
 " pentoxide " " " " " 80 " " 
 
 In both tables, nitrogen being constant, we see that 
 the oxygen varies in a simple multiple ratio. Hence 
 the law, of which many other examples could be 
 cited, that when two elements unite to form several 
 compounds, the higher proportions of each are even mul- 
 tiples of the lowest. 
 
 Two of these oxides, the third and the fifth, are 
 unimportant. The fifth is a white, crystalline, ex- 
 plosive body, which reacts with water so as to form 
 
AMMONIA AND THE OXIDES OF NITROGEN. 63 
 
 nitric acid. From the third, nitrous acid is simi- 
 larly derived. These two compounds need no fur- 
 ther notice here. The others are more important. 
 
 Nitrogen monoxide, commonly known as ni- 
 trous oxide, is a colorless, odorless, slightly sweetish 
 gas, twenty-two times heavier than hydrogen. By 
 great cold and pressure it can be liquefied, and 
 even frozen solid. The only available mode of prep- 
 aration is as follows : 
 
 EXPERIMENT 32. Arrange a test-tube and deliv- 
 ery-tube precisely as for the preparation of oxygen. 
 Fill the test-tube half full of dry ammonium nitrate 
 (see Experiment 31), and heat very gradually. The 
 ammonium nitrate will first melt, and then undergo 
 decomposition; the products of the latter change 
 being nitrogen monoxide and water. The nitrous 
 oxide can be collected in a gas-bag, or in bottles 
 over the water-pan. If the heating be conducted 
 too rapidly, the gas will be likely to contain delete- 
 rious impurities. 
 
 Although nitrous oxide is not really capable of 
 sustaining life, it may be breathed to a limited ex- 
 tent without danger. For this purpose, however, 
 it should be quite pure ; a condition best to be se- 
 cured by using only materials of good quality, evolv- 
 ing the gas very slowly, and washing it by causing 
 it to bubble through several bottles of water be- 
 fore it reaches the gas-bag. When inhaled in small 
 quantities, nitrous oxide produces a peculiar exhila- 
 ration, because of which it has received the popu- 
 lar name of " laughing gas." Prolonged inhalation 
 leads to unconsciousness, with complete insensi- 
 bility to pain. Hence its use by dentists as an an- 
 aesthetic. 
 
64 INORGANIC CHEMISTRY. 
 
 In nitrous oxide the elements are feebly united. 
 Strong heating, therefore, will decompose it, setting 
 oxygen free. By virtue of this fact it is capable 
 of supporting combustion. Immerse a splinter of 
 ignited charcoal in the gas, and it will burn almost 
 as brilliantly as in pure oxygen. The red-hot coal 
 first decomposes a little of the gas; the oxygen 
 thus liberated takes part in the combustion, devel- 
 oping more heat ; this leads to further decomposi- 
 tion, more oxygen becomes free, and so on to the 
 end of the reaction. To verify this point, repeat 
 Experiments 12, 13, and 15, using nitrogen monox- 
 ide instead of oxygen.. 
 
 Nitrogen dioxide, sometimes called nitric oxide, 
 is another colorless gas only fifteen times heavier 
 than hydrogen. Its odor is extremely suffocating, 
 and it supports combustion only in one or two ex- 
 ceptional instances. It is prepared thus : 
 
 EXPERIMENT 33. Put some copper scraps or 
 turnings in the flask previously used for generating 
 hydrogen, and cover them with a half-and-half mix- 
 ture of nitric acid and water. Connect the delivery- 
 tube with a glass jar full of water, and inverted in 
 the usual way over the water-pan. At first, heavy 
 brownish-red vapors will be evolved, but after a 
 few moments they will disappear, and the jar will 
 fill with colorless nitric oxide. 
 
 The most interesting property of this gas is its 
 power of absorbing oxygen. Lift the jar just filled 
 with it so as to admit the air, and it will change to 
 the deep-red suffocating gas which was noticed at 
 the beginning of the experiment. This colored gas 
 is nitrogen tetroxide, or hyponitric acid, and we 
 shall frequently encounter it in our experiments. 
 
AMMONIA AND THE OXIDES OF NITROGEN. 65 
 
 It appears whenever metals are dissolved or oxi- 
 dized by nitric acid. 
 
 In these experiments we have seen how inti- 
 mately the oxides of nitrogen are connected, and 
 also that all are derived either from nitric acid or 
 nitrates. We may now go a step further and obtain 
 even the strong base ammonia as a derivative of 
 nitric acid, as follows : 
 
 EXPERIMENT 34. Add some zinc filings to a 
 strong solution of caustic potash, and heat the mix- 
 ture in a flask, gently. Now put in a little nitric 
 acid, but not so much as to neutralize the alkali. 
 Ammonia will be given off, and it may be recog- 
 nized by its smell. In this experiment hydrogen is 
 produced by the action of the zinc upon the alkali ; 
 and this, at the instant of its liberation, so reacts 
 upon the nitric acid as to transform it into ammonia 
 and water. 
 
CHAPTER VIII. 
 
 ATOMIC WEIGHTS AND CHEMICAL FORMULA. 
 
 IN the foregoing chapters we have studied a 
 number of compounds, involving the consideration 
 of only three elements, hydrogen, oxygen, and nitro- 
 gen. If, now, we scrutinize their composition a lit- 
 tle more closely, some remarkable relations may be 
 brought out. 
 
 To 'facilitate study, let us begin by adopting a 
 set of abbreviations or symbols, by which the va- 
 rious elements may be concisely indicated. Such 
 symbols are a necessity to the chemist, and to each 
 element one is definitely assigned. Thus, H repre- 
 sents hydrogen, O oxygen, N nitrogen, and C car- 
 bon. Since several elements may have names be- 
 ginning with the same initial letter, double letters 
 are frequently employed, as follows : 
 
 C represents carbon, 
 
 Cd " cadmium, 
 
 Ca " calcium, 
 
 Cs " caesium, 
 
 Ce " cerium, 
 
 Cl " chlorine, 
 
 Cr " chromium, 
 
 Co " cobalt, 
 
 Cb " columbium, 
 
 Cu " copper. 
 
ATOMIC WEIGHTS, CHEMICAL FORMULA. 67 
 
 The last of these is derived from the Latin cu- 
 prum. So also we have Fe, from ferrum, for iron ; 
 Ag, from argentum, for silver ; Au, from aurum, for 
 gold ; Sn, from stannum, for tin ; and so on in sev- 
 eral other cases. These symbols should all be 
 learned by actual use, rather than by mere memor- 
 izing.* 
 
 Now, using these symbols, let us tabulate the 
 compounds thus far examined ; giving the compo- 
 sition of each both by volume and by weight : 
 
 By volume. 
 
 By weight. 
 
 Water. 
 
 2 vols. H, i vol. O. 2 parts H, 16 parts O. 
 
 
 Hydrogen dioxide. 
 
 2 
 
 H, 2 
 
 0. 2 
 
 H, 3 2 
 
 O. 
 
 
 Ammonia. 
 
 3 
 
 H, i 
 
 N. 3 
 
 H, 14 
 
 N. 
 
 
 Nitrogen monoxide. 
 
 2 
 
 N, i 
 
 0. 28 
 
 N, 16 
 
 0. 
 
 
 " dioxide. 
 
 2 
 
 N, 2 
 
 O. 28 
 
 N, 32 
 
 0. 
 
 
 " trioxide. 
 
 2 
 
 N, 3 
 
 O. 28 
 
 N, 48 
 
 O. 
 
 
 " tetroxide. 
 
 2 
 
 N |4 
 
 0. 28 
 
 N, 64 
 
 0. 
 
 
 " pentoxide. 
 
 2 
 
 N, 5 
 
 O. 28 
 
 N, 80 
 
 0. 
 
 
 Nitrous acid, i vol. H, 
 
 I 
 
 N, 2 
 
 0. i 
 
 H, 14 
 
 N, 
 
 32 parts O. 
 
 Nitric acid, i " H, 
 
 I 
 
 N, 3 
 
 0. i 
 
 H, 14 
 
 N, 
 
 48 " 0. 
 
 These numbers are very suggestive, especially 
 when we consider them in the light of the law of 
 multiple proportions. Hydrogen is represented by 
 i, 2, and 3 volumes, or i, 2, and 3 parts by weight. 
 Oxygen we find in the proportion of i, 2, 3, 4, and 
 5 volumes, or 16, 32, 48, 64, and 80 parts by weight. 
 Nitrogen occurs in i and 2 volumes, or 14 and 28 
 parts by weight. In brief, as far as our experience 
 goes, if we take hydrogen as our standard of com- 
 parison and put its combining value at unity, oxygen 
 always combines in the proportion of 16 parts by 
 weight or some even multiple thereof, and nitrogen 
 in the ratio of 14 parts or a multiple. Furthermore, 
 
 * See table of elements in Chapter II. 
 
68 INORGANIC CHEMISTRY. 
 
 these numbers, 14 and 16, which we may now call 
 the combining weights of nitrogen and oxygen, also 
 represent the specific gravity of these gases, referred 
 to hydrogen as unity. 
 
 As we extend our observations to the other 
 chemical elements, we shall find similar relations 
 holding good everywhere. For each element a 
 definite combining weight can be found, which will 
 apply in all the compounds into which the element 
 can enter. For example : 
 
 i part H unites with 35.5 parts Cl. 
 i " H " " 80 " Br. 
 i " H " " 127 " I. 
 
 These values, 35.5, 80, and 127, are the combining 
 weights of chlorine, bromine, and iodine respect- 
 ively ; and they also represent the specific gravity 
 of each element in the gaseous state compared as 
 before with hydrogen as unity. 
 
 But many of the elements do not combine di- 
 rectly with hydrogen, and therefore their combin- 
 ing weights need to be determined indirectly. This 
 is easily done through the medium of some other 
 element ; thus : 
 
 35.5 parts Cl unite with 23 of Na, 39 of K, or 108 of Ag. 
 
 80.0 " Br " " 23 " Na, 39 " K, " 108 " Ag. 
 
 127.0 " I " " 23 " Na, 39 " K, " 1 08 " Ag. 
 
 Hence 23 may be taken as the combining weight 
 of sodium, 39 of potassium, and 108 of silver; and 
 if we go further and examine the compounds of 
 these metals with oxygen, nitric acid, etc., we shall 
 find that the values here assigned are in perfect har- 
 mony with those previously found for hydrogen, 
 
ATOMIC WEIGHTS, CHEMICAL FORMULA. 69 
 
 oxygen, and nitrogen. The practical importance of 
 such numbers will appear as in subsequent chapters 
 we become familiar with their use.* 
 
 Now, what do these simple relations mean? 
 Why do we never find oxygen uniting in fifteen or 
 seventeen parts, but always in proportions repre- 
 sented by multiples of sixteen ? The answer to this 
 question was discovered by Dr. John Dalton, of 
 Manchester, England, who put forth in 1808 the 
 atomic theory which lies at the foundations of mod- 
 ern chemistry. If matter is, as we have already 
 supposed, made up of minute, indivisible atoms, it 
 is plain that in chemical union only whole atoms and 
 multiples of whole atoms can take part. Fractions 
 of atoms are impossible. If, then, hydrogen and 
 oxygen unite chemically, they must do so in pro- 
 portions representing either the relative weights of 
 their atoms, or simple multiples thereof, and similar 
 rules must govern the combination of all the ele- 
 ments. We assume, therefore, that the combining 
 weights really represent the relative weights of the 
 different atoms, compared with hydrogen as unity. 
 That is, an atom of oxygen weighs sixteen times as 
 much as an atom of hydrogen, an atom of nitrogen 
 fourteen times as much, an atom of silver one hun- 
 dred and eight times as much, and so on. These 
 values are called the atomic weights of the elements, 
 and a full table of them is given in Chapter II. As 
 to the real weights of the atoms we have no defi- 
 nite knowledge ; but concerning these comparative 
 weights we are quite certain. As we continue our 
 
 * The history of the discovery of the combining weights is admira- 
 bly given in the earlier chapters of Wurtz's "Atomic Theory" (" In- 
 ternational Scientific Series," vol. xxix). 
 
70 INORGANIC CHEMISTRY. 
 
 studies we shall find other lines of evidence confirm- 
 ing our present conclusions very strongly. 
 
 With the aid of the elementary symbols and 
 atomic weights we are now ready to approach the 
 subject of chemical formulas. First, let us render 
 our symbols a little more precise. Let H, for ex- 
 ample, represent not only hydrogen in general, but 
 exactly one unit weight of hydrogen, or one unit 
 volume, or, more definitely still, one atom. Let O, 
 N, C, etc., similarly stand for one atom of each ele- 
 ment respectively, and for 16, 14, 12, etc., parts by 
 weight, as the case may be. Furthermore, let us 
 express several atoms of an element by numerals 
 added to its symbol ; as, for example, H, H 2 , H 3 , H 4 , 
 etc., for one two, three, or four atoms of hydrogen. 
 Water, as we have already seen, contains two 
 unit weights, or two volumes of hydrogen, com- 
 bined with sixteen unit weights or one volume of 
 oxygen. Its formula, accordingly, is written H 2 O ; 
 the symbols being placed side by side to indicate 
 chemical union. Hydrogen dioxide, on like princi- 
 ples, becomes H 2 O 2 , and the nitrogen compounds are 
 easily formulated as follows : 
 
 Ammonia, NH 3 . 
 
 Nitrogen monoxide, N 2 O. 
 " dioxide, N 2 O 2 * 
 " trioxide, N 2 O 3 . 
 
 tetroxide, N 2 O 4 .* 
 " pentoxide, N 2 O 8 . 
 
 Nitrous acid, HNO 2 . 
 
 Nitric " HNO 3 . 
 
 These formulae almost explain themselves. For 
 example, let us consider the last one, because it is 
 
 * These two formulae should be halved, becoming NO and NO a 
 respectively, for reasons which will be presented further on. 
 
ATOMIC WEIGHTS, CHEMICAL FORMULA, fi 
 
 the most complicated. It shows, first, that nitric 
 acid contains one atom of hydrogen, one of nitro- 
 gen, and three of oxygen combined together ; and 
 next, that the gases are united by volume in the 
 same ratio of i : i : 3. By weight it indicates one 
 part of the first element, fourteen of the second, and 
 three times sixteen of the third. Finally, just as H 
 represents one atom of hydrogen, so HNO 3 stands 
 for one molecule of nitric acid, and the sum of the 
 atomic weights i -f- 14 + 4-8, or 63, is called the molecu- 
 lar weight of the compound. If we wish to indicate 
 two or more molecules of nitric acid, we may write 
 either 2HNO 3 , or (HNO 3 ) 2 ; but the former method 
 is customary. 
 
 All such formulas as these are capable of being 
 treated in a somewhat mathematical way, so that 
 chemical reactions may be written out in the form 
 of equations. On one side of an equation we write 
 the formulas of the substances with which our re- 
 action begins, and on the other the formulas of the 
 substances produced by the change. Thus, in mak- 
 ing oxygen we heat potassium chlorate, KC1O 3 , get- 
 ting potassium chloride and the gas sought for. 
 The equation is simple : 
 
 KC10, = KC1 + 3 . 
 
 Again, ammonium nitrate, N 2 H 5 O 3 , splits up, on 
 heating, into nitrogen monoxide and water, as fol- 
 lows : 
 
 N 3 H 6 O 3 = N 2 O + 2H 2 O. 
 
 Hydrogen is commonly prepared by the action of sul- 
 phuric acid, H 2 SO 4 , upon zinc ; zinc sulphate, ZnSO 4 , 
 being also formed. This reaction we may write : 
 
 Zn + H 2 SO 4 = H 2 + ZnSO 4 . 
 
72 INORGANIC CHEMISTRY. 
 
 It will be noticed that the plus sign, -)-, is used to 
 indicate addition, or mixture, as distinct from chemi- 
 cal union. The minus sign is sometimes used also, 
 to represent the withdrawal of certain elements 
 from a compound. 
 
 This class of chemical equations has very great 
 practical utility, inasmuch as they enable us to cal- 
 culate the results of reactions in advance. Suppose, 
 for instance, we wish to prepare a definite quantity 
 say one pound or one kilogramme of nitric acid 
 and desire to know just how much material to 
 use in order to avoid wasting. The reaction is as 
 
 follows : 
 
 KNO 3 + H 2 SO 4 = KHSO 4 + HNO 3 . 
 
 That is, one molecule of potassium nitrate and one 
 molecule of sulphuric acid yield one molecule of 
 potassium hydrogen sulphate and one molecule of 
 nitric acid. Now the molecular weight of KNO 3 is 
 39 + 14 + 48 = 101 ; that of H 2 SO 4 is 2 + 32 + 64 
 98 ; and that of HNO 3 is i + 14 + 48 == 63. Hence, 
 1 01 parts of KNO 3 , treated with 98 of H 2 SO 4 , will 
 give 63 parts of HNO 3 . For " parts " now read 
 " pounds," " ounces," " grammes," or " kilogrammes," 
 as the case may be, and the problem resolves itself 
 into an easy question in arithmetic. 
 
 Again, let us consider the preparation of oxy- 
 gen, for which the equation has recently been given. 
 The molecular weight of KC1O 3 is 39 -j- 35.5 + 48 = 
 122.5. Hence, 122.5 parts of KC1O 3 yield 48 parts 
 of oxygen. Suppose now we wish to make exactly 
 fifty litres of oxygen, measured at o and 760 mm. 
 In Chapter III we found the weight of one litre of 
 hydrogen, or one crith, to be 0.0896 gramme. A 
 litre of oxygen weighs 16 criths, and therefore fifty 
 
ATOMIC WEIGHTS, CHEMICAL FORMULAE. 73 
 
 litres must weigh 71.68 grammes. Hence, by a sim- 
 ple proportion 
 
 48 : 122.5 :: 71.68 : x, or, 
 O 3 : KC1O 3 :: 71.68 : x, 
 
 in which x represents the weight of potassium 
 chlorate needed to prepare the quantity of oxygen 
 sought for. If our oxygen is to be measured at a 
 temperature and pressure other than o and 760 
 mm. say at 21 and 755 mm. we must correct the 
 weight of our fifty litres by the aid of the formulae 
 given in Chapter III. Fifty litres of gas, at o and 
 760 mm., will become at 21 and 755 mm. : 
 
 50 x 760 x 294 
 
 This quantity, 54.2027 litres, weighs the same as be- 
 fore namely, 71.68 grammes, and fifty litres of the 
 expanded gas will weigh 
 
 54.2027 : 50 :: 71.68 : x, 
 
 x being the corrected weight of the volume of oxy- 
 gen desired. 
 
 The department of chemistry which deals with 
 these calculations is called stoichiometry. Many other 
 stoichiometrical problems will be taken up from time 
 to time as we proceed.* 
 
 * For a good outline of the principles of stoichiometry, see Chapter 
 VI of Cooke's " Chemical Philosophy," new edition, 1881. 
 
CHAPTER IX. 
 
 CARBON. 
 
 CARBON, one of the most common and most in- 
 teresting of the elements, is found in nature both 
 free and in a vast number of compounds. It is an 
 important constituent of limestone and many min- 
 erals ; it forms great beds of coal ; it is the element 
 chiefly characteristic of animal and vegetable mat- 
 ter. Chemistry is commonly divided into two great 
 branches injorganic and organic ; the former deal- 
 ing with substances formed in inanimate nature, the 
 latter with the products of organic life and their 
 derivatives. At present, organic chemistry is usu- 
 ally denned as " the chemistry of the carbon com- 
 pounds," and as such it might be fairly considered 
 here. For convenience, however, organic chemis- 
 try will be discussed separately later on ; and in 
 this chapter we may limit ourselves to carbon in 
 some of its inorganic aspects. 
 
 Carbon itself is one of the best examples of allo- 
 tropy, since it occurs in three distinct forms name- 
 ly, as diamond, as graphite, and as charcoal. In all 
 of its forms it is tasteless, odorless, infusible, non- 
 volatile, and insoluble. It is, however, combustible ; 
 readily so as charcoal, more difficultly in its other 
 modifications. But even the diamond burns in the 
 
CARBON. 
 
 75 
 
 oxyhydrogen-flame. The atomic weight of carbon 
 is 12. 
 
 The diamond is found in India, Borneo, South 
 Africa, and Brazil ; and occasionally in North Caro- 
 lina, Georgia, and California. It occurs in crystals, 
 more or less perfect, derived from the regular octa- 
 hedron (Fig. 19), and has in its purest state a spe- 
 cific gravity of 3.518. In color it ranges from a 
 pure limpidity well described in the phrase " a gem 
 
 FIG. 19. Crystals of Diamond. 
 
 of the -first water" through various shades of yellow, 
 blue, green, pink, etc., to black. Generally the col- 
 orless stones are most prized, the yellow diamonds 
 being of much less value. Occasionally a blue or 
 green diamond brings an enormous price, for these 
 tints are very rare. The black variety is called car- 
 bonado, and has a slightly lower specific gravity. 
 
 The diamond refracts light very strongly, and to 
 this property it owes its brilliancy as a gem. It is 
 the hardest of all known substances, and can be cut 
 and polished only with its own powder. Because 
 of its hardness it is used for cutting glass ; and the 
 coarser varieties, such as carbonado, serve to tip the 
 diamond-drills which are now employed in rock- 
 
76 INORGANIC CHEMISTRY. 
 
 boring machinery. In 1880 small diamonds were 
 produced artificially by Mr. J. B. Hannay, of Glas- 
 gow ; but the details of the process have only par- 
 tially been made public. 
 
 Graphite, also known as plumbago or black-lead, 
 is extensively mined in England, Ceylon, Siberia, 
 and California, and at Ticonderoga in New York. 
 There are many other localities in which it is found, 
 so that it may fairly be reckoned one of the com- 
 moner minerals. It occurs in some meteorites, and 
 it is frequently produced in the blast-furnace. In 
 the latter case it is dissolved by the molten iron, 
 and crystallizes out upon cooling. It differs from 
 the diamond in many particulars ; its color is black, 
 its specific gravity about 2.15, and it crystallizes in 
 six-sided plates. It is a good conductor of heat and 
 electricity, whereas the diamond conducts badly. 
 It may be more easily burned than diamond, less 
 easily than charcoal. In fine powder it has a greasy 
 feel, and is somewhat used as a lubricant for ma- 
 chinery. It is chiefly used in the manufacture of 
 lead-pencils, stove-polish, and crucibles, as a con- 
 ductor of electricity in the process of electrotyp- 
 ing, and as a glazing for the grains of gunpowder. 
 Gold and silver are usually melted in black-lead 
 crucibles. In the manufacture of coal-gas, a very 
 hard coating of gas-carbon is formed in the gas-re- 
 torts. This is commonly regarded as a variety of 
 graphite, and is used in the Bunsen galvanic bat- 
 tery, and for making the carbon-points of the elec- 
 tric light. 
 
 Amorphous (shapeless or non-crystalline) carbon 
 is always of organic origin. As charcoal it is pro- 
 duced by the imperfect combustion of wood, retain- 
 
CARBON. 77 
 
 ing the structure of the latter almost perfectly. A 
 purer charcoal may be prepared by heating pure 
 white sugar. Another variety, lamp-black, is made 
 by burning tar, rosin, turpentine, or petroleum, with 
 a deficient supply of air, and passing the smoke into 
 large chambers, in which the carbon is deposited. 
 It is simply soot prepared on a large scale, and it is 
 used as a black paint and for making printer's ink. 
 India ink is also made from lamp-black Animal 
 charcoal, as its name suggests, is produced by char- 
 ring animal matter in close iron cylinders, The 
 finest quality is made from blood, but bone-black, 
 containing with the carbon the earthy constituents 
 of bones, is more extensively prepared. 
 
 In all of its varieties amorphous carbon is black, 
 and easily combustible. Its specific gravity ranges 
 from 1.57 to 2.00; the variability resulting from the 
 fact that charcoal is always more or less porous. 
 This porosity confers upon charcoal an extraordi- 
 nary power of absorbing gases, to which property 
 its value as a disinfectant is due. For example, one 
 cubic centimetre of freshly-burned charcoal will ab- 
 sorb 17.9 cc. of oxygen, 67.7 cc. of carbonic acid, or 
 171.7 cc. of ammonia. Insert a bit of charcoal in a 
 tube of ammonia-gas filled over mercury, and an 
 immediate rise of the latter in the tube will indicate 
 the absorption. Suppose now that a quantity of 
 charcoal be brought into an atmosphere contami- 
 nated with the noxious gases resulting from a leaky 
 sewer or from animal decomposition. They will at 
 once be absorbed; and, coming into close contact with 
 oxygen which has been absorbed also, they will be 
 oxidized and rendered harmless. The vigor of this 
 action may be shown by the following experiment: 
 
78 INORGANIC CHEMISTRY. 
 
 EXPERIMENT 35. Heat a fragment of charcoal 
 to redness, so as to expel whatever gases it may con- 
 tain, and allow it to cool under mercury. Now 
 plunge it into a jar of sulphuretted hydrogen (Chap- 
 ter XV), and after a few moments transfer it to an- 
 other vessel containing oxygen. The two condensed 
 gases, meeting in the pores of the charcoal, will unite 
 with such intensity that the carbon will at once in- 
 flame. 
 
 The same principle may receive a number of 
 other less startling but more practical illustrations. 
 Rub a little powdered charcoal upon tainted meat, 
 and the unpleasant smell will disappear. Water 
 frequently has a fetid odor derived from organic 
 impurities ; this may be corrected by simply filter- 
 ing the water through a thick layer of charcoal. So, 
 also, by charring the lower end of a fence-post or 
 telegraph-post, it may be protected to a considerable 
 extent from rotting. 
 
 Charcoal also has a very remarkable power of 
 absorbing coloring - matters and many other sub- 
 stances. Animal charcoal is extensively used in 
 sugar-refineries for decolorizing raw brown sugar 
 and converting it into the finer white varieties. A 
 simple experiment will serve to illustrate this prop- 
 erty : 
 
 EXPERIMENT 36. Half fill a small bottle with 
 red wine, a solution of indigo, or a solution of cochi- 
 neal, and add an equal bulk of freshly-burned char- 
 coal-powder. Bone-black is better still if it can be 
 obtained. Shake vigorously, and filter ; the filtrate 
 will be colorless or nearly so. Beer or ale, similarly 
 treated, loses both its color and its bitterness. Even 
 a solution of quinine may be rendered nearly taste- 
 
CARBON. 
 
 79 
 
 less by filtering through charcoal, the quinine being 
 absorbed and retained. 
 
 Coke is a variety of amorphous carbon which 
 remains behind after coal has been heated for the 
 manufacture of illuminating gas. Coal itself is very 
 impure carbon, containing various compounds of 
 hydrogen, together with nitrogen, oxygen, sulphur, 
 and the various earthy substances which constitute 
 the ash. It varies much in composition, as the fol- 
 lowing percentage analyses show : * 
 
 
 Anthracite. 
 
 Soft coal. 
 
 Cannel-coal. 
 
 Lignite. 
 
 Carbon 
 
 Q2.SQ 
 
 80.33 
 
 80.07 
 
 66.31 
 
 Hydrogen 
 
 2.63 
 
 4.4.7 
 
 C.C7, 
 
 5.63 
 
 Oxygen 
 
 ^.WJ 
 
 1.61 
 
 3.25 
 
 8.10 
 
 22.86 
 
 Nitrogen 
 
 O.Q2 
 
 1.24. 
 
 2.IO 
 
 O. C7 
 
 Sulphur 
 
 
 o.^s 
 
 1. 10 
 
 W O/ 
 2.36 
 
 Ash 
 
 2 2? 
 
 1. 2O 
 
 2 7O 
 
 2 27 
 
 
 
 
 
 
 
 100.00 
 
 IOO.OO 
 
 IOO.OO 
 
 100.00 
 
 The compounds of carbon with hydrogen, the hy- 
 drocarbons, are very numerous, and are, in general, 
 of organic origin. Coal-oil and petroleum are vari- 
 able mixtures of hydrocarbons ; and the hydrogen 
 of coal exists partly combined with carbon and 
 partly in the form of water. Since the value of 
 coal for the manufacture of gas depends upon the 
 hydrocarbons which it contains, two or three of 
 these compounds may fittingly be described here, 
 while the others will be considered in connection 
 with organic chemistry, further on. 
 
 Methane,f also known as marsh-gas, fire-damp, 
 
 * In Dana's " System of Mineralogy " a large number of coal analy- 
 ses are given. The variations are extraordinary. 
 
 f The naming of the hydrocarbons is somewhat arbitrary. This 
 point will be considered under organic chemistry. 
 
8o 
 
 INORGANIC CHEMISTRY. 
 
 and light carbureted hydrogen, is a colorless gas 
 having the formula CH 4 . It burns readily with a 
 bluish-yellow flame, emitting much heat and but lit- 
 tle light. In nature it is often produced by the slow 
 decay of dead leaves at the bottoms of stagnant 
 pools ; hence the common name, marsh-gas. By 
 stirring up the mud beneath a jar of water inserted 
 in such a pool, the bubbles of gas may be collected 
 and identified (Fig. 20). It also frequently accumu- 
 lates in coal-mines, forming a dangerously explosive 
 
 FIG. 20. Collection of Marsh-gas. 
 
 mixture with the oxygen of the air. Such mixtures, 
 ignited by miners' lamps, have caused terrible loss 
 of life. Fire-damp is the miner's name for the gas, 
 distinguishing it from the suffocating carbonic acid, 
 or choke-damp. It sometimes issues in great quanti- 
 ties from the earth, and particularly from artesian 
 wells sunk in search of petroleum. In some such 
 
CARBON. 8 1 
 
 places it serves as a fuel, for driving steam-engines ; 
 and the town of Fredonia, New York, is mainly 
 lighted by gas of natural origin, Methane is artifi- 
 cially prepared as follows : 
 
 EXPERIMENT 37. Mix thoroughly two parts of 
 crystallized sodium acetate, four parts of caustic 
 soda, and eight parts of powdered quicklime. Heat 
 gently on an iron plate until the mixture is thor- 
 oughly dry and crumbly. Then heat it strongly in 
 a glass tube, such as was used for the preparation of 
 oxygen, and collect the gas over water. Test its 
 inflammability as in the case of hydrogen. In this 
 experiment the lime merely serves to render the 
 mass more porous, and to protect the glass from ex- 
 cessive corrosion by the caustic soda.* 
 
 Ethylene, C 2 H 4 , is another gaseous hydrocarbon 
 of great importance. It is fourteen times heavier 
 than hydrogen, whereas the density of methane is 
 only eight. Hence the old names of heavy and light 
 carburetted hydrogen respectively. It is easily pre- 
 pared by heating together alcohol and strong sul- 
 phuric acid, and it burns with a luminous, smoky 
 flame. It is also known as ethene and as olefiant 
 (oil-producing) gas. The last name was given it be- 
 cause it unites directly with another gas, chlorine, 
 to form an oily liquid. 
 
 Acetylene, C 2 H 2 , is another gas, of a disagreeably 
 pungent odor, which is formed by the direct union 
 of its elements. When a series of powerful electric 
 sparks are passed between two carbon-points in an 
 
 * A cheaper way of preparing impure methane is to soak lumps of 
 lime in vinegar, and then to heat, as above, the mixture of lime and 
 calcium acetate thus obtained. In this process a good deal of steam 
 is first given off. 
 
82 INORGANIC CHEMISTRY. 
 
 atmosphere of hydrogen, acetylene is produced. It 
 combines directly with hydrogen to form ethylene ; 
 thus : C 2 H 2 + H 2 = C 2 H 4 . It also unites with cer- 
 tain metals, such as copper or silver, yielding explo- 
 sive compounds of considerable interest. It burns 
 with a blue flame. All the hydrocarbons burn more 
 or less readily, and all form upon complete combus- 
 tion only carbonic acid and water. For example : 
 
 CH 4 + O 4 = CO, + ?H 2 O. 
 C 2 H 4 + O 6 = 2CO a + 2H 2 O. 
 CaHa + O 6 = 2CO 3 + H 2 O. 
 
 By the imperfect combustion of hydrocarbons, acety- 
 lene is often produced ; for example, when a candle 
 burns with a smoky flame its peculiar odor may be 
 detected. 
 
 Ordinary illuminating gas, distilled from coal, is 
 essentially a mixture, more or less impure, of hydro- 
 gen, carbon monoxide, methane, and ethylene. Its 
 production on a small scale may be illustrated by an 
 easy experiment. 
 
 EXPERIMENT 38. Fill the bowl of a common 
 clay tobacco-pipe with powdered soft coal, and cover 
 the latter tightly with a plug of clay. Heat the 
 bowl to redness over a Bunsen gas-flame or between 
 the bars of a grate. Gas will issue from the stem, 
 where it may be ignited. 
 
 In manufacturing gas on a large scale, bitumi- 
 nous or cannel coal is heated in retorts of fire-clay or 
 fire-brick which hold from one to two hundred pounds 
 at a time. Several retorts are heated at once over a 
 single fire, and the products of distillation pass out 
 into a series of pipes in which water, coal-tar, am- 
 monia, etc., are deposited. The tar and ammonia, 
 
CARBON. 83 
 
 being valuable, are thus saved. Twenty-five years 
 ago the tar was worthless ; now it serves as a source 
 of benzene, and of the superb aniline dyes. The 
 gas itself still contains a number of objectionable im- 
 purities, which are removed by passing it over some 
 absorbent substance, such as slaked lime.* Differ- 
 ent samples of gas differ widely in composition ; the 
 differences depending upon the quality of the coal 
 employed, the degree of heat applied to the retorts, 
 and so on. In percentages, the following figures may 
 represent a fair average : 
 
 Hydrogen, 50 
 
 Methane, 35 
 
 Carbon monoxide, 7 
 
 Ethylene, 3 
 
 Several impurities, 5 
 
 100 
 
 In Germany, gas is sometimes distilled from 
 wood ; and in our own country there are processes 
 in use which generate hydrogen from steam and 
 charge it with vapors from petroleum. The latter 
 give its flame illuminating power. In ordinary gas 
 the illuminating value depends mainly upon the 
 ethylene which it contains. 
 
 If we study a gas-flame closely we shall find that 
 its structure illustrates some important facts relat- 
 ing to the mechanism of combustion. In a common 
 burner the gas issues from a fine jet, and is ignited 
 in contact with a moderate amount of air (Fig. 21). 
 Near the jet we have a stream of gas not yet burned ; 
 and here the flame is comparatively cool and non- 
 
 * A good account of the manufacture and purification of coal-gas is 
 given in Roscoe and Schorlemmer's " Treatise on Chemistry," vol. i, 
 pp. 683-704. 
 
84 INORGANIC CHEMISTRY. 
 
 luminous. Insert a piece of slender glass tubing at 
 this part of the flame, and the unburned gas may be 
 
 FIG. 21. Structure of Common Gas-flame. 
 
 drawn off and kindled at the farther end (Fig. 22). 
 Above, and somewhat around this darker base, we 
 have the luminous portion of the flame ; and here 
 the light is partially due to imperfect combustion. 
 Hold a piece of cold porcelain over the jet for a 
 moment, and soot (that is, carbon) will be deposited 
 upon it. It is these solid particles in the flame which 
 become heated and luminous, and they result from 
 the partial combustion of ethylene and some of its 
 related hydrocarbons. Methane yields no free car- 
 bon under like circumstances, and of course hydro- 
 gen does not; hence their flames, containing only 
 gaseous matter, are non-luminous.* If we do any- 
 
 * In Experiment 7 the luminosity of a hot solid in a hydrogen-flame 
 was illustrated. 
 
CARBON. 
 
 thing to cut off the supply of air from a flame, it will 
 become fuller of carbon-particles and more smoky ; 
 a fact which may easily be verified by sliding a piece 
 
 FIG. 22. Withdrawal of Gas from a Flame-centre. 
 
 of sheet-iron or other convenient solid over the top 
 of a gas or kerosene lamp-chimney. As the air is 
 
 FIG. 23. Bunsen Burner. 
 
86 
 
 INORGANIC CHEMISTRY. 
 
 gradually excluded, smoke and soot will form copi- 
 ously. Conversely, if we render combustion more 
 perfect, and so prevent the deposition of carbon, a 
 flame will become hotter but less brilliant. This is 
 done in the Bunsen burner (Fig. 23), in which air is 
 allowed to enter at the base and become thoroughly 
 mixed with the gas before the latter is lighted. The 
 flame here emits very little light ; but if the holes at 
 the base are stopped up, then it becomes luminous 
 as usual. The Bunsen burner is the most conven- 
 ient source of heat for the minor operations of the 
 laboratory. Where gas can not be had, an alcohol 
 lamp is commonly used instead. Such a lamp is 
 easily improvised by perforating the cork of a small, 
 wide-mouthed bottle, and inserting through the per- 
 foration a glass tube carrying a wick (Fig. 24). 
 
 FIG. 24. Improvised Spirit Lamp. 
 
 In the mouth blow-pipe we have another illustra- 
 tion of the foregoing principles. By the aid of this 
 
CARBON. 87 
 
 little instrument air is blown from the cheeks into a 
 flame, and the latter is rendered much hotter (Fig. 
 25). Here, again, the flame may be divided into 
 two chief parts ; an inner blue cone and an outer 
 
 FIG. 25. Use of Blow-pipe. 
 
 portion. The greatest heat is at the apex of the in- 
 ner flame. A bit of tin or zinc, heated in the outer 
 part of the jet, is first melted and then converted 
 into oxide ; hence the name of oxidizing flame. On 
 the other hand, the oxide so formed, if heated in the 
 inner cone, will be reduced to the metal again, giv- 
 ing up its oxygen to assist in the burning of the car- 
 bonaceous matter there found. This part of the jet, 
 therefore, is called the reducing flame. Both parts 
 of the flame are important agents in blow-pipe analy- 
 sis ; and a little practice in heating bits of copper, 
 tin, zinc, lead, etc., supported on pieces of charcoal, 
 first in one and then in the other, will make the re- 
 lations of the two very clear. The stream of air 
 from the blow-pipe should be made as steady as pos- 
 sible ; and one can easily learn to blow lightly from 
 the muscles of the cheeks for several minutes at a 
 time without interrupting respiration. The flame 
 
 5 
 
88 INORGANIC CHEMISTRY. 
 
 of a lamp burning some animal or vegetable oil (lard, 
 whale, or rape-seed oil, for examples), is best for blow- 
 pipe work ; but alcohol or gas may be used. Kero- 
 sene is unavailable, because the chimney interferes. 
 
 In a strictly scientific sense a candle-flame is as 
 truly a gas-flame as any that issues from the tip 
 of a gas-burner. The wick, loosely made of cotton 
 threads, is first kindled ; and the heat thus gener- 
 ated melts a small quantity of the fat, wax, or paraf- 
 fine of which the candle is constructed. The liquid 
 oil thus produced is drawn up into the wick by 
 capillary attraction ; it is decomposed by the heat, 
 and the gaseous products of decomposition then 
 burn, depositing particles of carbon which become 
 luminous. These may be collected as soot ; and by 
 means of a glass tube the gas from the center of the 
 flame can be drawn off and ignited. If a sheet of 
 clean white cardboard be suddenly pressed down 
 upon a candle-flame and then withdrawn, it will be 
 found scorched in a ring, thus showing that at the 
 center of the flame there was no active combustion. 
 
 When bituminous coal is burned in a furnace, 
 the laws of combustion should be carefully consid- 
 ered. A smoky chimney always means imperfect 
 combustion and waste of carbon; and smoke-pre- 
 venting appliances, the so-called " smoke-consum- 
 ers," are getting to be more and more used in cities 
 where soft coal is the chief fuel. Many such appli- 
 ances have been patented, but all aim at the same 
 result namely, to bring about perfect combustion. 
 Sometimes, fine jets of steam are blown into the 
 furnace. These are decomposed at first, yielding 
 oxygen and hydrogen, which serve to make the fire 
 more intense. In other cases the coal is applied in 
 
CARBON. 89 
 
 such a way that the smoke from the fresh portions 
 of fuel is conducted over glowing beds of coke, the 
 latter being merely the earlier charges from which 
 the sooty hydrocarbons have been burned away. 
 In some metallurgical furnances the fuel is rendered 
 gaseous at the start, and the gases are then burned 
 with abundance of air. Such furnaces give great 
 heat and waste little or no fuel. 
 
 For every combustible substance there is a defi- 
 nite temperature below which it will not ignite. If 
 a flame be cooled below the ignition- 
 point of the gas which forms it, it will 
 go out. Press a piece of wire gauze 
 down upon a gas-flame, and the latter 
 will be flattened ; it can not penetrate 
 the metallic net-work. The gas itself 
 passes through, but the wire has con- 
 ducted so much heat away from it that 
 combustion is no longer possible. You 
 can hold the gauze over a jet of gas 
 and kindle the latter above, but the 
 flame can not then descend to the burn- 
 er. Or, you may hold two pieces of 
 gauze parallel to each other over a FIG. 26. Da- 
 stream of gas, and produce a flame be- 
 tween them which shall be unable to 
 pass either above or below. These facts find their 
 application in the safety-lamp of Sir Humphry 
 Davy (Fig. 26). This, which was invented for the 
 protection of coal-miners against fire-damp, is mere- 
 ly a lamp inclosed in a netting of fine-wire gauze. 
 This inclosure may be filled with flame, but the 
 latter can not penetrate its prison-walls and ignite 
 the explosive gaseous mixture without. 
 
CHAPTER X. 
 
 CARBON (continued}. 
 
 CARBON unites with oxygen in two proportions, 
 forming a monoxide, CO, and a dioxide, CO 2 . 
 
 Carbon monoxide, more commonly known as 
 carbonic oxide, is a colorless, odorless gas which 
 burns with a blue flame. It is not produced by the 
 direct union of its elements ; for when carbon, either 
 as diamond, graphite, or charcoal, is burned, only 
 carbon dioxide is formed. By passing the latter, 
 however, over red-hot coals, half of its oxygen may 
 be withdrawn, and carbon monoxide results from 
 
 the change : 
 
 C0 2 + C = 2CO. 
 
 This often happens in coal-stoves and furnaces, es- 
 pecially in the blast-furnace ; carbon dioxide being 
 produced by the combustion of the lowest layer of 
 fuel, and rising through the glowing coals above. 
 The blue flames which play over the surface of an 
 anthracite-fire are due to carbon monoxide, and the 
 product of the combustion is CO 2 : 
 
 CO + O = C0 2 . 
 
 Carbon monoxide may be artificially prepared 
 by various processes; but most conveniently by 
 heating either crystallized oxalic acid or potassium 
 
CARBON. 9 ! 
 
 ferrocyanide with strong sulphuric acid. By the 
 reaction which ensues, both oxides of carbon are 
 formed ; but, by passing the mixed gases through a 
 solution of caustic potash, the dioxide may be ab- 
 sorbed, leaving the monoxide pure. 
 
 The preparation of carbon monoxide should be 
 undertaken only with extreme care, because the gas 
 is dangerously poisonous. A trace of it in the air 
 we breathe will produce headache and dizziness, 
 and anything over one percent admixture might 
 prove fatal. It sometimes escapes from badly-con- 
 structed stoves into improperly-ventilated rooms, 
 and causes serious annoyance. Cheap cast-iron 
 stoves are especially liable to work this kind of 
 mischief, and deaths have resulted from the careless 
 use of such stoves in close sleeping-apartments. 
 All illuminating gas made from coal contains car- 
 bon monoxide as one of its ingredients. 
 
 The other oxide of carbon, carbon dioxide, is 
 met with under a great variety of conditions. We 
 find it ever present in the atmosphere ; it is always 
 produced when carbon or compounds of carbon are 
 burned ; we exhale it from our lungs ; it is evolved 
 from decaying animal and vegetable matter; and 
 we recognize it among the products of fermenta- 
 tion. 
 
 EXPERIMENT 39. Cover the bottom of a glass 
 jar with lime-water,* and suspend over it a burning 
 bit of candle. Close the jar, and the candle will 
 soon burn itself out. Now shake vigorously, and 
 the lime-water will become milky. Upon standing, 
 
 * Prepared by stirring powdered lime into water, leaving the mix- 
 ture to stand for at least an hour, and then filtering. The solution 
 should be perfectly clear. 
 
92 INORGANIC CHEMISTRY. 
 
 the milkiness will be deposited as a white sediment. 
 This sediment is calcium carbonate (carbonate of 
 lime), and its formation proves the presence of car- 
 bon dioxide in the air of the jar. A piece of wood 
 or charcoal burned in place of the candle will give 
 the same result. 
 
 EXPERIMENT 40. Pour some lime-water into a 
 tumbler, and through a piece of glass tubing blow 
 air into the liquid for several minutes from the 
 lungs. The lime-water will become milky, showing 
 that carbon dioxide has been exhaled. 
 
 EXPERIMENT 41. Mix in any convenient vessel 
 some very sweet molasses-and-water with a little 
 yeast. Fill a test-tube with the mixture, invert it in 
 the liquid, and let the whole stand in a warm place 
 overnight. Fermentation will occur, and bubbles of 
 carbon dioxide will rise into the tube. Close the 
 mouth of the latter with the thumb, remove it from 
 the vessel, and shake up its gaseous contents with 
 lime-water. 
 
 EXPERIMENT 42. In the same flask and appa- 
 ratus which previously served for the preparation 
 of hydrogen, put some fragments of chalk, lime- 
 stone, or marble, and pour over them a quantity of 
 dilute hydrochloric or sulphuric acid. Gas will be 
 given off with brisk effervescence ; and by passing 
 a few bubbles of it into lime-water it may be identi- 
 fied as carbon dioxide. Collect the remainder of 
 the gas as usual in bottles or jars over the water-pan. 
 
 The last experiment illustrates the only method 
 by which carbon dioxide is practically prepared 
 for use in the laboratory, The limestone, chalk, or 
 marble is calcium carbonate, CaCO 3 ; and the reac- 
 tion, when sulphuric acid is used, is as follows : 
 
CARBON. 93 
 
 CaCO 3 + H 2 SO 4 = CaSO* -I- H a O + CO 3 . 
 
 That is, calcium carbonate, treated with sulphuric 
 acid, yields calcium sulphate, carbon dioxide, and 
 water. Any other carbonate will give a similar re- 
 action with any strong acid, and carbon dioxide will 
 be evolved in the same way. For example, pour 
 vinegar (acetic acid) over common saleratus (a car- 
 bonate of sodium), and note the effervescence. As 
 the name indicates, a carbonate is a salt formed by 
 carbonic acid with a base. Since carbonic acid is a 
 very weak acid, any stronger acid can expel it from 
 its salts, as in the foregoing reactions. When free, 
 its formula should be H 2 CO 3 , but it is incapable of 
 existing independently, and therefore splits up at 
 the moment of its liberation into carbon dioxide 
 and water, CO 2 -f H 2 O. Many carbonates are easily 
 decomposed by heat ; for instance, lime, which is 
 calcium oxide, is made by burning limestone in a 
 kiln, when carbon dioxide is evolved freely : 
 
 CaCO 3 = CaO + CO 2 . 
 
 The lime and carbon dioxide thus separated can be 
 made to unite again only through the intervention 
 of water; the necessary reaction being one which 
 we have already observed in several experiments. 
 Filter off some of the sediment formed by carbon 
 dioxide in lime-water, and test it with a drop of any 
 common acid. It will effervesce, thereby revealing 
 its character as a carbonate. Carbon dioxide is fre- 
 quently miscalled carbonic acid ; indeed, " carbonic- 
 acid gas " is the commonest of its names. 
 
 Carbon dioxide is a colorless, odorless gas, which 
 by cold and pressure may be easily condensed to a 
 liquid. When the latter is allowed to escape from 
 
94 INORGANIC CHEMISTRY. 
 
 a fine jet a part of it evaporates instantaneously, 
 absorbing enough heat from the remainder to freeze 
 it into a white, crystalline solid, like snow. The 
 temperature of this solid is about 78 C., and if 
 it be pressed between the fingers it produces a pain- 
 ful blister, and sensations like a burn. 
 
 Carbon dioxide dissolves to a considerable ex- 
 tent in water, especially under pressure. Some 
 natural waters, from so-called mineral springs, are 
 heavily charged with it, and effervesce upon expos- 
 ure to the air. The Saratoga and Seltzer waters 
 are good examples. Soda-water is merely water 
 artificially charged with carbon dioxide ; and to the 
 same gas champagne owes its sparkle and beer its 
 foam. By standing in the open air these drinks 
 soon lose their gas, and become flat and valueless. 
 
 In the chemistry of cooking, carbon dioxide plays 
 an important part. As evolved by yeast it makes 
 bread light and porous ; and the same end is at- 
 tained less wholesomely and perfectly by the aid 
 of saleratus and baking-powders. All the latter 
 preparations owe their value to the carbon diox- 
 ide which they are capable of developing ; and all 
 leave residues behind which render bread inferior 
 in quality. 
 
 Like nitrogen, carbon dioxide is incapable of 
 sustaining either combustion or life. It is not in 
 any sense poisonous, like the monoxide it is sim- 
 ply inert. We throw it off from our lungs, and re- 
 place it with fresh oxygen ; it is no longer fit for 
 breathing. 
 
 EXPERIMENT 43. Lower a lighted candle into 
 a jar of carbon dioxide. The flame will at once 
 be extinguished. Chemical fire-engines are simply 
 
CARBON. 
 
 95 
 
 machines which generate carbon dioxide, and throw 
 it, mixed with water, upon fires. 
 
 Carbon dioxide sometimes accumulates in old 
 wells, vaults, and cisterns, and in the great vats of 
 breweries ; and the workman who descends into 
 such a place to clean it out may in consequence be 
 suffocated. Many fatal accidents of this kind have 
 happened ; so that it is always best, before entering 
 a place where carbon dioxide may be, to lower into 
 it a lighted candle. If the latter burns, the air is 
 fit to breathe ; if it goes out, then let the place 
 be thoroughly ventilated. The gas also collects at 
 times in unused galleries of coal-mines, where it is 
 known to the miners as choke-damp. In some places 
 it issues in quantity from crevices in the earth, as at 
 the Grotto del Cane* in Italy. Here it forms a 
 layer on the bottom of a small cave ; a man, enter- 
 ing, has his head above the level of the gas, and 
 does not notice it; but a dog, carried in by the 
 guide, when placed upon the floor, is immediately 
 overcome. 
 
 The fact that carbon dioxide is about half as 
 heavy again as air may easily be illustrated by ex- 
 periment. 
 
 EXPERIMENT 44. Slowly invert a jar of the gas 
 a short distance above the flame of a candle. The 
 latter will go out, showing that carbon dioxide de- 
 scends. So, also, we may pour the gas from one 
 vessel to another, almost as if it were a liquid. 
 
 EXPERIMENT 45. Put two glass jars in the pans 
 of a pair of scales, and balance them nicely against 
 each other. Pour carbon dioxide into one of the 
 jars and the latter will sink, having become the 
 
 * Grotto of the Dog. 
 
96 INORGANIC CHEMISTRY. 
 
 heavier (Fig. 27). The actual density of the gas, re- 
 ferred to hydrogen as unity, is 22 ; that of carbon 
 monoxide is 14. 
 
 In its relations to the atmosphere, and through 
 
 FIG. 27. Weighing Carbon Dioxide. 
 
 the atmosphere to life, carbon dioxide is a substance 
 of the greatest importance. Were its proportions 
 to be but moderately increased, all animals would 
 die ; were it wholly withdrawn, vegetable life would 
 perish. Fortunately, its quantity in the atmosphere 
 varies but little, in spite of the fact that every fire 
 and every breathing animal withdraws oxygen from 
 the air and replaces it with carbon dioxide. How 
 is the balance preserved ? 
 
 In organized life we have a steady circulation 
 of carbon. Directly or indirectly, all animals de- 
 pend upon vegetable food, the carbon of which 
 becomes a part of the animal tissues. These un- 
 dergo, through the medium of the lungs, a sort of 
 
CARBON. 
 
 97 
 
 slow combustion, whereby the animal heat is kept 
 up, and in consequence of which the carbon is con- 
 verted into carbon dioxide and thrown off into the 
 outer air. Now comes into play one of the most re- 
 markable functions of plant-life: the plant which 
 furnishes the animal with food, in turn seizes upon 
 the carbon dioxide which the latter has rejected, 
 and reconverts its carbon into vegetable tissue. 
 The leaf, in presence of sunlight, decomposes car- 
 bon dioxide, retaining its carbon and setting the 
 oxygen free. Without the help of the sunbeam 
 this work could not be done ; during the night the 
 leaves rest from their labors. In the manner thus 
 briefly outlined, the plant and the animal balance 
 each other in Nature, and help to keep even the 
 proportion of carbon dioxide in the air. 
 
 With nitrogen, carbon forms one compound a 
 colorless gas, having an odor suggestive of peach- 
 kernels, and burning with a beautiful purple flame. 
 Its formula is C 2 N 2 ; and its name, cyanogen, is de- 
 rived from two Greek words which indicate that it 
 forms some compounds which are blue. Prussian 
 blue is one of them. It unites with metals just as if 
 it were an element, forming salts which are known 
 as cyanides. Compounds which thus behave like ele- 
 ments are not infrequent, and are called compound 
 radicles. In the present case the true compound 
 radicle, however, is the half of C 2 N 2 , or CN, which 
 does not exist in the free state, but only in cyanides, 
 such as potassium cyanide, KCN, and so on. Some- 
 times the CN group is represented by an abbre- 
 viated symbol, Cy ; and on this plan free cyanogen 
 would be written Cy 2 . Hydrocyanic acid, popu- 
 larly called prussic acid, has the formula HCN. It 
 
98 INORGANIC CHEMISTRY. 
 
 is one of the deadliest poisons. Cyanogen and its 
 derivatives are best studied among organic com- 
 pounds, since they are commonly of organic origin. 
 Their further consideration, therefore, must be de- 
 ferred to the proper chapter. 
 
CHAPTER XL 
 
 COMBINATION BY VOLUME. 
 
 WE have already noticed the fact that the num- 
 bers 14, 1 6, 35.5, 80, and 127 represent not only the 
 atomic weights of N, O, Cl, Br, and I respectively, 
 but also the relative weights of equal volumes of 
 these elements, in the condition of gas or vapor, 
 compared with hydrogen as unity. In general, with 
 a very few exceptions to be noted hereafter, the 
 atomic weight of an element expresses also its vapor 
 density. 
 
 In carbon, however, we meet with an element 
 which does not readily vaporize, so that we can not 
 directly test the accuracy of the foregoing statement 
 with regard to it. Its atomic weight being 12, its 
 vapor should be just twelve times heavier than hy- 
 drogen ; but whether it is or not we are unable to 
 experimentally determine. We may, nevertheless, 
 study some of the gaseous compounds of carbon, and 
 see whether they can shed any light on the subject. 
 Or, in more general terms, we may try to discover 
 whether any simple relation connects the density of 
 a compound gas with the densities of the gaseous 
 elements contained in it. 
 
 If we refer back to the chapter upon atomic 
 weights, we shall see that the elementary gases hy- 
 
100 INORGANIC CHEMISTRY. 
 
 drogen, oxygen, and nitrogen, combine by volume 
 in very simple ratios. A few of these may well be 
 reconsidered here, with the addition of figures show- 
 ing the volumes of the resulting compounds in the 
 state of gases or vapors : 
 
 2 vols. H with i vol. O, in all 3 vols., form 2 vols. HaO. 
 
 3 " H " i " N, " " 4 " "2 " NH 3 . 
 2 " N " i " O, " " 3 " "2 " N 2 O. 
 
 2 " N " 3 " O, " " 5 " "2 " N a O 3 . 
 
 In short, in each of these cases, the elements 
 unite with condensation, and two volumes of a com- 
 pound result. So also with nitric acid, HNO 3 , in 
 which five volumes of H, N, and O condense to two 
 volumes of the compound vapor. In hydrochloric 
 acid, HC1, a substance to be described in a future 
 chapter, we have an example of a simpler kind. 
 One volume of H unites with one volume of Cl 
 without condensation, and here again two volumes of 
 the compound gas, HC1, are formed. 
 
 From these data, or rather from the two-volume 
 law in general, we can easily calculate the density of 
 any compound gas. For example, steam is formed 
 by the union of two unit volumes of hydrogen, 
 weighing two combining units, with one volume of 
 oxygen which weighs sixteen. The resulting two 
 volumes of course weigh eighteen units, and one 
 volume weighs half as much, or is nine times heavier 
 than hydrogen. Hence we may say that the density 
 of a compound gas or vapor, compared with hydrogen as 
 unity, is half its molecular weight* Thus 
 
 * To find the density referred to air as unity, divide the values 
 given according to this rule, by 1443. Why ? 
 
COMBINATION* 
 
 HC1. Mol. weight, I + 35.5 = 36.5. Density, 18.75. 
 HaO. " " 2 + 16 = 18. " 9. 
 
 H 3 N. " " 3 + 14 = 17. " 8.5, 
 
 N 2 O. " ' 28 + 16 = 44. " 22. 
 
 N 2 O 3 . " " 28 + 48 = 76. " 38. 
 
 HNO 3 . " " i + 14 + 48 = 63. " 31.5. 
 
 We may now apply this rule to the carbon com- 
 pounds, assuming the density of carbon vapor to be 
 12, and see whether the results obtained are correct : 
 
 CH 4 . Mol. weight, 12 + 4=16. Density, 8. 
 CaH 4 . " " 24+ 4 = 28. " 14. 
 
 CaH a . " " 24+ 2 = 26. " 13. 
 
 CO. " " 12 + 16 = 28. " 14. 
 
 COa. " " 12 + 32 = 44. " 22. 
 
 CaNa. " " 24+28 = 52. " 26. 
 
 These densities exactly agree with the results which 
 have been reached by direct experiment. Hence 
 we may conclude that just as 16 represents the den- 
 sity of oxygen, so also 12 stands for the density of 
 carbon in its gaseous compounds ; and the more we 
 study the latter the stronger the evidence will be- 
 come. In a similar way we can investigate the 
 volatile compounds of other non-volatile elements, 
 and prove that the two-volume law above indicated 
 is of universal application. The seeming exceptions 
 to it will be explained in another chapter. 
 
 Among the carbon compounds cited above are 
 three which deserve further consideration at this 
 point. Each of the formulae C 2 H 4 , C 2 H 2 , and C 2 N 2 
 is capable of being halved, and the simpler formulae 
 CH 2 , CH, and CN will represent just as well the 
 composition of these substances by weight. CH 2 
 indicates precisely the same ratio between C and H 
 as the more complex formula C 2 H 4 ; why, then, 
 
102 
 
 should we not by preference adopt it? Simply be- 
 cause the density of the gas, doubled, gives us its 
 molecular weight, and the latter agrees only with 
 the higher formula. So also with the other cases. 
 C 2 H 4 is one of a series of hydrocarbons C 2 H 4 , 
 C 3 H 6 , C 4 H 8 , C 5 H 10 , etc. in which the relative pro- 
 portions of hydrogen and carbon do not vary. But 
 in vapor density these substances differ widely, and 
 from it, as well as from other evidence to be con- 
 sidered under organic chemistry, we deduce the 
 formulas given above. In short, the same kinds of 
 atoms may combine in the same relative proportions 
 so as to form many different molecular groups or 
 compounds having different vapor density. If by 
 experiment we ascertain the latter, we are able in 
 any given case to assign a correct molecular weight, 
 and from that to draw conclusions as to the proper 
 formula. 
 
 Two of the oxides of nitrogen will illustrate the 
 application of these principles still further. In a 
 previous chapter we gave them provisionally the 
 formulae N 2 O 2 and N 2 O 4 , so as to bring out more 
 clearly the law of multiple proportions. Properly, 
 however, these particular compounds should be rep- 
 resented by the formulae NO and NO 2 respectively. 
 If the formula of the first were N 2 O 2 , its density 
 would be 30 ; whereas experiment shows it to be 
 only 15. Accordingly, we halve the formula, and so 
 get at the true molecular weight. So also with the 
 other oxide. 
 
 The more we study the properties of gases, the 
 more we shall be impressed with the simplicity of 
 the laws which govern them. They expand equally 
 by heat, and are affected equally by pressure ; and 
 
COMBINATION BY VOLUME. 
 
 103 
 
 between the molecular weight and the density we 
 have just recognized a very close relation. All 
 these regularities, with others which fall without 
 the scope of this book, suggest a general law for 
 gases, and such a law was announced by the Italian 
 physicist, Avogadrp, in 1811. It may be stated as 
 follows : 
 
 Equal volumes of gases, compared under identical 
 conditions of temperature and pressure, contain equal 
 numbers of molecules. 
 
 This law may be deduced both from chemical 
 and physical evidence, and has strong mathematical 
 foundations ; accordingly, it is accepted by chemists 
 and physicists alike. We, however, need to con- 
 sider it only in its chemical bearings, and in addi- 
 tion to what has already been said, especially with 
 regard to the difference between atoms and mole- 
 cules. " 
 
 So far, our standards of comparison have been 
 the atom of hydrogen for atomic and molecular 
 weights, and the unit volume of hydrogen for vol- 
 umes. Using these standards, we have found that 
 for all the elementary gases so far studied, density 
 and atomic weight have both been represented by 
 the same number ; which shows that equal volumes 
 of H, N, O, etc., contain equal numbers of atoms. For, 
 if an atom of O is sixteen times heavier than an atom 
 of H, and a litre of O sixteen times heavier than a 
 litre of H, then the litre of O arid the litre of .H must 
 contain precisely the same number of atoms. With 
 compound gases, on the other hand, a different re- 
 lation holds ; and, as we have seen, the molecular 
 weight is not equal to, but double, density. The 
 reason for this difference is, that we have been com- 
 
104 INORGANIC CHEMISTRY. 
 
 paring molecules with atoms ; whereas, in order 
 to verify Avogadro's law, we should compare mol- 
 ecules only with each other. 
 
 If, now, we assume that the molecule of hydro- 
 gen consists of two atoms, with a molecular weight 
 of two, and represent in a like manner the molecules 
 of the other elements by OO, NN, C1 2 , Br 2 , I 2 , etc., 
 we shall find that both elements and 'compounds 
 will come simply and regularly under Avogadro's 
 law. Then, for every gas or vapor, elementary or 
 compound, the density will be one half the molecu- 
 lar weight ; a ratio which is due to the fact that the 
 half-molecule, or atom of hydrogen, is taken as our 
 standard of comparison. 
 
 But the molecule of an element is not necessarily 
 a double atom. The density of ordinary oxygen, for 
 example, is 16; while that of ailotropic oxygen, or 
 ozone, is half as heavy again, or 24. We have here 
 two different molecular groups formed by the same 
 kind of atom ; and if the molecule of oxygen is O 2 , 
 then the molecule of ozone must be O 3 , with a mo- 
 lecular weight of 48. With mercury and cadmium, 
 the vapor density is half the atomic weight ; hence 
 the latter is identical with the molecular weight, 
 and the single atom and the molecule are the same. 
 Phosphorus and arsenic, on the other hand, form 
 vapors twice as heavy as their atomic weights 
 would indicate, and their molecules therefore contain 
 four atoms. These points will be considered more 
 fully when we come to describe these elements.* 
 
 * Fuller discussion of the points brought forward in this chapter 
 may be found in Cooke's "Chemical Philosophy," Cooke's "New 
 Chemistry," Wurtz's " Atomic Theory," or Remsen's " Theoretical 
 Chemistry. " 
 
CHAPTER XII. 
 
 VALENCY. 
 
 IF we examine the formulas of many chemical 
 compounds, we shall at first be struck with the 
 great diversity of character among them ; but, upon 
 a closer inspection, certain remarkable regularities, 
 of great theoretical importance, will appear. Let 
 us begin with some of the compounds of hydrogen : 
 
 I. II. III. IV. 
 
 HF. H 2 O. H 3 N. H 4 C* 
 
 HC1. H 2 S. H 3 P. H 4 Si. 
 
 HBr. H 2 Se. H 8 As. 
 
 HI. H 2 Te. H 3 Sb. 
 
 Here we have fifteen elements, which unite with 
 hydrogen in such manner as to fall into four well- 
 defined natural groups. These suggest the follow- 
 ing considerations : 
 
 Every elementary atom has a definite capacity 
 for uniting with other atoms, which we may call 
 its valency. f Let us again take hydrogen as our 
 standard of comparison, and assume its valency to 
 be unity. Then the elements in the first column of 
 
 * This particular hydrocarbon is given here because it contains a 
 higher proportion of hydrogen than any other. 
 
 f Also called by various writers " valence," " quantivalence," or 
 " atomicity." 
 
106 INORGANIC CHEMISTRY. 
 
 the table, which unite atom for atom with hydro- 
 gen, may be called univalent, those which take two 
 atoms of hydrogen bivalent, and those in the third 
 and fourth columns trivalent and quadrivalent re- 
 spectively. The atoms themselves, with reference 
 to their valency, may be concisely termed monads, 
 dyads, triads, and tetrads these names being derived 
 from the Greek numerals. Later on we shall meet 
 with quinquivalent and sexivalent elements, whose 
 atoms are called pentads and hexads respectively. 
 
 The proportions in which atoms combine to- 
 gether depend upon valency. Thus, one monad 
 can unite with one monad, one dyad with two 
 monads, one triad with three monads, and one tet- 
 rad with four monads. This is shown in the fore- 
 going table, and also in the following formulae. 
 The Roman numerals serve to indicate the valency 
 of the several elements : 
 
 K'Cl 1 . K'Br 1 . Na'F. AgT. 
 
 CyO". Ags'O' 1 . Na a 'S u . K 9 ! S". 
 
 FW. As^Cl, 1 . Sb m Br 3 '. Bi 111 !, 1 . 
 
 C'CU'. C'Br* 1 . Si iT F 4 1 . Si iT I 4 l . 
 
 Again, one dyad unites with one dyad, two triads 
 with three dyads, and one tetrad with two dyads, 
 thus: 
 
 Ca i! O il . Ba u S H . Zn"O". Hg"S". 
 
 B 2 m 3 ii . N 2 ii! 3 il . SW'S, 11 . BiV'S, 11 . 
 
 CW. C IT S, U . Si'W. Si lT S, !l . 
 
 In each of these cases the valencies of one element 
 exactly balance those of the other. Some of the 
 symbols used belong to metals which do not com- 
 bine with hydrogen, but of which the valency may 
 be determined with reference to univalent chlorine 
 or bivalent oxygen. Take, for example, some of 
 
VALENCY. 
 
 the compounds of potassium, calcium, bismuth, and 
 
 tin: 
 
 K'Cl 1 . Ca"Cl a '. BFCla 1 . Sn lT Cl4 l . 
 
 Ka'O". Ca u O". Bi a iU O 3 H . Sn iv O a u . 
 
 In many cases valency may be made clearer to the 
 eye by a different use of symbols. For instance, 
 carbon unites with hydrogen and chlorine to form 
 the following series of compounds : 
 
 Cl 
 Cl 
 Cl 
 H 
 
 Cl 
 Cl 
 Cl 
 Cl 
 
 Here we have the hydrogen-atoms successively re- 
 placed or substituted by chlorine-atoms, in such a 
 way as to show at a glance the equivalency of 
 these elements and the quadrivalency of the carbon. 
 Still another method of representing valency 
 consists in attaching to the symbol of each element 
 the necessary number of dashes, thus : 
 
 H- O=, N=, C i, etc. ; or thus : 
 
 H-, -O- -N- -C-etc. 
 
 i 
 
 From these symbols we may derive a system of 
 structural formulae, as they are called, of which the 
 following are good examples : 
 
 Free hydrogen, H - H, or H a . 
 " oxygen, O = O, or O a . 
 " nitrogen, N = N, or Ni. 
 Water, H-O-H. H H 
 
 Ammonia, H - N - H. Methane, H - C - H. 
 
 i 
 
 H 
 
 Carbon dioxide, O = C = O. Cyanogen, N = C - C = N. 
 Nitrogen monoxide, N = N. Nitrogen trioxide, O = N \ ~ 
 
 \(X = N/ etc. 
 
108 INORGANIC CHEMISTRY. 
 
 In some cases we encounter formulas in which 
 the conditions of valency are not satisfied. For in- 
 stance, in nitrogen dioxide, NO, we have 
 
 -N = 0, 
 
 and one of the valencies or bonds of affinity of the 
 nitrogen-atom is uncombined. Such a compound 
 is called an unsaturated compound, and it enters 
 into further union with other elements with very 
 great ease. Thus, from the compound just cited, 
 by combination with chlorine, we get a substance 
 having the formula Cl N=O, and in which we see 
 a triad united with a monad and a dyad in such 
 a way that the valencies exactly balance. It will 
 be seen at once that the molecules of free hydro- 
 gen, oxygen, and nitrogen are to be regarded as 
 saturated compounds, while the free atoms, if they 
 could exist separately, would be unsaturated. In 
 many chemical changes the elementary atoms are 
 probably set free, but immediately re-enter into 
 union with each other to form molecules. 
 
 In the case of cyanogen we meet with a group 
 of atoms which behaves like an element and is 
 called a compound radicle. The formula of the 
 gas is given above, and represents really two CN 
 groups united to C 2 N 2 . The CN group itself, the 
 true compound radicle, is univalent, thus : 
 
 and therefore is capable of combining with elements 
 in much the same way as chlorine. For example : 
 
 Chlorine, Cl - Cl. Cyanogen, CN - CN. 
 
 Hydrochloric acid, H - Cl. Hydrocyanic acid, N = C - H. 
 Potassium chloride, K - Cl. Potassium cyanide, K - CN, etc. 
 
VALENCY. 
 
 109 
 
 Care must be taken not to misapprehend the 
 meaning of these " structural " formulae. They are 
 not intended to represent the relative position of 
 the atoms in space, but merely to indicate to the 
 eye the chemical relations of the substances thus 
 symbolized. By their aid chemical reactions be- 
 come more easily intelligible, and in many cases 
 they help the chemist to predict the composition 
 and best mode of preparing compounds even in ad- 
 vance of actual discovery. The whole theory of 
 valency will become clearer when we study it in 
 the light of organic chemistry ; and one more illus- 
 tration of it will suffice for the present chapter. 
 
 A brief reference was made in a previous chap- 
 ter to three important classes of compounds, acids, 
 bases, and salts. So far we have studied but two 
 important acids namely, nitric acid, HNO 3 , and 
 carbonic acid, H 2 CO 3 . These have the following 
 structural formulae : 
 
 In these formulae we may regard the NO 3 group 
 of atoms, which is found in all nitrates, as univa- 
 lent ; while the CO 3 group, which characterizes the 
 carbonates, is bivalent, as the two hydrogen-atoms 
 united with it clearly show. Now, the salts of these 
 acids are really formed by replacing the hydrogen 
 by metals ; and just here the laws of valency come 
 into play. Thus, with univalent metals, nitrates are 
 formed having formulae like the subjoined : 
 
 H-NO 3 . K-NO 3 . Na-NO 3 . Ag-NO. 
 With bivalent metals we get salts like these : 
 
HO INORGANIC CHEMISTRY. 
 
 Pb(N0 3 ) 2 , or Pb < . Ca(N0 3 ) 2 , or Ca ( j. 
 
 And with a trivalent metal, like bismuth, we get 
 
 Bi(NO 3 ) 3 , orBi-NO 3 or BiN 3 O 9 . 
 
 X NO 3 , 
 
 Since these salts are called respectively potassium, 
 sodium, silver, lead, calcium, and bismuth nitrates, 
 it is plain that the acid itself might fairly be named 
 hydrogen nitrate. That is, in acids, hydrogen, 
 which is an essential constituent of every acid, be- 
 haves chemically like a metal, and gives us an addi- 
 tional argument in favor of its metallic character. 
 These formulas also show us that the nitrate of any 
 metal may be represented as resulting from the 
 combination of univalent NO 3 with the metal in a 
 proportion depending upon the valency of the lat- 
 ter. Hence, if we know the valency of a metal, we 
 can at once write the formula of its nitrate. 
 
 With carbonic acid similar rules hold good ; 
 only the hydrogen may be either partly or wholly 
 replaced. Thus, we have : 
 
 H a C0 3 . KHCOs. K 2 C0 3 . NaHCO 3 . Na 3 CO 3 . 
 PbCO 3 , CaCO 3 , etc. 
 
 As we become acquainted with more acids, we 
 shall find like principles always to be applicable ; 
 and that a knowledge of valency will enable us to 
 write a vast number of formulas which could not 
 possibly be remembered unless connected by some 
 such general law. 
 
CHAPTER XIII. 
 
 THE CHLORINE GROUP. 
 
 THE four univalent elements, fluorine, chlorine, 
 bromine, and iodine, are so similar in their chemi- 
 cal relations that they form an exceedingly definite 
 natural group. In their differences they exhibit a 
 remarkable gradation of properties, which follows 
 the order of their atomic weights. In the free state 
 fluorine is unknown, but chlorine is a greenish-yel- 
 low gas, brpmine is a heavy, brownish-red liquid, 
 and iodine is a black solid which forms beautiful 
 purple vapors. With hydrogen, fluorine unites so 
 strongly that the two elements can not be directly 
 separated from each other ; chlorine combines vig- 
 orously, bromine easily, and iodine only with diffi- 
 culty. In general, chlorine acts more energetically 
 upon other substances than bromine, while iodine is 
 the least active of all. As a rule, the compounds 
 of bromine have properties intermediate between 
 those of chlorine and iodine. These three elements 
 also resemble each other in odor. 
 
 FLUORINE is found in nature in various min- 
 erals, and minute quantities of its compounds also 
 occur in bones, milk, and blood. Its atomic weight 
 is 19, and its chief sources are the two minerals fluor- 
 spar and cryolite. The latter, which is brought in 
 6 
 
112 INORGANIC CHEMISTRY. 
 
 great quantities from Greenland, is a fluoride of 
 aluminum and sodium, 3NaF,AlF s ; and is used in 
 making soda, alum, and porcelain glass. Just as 
 the compounds of oxygen with other elements are 
 called oxides, the compounds of fluorine are termed 
 fluorides. So, also, we have chlorides, bromides, 
 and iodides, formed by chlorine, bromine, and iodine 
 respectively. With hydrogen these elements form 
 acids, as follow : 
 
 Hydrogen fluoride, or hydrofluoric acid, HF. 
 " chloride, " hydrochloric " HC1. 
 " bromide, " hydrobromic " HBr. 
 " iodide, " hydriodic " HI. 
 
 So far, all attempts to isolate fluorine have been 
 unsuccessful. Its chemical activity seems to be so 
 great that the moment it is set free it combines at 
 once with whatever substances may happen to be 
 near it. It is also the only element which has not 
 yet been made to combine with oxygen. 
 
 The only fluorine compound sufficiently impor- 
 tant for description here is hydrofluoric acid. This 
 is usually prepared by treating calcium fluoride, 
 CaF 2 , commonly known as fluor-spar, with sulphu- 
 ric acid. Any other metallic fluoride would do, 
 but this one is the most abundant. The reaction is 
 as follows : 
 
 CaF 2 + H 2 SO 4 = CaSO 4 + 2HF. 
 
 The pure acid is a very volatile liquid, having 
 the most violently corrosive properties. A drop of 
 it on the skin will produce a painful ulcer which 
 may not heal for several weeks. Even the weaker 
 acid containing water, such as is commonly pre- 
 pared, has to be handled with extreme care. 
 
THE CHLORINE GROUP. 113 
 
 Hydrofluoric acid is chiefly remarkable for its 
 power of attacking glass, which may be shown by 
 the following experiment : 
 
 EXPERIMENT 46. Cover a sheet of glass with 
 wax, and cut a design through the wax with the 
 point of a needle. Make a small dish or tray out 
 of a piece of. sheet-lead, and in it mix some pow- 
 dered fluor-spar to a paste with strong sulphuric 
 acid. Place the prepared glass over this dish, face 
 downward, and warm gently. Wherever the wax 
 has been scratched away, the glass will be corroded. 
 
 This process is practically used for etching de- 
 signs upon glass, for marking the graduation upon 
 the stems of thermometers, and so on. The com- 
 mercial acid contains much water, and is preserved 
 in bottles made of gutta-percha. 
 
 CHLORINE, the atomic weight of which is 35.5, 
 is by far the most important element of this group. 
 It is found in nature in many compounds, the most 
 abundant one being sodium chloride, NaCl, or com- 
 mon salt. This is the chemist's starting-point for 
 the preparation of chlorine and of all its other com- 
 pounds. 
 
 EXPERIMENT 47. In a large flask provided with 
 a delivery-tube mix one part of common salt, one of 
 manganese dioxide, two of sulphuric acid, and two 
 of water. Upon heating gently, chlorine gas will be 
 evolved in a continuous stream, and may be col- 
 lected by displacement (Fig. 28). It can not conve- 
 niently be collected over water or mercury, since it 
 is quite soluble in the one and it corrodes the other. 
 
 In this experiment two different reactions take 
 place. First, the sulphuric acid attacks the sodium 
 chloride, forming sodium sulphate and setting hy- 
 
INORGANIC CHEMISTRY. 
 
 drochloric acid free. The latter then reacts upon 
 the manganese dioxide, giving up its hydrogen to 
 
 FIG. 28. Preparation of Chlorine. 
 
 unite with the oxygen of the latter, and so liberat- 
 ing the chlorine. The whole change is as follows : 
 
 2NaCl + 2 H 2 SO 4 + MnO a = C1 2 + Na a SO 4 + MnSO 4 + 2H a O. 
 
 A simpler but no better mode of preparation, in- 
 volving the same apparatus, consists in treating the 
 manganese dioxide directly with common hydro- 
 chloric acid. The reaction then is 
 
 MnO 3 + 4 HC1 = MnCla + Cl a + 2 H 2 O. 
 
 In either equation we have two atoms that is, one 
 molecule of chlorine set free. There are still other 
 
THE CHLORINE GROUP. n$ 
 
 processes for the manufacture of chlorine which are 
 used on a large commercial scale, but they need no 
 extended notice here.* 
 
 Chlorine was discovered by Scheele in 1774. 
 It is a greenish-yellow gas, two and a half times 
 heavier than air, and having a highly irritating 
 odor. Even a trace of it, if inhaled, will produce a 
 painful sense of suffocation. By cold and pressure 
 it may be condensed to a heavy yellow liquid, but 
 it has not yet been solidified. 
 
 Cold water absorbs about two and a half times 
 its bulk of chlorine. The solution, which is known 
 in the laboratory as chlorine-water, is yellowish, and 
 smells strongly of the gas. It is a useful substance 
 in some of the processes of chemical analysis, but it 
 must be kept in the dark, or in a bottle covered 
 with black paper. Exposed to the light, chlorine 
 decomposes water, withdrawing hydrogen to form 
 hydrochloric acid, and setting oxygen free. 
 
 EXPERIMENT 48. Fill a small flask full of chlo- 
 rine-water, prepared by passing chlorine into water 
 as long as it dissolves, and invert it in a dish of the 
 same solution. Leave the liquid for some time ex- 
 posed to sunlight. Bubbles of oxygen will form, 
 and collect in the upper part of the flask (Fig. 29), 
 where they may easily be identified. 
 
 Chlorine unites vigorously with nearly all the 
 elements, and especially with the metals. A bit of 
 phosphorus, plunged into a jar of the gas, will spon- 
 taneously inflame ; and powdered antimony or thin 
 copper-foil will also ignite readily. 
 
 EXPERIMENT 49. Prepare some chlorine by 
 
 * A good outline of these processes is given in Wagner's " Chemi- 
 cal Technology." 
 
Il6 INORGANIC CHEMISTRY. 
 
 either of the methods previously described, and dry 
 it by allowing it to pass through a tube containing 
 
 FIG. 29. Formation of Oxygen from Chlorine-water. 
 
 lumps of calcium chloride. Into a jar of this per- 
 fectly dry gas throw some powdered antimony. 
 The latter will burn brilliantly, filling the jar with 
 dense fumes. Dip into another portion of the 
 chlorine a piece of paper moistened with warm 
 turpentine. This also will ignite and burn with 
 a sooty flame. Into a third jar of the gas plunge 
 a lighted candle. It will continue to burn with a 
 reddish flame, emitting dense clouds of smoke. 
 Combustion, then, although commonly due to ox- 
 
THE CHLORINE GROUP. 
 
 117 
 
 idation, is not always so. It is simply a phenom- 
 enon of violent chemical action, and may be pro- 
 duced by union either with oxygen or other ele- 
 ments. 
 
 Although chlorine has a considerable number of 
 uses in the arts, its chief practical importance is due 
 to its property of bleaching vegetable colors. This 
 is easily illustrated : 
 
 EXPERIMENT 50. Dip some slips of litmus-paper, 
 some bits of bright calico, and some highly-colored 
 flowers into chlorine-water. They will be bleached. 
 Add chlorine-water to a solution of indigo, and the 
 latter will be decolorized. Characters written in 
 ordinary ink may be obliterated by exposure to 
 chlorine; but printer's ink, which consists of car- 
 bon, is not affected. 
 
 Chlorine is also a vigorous disinfectant. This 
 property, and its value as a bleaching agent, both 
 depend upon its strong affinity for hydrogen, which 
 is partly illustrated in Experiment 48. The igni- 
 tion of turpentine and the burning of a candle in 
 chlorine are also due to the active union of this 
 element with the hydrogen which they contain. In 
 most cases chlorine is applied for bleaching or dis- 
 infecting purposes in presence of moisture. The 
 latter gives up its hydrogen, and the oxygen thus 
 set free acts with especial vigor, at the moment of 
 its liberation, upon the coloring-matter or putres- 
 cent substance which is to be destroyed. Chlorine, 
 therefore, may be regarded as indirectly an oxidiz- 
 ing agent ; although in some cases it acts destruc- 
 tively upon obnoxious compounds by withdraw- 
 ing hydrogen and so breaking up their molecules. 
 These uses of chlorine will be considered further 
 
Il8 INORGANIC CHEMISTRY. 
 
 on, when we study the properties of bleaching- 
 powder. 
 
 With hydrogen, chlorine forms but a single 
 compound, hydrochloric acid, HC1; and some of 
 the circumstances under which it is produced have 
 been already described. 
 
 When equal volumes of hydrogen and chlorine 
 are mixed together in the dark, they will remain 
 without action upon each other for an indefinitely 
 long time. If the jar or bottle containing them be 
 exposed to ordinary diffused daylight, they will 
 slowly and quietly combine ; but if they are sud- 
 denly brought from darkness into the full glare of 
 the sun, they will unite instantaneously with ex- 
 plosive violence. This may be experimentally veri- 
 fied by filling a flask in the dark with the gaseous 
 mixture, wrapping it in a cloth, and then in strong 
 sunlight pulling away the cloth by means of a long 
 string. The flask will be shattered by the explo- 
 sion which ensues. Light is frequently instrument- 
 al in bringing about chemical changes. In this 
 case it produces chemical union ; on the photo- 
 graphic plate it causes decomposition ; and the fad- 
 ing of colored fabrics in sunlight also illustrates the 
 same thing. Some of these matters will be further 
 discussed in other connections. 
 
 EXPERIMENT 51. An additional example of the 
 direct union of hydrogen and chlorine is furnished 
 by the combustion of the former "gas in the latter. 
 The apparatus may be arranged as in Fig. 30, hy- 
 drogen being generated in the flask in the usual 
 way, while the jet dips into a cylinder or jar con- 
 taining the chlorine. The hydrogen-flame should 
 be first kindled in the air, with the ordinary precau- 
 
THE CHLORINE GROUP. 
 
 119 
 
 tions (see Experiment 7), and then lowered into the 
 chlorine. 
 
 For practical purposes, however, hydrochloric 
 acid is prepared by a wholly different method. 
 
 FIG. 30. Combustion of H in Cl. 
 
 EXPERIMENT 52. In a glass flask provided with 
 a delivery-tube heat some perfectly dry common 
 salt with about twice its weight of strong sulphuric 
 acid. Hydrochloric acid will be evolved with much 
 effervescence, and may be collected over mercury. 
 If an aqueous solution of the gas is wanted, the de- 
 livery-tube may dip into a jar of water. As the 
 experiment is conducted in the school-room, the re- 
 action is as follows : 
 
 NaCl + H 2 SO 4 = NaHSO 4 + HC1. 
 
 In making the acid on a commercial scale, a higher 
 temperature is applied, and only half as much sul- 
 phuric acid is taken. The reaction then is : 
 
 2NaCl + H a SO 4 = Na.,SO 4 + 2HC1. 
 
120 INORGANIC CHEMISTRY. 
 
 When we study sulphuric acid and the sulphates, 
 the full significance of these equations will ap- 
 pear. 
 
 Hydrochloric acid is a colorless gas of pungent 
 odor, and density 18.75. In it the two component 
 gases are united without condensation. It dis- 
 solves very freely in water, and the commercial 
 hydrochloric or muriatic acid is merely its strong 
 aqueous solution. This solution emits acrid, suf- 
 focating fumes, and should be as colorless as 
 water; the common acid, however, is bright yel- 
 low, in consequence of impurities. It contains 
 from thirty to forty per cent of the gaseous 
 acid. 
 
 Hydrochloric acid is one of the strongest and 
 most important of acids. It is used extensively in 
 the manufacture of chlorine, and for a great variety 
 of other purposes. It dissolves many of the metals, 
 such as tin, zinc, and iron hydrogen being evolved, 
 and the chlorides of the metals being formed : 
 
 Zn + 2HC1 = ZnCl 2 + H 2 . 
 Fe + 2HC1 = FeCl 2 + H 3 . 
 
 In these reactions the metals replace the hydrogen 
 of the acid, just as in the cases previously noticed ; 
 only the salts formed are chlorides. In a similar 
 way hydrofluoric acid yields fluorides, hydrobromic 
 acid yields bromides, and hydriodic acid yields 
 iodides. The student may advantageously test the 
 solvent properties of hydrochloric acid upon sev- 
 eral of the commoner metals. Some will be dis- 
 solved, and others not attacked at all; and the solu- 
 tions of the former may be made by evaporation to 
 deposit crystals of chlorides. 
 
THE CHLORINE GROUP. 
 
 Hydrochloric * and nitric acids mutually decom- 
 pose each other, with evolution of chlorine : 
 
 HNO 3 + 3HC1 = 2H 2 O + NOC1 + Cl a . 
 
 The compound NOC1 was referred to in a previous 
 chapter. It is an orange-colored gas of slight im- 
 portance. The mixture of acids is, however, very 
 important ; since, by virtue of the chlorine which it 
 liberates, it has the power of dissolving gold. No 
 single acid will do this ; and so the alchemists gave 
 the mixture the name of aqua regia, or royal water, 
 gold being considered the king of metals. It also 
 dissolves platinum. 
 
 EXPERIMENT 53. In each of two test-tubes put 
 a bit of gold-leaf. Cover one with nitric and the 
 other with hydrochloric acid. Neither will be at- 
 tacked. Mix the contents of both test-tubes, and 
 warm gently. The gold will dissolve, forming a 
 yellow solution. 
 
 * When hydrochloric acid is spoken of, the aqueous solution is 
 usually meant. The pure HC1 is commonly specified as hydrochloric 
 acid gas. 
 
CHAPTER XIV. 
 
 THE CHLORINE GROUP (continued). 
 
 WITH oxygen chlorine does not combine direct- 
 ly ; but, by indirect processes, three oxides, C1 2 O, 
 C1 2 O 3 , and C1 2 O 4 , have been obtained. They are all 
 gases of irritating odor and dangerously explosive 
 character. With hydrogen and oxygen chlorine 
 yields a remarkable series of acids, of which hydro- 
 chloric acid may fairly be considered the first mem- 
 ber: 
 
 HC1, Hydrochloric acid. 
 
 HC1O, Hypochlorous " 
 
 HC1O 3 , Chlorous 
 
 HC1O S , Chloric 
 
 HC1O 4 , Perchloric 
 
 It will be observed that chlorous and chloric acids 
 resemble in formula nitrous and nitric acids, HNO 2 
 and HNO 3 . The prefix hypo, which we meet in 
 ^j/^chlorous acid, is often used to indicate com- 
 pounds which are relatively low in a series. For 
 example, ^//^sulphurous and /^/^phosphorous acids 
 contain less oxygen than sulphurous and phosphor- 
 ous acids respectively. The prefix/^/-, on the other 
 hand, as in perchloric acid, is expressive of higher 
 combination. Thus we have the terms /m)xide, 
 /^chloride, etc., applied to compounds more than 
 
THE CHLORINE GROUP. 12$ 
 
 ordinarily rich in oxygen or chlorine. These names 
 are somewhat arbitrary, and no definite rule gov- 
 erns them without exception. 
 
 Hypochlorous acid, HC1O, although unimpor- 
 tant by itself, forms some salts of the very highest 
 importance. When chlorine gas is passed into a 
 cold and dilute solution of caustic soda, it is copi- 
 ously absorbed, and a mixture of sodium chloride 
 and sodium hypochlorite, NaCIO, is produced. The 
 latter compound has a peculiar, sickish odor, and is 
 used for disinfecting purposes. It forms the " La- 
 barraque's solution " of the drug-stores. If chlorine 
 be passed over slaked lime, instead of into caustic 
 soda, a mixture of calcium chloride and calcium 
 hypochlorite results from the action, and this is the 
 well-known " chloride of lime," or bleaching-powder 
 of commerce. The reaction which forms it is as 
 follows : 
 
 2CaH 2 O a + 2Cl a = 2H 2 O + CaCU + CaCl 2 O 2 . 
 
 The last symbol in this equation may be written 
 
 O Cl 
 Ca^Q_pi ; and, when contrasted with H-O-C1 and 
 
 Na-O-Cl, it serves to illustrate the bivalency of cal- 
 cium. 
 
 Bleaching-powder is extensively used both for 
 bleaching and as a disinfectant. It has the peculiar 
 odor which is characteristic of all hypochlorites, 
 and it owes its efficiency in great measure to the 
 readiness with which it gives up its chlorine. In 
 short, it affords us a convenient means of storing 
 and transporting chlorine in an available form for 
 most of its practical applications. At the beginning 
 of this century all linen and cotton fabrics were 
 bleached by long exposure on the grass to the ac- 
 
124 INORGANIC CHEMISTRY. 
 
 tion of sunlight and moisture. To-day they are 
 bleached by chlorine, applied as a solution of cal- 
 cium hypochlorite ; and in a few hours, in a small 
 area, more bleaching can be done than was formerly 
 accomplished in several months on many acres of 
 grass-land. 
 
 EXPERIMENT 54. Shake up a quantity of " chlo- 
 ride of lime " with about four times its bulk of water ; 
 allow the mixture to settle thoroughly, and then 
 carefully pour off the clear solution. With this so- 
 lution repeat the bleaching experiments given under 
 the heading of Experiment 50. In each case,, how- 
 ever, first moisten the object to be bleached with 
 very dilute sulphuric acid or with vinegar. Acids 
 serve to liberate chlorine from bleaching-powder. 
 
 Chlorous acid and the chlorites are wholly un- 
 important; but in chloric acid and its salts we meet 
 with compounds of considerable utility and interest. 
 
 EXPERIMENT 55. Pass a stream of chlorine gas 
 into a weak and cold solution of caustic potash. Po- 
 tassium hypochlorite, K-O-C1, will be formed, and 
 may be recognized by its odor and bleaching prop- 
 erties. Now repeat the experiment with a hot and 
 strong solution of the caustic potash. Potassium 
 chlorate will be produced, and will be deposited in 
 tabular crystals when the solution cools : 
 
 6KOH + 3C1 2 = KC1O 3 + 5KC1 + 3H 2 O. 
 
 Chloric acid itself has never been prepared quite 
 free from water. In its most concentrated state it 
 is a colorless, sirupy, intensely sour liquid, resem- 
 bling nitric acid in many of its properties. It is so 
 powerful an oxidizing agent that when it is merely 
 dropped upon paper the latter will ignite. 
 
THE CHLORINE GROUP. 
 
 125 
 
 The chlorates of potassium and sodium, KC1O 3 
 and NaClO 3 , are compounds of commercial impor- 
 tance. Potassium chlorate is especially useful as a 
 source of oxygen in the manufacture of certain ex- 
 plosive mixtures, and as a medicinal agent. It is 
 one of the favorite remedies for sore-throat. We 
 have already met with it in Experiments 4 and n, 
 but the following experiments may also be profitably 
 tried : 
 
 EXPERIMENT 56. Allow a drop of strong sul- 
 phuric acid to fall upon a crystal of potassium 
 chlorate. There will be violent action, and an ev- 
 olution of yellow, pungent fumes. The latter con- 
 sist of chlorine tetroxide, C1 2 O 4 . If too much 
 chlorate be used, an explosion may ensue ; and if, 
 as in Experiment 4, the salt be mixed with sugar or 
 starch, the mass will take fire and burn brilliantly. 
 A mixture of potassium chlorate with sugar forms 
 a white gunpowder which, however, is too dan- 
 gerous for practical use. 
 
 EXPERIMENT 57. Put a bit of phosphorus as 
 large as a pea at the bottom of a conical glass filled 
 with water. A test-tube will answer, but is not 
 quite so convenient. Throw in a few crystals of po- 
 tassium chlorate, enough to cover the phosphorus, 
 and then pour in a little strong sulphuric acid 
 through a thistle-tube (Fig. 31). The phosphorus 
 will presently catch fire, and burn vividly under 
 water. The oxygen necessary for its combustion 
 is, of course, supplied by the potassium chlorate. 
 This experiment illustrates the ease with which chlo- 
 rates give up their oxygen. 
 
 EXPERIMENT 58. Rub vigorously together, in 
 a porcelain or iron mortar, a pinch of potassium 
 
126 
 
 INORGANIC CHEMISTRY. 
 
 chlorate and a pinch of sulphur. Explosions more 
 or less sharp will result from the friction. If a little 
 
 of the mixture be placed 
 on an anvil, or upon an 
 iron plate, and struck 
 with a hammer, the ex- 
 plosion will be almost 
 deafening. Care, there- 
 fore, should be taken not 
 to pulverize chlorates 
 with other substances, 
 although by themselves 
 they may be rubbed to 
 powder with safety. In 
 this experiment we see 
 that mechanical energy 
 may produce a vigorous 
 chemical action. All 
 these experiments illus- 
 trate the peculiarities of 
 chlorates in general, and 
 not merely those of the potassium salt in particular. 
 We have already learned that the most conven- 
 ient mode of preparing oxygen is to heat potassium 
 chlorate; the reaction being commonly written: 
 
 KC10 3 = KC1 + O,. 
 
 In reality, the reaction is much more complicated, 
 and consists of two stages : First, part of the chlo- 
 rate is decomposed by the heat, a portion of its oxy- 
 gen being liberated, while the remainder goes to 
 effect a further oxidation of some of the original 
 salt. The equation is as follows: 
 
 FIG. 31. Combustion of Phos- 
 phorus under Water. 
 
 2KC1O S = KC1O* + KC1 + O 2 . 
 
THE CHLORINE GROUP. 127 
 
 In the second stage the KC1O 4 is decomposed, 
 
 thus : 
 
 KC1O 4 = KC1 + 2O a . 
 
 The compound KC1O 4 is potassium perchlorate; 
 and from it, by proper means, perchloric acid, 
 HC1O 4 , may be obtained as an oily liquid of spe- 
 cific gravity 1.782. Thrown upon paper or wood, 
 the pure acid causes their immediate ignition ; 
 dropped upon charcoal, it explodes with terrific vio- 
 lence ; in contact with the skin, it produces wounds 
 which do not heal for months. 
 
 There is but one compound of chlorine with 
 nitrogen, the formula being probably NC1 3 . It is 
 an oily liquid of such terribly explosive properties 
 that it should never be prepared except by expe- 
 rienced chemists, and then only in very small quan- 
 tities. It was discovered by Dulong, who lost an eye 
 and three fingers in consequence of his discovery. 
 
 There are several compounds of carbon with 
 chlorine ; but as they are derivatives of hydrocar- 
 bons, they are usually described under the head of 
 organic chemistry. A few formulas will suffice for 
 present examples : 
 
 CH 4 yields CC1 4 . 
 C 2 H 4 C 2 C1 4 . 
 C 3 H 8 " C 3 C1 8 . 
 
 CeHe " Cede. 
 
 BROMINE, the third member of the chlorine 
 group, is the only element known, except mercury, 
 which is liquid at ordinary temperatures. It owes 
 its name to a Greek word signifying a stench, be- 
 cause of its terribly suffocating odor. Its atomic 
 weight is 80, its specific gravity in the liquid state 
 
128 INORGANIC CHEMISTRY. 
 
 is 3.187, and it boils at 63 centigrade. Its color 
 is dark red, almost black ; and it emits red fumes 
 which somewhat resemble nitrogen tetroxide. It 
 has some uses in analytical chemistry, and it is also 
 employed in the manufacture of certain organic 
 dyes. Some of the bromides, especially potassium 
 bromide, are important medicinal agents ; and they 
 are also considerably used in the art of photog- 
 raphy. 
 
 Bromine is chiefly found, as sodium or magne- 
 sium bromide, in sea-water and the waters of many 
 mineral springs. At present it is produced in large 
 quantities from some salt-wells in the Kanawha Val- 
 ley of West Virginia. After the common salt has 
 crystallized out from the brine, the remaining 
 " mother liquor " is heated with manganese dioxide 
 and sulphuric acid. These reagents liberate bro- 
 mine in precisely the same way that they liberate 
 chlorine ; and the bromine is distilled off into a well- 
 cooled receiver. 
 
 The compounds of bromine are strikingly simi- 
 lar to the compounds of chlorine, but are not quite 
 so numerous. No oxide of bromine is known, but 
 
 we have : 
 
 HBrOs, Bromic acid, 
 
 HBr, Hydrobromic acid, 
 
 NBr 3 , Nitrogen bromide, 
 
 CBr 4 , Carbon tetrabromide, etc. 
 
 Salts are also known corresponding to hypobro- 
 mous acid, HBrO (a bleaching acid), and perbro- 
 mic acid, HBrO 4 . 
 
 IODINE is found in minute quantities in sea- 
 water, from which, in the form of iodides, it is 
 taken up by marine plants. It is obtained, commer- 
 
THE CHLORINE GROUP. 129 
 
 cially, from the ashes of sea- weeds, which are first 
 treated with water. The solution thus obtained is 
 then heated with manganese dioxide and sulphuric 
 acid, and the iodine is thus set free. The reaction 
 is precisely like that by which chlorine and bromine 
 are prepared. 
 
 The element itself is a black solid with a metal- 
 lic luster, and an odor faintly resembling that of 
 chlorine. Its specific gravity is 4.95, and its atomic 
 weight is 127. It is slightly volatile at ordinary 
 temperatures, it melts at 115 C., and boils at 200. 
 Its vapor has a magnificent violet color ; to which, 
 from the Greek word meaning violet, it owes its 
 name. 
 
 EXPERIMENT 59. Put a fragment of iodine in 
 the bottom of a dry test-tube, and heat gently over 
 a flame. The violet vapors will recondense in the 
 upper and cooler part of the tube. This process, 
 by which a solid is vaporized and again condensed 
 without passing through the intermediate liquid 
 state, is called sublimation. The best commercial 
 iodine is commonly labeled " resublimed." 
 
 EXPERIMENT 60. Into the test-tube used for 
 the last experiment, pour a little alcohol. The io- 
 dine will presently dissolve. The solution thus ob- 
 tained is much used in medicine under the name of 
 " tincture of iodine." Water will dissolve only a 
 mere trace of the element. 
 
 EXPERIMENT 61. Make a little starch-paste by 
 warming common starch with water. A drop of 
 tincture of iodine added to this will strike a deep- 
 blue color. This is the ordinary test for free io- 
 dine.* Conversely, iodine is a test for starch. 
 
 * Refer back to the test for ozone in the chapter on oxygen. 
 
130 INORGANIC CHEMISTRY. 
 
 EXPERIMENT 62. Mix a solution of potassium 
 iodide with some of the starch-paste. Now add 
 a few drops of chlorine-water. Iodine will be 
 set free, and the mixture will become blue. Chlo- 
 rine and bromine both liberate iodine from io- 
 dides. 
 
 Iodine and its compounds are much used in 
 medicine, in photography, and in the preparation 
 of certain aniline dyes. In general, the com- 
 pounds resemble those of chlorine and bromine. 
 Hydriodic acid, HI, is a colorless gas soluble in 
 water. But one oxide is known the pentoxide, 
 I 2 O 5 , which is produced easily by the direct oxi- 
 dation of iodine. There are also two acids, iodic 
 and periodic, HIO 3 and HIO 4 , which are much 
 more stable than the corresponding compounds of 
 chlorine. 
 
 With nitrogen iodine forms a compound which 
 is curiously explosive. Its formula is probably NI 3 , 
 although it is rarely obtained perfectly pure. 
 
 EXPERIMENT 63. Pour a little strong ammonia- 
 water over some powdered iodine, and let it stand 
 for half an hour. Filter the black sediment off 
 upon several small niters, and spread these, while 
 still wet, at a distance from each other to dry. 
 When the powder, which is impure nitrogen io- 
 dide, is thoroughly dry, it will explode even at 
 the touch of a feather. It is by far the most sen- 
 sitive detonating substance known ; and never more 
 than a few grains of it should be prepared at a 
 time. 
 
 The following table of formulae may serve to as- 
 sist the memory concerning the chief compounds of 
 F, Cl, Br, and I : 
 
THE CHLORINE GROUP. 
 
 HF 
 
 HC1 
 
 "HPIO 
 
 HBr 
 
 HRrO 
 
 HI 
 
 
 HriOo 
 
 
 
 
 HClOo 
 
 HRrO<, 
 
 HTO, 
 
 
 Hrio, 
 
 HRrfh 
 
 HTfX, 
 
 
 Q of) 
 
 
 
 
 Q Do 
 
 
 
 
 Qr\ 
 
 
 
 
 3v_/4 
 
 
 TO K 
 
 
 
 NC1 3 
 
 ecu 
 
 NBr s 
 CBr 4 
 
 NI 8 
 CI 4 
 
 As we go on, we shall find that these elements 
 always form closely similar compounds. 
 
CHAPTER XV. 
 
 SULPHUR. 
 
 SULPHUR, selenium, and tellurium are three biv- 
 alent elements which, together with oxygen, form 
 a second well-marked natural group. A few formu- 
 las will show their chemical similarity : 
 
 H 2 
 HoOo 
 
 H 2 S 
 
 He 
 
 H 2 Se 
 
 H 2 Te 
 
 CO a 
 
 CSo 
 
 
 
 OOa (ozone) 
 
 S0 2 
 
 cr) 
 
 SeOa 
 
 TeOa 
 
 Tp>O 
 
 
 H <^O 
 
 LJ c p r 
 
 HTpn 
 
 
 H^O 
 
 HQpO 
 
 HT>n 
 
 
 
 
 
 SULPHUR occurs abundantly in nature, both free 
 and combined. Among the sulphides* we find the 
 chief ores of lead, mercury, silver, copper, and anti- 
 mony, and some of the commonest minerals con- 
 taining iron and zinc. Calcium sulphate, or gyp- 
 sum, exists in vast quantities, and other sulphates are 
 frequently met with. Sulphur is also found in such 
 animal substances as hair, albumen, etc., and in the 
 pungent oils to which garlic, mustard, and horse- 
 radish owe their biting flavors. The blackening of 
 
 * Formerly called sulphurets. 
 
SULPHUR. 
 
 133 
 
 silver spoons by eggs is due to the formation of sil- 
 ver sulphide by the sulphur which the eggs contain. 
 Nearly all the sulphur of commerce is native 
 sulphur from Southern Italy and Sicily. It is of 
 volcanic origin, and occurs sometimes in brilliant 
 crystals, but more commonly in opaque masses 
 mixed with dirt. By a simple process it is melted 
 out from its earthy impurities, after which it is re- 
 fined by distillation, as shown in Fig. 32. The vapor 
 
 FIG. 32. Distillation of Sulphur. 
 
 passes from the retort into a large brick chamber, 
 in which it condenses at once to the fine powder 
 known as " flowers of sulphur." By degrees the 
 walls of the chamber become heated, and then a 
 
134 INORGANIC CHEMISTRY. 
 
 part, or even all, of the sulphur assumes the liquid 
 state and is drawn off into molds. This gives the 
 round sticks called " roll-brimstone." Still another 
 variety of sulphur, " lac sulphur," is prepared by 
 adding hydrochloric acid to a solution of calcium 
 sulphide. It is precipitated as a fine white powder 
 which is used in medicine. 
 
 Sulphur is ordinarily a yellow, brittle solid, with- 
 out taste or odor. It dissolves in carbon disulphide, 
 but not in water; it melts at 114.5 C., and boils at 
 448. Its atomic weight is 32 ; but below 500 the 
 density of its vapor is three times this, or 96. Be- 
 tween 800 and 1,000 the vapor density becomes 
 normal, and agrees with the atomic weight. Hence, 
 applying Avogadro's law, and remembering that the 
 vapor density is always half the molecular weight, 
 we find that at ordinary temperatures the sulphur- 
 molecule is S 6 , but at very high temperatures it be- 
 comes S 2 . 
 
 Sulphur is a remarkable example of allotropy. 
 The natural crystals are rhombic octahedra, and 
 similar crystals are deposited from a solution of the 
 element in carbon disulphide. Their specific grav- 
 ity is 2.07. From fusion, however, sulphur solidi- 
 fies in slender prisms of sp. gr. 1.98. Accordingly, 
 sulphur is said to be dimorphous. A body capable 
 of crystallizing in three distinct forms would be tri- 
 morphous. 
 
 EXPERIMENT 64. Carefully melt a little sulphur 
 in a test-tube, and let it stand quietly to cool, Crys- 
 tals, like slender needles, will shoot out from the 
 sides of the tube toward the center, and form a 
 solid interlacing mass. A better plan, perhaps, is 
 to melt a considerable quantity of sulphur in an 
 
SULPHUR. 135 
 
 earthen crucible, and let it cool until a crust forms 
 over the top. Upon breaking this crust and pour- 
 ing out the still fluid material beneath it, the cruci- 
 
 FIG. 33. Crystals of Sulphur, both forms. 
 
 ble will be found to be lined with slender prismatic 
 crystals. This is a general method for crystalliz- 
 ing substances from fusion. Bismuth, thus treated, 
 yields superb crystals. 
 
 A third variety of sulphur, plastic sulphur, may 
 be obtained by pouring melted sulphur into cold 
 water. 
 
 EXPERIMENT 65. Fill a test-tube half full of sul- 
 phur, and heat gradually over a flame. At 114.5 
 it will melt to a clear, amber-colored fluid, which, 
 as the temperature rises, will become darker in tint 
 and quite viscid. At 230 it will be almost black, 
 and so thick that the test-tube may be inverted 
 without a drop running out. Above 250 it again 
 will become fluid, and if it be poured into cold 
 water it will assume the form of a brownish mass 
 which may be worked between the fingers like put- 
 ty, or even drawn out into slightly elastic threads. 
 By much kneading, or even by standing for a few 
 days, the plastic mass will crumble and pass back 
 into ordinary sulphur. 
 
 Sulphur combines easily with most of the other 
 elements. In Experiment i its union with a metal 
 
 7 
 
136 INORGANIC CHEMISTRY. 
 
 was shown ; and at this point the pupil may advan- 
 tageously repeat the experiment with the three met- 
 als copper, iron, and zinc.* The element has many 
 uses. It is an ingredient of gunpowder, of matches, 
 and of vulcanized rubber ; and immense quantities 
 of it are consumed in the manufacture of sulphuric 
 acid, and in the bleaching of silks and woolens. 
 
 With hydrogen, sulphur combines like oxygen 
 in two proportions, forming H 2 S and H 2 S 2 . The 
 latter is an oily liquid, of nauseous odor and power- 
 ful bleaching properties, but having only theoreti- 
 cal importance. 
 
 Hydrosulphuric acid, also known as sulphhy- 
 dric acid, or sulphuretted hydrogen, is a colorless 
 gas having the peculiar odor of rotten eggs. Its 
 density, as shown by the formula H 2 S, is 17; and 
 it burns with a blue flame to form sulphur dioxide 
 and water : H 2 S + $O = H 2 O + SO 2 . In the con- 
 centrated state it is poisonous to inhale ; and it may 
 be reckoned as one of the more objectionable prod- 
 ucts of animal putrefaction. For laboratory pur- 
 poses it is usually prepared by the action of dilute 
 sulphuric acid upon iron sulphide, which latter sub- 
 stance is made by heating together iron-filings and 
 sulphur. 
 
 EXPERIMENT 66. Place some iron sulphide, 
 broken into small fragments, in the flask previously 
 used for the preparation of hydrogen, and pour 
 over it some dilute sulphuric acid. The hydrosul- 
 
 * A mixture of 32 parts of flowers of sulphur with 65 parts of zinc 
 in the form known as " zinc-dust," may be ignited by a match. It 
 burns with a beautiful greenish flame, leaving a bulky residue of yel- 
 lowish-white zinc sulphide. In a confined space the combustion is ex- 
 plosive. 
 
SULPHUR. 
 
 137 
 
 phuric acid will be given off with effervescence, and 
 may be collected by displacement. Verify its com- 
 bustibility as in the case of hydrogen, bearing in 
 mind that it also makes an explosive mixture with 
 air. By passing a stream of the gas through water 
 a solution of it may be obtained, which will be of 
 use in subsequent experiments. The present experi- 
 ment may be represented by the subjoined equation : 
 
 FeS + H 3 S0 4 = FeS0 4 + H a S. 
 
 Hydrosulphuric acid is largely used as a test re- 
 agent in qualitative analysis, for the precipitation, 
 as sulphides, of lead, copper, tin, antimony, bismuth, 
 cadmium, etc. 
 
 EXPERIMENT 67. Dissolve in water, in separate 
 test-tubes or beaker-glasses, fragments of lead ni- 
 trate, copper sulphate, cadmium sulphate, and tar- 
 tar emetic, and acidulate each solution with a few 
 drops of hydrochloric acid. Now pass into each a 
 few bubbles of H 2 S, or add 
 a little of the solution of 
 the gas previously prepared, 
 and note the character of 
 the precipitates which form 
 (Fig. 34). Solutions con- 
 taining salts of other metals 
 may also be tested. Some 
 will yield precipitates and 
 some will not ; for example, 
 
 if we have compounds of FIG. 34. Precipitation by HaS. 
 
 lead and iron dissolved to- 
 gether, we may throw down all the lead as solid 
 lead sulphide, and filter it off, leaving the iron in 
 solution. Thus the two metals can be easily and 
 
138 
 
 INORGANIC CHEMISTRY. 
 
 completely separated from each other. Two equa- 
 tions will illustrate the nature of these precipita- 
 tions : 
 
 CuSO 4 + H 2 S = CuS + H 2 S0 4 . 
 
 Pb(NO 3 ) 2 + H 2 S = PbS + 2HNO 3 . 
 
 EXPERIMENT 68. Drop a solution of H 2 S upon 
 a bright silver coin or a bit of bright copper. A 
 sulphide will be formed, the metal will be black- 
 ened, and hydrogen will be set free : 
 
 Cu + H 2 S = CuS + H 2 . 
 
 Ag 2 + H 2 S = AgaS + H 2 . 
 
 Sulphuretted hydrogen occurs in many mineral 
 springs. The Blue Lick, White Sulphur, and Sha- 
 ron waters all emit the gas copiously ; and to it some 
 of their medicinal value is ascribed. 
 
 Four oxides of sulphur are known namely, SO 2 , 
 SO 3 , S 2 O 3 , and S 2 O 7 . Only the first two are impor- 
 tant. Sulphur dioxide, SO 2 , is formed whenever 
 sulphur burns, and to it the familiar " brimstone 
 odor " is due. It is a colorless gas, of density 32, 
 and is prepared either by the direct combustion 
 of sulphur, or by roasting iron pyrites, FeS 2 , in a 
 stream of air. It is used in the manufacture of sul- 
 phuric acid, as a disinfectant, and for bleaching 
 silk, wool, feathers, and straw, which would be in- 
 jured by chlorine. It also serves to check the fer- 
 mentation of wine or cider. As a disinfectant its 
 mode of action is exactly opposite to that of chlo- 
 rine. The latter in most cases oxidizes the bodies 
 which are to be destroyed, while sulphur^ dioxide 
 withdraws oxygen from them. As a bleaching 
 agent, however, it seems to combine with the color- 
 ing-matter to form an unstable compound ; and any 
 
SULPHUR. 
 
 substance which destroys the latter will bring the 
 color back again. For laboratory purposes sulphur 
 dioxide may be conveniently prepared as follows : 
 
 EXPERIMENT 69. Heat some scraps of copper 
 with strong sulphuric acid in the flask which was 
 previously used for making chlorine. When a tol- 
 erably high temperature has been reached, sulphur 
 dioxide will be freely evolved, according to the sub- 
 joined reaction : 
 
 Cu + 2H 2 SO 4 = CuSO 4 4- SO a + 2H a O. 
 
 The gas may be collected over mercury, or by dis- 
 placement. Instead of copper, charcoal may be 
 used, but the sulphur dioxide produced will be im- 
 pure. 
 
 EXPERIMENT 70. Pass a stream of the gas from 
 Experiment 69 into cold water. It will be absorbed, 
 and with the solution, which will have the charac- 
 teristic odor of SO 2 , some bleaching experiments, 
 like Experiments 50 and 54, may be tried. Sulphur 
 dioxide bleaches only in presence of moisture. 
 
 The aqueous solution of sulphur dioxide may be 
 formulated thus : H 2 O + SO 2 = H 2 SO 3 . The latter 
 symbol is that of sulphurous acid, which, like car- 
 bonic acid, unites with bases to form two sets of 
 salts. For example, we have 
 
 NaHSO 3 KHSO 3 
 
 Na 2 S0 3 K 2 SO 3 
 
 CaSO 3 , etc. 
 
 The salts which retain half of their hydrogen are 
 known as acid sulphites, or sometimes as ^sulphites. 
 Those in which the replacement of hydrogen is com- 
 plete are called normal or neutral salts. The sodium 
 
I 4 o INORGANIC CHEMISTRY. 
 
 hydrogen sulphite, NaHSO 3 , is sometimes used in 
 paper-mills and chlorine bleacheries, to neutralize 
 any excess of chlorine which might, if retained in 
 the fabric, tend to weaken its fibers. Substances 
 used for this purpose are termed " antichlors." 
 
 Sulphur trioxide, SO 3 , may be prepared by the 
 oxidation of SO 2 under peculiar circumstances, or 
 by heating a compound known as pyrosulphuric acid, 
 H 2 S 2 O 7 . It usually forms long, silky, white needles, 
 which unite with water, developing great heat, to 
 generate sulphuric acid : 
 
 H a O + SO 3 = HaSO 4 . 
 
 The similarity between this reaction and the one 
 which yields sulphurous acid should be carefully 
 noted. Although H 2 SO 4 is one of the strongest 
 acids known, SO 3 does not even redden litmus- 
 paper. By some chemists these acid-forming oxides 
 are termed anhydrides. Thus we have 
 
 N a O 6 , nitric anhydride, which with water yields HNO 3 . 
 I a O 6 , iodic " " " " " HIO 3 . 
 
 COa, carbonic " " " " " H 2 CO 3 . 
 
 SOa, sulphurous " " " " " H 2 SO 3 . 
 
 SO 3 , sulphuric " " " " " 
 
cid. ) 
 
 i 
 
 CHAPTER XVI. 
 
 SULPHUR (continued'). 
 
 SULPHUR is remarkable for the number of acids 
 which it forms by combination with hydrogen and 
 oxygen. They are as follow : 
 
 1. HaSOa, Hyposulphurous acid. 
 
 2. HaSO 3 , Sulphurous 
 
 3. HaSO 4 , Sulphuric 
 
 4. HaSaOT, Pyrosulphuric 
 
 5. HaSaOs, Thiosulphuric 
 
 6. HaSaOe, Dithionic 
 
 7. HaSaOe, Trithionic 
 
 8. H a S4O 6 , Tetrathionic 
 
 9. HaSsOe, Pentathionic * 
 
 Most of these are unimportant, and need no fur- 
 ther mention. Sulphurous acid has already been 
 described ; and thiosulphuric acid, which does not 
 exist by itself, is of consequence only in one or 
 two of its salts. Sodium thiosulphate, commercial- 
 ly known as " hyposulphite of soda," is very largely 
 used in the art of photography. It serves to dis- 
 solve out from the photographic plate those com- 
 pounds which have escaped the action of light, and 
 which, if they were allowed to remain, would cause 
 the photograph to fade. 
 
 * The existence of this acid has lately been called in question. 
 
142 INORGANIC CHEMISTRY. 
 
 In sulphuric acid, however, we find a compound 
 which is undoubtedly the most important yet dis- 
 covered by chemistry. It has so many and such 
 varied uses that, as has been well said, the advance- 
 ment of any nation in civilized arts may be meas- 
 ured by the amount of sulphuric acid which it 
 consumes. Its annual production must be over a 
 million tons ; * and it is used in the manufacture of 
 all the other strong acids, of chlorine, of soda, of 
 alum, of phosphorus, of quinine, and of the more 
 important fertilizers. It is also employed in refin- 
 ing fats and oils, in dyeing and bleaching, and as 
 an exciting liquid in several forms of the galvanic 
 battery. There is probably no great manufactur- 
 ing industry which does not, directly or indirectly, 
 make use of this acid. In nature it sometimes, 
 though rarely, occurs uncombined. The waters of 
 the Rio Vinagre, in South America, are rendered 
 appreciably sour by its presence ; and the Oak Or- 
 chard mineral spring at Medina, New York, con- 
 tains nearly a gramme and a half to the litre. It is 
 also found to a quite perceptible extent in the saliva 
 of certain mollusks. 
 
 Commercially, sulphuric acid is prepared by 
 oxidizing sulphurous acid with nitrous fumes. The 
 process is essentially as follows : 
 
 Sulphur dioxide, generated by the combustion 
 of sulphur, or by roasting iron pyrites in a suitable 
 furnace, is passed into a large chamber, or series 
 of chambers, lined with sheet-lead f (Fig. 35). Ni- 
 
 * In Great Britain alone more than 850,000 tons are annually made. 
 
 f Such a chamber may be thirty metres long, six or seven wide, and 
 five high ; but the dimensions and arrangement are different in differ- 
 ent places. An excellent account of the manufacture is given in Roscoe 
 and Schorlemmer's " Treatise on Chemistry," vol. i, pp. 319-338. 
 
SULPHUR. 
 
 143 
 
 trous fumes, produced by heating sodium nitrate 
 
 with a little sulphu- 
 
 ric acid, enter the 
 
 chamber at the same 
 
 time ; jets of steam 
 
 are blown in at sev- 
 
 eral points, and a 
 
 thorough draught 
 
 of air is kept up 
 
 throughout. The 
 
 sulphur dioxide, 
 
 meeting the nitric 
 
 acid which enters 
 
 the chamber with it, 
 
 becomes oxidized in- 
 
 to sulphuric acid, in 
 
 accordance with the 
 
 following reaction : 
 
 SO 2 
 
 2HNO 3 = H 2 SO 4 
 + 2NO a . 
 
 The NO 2 , in pres- 
 ence of steam, oxi- 
 dizes a fresh portion 
 of sulphur dioxide, 
 becoming itself re- 
 duced to NO; thus: 
 
 SO 2 + H 2 O + NO 2 = 
 H 2 SO 4 + NO. 
 
 The last substance 
 now takes up an 
 atom of oxygen from 
 the air, regenerating 
 NO 2 , but surrenders it at once to another portion of 
 
144 
 
 INORGANIC CHEMISTRY. 
 
 the sulphurous acid ; it is then reoxidized by more 
 air, again reduced, again oxidized, and so on indefi- 
 nitely. Theoretically a very small amount of NO 2 
 would serve to oxidize an infinite quantity of sul- 
 phurous acid ; but practically there is always some 
 loss, and fresh fumes are therefore constantly sup- 
 plied. It will be seen that the fumes act simply as 
 carriers of oxygen from the air to the mixture of 
 steam and SO 2 , which latter is being continually 
 transformed into sulphuric acid by the process. 
 The acid thus formed condenses on the floor of the 
 chamber, whence it is drawn off. 
 
 This " chamber acid," as it is called, is a brown- 
 ish, oily liquid of specific gravity 1.55. It still con- 
 tains much water, from which it is partly freed by 
 evaporation in leaden pans until its sp. gr. reaches 
 1.71. At this point it begins to attack the lead ; so 
 that further concentration is effected by heating in 
 retorts of glass or platinum, until it attains a sp. gr. 
 of 1.842. It is now pure enough for all commer- 
 cial purposes ; but, in order to render it chemically 
 pure, it has to be distilled. 
 
 In its purest state sulphuric acid is a colorless, 
 limpid, oily liquid, of specific gravity 1.854, which 
 boils at 338 centigrade, and freezes at 10.5. The 
 brown color of the commercial acid is due to or- 
 ganic matter derived from the dust of the air. It 
 is a powerful solvent, attacking many of the metals 
 and converting them into sulphates, and charring 
 such organic substances as wood, sugar, animal 
 matter, etc. There is an easy experiment to illus- 
 trate this point. 
 
 EXPERIMENT 71. Add to a very strong solution 
 of white sugar in water, its own bulk of sulphuric 
 
SULPHUR. 145 
 
 acid. In a few moments it will blacken, swell up, 
 and become a porous mass of charcoal. The ex- 
 planation of this phenomenon is simple. Sugar con- 
 tains carbon, hydrogen, and oxygen ; the last two 
 being present in just the proportions needful to 
 form water. Sulphuric acid unites with water with 
 intense avidity ; accordingly, it withdraws the hy- 
 drogen and oxygen from the sugar, leaving the car- 
 bon behind. The corrosive action of sulphuric acid 
 upon the skin and upon clothing is of the same gen- 
 eral character as the foregoing. 
 
 The strong affinity of sulphuric acid for water is 
 also indicated by the fact that when the two sub- 
 stances are mixed great heat is evolved. This may 
 be verified by experiment in a test-tube or small 
 beaker. The mixture, which often has to be made 
 in the laboratory, should always be effected care- 
 fully; best by pouring the acid slowly into the 
 water, and stirring the latter with a glass rod at 
 the same time. By allowing gases to bubble 
 through strong sulphuric acid, they may be thor- 
 oughly dried. For this purpose the arrangement 
 shown in Fig. 36 is commonly employed. The gas- 
 stream enters through the longer tube, which ex- 
 tends to the bottom of the flask, rises through the 
 acid, and issues from the shorter tube. The ease 
 with which sulphuric acid absorbs moisture from 
 the air may be simply illustrated as follows : 
 
 EXPERIMENT 72. Fill a test-tube one third full 
 of strong sulphuric acid, and carefully mark its level 
 on the side. Let it stand exposed to the air for a 
 day or two, and again note the level of the liquid. 
 The latter, by virtue of the absorbed water, will be 
 found to have increased in bulk very perceptibly. 
 
146 
 
 INORGANIC CHEMISTRY. 
 
 The affinity between sulphuric acid and water is 
 really due to a distinct chemical action ; for two 
 
 FIG. 36. Washing-Flask for Gases. 
 
 definite compounds, called hydrates, are formed. 
 Their formulae are written thus : 
 
 H 2 S0 4 , H 2 0, 
 H a S0 4 , 2H a O. 
 
 At low temperatures these hydrates crystallize in 
 characteristic forms. 
 
 Sulphuric acid was originally produced by a 
 process quite distinct from that which is carried on 
 in the leaden chambers. Sulphate of iron, or " vit- 
 riol," was distilled in earthen retorts, and an acid 
 having the formula H 2 SO 4 +SO 8 , or H 2 S 2 O 7 , col- 
 lected in the receivers. This was the "oil of vit- 
 riol " of the early chemists. It is now commonly 
 known as " Nordhausen sulphuric acid," from the 
 
SULPHUR. 147 
 
 town in Saxony at which it is still made. It is also 
 called " fuming sulphuric acid," from the fact that 
 it emits white fumes of sulphur trioxide. The latter 
 substance may be expelled by heating, when H 2 SO 4 
 remains behind. By many chemists the compound 
 H 2 S 2 O 7 is regarded as a distinct acid of sulphur, and 
 to it the name of pyrosulphuric acid is applied. 
 
 Like sulphurous and carbonic acids, sulphuric 
 acid is dibasic that is, it contains two hydrogen- 
 atoms which are replaceable by bases. Thus we 
 
 have 
 
 KHSO 4 NaHSO 4 
 
 K 3 SO 4 Na a SO 4 
 
 CaSO 4 , etc. 
 
 The sulphates of sodium, calcium, magnesium, ba- 
 rium, iron, zinc, copper, etc., are all important com- 
 pounds, which will be described in their proper 
 connection further on. 
 
 In the ordinary process for making sulphuric 
 acid, white crystals, called " lead-chamber crystals," 
 are sometimes formed. Their formation, which oc- 
 curs only when there is a deficiency of steam, may 
 be illustrated on a small scale as follows : 
 
 EXPERIMENT 73. Into a stoppered bottle, con- 
 taining dry sulphur dioxide, introduce a glass rod 
 moistened with nitric acid. Red fumes will appear, 
 and after a short time white crystals will be de- 
 posited on the sides of the glass. Upon the addi- 
 tion of water they will dissolve with effervescence, 
 giving off red fumes, and yielding sulphuric acid. 
 Their formula is HSO 3 NO 2 , and they give us an 
 important clew to the constitution or structure of 
 the sulphuric-acid molecule. 
 
 In SO 2 we have a compound which may be re- 
 
148 INORGANIC CHEMISTRY. 
 
 garded as a bivalent radicle. It unites with one 
 atom of bivalent oxygen to form SO 3 , and also with 
 two atoms of univalent chlorine to produce sul- 
 phuryl chloride, SO 2 C1 2 . With O and H^O it yields 
 sulphuric acid, which may be written structurally : 
 
 In this formula we meet with a peculiar group of 
 atoms, which is essentially water minus half its hy- 
 drogen, and in all acid molecules this group occurs. 
 It is called hydroxyl, and is necessarily univalent, 
 since the oxygen in it is only half satisfied. Hydro- 
 gen dioxide, H 2 O 2 , is probably hydroxyl in the un- 
 combined state ; (OH) 2 being a molecule similar to 
 H 2 , C1 2 , and (CN) 2 . Nitric acid, HNO 3 , is struct- 
 urally OH-NO 2 , the NO 2 being another univalent 
 radicle of great importance. Using these radicles, 
 SO 2 U , NO 2 , and OH 1 , we may now write the follow- 
 ing structural formulae : 
 
 S0 3 =0 S 2 <OH SO <SH 
 
 Sulphur trioxide. Sulphuric acid. Thiosulphuric acid. 
 
 /Cl /OH /NO, 
 
 so Jxci so^ q so, XQH 
 
 Sulphuryl chloride. Chlorosulphonic acid. Lead-chamber crystals. 
 
 SO< OH 
 )0 
 
 SOa \OH 
 
 Pyrosulphuric acid. 
 
 Some of these compounds have only theoretical 
 importance, and need not be specially described. 
 
 With nitrogen, chlorine, bromine, and iodine, 
 sulphur forms various compounds ; but only one of 
 them, the chloride, S 2 C1 2 , needs further mention here. 
 
SULPHUR. I 49 
 
 This substance is a volatile yellow liquid, produced 
 by the direct union of its elements. It is somewhat 
 used in a process for vulcanizing rubber. 
 
 With carbon, sulphur yields two compounds, 
 CS and CS 2 , analogous to CO and CO 2 . The disul- 
 phide, CS 2 , is produced by heating charcoal to red- 
 ness in a stream of sulphur- vapor. It is a colorless, 
 brilliant liquid of sp. gr. 1.29, which boils at 46. 
 Its odor suggests that of ether,* and its vapor forms 
 an explosive mixture with air. It is very combus- 
 tible, and burns according to the equation 
 
 CS 2 + 6O = CO 2 + 2SO 2 . 
 
 Its practical importance depends upon its solvent 
 properties, it having the power of dissolving easily 
 such substances as sulphur, phosphorus, rubber, fats, 
 and oils. A solution of rubber in it gives a conven- 
 ient water-proof varnish ; and it is also used on the 
 large scale for the extraction of fats from animal 
 refuse. The number of its useful applications seems 
 to be constantly increasing. 
 
 SELENIUM, atomic weight 79, is an element which 
 is found as an occasional impurity of sulphur, and as 
 a constituent of certain rare minerals. Its specific 
 gravity varies from 4.25 to 4.80, and like sulphur it 
 is allotropic. It has few uses, and these depend upon 
 its remarkable electrical properties. 
 
 Seleniuretted hydrogen, H 2 Se, is, like H 2 S, a gas 
 of intolerably nauseous odor. The dioxide, SeO 2 , is 
 a white solid which unites with water to form sele- 
 nious acid, H 2 SeO 3 . Selenic acid, H 2 SeO 4 , is very 
 similar to sulphuric acid, only not so strong. The 
 
 * Commercial carbon disulphide has a nauseous odor, which is due 
 to impurities. 
 
150 INORGANIC CHEMISTRY. 
 
 selenates are isomorphous with the sulphates that is, 
 they crystallize in precisely the same forms. 
 
 TELLURIUM is another rare element having semi- 
 metallic properties. It is tin-white, brittle, and has 
 a sp. gr. of 6.25. It occurs in nature free, and also 
 combined as tellurides with lead, bismuth, gold, 
 silver, and mercury. The tellurides of gold and 
 silver are important ores, especially in Colorado. 
 The compounds of tellurium in general resemble 
 those of selenium and sulphur. For example, H 2 Te 
 is a gas, and H 2 TeO 3 and H 2 TeO 4 are characteristic 
 acids. No uses have yet been found for either the 
 element or its compounds. 
 
CHAPTER XVII. 
 
 PHOSPHORUS. 
 
 JUST as sulphur, selenium, and tellurium belong 
 to the oxygen group of elements, so also phospho- 
 rus, arsenic, antimony, bismuth, and vanadium may 
 be classed with nitrogen. Only two of these sub- 
 stances, however, phosphorus and arsenic, will be 
 considered among the non-metallic elements. 
 
 Phosphorus exists in nature only in the com- 
 bined state. It is found in many rocks, in all fertile 
 soils, in plants, and in animals. Human bones con- 
 tain more than half their weight of calcium phos- 
 phate, Ca 3 P 2 O 8 ; and in other combinations phospho- 
 rus is an important constituent of nervous matter 
 and of the brain. Calcium phosphate is one of the 
 commoner minerals, apatite, and is often found in 
 large beds ; and the phosphates of lead, iron, alumi- 
 num, manganese, copper, uranium, and magnesium 
 form well-known mineral species. 
 
 The element itself was discovered by Brand of 
 Hamburg, in 1669. It is now prepared on a large 
 scale from bone-ash ; or from sombrerite, an im- 
 pure calcium phosphate found in West Indian gua- 
 no. The powdered material, which is essentially 
 Ca 3 P 2 O 8 , is mixed with sulphuric acid and water, 
 when calcium sulphate is formed and deposited as 
 
152 INORGANIC CHEMISTRY. 
 
 an insoluble white sediment. The remaining- liquid, 
 which is drawn off clear from this precipitate, con- 
 tains an acid calcium phosphate, CaHPO 4 , and is 
 concentrated by evaporation to a thick sirup. This 
 is mixed with powdered charcoal, thoroughly dried, 
 and distilled in an earthen retort. Phosphorus is 
 set free, vaporized, and recondensed under cold 
 water. It is finally cast into sticks, and sent in this 
 form into commerce. 
 
 As ordinarily seen, phosphorus is a yellowish- 
 white, waxy solid, of specific gravity 1.837. It melts 
 at 44.2, and boils at 290, giving a vapor of which 
 the density is 62, or double the atomic weight, _^-Tfie 
 molecule of phosphorus, therefore, is P 4 . Phosphorus^ 
 is highly inflammable, and on this account it is used 
 in enormous quantities for the manufacture of fric- 
 tion matches. In handling it, care must be taken 
 that it does not ignite in contact with the skin, for 
 the burns which it produces are very painful, and 
 troublesome to heal. It should never be cut except 
 under water ; and, indeed, it is always kept under 
 water to protect it from oxidation. Exposed to 
 the air at low temperatures, it oxidizes slowly, and 
 the chemical action which thus takes place gen- 
 erates a feeble light. Hence, phosphorus becomes 
 luminous in the dark ; whence its name, which sig- 
 nifies " light-bearer/' Whenever we rub a match 
 over the palm of the hand in the dark, we recognize 
 its luminous property. Although it is insoluble in 
 water, phosphorus dissolves slightly in olive-oil and 
 in ether, and freely in carbon disulphide. From its 
 solution in the last-named liquid it may be obtained 
 in crystals. 
 
 EXPERIMENT 74. Dissolve a bit of phosphorus 
 
PHOSPHORUS. 153 
 
 in CS 2 , and pour the solution over a piece of un- 
 glazed paper. In a few moments the disulphide 
 will evaporate, leaving the phosphorus spread over 
 the paper in a very finely divided state. Under 
 these circumstances it will ignite spontaneously, 
 and the paper will burst into flame. 
 
 EXPERIMENT 75. Cover a bit of phosphorus, no 
 larger than a pea, with about a teaspoonful of finely 
 powdered bone-black or lamp-black. The oxygen 
 condensed by the carbon will presently cause the 
 phosphorus to ignite. 
 
 When ordinary phosphorus is heated to 240 in 
 an atmosphere free from oxygen, it becomes convert- 
 ed into an extraordinary allotropic form. This is a 
 dark-red powder, which is opaque, insoluble in CS 2 , 
 non-luminous, and uninflammable. Its specific grav- 
 ity is 2.1 1 ; and it may be dissolved in melted lead ; 
 from which, upon cooling, it will separate out in 
 black crystals of metallic luster, and specific grav- 
 ity 2.34. It is odorless, whereas common phos- 
 phorus has a faint odor resembling that of garlic ; 
 and it is not poisonous, although the other variety 
 is a violent corrosive poison. Many rat and bug 
 poisons are merely pastes containing ordinary phos- 
 phorus ; and children have died in consequence of 
 nibbling the tips off of common friction matches. 
 By heating to 260, red phosphorus may be retrans- 
 formed into the common variety. Very recently 
 another modification of phosphorus has been de- 
 scribed by Remsen and Reiser. It is a white, flaky 
 substance, produced by distilling common phos- 
 phorus in an atmosphere of hydrogen. In some 
 respects it is analogous to flowers of sulphur, so 
 that " flowers of phosphorus " would be a fair name 
 
154 
 
 INORGANIC CHEMISTRY. 
 
 for it. A black phosphorus has also been obtained 
 by The"nard. 
 
 Although phosphorus forms three compounds 
 with hydrogen, only one of them, PH 3 , has any par- 
 ticular importance. This substance, phosphine, is a 
 colorless gas, having a very disagreeable odor, and 
 strongly resembling ammonia, NH 3 , in its structure 
 and chemical relations. Its formation is beautifully 
 illustrated in the following experiment: 
 
 EXPERIMENT 76. Arrange a small flask and de- 
 livery-tube, as in Fig. 37, and fill it nearly full of a 
 solution of either caustic soda or caustic potash. 
 
 FIG. 37. Preparation of PH 3 . 
 
 Milk of lime, a mixture of lime and water, will do 
 nearly as well. Add to the solution a few bits of 
 phosphorus, and pour upon its surface a dozen 
 drops of ether. The vapor of the latter merely 
 serves as an aid in expelling from the flask the oxy- 
 gen of the air. Upon boiling the solution, PH 3 will 
 be evolved, and each bubble of the gas, on rising 
 from the water of the water-pan, will ignite with a 
 brilliant flash, and form a beautiful white ring of 
 smoke. The absolutely pure gas is not spontane- 
 
PHOSPHORUS. 
 
 155 
 
 ously inflammable ; this property being really due 
 to the presence, as an impurity, of traces of P 2 H 4 . 
 Phosphine may also be formed by throwing calcium 
 phosphide into water, when the same inflammable 
 gas-bubbles will appear. 
 
 There are two oxides of phosphorus, P 2 O 8 and 
 P 2 O 5 , analogous to N 2 O 3 and N 2 O 5 . The first is 
 formed when phosphorus is oxidized slowly, the 
 latter is the sole product of the combustion of the 
 element. The one unites with water to form phos- 
 phorous acid, while from the other, under like cir- 
 cumstances, phosphoric acid is derived. The white 
 smoke produced in Experiments 21 and 76 consisted 
 of the pentoxide, which substance is chiefly remark- 
 able for its intense affinity for water. It is by far 
 the most powerful dehydrating agent known. 
 
 Phosphorus forms three distinct acids, as fol- 
 low : 
 
 Hypophosphorous acid, H 8 PO a . 
 
 Phosphorous " H 3 PO 3 . 
 
 Phosphoric " H 3 PO 4 . 
 
 Salts corresponding to the first acid, hypophos- 
 phites, are produced by the action of alkalies upon 
 phosphorus. One was formed in Experiment 76, 
 and remained in solution. Several hypophosphites 
 are used medicinally. Phosphorous acid and the 
 phosphites are unimportant, except theoretically. 
 
 Phosphoric acid, the highest of the acids of phos- 
 phorus, is remarkable because of its existence in 
 three distinct varieties having different formulas. 
 These may be represented simply as being formed 
 by the union of P 2 O 5 with one, two, and three mole- 
 cules of water successively, as shown in the sub- 
 joined equations : 
 
156 ' INORGANIC CHEMISTRY. 
 
 P 2 O 6 4- H 2 O =P 2 H 2 O = 2HPO 3 , w^taphosphoric acid. 
 P 2 O 6 + 2H 2 O = P 2 H 4 O7, /j/r0phosphoric " 
 
 P 2 O 6 + 3H 2 O = P 2 H 8 O 8 = 2H 8 PC>4, 
 
 The salts of these acids are called 
 /j/wphosphates, and 0r/&?phosphates respectively, 
 and they differ from each other in many particulars. 
 Orthophosphoric acid is especially interesting as 
 the first instance we have met with of a tribasic 
 acid. Thus it forms three salts with sodium, as 
 follows : 
 
 NaH 2 PO 4 . 
 
 Na 2 HPO 4 . 
 
 Na 8 P04. 
 
 All the more common phosphates, such as calcium 
 phosphate, Ca s II (PO 4 ) 2 , are orthophosphates. Such 
 salts as Ca u HPO 4 and KBa ii PO 4 are called double 
 salts; and some triple phosphates also are known. 
 For example, NaAmHPO 4 , sodium ammonium hy- 
 drogen phosphate, is a triple salt. The last sub- 
 stance is much used in blow-pipe analysis under the 
 name of microcosmic salt, or salt of phosphorus. 
 
 The compounds of phosphorus with the elements 
 of the chlorine group have very great theoretical 
 interest. Except in the case of the fluoride, they 
 are formed by the direct union of the elements, and 
 have the following formulae : 
 
 PF 6 . 
 
 PCI.. PCI.. 
 
 PBr 3 . PBr 6 . 
 
 P a T<. PI 3 . 
 
 There are also several oxychlorides, sulphochlo- 
 rides, oxybromides, etc., having formulae as follows: 
 
 POC1 3 . POBr 8 . PSC1 3 , etc. 
 
PHOSPHORUS. 
 
 157 
 
 Some of these bodies are very useful in the prepara- 
 tion of many organic compounds. 
 
 In the light of the foregoing formulae we are at 
 once led to ask a very serious question as to the 
 valency of phosphorus. In PH 3 it is apparently 
 trivalent, and also in PC1 3 , PBr 8 , and PI 8 ; but, in 
 the higher compounds, PF 5 , PC1 5 , and PBr 5 , it seems 
 to have a valency of five. Which is the true val- 
 ency, or are both equally correct ? 
 
 A complete answer to this question would in- 
 volve elaborate discussions entirely beyond the 
 scope of this book. Suffice it to say that most 
 chemists regard valency as a variable property of 
 the elements, and that this variability is well illus- 
 trated by phosphorus, nitrogen, and sulphur. Hy- 
 drogen and carbon seldom, if ever, vary in valency, 
 but the elements of the chlorine group seem to 
 change occasionally. In NH 4 C1, N 2 O 5 , etc., nitro- 
 gen is regarded as quinquivalent ; in SO S , the val- 
 ency of sulphur seems to be six ; in C1 2 O 3 and I 2 O 5 , 
 chlorine and iodine exhibit valencies of three and 
 five respectively. In general, the elements may be 
 divided into two great classes: one having valen- 
 cies represented always by even numbers, as 2, 4, 
 6; the other running in odd numbers, as I, 3, 5, 
 etc. The even class are called artiads, the odd 
 elements are called perissads. This division is, how- 
 ever, largely artificial, and represents no genuine 
 law. To the rule there are several striking excep- 
 tions. 
 
 Some of the phosphorus compounds cited above 
 may be assigned structural formulae agreeing with 
 a valency for the element of either three or five. 
 For example, P 2 O 5 may be written either 
 
158 INORGANIC CHEMISTRY. 
 
 Ill V 
 
 i x p_O-P^' or O=P-O^P=O 
 
 O x X O V O X 
 
 and POC1 3 may be represented by either 
 
 III V 
 
 ? /c . 
 
 P-O-Cl or O-P-C1 
 
 Cl " Cl 
 
 The aim of the chemist always is to select that 
 formula from among the possible formulas which 
 shall best indicate the relations of each compound 
 to the other compounds which may be derivable 
 from it.* In many cases a careful consideration of 
 structural formulas has led to important discoveries. 
 
 * The subject of variable valency is well discussed in Wurtz's 
 " Atomic Theory," Remsen's " Theoretical Chemistry," and Cooke's 
 " Chemical Philosophy." 
 
CHAPTER XVIII. 
 
 ARSENIC, BORON, AND SILICON. 
 
 ARSENIC, which is sometimes classed as a metal, 
 occurs in the mineral kingdom under a great vari- 
 ety of circumstances. The free element, its two sul- 
 phides, several arsenides, and a number of arsenates- 
 are common mineral species ; but, for commercial 
 purposes, it is chiefly obtained from arsenopyrite, a 
 sulphide of arsenic and iron. This mineral, finely 
 powdered, is heated in long earthen tubes ; when 
 arsenic, being volatile, sublimes, and is collected in 
 the form of a brilliant, steel-gray, brittle, seemingly 
 metallic mass. 
 
 Thus prepared, arsenic has a specific gravity of 
 5.7. There is also a black allotropic modification, 
 of which the specific gravity is only 4.71. When 
 heated under ordinary circumstances, it vaporizes 
 without first melting ; but, in a closed vessel, under 
 pressure, it may be fused. The density of the va- 
 por is 150, although the atomic weight of arsenic is 
 only 75. Hence the molecule of the free element 
 is As 4 , and similar in structure to the molecule of 
 phosphorus. The odor of the vapor resembles that 
 of garlic ; and its development before the blow-pipe 
 flame gives us an easy means of detecting arsenic in 
 minerals. A very impure arsenic is sometimes sold 
 
i6o 
 
 INORGANIC CHEMISTRY. 
 
 as a fly-poison, under the incorrect name of " co- 
 balt " ; but the only important use of the element is 
 for hardening lead shot. 
 
 In their chemical relations the compounds of 
 arsenic closely resemble those of phosphorus. They 
 are also in many respects quite similar to the corre- 
 sponding compounds of nitrogen. This is shown in 
 the following formulae : 
 
 NH 3 
 
 PH 3 
 
 AsH 3 
 
 N 2 3 
 
 P 2 3 
 
 As 2 O 3 
 
 N 2 6 
 
 P 2 6 
 
 As 2 O 6 
 
 HNO 8 
 
 HPO 
 
 
 
 H 3 PO 4 
 
 HaAsO 4 
 
 NC1 3 
 
 PC1 S 
 
 AsCl s , etc. 
 
 Like phosphorus, arsenic has a valency of either 
 three or five. 
 
 Arseniuretted hydrogen or arsine, AsH 3 , is a 
 colorless gas of terribly poisonous character. Its 
 discoverer, Gehlen, accidentally inhaled, a single 
 bubble of the pure compound, and died in conse- 
 quence. It is easily inflammable, depositing arsenic 
 upon any cold substance which may be inserted in 
 its flame ; and this fact is always applied in the de- 
 tection of arsenic. 
 
 EXPERIMENT 77. Generate hydrogen as in Ex- 
 periment 7 ; and, observing the necessary precau- 
 tions, kindle the stream of gas issuing at the jet. 
 Now pour into the generating-flask, through the 
 thistle-tube, a few drops of a solution of any com- 
 pound of arsenic. Hold a piece of cold porcelain 
 against the flame, and a black, mirror-like stain of 
 metallic arsenic will be deposited upon it. This 
 
ARSENIC, BORON, AND SILICON. 161 
 
 stain will be volatile, and may be driven away by 
 too much heat. Antimony compounds will give a 
 similar reaction, owing to the formation of SbH 3 ; 
 but the arsenic stain is soluble in a solution of so- 
 dium hypochlorite, whereas the antimony stain is 
 not. This test is known as Marsh's test for ar- 
 senic. 
 
 There are two oxides of arsenic, As 2 O 3 and 
 As 2 O 5 . The first of these, arsenic trioxide, is the 
 common white arsenic of commerce, well known on 
 account of its poisonous properties. It is formed 
 whenever arsenic is burned in the air; but it is 
 usually manufactured on a large scale by roasting 
 arsenopyrite, FeSAs. It is a white solid, which is 
 volatile at about 220 C., giving a colorless and 
 odorless vapor. It occurs in two different modifi- 
 cations one crystalline, the other amorphous; the 
 latter is the commercial form of the compound, 
 and usually is found in lumps which curiously re- 
 semble porcelain. It is slightly soluble in water, 
 forming probably arsenious acid, H 3 AsO 3 . From 
 this acid, many arsenites are derived, and some of 
 them have practical importance. Sodium arsenite 
 is used as a mordant in calico-printing ; and a dou- 
 ble salt of copper arsenite and copper acetate is 
 known commonly as Paris-green. This brilliant pig- 
 ment is used extensively for coloring wall-papers, 
 although the paper so tinted is certainly unwhole- 
 some. Whenever a sample of wall-paper is changed 
 from green to blue by a drop of ammonia-water, 
 or, when burned, gives a green tinge to the flame, 
 the presence of an arsenic green may safely be in- 
 ferred. The test is really a test for copper ; but 
 nearly all green pigments containing copper con- 
 
1 62 INORGANIC CHEMISTRY. 
 
 tain arsenic as well.* Paris-green is also used in 
 enormous quantities for the destruction of the Colo- 
 rado potato-beetle. Inasmuch as it is violently poi- 
 sonous, it should be handled with extreme care. 
 Arsenic trioxide itself is used in the preparation of 
 the foregoing compounds, in glass-making, and in 
 the manufacture of aniline red. When the last- 
 named color is carelessly made, it is apt to retain in- 
 jurious traces of arsenic. In cases of arsenical poi- 
 soning the best antidotes are freshly precipitated 
 ferric hydroxide and caustic magnesia. These sub- 
 stances unite with arsenious acid to form insoluble 
 arsenites, and thus prevent its absorption by the 
 system. An emetic is subsequently used to remove 
 the poison from the stomach. 
 
 Arsenic pentoxide, As 2 O 5 , is a white powder pre- 
 pared by oxidizing the trioxide with nitric acid. 
 It unites with water to form orthoarsenic acid, 
 H 3 AsO 4 , which is strictly analogous to orthophos- 
 phoric acid, H 3 PO 4 , and yields similar salts. No 
 acids of arsenic corresponding to pyrophosphoric 
 and metaphosphoric acids have yet been obtained ; 
 but pyroarsenates and metarsenates, resembling 
 the pyrophosphates and metaphosphates, are well 
 known. 
 
 The fluoride, chloride, and bromide of arsenic, 
 AsF 3 , AsCl 3 , and AsBr 8 , are all volatile liquids ; the 
 iodide, AsI 3 , is a solid compound. There are three 
 sulphides of arsenic, As2S 2 , As 2 S 3 , and AsgSg. The 
 first is a brilliant red mineral, called realgar ; and 
 the second, which is also a natural mineral, is the 
 
 * Brunswick-green, an oxychloride of copper, is the most important 
 exception to this statement. When doubt arises as to the presence of 
 arsenic, use Marsh's test for verification. 
 
ARSENIC, BORON, AND SILICON. ^3 
 
 golden-yellow orpiment. Both were formerly much 
 used as pigments. The trisulphide may be easily 
 produced artificially by adding a little hydrochloric 
 acid to a solution of the trioxide, and passing in a 
 stream of sulphuretted hydrogen. It forms a brill- 
 iant yellow precipitate. The pentasulphide is also 
 yellow, and is best known in combination with other 
 sulphides. For example, corresponding to sodium 
 arsenate, Na 3 AsO 4 , we have sodium sulpharsenate, 
 Na 3 AsS 4 . The latter is related to arsenic pentasul- 
 phide in the same way that the former is related to 
 arsenic pentoxide. Many similar double sulphides, 
 called by the general name of sulpho-salts, are well 
 known. 
 
 BORON, atomic weight 11, is a trivalent element 
 which occurs as a constituent of many minerals. It 
 is chiefly found, however, in boric (or boracic) 
 acid, H 8 BO 3 , and borax, an acid borate of sodium. 
 The element itself exists in two modifications ; the 
 one a dark-brown powder, the other a crystalline 
 variety. In the latter form, which is never quite 
 pure, boron has a specific gravity of 2.68, is infus- 
 ible, and is nearly as hard as diamond. The crys- 
 tals are square octahedra. 
 
 The compounds of boron are all formed upon a 
 simple trivalent type ; as, for example, the fluoride, 
 BF 3 , and the chloride, BC1 3 . The former is a color- 
 less gas, the latter is a volatile liquid. The hydride, 
 BH 3 , is also gaseous, and resembles NH 3 , PH 3 , and 
 AsH 3 in structure. From boron trioxide, B 2 O 3 , by 
 union with water, three acids are derived, as follows: 
 
 B 2 O 3 + H a O = 2HBO 2 , metaboric acid. 
 2B 2 O 3 + H 2 O = H 2 B 4 O 7 , pyroboric " 
 B 2 O 3 + 3H 2 O = 2H 3 BO 3 , orthoboric " 
 
1 64 
 
 INORGANIC CHEMISTRY. 
 
 Orthoboric acid, 
 B(OH) 8 , is chief- 
 ly obtained from 
 a volcanic region 
 in Tuscany. Jets 
 of steam, called 
 suffioni, there is- 
 sue from crevices 
 in a mountain- 
 side, bringing bor- 
 ic acid with them. 
 A tank of mason- 
 ry is built around 
 each jet, and filled 
 with cold spring- 
 water. This con- 
 denses the boric 
 acid, and then 
 flows to a lower 
 tank in which 
 more acid is re- 
 ceived, and so on 
 down to the foot 
 of the mountain 
 (Fig. 38). At the 
 bottom the water 
 is evaporated in 
 leaden pans, and 
 the acid is deposi- 
 ted in white, shin- 
 ing, crystalline 
 scales, which feel 
 something like pa- 
 raffin or sperma- 
 
ARSENIC, BORON, AND SILICON. 165 
 
 ceti. It is used for the manufacture of borax, or so- 
 dium pyroborate, Na 2 B 4 O7ioH 2 O. 
 
 Borax is by far the most important compound 
 of boron. It is not only made from boric acid, but 
 it is also found in great quantities in the water of 
 certain saline lagoons in Thibet, and in the Borax 
 Lake of California. It has a feebly alkaline reaction, 
 and is used to some extent in the household for 
 laundry purposes, and for driving away water-bugs. 
 Its important uses, however, are due to the power 
 which it possesses of dissolving, when in the fused 
 state, many metallic oxides. It serves as a flux in 
 metallurgical operations, and for cleansing metallic 
 surfaces which are to be brazed together. It is 
 also very largely employed in making colored glazes 
 and enamels for pottery and porcelain. Its use in 
 this direction is indicated on a small scale by its 
 applications to blow-pipe analysis. Make a small 
 loop on the end of a platinum wire, and fuse in it 
 enough borax to make a little, glassy bead. Add 
 to this a trace of any manganese compound, and 
 heat before the blow-pipe, and it will acquire an 
 amethystine tinge ; cobalt compounds will yield a 
 blue color, chromium compounds an emerald-green, 
 and so on. Each color gives a characteristic test 
 for the metal whose compounds produce it. 
 
 The ten molecules of water contained in borax 
 are called water of crystallization. Water so com- 
 bined forms an essential part of very many crys- 
 tallized salts, and is easily expelled by heating. 
 When borax is fused it first melts in its own water 
 of crystallization ; and when the latter is wholly 
 expelled, Na 2 B 4 O 7 remains behind. This anhydrous 
 borax, on account of its glassy appearance, is often 
 
1 66 INORGANIC CHEMISTRY. 
 
 called " glass of borax." When a solution of borax 
 is mixed with strong sulphuric acid, crystalline 
 scales of boric acid are deposited upon cooling. 
 
 EXPERIMENT 78. Dissolve a few crystals of 
 borax in the least possible quantity of water, and 
 add to the solution an equal bulk of strong sul- 
 phuric acid. Allow the mixture to cool, and note 
 the formation of boric acid. Transfer the whole to 
 a shallow porcelain or earthen dish, cover it with a 
 layer of strong alcohol, and ignite. The alcohol 
 will burn with a flame which is distinctly greenish, 
 especially upon the edges. By the production of 
 this green flame boric acid is easily detected analyt- 
 ically. 
 
 But one more non-metal remains to be con- 
 sidered ; namely, SILICON.* This element, after 
 oxygen, is the most important ingredient of the 
 earth's crust, and enters largely into the composi- 
 tion of all the commoner rocks except dolomite and 
 limestone. Granite, slate, clay, and sandstone are 
 all compounds of silicon. 
 
 The element itself has an atomic weight of 28, 
 and is, like carbon, quadrivalent. It is prepared by 
 heating together metallic potassium and potassium 
 silicofluoride, K 2 SiF 6 ; and, like carbon, may be ob- 
 tained in three different modifications. Of these, 
 one is an amorphous, dark-brown powder ; the sec- 
 ond forms hexagonal plates resembling graphite ; 
 and the third crystallizes in octahedrons. It fuses 
 at very high temperatures, and is insoluble in all 
 acids except hydrofluoric. It has no practical im- 
 portance. 
 
 The compounds of silicon are numerous and 
 
 * Sometimes called silicium. 
 
ARSENIC, BORON, AND SILICON. 167 
 
 complicated. With hydrogen it forms a colorless, 
 inflammable gas, SiH 4 ; with chlorine, bromine, and 
 iodine it yields the compounds SiCl 4 , SiBr 4 , and 
 SiI 4 . The compounds SiCl 3 Br, Si 2 Cl 6 , Si 2 Br 6 , and 
 Si 2 I 6 are also known. Silicon-chloroform, SiHCl 3 , 
 is interesting on account of its close similarity to 
 ordinary chloroform, CHC1 3 . There are several 
 series of silicon compounds which resemble in 
 chemical structure the organic compounds of car- 
 bon. 
 
 Silicon fluoride, SiF 4 , is a colorless, corrosive 
 gas which is produced whenever hydrofluoric acid 
 acts upon other silicon compounds. The corrosion 
 of glass by hydrofluoric acid is due to the forma- 
 tion of this fluoride. It is usually prepared by mix- 
 ing powdered fluor-spar, CaF 2 , with fine sand, and 
 heating the mixture in a glass flask with strong 
 sulphuric acid. If the gas is passed into water, a 
 complex reaction ensues ; a jelly-like mass of silicic 
 acid is deposited, and a new acid, hydrofluosilicic 
 acid, H 2 SiF 6 , remains in solution. This acid is much 
 used as a test reagent in chemical analysis. From 
 it, by replacement of hydrogen, a large series of 
 salts may be derived. 
 
 It is in its oxygen compounds, however, that 
 silicon is of the greatest importance. It forms one 
 well-defined oxide, SiO 2 , analogous to CO 2 ; and 
 this oxide is not only found by itself in nature, but 
 combined in a vast number of minerals. It also 
 occurs in the vegetable kingdom, giving strength 
 and stiffness to the stems of many plants. The 
 shiny surfaces of grass-stems, of rattan, and of the 
 scouring rush, are especially rich in silicon dioxide 
 or silica. 
 
1 68 INORGANIC CHEMISTRY. 
 
 In its purest form silica crystallizes in six-sided 
 prisms, and is called quartz or rock-crystal (Fig. 
 39). The crystals are often very large and very 
 limpid; and serve, when properly cut, for making 
 
 FIG. 39. Group of Quartz Crystals. 
 
 spectacle-lenses, or as substitutes for the diamond. 
 They are infusible, except before the oxyhydrogen 
 blow-pipe, and are hard enough to scratch glass. 
 Frequently quartz is colored by impurities, and 
 then is known by a variety of special names, such 
 as rose quartz, smoky quartz, etc. Yellow quartz 
 is called false topaz ; and the violet-colored variety 
 is the well-known gem amethyst. Chalcedony, 
 onyx, jasper, carnelian, agate, and flint, are merely 
 varieties of quartz ; sand and sandstone are the 
 same substance, more or less impure. Perfectly 
 white sand is nearly pure silica ; the yellowish and 
 reddish kinds owe their color to oxide of iron. 
 Opal is an amorphous silica, containing a little 
 water. 
 
 Silicon dioxide is insoluble in water, and is 
 attacked by no acid except hydrofluoric. Very 
 
ARSENIC, BORON, AND SILICON. 169 
 
 strong and hot alkaline solutions dissolve it slightly, 
 forming silicates ; but the latter compounds are best 
 prepared by fusing sand with sodium or potassium 
 carbonate. If the sand is not in excess, the fused 
 mass will dissolve in water, yielding a solution of 
 the alkaline silicate. These silicates of sodium and 
 potassium are known commonly under the name of 
 water-glass, and have various uses. They serve to 
 harden building-stones, and are used in making arti- 
 ficial stone ; they are introduced into certain kinds 
 of soap, and they are applied to mordanted calico 
 previous to dyeing. They vary in composition ; 
 but in general a silicate may be compared with the 
 corresponding carbonate, so that K 2 SiO 3 is similar 
 in structure to K 2 CO 3 . Most of the silicates, ex- 
 cept those just mentioned, are insoluble ; and the 
 majority of those known occur as natural minerals. 
 Feldspar, hornblende, mica, etc., are common exam- 
 ples; and garnet, emerald, topaz, and chrysolite 
 are well-known gems. Granite, syenite, trap, and 
 slate are mixtures of silicates, some of which are 
 exceedingly complicated in their composition. The 
 natural silicates are best described in the larger 
 treatises on mineralogy. 
 
 Glass, porcelain, and pottery are artificial mix- 
 tures of silicates. Porcelain and pottery, in general 
 terms, are more or less impure silicates of alumi- 
 num, and are infusible. Crown or window glass is 
 a silicate of calcium and sodium ; Bohemian glass is 
 a silicate of calcium and potassium ; flint or crys- 
 tal glass is a silicate of potassium and lead. Green 
 bottle-glass is like window-glass, except that it con- 
 tains silicates of iron derived from the cheap and 
 impure materials of which it is made. Other kinds 
 
i; INORGANIC CHEMISTRY. 
 
 of glass are also known, containing still other bases, 
 but they are unimportant.* 
 
 If hydrochloric acid be added to a strong solu- 
 tion of water-glass, a jelly-like mass of silicic acid 
 or silicic hydrate will separate out. To this mass 
 the formula Si(OH) 4 , which represents ortho-silicic 
 acid, is usually assigned ; but it rapidly loses wa- 
 ter and becomes converted into meta-silicic acid, 
 H 2 SiO 3 . If the solution of water-glass is sufficiently 
 dilute, no separation of silicic acid will occur, but 
 all will remain dissolved. Place such a solution in 
 a vessel made by tying a piece of bladder or parch- 
 ment-paper tightly over the bottom of a broad 
 wooden hoop, and partially immerse the latter in a 
 larger vessel of water for several days. The hydro- 
 chloric acid and the alkaline chloride will slowly 
 diffuse through the bladder into the water, and in 
 the hoop a clear, tasteless solution of silicic acid will 
 remain. This, upon long standing, will solidify to 
 a jelly. We have, then, two modifications of silicic 
 acid one soluble, the other insoluble and the 
 former is found in small quantities in many natural 
 waters. The geysers of Iceland and of the Yel- 
 lowstone Park contain it notably, and incrustations 
 of silicon dioxide are deposited around their edges. 
 The process by which the foregoing solution of 
 silicic acid was obtained is called dialysis. The hoop 
 and membrane constitute a dialyzer. Through such 
 a membrane crystallizable bodies, like salt, sugar, 
 etc., diffuse easily, while non-crystallizable bodies, 
 
 * The chemistry of glass and porcelain may be read up to advan- 
 tage in Roscoe and Schorlemmer's " Treatise on Chemistry," vol. ii, 
 part i, pp. 462-498 ; also in Wagner's * Chemical Technology," pp. 
 268-321. 
 
ARSENIC, BORON, AND SILICON. 171 
 
 like jellies, gum, glue, albumen, etc., can not pass 
 at all. These two classes of bodies are termed, re- 
 spectively, crystalloids and colloids ; and when they 
 occur in mixture they may be easily separated by 
 dialysis. 
 
CHAPTER XIX. 
 
 INTRODUCTORY TO THE METALS. 
 
 OF the seventy elements now known, fifteen 
 have been described as non-metallic ; the remaining 
 fifty-two being reckoned as metals. Of these, some, 
 like iron, copper, and lead, are familiar to every- 
 body ; while others, such as sodium and calcium, 
 are somewhat outside of ordinary experience. 
 
 Between the metals and the non-metals no sharp 
 line can be drawn. Neither group of elements can 
 be rigidly defined, for they shade off gradually into 
 each other. For example, arsenic and tellurium are 
 sometimes called metallic, and at other times non- 
 metallic ; and with good reasons either way. The 
 classification is merely one of convenience. 
 
 In general,, however, the metals are distinguished 
 by certain properties ; one of the most noteworthy 
 being the power of reflecting light in such a way as 
 to produce the brilliant metallic luster. This is best 
 seen on freshly-cut or scraped metallic surfaces be- 
 fore any film of rust or tarnish has had time to form. 
 This property is shared by two or three non-metals, 
 and by many compounds. * 
 
 In color, nearly all the metals are whitish or 
 grayish, like tin and silver. Calcium, strontium, and 
 gold, which are yellow, and copper, which is dull 
 
INTRODUCTORY TO THE METALS. 
 
 173 
 
 red, are the only distinct exceptions. All are 
 opaque, except occasionally in very thin layers. 
 For example, gold-leaf transmits a little light of a 
 greenish tinge. 
 
 Most of the metals are malleable and ductile ; 
 that is, they may be hammered into leaves and 
 drawn into wire. Antimony and bismuth, how- 
 ever, are brittle, and may be pulverized in a mor- 
 tar. In hardness they range from liquid mercury 
 and soft lead up to iridium, which will scratch the 
 hardest steel. In general, as compared with the 
 non-metals, they are good conductors of heat and 
 electricity. 
 
 In fusibility and specific gravity the metals dif- 
 fer widely. Mercury is liquid at all temperatures 
 above 39*5 C., while platinum and some allied 
 metals fuse only in the most intense heat of the 
 electric arc or the oxyhydrogen blow-pipe. In 
 lithium we have the lightest solid known, and in 
 osmium the heaviest. The subjoined table of spe- 
 cific gravity and melting-point will be found useful 
 for reference : 
 
 Melting-Point and Specific Gravity of some Metals. 
 
 NAME. 
 
 Melting- 
 point. 
 
 Specific 
 gravity. 
 
 NAME. 
 
 Melting- 
 point. 
 
 Specific 
 gravity. 
 
 Aluminum 
 Arsenic .... 
 
 850 
 
 2.583 
 e 727 
 
 Columbium .... 
 Copper % 
 
 IOQ1 
 
 7 .06 
 8.04.1: 
 
 Antimony 
 
 450 
 
 J ' ' 
 6.7OO 
 
 Didymium 
 
 
 6.S 44 
 
 Barium. . . . 
 
 
 3 71: 
 
 Gallium 
 
 10- is 
 
 C.OA 
 
 Bismuth 
 
 260 
 
 J'l 3 
 
 0.821 
 
 Glucinum 
 
 
 1.64 
 
 Cadmium. 
 
 3M 
 
 867 
 
 Gold 
 
 1200 
 
 10.208 
 
 Caesium 
 
 065 
 
 1.88? 
 
 Indium 
 
 176 
 
 7.421 
 
 Calcium 
 
 
 i t?8d 
 
 Iridium. 
 
 IQSO 
 
 22 421 
 
 Cerium . ... 
 
 
 6.728 
 
 Iron 
 
 ivy^VX 
 l800 
 
 7.8 
 
 Chromium 
 Cobalt . 
 
 1800 
 
 8.QS7 
 
 Lanthanum .... 
 Lead.. 
 
 112 
 
 6.163 
 
 II.W 
 
174 
 
 INORGANIC CHEMISTRY. 
 
 NAME. 
 
 Melting- 
 point. 
 
 Specific 
 gravity. 
 
 NAME. 
 
 Melting- 
 point. 
 
 Specific 
 gravity. 
 
 Lithium 
 
 1 80 
 
 0.585 
 
 Silver 
 
 IO4.O 
 
 IO.5I2 
 
 Magnesium 
 
 750 
 
 1.75 
 
 Sodium . 
 
 05.6 
 
 O.Q74. 
 
 Manganese 
 
 1000 
 
 8.013 
 
 Strontium 
 
 
 vx.y/ij. 
 
 2.58 
 
 Mercury 
 
 20.44 
 
 J 
 
 1^.506 
 
 Tantalum . 
 
 
 1078 
 
 Molybdenum . . . 
 
 
 8.60 
 
 Tellurium . 
 
 4.00 
 
 6.25 
 
 Nickel ... 
 
 l6oo 
 
 8 ooo 
 
 Thallium 
 
 200 
 
 1 1 QI 
 
 Osmium 
 
 
 22.4.77 
 
 Thorium . 
 
 
 1 1.2^ 
 
 Palladium 
 
 I 500 
 
 I2.O 
 
 Tin 
 
 215 
 
 7.3 
 
 Platinum 
 
 1770 
 
 21 5O4. 
 
 Tungsten 
 
 
 ' * 
 
 1 26 1 
 
 Potassium 
 
 62.5 
 
 0.871; 
 
 Uranium 
 
 
 18685 
 
 Rhodium 
 
 
 12 I 
 
 Vanadium 
 
 
 r r 
 
 Rubidium 
 
 38. 5 
 
 1. 52 
 
 Zinc 
 
 421 
 
 7 S iS 
 
 Ruthenium . . 
 
 
 J~, 
 12 2OI 
 
 Zirconium 
 
 
 A 1C 
 
 
 
 
 
 
 T" 1 5 
 
 The more important differences between the 
 metals and the non-metals, however, are not physi- 
 cal, but chemical. In general terms the oxides of 
 the non-metals unite with water to form acids, while 
 those of the metals produce bases. The only acid- 
 forming metallic oxides are those which contain 
 unusually large proportions of oxygen. In order 
 to make this matter clear, we must briefly consider 
 the subject of electro-chemistry. 
 
 Whenever a current of electricity is passed 
 through a compound liquid, the latter will be de- 
 composed into two parts. In Experiment 19, water 
 was so decomposed into oxygen and hydrogen, 
 which were collected in separate tubes placed over 
 the "poles," "terminals," or "electrodes," of the 
 galvanic battery. This method of decomposition 
 is called electrolysis, and the liquid which is analyzed 
 is known as the electrolyte. 
 
 In the battery itself, with which we effect elec- 
 trolysis, chemical action is taking place. In its 
 simplest form the galvanic battery consists of a 
 
INTRODUCTORY TO THE METALS. 175 
 
 plate of zinc and a plate of copper immersed in 
 dilute sulphuric acid, which acts unequally upon 
 the two metals. Whenever we have such an in- 
 equality of action between two conductors in a 
 conducting liquid, an electrical difference is pro- 
 duced which may be utilized as an electric current. 
 The greater the inequality of action the stronger 
 the current will be. In all cases the plate which is 
 most attacked will be electro-positive; the other 
 becoming at the same time electro-negative.* In 
 the forms of battery most generally in use, zinc is 
 the electro-positive element ; the material of the 
 other plate being varied. It would be possible, 
 however, to use with zinc a metal which should be 
 more vigorously attacked by sulphuric acid, and in 
 that case the zinc would become electro-negative. 
 When the terminal wires of a cell or battery are 
 connected, the current flows from the positive ele- 
 ment through the exciting liquid to the negative 
 element, and then through the wires back to the 
 positive plate to complete the circuit. 
 
 Now, when electrolysis takes place, as in the 
 decomposition of water, we have the two terminal 
 wires of the battery dipping separately into the 
 liquid. The latter is separated by the current into 
 two parts, one of which goes to one pole of the 
 battery, and the other to the other pole. The part 
 which appears at the pole connected with the zinc 
 plate, is electro-positive ; the part which appears at 
 the other pole is electro-negative. In short, all the 
 products of electrolysis exhibit electrical polarity ; 
 
 * For the full definition of these terms, as well as for the descrip- 
 tion of the different forms of battery, a work on physics must be con- 
 sulted. 
 
jy6 INORGANIC CHEMISTRY. 
 
 so that one becomes positive with respect to the 
 other. Oxygen is electro-negative, hydrogen is 
 electro-positive ; between the two there is a strong 
 chemical affinity. Between two electro-negative 
 or two electro-positive elements, affinity is weak. 
 Chemical affinity, then, bears a strong resemblance 
 to electrical and magnetic attractions. 
 
 If, now, we subject a great many compounds to 
 electrolysis, and note carefully at which electrodes 
 the products of decomposition appear, we shall be 
 able to arrange all the elements in an electro-chemical 
 series, as follows. For present purposes we may 
 ignore the rarer elements and confine our attention 
 to the commoner substances : 
 
 Electro-negative. 
 
 Oxygen. Antimony. Nickel. 
 
 Sulphur. Silicon. Iron. 
 
 Nitrogen. Hydrogen. Zinc. 
 
 Fluorine. Gold. Manganese. 
 
 Chlorine. Platinum. Aluminum. 
 
 Bromine. Mercury. Magnesium. 
 
 Iodine. Silver. Calcium. 
 
 Phosphorus. Copper. Strontium. 
 
 Arsenic. Bismuth. Barium. 
 
 Chromium. Tin. Lithium. 
 
 Boron. Lead. Sodium. 
 
 Carbon. Cobalt. Potassium. 
 
 Electro-positive. 
 
 In this series, which should be read as if it were 
 written in a single vertical column, each element is 
 negative to those which follow it, and positive to 
 those which precede it. Iodine, for instance, is the 
 negative element in potassium iodide, but positive 
 in its oxygen compounds. In general, however, 
 the non-metallic elements are strongly electro-negative, 
 
INTRODUCTORY TO THE METALS. 177 
 
 while the metals form the positive end of the chain. 
 Here we find the most essential difference between 
 the two classes of elements. It must never be for- 
 gotten that " positive " and " negative," as here 
 used, are only terms of comparison, and have no 
 final significance. An element is positive under 
 certain conditions, and negative under others, just 
 as a hill is said to be low when compared with a 
 mountain, and high when contrasted with a valley. 
 
 Electrolysis may be effected upon liquids under 
 very varying circumstances. The liquid may exist 
 at ordinary temperatures as a single, definite com- 
 pound ; it may be a substance kept in a state of 
 fusion at a high heat ; or it may consist of a salt 
 dissolved in some fluid like water. In the latter 
 case the chemical reactions may become quite com- 
 plicated, as the following experiment and its expla- 
 nation will show : 
 
 EXPERIMENT 79. Fill a U-tube (Fig. 40) with a 
 
 FIG. 40. Electrolysis of Na 2 SO 4 . 
 
 strong solution of sodium sulphate, colored with an 
 infusion of red cabbage. Into the solution, at the 
 two limbs of the tube, dip the terminals of a small 
 galvanic battery, and allow the current to pass. 
 
i;8 INORGANIC CHEMISTRY. 
 
 At the pole which is connected with the zinc of the 
 battery, the liquid will become alkaline, and turn 
 green ; at the other pole free acid may be detected, 
 and the color remains red. By electrolysis, then, a 
 neutral salt dissolved in water may be decomposed 
 into an electro-negative acid and an electro-positive 
 base. In the case under consideration, the reac- 
 tions are as follows : 
 
 First, the Na 2 SO 4 is split up into Na 2 and SO 4 . 
 The latter loses an atom of oxygen, which is given 
 off at the proper pole, leaving SO 3 . This unites at 
 once with water to form H 2 SO 4 . At the other side 
 of the equation the Na 2 decomposes some of the 
 water, evolving hydrogen, and forming sodium 
 hydroxide, NaOH, thus : 
 
 Na 2 + 2H 2 O = H 2 + 2NaOH. 
 
 The latter compound is a strong alkali, and readily 
 reunites with sulphuric acid, as follows : 
 
 2NaOH + H 2 SO 4 == Na 2 SO 4 + 2H 2 O. 
 
 Whenever any salt is electrolyzed, the acid por- 
 tion is separated as an electro-negative group of 
 atoms, and the basic portion as an electro-positive 
 group. The stronger the base or the acid, the 
 more distinctly marked its positive or negative 
 character will be. Most bases and most acids con- 
 tain hydroxyl, HO ; and when they unite they do 
 so with evolution of water, as in the equation last 
 given above. In forming a neutral salt, all of the 
 hydrogen contained in the hydroxyl of both acid 
 and base is thus removed. An acid salt retains 
 part of the hydrogen of the acid ; a basic salt re- 
 tains some oxygen from the hydroxyl of the base. 
 
INTRODUCTORY TO THE METALS. 179 
 
 In future chapters the applications of electroly- 
 sis to electrotyping and electroplating will be duly 
 described.* 
 
 The metals, like the non-metals, are best classi- 
 fied according to valency. Thus, sodium and po- 
 tassium are univalent, calcium and magnesium are 
 bivalent, gold is trivalent, and tin is quadrivalent. 
 The classification is most instructive, however, 
 when we consider all the elements together, and 
 ignore our old division into a metallic and a non- 
 metallic group. Let us begin by arranging some 
 of the elements in the order of their atomic weights, 
 starting with hydrogen, the lowest : 
 
 H ='i. 
 
 Li = 7. Gl = 9. B =11. C = 12. N=I4. O =16. F =19. 
 Na=23. Mg=24. Al=27. Si =28. P =31. S =32. Cl =35-5- 
 K =39. Ca=40. 80=44. Ti=48. V=5i.5. Cr=52. Mn=55. 
 
 If, now, we consider any horizontal line in this 
 table, we shall see that it begins with a univalent 
 element; the next is bivalent, the third trivalent, 
 the fourth quadrivalent, etc. Furthermore, the 
 elements which are closely related to each other 
 fall into the same vertical column, as Na and K, C 
 and Si, N and P, O and S, F and Cl. Toward the 
 left-hand side of the table the elements are strongly 
 basic; toward the right they are distinctly acid- 
 forming ; in the middle columns the electro-chemi- 
 cal character is less definitely marked. If we study 
 the chief oxides formed by these elements, some of the 
 regularities due to valency will become very clear : 
 
 Na 2 O. Mg 2 O 2 . Al a O 8 . Si 2 O 4 . P 2 O 6 . S 2 O. C1 2 O 7 . 
 K a O. Ca 2 O 2 . Sc 2 O 3 . Ti 2 O 4 . V 2 O 6 . Cr 2 O 8 . Mn a O 7 . 
 
 * Gore's work, " The Art of Electro-Metallurgy," is a most ex- 
 cellent little treatise upon this theme. 
 
180 INORGANIC CHEMISTRY. 
 
 Here the proportion of oxygen steadily increases 
 from one end of each line to the other. Six of the 
 formulas have been doubled in order to make this 
 ratio, which is only a ratio, more apparent. 
 
 We see, then, that the elements vary in their 
 chemical relations with a remarkable regularity, 
 and that they seem to be connected with each other 
 by some definite law. Were it not so, a bivalent 
 element might be followed by one which was quad- 
 rivalent, and its next neighbor in turn might have 
 any valency whatever. If we study the physical 
 properties of the elements, similar regularities will 
 confront us, at every step, of the most unmistak- 
 able character. In brief, it is now generally be- 
 lieved by chemists, although not as yet fully proved, 
 that all the properties of an element depend in some 
 way upon its atomic weight. For example, the 
 specific heat of an element is inversely proportional 
 to its atomic weight ; or, in other words, all the 
 elementary atoms have precisely the same capacity 
 for heat. This point will be brought out more 
 fully in another chapter. 
 
 On the opposite page a table of the elements 
 is given, based upon the principles developed in the 
 preceding paragraphs. This table is due chiefly 
 to a Russian chemist, D. Mendelejeff,* who was 
 able by means of it to predict the existence of 
 two new elements long before they were actually 
 discovered ; namely, gallium and scandium. Wher- 
 ever a blank occurs in the table, some element yet 
 to be discovered probably belongs. Such blanks 
 existed where gallium and scandium are now placed ; 
 
 * Similar tables were independently devised by Newlands and Lo- 
 thar Meyer. 
 
INTRODUCTORY TO THE METALS. 
 
 181 
 
 G ^ 
 
 >l 
 
 o co 
 
 HO 
 
 w 
 
 M 
 
 s- 
 
 So 
 
 * a 
 
 offi 
 
 4 
 
 ii 
 
 >., 
 N 
 
 
 Offi 
 
 c5 
 
 ^ 
 
 I! 
 
 g 
 O 
 
 to H 
 
 s 1! 
 
 u 
 
 
 II 2! 
 
1 82 INORGANIC CHEMISTRY. 
 
 and from their position Mendelejeff foretold not 
 only their existence, but also their leading proper- 
 ties. These predictions are now regarded as among 
 the most remarkable achievements of modern sci- 
 ence.* Unfortunately, the subject is not suited to 
 thorough treatment in an elementary text-book. 
 
 * For fuller discussions of Mendelejeff 's " Periodic Law," the 
 student may consult Roscoe and Schorlemmer's treatise, vol. ii, part 
 ii, p. 506; or Wurtz's "Atomic Theory," p. 154. 
 
CHAPTER XX. 
 
 THE METALS OF THE ALKALIES. 
 
 THE metals of the alkalies are five in number, 
 and form a very definite univalent group. They 
 exhibit a regular gradation in properties, which is 
 well indicated in the following: table : 
 
 
 NAME. 
 
 Atomic 
 
 weight. 
 
 Specific 
 gravity. 
 
 Melting- 
 point. 
 
 Lithium, 
 
 Li 
 
 7- ' 
 
 0.585 
 
 180. 
 
 Sodium, 
 
 Na (Natrium). . . . 
 
 27. 
 
 O 074. 
 
 05 6 
 
 Potassium, 
 
 K (Kalium) 
 
 ^o. 
 
 0.875 
 
 62.5 
 
 Rubidium 
 
 Rb 
 
 8c 5 
 
 1 52 
 
 l8 5 
 
 Caesium, 
 
 Cs 
 
 I?-z. 
 
 1.885 
 
 26 5 
 
 
 
 
 
 
 All of these metals are silver-white, and soft 
 enough to be easily cut with a knife. They are all 
 readily oxidizable so much so, that they have to 
 be kept under naphtha to preserve them from the 
 action of the air. Thrown upon water, they decom- 
 pose it, forming soluble hydroxides and setting hy- 
 drogen free. This is done quietly by lithium, very 
 violently by caesium ; the other metals of the group 
 being graded between these extremes. 
 
 EXPERIMENT 80. Throw into a vessel of cold 
 water a bit of potassium half as large as a pea. It 
 will fuse, move about rapidly on the surface of the 
 
 9 
 
1 84 INORGANIC CHEMISTRY. 
 
 water, and seemingly burst into violet-colored flame. 
 The flame is really due to the burning of the hydro- 
 gen which has been liberated. The color is caused 
 by the vapor of the potassium. Sodium, under simi- 
 lar circumstances, will act in much the same way, 
 only the action is not violent enough for the hydro- 
 gen to ignite. Thrown on wet paper, however, so 
 that the heat of action may be confined to one spot, 
 the hydrogen set free by the sodium will kindle, and 
 burn with a yellow flame. The yellow color is char- 
 acteristic of sodium and its compounds. 
 
 Concerning LITHIUM, RUBIDIUM, and CESIUM, 
 little need be said. All three are comparatively 
 rare. Lithium compounds are somewhat used in 
 medicine, and give a magnificent red color to a 
 flame. Rubidium and caesium resemble potassium 
 so closely that they are difficult to distinguish from 
 it. They were discovered by spectrum analysis, 
 which will be described in another chapter. The 
 best source of the three metals is the rare mineral 
 lepidolite. Csesium is the most electro-positive ele- 
 ment known. Hence it has a very strong affinity 
 for electro-negative oxygen. 
 
 Before the introduction of systematic names into 
 chemistry, soda, potash, and ammonia were known 
 as mineral alkali, vegetable alkali, and volatile alkali, 
 respectively. In 1807 Davy succeeded in decom- 
 posing soda and potash by means of a powerful elec- 
 tric current, and in isolating the metals which they 
 contained. Soon afterward, chemical methods of 
 preparing sodium and potassium were devised, the 
 best one consisting in heating the carbonates of the 
 metals with charcoal in an iron retort. The reac- 
 tion which takes place is as follows : 
 
THE METALS OF THE ALKALIES. 185 
 
 Na 2 CO 3 + 2C = Na 2 + SCO. 
 K a CO 3 + 2C = K a + 3CO. 
 
 The beak of the retort dips under naphtha in 
 which the vapor of the sodium or potassium, as it 
 distills over, is condensed. Both metals are easily 
 volatilized. As metals they have but few uses, al- 
 though their compounds are of the highest practi- 
 cal importance. Sodium is used to some extent in 
 the preparation of aluminum and magnesium, and 
 is also of value in some lines of chemical research. 
 
 SODIUM is one of the most abundant of elements. 
 The chloride exists in enormous quantities in sea- 
 water, in many salt-lakes and mineral springs, as 
 rock-salt, in marine plants, and in the various ani- 
 mal juices. The nitrate, the carbonate, and the bo- 
 rate occur in large natural deposits ; cryolite, a flu- 
 oride of sodium and aluminum, forms an inexhausti- 
 ble bed in Greenland ; many silicates contain sodi- 
 um as an essential ingredient. 
 
 The chief commercial source of sodium com- 
 pounds is sodium chloride, NaCl, or common salt. 
 Great beds of rock-salt, which is often perfectly 
 transparent, are worked at Northwich in England, 
 Wieliczka in Poland, Stassfurt in Germany, and 
 the Island of Petit Anse in Louisiana. Near Syra- 
 cuse, New York, Saginaw, Michigan, and in the 
 Kanawha Valley of West Virginia, salt is made in 
 vast quantities by the evaporation of natural brines 
 which rise through artesian wells from subterra- 
 nean springs. It is also prepared in many places 
 from sea-water. 
 
 Sodium chloride crystallizes in cubes, and has 
 a specific gravity of 2.15. As common salt, and in 
 its use as a food-preservative and condiment, it is 
 
1 86 INORGANIC CHEMISTRY. 
 
 familiar to every one. It is also used in great quan- 
 tities for the manufacture of chlorine and hydrochlo- 
 ric acid, as a fertilizer, and in the glazing of earthen- 
 ware. 
 
 Sodium forms two oxides, Na 2 O and Na 2 O 2 , but 
 neither is important. The hydroxide, NaOH, how- 
 ever, is of great importance. When sodium is 
 thrown into water, this substance, which is com- 
 monly called caustic soda, remains in solution ; but 
 practically it is usually prepared from the carbon- 
 ate. The latter is dissolved in water and mixed 
 with milk of lime ; calcium carbonate is deposited 
 as an insoluble white powder, and caustic soda re- 
 mains in solution. By boiling down in iron pans it 
 is obtained as a white solid, having a strong soapy 
 feel, and acting corrosively upon the skin. It is 
 one of the strongest alkalies. The reaction which 
 yields it may be written as follows : 
 
 Na 2 CO 3 + CaH 2 O 3 = 2NaOH + CaCO 3 . 
 
 Caustic soda is used in refining fats and oils, espe- 
 cially cotton-seed oil, and on a very large scale in 
 the manufacture of soap. Soap is a compound of 
 either alkali, with certain organic acids which are 
 found in fats and oils. The soda-soaps are hard 
 soaps, the potash-soaps are soft soaps. They are 
 produced by boiling the alkali with the fat ; and 
 from a chemical stand-point they are just as truly 
 salts of their respective acids as are the nitrates, 
 sulphates, or chlorides. A hard soap made from an 
 animal fat is mainly sodium stearate, QgH^NaC^. 
 
 Sodium carbonate, NagCOg, is a white solid hav- 
 ing a strong alkaline reaction. The base is so 
 strong, and the acid so weak, that in this salt the 
 
THE METALS OF THE ALKALIES. jg/ 
 
 basic character predominates. It crystallizes with 
 ten molecules of water of crystallization, Na 2 CO 3 , 
 ioH 2 O, and occurs in commerce both in this form 
 and dry. Crystallized sodium carbonate, or "sal 
 soda," is the common washing-soda of the laundries. 
 The dry carbonate is used in preparing other so- 
 dium compounds, and in enormous quantities in the 
 manufacture of glass and soap. Hence its prepara- 
 tion constitutes one of the largest chemical indus- 
 tries. 
 
 Sodium carbonate is commercially manufactured 
 by several processes ; but only one, the process in- 
 vented by Leblanc, is of sufficient importance to 
 warrant description here.* First, sodium chloride 
 is treated with sulphuric acid, yielding sodium sul- 
 phate and hydrochloric acid, thus : 
 
 2NaCl + H a SO 4 = 2HC1 + Na 2 SO 4 . 
 
 The operation is performed in a suitable furnace, 
 about half a ton of salt being treated at a time; 
 and the hydrochloric acid is in most establishments 
 
 FIG. 41. Black-ash Furnace. 
 
 condensed by water and saved. The crude sodium 
 sulphate is technically known as " salt-cake." 
 
 The second stage of the manufacture consists in 
 
 * Another process, the " ammonia-soda process," now bids fair to 
 supplant Leblanc's method. 
 
1 88 INORGANIC CHEMISTRY. 
 
 the conversion of the salt-cake into sodium carbon- 
 ate, and is called the " black-ash " process. Ten 
 parts of salt-cake, ten of limestone, in small frag- 
 ments, and seven and a half of coal, are heated 
 together in a reverberatory furnace until the mass 
 fuses, when it is taken out to cool. Two reactions 
 here take place ; first, the carbon of the coal with- 
 draws oxygen from the salt-cake, leaving sodium 
 
 sulphide : 
 
 Na 2 SO 4 + C 4 = Na 2 S + 4CO. 
 
 The limestone (calcium carbonate) next reacts upon 
 the sodium sulphide, forming by double decomposi- 
 tion calcium sulphide and sodium carbonate, as fol- 
 lows: 
 
 Na a S + CaCO 3 = Na 2 CO 3 + CaS. 
 
 By treating the black-ash with water, the sodium 
 carbonate is dissolved out, and afterward, by evap- 
 oration, it is obtained in crystals. These, calcined, 
 yield the dry carbonate, which is the soda-ash of 
 commerce. The calcium sulphide, which remains 
 undissolved, is worked over for the recovery of the 
 sulphur which it contains ; so that from first to last, 
 during the entire process, little or nothing is lost 
 or wasted. In Great Britain alone, at least half a 
 million tons of common salt are annually convert- 
 ed into sodium carbonate. In consequence of Le- 
 blanc's process sal-soda now costs less than one tenth 
 of what it did a century ago ; and, of course, glass 
 and soap have been proportionally cheapened. Al- 
 though the whole world has been benefited by the 
 invention, Leblanc himself was allowed to die in ab- 
 ject misery. 
 
 When the crystallized sodium carbonate is ex- 
 
THE METALS OF THE ALKALIES. 189 
 
 posed to the action of carbon dioxide, sodium 
 hydrogen carbonate, NaHCO 3 , or " bicarbonate of 
 soda " is produced. This is the common cooking- 
 soda of the household, and an important constituent 
 of all baking-powders. It is also used in medi- 
 cine, and in the preparation of various effervescent 
 drinks. 
 
 Only a few other sodium salts require especial 
 mention here. The sulphate, Na 2 SO 4 , is important 
 as salt-cake; and, crystallized, as Na 2 SO 4 ,ioH 2 O, 
 it is known as Glauber's salts, and has some me- 
 dicinal value. The acid sulphate, NaHSO 4 , is used 
 in chemical analysis. The nitrate, NaNO 3 , is found 
 in large beds in Chili, Peru, and Bolivia, whence 
 its commercial name of Chili saltpeter. It is used 
 as a fertilizer, in the manufacture of nitric acid, and 
 for the preparation of common saltpeter. Sodium 
 thiosulphate, Na 2 S 2 O 3 , 5H 2 O, has already been men- 
 tioned on account of its use in photography ; sodium 
 hypochlorite, NaCl 2 O 2 , has some applications as a 
 disinfectant ; the chlorate, NaQO 3 , is employed as 
 an oxidizing agent in dyeing with aniline black ; 
 and one of the phosphates, Na 2 HPO 4 , i2H 2 O, is an 
 important laboratory reagent, and also of value 
 medicinally. Borax, Na 2 B 4 O 7 , ioH 2 O, and sodium 
 silicate or water-glass, have been sufficiently de- 
 scribed in previous chapters. 
 
 POTASSIUM, although less widely diffused in na- 
 ture than sodium, is still one of the most abundant 
 elements. It is contained in most granitic rocks, 
 whence it finds its way into the soil, from which it 
 is extensively taken up by growing plants. For- 
 merly its compounds were almost exclusively ob- 
 tained from wood-ashes, whence the old name of 
 
190 INORGANIC CHEMISTRY. 
 
 vegetable alkali, as applied to its carbonate. To- 
 day, great quantities of potassium salts are derived 
 from the Stassfurt salt-beds. 
 
 There are two oxides of potassium, K 2 O and 
 K 2 O 4 . From the first, potassium hydroxide, KOH, 
 or caustic potash, is derived. Practically, however, 
 this important compound is prepared from potas- 
 sium carbonate by treatment with milk of lime, just 
 as in the preparation of caustic soda. It closely 
 resembles the latter substance, and is used for 
 similar purposes. 
 
 Potassium carbonate, K 2 CO 3 , is the familiar sub- 
 stance potash. The simplest mode of preparing 
 this compound is to boil wood-ashes with water, 
 and afterward to evaporate the solution. Until a 
 few years ago, nearly all the potash of commerce 
 was obtained from this source ; but now a variety 
 of other sources are available. First, potassium 
 chloride and potassium sulphate are found in large 
 quantities in the Stassfurt salt-beds. These are 
 treated by Leblanc's process in just the same man- 
 ner as the corresponding sodium compounds, and 
 yield potassium carbonate by precisely similar re- 
 actions. Secondly, the residues left behind in the 
 manufacture of beet-root sugar, yield annually some 
 thousands of tons of potash. Thirdly, there is the 
 most extraordinary source of all. Sheep, when 
 feeding, take up large quantities of potassium salts 
 from the soil. These are exuded in the perspira- 
 tion, and remain adhering to the wool. When the 
 wool is washed at some of the great European 
 centers of the woolen industry, the wash-water is 
 evaporated to dryness, and a substance known as 
 " suint " is obtained. This, which contains the 
 
THE METALS OF THE ALKALIES. 191 
 
 potassium salts of certain organic acids, is heated 
 in iron retorts, giving off a fair quality of illuminat- 
 ing gas. From the charred residue, water extracts 
 potassium carbonate. By this curious process, 
 which splendidly illustrates the way in which 
 chemistry utilizes seemingly worthless materials, 
 at least a thousand tons of potash are annually 
 made. 
 
 Potassium carbonate, when pure, is a white salt 
 containing no water of crystallization. It has a 
 strong alkaline taste and reaction, and is used for 
 preparing other potassium compounds, and for the 
 manufacture of glass and soft soap. By treatment 
 with carbon dioxide, it yields a " bicarbonate," 
 KHCO 3 . 
 
 Potassium chloride, bromide, and iodide, are all 
 white salts, which crystallize in cubes. The chloride 
 is chiefly used, as above indicated, in the prepara- 
 tion of the carbonate ; the bromide and iodide are 
 important medicinally. The formulae, potassium 
 being univalent, are naturally KC1, KBr, and KI. 
 
 Two other salts of potassium are of great practi- 
 cal importance, the chlorate and the nitrate, KC1O S 
 and KNO 3 . The properties of the chlorate, and its 
 uses for making oxygen and in pyrotechny, have 
 been sufficiently indicated in previous chapters. It 
 is also used in medicine, for allaying inflammation 
 of the throat, in calico-printing, and in the manufac- 
 ture of matches. 
 
 Potassium nitrate, popularly known as saltpe- 
 ter or as niter, is a salt which crystallizes easily in 
 long, white prisms. It occurs naturally in the soil 
 in many tropical countries, especially in Egypt and 
 the East Indies, and is extracted easily by solution 
 
192 
 
 INORGANIC CHEMISTRY. 
 
 in water. It originates from the oxidation of or- 
 ganic matter rich in nitrogen, in presence of potas- 
 sium compounds. In Sweden much saltpeter is 
 prepared artificially by piling up animal refuse- with 
 lime, soil, and a little potash ; and, after a proper 
 period of time, leaching the mass with water. It is 
 also made by double decomposition from the crude 
 potassium chloride of Stassfurt and the cheaper 
 Chili saltpeter. 
 
 KC1 + NaNO 3 = NaCl + KNO 3 . 
 
 It is used in the preservation of meat, and in the 
 manufacture of gunpowder. 
 
 Gunpowder is a mechanical mixture of char- 
 coal, sulphur, and saltpeter. A good average pow- 
 der is composed, by percentages, as follows : 
 
 KNO 3 , 75 
 C, 15 
 
 S, 10 
 
 IOO 
 
 When gunpowder burns, there is a great and sud- 
 den evolution of gas ; and to the expansion of the 
 latter the force of explosion is due. A cubic centi- 
 metre of powder gives about 280 cc. of gas ; and 
 the reaction, which in reality is very complicated, 
 is approximately represented by the subjoined equa- 
 tion : * 
 
 2KN0 3 + S + 3C = K 2 S + N 2 + 3 CO 2 . 
 
 The total explosive force of a pound of gunpow- 
 der, expressed in mechanical terms, is equivalent 
 
 * There is a good discussion of this subject in Roscoe and Schor- 
 lemmer's '* Treatise on Chemistry," vol. ii, part i, pp. 8 1-88. 
 
THE METALS OF THE ALKALIES. JQJ 
 
 to a power of lifting a weight of 486 tons one foot 
 high. 
 
 AMMONIUM, NH 4 , is a compound radicle which 
 is most conveniently studied in connection with the 
 alkaline metals. It plays the part of a metal, and 
 its salts in many respects are very similar to those of 
 potassium. When ammonia, NH 8 , is brought into 
 contact with HCl, union takes place, and NH 4 C1 is 
 formed. So also, when ammonia is passed into wa- 
 ter, the strongly alkaline solution may be regarded 
 as having the formula NH 3 , H 2 O, or NH 4 OH. In 
 one compound, we have the chloride of NH 4 , and 
 in the other an alkaline hydroxide similar in char- 
 acter to KOH and NaOH. Like the latter hy- 
 droxides the ammonium hydroxide or caustic am- 
 monia is capable of saturating the strongest acids, 
 and of forming crystalline salts in which the NH 4 
 plays precisely the same part as K or Na. In NH 4 , 
 which has not yet been obtained by itself, an atom 
 of quinquivalent nitrogen has four of its bonds of 
 valency saturated ; and by virtue of the one which 
 remains it is univalent. For convenience, we may 
 treat ammonium as if it were really a metal having 
 an atomic weight of 18, and designate it by the pro- 
 visional symbol Am. 
 
 Most of the ammonium salts are prepared by 
 saturating aqua ammonia with acids ; although in 
 practice there are some exceptions. The chloride, 
 AmCl, is a white salt which occurs in commerce in 
 tough fibrous masses. It is purified by sublimation, 
 being readily volatile. From its formula the den- 
 sity of its vapor should be - - = 26.75 ; 
 
 whereas experiment gives it a density only one half 
 
194 
 
 INORGANIC CHEMISTRY. 
 
 as great. That is, its vapor forms four volumes in- 
 stead of agreeing with the two-volume law. This 
 anomaly has been explained by showing that at 
 high temperatures the compound NH 4 C1 can not 
 exist ; but splits up into NH 3 and HC1, each repre- 
 sented by two volumes. On cooling, the parts re- 
 combine, again forming NH 4 C1. This splitting up 
 so as to give an unusual vapor-density is called dis- 
 sociation, and many examples of it are known. The 
 explanation is not wholly theoretical, but rests upon 
 solid experimental demonstrations. 
 
 Ammonium chloride has some medicinal use, 
 is largely employed in dyeing, and is a source 
 of other ammonium compounds. In soldering and 
 tinning it serves to cleanse the metallic surfaces. 
 Ammonium sulphate, Am 2 SO 4 , is important as a fer- 
 tilizer; the nitrate, AmNO 3 , is used in making ni- 
 trous oxide ; and a phosphate of sodium, hydrogen, 
 and ammonium, NaHAmPO 4 , 4H 2 O, microcosmic 
 salt, is a useful reagent in blow-pipe analysis. 
 
 When hydrogen sulphide, H 2 S, is passed into 
 aqua ammonia, ammonium hydrosulphide, AmSH, 
 is formed. There are also several sulphides of am- 
 monium, of which Am 2 S is the most typical. These 
 compounds are much used as test reagents in chem- 
 ical analysis. 
 
 EXPERIMENT 81. Dissolve in water, in separate 
 test-tubes, fragments of zinc sulphate, iron sulphate, 
 copper sulphate, manganese chloride, arsenious ox- 
 ide, and tartar emetic. Add to each solution a drop 
 of ammonium hydrosulphide, and note the color of 
 the precipitate. On adding an excess of the re- 
 agent, the arsenic and antimony precipitates will 
 redissolve. 
 
THE METALS OF THE ALKALIES. 
 
 195 
 
 Ammonium carbonate is another salt which is 
 used in medicine and as a reagent in analysis. It 
 has a complicated formula, and occurs in commerce 
 under the name of sal-volatile. It smells strongly 
 of ammonia, and is often met with in the form of 
 " smelling-salts/' 
 
 From ammonia and ammonium a number of 
 other strong bases are derived, which will be de- 
 scribed in connection with organic chemistry. 
 
CHAPTER XXI. 
 
 SILVER AND THALLIUM. 
 
 SILVER, which is also a univalent metal, is found 
 in nature both free and in a great variety of com- 
 pounds. The native metal, pure or nearly pure, 
 sometimes occurs in quite large masses ; but the 
 more important ores of silver are compounds. 
 Among them are found the chloride, bromide, io- 
 dide, sulphide, and telluride, and many double 
 compounds containing the sulphide united with 
 sulphides of arsenic and antimony. In some cases 
 the silver seems to be merely an impurity, as in 
 certain ores of copper and lead, from which the 
 more precious metal also may be extracted. 
 
 Silver is obtained from its ores by a great va- 
 riety of processes, concerning which a treatise on 
 metallurgy may be consulted. Only two of them 
 can be considered here. First, there is the amal- 
 gamation process, which is essentially as follows: 
 The finely-powdered ore is roasted in a reverbera- 
 tory furnace with a quantity of common salt, where- 
 by the silver is converted into chloride. The mass 
 is then mixed with water to a thin paste, and shaken 
 up with scrap-iron in revolving casks for several 
 hours. The iron withdraws the chlorine from the 
 silver, thus : 
 
SILVER AND THALLIUM. 
 2AgCl + Fe = FeCl 2 + Ag a . 
 
 197 
 
 Mercury is next added, and the agitation is contin- 
 ued until an amalgam of silver and mercury is ob- 
 tained. From this the mercury is distilled off, and 
 the silver, often containing gold, remains behind. 
 
 FlG. 42. Pattinson's Silver-Lead Process. 
 
 Secondly, there is the Pattinson process, by 
 which the traces of silver that often occur in lead- 
 ores may be separated from the lead. The latter is 
 first melted and allowed partially to cool ; crystals 
 of lead separate out, and are removed by a strainer, 
 and a richer alloy is left behind. This is remelted, 
 and the process of partial cooling and straining is 
 
198 INORGANIC CHEMISTRY. 
 
 continued until an alloy containing at least three 
 hundred ounces of silver to the ton is obtained. 
 This alloy is then cupelled a process in which it is 
 melted on a porous bed of bone-ash in presence of 
 a blast of air. The lead is oxidized, the fused ox- 
 ide is absorbed by the bone-ash, and at last a button 
 of pure silver remains. 
 
 Silver is a brilliant white metal, of atomic weight 
 108, and specific gravity 10.512. Its symbol is Ag, 
 from the Latin argentum. It melts at about 1040 
 C., and at very high temperatures it may be vapor- 
 ized and distilled. Its vapor has a bright blue color. 
 Melted silver absorbs many times its bulk of oxygen 
 from the air, and gives it out again upon cooling ; 
 often so suddenly as to cause an explosive spatter- 
 ing (called spitting] of the semi-fluid metal. Silver 
 is the best known conductor of heat and electricity, 
 and is exceedingly malleable and ductile. In the 
 arts it is usually alloyed with a little copper, which 
 hardens it. The American coinage standard is 900 
 fine that is, 1,000 parts of the metal used for coin- 
 ing contain 900 parts of silver to 100 of copper. 
 English silver coins are 925 fine. Jewelers' silver 
 is generally less fine. 
 
 The compounds of silver are, with a few excep- 
 tions, formed on the same type as those of the al- 
 kali metals. Thus, we have an oxide, Ag 2 O ; a sul- 
 phate, Ag 2 SO 4 ; a nitrate, AgNO 3 ; and a chloride, 
 AgCl. In general, the salts of silver do not con- 
 tain water of crystallization. The sulphide, Ag 2 S, 
 is interesting as a natural ore, and on account of 
 the ease with which it is produced artificially. The 
 blackening of silver-ware is due to H 2 S in the at- 
 mosphere ; and the blackening of spoons by eggs is 
 
SILVER AND THALLIUM. 
 
 199 
 
 caused by the sulphur which the latter contain. 
 Pass a bubble of H 2 S into a solution of silver ni- 
 trate, and a black precipitate of silver sulphide will 
 form. 
 
 The most important compounds of silver are the 
 chloride and the nitrate. Some of their relations 
 to each other and to the metal may be profitably 
 studied by experiment. 
 
 EXPERIMENT 82. Cover a small silver coin, 
 either in a glass beaker, flask, or porcelain dish, 
 with a mixture of half-and-half nitric acid and wa- 
 ter. Upon heating, the coin will dissolve, and the 
 solution will have a blue color due to the copper 
 which is present. Add a solution of common salt, 
 Nad, in considerable excess, and shake vigorously. 
 Silver chloride, which is insoluble, will be precipi- 
 tated, while all the copper will remain dissolved. 
 Filter, and wash the precipitate thoroughly by 
 pouring water over it until the liquid runs through 
 colorless. Transfer the silver chloride, still moist, 
 to a porcelain dish, add some clippings of zinc, and 
 cover the mixture with dilute sulphuric acid. By 
 the action of the latter on the zinc, hydrogen will 
 be evolved, which, at the instant of its liberation, 
 in the nascent state, will withdraw chlorine from the 
 silver chloride, forming hydrochloric acid, and set- 
 ting the metal free. When all the zinc has been 
 dissolved, silver will remain as a black, spongy mass, 
 which may be either melted into a globule before 
 the blow-pipe, or dissolved in nitric acid to form 
 pure AgNO 3 . From its colorless solution the latter 
 compound is deposited in tabular, transparent crys- 
 tals. This experiment shows, on a small scale, the 
 exact method by which the officers of a mint or 
 
200 INORGANIC CHEMISTRY. 
 
 silver-refinery prepare pure silver from crude bull- 
 ion. 
 
 The formation of silver chloride in the foregoing 
 experiment is according to the equation 
 
 AgNO 3 + NaCl = NaNO 3 + AgCl, 
 
 and well illustrates what is called double decomposi- 
 tion. Silver and sodium change places, as also do 
 the nitric-acid radicle and chlorine ; and two new 
 salts result from the mutual transfers. We have 
 already met with several examples of this sort 
 of chemical change, and we shall meet with many 
 more as we go on. They all come under one of 
 two laws, which, having been first announced by 
 Berthollet, are known as Berthollefs laws, and are as 
 follow : I . Whenever two substances in solution together 
 are capable of exchanging atoms so as to form a compound 
 insoluble in the solvent employed, that compound will be 
 produced and deposited as a precipitate. 2. Whenever 
 two substances in mixture are capable of exchanging 
 atoms so as to form a compound which is gaseous at the 
 temperature of the experiment, that compound will be 
 evolved as a vapor or gas. The case in point illus- 
 trates the first law ; the second may be exemplified 
 by heating together ammonium chloride and hy- 
 drogen sodium carbonate. Ammonium carbonate, 
 which is volatile, will be set free, and sodium chlo- 
 ride will remain. 
 
 NaHCO 3 + AmCl = NaCl + AmHCOs. 
 
 In the actual experiment the NH 4 , HCO 3 splits up 
 into NH 3 + CO 2 -t- H 2 O. This particular mixture 
 has been proposed, and slightly used, for a baking- 
 powder. 
 
SILVER AND THALLIUM. 2 QI 
 
 Silver chloride, as obtained in Experiment 82, is 
 a white, curdy precipitate which darkens on expos- 
 ure to light. If potassium bromide or iodide be 
 used in place of common salt, silver bromide or 
 iodide will be thrown down. The latter is yellow, 
 the bromide is yellowish white. All these com- 
 pounds are sensitive to light, and they are therefore 
 of great importance in the art of photography. 
 
 We have already seen, in studying the formation 
 of hydrochloric acid, that light may bring about 
 chemical union. It may also effect chemical de- 
 composition ; and this is especially the case with 
 most of the salts of silver. All, or nearly all of 
 them, when in contact with organic matter, are 
 blackened by light most where the light is strong- 
 est, less where it is weaker. This fact is the foun- 
 dation principle of photography,* which, in its 
 commonest form, is essentially as follows : 
 
 A glass plate is first coated with a film of collo- 
 dion, which is prepared by dissolving gun-cotton in 
 a mixture of alcohol and ether, and adding to it 
 certain bromides or iodides. The plate is next 
 dipped into a solution whereof silver nitrate is the 
 chief ingredient, and either the bromide or iodide 
 of silver is precipitated in the collodion-film. Hav- 
 ing been thus prepared in a dark room, the plate is 
 transferred to the photographic camera, and the 
 image of the scene or object to be photographed 
 is allowed to fall upon it. Where the object is 
 light, the plate is strongly affected ; where it is 
 
 * Captain Abney's " Treatise on Photography " is one of the best 
 of the smaller works on this subject ; Vogel's " Chemistry of Light 
 and Photography" ("International Scientific Series," vol. xiv) is also 
 very good. 
 
202 INORGANIC CHEMISTRY. 
 
 dark, the action is slighter; so that the picture 
 which is produced has all its lights and shadows 
 reversed, and is called a " negative." When first 
 taken from the camera, the plate shows no signs of 
 alteration ; but the image is brought out by pour- 
 ing over the plate a chemical solution known as 
 the developer. For this purpose various substances 
 are used, ferrous sulphate being the commonest.* 
 Finally, the plate is washed with a solution of sodium 
 thiosulphate, which dissolves out the silver salts 
 which have been unattacked, and the picture is thus 
 rendered permanent. In " printing " from this nega- 
 tive, a sheet of paper is rendered sensitive by silver 
 nitrate, and exposed underneath the plate to the 
 action of strong sunlight. Where the negative is 
 dark the paper remains light, and vice versa ; so 
 that an image which is correct as to lights and 
 shadows is produced. This, too, is " fixed " by so- 
 dium thiosulphate, and, after some little details of 
 finishing, the photograph is done. 
 
 EXPERIMENT 83. Soak a sheet of white paper 
 in a solution of silver nitrate. Place over it a piece 
 of lace or a fern-leaf, cover it by a sheet of glass, 
 and expose it to the sunshine until all the uncov- 
 ered portions are darkened. Wash it in a dark 
 room or closet, first with a solution of sodium thio- 
 sulphate, and afterward with pure water, continu- 
 ing the latter until the rinsings no longer have a 
 sweetish taste. A perfect copy of the lace pattern 
 or leaf will remain as a photographic print on the 
 paper. 
 
 Silver nitrate, which is always prepared by dis- 
 
 * The theory of the action of the developer is somewhat obscure, 
 and would be out of place in this treatise. 
 
SILVER AND THALLIUM. 203 
 
 solving silver in nitric acid, occurs in commerce 
 in two forms : First, we find it in large, trans- 
 parent, tabular crystals, in which form it is used 
 for various laboratory purposes, by the photogra- 
 phers, and in the art of electroplating ; second, 
 the fused salt is cast in small, round sticks, which 
 are used by physicians under the name of " lunar 
 caustic." It is applied to the cautery of inflamed 
 surfaces. 
 
 When a little potassium cyanide, KCN, is added 
 to a solution of silver nitrate, a precipitate of silver 
 cyanide, AgCN, closely resembling the chloride, is 
 formed. Upon the addition of more KCN, the 
 precipitate redissolves, and a solution is produced 
 which is much used in silver-plating.* In such a 
 solution, the preparation of which is subject to 
 many variations, the object to be plated is im- 
 mersed, together with a bar, rod, or plate of pure 
 silver. The latter is connected by a wire with the 
 negative element of a battery, while the object to 
 be plated is connected with the other pole. When 
 the current passes, electrolysis takes place, and sil- 
 ver is deposited upon the object in a thin, coherent 
 film. At the same time silver is dissolved off from 
 the plate at the opposite pole. The process con- 
 tinues until the plating has acquired whatever 
 thickness may be demanded ; afterward the plated 
 article is washed and polished. The same general 
 method, but with different solutions, is employed 
 in plating with gold, copper, platinum, or nickel. 
 
 THALLIUM, atomic weight 204, is one of the very 
 rare metals. It was discovered in 1861 by Crookes, 
 
 * For full details as to solutions and processes, see Gore's " Elec- 
 tro-Metallurgy." 
 
204 INORGANIC CHEMISTRY. 
 
 with the aid of the spectroscope, and in its general 
 properties it strongly resembles lead. Its com- 
 pounds give a brilliant green color to flame, and 
 are mostly poisonous. It forms two sets of salts 
 the thallious and thallic compounds ; behaving like 
 a univalent element in the first, and being trivalent 
 in the second. It occurs as an impurity in iron 
 pyrites and in native sulphur, and is usually ob- 
 tained from the flue-dust of sulphuric-acid works. 
 
CHAPTER XXII. 
 
 CALCIUM, STRONTIUM, AND BARIUM. 
 
 THE bivalent metals are quite numerous, and 
 form several well-defined sub-groups. In one of 
 these we find the three closely allied metals whose 
 names head this chapter. 
 
 
 Atomic weight. 
 
 Specific gravity. 
 
 Calcium Ca 
 
 4.O 
 
 1.58 
 
 Strontium, Sr 
 
 87.5 
 
 3 
 
 2.58 
 
 Barium Ba 
 
 1 17 
 
 -3 7C 
 
 
 
 
 In general, strontium and its compounds have 
 properties nearly midway between those of the 
 other two metals. For instance, strontium sulphate 
 is less soluble in water than calcium sulphate, and 
 more so than barium sulphate ; and in specific 
 gravity it also lies between the two. In short, if 
 we know the properties of two corresponding salts 
 of barium and calcium, we can make a close guess 
 as to what the properties of the similar strontium 
 salt will be. The metals themselves are unimpor- 
 tant, and difficult to obtain. Calcium is yellow, 
 strontium yellowish, barium white. All three are 
 fusible only above a red heat, all oxidize easily in 
 the air, all are malleable and ductile. 
 
206 
 
 INORGANIC CHEMISTRY. 
 
 CALCIUM is one of the most abundant of ele- 
 ments. As carbonate we find it in nature in the 
 form of limestone, marble, chalk, coral, marl, etc. 
 It enters into the composition of many silicates; 
 the sulphate, fluoride, and phosphate are abundant 
 minerals ; and the phosphate is also an important 
 ingredient of plants and of bones. 
 
 Calcium oxide, CaO, is commonly known as 
 quicklime. It is always prepared by heating the 
 carbonate, which is decomposed in accordance with 
 the following reaction : 
 
 CaCO 3 = CaO + CO a . 
 
 On a large scale, limestone is burned in a lime-kiln 
 (Fig. 43), and the lime remains behind. It is a 
 white, infusible solid, which 
 unites violently with water, 
 evolving great heat, and form- 
 ing the hydroxide, CaH 2 O 2 . 
 The latter formula may also be 
 written Ca(OH) 2 , to illustrate 
 the bivalency of the metal. 
 
 Calcium hydroxide, or 
 slaked lime, is a very useful 
 compound. The heat attend- 
 ing its formation may be ob- 
 served by sprinkling a lit- 
 tle cold water over a lump 
 of lime and noting that steam 
 is evolved. Fires are often 
 
 caused by the accidental contact of water with 
 lime which has been stored in leaky buildings. 
 Under such circumstances, in a closed space, the 
 heat may be sufficient to kindle wood. 
 
 FIG. 43. Lime-Kiln. 
 
CALCIUM, STRONTIUM, AND BARIUM. 207 
 
 Just as sodium hydroxide is called caustic soda, 
 so calcium hydroxide is often called caustic lime. 
 It has a strong- alkaline reaction, neutralizes acids, 
 and attacks organic matter vigorously. It is often 
 used as a fertilizer, inasmuch as it helps to rot or- 
 ganic substances in the soil ; and in tanneries it is 
 applied to hides to aid in the removal of hair. As 
 milk of lime that is, suspended in water it serves 
 as whitewash ; and it is also used in purifying coal- 
 gas, in making bleaching-powder and the caustic 
 alkalies, and for a great variety of other chemical 
 purposes. But the larger uses of slaked lime are 
 in the preparation of mortars and cements. Mortar 
 is made by mixing lime with water and sand ; for 
 interior plastering hair is added, to bind the mass 
 together. When first mixed, mortar is soft and 
 pasty ; on drying it hardens, absorbs carbon di- 
 oxide from the air, and forms a substance which in 
 time becomes almost as compact as stone. In very 
 old brick-work, the mortar is often harder and 
 stronger than the bricks themselves. Hydraulic 
 lime, which forms a cement capable of hardening 
 under water, is made by burning a limestone mixed 
 with clay. 
 
 The extensive occurrence of calcium carbonate 
 in nature has already been noticed. In its purest 
 state this substance forms transparent crystals, 
 which vary remarkably in character. One variety 
 is known as Iceland-spar (Fig. 44), and is doubly 
 refracting that is, a line or object seen through it 
 appears to be doubled. Iceland-spar is much used 
 in instruments for studying polarized light. In 
 pure water calcium carbonate is very slightly solu- 
 ble ; more so in water containing carbonic acid. 
 
208 INORGANIC CHEMISTRY. 
 
 EXPERIMENT 84. Into a test-tube filled with 
 lime-water pass a bubble of carbon dioxide. Cal- 
 
 FlG. 44. Double Refraction. 
 
 cium carbonate will be thrown down as a white 
 precipitate, but, if a stream of the gas be passed 
 in for a longer time, it will again dissolve. Upon 
 boiling the clear solution the excess of CO 2 will be 
 driven off, and CaCO 3 will be reprecipitated. 
 
 It is by this solvent action of water charged 
 with carbon dioxide that great limestone caverns, 
 like the Mammoth Cave of Kentucky, are formed. 
 From the roof of such a cave, especially during its 
 period of formation, water continually drips. Each 
 drop, in falling, leaves behind a particle of its dis- 
 solved limestone, and deposits another particle 
 upon the floor beneath. Thus, in the course of 
 ages, a stalactite grows slowly downward, like a 
 stone icicle, from above ; while from below a sta- 
 lagmite rises gradually to meet it. If the process 
 continues long enough, a column of semi-transpar- 
 ent calcium carbonate is the result. 
 
 Calcium sulphate, crystallized with two mole- 
 cules of water, occurs abundantly in nature as gyp- 
 sum, CaSO 4 , 2H 2 O. In white, translucent masses, it 
 is used as an ornamental stone, and is known as ala- 
 
CALCIUM, STRONTIUM, AND BARIUM. 209 
 
 baster ; in regular, transparent crystals, it is called 
 selenite. Gypsum is somewhat important as a fer- 
 tilizer ; and, when deprived of its water by calcina- 
 tion, it forms plaster of Paris. The latter substance, 
 when mixed to a thin paste with water, reabsorbs 
 the two molecules which were lost on calcination, 
 and " sets " to a compact, solid mass. In solidify- 
 ing it also expands ; and to this fact is partly due 
 its value in making casts. When poured into a 
 mold, it forces its way into every crack and crev- 
 ice, and thus a perfect copy is insured. 
 
 Like calcium carbonate, calcium sulphate is 
 slightly soluble in water ; and in natural waters 
 both compounds often occur. Such waters are 
 popularly known as " hard " waters, and are objec- 
 tionable for washing purposes or for use in the 
 steam-boiler. In the latter case, the lime-salts are 
 liable to be deposited on the sides of the boiler as 
 a hard, coherent coating, called boiler -crust or 
 boiler-scale, which, being a non-conductor of heat, 
 causes great waste of fuel. In the laundry, lime- 
 salts react upon the soap which is used, and insol- 
 uble lime-soaps are precipitated ; so that no good 
 soapy effect can be produced until all the calcium 
 compounds have been eliminated. 
 
 Calcium fluoride, CaF 2 , has already been referred 
 to in connection with fluorine. It is a mineral which 
 crystallizes in cubes, often brilliantly colored, and is 
 useful in the preparation of hydrofluoric acid. The 
 nitrate, Ca(NO 3 ) 2 , is found in the soil of some caves, 
 and when abundant may be profitably treated with 
 potassium carbonate, and made a source of salt- 
 peter. The phosphate, Ca 3 (PO 4 ) 2> is found in bones, 
 and also, combined with a little fluoride or chloride, 
 
210 INORGANIC CHEMISTRY. 
 
 in great beds as a mineral. It is valuable as a fer- 
 tilizer ; and, when treated with sulphuric acid, it 
 yields the so-called " superphosphate," CaHPO 4 , 
 which is much used in agriculture. 
 
 Calcium hypochlorite, chloride of lime, or bleach- 
 ing-powder, has already been described. Calcium 
 chloride, CaCl 2 , which is prepared by dissolving 
 chalk or marble in hydrochloric acid and evaporat- 
 ing to dryness, is a white, soluble compound much 
 used in the laboratory. It absorbs moisture with 
 great avidity ; enough in damp air to actually dis- 
 solve itself ; and is, therefore, of great value in 
 drying- gases. It is also employed in making 
 some kinds of artificial stone. The crystallized salt, 
 CaCl 2 , 6H 2 O, mixed with pounded ice or snow, 
 gives a powerful freezing mixture ; and with it a 
 temperature as low as 48.5 has been obtained. 
 
 STRONTIUM, as compared with calcium, is rare 
 and comparatively unimportant. Its sulphate and 
 carbonate occur as beautifully crystallized minerals. 
 Its compounds give a rich red color to flame, and 
 on this account its nitrate, Sr(NO 3 Xj, and its chlo- 
 rate, Sr(ClO 3 ) 2 , are used in the red-fire mixtures 
 of the pyrotechnist. Most of these mixtures con- 
 tain sulphur, and therefore smell badly when burn- 
 ing ; but the following experiment may be tried in 
 a room : 
 
 EXPERIMENT 85. Take two parts of potassium 
 chlorate, two of strontium nitrate, and one of shel- 
 lac. Powder them separately, and finely, and mix on 
 paper with as little friction as possible. Kindle the 
 mixture in any convenient vessel, and it will give 
 the brilliant strontium - flame. The ingredients 
 should be weighed out, and all should be scrupu- 
 
CALCIUM, STRONTIUM, AND BARIUM. 2 ll 
 
 lously dry.* If barium nitrate be used in place of 
 the strontium salt, a green-fire mixture will be made. 
 
 BARIUM is much more plentiful than strontium ; 
 but, like the latter metal, it occurs mainly as sul- 
 phate and carbonate. It is also found in a few 
 rather uncommon silicates. Several of its com- 
 pounds have practical interest. The chloride, BaCl 2 , 
 2H 2 O, and the carbonate, BaCO 3 , are useful reagents 
 in qualitative analysis ; and, as above indicated, its 
 nitrate is employed by the pyrotechnist in making 
 green fire. There are two oxides of barium, BaO 
 and BaO 2 , and these are easily transformable, the 
 one into the other. Upon this fact a " regenera- 
 tive " process for making oxygen has been based. 
 The monoxide, BaO, heated in a stream of air, is 
 converted by direct oxidation into BaO 2 . The lat- 
 ter, heated more strongly, gives up its extra atom 
 of oxygen, leaving BaO ready to be recharged in 
 another air-current. The operation may be re- 
 peated indefinitely. The BaO serves as a carrier 
 by which oxygen may be withdrawn from the at- 
 mosphere and transferred to a gas-holder. 
 
 Barium sulphate, BaSO 4 , is noted for its insolu- 
 bility. Add sulphuric acid or a solution of any 
 other sulphate to a solution containing barium, and 
 BaSO 4 will be thrown down as a heavy white 
 powder. Hence sulphuric acid serves as a test for 
 barium, and vice versa. The precipitated compound 
 is somewhat used as a white paint, under the name 
 of blanc fixe ; and the natural sulphate, which is 
 commonly called barytes or heavy spar, is ground 
 
 * A good list of recipes for different colored fires is given in Sadt- 
 ler's "Chemical Experimentation," p. 202. The book is a useful one 
 for either pupils or teachers. 
 
212 INORGANIC CHEMISTRY. 
 
 up as an adulterant for white-lead. By heating 
 the sulphate with charcoal, the sulphide, BaS, is 
 produced. This substance, exposed to a strong 
 light, is afterward luminous in the dark. The sul- 
 phides of calcium and strontium have similar prop- 
 erties, and from either of the three a luminous paint 
 may be made. 
 
CHAPTER XXIII. 
 
 SPECTRUM ANALYSIS.* 
 
 WHEN a beam of sunlight passes through a glass 
 prism, and falls upon a white screen, colors are pro- 
 duced, and the unaided eye readily distinguishes at 
 least seven tints. These are red, orange, yellow, 
 green, blue, indigo, and violet, and are popularly 
 known as the seven primary colors. If the prism 
 is placed in a dark chamber, and the light is ad- 
 mitted only through a narrow slit, the colors ar- 
 range themselves in a long band, side by side, with 
 the red at one end and the violet at the other, and 
 the remaining tints occupying their proper order 
 between. In the sunbeam these colors are all mixed 
 together, and the effect of the prism merely is to 
 separate them, by virtue of their differences in re- 
 frangibility. 
 
 Suppose now that, instead of sunlight, some 
 colored flame be studied with the prism, what sort 
 of a color-band or spectrum shall we obtain? In 
 every case we shall have, not a continuous band of 
 colors, but one or more bright-colored lines, sepa- 
 
 * In a treatise on chemistry this subject can be considered only on 
 its chemical side. The physical theory of the spectroscope, the nature 
 of luminous waves, etc., can be properly studied only as a branch of 
 physics. 
 
214 
 
 INORGANIC CHEMISTRY. 
 
 rated from each other by dark spaces ; and these 
 lines will be absolutely characteristic of the sub- 
 stance to which the tint of the flame is due. A 
 compound of sodium will give one bright-yellow 
 line ; potassium, a red and a violet ; thallium, a green 
 line ; strontium, a cluster in the red and orange, 
 and one brilliant line in the blue ; barium, a number 
 of lines near together, and mainly in the green 
 and y-ellow portions of the spectrum ; lithium, a 
 very rich line in the red, etc. There are also some 
 fainter lines which need not be mentioned here ; 
 and occasionally lines, which seem at first to be 
 single, prove when magnified to consist of several 
 closely huddled together. The yellow line of so- 
 dium, for instance, is really double. In no case does 
 any element give a line belonging to any other ; so 
 that if we insert any substance in a flame and exam- 
 ine its spectrum, we can determine at once which of 
 the above-named elements it contains. This meth- 
 od of examination is called spectrum analysis ; and it 
 is well illustrated by the colored chart of spectra 
 which is the frontispiece to this volume. 
 
 In order that spectra may be conveniently stud- 
 ied, an instrument called the spectroscope has been 
 devised. This, like most other great inventions, 
 grew up step by step, one discoverer after another 
 adding some point or detail ; but the honor of com- 
 pleting and perfecting the instrument is chiefly due 
 to Professor Bunsen, of Heidelberg in Germany. 
 In its simplest form it is constructed as follows 
 
 (Fig- 45) : 
 
 A prism and two small telescopes are mounted 
 
 upon a circular metallic plate and stand, as shown 
 in the illustration. One telescope, which serves for 
 
SPECTR UM ANAL YSIS. 2 1-5 
 
 receiving the light to be examined, is closed at its 
 outer end by two metallic knife-edges, which may 
 
 FIG. 45. One-Prism Spectroscope. 
 
 be moved nearer together or farther apart, and 
 which furnish the narrow slit as previously indi- 
 cated. The second telescope is used for observ- 
 ing the spectrum. The light enters the slit, passes 
 through the collecting-telescope, and falls upon the 
 prism. There it is refracted and dispersed, and is 
 seen through the observing eye-piece as the long 
 band which was described in a previous paragraph. 
 In nice instruments the observing eye-piece con- 
 tains a pair of cross-hairs, and is movable, with its 
 telescope, from side to side ; and the metallic plate 
 which supports it is provided with a graduated cir- 
 cle. Then, by moving the telescope so as to bring 
 each spectral line exactly across the intersection of 
 the cross-hairs, its position relatively to other lines 
 may be accurately measured. With these additions 
 the spectroscope becomes also a spectrometer, and is 
 a most convenient instrument for many optical in- 
 
2i6 INORGANIC CHEMISTRY. 
 
 vestigations. Instead of one prism, a spectroscope 
 may contain several prisms, and so be greatly in- 
 creased in power (Fig. 46). 
 
 Another convenient form of instrument is the 
 
 FIG. 46. Diagram of a Train of Prisms, with Telescopes. 
 
 direct-vision spectroscope. In the ordinary spectro- 
 scope the light is so refracted that the two tele- 
 scopes form an angle with each other; and it is 
 often a tedious matter to adjust them relatively to 
 the prism in the proper position. In the direct- 
 vision spectroscope the prisms, which may number 
 three, five, seven, or nine, are arranged as shown 
 in Fig. 47, and no adjustment is necessary. Such 
 spectroscopes are now made very cheaply, and 
 small enough to be carried in the vest-pocket. For 
 many purposes they are very handy and useful. 
 In the laboratory the spectroscope is mainly 
 
SPECTRUM ANALYSIS. 
 
 217 
 
 used for detecting Li, Na, K, Cs, Rb, Tl, Ca, Sr, 
 Ba, B, or Cu ; all of which substances impart defi- 
 nite colors to a gas or alcohol flame. The usual plan 
 is to put a little of the substance under examination 
 upon a piece of clean platinum wire, and insert it 
 in the flame of a Bunsen gas-burner. Then, al- 
 most at a glance, whatever spectra may be present 
 can be recognized. Some of the tests are inconceiv- 
 ably delicate for example, rgiFTjimnnr f a grain of 
 sodium, or OTirinnr of a grain of lithium, will reveal 
 
 FIG. 47. Section of a Direct -vision Spectroscope. 
 
 its presence immediately. Several of the rarer 
 metals have been discovered by means of the spec- 
 troscope namely, caesium, rubidium, thallium, in- 
 dium, and gallium. Caesium and rubidium were 
 discovered by Bunsen himself, shortly after the in- 
 vention of the instrument. He applied his spec- 
 troscope to the examination of a mineral water, and 
 observed certain lines which belonged to no known 
 element. He at once inferred that some new ele- 
 ment must be present ; and, carefully searching, 
 obtained the chlorides of the two metals. At the 
 high temperature of the electric arc all the ele- 
 ments give characteristic spectra, and most of them 
 have been carefully mapped and examined. 
 
 Another laboratory use of the spectroscope is in 
 the identification of dissolved coloring-matters. If 
 
2iS INORGANIC CHEMISTRY. 
 
 a beam of sunlight be passed through a solution of 
 blood, cochineal, logwood, etc., a red light will be 
 transmitted ; other solutions transmit green, yellow, 
 or blue tints mainly. If the transmitted light be 
 examined with the spectroscope, certain parts of 
 the complete spectrum will be found to be blotted 
 out, and what is called an absorption spectrum will be 
 seen. Such a spectrum is in most cases character- 
 istic of the coloring-matter which produces it, and 
 at once reveals the presence of the latter. The ar- 
 tificial color of an adulterated red wine may thus 
 (with some limitations) be detected. 
 
 Whenever we have a spectrum consisting of 
 bright lines with dark spaces between, it is pro- 
 duced by heated matter in the condition of a gas. 
 All the elements above mentioned, which color the 
 Bunsen flame, do so in the form of compounds 
 which are gaseous at its temperature. The other 
 elements, as was already stated, require much more 
 elevated temperatures for the production of bright- 
 line spectra. 
 
 If we study the light emitted by highly incan- 
 descent solids, such as the carbon of an electric arc 
 or the lime cylinder in the oxyhydrogen-flame, we 
 shall find that it gives a spectrum without lines, and 
 brilliantly continuous from the red end to the vio- 
 let. In the spectrum of sunlight, however, we have 
 something different still namely, a continuous spec- 
 trum intersected by a vast number of fine black lines, 
 each of which occupies a fixed and definite position.* 
 These lines were first described by Wollaston ; and 
 later they were carefully mapped by Fraunhofer ; 
 
 * Dark lines running lengthwise of the spectrum often confuse the 
 beginner. They are due to dust-specks on the slit of the spectroscope. 
 
SPECTRUM ANALYSIS. 
 
 2I 9 
 
 they are now known as Fraimhofer's lines. Each 
 of them corresponds in position exactly with one of 
 the bright lines obtainable from a chemical element ; 
 for example, Fraunhofer's line " D," in the yellow, 
 coincides precisely with the sodium-line, and, like 
 the latter, is really double. What does this mean ? 
 The explanation, discovered by the joint labors of 
 Professors Bunsen and Kirchhoff, is simple, and is an 
 application of the physical law that substances when 
 cold absorb the same rays which they give out when hot. 
 Let us consider a special case arising under this 
 law. Suppose we arrange a spectroscope as in Fig. 
 48, and place in front of the slit a strong light capa- 
 
 FIG. 48. Reversal of Sodium-line. 
 
 ble of giving a continuous spectrum. Now between 
 this light and the slit interpose a layer of sodium va- 
 por, produced by heating a little metallic sodium 
 in an iron spoon. The part of the spectrum corre- 
 sponding to the sodium-line will be absorbed, and 
 a dark line will be seen in its place. That is, sodium 
 vapor absorbs the yellow ray which more intensely 
 heated sodium vapor emits. This is commonly 
 
220 INORGANIC CHEMISTRY. 
 
 known as the reversal of the sodium-line ; and the 
 lines of other elements may be similarly reversed. 
 The spectrum of sunlight is merely a continuous 
 spectrum, with the reversed lines of over twenty of 
 the chemical elements distributed in their proper 
 places through it. The conclusion is, that the sun 
 contains these elements in the gaseous condition ; 
 and through such a gaseous envelope the light of the 
 solid or liquid interior is transmitted. In short, by 
 means of the spectroscope we can analyze the heav- 
 enly bodies, and tell of what substances they are com- 
 posed. 
 
 In the solar spectrum, so far, lines belonging to 
 the following elements have been identified : iron, 
 titanium, calcium, manganese, nickel, cobalt, chro- 
 mium, barium, sodium, magnesium, copper, hydro- 
 gen, palladium, vanadium, molybdenum, strontium, 
 lead, uranium, aluminum, cerium, cadmium, and 
 oxygen. The presence of still other elements in 
 the sun has been less clearly made out, but is highly 
 probable ; and in several of the fixed stars, which 
 resemble the sun in character, several substances 
 not discoverable in the sun have been distinctly 
 recognized. The bright star Aldebaran, for in- 
 stance, contains hydrogen, sodium, magnesium, cal- 
 cium, iron, antimony, mercury, bismuth, and tellurium. 
 
 At various points in the heavens are seen faint 
 clouds of light, called nebulas. Some of them are 
 star-clusters, so distant that only a powerful tel- 
 escope can recognize their true character ; and 
 such nebulae give regular star -spectra. Others, 
 however, when examined with the spectroscope, 
 prove to be immense clouds of incandescent gas, 
 and give a bright-line spectrum indicating hydro- 
 
SPECTRUM ANALYSIS. 2 2l 
 
 gen. This fact has a curious theoretical impor- 
 tance. It is commonly held by scientific men that 
 the solar system was once a vast nebula, which 
 gradually cooled and condensed into its present 
 condition ; and a great deal of evidence, physical 
 and mathematical, can be cited in favor of this neb- 
 ular hypothesis. In the heavens we see all stages of 
 development from the nebula itself, down to the 
 hotter stars, the sun, and the solid planets ; and ac- 
 companying this progression, we find a steady in- 
 crease in chemical complexity. The nebulae con- 
 tain but one or two elements ; the whitest and 
 hottest stars a few more ; stars like our sun a larger 
 number still ; and at last we find the earth with its 
 multitude of compound bodies. From these facts 
 we arrive at once at a startling conclusion, which, 
 though not yet absolutely proved, is sustained by 
 many lines of evidence, and is yearly becoming 
 more and more probable ; namely, that the evolu- 
 tion of planets from nebulae has been accompanied 
 by an evolution of the chemical elements from still 
 simpler forms of matter ; and that matter itself, like 
 force, instead of being many different things, is 
 really at bottom, in the final analysis, one.* 
 
 * The student who cares to pursue the subject of celestial spec- 
 troscopy further may profitably begin with two volumes in the " Inter- 
 national Scientific Series " : Young's work on " The Sun," and Lock- 
 yer's " Studies in Spectrum Analysis." 
 
CHAPTER XXIV. 
 
 GLUCINUM, MAGNESIUM, ZINC, CADMIUM, AND MER- 
 CURY. 
 
 ALTHOUGH the metals described in this chapter 
 are all bivalent, they do not form as definite a nat- 
 ural group as some that we have been considering. 
 Magnesium and zinc, indeed, are very closely re- 
 lated ; so are zinc and cadmium ; and, though less 
 strikingly, so also are cadmium and mercury. But 
 between magnesium and mercury, except as re- 
 gards valency, the resemblances are quite remote. 
 
 GLUCINUM, often called beryllium, is a rare metal 
 of specific gravity 2.1, and an atomic weight of 9. 
 It is found in a few minerals, among which the 
 beryl and the chrysoberyl are the only important 
 species. The beryl is a silicate of glucinum and 
 aluminum, and varies in color from white to yel- 
 low, and bluish to deep green. It is valuable as a 
 gem ; the bluish variety being known as aqua- 
 marine, and the green variety as the emerald. The 
 salts of glucinum are all formed on a simple biva- 
 lent type, and in their outward properties have 
 some resemblance to the compounds of trivalent 
 aluminum. The oxide, G1O, the chloride, G1C1 2 , 
 and the sulphate, G1SO 4 , are good examples of 
 their chemical structure. 
 
GLUCINUM, MAGNESIUM, ZINC, ETC. 223 
 
 MAGNESIUM, atomic weight 24, is one of the 
 more abundant elements, and forms an important 
 part of the earth's crust. It occurs in many sili- 
 cates, such- as talc and serpentine ; and in dolo- 
 mite, a double carbonate of magnesium and cal- 
 cium. The last-named species forms whole mount- 
 ain ranges, and is often confounded with limestone. 
 Some of its varieties resemble marble. Magnesium 
 minerals frequently have a soapy feeling, as in soap- 
 stone, and so may be recognized by touch. Salts 
 of magnesium are found in sea-water, and in many 
 mineral springs. 
 
 The metal itself is usually prepared by heating 
 the chloride with sodium; thus: 
 
 MgCl 3 + Na 2 = Mg + 2NaCl. 
 
 It is bluish-white, fusible at low redness, volatile at 
 higher temperatures, and has a specific gravity of 
 1.75. It is easily combustible, and burns with an in- 
 tensely brilliant light, emitting dense, white smoke- 
 clouds of its solid oxide, MgO. It is commonly sold 
 in the form of wire or ribbon, and may be kindled 
 with a common match. Its light gives a continuous 
 spectrum, but is brightest toward the violet end, 
 and abounds especially in those rays which possess 
 chemical activity. On this account it is available 
 for photographic purposes ; and is actually so used 
 as a source of illumination in photographing the in- 
 terior of caverns. 
 
 The compounds of magnesium are quite simple. 
 The oxide, MgO, also known as magnesia, is a white 
 powder somewhat used in medicine. Its popular 
 name well illustrates a common method of abbrevi- 
 ating the names of oxides; as, for example, SiO 2 , 
 
224 INORGANIC CHEMISTRY. 
 
 silica ; Na 2 O, soda ; K 2 O, potassa ; BaO, baryta ; 
 SrO, strontia ; A1 2 O 8 , alumina, etc. The superior 
 convenience of these names over such terms as 
 silicon dioxide, barium monoxide, etc., is evident. 
 Magnesia unites readily with water to form a 
 hydroxide, Mg(OH) 2 , which occurs naturally crys- 
 tallized as the mineral brucite. The carbonate, 
 MgCO 3 , is also found as a mineral, magnesite ; and, 
 artificially precipitated in union with hydroxide, as 
 the magnesia alba of pharmacy. The double carbon- 
 ate, MgCO 3 + CaCO 3 , has already been referred to 
 as dolomite. 
 
 The most important salt of magnesium is the 
 sulphate, MgSO 4 , 7H 2 O. It was originally found in 
 a spring at Epsom, England whence the common 
 name of Epsom salts. It is now prepared by treating 
 either magnesite or dolomite with sulphuric acid, 
 and evaporating the solution to the crystallizing 
 point. It is a useful reagent in chemical analysis, 
 and is a common household medicine. 
 
 The water of crystallization in magnesium sul- 
 phate deserves especial study. If the salt be heated 
 to about 120 C., six molecules of its water are ex- 
 pelled ; but the seventh molecule is retained with 
 great tenacity up to a temperature of nearly 200. 
 This molecule, therefore, is differently combined 
 from the others, and is known as water of constitu- 
 tion. It may be replaced by other sulphates ; as, 
 for example, K 2 SO 4 , yielding the double sulphate 
 MgSO 4 , K 2 SO 4 , 6H 2 O. 
 
 '' 
 
 This compound is the type of an important class of 
 double salts which result from the union of the 
 
GLUCINUM, MAGNESIUM, ZINC, ETC. 22$ 
 
 alkaline sulphates with the sulphates of magnesium, 
 zinc, iron, cobalt, nickel, and copper. These salts 
 show that there is some relationship between mag- 
 nesium and the last four metals. 
 
 ZINC, though far less abundant than magnesium, 
 is more familiar as a metal. It is found in many 
 
 FIG. 49. Zinc-Furnace. 
 
 minerals ; but its chief ores are the oxide, zincite ; 
 the sulphide, zinc blende ; the silicate, calamine ; 
 and the carbonate, smithsonite. These, in smelt- 
 ing, are first roasted, and then heated in either 
 earthenware tubes or fire-clay crucibles with coke 
 or charcoal. Zinc is set free, and distilled off into 
 suitable vessels. It is finally remelted and cast into 
 bars, which are known commercially as spelter. 
 Sometimes the zinc-vapor is condensed in the form 
 of zinc-dust, which is of use in some of the opera- 
 tions of organic chemistry. A mixture of zinc-dust 
 and sulphur may be used to illustrate chemical 
 
226 INORGANIC CHEMISTRY. 
 
 union, as in Experiment i. It can be kindled with 
 a match and burns almost like gunpowder, leaving 
 a residue of yellowish-white sulphide. 
 
 Zinc is a bluish-white metal of atomic weight 
 65, and a specific gravity from 6.8 to 7.3. It melts 
 at 423, and boils at 1,035. It is slightly combus- 
 tible, especially in thin sheets, and burns with a 
 greenish flame. At ordinary temperatures it is 
 brittle ; but at 125 to 150 it is malleable, and may 
 be rolled into sheets. At 205 it again becomes 
 brittle, and may be pulverized in a mortar. It is 
 largely used as sheet-zinc, for fire-screens, roofing, 
 etc. ; and it forms the positive plate in all voltaic 
 battc ies. Brass is an alloy of zinc and copper, and 
 German silver consists of zinc, nickel, and cop- 
 per. The so-called galvanized iron, used for roof- 
 ing, cornices, window-caps, water-pipe, etc., is mere- 
 ly iron which has been dipped in melted zinc, and 
 so coated with the latter. Granulated zinc is the 
 most convenient form of zinc for laboratory pur- 
 poses ; it is prepared by melting zinc in an iron 
 ladle, and pouring it gradually from a height of 
 about two metres into cold water. Other fusible 
 metals, like lead, tin, or cadmium, may be granu- 
 lated in the same way. 
 
 Chemically, the compounds of zinc resemble 
 those of magnesium. The oxide, ZnO, is white 
 when cold, yellow when hot. A large deposit 
 of it occurs at Franklin and Sterling, New Jer- 
 sey, in red masses which owe their color to man- 
 ganese as an impurity. The pure zinc oxide is 
 important as a white paint, which is not discolored 
 by atmospheric agencies. Zinc sulphide, ZnS, is 
 often produced in the laboratory as a white precipi- 
 
GLUCINUM, MAGNESIUM, ZINC, ETC. 227 
 
 tate, by adding ammonium sulphide to a solution of 
 any soluble zinc-salt. It occurs in nature as a very 
 common crystalline mineral, but is generally col- 
 ored yellow, brown, or black, by impurities. The 
 chloride, ZnClg, is a pasty solid, which is prepared 
 by dissolving zinc in hydrochloric acid and evapo- 
 rating to dryness. It is used in surgery as a caus- 
 tic, and by tinners for cleansing tin-plate previous to 
 soldering. It is also used on a large scale as an an- 
 tiseptic, in the preservation of wood from decay. 
 The process, which, from the name of its invent- 
 or, is called Burnettizing, consists in inclosing the 
 wood in strong iron cylinders, pumping out the air 
 by a powerful steam-pump, and then allowing the 
 solution of zinc chloride to flow in under very 
 heavy pressure. The wood is thus completely per- 
 meated by the preservative, and will last for years 
 without rotting. Copper sulphate, mercuric chlo- 
 ride, coal-tar, creosote, etc., are also applied to wood 
 in the same way and for the same purpose. 
 
 Zinc sulphate, ZnSO 4 , ;H 2 O, also called white 
 vitriol, resembles magnesium sulphate very closely. 
 It forms similar double sulphates, and its water of 
 crystallization behaves in the same way. Its uses 
 are chiefly medicinal, although in large doses it is 
 poisonous. Applied externally in weak solutions, 
 it quiets local inflammation ; and it is especially 
 used in treating diseases of the eye. Most of the 
 so-called " eye-waters " are merely preparations of 
 zinc sulphate. 
 
 CADMIUM, atomic weight 112, is a rare metal 
 which is chiefly found as an impurity in zinc. It is 
 bluish-white, brilliant, and of specific gravity 8.6. 
 It melts at 320 C., and boils at 860, forming a va- 
 
228 INORGANIC CHEMISTRY. 
 
 por having only half the density indicated by its 
 atomic weight. Hence its molecule consists of a 
 single atom. Cadmium is used in making certain 
 fusible alloys,* and in preparing a few compounds. 
 The iodide, CdI 2 , is employed to some extent in 
 photography ; and the sulphide, CdS, is a brilliant 
 yellow precipitate which is much prized by artists 
 as a pigment. 
 
 MERCURY, or quicksilver, being the only metal 
 liquid at ordinary temperatures, has always been an 
 object of both popular and scientific interest. It is 
 found in nature in the free state, and also in several 
 ores ; but only one of the latter, cinnabar, HgS, has 
 any practical importance. It is extensively mined 
 in Spain, Austria, China, Mexico, and Peru ; but 
 fully two thirds of the whole annual mercury-yield 
 of the world comes from a few localities in Califor- 
 nia. From cinnabar the metal is easily extracted 
 by a. process of roasting with lime. The mercury 
 volatilizes, and is condensed in suitable chambers 
 or pipes. It is purified by straining through linen, 
 and is sent into commerce in strong bottles made of 
 wrought-iron. 
 
 The specific gravity of mercury, at o, is 13.596. 
 At 39.5 it solidifies to a malleable mass, of spe- 
 cific gravity 14.19. At 357 it boils, yielding a vapor 
 of density 100, its atomic weight being, as in the 
 case of cadmium, twice as great, or 200. Hence 
 the mercury molecule consists of one atom. Pure 
 mercury does not tarnish in the air until heated 
 above 300, when it slowly unites with oxygen to 
 form the red oxide. It combines directly with chlo- 
 rine, bromine, iodine, and sulphur, and dissolves in 
 
 * Described under bismuth. 
 
GLUCINUM, MAGNESIUM, ZINC, ETC. 229 
 
 nitric and hot sulphuric acids. Its symbol, Hg, is 
 from the Latin hydrargyrum. It is used in making 
 thermometers, barometers, and other physical in- 
 struments, in silvering mirrors, in the manufacture 
 of many medicinal preparations, and in extracting 
 gold and silver from their ores. With many of the 
 metals it unites easily, forming a class of alloys 
 called amalgams. In handling mercury great care 
 should be taken to prevent it from coming in con- 
 tact with gold rings or other jewelry, on account of 
 the readiness with which gold amalgamates. A 
 bit of gold-leaf will dissolve in a drop of quicksilver 
 almost instantaneously (see Experiment 100). 
 
 Mercury forms two sets of compounds, which 
 are called mercurous and mercuric compounds re- 
 spectively. In the first set, which are unstable, it 
 seems to be a monad ; in the second it is unmistak- 
 ably bivalent. The following are its more impor- 
 tant compounds : 
 
 Mercum: oxide, HgO, is the well-known red 
 oxide formed by heating mercury in the air. At a 
 temperature above 350 it gives off its oxygen, and 
 is noted as the substance from which that gas was 
 first obtained pure (see Experiment 2, and Chapter 
 IV). Mercurous oxide, Hg 2 O, is black and unstable. 
 Mercuric sulphide, HgS, has already been referred 
 to as the ore cinnabar. When H 2 S is passed into a 
 solution of a mercuric salt, the same sulphide is 
 thrown down as a black precipitate. By subliming 
 a mixture of mercury and sulphur it is obtained in 
 a bright-red modification, called vermilion, which 
 is used as a scarlet pigment. 
 
 When mercury is treated with nitric acid in 
 quantity insufficient to dissolve the whole of it, 
 
230 INORGANIC CHEMISTRY. 
 
 mercurous nitrate, HgNO 8 , is produced in white 
 crystals. With an excess of nitric acid the mercu- 
 ric salt, Hg(NO 8 ) 2 , is formed. With hot sulphuric 
 acid mercury yields mercuric sulphate, HgSO 4 ; a 
 compound used in some forms of galvanic battery. 
 
 The chlorides of mercury, HgCl * and HgCl 2 , 
 are both important. Mercurous chloride is a white, 
 insoluble powder, much used in medicine under 
 the familiar name of calomel. Mercuric chloride, 
 which is prepared on a large scale by subliming a 
 mixture of mercuric sulphate and common salt, is 
 soluble in water, alcohol, and ether, and crystallizes 
 easily. It is the well-known violent poison, corro- 
 sive sublimate. The best antidote for this poison 
 is white of egg, administered raw, in large doses. 
 The albumen of the egg forms an insoluble clot 
 with the mercuric chloride, which may afterward be 
 removed from the stomach by means of an emetic. 
 
 Both of the mercury iodides are employed me- 
 dicinally. The mercurous compound is green ; the 
 mercuric salt is bright scarlet. The properties of 
 the latter substance are so extraordinary that, al- 
 though they were partly brought out in Experi- 
 ment 3, they deserve further experimental atten- 
 tion here. 
 
 EXPERIMENT 86. Dissolve in water, in separate 
 vessels, nine parts of mercuric chloride and eleven of 
 potassium iodide. Mix the two colorless solutions, 
 and a heavy precipitate, yellow at first, scarlet after- 
 ward, will form. Shake vigorously and divide into 
 
 TT /"M 
 
 * Many chemists write this HgaCla, or t regarding mercury 
 
 Hg-Cl, 
 
 as invariably dyad. Good arguments can be cited in favor of either 
 formula. 
 
GLUCINUM, MAGNESIUM, ZINC, ETC. 231 
 
 three portions. To one portion add an excess of 
 mercuric chloride solution, and to the second por- 
 tion an excess of potassium iodide. In each case 
 the precipitate will redissolve, leaving the fluid 
 colorless. Filter the third portion, and wash and 
 dry the precipitate. Heat a little of it gently on a 
 bit of porcelain or a slip of glass, and it will change 
 from scarlet to bright yellow. On cooling, it will 
 pass slowly back to its original color. Under the 
 microscope this change is very beautiful, inasmuch 
 as the scarlet may be seen to leap from particle to 
 particle of the yellow powder. 
 
 These color-changes are due to the fact that 
 mercuric iodide exists in two distinct modifica- 
 tions, having different optical properties and differ- 
 ent crystalline form. In Experiment 3 we have an 
 example of dry double decomposition, which is one 
 of the very rarest of chemical phenomena. 
 
 n 
 
CHAPTER XXV. 
 
 THE ALUMINUM GROUP. 
 
 ALUMINUM, as regards abundance, may be 
 ranked side by side with sodium, calcium, and 
 magnesium. It enters into the composition of all 
 the important primitive rocks, and all slates and 
 clays consist mainly of its silicates. In the crust of 
 the earth, only oxygen and silicon occur in larger 
 quantities. 
 
 The metal itself is prepared by passing the va- 
 por of a double chloride of aluminum and sodium 
 over metallic sodium. Sodium chloride is formed, 
 and metallic aluminum is set free.* It is a tin-white 
 metal, brilliant, malleable, and ductile, and has a 
 specific gravity of 2.583. It fuses at about 850, and 
 is an excellent conductor of heat and electricity. 
 It does not tarnish in the air, it is easily worked, 
 and it combines the properties of lightness and 
 strength to an extraordinary degree. If it could- 
 only be produced cheaply from common clay, it 
 would be one of the most useful of metals. Indeed, 
 it has been called "the metal of the future," al- 
 though at present it is only employed for a very 
 few purposes. An alloy of ten parts of aluminum 
 
 * Several modified processes for the manufacture of aluminum 
 have recently been patented in England. 
 
THE ALUMINUM GROUP. 233 
 
 with ninety of copper is known as aluminum bronze, 
 and is a dangerous imitation of gold. It is some- 
 what used in fine philosophical instruments. 
 
 Aluminum is trivalent, and has an atomic weight 
 of 27. It forms one set of compounds, of which the 
 oxide, alumina, A1 2 O S , is the type. Such oxides as 
 A1 2 O 3 , Fe 2 O 3 , Cr 2 O 3 , and Mn 2 O 3 , are termed sesqui- 
 oxides. 
 
 Alumina occurs crystallized in nature as the 
 mineral corundum, and is usually colored by im- 
 purities. The yellow variety is called " Oriental 
 topaz " ; the purple is the " Oriental amethyst " ; the 
 green is the " Oriental emerald." The sapphire is 
 merely blue corundum, and the ruby is a red vari- 
 ety. These gems can now be produced artificially. 
 Emery, which is so important as a polishing-pow- 
 der, is an impure corundum. 
 
 Aluminum forms several hydroxides, the com- 
 pound A1 2 (OH) 6 being the most characteristic. 
 When artificially precipitated, as by the addition 
 of ammonia to an aluminum salt, they possess the 
 property of uniting with organic dye-stuffs to form 
 insoluble substances called " lakes." Aluminum hy- 
 droxide, therefore, plays an important part in the 
 processes of dyeing, being thrown down in the fiber 
 of the cloth for the purpose of fixing and retaining 
 colors. 
 
 EXPERIMENT 87. Dissolve a crystal of alum in 
 water, and add ammonia to the solution. Warm, 
 and filter off the insoluble, gelatinous A1 2 (OH) 6 
 which is precipitated. Now pour over the precipi- 
 tate a solution of logwood or cochineal. The color 
 will be retained and can not be washed out. 
 
 In alumina we have an oxide which may play 
 
234 INORGANIC CHEMISTRY. 
 
 the part of either an acid-former or a base. With 
 strong acids it forms characteristic salts, like the 
 sulphate ; and with strong bases it unites to pro- 
 duce aluminates. 
 
 EXPERIMENT 88. To a solution of alum add a 
 very little caustic potash or caustic soda. A pre- 
 cipitate of hydroxide will be thrown down, which 
 will be redissolved upon the addition of more alkali. 
 Metallic aluminum itself may be dissolved, with evo- 
 lution of hydrogen, by potassium or sodium hydrox- 
 ide. In these reactions potassium or sodium alumi- 
 nate is formed. 
 
 The most important simple salt of aluminum is 
 the sulphate, A1 2 (SO 4 ) 3 , i8H 2 O. It is much used by 
 dyers as a mordant ; and an impure variety of it 
 occurs in commerce under the name of alum-cake. 
 It combines with the sulphates of the alkaline met- 
 als to form a class of double salts known as alums, 
 of which potassium alum, K 2 SO 4 , A1 2 (SO 4 ) 3 , 24H 2 O, is 
 the commonest example. The formula of this salt 
 may be halved, and written KA1(SO 4 ) 2 , I2H 2 O; or, 
 structurally 
 
 A1 ^So!-K I2Haa 
 
 With ammonium sulphate, ammonium alum is 
 formed ; and so also we may put either Na, Ag, Tl, 
 Cs, or Rb in place of K, or Cr, Ga, In, Fe, or Mn in 
 place of Al. In every case we shall have a salt con- 
 taining twelve molecules of water, and crystallizing 
 in regular octahedra ; and all of these salts may be 
 represented by the general formula 
 
 M'M^SO^a, i2H 2 O, 
 
 in which M 1 stands for a univalent metal and M ia for 
 a triad. The potassium and ammonium aluminum 
 
THE ALUMINUM GROUP. 235 
 
 alums are both important, and are used as mor- 
 dants in the art of dyeing. 
 
 In the mineral kingdom, in addition to the spe- 
 cies already mentioned, we find a number of highly 
 interesting aluminum compounds. The turquoise 
 is an aluminum phosphate, the garnet and emerald 
 are silicates containing aluminum, and the topaz 
 is a compound which may be represented by the 
 formula Al 2 SiO 4 F 2 . Another substance of special 
 interest is cryolite, a double fluoride of aluminum 
 and sodium, 6NaF, A1 2 F 6 , which forms a vast bed in 
 Western Greenland.* Thousands of tons of this 
 mineral are annually brought to the United States, 
 and worked over by a special process so as to yield 
 aluminum sulphate and an excellent quality of soda- 
 ash. A kind of glass which outwardly resembles 
 porcelain is also made by fusing cryolite with sand. 
 
 A beautiful blue ornamental stone, lapis lazuli, 
 is a silicate of aluminum and sodium containing sul- 
 phur. Formerly its powder was used by artists as 
 a paint, under the name of ultramarine ; but at pres- 
 ent this substance is produced artificially from very 
 cheap materials. First, a mixture of clay with so- 
 dium sulphate, soda, charcoal, and sulphur, is heated 
 in crucibles, and a valuable paint known as green 
 ultramarine is obtained. This, reheated with sul- 
 phur, yields blue ultramarine, which is much used 
 for water-colors and for paper-staining. In 1829 
 ultramarine was worth, in England, sixty dollars 
 a pound ; to-day its price is about twelve cents. 
 Nearly twenty million pounds are annually made. 
 Violet and red ultramarines have also been pre- 
 
 * Cryolite has recently been discovered near Pike's Peak, in Colo- 
 rado. 
 
236 INORGANIC CHEMISTRY. 
 
 pared ; but to none of these compounds can abso- 
 lutely definite chemical formulas as yet be as- 
 signed. 
 
 Pottery and porcelain, being made from clay, 
 are more or less impure silicates of aluminum. 
 Red bricks and red pottery owe their color to con~u 
 pounds of iron ; and fire-clay, from which the fire- 
 brick linings of furnaces are made, contains large 
 admixtures of silica. Porcelain differs from glass 
 in being non-transparent, or at best only translu- 
 cent, and exceedingly infusible. 
 
 Pure porcelain-clay or kaolin is a hydrous alumi- 
 num silicate, H 2 Al 2 Si 2 O 8 -f H 2 O. It is derived from 
 rocks containing feldspar (K 2 Al 2 Si 6 O 16 ), by the atmos- 
 pheric process known as weathering. When it is 
 baked in an appropriate furnace, it loses water and 
 hardens, and a porous mass is produced. In mak~ 
 ing porcelain the finely-powdered kaolin is mixed 
 with water to a very thick paste, and then molded 
 into the desired shape. A little feldspar, chalk, or 
 gypsum is also added to the clay, in order to form 
 a fusible silicate in quantity just sufficient to bind 
 the particles of the ware firmly together. Upon 
 firing, as the process of burning is called, a porous 
 " biscuit-ware " is obtained, which is afterward sub- 
 jected to a process of glazing. For the finest porce- 
 lain the glazing material is generally pure feldspar, 
 finely powdered and mixed with water to a very 
 thin consistency ; into this the biscuit is dipped, and 
 then fired over again. The feldspar, being fusible, 
 melts ; and a thin, smooth, glassy layer covers the 
 surface of the ware. A cheaper glaze for common 
 stone-china consists of a mixture of clay, chalk, 
 ground flints, and borax ; but many other recipes 
 
THE ALUMINUM GROUP, 237 
 
 are also used. Earthenware is generally salt-glazed, 
 a process which consists in throwing common salt 
 into the kiln just before the firing is finished. The 
 salt volatilizes, and a fusible silicate of aluminum 
 and sodium is formed all over the surface of the 
 pottery. The colors used in decorating porcelain 
 consist of various metallic oxides ; cobalt oxide for 
 blue, chromic oxide for green, etc. Some colors 
 are put on previous to glazing ; but the more deli- 
 cate tints, as well as any gilding, are imparted in a 
 separate firing over the glaze. 
 
 GALLIUM, which is chemically allied to alumi- 
 num, is an excessively rare metal, of atomic weight 
 69. It was discovered in 1875, and is interesting as 
 being one of the metals of which the existence and 
 properties were predicted in advance of actual 
 discovery. Its specific gravity is 5.9, and it melts 
 at 30 C. It becomes liquid in the heat of the 
 hand ! Its oxide is Ga 2 O 3 , and its sulphate forms 
 alums. 
 
 INDIUM, atomic weight 113.5, was discovered in 
 1875. Like gallium, it is exceedingly rare. The 
 metal has a specific gravity of 7.4, and outwardly 
 resembles zinc. Its sulphate forms an alum. Indi- 
 um and gallium were both discovered by spectrum 
 analysis, and both are trivalent. 
 
 Scandium, yttrium, terbium, erbium, and ytter- 
 bium are very rare metals having only theoretical 
 interest. They are all trivalent, forming sesqui- 
 oxides, which are strong bases. The existence of 
 scandium was predicted by Mendelejeff in advance 
 of its actual discovery by Nilson. 
 
 Cerium, lanthanum, and didymium are three 
 other rare metals which usually occur associated 
 
238 INORGANIC CHEMISTRY. 
 
 together. Lanthanum is a triad, cerium a tetrad, 
 and didymium a pentad. With didymium, in inti- 
 mate admixture, a fourth metal, samarium, has re- 
 cently been detected. Cerium oxalate has a limited 
 use in medicine. 
 
CHAPTER XXVI. 
 
 THE TETRAD METALS. 
 
 IN addition to cerium, which was mentioned in 
 the preceding chapter, titanium, zirconium, tin, 
 lead, and thorium are quadrivalent. In fact, they 
 may all be classed in a series of elements of which 
 carbon and silicon are the first and second mem- 
 bers. TITANIUM, atomic weight 50, is one of the 
 rarer metals. Its oxide, TiO 2 , is a natural mineral, 
 and has a limited application in giving a yellowish 
 tint to porcelain. Titanium occurs in many iron- 
 ores, and renders them more difficult of working. 
 In the blast-furnace it sometimes combines with ni- 
 trogen and carbon so as to form a nitrocyanide, 
 Ti(CN) 2 -f 3Ti 3 N 2 , which looks strikingly like metal- 
 lic copper. ZIRCONIUM, atomic weight 90, is even 
 rarer than titanium. Like alumina, zirconia (ZrO 2 ) 
 is sometimes basic and sometimes acid-forming. 
 The mineral zircon, ZrSiO 4 , is used, under the name 
 of hyacinth, as a gem. THORIUM, atomic weight 
 232, is exceedingly rare, and has no practical impor- 
 tance. Its oxide is a strong base. 
 
 TIN, atomic weight 118, is rarely found in the 
 metallic state, and occurs in only a few mineral 
 species. It has but one important ore, the mineral 
 cassiterite or tin-stone, SnO 2 . This ore varies in 
 
240 
 
 INORGANIC CHEMISTRY. 
 
 color from brown to black, and is quite heavy ; but 
 it is devoid of metallic luster, and might easily be 
 passed over as valueless by an untrained observer. 
 Tin is the only valuable metal which has not as yet 
 been found in paying quantities within the limits of 
 the United States. It is chiefly produced in Corn- 
 wall, Borneo, Malacca, and the Island of Banca. 
 Banca tin is almost chemically pure, while English 
 tin always contains a little iron and lead. 
 
 Tin is easily extracted from its ore by heating 
 the crushed mineral with coal or charcoal in a rever- 
 beratory furnace. 
 
 SnOa + C = Sn + CO a . 
 
 It is a white metal, of specific gravity 7.3, and a 
 melting-point of 235. Melted tin rea'dily absorbs 
 oxygen from the air, and becomes converted into 
 a white oxide, SnO 2 . When a bar of tin is bent, it 
 emits a peculiar crackling sound, called the " tin- 
 cry," which is caused by the friction against each 
 other of interlaced crystals. The crystalline char- 
 acter of the metal may be rendered evident to the 
 eye by washing the surface of a piece of tin-plate 
 with warm dilute nitro-hydrochloric acid. Crystal- 
 line markings will presently appear. Tin is ductile, 
 but not tenacious ; it is also highly malleable, and 
 is therefore much used in the form of foil. The 
 cheaper grades of tin-foil are adulterated with lead. 
 Tin-plate, or sheet-tin, is really tinned iron. 
 Sheets of rolled iron, chemically clean, are dipped 
 into melted tin, and acquire a coating of the latter. 
 Ordinary mirrors are covered with an amalgam 
 of tin and mercury ; bronze is an alloy of copper 
 and tin ; plumber's solder consists of tin and lead, 
 
THE TETRAD METALS. 
 
 241 
 
 and Britannia-metal is composed mainly of tin and 
 antimony. 
 
 The symbol of tin, Sn, is from the Latin stan- 
 num. There are two sets of tin compounds, which 
 are termed stannous and stannic compounds respect- 
 ively. Stannous oxide, or tin monoxide, SnO, is 
 basic, and from it a well-defined series of salts may 
 be derived. Stannic oxide, or tin dioxide, SnO 2 , is 
 weakly basic with strong acids, and weakly acid 
 with strong bases. Sodium stannate, Na 2 SnO 8 , 
 3H 2 O, is an important mordant in calico-printing. 
 Stannous chloride, SnCl 2 , 2H 2 O, and stannic chlo- 
 ride, SnCl 4 , 5H 2 O, are also much used as mordants. 
 The anhydrous stannic chloride, SnCl 4 , is a volatile 
 liquid ; but its hydrate is a crystalline salt. Stan- 
 nic sulphide, SnS 2 , forms golden scales which are 
 used for bronzing plaster casts. Its commercial 
 name is "mosaic gold." The close analogy be- 
 tween tin and other members of the same group is 
 shown by the subjoined formulae : 
 
 CO 
 
 
 
 SnO 
 
 CO, 
 
 SiO, 
 
 Ti0 2 
 
 SnO* 
 
 ecu 
 
 SiCU 
 
 TiCh 
 
 SnCl 4 
 
 Na a CO 3 
 
 NaaSiOa 
 
 Na a TiO 3 
 
 NaaSnOs 
 
 LEAD, although classed with the tetrads, is in 
 most of its compounds bivalent, and might fairly 
 be put in the same group with calcium and barium. 
 In chemical structure its commoner salts resemble 
 those of the latter metals ; but in certain organic 
 compounds it is unmistakably quadrivalent. 
 
 The carbonate, sulphate, phosphate, and arsen- 
 ate of lead all occur in nature as well-defined, crys- 
 
242 INORGANIC CHEMISTRY. 
 
 tallized, mineral species ; but the only ore of lead 
 having much practical importance is the sulphide, 
 PbS, which is commonly known as galena. This 
 ore is easily reduced by heating in a reverberatory 
 furnace, as follows : First, it is roasted with free ac- 
 cess of air, when a portion is oxidized to a sulphate, 
 PbSO 4 , and another to oxide, PbO, while a third 
 part remains unchanged. At the proper time the 
 air is excluded and the temperature is raised ; sul- 
 phur dioxide is given off, and lead is left behind, in 
 accordance with the subjoined equations. Both re- 
 actions occur simultaneously : 
 
 PbSO 4 + PbS = 2Pb + 2SO 3 . 
 2PbO + PbS = 3Pb + SO 3 . 
 
 In actual working a little lime is added in order to 
 form a fusible slag with the impurities of the ore. 
 In many cases the lead contains some silver, which 
 is afterward extracted by the process described in 
 the chapter upon that metal. 
 
 Lead is a bluish-white metal, of atomic weight 
 207, and specific gravity 11.38. It melts at 332, 
 and at ordinary temperatures is soft enough to be 
 scratched by the finger-nail. When freshly cut it 
 has a brilliant metallic luster; but it quickly tar- 
 nishes on the surface and becomes dull. It is mal- 
 leable and ductile, but its tenacity is so slight that 
 it is not available for wire or for very thin foil. 
 The symbol, Pb, is from the Latin plumbum. 
 
 The salts of lead are all poisonous ; and hence it 
 is often an important matter to determine whether 
 or not leaden water-pipes affect drinking-water in- 
 juriously. Even the slightest traces of lead, taken 
 day by day into the system, will in time accumulate 
 
THE TETRAD METALS. 243 
 
 so as to cause very serious illness. Perfectly pure 
 water, free from air, does not attack lead ; but wa- 
 ter containing air corrodes it slowly. Drinking- 
 waters all contain salts in solution, and these vary 
 with different localities and different sources of sup- 
 ply. Hard water, or water carrying either sul- 
 phates or carbonates dissolved in it, soon forms a 
 thin, insoluble coating on the surface of lead pipe, 
 and protects it from further action. Such waters, 
 therefore, are relatively safe. On the other hand, 
 water containing nitrates, chlorides, or free car- 
 bonic acid, will gradually take lead into solution, 
 and consequently may become unwholesome by 
 contact with that metal. In using lead pipes the 
 safest rule is never to drink water which has been 
 long standing in them. Always allow the water to 
 run until it flows relatively fresh from the cistern 
 or water-mains. If water is suspected of containing 
 lead, the impurity may be detected by adding a 
 few drops of hydrochloric acid and passing into 
 it a current of sulphuretted hydrogen. If lead is 
 present, a brownish tinge will be produced, which 
 may best be observed by looking through a very 
 thick layer of the liquid. With much lead in a so- 
 lution, sulphuretted hydrogen yields a heavy black 
 precipitate. 
 
 Lead forms a number of important compounds, 
 in most of which it plays the part of a dyad. For 
 example, there are the sulphate, PbSO 4 ; a nitrate, 
 Pb(NO 3 ) 2 ; a chloride, PbCl 2 , etc. The acetate, or 
 sugar of lead, will be described under acetic acid, 
 and the chromate, chrome-yellow, belongs in the 
 chapter with chromium. With oxygen lead com- 
 bines in three proportions, forming a monoxide, 
 
244 INORGANIC CHEMISTRY. 
 
 PbO ; a dioxide, PbO 2 , and the compound known 
 as red-lead or minium, Pb 3 O 4 . The last may be re- * 
 garded as a double oxide, 2 PbO + PbO 2 . 
 
 Lead monoxide, or litharge, is a yellowish pow- 
 der which is formed whenever lead is heated with 
 free access of air. It is a strong base, and combines 
 freely with most acids. It is very largely used as 
 an ingredient of flint-glass, which contains a color- 
 less lead silicate ; it is also employed in glazing 
 earthenware, in preparing other lead compounds, 
 and in medicine. The dioxide is a dark-brown 
 powder having powerful oxidizing properties. Red- 
 lead is made by heating litharge for several hours 
 to dull redness, and forms a valuable paint. It is 
 also used by the glass-makers, and in the prepara- 
 tion of some cements. 
 
 One of the most important compounds of lead 
 is the basic carbonate, 2PbCO 3 , Pb(OH) 2 , which 
 constitutes the valuable paint known as white-lead. 
 This may be prepared by several processes, the old 
 " Dutch method " being the best. Spiral coils of 
 sheet-lead are put in earthen pots with a little vine- 
 gar, and exposed for several weeks to the slow action 
 of carbon dioxide generated by the fermentation 
 of spent tan-bark or sawdust. First, a layer of the 
 bark is put down, and on this the earthen pots are 
 arranged in rows, covered with boards. On these 
 another layer of bark is spread, then a second series 
 of pots, and so on until many successive layers are 
 arranged. The entire pile is finally covered with 
 spent tan. After the proper lapse of time the lead is 
 found to be converted into white-lead, which is thor- 
 oughly washed, dried, and ground up with linseed- 
 oil. It is often adulterated with barium sulphate. 
 
THE TETRAD METALS. 245 
 
 Although white-lead is by far the most brilliant 
 of the white paints, it is subject to some objections. 
 It is readily blackened by sulphuretted hydrogen, 
 and it is poisonous to the workmen who handle it. 
 House-painters are often subject to the painful dis- 
 ease known as lead-colic, which is caused by the 
 slow absorption of small particles of white-lead into 
 the system. Baryta-white and zinc-white are less 
 beautiful than white-lead, but they do not blacken 
 and they are not unwholesome. 
 
 From solutions containing lead the metal is easily 
 thrown down. 
 
 EXPERIMENT 89. Suspend a rod or strip of zinc 
 in a solution of lead acetate. In the course of a few 
 hours the zinc will be covered with brilliant me- 
 tallic spangles of lead, forming what is called the 
 " lead-tree." For every atom of lead thrown down, 
 one atom of zinc goes into solution. If the process 
 be continued long enough, all the lead will separate 
 out, and zinc acetate will remain dissolved : 
 
 Pb(C 2 H 3 2 ) a + Zn = Zn(C a H 3 3 ) 3 + Pb. 
 
 Similarly, metallic mercury, placed in a solution of 
 silver nitrate, will precipitate metallic silver, and be 
 itself dissolved ; copper will precipitate mercury ; 
 iron or zinc will throw down copper, and so on. 
 With each pair of metals the one which is precipi- 
 tated is electro-negative to the one which displaces 
 it from solution. The more electro-positive a metal 
 is, the stronger will be its affinity for acids. 
 
CHAPTER XXVII. 
 
 THE ANTIMONY GROUP. 
 
 IN the same natural group of elements with ni- 
 trogen, phosphorus, and arsenic, we find the metals 
 vanadium, antimony, and bismuth. Each of these 
 substances, like phosphorus, may act either as a 
 triad or a pentad, and each is clearly related to the 
 others through a regular gradation of properties. 
 This is indicated in the following table of atomic 
 weights, specific gravity, and formulae : 
 
 Nitrogen . 
 
 Atomic 
 weight. 
 
 Specific 
 gravity. 
 
 N 2 O 3 
 
 N 2 O B 
 
 HNO 3 
 
 
 Phosphorus 
 Vanadium. 
 
 31 
 
 ci c 
 
 1.837 
 
 (j.;oo 
 
 P 2 3 
 V 2 O 3 
 
 P 2 5 
 V 2 O 6 
 
 HPOs 
 HVO 3 
 
 H 3 P0 4 
 H 3 VO 4 
 
 Arsenic 
 
 7C 
 
 15.700 
 
 As 2 O 3 
 
 As 2 O 6 
 
 
 H 8 AsO 4 
 
 Antimony . ... 
 
 1 2O 
 
 6.7O2 
 
 Sb 2 O 3 
 
 Sb 2 O 6 
 
 HSbO 3 
 
 
 Bismuth 
 
 208 
 
 0.823 
 
 Bi 2 O 3 
 
 Bi-zOs 
 
 HBiO 3 
 
 
 
 
 
 
 
 
 
 
 If we consider the series of compounds begin- 
 ning with nitric acid, we shall find that what may 
 be called the chemical intensity decreases as we 
 ascend. Nitric acid is a very strong acid ; phos- 
 phoric acid is a little weaker ; and so on, until we 
 reach bismuthic acid, HBiO 3 , which is exceedingly 
 feeble. In general, bismuth is a basic metal, and 
 
THE ANTIMONY GROUP. 247 
 
 antimony may act either as an acid-former or as a 
 base. 
 
 VANADIUM, although traces of it occur widely- 
 diffused in many rocks, is one of the very rare met- 
 als. Until quite recently its compounds had no 
 practical applications whatever, but now they are 
 rapidly coming into use for the preparation of a 
 very fine black ink, and in dyeing with aniline 
 black. Vanadic acid behaves like arsenic and phos- 
 phoric acids, and forms a similar variety of salts. 
 Like nitrogen, vanadium forms five oxides V 2 O, 
 VO, V 2 8 , V0 2 , and V 2 O 5 . 
 
 ANTIMONY, although not widely diffused, is nev- 
 ertheless quite abundant in some localities, and ranks 
 commercially as one of the cheaper metals. It is 
 found as native antimony, as sulphide, Sb 2 S 8 , as 
 oxides, and in a variety of other mineral species. 
 Some of the more important silver-ores are double 
 sulphides containing antimony. 
 
 The metal is' easily obtained from its sulphide 
 by heating the latter with scrap-iron. It melts at 
 450 C., and at a red heat is volatile. The vapor 
 oxidizes easily in the air, and forms dense white 
 clouds of Sb 2 O 3 . In color, antimony is bluish white, 
 and in texture it is highly crystalline. It is so 
 brittle that it may readily be pulverized in a mor- 
 tar. An allotropic variety of it, which is obtained 
 by electrolysis, is curiously explosive when either 
 scratched or heated. The symbol, Sb, is from stib- 
 ium. Metallic zinc precipitates antimony from its 
 solutions as a black powder, which, under the name 
 of antimony black, is used for giving to plaster 
 casts the appearance of steel. 
 
 Antimony is chiefly useful in its alloys. Type- 
 
248 INORGANIC CHEMISTRY. 
 
 metal is an alloy of antimony, lead, and tin, in 
 proportions which vary with different makers. In 
 solidifying from the fused state, type-metal expands, 
 insuring an accurate copy of the type-mold. Lead, 
 alone, contracts, and can not give sharp castings. 
 The tin toughens the alloy, the antimony imparts 
 the necessary hardness. Britannia-metal has al- 
 ready been referred to as composed of antimony 
 and tin ; and Babbit's anti-friction metal, which is 
 used by machinists, contains antimony, lead, tin, 
 and a little copper. 
 
 Antimony hydride, orantimoniuretted hydrogen, 
 SbH 3 , is a colorless gas resembling the correspond- 
 ing arsenic compound. Its properties were suffi- 
 ciently indicated under Experiment 77, and its forma- 
 tion affords a meansof detecting antimony in analysis. 
 
 With oxygen, antimony forms three oxides 
 Sb 2 O s , Sb 2 O 4 , and Sb 2 O 5 . From the trioxide, by 
 union with water, ortho-antimonious acid, H 8 SbO 3 , 
 and meta-antimonious acid, HSbO 2 , are derived ; 
 and in a similar way the pentoxide yields antimonic 
 acid, HSbO 8 . These acids are very weak, and their 
 salts are unimportant. There are still other salts 
 in which antimony is basic ; and one compound of 
 this kind, a tartrate of potassium and antimony, is 
 used in medicine under the name of tartar emetic. 
 The chlorides of antimony, SbCl 3 and SbCl 5 , are 
 easily formed by the direct union of the metal 
 with chlorine. The first is a pasty solid, sometimes 
 called " butter of antimony " ; the second is liquid 
 and volatile. 
 
 The sulphides of antimony, Sb 2 S 8 and Sb 2 S 5 , are 
 both interesting. Like the similar compounds of 
 arsenic, they form sulpho-salts ; thus : 
 
THE ANTIMONY GROUP. 249 
 
 NaaS + SbaSa = 2NaSbS 2 , sodium sulphantimonite. 
 3Na 3 S + Sb 2 S 5 = 2Na 3 SbS 4 , " sulphantimonate. 
 
 The trisulphide is the important ore of antimony, 
 stibnite, a heavy gray mineral of brilliant metallic 
 luster. In powder this mineral is an important inr 
 gredient of some fire-work mixtures. There is also 
 an orange-colored modification of the same sul- 
 phide, which is easily obtained in the laboratory, 
 thus: 
 
 EXPERIMENT 90. Dissolve some powdered an- 
 timony in aqua regia (HNO 8 + HC1), and dilute the 
 solution with water until it just begins to turn tur- 
 bid. Divide it into two parts, and saturate one 
 with a stream of hydrogen sulphide. Filter off the 
 orange-red precipitate, dry it, and heat gently in a 
 glass tube. It will be slowly transformed into the 
 black modification, thus showing the relation be- 
 tween the two. To the second part of the solution 
 add ammonium sulphide. The orange-colored pre- 
 cipitate will at first form, and then, upon the addi- 
 tion of more ammonium sulphide, will redissolve ; 
 this action being due to the production of am- 
 monium sulphantimonite, which is soluble. Simi- 
 lar experiments may be performed with a solution 
 of tartar emetic instead of the antimony solution 
 above described. Nitric acid alone will convert 
 antimony into a white oxide, which is insoluble. 
 
 The difference between the two varieties of 
 antimony sulphide is probably due to a different 
 arrangement of atoms in the molecule. The tri- 
 oxide is also dimorphous, and the dimorphism 
 in each case may be rendered clear by the sub- 
 joined structural formulae, in which antimony is 
 trivalent : 
 
250 INORGANIC CHEMISTRY. 
 
 QK^O O x QK ^S S v 
 
 ')0 Sb-O^Sb *>S Sb^S-Sb 
 S K X / Sb <S ^^ 
 
 A red paint, antimony cinnabar, is a double com- 
 pound of antimonious oxide and sulphide. Glass of 
 antimony, which is used for imparting a yellow tint 
 to glass and porcelain, is a substance produced by 
 fusing together the oxide and the sulphide. 
 
 BISMUTH is less abundant than antimony, and is 
 found in comparatively few minerals. The oxide 
 and sulphide occur as definite natural species, but 
 the metal itself is also found in nature, and furnishes 
 the chief supply of bismuth to commerce. It is sim- 
 ply melted out from the adherent rocky material, 
 and collected directly in the metallic state. 
 
 Bismuth is brilliant, brittle, and reddish white. 
 It melts at 264 C., and on solidifying from fusion 
 it expands, increasing about -fa in volume. It crys- 
 tallizes easily, and this fact has already been indi- 
 cated in Experiment 65. The crystals are rhombo- 
 hedral, but might readily be mistaken for cubes, 
 and often display brilliant iridescent colors on the 
 surface. 
 
 Bismuth is useful mainly in its alloys and its 
 compounds. Its alloys are remarkable for their 
 low fusibility, and several of them melt below the 
 boiling-point of water. Rose's alloy consists of 
 one part lead, one part tin, and two parts bismuth, 
 and melts at 93.7 C. Wood's alloy, which melts at 
 60.5, contains four parts bismuth, two of lead, one 
 of tin, and one of cadmium. These alloys expand 
 remarkably in solidifying from fusion, and are used 
 in making casts of medals and coins. A plaster 
 cast is first made, and then filled with the fusible 
 
THE ANTIMONY GROUP. 251 
 
 alloy, which, expanding, fills and reproduces every 
 line. Other alloys of this kind serve to make safety- 
 plugs for steam-boilers. When the boiler gets too 
 hot, the plug melts and the steam escapes harmlessly. 
 
 In its commoner compounds bismuth may be re- 
 garded as trivalent ; and in most of its salts it acts 
 distinctly as a base. Thus we have an oxide, Bi 2 O 3 , 
 a chloride, BiCl 3 , etc. ; and such salts as the nitrate, 
 Bi(NO 3 ) 3 , and the sulphate, Bi 2 (SO 4 ) 3 . When water 
 is added in large quantity to a solution of a bismuth 
 salt, the latter is decomposed, and a basic compound 
 is precipitated. The reaction is exceedingly char- 
 acteristic, and is applied analytically to the detec- 
 tion of bismuth. 
 
 EXPERIMENT 91. Dissolve some powdered bis- 
 muth in a little nitric acid, and divide the solution 
 into two parts. Leave one to crystallize, and add a 
 considerable quantity of water to the other. The 
 first portion will yield crystals of bismuth nitrate, 
 Bi(NO 3 ) 3 , 3H 2 O ; and the second will form a copious 
 white precipitate of the basic nitrate or subnitrate, 
 Bi(OH) 2 NO 3 . The relation of these compounds to 
 each other and to bismuth hydroxide may be ren- 
 dered clear by formulas, thus : 
 
 X OH N0 3 NO, 
 
 Bi-OH Bi-NOs ' Bi-OH 
 
 X OH 
 
 The basic nitrate is a very important medicinal 
 agent in the treatment of bowel disorders. If 
 water be added to the chloride of bismuth, BiCl 3 , 
 a similar white precipitate will be formed consist- 
 ing of bismuth oxychloride, BiOCl. This com- 
 pound has been used as a white face-powder, but 
 
252 INORGANIC CHEMISTRY. 
 
 is decidedly unwholesome. With sulphuretted hy- 
 drogen, bismuth solutions yield a black precipi- 
 tate of bismuth sulphide, Bi 2 S 3 . The same com- 
 pound is thrown down by ammonium sulphide, and 
 is insoluble in an excess of the reagent. 
 
 Two other very rare metals, being pentads, 
 properly belong in this chapter. They are colum- 
 bium,* atomic weight 94, and tantalum, atomic 
 weight 182. Their chlorides, CbCl 5 and TaCl 5 , and 
 their oxides, Cb 2 O 5 and Ta 2 O 5 , are characteristic 
 compounds. From the oxides, columbic and tanta- 
 lic acids are derived, and salts of these acids ex- 
 ist in a few rare minerals. 
 
 * Also known as niobium. The name columbium has priority. 
 
CHAPTER XXVIII. 
 
 THE CHROMIUM GROUP. 
 
 JUST as the metals of the preceding group are 
 classed with nitrogen and phosphorus, so the metals 
 of this group, chromium, molybdenum, tungsten, and 
 uranium, may be regarded as members of the same 
 elementary series with oxygen and sulphur. As 
 metals they have little importance ; but in many of 
 their compounds they are very useful. 
 
 CHROMIUM, atomic weight 52, owes its name to 
 a Greek word signifying color, and several of its 
 compounds are important paints. It occurs in vari- 
 ous minerals, but not very abundantly ; its chief ore 
 being chromite, FeCr 2 O 4 . The metal itself is ob- 
 tained with great difficulty, is almost absolutely in- 
 fusible, and has a specific gravity of 6.8 1. It forms 
 several distinct sets of compounds. 
 
 In chromous oxide, or chromium monoxide, CrO, 
 chromium appears to be bivalent. This oxide is 
 basic, and forms salts which are very unstable, and 
 rapidly absorb oxygen from the air. 
 
 Chromic oxide or chromium sesquioxide, Cr 2 O 8 , 
 is the most stable of the chromium compounds. It 
 is a brilliant-green powder, which is used in giving 
 a green color to glass and porcelain. The emerald 
 owes its hue to traces of this compound. From it 
 
254 INORGANIC CHEMISTRY. 
 
 as a base many salts may be derived ; for example, 
 there is a sulphate Cr 2 (SO 4 ) 3 , a chloride, Cr 2 Cl 6 , etc. 
 The chloride forms superb violet-colored scales. 
 Like aluminum sulphate, chromic sulphate forms 
 alums, of which common chrome alum, KCr(SO 4 ) 2 , 
 I2H 2 O, is the type. This may be obtained in violet- 
 colored octahedral crystals as follows : 
 
 EXPERIMENT 92. Dissolve about thirty grammes 
 of potassium pyrochromate * in the smallest possible 
 quantity of water, add forty grammes of sulphuric 
 acid, largely diluted, and boil with successive addi- 
 tions of small quantities of alcohol until the original 
 orange color of the solution is completely changed 
 to green. Upon moderately long standing, crystals 
 of chrome alum will be deposited. The reaction in- 
 volves the reduction of the highly oxidized chro- 
 mate to the lower oxidation of the chromic salt. At 
 the same time, the alcohol, which serves as the re- 
 ducing agent, is itself oxidized. 
 
 Chromium trioxide, CrO 8 , is the starting-point 
 from which chromic acid, H 2 CrO 4 , and a large num- 
 ber of chromates may be derived. These chromates 
 and the trioxide resemble the sulphates and sulphur 
 trioxide in chemical structure : f 
 
 OT? OT-T 
 
 S0 a = Cr0 3 = 
 
 qn /OK rn /OK 
 
 SOa \OK Cr0a \OK 
 
 i 
 
 Chromium trioxide is easily obtained from any 
 chromate by treatment with sulphuric acid ; thus : 
 EXPERIMENT 93. Add strong sulphuric acid, 
 
 * Commonly called bichromate of potash. 
 f Refer to Chapter XVI. 
 
THE CHROMIUM GROUP. 
 
 255 
 
 very gradually, to a strong solution of potassium 
 pyrochromate. Heat will be evolved ;. and, upon 
 cooling, superb crimson needles of the trioxide will 
 be deposited. These may be dried by draining on 
 a porous brick or tile, but should not be brought 
 in contact with any organic matter. Most organic 
 bodies are oxidized by them, Cr 2 O 3 being simultane- 
 ously formed. In Experiment 92 a reaction of this 
 kind took place, which may be further illustrated 
 by dropping strong alcohol upon the dry trioxide. 
 The alcohol will be ignited by the heat of the oxida- 
 tion. The aqueous solution of chromium trioxide 
 is yellow, and may be regarded as containing chro- 
 mic acid, H 2 CrO 4 , 
 
 (HaO + CrO 3 = H 2 CrO 4 ). 
 
 Nearly all of the chromates are either red, orange, 
 or yellow, and several of them are exceedingly im- 
 portant. 
 
 Potassium forms three chromates ; the first one, 
 K 2 CrO 4 , being the normal salt. The other two may 
 be represented as formed from this by the addition 
 of one and two molecules of CrO 3 respectively, as 
 follow : 
 
 K 2 CrO 4 -f CrOs = K 2 Cr 2 O 7 , potassium pyrochromate. 
 K 2 CrO 4 + 2CrO 3 = KaCr s O ie , " trichromate. 
 
 Structurally, the three salts may be represented 
 thus : 
 
 / OK CrOa \ r\ 
 
 
 The second of these chromates, the dichromate 
 or pyrochromate, is by far the most important of 
 
 12 
 
256 INORGANIC CHEMISTRY. 
 
 all the compounds of chromium, and from it the 
 others are prepared. It is made directly from chro- 
 mite (chrome iron-ore) by roasting the finely pow- 
 dered mineral in a strong oxidizing flame with po- 
 tassium carbonate and a little lime. Sometimes salt- 
 peter is added also. The roasted mass yields with 
 water a yellow solution of monochromate ; which, 
 treated with a quantity of sulphuric acid half suffi- 
 cient to set its chromic acid free, deposits, on cool- 
 ing, superb orange-red crystals of the desired salt. 
 
 Potassium pyrochromate is largely used in dye- 
 ing and calico-printing, in preparing the various 
 chromium paints, as an oxidizing agent in bleaching 
 discolored fats and oils, and in certain of the pro- 
 cesses of photography. Paper dipped in a solution 
 of it acquires a pale-yellow tint, but becomes brown 
 on exposure to light.* A film of gelatine saturated 
 with the salt becomes insoluble wherever it has 
 been acted on by light, but remains soluble in its 
 other portions. A photograph, therefore, taken on 
 such a film, may be made to stand out in actual re- 
 lief by simply dissolving away the unattacked parts ; 
 and then either copied in electrotype or in type- 
 metal, or transferred to a lithographic stone. This 
 fact is the basis of all the processes of photographic 
 printing, such as are used in the production of helio- 
 types, autotypes, photo-lithographs, etc.f 
 
 Another important chromate is lead chromate, 
 or chrome-yellow, PbCrO 4 . This useful paint is 
 prepared by mixing solutions of lead acetate and 
 potassium pyrochromate, and filtering off the bright- 
 
 * Repeat Experiment 83, using K 2 Cr a O7 instead of AgNOs- The 
 print may be rendered permanent by thorough washing with water. 
 I For details, see Abney's " Treatise on Photography." 
 
THE CHROMIUM GROUP. 257 
 
 yellow precipitate.* Boiling- with a caustic alkali 
 converts it into chrome-red, PbCrO 4 , PbO. Chrome- 
 orange is a mixture of chrome-red and chrome-yel- 
 low. 
 
 MOLYBDENUM, atomic weight 96, is one of the 
 rarer metals. Its chief ore is molybdenite, MoS 2 , 
 which strongly resembles graphite in its outward ap- 
 pearance. It forms complicated compounds, but its 
 leading oxide, MoO 3 , and molybdic acid, H 2 MoO 4 , 
 are analogous to the corresponding oxides and acids 
 of sulphur and chromium. Ammonium molybdate 
 is a very important, practically indispensable re- 
 agent, in the exact analysis of iron-ores and ferti- 
 lizers. 
 
 TUNGSTEN, atomic weight 184, is somewhat rare, 
 though more abundant than molybdenum. It is 
 found in several minerals, but chiefly in a tungstate 
 of iron, wolfram, FeWO 4 . The symbol, W, is de- 
 rived from wolfram ; but the name of the metal 
 itself, of Swedish origin, signifies a heavy stone. 
 Wolfram is a frequent and troublesome impurity 
 among tin-ores, and miners regard it as a sign of 
 tin. 
 
 Tungsten itself is a grayish metal, of specific 
 gravity 19.26, being almost as heavy as gold. Its 
 addition to steel in small quantities is said to give 
 the latter superior hardness and fineness. 
 
 Like molybdenum, tungsten forms very compli- 
 cated compounds. Some of them have great theo- 
 retical interest, but need no description here. Tung- 
 sten trioxide and tungstic acid, WO 3 and H 2 WO 4 , 
 show its relations to the other metals of the group, 
 and the hexchloride, WC1 6 , indicates its sexivalency. 
 
 * The experiment is a good and easy one for the pupil to try. 
 
258 INORGANIC CHEMISTRY. 
 
 One of the tungstates of sodium is sometimes used 
 as a mordant, and also for rendering cloth fabrics 
 uninflammable. 
 
 URANIUM, atomic weight 239, is another of the 
 rarer metals. When pure, it is silver-white, very 
 difficultly fusible, and of specific gravity 18.685. It 
 is found in a considerable number of minerals, but 
 is generally obtained from pitchblende, an impure 
 U 3 O 8 . This oxide is a compound of two others, 
 UO 2 and UO 3 ; and still another, UO 4 , has recently 
 been discovered. The trioxide, UO 3 , is a yellow 
 powder ; and from it a series of salts, similar in 
 composition to the pyrochromates, are derived. 
 The sodium and ammonium uranates, Am 2 U 2 O 7 and 
 Na 2 U 2 O 7 , both occur in commerce under the name 
 of "uranium yellow," and are used in coloring glass 
 and porcelain. The uranium glass has a peculiar 
 greenish-yellow color (canary glass), and is highly 
 fluorescent. In two other series of salts uranium is 
 basic. The uranic nitrate and acetate are useful 
 laboratory reagents. 
 
 Although uranium and its compounds have but 
 limited importance, the metal itself affords a good 
 illustration of the law of Dulong and Petit. This is 
 a physical law of much value in the determination 
 of atomic weights, and therefore it may be profita- 
 bly considered here. 
 
 If two different substances, equal in weight, be 
 exposed to the same source of heat, they will be 
 found to gain in temperature with very unequal 
 rapidity. A kilogramme of water, for example, re- 
 quires about thirty times as much heat to raise its 
 temperature one degree as is required to produce 
 the same effect upon the same quantity of mercury. 
 
THE CHROMIUM GROUP. 
 
 259 
 
 Hence the specific heat of mercury is said to be one 
 thirtieth of that of water. By the term specific heat 
 we express the relative amounts of heat needed to 
 raise equal weights of substances through equal 
 ranges of temperature. Water has the highest 
 specific heat of any substance known, and is taken 
 as the standard of comparison or unity. The spe- 
 cific heat of other substances is expressed in frac- 
 tions of unity. In other words, the quantity of 
 heat necessary to raise the temperature of one kilo- 
 gramme of water i C. is said to be one unit. The 
 fraction of such a unit which is required to raise the 
 temperature of a kilogramme of any other substance 
 i C. is called its specific heat. 
 
 Now, the law of Dulong and Petit is based upon 
 the fact that, when the specific heats of the metals 
 are multiplied by their atomic weights, the products 
 are sensibly equal. The product in each case is 
 called the atomic heat of the metal ; and the law 
 which is deduced is as follows : all the element- 
 ary atoms have equal capacities for heat* This is 
 shown in the table, which includes some of the 
 non-metals : 
 
 Table of Specific and Atomic Heat. 
 
 NAME. 
 
 .83 
 
 ff M 
 
 g 
 
 i d 
 
 | 
 
 i* 
 g 
 
 NAME. 
 
 3S 
 |f 
 
 iij 
 
 $ 
 $* 
 
 is 
 
 <-* 
 
 Aluminum 
 Antimony 
 Arsenic . . 
 
 27. 
 120. 
 
 75'. 
 
 .2253 
 
 Q.-23 
 .0822 
 
 6.08 
 6.28 
 
 6.16 
 
 Calcium .... 
 Cerium 
 Cobalt 
 
 40. 
 141. 
 
 CQ 
 
 .1686 
 .0448 
 .1062 
 
 6.74 
 6.32 
 626 
 
 Barium . . 
 Bismuth . 
 Cadmium 
 
 137- 
 208. 
 
 112. 
 
 .05 
 .0305 
 .0548 
 
 6.85 
 6.34 
 
 6.14 
 
 Copper 
 Didymium . . 
 Gallium 
 
 63.3 
 145- 
 6 9 . 
 
 .0951 
 .0456 
 .079 
 
 6.00 
 6.6 1 
 
 545 
 
 * For fuller discussions of this law, see Wurtz's " Atomic Theory, 
 and Chapter III of Remsen's " Theoretical Chemistry." 
 
2 6o INORGANIC CHEMISTRY. 
 
 Table of Specific and Atomic Heat (continued'). 
 
 NAME. 
 
 ii 
 
 <* 
 
 HL- 
 
 Z$ 
 eg* 
 
 .a . 
 
 I-S 
 
 NAME. 
 
 ,a5 
 
 efcJO 
 3 
 
 <* 
 
 o 
 
 1C . 
 
 HI 
 eg* 
 
 ^ 
 
 11 
 <* 
 
 Gold 
 
 106.5 
 
 .0316 
 
 6.T8 
 
 Platinum .... 
 
 *95- 
 
 0323 
 
 6.29 
 
 Indium 
 
 Iia C 
 
 .0565 
 
 6.61 
 
 Rhodium .... 
 
 104.? 
 
 .0580 
 
 6.O3 
 
 Iridium 
 
 193. 
 56. 
 
 .0326 
 .1116 
 
 6.29 
 6.25 
 
 Ruthenium . . 
 Selenium.. . . 
 
 104.? 
 
 79- 
 
 .0611 
 .0860 
 
 6-35 
 6.79 
 
 
 
 O^d.1 
 
 6 87 
 
 Silver . . 
 
 108 
 
 OCCQ 
 
 6 04. 
 
 
 178 
 
 OJ. l8 
 
 6 18 
 
 Sodium . ... 
 
 27. 
 
 2Q7A 
 
 6 75 
 
 Lead 
 
 2O7. 
 
 .03 I s ; 
 
 6.52 
 
 Sulphur.. . . 
 
 32. 
 
 .2026 
 
 6/]8 
 
 Lithium 
 
 7. 
 
 .0108 
 
 6.59 
 
 Tellurium . . 
 
 125. 
 
 475 
 
 5-94 
 
 Magnesium.. 
 Manganese.. 
 
 24. 
 
 55- 
 200 
 
 .2499 
 .1217 
 
 O777 
 
 6.00 
 6.70 
 666 
 
 Thallium. . . 
 Thorium . . . 
 Tin 
 
 204. 
 232. 
 118. 
 
 .0325 
 .0279 
 
 .0548 
 
 6.63 
 6.47 
 6 17 
 
 Molybdenum 
 Nickel 
 
 9 5. 
 
 58. 
 
 .0722 
 .IO75 
 
 6-93 
 6.23 
 
 Tungsten. . . 
 Uranium . . . 
 
 184. 
 
 239- 
 
 .0334 
 
 .0275 
 
 6.15 
 6.56 
 
 
 TOO ? 
 
 O3II 
 
 6 19 
 
 Zinc . .... 
 
 65. 
 
 .OQ7Q 
 
 6 OQ 
 
 Palladium. . . 
 Phosphorus . . 
 
 106. 
 Si- 
 
 .0592 
 .202 
 
 6.27 
 6.26 
 
 Zirconium.. . 
 
 90. 
 
 .0667 
 
 u.uy 
 
 6.00 
 
 There are a few apparent exceptions to the law, but 
 they need no notice here. The slight variations 
 from exact equality in the column of atomic heats 
 are due to unavoidable errors of experiment. 
 
 In the case of uranium there was until recently 
 some doubt as to whether its atomic weight was 
 239; or only half as great ; and the analyses of its 
 compounds gave formulae which agreed equally 
 well with either value. Thus, in UO 3 we have 239 
 parts of uranium, combined with 48 of oxygen ; 
 while, if U = 119.5, we should write the formula 
 U 2 Os, and express precisely the same ratio.* The 
 uncertainty was at last dispelled by a determination 
 of the specific heat of uranium, which Zimmermann 
 found to be .028. This, multiplied by 239, gives a 
 
 * The values 120 and 240 have commonly been given to U, but 
 119.5 and 239 are probably more nearly exact. 
 
THE CHROMIUM GROUP. 261 
 
 value for the atomic heat of 6.69, which agrees with 
 the other metals; whereas 119.5 would have given 
 a product very far too small. In many other cases 
 the atomic weights of elements have been unsettled 
 until the specific heats could be ascertained, and 
 that value selected which agreed best with Dulong 
 and Petit's law. 
 
CHAPTER XXIX. 
 
 MANGANESE AND IRON. 
 
 MANGANESE, iron, nickel, and cobalt are so 
 closely related that they may fairly be called the 
 iron group of metals. They are near each other in 
 metallic properties, and their compounds have very 
 many points of similarity. In valency they range 
 from two, to four, six, and eight. 
 
 MANGANESE is one of the commoner elements, 
 and is very widely diffused. It occurs in many 
 rocks and minerals, but its chief ores are pyrolusite, 
 MnO 2 , and manganite, Mn 2 O 3 , H 2 O. The metal it- 
 self is somewhat difficult to prepare, and in appear- 
 ance is similar to cast-iron. It oxidizes very easily, 
 is slightly magnetic, very difficultly fusible, and has 
 a specific gravity of 8.0. Its atomic weight is 55. 
 
 With oxygen, manganese combines to form the 
 oxides MnO, Mn 2 O 3 , Mn 3 O 4 , MnO 2 , and Mn 2 O 7 . 
 From the monoxide, MnO, a series of manganese 
 salts are derived, which are mostly rose-colored. 
 Manganous sulphate, MnSO 4 , 5H 2 O, and manganous 
 chloride, MnCl 2 , 4H 2 O, are the salts most often seen. 
 In solutions of manganese compounds ammonium 
 sulphide produces a flesh - colored precipitate of 
 MnS. From Mn 2 O 3 , which is also a basic oxide, the 
 manganic salts are prepared. Manganic sulphate, 
 
MANGANESE AND IRON. 263 
 
 Mn 2 (SO 4 ) 3 , unites with the alkaline sulphates to 
 form alums ; and in this particular manganese and 
 chromium may be classed in one group with alu- 
 minum and iron. Most of the manganic salts are 
 brown. 
 
 The oxides MnO 2 and Mn 3 O 4 are neutral oxides ; 
 that is, they form neither acids nor bases. The first 
 of these, commonly known as black oxide of man- 
 ganese, occurs abundantly in many localities, and is 
 simply ground up to powder and sent into com- 
 merce. Enormous quantities of it are used in mak- 
 ing chlorine and bleaching-powder, in the prepara- 
 tion of oxygen, and as a material from which all the 
 other compounds of manganese may be derived. 
 
 Manganese forms two acids : manganic acid, 
 H 2 MnO 4 , known only in its salts, and permanganic 
 acid, HMnO 4 , which is derived from the oxide Mn 2 O 7 . 
 Mn 2 O 7 -[-H 2 O=2HMnO 4 . Manganic acid belongs in 
 the same class with sulphuric and chromic acids; 
 while permanganic acid is similar in structure to 
 perchloric acid. The salts KC1O 4 and KMnO 4 are 
 isomorphous. The manganates are green ; the per- 
 manganates violet, red, or purple. 
 
 EXPERIMENT 94. Mix a little MnO 2 with so- 
 dium carbonate, and fuse the mixture in the outer 
 blow-pipe flame upon a slip of platinum foil. A 
 green mass of sodium manganate will be formed, 
 and by the production of this green color even the 
 smallest traces of manganese may be detected. Dis- 
 solve the fused mass in cold water, and let the solu- 
 tion stand freely exposed to the air. It will slowly 
 change color, passing from green through a series 
 of intermediate tints, until at last it becomes a su- 
 perb purple. These changes, which end in the pro- 
 
264 INORGANIC CHEMISTRY. 
 
 duction of sodium permanganate, caused the green 
 mass to receive the popular name of " chameleon 
 mineral." 
 
 Potassium permanganate, KMnO 4 , is an impor- 
 tant disinfectant. It forms nearly black crystals 
 with a semi-metallic reflection from their surfaces, 
 and it dissolves easily in water to an intense purple 
 fluid. Even a trace of the salt will impart a rosy 
 color to a large amount of water, and concentrated 
 solutions of it are opaque. It is a powerful oxidiz- 
 ing agent, and is much used as a reagent in chemical 
 analysis. Putrid water, or water which has acquired 
 an unpleasant, woody taste, from long keeping in 
 wooden cisterns or casks, may be rendered sweet by 
 the addition of a very little potassium permanganate. 
 
 IRON, atomic weight 56, is the most familiar and 
 useful of all metals, and one of the most abundant. 
 It is contained in a vast number of minerals, in 
 practically all rocks and soils, in the water of many 
 springs, in plants, and in the red coloring-matter of 
 blood. Occasionally it is found free in nature, and 
 a considerable proportion of the meteoric masses 
 which fall to the earth consist of metallic iron. One 
 such mass from Brazil weighed 32,000 pounds. 
 
 But, although iron is so widely diffused, it is 
 practically manufactured from only a very few ores. 
 These are essentially the magnetic oxide, Fe 3 O 4 ; 
 hematite, Fe 2 O 3 ; limonite, 2Fe 2 O 8 , sH 2 O ; and cha- 
 lybite or spathic iron, FeCO 8 . Of these, the mag- 
 netic ore is the richest, containing, when pure, 72.5 
 per cent of iron. 
 
 Pure iron is rarely seen. It is silvery white, 
 softer than wrought-iron, almost infusible, and has 
 a specific gravity of 7.8 to 8.0. It is extraordinarily 
 
MANGANESE AND IRON. 2 6$ 
 
 malleable and ductile, and at the same time very 
 tenacious ; so that, even in the finest wire, it can 
 support a considerable weight. The symbol, Fe, is 
 from the Latin ferrum. 
 
 All commercial iron contains carbon, and its 
 properties vary remarkably according to the pro- 
 portion of the latter. Wrought-iron, or malleable 
 iron, contains less than half a per cent of this im- 
 purity ; cast-iron contains from two to six per cent, 
 partly or wholly in chemical combination ; steel is 
 intermediate between the other two. 
 
 Wrought-iron is tough and fibrous in structure, 
 and can be worked at a red heat by rolling or ham- 
 mering. At the highest available temperatures it 
 does not fuse, but merely becomes pasty ; but, in 
 this condition, two masses may be compactly ham- 
 mered or welded together. This capability of weld- 
 ing is one of its most valuable properties. It is 
 sometimes prepared directly from the ore, by heat- 
 ing the latter in a proper furnace with charcoal, and 
 afterward purifying the pasty mass from adhering 
 fuel and slag by thorough hammering. This pro- 
 cess, which is known as blooming, has been in use 
 from the remotest antiquity, and yields a remarka- 
 bly fine quality of metal. It is, however, too ex- 
 pensive to be largely used at the present time ; and 
 to-day malleable iron is chiefly prepared by burning 
 out the carbon from cast-iron. The latter, mixed 
 with a certain amount of ferric oxide, is melted on 
 the floor of a reverberatory furnace, and constantly 
 stirred or shaken until it becomes pasty. The 
 spongy lumps are then taken out, and worked into 
 shape between heavy rollers. The whole process is 
 technically known 2& puddling. 
 
2 66 INORGANIC CHEMISTRY. 
 
 Cast-iron, which is a comparatively modern prod- 
 uct, is made in the blast-furnace (Fig. 50). This 
 consists of a tower from forty to ninety feet in 
 
 FIG. 50. Section of Blast Furnace. 
 
 height, having an interior diameter of from four- 
 teen to seventeen feet in the maximum. Internally 
 it is like two hollow cones placed base to base, 
 and it is lined with the most refractory fire-brick. 
 At the bottom, air is blown in by a powerful blast, 
 through pipes which are called tuyeres;* and ac- 
 
 * Pronounced " twyers." 
 
MANGANESE AND IRON. 2 6/ 
 
 cordingly, as hot or cold air is used, we have hot 
 and cold blast-furnaces respectively. The hot-blast 
 process is the more economical. 
 
 The furnace is fed at the top, and alternate lay- 
 ers of fuel, ore, and limestone are put in. The blast 
 of air from the tuyeres furnishes oxygen, vivid com- 
 bustion takes place, the oxides of iron are reduced 
 by the carbon,* and the metal is set free. The lat- 
 ter dissolves some carbon, fuses, and settles to the 
 bottom of the furnace, where it is drawn off from 
 time to time into molds made of sand. The object 
 of the limestone is to form an easily fusible slag 
 with the silica of the ore, and with this slag many 
 of the impurities are removed. When once kin- 
 dled, a furnace should burn continuously for months, 
 or even years ; were the semi-fluid mass to solidify 
 by too great a cooling, it would have to be dug out 
 at great expense and at the cost of serious delay to. 
 the iron-master. 
 
 Cast-iron or pig-iron occurs in several forms, but 
 is always crystalline in structure and more or less 
 brittle. White cast-iron is very hard, highly crys- 
 talline, and quite brilliant. Gray cast-iron is softer 
 and closer grained. Mottled iron is intermediate 
 between the other two. In white iron, most of the 
 carbon is combined chemically ; in gray iron, a part 
 has separated out in the form of fine .scales of graph- 
 ite. Spiegeleisen is a particularly brilliant white 
 iron, containing about six per cent of carbon and 
 some manganese. Common impurities in iron are 
 silicon, sulphur, and phosphorus. The last two ele- 
 
 * In reality, the chemical processes which take place in the blast- 
 furnace are quite complicated. In them, carbon monoxide plays an 
 important part. 
 
268 INORGANIC CHEMISTRY. 
 
 ments are particularly objectionable, especially if 
 the iron is to be either puddled or made into steel. 
 Sulphur, in wrought-iron, renders the metal brittle 
 when hot, or "hot-short"; the presence of phos- 
 phorus makes it brittle when cold, or " cold-short." 
 
 Steel may be made in several ways. Carbon 
 may be added to malleable iron, or carbon may be 
 withdrawn from cast-iron, or cast-iron and malle- 
 able iron may be melted together in the proportions 
 needed to form a mixture having the composition 
 and properties of steel. The last method is adopted 
 in what is called the Siemens-Martin process. Of 
 these methods, the first is by far the oldest. Bars 
 of iron are packed in charcoal in tight boxes of fire- 
 clay, and heated red-hot for a week or ten days. 
 Carbon is slowly absorbed, and at the end of the 
 operation the bars are found to have a curiously 
 blistered appearance. By melting them in black- 
 lead crucibles and casting them in ingots, cast-steel 
 is obtained. The whole process is known as the 
 cementation process, and cementation steel is con- 
 sidered the best for fine tools, knives, springs, etc. 
 
 The second process, by which carbon is taken 
 away from cast-iron, was invented by Bessemer in 
 1856. In this process, about five tons of melted pig- 
 iron are poured into an egg-shaped vessel called a 
 " converter " (Fig. 5 1), through which a powerful 
 blast of air can be blown. The converter is made 
 of the strongest wrought-iron, and lined with an in- 
 fusible layer of a silicious rock resembling fire-clay.* 
 As the air bubbles through the molten iron, forced 
 in from below, the temperature rises, carbon is 
 
 * In the Gilchrist-Thomas process, which removes the phosphorus 
 from the iron, the converter is given a " basic lining " of lime. 
 
MANGANESE AND IRON. 269 
 
 burned away, and the metal rapidly approaches the 
 malleable state. Just before the latter is reached, 
 however, a quantity of melted spiegel- 
 eisen is added, so as to supply just 
 the amount of carbon needed for the 
 production of good steel. The latter 
 is then poured out into molds, and the 
 operation is complete. By this pro- 
 cess iron may be transformed into 
 steel in less than half an hour, so that 
 
 f ,. . . .,, FIG. 51. Besse- 
 
 the saving of time in comparison with mer converter. 
 the cementation process is enormous. 
 To-day, in consequence of Bessemer's invention, 
 steel may be used for the manufacture of rails, car- 
 axles, bridge-girders, boiler-plates, and cannon, and 
 for a multitude of other purposes to which, thirty 
 years ago, it was too expensive to be applicable. 
 It is no exaggeration to say that the Bessemer pro- 
 cess is revolutionizing the iron industry.* 
 
 Steel owes its value to a variety of properties. 
 Like cast-iron it is fusible, like wrought-iron it is 
 malleable ; it is capable of high polish, and may be 
 rendered exceedingly hard. If heated to redness 
 and suddenly quenched in cold water, it becomes 
 both hard and brittle ; but upon reheating and cool- 
 ing slowly, it may again be rendered soft. By care- 
 fully regulating the heatings and coolings, interme- 
 diate degrees of hardness, brittleness, and elasticity 
 may be attained ; and by this process of " temper- 
 ing," steel is adapted to a wide diversity of uses. 
 
 Like manganese and chromium, iron forms two 
 
 * The best large treatise on the metallurgy of iron and steel is 
 Percy's. A good summary of the subject is given in Roscoe and Schor- 
 lemmer's " Treatise on Chemistry," vol. ii, part ii, pp. 34-83. 
 
2 70 INORGANIC CHEMISTRY. 
 
 distinct series of compounds, in which it plays the 
 part of base. It also forms a very unstable series of 
 salts, corresponding to ferric acid, H 2 FeO 4 , which 
 are analogous to the chromates and manganates. 
 
 The ferrous salts, in which iron is apparently biv- 
 alent, are similar in structure to the salts of zinc, 
 magnesium, and manganese. They may be regard- 
 ed as derived from ferrous oxide, FeO, and are 
 mostly pale green in color. By adding any caustic 
 alkali, KOH, NaOH, or AmOH, to a solution of a 
 ferrous hydroxide, Fe(OH) 2 , is obtained as a green- 
 ish precipitate. Ferrous chloride, FeCl 2 , 4H 2 O, is 
 easily prepared by dissolving iron in hydrochloric 
 acid, and is used in some processes of metallurgy. 
 Ferrous carbonate, FeCO 3 , is a crystalline mineral, 
 which, in a crude and impure state, is one of the 
 most important ores of iron. Ferrous sulphide, 
 FeS, is made by fusing iron and sulphur together 
 in the proportion indicated by their atomic weights, 
 and is employed in the laboratory for the genera- 
 tion of sulphuretted hydrogen. But the most im- 
 portant of the ferrous compounds is the sulphate, 
 FeSO 4 , 7H 2 O, which is commonly known as green 
 vitriol or copperas. It is prepared by dissolving 
 iron in sulphuric acid, or by slowly oxidizing iron 
 pyrites ; and forms large, pale-green crystals which 
 behave with regard to their water of crystallization 
 precisely like the sulphates of zinc and magnesium. 
 With tannin, or with solution of galls, ferrous sul- 
 phate strikes a deep-black color, on which account 
 it is used in great quantities for the manufacture of 
 ink. It also has some value as a disinfectant, acting 
 as an absorbent of oxygen. 
 
 All ferrous salts tend to take up oxygen from 
 
MANGANESE AND IRON. 2 Jl 
 
 the air, and to become converted into ferric com- 
 pounds, which are mostly red or yellow. Ferric 
 oxide, Fe 2 O 3 , is the important ore, hematite ; and 
 also, artificially prepared, is used both as a material 
 for polishing glass and precious metals, and as a 
 pigment under the name of Venetian-red. Jeweler's 
 rouge and crocus-powder are merely ferric oxide. 
 Several ferric hydroxides are found as mineral spe- 
 cies, and are valuable ores. An artificial hydroxide, 
 Fe 2 (OH) 6 , is produced by caustic alkalies in solu- 
 tions of ferric salts, as a reddish-brown precipitate. 
 It is used in some processes for purifying coal-gas, 
 and as an antidote for arsenical poisoning. Iron- 
 rust is another ferric hydroxide, produced by the 
 joint action of air and water upon metallic iron. 
 Ferric chloride, Fe 2 Cl 6 , and ferric sulphate, Fe 2 (SO 4 ) 3 , 
 are both important ferric salts. The chloride is used 
 as a reagent in the laboratory, and also in medicine 
 as a material to stop bleeding. The sulphate unites 
 with alkaline sulphates to form alums, which cor- 
 respond perfectly to the similar salts of aluminum 
 and chromium. 
 
 The magnetic oxide, Fe 3 O 4 , is a very important 
 ore, and is also met with as iron-scale in the black- 
 smith-shops. By heating iron in dry steam it may 
 be coated with a thin black film of this oxide and 
 protected against rust. Fe 3 O 4 is a neutral oxide, and 
 may be regarded as FeO -\- Fe 2 O 3 . Iron pyrites, 
 FeS 2 , is a common mineral, which is sometimes 
 called " fools' gold." It is yellow and metallic in 
 appearance, but, unlike gold, it may be pulverized 
 under a hammer. It is used as a source of copperas, 
 and also in the manufacture of sulphuric acid. 
 
 EXPERIMENT 95. Dissolve some iron filings in 
 
272 INORGANIC CHEMISTRY 
 
 dilute sulphuric acid, and divide the solution into 
 two parts. Add ammonia to one portion, and note 
 the color of the ferrous hydroxide which is thrown 
 down. Boil the other portion with a few drops of 
 strong nitric acid, and observe the change of tint. 
 Again precipitate with ammonia, and note the pe- 
 culiarities of the ferric hydroxide which will be ob- 
 tained. Nitric acid oxidizes ferrous compounds to 
 the ferric state. 
 
CHAPTER XXX. 
 
 NICKEL, COBALT, AND COPPER. 
 
 NICKEL and cobalt are comparatively rare met- 
 als, having a decided resemblance to iron. Both 
 are white and malleable, but cobalt has a very slight 
 reddish tinge. Both are strongly magnetic, and 
 their specific gravity is not far from 9. The atomic 
 weight of nickel is 58 ; that of cobalt is 59. 
 
 The chief supply of nickel comes from Ger- 
 many, Pennsylvania, and New Caledonia, and quite 
 recently valuable deposits of a nickel-ore have been 
 found in Oregon. The ores are mostly sulphides, 
 arsenides, and silicates of nickel, and the extraction 
 of the metal is a somewhat complicated matter. It 
 is used as an ingredient of small coins by several 
 nations, and German silver is an alloy of copper, 
 zinc, and nickel. Of late years the process of elec- 
 troplating with nickel has assumed considerable im- 
 portance. The metal forms a beautiful white sur- 
 face which does not rust, and is chiefly applied to 
 articles of copper, brass, or steel. 
 
 The compounds of cobalt and nickel resemble 
 those of iron, except that their lower salts do not 
 so readily oxidize to form the higher. The oxides 
 CoO, NiO, Co 2 O 3 , Ni 2 O 3 , yield series of derivatives 
 similar to the ferrous and ferric compounds. The 
 
274 INORGANIC CHEMISTRY. 
 
 nickelous salts are generally green, and the sulphate, 
 NiSO 4 , ;H 2 O, the chloride, NiCl 2 , 6H 2 O, and the ni- 
 trate, Ni(NO 3 ) 2 , 6H 2 O are the most important. The 
 salt employed in nickel-plating is the double sul- 
 phate NiSO 4 , Am 2 SO 4 , 6H 2 O. 
 
 The cobaltous salts are remarkable in regard 
 to their colors. They are rose-red when hydrat- 
 ed, blue when anhydrous. Heat cobalt sulphate, 
 CoSO 4 , 7H 2 O, until its water of crystallization is ex- 
 pelled, and its red color will pass into the blue tint 
 of CoSO 4 . 
 
 EXPERIMENT 96. Dissolve cobalt chloride in 
 water, and with a small brush apply the solution to 
 a sheet of white paper. When the latter is dry, 
 scarcely any color can be perceived upon it, but by 
 gently heating before a fire it will become distinctly 
 blue. The solution, therefore, may be used as a 
 " sympathetic ink " ; and a letter written with it will 
 be legible only when the paper is warm. 
 
 Some of the cobalt compounds are valuable col- 
 ors, especially for glass and porcelain. Smalt blue 
 is a silicate of cobalt, which withstands the highest 
 temperatures of the porcelain oven. Thenard's blue 
 contains the oxides of cobalt and aluminum. Rin- 
 mann's green consists of the oxides of cobalt and zinc. 
 
 EXPERIMENT 97. Place a crystal of alum on a 
 charcoal support, and heat it before the blow-pipe. 
 Moisten the infusible residue with a drop of cobalt 
 nitrate solution, and heat again. The mass will be- 
 come blue. Repeat the experiment, using zinc ox- 
 ide instead of alum, and a green will be produced. 
 Magnesia, treated in the same way with cobalt ni- 
 trate, gives a pale rose. By cobalt compounds a 
 borax bead is colored intensely blue. 
 
NICKEL, COBALT, AND COPPER. 275 
 
 COPPER, atomic weight 63.3, is a metal having 
 some relationship to the iron group on one side, 
 and closely allied to silver and mercury on the 
 other. Like mercury, it forms two sets of com- 
 pounds, a cuprous and a cupric series, but some of 
 its salts are quite analogous to similar compounds 
 of iron. The symbol, Cu, is from the Latin cu- 
 prum. 
 
 Copper is widely diffused in the mineral king- 
 dom, both as native metal and in a great variety 
 of compounds. Native copper is abundant in the 
 Lake Superior mining region, and a single mass 
 weighing four hundred and twenty tons was once 
 found. Important ores of copper are cuprous sul- 
 phide, Cu 2 S ; the oxides, Cu 2 O and CuO ; bornite, 
 Cu 3 FeS 3 ; copper pyrites, CuFeS 2 ; and malachite, 
 CuCO 3 , Cu(OH) 2 . The last-named mineral is often 
 used as an ornamental green stone. 
 
 The process of extracting copper from its ores 
 is generally somewhat complicated. The native 
 metal, of course, only needs to be put through a 
 refining operation in order to be prepared for 
 market ; and the oxides and carbonates of copper 
 may be easily reduced by heating with carbon ; but 
 in most smelting-works the metallurgist has to deal 
 with sulphides containing iron. These are com- 
 monly treated as follows: The ore is first roasted 
 in a reverberatory furnace, whereby the cuprous 
 sulphide is partly converted into oxide. It is then 
 mixed with sand, or with a fusible silicate, and 
 melted ; the copper regains sulphur, while the iron 
 is oxidized, and runs off as a part of the slag. The 
 cuprous sulphide, or " coarse metal," thus obtained 
 is re-roasted and re-melted, and so on, until all the 
 
2/6 INORGANIC CHEMISTRY. 
 
 iron contained in the ore has been slagged off, and 
 only a pure cuprous sulphide, or " fine metal," re- 
 mains. The latter is then partly oxidized by roast- 
 ing, and the mixture of oxide and sulphide is finally 
 fused ; sulphur dioxide is driven off, and metallic 
 copper is left behind. 
 
 2CuO + Cu 2 S = 4Cu + SO 2 . 
 
 In the Hunt and Douglas process the sulphides 
 of copper are roasted, and then treated, in pow- 
 der, with a solution of ferrous chloride. Copper 
 goes into solution, and is afterward precipitated 
 in the metallic state by the addition of scrap-iron. 
 The latter reproduces ferrous chloride, which 
 may be applied to another charge of ore, etc. 
 This process is an interesting example of a 
 class of metallurgical processes which are fast 
 assuming industrial importance. The precipita- 
 tion of copper by iron may be illustrated as fol- 
 lows : 
 
 EXPERIMENT 98. Dip a piece of bright iron or 
 steel into a solution of any salt of copper. Copper 
 will immediately be deposited in a thin, red coating 
 upon the surface of the other metal. 
 
 Copper is interesting on account of its being the 
 only red metal. It is very malleable and ductile, 
 and exceedingly tenacious; and, after silver, it is 
 the best conductor for heat and electricity. Bat- 
 tery-wires and lightning-conductors are usually 
 made of it. Its specific gravity is 8.945, and it 
 melts at about 1,050 C. At very high temperatures 
 it is slightly volatile ; and its vapor, either free or 
 in compounds, colors flame green. The best solv- 
 ent for copper is nitric acid ; boiling sulphuric acid 
 
NICKEL, COBALT, AND COPPER. 277 
 
 dissolves it also ; but hydrochloric acid attacks it 
 only with difficulty. 
 
 Copper is not only useful by itself, but also in 
 many alloys. Brass, bronze, German-silver, alumi- 
 num bronze, etc., have been already described.* 
 Copper is very easily deposited by electrolysis, and 
 this fact is applied in the process of electrotyping, 
 as follows : A page of type, set up in the usual way, 
 is first copied in wax or plaster. The mold thus 
 obtained, which is a perfect impression of the type, 
 is then dusted over with powdered graphite, in 
 order to render it a conductor of electricity, and 
 suspended in a solution of copper sulphate. It is 
 connected by a copper wire with the zinc-pole of 
 the battery, while the other pole terminates in a 
 copper bar or plate, which is also immersed in the 
 liquid. As the current passes, copper is deposited 
 upon the mold in a coherent film of any desired 
 thickness, and a perfect copy of the type is obtained. 
 By this process copper may be deposited to any 
 extent ; and even colossal statues may be electrically 
 copied by precipitating the metal gradually upon 
 their plaster casts. In electro-metallurgy copper 
 has many applications.f 
 
 The cuprous compounds have little importance, 
 except that cuprous oxide, Cu 2 O, is used for giving 
 a ruby-red color to glass. Most of the cupric salts 
 are green or blue when crystallized, but cupric 
 sulphate, CuSO 4 , 5H 2 O, is white when anhydrous. 
 This salt, which forms large blue crystals, may be 
 transformed into a white powder by careful heat- 
 ing. It is the most important of the copper com- 
 
 * See under zinc, tin, nickel, and aluminum. 
 
 t See Gore's work on electro-metallurgy, previously cited. 
 
2 ;8 INORGANIC CHEMISTRY. 
 
 pounds, and is commonly known as blue vitriol. It 
 is used in great quantities in galvanic batteries for 
 telegraph lines, in electro - metallurgy, in calico- 
 printing, in the manufacture of Paris green, etc. 
 
 Cupric oxide, CuO, is black ; but the hydroxide, 
 Cu(OH) 2 , is light blue. The relations between them 
 may be easily illustrated by experiment. 
 
 EXPERIMENT 99. Dissolve cupric sulphate in 
 water, and add a little caustic soda to the cold solu- 
 tion. A blue precipitate of Cu(OH) 2 will fall, which 
 will be transformed into black CuO, upon boiling. 
 
 CuSO 4 + 2NaOH = Na 2 SO 4 + Cu(OH) 2 . 
 Cu(OH) 2 = CuO + H 2 O. 
 
 Repeat the experiment, using ammonia- water in- 
 stead of caustic soda. The precipitate at first 
 formed will redissolve in an excess of the precipi- 
 tant, yielding an intensely deep-blue solution. This 
 reaction furnishes a most delicate test for copper. 
 
 In this experiment with ammonia a peculiar 
 compound is formed having the formula CuSO 4 , 
 2NH 3 . With other copper salts other similar com- 
 pounds will be produced ; all of which may be re- 
 garded as salts of a peculiar complex base, called 
 
 X NH 
 
 cuprammonium, Cu j^p^ 8 , derived from two am- 
 monium atoms by the replacement of two hydro- 
 gen atoms by one atom of dyad copper. Many 
 such complex bases are known, and they have great 
 theoretical interest. 
 
 All the copper compounds are very poisonous. 
 Hence cooking utensils of copper, such as preserv- 
 ing-kettles and the like, should be used only with 
 extreme care. They should always be kept clean 
 
NICKEL, COBALT, AND COPPER. 
 
 279 
 
 and bright, and acid fruits or preserves should not 
 be left long- in contact with them. This statement 
 applies also to brass. The dangerous pigments con- 
 taining arsenic and copper were described in a pre- 
 vious chapter. 
 
CHAPTER XXXI. 
 
 GOLD, AND THE PLATINUM GROUP. 
 
 GOLD, atomic weight 196.5, is almost invariably 
 found in the uncombined state. The only exception 
 is in the case of certain tellurides, which generally 
 contain both gold and silver. To some extent, gold 
 in dust, grains, or nuggets, is washed out from loose 
 soil and gravel, or found imbedded in rock; but 
 the larger yield is from invisible particles diffused 
 through veins of iron pyrites or quartz. The gold- 
 bearing rock is crushed to powder, and, if it contains 
 much pyrites, is roasted ; the mass is then agitated 
 with mercury, which readily amalgamates with the 
 more precious metal. The mercury is finally dis- 
 tilled off and recovered for use in future operations, 
 while metallic gold remains behind. 
 
 Gold, thus obtained, is rarely pure. It gener- 
 ally contains some silver ; and copper, iron, arsenic, 
 and other metals are common impurities. When 
 base metals are present, it is easily refined by forc- 
 ing chlorine gas through it while in the melted 
 state ; the impurities form chlorides, which either 
 volatilize or float in an easily removable scum, and 
 absolutely pure gold remains below. From silver 
 it is generally freed by a process known as quarta- 
 tion. The crude bullion is melted with an additional 
 
GOLD, AND THE PLATINUM GROUP. 281 
 
 quantity of silver, so that it shall consist of three 
 parts of the latter metal to one of gold ; the alloy is 
 then rolled into thin ribbons and treated with nitric 
 acid ; the silver is dissolved out as nitrate, and pure 
 gold is obtained. 
 
 Gold is bright yellow in color, softer than silver, 
 and malleable and ductile to an extraordinary de- 
 gree. One grain of gold can be made to gild two 
 miles of fine silver wire, or drawn into gold wire an 
 eighth of a mile long. It may be beaten into leaves 
 so thin that 280,000 would only make the thickness 
 of one inch. These thin leaves transmit light, and, 
 held between the eye and the sun, appear of a 
 greenish color. To glass, finely divided gold im- 
 parts a fine ruby-red tint. The specific gravity of 
 gold is 19.3, and it melts at about i , 100 C. For prac- 
 tical uses pure gold is too soft ; hence it is always 
 alloyed with copper or silver. The former alloy 
 renders it ruddier, the latter makes it paler in color. 
 The coin standard of the United States, for gold as 
 well as for silver, is 900 fine that is, 900 parts of 
 gold to 100 of alloy. Jeweler's gold is generally 
 less fine, and its character is indicated by a stand- 
 ard called the carat. Pure gold is said to be 24 
 carats fine ; three fourths pure would therefore 
 be 1 8 carats; two thirds fine would be 16 carats, 
 etc. With mercury gold amalgamates very readily ; 
 hence gold rings should never be worn when quick- 
 silver is being handled. 
 
 EXPERIMENT 160. Put a drop of mercury upon 
 a bit of gold-leaf. The latter will dissolve, forming 
 a white amalgam. 
 
 Gold is insoluble in all acids, except the mixture 
 known as aqua rcgia. It is trivalent, and forms two 
 
282 INORGANIC CHEMISTRY. 
 
 sets of compounds, of which the oxides Au 2 O and 
 Au 2 O 3 , and the chlorides AuCl and AuCl 3 are good 
 examples. The symbol Au is from the Latin aurum. 
 The aurous compounds are of slight importance 
 only. 
 
 The trichloride, AuCl 8 , is the most useful of the 
 gold salts. It is formed whenever gold is dissolved 
 in aqua regia, and may be obtained in orange-yellow 
 deliquescent crystals which are sensitive to light. 
 It is used in " toning " photographs, and in electro- 
 plating. As applied to gold the latter process is 
 almost exactly like the one described under silver ; 
 only a solution of the double cyanide of gold and 
 potassium is used, with a gold anode. 
 
 PLATINUM, atomic weight 195, is always more 
 or less associated with five other metals, iridium, 
 osmium, palladium, rhodium, and ruthenium. All 
 these metals are quadrivalent, and together they 
 are known as the platinum group. With one very 
 rare exception * they are found in the free state, or 
 rather alloyed with one another, and occasionally 
 with gold. 
 
 Platinum was originally brought from the gold- 
 washings of South America about the middle of the 
 last century. Its name, from platina, is the Span- 
 ish diminutive of plata, silver, and hence it means 
 " little silver." The greater part of the world's sup- 
 ply now comes from the Ural Mountains. The ore 
 occurs in grains and small lumps, mixed with vari- 
 ous impurities, from which it has to be separated by 
 a complicated process of refining. It is a steel-white 
 metal, fusible only at or above the temperature of 
 the oxy hydrogen-flame, and of specific gravity 21.5. 
 
 * The mineral laurite, ruthenium sulphide, found in Borneo. 
 
GOLD, AND THE PLATINUM GROUP. 283 
 
 Of all the other metals, iridium and osmium only are 
 heavier, and that but a trifle ; the specific gravity of 
 osmium, which is heaviest of all, is 22.5. 
 
 Platinum is, like gold, insoluble in all acids ex- 
 cept aqua regia. This property, together with its 
 infusibility, renders it extremely useful for the con- 
 struction of some pieces of chemical apparatus 
 such as dishes, crucibles, blow-pipe tips, foils, wire, 
 etc. The stills used for concentrating sulphuric 
 acid are made of platinum, and the metal is also 
 employed as the negative element in Grove's gal- 
 vanic battery. Without platinum utensils the chem- 
 ical analysis of many minerals would be practi- 
 cally impossible. Commercial platinum is generally 
 stiffened and hardened by the addition of a little 
 iridium. Platinum-black is a very finely divided 
 platinum, which possesses a remarkable power of 
 condensing gases within its pores. One volume of 
 this substance can absorb 800 volumes of oxygen ; 
 and hence it serves for some purposes as a powerful 
 oxidizing agent. 
 
 The compounds of platinum are many, compli- 
 cated, and theoretically interesting. There is a pla- 
 tinous series, corresponding to PtCl 2 and PtO ; and 
 a platinic series, represented by PtCl 4 and PtO 2 . 
 Platinic chloride, which is prepared by dissolving 
 platinum in aqua regia and evaporating to dry- 
 ness, is the most important of these compounds. 
 It is used in chemical analysis for the detection 
 of potassium and ammonium, and their separa- 
 tion from other bases. Potassium chloroplatinate, 
 K 2 PtCl 6 or 2KC1 + PtCl 4 , is a yellow precipitate 
 often produced in the laboratory. 
 
 The other metals of the group are rare and of 
 
284 INORGANIC CHEMISTRY. 
 
 little relative importance. An alloy of iridium and 
 osmium, called iridosmine, is often found in gold- 
 washings, and forms brilliant grains which are hard- 
 er than steel, and are used for tipping gold pens. 
 A process has recently been devised for fusing them 
 with phosphorus, and so obtaining a very hard and 
 refractory metal which may be used for a variety of 
 practical purposes. Iridium-plating has very lately 
 been patented, and may soon become a useful in- 
 dustry. 
 
 Platinum, iridium, and osmium are near each 
 other in atomic weight and specific gravity. Pal- 
 ladium, rhodium, and ruthenium form another trio, 
 having atomic weights from 103 to 106, and specific 
 gravities from 1 1 to 12. Palladium is a silver-white, 
 easily workable metal, which has been used to a 
 limited extent in philosophical apparatus. It has 
 the property of absorbing hydrogen, and forming 
 what is apparently an alloy with the latter. This 
 occluded hydrogen is commonly regarded as metal- 
 lic, and is sometimes called hydrogenium. 
 
PART II. 
 
 ORGANIC CHEMISTRY. 
 
 CHAPTER XXXII. 
 
 PRELIMINARY OUTLINE. 
 
 IN the early days of chemistry a sharp distinc- 
 tion was drawn between the compounds derived 
 from plants and animals and those obtained from 
 the inorganic or mineral kingdom. Such substances 
 as sugar, starch, the fruit acids, and albumen, to- 
 gether with many other bodies directly derived 
 from them, were termed organic ; while the min- 
 erals, metals, elements, and the commoner salts, 
 all of non-living origin, were classed as inorganic. 
 These classes of substances were regarded as per- 
 fectly distinct ; for it was thought that in the pro- 
 duction of organic bodies some peculiar vital force 
 was involved, and that no artificial means could 
 ever be discovered for their preparation. In 1828, 
 however, Woehler effected the synthesis of a well- 
 known organic compound, urea, from wholly inor- 
 ganic materials ; and since then a vast number of 
 similar syntheses have been successfully accom- 
 plished. One of the latest triumphs of synthetic 
 chemistry has been the artificial preparation of in- 
 digo. The old boundary between the organic and 
 
286 ORGANIC CHEMISTRY. 
 
 the inorganic has been thoroughly broken down, 
 and to-day the division is merely one of conven- 
 ience. 
 
 Organic compounds, so called, are remarkable 
 for their great number and complexity. They all 
 agree in containing carbon, generally in union with 
 hydrogen, oxygen, nitrogen, or all three. Occa- 
 sionally they contain sulphur and phosphorus also ; 
 and many of the artificial products contain chlorine, 
 bromine, iodine, boron, silicon, arsenic, or metals. 
 All of them, however, owe their chief characteris- 
 tics to carbon ; and on this account organic chem- 
 istry is now commonly defined as the chemistry 
 of the carbon compounds. Carbon, by virtue of 
 its quadrivalence, is capable of building up com- 
 plicated molecular structures ; and in doing so it 
 seems to combine with itself to form chains or 
 rings of carbon-atoms, that serve as centers around 
 which, in accordance with the laws of valency, 
 other elements can be grouped. This property of 
 carbon will become evident as we study its com- 
 pounds. 
 
 In general, organic substances may be most con- 
 veniently regarded as derived from compound radi- 
 cles, which, in most cases, are hydrocarbons having 
 unsatisfied bonds of valency. Cyanogen, however, 
 and carbon monoxide, being unsaturated compounds, 
 play an important part in organic chemistry ; and so 
 also, but in a different way, do ammonia and ammo- 
 nium. From the last two substances, and from the 
 compound NO 2 , many of the more important nitro- 
 genous bodies are derived. 
 
 Although hundreds of hydrocarbons are known, 
 and an almost infinite number are theoretically pos- 
 
PRELIMINARY OUTLINE. 287 
 
 sible, they may all be easily arranged in a small 
 number of comparatively simple series. Methane, 
 for example, CH 4 , is the compound of carbon and 
 hydrogen containing the highest proportion of the 
 latter element ; and in it the four bonds of the one 
 are exactly satisfied by the corresponding number 
 of the other. This compound is, however, the first 
 member of a series ; the higher terms being C 2 H 6 , 
 C 3 H 8 , C 4 H 10 , CgHtf, and so on up to C^H^. Here 
 each hydrocarbon differs from the one which pre- 
 cedes it by one atom of carbon and two of hydrogen ; 
 the second being the first plus CH 2 , and so on as far 
 as the series extends. Such a series is known as an 
 homologous series ; and it may be represented by one 
 general formula CnH^ + 2 . All other hydrocarbons 
 fall into similar series, and for each series a similar 
 formula may be assigned, as is shown in the follow- 
 ing scheme : 
 
 Series i. C n H 2n +2. Lowest member known, CH 4 . 
 
 " 2. CnHan. " " " C 2 H 4 . 
 
 " 3. CnHan-2. " " " C 2 H 2 . 
 
 4. CnHan-4. " " CeHo. 
 
 " 5- CnH 2n - 6 . " " " C 6 H 6 . 
 
 " 6. CnHa n -8. " " " C 8 H 8 . 
 
 " 7. CnHan-io. " " " C 8 H 8 . 
 
 " 8. CnHan-12. " " " C IO H 8 . 
 
 " 9- CnHan-i4. " " " C 12 H 10 . 
 
 " 10. CnHan-i 6 . " " " C 14 H 12 . 
 
 " II. CnHan-is. " " C 14 H 10 . 
 
 T -> /~" TJ tl f If 
 
 12. v^n rla n ao- Ci7rli 4 . 
 
 " T ? f~* T-T /^TT 
 
 13. ^n ilan 22. dcliio. 
 
 " T 4 C* T-I /" TT 
 
 14. L, n rl2n-24. CisHia. 
 " 15. CnHan- 26. " " " CaoHu. 
 
 " 1 6. C n H 2n -a 8 . " " " 
 
 " 17. C n H 2n _ 30 . " ' " C 22 H 14 . 
 
 l8. CnHan-sa. " " " C2eHao. 
 
288 ORGANIC CHEMISTRY. 
 
 All possible hydrocarbons are covered by this 
 system of formulas, although structural formulas of 
 a more definite kind are needed to bring out the 
 relations of these compounds fully. For one series 
 no representative has as yet been discovered, and 
 in several series the lowest possible members are 
 not known ; but some of these gaps will, doubtless, 
 be filled in due time. 
 
 From many of these hydrocarbons other com- 
 pounds are derived by a process known as substitu- 
 tion, in which atoms of hydrogen are successively 
 replaced by atoms of other univalent elements like 
 chlorine, bromine, or iodine. Thus, from methane, 
 CH 4 , we get substitution series as follows : 
 
 1. CH 4 . CH 3 C1. CH 2 C1 2 . CHC1 S . CCI 4 . 
 
 2. CH 4 . CH 3 Br. CHaBra. CHBr 3 . CBr 4 . 
 
 3. CH 4 . CHJ. CH a I 2 . CHI,. CI 4 . 
 
 For benzene, C 6 H 6 , the chlorine substitution series 
 is even more striking ; thus : 
 
 C 6 H 6 . C.H.C1. C 6 H 4 C1 2 . C.H.C1,. C 6 H 2 C1 4 . C 6 HC1 5 . C 6 C1 6 . 
 
 In many cases compound radicles serve as agents 
 of substitution, as in the case of the univalent group 
 NO 2 , which enters into numerous important sub- 
 stances. A few examples will suffice : 
 
 C 6 H 8 . C 6 H 5 (NO 2 ). C 6 H 4 (NO 2 ) 2 . 
 
 Benzene. Nitrobenzene. Dinitrobenzene. 
 
 C 3 H 8 3 . C 3 H 5 (N0 2 )30s. Etc. 
 
 Glycerin. Trinitroglycerin. 
 
 Still another class of substitution compounds of 
 the highest importance is derived from ammonia, 
 NH 3 , by replacing hydrogen with such radicles as 
 methyl, CH 3 , or ethyl, C 2 H 5 . They are called 
 amines, and are constituted as follows : 
 
PRELIMINARY OUTLINE. 
 
 28 9 
 
 (H 
 
 (CH 3 
 
 (CH, 
 
 (CH 3 
 
 N4 H 
 
 N.) H 
 
 N^ CH 3 
 
 N-! CH 3 
 
 (H 
 
 (H 
 
 (H 
 
 (CH 3 
 
 Ammonia. 
 
 Methylamine. 
 
 Dimethylamine. 
 
 Trimethylamine. 
 
 (C 2 H 6 
 
 ( C 2 H 6 
 
 (C 2 H 6 
 
 (CH 3 
 
 N-l H 
 
 N \ C 2 H 6 
 
 N \ C 2 H 6 
 
 N \ C 2 H 6 
 
 (H 
 
 IH 
 
 (C 2 H 5 
 
 ( C 2 H 6 . Etc. 
 
 Ethylamine. 
 
 Diethylamine. 
 
 Triethylamine. 
 
 Diethylmethylamine. 
 
 Similarly, from PH 3 we get a series of phosphines ; 
 from AsH 3 , arsines ; from SbH 3 , stibines, and so on. 
 Compounds of this kind are exceedingly numerous, 
 and others like them are derived from ammonium, 
 NH 4 : 
 
 NH 4 C1. 
 
 N(CH 3 ) 4 C1. 
 
 Ammonium chloride. Tetramethylammonium 
 chloride. 
 
 N(C.H.)C1. 
 
 Tetrethylammonium 
 chloride. 
 
 These few examples will suffice for present pur- 
 poses. 
 
 One other noteworthy feature of organic com- 
 pounds demands a brief consideration at this point 
 namely, isomerism. It often happens that two or 
 more entirely different substances are represented 
 by the same formula, both containing precisely the 
 same elements, united in precisely the same pro- 
 portions. Such compounds are called isoineric, and 
 owe their differences to different groupings of the 
 atoms within the molecules. Just as the same let- 
 ters may be so arranged as to spell several differ- 
 ent words, so the same atoms may be grouped in 
 several dissimilar clusters. For example, the em- 
 pirical formula C 2 H 6 O represents two substances 
 the one a gas, the other a liquid. One is the 
 oxide of the univalent radicle methyl, the other is 
 ethyl hydroxide, or common alcohol ; and their 
 
290 ORGANIC CHEMISTRY. 
 
 formulas, written side by side, show the difference 
 
 clearly : 
 
 (CH 3 ) 2 O. C 2 H 5 OH. 
 
 Methyl oxide. Alcohol. 
 
 In this instance both compounds have the same 
 molecular weight, and the same vapor density. In 
 some cases of imperfect isomerism, these properties 
 may differ in such a way that the compounds may 
 form a series of which the higher members shall 
 have molecular weights, even multiples of the low- 
 est. Such a case is furnished by the polymeric series 
 of hydrocarbons C n H 2n , in which, although all of 
 its members have the same percentage composition, 
 the molecular weights vary widely. Another ex- 
 ample of polymerism is afforded by the compounds 
 C 2 H 2 , C 6 H 6 , and C 8 H 8 , which represent three differ- 
 ent series. Other instances of isomerism and po- 
 lymerism will be considered by-and-by. 
 
CHAPTER XXXIII. 
 
 CYANOGEN AND CARBONYL COMPOUNDS. 
 
 FREE cyanogen, C 2 N 2 or (CN) 2 , is prepared by 
 heating mercuric cyanide. It is a colorless gas with 
 an odor resembling peach-kernels, and it burns with 
 a beautiful purple flame. In the chapter upon car- 
 bon it was shown that this gas behaved much like 
 an element of the chlorine group, and that the mol- 
 ecules (CN) 2 and C1 2 had many points of similarity. 
 Thus we have a hydrocyanic acid, HCN, and a 
 series of metallic cyanides such as KCN, Hg(CN) 2 , 
 and so on. Some of these compounds have practi- 
 cal importance. 
 
 Hydrocyanic acid, HCN, commonly known as 
 prussic acid, is obtained whenever a cyanide is 
 treated with a strong acid like sulphuric. In this 
 respect it resembles hydrochloric acid, as the sub- 
 joined equations show : 
 
 H 2 SO 4 + 2NaCl = 2HC1.+ Na 2 SO 4 . 
 H 2 SO 4 + 2NaCN = 2HCN + Na 2 SO 4 . 
 
 Practically, the yellow salt known as potassium fer- 
 rocyanide is distilled with dilute sulphuric acid in a 
 glass retort, and an aqueous solution of hydrocyanic 
 acid is collected in the receiver. This acid has a 
 strong odor resembling peach-kernels or bitter-al- 
 
2Q2 
 
 ORGANIC CHEMISTRY. 
 
 monds, and is intensely poisonous. A single drop 
 of the pure compound, which is a volatile liquid 
 boiling at 26.5, placed upon the tongue of a small 
 animal, such as a cat or rabbit, will cause death al- 
 most instantaneously. It is the most sudden and 
 one of the most fatal of all known poisons, and its 
 dangerous qualities are shared in a less degree by 
 many of its derivatives. It is very unstable, and 
 can be preserved only in dilute solutions. As an 
 acid it is exceedingly weak, and may be expelled 
 with ease from most of its compounds. 
 
 Potassium cyanide, KCN, is a white salt of con- 
 siderable importance. Great quantities of it are 
 used in the processes of gold and silver plating. 
 It is dangerously poisonous, and should be handled 
 with extreme care. It has, faintly, the characteris- 
 tic peach-kernel odor. Silver cyanide, AgCN, is a 
 white precipitate closely resembling the chloride. 
 
 With some of the metals of high valency cy- 
 anogen forms very curious and important double 
 salts. Of these, potassium ferrocyanide, K 4 Fe(CN) 6 , 
 is the most useful and noteworthy. To prepare 
 this salt, iron-filings, potash, and nitrogenous mat- 
 ter, such as scraps of horn, hides, leather-clippings, 
 hair, or refuse feathers, are heated together to the 
 temperature of fusion. The cooled mass is after- 
 ward treated with water, and the solution evapo- 
 rated to the point of crystallization. The ferrocya- 
 nide is thus obtained in large yellow crystals con- 
 taining three, molecules of water. It is sometimes 
 called the " yellow prussiate of potash," and is not 
 poisonous. Its uses may be illustrated by experi- 
 ment: 
 
 EXPERIMENT 101. To a solution of potassium 
 

 CYANOGEN AND CARBON YL COMPOUNDS. 293 
 
 ferrocyanide add a solution of ferrous sulphate. A 
 pale-bluish precipitate will form, which will rapidly 
 change to deep blue. Repeat the experiment, using 
 a ferric salt, and a deep-blue precipitate will be pro- 
 duced at once. 
 
 There are several different compounds pro- 
 ducible in the foregoing manner. One of them, 
 Fe 5 (CN) 12 , is an important paint, Prussian blue ; and 
 another, derived from the latter, Fe 7 (CN) 18 , is called 
 Williamson's blue. The chief use of potassium fer- 
 rocyanide is in the manufacture of these colors. 
 With solutions of copper, potassium ferrocyanide 
 gives a very characteristic reddish-brown precipi- 
 tate ; and by the production of this, very small traces 
 of copper may be detected. 
 
 Potassium ferrocyanide may be regarded as the 
 potassium salt of hydroferrocyanic acid, H 4 Fe(CN) 6 . 
 This acid is well known, and forms a large series of 
 salts. Having four replaceable hydrogen-atoms, it 
 is tetrabasic. In none of the ferrocyanides do the 
 ordinary tests for iron reveal the presence of the 
 later metal. It is completely masked. 
 
 By passing chlorine into a solution of the ferro- 
 cyanide a salt called potassium ferricyanide is pro- 
 duced. This compound forms large red crystals 
 having the formula K 3 Fe(CN) 6 , and from it a hydro- 
 ferri cyanic acid and a series of corresponding salts 
 may be derived. With ferrous solutions potassium 
 ferricyanide gives a blue precipitate, but in ferric 
 compounds it only produces a slight brownish col- 
 oration. It is a useful reagent in distinguishing be- 
 tween ferrous and ferric compounds, and it is also 
 employed in the preparation of blue paints. Like 
 iron, cobalt also forms interesting- series of cobalto 
 
2 9 4 
 
 ORGANIC CHEMISTRY. 
 
 and cobalticyanides, and most of the metals of the 
 iron and platinum groups behave in a similar way. 
 The platinocyanides are among the most beautiful 
 compounds known to chemistry. 
 
 With oxygen and sulphur, cyanogen forms two 
 quite similar acids namely, cyanic acid, CNOH, 
 and sulphocyanic acid, CNSH. Potassium sulpho- 
 cyanate, CNSK, is a white salt which yields a mag- 
 nificent red coloration with ferric solutions. It gives 
 no reaction with ferrous salts, and serves as a very 
 delicate reagent for the detection of ferric iron. 
 
 Some of the cyanogen compounds display in a 
 remarkable degree the power of polymerization. 
 For example, hydrocyanic acid, CNH, readily 
 changes into a solid compound, C 3 N 3 H 3 , called tri- 
 hydrocyanic acid. Cyanic acid, CNOH, similarly 
 is related to cyanuric acid, C 3 N 3 O 3 H 3 , and to a third 
 polymer of unknown molecular weight called cy- 
 amelide. So, also, there are two chlorides of cyano- 
 gen, one a liquid, CNC1 ; the other a solid, C 3 N 3 C1 3 . 
 On account of this tendency to polymerize, the de- 
 rivatives of cyanogen are very numerous and com- 
 plicated. 
 
 When ammonium cyanate, NH 4 CNO, is heated, 
 its atoms undergo a peculiar rearrangement, and it 
 is transformed into the isomeric compound, carba- 
 mide or urea : 
 
 H 2 N 
 H 2 N 
 
 Ammonium cyanate. Carbamide. 
 
 CN-0-NH 4 = CO \H 2 N 
 
 The latter compound, as will be seen, may be re- 
 garded as derived from two atoms of ammonia, by 
 replacing one hydrogen-atom from each by the 
 bivalent radicle CO. This radicle, known in inor- 
 
CYANOGEN AND CARBON YL COMPOUNDS. 
 
 295 
 
 ganic chemistry as carbon monoxide, is called car- 
 bonyl for brevity, and occurs in many organic com- 
 pounds. Some of its simpler derivatives are as fol- 
 lows : 
 
 co.o. coo, co< co<*- 
 
 Carbonyl oxide, or Carbonyl Carbonic acid. Carbamic acid, 
 
 carbon dioxide. chloride. 
 
 Carbamide is a white solid which is found in 
 many animal juices, and has great theoretical inter- 
 est. It was the first organic compound ever pro- 
 duced by synthesis from inorganic matter. It acts 
 like a weak base, uniting with nitric and oxalic acids 
 to form a nitrate and an oxalate, and it also yields 
 many complex derivatives. 
 
 If we heat ammonium sulphocyanate, NH 4 CNS, 
 instead of the cyanate, a sulphocarbamide or sulpho- 
 urea will be formed. 
 
 CN-S-NH* = CS <H*N 
 
 Ammonium sulphocyanate. Sulphourea. 
 
 This compound contains the radicle sulphocarbonyl, 
 CS, which yields derivatives similar in structure to 
 those obtained from CO. For example : 
 COCla. CSC1 2 . 
 
 Carbonyl chloride. Sulphocarbonyl chloride. 
 
 co /OH cs /SH 
 
 J \OH ^\SH. 
 
 Carbonic acid. Sulphocarbonic acid. 
 
 The greater number of these compounds are in- 
 teresting only from a theoretical point of view. In 
 the present instance they serve to illustrate in a sim- 
 ple way the convenience of structural formulae. By 
 means of the latter, many relations between different 
 substances may be most clearly brought out, and the 
 memory can thus be aided to a wonderful degree. 
 
 \ 
 
CHAPTER XXXIV. 
 
 THE METHANE SERIES. 
 
 THE methane or marsh-gas series of hydrocar- 
 bons, CnH2n + 2, is of the utmost importance, both 
 in theory and in practical work. Some of its mem- 
 bers constitute the greater part of petroleum ; and 
 from other members such noteworthy substances as 
 alcohol, ether, chloroform, and acetic acid, are de- 
 rived. Structurally, the series is very simple, the 
 carbon-atoms forming a regular chain around which 
 the hydrogen-atoms are symmetrically arranged. 
 A very few formulas will serve for illustration : 
 
 Methane, CH 4 . Ethane, C 2 H 8 . Propane, C 3 H 8 . Butane, C 4 H 10 . 
 
 H H H H 
 
 H-C-H H-C-H H-C-H H-C-H 
 
 H H-C-H H-C-H H-C-H 
 
 H H-C-H H-C-H 
 
 H H-C-H 
 
 i 
 H 
 
 And so on, regularly, up to C^H^. After butane 
 the hydrocarbons of this series receive numerical 
 names, based upon the number of carbon-atoms 
 which they contain. Thus, C 5 H 12 is pentane, C 6 H 14 
 is hexane, C 7 H 16 is heptane, C^H^ is decane, etc. 
 In properties, these hydrocarbons vary regularly. 
 
THE METHANE SERIES. 297 
 
 Methane, which was described under carbon, is a 
 gas, and ethane, propane, and butane are also gase- 
 ous. Pentane is a liquid boiling at 38, hexane boils 
 at 70, and so on through a series of liquids growing 
 less and less volatile as we ascend, until at last we 
 come to solid, waxy compounds which are known as 
 paraffins. The whole series is sometimes called the 
 paraffin group. Paraffin itself, such as is used for 
 making candles, is a mixture of these higher hydro- 
 carbons ; coal-oil, or petroleum, consists chiefly of 
 the liquid members of the series. The latter are 
 separated by a process of distillation, and the mixt- 
 ure which distills over at comparatively low tem- 
 peratures is known as naphtha or gasoline. Above 
 170. the distillate is used for illuminating oil or 
 kerosene ; higher still, heavier and denser products 
 are obtained, which serve for lubricating machinery. 
 Kerosene which has not been carefully freed from 
 the more volatile hydrocarbons is dangerous, and 
 none should be used which gives off inflammable 
 vapor at temperatures below 110 Fahr. Such va- 
 pors, like fire-damp, form explosive mixtures with air. 
 If, by proper reactions, we replace one atom of 
 hydrogen in each of the foregoing hydrocarbons by 
 a hydroxyl group, -O-H, we shall obtain a series of 
 most important compounds which are called alco- 
 hols. Thus : 
 
 OH 
 
 OH 
 
 OH 
 
 i 
 
 i 
 
 i 
 
 H-C-H 
 
 H-C-H 
 
 H-C-H 
 
 i 
 
 i 
 
 i 
 
 H 
 
 H-C-H 
 
 H-C-H 
 
 CH 4 O, methyl alcohol. 
 
 i 
 
 i 
 
 
 H 
 
 H-C-H 
 
 
 C a H 6 O, ethyl alcohol. 
 
 i 
 
 
 
 H 
 
 C 3 H 8 O, propyl alcohol. 
 
298 ORGANIC CHEMISTRY. 
 
 And so on through the series. These alcohols may 
 be conveniently regarded as the hydroxides of cer- 
 tain radicles, of which methyl, CH 3 , ethyl, C 2 H 5 , and 
 amyl, C 5 H n , are the most commonly encountered. 
 These radicles do not exist in the free state, but 
 their derivatives are of the highest importance ; and 
 most of them may be easily compared with the com- 
 pounds of the univalent metals. Thus : 
 
 KOH. CH 3 OH. C a H 6 OH. C 5 H n OH. Etc. 
 
 K 2 O. (CH 8 ) a O. (C 2 H 5 ) 2 O. (C B Hn) 2 O. " 
 
 KC1. CH 3 C1. C 2 H 6 C1. CH,iCl. 
 
 KNO 3 . CH 3 NO 3 . C 2 H 6 NO 3 . C 6 HnNO 8 . " 
 
 These alcoholic salts are mostly liquids, and are 
 called ethers. Their names, except in the series of 
 alcohols, are precisely like those used in inorganic 
 chemistry as, for example, methyl chloride, ethyl 
 oxide, propyl nitrate, amyl sulphate, etc. Nearly 
 every acid, organic or inorganic, can unite with 
 these radicles to form such ethers. 
 
 Three of the alcohols namely, those of methyl, 
 ethyl, and amyl have practical importance, and 
 therefore deserve especial mention. Methyl alco- 
 hol, CH 3 OH, commonly called wood-spirit, is a 
 colorless liquid obtained by the dry distillation of 
 wood. The latter, when distilled at a high tempera- 
 ture, yields a variety of liquid products, and from 
 the mixture methyl alcohol may be separated. It 
 has a specific gravity of .814, and boils at 55, and is 
 used partly as a cheaper substitute for common alco- 
 hol in various manufacturing processes, and partly 
 in the preparation of certain of the aniline colors. 
 
 Ethyl alcohol, C 2 H 5 OH, is the compound of 
 this series to which in common life the name of 
 
THE METHANE SERIES. 299 
 
 alcohol is especially applied. Although it may be 
 obtained from ethane, it is practically prepared only 
 by the fermentation of saccharine and starchy bodies, 
 such as cane-sugar, glucose, and the starch of pota- 
 toes or grain. These compounds, dissolved in wa- 
 ter, are fermented by yeast, and a weak solution of 
 alcohol is thus obtained. The latter is then concen- 
 trated by distillation, the process being repeated 
 until an alcohol containing only about 10 per cent 
 of water passes over. To obtain pure or " absolute " 
 alcohol the commercial product is again distilled 
 over caustic lime, which serves to retain the water. 
 
 EXPERIMENT 102. Mix alcohol and water in 
 equal proportions, place the mixture in a glass re- 
 tort, and distill until one half has passed over into 
 the receiver. Inasmuch as alcohol boils at 78.4 and 
 water at 100, the distillate will be found to contain 
 most of the alcohol, while the portion remaining in 
 the retort will be mainly water. Now repeat the 
 operation with the distillate, again distilling one half, 
 and a still stronger alcohol will be obtained. This 
 process, which is known as fractional distillation, is 
 continually employed in the laboratory for separating 
 liquids of different volatility. The most volatile dis- 
 till first, the least volatile remaining longest behind. 
 
 Pure alcohol is a colorless, inflammable liquid of 
 specific gravity .806. It boils at 78.4, but has never 
 been frozen;* hence its use in thermometers in- 
 tended for registering temperatures below the freez- 
 ing-point of mercury. It has a peculiar spirituous 
 smell and a burning taste, and in the pure state is 
 poisonous. In a diluted condition it is used as a 
 
 * Since this paragraph was written, alcohol has been frozen. At 
 130.5 C., it solidifies to a white mass. 
 
300 
 
 ORGANIC CHEMISTRY. 
 
 stimulant, and it is the intoxicating principle of all 
 wines, spirits, and malt-liquors. Beer and ale contain 
 from 4 to 7 per cent of alcohol ; wine from 6 to 20 
 per cent ; rum, brandy, and whisky from 40 to 50 per 
 cent. The stronger commercial alcohol, or spirits of 
 wine, contains from 50 per cent upward, and is used 
 as an antiseptic, as a burning-fluid, as a solvent for 
 gums and resins, in the manufacture of varnishes, per- 
 fumery, and medicinal preparations, and for a great 
 variety of other practical purposes. To the chemist 
 it is one of the most useful of chemical substances. 
 
 Amyl alcohol, C 5 H n OH, occurs as an impurity 
 in spirits distilled from potatoes. It is commonly 
 known as the chief constituent of a disagreeable 
 mixture called fusel-oil. When pure, amyl alcohol 
 is a colorless liquid which boils at 131, and has a pe- 
 culiarly suffocating odor. It is used in the prepara- 
 tion of valeric acid and some of its ethers.* 
 
 Propyl alcohol, C 3 H 7 OH, and butyl alcohol, 
 C 4 H 9 OH, lie between ethyl and amyl alcohols. 
 Cetyl alcohol, QeHggOH, is a solid compound 
 derived from spermaceti ; and melissyl alcohol, 
 CsoHflOH, is one of the constituents of beeswax. 
 Like the higher hydrocarbons of the methane series, 
 the higher alcohols and their derivatives are solid. 
 
 When common alcohol is cautiously mixed with 
 strong sulphuric acid, a compound known as ethyl- 
 sulphuric acid is formed. This is the type of a 
 series of acids, constituted as follows : 
 
 Sulphuric. Methylsulphuric. Ethylsulphuric. Propylsulphuric. Amylsulphuric. 
 
 etc. 
 * See next chapter. 
 
THE METHANE SERIES. 
 
 301 
 
 Heated with an additional quantity of alcohol, ethyl- 
 sulphuric acid undergoes a further change, and ethyl 
 oxide is formed. At the same time sulphuric acid 
 is reproduced, ready to act upon a fresh portion of 
 alcohol ; thus : 
 
 x o _u x ^o 
 
 / H // ^^ 4 * 
 
 These reactions are applied on a large scale to the 
 manufacture of ethyl oxide, which is commonly 
 known as ether.* This is a colorless liquid of pecul- 
 iar odor, specific gravity .74, and boiling-point 34.5. 
 Its. chief and important use as an anaesthetic, for 
 preventing the pain of surgical operations, is well 
 known. Allied to it are other ethereal oxides, which 
 the subjoined formulae may serve to illustrate : 
 
 CH 3 \ C 2 H 5 \ C 6 Hn\ CH 8 x C 2 H 6 x 
 
 CH 8 /L C 2 H 5 /U C 6 Hn /L C 2 H 5 /U C 5 Hn /U> 
 
 Methyl ether. Ethyl ether. Amyl ether. Methylethyl Ethylamyl 
 
 ether. ether. 
 
 The fourth and t fifth of these formulae represent 
 mixed ethers. Many such compounds are possible. 
 Besides these there are similar bodies containing 
 sulphur, most of which are liquids of exceedingly 
 nauseous odor. Their derivation may be illustrated 
 thus: 
 
 Ethyl sulphide. Amyl sulphide. Ethyl hydrosulphide. Amyl hydrosulphide. 
 
 The hydrosulphides resemble the alcohols in struct- 
 ure, and are called mercaptans. 
 
 * Erroneously called " sulphuric ether " in commerce. The true 
 sulphuric ether is ethyl sulphate, (Ca 
 
302 ORGANIC CHEMISTRY. 
 
 By the action of hydrochloric acid on the alco- 
 hols, the chlorides of the corresponding radicles may 
 be produced. With bromine and iodine, in pres- 
 ence of a little phosphorus, the alcohols yield simi- 
 lar bromides and iodides. Methyl chloride, CH 3 C1, 
 is a gas ; but the other chlorides, bromides, and 
 iodides of the commoner radicles of this series are 
 volatile liquids resembling chloroform in odor. 
 These compounds are often of use as steps in the 
 preparation of others. 
 
 When methyl or ethyl alcohol is heated with 
 bleaching-powder, chloroform is produced. This 
 compound, CHC1 3 , is a clear liquid of specific grav- 
 ity 1.52, and an agreeable smell. It boils at 62. 
 Like ether, it is an important anaesthetic, but is less 
 safe. lodoform, CHI 3 , is a yellow solid of some 
 value in medicine. Both of these compounds are 
 simple derivatives of methane : 
 
 H Cl I 
 
 H-C-H H-C-C1 H-C-I. 
 
 i i i 
 
 H Cl I 
 
 Methane. Chloroform. ' lodoform. 
 
CHAPTER XXXV. 
 
 THE FATTY ACIDS. 
 
 BY the action of oxidizing agents upon the fore- 
 going alcohols, two new series of compounds may 
 be obtained. The reactions, with any given alcohol, 
 are as follows : First, two atoms of hydrogen are 
 withdrawn, forming water, and leaving a compound 
 called an aldehyde : 
 
 C 2 H 6 O + O = C a H 4 O + H 3 O. 
 
 By further oxidation the aldehyde takes up an atom 
 of oxygen, and an acid is produced : 
 
 C a H 4 O + O = C 2 H 4 O 3 . 
 
 The relations of these sets of compounds to each 
 other, and to the methane series, may be repre- 
 sented structurally : 
 
 H 
 
 OH 
 
 H 
 
 OH 
 
 i 
 
 i 
 
 i 
 
 i 
 
 H-C-H 
 
 H-C-H 
 
 C = 
 
 c=o 
 
 i 
 
 i 
 
 r 
 
 1 
 
 H 
 
 H 
 
 H 
 
 H 
 
 Methane. 
 
 Methyl alcohol. 
 
 Formaldehyde. 
 
 Formic acid. 
 
 H 
 
 OH 
 
 H 
 
 OH 
 
 i 
 
 i 
 
 i 
 
 i 
 
 H-C-H 
 
 H-C-H 
 
 C = 
 
 c=o 
 
 i 
 
 i 
 
 i 
 
 1 
 
 H-C-H 
 
 H-C-H 
 
 H-C-H 
 
 H-C-H 
 
 i 
 
 i 
 
 i 
 
 i 
 
 H 
 
 H 
 
 H 
 
 H 
 
 Ethane. 
 
 Ethyl alcohol. 
 
 Acetaldehyde. 
 
 Acetic acid. 
 
 14 
 
304 ORGANIC CHEMISTRY. 
 
 Thus, corresponding to every hydrocarbon in the 
 methane series, we have an alcohol, an aldehyde (al- 
 cohol ^v^/rogenatum), and an acid. The aldehydes 
 are quite unstable bodies, and the one derived from 
 common alcohol is the best known. It is a very 
 volatile liquid, having a peculiar odor, which may 
 be recognized whenever alcohol is dropped upon 
 chromic acid. Its uses are few. 
 
 The acids of this series, however, are important. 
 The lower members are volatile liquids, the higher, 
 above QoH^Oa, are waxy or greasy solids. Inas- 
 much as some of them are essential constituents of 
 fats and oils, the entire series has been named the 
 fatty acids. The more important among them are 
 the following : 
 
 Formic acid, CH 2 O 2 , or HCOOH. Boils at 100. 
 
 Acetic " 
 
 C 2 H 4 O 2 , 
 
 " CHsCOOH. 
 
 " " 1 1 8. 
 
 Propionic " 
 
 C 8 H 6 2 , 
 
 " CaH 6 COOH. 
 
 " " 140. 
 
 Butyric " 
 
 C 4 H 8 O 3 , 
 
 " C 8 H 7 COOH. 
 
 " " 163. 
 
 Valeric 
 
 C 5 H 10 O a , 
 
 " C 4 H 9 COOH. 
 
 " 185. 
 
 Stearic " 
 
 Ci 8 H 36 O 2 , 
 
 " Ci 7 H 86 COOH. 
 
 Melts at 69. 
 
 In each of these acids we find the group COOH, 
 or, in detail, O=C OH, which is characteristic of 
 organic acids. In monobasic acids like these, it 
 occurs once ; in bibasic acids, twice ; in tribasic 
 acids, three times, etc. In the formation of salts 
 from these acids, it is only the hydrogen of the 
 COOH group which is replaceable by metals or by 
 bases. 
 
 Several of the fatty acids are important, either 
 by themselves or in their salts or ethers. Stearic, 
 margaric, and palmitic acids, are especially useful 
 in fats, oils, and soaps, and will be considered in 
 
THE FATTY ACIDS. 
 
 305 
 
 another chapter. Acetic acid, or vinegar, merits a 
 detailed notice here. It is commonly prepared by 
 
 FIG. 52. Manufacture of Vinegar. 
 
 the oxidation of dilute alcohol, such as cider, wine, 
 or weak whisky. In cider and wine the alcoholic 
 stage of fermentation is followed by an acetous stage, 
 and the change from alcohol to acetic acid takes 
 place without artificial assistance. This transforma- 
 tion of cider into vinegar is a matter of every-day 
 observation ; but only a small part of the vinegar in 
 use is made in this way. On a large scale, very 
 weak alcohol, such as the fermented mash from 
 which spirit is to be distilled, is allowed to trickle 
 slowly through large casks filled with wood-shav- 
 ings. The alcohol, diffused over the shavings, ex- 
 poses a very large surface to the oxidizing action of 
 the air, which latter enters the cask freely through 
 holes in the sides, and escapes through other holes 
 in the top. The oxidation from alcohol to acetic 
 acid is thus effected much more rapidly than by the 
 tedious process of fermentation which was previ- 
 ously referred to. 
 
3 o6 ORGANIC CHEMISTRY. 
 
 EXPERIMENT 103. Distill a little vinegar from a 
 glass retort. The distillate will be a weak acetic 
 acid free from the impurities which gave the vine- 
 gar its color. Pure acetic acid may be prepared by 
 distilling an acetate with sulphuric acid. A sul- 
 phate will be formed and acetic acid set free. 
 
 Perfectly pure acetic acid is a colorless liquid 
 which solidifies to an ice-like mass at 17. It has 
 the odor of vinegar to an increased degree, and has 
 all the properties of a strong acid. Dissolve sodium 
 or calcium carbonate in vinegar, and you will obtain, 
 with vigorous effervescence, a solution of sodium or 
 calcium acetate. Sodium acetate is a useful labora- 
 tory reagent ; lead acetate is the well-known " sugar 
 of lead"; copper acetate is "verdigris." These 
 salts (omitting water of crystallization) are formed 
 from acetic acid by substitution of hydrogen, pre- 
 cisely as in the domain of inorganic chemistry. 
 
 Thus : 
 
 Acetic acid, C 2 H 4 Oa. 
 
 Sodium acetate, C 3 H 8 O a Na. 
 Potassium " C a H 3 O a K. 
 Lead " (C 3 H 3 O 2 ) a Pb. 
 
 Copper " (C 2 HsO a )aCu. 
 
 With the alcohols of the methane series the fatty 
 acids yield a large number of compound ethers. 
 These are interesting, both because of their proper- 
 ties and on account of their bearing upon the sub- 
 ject of isomerism. Practically, several of them are 
 made for use in the manufacture of flavoring ex- 
 tracts. For instance, ethyl butyrate has the taste 
 and odor of pineapples; amyl acetate affords a 
 close imitation of bananas ; amyl valerate is made 
 as " apple-oil," etc. The peculiar flavors of many 
 
THE FATTY ACIDS. 307 
 
 fruits are doubtless due to the existence, naturally 
 formed, of some of these same ethers. Each ether 
 is isomeric with one of the acids, and in some cases 
 several ethers are isomeric with each other. The 
 cause of the isomerism, however, is easily under- 
 stood, as the following formulae for the compounds 
 C 7 H 14 O 2 will show : 
 
 (Enanthylic acid, C 6 Hi 3 , COOH = C 7 H 14 Oa. 
 
 Hexyl formate, CeHu, CHO 2 = 
 
 Amyl acetate, C B H n , C 2 H 3 O a = 
 
 Butyl propionate, C 4 H 9 , C 3 H 5 O 2 = 
 
 Propyl butyrate, C 3 H 7 , C 4 H 7 O 2 = 
 
 Ethyl valerate, C 2 H 6 , C 5 H 9 O 2 = 
 
 Methyl caproate, CH 3 , C 6 HnO 2 = 
 
 In these ethers the hydrocarbon radicles replace 
 hydrogen-atoms exactly as if they were univalent 
 metals. If the first compound in the column, which 
 is an acid, is treated with a solution of caustic soda, 
 its sodium salt is formed and water is set free. The 
 second compound, similarly treated, would give so- 
 dium formate and hexyl alcohol ; the third, sodium 
 acetate and amyl alcohol ; the fourth, sodium pro- 
 pionate and butyl alcohol, etc. So then, although 
 the seven compounds have the same percentage 
 composition and molecular weight, it is easy to 
 demonstrate experimentally that they differ in chemi- 
 cal structure, and to show wherein the differences 
 lie. Some cases of isomerism are less easily ex- 
 plained ; but all are explainable in some such gen- 
 eral way. 
 
 If from acetic acid, C 2 H 4 O 2 , we withdraw a hy- 
 droxyl group, OH, a compound radicle called acetyl, 
 C 2 H 3 O, will remain. This radicle does not exist in 
 the free state, but some of its compounds are inter- 
 
308 ORGANIC CHEMISTRY. 
 
 esting. Thus, it forms a chloride, C 2 H 3 OC1, which 
 is well known, and several amides. These resemble 
 the amines, with this difference, that whereas in the 
 latter compounds the hydrogen of ammonia is re- 
 placed by basic or positive radicles, in the amides 
 the replacement is effected by acid or negative 
 groups. Thus : 
 
 ( C 3 H 6 ( C 2 H B ( C 2 H 6 
 
 N ] H N \ C 2 H 6 N \ C 2 H 6 
 
 ( H ( H ( C 2 H 6 
 
 Ethylamine. Diethylamine. Triethylamine. 
 
 ( C 2 H 3 O ( C 2 H 3 O ( C 2 H 3 O 
 
 N 1 H N 1 C 2 H 3 N 4 C 2 H 3 
 
 ( H ( H ( C 2 H 3 O. 
 
 Acetamide. Diacetamide. Triacetamide. 
 
 From the other acids of the series, by withdrawal 
 of hydroxyl, other acid radicles are formed ; and 
 these have properties similar to acetyl. The amines 
 are all strong bases, the amides are neutral or acid. 
 By the action of chlorine upon acetic acid, three 
 substitution acids may be obtained. All are strong 
 acids, and yield important derivatives: 
 
 C 2 H 4 O 3 , acetic acid. 
 C 2 H 3 C1O 2 , monochloracetic acid. 
 C 2 H 2 C1 2 O 2 , dichloracetic " 
 
 C 2 HC1 3 O 2 , trichloracetic " 
 
 The fourth atom of hydrogen belongs to the COOH 
 group, and, although replaceable by metals, can not 
 be replaced by chlorine. This fact adds to the proof 
 that it is differently combined from the others. Just 
 as aldehyde is related to acetic acid, so also there is 
 a trichloraldehyde related to trichloracetic acid. It 
 is a liquid of formula C 2 HC1 3 O, and is more briefly 
 known as chloral. It combines with water to form 
 
THE FATTY ACIDS. 
 
 309 
 
 a solid crystalline hydrate which is much used in 
 medicine for producing quiet sleep. 
 
 One other compound may be noticed here as 
 the type of an important class. Whenever an ace- 
 tate is subjected to dry distillation, a volatile liquid 
 called acetone is formed. This compound, C 8 H 6 O, 
 is the first of a large series, members of which may 
 be obtained by a variety of reactions. They are all 
 known as ketones, and are structurally formed by 
 the union of two univalent radicles with bivalent 
 carbonyl, CO. Acetone may be called dimethyl- 
 ketone : 
 
 CH S CH 3 C a H* 
 
 i i i 
 
 c=o c=o c=o 
 
 CHs CaH 6 CaH 6 Etc. 
 
 Dimethyl-ketone. Ethylmethyl-ketone. Diethyl-ketone. 
 
 The ketones are isomeric with the aldehydes, but 
 have entirely different constitution. 
 
CHAPTER XXXVI. 
 
 THE OLEFINES. 
 
 THE C n H2n series of hydrocarbons is known as 
 the olefine series, from " olefiant gas " or ethylene, 
 its first member. Some of its relations to the me- 
 thane series and to the alcohol radicles are indicated 
 in the following formulas and the accompanying 
 nomenclature : 
 
 O Han + a. Ale. radicles* OH an . 
 
 CH 4 , methane. CH 3 , methyl. CH 2 , methylene.* 
 
 C a H 6 , ethane. C a H 8 , ethyl. C a H 4 , ethylene. 
 
 CsH 8 , propane. C 3 H 7 , propyl. C 3 H 8 , propylene. 
 
 C 4 Hio, butane. C 4 H 9 , butyl. C 4 H 8 , butylene. 
 
 CeHia, pentane. C 5 H U , amyl. C 6 Hi , amylene. 
 
 C 8 Hu, hexane. C 6 Hi 3 , hexyl. CeHia, hexylene. 
 
 C 7 Hi6, heptane. C 7 Hi 6 , heptyl. C 7 Hi 4 , heptylene. 
 
 CsHis, octane. C 8 Hi7, octyl. C 8 Hi 6 , octylene, etc. 
 
 The most important one of these olefines is ethylene, 
 which has already been described as a constituent 
 of coal-gas. In it the two carbon-atoms are united 
 by a double bond of affinity, as shown in the sub- 
 joined formula. The second formula is merely a 
 convenient abbreviation of the first. 
 
 H-C-H C = H a 
 
 ii or ii 
 
 H-C-H OH a . 
 
 * Known only in compounds ; can not exist free. 
 
THE OLEFINES. 3 1 1 
 
 These defines all behave as if they were biva- 
 lent radicles. Each one unites with two chlorine- 
 atoms to form a chloride, one oxygen-atom to form 
 an oxide, etc. They also take up two hydroxyl 
 groups to form a series of alcohols, which are some- 
 what better known as glycols. In all these deriva- 
 tives, however, the carbon-atoms are united by a 
 single bond only, the other bond, which is fixed in 
 the hydrocarbons themselves, being released to new 
 uses. Thus : 
 
 C=H a . C = H 3 C1. OH 3 OH. 
 
 Ethylene. Ethylene chloride. Ethylene alcohol. 
 CnHaNOa OH 2 C 2 H 3 O a C = H a 
 
 ' i i \O 
 
 Ethylene nitrate. Ethylene acetate. Ethylene oxide. 
 
 By the action of oxidizing agents the alcohols of 
 the olefine series, like the alcohols of the methane se- 
 ries, yield acids. Only, instead of a single set of acids, 
 each glycol yields two such derivatives. Thus : 
 
 CH 2 OH CH 2 OH COOH 
 
 i i i 
 
 CH 2 OH. COOH. COOH. 
 
 Ethylene alcohol. Glycollic acid. Oxalic acid. 
 
 Glycollic acid and its homologues, having but one 
 COOH group, are monobasic ; the acids of the ox- 
 alic series, on the other hand, are bibasic : 
 
 CH 2 OH COOH COOK 
 COOK. COOK. COOK. 
 
 Potassium Hydrogen potas- Neutral potas- 
 
 glycollate. sium oxalate. sium oxalate. 
 
 Some of these acids and their derivatives are 
 compounds of very great importance. In the gly- 
 collic series, for instance, we find lactic acid, which 
 
312 ORGANIC CHEMISTRY. 
 
 is the acid of sour milk ; while from oxalic acid the 
 more important acids of various natural fruits may 
 be rationally derived. 
 
 Lactic acid, C 3 H 6 O 3 , may be regarded as derived 
 from glycollic acid, C 2 H 4 O 8 , by the addition of CH 2 . 
 In reality, an atom of hydrogen in glycollic acid is 
 replaced by a methyl group, CH 3 . This is equiva- 
 lent to adding CH 2 , and all homologous series, 
 either of hydrocarbons or of their derivatives, are 
 built up by this process of substitution. Lactic 
 acid is a sirupy liquid, having a specific gravity of 
 1.215, an d is easily decomposed by heat. It may 
 be formed synthetically, but it is generally prepared 
 from sour milk. When the latter is used in cookery, 
 the free acid is neutralized by sodium bicarbonate, 
 and a soluble lactate of sodium is produced. Sev- 
 eral of the lactates are used medicinally, and all of 
 them are soluble in water. A baking-powder con- 
 taining lactic acid has recently been patented. 
 
 Oxalic acid, H 2 C 2 O 4 , is found in the juice of cer- 
 tain plants, such as the sorrel and rhubarb. It may 
 be prepared synthetically by a variety of methods, 
 but on a commercial scale only two processes are 
 used. One of these may be verified experimentally : 
 
 EXPERIMENT 104. Pour strong nitric acid over 
 a few grammes of white sugar contained in a large 
 flask or beaker. When the action has ceased, and 
 red fumes are no longer given off, evaporate the liq- 
 uid to a small bulk. On cooling, oxalic acid will crys- 
 tallize out. Starch may be used instead of sugar. 
 
 The second process, which is cheaper, and which 
 of late years has quite supplanted the first, is as 
 follows: When sawdust is heated with caustic pot- 
 ash, potassium oxalate is formed. This, treated 
 
THE OLEFINES. 
 
 313 
 
 with milk of lime, yields an insoluble calcium ox- 
 alate. The latter, treated with sulphuric acid, gives 
 calcium sulphate, while oxalic acid is set free, and 
 may be purified by recrystallization. 
 
 Oxalic acid is readily soluble, and crystallizes 
 with two molecules of water in prisms which re- 
 semble Epsom salt. It is intensely sour, a very 
 strong acid, and quite poisonous. Chalk or mag- 
 nesia, suspended in water, neutralizes the acid, and 
 is a good antidote in cases of poisoning. In the 
 household, oxalic acid is often used for removing 
 ink-stains or iron-rust from linen or clothing. As, 
 however, the acid attacks the fiber of the cloth, it 
 should be washed out as soon as it has produced 
 the desired bleaching effect. The oxalic acid which 
 was made in Experiment 104 may be used for veri- 
 fying its solvent property, either upon a rag spotted 
 w^ith ink or upon a sheet of written paper. On a 
 large scale, oxalic acid is used by calico-printers as 
 a means of discharging certain colors. 
 
 Oxalic acid is the first term of a long homologous 
 series. The second term, malonic acid, C 3 H 4 O 4 , is 
 unimportant ; but the third member, succinic acid, 
 C 4 H 6 O 4 , is interesting. This acid is obtained from 
 amber, and is noteworthy on account of its struct- 
 ural relations to two fruit-acids, malic and tartaric. 
 
 Succinic acid, C 4 H 6 O4. 
 Malic " C4H(,O6. 
 Tartaric " C 4 H 8 O fl . 
 COOH COOH COOH 
 
 CH a CHOH CHOH 
 
 CH a CH a CHOH 
 
 COOH. COOH. COOH. 
 
 Succinic acid. Malic acid. Tartaric acid. 
 
314 ORGANIC CHEMISTRY. 
 
 Malic acid is the acid of apples, pears, and 
 eral other fruits and vegetables. It is a white, crys- 
 talline body, which may be derived from succinic 
 acid by artificial means, but is more cheaply pre- 
 pared from mountain-ash berries. Tartaric acid is 
 the acid of grapes, and has considerable practical 
 importance. During the fermentation of wine its 
 potassium salt is deposited in an impure condition 
 on the sides of the wine-casks, and from this crude 
 tartar the acid itself may be obtained. It has also 
 been prepared synthetically from succinic acid. 
 
 Tartaric acid occurs in white crystals * having an 
 intensely sour taste. It is readily soluble in water, 
 and its solution effervesces strongly with carbonates. 
 In Seidlitz or Rochelle powders it forms the con- 
 tents of the smaller papers, while the other papers 
 contain a mixture of sodium hydrogen carbonate 
 and a tartrate known as Rochelle salt. The acid is 
 also used in the preparation of a variety of efferves- 
 cent drinks, and by calico-printers as a discharge 
 for certain mordants. 
 
 There are two sets of tartrates, a neutral and 
 an acid series, and some of these salts are practically 
 important. They may be represented in their rela- 
 tions to the acid by condensed formulas like the fol- 
 lowing : 
 
 C 4 H 4 6 . ^ C 4 H 4 6 . C 4 H 4 8 . ^ a C 4 H 4 0. 
 
 Tartaric acid. Hydrogen potas- Potassium Rochelle salt. 
 
 sium tartrate. tartrate. 
 
 The acid potassium tartrate is the well-known 
 cream of tartar, which is much used in cookery, and 
 as an ingredient of baking-powders. With a few 
 
 * Commercial tartaric acid occurs oftener as a white powder than it 
 does in the form of crystals. 
 
THE OLEFINES. 3x5 
 
 exceptions, the latter preparations are simply mixt- 
 ures of cream of tartar with sodium hydrogen car- 
 bonate, and when they are acted upon by the moist- 
 ure of dough, the following reaction takes place : 
 
 NaHCOs + KHC 4 H 4 8 = KNaC^Oe + CO a + H a O. 
 
 The carbonic-acid bubbles, escaping, render the 
 bread or cakes light ; the double tartrate, Rochelle 
 salt, remains behind.* 
 
 Several other tartrates are used in medicine, 
 and one of them, tartar emetic, is particularly im- 
 portant. It is a double salt containing potassium 
 and antimony, and is commonly represented as con- 
 taining the latter metal so united with oxygen as 
 to form a univalent radicle Sb m = O. Upon this 
 
 TC ) 
 basis, tartar emetic would be written, CUQ [ C 4 H 4 O 6 ; 
 
 but recent investigations show that its constitution 
 is more complicated. The salt is a powerful emetic, 
 and in large doses is poisonous. 
 
 One other fruit-acid, although not derived from 
 the foregoing acids, may fairly be described here. 
 Citric acid, C 6 H 8 O 7 , is found in oranges and lemons, 
 and, with malic acid, in such fruits as the currant 
 and gooseberry. It forms white, soluble crystals, 
 which contain three COOH groups, and therefore 
 three atoms of replaceable hydrogen. Hence it 
 can form various salts, thus : 
 
 ( H ( K ( K ( K 
 
 C 6 H 6 7 \ H C 6 H 6 7 \ H C 6 H 5 7 \ K C 6 H 6 O 7 \ K 
 
 (H (H (H (K 
 
 Citric acid. Monopotassic citrate. Dipotassic citrate. Tripotassic citrate. 
 
 Etc. 
 
 * Mrs. Richards's little book on " The Chemistry of Cooking and 
 Cleaning " may be profitably read in connection with this and the fol- 
 lowing chapter. 
 
CHAPTER XXXVII. 
 
 GLYCERIN AND THE FATS. 
 
 IN preceding- chapters we have become acquaint- 
 ed with two classes of alcohols, derived from univ- 
 alent and bivalent hydrocarbon radicles respect- 
 ively. These alcohols, we have seen, are simply 
 hydroxides, which, though very different in their 
 outward properties, may be compared as to struct- 
 ure with the hydroxides of the metals. Still other 
 series of alcohols are known, some of which cor- 
 respond to radicles of higher valency ; and these 
 we may compare with inorganic hydroxides, thus : 
 
 I. II. III. IV. 
 
 KOH. Ca(OH) 3 . Bi(OH),. Si(OH). 
 
 CHsOH. C 2 H 4 (OH) 2 . C 8 H 6 (OH) 3 . C 4 H 6 (OH) 4 . 
 
 There is also an alcohol, mannite, which is de- 
 rived from a sexivalent radicle. Its formula is 
 C 6 H 8 (OH) 6 ; but its description, as well as that of 
 the compound cited in the fourth column above, 
 erythrite, must be looked for in some of the larger 
 treatises upon organic chemistry. 
 
 The trivalent alcohol C 3 H 5 (OH) 3 , or C 3 H 8 O 3 , is, 
 however, a body of great practical and theoretical 
 importance. It is commonly known as glycerin ; 
 
GLYCERIN AND THE FATS. 
 
 and from it all the natural fats and fatty oils are sys- 
 tematically derived. 
 
 In Chapter XXXV it was shown that when a 
 compound ether is treated with caustic alkalies it is 
 decomposed, an alcohol being set free and an alka- 
 line salt formed. For example, ethyl acetate and 
 caustic soda yield sodium acetate and ethyl alcohol, 
 as follows : 
 
 C 2 H 6 C 3 H 3 O 2 + NaOH = NaC 2 H 3 O 2 + C 2 H 6 OH. 
 
 Now, the natural fats are simply ethers correspond- 
 ing to glycerin, and they may be decomposed in 
 precisely the same way. If we take stearin, which 
 is a tristearate of glyceryl, C 3 H 5 , sodium stearate 
 will be formed and stearic acid will be liberated. 
 
 C 3 H 6 (C i8 H 36 O 2 ) 3 + sNaOH = C 3 H 6 (OH) 3 
 
 This method of decomposition is known as saponifi- 
 cation, from the fact that the alkaline salts produced 
 by it are ordinary soaps. 
 
 On a large scale, glycerin is prepared either by 
 saponifying a fat or oil with lime or lead oxide, 
 which yield insoluble calcium or lead soaps and set 
 the glycerin free, or else by acting on fats under 
 great pressures with superheated steam. The latter 
 process readily decomposes a fat, and separates it 
 at once into glycerin and an acid in such a way that 
 both products are immediately recoverable. In the 
 preparation of stearic acid this method of decompo- 
 sition is practically applied, and both glycerin and 
 the acid are saved. The latter is used in the manu- 
 facture of candles.* 
 
 * For details about the stearine industry, see Wagner's " Chemical 
 Technology," pp. 620-636. 
 
3 i8 ORGANIC CHEMISTRY. 
 
 Glycerin is a colorless, sirupy liquid, of specific 
 gravity 1.28. It solidifies at low temperatures, and 
 distills, with partial decomposition, at 275-28o. It 
 distills more perfectly in a vacuum. It has a very 
 sweet taste, and mixes readily in all proportions with 
 water and alcohol. It has a great variety of uses, as 
 a solvent or as a lubricator, and its household appli- 
 cation to chapped lips or hands is universally famil- 
 iar. With feeble oxidizing agents it yields gly eerie 
 acid, C 8 H 6 O 4 . 
 
 The ethers derived from glycerin are numerous, 
 and, at first sight, complicated. Since the alcohol 
 itself is derived from a trivalent radicle, and has 
 three hydroxyl groups, it follows that with any 
 given monobasic acid it may form at least three 
 derivatives. Thus, with acetic acid, HC 2 H 3 O 2 , gly- 
 cerin yields three ethers, to which are given the 
 names that are written below the subjoined for- 
 mulae: 
 
 ( OH ( C 2 H S O 2 
 
 C 3 H 6 \ OH C 3 H B ] OH 
 
 (OH (OH 
 
 Glycerin. Monacetin. 
 
 ( C a H 3 2 ( C a H 3 3 
 
 C 3 H 6 \ C 2 H 3 O a C 3 H 6 ] C 2 H 3 2 
 
 ( OH ( C 2 H 3 O a 
 
 Diacetin. Triacetin. 
 
 With hydrochloric acid three compounds are 
 obtained, namely : 
 
 (9 ( cl ( cl 
 
 - C 3 H 6 1 OH C 3 H 6 1 Cl C 3 H 6 ] Cl 
 
 (OH (OH ( Cl 
 
 Chlorhydrin. Dichlorhydrin. Trichlorhydrin. 
 
 In fats and oils we generally encounter the triple 
 ethers of stearic, margaric, palmitic, or oleic acids. 
 
GLYCERIN AND THE FATS. 319 
 
 Stearic, margaric, and palmitic acids belong to the 
 regular fatty series, oleic acid stands in another 
 group. Stearic acid is the chief acid in beef-suet, 
 and has the formula QsHggOg ; margaric acid is one 
 step lower in the series ; and palmitic acid, C 16 H32O 2 , 
 is derived both from animal fats and from palm-oil. 
 Oleic acid, QsH^O^ is found in olive-oil and in sev- 
 eral other fatty substances. All these fats and oils 
 may be represented by the subjoined formulae : 
 
 ( C 16 H S1 2 ( C 17 H, 3 O a 
 
 C 3 H 6 \ C 16 H 3 iO a C 3 H 8 \ C 17 H 33 O a 
 
 ( Ci 8 H 81 O a ( Ci 7 H 33 O a 
 
 Tripalmitin. Trimargarin. 
 
 C 18 H 35 2 ( C 18 H 33 O a 
 
 Ci 8 H 3 6O a CsHs -s CisH 33 Oa 
 
 C 18 H 35 O a ( C 18 H 33 O a 
 
 Tristearin. Triolein. 
 
 They are commonly called by the briefer names of 
 palmitin, margarin, stearin, and olein, respectively. 
 The more stearin a natural fat contains, the more 
 solid it is ; the fluid or pasty fats are richer in olein. 
 Other glycerin ethers are often found, but they need 
 no full description here. 
 
 Soap is a mixture of the alkaline salts of the fore- 
 going acids, and is prepared by the direct action 
 of caustic soda or potash upon fats. A soap which 
 contains mostly soda salts and little of the oleate is 
 a hard soap ; potash soaps, or soaps containing much 
 oleic acid, are soft soaps. Sometimes, in making 
 cheap soaps, rosin is added ; and in some cases, a 
 solution of sodium silicate, or water-glass, is also 
 used. A pure soap is completely soluble in alcohol. 
 All soaps contain a considerable quantity of water. 
 
 When glycerin is treated with a mixture of strong 
 
3 20 
 
 ORGANIC CHEMISTRY, 
 
 nitric and sulphuric acids, an ether is formed which 
 is commonly known as nitroglycerin. This trini- 
 trin, as it is more properly named, is a yellow, oily 
 liquid having the formula C 3 H 5 (NO 3 ) 3 , and possesses 
 extraordinary explosive properties. When kindled 
 by a flame, it burns rather quietly ; but when struck 
 by a hammer, or ignited by a percussion-cap, it ex- 
 plodes with terrific violence. This explosion is sim- 
 ply a sudden decomposition, one effect of which is 
 to develop instantaneously a very large volume. of 
 gas, in accordance with the following equation : 
 
 4C 3 H 6 N 3 O9 = I2CO 2 + I2N + 20 + ioH 2 0. 
 
 Dynamite and several other explosive agents much 
 used in blasting are mixtures of nitroglycerin with 
 silica, fine sand, sawdust, or some other solid pow- 
 der. The oil itself is also used directly as an ex- 
 plosive. Nitroglycerin is a substance which should 
 only be handled with extreme care, for it is not 
 merely explosive but also very poisonous. A sin- 
 gle drop placed on the tongue will produce intense 
 headache ; and similar discomfort may arise from 
 mere contact of the liquid with the fingers. 
 
 When glycerin or any fat is heated to the point 
 at which decomposition begins, acrid vapors are 
 given off. These are produced by a substance called 
 acrolein, the odor of which may be recognized in the 
 unpleasant fumes emitted from the wick of an imper- 
 fectly quenched candle. Its formula is C 8 H 4 O, and 
 it is the aldehyde corresponding to allyl alcohol and 
 acrylic acid. These three compounds are related to 
 each other in the same way as are common alcohol, 
 aldehyde, and acetic acid, as the subjoined formulae 
 will show : 
 
GLYCERIN AND THE FATS. 321 
 
 Ethyl alcohol, C a H 6 O. Aldehyde, C 2 H 4 O. Acetic acid, C 2 H 4 O a . 
 Allyl " C 3 HO. Acrolein, C 3 H 4 O. Acrylic " C 3 H 4 O 2 . 
 
 Allyl alcohol, C 3 H 5 , OH, is interesting in several 
 ways. It is the hydroxide of a univalent radicle, 
 C 3 H 5 , which is isomeric with the trivalent radicle 
 of glycerin. These two radicles differ in structure, 
 however, as the following formulae for the alcohols 
 indicate : 
 
 CH 2 OH CH 3 
 
 CHOH CH 
 
 CH 2 OH. CHaOH. 
 
 Glycerin. Allyl alcohol. 
 
 A good many derivatives of allyl are known, 
 and some of them are important. Allyl sulphide, 
 (C 3 H 5 ) 2 S, is the natural oil to which garlic owes its 
 odor ; and allyl sulphocyanate, C 3 H 5 , CNS, is the oil 
 of mustard. The radish, horseradish, etc., also owe 
 their pungency to organic compounds of sulphur. 
 
CHAPTER XXXVIII. 
 
 THE CARBOHYDRATES. 
 
 IN sugar, starch, and a number of allied com- 
 pounds, the hydrogen and oxygen are combined in 
 just the proportions necessary to form water. By 
 reagents having very strong affinity for water this 
 hydrogen and oxygen may be removed, and char- 
 coal is left behind. For instance, strong sulphuric 
 acid reacts in this manner upon either sugar or 
 starch, as the pupil may easily discover by experi- 
 ment. Hence the term carbohydrates, or hydrates of 
 carbon, has been adopted as a convenient general 
 name for this class of substances, notwithstanding 
 the fact that it is somewhat misleading as to their 
 real chemical structure. 
 
 A considerable number of carbohydrates are 
 known, but, as some of them are isomeric with 
 others, all may be classed in three groups under 
 three simple formulae. These groups are known as 
 the sucroses, or sugars proper ; the glucoses ; and the 
 amyloses, or starches and gums : 
 
 Sucroses. Glucoses. Amyloses. 
 
 CiaHaaOn. C 6 H 12 O 8 . C 6 H 10 O6. 
 
 Cane-sugar. Grape-sugar. Starch. 
 
 Milk-sugar. Levulose. Dextrin. 
 
 Maltose. Etc. Gum. 
 
 Etc. Cellulose, etc. 
 
THE CARBOHYDRATES. 323 
 
 Cane-sugar, or sucrose, C^H^Ou, is found in the 
 sap of many plants, such as the sugar-cane, sorghum, 
 Indian corn, beet-root, sugar-maple, etc. From all 
 these sources, and perhaps from others, it may be 
 profitably extracted ; but sugar-cane is the most 
 important. Beet-root sugar is extensively made in 
 France, and maple-sugar in this country ; and the 
 manufacture of sugar from sorghum is an industry 
 which promises great development in the future.* 
 
 In the extraction of sugar from sugar-cane the 
 latter is first crushed between heavy iron rollers so 
 as to express the juice. To the latter a little lime is 
 immediately added, to neutralize certain vegetable 
 acids and to precipitate certain fermentable or de- 
 composable impurities. The liquid is next heated 
 to boiling, carefully skimmed, evaporated in copper 
 pans to near the crystallizing point, and filtered 
 through bags of cotton or linen. On cooling, a crys- 
 talline mass of moist brown sugar is deposited ; 
 and the remaining syrup, upon further evaporation, 
 yields still more. When the second crop of crystals 
 has been removed, a dark, thick molasses, rich in 
 uncrystallized sugar, remains behind. This is either 
 sent into market as it is, or else fermented and dis- 
 tilled into rum. 
 
 Brown sugar owes its color to organic impuri- 
 ties, which are removed by the following process of 
 refining : The sugar, dissolved in very little water, 
 is first heated in a copper pan. Albumen, generally 
 in the form of blood, is then added, which, coagu- 
 lating, carries down the impurities of the sugar in a 
 
 * The United States Department of Agriculture at Washington has 
 issued very valuable reports upon this industry, and also upon the sub- 
 ject of sugar from beets. 
 
324 
 
 ORGANIC CHEMISTRY. 
 
 sort of dense clot. The liquid is next heated to the 
 boiling-point with a little animal charcoal, and, after 
 running through a charcoal filter, is concentrated to 
 the point of crystallization. This concentration is 
 now generally effected in a vacuum-pan. Finally, 
 the purified sugar is drained of adhering syrup and 
 dried. 
 
 Pure sugar is a white, crystalline solid, of spe- 
 cific gravity 1.59. It melts at 160, forming the 
 amber-colored mass known as barley-candy. At 
 higher temperatures it turns brown, loses water, 
 and is converted into a substance called caramel, 
 which is somewhat used for coloring alcoholic 
 liquors. In rock-candy, sugar is highly crystal- 
 lized ; in granulated sugar the crystals are small 
 and separate ; in loaf or lump sugar the crystalline 
 character is evident throughout the mass. In all 
 of these forms sugar is easily soluble, and very 
 sweet. If a sample of commercial sugar fails to 
 dissolve completely in hot water, the insoluble resi- 
 due may be regarded as evidence of adulteration. 
 
 Chemically considered, sugar is the alcohol of 
 an octad radicle. Its eight hydroxyl groups may 
 be replaced by eight NO 8 groups, to form an explo- 
 sive octonitrate, or by eight acetic groups to pro- 
 duce an octoacetate. These derivatives, however, 
 have been incompletely studied. 
 
 Lactose, or milk-sugar, is obtained from the 
 whey of milk, and is isomeric with sucrose. It 
 forms hard, white crystals, which grit between the 
 teeth, and are less sweet than cane-sugar. They 
 contain one molecule of water of crystallization, so 
 that their formula is written C^H^On, H 2 O. Lac- 
 tose is used in preparing the little globules of the 
 
THE CARBOHYDRATES. 325 
 
 homoeopathic pharmacy. Several other isomers of 
 sucrose and lactose are known. 
 
 Cane-sugar itself does not undergo fermenta- 
 tion ; but by the action of yeast it is converted into 
 a mixture of two glucoses, both of which ferment 
 readily. In this transformation it takes up one 
 molecule of water, so that the whole change may be 
 written out as follows : 
 
 CiaHaaOi, + H 2 O = C 6 H 12 O 8 + C 8 H 12 O. 
 
 One of these glucoses is termed dextrose or grape- 
 sugar ; the other is called levulose or fruit-sugar. 
 The latter is the more readily soluble of the two, 
 and is uncrystallizable. Dextrose, together with 
 sucrose, occurs in many fruits ; with levulose it is 
 found in fruits and in honey. Commercial glucose 
 is commonly a mixture of both substances. 
 
 On a large scale, glucose is made by the action 
 of very dilute sulphuric acid upon starch. 
 
 EXPERIMENT 105. Add one cubic centimetre of 
 strong sulphuric acid to one hundred cubic cen- 
 timetres of water, and heat in a flask to boiling. 
 Mix ten grammes of starch to a thin paste with 
 water, and pour it very slowly into the acid, so 
 as not to check the boiling. Continue to boil for 
 about three hours, and then add powdered chalk 
 until all free acid has been neutralized. Filter off 
 the insoluble calcium sulphate thus formed, and 
 evaporate the filtrate to the consistency of a thick 
 syrup. The latter will be sweet, and will deposit 
 crystals of dextrose if left standing. By essentially 
 this process immense quantities of glucose are now 
 made from the starch of Indian corn. The prod- 
 uct is cheaper than cane-sugar, though less sweet, 
 
326 
 
 ORGANIC CHEMISTRY. 
 
 and is largely used to adulterate sugars and syrups, 
 in the manufacture of candies, by brewers for modi- 
 fying the quality of beer, and for a variety of other 
 more legitimate purposes.* 
 
 Starch, which has the formula C 6 H 10 O 5 or some 
 multiple thereof, is found in all grains, in such vege- 
 tables as the potato, in unripe fruits, and to a greater 
 or less extent throughout the whole plant-kingdom. 
 Beans, peas, and rice are especially rich in it ; sago 
 and tapioca are varieties of it ; and, in short, the 
 nutritive value of nearly all vegetables depends in 
 great part upon the amount of starch which they 
 contain. Pure starch is prepared chiefly from wheat- 
 flour or from potatoes. It consists of a white pow- 
 der made up of microscopic granules (Fig. 53), which 
 
 FIG. 53. -Starch Granules, Magnified. 
 
 are insoluble in water. If heated with water to 
 above 60, however, they burst, and form the jelly- 
 like starch-paste which is so familiar to the house- 
 keeper. With tincture of iodine starch forms a blue 
 compound ; and by this reaction it may be distin- 
 guished from all isomers.f 
 
 * The question whether artificial glucose is wholesome or not is 
 still under discussion. At the worst, it is not a dangerous article of 
 diet. 
 
 f The pupil may profitably apply this test for starch to flour, rice, 
 bread, potatoes, etc. Boil each article with a little water, and then 
 add a drop of the tincture. 
 
THE CARBOHYDRATES. 
 
 327 
 
 By heating to about 205 starch is converted 
 into an isomeric compound, dextrin. This sub- 
 stance is soluble in water, yielding a gummy solu- 
 tion which is applied to the backs of postage- 
 stamps and used for other similar purposes. Dex- 
 trin is largely manufactured under the name of 
 " British gum." Most of the natural gums are 
 isomers of starch and dextrin. Gum-arabic, how- 
 ever, is a mixture of the potassium and calcium 
 salts of arabic acid, (C 6 H 10 O 5 ) 2 . Pectin, which is 
 found in most fruits, and which enables their juice 
 to form jellies, is allied to the gums and starches ; 
 but its exact character is not yet definitely under- 
 stood. 
 
 Cellulose, (C 6 H 10 O 5 ) 3 , is the substance which 
 chiefly constitutes all vegetable fiber. Wood con- 
 sists mainly of cellulose, and cotton is cellulose 
 practically pure. By sulphuric acid cellulose may 
 be converted into glucose ; and the latter may be 
 made from old rags, or even from sawdust. 
 
 When cellulose is treated with a mixture of 
 strong nitric and sulphuric acids it is transformed 
 into nitrocellulose or pyroxylin. This compound, 
 C 6 H 7 (NO 2 ) 3 O 5 , is commonly known as gun-cotton, 
 and is remarkable for its explosive properties. 
 Outwardly, by the change from cotton to gun-cot- 
 ton, the vegetable fiber remains the same ; and it 
 may be spun into thread, woven into cloth, or made 
 into paper, the same as before. It explodes, how- 
 ever, either by percussion or upon the touch of a 
 flame, more violently than gunpowder; and it is 
 somewhat used as an explosive agent. 
 
 Gun-cotton dissolves easily in a mixture of al- 
 cohol and ether, forming a solution which is known 
 15 
 
328 ORGANIC CHEMISTRY. 
 
 as collodion. This liquid evaporates rapidly, leav- 
 ing- a film of gun-cotton behind ; and it is used for 
 a variety of surgical purposes and for photography. 
 The latter use was described in a previous chapter ; 
 its surgical value is due to its power of covering 
 raw or inflamed surfaces, as in the case of scalds 
 and burns, with a sort of artificial skin, and thereby 
 protecting them from contact with the air.* 
 
 * Details concerning many of the bodies described in this chapter 
 may be read up to advantage in Wagner's " Chemical Technology." 
 
CHAPTER XXXIX. 
 
 THE BENZENE DERIVATIVES. 
 
 BENZENE,* C 6 H 6 , is a hydrocarbon of remark- 
 able interest. It has been prepared by synthesis 
 from acetylene, C 2 H 2 , and by several other meth- 
 ods ; but it is chiefly obtained from the coal-tar 
 which accumulates in the gas-works. The benzene 
 is purified by several distillations, and forms a col- 
 orless liquid, lighter than water, and having a pe- 
 culiar odor resembling coal-gas. It boils at 80, and 
 solidifies at 3. Its vapor, as well as the liquid, are 
 highly inflammable. 
 
 Benzene is chiefly useful in the preparation of 
 its derivatives ; and these are of the highest impor- 
 tance. They are all derived from benzene by the 
 substitution of other elements or radicles for the 
 hydrogen, while the six carbon-atoms remain as a 
 permanent nucleus. These are supposed to be ar- 
 ranged in the form of a ring or closed chain, each 
 having three bonds of affinity satisfied. Thus, each 
 carbon-atom is still able to hold one hydrogen-atom, 
 as the following diagram will show : f 
 
 * Often called benz0/. The benzine of the shops is usually a mixt- 
 ure of volatile hydrocarbons of the C n H 2n + 3 series. It is obtained 
 from petroleum, and is very different from benzene proper. 
 
 f Other structural formulae are possible, but this one is the best for 
 present purposes. 
 
330 ORGANIC CHEMISTRY. 
 
 H 
 
 i 
 
 C 
 
 H-C X C-H 
 
 ii i 
 
 H-C C-H 
 
 i 
 H 
 
 From this formula the formulas of the derivatives 
 are easily deduced, as a few examples will indicate : 
 
 H H 
 
 i i 
 
 / C \ C \ 
 
 U-C \-CH 3 H-c' % C-OH 
 
 H-C C-H H-C C-H 
 
 \ # \ / 
 
 C C 
 
 I I 
 
 H H 
 
 Methyl-benzene, C 7 H 8 . Phenol, C 6 H 7 O. 
 
 H H 
 
 i i 
 
 C C 
 
 H-C X C-NH a H-C C-COOH 
 
 ii i ii i 
 
 H-C C-H H-C C-H 
 
 \ # \ <f 
 
 C C 
 
 H H 
 
 Aniline, C 6 H 7 N. Benzole acid, C 7 H O 2 . 
 
 Since every hydrogen-atom in benzene is thus re- 
 placeable, the possible number of benzene deriva- 
 tives is almost infinite. Thousands of them are 
 actually known ; hundreds are discovered every 
 year. Only a few of the more striking- and useful 
 can be described in this treatise. 
 
 Phenol, C 6 H 5 OH, commonly called carbolic 
 acid,* is a compound of great value as an antiseptic. 
 
 * It is not really an acid. 
 
THE BENZENE DERIVATIVES. 
 
 331 
 
 It is chiefly obtained from coal-tar by a process of 
 distillation, and forms white, deliquescent crystals 
 which melt at 39.5 and boil at 182. Commercial 
 phenol generally has a reddish tinge, due to im- 
 purities. It has a smoky odor and a burning taste, 
 and is much used in medicine and surgery for dis- 
 infecting sick-rooms, for preventing gangrene in 
 wounds, etc. It is highly poisonous. 
 
 By the action of strong nitric acid upon phenol 
 the latter is converted into trinitrophenol or pic- 
 ric acid, C 6 H 2 (NO 2 ) 3 OH. This substance occurs in 
 yellow, intensely bitter crystals, which are used for 
 giving a yellow color to silk. The picrates are 
 salts which explode violently by percussion, and 
 some of them have been used in gunnery and in 
 submarine torpedoes. 
 
 When nitric acid acts on benzene directly, ni- 
 trobenzene, C 6 H 5 NO 2 , is produced. This is a 
 volatile liquid, having an odor like that of bitter-al- 
 monds. Although somewhat poisonous, it is used 
 in the manufacture of cheap flavoring essences 
 and in perfumery. Three isomeric dinitrobenzenes, 
 C 6 H 4 (NO 2 ) 2 , all solid, are also known. 
 
 When nitrobenzene is mixed with iron-filings 
 and dilute sulphuric acid, the nascent hydrogen 
 evolved from the two latter substances reduces it 
 to amidobenzene,* or aniline, C 6 H 5 NH 2 . This 
 compound is sometimes called phenylamine, the 
 group C 6 H 5 being frequently known as phenyl. 
 Aniline is an oily liquid of specific gravity 1.036, 
 which boils at 181, and has a peculiar, soapy, dis- 
 
 * Compounds containing the group NH 2 are called "amido-com- 
 pounds." Many other nitro-compounds (containing NO a ) are similarly 
 reducible by hydrogen. 
 
332 ORGANIC CHEMISTRY. 
 
 agreeable odor. It is a powerful base, and unites 
 with nearly all acids to form highly crystalline 
 salts. With oxidizing agents it yields a great vari- 
 ety of derivatives ; and some of these are among 
 our most valuable and brilliant dyes. Nearly all 
 the gorgeous colors now used in silks and satins are 
 prepared indirectly from the benzene of coal-tar. 
 Some of them are salts of a complex base, rosani- 
 line, CjjoHjgNg ; which, though colorless itself, yields 
 compounds of marvelous beauty. For example, 
 rosaniline combines with hydrochloric acid to form 
 the color known as magenta. This substance, in 
 the solid state, forms crystals of a rich, metallic, 
 beetle-green color, which yield with alcohol a solu- 
 tion of a magnificent red. Other reds, purples, 
 violets, yellows, blues, greens, and a very stable 
 black are also found among the derivatives of ani- 
 line. Thirty years ago, coal-tar was worthless ; to- 
 day whole industries, giving employment to thou- 
 sands of men, depend upon it. 
 
 In some of the preceding chapters we have stud- 
 ied the relations of certain alcohols to derivatives 
 known as acids and as aldehydes. In all aldehydes 
 the group H C=O occurs, and in all acids we 
 
 find the more complex group O H C=O. In 
 
 each of these groups one carbon bond is free, by 
 means of which other groups can be chemically 
 held in union ; and whenever we find in any com- 
 pound either group, that compound will have the 
 properties of an acid or an aldehyde as the case 
 may be. Among the benzene derivatives we meet 
 many compounds illustrating these principles, and 
 a few formulae will make the subject clear : 
 
THE BENZENE DERIVATIVES. 333 
 
 H H 
 
 i i 
 
 C C 
 
 H-C X C-COOH H-C X C-COH 
 
 I! I II I 
 
 H-C C-H H-C C-H 
 
 \ s \ s 
 
 C C 
 
 H H 
 
 Benzoic acid. Benzaldehydc. 
 
 H H 
 
 i i 
 
 C C 
 
 H-C C-COOH H-C X C-COH 
 
 H-C C-OH H-C C-OH 
 
 \ <f \ ~ V 
 
 C C 
 
 I I 
 
 H H 
 
 Salicylic acid. Salicyl aldehyde. 
 
 These substances are of some importance. Ben- 
 zoic acid is obtained from gum-benzoin, and is of 
 some use in medicine ; benzaldehyde is the well- 
 known fragrant oil of bitter-almonds ; salicyl alde- 
 hyde is the odoriferous principle of the meadow- 
 sweet spiraea ; and salicylic acid, which is now 
 made synthetically from phenol, is a very impor- 
 tant remedy in the treatment of rheumatic disor- 
 ders. Sodium salicylate is often used instead of 
 the acid. Methyl salicylate is the natural oil of the 
 wintergreen or checkerberry. 
 
 When the hydrogen of benzene is replaced 
 by a radicle of the methyl series, new hydrocar- 
 bons, homologous with benzene itself, are pro- 
 duced. Thus, for example, we have : 
 
 Benzene, CeHe. 
 
 Methylbenzene, C 6 H 6 CH 3 , or C 7 H 8 . 
 
 Ethylbenzene, C 8 H 6 C a H 6 , " C 8 H 10 . 
 
 Propylbenzene, C 8 H 6 C 3 H7, " CHi 2 . 
 
334 ORGANIC CHEMISTRY. 
 
 Dimethylbenzene, C 8 H 4 (CH 3 ) 3 , or C 8 Hi . 
 
 Trimethylbenzene, C 8 H 3 (CH 3 ) 3 , " C 9 H 12 . 
 
 Tetramethylbenzene, C 6 H 2 (CH 3 )4, " Ci H 14 . 
 
 etc. 
 
 A great many of these hydrocarbons are known, 
 involving interesting cases of isomerism ; and a vast 
 number of others are possible. In each of them the 
 unreplaced hydrogen of the original benzene is still 
 replaceable by other atoms and radicles as before, 
 while the hydrogen of the methyl, ethyl, etc., groups 
 is also capable of substitution. Hence the deriva- 
 tives of these compounds are very complicated in 
 structure, and almost innumerable. The possible 
 benzene derivatives, containing no other elements 
 than carbon, hydrogen, oxygen, and nitrogen, would 
 have to be counted by millions. 
 
 Next to benzene, methyl benzene or toluene, 
 C 6 H 5 CH 3 , is the most important hydrocarbon of 
 the series. With nitric acid it yields nitrotoluene, 
 C 6 H 4 NO 2 CH 8 , which is easily reduced by nascent 
 hydrogen to amido-toluene, C 6 H 4 NH 2 CH 3 , a com- 
 pound which is more commonly known as toluidine. 
 This substance occurs to some extent in commercial 
 aniline, and it plays an essential part in the forma- 
 tion of the aniline dyes. 
 
 We have already noticed that benzene, minus 
 one atom of hydrogen, may behave like a univalent 
 radicle, and that this group, C 6 H 5 , is sometimes 
 known as phenyl. Now, phenyl may replace one 
 hydrogen-atom in ethylene, C 2 H 4 , yielding a hy- 
 drocarbon called phenylethylene, or cinnamene, 
 C 2 H 3 C 6 H 5 . From this hydrocarbon other com- 
 pounds may be in turn derived, and two of these 
 are noteworthy : 
 
THE BENZENE DERIVATIVES. 335 
 
 C = H 3 C = H a C = HCOH C = HCOOH 
 
 C = H a . CHCeH 6 . CHC 6 H 6 . CHC 6 H 6 . 
 
 Ethylene. Cinnamene. Cinnamic aldehyde. Cinnamic acid. 
 
 Cinnamic aldehyde, C 9 H 8 O, is the chief constituent 
 of the fragrant oil of cinnamon ; and from cinnam- 
 ic acid, by a series of synthetic processes, indigo 
 has been obtained. Indigo originally was prepared 
 from the leaves and stems of the indigo-plant, which, 
 covered with water and allowed to ferment, gradu- 
 ally yielded this valuable coloring-matter. When 
 absolutely pure its formula is C 16 H 10 N 2 O 2 ; and it is 
 probable that in the near future it will be largely 
 made artificially from among the hydrocarbon prod- 
 ucts of coal-tar.* Even at the date of writing, arti- 
 ficial indigo is being produced in Germany upon a 
 commercial scale. 
 
 In addition to the great number of hydrocar- 
 bons derivable from benzene by the substitution of 
 hydrogen, still others, even more complicated, are 
 formed by the combination of two or more benzene 
 rings with each other. A few formulae will illus- 
 trate this matter : 
 
 H H H H 
 
 i i i i C C 
 
 C-C C-C x \ / \ 
 
 ^ % # \ TT _ r* r* r* TJ 
 
 H-C C-C C-H 7 7 T~ 
 
 v / v r H ~ c c C - H 
 
 C = C C = C \ / \ s 
 
 i i i i C C 
 
 H H H H i i 
 
 Diphenyl, C 18 H 10 . H H 
 
 Naphthalene, C 10 H 8 . 
 
 * Full details concerning the synthesis of indigo would be too com- 
 plicated for introduction in a school text-book. For such matters the 
 larger treatises upon organic chemistry may be consulted. Strecker's 
 treatise is good. 
 
336 ORGANIC CHEMISTRY. 
 
 H H 
 
 i i 
 
 C H C 
 
 H-C C-C-C C-H 
 
 H-C C-C-C C-H 
 
 \ x i \ s 
 
 C H C 
 
 H H 
 
 Anthracene, Cj4H 10 . 
 
 From all such hydrocarbons as these a vast num- 
 ber of complicated derivatives may be obtained, and 
 some of them have great practical importance. 
 Naphthalene and anthracene are both white solids, 
 obtained from coal-tar oil, and from each some use- 
 ful dye-stuffs may be prepared. Thus, from naph- 
 thalene we get naphthalene-yellow, C 10 H 5 OH(NO 2 )2, 
 and, from anthracene, alizarin and purpurin are 
 artificially obtained. These latter substances are 
 found, naturally, in the madder-root, which has 
 been used from time immemorial as a red dye, and 
 which was cultivated over large areas in Eu- 
 rope. The familiar Turkey-red is simply the color 
 produced by madder. Alizarin has the formula 
 C 14 H 8 O 4 , and purpurin is C 14 H 8 O 5 . Both com- 
 pounds are now prepared commercially from the 
 anthracene of coal-tar, and the land upon which 
 madder was formerly grown is now released to the 
 production of food. By the single discovery of 
 artificial alizarin, made by two German chemists in 
 1868, hundreds of men have been given new em- 
 ployment, and the world's wealth has been percep- 
 tibly increased. 
 
 Enough has been said to illustrate the general 
 principles which govern the formation of the de- 
 rivatives of benzene. By a careful study of the 
 
THE BENZENE DERIVATIVES. 337 
 
 benzene ring, chemists are now able to predict the 
 existence of compounds in advance of actual dis- 
 covery, and to plan available methods for their 
 production. Alizarin, for example, was thus ob- 
 tained not by accident, but by a deliberate applica- 
 tion of principles with skill and foresight. Plainly, 
 then, the consideration of the structural formulae, 
 to which this chapter has been so largely devoted, 
 is not by any means a useless exercise of the imagi- 
 nation. The formulas may be capable of future 
 improvement, but, as they now stand, they are of 
 great use in the development of chemical science. 
 
CHAPTER XL. 
 
 THE TERPENES, CAMPHORS, ALKALOIDS, AND 
 GLUCOSIDES. 
 
 THE substances described in this chapter are all 
 products of plant-life. Some of them are struct- 
 urally related to benzene, but for the greater num- 
 ber the structure is as yet undetermined. 
 
 The terpenes are a class of volatile hydrocarbons 
 of the general formula C 10 H 16 . Most of them occur 
 as the so-called " essential oils " of plants ; and, al- 
 though they are isomeric, they differ widely in 
 their external properties. The oils of lemon, or- 
 ange, bergamot, lavender, pepper, etc., are exam- 
 ples. There are many others, and compounds con- 
 taining oxygen are often mixed with them. 
 
 In common turpentine, which exudes from cuts 
 made in the bark of several species of pine, we 
 have a mixture of terpenes. When it is distilled 
 with water, oil of turpentine, C 10 H 16 , distills over, 
 and rosin remains in the retort. The oil has a spe- 
 cific gravity of 0.86, and boils at 161. The rosin 
 contains oxygen, and consists in great part of sylvic 
 acid, CgoHgoCV In structure the terpenes are un- 
 doubtedly allied to the benzene series, but the 
 causes of isomerism remain to be made out. That 
 substances so different as turpentine, oil of orange- 
 
THE CAMPHORS AND ALKALOIDS. 339 
 
 flowers, and oil of pepper, should have the same 
 percentage composition, is certainly remarkable. 
 
 The camphors are closely related to the terpenes, 
 but contain oxygen. Ordinary camphor, which is 
 the best example, is a white solid, having the for- 
 mula C 10 H 16 O. It melts at 175, boils at 204, and 
 has a peculiar, characteristic odor. Nitric acid oxi- 
 dizes it to camphoric acid, C 10 H 16 O 4 . 
 
 In a great many plants, especially among those 
 which possess marked poisonous properties or me- 
 dicinal value, are found a class of compounds which 
 are termed alkaloids. Of these a few, containing 
 only carbon, hydrogen, and nitrogen, are liquids ; 
 the others, which contain oxygen also, are crystal- 
 lizable solids. They are all bases, and unite with 
 acids to form perfectly definite, well-characterized 
 salts. Only a few of them can be noted here. 
 
 Of the liquid alkaloids, conine, C 8 H 15 N, and nico- 
 tine, Ci H 14 N 2 , are the most noteworthy. Conine is 
 the active principle of the poison-hemlock (Conium 
 maculatum), and nicotine is contained in tobacco. 
 Nicotine is an oily liquid, of a disagreeable odor, 
 and is violently poisonous. Tobacco contains from 
 two to eight per cent of it ; but, in smoking, the 
 alkaloid is partly decomposed. 
 
 In tea and coffee we find a remarkable solid al- 
 kaloid, to which the stimulating effects of these 
 articles are due. This alkaloid, caffeine, C 8 H 10 N 4 O 2 , 
 crystallizes in silky needles, which melt at 178 and 
 sublime at higher temperatures. It is found also 
 in the leaves of the Ilex Paraguayensis, or Paraguay 
 tea, and in the drug known as guarana. It is a 
 curious fact that widely separated nations should 
 select as stimulants plants which belong to different 
 
34 ORGANIC CHEMISTRY. 
 
 genera and yet depend upon the same alkaloid for 
 their activity. In cocoa, theobromine, C 7 H 8 N 4 O 2 , is 
 found. Caffeine is theobromine with one hydrogen- 
 atom replaced by a methyl group. 
 
 In opium, which is extracted from certain spe- 
 cies of poppy, at least fifteen different alkaloids are 
 found. Some of these occur in very small quantity 
 and are unimportant, but the following are note- 
 
 worthy : 
 
 Morphine, CnH^NOs. 
 Codeine, Ci 8 H a iNO 8 . 
 Thebaine, Ci 9 HaiNO 8 . 
 Narcotine, Caa 
 
 With the alkaloids of opium, meconic acid, C 7 H 4 O 7 , 
 is combined. All of these alkaloids are useful in 
 medicine, and all form bitter crystals ; all are poi- 
 sonous, thebaine being the most so. Morphine is 
 chiefly used as sulphate, and is invaluable for 
 quieting pain. Heated under pressure with hy- 
 drochloric acid it yields a new base, apomorphine, 
 C 17 H 17 NO 2 , which is a violent emetic. Codeine is 
 methyl-morphine, C 17 H 18 (CH 3 )NO 3 . 
 
 Cinchona, or Peruvian bark, is another drug con- 
 taining a remarkable group of alkaloids. The trees 
 which yield it grow wild in the mountainous re- 
 gions of Peru and Ecuador, and are extensively 
 cultivated in Java and India. Quinine, C^H^NsC)^ 
 and cinchonine, C^K^NgO, are the most important 
 of its constituents. Both alkaloids are valuable 
 remedies in the treatment of fevers, although the 
 first named far surpasses the other. It is intensely 
 bitter, and is administered chiefly as sulphate. 
 
 EXPERIMENT 106. Dissolve in water, with the 
 aid of a drop of weak sulphuric acid, a little quinine 
 
THE ALKALOIDS. 
 
 341 
 
 sulphate. The solution will be colorless by trans- 
 mitted light, but with a reflected ray will appear of 
 a delicate, misty blue. This color does not exist in 
 the substance itself, but is produced by its action 
 upon the invisible rays of the spectrum beyond the 
 violet. The property of producing a color in this 
 peculiar way is termed fluorescence. The colorless 
 assculin, from horse-chestnuts, similarly fluoresces 
 with a brilliant blue, uranium compounds fluoresce 
 with a greenish yellow, etc. The phenomenon is 
 beautiful, and not uncommon. 
 
 A number of other alkaloids are important, but 
 space permits only the barest mention of them here. 
 In the nux vomica two bases exist namely, strych- 
 nine, C^H^NjjOg, and brucine, C^H^N^, 4H 2 O. 
 Both are violent poisons, and both are used in small 
 doses medicinally. Aconitine, from aconite ; atro- 
 pine, from belladonna ; hyoscyamine, and solanine, 
 are all interesting. Their names are sometimes 
 made to terminate in ia instead of ine, as atropia, 
 morphia, quinia, strychnia, etc. The termination is 
 only a matter of preference. 
 
 Although the chemical structure of the alkaloids 
 has not yet been definitely made out, chemists are 
 progressing rapidly toward a solution of the prob- 
 lem. Doubtless, within a few years, most of these 
 bases will be prepared by synthesis. At present, 
 the following points seem to be clear. In bone-oil, 
 produced by the distillation of bones, a series of 
 bases are found, of which pyridine, C 5 H 5 N, is the 
 first member. By the destructive distillation of 
 certain alkaloids, another base, chinoline, is formed ; 
 and this compound, C 9 H 7 N, is closely allied to pyri- 
 dine, as the subjoined formulae will show : 
 
342 ORGANIC CHEMISTRY. 
 
 H ^ . ? V 
 
 c c c 
 
 H -^ Y V H 
 
 H-C C-H H -x X , C - H 
 
 \ x N C 
 
 N i 
 
 Pyridine. H 
 
 Chinoline. 
 
 From these bases and their allied compounds the 
 alkaloids are in all probability derived, by a system 
 of hydrogen substitutions like that which serves to 
 explain the derivatives of benzene. The similarity 
 between pyridine and benzene, as regards structure, 
 is evident at a glance ; while chinoline is compara- 
 ble with naphthalene. 
 
 Of the glucosides, although many are known, but 
 little need be said. These compounds exist in many 
 plants ; and by the action of certain ferments they 
 are decomposed into glucose and other bodies 
 which are in general derivatives of benzene. The 
 ferments above mentioned are complex substances, 
 of which the exact composition remains to be de- 
 termined. The manner in which they act is also 
 little understood. The following glucosides are im- 
 portant : 
 
 Salicin, C 13 H 18 O 7 , is found in the bark of willows 
 and poplars. It forms colorless, bitter crystals, 
 which are easily split up by soluble ferments into 
 glucose and saligenin, C 7 H 8 O 2 . 
 
 H 2 O = C 7 H 8 O 2 + CoH 12 6 . 
 
 Amygdalin, CgoH^NOn, is the crystallizable bit- 
 ter principle of bitter-almonds. The latter also con- 
 tain a ferment called emulsin, and, when they are 
 
THE GLUCOSIDES. 343 
 
 crushed, the latter converts the amygdalin into ben- 
 zaldehyde (bitter-almond oil), hydrocyanic acid, and 
 glucose. 
 
 CaoHaTNOn + 2H 2 O = C 7 H 6 O + HCN + 2C 6 H 12 O 6 . 
 
 The oil of bitter-almonds does not exist in the per- 
 fect fruit, but is formed entirely by this reaction. 
 In the equation the emulsin does not appear. 
 
 In the cambium layer of coniferous trees, co- 
 niferine, C 16 H 22 O 8 , is found. This, with a ferment, 
 yields glucose, and coniferyl alcohol, C 10 H 12 O 3 . 
 The latter, upon oxidation, is converted into alde- 
 hyde and vanilline, C 8 H 8 O 8 . Vanilline is the fra- 
 grant principle of vanilla-beans, although it may 
 now be made .artificially from the coniferine of pine- 
 trees. Structurally, it is a derivative of benzene. 
 
 Populin, CaoH^Os, from the aspen-tree ; fraxin, 
 C 27 H 30 O 17 , from the bark of the ash ; phloridzin, 
 C^H^OK,, from various fruit-trees ; and assculin, 
 C^H^O^, from the horse-chestnut, are other com- 
 mon glucosides. There are also a group of these 
 compounds derived from oak-bark, nut-galls, etc., 
 which are known as the tannic acids or tannins. 
 These compounds all have an astringent taste, and 
 yield black precipitates with salts of iron ; they also 
 act upon the animal membranes (as, for example, 
 the skin) forming leather. Probably they all con- 
 tain the true tannic acid, C 14 H 10 O 9 , which is simply 
 derived from gallic acid, C 7 H 6 O S , a derivative of 
 
 benzene : 
 
 C 7 H fl O 5 = C 6 H 2 (OH) 3 COOH. 
 
 Tannin and gallic acid are both used in the manu- 
 facture of ink. 
 
CHAPTER XLI. 
 
 ANIMAL CHEMISTRY. FERMENTATION. 
 
 WHEN we study the compounds produced by 
 animal life, although we have but few elements to 
 consider, we meet with compounds of the very 
 greatest complexity. As a rule, subject to some 
 exceptions, they contain carbon, hydrogen, oxygen, 
 and nitrogen, and are uncrystallizable. Some of 
 them contain sulphur or phosphorus, and, except in 
 a few cases, we know little or nothing as to their 
 chemical structure. 
 
 Two groups of these compounds are especially 
 important, inasmuch as, together with water, fat, 
 and the earthy matter of the bones, they make up 
 the greater part of every higher animal organism. 
 These other substances we have already considered, 
 and we may now devote our attention to the two 
 groups in question, the albuminoids and the gela- 
 tins. 
 
 The albuminoids are a class of substances which 
 are best represented by the following compounds. 
 They all putrefy easily, coagulate or form clots 
 upon heating or by contact with alcohol, and are 
 soluble either in water or dilute hydrochloric acid. 
 
 Albumen, the chief compound of the group, is 
 found, dissolved in water, in the whites of eggs and 
 
ANIMAL CHEMISTRY. FERMENTATION. 345 
 
 the serum of blood. The change from fluid to solid 
 white, when an egg is boiled, illustrates the coagu- 
 lation by heat above referred to. When perfectly 
 freed from water, albumen is a yellowish, trans- 
 parent solid, having a composition which is toler- 
 ably well represented by the formula C 72 H 112 N 18 SO 22 . 
 A similar compound, not identical, however, is 
 found in all vegetable juices. It is called vegetable 
 albumen. 
 
 EXPERIMENT 107. Divide the white of an egg 
 into three portions, and put them into three different 
 test-tubes. Heat one, and add to the others a little 
 alcohol and an aqueous solution of mercuric chlo- 
 ride respectively. In each case coagulation will 
 ensue. Repeat the experiment, if convenient, with 
 a little blood. One drop of the latter in each test- 
 tube will suffice. 
 
 In blood, with albumen, are found two other 
 albuminoids, which so react upon each other as to 
 form a third substance, called fibrin. The latter 
 separates from blood very soon after the latter has 
 left the body, and forms the solid clot. The al- 
 bumen remains behind in the liquid serum. Fibrin 
 is best obtained by heating fresh blood until a clot 
 is produced, and washing the latter thoroughly un- 
 der a stream of water. It forms a mass of whitish 
 or grayish fibers. Blood also contains a crystalliza- 
 ble coloring-matter, called haemoglobin. The latter 
 decomposes easily into an albuminoid, and a body 
 called hematin, which contains iron. Its probable 
 formula is C^H^N^eO^ 
 
 Casein, the albuminoid constituent of milk and 
 cheese, separates in curds whenever, milk becomes 
 sour. With it, milk contains water, fat (or butter), 
 
346 ORGANIC CHEMISTRY. 
 
 milk-sugar, sodium chloride, calcium phosphate, etc. 
 The casein is held in solution by a little alkali, and 
 may be precipitated by acids. Gluten and legumin 
 are vegetable caseins. 
 
 In most foods the albuminoids play an important 
 part. When they are taken into the stomach they 
 first dissolve in the weak hydrochloric and lactic 
 acids of the gastric juice. The latter fluid also 
 contains a peculiar ferment, called pepsin, which 
 rapidly converts the albuminoids into substances 
 known as peptones, and these, unlike albumen it- 
 self, are capable of diffusion through membranes. 
 These chemical changes are essential to digestion, 
 and to the absorption of the valuable constituents 
 of the food into the system. All the albuminoids 
 dissolve in very dilute hydrochloric acid (one part 
 of acid in a thousand of water) to form acid albumen 
 or syntonin. This substance does not coagulate 
 upon heating, and from its solution alkalies repre- 
 cipitate albumen. 
 
 The gelatins, of which common gelatin is the 
 best example, are obtained from bone, cartilage, 
 connective tissue, etc. Common gelatin occurs in 
 commerce in sheets, which vary in color according 
 to purity. The finest qualities, made from the 
 " sounds " of certain fishes, are used for making jel- 
 lies ; the coarser grades form glue. Gelatin is also 
 valuable in various photographic processes, in mak- 
 ing hektograph plates, and for many other purposes. 
 It dissolves in hot water, and sets to a jelly on cool- 
 ing. By tannin it is precipitated from its solutions, 
 and the formation of leather is due to the action of 
 the tannin of the tan-bark upon the gelatinous mat- 
 ter of skins. Chondrin is a peculiar form of gelatin 
 
ANIMAL CHEMISTRY. FERMENTATION. 347 
 
 obtained from rib cartilage. It is precipitated from 
 solution by nearly all acids, whereas ordinary gela- 
 tin is not. 
 
 As might be naturally inferred from their great 
 complexity, the albuminoids and gelatins are very 
 unstable. Their unwieldy molecules tend to split 
 up into simpler groups of atoms ; and in the pro- 
 cess of putrefaction they are the compounds which 
 are first and most affected. Putrefaction, however, 
 is but a special kind of fermentation ; and this set 
 of phenomena we may now profitably consider. 
 
 Whenever the juice of fruits, such as grapes or 
 apples, is freely exposed to the air, a series of changes 
 occur which end in the formation of alcohol. If the 
 latter be left to itself, a further change takes place, 
 and vinegar is produced. Similar reactions are no- 
 ticed when yeast is allowed to act upon starch or 
 sugar, when milk turns sour or butter becomes ran- 
 cid, and all of them are ascribed to fermentation. 
 All of them are due to the action of minute living 
 organisms, microscopic plants or animals, and of 
 these the germs are found nearly everywhere. The 
 latter may be killed by extreme cold or extreme 
 heat, and no true fermentation can occur in bodies 
 from which they are excluded. Milk, fruit, meats, 
 vegetables, fish, etc., heated to boiling and sealed up 
 in air-tight tin cans, may be kept for years without 
 alteration ; but, when they are exposed to air con- 
 taining ferment-germs, fermentation and putrefac- 
 tion speedily ensue. Antiseptics, such as salt, phe- 
 nol, alcohol, etc., owe their power of preventing 
 decay to the fact that they kill all germs of fer- 
 ments ; and ice acts as a preservative by chilling 
 them below the temperatures at which they are 
 
348 
 
 ORGANIC CHEMISTRY. 
 
 capable of activity. Many contagious diseases, such 
 as small-pox, typhoid fever, etc., are also ascribed to 
 similar germs, which, when inhaled, set up processes 
 of fermentation in the living body ; and disinfectants 
 are used in the sick-room for the direct purpose of 
 destroying these dangerous creatures. Our knowl- 
 edge of them is as yet in its infancy, but new dis- 
 coveries are being made almost daily ; and we may 
 reasonably hope that in a few years many impor- 
 tant advances will be accomplished. 
 
 In putrefaction, the changes which the albumi- 
 noids undergo are so complex as to be outside the 
 range of an elementary treatise. The following 
 kinds of fermentation are simpler : 
 
 1. Alcoholic fermentation. The glucoses, when 
 exposed to the action of the yeast-plant, undergo 
 fermentation, yielding 'large quantities of carbon 
 dioxide and alcohol. Traces of succinic acid and 
 glycerin are formed at the same time. Sugar and 
 starch have first to be transformed into glucoses be- 
 fore fermentation can take place. In brewing, the 
 starch of the grain is converted into glucose by a 
 peculiar substance called diastase, which is formed 
 in the process of malting. Although this fermen- 
 tation produces alcohol, an excess of alcohol will 
 stop it. 
 
 2. Acetous fermentation. This produces acetic 
 acid, and is noticed when wine, cider, beer-mash, 
 etc., are transformed into vinegar. When vinegar 
 is made by allowing alcohol to trickle over wood- 
 shavings, the latter carry the ferment-germs upon 
 their surfaces. 
 
 3. Lactic fermentation. This occurs when milk 
 turns sour, and results in the formation of lactic acid. 
 
ANIMAL CHEMISTRY. FERMENTATION. 349 
 
 4. Butyric fermentation. This yields butyric 
 acid, and is observed in rancid butter and putrefy- 
 ing cheese. 
 
 5. Mucous fermentation, which produces gum 
 and mannite. 
 
 6. Nitric fermentation, recently discovered, by 
 which living organisms decompose nitrates, setting 
 nitrogen dioxide free. 
 
 For a full discussion of the subject of fermenta- 
 tion, Schlitzenberger's little treatise may profitably 
 be consulted.* 
 
 * " On Fermentations." No. 20 of the " International Scientific 
 Series." 
 
V 
 
APPENDIX I. 
 
 COMPARATIVE TABLE OF ENGLISH AND 
 METRIC MEASURES. 
 
 A. Measures of Length. 
 
 Standard unit, one metre. 
 
 i kilometre = 1,000 metres. i decimetre =0.100 metre, 
 
 hectometre = 100 " i centimetre = o.oio " 
 
 decametre = 10 " i millimetre = o.ooi " 
 
 metre = 39.37079 inches, 
 decimetre = 3-93708 " 
 centimetre = 0.39371 " 
 millimetre = 0.03937 " 
 
 i inch =2.53995 centimetres. 
 I foot = 3.04794 decimetres, 
 i yard = 0.914383 metre, 
 i mile = 1.609315 kilometres. 
 
 B. Measures of Surface. 
 
 i sq. metre = 10.7643 sq. feet. i sq. foot = 9.28997 sq. dm. 
 i sq. centimetre = 0.1550 sq. inch, i sq. inch = 6.45137 sq. cm. 
 I sq. millimetre = 0.0015 sq. inch, i sq.yard = 0.8361 sq. m. 
 
 C. Measures of Volume. 
 
 I litre = i cubic decimetre. 
 
 i " = 1,000 " centimetres. 
 
 i litre = 61.02705 cu. inches. i cu. inch = 16.38618 cu. cm. 
 i cu. cm. = 0.06103 cu - inch. i cu. foot = 28.31531 cu. dm. 
 I litre = 1.05672 U. S. qts. I U. S. qt. = 0.9469 litre. 
 16 
 
352 APPENDIX. 
 
 D. Measures of Weight. 
 
 The unit, one gramme, is the weight of one 
 cubic centimetre of distilled water, at the tempera- 
 ture of 4 C. 
 
 i kilogramme =i,ooogrs. i decigramme =o.iooogr. 
 
 i hectogramme = 100 " i centigramme = 0.0100 " 
 
 i decagramme = 10 " i milligramme = o.ooio " 
 
 i kilogr. = 2.204621 Ib. avoir. i grain =64.799 rnilligr. 
 
 I " =32.15073 oz. troy. i oz. troy =31. 1035 gr. 
 
 I gr. =15.43235 grains. I Ib. avoir. = 0.45359 kilogr. 
 
 One thousand kilogrammes vary but little 
 from the " long " ton of 2,240 pounds avoirdupois 
 (0.984206 ton). 
 
 The pound avoirdupois contains 7,000 grains. 
 
 The same figures which represent the specific 
 gravity of any solid or liquid, referred to water as 
 unity, also represent the weight of one cubic centi- 
 metre of the substance, expressed in grammes. 
 
 THERMOMETRIC RULES. 
 
 To reduce a Fahrenheit temperature to its 
 equivalent in centigrade degrees : Subtract 32, 
 and multiply the remainder by -|. 
 
 To reduce a centigrade temperature to its 
 Fahrenheit equivalent: Multiply by f, and add 32 
 to the product. 
 
APPENDIX II. 
 
 QUESTIONS AND EXERCISES. 
 
 To be amplified or increased at the discretion of the teacher. 
 
 CHAPTER I. i. How do chemical and physical changes differ? 
 2. Give an example of chemical combination. 3. Give an example of 
 chemical decomposition. 4. Give some points of connection between 
 heat and chemical change. 5. What points must be considered in the 
 complete study of a chemical change ? 6. What is understood by 
 matter? What by force? 7. Is either matter or force destructible? 
 8. Define chemistry. 9. Name some useful applications of chemistry. 
 
 CHAPTER II. i. Explain what is meant by analysis and synthesis. 
 2. Define elements and compounds. 3. Which of the following sub- 
 stances are elements ? Iron, oxygen, water, air, copper, wood, salt, 
 carbon, sugar, tin, iodine. 4. Explain what is meant by a molecule. 
 5. What is an atom? 6. What is a mass of matter? 7. From what 
 evidence do you infer the existence of atoms and molecules ? 
 
 CHAPTER III. i. Describe three methods for the preparation of 
 hydrogen. 2. How does hydrogen occur in nature ? 3. Describe the 
 hydrogen-flame. What precaution must be observed in kindling it ? 
 4. What compound is formed by the combustion of hydrogen? 5. 
 What substances are heavier than hydrogen? What does one litre 
 of hydrogen weigh ? 6. What law governs the expansion of gases by 
 heat? 7. How does the volume of a gas vary with pressure? 8. 
 What pressure and what temperature are taken as standards of com- 
 parison ? 9. Given one litre of gas at o, what will it become at 37 ? 
 What at 83 ? What at 273 ? 10. Seventy-two volumes of hydrogen 
 are measured at 16, what will they measure after cooling to o ? 
 What at 273 ? ii. Given ten litres of a gas at 22 and 748 milli- 
 
354 APPENDIX. 
 
 metres pressure, what will the volume be at o and 760 millimetres ? 
 12. How may gases be liquefied ? 13. What are the more important 
 properties of hydrogen? 14. Is hydrogen a metal or a non-metal? 
 
 CHAPTER IV. i. How does oxygen occur in nature ? 2. How is 
 oxygen best prepared ? What precautions are essential ? 3. What are 
 the chief properties of oxygen? 4. Define oxidation. What is an 
 oxide ? 5. Is oxygen necessary to combustion ? 6. Is oxygen essen- 
 tial to respiration? 7. Wherein is the solubility of oxygen in water 
 important? 8. What is ozone? Describe its properties. 9. What 
 does a litre of oxygen weigh ? 10. \Vhat volume will 87 grammes of 
 oxygen occupy at 15 and 774 millimetres pressure ? n. What will be 
 the weight of 17 litres of oxygen, measured at 12 and 755 millime- 
 tres? 
 
 CHAPTER V. i. What oxides does hydrogen form? 2. What 
 happens when a mixture of oxygen and hydro'gen is kindled ? 3. How 
 much heat is developed by the combustion of hydrogen ? Does any 
 other chemical change develop more heat ? 4. Explain the compound 
 blow-pipe. What are its uses ? 5. Describe the electrolysis of water. 
 6. Describe the synthesis of water. 7. In what proportions, by volume 
 and by weight, do oxygen and hydrogen combine to form water? 8. 
 Suppose thirty-six volumes of oxygen and hydrogen unite, what vol- 
 ume will be occupied by the resulting steam ? 9. What weight of 
 oxygen would be contained in one gramme of liquid water? What 
 volume would it occupy at o and 760 millimetres? 10. Given ten 
 litres of water of o, how much steam will it give at 100 ? What 
 volume of hydrogen can be obtained from that steam? What weight 
 of hydrogen? n. What are the chief properties of water ? 12. How 
 ^does water behave upon solidifying ? 13. Define a gramme. A litre. 
 A kilogramme. 14. Describe the centigrade and Fahrenheit scales. 
 15. How may impure water be purified ? 16. What is water of crystal- 
 lization ? Define deliquescence and efflorescence. 
 
 CHAPTER VI. i. How does nitrogen occur in nature? 2. How 
 may nitrogen be prepared ? 3. What is the composition of the atmos- 
 phere ? Does it vary in any way ? 4. Describe the chief properties 
 of nitrogen. 5. What is the weight of one litre of nitrogen, at o and 
 760 millimetres ? 6. What is the weight of 7.33 litres of air, measured 
 at 22 and 758 millimetres ? 
 
 CHAPTER VII. i. Describe ammonia gas. What is its exact com- 
 position? 2. What is aqua ammonia? 3. Name the oxides of nitro- 
 gen. 4. Describe nitric acid. What is a nitrate? 5. What action 
 has nitric acids on metals ? 6. Define " acid " and " alkali." 7. What 
 are salts and bases? 8. Explain the names nitrous and nitric. 9. 
 
QUESTIONS AND EXERCISES. 355 
 
 Give the law of definite proportions. 10. Give the law of multiple 
 proportions. Illustrate it. n. Describe nitrous oxide and its uses. 
 12. Describe nitrogen dioxide and nitrogen tetroxide. 
 
 CHAPTER VIII. I. What is a chemical symbol ? Give examples. 
 2. Explain the combining weights of oxygen and nitrogen. 3. Ex- 
 plain the combining weights of Cl, Br, I, K, Na, and Ag. 4. State the 
 atomic theory, and explain what is meant by atomic weight. 5. Give 
 and explain the formulae of several compounds. 6. What weight of 
 oxygen can be prepared from sixty grammes of KClOs ? What vol- 
 ume, measured at 10 and 740 millimetres ? 7. Explain this equa- 
 tion : Fe + H 2 SO 4 = H 2 + FeSO 4 . What weights of iron and of sulphu- 
 ric acid would be needed to give fifty grammes of hydrogen ? 8. Sixty- 
 five litres of oxygen are wanted, at 27 and 750 millimetres ; what weight 
 of KC1O 3 must be used ? 
 
 CHAPTER IX. I. Describe the different forms of carbon. 2. What 
 are the uses of graphite ? 3. What are the uses of amorphous carbon ? 
 
 4. How does charcoal affect coloring-matters ? How does it act as a dis- 
 infectant ? 5. What is coal ? 6. Describe methane. 7. What is ordi- 
 nary coal-gas ? 8. Describe a gas-flame. A candle-flame. 9. What 
 is a Bunsen-burner ? 10. Describe the mouth blow-pipe and its uses. 
 II. Explain the safety-lamp. 
 
 CHAPTER X. I. Describe carbon monoxide. 2. What compound 
 is formed when charcoal burns ? 3. How do you test for carbon 
 dioxide ? 4. How is COa best prepared ? 5. What percentage of 
 COa can be obtained from CaCO 3 ? 6. How does COa affect combus- 
 tion and respiration ? 7. Given a kilogramme of limestone, what volume 
 of COa will it yield, measured at 21 and 762 millimetres ? 8. How is 
 the atmosphere affected by plants and animals ? 9. What is cyanogen ? 
 10. Define a compound radicle. II. What volume of oxygen would be 
 required for the complete combustion of ten grammes of charcoal ? 
 What weight of COa would be produced ? 
 
 CHAPTER XI. i. How is the density of carbon-vapor determined ? 
 2. State the two-volume law. 3. Why should the formulae CH and CN 
 be doubled? 4. Why should the formulae N 2 O 2 and N 2 O 4 be halved? 
 
 5. What is the vapor density of C 2 H 6 O? ofC e H 6 ? ofC 6 H 7 N? 6. State 
 Avogadro's law. 7. How many atoms are there in most elementary 
 molecules ? 8. Explain the formula of ozone. 
 
 CHAPTER XII. i. Define valency. 2. In what proportion can two 
 monads combine? Two dyads? A dyad and a monad ? A dyad and 
 a triad ? A dyad and a tetrad ? 3. What valency has the metal in 
 each of the following formulae ? ZnBr 2 . SbH 3 . AuCl 3 . CdO. ThO a . 
 TiCl 4 . Al a O 3 . WC1 6 . BaCO 3 . Ag 2 CO 3 . RbNO 3 . Fe(NO 3 ) 2 . 
 
356 
 
 APPENDIX. 
 
 4. What is meant by a structural formula ? Give examples. 5. What 
 is an unsaturated compound ? 6. Explain the valency of cyanogen. 
 
 CHAPTER XIII. I. What elements form the chlorine group? How 
 are they related ? What are their atomic weights ? 2. Describe hy- 
 drofluoric acid. 3. How is chlorine best prepared? 4. What are the 
 properties and uses of chlorine ? 5. How does chlorine act as a bleach- 
 er or disinfectant ? 6. How is hydrochloric acid prepared ? Describe 
 it. 7. What weight.of HC1 can be made from one kilogramme of NaCl ? 
 How much H a SO4 would be used? What volume would the HC1 oc- 
 cupy at 17 and 771 millimetres ? 8. What action has hydrochloric 
 acid upon metals ? What salts are thereby formed ? 9. Describe aqua 
 regia. 
 
 CHAPTER XIV. I. Write the formulas of the oxides and acids of 
 chlorine. Explain their names. 2. What hypochlorites are useful, and 
 why ? 3. What are the properties and uses of the chlorates ? 4. De- 
 scribe bromine. What is its vapor density? 5. Describe iodine. 6. 
 What is a convenient test for iodine ? 7. Describe the chloride and 
 iodide of nitrogen. 
 
 CHAPTER XV. I. Point out the similarities between O, S, Se, and 
 Te. 2. Describe sulphur. What is the character of its molecule ? 3. 
 Describe H a S. What volume of H 2 S at O and 760 millimetres could 
 be evolved from 50 grammes of FeS ? 4. What weight of water and 
 of SO a would be formed by the combination of one litre of H a S. 5. 
 Explain, with equations, the precipitation of some metallic salts byH 2 S. 
 6. Which is the most important oxide of sulphur ? What are its prop- 
 erties and uses ? 7. Define the term anhydride. How do the anhy- 
 drides form acids ? 
 
 CHAPTER XVI. I. Give the names and formulae of the sulphur 
 acids. 2. Explain the manufacture of H 3 SO4, and write the equations. 
 3. State some uses of sulphuric acid. What is its action upon ordinary 
 organic matter? 4. What is Nordhausen acid? 5. Define a dibasic 
 acid. 6. Explain the composition of the lead chamber crystals. 7. 
 What is hydroxyl ? 8. Write structural formulae for several sulphur 
 compounds. 9. Describe CSa. 
 
 CHAPTER XVII. I. Describe the preparation and properties of 
 ordinary phosphorus. 2. What is red phosphorus ? 3. Describe phos- 
 phine. 4. Explain the formulae of the phosphoric acids. 5. How 
 many orthophosphates of sodium are possible? 6. What are double 
 and triple salts? 7. What is the valency of phosphorus? 8. What 
 volume of phosphorus-vapor will ten grammes of the solid element 
 yield ? 
 
 CHAPTER XVIII. I. Point out the similarities between P and As. 
 
QUESTIONS AND EXERCISES. 357 
 
 2. What are the oxides of arsenic? Which one is the more useful, and 
 in what ways ? 3. How does boron occur in nature ? Where and how 
 are its useful compounds obtained ? 4. What is borax ? What are its 
 uses? 5. How does silicon resemble carbon? 6. Describe silicon di- 
 oxide. 7. What is water-glass ? Crown glass ? Bohemian glass ? Flint 
 glass ? Bottle glass ? Porcelain ? 8. Describe dialysis. 9. Define the 
 terms crystalloid and colloid. 
 
 CHAPTER XIX. i. How do metals differ from non-metals? 2. 
 What is electrolysis? 3. Explain the galvanic battery. 4. What is 
 meant by electro-positive and electro-negative elements ? Give exam- 
 ples. 5. Which of the following pairs of elements would unite vigor- 
 ously, and which feebly ? O and Al. S and N. Pt and H. F and 
 Ba. Cl and K. Br and Cl. Si and Sb. 6. Explain the electrolysis of 
 NaaSCu. 7. How do neutral, basic, and acid salts differ in constitu- 
 tion ? 8. Explain Mendelejeff s classification of the elements, and his 
 prediction of the existence of undiscovered metals. 
 
 CHAPTER XX. I. Name and compare the metals of the alkalies. 
 What are their most noteworthy properties ? 2. Describe caustic soda. 
 
 3. What weight of NaOH can be prepared from 84 grammes of 
 Na 2 CO 3 ? 4. Describe the Leblanc soda process. What great indus- 
 tries has it benefited ? 5. Name the chief sources of potassium com- 
 pounds. 6. What is saltpeter ? What are its uses ? 7. Describe 
 gunpowder. 8. Explain the composition of the ammonium salts. 9. 
 Explain the vapor density of NH 4 C1. 
 
 CHAPTER XXI. i. How does silver occur in nature ? 2. De- 
 scribe an amalgamation process. 3. Describe the Pattinson process. 
 
 4. What weight of AgNOs can be made from 125 grammes of U. S. 
 coin silver? 5. How is silver bullion refined? 6. State and illustrate 
 Berthollet's laws. 7. Explain photography. 8. What process is used 
 in plating brass with silver ? 
 
 CHAPTER XXII. I. How do Ca, Sr, and Ba chiefly differ ? 2. 
 Describe CaO and Ca(OH) 2 . What are their chief uses? 3. De- 
 scribe CaCO 3 . 4. Describe gypsum and plaster. 5. What is "hard" 
 water? What is its action in the steam-boiler, and in the laundry. 
 6. What uses have the compounds of Sr? 7. Explain a regen- 
 erative process for making oxygen. 8. What are the properties of 
 BaSO 4 ? 
 
 CHAPTER XXIII. i. How is white light affected by a prism? 
 2. How is colored light affected by a prism ? 3. How may sodium or 
 barium be detected by the aid of a prism ? 4. Describe a common 
 spectroscope. 5. Describe a direct-vision spectroscope. 6. What ele- 
 ments are conveniently detected with the spectroscope ? 7. What ele- 
 
358 APPENDIX. 
 
 ments have Been discovered with the spectroscope ? 8. What is an 
 absorption spectrum ? 9. How does the light emitted by hot gases 
 differ from that emitted by solids ? What sort of a spectrum would 
 a candle-flame give? 10. Describe and explain the solar spectrum. 
 ii. Describe the reversal of the sodium-line. 12. W r hat do you know 
 of the spectra of stars and nebulae? 
 
 CHAPTER XXIV. i. What important gems contain glucinum ? 
 2. Give the valency and atomic weight of magnesium, zinc, cadmium, 
 and mercury. Illustrate the valency by some formulae. 3. How does 
 magnesium occur in nature ? What are its properties ? 4. Describe 
 magnesium sulphate. What is meant by water of constitution ? 5. 
 How is zinc extracted from its ores ? What are its properties ? 6. 
 Describe ZnO, ZnSO 4 , and ZnS. 7. What is meant by Burnettized 
 timber ? 8. What are the properties and uses of cadmium ? 9. Ex- 
 plain the vapor density of cadmium and mercury. 10. Where and 
 how is mercury obtained ? 11. Describe metallic mercury. What 
 classes of compounds does it form ? 12. Describe HgO, HgCl, HgCl 2 , 
 and Hgl a . 
 
 CHAPTER XXV. i. Describe aluminum and aluminum bronze. 
 State the atomic weight and valency of aluminum. 2. Describe A1 2 O 3 . 
 What is a sesquioxide ? 3. Describe alum and its uses. What other 
 alums are possible ? How do they resemble each other ? 4. What are 
 turquoise, topaz, cryolite, and lapis lazuli? What is ultramarine? 5. 
 Give a brief description of the chemistry of pottery and porcelain. 6. 
 Wherein are gallium and scandium especially interesting ? 
 
 CHAPTER XXVI. i. Name the tetrad metals in the order of their 
 atomic weights. 2, Describe tin. Where and how is it found in na- 
 ture ? 3. What is tin-plate ? What are solder and bronze ? 4. De- 
 scribe, with formulae, the more important useful compounds of tin. 5. 
 What ore of lead is most important ? How is it smelted ? 6. Describe 
 metallic lead. 7. Are lead water-pipes objectionable ? 8. What oxides 
 are formed by lead ? 9. Describe white-lead. What are its advantages 
 and disadvantages compared with other white paints? 10. In what 
 way may one metal precipitate another from solution ? 
 
 CHAPTER XXVII. i. Point out the relations connecting N, P, V, 
 As, Sb, and Bi. 2. Describe antimony and its uses. 3. Explain the 
 differences between the two forms of SbaOa. 4. Name and describe 
 the more useful antimony compounds. 5. Describe bismuth and its 
 uses. 6. Describe two fusible alloys of bismuth. 7. Describe the 
 oxides and nitrates of bismuth. 
 
 CHAPTER XXVIII. i. How do chromous and chromic compounds 
 differ? 2. Describe Cr a O 8 and CrO 3 . 3. Describe the useful chro- 
 
QUESTIONS AND EXERCISES. 359 
 
 mates. 4. How does K 3 CraO 7 behave with gelatin? 5. Name some 
 uses of molybdenum and tungsten compounds. 6. State the law of 
 Dulong and Petit. 7. Why is the atomic weight of uranium put at 239 
 rather than at 119.5? 
 
 CHAPTER XXIX. r. What oxides are formed by manganese? 
 What are the uses of the commonest one? 2. Describe MnSO*, Mn a 
 (804)3, and KMnO4. 3. How is iron found in nature? What are its 
 chief ores ? 4. How do wrought-iron, cast-iron, and steel differ from 
 each other? 5. How is wrought-iron prepared? 6. Describe the 
 blast-furnace. 7. Describe the chief methods of making steel. 8. How 
 do ferrous and ferric compounds differ? 9. Describe ferrou^sulphate. 
 10. Write at least six formulae for compounds of iron, and explain the 
 valency of the metal. 
 
 CHAPTER XXX. I. What are the sources and uses of nickel ? 2. 
 Write formulae to illustrate the similarity of the compounds of Fe, 
 Ni, and Co. 3. What' are the chief uses of cobalt compounds? 4. 
 How are the sulphide ores of copper smelted ? 5. Explain the Hunt 
 and Douglas process. 6. Name the leading alloys of copper. 7. De- 
 scribe metallic copper. 8. Describe the electrotype process. 9. How 
 may copper be detected in solutions containing it ? 10. Give an 
 example of an ammonio-metallic base. 
 
 CHAPTER XXXI. I. How does gold occur in nature? How is 
 it refined? 2. Describe the process of quartation. 3. What are the 
 properties of gold ? 4. Write formulae illustrating aurous and auric 
 compounds. 5. Describe gold trichloride and its uses. 6. Describe 
 briefly, in general terms, the metals of the platinum group. 7. De- 
 scribe platinum and its uses. What is platinum-black ? 8. W T hat 
 classes of compounds are formed by platinum ? 
 
 CHAPTER XXXII. I. Define organic chemistry. 2. Explain the 
 classification of the hydrocarbons. 3. What is an homologous series ? 
 4. What is a substitution series ? 5. What is an amine ? A phos- 
 phine? 6. Illustrate what is meant by isomerism. 7. What is a 
 polymeric series ? 
 
 CHAPTER XXXIII. I. Describe cyanogen. How does it resem- 
 ble chlorine ? 2. Describe the more useful double cyanides contain- 
 ing iron. 3. Describe the synthesis of carbamide. 4. What are car- 
 bonyl and sulphocarbonyl ? 
 
 CHAPTER XXXIV. I. Explain the structure of the methane 
 series. 2. Describe petroleum. 3. What is an alcohol ? What is an 
 ether? 4. Describe CH 3 OH. 5. Describe C 2 H 6 OH. 6. What is 
 fractional distillation? 7. Describe (C 2 H 6 )2O. 8. What is a mixed 
 ether? 9. Describe chloroform and iodoform. 10. Point out the 
 
360 APPENDIX. 
 
 resemblance in chemical structure between the compounds of the 
 univalent hydrocarbon radicles and the compounds of potassium. 
 
 CHAPTER XXXV. I. What is an aldehyde? 2. How are the 
 aldehydes and fatty acids derived from the alcohols? 3. What group 
 of atoms is characteristic of organic acids ? 4. Describe acetic acid. 
 
 5. Explain the isomerism of the fatty acids and their ethers. 6. What 
 is acetyl ? 7. What is an amide ? 8. What is a ketone ? 
 
 CHAPTER XXXVI. i. Point out the relations between paraffins, 
 alcohol radicles, and olefines. 2. What is the structure of C 2 H4 and 
 some of its derivatives ? 3. How are acids derived from the alcohols 
 of the otefines? 4. Describe lactic acid. 5. Describe oxalic acid. 
 
 6. Write formulae for succinic, malic, and tartaric acids. 7. What is 
 baking-powder? 8. Describe citric acid. 
 
 CHAPTER XXXVII. I. What is glycerin ? 2. Explain the struct- 
 ure of the ethers of glycerin. 3. What are stearin, margarin, palmitin, 
 and olein ? 4. What is a soap ? 5. What is nitroglycerin ? 6. Point 
 out the relations between allyl alcohol, acrolein, and acrylic acid. 
 
 CHAPTER XXXVIII. I. What are the carbohydrates? How are 
 they classified? 2. Describe sucrose. 3. Describe lactose. 4. De- 
 scribe glucose. 5. What is starch ? Dextrin ? Gum-arabic ? 6. 
 What is cellulose ? 7. Describe gun-cotton and collodion. 
 
 CHAPTER XXXIX. i. Explain the structure of benzene. 2. De- 
 scribe phenol. 3. Describe aniline. 4. Illustrate the derivation of 
 acids and aldehydes from benzene. 5. Illustrate the union of several 
 benzene rings with each other. 6. What do you know of indigo, alizarin, 
 and purpurin? 7. What are the uses of coal-tar? 
 
 CHAPTER XL. i. W 7 hat is a terpene ? Give examples. 2. What 
 are the alkaloids ? 3. Name the source from which each of the fol- 
 lowing alkaloids is derived : Strychnine, caffeine, quinine, morphine, 
 cinchonine, and nicotine. 4. Compare pyridin and chinolin with 
 benzene and naphthalene. 5. What is a glucoside ? 6. W T hat are the 
 useful properties of tannin ? 
 
 CHAPTER XLI. i. Describe albumen. 2. Describe casein. 3. How 
 are the albuminoids affected by the gastric juice ? 4. Describe gelatin. 
 5. What is fermentation ? 6. How do disinfectants check the spread 
 of disease ? 7. Name the different kinds of fermentation. 
 
INDEX. 
 
 Absorption spectra, 218. 
 
 Acetone, 309. 
 
 Acetyl, 307. 
 
 Acetyl chloride, 308. 
 
 Acetylene, 81. 
 
 Acid, 60. 
 
 acetic, 305. 
 
 acrylic, 321. 
 
 antimonic, 248. 
 
 antimonious, 248. 
 
 arabic, 327. 
 
 arsenic, 162. 
 
 arsenious, 161. 
 
 benzoic, 333. 
 
 boric, 164. 
 
 bromic, 128. 
 
 camphoric, 339. 
 
 carbamic, 295. 
 
 carbolic, 331. 
 
 carbonic, 93. 
 
 chloracetic, 308. 
 
 chloric, 124. 
 
 chlorous, 124. 
 
 chromic, 254. 
 
 cinnamic, 335. 
 
 citric, 315. 
 
 columbic, 252. 
 
 cyanic, 294. 
 
 cyanuric, 294. 
 
 dithionic, 141. 
 
 ethylsulphuric, 300. 
 
 ferric, 270. 
 
 gallic, 343. 
 
 gly collie, 311. 
 
 hydriodic, 130. 
 
 hydrobromic, 128. 
 
 Acid, hydrochloric, Ii8. 
 hydrocyanic, 97, 291. 
 hydroferrocyanic, 293. 
 hydrofluoric, 112. 
 hydrofluosilicic, 167. 
 hydrosulphuric, 136. 
 hypobromous, 128. 
 hypochlorous, 123. 
 hyponitric, 64. 
 hypophosphorous, 155. 
 hyposulphurous, 141. 
 iodic, 130. 
 lactic, 312. 
 malic, 314. 
 manganic, 263. 
 margaric, 319. 
 meconic, 340. 
 metaphosphoric, 156. 
 molybdic, 257. 
 muriatic, 118. 
 nitric, 58. 
 nitrous, 61. 
 oleic, 319. 
 oxalic, 312. 
 palmitic, 319. 
 pentathionic, 141. 
 perbromic, 128. 
 perchloric, 127. 
 periodic, 130. 
 permanganic, 263. 
 phosphoric, 155. 
 phosphorous, 155. 
 picric, 331. 
 prussic, 97, 291. 
 pyrophosphoric, 156. 
 pyrosulphuric, 141, 147. 
 
362 
 
 INDEX. 
 
 Acid, salicylic, 333. 
 
 selenic, 149. 
 
 selenious, 149. 
 
 silicic, 170. 
 
 stannic, 241. 
 
 stearic, 319. 
 
 succinic, 313. 
 
 sulpliocarbonic, 295. 
 
 sulphocyanic, 294. 
 
 sulphuric, 142. 
 
 sulphurous, 139. 
 
 sylvic, 338. 
 
 tannic, 343. 
 
 tantalic, 252. 
 
 tartaric, 314. 
 
 telluric, 150. 
 
 tellurous, 150. 
 
 tetrathionic, 141. 
 
 thiosulphuric, 141. 
 
 trithionic, 141. 
 
 tungstic, 257. 
 
 vanadic, 247. 
 Aconitine, 341. 
 Acrolein, 320. 
 yEsculin, 341, 343. 
 Agate, 168. 
 Air, 51, 53. 
 Alabaster, 209. 
 Albumen, 344. 
 Albuminoids, 344. 
 Alcohol, allyl, 321. 
 
 amyl, 300. 
 
 butyl, 300. 
 
 cetyl, 300. 
 
 ethyl, 298. 
 
 melissyl, 300. 
 
 methyl, 298. 
 
 propyl, 300. 
 Aldehyde, 304. 
 
 cinnamic, 335. 
 
 salicylic, 333. 
 Alizarin, 336. 
 Alkali, 60, 184. 
 Alkaloids, 339. 
 Allotropy, 29. 
 Alloys, fusible, 250. 
 Allyl, alcohol, 321. 
 
 sulphide, 321. 
 
 sulphocyanide, 321. 
 Alum, 234. 
 Alumina, 233. 
 Aluminum, 232. 
 
 Aluminum, bronze, 233. 
 
 hydroxide, 233. 
 
 sulphate, 234. 
 Amalgam, 229. 
 Amethyst, 168, 233. 
 Amides, 308. 
 Amidobenzene, 331. 
 Amidotoluene, 334. 
 Amines, 288. 
 Ammonia, 55, 65, 193. 
 Ammonium, 193. 
 
 carbonate, 195. 
 
 chloride, 56, 193. 
 
 cyanate, 294. 
 
 hydrosulphide, 194. 
 
 hydroxide, 193. 
 
 molybdate, 257. 
 
 nitrate, 194. 
 
 phosphate, 195. 
 
 sulphate, 55, 194. 
 
 sulphide, 194. 
 
 sulphocyanate, 295. 
 
 uranate, 258. 
 Amygdalin, 342. 
 Amyl, acetate, 306. 
 
 alcohol, 300. 
 
 valerate, 306. 
 Analysis, 8. 
 Anhydrides, 140. 
 Aniline, 331. 
 Anthracene, 336. 
 Anthracite, 79. 
 Antichlor, 140. 
 Antimony, 247. 
 
 cinnabar, 250. 
 
 chlorides, 248. 
 
 hydride, 249. 
 
 oxides, 248. 
 
 sulphides, 248. 
 Antozone, 31. 
 Apatite, 151. 
 Apomorphine, 340. 
 Apple-oil, 306. 
 Aqua ammonia, 57, 193. 
 Aqua fortis, 59. 
 Aquamarine, 222. 
 Aqua regia, 121. 
 Arsenic, 159. 
 
 compounds of, 161, 162. 
 Arseniuretted hydrogen, 160. 
 Arsenopyrite, 159. 
 Arsines, 160, 289. 
 
INDEX. 
 
 363 
 
 Artiads, 157. 
 Atmosphere, 53. 
 Atom, 12. 
 Atomic heat, 259. 
 
 theory, 69. 
 
 weight, 66. 
 
 weights, table of, 9. 
 Atomicity, 105. 
 Atropine, 341. 
 Avogadro's law, 103. 
 
 Babbit's metal, 248. 
 Baking-powders, 94, 200, 312, 314. 
 Barium, 205. 
 
 compounds of, 2 n, 212. 
 Barytes, 211. 
 Base, 61. 
 Beeswax, 300. 
 Belladonna, 341. 
 Benzaldehyde, 332, 343. 
 Benzene, 329. 
 Berthollet's laws, 200. 
 Beryl, 222. 
 Beryllium, 222. 
 Bessemer steel, 269. 
 Bismuth, 250. 
 
 compounds of, 251, 252. 
 Black-ash process, 188. 
 Black-lead, 76. 
 Blanc-fixe, 211. 
 Blast-furnace, 266. 
 Bleaching, 117, 123, 138. 
 Bleaching-powder, 123. 
 Blende, 225. 
 Blood, 345. 
 Blooming, 265. 
 Blow-pipe, compound, 34. 
 
 mouth, 86. 
 Blue vitriol, 277. 
 Bone-black, 77. 
 Borax, 165. 
 Bornite, 275. 
 Boron, 163. 
 
 Boyle and Mariotte's law, 22. 
 Brass, 226. 
 Brick, 236. 
 Brimstone, 134. 
 Britannia metal, 241, 248. 
 Bromine, 127. 
 Bronze, 240. 
 Brucine, 341. 
 Brucite, 224. 
 
 Brunswick-green, 162. 
 Bunsen burner, 86. 
 Burnettizing, 227. 
 Butane, 296. 
 Butyl alcohol, 300. 
 
 Cadmium, 227. 
 
 compounds of, 228. 
 Caesium, 184, 217. 
 Caffeine, 339. 
 Calamine, 225. 
 Calcium, 205. 
 
 carbonate, 207. 
 
 chloride, 210. 
 
 fluoride, 209. 
 
 hydroxide, 206. 
 
 hypochlorite, 123. 
 
 oxide, 206. 
 
 phosphate, 151, 209. 
 
 sulphate, 208. 
 
 sulphide, 188. 
 Calomel, 230. 
 Camphor, 339. 
 Caramel, 324. 
 Carbamide, 294. 
 Carbohydrates, 322. 
 Carbon, 74. 
 
 dioxide, 91. 
 
 monoxide, 90. 
 
 sulphide, 149. 
 Carbonado, 75. 
 Carbonic oxide, 90. 
 Carbonyl, 295. 
 Carburetted hydrogen, 81. 
 Carnelian, 168. 
 Carre's ice-machine, 58. 
 Casein, 345. 
 Cassiterite, 239. 
 Cast-iron, 266. 
 Catalysis, 26. 
 Cellulose, 327. 
 Cement, 207. 
 Cerium, 237. 
 Cetyl alcohol, 300. 
 Chalcedony, 168. 
 Chalk, 206. 
 Chalybite, 264. 
 Chameleon mineral, 264. 
 Change, chemical, I. 
 
 physical, I. 
 Charcoal, 76. 
 Chemical attraction, 6. 
 
INDEX. 
 
 Chemical calculations, 71. 
 
 combination, 3. 
 
 decomposition, 4. 
 
 formulae, 70. 
 Chemism, 6. 
 
 Chemistry defined, 6, 12. 
 Chili saltpeter, 189. 
 Chinoline, 341. 
 Chlorhydrins, 318. 
 Chloride of lime, 123. 
 Chlorine, 113. 
 
 acids of, 122. 
 
 oxides, 122, 125. 
 Chloroform, 302. 
 Choke-damp, 95. 
 Chondrin, 346. 
 Chromates, 255. 
 Chrome alum, 254. 
 
 orange, 257. 
 
 red, 257. 
 
 yellow, 256. 
 Chromite, 253. 
 Chromium, 253. 
 
 compounds of, 253, 254. 
 Chrysoberyl, 222. 
 Chrysolite, 169. 
 Cinchonine, 340. 
 Cinnabar, 228. 
 Cinnamene, 334. 
 Cinnamic aldehyde, 3^5. 
 Coal, 79. 
 
 gas, 82. 
 
 oil, 79- 
 
 tar, 82. 
 
 tar colors, 332. 
 Cobalt, 273. 
 
 salts of, 274. 
 Cobalticyanides, 294. 
 Cocoa, 340. 
 Codeine, 340. 
 Coffee, 339. 
 Coinage, 198. 
 Coke, 79. 
 Collodion, 328. 
 Colloid, 171. 
 Columbium, 252. 
 Combination, by volume, 99. 
 
 chemical, 3. 
 Combining weights, 68. 
 Combustion, 26. 
 Compounds, 9. 
 Compound blow-pipe, 34. 
 
 Compound radicles, 97. 
 Coniferine, 343. 
 Coniferyl alcohol, 343. 
 Conine, 339. 
 Copper, 275. 
 
 acetate, 306. 
 
 compounds in general, 277. 
 
 formate, 4. 
 
 pyrites, 275. 
 
 sulphide, 23. 
 Copperas, 270. 
 Coral, 206. 
 
 Corrosive sublimate, 230. 
 Corundum, 233. 
 Cream of tartar, 314. 
 Crith, 19, 72. 
 Cryolite, III, 185, 235. 
 Crystallization from fusion, 134. 
 
 water of, 48, 165. 
 Crystalloid, 171. 
 Cupellation, 198. 
 Cuprammonium, 278. 
 Cuprous compounds, 277. 
 Cyanides, 97, 291. 
 Cyanogen, 97, 291. 
 
 chlorides, 294. 
 
 Davy's safety-lamp, 89. 
 Decane, 296. 
 Decomposition, 4. 
 Definite proportions, 62. 
 Deliquescence, 48. 
 Density of gases, TOO. 
 
 of solids and liquids, 44. 
 Dextrin, 327. 
 Dextrose, 325. 
 Dialysis, 170. 
 Diamond, 75. 
 Didymium, 327. 
 Dinitrobenzene, 331. 
 Direct- vision spectroscope, 217. 
 Disinfectants, 77, 117, 123, 138. 
 Dissociation, 194. 
 Distillation, 46. 
 
 fractional, 299. 
 Dolomite, 223. 
 
 Double decomposition, 4, 200, 231. 
 Dulong and Petit's law, 259. 
 Dynamite, 320. 
 
 Efflorescence, 48. 
 Electrochemical series, 176. 
 
INDEX. 
 
 365 
 
 Electrolysis, 36, 174. 
 Electroplating, 203. 
 Electrotype, 277. 
 Elements, nature of, 221. 
 
 table of, 9. 
 
 Emerald, 169, 222, 233. 
 Emery, 233. 
 Emulsion, 342. 
 Erbium, 237. 
 Erythrite, 316. 
 Ether, 301. 
 Ethers, mixed, 301. 
 Ethyl, alcohol, 298. 
 
 butyrate, 306. 
 
 oxide, 301. 
 Ethylene, 81. 
 
 Fats, 318. 
 Fatty acids, 303. 
 Feldspar, 169, 236. 
 Fermentation, 347. 
 Ferric compounds, 271. 
 Ferrous compounds, 270. 
 Fibrin, 345. 
 Filtration, 45. 
 Fire-clay, 236. 
 Firedamp, 80. 
 Flame, 84. 
 Flint, 168. 
 Fluorescence, 341. 
 Fluorine, in. 
 Fluor-spar, 112. 
 Force, 5. 
 Formulae, chemical, 70. 
 
 structural, 107. 
 Fractional distillation, 299. 
 Fraunhofer's lines, 218. 
 Fraxin, 343. 
 Fruit-ethers, 306. 
 Fusel-oil, 300. 
 Fusible alloys, 250. 
 
 Galena, 242. 
 Gallium, 237. 
 Galvanized iron r 226. 
 Garnet, 169. 
 Gas, illuminating, 82. 
 
 laughing, 63. 
 Gas calculations, 21. 
 Gas-carbon, 76. 
 Gases, condensation of, 22. 
 
 expansion of, 20. 
 
 Gasoline, 297. 
 Gastric juice, 346. 
 Gelatin, 346. 
 German-silver, 226, 273. 
 Glass, 169. 
 Glucinunv, 222. 
 Glucose, 325. 
 Glucosides, 342. 
 Glue, 346. 
 Gluten, 346. 
 Glycerin, 318. 
 Glycols, 311. 
 Gold, 280. 
 
 chloride, 282. 
 Granite, 169. 
 Grape-sugar, 325. 
 Graphite, 76. 
 Green vitriol, 270. 
 Grotto del Cane, 95. 
 Guarana, 339. 
 Gum-arabic, 327. 
 Gun-cotton, 327. 
 Gunpowder, common, 192. 
 Gunpowder, white, 125. 
 Gypsum, 208. 
 
 Haemoglobin, 345. 
 
 Heat and chemical change, 5. 
 
 Heavy spar, 21 1. 
 
 Hematin, 345. 
 
 Hematite, 264. 
 
 Heptane, 296. 
 
 Hexane, 296. 
 
 Homologous series, 287. 
 
 Hornblende, 169. 
 
 Hyacinth, 239. 
 
 Hydraulic lime, 206. 
 
 Hydrocarbons, 79, 287. 
 
 Hydrogen, 14. 
 
 chloride, 118. 
 
 fluoride, 112. 
 
 oxides, 14. 
 Hydroxyl, 148. 
 Hyoscyamine, 341. 
 
 Ice, 43. 
 
 Ice-machines, 58. 
 Iceland-spar, 207. 
 Illuminating gas, 82. 
 Indigo, 335. 
 Indium, 237. 
 Ink, 270, 343. 
 
366 
 
 INDEX. 
 
 Ink, india, 77. 
 
 printer's, 77. 
 Iodine, 128. 
 
 pentoxide, 130. 
 lodoform, 302. 
 Indium, 284. 
 Iron, 264. 
 
 oxides, 270, 271. 
 
 pyrites, 271. 
 
 salts of, 270. 
 
 scale, 271. 
 
 sulphide, 270. 
 Isomerism, 289. 
 
 Kaolin, 236. 
 Kerosene, 297. 
 Ketones, 309. 
 
 Labarraque's solution, 123. 
 Lac-sulphur, 134. 
 Lactose, 324. 
 Lamp, safety, 89. 
 
 spirit, 86. 
 Lamp-black, 77. 
 Lanthanum, 237. 
 Lapis-lazuli, 235. 
 Laurite, 282. 
 Law, of Avogadro, 103. 
 
 of Boyle and Mariotte, 22. 
 
 of definite proportions, 62. 
 
 of Dulong and Petit, 258. 
 
 of multiple proportions, 62. 
 
 two-volume, 100. 
 Laws, Berthollet's, 200. 
 Lead, 241. 
 
 acetate, 306. 
 
 chromate, 256. 
 
 salts of, in general, 243, 244. 
 Lead-chamber crystals, 147. 
 Lead-tree, 245. 
 Leather, 343. 
 Legumin, 346. 
 Lepidolite, 184. 
 Levulose, 325. 
 Lime, 206. 
 Lime-light, 35. 
 Lime-water, 91. 
 Limonite, 264. 
 Litharge, 244. 
 Lithium, 184. 
 
 Madder, 336. 
 Magenta, 332. 
 
 Magnesia, 223, 224. 
 Magnesite, 224. 
 Magnesium, 223. 
 
 compounds of, 223, 224. 
 Magnetite, 264. 
 Malachite, 275. 
 Manganese, 262. 
 
 oxides, 262, 263. 
 
 salts of, 262, 263. 
 Manganite, 262. 
 Mannite, 316. 
 Margarin, 319. 
 Marsh-gas, 79. 
 
 Marsh's test for arsenic, 161. 
 Matter, 5. 
 
 Melissyl alcohol, 300. 
 Melting-point table, 173. 
 Mendelejeff's classification, 180, 
 
 181. 
 
 Mercaptans, 301. 
 Mercury, 228. 
 
 oxides, 229. 
 
 salts of, 230. 
 Metals, 10, 172. 
 Methane, 79. 
 Methane series, 296. 
 Methyl, alcohol, 298. 
 
 chloride, 302. 
 
 salicylate, 333. 
 Methylbenzene, 334. 
 Mica, 169. 
 Milk, 345. 
 Minium, 244. 
 Molecular weight, 71. 
 Molecule, II, 12. 
 Molybdenum, 257. 
 Morphine, 340. 
 Mortar, 207. 
 Mouth blow-pipe, 86. 
 Multiple proportion, 62. 
 
 Naphtha, 297. 
 Naphthalene, 336. 
 Naphthalene-yellow, 336. 
 Narcotine, 340. 
 Nascent state, 199. 
 Nature of the elements, 221. 
 Nebular hypothesis, 221. 
 Nickel, 273. 
 
 compounds of, 274. 
 Nicotine, 339. 
 Niobium, 252. 
 
INDEX. 
 
 367 
 
 Nitrates, 58. 
 Niter, 191. 
 Nitrobenzene, 331. 
 Nitrocellulose, 327. 
 Nitrogen, 49. 
 
 bromide, 128. 
 
 chloride, 127. 
 
 iodide, 130. 
 
 oxides, 62-64. 
 Nitroglycerin, 320. 
 Nitrosyl chloride, 121. 
 Nitrotoluene, 334. 
 Non-metals, 10. 
 Nux vomica, 341. 
 
 Oils, essential, 338. 
 
 fatty, 318. 
 defines, 310. 
 Olein, 319. 
 Onyx, 168. 
 Opal, 168. 
 Opium, 340. 
 Orpiment, 163. 
 Osmium, 284. 
 Oxygen, 24. 
 
 Oxyhydrogen blow-pipe, 34. 
 Ozone, 29, 104. 
 
 Palladium, 284. 
 Palmitin, 319. 
 Paraffin, 296. 
 Paris-green, 161. 
 Pectin, 327. 
 Pentane, 297. 
 Pepsin, 346. 
 Peptones, 346. 
 Perissads, 157. 
 Peruvian bark, 340. 
 Petroleum, 79, 297. 
 Phenol, 330. 
 Phenyl, 331. 
 Phenylamine, 331. 
 Phenylethylene, 334. 
 Phloridzin, 343. 
 Phosphates, 156. 
 Phosphine, 154, 289. 
 Phosphorus, 151. 
 
 chlorides, 157. 
 
 hydrides, 154. 
 
 oxides, 155. 
 
 oxychloride, 158. 
 Photography, 201. 
 
 Photolithography, 256. 
 Plant-respiration, 97. 
 Plaster, 207. 
 Plaster of Paris, 209. 
 Platinocyanides, 294. 
 Platinum, 282. 
 
 chloride, 283. 
 Plumbago, 7- 
 Polymerism, 290. 
 Populin, 343. 
 Porcelain, 236. 
 Porcelain-glass, 235. 
 Potash, 190. 
 Potassium, 183, 189. 
 
 bicarbonate, 191. 
 
 bromide, 191. 
 
 carbonate, 190. 
 
 chlorate, 124, 191. 
 
 chloride, 191. 
 
 chloroplatinate, 283. 
 
 chromates, 255. 
 
 cyanide, 292. 
 
 ferricyanide, 293. 
 
 ferrocyanide, 292. 
 
 hydroxide, 190. 
 
 iodide, 191. 
 
 nitrate, 191. 
 
 oxides, 190. 
 
 perchlorate, 127. 
 
 permanganate, 264. 
 
 silicate, 169. 
 
 sulphocyanate, 294. 
 
 tartrates, 314. 
 Pottery, 236. 
 
 Pressure, effect on gases, 22. 
 Propane, 296. 
 Propyl alcohol, 300. 
 Prussian blue, 293. 
 Puddling, 265. 
 Purpurin, 336. 
 Putrefaction, 347. 
 Pyridine, 341. 
 Pyrolusite, 262. 
 Pyrotechny, 210. 
 Pyroxylin, 327. 
 
 Quantivalence, 105. 
 Quartation, 280. 
 Quartz, 168. 
 Quicklime, 206. 
 Quicksilver, 228. 
 Quinine, 340. 
 
368 
 
 INDEX. 
 
 Realgar, 162. 
 Red-lead, 244. 
 Respiration, 28. 
 Reversal of sodium-line, 219. 
 Rhodium, 284. 
 Rinmann's green, 274. 
 Rochelle salt, 314. 
 Rock-crystal, 168. 
 Rosanilin, 332. 
 Rosin, 338. 
 Rubidium, 184, 217. 
 Ruby, 233. 
 Ruthenium, 284. 
 
 Safety-lamp, 89. 
 Salicin, 342. 
 Salicyl aldehyde, 333. 
 Saligenin, 342. 
 Sal-soda, 187. 
 Salt, common, 185. 
 Salt-cake, 187. 
 Saltpeter, 191. 
 Salts, defined, 61. 
 Samarium, 238. 
 Sand, 168. 
 Sapphire, 233. 
 Saratoga water, 45. 
 Scales, thermometric, 42. 
 Scandium, 237. 
 Seidlitz-powder, 314. 
 Selenite, 208. 
 Selenium, 149. 
 Serpentine, 223. 
 Silica, 168. 
 Silicates, 169. 
 Silicon, 166. 
 
 compounds of, 167. 
 Silver, 196. 
 
 bromide, 201. 
 
 chloride, 199. 
 
 cyanide, 203, 292. 
 
 iodide, 201. 
 
 nitrate, 199, 202. 
 
 oxide, 198. 
 
 sulphate, 198. 
 
 sulphide, 198. 
 Silver-plating, 203. 
 Slate, 169. 
 Smelling-salts, 195. 
 Smithsonite, 225. 
 Smoke-consumers, 88. 
 Snow, 43. 
 
 Soap, 186, 319. 
 Soda, 186. 
 Sodium, 183. 
 
 acetate, 306. 
 
 bicarbonate, 189. 
 
 borate, 165. 
 
 carbonate, 186. 
 
 chlorate, 125. 
 
 chloride, 185. 
 
 hydrogen sulphite, 140. 
 
 hydroxide, 186. 
 
 hypochlorite, 123. 
 
 hyposulphite, 141. 
 
 nitrate, 189. 
 
 oxides, 1 86. 
 
 phosphate, 189. 
 
 salicylate, 333. 
 
 silicate, 169. 
 
 stannate, 241. 
 
 sulphate, 189. 
 
 thiosulphate, 141. 
 
 tungstate, 258. 
 
 uranate, 258. 
 Solanine, 341. 
 Solder, 240. 
 Solution, 44. 
 Sombrerite, 151. 
 Spathic iron-ore, 264. 
 Specific gravity, 44. 
 
 table of, 173. 
 Specific heat, 259. 
 Spectrometer, 215. 
 Spectroscope, 214, 216. 
 Spectrum, absorption, 218. 
 
 bright line, 218. 
 
 continuous, 218. 
 
 nebular, 220. 
 
 solar, 220. 
 
 stellar, 220. 
 
 Spectrum analysis, 213. 
 Spelter, 225. 
 Spermaceti, 300. 
 Spiegeleisen, 267. 
 Spirit-lamp, 86. 
 Spirits of wine, 300. 
 Stalactite and stalagmite, 208. 
 Starch, 326. 
 Steam, 42. 
 Stearin, 319. 
 Steel, 268. 
 Stibines, 289. 
 Stibnite, 249. 
 
INDEX. 
 
 369 
 
 Stoichiometry, 73. Toluidine, 334. 
 
 Strontium, 205. 
 
 Topaz, 169, 233. 
 
 salts of, 210. 
 
 Trap, 169. 
 
 Structural formulae, 107. 
 
 Trinitrophenol, 331. 
 
 Strychnine, 341. 
 
 Tungsten, 257. 
 
 Substitution compounds, 288. 
 
 Turpentine, 338. 
 
 Sucrose, 323. 
 
 Turquoise, 235. 
 
 Sugar, cane, 323. 
 
 Type-metal, 248. 
 
 fruit, 325. 
 
 
 
 grape, 325. 
 
 Ultramarine, 235. 
 
 milk, 324. 
 
 Unsaturated compounds, 108. 
 
 Sugar of lead, 306. 
 
 Uranium, 258. 
 
 Saint, 190. 
 
 Urea, 294. 
 
 Sulphocarbamide, 295. 
 Sulphocarbonyl, 295. 
 Sulpho-salts, 163. 
 Sulphourea, 295. 
 Sulphur, 132. 
 
 Valency, 105, 157. 
 Vanadium, 247. 
 Vanilline, 343. 
 Venetian red, 271. 
 
 acids of, 141. 
 
 Verdigris, 306. 
 
 chloride, 148. 
 
 Vermilion, 229. 
 
 oxides, 138. 
 
 Vinegar, 305. 
 
 Sulphuretted hydrogen, 136. 
 
 Vitriol, blue, 277. 
 
 Sulphuryl chloride, 148. 
 
 green, 270. 
 
 Superphosphates, 210. 
 
 oil of, 142. 
 
 Syenite, 169. 
 
 white, 227. 
 
 Symbols of the elements, 9, 66. 
 Synthesis, 8. 
 
 Water, 32. 
 hard, 45. 
 
 Trtl nr*n 
 
 mineral, 45. 
 
 i ale, 223. 
 Tannin, 343. 
 Tantalum, 252. 
 
 of constitution, 224. 
 of crystallization, 48, 165, 224. 
 
 Tartar, 314. 
 
 rain, 45. 
 
 Tartar-emetic, 315. 
 
 sea, 45. 
 
 Tea, 339. 
 Tellurium, 150. 
 Terbium, 237. 
 Terpenes, 338. 
 Thallium, 203. 
 Thebaine, 340. 
 Thenard's blue, 274. 
 Theobromine, 340. 
 
 soft, 45' 
 Water-glass, 169. 
 White-lead, 244. 
 White-vitriol, 227. 
 Williamson's blue, 293. 
 Wolfram, 257. 
 Wood-spirit, 298. 
 Wrought-iron, 265. 
 
 Thermometric scales, 42. 
 
 Ytterbium, 237. 
 
 Thorium, 239. 
 Tin, 239. 
 
 Yttrium, 237. 
 
 compounds of, 240, 241. 
 
 Zinc, 225. 
 
 Tin-plate, 240. 
 
 compounds of, 226, 227. 
 
 Tinstone, 239. 
 
 granulated, 15, 226. 
 
 Titanium, 239. 
 
 Zincite, 225. 
 
 Tobacco, 339. 
 
 Zircon, 239. 
 
 Toluene, 334. 
 
 Zirconium, 239. 
 
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