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GIFT OF 
 
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 Complete in 1 vol., 8vo. With Problems and Index. 
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CLASS-BOOK 
 
 OF 
 
 CHE MISTRT 
 
 ON THE BASIS OF THE NEW SYSTEM, 
 
 BY 
 
 EDWARD L. YOUMANS, M. D., 
 
 ATTTUOB OK THE "HAND-BOOK OF HOUSEHOLD OCIEJiCE. 1 
 REWRITTEN AND REVISED. WITH MANY NJW ILLUSTRATIONS. 
 
 NEW YORK: 
 
 D. APPLETON AND COMPANY, 
 1, 3, AND 5 BOND STREET. 
 
 1880. 
 
C 
 
 ENTERED, according to Act of Congress, in the year 1863, by 
 
 D. APPLETON & CO., 
 
 In CLo Clerk's Office of the District Court of the United States for the 
 Southern District of New York. 
 
 ENTERED, according to Act of Congress, in the year 1875, by 
 
 D. APPLETON & COMPANY, 
 In the Office of the Librarian of Congress, at Washington. 
 
237382 
 
PEE F A E. 
 
 THE " Class-book of Chemistry," first published in 
 1852, was rewritten in 1863, and has now been again 
 thoroughly revised, so as to bring it into harmony with 
 the latest views, and adapt it more perfectly to the 
 wants of those for whom it was prepared. The first 
 edition represented the state of chemistry as it pre- 
 vailed at the time of publication, and had been long es- 
 tablished ; but the revised edition, though adhering to 
 the old theories, recognized that they were undergoing 
 important modifications. These modifications have 
 been long in progress, and having at length issued in a 
 new system of chemical doctrine, which has been gen- 
 erally accepted by chemists, it has been adopted in the 
 present volume, and explained and applied as fully as 
 the plan of the work will allow. The present position 
 of the science is, therefore, of special importance in. 
 relation to its exposition. 
 
 There can be no question that the new theories 
 mark an important step in the progress of chemistry. 
 They harmonize a wider range of facts, and give us a 
 more consistent philosophy of the subject, than the 
 theories they supersede. Yet they are far from being 
 complete. The present situation is the proverbially 
 
4 PREFACE. 
 
 uncomfortable one of transition ; the old house having 
 ceased to be habitable, while the new one is unfinished. 
 Prof. A. Crum Brown, of the Edinburgh University, 
 in a late address before the British Association, well 
 stated the present attitude of chemical theory in the 
 following words : 
 
 " It is impossible to make a certain forecast : looking back, 
 we see a logical sequence in the history of chemical speculation ; 
 and no doubt the next step will appear, after it has been taken, to 
 follow as naturally from the present position. One thing we can 
 distinctly see we are struggling toward a theory of chemistry. 
 Such a theory we do not possess. What we are sometimes 
 pleased to dignify with that name is a collection of generaliza- 
 tions of various degrees of imperfection. We cannot attain to a 
 real theory of chemistry until we are able to connect the science 
 by some hypothesis with tho general theory of dynamics." 
 
 This view of chemical science, as a body of thought 
 in process of development, more perfect at present than 
 ever before, but still imperfect in relation to the future, 
 should not now be lost sight of. It shows both the 
 reason and necessity of change, reconciles difficulties, 
 and enables us rightly to estimate the value of preced- 
 ing systems, which, although now displaced, were essen- 
 tial conditions of chemical advancement. We are not 
 to regard past theories as mere exploded errors, nor 
 present theories as final. The living and growing body 
 of truth has only moulted its old integuments in the 
 progress to a higher and more vigorous state. It is cer- 
 tainly desirable that this complexion of the subject 
 should be recognized in its presentation to ordinary 
 students. Practical text-books, intended for mastering 
 the subject experimentally, must, of course, be much 
 confined to existing facts and the principles by which 
 they are now interpreted ; but books designed to present 
 
PREFACE. 5 
 
 the science in its general relations for popular educa- 
 tional uses should not overlook the considerations sug- 
 gested in the above-quoted passage. In this volume, 
 therefore, I have aimed to preserve somewhat the tran- 
 sitional aspect of the subject, so that the " New Chem- 
 istry " may neither be regarded as an ingenious device 
 of yesterday, nor as a finality to be acquired with no 
 expectation of further improvement. 
 
 To prevent misconception respecting the claims of 
 this class-book, it is necessary to repeat what was said 
 in the Preface to the preceding edition. It is not de- 
 signed as a manual for special chemical students. It 
 aims to meet the wants of that considerable class, both 
 in and out of school, who would like to know something 
 of the science, but who are without the opportunity or 
 the desire to pursue it in a thorough experimental way. 
 Some acquaintance with the subject is now required as 
 a part of every good education ; but books designed for 
 laboratory use, and abounding in technical details, are 
 ill-suited to those who do not give special and thorough 
 attention to the subject. I have here attempted to fur- 
 nish such an outline of the leading principles and most 
 important facts of the science as shall meet the needs of 
 the mass of students in our high schools, seminaries, and 
 academies, who go no further with the subject than to 
 study a brief text-book, with the assistance perhaps of 
 a few lectures, and the observation of some accompany- 
 ing experiments. 
 
 The present edition has been much reduced in com- 
 pass, both by the use of larger type and fewer pages, 
 and it has thus been brought into more manageable 
 limits for school-use. Much new matter has, however, 
 been introduced under various heads. The rapid devel- 
 opment of spectrum analysis since the former edition 
 
6 PREFACE. 
 
 was published, and the great interest of the subject, have 
 led to considerable expansion of that topic. The treat- 
 ment of the chemistry of light is also amplified, and 
 the chapter on theoretical chemistry explaining the new 
 system is made as full as the proportions of the volume 
 will allow. Tables of the French system of weights 
 and measures are appended for the use of those who 
 desire to employ it. As the progress of investigation 
 is constantly bringing physics and chemistry into 
 closer relations, the division of chemical physics has 
 been retained, although the text has been much reduced. 
 
 Such a class-book can, of course, have little value 
 for the usual purposes of reference. It must be but a 
 brief compend of general principles and descriptions 
 of some of the most important substances, and is not to 
 be judged by the fullness of its details. Such are already 
 the vast proportions of the science, and such the enor- 
 mous rapidity of its growth, that nothing less than 
 works of encyclopedic scope have value for general 
 consultation. Watts' s invaluable " Dictionary of Chem- 
 istry," with its five volumes averaging a thousand 
 closely-printed pages, has already a thousand-paged sup- 
 plement ; and it would require such a volume every 
 year adequately to report the progress of the science. 
 The class-book should be supplemented by some such 
 ample treatises in every school-library. 
 
 I have to acknowledge especial indebtedness in 
 preparing the chapter on theoretical chemistry to the 
 admirable volume of Professor J. P. Cooke, entitled 
 " The New Chemistry " one of the finest pieces of 
 exposition in the language. It is a book that every 
 chemical teacher should study, and I would moreover 
 earnestly recommend them to place it in the hands of 
 their classes, aad have them go carefully through it. No 
 
PREFACE. 7 
 
 other work that I know of can put them in such thor- 
 ough possession of the later stand-points of chemical 
 study. 
 
 To many teachers and superintendents of schools 
 who have been anxious for the appearance of this re- 
 vised edition of the class-book, my apologies are due 
 for broken promises and a delay in publication that 
 may well have seemed without excuse. I have only to 
 plead that the volume would have been issued long 
 since but for the failure of my eyesight from overwork. 
 I have been greatly aided in this revision by my excel- 
 lent friend Professor Charles Froebel ; and I have also 
 to thank another friend, Miss Mary E. Shaw, for effi- 
 cient assistance in seeing the book through the press. 
 That errors may have crept in is probable, but I think 
 they will not be found serious, and shall be "glad to have 
 any inaccuracies pointed out for correction in future 
 editions. 
 
 E. L. Y. 
 
 NEW YORK, June, 1875. 
 
CONTENTS 
 
 PAGE 
 
 INTRODUCTION ........ .11 
 
 PART I. 
 
 CHEMICAL PHYSICS. 
 CHAPTER I. 
 
 GRAVITY. 
 
 1. Absolute Mass, Volume, and Weight ... .14 
 2. Specific Mass, Volume, and Weight 17 
 
 CHAPTER II. 
 
 MOLECULAR ATTRACTIONS. 
 
 1. Minute Constitution of Matter 23 
 
 2. Adhesion and Cohesion 25 
 
 8. Diffusion 28 
 
 4. Orystallizatwn 35 
 
 CHAPTER III. 
 
 HEAT. 
 
 1. Thermal Expansion Thermometers ..... 46 
 
 2. Transference of Heat 49 
 
 3. Changes of Molecular Aggregation . ..... 54 
 
 4. The Nature of Heat Gl 
 
 CHAPTER IV. 
 
 ELECTRICITY. 
 
 1. Frictional Electricity 65 
 
 2. Magnetism . 68 
 
CONTENTS. ix 
 
 PAGE 
 
 3. Voltaic Electricity . . ... 71 
 
 4 Electricity, Magnetism, and Heat . ... 76 
 
 CHAPTER V. 
 
 LIGHT. 
 
 1. Motion of the Radiant Forces 80 
 
 2. Interference and Polarization . ... 82 
 
 CHAPTER VI. 
 
 THE CHEMISTRY OF LIGHT. 
 
 1. The Chemical Rays . . - 
 
 2. Photographic Chemistry . 93 
 
 CHAPTER VII. 
 
 SPECTRUM ANALYSIS. 
 
 1. The Luminous Spectrum . .98 
 
 2. The Spectroscope ... . .103 
 
 3. Spectral Lines, - 105 
 
 4. Theory of Absorption . .110 
 
 5. Spectroscopic Applications . 116 
 
 PART II. 
 CHEMICAL PRINCIPLES. 
 
 CHAPTER VIII. 
 General Character of Chemical Action . . .127 
 
 CHAPTER IX. 
 
 THEORETICAL CHEMISTRY. 
 
 1. Theory of Atoms and Molecules ...... 134 
 
 2. Progress of Chemical Theory 138 
 
 3. Theory of Atomicity and Quantivalencs 141 
 
 4. Theory of Radicals 148 
 
 5. Theory of Adds, Bases, and Salts ...... 150 
 
 6. Theory of Isomerism and Allotropism . . . . .155 
 
 7. Theory of Combining Volumes ...... 158 
 
 CHAPTER X. 
 THE CHEMICAL NOMENCLATURE . . . . . . .163 
 
x CONTENTS. 
 
 PART III. 
 DESCRIPTIVE CHEMISTRY. 
 
 DIVISION I. PERISSAD ELEMENTS. 
 
 CHAPTER XL 
 
 PAGE 
 
 HYDROGEN ...... 169 
 
 CHAPTER XII. 
 
 THE CHLORINE GROUP. CHLORINE, FLUORINE, BROMINE, IODINE. 
 
 1. Chlorine and its Compounds . . . . . . .175 
 
 2. Fluorine " " ...... 180 
 
 3. Bromine 181 
 
 4. Iodine 183 
 
 CHAPTER XIII. 
 
 THE SODIUM GROUP. SODITTM, POTASSIUM, LITHIUM, RUBIDIUM, CAESIUM. 
 
 1. Sodium and Us Compounds . . . . . . .184 
 
 2. Potassium " " 188 
 
 3. Lithium, Rubidium, Caesium 193 
 
 CHAPTER XIV. 
 
 SILVER GOLD --BORON. 
 
 1. Silver and its Compounds ....... 194 
 
 2. Gold 196 
 
 3. Boron and its Compounds ....... 197 
 
 CHAPTER XV. 
 
 THE NITROGEN GROUP. NITROGEN, PHOSPHORUS, ARSENIC, ANTIMONY, BI5MUTH. 
 
 1. Nitrogen and its Compounds . . . . . . .198 
 
 2. Phosphorus " ...... 206 
 
 3. Arsenic " ....... 210 
 
 4. Antimony and Bismuth ....... 212 
 
 DIVISION II. ARTIAD ELEMENTS. 
 
 CHAPTER XVI. 
 
 OXYGEN. 
 
 1. Oxygen and its Compounds . . . . . . .214 
 
 2. The Atmosphere , 228 
 
CONTENTS. xi 
 
 CHAPTER XVII. 
 
 THE SULPHUR GROUP. SULPHUR, SELENIUM, TELLURIUM. 
 
 PAGE 
 
 1. Sulphur and its Compounds 
 
 2. Selenium and Tellurium . 240 
 
 CHAPTER XVIII. 
 
 COPPER AND MERCURY. 
 
 1. Copper and its Compounds 
 
 2. Mercury " " 242 
 
 CHAPTER XIX. 
 
 THE CALCIUM GROUP. CALCIUM, STRONTIUM, BARIUM, LEAD. 
 
 1. Calcium and its Compounds . 244 
 
 2. Strontium and Barium . .... 247 
 
 3. Lead and Us Compounds - 2 ^ 
 
 CHAPTER XX. 
 
 MAGNESIUM GROUP. MAGNESIUM, ZINC, CADMIUM. 
 
 1. Magnesium and its Compounds 
 
 2. Zinc and Cadmium . 2 51 
 
 CHAPTER XXI. 
 
 IRON, MANGANESE, NICKEL, COBALT. 
 
 1. Iron and its Compounds . . .253 
 
 2. Manganese, Xickel, and Cobalt . - 260 
 
 CHAPTER XXH. 
 
 CHROMIUM, ALUMINIUM, AND THE PLATINUM GROUP. 
 
 1. Chromium and its Compounds . 261 
 
 2. Aluminium " " 62 
 
 3. The Platinum Group ... .265 
 
 CHAPTER XXIII. 
 
 TIN, SILICON. 
 
 1. Tin and its Compounds . ... 266 
 2. Silicon " 967 
 
 CHAPTER XXIV. 
 
 1. CARBON AND ITS COMPOUNDS . 270 
 
 2. Combustion 279 
 
xii CONTENTS. 
 
 DIVISION III. ORGANIC CHEMISTRY. 
 
 CHAPTER XXV. 
 
 PAGE 
 
 1. Hydrocarbons and their Derivatives ... .287 
 
 2. Alcohols ... 292 
 
 3. Saccharine Bodies ........ 296 
 
 4. Fermentation . . 302 
 
 5. Ethers and Aldehydes 305 
 
 CHAPTER XXVI. 
 
 ORGANIC CHEMISTRY (CONTINUED). 
 
 1. Adds 308 
 
 2. Organic Alkaloids . . . ... 313 
 
 3. Albuminous Substances ........ 315 
 
 APPENDIX .......... 320 
 
 QUESTIONS .......... 326 
 
 PRONUNCIATION OF SOME TECHNICAL WORDS AND PROPER NAMES USED 
 
 IN THIS WORK ........ 340 
 
 INDEX . 342 
 
THE 
 
 CLASS-BOOK OF CHEMISTRY, 
 
 INTRODUCTION. 
 
 1. What is meant by Science. Science is a knowledge 
 of the phenomena of Nature. By Nature is understood 
 that vast and diversified array of things which exists 
 around us, and of which we form a part. The term phe- 
 nomena means literally appearances, but it is applied to all 
 the objects and actions of the natural world which we can 
 recognize in any way. Thus we speak of celestial phe- 
 nomena and material phenomena, the phenomena of sound 
 and the phenomena of thought. Natural things are con- 
 stantly undergoing changes. These changes do not take 
 place by chance or irregularly, but with inflexible uni- 
 formity. The uniformities of change are termed laws, and 
 the whole system of laws is known as the Order of Nature. 
 It is, therefore, the object of science to discover and ex- 
 plain the laws and order of natural phenomena. 
 
 2. The Test of Science, Knowledge grows ; ordinary, 
 loose information, is gradually developed into the more 
 perfect form of science. The qualities of things are first 
 studied, then their quantities ; first there is certainty, then 
 exactness. As the laws of Nature are regular, in propor- 
 tion as we understand them we can foresee their effects. 
 In the simplest science, astronomy, we can predict effects 
 
12 INTRODUCTION. 
 
 thousands of years -to fc come. In the more complicated 
 sciences, prediction is less complete, and, as each science 
 is perfected, it gives larger foresight. Prevision, or the 
 power of seeing beforehand what will take place in given 
 circumstances, is, therefore, the most perfect test of science. 
 
 3. Matter and Force. The phenomena of Nature pre- 
 sent themselves under two different aspects called matter 
 and force. Whatever occupies space, or has weight, is 
 termed matter, and different kinds and portions of it are 
 called substances, or bodies. The properties of matter are 
 the characters by which its different kinds are known. 
 Thus iron is known by one set of properties, glass by an- 
 other, and air by another. A fundamental property of 
 matter is its indestructibility. There is no evidence that, 
 in the course of Nature, or by the operations of art, any 
 particle of matter either comes into existence, or is annihi- 
 lated. But, while matter itself remains imperishable, all 
 its forms are mutable. Every substance is capable of being 
 altered in form or properties. 
 
 Whatever acts upon matter, to change it, is called force. 
 Thus the force of gravity causes bodies to change position 
 or fall to the earth ; the force of heat causes metals to 
 melt, or change form, and chemical force corrodes them, or 
 changes their metallic nature. Different kinds of force are 
 convertible into each other, but it is now believed that 
 force, like matter, is essentially indestructible, and only 
 changes its form. The total amount of energy in the uni- 
 verse, by which matter is changed, is held to be unal- 
 terable. 
 
 4. Physical Properties and Changes. Those various fa- 
 miliar characters by which bodies are known as color, 
 weight, hardness, temperature are termed physical prop- 
 erties ; and those various alterations of form and quality, 
 which bodies undergo without destroying their distinctive 
 characters, are termed physical changes. Thus iron may 
 be cut, melted, or magnetized, but it still remains iron. 
 
INTRODUCTION. 13 
 
 Gravity, cohesion, heat, light=, electricity, and magnetism, 
 are the forces chiefly concerned in modifying physical prop- 
 erties, and are therefore known as physical forces. 
 
 5. Chemical Properties and Changes. But matter is 
 capable of undergoing changes by which its distinctive 
 characters are destroyed. Thus bright iron, when exposed 
 to damp air, is converted into a brown rust. When vine- 
 gar and lime are brought together, they combine, losing 
 their properties, and producing a new and different sub- 
 stance. When wood is heated, in the absence of air, it is 
 changed to a black, brittle mass ; if heated in the presence 
 of air, it is changed to invisible gases and ashes. These 
 are examples of the chemical changes of matter. 
 
 Chemistry divides all substances into two kinds, simple 
 and compound. Compound bodies are such as can be sep- 
 arated or decomposed into simpler parts ; simple bodies, 
 on the contrary, are such as cannot be thus decomposed. 
 Water is a compound, and can be separated into two in- 
 visible gases ; but neither of these can be again resolved 
 into different kinds of matter ; they are, therefore, ranked 
 as simple bodies, or elements. Chemical science treats of 
 the composition of matter, of the nature and properties of 
 its elementary pirts, of the compounds which may be 
 formed from them, and of the laws by which combination 
 and decomposition are governed. 
 
 6, Chemical Physics. No chemical change can occur 
 without being accompanied by some kind of physical 
 change. So intimately are the forces of Nature connected, 
 that the disturbance of any one is certain to involve a vari- 
 ety of effects. Physical forces and conditions have so pow- 
 erful an influence over chemical actions, that some knowl- 
 edge of them is indispensable to the chemical student. 
 Accordingly, under the title of " Chemical Physics," we 
 shall first treat briefly of those physical agencies which 
 are most intimately connected with the subject of chem- 
 istry. 
 
PART I. 
 CHEMICAL PHYSICS. 
 
 CHAPTER I. 
 
 GEAVITY. 
 
 1. Absolute Mass, Volume, and Weight. 
 
 7. The Measurement of Matter. The science of chem- 
 istry is based upon numerical laws, and the chemist is al- 
 most always occupied in investigating quantities, amounts 
 of matter, or amounts of change ; and this is done by the 
 operations of weighing and measuring. The amount of 
 any material body occupying space is termed the mass, and 
 the quantity of space so occupied, the volume or bulk of 
 that body. The process by which the volume of any body 
 is determined is termed measurement, and the instruments 
 used for this purpose are called measures of capacity. 
 They consist of vessels of various shapes, always inclosing 
 the same or multiples of the same amounts of space. The 
 units or standard amounts of space to which volumes are 
 referred vary in different countries. For ordinary purposes, 
 gallons, quarts, pints, cubic inches, cubic feet, and cubic 
 yards, are most commonly used with us, but, in making 
 scientific investigations, the metrical scale, also called the 
 
MASS, VOLUME, AND WEIGHT. 15 
 
 decimal or French scale, of measures is now almost uni- 
 versally employed. 
 
 8. Metrical Measures. The basis of the metrical sys- 
 tem of measures is the linear metre^ a length equal to 
 39.368 American inches. To the decimal divisions of this 
 length, names composed of the word metre and a prefix 
 formed from Latin numerals have been given ; and the de- 
 cimal multiples of the same standard are similarly made up 
 by engrafting Greek numerals. The following are the des- 
 ignations: one-tenth of a metre is called one decimetre; 
 one-hundredth, one centimetre; one thousandth, one milli- 
 metre ; and ten metres are called one dekametre, one hun- 
 dred one hectametre, one thousand one kilometre, etc. 
 
 The cubic decimetre, or litre, is the unit most generally 
 used as the standard of volume, but the cubic centimetre is 
 also very often employed. To compare these measures 
 with one more familiar, it may be remembered that one 
 litre is equal to 61.016 cubic inches or 2.113 pints. 
 
 9. Gravity. The attractive force by which bodies are 
 drawn to the surface of the earth is called gravity. It 
 acts between masses of matter 
 
 FIG. 1. 
 
 of every kind, and at all dis- 
 tances. The mutual attraction 
 of masses of matter has been 
 thus illustrated : A pair of leaden 
 balls, two inches in diameter, 
 were attached to the ends of a 
 rod, which was suspended in the 
 middle by a fine wire (Fig. 1). / 
 Two other balls of lead, a foot 
 in diameter, were placed upon a 
 revolving platform, and, when 
 the larger and smaller balls were 
 brought near together, they were 
 
 mutually attracted, as was shown by the motion of the 
 rod. The force exerted did not exceed the twenty-millionth 
 
16 
 
 CHEMICAL PHYSICS. 
 
 of the weight of the lesser ball, but was sufficient to 
 slightly twist the wire, and give rise to a small oscillatory 
 movement. The force of gravity is proportional to the 
 quantity of matter; that is, if the earth had twice its 
 present mass, its attraction would be doubled, if but 
 one-half its mass, its force would be only half as great. 
 So with any body on the earth, the force with which it is 
 attracted increases or diminishes in exact proportion to its 
 quantity. 
 
 10. Weight. If a body, instead of being allowed to 
 fall, is supported, its tendency to descend is not destroyed. 
 It is drawn downward with the same force, but, as it is re- 
 sisted, and at rest, the force takes the shape of pressure. 
 This downward pressure of bodies is called their weight. 
 The weight of a body is the force it exerts in consequence 
 of its gravity, and, as this force depends upon the quantity 
 of matter, it is clear that, if the mass be doubled, the 
 weight will be doubled ; if the mass be halved, the weight 
 will be halved. Weights are therefore nothing more than 
 measures of the force of gravity in different objects, and 
 we measure the force to determine the quantity of matter. 
 
 11. The Balance. The instruments employed by chem- 
 ists in weighing are balances. The chemical balance (Fig. 
 
 2), used for analysis, consists 
 of an inflexible bar, delicate- 
 ly poised at a point exactly 
 midway between its extrem- 
 ities, from which the scale- 
 pans are suspended. Its 
 beam rests upon a fine edge 
 of hardened steel, which is 
 supported by a flat plate of 
 polished agate. This beam 
 
 The Chemical Balance. .-,, , , ., ,, 
 
 oscillates toward the earth 
 
 just as the rod in the preceding experiment oscillated 
 toward the larger balls. 
 
 FIG. 2. 
 
MASS, VOLUME, AND WEIGHT. 17 
 
 12. Standard Weights. The operation of weighing con- 
 sists in estimating the force with which any given body is 
 attracted toward the earth by comparing it with other 
 masses of matter already weighed and marked according 
 to some fixed standard, as Troy, Avoirdupois, or French 
 weight. These standard scales are quite arbitrary, there 
 being no natural starting-point, or unit. The grain-weights 
 were originally grains of wheat. The scales established 
 in this country are capriciously arranged, while the French 
 employ a decimal scale, which, being far more convenient, is 
 almost always used in scientific investigations, and is gradu- 
 ally being adopted by different states and countries as the 
 legal standard for the transaction of ordinary business. 
 
 13. Metrical Weights. The French or metrical system 
 of weights is based upon the metrical measures before 
 mentioned. The standard unit of the scale is the weight 
 of one cubic centimetre of pure distilled water at the tem- 
 perature of maximum density (39.2 Fahr.). The decimal 
 fractions and multiples of the scale are distinguished by 
 the addition of the same Latin and Greek prefixes already 
 mentioned above, to the name oi the unit. This is called 
 the gramme, or gram. The gramme is equal to .15.432 
 grains, and the kilogramme to 22.046 pounds avoirdupois. 
 Tables of equivalence of French and English weights are 
 given in the Appendix. 
 
 2. Specific Mass, Volume, and Weight. 
 
 14. Specific Volume. Different bodies of equal weight 
 do not occupy like amounts of space. Though a pound of 
 cork exactly counterpoises a pound of lead, yet the former 
 has a volume forty times greater than the latter. By com- 
 paring, therefore, the volumes of different substances with 
 the volume of any one body of equal weight taken as unity, 
 we may obtain their specific volumes. 
 
 15. Specific Weight or Gravity. Inversely, also, dif- 
 
18 CHEMICAL PHYSICS. 
 
 ferent bodies of equal volume do not weigh the same. 
 Thus 100 cubic inches 
 
 Pounds. Grains. 
 
 Of hydrogen weigh . . . . 2.14 
 
 Of air " . . . 31 
 
 Of water " . . S.604 
 
 Of iron " 28.11 
 
 Of platinum ' . . . . 75.68 
 
 Platinum, the heaviest body we know, is thus nearly a 
 quarter of a million times heavier than an equal bulk of 
 hydrogen, the lightest of known substances. 
 
 If we, then, determine, not the absolute gravity of a 
 substance, but its weight compared with another body of 
 equal size, we obtain its relative, or specific gravity. Any 
 solid substance when immersed in water displaces a volume 
 exactly equal to its own bulk, and, at the same time, loses 
 a portion of its own weight just equal to that of the vol- 
 ume of water displaced. Water, which is found every- 
 where upon the globe, and easily purified by distillation, is 
 therefore taken as the unit of comparison for solids and 
 liquids. As variations of temperature alter the bulk of 
 bodies, sp. g. is taken at the standard of 60 Fahr. In 
 the metrical S3^stem, the weight of one cubic centimetre of 
 water at 39. 2 Fahr. is equal to one gramme. The weight 
 of one cubic centimetre of any body at that temperature, 
 expressed in grammes, is therefore identical with its specific 
 gravity. 
 
 For determining the specific gravities of bodies various 
 methods are employed, differing according to whether the 
 body under consideration is a solid, a liquid, or a gas ; 
 whether it is heavier or lighter than water, or insoluble or 
 soluble in it. 
 
 16. Solids heavier than Water. Fill a vessel with wa- 
 ter (Fig. 3), and drop in it a piece of sulphur which has 
 been weighed. A quantity of water will then escape into 
 the dish below, equal in bulk to the sulphur. Weigh the 
 
SPECIFIC GRAVITY. 
 
 19 
 
 escaped water in the lesser vessel. If the sulphur weighed 
 two ounces, the water will weigh an ounce. That is, the 
 sulphur weighs twice as much as an equal volume of water ; 
 its specific gravity is therefore two. The best plan, how- 
 ever, is to suspend the solid to the scale-pan of a balance 
 by a fine thread or hair, and then counterpoise it, or get 
 its weight in the air. Immerse the suspended body in a 
 vessel of distilled water (Fig. 4), and, as it weighs less, re- 
 move weights enough from the opposite scale-pan to re- 
 store the lost equipoise. Now divide the original weight 
 
 FIG. 4. 
 
 FIG. 3. 
 
 The Solid displaces its Bulk of Water. 
 
 Weighing a Substance in Water. 
 
 in air by the loss in water, and the quotient is the specific 
 gravity of the substance. For instance, a piece of lead 
 weighs in air 820 grains, and loses in water 71 grains. The 
 weight in air divided by the loss in water gives 11.5 as the 
 specific gravity of the lead. 
 
 17. Solids lighter than Water. When the body to be 
 examined is lighter than water, it is first weighed and after- 
 ward attached to a piece of metal heavy enough to sink it, 
 and suspended from the balance. The weiglit of a bulk of 
 water equal to that of the piece of metal and light body 
 together is thus found, and, the operation being afterward 
 repeated with the piece of metal alone, the difference be- 
 
20 CHEMICAL PHYSICS. 
 
 tween the weights of the two bulks of water displaced 
 gives the weight of water displaced by the light body. 
 
 18. Powdered Solids, The specific gravity of any sub- 
 stance in powder as, for instance, a soil is obtained as 
 follows : Counterpoise a thousand-grain bottle and weigh 
 into it 150 grs. of soil to be tested. Fill with water and 
 weigh again ; water and soil give, say 1,096 grs., 150 of them 
 are soil, and 946 water ; consequently 54 grs. of water have 
 been displaced by 150 grs. of soil. The calculation is then 
 easy, 54 : 1.000 : : 150 : 2.777 sp. gr. of the soil. In practice 
 a precaution is to be observed. The soil contains air among 
 its particles, which would vitiate the result. To obviate 
 this, fill the bottle but half full of water at first, and shake 
 it well with the soil ; the air escapes, and the bottle may 
 then be filled with water. 
 
 19. Soluble Solids. When the substance to be examined 
 is dissolved by water, its specific gravity is determined by 
 substituting for the water some other liquid that does not 
 dissolve it, and the specific gravity of which has been ac- 
 curately established. The bulk of water corresponding to 
 the bulk of the substituted liquid displaced may be found 
 by simple proportion. The liquids most generally used in 
 these determinations are alcohol and oil of turpentine. 
 
 20. Liquids and Gases. To determine the specific gravity 
 of liquids, procure a small bottle, and make a fine mark wilh 
 a file and ink upon its neck. Counterpoise it in the bal- 
 ance. Fill to the mark with distilled water at 60 Fahr., and 
 weigh it. Empty and fill again with the liquid, the specific 
 gravity of w r hich is required. Its weight, divided by that 
 of the water, gives the desired result. Suppose the bottle 
 holds a thousand grains of pure water, it will be found to 
 hold 1,845 grains of sulphuric acid, which therefore has a 
 sp. gr. of 1.845. For 1000 : 1.000 : : 1845 : 1.845. It will 
 hold 13,500 grs. of mercury, the sp. gr. of which is hence 
 13.5 ; or 1,030 grs. of milk, sp. gr. 1.03. In practice it is 
 usual to employ a bottle (Fig. 5), holding exactly 100 or 
 
SPECIFIC GRAVITY. 21 
 
 1,000 grains of distilled water at 60, which shows the re- 
 sult at once without calculation. 
 
 The specific gravity of gases is obtained in a similar 
 manner. A flask or globe suspended from 
 the arm of a balance is weighed when 
 empty, and again when filled with air. 
 This gives the weight of air, which is 
 taken as unity. Other gases are then sub- 
 stituted for the air, and their comparative 
 weights ascertained. Gases are subject to 
 variations of density, not only by altera- 
 tions of temperature, but by changes of 
 atmospheric pressure; these weights are 
 therefore taken at the standard barometric pressure of 30 
 inches. 
 
 21. Hydrometer, Take a tumbler, or a light, slender- 
 necked bottle, loaded with some shot, and float it in pure 
 rain-water ; it will sink to a certain depth, which may be 
 accurately marked upon the glass. If now Flo 6 
 
 placed in brine or milk, the mark will stand 
 above the surface ; the vessel not sinking 
 so deeply as before, because the liquids 
 are heavier. Place it in alcohol, and the 
 mark will disappear below the surface ; it 
 sinks deeper than at first, because the li- 
 quid is lighter than water. Instruments 
 arranged on this principle, and called hy- 
 drometers, are used to measure the specific 
 gravity of fluids. They usually consist of 
 a glass stem (Fig. 6), terminating in a bulb 
 below, loaded with shot or mercury, and 
 floating in a narrow glass vessel, contain- 
 ing the liquid to be tested. Scales are fixed within the stem, 
 zero being the point at which the instrument sinks in dis- 
 tilled water at 60 Fahr. In lighter liquids it sinks deeper, 
 and the scale ascends from zero. In heavier liquids it 
 
22 CHEMICAL PHYSICS. 
 
 floats higher, and the scale is reversed. These scales are 
 arbitrary and different in the various instruments. Tables 
 accompany them, so that we see at a glance the sp. gr. 
 which corresponds to any number upon the scale. Instru- 
 ments of this kind are much used by manufacturers and 
 dealers to determine the specific gravity or strength of 
 liquors, syrups, oils, lyes, etc. 
 
 22, Importance of Specific Gravity. Specific gravity is 
 among the most important of the physical properties of 
 bodies. It affords an important means of identifying them. 
 The mineral, iron pyrites, for example, is in color almost 
 exactly like gold, and is frequently mistaken for it. But it 
 is at once distinguished by the difference in specific grav- 
 ity, an equal bulk of gold being nearly four times heavier 
 than pyrites. So, if gold is debased by alloying it with a 
 cheaper metal, taking the specific gravity promptly detects 
 the fraud. The proportion of alcohol in spirituous mix- 
 tures, the richness of milk, the strength of various solu- 
 tions employed in the arts, and the identity and purity of 
 many substances, are determined with more or less accuracy 
 by finding this property. 
 
 23. Density. Specific gravity is often confounded with 
 density, but there is an important difference. The specific 
 gravity of a body is the ratio of its weight to that of an 
 equal volume of some substance selected as the standard, 
 and it implies no unit of volume in the determination. 
 The density of a body, on the other hand, is the amount of 
 matter by weight that it contains in a fixed unit of volume 
 compared with some substance taken as a standard. In the 
 English system it is the weight in grains of a cubic inch, 
 and may be expressed as a ratio by comparing it to the 
 weight of a cubic inch of water. In the French system 
 density is the weight in grammes of a cubic centimetre. 
 
CHAPTER II. 
 
 MOLECULAR ATTRACTIONS. 
 
 1. Minute Constitution of Matter. 
 
 24. Its Interior Structure. From the force which acts 
 between masses at all distances, we now pass to the study 
 of a class of forces which only come into play when bodies 
 are in contact. They seem to pertain to the interior struct- 
 ure of substances, and hence, before treating of them, it 
 becomes important to refer to that interior structure, or 
 how matter is believed to be constituted. 
 
 25. Porosity of Matter. If we place a little water upon 
 chalk or cloth, it disappears ; in a certain sense it pene- 
 trates them, but it only passes into vacant places termed 
 pores. Not only loosely-composed substances, as soil and 
 flesh, but wood, rocks, stones, and even dense metals, have 
 the same porous texture. Liquid mercury passes through 
 lead, and water has been also forced through the pores of 
 gold. Matter is, therefore, held to be universally porous. 
 
 26. Motions of Internal Parts. If a closed India-rubber 
 bag, filled with air, be squeezed, it will be compressed into 
 less bulk that is, the particles of air will be forced nearer 
 together. If alcohol and water be commingled, the mixture 
 occupies a smaller space than did the separate liquids ; their 
 particles have, therefore, approached closer to each other. 
 If iron be hammered, it will be driven into less compass, 
 the metallic particles being forced into closer relation. A 
 
24 CHEMICAL PHYSICS. 
 
 certain amount of heat added to bodies in either the solid, 
 liquid, or gaseous form, will cause a certain aegree of ex- 
 pansion that is, will cause the constituent particles to re- 
 cede from each other; and, when the heat is withdrawn, 
 the particles again approach. 
 
 27. It is concluded from such facts as these that mat- 
 ter consists of exceedingly minute particles which are 
 never in absolute contact, but are surrounded by unoccu- 
 pied spaces, in which they are free to move under the 
 action of forces. These ultimate separated material points, 
 which are of great minuteness, are termed molecules, a 
 word signifying a small mass. To the physicist molecules 
 are not imaginary, but actual things -vith weights and mag- 
 nitudes, and which do not change in the physical transform- 
 ations of matter. Molecules play a prominent part in mod- 
 ern physical theory ; and have made familiar the phrases 
 molecular attractions, molecular forces, molecular constitu- 
 tion of mutter. The chemical aspect of molecules will be 
 considered in the chapter on Theoretical Chemistry, Part II. 
 
 28. Divisibility of Matter. The division of matter may 
 be carried to an amazing extent. Gold may be drawn out 
 as a coating upon silver wire until the 492-thousand-mill- 
 ionth part of an ounce is still visible, with its proper me- 
 tallic color and lustre. It has been estimated that, in a 
 drop of the blood of the musk-deer, such as would remain 
 suspended upon the point of a fine needle, there are one 
 hundred and twenty millions of globules. But these ex- 
 amples of the divisibility of matter bring us only to the 
 threshold of a world of wonders. Microscopic researches 
 have introduced us to a realm of life peopled with animate 
 beings, which are born, grow, reproduce their kind, and 
 die ; and yet so minute that many millions of them heaped 
 together would not exceed in size a grain of sand. 
 
 We will now notice some of those forms of force which 
 are exerted between bodies only when in contact, and 
 which are known as molecular attractions. They are mani- 
 
ADHESION AND. COHESION 25 
 
 fested in the forms of matter, solid, liquid, and gaseous, 
 which are known as states of aggregation. 
 
 2. Adhesion and Cohesion. 
 
 29. Their Differences, Though the molecules of a solid 
 are separated, yet it does not crumble to pieces. They are 
 held together by a force which reaches across their inter- 
 stices and binds them in a fixed relation. When this force 
 unites bodies dissimilar in kind, it is called adhesion. The 
 sticking of chalk to a black-board, of mortar to bricks, of 
 glue to wood, etc., are examples of adhesion. The same 
 force, when acting between particles of the same kind, is 
 termed cohesion. The form, solidity, hardness, elasticity, 
 brittleness, malleability, and ductility of solids, are the re- 
 sult of various unknown modifications of cohesive force. 
 There is also a mutual attraction among the particles of 
 liquids. In a drop of liquid, cohesion attracts the particles 
 into a rounded figure, against the influence of their weight, 
 which would spread them out ; pendant drops still further 
 exemplify the same force. 
 
 30. Adhesion of Liquids to Solids. If a glass rod be 
 dipped in water, the liquid will rise round it above its level 
 in the vessel (Fig. 7), and, when with- 
 drawn, it will be wet. But, if the same 
 
 rod be dipped in mercury, there is an 
 apparent repulsion (Fig. 8), and the rod 
 when withdrawn is dry. If a rod of 
 gold be dipped in the mercury it is 
 wetted, or covered with a mercurial 
 
 The Glass Eod in Water. 
 
 film. The wetting in this case shows 
 an attraction between the liquid and the solid, and that it is 
 sufficiently strong to produce adhesion. But there may be 
 attraction without wetting ; glass is not wet by mercury, 
 and still they are attracted, as may be thus shown. Suf- 
 pend a flat, circular plate of glass to the arm of a bal::t;cr, 
 
26 CHEMICAL PHYSICS. 
 
 counterpoise it, and lower the plate (Fig. 9) over a cup of 
 mercury. No matter how near the glass approaches, while 
 there is no contact, there is no attraction. But, as soon as 
 thev are made to touch, a slight adhesion occurs, sufficient 
 to lift a portion of the mercury above its level in the ves 
 
 FIG. 9. 
 
 FIG. 8. 
 
 Glass Rod in Mercury. Attraction of Glass and Mercury. 
 
 sel, the amount of which may be exactly measured by the 
 number of weights required to be placed in the opposite 
 scale-pan to separate them. 
 
 31. Conditions of Wetting. If the adhesive force of any 
 solid for any liquid exceeds half the cohesive force of the 
 liquid particles for each other, the solid will be wet. Thus, 
 the adhesion of gold for mercury and of water for wood 
 exceeds half the cohesive force of the mercurial and watery 
 particles for each other, consequently water wets wood, and 
 mercury wets gold. But, if the adhesion of the solid be 
 less than half the cohesion of the liquid, wetting does not 
 follow contact, as is exemplified by glass and mercury. 
 
 32. Capillary Attraction. If glass rods with small aper- 
 tures, open at both ends (Fig. 10), be dipped in water, the 
 liquid immediately rises through the orifices to a height 
 which increases in proportion to the smallness of the open- 
 ings. The same thing may also be beautifully exhibited 
 by placing two plates of glass (Fig. 11) upon their edges 
 in a dish of colored water, one end being joined, and the 
 other slightly separated. The influence of the gradually- 
 approaching sides of the glass in attracting the liquid up- 
 
CAPILLARY ATTRACTION. 
 
 27 
 
 ward is seen in the course of the curve. From the circum- 
 stance that this effect is best produced by tubes with very 
 
 FIG. 10. 
 
 FIG. 11. 
 
 Capillary Tubes. 
 
 Rise of Liquid between Plates. 
 
 FIG. 12. 
 
 fine apertures, the attraction that causes these phenomena 
 is called capillary (from capittm, a hair). 
 
 33. Reversed Capillarity. If, now, a glass tube be 
 dipped in mercury, we have again a disturbance of liquid 
 equilibrium, but the effect is reversed. The interior col- 
 umn of mercury is depressed below the outside level, and 
 its surface exhibits a convex shape, as seen in Fig. 12. The 
 same thing occurs if the tube be greased and dipped in 
 water, and in all cases where the liquid cannot wet the 
 solid. The common belief, that depression 
 in this case (as in that of the glass and 
 mercury) is caused by repulsion, is quite 
 erroneous. We have proved that, instead 
 of repulsion, there is a strong attraction 
 between glass and mercury. The reversed 
 capillary action simply results from the 
 preponderance of the cohesive over the 
 adhesive force. 
 
 each particle is kept in place by the mutual 
 action of all the surrounding particles. But, if a column 
 of fluid be separated from the surrounding mass by inter- 
 posing the walls of a tube, the sides of which exert no 
 equivalent adhesive for ce, the cohesion of the mass below 
 draws down the upper and outer particles, and produces a 
 roundness or convexity at the top. 
 
 In every body of fluid, Convex Liquid Sur- 
 
28 CHEMICAL PHYSICS. 
 
 34. Adhesion of Gases to Liquids. When a liquid is 
 poured from one vessel to another, the gases of the air ad- 
 here to the descending stream, are carried downward, and 
 a portion of them remain combined with it. The force to be 
 overcome by this adhesion is the elasticity of the gases, or 
 the mutual repulsion of their particles. Pressure and cold 
 lower the elastic force, and therefore favor absorption. As 
 the temperature rises, adhesion is diminished, and hence 
 the readiest means of driving out a gas from solution is by 
 boiling. 
 
 35. Adhesion of Gases to Solids. If iron filings are 
 gently dusted over the surface of water, they float, though 
 iron is eight times heavier than water. This is because of 
 the adhesion and condensation of a layer of air upon their 
 surface, which prevents the water from wetting them. The 
 condensed air around the particles forais a capillary cavity, 
 and thus displaces a large volume of the liquid in com- 
 parison with that of the solid. Insects walk upon water 
 and skim over its surface, because the air adhering to their 
 feet forms capillary cavities, and prevents them from be- 
 coming wetted. 
 
 3. Diffusion. 
 
 36. Diffusion. Whenever the cohesive force subsisting 
 between the molecules of any body is exceeded by the ad- 
 hesive force subsisting between its molecules and those of 
 another body, the cohesion of one or both bodies is over- 
 come, their molecules separate, and become evenly inter- 
 mixed. The bodies in this case are said to be dissolved in, 
 or diffused through, one another, the process by which 
 their particles become intermingled being termed diffusion. 
 When diffusion takes place between bodies in unlike states 
 of aggregation, one of the two, under the influence of ad- 
 hesive attraction, assumes the state of the other. Thus, a 
 solid or liquid, in order to become diffused through a gas, 
 must first assume the gaseous state ; gases and solids, to be- 
 
DIFFUSION OF GASES. 
 
 29 
 
 FIG. 13. 
 
 come diffused through liquids, the liquid state; and gases 
 and liquids, to become diffused through solids, the solid 
 state of aggregation. The term diffusion is generally lim- 
 ited to the molecular union or intermingling of bodies al- 
 ready in a like condition of aggregation. 
 
 37. Diffusion of Gases. The molecules of gases exercise 
 upon each other no cohesive attraction. Consequently, all 
 gases when brought in contact will intermix, or diffuse 
 through each other uniformly, and in all 
 proportions, the process setting in even in 
 
 opposition to their specific gravities. Thus, 
 if two jars be connected by a narrow tube 
 (Fig. 13), and the lower filled with carbon 
 dioxide, the upper containing hydrogen, dif- 
 fusion takes place through the narrow pas- 
 sage. The light hydrogen descends, and the 
 carbon dioxide, though twenty times heav- 
 ier, rises, and they become equally mingled 
 in both jars. Our atmosphere owes its sta- 
 bility to this principle, its constituents 
 being perfectly intermingled. The bane- 
 ful products of respiration, combustion, 
 and decay, instead of accumulating, are 
 incessantly dissolved away and dispersed Diffusion of Gases 
 in the atmospheric ocean. 
 
 38. Rate of Diffusion of Gases. All gases do not, how- 
 ever, diffuse with equal facility, There is a very simple re- 
 lation between the density of gases and the rapidity of 
 their diffusion, which is expressed by saying that the dif- 
 fusive power of gases varies inversely as the square root 
 of their densities. 
 
 39. Osmose of Gases. If a vessel be divided into two 
 portions by a diaphragm or partition of dry plaster of 
 Paris or some other porous substance, and each half filled 
 with a different gas, diffusion will immediately commence. 
 The rate of diffusion is governed by the law already men- 
 
30 CHEMICAL PHYSICS 
 
 tioned, so long as tue porous plate be very thin, but, when 
 the plate is thick, the law observed is different. A distinc- 
 tion must also be carefully drawn between real diffusion 
 through small apertures and the apparently similar passage 
 of gases through membranous diaphragms, such as caout- 
 chouc or bladder. In this mode of passage, which is called 
 osmose, the rate of interchange de- 
 pends partly on the relative diffusi- 
 bilities of the gases, partly on the 
 different degrees of adhesion ex- 
 erted by the membrane, the gas 
 which adheres most powerfully 
 penetrating the diaphragm most 
 easily. A sheet of India-rubber 
 tied tightly over the mouth of a 
 Passage of (^e^throu-h Mem- wide - mouthed jar containing hy- 
 drogen is soon pressed inward, even 
 
 to bursting. If the jar be filled with air, and placed in an 
 atmosphere of hydrogen, the swelling and bursting take 
 place outward (Fig. 14). If the membrane is moist, the 
 result is likewise affected by the different solubilities of the 
 gases in the water or other liquid which wets it. Though 
 the diffusive power of carbon dioxide is small compared 
 with that of air, yet it easily passes into the latter through 
 wet bladder. This process appears to be brought into 
 play in atmospheric respiration. There is air on one side 
 of the moist lung-membrane, and blood on the other ; oxy- 
 gen is transmitted from the air to the blood, and carbon 
 dioxide from the blood to the air. 
 
 40. Diffusion of Liquids and Solids through Gases The 
 
 diffusion of liquids through gases is a phenomenon of com- 
 mon observation. Water, as well as other liquids, at all 
 temperatures, gives off vapors, which diffuse through the 
 air as fast as they are formed. Solids in some cases do the 
 same thing ice, for example, evaporating very fast when 
 in contact with a current of dry air. The law which gov- 
 
DIFFUSION OF LIQUIDS 31 
 
 erns these diffusions is indentical with that under which 
 other gaseous bodies intermingle. 
 
 41. Diffusion of Liquids. That the molecules of liquids 
 cohere may be seen in the formation and persistence of 
 drops. But, though thus held together by cohesive force, 
 the amount of its action in liquids is never sufficient 
 to unite large masses. The adhesive attraction of the 
 molecules of dissimilar liquids, on the other hand, is in 
 many cases very considerable. Diffusion of liquids through 
 each other, though not universal as that of gases, may be 
 observed in many cases. Thus, if a colored fluid, heavier 
 than water as, for example, ink be placed in the bottom 
 of a tall glass jar filled with water, taking care not to mix 
 the two liquids by agitation, they will, after a time, be 
 found commingled. 
 
 42. Rate of Diffusion of Liquids. Different liquids 
 under entirely like conditions diffuse with very unequal ve- 
 locity. According to Graham, who placed small 
 
 jars, filled with liquids to be tested, in larger FIG. is. 
 ones containing distilled water, as in Fig. 15, 
 and determined the amount of the inner solu- 
 tion that diffused into water in a given time, 
 substances were found to differ greatly in 
 diffusibility, chlorohydric acid proving to be 
 the most diffusible. The equal diffusion of 
 several solutions took place in the following 
 times : Chlorohydric acid, 1 ; common salt, 
 2.33 ; sugar, 7 ; albumen, 49 ; caramel, 98. Substances 
 thus tested are called diffusates. 
 
 Diffusion is generally found to take place more rapidly 
 at high than at low temperatures. It is particularly rapid 
 with solutions of crystallized substances, like sugar, salt, 
 etc., and slowest with those of non-crystalline bodies, which, 
 like gelatine, gum, etc., are capable of forming jellies. 
 The substances of great diffusibility have accordingly been 
 designated as crystalloids, those of low diffusibility as 
 
32 CHEMICAL PHYSICS. 
 
 colloids. Crystalloid bodies form solutions which are mo- 
 bile, the solutions of colloids are viscid. When solutions 
 of colloids are in contact, they hardly diffuse through each 
 other, while the solutions of crystalloids not only diffuse 
 with rapidity through the solutions of other crystalloids, 
 but also through those of colloids. 
 
 43. Osmose of Liquids. When a piece of moistened 
 bladder is tied tightly over the end of a tube placed in a 
 vessel of water, and then filled with alcohol up to the level 
 of the outer liquid, the fluid in the tube will shortly begin 
 to ascend, and may rise to a considerable height (Fig. 16). 
 The external water passes through the membrane and mixes 
 
 with the alcohol, while at the same 
 time a feeble current of alcohol flows 
 the other way and commingles with 
 the water. When different liquids 
 are separated by a membrane in this 
 manner, the one is transmitted fastest 
 which wets the barrier most perfectly. 
 D'ltrochet, who first drew attention to 
 Osmose of LiquM. this matter, named the inflowing cur- 
 rent endosmose, and the outflowing 
 one exosmose ; but these terms are lately less employed, 
 and the phenomena are now known simply as osmose, from 
 a Greek word signifying impulsion. The osmose of liquids 
 is due partly to their adhesive attractions for each other, 
 and partly to the difference of their adhesive attractions for 
 the membrane or diaphragm, the pores of which act as 
 short capillary tubes. 
 
 44. Diffusion of Gases through Liquids, Absorption, The 
 diffusion of gases through liquids is called absorption. 
 It is a phenomenon often noticed, the most common liquid, 
 water, being possessed of high absorptive power. The 
 power of absorption of liquids varies for different gases; 
 pressure or cold increases it, heat diminishes it. The 
 effect of pressure is often employed to induce absorp- 
 
SOLUTION. 33 
 
 tion, as, for example, when water is impregnated with car- 
 bon dioxide to form the common beverage known as soda- 
 water. When a mixture of different gases is brought in 
 contact with a liquid, the absorptive power of the latter 
 for each gas contained in the mixture will, however, be 
 only proportional to the pressure of that gas. and not to 
 that exercised by all the gases present. 
 
 45. Diffusion of Solids through Liquids. The diffusion 
 of solids through liquids, which is termed solution, is fa- 
 miliarly known. In this case the solid, assuming itself the 
 fluid state, disappears, mixing uniformly with the liquid, 
 which remains transparent. The solid is then said to have 
 been dissolved by it, and the liquid employed is called the 
 solvent. A liquid which dissolves one substance may 
 refuse to dissolve another, while substances insoluble in 
 one liquid are dissolved in others. A distinction must, 
 however, be drawn between solution which depends en- 
 tirely on diffusion and solution which is owing in part to 
 chemical change. In the former case, as when sugar is 
 dissolved in water, the sugar may be again obtained in an 
 unaltered condition by the vaporization of the water, while 
 in the latter instance, as when zinc is dissolved in sulphuric 
 acid, the vaporization of the excess cf the solvent will not 
 yield the solid zinc, but an entirely different substance 
 known as zinc sulphate. 
 
 46. Conditions favorable to Solution. Whatever weak- 
 ens cohesion favors solution. Thus, by powdering a sub- 
 stance, cohesion is partially destroyed and the surface in- 
 creased ; solution is consequently promoted. Heat, in 
 most cases, contributes powerfully to solution, its effect 
 being, as is supposed, to weaken cohesion by increasing 
 the distance between the particles of the solid ; yet there 
 are marked exceptions. Water just above the freezing- 
 point dissolves twice as much lime as at the boiling-point, 
 while the solubility of common salt seems hardly affected 
 by temperature. Some substances increase in solubility 
 
34 CHEMICAL PHYSICS. 
 
 regularly as the temperature increases ; in many cases the 
 solubility increases faster than the temperature, and in 
 others it rises with the increasing heat to a certain point, 
 and then declines, while the temperature continues to 
 ascend* 
 
 47. Saturation. A liquid is said to be saturated when 
 it has taken up as large a quantity of a solid as it can dis- 
 solve; in which case the force of cohesion between the 
 particles of the solid is equaled by the adhesion of the 
 solid and liquid to each other. The solvent power of liquids 
 varies much. Water is the great solvent, and so general 
 and important is its use that, in speaking simply of the 
 solubility of a body, water is always understood. 
 
 48. Separation of Solids from Solution. If the adhesive 
 attraction between the solvent and the dissolved solid can 
 be overcome, cohesive attraction resumes its sway, and re- 
 unites the molecules of the solid. This change may be 
 effected in various ways as, when the solvent is removed 
 by evaporation, or, when another liquid, having no chemical 
 effect upon the solid, is mixed with the solution. When a 
 solution is evaporated, the solid is deposited either during 
 the process, or remains at its close. The former is generally 
 the case with crystalloid, the latter with colloid bodies. 
 When the solid is separated by the addition of another 
 liquid, the separation is due to the insolubility of the solid 
 in the liquid added. Thus, if water be mixed with a solu- 
 tion of camphor in alcohol, the camphor separates as a 
 white cloud, at first rendering the liquid turbid, but, after 
 some time, depositing on the bottom of the vessel. The 
 instantaneous separation of a solid from a clear liquid is 
 termed precipitation, and, the deposit formed, a precipitate. 
 As most frequently observed, however, precipitation is not 
 due only to a reversal of solution, but also involves various 
 forms of chemical action. 
 
 49. Diffusion of Solids. The cohesive attraction sub- 
 sisting between the molecules of any solid is much greater 
 
DIFFUSION. 35 
 
 than the like attraction between the molecules of liquids. 
 Their molecules being so much less mobile, diffusion can- 
 not take place directly between solid substances ; but, when 
 they have been first diffused through liquids, and, the re- 
 sulting solutions being mingled together, the mixed liquids 
 are exposed to conditions under which the solids are com- 
 pelled to again separate from the solvent, they will in 
 some cases remain blended with, dissolved in, or diffused 
 through, one another. This takes place, for example, when 
 mixed solutions of magnesic sulphate and zinc sulphate 
 in water are evaporated, and likewise with the mixed so- 
 lutions of many other salts. 
 
 50. Diffusion of Gases through Solids. Occlusion. The 
 fact that gases adhere to solids has already been noticed. 
 Under some conditions, certain solids absorb large quanti- 
 ties of gases, which appear to be truly diffused through the 
 mass of the solid. Thus, the metals iron, platinum, and 
 palladium, have the power of taking up various gases ; the 
 last-named metal is said to be capable of uniting in this way, 
 at ordinary temperatures, with several hundred times its 
 own bulk of hydrogen gas. Although not directly demon- 
 strable by experiment, it is maintained that the hydro- 
 gen, having undergone intense condensation, must be in a 
 state of solidity. This diffusion of gases through solids is 
 termed " occlusion" No phenomena bearing the character 
 of true diffusions of liquids through solids have so far been 
 noticed. 
 
 4. Crystallization. 
 
 51. Under various conditions, and particularly when 
 bodies pass from the liquid or gaseous state to the solid 
 state, their molecules tend to arrange themselves in reg- 
 ular geometrical forms termed crystals, of which Fig. 17 
 may be taken as an example. The substances in which 
 this tendency is marked are said to be crystattizable, and 
 
36 CHEMICAL PHYSICS. 
 
 the process of their formation is called crystallization. 
 Many substances, however, do not crystal- 
 lize. They are, in that case, said to be amor- 
 phous^ their molecular condition being dis- 
 tinguished as amorphism. Water, salt, sugar, 
 are examples of crystallizable, gum and glass 
 of amorphous bodies. 
 
 52. Crystals in Nature. Nature teems with 
 crystals. When it snows, the heavens shower 
 Crystal of tnem down, and ice is a mass of crystals, only 
 Quartz. so blended that we cannot distinguish them. 
 Geology teaches that the materials of the globe were for- 
 merly in a melted state, so that in the slow process of solidifi- 
 cation the opportunity was offered on the grandest scale for 
 the formation of crystals. Hence vast rocky systems have 
 their constituents crystallized, and are known as the crystal- 
 line rocks. Metallic ores are nearly all crystallized, and im- 
 mense regions of granite are but mountains composed of 
 crystals, varying in size from particles that can only be 
 distinguished by the aid of the microscope up to masses 
 sometimes weighing several hundred pounds. 
 
 53. Artificial Crystals. Crystals may be artificially 
 produced in various ways, as from solutions, by the slow 
 cooling of bodies ii a state of fusion, by the condensation 
 of gases, or even by rearrangement of the molecules of 
 solids. When chemical action produces bodies not before 
 present, they very frequently make their appearance in the 
 form of crystals. 
 
 54. Crystals by Solution. It has already been stated 
 that the solvent power of liquids for any solid body is gen- 
 erally greater at high than at low temperatures. When, 
 therefore, a hot, saturated solution of anv such substance 
 as, for example, alum in water is allowed to cool, a por- 
 tion of the solid separates, and, in doing so, assumes the 
 form of crystals. The liquid which remains after their forma- 
 tion has ceased is called the mother-lye, or mother-l 'qitor. 
 
FORMATION OF CRYSTALS 37 
 
 55. Crystals by Fusion. Nearly all bodies when cooled 
 after melting take the crystalline form, though this may 
 not be at first perceptible. The spaces left between the 
 crystals which first form are completely filled up by the 
 portions which solidify afterward, so that 
 
 fracture reveals only a general crystalline 
 structure, as may be observed in broken 
 cast-iron and zinc. Common sheet-tin is 
 beautifully crystallized, though it is not 
 apparent. If with weak acid we wash off 
 the thin surface-film of metel, which had 
 cooled too rapidly to crystallize, the struct- sulphur-Crystals. 
 ure will be revealed of a beautiful feathered 
 appearance. To obtain crystals by fusion, the excess of 
 liquid must be removed from around those which are first 
 formed. In this way beautiful sulphur-crystals are pro- 
 duced. If a quantity of this substance be melted, and 
 then allowed to cool till a crust forms upon the surface and 
 sides of the vessel, crystals will be formed within, which 
 may be seen either by breaking the vessel (Fig. 18), or by 
 piercing the crust and draining off the interior liquid. 
 
 56. By Sublimation. Solid substances vaporized (sub- 
 limed) may be condensed in the crystalline form, as iodine, 
 sulphur, arsenic. Camphor thus vaporizes and condenses 
 in brilliant crystals upon the sides of apothecaries' jars by 
 the rise and fall of common temperatures. 
 
 57. Crystallization in the Solid State. The strong ten- 
 dency of molecules to assume crystalline shape is mani- 
 fested even in solids. Thus sugar-candy, at first transparent 
 and amorphous, after some time becomes opaque and crys- 
 talline. Glass, by long-continued heat, though it does not 
 melt, becomes also opaque and crystalline (JReaitmur^s por- 
 celain). Brass and silver, when first cast, are tough and 
 uncrystalline, but, when repeatedly heated and cooled, they 
 become brittle, and show traces of crystallization. Even 
 the little liberty the particles obtain by the motions of 
 
38 CHEMICAL PHYSICS. 
 
 heating and cooling they improve to assume the crystal- 
 line condition. Tins is still better seen where the particles 
 of bodies are thrown into motion by blows and vibration. 
 Metals, by hammering, lose their ductility and tenacity, 
 and become brittle and crystalline. Coppersmiths, when 
 hammering their vessels, frequently anneal them, to pre- 
 vent their flying to pieces ; that is, they heat them, and 
 then allow them to slowly cool. Thus also bells, long 
 rung, change their tone ; cannon, after frequent firing, lose 
 their strength, and are rejected ; and so the perpetual jar 
 and vibration of railroad-axles and the shafts of machinery 
 gradually change the tough, fibrous w rough t-iron into the 
 crystalline state, weakening them and increasing their lia- 
 bility to fracture. 
 
 58. Crystals by Decomposition. It is also possible, by 
 the decomposition or other chemical change wrought in 
 various bodies, to obtain substances not before present in 
 the shape of crystals. Thus, many compound gases, when 
 passed through red-hot tubes, deposit crystals, and solutions 
 of metallic salts are decomposed by the galvanic current, 
 with the separation of the metals in the crystalline form. 
 
 59. Phenomena attending Crystallization. This change 
 of state is usually attended by change of bulk. Water in 
 freezing expands to a considerable degree, and with great 
 power ; 1,000 parts of water are dilated to 1,063 parts of 
 ice ; and the force exerted by the particles in changing po- 
 sitions is so enormous as to burst the strongest iron vessels. 
 Heat is always manifested when crystals are formed, in 
 proportion to the rapidity of the change from the liquid to 
 the solid state. Light has also occasionally been noticed 
 to accompany the process, but its cause is not explained. 
 Muddy and impure solutions often yield the largest crystals, 
 and the presence of foreign bodies which do not themselves 
 crystallize may thus modify the form which the crystal as- 
 sumes. For example, common salt usually crystallizes in 
 the form of a cube (Fig. 27), but, if urine be present in the 
 
CONDITIONS OF CRYSTALLIZATION. 39 
 
 solution, it takes the form of the octahedron. When a 
 crystal is broken, there is a tendency to repair it ; it con- 
 tinues to increase in every direction, but the growth is 
 most active upon the fractured surface, so that the proper 
 outline of the figure is restored in a few hours. 
 
 60. Favorable and Unfavorable Conditions. Vibratiou 
 may so disturb the process as to check the growth of those 
 which have commenced, and start a second crop upon them. 
 Crystals are seldom found perfect, being generally irregular, 
 
 FIG. 20. 
 FIG. 19. 
 
 Crystal of Alum. Masses of Imperfect Alum-Crystals. 
 
 disguised, and distorted. Perfect alum-crystals, for ex- 
 ample, are regular octahedrons (Fig. 19), but Fig. 20 shows 
 how they appear in the large vat of the manufacturer. 
 Sometimes the attractions are so balanced that a jar or 
 agitation is needed to start the action. In a perfectly still 
 atmosphere, water may be cooled eight or ten degrees 
 below the freezing-point without congealing, but the vibra- 
 tion of the vessel produces a sudden crystallization of part 
 of the liquid into ice. Any solid body intruded into the 
 liquid, by adhesion, may destroy the equilibrium and begin 
 the play of the crystallizing attractions. Thus, threads 
 are stretched across vessels containing solutions of sugar, 
 and form a nucleus around which rock-candy is crystal- 
 lized. 
 
40 CHEMICAL PHYSICS. 
 
 61. Forms of Crystals. Leaving disturbing influences 
 out of view, all liquids tend to assume the spherical shape 
 of drops, We might, therefore, anticipate that, in return- 
 ing to the solid state, their molecules would still group 
 themselves round centres into spheres. But, although 
 something of this kind may take place with amorphous 
 bodies, the forms produced in the solidification of crystal- 
 lizable substances are angular, and bounded on all sides by 
 plane surfaces symmetrically arranged. 
 
 62. Elements of Crystalline Form. Although there is 
 an almost endless diversity in the forms which substances 
 take when crystallizing, crystals are built i; p in obedience 
 to universal geometrical laws, and present in the most 
 varied forms certain constant elements of construction. All 
 crystals are solids of the class known to geometry as 
 polyhedrons they are bounded by plane surfaces, or faces, 
 which meet by twos in stright lines, or edges, inclosing be- 
 tween them interfacial angles. The faces, polygons in 
 shape, present three or more plane angles, and three or 
 more of these, having a common apex, inclose a solid 
 angle. 
 
 63. Axes of Crystals. Single crystals often present a 
 large number of faces, but the position of all of these bears 
 a fixed mathematical relation to that of the faces of simpler 
 forms, so that the former may be calculated when the latter 
 are known. These simple shapes, from which the others 
 are said to be derived by modification, are termed primary 
 forms. The primary forms, as usually assumed, are solids 
 bounded by six quadrilateral faces meeting in twelve edges 
 and eight solid angles. Every one of the faces will be 
 opposite and parallel to another ; therefore when their 
 centres are connected by straight lines, these must be three 
 in number, and intersect each other in the centre of the 
 primary. In some cases it has been found more convenient 
 to assume four. They are termed the axes of the crystal, 
 and it is known that all the faces observed in any crystal, 
 
FORMS OF CRYSTALS. 
 
 41 
 
 when extended to meet them, will always do so at- dis- 
 tances from the centre, bearing a very simple numerical re- 
 lation to the distances at which they are met by the faces 
 of the primary form. The different geometrical elements 
 of crystalline form are thus mutually dependent ; hence, 
 when a certain number of these are known, the rest may 
 be computed. Accordingly, when it is desired to deter- 
 mine the position of all the faces, the length of the axes, 
 etc., of any crystal, all that is required is the measurement 
 of some of the interfacial angles, an operation performed 
 by the aid of certain instruments called goniometers. 
 
 64. Systems of Crystallization. All the different crys- 
 talline forms which have been observed have been classified 
 and arranged in a number of groups termed systems of 
 crystallization. There are six of these systems, and the 
 forms belonging to each of these differ from the forms be- 
 longing to the other systems, either in the number or the 
 relative length of the axes, or in re- 
 gard to the angles which the axes 
 
 form at their intersection in the cen- 
 tre of the crystal. 
 
 65. Monometric or Regular Sys- 
 tem. In the forms of this system 
 (Fig. 21) the axes are three in num- 
 ber, of equal length, and intersect 
 
 each other at right angles. Crystals of this system ex- 
 pand equally in all directions by heat, and refract light 
 in the ordinary manner. Common 
 salt and iron pyrites are exam- 
 ples. 
 
 66. Dimetric, Quadratic, or Square 
 Prismatic System. In this system 
 there are three axes intersecting each 
 other at right angles. Two are equal, 
 the third is of a different length. Its 
 forms expand by heat equally in two directions only, and split 
 
 FIG. 21. 
 
 Regular System. 
 
 FIG. '2-2. 
 
 Square Prismatic System. 
 
CHEMICAL PHYSICS. 
 
 the ray of light passing through them (double refraction), as 
 do also the forms of the four systems remaining to be no- 
 ticed. Examples : stannous oxide and mercuric cyanide. 
 Trimetric, Rhombic, or Right Prismatic System. In 
 
 67 
 
 FIG. 23. 
 
 Right Prismatic System. 
 FIG. 24. 
 
 Oblique Prismatic System. 
 FIG. 25. 
 
 the forms of this system, the three 
 axes are also at right angles to 
 each other, but all three of unequal 
 length. Crystals of this system 
 (Fig. 23) expand unequally in the 
 three directions of the axes. Nitre 
 and topaz may be taken as examples. 
 
 68. Oblique Rhombic or Oblique 
 Prismatic System, The forms of 
 this system have three axes, which 
 may be unequal (Fig. 24). Two 
 are placed at right angles to each 
 other, and the third is oblique to 
 one and perpendicular to the other. 
 Sodic sulphate and borax are com- 
 mon examples. 
 
 69. Oblique Rhomboidal or Dou- 
 bly Oblique Prismatic System. In 
 this there are three axes, which may 
 be all unequal and all oblique (Fig. 
 
 Doubly Oblique Prismatic System. 35). Examples I CUpHc sulphate 
 
 and bismuthous nitrate. 
 
 70. Rhombohedral or Hexagonal 
 System. The forms of this system 
 (Fig. 26) differ from those of the 
 others in having fotir axes, three of 
 which are equal, in the same plane, 
 
 Khombohedrai System. an( j i nc li ne d at angles of 60, while 
 the fourth is of different length and perpendicular to the 
 other three. Examples : quartz, Iceland spar, and ice. 
 
 71. Axial Polarity. The axes of crystals are not mere 
 imaginary lines. The force which builds the crystal works 
 
 FIG. 2(5. 
 
POLARITY IN CRYSTALLIZATION. 43 
 
 unequally, and endows it with different powers in different 
 directions. In those crystals where the axes are all equal, 
 light, heat, and electricity, are conducted equally in every 
 direction. But, where the axes are unequal, conduction 
 of heat and electricity, hardness, elasticity, transparency, 
 expansion by heat, and luminous refraction, are corre- 
 spondingly unequal, showing an actual difference of struct- 
 ure in the different directions, just as wood varies in quali- 
 ties when tested with or across the grain. This perfect 
 regularity of structure in crystals, by which they manifest 
 different powers in different directions, can only be ex- 
 plained by supposing that attraction, in causing molecules 
 to cohere in crystalline combination, does not act equally 
 all around each molecule, but between certain sides or 
 parts of one and corresponding parts of another ; so that, 
 when allowed to unite according to their natural tenden- 
 cies, they always assume a certain definite arrangement. 
 This property of molecules is called polarity, because in 
 these circumstances they seem to resemble magnets^ which 
 attract each other by their poles. 
 
 72. Cleavage. If we apply the edge of a knife to a 
 piece of mica, it may be cleft into thinner plates, and these 
 may again be separated into the thinnest films. Nearly all 
 crystals will thus separate in certain directions, disclosing 
 polished surfaces, and showing the order of formation of 
 successive parts. This mechanical splitting of crystals is 
 termed cleavage. Amorphous solids do not cleave, but 
 fracture irregularly and in any direction. 
 
 73. Derivation of Form. The cube (Fig. 27) may be 
 taken to illustrate change of figure, and this is chiefly ef- 
 fected by replacing edges and angles by planes. The cube 
 has twelve edges and eight solid angles. If plane-surfaces 
 are substituted for the edges, we get the secondary form 
 (Fig. 28). If we replace the solid angles by planes, we 
 have the form Fig. 29. If both these replacements occur 
 together, the more complex (Fig. 30) results. If the 
 
44 
 
 CHEMICAL PHYSICS. 
 
 edges of the cube be replaced until all traces of the original 
 planes disappear (Fig. 31), the rhombic dodecahedron is 
 formed. And, if the solid angles be replaced by planes to 
 the same extent, we get (Fig. 32) the regular octahedron. 
 
 FIG. 27 
 
 FIG. 28. 
 
 FIB. 30. 
 
 FIG. 81. 
 
 Transformations of the Cube. 
 
 We have said that the secondary or derived forms of 
 crystals are almost innumerable. Six hundred modifica- 
 tions of the six-sided prism have been enumerated by Dr. 
 Scoresby among snow-flakes, while M. Bournon, in a two- 
 volume treatise, has delineated eight hundred different 
 forms of the mineral calcite (calcic carbonate). Hauy has 
 described a single crystal which had one hundred and 
 thirty-four faces. 
 
 74. Isomorphism. When different substances take upon 
 them the same primary form or modifications of it, they 
 are said to be isomorphous, and the law which governs 
 their identification is called isomorphism, from the Greek 
 isos, equal, and morphe, form. Thus gold, silver, copper, 
 alum, salt, and many other bodies, all crystallize in forms 
 of the monometric system, which perfectly resemble each 
 other. Such perfect identity is, however, only met with in 
 forms of this system ; in all others, the lengths of the axes, 
 
DIMORPHISM. 45 
 
 or their inclinations, or both, varying slightly, produce al- 
 ways small differences in the geometrical elements of their 
 forms. For this reason the term homceomorphous, signify- 
 ing similarly formed, has sometimes been employed in 
 place of the one above mentioned. Isomorphous bodies, 
 when crystallizing from mixed solutions, frequently remain 
 diffused through one another in the solid state. Some 
 substances crystallize in two different forms, and are called 
 dimorphous. Thus, sulphur deposited from solution takes 
 one form, and when cooled from melting, another. Nitre 
 crystallizes in one shape in large quantities, and takes an- 
 other shape in small quantities. Substances crystallizing 
 in three forms are called trimorphous. 
 
 75. Molecular Motions. The changes considered in this 
 chapter are resolvable into molecular movements. It is 
 held that the molecules are always in motion, and by vir- 
 tue of their motions are centres of molecular energy. The 
 molecular units are supposed to have three kinds of mo- 
 tion. In solids they maintain their relative places, but 
 vibrate at such varying rates as to emit all the colors of 
 the spectrum. In liquids the molecules are loosened from 
 their structural relations, and circulate among each other 
 so rapidly as to give rise to energetic liquid diffusion. 
 When the violence of these motions is increased by heat, 
 the molecules are shot beyond cohesive restraint, and as- 
 sume the condition of gas. No longer influenced by mu- 
 tual attractions, they are now supposed to move with far 
 greater energy, flying about in all directions, in extremely 
 short, straight paths, striking and repelling each other, and 
 giving rise to an expansive pressure, known as gaseous 
 tension. This is the molecular explanation of the phe- 
 nomena presented by the three states of matter. 
 
CHAPTER III. 
 
 II EAT. 
 
 1. Thermal Expansion. Thermometers. 
 
 76. HEAT exerts a very powerful influence over the 
 states of matter, and is so important for the production 
 of chemical effects, that the chemist has been called the 
 " Philosopher by Fire." The general science of heat is 
 termed Thermotics, from the Greek thermos, hot, which 
 gives us also the words thermal, thermometer, etc. 
 
 77. Expansion of Solids. Heat is a force of repulsion, 
 and its general effect upon matter is to separate its parti- 
 cles, or to expand it. All bodies of uniform constitution 
 expand equally in all directions, when heated, while other 
 substances, as crystals and wood, in which the particles 
 are differently arranged in different directions, expand un- 
 equally. With a given amount of heat, the same sub- 
 stance always expands to the same 
 
 FIG. 33. degree ; but the same quantity of 
 
 ( ' ' ' 'L-J l^lll ' "-"-^ heat causes different substances to 
 expand unequally. This may be 
 shown by riveting together thin 
 
 Expanston of Compound Bars. sli P s of different metals, for in- 
 stance zinc and iron, into a straight 
 
 bar, Fig. 33. When dipped into hot water it is warmed, 
 and the zinc, expanding most, becomes longest ; the bar 
 curves, the zinc forming the convex side. If placed in ice- 
 water, the zinc contracts most, and the bar curves in the 
 opposite direction. Heat thus antagonizes cohesion : and 
 
MEASUREMENT OF HEAT. 47 
 
 a quantity of heat, applied at a high temperature, produces 
 more expansion than the same amount at a low one. 
 
 78. Expansion of Liquids. If sufficient heat be imparted 
 to a solid, it overcomes cohesion, and liquefies it. Liquids, 
 thus produced by heat, are also expanded by it, and to a 
 much greater degree than solids. While iron increases 
 from freezing to boiling but -^ of its volume, water ex- 
 pands ^5, and alcohol . 
 
 79. Expansion of (rases. But liquids cannot be indefinite- 
 ly expanded ; a sufficient repulsion of their atoms changes 
 them into gases. As a general law gases expand much 
 more than liquids, although certain liquids, as sulphur 
 dioxide, are among the most expansible bodies known. 
 As there are no varying cohesions to overcome, gases ex- 
 pand very nearly alike, increasing from the freezing to the 
 boiling of water more than one-third of their bulk. 
 
 80. Measurement of Heat As the effect of heat is ex- 
 pansion, the measurement of expansion becomes the meas- 
 urement of the force. The common instruments for meas- 
 uring heat are called thermometers. They measure not 
 quantity of heat, but temperature. Heat is the force pro- 
 ducing the effect ; and temperature the intensity with 
 which it acts. Liquids are better adapted as heat-meas- 
 urers than either solids or gases ; as in solids the expan- 
 sion is too slight to be easily perceptible, and gases are 
 too sensitive to changes of atmospheric pressure to fit them 
 for this purpose. 
 
 81. Mercurial Thermometer. To make this instrument, 
 a fine glass tube, with a bulb upon the end, is partly filled 
 with mercury. The air is expelled from the rest of the tube 
 by heating it till the mercury rises by expansion to the 
 top, and at that moment the glass is hermetically sealed 
 by melting the end of it with a blow-pipe. As it cools, 
 the mercury falls in the tube, leaving a vacuum above. 
 
 Mercury has several important advantages as a ther- 
 mometric fluid. It is readily obtained pure, and does not 
 
48 
 
 CHEMICAL PHYSICS. 
 
 FIG. 84. 
 
 adhere to the tube ; it is sensitive to heat, expands witli 
 greater regularity than most liquids, and has a range of 
 700 between freezing and boiling. Temperatures below 
 the freezing point of mercury are usually determined by 
 thermometers filled with alcohol, tinged with some col- 
 oring matter, to make it visible. As mercury boils at 660, 
 temperatures above that point are measured by the expan- 
 sion of the air, or by the aid of thermo-electric currents, the 
 metals iron and platinum being sometimes selected for the 
 combination. 
 
 82, Thermometric Scales, The sealed tube is attached 
 to a brass plate engraved with the thermometric scale, Fig. 
 34, or, for chemical work, the divisions are en- 
 graved directly on the glass tube. It is then 
 dipped into ice-water, and a mark made oppo- 
 site the top of the column of mercury, called 
 the freezing-point. It is now introduced into 
 boiling water, and the height to which the col- 
 umn rises is marked as the boiling-point. These 
 are natural standard points which serve as a 
 basis for the division of the scale. In the Cen- 
 tigrade thermometer of Celsius, the freezing- 
 point is called zero, and the interval between 
 that and the boiling-point is marked off into 
 100 equal spaces called degrees. In Reaumur's 
 scale the same space is divided into 80 degrees. 
 The scale named after its inventor, Fahren- 
 heit, and which has, unfortunately, come into 
 general use in England and this country, is 
 not so simple. He divided the space between 
 freezing and boiling into 180 degrees ; but, 
 instead of starting at the freezing-point, he 
 (^Appendix.) thought he would find the lowest possible cold, 
 and make that zero. So with snow and ice he got the 
 mercury down to 32 below the freezing-point, and com- 
 menced counting there. On this scale, therefore, freezing 
 
 40-B-40 
 
CONDUCTION OF HEAT. 49 
 
 occurs at 32, and boiling at 212. The several scales are 
 distinguished by their initial letters F., C., and R. The 
 Centigrade, affording decimal subdivisions, is the most 
 simple and rational, and is gradually coming into use for 
 scientific purposes. In all of these scales, degrees belcw 
 zero are distinguished from those above by prefixing the 
 minus-sign ( ). 
 
 2. Transference of Heat. 
 
 83. Conduction of Heat. Heat moves, or is transferred, 
 in several ways, known as conduction, convection, and ra- 
 diation. If several marbles are stuck by wax to a copper 
 
 FIG. 36. 
 FIG. 85. 
 
 Conduction of Heat Non-conduction of Liquids. 
 
 rod, Fig. 35, and heat be applied to one end, it gradually 
 passes along the rod, the wax is melted, and the marbles 
 drop off successively. The heat, in this case, is said to be 
 conducted. Generally, the more dense a body is, the better 
 it conducts ; solids are better conductors than liquids, and 
 liquids than gases. As a class, metals are the best con- 
 ductors, but they differ much among themselves in this re- 
 spect. The imperfect conduction of liquids may be shown 
 by filling a glass tube with water, inclining it over a lamp, 
 and applying the flame at the upper end, Fig. 36. The 
 water will boil at the surface, while at the bottom there 
 may still be ice for a considerable time. Dry air is one of 
 the poorest conductors. Loose materials, as wool, cotton, 
 
50 CHEMICAL PHYSICS. 
 
 sawdust, are bad conductors, chiefly owing to the air in- 
 closed in their spaces. 
 
 81 Influence of Internal Arrangement. A slice of 
 quartz cut across its axis, Fig. 37, was perforated with a 
 small hole and covered with a layer of white wax. A wire 
 was then inserted through the orifice and heated by an 
 electric current. The wax melted in an exact circle, which 
 showed equal conduction in all directions. A slice cut 
 
 FIG. ST. FIG. 38. 
 
 Equal Conduction. Unequal Conduction. 
 
 parallel with the axis, as in Fig. 38, treated in the same 
 way, gave an oblong outline of the melted wax, showing 
 that heat travels with more facility along the crystalline 
 axis than across it. The metal bismuth conducts both 
 heat and electricity better along the planes of cleavage 
 than across them. The same thing has been found in 
 reference to wood ; it transmits heat better along the 
 course of the fibres than across them. 
 
 85. Conduction influences Sensation. The carpet feels 
 warmer to the naked feet than oil-cloth, because the latter 
 conducts away the heat faster from the skin, although both 
 are at the same temperature. If the hand be placed upon 
 silver at 120, it will be burned, owin^ to the rapidity with 
 which heat leaves the metal and enters the flesh. Water 
 will not scald the hand if it be held quietly in it till it 
 reaches 150, while the contact of air at 250 or 300 may 
 be endured. 
 
 86. Convection. Although liquids and gases are poor 
 conductors, yet, from the mobility of their particles, they 
 may be rapidly heated by a process of circulation or con- 
 
CONVECTION OF HEAT. 51 
 
 section. If heat be applied to the bottom of a vessel con- 
 taining water, the lower portion of the liquid is warmed, 
 expands, becomes lighter, and ascends, 
 its place being taken by the colder 
 liquid at the sides thus forming a set of 
 currents which diffuse the heat through 
 the whole mass. 
 
 Gases are heated in the same man- 
 ner. The warm air in contact with a 
 stove or other heated body becomes 
 lighter, and ascends, while the colder 
 and heavier air rushes in to supply its 
 place. This, becoming heated, also as- 
 
 Circulation of Heat 
 
 cends, and thus a system of currents is 
 established, which diffuses warmth through the apart- 
 ment. 
 
 87. Badiation of Heat While standing at some dis- 
 tance from a hot stove we are warmed by it. It emits a 
 constant stream of heat-rays in straight lines, at a very 
 high velocity, and which have the power of raising the 
 temperature of any body that receives them. Heat moving 
 in this way is called radiant heat, and the act of transfer- 
 ence radiation. All bodies radiate heat at all times, the 
 rate of emission depending upon the temperature. If a 
 cannon-ball, at 1,000, be placed near another at 100, they 
 radiate heat to each other, but that at 1,000 loses it faster 
 than it receives it, and its temperature falls ; while that 
 at 100 receives heat faster than it parts with it, and its 
 temperature rises. After a time they both come to the 
 same temperature, the radiations are equal, and an equilib- 
 rium is established. All bodies are thus exchanging heat 
 with each other, and tending to an equilibrium of temper- 
 ature. 
 
 88. Influence of Surface. Radiation is influenced by 
 surface. A cubical vessel of tin had one of its sides coated 
 with a layer of gold, a second with silver, a third with cop- 
 
52 CHEMICAL PHYSICS. 
 
 per, and a fourth with varnish. The vessel was then filled 
 with hot water, and placed at a little distance from the 
 thermometer. When the hot gold surface is turned to it, 
 scarcely a trace of effect is observed, and so with the cop- 
 per and silver ; but, when tlie varnished surface is brought 
 round, a stream of heat strikes the bulb, and the mercury 
 quickly rises. The physical condition of the surface also 
 influences radiation rough, uneven surfaces being more 
 active than bright polished ones ; hence, if the metal is 
 covered with woolen or velvet, its radiant power is in- 
 creased. Bright metallic vessels, therefore, retain the 
 heat much longer than those which are tarnished. 
 
 89. Absorption. Good radiators are good absorbers of 
 heat ; that is, the surfaces which can easily give out heat 
 will easily take it in. On the contrary, a bad radiator, as 
 a bright metallic surface, is a bad absorber, and therefore 
 a good reflector. Hence, the thinnest metallic film upon 
 a surface powerfully protects it from the action of radiant 
 heat. 
 
 90. Dew. When the radiation of bodies is not com- 
 pensated, their temperature sinks. Such is the case with 
 objects exposed to the sky on clear nights. If good radia- 
 tors, they rapidly lose heat, and, cooling below the tem- 
 perature of the air, at length begin to condense its moist- 
 ure upon their surfaces : this is dew. The best radiators, 
 as grass, leaves of trees, and porous soils, receive the most 
 dew, while poor radiators, as smooth stones, and hard, com- 
 pact soils, remain almost dry. Clouds radiate back the 
 heat received from the earth, so that cloudy nights are 
 warm and dewless. If the temperature sinks lower than 
 32, the moisture is frozen, and becomes frost. 
 
 91. Two Kinds of Radiant Heat. It is well known that 
 radiant heat is constantly associated with light, and the 
 laws of its movement are the same as those of light. That 
 which accompanies light is called luminous heat ; but that 
 which is emitted from dark bodies, as from a stove below 
 
RADIATION OF HEAT. 53 
 
 redness, or from the hand, is called obscure, or dark heat. 
 But dark radiant heat obeys the same laws of motion as 
 light and luminous heat. 
 
 92. Diathermancy. Bodies which transmit heat freely 
 are called diathermic,' those which arrest it, athermic. 
 Rock-salt (common salt in blocks) is the most perfect dia- 
 thermic body, allowing all the heat-rays those from the 
 sun and the hand to pass through with equal freedom. 
 What glass is to light, a plate 
 
 of rock-salt is to heat, and it has FlG - 40- 
 
 hence been aptly termed " the 
 glass of heat." This substance 
 is therefore adapted to make 
 prisms and lenses for the con- 
 centration and dispersion of 
 dark heat. If a heated ball 
 
 , , j , , , f Glass intercepting, and Rock-Salt 
 
 be placed between a plate ot transmitting Heat, 
 
 glass and one of rock-salt, Fig. 
 
 40, and bits of phosphorus be laid upon stands beyond, 
 though the salt be many times thicker than the glass, the 
 dark heat passes freely through it, igniting the phos- 
 phorus, while it is quite arrested by the glass. 
 
 93. Absorption of Heat by Aqueous Vapor. Aqueous 
 vapor, when condensed to minute particles of water, is 
 highly opaque to the dark radiations. Where the atmos- 
 pheric gases arrest one ray of obscure heat, the small pro- 
 portion of water suspended in the air stops sixty or seventy 
 rays. Luminous solar heat penetrates the air, and, falling 
 upon the earth, is changed into obscure heat, which cannot 
 be radiated back into space. The watery particles are thus 
 the " barb " of the atmosphere which prevents the escape of 
 the heat, and thus maintains the temperature of the earth. 
 It follows that, if aqueous vapor were withdrawn from the 
 air, the terrestrial heat would so quickly radiate away 
 that the earth would soon become uninhabitable ; the in- 
 visible watery element of the air is, therefore, the blanket 
 
54 CHEMICAL PHYSICS. 
 
 which keeps the world warm. In all those localities where 
 the atmosphere is dry, the nightly loss of radiant heat is 
 great, so that even in the burning desert of Sahara there 
 is nocturnal freezing. 
 
 3. Changes of Molecular Aggregation. 
 
 94. Liquefaction, Heat applied to solids overcomes 
 their cohesion and changes them to liquids. That degree 
 of temperature which is required to liquefy a substance is 
 called its melting-point. From hundreds of degrees below 
 zero up to thousands above, the various substances of Na- 
 ture melt at diiferent temperatures, showing that each re- 
 quires its particular amount of heat-force to throw it into 
 the liquid state. 
 
 95. Latent Heat. In effecting this change, a certain 
 imount of heat disappears, or seems to be used up in the 
 process ; and, as it can no longer be detected as sensible 
 heat, it is spoken of as latent heat. If we take an ounce of 
 ice at 32, and one of water at 174, and put them together, 
 when the ice is melted, we shall have two ounces of water 
 at 32. The ounce of hot water has, therefore, lost 142 
 of its heat in melting the ice, which amount is the " latent 
 heat " of the resulting water. The amount of heat thus 
 consumed in altering the form of bodies, without raising 
 their temperatures, is different in different cases. 
 
 96. Specific Heat. If we expose equal weights of differ- 
 ent substances to the same source of heat, they do not all 
 receive it with equal readiness or in equal amounts ; some 
 will receive more than others. Water requires thirty times 
 as much heat as mercury to raise an equal weight of it 
 through the same number of degrees. Hence bodies are 
 said to have different capacities for heat, and, as each sub- 
 stance seems to require a particular quantity for itself, that 
 quantity is called its specific heat. The art of measuring 
 the specific heat of bodies is called calorimetry. 
 
CHANGES OF STATE. 55 
 
 97. Heat liberated by Freezing. If the change of a 
 solid to a liquid consumes force, the reverse change must 
 produce it j the force therefore reappears as heat, upon 
 freezing. As the thawing of snow and ice in spring is de- 
 layed by the large amount of heat that is expended in the 
 forming of water, so the freezing processes of autumn are 
 delayed, and the warm season -prolonged, by the large 
 quantities of heat that escape into the air, from the chang- 
 ing of water into ice. 
 
 98. Freezing Mixtures. Advantage is taken of the ab- 
 sorption of heat in liquefaction to produce freezing mix- 
 tures, the most common example of which is salt and ice. 
 In this case the salt melts the ice to unite with its water, 
 which in turn dissolves the salt, so that both solids are 
 changed to liquids. These changes require large amounts 
 of heat, which is absorbed from surrounding bodies ; the 
 cold produced sinking the thermometer 40 below zero. 
 
 99. Ebullition. When water is gradually heated, minute 
 bubbles are formed at the bottom of the vessel, which rise 
 a little way, are crushed in, and disappear. These consist 
 of vapor or steam, which is formed in the hottest part of 
 the vessel, but, as they rise through the colder water above, 
 are cooled and condensed. As the heating continues, these 
 rise higher and higher until they reach the surface and 
 escape into the air, producing that agitation of the liquid 
 which is called boiling or ebullition. 
 
 100. Boiling-Point. The temperature at which this 
 takes place is called the boiling-point, and it varies with 
 different liquids and in different circumstances. It is 
 slightly influenced by the nature of the containing vessel. 
 To glass and polished metallic surfaces liquids adhere with 
 greater force than to rough surfaces ; and, before vaporiza- 
 tion can occur, this adhesion must be overcome. Sub- 
 stances dissolved in a liquid also raise its boiling-point on 
 account of their adhesion. Under ordinary circumstances, 
 water boils at 212, but, saturated with common salt, its 
 
56 CHEMICAL PHYSICS. 
 
 boiling-point is 224. It has lately been shown that the 
 amount of air dissolved in the water affects its boiling- 
 point, as it presses the watery particles asunder, and thus 
 aids them to take on the gaseous state. Water purged 
 of its air by long ebullition has been heated to 275 with- 
 out boiling. When it did boil, the water was instantly 
 changed into vapor with a loud explosion, the cohesion of 
 its particles being suddenly overcome, like the snapping 
 of a spring, by the repulsive power of the accumulated 
 heat. But the most important circumstance that influences 
 the boiling-point is the pressure of the atmosphere. This 
 resists the rising vapor, and, as it fluctuates, the boiling- 
 point varies. The pressure becomes lighter as we ascend 
 into the atmosphere, and the temperature of the boiling- 
 point is correspondingly diminished, so that boiling water 
 is less hot in high altitudes than in low ones. 
 
 101. The Spheroidal State. Water adheres to most 
 surfaces, but heat destroys this attraction, and, if drops 
 of it fall upon a red-hot plate of metal, they gather into 
 spheroids, roll about, and evaporate very slowly. Fig. 41 
 represents a mass of water in the spheroidal state. In this 
 
 FIG. 42. 
 FIG. 41. 
 
 Spheroid of Water. Its Explosion. 
 
 case the heat of the metal produces a layer of vapor which 
 supports the drop, so that it does not touch the surface, 
 but is driven about by currents of heated air. The tem- 
 perature of the spheroid never reaches the .boiling-point of 
 the liquid, as the vapor, being a non-conductor, does not 
 transmit the heat from the metal, and, besides, it is kep| 
 
HEAT IN EVAPORATION. 57 
 
 cool by evaporation from its surface. If the temperature 
 of the plate be allowed to fall to a point at which the 
 water wets its surface, it will be suddenly scattered in a 
 kind of explosive ebullition, Fig. 42. 
 
 102. Vaporization. The change of solids or liquids by 
 the force of heat to vapor is called vaporization. Sub- 
 stances which are readily converted into vapor are said to 
 be volatile, while those which are vaporized with difficulty 
 are termed fixed or non-volatile. The slow formation of 
 vapor from the surfaces of bodies is called evaporation. It 
 goes on at all temperatures, even from the surface of ice 
 and snow, but is rapidly increased as the temperature rises. 
 
 103. Heat of Vaporization. A much larger amount of 
 heat is spent in converting liquids into vapors than in 
 changing solids to liquids, while the vapors are no hotter 
 than the liquids from which they are formed. The heat 
 has been consumed in producing the repulsive motion and 
 the consequent enormous expansion of the gaseous body. 
 If the liquid is exposed to the air, it is impossible to raise 
 its temperature above its natural boiling-point. All the 
 heat added after boiling commences is carried away by the 
 vapor. Water boiling violently is not a particle hotter 
 than that which boils moderately. 
 
 104. The quantity of heat which disappears during 
 evaporation is very large. With the same intensity it 
 takes 5 times as long to evaporate a pound of water as it 
 does to raise it from freezing to boiling ; it hence receives 
 5| times as much heat. If, therefore, 180 were required 
 to boil the pound of water, nearly 1,000 are necessary to 
 change it to vapor, and, being spent in producing the 
 change of state, it of course disappears as sensible heat. 
 This quantity is, therefore, the " latent " heat of steam. If 
 the process be reversed, and the vapor be made to reas- 
 sume the liquid form, the heat reappears. The condensa- 
 tion of a pound of steam will raise 5^ pounds of water 
 from the freezing to the boiling point. 
 
58 CHEMICAL PHYSICS. 
 
 105. Cooling Effects of Evaporation. As evaporation 
 consumes heat, it is a cooling process. We experience 
 this in the cold sensation of evaporating a few drops of 
 ether from the hand. As the perspiration evaporates from 
 the skin, it becomes a powerful cooling agency and regu- 
 lator of bodily temperature, while the vapor which escapes 
 from the breath, by its absorption of heat, exerts a cooling 
 effect within the body. 
 
 106. The Cryophorus, or Frost-Bearer, is an instrument 
 which strikingly illustrates this principle. It consists of a 
 
 tu ^ )e w ^k a gl ass bulb at eacn extremity, 
 one of which contains a little water. Air 
 is expelled from the instrument by boiling 
 the water, the aperture through which the 
 steam escapes being sealed, while the re- 
 maining space is filled with vapor. The 
 empty bulb is then placed in a freezing mix- 
 ture, Fig. 43, and the vapor condenses, its 
 place being supplied by vapor from the 
 water-bulb above. Condensation and evap- 
 oration go on so rapidly that the water is 
 
 The Cryophorus. SOO11 f rozen . 
 
 107. Dew-Point. The air always contains moisture, 
 the amount of which varies with the temperature. The 
 power of the air to absorb moisture is called its capacity 
 for absorption. When it contains as much as it is capa- 
 ble of holding at a given temperature, it is said to be 
 saturated, and any lowering of the temperature condenses 
 it in the form of clouds, mist, fogs, dew, etc. The degree 
 of temperature at which the moisture is condensed is called 
 the dew-point. If the temperature of the air has to fall 
 but a few degrees before moisture is deposited, the dew- 
 point is said to be high, and there is much moisture in the 
 air ; while, if the temperature must fall far, the dew-point 
 is low, and the air contains less moisture. It is obvious, 
 therefore, that, by finding these two points of tempera- 
 
ACTION OF THE HYGROMETER. 
 
 59 
 
 FIG. 44. 
 
 ture, one can easily obtain the amount of atmospheric 
 humidity. 
 
 108. The Hygrometer. This is an instrument for meas- 
 uring atmospheric moisture. Daniell's hygrometer, Fig. 44, 
 is constructed on the principle of the cryophorus. The long 
 limb ends in a glass bulb b half filled with ether, into which 
 dips a small thermometer. The bulb a 
 
 on the short limb is empty and covered 
 with muslin. The temperature of the 
 air is shown by another thermometer, 
 c, affixed to the stand of the instru- 
 ment. When an observation is to be 
 made, a little ether is poured upon the 
 muslin, and, as it evaporates, the tem- 
 perature of the other bulb becomes re- 
 duced. When it is sufficiently cold to 
 condense the moisture of the air, it will 
 be covered with dew. The thermome- 
 ter in the tube b shows at what tem- 
 perature this deposition takes place, 
 and, of course, gives the dew-point. 
 
 The amount of moisture in the air of our artificially- 
 heated rooms is a matter of great importance to health, 
 and the hygrometer is very valuable in enabling us to de- 
 termine it. 
 
 109. Volume and Density of Vapor. Equal bulks of dif- 
 ferent liquids generate unequal volumes of vapor. Water 
 yields a larger amount than any other liquid. While a 
 cubic inch of water gives 1,694 inches of vapor, a cubic 
 inch of alcohol yields 528, one of ether 298, and of oil of 
 turpentine 193. But, the less the volume of vapor, of 
 course the greater its density. The density of vapor is 
 increased, either by cold or pressure. The point at which 
 its temperature cannot be further lowered, without return- 
 ing to the liquid state, is called its maximum density. 
 
 110. Elastic Force of Vapors. All vapors are elastic, 
 
 DauielPs Hygrometer. 
 
60 
 
 CHEMICAL PHYSICS. 
 
 FIG. J5. 
 
 and have a tendency to diffuse themselves through space, 
 exerting more or less force against any obstacle that re- 
 sists their expansion. This expansive force of vapors is 
 called their elastic force or tension. The expansive force 
 of heat, acting through the vapor of water, is the impelling 
 power of the steam-engine. 
 
 111. Distillation consists in vaporizing a liquid by heat 
 in one vessel, and condensing it by cold in another, Fig. 
 
 45. The object may be either 
 to separate a liquid from non- 
 volatile substances dissolved in 
 it, as in distilling water, to purify 
 it from foreign ingredients, or to 
 separate two liquids which evap- 
 orate at different temperatures, 
 as alcohol and Avater. In the 
 latter case, the heat is carried 
 just high enough to vaporize the 
 most volatile liquid. The product 
 of the process is called the distil- 
 late. When solids are vaporized, the process is termed 
 sublimation, and the condensed vapor a sublimate. 
 
 112. Condensation of Gases. When a gas loses heat 
 enough to change it to the liquid or solid state, it is said to 
 
 be condensed. Under the joint effect of 
 pressure and extreme cold, many gases 
 once considered permanent have been re- 
 duced to liquids, and some even to the solid 
 condition. Dr. Faraday effected this by 
 a very simple method. He placed the ma- 
 terials from which the gas was to be gen- 
 erated in one end of a glass tube bent in the middle, which 
 was then hermetically sealed, Fig. 46. The expanding gas 
 confined in so small a space exerted a tremendous pressure, 
 the force of which condensed a portion of it into a liquid 
 in the other end of the tube, which was immersed in a 
 
 Distillation. 
 
 FIG. 46. 
 
 Condensation Tube. 
 
CHEMICAL INFLUENCE OF HEAT 61 
 
 freezing mixture to facilitate the process. By this method, 
 and at a temperature of 166, he succeeded in liquefying 
 carbonic dioxide, chlorine, ammonia, and several other gases, 
 More recently M. Natterer, of Vienna, applied a cold of 
 220 F., and a pressure of 3,000 atmospheres ; but some 
 of the gases, as oxygen, hydrogen, nitrogen, refused to 
 liquefy, even under this tremendous force. 
 
 113. Heat and Chemical Action. Besides these physi- 
 cal changes and transformations, heat is also employed to 
 effect innumerable chemical changes. By means of lamps, 
 baths, and furnaces, the chemist is able to subject bodies 
 to all degrees of temperature, and to promote and modify 
 their action on each other. By its repellant action upon 
 the constituent parts of matter, heat overcomes chemical 
 attraction, destroys compounds, and brings new affinities 
 into play with the production of new substances. At a 
 sufficiently high temperature, indeed, we can conceive the 
 repulsion to be so great that all affinities are suspended, 
 and the chemical elements are dissociated. 
 
 4. The Nature of Heat. 
 
 114. Heat and Cold. The difference between heat and 
 cold is merely one of degree, and we must be careful not 
 to misinterpret their impressions upon ourselves. If we 
 plunge one hand in ice-water and the other in hot water, 
 and then transfer both to water intermediately warm, it 
 will seem hot to the one and cold to the other. Indeed, 
 if we trusted our ordinary sensations, we should believe in 
 two opposite principles of heat and cold, a doctrine which 
 was long advocated until it was found that these are mere- 
 ly relative, and that cold is but the absence of heat. In- 
 tense heat and intense cold produce the same sensations ; 
 fro/en mercury blisters the flesh like hot iron. Putting 
 aside, then, our sensations, what is it that we know con- 
 cerning the n:iture of heat ? 
 
62 CHEMICAL PHYSICS. 
 
 115. The Caloric Hypothesis. In the foregoing brief 
 statement of the actions and effects of heat, we have con- 
 fined ourselves to facts which can be shown by experi- 
 ment, and have spoken of heat merely as a force, or agent. 
 But how are its effects produced ? It has long been re- 
 garded as a kind of matter a subtile fluid an imponder- 
 able element, whose entrance into our bodies produces 
 warmth, and its escape cold. This fluid caloric was sup- 
 posed to be stored up in the interstices of bodies, some 
 holding more than others, according to their various capaci- 
 ties. It was assumed to have an attraction for the parti- 
 cles of matter, and to combine with them, while its own 
 particles are self-repulsive, and thus cause the atoms with 
 which they unite to repel each other. This notion of the 
 materiality of heat is now generally abandoned in the 
 scientific world. 
 
 116. Grounds of a New Theory. Facts were pointed 
 out in the last century by Count Rumford which were 
 wholly inconsistent with the caloric hypothesis > and many 
 other facts of similar import have been since observed. 
 If an iron bar is struck upon an anvil, its temperature is 
 raised, and, if it continues to be hammered, it may be 
 made red hot. Two sticks may be rubbed together till 
 they take fire ; and water may be agitated by friction till 
 it boils. It is a general law, that arrested mechanical mo- 
 tion produces heat, and that the amount of heat produced 
 depends not at all upon the capacities of bodies for heat, 
 but upon the amount of mechanical force expended. Prof. 
 Rood made the following beautiful experiment : A ball 
 weighing a pound is allowed to fall from a height of one 
 or two inches on a thermo-electric couple made by solder- 
 ing together German-silver and iron. The heat thus de- 
 veloped generates a current of electricity which is meas- 
 ured by a galvanometer. The amount of heat generated 
 was found to be directly proportional to the distance 
 through which the ball fell. It has been demonstrated 
 
THE LATER VIEWS OF HEAT. 63 
 
 that 772 pounds falling through one foot of space pro- 
 duces sufficient heat to raise one pound of water 1 F. ; 
 and it has been further proved that one pound of water 
 falling through one degree of temperature gives out suffi- 
 cient heat to raise 772 pounds one foot high. This is 
 known as the mechanical equivalent of heat, and was estab- 
 lished by Dr. J. P. Joule, of Manchester, England, in 1850. 
 
 117. Heat as a Mode of Motion. It is, therefore, now 
 held that heat and mechanical force are convertible into 
 each other, and this puts an end to the conceptions of heat 
 as a material fluid ; for, to be interchangeable, their forces 
 must have a common nature. The convertibility is between 
 molar motions and molecular motions the motion of 
 masses and the motion of particles. When a body is 
 struck, the mechanical motion is arrested, but there is no 
 destruction of force ; it is only communicated to the parti- 
 cles of the body which are thrown into internal motion, 
 and this is manifested as heat. Heat is, therefore, now 
 defined as a " mode of motion " among the constituent 
 parts of matter. We say that bodies are heated and 
 cooled, and that one warms another near it. But we 
 strictly mean only that they expand and contract, and 
 that a body in expanding contracts others, and in contract- 
 ing expands them. Hence, we find the effect of heat to be 
 simply a motion of expansion in matter communicable 
 from body to body. The motion of a mass implies the 
 motion of its parts. If a body expands, it is because its 
 parts have receded farther from each other, that is, have 
 moved. Heat is therefore such a motion among the mole- 
 cules of a body as gives rise to expansion. 
 
 The later views of the relations of force all favor the 
 idea that the minute molecules of matter are in a state 
 of incessant movement. As nothing around us is at rest, 
 the idea of the quiescence of the internal parts of matter 
 would seem to contradict the whole course of Nature. 
 Tlie celestial bodies are in perpetual oiderly movement, 
 
64 CHEMICAL PHYSIC -. 
 
 and it seems highly probable that at the other extreme of 
 being there is also an order of motions equally regular and 
 systematic. 
 
 118. As heat is a molecular motion, intensity of this 
 motion determines temperature. When a body is heated, 
 the vibration of its molecules is augmented ; the particles 
 move through larger spaces ; are urged apart, and thus 
 cause the body to expand in bulk. When the vibrations 
 of the particles of solids become sufficiently violent, they 
 are loosened from the cohesion, and, continuing to oscillate 
 as before, they are now at liberty to slip or flow around 
 and among each other. This is the liquid state, in which 
 rigidity has disappeared. A further augmentation of heat 
 increases the swing of the molecules until they are thrown 
 quite beyond the sphere of cohesion, and fly asunder into 
 the vaporous or gaseous state. 
 
 119. The Railway-Train. In this case the heat of 
 combustion is spent in communicating to water the molec- 
 ular vibration, which changes it to steam, and this molecu- 
 lar motion is then converted into the mechanical move- 
 ment of the piston and the flight of the train. W r hen the 
 train is to be stepped the breaks are applied, heat and 
 sparks are produced, and the motion of the cars is con- 
 densed back again into the molecular vibrations of heat. 
 This explanation of the nature of heat is known as the 
 dynamical theory. 
 
 120. Heat of Combustion, The chief source of artificial 
 heat is combustion. Combustion is that particular form of 
 chemical action which takes place when the simple ele- 
 ments of which certain substances, as wood, coal, fats, il- 
 luminating gas, etc., are composed, enter into new combi- 
 nations with oxygen, one of the constituents of our atmos- 
 phere, or any other gaseous body, with so much energy as 
 to involve the conversion of the excess of chemical force, 
 brought into play, into other modes of motion, chief among 
 which are heat and light. 
 
CHAPTER IV. 
 
 ELE CTRICITY. 
 
 1. Frictional Electricity. 
 
 121. Electrical Excitation. If a dry, warm glass tube 
 be rubbed with a silk handkerchief, a feeble, crackling 
 noise is heard ; and, if it be dark, faint sparks will appear 
 to dart from the surface of the glass. If the tube be now 
 presented to any light substances, as bits of paper or 
 feathers, they are attracted to the glass. The force or 
 affection of matter thus made active is called electricity. 
 Bodies in which it is displayed are said to be electrically 
 excited or electrified, and are termed electrics. They are 
 numerous, including all resinous, gummy, and glassy sub- 
 stances, hair, silk, dry gases, and air. 
 
 122. Conductors and Insulators. Some bodies, as the 
 metals, water, charcoal, etc., allow electricity to pass read- 
 ily through them, and are hence called conductors. Other 
 substances, such as glass, resins, wool, do not readily allow 
 its passage, and are termed non-conductors. As the latter 
 tend to arrest or confine electricity, they are called insu- 
 lators. Air is a non-conductor, and acts as a universal in- 
 sulator. All electrical manifestations around us depend 
 upon this, for, if air were a good conductor, no body could 
 preserve its electricity. Yet moisture conducts, so that 
 the air, when charged with dampness, carries off electricity 
 quite rapidly. For successful experiments, therefore, the 
 air must be dry. 
 
66 
 
 CHEMICAL PHYSICS. 
 
 123. Two Electricities. There are two kinds of elec- 
 tricity ; that from glass is called vitreous, and that from 
 wax resinous. Each is self-repulsive, but bodies excited 
 both ways attract each other ; or, as it is commonly ex- 
 pressed, like electricities repel, and unlike attract. Frank- 
 lin held that bodies vitreously electrified have an excess 
 of it above their natural share, which excess he called the 
 positive state; while bodies resinously electrified are de- 
 ficient in the fluid, or in a negative condition. The posi- 
 tive electrical state he distinguished by the plus sign ( + ), 
 and the negative by the minus sign ( ). Positive elec- 
 tricity is, however, no more positive, real, or powerful than 
 negative, and the terms might be reversed so far as the 
 character of the electricities is concerned. 
 
 124. Electric Tension. The electrical excitement of a 
 body may rise so high as to overcome the resistance which 
 confines it and escape, rending a passage through the 
 air, when all excitement disappears. A body electrically 
 excited is said to be charged ; the restoration of equilib- 
 rium is called discharge, and is seen in the electric spark 
 
 and the flash of lightning. The 
 degree of excitement or intensity 
 of the charge is called electrical 
 tension, and may be compared to 
 the pressure of steam, or the bend- 
 ing of a bow or spring ; its dis- 
 charge, to their release. 
 
 125. Electrical Induction. Elec- 
 trical bodies act at a distance to 
 disturb the equilibrium of neigh- 
 boring bodies. If an excited glass 
 rod be brought near an electro- 
 scope, though there be no con- 
 tact, the gold leaves suspended in 
 the jar below will diverge, Fig. 47, and, upon examination, 
 it will be found that the cap is negatively electrified, and 
 
 FIG. 47. 
 
 Induced Electricity. 
 
POLAR STATES OF MOLECULES. 67 
 
 the leaves positively. The approach of the excited tube 
 decomposes their natural electricity, the negative element 
 being attracted, and the positive repelled. This action of 
 an excited body, without discharge, through a medium 
 upon distant bodies, is known as electrical induction. 
 
 Induction is a kind of preparation for discharge. When 
 electricity is about to move, or discharge to occur, the 
 whole course through which it will pass is, as it were, felt 
 out beforehand ; at first and infallibly the line of least re- 
 sistance is found and pursued. If two conductors are be- 
 fore it, it takes the easiest course at the outset. 
 
 126. Course of the Discharge. Fig. 48 represents frag- 
 ments of gold leaves casually laid upon paper, and produ- 
 cing with the paper a series of bad and good 
 conductors. A discharge finds its path across FlG - 48< 
 the interrupted circuit from P to j\^ burning 
 
 up the leaves and parts of leaves, as shown by H n 
 
 the shaded track. These remarkable results </> 
 
 are necessary consequences of the principle 
 of induction. The charged body induces at- 
 tractions in all directions, and the discharge 
 will, of course, be determined through that %. 
 range of materials which, from their nature ^ 
 and position, are most excited ; which present ** 
 the strongest attractions, and, of course, the 
 least obstruction. H 
 
 127. Theory of Induction. As there are 
 
 all degrees of conduction and insulation, Dr. N 
 Faraday held that we must look upon con- 
 duction and induction as only different de- 
 grees of the same mode of movement ; in all cases, it is 
 an effect communicated through molecules. If, when a 
 body is electrified, its particles discharge instantaneously 
 into each other, conduction is the consequence. If the 
 molecules do not readily discharge, but hinder the course of 
 the electricity, they are immediately forced into positions 
 
68 CHEMICAL PHYSICS. 
 
 of constraint : they become polarized, their opposite sides 
 having opposite properties, and, as each particle induces a 
 state of polar tension in its neighbor, the effect is trans- 
 ferred to a distance. In Fig 1 . 49, P represents a 
 
 FIG. 49. 
 
 positively charged body, and abed intermedi- 
 ate particles of air. These are thrown into op- 
 posite states or polarized, as is represented by 
 
 the white and black sides of the spheres, and 
 Q Q Q $ 
 
 thus the effect is propagated to the body JVJ 
 
 , which is electrically excited. We have said 
 that insulators arrest electricity, but en this 
 view they only stop movement by conduction ; 
 they transmit it by induction through the polari- 
 of Atoms" zation of their particles. As the polar particles 
 are in active relations of force to those around, it 
 is obvious that the effects may be propagated in various 
 directions. Hence the polarization may occur in curved 
 lines, and induction take place round corners and behind 
 obstacles. 
 
 2. Magnetism. 
 
 128. Natural and Artificial Magnets. If a fragment 
 of iron-ore called the loadstone is suspended, it turns one 
 of its sides to the north, and the opposite to the south ; it 
 attracts to itsslf particles of iron or steel, and is called a 
 natural magnet. If a steel bar be rubbed by a natural 
 
 magnet, it acquires magnetic prop- 
 erties, and becomes an artificial 
 magnet. If properly shaped and 
 poised upon a pivot, Fig. 50, it 
 takes a northerly and southerly 
 direction. The extremity which 
 Magnetic Needle. points northward is called the 
 
 north pole of the magnet, and 
 that which turns southward, the south pole. 
 
 129. Polarity. If a second needle be brought near the 
 first, it will be noticed that they exert a powerful influence 
 
INDUCED MAGNETISM. 
 
 FIG. 51. 
 
 over each other. The north pole of each attracts the south 
 pole of the other, while north pole repels north pole, and 
 south pole repels south pole. In short, like poles repel, 
 and unlike attract each other. These influences are ex- 
 erted through all kinds of matter glass, wood, metals, 
 or the human body and through a vacuum. The magnetic 
 force is manifested chiefly 
 at the poles. If a sheet of 
 paper be laid upon a mag- 
 netic bar, and iron filings 
 be dusted over it, on gen- 
 tly tapping the paper, they 
 gather thickly around the 
 poles, extending away in Magnetic Curves. 
 
 curved lines, called mag- 
 netic curves, Fig. 51. Thus the two magnetic forces are 
 always produced simultaneously ; are equal in amount, but 
 opposite in direction ; and as these opposite powers are 
 manifested in the poles of the magnet, they are called 
 polar forces, while the property excited is termed polarity. 
 130. Magnetic Induction. The preceding experiments 
 show that the magnet has the power of exciting magnet- 
 ism in adjoining bodies ; P, fl 53 
 in fact, each of the little 
 particles of iron becomes 
 a magnet with a north 
 and south pole. This 
 may be proved by pla- 
 cing several bars of soft 
 iron around the pole of 
 a magnetic bar, Fig. 52, 
 when they all become 
 temporarily magnetic. 
 The permanent magnet 
 induces the influence in Ma ^ netic ucttan. 
 
 FIG. 52. 
 
 Magnetic Chain. 
 
 the adjacent bars, which are hen 33 said to be magnetized 
 
70 
 
 CHEMICAL PHYSICS. 
 
 FIG. 54. 
 
 IS NiiS NjJS 
 
 A Broken Magnet. 
 
 by induction. A key may be suspended by a magnet, 
 Fig. 53, and this will hold a second smaller key, this 
 a nail, and the nail a tack, all receiving their magnet- 
 ism by induction from the bar, and each possessing its 
 separate north and south polarity. 
 
 131. Polarity of Particles. Now, the particles of the 
 magnet are in the same condition as the magnet itself. 
 If a magnet is broken, as in Fig. 54, and the pieces are 
 
 broken again and again, the small- 
 est particles still have opposite 
 poles. Each particle acquires po- 
 larity, and acts by induction upon 
 all the others, the opposite pow- 
 ers becoming accumulated at the opposite extremities of 
 the bar. It may be observed that while steel retains its 
 magnetism that is, its particles remain fixed in their polar 
 relation soft iron, on the contrary, only remains a magnet 
 while immediately acted upon. 
 
 132. Diamagnetism. Magnetic bars are usually bent in 
 the shape of a horseshoe, and their poles are connected 
 by a piece of iron called an armature. The space between 
 
 the poles is called the mag- 
 netic field / a line joining the 
 poles the axis ; the line at 
 right angles with this, the 
 equator. All substances which, 
 when freely suspended between 
 the poles, of a magnet, arrange 
 themselves axially, are classed 
 as magnetic. Iron, nickel, co- 
 balt, and oxygen, are the most 
 important. Certain bodies, 
 when suspended in the mag- 
 netic field, assume an equa- 
 torial direction, as if repelled 
 by the poles, and these are said to be diamagnetic. In 
 
 FIG. 55. 
 
 Diamagnetism. 
 
CUR KENT ELECTRICITY. 71 
 
 Fig. 55, b represents a bar of diamagnetic bismuth sus- 
 pended by fibres of unspun silk between the two poles of 
 a magnet. This property is also manifested by antimony, 
 wood, leather, water, etc. ; in fact, all substances not mag- 
 netic are now regarded as diamagnetic. 
 
 3. Voltaic Electricity. 
 
 133. The Voltaic Circuit. We are now to consider 
 electricity in a form more closely related to chemical 
 action. Tt was first discovered by Galvani, and has been 
 called after him galvanism ; but its most illustrious culti- 
 vator was Volta, from whom it is also called voltaic elec- 
 tricity. A strip of zinc and one of copper are placed in a 
 vessel containing water, to which has been added a little 
 sulphuric acid. If not permitted to touch each other, as in 
 Fig. 56, there is no effect. But, if brought into contact, as 
 seen in Fig. 57, several results ensue. The acid in the 
 water grows weaker ; the zinc strip is corroded, and bub- 
 
 F,o. K 
 
 No Effect. The Voltaic Circuit. 
 
 bles of gas are seen to escape from the surface of the copper. 
 If the metals are separated, the action ceases ; and, if this 
 is done in the dark, a minute spark will be seen. Electrici- 
 ty seems to flow round and round in the direction of the 
 arrows, like an invisible stream. The combination through 
 which it passes is termed a voltaic circuit, and the circulat- 
 ing force an electric or electromotive current. The electric 
 current originates in chemical changes, and requires a com- 
 pound liquid capable of decomposition by one of the metals. 
 4 
 
72 CHEMICAL PHYSICS. 
 
 The source of the electricity, in this case, is the decom- 
 position of the sulphuric acid forming zinc sulphate, and set- 
 tiug free hydrogen gas. The zinc sulphate being dissolved 
 in the liquid, the plate is kept clean and the action main- 
 tained, till the metal is consumed, or the acid all neutralized. 
 
 134. Electrodes. To the plates are often soldered wires 
 with terminals of platinum to withstand the action of cor- 
 rosive liquids. The ends of these wires are known as the 
 poles of the circuit, from an idea that they exerted an at- 
 tractive and repellant action, like the poles of a magnet. 
 But Faraday has proved that there is no attraction or re- 
 pulsion in the case, and suggested the better term elec- 
 trodes^ which means simply a door or way for the elec- 
 tricity. The copper pole is termed positive, and the zinc 
 pole negative. Whatever be the metals used, that which 
 is chemically acted upon and originates the electricity is 
 termed positive. 
 
 135. The Voltaic File. The power of the circuit may 
 be increased by repeating its elements. The pile discov- 
 ered by Volta and named after him was the first con- 
 trivance for ausrmenting 1 the force of the elec- 
 
 FIG. 58. 
 
 trie current. It is made by preparing small 
 plates or disks of metal, usually copper and 
 zinc, and placing between them pieces of flan- 
 nel moistened with an acid or saline soluiion. 
 >c Such a pile is represented in Fig. 58. The 
 cloth is placed between the metals, and the 
 order begun is preserved. Commencing at 
 the bottom there is copper (c), flannel (/"), 
 zinc (2), and upon that copper, flannel, zinc, 
 Voltaic Pile, and so on to fifty or a hundred sets, as may be 
 desired (Fig. 58). The lower or copper end is 
 positive, and the other negative ; a current, therefore, moves 
 in the direction of the arrows. This form of instrument 
 gives a strong effect at first, but rapidly declines in power. 
 
 136. The Galvanic Battery. To augment the electrical 
 
ELECTRICAL BATTERIES. 
 
 73 
 
 FIG. 50. 
 
 Voltaic Battery. 
 
 FIG. 60. 
 
 effect, and at the same time secure steadiness of action and 
 convenience of management, 
 the compound circuits are ar- 
 ranged in other forms known 
 as voltaic or galvanic batter- 
 ies. A series of vessels, called 
 cells, containing an acidulated 
 liquid, is arranged, in each 
 of which there is a plate of 
 copper and another of zinc ; the copper plate of one cell 
 being connected by a copper wire with the zinc plate of 
 the preceding cell, Fig. 59. 
 
 137. Daniell's Battery. Prof. Daniell made an impor- 
 tant improvement in the battery by using two different 
 fluids separated by a porous partition. 
 Fig. 60 exhibits a section of Darnell's 
 cell : a is an outer cylinder of copper 
 rilled with b, an acid solution of blue 
 vitriol, which is kept saturated by crys- 
 tals resting upon the perforated shelf 
 /; c is a tube of porous ware, or un- 
 oiled leather, filled with tf, 1 part of sul- 
 phuric acid to 7 of water, and into this 
 is plunged a rod of amalgamated zinc e. 
 To the copper and zinc are attached 
 binding screws for wire connections. 
 When the action commences, a double set of changes 
 rakes place in the liquid. Oxide of zinc is formed in the 
 inner vessel, and the polarizing action taking place through 
 the porous wetted body c, the sulphate of copper is decom- 
 posed in the outer vessel. The sulphuric acid set free is 
 gradually transferred to the inner vessel, while the hydro- 
 gen, instead of being set free, combines with the oxygen 
 of the oxide of copper, precipitating metallic copper upon 
 the surface of the outer cylinder. A variety of improved 
 batteries, such as Grove's and Bunserfs, are now in use. 
 
 Danieirs CelL 
 
74 CHEMICAL PHYSICS. 
 
 138. Quantity and Intensity. In the battery the quan- 
 tity of electricity depends upon the size of the plates ; the 
 intensity, upon the number of them. If we increase the 
 size of a pair of zinc and copper plates, we increase the 
 quantity of the electricity they produce, but not its inten- 
 
 sit}- ; while, if we reduce 
 FlG - 61 - the size, we reduce the 
 
 quantity, the intensity re- 
 maining the same. On 
 the contrary, if we multi- 
 ply the number of pairs 
 of equal size, the inten- 
 sity is augmented at an 
 
 Accumulating Intensity. > 
 
 equal rate, while the quan- 
 tity is unchanged. The electricity developed by a single 
 pair is exceedingly feeble ; the second cell adds no more 
 to it, but intensifies its power. In Fig. 61 the arrows illus- 
 trate the accumulating intensity. 
 
 139. Induced Currents. If two conductors are placed 
 near and parallel to each other, a current sent through one 
 induces an opposite current in the second. At the mo- 
 ment the circuit is formed and the primary current passes, 
 a secondary current is produced in the opposite direction 
 in the second wire. If one or two hundred feet of stout 
 copper wire are wound into a close coil, and then twenty 
 or thirty thousand feet of much finer wire (both well cov- 
 ered with silk) be wound into a secondary coil around the 
 first, a current sent through the inner wire, and rapidly in- 
 terrupted, induces very powerful currents in the outer coil, 
 which give rise to a stream of brilliant sparks. This is the 
 principle of the Ruhmkorif coil, which has been greatly 
 improved by Mr. Ritchie, of Boston, and is now one of the 
 most energetic of electrical machines yet devised, pro- 
 ducing electricity in large quantity and of extraordinary 
 intensity. 
 
 140. Voltaic electricity will travel through a con- 
 
ELECTRICAL DECOMPOSITION. 
 
 FIG. G2. 
 
 ductor thousands of miles rather than penetrate a barrier of 
 air a small fraction of an inch in thickness, while frictional 
 electricity will leap through miles of intervening atmos- 
 phere. For sustained effects, as in chemical decomposi- 
 tions and telegraphy, where vast quantities of electricity 
 are required, the battery is employed, its current being 
 raised to the requisite tension by multiplying the cells. 
 
 141. Electrolysis. If the ends of the platinum wires 
 connected with a battery are placed near each other in a 
 vessel of water containing a little sulphuric 
 acid to aid conduction, bubbles of gas will 
 be seen to rise from the terminals and es- 
 cape at the surface. A couple of glass 
 tubes filled with water, and inverted in the 
 vessel over the poles, serve to collect the 
 rising gases, Fig. 62, which, upon examina- 
 tion, prove to be pure hydrogen and pure 
 oxygen, the bulk of the former being twice 
 that of the latter. The source of the gases 
 is the water which is decomposed. This 
 operation is termed electrolysis (analyzing 
 by electricity), and any substance that is 
 capable of this decomposition is called an electrolyte. 
 
 142. When compounds are electrolvzed, their ele- 
 ments are found in opposite electrical states. Some, as 
 oxygen, chlorine, sulphur, appear at the positive electrode, 
 and are called electro-negative bodies ; while others, as 
 hydrogen and the metals, appear at the negative electrode, 
 and are called electro-positive. Oxygen heads the first 
 list, or is the most powerful electro-negative body, while 
 the newly-discovered caesium heads the other, being the 
 strongest electro-positive substance. The elements may 
 be arranged in such an order that each will be electro- 
 negative to all which follow it, and electro-positive to all 
 which precede it. As the electric current thus originates 
 in chemical changes and produces them, and as the atoms 
 
76 
 
 CHEMICAL PHYSICS. 
 
 FIG. 
 
 seem to be in opposite electrical states, it is obvious 
 that electrical force is very closely allied to chemical 
 power. 
 
 143. Electrotype. When a salt of copper, silver, nickel, 
 or gold, is dissolved in water, if a current of electricity be 
 passed through the liquid, it decomposes the saline body, 
 and the metal is deposited. In this way medals may be 
 copied (electrotype) ; or new metallic surfaces may be 
 imparted to articles, as in electro-gilding and electro- 
 plating. 
 
 144. Heating Effects of the Current 
 A current passing through a conductor 
 raises its temperature in proportion to 
 the electricity arrested. A wire which 
 is but little heated by a current, if con- 
 siderably reduced in diameter, becomes 
 instantly white hot. The arrested elec- 
 tricity appears as heat. Two carbon 
 points brought into contact in the circuit, 
 arid then slightly separated, emit a light 
 of dazzling splendor, Fig. 63, known as 
 Electric Light. the electric light. 
 
 4. Electricity, Magnetism, and Heat. 
 
 145. Electro Magnetism. If a magnetic needle be 
 
 brought near a wire along which an electric current is 
 
 passing, the needle will be caused to move. The degree 
 
 FlG 64 of the motion will depend upon the 
 
 |+Jt > strength of the current, and its 
 
 ~lj\ direction upon the relative position 
 of the needle and wire. If the 
 wire be above and parallel to the 
 
 Current and Needle. 
 
 needle, the pole next the negative 
 
 electrode will move westward ; if beneath the needle, 
 it will move eastward. If the wire is on the east side, 
 
 f 
 
ELECTRO-MAGNETISM. 77 
 
 this pole will be elevated ; if on the west, it will be de- 
 pressed. In all cases it tends to place itself at right an- 
 gles, or transverse, to the wire. If the wire be bent, so as 
 to pass above and below the needle, Fig. 64, the effect is 
 increased ; and, if it be coiled round many times in the 
 same manner, it becomes still more powerful. 
 
 146, The Astatic Needle. A single needle keeps its 
 place in the magnetic meridian with considerable force, so 
 that a very faint current will not move it ; but, if two 
 needles are placed parallel, near each other, with reversed 
 poles, their directive force is mutually neutralized. Two 
 needles thus fixed upon an axis, Fig. 65, form the astatic 
 (unstable) needle. If one is slightly 
 
 stronger than the other, it still retains 
 
 a feeble tendency to keep its north and 
 
 south position. If, now, the wire of 
 
 Fig. 65 were folded round both these 
 
 needles, the same current would urge 
 
 them in opposite directions, and there 
 
 would be no motion ; but, when the coil Astatic Needle. 
 
 incloses only one of the needles, as the 
 
 lower, for example, the current impels both needles in the 
 
 same direction. If the needles be suspended by a single 
 
 fibre of silk, it affords the means of detecting the faintest 
 
 electrical current, and forms the galvanometer. 
 
 147. Thermo-Electricity. Heat, applied to unlike met- 
 als when in contact, produces a current known as thermo- 
 electricity. A B, Fig. 66, is a bar of antimony, and B C 
 a bar of bismuth, soldered together at one extremity, and 
 connected by the wire D at the other. When the place 
 of junction is warmed, an electric current is produced, 
 which moves in the direction of the arrows. If the junc- 
 tion B is chilled, the current moves in the opposite direc- 
 tion. Such a combination forms a thermo-electric pair. 
 The effect is increased if several of these are united, form- 
 ing what is known as the thermo-electric pile. To secure 
 
78 
 
 CHEMICAL PHYSICS. 
 
 FIG. 66. 
 
 a compact arrangement, they are soldered together, and 
 combined as in Fig 67, A representing one of the faces 
 of the pile. When both faces are equally 
 heated, there is no current. If the face, A, 
 is warmed, there is a current in one direc- 
 tion, due to the difference of temperatures 
 between the two faces. If the opposite face 
 , is warmed, or, what is the same thing, if 
 
 Thermo electric Pair. 
 
 Arrangement of the Bars. 
 
 the face, A, is cooled, there is a reverse current. 
 
 148. In Fig. 68, A B represent the thermo-electric 
 pile as mounted for lecture-room use. A shows one of 
 
 FIG. 63. 
 
 Thermo-electric Pile as mounted for Use. 
 
 the faces ; w w are wires connecting it with the galva- 
 nometer, The needle in n is suspended by a fibre of un- 
 
ACTION OF THE GALVANOMETER. 79 
 
 spun silk, s s, and protected from currents of air by the 
 glass shade G. To one end of the needle is fixed a piece 
 of red paper, and to the other a piece of blue. If the face 
 of the pile is merely breathed upon, the warmth swings 
 the needle round to 90, or at right angles to the cur- 
 rent the pieces of paper making the movement visible 
 throughout the room. This important instrument detects 
 heat radiation from sources much lower than the human 
 body, and announces the heat emitted from the bodies of 
 insects. Lately it has been used to detect the heat from 
 the fixed stars. 
 
 148a. Animal Electricity, Certain fish possess the re- 
 markable power of giving electrical shocks. They have 
 internal organs for this purpose, which play the part of 
 batteries, and the discharges from them produce all the 
 effects of ordinary electricity. In the torpedo the electri- 
 cal organs are situated on each side of the head, and con- 
 sist of a mass of cells filled with a dense fluid consisting 
 of water, albumen, and common salt. These organs give 
 rise to electricity just as the muscles do to mechanical mo- 
 tion. A dense mass of nerves links them with the brain, 
 which controls the electrical discharges in the same way 
 as it does the mechanical movements. 
 
 It has been proved that currents of electricity circulate 
 in the frames of all animals, and that different parts or 
 sections of the muscles are in different electrical states. 
 The smallest shreds of muscular tissue have been proved 
 by Prof. Du Bois-Raymond to manifest currents, the longi- 
 tudinal section being alwa\ r s positive to the transverse sec- 
 tion. By arranging a series of half-thighs of frogs, alter- 
 nately connecting the exterior and interior surfaces, he ob- 
 tained an electrical current that decomposed potassic iodide, 
 deflected a magnetic needle 90, and caused the gold leaves 
 of an electroscope to diverge. Many have supposed that 
 the nervous force is electrical, but this is disproved by the 
 comparatively slow rate of its motion. It is, however, 
 probably an analogous polar force. 
 
CHAPTER V. 
 
 LIGHT. 
 
 1. Motion of the Radiant Forces. 
 
 149. Their Motion. Light is that agent which, acting 
 on the eye, produces vision. Other forces are generally 
 associated with it that obey the same laws of motion ; and, 
 as that motion is in rays, they are known as radiant forces ; 
 their laws of movement are the same. Light moves in 
 straight lines and in all directions from the point of emis- 
 sion diminishing in intensity in inverse ratio to the square 
 of the distance. Its velocity is about 190,000 miles per 
 second. When light falls upon bodies, some reflect it, 
 others absorb it, and others transmit it. The laws of these 
 motions are explained in books upon optics. 
 
 150. The Analysis of Light. By the prism a triangu- 
 lar piece of glass, or other transparent substance the white 
 ray is decomposed into a series of colors. A beam of solar 
 light passing through such a prism, Fig. 69, is refracted by 
 
 it, and produces an oblong 
 Fl - 69> colored image called the 
 
 solar spectrum. It is usu- 
 ally considered to comprise 
 the seven colors enumer- 
 ated in the accompanying 
 diagram. White light is, 
 therefore, held to be a com- 
 
 pound consisting of these colored lights, which are only 
 separated by the prism. Each color has its own peculiar 
 
ANALOGIES OF LIGHT AND SOUND. 81 
 
 refrangibility, or degree of divergence from the original 
 source, the red being least refracted, and the violet most. 
 Certain of the rays accompanying light produce heating 
 effects, and others chemical effects. These rays are gov- 
 erned by the same laws of motion as light itself, but by 
 the prism the heat is mainly distributed through the red 
 end of the spectrum, and the chemical force through the 
 violet extremity. (162.) 
 
 151. The Wave Hypothesis. The motion of the ra- 
 diant forces is explained by what is called the wave- 
 theory. It is known that sound is propagated through 
 the air by means of the vibration of its particles ; and it 
 is supposed that light moves by a similar mode of action. 
 There is a great amount of evidence to show that the 
 radiant forces are propagated by some kind of undulatory 
 movement, but the hypothesis implies a medium that is 
 capable of this kind of motion. This medium is assumed 
 to be an infinitely rare and elastic ether that fills all space 
 and pervades all matter. 
 
 152. Cause of Colors. According to this hypothesis, 
 light is transmitted by ethereal undulations just as sound is 
 by those of the atmosphere ; with only this difference, that, 
 while the air-particles move backward and forward in the 
 same direction as the advancing wave (longitudinal vibra- 
 tions), the ethereal particles move across the course of the 
 wave (transverse vibrations). Thus the spectrum is to the 
 eye what the gamut is to the ear. As the pitch of sound 
 depends upon the length of the air-wave, so the color of 
 light depends upon the length of the ethereal wave; and 
 as loudness of sound depends upon the extent of the Swing 
 of air-particles, so the brightness or intensity of color re- 
 sults from the extent of the excursions of the ethereal 
 particles. 
 
 By several refined methods which cannot be detailed 
 here, the lengths of the ethereal waves upon which colors 
 depend have been estimated. The motions which produce 
 
82 CHEMICAL PHYSICS. 
 
 red are slower, and the undulations longer than those 
 which produce violet. It is found that 40,000 waves of 
 red light would measure an inch, while 60,000 waves of 
 violet light would fill the same space. The other colors 
 are intermediate, their number of waves increasing grad- 
 ually from red to violet. As light moves 190,000 miles 
 per second, that length of ray streams into the eye each 
 second. If this distance be reduced to inches, and the 
 product be multiplied by 40,000, we shall have the number 
 of waves which beat against the retina each second, when 
 we look upon a red color. If the same product is multi- 
 plied by 60,000, we get the number of pulses per second 
 which strike the retina when looking upon a violet color. 
 
 153, Transmission of Radiant Motion. In this view it 
 is necessary to distinguish between vibrations and undula- 
 tions. In the case of sound, the vibrations of a sonorous 
 body, as a bell, produce undulations in the air which, when 
 striking against distant bodies, may set them also into 
 vibration. The vibrations of the bell, transmitted as air- 
 waves, are taken up by the tympanum of the ear, which, 
 when set to vibrating, gives rise to the sensation of sound. 
 So the vibration of atoms in a flame produces undulations 
 in the ether ; these are transmitted to the nerve of vision, 
 and, breaking against it, throw its atoms into the vibi^- 
 tions which produce sight. In the same way the particles 
 of a heated body are supposed to be in a state of vibra- 
 tion, which are transmitted by ethereal undulations, and 
 these, falling upon other bodies, set their particles into 
 vibration, and raise their temperature. This is the ex- 
 planation afforded of radiant heat. 
 
 2. Interference and Polarization. 
 
 154. Interference of Waves, When two sets of water- 
 waves are made to flow together, if they coincide, that is, 
 if ridge corresponds to ridge, their height will be increased; 
 
INTERFERENCE OF WAVES. 
 
 83 
 
 PIG. 70. 
 
 but, if the ridge of one corresponds with the trough of an* 
 other, they will neutralize each other, and the water be- 
 come still. This is called interference. 
 
 Again, two stretched strings, or two tuning-forks, may 
 be so placed, that, when simultaneously struck, they do 
 not give forth a continuous sound ; but there is produced 
 a series of alternating swells and depressions of tone. 
 During the pauses, there is still rapid vibration, so it is 
 certain that the sounds are extinguished by interference 
 of their waves. 
 
 155. Interference of Light. If a beam of colored light 
 be admitted into a dark room by two pin holes made near 
 each other in a thin sheet of metal, and be made to fall 
 upon a screen at a short distance, the rays intersect each 
 other, and a series of dark bands alternating with bright 
 stripes will be formed upon 
 the screen by interference of 
 the ray from the two orifices. 
 In Fig. 70, a f represent the 
 two pinhcles, and c d e b a 
 portion of the screen, c g be- 
 ing a line joining the two 
 surfaces at right angles, and 
 midway between the pin- 
 holes. The rays, a C, f C, Interference of Light. 
 
 pass through equal paths ; 
 
 their waves coincide at c, and, heightening each other's 
 effect, a bright band is produced at c ; a d^fdwill differ 
 by the length of one wave, a e,fe by the length of two 
 waves, and a 6, f b by the length of three waves ; hence, 
 there will be also bright bands at rf, e, and b. But the 
 rays from the two orifices, meeting at 1, 2, 3, differ in 
 length successively by half a wave, a wave and a half, and 
 two waves and a half, and, by thus interfering, extinguish 
 each other and produce darkness. As the rays which meet 
 ut c are equal, it is obvious that all the other rays coming 
 
84 CHEMICAL PHYSICS. 
 
 from a are lengthened, and all others coming from f are 
 shortened. As this variation of length is gradual, there 
 will be a gradual passage from the brightest light to com- 
 plete darkness. This effect is exhibited by the shaded 
 portion of the diagram. If the light from one aperture is 
 intercepted, all the dark bands disappear. 
 
 Thus we have seen that motion added to motion pro- 
 duces rest ; that sound added to sound produces silence ; 
 that light added to light produces darkness ; and it has 
 also been proved that heat added to heat produces cold, 
 heat-rays being liable to interference, like light. 
 
 156. Polarization of Light. When light is reflected at 
 certain angles from the surface 
 
 r IG- 71. 
 
 of glass, water, marble, polished 
 wood, etc., a portion of it under- 
 goes a remarkable change. Al- 
 though taking place all around 
 us constantly, we do not per- 
 ceive it, but it may be detected 
 in various w r ays. Two plates of 
 glass are blackened on one side 
 so as to have but a single re- 
 flecting surface, and then placed 
 FlG 73 as shown in Fig. 71, <7, 5, with 
 
 their edges toward the eye. A 
 ray of common light falling upon 
 a in the direction of the arrow 
 is reflected, and, upon being 
 -74. thrown upon &, is again reflect, 
 
 ed. The ray is changed at a, as 
 the altered structure of the line 
 shows, but the effect is not ap- 
 parent. If now &, or the second 
 Light polarized by Reflection. platej is turned a quarter round, 
 its angle with the ray being preserved, reflection ceases, 
 and the beam is extinguished, Fig. 72. Turning it anothei 
 
POLARIZATION OF LIGHT. 
 
 85 
 
 quarter round, Fig. 73, the ray is again reflected; and still 
 another quarter revolution, Fig. 74, brings it on the oppo- 
 side side to Fig. 71, and again extinguishes it. The beam 
 may be reflected from surface to surface any number of 
 times in the same plane but it has lost the ability of 
 being reflected in planes at right angles to that plane, 
 while common light may be reflected in all directions. It 
 thus appears that the ray has acquired different properties 
 on different sides. From its analogy to magnetic polarity, 
 this change is called polarization, and the ray thus affected 
 is said to be polarized. The angle at which the ray falls 
 upon the polarizing surface is called the polarizing angle, 
 and differs in different substances : for glass, it is 56 45', 
 while for water it is 53 11'. 
 
 157. Polarizing by Transmission, 
 Light transmitted obliquely through a 
 bundle of thin glass plates, Fig. 75, is 
 polarized, and the same effect is also 
 produced by its passage through certain 
 crystals. A stone, called the tour IK a- 
 line, is much used for polarizing pur- 
 poses. A thin polished plate of it po- 
 larizes the light which passes through 
 it, as in Fig. 76. If a second plate is 
 placed parallel to the first, Fig. 77, the light passes 
 
 FIG. 75. 
 
 Polarization by Thin 
 Plates. 
 
 FIG. 7( 
 
 FIG. 77 
 
 FIG. 78. 
 
 Polarization by Tourmalines. 
 
 through both ; but if the second plate is turned a quarter 
 round, Fig. 78, the light is stopped. " The rays of the 
 meridian sun cannot pass through a pair of crossed tour- 
 
86 
 
 CHEMICAL PHYSICS. 
 
 FIG. 79. 
 
 malines." The plate polarizing the light is called a polar- 
 izer / that which tests or detects it after it, is changed, is 
 termed the analyzer. 
 
 158. Theory of Polarization. The wave-theory thus 
 explains the phenomena. We can vibrate a cord up and 
 
 down, horizontally, 
 or in any direction 
 transverse to its 
 length, Fig. 79. In 
 common light the 
 undulations take 
 place practically in all these directions at once. It has 
 been suggested that common light may be represented by 
 a round rod ; polarized light by a flat lath. Supposing 
 
 Vibration in Different Planes. 
 
 FIG. 80. 
 
 FIG. 81 
 
 FIG. 82. 
 
 Illustrations of Planes of Vibration. 
 
 the round rod to image to us the common ray, the radii, 
 Fig. 80, will exhibit the system of transverse vibrations 
 taking place in all planes. But the effect is just the same 
 if we regard the vibrations as taking 
 place in two planes only, at right angles 
 to each other, as in Fig. 81. Now, when 
 common light is reflected in certain po- 
 sitions, which we have just noticed, one 
 of its planes of vibration is destroyed, 
 Motion in a Single and the beam is polarized, its vibrations 
 taking place all in one plane, Fig. 82. 
 We can now easily understand the action of the tourma- 
 line upon light. A plate of this crystal suppresses one of 
 the planes of vibration, and therefore transmits a polar- 
 
POLARIZATION AND REFRACTION. 
 
 87 
 
 ized ray. This will pass through a second plate if it is 
 held in such a manner that its structure coincides with the 
 motion ; but. if it is turned so as to cross the waves, the 
 ray is obstructed. A card which readily slips through a 
 grate when its plane coincides with the bars, will be 
 stopped if it is turned a quarter round, Fig. 83. 
 
 159. When a ray falls upon a transparent surface at 
 a certain angle, its planes of vibration are resolved into 
 
 FIG. 84. 
 
 Fio. 85. 
 
 Polarized Eays. 
 
 Double Refraction. 
 
 FIG. 86. 
 
 two, one of which is reflected, and the other transmitted. 
 Fig. 84 ; both are polarized, but one ray vibrates in one 
 direction, and the other at right angles to it. 
 
 160. Double Refraction. Some 
 substances possess the singular prop- 
 erty of splitting the ray which passes 
 through them, producing an effect 
 which is known as double refrac- 
 tion. Fisr. 85. Iceland spar and 
 
 Effect of Double Refraction. 
 
 many crystals possess this power; 
 
 printed words, or a candle-flame, seen through them, ap- 
 pearing double, Fig. 86. The effect is supposed to be due 
 to the molecular structure of the body. 
 
 161. Phosphorescence. This is a property possessed by 
 various bodies of emitting a faint light at ordinary or low 
 temperatures, and is so named from phosphorus, which 
 exhibits it in a remarkable degree. Phosphorescence is 
 manifested by certain insects, as the firefly and glow-worm, 
 by several species of plants, by various animal and vege- 
 
88 CHEMICAL PHYSICS. 
 
 table substances in a state of decay, and by exposure of 
 many substances to sources of light. If calcined oyster- 
 shells be placed for a short time in sunshine, and then 
 withdrawn into darkness, they will continue to glow for 
 some time, while other bodies, as the diamond and chloro- 
 phane, after exposure, remain for a long time luminous. 
 Recent investigations have shown that the same property 
 exists in a much lower degree in a great number of bodies, 
 their phosphorescence continuing in most cases for the 
 briefest moment sometimes only for the ten-thousandth 
 of a second. It would seem that, in cases where the lu- 
 minosity continues, the molecules of matter are set in mo- 
 tion by the ethereal undulations, and continue to move 
 after the withdrawal of the exciting cause. Fluorescence 
 is a kind of phosphorescence, in which the highly-refrangi- 
 ble dark rays of the solar spectrum, next to be considered, 
 are turned to light when falling upon certain substances, 
 as fluor-spar, or sulphate of quinine solution. 
 
 CHAPTER VI. 
 
 THE CHEMISTRY OF LIGHT. 
 
 1. The Chemical Rays. 
 
 162. A Third Radiant Force. Besides the heat-rays, 
 which take effect upon all kinds of matter, and the lumi- 
 nous rays, which act only upon special forms of nerve- 
 substance producing the sensation of vision, there is a 
 third class of rays which act upon certain chemical bodies, 
 producing combination and decomposition. These have 
 been called actinic rays, and the agency actinism / but 
 they are better known as chemical rays. They accompany 
 the light of the sun and stars, and are produced in arti- 
 
THE CHEMISTRY OF LIGHT. 
 
 89 
 
 FIG. 87. 
 
 ficial illumination ; but they are, nevertheless, distinct 
 from light. The art of photography depends upon them, 
 and has given a great stimulus to their recent investiga- 
 tion. Like light and heat, the chemical radiations are 
 measurable in their effects, and have given rise to an in- 
 dependent branch of scientific inquiry. 
 
 163. Refrangibility of the Invisible Radiations. The 
 heat-rays and the chemical rays are reflected and refracted 
 like light, and like the colored rays the}' exhibit marked 
 differences in their degrees of refrangibillty. When the 
 sunbeam is passed 
 through a prisrn 
 (Fig. 87) not only 
 is there an oblong 
 visible image 
 thrown upon the 
 screen, but there 
 is also an invisi- 
 ble heat - image, 
 and an invisible 
 chemical image, 
 which are revealed 
 in different ways. 
 The position and 
 varying intensity 
 of the heat-spec- 
 trum may be 
 traced out by a 
 delicate galvanom- 
 eter, and it is found that it begins down in the neigh- 
 borhood of a, and runs up into the luminous region. A 
 large portion of the heat-rays are hence of a lower refrangi- 
 bility than the red, and are dark radiations. If, now, a 
 solution of argentic nitrate is washed over a large sheet of 
 paper, which is then placed upon the screen so as to re- 
 ceive the visible spectrum and extend through the space 
 
 Positions of the Three Spectra. 
 
90 CHEMICAL PHYSICS. 
 
 above it, a chemical change takes place upon its surface, 
 producing a blackening, which defines the outline of the 
 chemical spectrum. It is now found that the chemical 
 rays are more refrangible than the luminous ; and that, 
 while the blackening takes place in the colored spectrum, 
 it extends also through the dark space up to b. That the 
 heat of the spectrum is greatest in the red, and that there 
 are dark thermal rays of still lower refrangibility, was shown 
 by Sir William Herschel, in the year 1800. That the chem 
 ical rays of the luminous spectrum are most active in the 
 violet region was pointed out by Scheele, in 1777; while 
 their extension into the dark space beyond, was discov- 
 ered by Ritter, in 1801. 
 
 164. Distribution of the Forces. The forces of the spec- 
 trum are thus very unequally distributed, as is illustrated 
 in Fig. 88, where they appear to rise like the peaks of 
 mountains. The middle curve shows the varying intensitv 
 
 Varying Intensities of the Spectrum Forces 
 
 of the luminous force. The maximum is at B in the yel- 
 low space, and from this point the intensity of the light 
 rapidly declines each way ; its extent being shown by the 
 space shaded with oblique lines. The curve A, with the 
 vertical lines, represents the position and varying force of 
 the heat; and the curve (7, horizontally shaded, exhibits 
 the distribution and unequal energy of the chemical force. 
 The three maxima are widely separated, as if there were 
 some antagonism among them ; and it is noticeable that 
 where the light is strongest the chemical force seems quite 
 
THE CHEMISTRY OF LIGHT. 91 
 
 neutralized. Different kinds of prisms (180) give some- 
 what different effects, but do not change their order. 1 The 
 mode of action of all these radiations is unquestionably 
 the same. Heat-rays, light-rays, and chemical rays, differ 
 from each other only as yellow differs from green, that 
 is, by wave-length and intensity of vibration. They all 
 exhibit the effects of interference and polarization which 
 proves the mode of ray-action to be alike in all. 
 
 165. Actinoinetry. It has been stated that the chemi- 
 cal rays are measurable in their force, and for this impor- 
 tant step of research we are indebted to Dr. J. W. Draper. 
 If hydrogen and chlorine gases be mixed in equal propor- 
 tions in a glass vessel, and kept in the dark, they will not 
 combine ; but, if exposed to the light, they unite with each 
 other, forming a compound. Upon such a mixture, how- 
 ever, the red rays produce no effect, while the violet rays 
 cause the gases to combine explosively. It is the chemi- 
 cal rays that are here active, and Dr. Draper employed a 
 mixture of these gases to test, by the rate of combination, 
 the varying intensity of the force. Instruments for this 
 purpose have been called actinometers. Roscoe and Bun- 
 sen afterward employed papers, made sensitive by silver 
 nitrate, which were blackened in given times to certain 
 shades as standard tests of the varying force of the chemi- 
 cal rays. 
 
 166. Variation of Chemical Rays in England. Observa- 
 tions were made at the Kew Observatory, near London, to 
 determine the changes of chemical activity in the solar 
 rays at different hours of the day, and different seasons of 
 the year. The diagram (Fig. 89) represents the results 
 graphically. The experiments were made from 6 A. M. to 
 6 P. M. throughout the year 1866. The figures below give 
 the hour of the day, and each curve represents the daily 
 change in intensity for the average of a month the hori- 
 zontal lines marking the scale of effects. The maximum 
 effect occurs at twelve o'clock, and the forenoon rise and 
 
 1 See note on this subject in the Appendix. 
 
CHEMICAL PHYSICS. 
 
 Curves of Variation at Kew. 
 
 afternoon decline are very nearly equal. But by comparing 
 the highest and lowest curves it will be seen that the chem- 
 FrG 89 ical intensity was fully 
 
 seven times as great 
 in July as in Decem- 
 ber. 
 
 167. Effects at the. 
 Equator. As we go 
 south, though the light 
 increases in brilliancy, 
 the chemical action is 
 impeded or interfered 
 with, so that it is said 
 to take ten or twenty 
 times longer to get a 
 picture under the blaze of the Mexican sun than in New 
 York. Yet tlie effect seems not due to lack of intensity 
 of the chemical rays, 
 but, perhaps, to some 
 obscure cause of irreg- 
 ular action. Fig. 90 
 represents the effects 
 obtained at Para, in 
 North Brazil, situated 
 nearly under the equa- 
 tor. The zigzag lines 
 show the sudden chan- 
 ges of intensity from 
 hour to hour, which 
 were accompanied by 
 heavy showers. The 
 dotted line below rep- 
 resents the chemic alre- 
 
 Sults at Kew at the Fluctuations at the Equator. 
 
 same time. 
 
 168. Relation to Vegetation. Of the effects produced 
 
 FIG. 90. 
 
THE CHEMISTRY OF LIGHT. 93 
 
 by these rays in Nature little is understood. It has long 
 been known that light exerts a powerful influence upon 
 the organic world. Vegetation languishes in the absence 
 of light, and flourishes when exposed to it. It was at first 
 supposed that this power over plants resided in the chemi- 
 cal ravs ; but it is now known that the force that decom- 
 poses carbon dioxide in green leaves, and which is the 
 foundation of the vegetative processes, is most active, not 
 in the blue, but in the yellow space of the spectrum, where 
 the actinic force is absent. 
 
 2. Photographic Chemistry. 
 
 169. Chemical Eeactions of Light. It was long sup- 
 posed that the chemical rays act only upon a few sub- 
 stances, but the contrary is really the fact. So many sub- 
 stances are affected by it, and in so many different ways, 
 that some think a ray of light cannot fall upon the surface 
 of any solid without impressing upon it an enduring mo- 
 lecular change. Four kinds of effect may be here referred 
 to : First, the elements, such as phosphorus, are altered by 
 light in their allotropic forms (271). Second, light promotes 
 chemical combination of the elements, as already shown 
 (165). Third, it produces mechanical effects. If the beau- 
 tiful ruby-colored crystals of arsenic disulphide are exposed 
 to light for some months, they become pliant and fall to 
 powder. Fourth, chemical compounds, as silver nitrale, 
 are decomposed under the influence of light, and new com- 
 pounds are formed. 
 
 170. Substances at the Basis of Photography. By ex- 
 ploring this subject, chemists have founded a new art of 
 great importance, that of taking pictures quickly, cheaply, 
 and accurately, by the direct action of light. Experi- 
 menters began to feel their way toward this result early in 
 the present century ; but the process only became success- 
 ful in the hands of M. Daguerre, a Frenchman, who made 
 it public in August, 1839 ; and since then it has undergone 
 
94 
 
 CHEMICAL PHYSICS. 
 
 FIG. 91. 
 
 the most rapid extension and development. For photo- 
 graphic purposes the salts of silver are mainly used sil- 
 ver iodide, bromide, and chloride, being the substances most 
 generally employed. The unequal susceptibility of these 
 compounds to the action of light gives great resources to 
 the operator, and is the basis of this modern art. 
 
 171. Production of the Invisible Image. Photographic 
 pictures are taken, as is well known, by means of a camera- 
 obscura, an instrument by which inverted images of ex- 
 ternal objects are 
 produced in a dark 
 chamber in their 
 natural colors. In 
 Fig. 91 G represents 
 a ground-glass slide 
 upon which the im- 
 age is formed, and 
 which is viewed by 
 the operator from 
 behind. The glass 
 plate is brought to 
 the exact focus, first 
 by sliding the part M of the box in the part N, and 
 then by turning the pinion ~V, which moves the lenses in 
 the tube A B. Fig. 92 represents the lenses E L in 
 the tube A B ; two lenses having the 
 effect of allowing a larger aperture, 
 and increased light, with the same focal 
 distance. A metallic or glass plate is 
 then prepared in an obscurely lighted 
 place, by coating it with the proper 
 chemicals, and it is then said to be 
 sensitive that is, it is very susceptible to changes from 
 the action of light. It is, therefore, kept protected 
 from the daylight, until substituted for the glass slide 
 G in the camera. The cap being then removed from be- 
 
 Photographic Camera. 
 
 FIG. 92. 
 
 Position of Lenses. 
 
THE CHEMISTRY OF LIGHT. 95 
 
 fore the lenses, the light from the object to be taken falls 
 upon the sensitive surface. If silver iodide be used, such 
 as Daguerre employed, twenty minutes will be necessary 
 to get an impression. But if silver bromide, or chloride, be 
 used, which are far more sensitive, the operation is quick- 
 ened, and by mixing different chemicals any degree of sen 
 sitiveness may be secured. If required, an impression 
 may be obtained in the hundredth part of a second. 
 
 172. Developing the Picture. When the plate is re- 
 moved from the camera, no effect is visible; the image has 
 to be brought out or developed by a subsequent process. 
 Daguerre effected this by exposing the plate to vapor of 
 mercury, which, being condensed unequally upon the 
 changed surface, evolved the lights and shadows, that be- 
 came visible when the plate was washed with sodic hypo- 
 sulphite, by which the unchanged silver iodide is dissolved 
 away. At present the plates exposed in the camera are 
 coated with collodion, in which the sensitive chemicals are 
 contained. The pictures are developed by washing the 
 surface with a solution of green vitriol, which, becoming 
 mixed with the silver compounds, decomposes them, and 
 precipitates the silver in the form of a fine black powder, 
 that adheres to the exposed surfaces of the plate. 
 
 173. Negatives and Positives. Pictures are now gen- 
 erally taken upon a transparent glass plate, in which the 
 lights and shades are reversed, and these are called nega- 
 tives. But from these negatives others are taken, and the 
 effects are again reversed, which makes them true to na- 
 ture lights answering to lights, and shadows to shadows : 
 these are called positives. They are copied, or printed 
 from the negative, by placing sensitively-prepared paper 
 surfaces against the negative, and exposing to sunlight. 
 In this way, from a single negative, many positives may be 
 obtained, while a little delicate retouching of the negative, 
 with Indian-ink or a pencil, may remove defects, and im- 
 prove all the positives printed from it. This is often de- 
 
96 CHEMICAL PHYSICS. 
 
 sirable, as freckles and pimples upon the face are liable to 
 be exaggerated in the photographic negative. 
 
 174. Varying Affect of Colored Lights. Yellow and red- 
 dish light being chemically inoperative, the artist can carry 
 on his manipulations by a dingy lamp-light or daylight 
 passing through yellow glass ; and as blue light is chemi- 
 cally most powerful, the reflected illumination of the sky 
 is favorable for photographic effects. White clouds in- 
 crease thu chemical intensity of light, while gray clouds 
 diminish it. Blue, indigo, and violet colors generally come 
 out light in photographs, while yellow and red work dark. 
 Hence dark-blue flowers on a light-yellow ground produce 
 light flowers on a dark ground. Red, and also fair golden 
 hair, becomes black, and yellow specks in the face produce 
 black points in a picture. It is obvious from this unequal 
 working of light that mai^-colored toilets must produce 
 discordant photographic results. " Persons of dark com- 
 plexions, also stout persons, should prefer dark clothes; as 
 it is well known that white clothing increases in appear- 
 ance the fullness of the figure. Thin and pale persons are 
 advised, on the contrary, to wear light clothes, as a pale 
 complexion would appear even paler when contrasted with 
 black." (Vogel.) 
 
 175. Celestial Photography. The applications of pho- 
 tography in the arts are becoming constantly more valu- 
 able, and it is also an important resource of science in 
 making quick and accurate representations, and in record- 
 ing the workings of self-registering apparatus. Its astro- 
 nomic indications are of especial interest. Enlarged pho- 
 tographs of the moon represent the details of its surface 
 with surprising minuteness ; and photographs of the stars 
 are taken, which define their position with the greatest 
 accuracy. In observing eclipses of the sun, this power of 
 producing instantaneous pictures is invaluable ; for the 
 display in a total solar eclipse is grand, complex, and mo- 
 mentary chromosphere, prominences, and corona, all burst 
 
SPECTRUM ANALYSIS. 
 
 97 
 
 upon the view at once, and baffle every attempt at delinea- 
 tion. The corona is a vast, irregular luminous appendage 
 surrounding the sun, reaching away to immense distances, 
 only visible in eclipses, of unknown nature, and presenting 
 the greatest diversity of aspects at different times. Pho- 
 tography is therefore eminently adapted to seize its pecul- 
 iar and varying ap- 
 pearances. Fig. 93 
 represents a picture 
 of the eclipse of 1868, 
 taken in a few sec- 
 onds, and selected 
 because its aspect is , 
 very marked. The 
 great coronal halo 
 is seen to have the 
 appearance of rays, 
 with deep gaps or 
 rifts; and the curious 
 effect of an oblique 
 luminous line cutting the lower stratum of light was re- 
 corded upon the plate. Other photographs give a more 
 even outline, and a wider circle of white light around the 
 central body. The multiplication of such impressions in 
 different places, and at different times, will be of the ut- 
 most service in the investigations of solar physics. 
 
 Photograph of Total Solar Eclipse of 1S68. 
 
 CHAPTER VH. 
 
 SPECTRUM ANALYSIS 
 
 176. Interest of the Subject The progress of science 
 is full of surprises. A step is taken that seems so wonder- 
 ful that nothing can surpass it ; but it is soon eclipsed by 
 something still more wonderful. With the remarkable 
 
98 CHEMICAL PHYSICS. 
 
 discovery that the radiations of space can produce endur- 
 ing images by the chemical alterations of matter, it was 
 thought that the marvels of light were exhausted; but, 
 twenty years after photography, came spectrum analysis 
 the most brilliant and startling of all modern discoveries. 
 It has endowed the chemist with a power of research of hith- 
 erto unapproachable delicacy, by which new elements have 
 been discovered, and our knowledge of the composition of 
 matter greatly extended and refined. And, what is much 
 more astonishing, it has revealed the chemical elements 
 in the atmospheres of the sun and the stars; and thus 
 made chemistry a cosmical instead of a terrestrial science. 
 In spectrum analysis, chemistry and physics become most 
 intimately united, so that an account of it becomes neces- 
 sary before closing the subject of Chemical Physics. 
 
 1. The lAiminous Spectrum. 
 
 177. Newton's Experiment. The analysis of the solar 
 beam into its elemental colors by the prism has been re- 
 ferred to in speaking of the general properties of light 
 (150) : we have now to study the spectrum more carefully. 
 
 FIG. 94. 
 
 Kecom position of Light by a Lens. 
 
 Spectral phenomena, as seen in rainbow-tints, in the sparkle 
 of jewels, the chromatic flashes of cut-glass, and the gleam- 
 
SPECTRUM ANALYSIS. 
 
 ing hues of clouds at sunset, have ever been familiar ; But 
 they were first explained by Newton in his treatise en 
 optics, presented to the Royal Society in 1675, exactly 
 two hundred years ago. He showed that white light, in 
 passing through the prism (Fig. 69), is resolved into its 
 elements, forming a splendid colored image, such as is 
 shown in the plate at the beginning of the volume. This 
 is proved by reversing the process. If the separated col- 
 ored rays are recombined by a lens, as illustrated in Fig. 
 94, they reproduce the spot of white light. 
 
 178. The Solar Spectrum The colors produced by 
 prismatic analysis are ultimate elements. Those seen in 
 the perfect solar spectrum are in the highest degree brill- 
 iant and pure. They blend with each other in impercepti- 
 ble gradations, so that their number and limits are indeter- 
 minate. For convenience they are designated as forming 
 seven principal groups; but, as Baden Powell remarked, 
 " the fact is, the number of 
 
 primary rays is not really 
 seven but infinite." That 
 the colors produced are in- 
 capable of further decom- 
 position may be show r n by 
 passing a beam of the spec- 
 trum through a second 
 prism, as represented in 
 Fig. 95. The white ray 
 refracted by the prism, $, 
 gives the spectrum on the screen, A B. Tf, now, an aper- 
 ture is made in the screen, and a colored pencil passed 
 through a second prism, P, it will not be further ana- 
 lyzed, but only diverted in its course. 
 
 179. Spectrum of the Plectric Light. Any source of 
 light may be employed to produce a spectrum ; but next 
 to the sun, which is by far the most brilliant, the spec- 
 trum of the electric light is most powerful, and is gen- 
 
 FIG. 
 
 Effect of Second Prism. 
 
100 
 
 CHEMICAL PHYSICS. 
 
 FIG. 96. 
 
 erally used where intense effects are required. If two 
 carbon cylinders (Fig. 96) are brought near each other, 
 and the current of a powerful vol- 
 taic battery be sent through them, 
 the stream of discharge takes the form 
 of a brilliant arc of fire between the 
 points with the emission of a dazzling 
 light. This has to be inclosed in a 
 box or lantern, one of the forms of 
 which is shown in Fig. 97. As the 
 carbon-points gradually waste away, 
 the distance between them would be- 
 come too great, and they are kept in 
 the proper position by the machinery 
 of the lamp. The intensity of the 
 light from the voltaic arc depends 
 
 Electric Arc 
 
 chiefly upon the 
 amount of elec- 
 tricity generated, 
 and the purity of 
 the carbon-points. 
 Measured by its 
 chemical effects, 
 it has been found 
 that the electric 
 light from a Bun- 
 sen battery of for- 
 ty-six elements 
 has nearly one- 
 fourth the inten- 
 sity of sunlight 
 at noon in Au- 
 gust. The elec- 
 tric light is con- 
 venient for dis- 
 playing the spec- 
 
 FIG 97. 
 
 Klectric Lamp. 
 
SPECTRUM ANALYSIS. 
 
 tra produced by various substances. Fig. 96 shows a 
 piece of sodium placed for volatilization on the lower 
 carbon. 
 
 180. Dispersion. Although in prismatic analysis the 
 colors are always refracted in the same order, yet different 
 substances have very unequal refractive power, and separate 
 the rays unequally. The degree of separation is called dis- 
 persion. The dispersive power of water is low. A hollow 
 prism filled with water gives a short spectrum, as shown 
 in Fig. 98 (the lettered lines of which will be presently ex- 
 plained). The dispersion is seen to be much greater with 
 
 FIG. 9b. 
 
 Unequal Dispersion. 
 
 a prism of crown-glass. Again, the dispersive power of a 
 prism of flint-glass is twice as great as one of crown-glass : 
 and a hollow prism filled with bisulphide of carbon gives 
 a spectrum twice as long as that of flint-glass. The denser 
 the glass the greater the dispersion ; and the greater the 
 angle in prisms of all materials, the greater also is the 
 dispersion. But the spectrum loses in sharpness and brill- 
 iancy, in proportion as it is extended. 
 
 181. Combination of Prisms. Dispersion may be in- 
 creased by adding one prism to another in such a way that 
 the refracted light of the first shall pass on through the 
 second. Fig. 99 shows how this may be effected. The 
 electric light emerging through a slit, is directed by the 
 double-convex lens upon a flint-glass prism, and having 
 
102 
 
 CHEMICAL PHYSICS. 
 
 undergone one refraction, falls upon a second prism P 
 filled with bisulphide of carbon, which then forms the im- 
 age V R upon the screen. The image is seen to be di- 
 verted more than 90 to one side. With a spectrum thus 
 
 FIG. 99. 
 
 Spectrum formed by Two Prisma. 
 
 produced, eight feet long, the colors would be distinguish- 
 able, but will have lost much of their brilliancy. 
 
 182. Trains of Prisms. For the usual purposes of 
 examination, a single prism suffices ; but, in delicate re- 
 searches, it is often desirable to increase the dispersion 
 to a high degree. This is especially the case in working 
 with the feeble light from the stars, comets, nebula, and 
 the aurora. Three, four, and sometimes a dozen prisms, 
 are therefore combined when such delicate observations 
 are required ; and the whole effect may be doubled by re- 
 flecting the light back through the same train, as will be 
 shown when we come to speak of the applications of the 
 spectroscope to celestial bodies (204), 
 
SPECTRUM ANALYSIS. 103 
 
 2. The Spectrosco%>e. 
 
 183, Its Essential Parts. The spectroscope is- an in- 
 strument for observing the spectrum. Fig. 100 shows its 
 simplest form, and the relation of its parts. L represents 
 the light, winch may be from any source, natural or arti- 
 ficial, the spectrum of which is to be examined. A is a 
 tube, closed at $, but in the end of which there is a vertical 
 
 The Simple Spectroscope. 
 
 slit, opened and adjusted by a slide or screw (205). This 
 slit is a very important part of the instrument, and is 
 formed by knife-edges of the most unchangeable material, 
 finished with great accuracy, so as to give a perfect line, 
 though not more than ^ of an inch in thickness. The 
 light entering the slit, passes through a tube called the 
 collimator, containing a lens, by which the rays are made 
 parallel before falling upon the prism. The rays emerge 
 from the opposite face of the prism refracted, yet only 
 slightly dispersed, so that the spectrum S is but little 
 larger than the width of the slit. In order to observe 
 it of a sufficient size, at a short distance, a magnifying- 
 glass or small telescope, F, is employed. The collima- 
 tor, the prism, and the spy-glass, are therefore the es- 
 sential parts; and in use the prism requires to be covered 
 to exclude the interfering light. 
 
 184. Measuring the Spectrum. But for scientific pur- 
 poses the instrument requires the most accurate means of 
 measuring the spaces of the spectrum. For this purpose a 
 third tube has been added, as shown in Fig. 101 at S. At 
 its outer end there is a glass plate, m, upon which is en- 
 
104 CHEMICAL PHYSICS. 
 
 graved or photographed a scale of minute divisions. A 
 lamp, JT, throws the image of this scale through the tube 
 and lens, so that it falls upon the face of the prism at n 9 
 at such an angle as to be reflected by the polished surface of 
 glass through the telescope Fio the eye. The scale is per- 
 manent, and parallel with it the observer sees the spectrum 
 
 Compound Spectroscope. 
 
 of whatever light is employed, and can thus fix and com- 
 pare the position of the lines with exactness. 
 
 185. The Mounted Instrument. The foregoing figures 
 show a mere skeleton of the parts, for explanation : Fig. 
 102 represents the construction of the instrument as ready 
 for use. A is the collimator-tube, the slit not being vis- 
 ible. A gas-burner is represented as the source of light ; 
 and a stand is shown beside it, with an arm for supporting 
 in the flame any substances it is desired to experiment 
 with. B is the telescope furnished with a guard to screen 
 the eye from extraneous light. C is the tube with the 
 scale for measurement, and a candle for projecting the 
 image. 
 
 186. Direct-Vision Spectroscopes, It would obviously 
 be an advantage if the slit, lens, prism, and telescope, were 
 
SPECTRUM ANALYSIS. 
 
 105 
 
 all in a straight line, so that the instrument could be ap- 
 plied directly to the light to be examined. This result is 
 gained in the direct-vision spectroscope. If two exactly 
 
 FKJ. 102. 
 
 The Common Mounted Spectroscope. 
 
 similar prisms are combined in opposite positions, as in Fig. 
 103, A B, the changes impressed upon a ray by the first will 
 be counteracted by the second. But, if the prisms differ in 
 refractive angles, or density of material, this counteraction 
 will not be complete. The deviation may be corrected, 
 which will give a straight path for the light, but the dis- 
 persion may be but partially corrected, which will leave a 
 spectrum. This depends upon the principle that the disper- 
 
106 
 
 CHEMICAL PHYSICS. 
 
 Fig. 103. 
 
 Counteraction of Prisois. 
 
 sive power of various kinds of prisms is not exactly in the 
 
 proportion of their refractive 
 power. Hence, if two crown- 
 glass prisms, P P (Fig. 104), 
 are combined with a flint glass 
 prism, P', of greater angle, and 
 in a reversed position, the com- 
 bination will give a spectrum 
 in the line of sight. A train 
 of prisms thus arranged, and 
 combined with a spyglass, 
 
 forms the direct-vision spectroscope, which is shown mount- 
 ed upon a stand, S, FIQ 1Q4 
 
 in Fig. 105. It may 
 
 be detached from the 
 
 stand, unscrewed at 
 
 the centre, and placed 
 
 in a portable case. 
 
 These spectroscopes 
 
 are sometimes made straight Course of Ray. 
 
 so small that they may be conveniently carried in the 
 pocket. 
 
 3. Spectral Lines. 
 
 187. Newton's Spectrum imperfect. Newton used the 
 light from a round hole in a window-shutter, so that his 
 spectrum consisted of a series of 
 overlapping images of the aper- 
 ture, by which the colors were 
 slightly mixed. In this way the 
 deeper mysteries of the spectrum 
 could not be disclosed ; and for 
 g one hundred and twenty-seven 
 
 ==ssas ^ _ ^ 1 years no progress was made in 
 
 this branch of knowledge. But 
 Direct- Vision Spectroscope. * n 1802, Dr. Wollaston examined 
 
SPECTRUM ANALYSIS. 
 
 107 
 
 the spectrum formed by a nar- 
 row opening, and found that, in- 
 stead of being so pure as was al- 
 ways supposed, it was crossed in 
 various places by dark lines. The 
 discovery, however, although it 
 was the initial step of modern 
 spectrum analysis, excited no in- 
 terest at the time. 
 
 188. Fraunhofer's Lines. The 
 dark lines were afterward redis- 
 covered, in 1814, by a German 
 optician named Fraunhofer, who 
 explored them so carefully that 
 they have since been called after 
 his name. He studied the spec- 
 trum, formed by a fine slit, with 
 the telescope, and found that 
 the lines were very numerous, 
 that they varied in thickness and 
 were distributed in unequal 
 groups through the spectrum. He 
 counted 590 from the red to the 
 violet, and made a map of them 
 (Fig. 106), designating the most 
 important by the letters of the 
 alphabet. Fraunhofer further 
 found that the lines did not vary 
 in sunlight, examined at differ- 
 ent times ; that the reflected light 
 from the moon, or from Venus, 
 gives the same distribution of 
 them as the sun, while the spec- 
 tra of the fixed stars differ from 
 those of the sun, and from each 
 other. From these considerations 
 
108 CHEMICAL PHYSICS. 
 
 Fraunhofer drew the important conclusion that the cause 
 of the dark lines in the solar spectrum exists in the sun, 
 although what that cause could be seemed an impenetra- 
 ble mystery. 
 
 189. Dr. Draper's Investigations, The next most im- 
 portant step, after Fraunhofer, was taken by Dr. Draper, 
 of New York. He was the first to use Fraunhofer's 
 spectroscope in this country, more than thirty years ago. 
 He modified it in 1842, in such a manner as to cast the 
 fixed lines upon the sensitive surface of photographic 
 plates, and published a map of the results, showing four 
 great groups of these lines beyond the limit of the violet 
 ray, and probably doubling the number of lines up to that 
 time known. But, what is more important, he passed to the 
 examination of spectra formed by incandescent terrestrial 
 bodies, and discovered a principle which is fundamental in 
 the philosophy of the subject. He determined the temper- 
 ature at which a solid body begins to give off light, 
 showed that it is the same for all solids ; that, as the tem- 
 perature increases, the colored rays are emitted in the 
 order of their refrangibility, from red up to violet; and 
 that the spectra cf all incandescent solids are continuous, 
 or without lines or breaks. 1 
 
 190. Spectra of Gaseous Bodies. But when a solid body 
 is volatilized, its spectrum is changed, becoming discon- 
 tinuous, or broken up into separate lines ; and these are 
 not dark, but bright, and of various colors. If a little 
 sodium is introduced into the gas-flame (Fig. 102), and the 
 
 1 As but very imperfect justice has been done to the work of Draper 
 abroad, I am glad to notice the following admission from a recent and 
 English work of high character : " It has been found that all solid and 
 liquid substances act in the same way with regard to the increase of heat ; 
 they all begin to be visibly hot at the same temperature, and the spec- 
 trum is in every case a continuous one. This law was discovered by 
 Draper (Philosophical Magazine, 1847). The only known exception to 
 this law is glowing solid Erbia, whose spectrum exhibits bright lines." 
 (Roscoe's " Spectrum Analysis," third edition, p. 51.) 
 
SPECTRUM ANALYSIS. 109 
 
 spectrum be then observed through the telescope, a bright- 
 yellow line of light will appear, always in the same po- 
 sition ; and, if a higher dispersive power is applied, this 
 yellow line will be resolved into two, forming the double 
 line which is the distinguishing spectral mark of sodium. If, 
 now, potassium be submitted to the light, three lines appear, 
 two red at one extremity of the spectrum, and a purple line 
 at the other, all else being darkness. If electric currents 
 are sent through pure hydrogen, oxygen, or nitrogen gas, 
 each produces a spectrum of different lines, as shown in the 
 colored frontispiece. The colors of the lines are as variable 
 as the tints of the spectrum, and they vary in numbers 
 through an immense range : while sodium gives but two 
 lines, iron yields several hundreds. 
 
 191. What the Lines indicate. The spectral lines indi- 
 cate first, chemical identity, and serve as tests of chemi- 
 cal substances. Each element gives a peculiar spectrum, 
 distinguishable from all others in the number, color, breadth, 
 and grouping of its lines. So distinct are they, that when 
 a compound is vaporized all its elements are at once dis- 
 closed. If several substances are volatilized together, all 
 the spectra can be identified. Most of the lines are mere 
 films, like the finest spider's web, so that they really occupy 
 but a very small portion of the spectrum space. In some 
 cases, however, several of the bright lines cf different 
 bodies seem to coincide ; but upon narrower scrutiny these 
 have been generally found to show real though slight 
 differences of refrangibility. Such coincidences as are still 
 unsolved will probably disappear under higher instrumental 
 power. 
 
 192. Physical Indications. The spectral lines are also, 
 to some extent, indices of physical states. With increasing 
 temperature there is increasing brilliancy of the lines, and, 
 with some metals, lines come out under intense heat that 
 do not appear at lower degrees. Pressure or density also 
 affects the spectrum. If the particles of a gas are forced 
 
110 CHEMICAL PHYSICS. 
 
 together so as to approach the solid state, the spectrum- 
 lines are widened into band?, so as to approach the con- 
 tinuous spectrum. The spectrum of hydrogen may be thus 
 made continuous by great pressure. But this in no way 
 interferes with the fixity of the bright lines, or their value 
 as chemical tests. 
 
 4. Theory of Absorption. 
 
 193. What are the Spectrum Lines? The optical answer 
 to this question is, that they are images of the slit. A 
 slit of say the fiftieth of an inch would of course give on a 
 screen a very fine white line, which would be simply an 
 image of the aperture. Now, if that filmy ribbon of white 
 light is passed through a prism, the spectrum formed 
 will be a succession of colored lines into which the white 
 line has been resolved, and the whole spectrum will be 
 but a series of images of the slit, either continuous or 
 broken. It is easy to recognize that the bright-colored 
 lines are images, but it may be asked, what are the dark 
 solar lines images of? Darkness is absence of light, and 
 the dark lines of the spectrum simply indicate the absence 
 of luminous rays. It is sometimes supposed that there are 
 dark lines of gossamer delicacy in the sunlight, but this is 
 a misconception. There are rays wanting in the sunlight, 
 and in the spectrum these vacancies come out as lines of 
 darkness. If the slit is changed to a cross, then, as the 
 mark of sodium, we have a yellow cross, instead of a line, 
 and black crosses in the spectrum of sunlight. 
 
 194, Coincidence of Bright and Dark Lines, We thus 
 reach the vital question of Spectrum Analysis, What has 
 become of the missing rays of sunlight ? and what is the 
 relation between the dark solar lines and the bright lines 
 produced by burning terrestrial substances? That there 
 is some close relation was suspected by Fraunhofer, and 
 maintained bv others after him. The exact coincidence in 
 

 SPECTRUM ANALYSIS. 
 
 Ill 
 
 position of the double dark line D of the solar spectrum 
 and the double bright line of sodium attracted frequent at- 
 tention, and it was thought it could not be accidental. 
 This conclusion was at length reenforced by overwhelming 
 evidence. The solution of the problem was given bv Kirch- 
 
 Fio. 107. 
 
 Coincidence of Bright Iron Lines with Dark Solar Lines. 
 
 hoff in 1859. In order to map the positions of the bright 
 lines of various metals, he employed the dark lines of the 
 solar spectrum as his guide. Upon placing one spectrum 
 over the other, he was astonished to find that whole sys- 
 tems of lines in the two spectra were coincident in position 
 and gradation. The coincidence of more than sixty bright 
 lines of vaporized iron with the same number of dark solar 
 lines, the brightest corresponding to the darkest, was 
 shown as represented in Fig. 107, and Kirchhoff proved 
 mathematically that the chances are more than 1,000,000,- 
 000,000,000,000 to 1 that this could not happen without 
 some causal connection. Angstrom has since identified 470 
 bright iron lines with the dark solar lines, and it has been 
 established that 75 lines of calcium, 57 of manganese, 33 
 of nickel, and 170 of titanium, exactly correspond in group- 
 ing, breadth, and degree of shade, with the same number 
 of dark lines of the solar spectrum, 
 
112 CHEMICAL PHYSICS. 
 
 195, Absorption Lines. It was thus proved that both 
 orders of lines belong together, and must have a common 
 cause ; but what is that cause ? A step toward the answer 
 was taken by producing the dark lines experimentally. 
 When light is transmitted through certain vapors, and the* 
 
 FIG. 108. 
 
 Absorption by Vapor of Iodine. 
 
 passed through the prism, the spectra exhibit dark lines, 
 which vary in the different cases. Fig. 108 represents the 
 spectrum thus formed by the vapor of iodine. The dark- 
 lines, in the lunar band, show the rays that have been in- 
 tercepted, or absorbed, on their passage through the vapor, 
 and they are hence culled lines of absorption. 
 
 196. What Lines are absorbed? Vapors absorb the 
 kind of light that they emit, and let all other rays pass. 
 Sodium-vapor gives out yellow light, and so it stops yellow 
 light. This principle is so important that we must show 
 how it may be proved. In Fig. 109 suppose the part ^V G 
 removed, we shall then have the oil-lamp L giving light 
 which produces a continuous spectrum, which is observed 
 by the direct-vision spectroscope $, the light entering at 
 the slit s. If now the glass tube N' is interposed (which 
 is rilled with hydrogen, instead of air, to prevent combus- 
 tion), and a little sodium is placed in it and heated by the 
 gas-burner 6r, the tube becomes filled with sodium-vapor. 
 Upon now observing the spectrum, it will be found that 
 th red, orange, green, blue, and violet, have passed through 
 
SPECTRUM ANALYSIS. 
 
 113 
 
 unimpaired, while the yellow is absent, having been ab- 
 sorbed by the vapor. If vapors of lithium, strontium, 
 
 FIG. 109. 
 
 Absorption by Sodium Vapor. 
 
 or barium, are substituted, the colors that they emit when 
 luminous are in like manner extinguished. 
 
 197. Reversal of the Lines. The change from bright to 
 dark, or, as it is called, " the reversal of the spectrum," by 
 absorption, may be more fully shown with the apparatus 
 represented in Fig. 110. Suppose, again, the gas-burner G 
 removed, and a little sodium placed upon the carbon of the 
 electric-lamp. The rays emerging from the slit E pass 
 through the lens Z, and the prism P, and, falling upon the 
 large screen, will give the yellow line of sodium, the posi- 
 tion of which is marked at m. When the sodium has been 
 all volatilized, its yellow line disappears, and there remains 
 the continuous spectrum r V. Now restore the gas-burner 
 6r, into which there is inserted the spoon /, containing a 
 bit of sodium, which soon tinges the flame yellow. The 
 lesser screen $, which allows the rays to pass through 
 its opening, shades the larger screen from the diffused 
 light, and we have the dark line D exactly in the position 
 it occupies in the solar spectrum. In the same way the 
 spectral lines of potassium, lithium, strontium, and other 
 elements, have been reversed by absorption, from which it 
 
114 
 
 CHEMICAL PHYSICS. 
 
 is concluded that the dark solar lines are due to the same 
 cause, or are reversed lines. It is, however, to be observed 
 that these dark lines are only relatively dark. The sodium- 
 vapor in the experiment continues to emit its bright rajs, 
 but the light intercepted is so much more brilliant than 
 
 FIG. 110 
 
 Eeversal of the Sodium Liue. 
 
 that emitted that the lines appear as dark spaces in con- 
 trast with the adjacent colors. 
 
 198. Theory of Absorption. Spectrum analysis is thus 
 based theoretically upon a broad principle of physics. We 
 have seen (89) that there is a fixed relation between the 
 absorption and radiation of heat ; that is, at a given tem- 
 perature, as bodies absorb, so they radiate. We are more 
 familiar with the principle in acoustics. Resonant bodies 
 absorb only the vibrations they can give out. If we sing 
 near the piano, the strings sometimes respond, but the re- 
 sponse is alwa} r s a note that has been sung. The note 
 sung is not taken up by strings that vibrate differentlv. 
 The string affected absorbs the vocal vibrations that strike 
 
SPECTRUM ANALYSIS. 115 
 
 them in one direction, and emits the same vibrations in 
 all directions. So also with light The rays to which an 
 incandescent gas is transparent it cannot emit ; only those 
 which it stops, or absorbs, can it again give out. This is 
 explained by the wave-hypothesis, on the principle that 
 incandescent molecules can only absorb and emit undula- 
 tions that are timed to their rates of vibration. 
 
 199. Fraunhofer's Lines explained. The early and saga- 
 cious conjecture of Fraunhofer that the cause of the dark 
 solar lines exists in the sun, and that they are lines of ab- 
 sorption, is thus verified ; and, moreover, the explanation 
 that is forced upon us gives a clew to the constitution of 
 the sun itself. The solar metals must be in a volatile state, 
 which implies an atmosphere surrounding the sun, and 
 laden with metallic vapors. Below this there must be a 
 liquid or solid nucleus of far greater heat, the main source 
 of illumination, and that yields a continuous spectrum. 
 This is called the photosphere, or light-giving stratum. As 
 its light shines through the atmosphere above, the metallic 
 vapors intercept the rays they can themselves emit, and 
 thus fill the solar spectrum with dark lines, or lines of ab- 
 sorption (206, 207). 
 
 5. Spectroscopic Applications. 
 
 200. Delicacy of the Chemical Indications. Spectrum 
 analysis affords a ready, certain, and delicate means of test- 
 ing chemical bodies. There are various rare metals which 
 resemble each other so closely, that they are distinguished 
 with difficulty by the ordinary methods ; but, however mixed 
 together, or with other substances, when vaporized their 
 characteristic spectral lines are detected at a glance. The 
 amazing sensitiveness of the reactions has led to new 
 results which would, a short time ago, have been regarded 
 as incredible. The spectroscope will easily detect the one- 
 eighteen-millionth of a grain of sodium, and it has shown 
 that sodic chloride (common salt) is almost omnipresent. 
 
116 CHEMICAL PHYSICS. 
 
 It pervades the atmosphere in its dust, and we breathe it 
 in the air we inhale. If we clap our hands, or shake our 
 clothing, or jar the furniture, the dust set in motion contains 
 sodium enough to affect the flame and give its reaction in 
 the spectrum. Again, the six-millionth part of a grain 
 of lithium is sufficient to reveal its beautiful red line, and 
 it would be detected though mixed with ten thousand 
 times its weight of other substances. It was formerly 
 regarded as a very rare element, known to exist in only 
 four minerals ; now it is found almost everywhere in the 
 juices of plants, fruit, bread, tea, coffee, wine, tobacco, 
 milk, and blood ; also in meteoric stones, and the water of 
 the Atlantic. Dr. Miller found that the stream of one 
 spring poured out eight hundred pounds of lithic chloride 
 everv twenty- four hours. 
 
 201. New Elements. That elements which had hitherto 
 eluded chemists should be caught by the spectrum tests 
 was to be expected. Bunsen, in examining the spectra 
 of alkalies from the ashes of a spring, at Durkheim, noticed 
 some new lines, from which he inferred a new substance. 
 He accordingly evaporated forty-four tons of the water, 
 and from its residue extracted two hundred grains of what 
 turned out to be the chloride of a new metal, which he 
 called ccesium, from its bluish-gray spectral line. Three 
 other metals, before unknown, and named Rubidium, Thal- 
 lium, and Indium, from the colors of their lines, were sub- 
 sequently found by the same means. 
 
 202. The Spectroscope in Steel-Making. By what is 
 called the "Bessemer process " cast-iron is changed directly 
 into steel, by burning out its excess of carbon. A large 
 amount of cast-iron five tons at a time is placed in a 
 suitable vessel, called a "converter," where it is melted, 
 and a copious stream of air is thrown into the bottom of 
 the vessel by a powerful blowing apparatus. The atmos- 
 pheric oxygen burns away the carbon and silicon from the 
 molten cast-iron, and the heated gases issue in flame at 
 
SPECTRUM ANALYSIS. 117 
 
 the mouth of the converter. The operation lasts about 
 twenty minutes, but it must be stopped at a certain point, 
 and if it is done ten seconds too early or too late the whole 
 mass is spoiled. The flame changes with the progress of 
 the combustion, and, although a quick and experienced 
 observer can judge very nearly when the time has come to 
 stop the blast, yet the spectroscope shows the exact mo- 
 ment at which the carbon disappears, and the combustion 
 must be arrested. 
 
 203. Organic Indications. The investigations of the 
 spectra of organic substances produced by burning, or by 
 the absorptive action of their solutions, are already fruit- 
 ful, and promise to be of great future importance. Solu- 
 tions of blood, magenta, and various coloring-matters, are 
 identified in extremely small proportions by the absorp- 
 tion-bands they produce ; and, by a combination of the 
 spectroscope with the microscope, blood-stains may be de- 
 tected in which the spot contains only the thousandth of a 
 grain of blood, and is fifty years old. The vintages of 
 wine differ so considerably in successive years as to be at 
 first readily distinguished, but as they grow old the dis- 
 crimination becomes difficult and uncertain by ordinary 
 means. A skillful English spectroscopist, Mr. Sorby, has, 
 however, shown that, by this mode of testing, old vin- 
 tages can be as well identified as recent ones. Again, this 
 process has been made to throw light on physiological 
 changes, such as the circulation, and the rate of diffusion 
 in the animal system. Dr. Bence Jones injected salts of 
 lithia under the skins of Guinea-pigs, and then, by the com- 
 bustion of the tissues, at different times, the appearance 
 of the red lithium-line showed the rate of diffusion of the 
 substance. Three grains being thus injected, in four min- 
 utes it was found to have made its way into the bile and 
 the aqueous humors of the eye, and in ten minutes traces 
 of it were detected in the crystalline lens. 
 
 204. The Tele-Spectroscope. But by far the most im- 
 
118 CHEMICAL PHYSICS. 
 
 pressive of all the applications of spectrum analysis is to 
 the heavenly bodies. An instrument adapted for this pur- 
 pose, and attached to the telescope, is called the tele-spec- 
 troscope. Fig. Ill represents the one employed by Prof. 
 
 FIG. 111. 
 
 Spectroscope, with Train of Prisms. 
 
 C. A. Young-, of Dartmouth College, in his solar researches: 
 a a are clamping-rings, which slide upon a strong metal 
 rod firmly fastened to the telescope, and which brings the 
 slit s of the instrument exactly in the focus of the object- 
 glass, where the image of the celestial object is formed. 
 The light passes through the collimator c (about an inch in 
 diameter and ten inches long) and traverses the train of 
 six prisms p near their bases. It is then twice reflected by 
 a rectangular prism r, and sent back through the upper por- 
 tions of the same prisms, by which the effect is doubled. 
 After this twelvefold dispersion the rays pass through the 
 lesser telescope t, and, being again reflected for conven- 
 ience of observation, are received by the eye at e. The 
 tangent screw m serves to adjust the position of the 
 prisms. 
 
 205. Viewing a Solar Prominence, Fig. 112 represents 
 the slit-plate of the spectroscope, of its actual size, the ob- 
 long bl ick square being the slit widely opened by the 
 
SPECTRUM ANALYSIS. 
 
 119 
 
 FIG. 112. 
 
 screw. This is brought to the edge or limit of the sun's 
 image represented by the white circular space. A sun- 
 spot is shown near by, and these 
 are often accompanied by promi- 
 nences. The slit is shown in Fig. 
 113 on an enlarged scale. If the 
 instrument is so adjusted as to 
 bring the Fraunhofer line C into 
 the centre of the field of view, then 
 on looking into the eye-piece an 
 effect resembling that in the figure 
 
 Opened Slit of the Spectroscope. 
 
 FIG. 113. 
 
 may be seen. Prof. Young says : " The red portion of the 
 spectrum will stretch athwart the field of vision like a 
 scarlet ribbon with a darkish band across it, and in that 
 band will appear the prominences like scarlet clouds; so 
 like our own - terrestrial clouds, indeed, in 
 form and texture, that the resemblance is 
 quite startling ; one might almost think he 
 was looking out through a partly-opened 
 door, upon a sunset sky, except thai there 
 is no variety or contrast of color; all the 
 cloud-tints are of the same pure sunset 
 hue." 
 
 206. The Solar Envelope. To the eye of 
 c . science the sun is a very different object 
 
 Spectroscopic As- 
 pect of a Promi- from that which appears to common observa- 
 nence. 
 
 tion. The light-giving portion, which seems 
 to form his true surface, and is called the photosphere, 
 while it incloses the chief mass of the sun, is estimated to 
 indicate but half its real diameter, and but one-seventh of 
 its volume. It is surrounded by a vast, irregular, variable 
 atmosphere, or envelope, in the most violent agitation, and 
 sending out eruptive masses at a rate of motion and on a 
 scale of magnitude that are almost inconceivable. This 
 envelope consists of different parts, which, though they 
 can hardly be regarded as stratified, yet conform to a gen- 
 
120 CHEMICAL PHYSICS. 
 
 eral order of position. Lying upon the photosphere is 
 what appears like a layer of scarlet fire, called the chromo- 
 sphere, which is five or six thousand miles in thickness. 
 Its appearance, according to Young, " is as if countless 
 jets of heated gases were issuing through the vents and 
 spiracles over the whole surface, thus clothing it with 
 flame, which heaves and tosses like the blaze of a confla- 
 gration." At different points are thrown up enormous 
 
 FIG. 114. FIG. 115. 
 
 .Vertical Eruption. 100.000 miles to Filamentary Prominence, 
 
 the inch. 
 
 masses of gaseous matter to various elevations, which are 
 called prominences, or protuberances. Many hundreds of 
 them have been observed and measured, and the most of 
 them vary from fifteen to seventy -five thousand miles in 
 height. Numerous instances are recorded of their reach- 
 ing an elevation of one hundred thousand miles, and Prof. 
 Young saw one over two hundred thousand miles high. 
 Their motions often have a velocity of one hundred miles 
 per second, and sometimes of double that rate. " Their 
 form and appearance frequently change with great rapid- 
 ity, so that the motion can almost be seen with the eye 
 an interval of fifteen or twenty minutes being often suf- 
 ficient to transform, quite beyond recognition, a mass of 
 these flames fifty thousand miles high, and sometimes em- 
 bracing the whole period of their complete development 
 or disappearance. Sometimes they consist of pointed 
 raySj diverging in all directions, like hedgehog-spines. 
 Sometimes they look like flames ; sometimes like sheaves 
 
SPECTRUM ANALYSIS. 121 
 
 of grain; sometimes like whirling water-spouts, capped 
 with a great cloud; occasionally they present most ex- 
 actly the appearance of jets of liquid fire, rising and fall- 
 ing in graceful parabolas ; frequently they carry on their 
 edges spirals like the volutes of an Ionic column ; and con- 
 
 FIG. 117. 
 
 Stemmed Prominence. Cyclonic Prominence. 
 
 tinually they detach filaments which rise to a great eleva- 
 tion, gradually expanding and growing fainter as they as- 
 cend, until the eye loses them." YOUNG. 
 
 207. Elements in the Sun. The principal constituent 
 of the chromosphere is hydrogen gas, which is always 
 present, as shown by the length and brilliancy of its 
 spectral lines. The prominences are regarded as local ac- 
 cumulations of the chromosphere, which seem to force 
 their way up from the interior of the sun with great vio- 
 lence, in the form of monster irruptions, which consist 
 mainly of incandescent hydrogen. There is no evidence 
 of oxygen, nitrogen, or carbon, in the sun. Besides hy- 
 drogen, the spectrum reveals the following solar elements, 
 as lately stated by Professor Roscoe : 
 
 1. Sodium. 5. Iron. 9. Zinc. 13. Rubidium. 
 
 2. Calcium. 6. Chromium. 10. Strontium. 14. Manganese. 
 
 3. Barium. 7. Nickel. 11. Cadmium. 15. Aluminium. 
 
 4. Magnesium. 8. Copper. 12. Cobalt. 16. Titanium. 
 
122 CHEMICAL PHYSICS. 
 
 These elements exist in a condition of ignited lumi- 
 nous vapor, most abundant in the lower parts of the chro- 
 mosphere, but many of them are thrown up to great 
 heights in the prominences. They, no doubt, undergo 
 condensation by cooling, and pour back upon the liquid 
 photosphere dense sheets of metallic rain. Prcf. Young 
 states that sulphur is probably present in the 'chromo- 
 sphere, and traces of other elements are reported. There 
 are also solar lines which correspond to no known terres- 
 trial substance. 
 
 208. Elements in the Stars. Light is the same through- 
 out the visible universe ; its nature is not changed by the 
 distances through which it travels. In the case of the 
 stars we have to deal with radiations, greatly weakened 
 in intensity, yet, such is now the wonderful delicacy of the 
 tests, that it has been lately proved that heat-rays are as- 
 sociated with the stellar light, and, as we have already 
 seen> the chemical rays, also. When the light of the stars 
 is studied by the spectroscope, it testifies, still further, to 
 the physical unity of the universe, by showing that the 
 same chemical elements which exist upon earth, and in the 
 sun, are found, also, in these distant bodies. In the spec- 
 trum of one star, Aldebaran, the lines of nine elements 
 have been identified, viz., hydrogen, sodium, magnesium, 
 calcium, iron, antimony, mercury, bismuth, and tellurium 
 the two latter not having been found in the sun. Other 
 stars give different spectra ; many hundreds have been ob- 
 served, and hydrogen discovered in all except two. The 
 stellar lines are both dark and bright, the former indicating 
 a white-hot nucleus, sending its light through absorbing 
 vapors, and the latter indicating a chromosphere. Spec- 
 trum analysis thus adds its powerful evidence to that al- 
 ready existing, to show that the stars are suns, similar in 
 constitution to our own. 
 
 209. A Star in Conflagration. In May, 1866, a star in 
 the constellation of the "Northern Crown," of the tenth 
 
SPECTRUM ANALYSIS. 123 
 
 magnitude, and so small as to be hardly known, was ob- 
 served to suddenly blaze out, and attain an apparent mag- 
 nitude equal to that of the largest stars. Examined by 
 the spectroscope it was found that, in addition to the usual 
 dark lines, there were the bright linfes of hydrogen, re- 
 markably clear. The star, however, soon began to fade, 
 and the bright lines to dwindle, and after the lapse of 
 twelve days, when it had fallen to the eighth magnitude, 
 these lines had totally disappeared. It seemed like the 
 outburst of prominences upon our own sun, though on a 
 far more stupendous scale. 
 
 210. Marvelous Delicacy of the Investigation. In the 
 case of the sun, the spectroscopist has to deal with light 
 of overpowering brilliancy, his meridian rays being many 
 times more intense than can be produced by any artificial 
 means ; but the light of the stars is at the opposite ex- 
 treme. We shall appreciate the difficulty of these observa- 
 tions by remembering that the light of a star emanates 
 from a mere point that is, it has no sensible magnitude, 
 and has to be kept steadily upon a slit only the 3^ part of 
 an inch in breadth, and which is constantly altering its po- 
 sition with the motion of the earth. Moreover, this faint 
 line of light has to be still further weakened by being 
 spread out into a band. The air, besides, is so unsteady 
 as to cause flickering, and confusion of the spectrum. Yet 
 over all these embarrassments skill and patience have 
 proved victorious. Roscoe says the spectrum of the star 
 Sirius has been photographed by Huggins. The inten- 
 sity of the light of this star is, according to the best 
 measurements, the -g-.Trw.TiW.Tnnr P art f ^at f ^ e sun 5 
 and, although probably not less in size than sixty of our 
 suns, it is estimated to be at the enormous distance of 
 more than 130,000,000,000,000 miles; and yet even this 
 immense distance does not prevent us registering the 
 chemical intensity of the rays which left Sirius twenty- 
 one years ago (MILLER). 
 
124: 
 
 CHEMICAL PHYSICS. 
 
 FIG. 118. 
 
 The Two Solar Spectra. 
 
 211. The Double Solar Spectrum. Another remarkable 
 result remains to be noticed, the spectroscopic proof of the 
 motions of celestial masses ; and to explain this we must 
 refer again to the sun. As from his photosphere we get 
 dark lines, and frofn his chromosphere bright ones, how are 
 they related to each other ? The lines from the same 
 elements having the same positions, if the bright and 
 dark spectra are brought together they should be continu- 
 ous, and such is the fact. If 
 the spectroscope be placed ra- 
 dially (Fig. 118), so that the 
 slit s s covers the photosphere 
 p and the chromosphere c, a 
 double spectrum will be seen, 
 and the dark lines will coincide 
 with the bright lines. In Fig. 
 
 119 the dark Fraunhofer line (7 is continuous with the scar- 
 let hydrogen-line, and the same continuity is observed 
 with the lines of other elements. 
 
 212. Variations of the Bright 
 Solar Lines. It has been stated 
 that the changes in the aspects 
 of the lines may indicate physical 
 alterations in the substances pro- 
 ducing them, the hydrogen-lines, 
 for example, being widened when 
 the gas is under pressure. The 
 bright solar hydrogen - line H 
 (Fig. 119) is generally more slen- 
 der than the dark line C", which is 
 explained by the greater rarity of 
 the hydrogen in the higher region 
 of the chromosphere. At the base, 
 
 however, it is seen to be widened, an effect due to the 
 pressure of the superincumbent mass. But it is also 
 observed that the bright hydrogen-lines are often bent, 
 
 mosphere above, near the C- 
 line. 
 
SPECTRUM ANALYSIS. 
 
 125 
 
 Changes in the ^-fine. 
 
 FIG. 121. 
 
 widened, twisted, and displaced, in a very remarkable way. 
 Fig. 120 represents F, as pictured by Lcckyer, strongly 
 bulged and contorted ; and Fig. 
 121 shows it as affected by a 
 solar cyclone. These alterations 
 of the positions of lines, in the 
 spectrum, are simply changes of 
 refrangibility, and, as the corre- 
 sponding dark lines suffer no dis- 
 turbance, at the same time we have 
 to seek the cause of the altered re- 
 frangibility in some change of the 
 hydrogen-mass above. An illus- 
 tration from sound will help us 
 to understand the cause of this. 
 When in a railway-train we listen to the whistle of a 
 rapidly-approaching engine, as it passes, 
 the pitch of the sound falls. This is be- 
 cause, with the advance of the engine, the 
 rate of air- vibrations striking upon the 
 ear is increased. In the same way, if a 
 luminous body is very rapidly approaching 
 the eye, the ethereal waves that enter it 
 are increased in number, and, as color de- 
 pends upon their rate, the pitch of color, 
 so to speak, will be altered. In the spec" 
 trum the effect would be to change the refrangibility of the 
 rays, and consequently the position of the lines. With the 
 swift approach of the body the more rapid wave-beats 
 would displace the lines toward the violet, while the reces- 
 sion of the body would shift them toward the red. From 
 this cause of variation in the lines, it becomes possible to 
 trace the direction of gas-streams, cvclones, and the course 
 of eruptive masses, and to account for the otherwise inex- 
 plicable mutations of the bright solar line?. 
 
 213. Motions of the Stars. Perhaps the most splendid 
 
 The F-line in a Solar 
 Cyclone. 
 
126 CHEMICAL PHYSICS. 
 
 triumph of spectrum analysis is the application of this prin- 
 ciple to the determinations of the motions of the stars. 
 Hitherto observations have been limited to movements 
 across the field of vision. Spectrum analysis proves the 
 approach and retreat of the stars by the displacement of 
 the hydrogen-lines. Mr. Huggins first established this by 
 a series of observations upon Sirius of the most consum- 
 mate delicacy. A powerful spectroscope being applied, a 
 slight displacement of H toward the red was discovered arid 
 verified by numerous observations. Fig. 122 shows the po- 
 sition of this line in Sirius, as 
 violet compared with its other deter- 
 mined positions. The normal 
 A position is obtained by sealing 
 up pure hydrogen in a vacuum- 
 is tube, free from pressure, and 
 passing through it a stream 
 c of electric sparks. It will be 
 seen that the 7^-line of Sirius is 
 started toward the red, as com- 
 .' pared with both its normal and 
 
 lu.; Celine in Solar Spectrum. ^ ^^ positk)ns , TMs dig . 
 
 placement exactly measured corresponds to a receding mo- 
 tion of the star of twenty-nine miles per second. ^ Later 
 observations by Mr. Huggins, with instruments of still 
 higher power, confirm and extend these results. Arcturus 
 is shown to be approaching us at the rate of fifty-five miles 
 per second, and the motions of various other stars have 
 been established. 
 
 Only a meagre outline of spectrum analysis has here 
 been giv r en, and it can convey but an imperfect idea of the 
 extent, precision, and surprising harmony, of the knowl- 
 edge that has so quickly arisen upon this interesting sub- 
 ject. Those who care to pursue the subject further, are 
 referred to the works of Schellen, Roscoe, and Lockyer, 
 
PART II. 
 CHEMICAL PRINCIPLES. 
 
 CHAPTER VIII. 
 
 GENERAL CHARACTER OF CHEMICAL ACTION. 
 
 214. FROM the study of those molecular forces which 
 determine the forms of matter, and variously influence chemi- 
 cal phenomena, we now pass to the consideration of chemi- 
 cal changes themselves. There are, however, certain ele- 
 mentary facts and principles of the subject, leading to im- 
 portant theoretical views, which it is necessary to consider 
 before stating the peculiar language of chemistry, or enter- 
 ing upon the detailed description of chemical substances. 
 
 215. The Chemical Force. Affinity, chemism, or chemi- 
 cal force, are names given to that power in Nature which 
 produces transformations of matter by altering its compo- 
 sition. It acts only at insensible distances, or when differ- 
 ent substances are brought into the closest relation with 
 each other ; but its effects are conspicuous, numberless, and 
 of the highest importance. It is an inherent and universal 
 energy of the natural world, from which no form of matter 
 is exempt, and causes incessant and innumerable changes 
 everywhere, around and within us. In the production of 
 all its effects, the chemical force conforms to exact and in- 
 flexible laws, forming a science equally remarkable for the 
 beauty of its principles, the depth of its philosophy, and 
 the practical value of its applications. 
 
128 CHEMICAL PRINCIPLES. 
 
 216. Elements and Compounds. Chemical force comes 
 into play only between different kinds of matter. If there 
 were but one kind of matter in the universe, there might 
 be physics, but no chemistry; this science, therefore, deals 
 with composition, and implies elements and compounds. 
 As the letters of its alphabet make up all the words, sen- 
 tences, and books of a language, so a small number of 
 chemical elements compose all the objects of Nature, and 
 many thousand artificial compounds made by chemical 
 experiment. All chemical changes consist in producing, 
 altering, or destroying compounds. The separation of 
 compound bodies into simpler ones is called decomposi- 
 tion / the process of separation, analysis. A highly-com- 
 plex body, like flour, may be first separated into simpler 
 substances, as gluten, starch, oil, and water, and this would 
 be proximate analysis ; these bodies may be again separ- 
 ated into their final elements, which is ultimate analysis. 
 Synthesis is the reverse process, by which simpler bodies 
 are built up into those of greater complexity. Qualita- 
 tive analysis determines of what elements a compound 
 consists ; quantitative analysis ascertains their propor- 
 tions. 
 
 217. Characteristic Effects of Chemical Force. It has 
 been stated that the physical forces alter only the forms 
 of bodies, but do not affect their nature. Chemism goes 
 deeper, destroying the distinctive qualities of substances 
 and producing new ones. Newness of properties in the 
 bodies formed is a consequence of all chemical action. It 
 may convert two solids into a liquid, two liquids into a 
 solid, or even two gases into a solid. Thus, when black 
 charcoal and yellow sulphur combine, the compound formed 
 is colorless as water, and highly volatile. Sulphur and 
 quicksilver unite to form the bright-red vermilion. Nitro- 
 gen and oxygen are neutral and tasteless, separate or 
 mixed ; yet one of their compounds, laughing-gas, is sweet, 
 producing delirium when breathed ; and another, nitric 
 
CHARACTER OF CHEMICAL ACTION. 129 
 
 acid, is an intensely sour corrosive poison. Carbon and 
 hydrogen are odorless, yet they combine to produce our 
 choicest perfumes. Mild and scentless hydrogen and nitro- 
 gen form the pungent ammonia ; while suffocating and poi- 
 sonous chlorine, united with a brilliant metal, gives rise to 
 common salt. There is, however, a gradation in these 
 effects. Substances resembling each other only lose their 
 properties partially; and the wider their differences, the 
 more complete is the transformation. If the elements are 
 very similar, the compound will show its parentage, as, for 
 example, in the union of metals forming an alloy ; if quite 
 unlike, all traces of its derivation will be lost. 
 
 218. Gradations in Chemical Attraction. When two 
 bodies unite to form a new substance, the chemical force 
 may not be satisfied, and the compound may again unite 
 with other substances, forming bodies still more complex. 
 But in such cases the combining power is progressively 
 weakened. Hence highly-complex bodies are generally 
 less stable than simpler ones. Thus, for example, crystal- 
 lized alum, a complex substance, may be easily decomposed 
 into the simpler compounds, water and burnt alum. The 
 latter, again, may be separated into potassic sulphate, and 
 aluininic sulphate. But it requires greatly-increased power 
 to decompose these into sulphur, potassium, oxygen, and 
 aluminium ; while no power hitherto applied has been suffi- 
 cient to decompose these substances, and they are hence 
 classed as elements. So far, only sixty-three of these sim- 
 plest forms of .matter have been brought to light, most 
 material objects being, therefore, compounds. A list of 
 the elements is given in the Appendix. 
 
 219. Conditions of Chemical Action. These are many 
 and various. Such is the range of intensities manifested 
 by chemical substances, that, while a mere touch, or a beam 
 of light falling upon a body, will sometimes destroy its com- 
 position, in other cases decomposition can only be brought 
 about by the intense and prolonged application of force. 
 
130 CHEMICAL PRINCIPLES. 
 
 220. Influence of Cohesion, As chemical combination 
 involves a total change in the arrangement of the internal 
 parts of bodies, it is clear that cohesion, which tends to hold 
 'them in certain fixed positions, must be opposed to chemi- 
 cal union ; and, on the contrary, any thing which gives mo- 
 bility to the particles of different substances and enables 
 them to approach within shorter distances of each other, 
 must tend to promote it. Hence it is only in few instances 
 that solids combine directly. Their combinations are fa- 
 cilitated by pulverization and grinding in mortars, or by 
 the aid of heat or other forces. Usually, one at least of 
 the combining bodies must be in the liquid or the gaseous 
 state before chemical action can take place. 
 
 221. Influence of Heat and Light. Heat is a potent 
 agent of chemical change from its control over the forms of 
 matter ; and so constantly is it used in the laboratory that 
 the chemist used to be called the " Philosopher by fire." 
 Sometimes it brings bodies into conditions favorable for 
 union, and then it may set up repulsive actions by which 
 combination is overcome. Sulphur, in the melted state, 
 will not combine with carbon ; it must be converted into 
 vapor, and the carbon heated to redness, before they can 
 be made to unite. The chemical action of light has been 
 already considered. 
 
 222. Influence of Electricity. Electricity also deter- 
 mines the combination of many substances, especially gases, 
 acting perhaps indirectly by elevation of temperature. By 
 passing through the mixture an electric spark, the union of 
 oxygen with hydrogen, and of chlorine with hydrogen, is 
 instantaneously brought about. The voltaic current also, 
 as has been before pointed out (141, 142), is one of the 
 most powerful agen j s of decomposition possessed by the 
 chemist. 
 
 223. Chemical Induction. A body in the act of chemi- 
 cal combination or decomposition often induces the same 
 kind of activity in another body, producing changes in 
 
CHARACTER OF CHEMICAL ACTION. 131 
 
 them by a kind of induction. Thus pure copper does not 
 dissolve in dilute sulphuric acid, while zinc does. But 
 when one part of copper is alloyed with three times its 
 weight of zinc, both metiils pass into solution. Again, 
 the compounds of several metals with oxygen, perfectly 
 stable by themselves at ordinary temperatures, may be de- 
 composed with almost explosive violence by being brought 
 into contact with a very unstable compound of hydrogen 
 and oxygen hydrogen dioxide both compounds being 
 decomposed together. 
 
 224. The Nascent State. The moment in which sub- 
 stances are liberated from union with each other is called 
 the nascent (forming) state, and, at this time, they often 
 enter into combinations which could not be formed under 
 other circumstances. Nitrogen and hydrogen gases, if 
 mingled, do not unite; but when set free from their 
 combinations they readily recombine, at the moment of 
 chemical change, to form ammonia. 
 
 225. Catalysis. The chemical union of bodies is often 
 effected or aided by the bare presence of a substance which 
 does not itself undergo any alteration during the process. 
 Thus the presence of finely-divided platinum brings about 
 the combination of oxygen and hydrogen gases at ordinary 
 temperatures, which would otherwise take place only at 
 red heat. This is apparently due to the power of finely- 
 divided and porous bodies to condense gases on their 
 surface, whereby the atoms of the combining bodies are 
 brought into closer contact. This form of chemical in- 
 duction is termed catalysis, or contact action. 
 
 226. Intensities of Chemical Action. Chemical force 
 acts through an infinite range of intensity. Sometimes 
 the changes proceed slowly, as in rocks and soils ; some- 
 times rapidly, as in growth, decay, or putrefaction ; and 
 sometimes with great violence, as in combustions and ex- 
 plosions. Our life depends upon that quiet rate of chemi- 
 cal change which takes place in breathing or respiration. 
 
132 CHEMICAL PRINCIPLES. 
 
 But the same force may act with such terrific power that a 
 few ounces of nitro-glycerine exploded upon the surface 
 of a rock will shatter it to fragments. That such forces 
 may be dealt with, and such operations controlled, is be- 
 cause they are governed by inflexible laws. 
 
 227. The Mathematical Basis of Chemistry, One of the 
 greatest discoveries of modern times is the truth that Na- 
 ture works with the same exactness on the small scale as 
 on the large. It is the glory of Newton to have proved 
 that the material objects of the universe attract each other 
 according to a definite mathematical law by which all the 
 celestial and terrestrial motions of bodies are regulated. 
 It has been established by chemists that the minutest par- 
 ticles of matter, in their actions and reactions, obey a cor- 
 responding law, and that every chemical compound has a 
 mathematical constitution as fixed as that of the solar sys- 
 tem itself. The stones and soil beneath our feet, and the 
 ponderous mountains, are not mere confused masses of mat- 
 ter ; they are pervaded throughout their innermost constitu- 
 tion by the harmony of numbers. The fuel we burn wastes 
 away before us, dissolves in air, and passes beyond the 
 reach of sight ; but the invisible changes among the un- 
 seen particles are definite, exact, and harmonious. And 
 so it is with all chemical mutations. When instruments 
 of weighing had attained sufficient perfection, it was found 
 that, however often matter might change its form, nothing 
 was either gained or lost that its quantity remained the 
 same ; and it was soon found.that the constituents of chemi- 
 cal compounds always combine in the same proportions. 
 
 228. The law of Definite Proportions. When, the com- 
 position of a sample of pure water, common salt, lime, or 
 any other substance, is once accurately determined, the 
 knowledge applies to all these substances their elements 
 enter into them in constant and invariable proportions. 
 Pure water consists of 1 part by weight of hydrogen, and 
 8 parts by weight of oxygen ; common salt of 35.5 parts of 
 
CHARACTER OF CHEMICAL ACTION. 133 
 
 chlorine to 23 of sodium. This principle is known as the 
 law of definite proportions, and its consequence is that 
 every chemical element has a numerical property by which 
 it is governed when entering into combination. These 
 quantities are known as combining numbers. The princi- 
 ple holds, moreover, in the union of compounds with each 
 other, as well as with elements ; the combining number of 
 a compound being determined by adding together the com- 
 bining numbers of its constituents. 
 
 229. The Law of Multiple Proportions. The old idea, 
 that chemical combination was indefinite, long held its 
 ground against the gradually accumulating proofs that 
 all combination is definite and constant. But, when this 
 principle was established, it soon led to the discovery 
 of another, known as that of the multiple proportions of 
 combination. It was found that two elements may com- 
 bine so as to produce several different substances, and 
 that the proportions of one or both elements will be vari- 
 able in the different compounds. ' But these variations are 
 in simple numerical proportions, each part being exactly 
 doubled or tripled in its quantity. Hence, when combi- 
 nations occur in more proportions than one, the larger 
 quantities are multiples of the smaller by a whole num- 
 ber. This principle is formulated as the law of multiple 
 proportions, and is illustrated by the following example of 
 the ratios in which carbon and oxygen unite : 
 
 Carbon. Oxygen. 
 
 Carbonic monoxide 12 : 16 
 
 Carbonic dioxide 12 . 32 
 
 The law is still more marked in the case of a series 
 of compounds of nitrogen and oxygen : 
 
 Nitrogen. Oxygen. 
 
 Nitric mon-oxide... 14 : 8 
 
 Nitric dioxide ...14 : 16 
 
 Nitric trioxide 14 : 24 
 
 Nitric tetraoxide 14 : 32 
 
 Nitric pentoxide 14 : 40 
 
134 CHEMICAL PRINCIPLES. 
 
 230. Equivalent Proportions. It results, from the fore- 
 going, that the proportions, or multiples of them, in which 
 two bodies combine with a third, are those in which they 
 combine with each other. For example, 71 parts of chlo- 
 rine unite with 32 parts of sulphur, and with 56 parts of 
 iron; but 32 to 56 is the ratio in which sulphur combines 
 with iron. These relative numbers have been called equiv- 
 alent proportions, or equivalents ; but this idea has re- 
 cently undergone very important modifications, and an 
 enlarged and more accurate conception of it has become 
 the basis of the new system of theoretical chemistry now 
 to be considered. 
 
 CHAPTER IX. 
 
 THEORETICAL CHEMISTRY. 
 
 1. Theory of Atoms and Molecules. 
 
 231. The Old Atomic Theory. It was an ancient specu- 
 lation that all matter is made up of atoms, or exceedingly 
 minute particles, which are endowed with powers and vir- 
 tues that explain all the properties of things, and the effects 
 they produce. It was warmly disputed whether these 
 particles are capable of being divided and subdivided to 
 infinity; but there were no data for determining this ques- 
 tion, and the vague notion of the atomic constitution of 
 matter remained for thousands of years nothing more than 
 an ingenious guess. 
 
 232. Dr. Dalton revives it. But, when science had ex- 
 perimentally proved that there are definite numerical rela- 
 tions among the minutest parts of matter, this old problem 
 was placed in a new light. The idea of the definite propor- 
 tions of chemical combination, at first strongly resisted, was 
 established near the close of the last century. It was soon 
 
THEORETICAL CHEMISTRY. 135 
 
 extended by Dr. Dalton, of Manchester, England, who dis- 
 covered the law of multiple proportions ; and, to explain 
 it, he went back to the old Greek conception of atoms. 
 He assumed 1. That all matter consists of ultimate and 
 unchangeable particles or atoms; 2. That atoms of the 
 same element have a uniform weight, but that in different 
 elements they have different weights ; 3. That the combin- 
 ing numbers of chemistry represent these relative weights; 
 and, 4. That between these different atoms there are attrac- 
 tions, which unite them by juxtaposition in the formation 
 of chemical compounds. Dr. Dalton maintained that, if 
 these ideas are accepted, the constancy of chemical charac- 
 ters and the definite and multiple proportions of combina- 
 tion follow as necessary consequences. This theory has 
 been of great service in the modern development of the 
 science ; but it has been gradually extended and altered, 
 until it now assumes a, quite different form from that 
 which it had at first. 
 
 233. The Molecule in Physics. The extension of the 
 atomic theory has consisted in the far greater prominence 
 and distinctness recently given to the conception of the 
 molecule ; a conception which has become fundamental, botli 
 in physics and chemistry. We have seen (26, 27, 75) that 
 the physicist regards all matter as made up of separated 
 units, with intervening spaces that allow a varied freedom 
 of movement ; and that upon this idea is based the mo- 
 lecular dynamics of the three states of matter. To the 
 physicist, therefore, molecules are not abstractions, but 
 actual things, having definite magnitudes (274), and he 
 defines them as the smallest particles of matter which 
 move a$ units from state to state, under the operation of 
 phys ical forces. 
 
 234. The Molecule in Chemistry. To the chemist the 
 molecule has also become no less a real thing, but he views 
 it in a different aspect. The physicist takes it as a unit, 
 and asks no questions as to what it is made of; but this is 
 
}36 CHEMICAL PRINCIPLES. 
 
 exactly the question of the chemist. He is to find out 
 whether the molecule be simple or compound, what kino, 
 or kinds of matter it contains, and what is its constitution. 
 The physicist, for example, grinds a bit of sugar down to the 
 finest particles of microscopic dust not the ten-thousandth 
 of an inch in diameter, but each particle still presents all the 
 properties of the lump, and he is very far from having yet 
 arrived at the molecule. He now puts it into water and it 
 disappears, changing to the liquid state. The visible parti- 
 cle may be thus divided into perhaps millions of molecules, 
 and when the water is evaporated the sugar returns to the 
 solid state, with all its properties unchanged. Again, a bit 
 of common salt, if sufficiently heated, passes into the state 
 of vapor, its molecules being driven widely asunder ; but 
 when condensed we again have the substance, with its 
 characters unaltered. The chemist now puts the sugar to a 
 test from his point of view. He heats it, or acts upon it 
 by a strong chemical agent, and finds that it contains three 
 kinds of matter, carbon, oxygen, and hydrogen. The sugar 
 is destroyed, and the three new substances produced from 
 it exactly equal it in weight. The sugar-molecule, he says, 
 is therefore not chemically a unit, but a compound. He 
 proves that the soda-molecule is a compound also, consist- 
 ing of two different kinds of matter, oxygen and sodium. 
 To the chemist, therefore, the molecule is not an ultimate 
 unit, but a group of units of a still lower order ; and he 
 defines the molecule to be the smallest particle of a sub- 
 stance which is capable of existing in a separate condition, 
 and in which its properties are preserved. 
 
 235. The Atom in Chemistry. The ultimate unit of the 
 chemist is the atom. Molecules and atoms have hitherto 
 been confounded together; but in the present state of 
 chemical science they represent totally different things. A 
 molecule is a group of atoms united by chernism, and capa- 
 ble of existing by itself ; an atom is the smallest quantity 
 of a substance that can enter into combination to produce 
 
THEORETICAL CHEMISTRY 137 
 
 the molecule. Atoms are indestructible, molecules sus- 
 ceptible of endless change. All chemical reactions are 
 therefore operations on molecules which are expressed in 
 terms of the atoms that compose them. A group of the 
 same kind of atoms forms an elemental molecule ; a group 
 of different kinds of atoms forms a compound molecule. 
 The breaking up of a molecule into its component atoms is 
 analysis ; the binding together of atoms to form mole- 
 cules is synthesis ; and the interchange of atoms between 
 different molecules is known as metathesis. 
 
 236. Symbols of Atoms. The chemical elements are 
 represented by symbols which are the first letters of their 
 names, and where different elements have the same initial 
 letter a small letter is added, or the first letter of the Latin 
 synonyms. Thus, N stands for nitrogen, B for boron, Br 
 for bromine, and Fe for iron (ferrum). 
 
 But the letter does not merely represent the substance ; 
 it stands for a certain quantity of it, the smallest that can 
 enter into combination the atom. H not only symbolizes 
 hydrogen, but one atom of it, the weight of which is taken 
 as 1. C stands for the carbon-atom, which has a combin- 
 ing weight of 12 ; and O for the oxygen-atom, weighing 
 16. These are the proportional numbers of combination, 
 and are also called atomic numbers. The molecules will, 
 therefore, be represented by writing together the symbols 
 of the atoms of which they consist, thus : H, hydrogen, and 
 Cl^ chlorine, combine to form hydric chloride, HC1, the sym- 
 bol of the molecule. The single letter always signifies one 
 atom, but, if several atoms are to be indicated, small Arabic 
 numerals are employed, thus : S 6 means six atoms of sul- 
 phur, P 4 four atoms of phosphorus ; H a O represents the 
 molecule of water, and CO a the molecule of carbonic diox- 
 ide. To represent several molecules a large figure is pre- 
 fixed, thus : 2H a O indicates two molecules of water, 4CO 2 
 four molecules of carbonic dioxide, and 10 (C 2 H 6 O) ten mol- 
 ecules of alcohol. By adding together the atomic weights 
 
138 CHEMICAL PRINCIPLES. 
 
 of the elements, in a molecule, we get the molecular weight 
 Thus for water, H 2 O, it is 18; for carbonic dioxide, CO 2 , 
 it is 44. The symbols and atomic numbers of all the ele- 
 ments are given in a table in the Appendix. 
 
 2. Progress of Chemical Theory. 
 
 237. Earlier Views The progress of chemistry has con- 
 sisted in the advance of theory, that is, in an ever-widening 
 view of facts, and a deeper insight into their relations. 
 The most ancient theories of material things referred 
 them to some essential principle, as air, water, or fire; and 
 then, later, these ideas were combined. The objects of Na- 
 ture were held to be formed of various commixtures of 
 four elements, fire, air, earth, and water; and for mai:y 
 centuries the properties and changes of all substances, ani- 
 mate and inanimate, were explained on this hypothesis. In 
 the seventeenth and eighteenth centuries, alchemy, the old 
 mystical pursuit of the art of gold-making, gradually grew 
 into a rough science of experiment by which much became 
 known of the qualities of different kinds of matter. For a 
 hundred years the explanation of chemical changes was 
 given by the theory of phlogiston. This was held to be a 
 kind of subtile matter, present in all combustible bodies, 
 and absent in all incombustible bodies, and which caused 
 combustion-changes by its escape. The doctrine is now re- 
 garded as a very crude one, but it contained truth, and was 
 of great service, in its time. A chemical belief that the 
 discoverer of oxygen, Dr. Priestley, held to the day of his 
 death, could certainly not have been an absurdity. Prof. 
 Cooke has the following excellent remarks on this early 
 theory : " That it was not absurd a single consideration 
 will show. Translate the word phlogiston, energy, and in 
 Stahl's work on chemistry and physics, of 1731, put energy 
 where he wrote phlogiston, and you will find there the 
 germs of our great modern doctrine of conservation of en- 
 ergy one of the noblest products of human thought, It 
 
THEORETICAL CHEMISTRY. 139 
 
 was not a mere fanciful speculation which ruled the scien- 
 tific thought of Europe for a century and a half. It was a 
 really grand generalization ; but the generalization was 
 given to the world clothed in such a material garb that 
 it has required two centuries to unwrap the truth." 
 
 238. The Binary Theory ; Dualism. With the abandon- 
 ment of phlogiston as a ruling principle of chemical change 
 the conception of affinity came forward, and chemical effects 
 began to be referred to inherent attractions among different 
 kinds of matter. At the epoch of Lavoisier, affinity was 
 thought of simply as a coupling force. Combination and 
 decomposition were supposed to take place directly among 
 bodies in pairs ; elements uniting with elements to form 
 binary compounds, and these uniting again by twos to form 
 double binary or ternary compounds ; and, when these were 
 made to act on each other, the reaction was represented as 
 a double decomposition. This was known as the dual 
 theory, and was commended for its simplicity and strongly 
 confirmed both by the beautiful nomenclature which was 
 adapted to it, and by the atomic theory which followed 
 soon after. Powerful aid was also subsequently lent to it 
 by electro-chemistry. Compounds were resolved into pairs 
 by galvanic decomposition, and their elements were sup- 
 posed to be in opposite electrical states, and to be united 
 by polar forces. In this system the controlling idea was 
 the properties of the elements, which were supposed to give 
 character to compounds, and the main question was, What 
 bodies does a substance yield upon analysis ? The proper- 
 ties of compounds were referred to the presence of pre- 
 dominating constituents, and hence oxygen was named as 
 the acid-former, and hydrogen as the water-former. The 
 question as to how the constituents of a compound were 
 grouped was hardly raised ; yet it now turns out to be a 
 question of very great importance. 
 
 239. Unitary or Substitution Theory. But, as chemical 
 changes were more closely studied, it was increasingly felt 
 
140 CHEMICAL PRINCIPLES. 
 
 that dualism, or mere splitting and pairing, gave a totally 
 insufficient account of them. There was a truth in this idea, 
 but it was not the whole truth. The conception of atomic 
 groupings in a molecule, and of the molecule as having 
 a unitary constitution, gradually rose into clearness. It 
 was found that the changes that take place among chemi- 
 cal compounds were rather of the nature of replacements 
 and substitutions, which left the structure of the molecule 
 intact. The constitution of the molecule, therefore, became 
 the main object of investigation. It was found, more- 
 over, that the most opposite elements could replace each 
 other in a group without altering its chemical character. 
 Chlorine, a powerful electro-negative element, could be sub- 
 stituted for hydrogen, a strong electro-positive element, in 
 a compound, without changing its characteristic properties. 
 Chemical compounds, instead of being likened to magnets, 
 with a twofold attraction of opposite poles, were now 
 likened rather to crystals whose angles and edges may be 
 replaced by new matter, the form being maintained. 
 
 240. Theory of Chemical Types, The unitary theory 
 attained fuller expression in the theory of types, in which 
 molecular structure first became a basis of classification. 
 Most chemical changes were viewed as replacements, which 
 conformed to a few general modes. As the stones of an 
 edifice may be successively exchanged, leaving the style of 
 architecture undisturbed, so atoms may replace atoms, leav- 
 ing the types of molecular structure unaltered. This im- 
 portant idea was at the basis of the theory. Gerhardt 
 proposed four such general types or patterns, taking hy- 
 drogen, hydric chloride, water, and ammonia, as repre- 
 sentative bodies, and classing with them all substances 
 which exhibit analogous reactions. But the exceptional 
 compounds were so numerous that the system was held 
 to be inadequate for classification, though invaluable as 
 a transition-step to something broader and more satisfac- 
 tory. 
 
THEORETICAL CHEMISTRY. 141 
 
 3. Theory of Atomicity and Quantivalence. 
 
 241. Variable Combining Capacity. The general theory 
 of chemistry now adopted is the outgrowth of preceding 
 theories, and embodies the truths they have severally at- 
 tained. But it adds an important principle which throws 
 further light upon chemical operations, and serves to or- 
 ganize into a better system the later facts and ideas of 
 the science. The notion of equality between combining 
 elements, and of equivalence among their atoms, has long 
 been fundamental in chemistry. When the substitution 
 theory arose it was still maintained that the replacements 
 were, atom for atom. But it is now recognized that the 
 replacing power of different kinds of atoms is unequal, 
 through a very considerable range. The idea of variable 
 combining capacity of atoms and molecules has been 
 worked out with great clearness, and is the distinctive 
 feature of what is now known as the New Chemistry. 
 
 242. Atomicity. While certain kinds of atoms inter- 
 change with each other as true equivalents, atom for atom, 
 it is found that in other cases it takes two, three, or 
 half a dozen atoms of one kind to equal one of another 
 kind in combining power. To determine these degrees of 
 equivalence of different bodies, we have but to take some 
 one, which will serve as a measure of comparison between 
 them. Hydrogen answers this purpose. It unites with 
 chlorine, atom to atom, forming the molecule of hydric 
 chloride, HC1 ; but oxygen cannot combine with hydrogen 
 in this w r ay; it must take two hydrogen-atoms, forming 
 the molecule of water, H 2 O. Nitrogen again takes three 
 atoms of hydrogen, forming the molecule of ammonia, 
 H 3 N ; and carbon behaves still differently, demanding four 
 hydrogen-atoms as in the molecule of marsh-gas, H 4 C. 
 We have, therefore, the four following molecular construc- 
 tions : 
 
 HC1 H 2 O H 3 N H 4 C 
 
 Hydric Chloride. Water. Ammonia. Marsh-Gas. 
 
142 
 
 CHEMICAL PRINCIPLES. 
 
 which vary in a regular numerical order. This may 
 seem to be accidental, but it is not so, for, if we take 
 chlorine instead of hydrogen as a measure, we shall get 
 similar results, as follows : 
 
 NaCl HgCl 2 SbCl 3 OC1 4 PC1 6 
 
 Sodic 
 Chloride. 
 
 Mercuric 
 Chloride. 
 
 Antimonic 
 Chloride. 
 
 Carbonic 
 Chloride. 
 
 Phosphoric 
 Chloride. 
 
 Now this is not something that merely happens among 
 a few selected substances; it illustrates a law that has 
 bet n traced through the whole chemical field. It is ob- 
 vious that in the first four groupings, the elements chlo- 
 rine, oxygen, nitrogen, and carbon, can no longer be re- 
 garded as equivalents of each other; nor are the sodium, 
 mercury, antimony, carbon, and phosphorus, of the second 
 group, equivalents of each other. Each element seems to 
 have its own atomic capacity. Hydrogen, sodium, and 
 chlorine, go together in ones ; oxygen and mercury take 
 hydrogen and chlorine by twos; nitrogen and antimony 
 take them by threes ; carbon takes both by fours ; and 
 phosphorus takes its chlorine in fives. This varying atomic 
 capacity is called atomicity, and the powers of the differ- 
 ent elements in this respect are known as their atomicities. 
 
 243. ftuantivalen.ee, and its Expressions. To these 
 chemical relations the general term quantivalence has also 
 been applied ; and different modes are employed to indi- 
 cate the several atomicities of the different elements. 
 They are as follows : bodies whose atomic capacity is 
 
 One, are termed Monads, Monatomic, Monadic, or Univalent. 
 
 Two 
 
 Three 
 
 Four 
 
 Five 
 
 Six 
 
 Seven 
 
 Dyads, 
 Triads, 
 
 Diatomic, 
 Triatomic, 
 
 Dyadic, 
 Triadic, 
 
 Tetrads, Tetratomic, Tetradic, 
 
 Pentads, Pentatomic, Pentadic, 
 
 Hexads. Hexatomic, Hexadic, 
 
 Heptads, Heptalomic, Heptadic, 
 
 Bivalent. 
 
 Trivalent. 
 
 Quadrivalent. 
 
 Quinquivalent. 
 
 Sexivalent. 
 
 Septivalent. 
 
 Bodies with a higher atomic capacity than one are said 
 to be polyatomic or multivalent. Hydrogen, in the single 
 
THEORETICAL CHEMISTRY. 143 
 
 compound it forms with chlorine, is assumed as the stand- 
 ard of atomicity. 
 
 Quanti valence is also expressed in different ways, as 
 follows : 
 
 Monads. Dyads. Triads. Tetrads. Pentads. Hexads. 
 
 H 1 O 11 N m C IV P Fe VI 
 
 01' S" B"' Si"" Bi"'" Mn""" 
 
 F- Ca= Ste Sm Tai Tel 
 
 With the monadic elements the indices of atomicity 
 are generally assumed and not written. 
 
 244. Bonds. To illustrate more clearly the meaning 
 and use of these indices of atomicity in representing 
 chemical combinations and changes, let us represent the 
 atom as a circle. Its attractions, polarities, or quantiva- 
 lence, may then be symbolized by radial lines, which be- 
 come the links of union, and appear as follows : 
 
 Monad. Dyad. Triad. Tetrad. Pentad. Hexad. 
 
 But as the links are the main things, the circles 
 (which were formerly much used) may be dispensed with, 
 and the dashes alone retained to mark the quantivalence, 
 thus : 
 
 H- -O- V N X -0- >P( )Fe< 
 i i i 
 
 These links or dashes are termed bonds. When chem- 
 ism takes effect it is assumed that the bonds of different 
 atoms are joined together, and they are said to be satisfied, 
 or closed ; when not so joined they are unsatisfied, or free. 
 The previous examples, in which numerals were used, 
 would be represented as follows by the use of bonds : 
 
 H 
 
 H H-O-H 
 
 H-C1 H-O-H H-N-H H 
 
 Hydric Chloride. Water. Ammonia. Marsh-Ga*. 
 
144 CHEMICAL PRINCIPLES. 
 
 ci 01-0-01 c \^9 l 
 
 Na-01 Cl-Hg-Cl Cl-s'b-01 01 01 01 
 
 Sodic Mercuric Antiraonic Carbonic Phosphoric 
 
 Chloride. Chloride. Chloride. Chloride. Chloride. 
 
 245. The Bonds control Combination. We have here 
 a controlling and limiting principle of all chemical 
 changes. In every transformation each bond requires to 
 be satisfied, and an atom can link itself to others only to 
 the extent of its bonds. Only those elements can unite 
 with each other, atom to atom, which have the same num- 
 ber of bonds. "The hydrogen, sodium, and chlorine atoms 
 have only one bond or pole, and hence, in combining with 
 each other, they can only unite in pairs. The oxygen- 
 atom has two bonds or poles, and can combine, therefore, 
 with two hydrogen-atoms, one at each pole. The mercury- 
 atom has also two bonds, and takes, in a similar manner, 
 two atoms of chlorine; but it can only combine with a 
 single atom of oxygen, for the two poles of one just satisfy 
 the two poles of the other. Again, the atom of carbon 
 has four bonds, which may be satisfied by either four 
 atoms of hydrogen, or four atoms of chlorine, or two atoms 
 of oxygen ; or one atom of oxygen and two of chlorine ; 
 or, lastly, one atom of oxygen and two of hydrogen. 
 Further, the atom of phosphorus has five bonds, and holds 
 five atoms of chlorine, or three atoms of chlorine, and one 
 of oxygen." On this theory, we view every chemical 
 compound as a molecule which can exist separately in con- 
 sequence of the equipoise of all its attractions, as shown 
 by the closing of the bonds of all its atoms. 
 
 246. Varying Quantivalence in the Same Element. Ele- 
 ments are not limited to one degree of quantivalence. 
 Thus nitrogen may act either as a triad or a pentad ; iron 
 as a dyad, tetrad, or hexad, and most of the other ele- 
 ments may assume different quantivalent relations. It is 
 remarkable that the same element in changing its quantiv- 
 
THEORETICAL CHEMISTRY. 145 
 
 alence changes its chemical relations almost as if it be- 
 came a new element, giving rise to widely different classes 
 of compounds in its different states of atomicity. Thus 
 triatomic nitrogen in ammonia, and 
 
 H H 
 
 i H x i 
 
 H-N >tf-Cl 
 
 i H i 
 
 H H 
 
 Ammonia Gas. Ammonic Chloride. 
 
 pentatomic nitrogen in ammonic chloride, give rise to two 
 series of compounds, with a marked contrast of properties. 
 Again, manganese unites with fluorine as a dyad, a tetrad, 
 and a hexad, as shown by the following graphic symbols ; 
 and the difference between the chemical relations of the 
 
 F F F 
 
 F-Mn-F F-Mn-F 
 
 F-Mn-F F F ^F 
 
 Mn. Dyadic. Mn. Tetradic. Mn. Hexadic. 
 
 diatomic and the hexatomic-atom is said to be " almost as 
 great as that between the atom of zinc and the atom of 
 sulphur." But the replacing and atom-fixing power of an 
 element in its different states is very unequal. Thus, 
 sulphur acts as a hexad, and lead as a tetrad ; but the 
 most common condition of both is diatomic. Nitrogen is 
 a pentad, but much more frequently a triad. Bodies have 
 thus a higher and lower quantivalence, and it has been 
 proposed to limit the term atomicity to the highest quan- 
 tivalence that they ever exhibit. But this is a less im- 
 portant property of an element than the leading or pre- 
 vailing quantivalence. 
 
 247. Perissads and Artiads. Variation in the degrees 
 of quantivalence in an element is always dual, that is, it in- 
 creases or diminishes by two. Hence, there are two series 
 of steps, an odd series one, three, five, and seven, and an 
 even series two, four, and six. Elements, whose quan- 
 
146 CHEMICAL PRINCIPLES. 
 
 tivalence is odd, are termed perissads ; elements, whose 
 quantivalence is even, are called artiads. It seems to be 
 a principle, almost, if not quite universal, that an artiad 
 can never become a perissad, nor a perissad an artiad. 
 There may be a few exceptions, but the distinction is re- 
 garded as fundamental, and as so completely separating 
 chemical bodies into two great divisions, that it is taken 
 as the basis of present classification. 
 
 248. Theory of Change by Pairs. The analogies of po- 
 larity offer an explanation of the changes of quantivalence 
 by pairs of attractions. When the opposite poles of a 
 magnet are brought together they neutralize each other ; 
 and so it is thought that the bonds of an atom, when not 
 closed by other atoms, may neutralize and satisfy each 
 other, in pairs conversely, the neutralized bonds may be 
 aroused by induction of more strongly polaiized atoms 
 (125). Thus, phosphorus unites with chlorine both as a 
 triad and a pentad ; and, if the atoms of the chlorine mole- 
 cule are assumed to be in opposite polar states, the change 
 of P m to P v is explained, thus : 
 
 c, 
 - 
 
 T Cl 
 ci-^i-v = CI-P< 
 
 01 01 01 
 
 The fact that a single bond is never suppressed is thus 
 accounted for, and a reason given why artiads and pe- 
 rissads are inconvertible. As the bonds can only be satu- 
 rated in pairs, a pentad can become a triad and a monad 
 successively ; and a hexad may be converted into a tetrad 
 or a dyad, as follows : 
 
 Perissads. Artiads. 
 
 , A k , A . 
 
 Pentad. Triad. Monad. Hexad. Tetrad. Dyad. 
 
THEORETICAL CHEMISTRY. 147 
 
 249. The Free State of Elements. As an atom or a 
 molecule can only exist separately when its bonds are all 
 closed, that is when saturated, it follows that perissads 
 cannot exist free. The odd bond must be satisfied. In 
 hydrogen gas, therefore, the condition is not atomic, as H- 
 is impossible ; but it is molecular, or H - H. So free chlo- 
 rine, Cl - Cl, and sodium, Na - Na, are self-saturated mole- 
 cules. As the even bonds of the artiads can close each 
 other, these elements may exist as separate atoms ; oxygen 
 being either O = O, or O >. 
 
 250. Importance of Mode of Linking. The quantiva- 
 lence of a molecule does not depend entirely upon the 
 atomicity of its elements, but partly upon the manner in 
 which they are united. When multivalent atoms are con- 
 nected together only by single bonds, the remaining bonds 
 will be free, and determine the quantivalence of the group. 
 Thus the molecule C 3 H 4 may be saturated, or diatomic, 
 accordingly as two bonds of the carbon-atoms are disposed 
 of. This is seen by comparing the following symbols : 
 
 i 
 
 H-C-H ~V~ 
 
 H-C-H H-C-H 
 
 Saturated. Diatomic. 
 
 251. Structure of Molecules. On this view it is impos- 
 sible to avoid the idea of the great importance of the 
 grouping of atoms in molecules. If the relations among 
 atoms are such that they can be most accurately repre- 
 sented by the mechanical conception of bonds and clamps, 
 that of structure in the molecules inevitably follows. These 
 structures are of different orders. With monads we can 
 only get molecules of the simplest construction, in which 
 the atoms are paired, as K-C1, H-I. As a monad has 
 but one bond, it can never join other atoms together; but 
 when dyads are introduced the molecular structure becomes 
 more complex. The dyad performs a linking function, and 
 
148 CHEMICAL PRINCIPLES. 
 
 in union with monads produces molecular chains. Oxygen 
 acts extensively in this way, as in 
 
 H-O-H H-0-Ca-O-H 
 
 Water. Calcic Hydrate. 
 
 and, by introducing more cxygen-links, such chains may be 
 indefinitely extended. With atoms of higher quantiva- 
 lence the complexity is increased in a still greater degree, 
 the muLivalent atom playing the part of a nucleus. The 
 following scheme represents the constitution of common 
 alum as a saturated molecule : 
 
 O O 
 
 V 
 
 O O O O 
 
 K-O-S-O-A1-A1-O-S-O-K 
 
 ii ii ii 
 
 O O O 
 
 \ / 
 
 s 
 
 # \ 
 
 O O 
 
 Potassic-Aluminic Sulphate (Alum). 
 
 The double atom of aluminium is the nucleus of the 
 group, and combines four subordinate groups, each having 
 a nucleus of hexadic sulphur. It matters nothing how 
 such a scheme is drawn, so that the atomicities are all 
 satisfied, but from the way such complex molecules break 
 up in decomposition it is inferred that there must be some 
 definite order of arrangement among the atoms. 
 
 4. Theory of Radicals. 
 
 252. Simple Radicals. The term radical has long been 
 applied to any chemical body which is regarded as a com- 
 mon ingredient, or basis of a series of compounds. Thus 
 potassium, sulphur, and, in fact, any element may be taken 
 as the starting-point, or root, of such a series. The sim- 
 ple radicals, or elements, may be divided into two great 
 
THEORETICAL CHEMISTRY. 149 
 
 classes, which stand in opposite relations, the metals and 
 the non-metals, the former being electro-positive, or posi- 
 tive radicals, and the latter electro-negative, or negative 
 radicals. 
 
 253. Compound Radicals. But it has been established 
 that there are groups of elements so bound together that 
 they play the part of simple bodies, and are therefore 
 called compound radicals / thus carbon and nitrogen com- 
 bine to form the radical cyanogen CN, which is the root of 
 a series of compounds much resembling those formed by 
 chlorine. Ammonium, NH 4 , is a compound radical which 
 behaves in chemical reactions closely like the metals, com- 
 bining with chlorine, sulphur, and cyanogen. Methyl, 
 CH 3 , is the radical of methylic alcohol ; and ethyl, C a H 6 , is 
 the root of ethylic alcohol, both of which are traceable 
 through numerous affiliated compounds. These compound 
 radicals are classed as positive and negative, like the sim- 
 ple ones. 
 
 254. Quantivalence of Compound Radicals. Compound 
 radicals also obey the laws of quantivalence like simple 
 radicals. In general they cannot be isolated, as they are 
 unbalanced molecules ; but some of them pair with each 
 other like elementary atoms, forming saturated molecules 
 which can exist separately. The radical hydroxyl, H - O -, 
 cannot, as it has an unsaturated bond, exist free, but 
 coupled as H-O-O-H it forms the compound known as 
 hydric peroxide. The compound radicals interchange with 
 each other, and with the simple radicals, under the usual 
 limitations of atomicity, or, according to the number of 
 free bonds. As represented by the graphic symbols, the 
 following radicals are monatomic : 
 
 H H H H H 
 
 N H-C- H-C 0- 
 
 H /X H H H H 
 
 Ammonium. Methyl. Ethyl. 
 
150 CHEMICAL PRINCIPLES. 
 
 5. Theory of Acids, Bases, and Salts. 
 
 255. The Old View, These numerous and important 
 bodies were long explained in a very simple way on the 
 dual theory, already noticed. The primary elements were 
 divided into the metals and non-metals, which, uniting with 
 each other in pairs, give rise to binary compounds, acids 
 and bases. Acids are sour, corrosive substances, that 
 turn vegetable blue colors to red, and have a strong chem- 
 ical attraction for bases. Bases, on the other hand, are a 
 class of bodies, (including alkalies, which have a hot, acrid 
 taste, and restore the blues discharged by acids,) that are 
 marked by their powerful chemical attraction for acids. 
 The union of acids and bases gives rise to the ternary com- 
 pounds known as salts bodies, generally, with a saline 
 taste, and in which the acid and basic constituents are 
 partially or totally neutralized. For example, the element 
 oxygen, " the centre of the chemical world,*' and long re- 
 garded as the acidifying principle of Nature, unites with 
 sulphur to form sulphuric acid, SO 3 . Oxygen also com- 
 bined with potassium to form basic potash, KO. These 
 binaries then paired in the production of the ternary salt, 
 sulphate of potash, KO, SO 3 . 
 
 Even in salts affinity is often not exhausted. They 
 may be again coupled, producing quaternary compounds, 
 or double-salts. Most of the bodies of Nature were viewed 
 as composed of these four great groups, primaries, binaries, 
 ternaries, and quaternaries ; and chemistry, for half a cen- 
 tury, consisted in extending chemical knowledge under the 
 guidance of this system. But, as facts have accumulated, 
 it has undergone a profound modification. 
 
 256. Water in Relation to the Theory. Water was long 
 supposed to act only as a solvent medium, facilitating the 
 reactions of other bodies, but not participating in the 
 changes, except that its particles were sometimes taken 
 up, and appended to other compounds, as " water of hy- 
 
THEORETICAL CHEMISTRY. 151 
 
 dration," or " water of crystallization." But at length it 
 began to be recognized that the elements of water are 
 themselves seriously implicated in the transformations. It 
 turned out, in fact, that, in regard to the constitution of 
 acids, alkalies, and salts, water holds a controlling relation ; 
 its molecule being the pattern upon which they are all 
 constructed. It was, moreover, found that the union of 
 acids and bases in the production of salts is not a direct 
 combination, or pairing ; but that acids, bases, and salts, 
 are all alike formed by the substitution of different kinds 
 of atoms for atoms in the water-group ; the replacements 
 occurring without disturbing the type of the water-mole- 
 cule. The water-group may be regarded either as a mo- 
 lecular chain, with hydrogen-atoms at each end, linked by 
 dyadic oxygen, H - O - H ; or, as a compound of the radi- 
 cal hydroxyl H - O -, with hydrogen ; and the substitution 
 may be either for one hydrogen-atom, for the two hydro- 
 gen-atoms, or for the hydroxyl group. 
 
 257. Constitutions of Acids. By comparing the water- 
 molecule with acid molecules, the relations are shown at a 
 glance : 
 
 Water. H-O-H 
 Hypochlorous Acid. H - O - Cl 
 
 Nitric Acid. H-O-(NO a ) 
 
 Here the hydrogen at one end of the water-chain has been 
 simply replaced by chlorine, and an acid molecule is the 
 result. The chlorine is a simple radical, powerfully elec- 
 tro-negative, which, by replacing hydrogen in the water- 
 molecule, produces an acid. Nitryl (NO 2 ) is a negative 
 compound radical, which also replaces hydrogen in the 
 water-molecule, producing the powerful nitric acid. An 
 acid molecule is therefore one in which a negative radical, 
 simple or compound, is united by oxygen to hydrogen, and 
 it has the general formula K - O - H . 
 
 258. Constitution of Bases. When pure metallic sodium 
 
152 CHEMICAL PRINCIPLES. 
 
 is added to pure water, energetic chemical action ensues, 
 hydrogen is set free, and the water becomes alkaline or 
 basic. If it is evaporated, a white powder is obtained, 
 which is caustic soda, or sodic hydrate. We begin with 
 sodium and water, and get sodic hydrate thus : 
 
 H-O-H 
 Na-O-H; 
 
 that is, the reaction has consisted simply in the substitu- 
 tion of Na for H in the water-molecule, which has not 
 changed its type. But, as the sodium is a diatomic mole- 
 cule, it engages two molecules of water, as may be graphi- 
 cally represented : 
 
 H-O-H Na Na-O-H H 
 H-O-H Na Na-O-H H 
 
 The new molecules have thus exactly the same struct- 
 ure as the old. Had potassium been used, instead of so- 
 dium, the reaction would have been the same, with the pro- 
 duction of another basic molecule. But sodium and po- 
 tassium are positive radicals. A basic molecule, therefore, 
 is one in which a positive radical, simple or compound, is 
 united by oxygen to hydrogen, and its general formula is 
 
 R-O-H. 
 
 259. Constitution of Salts. If, now, an acid molecule 
 and a basic molecule are brought together, a strong reac- 
 tion takes place ; but, again, it is a substitution that does 
 not impair the molecular type. We get a salt which has 
 
 the general formula R - O - R. Thus, an 
 
 acid, R-O-H) (R-O-R a salt, and 
 
 + c give < 
 
 and abase R-O-H \ (H-O-H water. 
 
 Compounds in which a positive element, or radical, is linked 
 to a negative element or radical by oxygen, or some analo- 
 gous dyad, are termed salts. 
 
THEORETICAL CHEMISTRY. 153 
 
 260. Hydrates. On the foregoing view acids and bases 
 belong to the same class of compounds, and are called hy- 
 drates acid hydrates and basic hydrates. Caustic potash 
 and nitric acid are opposite extremes of the same series 
 which are connected by bodies of intermediate gradation. 
 Hydrogen is an essential constituent of all acids and 
 bases. Salts contain no hydrogen, and possess neither 
 acid nor basic properties. 
 
 261. Quantivalence of Hydrates. The hydrogen, which 
 is directly linked to the atomic group by oxygen in acids, 
 is termed basic hydrogen ; that in bases, acid hydrogen. It 
 is readily replaceable in the former case by other positive 
 elements ; in the latter case by other negative elements or 
 radicals. Hydrates are univalent, bivalent, trivalent, etc., 
 according to the number of these replaceable hydrogen- 
 atoms, or hydroxyl groups ; arid acids are said to be mono-, 
 di-, or tri-basic; and bases, mon-, di-, or tri-acid, in the 
 same conditions. 
 
 262. Kinds of Acids and Bases. Acids or bases in which 
 all the oxygen (or analogous element) performs a linking 
 function, are called ortho-^ those which also contain oxygen 
 that is not linking, are termed meta-, acids or bases. The 
 atoms of ternary molecules may be connected by the nega- 
 tive dyads, sulphur and selenium, as well as by oxygen, 
 giving rise to sulphur and selenium acids, bases, and salts. 
 
 263. Classes of Salts. Salts containing neither acid nor 
 basic hydrogen are said to be normal. Acid salts are 
 those which contain basic hydrogen, and manifest acid re- 
 actions ; basic salts contain acid hydrogen, and produce 
 basic effects. Double salts are such as contain two or 
 more positive atoms. 
 
 264. Anomalous Bodies. As common salt, the sub- 
 stance which, above all others, was long considered as the 
 type of saline character, contains no oxygen whatever, it 
 cannot properly be included in this class of bodies. It 
 consists of one atom of each of the monad elements, so- 
 
154 CHEMICAL PRINCIPLES. 
 
 dium and chlorine, directly united. Substances of analo- 
 gous composition have been called haloids bodies re- 
 sembling salt. As the compounds of hydrogen with chlo- 
 rine, and other elements analogous to it, likewise contain 
 no oxygen, though often termed acids, they must also be 
 excluded from this group as above defined. They are 
 sometimes distinguished as hydr acids. 
 
 265. The Ammonia Type. In acids, bases, and salts, 
 the radicals are linked by dyads, but triadic elements, as 
 nitrogen, phosphorus, or arsenic,-, may perform a similar 
 linking function, and then we have a corresponding series 
 of bodies on a new type. Nitrogen is the nucleus of the 
 most important group, and its molecule in ammonia, 
 
 H 
 
 l is the type of a large class of compounds. If 
 
 H N H 
 
 the hydrogen is replaced by negative radicals, an amide is 
 produced ;. if by positive atoms, an amine results ; if by 
 one positive and one negative radical, an alkalamide is the 
 product. By thus substituting simple or compound radi- 
 cals for the hydrogen of the ammonia-molecule, we get the 
 
 H) 
 derived ammonias. If we write ammonia as H > N, and 
 
 H) 
 
 then substitute for its hydrogen the negative radicals, cyano- 
 gen, iodine, and chlorine, the formation of the amides will 
 be made clear : 
 
 (ON)' ) I ) 
 
 HkN IVN 
 
 H) Hi 
 
 Cyanamide. Din-iodamide. 
 
 By replacing the hydrogen with positive radicals, we get 
 the amines, as follows : 
 
 Na ) Rb ) 
 
 Na f- N Rb \ N 
 
 H ) Rb) 
 
 Di-iodamin. Tri-rubidamine. 
 
THEORETICAL CHEMISTRY. 155 
 
 6. Theory of Isomerism and Allotropisin. 
 
 266. Inorganic Chemistry in Relation to Theory. 
 Chemical science has been long divided into two great 
 branches inorganic chemistry, which treats of non-living 
 or mineral substances, and organic chemistry, which treats 
 of matter that composes the parts of organized things. In 
 the former department the chemist deals with all the ele- 
 ments of Nature in their simple physical conditions; in 
 the latter he is occupied with only a very few elements in 
 circumstances of great obscurity and complexity. In fact, 
 organic chemistry was long regarded as an impossibility, 
 under the belief that the vital force dominates in the or- 
 ganic sphere, and suspends the ordinary laws of chemical 
 action. It was therefore natural, and indeed inevitable, 
 that inorganic chemistry should be cultivated first, and that 
 the earlier theories of the science should be framed upon 
 the knowledge obtained by studying the simpler and more 
 general phenomena. Yet the domain was partial, and the 
 knowledge limited ; organic chemistry was a legitimate 
 and most important division of the science, and its numer- 
 ous and remarkable facts being left out, the prevailing 
 theories were necessarily defective. 
 
 267. Organic Chemistry in Relation to Theory. But it 
 was impossible to confine the chemists within these early 
 and arbitrary limits ; they pressed into the organic field, 
 and were rewarded by the discovery of multitudes of new 
 substances, many of them of great importance. They also 
 made an unexpected conquest by forming, artificially, in 
 the laboratory, various compounds which had hitherto been 
 regarded as producible only under the influence of life. 
 Much ingenuity was, however, at first expended in the 
 offort to bring the new facts into harmony with preexisting 
 theoretical views. The efforts, however, proved futile. A 
 new chemistry sprang up in the new province, which, in- 
 stead of being subordinated to old theories, powerfully re- 
 
156 CHEMICAL PRINCIPLES. 
 
 acted upon them. And thus, from a neglected region, long 
 supposed to lie beyond the bounds of the science, there 
 came an influence that has changed its whole theoretical 
 character. The modern ideas that are distinctive of the 
 new system changes by substitution, types, unitary 
 groups, atomicity, and the controlling importance of mo- 
 lecular structure have all arisen through the modern in- 
 vestigation of organic substances. 
 
 268. The Organic Elements, Four substances make up 
 the main bulk of organized bodies throughout the entire 
 vegetable and animal kingdoms, viz., hydrogen, oxygen, 
 nitrogen, and carbon. The properties of these bodies are 
 remarkable. The three gases have never been condensed 
 to the liquid or solid state by any application of mechani- 
 cal force, although they are constantly reduced to these 
 conditions by chemical action. Carbon, on the other hand, 
 is an equally invincible solid, never having been liquefied 
 or vaporized in its separate state. Hydrogen is the most 
 attenuated of bodies, the unit of the chemical system, and 
 the most widely-diffused element in Nature. Oxygen is 
 the most abundant element on the globe we inhabit, has an 
 extreme range of attractions, and forms compounds of all 
 grades of stabilitj'. Nitrogen performs peculiar offices of 
 the highest importance in the world of life, giving quality 
 to the most complex and changeable organized compounds. 
 Carbon is the common solidifying element in all organ- 
 ized products, and by its peculiar chemical relations stamps 
 the character of this division of chemistry. Hydrogen is 
 monadic, oxygen dyadic, nitrogen triadic, and carbon te- 
 tradic. The latter element, by its high multivalence, com- 
 bines with itself in interminable series of radical groups, 
 which become the skeletons or nuclei of a countless host 
 of compounds by linking with atoms and groups of other 
 elements. Organic chemistry, under this title, has in fact 
 now disappeared, and so important is the part played bv 
 carbon that this division of the subject is known as the 
 
THEORETICAL CHEMISTRY. 157 
 
 " Chemistry of the Carbon-compounds." Prof. Cooke, in- 
 deed, does not hesitate to say that " the number of known 
 compounds of this one element is far greater than those 
 of all the other elements besides." 
 
 269. Isomerism. The old conditions of analytic in- 
 quiry here obviously failed. It was not enough merely to 
 analyze organic substances, and state the elements and the 
 proportions of the elements that they contained. Analysis, 
 in fact, now broke down so completely as to leave no alter- 
 native to chemists but to seek the explanation of the prop- 
 erties of bodies in their atomic arrangements; for com- 
 pounds of the most diverse properties were found to con- 
 sist of exactly the same elements in exactly the same pro- 
 portions. Butyric acid, an oily liquid, not easily inflam- 
 mable, which has the disgusting smell of rancid butter, and 
 gives the acid reaction, has the formula C 4 H 8 O 2 ; while 
 acetic ether, a limpid liquid, non-acid, easily inflammable, 
 and having the pleasant, fruity smell of apples, has also 
 the formula C 4 H 8 O 3 . These substances are therefore said 
 to be isomeric, a term meaning equal measure. There is 
 no way of explaining this difference of properties, except 
 on the theory that the constituent atoms are differently 
 grouped in the two cases. And this is proved by acting 
 on the two molecules with chemical agents, when they 
 break up in very different ways, and give rise to different 
 products. Isomeric compounds are often convertible into 
 each other without loss or addition ; their different proper- 
 ties must therefore be ascribed, not to the presence or 
 proportions of certain elements, but to the influence of mo- 
 lecular clustering and structure. 
 
 270. Kinds of Isomerism. Isomeric phenomena are so 
 important that they have been discriminated as of different 
 kinds. If bodies have the same absolute composition, as 
 in the example just quoted, they are said to be metameric 
 compounds. But substances sometimes have not the same 
 atomic composition, although represented as identical on a 
 
158 CHEMICAL PRINCIPLES. 
 
 percentage scale. They have only the same proportions 
 of elements, and are then said to be polymeric compounds. 
 Isomeric bodies are called isomerides or isomers. 
 
 271. Allotropism. Closely allied to isomerism, in fact, 
 the same thing, only limited to elementary bodies, are the 
 phenomena of allotropism, or allotropy. The word means 
 different states, and denotes different conditions, into which 
 the elements are observed to pass with the manifestation 
 of diverse properties. Thus phosphorus, sulphur, and car- 
 bon exist, each in several different allotropic forms, with 
 totally unlike sets of characters. It was at first supposed 
 that but few of the elements were aliotropic, but it is now 
 found that a considerable number of them take on this 
 doubleness of condition. The only theory of these effects 
 hitherto offered, is that of varying atomic or molecular 
 arrangement. 
 
 7. Theory of Combining Volumes. 
 
 272. Space-Relations of Molecules. It has been stated 
 that the physicist and the chemist agree in regarding mole- 
 cules as actual things, pieces of matter, amazingly minute, 
 but just as real as planets and stars are to the astronomer. 
 Thus far we have considered them only in relation to 
 weight ; but if they are things of weight they must occupy 
 space, and have dimensions. Something has been done 
 toward elucidating this problem of the space-relations of 
 molecules ; and physics and chemistry have both contrib- 
 uted to the result. 
 
 273. The Law of Avogadro. When a given amount 
 of heat is applied to a given amount of matter in the solid 
 or liquid state, the expansions are unequal. If, for exam- 
 ple, the same amount of heat is applied to equal volumes 
 of water, alcohol, and ether, they expand differently ; but 
 if these substances are converted into vapor, and then 
 the same amount of heat is applied to equal volumes, 
 
THEORETICAL CHEMISTRY. 159 
 
 a new result appears : the vapors now all expand alike. In 
 the change to the gaseous state the molecules have got 
 free of each other's attractions, and enter upon a common 
 condition of mutual repulsion. In this state all gases and 
 vapors obey common laws, both in expanding under the 
 influence of heat, and in contracting under the influence 
 of pressure. What can be the cause of these remarkable 
 uniformities ? This question was answered by the Italian 
 physicist, Avogadro, as early as 1811, as follows : "Equal 
 volumes of all substances when in the state of gas, and 
 under like conditions of temperature and pressure, contain 
 the same number of molecules" This is known as Avo- 
 gadro's law. The law of Avogadro cannot be directly 
 proved, but it is indirectly established by the most con- 
 vincing evidence ; and it harmonizes and explains so great 
 a number of physical and chemical facts, that it is now 
 accepted by both physicists and chemists as a fundamental 
 principle. 
 
 274. Size of Molecules. That molecules have magni- 
 tudes is self-evident, and if the principle be true that 
 equal numbers occupy equal spaces, it is inferable that 
 they all have equal magnitudes. What those dimensions 
 are may be thought an impossible problem, and cer- 
 tainly it must be one of great difficulty, and uncertain 
 results. Yet the ablest physicists do not regard its diffi- 
 culties as insuperable, and claim to have already arrived at 
 approximate conclusions that are entitled to reasonable 
 confidence. Great advances have been made in recent 
 times in minute measurements. Time is measured in mill- 
 ionths of a second, and lines have been ruled on glass plates 
 numbering 224,000 to the inch several times finer than 
 the scale of wave-lengths. From various lines of research 
 of exquisite delicacy, among others, the relations of light 
 to thin films, the conclusion has been reached that the 
 diameters of gaseous molecules will not greatly vary from 
 the yoT,y}r f ToT f an * nc ^ According to a theorem of 
 
160 CHEMICAL PRINCIPLES. 
 
 molecular mechanics deduced by Clausius, the number of 
 molecules, in a perfect gas, at the freezing-point, and with 
 a barometric pressure of thirty inches, is about one hun- 
 dred thousand million million million, or 10 23 to a cubic 
 inch. Sir William Thomson, who has been prominent in 
 these investigations, says: "If we conceive a sphere of 
 water as large as a pea to be magnified to the size of the 
 earth, each molecule being magnified to the same extent, 
 the magnified structure would be coarser grained than a 
 heap of small lead shot, but less coarse grained than a 
 heap of cricket-balls." 
 
 275. Chemical Application of Avogadro's Principle. 
 If equal measures of two different gases or vapors contain 
 the same number of molecules, then we have but to weigh 
 these equal volumes to get the relative weight of the 
 molecules. For example, a cubic inch of oxygen weighs 
 sixteen times as much as a cubic inch of hydrogen, under 
 the same conditions ; but, if in every cubic inch there is 
 the same number of molecules, each molecule of oxygen 
 must weigh sixteen times as much as each molecule of hy- 
 drogen. We have thus a simple means of determining 
 the molecular weight of all bodies that are capable of 
 passing into the aeriform state. 
 
 276. The Unit of Molecular Weight If the hydrogen- 
 molecule were taken as the standard, then the specific 
 gravity of any gaseous body compared with it would give 
 its molecular weight. But the half-molecule of hydrogen 
 has been adopted as the unit, or 1, so that the hydrogen- 
 molecule will have to be represented by 2. This makes it 
 necessary to double the specific gravities of gases in order 
 to get the molecular weight. The volume of the hydrogen- 
 molecule being represented by 2, as all molecules have the 
 same volume, they must also be represented by 2. As the 
 molecule of hydrogen weighs 2, the molecule of oxygen, 
 which is sixteen times heavier, weighs 16 times 2, or 32. 
 The specific gravity of nitrogen, compared with hydrogen, 
 
THEORETICAL CHEMISTRY. 161 
 
 is 14; its molecular weight is therefore 28. As density 
 is weight referred to a unit-volume, a litre of hydrogen is 
 taken as the unit of density of gases, and is called a crith. 
 The numbers expressing specific gravity also express the 
 density or weight in criths, consisting of one litre of the 
 gas or vapor, under standard conditions, thus : 
 
 Hydrogen. Nitrogen. Oxygen. Chlorine. 
 
 Specific Gravity. 1 14 16 35.5 
 
 Density. 1 crith. 14 criths. 16 criths. 35.5 criths. 
 
 277. Physical Verifications. This method is of great 
 importance in chemical investigations, where molecular 
 weights and formula are to be determined. Analysis, 
 as we have before seen, gives us only the proportions 
 of elements in a compound. It tells us, for example, 
 that water consists of 88.89 parts, by weight, of oxygen, 
 and 11.11 parts of hydrogen, but this is only a ratio, and 
 may be expressed as 8 to 1, or 16 to 2, or 24 to 3, so that 
 the actual molecular weight of the water might be either 
 9, 18, or 27. But if now water is vaporized, and the vapor 
 weighed, its density turns out to be 9 times that of hy- 
 drogen ; and this number multiplied by 2 gives 18 as the 
 actual molecular weight of water. The molecular weights 
 of solid and liquid substances can only be chemically ascer- 
 tained by combining them with other substances, and finding 
 the lowest proportions in which such combination ever takes 
 place, which is the molecular weight. Such results are, 
 however, indecisive, as new combinations may give new 
 numbers. But, if the substance is capable of being vapor- 
 ized, the indications that may be obtained are usually re- 
 garded as conclusive. It may here be stated that there is 
 a kindred closeness in other numerical relations of physics 
 and chemistry. A striking connection is found to subsist 
 between the atomic weights and the specific heats of the 
 elements, known as atomic heat. That is, the numbers ex- 
 pressing the relative amounts of heat required to raise 
 
162 
 
 CHEMICAL PRINCIPLES. 
 
 equal weights of iron, copper, and lead, for example, 
 through equal degrees of temperature, coincide with the 
 atomic numbers of these elements. Moreover, the quanti- 
 ties of electricity expended in decomposing compounds 
 are found to be also in definite relation to the atomic 
 weights of the bodies set free. 
 
 278. Combining Volumes. Gases combine by volume 
 in very simple ratios ; in some cases in equal measures 
 without condensation ; but if condensation occurs it is by 
 whole units, as 2 to 1, 3 to 1, or 4 to 1, as is illustrated in 
 the following cases : 
 
 Hydrogen. Chlorine. 
 
 Ch 
 
 Hydric 
 loride 
 
 Water. 
 
 Hydrogen. 
 
 Nitrogen. 
 
 Carbon. 
 
 Marsh-Gas. 
 
 279. Theory of these Effects. The foregoing ratios of 
 combining volume are simple results of experiment ; but if 
 Avogadro's law is assumed, that equal gas-volumes contain 
 equal numbers of molecules, the theory of quantivalence 
 explains the effects. In the first case we have monadic 
 atoms with diatomic molecules H - H and Cl - Cl, and in 
 equal volumes an equal number of these molecules. When 
 the gases are mingled, the molecules interchange atoms 
 
THE CHEMICAL NOMENCLATURE. 163 
 
 producing H - 01 and H - Cl, but, as the number of mole- 
 cules remains the same, the volumes remain unaltered. In 
 the second case we have the dyad oxygen, the molecule 
 of which is O=O. Each of its atoms links two of hydro- 
 gen, forming the triatomic molecule H 2 O. The total num- 
 ber of molecules is thus diminished a third, and the three 
 volumes are consequently reduced to two. In the third ex- 
 ample we have triadic nitrogen, the molecule of which is 
 N^N. Each nitrogen-atom takes three hydrogen-atoms, 
 forming ammonia, H 3 N. All the molecules at first con- 
 tain two atoms, and the resulting molecules contain four. 
 There is, therefore, but half the number of molecules, 
 and the four volumes are reduced to two. Lastly, each 
 atom of the tetrad carbon molecule, OC, unites with four 
 atoms of monadic hydrogen, and the resulting molecule 
 contains five atoms. The number of molecules formed 
 equals the number of carbon-atoms, or twice the number 
 of the carbon-molecules, and hence the five volumes are 
 condensed to two. 
 
 CHAPTER X. 
 
 THE CHEMICAL NOMENCLATURE. 
 
 280. The Science reflected in its Language. The terms 
 used in chemistry bear the impress of the various theoreti- 
 cal stages of the science. Some of them, as gold, silver, 
 iron, were applied to substances thousands of years ago, 
 before the science had taken a separate form. The al- 
 chemists were the first chemists, and they worked under 
 the mystical influence of astrology. Terms still survive 
 that indicate the fancied relations of substances to celestial 
 bodies. Quicksilver was associated with Mercury ; silver 
 with Luna or the moon (hence lunar caustic) ; and crocus 
 
164 CHEMICAL PRINCIPLES. 
 
 Martis, a compound of iron, is a vestige of the old associa- 
 tion of this metal with Mars. The alchemists had a crude 
 theory of the action of spirits in Nature, and named vari- 
 ous products accordingly, as spirit of wine, spirit of salt, 
 spirit of hartshorn, spirit of nitre, etc. The first general 
 chemical theory, that of phlogiston, gave rise to a termi- 
 nology which has disappeared with the system, and which 
 renders many of the chemical books of the eighteenth cen- 
 tury almost unintelligible to a modern student. The 
 system of naming chemical substances called the Nomen- 
 clature, which originated with the French about a hundred 
 years ago, has been of immense service, both in the ad- 
 vancement and the diffusion of the science. When the 
 facts of chemistry were comparatively few, and its theory 
 simple, the terminology, which conformed to the dual doc- 
 trine, was also simple and highly effective. But as facts of 
 all orders rapidly multiplied, and assumed new relations, 
 the old system of expression was disturbed ; and now, 
 with the changes of theor}^ the nomenclature has been 
 unsettled at various points, and there is some want of 
 uniformity among authorities in the use of chemical terms. 
 The main principles, however, remain in full force. 
 
 281. Naming the Elements. The names of the ele- 
 ments generally given have been expressive of some lead- 
 ing quality, real or imaginary. Thus, oxygen, as has been 
 stated, received a name signifying acid-former, while chlo- 
 rine takes its name from its greenish color ; iodine, from its 
 purple vapor, and phosphorus from its being luminous in 
 the dark. Analogy of properties is sometimes indicated 
 by similarity of termination, as chlorine, brormwe, iodine ; 
 while the metals discovered in modern times are marked 
 by the termination um, as platinum, thallium, etc. 
 
 282. Naming of Compound Radicals, These sub- 
 stances, which, as we have seen, are analogous to elements, 
 are generally named from one or more of their constitu- 
 ents, or from some compound into which they enter. The 
 
THE CHEMICAL NOMENCLATURE. 165 
 
 terminal syllable, generally, is yl. Thus, the radical com- 
 posed of one atom of hydrogen and one of oxygen is .called 
 hydroxyl, and that composed of one atom of oxygen and one 
 of carbon, carbonyl. Ethylene and benzylene are exam- 
 ples of compound radicals whose names terminate in ylene. 
 Exceptions to the forms given are found in the case of 
 cyanogen, and in the numerous compounds formed of 
 carbon and hydrogen, or of carbon, oxygen, and hydro- 
 gen, whose names frequently bear reference to the 
 number of their carbon-atoms, as, for example, trityl, 
 tetryl, etc. 
 
 283. Naming of Binary Compounds. Binary com- 
 pounds, strictly speaking, result only from the union of 
 two elementary substances, but the term is frequently ex- 
 tended to include combinations of two compound radicals. 
 Thus, silicon and fluorine combine to form silicic-fluoride ; 
 while methyl and ethyl form methylic-ethide. All of these 
 compounds are named by placing the positive element Jirst, 
 and the negative element, with its termination changed 
 to ide, after it. Thus : 
 
 Compounds of Chlorine are called Chlorides. 
 
 Bromine " 
 
 Bromides. 
 
 Iodine 
 
 Iodides. 
 
 Fluorine " 
 
 Fluorides. 
 
 Sulphur " 
 Nitrogen " 
 Phosphorus " 
 Antimony ' 
 
 Sulphas. 
 Nitrides. 
 Phosphides. 
 Antimom'des. 
 
 Carbon " Carbonides. 
 
 The termination of the name of the positive element is 
 changed to ic, except in compounds, in which the positive 
 element unites with the negative element in variable pro- 
 portions, when the ending ic is confined to the compound 
 containing the smaller proportion of it, while the termina- 
 
166 CHEMICAL PRINCIPLES. 
 
 tion OKS expresses the larger quantity of the positive ele- 
 ment. Thus : 
 
 Ferrous oxide, FeO. 
 Fem> oxide, Fe 2 0a. 
 
 Stannow chloride, SnCl a . 
 Stanm'c chloride, SnCl 4 . 
 
 In some cases the terminations OKS and ic are affixed 
 to the ,ttames of the elements, as, for example, in the well- 
 known compounds sulphurous and sulphuric oxide. When 
 the name of the positive element is not derived from the Lat- 
 in or Greek language it is translated into the former be- 
 fore changing the termination ; thus, the Latin for gold is 
 durum, and it forms two compounds with chlorine, one of 
 which is termed aurous, and the other auric chloride. When 
 the number of compounds formed of two elements exceeds 
 two, hypo, under, and per, over, are employed to distin- 
 guish them ; thus, a compound containing less oxygen 
 than chlorous oxide is known as hypochlorous oxide, while 
 one containing more oxygen than chloric oxide would be 
 known as perchloric oxide. 
 
 284. Prefixes. A system of naming much used in 
 the following pages consists in the use of numerical 
 prefixes, expressing the number of atoms of the ele- 
 ment. The compounds of nitrogen and oxygen, all con- 
 taining two atoms of nitrogen, united with respectively 
 one, two, three, four, and five atoms of oxygen, are distin- 
 guished as nitrous monoxide, dioxide, trioxide, tetroxide, 
 and pentoxide ; while a compound containing three atoms 
 of iron and four atoms of oxygen is termed tri-ferric- 
 tetroxide. An exception to the previous rules is found 
 in compounds consisting of carbon and hydrogen these 
 are so very numerous that the methods given cannot be 
 rigidly applied. The termination adopted is generally ene. 
 
 285. Naming of Salts, Acids, and Bases. The consti- 
 tution of these compounds has been already explained (257), 
 
THE CHEMICAL NOMENCLATURE. 167 
 
 and the method of naming them is a modification of the 
 old system, which was derived from the dual view of 
 their constitution. They are named, like binaries, from 
 their constituent atoms. In the case of the negative ele- 
 ment the termination is changed to indicate that the atoms 
 are linked by oxygen. These negative terminations are 
 at 2 and ite / the positive element follows the rule given 
 (283). Thus, hydric nitride becomes, by the introduction 
 of more oxygen, hydric nitrate; by less oxygen, hydric 
 nitrite both acids. In salts the element which replaces 
 t'.ie hydrogen of the acid becomes the first term of the 
 name. For example, when the element sodium replaces 
 the hydrogen of hydric nitrate, we obtain sodic nitrate ; 
 when it replaces the hydrogen of hydric nitrite, we obtain 
 sodic nitrite. Bases are named like the salts, water taking 
 the place of the second term of the name. Thus, the base 
 which consists of calcium and hydrogen, linked by oxygen, 
 is termed calcic hydrate. 
 
 The common names of the acids are derived from those 
 of binary compounds containing oxygen by merely substitut- 
 ing the word acid for the word oxide, thus ignoring, in the 
 naming of the compound, the oxygen ; but, when the link- 
 ing element is not oxygen, but some of its analogues, a 
 prefix is used. Arsenic acid is composed of arsenic and 
 hydrogen, linked by oxygen ; sulpho-arsenic acid of arsenic 
 and hydrogen linked by sulphur. 
 
 286. Naming of Amides, Amines, and Alkalamides. 
 It will be remembered that these bodies are derived from 
 ammonia (265) by replacing one or more of the hydrogen- 
 atoms by other elements or radicals. They are named by 
 joining the names of the substituted elements, either with 
 or without their terminal syllable, with the termination 
 amide or amine. Thus, we have Cyanamide, Potassamine : 
 and the replacing of more than one element or radical is 
 indicated by numerical prefixes, thus : Di iodamide, Di-so- 
 damine ; and, when these compounds are derived from more 
 8 
 
168 CHEMICAL PRINCIPLES. 
 
 than one molecule of ammonia, the numerical prefix is in- 
 serted between the names of the elements or radicals taking 
 the place of hydrogen arid the word amide or amine. 
 
 287. Chemical Formula. The notation and use of sym- 
 bols have been already explained (236). Chemical com- 
 position and reactions are expressed by writing them to- 
 gether ; and such written expressions, are called chemical 
 
 i formula. An empirical formula is one which states only 
 what substances and what proportions of them or number 
 of atoms form a compound ; a rational formula aims to ex- 
 press the manner of atomic grouping, or the way the ele- 
 ments are combined. The empirical formula for alcohol 
 is C 2 H 6 O, the rational formula is C 2 H 6 .OH, a compound of 
 ethyl and hydroxyl. When the atoms of a group are more 
 closely connected among themselves than with the other 
 constituents of the compound, or when they play the part 
 of a compound radical, they are separated from the rest by 
 commas, inclosed in a parenthesis, or a single symbol (Cy), 
 as in the case of cyanogen (C a N 2 ), is substituted for the 
 group. Thus the following equation may be written 
 
 Eg, C a tf 2 = Hg + 2 ON or 
 Hg (Cy,) = Hg + 2 Cy 
 
 The plus-sign ( + ) is also used to separate atomic groups. 
 
 288. Chemical Equations. The results of chemical re- 
 action are represented in the form of equations, which de- 
 pend upon the principle that nothing is lost in the course 
 of transformation. The bodies to be acted upon are placed 
 at the left, and connected by the sigh of addition +. 
 The sign of equality = signifies that the products of the 
 change which are written at the right equal the bodies at 
 the left. The equation also implies that the molecules at 
 the left side are convertible into those written upon the 
 right. The equation CaO 4- H 2 O = CaO 2 H 3 represents 
 simply that, if a molecule of lime be added to a mole- 
 cule of water, the product formed will be a molecule of 
 calcic hydrate or slacked lime. 
 
PART IIL 
 DESCRIPTIVE CHEMISTS Y 
 
 DIVISION I. PERISSAD ELEMENTS. 
 
 CHAPTER XI. 
 
 HYDROGEN. 
 
 Symbol, H. Atomic Weight, 1 ; Quantivalence, 1 ; Specific Gravity, 1 ; 
 Molecular Weight, 2 ; Molecular Volume, 2. 
 
 289. Its Position. In entering upon the description 
 of the properties of chemical substances we begin with 
 hydrogen, which is taken as the unit, or starting-point of 
 the established system. It is an element of great impor- 
 tance in Nature, as well as in chemical theory ; and is so 
 individual in its character that it is difficult to classify with 
 other elements, and so will be most conveniently considered 
 at first and by itself. 
 
 290. History. It was known by Paracelsus, in the 
 sixteenth century, that when iron is dissolved in sulphuric 
 acid an air is given off; this air was shown by Boyle, in 1672, 
 to be inflammable ; and by Lemery, in 1700, to have deto- 
 nating properties. But the first exact experiments upon 
 it were made by Cavendish in 1766, and it was called by 
 him inflammable air. In 1781 Cavendish made the great 
 discovery that water is the sole product of the combustion 
 of this gas, and Lavoisier therefore gave it the name 
 
170 
 
 DESCRIPTIVE CHEMISTRY. 
 
 hydrogen, from two Greek words signifying water-gen- 
 erator. 
 
 291. Occurrence in Nature, Hydrogen is universally 
 diffused, and takes an active and varied share in the chemi- 
 cal operations of Nature. Existing in water, which is de- 
 composed with facility, it pervades the crust of the earth, 
 and ministers to the transformation of minerals ; while, as 
 a large constituent of all living things, its changes con- 
 tribute to carry on the processes of life. It is present in 
 nearly all kinds of compounds, combined with other ele- 
 ments. It forms one-ninth of the weight of water, and 
 the body which contains the largest proportion of it is 
 hydric carbide (marsh-gas), of which it forms one-fourth. 
 It was formerly held that hydrogen does not exist free in 
 Nature ; but it is now found uncombined in volcanic gases, 
 in meteoric stones, and, as we have seen, exists free in 
 immense masses in the atmospheres of the sun and 
 stars. 
 
 f ** 128 - 292. Preparation. 
 
 Hydrogen is generally 
 obtained by decompos- 
 ing water and setting 
 the gas free. It is usu- 
 ually collected in in- 
 verted jars filled with 
 water, as represented 
 in Fig. 123. If a bit 
 of the metal sodium 
 in a spoon be placed 
 under the mouth of 
 such a jar, it decom- 
 poses the water rapid- 
 ly, combining with its 
 oxygen, and setting free the hydrogen, which rises in 
 bubbles and displaces the water in the jar. Steam passed 
 through a red-hot gun-barrel is decomposed by the iron, 
 
 Liberation of Hydrogen by Sodium. 
 
HYDROGEN. 171 
 
 which combines with the oxygen and sets the hydrogen 
 free. A current of electricity passed through water severs 
 its constituents, and liberates both oxygen and hydrogen, 
 when they may be collected separately (141). 
 
 293. By the Use of Zinc. Hydrogen is commonly pre- 
 pared, however, by the action of dilute hydric sulphate (sul- 
 phuric acid) upon bits of zinc. The zinc is placed in a two- 
 
 FIG. 124. 
 
 Preparation of Hydrogen. 
 
 necked bottle (Fig. 124) and covered with water. The 
 tube, with a funnel at top, admits the acid, when the action 
 begins at once, the gas bubbles up freely and passes off 
 through the curved tube, which delivers it under the mouth 
 of an inverted jar, as before, but which now rests upon a 
 support below the surface of the water. A vessel for the 
 collection of gases, in this way, is called a pneumatic 
 trough. It is usually a tank (represented in the cut as 
 having glass sides), in which jars are filled with water, 
 inverted, and then slid upon the shelf, the water being 
 supported above its level by atmospheric pressure. When 
 the jars are filled with gas they may be slipped off, mouth 
 downward, into shallow vessels containing a little water, 
 and kept for use. In the foregoing reaction the hydric 
 
172 DESCRIPTIVE CHEMISTRY. 
 
 sulphate is decomposed by the zinc, while the hydrogen 
 is liberated, and zinc sulphate formed. The changes are 
 represented by the following equation : 
 
 H 2 =S0 4 + Zn. = Zn.=S0 4 + H-H. 
 
 Sulphuric Acid. Zinc. Zinc Sulphate. Hydrogen Gas. 
 
 294 Chemical Properties. As usually prepared, hydro- 
 gen has a disagreeable odor, arising from the impurities of 
 the materials employed; but pure hydrogen is a transpar- 
 ent, tasteless, inodorous gas, very slightly soluble in water, 
 inflammable, and having great chemical activity. It is an 
 essential constituent of bases and acids, the latter being 
 properly salts of hydrogen. It unites with metals and 
 organic radicles, forming compounds called hydrides. It 
 does not support respiration, and animals immersed in it 
 soon die. When mixed with air it may be breathed 
 without immediate injury, but from its tenuity it imparts a 
 squeaking tone to the voice. All attempts to liquefy it, 
 either by pressure or cold, have failed. In the gaseous 
 state hydrogen is combined with itself, forming the mole- 
 cule, H-H. 
 
 295. Its Lightness. Hydrogen is the lightest of all 
 known substances, being 14-J- times lighter than air, 16 times 
 lighter than oxygen, and 11,000 times lighter than water. 
 Hence it may be carried in jars with the open mouth 
 downward, and transferred to other vessels by pouring 
 upward. Soap-bubbles filled with it rise to the ceiling, 
 and it gives the greatest levity to balloons ; though they 
 are usually inflated with a hydrocarbon gas, the lightness 
 of which is due to the hydrogen it contains. Owing to 
 the fineness of its molecules it will escape through the 
 joints of apparatus that are perfectly tight to other gases ; 
 and a stream of it directed against one side of a piece of 
 gold-leaf passes through so rapidly that it may be ignited 
 on the other side. 
 
 296, Inflammability and Explosiveness. If a jet of hy- 
 
HYDROGEN. 
 
 173 
 
 FIG. 125. 
 
 Exploding Soap-Bubble* 
 
 drogen in the air is ignited it burns with a pale-blue flame, 
 which brightens as the pressure of the air is increased. 
 But, though the light emitted is small, the heat produced 
 is intense. The result of the combustion is pure water. 
 If hydrogen and 
 oxygen gases are 
 mixed in the pro- 
 portion to form 
 water, that is, 
 two volumes of 
 H to one of O, 
 and the mixture 
 is then ignited by 
 an electric spark, 
 or the application 
 of fire, the gases 
 
 combine explosively with a sharp report. The same effect, 
 though less intense, is produced by mingling 6ve volumes 
 of air with two of hydrogen. Soap-bubbles blown with 
 such a mixture detonate when 
 ignited. (Fig. 125.) In ex- 
 perimenting with hydrogen, it 
 is therefore necessary to guard 
 against the accidental intermix- 
 ture of air with the gas. The 
 lightness, explosiveness, and in- 
 flammability of hydrogen, and 
 that it cannot itself sustain com- 
 bustion, may be all shown by a 
 very simple experiment illus- 
 trated by Fig. 126. If a jar of 
 hydrogen be held mouth down- 
 
 , , ,. , , , . i Experiment illustrating the Proper- 
 
 Ward, and a lighted taper be ties of Hydrogen. 
 
 introduced, it is extinguished, 
 
 while the gases are ignited and burn at the mouth of 
 
 the jar. If, now, the jar is inverted, the escaping hy- 
 
 FIJ. 126. 
 
174 DESCRIPTIVE CHEMISTRY. 
 
 drogen unites with air, and there is a slight explo 
 sion. 
 
 297. Condensation of Hydrogen. But hydrogen and 
 oxygen may be ignited without the application of fire. 
 The metal platinum can he converted into a kind of pow- 
 dery condition known as platinum-sponge. If, now, a jet 
 of hydrogen be directed against a little ball of this 
 sponge, it instantly becomes red-hot, and remains so as long- 
 as the current lasts. Dobereiner's lamp depends upon this 
 principle. The theory of it is that oxygen is condensed 
 within the fine pores of the metal, and the hydrogen also 
 being condensed by it, their molecules are brought within 
 combining range, and union results. But the porous condi- 
 tion of the metal is not essential to this action. Clean 
 strips of platinum will condense the gases upon their sur- 
 face sufficiently to cause rapid combination. 
 
 298. Occlusion of Hydrogen. Red-hot platinum, palla- 
 dium, and iron, are freely permeable by hydrogen, and 
 when cold are capable of retaining considerable portions 
 of the gas. These metals are also capable of absorbing 
 and retaining more or less of hydrogen when it is pre- 
 sented to them in a nascent state. Graham, who terms 
 this effect occlusion, has shown that palladium takes up 
 more than 900 times its volume of hydrogen, and that the 
 product is a white metallic solid. Graham regarded this 
 compound as an alloy, consisting of palladium and solidi- 
 fied hydrogen, which he believed to be a metal, and called 
 it hydrogenium. Hydrogen in combination is replaced by 
 metals, and undoubtedly has strong analogies with them ; 
 but it is also replaced by chlorine, and its analogies with 
 the chlorous elements are as numerous, as strongly marked, 
 and as important, as with those of the basilous class. 
 
 In the earlier stages of the science oxygen held the 
 leading place ; but, as we have seen, hydrogen has usurped 
 its office as acid-former, and now occupies by far the most 
 important chemical position. 
 
CHLORINE. 
 
 175 
 
 CHAPTER XII. 
 
 THE CHLORINE GROUP. CHLORINE, FLUORINE, BROMINE, 
 
 IODINE. 
 
 1. Chlorine and its Compounds. 
 
 CHLORINE. Symbol, Cl. Atomic Weight, 35.5 ; Quantivalence, I., III., 
 V. and VII. ; Molecular Weight, 71 ; Molecular Volume, 2 ; Specific 
 Gravity, 2.47. 
 
 299. History. Chlorine was discovered by Scheele, in 
 1774, but was long regarded as a compound. In 1810 Davy 
 established its elementary character, and gave it the name 
 it bears, from the Greek chloros, yellowish green. It is 
 never found free in Nature, but exists abundantly in the 
 mineral world, chiefly in combination with the metal so- 
 dium, as common salt. 
 
 FIG. 127. 
 
 Preparation of Chlorine. 
 
 300. Preparation. Scheele's method of obtaining chlo- 
 rine by the action of hydric chloride on manganic di- 
 
176 DESCRIPTIVE CHEMISTRY. 
 
 oxide is still generally adopted. The manganic dioxide 
 is placed in a flask provided with a safety-tube for pouring 
 in the acid, and one for the delivery of the gas. To the 
 delivery-tube is attached an intermediate bottle containing 
 sulphuric acid, which is a powerful absorbent of water, and 
 which dries the gas by separating its adhering moisture. 
 From this bottle it passes through a long glass tube to 
 the receiver (Fig. 127). A little acid is first poured in 
 and well shaken up with the manganese, in order to wet 
 every portion of it ; more acid is then added, and a gen- 
 tle heat applied, when the gas is given off copiously. It 
 may be collected by displacement, or over warm water 
 in a pneumatic trough. The chlorine, being heavier than 
 air, collects at the bottom of the vessel, and the greenish 
 color of the gas will indicate when the vessel is filled. 
 The reaction may be thus expressed : 
 
 MnO, + (HC1) 4 = MnCl a + (H 2 O) 3 + Cl a . 
 
 Chlorine may also be prepared from common salt by 
 the aid of sulphuric acid and manganic dioxide. 
 
 301. Properties. Chlorine is one of the most energetic 
 of bodies, surpassing even oxygen under some circum- 
 stances. At ordinary temperatures chlorine (C1-C1) is a 
 yellowish-green gas, but by a pressure equal to four atmos- 
 pheres, or by exposure to a cold of 40 C., it may be con- 
 densed to a transparent, yellow liquid, of 1.38 specific 
 gravity, which remains unfrozen at 110 C. The gas has 
 a peculiar, suffocating odor, and if inhaled, even when con- 
 siderably diluted, produces distressing irritation of the 
 throat and lungs. When respired, however, in very minute 
 quantities, it is not only harmless, but is said to be benefi- 
 cial to those affected with pulmonary disease. Chlorine 
 maintains combustion ; many bodies burn in it readily 
 and some take fire in it spontaneously, such as phosphorus, 
 finely-powdered antimony (Fig. 128), zinc, and arsenic. 
 Many organic compounds, rich in hydrogen, are decon> 
 
CHLORINE. 
 
 177 
 
 FIG. 128. 
 
 C 
 
 posed by it so rapidly as often to burst into flame. A 
 piece of paper saturated with oil of turpentine and plunged 
 into a vessel filled with chlo- 
 rine (Fig. 129), emits a dense, 
 black smoke, and usually ig- 
 nites, from the rapid decom- 
 position of the turpentine. 
 Hydric chloride is formed and 
 carbon deposited. 
 
 Cold water absorbs about 
 two and a half times its own 
 bulk of chlorine, the solution 
 acquiring the color, taste, and 
 smell of the gas. If this so- 
 lution is cooled down to C., 
 a definite crystalline hydrate 
 of chlorine is formed, having 
 the formula Cl 5 + H 2 O. Liq- 
 uid chlorine may be readily 
 obtained from these crystals by hermetically sealing them 
 in a curved tube, and applying a gentle heat. This 
 liberates the chlorine, which, pressing upon itself, as- 
 sumes the condition of a liquid. It may be distinguished 
 from the water present by its yellow color. Chlorine solu- 
 tion readily dissolves gold. Light decomposes chlorine- 
 water, giving rise to hydric-chloride solution and free oxy- 
 gen ; hence it is necessary that it be kept in bottles pro- 
 tected by some opaque covering. 
 
 302. Uses. One of the most valuable qualities of chlo- 
 rine is its bleaching power. Chlorine-water, or the moist 
 gas, immediately discharges the colors of ordinary fabrics, 
 indigo, common ink, etc. It is principally used in bleach- 
 ing cotton cloth and rags of which paper is to be made. 
 Not only does chlorine destroy the coloring-matter by 
 uniting with its hydrogen, but it decomposes the associ- 
 ated water, setting free oxygen, which, in its nascent 
 
 Combustion of Antimony in Chlorine. 
 
178 
 
 DESCRIPTIVE CHEMISTRY. 
 
 FIG. 129. 
 
 state, acts powerfully to oxidate and destroy the coloring 
 particles. Dry chlorine will not bleach ; it acts only 
 through the agency of water. But it is so 
 powerful that, if the bleaching solution is not 
 quickly removed, it corrodes and weakens the 
 fabric. It has no action upon carbon, and 
 therefore does not bleach printer's ink. Ar- 
 gentic nitrate (lunar caustic) added to a solu- 
 tion containing chlorine, or a soluble chlo- 
 ride, gives a white precipitate of argentic 
 chloride, AgCl, which on exposure to light 
 changes first to violet, and then to black, 
 combustion of oil Argentic nitrate is the test for chlorine. 
 ChKme entine in This element is largely used in the prepara- 
 tion of chloride of lime, in which form it is 
 made available as a bleaching agent. 
 
 303. Hydric Chloride, HC1 (Muriatic Acid). This is the 
 only compound of chlo- 
 rine and hydrogen known. 
 It was discovered by 
 Priestley in 1772. It oc- 
 curs in Nature among the 
 gaseous products of vol- 
 canic eruptions. A mixt- 
 ure of chlorine and hy- 
 drogen gases, when ex- 
 posed to direct sunlight, 
 is converted, with violent 
 explosion, into hydric 
 chloride. Each of the 
 gases also burns freely 
 in an atmosphere of the 
 other. If a jar be filled 
 one half with hydrogen, 
 and the other half with chlorine, and the gases ignited at 
 the mouth, an explosion takes place; and white fumes of 
 
 Direct Union of Chlorine and Hydrogen. 
 
COMPOUNDS OF CHLORINE. 
 
 179 
 
 FIG. 131. 
 
 hydric chloride are formed. A towel should be wrapped 
 around the jar to prevent the pieces from scattering in case 
 of explosion (Fig. 130). Hydric chloride is generally 
 prepared by the action of sulphuric acid on sodic chloride 
 (common salt). The reaction is expressed by the equa- 
 tion: 
 
 2 (NaCl) + H a S0 4 = + Na,SO 4 + 2 (HC1). 
 
 As the gas is greedily absorbed by water, it must be col- 
 lected over mercury, or by dis- 
 placement. Fig. 131 shows a 
 convenient arrangement for its 
 preparation. 
 
 304. Properties and Uses. 
 Hydric chloride is a colorless, 
 pungent, acid gas, irrespirable, 
 very irritating to the eyes, and 
 extinguishes flame. It is some- 
 what heavier than air, having a 
 specific gravity of 1.24. Under a 
 pressure of 40 atmospheres at 
 
 10 C., or of 2 atmospheres at 70 C.,it condenses into 
 a colorless liquid of 1.27 specific gravity, which has never 
 been frozen. Hydric chloride is exceedingly soluble in 
 water, which, at 4 C., absorbs 480 times its volume of the 
 gas. This solution is much used in the laboratory as a 
 chemical reagent. 
 
 305. Compounds of Chlorine and Oxygen. The com- 
 pounds of chlorine and oxygen are unstable, and most of 
 them explosive. Chlorine may act as a monad, a triad, a 
 pentad, or a heptad, and its compounds with oxygen, to- 
 gether with the corresponding acids, are as follows : 
 
 Chloric monoxide, C\\O Hypochlorous acid, HCl'O* 
 Chloric trioxide, Cl in 2 O 3 Hydric chlorate, HC1 IU O 3 . 
 Chloric tetroxide, C1%O 4 Hydric perchlorate, HC1 T O 4 . 
 
180 DESCRIPTIVE CHEMISTRY. 
 
 306. Chloric Monoxide, C1 2 O. This compound, also 
 known as hypochlorous oxide, may be obtained by pass- 
 ing dry chlorine through a tube filled with mercuric oxide. 
 A portion of the chlorine takes the place of the oxygen, 
 forming mercuric chloride, while another portion unites 
 with the oxygen, at the moment of its liberation, forming 
 chloric monoxide. As a gas, its color is a shade darker 
 than that of chlorine, and it has a similar pungent odor. 
 It is a powerful oxidizing agent, and possesses remarkably 
 strong bleaching power. 
 
 307. Chloric Tetroxide, C1 2 O 4 . When potassic chlo- 
 rate, KC1O 6 , is made into a paste with sulphuric acid and 
 cooled, and this paste is cautiously heated in a glass retort, 
 over a water-bath, a deep-yellow gas is evolved, which can 
 only be collected by displacement. Chloric tetroxide has 
 a powerful odor, and, if heated, explodes with great vio- 
 lence. It may be liquefied by cold. It is absorbed by 
 water, the solution possessing strong bleaching properties. 
 
 308. Chloric Acid, Hydric Chlorate, HC1O 3 . This com- 
 pound may be obtained by decomposing a solution of 
 potassic chlorate with a solution of hydro-fluosilicic acid, 
 the products being an insoluble potassic fluosilicate, and a 
 dilute solution of chloric acid, which, by cautious evapora- 
 tion at a low temperature, may be concentrated to the 
 consistence of a syrup. It is a very unstable compound, 
 being easily decomposed, especially by organic matter, 
 which it sometimes ignites. 
 
 2, Fluorine and its Compounds. 
 
 FLUORINE. Symbol, F. Atomic Weight, 19 ; Quantivalence, I. ; Molecu- 
 lar Weight, 38 (?) ; Molecular Volume, 2 (?). 
 
 309. History. This substance does not occur in Nature, 
 uncombined, and very little is known in regard to it. Its 
 most frequent compound is calcic fluoride (fluor-spar), and 
 from this it receives its name. In consequence of its great 
 
FLUORINE. 181 
 
 affinity for other substances, it has never been satisfactorily 
 isolated. 
 
 310. Hydric Fluoride, HF. Hydric fluoride is produced 
 when a metallic fluoride (as fluor-spar) is acted upon by 
 hydric sulphate with the application of heat. Hydric 
 fluoride attacks and corrodes glass, and the process must, 
 therefore, be conducted in vessels of lead or platinum. 
 As thus obtained it is a colorless gas, which does not 
 condense to a liquid at 12 C. On account of its strong 
 affinity for water, it fumes in the air, and, if inhaled, 
 produces intense irritation of the lungs. The distinguish- 
 ing characteristic of hydric fluoride is its corrosive action 
 on glass. This may be shown by placing some pow- 
 dered calcic fluoride, made into a paste 
 
 * rir,. 164. 
 
 with sulphuric acid, in a leaden cup 
 (Fig. 132), and covering it with a 
 plate of glass, previously smeared on 
 one side with beeswax, through which 
 characters have been traced with a Action of Fluorine . 
 fine-pointed instrument. The waxed 
 side is placed next the mixture, and a gentle heat applied 
 to the cup. After the lapse of half an hour, on removing 
 the glass, and cleaning off the wax with the aid of a little 
 oil of turpentine, the letters will be found corroded into 
 the glass. The hydric fluoride has reacted upon and de- 
 composed the silica of the glass at the exposed points. 
 This quality is taken advantage of to etch the labels on 
 glass bottles that are to be used in laboratories and drug- 
 shops, where corrosive substances abound. 
 
 3. JBromine. 
 
 Symbol, Br. Atomic Weight, 80 ; Quantivalence, I., V., and VII. ; Molecu- 
 lar Weight, 160 ; Molecular Volume, 2 ; Specific Gravity, 3.187. 
 
 311. History and Preparation. This substance was first 
 obtained by a French chemist in 1826. The name bro- 
 
182 DESCRIPTIVE CHEMISTRY. 
 
 mine is derived from the Greek bromos, " stench." It is 
 not found native. After the extraction of the crystal- 
 lizable salts from the sea-water, there is left a solution of the 
 more soluble salts, called the mother-liquor or bittern. This 
 bittern is rich in bromides, and, by heating this with man- 
 ganic dioxide and hydric sulphate, chlorine is liberated 
 from the decomposed chlorides. The chlorine, in its turn, 
 sets free the bromine from the bromides, and the vapors 
 are collected in a cooled receiver, where they condense into 
 a liquid. 
 
 312. Properties and Uses. Bromine, at ordinary tem- 
 peratures, is a liquid of a deep brownish-red color. It has 
 a peculiar, irritating, disagreeable odor. At 22 C. it 
 solidifies to a hard, brittle, laminated mass, having a dark 
 lead-gray color and semi-metallic lustre. At about 122 
 (50 C.) it boils, forming red vapors. It dissolves spar- 
 ingly in water, more readily in alcohol, and in all pro- 
 portions in ether. It is an active chemical agent, and a 
 violent poison. Bromine is used in photography, and 
 occasionally as a disinfectant. 
 
 4. Iodine. 
 
 Symbol, I. Atomic Weight, 127; Quantivalence, I., III., V., and VII.; 
 Molecular Weight, 254 ; Molecular Volume, 2 ; Specific Gravity, 4.94. 
 
 313. History. Iodine was discovered in 1811, in prod- 
 ucts of decomposition obtained from the mother-liquor, 
 which remains when the ashes of sea-weed, known as 
 " kelp," are leached, and allowed to crystallize. The name 
 iodine is derived from the Greek ion, " V 7 iolet," and refers 
 to the color of its vapor. It is not found native. The prep- 
 aration is similar to that of bromine. The mother-liquors 
 are distilled with manganic dioxide and hydric sulphate, 
 and the vapors condensed. 
 
 314. Properties and Uses. Iodine is a grayish-black 
 solid of metallic lustre, and crystallizing in forms of the tri- 
 
IODINE. 183 
 
 metric system. It melts at 225 (107 C.), and boils at 
 356 (180 C.), rising in dense, beautiful, deep-violet vapor, 
 which is 8.72 times heavier than air. Iodine volatilizes 
 even at ordinary temperatures, diffusing an odor somewhat 
 similar to that of chlorine, though easily distinguished 
 from it. It is sparingly soluble in water, more easily in 
 alcohol and ether, or aqueous solutions of iodides. Iodine 
 colors starch-paste a beautiful deep-blue, this reaction con- 
 stituting the most delicate test of its presence. It stains 
 the skin yellow, but is not so corrosively poisonous as 
 chlorine or bromine. It is a non-conductor of electricity. 
 
 Iodine is extensively used in photography, in the prep- 
 aration of iodides, as a chemical reagent, and in medicine. 
 A dark- brown solution of iodine in alcohol (containing also 
 potassic iodide) is familiarly known as tincture of iodine, 
 and much used as a liniment. 
 
 315. Hydric Bromide, HBr., and Hydric Iodide, HI. 
 These bodies are produced by the action of dilute sulphuric 
 acid on bromides and iodides, but the compounds, espe- 
 cially the hydric iodide, are liable, under these circum- 
 stances, to be further decomposed. By heating bromine 
 or iodine with hydrogen, these bodies are also formed, but 
 for practical purposes they are best prepared by allowing 
 bromine and iodine to react upon phosphorus in the pres- 
 ence of water. The properties of hydric bromide and 
 iodide are similar to those of hydric chloride. 
 
 316. The Halogen Group. The elements fluorine, chlo- 
 rine, bromine, and iodine, constitute a well-marked chemi- 
 cal series, exhibiting a regular progression of properties. 
 Chlorine is a gas, bromine a liquid, and iodine a solid, 
 at ordinary temperatures. Their molecules are all dia- 
 tomic. Chemically they are highly active bodies, and, 
 when brought in contact with certain metals, readily give 
 rise to a class of compounds, of which common salt is the 
 type. Hence they have been named halogens, from Greek 
 words meaning salt-formers. The hydrogen compounds 
 
184 DESCRIPTIVE CHEMISTRY. 
 
 of these elements, represented by HF, HC1, HBr, and 
 HI, also form a well-marked series. At ordinary tempera- 
 tures they are all colorless gases, of pungent, suffocating 
 odor, and powerful acid properties, hydric fluoride being 
 chemically the most, and hydric iodide the least, active. 
 
 CHAPTER XIII. 
 
 THE SODIUM GKOUP SODIUM, POTASSIUM, LITHIUM, RUBID- 
 IUM, CAESIUM. 
 
 1. Sodium and its Compounds. 
 
 SODIUM. Symbol, Na. (Natrium). Atomic Weight, 23; Quantivalence, 
 I. and III. ; Specific Gravity, 0.98. 
 
 317. Preparation and Properties. Metallic sodium, 
 Na-Na, was first obtained by Davy, in 1807, by decom- 
 posing sodic hydrate (NaHO) by the electric current. 
 Sodium does not occur native, but is now manufactured on 
 a large scale, by distilling a mixture of sodic carbonate and 
 
 charcoal at a high temperature. 
 Sodium, when freshly cut, presents 
 a silvery appearance, and, if cast 
 upon hot water, bursts into a beau- 
 tiful yellow flame, and is converted 
 into sodic oxide, or soda (Fig. 133). 
 Sodium is a very abundant metal, 
 constituting more than two-fifths 
 of common salt, and existing: as a 
 
 Combustion of Sodium. 
 
 large ingredient of rocks and soils. 
 
 318. Sodic Chloride (NaCl) (Common Salt) may be 
 formed by the direct union of its constituents, and is ob- 
 tained commercially, either by mining it in the form of 
 rock-salt, or by evaporating the water of salt-springs. Sea- 
 
SODIUM AND ITS COMPOUNDS. 185 
 
 water contains in every gallon about four ounces of salt. 
 Estimating the ocean at an average depth of two miles 
 (Lyell), the salt it holds in solution would, if separated, 
 form a solid stratum 140 feet thick. Saline springs in 
 various localities in this country yield enormous quantities 
 of salt by the process of evaporation. The springs in the 
 State of New York, alone, furnish an annual supply of about 
 6,000,000 bushels. As a solid it occurs in extensive beds 
 in various localities in Europe. The celebrated bed at 
 Wielitzka, Poland, is said to be 500 miles long, 20 miles 
 broad, and 1,200 feet thick, containing salt enough to sup- 
 ply the entire world for thousands of years. 
 
 319. Salt exists in small quantities in plants, and some- 
 times promotes their growth by being applied to the soil. 
 It is also an ingredient of animal bodies, being contained 
 in the blood. It forms an important constituent of the 
 food of both man and beast, an adult consuming about live 
 ounces per week. (PEEEIRA.) 
 
 Common salt is readily soluble alike in hot or cold 
 water, and usually crystallizes in cubes. A peculiar-shaped 
 
 FIG. 134. FIG. 185. 
 
 Crystallization of Common Salt. 
 
 crystal, or aggregation of crystals, is often formed when 
 the salt is allowed to crystallize from concentrated solu- 
 tions. A small cube is first formed which sinks so as to 
 
186 DESCRIPTIVE CHEMISTRY. 
 
 bring its upper surface on a level, or a little below the 
 surface of the water (Fig. 134). Other cubes form on this, 
 and, as the mass sinks, others still are deposited, each layer 
 being attached to the upper and outer edge of the layer 
 next below, until the hopper-like form shown in Fig. 138 
 is obtained. 
 
 320. Uses. Salt is used lor packing and preserving 
 meat, as it prevents putrefaction, by absorbing water from 
 the flesh. It is also used as a source of sodium in the 
 manufacture of sodic hydrate, and as a source of chlorine 
 in the production of hydric chloridQ, It fuses at a red 
 heat, and hence is used for glazing stone-ware, earthen- 
 ware, etc. 
 
 321. Sodic Carbonate (Na 2 CO 3 ). Sodic compounds are 
 supposed to perform the same function in the economy of 
 marine plants that the corresponding potassium compounds 
 perform in land plants, and sodic carbonate was formerly 
 obtained by leaching the ashes of the former. It is now 
 manufactured almost entirely from common salt, by Le- 
 blanc's process. This consists, first, in treating sodic chlo- 
 ride with sulphuric acid, forming crude sodic sulphate, or 
 salt-cake, and hydric chloride. The next step in the process 
 is to convert sodic sulphate into a crude carbonate. This 
 is effected by heating the salt-cake with finely-ground coal 
 and calcic carbonate (chalk) in a reverberatory furnace, 
 constructed for the purpose. After the mass is thoroughly 
 fused it is raked out into wooden troughs, and allowed to 
 cool, forming ball-soda or black-ash. 
 
 In this operation, calcic sulphide and carbonic mon- 
 oxide are also formed, the reaction taking place according 
 to the equation : 
 
 Na,SO 4 + Ca" CO 3 + 40 = Na 2 CO 3 + Ca" S + 4CO. 
 
 The sodic carbonate being the only constituent of the 
 black-ash that is readily soluble, is separated by leaching 
 with warm water ; and lastly, the solution is evaporated to 
 
SODIUM AND ITS COMPOUNDS. 187 
 
 dryness, yielding the soda ash or crude carbonate of com- 
 merce. When a hot, filtered solution of this is allowed to 
 cool quietly, large transparent crystals of a decahydrated 
 salt (Na a CO 3 + 10H 2 O) are obtained. These are known 
 as sal-soda. Sodic carbonate is extensively used in the 
 manufacture of soap and glass, being both cheaper and 
 purer than the ordinary potash. It is also used as a deter- 
 gent, both in calico-printing and in the laundry. 
 
 322. Hydro-Sodic Carbonate (NaHCO,). This is pro 
 duced by passing carbonic dioxide through a solution of 
 sodic carbonate. It is used under the name of saleratus, 
 forms part of effervescing soda-powders, and is used in 
 bread making.- 
 
 323. Sodic Hydrate, NaKO (Caustic Soda). This com- 
 pound is obtained by decomposing a solution of sodic 
 carbonate (Na a CO 3 + H 3 O) with calcic hydrate (slacked 
 lime, CaH a O a ) at the boiling temperature, allowing the 
 calcic carbonate formed to subside, drawing off the clear 
 solution of sodic Irydrate, and concentrating by evaporation. 
 Thus prepared it is a white, opaque, brittle substance, 
 which melts below red heat, and volatilizes at higher tem- 
 peratures. It is also formed by the action of sodium upon 
 water. 
 
 324. Sodic Sulphate (Na a SO 4 + 10H a O) (Glauber's Salt). 
 This well-known salt may be formed by adding sulphuric 
 acid to soda, and is chiefly procured in the manufacture of 
 hydric chloride. It has a bitter, saline taste, and loses its 
 water of crystallization on exposure to the air. 
 
 325. Sodic Nitrate, NaNO 3 ( Soda-Saltpetre). Pro- 
 cured native from parts of Brazil and Chili. Attempts 
 have been made to substitute this salt for nitrate of potash 
 in the manufacture of gunpowder, but its tendency to at- 
 tract moisture from the air has rendered it impracticable. 
 Nitric acid is obtained from sodic nitrate, and it has been 
 somewhat used as a fertilizer. 
 
188 DESCRIPTIVE CHEMISTRY. 
 
 2. Potassium and its Compounds. 
 
 POTASSIUM. Symbol, K. (Kalium). Atomic Weight, 39 ; Quantivalence, 
 I., III., and V. ; Specific Gravity, 0.86. 
 
 326. History and Occurrence. This metal was discov- 
 ered by Sir Humphry Davy in 1807. He first obtained it 
 by subjecting moistened potash to the action of a powerful 
 voltaic battery ; the positive pole gave off oxygen, and 
 metallic globules of pure potassium appeared at the nega- 
 tive pole. It is found abundantly in Nature, but never 
 uncombinecl. It is obtained by the action of charcoal upon 
 potassic carbonate at a very high temperature. The potas- 
 sic carbonate is decomposed with liberation of potassium, 
 carbonic monoxide, and small quantities of other com- 
 pounds but little known. Leaving these out of view, the 
 reaction may be represented by the equation : 
 
 K a CO 3 + 2C = 300 + K 2 . 
 
 327. Metallic Potassium (Molecule) (K-K), at common 
 temperatures, is a silver-white metal, and so soft that it 
 
 may be moulded like wax. If thrown 
 > 
 
 upon the surface of water, instant 
 decomposition takes place (Fig. 139), 
 potassic oxide being at first formed. 
 The liberated hydrogen, together 
 with a small quantity of volatilized 
 metal, is ignited by the heat evolved 
 during the decomposition, and burns 
 with a beautiful lilac flame as the 
 Combustion of Potassium, g^ule floats about on the surface of 
 the liquid. At the close of this reac- 
 tion a second change ensues : the potassic oxide, which had 
 been kept above the surface of the water, coming in contact 
 with the liquid, gives rise to the formation of potassic hy- 
 drate, which becomes red-hot, and scatters with a violent 
 explosion. Potassium decomposes nearly all compounds 
 
POTASSIUM AND ITS COMPOUNDS. 189 
 
 containing oxygen, if brought in contact with them at high 
 temperatures, and many even at ordinary temperatures. 
 Hence, to preserve it pure, it is kept in naphtha, a liquid 
 containing no oxygen. 
 
 328. Potassic Monoxide (K 2 O). This compound is ob- 
 tained by exposing metallic potassium to perfectly dry air, 
 free from carbonic dioxide, at ordinary temperatures. It 
 is a white solid, which melts at a red heat, and volatilizes at 
 higher temperatures. It is very deliquescent ; brought in 
 contact with water it becomes incandescent, potassic hy- 
 drate being produced. 
 
 329. Potassic Hydrate (KHO) ( Caustic Potash). The 
 method of obtaining this important substance is similar to 
 that of obtaining caustic soda. The solution of potassic 
 hydrate, after being boiled until the temperature of the 
 liquid is near a red heat, flows without ebullition, and may 
 be run into moulds, solidifying on cooling to a white, 
 hard, brittle substance, which melts, below redness, to an 
 oily liquid, and volatilizes at a full red heat in white, pungent 
 vapors. Potassic hydrate dissolves freely in water, with 
 great evolution of heat. It has a peculiar nauseous odor, and 
 acrid taste. It decomposes acids with formation of corre- 
 sponding potassic salts and elimination of water, changes 
 vegetable yellows to brown, restores the blues discharged 
 by acids, and decomposes animal and vegetable substances, 
 whether living or dead. It is used in medicine to cauterize 
 and cleanse ulcers and foul sores ; hence its name, caustic 
 potash. If a solution of potash be shaken in a bottle with 
 any fixed oil, the two unite, forming a soap. This accounts 
 for the soft, greasy feel it has when touched by the fingers, 
 as it decomposes the skin and forms a soap with its oily 
 elements. When taken into the system, potash acts as a 
 powerfully corrosive poison. Its active chemical character 
 renders it an indispensable reagent in the laboratory. 
 
 330. Potassic Chloride (KC1) is known as the mineral 
 sylvite, and is isomorphous with NaCl. Potassic iodide 
 
190 DESCRIPTIVE CHEMISTRY. 
 
 (KI) may be formed by adding iodine to a solution of pot- 
 ash, and gently warming until the solution assumes a 
 brown tint. It is a very soluble, white solid, which crys- 
 tallizes in cubes, and is much used in medicine. 
 
 331. Potassic Carbonate (K 2 CO 3 ). Potassic salts of 
 various kinds exist in the juices of plants. By the com- 
 bustion of the plants, most of these are decomposed with 
 the formation of potassic carbonate, which may be obtained 
 from their ashes. This is a highly alkaline, deliquescent 
 salt, and is used largely in the manufacture of soap and 
 glass, in preparing caustic potash, etc. It is also an im- 
 portant reagent in the laboratory, and a most valuable 
 fertilizer. This salt rarely forms less than 20 per cent., 
 and sometimes more than 50 per cent., of the weight of 
 wood-ashes. The ashes of different plants, and even dif- 
 ferent parts of the same plant, yield it in varying quantities. 
 Wood ashes furnish the principal source of the potassic 
 carbonate of commerce, from which it is obtained by leach- 
 ing them and boiling the solution to dryness in iron pots. 
 The residue is called potashes, and these, when calcined, 
 afford the impure carbonate known as pearlash. Potash, 
 or pearlash, therefore represents the readily soluble portion 
 of wood-ashes, and consists chiefly of potassic carbonate 
 with small amounts of sodic carbonate and common salt. 
 
 332. Hydro-Potassic Carbonate (KHC0 3 ). This is 
 formed by passing carbonic dioxide through a strong solu- 
 tion of potassic carbonate. It is employed as a source of 
 potassium in the formation of many of its other compounds, 
 and is also used for making effervescing draughts, by add- 
 ing citric or tartaric acid to its solution. 
 
 333. Potassic Nitrate (KNO 3 ) (Nitre, Saltpetre). This 
 salt occurs as a native product in the earth of various dis- 
 tricts in the East Indies, and is separated therefrom by 
 leaching the soil, and allowing the nitre to crystallize. It 
 is artificially formed by heaping up organic matter with 
 lime, ashes, and soil, and keeping the mass well moistened 
 
POTASSIUM AND ITS COMPOUNDS. 191 
 
 with urine for a period of two or three years, when the 
 heap is lixiviated and the salt crystallized out. Besides 
 these sources, nitre occurs in the sap of certain plants, such 
 as the sunflower, tobacco-plant, etc. Nitre dissolves in 
 about three times its weight of cold and one-third its 
 weight of boiling water. When thrown upon burning 
 charcoal it is decomposed and deflagrates violently. Paper 
 dipped in a solution of sodic nitrate, and dried, forms what 
 is known as touch-paper. When ignited, it burns slowly 
 and steadily until consumed ; hence its use in lighting 
 trains of gunpowder, fireworks, etc. Nitre has a cooling, 
 saline taste and strong antiseptic powers. Owing to the 
 latter quality it is used extensively in packing meat, to 
 which it imparts a ruddy color. It is chiefly consumed, 
 however, in the manufacture of gunpowder. 
 
 334. Gunpowder is an intimate mechanical mixture of 
 about 1 part nitre, 1 part sulphur, and 3 parts charcoal. 
 These proportions, however, vary somewhat in different 
 countries, as well as in different sorts of powder. More 
 charcoal adds to its power, but also causes it to attract 
 moisture from the air, which of course injures its quality. 
 For blasting rocks, where a sustained force, rather than an 
 instantaneous one, is required, the powder contains more 
 sulphur, and is even then often mixed with sawdust to 
 retard the explosion. The nitre, sulphur, and charcoal, 
 having been ground and sifted separately, are thoroughly 
 mixed and then made into a thick paste with water. This 
 is ground for some hours under edge stones, after which it 
 is subjected to immense pressure between gun-metal plates, 
 forming what is known as press-cake. These cakes are 
 then submitted to the action of toothed rollers, whereby 
 the granulation of the powder is effected. The grains 
 thus formed are sorted by means of a series of sieves, 
 and thoroughly dried at a steam heat. The last opera- 
 tion, that of polishing, is accomplished in revolving bar- 
 rels, after which the powder is readv for market. The 
 9 
 
192 DESCRIPTIVE CHEMISTRY. 
 
 heavier the powder, the greater is its explosive power. 
 Good powder should resist pressure between the fingers, 
 giving no dust when rubbed, and have a slightly glossy 
 aspect. The explosive power of gunpowder is due to a 
 sudden formation of a large volume of nitrogen and car- 
 bonic dioxide; one volume of the powder giving about 
 1,800 volumes of vapor. Fireworks contain nitre as a 
 chief ingredient, mixed with charcoal, sulphur, ground 
 gunpowder, and various coloring substances. 
 
 335. Potassic Sulphate (K 2 SO 4 ) is obtained in the man- 
 ufacture of hydric nitrate, and is of limited use in the 
 arts. Potassic chlorate (KC1O 3 ) may be formed by pass- 
 ing chlorine gas through a solution of potassic carbonate 
 (K 2 CO 3 ). Potassic chlorate is soluble in water, has a taste 
 resembling that of nitre, melts at about 700, and, if heated 
 above that temperature, decomposes with formation of po- 
 tassic chloride and perchlorate, and oxygen gas. It is used 
 in the manufacture of lucifer matches, in certain operations 
 of calico-printing, and as a source of oxygen. 
 
 336. Sodic and Potassic Silicates. If 8 or 10 parts of 
 sodic or potassic carbonate are mixed with 12 or 15 parts of 
 sand and 1 of charcoal, on being heated they melt, and form 
 a mass resembling ordinary glass ; but it entirely dissolves 
 in hot water. This is known as soluble glass, and when 
 applied to wood and other substances answers the protec- 
 tive purpose of a varnish or paint. 
 
 337. Soap. When caustic potash, or soda, acts upon 
 certain organic acid radicles, chiefly oleine and stearine, 
 which are present in fats and oils, the resulting salts are 
 termed soaps, and the process by which they are produced 
 is called saponification. The consistence of soap depends 
 chiefly upon its alkali. Hard soaps are made of soda, or a 
 mixture of soda and potash, while in soft soaps potash 
 alone is used, the soaps made with this base being deliques- 
 cent and consequently attracting water, which renders the 
 soap liquid. The quality of hardness is due to the con- 
 
LITHIUM, RUBIDIUM, (LESIUM. 193 
 
 sistence of the oil or fat. The compounds containing a large 
 proportion of stearin and palmitin, like tallow, form hard 
 soaps, while those in which olein predominates, as the soft 
 fats and oils, produce soap of softer consistence. The 
 glycerin which is retained in soft soap also adds to its 
 fluidity. Soap has a powerful affinity for water, and may 
 retain from 50 to 60 per cent, of it and still continue solid ; 
 hence dealers frequently keep it in damp places where it 
 will absorb moisture. It is soluble in fresh water, but, 
 with the exception of cocoa-soap, is insoluble in salt-water. 
 
 338. Mode in which Soap acts in Cleansing. As water, 
 having no affinity for oily substances, will not dissolve 
 them, of course it cannot alone remove them from surfaces 
 to which they may adhere. The oily matters which are 
 constantly exuding from the glands of the skin, uniting 
 with the outer dust, form a film over the body. The alkali 
 of the soap acts upon the oil during ablution, partially 
 saponifies it, and renders the unctuous compound freely 
 miscible with water, so as to be easily removed. The cuti- 
 cle or outer layer of the skin is chiefly composed of albu- 
 men, which is soluble in the alkalies. The alkali of the 
 soap, therefore, dissolves off a portion of the cuticle with 
 the dirt ; every washing with soap thus removing the old 
 face of the scarf-skin and leaving a new one in its place. 
 The action of soap in cleansing textile fabrics is of a similar 
 nature. Alkalies not only act upon greasy matter, but, as 
 is well known, dissolve all organic substances. In the case 
 of soap, however, the solvent power of the alkali is in part 
 neutralized, thus preserving both the texture and color of 
 the fabric exposed to its action. The oily nature of the 
 soap also increases the pliancy of the articles washed. 
 
 3. Lithium, Rubidium, Caesium. 
 
 339. History. These three rare elements are found 
 associated with potassium and sodium, to which they are 
 closelv allied in all their chemical Delations. Lithium is a 
 
194 DESCRIPTIVE CHEMISTRY. 
 
 brilliant, silver- white metal, softer than lead, remarkably 
 light, having a specific gravity of 0.578. We have already 
 referred to its distribution (201). 
 
 Rubidium, also a soft, white metal, was discovered by 
 means of the spectroscope. Its spectrum contains two 
 dark-red lines; hence its name, from the Latin rubidus, 
 meaning dark-red. Rubidium has been found in the ashes 
 of many plants, in mineral water, in tobacco-leaves, in 
 coffee, tea, cocoa, and crude tartar. 
 
 Caesium was discovered at the same time with rubidium. 
 The name comes from ccesius, sky-blue, and has reference 
 to two blue lines in the spectrum. 
 
 CHAPTER XIV. 
 
 SILVER. GOLD. BORON. 
 
 1. Silver and its Compounds. 
 
 SILVER. Symbol, Ag. (Argentum). Atomic Weight, 108; Quautivalence, 
 I. and III. ; Specific Gravity, 10.5. 
 
 340. Metallic Silver (Molecule) (Ag-Ag). This well- 
 known metal is frequently found native in fibrous crystal- 
 line masses. It is also found in combination with chlorine, 
 sulphur, arsenic, or antimony. The principal silver-mines 
 are those of Mexico and Peru. Silver is obtained from its 
 ores by various processes, in some of which the ore is 
 roasted with common salt, by which argentic chloride is 
 formed ; then, together with water, iron-scraps, and mer- 
 cury, put into casks which revolve on their axes. The iron 
 removes the chlorine, and the mercury amalgamates with 
 the silver, from which it is afterward freed by distillation 
 
 (in.). 
 
 From plumbic sulphide, which is by far the most im- 
 portant source of silver, it is obtained by first smelting for 
 lead, and then volatilizing the lead by cupellation, a pe- 
 
SILVER AND ITS COMPOUNDS. 195 
 
 culiar process, conducted in a furnace, the shallow, basin- 
 shaped bottom of which is covered with a thick layer of 
 bone, ashes, marl, or some other porous, infusible material. 
 When the lead, alloyed with a small quantity of silver, is 
 melted on this hearth, in a current of air, most of the lead 
 oxidizes ; the oxide or litharge melts, and, being absorbed 
 by the cupel, leaves the silver pure. 
 
 341. Properties and Uses. Silver is the whitest of the 
 metals, with a bright, metallic lustre. It is very malle- 
 able, ductile, and tenacious. It may be extended into 
 leaves not exceeding 1 6 * of an inch, or ^^5^5- of a milli- 
 metre, in thickness; and one grain, or ^ of a gramme, 
 may be drawn out into 400 feet, or 122 metres of wire. 
 Silver does not oxidize in the air at any temperature, hut 
 absorbs oxygen when melted, holding it mechanically, and 
 giving it off on solidifying. It is a good conductor of heat 
 and electricity, and its polished surface is one of the best 
 reflectors of light. Silver is chiefly consumed in the manu- 
 facture of allo}-s used for coinage and silver-plate. Being 
 too soft, pure silver is never employed for these purposes. 
 
 342. Argentic Chloride (AgCl.) (Chloride of Silver) is 
 occasionally found native in mines, and is called horn 
 silver, from its tough, horny texture. It may be prepared 
 artificially by adding a solution of common salt to a solu- 
 tion of argentic nitrate, and appears as a white powder 
 which darkens in color on exposure to light. Argentic 
 bromide (AgBr-) and argentic iodide (Agl) resemble the 
 previous compound, and are found in a similar way. 
 
 343. Argentic Monoxide (Ag 2 O) (Silver Oxide). This 
 substance is best prepared by mixing concentrated hot 
 solutions of argentic nitrate and potassic hydrate. It is a 
 black or bluish-black, heavy powder, slightly soluble in 
 water. It is also formed when silver is heated in the 
 air, but at a red heat, or even lower temperatures, it is 
 completely decomposed, with formation of metallic silver 
 and oxygen gas. 
 
196 DESCRIPTIVE CHEMISTRY. 
 
 344. Argentic Nitrate (AgNO 3 ) (Lunar Caustic). 
 This interesting salt may be obtained by dissolving metal- 
 lic silver in nitric acid ; colorless, anhydrous crystals being 
 formed, which are readily soluble in an equal weight of 
 cold water. These crystals, when melted and cast into 
 small sticks, form the lunar caustic of surgery. Argentic 
 nitrate solution is decomposed by organic matter, with 
 separation of black, finely-divided metallic silver, the reac- 
 tion being most rapid when taking place in the light. 
 Advantage is taken of this property in making indelible 
 ink and hair-dye. A solution of potassic cyanide removes 
 the stain thus produced. 
 
 2. Gold. 
 
 Symbol, Au. (Auruin). Atomic Weight, 196.6 ; Quantivalence, I. and 
 III. ; Specific Gravity, 19.34. 
 
 345. Gold (molecular symbol of metal probably [Au=Au]). 
 This is one of the most widely diffused of the metals, and 
 generally occurs in minute grains, though sometimes in 
 masses weighing many pounds. In 1851 a lump weighing 
 106 pounds was found in Australia, embedded in a matrix 
 
 of quartz. It sometimes occurs in crys- 
 talline form, as shown in Fig. 140. As 
 found in Nature, gold is rarely pure, but 
 generally mixed with a variable quantity 
 of silver. Gold is separated from all the 
 constituents of its ores except silver, by 
 amalgamation with mercury. It is ob- 
 tained from silver by boiling the alloy in 
 nitric acid, which dissolves out the silver, 
 Crystal of Gold. leaving the gold pure. In this operation, 
 in order to prevent the silver from being 
 mechanically protected from the action of the acid, it is 
 necessary that there should be three times as much silver 
 
BORON AND ITS COMPOUNDS. 197 
 
 as gold. As the gold constitutes only one quarter of the 
 mass, the process is known as quartation. 
 
 346. Properties. Gold is the only metal of a yellow 
 color, it has a brilliant lustre, and high specific gravity. 
 It is the most malleable of the metals, and to its ductility 
 there is scarcely a limit ; when pure it is nearly as soft as 
 lead. It fuses at about 1200 C., and does not oxidize in 
 the air at any temperature. Gold is not dissolved by any 
 single acid, but is acted upon by chlorine, or any solution 
 which liberates the gas. Its usual solvent is a mixture of 
 four parts of hydric chloride and one of hydric nitrate, 
 called, on account of its power to dissolve gold, aqua regia. 
 The compounds of gold have little chemical interest to the 
 ordinary student. AuCl, is somewhat used in the labora- 
 tory, and a solution of auric cyanide in potassic cyanide is 
 used in electro-gilding. 
 
 3. Boron and its Compounds. 
 
 BORON. Symbol, B. Atomic Weight, II. ; Quantivalence, III. ; Molecular 
 Weight, 22 (?) ; Molecular Volume, 2 ; Specific Gravity, 2.68. 
 
 347. Boron. This substance is not found native, but 
 may be prepared by decomposing fused boric oxide (B 2 O 3 ) 
 with sodium or aluminium. It exists in several modifica- 
 tions, being either brown, amorphous, and slightly soluble 
 in water, or crystalline, and entirely insoluble. One of the 
 two crystalline modifications known is exceedingly hard 
 and brilliant, resembling the diamond in this respect. 
 
 348. Boric Acid, H 3 BO 3 . This acid is found as a 
 natural constituent of hot mineral springs, the principal 
 locality being the " lagoons " of the volcanic district of 
 Tuscany, where the acid issues from the earth with jets 
 of steam, and is collected by throwing the jets into 
 water. The acid is afterward separated from the water 
 by evaporation in leaden pans so arranged that they are 
 heated by the vapors as they escape from the earth. It is 
 
198 DESCRIPTIVE CHEMISTRY. 
 
 deposited in white, scaly crystals, which are purified by 
 repeated crystallizations. These crystals have a glassy- 
 appearance, and are soapy to the touch. They dissolve 
 much more readily in boiling" than in cold water, and form 
 a solution having feebly acid properties. 
 
 349, Hydro-Sodic Borate (Na 2 H 2 B 4 O 8 + 9H 2 O) (Borax). 
 This salt is found native at the bottom of certain lakes 
 in Thibet and California. It is procured artificially by 
 heating boric acid with sodic carbonate, decomposition 
 taking place with evolution of carbonic dioxide. Borax 
 has an alkaline taste and reaction, and in the fused state, 
 at a high heat, possesses the property of dissolving many 
 metallic oxides ; hence its use as a flux in the welding of 
 metals. It dissolves the coating of oxide formed when 
 the metals are heated, which thus constantly present a clean 
 surface. On account of the same property it is one of the 
 most important reagents, being chiefly employed in blow- 
 pipe analysis. 
 
 CHAPTER XV. 
 
 THE NITROGEN GKOUP. NITROGEN, PHOSPHORUS, ARSENIC, 
 ANTIMONY, BISMUTH. 
 
 1. Nitrogen and its Compounds. 
 
 NITROGEN. Symbol, N. Atomic Weight, 14 ; Quantivalence, L, III., and 
 V. ; Molecular Weight, 28 ; Molecular Volume, 2 ; Specific Gravity, 
 0.972. 
 
 350. Nitrogen Gas (Molecule) (NiN). This gas was 
 discovered by Rutherford, in 1772. Chaptal afterward 
 gave it the name nitrogen, signifying generator of nitre. 
 It is very extensively diffused in Nature, forming about 
 four-fifths of the atmosphere, in which it plays the impor- 
 tant part of diluting the oxygen, and adapting it to the 
 conditions of life. It is the characteristic ingredient of 
 
NITROGEN AND ITS COMPOUNDS. 
 
 FIG. 141. 
 
 Preparation f Nitrogen. 
 
 animal tissue, and is never entirely absent from plants, 
 while of many important vegetable products it is an essen- 
 tial constituent, as for example, of the vegetable alkaloids. 
 
 351. Preparation. Nitrogen is most commonly pre- 
 pared by withdrawing the oxygen from a portion of air. 
 A small bit of phosphorus is 
 
 placed in a little cup and 
 floated on the water in a pneu- 
 matic trough. It is then set 
 on fire and a jar placed over 
 it, as in Fig. 141. The phos- 
 phorus takes the oxygen, 
 forming phosphoric pentox- 
 ide, which fills the jar with a 
 white vapor ; but this is soon 
 absorbed by the water, and 
 nitrogen alone is left, the 
 water rising to occupy the 
 space of the vanished oxygen. 
 
 352. Properties. Nitrogen is a transparent gas, without 
 taste or color, and has never been condensed into a liquid. 
 It is remarkable for chemical inertness. It is irrespirable ; 
 animals placed in it quickly die, not from its poisonous 
 action, but from lack of oxygen. It supports the com- 
 bustion of but few substances; a lighted taper introduced 
 into it is immediately extinguished. Boron, titanium, and 
 a few other rare bodies, burn in it, with the formation of 
 nitrides. It is slightly soluble in water, one hundred 
 volumes of the latter, at 15 C., taking up about one and 
 a half volume of the gas. Although nitrogen combines 
 directly with only two elementary substances, boron and 
 titanium, it has great capacity for combination, and is 
 distinguished by the large number and variety of its com- 
 pounds. 
 
 353. Hydric Nitride or Ammonia (H 3 N). This sub- 
 stance was first described by Priestley, in 1774. It is 
 
200 DESCRIPTIVE CHEMISTRY. 
 
 frequently met with in Nature, being a constant product 
 of the decomposition of organic substances which contain 
 nitrogen. It is produced from the destructive distillation 
 of horns and hoofs, which are rich in nitrogen, but the 
 chief source of commercial ammonia is the liquor of the 
 gas-works. Ammonia gas is conveniently obtained by the 
 action of one part of quick-lime, CaO, upon two parts of 
 ammonic chloride, NH 3 HC1, in a glass flask or retort. The 
 reaction is thus shown : 
 
 (NH 3 HC1) 2 + CaO = CaCl 2 + H 3 O + (H 3 N) 2 . 
 
 It will be seen that the lime takes the hydric 
 chloride, forming calcic chloride, while water and 
 ammonia are set free. The gas may be collected 
 in jars in the pneumatic trough, but it must be 
 over mercury, as water absorbs it. It is, how- 
 ever, more convenient to procure it by what is 
 called the method of displacement. The gas 
 generated in the lower vessel (Fig. 142) being 
 lighter than the air, accumulates in the upper 
 portion of the inverted jar, displacing the air 
 and expelling it downward. 
 
 354. Properties. Ammonia is a colorless, ir- 
 respirable gas of a pungent, caustic taste, lighter than air 
 (sp. gr. 0.59), and possesses strong alkaline properties, 
 changing vegetable blues to green and yellows to brown, 
 whence it is called volatile alkali. It does not support com- 
 bustion or respiration ; a thin stream of the gas may be ig- 
 nited in the air, and burns with a pale flame. It may be con- 
 densed by cold or pressure, both to the liquid 
 and the solid state. Liquid ammonia is a 
 colorless, mobile fluid. In the solid state it 
 is white, transparent, and crystalline. From 
 the circumstance that it was derived from the 
 horns of harts, it was called spirits of harts- 
 horn. Ammonia is recognized by its odor. Testing Ammonia. 
 
 
 
NITROGEN AND ITS COMPOUNDS. 
 
 201 
 
 If a rod dipped in hydric chloride be brought near a source 
 of ammonia, a white cloud is produced by the formation of 
 ammonic chloride (NH 4 C1). (Fig. 143). 
 
 355, Uses. Ammonia is used medicinally in various 
 ways. It is administered internally as a stimulant, and 
 applied externally as a counter-irritant. Mixed with 
 olive-oil, it forms volatile liniment. It is the best antidote 
 to prussic acid, but in large doses it is poisonous. It is of 
 many uses to the chemist. 
 
 356. Oxides and Acids of Nitrogen. Nitrogen combines 
 with oxygen, forming : 
 
 Nitric monoxide, N' 2 O. 
 Nitric dioxide, N in ,O a . 
 Nitric trioxide, N in 2 O 3 . 
 Nitric tetroxide, N v a O 4 . 
 Nitric pentoxide, N V 3 O 5 . 
 
 Nitrous acid, HN'"O,. 
 Nitric acid, HN V O 8 . 
 
 FIG. 144. 
 
 357. Nitric Monoxide (N a O) (Nitrous Oxide). This 
 compound was discovered, in 1776, by Priestley, and 
 further examined by Davy in 1800, who noticed the ex- 
 hilarating effects produced 
 by the respiration of this 
 gas, from which its popular 
 name, "laughing gas" is 
 derived. It is prepared 
 from ammonic nitrate, by 
 moderately heating this salt 
 in a flask. The gas escapes 
 through a tube, and is col- 
 lected in jars Over Water 
 (Fig. 144). It should be 
 
 allowed to stand for some time over water, to absorb any 
 nitrous acid that may chance to be formed. The chemical 
 change may be represented by the equation, 
 
 N,H 4 8 = 2H 9 + N 3 0, 
 
 Preparation of Nitrous Oxide. 
 
202 DESCRIPTIVE CHEMISTRY. 
 
 one molecule of ammonic nitrate yielding two molecules 
 of water and one of nitric monoxide. 
 
 358. Properties. At ordinary temperatures nitric mon- 
 oxide is a neutral, colorless, transparent gas, of a slightly 
 sweetish taste, and very soluble in water cold water 
 absorbing about three-fourths of its volume. Sp. gr. 1.527. 
 It is an active supporter of combustion, relighting a glow- 
 ing candle when plunged into it, and intensifying the 
 combustion of phosphorus almost equally with pure oxy- 
 gen. A pressure of 50 atmospheres at 45 F. condenses it 
 into a clear liquid which boils at about 1126 F., and may 
 be frozen at about 150 F. When breathed in small 
 quantities this gas produces a transient intoxication, at- 
 tended sometimes by an irresistible propensity to laugh, 
 and at others by a tendency to muscular exertion, indi- 
 viduals being variously affected according to temperament. 
 The gas should be pure, and even then the experiment 
 is not a safe one for some constitutions. Inhaled in larger 
 quantities it produces insensibility, hence it is now much 
 employed by dentists as an anaesthetic. 
 
 359. Hydric Nitrate or Nitric Acid (HNO 3 ). This 
 compound, familiarly known as aqua-fortis, is not found in 
 Nature, but has been known since very early times. It is 
 
 FIG. 14.-. 
 
 Liberation of Nitric Acid. 
 
 produced on a large scale by the decomposition of sodic 
 nitrate with sulphuric acid : 100 parts, by weight, of sodic 
 
NITROGEN AND ITS COMPOUNDS. 203 
 
 nitrate, 117 parts concentrated sulphuric acid, and 30 parts 
 of water, are placed in a glass retort which is supplied with 
 a receiver .Z?, kept cool by cold water flowing over it from 
 the tube /, by means of a netting (Fig. 145). With the 
 application of heat, the nitrate is decomposed, and the 
 acid distils over into the receiver. The change is thus 
 shown : 
 
 NaNO, + H 2 SO 4 = NaHSO 4 + HNO s . 
 
 That is, one molecule of sodic nitrate and one of sulphuric 
 acid furnish one molecule of nitric acid and one of hydro- 
 sod ic sulphate. 
 
 360. Properties. Nitric acid is a colorless, mobile 
 liquid, of 1.52 specific gravitj r , fuming in contact with 
 the air, and possessed of an intensely sour taste and pe- 
 culiar sweetish-nauseous pungent smell. It becomes solid 
 at very low temperatures, and boils at 86 C., with partial 
 decomposition. It is highly corrosive, and stains of a yellow 
 color the skin, nails, and many other animal substances; 
 it is therefore used to produce yellow patterns upon 
 woolen fabrics. It is also employed for etching on copper, 
 for assaying or testing metals, and, by dyers and calico- 
 printers, as a solvent for tin. In consequence of its large 
 proportion of oxygen, it corrodes the metals with great 
 energy, and hence is the most powerful of oxidizing 
 agents. It ignites powdered charcoal and oil of turpen- 
 tine, and oxidizes phosphorus so rapidly as to produce an 
 explosion. 
 
 361, A mixture of chlorohydric acid with nitric acid 
 constitutes the aqua regia, or royal water, of the alchemists, 
 so named from the power it possesses of dissolving gold, 
 the "king of metals," a property due to the presence of 
 chlorine, which, at the moment of its formation, attacks 
 metals with great energy. The proportions for the mixt- 
 ures are four measures of hydric chloride to one of nitric 
 acid. 
 
204 DESCRIPTIVE CHEMISTRY. 
 
 362. Ammonic Chloride (NH 4 C1) (Sal-ammoniac). This 
 substance is found native in many volcanic regions, in the 
 vicinity of burning coal-mines, and in guano-deposits. 
 
 FIG. 146. 
 
 Formation of Ammonic Chloride. 
 
 When hydric chloride and ammonia are brought together, 
 they form dense white clouds of sal-ammoniac, as may be 
 seen in Fig. 146. The reaction is expressed thus : 
 
 NH, + HC1 NH 4 C1. 
 
 Ammonia Gas. Hydric Chloride. Ammonic Chloride. 
 
 When a solution of ammonic hydrate is neutralized by 
 hydric chloride, crystals of ammonic chloride are produced, 
 which have a sharp taste, and dissolve in thrice their 
 weight of cold water. Sal-ammoniac is chiefly obtained 
 by neutralizing the ammoniacal liquor of the gas-works by 
 hydric chloride. On evaporating the resulting solution, 
 the salt appears in the form of the tough, fibrous crystals 
 of commerce. It is volatilized by heat. Mixed with lime, 
 which decomposes it and expels the ammonia, it is used in 
 smelling-bottles. 
 
 363. Ammonic Hydrate (NH 5 O) (Aqua Ammonia). 
 This compound is prepared by passing ammonia gas (NH g ) 
 into water, which absorbs it rapidly to the extent of 700 
 times its own volume. The gas is evolved by gently heat- 
 
NITROGEN AND ITS COMPOUNDS. 
 
 205 
 
 FIG. 147. 
 
 ing a mixture of slacked lime and sal-ammoniac, and pa&s- 
 ing it through a series of bottles. la making solutions of 
 the absorbable gases several difficulties have to be guarded 
 against. The action in the 
 evolution-flask is liable to 
 various interruptions, while 
 the water present in the 
 apparatus rapidly absorbs 
 the gas. This creates a 
 partial vacuum, and the 
 consequence is, that the 
 water in the jar flows back 
 into the flask, thus putting 
 an end to the process ; also, Wouifes Bottles, 
 
 if the gas is generated fast- 
 er than it is absorbed, there arises the danger of an explo- 
 sion, unless there is a free outlet to the apparatus. These 
 dangers are obviated by the arrangement known as Woulfe's 
 bottles (Fig. 147). 
 
 The flask in which the gas is generated is provided with 
 a safety tube which serves both as a means of introducing 
 a liquid and as a protection against the above-mentioned 
 accidents. When the liquid is poured in, a portion of it is 
 retained in the bend of the tube, acting there as a valve to 
 prevent the access of air to the flask. Each bottle has an 
 upright tubs in the middle neck which acts as a safety- 
 tube, allowing the air in case of a vacuum to pass in, or 
 the liquid in flow out, if the pressure of the gas becomes 
 too great. The other tubes serve to connect the bottles 
 with the flask and with each other. 
 
 364. Properties. Ammonic hydrate is a colorless, trans- 
 parent liquid, of 0*85 specific gravity, with the pungent 
 odor of ammonia, and a sharp, burning taste. As usually 
 met with, it is rarely a definite compound, being liable to 
 contain either more water or gas than the above formula 
 implies. A saturated solution freezes between 38 and 
 
206 DESCRIPTIVE CHEMISTRY. 
 
 41 C., forming shining, flexible, needle-shaped crystals. 
 It boils at 130 F., but is, at the same time, decomposed 
 with evolution of ammonia. The graphic formula of am- 
 monic hydrate is (HJsN-O-H. The single atom of hydro- 
 gen which is linked to the one oxygen-atom is replaceable 
 by negative radicles ; the resulting compounds are termed 
 ammoniacal salts. These salts are remarkable as being 
 isomorphous with certain potassic compounds, and when 
 the formulas of any two of these isomorphous salts are 
 compared, it is found that the atomic group H 4 N exactly 
 corresponds in function to the radical potassium. Thus in 
 comparing the formulas of the two well-known isomorphous 
 salts 
 
 Potash-alum K A1S 2 O 8 + 12H 2 O, and 
 Ammonia-alum H 4 N A1S 3 O 8 + 12H a O, 
 
 we readily observe this analogy. On account of this re- 
 markable fact, it has been assumed that the atomic group, 
 H 4 N, or its double molecule (H 8 N 2 ), must be very similar 
 in character to potassium, and possessed of metallic prop- 
 erties. This radical has been named ammonium. 
 
 365. Ammonic Nitrate, (H 4 N) NO 3 , is formed in small 
 quantities during thunder-storms, and is sometimes con- 
 tained in rain-water. Ammonic sulphate, (H 4 N) 3 SO 4 , is a 
 valuable fertilizer. Several ammonic carbonates are known, 
 and the commercial ammonic carbonate, when purified, 
 constitutes the volatile salts, or smelling-salts, of the shops. 
 
 2. Phosphorus and its Compounds. 
 
 PHOSPHORUS. Symbol, P. Atomic Weight, 31 ; Molecular Weight, 124; 
 Molecular Volume, 2 ; Quantivalence, I., III., V. ; Specific Gravity, 
 1.82. 
 
 366. Distribution, Phosphorus is found in Nature 
 chiefly in combination with calcium. It is a never-failing 
 constituent of the plants used by man and the domestic 
 animals. It is an equally important ingredient of animal 
 
PHOSPHORUS AND ITS COMPOUNDS. 207 
 
 skeletons, which owe their strength to calcic and magnesic 
 phosphates, while it also exists in other combinations in 
 the blood, flesh, milk, and other tissues, and secretions of 
 animals. Phosphorus exists in several allotropic states. 
 Ordinarily, it is a white solid, with a faint-yellow tinge, 
 and almost transparent; when exposed to light under 
 water, it gradually becomes white, opaque, and scaly. 
 Exposed to direct sunlight under water, phosphorus be- 
 comes covered with a red coating, and the same modifica- 
 tion is formed when ordinary phosphorus is heated to a 
 temperature below 250 C., in a gas which has no action 
 upon it. None of the modifications are found native. 
 
 367. Ordinary Phosphorus (P 4 ). This interesting body 
 was discovered in 1669 by Brandt, who obtained it by dis- 
 tilling the residue of evaporated urine with charcoal. Most 
 of the phosphorus of commerce is obtained by the decompo- 
 sition of the bones of animals, which consist largely of calcic 
 phosphate (Ca 3 P 3 O 8 ). The bones are first burned, and, the 
 organic matter being consumed, they are reduced to pow- 
 der and soaked in concentrated sulphuric acid. This de- 
 composes the phosphate, with formation of insoluble calcic 
 sulphate, and soluble acid calcic phosphate (CaH 4 P a O 8 ). 
 The solution of this compound, after being separated from 
 the sulphate, evaporated to sirupy consistence, mixed with 
 charcoal, and heated in an iron pot, is distilled at a bright- 
 red heat. The carbon unites with the oxygen, liberating 
 the phosphorus, which rises in vapor, and is condensed in 
 water in the shape of yellow drops. These are melted 
 under water and forced into tubes, thus forming the ordi- 
 nary stick-phosphorus. 
 
 368. Properties. Phosphorus is a soft, colorless, half- 
 transparent, waxy solid, so extremely inflammable that it 
 takes fire in the open air by the heat of the slightest fric- 
 tion, and burns with great violence, emitting a brilliant 
 flame, and dense, white fumes of phosphoric pentoxide. 
 If quietly exposed to the air, it undergoes slow oxidation, 
 
208 DESCRIPTIVE CHEMISTRY. 
 
 emitting white vapors of a garlic odor and shines in the 
 dark, whence its name, phosphorus, bearer of light. It must 
 he handled with caution, as the burns it produces are deep 
 and difficult to heal. It is insoluble in 
 water ; partially soluble in ether, but 
 dissolves readily in carbonic disulphide 
 and various oils. It melts at 44 C., form- 
 ing a viscid, oily liquid. In warm weath- 
 er phosphorus is flexible, and may be 
 bent without breaking, but near the freez- 
 ing-point of water it becomes brittle, ex- 
 hibiting a cystalliue fracture. On ac- 
 count of its inflammability it is kept under water. It 
 crystallizes from its solution, in forms of the monometric 
 system (Fig. 148). Solutions of phosphorus, as well as 
 the solid itself, are luminous in the dark. Phosphorus is 
 a violent poison. The chief use of this substance is in the 
 manufacture of friction-matches ; and vast quantities are 
 consumed in this way among all civilized nations. 
 
 369. Red Phosphorus. This substance may be obtained 
 by exposing ordinary phosphorus to sunlight, or heating 
 it to near its boiling-point in an atmosphere free from oxy- 
 gen. As thus prepared, red phosphorus, also known as 
 amorphous phosphorus, is a red powder, of about 2.18 spe- 
 cific gravity, much less fusible than ordinary phosphorus, 
 but reverting into the latter at about 260 C. It exhales no 
 vapor or odor ; oxidizes but very slowly in the air, does 
 not change oxygen into ozone, is chemically indifferent, 
 may be handled with impunity, or carried exposed in the 
 pocket, and is not poisonous. Phosphorus forms three 
 compounds with hydrogen, but only one is of importance 
 to the ordinary student. 
 
 370. Hydric Phosphide (H 3 P) (Phosphu retted Hydro- 
 gen). This is a colorless gas, with a very offensive odor, 
 like rotten fish. It is found in Nature, being produced in 
 small quantities by the decay of animal matter, and ap- 
 
PHOSPHORUS AND ITS COMPOUNDS. 
 
 2C9 
 
 pears to be the cause of the will o' the wisp. It may be 
 prepared by heating small fragments of phosphorus with 
 a strong solution of 
 potash in a 
 The end of 
 dips 
 and, 
 
 FIG. 149. 
 
 Wreaths of Flaine. 
 
 caustic 
 retort. 
 
 the retort-tube 
 beneath water, 
 as the gas passes out 
 in bubbles, it rises to 
 the surface and takes 
 fire spontaneously. 
 If some pieces of cal- 
 cic phosphide are thrown into a glass of water, the same 
 thing takes place. Double decomposition with the water 
 produces hydric phosphide, which ignites at the surface 
 and forms beautiful wreaths of vapor (Fig. 149). Pure 
 hydric phosphide (H 3 P) is, however, not spontaneously 
 inflammable, this property being due, in this case, to the 
 admixture of a minute quantity of a liquid compound 
 (H 4 P 2 ). It is poisonous. In many cases the combining 
 weights and the unit-volume weights are identical. But 
 the atomic weight of phosphorus is 31 ; while the specific 
 gravity of its vapor has been found to be 62.1. The volu- 
 metric composition of hydric phosphide will be readily 
 understood by reference to the accompanying diagram : 
 
 H 
 1 
 
 H 
 1 
 
 "H 
 
 i 
 
 }> + 
 
 PH 3 34 
 
210 
 
 DESCRIPTIVE CHEMISTRY. 
 
 FIG. 150. 
 
 Combustion of Phosphorus. 
 
 371. Phosphoric Pentoxide (P a O & ).-~When phosphorus 
 
 is burned in dry oxygen (Fig 1 . 
 150), the dense, white vapors 
 which are formed condense 
 upon the glass in snow-like 
 flakes. This is phosphoric 
 pentoxide. Tt has a power- 
 ful attraction for moisture, 
 absorbing it from the air, or, 
 if brought into contact with 
 water, seizing it with such 
 violence as to emit a hissing 
 sound. By the union of phosphoric pentoxide with water, 
 there are formed three distinct acids: meta-phosphoric 
 acid (HPO 3 ), pvro-phosphoric acid (H 4 P 2 O 7 ), and ortho- 
 phosphoric acid (H 3 PO 4 ). 
 
 3. Arsenic and its Compounds. 
 
 ARSENIC. Symbol, As. Atomic Weight, 75; Quantivalenee, III. and V. 
 Molecular Weight, 300 ; Molecular Volume, 2 ; Specific Gravity, 5.79. 
 
 372. Arsenic. This element is found native, but most 
 of the arsenic of commerce is obtained by the decomposi- 
 tion of the arsenides. The compounds are heated in retorts 
 of earthen-ware ; the arsenic sublimes and collects in iron 
 tubes and earthen receivers. 
 
 Arsenic is a brittle metal, of a steel-gray, or nearly 
 white color. The coarse, gray powder, sold under the 
 name of " fly-poison," or " cobalt," is an impure arsenic. 
 When arsenic is heated in a close vessel to 356 F., it vola- 
 tilizes without fusion, giving off a dense, colorless vapor, 
 having the peculiar odor of garlic, and corresponding to 
 the formula As 4 . If heated in the open air it takes fire, 
 burning with a blue flame, with formation of arsenic tri- 
 oxide. Tt is highly poisonous. 
 
 373. Hydric Arsenide (H 8 As.) (Arseniuretted Hy- 
 
ARSENIC AND ITS COMPOUNDS. 211 
 
 drogeri). This gas may be formed by decomposing an 
 allov of arsenic and iron with dilute sulphuric acid, or by 
 introducing a solution of arsenic into a FIG. isi. 
 
 flask in which hydrogen is being evolved. 
 It burns with a bluish white flame, is high- 
 ly poisonous, and of a disgusting odor. 
 The formation of this gas is used for the 
 detection of arsenic by Marsh's test. 
 Fig. 151 shows the form of an appa- 
 ratus which answers, in a rough way, 
 very well for this purpose. Bits of zinc 
 and a little water are placed in the 
 vessel, which is provided with a cork 
 through which a tube is inserted. Sul- 
 phuric acid is now poured in through the 
 funnel-tube, and the evolution of hydro- 
 
 , ,, A , . , , Marsh's Test. 
 
 gen commences. Atter the air has been 
 completely expelled from the flask, the gas may be lighted 
 at the jet. If the solution containing arsenic be now 
 poured in through the funnel-tube, the color of the flame 
 immediately changes, and a cold, white surface, held so as 
 to cut the flame in half, is stained with a black or brown 
 spot by the deposition of metallic arsenic. Antimony 
 produces a similar effect, but a solution of calcic or sodic 
 hypochlorite dissolves the arsenical stain, leaving that 
 made by antimony unchanged. This is a very delicate 
 test, but great care should be taken that the sulphuric acid 
 and zinc do not contain any previous traces of arsenic. It 
 is estimated that g() ^ 00 of a grain of arsenious oxide in one 
 hundred grain measures of the solution may be detected 
 by this test. 
 
 374. Arsenic Trioxide (As 2 O 3 ) (Arsenious Acid). 
 This compound occurs native, but is also prepared on a 
 large scale by roasting certain ferric arsenides, and other 
 arsenical ores. Thus obtained, it constitutes the well- 
 known white arsenic or ratsbane of commerce, ,a white 
 
212 DESCRIPTIVE CHEMISTRY. 
 
 solid body, capable of existing in three isomeric forms. It 
 is soluble in about ten parts of hot water, the solution 
 having a slightly sweetish taste, and acid reaction. It 
 also dissolves readily in hot hydric chloride, and in solu- 
 tions of the alkaline arsenites. It is used in dyeing and 
 calico-printing, in glass-making, and for the preparation 
 of arsenical soap, which is employed for preserving stuffed 
 animals. Though a violent, corrosive poison, it is used in 
 medicine ; its most effectual antidotes are the moist hy- 
 drated ferric oxide and caustic magnesia. Ortho-arsenic, 
 acid (H 3 AsO 4 ) is formed by oxidizing arsenious oxide by 
 means of nitric acid. It has strongly acid properties, 
 decomposing the carbonates with effervescence. Arsenic 
 disulphide (As 2 S 2 ) has been known since very remote 
 times, and is found native as realgar, a mineral crystal- 
 lizing in translucent, oblique, rhombic prisms, of beau- 
 tiful orange-yellow, or ruby-red, color. It is produced 
 artificially, is used as a pigment, and in the preparation 
 of the pyrotechnical mixture known as "Bengal white- 
 light." Arsenic trisulphide (As 2 S 3 ), familiarly known 
 as "orpiment," is found native, but is also prepared 
 artificially. It is a bright-yellow substance, and is used 
 in dyeing to reduce indigo, and also in the prepara- 
 tion of "rusma," a paste employed to remove the hair 
 from skins. 
 
 4. Antimony and Bismuth. 
 
 ANTIMONF. Symbol, Sb. (Stibium). Atomic Weight, 122; Quantivalence, 
 III. and V. ; Molecular Weight, 488 (?); Molecular Volume, 2; Spe- 
 cific Gravity, 6.78. 
 
 375. Antimony is found native, though most of the 
 antimony of commerce is obtained from the trisulphide 
 (Sb 2 S 3 ). It exists in two modifications ; ordinarily it is a 
 brittle, brilliant, bluish-white metal, crystallizing in rhom- 
 bohedrnns. The other form is obtained by electrolysis, and 
 
ANTIMONY AND BISMUTH. 213 
 
 has a specific gravity of 5.78. When struck or heated it 
 suddenly reverts to the previous modification, with great 
 evolution of heat. Antimony melts at 450 C., and va- 
 porizes at a white heat. Heated in the air it burns with a 
 white flame. The alloys of antimony are of great use in 
 the arts. Of these, type-metal, an alloy of lead and anti- 
 mony, is the most important. The detection and separa- 
 tion of arsenic and antimony is a subject cf much impor- 
 tance as both alike exhibit poisonous characters and similar 
 reactions (373). Stibic trioxide (Sb 2 O 3 ) is produced when 
 metallic antimony burns in the air. It is white, crystal- 
 line, isomorphous with arsenic trioxide, sparingly soluble in 
 water. It is used as a pigment in place of white lead, 
 and gives rise to the salts of antimony so much used 
 in medicine. Stibic trisulphide (Sb 2 S 3 ) is employed in 
 veterinary surgery, in pyrotechny, and in the preparation 
 of the percussion pellets used in the cartridges of the 
 Prussian needle-gun. 
 
 BISMUTH. Symbol, Bi. Atomic Weight, 210 ; Quantivalence, III. and V. ; 
 Specific Gravity, 9.8. 
 
 376. Bismuth. This metal, which has long been known, 
 is found, in the metallic state, in veins in gneiss, clay, 
 slate, and other crystalline rocks, chiefly in Saxony and 
 Bohemia. The commercial material is derived from the 
 native metal by purification. It is hard, brittle, reddish- 
 white in color, and crystallizes from fusion in rhombohe- 
 drons. It melts at 264 C., and on solidifying expands 
 one thirty-second of its bulk. It is volatile at high tem- 
 peratures. Heated in the air it burns with a bluish flame, 
 giving rise to yellow fumes. Bismuth is used in the arts 
 alloyed with other metals, and its compounds are used in 
 medicine and as pigments. 
 
DIVISION II.-ARTIAD ELEMENTS. 
 
 CHAPTER XVI. 
 
 1. Oxygen and its Compounds. 
 
 OXYGEN. Symbol, 0. Atomic Weight, 16; Quanti valence, II.; Molecu- 
 lar Weight, 32 ; Molecular Volume, 2 ; Specific Gravity, 1.1056. 
 
 377. Modifications of Oxygen. Oxygen is known to us 
 in three modifications, consisting, apparently, of one, two, 
 and three atoms of the radical bearing the same name. 
 The second, only, of these is generally termed oxygen ; 
 the molecule containing three atoms of the radical oxygen 
 is known as ozone, and the body containing only one 
 atom as antozone. 
 
 378. Oxygen (Ordinary Modification) (O 2 ). This gas 
 was discovered in 1774, by Dr. Priestley, and the following 
 year it was discovered, independently, by Scheele. Its 
 discovery was also claimed by Lavoisier, who, in 1781, 
 gave it the name oxygen, from two Greek words, meaning 
 acid-former. This has been justly pronounced the capital 
 discovery of the last century, rivaling in importance the 
 great discovery of gravitation, by Newton, in the pre- 
 ceding century. It formed one of the great eras in the 
 progress of human knowledge; it put an end to old 
 theories, laid the foundation of modern chemical science, 
 and furnished the master-key by which man has been 
 enabled to open the mysteries of Nature. But while the 
 discovery of gravitation is unsurpassed in grandeur, that 
 of oxygen is far more vitally linked with the course of 
 earthly affairs. 
 
OXYGEN AND ITS COMPOUNDS. 215 
 
 379. Of its vast practical consequences, Professor Lie- 
 big observes : " Since the discovery of oxygen, the civil- 
 ized world has undergone a revolution in manners and 
 customs. The knowledge of the composition of the at- 
 mosphere, of the solid crust of the earth, of water, and 
 of their influence upon the life of plants and animals, 
 was linked with that discovery. The successful pur- 
 suit of innumerable trades and manufactures, the prof- 
 itable separation of metals from their ores, also stand 
 in the closest connection therewith. It may well be 
 said that the material prosperity of empires has increased 
 manifold since the time oxygen became known, and the 
 fortune of every individual has been augmented in pro- 
 portion." 
 
 380. Occurrence. Oxygen is the mos. abundant ele- 
 ment in Nature. It is of universal distribution through 
 our atmosphere, forming one-fifth part of the air we breathe. 
 The total quantity contained in the atmosphere has been 
 computed to be about 1,178,158,000,000,000 tons, which, 
 if forming a separate layer of uniform density upon the 
 earth's surface, would be one mile deep. It constitutes 
 eight-ninths of water by weight, besides being a con- 
 stituent of nearly all the rocks of the globe; and en- 
 tering largely into the organized structure of plants and 
 animals. 
 
 381. Preparation. Oxygen may be procured in many 
 ways. Mercuric oxide and manganic dioxide readily yield 
 it when they are exposed to a high temperature. It can 
 be obtained in larger quantity, and very pure, from potas- 
 sic chlorate. Two hundred grains of the salt, or about 
 fourteen grammes, are placed in a glass flask, which is fitted 
 tightly with a cork, containing a glass tube, bent so as to 
 dip under the shelf of the pneumatic trough (Fig. 152). 
 The flask is heated, and the chlorate gives off more than a 
 third of its weight of gas. This salt consists of potassium, 
 chlorine, and oxygen, and in the change the whole of the 
 
 10 
 
216 
 
 DESCRIPTIVE CHEMISTRY. 
 
 oxygen is disengaged, potassic chloride remaining be- 
 hind. 
 
 2KC1O 3 = 2KC1 + 3O 2 . 
 
 The decomposition of the chlorate is much facilitated by 
 mixing with it one-fourth its weight of cupric oxide, or 
 
 FIG. 152. 
 
 Generating Oxygen Gas. 
 
 manganic dioxide, thoroughly dried. These substances 
 take no active part in the change, but seem to aid the 
 decomposition by simple presence (catalysis). 
 
 382. Properties. Oxygen is a transparent, colorless, 
 tasteless, inodorous gas. It is about ^ heavier than at- 
 mospheric air. It has never been condensed into a liquid. 
 The refractive power of oxygen compared with that of air 
 as unity is 0.8616. It possesses magnetic properties, but 
 loses them at a high temperature. Oxygen is slightly sol- 
 uble in water, 100 volumes of which absorb about 4J of 
 the gas. 
 
 Oxygen is perfectly neutral, possessing neither acid nor 
 alkaline qualities, but, though apparently the very type of 
 passiveness, this substance is endowed with the most in- 
 tense power. The two atoms of the radicle, which together 
 
OXYGEN AND ITS COMPOUNDS. 
 
 217 
 
 FIG. 153. 
 
 Taper in Oxygen. 
 
 form a molecule of oxygen gas, are held by but feeble 
 attraction, and are easily severed, when they enter into 
 new and firmer combinations. 
 
 383. Combustion in Oxygen. The oxygen of the air 
 
 (about one-fifth of its weight) is equal- 
 ly diffused throughout it. All com- 
 bustion in the open air is the result of 
 the action of oxygen. It has a power- 
 ful affinity for the elements of which 
 fuel is composed, and unites with them 
 with such violence as to give rise to 
 the heat and light of our ordinary 
 fires. All substances which burn in 
 air, burn in pure oxygen with greatly 
 increased brilliancy. If the flame of 
 a taper (Fig. 153) be extinguished, 
 
 and a single spark remain upon the wick, on plunging it 
 
 into a jar of pure oxy- 
 gen, it will be relighted 
 
 and burn with extreme 
 
 vividness ; and this may 
 
 be repeated many times 
 
 in the same vessel of 
 
 gas. The combustion 
 
 of a splinter of wood is 
 
 brilliant, and a piece of 
 
 bark charcoal glows and 
 
 scintillates in the most 
 
 beautiful manner. 
 
 384. Substances 
 usually considered in- 
 combustible also burn 
 violently in oxygen. If 
 
 * n . Combustion of Iron in Oxygen. 
 
 a piece ot hne iron wire 
 
 (or, better still, a steel watch-spring) be coiled into a spiral 
 
 and then tipped with sulphur, ignited and introduced into 
 
 FIG. 154. 
 
218 
 
 DESCRIPTIVE CHEMISTRY. 
 
 FIG. 155. 
 
 FIG. 156. 
 
 a jar of oxygen, it burns with dazzling brilliancy and splen- 
 did corruscations (Fig. 154). Occasionally globules of 
 white-hot iron fuse into the glass even through an inch 
 depth of water. If a jar of oxygen be inverted over a stand 
 upon which there is a little burning sulphur, a beautiful 
 blue light is emitted, and the fumes produced circulate 
 
 round in curious rings (Fig. 155). 
 
 If phosphorus be burned in the 
 
 same manner, a blinding flood of 
 
 light is produced, accompanied 
 
 by great heat (Fig. 156). In 
 
 all these cases, the effects are 
 
 due simply to the union of 0x3^- 
 
 gen with the burning body, and, 
 
 could we have weighed them be- 
 
 fore the experiment, and the prod- 
 ucts of combustion afterward, they would have been found 
 precisely equal. 
 
 385. Eremacausis. The cause of decay in vegetable 
 and animal substances is the action of oxygen, which 
 breaks them up into simpler and more permanent com- 
 pounds. This slow combustion is called by Liebig erema- 
 causis. Oxidation is also the grand process by which the 
 earth, air, and sea, are purified from contaminations ; nox- 
 ious vapors and pestilential effluvia being destroyed by a 
 process of burning, more slow indeed, but as real as if it 
 took place in a furnace. The offensive impurities which 
 constantly flow into rivers, lakes, and oceans, as well as 
 the decaying remains of the living tribes which inhabit 
 them, are perpetually oxidized by the dissolved gas, and 
 the water thus kept pure and sweet. In this way waters 
 that have, become foul and putrid are purified and sweet- 
 ened by exposure to the action of air. This effect, how- 
 ever, is largely dependent upon the presence of ozone. 
 
 386. Relation of Oxygen to Life. Oxygen is the uni- 
 versal supporter of respiration, and hence, as this is the 
 
OXYGEN AXD ITS COMPOUNDS. 219 
 
 most important of the vital processes, it is the immediate 
 supporter of life. From this circumstance it was first 
 known as vital air. An animal confined in a given bulk 
 of common air, having consumed its oxygen, dies. If im- 
 mersed in pure oxygen, it lives much longer, but the effect 
 is too powerful over-action, fever, and in a short time 
 death, are the result. As the introduction of oxygen is the 
 prime physiological necessity of animal life, the mechanism 
 of all living beings is constructed with reference to this 
 fact. The lungs of the higher races, the spiracula of in- 
 sects, and the gills of fishes, are all adapted to the same 
 purpose the absorption of oxygen, either from the air or 
 water. The animal organism is chiefly composed of com- 
 bustible constituents, and we introduce this wonderful 
 element incessantly, day and night, from birth to death, 
 that it may perform its chemical work. The animal body 
 is an oxidizing apparatus, in which the same changes occur 
 that take place in the flame, only in a lower degree, and a 
 more regulated way. Every organ, muscle, nerve, and 
 membrane, is wasted away, burnt to poisonous gases and 
 ashes, and thrown from the system as dead and dangerous 
 matter. If these constant losses are not repaired by the 
 due supply of food, emaciation, decay, and finally death 
 ensue. Starvation is thus unimpeded oxidation slow 
 burning to death. 
 
 387. Ozone (O 3 ). When electric sparks are passed 
 through dry air, a peculiar odor is perceived, which has 
 been called the " electrical smell." There was much doubt 
 about the cause of it, until the investigations of Schonbein, 
 and of Marignac, and De la Rive, showed that it was due to 
 an allotropic form of oxygen. From its peculiar odor, its 
 discoverer named it ozone. In Nature this modification of 
 oxygen is found principally during and after thunder- 
 storms; but the quantity contained in the atmosphere 
 varies considerably, and is always small. Winds blowing 
 from the sea are said to contain more of it than those 
 
220 DESCRIPTIVE CHEMISTRY. 
 
 which sweep over large tracts of land. Oxygen may be 
 converted into ozone not only by electricity, but in various 
 other ways. Thus, when a spiral of 
 platinum wire is heated in air, or when 
 light acts upon some essential oils, in 
 contact with air, ozone is formed. If 
 a piace of phosphorus be placed in a 
 jar, and partially covered with water, 
 its slow oxidation will soon produoe 
 ozone. Or, if we place a little ether in 
 an open vessel, and then introduce into 
 Preparation of Ozone. its vapor a moderately heated glass rod 
 
 (Fig. 157), ozone promptly appears. 
 388, Properties. In most of its physical properties 
 ozone resembles the ordinary modification of oxygen. It 
 differs from it in possessing a powerful odor, somewhat 
 resembling dilute chlorine gas. Its molecular weight is 
 48, and its density 24. It is soluble only in oil of turpen- 
 tine. The most remarkable property of ozone is its power- 
 ful oxidizing action. In fact, it is oxygen greatly intensi- 
 fied in activity. It corrodes metals upon which ordinary 
 oxygen could not act, for example, silver; it quickly 
 bleaches colors, which are comparatively permanent in the 
 air; it deodorizes tainted flesh, destroying its effluvium 
 instantlj T , and carries woody fibre in a short time through 
 a course of decomposition, which, with common oxygen, 
 would require years. It decomposes potassic iodide, set- 
 ting the iodine free. Free iodine combines with starch, 
 turning it blue ; therefore, a test of ozone is made by soak- 
 ing slips of paper in a mixture of starch and potassic iodide. 
 The slightest trace of ozone turns it immediately blue. 
 Prepared paper, exposed for a few minutes to the open air, 
 will frequently turn blue, which is supposed to be due to 
 the presence of ozone. It is probable that it is generated 
 on a large scale in the atmosphere, and that it subserves a 
 high purpose in the economy of the globe as a purifier of 
 
OXYGEN AND ITS COMPOUNDS. 221 
 
 the air, and hastener of decay. Ozonized air irritates the 
 respiratory organs, and a minute quantity kills a rabbit. 
 At a temperature of 290 C., ozone is reconverted into 
 ordinary oxygen. 
 
 389, Antozone (O,). The existence of this substance 
 is yet somewhat doubtful. It is supposed to be produced, 
 together with ozone, by the action of the silent electric 
 discharge upon oxygen. On passing the electrized gas 
 through a solution of potassic iodide, the ozone is absorbed, 
 and the antozone mixed with the excess of unaltered 
 oxygen remains. When this is passed through water it 
 forms a peculiar dense mist, which, collected by itself, dis- 
 appears after a little time, depositing only pure water. 
 Antozone is reconverted into ordinary oxygen, under the 
 same conditions as ozone, but the reconversion takes 
 place more readily in the presence of the latter. Ant- 
 ozone has an odor similar to ozone, but is much more 
 repulsive. 
 
 The molecule of ordinarv oxygen is regarded as con- 
 stituted according to the graphic formula O=O. As the 
 density of ozone is to that of ordinary oxygen as 3 :" 2, the 
 ozone-molecule is assumed to be made up of three atoms of 
 the radicle oxygen. When two molecules of ordinary 
 oxygen are ozonized, three of the four constituent atoms 
 combine to form ozone. It is, therefore, held that ant- 
 ozone consists of the one remaining atom. The molecular 
 and graphic formulas of the three forms of oxygen exhibit 
 the following relations : 
 
 Antozone. Oxygen. Ozone. 
 
 Molecular, O l O 2 O 3 
 
 A 
 
 Graphic, O> OO O-O. 
 
 390. Hydric Oxide (H Q O), Water. Of the importance 
 of water in the economy of Nature little need be said ; it is 
 obvious to all. It is the most abundant substance that we 
 
2% DESCRIPTIVE CHEMISTRY. 
 
 know, and it seems as if the whole scheme of Nature were 
 conformed to its properties. Turning to solid ice, or ex- 
 haling into invisible vapor, its changes of form involve the 
 very history of the globe. Rising from the ocean, con- 
 densed upon the land, and flowing back again to the sea, 
 it carries on in its circulation the grand processes of the 
 world. Constituting four-fifths the weight of the vegetable 
 kingdom, and three-fourths that of the animal, it is the 
 first condition of all organization, and by innumerable 
 transformations and decompositions it is essential to the 
 continuance of organic life. Nor is it less indispensable in 
 the laboratory of the chemist. It is the ready, invaluable 
 medium of a thousand operations, and is involved in nearly 
 every chemical process. 
 
 391. Production of Water. If hydrogen is generated 
 in a jar and allowed to escape through a fine 
 tube (Fig. 158) into the air, it burns, when ig- 
 nited, with a small, steady flame, giving out but 
 little light, though producing intense heat. In 
 all cases where hydrogen is burned with oxygen. 
 water is the product. If a cold, dry glass is held 
 over the jet, it is quickly covered with a film of 
 dew, which rapidly increases to drops of water. 
 ^ e gases unite to form steam, which then con- 
 denses into the liquid state. 
 
 Oxygen and hydrogen burn quietly when brought 
 cautiously in contact and ignited, but, if the gases are 
 mixed, before ignition, in the proportion of one volume 
 of the first to two of the second, a violent explosion re- 
 sults. Soap-bubbles, if blown with this mixture from a 
 bag and fired with a candle, detonate like a pistol (Fig. 
 
 392. Composition, Water is a compound of 8 parts by 
 weight of oxygen to 1 of hydrogen, or by bulk 1 of oxy- 
 gen to 2 of hydrogen. Its composition may be proved in 
 many ways, but one of the most simple is to throw a 
 
OXYGEN AND ITS COMPOUNDS. 223 
 
 little metallic potassium upon its surface. The metal in- 
 stantly decomposes it, seizing upon the oxygen, and set- 
 ting hydrogen free with such violence as to produce the 
 vivid combustion of the latter (Fig. 
 159); the water seems set on fire. FlG - 159 - 
 
 Water is also decomposed by so- 
 dium, iron, zinc, and many other 
 metals ; in fact, they have been long 
 classified according to their degrees 
 of power in this respect. In num- 
 berless operations of chemistry, the 
 elements of water are separated and 
 reunited, and the same thing is going 
 on perpetually in vegetable and ani- Decomposing Water, 
 mal organisms. 
 
 But the composition of water may be shown in the most 
 perfect manner by sending an electric current through a 
 vessel of it (Fig. 62), as already described (141). The 
 gases are set free in the exact proportions given above, 
 and, if mixed together and ignited, they combine with a 
 loud and sharp explosion, the product being pure water. 
 The composition of water is thus demonstrated by both 
 analysis and synthesis. 
 
 393. General Properties. Pure water is a transparent, 
 tasteless, inodorous liquid. It is but very slightly con- 
 densible according to Regnault, being compressed 1-47 
 millionth of its bulk for each atmosphere of pressure and 
 is perfectly elastic, as it regains its full dimensions when 
 the pressure is removed. It evaporates at all tempera- 
 tures; boils at 100 C. or 212 F., and freezes at C. or 
 32 F. It is 815 times heavier than an equal bulk of air. 
 An imperial gallon weighs 70,000 grains, or just 10 Ibs. 
 The American standard gallon of pure distilled water at 
 the maximum density weighs 58,972 grains. In thin sheets, 
 water is colorless, but when viewed in thick masses it has 
 a decided tint. Light passed through fifteen feet of pure 
 
224: DESCRIPTIVE CHEMISTRY. 
 
 distilled water emerges of a bright and delicate blue-green, 
 and, by augmenting the thickness, the color is deepened. 
 
 394. Snow Crystals. Water, in freezing, crystallizes. 
 The aqueous vapor of the atmosphere, condensed by cold 
 in winter, or at great heights in summer, assumes the most 
 beautiful crystalline forms those of snow-flakes. Perfect 
 snow-flakes are six-sided stars modifications of an hexa- 
 gonal prism which shoot out an infinity of delicate 
 needles, all diverging from each other at an angle of 60. 
 These frozen blossoms, as they have been aptly termed, 
 are seen in an endless variety of most exquisite forms, a 
 few of which are shown in Fig. 160. 
 
 FIG. 160. 
 
 Forms of Snow-Flakes. (GLAISHER.) 
 
 When a ray from the sun or an electric lamp is made to 
 pass through a block of pure ice, a portion of the heat is 
 arrested, and must, of course, produce change. As it cannot 
 warm the ice, it melts it. But the ice-particles return to the 
 liquid state in definite order, and, upon examining it with 
 a magnifier, the ice is seen to be filled with beautiful 
 flower-like figures. These consist of water, but as the 
 
OXYGEN AND ITS COMPOUNDS. 225 
 
 liquid formed cannot quite fill the space of the melted ice, 
 there occurs a little vacuum, which looks like a globule of 
 burnished silver in the centre of the flower. 
 
 395. Unequal Expansion of Water. This liquid con- 
 tracts as its temperature falls from the boiling-point till it 
 reaches 39 F., when it remains stationary for a time. It 
 then begins to expand, and, in cooling through 7 to 
 the freezing-point, it reaches the same volume it had at 
 48. The point of greatest contraction is called the maxi- 
 mum density of water. This fact is of great importance 
 in Nature. If water continued to contract as it cooled, it 
 would be denser and heavier at the freezing-point, and, 
 consequently, sink. Lakes and rivers would then begin to 
 freeze at the bottom first, and, in the course of the winter, 
 would become solid masses of ice ; while the length of time 
 required to thaw them would greatly prolong the cold 
 season. But as the surface stratum of water approaches 
 the freezing-point and freezes, it expands, and, becoming 
 lighter, floats, and thus the coldest water and ice are kept 
 at the surface, where, as they are almost perfect non-con- 
 ductors of heat, they protect the mass of water below from 
 the cold above. In freezing, water expands with such 
 power as to burst the strongest vessels. Percolating 
 the minute crevices and fissures of rocks in summer, it 
 freezes in winter, and expands with a force which breaks 
 the solid stones, crumbling them into soil fit for the sup- 
 port of vegetable life. 
 
 396. Its Specific Heat. The great specific heat of water 
 is a powerful agency in controlling climate. It is four times 
 greater than that of air ; that is, a pound of water, in cool- 
 ing one degree, would warm four pounds of air one degree. 
 But, as water is 770 times heavier than air, it is obvious that 
 a cubic foot of water, in cooling one degree, would warm 
 four times 770 cubic feet of air, or 3,080 cubic feet one 
 degree. Hence, the vast amount of heat stored up in 
 oceans and lakes, being gradually imparted to the air 
 
226 DESCRIPTIVE CHEMISTRY. 
 
 during winter, modifies the severity of the cold, and ex- 
 plains the fact that island winters are less severe than 
 those of continents or inland places. 
 
 The very stability of Nature seems to depend upon this 
 quality of the earth's aqueous element. If the watery 
 masses of the globe, and that large proportion of it con- 
 tained in our own bodies, lost and acquired heat as promptly 
 as mercury, the variations in temperature would be incon- 
 ceivably more rapid than now ; the inconstant seas would 
 freeze and thaw with the greatest facility, while the slight- 
 est changes of weather would send their fatal undulations 
 through all living systems. But now the large amount of 
 heat accumulated in bodies of water during summer is 
 given out at a slow and measured rate; the climate is 
 tempered, and the transitions from heat to cold are gradual 
 and moderated. 
 
 397. Its Solvent Power. Water possesses the power 
 of dissolving many solid, liquid, and gaseous substances. 
 This solvent power is variable for different substances, and 
 at different temperatures. Thus, a pound of cold water 
 will dissolve two pounds of sugar, while it will only take 
 up two ounces of common salt, two and a half of alum, or 
 eight grains of lime. Heat generally increases the solvent 
 power of water; thus boiling water will dissolve 17 times 
 as much saltpetre as ice-water. But there are exceptions 
 to this rule; ice-water dissolves twice as much lime as 
 boiling water. 
 
 Water dissolves gases in the most diverse proportion, 
 taking up 700 times its bulk of ammonia ; its own bulk of 
 carbonic dioxide ; ^ its bulk of oxygen, and still less of 
 nitrogen. There is, therefore, an atmosphere diffused 
 throughout all natural waters, which is richer in oxygen 
 than common air, and hence better adapted for supporting 
 the life of aquatic animals. The gases absorbed by water 
 give it a brisk, agreeable flavor, and, if driven off by boil- 
 ing, the liquid becomes insipid. 
 
OXYGEN AND ITS COMPOUNDS. 227 
 
 398. Purification of Water. Water, as found in Nature, 
 is never perfectly pure, but always contains variable quan- 
 tities of mineral and organic substances which are" either 
 held in suspension mechanically, or are dissolved in it. It 
 is also inhabited by myriads of minute living organisms 
 known as infusoria. 
 
 During freezing, the substances dissolved in water are 
 expelled ; hence the ice of sea-water (as is well known to 
 sailors), when melted, becomes fresh water. For the same 
 reason, water from melted ice contains neither air nor gas 
 fish cannot live in it. 
 
 399. The best method of purifying water is by distilla- 
 tion (111) ; to render it perfectly pure, it must be redis- 
 tilled at a low temperature, in silver vessels. By filtration 
 through sand, crushed charcoal, or other closely porous 
 media, water may be deprived cf suspended impurities, 
 and of all living beings. Boiling kills all animals and 
 vegetables, expels gases, and precipitates calcic carbonate, 
 which constitutes the fur or crust, often seen lining tea- 
 kettles and boilers. Alum (two or three grains to the 
 quart) is often used to cleanse muddy or turbid water, but 
 it does not purify it, being merely decomposed by the 
 calcic carbonate contained in the water, while the alumina 
 set free carries down the impurities mechanically ; but the 
 sulphuric acid of the alum, combining with the lime, forms 
 calcic sulphate, and renders the water harder than before. 
 The alkalies, potash, or soda, soften water by decomposing 
 and precipitating the earthy salts ; but in their turn re- 
 main themselves in solution. 
 
 400. Chemical Properties. Although water is neither 
 acid nor alkaline in its action on vegetable colors, it is 
 chemically an exceedingly active body, inducing and under- 
 going decomposition, w r hen brought in contact with a great 
 number of different substances. When one atom of hydro- 
 gon in the water-molecule is replaced by an atom of a posi- 
 tive radicle, it gives rise to a hydrate ; when by a negative 
 
228 DESCRIPTIVE CHEMISTRY. 
 
 radicle, to an acid (hydric salt). Water combines directly 
 with many substances, especially those which are crystal- 
 lizable from aqueous solutions. Thus held in combination, 
 it is termed water of crystallization. From this, it appears 
 that the radicle oxygen contained in water is capable of 
 performing a tetradic linking function, which view may 
 be graphically expressed by assigning to it the formula 
 H-O-H, instead of H-O-H. 
 
 IV 
 
 401. Hydric Dioxide (H 2 O 2 ) is a transparent, colorless, 
 syrupy liquid, of 1.452 specific gravity, which does not 
 solidify at 30 C., and may be evaporated at low tem- 
 peratures in a vacuum. It has an astringent taste, a 
 decided odor, and possesses active bleaching properties. 
 It is a very unstable compound, decomposing slowly at 
 15 C., while higher temperatures, or the contact of various 
 substances, causes it to separate into water and oxygen 
 with explosive violence. It may be regarded as free 
 hydroxyl (HO), composed of two atoms of a compound 
 monad radical. 
 
 2. The Atmosphere. 
 
 402. Its Composition. It was not until the year 1774 
 that Lavoisier pointed out the true composition of the 
 atmosphere. Up to this time it was spoken of as one of 
 the four elements ; but the careful observations of Priestley 
 and Scheele, and their discovery of oxygen gas, prepared 
 the way for a knowledge of its exact composition. It is 
 now regarded as a mixture of several gases, nitrogen and 
 oxygen constituting its bulk the one incapable of sup- 
 porting combustion or respiration, and the other essential 
 to life. 
 
 Air contains, Composition by Volume. Composition by Weight. 
 
 Oxygen, 20.96 23.185 
 
 Nitrogen, 79.04 76.815 
 
 100.00 100.000 
 
THE ATMOSPHERE. 229 
 
 That the air is made up of these gases may be ascertained 
 both by analysis and synthesis. That it is a mixture and 
 not a chetnical compound is made manifest by the facts 
 that its components are not united in the ratio of their 
 atomic weights, and that each gas dissolves in water, inde- 
 pendently of the other ; but the analyses of air collected 
 from different parts of the earth, and at different heights, 
 show a remarkable uniformity in its composition. In addi- 
 tion to the oxygen and nitrogen present in the atmosphere, 
 there is always a small proportion of aqueous vopor, car- 
 bonic dioxide, and ammonia. 
 
 403. The proportion of watery vapor in the atmosphere 
 varies with the temperature. It usually ranges from the 
 fa to the ^-J-Q of the bulk of the air. By passing known 
 quantities of air through carefully-weighed tubes of po- 
 tassic hydrate, the carbonic dioxide is absorbed, and its 
 proportion determined. It varies from 3 to 6 paits in 
 10,000 of air, and averages about one volume in 2,500. 
 The quantity is variable within the limits above stated. 
 It increases as we rise from the earth, and is less after a 
 rain, which washes it down from the air; it increases 
 during the night, and diminishes after sunrise, is less over 
 large bodies of water than over large tracts of land, and is 
 more abundant in the air of towns than in that of the 
 country. 
 
 404. The Carbonic Acid which is poured into the at- 
 mosphere in prodigious quantities and from innumerable 
 sources, is as necessary to the vegetable w r orld, as is oxy- 
 gen to the animal world. It is absorbed by the leaves, 
 and minute as is its proportion, if it were withdrawn, the 
 vegetable world would quickly perish. Liebig has shown 
 that the air contains minute traces of ammonia, which are 
 washed down, and may be detected in rain-water. Traces 
 of nitric acid have also been frequently detected. This 
 substance is thought to be formed by electricity, every 
 flash of lighting which darts across the sky combining a. 
 
230 DESCRIPTIVE CHEMISTRY. 
 
 portion of the oxygen and nitrogen along the line of its 
 course, and forming this acid. The saline particles of the 
 ocean-waves, as they are dashed into foam and- spray, are 
 carried by the winds far inland. All these substances are 
 brought down by the rains, and help to quicken the growth 
 of vegetation. 
 
 405. Resulting Properties. Each of the constituents 
 of the air is essential to the present order of things. 
 Oxygen is preeminently its active element. To duly re- 
 strain this activity, the oxygen is diluted and weakened 
 by four times its bulk of the negative element, nitrogen. 
 Their properties are thus perfectly adjusted to the require- 
 ments of the living world. Were the atmosphere wholly 
 composed of nitrogen, life could never have been possible ; 
 were it to consist wholly of oxygen, other conditions re- 
 maining as they are, the world would run through its 
 career with fearful rapidity ; combustion once excited, 
 would proceed with ungovernable violence ; animals would 
 live with hundred-fold intensity, and perish in a few hours. 
 
 406. The Atmosphere and the Living World. The re- 
 lations of the atmosphere to living beings, the stability of 
 its composition, and the wonderful forces that are displayed 
 within it, are full of surpassing interest. The vegetable 
 world is derived from the air ; it consists of condensed 
 gases that have been reduced from the atmosphere to the 
 solid form by solar agency. On the other hand, animals, 
 which derive all the material of their structure from plants, 
 destroy these substances while living, by respiration, and 
 when dead, by putrefaction, thus returning them again in 
 the gaseous form to the air whence they came. 
 
SULPHUR AND ITS COMPOUNDS. 231 
 
 CHAPTER XVII. 
 
 THE SULPHUR GKOUP. SULPHUR, SELENIUM, TELLURIUM. 
 
 1. Sulphur and its Compounds. 
 
 SULPHUR. Symbol, S. Atomic Weight, 32 ; Quantivalence, II., IV., VI. ; 
 Molecular Weight, 64 ; Molecular Volume, 2 ; Specific Gravity, 2.05. 
 
 407. Modifications of Sulphur. Sulphur, like oxygen, 
 is capable of existing in several different modifications. 
 At ordinary temperatures it is solid, or nearly so. At 
 115 C., it melts to a pale-yellow liquid. As the tempera- 
 ture rises this liquid becomes viscid, until, between 200 
 and 250 C., it is too thick to flow. At a still higher 
 temperature it again becomes fluid, and finally boils at 
 440 C. The density of the vapor then diminishes grad- 
 ually, until, at 1000 C., a point is reached where it is 
 32 times as great as that of hydrogen at the same tem- 
 perature. Sulphur in all its forms is insoluble in water 
 and alcohol, a poor conductor of heat, and a non-conductor 
 of electricity. When heated in the air to 260 C., it takes 
 fire, burning with a pale-blue flame. The vapor of sulphur 
 supports combustion, many metals taking fire in it, and 
 burning actively. When combined with metals or positive 
 radicals, sulphur is a dyad, but in other combinations it 
 may be either a tetrad or hexad. 
 
 408. Ordinary Modification (S a ) In this form, sulphur 
 is one of the oldest known substances, being mentioned in 
 the Bible, and in the writings of the ancients. It exists 
 abundantly in Nature ; is found in various volcanic regions, 
 as in the island of Sicily, where it is mined in immense 
 quantities for the market. It is deposited by many springs 
 and small lakes, being produced by the decomposition of 
 hydric sulphide. The sulphur of commerce is prepared 
 from the impure native material, by subjecting it to a rough 
 distillation in earthen retorts which separates it from min 
 
232 DESCRIPTIVE CHEMISTRY. 
 
 eral impurities. It is also obtained from a native ferric sul- 
 phide. This is generally done by piling the ferric sulphide 
 with wood, in large heaps in the open air, and setting these 
 on fire. A portion of the ferric sulphide burns, and, through 
 the heat attending its combustion, the remainder is also 
 decomposed with the liberation of sulphur, which volatalizes 
 and collects in the fluid state, in basin-shaped cavities on 
 the surface of the heap. In commerce, sulphur exists in 
 forms due to the different modes of its preparation : first, 
 as roll-sulphur or brimstone, obtained by running melted 
 sulphur into moulds; second, as flour of sulphur, a pale 
 yellow gritty powder, obtained by sublimation ; and, third, 
 as milk of sulphur, produced by the decomposition of solu- 
 tions of certain sodic and potassic sulphides with acids. 
 409. Properties. In its ordinary modification sulphur 
 F, G . i6i is a brittle, yellow solid, crystallizing 
 
 in transparent right rhombic octohe- 
 dra, or allied forms (Fig. 161). It is 
 soluble in carbonic disulphide, and the 
 crystals may be obtained from this 
 solution by evaporation. 
 
 410. Oblique Prismatic Sulphur 
 Sulphur-Crystals. (S^). This modification may be ob- 
 tained by melting ordinary sulphur in a crucible, allowing it 
 to cool until a crust is formed, then breaking the crust and 
 pouring out the still fluid portion. The walls of the crucible 
 will then be found lined with a mass of transparent yellow- 
 ish-brown, needle-shaped crystals (Fig. 162). They are ob- 
 lique rhombic prisms, or modifications of Pio 162 
 these, have a specific gravity of 1.98, and 
 in the course of a few days pass sponta- 
 neously into the ordinary octahedral modi- 
 fication. They are readily soluble in car- 
 bonic disulphide. 
 
 411, Plastic Sulphur (Sy). This va- 
 riety is produced by heating melted sul- Crystals by Fusion. 
 
SULPHUR AND ITS COMPOUNDS. 
 
 233 
 
 FIG. 163. 
 
 phur to a temperature of from 260 to 300 C., and then sud- 
 denly cooling it by pouring it in a thin stream into water 
 (Fig. 163). It is a dark-brown tenacious mass, which may be 
 drawn into threads like In- 
 dia-rubber. It has a specific 
 gravity of 1.95, and is inso- 
 luble in carbonic disulphide. 
 It gradually changes to the 
 ordinary modification. Sul- 
 phur is consumed largely in 
 the manufacture of hydric 
 sulphate, of gunpowder, and 
 of friction-matches. Milk of 
 sulphur is extensively used 
 in medicine. The plastic 
 modification is often em- 
 ployed to take impressions 
 of medals, coins, and simi- 
 lar objects. 
 
 412. Hydric Sulphide (H 2 S) (Sulphuretted Hydrogen). 
 Hydric sulphide was discovered by Scheele, in 1777. 
 It is found abundantly in Nature as a volcanic product, 
 as the essential ingredient to which the waters of so-called 
 sulphur-springs owe their flavor, and as one of the bodies 
 resulting from the decay of organic matter. 
 
 413. Preparation and Properties. It is usually obtained 
 by the action of dilute hydric sulphate on ferrous monosul- 
 phide. 
 
 Fe'S + H a S0 4 = Fe"SO 4 + H 2 S 
 
 Fig. 164 represents a convenient arrangement for its evo- 
 lution. The ferric monosulphide should be broken into 
 small lumps and placed in the flask. The cork and tubes 
 may then be adjusted, and, first, water, and then hydric 
 sulphate poured in through the funnel-tube. The gas is 
 absorbed by the water of the second vessel. The solution 
 must be kept in tightly-secured bottles, as, if exposed 
 
 Amorphous Sulphur. 
 
234 
 
 DESCRIPTIVE CHEMISTRY. 
 
 FIG. 164. 
 
 to the air, it is gradually decomposed. Hydric sulphide 
 is a colorless transparent gas, having the well-known odor 
 of rotten eggs. Cooled to 74, or submitted to a pressure 
 of 17 atmospheres at 10, it con- 
 denses to a colorless mobile liquid 
 of 0.9 specific gravity, which freez- 
 es at 85, the frozen portion sink- 
 ing in the liquid. It readily dis- 
 solves in water, imparting to the 
 solution its taste and smell. Its 
 reaction on vegetable colors is 
 slightly acid, and heated in the air 
 it burns with a pale-blue flame. 
 When breathed it is highly poi- 
 sonous, and even when much di- 
 luted with air it has proved fatal to many of the lower 
 animals. Hydric sulphide is used extensively in chemical 
 operations as a re-agent. Its action upon solutions of the 
 metals may be shown by the apparatus represented in the 
 
 FIG. 165. 
 
 Liberation of Hydric Sulphide. 
 
 Precipitation of Metals by Hydric Sulphide. 
 
 accompanying cut (Fig. 165). The gas is evolved from 
 ferrous sulphide in a two-necked bottle, and passed through 
 
SULPHUR AND ITS COMPOUNDS. 235 
 
 a second bottle containing a little water, after which it suc- 
 cessively passes through bottles containing solutions of 
 cupric sulphate, zinc sulphate, ferrous sulphate, and lead 
 sulphate. The cupric sulphate in the first bottle will give 
 a black precipitate, that in the second a white, while the 
 last ones yield black precipitates. 
 
 414. Chloric Bisulphide, C1 2 S 2 . This compound, more 
 generally termed chloride of sulphur, is obtained by passing 
 dry chloric gas over melted sulphur. It is a deep orange- 
 yellow liquid of peculiar disagreeable odor, boiling at 
 136 C. It is instantly decomposed by water. Chloric 
 disulphide is employed in the vulcanization of caoutchouc. 
 
 415. Sulphur and Oxygen. Sulphur may unite with 
 oxygen as a dyad, tetrad, or hexad. The following are the 
 oxides and acids with which we are acquainted : 
 
 Sulphurous oxide, S IV O 2 . Sulphurous acid, H a S IV Oj. 
 
 Sulphuric " S VI S . Sulphuric u H 3 S VI O 4 . 
 
 416. Sulphurous Oxide, SO 2 . This substance occurs 
 among the products of volcanic action, and is always 
 formed by the combustion of sulphur in air, or in pure 
 oxygen, th us : 
 
 S, + 0.=2(S0 3 ) 
 
 It is a transparent, colorless gas, of 2.25 specific gravity, 
 having a pungent, suffocating odor, familiarly known in the 
 case of a burning match. It extinguishes combustion; 
 hence sulphur is often thrown into the fire to quench the 
 burning soot of chimneys. It has a strong attraction for 
 water. Allowed to escape into the air, it forms white fumes 
 with its moisture, and a piece of ice thrust into the gas is 
 instantly liquefied. Water at 60 F. takes up large quan- 
 tities of this acid, the solution formed having the taste and 
 smell of the gas. By cold or pressure it condenses into a 
 liquid, of 1.49 specific gravity, which evaporates so fast 
 that the cold generated will freeze water even in a red-hot 
 crucible. At 76 C. it becomes solid. 
 
236 
 
 DESCRIPTIVE CHEMISTRY. 
 
 FIG. 166. 
 
 Bleaching by Sulphurous Oxide. 
 
 417. Uses. Sulphurous oxide is used as a disinfectant, 
 and in bleaching woolen and straw fabrics. The goods are 
 
 moistened, and suspended in 
 large chambers, or, in a small 
 way, they are put into inverted 
 barrels, and exposed to the 
 fumes of burning sulphur. The 
 effect is produced, not by de- 
 stroying the coloring matter, as 
 in the case of chlorine, but by 
 the union of the acid with the 
 coloring matter, which forms a 
 white compound. If a red rose 
 is held over burning sulphur, 
 it is whitened, but the color is 
 at once restored by weak sul- 
 phuric acid, which, being stronger, discharges sulphurous 
 oxide from combination. The bleaching power of sul- 
 phurous oxide upon flowers may be illustrated by burning 
 sulphur under a glass, within which are some highly- 
 colored flowers. (Fig. 166.) If woolens, after sulphur- 
 bleaching, are washed with a strong alkaline soap, the acid 
 is neutralized by the alkali, the coloring matter liberated, 
 and the yellowish color restored. 
 
 418. Sulphurous Acid, Hydric Sulphite, H 2 SO 3 . The 
 solution of sulphurous oxide in water contains a definite 
 compound of the form H 2 SO 3 , which is possessed of strong 
 acid properties. It is sometimes used for the same purposes 
 for which sulphurous oxide is employed. The hydrogen 
 in this compound is replaceable wholly or in part by me- 
 tallic elements, giving rise to numerous salts known col- 
 lectively as sulphites. 
 
 419. Sulphuric Oxide, SO 3 . This may be obtained in 
 the form of a white snowy solid, by heating disulphuric 
 acid, and collecting the fumes which pass over into a 
 receiver surrounded by a freezing mixture. While in this 
 
SULPHUR AND ITS COMPOUNDS. 
 
 237 
 
 condition, it exhibits no acid properties, and may be handled 
 with impunity, if the hands are dry. But it fumes in the 
 air, and rapidly absorbs moisture. When thrown into 
 water it hisses like a hot iron, and the solution thus formed 
 possesses all the properties of the ordinary acid. 
 
 420. Sulphuric Acid, Hydric Sulphate, H 2 SO 4 . This 
 important chemical compound was known as early as the 
 fifteenth century. It is found native in a dilute condition, 
 in volcanic regions, and in the waters of some springs and 
 rivers. Sulphuric acid may be prepared on a small scale 
 
 FIG. 167. 
 
 FIG. 16$. 
 
 Preparation of Sulphuric Acid. 
 
 in an apparatus represented by Fig. 167. A large glass 
 balloon, #, is connected by tubes with three flasks. Flask 
 b supplies it with sulphurous oxide; c, with nitric dioxide; 
 d, with steam, and the short tube furnishes air. These 
 four substances re- 
 act upon each other 
 with the continued 
 production of sul- 
 phuric acid. In 
 
 the manufactory the ' Liberate sulphuric Acid. 
 
 balloon is represent- 
 ed by large chambers lined with sheet-lead, and the flasks 
 by furnaces (Fig. 168). In one furnace sulphur is heated, 
 
238 DESCRIPTIVE CHEMISTRY. 
 
 and pours into the chamber sulphurous oxide, SO,. In 
 another nitre is heated in an iron pot with sulphuric acid, 
 by which fumes of nitric acid, HNO 3 , are produced and 
 delivered into the chamber. The HNO 3 is quickly deprived 
 of an atom of oxygen by the sulphur, yielding water and 
 nitrogen tetroxide, N C O 4 , Steam and air are thrown into 
 the chamber by another flue, and thus the conditions of 
 action are secured. 
 
 421. The process depends upon the property possessed 
 by the higher oxides of nitrogen of oxidizing sulphurous 
 oxide, at the expense of the oxygen of the atmosphere. 
 The sulphurous oxide is converted into the sulphuric, the 
 oxygen being derived from the air, and the nitric dioxide 
 being the carrier that transports it. A small quantity of 
 N a O 2 may thus form an endless quantity of SO 3 , which 
 unites with the water present to form sulphuric acid, H 2 SO 4 . 
 These changes are represented in the following scheme : 
 
 FROM AIR, O 
 FBOM THE 
 
 FURNACE, N 2 2 - N 2 4 ^ N 2 2 * N 2 4 ^ N 2 8 
 
 AS STEAM, H 2 O v \ H 2 0, 
 
 FROM THE ^V \ 
 
 FURNACE, S Oj^^X^ \ 8 O a 
 
 ~ H 2 S0 4 
 
 The large chambers of the manufactory are divided by 
 leaden partitions with narrow openings, which serve to 
 facilitate the intermixture of the gases as they pass on 
 through the apartments. The bottom of the chamber is 
 always kept covered with water to the depth of two or three 
 inches, to absorb the acid as it falls. When the water has 
 acquired a density of 1.5, by the absorption of acid, it is 
 drawn off and boiled down in glass or platinum retorts, 
 until it has a specific gravity of about 1.8. The acid thus 
 obtained has the formula H 2 SO 4 , and constitutes the or- 
 dinary sulphuric acid of commerce. 
 
SULPHUR AND ITS COMPOUNDS. 239 
 
 422. Properties. Sulphuric acid is a thick, oily liquid 
 of 1.85 specific gravity, without odor, and has at first a 
 soapy feel, but it speedily corrodes the skin, causing an 
 intense burning sensation. It is the most powerful of acids, 
 and has an intense affinity for water. When a splinter of 
 wood is dipped into it for a short time, it turns black, the 
 acid taking away from it the elements of water, and leaving 
 the carbon. In like manner, it decomposes and chars the 
 skin and most other organic substances by removing their 
 water. If a little concentrated acid is exposed to the open 
 air in a shallow dish it will soon double its weight 
 
 from the moisture absorbed. When sulphuric acid FlG - 
 and water are mixed they shrink in bulk, and heat 
 is produced. A mixture of four parts concentrated 
 acid to one part water (Fig. 169) evolves sufficient 
 heat to boil the ether in a test-tube. The concen- 
 trated acid freezes at about 30 F., and boils at 
 640 F. Pure sulphuric acid is colorless, but slight 
 traces of organic matter, as dust or straws, turn it of the 
 dark shade usually seen in commerce. The commercial 
 acid is cheap, but impure, containing traces of lead, arsenic, 
 potash, hydric chloride, and sulphurous oxide. The test 
 for sulphuric acid is a solution of baric chloride (440). 
 
 423. Uses. Sulphuric acid is the most important sub- 
 stance used in manufactures. It is employed to make 
 sodic and chloric carbonate, citric, tartaric, acetic, and nitric 
 acids, sodic and magnesic sulphate, and various paints; 
 also, in dj eing, calico-printing, gold and silver refining, 
 and in purifying oil and tallow. Its chemical uses are in- 
 numerable. Disulphuric acid, H S S S O 7 , is also known as 
 Nordhausen sulphuric acid, or fuming sulphuric acid, and 
 is manufactured by the original process the distillation of 
 dried ferrous sulphate in earthen retorts. It is a heavy, oily 
 liquid, of 1.9 specific gravity, fuming strongly in contact 
 with the air. Heat decomposes it into sulphuric acid and 
 sulphuric oxide. The method by which this acid is ob- 
 
 11 
 
240 DESCRIPTIVE CHEMISTRY. 
 
 tained from ferrous sulphate, or " green vitriol," has given 
 rise to the name of "oil of vitriol," by which sulphuric acid 
 is generally known. 
 
 2. Selenium and Tellurium. 
 
 424. History. Selenium and Tellurium are elements 
 closely allied to sulphur. They form compounds with dry 
 hydrogen, H 2 Se, and H 2 Te, similar to H 2 S ; and also com- 
 pounds with oxygen and hydrogen, resembling sulphurous 
 and sulphuric acids. Selenium is a rare substance, existing 
 in several modifications, apparently analogous to those of 
 sulphur. Its name is derived from a Greek word, meaning 
 the moon. At ordinary temperatures it is a solid of a 
 brownish-red color, and with a lustre somewhat resembling 
 that of the metals. Selenium boils at 700 C. Heated in 
 the air it burns, emitting an intolerable odor resembling 
 decayed horse-radish. Tellurium was first distinguished in 
 1798, by Klaproth, who named it tellurium, from the Latin 
 " tellus," the earth. It is found in Nature, but is exceed- 
 ingly rare. It is a tin-white brittle metal, crystallizing in 
 rhombohedrons, melting at about 500 C., and volatilizing 
 at a white heat. Heated in the air it takes fire, and burns 
 with a lively blue flame, edged with green. The vapor of 
 tellurium has a greenish-yellow color. 
 
COPPER AND ITS COMPOUNDS. 241 
 
 CHAPTER XVIIL 
 
 COPPER AND MERCURY. 
 
 1. Copper and its Compounds. 
 
 COPPEB. Symbol, Cu. Atomic Weight, 63.5 ; Quantivalence, II. ; Specific 
 Gravity, 8.9. 
 
 425. Copper. This metal, well known since earliest 
 times, is often found native in masses of considerable mag- 
 nitude. It is obtained on a large scale by the decomposi- 
 tion of ores, of which copper pyrites (Cu 2 Fe 2 S 4 ), cuprous 
 oxide (Cu 2 O), and malachite (Cu 2 H 2 CO 5 ), are among the 
 most important. The processes of its extraction are very 
 complicated. Metallic copper is tough, malleable, and of a 
 red color. The metal may be stiffened by hammering, and 
 softened by heating and suddenly cooling in water ; the re- 
 verse of the effect produced upon steel. In dry air it is 
 hardly acted upon, but in a damp atmosphere it acquires 
 a green crust of a cupric carbonate familiarly known as ver- 
 digris. Copper is an excellent conductor of heat and elec- 
 tricity, and is extensively used for telegraph-wires. Being 
 little affected by the air, it is better adapted for culinary uten- 
 sils than iron. Vegetable acids, however, dissolve it in the 
 cold state ; hence sauces containing vinegar, and preserved 
 fruits or jellies, should not be allowed to remain in copper 
 vessels, as the salts produced are poisonous. Copper forms 
 alloys with other metals, among which may be mentioned 
 brass, German-silver, bronze and speculum metal. 
 
 426. Cupric Oxide, CuO. This oxide is found native 
 as the mineral melaconite. It may be artificially prepared 
 by strongly heating cupric nitrate (CuN 2 O 6 + 3H 2 O). It is 
 a black or brownish-black powder, fusible at red-heat. It 
 is used in organic analysis as a source of oxygen, and in 
 the manufacture of glass and porcelain to impart a green 
 
DESCRIPTIVE CHEMISTRY. 
 
 color. Cupric sulphate (Blue Vitriol), (CuS0 4 + 5H 2 O), 
 is obtained by heating cupric sulphide in contact with air, 
 or by the action of sulphuric acid on metallic copper. 
 It is used largely in dyeing and calico-printing, and as 
 a source of many of the pigments containing copper. 
 Cupric arsenite, or Scheele's green, is obtained by mixing 
 solutions of cupric sulphate with sodic arsenite. It is of 
 bright-green color, exceedingly poisonous, and is used as 
 a pigment. In commerce it is called Paris green. 
 
 2. Mercury and its Compounds. 
 
 MERCURY. Symbol, Hg. (Hydrargyrum). Atomic Weight, 200 ; Quan- 
 
 tivalence, II.; Molecular Weight, 200 ; Molecular Volume, 2 ; 
 
 Specific Gravity, 13.59. 
 
 427. History. This remarkable element is often found 
 native in little globules, disseminated through certain 
 ores, particularly cinnabar, or mercuric sulphide (HgS). 
 It is obtained on a large scale by distillation of the cin- 
 nabar-ore, either alone or mixed with burnt lime or forge- 
 scales. Mercury has a silver-white color, and a brilliant 
 lustre, and is remarkable in being a liquid at ordinary 
 FIG 170 temperatures. Its specific grav- 
 
 ity is nearly twice that of iron, 
 a ball of which will sink half-way 
 into the liquid mercury, while 
 wood will float upon its surface 
 (Fig. 170). 
 
 It solidifies when cooled to 
 -40 C., and is then soft and mal- 
 
 Ball sinking in Liquid. ^^ ^ . f ^^ ^ & ^^ 
 
 lower temperature it becomes brittle. It boils at about 
 350 C., and slowly volatilizes at all temperatures above 
 15 C. Metallic mercury is used extensively in the manu- 
 facture of philosophical instruments, thermometers, barom- 
 
MERCURY AND ITS COMPOUNDS. 243 
 
 eters, and to form an alloy with tin for coating the backs 
 of mirrors. It is also used largely in the extraction of 
 gold and silver by the process of amalgamation. The 
 alloys of mercury are called amalgams. 
 
 428. Mercuric Oxide, HgO. This substance, commonly 
 known as red oxide of mercury, or red precipitate, may be 
 formed by heating metallic mercury up to 600 F., with 
 free access of air. A still higher heat decomposes it, 
 liberating the oxygen, and reducing the mercury to the 
 metallic state. This oxide furnishes a ready source of 
 oxygen gas, being the compound from which oxygen was 
 first obtained by Priestley, and by which Lavoisier proved 
 the composition of air. 
 
 429. Mercuric Chloride, HgCl 2 (Corrosive Sublimate). 
 This compound is prepared by mixing mercuric sulphate, 
 HgSO 4 , with an equal weight of common salt, and apply- 
 ing heat to the mixture. It is soluble in water and in 
 alcohol. Its solution has a metallic, acrid taste, and an 
 acid reaction. It is a deadly poison, and accidents have 
 occurred from its substitution for calomel. The proper 
 antidote for it is white of egg, which forms with it an in- 
 soluble inert compound. This substance is used in a 
 process for preserving wood, by impregnation with its 
 solution, which is termed kyanizing. 
 
 430. Mercurous Chloride (Calomel), Hg 8 Ci 2 . This 
 compound is found native as " horn quicksilver" It is 
 prepared by triturating mercuric chloride, HgCl 2 , with 
 mercury, or is precipitated whenever solutions of any mer- 
 curous compounds and a soluble chloride are mixed 
 together. Sublimed calomel is a crystalline powder, white 
 or dirty white in color ; very heavy, tasteless, and inodor- 
 ous. Calomel is decomposed by light. It has been very 
 extensively used in medicine, and is much less poisonous 
 than " corrosive sublimate." 
 
 431. Mercuric Sulphide (Cinnabar), HgS, occurs in 
 large beds at Almaden, in Spain, and is also found in 
 
244 DESCRIPTIVE CHEMISTRY. 
 
 extensive deposits in California. It is produced in con- 
 siderable quantity by artificial means, and sold as a pigment 
 under the name of vermilion. 
 
 CHAPTER XIX. 
 
 THE CALCIUM GROUP CALCIUM, STRONTIUM, BARIUM, LEAD. 
 
 1. Calcium and its Compounds. 
 
 CALCIUM. Symbol, Ca. Atomic Weight, 40 ; Quantivalence, II. and IV. ; 
 Specific Gravity, 1.57. 
 
 432. History. Calcium is one of the most abundant 
 constituents of the crust of the earth. It occurs in the 
 extensive layers of limestone, marble, and chalk, as a car- 
 bonate. In gypsum and alabaster it is found as a sulphate, 
 while as a phosphate it forms an important constituent of 
 the bones of animals. The metal itself is rare, and is 
 prepared by passing a galvanic current through fused calcic 
 chloride. It is a light-yellow metal, somewhat harder than 
 lead, very malleable, melts at a red heat, and oxidizes in 
 the air. 
 
 433. Calcic Oxide, CaO (Lim*). This well-known sub- 
 stance do3s not occur in Nature, but is prepared by burning 
 calcic carbonate, limestone (CaCO 3 ), in large masses in 
 kilns. The carbonic dioxide is driven off by the heat, and a 
 white, stony substance remains, called quick-lime, or caustic 
 lims. One ton of good limestone yields 11 cwt. of lime. 
 When this is exposed to the air it first rapidly imbibes 
 moisture and crumbles to powder. This gradually absorbs 
 carbonic dioxide, and, becoming less and less caustic, 
 regains the neutral condition of the carbonate. 
 
 434. Calcic Hydrate. When water is poured upon 
 quicklime it absorbs it (every 28 Ibs. of lime taking nine 
 
CALCIUM AND ITS COMPOUNDS. 345 
 
 pounds of water), swells to thrice its original bulk, crum- 
 bles to a fine white powder, and is converted into calcic 
 hydrate, CaH 2 O 2 . This process is called slacking, and 
 sufficient heat is often produced by the chemical action to 
 ignite wood. Lime-water is a saturated, transparent solu- 
 tion of calcic hydrate in water. Cream or milk of lime is 
 a thick mixture of the hydrate with water, such as is used 
 in whitewashing. In tanneries the hides are immersed in 
 milk of lime, which partially decomposes them, so that the 
 hair may be easily removed. Calcic hydrate exhibits the 
 properties of a strong alkali, decomposing organic tissues 
 and saturating the strongest acids. It is more soluble in 
 cold than in hot water. Hence, when cold saturated lime- 
 water is boiled, a portion of the hydrate is deposited. 
 Slacked lime is extensively used in chemical manufactures, 
 and as a fertilizer. Its value as a fertilizer is due to the 
 property which it has of decomposing organic and inor- 
 ganic constituents of soil. 
 
 435. Mortar and Cement. Lime, mixed with sand, 
 forms the mortar employed by builders to cement stones 
 and bricks. To make the best mortar, the lime should be 
 perfectly caustic and the sand sharp and cross-grained. 
 The nature of the changes by, which the mortar becomes 
 hardened is not satisfactorily explained. It is supposed to 
 be owing in part to the absorption of carbonic dioxide from 
 the air by the lime, and the subsequent hardening into a 
 calcic carbonate. In time the lime also partially combines 
 with the silica of the sand, forming an exceedingly hard sili- 
 cate of lime. Common mortar, when laid in water, not only 
 refuses to harden, but its lime gradually becomes dissolved 
 out and washed away. Hydraulic cement possesses the 
 property of solidifying under water. This quality is 
 owing to the presence of clay (aluminic silicate) in the lime 
 of which it is composed. 
 
 436. Bleaching-Powder. When chlorine is passed 
 through recently-slacked lime, large quantities of the gas 
 
246 DESCRIPTIVE CHEMISTRY. 
 
 are absorbed, forming the bleaching -poivder of commerce. 
 The chemical constitution of this substance is yet a matter 
 of doubt. It is generally regarded as a mixture of calcic 
 hypochlorite with calcic chloride, but it is not impos- 
 sible that it may correspond to the graphic expression 
 Cl-Ca-O-Cl. It is a white, sparingly soluble powder, 
 used in great quantities for bleaching purposes. In the 
 bleaching of cotton fabrics, the goods are first freed 
 from all greasy impurities, and then digested in a solu- 
 tion of this powder. They are next dipped into very 
 dilute sulphuric acid, by which chlorine is liberated, and 
 exerts its bleaching power. This process requires to be 
 repeated several times before the color is entirely dis- 
 charged ; after which the goods are thoroughly washed in 
 water, in order to remove all trace of acid from the fibre 
 of the cloth. 
 
 437. Calcic Sulphate, CaSO 4 . This salt occurs native 
 as the mineral anhydrite, and is produced artificially on a 
 large scale by calcining powdered gypsum (CaSO 4 + 2H 2 O), 
 at about 250 C. Thus prepared it constitutes " plaster of 
 Paris," and possesses the property of combining with water 
 when made into a paste. It is used for taking casts by 
 running the mixture into hollow moulds, and colored and 
 mixed with glue, for producing the ornamental designs 
 known as stucco-work. Calcic sulphate dihydrate (gyp- 
 sum, alabaster), CaSO 4 + 2H 2 O, occurs in many parts of 
 the world, forming extensive rocky beds. In its pure, 
 transparent form, it is known as selenite, and in its com- 
 pact and earthy varieties as gypsum and alabaster. Gyp- 
 sum is used extensively as a fertilizer. 
 
 438. Calcic Carbonate, CaOO 3 . Vast deposits of this 
 substance are distributed all over the globe in the form of 
 limestones, marbles, chalks, marls, coralreefs, shells, etc. 
 Numerous and extensive as are these deposits, it is con- 
 jectured that they are all of animal origin. The densest 
 limestone and the softest chalk are found to consist of the 
 
STRONTIUM AND BARIUM. 247 
 
 aggregated skeletons or shells of myriads of tribes of the 
 lower animals, which have existed in some former period 
 of the world's history. The formation of coral-reefs, which 
 are sea-islands of calcic carbonate, built up from the depths 
 of the ocean by minute aquatic animals, is an example of 
 similar deposits now in process of formation. Calcic car- 
 bonate is decomposed by heat into calcic oxide and car- 
 bonic dioxide. Hydro-calcic carbonate, CaH 2 C 2 O 6 . When 
 calcic carbonate is acted upon by water containing carbonic 
 dioxide in solution, it dissolves with the formation of this 
 compound. This solution, naturally formed, constitutes one 
 of the varieties of hard water, which is generally met with 
 in limestone districts. 
 
 439. Calcic Phosphate, Ca 3 (PO 4 ) 2 . This is the earthy 
 constituent of the bones of animals. They obtain it from 
 the plants, and the plants in turn take it from the soil. 
 It is found abundantly in the grains of cereals, which, as 
 the supply is limited in the soil, rapidly exhaust it, when 
 they are cultivated, year after year; hence the importance 
 of restoring to the land the phosphates when they are re-r 
 moved by the crops. 
 
 2. Strontium a/id Barium. 
 
 440. Strontium Resembles calcium, both in appear- 
 ance and properties. It is obtained from its chloride, and 
 is a pale-yellow metal, of specific gravity 2.54. It does 
 not change in dry air", but decomposes water readily, 
 evolving hydrogen. Barium is a light-yellow metal, which 
 rapidly oxidizes in the air, decomposes water, and has 
 a specific gravity of 4.0. The compounds of these elements, 
 though less widely distributed, are allied to the correspond- 
 ing compounds of calcium. The nitrate of strontium is 
 used in pyrotechny, and imparts to flame a beautiful crim- 
 son color. Baric oxide, or baryta (BaO), is a gray powder 
 having a strong attraction for water^ which it absorbs on 
 
248 DESCRIPTIVE CHEMISTRY. 
 
 exposure to the air, forming baric hydrate. Baric chloride 
 dihydrate (BaCl 2 + 2H 2 O) is interesting chiefly as the 
 usual test for sulphuric acid, with which it gives a dense, 
 white, insoluble precipitate of baric sulphate. It has been 
 employed in medicine. Baric sulphate, or heavy spar, 
 occurs in large quantities, and when ground is extensively 
 consumed under the name of barytes, in the adulteration 
 of paints. 
 
 3. Lead and its Compounds. 
 
 LEAD. Symbol, Pb. (Plumbum). Atomic Weight, 207 ; Quantivalence, 
 II. and IV. ; Specific Gravity, 11.44. 
 
 441. Lead. This useful and common metal is of doubt- 
 ful native occurrence, but is obtained from various ores, of 
 which the mineral galena, a plumbic sulphide, is the most 
 important. Lead is a soft, blue metal, easily scratched by 
 the nail, and leaving a stain when rubbed upon paper. 
 It is highly malleable, but not very ductile. In the air a 
 film of oxide rapidly forms on its surface, which protects it 
 from further corrosion. It melts at about 330 C., and on 
 solidifying contracts to such an extent as to render it unfit 
 for castings. Lead is much used in the manufacture of 
 pipe for conducting drinking-water to the different parts 
 of dwellings. 
 
 If lead is exposed to the combined action of pure water 
 and air, plumbic hydrate is formed on the exposed surface, 
 which is dissolved by the water with which it is in contact. 
 This solution of plumbic hydrate absorbs carbonic dioxide 
 with formation of plumbic carbonate, a highly-poisonous 
 compound. The presence of chlorides or nitrates assists 
 this corroding action, while it is retarded by the sulphates, 
 phosphates, or carbonates. Hydro-calcic carbonate, a salt 
 found in many spring-waters, also prevents this corrosion 
 by depositing a coating on the exposed surface. As all 
 lead-salts are poisonous, it is not safe to use water which 
 
LEAD AND ITS COMPOUNDS. 249 
 
 has been kept in cisterns lined with lead, or which has 
 been conveyed through lead pipes, unless it has been care- 
 fully ascertained that the water contains such foreign 
 matters as will prevent its action upon the metal. Lead 
 in the presence of air and moisture is acted upon by feeble 
 acids. Hence the use of vessels made of lead should be 
 carefully avoided in the culinary department. This metal 
 is extensively used in the arts, both alone and alloyed with 
 other metals. An alloy prepared by mixing 2 parts of 
 arsenic with 100 parts of lead is employed in the manu- 
 facture of shot. 
 
 442. Plumbic Monoxide, Pb n O. This substance is 
 found native as lead-ochre, a yellow massive mineral of 
 crystalline structure. It is obtained on a large scale by 
 heating lead to a point a little below redness, or in the 
 process of cupellation. The former product is known as 
 massicot, the latter as litharge. Plumbic monoxide is met 
 with in several isomeric modifications, as a yellow or red 
 crystalline substance, or as an amorphous powder. At 
 a red-heat plumbic monoxide melts to a clear, dark-red 
 liquid. In water it is slightly soluble with formation of 
 lead hydrate. Acids dissolve it readily, giving rise to 
 plumbic salts. It is much used in glass-making, and in 
 glazing earthen-ware. Triplumbic tetroxide (Pb 3 O 4 ), (min- 
 ium or red lead), occurs native, and is formed when plum- 
 bic monoxide is for some time exposed to a low red heat 
 in contact with air. It is extensively used as a pigment, 
 and in the manufacture of flint-glass. 
 
 443. Plumbic Carbonate, PbCO 3 ,TFAiYe Lead. This 
 salt it found beautifully crystallized in Nature, but it is 
 largely manufactured as a paint. It is produced in several 
 ways, but the following, which is known as the Dutch 
 method, is considered the best : Thin sheets of lead, rolled 
 up into loose scrolls, are placed in earthen pots with weak 
 vinegar or acetic acid. Thousands of these pots, fitted 
 with lead covers and closely packed, are then buried in 
 
250 DESCRIPTIVE CHEMISTRY. 
 
 spent tan-bark. The acetic acid corrodes the metal, form- 
 ing a superficial coating of plumbic acetate, and the carbon 
 dioxide set free by the decomposing vegetable matter de- 
 composes the acetate with formation of plumbic carbonate 
 and free acetic acid. The acetic acid attacks more metal, 
 which is again converted into carbonate ; and thus, with a 
 small charge of vinegar, the operation is continued a long 
 time, and a large quantity of lead changed. White lead is 
 extensively adulterated with baric sulphate ; it may be de- 
 tected by adding nitric acid, which dissolves the lead, 
 leaving the baric sulphate as an insoluble residue. 
 
 444. Plumbic Acetate, Pb (C 3 H 3 O 2 ) 2 . This important 
 salt of lead is easily procured by dissolving plumbic mon- 
 oxide (PbO) in acetic acid. It receives its common name 
 " sugar of lead " from its sweet taste, and its general like- 
 ness, in appearance, to loaf-sugar. It is exceedingly poi- 
 sonous. The soluble salts of lead are most of them color- 
 less, and redden litmus-paper. Metallic lead is easily pre- 
 cipitated from solutions of its salts by means of iron or 
 zinc. 
 
 CHAPTER XX. 
 
 MAGNESIUM GROUP MAGNESIUM, ZINC, CADMIUM. 
 
 1. Magnesium and its Compounds. 
 
 MAGNESIUM. Symbol, Mg. Atomic Weight, 24 ; Quanti valence, II. ; 
 Specific Gravity, 1.74. 
 
 445. History and Occurrence. This metal was first ob- 
 tained by Davy, in 1808. It does not occur native, but 
 may be obtained by decomposing magnesic chloride by 
 metallic sodium. Magnesium is a white or bluish-gray 
 crystalline metal ; malleable and ductile, melts at a mod- 
 erate red-heat, and volatilizes at higher temperatures. 
 
ZIXC AND CADMIUM. 251 
 
 Heated in the air it burns with a dazzling bluish-white 
 light, and is on this account much used for signaling, and, 
 as a source of artificial light in photography. 
 
 446. Magnesic Oxide, MgO, Magnesia. This compound 
 is obtained by strongly heating magnesic carbonate. It is 
 a white, light powder, with feeble alkaline properties, very 
 sparingly soluble in water, but dissolving readily in acids. 
 It is found native as the mineral periclase. It is used 
 principally in medicine as a mild aperient and antacid. 
 Magnesic Sulphate, Mg SO 4 + 7H 2 O (Epsom Salts), is a 
 common ingredient of mineral waters, and takes its name 
 from the circumstance of its being contained in great quan- 
 tities in the springs near Epsom, in England. The com- 
 mercial supply is chiefly derived from sea-water, by de- 
 composing the magnesic compounds with lime, and then 
 adding sulphuric acid. It may also be obtained from 
 magnesian limestone. It is soluble in water, has a bitter, 
 saline taste, and is used in medicine as a cathartic and an 
 antidote to various poisons. It has also been used as a 
 fertilizer. 
 
 2. Zinc and Cadmium. 
 
 ZINC. Symbol, Zn. Atomic Weight, 65 ; Quantivalence, II. ; Molecular 
 Weight, 65 ; Molecular Volume, 2 ; Specific Gravity, 7.0. 
 
 447. History and Occurrence. This element is not 
 found native, but is obtained on a very extensive scale by 
 the decomposition of certain ores, among which zincic sul- 
 phide or "blende" (ZnS), zincic carbonate (ZnCO 3 ), zincic 
 oxide (ZnO), and a zincic silicate, are the most important. 
 It is a brilliant, bluish- white metal. At common tempera- 
 tures it is brittle, but, when heated from 212 to 300 F., it 
 may be rolled out into thin sheets, and retains its malle- 
 ability when cold. At 400 it again becomes quite brittle ; 
 at 770 it melts, and at a red heat volatilizes. When 
 strongly heated in the air it takes fire, burning with a 
 whitish-green flame and production of zincic oxide. Zinc 
 
252 DESCRIPTIVE CHEMISTRY. 
 
 soon tarnishes in a moist atmosphere, forming a thin film 
 of oxide, which resists further change. This property ren- 
 ders it useful for a variety of purposes, such as for gas- 
 pipes, gutters, roofing, and for galvanizing iron, thus 
 preventing it from oxidation. It is also used in the prep- 
 aration of hydrogen gas. 
 
 448. Zincic Oxide, ZnO. This compound is found when 
 zinc is burned with free access of air. It is a fine white 
 powder, familiarly known as zinc white. It is largely 
 used as a paint, Zincic Chloride, ZnCl 2 , may be pre- 
 pared by distilling an intimate mixture of zincic sulphate 
 and sodic chloride. Zincic chloride is a whitish-gray 
 translucent substance, soft like wax, and of 2.7 spec. grav. 
 It melts easily and distills at a red heat ; it is deliques- 
 cent, dissolves easily in water and alcohol ; has a burning 
 taste, and is poisonous. It is used in various chemical 
 manufactures. Wood, impregnated with a crude solution 
 of zincic chloride known under the name of " Sir William 
 Burnett's Fluid," is effectually preserved from decay, this 
 process being called Burnettizing. Zincic sulphate, Zn 
 SO 4 4-7H 2 O (White Vitriol), may be prepared either by 
 roasting zincic sulphide, or by the action of sulphuric acid 
 on metallic zinc. It strongly resembles magnesic sulphate, 
 and is used in medicine, and in certain operations of calico- 
 printing. 
 
 CADMIUM. Symbol, Cd. Atomic Weight, 112; Quantivalence, II. ; Mo- 
 lecular Weight, 112; Molecular Volume, 2; Specific Gravity, 8.6. 
 
 449. Cadmium. This metal does not occur native, but 
 may be obtained from ores of zinc, and from some of the 
 secondary products of zinc-manufacture. It is a bluish- 
 white, strongly lustrous metal, tarnishing in the air. It is 
 soft, flexible, malleable, and ductile, melts at 315 C., is 
 volatile, and crystallizes from the fused state, in regular 
 octahedrons. In the air at higher temperatures it burns, 
 cadmic oxide (CdO) being formed. 
 
IRON AND ITS COMPOUNDS. 253 
 
 CHAPTER XXI. 
 
 IRON, MANGANESE, NICKEL, AND COBALT. 
 
 1. Iron and its Compounds. 
 
 IRON. Symbol, Fe. (Ferruni). Atomic Weight, 56 ; Quantivalence, II., 
 IV., and VI. ; Specific Gravity, 7.8. 
 
 450. History and Occurrence. Were we to seek for 
 that circumstance which might best illustrate the peculiar- 
 ities of ancient and modern civilization, we should perhaps 
 find it in the history of this metal. The ancients, imbued 
 with a martial spirit and passion for conquest, made iron 
 the symbol of war, and gave it the emblem of Mars. And 
 if it were required also to symbolize the pacific tendencies 
 of modern society, its triumphs of industry and victories 
 of mind over matter, its artistic achievements and scientific 
 discoveries, we should naturally employ the same metal, 
 iron. As gold and jewels have long been the type of bar- 
 baric and empty pomp, so iron may now be well regarded 
 as the emblem of beneficent and intelligent industry. 
 
 Native iron of meteoric origin has frequently been found, 
 and instances of its occurrence on the earth have been 
 reported, but usually in these cases the iron is combined 
 with nickel. We are, however, acquainted with numerous 
 ores of iron, among which are magnetite, red hematite, 
 and specular iron, brown iron-stones, spathic iron, and clay 
 iron-stone. 
 
 451. Preparation. Metallic iron or wrought-iron has 
 been obtained from iron-ores, and to some extent this is 
 still its source, but by far the largest portion brought into 
 the market is derived from the decomposition of cast-iron, 
 which is essentially a ferric carbide, but also contains vary- 
 ing quantities of other substances. The operation is usu- 
 ally conducted in reverberatory furnaces. In this process, 
 
254 
 
 DESCRIPTIVE CHEMISTRY. 
 
 Fitt. 171. 
 
 Puddling-Furnace. 
 
 the cast-iron is melted on a flat hearth by causing the 
 flame to impinge upon it from above on its way through 
 the furnace, as shown in Fig. 171. A workman, with a 
 long, oar-shaped implement of iron, stirs (puddles) the 
 melted mass until the carbon and other impurities of a like 
 
 nature are burned away or con- 
 verted into a slag, and the met- 
 al becomes thick and pasty. 
 This is called puddling. The 
 puddler then rolls up from the 
 mass a ball of about 75 Ibs. 
 weight, which he transfers to 
 the tilting or trip hammer, 
 where it is beaten by heavy 
 blows into a crude bar. By 
 this operation the liquid slag, 
 consisting chiefly of ferrous silicate, is squeezed out, as 
 water is expelled from a compressed sponge. The metal, 
 still hot, is then passed between grooved cylinders, where 
 it is rolled out into bar-iron. The quality of metal is 
 greatly improved when these bars are broken up, bound 
 together, reheated to the welding-point, and again passed 
 through the rolling-mill. This latter operation is often 
 repeated several times, and is known as piling OY fagoting. 
 452. Properties. Pure iron is of a silver-white color, 
 while ordinary wrought-iron is grayish-white, and when 
 polished has a perfect lustre. In the absence of im- 
 purities, iron is so malleable that books have been made 
 of it with leaves as thin as paper, and so ductile that 
 it may be drawn out into wires as thin as a hair. Its 
 most useful quality, however, is its superior tenacity, or 
 power of resisting strain ; no other metal being equal to 
 it in this respect. Hence the value of iron in the manu- 
 facture of cannons and mortars, where the immense ex- 
 pansive force of gunpowder is to be resisted, and in the 
 making of wire cables for suspension bridges. So great is 
 
IRON AND ITS COMPOUNDS. 355 
 
 its tenacity that an iron wire 0.075 of an inch in diameter 
 is capable of supporting a weight of 449 pounds. 
 
 Wrought-iron has a fibrous text- 
 ure, and rough, hackly fracture, Fig. 
 172. It is said that the effect of con- 
 stant jarring is to cause it to lose 
 this tough, fibrous character, and to 
 become crystalline. It usually con- 
 tains a small quantity of carbon, which 
 hardens the iron without affecting its 
 other properties to any great extent ; 
 
 , .** Texture of Wrought-Iron. 
 
 but if the amount exceeds per cent., 
 
 it renders the iron cold-short, that is, brittle and liable to 
 snap asunder when cold. The presence of sulphur, even in 
 so small a proportion as y^Vor? un fi ts tne i ron f r being 
 worked at a red heat, as it is liable to split when ham- 
 mered ; it is then said to be hot-short. 
 
 453. When w rough t-iron is heated to whiteness, it be- 
 comes soft, pasty, and adhesive, and two pieces in this 
 condition may be incorporated, or hammered into one. 
 This is called welding. During the heating a film of triferric 
 tetroxide is formed upon the surface of the metal, which 
 would obstruct the ready cohesion of the separate masses. 
 To prevent this, the smith sprinkles a little sand upon the 
 hot iron, which gives rise to the formation of a fusible 
 silicate, easily forced out by pressure, leaving clean sur- 
 faces that unite without difficulty. This important quality 
 is possessed only by iron, platinum, and sodium. All the 
 other metals pass suddenly from the solid to the liquid 
 state, at their respective melting-points. In its ordinary 
 condition iron oxidizes rapidly in the air, and dissolves in 
 nitric acid. But under several circumstances it assumes 
 different, and peculiar chemical relations. If momen 
 tarily immersed in a strong mixture of nitric and sul- 
 phuric acids it retains its metallic lustre, but has lost the 
 power of either being oxidized in the air or of dissolving 
 
256 
 
 DESCRIPTIVE CHEMISTRY. 
 
 in ni'ric acid; it has become passive, or assumed an allo- 
 tropic form. 
 
 454. Uses Iron in some of its innumerable forms 
 ministers to the benefit of all. The implements of the 
 miner, the farmer, the carpenter, the mason, the smith, the 
 shipwright, are made of iron and with iron. Roads of iron, 
 traveled by iron steeds, which drag whole townships after 
 them and outstrip the birds, have become our commonest 
 highways. Ponderous iron ships are afloat upon the ocean, 
 with massive iron engines to propel them ; iron anchors to 
 stay them in storms; iron needles to guide them, and 
 springs of iron in chronometers by which they measure the 
 time. Ink, pens, and printing-presses, by which knowledge 
 is scattered over the world, are alike made from iron. 
 
 455. Ferric Carbides (Cast-Iron}. As already stated, 
 most of the wrought iron of commerce is obtained from the 
 ore indirectly, the latter being first decomposed in such a 
 manner as to yield certain ferric carbides, etc., known as 
 cast or pig-iron. 
 
 The operation is conducted in tall chimney-like struct- 
 ures, termed blast - furnaces. 
 They are constructed of stone, 
 and lined with the most re- 
 fractory fire-brick, having the 
 form seen in Fig. 173. The top 
 or mouth of the furnace serves 
 for charging it, and for the es- 
 cape of smoke ; it is both door 
 and chimne^v. The tubes or tu- 
 yere pipes at the bottom serve 
 to supply the air, which is forced 
 in by means of immense blow- 
 ing cylinders driven by water 
 or steam power. The amount 
 of air thus forced through some 
 Smeiting-Furnace. large furnaces exceeds 12,000 
 
 FIG. 173. 
 
IRON AND ITS COMPOUNDS. 57 
 
 cubic feet per minute. Formerly the air was used at the 
 ordinary temperature (cold blast), but within a few decades 
 an immense improvement has been effected by heating the 
 air before it enters the furnace (hot blast). 
 
 456. In some cases the materials are drawn up an in- 
 clined plane to the mouth of the shaft by the same engine 
 that impels the blast mechanism. The furnace is supplied 
 with ore, coal, and limestone, broken into small fragments. 
 When the heat is sufficiently intense the carbon of the fuel 
 deoxidizes the iron, and the limestone being decomposed 
 into carbonic dioxide gas, which escapes, and " burnt lime," 
 which in its turn acts upon the ore, unites with the sand, 
 clay, silica, and other impurities, to form a slag or scoria, a 
 crude semi-vitreous, easily-fusible product. The melted 
 cast-iron, falling to the bottom of the 
 
 furnace, accumulates and is drawn off 
 by taking out a tap or plug. It is al- 
 lowed to run into a bed of sand, con- 
 taining straight channels and furrows 
 running at right angles. The former 
 are called by the workmen the sow, and 
 the latter the pigs; hence the term Texture of Cast-iron. 
 pig-iron. As the contents of the furnace are removed from 
 below, crude-ore, limestone, and fuel are constantly supplied 
 from above, and the operation goes on day and night un- 
 interruptedly for a course of years, or until the fabric 
 demands repair. 
 
 457. Cast-iron has a granular texture (Fig. 174), and 
 is so brittle that it cannot be forged, but may be remelted 
 and cast into moulds. It expands when first poured into 
 the mould, so as to copy it perfectly, but subsequently 
 contracts. The expansion is caused by the particles as- 
 suming a crystalline arrangement while consolidating ; the 
 contraction by the cooling of the metallic mass when solidi- 
 fied. There are several varieties of cast-iron. The so-called 
 " Spiegeleisen " (mirror-iron) of Germany is a nearly pure 
 
258 DESCRIPTIVE CHEMISTRY. 
 
 tetraferric carbide, Fe 4 C. Other varieties appear to be 
 mixtures of this compound with artificial plumbago (a 
 variety of carbon), or with true metallic iron. 
 
 458, Steel. This is a compound of the metal with about 
 one and a half per cent, of carbon. It is produced in dif- 
 ferent ways. One variety is made by imbedding bars of 
 the best wrought-iron in powdered charcoal, in boxes or 
 sand-furnaces, which exclude the air, and heating it in- 
 tensely for a week or ten days. The chemical changes are 
 obscure; probably carbonic oxide penetrates the heated 
 metal, is decomposed, surrenders part of its carbon and 
 escapes as carbonic dioxide. The steel when withdrawn 
 has a peculiar rough, blistered appearance, and is therefore 
 known as blistered steel. This method of making steel is 
 called the process of cementation. When this quality of 
 steel is melted and cast into ingots, it constitutes cast-steel. 
 
 A great improvement in the manufacture of steel has 
 been introduced, called from its inventor the Bessemer 
 process. By means of this, steel is produced directly from 
 the cast-iron, without previous casting into pigs. The 
 melted cast-iron is run from the shaft-furnace into egg- 
 shaped vessels made of boiler-plate, lined with tire-clay, 
 which are termed "converters." An intense blast of 
 compressed air is forced into the molten mass, and ten to 
 twenty-five minutes of this operation suffice to decarbonize 
 the cast-iron so as to convert it into steel, or wrought-iron, 
 as may be desired. 
 
 459. In its properties steel, combines the fusibility of 
 cast-iron with the malleability of bar-iron. Its value for 
 cutting instruments, springs, etc., depends upon its quality 
 of being tempered. When heated to redness and suddenly 
 quenched in cold water, it becomes so hard as to scratch 
 glass. If again heated and cooled slowly, it becomes as 
 soft as ordinary iron, and between these two conditions 
 any required degree of hardness can be obtained. As the 
 metal declines in temperature, the thin film of oxide upon 
 
IRON AND ITS COMPOUNDS. 259 
 
 its surface constantly changes its color. The workmen are 
 guided by these tints. Thus a straw-color indicates the 
 degree of hardness for razors ; a deep blue for sword-blades, 
 saws, and watch-springs. Steel receives a higher polish 
 than iron, and has less tendency to rust. Nitric acid placed 
 upon steel corrodes it, and leaves the carbon as a dark-gray, 
 stain; hence it is often used for writing and ornamental 
 shading upon this metal. 
 
 460. Ferrous Oxide, FeO. This compound is not found 
 native, but is obtained when ferrous oxalate is heated in a 
 close vessel, as a black powder, which in the air ignites 
 spontaneously, burning to ferric oxide, Fe 2 O 3 (diferric tri- 
 oxide), which is of very wide distribution as the minerals 
 red hematite and specular iron, from which a large propor- 
 tion of the iron of trade is derived. Red hematite is mas- 
 sive, earthy, or fibrous, and brick-red in color. Specular 
 iron is extensively employed under the names of colcothar 
 and jewelers' rouge, as a pigment, and for polishing jewel- 
 ry, glass, and metallic objects. 
 
 461. Triferric Tetroxide, Fe 3 O 4 , Magnetic Oxide 
 This substance occurs native as the mineral magnetite, the 
 most valuable of the ores from which iron is produced. 
 This appears as a black, crystalline powder, in Nature it 
 forms large masses, and is frequently found in distinct 
 octahedral crystals of considerable size. The triferric 
 tetroxide is strongly magnetic, and the black oxide which 
 forms on iron when heated in aqueous vapor consists of 
 this compound, which is also produced by the combustion 
 of iron in oxygen gas. 
 
 462. Ferric Bisulphide, FeS 2 . This compound occurs 
 native in two isomeric modifications, one, the mineral mar- 
 casite, the other, iron pyrites. Both forms are widely dis- 
 tributed. Iron pyrites crystallizes in cubes or other 
 forms of the monometric system, of a golden-yellow color 
 and strong metallic lustre. Heated in the air, iron pyrites 
 burns with evolution of sulphurous oxide, and it is much 
 
260 DESCRIPTIVE CHEMISTRY. 
 
 used in the manufacture of sulphuric acid. Sulphur and 
 copperas are also obtained from it, but it is never worked 
 for iron. Marcasite is a mineral possessed of a white color 
 and metallic lustre, which in moist air decomposes rapidly, 
 with formation of ferrous sulphate (FeSo 4 + 7H 2 O) and 
 evolution of heat. It occurs in coal-beds, and sometimes 
 causes their spontaneous ignition. 
 
 463. Ferrous Sulphate, FeSo 4 + 7H 2 O, Green Vitriol, 
 Copperas. This salt is largely manufactured from iron 
 pyrites. It is used in dyeing, for making ink and Prussian 
 blue, and in medicine. It often exists in soils to a perni- 
 cious extent, but is decomposed by lime, gypsum being 
 formed. Ferrous Carbonate, FeCO 3 . This is a very abun- 
 dant mineral known as spathic iron. It is grayish-white, 
 opaque, and crystallizes in rhombohedrons. When found 
 in large masses it constitutes one of the most valuable 
 iron-ores. Steel has been made directly from it, hence it is 
 known as steel-ore. 
 
 2. Manganese, Nickel, and Cobalt. 
 
 MANGANESE. Symbol, Mn. Atomic Weight, 55 ; Quantivalence, II., 
 IV., and VI. ; Specific Gravity, 8. 
 
 464. This metal never occurs in Nature, but can be 
 obtained by making manganic oxide into a paste with oil 
 and lamp-black and heating this mixture to whiteness in a 
 covered crucible. It is a hard, brittle metal of a grayish- 
 white color, and rapidly oxidizes when exposed to the air. 
 It is best preserved in naphtha. Manganic Dioxide, 
 MnO 2 , occurs in Nature as the mineral pyrolusite. It is an 
 iron-black or steel-gray, brittle substance, crystallizing in 
 forms of the trimetric system. It is mined extensively, 
 being employed in the manufacture of chlorine and bleach- 
 ing-powders, as a source of oxygen, and for discharging 
 the brown and green tints of glass. 
 
 465. Nickel and Cobalt. These two metals are closely 
 
CHROMIUM AND ITS COMPOUNDS. 261 
 
 related by their properties. Their atoms have identical 
 weights, and their reactions are so similar that there is 
 difficulty in separating one from the other. They occur 
 associated together, and are found alloyed with the iron of 
 meteoric origin. 
 
 They may be obtained by the decomposition of ores, 
 chiefly nickelic and cobaltic arsenides, sulphides, and 
 sulph-arsenides. They are both magnetic, and resemble 
 iron in many of their properties. Nickel is a silver-white, 
 ductile and malleable metal, of about 8.4 spec, grav., not 
 much more fusible than iron. It is used principally in the 
 manufacture of german silver, of coinage, and other similar 
 alloys. Cobalt is a reddish or grayish-white metal, of 
 about 8.9 spec. grav. ; hard and somewhat malleable at a 
 red heat. It has not been applied to any useful purpose. 
 Cobaltous Chloride, CoCl 2 + 6H 2 O, may be obtained in 
 ruby-red octahedral crystals from solutions of cobaltous 
 oxide or carbonate, in hydric chloride. The dilute solution 
 of these is used as a sympathetic ink, the characters writ- 
 ten with it being so pale as to be invisible till warmed, 
 when they appear blue, owing to the formation of the an- 
 hydrous chloride (CoCl 2 ). On cooling, they absorb moist- 
 ure and again disappear. 
 
 CHAPTER XXn. 
 
 CHROMIUM, ALUMINIUM, AND THE PLATINUM GROUP. 
 
 1. Chromium and its Compounds. 
 
 CHROMIUM. Symbol, Cr. Atomic Weight, 52.5 ; Quantivalence, II., IV., 
 and VI. ; Specific Gravity, 6.8. 
 
 466. Occurrence. This metal may be prepared by ex- 
 posing chromic compounds to intense heat in a current of 
 hydrogen gas or by fusing its oxide with charcoal in a 
 
262 DESCRIPTIVE CHEMISTRY. 
 
 charcoal-lined crucible. When the oxide is reduced by 
 carbon the metal obtained is of steel-gray color, exceed- 
 ingly hard, and not easily fused. Many of the compounds 
 have a brilliant color and are used as paints. It gives 
 color to the emerald. 
 
 467, Dichromic Trioxide, Cr 2 O s , Chromic Oxide. This 
 compound may be obtained, by strongly heating a chromic 
 hydrate, as a bright-green powder, or in the form of green- 
 ish-black rhombohedral crystals of metallic lustre, 5.2 spec, 
 grav., and great hardness. It is used in coloring glass and 
 porcelain, and also in ordinary painting under the name of 
 
 VI 
 
 chrome-green. Chromic Trioxide^ CrO 3 , is obtained in 
 splendid crimson needle-shaped crystals often an inch in 
 length, easily soluble in water, melting at 190 C., and de- 
 composing at 250 C. It is a powerful oxidizing agent. 
 
 2. Aluminium and its Compounds. 
 
 ALUMINIUM. Symbol, Al. Atomic Weight, 27.5 ; Quantivalence (A1 2 ) VI ; 
 Specific Gravity, 2.5. 
 
 468, History. This important metal was discovered by 
 the German chemist Wohler in 1827. It is not found 
 native, but may be obtained by decomposing either the 
 chloride or the fluoride with metallic sodium. It is one of 
 the most abundant elements, being the metallic base of 
 alumina, which forms the argillaceous rocks, beds of clay, 
 and a large proportion of granite. It is a shining, white 
 metal, of a shade between silver and platinum, harder than 
 zinc and of remarkable strength and stiffness. It resists, 
 like silver, the oxidizing influence of moist air, melts at a 
 still lower temperature than that metal, and, pound for 
 pound, occupies four times its space. It is the most sonor- 
 ous of metals, giving forth a clear musical sound when 
 struck. It is malleable and ductile like iron, exceeds it in 
 tenacity, and combines with carbon, forming a east metal, 
 which is not malleable. 
 
ALUMINIUM AND IIS COMPOUNDS. 63 
 
 It conducts electricity nearly as well as silver, and 
 unlike silver is not tarnished by hydric sulphide. Ni- 
 tric and sulphuric acids, when cold, do not act upon 
 this metal. It dissolves in hydric chloride, forming alu- 
 minic chloride, and in potassic or sodic hydrate solu- 
 tions with production of corresponding aluminates. At 
 present, aluminium is principally employed in the manu- 
 facture of aluminium bronze, small weights, and optical 
 instruments. 
 
 469. Aluminic Oxide, A1 2 O 3 , Alumina. This com- 
 pound is found native. Crystallized and colored by chro- 
 mic oxide it forms the ruby and sapphire, which rank next 
 to the diamond in hardness and value. In a pur,- massive 
 form it is known as corundum, and this when ground con- 
 stitutes emery. It may be artificially prepared by heating 
 aluminic hydrate. It is a white powder, insoluble in water, 
 inodorous and tasteless. 
 
 470. Aluminic Silicates. These bodies form the chief 
 constituents of clays, which result from the decomposition 
 of feldspathic and silicious rocks, and are the basis of all 
 kinds of pottery. Their adaptation for this purpose de- 
 pends upon their plasticity when mixed with water, the 
 readiness with which they may be moulded, and also upon 
 their capability of solidifying when exposed to a high heat. 
 After burning, the ware, though hard, is porous, and ab- 
 sorbs water with avidity, even allowing it to filter through. 
 To prevent this, the ware is covered with a glassy coating, 
 or glazed. 
 
 471. Porcelain consists of a mixture of decomposed 
 feldspar (called kaolin), silica, and a small proportion of 
 lime, the ingredients being carefully selected, and thor- 
 oughly ground and incorporated. When moulded into 
 the proper form, the articles are dried and subjected to a 
 high heat in a furnace, in which state the ware is called 
 biscuit. They are then glazed by dipping them into a 
 solution of powdered quartz and feldspar, which, when 
 
 12 
 
264 DESCRIPTIVE CHEMISTRY. 
 
 heated, fuses into the ware, giving it a vitreous coating 
 which adds to its compactness and strength. The partial 
 fusion of the materials gives porcelain the beautiful semi- 
 transparency which distinguishes it from earthen-ware. In 
 coloring porcelain, the patterns are printed on paper which 
 is applied to the biscuit while the color is still moist. 
 When the color is absorbed, the porcelain is subjected to 
 another baking, which fixes the tint. In the finer kinds of 
 porcelain the colors are mixed with a fusible glaze, and 
 applied with a hair pencil. Common red pottery ware 
 owes its color to ferric oxide (Fe 2 O 3 ), and is glazed with a 
 preparation of clay and plumbic oxide. Vessels thus 
 coated are objectionable for domestic use, as the lead-glaze 
 is sometimes dissolved by acids, producing poisonous 
 effects. Bricks are unglazed. Stone-ware is a coarse kind 
 of porcelain glazed with salt. Fire-bricks, muffles, and 
 Hessian crucibles, are made of a pure, infusible clay, con- 
 taining a large amount of silica. The beautiful blue pig- 
 ment ultramarine is one of the aluminic silicates supposed 
 to be colored by a sodic sulpho-ferrate. A variety of clay 
 known as fuller's-earth is also used to remove grease from 
 woolen cloths. t iy 
 
 472. Potassio-Aluminic Sulphate. KA1S 2 O 8 + 12H 2 O, 
 Alum. Small quantities of this important salt are found 
 native, but for commercial purposes it is prepared artifi- 
 cially by several different methods. In this country it i/ 
 formed by treating alumina or clay with sulphuric acid, 
 and, after the lapse of a few months, adding potassic sul- 
 phate or carbonate. The whole is then leached, and the 
 alum separated from the solution by crystallization. Alum 
 is used .largely for purifying and preserving skins, for mor- 
 dants in dyeing and calico-printing, for glazing paper, for 
 hardening and whitening tallow, clarifying liquors, and in 
 medicine as an astringent and caustic. Wood impregnated 
 with it is almost incombustible. Alum has a sweetish, 
 styptic taste, and is soluble in 18 parts of cold water, or in 
 
THE PLATINUM GROUP. 265 
 
 its own weight of boiling water, the solution having an 
 acid reaction. When heated, alum swells up into a light, 
 puffy condition, at the same time giving off its water of 
 crystallization, and leaving a wbite, anhydrous, infusible 
 mass known as burnt alum. 
 
 3. The Platinum Group. 
 
 PLATINUM. Symbol, Pt. Atomic Weight, 197 ; Quantivalence, II. and 
 IV. ; Specific Gravity, 21.5. 
 
 473. This rare metal is always found native, and 
 usually associated with palladium, rhodium, and iridium. 
 It also occurs alloyed with gold, copper, iron, and lead. 
 Its chief sources are the mines of Mexico, Brazil, and the 
 Ural Mountains. Platinum is of a grayish-white color, and 
 closely resembles silver in appearance. It is one of the 
 heaviest of metals, and when pure it scarcely yields in malle- 
 ability to gold and silver; is very ductile, and takes a good 
 polish. But the qualities which render it so useful, and in 
 some cases indispensable to the chemist, are its extreme 
 difficulty of fusion (being unaffected by any furnace heat), 
 and the perfect manner with which it resists the action of 
 almost all acids. It does not oxidize in the air at any 
 temperature, and is not acted upon by simple acids. It is 
 slowly dissolved by aqua regia. We have already alluded 
 (259) to the power possessed by spongy platinum of con- 
 densing gases and causing the union of oxygen and hydro- 
 gen. Platinum-black is a preparation of the metal in a 
 still more minute state of subdivision, and has the property 
 of effecting chemical changes more energetically than plat- 
 inum sponge. It may be produced by electrolyzing a 
 dilute solution of the metal. 
 
 474. Platinic Tetrachloride, PtCl 4 , is obtained by dis- 
 solving platinum in aqua regia and evaporating the solution 
 over the water-bath. It is a brownish-red substance, solu- 
 ble in water and alcohol, forming a reddish-yellow solution. 
 
266 DESCRIPTIVE CHEMISTRY. 
 
 It is a valuable reagent for potassic, rubidic, and caesic 
 compounds. 
 
 Rhodium, Ruthenium, Palladium, Iridium, and Os- 
 mium, are rare and generally found associated with plati- 
 num, which they resemble both in appearance and prop- 
 erties. 
 
 CHAPTER XXIII. 
 
 TIN, SILICON. 
 
 1. Tin and its Compounds. 
 
 TIN. Symbol, Sn. (Stannum) Atomic Weight, 118 ; Quantivalence, II. 
 and IV. ; Molecular Weight 236 (?) ; Specific Gravity, 7.29. 
 
 475. History and Occurrence. Tin is a brilliant, silver- 
 white metal, which has been found native only in small 
 quantities, and in few localities. It is obtained on a large 
 scale by the decomposition in furnaces of various ores, of 
 which the mineral cassiterite is the most important. It is 
 softer than gold, slightly ductile and very malleable, and 
 may be beaten into leaves one-fortieth of a millimetre 
 thick. It melts at 442 F. The peculiar crackling sound 
 given by tin when bent is due to a disturbance of its crys- 
 talline structure. It tarnishes but slightly on exposure to 
 the air or moisture, and is therefore very valuable for 
 domestic utensils. This propertv also renders it useful for 
 coating other metals to prevent them from oxidizing. 
 Sheet-iron coated with tin, with which it forms an alloy, 
 constitutes common tin-ware. 
 
 476. Stannic Dioxide, SnO 2 , Oxide of Tin. This com- 
 pound exists in several modifications. It is found native, 
 as the mineral cassiterite, in broad square prismatic crystals. 
 More or less rounded by attrition, these crystals are met 
 with in the alluvi.il deposits of rivers forming "stream-tin," 
 
SILICON AND ITS COMPOUNDS. 267 
 
 from which metallic tin is obtained. Another modification 
 may be obtained in the form of colorless prisms of the 
 trimetric system, which are very hard and brilliant. Stan- 
 nic dioxide is much used in the manufacture of enamels 
 and opaque glasses. Britannia metal is a white alloy 
 much resembling German-silver in appearance. It consists 
 chiefly of tin and antimony in the proportion of 9 parts of 
 the former to 1 part of the latter. 
 
 Titanium, Zirconium, Thorium, are but little known 
 and comparatively unimportant. They are allied to tin by 
 many of their properties. 
 
 2. Silicon and its Compounds. 
 
 SILICON. Symbol, Si. Atomic Weight, 28 ; Quantivalence, IV. ; Molec- 
 ular Weight 56(?); Molecular Volume, 2; Specific Gravity, 2.49. 
 
 477. Silicon. This element is never found native, but 
 may be prepared by decomposing silicic fluoride or chloride 
 with sodium or aluminium. It has three allotropic states : 
 first, amorphous silicon a brown powder; second, a crys- 
 talline hexagonal variety resembling graphite; and a third, 
 octahedral form which is exceedingly hard. It is of no 
 importance except to the scientific chemist. 
 
 478. Silicic Dioxide, SiO 2 , Silica. This compound is 
 one of the most important and widely-distributed of sub 
 stances ; forming the bulk of the minerals, quartz, flint, 
 agate, chalcedony, opal, etc., and of most sandstones, and 
 sandy soils. It is also an essential and sometimes predom- 
 inating ingredient in granite, and many other rocks. It 
 exists in two modifications: one crystalline, the other 
 amorphous. In both of these conditions it is almost infu- 
 sible. By the intense heat of the oxy-hydrogen blow-pipe 
 it is reduced to a transparent glass, and may be spun out 
 into threads. 
 
 Both modifications of silica are insoluble in water, and 
 in all acids, except the fluohydric, but it is dissolved by solu- 
 
268 DESCRIPTIVE CHEMISTRY. 
 
 tions of alkaline silicates. Hence, all natural waters which 
 contain alkaline silicates may also contain a little silica. 
 When water containing even small quantities of alkaline 
 carbonates acts upon silica under pressure and at tempera- 
 tures from 300 to 400 C., it is capable of dissolving a 
 large quantity of it, which is again deposited when the 
 pressure and heat are removed. This is the cause of the 
 siliceous deposits formed by certain hot springs, as the 
 geysers of Iceland. If wood be present in such waters, as 
 it decays, the particles of silica are deposited in place of 
 those that escape, and thus a copy of the wood in stone, or 
 a petrifaction, is produced. 
 
 479. Crystalline Modification. This is found in Nature 
 as quartz, amethyst, etc., forming- rhombohedra or hexag- 
 onal crystals terminated by six-sided summits (Fig. 175), 
 which are sometimes of enormous size. It is very hard, 
 colorless when pure, and often quite transpar- 
 ent. The amorphous modification of silicic 
 dioxide is a pure white powder. This com- 
 pound, with varying quantities of water held 
 hygroscopically, constitutes the opal. 
 
 480. Silicic Fluoride, SiF 4 . This is a 
 colorless gas produced when hydric fluoride 
 acts upon silica. When passed into water 
 the g;as is decomposed, with formation of hy- 
 
 Quartz-Crystal. ,.%. ' ,, J 
 
 dnc silicate, and a peculiar compound known 
 as hydric fluo-silicate, H,SiF 6 . 
 
 Silicic Acids. If to a solution of sodic or potassic 
 silicate hydric chloride be added, silicic acid separates as a 
 transparent jelly, which is nearly insoluble in water or 
 acids. By reversing the operation, that is, by pouring the 
 sodic, etc., silicate solution into the hydric chloride, no pre- 
 cipitate results, but by subjecting this mixture to dialysis a 
 clear aqueous solution of silicic acid may be obtained. The 
 exact composition of these hydric silicates is not known. 
 This gelatinous state may be continued by keeping it 
 
SILICON AND ITS COMPOUNDS. 269 
 
 moist, but as soon as it is deprived of water it falls to a 
 gritty powder. 
 
 481. Glass. When mixtures of pure quartz-sand with 
 potash, or soda, and various metallic oxides, are strongly 
 heated, they fuse to a liquid, which on being gradually 
 cooled before solidifying passes through a thick, viscous, 
 semi-fluid condition. While in this s ,ate they may be 
 moulded into any desired shape, retaining their form and 
 transparency when cold. Thus we have a compound easily 
 moulded at a certain stage of fusion, uncry stall ine when 
 cold, but transparent, hard, strong, insoluble, and durable 
 that is, common glass. The materials for the manufacture 
 of glass are, first, pulverized quartz or sand for the 
 manufacture of the finest varieties of glass a pure white 
 sand free from ferric oxide is employed second, the basic 
 constituents, potash, soda, lime, magnesia, and lead-oxides 
 more or less pure, according to the quality of the glass 
 required. Various metallic oxides are also employed as 
 coloring agents. Thus cupric oxide gives a green color, 
 gold oxide a ruby, uranic oxide a yellow, cobaltic oxide a 
 deep-blue, manganic oxide a purple, and a mixture of co- 
 baltic and manganic oxides a black glass. Enamel watch- 
 dials and semi-opaque transparencies are glass rendered 
 milk-white by stannic oxide or bone earth. 
 
 482. Varieties of Glass. The silicates of lime, magne- 
 sia, iron, soda, and potash, in their impure form, produce 
 the coarser kinds of glass of which green bottles are made. 
 The silicates of soda and lime give the common window- 
 glass and French plate. Lime hardens glass, and adds to 
 its lustre; soda tends to give it a greenish tinge. Bohe- 
 mian glass, the most beautiful variety, hard and highly in- 
 fusible, is a silicate of potash and lime. Crystal glass, or 
 
 flint glass, so called because pulverized flints were formerly 
 used in making it, is a potassio-plumbic silicate. The red 
 plumbic oxide renders it very soft, so as to be easily 
 scratched, but greatly increases its transparency, brilliancy, 
 
270 DESCRIPTIVE CHEMISTRY. 
 
 and refractive power. Sometimes the proportion of oxide 
 of lead used rises as high as fifty-three per cent. Glass of 
 this composition forms what is called paste, and, when 
 suitably cut, is used to imitate the diamond. By the addi- 
 tion of a trace of ferric oxide the yellow of the topaz is 
 imitated, and by cobaltic oxide the brilliant blue of the 
 sapphire is produced. 
 
 CHAPTER XXIV. 
 Carbon and its Compounds. 
 
 CARBON. Symbol, C. Atomic Weight, 12 ; Quantivalence, II. and IV. ; 
 Molecular Weight 24(?); Molecular Volume, 2; Specific Gravity 
 (Diamond), 3.5. 
 
 483. History and Properties. Carbon, from the Latin 
 carbo, coal, is the name applied to the solid with which 
 we are familiar in the various forms of charcoal, min- 
 eral coal, lamp-black, etc. It is met with in three well- 
 marked allotropic forms the diamond, graphite, and char- 
 coal. The purest form of carbon is the diamond a very 
 extraordinary kind of matter. It crvstallizes in regular 
 octahedrons or other forms of the monometric system, 
 the faces being frequently convex (Figs. 176, 177, and 
 178), and is the hardest body known. Diamonds are 
 
 FIG. 176. FIG. 177. FIG. 178. 
 
 found in the earth in various places, usually in the form of 
 rounded pebbles covered with a brownish crust. Of their 
 
CARBON AND ITS COMPOUNDS. 271 
 
 mode of production nothing whatever is known. The finest 
 specimens are perfectly colorless and limpid, but they are 
 also of various colors. The diamond has a very high 
 refractive and dispersive power by which it flashes the 
 most varied and vivid colors of light. It is a non-con- 
 ductor of electricity, and resists the action of all known 
 chemical substances. The diamond remains unchanged at 
 a very high degree of heat ; but, if made red-rot and car- 
 ried into pure oxygen, it burns with a steady glow, like a 
 little star, the product being carbonic dioxide. From its 
 high refractive power, resembling in this respect some or- 
 ganic substances, Newton predicted that it would prove 
 not only combustible, but of organic origin. This view 
 seems to be supported by the fact that the crystal on 
 being burned leaves a trace of ash in the form of a cellu- 
 lar net-work. In the flame of the voltaic arc, the diamond 
 becomes white-hot, swells, and is converted into a black, 
 coke-like mass. The diamond is the most brilliant and 
 precious of gems. Being a powerful refractor of light, it 
 has been sometimes employed for the lenses of micro- 
 scopes, but it is chiefly used for cutting glass and drilling 
 apertures through other gems. 
 
 484. Graphite, or Plumbago, is another allotropic form 
 of carbon. It is found in rocks, sometimes in considerable 
 masses, and crystallizes in six-sided plates 
 of a metallic lustre, resembling lead, Fig. 
 179; hence it is called black-lead. Its 
 spec. grav. is about. 2.1. Like the dia- 
 mond, it resists the action of intense 
 heat, and is useful to the chemist in 
 making crucibles. It is friable, has an unc- 
 tuous feel, and is used instead of oil to 
 relieve the friction of machinery. It is unaffected by the 
 weather, and hence forms a valuable coating to protect 
 iron-work from rust; and, as it resists heat, it is fitted 
 for stove-polish. It is, however, often adulterated largely 
 
272 DESCRIPTIVE CHEMISTRY. 
 
 with lamp-black, which may be detected by heating the 
 suspected sample to redness, when the lamp-black burns 
 away. Its most important use is in the manufacture of 
 pencils. The powder, subjected to enormous pressure, 
 coheres in masses, and is then sawed into thin slices, and 
 again into small bars, which are placed in grooved cedar- 
 sticks for use. Though apparently so soft, the particles 
 of graphite are extremely hard, and soon wear out the 
 steel saws with which the mass is cut. 
 
 Graphite, unlike diamond, may be artificially produced. 
 When cast-iron, which has been melted in contact with an 
 excess of carbon, is allowed to cool slowly, the carbon 
 crystallizes out in the form of graphite. In the manufact- 
 ure of coal-gas, a layer of pure, dense carbon, having a 
 metallic lustre, is deposited upon the hottest parts of the 
 retort. It is called gas-carbon, and seems to be a variety 
 of graphite, if, indeed, it be not itself an allotropic form of 
 carbon. 
 
 485. Charcoal, the third well-settled allotropic variety 
 of carbon, is obtained when any organic substance, as 
 wood, bones, or sugar, is strongly heated or burned with a 
 partial exclusion of air. It is ordinarily prepared by covering 
 large heaps of wood with ashes or turf, and burning them 
 with a restricted supply of air, so as to prevent complete 
 combustion, and only char the wood. The finer kinds of 
 charcoal, such as are used for making gunpowder, are pro- 
 duced by distilling the wood in close iron retorts. Char- 
 coal is a black, brittle, inodorous, tasteless solid; a 
 good conductor of electricity, but a bad conductor of 
 heat, and perfectly insoluble in all liquids. It is oxidized 
 by strong hydric nitrate, but resists the action of air and 
 moisture, and is, therefore, very unchangeable. The tim- 
 bers, and grains of wheat and rye, converted into charcoal 
 eighteen hundred years ago, at Herculaneum, remain as 
 entire as if they had been charred but yesterday. Wooden 
 posts are rendered more durable by charring their ends 
 
CARBON AND ITS COMPOUNDS. 273 
 
 before placing them in the ground. The interiors of tubs 
 and casks are often charred for the same reason. 
 
 486. Uses. The chief use of charcoal is as a fuel. 
 When pure, it burns without flame, although it usually 
 contains water which, during the combustion, is partially 
 decomposed and hydric carbide is foinaed which burns with 
 a slight flame. A cubic foot of charcoal from soft wood 
 weighs from 8 to 9 Ibs. ; from hard wood, from 12 to 13 Ibs. ; 
 hence, hard-wood coal is best adapted to produce a high 
 heat in a small space. At high temperatures, charcoal has 
 a very powerful affinity for oxygen ; therefore, it is of great 
 value in reducing metals from their oxides, in the smelting- 
 furnace. 
 
 Having the structure of the wood from which it was 
 derived, charcoal is very porous, and possesses in a remark- 
 able degree the power of absorbing gases, and condensing 
 them within its pores. It will absorb 90 times its bulk of 
 ammonia ; 35 times its bulk of carbonic dioxide ; and 9 
 times its bulk of oxygen. Freshly-burned charcoal im- 
 bibes watery vapor from the air very greedily, and by a 
 week's exposure increases in weight from 10 to 20 per 
 cent. Charcoal, having the finest pores, possesses this 
 power of absorption in the greatest degree ; the spongy 
 sort least. " A cubic inch of charcoal," says Liebig, " must 
 have, at the least computation, a surface of 100 square 
 feet." Charcoal absorbs noxious gases and offensive odors ; 
 and, when crushed, foul water filtered through it, and 
 tainted meat packed in it, are restored to sweetness. The 
 charcoal from bones (bone-black) is superior to wood-char- 
 coal for purifying purposes. It is extensively used in 
 sugar refineries to decolorize syrups. Vinegars, wines, 
 etc., are bleached in the same way. 
 
 Charcoal is a powerful deodorizer and disinfectant, but 
 it is not an antiseptic, or preventer of change, as has 
 been supposed. In fact, it is an accelerator of decomposi- 
 tion. It was formerly thought that charcoal acted by 
 
274 DESCRIPTIVE CHEMISTRY. 
 
 simply sponging up the deleterious gases, and retaining 
 them in its pores ; but it has been lately shown that, by 
 means of its condensing power, it is a powerful agent of 
 destructive change. The condensed oxygen seizes upon 
 the other gases present, and, oxidizing them, forms new 
 products. It thus changes ammonia to hydric nitrate, and 
 hydric sulphide to hydric sulphate. The body of a dead 
 animal packed in charcoal emits no odor, but, instead of 
 being preserved, its decomposition is much hastened. This 
 property has been made medically available in the form of 
 charcoal-poultice, to aid in the removal of sloughing and 
 gangrenous flesh in malignant wounds and sores. Lamp- 
 black is an impure variety of charcoal. It is the soot de- 
 posited from the burning of pitchy and tarry combustibles. 
 The smoke is conducted through long horizontal flues ter- 
 minating in chambers hung with sacking, upon which the 
 lamp-black is deposited. It is used for making printers' 
 ink and black paint. 
 
 487. Carbonic Monoxide, CO, Carbonic Oxide, is a 
 colorless, almost inodorous gas, which burns with a pale- 
 blue flame. It is produced by burning carbon with an im- 
 perfect supply of air, and its formation may be observed in 
 an open coal-fire. At the lower part of the grate, where 
 the air is abundant, carbonic dioxide is formed. As it 
 ascends into the hot mass above, it loses half of its oxygen, 
 becoming carbonic monoxide. The liberated oxj-gen, com- 
 bining with the carbon of the fuel, also produces an equal 
 quantity of the gas. As the carbonic monoxide thus 
 formed rises to the surface of the fire, it burns to carbonic 
 dioxide, with a lambent, blue flame. This gas may be ob- 
 tained pure and in great quantities by heating 1 part of 
 potassic ferrocyanide with 10 of hydric sulphate in a capa- 
 cious retort. Carbonic monoxide, when respired, acts as a 
 violent poison. Even when mixed with a very large quan- 
 tity of air its inhalation produces giddiness and headache, 
 and has in many instances proved fatal. 
 
CARBON AND ITS COMPOUNDS. 275 
 
 488. Carbonic Dioxide, CO S , Carbonic Acid. This 
 compound was discovered by Van Helmont about the be- 
 ginning of the seventeenth century. It is a normal con- 
 stituent of the atmosphere, to the average amount of 4 
 volumes in 10,000. Wherever carbon in any of its modifi- 
 cations, or any carbonic compounds, burn, with free access 
 of air, carbonic dioxide is produced. The combustion of a 
 bushel of charcoal produces 2,500 gallons of the gas. It 
 is produced by fermentation, and the slow decomposition 
 of organic bodies, and also by the respiration of animals. 
 Each adult man exhales about 140 gallons per day. It 
 is also produced by chemical changes which take place 
 in the interior of the earth, and it comes up with the waters 
 which rise to the surface. In volcanic regions it is occa- 
 sionally met with, unmixed with other gases. Rising to 
 the surface, often more rapidly than it is diffused into the 
 air, it accumulates in invisible pools and ponds. Through 
 the celebrated Grotto del Cane, in Italy, a man may walk 
 unharmed, but a dog with its nostrils near the earth is suffo- 
 cated on entering. The poison valley of Java is a lake of 
 carbonic dioxide filled with the bleached bones of dead 
 animals. 
 
 489. Preparation. Carbonic dioxide is most conven- 
 iently obtained by the action of an acid upon small frag- 
 ments of marble, limestone, or chalk. Any strong acid 
 will answer the purpose, but hydric chloride is the best. 
 The powdered mineral is placed in a jar and covered with 
 water. A little dilute acid is then poured down through 
 the tube, Fig. 180. Effervescence immediately takes place, 
 and the gas escapes through the bent tube. It may be 
 collected over water in the pneumatic trough, or, as it is 
 heavier than the air, it will quickly displace it in an open 
 vessel. The change is thus shown : 
 
 CaC0 3 + 2HC1 = CaCl, + H 3 O + CO,. 
 A cubic inch of marble will yield four gallons of the gas. 
 
276 
 
 DESCRIPTIVE CHEMISTRY. 
 
 FIG. 180. 
 
 Jar for generating Carbonic Dioxide. 
 
 490, Properties, Carbonic dioxide is, at ordinary tem- 
 peratures and pressures, a colorless, inodorous gas, of 1.52 
 
 specific gravity. It 
 does not support 
 combustion. To 
 prove this, and to 
 show also that it is 
 heavier than air, we 
 have but to place 
 a lighted taper in a 
 jar, and pour in 
 carbonic dioxide 
 from another ves- 
 sel, Fig. 181; the 
 invisible current 
 promptly puts out 
 the light. 
 
 When respired, 
 carbonic dioxide is fatal to life. If pure, it produces spasm 
 of the glottis, closes the air-passages, and thus kills sud- 
 denly by suffocation; but, though it has been held that 
 carbonic dioxide exerts a poisonous 
 action, it is more probable that these 
 effects a re merely due to deprivation 
 of oxygen. This gas often accumu- 
 lates at the bottom of wells, and in 
 cellars, stifling those who may un- 
 warily descend. To test its pres- 
 ence in such cases, it is common to 
 lower a lighted candle into the sus- 
 pected place, and, if it is not extin- 
 guished, the air may be breathed 
 safely for a short time. If the light goes out, it will be ne- 
 cessary before descending to let down dry-slacked lime, 
 or pans of freshly-burned charcoal, to absorb the gas. 
 When carbonic dioxide is brought into contact with 
 
 FIG. 181. 
 
 Pouring Carbonic Acid. 
 
CARBON AND ITS COMPOUNDS. 277 
 
 calcic hydrate solution (lime-water), the liquid turns milky, 
 from the production of calcic carb juate. Thus, if we 
 expose a saucer of lime water to the air, in a short time its 
 surface is covered with a thin film of calcic carbonate, 
 proving that there is carbonic dioxide in the atmosphere. 
 If we blow through a tube into a jar of lime-water, it quickly 
 becomes turbid from the same cause, thus showing that 
 there is carbonic dioxide in the expired breath. Under a 
 pressure of 36 atmospheres at 32 F., carbonic dioxide 
 shrinks into a colorless, limpid liquid lighter than water. 
 When this pressure is removed, it does not suddenly 
 resume its gaseous state, but evaporates with such ra- 
 pidity, that one portion absorbs heat from another, and 
 freezes it to a white solid, like dry snow. This solid car- 
 bonic dioxide wastes away but slowly, and may be handled, 
 though, if it rests long upon the skin, it disorganizes it like 
 red-hot iron. 
 
 491. Uses. The sparkling appearance and lively, pun- 
 gent taste of various mineral waters are due to the carbonic 
 dioxide they contain. Water absorbs nearly its own 
 volume of carbonic dioxide, but by means of a forcing-pump 
 it may be made to receive a much larger proportion. " Soda- 
 water " is, ordinarily, only water charged with carbonic di- 
 oxide. Being overcharged, when the pressure is withdrawn, 
 the gas escapes with violent effervescence. The effect is 
 the same whether the carbonic dioxide is forced into the 
 water from without, or generated in a tight vessel, as is 
 the case with fermented liquors; the gas gradually formed 
 is dissolved by the water, and, escaping when the cork is 
 withdrawn, produces the fuming and briskness of the 
 liquor. 
 
 Carbonic dioxide is also used to extinguish fires. In 
 one case an English coal-mine, which had been on fire 
 thirty years, was completely extinguished by pouring into 
 it eight million cubic feet of this gas. In the " fire- 
 annihilators " or " extinguishers," the gas is generated at 
 
278 DESCRIPTIVE CHEMISTRY. 
 
 the time when wanted, in a suitably-constructed metallic 
 vessel, and discharged into the fire under pressure. 
 
 492. Carbonic Bisulphide, CS 2 . This is a very volatile, 
 colorless liquid, of about 1.27 specific gravity, which boils at 
 118.5 F. It has a peculiar, very unpleasant odor and pun- 
 gent taste. It lias never been frozen, and is used in ther- 
 mometers which are to measure very intense degrees of 
 cold. It is highly inflammable, burning with a blue flame, 
 and yielding carbonic dioxide and hydric sulphate. It dis- 
 solves sulphur, phosphorus, and iodine, and is dissolved in 
 ether, but not in water. It is produced by bringing vapor 
 of sulphur into contact with red-hot charcoal, the compound 
 vapor being condensed in cold vessels. From its high dis- 
 persive power over light, it is used to fill hollow prisms of 
 glass for spectroscopic observations. It is also applied in 
 chemical manufactures, to a variety of purposes. 
 
 493. Cyanogen, C 2 N 2 . This substance may be best pro- 
 cured by heating mercuric cyanide (HgC 2 N 2 ) in a glass 
 tube or retort. The compound is decomposed, the cyano- 
 gen being evolved as a colorless gas, which 
 may be ignited, burning with a beautiful 
 blue flame, edged with purple, Fig. 182. 
 Cyanogen is a transparent, colorless gas, 
 poisonous if respired, and with a strong 
 odor. It is very soluble in water, and hence 
 must be collected in the pneumatic trough 
 over mercury. It is reduced to a colorless, 
 limpid liquid by a pressure of four atmos- 
 pheres, and freezes into a transparent crys- 
 talline solid at 30 C. 
 
 cyanogen. * H y dric Cyanide, HCN (Prussic 
 Acid). This substance is found, in very 
 small quantities, in the leaves, bark, blossoms, and fruit of 
 the peach, cherry, sloe, and many other plants. It is best 
 obtained by the decomposition of various metallic cyanides 
 with a strong acid, and subjecting the mixture to distilla- 
 
COMBUSTION. 279 
 
 tion. Hydric cyanide, when pure, is at common tempera- 
 tures a colorless liquid, which solidifies at 15 C., and 
 boils at 26 C. It has the peculiar odor of bitter almonds 
 or peach-blossoms. It is exceedingly poisonous, one drop 
 producing instant insensibility, and almost instant death. 
 The inhalation of the vapor should, therefore, be most 
 carefully guarded against. The prussic acid of the shops 
 is a more or less dilute solution of hydric cyanide, in water. 
 The hydrogen of hydric cyanide is replaceable by simple 
 or compound monad radicles, giving rise to a series of 
 compounds termed cyanides. 
 
 495. Potassic Cyanide, KCN. This compound is formed 
 when potassium is heated in cyanogen gas, or hydric 
 cyanide vapor, but it is obtained on a large scale by the 
 decomposition of potassic ferrocyanide (yellow prussiate of 
 potash) (K 4 FeC 6 N 6 ), by heat. It is a \\hite crystalline 
 body, very soluble in water, and exceedingly poisonous. 
 It is much used in the arts in electroplating and gilding, 
 and in the laboratory as u reagent. 
 
 2. Combustion. 
 
 496. Combustion a Chemical Process. Combustion, in 
 its popular sense, is that form of chemical action which is 
 accompanied by the disengagement of heat and light, and 
 which usually takes place between the oxygen of the air 
 and certain organic bodies, as wood, coal, oil. etc. The 
 chemist, however, gives to the term a wider meaning, 
 which includes all those forms of chemical action which 
 result in the combination of bodies, with one or all of the 
 constituents of a surrounding gaseous atmosphere; thus 
 the violent burning of iron in oxygen, or its slow rusting in 
 the air, the rapid consumption of wood in the furnace, or its 
 gradual decay, are all alike, to him, cases of combustion. 
 The nature of the gaseous atmosphere also makes .no 
 difference, and phosphorus or arsenic burning in chlorine 
 gas, hydrogen, or iron in sulphur-vapor, are instances of 
 
80 DESCRIPTIVE CHEMISTRY. 
 
 this form of chemical action, as well as the corresponding 
 changes taking place in air, or oxygen gas. Bodies were 
 formerly divided into combustibles and supporters of com- 
 bustion. Oxygen was held to be the universal supporter 
 of combustion, while hydrogen, carbon, and iron, which 
 burn in it, were called combustibles. But if the atmos- 
 phere were hydrogen, the so-called supporters of combustion 
 would burn in it equally well, and the fact is, the action is 
 mutual and of the same kind on the part of both. 
 
 497, Rapid Combustion. The beginning of rapid com- 
 bustion is termed ignition. In order to induce ignition 
 a certain elevation of temperature is required, and the 
 maintenance of this temperature is essential to the con- 
 tinuance of the combustion. After a substance is once 
 kindled, the heat given off by the rapid chemical action is 
 usually more than sufficient to maintain the combustion 
 until the burning body is consumed. The temperature at 
 which rapid combustion may take place differs with dif- 
 ferent bodies. Thus, in atmospheric air, phosphorus ignites 
 at 150 F., sulphur at 480 F., while the hydrocarbons re- 
 quire a temperature of nearly 1000 F. to kindle them. 
 The stability of the order of Nature depends upon the gra- 
 dation of the affinities between atmospheric oxygen and 
 the hydrogen and carbon of organic bodies. These are 
 only brought into action at high temperatures. Did these 
 bodies, like phosphorus, ignite at a much lower degree, 
 conflagrations, which are now comparatively rare, would 
 become universal. 
 
 498. Explosive Combustion. When two gaseous bodies, 
 combustible in each other, are mixed and ignited, an ex- 
 plosion ensues. This is because the constituents of the 
 gaseous mixture are so intimately blended that the heat 
 evolved by the particles first ignited passes to those ad- 
 joining, and so on through the entire mass, with such 
 velocity as to cause an almost instantaneous completion 
 of the process. The products pf this form of combus^ 
 
COMBUSTION. 281 
 
 tion are always in the form of highly-expanded gases or 
 vapors, the intense rarefaction of which gives rise to a 
 vacuum, and the particles of air rushing in to fill thiy, in 
 colliding with each other produce the noise of the explosion. 
 
 499. Slow Combustion. Oxygen, as well as other ele- 
 ments, frequently enters into slow combination at ordinary 
 temperatures and without perceptible heat, as in the rust- 
 ing of iron in the air. The cause of decay in vegetable 
 and animal substances is the slow action of oxygen. This 
 slow combustion is termed eremacausis. Heat, however, 
 always accompanies this slow form of combustion. An 
 ounce of iron rusted in air, or burnt in oxygen, produces 
 the same amount of heat, but in the former case it requires 
 years for its development, and in the latter only as many 
 minutes. Sometimes, under favorable circumstances, the 
 combination becomes so rapid that the accumulated heat 
 produces ignition, causing the phenomenon called spon- 
 taneous combustion. This is most liable to occur with 
 porous substances which expose a large surface to the air. 
 The tow or cotton used for wiping the oil from machinery, 
 and then laid away in heaps, often ignites in this manner, 
 especially if exposed to the sun. 
 
 500. Heat of Combustion. The complete burning of a 
 combustible body requires the consumption of the same 
 quantity of oxygen, whether the process goes on rapidly or 
 slowly, and, in either case, the amount of heat set free is 
 the same. Therefore, the intensity of the heat depends 
 upon the rapidity of the combustion. Heat would be 
 liberated from the burning of a pound of coal in ten minutes, 
 six times as fast as if its combustion occupied an hour. 
 The burning in air of one pound of wood-charcoal will 
 raise from the freezing to the boiling point 73 Ibs. of water; 
 one pound of mineral coal will correspondingly heat 60 Ibs. 
 of water ; and one pound of dry wood will raise 35 Ibs. of 
 water through the same number of degrees. These are the 
 highest results by careful experiments ; in practice we pb- 
 
282 DESCRIPTIVE CHEMISTRY. 
 
 tain a much lower eff-.ct, both on account of imperfect 
 combustion, and from the fact that a large proportion of 
 the heated air escapes through the chimney, before it has 
 given off as great an amount of heat as it is capable of 
 producing. 
 
 501. Cause of the Heat. It has been explained that 
 chemical action produces heat by conversion of the motion 
 of chemical atoms into heat-vibrations. We have atoms 
 separated and powerfully attracted, like lifted weights ; 
 they rush together, collision arrests motion, and their force 
 is given out as heat. It is the clash or impact of the atoms 
 of oxygen against the elements of burning bodies, which 
 gives us the heat and light of combustion. By figuring 
 to ourselves the atoms shot across the molecular spaces 
 with intense force, and thus parting with their motion, we 
 have an explanation of the source of heat in combustion, 
 which is in harmony with our latest knowledge of the 
 nature of heat, and of its other modes of production, while 
 in no other way is it possible to explain its chemical origin. 
 
 502. Nature of Flame. Flame is produced by the com- 
 bustion of gas?s. Substances which burn with flame are 
 either gases already, or they contain a gas which is set 
 free by the heat of combustion. But flame does not ne- 
 cessarily produce light. In the burning of pure oxygen 
 and hydrogen, there is intense flame, but so little light that 
 it can hardly be seen. ]f, into this non-luminous flame, we 
 sift a little charcoal-dust, the particles of solid carbon are 
 instantly heated to incandescence, and there is a bright 
 
 flash of liffht. The conditions of 
 
 .PIG. loo. 
 
 illumination are, therefore, first, an 
 intense heat ; and, second, a solid 
 placed in the midst of it, which 
 remains fixed, a,nd gives out the 
 light. 
 
 503, The Compound Blow-pipe, 
 -pipe, These conditions are fulfilled 
 
COMBUSTION. 
 
 most perfectly by means of the compound blow-pipe of Dr. 
 Hare. The two gases are collected in gasometers, or India- 
 rubber bags, Fig. 183, which are connected by flexible tubes 
 with the brass jet. Fig. 184 ; the 
 flow being increased by pressure 
 on the bags, and controlled by 
 stop-cocks. The gases are emit- 
 ted together and burned at the 
 orifice, a. When ignited, they 
 give rise to a blue flame which 
 is hardly visible, but which has Blow-pipe Jet. 
 
 intense heating power, and pro- 
 duces the most remarkable effects. A steel watch-spring 
 burns in it with a shower of scintillations. Substances 
 which do not fuse in the hottest blast-furnaces melt in 
 this heat like wax, or dissipate in vapor. 
 
 504. The Lime-BalL A little ball of lime, however, of 
 the size of a pea, remains unaltered in the flame. It glows 
 with a blinding brilliancy, producing what is known as the 
 " Drummond light," or the " calcium light." It is em- 
 ployed as a substitute for the rays of the sun in the solar, 
 or oxyhydrogen microscope, and is used in coast-surveys 
 for night-signals. In all ordinary illuminations the prin- 
 ciple is the same as that of the lime-light. The substances 
 employed are compounds of carbon and hydrogen; the 
 union of oxygen and hydrogen gives rise to heat, and the 
 luminous carbon-particles at the same time set free in the 
 heated space are the source of the light. 
 
 505. How the Candle burns. The materials used for 
 illumination, whether solids or liquids, are always con- 
 verted into gas before burning. The candle first becomes 
 a lamp, and then a gas-burner. "When lighted, the heat 
 radiates downward, so as to melt the material of the can- 
 dle and form a hollow cup filled with the liquid combus- 
 tible, Fig. 185, and thus the candle becomes an oil-burner. 
 From this reservoir, the wick draws up the oil into the 
 
284 
 
 DESCRIPTIVE CHEMISTRY. 
 
 FIG. 185. 
 
 Burning 
 Candle. 
 
 flame. Here, in the midst of a high heat, and cut off from 
 the air, it undergoes another change exactly as if it were 
 inclosed and heated in a gas-maker's retort ; it 
 is converted into gas, and in this form finally 
 burned. As the wick rises into the flame, it 
 fills the interior with a sooty mass, and inter- 
 feres with the combustion. 
 
 506. Structure of the Flame, As the wick 
 remains thus unconsumed in the interior of 
 tha flame, it is obvious there can be no fire 
 there. If we lower a piece of glass or a wire 
 gauze over a candle or gas flame, as in Fig. 186, 
 we shall see an interior dark space surround- 
 ed by a ring of fire. This inner sphere is filled 
 with dark unburned hydrocarbon vapors, which 
 are inclosed by a shell of fire, or burning gas. 
 If one end of a small glass tube be introduced into the 
 candle-flame, as in Fig. 187, these in- 
 terior gases will be conveyed away, 
 and may be lighted at the other end. 
 
 507. Order of the Combustion. 
 There is an order of combustion in 
 the flame, which depends upon the or- 
 der of affinities. In Fig. 188, a repre- 
 sents the nucleus of hydrocarbon va- 
 por. If, now, oxygen from without 
 had the same affinity for both its ele- 
 ments, they would be consumed to- 
 gether, with but little luminous effect. 
 But the oxygen decomposes the gas- 
 eous compound, and, seizing upon 
 the hydrogen first, surrounds a with 
 the intensely heated space, b. At the 
 same time the carbon-particles are set 
 free, and, being heated white-hot, give 
 
 Out the motion of light. The COne b Gas from Flame. 
 
 FIG. 186. 
 
 The Flame hollow. 
 FIG. 1ST. 
 
COMBUSTION. 
 
 285 
 
 FIG. 188. 
 
 FIG. 189. 
 
 is therefore the place of burning hydrogen and the seat of 
 illumination. The incandescent carbon-particles, as they 
 pass outward, meet with oxygen at c, and are 
 converted into carbonic dioxide in the outer cone. 
 To prove the constant presence of free carbon in 
 the flame, it is only necessary to introduce into 
 it any cold body, as a piece of porcelain, when 
 carbon will be copiously deposited upon it as 
 soot. Fig. 189 represents a cross-section of the 
 flame and the arrangement of its parts ; CH the 
 unburned carbon and hydrogen, H the sphere of 
 burning hydrogen across which the carbon-parti- 
 cles float, and lastly the sphere of burning car- 
 bon. It will be observed, by noting any com- 
 mon flame, that at the base it burns blue, and 
 
 yields but little light. This is because the 
 oxygen at this point is so abundant that 
 it burns simultaneously both hydrogen 
 and carbon. A candle-flame moved swift- 
 ly through the air gives a diminished light 
 for the same reason. 
 
 508. Effect of Temperature on the 
 Flame. The amount of light produced 
 depends upon the intensity of the heat. 
 Dr. Draper found that a body at 2,600 emitted almost 40 
 times as much light as at 1,900. If 
 by any means the temperature of the 
 flame falls below a certain limit it is im- 
 mediately extinguished. The flame of a 
 candle may be put out by lowering over 
 it a coil of cold copper wire, Fig. 190. A piece of fine 
 wire gauze held across the flame of a candle cools the com- 
 bustible gases below the point of ignition, so that they 
 rise through the meshes in the form of smoke, Fig. 191. 
 The gauze may become red-hot and still not allow the flame 
 to pass, so rapidly is the heat conducted away by the wire. 
 
 Cross-Section of the 
 Flame. 
 
 FIG. 190. 
 
 Copper CoiL 
 
286 
 
 DESCRIPTIVE CHEMISTRY. 
 
 FIG. 191. 
 
 Gauze stops the Flame 
 
 Yet the cooled gases may be rekindled above, when the 
 flame will go on burning as before, Fig. 192. 
 
 509, Safety -Lamp. On this principle the safety-lamp is 
 
 constructed. The explosions 
 of hydric carbide in coal- 
 mines caused immense de 
 struction of life, and various 
 arrangements had been fruit- 
 lessly contrived to prevent 
 these terrible accidents when 
 Sir Humphry Davy took hold 
 of the subject. He com- 
 menced a series of research- 
 es upon flame in August, 
 1815, and with such success 
 as to produce the perfected 
 lamp at the Royal Institution of London in the succeeding 
 November. The safety-lamp consists simply of an ordi- 
 nary oil-lamp inclosed in a cage of wire 
 gauze which permits the light 
 to pass, out, but prevents all 
 exit of flame, Fig. 193. The 
 space within the gauze often 
 becomes filled with flame, 
 from the burning of the 
 mixed gases which penetrate 
 the net-work; but the isola- 
 tion is so complete that the 
 explosive mixture without is not fired. Fatal 
 explosions still occasionally take place, but 
 they are due to carelessness of the miners. 
 As the intensity of light depends upon the 
 rapid consumption of oxygen, there must be a 
 free supply of air, and provision for the escape 
 Safety -Lamp of combustion products. 
 
 FIG. 192. 
 
 FIG. 193. 
 
 Ga. hums above. 
 
HYDROCARBONS AND THEIR DERIVATIVES. 287 
 
 DIVISION III.-ORGANIC CHEMISTRY. 
 
 CHAPTER XXV. 
 
 1. Hydrocarbons and their Derivatives. 
 
 510. The Marsh-Gas Series (Paraffins). When the unit- 
 weight of carbon combines with four unit-weights of hy- 
 drogen the result is the simplest known hydride of car- 
 bon, and since this is a saturated compound, or molecule, 
 it is incapable of combining with chlorine, bromine, or 
 any monad element, but it may exchange the whole or a 
 
 Fir. 194. 
 
 March-Gas. 
 
 part of its hydrogen for an equivalent quantity of another 
 element. It is from these hydrocarbons, or compounds 
 having this composition, that more or less directly the 
 13 
 
288 DESCRIPTIVE CHEMISTRY. 
 
 organic substances, to be hereafter described, may be 
 built up. 
 
 Methane, CH 4 (Marsh-Gas)^ is the first member of a 
 series, each term of which differs from the term next below 
 by CH,. 
 
 It is a colorless, inodorous, tasteless, inflammable gas, 
 which burns with a yellow, luminous flame. If diluted 
 with air, it is not injurious to life. It may be produced by 
 heating in a glass flask a mixture of two parts of sodic 
 acetate, three parts of potassic hydrate, and three of quick- 
 lime. It is called marsh-gas because it is a product of the 
 decomposition of vegetable matter contained in the mud of 
 stagnant pools. It may be collected by inverting a jar and 
 funnel in the water, and stirring the mud beneath, Fig. 194, 
 when the gas rises into the jar in bubbles. It is often dis- 
 engaged in large quantities in coal-mines : mixed with the 
 air it becomes explosive, and constitutes the fatal fire- 
 damp. If the air is more than six times or less than four- 
 teen times the bulk of the gas, the mixture explodes vio- 
 lently. Carbonic dioxide is produced by the combustion, so 
 that those who are not killed by the burning or shock are 
 generally suffocated by the choke-damp. 
 
 In some places, this gas rises from the earth in such 
 quantities as to be utilized for purposes of illumination ; as 
 in the village of Fredonia, N. Y. In the deep wells sunk 
 for brine and mineral oil, it often rises in such quantity as 
 to be employed for driving the pumping-engines, or for 
 evaporating the liquids. 
 
 Petroleum (Rock- Oil) is a natural product found on 
 this continent, in Canada, and in Pennsylvania. In some 
 cases it rises to the surface of the earth, but more general- 
 ly it is obtained by sinking wells into the strata in which 
 it occurs. It is a thick, greenish, oily liquid, of variable 
 composition. 
 
 511. Coal-Oil consists, to a great extent, of a mixture 
 of various compounds of the Paraffin Series. It is a prod- 
 
HYDROCARBONS AND THEIR DERIVATIVES. 289 
 
 uct of the distillation of bituminous coal, bituminous 
 shales, and asphalt. The material is placed in iron retorts, 
 in large pits holding a hundred tons, or in kilns of brick 
 containing twenty-five tons. The retorts are heated from 
 without, like gas-retorts, while the kilns are fired within, 
 like the tar-pits. The first product collected in the reser- 
 voirs resembles the natural oil from the wells, and is re- 
 fined by the same method. It is first distilled at a tem- 
 perature of 600 or 800 F., and the product, conveyed to 
 cisterns holding 3,000 gallons, is agitated with 5 or 6 per 
 cent, of hydric sulphate. The acid and settled impurities 
 being drawn off at the bottom, the mass is again agitated, 
 first with water, and afterward with alkaline lye ; it is then 
 redistilled, and constitutes the " kerosene " or "petroleum- 
 oil" of commerce. It has been found by experience that 
 it is not safe to use a paraffin-oil which will take fire on 
 the application of a match, and burn continuously at a 
 temperature below 100 F. The reason for this may be 
 found in the fact that the oils obtained by the distillation 
 of coal, at low temperatures, are mixtures of paraffins, dif- 
 fering in volatility, and unless the volatile members of the 
 series have been driven off by proper distillation, the oils 
 take fire easily, give off inflammable vapors which, mixing 
 with air in the body of the lamp, form compounds which 
 are dangerously explosive. 
 
 Paraffin is a crystalline, colorless, inodorous, tasteless, 
 and fatty substance, probably a mixture of several of the 
 higher terms of this series. It is found native in coal-beds 
 and other bituminous strata, as fossil wax, mineral tallow, 
 etc. It may also be procured from petroleum and from 
 coal-oil. As it burns with a bright flame and is hard, it 
 makes excellent candles. It is used as a substitute for sul- 
 phur in dipping matches, and to render woolen cloths 
 stronger and water-proof. 
 
 512, Olefine Series of Hydrocarbons. This series in- 
 cludes a number of interesting bodies. The lowest terms 
 
290 DESCRIPTIVE CHEMISTRY. 
 
 of the series are gaseous at ordinary temperatures; the 
 highest solid, and the intermediate compounds liquid. 
 
 Ethylene^ C 3 H 4 (Olefiant Gas). This gas may be pre- 
 pared by mixing strong alcohol with five or six times its 
 weight of sulphuric acid in a retort, and applying heat. It 
 is colorless, tasteless, nearly as heavy as air, with a marked 
 odor, very inflammable, and burns with a bright and in- 
 tensely luminous flame. When mixed with air it is explo- 
 sive, and derives its name (oil-former) from the fact that it 
 forms an oily compound with chlorine. It was liquefied 
 under great pressure by Faraday. It is decomposed by 
 electric sparks into carbon and methane. 
 
 Illuminating gas consists of a mixture of various gases 
 hydrogen, methane, nitrogen, ethylene, carbonic monox- 
 ide and dioxide, and hydric sulphide being represented in 
 the largest quantities. The illuminating power of the 
 gas is nearly proportional to the quantity of ethylene 
 which it contains. It is commonly produced from bitu- 
 minous coal, placed in cast-iron retorts, fixed in furnaces, 
 and heated to redness by an external fire. Each retort 
 receives a charge of 100 to 150 Ibs. of coal every six 
 hours, and in large gas-works several hundreds of them are 
 kept at work day and night. At a moderate heat, tar and 
 oil are produced, but, at a high temperature, gases are 
 formed in large quantities. Besides the products of this 
 destructive distillation above mentioned, there are present 
 a thick, black liquid, known as coal-tar, steam, various arn- 
 moniacal compounds and a solid, friable, carbonaceous mass 
 known as coke. 
 
 Illuminating gas has come into use entirely within the 
 present century, it having been first employed in London 
 in 1802. How wonderful that sunbeams absorbed by vege- 
 tation in the primordial ages of the earth, and buried in its 
 depths as vegetable fossils through immeasurable eras of 
 time, until system upon system of slowly-formed rocks 
 have been piled above, should come forth at last, at the 
 
\ 
 HYDROCARBONS AND THEIR DERIVATIVES. 291 
 
 disenchanting touch of Science, and turn the night of civil- 
 ized man into day ! 
 
 513. Acetylene, C 2 H,. This compound is of special 
 interest as a hydrocarbon which can be obtained by the 
 direct union of its elements. It is formed when the 
 current from a powerful battery passes, in an atmosphere 
 of hydrogen, between carbon-poles. It is also the product 
 of decomposition by heat or imperfect combustion of or- 
 ganic compounds. 
 
 514. Turpentine Series. This series is interesting as 
 including an isomeric group of the composition C 10 H 16 , 
 called Terpenes, which occur, widely distributed through 
 the vegetable kingdom, as the essential oils, to the pret- 
 ence of which the peculiar odor of certain plants is due. 
 
 Terpenes, C 10 H 16 . The volatile oil of turpentine, also 
 known as " spirits of turpentine," may be taken as a type 
 of this class of substances. It is obtained by distilling with 
 water the pitchy matter that exudes from various species 
 of pine and other trees. Oil of turpentine is a colorless, 
 limpid fluid, having a strong odor and disagreeable taste. 
 It boils at 320 F., and has a specific gravity of 0'86. It is 
 highly inflammable, and when purified is used for illumi- 
 nating purposes, under the name of camphene. Burning 
 fluid is rectified turpentine or camphene, dissolved in alco- 
 hol, which admixture renders it less smoky when burned. 
 Spirits of turpentine is also used in varnishes as a solvent 
 for resins and gums. The oils of lemon and orange are also 
 terpenes. 
 
 515. Benzine Series. The hydrocarbons of this class 
 are found in coal-tar and in the petroleum which is ob- 
 tained from Rangoon, in the kingdom of Burmah. Benzol, 
 or benzene (C 6 H e ), is very much used in the arts. It is a 
 colorless, volatile liquid, the vapor of which is very inflam- 
 mable. It burns with a smoky flame. Benzol is valuable 
 as a solvent, readily dissolving phosphorus, sulphur, and 
 caoutchouc, as well as wax and all fatty bodies. 
 
292 DESCRIPTIVE CHEMISTRY. 
 
 By the action of nitric acid on benzene, a heavy oily 
 liquid called nitro-benzene is produced. It has an odor re- 
 sembling that of bitter almonds, and is used in perfumery, 
 but it is chiefly interesting as being a stepping-stone in the 
 production of aniline, C 6 H 7 N, which has of late years ac- 
 quired special importance as the basis of the well-known 
 aniline colors. Aniline is obtained indirectly from benzene, 
 one of the chief constituents of coal-tar, though it also 
 occurs in the coal-tar, ready formed, in small quantities. 
 It is a colorless, mobile, oily liquid of faint, agreeable, 
 vinous odor, and aromatic, burning taste. It boils at 182 
 C., solidifies at very IOAV temperatures, is easily soluble in 
 alcohol and ether, and slightly soluble in water. It is 
 poisonous. 
 
 Naphthalene, C 10 II 8 , closely resembles benzene in chem- 
 ical reactions. It is a product of the decomposition of 
 many hydrocarbons by a red heat, and is obtained abun- 
 dantly in the distillation of coal-tar. It is solid at ordi- 
 nary temperatures, insoluble in water, but dissolves in al- 
 cohol. 
 
 Anthracene, C 14 H 10 , is a white solid, and is one of 
 the last products of the distillation of coal-tar. It has 
 lately attracted much attention owing to the fact that 
 alizarine, the red coloring substance of the madder-roots, 
 has been obtained from it. Carminic acid the coloring- 
 matter of cochineal is used for dyeing wool and silk 
 crimson or scarlet, but the colors, though brilliant, are not 
 durable, 
 
 2. Alcohols. 
 
 516. The term alcohol, which originally designated only 
 one substance, viz,, spirit of wine, has now a much wider 
 meaning, and is applied to quite a large number of com- 
 pounds, many of which in their external characteristics 
 exhibit but little likeness to common alcohol. They are 
 all compounds of oxygen, hydrogen, and carbon, and may 
 
ALCOHOLS. 293 
 
 be regarded as derived from the hydrocarbons of the rnarsh- 
 gas series by substituting for a single atom of hydrogen 
 the radicle hydroxyl (HO), as, for example, common al- 
 cohol. 
 
 H H ! 
 
 H-C-C- 
 A A 
 
 -0-H 
 
 Methyl Alcohol, CH 4 O ( Wood- Spirit). This is one of 
 the chief products of the dry distillation of wood. When 
 pure it is a thin, colorless liquid, very similar in smell and 
 taste to common alcohol. Crude wood-spirit, however, is 
 always impure, has an offensive odor, and a nauseous, burn 
 ing taste. It is employed in the arts for many of the pur- 
 poses for which ordinary alcohol is used, especially in the 
 manufacture of varnishes. 
 
 517. Ethyl Alcohol, C a H 6 O (Common Alcohol, Spirits 
 of Wine). When solutions of sugar (C ia H M O n ), or the 
 sweet saccharine juices of plants, are acted upon by fer- 
 ments, they are decomposed, with evolution of carbonic 
 dioxide, and formation of alcohol. This substance may 
 also be obtained from ethylene ; ethylene may be prepared 
 from acetylene (513), and thus it will be seen that it is 
 possible by a series of simple reactions to build up alcohol 
 from the elements carbon, oxygen, and hydrogen. It is a 
 colorless, mobile fluid, of 0.77 specific gravity, having a 
 pleasant, fruity smell, and a burning taste. It is very vola- 
 tile, and has a strong tendency to absorb moisture from the 
 air or from bodies immersed in it, thus rendering it valu^ 
 able as an antiseptic. It is highly combustible, burning 
 with a pale-blue flame, and producing intense heat without 
 smoke ; it is therefore well adapted to burn in lamps for 
 chemical use. Alcohol has great value as a solvent, as it 
 acts upon many substances which water does not dissolve, 
 and is easily separated from them on account of its extreme 
 volatility. It boils at 173 F., and has never been frozen, 
 
294 DESCRIPTIVE CHEMISTRY. 
 
 although at 166 it becomes viscid. In a concentrated 
 form it is a potent poison, but, when sufficiently diluted, it 
 acts upon the animal system as a stimulant. Taken freely 
 in this form it produces inebriation, and is the active prin- 
 ciple of all intoxicating liquors. 
 
 518. Amyl Alcohol, C 6 H 12 O (Fusel Oil). This alcohol 
 is produced together with ordinary alcohol in fermentation. 
 It is a transparent, colorless liquid, of unpleasant, mouldy, 
 spirituous odor, and burning taste, and is poisonous. It 
 burns with a white, smoky flame, and has been used for 
 illuminating purposes. 
 
 519. Wines are obtained from the expressed juice of 
 the grape and other fruits. The fresh grape-juice, or must, 
 is placed in vats in cellars, where the temperature is so 
 low that the fermentation proceeds very slowly. Some- 
 times the wines are bottled before the fermentation is 
 quite complete, and they continue to generate carbonic 
 dioxide, which remains compressed within the liquid. If 
 the carbonic dioxide is so abundant as to produce efferves- 
 cence when uncorked, the wine is said to be " sparkling " 
 if otherwise, it is termed "still" wine. 
 
 520. Lager-Beer is freed from nitrogenized products by 
 a slow and long-continued fermentation ; hence it may be 
 preserved for years without further decomposition. Before 
 consumption it lies stored in vaults for months, from which 
 circumstance its name is derived (lager, lair). The differ- 
 ence in color of malt liquors is owing to the various degrees 
 of heat employed in malting. Ale is made from pale malt, 
 while that used for porter is partially charred, giving it a 
 brownish color and bitter flavor. 
 
 521. Distilled Liquors are obtained by subjecting cer- 
 tain fermented mixtures to distillation. Brandy is derived 
 from the distillation of wine ; rum from that of fermented 
 molasses, and arrack from the distillation of fermented rice- 
 infusion. Whiskey is obtained from corn, rye, and potatoes, 
 by first converting their starch into sugar, then into spirit, 
 
ALCOHOLS. 295 
 
 and distilling the product. Grin is produced from the dis- 
 tillation of the spirit of a mixture of barlev and rye, and 
 owes its peculiar flavor to juniper-berries. 
 
 522. Phenol, C e H 8 O. A substance familiarly known as 
 carbolic acid is regarded by the chemist as the alcohol of 
 benzene : 
 
 Benzene, C 6 H e . Phenol, C 6 H 6 OH. 
 
 The chief source of phenol is coal-tar, from which it is 
 obtained by distillation. Pure phenol crystallizes at or- 
 dinary temperatures in long, colorless, needle-shaped prisms, 
 which attract moisture from the air, deliquescing to an oily 
 hydrate. The crystals melt at 35 C., and boil at 180 C., 
 are slightly soluble in water, more freely in alcohol. They 
 have a penetrating, smoky odor and a burning acrid taste. 
 Phenol and its solutions have in an eminent degree the 
 property of preserving animal substances from decay, and 
 are on this account much employed as antiseptics and dis- 
 infectants. A considerable portion of the creosote of com- 
 merce consists of phenol. Genuine creosote is a colorless, 
 oily liquid with a smoky odor and burning taste. It is a 
 powerful antiseptic, and meat, steeped for a few hours in 
 a solution of one part creosote to 100 parts water, remains 
 sweet and will not putrefy. Creosote is used very exten- 
 sively in medicine, both inwardly and as an external appli- 
 cation, but an overdose is a corrosive poison. Crude pyro- 
 ligneous acid, on account of the creosote it contains, is 
 used to preserve meats, to which it imparts a smoky flavor. 
 The curing quality of the smoke of green wood is also 
 owing to this cause. It is the vapor of creosote which 
 renders smoke so irritating to the eyes. 
 
 523. Fats and Oils. Most of the fixed oils, and the fats, 
 both animal and vegetable, are compounds of glycerine, 
 and acids of the acetic and oleic type. Thus beef and 
 mutton fat consist mainly of stearic glyceride (stearin) ; 
 olive-oil is oleic glyceride (olein) ; palm-oil is chiefly pal- 
 
296 DESCRIPTIVE CHEMIS:RY. 
 
 mitic glyceride (palmitine). These glycerides, when de- 
 composed, by heating with water yield glycerine and an 
 acid. 
 
 Glycerine (C g H 8 O 3 ). When pure this substance is a 
 nearly colorless, inodorous, sirupy liquid, of intensely sweet 
 taste. It is readily soluble in water and alcohol, and is a 
 powerful solvent and antiseptic. Of late years, it has been 
 employed as a medicine ; and, on account of its solvent 
 power, it is also largely used as a vehicle for administering 
 other medicines. It is extensively employed in the manu- 
 facture of cosmetics and perfumery. Glycerine is non- 
 volatile, and, when heated over 600 F., is decomposed, 
 giving off among other products a peculiar acrid substance 
 termed acroleine (C 3 H 4 O). This is the body which causes 
 the irritating fumes of a smouldering candle-wick and of 
 burning fats when the combustion is in complete. 
 
 524. Nitro-glycerine, C S H B (NO 3 ) 3 . When a mixture 
 of strong sulphuric and nitric acids acts on glycerine, at low 
 temperatures, a violently explosive, oily liquid of light- 
 yellow color is produced. This compound has a specific 
 gravity at 15 C. of 1.6, is inodorous, but has a sweet, 
 pungent, aromatic taste, and, placed upon the tongue, pro- 
 duces headache. Nitro-glycerine is exploded not by the 
 direct application of heat, but by sudden concussion, and 
 proper care in its preparation greatly lessens the danger 
 accompanying its use. 
 
 3. Saccharine Bodies. 
 
 525. Saccharine bodies, sometimes called carbo-hy- 
 drates, constitute an important class of substances, inter- 
 esting on account of their wide distribution in the vege- 
 table world. Among these substances we have the sugars 
 proper, grape-sugar, gum, starch, and woody fibre. These 
 are probably related to the alcohols, though their exact 
 composition has not in all cases been ascertained. Two 
 
SACCHARINE BODIES. 297 
 
 of these compounds, grape and fruit sugar, break up into 
 alcohol and carbonic dioxide under the influence of yeast. 
 Dextrose, or grape-sugar, C 6 H 12 O e , is widely distributed 
 in all ripe fruits, and may be prepared by boiling starch in 
 dilute sulphuric acid. Isomeric with this compound is 
 Icevulose, or fruit-sugar, which occurs mixed with other 
 varieties of sugar in the juices of ripe fruit, honey, etc. 
 Both of these compounds belong to the group of glucoses. 
 
 526. Cane-Sugar, C ia H M O n , is produced chiefly from 
 the cane, beet-root, sorghum, and the palm and maple 
 trees; but by far the largest portion is from the sugar- 
 cane. The canes are crushed by passing them between 
 grooved iron cylinders. The juice, when first expressed, 
 is liable to rapid decomposition from the heat of the cli- 
 mate. This is prevented by the addition of a small quan- 
 tity of lime, which neutralizes acids and coagulates impu- 
 rities. The juice is evaporated by boiling in large, open 
 vessels, and, when reduced to a proper consistency, is trans- 
 ferred to coolers, where a portion of it crystallizes, forming 
 raw or brown sugar. On an average, a gallon of juice 
 produces a pound of sugar. 
 
 Crude sugars are purified, or refined, by reducing them 
 to a sirup, which is first filtered through twilled cotton, to 
 separate mechanical impurities. The same effect is further 
 promoted by the use of serum of blood. To decolorize the 
 sirup it is again filtered through a bed of coarsely-pow- 
 dered bone-black or animal charcoal. It is then evaporated 
 in vacuum-pans the air being exhausted, so that it will 
 boil at a lower temperature and finally recrystallized. 
 The drainage of the raw sugar forms molasses. 
 
 527. Properties. Pure cane-sugar has a specific gravity 
 of 1.6, is soluble in about one-third of its weight of cold 
 water, forming a thick sirup, and separates from concen- 
 trated solutions in large, transparent, colorless crystals, 
 having the shape of oblique rhombic prisms or modified 
 forms. It melts at about 320C., and solidifies, on cooling, 
 
298 DESCRIPTIVE CHEMISTRY. 
 
 to a transparent, amber-colored substance, known as bar- 
 ley-sugar. If the melted sugar be heated to 420C., it 
 changes to a dark-brown mixture of several different bodies, 
 which is termed caramel, and is much used for coloring 
 sirups and liquors. 
 
 528. Lactose (Milk-Sugar), C If H M O n + H a O, is ob- 
 tained only from the milk of the mammalia, to which it 
 gives the sweetish taste. It is obtained by evaporating 
 clarified whey till it crystallizes. It is much less soluble, 
 and therefore much less sweet, than cane-sugar, and its 
 crystals are hard and gritty. It is much used in the prep- 
 aration of homoeopathic medicines. 
 
 529. Gum, C 19 H M O n (Arabin). These terms are ap- 
 plied to a class of substances which are often seen exud- 
 ing in globular masses from the bark of trees, as the plum 
 and cherry. Gum is translucent, tasteless, inodorous, and 
 either dissolves in water, cr swells up and forms with it a 
 thick mucilage. It exists in small proportion in the cereal 
 grains, but its chief source is certain tropical trees, from 
 the bark of which it flows in such quantity as to be gath- 
 ered for commercial purposes. Gum-arabic, the product ol 
 a species of acacia, is a hard, brittle substance, and is, per- 
 haps, the best known of the gums. Its solution being 
 very adhesive, is used as a substitute for paste or glue. 
 Mucilage or bassorin is a kind of gum insoluble in water, 
 but which swells into a gelatinous mass when moistened. 
 It abounds in gum-tragacanth, and also in quince-seeds 
 and linseed. Pectin, or the jelly of fruits, is in its physi- 
 cal properties closely allied to the gums, but its exact 
 chemical composition has not yet been established with 
 certainty. 
 
 Balsams are complex substances which exude from the 
 bark of certain trees ; they consist for the most part of an 
 essential oil which holds in solution peculiar substances 
 known as resins. Gum-copal, mastic, and shellac, belong 
 to this class ; they are insoluble in water, but dissolve in 
 
SACCHARINE BODIES. 
 
 299 
 
 FIG 195. 
 
 alcohol, naphtha, and oil of turpentine. The solutions 
 thus formed constitute varnishes. 
 
 Caoutchouc, or India-rubber, is a compound of hydrogen 
 and carbon, of great value to the chemist. It is the hard- 
 ened juice of several tropical trees, and when pure is 
 white. Combined with sulphur in variable proportions it 
 forms the vulcanized caoutchouc or vulcanite of commerce. 
 
 530. Starch, C 6 H 10 O a .- 
 This substance is found univer- 
 sally distributed in the vegeta- 
 ble kingdom in grains, seeds, 
 roots, and the pith and bark of 
 plants. When pure it is a snow- 
 white, glistening powder. Ex- 
 amined by the microscope, it is 
 found to consist of exceedingly 
 minute round or oval grains, 
 which vary in size from YJ-g- to 
 T _^_ J . of an inch in diameter. 
 The starch-granules of potatoes 
 are much larger than those of 
 wheat or rice. Starch-grains 
 from different sources vary also 
 in form and structure. Those 
 of the potato are egg-shaped ; 
 those of wheat are lens-shaped ; 
 those of rice angular ; while 
 several kinds have a grooved 
 aspect, and consist of concen- 
 tric layers, like the coats of an 
 onion. As each variety has some 
 peculiarity by which it may be 
 identified, the adulteration of 
 wheat-flour by potato, or other 
 starches, may thus be detected. 
 
 531. Properties and Uses, Starch is insoluble in cold 
 
 Starch-Grains of Potatoes. 
 FIG. 196. 
 
 Ctarch-Grains of Plantain. 
 
 FIG. 19T 
 
 * 
 
 Starch-Grains of Rice 
 
300 DESCRIPTIVE CHEMISTRY. 
 
 water, alcohol, and ether, but swells up and is converted 
 into a paste in water containing 2 per cent, of alkali. If 
 heated in water to 140 F., the grains swell and burst, pro- 
 ducing a jelly-like mass (gelatinous starch, or amadin), 
 which is used to impart a gloss to textile fabrics. The 
 test of starch is iodine, which combines with it, forming a 
 blue compound. The uses of starch are varied ; the most im- 
 portant, however, is that of nutrition, the comparative value 
 of different articles of vegetable diet depending largely on 
 the proportion of this proximate principle which they con- 
 tain. When vegetable food is prepared for the table by 
 the various processes of cooking, the starch is slightly 
 modified. 
 
 532. Dextrine. When commercial starch is heated un- 
 der pressure to 400 F. for some hours, it becomes soluble 
 in cold water, and is changed into a gurnmy substance 
 called dextrine, which, under the name of British gum, has 
 been successfully substituted for gum-arabic by calico- 
 printers in thickening their colors. Dextrine is also pro- 
 duced when starch-paste is boiled for a few minutes with 
 weak sulphuric acid. It is a transparent, brittle solid, iso- 
 meric with starch, soluble in water, incapable of fermenta- 
 tion, and produces right-handed rotation in a ray of polar- 
 ized light; hence its name. When solutions of dextrine 
 are boiled with dilute acids for some hours, the dextrine is 
 converted into glucose. Dextrine is also formed from 
 starch, by the action of animal secretions such as saliva, 
 bile, and pancreatic juice. 
 
 Glycogen, C 6 H 10 O 5 , was first obtained by Bernard from 
 the livers of animals. It is a white, amorphous, starch-like 
 substance, odorless and tasteless, and is converted into 
 glucose by boiling with dilute acids, or by contact with 
 blood, saliva, or pancreatic juice. 
 
 Inulin is a substance obtained from the roots of many 
 plants, among which are the dahlia, dandelion, and chiccory. 
 It has the same composition as common starch, but differs 
 
SACCHARINE BODIES. 301 
 
 from it in some important particulars. Inulin may be ob- 
 tained by washing the rasped roots on a sieve, when it will 
 settle to the bottom of the liquid. It is a white, tasteless 
 substance, which is not soluble in cold water, but freely 
 dissolves by the aid of heat. It exists in the plant in a 
 liquid form, and is converted by the action of dilute acids 
 into laevulose. Iodine does not turn inulin blue. 
 
 533. Cellulose, C 18 H 30 O 1B ( Woody Fibre, Lignine).^^ 
 is the most abundant product of vegetation. Besides form- 
 ing the chief bulk of all trees, it exists in the straw and 
 stalks of grain, in the membrane which envelops the kernel 
 (bran), in the husk and skin of seeds, and in the rinds, 
 cores, and stones of fruit. Wood consists of slender fibres, 
 or tubes closely packed together. When first formed these 
 tubes are hollow and serve to convey the sap, but in the 
 heart- wood of trees they become filled up and consolidated, 
 the circulation of fluids taking place in the white external 
 sap-wood (alburnum). Upon the density with which the 
 fibres are imbedded depends the property of hardness or 
 softness of wood. Cellulose is the fibrous portion of the 
 woody tissue. 
 
 534. Properties and Uses. The properties of cellulose 
 may be conveniently studied in fine linen and cotton, which 
 are almost entirely composed of it. When pure it is taste- 
 less, insoluble in water and alcohol, and not sensibly af- 
 fected by boiling water. By cold concentrated sulphuric 
 acid, it is converted into dextrine. The uses of cellulose 
 are almost numberless. It forms the chief bulk of the 
 wood we burn, of the linen and cotton fabrics we wear, and 
 of the paper we write and print upon. Besides these uses 
 of unaltered cellulose, a multitude of useful chemical bodies 
 are derived from its decomposition ; charcoal, illuminating 
 gas, tar, wood-spirit, wood-vinegar, creosote, and oxalic 
 acid, being among the most important. Grape-sugar and 
 alcohol have also been made from it. 
 
 535. Pyroxylene. If pure cellulose (C 18 H 30 O 15 ), as cot- 
 
302 DESCRIPTIVE CHEMISTRY. 
 
 ton, linen, sawdust, or paper, be steeped for a few minutes 
 in a mixture of nitric and sulphuric acids, then squeezed, 
 washed, and dried by gentle heat, a part of the hydrogen 
 of the cellulose is oxidized by the action of the nitric acid, 
 and eliminated as water, while its place in the compound is 
 occupied by a corresponding quantity of the radicle nitryl 
 (NO ). This quantity is greater in proportion to the con- 
 centration of the acid. When a mixture of concentrated 
 sulphuric acid with nitric acid of 1.52 specific gravity is 
 used, pyroxyline, C 18 H Q1 (N 2 O 2 ) 9 O 1B , a highly-explosive com- 
 pound, is produced, which constitutes the well-known gun- 
 cotton, discovered a few years ago by Prof. Sch5nbein. It 
 ignites at 400 F. (200 below gunpowder), and disappears 
 in an instantaneous flash, leaving- hardly a trace of residue. 
 Authorities vary in estimating its explosive force, but the 
 latest make it about three times that of gunpowder. The 
 extreme suddenness of the propulsive force overstrains the 
 gun and produces less effect upon the ball than gunpowder. 
 Collodion is formed by dissolving gun-cotton in ether, 
 containing a small proportion of alcohol. On evaporating 
 the ether, a transparent, adhesive film is left, which is in- 
 soluble in water and is used in surgery for protecting 
 wounds from the air. The chief use of collodion, however, 
 is in photography. 
 
 4. Fermentation. 
 
 536. When certain compound substances, derived chief- 
 ly from plants and animals, are exposed to the action of air 
 and water, at a given temperature, they undergo decompo- 
 sition, which, when involving the formation of useful prod- 
 ucts, is generally known as fermentation, but when result- 
 ing in the production of useless and ill-flavored bodies is 
 distinguished as putrefaction. These changes all agree in 
 having a peculiar self-sustaining and contagion-like charac- 
 ter. The true nature of these processes is not yet thor- 
 oughly understood. But careful investigation has shown. 
 
FERMENTATION. 303 
 
 that, in by far the largest number of cases, we may recog- 
 nize the presence of living organisms. The exciting cause 
 of fermentation has been sought in the oxygen of the air, 
 but it appears from recent experiments that air which has 
 been passed through a red-hot tube does not induce fer- 
 mentation even in those bodies which are most liable to 
 this change. It has been proved, however, that ordinary 
 air contains the germs of microscopic plants and animals, 
 and it seems almost certain that the excitation of the pro- 
 cesses in question is due to their action. 
 
 537. Ferments and Fermentable Bodies. The sub- 
 stances most disposed to putrefaction are certain compounds 
 rich in nitrogen, contained largely in flesh, blood, cheese, 
 milk, white of egg, gelatine, and other animal products. 
 These bodies require only the presence of water, and free 
 access of air at the commencement, to induce in them a 
 process of decomposition. Of those compounds which con- 
 tain no nitrogen there are but few, as for example sugar, 
 gum, and starch, that may be brought into a state of fer- 
 mentation by mere contact with air and water. But many 
 substances, incapable of fermenting by themselves, undergo 
 that change when brought in contact with a minute quan- 
 tity of the above-mentioned nitrogenous bodies. The lat- 
 ter are, for this reason, termed ferments, the former fer- 
 mentable bodies. 
 
 As a spark may kindle a conflagration that shall con- 
 sume a city, so the minutest quantity of fermenting or pu- 
 trescent matter is often sufficient to affect an indefinite 
 quantity of changeable substance. The remarkable com- 
 municability of these effects is well observed in the action 
 of leaven upon dough. It is also painfully illustrated by 
 physicians, who sometimes wound themselves while dissect- 
 ing. The small trace of decomposing matter from the dead 
 body which clings to the dissecting-knife is sufficient to 
 establish a rapid decomposition in the living system, which, 
 in many cases, quickly terminates in death. 
 
304 DESCRIPTIVE CHEMISTRY. 
 
 The part played by yeast, and the nature of vinous fer- 
 mentation, has been a matter of much speculation. Yeast 
 consists of round or egg-shaped cells about T oVg- f a m ^~ 
 lirnetre in diameter ; these consist of an outer wall of cellu- 
 lose, inclosing a liquid. The yeast-cells grow and multiply 
 in a fermenting liquid, but the presence of nitrogen, phos- 
 phorus, sulphur, potassium, and magnesium, in combined 
 form, seems to be necessary to their growth. Several dif- 
 ferent kinds or modes of fermentation have been observed, 
 varying in the character of the products formed. The pro- 
 cesses are, moreover, very much modified by temperature 
 and other atmospheric conditions. The modes of fermen- 
 tation best known are the vinous, acetous, lactous, and sac- 
 charous. 
 
 538. Vinous Fermentation. When the sweet juice of 
 fruits or plants is exposed to the air at the temperature of 
 70 or 80 F., in the course of a few hours a change com- 
 mences : small bubbles consisting of carbonic dioxide rise 
 to the surface, the liquid becomes turbid, and begins to 
 ferment, or, as is commonly said, to " work" After a time 
 the bubbles cease to rise and the liquid is no longer sweet, 
 but has acquired a spiritous taste. If, now, it be distilled, 
 an inflammable body is separated, which is known as spirits 
 of wine, or alcohol, a product of the decomposition of 
 sugar. Besides the alcohol the fermented liquid generallv 
 contains two other bodies, known respectively as glycerine 
 and succinic acid. Other compounds are also in some in- 
 stances produced. 
 
 539. Saecharous Fermentation. But sugar itself may 
 be a product of fermentation. When seeds are exposed 
 to air and moisture at a suitable temperature, germina- 
 tion commences. This consists in a series of changes, of 
 which the first is an alteration of a portion of the nitro- 
 genous matter and the production of a compound not well 
 understood, called diastase. This is an active ferment, and, 
 taking effect upon the starch, changes it to sugar and dex- 
 
ETHERS AND ALDEHYDES. 305 
 
 trine. When barley is treated in this way it swells and 
 becomes sweet. Diastase is formed, and the barley is 
 termed malt. When the germ is about half an inch long 
 the process is arrested by heat, but the dextrine is not 
 destroyed. 
 
 540. Acetous Fermentation. If the vinous fermenta- 
 tion is not checked at the proper time, it passes on to a 
 second stage, the acetous fermentation ; the liquid loses its 
 spirit and quality, and becomes sour. Oxygen is absorbed, 
 and the alcohol converted into vinegar or acetic acid, 
 C,H 4 O 9 . Pure diluted alcohol does not absorb oxygen 
 when exposed to the atmosphere ; it is affected only by 
 adding some matter in a state of change, or which absorbs 
 oxygen. The action proceeds slowly at first, but by de- 
 grees a peculiar body, a kind of slimy vegetable mould, is 
 formed, which is known as mother of vinegar, and which 
 acts something like a ferment to hasten the process. It is 
 supposed that this acetous ferment acts as a carrier of 
 atmospheric oxygen, which it absorbs within its pores, 
 thus bringing it into intimate contact with the alcohol. In 
 this respect the action of the ferment is like that of plati- 
 num, which causes the union of oxygen and hydrogen, 
 when these gases are condensed within its pores. 
 
 5. Ethers and Aldehydes. 
 
 541. The ethers may be regarded as oxides of the alco- 
 hol radicles, and they bear the same relation to the alcohols 
 that metallic oxides bear to the metallic hydrates, thus : 
 
 C.H. 
 
 a i 
 
 c, c CH 
 
 Ethylic Oxide. Ethylic Hydrate. 
 
 (Ethylic Ether.) (Ethylic Alcohol.) 
 
 Ethylic Ether, C 4 H 10 O (Sidphuric Ether). When equal 
 weights of strong sulphuric acid and alcohol are heated in 
 a retort, a yapor passes over which may be condensed into 
 
306 
 
 DESCRIPTIVE CHEMISTRY. 
 
 a limpid fluid, called ether from its volatility, and sulphuric 
 ether, because in obtaining it sulphuric acid is employed. 
 Ether is colorless, with a fragrant odor, a hot, pungent 
 taste, and, when inhaled, produces insensibility to pain ; 
 hence it is much used as an anaesthetic. It is so vola- 
 tile that it disappears when poured through the air from 
 one vessel to another, and, when placed upon the hand, 
 produces cold by rapid evaporation. It boils at 96 Fahr., 
 or when exposed to the air in summer, and is very com- 
 bustible, burning with more light than alcohol and some 
 smoke. Its vapor, when mixed with air, is explosive. It 
 readily dissolves fats and oils. 
 
 542. Aldehydes. The aldehydes are a class of com- 
 pounds intermediate between acids and alcohols, and they 
 are produced by the oxidation of the latter. Example, 
 acetic aldehyde : 
 
 HO 
 H-C-C 
 
 FIG. 198. 
 
 Acetic aldehyde, C 3 H 4 O, the best known 
 compound of this series, may be produced by 
 the gradual oxidation, in various ways, of or- 
 dinary alcohol, or by transmitting a mixture 
 of alcohol and air through a porcelain tube 
 at a low red heat. When a few drops of al- 
 cohol are placed in a cup, its vapor will 
 mingle with the air. If, now, a red-hot coil 
 of platinum wire be introduced into the cup, 
 Fig. 198, the oxidation of the vapor com- 
 mences, pungent odors of acetic aldehyde are 
 given off, and the wire is kept at a red heat by the con- 
 tinued oxidation. If the coil be suspended over the wick 
 of an alcohol or ether lamp, Fig. 199, it will continue to 
 glow for hours after the flame is extinguished, from the 
 
ETHERS AND ALDEHYDES. 307 
 
 same cause. Acetic aldehyde is a highly- FlG - 199 - 
 volatile, inflammable liquid, with a pungent, 
 apple-like odor. 
 
 543. Camphor, C 10 H 16 O. This well-known 
 substance has the composition of an aldehyde, 
 but its reactions are different from .the other 
 aldehydes. It is obtained by distilling the 
 wood of the camphor- tree (found in Japan 
 and other parts of the East) with water, and 
 collecting the vapors in a vessel containing rice-straw. 
 It condenses in the straw and is again sublimed, after 
 which it is thrown into commerce ; but it requires subse- 
 quent purifications to fit it for use. Camphor is quite vola- 
 tile and readily soluble in alcohol, with which it forms a 
 solution known as spirits of camphor. Taken in large 
 doses it acts as a poison. 
 
 544. Chloral, C,HC1 3 O. By replacing a single atom of 
 the hydrogen in the formula of aldehyde, by chlorine, the 
 formula for a compound known as chloral is obtained. It 
 is formed by the action of pure and dry chlorine gas on 
 absolute alcohol. It is a thin, colorless oil, which boils at 
 about 96 C. It has a peculiar, pungent odor, and excites 
 a copious flow of tears. Its taste is greasy, and slightly 
 astringent. The vapor acts powerfully upon the skin. 
 Mixed with a small quantity of water it becomes heated 
 and solidifies to a white crystalline mass, chloral hydrate, 
 which is soluble in a large quantity of water, volatilizes 
 gradually in the air, and may be distilled without decom- 
 position. It has been recentty introduced into medicine, 
 as a means of producing sleep. 
 
 545. Chloroform, CHC1 3 , is prepared by distilling alco- 
 hol with a solution of chloride of lime. It is a colorless, 
 volatile liquid, of a strong, agreeable odor, and a sweet, 
 penetrating taste. It dissolves sparingly in water, but 
 freely in alcohol and ether. It is extensively employed in 
 medicine, but for this purpose it should be perfectly pure, 
 
308 DESCRIPTIVE CHEMISTRY. 
 
 as the fatal effects which have sometimes attended its use 
 are doubtless chiefly owing to its contaminations. It 
 should be colorless acd free from a chlorous smell, or any 
 unpleasant odor, when a few drops are evaporated on the 
 hand. 
 
 Chloroform is one of the most important representatives 
 of a class of bodies, the vapor of which when inhaled pro- 
 duces temporary insensibility to pain, or ancesthesia / these 
 substances are known as anaesthetics. 
 
 CHAPTER XXVI. 
 
 ORGANIC CHEMISTRY (CONTINUED). 
 
 1. Acids. 
 
 546. A LARGE number of organic acids are known, some 
 of which exist in a free state, as, for example, formic acid, 
 which is secreted by ants and 'is found in nettles. These 
 compounds constitute several series, which are all regard- 
 ed as derived more or less directly from the hydrocarbons. 
 Formic acid, CH 2 O a , is a clear, pungent, volatile, strongly 
 acid liquid, which was first obtained by distilling the bod' 
 ies of red ants (Formica rubra) in water, hence its name 
 formic acid. It is also found in human blood, urine, and 
 other secretions, in the juices of many plants, and in the 
 waters of certain mineral springs. 
 
 547. Acetic Acid, C 2 H 4 O 2 . This acid is one of the most 
 important organic compounds. /It is the essential constitu- 
 ent of vinegar, which is merely ashore or less impure solution 
 of acetic acid, common table-vijfegar containing from three 
 to four per cent. Pure acetic swid is, at ordinary tempera- 
 tures, a colorless, intensely souifc liquid, having a pungent 
 odor, and capable of raising a brfeter on the skin. It solidi- 
 
ACIDS. 309 
 
 fies at or below 17 C. to a crystalline, ice-like body, known 
 as " glacial acetic acid," and boils at about 119 C. Vine 
 gar is usually obtained by the spontaneous oxidation of 
 dilute alcoholic liquors, saccharine solutions, etc. If, in 
 the process of its manufacture, the air comes in contact 
 with only a small portion of the liquid, months may be re- 
 quired to produce the change. Wdod-vinegar, or pyrolig- 
 neous acid, is obtained by the destructive distillation of 
 wood, dry beech-wood being the best, a pound yielding 
 nearly half a pound of the acid. It is a brown liquid, with 
 a strong smoky taste and odor. It is extensively used to 
 form salts the acetates used by dyers. 
 
 548. Butyric Acid, C 4 H 8 O 2 , is prepared by allowing a 
 mixture of sugar, chalk, and cheese, to ferment. It is 
 found in small quantity in butter, in perspiration, in some 
 plants, and in the juice of human flesh. It resembles 
 acetic acid in appearance, has a peculiar rancid odor, and 
 is soluble in water. 
 
 Glycocholic Acid, C a H 4 O 3 , constitutes the great mass 
 of the resinous matter of ox-bile; it forms silky white, 
 needle-shaped crystals, of a bitter-sweet taste, which are 
 soluble in water and alcohol, and have an acid reaction. 
 
 549. Lactic Acid, C 8 H fl O 3 . This acid is so called be- 
 cause it occurs in sour milk. It is formed from sugar by 
 lactic fermentation, and is a colorless, sirupy, very acid 
 liquid. Succinic acid, C 4 H 6 O 4 , is also one of the products 
 of the fermentation of sugar (538), and is obtained by the 
 distillation of amber. It occurs in certain resins, in worm- 
 wood, and in small quantities in animal juices. Inti- 
 mately connected with this Jacid are two of much impor- 
 tance, viz., malic acid, C 4 HA 6 , and tartar ic acid, C 4 H e O 6 . 
 The former is found in mai acid fruits and in the stalks 
 of rhubarb, but is usually (ained from the unripe berries 
 of the mountain-ash. ItS a colorless solid, dissolves 
 readily in water and alcohoind crystallizes with difficulty. 
 The solutions of all the Jjfas named have an agreeable 
 
310 DESCRIPTIVE CHEMISTRY. 
 
 acid taste, but become mouldy if long kept, and gradually 
 undergo decomposition. 
 
 Tartaric acid is found abundantly in the juices of many 
 fruits. It is obtained by the decomposition of calcic tar- 
 trate with sulphuric acid. Its crystals, when pure, are 
 colorless, transparent, permanent in the air, and dissolve 
 readily in water or alcohol. It is extensively used by the 
 calico-printer and dyer for the removal of mordants. 
 Mixed with the bicarbonates of the alkalies, it forms the 
 soda-powders of effervescing draughts. 
 
 550. Benzoic Acid, C 7 H 6 O 2 , obtained exclusively at one 
 time from gum-benzoin, is now procured from hippuric 
 acid, which occurs in the urine of herbivorous animals. 
 
 551. Salicylic Acid, C 6 H 4 OH CO 2 H, is one of the deriva- 
 tives of salicine, which is a neutral vegetable principle, 
 discovered in 1830 in the bark of the willow, Salix, whence 
 its name. The acid was early obtained from the flowers 
 of the meadow-sweet (Spirea ulmarid), and it occurs in 
 the oil of winter-green. It is now regarded with great 
 interest, on account of its valuable qualities as an anti- 
 ferment and antiseptic. As its practical value became 
 known, the sources from which it had been obtained were 
 found utterly inadequate to the increased demand; and 
 the reconstructive power of the modern chemist sought 
 for a compound, which might be split up, or reorganized 
 in such a way as to yield the desired salicylic acid. The 
 German chemists found this in phenol or carbolic acid, a 
 substance long known for its valuable qualities as an anti- 
 ferment. The agent selected to reconstruct the molecule 
 of phenol was carbonic dioxidl The pure acid is obtaii 
 
 in minute acicular crystals, white, odorless, and nej 
 tasteless ; insoluble in cold Biter, more soluble in hot 
 water, and in still greater dee soluble in alcohol and 
 ether. It melts at about 25 F. It is used in medicine 
 and in surgical operations, wh^fc it is said to be more effec- 
 tive in smaller quantities thanBiy other antiseptic, and to 
 
ACIDS. 311 
 
 be devoid of all irritating action upon the living tissues. 
 Tn cases of decomposition which cannot be reached by any 
 other antiseptic, salicylic acid is claimed to be especially 
 valuable. 
 
 552. Citric Acid, C 6 H 8 O 7 , is found principally in fruits 
 of the orange family, but is of frequent occurrence in goose- 
 berries, currants, and other acid fruits. It may be readily 
 procured from the juice of the lemon by the aid of chalk 
 and sulphuric acid. It has a pleasant acid taste, is very 
 soluble in water, and is used in medicine, calico-printing, 
 and for effervescing draughts. Gallic acid, C 7 H,O 6 , oc- 
 curs in sumach, acorns, tea, and many plants. It crystal- 
 lizes in silky needles, is freely soluble in boiling water, and 
 does not precipitate gelatine. Heated to about 215 C., 
 gallic acid is decomposed into carbonic dioxide and pyro- 
 gallol, C 6 H 6 O 3 . This acid is extensively used in photog- 
 raphy. Both gallic acid and pyrogallol decompose the 
 salts of silver, gold, and platinum ; hence they are exten- 
 sively employed in photography, and in the manufacture 
 of hair-dves. 
 
 553. Tannins (Tannic Acids). There are several dis- 
 tinct compounds known under the Dame tannin, which 
 resemble each other in character and possess an acid reac- 
 tion. They are found extensively diffused throughout the 
 vegetable kingdom, and are all distinguished by an astrin- 
 gent taste. The bark and leaves of most forest-trees, as 
 well as of many fruit-trees, contain a large quantity of 
 tannin ; it, is found in various roots, shrubs, and seeds, and 
 is the astringent principle of tea and coffee. The most 
 important of these compounds, obtained from gall-nuts, 
 is generally known as gallotannic acid, C 27 H 22 O 17 . It 
 has an intensely astringent taste, reddens litmus-paper, 
 and is very soluble in water. When a solution of gal- 
 lotannic acid is mixed with a solution of a ferric com- 
 pound, it produces a deep bluish-black precipitate, which 
 is the basis of writing-ink. The gradual darkening of pale, 
 
 14 
 
312 DESCRIPTIVE CHEMISTRY. 
 
 watery ink is due to the oxidation of the iron it contains. 
 Tannins form insoluble compounds with starch, gelatine, 
 and other organic bodies, the most remarkable being those 
 with gelatine, which form the basis of leather. 
 
 554. Oxalic Acid, C 2 H 2 O 4 , is met with in the juice of 
 the sorrel, rhubarb, and many plants, sometimes in the free 
 state, but more frequently in the compound known as calcic 
 oxalate. It is commonly prepared by the oxidation of sugar 
 or starch with nitric acid : one part of sugar is dissolved in 
 eight parts of nitric acid, and gently heated, when intense 
 action ensues, with a copious disengagement of nitrous acid 
 fumes. By evaporating the solution, oxalic acid may be ob- 
 tained in large, transparent, and intensely sour crystals. 
 Oxalic acid is poisonous, and its crystals resemble those 
 of Epsom salts, for which it is sometimes mistaken. In 
 cases of poisoning with it, chalk or magnesia, mixed in 
 water, is the proper antidote. Oxalic acid is largely used 
 in calico-printing ; it is also employed as a delicate test 
 for the presence of lime, with which it forms an insoluble 
 salt. It removes ink and iron stains from linen by forming 
 a soluble oxalate of iron, but the acid is so corrosive as to 
 injure the fibre if not immediately removed by washing. 
 
 555. Alkaline Organic Salts. The compounds of this 
 group are derived from the organic acids by the substitu- 
 tion of a radicle of the Lithium group for the basic hydro- 
 gen of the acid. The most important salt of the acid series 
 is hydro-potassic tartrate (cream of tartar), (HK), (C 4 H 4 O 4 ) 
 O 3 . It is deposited in an impure state from wine consti- 
 tuting the tartar or argol of commerce. When purified by 
 recrystallization, it forms a white crystalline powder, or 
 larger crystals, soluble with difficulty in cold water, more 
 readily in hot water, and possessing a pleasant sour taste. 
 Among the salts of the neutral series, sodio-potassic tartrate 
 (Rochelle salts), (NaK) (C 4 H 4 O 4 ) O a + 4 H 2 O, deserves spe- 
 cial notice. It is obtained in beautiful large crystals, per- 
 fectly colorless when pure, of mild saline taste, by crystal- 
 
ORGANIC ALKALOIDS. 313 
 
 lizing mixed solutions of argol and soda-ash. It is largely 
 used in medicine, forming the chief constituent of Seidlitz 
 powders. 
 
 2. Organic Alkaloids. 
 
 556. The term alkaloid has been applied to a large 
 number of bodies having the general constitution of amines. 
 They contain carbon, oxygen, hydrogen, and nitrogen, and 
 act as bases. Many compounds analogous to these have 
 been artificially prepared, but the vegetable alkaloids have 
 as yet defied the constructive power of the chemist. They 
 include some of our most violent poisons, and act power- 
 fully on the animal economy. Most of the alkaloids dis- 
 solve sparingly in water, but freely in boiling alcohol ; are 
 intensely bitter, and usually restore the reddened color of 
 litmus. They are the most powerful medicines and poi- 
 sons known. Gallotannic acid precipitates most of the 
 organic bases, forming, with them, insoluble compounds ; 
 hence it is an excellent antidote when they have been 
 taken in poisonous doses. We shall notice only the more 
 important alkaloids found in vegetable substances. 
 
 557. Nicotine, C 10 H 14 N 9 . This compound is of inter- 
 est, as the chief alkaloid contained in the smoke of tobacco, 
 and, in fact, is the proximate cause of the narcotic effects 
 produced by the use of that plant, which contains it in 
 quantities varying from two to eight per cent. It is a 
 colorless, transparent oil, which boils at 250 C., giving 
 off very irritating vapors. It is soluble in water, alcohol, 
 and oils. It has a burning taste, even when much diluted, 
 and is one of the most violent poisons known. The effect 
 is said to be produced upon the motor nerves, producing 
 convulsions, and afterward paralysis. Five milligrammes 
 has been found sufficient to kill a medium-sized dog in 
 three minutes. 
 
 558. Morphine, C 17 H 19 O 3 N. This is the chief active prin- 
 ciple of opium, which is the hardened, milky juice of the 
 
314 DESCRIPTIVE CHEMISTRY. 
 
 poppy. Opium is a very complex body, containing, besides 
 morphine, a large number of other alkaloids. Morphine 
 (from Morpheus, in consequence of its sleep-inducing prop- 
 erty) is a crystallizable, resin-like body, without odor, and 
 possessing a bitter, disagreeable taste. It is a powerful nar- 
 cotic and poison, and, in the form of the acetate, sulphate, 
 and hydrochlorate, is largely used in medicine. Piperine, 
 C 17 H 19 NO 3 , is a substance isomeric with morphine, found in 
 common black and white pepper. It is nearly insoluble in 
 cold water, has an acrid taste, and, when acted upon by 
 nitric acid, develops an odor of bitter-almonds. Capsicine 
 is an alkaloid obtained from Cayenne pepper. It forms 
 crystallizable salts, with acetic, nitric, and sulphuric acids. 
 
 559. Strychnine, C 21 H 22 O 2 N 2 , is chiefly obtained from the 
 beans of the strychnos nux-vomica, a small East India 
 tree, but is found in several other plants belonging to that 
 tribe. Cold water dissolves only ^-^QQ of its weight of 
 strychnine, but it is more readily soluble in essential oils 
 and chloroform. From its solutions it crystallizes in small 
 brilliant octahedrons, of exceedingly bitter taste. Such is 
 its intense bitterness, that it imparts it perceptibly to 700,- 
 000 times its weight of water. It is a deadly poison, ^ of 
 a grain killing a dog in thirty seconds. It takes effect upon 
 the nerve-centres of the spinal axis, producing fearful con- 
 vulsions. The terrible woorara poison, with which the 
 South American natives poison their arrows, and which has 
 been lately used as a remedy for tetanus, appears to con- 
 tain a principle nearly allied if not identical with strych- 
 nine. Jlracine is an alkaloid closely allied to strychnine, 
 and obtained from the same genus of plants. 
 
 560. Quinine, C 90 H Q4 O 3 N 2 , is extracted from pulverized 
 Peruvian bark by acidulated water. It is a white, crystal- 
 line substance, which unites with acids, producing intensely 
 bitter salts. Quinine sulphate, which forms light, bulky 
 crystals, is the salt employed in medicine. It dissolves 
 sparingly in water, but freely in dilute sulphuric acid and 
 
ALBUMINOUS SUBSTANCES. 315 
 
 alcohol. Cinchonine is another alkaloid from the same 
 source. 
 
 561. Caffeine Series. Two terms of this series are known. 
 Tkeobromine, C 7 H 8 O 2 N 4 , is a crystalline alkaloid, obtained 
 from cacao-beans, the source of chocolate. Caffeine or 
 theine, C 8 H 10 O 2 N 4 , is an alkaloid, which may be obtained 
 from coffee, tea, and several other plants, the stimulating 
 effects of which are in part due to the presence of caffeine 
 compounds. Coffee seldom contains more than one per 
 cent, cf the principle, while tea furnishes three or four. 
 Caffeine crystallizes in long, flexible, silky needles, has a 
 slightly bitter taste, and dissolves sparingly in cold water, 
 but freely in hot water. 
 
 The stimulating effects of coffee and tea are, however, 
 not due to the caffeine alone, but are modified by various 
 other ingredients. In tea, the alkaloid is associated prin- 
 cipally with tannin and an essential cil ; in coffee, with 
 empyreumatic and essential oils. 
 
 3. Albuminous Substances. 
 
 562. Under this head are classed a number of com- 
 pounds, some of which form essential portions of the 
 bodies of animals, and occur in certain parts of vegetables ; 
 while others, not properly albuminoids, are obtained, di- 
 rectly or indirectly, from the animal organism. The albu- 
 minoids possess constitutions very complicated, and our 
 knowledge of their chemical relations is limited. They do 
 not crystallize, but are found in amorphous, jelly-like form. 
 They contain, in addition to carbon, oxygen, hydrogen, 
 and nitrogen, small quantities of sulphur and phosphorus. 
 Strong mineral acids dissolve all of the albuminoids. 
 
 563. Albumen is the chief and characteristic constituent 
 of the serum of the blood, and of white of egg, and occurs 
 in all the fluids which supply nutritive material for the 
 renovation of the animal tissues. It forms about seven 
 
316 DESCRIPTIVE CHEMISTRY. 
 
 per cent, of blood, and twelve per cent, of the white of egg. 
 Albumen exists in two modifications the soluble form, 
 and the insoluble variety into which it may be brought by 
 the action of heat, as when white of egg is boiled. These 
 two modifications are identical in chemical composition, 
 and the difference is thought to be due to the presence of 
 certain mineral salts which are associated with the soluble 
 variety. A solution of albumen, heated to 72 C., is co- 
 agulated. 
 
 Vegetable albumer abounds in the juice of many soft, 
 succulent plants used for food ; it may be extracted from 
 potatoes by macerating the sliced tubers in cold water con- 
 taining a little sulphuric acid. 
 
 564. Musculine is the name given to the substance 
 which forms the basis of muscular tissue. This occurs in 
 FIG 20Q bundles, as shown in Fig. 
 
 200, the parallel fibres hav- 
 ing wrinkles or cross-mark- 
 ings. If a piece of lean 
 beef be washed in clean wa- 
 ter, its red color, which is 
 due to blood, ffraduallv dis- 
 
 Fibres of Lean Meat, magnified. . 
 
 appears, leaving a whitish 
 
 mass composed of musculine, and the areolar tissue which 
 binds the fibres of the muscle together. Like albumen, it is 
 capable of being converted into an insoluble body. Fibrine 
 is a constituent of blood, forming in the healthy state about 
 two parts in 1 ,000 parts of that liquid. The clotting of blood, 
 when freshly drawn, is due to the coagulation of its fibrine, 
 which solidifies into a net-work of fibres. Dilute solutions 
 of potash and soda dissolve fibrine, as they do albumen. 
 When wheat-flour is made into dough, and then kneaded 
 on a sieve, or a piece of muslin under a stream of water, 
 its starch is washed away, and there remains a gray, tough, 
 elastic substance, almost resembling animal skin in appear- 
 
ALBUMINOUS SUBSTANCES. 317 
 
 ance. When dried it has a glue-like aspect, and is there- 
 fore called gluten. The crude gluten thus prepared, when 
 freed from oil, albumen, etc., proves to be identical with 
 animal albumen. 
 
 The effect of boiling upon fibrine is to render it hard 
 and tough. Heat, a we have seen, converts soluble into 
 coagulated albumen which is insoluble in water, either hot 
 or cold. 
 
 565. Caseine is an essential constituent of milk, exist- 
 ing in it to the extent of about three per cent., and form- 
 ing its curd, or cheesy principle. In milk it is held in 
 solution by the presence of a small portion of free alkali, 
 and, when this is neutralized by an acid, the caseine is pre- 
 cipitated, or the milk curdles. By neutralizing the acid, 
 the caseine is redissolved. Almonds, peas, beans, and 
 many other seeds, contain an albuminoid closely resembling 
 caseine, sometimes known as legumine, or vegetable case- 
 ine. This is not coagulable by heat, but by alcohol and 
 acetic acid. The coagulated legumine resembles the curd 
 of milk. The Chinese make a cheese from peas, which 
 gradually acquires the smell and taste of milk-cheese. 
 
 Milk is a secretion of special interest from the circum- 
 stance that it constitutes the entire food of the young ani- 
 mal for some months, and consequently must contain all 
 the elements necessary for the rapid development of the 
 various tissues of the body. It has essentially the same 
 constituents in carnivorous animals that it has in the her- 
 bivorous, although the proportions are somewhat variable. 
 When examined under a microscope it is seen to consist 
 of a transparent fluid, in which float transparent globules 
 consisting of fat, surrounded by an envelope of albumen. 
 When milk is allowed to remain at rest for a few hours, at 
 the ordinary temperature of the air, the fat-globules rise 
 to the surface ; and, if the layer of cream thus formed be 
 removed and subjected to mechanical action, the albumi- 
 nous envelope is broken, and the globules of fat coalesce 
 
318 DESCRIVTIVE CHEMISTRY. 
 
 into a mass forming butter. Good milk, when perfectly 
 fresh, is always feebly alkaline ; when left to itself, how- 
 ever, it soon becomes sour, and is found to contain lactic 
 acid. The quantity and quality of milk vary. We give 
 below a statement of the composition of cow's-milk, from 
 an analysis made by Haidlen : 
 
 Water 873.00 
 
 Butter ...... 30.00 
 
 Caseine ..... 48.20 
 
 Milk-sugar . . . . .43.90 
 
 Calcic phosphate .... 2.31 
 
 Magne?ic phosphate .... 0.42 
 
 Iron phosphate .... 0.07 
 
 Potassic chloride .... 1.44 
 
 Sodic chloride .... 0.24 
 
 Soda combined with caseine . . 0.42 
 
 1000.00 
 
 566, Gelatine. Animal membranes, skin, tendons, and 
 even bones, dissolve in water at a high temperature, more 
 or less completely, but with very different degrees of facil- 
 ity, giving solutions which on cooling acquire a soft-solid, 
 tremulous consistence. The substance so produced is 
 called gelatine. It does not preexist in the animal system, 
 but is generated from the membranous tissue by the action 
 of hot water. Cut into slices and exposed to a current of 
 dry air, it shrinks much in volume, forming a transparent, 
 glassy, brittle mass soluble in hot water. The aqueous so- 
 lution is precipitated by alcohol, tannin-solution, and many 
 other substances. Gelatine is largely employed as an ar- 
 ticle of food, and in manufactures as " size " and " glue." 
 The cartilages of the joints, the cornea of the eye, and 
 the ribs, yield a gelatine, called, by way of distinction, 
 chondrine. 
 
 Chitine, C 9 H ]2 HO 6 , constitutes the skeletons of insects 
 and Crustacea. It is a white substance which retains the 
 
ALBUMINOUS SUBSTANCES. 319 
 
 form of the texture from which it is obtained ; the word 
 chitine means a mantle. 
 
 567. Urea, CH 4 ON 2 , is one of the chief solid constitu- 
 ents of urine, from which it may be obtained. It is also 
 produced by heating ammonic cyanate (H 4 N,CNO), with 
 which it is isomeric. Urea crystallizes in transparent 
 colorless prisms soluble in water and alcohol. It is in- 
 odorous, and has a cooling 1 , saline taste. By heat it is de- 
 composed into ammonia, amrnonic cyanate, and C3 r anuric 
 acid. This compound is of special interest as the first or- 
 ganic compound artificially produced. 
 
 568. Creatine, C 4 H n O 4 N s . Creatine occurs in the juice 
 of flesh. When pure, it forms colorless brilliant prismatic 
 crystals, readily soluble in hot water. The aqueous solu- 
 tion has a slightly bitter and acrid taste, and a neutral re- 
 action. It forms no salts with acids. By the action of 
 strong acids, it is converted into creatinine. 
 
 569. Pepsine, is a nitrogenous substance contained in the 
 gastric juice, and has never been perfectly isolated. It is the 
 active agent concerned in digestion. An artificial gastric 
 juice which acts upon albuminoid substances is obtained 
 by digesting the mucous membrane of the stomach (usually 
 of a pig) with a warm, dilute solution of hydric chloride. 
 
 570. Haemoglobins, also called hcemato-crystalline, is 
 made up of carbon, hydrogen, iron, nitrogen, oxygen, and 
 sulphur, and forms the chief part of the red globules of the 
 blood of vertebrate animals. Usually it is amorphous, 
 but from some animals it can be separated in crystalline 
 form. Dilute solutions of this substance may be heated to 
 160 F. without marked change, but if the heat is continued 
 the haemoglobine is disorganized and splits up into hmma- 
 tine, CggHj^N^Fe^jg, and coagulated albumen. Alcohol 
 also decomposes it. 
 
 571. Putrefaction. The exact character of the fermen- 
 tation which takes place when animal bodies putrefy is but 
 little known. Among the products of these changes are hy- 
 
320 DESCRIPTIVE CHEMISTRY. 
 
 drogen, nitrogen, carbonic dioxide, ammonia, hydrogen car- 
 bides, sulphides, and phosphides. The gaseous combinations 
 of sulphur and phosphorus are the chief causes of the offen- 
 sive odor of putrefying bodies. As the presence of moist- 
 ure, a favoring temperature, and access of air, are essential 
 conditions of putrefaction, if any of them are withdrawn, 
 the effect is prevented. It is well known that the most 
 perishable organic substances, both vegetable and animal, 
 may be indefinitely preserved by drying. Cold checks de- 
 composition, and it is entirely arrested by freezing. So, if 
 the prime inciter of change, the air with its floating organic 
 germs, is excluded, putrefaction cannot take place. This 
 fact is illustrated by the general practice of preserving all 
 kinds of alimentary substances, meat, fruits, and vegetables, 
 in vessels which exclude the air. It is not enough, how- 
 ever, to exclude these agents from the surface of ferment- 
 able bodies, the germs which have already been absorbed 
 must also be destroyed. This may be done by a sufficient 
 elevation of temperature. In some cases boiling is effect- 
 ual, in others a much higher temperature is required. 
 
 572. Ferment -Diseases. The foul accumulations of 
 neglected towns, and the decomposing organic matter of 
 many swampy districts, give off invisible emanations know 7 n 
 as miasms and malaria, which fill the air, and often occa- 
 sion fatal epidemics. Of their composition, nature, or 
 mode of action, nothing very definite is known, but it has 
 been held that the effects produced by them are due to 
 the presence of a large quantity of ferment-germs which, 
 being inhaled, develop and induce a condition somewhat 
 similar to fermentation in the living system. Intermittent 
 fever, typhoid fever, and cholera, have been ascribed to this 
 cause. Various other diseases, as small-pox, hydrophobia, 
 etc., have also with much reason been considered as con- 
 sisting in processes of fermentation running their course 
 in the living organism. 
 
APPENDIX. 
 
 The Metrical System of Weights and Measures. 
 
 LENGTH. 
 
 Kilometre = 1000 metres. 
 
 Hectometre = 100 " 
 
 Decametre = 10 " 
 
 METRE (m.) = 1 metre. 
 
 Decimetre = 0.1 " 
 
 Centimetre (cm.) = 0.01 u 
 
 Millimetre (mm.) = 0.001" 
 
 VOLUME. 
 
 Kilolitre =1000 litres. 
 
 Hectolitre = 100 " 
 
 Decalitre = 10 " 
 
 LITRE = 1 litre. 
 
 Decilitre = 0.1 " 
 
 Centilitre = 0.01 " 
 
 Millilitre (or cubic centimetre) (c. c.) = 0.001 " 
 
 WEIGHT. 
 
 Kilogramme = 1000 grammes. 
 
 Hectogramme = 100 
 
 Decagramme 10 
 
 GRAMME (grm.) = 1 gramme. 
 
 Decigramme = 0.1 
 
 Centigramme = 0.01 " 
 
 Milligramme = 0.001" 
 
 The metre = 39.368 inches. 
 
 The litre = 1.76 pints. 
 
 The gramme = 15.432 grains, 
 
323 
 
 APPENDIX. 
 
 Relation of the Scales of the Centigrade and Fahrenheit 
 Thermometers. 
 
 Cent. 
 
 Fahr. 
 
 Cent. 
 
 Fahr. Cent. 
 
 Fahr. 
 
 Cent. 
 
 Fahr. 
 
 + 100 = 
 
 + 212 
 
 + 64 = 
 
 + 147.2 
 
 4- 29 = 
 
 + 84.2 
 
 6 = 
 
 = + 21.2 
 
 99 = 
 
 210.2 
 
 63 = 
 
 145.4 
 
 28 = 
 
 82.4 
 
 7 = 
 
 19.4 
 
 98 = 
 
 208.4 
 
 62 = 
 
 143.6 
 
 27 = 
 
 80.6 
 
 8 = 
 
 17.6 
 
 97 = 
 
 206.6 
 
 61 = 
 
 141.8 
 
 26 = 
 
 78.8 
 
 9 = 
 
 15.8 
 
 96 = 
 
 204.8 
 
 60 = 
 
 140 
 
 25 = 
 
 77 
 
 10 = 
 
 14 
 
 95 = 
 
 203 
 
 59 = 
 
 138.2 
 
 24 = 
 
 75.2 
 
 11 = 
 
 12.2 
 
 94 = 
 
 201.2 
 
 58 = 
 
 136.4 
 
 23 = 
 
 73.4 
 
 12 = 
 
 104 
 
 93 --= 
 
 199.4 
 
 57 = 
 
 134.6 
 
 22 = 
 
 71.6 
 
 13 = 
 
 8.6 
 
 92 = 
 
 197.6 
 
 56 = 
 
 132.8 ! 
 
 21 = 
 
 69.8 
 
 14 = 
 
 6.8 
 
 91 = 
 
 195.8 
 
 55 = 
 
 131 
 
 20 = 
 
 68 
 
 15 = 
 
 5 
 
 90 = 
 
 194 
 
 54 = 
 
 129.2 
 
 19 = 
 
 66.2 
 
 16 = 
 
 3.2 
 
 89 = 
 
 192.2 
 
 53 = 
 
 127.4 
 
 18 = 
 
 644 
 
 17 = 
 
 1.4 
 
 88 = 
 
 190.4 
 
 52 = 
 
 125.6 
 
 17 = 
 
 62.6 
 
 18 = 
 
 = 0.4 
 
 8T = 
 
 188.6 
 
 51.= 
 
 123.8 
 
 16 = 
 
 60.8 
 
 19 = 
 
 2.2 
 
 86 = 
 
 186.8 
 
 50 = 
 
 122 
 
 15 = 
 
 59 
 
 20 = 
 
 4 
 
 85 = 
 
 185 
 
 49 = 
 
 120.2 
 
 14 = 
 
 57.2 
 
 21 = 
 
 5.8 
 
 84 = 
 
 188.2 
 
 48 = 
 
 118.4 ! 
 
 13 = 
 
 55.4 
 
 22 = 
 
 7.6 
 
 83 = 
 
 181.4 
 
 47 = 
 
 116.6 | 
 
 12 = 
 
 53.6 
 
 23 = 
 
 9.4 
 
 82 = 
 
 179.6 
 
 46 = 
 
 114.3 ! 
 
 11 = 
 
 51.8 
 
 24 = 
 
 11.2 
 
 81 = 
 
 177.8 
 
 45 = 
 
 118 
 
 10 = 
 
 50 
 
 25 = 
 
 13 
 
 80 = 
 
 176 
 
 44 = 
 
 111.2 i 
 
 9 = 
 
 48.2 
 
 26 = 
 
 : 14.8 
 
 79 = 
 
 174.2 
 
 43 = 
 
 109.4 | 
 
 8 = 
 
 46.4 
 
 27 = 
 
 16.6 
 
 78 = 
 
 172.4 
 
 42 = 
 
 107.6 ' 7 = 
 
 44.6 
 
 28 = 
 
 18.4 
 
 77 = 
 
 170.6 
 
 41 = 
 
 105.8 ! 
 
 6 = 
 
 42.8 
 
 29 = 
 
 20.2 
 
 76 = 
 
 163.8 
 
 40 = 
 
 104 
 
 5 = 
 
 41 
 
 30 - = 
 
 22 
 
 75 = 
 
 167 
 
 39 = 
 
 102.2 
 
 4 = 
 
 39.2 
 
 31 = 
 
 23.8 
 
 74 = 
 
 165.2 
 
 83 = 
 
 103.4 
 
 3 = 
 
 37.4 
 
 82 = 
 
 25.6 
 
 73 = 
 
 163.4 
 
 37 = 
 
 9S.6 
 
 2 = 
 
 85.6 
 
 33 = 
 
 27.4 
 
 72 = 
 
 161.6 
 
 36 = 
 
 96.8 
 
 -I 
 
 33.8 
 
 34 = 
 
 29.2 
 
 71 = 
 
 159.8 
 
 35 = 
 
 95 
 
 = 
 
 32 
 
 35 = 
 
 81 
 
 70 = 
 
 158 
 
 34 = 
 
 932 
 
 1 = 
 
 80.2 
 
 36 = 
 
 32.8 
 
 69 = 
 
 156.2 
 
 83 = 
 
 91.4 
 
 2 = 
 
 28.4 
 
 37 = 
 
 34.6 
 
 68 = 
 
 154.4 
 
 82 = 
 
 89.6 
 
 3 = 
 
 26.6 
 
 38 = 
 
 86.4 
 
 67 = 
 
 152.6 
 
 31 = 
 
 87.8 
 
 4 = 
 
 24.3 
 
 39 r 
 
 88.2 
 
 66 = 
 
 150.8 
 
 80 = 
 
 86 
 
 5 = 
 
 23 
 
 40 = 
 
 40 
 
 65 = 
 
 149 
 
 
 
 
 
 
 
 It is often necessary to convert temperatures expressed on the Fahren- 
 heit scale into the corresponding temperatures on the Centigrade scale, 
 and the following rules will assist the pupil in transforming one scale 
 into the other : 
 
 (1.) To convert Fahrenheit Degrees into Centigrade Degrees. Subtract 
 32 from the number of degrees, and multiply the remainder by f (or 0.5). 
 
 (2.) To convert Centigrade Degrees into Fahrenheit Degrees. Multiply 
 the number of degrees by g (or 1.8), and add 32 to the product. 
 
APPENDIX. 
 
 323 
 
 Table for the Conversion of Grammes into Grains , Cen- 
 timetres into Inches, and Litres into Quarts. 
 
 CONVERSION. 
 
 1. 
 
 2. 
 
 3. 
 
 4. 
 
 5. 
 
 Grammes into Grains 
 
 15.4346 
 
 80.8692 
 
 46.3038 
 
 61.7384 
 
 77.1730 
 
 Centimetres into Inches 
 
 .3937079 
 
 .7374153 
 
 1.1811237 
 
 1.574S316 
 
 1.9685395 
 
 Litres into Imperial Quarts.. 
 
 O.SS066 
 
 1.761:32 
 
 2.64193 
 
 3.52264 
 
 4.40330 
 
 Litres into U. 8. Quarts 
 
 1.05708 
 
 2.11415 
 
 3.17123 
 
 4.22830 
 
 5.2SSa3 
 
 Table of Elementary Atoms and Molecules. 
 
 NAMES OF 
 PERISSAD ELEMENTS. 
 
 Symbols of 
 Atoms. 
 
 11 
 
 ll 
 
 Quantivalence. 
 
 Atomic 
 Weight. 
 
 Hydrogen 
 
 H 
 
 li-H 
 
 1. 
 
 1.0 
 
 Fluorine 
 
 Fl 
 
 F-F 
 
 I. 
 
 19.0 
 
 Chlorine 
 
 Cl 
 
 Cl-Cl 
 
 I.. III., V., VII. 
 
 35.5 
 
 Bromine 
 
 Br 
 
 Br-Br 
 
 I. III. V., VII. 
 
 80.0 
 
 Iodine 
 
 I 
 
 I-I 
 
 L, IIL, V., VII. 
 
 127.0 
 
 Lithium 
 
 Li 
 
 Li-Li 
 
 I. 
 
 70 
 
 Sodium (Natrium) 
 
 Na 
 
 Na-Na 
 
 I., III. 
 
 23.0 
 
 Potassium (Kalium) 
 Rubidium . 
 
 K 
 
 Rb 
 
 K-K 
 Rb-Kb 
 
 I., III., V. 
 I. 
 
 39.1 
 85.4 
 
 Caesium 
 
 Cs 
 
 Cs-Cs 
 
 I. 
 
 133.0 
 
 Silver (Argentum) 
 
 Ag 
 
 Ag-Ag? 
 
 I., III. 
 
 103.0 
 
 Thallium 
 
 Tl 
 
 T1-T1 ? 
 
 I., III. 
 
 204.0 
 
 Gold (Auruni) 
 
 Au 
 
 Au=Au? 
 
 I.. III. 
 
 197.0 
 
 Boron 
 
 B 
 
 B=B? 
 
 III. 
 
 11.0 
 
 Nitrogen 
 
 N 
 
 N=N 
 
 I., III., V. 
 
 14.0 
 
 Phosphorus 
 
 P 
 
 
 I.. III., V. 
 
 81.C 
 
 
 As 
 
 
 I , III. V. 
 
 750 
 
 Antimony (Stibium) 
 Bismuth 
 
 Sb 
 Bi 
 
 2 ? 
 ? 
 
 III., V. 
 III., V. 
 
 122.0 
 210.C 
 
 Vanadium 
 
 Va 
 
 V=V? 
 
 III., V. 
 
 51.37 
 
 Uranium 
 
 TTr 
 
 UiU? 
 
 III., V. 
 
 120.0 
 
 Columhium 
 
 Cb 
 
 CbiCb? 
 
 V. 
 
 94.0 
 
 Tantalum 
 
 Ta 
 
 TafTa? 
 
 V. 
 
 1820 
 
 
 
 
 
 
324 
 
 APPENDIX, 
 
 NAMES OF 
 ARTIAD ELEMENTS. 
 
 Symbols of 
 Atoms. 
 
 8 
 
 Ej 
 
 ooS 
 
 Quantivalence. 
 
 Atomic 
 Weight. 
 
 Oxygen 
 
 O 
 
 OO 
 
 II. 
 
 16.0 
 
 Sulphur. 
 
 s 
 
 8=8 
 
 II IV VI 
 
 32 
 
 Selenium 
 Tellurium 
 
 Se 
 Te 
 
 Se=Se 
 To=Te 
 
 II., IV., VI. 
 II., IV., VI. 
 
 79.4 
 128.0 
 
 Molybdenum 
 Tungsten ( Wolfram) 
 
 Mo 
 W 
 
 Mo? 
 W? 
 
 II., IV., VI. 
 IV., VI. 
 
 96.0 
 184.0 
 
 Copper (Cuprum) 
 Mercury (Hydrargyrum) . 
 
 Cu 
 Hg 
 
 Cu? 
 Hg 
 
 II. 
 II. 
 
 63.4 
 200.0 
 
 Calcium . 
 
 Ca 
 
 Ca? 
 
 II. 
 
 40 
 
 Strontium 
 
 Sr 
 
 Sr? 
 
 ii., rv. 
 
 87.6 
 
 Barium 
 
 Ba 
 
 Ba? 
 
 ii. 
 
 137 
 
 Lead (Plumbum) 
 
 Pb 
 
 Pb? 
 
 II., IV. 
 
 207.0 
 
 Magnesium 
 
 Mg 
 
 Mg? 
 
 ii 
 
 24 
 
 Zinc 
 
 Zn 
 
 Zn? 
 
 ii. 
 
 66.2 
 
 Indium . 
 
 In 
 
 In 9 
 
 II IV VI 
 
 72 
 
 Cadmium 
 
 Cd 
 
 Cd 
 
 II.' 
 
 112.0 
 
 Glucinum 
 
 G 
 
 G? 
 
 II. 
 
 9.8 
 
 Yttrium 
 
 Y 
 
 Y? 
 
 II. 
 
 61.7 
 
 Erbium 
 
 E 
 
 E? 
 
 II. 
 
 112.6 
 
 Cereum . . . 
 
 Ce 
 
 Ce? 
 
 11. IV 
 
 92 
 
 Lanthanum 
 
 La 
 
 La? 
 
 II 
 
 98 6 
 
 Didymium 
 
 D 
 
 D? 
 
 II. 
 
 95.0 
 
 Nickel . . 
 
 Nl 
 
 Ni? 
 
 II., IV. 
 
 58.8 
 
 Cobalt 
 
 Co 
 
 Co? 
 
 II., IV. 
 
 58.8 
 
 Manganese 
 Iron (Ferrum) 
 
 Mn 
 Fe 
 
 Mn? 
 Fe? 
 
 II., IV., VI. 
 II., IV., VI. 
 
 55.0 
 56.0 
 
 Chromium 
 
 Cr 
 
 Cr? 
 
 II., IV VI 
 
 52 2 
 
 Aluminium 
 
 Al 
 
 Al? 
 
 IV. 
 
 27.4 
 
 Ruthenium 
 Osmium 
 
 Ku 
 Os 
 
 Eu? 
 Os? 
 
 II., IV., VI. 
 11., IV., VI. 
 
 104.4 
 199.2 
 
 Rhodium . . 
 
 Eo 
 
 Eo? 
 
 II IV VI 
 
 104 4 
 
 Iridium 
 
 Ir 
 
 Ir? 
 
 II.. IV., VI. 
 
 196.0 
 
 Palladium 
 
 Pd 
 
 Pd? 
 
 II IV 
 
 106 6 
 
 Platinum 
 
 Pt 
 
 Pt? 
 
 II., IV. 
 
 197.4 
 
 Titanium 
 
 Ti 
 
 Ti ' 
 
 II IV 
 
 50 
 
 Tin (Stannum) 
 
 Sn 
 
 Sn? 
 
 II., IV. 
 
 118.0 
 
 Zirconium 
 
 Zr 
 
 Zr? 
 
 IV. 
 
 89.6 
 
 Thorium 
 
 Th 
 
 Th? 
 
 II. 
 
 115.72 
 
 Silicon 
 
 Si 
 
 Si? 
 
 IV. 
 
 28.0 
 
 Carbon 
 
 c 
 
 C? 
 
 II , IV. 
 
 12.0 
 
 
 
 
 
 
 NOTE TO PAGE 91. 
 
 The views presented in the text concerning the distribution of the 
 spectrum forces have long been regarded as established. But Dr. J. W. 
 Draper maintains that, while the effects described are true as matters of 
 observation, they are variously interpreted. He says that the accumula- 
 
APPENDIX. 325 
 
 tion of heat at one end of the spectrum is due to the same cause as the 
 unequal spaces of the colors that is, to the distorting action of the 
 prism. With a diffraction spectrum produced by finely-ruled surfaces, 
 he claims to have found, by many experiments, that the luminous spaces 
 are equal ; that, from the centre of the spectrum, near the sodium-line D, 
 there are equal amounts of heat on the two sides ; and, finally, that all 
 the rings of the spectrum, irrespective of their color or wave-length, have 
 equal heating-power. 
 
QUESTIONS. 
 
 INTRODUCTION. 
 
 1. WHAT is meant by the terms phenomena and order of Nature ? 
 2. What purpose does prevision serve in science ? 3. Define matter and 
 force. 4. What are physical changes ? 5. Give examples of chemical 
 changes of matter. Give the distinction between compound and sim- 
 ple bodies. 6. Are the forces of Nature in any way connected ? 
 
 CHAPTER I. GRAVITY. 
 
 7. SHOW how the processes of weighing and measuring are impor- 
 tant to the chemist. What system of measurement is now in ordinary 
 use? What is the metrical scale? 8. What is its basis ? Describe this 
 scale fully. 9. What is gravity ? Give illustration showing mutual at- 
 traction of masses of matter. What relation exists between the quan- 
 tity of matter and the force of gravity? 10. What is weight? 11. De- 
 scribe the balance. 12. In what does the operation of weighing con- 
 sist? 13. Give the unit of the French scale of weights. The gramme 
 is equal to how many grains ? 14. How may specific volumes be ob- 
 tained? 15. How is volume related to weight? How is platinum re- 
 lated to hydrogen ? What is specific gravity? 16. How is the specific 
 gravity of solids heavier than water obtained? 17. How is the specific 
 gravity of solids lighter than water obtained ? 18. What precaution 
 should be taken in finding the specific gravity of powdered solids ? 19. 
 How may the specific gravity of soluble solids be obtained ? 20. How 
 may the specific gravity of gases be obtained ? 21. Explain the prin- 
 ciple on which the hydrometer is constructed. 22. How does specific 
 gravity afford means of identifying bodies ? 23. Give distinction between 
 specific gravity and density. 
 
QUESTIONS. 327 
 
 CHAPTER II. MOLECULAR ATTRACTIONS. 
 
 25. WHAT reason can be given for the conclusion that matter is 
 universally porous ? 27. What are atoms ? How are they distinguished 
 from molecules ? 28. State what you can of the divisibility of matter ? 
 29. Give distinction between adhesion and cohesion. 31. Explain con- 
 ditions of " wetting." 32. What is capillary attraction ? 33. What is 
 said of reversed capillarity ? 34. How may a gas be driven out from 
 a solution ? 35. How may insects walk upon water ? 36. Explain 
 what takes place in diffusion. 37. What principle explains the 
 stability of our atmosphere? 38. What is the law of the diffusion 
 of gases? 39. What is osmose? Explain Fig. 14. What occurs in 
 atmospheric respiration? 40. May liquids and solids diffuse through 
 gases? 42. What are diffusates? What are crystalloids and colloids? 
 43. Explain endosmose and exosmose. 44. What is the difference be- 
 tween absorption and osmose? 45. What is meant by the terms solu- 
 tion and solvent ? 46. What conditions favor solution ? 47. When 
 is a liquid saturated ? 48. How may solids be separated from solution ? 
 Give examples. 50. What is occlusion? 51. What are crystals? 
 What are substances called which do not crystallize? 53. How may 
 crystals be artificially produced ? 54. What is mother-liquor ? 55. 
 What is said of crystals by fusion ? 57. Does crystallization ever take 
 place except in liquids ? 58. State phenomena attending crystallization ? 
 61. What forms do liquids tend to assume on crystallizing? 62. Crystals 
 are solids of what class ? 63. What are primary forms ? What is a 
 goniometer ? 64. How many systems of crystallization are there ? 65. 
 Describe the monometric system. 66. How are the axes arranged in the 
 dimetric system? 67. Give examples of, and describe, the trimetric 
 system. 69. Give characteristics of rhombohedral and hexagonal sys- 
 tems. 71. What evidence is there that the axes of crystals are not 
 mere imaginary lines ? 72. What is cleavage ? 73. What example of 
 the derivation of form is given ? 74. What is isomorphism ? 75. What 
 is dimorphism ? 
 
 CHAPTER III. HEAT. 
 
 76. GIVE the term which is applied to the science of heat. 77. 
 What is the general effect of heat upon matter ? 78. How may the cohe- 
 sion of a solid be overcome ? 79. May gases be expanded indefinitely ? 
 80. What do thermometers measure ? 81. What advantages has mer- 
 cury as a thermometric fluid ? 82. Give the different thermometers in 
 use, and state the peculiarity of each. 83. How is heat transferred ? 
 What are the best conductors ? 84. Does heat travel with more facil- 
 
328 QUESTIONS. 
 
 ity across the axis than in other directions ? 85. Why do some sub- 
 stances feel so much warmer than others ? 86. Explain what takes place 
 when gases and liquids are heated. 87. What is radiation ? How may 
 equilibrium of temperature be obtained ? 88. What effect does surface 
 have on radiation ? 89. What substances are good absorbers of heat ? 
 90. What is dew ? 91. What two kinds of radiant heat are there ? 92 
 Define the terms diathermic and athermic. 93. How does the aqueous 
 vapor affect the temperature of the earth ? 94. What is the melting- 
 point of a substance ? 95. Give the distinction between latent heat 
 and sensible heat. 96. What is sensible heat ? 97. Explain how freez- 
 ing is a warming process. 98. What is a freezing mixture ? 99. Ex- 
 plain the process called " boiling." 100. What circumstances affect the 
 boiling-point? 101. What is the spheroidal state? 102. What sub- 
 stances vaporize readily ? 103. What becomes of the heat which has 
 been consumed in converting liquids into vapors ? 104. On reversing 
 the process what occurs ? 105. What is the effect of evaporation ? 
 106. Explain the cryophorus. 107. How can the amount of atmospheric 
 humidity be obtained ? 108. Explain the hygrometer. 109. What re- 
 lation is there between the vapor from a cubic inch of water, one of 
 alcohol, and one of ether ? 110. What is meant by elastic force? 111. 
 Explain distillation, and give the meaning of the terms distillate and 
 sublimate. 112. How may gases be reduced to liquid or solid condi- 
 tions? 114. What is the difference between heat and cold? 115. 
 Give an idea of the caloric hypothesis. 116. Give the facts which 
 led to the new theory. 117. Heat is now how regarded ? What is sup- 
 posed to be true of the atoms? 118. What follows from this theory 
 with regard to the temperature of bodies ? 119. What is the dynamical 
 theory? 120. What is combustion ? 
 
 CHAPTER IV. ELECTRICITY. 
 
 121. STATE what is said of electricity? 122. What are conductors 
 and insulators ? 123. How do the electricities affect each other? 124. 
 Explain the terms "charged" and "discharged." 125. What is the 
 effect of bringing an excited glass tube near an electroscope ? What is 
 electrical induction? 126. Explain Fig. 48. 127. State Faraday's theory 
 of induction. 128. What is a natural magnet? 129. What is the law 
 of polarity? 130. Explain the term magnetic induction by reference 
 to the figure. 131. What is the result of breaking a magnet? 132. 
 What are those substances, which arrange themselves axially, called? 
 133. What is voltaic electricity, and whence the name? Describe the 
 voltaic circuit. 134. What are the poles of the circuit? 135. How 
 may the power of the circuit be increased? 136. How may increased 
 
QUESTIONS. 329 
 
 effect, combined with steadiness of action, be secured ? 137. Describe 
 DanielFs battery. 138. Upon what does quantity of electricity depend? 
 139. Explain the principle of the Ruhmkorff coil. 140. Will voltaic 
 electricity travel through air ? 141. What is electrolysis? 142. Which 
 bodies are termed electro-negative, which electro-positive? 143. Explain 
 electro-gilding and electro-plating. 144, What relation exists between 
 arrested electricity and heat? 145. Upon what do the degree and 
 direction of the motion of the needle depend ? 146. What is the astatic 
 needle ? 147. What is thermo-electricity ? 
 
 CHAPTER V. LIGHT. 
 
 149. STATE what you can of light; give its velocity. 150. How is 
 light affected by the prism? What is the order of refrangibility of 
 the rays? 151. Give the wave-hypothesis. 152. What to the eye is the 
 same as the gamut to the ear ? How do the number of waves of red 
 light compare with those of blue light in a given space? 153. What 
 explanation is given of radiant heat? 154. What is interference? 
 155. Explain Fig. 70. The principle of interference leads to what con- 
 clusions regarding silence, darkness, etc. ? 1 56. What happens when 
 light is reflected at a certain angle ? How may the change be detected ? 
 157. In what other ways may light be polarized? 158. Show how the 
 wave-theory explains polarization. 
 
 CHAPTER VI. CHEMISTRY OF LIGHT. 
 
 162. UPON what rays does the art of photography depend? 163. 
 Describe Fig. 87, and state the facts regarding invisible radiations. 
 164. How do heat-rays, light-rays, and chemical rays, differ from each 
 other? 165. What are actinoroeters ? 166. What changes take place 
 in the chemical activity of the solar rays, at different times of the day 
 and year? 167. What is said of chemical action at the equator? 168. 
 Where does the force which is most active in vegetative processes 
 reside? 169. State the chemical effects of light? 170. What chemi- 
 cals are employed in photography? 171. State how the invisible image 
 is produced. 172. How is the invisible image brought out? 173. 
 What are negatives and positives ? 174. Give some idea of the varying 
 effects of colored lights. 175. How is photography, in its applications, 
 related to science ? 
 
 CHAPTER VII. SPECTRUM ANALYSIS. 
 
 176. How is spectrum analysis related to other modern discov- 
 eries? 177. What is proved by recombining, by means of a lens, the 
 
330 QUESTIONS. 
 
 separated colored rays? 178. May the colors of the solar spectrum be 
 still further decomposed? 179. What is said of the spectrum of the 
 electric light? 180. What is dispersion? How does the dispersive 
 power of flint-glass compare with that of crown-glass ? 181. How may 
 dispersion be increased? 182. When may four or five prisms be used 
 to advantage ? 183. Describe the spectroscope, and explain Figs. 100, 
 101, and 102. 187. What was Dr. Wollaston's discovery? 188. 
 State what is said of Fraunhofer's lines. 189. Give the results of Dr. 
 Draper's investigations. ,190. How do the spectra of gaseous bodies 
 differ from those of solids ? What is the difference in the spectra of 
 sodium and iron? 191. These spectral lines may serve as tests for 
 what ? 192. Increasing temperature and added pressure have what 
 effect on the spectrum? 193. What are the spectrum-lines? 194. 
 What relation exists between the dark solar lines and the bright lines 
 produced by burning terrestrial substances ? 195. What are absorption- 
 lines ? 196 What kind of light do vapors absorb ? Explain Fig. 109. 
 
 197. What is meant by the reversal of the lines? Describe Fig. 110. 
 
 198. What principle of physics underlies the theory upon which spec- 
 trum analysis is based? 199. What clew is given us by Fraunhof- 
 er's lines ? 200. Give illustrations showing the delicacy of spectrum 
 analysis, when used as a means of testing chemical substances. 201. 
 Mention the names of the new elements discovered by this means. 
 202. Explain use of spectroscope in steel-making. 203. Give organic 
 indications of the spectroscope. 204. Give description of telespeotro- 
 scope. 205. How does Prof. Young describe the red portion of the 
 spectrum ? 206. Describe the solar envelope. 207. What elements are 
 found in the sun ? 208. What evidence does spectrum analysis give us 
 that stars are suns? 211. Give the spectroscopic proof of the motions 
 of celestial bodies. 212. How does spectrum analysis prove the motions 
 of the stars. 
 
 CHAPTER VIII. GENERAL CHARACTER OF CHEMICAL ACTION. 
 
 GIVE a general idea of chemical force. 216. Define analysis, prox- 
 imate, ultimate, qualitative, and quantitative. 217. How do the effects 
 of chemical force differ from those of the physical forces? 218. Why 
 are some substances called elements, and others compounds ? 220. 
 How is chemical action affected by cohesion, heat, light, and electricity ! 
 223. What is chemical induction ? 224. When will nitrogen and hydro- 
 gen unite to form ammonia ? 225. Define catalysis. 226. Is there any 
 variation in the intensity of chemical action ? 227. Has chemistry any 
 mathematical basis? 228. Give the principle underlying the law of 
 
QUESTIONS. 331 
 
 definitive proportions. 229. Explain the law of multiple proportions. 
 230. Give example of equivalent proportion. 
 
 CHAPTER IX. THEORETICAL CHEMISTRY. 
 
 231. GIVE an idea of the old atomic theory, and of the theory as 
 revived by Dr. Dalton. 233. Define the term molecule as used by the 
 physicist. 234. Define the term molecule as used by the chemist. 235. 
 What is the ultimate unit of the chemist called ? Define the terms anal- 
 ysis, synthesis, and metathesis. 236. What quantity of an element does 
 the symbol represent ? 
 
 237. What theory was first given in explanation of chemical changes ? 
 238. Give a general idea of the binary theory. 239. What theory 
 was the outgrowth of the binary theory? 240. Give a statement of 
 the theory of types. 241. Do substitutions take place, atom for atom ? 
 242. Define the term atomicity, and give groupings illustrating the 
 subject. 243. What is quantivalence ? How is it expressed? 244. 
 What is the significance of bonds ? 245. What relation exists between 
 the number of bonds and the ability of the atoms to combine with 
 each other ? 246. To what is the term atomicity limited ? 247. Define 
 terms perissad and artiad. May a perissad ever become an artiad? 
 248. How is it supposed that changes of quantivalence may be ex- 
 plained ? 249. When may an atom or molecule exist free ? Does the 
 quantivalence of a molecule depend upon the atomicity of its elements ? 
 251. How may molecular chains be formed? 252. What are radi- 
 cals? 253. Define compound radicals. 254. Can compound radicals 
 exist free? 255. On what theory were acids, bases, and salts, for- 
 merly explained ? 256. What is the relation of water to the acids and 
 bases ? 257. Give the constitution of the acids. 258. What is the con- 
 stitution of a base? 259. Give formulas for acids, bases, and salts. 
 260. What are hydrates? 261. Is hydrogen an essential constituent of 
 acids, bases, and salts? 262. What are ortho-acids and meta-acids? 
 263. What are normal salts ? 264. Is common salt properly a salt ? 
 265. Explain the constitution of the amides, amines, and alkalamides? 
 
 267. Show how the modern ideas of changes by substitution, types, 
 atomicity, etc., are the result of investigations in organic chemistry. 
 
 268. What are the important organic elements ? 268. What is the rela- 
 tion of carbon to organic chemistry ? 269. How are isomeric phenomena 
 explained? 270. When are compounds said to be polymeric? 271. 
 Define allotropism. 272. Are molecules to be regarded as having di- 
 mensions? 273. What is the law of Avogadro? 274. What conclusion 
 has been reached regarding the diameters of gaseous molecules ? 275. 
 Explain how the molecular weight of all aeriform bodies may be deter- 
 
332 QUESTIONS. 
 
 mined. 276. What is the standard of molecular weight ? What is the 
 crith ? 277. How is atomic heat related to specific heat ? 278. In what 
 ratios do gases combine by volume ? 
 
 CHAPTER X. THE CHEMICAL NOMENCLATURE. 
 
 280. SHOW how the science of chemistry is reflected in the language. 
 281. How have the elements generally been named? What is the sig- 
 nificance of the terminations um and ine? 282. What termination is 
 given to the compound radicals ? 283. In the naming of binary com- 
 pounds which element is placed first ? What change takes place in the 
 termination of the positive element? What significance have the pre- 
 fixes hypo and per ? 284. Illustrate the use of numerical prefixes. 285. 
 How are acids named ? How salts ? How bases ? 286. Give examples 
 of the names of amides, amines, and alkalamides? 287. Define em- 
 pirical formula and rational formula. How are atomic groups sepa- 
 rated ? 288. In what form may chemical reactions be expressed ? 
 
 CHAPTER XI. HYDROGEN 
 
 289. WHAT are the quantivalence and atomic weight of hydrogen ? 
 290. What is the significance of the term hydrogen? 291. To what ex- 
 tent is hydrogen found in Nature? 292. In what different ways may- 
 hydrogen gas be obtained? 293. Describe a pneumatic trough. 294. 
 Give properties of hydrogen. 296. How does hydrogen compare with 
 other elements in weight ? 296. What is known of its inflammability 
 and explosiveness ? 297. How may hydrogen be ignited without the ap- 
 plication of heat ? 298. What is occlusion ? 
 
 CHAPTER XII. CHLORINE, FLUORINE, BROMINE, IODINE. 
 
 299. WHERE is chlorine chiefly found? 300. How is the gas ob- 
 tained? 301. What are the properties of chlorine? 302. Its uses? 
 How does chlorine act as a bleaching agent ? 303. What is the composition 
 of muriatic acid ? Give the reaction which takes place when sulphuric acid 
 acts on sodic chloride. 305. How may chlorine combine with oxygen ? 
 306. What use is made of chloric monoxide? 308. What are the 
 properties of chloric acid ? 309. Is fluorine found uncombined in Na- 
 ture? 310. What is the distinguishing characteristic of hydric fluo- 
 ride? 311. How is bromine obtained? 312. Give properties and uses 
 of bisemine. 313. What does the term iodine refer to ? 314. What is 
 the test for iodine? For what is iodine used? 315. When bromine 
 and iodine are heated with hydrogen, what compounds are formed ? ?16. 
 What an you say of the halogen group ? 
 
QUESTIONS. 333 
 
 CHAPTER Xin. SODIUM, POTASSIUM, LITHIUM, RUBIDIUM, CAESIUM. 
 
 317. WHAT was the first method of obtaining metallic sodium? 
 318. What is the chemical name of common salt? From what source is 
 salt chiefly obtained ? 320. Give uses of common salt. 321. How are 
 sodic compounds distinguished from potassic compounds ? What is the 
 composition of sodic carbonate? 322. Give common name of hydro- 
 sodic carbonate. 323. How is caustic soda obtained? 324. What is 
 the chemical name for Glauber's salt ? 325. Give symbol of sodic ni- 
 trate. 326. How was potassium first obtained? 327. What takes 
 place when potassium is thrown upon water ? Why is this metal kept 
 in naphtha? 329. Give the properties of potassic hydrate. 331. 
 Where are the potassic salts found ? What use has potassic carbonate ? 
 332. How may hydro-potassic carbonate be formed ? 333. Give common 
 name for potassic nitrate. What is it used for ? 334. Give composition 
 of gunpowder. 335. What use has potassic chlorate in the laboratory ? 
 336. What is soluble glass ? 337. Describe the process of soap-making. 
 Upon what does the consistence of the soap depend ? 338. How does 
 soap act in cleansing ? 339. What elements are found associated with 
 sodium and potassium ? Where is rubidium found ? What does the 
 word caesium mean ? 
 
 CHAPTER XIV. SILVER, GOLD, BORON. 
 
 340. WHAT is silver associated with ? 341. Give its properties and 
 uses. 342. What is the common name of argentic chloride? 344. 
 Give composition of lunar caustic. How may the stains of indelible 
 ink be removed ? 345. What is the method employed to separate gold 
 from its ores ? 346. How does gold compare with other metals in 
 malleability and ductility ? What is aqua regia ? 347. What does one 
 modification of boron resemble ? 348. Where is boric acid found ? 349. 
 What is borax ? What property renders borax a valuable reagent ? 
 
 CHAPTER XV. NITROGEN, PHOSPHORUS, ARSENIC, ANTIMONY, BISMUTH. 
 
 350. How is nitrogen obtained ? 352. For what is nitrogen re- 
 markable ? 353. Give the composition and method of obtaining am- 
 monia. 354. Why was it called spirits of hartshorn ? 356. Nitrogen 
 combines with oxygen forming what compounds ? 357. What is laugh- 
 ing gas ? 358. What effect is produced on the nervous system by nitric 
 monoxide ? 359. Give composition of nitric acid. 360. Its properties 
 and uses. 362. When hydric chloride and ammonia are brought together, 
 what substance is formed ? Give the equation which expresses the reac- 
 tion when ammonic chloride is formed. 363. How is ammonic hydrate 
 
334 QUESTIONS. 
 
 formed? Describe Woulfe's bottles. What atomic- group resembles 
 potassium? 366. What are the sources of phosphorus in Nature? 
 367. What is the molecular symbol of ordinary phosphorus ? 368. Give 
 the properties of this element. 369. How may red phosphorus be ob- 
 tained ? 370. Name the compounds of phosphorus and hydrogen. 
 What takes place when calcic phosphide is thrown into water ? 371. 
 How does phosphoric pentoxide behave when it is brought in contact 
 with water? 372. Describe arsenic. 373. To the formation of what 
 gas is the detection of arsenic, by Marsh's test, due? How may the 
 presence of antimony be distinguished from that of arsenic? 374. 
 What is the composition of ratsbane ? 375, 376. Give the characteris- 
 tics of antimony and bismuth. What are the uses of bismuth? 
 
 CHAPTER XVI. OXYGEN. 
 
 377. GIVE the quantivalence of oxygen. State what you can of the 
 modifications of oxygen. 378. What does the word oxygen mean ? 
 380. To what extent is it distributed in Nature? 381. From what sub- 
 stances can oxygen be obtained ? 382. Give properties of oxygen. 383. 
 What effect has oxygen on combustion ? 385. Under what conditions 
 may iron wire or a steel spring be made to burn with brilliancy ? 385. 
 What is the cause of decay in animal and vegetable substances ? 386. 
 How is oxygen related to the vital processes ? 387. How is ozone differ- 
 ent from oxygen? 389. What can be said of autozone? Give formulas 
 illustrating the three forms of oxygen. 390. What is the common name 
 of hydric oxide ? 391. When hydrogen is burned with oxygen, what is 
 the product ? 392. In what two ways may the composition of water be 
 demonstrated ? 393. Give properties of water. 394. Describe the forms 
 which are the result of freezing water. 395. What is said of the une- 
 qual expansion of water ? 396. Is there any relation existing between 
 specific heat of water and climate? 397. What can be said of the 
 solvent power of water ? 398. How may water be purified ? 400. Give 
 the chemical properties of water. 401. State what you can of hydric 
 dioxide. 402. What is known of the composition of the atmosphere ? 
 What considerations lead us to the conclusion that the atmosphere is a 
 mixture of gases? 403, 404. Are the watery vapor and carbonic acid 
 present in the atmosphere a constant quantity ? 405. What office does 
 oxygen perform in the atmosphere ? What nitrogen ? 
 
 CHAPTER XVII. SULPHUR, SELENIUM, TELLURIUM. 
 
 STATE the quantivalence of sulphur. 407. Describe modifications of 
 sulphur. 408. How is the ordinary form obtained ? 410. Under what 
 
QUESTIONS. 335 
 
 conditions will ordinary sulphur pass into the other forms? 411. Of 
 what use is plastic sulphur in the arts? 412. Where is hydric sul- 
 phide found? 413. Explain the method of liberating hydric sulphide? 
 414. Of what use is chloric disulphide in the arts ? 415. How may 
 sulphur unite with oxygen ? 416. When is sulphurous oxide liberated? 
 417. For what is S0 2 used? 418. How may the sulphites be obtained ? 
 419. Give composition of sulphuric oxide. 420. How early was sul- 
 phuric acid known ? How is it prepared ? 422. What are the proper- 
 ties of this acid ? State phenomena which occur when sulphuric acid 
 and water are mixed together. What can you state of disulphuric acid ? 
 424. What do the words selenium and tellurium mean ? 
 
 CHAPTER XVIII. COPPER AND MERCURY. 
 
 425. FROM what ores is copper obtained? What are the prop- 
 erties of metallic copper ? What is verdigris ? What salts should be 
 avoided in the culinary department ? 426. Give preparation and uses 
 of cupric oxide. Give common names for cupric sulphate and cupric 
 arsenite. 427. State the properties and uses of mercury. What are 
 amalgams ? 428. What use did Priestley and Lavoisier make of mer- 
 curic oxide. 429. What is the antidote for mercuric chloride? 430. 
 Give properties of calomel. 431 Under what name is mercuric sulphide 
 sold? 
 
 CHAPTER XIX. CALCIUM, STRONTIUM, BARIUM, LEAD. 
 
 432. WHERE is calcium found ? 433. How is lime obtained ? 434. 
 Describe the process of slacking. What is milk of lime ? Give prop- 
 erties of calcic hydrate. 435. Of what is the best mortar made? 
 To what is the hardening of the mortar supposed to be due ? 436. 
 What is bleaching-powder ? 437. Give composition of gypsum. Give 
 its uses. 438. What is the source of calcic carbonate ? What is hard 
 water? 439. Through what mutations does calcic phosphate pass? 
 440. Give properties of strontium and barium. What is the test for 
 sulphuric acid ? What are the uses of nitrate of strontium and baric 
 sulphate ? 441. What is galena ? Give the uses of lead. What dan- 
 ger may arise from the use of lead pipe ? The presence of what salts 
 in the water protects the lead against its corroding action ? 442. Give 
 composition of plumbic monoxide and tetroxide. 443. How is white 
 lead obtained ? 444. Give properties of plumbic acetate. 
 
 CHAPTER XX. MAGNESIUM, ZINC, CADMIUM. 
 445. WHERE does magnesium occur ? Of what use is it in the arts ? 
 15 
 
336 QUESTIONS. 
 
 446. What are the common names of magnesic oxide and sulphate ? 
 
 447. How is zinc obtained ? Give properties. 448. State symbols for 
 zincic oxide, chloride, and sulphate. Give common name of zincic sul- 
 phate. 449. Describe cadmium. 
 
 CHAPTER XXI. IRON, MANGANESE, NICKEL, AND COBALT. 
 
 450. GIVE history and occurrence of iron. 451. Describe the pro- 
 cess of obtaining wrought-iron from cast-iron. 452. Give properties 
 of iron. What is the effect of constant jarring on wrought-iron ? 453. 
 What is welding ? What quality belongs only to iron, platinum, and 
 sodium? 455. How is cast-iron obtained from the ore? 456. Give the 
 origin of the term pig-iron. 457. Properties of cast-iron. 458. What 
 is steel ? How produced ? Describe the Bessemer process. 459. What 
 quality renders steel valuable in the arts ? 460. State uses of ferrous 
 oxide. 461. Which is the most valuable iron-ore ? 462. What is the 
 scientific name of iron pyrites ? 463. Give uses and composition of 
 green vitriol. 464. State what you can of manganese. 465. How are 
 nickel and cobalt related ? 
 
 CHAPTER XXII. CHROMIUM, ALUMINIUM, AND PLATINUM. 
 
 466. FOR what are the compounds of chromium used ? 467. Give 
 composition of dichromic trioxide and chromic trioxide. 468. Give 
 history and properties of aluminium. Its uses. 469. What compound 
 gives color to the ruby and sapphire ? What are emery and corundum ? 
 470. What constitutes the basis of pottery? 471. How is porcelain 
 made ? What gives color to common red pottery- ware ? 472. Give 
 properties of alum. What is the difference between alum burnt and 
 unburnt ? 473. What are the associates of platinum ? What acid acts 
 upon platinum ? What power has spongy platinum ? Its uses, in the 
 arts. 474. How may platinic tetrachloride be obtained ? 
 
 CHAPTER XXIII. TIN, SILICON. 
 
 475. WHICH is harder, gold or tin? What is the cause of the 
 peculiar crackling sound given by tin when bent ? 476. What is Bri- 
 tannia metal? What elements are allied to tin? 477. What three 
 different modifications has silicon ? 478. Give composition of silica. 
 It forms the bulk of what minerals? 479. What is the composition 
 of the opal? 480. When hydric fluoride acts upon silica, what gas is 
 produced? 481. What is glass? How colored? 482. State how the 
 different varieties of glass are produced. 
 
QUESTIONS. 337 
 
 CHAPTER XXIV. CARBON. 
 
 483. WHAT are the allotropic forms of carbon? Which is the 
 purest form ? State what you can of the diamond. 484. Give the prop- 
 erties of graphite. 485. How is charcoal obtained ? 486. Its uses. Is 
 it an antiseptic ? What is lamp-black ? 487. How is carbonic monox- 
 ide produced ? What is the character of its flame ? 488. Give compo- 
 sition of carbonic monoxide. 489. How is carbonic acid prepared ? 
 490. How can you prove that G0 2 is not a supporter of combustion, and 
 that it is heavier than air? What experiment shows that carbonic diox- 
 ide is in the expired breath ? 491. What is soda-water ? 492. Give prop- 
 erties and uses of carbonic disulphide. 493. What is the symbol of 
 cyanogen ? 494. Where is prussic acid found ? 495. Describe potassic 
 cyanide. 496. What is the popular meaning of combustion ? How 
 does the chemist use the term ? 497. State what is said of the gradation 
 of affinities between oxygen and the elements of combustible bodies. 
 498. Show how explosive combustion takes place. 499. What is ere- 
 macausis ? 500. What does intensity of heat depend upon ? 501. How 
 does chemical action produce heat ? 502. What kind of substances pro- 
 duce flame? State the conditions of illumination. 503. Describe the 
 compound blow-pipe. 504. What constitutes the Drummond light ? 
 505. How does the candle burn ? 506. Give a statement of the struct- 
 ure of flame. 507. How may the constant presence of free carbon in 
 the flame be proved ? 508. Upon what does the amount of light pro- 
 duced depend ? 509. What is the principle on which the safety-lamp i.-< 
 constructed ? 
 
 CHAPTER XXV. HYDROCARBONS AND THEIR DERIVATIVES. 
 
 510. GIVE the composition of the hydrocarbons ? Describe marsh- 
 gas? Where is rock-oil found? 511. What is ordinary "kerosene?" 
 When is it safe to use a paraffin-oil ? For what is paraffin used ? 
 512. Describe ethylene. What is illuminating gas? 513. Why is 
 acetylene of special interest? 514. To what series do the terpenes be- 
 long? What are the oils of lemon and orange? 515. Give the proper- 
 ties of benzene. What compound is a stepping-stone to the production 
 of aniline ? What use is made of aniline ? What other coloring sut- 
 stances are mentioned ? 516. Give the general composition of the 
 alcohols. From what is wood-spirit obtained ? 517. Give formula for 
 common alcohol. Its properties. 518. What is fusel-oil ? 519. When 
 is wine said to be sparkling ? 520. Give what information you can re- 
 garding lager-beer, ale, and porter. 521. How does brandy differ from 
 wine ? 522. Give the composition of phenol. Mention substances valu- 
 
338 QUESTIONS. 
 
 able as antiseptics. 523. What is the composition of the fats and oils ? 
 For what is glycerine used ? 524. How is nitro-glycerine exploded ? 
 
 525. Mention some of the carbo-hydrates. What are the glucoses ? 
 
 526. Give formula and properties of cane-sugar. 528. What is lactose 
 used for ? 529. Mention some substances having the composition Ci 2 - 
 Haa On. What is varnish ? 530. How does starch differ from sugar in 
 its composition? 531. What are the properties and uses of starch? 
 532. How may commercial starch be converted into dextrine? Men- 
 tion substances isomeric with starch. 533. From what may cellulose 
 be obtained ? 534. Give the uses of cellulose. 535. How may cellu- 
 lose be converted into pyroxylene ? How does the explosive force of 
 pyroxylene compare with that of gunpowder ? What is collodion ? 536. 
 What distinction is made between the terms fermentation and putrefac- 
 tion ? What is the exciting cause of fermentation ? 537. Give examples 
 of ferments and fermentable bodies. What is said of yeast ? Mention 
 different modes of fermentation. 538. What are the products of vinous 
 fermentation ? 539. How is diastase formed ? 540. To what does vinous 
 fermentation, if not checked, pass? What other name has vinegar? 
 541. How are ethers regarded by the chemist? Describe sulphuric 
 ether. 542. How are aldehydes related to acids and alcohols ? What 
 are the properties of acetic aldehyde ? 543. From what is camphor ob- 
 tained ? 544. Give composition and properties of chloral. 545. What 
 are anaesthetics ? What important representative of this class have we ? 
 
 CHAPTER XXVI. ORGANIC CHEMISTRY. (Continued.) 
 
 546. FROM what is formic acid obtained ? 547. What is the com- 
 position of acetic acid ? 548. Give method of preparing butyric acid, 
 and its properties. Where is glycocholic acid found ? 549. What can 
 be said of lactic acid and succinic acid ? Where is malic acid found ? 
 What are the uses of tartaric acid ? 550. Give composition of benzoic 
 acid. 551. Give history of salicylic acid. 552. What is the acid ob- 
 tained from the fruits of the orange family called? For what purposes 
 is gallic acid used? 553. What is the distinguishing characteristic of 
 tannic acids ? What is the basis of writing-ink ? 554. Give the anti- 
 dote for oxalic acid. Its uses. 555. What can be said of Rochelle 
 salts and cream-of-tartar ? 556. Have the organic alkaloids been arti- 
 ficially produced ? What substance precipitates the organic bases ? 
 557. Give the name of the alkaloid contained in tobacco. 558. What 
 narcotic is the active principle of opium ? 559. From what is strych- 
 nine obtained ? How does this alkaloid affect the nervous system ? 
 560. What organic bases are obtained from Peruvian bark? 561. To 
 what are the stimulating effects of tea and coffee due ? 562. Describe 
 
QUESTIONS. 339 
 
 the albuminoids. 563. Where is albumen found ? In what two modifi- 
 cations does it exist ? 564. What is said of musculine, fibrine, and glu- 
 ten ? 565. Give the essential constituent of milk. What is said of the 
 constitution of cow's milk ? 566. What use is made of gelatine ? From 
 what is chitine obtained ? 567. What was the first organic compound 
 artificially produced ? 568. Give the name of the compound occurring 
 in the juice of flesh. 569. Has pepsine ever been perfectly isolated? 
 
 570. What constitutes the chief part of the red globules of the blood ? 
 
 571. What are some of the products of putrefactive changes? How 
 may putrefaction be prevented ? 572. What is said of ferment diseases ? 
 
PRONUNCIATION OF SOME TECHNICAL WORDS 
 AND PROPER NAMES USED IN THIS WORK. 
 
 TECHNICAL WORDS. 
 
 A9'-e-tate. 
 
 A-cet'-ic. 
 
 A-ce'-tous. 
 
 A-cet'-y-lene. 
 
 Al-bu'-men. 
 
 Al'-de-hyde. 
 
 Al-iz'-avine. 
 
 Al-kal'-am-ide. 
 
 Al-lo-trop'-ic. 
 
 Al-lot'-ro-pism. 
 
 Al-u'-min-a. 
 
 Al-u'-min-ic. 
 
 Al-u-min'-i-um. 
 
 Am'-ad-in. 
 
 Am'-ide. 
 
 Am'-ine. 
 
 Am-mo'-nic. 
 
 Am-yl'-ic. 
 
 An-ses-thet'-ics. 
 
 An'-il-ine. 
 
 Ant'-o-zone. 
 
 Ar'-ab-in. 
 
 Ar-gen'-tic. 
 
 Ar'-sen-ic (noun). 
 
 Ar-sen'-ic (adj.). 
 
 A-ther'-mic. 
 
 A-tom'-ic. 
 
 At-om-i9'-it-y. 
 
 Ben-zo'-ic. 
 
 Bo-ra9'-ic. 
 
 Bro'-mine. 
 
 Bu-tyr'-ic. 
 
 Caf-fe'-me. 
 
 Cam'-er-a ob-scu'-ra. 
 
 Caoutchouc (Koo'-chook) 
 
 Cap'-il-la-ry. 
 
 Cap'-si-cme. 
 
 Chi tine (ki'-teen). 
 Chlorine (Klo'-rin). 
 Co'-balt. 
 Col-li-ma'-tor. 
 Col-loid'. 
 Cry-oph'-o-rus. 
 Di-al'-y-sis. 
 Di'-as-tase. 
 Di-a-ther'-man-cy. 
 Dif-fu'-sate. 
 Dy-ad'-ic. 
 E-lec-trol'-y-sis. 
 Er-e-ma-cau -sis. 
 Eth'-yl. 
 Eth'-yl-ene. 
 Flu'-o-rme. 
 Gly9'-e-rine. 
 Gly-co-chol'-ic (/col). 
 Gly '-co-gen. 
 Go-ni-om'-e-ter. 
 Has-mo-glo'-bme. 
 Hep'-tad. 
 Hip-pu'-ric. 
 Ho-mo3-o-mor'-phous. 
 Hy-dray'-id. 
 Hy-drox'-yl. 
 I'-o-dine. 
 I-som'-er-ides. 
 I-som'-er-ism. 
 I-so-mor'-phism. 
 j Laev'-u-lose. 
 Lith'-arge. 
 Lith'-i-um. 
 Mer-cu'-ric 
 Mer'-cu-rous. 
 Met-ath'-e-sis. 
 Meth'-yL 
 
PRONUNCIATION, ETC. 
 
 341 
 
 Mol'-e-cule. 
 
 Mon-ad'-ic. 
 
 Mor'-phine. 
 
 Mo-lyb-de'-num. 
 
 Nic'-o-tine. 
 
 Ni-trog'-e-uous. 
 
 Ni'-tryl. 
 
 O-le-fi'-ant. 
 
 Par'-af-fin. 
 
 Per-is'-sad. 
 
 Phe'-nyl. 
 
 Phos-phor'-ic. 
 
 Pho'-to-sphere. 
 
 Pip'-er-me. 
 
 Plat in'-ic. 
 
 Plat'-i-num. 
 
 Py-ri'-tes. 
 
 Pyr-o-gal'-lic. 
 
 Quan-tiv'-a-lence. 
 
 Quinine (Kwe-mne 1 , or Kurin'-in). 
 
 Saccharine (Sak 1 -a-rin). 
 
 Sa-li-cyl'-ic. 
 
 Sa-li'-va. 
 
 Sel'-e-nite. 
 
 Se-le'-ni-um. 
 
 Sil-i9'-ic. 
 
 Sil'-ic-on. 
 
 Spec'-tro-scope. 
 
 Spiegeleisen (Spe' -ghel-i-sen). 
 
 Sta-lac'-tite. 
 
 Sta-lag-mite. 
 
 Ste'-ar-me. 
 
 Strychnine (Strik -nin}. 
 
 Suc-9in'-ic. 
 
 Sul-phu'-ric. 
 
 Sul'-phur-ous. 
 
 Tar-tar'-ic. 
 
 Tet'-rad. 
 
 The'-ine. 
 
 Ther-mot'-ic. 
 
 Tho-ri'-num. 
 
 Tourmaline (Toor'-ma-lin}. 
 
 U-niv'-a-lent. 
 
 U'-re-a. 
 
 PEOPEK NAMES. 
 
 Al-deb'-a-ran. 
 
 Ampere (Ang-pdre 1 ). 
 
 A-vo-gad'-ro. 
 
 Berthelot (Ber 1 -tel-o). 
 
 Bes'-sem-er 
 
 Bournon (Boor-nong). 
 
 Bunsen (Boon -sen). 
 
 Chaptal (Shap'-tal). 
 
 Clausius ( Clow -si -us). 
 
 Daguerre (Day-yair). 
 
 De la Rive (Reeve\ 
 
 Descartes (Day-cart'}. 
 
 Du Bois-Reymond (X>u-bwd-Ray' 
 
 mong}. 
 
 Dumas (Du-mah'}. 
 Durkheim (Door'-kime). 
 Dutrochet (Du-tro'-shay). 
 Ehrenberg (A '-ren-berg}. 
 Fraunhofer (Frown' -ho- fer). 
 Galvani ( Gal-vah' -nee}. 
 Gay-Lussac ( Gati-ee-lti&'-sac}. 
 Gerharat ( Gair'-hart). 
 
 Haidlen (Hlde-Un). 
 Hauy (Ah'-ii-y}. 
 Joule (Jole). 
 
 Klaprcth (K lap' -rote}. 
 Leverrier (Le-ver -re^a). 
 Leyden (Li' -den). 
 Liebig (Lee -big}. 
 Marignac (Mar-in 1 -yac}. 
 Matteucci (Mat-tu'-tshee). 
 Mayer (My'-er). 
 Montgolfier (Afona-gol '-fec-ct}. 
 Oersted ( Ur'-sted}. 
 Par-a-cel'-sus. 
 Reaumur (Ray -o-mur). 
 Regnault (Rain'-yole}. 
 Ruhmkorff (Room'-korf) 
 Scheele (Shay 1 Jay). 
 Schellen (Shel'-len}. 
 Schonbein (Shane 1 -bine). 
 Vogel (Fo'-ghet). 
 Wohler ( Vatt-er). 
 
INDEX. 
 
 Absorption of heat, 52, 53; of spectral 
 
 lines, 110-114. 
 Acetate of lead, 250. 
 Acetic acid, 308. 
 
 aldehyde. 306. 
 Acetylene. 291. 
 
 Acids, constitutions of, 151 ; kinds of, 153. 
 Acid, arsenious, 211. 
 
 acetic, 305, 30S. 
 
 benzole, 310. 
 
 boric, 197. 
 
 butyric, 309. 
 Acid, carbolic, 295. 
 
 carbonic, 275. 
 
 carminic, 292. 
 
 citric, 311 
 
 di sulphuric, 239. 
 
 formic, 303. 
 
 gallic, 311. 
 
 gallotannic, 311, 313. 
 
 glycocholic, 309. 
 
 hippuric, 310. 
 
 hypochlorous, 179. 
 
 lactic, 309. 
 
 malic, 309. 
 
 meta -phosphoric, 210. 
 
 muriatic, 178. 
 
 nitric, 202. 
 
 nitrous, 201. 
 
 Nordhausen, 239. 
 
 ortho-arsenic, 212. 
 
 ortho-phosphoric, 210. 
 
 oxalic, 312. 
 
 prussic, 278. 
 
 pyroligneous, 309. 
 
 pyrophosphoric, 210. 
 
 silicylic, 310. 
 
 silicic, 268. 
 
 succinic, 304, 309. 
 
 su phuric, 237. 
 
 sulphurous, 236. 
 
 tannic, 311. 
 Acid-former, 139. 
 Acroleine, 296. 
 Actinism, 88. 
 Actinometry, 91. 
 
 Adhesion, 25; of liquids to solids. 25; of 
 gases to liquids, 28; of gases to solids, 28. 
 Alabaster, 246. 
 
 Albumen, 315 ; vegetable, 316. 
 Albuminous substances, 315. 
 Alcohols, 292-296. 
 Alcohol, common, 293. 
 Alcohol, methyl, 293. 
 
 ethyl, 293. 
 
 amyl, 294. 
 
 Aldehydes, 305, 306. 
 Ale, -294. 
 Alizarine, 292. 
 
 Alkalamides, naming of, 167. 
 Alkaloids, organic, 313. 
 Allotropism, 153. 
 Alum, 264. 
 Alumina, 263. 
 Aluminic oxide, 263. 
 
 silicates, '2(!3. 
 Aluminium, 26J. 
 Amadin, 300. 
 Amethyst, 268. 
 Amides, naming of, 167. 
 Ammonia, 199. 
 Ammonic chloride, 204 
 
 hydrate, 204. 
 
 nitrate, 206. 
 
 sulphate, 206. 
 
 carbonates, 206. 
 Ammonium, 206. 
 Anaesthetics, 308. 
 
 Analysis ; proximate , ultimate : qualita- 
 tive ; quantitative, 1.8 ; of molecule, 137. 
 Aniline. 292. 
 Animal electricity. 79. 
 Anomalous bodies, 153. 
 Anthracene, 292. 
 Antimony, 212. 
 Antozone, 221. 
 Aqua ammonia, 204. 
 Aqua regia. 197, 203. 
 Argentic chloride, 195. 
 
 mom xide, 195. 
 
 nitrate, 196. 
 Arrack, 294. 
 Arsenic. 210-212. 
 
 trioxide, 211 
 
 disulphide, 212. 
 
 trisulphide, 212. 
 Arseniuretted hydrogen, 210. 
 Artiads, 145, 214. 
 Astatic needle, 77. 
 Atmosphere, 228. 
 
INDEX. 
 
 343 
 
 Atom, 24, 134. 135; in chemistry, 136; 
 
 symbols of, 187. 
 Atomic heat, 162. 
 
 theory, 134 ; revival of, 185. 
 Atomicity, 141. 14'2, 145. 
 Attractions, 15; molecular, 24 ; capillary, 
 
 26; chemical, 12t>. 
 Auric chloride, 197. 
 
 cyanide, 197. 
 Avogadro'a law, 158 ; chemical application 
 
 oi?180. 
 
 Balance, 16. 
 Balsams, 298. 
 Baric oxide, 247. 
 
 chloride dihydrate, 248. 
 
 sulphate, 248. 
 Barium, 247. 
 
 Bases, constitution of. 151 ; kinds of, 153. 
 Bassorin, 298. 
 
 Battery, galvanic, 72 ; DanielPs, 78. 
 Benzine series, 291. 
 Benzoic acid, 310. 
 Benzol, 291. 
 Bessemer process, 258. 
 Binary theory, 139. 
 Bismuth. 213. 
 Bleaching-powder, 245. 
 Blow-pipe. 232. 
 Blue vitriol 242. 
 
 Bodies, compound and simple, 13. 
 Boiling-point 55. 
 Bonds, 143. 144. 
 Boric acid, 197. 
 Borax, 198. 
 Boron, 197. 
 Brandv, 294. 
 Brass, 241. 
 Britannia metal, 267. 
 Bromine, 181. 
 Bronze. 241. 
 Brucine. 314. 
 Burning-fluid. 291. 
 Butyric acid, 309. 
 Butter, 318. 
 
 C. 
 
 Cadmium. 252. 
 Caesium, 193. 
 Caffeine, 315. 
 Calcic oxide, 244. 
 
 hydrate, 244. 
 
 sulphate, 246. 
 
 " dihydrate, 246. 
 
 carbonate, 246. 
 
 phosphate, 247. 
 
 pxalate; 312. 
 Calcium group, 244. 
 Calomel, 243. 
 Caloric, 62. 
 Camera-obscura, 94. 
 Camphene. 291. 
 Camphor. 807. 
 Candle, how it burns, 283. 
 Caoutchouc, 299. 
 Capillarity, reversed, 27. 
 
 Capillary attraction, 26, 27. 
 
 Capsicine, 314. 
 
 Carbolic acid, 295. 
 
 Carbon, 270-287 ; history and properties 
 
 of, 270; allotropic forms of, 270. 
 Carbonate of lead, 249. 
 Carbonic acid, 275. 
 Carbonic monoxide, 274. 
 dioxide, 275. 
 disulphide, 278. 
 Caseine, 317. 
 Cast-iron, 256. 
 Catalysis, 131. 
 Caustic potash, 189. 
 Caustic soda, 187. 
 Cellulose, 301. 
 Cement, 245. 
 Cementation, 258. 
 Change by pairs. 146. 
 Charcoal, 272. 
 
 uses of, 278. 
 
 Chemical action, character of, 127; con- 
 ditions of, 129; intensities of, 131. 
 attraction, gradations in, 129. 
 equations, 16s. 
 force, 127; characteristic effect* of, 
 
 128; range of, 131. 
 formula, 168. 
 physics, 13. 
 
 rays. 83 ; variations of, 91, 92. 
 reactions of light, 3. 
 types, 140. 
 Chemism, 127, 128. 
 Chemistry, basis of; 132; theoretical, 134 
 
 of carbon compounds, 157. 
 Chitine, 318. 
 Chloral, 807. 
 
 hydrate, 307. 
 Chloric disulphide, 235. 
 monoxide, 180. 
 tetroxide, 180. 
 acid, 180. 
 trioxide. 179. 
 
 Chlorine, 175; preparation of, 176; prop- 
 erties of, 176 ; uses of, 177 ; combustion 
 of turpentine in, 178. 
 Chloroform, 807. 
 Chondrine, 318. 
 Chromic oxide. 262. 
 
 trioxide, 262. 
 Chromium, 261. 
 Cinchonine, 315. 
 Cinnabar, 243. 
 Citric acid, 311. 
 Cleavage. 43. 
 Coal-oil. 238. 
 Coal-tar. 290. 
 Cobalt, 260. 
 
 Cobaltous chloride, 261. 
 Cohesion, 25, 26 ; influence of, 130. 
 Coke, 290. 
 Collimator, 103. 
 Colloids. 31. 
 
 Colored lights, varying effects of, 96. 
 Collodion, 802. 
 Colors, cause of 81 . 
 
 Combining capacity. 141 ; volumes, 162. 
 Combination, control of. 144. 
 Combining volumes, theory of, 158, 162. 
 
344 
 
 INDEX. 
 
 Combustion, 64, 279; rapid, 280; slow, 
 281 ; heat of, 281 ; spontaneous, 281. 
 
 Common salt, 185. 
 
 Compounds, 128; metameric, 157; poly- 
 meric, lob. 
 
 Compound blow-pipe. 282. 
 
 Condensation of gases, 60. 
 
 Conductors, 65. 
 
 Copper, 241. 
 
 Corrosive sublimate, 243. 
 
 Cream-of-tartar, 312. 
 
 Creosote, 295. 
 
 Crith, 161. 
 
 Cryophorus, 58. 
 
 Crystallization, 35-46 ; phenomena attend- 
 ing, 38. 
 
 Crystalloids, 81. 
 
 Crystals, natural, 86; artificial, 36; by 
 solution, 86 ; by fusion, 37 ; by sub- 
 limation, 37 ; in the solid state, 87 ; by 
 decomposition, 38 ; forms of, 40 ; axes 
 of, 40 ; elements of crystalline form, 40 ; 
 systems of, 41, 42. 
 
 Cupric oxide, 241. 
 sulphate, 242. 
 arsenite, 242. 
 
 Cyanogen, 278. 
 
 D. 
 
 Daguerreotype, 95. 
 
 Decomposition, 128. 
 
 Definite proportions, law of, 132. 
 
 Density, 22. 
 
 Derivation of form, 43. 
 
 Developing a photograph, 95. 
 
 Dew, 52 
 
 Dew-point, 58. 
 
 Dextrine, 300. 
 
 "Dextrose, 297. 
 
 Diamagnetism, 70. 
 
 Diamond, 271. 
 
 Diastase, 304. 
 
 Diathermancy, 53. 
 
 Dichromic trioxide, 262. 
 
 Diffusion, of gases, 29; rate of, 29; of 
 liquids and solids through gases, 30 ; of 
 liquids, 31; rate of, 31; of gases thronrrh 
 liquids. 32 ; of solids through liquids, 
 33 ; of gases through solids, 35. 
 
 Dimorphism, 45. 
 
 Dispersion, 101: power of crown-glass. 
 101; of flint-glass, 101; of bisulphide of 
 carbon, 101. 
 
 Distillation, 60. 
 
 Distilled liquors, 294. 
 
 Double solar spectrum, 124. 
 
 Draper's researches, 108. 
 
 Prummond light, 283. 
 
 Dualism, 139. 
 
 E. 
 
 Ebullition, 55. 
 
 Electricity, 65-80 : animal, 79 ; magnetic. 
 
 73 ; thermo, 77 ; voltaic, 71 ; influence of, 
 
 130. 
 Electric light, spectrum of, 99. 
 
 Electric lamp, 100. 
 
 tension, 66. 
 Electrodes, 72. 
 Electrolysis, 75. 
 Electro-magnetism, 76. 
 Electrotype, 76. 
 Elements, 128, 129; organic, 156; in a 
 
 free state, 147; naming of, 164; peris - 
 
 sad, 169 ; artiad, 214. 
 Elements in sun, 121 ; in stars, 122. 
 Epsom salts, 251, 312. 
 Eremacausis, 218. 
 Ethers, 805. 
 Ethyl, 149. 
 Ethylene, 290. 
 Ethylic ether, 305. 
 Expansion of solids, 46 ; of liquids, 47 ; of 
 
 gases, 47. 
 
 F. 
 
 Fats and oils, 295. 
 Fermentation, 302-305. 
 
 vinous. 304. 
 
 saccharous, 304. 
 
 acetous. 805. 
 
 lactic, 309. 
 Ferments, 303. 
 Fermentable bodies, 303. 
 Ferment diseases, 320. 
 Ferric carbides, 256. 
 
 disulphide, 259. 
 Ferrous oxide, 259. 
 
 sulphate, 260. 
 
 carbonate, 260. 
 Fibrine, 816. 
 Fire-damp, 288. 
 Flame, 282; structure of, 284; effect of 
 
 temperature on, 285. 
 Fluorescence, 88. 
 Fluorine, 180. 
 Force, indestructible, 12. 
 Forces, radiant, motions of, 80. 
 Formic acid, 808. 
 Fraunhofer's lines, 107, 111, 115. 
 Freezing mixtures, 55. 
 Fusel-oil, 294. 
 
 G. 
 
 Gallotannic acid, 312. 
 Galvanic battery, 72. 
 Galvanism. 71 ; quantitv and intensity 
 
 of, 74. 
 
 Gas, illuminating, 290. 
 Gases, 20, 21 ; condensation of, 60. 
 German silver, 241. 
 Gelatine, 318. 
 Gin. 295. 
 
 Glass, 269 ; varieties of, 269. 
 Glauber's salt, 187. 
 Gluten, 316. 
 Glycerine, 296, 304. 
 Glycocholic acid, 309. 
 Glycogen, 800. 
 
 Gold, 196 ; properties of, 197. 
 Graphite. 271. 
 Gravity, 15. 
 Green 'vitriol, 260. 
 
INDEX. 
 
 345 
 
 Gum, 298. 
 Gum-arabic, 298. 
 Gun-cotton, 302. 
 Gunpowder, 191. 
 Gypsum, 246. 
 
 , Isomerid.es, 158. 
 Isomerism, 155, 157. 
 Isomorphism, 44. 
 
 II. 
 
 ip, 183. 
 Haloids, 154. 
 Haemato-crystalline, 319. 
 Haemoglobine. 319. 
 
 Heat, 46-65 ; its effects. 46 ; expansion 
 by, 47; measurement of, 47; transfer- 
 ence, 49 ; conductions of, 49 ; convec- 
 tion of, 51 ; radiation of, 51 ; kinds of 
 radiant. 52; absorption of, by aqueous 
 vapor, 53; latent, 54; specific, 54; na- 
 ture of, 61 ; relation to chemical action, ; 
 61 ; as a mode of motion, 63. 
 Heavy spar, 248. 
 Horn silver, 195. 
 Hydracids, 154. 
 
 Hydrates. 152, 153 ; quantivalence of, 153. 
 Hydric chloride, 17S. 
 chlorate, 179, 180. 
 perchlorate, 179. 
 fluoride, 181. 
 bromide, 183. 
 iodide, 183. 
 nitride, 199. 
 nitrate, 202. 
 phosphide, 208. 
 arsenide, 210. 
 oxide. 221. 
 dioxide, 228. 
 sulphide, 283. 
 sulphite, 236. 
 sulphate, 237. 
 cyanide, 278. 
 Hydrides, 172. 
 
 Hydrocarbons and their derivatives, 287- 
 292. 
 
 Hydrogen, 169-175; occurrence in Nature, j 
 170; preparation of, 170; chemical prop- 
 erties of, 172; condensation of, 174; 
 occlusion of, 174. 
 
 Hvdrogenium. 174. 
 
 Hydrometer, 21. 
 
 Hydro-sodic borate, 198. 
 
 Hygrometer, 59. 
 
 Illuminating gas. 290. 
 
 India-rubber, 299. 
 
 Induction, electrical 66; magnetic, 69; 
 
 chemical, 130; theory of, 67; induced 
 
 currents, 74. 
 Inflammable air, 169. 
 Insulators, 65. 
 Interference of light, 82. 
 Inuline, 300. 
 Invisible image, 94. 
 Iodine, 182. 
 Iridium, 266. 
 Iron, 253; history and occurrence of, 253; 
 
 properties, 254; preparation of, 253; 
 
 uses of, 256. 
 
 Kerosene. 
 
 Lactic acid, 309. 
 
 Lactose, 298. 
 
 Laevulose, 297. 
 
 Lager-beer, 294. 
 
 Lamp-black, 274. 
 
 Latent heat, 54. 
 
 Laughing gas. 201. 
 
 Law defined. 11. 
 
 Law of Avogadro, 158; of definite propor- 
 tions, 132 ; multiple proportions, 133. 
 
 Lead, 248. 
 
 Legumine, 317. 
 
 Light, 80-127; analysis of, 80 ; wave-theory 
 of, 81 ; interference of, 82 ; polarization 
 of, 83; double refraction of, 87 ; chemis- 
 try of, 88; refrangibility of, 89 ; effect, on 
 vegetation, of rays of, "92 ; chemical re- 
 actions, 93; ifcomposition of, 98; ab- 
 sorption of, 110. 
 
 Ugnine, 301. 
 
 Lime, 244. 
 
 Limestone. 246. 
 
 Lines, absorption, 112; reversal of, 113; 
 what indicated by, 109. 
 
 Liquefaction, 54. 
 
 Liquids, 20. 
 
 Litharge, 249. 
 
 Lithium, 193. 
 
 Litre, 15. 
 
 Luminous spectrum, 98. 
 
 Lunar caustic, 196. 
 
 M. 
 
 Magnesia. 251. 
 Magnesic oxide. 251. 
 
 sulphate, 251. 
 Magnesium group, 250. 
 Magnetic induction, 69. 
 
 oxide. 259. 
 Magnetism, 63-71 ; kinds of magnets, 68 ; 
 
 induction of, 69. 
 Malic acid, 309. 
 Malt, 305. 
 Manganese. 260. 
 Manganic dioxide, 260. 
 Marsh-pas, 287, 288. 
 Marsh's test, 211. 
 Matter denned, 12. 
 
 indestructible, 12. 
 
 interior structure, 23 ; porosity of 23 ; 
 motions of internal parts of, 23 ; divisi- 
 bility of, 24. 
 
 measurement, 14. 
 Matter and force, 12. 
 Melting-point, 54. 
 Mercuric oxide, 243. 
 
 chloride, 243. 
 
 sulphide, 243. 
 
346 
 
 INDEX. 
 
 Mercurous chloride, 243. 
 
 Mercury, 241. 
 
 Metathesis, 13T. 
 
 M eta-acids, 153. 
 
 Methane, 288. 
 
 Methyl, 149. 
 
 Metrical measures, 15. 
 
 Metre, 15. 
 
 Miasms, 320. 
 
 Milk, 317. 
 
 Milk-sugar, 298. 
 
 Molecular motions, 45. 
 weight, unit of, 160. 
 
 Molecule, 24, 134, 135 ; in physics, 135 ; in 
 chemistry, 135 ; structure of, 147 ; space 
 relations of, 158 ; size of, 159. 
 
 Morphine, 313 
 
 Mortar and cement, 245. 
 
 Mucilage, 298. 
 
 Multiple proportions, law of, 133. 
 
 Muriatic acid, 178. 
 
 Musculine, 316. 
 
 N. 
 
 Naming elements, 164; compound radi- 
 cals, 164; binary compounds, 165; salts, 
 acids, and bases, 167 ; amides, amines, 
 and alkalamides, 167. 
 Naphthaline, 292. 
 Nascent state, 181. 
 Nature, order of, 11. 
 Negatives and positives, 72, 95. 
 Nickel, 260. 
 Nicotine, 313. 
 Nitre, 190. 
 Nitric acid, 202. 
 
 monoxide, 201. 
 
 dioxide, 201. 
 
 trioxide, 201. 
 
 tetroxide, 201. 
 
 pentoxide, 201. 
 
 Nitrogen, 198; preparation and proper- 
 ties of, 199. 
 
 Nitrogen group, 198-213. 
 Nitro-benzine, 292. 
 
 glycerine, 296. 
 Nitryl, 151, 302. 
 Nomenclature, 163-169. 
 Normal salts, 153. 
 
 O. 
 
 Occlusion, 35, 174. 
 
 Olefiant gas, 290. 
 
 Olefine series, 289. 
 
 Olein, 295. 
 
 Opal, 268. 
 
 Opium, 314. 
 
 Organic alkaloids, 313. 
 
 Organic elements, 156. 
 
 Orthoacids, 153. 
 
 Osmium, 266. 
 
 Osmose, of gases, 29; of liquids, 82. 
 
 Oxalic acid, 313. 
 
 Oxygen, 214-231 ; modifications of, 214 ; 
 
 occurrence of, 215; preparation of, 215; 
 
 properties of. 216; combustion in, 217; 
 
 relation to life of, 218. 
 Ozone, 219 ; properties of, 220. 
 
 P. 
 
 Palladium, 266. 
 Palmitine, 296. 
 Paraffins, 287, 289. 
 Paris green, 242. 
 Pearlash, 190. 
 Pectin, 298. 
 
 Ferissads, 145 ; inconvertible, 146. 
 Petrifaction, 268. 
 Petroleum, 288. 
 Phenol, 295. 
 
 Phenomenon defined, 11. 
 Phlogiston, 138. 
 Phosphorescence, 87. 
 Phosphoric pentoxide, 210. 
 Phosphorus, 206; distribution of, 206; 
 properties of, 207 ; modifications of, 207. 
 208. 
 
 Phosphuretted hydrogen, 208. 
 Photography, 98; celestial, 96. 
 Physical verifications, 161. 
 Physical properties of matter, 12. 
 Pig-iron, 257. 
 Pile, voltaic, 72. 
 Piperine, 314. 
 Platinic tetrachloride, 265. 
 Platinum-black, 265. 
 Platinum group, 265. 
 Plumbago, '271. 
 Plumbic monoxide, 249. 
 
 carbonate, 249. 
 
 tetroxide, 249. 
 
 acetate, 250. 
 Pneumatic trough, 171. 
 Polarity, 146. 
 Polarization, 85. 
 Porcelain. 263. 
 Porter. 294. 
 Potassic monoxide, 189. 
 
 hydrate, 189. 
 
 chloride, 189. 
 
 carbonates, 190. 
 
 nitrate, 190. 
 
 sulphate, 192. 
 
 silicate, 192. 
 
 cyanide, 279. 
 
 Potassio-aluminic sulphate, 264. 
 Potassium, 188. 
 Prefixes. 166. 
 Press-cake. 191. 
 
 Prevision the best test of science, 12. 
 Primary rays. 99. 
 Prisms, 8'); combination of, 101; trains 
 
 of, 102. 
 Proportions, definite, 132; multiple, 133; 
 
 equivalent, 184. 
 Prussic acid, 278. 
 Puddling, 254. 
 Putrefaction, 802. 
 Pyroxylene, 301. 
 
 Q. 
 
 Quantivalence, 141, 142; its expressions, 
 
 142 ; varying, 144. 
 Quinine, 314. 
 Quartation, 197. 
 Quartz, 268. 
 
INDEX. 
 
 347 
 
 Radiant motion, transmission of, 82. 
 Radicals, theory of, 148; simple, 148; 
 compound, 149 ; quantivalencs of, 149. 
 Rays, chemical. S3. 
 Refraction, double, 87. 
 Refrangibility of invisible rays, 89. 
 Resins, 298. 
 Rhodium, 266. 
 Rochelle salts, 312. 
 Rubidium, 193. 
 Rum, 294. 
 Ruthenium, 266. 
 
 Saccharine bodies, 296-502. 
 Safety-lamp, 2S6. 
 Sal-ammoniac, 204. 
 Sahcine, 310. 
 Salicylic acid, 310. 
 Saltpetre, 190. 
 
 Salts, constitution of, 152 ; classes of, 153. 
 Saturation, 34. 
 Science defined, 11. 
 Selenium, 240. 
 
 Separation of solids from solution, 34. 
 Silica, 267. 
 Silicic acid, 268. 
 dioxide, 267. 
 fluoride, 268. 
 Silicon, 267. 
 Silver, 194 ; properties and uses, 195. (See 
 
 ARGENTIC.) 
 Snow-crystals, 224. 
 Soap. 18^, 192, 193. 
 Sodic chloride, 184. 
 
 carbonates, 136, 187. 
 hydrate, 1S7. 
 sulphate, 187. 
 nitrate, 187. 
 silicates, 192. 
 Sodium group, 184., 
 Solar envelope, ItSr* 
 
 prominences, 120. 
 Soluble glass, 192. 
 Solution. 33. 
 Specific gravity, of liquids, 20 ; of gases, 
 
 20. 
 Specific heat, 54. 
 
 volume, 17 ; weight, 17. 
 Spectral lines, 106; indications of, 109; 
 
 coincidence of bright and dark. 110. 
 Spectroscope, 103: essential parts of, 103: 
 
 direct vision, 104 ; mounted, 104. 
 Spectroscope in steel-making. 116. 
 Spectrum, solar, 99; luminous, 98; of the 
 
 electric light 99; measuring the, 103: 
 
 Newton's, 106 ; affected by pressure or 
 
 density. 109 ; lines. 110 ; double, 124. 
 Spectrum analysis. 99-127. 
 Speculum metal, 241. 
 Spheroidal state. 56. 
 Spieseleisen, 257. 
 Stannic dioxide, 266. 
 Star, conflagration of a, 122. 
 Starch, 299. 
 Stars, motions of, 125, 
 
 Stearine. 295. 
 
 Steel, 258. 
 
 Stibic trioxide, 213. 
 
 trisulphide, 213. 
 Stone-ware. 264. 
 Strontium, 247. 
 Strychnine, 814. 
 Substitution theory, 140. 
 Succinic acid. 309. 
 Sugar, grape, 297. 
 
 fruit. 297. 
 
 cane. 297. 
 
 milk. 298. 
 
 Sulphur group. 231-241. 
 Sulphuretted hydrogen, 233. 
 Sulphuric oxide", 236. 
 
 acid. 237 ; manufacture oi, 237, 238. 
 
 properties and uses, 239. 
 Sulphurous oxide, 235. 
 
 acid. 236. 
 
 Sun, elements in, 121. 
 Symbols of atoms, 137. 
 Synthesis. 137. 
 Systems of crystallization, 41. 
 
 T. 
 
 Tannic acid, 311. 
 
 Tannin. 311. 
 
 Tartaric acid. 309. 
 
 Tele-spectroscope, 117. 
 
 Tellurium. 240. 
 
 Terpenes, 291. 
 
 Tetraferrio carbide, 258. 
 
 Theine. 315. 
 
 Theobromine, 315. 
 
 Theory of acids, bases, and salts. 151: 
 of radicals, 148; of polarization, 86: ot 
 absorption, 114; atomic, 134; progress 
 of chemical 138; binary, 139; unitary. 
 139; substitution. 139"; of chemical 
 types, 140 ; of isomerism and allotro- 
 pism. 155; of combining volumes, 158; 
 of effects, 162. 
 
 Thermo-electricity, 77. 
 
 Thermometer, 47": mercurial, 47; scales, 
 48. 
 
 Thorium, 267. 
 
 Tin. 266. 
 
 Titanium. 267. 
 
 Touch-paper. 191. 
 
 Triferrc tetroxide. 259. 
 
 Turpentine series. 291. 
 
 Type-, chemical, 140. 
 
 U. 
 
 Unitary theory. 139. 
 
 Vapor, volume and density of, 59 ; elastic 
 force of, 59. 
 
 Vaporization, 57; heat of, 57 ; cooling ef- 
 fects of. 58. 
 
 Varnishes, 299. 
 
 Vegetation, influence of light on, 92. 
 
 Verdigris, 241. 
 
 Vermilion, 244. 
 
348 
 
 INDEX. 
 
 Vinegar, 309. 
 Volatile liniment, 201. 
 Volumes, combining, 162. 
 Voltaic electricity, 71-76. 
 
 W. 
 
 Water, 221 ; production of, 222 ; compo- 
 sition of, 222; properties of, 22>; un- 
 equal expansion of, 225; specific heat 
 of, 225; solvent power of, 226; purifica- 
 tion of, 227; chemical properties of, 227 
 
 Water-former, 139. 
 
 Weights, 16 ; metrical standard, 17. 
 
 Welding, 255. 
 
 Whiskey, 294. 
 
 White lead, 249. 
 
 White vitriol, 252. 
 Wine, 294. 
 Wood-spirit, 293. 
 
 Yeast, 304. 
 
 Zinc, 251. 
 
 Zincic sulphide, 251. 
 
 carbonate, 2c,l. 
 
 oxide, 252. 
 
 silicate, 251. 
 
 chloride, 252. 
 
 sulphate, 252. 
 Zirconium, 267. 
 
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 Symptomatology of Insanity ; Clinical Groups of Mental Disease; The Morbid Anat- 
 omy of Mental Derangement ; The Treatment of Mental Disorders. 
 
 THE CHEMISTRY OF COMMON LIFE. By the 
 
 late JAMES F. W. JOHNSTON, F. R. S., etc., Professor of Chemistry hi 
 the University of Durham ; author of " Lectures on Agricultural 
 Chemistry and Geology " ; " Catechism of Agricultural Chemistry 
 and Geology," etc. A new edition, revised, enlarged, and brought 
 down to the Present Time, by ARTHUR HERBERT CHURCH, M. A., 
 Oxon.. author of "Food: its Sources, Constituents, and Uses"; 
 " The Laboratory Guide for Agricultural Students " ; " Plain Words 
 about Water," etc. Illustrated with Maps and numerous Engravings 
 on Wood. In one vol., 12mo, 592 pages. Price, $2.00. 
 
 SUMMARY OF CONTENTS : The Air we Breathe; The Water we Drink ; The Soil we 
 Cultivate: The Plant we Rear ; The Bread we Eat; The Beef we Cook ; The Beverages 
 we Infuse; The Sweets we Extract; The Liquors we Ferment; The Narcotics we In- 
 dulge in; The Poisons we Select; The Odor? we Enjoy; The Smells we Dislike; The 
 Colors we Admire; What we Breathe and Breathe for; What, How, and Why we 
 Digest; The Body we Cherish; The Circulation of Matter. 
 
 in. 
 
 PROGRESS AND POVERTY. An Inquiry into the 
 Cause of Industrial Depressions and of Increase of Want with In- 
 crease of Wealth: The Remedy. By HENRY GEORGE. One vol., 
 12mo. 512 pages. Cloth. Price, $2.00. 
 
 I propose to seek the law which associates poverty with progress, and increases 
 
 in th 
 
 want with advancing wealth; and I believe that in the explanation of this paradox we 
 shall find the explanation of those recurring seasons of industrial and commercial pa- 
 ralysis which, viewed independently of their relations to more general phenomena, 
 seem so inexplicable." Extract from Introduction. 
 
 GREAT LIGHTS IN SCULPTURE AND 
 
 PAINTING. A Manual for Young Students, By S. D. DOREMUS. 
 
 One vol., 1 2mo. Cloth. Price, $1.00. 
 
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 For sale by all booksellers ; or sent, post-paid, to any address in the lifted States, 
 on receipt of price. 
 
 D. APPLETON <fe CO., PuUi$hJr9, Neu Tort. 
 
MEMOIRS 
 
 MADAME DE REMUSAT, 
 
 1802-1808. 
 
 WITH PREFACE AND NOTES BY HER GRANDSON. 
 
 TRANSLATED BY 
 
 Mrs, CASHEL HOEY and JOHN LILLIE. 
 
 In three volumes, 8vo. Paper, $1.50 ; each volume separately, 50 cents; 
 or in one volume, 12mo, cloth, $2.00. 
 
 "The literary event of the day," remarks a Paris correspondent, "is the 
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 whom she remained from 1802 to 1808, and so followed her in her imperial for- 
 tunes." 
 
 " It would he easy to multiply quotations from this interesting hook, which no 
 one will take up without reading greedily to the end ; hut enough has heen said 
 
 ' These Memoirs are unusually attractive. As illustrating the interior history 
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 the personality of their writer is not the least interesting revelation." From 
 leading article in the Daily News. 
 
 "The most fascinating personal narrative which has been published since 
 Madame d'Arblay's Memoirs." May/air. 
 
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 "To thoughtful readers the most entertaining as well as the most valuable 
 parts of the book are those which graphically and piquantly depict traits of 
 character, manners, and life, and of such things this work is fall.'' 2fel0 York 
 Evening Post. 
 
 "It brings into broad relief the smallnesses of the great Napoleon ; the in- 
 trigues and scandals of court-life under the First Empire ; the jealousies of the 
 Bonapartes of Josephine and her family; the listlessness and indolent character 
 of the latter, and the base uses employed by Napoleon to subordinate all around 
 him to his will." New York Commercial Advertiser. 
 
 "No book of the year is calculated to create the sensation that this will. It 
 is from the pen of an observer who writes of what she knew and saw and 
 heard." Brooklyn Daily Union-Argw. 
 
 "Notwithstanding the enormous library of works relating to Napoleon, we 
 know of none which cover precisely the ground of these Memoir?. Madame 
 de Remnsat was not only lady-in-waiting to Josephine during the eventful 
 years 1802-1808, hut was her intimate friend and trusted confidant. Thus we get 
 a view of the daily life of Bonaparte and his wife and the terms on which they 
 lived not elsewhere to be found." New York Mail. 
 
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PEOGEESS AID POYEETY, 
 
 A A' INQUIRY INTO THE CAUSE OF INDUSTRIAL DE- 
 PRESSIONS, AND OF INCREASE OF WANT 
 WITH INCREASE OF WEALTH: THE 
 REMEDY. 
 
 By HENI^Y GEORGE. 
 
 One vol., 12mo, 512 pages. Cloth. Price, $2.00. 
 
 From The Popular Science Monthly. 
 
 "In 'Progress and Poverty ' Mr. Henry George has made a careful and sys- 
 tematic inquiry into the conditions of the production and distribution of wealth, 
 the relations of labor and capital, and has traced out the action of what he con- 
 siders the cause of the continued association of poverty with advancing wealth. 
 However unpalatable its conclusions to certain large classes of the community, 
 this book must, from its clearness of statement, ingenuity of argument, its large 
 human sympathy, aud the broad and philosophic spirit with which the question 
 is treated, claim the attention of all who realize the paramount importance of 
 the subject and the value of a thoughtful contribution toward its elucidation. . . . 
 I am not here concerned with criticising Mr. George's work: my purpose is served 
 if I have succeeded in drawing attention to what seems to me one of the most 
 important contributions yet made to economic literature. 
 
 " G. M. LTJNGREN." 
 From the New York Sun. 
 
 " Let us say, at the outset, that this is not a work to be brushed aside with 
 lofty indifference or cool disdain. It is not the production of a visionary or a 
 sciolist, of a meagerly-equipped and ill -regulated mind. The writer has brought 
 to his undertaking a comprehensive knowledge cf the data and principles of 
 science, and hie skill in exposition and illustration attests a broad acquaintance 
 with history and literature. His book must be accounted the first adequate pres- 
 entation in the English lansnase of that new economy which has found powerful 
 champions in the German universities, and which aims at a radical transfor- 
 mation of the science formulated by Adam bmith. Ricardo, and J. S. Mill. The 
 author does not expect the scheme which he propounds in this remarkable book 
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 and respectful hearing. This much he unquestionably deserves. Few books 
 have, in recent years, proceeded from any American pen which have more 
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 tion ; or, we venture to affirm, without a twinge of misgiving and regret." 
 
 From the Chicago Tribune. 
 
 "Mr. George's book is welcome, because it will cause a discussion of a sub- 
 ject the magnitude and importance of which none will deny. It is a bold and 
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 moreover, the writer is in earnest, and he is also original." 
 
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IMPORTANT WORKS. 
 
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 The Life and Words of Christ. By CUNNINGHAM GEIKIE, 
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