UC-NR SB John Sv;ett 1. Solar Spectrum. 2. Spectrum of Potassium 3. Spec ir 4 Spec Harpe H Hi 150 160. , 170 93 100 110 120 130 140 150 160 HO lllllllllllllllil.lltlllllllllllllllllllllllllllliilllllllillllllllllllllllllll'llllll 100 110 120 130 140 150 If 110 120 130 140 150 160 100 110 1ZO 130 140 ISO 160 170 100 11C 1ZO 130 140 150 TL of Sodium, of Strontium. Brother s .TfewYork . 5. Spectrum, of Calcium. 6. Spectrum of Barium. See page 286. SCIENCE FOB THE SCHOOL AND FAMILY. PART II. CHEMISTRY. BY WORTHINGTON HOOKER, M.D., PROFESSOR OF THE THEORY AND PRACTICE OF MEDICINE IN YALE COLLEGE, AUTHOR OF "HUMAN PHYSIOLOGY," "CHILD'S BOOK OF NATURE," "NATURAL HISTORY," ETC. Ellustrateti b$ Numerous SECOND EDITION, REVISED AND CORRECTED. NEW YORK: HARPER & BROTHERS, PUBLISHERS, FRANKLIN SQUARE. 1876. ,UCATION By DR. WOETHINaTON HOOKER. THE CHILD'S BOOK OF NATURE. For the Use of Families and Schools ; intended to aid Mothers and Teachers in training Children in the Observation of Nature. In three Parts. Engravings. The Three Parts complete in one vol., small 4to, Cloth, $1 CO ; Separately, Part, L, 60 cents ; Parts II. and III., 65 cents each. PABT L PLANTS. PABT IL ANIMALS. PABT IIL AIK, WATER, HEAT, LIGHT, &o. FIRST BOOK IN CHEMISTRY. For the Use of Schools and Families. Engravings. Square 4to, Cloth, 90 cents. NATURAL HISTORY. For the Use of Schools and Families. Nearly 300 Engravings. 12mo, Cloth, $1 50. SCIENCE FOR THE SCHOOL AND FAMILY. PART I. NATURAL PHILOSOPHY. Engravings. 12mo, Cloth, $1 50. PABT II. CHEMISTRY. Engravings. 12mo, Cloth, $1 50. PABT III. MINERALOGY AND GEOLOGY. Engravings. 12mo, Cloth, f!50. Published by HARPER & BROTHERS, Franklin Square, ff. T. B^P* HABPEK & BEOTm?ns will send any of the above works by mail, postage prepaid, to any part of the United States or Canada, on receipt of the price. Entered according to Act of Congress, in the year 1875, by HARPER & BROTHERS, in the Office of the Librarian of Congress, at Washington. PREFACE TO THE FIRST EDITION. THIS book differs from all other text-books on Chemistry in several particulars. 1st. It includes only that which every well-informed person ought to know on the subject, and excludes whatever is of value only to those who are to be chemists, or who intend to apply chemistry to specific branches of busi- ness, as medicine, metallurgy, etc. For the extended and specific knowl- edge required for such purposes other books can be studied afterward, this book being suitable for a preliminary preparation. I will give a single ex- ample of the sort of selection I have practiced in carrying out my plan. I exclude the consideration of the tests of the presence of arsenic in cases of poisoning, because the application of them is so complicated that none but a professed chemist can make the investigation. On the other hand, I notice very particularly the chemical action of the whites of eggs upon corrosive sublimate, because, as poisoning with this substance is quite fre- quent, and promptness in the use of the antidote is all-important, every one ought to know what the antidote is, and he will certainly be the more prompt to apply it if he understand its modus operandi. 2d. I recognize fully the distinction between a book for reference and a book for study. The pupil should have his book specially adapted for study ; and the teacher should have, in addition to this, books for refer- ence, so that his knowledge may be wider than that included in the text- book, in order that he may meet any inquiries that may arise, or add to the facts and illustrations which the text-book furnishes, as occasion may offer. Most text-books are too extensive, because the distinction referred to is not observed. The attempt sometimes made to draw the line between the mat- 541767 JV PEEFACE. ter for the pupil to learn and other matter not so essential by a difference in type is always awkward, and is not fully effectual. 3d. While most books on Chemistry are illustrated chiefly from phenom- ena developed in the laboratory of the chemist, I have taken great pains to have abundant illustrations from common every-day phenomena, so that this book is largely a Chemistry of Common Things. As an illustration of the general neglect on this point, I find that very few of all who have studied ordinary chemical books, or have attended lectures, can explain the chemistry of so very common a thing as striking fire. 4ith. The arrangement of topics is entirely different from that of any other text-book on Chemistry. It is such that the most simple and inter- esting topics come first, and each page enables the pupil to understand bet- ter the pages that follow. I begin with making the pupil familiar with the four grand elements, oxygen, nitrogen, carbon, and hydrogen, and their combinations with each other. This brings out fully those most interesting of chemical subjects, combustion, water, and the chemistry of the atmos- phere. I then pass to the combinations of these four elements with other elements, and the combinations of these latter with each other. In this portion of the book I notice first the metals and their compounds with oxy- gen the oxides ; then the metalloids sulphur, phosphorus, etc., and their combinations with oxygen the oxygen acids, and also the hydrogen acids. Then in natural sequence come to view the salts formed by the union of these acids and oxides, and in connection with these the salts of the chlorine family. Now follows a development of the laws of chemical affinity, the examples being taken from the facts already brought out, so that we have here in part a review of what is gone before, which is of great advantage to the student. In this connection I introduce the consideration of chemical equivalents, symbols, and the atomic theory. All of this is commonly in- troduced into the first part of Chemistry, and hence is generally but par- tially understood, and is very diy and uninteresting ; but on the plan which I have adopted the pupil easily comprehends it, and is interested at every step. Then comes in. naturally the influence of the modifiers of chemical affinity heat, light, electricity, and magnetism which before have been al- luded to here and there, but now are fully treated of. The hook concludes with the consideration of Organic Chemistry. PBEFACE. V The only text-book which has any resemblance to this in its plan is Stb'ckhardt's, and the resemblance touches only a few points. The coinci- dence, so far as it goes, gave me great gratification when my attention was called to it by a friend to whom I was developing my plan. A large proportion of the experiments can be tried with very simple ap- paratus, and a few dollars' worth of materials obtained from the druggist ; but it will be well for the teacher to purchase a few articles such as re- torts, a retort-stand, thin flasks, glass tubes, etc. at some chemical shop, and also such materials as druggists do not usually have as potassium, sodium, oxide of manganese, phosphorus, etc. A pneumatic trough can be easily made by any tinman or cabinet-maker from the teacher's directions, or he can even construct one himself by fixing a perforated shelf in a small tub. At the same time, it may be said that the book can be profitably read or studied with only trying such experiments as the most common materi- als and apparatus which any household may furnish, because the illustra- tions are drawn so abundantly from ordinary phenomena within the obser-" vation of all. There are around us, and even within us, chemical reactions which are the counterpart of a large proportion of the experiments which the chemist performs in the laboratory. Questions are appended for the use of teachers if they desire them, and also a full Index. There is a glossary, or rather a list of terms, with the numbers of the sections where their explanation may be found. With the present degree of instruction in natural science in our general system of education, this book is rather too far advanced for the oldest scholars in common schools, though it would not be if they had gone through with the previous books of the series* which I have prepared. Until the different gradations which I have aimed at in this series are fairly intro- duced, the proper place for this book and Part III. is the High School and the Academy, while Part I. is within the comprehension of the next grade below. But it is to be hoped that the time will very soon come when nat- ural science shall have its due prominence during the whole course of edu- cation, and then the books of this series, or other similar books, will find All the books of this series are mentioned in the Preface of Part I. See also back of the title of the present volume. VI PEEFACE. their appropriate places; and thus those pupils who in so large numbers stop short of the High School and Academy, will not go out into the world, as they now do, destitute of that knowledge which not only embraces the principles lying at the basis of the arts and trades into which many of them will enter, but will add greatly to their usefulness and happiness, even if their business be such as to call for no practical application of this knowl- edge. W. HOOKER. November, 1863. PREFACE TO THE SECOND EDITION. THE rapid progress made by Chemistry within the last decade, and the changes in the methods of instruction, hare necessitated a new edition of this standard work. The alterations deemed advisable have been chiefly of four kinds omission of sections, insertion of new ones, introduction of the latest nomenclature and chemical formulae throughout, and a com- plete rearrangement of the matter. A rearrangement of the chapters re- lating to Organic Chemistry on a strictly scientific basis was found imprac- ticable, consequently the empirical plan adopted by the author has been re- tained, while the editor has endeavored to point out the desirable method of classification of organic bodies in Chapter XXTV. The sections relating to Chemical Philosophy, especially in Chapters II. t III., and IV., have been entirely rewritten ; the chapter on Galvanism in the first edition has been omitted, the subject being now treated in connec- tion with Physiqs ; a brief chapter on Spectrum Analysis has been added ; and, lastly, the Metric System of Weights and Measures and the Centigrade Thermometer have been adopted as standards throughout the work. Tables explaining these standards are given in an Appendix. Many wood-cuts have been added, and nearly all are new. The intro- duction of two sizes of type may aid the teacher in the instruction of young- er scholars. The questions in this edition are placed at the end of each chapter, instead of being collected at the end of the book. Finally, the editor expresses the hope that he has not entirely obliterated the pleasant, familiar manner of treating the subject so happily adopted by the author and so successfully carried out. H. CAKBINGTON BOLTON, Ph.D. SCHOOL OF MINES, COLUMBIA COLLEGK, ) September, 1ST5. CONTENTS. CHAPTW *AO ^ I. INTRODUCTORY 11 IL CONSTITUTION OP MATTER 23 III. LAWS OF CHEMICAL COMBINATION. NOTATION 30 IV. CHEMICAL PHILOSOPHY (CONTINUED) 42 V. OXYGEN AND OZONE 49 VI. NITROGEN AND ITS OXIDES 61 VII. CARBON AND CARBONIC ANHYDRIDE 76 VTII. THE CHEMISTRY OF THE ATMOSPHERE 92 IX. THE CHEMISTRY OF WATER. HYDROGEN 110 X. COMBUSTION 131 XI. CHLORINE, BROMINE, IODINE, AND FLUORINE 158 XH. SULPHUR 172 XTTT V PHOSPHORUS 184 XIV. SILICON AND BORON 190 XV. METALS 197 XVI. GROUP I. POTASSIUM AND SODIUM 206 XVH. GROUP II. BARIUM, STRONTIUM, CALCIUM. GROUP m. ALUMINIUM, ETC. GROUP IV. MAGNESIUM AND ZINC. 222 XVUI. GROUP V. MANGANESE, IRON, COBALT, NICKEL, CHROMI- UM. GROUP VI. TIN 240 XIX. GROUP VH. ARSENIC, ANTIMONY, AND BISMUTH. GROUP Vm. COPPER AND LEAD 253 XX. GROUP IX. MERCURY, SILVER, GOLD, AND PLATINUM.. 264 XXI. CHEMICAL INFLUENCE OF LIGHT 274 XXTT. SPECTRUM ANALYSIS 282 XXill, ORGANIC CHEMISTRY 29(^ XXIV. CLASSIFICATION OF ORGANIC SUBSTANCES 301 XXV. CONSTITUENTS OF PLANTS, ETC 313 A2 X CONTENTS. CHAPTER PAGE XXVI. CONSTITUENTS OP PLANTS (CONTINUED) 327 XXVII. VEGETATION 341 XXVIII. SOILS AND MANURES 350 XXIX. OILS AND FATS 364 XXX. FERMENTATION 380 XXXT. ANIMAL CHEMISTRY 394 APPENDIX. METRIC SYSTEM OF WEIGHTS AND MEASURES.. 415 INDEX.. . 419 CHEMISTRY. CHAPTER I INTRODUCTORY. 1. Difference between Chemistry and Natural Philosophy. Chemistry treats of the composition of substances, while in Natural Philosophy, or Physics, their mechanical con- ditions and relations alone are regarded. For example, in Natural Philosophy we look at the laws governing the pressure and movements of water, while in Chemistry we inquire of what water is composed, and into the composi- tion of what substances it enters. And so of other sub- stances solid, liquid, and gaseous. 2. Elementary Substances. In making its investigations, chemistry decomposes such substances as are composed of two or more things. When any substance is found that can not be decomposed or separated into two or more things, it is termed an element, or an elementary substance. On the other hand, all those substances which can be de- composed are called compound. Iron is an element, for it can not be decomposed : it is one thing. But iron rust is a compound substance composed of three things, for water and a gas called oxygen, existing in the air, unite with iron to form rust. 12 v ..,,:; CHEMISTRY. 3. Idea ^ of Elements among the Ancients. The ancients full what is said of the influ- ence of heat on the forms of substances. 10. Illustrate the fact that no chemical changes accompany the changes of form just mentioned. 11. Give examples of the nature of chemical changes. What is iron rust ? Do gases unite with solid substances ? What are oxides ? 12. State in full what is said of the extent and variety of chemical action. 13. What is said of changes in the rocks ? 14. What of the sun's agency in chemical changes? 15. Sum up the five characteristics of chemical change. 16. What is meant by analysis and synthesis? 17. Contrast the old and modern systems of nomenclature. Who introduced the present method ? How are new compounds named? 18. On what principles are names of compound bodies formed ? Give examples sulphur and sodium ? barium and chlorine ? What do the terminations ous and tc signify ? CONSTITUTION OF MATTER. 23 CHAPTER II. CONSTITUTION OF MATTER. [Note to the Teacher. In pursuing a logical arrangement of matter, the principles of chemical philosophy appropriately precede the descriptive por- tion of chemistry, and yet to some minds abstract ideas are exceedingly difficult of comprehension, and can best be grasped after having acquired a number of facts and phenomena with which to connect them. It is hard- ly to be expected, then, that all young pupils will be able to intelligently learn many parts of this and the two succeeding chapters ; it is recommend- ed, therefore, that these chapters be carefully reviewed after having com- pleted the study of the first ten chapters. Nomenclature and notation should, however, be dwelt upon on the first perusal until the pupil is per- fectly familiar with the systems employed. EDITOR.] 19. Constitution of Matter. You have already learned in Part I, p. 17, that matter is in the abstract any thing which is perceptible by the senses, but that we do not know any thing of its nature ; we can only observe its phenomena and learn its properties. In order to interpret facts and to aid in their classification, theories have been formed regarding the nature of matter, and one of these is of importance to us. Theories, you should bear in mind, are not to be considered as having the same weight of authority as facts, but as mere matters of convenience, which are liable to be supplanted by other and new theories so soon as the old ones prove in- sufficient. We do not propose to trouble you with meta- physical speculations, but will explain the so-called atomic philosophy simply and briefly, both because it is interesting and apparently true, and also because its consideration will 24 CHEMISTRY. serve to impress upon your minds more strongly some of the great principles and facts of chemistry. 20. Molecules. The atomic philosophy assumes that mat- ter can not be infinitely divided that is, you may cut and pulverize any thing as fine as you please, and you may then think the smallest attainable particles divided again and again, smaller and smaller, until you reach a certain limit, beyond which matter can not be subdivided. Hence bod- ies consist of an immense number of little particles called molecules literally, little masses. These molecules do not touch each other, but are separated by empty spaces, and these void spaces are very large compared with the dimen- sions of the molecules themselves. These little particles are held near each other by some force, or attraction, as it is often called, and this force varies considerably in power in the three different states of matter with which you are fa- miliar. It is supposed that if it were not for the fact that these molecules do not touch each other, we would be un- able to cut any substance into pieces, for the small parti- cles of matter are considered to be impenetrable ; and when a knife-edge is forced into a body, it simply enters the void spaces between the molecules and makes them separate it does not penetrate the substance of the molecules them- selves. It seems strange at first to think of hard substances like iron and silver as made up of particles which do not touch each other; but this is a way of regarding them which you will find easier to accept the longer you study. Do not for an instant think that these little particles are ever visible to any one, even with the aid of a most powerful microscope. They are so small that we can only think them. "What we do see are immense numbers of these molecules aggregated. To give you a faint idea of the littleness of these particles, we will tell you that philosophers have conjectured that fifty million million molecules placed in a row would occupy the CONSTITUTION OF MATTER. 25 space of one inch, and the weight of a million million mole- cules of hydrogen gas (the lightest substance known) is supposed to be equal to about three pennyweights. Or, if you prefer another way of looking at it, imagine a drop of water the size of a pea magnified to the size of the earth, then the molecules in it increased in the same proportion would be coarser than fine shot, but probably not so coarse as cricket-balls. These speculations may seem rather extrav- agant ; but three trains of thought have led philosophers to nearly similar conclusions. These molecules are con- ceived to be continually in motion, so that the interior of a body presents to our imagination some resemblance on a small scale to the vast system of the universe. In fact, we see in the latter case stars held in certain positions deter- mined by the law of universal attraction, and revolving one about another. Repeating briefly what we have told you in this section, masses of matter are made up of excessively small particles, called molecules, separated from each other by void spaces, mutually attracting and constantly in mo- tion. 21. Advantages of this Theory. We have already alluded to the fact that this theory enables us to explain intelli- gently the divisibility of matter, bftt besides this it accounts in a satisfactory manner for many of the facts of physical science. When you heat iron, it expands ; this you remem- ber was explained fully in Part I., just as we do now by saying that the particles are put farther apart by the heat, which is really but an increase of motion imparted to them. When any thing is cooled down, on the other hand, it con- tracts that is, the particles approach each other. This theory, then, accounts for the changes of volume caused by changes of temperature. Then, again, the very existence of three states of matter solid, liquid, and gaseous depends on the relative position of the molecules. In solid bodies, B 26 CHEMISTRY. force is required to move the molecules and separate them ; in liquid bodies the relative position of the particles is no long- er permanent they glide past each other with perfect ease, and less force is required than in the case of solids ; in gases the mobility of the molecules is still greater than in liquids, and the molecules tend constantly to recede from each other. In Fig. 2 you have a rough representation of the way molecules are separated from each other by heat. o e e Fig. 2. 22. Atoms. As minute and intangible as these mole- cules are, they are believed to be composed of still smaller particles called atoms. We have already alluded to the difference between Chemistry and Physics (or Natural Phi- losophy), but this difference is now clearer when we state that physical phenomena affect mainly the molecules, while chemical science deals with atoms. Thus the physical properties of an object refer to its condition, whether solid, liquid, or gaseous ; crystalline form, color, hardness, specific gravity, transparency or opacity, and the relations of the body to heat, light, and electricity, are physical properties. These you have studied in Part I. CONSTITUTION OF MATTEE. 27 The phenomena of combustion, fermentation, putrefaction, decomposition, etc., belong to the science of chemistry. In short, all the phenomena in which the molecule remains un- changed belong to the science of physics, while the phenom- ena in which the molecule is changed or modified in its nat- ure belong to the science of chemistry. 23. Illustration. If you examine a piece of iron from a purely physical point of view, you may describe it as black or steel gray, opaque, hard, of a specific gravity of 7.8 i. e., nearly eight times as heavy as water and a fair conductor of heat, as you will find on heating one end red-hot. Be- sides these qualities, it is a conductor of electricity, and may be converted into a magnet possessing the power of attract- ing and repelling other pieces of iron. It is also fusible, malleable, ductile, elastic, capable of crystallization. In all this, however, its nature is not changed it still remains iron, its molecules are intact. Again, here you have some sul- phur : it is, physically considered, yellow, brittle, electric, easily fusible, readily crystallized, soluble in certain liquids, etc., etc. Now take some iron filings having the physical qualities named, and mix these with powdered sulphur having its own properties ; mix and pulverize as fine as you please ; each grain of the mixture will contain a particle of iron and a particle of sulphur. The iron may be withdrawn by a magnet, and the sulphur may be dissolved out in car- bon disulphide. Examined under a powerful microscope, each particle will be seen to consist of two distinct substan- ces, iron and sulphur. Now apply heat to this mixture, and thus set chemical force at work : the mass glows, a kind of combustion takes place, and on cooling you have a dark sub- stance which possesses physical and chemical properties of its own. The iron has disappeared, the sulphur has gone, each has united with the other, atom to atom. The magnet will not now withdraw the iron, nor can the sulphur be dis- 28 CHEMISTRY. solved out ; the microscope reveals a homogeneous mass, and the whole is soluble in acids, evolving a very disagreeable odor. The new substance, while containing iron and sul- phur, is neither iron nor sulphur ; chemists call it sulphide of iron. 24. Two Kinds of Molecules. Molecules may be com- pound or simple. Simple molecules are made up of atoms of one and the same substance. By exposing the sulphide of iron to the action of other substances, with the agency of heat and chemical force it may be resolved into its constit- uents, iron and sulphur ; sulphide of iron, then, is a com- pound molecule composed of atoms of iron and atoms of sulphur. Iron is not capable of being decomposed, nor is sulphur that is, their molecules are simple, or compounded only of like atoms. They are elementary bodies, as you were told in the first chapter ; but you now learn to regard the elements from another and peculiar point of view. 25. Further Properties of Atoms. These atoms, it is sup- posed, can not be destroyed or altered or divided, but have remained precisely the same since their first creation. The atoms of some elements have been continually uniting with the atoms of others, changing from one kind of combination to another, and yet, after myriads of such changes, they have not altered in shape or character. Take oxygen for example. When its atoms unite with those of hydrogen to form water, it is not by any change in the atoms them- selves that a fluid so different from each of these gases is produced, but it is only by some arrangement of these atoms. So when potassium is thrown upon water, and pro- duces fire and smoke, amid all the commotion and burn- ing not an atom of either the potassium or oxygen or hy- drogen is lost or injured, but they simply form new associ- ations. The disturbance is the mere result of the eagerness of the atoms of oxygen and potassium to unite together. CONSTITUTION OF MATTER. 29 So, too, when a mixture of oxygen and hydrogen explodes on the application of a light or electricity, the atoms of the two gases merely unite in a very hurried manner, forming water, and none of them experience the slightest change. These ultimate atoms unite together to make molecules or particles, which, unlike the atoms, can be both changed and divided if the atoms composing them be of two or more kinds, and can at least be divided if their atoms are of one kind alone. 26. Weight of Atoms. A most important attribute of atoms has not yet been mentioned, viz., weight. Every ele- mentary body is supposed to be made up of atoms of ex- actly the same size and weight in the same body. The weight of the atoms of different elements varies greatly ; if we call the weight of the hydrogen atom l,then that of oxygen is 16, while mercury is 200, gold 19 7, carbon 12, etc. How it is that chemists are able to determine that the atoms of the various elements differ in weight we can not ex- plain to you in this work, but you must not imagine that sin- gle atoms are ever weighed, only immense numbers of them taken together. Nor is there any thing absolute with ref- erence to their weight it is merely relative ; that is, the figures for hydrogen and oxygen named, viz., 1 and 16, do not stand for any particular quantity, say pounds or grammes, but they signify that if the hydrogen atom weighs 1 gramme or 1 pound, then the oxygen atom, being sixteen times as heavy, weighs 16 grammes or 16 pounds. Any other unit than hydrogen might be taken; and actually many years ago oxygen was placed equal to 100, and the weights of the other atoms were proportionally heavier hydrogen becoming 12.5, since 8 : 100 = 1 : 12.5. All the fig- ures representing the relative weights of the atoms were then 12.5 times heavier. Chemists now universally adopt hydrogen as the standard, and make it unity. 30 CHEMISTEY. QUESTIONS. 19. What is the use of theories ? 20. What is said of the divisibility of matter ? What are molecules ? Give the reason for their not touching each other in masses. State what is given as the probable size of mole- cules ? Are molecules motionless? 21. What are the advantages of this theory ? Why do bodies expand by heat ? 22. Of what are molecules made up ? Show the difference between Chemistry and Physics ? 23. De- scribe the illustration of this difference in the example given. What is sulphide of iron ? 24. Explain the nature of elements with reference to the atomic theory. 25. What other properties are ascribed to atoms ? Is any thing lost or destroyed when burned up ? 26. What is the most im- portant attribute of atoms ? Are these absolute weights ? What is the standard now adopted ? CHAPTER III. LAWS OF CHEMICAL COMBINATION. NOTATION. 27. Law of Definite Proportions. Chemists have made innumerable experiments and analyses by which it is proved that elementary bodies unite in definite proportions by weight. Thus, if you take 32 pounds of sulphur and heat it with iron filings to make sulphide of iron, as in the experi- ment noticed in 23, you will require just 56 pounds of iron, no more and no less. If you should take 32 pounds of sul- phur and GO pounds of iron, you will have four pounds of iron left over, i. e., uncombined ; or if you take 50 pounds of sulphur and 56 of iron, you will have 18 pounds of sulphur too much. While, therefore, there may be great indefinite- ness in mere mixtures, there is none in the formation of compounds. Every compound always has exactly the same composition. No matter under what circumstances the compounds are produced, this exactness is preserved. The carbonic anhydride formed by combustion, by respiration, LAWS OP CHEMICAL COMBINATION. NOTATION. 31 by fermentation, or by the explosion of gunpowder, always possesses the same definite composition. This is one of the four great laws governing chemical combination, and is known as the Law of Definite Proportions. Before taking up the study of the other laws you must understand the meaning of chemical symbols. 28. Chemical Symbols. Now turn to the table on page 13, and we will tell you how to use it. First you have a list of all the elementary substances, and opposite each name you find letters placed, which are either the first two letters of the full name or some other abbreviation, the meaning of which you will now learn. These letters are the symbols used so much in chemistry, and we will explain some of them. Take those elements whose names begin with S. We call sulphur S, and we must therefore designate the others in such a way as to distinguish them from this and from each other. "We call, then, silver Ag, from Argentum, the Latin for silver ; and sodium N"a, from an old Latin name for soda, Natrium. Phosphorus is set down as P, being a prominent element with a name beginning with that letter. Then Po- tassium is designated by K, from JTalium, an old Latin name for potash. Several of the elements take their sym- bols from their Latin names. Thus the Latin for Antimony is Stibium, Sb ; for Mercury, Hydrargyrum, Hg; Lead, Plumbum, Pb ; Copper, Cuprum, Cu ; Gold, Aurum, Au ; Iron, Ferrum, Fe ; and Tin, Stannum, Sn. Generally those which are most important are represented by a single let- ter; as, for example, the four grand elements, oxygen, ni- trogen, carbon, and hydrogen. We use these symbols as a kind of short-hand for expressing chemical reactions, and it is necessary to become familiar with this method of writ- ing from the very outset. Thus, instead of writing Potas- sium in full, we write K, or in place of Hydrogen we write H. This is not all they signify, however : each letter stands 32 CHEMISTRY. for one atom of the element it represents. IT, then, means one atom of hydrogen no more and no less. If we want to express two, three, or more atoms, we place a little 2 or 3 to the right hand of the symbol ; thus Na 2 stands for two atoms of sodium, and O 3 means three atoms of oxygen. Sometimes large figures are placed in front, as 5N, which means five atoms of nitrogen. Now unlike atoms unite to form molecules of new bodies, and to represent this we write the symbols alongside of each other. Thus HC1 will signify the body having one atom of hydrogen united to one atom of chlorine ; you will learn farther on that this body is call- ed hydrochloric acid. 29. The Symbols in Formulae. The example given in the last paragraph, HC1, is called the formula of the body. In place of writing "one atom of hydrogen united to one atom of chlorine," we say "HC1," which is certainly much short- er. In the same way CO stands for a gas called carbonic oxide, containing as you see one atom of carbon and one atom of oxygen. ISTaCl signifies chloride of sodium; CaO, oxide of calcium. These examples anticipate of necessity the method of forming the names of compounds, which you will learn more fully in the section on nomenclature. In the examples we have taken so far, only one atom unites with one atom of another substance; it frequently happens, however, that several atoms of an element unite with one of another element, and to show this we use the little figure referred to in 28, and which is called a coefficient. Thus water is made up of two atoms of hydrogen and one of oxy- gen, hence it is written H 2 O ; marsh gas is CH 4 , sulphuric acid is H 2 SO 4 , etc., etc. Interpreting the last formula, we would say that two atoms of hydrogen, one of sulphur, and four of oxygen, held together by chemical attraction, make one molecule of sulphuric acid. Potassium nitrate is KNO 3 , gypsum is CaSO 4 , sodium carbonate is N"a 2 CO 3 . If a snb- LAWS OF CHEMICAL COMBINATION. NOTATION. 33 stance crystallizes with water, we usually write the mole- cules of water separately, thus : Xa 2 CO 3 . 10H 2 O, a period separating them ; in place of a period, a plus sign is some- times used. CaSO 4 -f 2H 2 O is the formula, then, of crystal- lized gypsum, the sign + indicating that the connection be- tween the gypsum and the water is not so close as that of the remaining elements. We know this to be a fact, because if crystallized gypsum containing water be heated red-hot, the water is driven off, but the C, the S, and the O 4 are not thus separated. Notice that the 10 prefixed to the H 2 O in the case of sodium carbonate, and the 2 prefixed to the H 2 O in the other formula, multiplies the O as well as the H 2 ; it is the same as if w^e had written H 20 O 10 , or H 4 O 2 , and means that ten and two molecules of water respectively are taken. From what we have said about formulae, it is plain that a group of atoms constitutes a molecule, and that the number of atoms in a molecule varies considerably; in HC1 we have two, w r hile in Fe 2 (SO 4 ) 3 , for example, there are seventeen. In the chapters on organic chemistry, you w T ill learn that frequently the organic bodies contain a much larger num- ber of atoms in a molecule. 30. Further Explanation of Symbols. Since the atoms have definite weights, and elementary bodies unite in fixed proportions by weight, these symbols stand not only for the atoms of the respective elements, but also for definite weights of the elements. The third column in the Table on page 13 gives these weights. S, then, means not only one atom of sulphur, but also 32 parts by weight. Na stands for 23 parts by weight of sodium, and so on. In this light, formulae have a new significance. HC1 means 1 part by weight of hydrogen, and one atom or 35.5 parts by weight of chlorine. In sulphuric acid, or H 2 SO 4 , we have the following composition : B2 34 CHEMISTRY. 2 atoms of hydrogen, or II 2 , weigh 2 1 atom of sulphur, or S, weighs 32 4 atoms of oxygen, or O 4 , weigh 64 1 molecule of sulphuric acid, or H S SO 4 , weighs 98 You notice that we have drawn a line under the weights of the atoms and added them together, obtaining the weight of a molecule of sulphuric acid. Atoms, you remember, unite to form molecules, and here you see that the sum of the atomic weights of the elements composing the mole- cule of a body gives the weight of a molecule of that body. This is called the Law of Molecular Weights. Take another example : Common limestone, you will learn farther on, is a compound of calcium, carbon, and oxygen, in the proportions represented by the formula CaCO 3 : 1 atom of calcium, or Ca, weighs 40 1 atom of carbon, or C, weighs 12 3 atoms of oxygen, or O 3 , weigh 48 1 molecule of calcium carbonate, or CaC0 3 , weighs 100 The molecular weight of crystallized gypsum can be cal- culated in like manner, the weight of two molecules of water (2H 2 O = 36) being added to that of one molecule, of gypsum. Use the Table on page 13 to make this calcula- tion. These examples also make the Law of Definite Pro- portions much clearer. 31. Other Laws of Chemical Combination. In explaining the meaning of symbols, we have somewhat anticipated the other laws of chemical combination. The Law of Multiple Proportions may be thus stated: When one body com- bines with another in several proportions, the higher propor- tions are multiples of the first or lowest. This results from the fact that one, two, three, or more atoms of one element often unite with a single atom of some other element, form- ing three or more bodies having very different properties. LAWS OF CHEMICAL COMBINATION. NOTATION. 35 Examples of this law are abundant; to take the case most familiar to us, iron and sulphur unite not only in the proportions of atom to atom, but also of one atom of iron to two atoms of sulphur consequently in the ratio of 56 parts by weight to twice 32 parts. This is shown in the follow- ing manner : . i unites with \ ... (to make > 1 atom iron, weighing Fe, 56, , gj / unites with \ ... (to mane \ J 1 atom sulphur, i S hin * J a molecule, i ( S, i 32 ' I FeS, ) 1 atom iron, weighing j su lphur, i weighing] Fe > 56 ' I S 2 , i <* I FeS 2 , ) When there are two elements forming different com- pounds, generally one remains the same in all the combina- tions, while the other is varied, not irregularly, but regular- ly. When two elements unite to form a series of com- pounds, this law of multiples is very noticeable. Oxygen and nitrogen furnish such a series, which you will find on page 63. Sometimes the series is complete, as in the case of the combinations of hydrogen with oxygen and chlorine, which may be stated thus : Composition by weight Names. Formulae. Hydrogen. Chlorine. Oxygen. Hydrochloric Acid HC1 1 35.5 Hypochlorous " HC1O 1 35.5 16X1=16 Chlorous " HC1O 2 1 35.5 16X2=32 Chloric " HC1O 3 1 35.5 16X3=48 Perchloric " HC1O 4 1 35.5 16x4=64 Here the proportions of oxygen, 16 xl, 16 x 2, 16x3, 16x4, are respectively the multiples of 16 viz., 32, 48, and 64. The remaining law is that of Reciprocal Proportions, which may be thus stated: If two bodies combine with a third, the proportions in which they combine with that third body are measures or multiples of the proportions in which they may combine with each other. 36 CHEMISTRY. Referring again to the Table of Atomic Weights, we find that 32 parts by weight of sulphur combine with 56 parts by weight of iron and with 16 parts by weight of oxygen, consequently 56 parts by weight of iron combine with 16 parts by weight of oxygen. Or, using less wordy language, since one atom of sulphur (32) combines with one atom of iron (56) and with one atom of oxygen (16), these bodies, iron and oxygen, combine with each other atom, to atom (56 and 16). Actually the relation is not quite so simple, for oxygen and sulphur combine usually in the proportion of two atoms of the former to one of the latter, and this necessitates the use of the word " multiples " in the law as just stated. We might in a similar way go through the whole list of elements, showing that their atomic weights express their value in satisfying the demands of each other in their com- binations. 32. Summary. We will sum up in four propositions the facts which we have developed in this chapter in regard to the combinations of substances. l.When substances com- bine with each other, it is always in certain fixed and in- variable proportions. In other words, every compound al- ways has precisely the same composition. This is called the law of definite proportions. 2. When two substances unite in more proportions than one, these proportions bear a simple arithmetical relation to each other. This is called the law of multiple proportions. Commonly, as you have seen, one of the substances remains the same, while the other is in different proportions, usually as 1,2, 3, etc. Sometimes the relation is as 1 J, 2-J-, 3J, etc.; but this we shall speak of in another place. 3. When several substances, B, C, D, etc., unite with a substance, A, the proportions in which they unite with it are expressed by numbers, which represent the proportions in which they unite with each LAWS OF CHEMICAL COMBINATION. NOTATION. 37 other. This is called the law of equivalent or reciprocal proportions. 4. The molecular weight of a compound is the sum of the atomic weights of its constituents. This is the law of molecular weights. 33. Chemical Equations. Returning to the symbols, there is a further great advantage to be derived from their use which we have not yet mentioned. By writing formulae in a particular way, they place before the eye in small com- pass the exact changes which occur when chemical action takes place between two substances. We will give only very few examples here, but you will become familiar with them as you progress. The formula for water, you know, is H 2 O; now potassium is simply K. In Chapter XVI. you will learn that potassium decomposes water, forming potassium hydrate, and setting half the hydrogen free ; this is expressed in symbols thus : Potassium and Water yield Potassium hydrate and Hydrogen K + II 2 O KHO + H The plus sign between potassium and water signifies " mixed with " or " in contact with," or " acted upon by," and not " combined with." The sign of equality means " yields " or " produces," and has not the precise meaning of " equal to " as when used in algebra. Notice particu- larly that you have the same elements on both sides of the equation, viz., O, H 2 , and K,but they are arranged different- ly. K+H 2 O expresses the condition of the substances be- fore they come in contact, and KHO-fH their condition after the chemical action. The most important meaning conveyed by the chemical equations remains still to be explained. Bearing in mind that the symbols stand for definite weights of the bodies they represent (referred to hydrogen as unity), the equa- tions give the actual proportion by weight of the elements 38 CHEMISTRY. concerned, and of the bodies produced by the chemical change. This is shown thus : Potassium Potassium Water yield hydrate K + H 2 O KHO 39.1 + (1) 2 + 16 = 39.1 + 1 + 1G Hydrogen + H 57.1 57.1 The 39.1 stands for so many grammes, pounds, tons, etc., of potassium, the 18 (obtained by adding the weights of the atoms) for so many grammes, pounds, tons, etc., of water; now when chemical action takes place, nothing is lost, so we must find just as many grammes or pounds of these ele- ments taken together, viz., 57.1, on one side of the equation as on the other. That this is the case is evident ; only the atoms are arranged differently on the right-hand side we have 56.1 grammes, pounds, or tons of potassium hydrate, and 1 pound, etc., of hydrogen. 34. Combination by Volume. "We have hitherto considered only the laws governing combination by weight, but the elementary bodies which exist in a gaseous state combine by volume in simple ratios, and the vol- ume of the resulting body bears a simple ratio to the volume of its constit- uents. A full examination of the laws of combination by volume can not be entered upon in this work. We can give you only a few illustrations to show that the volume relations of gaseous compounds are very simple. Thus one volume of H and one volume of Cl unite to form two volumes of hydrochloric acid, two of H and one of O form two of water, three of II and one of N form two of ammonia, and, finally, four of H and one of C form two of marsh gas. This, you will see, is in direct connection with the atomicity of the elements explained in 44. Now there is a law in physical science that all molecules in the gaseous state occupy the same volume ; and taking the volume of an atom of hydrogen as unity, the volume occupied by molecules is two. Chemical formulae, then, dealing with molecules of bodies, as well as the atoms, represent the volumes of the constituents as well as the weights. If we represent the volumes by squares, as on the next page, this will be somewhat clearer ; we take for examples the formation of the bodies HC1, H 2 O, NH 3 , and CII 4 , just mentioned : LAWS OF CHEMICAL COMBINATION. NOTATION. 39 H + ci = H Cl or H + C1 = HC1 (hydrochloric acid). - 1 + I O I = HlO or H,+O = H 2 O (water). I H I ' ' l ' 2LI _ H | + | N | = I N'H 3 | or H 3 +N = NH 3 (ammonia). 1"! = C HJ or H<+C = CH 4 (marsh gas). 35. Significance of Equations. Every chemical equation expresses a great deal in an exceedingly condensed manner. It shows : 1st. What and how many elements are concerned in the reaction. 2d. How these elements are combined before and after the chemical change has taken place. 3d. The proportion by weight of every constituent in the compounds. Iii the case of gases a fourth point is shown, to which we have just alluded, viz., the proportion by volume. We will give you one more example to study; try to determine the application of the three points above named. The names of the bodies are not familiar, but that need not be a source of confusion : Calcium Hydrochloric Calcinm Carbonic Carbonate. Acid. Chloride. Water. Anhydride. CaCO 3 + 2HC1 = CaCl 2 + H 2 O + CO 2 40 + 12 + (1GX3) 2(1+35.5) 40+(35.5X2) (1X2) + 16 12+(16x2) 100 73 "Til 18 44 ~17Z~ ~173 40 CHEMISTRY. 36. Mathematical Calculations. You have already obtained some insight into the numerical relations of the atoms ; the calculations made from the atomic weights and molecular weights of bodies belong to a special branch of chemical philosophy called stoichiometry, a word made up of two Greek words meaning "an element" and " a measure." These mathemat- ical calculations are of the greatest importance both to the scientific and manufacturing chemist ; the former is enabled to determine the composi- tion of new bodies, or the purity of known substances ; the manufacturer is enabled to estimate how much of any given material it is necessary to use in order to manufacture a certain product. A knowledge of a few simple rules, seldom requiring higher arithmetic than Proportion, properly ap- plied to questions of practical import in manufacturing chemical products, saves the capitalist thousands of dollars, and dollars and cents are items of no small consideration. We can not explain all these calculations to you, nor is it necessary for any one except a working chemist to master them, but you should endeavor to realize their importance. We will give only a single case, and illustrate it by two examples. Turn to page 38 ; you find there an equation for the reaction of potassium in water, with the nu- merical values of each atom and molecule attached. Now suppose this was a good method for manufacturing potassium hydrate (or caustic potash, as it is commercially known), and we should want to know how much of it can be made from 10 pounds of metallic potassium, the question would be solved thus : From the equation cited it is evident that one atom of potassium yields one molecule of potassium hydrate ; but one atom, or K, weighs 39.1, and the molecule KHO weighs 56.1, therefore we have the proportion : Atomic oecuar The number 39.1 : 56.1 :: 10 : the answer; 56 1x10 whence ' ~-. =14.3; consequently 10 pounds of potassium would oJ. 1 furnish 14.3 pounds of potassium hydrate. Supposing, again, that this was an economical method for manufactur- ing hydrogen gas, how much potassium is required to make 100 grammes of hydrogen ? By examining the equation on page 38, you will find as before that one atom of potassium weighing 39. 1 takes place in the re- action setting free one atom of hydrogen weighing 1 , hence the propor- tion : LATVS OF CHEMICAL COMBINATION. NOTATION. 41 ( A ^ ( A^ m - 1 f The given "\ C Number of ^ A ) -k-T^V * 5 M f I ^ -a 3 number of f ... } grammes off As -< weight of > is to 4 weight of s so is < CTamraes of ( to ^ potassium T (hydrogen) (potassium,) ( g h ydJeu ) ( required. ) 1 : 39.1 :: 100 : the answer ; whence - - =3910 grammes of potassium. Such calculations are very useful as a discipline for students, impressing on their minds the four great laws of chemical combination, particularly the law of definite pro- portions. Examples may be multiplied at the discretion of the teacher, employing from time to time the equations given in different parts of the book. The questions of percentage composition and of volume relations can not be entered upon in an elementary work. QUESTIONS. 27. How do elementary bodies unite ? Illustrate by taking iron and sul- phur. What is the first great law governing chemical combinations? 28. Explain the nature of symbols ? How are they used ? What do they sig- nify ? Write five atoms of nitrogen. How are molecules expressed ? 29. What is a formula of a body ? What is the formula for common salt ? What of sulphuric acid ? Explain the small figure in the latter formula. What is the use of the period ? AVhat of the plus sign ? How are several molecules of one substance written ? Do molecules ever contain several atoms ? 30. What else do the symbols stand for ? Explain the law of molecular weights. (The teacher should place examples on the black- board.) 31. Give the law of multiple proportions. Illustrate with iron and sulphur. What is the law of reciprocal proportions ? Explain by referring to a Table of Atomic Weights. 32. Recapitulate the four laws. 33. Give in your own language the use of chemical equations. Write the action of water on potassium. Explain this equation. 34. How do the elements combine as regards volumes ? 35. What three points are expressed by equations ? 36. What is stoichiometry ? Calculate how many pounds of caustic potash can be made from 100 pounds of potassium. How many grammes of potassium are required to make 100 grammes of hydrogen ? Explain the calculation. 42 CHEMISTRY. CHAPTER IV. CHEMICAL PHILOSOPHY (CONTINUED). 37. Forces. The force which binds unlike molecules to- gether is called cohesion; it is this power which gives rigid- ity to solid bodies, and which, though weaker in fluids, pre- serves their particles in contact. The attraction exerted be- tween unlike molecules is called adhesion; this is the force which makes water adhere to solid bodies, and which you Lave already studied in Part I. The power which unites atoms within the molecule is called chemical attraction^ though sometimes spoken of as affinity. To illustrate these different forces, we may say that the molecules of a pane of glass are held together by cohesion ; dip the pane in water, and the water sticks to it by adhesion ; while the atoms of silicon, calcium, potassium, and oxygen (of which the mole- cules of glass are composed) are held together by chemical attraction. Observe that in the attraction of adhesion and of cohesion the particles are merely held together, without producing any change in the nature of the substances which attract each other, however different they may be. But when two substances attract each other chemically, in the union that occurs a change is produced in both. Moreover ordinary attraction operates at all distances, in masses as well as in particles, while chemical attraction operates only when the particles of substances are intimately mingled as we usually say, in actual contact. Note, also, that chem- ical attraction has nothing in common with electrical or magnetic force about which you studied in Part I, for the CHEMICAL PHILOSOPHY. 43 latter produce no change in the actual constitution of the metals themselves. 38. Chemical Affinity. There is great variety in the range and degrees of chemical attraction. Between some sub- stances there appears to be no disposition to unite under any circumstances: thus no compound of fluorine and oxy- gen is yet known. We say yet known, for such a compound may be discovered to-morrow, as we have no proof of the absolute impossibility of the union taking place. In a gen- eral way substances which are alike are not eager to unite ; thus the metals form few definite compounds, their alloys being mainly mixtures. Bodies belonging to the same group, and therefore chemically similar, as chlorine, io- dine, and bromine, are not very prone to form definite com- pounds. The widest range of aflinity is possessed by oxygen ; it unites with every known element except fluorine, as just stated. Sulphur has a very wide range of attraction, unit- ing with nearly all the metals, forming an important class of bodies called sulphides. Oxygen and nitrogen show a marked contrast in this respect, the latter having very lit- tle tendency to enter into combination, particularly in its free state, as it exists in the atmosphere. Chemical attraction varies much in its degrees, or power, between different substances. This is seen strikingly in the affinity of oxygen for the various metals. At one end we have the so-called noble metals, gold, platinum, etc., uniting with oxygen only under compulsion ; while at the other ex- treme we have potassium, sodium, etc., so eager to unite with oxygen that they are never found uncombined in nat- ure. Between these two extremes at various points we have iron, zinc, copper, lead, etc. The same variation in the degrees of the attraction of oxygen is shown in relation to other substances besides the metals ; we shall learn how 44 CHEMISTRY. this is the case with sulphur, phosphorus, and carbon far- ther on. Oxygen lias a great attraction for hydrogen, and is continually uniting with it, on every hand produc- ing water. Some substances can be made to unite with each other only under the most extraordinary circumstances. This is the case with oxygen and nitrogen. No degree of heat to which we may subject them together can force them to unite. Lightning does it to a small extent, as it shoots through the atmosphere, forming nitric acid. And the pow- er of this and many other analogous compounds consists, at least for the most part, in the looseness of the affinity which holds their constituents together. They destroy by falling to pieces, their elements uniting with other substances for which they have an affinity. This is the explanation of the action of all caustics they do not eat and themselves re- main whole, but they are decomposed in the destruction which they cause. So, too, the efficacy of gunpowder de- pends upon looseness of affinity in the nitre, and the conse- quent readiness with which it furnishes one of its elements, oxygen. 39. Providence Seen in Affinity. The various degrees of affinity between different substances are adjusted by the Creator, as all other forces in nature are, with an obvious reference to the comfort and welfare of man. Take, for ex- ample, the different degrees of affinity which oxygen has for hydrogen and nitrogen. With hydrogen it is uniting every where and continually to form water. This is done, as you will see, in all ordinary combustion. Now if oxy- gen united with nitrogen with the same ease if the heat of ordinary combustion could cause them to combine, form- ing nitric anhydride with the great abundance of these gases in the air the most disastrous effects would result every where. So, also, if sulphur had the same degree of CHEMICAL PHILOSOPHY (CONTINUED). 45 affinity for oxygen that phosphorus has, the abundance of this substance in the earth would occasion wide-spread con- flagrations. Examples illustrating the same truth could be cited to any extent, but these will suffice. 40. Modifiers of Chemical Attraction. The force of chem- ical attraction varies not only with respect to the different substances between which it is exerted, but it is greatly influenced by certain circumstances independent of the sub- stances themselves. Solution has so much influence upon affinity, or the disposition of substances to act chemically upon each other, that it has given rise to a maxim set down by the older chemists, " Coipora non agunt nisi sint soluta" substances do not act unless dissolved. A famil- iar illustration of this we have in the mixture of common soda powders. If the powders of tartaric acid and sodium carbonate be mingled dry, there will be no action ; but if each be dissolved before they are mixed, the action will be immediate, producing a brisk effervescence. There are two reasons for this : First, the particles are brought nearer to- gether in solution than they can be mixed in powder, how- ever finely they may be pulverized ; and, secondly, they are free to move about among each other. Water, aside from the chemical actions which itself produces, exerts a very great agency as a solvent in the chemical changes ever going on in all parts of the earth ; and not only so, but it acts as a distributor, often bringing substances to- gether which otherwise could never have come within the range of each other's chemical action. 41. Influence of Heat. Alteration of temperature is an- other of the causes which modify the attractive force ex- erted between atoms. Both composition and decomposi- tion are effected by the influence of heat. How this can be we will explain. Heat expands all bodies, or, in other words, spreads the molecules farther apart; but, as you 46 CHEMISTRY. have already learned, it is necessary that the particles of different substances should be in immediate contact, or ex- ceedingly near to each other, in order that they may exert their combining power. Now if any substance is heated so hot that the atoms of which it is composed are separated so widely that they pass beyond the range of their attrac- tion, and new molecules form by a re-arrangement of the atoms, the body is said to be decomposed by heat. 42. Influence of the Nascent State. When the molecules of a body are acted upon by any force which separates its constituent atoms, the latter momentarily possess unusual attractive force, and are said to be in the nascent state, or just born. The reason that a gas is so active in its nascent state is supposed to be that at the very instant of its production from some solid or liquid it is for that instant in a highly concentrated state, not yet having expanded to the dimensions which it has in the gas- eous state. Many gases which will not show any affinity for each other under ordinary circumstances, if at the instant of their production, the mo- ment of their birth, they are in immediate neighborhood of each other, unite at once. The particles of the two gases thus produced are, in their momentary concentrated state, so pressed in among each other that they must unite if they have any affinity at all. When they are expanded there is none of this pressure to bring the particles within the range of their at- traction in other words, they are removed too far apart to exert a chem- ical attraction upon each other. This being so, perhaps some one might think that if a mixture be made of two gases, and great pressure in some way be exerted upon it, these gases could be made to unite as they would do in their nascent state. But the difficulty would be that no artificial press- ure can bring them into so concentrated a state as they are in at the mo- ment that they are produced in some fluid or solid. The state of conden- sation in which gases are, as forming a part of solids or fluids, is far be- yond any thing which mere pressure can produce. There are twenty-seven gallons of oxygen in a single pound of iron rust. Is there any pressure which man can produce in any way that can condense such a body of gas into so small a space ? 43. Catalysis Dissociation. There are other circumstances which influence chemical attraction, among which should be mentioned what is termed catalysis. This word is derived from two Greek words, viz., kata "down," and luein, "to loosen," and is applied to the peculiar power ex- CHEMICAL PHILOSOPHY (CONTINUED). 47 erted by some substances which assist chemical action without themselves undergoing any chemical change. Dissociation is another term applied to a special kind of chemical change effected by heat alone. But a full dis- cussion of these points is here out of place. 44. Atomicity. After you have become familiar with the multitude of compounds formed by the union of the elementary bodies, it will appear that there is a large class of elements which invariably combine with each other in the proportion of one atom to one atom. Hydrogen, chlorine, bromine, iodine, sodium, potassium, and silver belong to this class ; there are such bodies, for example, as HC1, Agl, KBr, NaCl, etc., in which the elements are combined in the simple ratio of one to one. Moreover, chem- ists are not able to make any such bodies as H 2 C1, or HC1 2 , or NaCl 2 , or K a Br 3 ; hence it is supposed that this class of bodies are monatomic, and are said to possess only one bond of affinity. There is a second class of elements which are prone to unite with two of these monatomic elements, and are hence called diatomic, and are said to have two bonds or tint to of affinity. Oxygen, sulphur, calcium, etc., belong to this class ; thus water contains two atoms of H to one of O, and is writ- ten, as you know, H 2 O. We have other examples in the following bodies, CaCl 2 , H 2 S, K 2 O, Na 2 O. These diatomic elements may also unite with two dissimilar monatomic elements, giving rise to such bodies as KHO, NaHS, etc. ; in this case, however, hydrogen is generally one of the mon- atomic elements. Besides these monatomic and diatomic elements, there are several other classes the tri-, tetr-, pent-, and hex-atomic which combine respectively with three, four, five, and six monatomic elements. A triatomic element may unite with one monatomic element and one diatomic ; a tetratomic element may combine with two diatomic elements, or with one triatomic and one monatomic element, etc. This combining capacity, or atom-Jixing power, is generally believed to point to a real difference of chemical power ; it has nothing to do with the atomic weights, nor with the combination by volume. This idea of atomicity is represented in symbols by a very simple method ; a single stroke attached to the symbol, thus H' or H-, signifies that the element named has only one bond of affinity, or is monatomic. T\vo strokes connected with a symbol, thus O'', or -O-, or O=, represent a diatomic element; three, N'" or X N', a triatomic ; four, C iv or -C-, a tetr- atomic, etc. You may, if you please, regard these strokes as so many arms stretched out to grasp some other element. Water is often represented 48 CIIEMISTEY. thus, H-O-H, which is the same thing as H 2 O, only it shows the rel- ative atomicity of its constituent elements. The atom-Jixiny power of the elements is not a fixed quantity for each element; nitrogen, for instance, may be pentatomic or triutomic ; sulphur may be hexatomic, tetratomic, or even diatomic, according to circumstances ; the maximum is generally taken as the true atomicity of the element. This variation is in- geniously accounted for by supposing that in the lower powers the bonds are neutralized by self-saturation, or by combining with themselves ; thus, if in pentatomic nitrogen, ^N^, two of the bonds unite, it may become triatomic, ,N> The bonds are said to be saturated when joined to them- V X selves or to the bonds of some other element. It scarcely ever happens that an element possessing an even atomicity can assume an odd atomicity, nor can the reverse take place, consequently the elements are divided into two great classes those of even atomicity, called artiads, and those of odd atomicity, called perissads. The following table embraces all the commonly occurring elements which are thus grouped. The symbols only are given, in order to familiarize you with them. This whole subject of atomicity is a theory which is as yet only in its infancy, and is so replete with exceptions to the rule that the longer it is studied the more unsatisfactory it becomes. We have only sketched its fundamental principles, and we do not propose to apply them in the body of this work, notwithstanding they have been of great advantage to the progress of the- oretical chemistry. In the following table the monatomic elements are called monads; the triatomic, triads; the diatomic, dyads, etc., in accordance with custom. TABLE OF ATOMICITY. PERISSADS. ARTIADS. Monads. Triads. Pentads. Dyads. Tetrads. Hexads. II Bo N C Cr Fl Au P S Si Mn Cl As Ca Sn Fe Br Sb Sr Al Ni I Bi Ba Ft Co Li Mg Fb Na Zn K Cd Ag Cu Hg OXYGEN AND OZONE. 49 QUESTIONS. 37. Explain the difference between cohesion and adhesion. What is chemical attraction? Illustrate these forces. 38. What is said about the variety of chemical attractions? What element has the widest range of affinity ? What about the compounds of oxygen with the metals ? Under what circumstances do oxygen and nitrogen combine? 39. What advan- tages result to mankind from the various degrees of affinity? 40. How does solution affect chemical attraction ? Give an example. How does water act on the earth? 41. How does heat modify the attractive force? i2. What is meant by the nascent state ? Why are gases active in this condition ? 43. Name two other circumstances which influence chemical attraction. 44. What are monatomic bodies? Give examples of com- pounds of monatomic elements. What other classes are named? How do these mono-, di-, tri-, and tetr-atomic elements combine ? How is at- omicity expressed in symbols ? What is said of the variableness of this atom-fixing power ? Explain the division into artiads and perissads. What is the atomicity of oxygen ? what of phosphorus ? what of hydrogen ? CHAPTER V. OXYGEN AND OZONE. 45. Composition of the Air. The air is composed chiefly of two ingredients, oxygen and nitrogen, which are ele- mentary substances, gaseous in form. These are not united chemically in the air, but are only mingled together. The atmosphere is a mere mixture of gases, just as alcohol and water form a fluid mixture. We will now study oxy- gen at some length, and then take up nitrogen in the next chapter. 46. Abundance and Importance of Oxygen. Oxygen is the most abundant of all substances. It forms nearly one half the whole bulk of material substances in our earth. It constitutes by weight nearly one fourth of the atmos- phere, eight ninths of the waters of the earth, and about C 50 CHEMISTRY. one third of the earth's solid mass. It is one of the chief components, also, of all vegetable and animal substances. It enters into more combinations with other substances than any other element. There is but one element with which it does not combine. This is not true of any other of the sixty-four elements. Oxygen, therefore, may be said to be the most important substance in nature. This will be still more apparent when we come to consider its agency in the chemical operations every where going on, especially in those of living substances. 47. One Way of Obtaining Oxygen. Oxygen can be read- ily obtained from many substances which have a great deal of it in them. The red oxide of mercury, formerly called red precipitate, is one of these. This is mercury united with considerable oxygen ; its formula is HgO. By heating this oxide the ox- ygen can be made to leave the mercury. One way in which this can be done is shown in Fig. 3. We have here a glass vessel full of mercury, containing the mer- curic acid at the top, stand- ing in the mercury in the dish, B. The heat applied is that of the sun's rays con- Fig, s. cent-rated by a burning-glass, C. The result is the decomposition of the red substance, the oxygen of which accumulates in the upper part of the glass vessel, pushing the mercury down before it. Expressed in symbols, the decomposition is very simple : Mercuric Oxide. Mercury. Oxygen. HgO Hg O 48. Discovery of Oxygen. The above was the original ex- OXYGEN AND OZONE. 51 periment by which Dr. Priestley, an English chemist, made the discovery of this gas a little more than a hundred years ago, on the 1st of August, 1774. It was discovered also by Scheele, a Swedish chemist, shortly after, he not having heard of the discovery by Priestley. The gas was called by Priestley dephlogisticated air, for reasons which we will explain to you. Very crude and fanciful notions prevailed at that time, and among others that of Stahl, a German chemist, who maintained that all combustible substances burn in consequence of an element in them which he called phlogiston. Now as this gas, while it makes other things burn brightly, does not burn itself, Priestley considered it as destitute of phlogiston, or dephlogisticated. Some years after, the investigation of the qualities of this gas having in the mean time been diligently prosecuted, Lavoisier, a French chemist, gave it the name which it has retained to this day, and which it probably always will retain viz., oxygen. It is derived from two Greek words, oxus, acid, and gennao, I give rise to. His idea was that this gas is a component of all acids. This has since been found not to be true ; but the name is nevertheless retained. 49. Another Mode of Obtaining Oxygen. A more easy and convenient way of obtaining oxygen from oxide of mer- cury than that described in 47 is represented in Fig. 4 (p. 52). Here the oxide is put into a retort, a, where it is heated by the flame of a spirit-lamp. You see also a re- ceiver, b, from which a bent tube, c, passes under the water in the pneumatic trough, g, where its end is directly under the open mouth of a glass jar. The heat of the lamp de- composes the oxide, so that in place of this compound sub- stance we have two elements, mercury and oxygen. But the mercury, as it separates from the oxygen, is, on account of the heat, in the form of vapor, and therefore passes on with the oxygen gas through the tube of the retort. By 52 CHEMISTRY. Fig. 4. the time, however, that it arrives at the end of the tube it is so far cooled as to become liquid, and drops into the receiver, b. But the gas moves on through the tube, c, and goes up the glass jar, forcing the water in it down as fast as it collects. 50. Difference between Gases and Vapors. You see in the above process what the difference is between a gas and a vapor. The mercury rises in vapor with the oxygen gas, and both are invisible as they pass mingled together through the tube of the retort. This is because the parti- cles of the mercury are so much separated from each other by the action of heat, just as it is with water when it is converted into steam. But these particles are condensed or brought near together again, and appear in the liquid form in the receiver, b. Meanwhile the gas, though cooled equally with the mercury, retains its gaseous form, and passes on. You see that the vapor has its gaseous form dependent upon a certain range of temperature, but the gas retains it under all temperatures. No degree of cold (that is, diminution of heat) can condense the gas into a liquid form. The form of the gas, then, is not accidental and temporary, but permanent. The range of temperature in which vaporization can take place is different in different substances. Water can evaporate at all temperatures, while OXYGEN AND OZONE. 53 mercury will not evaporate under 40. The space above the mercury in a barometer or a thermometer is spoken of as a vacuum ; but it is not strictly so, for there is some little of the vapor of mercury diffused through that space. While it is proper, then, to speak of substances appearing, under certain circumstances, in the form of vapor as being gaseous or aeriform, they can not properly be called gases. This name belongs only to those substances which main- tain this state under all circumstances ; or perhaps we should say under all ordinary circumstances, for some of the gases under extraordinary circumstances have been made to take on another form, either solid or liquid. 51. Obtaining Oxygen from Oxide of Manganese. The chemist does not now get his oxygen from mercuric oxide, for there are other compound substances that contain more of it, and furnish it more readily and abundantly. One of these is an oxide of a metal called manganese ; there are several oxides of this metal containing different propor- tions of oxygen ; the one used for the preparation of oxy- gen is called the dioxide, MnO 2 . Manganese dioxide oc- curs native as a mineral, and when ground fine it is a con- venient and cheap source of oxygen ; it is not now so much used as formerly, for still better methods have been invented. In obtaining oxygen from it great heat is em- ployed ; it must there- fore be heated in an iron retort, such as you see in Fig. 5, placed in a furnace. Only one Fig. 5. third of the oxygen in the dioxide is driven off, leaving behind the red oxide of manganese. The dioxide is of a dark color, and is commonly called the black oxide. 54 CHEMISTRY. 52. Preparation of Oxygen from Potassium Chlorate. The most common way of obtaining this gas is by heating a substance called potassium chlorate. This contains a large quantity of oxygen. In every hundred grammes of it there are thirty-nine grammes of this gas. This is more than four times as much as there is in the mercuric oxide, the sub- stance from which Priestley obtained the oxygen for his experiments. Over a gallon and a half of oxygen can be obtained from an ounce of potassium chlorate. There is only a little more of this gas in this substance than in the diox- ide of manganese ; but the former gives up all its oxygen on being heated, while the latter, as we told you in 51, gives up but a third part of what it contains. And, besides, the potassium chlorate needs to be heated but little compared with the manganese dioxide to evolve the gas. The heat of a spirit lamp or of a Bunsen burner is sufficient. Fig. 6 shows the method of generating and collecting the gas. 53. Explanation of the Process. The potassium chlorate is composed of three elements the two gases, oxygen and chlorine, and the metal potassium, in the proportion KC1O 3 . The oxygen is driven off by heat, and the chlorine remains united with the potassium, making what we call potas- sium chloride. Expressed in formulae thus: KClO 3 +heat KCl-f-O 3 . Of chlorine and potassium we shall speak par- ticularly hereafter. There is some danger of explosion in obtaining oxygen from potassium chlorate alone, because OXYGEN AND OZONE. 55 large quantities of the gas are apt to be set free suddenly. This danger is prevented by mixing with it an equal weight of manganese dioxide. What is singular is that the diox- ide does not part with any of its oxygen, and yet it regu- lates and renders more easy the separation of the oxygen from the potassium chlorate. Less heat is required than when the chlorate is used alone, and the gas is driven off gradually and yet very readily. 54. Other Methods of Preparing Oxygen. There are many other ways of preparing oxygen gas, and by some of them we obtain it indirectly from the atmosphere. One way in which this is done is (1) by passing air over a heated mixture of manganese dioxide and sodium hydrate, and then (2) heat- ing the materials hotter while a current of steam is passing over them. In the first part of the operation sodium man- ganate is formed ; this gives up its oxygen in the second part of the operation, thus reproducing the original materi- als, when the process is repeated. This method was invent- ed by a Frenchman named Tessie du Hotay, and has been tried on a very large scale. Oxygen can also be prepared by decomposing sulphuric acid, by heating barium dioxide, and in other ways of less value. Oxygen gas is now a commercial article in great cities, being manufactured for use in the arts. 55. Properties of Oxygen. Oxygen gas is heavier than that mixture of oxygen and other gases which we call air. If we take 1 as representing air, oxygen would be repre- sented by 1.106. This is said to be the specific gravity of oxygen, air being the standard in reckoning the weight of all the different gases. Oxygen is, like the air, transparent, and without color, odor, or taste. 56. Oxygen a Supporter of Combustion. It is this ingre- dient of the atmosphere which, to use common language, ordinarily makes things burn. If any thing that is burning 56 CHEMISTRY. be introduced into a jar filled with oxygen, it will burn much more briskly and brilliantly than in the air. For the same reason, if a candle or taper be blown out, it will at once be rekindled if put into ajar of oxygen, though there be only a slight spark on the wick. This may be done many times in the same jar of oxygen. After a while this effect will not be produced, because the oxygen is used up ; for every time the candle is in- troduced some of the oxygen unites with the wick and the tallow. It is this union that produces the phenomenon which we call combustion. A very con- venient way of introducing a taper or a candle into .r. j ars filled w jth gas is represented in Fig. 7. 57. Charcoal Burned in Oxygen. If a piece of charcoal be ignited in the air, it will exhibit only a dull red color ; but the moment that it is introduced into oxygen gas it burns brilliantly, casting off sparks with great rapidity, as seen in Fig. 8. Charcoal made from bark is better for this experiment than that made from wood. In this case, as in that mentioned in 56, the oxygen is used up by uniting with the burning substance. In doing this it forms with the charcoal or carbon carbonic anhy- dride, a gas which we shall speak of particularly in the next chapter. This union is very simple : C + O 2 =CO 2 . 58. Phosphorus Burned in Oxygen. One of the most splendid experiments with oxygen is the burning of phos- phorus in it. On introducing the ignited phosphorus into a vessel filled with oxygen, Fig. 9, thick white fumes arise, illuminated by a most intense brightness. In the combus- tion here the oxygen unites with the phospho- rus to form phosphoric anhydride, the parti- Fig. 9. cles of which make the fumes that you see. In this case we have P 2 +O 3 =:P 2 O 5 . OXYGEN AND OZONE. 57 59. Combustion of Steel in Oxygen. Some things which will not burn at all in common air will do so in oxygen gas. This is the case with even so hard a substance as steel. Take an iron wire, or, better, a steel watch-spring, which you can get at any jeweler's, melt a little sulphur and drop it on one end of the spring, ignite the sulphur, and introduce it into the oxygen in the manner represented in. Fig. 10. The com- bustion will at once be communicated to the wire, and it will go on, throwing off sparks of intense brightness till most of the oxygen is united with the iron. The experiment will be very brilliant if the steel spring be coiled. Fig< 10 * The result of the combustion in this case is a solid, for the oxygen unites with the iron to form an oxide of iron. The sparks which fly from the red-hot iron struck by the black- smith's hammer are the same, being formed by the union of the oxygen of the air with some of the iron. But there is this difference : The sparks emitted from the iron in the oxygen are much hotter, because the combustion is more brisk and perfect. Some of the iron falls in small burning globules, which are so intensely hot as to be imbedded in the glass, or they may even go through it if it be thin. We have spoken of iron as not burning at all in air. This is not strictly true, for every time that we strike fire with a steel and flint, or with the heel of the shoe upon the sidewalk, we set fire to a particle of steel. It is not only an exceedingly little fire, but it is also momentary. It would be continuous if the air were all oxygen, and the shoes on our feet would be constantly taking fire from this cause. 60. Oxygen Essential to Life. As ordinary combustion can not go on without oxygen, so also is its presence essen- tial to the continuance of life. It is the oxygen of the air that supports life in all breathing animals, and no other gas C2 58 CHEMISTRY. can take its place in that respect. Cut off the supply of oxygen to our lungs for only a minute or two, and life is extinct. When death occurs by drowning, it is because oxygen is shut out from the lungs. 61. Oxides. Among the most common chemical com- binations are the oxides of metals. Most metals have such an affinity for oxygen that they readily unite with it and form oxides, some much more readily than others. Ex- posed to the air, they tarnish, that is, unite with oxygen. Gold, silver, mercury, and platinum do not oxidize in this way, and therefore are called the noble metals. Gold and platinum are so reluctant, as we may express it, to be united with oxygen, that when the chemist by certain processes forces them to a union with it, they very easily part with the oxygen and return to their metallic state. Such oxides are said to be unstable compounds. On the other hand, there are some metals which have so strong an affinity for oxygen that they are never found native, and can only be obtained by separating them from the ox- ygen with which they are combined. Such are the metals of which lime, potash, and soda are oxides. 62. Different Degrees of Oxidation. While some of the metals have but a single oxide, most of them have two or more, made by having different amounts of oxygen united with the metal. Thus while there is but one oxide of zinc, lead has three, mercury two, copper three, etc. If there be two or more oxides of a metal, they are named thus: Monoxide, dioxide, trioxide, etc., the prefixes being derived from Greek words meaning one, two, three, etc. Thus the dioxide has twice as much oxygen as the mon- oxide, the trioxide three times as much, and so on, the rel- ative amount of the metal being the same in all cases. In some cases another system of nomenclature is em- ployed, as mentioned in 18. Thus we have nitrous oxide, OXYGEN AND OZONE. 59 nitric oxide, and nitric peroxide, according to the propor- tion of oxygen in them, as you will learn in the next chap- ter. A peroxide, is an oxide having the highest amount of oxygen, or at least a higher amount than the nitric oxide in the series named. In the case of the compounds of ox- ygen with the metals, sometimes an oxide is discovered containing less oxygen than the monoxide, and this is call- ed a suboxide, the prefix sub being the Latin for under. Some metals form compounds having one and a half times as much oxygen as the monoxide ; or, what is the same thing, since we can have no half atoms, these compounds contain two atoms of metal to three of oxygen ; they are then called sesquioxides, the prefix sesgui being the Latin for one and a half. Iron gives us an example of this, form- ing Fc 2 O 3 , which you see is a sesquioxide. 63. Ozone. This is oxygen gas in a peculiar condi- tion, distinguished from common oxygen by its pungent smell and its very active chemical properties. You may perceive the peculiar smell when an electrical machine is in action, owing to the partial conversion of the oxygen of the air into ozone. The easiest way of effecting this change is by means of phosphorus. Place a clean stick of phosphorus in a corked flask having a little water in the bottom, and let the flask stand half an hour. Remove the phosphorus with a pair of pincers, and notice the peculiar odor of the gas in the flask. The phosphorus very slowly oxidizes and induces the formation of a little ozone. Pure ozone has never been made it is always mixed with much oxygen. Ozone when breathed irritates the lungs, and corrodes organic matter. It immediately oxidizes metals which ordinarily unite with oxygen at high temperatures only. 64. Experiment. Boil as much starch as will cover the point of a penknife with about fifty cubic centimeters of 60 CHEMISTRY. water, and add a very little potassium iodide. Now steep some slips of paper in the mucilage thus prepared, and you have a test-paper for ozone. Place a strip of this paper in the flask containing ozone prepared by phosphorus, and it will soon turn blue, owing to the action of the ozone. The explanation is this : Ozone first decomposes the potas- sium iodide, setting iodine free ; now free iodine forms a blue substance with starch, called iodide of starch, and hence the color produced. Ordinary oxygen will not act thus. Traces of ozone are found in the atmosphere, partic- ularly in the country, and it is tested for with this same iodine-starch paper. Ozone has strong bleaching properties, and advantage has been taken of this to bleach sugar on a large scale, the ozone being formed by electricity. 65. Nature of Ozone. Exactly how phosphorus or elec- tricity act in converting oxygen into ozone is not under- stood by chemists. But it has apparently to do with the question of the arrangement of atoms, for the mere arrange- ment of atoms in the molecule of a substance has much to do with the production of the various qualities presented by different substances. Thus in oxygen we have two atoms in one molecule, arranged thus, O=O, the two lines indicating the supposed points of union ; but in ozone we have three atoms of oxygen to a molecule, and ar- ranged thus, / \ You will meet with other cases of allo- tropism, as this is called, where a fuller explanation will be attempted. QUESTIONS. 45. Of what does air consist? 46. What is the most abundant of ele- ments ? 47. Describe one way of obtaining oxygen. Write the equation and explain its significance. 48. What makes this method of making ox- NITEOGEN AND ITS OXIDES. 61 ygen of interest ? 49. Describe a more convenient way of obtaining oxy- gen from the same material. 50. How do gases and vapors differ ? What is a permanent gas? 51. How is oxygen prepared from manganese di- oxide? 52. How from potassium chlorate? 53. Explain the process. Why is there danger of explosion ? How is explosion avoided ? Write and explain the equation. 54. Name two other methods of making oxy- gen. Who invented a commercial process ? 55. What are the properties of oxygen ? 5G. What is said of oxygen as a supporter of combustion ? 57. What of burning charcoal in it ? What becomes of the oxygen in this case ? 58. What forms when phosphorus burns in oxygen ? 59. How may steel be burned in oxygen ? What is striking fire ? CO. Why is oxygen essential to life ? 61. What are oxides? Mention an unstable oxide. 62. What is said of metals uniting with oxygen in different ratios ? What is a peroxide? What a suboxide? What a sesquioxide? 63. How may ozone be prepared ? 64. How does ozone act on potassium-iodide-starch paper ? 65. What are the properties of ozone ? What is said of its nat- ure? CHAPTER VL NITROGEN AND ITS OXIDES. 66. Abundance of Nitrogen and its Combinations. Nitro- gen gas forms about four fifths of the atmosphere. It is one of the elements in all animal substances, constituting about one fifth of the flesh of animals when dried that is, when freed from the water that is in it. It enters also into the composition of many of the vegetable substances that are designed for food for animals. It forms some important substances by uniting with oxygen and other elements, as nitric acid, ammonia, etc. It does not enter into any thing like the number of combinations that oxygen does. For example, while oxygen makes with the metals a multitude of substances called oxides, there are very few compounds of the metals with nitrogen. 66 . How Nitrogen can be Obtained. Nitrogen gas can 62 CHEMISTRY. be readily obtained from common air in the mode represent- ed in Fig. 11. Let a cork, with a cup-shaped piece of chalk on it for the reception of a bit of phosphorus, float in a pneumatic trough, d. Aft- er igniting the phosphorus, hold over it a glass jar, a, keeping the edge of its mouth immersed in the water. After a little time there is nothing Fig. 11. - n tne j ar k u fc nitrogen gas nearly pure. The explanation is this : As the phosphorus burns, it unites with the oxygen of the air in the jar, thus making phosphoric anhydride, as phosphorus burned in pure oxy- gen does ( 58). This rises in fumes, and is mingled with the nitrogen. We have then nitrogen "and phosphoric an- hydride in the jar. How do we get the nitrogen separate ? Wait a little, and the fumes disappear, for the phosphoric anhydride dissolves readily in the water in the pneumatic trough, leaving the nitrogen alone in the jar. The nitrogen occupies less space by one fifth than the air in the jar did, for the oxygen that has disappeared was one-fifth part of the air. The cork, therefore, rises somewhat in the jar during the process, being pushed up by the water to take the place of the oxygen. The water now contains phosphoric acid. 67. Properties of Nitrogen. Nitrogen is lighter than air, its specific gravity being .972. Like oxygen, it is transpar- ent, without color, taste, or smell. But it is very different from oxygen in some of its properties. Nothing will burn in it. The contrast between the two gases in this respect can be very prettily shown if you have two jars filled with them. If you let a lighted taper down into the jar of ni- trogen, it will go out. If now you introduce it quickly into the jar of oxygen, it will light up again and burn brilliant- ly ; and you can pass it back and forth from one jar to the NITROGEN AND ITS OXIDES. 63 other many times, producing the same results. The brill- iancy of the lighting-up will diminish each time, because the combustion of the taper uses up the oxygen. 68. Nitrogen in Respiration. As nitrogen can not sup- port combustion, so it can not support life. If we put an animal a mouse, for example into ajar of nitrogen, it will die speedily. But nitrogen does not act as a poison. The air which animals take into their lungs is four fifths nitro- gen, but it does them no harm. The reason that animals can not live in nitrogen alone is simply that they can not live without having some oxygen in the air which they breathe. Because this gas can not support life it is some- times called azote, from two Greek words , privative, and zoe, life. 69. Compounds of Nitrogen with Oxygen. Nitrogen forms five compounds with oxygen. Those which are of the most interest to us are nitric anhydride, which unites with water to form nitric acid (formerly called aqua fortis, the Latin for strong water), and nitrous oxide, the so-called laughing-gas. The following table shows us the names and formulae of these five oxides of nitrogen : Names. Formulae. Composition. 1. Citrous oxide (or laugh-) __ ing-gas) . . . ; N ' 28 Parts N ' 16 P artS ' 2. Nitric oxide N a O a (orNO)* 28 " " 32 " " 3. Nitrous anhydride N a O 3 28 " " 48 " " 4. Nitric peroxide N 2 O 4 (or N0 a )* 28 " " 64 " " 5. Nitric anhydride N 2 O 3 28 " " 80 " " This table illustrates the regularity in proportions which prevails in all chemical combinations, explained in Chapter III. In order to learn all about these oxides of nitrogen, you * For reasons which we can not explain here, the formula? of these bod- ies are of necessity halved as indicated. 64 CIIEMISTKY. will understand them best by taking up nitric anhydride first, and then following the others in the order given above. 70. Nitric Anhydride, N 2 O 5 . This body is a great curios- ity even to a chemist ; it is difficult to obtain, and hard to keep when prepared ; and, since it has no good uses, you do not care to learn much about it. When, however, we have this substance united with water, we get the very impor- tant acid known as nitric acid. We will give you the reaction, although nitric acid is never prepared in this manner, as you will presently see : N 2 5 +H 2 0=2(HNO 3 ). One molecule of nitric anhydride unites with one of wa- ter, forming two molecules of nitric acid. 71. Preparation of Nitric Acid. Potassium nitrate, com- monly called either nitre or saltpetre, and sodium nitrate, are the chief sources of nitric acid ; they are natural products, but may also be made artificially, as you will learn hereafter. Nitrate of sodium, heated with sulphuric acid also called oil of vitriol gives us nitric acid and sodium sulphate : Sodium nitrate. 2NaNO 3 Sulphuric acid. H 2 SO 4 Sodium sulphate. Nitric acid. 2HNO 3 The process is represented in Fig. 12. In the retort, A, are the saltpetre and the sulphuric acid. The heat ap- plied serves the double purpose of facilitating the chemical change, and of driving the nitric acid as it is generated over into the receiver, B, in Fig. 12. NITEOGEN AND ITS OXIDES. 65 the form of vapor. There it is condensed into the liquid form. To produce this condensation the receiver is kept cool by a stream of water flowing from the pipe, *, over its surface, a netting being spread over it to distribute the water evenly. As the water accumulates in the vessel, c c, in which the receiver rests, the waste runs off by the pipe, I. 72. Properties of Nitric Acid. This is a nearly colorless fluid, intensely acid, and very corrosive. It stains the skin yellow the moment that it touches it, and if it continue to be applied, it eats the skin, as it is commonly expressed, or, in chemical language, decomposes it. It also attacks and dissolves most metals. These active properties result from the quantity of oxygen in nitric acid, and the readiness with which it parts with a portion of it. What we call the strength, then, of this substance is really its weakness that is, the weakness with which it holds on to one of its in- gredients. If it held on to its oxygen strongly, instead of parting with a portion of it readily, it would not produce such powerful effects upon other substances. We will pro- ceed to illustrate this explanation of its power by its action on metals, and on certain combustible substances. 73. Action of Nitric Acid on Metals. If you put a bit of copper (a copper cent will answer) in a saucer, and pour upon it some nitric acid, it will at once begin to dissolve the copper. But you do not really get a mere solution, as salt is dissolved in water. The copper acted upon by the nitric acid is no longer copper. It is chemically changed. What the change is we will explain. The acid immediately in contact with the copper lets go a portion of its oxygen, which unites at once with the copper, forming an oxide of copper. The acid that does this is of course no longer nitric acid, for it has lost a portion of one of its ingredients. It becomes nitric oxide, and passes off in fumes. Observe now what becomes of the oxide of copper that is formed. This 66 CHEMISTRY. does not remain an oxide. It is immediately laid bold of by some of the acid, and they together make a substance called nitrate of copper and water. And so the process goes on, some of the particles of nitric acid constantly giv- ing oxygen to the copper, and other particles as constantly seizing upon the oxide of copper thus formed, till the cop- per is all changed to nitrate of copper. This lengthy ex- planation is conveniently abridged in the following equa- tions : Copper. Nitric acid. Oxide of copper. Nitric oxide. Water. 3Cu + 2HNO 3 = 3CuO + 2NO + H 2 O Oxide of copper. Nitric acid. Nitrate of copper. Water. 3CuO + 6HNO 3 = 3(Cu(N0 3 ) 2 ) + 3H 2 O The hydrogen of the acid takes to itself oxygen and forms water in each case. It is this action of nitric acid upon the oxides of metals which makes it so useful in cleansing the surface of instruments or vessels made of metals, as brass and copper, when they have become oxi- dized from exposure or any other cause. The acid dissolves the oxide, forming a salt with it, and thus makes the sur- face bright. 74. Exceptions. Most of the metals are acted upon in the same way by nitric acid. The action upon tin and an- timony is different from that which we have described in the case of copper. Only one step of the process is taken with these metals. The nitric acid merely parts with a portion of its oxygen, and forms oxides of these metals. No solu- tion is made, but we have the oxides in the form of a white powder. Gold and platinum are not acted upon at all by this acid. The reason is that they are not oxidizable, and so the acid keeps all its oxygen to itself. 75. Nitrates. These bodies are formed either by direct union of nitric acid with the oxides or by the action of the NITROGEN AND ITS OXIDES. 67 acid upon the metals themselves. In the latter case the acid in immediate contact with the metal gives some of its oxygen to the metal forming an oxide, and the moment that this is done another portion of the acid seizes this oxide, forming with it the nitrate ; and this double process goes on continually until the action stops. You see, then, that a part of the acid is decomposed in order to provide an ox- ide to unite with the other part. In this decomposition, the acid losing a portion of its oxygen, fumes of nitric oxide pass off. We will study the nitrates of the metals in connection with the metals themselves. F6. Combustion by Nitric Acid. As this acid so read- ily parts with some of its oxygen, it can set fire to certain substances oh being applied to them. If you heat some powdered charcoal, on pouring nitric acid upon it combus- tion will at once take place. The cause is the rapid union of the charcoal with the oxygen, which it takes from the nitric acid. The reason that it is necessary to heat the charcoal is that the union would not be sufficiently rapid to produce a fire without the aid of heat. So, too, if you pour some of the acid upon warmed oil of turpentine, the oxygen which the turpentine takes from the acid sets it all ablaze. Some caution is required in trying this experiment. The test-tube containing the acid should be fastened to the end of a stick a yard long, so that the experimenter may be at some distance from the turpentine as he pours the acid upon it. Phospho- rus, if thrown upon some nitric acid in a plate, will be set on fire, as seen in Fig. 13. The bits of phosphorus must be very small, or some harm will be done by the violence of the combustion. If the acid be rather weak, as that which is bought at the shops often 68 CHEMISTEY. is, it may be necessary in this experiment to heat it before dropping the phosphorus upon it. In all these cases oxides of the bodies named are formed. 77. Nitric Acid in the Atmosphere. Nitric acid can not be made by mixing together its ingredients, oxygen, hydro- gen, and nitrogen. No degree of heat, however severe, will make them unite to form the acid. Accordingly they ex- ist together in the air without uniting, except under ex- traordinary circumstances. If they could be made to unite readily, producing every now and then nitric acid in con- siderable amounts, the most destructive effects would result from the corrosive acid as it descended in showers upon the earth. As it is, there is only one agent that can cause them thus to unite, and that is electricity. Even this does it, as we may say, with difficulty. It is only when this agent acts with violence that the effect is produced. Nitric acid is, therefore, generated in the air only in small quantity, and it is carried down by the rain into the earth, where it answers a valuable purpose in vegetation, as you will see in another part of this book. Its formation then, small as the quantity is, is not a mere accident, but a provision of Providence for a special purpose of a marked character. 78. Acids. Nitric acid being the first acid you have studied, we can now tell you about the class of bodies called acids. But first make a simple experiment. Purple cab- bage, certain lichens, and other vegetables, when boiled with water, furnish blue infusions. Paper steeped in this strong blue solution, and dried, gives us a test-paper for acids which is very useful. The substance usually em- ployed is called litmus, and the paper, prepared as above, litmus paper. Now this blue coloring matter is turned red by the action of even a very small quantity of acid. Dip some litmus paper in a very weak solution of acetic, sul- NITROGEN AND ITS OXIDES. 69 phtiric, nitric, or any other acid, and you find the blue paper will turn red. This is a characteristic property of acids. Another and important distinction is this : all acids contain hydrogen. Nitric anhydride, which has just been men- tioned, contains no hydrogen, as its very name indicates ; when, however, it comes in contact with water, a new body is formed containing hydrogen, and this is nitric acid. The hydrogen in acids may be replaced, as it is termed, by metals forming new bodies called salts, as you will further learn in 80. All the non- metallic elements, except hy- drogen and fluorine, unite with oxygen, forming anhydrides, which, dissolved in water, yield acids. 79. Names given to Acids. Just as we have ous and ic compounds of oxygen, so we have ous and ic acids named in like manner from the proportion of oxygen in them (see 62). Thus nitric anhydride gives us nitric acid, while nitrous anhydride gives us nitrous acid. The compounds of sulphur and oxygen are similar ; sulphurous anhydride yields sulphurous acid, and sulphuric anhydride yields sul- phuric acid. The prefix hypo is used to name certain acids having less oxygen than the ic or ous acid as hypophos- phorus acid. When the acids combine with the metals with elimina- tion of hydrogen, we have bodies whose names correspond in a certain way to the acids whence they are derived. The rule is as follows : Compounds of acids ending in ic are indicated by names ending in ate, and compounds of acids ending in ous are distinguished by names terminating in ite. More concisely stated : ic acids form ates, ous acids form ites. Examples are abundant : nitric acid forms ni- trates, nitrcws acid forms nitrites; chloric acid forms chlo- rates, chlorous acid forms chlorates. The termination ite must never be confounded with the ending ide, as sulphide, chloride, etc. ; these bodies contain no oxygen. 70 CHEMISTRY. Acids containing one atom of hydrogen are said to be mono-basic ; when they contain two or three atoms of hydrogen, they are called di-basic or tri- basic. Thus nitric acid, HN0 3 , is mono-basic, and sulphuric acid, H 2 S0 4 , is di-basic. 80. Bases and Salts. You have seen that blue litmus is turned red by acids ; now there is another class of bodies which turns reddened litmus to blue again. These bodies, chemically opposed to the acids, are called bases. They are either oxides or hydrates of the metals. Thus sodium oxide, Na 2 O, and potassium hydrate, KHO, and calcium hy- drate, CaH 2 O 2 , are bases. The soluble hydrates are called alkalies, and possess strong caustic properties. Now when the hydrogen of an acid is exchanged for a metal, or when the acids act upon these bases, a third class of bodies is pro- duced, called salts. Thus the hydrogen in nitric acid may be replaced by silver, forming silver nitrate, which is a salt. When the hydrates or the oxides are acted upon by acids, water is formed at the same time with the salts, as shown in the two examples below : Potassium hydrate, Nitric Potassium nitrate, Water. A base. Acid. A salt. KHO + HN0 3 = KNO 3 + II 3 Calcium oxide, Nitric Calcium nitrate, Water. A base. Acid. A salt. CaO + 2HNO 3 = Ca(NO 3 ) a + H 2 O Having in the second example taken a dyad metal and an acid contain- ing only one atom of hydrogen, two molecules of the acid are necessary to complete the equation and form the salt. When an acid acts upon a base to form a salt, a remark- able change in the properties of both the acid and the base takes place ; the acid loses its corrosive, acid properties, and the base loses its alkaline and caustic nature, the re- sulting body being neutral. Neither reddened nor blue litmus are affected by neutral salts. XITEOGEX AXD ITS OXIDES. Some acids contain two or more atoms of hydrogen, which may be re- placed successively by a metal ; if only one atom of hydrogen is thus exchanged, an acid salt is formed ; if both atoms of hydrogen are ex- changed for two atoms of a monad or one atom of a dyad metal (see 44), a neutral salt results. You will observe this in the study of sulphuric acid. 81. Nitrous Oxide, or Laughing-Gas. This gas is the com- pound of oxygen and nitrogen, which has the smallest pro- portion of oxygen. It is obtained by heating ammonium nitrate in a re- tort or flask, a. Complete decomposition ensues; the gas is washed in the flask, b, and collected in the receiver, c. "We obtain two substances en- tirely different from each oth- Fig. 14. er and from the substance from which they come, viz., water and the nitrous oxide gas : Ammonium nitrate. NH 4 N0 3 Nitrous oxide. N S O Water. The vapor of the water and the gas pass together into the second flask ; but there the vapor is condensed into water, and the gas bubbles up into the glass jar set in the trough to receive it. Some caution is necessary in preparing this gas, or it may be impure, and therefore injurious to those who may inhale it. To avoid this the material must be pure, the heat must not be so great as to cause fumes to rise in the retort, and the gas should be passed through 72 CHEMISTRY. solutions of potassium hydrate and ferrous sulphate before collecting it in a receiver. 82. Properties of Laughing-Gas. The nitrous oxide gas is as colorless and transparent as air, and has a sweetish taste. A lighted taper burns almost as brightly in it as in oxygen, and if there be but a spark on the wick, on introducing it into a jar of this gas it lights up instantly. When breathed, it occasions no irritation in the lungs, but produces a sin- gular excitement, a delicious intoxication, which lasts but two or three minutes. Individuals under the influence of it act variously. Some dance, some laugh, some declaim, some fight, etc. The excitement is very commonly of a pleasant kind, and hence this gas is called in common lan- guage laughing-gas. It also possesses the property of causing insensibility to pain, and is now much used by den- tists. 83. Nitric Oxide. This is a colorless gas which has just twice as much oxygen in it as the nitres oxide. It can be obtained from nitric acid and copper in the apparatus rep- resented in Fig. 15. Bits of copper and nitric acid, some- what diluted, are in- troduced into a flask. The gas passes out through the tube, and may be collect- ed in the usual way in jars in the pneu- matic cistern. The first gas that passes over will be orange- colored, and we must not begin to collect till the gas is colorless. The object of NITROGEN AND ITS OXIDES. 73 the funnel is to enable us to add more nitric acid as the ac- tion moderates. Copper. Nitric acid. Nitrate of copper. Nitric oxide. Water. 3Cu + 8HNO 3 = 3(Cu(NO 3 ) 2 ) + 2NO + 4H 3 O Though this gas is colorless, the moment that it is ex- posed to the air it is changed into orange fumes. This is very prettily shown if a jarful of this gas be raised out of the water in the pneumatic trough. The air, entering the jar, diffuses an orange-red color in every part of it. The explanation is this : The oxygen of the air unites with the nitric oxide, converting it into a mixture of nitrous anhy- dride and mtric peroxide, 3(NO) + O 2 =N 2 O 3 +NO 2 . You can now understand why the first gas that rises in the flask is colored. There is some air in the flask, and when the gas begins to rise-it takes the oxygen from this air, and be- comes nitrous anhydride. When this is driven off the ni- tric oxide will come along pure. In making these experiments you must be very careful not to breathe the reddish fumes of nitrous anhydride mixed with nitric peroxide, for they irritate the lungs. Indeed, they smell so horribly we think you will not need to be warned. 84. Explanation of a Former Experiment. You will see that in the above process the same materials are used as in the experiment given in 73. Nitric oxide was formed in that experiment, as well as in this process, and yet reddish fumes arose from the copper and the acid. The nitric ox- ide at once united with the oxygen of the air, and so was changed into nitrous anhydride and nitric peroxide, as ex- plained in 83. In the process for obtaining the nitric oxide we prevent this change, as you see, by shutting out the air. 85. Air and Nitric Oxide Contrasted. The two great in- gredients of air are those which compose nitric oxide. And yet how entirely opposite these two substances are in their D 74 CHEMISTEY. qualities! one being one of the blandest of all substan- ces, flowing into the lungs without irritating in the least the delicate air-cells, while the other is powerfully acid, and dangerous to breathe. The chief reason of this differ- ence is that the air is a mere mixture of oxygen and nitro- gen, and therefore partaking of the properties of both of these gases, while nitric oxide is a compound, a new sub- stance formed by the chemical union of the two gases. You have here illustrated in a striking manner the grand difference between mixtures and compounds, the mixture having properties intermediate between those of its ingre- dients, while the compound generally has properties differ- ing widely from those of either of the substances of which it is composed. 86. Nitrous Anhydride. This is a thin, mobile, blue liquid at a very low temperature, otherwise it is an orange-red gas. Dissolved in water, it combines with it and forms nitrous acid, which is of no great importance, though some of its compounds are useful in the arts ; they are called nitrites. 87. Nitrous Anhydride in Nitric Acid. It is the nitrous anhydride that gives the yellow color which nitric acid so commonly has. But how is this gas generated in the nitric acid ? The explanation is easy. Nitric acid, we have told you, is very ready to part with a portion of its oxygen. Even exposure to light will make it do this ; so that if we wish to preserve the acid pure, we must keep it in a dark place or in dark-colored bottles. As we commonly see it, a portion of it has become, by a loss of one fifth of its oxy- gen, nitrous anhydride, which, readily dissolving in the nitric acid, gives it a yellow color. Sometimes the oxygen which is disengaged in this decomposition of the nitric acid, to- gether with some of the nitrous anhydride, forces out the stopper of the bottle. 88. Nitric Peroxide. To obtain this substance in a liquid NITROGEN AND ITS OXIDES. 75 form you can heat nitrate of lead in a glass retort and col- lect the deep red fumes in a tube surrounded by a freezing mixture. At a low temperature the fumes condense to a red liquid. The proc- ess is represented in Fig. 16. It also forms in the gaseous state by exposing nitric oxide Fitr 1(J to the oxygen of the air. This does not form an acid on dissolving in water. QUESTIONS. 66. Where does nitrogen occur in nature ? 66 a. How can it be obtained? 67. What are the properties of nitrogen? 68. WTiat are its relations to life ? 69. How many and what are the compounds of nitrogen with oxy- gen ? W r hat are the proportions of these elements in laughing-gas ? What in nitric oxide ? 70. What is said of nitric anhydride ? What does it form when dissolved in water ? 71. Describe the preparation of nitric acid. 72. What are its properties ? 73. Explain the action of nitric acid on met- als. 74. What metal does not dissolve in nitric acid ? WTiy ? 75. What are nitrates ? 76. Give an example of combustion produced by nitric acid. 77. What is said of the formation of nitric acid in the air ? 78. What is the action of acids on blue vegetable solutions ? How do anhydrides form acids ? 79. Explain the method of naming acids. What does the prefix * ' hypo " mean ? How are bodies derived from acids by replacement of hydro- gen named ? 80. W T hat are bases ? How do they act on reddened litmus ? What is a salt ? What do nitric acid and potassium hydrate form by com- bining ? What is a neutral salt ? W T hat an acid salt ? 81. How is nitrous oxide prepared ? 82. WTiat are its properties ? 83. How is nitric oxide obtained ? 84. What are the reddish fumes given off when copper is put into nitric acid ? 85. What is said of the contrast between air and nitric oxide ? What does this illustrate ? 86 and 87. What is nitrous anhydride ? How does it occur in nitric acid ? 88. How is nitric peroxide obtained ? 76 CHEMISTRY. CHAPTER VII. CARBON AND CARBONIC ANHYDRIDE. 89. Abundance of Carbon. The two elements which we have described to you in Chapters V. and VI. are gaseous. Carbon, the element which we are now to consider, is a solid. This is present almost every where. It forms nearly one half of all the solid part of all vegetable and animal substances. The different varieties of coal are nearly pure carbon. This element is one of the ingredients of all limestones and mar- bles. All shells are composed in part of it. It is present every where in the air, united with oxygen to form a gas, carbonic anhydride, which we shall speak of particularly in the latter part of this chapter. 90. Charcoal. One of the most common forms in which we see carbon is charcoal. Before hard coal was introduced into use it was the most common form ; and it is for this reason that the word charcoal is often used as being syn- onymous with carbon. Charcoal is ordinarily made from wood ; or, to speak more correctly, it is obtained from wood, for no new substance is formed, but there is merely a sep- aration of the components of the wood. All the compo- nents except the carbon are driven off, for the most part. This is done by a smothered and imperfect combustion. The wood is piled together and covered over with turf. It is then set on fire from below, and suitable openings are kept in the covering to allow the proper degree of combus- tion. Figs. 17 and 18 (p. 77) illustrate the manner of piling the wood and conducting the operation. Some of the car- CARBON AND CARBONIC ANHYDRIDE. 77 bon is lost in this process, for it unites with the oxygen of the air that is admitted in the openings, forming a gas, and so passes out at the upper openings with the other matters that are driven off by the heat. About 40 per cent, of the wood is carbon, and the char- coal obtained is from 20 to 25 per cent., so that the loss of carbon is nearly, often quite, one half. The best charcoal is made by heating wood in tight iron vessels till all the vapors and gases are driven off. The proc- ess of making char- Fi - 1S - coal can be illustrated by holding a burning slip of wood in a test-glass, as represented in Fig. 19. The portion within the glass, not hav- ing a free access to air, is subjected to a partial smothered combustion, and therefore becomes charcoal. 91. Soot. In burning wood there is more or less smoke. This arises from the imperfection of the combustion, and is dense in proportion to that im- perfection. If the combustion were Fig. 19. perfect, there would be nothing visi- ble, for the substances passing off in the air would be, as you will learn more particularly in another chapter, vapor and 78 CHEMISTRY. gases only, and all that would be visible is the ashes. But, as it is, there pass upward in this body of vapor and gas solid particles of carbon that failed to be burned, and it is these that you see and call smoke. These accumulate to some extent in a chimney upon its sides. The soot thus formed is not pure carbon, for there are some other substances creosote, etc. mingled with it. The reason that we do not have smoke and soot from hard coal is that the combustion is more perfect than in the case of wood. So, too, there is more of smoke, and therefore soot, from green wood than there is from dry wood. For this reason green or wet wood is used in smok- ing meat. When a lamp smokes from having the wick too high, it is because the carbon of the oil is furnished in too large quantity for the oxygen that is in the air around the wick. Whatever this smoke touches has soot deposited upon it. When the combustion is perfect, all the carbon, as it rises in the heated wick, is made by the heat to unite with the oxygen of the air, and form carbonic anhydride, which passes upward unseen. 92. Lampblack. This substance, so much used in making printing-ink, is a fine kind of soot made from pitch or tar. In Fig. 20 is represented an apparatus for mak- ing lampblack. In the iron pot, a, some pitch or tar is heated to boil- ing, and, as a little air is admitted through small openings in the brick- work around the pot, an imperfect combustion takes place. The carbon of the tar passes in a dense cloud of smoke into the chamber, b c. In this hangs a cone of coarse cloth, the height of which may be regulated, as you see, by a pulley. The lampblack or car- bon is deposited in powder on the cone and on the sides of CARBON AND CARBONIC ANHYDRIDE. 79 the chamber, which are lined with leather. There are two objects in having the cone one to prevent the smoke from passing upward too rapidly, and the other to present a large surface for the deposition of the powder in addition to that of the walls of the chamber. 93. Bone-Black. Bone or ivory black is a powdered char- coal prepared from bones. It is far from being pure char- coal, as you will see as we explain its preparation. A bone is composed of two parts mingled together, a mineral and an animal part. These can be obtained separate from each other, as has been fully shown in the " First Book of Physi- ology." It is the animal part alone that really furnishes charcoal ; but in the preparation of bone-black both parts are used together. The bones are heated in iron vessels, and the heat, driving off all the volatile ingredients of the animal part, leaves the carbon mingled with the mineral portion the phosphate of lime. The advantage of this form of charcoal is that the carbon is very minutely divided by being thus mingled with the mineral powder. Besides other uses soon to be noticed, bone-black is used in the manufact- ure of blacking, being mixed for this purpose with oil of vitriol and sirup. 94. The Carbon in Animal Substances. As there is car- bon in the animal part of bone, so it is in all animal sub- stances. It exists in combination with other elements, and therefore does not appear as carbon. It is only by some chemical process which separates it from these combina- tions that it can be made manifest, and combustion is one of the processes that can do this. When animal skin or flesh is charred that is, partially burned the charcoal that appears is produced essentially in the same way that it is when made from wood. It is not really made, but it is sepa- rated by the heat from the substances with which it is com- bined, the heat for the most part driving these off into the 80 CHEMISTEY. air. Whenever meat is overcooked in roasting, some of the outside exhibits this separation of carbon by chemical de- composition. 95. Properties of Charcoal. Although charcoal is so com- bustible, it is in some respects a very unchangeable sub- stance, resisting the action of a great variety of other sub- stances upon it. Hence posts are often charred before be- ing put into the ground. Grain has been found in the ex- cavations of Herculaneum which was charred at the time of the destruction of that city, 1800 years ago, and yet the shape is perfectly preserved, so that you can distinguish between the different kinds of grain. While charcoal is itself so unchangeable, it preserves other substances from change. Hence meat and vegetables are packed in char- coal for long voyages, and the water is kept in casks which are charred on the inside. A ham was kept, by a friend of the author, packed in charcoal-dust eight years, and on be- ing cut was found as fresh and sweet as when first put in. Charcoal is also a great purifier. Tainted meat can be made sweet by being covered with it. Foul and stag- nant water can be deprived of its bad taste by being fil- tered through it. Charcoal is a great decolorizer. Ale and porter filtered through it are deprived of their color, and sugar-refiners decolorize their brown sirups by means of charcoal, and thus make white sugar. Animal charcoal, or bone-black, is the best for such purposes, although only one tenth of it is really charcoal, the other nine tenths be- ing the mineral portion of bone. Other substances besides those which give color are often extracted by charcoal. Thus brandy is rendered pleasanter in taste and smell by being filtered through charcoal, because an acrid volatile oil, called fusel-oil, is extracted. So charcoal takes away from beer not only its color, but that which causes its bitter taste. CARBON AND CARBONIC ANHYDRIDE. 81 96. Absorbing Power of Charcoal. Most, if not all, of the effects above mentioned are attributed to the absorbing power of charcoal. This power is very great. Charcoal will absorb of some gases from eighty to ninety times its own bulk. This constitutes a protection to substances which are covered with charcoal, for gases are the grand agents in decay. Absorbed by the charcoal, they are put out of the way ; and not only so, but they constitute a part of the wall of defense together with the charcoal, filling up as they do all its spaces. Charcoal thus saturated with gases defends the substance that it covers from access of the air. When decay has already begun before the char- coal is applied in the work of purification, it absorbs all the gases tli at have been produced in the decay, and thus puts a stop to the process. 97. Explanation. The question arises as to what gives this power of absorption to charcoal. It is generally sup- posed that it is owing to its great porosity. Charcoal is full of minute spaces, and is therefore intersected by num- berless partitions. If these were spread out they would con- stitute a surface perhaps a thousand times larger than the external surface of the charcoal. As every point of this sur- face is a point of attraction, it is supposed to account for the enormous accumulation of gases in the spaces of the charcoal. But this accounts for it only in part. If it were the only cause of the absorption, there should not be such a great difference in absorbing different gases. Of some gases it absorbs nearly fifty times as much in bulk as it does of some others. When great quantities of gases are absorbed, there must be great condensation, and this would hardly come from mere common attraction. There must be some peculiar power in the charcoal to change in some way the condition of a gas of w r hich it absorbs ninety times its own bulk. And, besides, it seems to show some sort of affinity D 2 82 CHEMISTEY. for certain substances in separating the'm from others, as, for example, in separating the coloring substance from ale, and also that which gives it its bitter taste. 98. Coal. All the different varieties of coal anthracite, bituminous, etc. are carbon, more or less mixed with compounds of hydrogen and carbon called hydrocarbons. Anthracite burns without smoke, and when fully ignited without flame, for it is destitute of the volatile hydrocar- bons that are present in bituminous coal. The reason of the difference is that these volatile substances have been driven off by heat in the formation of the anthracite. When the anthracite is burned the carbon all passes upward, unit- ed with the oxygen of the air, forming carbonic anhydride. The impurities combined with this carbon in the coal fall below, making the ashes. The bituminous coal is used in making illuminating gas. What is left after the volatile matters are driven off is a very impure charcoal called coke. 99. Graphite. Graphite, or plumbago, sometimes called black-lead, contains not a particle of lead, but is crystallized carbon, having commonly a very little iron mingled with it. It is a grayish black substance having a metallic lus- tre. It is used for making the so-called lead-pencils, and for giving a polish to stoves and other iron articles. When powdered it is so soft and lubricating that it is added to grease for the prevention of friction in wheels and machin- ery. It is a very incombustible article, and therefore the coarser kinds are manufactured into crucibles, or melting- pots. There are famous mines at Cumberland, in England, and in Siberia, which furnish very fine graphite for pencils. It is quite a common mineral in this country, appearing in many localities. At Ticonderoga, in New York State, an extensive deposit occurs, most of which is worked up into crucibles and stove-polish. 100. The Diamond. In the diamond we have pure carbon CARBON AND CARBONIC ANHYDRIDE. 83 crystallized, but differently from what it is in graphite. It is the hardest of all substances. It has not the least resem- blance to coal, yet it can be burned up in oxygen, car- bonic anhydride being the result, as in the burning of coal and other forms of carbon. It was discovered to be carbon in this way by Lavoisier, a French chemist. He threw the sun's rays, concentrated by a large lens, upon a diamond in a vessel of oxygen gas. It was consumed, and carbonic an- hydride alone resulted, showing that the substance that had thus united with the oxygen was nothing but carbon. No one has ever yet been able to convert coal into diamonds. The difficulty seems to be that coal can neither be dissolved nor melted, for, in order to crystallize any substance, it must first be in a liquid state. It is indeed stated that a French- man, M. Despretz, has with a galvanic battery melted and crystallized carbon, and thus made diamonds; but they were so small as to be visible only with a microscope. 101. Allotropism. You have learned that the elementary body carbon appears under three very different forms dia- mond, graphite, and charcoal varying in color, hardness, specific gravity, and other physical properties. "We can not explain exactly how and why this is so, but we know that some other elements appear in two or more distinct forms, and the peculiarity is not confined to carbon. Bear in mind that, chemically, diamond, graphite, and charcoal are one and the same, but they differ in their physical as- pects. Bodies having this power of taking different forms are said to be allotropic, and the phenomenon is called allo- tropisra. These words are made up from two Greek words, allos," other," and tropos, "way," because the body exists in some "other way." When we say that carbon exists in three allotropic forms, we do not explain any thing; we rather conceal our ignorance of the truth by employing a high-sounding word coined for that purpose. 84 CHEMISTRY. 102. Carbonic Anhydride. Having given you an account of the element carbon, we will now notice a gas formed by the union of this element with oxygen, viz., carbonic anhy- dride.* This is formed whenever carbon is burned in oxy- gen, as in the experiment in 57. So, also, when a diamond is burned in oxygen, this, being pure carbon, unites with the oxygen to form carbonic anhydride. This gas is one of the products of all ordinary combustion, the result of the union which takes place between the oxygen of the air and the carbon in the combustible substance. Thus the carbon of wood, oil, tallow, illuminating gas, etc., unites, in the act of burning, with the oxygen of the air, and forms this gas. 103. Common Mode of Obtaining Carbonic Anhydride. Put into a flask, Fig. 21, some small bits of chalk or marble, Fig. 21. and pour upon them some hydrochloric acid. The gas will bubble up, and, forcing out the air before it, will pass through * This gas used to be called carbonic acid, but chemists have decided that it is not a true acid because it contains no hydrogen, hence it is now known as carbonic anhydride. CARBON AND CARBONIC ANHYDRIDE. 85 the bent tube, and so can be collected in jars in the pneu- matic cistern. The explanation is this : The chalk and mar- ble are two forms of the same substance, calcium carbon- ate, which contains carbonic anhydride united to the oxide of calcium, commonly called lime. Now the hydrochloric acid decomposes the calcium carbonate, forming water, the gaseous carbonic anhydride, and a new body, calcium chlo- ride, which remains dissolved in the water. We do not see the water formed, for it mixes with that in the flask ; nor do we see the calcium chloride, for it is very soluble, and remains in the water ; we can easily prove it is there, how- ever, by evaporating the watery solution, when we will ob- tain a white solid mass. The carbonic anhydride set free is seen as it bubbles up through the water. Expressing this in symbols, we write thus : ,, ., Hydrochloric Calcinm \xr^ a Carbonic Marble - ' acid. chloride. Water * anhydride. CaCO 3 + 2HC1 = CaCl 3 + HsO + CO a Sodium carbonate, potassium carbonate, or any other car- bonate, will serve equally well; so, also, sulphuric or nitric acid may be used instead of hydrochloric. 104. Properties of Car- bonic Anhydride. This gas is, like air, transparent and without color. It has a slightly acid and agreea- ble taste. Its specific grav- ity is 1.527 that is, it is about one and a half times as heavy as air. Because it is so much heavier than air it can be collected by dis- Fi s- 22 - placement, as it is termed. This is represented in Fig. 22. The gas produced in the flask passes over in the tube and 86 CHEMISTRY. displaces the air in the jar, pushing it upward as water would oil. In order that it may do this quietly and ef- fectually, the jar is so placed that the end of the tube is near the bottom. So, also, we can pour this heavy gas from one vessel into another, the same displacement of air taking place in this case. The comparative weights of air and this gas may be shown by the experiment represented in Fig. 23. An empty beaker that is, a glass vessel full of air is first balanced on a scale; then carbonic anhydride is poured into it, of course causing the beaker to go down. Fig. 23. 105. Liquefaction and Solidification of Carbonic Anhydride. By an apparatus which subjects carbonic anhydride to great pressure and cold this gas can be made fluid, and even solid. As a solid it is a very peculiar substance, of a white color, appearing much like dry snow. If held in the hand it will destroy the skin like red-hot iron. The enormous degree of pressure required to liquefy carbonic anhydride is shown by the fact that the apparatus once exploded in Paris, killing an assistant engaged in the experiment. CARBON AND CARBONIC ANHYDRIDE. 106. Carbonic Anhydride not a Supporter of Combustion. A lighted taper introduced into a jar of this gas is extin- guished as quickly as it would be if it were dipped into wa- ter. This is simply because oxygen is absolutely necessary to the continuance of the combustion. There is, it is true, a sufficient quantity of oxygen in the carbonic anhydride, but it is so thoroughly united with carbon that not a par- ticle will quit it to unite with the carbon of the taper. A very pretty way of showing that this gas is not a support- er of combustion, and at the same time that it is heavier than air, is to pour it, as seen in Fig. 24, from one jar down into another in which there is a lighted taper. Notwith- standing that carbonic anhydride does not support ordinary combustion, a few substances having a great attraction for oxygen will burn in it. A piece of magnesium wire lighted and plunged into a jar of the gas burns brilliantly, taking the oxygen to itself and leaving the carbon, which appears as a black powder on the sides of the glass jar. The decomposition of the carbonic anhydride is thus ex- pressed : Carbonic anhydride, Magnesium, Carbon, Magnesium oxide, CO 2 " + 2Mg C + 2MgO. 107. Effects of Carbonic Anhydride when Respired. As it is with nitrogen ( 68), so with this gas no animal can live in it. But it destroys life not merely because, like nitrogen, it shuts out oxygen from the blood in the lungs, but it acts also as a positive poison. It produces an effect upon the sys- tem similar to that of some narcotics. Nitrogen is constant- ly taken into the lungs in large quantities without doing any harm, for about four fifths of the air is nitrogen; but if car- Fig. 24. 88 CHEMISTRY. bonic anhydride be present in the air to the amount of one tenth of the whole, its poisonous influence is very manifest. And even when it is present only in the small quantity of one or two per cent., bad effects show themselves on breath- ing such an air for some little time. This gas is always present in the atmosphere, but in so very small amount, as you will see in the next chapter, that it produces no effect as a poison. 108. Carbonic Acid in the Stomach. While this gas is thus a poison in the lungs, it is far otherwise in the stomach. It produces an agreeable tonic effect there, as it is intro- duced in effervescing drinks. The chemistry of these two organs is different. The lungs can use oxygen chemically to advantage ; while carbonic anhydride, which is a deadly poison to the blood in the lungs, is beneficial in the stomach, or at least is not injurious there. 109. Absorption of Carbonic Anhydride by Liquids. Wa- ter readily absorbs or dissolves about its own bulk of car- bonic anhydride. By means of pressure it can be forced to absorb more than this, the amount absorbed being in propor- tion to the amount of pressure. Thus " soda-water " is com- monly only water into which a large quantity of carbonic anhydride has been forced, and the effervescence is owing to the escape of this gas on taking off the pressure. The wa- ters of many natural springs have considerable of this gas, which, being generated under pressure in the earth, is there- fore largely dissolved in the water, and, escaping from this pressure as the water issues forth, causes an effervescence. In beers and sparkling wines the carbonic anhydride is made by the fermentation of the liquid as it is confined. The bursting of bottles, which sometimes occurs, is pro- duced by the generation of too large an amount of this gas, or by its undue expansion by exposure to heat. 110. No True Carbonic Acid. Carbonic anhydride is one CARBON AND CARBONIC ANHYDRIDE. 89 of a class of bodies which unite with water to form acids. You have learned in 70 that nitric anhydride combines with water, forming nitric acid ; thus N 2 O 5 -f-H 2 O=2HNO 3 . But carbonic acid does not seem to have any definite ex- istence ; the solution of CO 2 in H 2 O may be regarded as H 2 CO 3 , but the acid, if it exist at all, is decomposed at ordi- nary temperatures, and quickly by boiling. Although car- bonic acid has a doubtful existence, the carbonates derived from it are a most important and numerous class of bodies. From these carbonates the stronger acids, hydrochloric and nitric, for example (or even acetic), do not drive out carbon- ic acid, but carbonic anhydride, and the reaction is accom- panied by the formation of water. 111. An Apparent Inconsistency. Notwithstanding the comparative weakness of carbonic acid, it adheres to its union with some substances in spite of the most intense heat. No degree of heat can drive off the carbonic acid from potassium or sodium carbonates. Why this is we know not, neither do we know why lime will take carbonic acid away from potash. It would seem from this that car- bonic acid has a stronger attraction for calcium than for potassium, and yet, from the effect of heat upon carbonate of lime, we should make exactly the opposite inference. This is one of the apparent contradictions in affinity which we can not explain, though the object which the Creator had 'in making such differences is generally quite obvious. 112. Carbonic Oxide. This is a gas which has but half as much oxygen in it as carbonic anhydride, its formula be- ing CO. It is a transparent colorless gas, and burns with a beautiful blue flame, which you have often seen playing over the surface of an anthracite fire as it kindles. The ex- planation of its formation in this case is this : The closely packed coal does not get sufficient oxygen from the air to make carbonic anhydride, and so carbonic oxide is formed. 90 CHEMISTRY. When, however, it emerges into the air, if the heat be suffi- cient to inflame it, it takes from the air an additional quan- tity of oxygen, and thus becomes carbonic anhydride. When the whole body of the coal has become thoroughly ignited, there is no more carbonic oxide formed, but only carbonic anhydride, and hence there is no longer any flame. When charcoal burns without a good supply of air, carbonic oxide is produced, mingled with carbonic anhydride. This gas is very poisonous, much more so than the carbonic an- hydride. It is the mixture of the two gases that produces such injurious effects when charcoal is burned in a chafing- dish or an open furnace in a close room. We have known similar effects produced when a damper of an anthracite coal- stove was closed before the coal was well ignited, thus pre- venting the carbonic oxide as it rises from being fully con- verted into carbonic anhydride, and forcing some of both of these gases out into the room. 113. Preparation of Carbonic Oxide. This gas is common- ly obtained from oxalic acid, the acid which gives the sour taste to sorrel. This is composed of carbon, oxygen, and hy- drogen, the same ingredients which we have in carbonic an- hydride and carbonic ox- idephts water, but in differ- ent propor- tions. The chemist by means of sul- phuric acid splits up, as we may say, the oxalic acid into these two CARBON AND CARBONIC ANHYDRIDE. 91 gases, and then, by taking away the carbonic anhydride, he has the carbonic oxide by itself. The way in which he does this is represented in Fig. 25 (p. 90). The oxalic acid and the sulphuric acid are put into the flask, a, and on the application of gentle heat the two gases, carbonic anhydride and carbonic oxide, are produced, and pass over through the tube into the bottle, b. Here there is a solution of potassium hydrate; and as the gases pass into it the carbonic anhy- dride unites with the potassium to form potassium carbon- ate, and the carbonic oxide goes on alone into the jar, c, where it is received for experiments. 114. Experiment. If you take a jar of this gas, Fig. 26, and apply a lighted taper to its mouth, the gas will burn with a beautiful blue flame. You can make the flame very large by pouring water in, for this forces the gas out rapidly. As it burns it becomes carbonic anhydride by taking oxygen from the air. Fig. 20. Carbonic oxide. Oxygen. yield Carbonic anhydride. CO + O = CO 2 QUESTIONS. 89. In what forms does carbon occur in nature ? 90. How is charcoal made? How illustrated? 91. What is soot? What is said of imperfect combustion ? Why do lamps smoke when the wick is too high ? 92. How is lampblack made ? 93. What is bone-black ? What does it contain be- sides charcoal ? What are some of its uses ? 94. What is said of the pres- ence of carbon in animal substances ? What is the chemical explanation of the charring of flesh and skin ? What is said of overcooking meat ? (>."). What of the unchangeably of charcoal ? What of its preservative power? What of its purifying and decolorizing powers? What other 92 CHEMISTRY. effects does it produce ? 9G. What is said of its absorbing power ? 97. How is this power to be explained? 98. What is the difference between anthracite and bituminous coal ? What is coke ? 99. What is said of black-lead? 100. What of the diamond? 101. What is meant by allo- tropism ? Whence is the word derived ? 102. State various cases in which carbonic anhydride forms ? 103. Describe and explain the common mode of obtaining it? Write the equation given. 104. What are the properties of carbonic anhydride? How is it collected? Show it has weight. 105. What is said of converting gases into solids ? 106. What effect does car- bonic anhydride have on combustion? Illustrate this. 107. What effect on respiration ? How does it differ from nitrogen in this respect ? 108. How does carbonic anhydride act on the stomach? 109. What is "soda- water?" 110. Why is there no true carbonic acid? 111. State what is said of an apparent inconsistency. 112. What is the composition and nat- ure of carbonic oxide? Where do we often see it burning? Explain its production and burning in this case. 113. How may it be prepared ? Why will it burn when forced out of a jar by pouring in water ? Is it poisonous ? CHAPTER VIII. THE CHEMISTRY OP THE ATMOSPHERE. 115. Ingredients of the Atmosphere. The air is a mixture of three gases oxygen, nitrogen, and carbonic anhydride. The proportions of these ingredients are changed by cir- cumstances, as you will soon see, and yet wherever the air is free the proportions are always the same. About one fifth of the air is oxygen, and the remaining four fifths nitrogen. The amount of carbonic acid is very small, there being only 4 vol- umes in every 10,000 volumes of air. These proportions are repre- sented to the eye in Fig. 27, the largest square representing the nitrogen, the one at its side the oxygen, and the smallest the carbonic anhydride. THE CHEMISTRY OF THE ATMOSPHERE. 93 116. Quantity of Carbonic Anhydride in the Atmosphere. As the air encircling the earth is from 45 to 50 miles in height, the quantity of carbonic acid, although proportion- ably small, is really in the whole very great. It has been estimated that there is seven tons' weight of this gas over every acre of the earth's surface. 117. Chief Use of Nitrogen in the Air. Oxygen, you have seen, is a very active substance, supporting life and com- bustion every where. It is so active that it needs to be diluted in the air with four times its bulk of nitrogen gas. If it were not thus diluted the world would be one vast scene of continued conflagrations. Combustible substances would take fire five times as easily as now, and when once on fire it would be difficult to put them out. Iron would burn as readily as wood now does. So also the operations of life would be attended with five times the amount of heat that they now are, and the tendency in every animal would be to fever and inflammation. As oxygen is so stimulat- ing, it has sometimes been used successfully in reviving persons who have been drowned or suffocated. In such cases, the more of this gas you can introduce into the lungs for a little while the better. It is easily introduced by a pipjB from a bladder filled with it. The remedy, however, has seldom been used, because it is not at hand unless the accident occur near the laboratory of a chemist. 118. Analysis of the Air. We will describe two modes of analyz- ing the air. The first is this : A certain volume of air is allowed to pass slowly through a tube containing potassium hydrate. This has a very strong attraction for one of the ingredients of the air, carbonic anhydride, and has none for either the oxygen or nitrogen. It takes, therefore, the carbonic anhydride, and the weight of the tube compared with its weight before the experiment shows how much there is of this ingredient in the volume of air employed. And now the air, thus deprived of its carbonic anhydride, is made to pass through a tube filled with red-hot copper-filings. The copper in this state attracts to itself the oxygen, but having no tendency 94 CIIEMISTEY. to unite with the nitrogen, this passes on. The weight of this tube com- pared with its weight before the experiment shows the amount of oxygen in the air. Then subtracting the sum of the weights of the oxygen and carbonic anhydride from the weight of the air examined, we have the weight of the nitrogen. Another mode which ascertains the proportionate volumes of the gases as well as their weights is represented in Fig. 28. We have here a tube, a b c, with a very minute opening at a, a bulbous enlargement at 6, and its larger orifice, c, made to fit air-tight in the top of the vessel, d. This vessel is filled with mercury, and is graduated, as you see. There is a cock at e, by which you can let the mercury run out in as small a stream as you please. Before fitting the tube, a ft c, to the vessel, it is filled with loose cotton having bits of phosphorus scattered in it, which, by warming, is spread over the fibres of the cotton, and then the tube is accurately weighed. Fitting the tube to the vessel, the cock, e, is now slight- Fig. 23. ]y opened. AS the mercury flows slowly out, air pass- es in at a to take its place, and in passing in it loses all of its oxygen, for the phosphorus which it finds every where in the cotton takes it, forming with it phosphorous anhydride, which remains in the cotton. We have therefore nitrogen alone in the vessel, surface and hold it across the flame, the tarnish will be removed from its middle portion, while it will be increased each side of this where the metal is in contact with the very outer part of the flame. The explanation is this : In this outer faint blue part of the flame there is plenty of oxy- gen from the surrounding air, and some of this unites with the metal, increasing the oxide or tarnish. But in the inner 138 CHEMISTRY. part, where the iminflamed gas is, there is no oxygen, and the heated hydrogen and carbon are ready to unite with oxygen, and so take it from the surface of the metal. Then, too, in the bright part of the flame there is not a free access of oxygen, and therefore the oxygen combined with the metal is taken and used in the burning. The portions of the flame, then, marked 2 and 3 in Fig. 52, are deoxidizing ; that is, they take oxygen, de, from metallic oxides, while the outer portion of the flame is oxidizing. The above experi- ment is more satisfactory with a spirit-lamp than with a candle, because in that there can be no trouble from soot. A tarnished copper cent will answer for this experiment if held with a pair of pincers horizontally in the flame. 175. Combustion of Wood. The flame of burning wood is essentially the same as that of the candle. It is not really the wood that burns. As the tallow is turned into gas by the heat before combustion occurs, so a part of the wood is changed into gas, and this, burning, makes the flame. You often see this illustrated in the kindling of wood. As it lies with the bright coals beneath it, at first its under sur- face smokes, but there is no flame. What is this smoke? It is gas made visible by panicles of carbon, and perhaps also by vapor from the water in the wood. Soon this smoke takes fire, not from contact with the coals, but from their heat radiated upward against it. We often see the same thing in conflagrations. A wooden building, perhaps across the street from the one that is on fire, begins to scorch and smoke, and soon bursts into a flame. In these instances you have clear illustrations of the fact that the formation of gas and its combustion are two distinct processes. As an- other example, we often see jets of gas blowing out from some crevice in the wood, and set on fire by the heat. The gas is generated in the wood by the heat, and comes out of the crevice as from a gas-burner. If you hear the sound of COMBUSTION. 139 such a blowing forth of gas, and sec no flame, you can at once produce a flame by applying a burning match to the crevice, just as you do by applying it to the opened orifice of a common gas-burner. 176. Nature of Flame. To understand the cause of flame we must remember that it is produced by burning gases only ; solid bodies, heated ever so intensely, emit light and may burn, but they can not make flame if they are incapable of being converted into vapor. Thus a piece of iron or sil- ver may be heated hot enough to give out light, but can not burn with a flame. So with carbon, which burns without flame when alone. In the examples mentioned the flame is caused by the combustion of the gaseous hydrocarbons. 177. Combustion of Coal. In the combustion of anthracite coal when fully ignited there is no flame, for it contains no hydrogen, but is nearly pure carbon. Its combustion is like that of wood-coals, or charcoal. The reason that an- thracite contains no hydrogen is that in its formation all volatile matters were driven off by heat. There is a blue flame given off by anthracite coal when it is kindling, and especially w r hen a hot fire is freshly fed with coal, arising from the generation of carbonic oxide, noticed in 112 ; but when the coal is fairly ignited it burns without flame. Bituminous coal, on the other hand, burns with a flame because it contains hydro- gen as well as carbon. 178. Manufacture of Gas. If you place some shavings in a test-tube, Fig. 57, with a cork in its mouth having a tube fixed into it, and ap- ply heat, illuminating gas will pass out through the tube, and you can Fig. si. 140 CHEMISTRY. light it. The same effect will be produced if you use bitu- minous coal, or oil, or tallow. The explanation is this : The heat sets free the hydrogen and the carbon in the form of carburetted hydrogen, just as it does in the case of the can- dle. The gas that we bum in our houses is made from coal substantially in the way indicated in the above experiment. It is made in large iron retorts. It has many impurities mingled with it, which are removed by certain chemical processes before the gas is distributed in the pipes. Gas which is made from oil is purer, and gives a stronger light, than that which is made from coal. 179. Results of Combustion. The results of combustion are of two kinds those which pass off in the form of gas or vapor, and those which are deposited in a solid form. When a gas burns, the results are all aeriform. The vapor, how- ever, that is formed by the burning of hydrogen may be condensed into a liquid form, or even be made solid in the form of snow, hail, or ice. The results of the combustion of some solids are wholly aeriform, as, for example, in the case of the candle, whether it be tallow, wax, or stearine. The results in the case of some solids, on the other hand, are wholly solid. When a metal, as iron, burns, not a par- ticle of it passes off as gas, but it all falls as a solid oxide. When wood or coal burns, the results are both aeriform and solid, the latter being in the form of ashes. The ashes of different substances vary much both in character and in quantity. When wood is burned, out of every 100 pounds about 2 are ashes, while 98 pounds fly off into the air by uniting with oxygen to form carbonic anhydride and water. Of what ashes are composed we shall speak particularly in another place. 180. Expedients for Increasing Combustion. When any thing is burning, the greater the supply of oxygen the more brisk and perfect will be the combustion. If we blow COMBUSTION". 141 a fire, we bring more air, and therefore more oxygen, to it. The coals therefore brighten, the combustion being made more active, and this increasing the heat, the wood burns more briskly, or, if not burning at all, soon bursts into a flame. It is chiefly for the same reason that when a build- ing takes fire there is great danger that the fire will extend to other buildings. So, also, whatever increases the draught of a chimney makes the fire more brisk. On this account the chimneys of foundries and other factories, in which a very hot fire is needed, are made very tall. For the same reason the tall chimneys of lamps cause them to give a very bright light. If you should take the chimney from a lamp that is burning brightly, leaving the wick at the same height, there would be a great smoke, because the oxygen would not come to the wick with sufficient rapidity to unite with all the carbon and hydrogen that go up from it. A flat wick gives a brighter light than a round one, because it presents a larger surface to the oxygen of the air. Still more light is given if a flat wick have a circular arrange- ment, the air being admitted inside as well as outside of the circle. This is the construction of the well-known Ar- gand burner. 181. Bunsen's Burner. By increasing the supply of oxy- gen to a flame we increase its luminosity ; but if we mix the combustible gases with oxygen before igniting them, the resulting flame gives scarcely any light at all. This will not seem so strange if you understand that the par- ticles of carbon are completely burned np in the mixed gases. Such a flame is not only smokeless, but deposits no soot on cold surfaces placed in it, and consequently is a very clean flame to cook or heat with. Many forms of stoves and lamps have been contrived which produce this color- less and very hot flame ; the one commonly used in chem- ical laboratories is called Bunsen's Burner, after the great 142 CHEMISTRY. Fig. 68. German chemist who invented it. Coal gas enters at , Fig. 58, and air enters at #/ they mix in the tube before they issue at c, and on applying a light at this orifice we have a very clean hot flame. By stop- ping up the hole, , with your fingers you can cut off the supply of air, and conse- quently of oxygen, and the flame will in- stantly change its appearance, burning with the usual partially smoky yellow light of ordinary coal gas. Removing your fingers, oxygen enters, a perfect com- bustion of the carbon particles takes place, and the flame is colorless again. In all chemical laboratories where gas is to be had, these burners, and stoves constructed on the same principle, are in constant use, being clean, cheap, and needing no attention. After a Bunsen burner has been long in use it sometimes burns badly, the gas igniting at the base of the tube, c, and burning within it with an illuminating flame. This is be- cause there is too much air in proportion to the gas, and by cleaning the little hole in the jet at the base of the tube, . to make the phosphorus burn, or, in other words, unite with the oxygen. 187. Fire Extinguishers. Since carbonic anhydride is not a supporter of combustion, it may be used for extinguishing fires. It is usually employed in solution in water under pressure, and various contrivances have been made for gen- erating the gas quickly when needed, and throwing a stream of it mixed with water in any direction desired. The " plain soda-water" sold in apothecary shops would serve just as well, for it is really the same thing. The pure dry gas has G 146 CHEMISTRY. also been used as a fire extinguisher. For example, a Mr. Gurney, in the case of a fire which nad been burning for a long time in a coal-mine in Scotland, contrived to generate a large quantity of carbonic anhydride, so that it should flow to the spot where the fire was raging, and thus extin- guished it. Here water could not be made to reach the to fire, but the gas went to it without any difficulty. 188. Oxyhydrogen Blow-pipe. When a jet of hydrogen gas is lighted, and a jet of oxygen is made to mingle with it, the union of the two gases produces the greatest heat known, with the exception of that which is produced by the galvanic battery. The sole product of this energetic com- bustion is water, the grand extinguisher of combustion. In Fig. 61 is represented an extemporaneous contrivance for Fig. 61. burning these gases. The oxygen is contained in the bag, which has a weight upon it to press the gas out through the pipe. At the same time hydrogen gas is coming up from the bottle below through another pipe. Here you have the essentials of the blow-pipe invented by Dr. Hare, of Phila- COMBUSTION. 147 delphia. The common arrangement of this instrument is, however, repre- sented in Fig. 62. In one reservoir is the oxygen, and in the other the hydrogen ; flexible tubes lead to a common jet, where the gases issue and are set on fire. The flame, not- withstanding its heat, has very little brightness. It melts almost all sub- stances, even the most refractory, dissipating many of them in vapor. Platinum, which can not be melted in the hottest furnace, readily melts Fig. 62. here. Most of the metals are oxidized as they bum in this flame. Though the flame itself is so nearly colorless and destitute of light, a dazzling light, variously colored, is pro- duced as it burns the metals. Copper gives a beautiful green light, and platinum a delicate white. The scintilla- tions of iron are of a more dazzling brightness than when it is burned in a jar of oxygen, as noticed in 59. 189. Drummond Light. There are some of the earths, as lime and magnesia, that resist the heat of the oxyhydrogen blow-pipe, and one of these, lime, placed in the flame, gives a light which rivals in brightness the noonday sun. An arrangement having a burning jet of the two gases thrown upon a ball of lime is called the Drummond Light, because Lieutenant Druramond, of the English navy, if he did not first discover the fact that such an intense light could be thus produced, was at least the first to discover and recom- mend its use for most of the purposes to which it is now applied. The light can be seen at such great distances that it is exceedingly useful for signaling. In one case the light was seen at the distance of 70 miles. That a flame which gives so little light of itself should be made so intensely 148 CHEMISTRY. luminous by merely striking against a solid substance, with- out in the least altering it, confirms what we have before learned, that the light-giving power of flame is dependent chiefly on the presence of incandescent solids. Instead of using pure oxygen and pure hydrogen, an ex- cellent light for all practical purposes is obtained by em- ploying oxygen and coal gas. Strong metallic cylinders (see Fig. 62, p. 147) containing these gases under pressure are now sold in the large cities to any one wanting a bright light or intense heat. This light, also called the oxycalcium light, is very frequently seen in theatres, torchlight proces- sions, and even as a' means of advertising. The stereopti- con used in illustrating public lectures is simply a magic- lantern provided with a calcium light. 190. Cause of Explosions. So long as the two gases hy- drogen and oxygen are kept separate before burning them no explosion takes place ; but if oxygen and hydrogen be mingled together and then fire be applied there is a violent action, and a report proportioned to the amount of the gases. The combustion is alike in both cases, oxygen and hydro- gen uniting to form water, and the explosion is due to the sudden expansion of the gases caused by the intense heat generated by their chemical union. The noise is pro- duced by the sudden collision of the instantaneously ex- panded vapor with the air surrounding the vessel contain- ing it. 191. Experiments. Some interesting experiments can be tried illustrative of the explosive combustion of gases. If into a strong brass vessel, a, Fig. 63, we in- troduce a mixture of oxygen and hydrogen, and, having pushed the cork, c, in tightly, pass electricity by the ball and wire at b, an explosion will occur. The cork will be violently driven out by the expansive force of the heated vapor produced. Such COMBUSTION. 149 an apparatus is called a " hydrogen pistol," but it ought really to be called an " oxyhydrogen pistol," for only a mixture of these gases explodes. The two gases can be mingled in a bag, and by the aid of a common tobacco-pipe, as seen in Fig. 64, soap-bubbles can be formed, which on flying upward can be ex- ploded by touching them with a light. To obtain good soap-bubbles mix a little glyc- erine with the soap-water before using. In such experiments we use in bulk twice as much hydrogen as oxygen, for it is in this proportion that these gases unite to form water ( 140). Common air is often used in place of oxygen, and answers the purpose be- cause it contains this gas. When this is used we introduce about equal bulks of the air and the gas. In all such ex- periments great care should be exercised. For example, in the bubble experiment we should be careful not to bring the light near the pipe of the gas-bag, else the whole might- be exploded at once. 192. Spontaneous Combustion. We mean by spontane- ous combustion the taking fire of any substances without the application of heat to them. We will give you some ex- amples, and explain them. If you place a bit of phosphor- us of the size of a pea upon blotting-paper, and sprinkle over it some soot or powdered charcoal, it after a while melts and bursts into a flame. This is owing to the large absorption of oxygen gas by the carbon, as noticed in 96. Much oxygen is thus introduced to the phosphorus, for which it has a strong affinity ; and a union is therefore readily effected between them, which union is combustion. Heat is generated by the absorption of the gas ; and as car- bon is a non-conductor, the heat is retained, and is sufficient to start the combustion of the phosphorus. Indeed, where there is a large amount of powdered charcoal heaped to- 150 CHEMISTRY. getlier,the heat thus developed and retained may be suffi- cient to set fire to it. Gunpowder factories have sometimes exploded from this cause. For the same reason spontane- ous combustion may occur in a mixture of lamp-black and linseed-oil, if the lamp-black be in excess, or if a portion of it be dry. Any substances in which chemical action is apt to take place, if heaped together so as to shut in the heat which this action produces, may take fire spontaneously. This is the case with oiled cotton and rags if there be in them any drying oil, or even with damp goods packed to- gether. Damp hay may take fire for the same reason. More often, in this case, the combustion is imperfect, and the hay is turned black that is, charred or changed into charcoal, just as wood is in the coal-pit. Spontaneous combustion of the human body, often referred to by ignorant people, is a fiction. 193. Combustion without Oxygen. We have seen that ordinary combustion is the union of a substance with oxy- gen, accompanied by the development of light and heat. The presence of oxygen, however, is not indispensable to combustion, for we have many examples of chemical com- bination taking place, with such intensity as to generate light and heat, where oxygen is absent. Thus carbon will burn when heated in the vapor of sulphur, and a yellowish green gas called chlorine supports the combustion of metals and even of a candle. But of this we will learn more far- ther on. 194. Requisites for Combustion. The variations in the readiness with which ordinary combustion goes on depend chiefly on three things: 1. The comparative affinity of the substance for oxygen. 2. The amount of oxygen supplied. 3. The temperature to which the combustible body is raised. Thus in the case of phosphorus, the slight heat caused by friction is sufficient to make it take fire. Wood, on the oth- COMBUSTION. 151 er hand, requires a much higher temperature to ignite it. Friction will do it, but it must be brisk and long continued. By increasing the quantity of oxygen present combustion will take place with less heat than is ordinarily required. This is the cause of spontaneous combustion in many cases, as noticed in 192. In the brisk and continued burning of iron or steel in oxygen gas, 59, we see the influence of an abundance of oxygen about the iron, in contrast with the mere spark that flies off in striking fire in the air, which is only one-fifth part oxygen. 195. Ordinary Oxidation a Slow Combustion. As carbon and hydrogen in burning unite with oxygen, forming car- bonic anhydride and water, so do the metals, forming ox- ides. It is indeed this union which is the combustion. It follows, then, that the gradual oxidation of the metals, the rusting of iron, copper, zinc, etc., is a combustion a slow fire. And it undoubtedly produces as much heat in the ag- gregate as rapid oxidation does, though the process is so very slow that the heat at any one moment is so little as to be imperceptible. 196. Sun-Bleaching is Combustion. The old mode of bleaching by exposure to the sun, grass-bleaching as it is termed, is an example of oxidation that is, combustion. By the influence of the sun's light the oxygen of the air is made to unite with the coloring matter of the cloth, and so this is burned up, the product passing off in the air, just as the products of ordinary combustion do. If the cloth be exposed too long, some of the substance itself is burned up, lessening the strength of the cloth, or rotting it, as it is commonly expressed. The reason that the coloring matter is affected before the substance is that it is more combusti- ble, or, in other words, more readily oxidized. 197. Animal Heat. The heat of the body is maintained by a real combustion, though without light. To produce 152 CHEMISTRY. this heat the same chemical unions take place as in the burn- ing of a common candle. We have told you something al- ready about the introduction of oxygen into the body in breathing. It enters the blood in the lungs, and courses about in search of carbon and hydrogen. It finds these every where, and unites with them, forming with the car- bon carbonic anhydride, and with the hydrogen water, as in the case of the candle. In effecting this union heat is produced, and thus the body is kept warm. 198. The Lungs not the Body's Furnace. It was for a long time supposed that the chemical combinations produc- ing the heat occurred in the lungs, and that the heat gener- ated there was carried with the blood all over the body. But there were some facts observed that were inconsistent with this doctrine. If it were the true doctrine, the lungs should be hotter than any other organ in the body, just as a furnace is always hotter than the apartments to which the heat from it is carried. But it was found that the lungs were no warmer than other organs, and that therefore they were not the furnace of the body. Then, again, it was ob- served that the heat of different parts of the body is often temporarily increased. Thus when an inflammation occurs there is more heat than usual. So, also, blushing will make the face to burn. In such cases the increased heat is of course produced where it manifests itself, and not in the lungs. It was therefore found, on further investigation, that the animal heat is produced in all parts of the body, every little vessel being a chemical laboratory for this as well as other purposes. 199. Temperature of the Body. The heat of the body is maintained quite uniformly at 98.* You observe that this * The temperatures named in this section are given in Fahrenheit de- grees. See Appendix. COMBUSTION. 153 is much above the ordinary temperature of the atmosphere, so that our bodies are almost always giving out consider- able heat to the air around us. This is very obvious where there are many persons gathered together. A room that is just comfortably warm with but few in it, becomes uncom- fortably so very soon when it is crowded full of company. It is very seldom that the air around us is as hot as our bodies, and therefore very seldom that we are not giving off heat. We are most comfortable when the air around us is at about 70 (Fahrenheit), and as this is 28 below the heat of our bodies, we may say that we are comfortable only when we are giving off considerable heat to the air. As this heat is given off from the surface, the outer parts of the body are not as warm as the inner. And as heat is constantly lost, so it is constantly made. The myriads of furnaces are at work all the time, night and day. The fires within us never go out while life continues. 200. Sources of the Fuel. The fuel used in producing animal heat is carbon and hydrogen, as already intimated. There are two sources from which these come : 1. The waste of the body. In the wear and tear of the animal machine there are particles every where that have ceased to-be use- ful. They must be got rid of to make way for other par- ticles to be deposited in their place. How is this done? The oxygen that enters the lungs in breathing does it. This goes in the blood to these useless particles, and burns up, that is, unites with their carbon and hydrogen. This makes heat just where the particles are, and the products of the combustion, the carbonic anhydride and water, are carried off in the blood that sweeps along in the veins. What be- comes of them we will soon tell you. 2. A part of our food furnishes fuel to feed the fires within us, the starchy, sug- ary, and fatty articles. We shall speak particularly of this subject in another part of this book, and so will not dwell G2 154 CHEMISTRY. upon it here. Occasionally the fat which is deposited in various parts of the body is used as fuel, the oxygen in the blood seeking it out, and uniting with its constituents, car- bon and hydrogen. This is done in sickness, when the ac- cumulated fat disappears, and also in the hibernation of many animals, as will be noticed farther on. 201. Amount of Fuel Consumed. Some calculations have been made in regard to the amount of fuel consumed in keeping up animal heat. This is more easily done in regard to carbon than hydrogen. A full-grown man requires about 100 kilogrammes of charcoal to keep him warm through the year. A horse needs about five times as much 500 kilogrammes. 202. The Windpipe the Smoke-pipe of the Body. We have told you that in the combustion that is every where going on in the body carbonic anhydride and water are formed, and pass into the blood in the veins. Observe how they are disposed of. They are for the most part carried in the blood to the lungs,* where they are discharged through the windpipe into the air. The water comes out in the form of vapor mingled with the carbonic anhydride, just as the two rise together from the flame of a candle. As these products of combustion are discharged from the body by the wind- pipe, this may be termed the body's smoke-pipe. It acts thus as we breathe out, but when we breathe in it serves to introduce to all the little heat-laboratories of the body oxy- gen, the supporter of their combustion. 203. Influence of Exercise on Animal Heat. When the body is in a state of activity the heat is increased, or, in other words, the fires within us burn more briskly. This is * For a particular description of the manner in which this is done we refer to either Hooker's "Human Physiology" or his "First Book in Physiology. " COMBUSTION. 155 because the circulation is quickened, and with it the breath- ing, and so more of the oxygen is introduced into the blood, and thus to the carbon and hydrogen- The same effect is produced in this way upon the combustion of the body as upon an ordinary fire by blowing it. It is simply increasing one of the three requisites for combustion mentioned in 194. 204. Cold-blooded Animals. Reptiles and fishes are cold-blooded animals that is, they have nearly the same temperature with the medium in which they live. The fires in them are not at all brisk, and they use little oxygen in comparison with warm-blooded animals. They have need of but little, for they live a comparatively sluggish life, as you may fully realize in relation to reptiles if you observe the difference in activity be- tween a bird and a frog or toad. It may appear to you that this is not true of fishes, as their motions are often very quick. But it must be re- membered that it requires but little exertion really for them to move with rapidity, because they live in a medium of a specific gravity so near their own. For further illustration of this point we refer you to Chapter XX. of Hooker's " Natural History." 205. Hibernation. Animals are said to hibernate who go into a torpid state in the winter. The degree of torpidity varies much in differ- ent animals. In cold-blooded animals respiration and circulation may cease altogether, and the operations of life may be as thoroughly suspend- ed as in a seed that is kept from heat and moisture. They may be pre- served in this state for a long time. Frogs and serpents have been kept in ice for years without any signs of life, and then have been revived by ex- posure to a warm atmosphere. While animals are in such a state, the ma- chinery of life being stopped, there is no wear and tear, and therefore no waste to be got rid of. As there is nothing to bum, no oxygen is needed. In hibernating warm-blooded animals the torpidity is not so thorough, and in proportion to the movements of life there is waste, and therefore need of oxygen to burn it. Hence there is occasional respiration. In such cases of imperfect torpidity the fat which has been acquired in summer is burned up for the purpose of maintaining the requisite warmth, and such animals therefore come out in the spring from their hiding-places in quite a lean condition. 206. The Chief Elements. The four elements with which you have become so familiar in the previous chapters 156 CHEMISTRY. viz., oxygen, nitrogen, carbon, and hydrogen are the chief elements concerned in the formation of the earth. Especial- ly is this true of orgianic substances, both vegetable and ani- mal. In some of these, it is true, there are lime, phosphorus, sulphur, iron, etc. ; but these are generally in small quan- tities, while the great bulk of them is made up of combina- tions of the four grand elements which we have mentioned. Then of substances not living, the earth's envelope of air, fifty miles thick, is a mixture mostly of two of these ele- ments, oxygen and nitrogen, and all the water is composed of oxygen and hydrogen. And to come to the solid crust of the earth, carbon is seen in the enormous quantities of coal treasured up in the bowels of the earth for the use of man; carbon and oxygen united with a metal form the limestone rocks and ranges of mountains ; oxygen is a large constituent of the granite and other hard rocks ; and of the compound mixture under our feet which we call earth the four grand elements form a very large proportion. 207. Chemical Changes in Air and "Water. These elements are continually the subjects of chemical changes. You have already seen how that mixture of gases, the air, is constantly changing by means of the chemical operations going on in the lungs of animals, in the leaves of vegetables, in combus- tion, in the various arts of man, and in the decay of animal and vegetable substances. Though, therefore, the atmos- phere which envelops the earth is to-day composed of oxy- gen, nitrogen, and carbonic anhydride, in precisely the same proportions as that which enveloped it when our first parents were in the Garden of Eden, yet it is not the same air, but its elements have from that time to this been going through many changes, entering into the composition now of liquids, now of solids, and now of gaseous substances. The ele- ments of water are also continually changing, though per- haps not to such an extent as those of air. In 9, Part L, COMBUSTION. 157 we spoke of the exceeding movability of water. As it courses about much of it becomes resolved into its elementary gases, oxygen and hydrogen, to engage in the formation of other substances, gaseous, liquid, and solid; and just as constantly new water is forming to take the place of that which is thus resolved. Especially do such changes in water take place when it enters living substances. The constituents of water form a part of all vegetable and animal substances, and it is, therefore, decomposed continually to furnish these in the growth that is every where going on. QUESTIONS. 167. Mention some of the various effects of combustion. 1G8. What was Stahl's theory of phlogiston ? How long did his theory prevail ? 169. What takes place in ordinaiy combustion? 170. Explain the experiment repre- sented in Fig. 50. State what takes place in the burning of illuminating gas. 171. State the processes involved in the burning of a common candle. How can you prove that water is formed in the burning of u candle ? How that carbonic anhydride is formed ? 172. Describe the structure of a can- dle's flame as mapped in Fig. 52, and the processes involved in the burning. 173. State the experiments shown in Figs. 53 and 54. Give the experi- ment with the slip of wood. That with the match. State the experiment represented in Fig. 55. 174. That represented in Fig. 56. State and ex- plain the experiment with a slip of copper. 175. Illustrate the fact that in the combustion of wood the formation of gas and its combustion are two distinct processes. 176. What is the cause of flame ? 177. What is said of the burning of anthracite ? What of the difference between anthracite and bituminous coal? 178. What of the making of gas? 179. Mention cases of combustion in which the results are aeriform ; cases in which they are solid ; and cases in which they are partly solid and partly aeriform. What proportion is there of solid when wood is burned? 180. How may combus- tion be increased ? What is said of the chimneys and wicks of lamps ? 181. Describe the gas-lamp known as Bunsen's Burner. What are its ad- vantages ? 182. Describe a blow-pipe. What is said about oxidizing and reducing flames? How is a blow-pipe useful to chemists? 183. What is said of improper management at fires ? 184. What of blowing out a can- dle ? Explain the expedients resorted to for preventing lights from going 158 CHEMISTRY. out as we carry them about. 1 85. In what two ways does water act in put- ting out fires ? Explain other means of putting out fires. 186. How can a fire be made under water? 187. What is said about fire extinguishers? Explain the extinguishing of a fire in a Scotch coal-mine. 188. What is the oxyhydrogen blow-pipe? \Vhat is its use? 189. What is the Drummond Light? What the oxycalcium light? When are they used? 190. Ex- plain the cause of explosions. What causes the noise? 191. Describe the hydrogen pistol, and the experiment with soap-bubbles? 192. What is spontaneous combustion? State and explain the experiment with phos- phorus and charcoal. Give various examples of spontaneous combustion. 193. Is oxygen indispensable to combustion ? 194. What are the requi- sites for ordinary combustion ? Give examples illustrating the variation of these in different cases. 195. What is said of ordinary oxidation ? 196. What of sun-bleaching ? 197. How is animal heat the result of combus- tion? 198. What facts show that animal heat is not made in the lungs? Where is it made? 199. What is the temperature of the body? What is said about the body's giving out heat ? 200. What is the fuel of the fire in the body ? What is said of the sources of the fuel ? What of the uses sometimes made of the fat of the body? 201. What of the amount of the fuel used ? 202. How is the windpipe the smoke-pipe of the body ? 203. Show how exercise influences animal heat. 204. What is said of cold- blooded animals ? 205. What is said of hibernating cold-blooded animals ? What of hibernating warm-blooded animals ? 206. What is said of the four chief elements ? 207. What is the nature of the changes in air and water? - CHAPTER XL CHLORINE, BROMINE, IODINE, AND FLUORINE. 208. A Natural Group. Having now studied somewhat at length the most important and widely distributed ele- mentary bodies oxygen, nitrogen, carbon, and hydrogen together with many of the compounds which they form, we will now take up the remaining elements one by one, and, for convenience' sake, will begin with the non-metals not yet described. Four of these non-metals chlorine, bromine, io- dine, and fluorine resemble each other, chemically speak- CHLORINE, BROMINE, IODINE, AND FLUORINE. 159 ing, to a remarkable degree, and are said to form a natural group; the most important member of this group is chlo- rine. 209. Occurrence of Chlorine. All common salt is made up of this element and a metal called sodium. Afterward, when you have learned the remarkable properties of the constituents of salt, how one is a suffocating yellow gas, and the other a very light, soft metal which burns on water, it will seem rather strange that a union of these two bodies, both of them so corrosive and dangerous, should produce such a mild, healthful substance as common salt. And yet this is only another example of the marvelous change which elements experience when united, each one losing its iden- tity, and the compound having the properties of neither of them. Chlorine forms more than one half of common salt ; so that, as salt is abundant in sea-water and in salt-mines, and is also present to some extent in the soil and in animals and vegetables, chlorine is one of the elements that exists in large quan- tities in the earth. 210. Preparation of Chlorine. Chlorine is never found free in nat- ure ; we can make it from common salt. Mix some common salt, or chloride of sodium, with manganese dioxide, put the mixture into a flask fitted with a tube, as in ^ Fig. 65, and then add some sulphuric acid somewhat diluted. K"ow Fig. G&. 160 CHEMISTRY. heat the contents of the flask, and yellowish-green vapors of chlorine will arise and pass over into the jar arranged to collect it. The reaction which takes place is somewhat complex, but you will understand it by studying this equation: Sodi Sulphuric ^anpi. Hydro-sodium w Chlo- dioxide. chlorlde ' acl(L sulphate. sulphate. ' ter - r ine. MnO a + 2NaCl + 3H 2 SO 4 = MnSO 4 + 2(NaIISOJ + 2H a O + C1 2 The manganese dioxide is necessary to furnish oxygen to unite with the hydrogen of the sulphuric acid, forming wa- ter. What happens when we omit the addition of manga- nese dioxide you will see very soon. 211. Another "Way of Obtaining Chlorine. Chlorine gas may also be obtained by heating hydrochloric acid with manganese dioxide. The heat required is not high plac- ing the flask in a bowl of hot water is sufficient. If the gas stops coming over, add more hydrochloric acid, for this is the source of the chlorine. As the gas is about two and a half times as heavy as air, it can be collect- ed in ajar, as rep- resented in Fig. 66, the lighter air being driven out to give place to it. The ex- planation of the chemical change in the flask is this: There is a large amount of oxygen in the ox- ide of manganese, which is therefore loosely attached to the metal, and ready Fig. CO. CHLORINE, BKOMINE, IODINE, AND FLUORINE. 161 to leave it at the slightest invitation. The hydrogen of the hydrochloric acid, therefore, at once strikes up a union with this oxygen, and the chlorine of the acid being there- fore forsaken by the hydrogen, a part of it unites with the manganese to form a chloride of that metal, and a part of it escapes and passes out through the tube. Manganese Hydrochloric Manganese w CM rf dioxide. acid. chloride. MnO 3 + 4HC1 = MnCl 2 + 2H 2 O + Cl a 212. Breathing Chlorine. This gas can not be breathed with safety unless very largely diluted with air. If breathed when'but little diluted, it occasions violent coughing and a suffocating effect. Great care, therefore, is requisite in pre- paring it and in experimenting with it. The very small quantity that is in the air where bleaching is carried on, or where it is disengaged from chloride of lime for disinfecting purposes, though decidedly appreciable to the sense of smell, occasions no embarrassment in the respiration. 213. Chlorine "Water. Water will dissolve twice its bulk of chlorine. This solution, called chlorine water, may be used in a variety of interesting experiments. You can make it very readily by passing the gas generated by either method described into a bottle containing water. The gas will be absorbed, and will communicate a yellow color to the water. Chlorine water keeps best in the dark, so some black paper may be pasted around the bottle. 214. Action of Chlorine on Metals. This gas has a strong disposition to combine with the metals, forjning chlorides. If you put some pure gold-leaf into chlorine water it will soon disappear, because the chlorine forms with the gold a chloride, which is dissolved in the water as fast as it forms. In some cases so eager are the chlorine and the metal to unite that the violence of the action occasions the phenom- enon of combustion. Thus if antimony in fine powder be 162 CHEMISTEY. Fig. 6T. dropped into a vessel of chlorine gas, it will fall in a show- er of fire, and the vessel will be filled with a white smoke which is made up of small par- ticles of chloride of antimony. (Fig. 67.) If a fine brass wire, with a little bit of tinsel fast- ened to its end, be introduced into a vessel of chlorine gas, the wire will burn briskly, the tin- sel of course taking fire first and kindling the wire, as shavings do wood. In this combustion the zinc and copper, of which brass is composed, unite with chlorine to form chlorides of zinc and copper. 215. Attraction for Hydrogen. Fill a jar with chlorine water, and invert it in a vessel of water. If this be kept in the dark no change will occur ; but if it be exposed to the sun for a few days there will collect a colorless gas in the upper part of the jar, and the water will be found to have lost its chlorine and to have become sour. This is because the chlorine in the solution has decomposed some of the water by taking to itself its hydrogen to form hydrochloric acid, while the other constituent of the water, oxygen, has collected in the upper part of the jar. That this gas is oxy- gen can be readily proved by setting the jar upright and introducing into it a taper which is merely in a glow, and not in a flame. It will burst into a bright flame at once. Water. Chlorine. Hydrochloric acid. Oxygen. H 2 O + C1 2 2HC1 + O 216. Bleaching. The powerful attraction between chlo- rine and hydrogen, and the consequent decomposition of water, furnish us the explanation of chlorine bleaching. The CHLORINE, BROMINE, IODINE, AND FLUORINE. 163 first step in the process is the decomposition of water, and hence the necessity for having the substance to be bleached moist. If a colored rag be introduced into chlorine gas dry, the chlorine will have no effect upon it; but if it be moist- ened, it will lose its color. The explanation of bleaching is this : The chlorine, taking the hydrogen of the water, sets free oxygen, and this in its nascent state ( 42) has special chemical power, and attacks the coloring matter, destroy- ing it, or burning it up, as we may say, for the union of oxygen with other elements is, as you have seen, essential- ly a combustion. It is oxygen, then, that really does the bleaching here, just as in the case of sun-bleaching ( 196). But the question arises, Why does the oxygen burn up the coloring matter, and not the cloth itself? This is from a principle which is well established in chemistry, viz., that the more ingredients there are in a compound the more easily it is decomposed. While the vegetable tissue or sub- stance is composed of three elements, carbon, oxygen, and hydrogen, the coloring matter is composed of these with ni- trogen in addition, and therefore is more readily demolished by the oxygen than the cloth is. 217. Carrying the Bleaching too Far. But sometimes the cloth is somewhat burned in the process that is, some of the tissue is destroyed by the released oxygen, and the cloth consequently weakened. This is done whenever, after the chlorine has released sufficient oxygen to destroy the coloring matter, it continues to release more. The point, then, to be aimed at by the bleacher is to set free only just enough oxygen by means of the chlorine to oxidize the col- oring matter, and not the substance. There is the same danger that the process may be carried too far in the com- mon sun -bleaching, or grass -bleaching, as it is usually called. 218. Comparison with Grass-Bleaching. The old mode 164 CHEMISTRY. of bleaching was very tedious and uncertain, but chlorine bleaching is both an expeditious and certain process. Pro- fessor Pepper, an English author, thus remarks on the bene- fits which the discovery of this process has conferred upon English manufacturers : " All our linen used formerly to be sent to Holland, where they had acquired great dexterity in the ancient mode of bleaching, viz., by exposure of the fabric to atmospheric air, or the action of the damps and dews, assisted greatly by the agency of light. Some idea may be formed of the present value of chlorine when it is stated that the linen goods were retained by the Dutch bleachers for nine months ; and if the spring and summer happened to be favorable, the operation was well conduct- ed ; on the other hand, if cold and wet, the goods might be more or less injured by continual exposure to unfavor- able atmospheric changes. At the present time as much bleaching can be done in nine weeks as might formerly have been conducted in the same number of months ; and the whole of the process of chlorine bleaching is carried on inde- pendent of external atmospheric caprices; while the money paid for the process no longer passes to Holland, but re- mains in the hands of our own diligent bleachers and man- ufacturers." Quite as great is the usefulness of chlorine bleaching in the art of paper-making in the preparation of its material. A most valuable present, then, did the Swed- ish chemist Scheele make to the arts when he discovered chlorine and its application in bleaching. 219. Difference between Chlorine Bleaching and Sulphur Bleaching. In chlorine bleaching the coloring matter is actually de- stroyed burned up that is, its elements are dispersed in new combinations. But in sulphur bleaching, as you will learn, the coloring matter remains. It is only changed, not dispersed, and therefore it can be restored as before by certain chemical actions. Chlorine bleaching is inapplicable to straw, because for some reason it imparts a brown tinge to the material. There- fore for straw goods sulphur bleaching continues to be used. CHLORINE, BEOMINE, IODINE, AND FLUORINE. 165 220. Chlorine a Disinfectant. Chlorine not only decom- poses colors, but also, and probably for the same reason, the volatile compounds which are formed in decay, and which are so disagreeable to the smell and injurious to the health. It may be used, therefore, for purifying all morbid matters and infected atmospheres, and even for arresting decay. Musty casks may be cleansed by washing them first with chlorine water, and then with milk of lime. Mouldy cellars, in which milk readily turns sour, can be purified by fumi- gating them with chlorine gas, or washing them with chlo- rine water or a solution of chloride of lime. 221. Combustion in Chlorine. It was formerly supposed that oxygen is the sole supporter of combustion, but we have an example to the contrary in chlorine. You have already seen in 214 that certain metals spontaneously burn in this gas. In the burning of ordinary substances in chlorine the flame comes from the union of chlorine and hydrogen, no union with the carbon, so commonly attending combus- tion, taking place in this case. Thus, if a candle be let down into a jar of this gas, Fig. 68, it burns as it enters with a dull red flame, but a dense cloud of smoke arises, and the light is soon extinguished. The ex- planation is this : The hydrogen of the tallow unites with the chlorine, giving aflame; and the carbon, being separated from the hydrogen, flies off in minute particles, and soon ex- tinguishes the flame. The results of the combustion are hydrochloric acid and lamp-black, the former com- ing from the union of the hydrogen of the candle and the chlorine, and the latter from the carbon of the caudle, which can find nothing in the jar to unite with, and so takes this form, some of it being deposited in a dark film upon the sides of the jar. If you moisten a slip of paper with oil Fig. ca. 166 CHEMISTRY. of turpentine, which is composed of carbon and hydrogen, and put it into a jar of chlorine, it will burn spontaneously (Fig. 69, p. 165), the hydrogen making the flame, and the re- leased carbon producing a cloud of heavy smoke. 222. Hydrochloric Acid, HC1. We have already had so much to do with this acid that you know its composition and nature. We have hitherto always used a solution of gaseous hydrochloric acid in water without further expla- nation. Hydrochloric acid, then, is a colorless gas, with acid properties, pungent odor, and very soluble in water ; in fact, water is capable of taking up 500 times its bulk of this gas. Commercially this solution is called muriatic acid a name a hundred years old. Hydrochloric acid dissolves many metals, forming chlorides. It is of great value in the arts. 223. Production of Hydrochloric Acid. It can be pro- duced synthetically, i. e. y by the direct combination of its elements, and it is curious that light is the agent that makes them combine. If equal quantities in bulk be mixed by candle-light, and be kept in the dark, no combination will take place, but the two gases will remain simply mixed to- gether. If now the jar containing the gases be exposed to the direct rays of the sun, the union will be so sudden as to cause an explosion. Sometimes this result occurs by expos- ure to the diffuse light of the sun, but commonly the di- rect rays are required. Of course in this very dangerous experiment the jar should be inclosed in a wire screen to guard against injury. 224. Common Mode of Preparation. Hydrochloric acid is commonly prepared by mixing together common salt and dilute sulphuric acid, and applying heat to the mixture. The chemical reaction is as follows : Sodium Sulphuric Hydro-sodium Hydrochloric chloride. acid. sulphate. acid gas. NaCl + H 2 S0 4 = NaHS0 4 + HC1 CHLORINE, BBOillNE, IODINE, AND FLUOBINE. 167 Fig. 70. You see the chlorine of the sodium chloride unites with part of the hydrogen of the sulphuric acid, forming hy- drochloric acid ; and the sodium takes the place of the hy- drogen which left the acid, forming an acid salt hydro- sodium sulphate. Now you see what would have taken place had we omitted the manganese dioxide in the prepara- tion of chlorine in 211. Compare the two equations. 225. Aqua Regia. This is a mixture of nitric and hydro- chloric acids in the proportion of one part of the former to three of the latter. Neither of these acids alone will dis- solve gold or platinum, but this mixture of them will do it ; and as gold is considered the king of metals, the liquid that can dissolve it has been styled aqua regia, or royal water. But we do not have in this case, in reality, a mere physical solution of gold. It is something more. A chemical change takes place by which a union is effected between the gold and the chlorine of the hydrochloric acid, making chloride of gold, and it is this salt of gold which is dissolved, and not gold itself. The explanation is this : While gold put into hydro- chloric acid can not take its chlorine, the nitric acid which 168 CHEMISTRY. is added in making aqua regia forces the hydrochloric acid to give up its chlorine, which at once unites with the gold. 226. Compounds of Chlorine with Oxygen. Chlorine unites with oxygen in several properties, forming anhydrides. These form with water four acids : hypochlorous, IIC1O ; chlorous, HC1O 2 ; chloric, HC1O 3 ; and perchloric, HC1O 4 , as shown in the table on p. 35. Two of these acids are formed on passing chlorine gas into a solution of potassium hydrate; thus: ^i , . Potassium Potassium Potassium Potassium w ine ' hydrate. chloride. hypochlorite. chlorate. C1 8 + 8KHO = 6KC1 + KC10 + KC1O 3 + 4H 2 O You see that part of the oxygen of the potassium hydrate oxidizes the chlorine and combines with the potassium. Ac- cording to the strength of the potassium solution you ob- tain more of the hypochlorite or of the chlorate, the weaker solution giving more of the former. Hypochlorous acid is a powerful bleaching agent ; combined with calcium it makes the so-called chloride of lime, of which you will learn more later. Potassium chlorate, you remember, was used in the preparation of oxygen gas. It is also used in medicine to a limited extent. The anhydrides corresponding to the first three acids named are unstable gases ; all have a red or yellow color and a pungent odor. We will not describe them further, but will notice the preparation of one of them hy- pochlorous anhydride. It is best prepared by the action of chlorine upon dry mercuric oxide: Mercuric oxide. Chlorine. 2 dride" 8 Mercuric chloride. 2HgO + C1 4 = C1 2 + HgCl 2 227. Other Compounds of Chlorine. Chlorine also forms com- pounds with carbon and with nitrogen, but they are far too rare and unin- teresting to describe here. Chloride of nitrogen is one of the most danger- ously explosive substances known, and must never be prepared by students 11 for fun." So we will not tell you how to make it. CHLORINE, BROMINE, IODINE, AND FLUORINE. 169 228. Iodine. While chlorine is a constituent of the salt of the sea, iodine is found in many of the sea's products, as sea- weed, sponge, etc., in combination with sodium and other metals. It is commonly obtained by making a lye from the ashes of sea-weeds, called kelp, and separating the iodine from this lye by a chemical process. The lye is evaporated till all the sodium carbonate and other salts in it are crys- tallized, and the remaining liquor, after being treated with sulphuric acid, is heated gently with manganese dioxide in a leaden retort, a b c,Fig. 71, the iodine passing out in va- Fig. 71. por, and being condensed in the successive receivers, d. The action of the manganese dioxide is the same as in the cor- responding method of preparing chlorine. After the dis- covery of iodine, in 1811, by M. Courtois, of Paris, the prep- aration of kelp became quite a large business on the coast of Scotland. Iodine is chiefly used in the arts in the proc- ess of dyeing and in the making of photographic pictures. It is also used in medicine. H 170 CHEMISTEY. 229. Properties. Iodine is a solid substance of a deep- blue color, with a somewhat metallic lustre. By the ap- plication of heat it may be made to rise in a beautiful vio- let vapor or gas. This gives it its name, which comes from a Greek word meaning violet-colored. The vapor of iodine is nearly nine times as heavy as air, and is one of the heav- iest of the gases. Iodine is not very soluble in water, but is quite soluble in alcohol, and forms with it a tincture much used in medicine. 230. Iodine a Supporter of Combustion. Combustion in iodine is much the same as in chlorine. For purposes of experiment in this respect you can prepare the gas by placing a few grains of the solid iodine in a jar, , Fig. 72, and heating the jar by a sand-bath, b, and spirit-lamp, c. The jar will become gradually filled with the violet- colored gas, the air in the jar being pushed up before it. If a lighted taper or candle be let down into the jar it burns, but dimly, however. A piece of phosphorus introduced into it takes fire spontaneously. 231. Bromine. Bromine is contained in sea-water, where it exists in small quantity, combined with magnesium. It is the only elementary substance, save mercury, which is liquid at ordinary temperatures. It is of a dark brown-red color, and very heavy ; it has a powerful, irritating odor, whence it receives its name, bromos being the Greek word for bad odor. It is a corrosive and deadly poison. It is used in medicine and in photography, chiefly as sodium bro- mide. Iodine and bromine form hydrogen compounds and oxygen compounds almost exactly the same as chlorine. These three elements are always found associated, and seem to be members of the same family. 232. Fluorine. This element has never been prepared in a free state, and is known to chemists only in combination. CHLORINE, BROMINE, IODINE, AND FLUORINE. 171 It occurs rather abundantly in nature, combined with cal- cium chiefly. The beautiful mineral fluor-spar is calcium fluoride. The hydrogen compound of fluorine is of great importance to the chemist and in the arts, owing to its val- uable property of dissolving silica and attacking glass. This hydrofluoric acid, as it is called, HF1, is a colorless, acid gas, soluble in water. You can make a pretty experi- ment with it, but be careful not to breathe the fumes. Take a small leaden dish, and put into it some powdered fluor-spar, calcium fluoride. Next take a watch-glass, warm it gently, and make beeswax to flow evenly over the convex surface. Now write a word, or scratch any thing you please with a pin on this wax-covered glass, removing the wax only where you wish lines to be eaten into the glass. Pour some strong sulphuric acid into the leaden dish containing the calcium fluoride, heat gently, and, as soon as you see white fumes, cover the dish with the wax-covered glass. The gaseous hydrofluoric acid will eat away the glass where not covered by the wax. Remove the glass after some minutes, scrape off the wax, wash the rest off with benzol, and you will have an etched surface exposed. Par- affin may be used instead of wax. QUESTIONS. 208. What four bodies form a natural group ? 209. Where and how does chlorine occur in nature? Is it abundant? 210. Describe and ex- plain a method of obtaining chlorine from common salt. 211. From hy- drochloric acid. 212. What is said about breathing chlorine ? 213. What about chlorine water? 214. State what action chlorine has on some met- als. 215. Show its attraction for hydrogen by describing the experiment named. 216. How is advantage taken of this attraction in bleaching? What really does the work? 217. What happens if the chlorine be in too great excess? 218. What advantages has this method over grass-bleach- ing? Who discovered chlorine? 219. Explain the difference between chlorine bleaching and sulphur bleaching. 220. How is chlorine used as a 172 CHEMISTRY. disinfectant? 221. Describe a case of combustion in chlorine. Why does a candle smoke so badly in chlorine ? How does oil of turpentine act in chlorine gas? 222. What is hydrochloric acid, and what are its properties? What is its commercial name ? 223. Show how this acid can be obtained synthetically. 224. Describe the common mode of preparing hydrochloric acid. What will be formed if you add manganese dioxide to the materials employed ? 225. What is aqua regia ? Whence comes its name ? 22G. What is said of the oxygen compounds of chlorine ? What bodies form when chlorine gas is passed into a solution of potassium hydrate ? 228. What is said of iodine ? 229. What of its properties ? 230. How does it support combustion? 231. What is noticeable about bromine ? 232. Of what use is fluorine itself? Explain a method of etching glass. CHAPTER XII. SULPHUR. 233. Occurrence of Sulphur. Sulphur is a very abundant substance in nature. In the combinations of sulphur with copper, lead, silver, and many other metals, forming sul- phides, we have their most important ores. Much of the sul- phur which is used is obtained from a sulphide of iron, or iron pyrites. Large beds of native sulphur are often found, especially in volcanic localities. Combined with oxygen as sulphuric acid, it exists in great amount in the sulphates, the most abundant of which is the sulphate of lime, called gyp- sum or plaster of Paris. It enters also in small proportion into the composition of both vegetable and animal substan- ces, being in considerable quantity in some of them, as in beans, pease, horseradish, onions, etc., in the vegetable world, and in eggs, hair, horns, hoofs, etc., in the animal. 234. Forms of Sulphur. Sulphur is disposed to take a crystalline arrangement, and always does to a greater or less degree. Even when cast in roll there is some crystal- lization, imperfect and irregular, so that when it is held in SULPHUR. 173 the warm band the expansion occasioned by the heat causes a separation and friction of the crystals, and consequently a crackling sound. So, also, when the roll is broken the sur- face presents a glistening appearance, because of the multi- tude of surfaces of crystals. Even in the flowers of sulphur, though apparently a fine powder, there is really the crystal- line state, as may be seen by examining the pow- der with a microscope. When a fair opportunity is given to the particles of sulphur to arrange them- selves without disturbance, crystals are formed of considerable size and of great beauty. In the fis- sures and cavities of the beds of sulphur in vol- canic countries there are collections of crystals of Fig> T3 * the shape seen in Fig. 73. It is curious that the crystals are of a different shape if they are formed artifi- cially. Melt some sulphur in a crucible, then, let- ting it stand till a crust forms over the surface, quickly break the crust, and pour out all the sul- phur that is yet liquid. On breaking the cruci- ble afterward you will find the cavity of the sulphur covered with fine crystals in the form of lengthened pillars, as represented in Fig. 74. Sulphur is said, therefore, on account of its taking these two crystalline forms, to be dimorphous, from the Greek dis 9 twice, and morphe, form. Amorphous Sulphur. Twist a wire the mouth of a test-tube, Fig. 75, so that you can conveniently hold it, and, filling the tube with flowers of sulphur, hold it over a Bunsen burner. The sulphur as it melts but half fills the tube. At first it is thin like water, but on heating it more it becomes brown and thick. If now you heat it a little farther it becomes fluid again, Fig. 75. Fig. T4. 235. around 174 CHEMISTEY. and then on being poured into water it becomes a soft waxy mass, which slowly hardens. This sulphur, not being at all crystalline, is said to be amorphous, from the Greek a, without, and morphe, form. When in its waxy state it is used for copying coins and medals, the copy becoming hard in a few hours. 236. Flowers of Sulphur. The two common forms of sul- phur in commerce are the roll sulphur and the flowers of sulphur. The roll sulphur is obtained by distillation in the manner shown in Fig. 76, or by sim- ply melting tho crude sulphur, and as the impurities sink in the liquid the sulphur is poured into moulds, where it is left to cool. The apparatus for making the flowers of sulphur is represented in Fig. 77 (p. 175). The crude sulphur is melted in the iron pot, a, whence it flows into the retort, c / here it is heated to boiling by the fire, d, and the vapors pass into the large chamber, e e e. After a while the sulphur vapor cools and condenses on the sides of the chamber in the form of very small crystals, so minute as to appear like a powder. When a sufficient quantity of the flowers is thus formed they are removed by the door at p. Some melted sulphur accumu- lates at the bottom, and is drawn off into moulds and cooled. This constitutes roll sulphur. If the mixture of sulphur vapor and air should inflame, the consequent explosion will Fig. 70. SULPHUR. 175 Fig. 77. do no harm, for it opens at once the valve, s, and the gases escape. This process of raising a solid in vapor, and then condensing it in the form of a powder, is called sublimation. 237. Properties of Sulphur. Sulphur is familiar to you as a brittle yellow solid. It is insoluble in water and alcohol. It takes fire readily, or, in other words, its attraction for oxygen is such that it requires but little heat comparatively to render its union with oxygen sufficiently rapid to occa- sion the phenomena of combustion. For this reason it has been much used for kindling purposes. By means of it other substances that unite less readily with oxygen may be heated to the degree of temperature requisite to set them on fire. The kindling of a coal fire in the times of the old- fashioned tinder-box illustrates well the different degrees of combustibility in various substances. The iron spark cast off by the blow of the flint sets fire to the finely divided charcoal of the tinder ; this kindles the sulphur on the match, 176 CHEMISTRY. by means of which the paper, the wood, and the coal are successively brought to the degree of heat requisite for combustion. The following, then, is the order of these arti- cles in relation to the degree of heat necessary to produce their combustion tinder, sulphur, paper, wood, coal. If the phosphorus so much used at the present day in the lucifer- matches be put in this list, its place will be at the head of it. 238. Sulphurous Anhydride, SO 2 . This gas is produced whenever sulphur is burned. You are familiar with its smell and its suffocating power. The gas un- mixed with air can not be breathed at all. It extinguishes at once a lighted taper, as may be seen when it is introduced into a jar of it, as represented in Fig. 7& For this reason, when a chimney takes fire, it may be extinguished by sprinkling some sulphur upon the coals. The sulphurous anhydride, rising, drives out all the air, and, thus preventing the burning soot from being sup- plied with oxygen, puts out the fire. The fact that the gas is very heavy helps to produce this result, for while it fills the chimney it is not disposed to pass rapidly upward. 239. Preparation of Sulphurous Anhydride. This gas, though easily obtained on a large scale by burning sulphur, is usually prepared in the chemist's laboratory by heating copper with concentrated sulphuric acid. The reaction is as follows : S u,phuricacid. Copper. 2H 2 S0 4 + Cu = CuS0 4 + S0 2 + 2H 2 O The sulphuric acid is decomposed, some of it furnishing S0 a and 2 to form water with H 4 , while some of it forms copper sulphate with the metal. Charcoal can be used in place of copper, the reaction being different : Pfli-hnn Sulphuric Sulphurous Carbonic WntPr acid. anhydride. anhydride. C + 2H 2 S0 4 = 2S0 2 + C0 2 + 2H S O You see that more sulphurous anhydride is obtained by this method from SULPHUB. the same amount of sulphuric acid, but it is mixed with carbonic anhydride, which is not wanted in many experiments. Sulphurous anhydride is very eagerly absorbed by water, which takes up 40 volumes. This solution is an unstable acid, like carbonic acid : Sulphurous anhydride. Water. Sulphurous acid. S0 3 + H 3 = H 3 SO 3 Yet many salts are formed by replacement of the hydrogen in this acid; such salts are called sulphites, " ous " acids making "ites," as you learned in 79. 240. Bleaching Properties of Sulphurous Anhydride. It is the sulphurous anhydride which is the bleaching agent when straw goods are placed in a chamber in which sulphur is burned. The gas unites chemically with the oxygen of the coloring matter, and turns it white. The bleaching power of this acid may be very prettily illustrated by holding a red rose or peony over a burning stick of sulphur. The coloring matter is not destroyed in bleaching, but there is a chemical union between it and the acid ; and it is a union that can be broken up either gradually by the action of light and air, as is manifested in the return of color after a time to the bleached articles, or quickly by the action of some powerful agent, as sulphuric acid. We will give a single illustration of the latter. If you pour a solution of sulphur- ous anhydride in water into an infusion of logwood shav- ings, the infusion loses its dark color ; but if you pour into it a little sulphuric acid, the color will be at once restored. 241. Sulphuric Anhydride, SO 3 . This body, which may be considered as sulphuric acid less the elements of water, is a glistening white solid. It can not be kept unless it be shut in from the air in glass tubes hermetically sealed. On exposure to the air it fumes violently, and soon becomes fluid by attracting the moisture of the air. If it be thrown II 2 178 CHEMISTRY. into water it hisses like red-hot iron, and forms sulphuric acid : Sulphuric anhydride. Water. Sulphuric acid. SO, + H a O = H 3 SO 4 This anhydride dissolved in common sulphuric acid forms the so-called Nordhausen or fuming sulphuric acid, gen- erally obtained by distilling ferrous sulphate (sulphate of iron) : Ferrous sulphate. Ferric oxide. Sulphuric Sulphurous anhydride. anhydride. 2(FeSOJ Fe 3 3 + SO 3 + SO 3 When water is present, and this is generally the case, some of the sulphuric anhydride dissolves in it, forming sulphuric acid (as above), and some of this anhydride dissolves in the acid thus formed. This acid is called Nordhausen acid, after the town in Saxony where it has been made for many years. This was one of the earliest ways of making sulphuric acid, but common oil of vitriol is manufactured differently. 242. Manufacture of Sulphuric Acid. This acid has one more atom of oxygen in it than sulphurous acid, and there- fore can be made from the latter by adding this amount of oxygen to it. When sulphur burns it forms sulphurous an- hydride, and will not take up any more oxygen from the air; hence this oxygen must be added in an indirect manner, as shown in the following sentences : Sulphurous anhydride produced by burning sulphur, or by roasting iron or copper pyrites, is conducted together with steam into an apartment lined with lead, on the floor of which is some water. But there is sent in with this some nitric acid; this acid on meeting the sulphurous anhydride gives up to it a part of its oxygen, and the sulphuric anhydride thus formed dis- solves in the watery vapor present, making sulphuric acid. Meanwhile the nitric acid, having parted with some of its SULPHUR. 179 oxygen, is no longer nitric acid, but nitric oxide ; this imme- diately absorbs oxygen from the air in the leaden chamber, becoming nitric peroxide. Then this nitric peroxide, meet- ing sulphurous anhydride, again gives up its oxygen; and this process is repeated over and over. Thus you see the nitric peroxide answers simply as a medium for delivering over to the sulphurous anhydride the oxygen from the air. Fig. 79. The sulphuric acid that is formed becomes dissolved as fast as it is made in the water in the lead chamber. In order to facilitate this solution steam is constantly admitted into the chamber, so that each particle of the acid may be dis- solved as soon as it is formed. The water is in this way sent in search of the acid. 243. Explanation in Formulae. There are three stages : !Sr *. water. SU 'P!T C *** annjduue. acid. oxide. (1) 3(S0 3 ) + 2(HN0 3 ) + 2(H 3 0) = 3(H 3 SOJ + 2(NO) Nitric oxide. Oxygen. Nitric peroxide. (2) NO + O N0 3 Nitric Sulphurous w Sulphuric Nitric peroxide. anhydride. acid. oxide. (3) N0 3 + SO a -f H 3 O = H 3 S0 4 + NO then (2) is repeated, (3) follows, and so on. 244. Properties. Sulphuric acid is the most powerful of all the acids, and is therefore one of the most important 180 CHEMISTEY. agents of the chemist in his operations. " What iron is to the machinist," says Stockhardt, "sulphuric acid is to the chemist. It stands, as it were, the Hercules among the acids, and by it we are able to overpower all others, and expel them from their combinations." It chars most vegetable JD and animal substances. If a bit of wood be introduced into it, it becomes black, and in fact is reduced to coal, as if it had been burned ; for, being composed of carbon, oxy- gen, and hydrogen, the sulphuric acid takes away the two latter, combining them to form water, and leaves the car- bon untouched. It does the same thing to sugar, as that is composed of the same ingredients as wood. 245. Development of Heat. If water and sulphuric acid be mixed together, considerable heat is evolved by the chemical union which takes place between them. This may be shown very prettily by the following experiment : Put some tow or cotton around a wine-glass, with some little bits of phosphorus placed in it in such a way as to be in contact with the glass. If now you pour into it some sul- phuric acid, and then some water, the heat produced will burn up the combustible material around the glass. It is supposed that the heat is caused by a condensation which takes place in the union of the acid and the water. If 50 measures of the acid are mixed with 50 of water, we do not have as the result 100 measures of the mixture, but only 97, showing a contraction or condensation which is considered adequate to the production of the heat. 246. A Practical Direction. The heat caused by the union of water and sulphuric acid explains the reason of a practi- cal direction that may be given in regard to an accident which sometimes happens with sulphuric acid. If some of the acid be spilled upon the skin, just wipe off as much of it as you can with a piece of dry cloth or paper, and then use a large quantity of water in washing off the rest, so that SULPHUR 181 the acid may be well diluted. If you should apply water at first, the heat produced by its union with so much acid would cause an immediate corrosive action upon the skin. That the acid itself acts rather slowly, and its action may be greatly hastened by putting some water with it, may be seen in the following experiment. Drop a little of the acid upon paper, and you will see that the decomposition takes place slowly ; but add a few drops of water, and the decom- position or corrosive action will be instantaneous from the influence of the heat produced. 247. Uses of Sulphuric Acid. The sulphuric acid that we commonly use is, when it is the strongest, nearly one fifth water by weight, and its tendency to absorb water makes it very difficult to keep it of this strength. Exposed to air it will continually absorb its moisture, and of course increase in bulk. In air that seems to us perfectly dry this acid will find some moisture to drink. The chemist sometimes wishes to obtain some gas in an entirely dry state, and for this purpose lets it pass through sulphuric acid. The work is thoroughly done. As the gas bubbles up through the acid it loses every particle of water, and comes out perfectly dry. As sulphuric acid has such strong and varied chemical powers, it is largely used in the arts. It is used, for exam- ple, in bleaching, in dissolving indigo for use in dyeing and calico printing, in manufacturing sodium carbonate and ni- tric and hydrochloric acids, in the refining of gold and sil- ver, in the purification of oils, in the manufacture of super- phosphate of lime, so much used now in agriculture, etc. Sulphuric acid having two atoms of hydrogen which can be replaced by a metal, forms two classes of salts, neutral and acid. Thus we have sodium sul- phate, Na 2 S0 4 , which reacts neutral, and hydro-sodium sulphate, NaHSO 4 , which reacts acid. The second forms when excess of acid is present ; on heating the acid salt to redness, sulphuric acid is expelled and the neutral salt remains. 182 CHEMISTRY. Hydro-sodium sulphate. Sodium sulphate. Sulphuric acid. 2NaHS0 4 = Na a SO 4 + H a SO 4 A large number of the sulphates are very soluble ; the sulphates of the alkaline earths are notable exceptions. Sulphates are often formed in nature from the sulphides by the latter taking up oxygen from the air. 248. Sulphuretted Hydrogen, H 2 S. This may best be pre- pared by acting on ferrous sulphide with hydrochloric or sulphuric acids ; heating is not necessary. Ferrous sulphide. Sulphuric acid. Ferrous sulphate. FeS + H a S0 4 FeS0 4 + H a S The apparatus used is shown in Fig. 80. The gas which comes over is colorless, and has a very strong odor of rotten eggs. It is produced in the decomposition not only of eggs, but of other animal substances, and also of such vegetable substances as contain s u 1 p h u r, as pease, beans, onions, etc. When at all concen- trated this gas has a very decided effect upon various metals and their salts. Thus it blackens white paint because it attacks the _ white-lead in it, form- Fig. so. ing a sulphide of lead. Silver or copper vessels exposed to it become dark from the formation of sulphurets of these metals. There is some lit- tle of this gas very generally in the atmosphere, and hence silver articles become slowly tarnished. When much con- centrated it is a very deadly gas, and it is this which oc- casionally destroys the lives of men engaged in cleaning SULPHUB. 183 out vaults and sewers. Sulphuretted hydrogen burns with a pale blue flame, producing sulphurous anhydride and water, H 2 S+O 3 =H 2 O-f SO 2 . It dissolves in water freely, and the solution is of great service to the analytical chemist as a reagent, for it forms colored sulphides with solutions of many of the metals. This solution does not keep perfectly, sulphur precipitating, and hydrogen escap- ing or uniting with oxygen. QUESTIONS. 233. How does sulphur occur in nature in the mineral kingdom ? How in the vegetable ? How in the animal ? 234. What is said about the forms of sulphur ? What is the meaning of dimorphous ? 235. How can soft sul- phur be made ? Why is it called amorphous ? 236. How are flowers of sulphur made ? 237. What are the properties of sulphur ? 238. What does burning sulphur produce ? 239. How is sulphurous anhydride prepared ? How are sulphites formed ? 240. Explain the bleaching power of sulphur- ous anhydride. 241. What are the properties of sulphuric anhydride? How is it prepared ? What is Nordhausen oil of vitriol ? 242. State in full the process of manufacturing sulphuric acid. 243. Explain the reac- tions by equations. 244. What are the properties of sulphuric acid? 245. What happens when you mix concentrated sulphuric acid with water? 246. What remedy should be employed to prevent the corrosive action of sulphuric acid on the skin ? 247. Name some of the uses of sulphuric acid. What is the distinction between neutral and acid salts ? 248. How is sul- phuretted hydrogen best prepared ? What is the equation ? What are its properties ? What is said of its burning ? What of its solution ? 184 CHEMISTRY. CHAPTER PHOSPHORUS. 249. Properties of Phosphorus. This substance, discov- ered more than two hundred years ago, and obtained now extensively from bones, has very remarkable properties, with which you have already become somewhat acquainted. It is a nearly colorless substance, having a waxy appear- ance. Exposed to the air it smokes, and in the dark emits light, from which it gets its name, derived from two Greek words signifying together to bear light. It is, you remem- ber, inflammable at ordinary temperatures, and therefore in order to preserve it we must keep it in water. From the readiness with which it takes fire, and the violence with which it burns, it is necessary to be careful in handling it. It should be cut under water, and when taken from the water it should be held by a forceps or on the point of a knife, as even the warmth of the hand may set it on fire. We should use small quantities in experimenting, and have a vessel of water at hand to quench it in case it should take fire accidentally \vhen we do not wish it. Phosphorus is a violent poison, and is therefore used in getting rid of rats and mice. The common rat electuary is made of a dram of phosphorus and eight ounces each of hot water and flour. Phosphorus is insoluble in water, but is soluble in ether, alcohol, and oils. 250. Experiments. Observing the cautions given, you can try many interesting experiments with phosphorus, some of which we will notice. PHOSPHORUS. 185 Put into a phial half an ounce (a tablespoon ful) of ether, and then a piece of phosphorus twice the size of a pea. Cork the phial, and put it aside for several days, occasionally shaking it. Pour the clear liquid now into another phial, and it is ready for use. If you moisten your hands with some of this solution, the ether will speedily evaporate, leaving the phosphorus in small quantities all over the skin, which of course combines with the oxygen of the air, and in doing so-gives out a light which in the dark is very bright. By rubbing the hands you make the light more vivid, be- cause you quicken this union of the phosphorus and oxygen. The quantity of phosphorus used in this case is so small that little heat is evolved, and we have a slow combustion, producing phosphorous anhydride. Moisten a lump of sugar with this solution, and throw it into hot water. The ether and phosphorus rise together to the surface, and the moment they reach the air they take fire. The combustion is here rapid and perfect, and there- fore phosphoric anhydride, which has more oxygen in it than the phosphorous anhydride, is formed. Pour some of the solution upon fine blotting-paper, and it will burst into flame as soon as the ether is evaporated. If you boil water in a flask with some phosphorus in it, the escaping steam will be luminous. 251. Amorphous Phosphorus. When ordinary waxy phos- phorus is heated for many hours in tightly closed vessels in such a manner that it can not burn, a great change in its properties takes place, and we obtain what is known as amorphous phosphorus. This is dark-red in color, is opaque instead of transparent, its specific gravity is higher, it is insoluble in the liquids which dissolve ordinary phosphorus, and, most remarkable of all, it no longer takes fire in the open air at low temperatures. It may be heated quite hot, beyond 200 C., without inflaming. This red phosphorus 180 CHEMISTRY. is another case of allotropism, which, you remember, in the case of ozone and carbon was attributed to a difference in the arrangement of the atoms. 252. Lucifer-Matches. As phosphorus can be ignited by friction, it is used in the manufacture of hicifer-matches. The substance on the ends of the matches is a mixture of phosphorus with other substances that contain considerable oxygen, the composition being done up in mucilage of gum arabic. The object is to supply oxygen in the immediate neighborhood of the phosphorus, that the friction may read- ily produce combustion. The particles of the phosphorus are so much shut in from the air in the dried mass that the oxygen of the air can get admission to comparatively a small portion of them. The substances containing oxygen that are commonly used are red-lead (oxide of lead), potas- sium nitrate, and potassium chlorate. A formula given by Stockhardt is this: If parts of phosphorus, 4 each of gum- arabic and water, 2 of nitre, and 2 of red -lead. Safety matches are made with amorphous phosphorus, which is less liable to be set on fire by accidental friction. Some- times the phosphorus composition is applied only to the surface of the box, and then the matches ignite only when rubbed on this surface. 253. Mode of Obtaining Phosphorus. As already stated, phosphorus is obtained from bones. These are composed mostly of an animal substance, gelatine, and a mineral sub- stance, phosphate of lime. The gelatine is first burned out, and the phosphate of lime which is left is reduced to pow- der. This powder is digested with dilute sulphuric acid, and in consequence a sulphate of lime is formed, which is an insoluble substance. As, therefore, phosphate of lime is composed of phosphoric acid and lime, the lime being re- moved, we have the phosphoric acid dissolved in the dilute sulphuric acid. This solution, after being strained, is mixed PHOSPHOEUS. 187 Fig. 81. with powdered charcoal, and when the mixture is dry it is put into a stone-ware retort, a, Fig. 81, to the neck of which is attached a copper tube, , the mouth of which dips under wa- ter in a vessel. The retort be- ing subjected to a white heat, the charcoal unites with the oxygen of the phosphoric acid to form carbonic oxide, and the disengaged phosphorus be- comes vaporized. The vapor and the gas pass over together through the tube, b, the phos- phorus becoming condensed and dropping into the water, and the gas passing out through the small tube in the vessel. Phosphorus is com- monly in the form of small round sticks, this form being given to it by melting it in glass tubes in warm water. 254. Diffusion of Phosphorus in Nature. Phosphorus is quite widely diffused, not as phosphorus, for it is never found as an element, but in combination with other sub- stances. There is in the body of an adult man from 500 to 800 grammes of phosphorus. It is not all in the bones, but there is some in the blood and the flesh, and especially in the brain. Now the phosphorus that is in animals must come from vegetables, and these must get it from the min- eral world. The phosphate salts appear in all kinds of grain, and in leguminous and many other plants, especially in their seeds. If there were no such salts in the soil these seeds could not be produced, and hence in part the great usefulness of bones, in many cases, as a manure, supplying the deficiency of these salts in the soil. From all this you see that phosphorus has a wide and constant circula- 188 CHEMISTRY. tion in the chemical and vital operations going on in the world. 255. Phosphoretted Hydrogen, H 3 P. This is a colorless gas having the odor of garlic. A beautiful phenomenon attends its production if it be allowed to escape into the air. Let about 30 grammes of potassium hydrate be put into a small retort, Fig. 82, and pour in upon it half a tumbler of Fig. 82. water ; then add a bit of phosphorus-stick half an inch long and a teaspoonful of ether, and apply the heat, the beak of the retort being under the surface of the water in the bowl. The ether has nothing to do with making the gas, but this is made by the action of the phosphorus and potassium hy- drate and water together. The object of the ether is to prevent an explosion, which would be liable to occur if the gas escaped directly into the air in the retort. The ether does this very effectually, for, being vaporized by the heat, it rises, driving the air out before it, and then the gas, which is generated as the heat increases, passes out behind the ether, which acts thus as a sort of advance-guard. The gas, as it comes up out of the water in the bowl, takes fire spon- PHOSPHOBUS. 1 89 taneously, emitting a bright yellow light ; and the smoke rises in rings, which enlarge as they go up, exhibiting at the same time a singular rotary movement. The reaction is complicated : ,,, . Potassium Phosphoretted Potassium Phosphorus. Water. hydrate> hydrogen, hypophosphite. P 4 + 3H 2 + 3KHO = H 3 P + 3KPH 3 O 3 It is this gas, forming with hydrogen and nitrogen in the decomposition in the mud of marshes, which causes the light called " will-o'-the-wisp." 256. Another "Way of Making Phosphoretted Hydrogen, Phosphide of calcium thrown into water acidulated with hydrochloric acid gives off phosphoretted hydrogen, which ignites spontaneously. This experiment can be made in a wine-glass without danger. 257. Compounds of Phosphorus -with Oxygen. These are two in number. First we have phosphorous anhydride, formed by slow combustion, as exemplified in the first ex- periment in 250. Then we have phosphoric anhydride, the result of perfect combustion, as in the second experi- ment, and in the burning of phosphorus in oxygen gas, no- ticed in 58. Both of these anhydrides dissolve in water, forming corresponding acids. Phosphoric acid is made in another way, however, as this is inconvenient. Phosphorus is heated with moderately strong nitric acid, the phosphor- us is oxidized by the acid, and on concentrating the solu- tion the excess of nitric acid is expelled and a sirupy liquid remains. Phosphoric acid, H 3 PO 4 , containing three atoms of hydrogen, is a tri-basic acid, and forms a great variety of salts. A third acid is known, hypophosphorous acid, the compounds of which are used in medicine. Its anhydride has not as yet been prepared. 1 90 CHEMISTRY. QUESTIONS. 249. How long has phosphorus been known ? What are its properties ? How does it act physiologically? In what is it soluble? 250. Describe some experiments with a solution of phosphorus. 251. How is amorphous phosphorus obtained ? What is allotropism ? 252. What is the chief use of phosphorus? 253. Detail the method of obtaining phosphorus. 254. Where and in what state does phosphorus occur in animals ? How do an- imals get it ? 255. What is the composition of phosphoretted hydrogen ? What is its nature ? Explain a method of obtaining it. What name is given to it when occurring in marshes ? 256. Mention another way of making this gas. 257. What compounds does phosphorus form with oxy- gen ? What is said of the acids ? CHAPTER XIV. SILICON AND BORON. 258. Silicon. This element never occurs in nature in a free state, but its compound with oxygen silicic anhydride, SiO 2 is most important and abundant. Silicon itself is ca- pable of existing in three allotropic forms, like carbon ; the form corresponding to lampblack is a dark-brown powder, destitute of lustre ; the diamond form is crystalline, and so hard as to scratch glass. These substances are mere chem- ical curiosities, and their preparation does not interest us. United with oxygen it forms silicic anhydride, commonly called silica ; this unites with the elements of water, form- ing a true acid, which, when freshly prepared, appears like a transparent jelly. On igniting, water is driven off and sil- ica remains. Compounds of silicic acid and metallic oxides are called silicates. 259. Abundance of Silica. It is estimated that silica con- stitutes about one sixth of the bulk of the earth. It ap- pears in various forms and combinations. It is nearly pure SILICON AND BORON. 191 in quartz and flint. Various precious stones, carnelian, am- ethyst, opal, jasper, etc., are silica, their different colors be- ing caused by the presence of metallic oxides. Common sand is silica, generally rendered yellow by the hydrated oxides of iron or iron rust. Then silica is present in many salts called silicates, constituting part of an abundant class of rocks. In the granite rocks we have mingled with the quartz, which is silica, two silicates feldspar and mica. There are silicates in many other rocks also. In clays there are variable quantities of various silicates ; but the silicate of alumina is largely predominant, and is the essential basis of all clays. The best porcelain clay, which is perfectly white, is nearly pure silicate of alumina. As earthenware is made of clay, it is composed of silicates. The same thing is true of the various kinds of glass. 260. Silica in "Water and in Plants. Through the agency of potash silica is rendered soluble to some extent, and therefore is found in water and in plants. If spring-water be evaporated, what remains in solid form is in part silica ; and so if we burn plants, it is found in their ashes. There is considerable silica in grasses and the various kinds of grain, and they have therefore been called silicious plants. Absorbed by the root, it goes up in the plant dissolved in the sap, and is deposited chiefly in the stalks, giving to them their requisite firmness. It is to them what the mineral matter, the phosphate of lime, in our bones is to us. Silica is also present to a considerable extent, especially in the frame- work of those minute animals, which can be seen only by means of the microscope, called infusoria. 261. Silicified Wood. A singular result occurs when wood decays in water that has considerable silica dissolved in it. The water, of course, soaks into every part of the wood, taking the silica along with it. Now, as the parti- cles of wood are loosened one after another and carried 192 CHEMISTRY. away, a particle of silica takes the place of every removed particle of wood, so that at length all the wood is gone, and is wholly replaced by silica. Because the shape and all the lines of the wood are preserved, the common idea is that the wood is turned to stone ; but, as you see, stone has merely taken the place of wood. Silicified wood is found in great quantity in certain parts of California and Oregon. Large trunks of trees are found completely silicified. Such speci- mens are erroneously called petrifactions, as if they were the result of turning into stone. 262. Glass. In making glass, the silica or silicic anhydride is made, by an intense and long-coatinued heat, to unite with various bases, according to the kind of glass required. Window-glass is made by uniting silica with soda and lime ; plate-glass, crown-glass, and the beautiful Bohemian glass, by uniting silica with lime and potash ; and green-bottle glass is commonly a silicate of lime and alumina, combined with oxides of iron and manganese, and sodium and potas- sium, its green color being produced by the oxide of iron. Glass is in reality a very complex mixture of true salts. What is called enamel is an opaque glass, made so by some substance which, though it be thoroughly mixed with the glass in melting, does not melt with it. Stannic oxide is commonly used for this purpose. The silica used in mak- ing glass is in the forms of sand, quartz, flint, and old broken glass. The materials are subjected to intense heat in clay pots for about forty-eight hours, in order to bring the mass into a proper state to be worked. The manner in which the melted glass is made into various articles we will not detail. The common mode of making window-glass is de- scribed in Part I, 216. 263. Coloring Glass. The various colors are given to glass mostly by metals. We have already mentioned the bottle- green color imparted by the ferrous oxide. Ferric oxide gives SILICON AND BORON. 193 a yellowish-red color, oxide of cobalt blue, oxide of manga- nese purplo and violet, oxide of copper a ruby red, etc. 264. Annealing. Glass, like steel, must be annealed to de- prive it of its brittleness. For this purpose the articles that are made are placed in the annealing furnace, which is a very long gallery containing iron trays that are moved very slowly through it by means of an endless chain. The heat at the end where the articles are put in is very great, and gradually lessens toward the other end. Every article is from twenty- four to forty-eight hours in passing through the gallery, and the particles of the glass have time, in this slow cooling, to assume such an arrangement as to give them their highest degree of firmness. We see the opposite result in what are called "Prince Rupert's Drops," which are prepared by taking up on an iron rod some melted glass and allowing the drops of it to fall into cold water. They assume the shape given in Fig. 83. The particles in this case, solidifying hastily, have an exceedingly unstable ar- rangement, which can be wholly destroyed by a very slight disturbance. If, therefore, you scratch the surface or break off the lit- tle end, the whole flies into powder so quick- ly as to cause a considerable report. 265. Slag. The slag which is so often seen in reducing metallic ores is composed of silicates, and is a kind of glass. In the process of reducing iron ore, described in Chapter XVIIL, the lime is used, because it makes, with the silica that is mixed with the ore, a glass that is very fusible, and is therefore easily removed. It is for this reason that oys- ter-shells, introduced among the anthracite coal in a stove, remove the clinker. The lime unites with the silica, and the silicate formed, melting easily, runs down and min- I 194 CHEMISTKY. gles with the ashes. So, also, if there be much lime in the clay that is used for making bricks, they will be apt to be spoiled in burning, from the too great fusibility of the silicate that is thus formed. 266. Soluble Glass. Glass, as commonly made, is wholly insoluble; but soluble glass can be produced by using a very large proportion of alkali ; and a solution of it was known a long time ago as the liquor of flints. Such a solu- tion is sometimes employed as a fire-proof varnish for wood, canvas, etc. 267. Earthenware. All earthenware is made of clay, which has as its essential ingredient silicate of aluminium. There are mingled with this in different clays silicates of po- tassium, sodium, calcium, etc. The coarsest clay employed is used in making bricks and common flower-pots, and the finest in making porcelain. The plastic nature of clay, and its hardening by heat, are the causes of its peculiar adapta- tion to the manufacture of earthenware. The moistened clay, after being well kneaded, is shaped, either by pressure in moulds, as in brick-making, or by the hand of the potter as he makes it revolve with his lathe, thus pressing into his service centrifugal force, as indicated in Part I., 213. The articles are first dried in the sun, and then are baked in furnaces, both of which processes cause considerable shrinking, especially the baking. The reddish-brown color of bricks and flower-pots is owing to the presence of ferric oxide. The bricks of the Egyptians, in the making of which straw was used as one of the constituents, were merely sun- dried. The bits of straw mingled with the clay were of the same use as hair is in mortar which is used in plaster- ing. 268. Glazing. Although earthenware by baking becomes hard and firm, it is quite porous, so that water can exude through it. This is not objectionable in the case of flower- SILICON AND BOEON. 195 pots, but would be decidedly so for most of the purposes to which earthenware is applied. To remedy this defect the ware is covered with a coat of glass. This glazing, as it is called, is done in various ways. Common earthenware is often glazed with oxide of lead. This is very dangerous if the vessels are to be used in cooking or in preserving any eatables, for the lead may be dislodged by some chemical action of the contents, and act as a poison. Common salt is also used. Being thrown into the kiln, it is raised in va- por by the heat, and is decomposed on coining in contact with the surface of the ware. The chlorine leaves the salt, and its sodium becoming soda by attracting oxygen, the soda unites with the silica of the ware and forms a glass. For finer articles another mode is followed : A paste is made of such materials as will, under the influence of powerful heat, form a glass. These materials are reduced to an ex- ceedingly fine powder, and this being diffused in water, the article to be glazed is dipped into it. By this means it gets a very thin coating of the glaze, for the clay absorbs at once the moisture, and the fine powder remains uniformly diffused over the surface. By intense heat this is converted into a smooth coating of glass. The paste used is often composed of feldspar, quartz, and borax. Glazing is not necessary in the case of porcelain and some kinds of stone- ware, for certain materials which form glass are mingled with the clay, so that the heat of the baking fills up all the minute spaces in the clay with glass. Still, the glazing is usually done for the sake of adding to the beauty of the ware. 2C9. Boron. The element called boron is a gray amor- phous powder. It is never found in nature, but the acid which it forms, boracic acid, is sometimes exhaled from vol- canic openings in the earth. The hot vapors of the lagoons of Tuscany contain it in large quantity. In collecting it, 196 CHEMISTRY. Fig. 84. Lagoons of Tuscany these vapors are made to pass into water, which condenses them, and then the water is evaporated, which leaves the boracic acid in large crystalline flakes, having the feeling somewhat of spermaceti. Boracic acid is not volatile when it is by itself. If heat be applied to it, it will melt, and be- come a vitreous mass, but no degree of heat will make it fly off in vapor. But it is volatile when it is in volatile com- pany, as we may say ; which is often true of other substan- ces, and, we may add, persons also. Thus, if we mix some of it with alcohol in a mortar, and then set fire to the alco- hol, it will burn with a green flame, because some of the boracic acid rises in vapor with it. Boracic acid forms with sodium a bi-borate, commonly called borax, which we shall notice hereafter. QUESTIONS. 258. In what does silicon resemble carbon ? What are silicates ? 259. What is said of the occurrence and abundance of silica ? What is quartz ? What is granite ? What is clay ? 2GO. What is said of the presence of sil- ica in plants ? What animals contain silica ? 261. What is silicified wood ? Explain the error of common opinions regarding it. 2G2. How is glass METALS. 197 made ? 263. What materials are used to color glass ? 264. How is ing done, and with what object ? Describe the experiment with Prince Bu- pert's Drops. 265. What is slag ? Why do oyster-shells remove clinker in a furnace ? 266. What is said of soluble glass ? 267. Of what is earthen- ware made ? Whence comes the reddish color of bricks ? Why did the Egyptians use straw in making bricks ? 268. How is glazing done ? How are finer articles glazed ? 269. What is said of the occurrence of boracic acid? What is borax? CHAPTER XV. METALS. 270. Characteristics of the Metals. Metals as a class of substances have certain general characteristics. 1. In masses they are opaque bodies. It has been thought by some that gold is an exception, for they assert that light is transmitted through it when made into lea.even when the leaf is not so thin as to permit transmission through multitudes of lit- tle openings. 2. Metals are not soluble. It is commonly stated that they are not soluble in water. But it may be said with truth that they are not soluble in any liquid ;* for, as you will see farther on in this book, in those cases in which metals are spoken of as being dissolved, it is not really the metal which dissolves, but a chemical compound is formed with the metal by the liquid, and then this com- pound is dissolved. 3. Metals have more or less of a certain brilliancy, which is termed, whenever it is found in other substances, the metallic lustre. 4. Metals are better con- ductors of heat and electricity than the non- metals, -and most of them have a higher specific gravity. Some of the properties of metals require a closer examina- Certain TymaA^Kte rnqgs excepted. 198 CHEMISTRY. tion, especially malleability, ductility, fusibility, density or specific gravity, and tenacity. 271. Density. Most of the metals are dense, and there- fore heavy substances. The idea of most people is that a metal is of course heavy, and this was the idea also of phi- losophers until Sir Humphrey Davy, in 1807, made his dis- covery that potash and soda are oxides of metals. This is illustrated in an anecdote of Dr. Wollaston, a celebrated English chemist. Davy, just after he had succeeded in ob- taining by a chemical process the metal potassium, of which potash is the oxide, put a bit of it into the hands of Dr. Wollaston, who spoke of it as being quite heavy, and was surprised to learn that it was lighter than water. There is a wide range in the specific gravities of the metals, as may be seen from the following table, which contains a portion of them : SPECIFIC GRAVITIES OP METALS. Sp. Gr. at 15.5 C. Platinum 21.50 Gold 19.50 Uranium 18.40 Mercury 13.59 Thallium 11.90 Palladium 11.80 Lead 11.45 Silver 10.50 Bismuth 9.90 Copper 8.96 Nickel 8.80 Cadmium 8.70 Cobalt 8.54 Sp. Gr. at 15.5 C. Manganese 8.00 Iron 7.79 Tin 7.29 Zinc 7.10 Antimony 6.80 Arsenic 5. 88 Aluminium 2.67 Magnesium 1.75 Calcium 1.58 Rubidium 1.52 Sodium 972 Potassium 865 Lithium.. 593 The comparison in this table is made with water, that being considered 1. There is, you observe, a gradual diminution in specific gravity in the list till we come to the last seven. These are very light, three of them are even lighter than METALS. 199 water, and one of them, lithium, being lighter than any known liquid. 272. Color. The colors of almost all the metals are vari- ous shades between the pure white of silver and the bluish gray of lead. Bismuth has a reddish-white color. There are only two metals that have very decided colors gold, which is yellow ; and copper, which is red. 273. Tenacity.- There is great variety in different metals in their tenacity or power of holding together, iron being the strongest and lead the weakest. This quality is tested by using wires of the different metals of the same size and appending weights to them, observing how much each wire can possibly hold without breaking. In the following table the experiments were made on wires one millimetre in di- ameter: Metals. Breaking weight : wires one millimetre in diameter. Lead 3.1 Ibs Tin 6.9 Cadmium 9.5 Aluminium 18.0 Zinc 23.5 Gold 27.0 Silver 29.0 Copper 37.0 Platinum 44.0 (Brass 56.0 Iron 56.5 (Steel 96.0 Relative tenacity. 1.00 2.20 3.06 5.80 7.58 8.71 9.35 11.90 14.20 18.00) 18.20 30.00) 274. Malleability. Malleability, derived from the Latin word for hammer, is the capability of being beaten into leaves. Laminability, from the Latin for leaf, lamina, is sometimes used for the same quality, as exhibited when the leaves are made by pressure rather than by blows, as when iron and other metals are flattened by passing between heavy rollers of steel. More properly it should be used as 200 CHEMISTRY. including both this and malleability, for in either case la* minse or leaves are formed. Gold is the most malleable of all the metals. It has been beaten so thin as to require nearly 300,000 leaves to make an inch in thickness if they could be pressed into a solid mass. A leaf of this book equals forty or more of such leaves in thickness. Some metals are perfectly malleable when cold, as gold, silver, lead, and tin ; while others, as iron and platinum, are only slightly malle- able when cold, but very much so when heated. 275. Ductility. This quality, named from the Latin word duco, to lead or draw, is the capability of being drawn out in the form of wire. It is very nearly allied to malleability. Wires are made small by being drawn successively through smooth conical holes in a steel plate, each hole being a little smaller than the one through which the wire was previously drawn. Dr. Wollaston made a gold wire so fine that one hundred and sixty-one metres (five hundred and thirty feet) of it weighed but sixty-four milligrammes (one grain), and he succeeded in making a wire of platinum six times as fine as this. This, then, is more ductile than gold, while it is not by any means as malleable. 276. Relations of the Metals to Heat. The melting points of the metals, or the degrees of temperature at which they melt, are very different. Thus it requires a much less de- gree of heat to melt lead than it does iron ; and platinum resists the heat of the hottest furnace, and can only be melted in the flame of the oxyhydrogen blow-pipe or the current of a galvanic battery. This metal stands at one extreme in regard to fusibility, while mercury stands at the other. So low is the degree of temperature at which this latter melts, or, in other words, so little heat is required to melt it, that it is in the solid state in no weather except that of winter in the arctic regions. Many metals are quite volatile that is, capable of being made to fly off in vapor METALS. 201 by the application of heat ; some of them at quite a moder- ate temperature. Thus mercury, arsenic, and zinc are vol- atile below a red heat. Indeed, at ordinary temperatures mercury is somewhat volatile, and there is always a thin vapor of this metal in the vacuum of the thermometer, so that it is not strictly a vacuum. TABLE SHOWING THE FUSING POINTS OP METALS. F. C. Mercury. 39 39.4 Rubidium 101.3 38.5 Potassium 144.5 62.5 Sodium 207.7 97.6 Lithium 356 180 Fusible Tin 442 235 below a - Bismuth 497 258 red heat. Thallium 561 294 Cadmium 599 315 Lead 626 330 Arsenic. Unknown. Zinc 773 412 Antimony 842 450 fSilver. 1873 1023 Copper 1996 1091 Infusible Gold 2016 1102 22T*"; * 2786 153 red heat. Manganese, f Hi hest heat .Palladium, J Chromium, Titanium, Osmium, [ Infusible in ordinary blast-furnaces. Iridium, Platinum, 277. Welding. Some of the metals, as they approach to the melting point, become semi-fluid or pasty. This is the case with iron. In this state it can be welded that is, two pieces of it can be made to unite by hammering them to- 12 202 CHEMISTRY. gether. Lead, potassium, and sodium can be welded without being heated, and mercury can be welded when it is frozen. 278. Alloys and Amalgams. Metals unite together to form alloys. Some of the most common of these we will mention. Brass is an alloy composed of copper and zinc, the copper making from two thirds to three fourths of the whole. The color of the mixture is intermediate between the deep color of the copper and the light color of the zinc. What is called pinchbeck is a kind of brass, with a larger proportion of zinc than ordinary brass. What is called German silver is a sort of brass with the addition of another metal, nickel, the whiteness of which gives this alloy its re- semblance to silver. Bronze is an alloy of copper and tin, the latter being commonly one tenth of the whole. Bell- metal is the same, with a larger proportion of tin. Common type-metal is an alloy of lead with different proportions of zinc, tin, bismuth, and antimony. Solders are commonly al- loys of lead and tin. Pewter is tin alloyed with lead or antimony. What is called Britannia ware is a kind of pew- ter. The alloys which various metals form with mercury are called amalgams. A familiar example you have in the silvering of mirrors. The amalgam is formed in this case by pouring mercury upon tin-foil laid over the glass. 279. Nature of Alloys. An alloy is generally considered as a mixture, and not a compound, for two reasons: 1. In making alloys there are no fixed proportions in which the metals must be combined. 2, The qualities of alloys are in- termediate, for the most part, to those of their constituents. Thus the color of brass is intermediate to the colors of the copper and the zinc, and the hardness of type-metal to that of the copper and that of the lead. But there are some marked exceptions to this second characteristic of mixtures, which seem to indicate the existence of some degree of chemical affinity, sufficient to produce decidedly new quali- METALS. 203 ties. For example, an alloy of copper and tin, in the pro- portions of 90 of the former and 10 of the latter, called speculum metal, is as brittle as glass and almost white. Now if it were merely a mixture, its color should be that of copper lightened by the small proportion of tin, as zinc lightens the copper-color in brass, and the tin should give to it but a slight degree of brittleness. A single example more will suffice. There is an alloy which is sometimes used as a source of amusement, for teaspoons made of it will melt in a cup of very hot tea. It is composed of 8 parts of lead, 15 of bismuth, 4 of tin, and 3 of cadmium. If it were only a mixture, the melting point of the alloy would be somewhere between the melting points of its constituents. But in fact it is far below them. Lead must be heated to 330 to melt it, bismuth to 258, tin to 235, and cadmium to 315; but this alloy melts at about 70 that is, 30 be- low the boiling point of water. 280. Ores. The ores of metals are certain compounds from which the metals are usually obtained. These com- pounds are commonly oxides or sulphides. When any metal is found in its uncombined state it is said to be native. Some metals, as gold and platinum, are always found in this state, and therefore, strictly speaking, have no ores, though this word is sometimes loosely applied to them. Such metals are often found alloyed with other metals. Thus gold is usually alloyed with silver, copper, etc. Silver is found in the three conditions, native, alloyed, and com- bined. The word ore is not applied to all combinations of metals, but only to those which are used in obtaining the metals. Thus the carbonate of iron is an ore ; but the car- bonate of calcium, occurring in the different forms of chalk, limestone, marble, etc., is not an ore. So while an oxide of iron is an ore, limestone, the carbonate of calcium, is not. 204 CHEMISTRY. 281. Classification of Metals. Metals may bo divided for the sake of convenience into nine groups, according to their attraction for oxygen and their chemical relations generally : GROUP I. The Metals of the Alkalies: Potassium, Sodium [and the very rare metals Lithium, Caesium, and Rubidium]. GKOUP II. Metals of the Alkaline Earths: Barium, Strontium, and Cal- cium. GROUP III. Metals of the Earths : Aluminium [and the very rare met- als Glucinum, Yttrium, Erbium, Cerium, Lanthanium, Didymium]. GROUP IV. Magnesian Metals. Magnesium, Zinc [Cadmium, and In- dium]. GROUP V. Iron Group. Manganese, Iron, Cobalt, Nickel, Chromium [and Uranium]. GROUP VI. Tin Group. Tin [and the exceedingly rare metals Titanium, Zirconium, Thorinum, Columbium, Tantalum, Molyb- denum, and Tungsten]. GROUP VII. Arsenic Group. Arsenic, Antimony, Bismuth [and Vana- dium]. GROUP VIII. Three Metals not closely related. Copper, Lead [and Thallium]. GROUP IX. Noble Metals. Mercury, Silver, Gold, Platinum [and the accompanying metals Palladium, Rhodium, Ruthenium, Iridium, and Osmium]. Of these forty-nine elementary substances we shall study only twenty-three, the remainder (inclosed in brackets in the above paragraphs) are far too rare and of too little im- portance and interest to engage our attention. Sometimes arsenic and antimony are placed for chemical reasons among the non-metallic bodies alongside of phosphorus, but this is only a matter of taste. The line drawn between the non- metals and the metals is not absolute, but merely a con- venient way of distinguishing them. There is another way of grouping metals often followed, viz., with refer- ence to their atomicity ; but this separates metals which seem to belong nat- METALS. 205 urally in one class, as you see in the following list, where all the metals are thus arranged, the rare ones being in brackets : MONADS. DYADS. TEIAD8. TETRADS. PENTADS. IIEXADB. K Ba [Tl] Ft As Cr Na Sr [In] [PI] Sb [U] [Li] Ca Au [Ir] Bi [W] [Cs] Mg [Bo] [Vd] [Mo] [Kb] Zn [Ru] [Ta] Ag Cd [Os] [Cb] Hg Sn Cu [Ti] [Gl] Pb [Yt] [Zr] [Er] [Th] [La] Al [Dd] Fe Mu Co Ni [Ce] QUESTIONS. 270. What are the chief characteristics of metals? 271. Illustrate the fact that metals are not necessarily dense. Name the heaviest metal and the second heaviest. Name the lightest metal. 272. What three metals have distinct colors? 273. What is meant by tenacity? Which is the least tenacious metal ? Which the strongest? 274. What is meant by mallea- bility ? Which is the most malleable of metals ? 275. What is ductility ? How fine a platinum wire did an English chemist make ? 276. How does a difference of temperature affect metals? Which metals are volatile? Which is the most fusible metal ? Which the most infusible ? 277. What is welding ? 278. What is said of alloys and amalgams ? Of what is solder made? Of what German silver? 279. Is an alloy a true chemical com- pound ? Why not ? What are the ingredients of fusible metal ? At what temperature does it melt? 280. Give in full what is said of ores. 281. Into how many groups may the metals be divided ? What two bodies are sometimes placed among the non-metals ? 206 CHEMISTRY. CHAPTER XVI. GROUP I. POTASSIUM AND SODIUM. 282. Potassium and Sodium. These metals have so great an attraction for oxygen that they are never found native. They occur only in combination, usually as salts. They de- compose water at ordinary temperatures, setting hydrogen free ; this is of itself a sufficient reason for their not existing native. Their oxides and hydrates are exceedingly soluble in water, forming intensely alkaline caustic solutions. They form important compounds with the non-metals and with the principal acids. 283. How Potassium is Obtained. Potassium was origi- nally obtained by Davy by decomposing the hydrate, by means of a galvanic battery. But it is now commonly ob- tained by decomposing potassium carbonate by a process which we will describe. The carbonate and some charcoal .finely pulverized and well mixed are exposed to a white heat in an iron retort, a, Fig. 85 (p. 207). Observe now what the chemical changes are. Potassium carbonate is composed of K 2 CO 3 . This is decomposed, the oxygen uniting with the carbon to form carbonic oxide. We have then formed two things, carbonic oxide and the metal potassium : Potassium carbonate. Carbon. Potassium. Carbonic oxide. K 2 CO 3 + 2C K 2 + SCO Now the heat is so great that the metal is in the state of vapor, and this vapor and the carbonic oxide gas pass out together through the tube, , into the copper receiver, h. The upper part of this receiver is surrounded by a wire POTASSIUM AND SODIUM. 207 Fig. 85. basket, b x c c?, which is filled with ice. The object of this is to condense the vapor of the metal, while the gas, the car- bonic oxide, is allowed to escape through an opening. The condensed metal falls to the bottom of the reservoir into some mineral naphtha. This is a liquid which contains no oxygen, its ingredients being only carbon and hydrogen, and therefore it will not have any effect upon the potassium. There are some minute details in this process w T hich we have omitted in order that the main points may be clear to you. The process is expensive and difficult, and the metal is obtained in small quantities, and therefore it bears a high price. 284. Properties of Potassium. Potassium is so light that it floats on water. It is a white metal with a cast of blue, and is very brilliant in its lustre if a piece be cut so as to expose a fresh surface. But so great is its attraction for oxygen that the cut surface immediately tarnishes from uniting with the oxygen of the air, and if left exposed to 208 CHEMISTRY. the air the oxide absorbs moisture, and very shortly becomes potassium hydrate. It can not be kept in the air at all, and is ordinarily kept in naphtha for the same reason that it is received into that liquid when it is made. It is so soft that it can be worked by the fingers like wax. 285. Potassium Set on Fire by Water. When a little piece of this metal is thrown upon water it instantly decom- poses the water, taking the oxygen to itself to form an ox- ide. Hydrogen, the other ingredient of water, being set free, immediately takes fire, Fig. 86, from the heat which is produced by this sudden union of the oxygen and potassium. The flame of the burning gas is of a beautiful violet color. Fig. so. rpjjjg j s Because the heat changes some of the metal into vapor, and this rises with the burning hydrogen. As the metal burns it runs about on the surface rapidly. This is owing to the hydrogen gas which is constantly devel- oped from the water, the steam produced from the water by the heat, and the vapor of the metal. These act on the lit- tle bit of potassium as the gases of burning powder do on a rock. The motion is irregular, because the production of the gas and steam and vapor is going on upon all sides of the piece of metal. The results of this energetic action are potassium hydrate and free hydrogen ; the latter, however, immediately burns, i. ., unites with oxygen, forming water. K+H 2 O=:KHO+H and H 2 +O=H 2 O. The same phenom- ena and results occur if potassium be thrown upon ice. So strong is its attraction for oxygen that the coldness of the ice makes no difference. 286. Caustic Potash. What is commonly termed caustic potash is a hydrate of potassium, KHO. So strong is the disposition of the oxide of potassium to become hydrated, that the anhydrous oxide can be obtained only by exposing the metal potassium to air or oxygen that is perfectly dry. POTASSIUM AND SODIUM. 209 This is of course an expensive process, as potassium is a costly metal. And, besides, this anhydrous oxide rapidly becomes hydrated on exposure to common air by attracting its moisture. The hydrate is a white solid. It has a soapy feeling, owing to its dissolving the cuticle, forming with it a kind of soap. It is a strong caustic, decomposing and dissolv- ing the flesh, and making with it a soapy jelly. It eagerly absorbs water from the air, and becomes dissolved in it. It can therefore be kept in its solid state only by keeping it shut in from the air. It can be dissolved in half its weight of water. It has strong purifying powers, and hence is used in making soap, which will be spoken of particularly in an- other part of this book, when we show what the chemical union is that it forms with fatty substances. This and the other alkalies turn reddened litmus solution blue, as stated in 80. 287. How Potash is Obtained. Neither potassium nor po- tassium hydrate occur native, but are always found com- bined with acids forming salts, as potassium chloride, car- bonate, nitrate, etc. Thus combined it is a very abundant substance in nature. Potassium carbonate abounds in veg- etables, and the name potash comes from the pots in which the vegetables from which it was obtained used formerly to be burned, the alkaline carbonate remaining with the ashes at the bottom of the pots. It is from this carbonate that the caustic potash is ordinarily obtained. The carbonic acid can not be driven off by heat, but it can be taken away by some substance which has a stronger affinity for it than the potash has. Such a substance is lime. This added to a solution of potassium carbonate in proper quantity takes the carbonic acid, forming calcium carbonate, and leaves the potassium hydrate free in solution. On evaporating this solution, by heating it in a basin of iron, we obtain caustic potash : 210 CHEMISTRY. Potassium ^ i v j t Calcium Potassium carbonate. Calcmm W ie ' carbonate. hydrate. K 8 CO 3 + CaII 2 O 3 CaC0 3 + 2(KHO) The same thing is done in part in the common leach-tubs. Lime is put into the lower part of the tub, so that as the dissolved carbonate of potash comes down a part of it is deprived of its carbonic acid, and therefore becomes caustic potash. The lye thus produced is then a solution of the caustic potash and the carbonate together. 288. Potassium Carbonate, K 2 CO 3 . If a lye be obtained from wood-ashes, and be evaporated to dryness, we .have in the mass which is left the common crude potash of com- merce. There are in this many impurities mingled with the potassium carbonate, for there are other soluble salts in the ashes which appear in the lye. Pearlash is this common potash partially purified from these impurities. Potassium carbonate is decidedly alkaline, having an alkaline taste, and turning red litmus paper blue. It has to some little extent the cleansing power of caustic potash. Though quite insoluble in alcohol, it is very soluble in water, though not so much so as potassium hydrate. It dissolves in twice its weight of water, while potassium hydrate requires only half its weight of water to dissolve it. It is a very deliquescent salt, and therefore to preserve it dry it must be kept in well- stopped bottles. 289. Experiment. You learned in 287 that although no degree of heat can drive away carbonic anhydride from po- tassium carbonate, it can be taken away by a substance which has a stronger affinity for it than potassium has, as, for example, lime. It can also be driven off by any acid stronger than carbonic acid. Such an acid we have in acetic acid, the acid of vinegar, as may be shown by the simple experiment represented in Fig. 87 (p. 211). Put a teaspoonf ul or more of pearlash into a tumbler containing POTASSIUM AND SODIUM:. 211 vinegar. There will be an effervescence, because the acetic acid expels the car- bonic anhydride and forms potassium ace- tate. As the gas fills the tumbler it will extinguish a burning taper introduced into it. 290. Saleratus. This is the bicarbonate of potash, or, strictly speaking, hydro- potassium carbonate, KHCO 2 , containing precisely twice as much carbonic acid as the common car- bonate. It is formed by passing carbonic anhydride through a cold solution of potassium carbonate, and then evapo- rating the solution. On heating the hydro-potassium car- bonate, the extra amount of carbonic acid may be driven off. It therefore loses some of its carbonic acid if it be dis- solved in hot" water ; or, rather, some of it is converted into the carbonate, and you have in the solution a mixture of the two salts. The amount of carbonic anhydride in this salt makes it useful in raising bread and cake. The acid which is employed with it takes the potash to itself, and sets free the gas, which by its expansive force puffs out the dough, forming in it innumerable air-cells, and thus makes it " light." The acid which is in sour milk is as good as any other for this purpose. 291. Potassium Nitrate, or Saltpetre. This salt, also called nitre, is of special interest to us as being one of the ingre- dients of gunpowder. It is a natural product in some soils in hot climates, as in India and South America. The man- ufacture of potassium nitrate is a curious chemical process. First a calcium nitrate is produced in the following manner: Animal substances, flesh, hides, etc., are mixed with lime and earth, and this mixture is moistened and left to putrefy. Ammonia results, the elements of which, nitrogen and hy- drogen, unite with the oxygen of the air to form two things 212 CHEMISTBY. water and nitric acid. You see how this is. The oxy- gen unites with the hydrogen of the ammonia to form water, and with its nitrogen to form nitric acid. Then as lime is ready on the spot, the acid at once unites with it, forming calcium nitrate. This is obtained in solution from the mass, and converted into potassium nitrate by treating with potassium carbonate. Insoluble calcium carbonate is precipitated, and potassium nitrate goes into the solu- tion. 292. Gunpowder. Gunpowder is composed of potassium nitrate, charcoal, and sulphur, each carefully ground, and the three well mixed in proper proportions. The effectiveness of saltpetre as a constituent of gunpowder depends on the fact that it quite readily parts with its oxygen gas, which constitutes nearly one half of the salt. Bloxam thus ex- plains the chemistry of the explosion of gunpowder: "The oxygen of the saltpetre converts the carbon of the charcoal chiefly into carbonic anhydride, part of which assumes the gaseous state, while the remainder combines with the po- tassium of the nitre to form potassium carbonate. The greater part of the sulphur is converted into sulphuric acid, which forms sulphate of potassium. The chief part of the nitrogen contained in the potassium nitrate is evolved in the uncombined state." Several other substances are form- ed in small quantity besides those named, among which are carbonic oxide, marsh gas, potassium sulphide, and sulphu- retted hydrogen. The disagreeable odor of burned gun- powder comes from the formation of sulphuretted hydrogen by the action of the moisture of the air upon the sulphide of potassium. The blackening of the surface of the gun- barrel comes from the formation of sulphide of iron. There is no water of crystallization in nitre. If there were any, it would unfit it for being an ingredient in gunpowder ; for this water, being released by the heat, would tend to put . POTASSIUM AND SODIUM. 213 out the fire which the oxygen and carbon are disposed to get up together. 293. The Explosion Explained. If the gases thus evolved by the burning of gunpowder could remain condensed, occupying the same space that they do in the powder, there would be no explosion. But the moment they are evolved they immediately expand so as to occupy a space sev- eral thousand times greater than before. And it is this expansive force which causes the sound of the explosion, and which constitutes the power of the burning powder in propelling balls, rending rocks, etc. It is the con- cussion or blow which the suddenly expanding body of gas gives to the sur- rounding air that causes the detonation. Observe the difference between this explosion and that which occurs when gases unite suddenly to form a liquid, as in the formation of water by the explosion of oxygen and hydro- gen ( 144). In the latter case there is condensation, while there is none in the former. Now if the condensation were the sole cause of the detona- tion, the explanation would be this : A vacuum is created by the condensa- tion, and the air rushing into it from all quarters, and therefore coming to- gether, produces a sound very much as clapping two hands together does. But this explanation will not hold, for there is not only no evidence of col- lapse at the moment of explosion, but, on the other hand, decisive evidence of expansion. For example, when the gases are discharged in the gun, in the experiment in 191, the cork is driven out, showing that there must be expansion at the first, although eventually there is condensation. But how is this expansion produced ? It must come from the fact that the water is formed in the midst of the great heat which always attends the combustion of oxygen and hydrogen together, and is therefore steam largely expanded, to be condensed, however, at the next instant. Whether this condensation has any agency in the production of the sound is uncertain. 294. Sodium. This is a soft, light metal, somewhat re- sembling potassium, and, like it, never occurs in a free state in nature owing to its powerful attraction for oxygen. This attraction is not quite so strong as in the case of potassium ; so when sodium is thrown upon cold water it runs about with a hissing sound, but does not usually set fire to the hydrogen evolved. By using hot water, the sodium will set the hydrogen on fire, which then burns with a bright 214 CHEMISTRY. yellow flame. Compounds of sodium are most abundant in nature. 295. Experiment. A very neat experiment can be tried showing the decomposition of water by sodium. Boil some water for about fifteen minutes in order to expel the air from it, and after it is cool fill a bowl and a test-tube with it. Close the test-tube with the finger, and invert it under the water in the bowl, as seen in Fig. 88. Throw a bit of sodium on the wa- ter, catch it witli a spoon of wire gauze, and thrust it quickly to the opening of the test- tube, and disengage it from the spoon by turning it over. As it is lighter than water, it will rise at once to the top of the tube, and there will busy itself in decomposing the water. By taking the oxy- gen of the water and half the hydrogen the sodium becomes sodium hydrate, and the rest of the hydrogen, being thus set free, accumulates in the tube, forcing down the water that is in it. When the sodium has all disappeared, close the tube with the finger, and remove it from the vessel. If now, holding the tube with its, opening upward, you apply a light to it, the hydrogen will burst into a flame. 296. Common Salt. The chloride of sodium, NaCl, is the most abundant and important of the compounds of this metal. This salt is composed of two elements that are en- tirely different from the compound which they form. One of them is a gas, which is so suffocating that no one can breathe it undiluted and live. The other is a metal, which has such an affinity for oxygen that if it were introduced into your mouth it would set the moisture there on fire in seizing its oxygen. And yet the compound which these two elements make is a very mild substance, which we take into our mouths every day in our food. It is most widely dif- fused in the animal and vegetable as well as the mineral POTASSIUM AND SODIUM. 215 world. It all originally comes from the mineral world, and being absorbed from the soil by plants, through them it gets into the blood of animals by their food. What its special uses are in animals, beyond the fact that no food can be digested without it, we know not; but that it is essen- tial its constant presence in the blood shows. Salt is suffi- ciently soluble for all practical purposes. It does not deli- quesce easily, troubling us in this respect only when the air happens to be very damp. Unlike most other salts, it dis- solves almost equally well in cold and hot water. It is scarcely soluble at all in alcohol. It crystallizes in the,form of cubes. Sometimes the crystals have an arrangement which is hopper-shaped, as represented in Fig. 89. This is be- cause that which is first formed on the surface sinks a little in the solution, and then there is an addition upon its outer Fi s- edge all around; and this goes on continually, the outer edge all the time enlarging, and the solid salt all the time sink- ing as it increases. The upper edge is during the whole process just at the surface, evaporation adding continually to it. 297. Decomposition of Salt. Salt is decomposed in many chemical operations, but its elements are so firmly united that it is by no means easily decomposed. Heat, for ex- ample, can not drive off the chlorine, as it does carbonic anhydride, from limestone. Most of the substances with which salt is apt to come in contact can not decompose it. Strong as is the attraction of oxygen for sodium, it can not take it away from chlorine. If now, on the other hand, salt were easily decomposed, as it circulates by means of water constantly among a great variety of substances in the sea, in the soil, and in the fluids of vegetables and animals it would be a source of continual danger. The evolution of 216 CHEMISTRY. the suffocating chlorine, which would take place here and there, would produce the most disastrous results. 298. Localities of Salt. While salt is so widely diffused, there are some localities where it is found in great abund- ance. There are extensive beds of it in Spain, in some cases rising in hills three or four hundred feet high. The same is true of the north part of Africa. Then there are extensive beds in various parts of the continent of Europe, in Cheshire, England, in Persia, China, India, and South America. The most remarkable salt-mines are in Prussia, Poland, and Hun- gary. Some deposits have been found in this country, in Virginia and Louisiana. There are extensive salt lakes in Africa and South America. In this country there is the famous Great Salt Lake, on a height among the Rocky Mountains, 4200 feet above the level of the sea. There are in this country some salt springs which are very productive. The most celebrated are those at Salina and Syracuse, the latter producing annually five millions of bushels of salt. 299. Modes of Obtaining Salt. The rock-salt is sometimes nearly pure, as at Norwich, in Cheshire, England, where large masses from five to eight feet in diameter are found, and it is prepared for use by crushing between rollers. Commonly, however, it is impure, and to purify it the salt is dissolved in water; and when the impurities have settled, the solution is drawn off and evaporated, that the solid salt may be obtained. In this country the salt is gathered by evaporating the brine which is flowing continually in. For this purpose wells are made from 50 to 150 feet deep, and the brine, as it is pumped up, is conducted by troughs to large boilers. Sometimes the evaporation is left to occur without the application of heat, by exposing the brine to the sun in large shallow vats. This process is often made use of in hot climates for obtaining salt from sea-water. A number of extensive shallow basins having a smooth bot- POTASSIUM AND SODIUM. 217 torn of clay are made near the sea, all communicating with each other. The water is let into the one adjoining the sea at high tide, and when they are all filled it is shut off. The sea-water affords a bushel of salt to every 300 or 350 gallons, while the brine from the best springs gives a bushel to every 40 gallons. 300. Amount of Salt in the Sea. About one thirty-sixth part of sea-water is common salt. The proportion in the best of our salt springs is one seventh ; in the water of the Great Salt Lake it is over one fifth ; and in the Dead Sea it is even more than that. The whole amount of salt in all the seas and oceans of the earth is estimated to be at least five times the mass of the Alps. It is enough to cover an area of seven millions of square miles with a layer a mile in thickness. 301. Sodium Carbonate, Na 2 CO 3 . This salt is contained in the ashes of sea-plants, as the carbonate of potassium is in those of land-plants ; and originally it was obtained almost wholly from that source by lixiviation that is, by making a lye. But it is now obtained entirely, because more easi- ly, from common salt by certain chemical reactions, which are somewhat complicated ; briefly, however, the process is as follows: (1) Sodium chloride is heated with sulphuric acid, forming sodium sulphate, or, as it is technically called, "salt cake;" (2) this is mixed with coal and limestone, heated in a furnace of peculiar form, and thereby converted into very crude sodium carbonate ("black ash"); (3) this is then purified by solution in water and crystallization (" soda ash "). During the first step, the manufacture of salt cake, immense quantities of hydrochloric acid gas are given off, which are condensed in water. During the sec- ond step abundance of calcium sulphide is formed as a waste product. The importance of this manufacture will be faintly ap- K 2 1 8 CHEMISTRY. predated by learning that 200,000 tons of "soda ash" (crude sodium carbonate), worth ten million dollars, are made an- nually in Great Britain alone. Carbonate of soda, when crystallized, has a remarkably large amount of water com- bined with it 63 parts in every 100. When it is wholly anhydrous that is, when it has lost all its water of crystal- lization it is of more than twice the strength of the crys- talline salt. If the crystals be heated, they fuse in their own water of crystallization. Many mineral waters contain con- siderable of this salt. 302. Sodium Bicarbonate. This salt is, strictly speak- ing, hydro-sodium carbonate, NaHCO 3 . It is much used in making soda-powders. The powder in the blue paper is the bicarbonate of sodium, while that in the white paper is tartaric acid. When these are dissolved in water in separate tumblers, and the two solutions are poured together, the tartaric acid at once seizes the soda, forming tartratc of sodium, and the carbonic anhydride, set free, effervesces strongly. The same effect is produced if you mingle the two powders intimately, and then throw the mixture into the water. 303. Sodium Sulphate, or Glauber's-Salt, Na 2 SO 4 -f 10lI 2 O. This salt received the name of Glauber's-salt because it was first obtained by means of a chemical process by a Ger- man chemist of that name. It occurs in nature, but not abundantly, except in a few localities, one of which is a cave in the island of Hawaii, from which the natives gather it for medical use. Ordinarily it is obtained by the action of sulphuric acid upon common salt. More than half of this salt in its crystalline state is water, and exposed to the air the crystals effloresce, and fall to powder. There is another sodium sulphate containing less sodium, NaHSO 4 ; this is formed when the sulphuric acid is used in excess. It has a very acid reaction. POTASSIUM AND SODIUM. 219 304. Borax. Chemically this substance is sodium bibo- rate. It is found native in some of the lakes of Asia and of California, and is also prepared by neutralizing with sodi- um carbonate boracic acid obtained from hot springs in Italy. It contains half its weight of water of crystalliza- tion, having the composition Na 2 B 4 O 7 -f 10H 2 O. Borax is much used in the trades for soldering. If you hold with pincers over a spirit-lamp a piece of copper on which are placed a bit of tin and of iron wire, the tin will melt, but will not adhere to either metal. But if you smear the three metals over with a paste made of moistened borax, and repeat the experiment, you will find that the wire is firmly soldered to the copper. The explanation is this : Metals will adhere to each other only w r hen they have a pure surface ; but heating them always produces at once a film of oxide, and so prevents their adhering. Now the borax serves to keep the surfaces bright by forming with this oxide a sort of melted glass, which is easily pushed aside by the melted solder. There are various substances used in soldering, and they all act by removing in some way the oxides produced by the heat. 305. Soda Saltpetre. This salt, sodium nitrate, NaNO 3 , resembles common saltpetre. It is found in large quanti- ties in South America, where extensive plains are covered with it, and it is exported to other countries under the name of Chili saltpetre. It has the same amount of oxy- gen in it that nitre has, and parts with it as readily, as is shown by its brisk deflagration on glowing coals. But it will not answer in place of nitre in gunpowder, simply be- cause it is strongly disposed to attract water from the air. Keeping the powder dry would be difficult if one of its ingredients be deliquescent. 306. Ammonium. With the group of metals we are study- ing, the salts of ammonium may be conveniently ranged. 220 CHEMISTBY. The alkaline gas ammonia is composed, you remember, of hydrogen and nitrogen, or is NH 3 . Now a solution of this gas in water acts like the hydrate of an alkaline metal, combining with acids to form crystallizable salts. This analogy has caused chemists to conjecture that, since NH 3 -f H 2 O is the same as NH 4 HO, there is a metal NH 4 , of which NH 4 HO is the true hydrate, just as KHO is the hydrate of potassium. This compound metal reminds us of cyanogen, which, you remember, was a compound also, and was called a radical. Note that if there be an ammoniacal metal, it is not an element, as all other metals are, but a compound. It is composed of nitrogen and hydro- gen, just as is the ammoniacal gas, and it differs in composition from this gas only in having one third more hydrogen in it. Though no one has ever succeeded in obtaining this metal, all chemists seem to believe in its existence. The evidence on which this belief is based is twofold. First, the salts of ammonia are so much like other salts that have a metallic base that it would be a very strange thing if they did not also have such a base. Thus in sal ammoniac we have a salt so similar to other salts that we should expect to find, as we do in them, that one of the constituents is a metal. But it is composed of three gases chlorine, nitrogen, and hydrogen. It is supposed, therefore, that as common salt is composed of chlorine and the metal sodium, so this salt is composed of chlorine and a metal ammonium, the nitrogen and hydrogen being so combined as to act in this latter capac- ity. But by whatever method the chemist separates the chlorine from this combination, the metal eludes his grasp, and he gets only nitrogen and hy- drogen, each by itself. The evidence, therefore, that there is a metal here is incomplete. But there is, secondly, another proof of a more decided character. If sal ammoniac that is, chloride of ammonium be mixed with an amalgam of mercury and sodium, a change takes place resulting in the formation of common salt, or chloride of sodium, and an amalgam different from that which was put into the mixture. How is this ? The sodium has left the mercury to unite with the chlorine of the sal ammoniac. What has taken its place in the amalgam? Something from the sal ammoniac, and that something must be a metal, for nothing but a metal has ever been known to form an amalgam with mercury. The proof, therefore, is quite decided that sal ammoniac is a chloride of a metal, and therefore its proper name is chloride of ammonium. POTASSIUM AND SODIUM. 221 307. Ammonium Salts. This hypothetical metal forms a whole series of important salts. Thus we have ammonium sulphate, ammonium nitrate, which was used in the prepa- ration of laughing-gas, ammonium phosphate, ammonium carbonate, etc. This last-named salt is the common sal vol- atile of the pharmaceutist, used as smelling-salts. It is so volatile that it slowly passes away in the air in the form of vapor. It is evolved in the decay of all animal and vegeta- ble substances that contain nitrogen, and gives the peculiar pungent odor to the stable and the manure heap. As pro- duced in manures and brought down from the air in the rain, it is a valuable agent in vegetation, and will be consid- ered in this light in another part of this book. QUESTIONS. 282. Why does potassium never occur native ? 283. How is potassium obtained ? Write the equation showing the reaction. 281. What are the properties of potassium ? Under what liquid is it kept ? 285. What hap- pens when potassium is thrown into water ? Explain. 286. What is the composition of caustic potash ? 287. How is it obtained ? 288. How is potassium carbonate made ? What are its properties ? 289. How does acetic acid act on potassium carbonate ? 290. What is saleratus ? What raises bread and cake? 291. Where does saltpetre occur? How is it made ? 292. Of what is gunpowder made ? Explain the chemistry of the explosion. 293. Whence comes the power when gunpowder is burned? Whence the noise ? 291. Mention the properties of sodium. 295. De- scribe the decomposition of water by sodium. 29G. What is the most abun- dant and useful compound of sodium ? What is said of it ? 297. What would happen if salt were easily decomposed ? 298. Mention the principal localities of salt deposits. 299. Describe the modes of obtaining salt. 300. What is said of the amount of salt in different kinds of salt water? 301. Name the three steps in the manufacture of carbonate of sodium. How much water of crystallization does it contain ? 302. What is hydro-sodium carbonate? 303. What is Glauder's-salt ? 301. What is borax, and whence comes it ? What is the philosophy of its use by blacksmiths ? 305. What is said of sodium nitrate ? 30G. Explain what is said of the ammonium theory. 307. Name some ammonium salts. 222 CHEMISTRY. CHAPTER XVII. GROUP II. BAKIUM, STRONTIUM, AND CALCIUM. 308. Barium and Strontium. These metals do not occur native, their properties being in this respect much like those of Group I. Barium salts are widely distributed, but not in very great quantity. Strontium compounds are comparatively rare. Both occur as sulphates and car- bonates. Barium sulphate or larytes is used to adulter- ate white-lead paint. Barium salts are poisonous. Bari- um nitrate is used in making the green fire of fireworks, and strontium nitrate for the red fire. AVe will give you a receipt for a red fire if you will be careful in making it : Take 80 parts of dry strontium nitrate, 22 of sul- phur, and 5 of lampblack ; mix these intimately in fine powder ; then add 20 parts of potassium chlorate cau- tiously and without rubbing. Mix well on paper. This burns with a brilliant crimson flame. Make no more than you want to burn, for it is dangerous to keep it. 309. Fire Under Water. If this mixture be put into a paper case, A, well stopped with varnish at the end, and then, after being set on fire, be introduced into a jar of water, CC, it Fig. so. w ill continue to burn under water, BARIUM, STRONTIUM, AND CALCIUM. 223 the red flames making a brilliant display. B is a piece of lead pipe fastened with copper wire to the case to hold it, with its orifice downward. The oxygen in this mixture is contained in the potassium chlorate and the strontium ni- trate, while the sulphur and carbon are the combustible substances. The red color is given to the flame by the strontium nitrate. 310. Calcium. This metal has no interest for us, but its oxide and its hydrate, as well as many other of its com- pounds, are of the greatest importance. Quicklime is cal- cium oxide, CaO ; slaked lime is calcium hydrate, CaIT 2 O 2 . We often use the word lime when we ought strictly to say calcium. Lime is never found in nature, but abounds in combination with acids. In this way it forms more than half of chalk, limestone, and marble, is the base of plaster of Paris and alabaster, and constitutes the greater part of the mineral portion of the bones of animals. Lime is con- sidered as occupying a middle place between the alkalies and the earths. It is, therefore, called an alkaline earth. The earths are insoluble, the alkalies are very soluble, but the alkaline earths are but sparingly soluble. The alkaline earths are also midway between the earths and the alkalies as to being caustic, for they are somewhat caustic, while the alkalies are very much so, and the earths not at all, but perfectly inert. That lime is somewhat caustic you can perceive by the feeling occasioned when you rub a little of it, made into paste, between your fingers. It is from this caustic quality that the milk of lime that is, lime dif- fused in water is used to remove the hair from hides. So, also, lime is often mixed with weeds to quicken their de- composition. 311. Manufacture of Lime. Quicklime is obtained from the carbonate in its various forms chalk, limestone, marble, oyster-shells, etc. simply by the application of strong heat, 224 CHEMISTRY. the carbonic acid being driven off. The operation is car- ried out on a large scale in a kind of furnace called a lime-kiln, shown in Fig. 91. The decomposition takes places at a lower temperature in a current of air than otherwise, and this is effected by building a tall kiln. Fig. 91. How simply heating their bodies effects their decom- position we will explain : Heat expands all bodies, or, in other words, puts the particles in them farther apart. But, as you have already learned, it is necessary that particles of different substances should be in immediate contact, or exceedingly near to each other, in order that the attractive force may come into action. Now it is supposed that in the case of the carbonate of lime the heat, in expanding it, puts the particles of the carbonic anhydride at such a dis- BARIUM, STRONTIUM, AND CALCIUM. 225 tance from the particles of the lime that they are out of the range of their attraction, and so they escape. The ef- fect of heat is, you see, just opposite to that of solution, the latter bringing particles more nearly together. The carbonate of lime is quite in contrast with the carbonate of potassium in this respect, for no heat, however great, can drive the carbonic acid away from the potassium hy- drate, as you learned in 287. And yet, strange as it may seem, lime, as you also there learned, can take away the carbonic acid from the potassium carbonate. 312. Attraction of Lime for Water and Carbonic Anhydride. The eagerness with which lime unites chemically with water is shown in its slaking. So great is the heat pro- duced by the rapid union that takes place that even gun- powder has been ignited by it. It very readily ignites phosphorus. Put a little quicklime in a heap upon a board, and place on the top of it a bit of phosphorus. To avoid wetting the phosphorus moisten the heap at the bottom, and as the moisture spreads through the lime it will very soon produce heat enough to set the phosphorus on fire. Another experiment, showing the amount of heat produced, may be tried as follows : Put some lime in a bowl, and, moistening it, place a glass bell- jar over it, Fig. 92. At first the steam which rises from the slaking lime will be condensed upon the inside of the glass. But soon the heat will be so great that the - steam in the bell-jar will form a transparent atmosphere in it. If now you raise the Fig. 92. glass, the steam as it escapes loses its transparency, and becomes a thick cloud, because it is changed into a kind of fog by the condensing influence of the cold air. By the union of lime with water there is formed a hydrate of lime, there being in every 100 grammes of dry slaked lime about K2 226 CHEMISTRY. 25 grammes of water. Lime has also a considerable affinity for carbonic acid. When, therefore, it is exposed for some time to the air, it unites with the carbonic anhydride of the air as well as its moisture, and air-slaked lime is there- fore a mixture of hydrate and carbonate of lime. 313. Solubility of Lime. While lime has so great an af- finity for water, the dry substance which results after its thirst is slaked is very sparingly soluble. It is in strong contrast in this respect with the alkalies. While potas- sium hydrate is soluble in half its weight of water, the hydrate of lime requires one thousand times its weight of water to dissolve it. It is very remarkable that cold water will dissolve more of it than warm. Lime-water, as the solution of lime and water is called, is sometimes used as a medicine. With sweet-oil it makes a soapy mixture which is often used as an application to burns. 314. Mortar. The most important use of lime is in mak- ing mortar. As glue holds pieces of wood together, so does mortar bricks and stones. In the making of mortar w r e stir sand, lime, and water together, and the sand becomes in- timately mixed with the hydrate of lime while it is form- ing. As the mortar becomes dry by the evaporation of all the water that is not used up in the formation of the hydrate, there occurs also another chemical change car- bonic anhydride is attracted from the air, and unites with a portion of the lirne ; so that we have in the mortar a mixture of carbonate and hydrate of lime, which has more firmness than either of these substances separately. Then, again, mortar becomes hard gradually, from a chemical action between the sand and lime, whereby silicate of lime is formed. The sand serves to give both body and firm- ness to the mortar. When mortar is used as plastering, hair is added, the fibres serving to hold the mortar more thoroughly together. BAEIUM, STRONTIUM, AND CALCIUM. 227 315. Carbonate of Calcium, CaCO 3 . This salt presents it- self in various forms chalk, common limestone, and the beautiful granular marble. The mineral calcite, which sometimes appears in large, magnificent crystals of various colors, is one of the forms of this salt. The variety of form which this salt presents is analogous to the variety that we so commonly see in sugar, which is perfectly crys- talline in rock -candy, like calcite, imperfectly so in the granular loaf-sugar, like marble, and without any trace of crystallization when pulverized finely, like common chalk. Carbonate of lime is very abundant, and is in fact one of the chief constituents of our earth. There are hills and ridges of mountains built up with limestone. In a pul- verized state it exists extensively in the soil, in some dis- tricts being very prominent, making what is called a cal- careous soil. Oyster- shells, and the shells of shell-fish generally, are composed almost entirely of carbonate of lime. So are the shells or frame-work of many very small animals, some of them exceedingly minute, and yet, by their numbers, occupying much space in the earth. The skeletons of the coral animals, of which so much of some portions of the earth has been built up, are made chiefly of this salt. 316. Depositions of Carbonate of Calcium. If you breathe into lime-water there will be precipitated carbonate of cal- cium, or chalk, as you learned in 125. If, after this pre- cipitate is formed, however, you continue to breathe into the lime-water, some of the precipitate will disappear, a part of it being dissolved again. How is this, when carbonate of calcium is insoluble in water ? It is because you have now something more than water in the vessel ; it is water considerably charged with carbonic anhydride. Now, while pure, simple water can not dissolve carbonate of calcium, water charged with this gas can do it. Hence the 228 CHEMISTRY. disappearance of a part of the precipitate. If now you let the liquid stand for a time exposed to the air, it becomes turbid again, because the carbonic anhydride escapes, which takes from the water its power of keeping the car- bonate in solution, and this salt is therefore again pre- cipitated. And here we have a key to the explanation of some very interesting phenomena. Water, as it makes its way among the particles of the soil, finds carbonic acid as one of the results of decay, and dissolves it ; and there- fore, as it issues from the earth in springs, it contains not only carbonic acid, but also carbonate of lime, which it has found in the soil and dissolved by the aid of the acid. But as soon as the water is fairly exposed to the air the carbonic anhydride begins to escape from it, and ac- cordingly the carbonate of lime begins to be deposited. Hence comes the grand difference between the hard water of springs and wells, and the soft water that runs in brooks and rivers. The water as it runs along exposed to the air has discharged much of its carbonic acid upward, and therefore precipitated much of its carbonate of lime down- ward. Water can be more thoroughly freed of its car- bonic acid, and therefore of its carbonate of lime, by boil- ing it than by 'mere exposure to the air, which explains the considerable deposition of this salt in large steam-boil- ers when hard water is used, collecting gradually as a hard crust. Such incrustations are of course particularly apt to occur in limestone districts. 317. Stalactites and Stalagmites. The roofs of caverns in limestone regions often have stalactites of carbonate of lime suspended from them like icicles in shape. The rea- son is obvious. The water, as it percolates through the soil above the cavern, becomes charged with carbonic acid from decaying vegetable matter, and therefore dissolves some of the limestone ; and then., as it is exposed to the air BAKIUM, STRONTIUM, AND CALCIUM. 229 in dripping, losing in part its carbonic acid, and therefore its solvent power, deposits some of its carbonate, which ac- cumulates gradually in the stalactite form. But as the solvent power of the water is not all lost, some of the car- bonic acid still remaining, the water, as it falls upon the floor of the cavern, loses another portion of the acid, and so deposits more of the lime in eminences called stalag- mites. These are of course less slender and pointed than the stalactites. You see the same difference in form be- tween icicles and the accumulations below them. There are splendid displays of these formations in many of the caves of the earth. Some of the most celebrated are, Weyer's Cave, in Virginia ; the Cave of Thor, in Derby- shire, England ; and the Grotto of Antiparos, on an island of the same name in the Grecian Archipelago. A part of this grotto is represented in Fig. 93. You can get an Fig. 93. The Grotto of Antipnros. 230 CHEMISTRY. idea of the size of these formations, the accumulations of constant dripping for ages, by the human figure at the foot of one of them. 318. Carbonate of Calcium in the Sea. Though rain-water may be free from carbonate of lime, water which has per- colated through the earth is never wholly free from it. Though it may deposit it as it comes out of the springs and runs along brooks and rivers to the ocean, yet even when, it arrives there it retains some of it in solution, for it has still dissolved in it some of the carbonic acid which it derived from the soil. If it were not so, the shell-fish would have no material for the formation of their external skeletons, or houses, as they may more properly be called. 319. Sulphate of Calcium, CaSO 4 . The common name of this salt is gypsum. It has also the name of plaster of Paris, which it received from the fact that it was first used in the form of plaster in Paris, there being immense quantities of it in the neighborhood of that city. It is a white and quite soft mineral, occurring in various forms, some of them very beautiful. One of its forms, alabaster, which is snowy white, is cut into vases and ornaments of various kinds. Sometimes it is crystallized in exceedingly thin leaves, laid together so nicely that a multitude of them make a white crystal clearer than the clearest glass. Then there is the satin-spar, so called from the splendid lustre of its fibrous arrangement. Gypsum is about one fifth water. This wa- ter can be driven off by heat, and then this powdered an- hydrous gypsum has the property of "setting" with wa- ter; or, in other words, becoming with water a firm, coher- ent, and dry mass. For this purpose it is moistened with water to about the consistency of cream. In this state it can be poured into moulds, or it can be put upon walls as hard finish, the water disappearing as it hardens, partly by evaporation, and partly by becoming a part of the solid, BARIUM, STRONTIUM, AND CALCIUM. 231 dry substance. The hardening takes place quite rapidly. The moistened plaster can also be moulded into casts, plas- ter heads, ornamental work for walls, called stucco-work, etc. It is remarkable that, in making the gypsum anhy- drous, if the heat be carried above a certain point, its affin- ity for water will be destroyed, and there will be no " set- ting" of the plaster. 320. Casts of Coins. Copies of coins and medals can be taken very readily with the moistened plaster. For this purpose put the coin into a paper box, or, if you have not one of the proper size, fasten a slip of paper around the coin, securing the loose end by a little sealing-wax, and pour the plaster in upon the coin. After a few minutes it will become so*hard that both the paper and the coin can be removed. A reversed impression will be formed on the under surface of the plaster. To get from this a real copy of the coin, smear the impression with a very little of a strong solution of soap, having a few drops of oil mixed with it, and then pour upon it some of the plaster. The use of gypsum in agriculture will be spoken of in another part of this book. 321 . A Singular Case. If sulphate of calcium (gypsum) and carbon- ate of ammonium be mingled together in solution, there will result car- bonate of calcium, or chalk, and sulphate of ammonium. Now if we take these two substances thus resulting, and, powdering them finely, mix them together, and expose the mixture to a red heat in a close vessel, we shall have the original sulphate of calcium and carbonate of ammonium pro- duced again. Here we have heat occasioning a chemical process exactly the reverse of that caused in a solution at an ordinary temperature. 322. Chloride of Lime. The salt which sometimes goes by this name, and sometimes by the name of bleaching powder, is a white powder, having the odor of chlorine gas, because this gas escapes from it continually in a small amount. The reason of its escape is that the carbonic an- 232 CHEMISTRY. hydride of the air unites with the lime gradually, thus lib- erating the chlorine. In using this salt for bleaching the gas is liberated by some acid which is applied. The arti- cle to be bleached is first soaked in a solution of the chlo- ride, and then in a dilute sulphuric acid. Here you have chloride of lime and sulphuric acid brought together, and the result is that the acid takes the lime and releases the chlorine. What does the released chlorine do ? Being set free in immediate contact with the cloth, it acts at once upon the coloring matter. The operation is not all done at once; but as strong solutions are apt to injure the cloth, the solutions are made weak, and the articles are moved back and forth from one solution to the other several times. White figures are sometimes made on colored cloth by this bleaching process. The figures are first stamped upon the cloth with a mixture of tartaric acid and gum-water, and then the cloth is soaked in the solution of the chloride. You see what the result is. The chloride is decomposed by the acid, and therefore the chlorine whitens only where the figures are stamped. This bleaching powder is very valuable because we have the bleaching gas condensed in it, a form convenient for transportation, which would not be true of either chlorine gas or chlorine water. 323. Composition of Chloride of Lime. The name which is so universally given to this preparation is a very incor- rect one. It is impossible to have a real chloride of lime, for the chlorine can not be made to unite with an oxide of a metal, but will unite only with the metal itself. If there- fore this salt be a chloride, it must be chloride of calcium, the metal of which lime is the oxide. But it has been found that it is composed only in part of this chloride. It is a mixture of chloride of calcium, calcium hydrate, and a salt called hypochlorite of calcium. This latter salt is a compound of calcium with hypochlorous acid, an acid com- BARIUM, STRONTIUM, AND CALCIUM, 233 posed of chlorine and oxygen. Perhaps the reason that the old name chloride of lime is retained is that it is diffi- cult to fix upon a proper name for this mixture of two salts. Chloride of lime is made by exposing slaked lime, slightly moistened, to chlorine gas ; this is eagerly absorbed by the lime, forming calcium hypochlorite and calcium chloride, while some of the calcium hydrate remains unchanged. The bleaching powder thus prepared is very uncertain as to the amount of its bleaching properties, and these are very liable to be impaired by exposure to air and other circumstances. As offered in the market it varies much in its value according to its age, care in keeping it, and also care in its original preparation. 324. Calcium Phosphate, Ca 3 (PO 4 ) 2 . While carbonate of lime is the mineral out of which all shells are made, the phosphate of calcium, mixed with very small quantities of the carbonate and sulphate and fluoride, forms the mineral portion of bones. It is estimated that the amount of phos- phorus contained in this salt in the bones of a full-grown man is from 500 to 800 grammes. Phosphorus is obtained from bones, and the process is described in 253. As phos- phate of lime exists so largely in animals, it is necessary that it be provided for them in the food that they eat. Accordingly it is present in all cereal grains, in leguminous plants, and many other vegetables, the soil of course fur- nishing it to them. It is not only, then, the animal sub- stance in bones, the gelatine, that makes them a good ma- nure ; but the mineral part is of essential service, to some crops especially, if the soil be at all deficient in phosphate of lime. Calcium phosphate occurs abundantly also in the min- eral kingdom, as you will learn more particularly in the study of Mineralogy, Part III. 234 CHEMISTEY. GEOUP III. ALUMINIUM (ETC.). GEOUP IV. MAGNESIUM AND ZINC. 325. Aluminium. This metal, the base of the oxide alu- mina, though it was unknown until a few years ago, is al- ready used for a variety of purposes. It is a white metal, resembling silver in color and hardness, as well as in its power of resisting the action of air and water, but differ- ing from it greatly in weight, silver being four times as heavy. It is admirably fitted for ornamental purposes, and has already been so employed to a considerable extent. It is very sonorous, and therefore will make good bells. The French government at one time used it for helmets and cuirasses, for which it is well fitted, as it is both light and strong. Formerly this metal was very costly, but in the year 1854 M. Deville, who had charge of the private lab- oratory of the Emperor of France, discovered a process by which it can be obtained in large quantities, and at com- paratively low price. And as silver is four times as heavy, articles can be made of this beautiful metal for less than the cost of silver. 326. Aluminium Oxide, or Alumina, A1 2 O 3 . This earth is the essential ingredient of all clays, and is present more or less in all fertile soils and in many of the slaty rocks. The metal of which this is an oxide is therefore quite abun- dant, and widely diffused in the earth, though it is never found in its metallic state, but is always in combination with other substances. Alumina appears in some beauti- ful forms. The sapphire, which in some of its varieties is, next to the diamond, the most costly of gems, is pure alu- mina crystallized. Blue is the true sapphire color. * When this gem has other colors it receives other names : when red, Oriental niby ; when yellow, Oriental topaz ; when vio- let, Oriental amethyst; and when green, Oriental emerald. ALUMINIUM. MAGNESIUM AND ZINC. 235 The largest Oriental ruby yet found came from China, and is now a jewel in the imperial crown of Russia. Emery is nearly pure alumina. This, besides being used by the ladies in their "emery-bags," is extensively employed in polishing metals and precious stones. 327. Common Alum. In this salt we have sulphuric acid united with two bases, potassium and aluminium, forming a sulphate. It is therefore said to be a double salt, and has the composition Al 2 K 2 (SO 4 ) 4 -f-24H 2 O. It is not a mere mixture of the two salts, but a chemical compound always precisely the same in the proportions of its constituents. The water of crystallization in this salt constitutes nearly one half of it. If it be heated, the escape of this water causes it to foam and melt, and swell up into a large porous mass. This is what is called burnt alum. This salt, like all the salts of aluminium, has an astringent taste. Warm water will dissolve much more of it than cold. It is much used in dyeing and calico-printing for the purpose of fasten- ing the colors, or, in other words, making the colors unite thoroughly with the fibre of the cloth. It is not, however, the alum that does this, but the alumina which is in it. The alum is decomposed in preparing the lakes, or fast col- ors. Thus an infusion of Brazil-wood, with alum dissolved in it, presents a brilliant red color. If now there be added a solution of carbonate of potassium or sodium, a precipitate is produced, which is the alumina of the alum united with the red coloring matter. This dried is the Brazil-wood lake of commerce. In like manner other lakes are prepared from other vegetable coloring substances. The alumina is said to act in these lakes as a mordant, a word which is de- rived from the Latin verb meaning to bite. It is because the compound which it forms with the coloring -matter takes such strong hold of the cloth. Alumina is also em- ployed in the production of those beautiful blue pigments called stnalts and ultramarine. 236 CHEMISTRY. 328. Other Alums. Although there is but one substance which is commonly called alum, the chemist recognizes sev- eral different salts as alums. The common alum he calls potassium alum. Then there is a sodium alum, in which sodium has taken the place of potassium, and the salt is therefore sulphate of aluminium and sodium, Al 2 Na 2 (SO 4 ) 4 -f 24II 2 O. We have also an ammonium alum, in which am- monium takes the place of the potassium, making a sulphate of aluminium and ammonium. There are others which we will not mention. Now in all these different alums the water of crystallization is exactly the same. And what is more remarkable still, the crystals are alike in all these salts. They are therefore termed isomorphous salts, this name com- ing from two Greek words, isos, equal, and morphe, form. 329. Magnesium. This is a white malleable and ductile metal, somewhat resembling aluminium, but far lighter and more readily oxidizable. A wire or tape of this metal burns with a magnificent white light, which is sometimes used for lighting up the interior of buildings for the pur- pose of photographing. Magnesium oxide, hydrate, carbonate, sulphate, chloride, and iodide are all used in the arts. Magnesium oxide, ob- tained by heating the carbonate to redness, is often called calcined magnesia. This carbonate occurs native, but is generally prepared artificially. Mixed with magnesium hy- drate, it forms the magnesia alba of pharmacy. The sul- phate of magnesia was originally called Epsom-salt, be- cause the waters of Epsom Spa, in England, contained so much of it. In its crystalline state, MgSO 4 -fVH 2 O, more than one half of it is water, and it is efflorescent. 330. Other Earths. There are several other earths, but they are all rare, some exceedingly so. One of them, glucina, is one of the constitu- ents of the precious stones called emerald, beryl, and chrysoberyl. Crys- tals of another, zirconia, are in common use in jewelry. ALUMINIUM. MAGNESIUM AND ZINC. 237 331. Zinc. The principal ores of this metal are the sul- phide, the silicate called calamine, the oxide, and the car- bonate. In obtaining the metal, if the sulphide and carbonate are used, they are first roasted, the heat driving off the carbonic acid from the car- bonate, and the sulphur from the sulphide, in the form of sulphurous anhydride. This leaves the ore in the state of oxide. The ore is now mixed with charcoal, and introduced into an iron cruci- ble, a vertical section of which is given in Fig. Fi s- 94 94. The crucible is closed at the top, and has an iron tube passing through a hole in the bottom, and also down through the floor of the furnace in which the crucible is placed. The upper opening of this tube is above the sur- face of the mixed ore and charcoal, and the lower opening is very near to the surface of water in a reservoir. When the heat is applied the carbon, uniting with the oxygen of the oxide, forms carbonic oxide and anhydride, which pass out through the tube and escape. Now as the zinc is vola- tile, it passes out also with them in the form of vapor, but, condensing as it gets in the tube below the fire of the fur- nace, it drops as a liquid into the reservoir of water, where it becomes solid. Zinc is a bluish-white metal. It has but a single oxide, ZnO. It takes fire when heated to a bright red heat, and burns with a brilliant white flame, with a tinge of green. As it burns the oxide formed flies off in flakes, which the alchemists fancifully called lana philosophica, philosopher's wool, and nihil album, white nothing. 332. Carbonate of Zinc, ZnCO 3 . The thin whitish film which forms over the surface of zinc by exposure to air is a carbonate of zinc, the water and the carbonic anhydride of the air both entering into its composition. The carbon- ate of zinc, under the name of smithsonite, is an important ore of this metal. 238 CHEMISTRY. . 333. Chloride of Zinc, ZnCI 2 . This is a white substance which is quite soft, and melts, if heated, a little above the boiling point of water. "When the old names in chemistry were in vogue, this substance, on account of its softness and fusibility, had the name of butter of zinc. It has a great attraction for water, and therefore is active as a caus- tic, a use to which it is appropriated. While it thus de- stroys when concentrated, if diluted it acts as a preserva- tive against putrefaction, and is employed by the anatomist for preserving bodies for dissection. Sulphate of zinc ZnSO 4 sometimes called white vitriol, is a powerful emetic. It crystallizes in long, white needles, and is very soluble in water. It is often obtained in the laboratory as a residue in making hydrogen gas. Zinc, sulphuric acid, and water yielding zinc sulphate and hy- drogen, thus : Zn + H 2 S0 4 = ZnS0 4 + H a 334. Uses of Zinc. Though zinc is quite an abundant metal, it was formerly used but for little else than making brass and pinchbeck. The variety of uses to which it is now applied comes from a discovery which was made in regard to its malleability. When cold it is very brittle; but when heated to within a certain range of temperature (100 to 150 C.), it becomes quite malleable, and may be rolled into thin sheets. It retains the malleability thus acquired after it becomes cold. It is a curious fact that if this metal be carried beyond the range of temperature al- luded to, it becomes brittle again. When in this range it becomes ductile as well as malleable. The discovery of these facts has introduced this metal to very numerous valuable uses. It is now used in the manufacture of many articles which were formerly made of lead, copper, and iron as nails, gasometers, gas-pipes, gutters, roofing, lining for refrigerators and sinks, etc. It is harder and yet lighter ALUMINIUM. MAGNESIUM AND ZINC. 239 than lead. It is cheaper than copper. It is not affected by air and water as readily as iron. Zinc melts at 412, and boils at 1040. At a still higher heat it may be dis- tilled. So-called galvanized iron is merely sheet iron coated with zinc. QUESTIONS. 308. What is said of barium and strontium compounds ? 309. Describe an experiment in which strontium nitrate is used. 310. Where and how does calcium occur in nature? What is quicklime? What is said of al- kaline earths? What of the caustic power of lime? 311. Explain the manufacture of quicklime. How does heat effect this decomposition ? 312. Illustrate the attraction of lime for water, and for carbonic anhy- dride. 313. What is stated as to the solubility of lime? To what uses is lime-water applied? 314. What are the ingredients of mortar? What chemical changes occur in mortar as it hardens and dries ? 315. Under what forms is carbonate of calcium found ? Mention some animals which furnish it.-*-316. Explain the deposition of carbonate of calcium from natural waters. 317. What are stalactites? What stalagmites? Where found? How formed? 318. What is said of calcium carbonate in the sea? 319. What is gypsum? How is plaster made? Explain the "set- ting" of plaster. 320. How may casts of medals be made? 321. De- scribe the mutual reactions of sulphate of calcium and carbonate of am- monium under different circumstances. 322. How is chloride of lime used in bleaching ? 323. Of what is it composed ? How made ? 324. How does calcium phosphate occur in nature ? 325. What are the properties of aluminium ? 326. What is clay ? Name some precious stones containing alumina. 327. Of what is common alum composed? How is it used in dyeing? What is a mordant ? 328. Name some other alums. 329. What are the properties of magnesium ? What is Epsom-salt ? 330. Name some of the rare earths occurring in precious stones. 331. How is zinc obtained? What is "philosopher's wool?" 332 and 333. What is said of the salts of zinc ? 334. What of its uses ? 240 CHEMISTRY. CHAPTER XVIII. GROUP V. MANGANESE, IRON, COBALT, NICKEL, CHROMIUM. 335. Manganese. This metal is never found in nature, and it is rather difficult to obtain it from its ores on account of the great stability of its oxides and its high melting- point. It is remarkable for the number of the compounds which it forms with oxygen. There are six of them. Here follow their names and formulae : 1. Manganous oxide MnO. 2. Manganese sesquioxide Mn 2 O 3 . 3. Manganous manganic oxide Mrt^O 4 . 4. Manganese dioxide MnO 2 . 5. Manganous anhydride MnO.,. 6. Permanganic anhydride Mn 3 O 7 . The first two form numerous compounds. Number 4 we have already used for preparing oxygen. Numbers 5 and 6 are not known in the free state, but their compounds are important; they combine with bases forming manganates and permanganates respectively. Potassium permanganate is used in dilute solution as a tooth- wash. Its solution has a magnificent purple color. It is a powerful oxidizing agent. 336. Iron. Iron when pure is almost white, and is rather soft, but very tenacious. It is quite malleable. It can be made into leaves so thin that it would take over three hun- dred of them to make half an inch in thickness. But even the best of iron found in the market is far from being pure. It contains small amounts of carbon and other substances. Perfectly pure iron is never obtained except in small quan- MANGANESE, IRON, COBALT, NICKEL, CHROMIUM. 241 titles, and by the chemist in his laboratory. The most striking property of iron is its magnetic power. 337. Importance and Abundance of Iron. As iron can be applied to a greater variety of uses than any other metal, it is very abundant. Stockhardt says of it, " If gold is called the king of metals, iron must be deemed by far the most important and useful subject in the metallic realm. It is not only converted into swords and cannons, but into plowshares and chisels, and into a thousand other imple- ments and machines, from the simple coffee-mill to the won- derful steam-engine. It is the ladder upon which the arts and trades have mounted to such an extraordinary height. It is the bridge upon which we now glide over mountains and valleys with the rapidity almost of magic." Besides all this, it is present in all soils and in almost all plants, and is an ingredient of the blood in a large portion of the ani- mal world. Although we understand but little in regard to its influence upon plants and animals, we have sufficient facts to show that, small as its amount is, it is as essential in the chemical operations of the living world as are com- mon salt, lime, and some other substances. 338. Oxides of Iron. There are three oxides of iron : the monoxide, FeO ; the sesquioxide, Fe 2 O 3 ; and the so-called magnetic oxide, Fe 3 O 4 . The first named has not been pre- pared in a pure state owing to the rapidity with which it takes up oxygen and passes to the sesquioxide. It occurs in nature in combination with acids, forming important minerals. Ferrous sulphate, or green vitriol ; ferrous car- bonate, or spathic iron ore ; ferrous sulphide, FeS 2 , also called iron pyrites, are the most abundant. On adding am- monium hydrate to a solution of a ferrous salt, a white pre- cipitate forms consisting of ferrous hydrate, but this imme- diately begins to change in color, passing through green to brownish red by absorption of oxygen from the air, and L 242 CHEMISTRY. becoming ferric hydrate. The second oxide, called sesqui- oxide, forms one of the abundant ores of iron. It is some- times crystallized, as in iron-glance; or compact, as in red iron-stone ; or radiated, as in red hematite ; or earthy, as in red ochre. When mixed with clay it is the clay iron-stone. It is that which gives the red color to so many stones and bodies of earth. The red chalk, so called, used in making: red pencils, is one form of this oxide. This sesquioxide may be prepared artificially by heating ferrous sulphate to redness, or by igniting ferric hydrate, obtained by precip- itating a ferric solution with an alkaline hydrate. Ferric hydrate Fe 2 O 3 .3H 2 O also occurs in nature; in large masses it is the brown iron ore, or limonite, from which the metal can be profitably obtained. Mixed with clay it forms the yellow day iron-stone, yellow ochre, etc. The yellow or brown color of soils and of stones which have been long exposed to the air is owing to ferric hy- drate. The ochrey deposit which is seen always about the edges of chalybeate springs is ferric hydrate, made in this case chiefly from the carbonate, the carbonic acid passing off and leaving the oxide to become a hydrated sesquioxide. Observe the difference in color between the hydrated ses- quioxide and that which is not hydrated ; the former is yel- low, the latter red. The reason that bricks become red by burning is that the water is expelled from the iron rust which is in the clay, and it therefore becomes anhydrous. This term, which is much used in chemistry, means dry, or without water, the prefix an meaning without. Iron rust is the ferric hydrate, 2Fe 2 O 3 .3H 2 O. This water is a part of the dry solid, being combined intimately with its ingredi- ents. It is really, therefore, water solidified without freez- ing. In every hundred grammes of it there are about fourteen and a half grammes of water, and nearly forty grammes of oxygen. Both are condensed in uniting with MANGANESE, IKON, COBALT, NICKEL, CHROMIUM. 243 the iron, the oxygen very much so. As about twenty-seven gallons of this gas are used up in forming a pound of rust, it must be vastly condensed to occupy so little space. This remarkable condensation of oxygen takes place in the for- mation of all the solid oxides. The third oxide, Fe 3 O 4 , is sometimes considered as a combination of the first and the second oxides, FeO.Fe 2 O 3 , and hence is also called ferroso-ferric oxide. This oxide forms no salts, but it occurs in nature very largely, forming an important ore. This is endowed with magnetic proper- ties. The common loadstone is ferroso-ferric oxide. Its color is black, and many dark and green stones owe their color to it. The celebrated Swedish iron is mostly made from it. The scales thrown off from heated iron by the hammer of the blacksmith are formed of this black oxide. 339. Meteorites. Abundant as iron is, it is never found in metallic form except in meteorites, and then it is alloyed with nickel and some other metals. In the large meteorite in the cabinet of Yale College, brought from Texas, and weighing nearly two tons, there is from eight to ten per cent, of nickel, the mixture of the two metals not being uniform throughout. 340. Production of Iron from its Ores. In order to obtain iron from its ores they must be deprived of their oxygen, and of the impurities that are mingled with them. The oxygen is removed by subjecting the ores to intense heat in a furnace with charcoal. This causes the oxygen to leave the iron, and unite with the carbon of the charcoal to form carbonic oxide and anhydride, which fly off. But an- other thing is necessary to remove the impurities, silica, clay, etc. For this purpose limestone is introduced into the furnace, which forms with the impurities a slag or glassy substance, which, as the iron is permitted to run out, floats on the surface of the melted metal, and is raked off. The 244 CHEMISTRY. stream of iron runs off into channels made in sand, and when it becomes cool it forms what is called pig-iron. Fig. 95 represents a common form of the blast-furnace Fig. 95. Blast-furnace. MANGANESE, IKON, COBALT, NICKEL, CHROMIU3I. 245 used. Ore and fuel are dumped in at the top, the material gets hotter and hotter as it descends, reduction of the ore takes place, and the melted iron settles down into the lower part of the tall furnace, whence it is run off from time to time on the inclined plane to the left. The arrangement for the blast of air, by means of which the combustion is accelerated, is seen at the right hand in the lower portion of the picture. 341. Cast Iron. This pig-iron is used for making castings. It is fit for this purpose from having had combined with it in the process above described about five per cent, of car- bon. It is from this addition that the metal runs so readily into the moulds. If it were pure iron, or if it contained much less carbon, it would not do this. Besides, this com- bination of carbon and iron, as it passes from the liquid to the solid state in cooling, increases a little in bulk, and so fills out the mould in every line. This is owing to the crys- tallization which takes place every where in it. Cast iron is very brittle, and is not in the least malleable or ductile. Its hardness and its capability of being cast in moulds fit it for a great variety of uses, while its brittleness unfits it for many uses to which other modifications of this metal are especially adapted. 342. 'Wrought Iron. This is obtained from cast iron by taking advantage of the fact that carbon is more combusti- ble than iron. The carbon is mostly burned out of the cast iron. It is done by exposing the iron to a current of air when it is strongly heated in what is called a reverberatory furnace. The result is that the oxygen of the air unites with the carbon of the cast iron, and passes off as carbonic oxide. Fig. 96 (p. 246) will give you an idea of the con- struction of the furnace. The upper figure is a vertical, and the lower a horizontal section. At a is the fire, and b is the ash-pit ; at c is a wall called the bridge, which serves to direct 246 CHEMISTRY. the body of flame and heated air strongly against the arched ceiling of the furnace, whence it rebounds, or is reverberated down upon the iron which lies on the floor or hearth, d. The openings, g and i, are for the introduction of the iron, and at p is a damper by which the draught is regulated. "When the "puddling" is finished the metal is taken out in the shape of a ball, and aft- er being subjected to great pressure by machinery, to squeeze out the slag, it is passed through a succes- sion of rollers, each pair having a smaller space be- tween them than the pre- ceding. The conclusion of all this is the formation of the soft bar-iron of com- merce. Its qualities are the Flg - 96 - very opposite of those of cast iron. It is soft, flexible, ductile, and malleable, while cast iron is hard and brittle. When strongly heated it be- comes only semifluid, and therefore can not be made to run into moulds like cast iron. It is also different in its text- ure. "While cast iron is granular, as you can see by ex- amining a broken edge, the structure of wrought iron is fibrous. It is a curious fact that long-continued jarring will sometimes change the fibrous texture of wrought iron into the granular arrangement peculiar to cast iron, show- ing that it is not the mere absence of carbon that makes wrought iron what it is. This has sometimes taken place in the axles and wheels of railway cars, and the brittleness induced has caused serious accidents. It is on account of the peculiar structure of wrought iron that it can be welded, which can not be done with cast iron. In welding MANGANESE, IRON, COBALT, NICKEL, CHROMIUM. 247 the fibres of the iron intermingle. For this reason welding adds to the strength of the material, and accordingly arti- cles which require to be very strong, such as anchors, are made not in a single piece, but by welding together a bundle of bars of iron. 343. Steel. Steel is a form of iron midway between wrought and cast iron as to the quantity of carbon it con- tains, which is from one to two per cent., while that of cast iron is five per cent. It may be made from cast iron by burning out half of its carbon, or from wrought iron by re- storing half of the carbon of which it was deprived in its preparation. The latter is the usual process, and consists in heating the wrought iron in close iron boxes containing charcoal for several days. Steel can be made to have dif- ferent properties according to the uses to whicli we wish to put it. If it be heated to redness, and then be quickly quenched, it is rendered hard and brittle ; if cooled rather gradually it becomes elastic ; and if cooled very slowly it becomes soft, ductile, and malleable, like bar-iron. When it is cooled slowly it is said to be annealed. 344. Bessemer Process. This is a new and very rapid method of preparing cast steel, of the greatest industrial importance. It consists in burning out all the carbon and silicon in cast iron by passing a blast of atmospheric air through the molten metal, and then in adding such a quan- tity of a pure cast iron as is necessary to give carbon enough to convert the wrought iron into steel ; the melted steel is then at once cast into ingots. In this way six tons of cast iron can be converted into steel in one operation lasting twenty minutes. This process has in large measure revolutionized the old iron industry. 345. Tempering. Steel when hardened, as mentioned above, is not fit for use till it is tempered, as it is termed, to the particular use for which it is designed. This tern- 248 CHEMISTRY. pering process consists in reheating the steel and then let- ting it cool slowly. The character of the effect depends upon the degree of heat to which it is carried, and this is measured by the workmen by the color caused by the heat. You can see the various colors by experimenting with a common knitting-needle. First heat it to redness in the flame of a spirit-lamp, and quench it in cold water. Now hold it again in the flame, and observe the changes of color. It first becomes a pale yellow, then orange, crim- son, violet, blue, and finally dark gray. The explanation is this : A film of oxide forms, which, being at first exceed- ingly thin, is pale yellow, and deepens in its tint as the in- creased heat thickens it. The final dark-gray coating is scales of the oxide of iron. Now there is a definite degree of hardness on the one hand, and of elasticity on the other, corresponding to each one of these colors, the yellow giv- ing the most brittleness and hardness, and the blue the most softness and elasticity, the other colors giving inter- mediate results. Accordingly, tools for cutting metal, which require to be very hard, are heated till they become a pale yellow ; knives and planes to an orange ; chisels, hatchets, etc., to a crimson ; and springs to a violet or blue tint. 346. Sulphides of Iron. There are three sulphides of iron. One of them, the disulphide FeS 2 , is what is usually called iron pyrites. It received this name among the an- cients because it strikes fire, pur being the Greek for fire. The idea which they had of it may be gathered from what Pliny says, who states that " there was much fire in it." It crystallizes, and has a brilliant yellowish brassy color. It has sometimes been supposed by the ignorant to be gold, and so has received the name of fool's gold. It is of great value in the arts in obtaining several important substances, as sulphur, ferrous sulphate, and sulphuric acid. As more MANGANESE, IRON, COBALT, NICKEL, CHROMIUM. 249 than half of this salt is sulphur, heat will drive off a large portion of it. It is therefore usually heated in clay retorts, and the sulphur which passes off in vapor is collected. The residue is taken out and thrown into heaps, and is simply left exposed to the air. By the absorption of oxy- gen from the air this sulphide gradually becomes a ferrous sulphate, the oxygen converting the sulphur into sulphuric acid, and the iron into oxide of iron, which unite to form the sulphate. 347. Other Salts of Iron. Metallic iron dissolves readily in nitric and hydrochloric acid, forming nitrate and chloride of iron. Two of each can be obtained, one in the ferrous and the other in the ferric state. Ferric chloride is much used in medicine and in the arts ; it is a valuable disinfect- ant. Ferric solutions are usually yellowish red in color, and ferrous solutions pale green. 348. Cobalt. This is a brittle metal of a reddish-white color. It exists in nature in combination with arsenic and sulphur. There are two oxides, one of which, the monox- ide, gives a beautiful blue color to glass. It is this colored glass ground to a fine powder that constitutes the smalt which is used to give. to writing-paper and linen a delicate shade of blue. The blue colors on porcelain are also pro- duced by cobalt, and the zaffer used to give a blue color to common earthenware is an impure oxide of this metal. The fly-poison, so commonly called cobalt by apothecaries, is arsenic, and has not a particle of cobalt in it. The name which this metal bears was given to it in a singular way. When the superstitious miners of the Middle Ages found the ores of cobalt, they expected, from their brilliancy, that they should obtain something very valuable from them; but they were disappointed in finding them crumble in their smelting-furnaces into gray ashes, emitting at the same time a disagreeable odor of garlic. They imagined, L2 250 CHEMISTRY. therefore, that they were mocked in these results by the earth-spirits of the mines, the Kobolds, as they were called, and so named the ore after them. The name which the metal now bears is a corruption of that which was orig- inally bestowed by the miners upon the ore. 349. Chloride of Cobalt. The solution of this salt makes a beautiful sympathetic ink. It being of a pink color, what is written upon pink paper will be invisible. If the paper be warmed, the letters will become of a bright blue color, and then they will fade again as the paper becomes cool. This is owing to the difference of color between the hy- drated and the anhydrous salt. 350. Nickel. This is a white metal, and takes a good polish. One of its chief uses is in making the alloy called German silver. It is an ingredient in the meteorites, as already noticed. Both cobalt and nickel are commonly found in company with iron, and these three metals are the only ones which are magnetic. The beautiful stone called chrysoprase is quartz colored an apple-green by oxide of nickel. Nickel almost deserves to be classed among the noble metals, it is so little prone to oxidize. Since nickel-plating has been perfected we see nickel -covered objects in com- mon use. The one-cent and five-cent coins are alloys of copper and nickel. Nickel forms two oxides, only one, NiO, being of importance. 351. Salts of Nickel. The most abundant ore of nickel is niccolite, an arsenide of nickel. Nickel dissolves in ni- tric acid, forming a beautiful green nitrate of nickel. The carbonate, sulphate, chloride, hydrate, etc., are well-known salts, which have not obtained any extensive use in the arts. A double salt, sulphate of nickel and ammonium, is used in nickel-plating. 352. Chromium. This is not very abundant in the earth. TIX. 251 It occurs near Baltimore combined with iron, forming so- called chromic iron. Chromium forms a great many oxides, like manganese. That having most oxygen plays the part of an acid. Some of the salts of chromic acid are valuable. Chrome yellow, a well-known pigment, is a chromate of lead. Chrome or- \anye is made by digesting chrome yellow with potassium carbonate, the effect of which is to remove a part of the chromic acid from the salt. The most important of the chromates, however, is the potassium dichroniate, K 2 Cr 2 O 7 , a beautiful yellowish-red crystalline substance. All the compounds of chromium are strongly colored, and many of them are very beautiful. The green color of our "greenbacks" is due to the sesqui- oxide of chromium, Cr 2 O 3 , which is a very fast color, and not easily attacked by acids or alkalies. GROUP vi. TIN. 353. Tin. Tin is one of the most extensively useful of the metals, for it is soft and malleable, and does not easily tarnish. The tin-foil which you so often see shows how malleable it is. Tin is used in making many of the alloys. Our common tin-ware is not tin alone, but thin sheet-iron covered with tin, the sheets having been dipped into the melted metal. The object of the covering of tin is to pre- sent a surface to the air and to liquids that is not easily oxidized. For the same reason iron chains are often cov- ered with tin. Pins are made of brass, and are coated with an exceedingly thin covering of tin by a chemical process which has been described in Part L Tin is a brilliant white metal. It is quite disposed to crystallize, as may be seen by a single experiment. Sponge a perfectly clean piece of tin which has been slightly heated quickly over with nitre-muriatic acid. After washing it in clean water 252 CHEMISTRY. and drying it, the crystalline arrangement can be very plainly seen. Ware which has been treated in this way is called moire metallique. If a bar of tin be bent it gives a peculiar sound, which is owing to the friction of the mi- nute crystals of the metal against each other. This sound has been fancifully called "the cry of tin." There are three oxides of tin, one of Avhich, the dioxide, SnO 2 , is its common one. The most famous and most abundant tin- mines are those of Cornwall, in England. It is supposed that they were worked long before the Christian era. 354. "Tin Salts." By dissolving tin in hydrochloric acid, stannotis chloride, SnCl 2 , separates from the solution in needle-shaped crystals containing water. This forms the "tin salts" so largely used by the calico-printer and dyer as a mordant. Stannic chloride, SnCl 4 , is a fuming, color- less, heavy liquid. 355. Sulphides of Tin. There are two sulphides of tin, a mono- and a di-sulphide. Stockhardt tells us how to obtain them. To obtain the first inclose 2 grammes of flowers of sulphur in a piece of tin-foil weigh- ing 4 grammes, and introduce the package into a test-tube. On heating the tube, half of the sulphur will burn up, and the other half will unite with the tin with a lively glowing, forming a brownish-black mass, which is the monosulphide. If you sprinkle the glass, while still hot, with water, it is rendered friable, and is easily separated from the fused salt, which will be found to weigh about 5 grammes. Pulverize this, and mix intimately with the powder 1 gramme of sulphur and 2 of sal ammoniac. Put this into a thin flask, and let it be heated in a sand-bath for an hour and a half. The disulphide will be found in the bottom of the flask in a mass having a gold- en lustre, and the sal ammoniac will appear in the upper part of the flask, deposited there by sublimation. The latter is not altered at all in compo- sition, but it in some way serves to give the disulphide its golden color. The beautiful substance thus obtained has been called aurum musivum, or mosaic gold, and it may be used for giving a gold-like coating to wood, plaster of Paris, etc. ARSENIC, ANTIMONY, BISMUTH. COPPER AND LEAD. 253 QUESTIONS. 335. Give the names and formulae of the oxides of manganese. Which ones form salts? 336. What are the properties of pure iron? 337. What is said of the abundance and importance of iron ? 338. What oxides does iron form ? What is said of ferrous hydrate ? Mention some of the ores of the monoxide of iron. Of the sesquioxide. Of ferric hydrate. How many grammes of water are there in 100 grammes of ferric hydrate ? How many grammes of oxygen ? How many gallons of oxygen in one pound of rust ? What is the composition of the so-called magnetic oxide of iron ? What are its properties ? 339. What are meteorites ? 340. Describe the process of making pig-iron. Why is limestone added ? 341. What is said of cast iron ? 342. What is the process of converting cast iron into wrought iron? Describe the change in properties thus produced. Why can wrought iron be welded ? 343. In what does steel differ from iron ? What are its properties ? What is annealing ? 344. In what does the Bessemer process consist? 345. What is said of tempering steel? What colors does it assume? 346. Name and describe the principal sulphide of iron. Of what use is it ? 347. Name some other salts of iron. 348. What is the nature of cobalt ? Whence its name ? 349. What is said of sympathetic ink? 3.">0. What are the properties of nickel? 351. Name some of its salts. 352. What are the most important oxides of chromium ? What is said of the chromates? 353. What are the uses of tin ? How are pins made ? What is moirt metalllgue * What peculiar property has a bar of tin ? 354. What is known as " tin-salts ?" How used ? 355. What is mosaic gold ? How made ? How is the monosulphide obtained ? CHAPTER XIX. GROUP VII. ARSENIC, ANTIMONY, AND BISMUTU. GROUP VIII. COPPER AND LEAD. 356. Arsenic. What is known as arsenic in common lan- guage is a compound of this metal with oxygen, called by the chemist arsenious anhydride, As 2 O 3 . This arseniotis anhydride is a deadly poison, so that " poisonous as arsenic" is a common expression. It is used for the destruction of 254 CHEMISTRY. life more often than any other poison. It is much used for killing rats, moles, and other troublesome animals, and hence the name ratsbane which is often given to it. It looks much like sugar and flour, and its taste is rather sweet. The metal arsenic is crystalline, of a bright steel-gray color. It is not poisonous when free from oxide. It very soon tarnishes when exposed to the air, and at length becomes a coarse gray powder, which is a mixture of the metal and its oxide. It is sometimes sold by druggists under the names of " fly -powder," "cobalt," and "mercury." This is wrong, for people who buy it are not as cautious in its use as they would be if they knew that it w r as arsenic. 357. Antidotes to Arsenic. Every one ought to know what to do if he chance to be with any person who has taken arsenious anhydride white arsenic, as it is called. He should administer at once in considerable quantities the whites of eggs, or milk, or flour and water, or soap- suds. These, however, are but partial antidotes, doing little, if any thing, more than sheathing the membranes of the stomach from the arsenic. There is only one true chemical antidote to this poison ferric hydrate ; but it is good for nothing unless it has been freshly prepared. Its efficacy results from its forming with the arsenic a com- pound which is insoluble, and therefore inactive. There are some sure chemical tests of the presence or ab- sence of arsenic in the bodies of those who are supposed to have been killed by this poison ; but such investigations belong properly only to the professional chemist, and there- fore are not suited to this work. 358. Antiseptic Powers of Arsenic. When arsenious an- hydride is taken as a poison and destroys life, it has a marked effect in preserving the body from putrefaction. This is shown in various ways. Sometimes the whole body is remarkably preserved for a long time after death. ARSENIC, ANTIMONY, BISMUTH. COPPER AND LEAD. 255 Iii this case the person lives so long after taking the poison that it goes every where in the circulation, and pervades the whole body. But sometimes, on the other hand, the stomach and intestines alone have been found preserved even after the rest of the body was far gone in decompo- sition. Here the person died soon after taking the ar- senic, and therefore its antiseptic influence was exerted locally. It is on account of this preservative power that skins intended for shipping have arsenic rubbed on the flesh side. 359. Arsenic-Eating. There is a strange habit of eating arsenic prevalent among the inhabitants of Styria, a mount- ainous district in Austria. The effects which are ascribed to it are hardly credible, but the statements seem to be well authenticated. It is said that the arsenic-eaters con- tract the habit for the purpose of improving their personal appearance. Another effect is that the respiration is im- proved, so that mountains can be climbed with much less embarrassment of the breathing than is usual. But the habit is attended with great dangers. The arsenic-eater begins with small doses, and gradually increases them. Great caution is required, and very often too much is taken ; aitd then symptoms of poisoning appear, perhaps resulting in death. Then, again, when the habit is once formed, any intermission in the regular taking of the ar- senic is dangerous, bringing on at once the common symp- toms of arsenic-poisoning. It is said that the same results are produced on brute animals, and that in the city of Vi- enna men sometimes throw a pinch of arsenic into the food of horses. It makes them fat, sleek, and of good wind ; but the practice once begun must be kept up. Notwithstand- ing all this, thorough investigation would undoubtedly show that arsenic-eating very considerably shortens life, although cases are cited in which persons who for a long 256 CHEMISTRY. time Lave been slaves to the habit are in good health even at the age of sixty years or more. 360. Arsenetted Hydrogen. Arsenic, like nitrogen and phosphorus, combines with hydrogen in the proportion of one atom to three. This body, arsenetted hydrogen, AsH 3 , or hydrogen arsenide, as it is sometimes called, is a gas, neither acid nor alkaline, and very poisonous. A German chemist, named Gehlen, was fatally poisoned by it in 1815, while investigating its properties. It is easily obtained by throwing a little arsenious anhydride into an apparatus for generating hy- drogen by means of zinc and sul- phuric acid. The arsenious oxide is deprived of its oxygen, and part of the metal com- bines with the hy- drogen, forming ar- senetted hydrogen. This gas is inflam- Fi s- 97 - mable, and burns with a lambent flame ; if a cold porcelain plate be held in the flame a moment, the gas being decomposed by the combustion, metallic arsenic will be deposited on the por- celain, forming gray-black spots. This formation of ar- senetted hydrogen and of a metallic deposit by the flame is made use of in testing for arsenic. The delicacy of the test is remarkable : -^^-QQ of a gramme can be detected in this manner, using suitable precautions not necessary to describe here. Antimony forms a similar compound with hydrogen, SbH 3 , and the flame of this gas deposits a black metallic coating on a cold porcelain surface just like ar- AKSENIC, ANTIMONY, BISMUTH. COPPER AND LEAD. 257 senic, but somewhat deeper black in color. The methods of distinguishing between arsenic and antimony, however, belong to works on analytical chemistry. You can easily see, however, that when a chemist is called upon to deter- mine whether a person has been poisoned by arsenic or not, the chemist must be very careful not to mistake anti- mony for arsenic, for antimony, as you will learn in 363, is a component of tartar emetic, which is sometimes given to produce vomiting when poisoning is suspected. 361. Arsenical Pigments. Arsenious acid in combina- tion with copper makes several splendid green pigments. Scheelds Green is an arsenite of copper formed by adding an alkaline solution of arsenious acid to a hot solution of copper sulphate. Paris Green is nearly the same, but con- tains acetate of copper also. This brilliant color is exten- sively used as a pigment. It is a very poisonous substance, and its use is dangerous. "It may even prove danger- ous," Stockhardt says, " as a green paint for rooms, since, under some circumstances, volatile combinations of arsenic are formed from it and mix with the air." Brunswick Green is another arsenical pigment, prepared like Scheele's Green, only some cream of tartar is added to the copper sulphate, and some slaked lime to the arsenious solution. The facility with which compounds of arsenic can be obtained by the common people, and their cheap- ness, is much to be deplored. 362. Antimony. This metal is not so well known as one of its salts called tartar emetic ; and yet in some of the arts it is largely used. It is one of the constituents of type- metal. The alloy of lead and antimony which we have in type-metal at the moment that it becomes solid in casting expands, so that the mould is well filled out, and the type is therefore complete, with well-marked lines and angles. But neither of these metals when alone makes a good cast- 258 CHEMISTRY. ing, because they shrink in becoming solid, instead of swell- ing as they do when mixed in alloy. The metal plates on which music is sometimes engraved is an alloy of tin and antimony. The Britannia Metal, which has taken the place of the old-fashioned pewter, is composed of one hundred parts of best block-tin, eight of the metal antimony, and either two and a half parts each of copper and brass, or two of copper and bismuth. Antimony is obtained chiefly from its sulphide, which is quite an abundant ore. It is associated commonly with ores of silver, copper, lead, zinc, etc. 363. Compounds of Antimony. Antimony forms two chlorides, one of them, SbCl 3 , has long been known under the name of butter of antimony. It forms also two oxides, Sb 2 O 3 and Sb 2 O 5 , and two sulphides of corresponding com- position. Tartar emetic is a double tartrate of antimony and potassium, K(SbO)C 4 H 4 O 6 . It is obtained by boiling antimonious oxide with cream of tartar (hydro-potassium tartrate), and evaporating the solution. Nearly all the salts of antimonious oxide are decomposed on adding wa- ter to their acid solutions. Antimonetted hydrogen has been mentioned in 360. 364. Bismuth. This metal is found in but few localities, and mostly in the metallic state. By far the largest part of it comes from one locality, Schneeberg, in Saxony. It is obtained from the rocks in which it is present by reducing them to a coarse powder, which is burned in a sort of kiln. The bismuth, which is quite fusible, is thus melted out, and is collected in a trough at the bottom of the kiln. It is a white metal with a peculiar reddish tint, and a remarkable crystalline structure. It is used chiefly in forming certain alloys, as one kind of type-metal, and the metal for stereo- type plates. 365. Nitrate of Bismuth. If a solution of this salt be ARSENIC, ANTIMONY, BISMUTH. COPPEE AND LEAD. 259 turned into a large quantity of water, the salt loses a part of its nitric acid, and so becomes basic, and is called a sub- nitrate. This appears in the form of a white precipitate. This has been sometimes used as a cosmetic. It would be dangerous for a lady who had used it for this purpose to attend a chemical lecture at which any sulphuretted hydro- gen should escape, for this gas blackens at once this salt. 366. Copper. This metal is next to iron in strength. It is one of the very few metals which have a decided color. It is very malleable and ductile, and is therefore much used in the forms of sheet and wire. It is largely used in sheath- ing ships. It is a constituent of many alloys, as brass, bronze, German silver, etc. Gold and silver, both in coins and articles for use, are alloyed with copper, to give them the requisite hardness. Native copper is found in abun- dance in the neighborhood of Lake Superior. A mass of it has been taken thence to Washington which weighed 3704 pounds, and a mass has been uncovered in one of the mines which has been estimated to weigh 200 tons. The metal is also largely obtained from copper pyrites, a double sul- phide of iron and copper that is, an ore in which the sul- phur is chemically combined with both of these metals, the particles of the .two sulphides being most intimately min- gled together. There are also other ores of copper the pure sulphide, red oxide, carbonate, etc. There are two oxides of copper the monoxide, which is black, and the suboxide, which is red. The latter is used in the manu- facture of glass, giving it a splendid ruby-red color. We have already named many of the salts of copper; the sulphate sometimes called blue vitriol forms beautiful blue crystals containing water. It is used in calico-print- ing and in the manufacture of green pigments, some of them containing arsenic, as you have just learned. Ace- tate of copper, sometimes called verdigris, is another green 260 CHEMISTRY. pigment. It is a very poisonous substance. It is formed whenever acetic acid is brought in contact with copper. No article of food, then, in which there is vinegar should be cooked or kept in a copper vessel. 367. Experiment -with Sulphate of Copper. If you hold a knife -blade for a few minutes in a strong solution of sul- phate of copper, it will be covered with a coating of metal- lic copper. The copper is precipitated upon the iron, while the iron goes into the solution. This is shown as follows : Sulphate of copper. Iron. Ferrous sulphate. Copper. CuSO 4 + Fe = FeSO 4 + Cu This experiment was tried on a large scale some years ago in Ireland. In some pits at a mine in Wicklow there was a large amount of the solution of sulphate of copper. In order to get the metallic copper from this, 500 tons of iron were placed in the pits and left there for a year. The re- sult was that the iron was all united to the sulphuric acid, forming ferrous sulphate, which was dissolved in the water, and the metallic copper lay in the form of a reddish mud at the bottom of the pits. This was taken out, and, after being freed from its impurities, was melted and cast in bars. The same expedient has been adopted in other mines. 368. Test for Copper. Polished steel, as shown by the experiment with the knife-blade, is a good test of the pres- ence of salts of copper. If pickled cucumbers or preserved fruit have been prepared in copper vessels, we can ascer- tain whether copper be present in them by introducing a slip of polished steel, or, what is the same thing, a bright knife-blade. If there be any salt of copper, the metal it- self will be deposited upon the steel. Of course, as the quantity, if there be any, must be small, the steel must re- main in the liquid for some little time, and the deposit must necessarily be small. If the salt be acetate of copper, as it ARSENIC, ANTIMONY, BISMUTH. COPPER AND LEAD. 261 is very likely to be, the copper is set free by the formation of an acetate of iron. 369. Lead. Next to iron, lead is one of the most abun- dant metals. Its softness and low melting-point are its chief characteristics. It is used for a great variety of pur- poses. It is the chief ingredient in type-metal. Bullets and shot are made from it. The mode of manufacturing shot is given in 60, Part I. It is also largely used for pipes for conducting water and other liquids. In the form of sheet-lead it is applied to various uses. This metal is obtained principally from its sulphide, called galena. One mode of obtaining it is to mix the ore with iron, and then apply heat. The sulphur, having a greater attraction for iron than for lead, leaves the lead to unite with the iron. The action of water upon lead we shall speak of in another place. 370. Oxides of Lead. The monoxide of lead, PbO, is a yellow substance called massicot. If this be melted with a strong heat it solidifies, on cooling, into a reddish-yellow mass composed of brilliant scales, and is called litharge. It is used extensively in the arts, in the manufacture of glass, in making the lead plaster of the apothecary, in form- ing a varnish with linseed-oil for the cabinet-maker, in the manufacture of wliite-lead, red-lead, etc. The red oxide is prepared by exposing for some time to a faint red heat the monoxide which has not been fused. A brilliant red and very heavy powder results called minium, which is used as a cheap substitute for vermilion in painting. The composition of the red oxide is 2PbO.PbO 2 , being a compound of the monoxide and of a chocolate-colored ox- ide, PbO 2 , not previously mentioned. 371. "White-Lead, or Carbonate of Lead, PbCO 3 . This may be prepared by mixing a solution of lead acetate or nitrate with one of sodium carbonate, a white precipitate settling. 262 CHEMISTEY. The commercial white-lead is prepared differently, usually by exposing sheet-lead to the influence of the oxygen of the air in the presence of acetic acid or vinegar. The agency of the acetic acid of the vinegar is interesting. It dissolves successive portions of the oxide of lead, forming with it an acetate, and the moment that it does this the carbonic acid takes away the oxide from it; so that the office of the acetic acid is simply to take the oxide and deliver it over to the carbonic acid. It is very much as the nitric acid in the formation of sulphuric acid ( 242) continually takes oxygen from the air and delivers it over to the sulphurous acid. 372. Lead-Poisoning. The carbonate of lead is a poison, producing, when introduced into the system, lead colic, paralysis, and many other bad affections. Many persons have been subjected to protracted suffering, and many lives have been lost from this poison. Painters are liable to be poisoned by it, but the liability has been much diminished by precautions in the use of the article in their business. The poisonous influence more often comes from drinking water brought in lead pipes, and in that case is commonly slow and insidious. And, as a general rule, the purer the water, the more apt is it to be rendered poisonous by the lead. The reason of this is obvious. You will remember that we told you that there is always some carbonic anhy- dride in water. Now this acts upon the metallic lead in connection w 7 ith the water, and, forming carbonate of lead, makes it poisonous. It will do so unless there be some- thing to prevent it. If the water be quite pure, there is nothing in it to prevent the carbonic anhydride from thus acting ; but if there be certain impurities, as, for example, sulphate of lime, there will be formed a thin coating over the surface of the metal, which effectually shields it. Lead pipes ought never to be used unless the water to be brought ARSENIC, ANTIMONY, BISMUTH. COPPER AND LEAD. 263 through them has been ascertained by a skillful chemist to have the protective ingredients alluded to in it. There has been great carelessness in this matter. Because in the majority of cases there is no hazard, people have presumed on safety without any examination, foolishly running the risk of having the exception occur in their case. Tin-lined pipes are said to be safer than ordinary lead pipes. 373. Sugar of Lead, or Lead Acetate, Pb(C 2 H 3 O 2 ) 2 . Ace- tate of lead is commonly called sugar of lead, on account of its sweet taste. A very pretty experiment may be tried with a solution of this salt. Dissolve 15 grammes of sugar of lead in ISO cubic centimeters of water, making the liq- uid clear by adding a few drops of acetic acid. If this be poured into a phial, and a slip of zinc be fastened to the cork, as seen in Fig. 98, brilliant metallic branches will grow upon the zinc, filling the phial in a day or two. These are crystals of lead which have arranged them- selves in this arborescent form. This is because the zinc replaces the lead in the lead acetate, forming zinc ace- tate, which takes the place of the lead acetate in the liquid. This leaves the lead uncombined, and its particles, as fast as they are released, gather in crystals, the process taking its start from the zinc where the chemical change occurs. Acetic acid is H.C 2 H 3 O 2 , being an organic acid composed of carbon, hy- drogen, and oxygen, in the proportions named. Lead ace- tate is Pb(C 2 H 3 O 2 ) 2 , therefore the reaction above described may be expressed in an equation thus : Lead acetate. Zinc. Zinc acetate. Lead. rb(C a II,O a )a + Zn = Zn(C 3 H 3 3 ) 2 + Pb 264 CHEMISTRY. QUESTIONS. 356. What is said of the metal arsenic ? What is the composition of ratsbane ? 357. What are the antidotes to arsenic poisoning ? 358. What is said of the antiseptic properties of arsenic ? 359. What of arsenic eat- ing ? 3GO. What is the composition of arsenetted hydrogen ? How is it made ? What are its properties ? How delicate is this as a test for ar- senic ? What is said of the danger of mistaking antimony for arsenic ? 361. Name some pigments containing arsenic. Of what are they com- posed ? 362. What is said of the uses of antimony ? 363. Describe some salts of antimony. What is tartar emetic ? 364. What is said of bismuth ? 365. What of its nitrate ? 366. What are the properties of copper ? What its uses ? What is said of native copper ? What other ores of copper are mentioned? What is said of the salts of copper ? 367. Describe an experi- ment with sulphate of copper. Where and why was this done on a large scale ? 368. What is a good test for copper ? 369. How is lead obtained ? For what is it used ? 370. What is said of the oxides of lead ? What is minium? 371. What is white-lead? How made? 372. Why is poison- ing by lead so insidious? What danger is there in using lead pipes for conveying drinking-water? What pipes are safer? 373. What is the sci- entific name of sugar of lead ? What is its composition ? How can a lead tree be made ? What is the theory of its formation ? CHAPTER XX. GROUP IX. MERCURY, SILVER, GOLD, AND PLATINUM. 374. Mercury. This metal was thus named from its quickness of movement, because Mercury was considered by the ancients the most active of the gods. The alche- mists called it quicksilver, because they thought it to be an enchanted kind of silver, and they endeavored by vari- ous processes to obtain from it solid silver. Mercury is the only metal which is liquid at ordinary temperatures. It freezes or solidifies at about 39-j- degrees below zero, and then it is malleable like lead. It evaporates like water, MERCURY, SILVER, GOLD, AND PLATINUM. 205 though not as rapidly, at ordinary temperatures. This you can prove by a simple experiment. Put some mercury in a phial, and fasten to the cork a little bit of wood having some gold-leaf attached to it. The gold, after a few days, will have a white color, because the mercury has risen in vapor and united with the gold, forming an amalgam. There are two oxides of mercury, one of which, called red precipitate, is with its bright red color a striking example of the great difference which is so often seen between the properties of a compound and those of its constituents. Mercury is sometimes found native. It is said that the mines of Mexico were discovered by a hunter, who, as he took hold of a shrub in climbing a mountain, tore it up by the roots, and a stream of what he supposed to be liquid silver burst forth. But the metal is commonly obtained from the ore called cinnabar, a sulphide. So readily does the mercury in cinnabar part with the sulphur that merely roasting it in a current of heated air answers to reduce it. Sulphurous anhydride is formed by the union of the sulphur with the oxygen of the air, and this gas passes together with the vapor of the mercury into a cool chamber, where the liquid mercury collects by the condensation of the vapor. 375. Vermilion. Cinnabar is of a beautiful red color, but precipitated mercuric sulphide is black. If this artificial sulphide is sublimed, then, without any chemical change, it becomes a brilliant red, and is the so-called vermilion. This substance is sometimes adulterated with minium or red- lead, but the fraud can be easily detected. If a little of pure vermilion be thrown upon a live coal, it is entirely volatilized or sublimed with a blue sulphurous flame ; but if it be adulterated with minium it will not all volatilize, and beads of metallic lead will remain on the coal. 376. Chlorides of Mercury. Mercurous chloride, Hg 2 Cl 2 , M 266 CHEMISTRY. is also called calomel. Mercuric chloride is commonly call- ed corrosive sublimate ; it contains twice as much chlorine as the first-named chloride, and is written HgCl 2 . Calomel is an insoluble and mild substance ; but corro- sive sublimate, merely by having this additional quantity of chlorine, is soluble, and acts as a corrosive poison, burn- ing and eating wherever it goes. It is much used for the destruction of vermin. It has sometimes been swallowed by mistake. It produces most distressing symptoms, end- ing very commonly in death. The accident happens usu- ally in one or the other of two ways : either a bottle which has had a solution of corrosive sublimate in it is carelessly put aside, and is afterward used for some other purpose, perhaps for bottling cider ; or the bottle containing the so- lution is put among other bottles without being properly labeled, and, if the solution is made with alcohol, some of it may be swallowed on the supposition that it is some kind of liquor. It is in this latter case that such intense suffer- ing is produced, because the poison is so concentrated. But little is swallowed, for the individual is affected at once by an intense burning in the throat, extending down into the stomach. Every one ought to know the effectual antidote which they have to this poison, for the earlier it is used the better, and every moment's delay adds to the dan- ger of the case. Fortunately the antidote is generally at hand. It is the whites of eggs, which should be swallowed freely. The albumen in this substance acts chemically upon the corrosive sublimate, producing a compound that is not poisonous. If there be no eggs at hand, give milk, or flour stirred up in water, for there is some albumen in these. 377. Amalgamation. You have already learned ( 278) that mercury forms with some of the metals alloys called amalgams. This fact is made use of in freeing certain MEECUEY, SILVEE, GOLD, AND PLATINUM. 267 metals from substances with which they happen to be min- gled. Silver and gold are often obtained by this process, which is called amalgamation. Suppose, for example, that we have some quartz with gold finely scattered through it. The quartz is first powdered, and then the powder is agi- tated with mercury, which seeks out, as we may say, all the gold, and unites with it to form an amalgam. Suf- ficient mercury is used to have the amalgam liquid, so that it may be readily separated from the powder. This liquid amalgam, which is really a solution of gold in mercury, is poured upon buckskin or a closely woven cloth, which al- lows most of the mercury to run through, leaving the gold alloyed with a small part of the mercury. The remaining mercury is driven off by heat, and the gold is obtained pure. The dust of jeweler-shops is often treated in this way to save the gold which has been scattered by filing and other processes. 378. Silver. This metal stands in regard to hardness be- tween gold and copper, and requires to be alloyed with copper to make it wear well In the coinage of the United States the proportion of copper is one tenth. Silver is very ductile and malleable. Its polished surface reflects both light and heat better than any other metal, and accordingly it is used for reflectors. The tarnishing which gradually occurs is not from oxidation, but from the formation of a sulphide of silver by the sulphuretted hydrogen which is generally in the air in small quantity. When this gas is present in the air in considerable amount, as in the neigh- borhood of some sulphur springs, silver tarnishes rapidly. It is the sulphur in the egg that discolors the spoon with which you eat it, forming a sulphide. Silver is sometimes found native, but is usually obtained from ores. The most common of its ores is the sulphide called argentite. This occurs abundantly in Nevada. It is sometimes combined 268 CHEMISTRY. with antimony and arsenic. There is always some silver in the common ore of lead, galena, and sometimes there is so much of it that it is profitable to submit the lead ob- tained from this ore to certain chemical processes for ex- tracting the silver alloyed with it. 379. Extraction of Silver from Galena. We have already told you, in 369, how the galena is freed from the sul- phur. This gives you an alloy of lead and silver. This is melted in a large basin and allowed to cool slowly. As it cools a crust continually forms over the surface, which is composed of crystallized lead without any of the silver, this settling down in the liquid below simply because it does not crystallize as readily as lead does. This crust is taken off with an iron colander as fast as it forms, until there is left only a small amount of the melted metal. You see what the result is. You have an alloy containing much more silver in proportion than the mass which you melted. This alloy, after cooling, is submitted to a proc- ess called cupellation. The cupel is a shallow dish made of bone ashes, and is very porous. In this is placed the alloy, and it is submitted to a strong heat. When it is at a full red-heat a powerful current of air is thrown across it by bellows in order to blow away the litharge or oxide of lead which forms on the surface. What is not thus blown away is absorbed by the pores of the cupel. When the lead is all disposed of, and the silver is left alone, the surface suddenly becomes brilliant, and the workman, see- ing this flashing or lightening, as it is technically termed, knows that the process is completed, and withdraws the cupel from the fire. 380. Salts of Silver. Silver forms many useful salts. Silver nitrate is often called by physicians lunar caustic, being used as a caustic by the surgeon. As it grows black rapidly when exposed to the light in contact with MERCURY, SILVER, GOLD, AND PLATINUM. 269 vegetable fibre, it is much used in solution as an indelible ink for marking linen and cotton. Mercury introduced into a weak solution of it precipitates the metallic silver in beautiful tree-like forms called arbor Diance. There have been cases in which nitrate of silver (lunar caustic) has been swallowed in considerable quantity by mistake. The sure antidote is common salt, producing two harmless articles, chloride of silver and nitrate of sodium. 381. The Silver Assay. The process by which the amount of al- loy in silver is ascertained is called the silver assay. A sample of the sil- ver to be examined is first dissolved in nitric acid. The assayer then in- troduces salt (chloride of sodium) into this solution, and a curdlike sub- stance is precipitated. This substance is chloride of silver, formed by the union of the chlorine of the salt with the silver. He adds the salt slowly till there ceases to be any precipitation, and then Stops, because he knows that there is no more silver for the chlorine to unite with. Now observe how he tests by this process the amount of silver in the specimen. Of course, the more silver there is and the less alloy, the more salt is required to precipitate all the silver. The assayer, therefore, judges of the purity of the specimen by the amount of salt which he is obliged to use to com- plete the process, and in order to ascertain this accurately he employs a so- lution of a certain strength, which he pours from a graduated glass. He knows beforehand just how much of this is required to precipitate a cer- tain amount of pure silver for example, a gramme. If now he is obliged to use only half as much for a gramme of any sample, he infers that it is only half silver ; if three fourths, it is three fourths silver, etc. The explanation of the process is this : The solution of the silver in nitric acid is a solution, not of silver, but of the salt called nitrate of silver. This is decomposed, as is also the chloride of sodium when the two solutions min- gle, producing chloride of silver and nitrate of sodium, as indicated in the equation : AgXO, + NaCl = AgCl + NaNO 3 . 382. Gold. Gold is nearly always found in its metallic state. It is usually, however, alloyed with silver. Some- times it occurs in masses, but commonly in small round or flattened grains. It is also found in veins in various rocks. 270 CHEMISTRY. Its properties are, a splendid yellow color, brilliancy, high specific gravity, softness, great malleability and ductility, and indisposition to combine chemically with other sub- stances, especially oxygen. Gilding is usually performed by means of gold-leaf, except in case of the metals, on which it is commonly done by amalgamation, a process just ex- plained. Gold is so soft a metal that it is not fit for use in its pure state, and is therefore always alloyed with sil- ver and copper to give it the requisite hardness. The gold coin of this country is one-tenth part an alloy of silver arid copper. The word carat, used so much in express- ing the degree of purity in specimens of gold, signifies one twenty-fourth. If, therefore, it is said of any specimen of gold that it is 18 carats fine, it means that the pure gold in it is 18 parts out of the 24, or that it is three fourths gold. Perfectly pure gold is, of course, 24 carats fine. The word is of Eastern origin, and comes from a word meaning bean. Gold is not soluble in nitric acid, nor in hydrochloric, but in a mixture of the two it dissolves readily, as ex- plained in 225. 383. Chloride of Gold. This salt can be made in two ways. If gold-leaf be put into chlorine water, the chlorine will unite with it, and chloride of gold will be found in the solution. But it is most commonly made by treating gold with aqua regia. The chemical action is described in 225. If the solution thus obtained be evaporated, a brownish-red salt will appear, which is the chloride of gold. It is very easily decomposed, as can be shown by the following exper- iment : Dip a test-tube which has been wiped dry into a dilute solution of chloride of gold, and then heat it over a spirit-lamp. It will become gilded, showing that heat suf- fices to disengage the chlorine from the gold. The chloride of gold is quite in contrast with the chloride of sodium in MERCURY, SILVER, GOLD, AND* PLATINUM. 271 this respect, for no heat can decompose the latter. The compound, then, of gold with chlorine can be called an un- stable compound, as are its compounds with oxygen. Chloride of gold is used to a limited extent in the arts, chiefly in photography. 384. Platinum. The color of this metal is between tin and steel. It is the heaviest of all substances ; it has great ductility and tenacity ; it is very malleable, especially when heated, and it may then be welded, though not as perfectly as iron. In fusibility this metal stands at one end of the scale of metals, mercury being at the other. Mercury may be said to melt at about 40 below zero ; while, on the other hand, platinum withstands the heat of the hottest furnace, and requires the intense heat of the oxyhydrogen blowpipe to melt it. Hence the crucibles of the chemist are often made of this metal. It is used, also, somewhat in the arts in the manufacture of apparatus for the distillation of sulphuric acid, and in enameling glass and porcelain. If it were an abundant metal, it might be put to many common uses, and be a great convenience, for the utensils made of it would never rust, and would not be in any danger of melting, and when they became dirty they could be cleaned and made bright again by heating them red-hot. Platinum, like gold, dissolves in aqua regia only ; the so- lution on evaporation gives a deliquescent brown-red mass consisting of platinic chloride, PtCl 4 . This is used in chem- ical laboratories as a test solution, and in photography to a limited extent. 385. " Dobereiner's Lamp." By a certain chemical process platinum may be obtained in a finely divided state, furnish- ing a soot-like substance called " spongy platinum." This produces remarkable effects upon certain gases. If a little of it be introduced into a mixture of oxygen and hydrogen gases, an explosion is produced as quickly as if a lighted 272 CHEMISTRY. taper had been introduced. So, also, if a piece be held in a current of hydrogen it becomes red-hot, and then sets fire to the gas. This is what takes place in Dobereiner's Lamp, so called after the inventor. By turning a stop-cock in this lamp you let a current of hydrogen strike upon a bit of spongy platinum, and you have the result just men- tioned. In Fig. 99 you have a plan of this lamp, a being a glass jar covered by a brass lid, e, which has a stop-cock, c, with its opening opposite to a brass cylinder, d, which contains the spongy platinum. There is a small bell-jar, /, communicating at the top with the stop- cock, and having suspended in it a cylinder of zinc, z. "When the lamp is to be used the jar, a, is two thirds filled with a mixture of one part sulphuric acid and four parts wa- ter, as indicated by the circular line. As the bell-jar is open at the bottom, the acid and water attack the zinc in it, producing hydrogen gas, just as it is produced in the apparatus described in 143. If the cock be opened the hydrogen gas will escape, and be directed against the spongy platinum in c7, and will make it red-hot, and then this will set fire to the gas. 386. Other Illustrations. This curious property is not confined to spongy platinum, but the metal in its ordinary condition shows it to some extent. For example, if some ether be poured into a glass jar, Fig. 100, and a coil of platinum wire recently ig- nited be put into it, the metal will glow so long as there is any ether present. Ozone is formed at the same time. In Fig. 101 (p. 273) you have essentially Fig. 100. the same experiment in a prettier form. Fig. 99. MERCURY, SILVER, GOLD, AND PLATINUM. 273 Take a common alcohol lamp, and, cutting the wick rather short, surround it with a coil of small platinum wire about half an inch high. Light the lamp, and when the wire be- comes red-hot blow it out. The wire, in- stead of cooling at once, as any common wire would, will continue to glow till all the alcohol is consumed. These curious phenomena depend upon the power pos- sessed by platinum of condensing gases upon its surface. 387. Iridium and Osmium. There are sev- eral very rare metals found associated with platinum, and having similar properties. Two of these, iridium and osmium, form the hardest alloy known, a mineral called by the mineralogist iridosmine, a name compounded of the names of the two metals. One use has been found for this mineral : it is used to point gold pens, its great hardness fitting it admirably for that purpose. QUESTIONS. 374. Whence the name mercury ? How can the evaporation of mercury be shown? What is cinnabar? How is mercury obtained from it? 375. What is vermilion ? When is it black ? W^hen red ? 376. What is the com- position of calomel ? What of corrosive sublimate ? What are their prop- erties ? What antidote is recommended ? How does it act ? 377. What is amalgamation ? How carried on ? 378. What is said of the properties of silver ? Its uses ? Explain the tarnishing of silver. 379. In what min- eral does silver occur ? How is it extracted ? What is cupellation ? 380. What is the composition and nature of lunar caustic, so called? 381. De- scribe the silver assay. 382. How is gold found in nature ? With what is it alloyed ? What are its properties ? Explain the term carat. 383. How is gold chloride made? For what used? 384. Give in full what is said of the properties and uses of platinum. In what acids does it dissolve ? 385. Describe and explain Dobereiner's Lamp. 386. Describe the experi- ment with ether and a coil of platinum wire. Explain this briefly. 387. What other metals belong to the platinum group ? M 2 274 CHEMISTRY. CHAPTER XXL CHEMICAL INFLUENCE OP LIGHT. 388. Chemical Influence of Light. You have already had some illustrations of the fact that the rays of the sun not only give light and heat to the earth, but also stimulate many chemical operations. For example, you saw in 223 that chlorine and hydrogen are very ready to unite under the stimulus of light, when, if light be shut out, no such union takes place. So strong is this disposition to unite under this stimulus, that if a mixture of the two gases be exposed to the direct rays of the sun, the union is so sud- den as to occasion an explosion. A solution of ferrous sulphate may be kept a long time in the dark without any change ; but expose it to sunshine, and a precipitation of ferric oxide at once begins. Indeed, it is ascertained that precipitation in many cases may be quickened by the rays of the sun. You have a familiar example of the chemical influence of solar light in the blackening of common mark- ing-ink when the marked articles are exposed to the light. In sun-bleaching, also, the sun's rays stimulate the chemical changes which take place. 389. Universality of this Influence. Wherever light goes it acts chemically. It was said by Niepce, who was asso- ciated with Daguerre in the investigations which led to his great discovery, that " no substance can be exposed to the sun's rays without undergoing a chemical change." Though, with the common notion which was prevalent that the sun, the great source of light and heat, had little to do CHEMICAL INFLUENCE OF LIGHT. 275 with chemical results in nature, the remark of this philos- opher when it was made was considered extravagant, and his light-pictures were looked upon by his friends as mere pleasant curiosities, there is at the present time every day more and more realization among chemists of the great truth which he uttered. The solar ray is now regarded as one of the grand chemical powers of our earth. 390. Chemical Influence of Light on Vegetables. Light produces chemical results in all of the three kingdoms of nature, but they are perhaps the most observable in the vegetable world. The green coloring substance called chlorophyll, which, appearing in the leaves and other parts of plants, makes the general face of nature so pleasant to the eye, is entirely dependent upon the stimulus of light, as may be seen in many common facts. The sprouts of vegetables in our cellars, for example, are destitute of this coloring substance exactly in proportion to the exclusion of light. This explains the deep green of leaves in trop- ical countries, where " the sun shines forever unchangeably bright." Light has the same influence upon other colors, and hence the rich deep colors of tropical fruits and flowers, and the subdued tints of those of colder regions. But the stimulus of light not only acts thus upon the colors of veg- etables, but it is absolutely essential to the formation of their substance. That chemistry of the leaves which, as you learned in 128, furnishes to plants from the air so large a part of their carbon, can not go on without the in- fluence of light. Indeed, as stated in 129, the leaves rest from this chemical work, this laying in of carbon, when the light is withdrawn at night. 391. Light and Locomotives. It was in relation to the in- fluence of light upon vegetable growth that George Ste- phenson, the great inventor of locomotives, said that light was the power that moved them. The conversation in 276 CHEMISTRY. which he said this is thus related : Mr. Stephenson asked the late Dean Buckland, " Can you tell me what is the power that is driving that train ?" alluding to a train which happened to be passing at the moment. The learned dean answered, "I suppose it is one of your big engines." "But what drives the engine?" "Oh, very likely a canny New- castle driver." "What do you say to the light of the sun ?" " How can that be ?" asked Buckland." It is noth- ing else," said Stephenson. " It is light bottled up for tens of thousands of years ; light absorbed by plants and veg- etables, being necessary for the condensation of carbon dur- ing the process of their growth, if it be not carbon in an- other form ; and now, after being buried in the earth for long ages in fields of coal, that latent light is again brought forth and liberated, made to work as in that locomotive for great human purposes." 392. Chemical Influence of Light on Animals. The influ- ence of light upon color is very much the same in animals as in vegetables. Accordingly, the plumage of birds in tropical climates presents the richest hues, while the pre- vailing color in the colder regions is a russet brown. So, also, those fishes that swim near the surface have various and rich colors, while those that live in deep water are gray or brown or black. Those that live at so great a depth that very little light reaches them are nearly color- less. It is pretty well ascertained that at depths where no light can penetrate there are no fishes or other animals of a high order, showing how dependent animal life is upon light. The influence of light upon life and health has at- tracted considerable attention of late ; and, although some extravagant things have been said about it by superficial enthusiasts, there is no doubt that it is an influence which should be seriously taken into the account in the arrange- ment of our houses and workshops, and in the formation of our habits of living. CHEMICAL INFLUENCE OF LIGHT. 277 393. Light Dissected. Light that does all this is not one thing ; but in every ray, besides the seven colors which, blended together, make the white light, there are two dis- tinct powers heat and chemical power. The dissection of light effected by the prism is depicted in Fig. 102. We Proportionate width of th ^^^ .... Greatest Chemical Action. of Colors* Yellow 40 | I ....Greatest Light. Greatest Heat Fig. 102. have in Part I. described the manner in which this spec- trum, so called, is made, and commented upon the colors that compose white light, and we need to say no more hero on these points. The chemical power is what concerns us now. This is greatest at the violet end of the spectrum, diminishing as you go from there toward the other end. The greatest heat, on the other hand, is at the red end. We have, then, bound up in every ray of light that comes from the sun three powers viz., light, heat, and chemical power. This last has been called actinism, or the actinic power. The reason that these three powers can be par- tially separated in the spectrum, as well as the different colors, is that different parts of the ray are differently re- frangible the calorific part the least, the actinic part the most, and the illuminating part between the two. Then of the colors, the least refrangible is the red, the most so the violet. You observe that we speak of the separation of 278 CHEMISTRY. the three forces or powers in the spectrum as being par- tial. We will explain this. As the ray of light is bent out of its course by the prism, and the spectrum is formed on the screen, each of the three powers has a point in the spec- trum where its influence is most concentrated. On each side of this it lessens till you come to a point where it is comparatively feeble. "The result of the action of any ray depends, however, greatly on the physical state of the surface upon which it falls and in the chemical constitution of the body ; indeed, for every kind of ray a substance may be found which under particular circumstances will be af- fected by it; and thus it appears that the chemical func- tions are by no means confined to any set of rays to the exclusion of the rest " (Fownes). 394. Experiments. Many interesting experiments can be tried with the spectrum, some of which we will detail : Brush over some paper with a solution of nitrate of sil- ver, and then expose strips of it to different parts of the spectrum. A strip applied at the lower part where the red color or ray is will be scarcely affected, for the chemical rays there have little or no power to affect this substance. A strip at the violet end, on the other hand, will be dark- ened quite rapidly, because there is the centre of the influ- ence of this power. So, also, a strip in the green ray will not be affected so much as one in the blue, because the lat- ter is nearer to that centre. Paper charged with chloride of silver is still more sensi- tive to light than that charged with the nitrate, and there- fore gives more decisive results. It may be charged in the following manner: The paper is first wet in a solution of common salt or chloride of sodium. Then it is brushed over with a solution of nitrate of silver. This decomposes the salt, leaving on the paper chloride of silver in place of the chloride of sodium : CHEMICAL INFLUENCE OF LIGHT. 279 Chloride of Nitrate of Chloride of Nitrate of sodium. silver. silver. sodium. NaCl + AgN0 3 = AgCl + NaNO 3 Strips of paper thus prepared, placed in parts of the spec- trum where the chemical power resides, will be darkened, because the chloride of silver is decomposed, the chlorine passing off and leaving the silver attached to the fibres of the paper. It is to be remembered in preparing these pa- pers that exposure to the light has the same effect upon them that placing them in the chemical limits of the spec- trum does, for every ray of white light has the chemical power bound up in it. For this reason the papers must be prepared in a dark room, and, after being dried by blot- ting-paper, must be put between the leaves of a book to prevent the light from coming to them. Some other experiments akin to these may be tried with colored glasses. Glass stained dark blue with oxide of co- balt lets scarcely any light pass through, but offers no hin- derance to the passage of actinism, as may be seen by using the papers charged with chloride of silver. Yellow glass, on the other hand, will let the light and heat pass, but not the actinism. You remember that a mixture of hydrogen and chlorine exposed to the direct light of the sun explodes, so rapid is their union, while they do not unite at all if the mixture be kept in the dark. Now when the mixture of the two gases is exposed to the sun in a vessel or tube of red glass scarcely any effect is produced ; but if it be ex- posed in a tube of violet-colored glass the gases combine rapidly with an explosion, just as they do when the glass is without color. 395. Light-Pictures. If lace be spread over paper charged with chloride of silver, on exposure to light for a few min- utes its whole shape, to the minutest thread, will be traced in white lines. The explanation is this: The chemical 280 CHEMISTRY. Fig. 103. power of the sunlight acts upon the chloride of silver, dark- ening it, except where the threads of the lace prevent it from doing so. The tracings of the lace consist, then, of the chloride of silver un- changed ; while in the dark parts there is me- tallic silver minutely di- vided. In the same way skeletons of leaves, or even the leaves them- selves, may be copied. So, also, we may copy engravings, if we oil them so that the light may shine through the unprinted portions. The dark parts of the engraving will of course be light, and the light parts dark in the copy. This constitutes what is called a " negative ;" and a "positive" or true copy can be obtained by dealing with the " nega- tive" as you do at first with the engraving it- self. In Fig. 103 you have represented a "neg- ative" of a leaf, the dark- est parts of the picture corresponding to the thinnest parts of the leaf, as the light coming through them decomposes the Fig. 104. CHEMICAL INFLUENCE OP LIGHT. 281 chloride of silver. In Fig. 104 (p. 280) you have the " posi- tive " of the same leaf. 396. Fixing the Picture. The figures of which we have spoken can not be permanent, for exposure to light will destroy them by making the whole surface equally dark. To verify this, take a copy of lace and hold it up to a win- dow. The white lines of the tracery will disappear quick- ly, the whole surface being subjected to the chemical power of the light, and becoming therefore covered with the dark silver. This effect, however, will not occur if the window be covered with a heavy yellow curtain, for this will not allow the chemical power to pass through. Now if after a picture is made we could by means of any substance re- move from it all the chloride of silver, and at the same time leave the metallic silver untouched, we should have a pict- ure which the light can not affect. Such a substance we have in sodium hyposulphite. This dissolves out the un- decomposed chloride of silver, but produces little or no effect upon the metallic silver which constitutes the parts of a " positive " picture. 397. Photography. We have given you a brief outline of the principles on which the beautiful art of photography is based. To pursue this interesting subject any farther will lead us too deeply into this important branch of Ap- plied Chemistry. QUESTIONS. 388. Give some examples of the chemical influence of light. 389. What is said of the universality of its influence ? 390. State in full what is said of its influence on vegetables. 391. Give the anecdote of George Stephen- son. 392. State in full what is said of the influence of light on animals. 393. What three powers are there in the sun's rays ? Show how these are arranged in the spectrum. Why can they be thus partially separated ? What is actinism ? Where in the spectrum is the point of greatest light ? 282 CHEMISTRY. Where the centre of actinic power ? Where the point of greatest heat ? 394. State the experiments with paper charged with nitrate of silver. How can you charge paper with chloride of silver ? What is said of the effect of light upon it ? What experiments can be tried with variously colored glasses? 395. State in full what is represented in Figs. 103 and 104. 396. What is said of "fixing" the picture obtained with the chloride of silver ? CHAPTER XXII. SPECTEUM ANALYSIS. 398. Continuous Spectra. You have learned in Part I. that when light from the sun passes through a prism it is separated into its different colors, because rays of differ- ent colors are unequally refracted. The first band in the figure on p. 287 represents roughly the spectrum thus ob- tained. Suppose light from other sources than the sun is thus analyzed by a prism, what are the results ? Briefly, the results vary according to the nature of the light emitted ; how this is we will now explain to you. In the first place, the emission of light is a question of temperature ; any solid body heated high enough emits light. Now it is found that all solid bodies heated to incandescence that is, until they glow with light produce spectra resembling in the main that of the sun, at least so far as the nature and order of the colors are concerned. For example, a glowing plat- inum wire, a candle, and a gas flame give the same sort of spectrum, uninterrupted in the shading of its colors and containing them all. Such spectra are termed continuous. 399. Discontinuous Spectra. There is another kind of spectrum called discontinuous or broken. These are pro- duced by glowing gases. You have already learned that SPECTRUM ANALYSIS. 283 some chemical substances burn with colored flames ; po- tassium with a violet flame, and sodium with a yellow flame, as seen when burning on water, or when common salt is thrown into a fire. Then, again, strontium com- pounds burn with a beautiful red flame, and barium with a green flame, so that they are used in making fireworks. Now in all these cases the flames are colored by the bodies named in the state of gases. If you examine the light from burning sodium by means of a prism -that is, allow the light from incandescent sodi- um vapor to pass through a prism you will obtain a dis- continuous or broken spectrum: only one color will be seen, viz., yellow, and this yellow color will fall at the same point in the spectrum that the yellow rays of the sun spectrum would strike. It appears, then, that sodium vapor heated red-hot gives out rays of a particular re- frangibility ; now this illustrates a well-defined law : That every chemical element in the state of gas, when heated until it becomes luminous, gives off a peculiar light. In the example taken, light of all one color was given out by the substance heated ; this is not the rule, however, but rather exceptional, for most bodies emit light of various kinds, possessing different degrees of refrangibility ; thus the light from glowing strontium vapor analyzed by a prism gives a spectrum made up of several yellow and red rays, together with one blue one. 400. Use of the Slit. The appearance of a continu- ous spectrum, obtained from light of any source, depends much upon the size and shape of the opening through which the light passes before passing through the prism. If a round opening be used, a series of disks will be seen overlapping each other, as shown in Fig. 105 (p. 284). If an opening having parallel sides be employed, the dif- ferent colors will shade off into each other imperceptibly, 284 CHEMISTRY. Fig. 105. the brightest light appearing in the centre of the yellow portion. By making an opening of this shape very narrow, there is less overlap- ping of the different colors, and a purer spectrum is obtained. A very narrow open- ing with parallel sides, called a slit, is gener- ally employed in ex- amining the spectra of different bodies ; and in the case of discontinuous or broken spectra, the colored image of the slit is what produces the banded appearance of such spec- tra. A narrow ray of yellow light produces a yellow band of light in the spectrum, a red or a blue bundle of rays produce a red or a blue line or band in the spectrum. This is shown in Fig. 105. 401. The Spectroscope. This is the name of the instru- ment employed for thus analyzing the light emitted from different sources. A brief description of Fig. 106 (p. 285) will suffice. A spectroscope consists essentially of a prism, a telescope, and a slit. In the figure before you the prism, A, is placed on a plate of metal supported by a tripod, the telescope is at B, and the slit is attached to the tube C, which contains also a lens at the end next to the prism. The substance to be examined, held on a platinum wire sup- ported by the stand /*, is heated in the non- illuminating flame of a Bunsen burner, I the cone, w, at the top of the burner serving simply to steady the flame. The light passes from the flame, /, through the slit at the end of the tube C into this tube ; the rays are made parallel by the lens in this tube before they fall upon the prism, A. The SPECTRUM ANALYSIS. 285 Fig. 106. The Spectroscope. rays are then refracted, and the image of the refracted rays is observed through the telescope, B. In the instrument here pictured, a third tube, D, contains a scale engraved on a glass plate, and this being illuminated by the candle flame, <7, can be seen at the same time with the spectrum ; one face of the prism reflecting this scale through the telescope, B, to the observer. 402. Spectrum Analysis. The spectroscope, invented in 1859 by two distinguished Germans, a chemist (Bunsen) and a physicist (Kirchhoff ), is of great importance to the chemist, for it places in his hands a means for detecting certain substances with great accuracy and extraordinary 286 CHEMISTEY. delicacy. It follows from what we have told you in the preceding sections that any chemical substance capable of being converted into an incandescent vapor by the heat of a Bunsen burner must give out light of a particular degree of ref rangibility ; and consequently any one look- ing through the telescope, B, will see a pictorial image in brilliant colors characteristic of that particular substance. Practically this is done as follows : Dip a small platinum wire into the material you wish to examine, insert the sub- stance into the flame (which, being non-luminous, gives no spectrum), and place your eye at B. Now it is found that only a certain number of chemical substances are capable of being volatilized in the heat of a Bunsen burner or of an alcohol lamp ; these are the salts of the alkalies, many of the salts of the alkaline earths, besides some other bodies not classifiable ; or, stating it differently, spectrum analysis, under the circumstances described, enables the chemist to detect sodium potassium (lithium, caesium, rubidium), calci- um, strontium, barium, copper, boracic acid, and some other bodies. The spectra seen are shown in Fig. 107 (p. 287), and in the frontispiece to this work. The first band represents the spectrum of the sun, the vertical black lines in which you may for the present dis- regard. Sodium gives a single yellow line or band, occurring at a on the scale ; potassium gives a red line at the right end of the spectrum, a blue one at the extreme left, and a long luminous band between. Barium gives a large number of lines and bands, several red, orange, yellow, and four very bright green ones. These lines and bands al- ways occur at the same point on the scale of the same spectroscope ; the scales of various instruments vary, but the positions of lines can be compared by preparing maps of the various spectra referred to a constant scale. Thus XJf SPECTRUM ANALYSIS. P' IE 287 C JJ a A Ba Tl Fig. 107. you see the accuracy of the analysis is all that can be desired. We have referred to the delicacy of this method of anal- ysis. This delicacy varies with different substances ; of so- dium, the one three-millionth of a milligramme ( 3>ow>( ! w>OU u gramme) can easily be detected. Sodium in some shape, combined with chlorine chiefly, is always present in the 288 CHEMISTRY. air in sufficient quantity to be seen very readily in the spectroscope by agitating the air ; clapping the hands to- gether or dusting a book will make the yellow line flash out brilliantly, the particles of dust always containing salt. Of strontium, the -^-^ of a milligramme is capable of detection ; of calcium the same ; of lithium, the ^-^ of a milligramme. 403. Discovery of New Elements. So great is the deli- cacy of spectrum analysis that many known elements have been found more widely distributed than was previously supposed, and four new elementary substances have been discovered which existed in such minute quantities as to be overlooked by the ordinary methods of examination. Bunsen and Kirchhoff, the discoverers of spectrum analy- sis, almost immediately after their invention discovered two elements, ca3sium and rubidium, which belong to the class of alkaline metals. Caesium was recognized by two blue lines in its spectrum, which did not correspond in position to the blue line of strontium, and rubidium by two red lines. The material examined was the residue from the evaporation of certain mineral waters. Since then thallium has been discovered by Prof. Crookes, of London, and indium by Profs. Reich and Richter, of Sax- ony. These bodies are mere chemical curiosities, occur- ring in far too small quantities to become of commercial value unless some unexpected and rich source is awaiting discovery. In the chapters on metals we have barely al- luded to them by name. 404. Spectra of the Heavy Metals. The heavy metals and their salts as a rule do not give spectra when heated in the non-illuminating flame of a Bunsen burner, but this is only because the temperature is not high enough to vol- atilize them. To obtain spectra of these substances, there- SrECTEUM ANALYSIS. 289 fore, a strong current of electricity is used, excited by a powerful galvanic battery, and the material heated in the electric arc is converted into incandescent vapor, and thus yields a spectrum. Maps have been made showing the thousands of lines which are seen in the spectra of nearly all the elements. The apparatus is difficult to manage and very expensive, so for ordinary work the chemist depends upon the Bunsen burner or alcohol lamp, and confines his research to the lighter metals. 405. Celestial Spectroscopy. "We have not previously re- ferred to certain peculiarities in the sun's spectrum, be- cause we did not want to tell you too many things at once. If you examine the sun's spectrum with a good spectro- scope having a narrow slit, you will see fine black lines crossing the spectrum. These were observed many years ago by Fraunhofer, a German optician, but no attempt was made to explain them until after the perfection of the spectroscope by Kirchhoff. For good and sufficient rea- sons, which we can not explain to you in this book, it is be- lieved that those black lines give us indications of the ele- mentary bodies burning in the sun. A careful study of these lines by many eminent men has led to a remarkably accurate knowledge of the constitution of the sun. Thus, wonderful as it may appear, we have good reason for be- lieving that the sun contains sodium, calcium, magnesium, iron, copper, zinc, hydrogen, and many other metals; and that the sun does not contain gold, silver, mercury, po- tassium, lead, arsenic, or platinum. More perfect instru- ments may eventually remove some element from this last list and place it among the bodies known to exist in the sun. Not only have astronomers, thus aided by the chem- ist, examined the light of the sun, but they have studied the fixed stars, the nebula?, and comets, thus developing a special branch of spectrum analysis called celestial spectro- N 290 CHEMISTRY. scopy. A description of the methods employed, the instru- ments used, and the results obtained would be interesting, but must be passed by in the present work. QUESTIONS. 398. Do lights from other sources than the sun yield spectra ? Upon what does the emission of light depend ? Give examples. What are continuous spectra ? 399. What produces discontinuous spectra ? What bodies color flames ? What kind of a spectrum does sodium give ? What strontium ? 400. Explain the use of a narrow opening for the passage of light. What produces the banded appearance of discontinuous spectra ? 401. Describe and explain the spectroscope. How does the light pass ? 402. Who invented this instrument ? When ? How is it made prac- tical ? What can be detected by it at the temperature of a Bunsen burn- er ? What kind of a spectrum does barium yield ? What is said of the delicacy of this instrument ? 403. What elements were discovered by Bunsen and Eirchhoff? How? From what source? What other ele- ments have been discovered by this means ? 404. How can spectra of heavy metals be obtained ? 405. State in full what is said of celestial spectroscopy. CHAPTER XXIII. ORGANIC CHEMISTRY. 406. Introduction. Formerly the term Organic Chemistry was applied to that branch of chemistry treating of sub- stances which derived their existence from the operations of either vegetable or animal life ; it was erroneously sup- posed that the production of these substances was due to a mysterious power, called vital force, residing in the organs of plants and animals, and that this class of substances could not be artificially formed. Under this view organic chem- istry was considered as the Chemistry of Life. Within from twenty to thirty years, however, many sub- ORGANIC CHEMISTRY. 291 stances Lave been made in the chemist's laboratory which were formerly regarded as solely the products of the agency of life, and consequently the theory of a special vital force governing the attractions of matter in plants and animals has been gradually abandoned. Urea (a constituent of urine), alcohol, acetic acid, alizarine (a beautiful dye-stuff), and indigo, are some of these organic bodies which have been synthetically prepared that is, by a putting together of so-called inorganic materials. The branch of chemistry you have been studying is some- times called Inorganic, because opposed to Organic Chem- istry; another and very suitable name is Mineral Chem- istry, since it concerns chiefly mineral substances. This division into Mineral and Organic Chemistry is, however, a mere matter of convenience, and not countenanced by Nature. The same elements compose the bodies and sub- stances existing in the three kingdoms mineral, vegetable, and animal; and the same laws of attraction hold these elements together, and govern their combinations. Certain organic substances do, indeed, differ radically in their nature and formation from mineral bodies, exhibiting O a fibrous and cellular structure, and forming parts of organs peculiarly the product of life ; these are termed organized bodies, and must not be confounded with organic bodies. As an example of this difference take the case of a fruit ; the fibrous, cellular, pulpy matter forming the woody frame- work of the fruit is an organized body ; but the acids, the sugar, the gum, the starch, the coloring matter, etc., con- tained in these living organs are organic bodies. Whether the chemist will ever be able to imitate organized struct- ure is exceedingly problematical. The distinguishing pow- er between organic and organized bodies lies in the micro- scope. 407. Constituents of Organic Substances. "We have stated 292 CHEMISTRY. that organic bodies are composed of the same elements as mineral bodies, and while this is perfectly true, the state- ment must be qualified. The number of elements which enter into the composition of organic bodies is compara- tively small. You remember there are sixty-three element- ary substances at present known to the chemist : now of these four build up nearly the whole of the innumerable organic bodies ; these four are carbon, hydrogen, oxygen, and nitrogen. Some of the other elements occur, it is true, but to a comparatively limited extent. Thus we have calcium and phosphorus in the bones, iron in the blood, silicon in tho stalks of grains and grasses, and various other elements in very small quantities for various purposes. The four grand elements C, H, O, and N we have learned about in studying mineral chemistry; one of them, you observe, is a solid, while the other three are gases. They are all with- out taste or smell, and the solid element is in its ordinary form of a dark color ; and yet from these few materials what an endless variety in taste, smell, color, and other properties is produced in the vegetable and animal world ! Let us not be understood to say that other elements be- sides the four C, II, O, and N are of little importance. They are not only of use in their place, but they are essen- tial, some of them as much so within a certain range as the grand elements. 408. Sources of the Elements in Organized Substances. The elements of which vegetable and animal substances are composed come from three sources earth, air, and water. In the case of the plant they enter by the root and the leaves. By the root, with its millions of little mouths, they are drunk up dissolved in water, and in the sap they flow upward to the leaves, where carbon is added from the air. It is in the leaves that the sap, the build- OEGANIC CHEMISTRY. 293 ing material of the plant, is completed, so as to be fit for use in constructing all the various parts the wood, the bark, the flowers, the fruit, etc. Animals, also, receive their elements in part from the earth, but not in a direct man- ner. They receive them from the plants which they eat. The plant, then, gathers up, as we may say, the elements from the earth for the use of the animal. They are com- bined together in the blood, which is to the animal what the sap is to the plant the common building material of the body. But as in the case of the plant, so with the an- imal, all is not derived from the earth. A part of the ox- ygen needed comes from the air, being admitted by the pores of the lungs, as part of the carbon of the plant goes into it by the pores of the leaves. It is believed that the leaves of plants decompose the carbonic acid that comes to them from the lungs of animals, separating it into its ele- ments, carbon and oxygen, and that the carbon is absorbed to make a part of the plant, while the oxygen thus set free again returns to the lungs of animals. Every leaf, there- fore, is a laboratory to purify the air, and maintain its prop- er supply of oxygen for the use of the animal kingdom. 409. Subservience of Plants to Animals. You see, then, that the subservience of plants to animals is twofold. First, they supply to animals the elements of their growth by gathering them from earth, air, and water into their own substance. This subservience is direct in the case of herbivorous animals. It is no less real, though indirect, in the case of the carnivorous, for they eat the flesh of the herbivorous. Secondly, plants, by their chemical action upon the air, keep up that supply of oxygen which is need- ed by animals. 410. Difference of Vegetable and Animal Structures in Composition. In this subservience of plants to animals there is one very interesting fact to be noted in regard to 294 CHEMISTRY. the difference in their composition. All the four grand elements carbon, hydrogen, oxygen, and nitrogen enter into the structure of animals, but only the first three are found in the structure of vegetables. The inquiry then arises in what way the nitrogen is supplied to animals. Nitrogen constitutes four fifths of the air which is so con- stantly entering their lungs, and yet not a particle of it is supplied to their bodies in this way. The blood in the lungs receives oxygen from the air, but no nitrogen, as you learned in 132. The nitrogen which is needed is supplied through the agency of plants. For this purpose, though there is none of this element in their structure, many of them have it in their juices and fruits. It is especially present in Indian corn, the grains, pease, beans, etc., so ex- tensively used for food. In such cases the plant may be said to gather up this element, and deposit it, not in its own structure, for it is not wanted there, but in repositories, where man and other animals can take it and appropriate it to their use. There is no case in which the design of the Creator is manifested in a more marked manner than it is here. 411. Definition of Organic Chemistry. Of the four ele- ments C, H, O, and N" playing such a wonderful part in the vegetable and animal kingdoms, the first of these, carbon, is by far the most important, its presence being character- istic of organic substances. Hence organic chemistry is often defined as the Chemistry of Carbon Compounds. This definition includes the simple carbon compounds, carbonic oxide, carbonic anhydride, and others which we have just studied under the head of mineral chemistry ; but it is im- possible to draw any precise line of distinction, especially since the same elements and laws of union are common to the two divisions. Organic bodies are characterized by great complexity and instability of the molecules. ORGANIC CHEMISTRY. 295 412. Molecules In Organic Bodies. Organic substances arc generally more complex in their constitution than min- eral substances, their molecules containing a far larger number of atoms. For example, while carbonic anhydride has in each molecule one atom of carbon and two of oxy- gen, CO 2 , and sulphuric acid two of hydrogen, one of sul- phur, and four of oxygen, H 2 SO 4 , making 7 atoms in the molecule, each molecule of tartaric acid contains 16 atoms, as indicated in the formula H 2 C 4 H 4 O 6 ; while a molecule of starch is believed to contain 63 atoms (starch = C 18 H 30 O 15 ), and of stearin 173 atoms. One of the most complex of organic bodies is albumen, which is supposed to contain several hundred atoms in a molecule ; but this number will probably be reduced when, its composition is better understood. 413. Instability. Organic substances are unstable com- pounds, that is, very easy to decompose, because they are so complex. It is with them as it is with machinery. The greater the complication, the greater is the liability to derangement. The more atoms there are in a molecule, therefore, the more easily can it be broken up, and the more kinds of atoms there are in it the greater is the lia- bility to this result. Not only do organic substances differ from the inorganic in this respect, but they differ among themselves. We have a good example of this in bleach- ing. The coloring matter of the cloth is broken up and dissipated, while the cloth itself remains, for the simple rea- son that the molecule of the coloring matter is composed of four elements carbon, hydrogen, oxygen, and nitrogen M'hile that of the vegetable tissue, the substance of the cloth, is composed of only three carbon, hydrogen, and ox- ygen. The more complex substance is decomposed first ; but if the process be continued after the cloth has become white that is, after the coloring substance is all destroyed CIIEMISTEY. the vegetable tissue will be attacked, and the cloth will become more or less rotten from the destruction of some of its molecules. 414. Difference in Properties with Similarity of Composi- tion. There is often found in organic chemistry great sim- ilarity of composition with wide difference in properties. We will give a few examples. Alcohol, cotton, sugar, and acetic acid are four substances certainly not much alike in their properties, and yet these widely dissimilar bodies are made of the same elements carbon, hydrogen, and oxygen. By examining the formulae of these bodies, here given, Alcohol C 2 H 6 O I Grape sugar .C 6 H 12 O 6 Cotton C 6 H 10 O 5 Acetic acid C 2 H 4 O 2 you will see that these three elements are combined in very different proportions ; and this illustrates as well the com- plexity of the molecules referred to in 412, for each of the formulae above represents one molecule. We have select- ed only four bodies made of these three elements, but act- ually there are many thousands of bodies composed of these three elements only. 415. Isomerism. Strange and mysterious as these facts appear, a much more apparently inexplicable feature re- mains to be shown. Examine closely the formulae of the last two bodies named, grape sugar and acetic acid ; you see that if we should multiply by three the little figures, or co-efficients, of the atoms of C, H, and O in acetic acid, we will get the formula of grape sugar ; thus : Acetic acid = C 2 H 4 O 3 . 3 Grape sugar = C 6 H 12 O 6 Here, then, we have two bodies made up of the same elements in the same proportion, and differing only in their molecular weights, and yet how different in their proper- ORGANIC CHEMISTRY. 297 ties! One is sweet, crystalline, capable of fermenting, neutral to litmus paper, being neither an acid, a base, nor a salt ; the other is sour, liquid at ordinary temperatures, and capable of combining with bases to form a large series of salts. We have said these bodies differ in their molecular weights ; we will explain why this is. You learned in 30 that the molecular weight of a body is equal to the sum of its atomic weights; hence we calculate thus: Acetic acid. Grape Sugar. ' C - 12; C 3 = 2 C 6 = 72 H = 1; II 4 = 4 H 18 - 12 O = 16; O 3 = 32 O = 9G Molecular weight = CO Molecular weight = 180 Substances which thus have the same chemical constitu- tion, and yet are dissimilar in their qualities, are called iso- meric substances, this term coming from two Greek words, tsos, equal, and meros, part. Isomeric substances may even have the same molecular weight ; they are then said to be metamerlc. Thus the molecular formula C 3 H 6 O 3 represents three different bodies possessing different properties and different constitutions ; how this can be is shown in the following formulas : C 3 H 6 O 2 may be arranged thus: C 3 H 5 O. HO which is Propionic Acid. " C 2 H 3 O.CH 3 " Methyl Acetate. " " CHO.C a H 3 O " Ethyl Formate. It is not necessary to know the nature of these bodies their names show you that they are essentially distinct. One, you observe, is an acid, the other two are compound ethers belonging to the class described in 423. 416. Explanation of Isomerism. The explanation which the atomic theory affords of this isomeric state is illustrated by Stockhardt by the various grouping of white and black squares which can be made on a chess-board, as seen in N 2 Fig. 108. Fig. 108. Here each figure is composed of eight white and eight black squares; but though the number is the same in all, the grouping is different. In a one and one; in b two and two, in c and d four and four squares are so joined to- gether as to make the figures look very different from each other. If we imagine these squares to be atoms we obtain an idea of isomeric substances, and can see how there may be bodies of the same constitution and form, yet presenting an entirely different appearance, and having very different properties. Isomeric bodies are far more numerous in organic than in mineral chemistry, because the molecules of organic sub- stances are more complex than those of inorganic ; for the difference in properties can not be owing to any thing else than a difference in arrangement of the atoms, and the more atoms there are in a molecule obviously the greater is the range afforded for differences in arrangement. This may be illustrated by reference to Fig. 108. Each of the squares contains eight small black squares, and eight white ones, sixteen in all. It is obvious that more and greater changes in arrangement can be made here than there could be if the number of small squares were less four, for example; and so, also, more differences in arrangement can be had in a molecule if it be composed of sixteen atoms than there can be if there be only four atoms in it. 417. Graphic Formulae. Another method of explaining isomerism makes use of so-called graphic formula. You learned in 44 that the elements differ in atom-fixing power, and that they are divided into groups, monads, dyads, triad?, tetrads, etc., according to this power. The four ORGANIC CHEMISTRY. 299 grand elements of which most of the organic world is constituted are rep- resentatives or types of these four classes, hydrogen being a monad, H' ; oxygen a dyad, 0" ; nitrogen a triad, N'" ; and carbon a tetrad, C iv . By taking advantage of these points of attraction, a peculiar kind of pictorial formulae may be constructed, called "graphic formulae." Thus the ordi- nary formula for water is H 2 O; but if we represent the dyad oxygen by O , and the monad hydrogen by H , we have by combining them H O II, a graphic formula for water. Take a more complex example, from organic chemistry. Alcohol has the formula C a H 5 .HO, graphically represented thus : H I H-C-H I H-C-O-H I H ! being a tetrad, O a dyad, and the rest monad hydrogen, each bond of affinity is satisfied by arranging the atoms in this manner. Now you will see how graphic formulae help to explain metamerism, the highest kind of isomerism. Take the three bodies which have already served us as examples. On the following page you have the ordinary formulae, the constitutional formulae, and the graphic formulae side by side, showing how differently the atoms are arranged in the molecules of each body. We can not explain to you how chemists are able to arrive at any probable knowl- edge of the arrangement of atoms in the interior of a molecule, for the sub- ject belongs to the highest branch of chemical philosophy. Of late years the most wonderful progress has been made in precisely this field, and indeed the whole aim of modern investigators is directed to this study of internal atomic structure. 300 CHEMISTRY. GRAPHIC EXPLANATION OF ISOMERISM. !._. Constitutional Substances. Formula;. Graphic Formulae. Propionic ^ f C 3 H 5 O. HO, H Acid or 1 CH 3 H-C-H 1 1 pj* 2 CH 2 H-C-H * *S 1 1 'o -i COOH O=C-O-H S "^ Methyl 1 8 O | Acetate I ^ * C 2 II 3 O.CH 3 O, or II 1 H-C-H II " fe CII 3 1 1 2 ^ 1 0=C-O-C-H CO(OCHs) 1 S H ^ ^ Ethyl Formate . iCHO.C 2 H 5 O, II II II or 1 1 1 H O=C-O-C-C-H 1 1 I CO(OC 2 H 5 ) II II QUESTIONS. 406. Explain the change of views which has taken place with reference to organic substances. What examples of synthesis are given ? What is said of the division into mineral and organic chemistry ? What are or- ganized bodies? How do they differ from organic bodies? Give exam- ples. 407. What are the four chief constituents of organic bodies ? What others occur also ? 408. What is said of the sources of the elements in or- ganized bodies? Show how leaves purify the air for animal life. 409. Show that the subservience of plants to animals is twofold. 410. How is nitrogen furnished to animals ? 411. Give a definition of organic chem- istry. Explain it. 412. Show that the molecules of organic bodies are complex in constitution. How many atoms in a molecule of tartaric acid ? Of starch ? Of stearine? 413. What is said as to the instability of or- ganic substances? Give an example from bleaching. 414. Of what three CLASSIFICATION OF OKGAXIC SUBSTANCES. 301 elements are cotton, alcohol, sugar, and acetic acid composed ? How do you account for the difference in their properties? 4 Jo. Show what is meant by isomerism. Take acetic acid and grape sugar as examples. When are substances metameric ? Give examples. 41 6. Explain isomer- ism by reference to a chess-board. Why is isomerism more common in organic than in mineral chemistry? 417. What are graphic formulae? Illustrate by the graphic formula of water. Explain it. What is said of the arrangement of atoms in the molecule ? Explain the table on page 300. CHAPTER XXIV. CLASSIFICATION OF OEGANIC SUBSTANCES. 418. Scientific Classification. Two methods of classify- ing organic bodies for the convenience of study may be followed ; in one an empirical arrangement connects sub- stances which are closely related in nature, and treats in groups bodies possessing similarity of origin or properties ; the other is a strictly scientific classification based on the atomicity of the tetrad carbon. In this work we will fol- low the former arrangement, prefixing it, however, with a brief synopsis of the scientific method, in order to introduce to you a number of bodies which would otherwise find no place in the so-called natural system. Scientifically con- sidered, organic bodies may be classified as follows : I. Hydrocarbons. II. Alcohols. III. Ethers. IV. Aldehydes (and Ketones). V. Acids (and Anhydrides). VI. Amines (including Alkaloids). VII. Organo-metallic Compounds. This is a greatly abbreviated scheme, and does not include many bodies produced in the living organism, the chemical 302 CHEMISTEY. relations of which are not yet well enough understood to bring them within a scientific system: such are gelatin, albumen, vegetable resins, and other compounds formed in the bodies of plants and animals. . We will now review briefly the chemical relations of the above-named groups, reserving details until we meet with them again farther on. 419. Hydrocarbons. You have already become somewhat familiar with two important hydrocarbons in the first part of this work marsh gas, CH 4 , and defiant gas, C 2 H 4 . But besides these there is an immense number of other bodies, solid and liquid as well as gaseous, made up solely of C and H in various proportions. No two elements are capable of combining in so many different forms as carbon and hydrogen. On page 324 you will find a table giving the names and formula of a large number of hydrocarbons of the so-called Marsh Gas Series, occurring in American petroleum. On examining the formula you will notice that in each of the two series the hydrocarbons differ by exactly CH 2 ; that is, each successive formula may be ob- tained by adding CH 2 to the preceding one ; this is another and striking example of isomerism. Besides the long series of hydrocarbons given on page 324, there are several other series differing from each other by H 2 , and the members in each differing by CH 2 . Thus olefiant gas, C 2 H 4 , belongs to a series which takes its name from this its important member. In the following table you have this series with the formula?, and the correspond- ing alcohol and acid, to which we will have occasion to re- fer a little later. In this table olefiant gas is called Ethy- lene. CLASSIFICATION OF ORGANIC SUBSTANCES. 303 THE OLEFINES, OR ETHYLEXE SERIES OF HYDROCARBONS. NAME. FORMULA. BOIT.TNQ POINT. COEBE8PONBIXQ A1X3O110L. CORRESPOND- ING AOID. Methylene. CH 2 Gas Wood-Naphtha Formic. Ethylene CH. Gas Alcohol Acetic. Propylene. . C 3 H 6 17.7 Propvlic Propvlic. Butvlene. . . C 4 H 8 +3 Butylic Butyric. Amylene. . . C 5 H 10 35 Amylic (Fusel-Oil). . Valerianic. Hexvlene C H 69 Caproic. . Caproic Heptvlene C H 9 > CEnanthic CEnanthic Octvlene. . . (TH 1fi 115.5 Caprylic Caprylic Xonylene . . C 9 H 18 140 Pelargonic. Decatylene. C 10 H 20 160 Cetvlene. . . c lfi u,. 275 Ethal. Palmitic Cerotene. . r H Solid Cerotene. Cerotic Melissene. . C, H SO Solid Melissene. Melissic 420. Homologues and Isologues. The members of a group of hydrocarbons which differ regularly by CH 2 , as in this table, are said to be homologues, or to form a homologous series. Two or more series, on the other hand, differing from each other by H 2 , are said to be isologites, or to form an isologous series. Thus the members of the Ethylene or Olefiant Gas Series are homologous among themselves, but isologous with respect to the Marsh Gas Series on page 324. Many of the hydrocarbons of such isologous series are rare bodies, mere chemical curiosities; but we will give you a table showing some of these, that you may the better understand the terms homologous and isologous, and that you may see at a glance the enormous number of com- pounds of hydrogen and carbon which are capable of ex- 304 CHEMISTRY. HOMOLOGUES- be o- *-. p" d i . c> c5 i ; IS *- p K | ^ p ^* !3 5 : I1 c TEREBENE8. C n H 2n -4 - s" M K S n g. S 1 c3 ta I r * S 6* S c r-% y. a* . K i oTc5 ^ 5 o s fl f| c5 j S -r S3 .2 o 1 S ^ c3 S3 ",.5 sT M* r 1 ^* *"* r -^ " >^ *^ r ^ C "^ y 3 *- s (O J/ d " T! ^ . o ^ 3 ^ 2 * W S iJ O o * CH 2 Methylene, or Methene. C 2 H 4 Ethylene, or Ethene. rf! .gi" C 5 H 10 Amylene, or Quintene. C 6 H 12 Caproylene, or Sextene. ARAFFIN8. C n H 2n +2 ell oT .1 ss ^..3 S-|l aT ,ij Is B 2 |-| "?,( oT r S o"?J ^ s S o I s . ^s 51 CLASSIFICATION OF ORGANIC SUBSTANCES. 305 isting. The bodies marked ? are not as yet known to chemists. At the head of each column is placed an algebraic for- mula expressing the formula of the series in general terms. By making n=l, n=2, n = 3, etc., each member of the ho- mologous series can be obtained. Two sets of names are given : the first are in general use among chemists, and the second is a very ingenious plan proposed by Dr. A. W. Hofmann, where the vowels a, e, i, o, and u are successively used in the final syllable to indicate the position of any member of the isologous series. The Marsh Gas Series, or Paraffin Series, as it is called, and the Olefin Series, are of first importance, next comes the Benzol Series ; of benzol itself you will learn more farther on. 421. Substitution. Marsh gas, you know, is CH 4 , but it may be considered as CHHHH, which is really the same thing. Each H represents one atom of hydrogen. Now certain bodies, as chlorine, bromine, cyanogen, etc. (provided they are monatomic ; see 44), may take the place of these atoms of H ; or, as we say, may be substituted, by means of appropriate processes, for each atom of H in the compound CHHHH; this substitution may take place all at once or gradually, as shown below : CHHHH or CH 4 (1) CHHHC1 or CH 3 C1 (2) CHHC1C1 or CH 2 Cl a (3) CHC1C1C1 or CHC1 3 (4) CC1C1C1C1 or CC1 4 (5) thus giving rise to a large number of so-called substitution compounds. The bodies numbered (1), (2), (3), (4), and (5) really exist, one of them, (4), being the well-known and valuable substance chloroform. Thus you see how the theory of substitution is made use of to explain the forma- tion of organic bodies. One more example, however, will be given. 306 CHEMISTRY. Ammonium, (NH 4 )', and cyanogen, (CN)', you have learn- ed, are called radicals, because they act like simple elements in certain cases. Now water is H O H; if you remove one H, you have left O H, or (OH)', which acts also like a radical, taking an important part in the building up of or- ganic bodies. This radical, called hydroxyl, is monatomic, or has one bond of affinity, as indicated above, and hence may take the place of one atom of hydrogen in any com- pound. Suppose, then, we substitute one atom of hydroxyl, (HO)', for one atom of H in the hydrocarbon we have been studying, CHHHH, what kind of a body will result? This question can of course be answered by experience only, and experience has taught the chemist that a body very closely resembling common alcohol is formed. Act- ually the substance is methylic alcohol, or CH 3 (OH). This leads us to the next subdivision of the scientific classifica- tion, which is that of alcohols. 422. Alcohols. You are now prepared to understand the relation between alcohols and hydrocarbons; for common alcohol has become the type of a vast number of bodies, some of which resemble it in its physical properties, but many of which are crystalline solids, and have no apparent connection with it. This relation is not founded on resem- blance in properties, but on similarity of constitution, which, indeed, is the key to this scheme of classification. Alcohols, then, are substances derived from hydrocar- bons by the substitution of one or more groups of hy- droxyl, (OH)', for hydrogen. Take the case of common alcohol : the formula of this body determined by analysis is C 2 H 6 O ; certain facts show its relations to ethane, which is C 2 H 6 . Now follow carefully the following formulae, and you will see how common alcohol is a derivative of ethane : CCHHHHHH = ethane ; remove one H and substitute CLASSIFICATION OF ORGANIC SUBSTANCES. 307 one (OH), and you have CCHHHHH(OH), which is the same as C 2 H 5 (OH) or C 2 H 6 O, the formula for common alcohol. This way of writing formulae has a great disad- vantage : it does not bring out the idea of atomicity, so we will repeat this explanation with graphic formulae. (See 41 7.) II H I I H-C-H H-C-H I I H-C-H II-C-O-H I I II H Ethane. Common alcohol. Of course it makes no difference which atom of H in the formula is replaced. This is a matter of theory solely, and is apt when thus briefly treated to leave rather crude no- tions, of which we must beg you to beware. 423. Ethers. From what has been said it is evident that if we regard (C 2 H 5 ) as a compound radical, alcohol may be regarded as a hydrate; this similarity to the hydrates of mineral chemistry is shown thus : Radical K Na (NH 4 ) (C a H 5 ) Hydrate KHO NaHO (NHJHO (C a H 5 )HO Alcohols may therefore be looked at in another light, viz., as hydrates of organic radicals. Now if alcohols are hydrates, ethers are oxides. Here again we must ask you to bear in mind that the term ethers is a general one, applied to a great number of bodies sim- ilar in constitution to common ether, though not at all alike in other respects. You have probably been in the habit of considering ether as a very mobile, volatile, odor- ous, inflammable liquid used in medicine and photography ; it will therefore be difficult to conceive of ethers which 308 CHEMISTRY. are crystalline solids, some of them with a texture resem- bling organized bodies. And yet this is the case, the word ether having acquired a general meaning, just like oxide. Common ether, then, is oxide of ethyl, the name of the radi- cal C 2 H 5 just mentioned, and its formula is (C 2 H 5 ) 2 O, just like K 2 0, or (NH 4 ) 2 O. 424. Acids. We will pass over aldehydes and ketones, as they are of no great importance to you. The number of organic acids is enormous. To print their names alone would require many pages* of this book. But it is important to learn their general relations to the preceding bodies. Take the simple example, acetic acid ; analysis shows it to be composed of C 2 H 4 O 2 ; now alcohol is C 2 IT 5 (OH) ; com- pare these two formulae, and you will find one more atom of oxygen in the acid than in the alcohol, and two atoms less of hydrogen. This is the result of substitution, for one O atom, being a dyad, may replace two II atoms, being mo- nads. This is indeed the way acids are regarded; they are derived from their corresponding alcohols by one atom of oxygen replacing two atoms of hydrogen. Let us have recourse once more to graphic formula? : II II II 1 1 1 H-C-H II-C-H H-C-H 1 1 1 H-C-H H-C-O-H 0-C-O-H 1 1 H H or C 2 H 6 or C.,H 6 O or C 2 IT 4 O 2 Ethane. Alcohol. Acetic acid. Observe that the two atoms of H in the lower left-hand corner of the formula of alcohol disappear in the formula of acetic acid, one atom of O taking their place, and held fast to the carbon by two strokes, signifying its diatomic power. CLASSIFICATION OF ORGANIC SUBSTANCES. 309 Now we have said that alcohols and ethers are names given to classes of bodies ; this is also the case with acids. Acetic acid may be regarded as the type of one class of acids. We can not here go deeper into this abstruse sub- ject ; if you wish to learn about mono- and di-basic, mon- atornic and diatomic acids, we refer you to larger works, especially to Fowne's Manual of Chemistry. All the acids with which you will become familiar citric (from lemons), tartaric (from grapes), malic (from apples), formic (from ants), and a host of others belong to this division, and are regarded as similarly constituted, their basicity, etc., excepted. Examine also the table, page 303, giving acids and alcohols corresponding to the hydrocarbons of the Ethylene Series. TABLE Showing the Chemical Relations of Hydrocarbons, Alcohols, Acids, and Ethers in the First Three Members of the Marsh Gas Series: HYDROCARBONS. ALCOHOLS. ACIDS. ETIIEliS. H 1 (or CHJ CII 3 Marsh gas, or methane. H 1 CH 2 (OH) Wood-spirit, or methylic alcohol. H 1 CO(OH) Formic acid. H 1 CH a (OCH 3 ) Methylic ether. CH 3 1 (or C 2 H 6 ) CH 3 Ethane. CH 3 CH 2 (OH) Common, or ethylic alcohol. CH. CO(OH) Acetic acid. CH 3 CH 2 (OC 2 II 5 ) Common ether. CH 3 CH 3 (or C 3 H B ) CH, Propane. f' CH. CH./OH) Propylic alcohol. CH 3 fr co(OH; Propionic acid. CH 3 CH 2 (OC 3 H 7 y Propionic ether. 310 CHEMISTRY. 425. Amines. These are bodies containing nitrogen, and patterned after ammonia. Up to this point carbon, a tet- rad, has been the foundation on which the organic bodies are built up, but now we will assume that nitrogen takes [ H this position. Ammonia is NH 3 , NHHH, or N < H ; it mat- IH ters not how it is written. Now the hydrogen atoms in ammonia are capable of being replaced by organic groups, which we have called radicals, either successively or all at once. Suppose we take, for example, the same radical C 2 IT 5 which is supposed to exist in alcohol, ether, etc. Now if fH we substitute C 2 H 5 for one of the IT atoms in N i H, we fH [H get N j H , and this is called an amine / actually it is [C 2 H 6 ethylamine, for the radical C 2 U 5 is called ethyl. Now what do you suppose are the properties of ethylamine ? They re- semble those of ammonia very closely ; it is a gas, with a pungent, not disagreeable odor, very soluble in water, unites with acids to form crystalline salts, etc., just like ammonia; so that the substitution of the group C 2 H 5 for H has made but little change in the properties. Do you ask how this exchange is actually performed in a laboratory ? We will tell you. A liquid called ethyl iodide, C 2 H 5 T, is put into a strong glass tube with a solution of ammonia ; the tube is then sealed, and heated by immersion in boiling water. In a short time a new body is formed, having a very long name. The tube is then opened, and its contents heated in a retort with potassium hydrate, when the ethyl- amine distills over and dissolves out in the water, which condenses at the same time. We have explained roughly this operation in order to give you some idea how a chem- CLASSIFICATION OF ORGANIC SUBSTANCES. 311 ical reaction of this nature is practically carried out, and to enable you to understand that the " substitution " is not merely a new arrangement of letters on paper, but an act- ual rearrangement of the atoms of tangible matter. Now as a matter of fact, when the above operation is carried out the liquid which distills over, on heating with potassium hydrate, contains other bodies besides ethyl- amine. For not only is one atom of H replaced by C 2 H 5 , but two, and all three atoms are likewise replaced, yielding bodies having the composition shown in the formulaB fol- lowing : (H (H (C 3 H 5 N < H N < C a H 5 N -j C 2 H 5 (C 2 U 5 (C 2 H 5 (C 3 H 5 Ethylamine. Diethylamine. Triethylamine. These bodies are chemical curiosities; but we have explain- ed their formation and constitution in order that you may have some idea of the group of Amines, for to this class of bodies it is believed that the Alkaloids belong; and the al- kaloids you will learn are of immense importance, includ- ing as they do the valuable and interesting bodies quinine, strychnine, morphine, etc., occurring in plants. When the replacing radical contains oxygen, the new body formed is called an amide, but these are of less importance. 426. Organo-metallic Compounds. These are compounds of hydrocarbon radicals with monad, dyad, and tetrad met- als, but, being mere chemical rarities for the most part, do not interest us. One of them, called zinc-ethyl Zn(C 2 H 5 ) 2 is a volatile liquid with a disagreeable odor, and possesses the property of igniting spontaneously in contact with the air, like phosphoretted hydrogen. "We will not return to this class of bodies. 427. Organic Analysis. Analytical chemistry does not come within the scope of this work, but we will tell you 312 CHEMISTRY. briefly how chemists determine the constitution of organic bodies. There are two kinds of organic analysis : first, proxi- mate analysis separates the several definite compounds or proximate elements of which a complex substance is com- posed ; second, ultimate analysis determines the number of atoms of the elementary bodies in the molecule of & proxi- mate constituent. For example, starch, cellulose, gluten, sugar, coloring matters, alkaloids, etc., are proximate prin- ciples of plants, while carbon, oxygen, and hydrogen in cer- tain ratios are the ultimate elements of starch, sugar, and other proximate principles. The methods in use for separating proximate principles of vegetables and animals vary with nearly every sub- stance examined; no scientific scheme has been yet de- vised, nor can be until our knowledge of this branch of or- ganic chemistry is vastly increased. On the other hand, ultimate organic analysis has been brought to great perfection. The principles on which the process is based are as follows : Organic bodies may be considered as mainly made up of carbon, hydrogen, and oxygen ; now when such a body is completely burned, or oxidized (which is the same thing), the carbon, as you know, burns to form carbonic anhydride, the hydrogen burns to form water, and the oxygen escapes as such, or assists in the oxidation. By taking a weighed amount, therefore, of an organic substance, and oxidizing it carefully (by heating with an oxidizing agent, or in a current of pure dry oxygen) in a gas-tight apparatus, so arranged that all the carbonic anhydride and water formed can be collected and weighed, it is not difficult to calculate from the amounts of these products the actual amount of carbon and of hydrogen in the substance taken. How the operation is conducted, and how the calculation is made, is a matter foreign to the character of this work. 313 QUESTIONS. 418. "What two methods of classifying organic bodies may be pursued? Give the scientific classification in seven groups. 419. What is said of the compounds of hydrogen and carbon as to number and variety ? How do these isomeric bodies differ in constitution ? Name some of the hydro- carbons of the Ethylene Series. 420. Explain the terms homologous and isologous. 121. Show how bodies are formed by substitution. What is CHC1 3 ? What is hydroxyl? 422. Show the relation between alcohols and hydrocarbons. Explain, taking common alcohol as an illustration. 423. What are ethers ? 424. What are the relations of acids to alcohols ? Illustrate with acetic acid. 425. Whence are amines derived ? How ? How is ethylamine practically prepared? How theoretically derived? What important constituents of plants belong to this class of bodies ? 426. What is said of zinc-ethyl? 427. What are the divisions of organic analysis ? Illustrate. Explain briefly the method of ultimate analysis. CHAPTER XXV. CONSTITUENTS OP PLANTS, ETC. 428. Variety of Vegetable Substances. There is a great variety in the substances which are produced in plants. They are wood, starch, gums, gluten, fatty substances, vola- tile oils, coloring matters, alkaloids, etc. Then from many of these are developed other compounds. A very wide field is thus opened ; and, numerous as are the valuable combinations already discovered, we know probably but little as yet of the extent of the discoveries which are to be made in this field. Stockhardt says on this point: " Thousands of such new combinations have been discovered within the last twenty years ; our posterity will probably count them by millions." Of the products of vegetation, there are some which are O 314 CHEMISTRY. so widely diffused that they can be considered essential constituents of plants every where ; while others appear only in particular plants, and though essential, are not uni- versally so. It is the former class, which may properly be called the constituents of plants, that we shall speak of now, reserving the consideration of the latter class for another chapter. In treating of them, we shall speak of the changes effected in them by the operations both of nature and of art. 429. "Wood. What is termed wood in chemistry is the vegetable tissue which makes the framework of all vegeta- ble growths in all their parts, giving to them their shape and firmness. It is the solid part of all vegetable organs. It is to plants what bones, muscles, tendons, skin, etc., are to animals. Woody fibre is present even in the most deli- cate and tender fruits, holding in its interstices the juices. It is sometimes so exceedingly delicate that in crushing the fruit there seems to be almost nothing but juice. In some fruits, as the orange, the woody tissue is beautifully ar- ranged in long and slender sacs or bottles containing the fluid for our use, the sacs being packed into several differ- ent compartments, and each compartment being made of woody tissue. This same tissue, which is so soft and finely divided in the pulp of fruits, in leaves, and flowers, is con- densed and hard in what is ordinarily called wood, in bark, in straw, and the husks of grain, and especially in the shells of nuts and the stones of cherries, peaches, etc. The so- called vegetable ivory is chiefly condensed wood. In cork we have wood in a very light, porous, and elastic form. 430. Cellulose. The essential part of woody fibre is called cellulose; this has the composition C 6 H 10 O 5 ; it is nearly pure in cotton, paper, and wood pulp, provided they are not colored with any thing and are not starched. Pure cellulose may be obtained by washing white cotton, CONSTITUENTS OF PLANTS, ETC. 315 unsized paper or old linen with a warm solution of po- tassium hydrate, then with cold dilute hydrochloric acid, then with ammonia water and alcohol, repeating the process several times. Thus purified it is white, translucent, and unalterable in the air; it is insoluble in water, alcohol, ether, and oils, but is decomposed by strong acids. Nitric acid converts it into gun-cotton, as explained in 433 ; sul- phuric acid diluted with about one half its volume of water acts upon cellulose in a peculiar manner, converting it with- out change of composition into a tough substance resem- bling animal parchment and applicable to the same pur- poses. This so-called "vegetable parchment" is manu- factured on a large scale. 431. Linen and Cotton. These are composed of fibres of wood, long and pliant. Hemp is also another form of a similar kind. Linen is the inner bark of the flax plant. It is separated from the outer bark by rotting and breaking. In rotting there is long exposure to moisture and air, which rots the outer bark, and in the breaking this is beaten and rubbed off. Then follows the hatcheling, by which the fine fibres are separated from each other but left parallel, and the tangled ones are taken out, making what is called the tow. The flax thus obtained has a gray color, which is re- moved by bleaching and boiling with lye. Cotton is in the form of fine hollow hairs, which are beautifully arranged in the cotton-plant around the seeds. All cotton, except the Nankin cotton, which is yellow, is so white that it would need no bleaching were it not that in spinning and weaving it oil and dirt are necessarily gathered upon it. 432. Uses of "Wood. We put woody fibre to a great va- riety of uses. We build houses with it, and fill them with wooden furniture. Out of this fibre we make thread, twine, cordage, and fabrics of every variety. We clothe ourselves with it ; we write and print upon it ; we even eat it as a 316 CHEMISTKY. part of much of our food. We burn it to keep ourselves warm and to do our cooking. We spread it out in huge sheets to the wind in our boats and ships. 433. Gun-Cotton. If any form of cellulose in a divided state, as cotton, linen, saw-dust, etc., be submitted for a short time to the action of strong nitric acid, it becomes a more explosive substance than even gunpowder. When the discovery was first made it was proposed to use it in place of powder, but this was found impracticable on two accounts. First, it ignites so readily that it is very apt to explode when we do not wish it. Secondly, its explosion is too forcible and rapid, or, in other words, the gases pro- duced expand too rapidly four or five times more so than they do in the case of gunpowder. The consequence of this quick expansion is that there is danger that the gases will not have time to escape, as in the case of gunpowder, at the outlet of the gun-barrel, and therefore the barrel is very apt to burst. Gun-cotton can be prepared by immers- ing cotton for about five minutes in strong nitric acid, and then washing it thoroughly, and drying it. Care must be taken to use but a moderate heat in drying it, lest it should explode. The explanation of its explosiveness is that the cotton loses a portion of its hydrogen and takes in its place nitric peroxide, thereby increasing the number of atoms in the molecule and its consequent instability. 413. The reaction is shown in the following equation : Cellulose. Nitric acid. Gun-cotton. Water. C 6 H 10 5 + 3(HN0 3 ) = C 6 H 7 (NO 3 ) 3 5 + 3H 3 O Gun-cotton is often called trinitro-cellulose on account of its composition, as shown in the formula just given. It contains much more both of oxygen and nitrogen than common cotton does. It is, then, like potassium chlorate, a substance highly charged with oxygen, and on that ac- count explosive. It is the oxygen that produces the com- CONSTITUENTS OP PLANTS, ETC. 317 bastion when the heat is applied; and the nitrogen, being set free, expands with the other gases, and helps to give force to the explosion. Sulphuric acid is commonly used with the nitric acid in preparing gun-cotton. It is of use only in taking the water from the cotton, by virtue of its strong attraction for water ( 244), thus making more room for nitric acid, and securing a larger combination of this acid with the cotton than it could otherwise obtain. Collodion is a solution of gun-cotton in ether, making a sirupy liquid. It is often used for court-plaster, and also* for making small air-balloons. If it be put upon any thing the exposure to the air causes an evaporation of the ether at once, and the cotton is left in the form of a transparent coating. 434. Products from Wood by Heat When wood is con- sumed with free access of air, it is decomposed, as you have already learned, into its elements carbon, oxygen, and hy- drogen ; and these, together with some oxygen from the air, form carbonic anhydride and water in the condition of va- por. When, however, there is imperfect combustion from a restricted access of air, the products are different. They are four in number: 1. Charcoal ; 2. Illuminating gas, which is a mixture of several hydrocarbons with some carbonic ox- ide and carbonic anhydride ; 3. Pyroligneous acid, or wood- vinegar ; 4. Wood-tar. In the common burning of wood the combustion is not perfect, and we have three of these prod- ucts deposited in the form of soot, for this substance is composed of particles of carbon which have passed off un- burned in the current of smoke, having united with them some of the pyroligneous acid and the wood-tar. In the case of the air-tight stoves, so called, soot forms which con- tains a much larger proportion of the acid and the tar than the soot of an open fire, because the current up the chimney is too sluggish to carry up much of the carbon. 318 CHEMISTRY. 435. Dry Distillation of "Wood. These products can be obtained separate from each other by a process called dry distillation, repre- sented in Fig. 109. Some pieces of wood are heated in a retort, and the volatile matters pass over through the tube into a receiver. The il- luminating gas passes on through the bent tube, and is col- lected in the usual manner. One of these, the wood-tar, is very thick ; and the other, the wood-vinegar, is a thin, wa- tery substance. Charcoal, not being at all volatile, is left behind in the retort. Wood is composed of the three ele- ments, carbon, oxygen, and hydrogen ; and it is out of these that the products above mentioned are formed by the in- complete combustion produced by the heat. They did not exist in the wood, and therefore may be properly called products. Even the carbon left in the retort may be called a product, for in the wood it does not exist as carbon, but is in combination with the other elements forming the com- pound, wood; just as oxygen does not exist in water as oxygen, but is in combination with hydrogen, forming the compound, water. Two of the above products charcoal and illuminating gas have already been sufficiently described in other parts of this book, and therefore we will now notice only the other two. 436. Pyroligneous Acid. The name of this acid is de- rived from a Greek word, pur, fire, and a Latin word, lig- num, wood. Its acidity comes from acetic acid, and hence the propriety of calling this liquid wood-vinegar, Its pe- CONSTITUENTS OP PLA.NTS, ETC. 319 culiar strong smell comes from creosote, wood-naphtha, and other bodies. The same smell we have in smoke, and from the presence of the same substances. It is the creosote which makes smoke so irritating to the eyes. It is this substance which, both in smoke and in pyroligneous acid, acts upon meat as an antiseptic. Creosote is a liquid of an oily consistency, and colorless when freshly prepared, but it gradually becomes brown by age. It is a very powerful substance when obtained pure, and is an irritating poison. If taken into the mouth it has a very burning taste, and de- stroys the tender membrane which lines the tongue and mouth. Great care, therefore, should be exercised when it is employed, as it often is, as a remedy for the toothache. 437. Wood-Naphtha. The liquid portion of the products of the distillation of wood contains, besides acetic acid and creosote, eight or ten other substances; one of these, wood- naphtha, is of considerable importance. It is a volatile, odorous, mobile liquid, resembling alcohol, and yet having a different composition. If it be purified by treatment with lime to remove acetic acid, etc., and then by distilla- tion, a pure substance is obtained, known as methylic alco- hol. This is the first of a series of bodies called alcohols, with one member of which you are familiar, viz., common alcohol. Its composition is CH 3 HO, while common or ethylic alcohol is C 2 H 5 HO. Methylic alcohol burns with a flame much like that of common alcohol, is a good solvent of resinous substances, and, being cheaper than ethylic alco- hol, is of great nse in the arts. 438. Wood-Tar. This is a resinous substance, and is therefore soluble in alcohol, but not in water. If it be dis- tilled, a volatile oil passes over, called oil of tar, and there is left behind a black pitch. This separation takes place gradually when wood is besmeared with tar, the volatile oil flying off into the air, and the pitch becoming, there- 820 CHEMISTRY. fore, solid on the wood and in its pores. There is always some creosote in the tar, and this preserves the wood from decay or putrefaction. You see, then, the object of apply- ing tar in the calking of ships. 439. Coals found in the Earth. These are conveniently divided into three classes: lignites, bituminous coals, and anthracites. The first named has more nearly the compo- sition of wood ; the second is an intermediate state ; and the last, anthracite, is nearly pure carbon, having under the combined influence of heat and pressure lost most of its hydrogen and nearly all of its oxygen. Lignite is of a browner color than the others, and retains in some degree its woody structure. Bituminous or soft coal burns with a smoky flame containing some hydrocar- bons, and hard coal burns with scarcely any flame at all. All three were made from woody substance, and were brought into their present state by an imperfect combus- tion. We see the same process essentially going on at the present time, to a certain extent, in the formation of peat. This substance is formed from marsh plants. There is a growth of these every year, which, rotting in the water, sink to the bottom. There occurs, therefore, in the course of time, a large accumulation of vegetable substance, most- ly woody fibre, in the form of a brown net-work, in which the separate parts of the plants are discoverable. By the partial decay that is, incomplete combustion of this mass it is converted into peat, which is a half-formed coal, being mostly carbon, having some oxygen and hydrogen combined with it. The formation of coal in the earth will be particularly noticed in Part III. 440. Imperfect Combustion of Bituminous Coal. When bituminous coal is heated with the air excluded, products are obtained very similar to those which result from wood CONSTITUENTS OF PLANTS, ETC. 321 when subjected to this process. They are these: 1. Coke, which is nearly pure carbon ; 2. Illuminating gas ; 3. Tar- water, a watery empyreumatic liquid containing some am- monia ; 4. Coal-tar, a dark, viscid liquid. This process of dry distillation of bituminous coal is employed for the pro- duction of the gas so much used for illumination. The coke which is left in the retorts of the gas-works is a valu- able article of fuel. The ammonia in the tar-water is the chief source of the commercial article ; it is derived from the nitrogen, which is always present in coal in small quan- tities, uniting with the hydrogen during the distillation. Coal-tar is used for covering roofs, to protect them from moisture, and, mixed with chalk and other substances, it is employed as a cement. A great variety of products can be obtained from it. By distilling it we can obtain two oils, one of them a light oil, called benzol, which can be- used for many purposes in place of spirits of turpentine ; the other a heavy oil, used in the arts for lubrication and for dissolving India rubber, and also sometimes for illumi- nation. Benzol is one of the large class of bodies called hydro- carbons, so many of which are found in petroleum. Its for- mula is C 6 H 6 . It is a colorless, volatile liquid, having a low boiling-point. By treating it with nitric acid it is con- verted into nitro-benzol C 6 H 5 (NO 2 ) commonly called ar- tificial oil of almonds, from its odor, which resembles bitter almonds. It is much used in perfumery. Aniline is made from benzol, and is the basis of many of the beautiful dye- stuffs which have been introduced of late years. These dyes are called aniline colors, or simply coal-tar colors; their manufacture is interesting, but too complicated to give here. Aniline is also a constituent of the heavy oil mentioned above. This heavy oil also contains naphtha- line, a solid hydrocarbon also yielding dye-stuffs, and car- 02 322 CHEMISTRY. bolic acid (phenol), a substance of great value as a disin- fectant. By acting on phenol with nitric acid, a beautiful yellow dye is obtained called picric acid. The pitch which is left after distilling off these oils is much used in Europe as a cement for refuse coal-dust. The mixture thus made is cut up into cakes for fuel. 441. Nature's Products from Bituminous Coal. The re- sults of the dry distillation of bituminous coal by art have their counterpart in nature. Volcanic heat is the agent. The anthracite coal is very much like the coke formed in the retorts of the gas-works, except that immense pressure has condensed and hardened it during the action of the heat. Then we have inflammable gases issuing from crev- ices of rocks, answering to the illuminating gas produced by art. The oil of coal-tar has its representatives in nat- ure in the naphtha that oozes out of the ground in Persia, and in the mineral tar found in France as well as in Persia. Then, to compare with the pitch, the artificial asphaltum obtained from the coal-tar, we have the natural asphal- tum of the Dead Sea of Judea, found also in other seas in Asia. 442. Petroleum. Petroleum has been known from a very early period in the history of the earth, but it was reserved for American enterprise to discover the inexhaustible sup- ply beneath the surface. Evidences of the use of petro- leum are found near the ruins of Nineveh and Babylon ; the springs of Rangoon, in India, have been worked for ages ; and in our own country the Indians collected petro- leum for various purposes, chiefly medicinal. In 1854 a company was formed for collecting "rock oil" at Oil Creek, Pennsylvania ; but the process of gathering it from ditches in blankets and squeezing it into tubs was too ex- pensive. In 1858 Colonel Drake began to bore an artesian well for oil, believing that that which oozed out of the CONSTITUENTS OP PLANTS, ETC. 323 Fig. 110. A View on Oil Creek, Penu., showing Oil- Wells, Derricks, etc. ground and ran along the surface might be obtained in great quantity by digging down to its source. His expec- tations were more than realized ; and a well which yielded 400 gallons of oil a day, worth at the time 55 cents per gallon, rewarded his exertions, and successfully answered the ridicule of his neighbors. The eleven years succeeding this discovery produced more than thirty-five million bar- rels of this useful article. 443. Composition of Petroleum. Petroleum is a mixture of a great number of hydrocarbons, differing from each other in volatility and density. These hydrocarbons be- long to two series, one called the Marsh Gas Series and the other the Olefiant Gas Series, because these bodies are the first members of their respective series. The table 324 CHEMISTRY. .s=' IS |8J > 8 S 5 O5 1 ^^?*^ S cJ* c5* c5* S^ ^w' ^^ P) P"4 1 cc i O 11 B r~u a" 5 w 3 o I S S cL IS , t-j c? p^ ^3 *^ Q o c> c s ^* o o g P P P ^ M S fc b r/> "a 1 8 1 PH M a o 5 0* ^S^^^QQ PQ 'w a,'~ l cooc5^-cooQocn eo o '^ < S O P ^ < >" H S cs i co "3 M HI 09 *a ( sugar, etc. P2 346 CHEMISTRY. The materials of growth, then, are produced by decay, which is really not destruction, but a set of chemical changes for the purpose of a recombination of the elements in new forms of life and beauty. It is thus that life con- tinually springs out of what we call death. 479. Nitrogen from Nitric Acid. Considerable nitrogen is furnished to plants from the nitric acid, which we have stated is formed in the air and brought down in the rain. As long ago as 1785, Cavendish, an English chemist, dis- covered that by passing a succession of electric sparks through a mixture of nitrogen and oxygen in presence of aqueous vapor in a glass tube, a little nitric acid is formed. This is a small representation of what takes place on a large scale in the atmosphere, for traces of nitric acid have been found in samples of rain collected during and after thunder-storms. As one of the elements of nitric acid is nitrogen, its decomposition furnishes this element to plants to be used in their growth. 480. Green Manuring. Land which has been impover- ished is often rendered fertile by raising some crop upon it, as buckwheat, barley, rye, etc., and plowing it in while green. The manner in which this process, called green manuring, enriches the soil will be clear to you by referring to what we have said of the sources of the materials for growth. In the first place, all the ammonia and nitric acid which are washed down by the rain are used by the plants, and as these are plowed in there is really a store of nitro- gen laid up in the ground for the next crop. Then, again, every leaf of the plants is gathering in, by its multitude of open mouths, carbon from the air ; and this carbon is plowed in, therefore, with the nitrogen. But, besides all this, the roots as they are pushed down by the living pow- er of the plant break up the mass, and then thoroughly mix with it in their decay. We have, therefore, a loosen- VEGETATION. 347 ing and rearrangement of the soil which are favorable to fertility. 481. Inorganic Food of Plants. The materials of which we have spoken as ministering to the growth of plants are said to be their organic food. They are composed of the four grand elements carbon, oxygen, hydrogen, and nitrogen. But there are other substances which are absorbed in va- rious quantities in different plants, as silica, potash, lime, phosphorus, etc. These are said to be their inorganic food. Although the inorganic are not as essential to the growth of plants as the organic substances, still the fact that the most important of them are present to some ex- tent in all plants shows that every plant requires some amount of them for its full development. If a plant fails to find them its growth is feeble, and it withers before at- taining maturity. 482. Ashes of Plants. If a plant be burned, we obtain in the ashes the inorganic portion of it. The organic part has flown off in the form of gas, the carbon having formed carbonic anhydride with oxygen, the hydrogen water with oxygen, and ammonia with nitrogen. The ashes show how small a proportion of the substance of plants is inorganic. Ordinarily every hundred grammes of wood affords but two of ashes, the other ninety-eight grammes having been dissipated in the air. 483. Mineral Classification of Plants. The ashes of differ- ent plants differ very much in their inorganic constituents. A knowledge, therefore, of their composition in this respect, derived from a chemical examination of their ashes, is very important for an intelligent application of manures in rais- ing different crops. The inorganic substances which are found to predominate in the ashes of a plant must be con- sidered as indispensable to its nourishment ; and if the soil be deficient in them they must be supplied by the culti- 348 CHEMISTRY. vator. If the soil be destitute of potash, neither turnips nor grape-vines will grow well in it. If it be destitute of lime, it will not answer for clover or pease. Liebig divides all cultivated plants into three classes, according to the chemical character of their ashes: I. Potash plants, the ashes of which contain more than half their weight of salts, having alkaline bases (potassium and sodium), soluble in cold water. The beet, mangel-wurzel, and turnip belong to this class. 2. Lime plants, the ingredients of which are salts of lime and magnesia, soluble in acids. In this class we have clover, beans, pease, tobacco, etc. 3. Silica plants, in which silica predominates in the ashes. Wheat, barley, rye, and oats are in this class. 484. Water in Plants. In the processes of vegetation water not only furnishes some of the material, but it is the common carrier, as we may say, of all the other materials. What is taken in by the roots and the leaves is carried to all parts of the plant by the water. In doing this work the water courses through the plant in larger quantity than is commonly supposed. We can get some idea of this by looking at the amount which is exhaled from the leaves of plants into the air. Some investigations have been made on this point. It was found that from the leaves of a sin- gle cabbage there passed into the air nearly a quart of wa- ter in twenty-four hours. With this great exhalation from plants there must be a large amount of water passing up from the earth through them in a rapid but quiet circula- tion. 485. Annual Changes in Plants. When annual plants have stored up in their seeds a sufficient quantity of starch and albuminous substance for the germs of a new race of plants their work is done, and they fall to decay. But in perennial plants, such as shrubs, fruit and forest trees, after their fruit or seed has ripened, the woody fibre which has VEGETATION. 349 been formed in the spring becomes harder by continued woody deposit. At length, however, there ceases to be any formation of wood, and in its stead starch is made, and dif- fused through every part of the plant by the autumnal sap, the buds of the next year being formed at the same time. In the following spring this starch thus stored up is con- verted into dextrine and sugar, from which the leaves and tender branches are constructed, and the whole plant in- creased in bulk. QUESTIONS. 471. What is said of the dormant seed, and of its stimuli? What are the constituents of the seed ? What changes do the stimuli effect in these ? 472. What familiar examples have we of such changes? 473. State the contrast between the formation of the lead-tree and that of the root and germ of the plant. From whence are the materials for their growth de- rived? 474. What is said of the supply of carbon to plants? 475. What of the sources of their oxygen and hydrogen ? What is said of the decom- position of water in plants and in the laboratory of the chemist ? 476. Explain how plants can grow without earth. In what respects is their growth defective, and why ? 477. What is said of the nitrogen in the air in relation to the supply of plants with it ? From what source is it sup- plied, and how ? What is said of the presence of carbonate of ammonium in the air? 478. Give the summary in regard to growth and decay. 479. What is said of nitric acid as supplying nitrogen to plants ? 480. What is green manuring? How does it fertilize land? 481. What is said of the inorganic food of plants ? 482. What of the ashes of plants ? 83. Of what use is the chemical examination of the ashes of plants to the culti- vator? What are Liebig's three classes of plants ? 484. What are the offices of water in plants ? What is said of the quantity of water that circulates in them ? 485. WTiat provision is made by annual plants for the following year ? What is the provision in perennial plants ? 350 CHEMISTRY. CHAPTER XXVIII. SOILS AND MANURES. 486. Soil the Food of Plants. There is a striking analogy between the root of a plant and the stomach of an animal. In both there are minute absorbents which take up the material for growth. As the food put into the stomach is not all nutritious, and the absorbents take from it that which is so, so also the soil, the food of plants, as it is min- gled with the fine branches of the roots, has its nutritious portion absorbed by the little mouths which are there ever open to receive it. The root, therefore, may be regarded as the stomach of the plant. The proportion of nutritious substance is much greater in the food of the animal than in that of the plant, and therefore the stomach of the latter is a much more extensive organ than that of the animal. 487. Loosening the Soil. As food put into the stomach of an animal more readily furnishes its nutritious part to the absorbents if it be well masticated, so it is with the food of the plant. Hence the necessity of preparing the ground for plants by plowing, digging, etc. ; and hence y also, the usefulness of loosening the ground about plants so well known to the gardener. One of the evils of an abundance of clay in a soil is the close, compact character which the clay gives to it. The cold of winter has much influence in preparing the soil for the coming growth of spring, for, as the ground freezes, the expansion of the wa- ter, which is mingled up with its particles as it changes into ice, separates these particles from each other, and thus SOILS AXD MANURES. 351 loosens the compact soil. It is thought that earth-worms are more beneficial than injurious, because the benefit which they confer by loosening the soil is greater than the dam- age which they do by extracting nutriment from it. 488. "Water in the Soil. Food for either plant or animal needs to be dissolved to be available, and the great solvent is water. If a drought prevail plants languish, not because there is a deficiency of nourishment in the soil, but because there is not sufficient water to present the nutritious mat- ter in good quantity to the absorbents, and to carry it up in the tubes of the plants. You saw in 484 that a large amount of water is required for this. The solid matter of nutrition must be carried along on a full tide in the chan- nels made for it. 489. Soil as Generally Constituted. Soil is commonly made up of many substances mingled together, but derived from two sources. The first is the rocks. The great bulk of the soil conies from this source. This is very manifest in gravelly and sandy soils, for in them a mere glance shows you the broken pieces and grains which carrie from the rocks. But it is true even of fine rich earth that the most of it is mineral, and therefore that the rocks furnished it. You can see this to be so if you take some earth in your hand and examine it after it is dry. You will find that the grains of stone predominate over the other ma- terials. An analysis of the earth will develop the fact more thoroughly, for two reasons. First, some of the in- gredients from the rocks are dissolved in the water of the earth ; and, secondly, some of them are very finely divided, and therefore their mineral character is not manifest to the naked eye. The second source of soil is the decay of veg- etable and animal matters. All wood, leaves, bones, flesh, etc., as they decay form a part of the soil. 490. Humus. This second part of the soil is called hu- 352 CHEMISTRY. mus. It is of a dark color, and hence fertile earth has a darker color than sand. The substances forming humus are chiefly those that are composed of carbon, oxygen, and hydrogen, vegetable fibre as contained in wood, bark, leaves, etc., being the principal. There is some nitrogen, of course, in humus, from the juices of plants and the seeds, and also from the decomposition of animal substances. The immediate products of the decomposition of humus are humic acid, so called, humic acid salts, carbonic acid, water, ammonia, etc. The decomposition produces a good effect mechanically upon the whole body of the soil, loosen- ing it, and so making it mellow, as it is commonly termed. Humus is also a great absorbent of water, swelling up as a sponge, and this helps the mechanical effect produced by the generation of gases by decay. Heat also is developed by the chemical changes, which is often of very material benefit when the soil is naturally a cold one. 491. How Soil was Originally Made. All the soil, with the exception of that portion of the carbon which has been supplied from the air, and also the water which is diffused in it, came originally from the rocks. There was a time when there was nothing but rocks and water and air. Some of the rocks became at length broken and ground up by processes which the geologist describes, and thus was furnished the soil on which the plants first grew. Soil be- ing thus prepared, seeds were supplied by the Creator, the plants from which, sending down their roots into the pow- dered rock, took up there the soluble matters, and sending up branches and leaves into the air, collected carbon there with their outspread nets. And now the plants, decaying, added humus to the soil, which, increasing year after year, at length made the soil a fertile one. Besides those agita- tions which break up and scatter fragments of rocks and grind them to powder, there is another process, called SOILS AND MANURES. 353 weathering, which is necessary in preparing the soil for vegetation. This consists in the action of chemical forces, in connection with heat and moisture, which not only aid in the pulverization, but also render some of the materials soluble, and therefore available for vegetation. 492. The Process Seen in Volcanic Countries. The forma- tion of soil is continually going on in all parts of the earth in the manner indicated. It can be best seen in the neigh- borhood of volcanoes. The lava that has issued from a volcano lies barren for years; but the varying tempera- ture, the water, and the oxygen of the air at length pro- duce sufficient disintegration and chemical change to make a soil for lichens. These succeed each other year after year for generations, from which there is a gradual accumula- tion of humus. This by its decay assists the other agencies of disintegration, and so there is a yearly addition to the soil on the rocky lava. Thus is preparation made for other plants, and so the accumulation goes on till at length, per- haps- in the lapse of centuries, the soil becomes deep enough for shrubs and afterward trees. The various steps of this process, thus briefly described, may often be observed in deposits of lava of different ages in the neighborhood of volcanoes. 493. Different Kinds of Soil. In the agitations by which rocks were broken up there was so wide a scattering of the broken materials that the varied mineral ingredients of soil are well mixed up in all parts of the earth. Still there are peculiarities in soils here and there, owing to the predominance sometimes of one and sometimes of another mineral ingredient. For example, in the regions of lime- stone formations there is apt to be a predominance of lime in the soil. The three chief mineral ingredients of soil are these: 1, Silica, in the shape of sand; 2, Alumina, mixed or combined with sand, as clay ; and 3, Lime, in the form 354 CHEMISTRY. of carbonate, as limestone, chalk, etc. Soils are named ac- cording to the proportions of these ingredients. Thus if an ordinary soil, dried, is found to contain but 10 per cent, of clay, it is a sandy soil; if from 10 to 40 per cent, a sandy loam ; if from 40 to 70, a loamy soil; if from 70 to 85, a clay loam; and if from 85 to 95, a strong clay, fitted for making bricks. If a soil contains from 5 to 20 per cent, of carbonate of lime it is called a marl, and if more than 20 per cent., a calcareous soil. Sometimes the only difference in the character of two soils may be me- chanical, while the one is barren and the other fertile. Thus there are sandy soils in Ohio which for fifty years have yielded, without manuring, eighty bushels of corn to the acre, and yet they do not differ in chemical char- acter, so far as inorganic matters are concerned, from sandy soils in the Eastern States which are nearly barren. The only difference discovered between the two soils is that the barren consists mostly of coarse grains, while the other is a very fine powder. Commonly, however, when there is a marked difference in fertility, there is a considerable difference in chemical composition. 494. Rotation in Crops. The differences in soil are af- fected by the crops which we raise. If, for example, a crop be raised year after year upon a soil which contains in due quantity a chemical ingredient particularly adapted to that crop, the ingredient will be at length exhausted. Hence comes the good policy of rotation of crops. Potassium compounds are particularly needed in the raising of tur- nips, but if turnips be cultivated on the same field year after year, the potassium salts will finally become deficient, and you will have poor crops of turnips. So, also, if pease be raised successively on the same land, the soluble lime in the soil will be at length exhausted. But change these two crops on the two fields, and there will be no difficulty. SOILS AND MANURES. 355 The turnips will flourish in the pea-field, because there is plenty of potash there; and the pease will flourish in the turnip-field, because the turnips have not used up the lime. 495. Manures. You have seen in 486 what analogy there is between the stomach of the animal and the root of the plant. Let us follow out this analogy a little far- ther. If we give an abundance of proper food to the ani- mal it grows well, but with scanty and improper food it becomes lean and languishing. So it is with the plant. If its root be supplied in the soil with a proper amount of those substances which are fitted for its nutrition, it grows vigorously, and its leaves, flowers, and fruit are abundant. The object of manures is to supply to the soil whatever of these substances are deficient. In doing this we must have regard to the kinds of food which different kinds of plants need. There are certain substances the presence of which in the soil is required by all plants in order to secure vig- orous growth. But then in regard to many substances the wants of plants are very different. A potash-plant, for ex- ample, must have a soil that has considerable potash in it ; while a lime-plant must have one that contains considera- ble lime. If lime or potash be deficient where it is wanted, it must be supplied in the form of manure. And the same can be said of other substances. The term manure is applied to any substance which acts as a fertilizer. Sometimes such substances act indirectly by producing some mechanical effect upon the soil, or by modifying the action of other substances, instead of afford- ing a direct supply of nutriment, as is generally done by manures. 496. Chemical Knowledge Requisite. In order to apply manures appropriately we must know something of the chemical characters of the soils, of the plants, and of the 356 CHEMISTRY. , manures. From a deficiency of this knowledge mistakes are made continually by farmers. For example, lime has been often applied where there was already enough of it, as might be shown by a chemical analysis of the soil, and so has proved, not merely a waste, but a positive injury to the land. A very simple test will often give valuable in- formation. Suppose, for instance, we take a pound of earth, and after boiling it for some time in about a pint of water, so that the lumps may be all destroyed, and the earth uni- formly diffused in the water, introduce into the mass a strip of blue litmus paper. If this after a little time turns red it shows that the soil is sour, and that the humic acid in it requires the application of lime to neutralize it. Chem- istry may be made use of often by the farmer in discover- ing rich materials for fertilizing his land. Beds of marl have been found here and there which have proved of great value as furnishing a fertilizer for certain soils. We will quote here some remarks of Stockhardt on these dis- coveries : " Probably such treasure still lies hidden in the ground in many other places ; it appears only to require the divining-rod to indicate where it lies, and the touch- stone by which it can be ascertained whether it really is what it appears to be. Yet both are close at hand : the divining-rod is called 'look for it,' and a wine-glass of 'hydrochloric acid' serves as a touch-stone. How many accidental opportunities the farmer has of penetrating a little deeper than usual into the earth ! Here a well is dug, or a ditch ; there a hill is leveled or cut through in road-making ; in other spots a stone-quarry, a sand or loam pit, is opened. These are all excellent opportunities and even deep -plowing' and ordinary work with the subsoil plow not unfrequently furnish others to make acquaint- ance with the kind of earth lying beneath the cultivated Boil. If an earth of different character is met with under SOILS AND MANUKES. 357 the surface soil, a few drops of hydrochloric acid should be poured upon a specimen of it; if this produces an efferves- cence, it is a sure sign of the presence of carbonate of lime, and the earth probably belongs to the useful kinds of marl, which may then readily be ascertained more ex- actly by a chemical examination." 497. Volatile Substances in Manures. There are some valuable substances in some manures which are volatile, and the skill of the farmer is called in requisition to pre- vent their flying off, or to fix them, as it is expressed. If he carelessly leave his manure heaps to putrefaction, he will lose a large part of some of their most valuable mate- rial. He will lose, for example, much of the ammonia. It will pass off into the air, and so will be lost to him, though it will not be lost to the earth, for it will be brought down by the rain. By losing it he will unwittingly benefit oth- er farmers over a wide extent of territory, for the volatile matter will be largely diffused. There are means of fixing the ammonia, which are applied sometimes in the manure heap, and sometimes in the field with the manure as it is scattered. These means will be noticed hereafter. 498. Animal Manures. These are of two kinds the sub- stances composing the body of the animal, and the excre- tions. They are generally the most valuable manures that we have, for they contain, besides other ingredients, a con- siderable amount of that very important element, nitrogen. The excretions of different animals vary much according to the kinds of food upon which they live. This is of course to be taken into consideration by the farmer in the application of these manures, and in the mixture of other manures with them. 499. Guano. This is the manure of sea-birds, which has been accumulated during a long period of time in deep layers upon uninhabited islands and rocks. There are im- 358 CHEMISTRY. raense quantities of it in different parts of the earth. It is calculated that the deposits of it in South and Middle Peru amount to more than twenty millions of tons. The value of this manure, when it is good, is very great. Its good- ness depends upon the amount of nitrogen it contains lock- ed up in its ammonia. Next to nitrogen, phosphoric acid, contained in phosphate of lime, must be considered as the most valuable constituent of guano ; but of so much more value is the nitrogen than this, that we may lay it down as a rule that the more of ammoniacal salts and the less of phosphate of lime guano contains, the higher is its value. Peruvian guano is better on this account than the guano of Patagonia and that of Africa. The reason that these latter have so small a proportion of ammoniacal salts in them is that by exposure to the action of air and water these salts have been to a great extent washed out. Guano is deficient in potash, and therefore in its application wood- ashes make a useful addition. 500. Tests of Guano. Guano varies much in its char- acter, and on account of its pecuniary value is often adul- terated, hence it is well that certain plain tests of its chem- ical composition should be known, that they may be applied by buyers of the article. We will mention some of them. 1. Test by Combustion. Put fifteen grammes of the guano to be examined in an iron spoon, and hold it over some red- hot coals until a white or grayish ash is left. The weight of the ash, subtracted from that of the guano, gives you the proportion of nitrogenous substance, for this has been burned tip and volatilized, while the phosphate of lime makes the ash. In this application of heat the odor differs according to the character of the guano. That from a good specimen is pungent, like the vapor from spirits of harts- horn, while the odor from a poor specimen is like that of singed hair. 2. Lime Test. Put a teaspoonful of guano SOILS AND MANURES. 359 into a wine-glass, and upon this a teaspoonful of slaked lime, and, adding a few teaspoonfuls of water, shake the mixture briskly. The stronger the smell of ammonia the better is the guano, for the lime, by taking away the acids that are united with the ammonia, sets that pungent sub- stance free. 3. Vinegar Test. If on pouring vinegar upon guano a strong effervescence ensues, we infer that there has been an intentional adulteration with carbonate of lime. 4. Test with Hot Water. Make a filter of blot- ting-paper, folded together in the form of a cone, and put it into a common funnel. Put into this fifteen grammes of guano well dried, and pour upon it hot water as long as it passes through of a yellow color. Now dry the filter, and, weighing the dried powder which is upon it, you find what proportion of the guano is dissolved, or, in other words, what proportion of ammoniacal salts it contains, for it is this part of the guano alone that is soluble. 501. Ammoniacal Salts. The salts of ammonium, some of which, as you have seen, are the principal source of the fertilizing power of guano, are chiefly the chloride, or sal ammoniac, the sulphate, the nitrate, the humate (formed with the acid of humus), and the carbonate or salt of harts- horn. These salts are present in stable manure, and in oth- er fertilizing substances which furnish nitrogen to plants. There is considerable ammonia in the gas-liquor which is formed in the process of cooling and purifying the gas. This liquor is very valuable for manure. There also is con- siderable ammonia in soot, and hence this substance is a good fertilizer. 502. Bone-Dust. The powder of bones is an exceedingly valuable manure, as you can readily see it would be from observing the composition of bone. A bone is composed of an animal part, gelatin, and a mineral part, nine tenths of which is phosphate of lime, and one tenth the carbonate. 360 CHEMISTRY. These two parts can be obtained separate from each other by processes which are described in the first chapter of Hooker's "First Book in Physiology." The gelatin is of great value as a fertilizer for any crop because of the nitro- gen which it contains ; and the phosphate of lime is espe- cially favorable to the development of seeds, and therefore bone-dust is peculiarly appropriate as a manure for grain- fields. It is on account of this phosphate of lime that bone- dust is so beneficial to dairy lands. Milk and cheese both contain this substance. There is about half a pound of it in ten gallons of milk. Bone-dust is also an excellent ma- nure for wheat; for though this is a silica plant ( 483), the presence of phosphates in the soil is essential to the formation of the seeds. If the soil be rich in silicates but deficient in phosphates, excellent straw will be obtained, but the grain will be small in amount : it will be a crop better calculated to make bonnets than bread. It is calcu- lated that 1 cwt. of bone-dust is equal to 25 or 30 cwt. of stable-manure. Although bones contain such fertilizing materials, they must be well pulverized in order that they may be immediately available for the nutrition of plants. It often takes even twenty or more years for the soil to disintegrate fragments of bone of the size of a hazel-nut or a pea, and yet such fragments arc frequently seen in the bone-dust of commerce. 503. Lime. While guano, bone-dust, stable-manure, etc., act as direct nutrients, giving actual substance to the plant, the action of lime is for the most part indirect. It acts in many ways. In some cases its chief effect upon the soil is mechanical, rendering it loose and porous. In other cases, as stated in 496, it neutralizes the acidity of the soil, and thus makes it fertile. In still other cases it excites a more rapid decay of the humus, and thus provides more nutri- tious matter in the soil for the plants. And still again it SOILS AND MANURES. 361 does good service often in aiding the weathering (491) of the mineral substances in the soil, and thus acts as a sol- vent for matters which the plants need but can not get un- less they are dissolved. The direct manures, you observe, act with their own power, and furnish some of their own material to plants ; but lime, on the other hand, does not work with its own material, but at the expense of other matters in the soil. Lime, therefore, tends eventually to make the soil poorer unless other manures are applied at the same time, and hence the maxim current among the Belgian farmers : "Much lime and no manure Makes both farm and farmer poor." 504. Marl. "VYe have alluded to this manure in 493. Marl is a lime mud which was deposited in the last over- flowings of the surface of the earth in its preparation for man. It is sometimes tolerably pure, but is commonly mingled with clay, stones, shells, etc. The lime in it is in the form of carbonate. Its effects upon soils are very similar to those of quick-lime, just described. There are, however, other substances mingled with the carbonate of lime, which modify its effects, and render the marl more valuable as a fertilizer than it otherwise would be. Yet these are so small in amount that the Belgian proverb is nearly as true of marl as it is of lime. 505. Gypsum. The fertilizing properties of sulphate of lime were known in Europe long before they were in this country. Franklin, when abroad, was struck with the rich- ness of the crops raised in fields manured with gypsum, and endeavored to persuade American farmers to use it, but in vain. To convince them of the truth of his statements he resorted to the following expedient : He strewed gypsum on a sloping field in such a way as to form in enormous letters the words Effects of Gypsum. The abundant growth Q 362 CHEMISTRY. on the part so prepared, making the letters legible to every passer-by, brought the new manure at once into popular favor. There has been much dispute as to the manner in which gypsum acts as a fertilizer. One thing is quite set- tled about it it answers a good purpose infixing the am- monia in the soil. This is effected by a double decompo- sition between the sulphate of lime and the carbonate of ammonium, the result being carbonate of lime and sulphate of ammonium. In this connection we will mention that sul- phuric acid is often used for fixing ammonia in manures, forming with it a sulphate, which is not volatile like the carbonate. 506. Vegetable Refuse. In every garden and on every farm all vegetable matter which is useless should, so far as it can be done, be made to add to the stock of humus by its decay. It is convenient to have in a garden a pit into which all weeds, small trimmings, etc., can be thrown, where, covered up, they may be left to decay, forming rich humus. The decay may be hastened by the occasional ad- dition of some lime. On most farms there is a large quan- tity of vegetable matter left to decay on the surface of the ground, and thus waste by volatilization a part of its fer- tilizing material. This refuse might be of great value if gathered up and mingled in a compost heap with other materials. 507. Sewer- Water. This always contains a great variety of fertilizing substances, and therefore is one of our most valuable manures. Yet it is very generally wasted. Vast quantities of it in our towns and cities run off into the wa- ter, where it is not only lost, but sometimes does much harm. The water of the River Thames is becoming more impure every year from this cause. It is calculated that the London sewers pour into it fertilizing materials of the annual value of over half a million pounds sterling. Great SOILS AND MANURES. 363 attention has been attracted to this subject, and plans have been broached for avoiding this enormous waste. QUESTIONS. 486. State the analogy between the stomach of an animal and the root of a plant. What is said of the difference in the proportion of nutritious substance ? 487. State the analogy in regard to loosening the soil. What influence has clay upon soil ? What effect has the cold of winter upon it ? What is said of earth-worms ? 488. What of water in the soil ? 489. From what source comes the principal part of the soil ? In what two ways can you see what its chief source is ? 490. What is the second source of the soil ? What name is given to the product from this source ? What is said of its chemical character ? What are the products of its decompo- sition ? What mechanical effect does this decomposition produce ? What other effect is mentioned ? 491. State in full how soil was originally made. What is weathering ? 492. Describe the process of making soil as seen in volcanic countries. 493. How are peculiarities in soil produced? What are the three chief mineral ingredients in soil ? What are some of the dif- ferent soils made by different proportions of these ingredients ? What is said of the mechanical differences of soils ? 494. What is said of the rota- tion of crops ? 495. Follow out the analogy between stomachs and roots in regard to amount of food. W T hat is the object of manures ? What cir- cumstances should govern the selection of the kind of manure ? What is said of the term manure, and of the modes in which manures act ? 496. Illustrate the truth that a knowledge of chemistry is necessary to a suita- ble application of manures. What opportunities often offer for ascertain- ing the chemical character of subsoils ? What is said of hydrochloric acid as a test of the character of soils ? 497. What of the management of vola- tile substances in manures ? 498. What of animal manures ? 499. What is guano ? What is said of its abundance ? What are the chemical in- gredients that give it its value ? Why is the guano of Peru better than that of Africa and Patagonia ? Why are wood-ashes a good addition to guano when used ? 500. State the test of guano by combustion. State the lime test. The vinegar test. The test with hot water. 501. What are the ammoniacal salts present in various manures? What is said of gas-liquor? 502. What is the composition of bone? What is said of the fertilizing powers of the ingredients ? What of their use in regard to dif- ferent crops ? What of the value of bone-dust ? What of its degree of 364 CHEMISTRY. pulverization ? 503. How does lime differ from most other manures in its action? Give the maxim in regard to lime, and the ground for it. 504. What is marl ? What is said of its effects on soils ? 505. Give the anec- dote of Franklin in regard to gypsum. What is said of the manner in which gypsum acts as a fertilizer ? 506. What is said of vegetable refuse ? 507. What of sewer-water? CHAPTER XXIX. OILS AND FATS. 508. Acids. The common idea that acids are sour bodies must now be given up, for under this head are included many oily and fatty substances which do not react acid at all. The sources of organic acids are exceedingly vari- ous; thus formic acids can be extracted both from red ants and from nettles ; acetic acid is a product of fermen- tation, as you will learn in the next chapter ; butyric acid is contained in rancid butter, palmitic acid in palm-oil, stearic acid in tallow, and melissic acid in beeswax. These form part of a series called the Fatty Acid Series.* The first one is a liquid, with a low boiling-point ; the rest in- crease in density, becoming oily and finally solid. The first acids of this series mix with water, but the last acids are quite insoluble in water; thus a gradual transition of properties is noticeable, and their formulae become heavier and more complex as you ascend the series. Formic acid is CH 2 O 2 , acetic acid C 2 H 4 O 2 , etc., while the last named, melissic acid, has the formula C 30 H 60 O 2 . There are many other acids which do not belong in this series, also derived from various sources ; thus tartaric acid * See last column in Table on page 303. OILS AND FATS. 365 is found in grapes, citric acid in lemons and some other fruits, malic acid in apples, lactic acid in sour milk, etc. These organic acids form salts by replacement of hydro- gen with a base just like the mineral acids. In fact the acids mentioned as found in fruits do not exist as such, but combined with potassium, sodium, or possibly calcium. Thus in the case of tartaric acid it is combined with potas- sium in the plant. Acid potassium tartrate, or so-called cream of tartar, is gradually deposited in wine-casks from the wine, and this is one cause of the improvement of wine by age. Rochelle salt is a double salt a tartrate of potas- sium and sodium. So tartar emetic is a tartrate of potas- sium and antimony. Then there is a double tartrate of potassium and iron, which is a valuable medicine. Many of the organic acids char on heating, owing to the imperfect combustion of the carbon. If they are heated more strongly complete decomposition ensues, just as in the case of wood, sugar, etc. This distinguishes them in their reactions from the mineral acids. 509. Tannic Acid. This body is not a true acid, and strictly belongs to another group of bodies called gluco- sides, but it is of so much importance in many ways in the arts that it should not be passed by. It exists extensively in the bark of many trees, as the oak, horse-chestnut, hem- lock, birch, etc., and is also found in some roots, and in the leaves of roses and pomegranates. It exists most abun- dantly in the gall-nut of the oak. Here we have a valuable vegetable product as the result of disease, for the gall-nut is a morbid growth which comes from the wound of an insect made in the oak for the purpose of depositing its eggs.* Tannin, as this body is commonly called, is a very astringent substance. By the decomposition of tannic acid another * See Hooker's "Natural History," page 270, for further particulars. 366 CHEMISTRY. acid called gallic acid is obtained, and then by the decompo- sition of this latter several other acids can be produced. 510. How Obtained. The mode of obtaining tannin is as follows: Into a globular funnel, 5, Fig. 115, which can be closed at the top by a stopper, is introduced a quantity of powdered nut-galls after the tube of the funnel, c, has been stopped with a little cotton. The funnel is then placed in the bottle, a, and is filled up with the ether of the shops, which is about one tenth water. The apparatus being allowed to stand several days, there appear two layers of liquid. The lower one, which is as thick as sirup, is a con- centrated solution of the tannin in water, with very little ether in it, while the upper is ether containing a mere trace of tannic and gallic acids. The theory of this process is that the tannin has such a greedy affinity for water that, as the liquid passes through the powder, the tannin in it seizes the water, withdrawing it from the ether. The tannin is obtained from this sirup-like solution by evaporation. 511. Tanning. In the common process of tanning the tannic acid in the bark is the effective agent. It is a chem- ical union of this acid with the gelatin of the skin that converts the skin into leather. This combination prevents the decay or putrefaction which would otherwise take place in the skin, just as the chemical union of corrosive subli- mate with the albumen of the wood in kyanizing prevents the decay of the wood. A black color is given to the leath- er by washing it with a solution of iron, the tannin of the leather imiting w^ith the iron to form a tannate of iron. The reason that drops of tea upon a knife-blade become of a dark color is that the tannic acid in the tea forms a tan- nate with the iron. OILS AND FATS. 367 512. "Writing-Ink. Common writing-ink is prepared from nut-galls and ferrous sulphate. A solution of the tannic acid is obtained by boiling the galls in water, and this is mixed with a solution of ferrous sulphate. A feriws tan- nate results, which makes a very pale solution ; but by ex- posure to the air the tannate becomes more highly oxidized, and thus changes to a feme tannate, which is of a very dark color. It is desirable, for the permanency of the writ- ing, that this change should take place in part in the fibres of the paper, and not wholly in the ink before it is used. The ink is, therefore, bottled, and thus shut in from the air before the change is completed, so that when used in writ- ing it may be rather pale, and become gradually dark on the paper. To keep the tannate from settling gum is added to the ink, and to prevent moulding oil of cloves or creosote is introduced in small quantity. Corrosive sublimate is a very effective preventive of moulding, but it is obviously danger- ous to employ it with the ordinary careless habits of people in using ink. It is from the action of tannin on ferrous sul- phate and other salts of iron that it is used in dyeing. 513. Oils and Pats. These substances are found widely distributed in both the vegetable and the animal kingdoms, and are constituted very much alike in both. In plants they are generally contained in the investing membranes of seeds or in the cellular substance of fruits. There is sel- dom any fatty matter in leaves or in roots. The principal vegetable oils and fats are as follows : Linseed-oil, which is pressed out from flax-seed ; Olive-oil, from the pulp of the fruit of the olive-tree; Palm-oil, a yellow fat, similar to butter, from the fruit of a species of palm-tree; Castor-oil, from the seeds of the castor-oil plant ; Butter of Cacao, the tallow-like fat of the cacoa-nut, the cause of the fat particles which rise on boiled chocolate; Hemp-oil, from hemp-seed, etc. Oils can also be obtained from pumpkin- 368 CHEMISTEY. seeds, walnuts, sunflower-seeds, hazel-nuts, even apple-seeds, plum and cherry stones, etc. 514. Composition. The oils and fats are composed most- ly of three ingredients, called stearin, palmitin, and olein. The stearin, when separated from the others, is a solid at all ordinary temperatures, while the olein is a liquid ; the palmitin is midway between the other two. In very cold weather, when a portion of lamp-oil becomes solidified, we have a partial separation between the stearin and the olein. The consistency of fatty substances depends upon the proportions of olein and stearin in them, the former predominating in the liquid, and the latter in the more solid bodies. But these constituents of fats are far from being simple substances. They are compounds formed by the union of acids with a certain b.ase or radical called glyceryl. Thus stearin is a combination of stearic acid with this base, a glyceryl stearate, just as pearlash is potassium carbonate. Likewise olein is glyceryl oleate. Bodies formed after this pattern are called salts in organic chemistry just as in mineral chemistry, the only real differ- ence being that the radicals and the acids in one instance are far more complex than in the other. This the formula) for stearin, palmitin, and olein show : Glyceryl, a hydrocarbon radical, (C 3 H 5 )'" Stearin, or glyceryl stearate, (C 3 H 5 )"'(C 18 H 35 2 )3 Palmitin, or glyceryl palmitate, (C 3 H 5 )"'(C 16 H 31 O 2 ) 3 Olein, or glyceryl oleate, (C 3 H 6 )'"(C 18 H 33 O 2 ) 3 515. Glycerin. This is a colorless, sirupy liquid, of a sweet taste ; this latter quality gives it its name, which is de- rived from a Greek word glukus^ sweet. It belongs to the class of bodies called alcohols, but is described in this con- nection because it is a product of the decomposition of oils and fats. It is a hydrate of glyceryl, and has the formula C 3 H 5 (IIO) 3 . OILS AND FATS. 369 Glycerin is soluble both in water and alcohol. It can be obtained by boiling stearin and olein with a solution of potassium hydrate. The fat (or stearin) is decomposed by the substitution of potassium for glyceryl, and the re- sulting products are potassium stearate and glyceryl hy- drate or glycerin. We will explain this further in the section on soaps. Glycerin has remarkable solvent powers, dissolving readily the greatest variety of substances, min- eral and organic. Nitrogtycerin is a powerfully explosive oily liquid, made by the action of nitric acid on glycerin, much as in the case of gun-cotton. It is very dangerous to manufacture and to handle, and at the same time very use- ful for blasting rocks. Mixed with porous silica and some other substances it is called Dynamite. 510. Candles made of Stearin and Stearic Acid. Stearin may be obtained from lard and tallow by a simple process. If the fat be melted, as it cools it hardens, forming a mass from which the fluid olein can be pressed out, leaving the stearin alone by itself. The stearin is used for making can- dles, while the expressed olein is the well-known lard-oil. But a better material for candles can be obtained by de- composing the stearin with lime, thus forming a stearate of lime, and then decomposing this with sulphuric acid. In this way we obtain stearic acid, for the sulphuric acid takes the lime away from the stearate of lime, and thus sets the stearic acid free. This acid is a white, crystalline, translu- cent substance with a brilliant lustre. It is a better ma- terial for candles than stearin, because it is not so readily softened by heat, its melting point being about ten degrees higher than that of stearin. 517. Soaps. In the preparation of glycerin, described in 5 15, we did not tell you any thing about the potassium stearate which was produced along with the glycerin ; this substance is soap. Soap, then, as well as oils and fats, is a Q2 370 CHEMISTKY. true chemical salt. In the manufacture of soap, lime, so- dium hydrate, or potassium hydrate may be used ; calcium, sodium, or potassium stearate being formed. Natural fats, however, are composed of stearin, palmitin, and olein, con- sequently the soaps are mixtures of stearates, palmitates, and oleates of the bases named, and not pure stearates. If we consider the formation of only one of these bodies, it can be expressed in a rather complex equation, thus : Caustic soda or Olive-oil or Gn ^- , i i rn Sodium hydrate. Glyceryl oleate. Sodmm oleate ' Glycerin. 3(NaHO) + (C,H.)" / (C 18 H,,0 1 ), = 3(NaC 19 H 33 O 2 ) + (C 3 H 5 )"'(HO) 3 518. Hard and Soft Soap. Hard soaps are formed by soda, and soft by potash. A potash soap can be converted into a soda soap by means of common salt. This is often done by soap-makers on a large scale. The soft soap is dissolved in boiling water, and salt is thrown into it. There is a collection of soda soap on the surface of the wa- ter, which on cooling becomes hard. The chemical change is this : The chlorine of the salt goes to the potassium of the soap, forming potassium chloride, while its sodium goes to the stearic and oleic acids to form stearate and oleate of sodium. The cleansing power of soap in washing depends chiefly upon the fact that the water used with them sets free some of the alkali from its combination with the fatty acids, so that we have a mixture of caustic alkali and fat-salts, the alkali by its union with the greasy matters in the cloth cleansing it, and the salts the stearate and oleate by their lubrication, keeping the cloth pliant, and thus making the operation easy. The alkali would not answer alone, be- cause it would by shrinking the fibre of the cloth render it rigid, and thus prevent its perfect cleansing, and at the same time would injure it .by its too great causticity. Alcohol dissolves soaps, and the common soap liniment OILS AND FATS. 371 is a solution of soap in alcohol. Camphor added to this makes the liquid opodeldoc. Volatile liniment is a sort of soapy mixture made of oil and the volatile alkali ammonia. Equal parts of lime-water and sweet-oil make a soapy mixt- ure which is one of our best applications for a burn. A solution of ammonia in alcohol is very effective in remov- ing grease spots from woolen clothes, because it unites with the grease to form a soap, which readily washes out with the application of a little \vater. 519. Properties of Fats. Fatty or oily substances have some peculiar properties which fit them for many valuable uses. They spread readily in the pores of substances, and as they are not volatile they answer a valuable purpose in keeping leathern and other articles soft and pliable for a long time. As the fats float upon water, they can be used for excluding air from various substances, thus preserving them from chemical change. Thus a layer of oil is some- times poured over preserved fruits. As the fats are not only insoluble in water, but have a sort of repulsion for it, they are extensively used for preserving substances from being penetrated by water. Shoe-leather is rendered im- pervious to water by greasing. Iron is oiled to protect it from the damp air, and thus keep it from rusting. Tim- bers saturated w r ith oil will be preserved a long time from rotting in the damp earth. 520. Varnish Oils. All fatty substances on exposure to the air grad- ually absorb oxygen and evolve carbonic acid; and as there is always a cer- tain amount of nitrogenous substance in them, a sort of fermentation occurs, producing acids, and thus making the fats rancid. There are some oils, however, that instead of changing thus gradually in the air, absorb oxygen rapidly and become dry and hard. These drying oils are called varnish oils, because they are so much used in mixing varnish. Linseed-oil is one of the most important of them. It is prepared for varnishing by freeing it from all mucilaginous matter by heating -it with litharge or oxide of lead in it, and mixing it, after this clarifying, with some coloring substance. 372 CHEMISTRY. Oil-cloth is cotton cloth covered with colored varnish, and oil-silk is var- nished silk. Drying oils are used in painting, and mixed with lampblack they constitute printers' ink. 521. Spontaneous Combustion. It is because of the rapid absorption of oxygen from the air that the drying oils are sometimes the cause of spontaneous combustion. This com- monly occurs in waste thrown together in a heap. The heat produced by the absorption of the oxygen sets fire to the combustible substance cotton or linen or woolen that is impregnated with the oil, and the oil, being itself com- bustible, burns also. The reason that the heat is adequate to produce this effect is that it is so shut in among the parts of the heap where it is generated that it accumulates, reaching at length the point of combustion. The oil in drying always produces heat; for condensation of a gas, as it combines with a fluid or solid substance, can not take place without this effect ; but the heat in all ordinary cir- cumstances quietly escapes into the air as fast as it is pro- duced. In the drying of paint upon any surface heat is formed at every point of it, but it produces no combustion because it escapes instead of accumulating. 522. Combustion of Fats. As both the fat acids and their base, glyceryl, are compounds of carbon, oxygen, and hy- drogen, we have in them the same elements as in wood and coal, and therefore their combustion is attended with the same phenomena and the same results. The facts stated in Chapter X. fully illustrate this, and we need not dwell upon the point here. 523. Wax. This substance has so decided a resemblance in some respects to the fats that it may be classed with them. It is a mixture of two substances cerin and myri- cin. A soap can be formed with cerin by boiling it in a solution of potassium hydrate. Wax occurs in small quan- tity in all plants. It gives a shining appearance to leaves, OILS AND FATS. 373 stalks, and fruits, which in some cases is very decided. Some plants in South America and China contain so much wax that it is obtained from them by boiling and pressure, and is sold under the name of vegetable or Chinese wax. But most of the wax in use in the world is made by bees. It has been supposed that the bees simply gathered the wax from flowers as it exists in the pollen; but this is certainly not true in regard to all of it, for it has been sat- isfactorily proved that the bees actually convert the sug- ary substance into wax in their abdominal sacs. 524. Volatile Oils. The oils which we have already no- ticed are called faced oils, because they have no tendency to pass off into the air. The volatile oils, of which oil of turpentine, oil of peppermint, and oil of lemons are familiar examples, nearly all possess the same chemical composition C 10 H 16 ; they differ from the fixed oils in three important respects : 1. As their name imports, they are readily dissi- pated in the air. Some of them are exceedingly volatile. Sometimes a volatile oil is adulterated with some fixed oil; but this can be readily detected by dropping some of the specimen on paper, for if it be adulterated it will leave a grease spot upon it. 2. Volatile oils dissolve in alcohol. Such solutions form the bases of essences and cordials and perfumed waters, such as the Eau de Cologne. 3. They are hydrocarbons, and not salts of fatty acids like the fixed oils. The volatile oils are very numerous, as you -may readily see from the fact that all the varied odors of plants are due to their presence. They are most frequently pro- duced in flowers and seeds, sometimes in the stalks and leaves, and in some plants in the roots. Sometimes there are several sorts of oil in the same plant. Thus there are three different kinds of oil in the orange-tree one in the leaves, another in the blossom, and still another in the peel of the fruit. 374 CHEMISTRY. 525. Composition. The volatile oils are divided into three classes, according to their composition: 1. Oxygen- ated oils. These, which are by far the most numerous class, are composed of carbon, hydrogen, and oxygen. 2. Non- oxygenated oils, which are composed only of carbon and hydrogen, and are therefore called hydrocarbons. The principal of these are the oils of turpentine, savin, juniper, lemons, etc. 3. Sulphuretted oils, which are composed of carbon, hydrogen, and sulphur. Nitrogen is a component of some of them. These oils exist in mustard, horseradish, garlic, onions, hops, etc. They have a very pungent smell, causing lachrymation, and are so acrid that they raise blis- ters when applied to the skin. 526. Camphor. Camphor is obtained by distilling with water the wood of the laurus camphora. This forms when pure a white, crystalline, translucent solid, having a pecul- iar odor which is familiar to every one. It gradually sub- limes at ordinary temperatures, and often forms beautiful crystals on the sides of the bottles in which it is kept. 527. Resins. Where an essential or volatile oil is ex- posed to the air, a part of it evaporates, diffusing an odor, but a part combines with the oxygen of the air, forming a resin. The pure rosin, or colophony, is thus produced from the oil of turpentine. It is really a mixture of two acids. This oxidation is, however, only partial, so that the turpen- tine when gathered is a mixture of the oil and the resin. Some of the resins are called balsams. The resins are very indestructible, and have also the power of preserving other substances from decay. The mummies found in the pyra- mids of Egypt are bodies which were embalmed with res- ins. Amber furnishes the most striking illustration of this indestructibility. This resin was formed in the early ages of the world, it having survived the destruction of the trees from which it exuded. Insects are often seen inclosed in OILS AND FATS. 375 pieces of it, embalmed, as we may say, centuries upon cent- uries before the Egyptians lived whose mummies are found in the pyramids. 528. Uses of the Resins. The resins are chiefly used for making varnishes. In spirit varnishes the solvent is alco- hol ; in oil varnishes it is some drying oil. As the resins are soluble in fat oils, they enter into the composition of many ointments and plasters. Sealing-wax is mostly the resin called shellac, with a little turpentine to make it melt and burn more readily, and some cinnabar, lampblack, or other substance to color it. 529. Caoutchouc and Gutta-Percha. These are mixtures of several hydrocarbons, and are in their composition very much like turpentine oil. The caoutchouc is the milky juice which exudes from incisions made in several kinds of large trees in South America. This, when left to dry in the air, becomes a white elastic mass. The drying is more rapid when the exuded substance is spread upon moulds of clay and suspended over a fire, as is commonly done. The soot, which thus becomes incorporated with it, gives it a dark color. Gutta-percha is obtained from certain trees in the East Indies. Like the caoutchouc, it exudes as a milky juice. It differs from caoutchouc in three respects it is very tough, has little elasticity, and becomes soft and plastic with a moderate heat, hardening again as it grows cool. This difference in properties fits these two substances for different uses in the arts. 530. Vulcanized India-Rubber. This substance is a com- pound of sulphur and caoutchouc, which has received pecul- iar qualities from being subjected to a certain degree of heat. Unless this be done it is too soft for use. Shoes and other articles of this material are therefore, after being made, brought up to the required temperature, and on cool- ing they have the two qualities of firmness and pliability. 376 CHEMISTRY. The discovery of this effect of heat, so important in the manufacture of India-rubber goods, is said to have been made by our countryman, Goodyear, in consequence of an accidental circumstance. As he was talking earnestly with a friend, in making a gesture he threw into the tire a bit of the compound of sulphur and caoutchouc. On taking it out of the fire he observed that its properties were essentially altered, and this observation led to experiments which re- sulted in the discovery alluded to, and to its wide applica- tion in the India-rubber manufacture. 531. Vegetable Alkaloids. There are certain organic bases, that is, bases which are extracted from the seeds, bark, roots, and other parts of plants. They are called al- kaloids, because, like the alkalies, they produce a basic re- action on red litmus paper. We will mention a few of the most prominent of them. There is morphine, which we get from opium, and quinine, which we get from the cin- chona bark. Caffeine, or theme, is the alkaloid found both in the leaves of the tea-plant and the berries of the coffee- plant. Strychnine, which is so exceedingly poisonous, is obtained from the seeds of the strychnos mix vomica. Nicotine is found in tobacco. It is an oily, colorless sub- stance, which is so poisonous that a fourth part of a drop will kill a rabbit. Most of these bases are crystalline, and the crystals of some of them are beautifully delicate. Thus the crystals of caffeine are fine white prisms of a silky lus- tre ; and those of piperine, the active principle alike of white, black, and long pepper, are white and needle-shaped. Most of the organic bases, like the inorganic, unite with acids to form salts. Thus morphine and quinine unite with sulphuric acid to form sulphates. The formula of these bodies are very complex. They all contain nitrogen, however, besides C, H, and O, and belong to the class of bodies called Amines, as mentioned in 425. OILS AND FATS. 377 What the organic radicals are of which these alkaloids are composed is not definitely known. "When the exact con- stitution of quinine, for instance, is discovered, it will be pos- sible to prepare it artificially, instead of extracting it from cinchona bark. This discovery will be of immense impor- tance, and will doubtless prove a fortune to the happy dis- coverer. 532. Coloring Matters. There is a great variety of these in the vegetable world. A portion of them are composed of C, H, O, and N, but some of them contain no N. The former are called nitrogenous because they contain nitro- gen, and the latter non-nitrogenous. The principal of the latter class are madder, hematoxyline, which is the color- ing principle in logwood, Brazil-wood, and camwood, gam- boge, etc. Indigo is the most important of the nitrogenous class. This is derived from the juice of several species of the plants called indigofera. The indigo is not, however, of a blue color in the plants, but is almost colorless. It ac- quires the brilliant blue color that we see it have by a fer- mentation, to which the leaves of the plants are subjected in the extraction of the indigo. Blue indigo is, therefore, oxidized indigo, and by depriving it of its oxygen we can restore it to its colorless state. When thus deoxidized it is soluble, as it is in its natural state in the plant; but by exposure to the air it absorbs oxygen rapidly, and so be- comes blue and insoluble. The blue litmus, so much used by the chemist in testing acids and bases, is a nitrogenous coloring matter which is derived from certain lichens. Al- most the only coloring matter of animal origin is cochineal an insect. The color from this insect is called carmine. 533. Mordants. Some coloring matters have such an affinity for the substance of cloth that they will unite inti- mately and firmly with the fibres, and so make fast colors. But some have not this power. In order to fix the colors 378 CIIEMISTKY. in such cases, some substance must be employed which has a strong attraction for both the coloring matter and the substance of the cloth, and can therefore unite the two firm- ly together. Such a substance is called a mordant, for rea- sons already given. The cloth to be dyed is first charged with the mordant, and then is immersed in the dye. 534. Colors Modified by Mordants. The mordant not only fixes the color, but modifies it, so that with different mordants different colors can be produced with the same dye. Thus, by using with madder the acetate of aluminium, produced by mixing common alum with acetate of lead, a red color is obtained ; but if ferrous sulphate be mixed with the acetate of lead instead of the alum, a deep black color is the result. Then, again, if some arsenious acid be added, together with the ferrous sulphate, the madder gives a rich purple color. Now all of these madder colors can be pro- duced upon the same piece of calico by printing the different figures with different mordants before introducing it into the dye. The printing is done by rollers, between which the calico is passed. These rollers are engraved with the fig- ures, and the pastes containing the mordants are each put upon its appropriate set of rollers. The calico is passed through the several sets successively. After all the mor- dants are thus printed upon the cloth it is immersed in the dye. The process is not finished yet, for the common color of the madder is in all those parts of the cloth not touched by the mordants. But the color is not fast, and is easily washed out, leaving a white ground, the washing out not affecting at all the colors fastened by the mordants. QUESTIONS. 508. Why must the common idea that acids are sour be abandoned ? Name some of the sources of organic acids. What is said of the proper- ties of the members of the fatty acid series ? In what conditions do the OILS AXD FATS. 379 acids of fruits, etc., exist in the plant? How may some organic acids be distinguished from mineral acids ? 509. From what sources is tannic acid obtained ? What is its character? What is said of the products of its de- composition ? 510. Describe the mode of obtaining it. 511. What is tan- nin ? To what is it compared ? Give the chemical explanation of the black color of leather. Why do drops of tea on a knife-blade become dark? 512. Explain the common mode of making writing-ink. What is said of securing permanency in writing ? What substances are added to ink, and for what purposes ? 513. In what parts of plants are oils and fats formed ? Name some of the principal ones, with their sources. 5U. What is said of their composition ? What is stearin ? Olein ? 515. What are the properties of glycerin ? To what class of bodies does it belong ? What is nitroglycerin ? What is dynamite? 516. How can stearic acid be ob- tained ? Of what are candles best made ? 517. What is soap, chemically considered ? Explain the action of caustic soda on olive-oil. Of what are natural fats composed ? 518. What is the difference between hard and soft soaps ? Upon what does the cleansing power of soap depend ? Mention some of the uses of soap. What is the best application for burns? 519. What is said of the properties of fats, and of the uses to which they are ac- cordingly applied ? 520. How do fats become rancid ? What are varnish oils? How is linseed-oil prepared for varnishing? What are oil-cloth and oil-silk? 521. State in full what is said of spontaneous combustion. 522. What is said of the combustion of fats ? 523. What are the nature and composition of wax ? What is said of its occurrence in plants ? What of its preparation by bees ? 524. How do volatile oils differ from fixed ? How can adulteration of a volatile with a fixed oil be detected? In what parts of plants are the volatile oils found ? 525. Give the three classes of volatile oils, and what is said of them. 526. What is said of camphor? f>27. What are resins ? What is said of their indestructibility ? 528. What of their uses ? 529. What is said of caoutchouc ? What of gutta-percha ? 530. What of vulcanized India-rubber. 531. What are vegetable alkaloids? Mention some of them, and the sources from which they are obtained. What is said of their crystals? What of their composition? 532. What are the two classes of coloring matters ? What is said of indigo ? 533. What is said of mordants? 534. What is said of modifying color by mor- dants ? In what way can different colors be put upon the same piece of calico ? 380 CHEMISTRY. CHAPTER XXX. FERMENTATION. 535. Different Kinds of Fermentation. The word fermen- tation is applied to various decompositions and changes which occur in organic substances. We have the alcohol- ic fermentation, producing alcohol; the acetous, producing vinegar, etc. It is of these two kinds that we shall speak in this chapter. By the alcoholic fermentation sugar is converted into alcohol, and by the acetous alcohol is con- verted into acetic acid, the sour principle of vinegar ; or, strictly speaking, alcohol is made from sugar, and acetic acid from alcohol. Putrefaction and fermentation are really the same thing, only the former name is given to the decomposition when accompanied by an offensive odor. Some fermentations give rise to evolution of gases, derived from the constitu- ents of the decomposing substance ; when these gases have a disagreeable odor, as sulphuretted hydrogen, certain hy- drocarbons, and ammonia, for example, produced in the decomposition of animal matter, the term putrefaction is used. Nitrogenous bodies are the most disposed to this kind of decomposition. Substances which arrest fermen- tation already begun, or deprive bodies of the power of fermenting, are called antiseptics. Such are ferric chlo- ride, arsenious anhydride, carbolic acid, etc. 536. Ferments. There must always be a fermenting agent to produce the change. Neither sugar nor alcohol has any tendency to ferment of itself, but they very readily FERMENTATION. 381 do so on the application of a small amount of some fer- ment. This ferment may be either of the albuminous sub- stances gluten, albumen, or casein. The manner in which these bodies act in exciting fer- mentation is very imperfectly understood; "they neither add any thing to the fermenting body nor take any thing away from it, but the motion or disturbance of their par- ticles, while undergoing putrefaction, is supposed to be communicated to the particles of the fermenting body with which they are in contact, and thus induce decomposition." Fermentation is always accompanied by the growth of organized bodies called fungi when vegetable, and infu- soria when animal. In fact, their development is regarded as the exciting cause of fermentation and putrefaction. 537. The Chemical Change in Alcoholic Fermentation. Alcohol is composed of the same elements as sugar, but in different proportions. The production of alcohol by the fermentation of sugar is not really a conversion of sugar into this substance, but a splitting up of the sugar into al- cohol and carbonic anhydride. Cane-sugar does not thus break up, but is converted first into glucose, or grape-sug- ar, and this is decomposed in the following manner: Grape-sugar. Alcohol. Carbonic anhydride. C 6 H la O 6 = 2C 2 H 6 O + 2CO 3 " Some other substances are formed at the same time, but only in small quantity ; and their production has been dis- regarded in the equation. 538. Yeast. What is commonly called yeast is really a growth, for yeast is a collection of very minute plants ; so minute that it is estimated that a cubic inch contains twelve hundred millions of them. This plant, revealed to us by the microscope, multiplies itself with exceedingly great rapidity, and will continue to do so as long as there is ni- trogenized matter to supply it with the means of growth. 382 CHEMISTRY. Thus in a brewery the quantity of yeast continually in- creases, and it is sold largely for the raising of bread, a fer- menting process to be noticed soon. There is a difference of opinion as to the mode in which yeast causes fermenta- tion. Some suppose that it is the yeast-plants that produce this effect, while others suppose it is their decomposition. 539. Wines, Cider, etc. In making these no addition of yeast is required, for there is nitrogenous matter in the juices from which they are made, which by exposure to the air becomes a ferment. In making Champagne and other sparkling wines, the wine is bottled before the fer- mentation is finished. Of course the process goes on in the bottle, and the carbonic acid produced is pent up in the liquid, ready to expand and escape the moment the way is opened. Sweet wines are those in which there is some sugar that has not been decomposed in the fermen- tation. Wines are called dry when they contain very little sugar. Wines are made from other fruits as well as the grape, as, for example, the currant, the gooseberry, the elderberry, etc. Cider is essentially a wine made from apples. Much of the so-called Champagne wine is really cider, to which a peculiar flavor is given. Other wines are counterfeited, and there is probably no class of men more often cheated than wine-drinkers. 540. Flavor of Wines. The flavor which distinguishes grape wines as a class from other spirituous drinks is produced by a very small amount of an ethereal substance called cenanthic ether. When obtained in a sep- arate state it is a very fluid liquid, having a sharp, disagreeable taste, and a vinous odor so powerful as to be almost intoxicating. It does not exist in the grape, but is one of the products of the fermentation, and increases with the age of the wine. You can have some idea of the power of this sub- stance from the fact that in few wines does it constitute more than the one four-thousandth part of their bulk. It is often obtained by manufacturers of wines from grain spirit and cheap wines, and is used by them for produc- ing imitations of wines of higher prices with such cheap articles as potato FERMENTATION. 383 whisky. Besides the general wine flavor given by the oenanthic ether, there are other flavors imparted by other substances giving to the various wines individual characteristics. 541. Acidity of "Wines. The acidity of grape wines is owing to the presence of tartaric acid in combination with potassium, forming the acid tartrate of potassium, or cream of tartar. As this gradually separates from the wine, and collects as a crust on the sides of the casks and bottles, the longer wines are kept the less acid they become, and hence in part the val- ue which age gives to them. The acid which is present in small amount in malt beer is acetic acid, the acid of vinegar ; and that which we have in cider is lactic acid, the acid which is present in soiir milk ; so that wine, malt beer, and cider each has a different acid. When, however, the fer- mentation goes in either of these beyond the production of alcohol, acetic acid results, for then we have the acetous fermentation. 542. Amount of Alcohol in Wines. The proportion of alcohol varies very much in different wines. Even in the strongest wines more than three fourths of the liquid is water. The proportion, by measure, of alcohol in the most prominent wines is as follows : Per Cent. Port 21 to 23 Sherry 15 to 25 Madeira 18 to 22 Marsala 14 to 21 Malmsey 16 Per Cent . Tokay 9 Khenish 8 to 13 Moselle 8 to 9 Champagne 5 to 15 Burgundy 7 to 13 Claret 9 to 15 543. Production of Alcohol from Starchy Substances. In the production of alcoholic liquors from barley, rye, pota- toes, etc., in which starch is the chief ingredient, and sugar is only present in very small amount, a preliminary process is necessary in order to change the starch into sugar. In making beer from barley this is done in the following man- ner : The grain is first moistened in heaps, and spread upon a floor in a dark room. It sprouts, and in doing this some of the starch in it is turned into sugar by the action of the diastase ( 472), so that the barley has quite a sweet taste. The process is arrested by drying in the kiln just as the germs are about to burst from the seed, for if it be left to 384 CHEMISTRY. go on beyond this some of the sugar will be lost by being converted into vegetable fibre. The malt for so this sug- ared barley is called after being dried, is bruised and put into the mash-tun with water in the requisite quantity, which is gently warmed. Here the sugar and diastase are dissolved, the latter at the same time converting the remaining starch of the seeds into grape-sugar. The liquor, or wort, as it is called, is now put into the boiler, and boiled with the hops, which not only give to the liquor its bitter taste, but also help to clarify it. The boiled liquor is run off into shallow vats, where it is cooled, and then it is poured into the fermenting tun, where, with the addition of yeast, the requisite fermentation is produced. In like manner in making whisky from the potato the starch must first be converted into sugar to prepare for the alcoholic fermentation. 544. Distillation. In the operations of which we have spoken alcohol is obtained mingled with a large amount of water. By the process of distillation this amount of water can be much diminished, giving us the stronger spir- ituous liquors called by the common names of distilled liquors and ardent spirits. Brandy, for example, is distill- ed from wine, and has from 50 to 54 per cent, of alcohol, while the strongest wine has but 25 per cent. In rum, dis- tilled from fermented molasses, there is from 72 to 77 per cent, of alcohol. A common form of apparatus for distill- ing brandy and spirits of wine is represented in Fig. 116 (p. 385). It consists of a copper still, A, having a dome- shaped head, B, which by a tube, C, communicates with the worm, D. Heat being applied to the still by the Bunsen burner, the alcohol passes over to the worm more freely than the water because it is more volatile. For the purpose of condensing the vapor as it passes into the worm, the worm is inclosed in a cylindrical vessel, E, which is full FERMENTATION. 385 Fig. 116. of water. To prevent the water from becoming hot a con- stant supply of cold water flows in by the tube H to the bottom of the vessel, the heated water rising and flowing out by the tube G. The condensed liquor, passing out at F, drops into the receiver. 545. Fusel-Oil. This oily substance, which is very poisonous, was first discovered in the distillation of liquor made from potatoes, and hence has sometimes been called potato-oil. In reality it is amylic alcohol, one of the large class of alcohols mentioned in the fourth column of the table on page 303. Amylic alcohol is produced in the distillation of liquors made from the grains, and occasionally at least in other distillations also. It may be separated from the spirit by filtration through charcoal, this substance absorbing the poison into its pores. But not only is this process often omitted, thus leaving this poison to aggravate the deleterious effects of the alcohol itself, but the fusel-oil is made use of to a large extent by unprincipled manufacturers, of whom there are a great number, in getting up factitious liquors, wines, and cordials. The enormous cheating and destructive poisoning to which the drinkers of spirituous liquors are thus subjected, though extensively known, seem to be little heeded. 546. Fermentation in Bread. The "raising" is ordinarily accomplished by alcoholic fermentation. The yeast first R 386 CHEMISTRY. converts some of the starch of the dough into sugar, and then makes from this sugar alcohol and carbonic anhydride. It is the expansion of the gas thus produced in every part of the mass that makes the numberless cells in it, and thus causes the "raising;" the volatile alcohol escapes at the same time. In the baking of bread part of the starch of the flour is converted by the heat into dextrin. A shining coat is given to the loaf by dissolving some of this gum on the surface by moistening the loaf after it is baked, and then subjecting it for a few minutes to heat again, which quickly dries and hardens the gum. Bread is often raised by other means than fermentation. Tartaric acid and hy- dro-sodium carbonate are used for this purpose. If the bi- carbonate, as it is commonly called, be thoroughly mixed with the dough, and the tartaric acid be then added, it will seize the soda, and the released carbonic anhydride, as it ex- pands into its gaseous state, raises the bread, as it does when generated by yeast. Bakers sometimes use ammonium carbonate to raise their light, spongy cakes. There is no need of any acid in this case, for the heat volatilizes the carbonate, and as it escapes it makes the cakes porous. Hum and alcohol have sometimes been employed, the vapor produced by the heat answering the purpose. There is considerable water in bread. In every 100 pounds of flour there are 16 of water. Then in the making of the flour into bread there are added 50 pounds more of water, so that there are 66 pounds of water in 150 pounds of bread. When bread becomes "stale," its dryness is not owing to an es- cape of water, but to a more thorough incorporation of the water with the bread. 547. Ether. This singular fluid, so different from alcohol in its properties, is prepared from alcohol, and differs from it but little in its composition having the same ingredi- ents, though not in the same proportions. Alcohol being FERMENTATION. 387 C 2 H 5 (HO), ether is (C 2 H 5 ) 2 O. As stated in 423, if we re- gard alcohol as a hydrate of the radical ethyl C 2 H 5 , ether may be regarded as the oxide of this radical. Ether is a very light liquid. If exposed to a heat of 35.6, two de- grees less than blood heat, it boils, and it has never yet been frozen. It is exceedingly volatile. On account of its volatility and the effect of heat upon it, it must be kept in a cool place and in tightly closed bottles. If the hand be moistened with it, there ensues a sensation of great cold, owing to the rapid evaporation. It is very combustible, and its vapor mingled with the air forms an explosive mixture. The inhalation of it in considerable amount produces in- sensibility, and it is therefore much used in surgery to pre- vent the patient from suffering while undergoing an oper- ation, and also to some extent in medicine to relieve the pain of disease. It is also used to dissolve gun-cotton, or pyroxyline ; the solution is largely employed by photog- raphers to form the collodion films of the glass plates on which the negative pictures are produced. 548. Compound Ethers. As ether is an oxide it unites with acids to form compounds which may properly be termed salts. That very common medicine, the sweet spirits of nitre, is one of these salts diluted with alcohol. The essences used in flavoring wines, cordials, and in cook- ing food, are really compound ethers, artificially prepared on a large scale. In the following table (p. 388) you have a list of some of these perfume ethers, their formulaa, and the flavors they imitate. By mixing these ethers with each other, and with essential oils in various proportions, the odor and flavor of nearly every fruit may be imitated. Dilution with alcohol best develops the flavor. Salicylol is not an ether, but finds a place in this table for obvious reasons. 549. How Ether is Obtained. It is by the action of sul- 388 CHEMISTRY. PERFUME ETHERS; FRUIT ESSENCES. NAME. FORMULA. FLAVOB. Ethyl butyrate. Pine-apple Ethyl cenanthylate. . C 2 H 5 .C 7 H 13 O 2 Greengage. Ethyl pelargonate . . GjHs.Ogllj^Oa Quince. Ethyl suberate. . . C,H 5 .C S H 12 O, Mulberry Aroyl acetate. . . P FT f 1 TT O Pear .Amyl valerate C-H n C 5 H 9 O 2 Salicylol H.C 7 H 4 O.HO Meadow-sweet Methyl salicylate . . . C 7 H 4 O.CH 3 .H.O 2 Winter-green. phuric acid upon alcohol that ether is generally obtained. The process is represented in Fig. 117. Equal quantities by Fig. 117. weight of alcohol and the acid are introduced into a retort, A, to which heat is applied by a ring-burner, or, better, by means of a sand-bath. The retort is connected with an ap- paratus for condensing the vapor of the ether, known as Liebig's Condenser, and consisting essentially of two glass tubes, C and D, one fitted into the other by means of corks ; water entering the space between these tubes through the FERMENTATION. 389 funnel, E, cools the vapor of the ether, and passes off through the outlet, F. The ether condensing in the inner tube flows into the two-necked receiver, G, and thence into a flask, H. The Liebig condenser is supported by a stand, B ; the outer tube of the condenser is often made of metal. The stopper in the tubulure of the retort, A, may be removed, and more alcohol added as may be needed for the continuance of the formation of the ether to any considerable amount. The chemical process here is this: Sulphuric acid takes away the elements of water from the alcohol and leaves ether, thus: 2(C 2 H 6 O) - H 2 O = (C 2 H 5 ) 2 O. At least this is the simplest explanation which we can give you. Ether is very commonly called sulphuric ether, but the name is improper, as it contains neither sulphuric acid nor sulphur. By man- aging the alcohol and sulphuric acid differently a gas may be produced which is a very different substance from ether. The amount of sulphuric acid used for this purpose is five times that of the alcohol. This gas is olefiant gas, one of the hydrocarbons obtained by distillation of wood and coal. The reaction in this case is a dehydration or abstraction of water from the alcohol : Alcohol. Olefiant gas. Water. C a H 6 = C 3 II 4 + H 2 O 550. Chloroform. This valuable substance can be ob- tained in various ways. It is commonly produced by distilling alcohol with water and chloride of lime. Its molecule contains one atom of carbon, one of hydrogen, and three of chlorine, and its composition is therefore ex- pressed thus : CHC1 3 . We have seen in 421 how it may be regarded as a substitution product of marsh gas. It is, like ether, a colorless and very volatile liquid, having a peculiar sweetish smell. Its inhalation produces insensi- bility more readily than ether. 551. Vinegar. This is a mixture of acetic acid with wa- 390 CHEMISTEY. ter, there being diffused through the water also more or less of some other matters. But a small percentage of the whole is acetic acid. Common table vinegar contains but from two to five per cent. As acetic acid is little if any more volatile than water, it can not be obtained pure from vinegar by distillation. The only way in which the chem- ist can obtain it is to decompose some of the acetates, as acetate of lead the common sugar of lead by an acid which is strong enough to seize the base, and thus release the acetic acid. 552. The Acetous Fermentation. Vinegar is commonly made by the exposure of some spirituous liquor, as cider or wine, to the air. This occasions what is called the acetous fermentation. This, like the alcoholic fermentation, can not take place without the presence of a ferment. For this reason, if a solution of alcohol in perfectly pure water be exposed to the air, there will not be the least fermentation. In the case of cider, wine, etc., there is no need of adding any ferment, for there is one already present in the liquid, the same which acted in its alcoholic fermentation. It is the decomposition of this which produces that gelatinous mass called the mother. As one of the results of this de- composition we have the generation of infusoria, or vinegar eels, as they are commonly called, which can often be seen by the naked eye when a glass of vinegar is held up to the light of the sun. When the acetous fermentation takes place in liquids containing starch and sugar, it is always really preceded by the alcoholic fermentation. For exam- ple, when preserved fruits become acid there is first an al- coholic fermentation, which passes into the acetous, pro- ducing vinegar. The effervescence which occurs, causing bubbles on the surface, is occasioned by the carbonic anhy- dride generated by the preliminary alcoholic fermentation. The more thoroughly the air is shut out from preserves the FERMENTATION. 391 less apt will they be to ferment. Exposure to heat favors fermentation, and hence preserves should be kept in a cool place. A high degree of heat will, however, destroy the power of the ferment, and hence preserves are scalded when there is a suspicion that fermentation is commencing in them. For the same reason vinegar is boiled to arrest the formation of the mother in it. 553. Sour Bread. When bread is sour it is because the vinous fermentation has been followed by the acetous. This may arise from two causes. Either the fermentation has been allowed to go on too long before the bread was baked, or the ferment used has been kept so long as to enter into that state which makes it capable of producing the acetous fermentation. If a flour paste stand in a ves- sel covered with a board for six or eight days, it acquires a pleasant smell in the change which has taken place in it, and is now fit to act as an alcoholic ferment. Bread raised by it will be sweet. But if this paste or dough be left to stand a little longer, it acquires an acid taste, and will now, indeed, excite an alcoholic fermentation in sugared water or in bread, but this will at once pass on to the acetous fer- mentation. 554. Explanation of Acetous Fermentation. The change which alcohol undergoes on conversion into acetic acid is not strictly a result of fermentation, because this conversion may be effected in various ways which exclude the idea of any vegetable or animal growth. It is rather a case of oxidation, for alcohol contains more oxygen and less hydro- gen than acetic acid, as shown in the following equation : Alcohol. Oxygen. Acetic acid. Water. C a H 6 + O a = C a H 4 O a + H0 a Since, however, pure alcohol may be exposed to the air> either alone or mixed with water, for any period without suffering oxidation, and the change is induced by the pres* 392 CHEMISTRY. ence of unstable organic substances, the conversion may be regarded as a sort of fermentation. Actually the change is not so simple as represented in the equation just given. It has two stages. As when starch is converted into sugar there is an intermediate substance dextrin into which it is changed prepara- tory to its conversion into sugar, so also, in the formation of acetic acid, the alcohol is first changed into an intermediate substance called aldehyde. The two changes may be expressed thus : Alcohol. Oxygen. Aldehyde. Water. C 3 H 6 O + O = C 2 H 4 O + H 2 O Aldehyde. Oxygen. *0 Acetic acid. C a H 4 2 Compare the equations in 537 explaining alcoholic fermentation. 555. Quick Mode of Making Vinegar. Alcohol can be converted into acetic acid in a very short time by provid- ing for a very free exposure of it to the air, so that the ox- ygen may act upon every drop of it at once. This is done in the manner repre- sented in Fig. 118. A bar- rel is filled with shavings which have been steeped in vinegar. Near the top of the barrel is a shelf, perfo- rated with holes, in which there are fastened either bits of string or straw, that the liquid poured in, which is alcohol and water with a little yeast, may trickle down upon the shavings. A free access of air is secured to the whole surface of the shavings by holes made in the side of the barrel, and some holes in the perforated shelf large enough to admit glass tubes of considerable size. Now as the fermentation creates heat, the cold air admitted in FERMENTATION. 393 the holes becomes expanded by the heat, and so rises to pass out through the glass tubes ; and in this way quite a brisk circulation of air is kept up, bringing, therefore, oxygen to the whole surface of the shavings with con- siderable rapidity. The fluid as it runs out below passes into the receiver. Of course the barrel is whole as used ; in the figure a portion of it is represented as cut away, merely that you may see the interior arrangement. 556. Adulteration of Vinegar. Even vinegar is some- times adulterated. When a manufacturer desires to sell poor vinegar as good he gives the requisite sharpness to it by adding some substance, as, for example, sulphuric acid. Adulteration with this article can be very easily detected. Fill a jar or mug half full of water, and set upon it a cup containing some of the vinegar with grape-sugar in it. If you set the mug upon a hot stove the vinegar in a little time will be all evaporated. If now what is left in the cup be of a black color, there is proof of the presence of free sulphuric acid. The explanation is this : As the vinegar evaporates, the sulphuric acid, not being volatile, remains in the cup, and at length, when all the water is gone, is so concentrated that it carbonizes the non-volatile organic matter. (See 244.) Great care must be taken not to heat the contents of the mug too hot, or the organic matter may be charred by the heat alone. QUESTIONS. 535. What is said of different kinds of fermentation ? What is the dif- ference between fermentation and putrefaction ? What are antiseptics ? 536. Explain the nature and action of ferments. What is said of the growth of organized bodies? 537. Explain the chemical change in alco- holic fermentation. Give the equation. 538. What is yeast ? 539. What is said of the fermentation of wines ? When are wines dry ? 540. What R2 394 CHEMISTBY. gives peculiar flavor to grape wines ? How much of this ether do wines contain? 511. To what is the acidity of grape wines due? 542. What is said of the amount of alcohol in wines ? 543. What is the first step in making alcohol of starchy substances ? What is malt ? How is it made ? 544. Describe the process of distillation. 545. What is fusel-oil ? How produced? 546. Explain the raising of bread by yeast. What other means are employed to raise bread ? How much water is there in bread ? What makes bread stale ? 547. What is ether ? What are its properties ? For what is it used ? 548. How may compound ethers be regarded ? Give the names and flavors of some of the so-called fruit essences. 549. De- scribe the process of making ether. Explain the chemical reaction which ensues. What is obtained by managing the alcohol and sulphuric acid dif- ferently? 550. How is chloroform made? Of what composed? 551. What is vinegar ? Why can not acetic acid be obtained from it by distil- lation? How is it obtained by the chemist? 552. What is said of the common mode of making vinegar ? What is the mother of vinegar ? What are vinegar eels, and how are they produced ? State in full what is said of the acetous fermentation in preserves. 553. Explain the chemistry of sour bread. 554. Explain in full the chemical changes of the acetous fer- mentation. In what two stages does this change take place? 555. De- scribe and explain the quick mode of making vinegar. 556. How is vinegar commonly adulterated, and how can the adulteration be detected ? CHAPTER XXXI. ANIMAL CHEMISTRY. 557. Materials. The elements which enter into the com- position of the various substances found in animals are the same with those which compose vegetable substances. Wo have first the four grand elements carbon, oxygen, hydro- gen, and nitrogen. There are also chlorine, sulphur, and phosphorus, and also the metals calcium, potassium, so- dium, and iron. As in vegetables, so in animals, these ele- ments never appear as elements, but always in combina- tion. Thus we never have chlorine alone, but it exists in ANIMAL CHEMISTRY. 395 combination chiefly with sodium, forming the chloride or common salt, which, as you will soon see, plays quite a part in the animal economy. So phosphorus is mostly united with oxygen and calcium, so as to form a phosphate of calcium, and is never found as phosphorus. The com- binations of the four grand elements are very various in their character, for out of them are built animal structures of every kind. It is not commonly the elements them- selves, but the combinations of the elements, derived from various sources vegetable, animal, and mineral that an- imal chemistry works upon as materials in evolving ani- mal substances, both liquid and solid. Thus phosphorus and oxygen and calcium are not introduced into the an- imal system separately, and there united to form phos- phate of calcium; but this salt is introduced as such in both vegetable and animal food. So the carbon, oxygen, hydrogen, nitrogen, and sulphur which compose albumen do not unite in the animal to produce this substance, but it is formed in the vegetable for use in the animal. 558. How Animal and Vegetable Chemistry are Alike. They are alike, as you have just seen, in the elements which are employed. They are also alike in many of the com- binations of these elements. The chloride of sodium and the phosphate of lime found in animals are also present in vegetables. One of the principal constituents in animals is like vegetable gluten. Then there are albumen and casein, corresponding with substances of the same name in vegetables. This resemblance between animal and vege- table chemistry comes in consequence of the fact that the vegetable world is so largely engaged in preparing for the animal world what it gathers up from the mineral world. It not only transfers, but prepares, and many of its prepa- rations are combinations which enter with little or no al- teration into the composition of animal substances. 396 CHEMISTEY. 559. How they Differ. Animal and vegetable chemistry differ in several important particulars. The former is much more complex and mysterious than- the latter. Certain substances, as starch and sugar, found in such abundance in some vegetables, are not present in animals in their normal state. When taken into the animal they are changed into fat and other substances. Then there is not only difference but opposition between the chemical action of leaves and that of lungs, carbon being given out by lungs and taken in by leaves, and oxygen being given out by leaves and taken in by lungs, as stated in 128. Besides all this, the plant lives upon unorganized materials, while the animal lives upon organized materials built up by the plant. 560. The Blood. This universal building material of the animal contains all the constituents needed for the construction and repair of every part. There is fibrin, out of which chiefly the various textures of the body are formed. This is the firm part of the coagulum or clot that separates when blood is left standing, there being in- corporated with it the coloring matter of the blood. The clot swims in a watery fluid called serum, which contains albumen in solution. Besides these there is a variety of materials in small amounts in the blood. There is iron, which is contained in the matter which gives the blood its red color. Then there are mineral materials for the manu- facture of bones, teeth, etc., and various other substances. Water constitutes about four fifths of the blood. Without this the materials which we have mentioned could not be carried to all parts of the body. In this they are sent to their destination through innumerable tubes by the heart, the great central pump of the circulation. 561. How the Blood is Made. The blood is made mostly from our food. We say mostly, because that important sub- ANIMAL CHEMISTRY. 397 stance, oxygen, is partly furnished from, the air that enters the lungs. The process of digestion, by which the blood is made from the food, we shall not particularly describe here, but will refer you to Hooker's two works on Physi- ology. It is sufficient to speak of it here very briefly and generally. The food on being ground up by the teeth is at the same time mixed with the saliva, which is poured into the mouth by several glands, or saliva factories, as they may be called. In the stomach the ground and moist- ened mass is acted upon by the gastric juice, a fluid which oozes out from myriads of minute glands set into the inner surface of the organ. This is a chemical operation, and it is promoted by a constant motion which is kept up in the stomach, thus stirring up the food so that the gastric juice may be well mixed with it. After the proper chemical change is effected the nutritious part of the mass is ab- sorbed and poured into the blood, and becomes a part of it. 562. Albumen. The protein compounds, or albuminoids, are very nearly identical in composition, as you have al- ready learned, and they are convertible into each other. In the animal the various tissues or structures, as we have stated in 560, are made chiefly of fibrin. Exactly how fibrin is formed in the animal economy is an unsettled ques- tion. It was formerly supposed that albumen was trans- formed into fibrin, and that all other protein bodies were first converted into albumen in the stomach, but this lacks demonstration. Albumen is held in solution in the blood by means of chloride of sodium associated with it. It does not occur in the animal in the free state, jbut as an alkaline albuminate. It forms about seven per cent, of blood, and occurs in the brain, in the juice of the flesh, and in a greater or smaller quantity in all the liquids effused from the blood- vessels into different parts of the system. 398 CHEMISTRY. 563. Formation of the Bird in the Egg. In the formation of the bird in the egg we have a marked illustration of the prominent part which albumen plays in nutrition. Both the yolk and the white are composed chiefly of albumen dissolved in water. The white is seven eighths water, and only one eighth albumen. In the yolk we have the same solution of albumen holding yellow globules of oily matter suspended in it. There are in both the yolk and the white minute amounts of various mineral substances, as common salt, phosphate of lime, carbonate of soda, etc. These form the ash of the egg when it is burned. It is the albumen of the egg from which all the varied structures of the bird are formed the muscles, the skin, the feathers, etc. The oily matter of the yolk, it is true, is diffused in the inter- stices of many of the tissues, but it does not really form a part of them, unless it be in the case of the brain. The phosphate of lime also is deposited in the texture of the bones, but it is the albumen that first forms that texture. As we look at the white of an egg, so simple is it that we can hardly believe that such a variety of tissues can be evolved from it by the chemistry of life. And yet the ev- idence is clear that it is so ; for shut up in the shell noth- ing can gain admission to it but the oxygen of the air, which acts upon it through the pores of the shell, and thus materially aids in the process, as may be proved by the interruption of it by a coat of varnish shutting up the pores. 5G4. Gelatin. There is considerable doubt as to the nat- ure of this substance, which enters largely into the struct- ure of some portions of animals. It is supposed that it is formed from albumen and fibrin, as the gelatinous struct- ures are well developed in animals which are fed upon these substances alone. Its composition is nearly the same as theirs, although its properties are very different. It forms ANIMAL CHEMISTRY. 399 about one third of the substance of the bones, phosphate of lime being almost all of the remaining two thirds. It is the gelatin in the skin that tannin so firmly unites with, converting it into leather. What is commonly called glue is gelatin. This substance dissolves readily in water. The various jellies that we use prepared from animal substances are gelatin. The gelatin is first separated from them and dissolved by hot water, and then the solution on cooling leaves a jelly. Isinglass, so called, is chiefly gelatin pre- pared from the sounds or air-bladders of certain fresh-wa- ter fishes, particularly one of the sturgeon class found in the rivers of Russia, 565. Two Kinds of Food. All the varieties of food are divided into two classes according to the purpose which they serve, the one class serving to build up the tissues, and the other to maintain the animal heat. To the former class belong those substances that contain nitrogen, as the gluten of bread, the fibrin of meat, the casein of milk, etc. The other class comprises those substances that have no ni- trogen in them, as starch, sugar, and oily substances. These all serve to maintain the warmth of the body, and it is sup- posed have little or nothing to do with building its struct- ures. They are burned up, as we may express it, in creat- ing heat, which is just as essential to the maintenance of life as nutrition is. This food is called respiratory food, because it is supposed that the oxygen introduced by the respiration is employed in consuming or burning it. The products of this flameless combustion are the same with those of ordinary combustion with flame, water, and car- bonic anhydride. The heat-making food is often called carbonaceous from the predominance of carbon in it, while the building food is called nitrogenous because it is dis- tinguished from the other by containing nitrogen. While the view thus presented is generally true, there 400 CHEMISTRY. is ground for doubt whether the distinction can be as strictly carried out as is attempted by Liebig and others. The reasons for this doubt will be noticed soon. 566. Climate and Food. If the view above presented be substantially correct, climate must have a great influence upon the choice of food, the necessities of the case influ- encing that choice to a considerable extent through the instincts. Accordingly we find that oily and fatty food is largely used by the inhabitants of the arctic regions, from the great demand of the system for heat -making food amid the surrounding cold. And provision is made by the Creator for this want ; for the animals from which the Esquimaux, the Greenlanders, etc., obtain their chief nutriment as bears, seals, and whales are loaded with fat, while there is but little of this substance in those animals which furnish meat to the inhabitants of hot climates. 567. Warmth in Hibernation. It is observed that the woodchuck and other warm-blooded animals that are in a torpid state in the winter mouths are lean when they come out of this state in the' spring, though they were very fat when they went into it. This is because the fat is burned up during the winter in maintaining the warmth requisite for the continuance of life in this torpid state. So, also, in disease, the fat previously accumulated in the system is often used in the production of animal heat, the other sources being in part cut off by the impaired ability to ap- propriate food. 568. Corpulency. In this state of body there is an ac- cumulation to a larger degree than usual of fatty matters in all quarters of the system. This is supposed to arise from the fact that the heat-making food is provided in so great amount that the oxygen introduced into the system is far from being sufficient to burn it up. In this case the ANIMAL CHEMISTEY. 401 accumulation of fat does not corne from oily food alone, for starch and sugar can be converted into fat by the chem- istry of life. It is on account of this conversion that pota- toes increase the butter or fatty part of the milk in the cow. For the same reason the butter in milk is greater in amount in the morning milk than in that of the evening, when in cold weather the cow is kept in a warm stall through the night, there being more starchy and sugary matters converted into fat when there is less necessity for their consumption in the production of heat. For the same reason, also, in the fattening of animals in cold weath- er, the more comfortably they are housed the less food will it take to fatten them. 569. Heat in Carnivorous and Herbivorous Animals. It is obvious that carnivorous animals do not eat as much heat-making food as herbivorous animals do, while they eat more of building-food; and yet they have as much heat as the herbivorous animals, and do not have any greater development of structure. This seems to be in contradiction to the views presented of the purposes of food ; but the apparent discrepancy, for it is only apparent, can be easily explained. There are two sources of the fuel used in maintaining animal heat, viz., the food and the waste of the tissues of the body. Now the heat in carnivorous animals is derived almost wholly from the latter source, for they are so active in their habits that there is much greater wear and tear of the tissues than in herbivorous animals. You can realize this difference in activity if you observe the constant restlessness which lions, tigers, hyenas, etc., manifest in their cages in a menagerie. Herbivorous animals are so inactive that when they are left to their natural habits they can live on food which contains but very little nitrogenous substance, as common grass, potatoes, etc. But when they are worked by man, if they are not fed in part on some of the grains, they will lose flesh for want of building-food. But there is another difference between carnivorous and herbivorous animals, which accounts for the absence of that overheating that we might reasonably expect from such an amount of heat-food as is commonly eaten by herbivorous animals. They perspire freely, much more so than carnivorous animals, and a large part of the heat made by their food passes off therefore as latent heat in the vaporization of the perspired matter. 402 CHEMISTRY. 570. Relation of Food to Labor. This topic, incidentally touched upon in 569, merits a more particular notice. If a horse is not worked he will retain his good condition on such food as hay and potatoes. If oats or corn be added he will gain in flesh ; that is, the tissues will be more fully developed by this addition of plastic food, and at the same time the fat will be increased, as his heat-making food is not used up freely in pro- ducing heat. If now with this mixed diet he is put to work, he will retain from day to day his usual bulk both in respect to fat and muscular fibre. Laboring men require a larger proportion of nitrogenous food than those who are inactive. It is for this reason that when men live almost wholly on such articles as potatoes or rice or plantains there is the same failure both in bulk and power as in the working horse that is fed on hay alone. The Israelites could not have endured their journey if their manna had been like the article now called by that name. They needed food which was in part nitrogenous, and such was the manna miraculously furnished to them, as the change in it when it was kept for any length of time clearly showed ( 4G6). It is calculated by Liebig that the proportion of nitrog- enous to non-nitrogenous food most suitable to the wants of a laboring man is about as one to four. If he eat too much of the former, like the sav- age hunter who lives almost wholly on meat, there is deficiency of heat- making food, and he is obliged to eat a larger amount of nitrogenous food than is needed for nutrition, in order to get a sufficiency of that non-nitrog- enous food which is combined with it, unless he pursue, like carnivorous animals ( 569), so active a life that the waste of the tissues shall supply the requisite amount of fuel. The use of so large a quantity of animal food by no means proportionally develops the tissues, for it burdens the digest- ive and other organs with too much labor, and therefore produces disease in spite of the invigorating influences of an outdoor life. 571. Mingling of Heat -Pood and Building -Food. Gen- erally in articles which are eaten the two kinds of food are mingled together. Thus even in the lean part of meat there is always some fat in addition to that which is de- posited in masses in the neighborhood of the muscles ; and gluten and starch are mingled in the grains. That mixture of nitrogenous and non-nitrogenous food which we have in bread is so especially suited to man that this article of diet has from remote antiquity been styled " the staff of life." The instincts of men seem to lead them to mingle the two ANIMAL CHEMISTRY. 403 kinds of food together. Thus the Irishman eats with his potatoes buttermilk for the casein it contains, or cabbage, which is one of the vegetables that is rich in nitrogen. The Italian for the same reason adds cheese to his macaroni, and the wayfaring Spaniard eats with his bread an onion or two, this vegetable containing much nitrogen, like the cabbage of the Irishman.* So pork, which is only heat-food, is eaten with cabbage or beans, butter with bread, and oil with salad. Experiments which have been tried show decidedly that life can be sustained only on mixtures of food. Animals have been fed on various single substances extracted from articles of food, and the results have always been bad, even to the destruction of life. This is true of the nitrogenous constituents as well as the carbonaceous. The fibrin ex- tracted from meat is far from answering the same purpose as the meat itself. The juices of the meat are needed in combination with the fibrin to accomplish the full pur- poses of nutrition. It may be laid down as a general truth that no separated principles of food answer the same end as the mixtures which are produced in nature. The gluten of wheat does better than any other one thing, but this alone is by no means as good food as its mixture in the grain with starch and albumen. 572. Milk. It is worthy of remark here that milk, the only mixture of food which nature has provided as the sole means of nutrition for some animals the mammalia in their infancy, has the two kinds of food combined, the * The dish so common in Ireland called Kol-cannon is prepared by beat- ing potatoes and boiled cabbage together, putting in a little pork-fat, salt, and pepper. Johnston says of this, " Take a pot-bellied potato-eater and feed him on this dish, and he will become not only stronger and more act- ive, but he will cease to carry before him an advertisement of the kind of food he lives upon, and his stomach will fall to the dimensions of the same organ in other men." 404 CHEMISTEY. cheesy matter or casein being the nitrogenous part, and the oily matter or butter the non-nitrogenous part. And the proportions of the two, being as one of the former to four of the latter, furnish a clear indication of what they should be in food generally, making allowances, of course, for varying circumstances. Milk must contain, besides the casein and the oily matter, all the other materials required in both the solids and fluids of the body, else there would be some defect in the nutrition of an animal that lives en- tirely upon milk. We have therefore in this liquid iron for the blood, salt for this and various other fluids in the body, phosphate and carbonate of lime for the bones, etc. The milk, though of a white color, contains in fact all the elements that are present in the red blood of the animal, and in the same proportions, with the exception of that portion of the oxygen which is added to the blood in the lungs. A great error is often committed in confining a child too exclusively to starchy articles of food, such as arrow-root, thus depriving it not only of the albuminous substances, but also of the iron, the phosphate of lime, etc., which are all contained in the complex food furnished it by nature. 573. Proportions of Heat-Food and Building-Food in Dif- ferent Articles. In the following articles to every 10 parts of nitrogenous substance there are the parts named of non- nitrogenous substance: Cow's milk, 30; pease, 23; beef, 17; veal, 1; eggs, 15; wheat flour, 46; oatmeal, 50; rye flour, 57; potatoes, 86; rice, 123; buckwheat flour, 130. There are some variations according to circumstances, but these are the average proportions. The percentage of nitrogenous and non-nitrogenous substance, in three forms of food used largely in three different quarters of the world, may be thus stated : ANIMAL CHEMISTBY. 405 Rice. Potato. Plantain. Gluten 7^ 8 5| Starch,etc 92^ _92 94| 100 100 100~ The percentage is reckoned here upon the dry food, that is, the substance freed from the water which is naturally in it. The albuminous material in cabbage is much great- er than in these articles, being from 30 to 35 per cent., and in cauliflower it is still greater. In the onion it is from 25 to 30 per cent. In tea-leaves it is 25 per cent., so that if they were eaten they would prove good building-food. Figs as imported, that is, partially dried, are thus com- pared with wheat bread : Figs. Wheat bread. Waters 21 48 Gluten 6 5| Starch, sugar, etc 73 46J 100 100. Figs, therefore, have less water than the bread, a little more gluten, and 27 per cent, more of starch and sugar. There is a larger proportion of gluten in the covering or husk of the wheat than in the grain itself, and therefore the separation of the bran from the flour by bolting im- pairs the nutritive power of the bread, that is, so far as the building of structure is concerned. 574. Is the Division of Food into Two Kinds Correct? The classification of food given in 565, which is that of Liebig, though generally received, is considered by some as without foundation. One of the chief objections to it is that the large proportion of heat-food which is used in warm climates in the form of starch, in such articles as rice and the plantain, is in opposition to it. But the objector forgets that man is always throwing off heat freely into the air even in hot climates ; for when in such climates the atmosphere is at a higher degree of temperature than 36.6 C., the animal heat passes off in the abundant perspiration, both sen- sible and insensible. If it were not for this, disastrous consequences would result from exposure to excessive heat, either in a hot climate or in the 406 CHEMISTEY. heated apartments in which some manufactures are carried on. There are other objections to Liebig's classification, but we will not dwell on them. The division is probably in the main correct, and yet there are some facts that seem to show that plastic food is sometimes used for the production of heat, and that fuel -food is sometimes used for build- ing. If so, it is an exception to a general rule, and indicates that the chemistiy of life is not bound by such strict lines as is inorganic chem- istry. 575. Amount of Animal Heat. At first thought it seems strange that so much of the food, ordinarily four fifths, should be expended as fuel in producing heat, because we are in the habit of thinking of food as doing good only in building up and repairing the system. This is the com- mon popular view of nourishment, and it is only the in- vestigations of the chemical physiologist that make us realize of what importance heat is in the maintenance of living action. It is calculated that the amount of heat produced in the body of an adult man in one year would suffice to raise from twenty to twenty-five thousand pounds of water from the freezing to the boiling point. The heat, then, required to run the animal machine, as we may ex- press it, is very great, and therefore there must be a large provision of fuel. 576. Uses of Pat in the System. There is one form of heat-food fatty matter which is used quite extensively in building up the structures of the system, though in the wear and tear of these structures it may eventually serve as fuel. But it is Liebig's idea that the fat which is so largely present in many tissues is not really a part of them, but is contained in them very much as water is contained in the interstices of a sponge. The combination, however, is certainly more intimate than this; perhaps it may be considered like that of phosphate of lime with gelatin in bone. And in the case of the brain there seerns to be even a chemical combination of fatty matter with phosphoric ANIMAL CHEMISTRY. 407 acid. More than one fifth of the solid matter of the brain is fat, and this substance constitutes more than a sixth part of the solid matter of muscle. It is present in con- siderable quantity, also, in other structures. It must, then, have other uses besides heat-making. Besides its useful- ness in the textures of organs, it is of some local benefit as deposited in masses. Thus the eyeball rests in its socket upon a cushion of fat. 577. Phosphorus and Sulphur. Phosphorus does not ex- ist as such in animals, but is in combination with soda and lime. The phosphate of lime is present in large quantity in the bones. In the body of an adult man there is in the bones from 2 to 3 kilogrammes of this salt, and the phos- phorus in it amounts to from 500 to 800 grammes. Phos- phorus forms one of the most important constituents of cer- tain complex fatty bodies in the brain. It is extensively provided for animals in their articles of food, mostly in the form of phosphate of lime. Phosphorus exists in eggs, and in all animal food. It is one of the components of milk, the universal and sole food of the mammalia in their infancy. It is also present in many seeds. So abundant is it in oats that the horse is liable to an earthy concretion in the bowels, of which phosphorus is a chief ingredient. Sulphur also occurs in combination in animals, chiefly in the albuminous or protein substances, and in some of the tissues. It comes from both animal and vegetable sources. Like phosphorus, it exists in flesh, eggs, and milk. It is also in the nitrogenous compounds of plants, gluten, albumen, and casein ; and, combined with lime in the form of a sul- phate, it is in most of the water that we drink. 578. Lime. This is one of the most widely diffused min- eral substances both in the animal and vegetable kingdoms. It exists largely in the seeds of most grasses, especially in the grains of wheat. Beans and pease have more nitroge- 408 CHEMISTRY. nous matter than wheat, and therefore would be more nutri- tious were they not deficient in a salt of lime, the phosphate. There is considerable lime supplied to plants and animals from water in the forms of the carbonate and the sulphate, these salts being present in all hard water. The thickness of the shells of aquatic mollusks depends very much upon the amount of carbonate of lime in the water. Those which live in the sea have as much as they need, and their shells have considerable thickness ; but those which are found in fresh-water lakes, where there is but little lime, have thin shells. There are some lakes, however, where, from local causes, the water is greatly impregnated with calcareous matter, and the mollusks that inhabit them have shells of uncommon thickness. Hens require more lime than usual when they are laying eggs, and they therefore instinctive- ly at such times eat chalk, mortar, or any substance they can find which contains carbonate of lime. If they are shut up where they can not obtain this they lay eggs without shells, and if they obtain it sparingly the shells are thin. 579. Iron. This metal is absolutely essential to the blood, and is present in all the pigments of the body, in the bile, and in various tissues, especially the hair. The quantity of iron in the blood is very small, it being only about the one four-hundredth part of its solid matter. It varies in different persons, being greater in the sanguineous than the lymphatic, in the well-fed than those who live on a poor diet. It is found more or less in most articles of food. It is in the yolk of eggs and in milk, as well as in animal flesh. It is present in most of the vegetable substances used as food by man, such as potatoes, cabbage, pease, mustard, etc. We have said that iron is essential to the blood. It is there not so much to be supplied to the tissues as to execute certain offices in the blood itself. ANIMAL CHEMISTRY. 409 These offices we will indicate so fur as they are ascer- tained. The blood, examined by the microscope, is seen to consist of two parts, an almost colorless liquid called liquor sanguinis, or liquor of the blood, and floating in this are multitudes of rounded particles called globules of the blood, or blood-disks. These are little sacs or vesicles con- taining a fluid, and the iron forms one of the constituents of certain crystalline principles suspended in this fluid. These globules convey the oxygen received in the lungs to all parts of the body, and the liquor sanguinis probably brings back to the lungs the carbonic acid which is to be discharged there. The crystalline bodies containing iron act as common carriers for oxygen. When iron is deficient in the blood some form of iron medicine is administered by the physician. 580. Salt. The amount of salt in the blood is about three times that of iron. Though it is nowhere present as a part of any tissue, it is of much service in the formative processes, both as salt and by its elements, it being to some extent decomposed in the body. There is no salt found in the juices of muscles, but one of its elements, chlorine, is found there combined with potassium, and this element is undoubtedly derived from the salt in the blood. In the bile of land animals there is soda, derived from the same source. Then there is hydrochloric acid, an efficient part of the gastric juice in the process of digestion, which is furnished in some way from the decomposition of salt. We use salt instinctively with our food with some articles, as potatoes, more than with others. As it is not as abundant in plants as it is in animal food, considerable pains are taken to supply our domestic herbivorous animals with a suf- ficiency of this important article of diet. And, to meet the instinctive desire of the wild animals for it, there are places where it exists in the soil, to which they can resort for it. S 410 CHEMISTRY. Such are the " buffalo-licks " of this country. The results of some experiments which have been tried with cattle in relation to salt as an article of food are interesting and instructive. The salt had no influence on the flesh or on the amount of milk obtained ; but the set which had salt mixed with their fodder had a much better coat, and were much more lively than the set from which salt was with- held. 581. Water. This is the largest ingredient in animal bodies. It constitutes nearly 80 per cent, of the blood, and the same of the brain, and nearly 75 per cent, of the muscles. The body of a human being is about three fourths water. One great use of this abundant substance in the animal is to furnish a proper vehicle for the solid substances in their circulation. The materials for growth are carried every where in it, and the worn-out particles are conveyed to their natural outlets. It also serves various purposes in the tis- sues, giving transparency to some, as the cornea, the beau- tiful clear front-covering of the eye, and giving to the mus- cles and the membranes their softness, flexibility, and elas- ticity. Water is in these respects as essential to life as any other substance. Being thus needed in the animal, it is largely present in all the vegetable substances which are used as food ; and as in vegetables it furnishes in its decomposition its elements for the formation of the com- pounds which they contain, so it may do to some extent in animals. 582. Endosmose and Exosmose. In connection with water, it is proper to notice an agency which has a wide influence on the circulation of matter, both in vegetable and animal substances. This agency is exhib- ited in the following experiment: B C (Fig. 119, p. 411) is a glass tube expanded at its lower end, which has a piece of moist membrane, as fresh bladder, tied over it. If we pour some water into the vessel, and also so much into the tube as will make it at the same level with that in the vessel, there will be no change in the levels, however long the apparatus mny be left ANIMAL CHEMISTRY. 411 Fig. 119. to stand. But if we add salt to the water in the tube, the solution thus made will in a few minutes rise in the tube, while the water in the vessel will fall. This is because some of the water, attracted by the solution of salt, passes through the pores of the bladder. The salt has given the water in the tube something like a power of suction. We can vary this experiment in several ways. If the salt be put into the vessel, the contrary effect will be produced the water in the tube will fall below the level of the fluid in the vessel. If salt be put into both ves- sel and tube in equal proportions, no change will follow ; but if in unequal proportions, the suction will be toward the strongest solution. Suppose now that instead of salt you put a solution of gum or sugar into the tube, holding it so that the level shall be the same with that of the water in the vessel. Here the fluid in the tube will rise, because the water from without presses in through the bladder. This passing inward is called by Dutrochet, who first developed this subject, endosmose, from two Greek words endon, inward, and osmos, impulsion, or pressure. But some of the gum or sugar is found, after a time, in the water outside. There is, therefore, also a transmission from within outward, though less than that from without inward, and this he called exosmose, ex meaning from or outward. The membrane used in such experiments is called the septum. Similar phenomena are seen with other substances ; as, for example, albumen, a substance which is largely present in animals. You can readily see, then, that the agency which we have described must have a very wide influence on the circulation of fluids in both the animal and vegetable world, for salt, gum, sugar, albumen, etc., are common substances in these fluids, and there are soft and porous mem- branes every where ready for this endosmotic and exosmotic action. And we may remark, in passing, that the influence of this agency is very consid- erable, also, in the mineral world, for gases as well as liquids are affected by it, and it may act through almost any porous substance. 583. Circulation of Matter. You have seen in this book that in the ministration of nature to the wants of man and other animals there is a constant circulation and inter- change of matter between the three kingdoms of nature. First there is a circulation in the strict sense of that word, for there is a movement in a circle. As the vegetable re- 412 CHEMISTRY. ceives its materials from the mineral world, and the ani- mal from the vegetable, there is a continual return in de- cay from the animal to the mineral world. Death is thus constantly ministering to life, and life to death ; and life may be considered as being maintained by a constant suc- cession of resurrections, not a particle of matter being lost in all the changes that take place, even in those where there is apparent destruction. As that which is made of dust returns to dust, a new life rises up out of that dust, exhib- iting a reality more wonderful than that of the fabled Phoenix which shadows it forth. But there is interchange as well as circulation. The animal kingdom does not re- ceive all its material through the vegetable, but some of it comes directly from the mineral kingdom. And then the vegetable, standing as it does between the animal and mineral kingdoms, receives from both, and gives to them in return. It yields back to the mineral world in decay what it receives from it ; and while it receives from the lungs of animals carbonic acid, it gives back to them the oxygen which they need every moment for the maintenance of life. It is thus that the earth, with all its stability, has vast changes going on continually and every where upon its surface, in which air and water and heat and light and electricity and chemical and vital agencies are ever busy ; and yet, extensive as these changes are, and accompanied with disturbance, conflict, and decay, the Creator, who seeth the end from the beginning, preserves amid it all a wonderful balancing and harmony, so that from age to age we see the impress which he put upon creation at the first, and bear witness that it is all " very good." ANIMAL CHEMISTRY. 413 QUESTIONS. 557. What is said of the elements which come into play in animal chem- istry ? Give examples of the combinations of elements that are introduced into animals. 558. Indicate some of the points in which animal and veg- etable chemistry are alike. 559. Indicate some in which they differ. SCO. Give in full- what is said of the composition of the blood. 561. De- scribe in full the way in which the blood is made. 562. What is said of the occurrence of albumen in animals ? 563. What are the constituents of the contents of an egg ? What is said of the formation of the bird in the egg ? 564. What of gelatin ? 565. Into what two classes are the various kinds of food divided? State what is said of the heat -making class. 566. What relation has climate to food? 567. How is the warmth of some hibernating animals maintained in their torpid state ? What is said of the fat of the body in disease ? 568. What of corpulency ? What of the butter in milk ? What of fattening animals ? 569. What apparent discrepancy is there in regard to the food and the animal heat of carnivo- rous and herbivorous animals ? State in full what is said to clear up this discrepancy. 570. What is said of the relation of food to labor? What is said of the manna of the Israelites ? What of the proportion of nitrog- enous to heat-making food ? What of the use of an excess of animal food ? 571. What of the mingling of the two kinds of food ? What is said of feeding animals on some single substance alone ? 572. What of the com- bination in milk? What error is frequently committed in the diet of chil- dren ? 573. State in full what is said of the proportions of the two classes of food in different articles. 574. What is said of the chief objection to Liebig's classification? 575. What is said of the amount of animal heat? 576. What of the uses of fat in the system ? 577. What is said of phos- phorus in animals and in their food? What of sulphur? 578. What of the diffusion of lime in nature ? What is said of the thickness of the shells of mollusks ? What of the shells of hens' eggs ? 579. What of the pres- ence of iron in animals? W T hat of its presence in food? What of its of- fices in the blood ? 580. What is said of the presence of salt in animals ? What of its use as an accompaniment of food? 581. State in full what is said of water as an ingredient of animal and vegetable substances ? 582. Explain in full endosmose and exosmose. 583. Give in full what is said of the circulation of matter ? Also what is said of its interchange. And what is said of the harmony of creation in the midst'-of all its change. APPENDIX. METRIC SYSTEM OF WEIGHTS AXD MEASURES. (FROM: MILLER'S "INORGANIC CHEMISTRY.") THE weights and measures used in this work are those of the metric system, which, on account of their simplicity and convenience, are now commonly employed by men of science throughout the world. The unit of length in this system is the meter, which is equal to 3.937 English inches. From this integer all meas- ures of surface capacity and weight are derived. The sub- divisions of the meter are marked by the Latin prefixes deci, ten, centi, a hundred, and mitti, a thousand ; so that the tenth of a meter is called a decimeter, the hundredth of a meter a centimeter, and the thousandth of a meter a mil- limeter. The higher multiples are indicated by the Greek prefixes deca, ten, hecto, one hundred, kilo, one thousand ; but the prefix kilo, or multiple by one thousand, is almost the only one used in practice. For instance, the higher multiple, or 1000 meters, is called a kilometer. It is used as a measure of distance by road, and represents about 1094 yards, 16 kilometers being equal to nearly 10 English miles. 416 METEIC SYSTEM OF WEIGHTS AND MEASURES. Each side of this square measures 1 Decimeter, or 10 Centimeters, or 100 Millimeters, or 3.937 English inches. A liter is a cubic measure of 1 decimeter in the side, or a cube each side of which has the dimensions of this figure. When full of water at 4 C. a liter weighs exactly 1 kilogramme, or 1000 grammes, and is equivalent to 1000 cubic centimeters, or to 61.024 cubic inches, English. A gramme is the weight of a centimeter cube of distilled water ; at 4 C. it weighs 15.432 grains. 100. Centim- eter. -1 -5 -in - 4 inches. The measures of capacity are connected with those of length by making the unit of capacity in this series a cube of one decimeter, or 3.937 English inches, in the side; this, which is termed a liter, is equal to 1.7637 imperial pints, or to 61.024 cubic inches. Finally, the system of weights is connected with both the preceding systems by taking as its unit the weight of a cubic centimeter of distilled water at 4 C.: it weighs 15.432 English grains. The gramme^ as this quantity is called, is APPENDIX. 417 further subdivided into tenths or decigrammes, hundredths or centigrammes, and thousandths or milligrammes, the mil- ligramme being equal to about ^ of a grain. The higher multiple of 1000 grammes constitutes the kilogramme. It is the commercial unit of weight, and represents 15,432 English grains, or rather less than 2^ Ibs. avoirdupois. The weight of 1000 kilogrammes, or a cubic meter, of water, is 0.9842 of a ton, which is sufficiently near to a ton weight to allow of its being reckoned as one ton in rough calculations. Various plans have been devised for converting the French weights and measures into their English equiva- lents. The following tables will be found useful for this purpose : MEASURES OF LENGTH. Millimeter English inches. = .03937 DccaniGtcr. ... English inches. = 393.70790 Centimeter .... = .39371 Hectometer. . . = 3,937.07900 Decimeter = 3.93708 Kilometer .... = 39,370.79000 Meter . . . - 39.37079 Mvriameter. . . = 393,707.90000 MEASURES OF VOLUME. Milliliter, or 1 cubic centimeter Centiliter, or 10 cubic centimeters Deciliter, or 100 cubic centimeters Liter, or 1 cubic decimeter, or 1000 cubic centimeters. Decaliter Hectoliter Kiloliter Myrialiter Milligramme Centigramme Decigramme = 1.54323 Gramme... . = 15.43235 MEASURES OF WEIGHT. English grains. = .01543 = .15432 Decagramme.. Hectogramme. Kilogramme . . Myriagramme. Cubic inches. .06103 .61027 6.10271 61.02705 610.27052 6,102.70515 61,027.05152 010,270.51519 English grains. 154.32349 1,543.23488 15,432.34880 154,323.4880 S2 418 METEIC SYSTEM OF WEIGHTS AND MEASUEES. The temperatures given in this book are expressed throughout in degrees of the Centigrade thermometer, un- less otherwise specified. The following is a short compara- tive table of the two scales, Centigrade and Fahrenheit. c. F. C. F. C. F. C. F. 20 -4 15 59 45 113 75 107 J5 +5 20 68 50 122 80 176 -10 14 25 77 55 131 85 185 5 23 30 86 60 140 90 194 32 35 95 65 149 95 203 5 41 40 104 70 158 100 212 10 50 The formula for converting degrees on Fahrenheit's scale to corresponding degrees on the Centigrade scale is (F. 32) = C.; and for converting Centigrade to Fah- renheit, | C. +32 = F.. For further data with regard to thermometer scales, see Part L INDEX. [The numbers refer to the sections.] A. Absorbent power of charcoal, 96. Acetates, 508. Acetous fermentation, 552. Acetous fermentation explained, 554. Acid, boracic, 269. Acid, carbonic (foot-note on page 84), 102, 110. Acid, hydrochloric, 222. Acid, hydrochloric, preparation of, 224. Acid, hydrocyanic, 166. Acid, muriatic, 222. Acid, nitric, 71. Acid, phosphoric, 257. Acid, picric, 440. Acid, prussic, 166. Acid, pyroligneous, 436. Acid salts, 80. Acid, stearic, 514. Acid, sulphuric, fuming, 241. Acid, sulphuric, manufacture of, 242. Acid, sulphuric, Nordhausen, 241. Acid, sulphuric, properties of, 244. Acid, sulphuric, uses of, 247. Acid, tannic, 509. Acidity of wines, 541. Acids, nomenclature of, 79. Acids, organic, 508. Acids, organic, how derived, 424. Acids, tests for, 78. Actinism, 393. Adhesion, 37. Affinity, bonds of, 44. Affinity, chemical, 38. Affinity, Providence seen in, 39. Air, a mixture proved, 139. Air, analysis of, 118. Air and nitric oxide contrasted, 85. Air, composition of, 45. Air, impurities in the, 138. Air in water, composition of, 134. Air, water in the, 137. Albumen, 562. Albumen, vegetable, 468. Albuminoids, 470. Alcohol, amount of, in wines, 542. Alcohol, amylic, 545. Alcohol made from starchy substan- ces, 543. Alcohol, methylic, 437. Alcoholic fermentation, 537. Alcohols, how derived, 422. Alkaline earths, 310. Alkaloids related to amines, 425. Alkaloids, vegetable, 531. Allotropism, 65, 101. Alloys, nature of, 279. Alum, common, 327. Alumina, 326. Aluminium, 325. Amalgamation, 377. Amalgams, 278. Amber, 527. Amines defined, 425. Ammonia in guanos, 501. Ammonia in rain-water, 477. 420 INDEX. Ammonia, preparation of, 162. Ammonia, production of, 160. Ammonium salts, 307. Ammonium, the metal, 306. Amorphous sulphur, 235. Amylic alcohol, 545. Analysis, 16. Analysis, organic, described, 427. Animal and vegetable structures compared, 410. Animal heat, 197. Animal heat, amount of, 575. Animal heat, exercise and, 203. Animal substances, carbon in, 94. Animals and vegetables compared, 558. Animals, carnivorous and herbivo- rous, 569. Animals, cold-blooded, 204. Animals, influence of light on, 392. Animals, materials used in structure of, 557. Animals, subservience of plants to, 409. Anthracite, 439. Antimony, 362. Antiseptics, 535. Aqua regia, 225. Arbor Dianas, 380. Arsenetted hydrogen, 360. Arsenic, 356. Arsenic, antidotes to, 357. Arsenic, antiseptic properties of, 358. Arsenic-eating, 359. Arsenical pigments, 361. Artiads, 44. Asphaltum, 441. Assay of silver, 381. Atmosphere, carbonic anhydride in the, 116. Atmosphere, ingredients of the, 115. Atmosphere, nitric acid in the, 77. Atmosphere, nitrogen in the, 117. Atmosphere, sources of carbonic an- hydride in the, 127. Atomicity, table of, 44. Atomic philosophy, 20. Atoms, 22. Atoms, properties of, 25. Atoms, weight of, 26. Attraction, chemical, 37. Attraction, chemical, action of heat on, 41. Attraction, chemical, modifiers of, 40. B. Ballooning, 147. Barium, 308. Barytes, 308. Bases and salts, 80. Benzol, 440. Bessemer process for steel, 344. Bismuth, 364. Bismuth nitrate, 365. Bituminous coal, distilled, 440. Black ash, 301. Blast-furnace, 340. Bleaching, 196, 216. Bleaching powder, 322. Blood, 560. Blood disks, 579. Blood, how made, 561. Blowpipe, use of, 182. Blowpipe, oxy hydrogen, -188. Blue vitriol, 366. Body, temperature of the, 199. Bonds of affinity, 44. Bone-black, 93. Bone-dust, 502. Boracic acid, 269. Borax, 304. Boron, 269. Bread, raising of, 546. Bread, sour, 553. Britannia ware, 278. Bromine, 231. Bronze, 278. Brunswick green, 361 . Bunsen and Kirchhoff, 402. Bun sen's burner, 181. INDEX. 421 Burner, Argand, 180. Burner, Bunsen's, 181. Butter of zinc, see Zinc chloride, 333. C. Cadmium, 281. Caffeine, 531. Calamine,331. Calcium, 310. Calcium carbonate, 315. Calcium, phosphate of, 324. Calcium, phosphide of, 256. Calcium, sulphate of, 319. Calculations, mathematical, 3G. Calico-printing, 534. Calomel, 376. Camphor, 526. Candle, chemistry of a, 171. Candle, experiments with a, 173. Candle, extinguishing a, 184. Candles made from stearin, 516. Cane-sugar, 458. Caoutchouc, 529. Carat, 382. Carbon, 89. Carbon, abundance of, 89. Carbon, sources of, in plants, 474. Carbonate of lead, 371. Carbonic anhydride, 102. Carbonic anhydride, absorption of, 109. Carbonic anhydride and combustion, 106. Carbonic anhydride and digestion, 108. Carbonic anhydride and respiration, 107. Carbonic anhydride, preparation of, 103. Carbonic anhydride, properties of, 104. Carbonic anhydride, solidification of, 105. Carbonic oxide, 112. Carbonic oxide, preparation of, 113. Carburetted hydrogen, 154. asein, vegetable, 469. ast iron, 341. Casts of coins, 320. atalysis, 43. Caustic potash, 286. Cavendish, 147, 479. elestial spectroscopy, 405. Cellulose, 430. Centigrade thermometer compared with Fahrenheit, see Appendix, p. 418. Chalk, 316. Champagne, 539. Charcoal, absorbent power of, 96. Charcoal burned in oxygen, 57. Charcoal, fumes of, 124. Charcoal, manufacture of, 90. Charcoal, properties of, 95. Chemical action, characteristics of, 15. Chemical action, nature of, 10. Chemical action, variety of, 12. Chemical affinity, 38. Chemical attraction, modifiers of, 40. Chemical combination, laws of, 32. Chemistry and Physics, difference between, 23. Chloride of lime, composition of, 323. Chloride of sodium, 296. Chlorine, 208. Chlorine a disinfectant, 220. Chlorine and respiration, 212. Chlorine, attraction of, for hydrogen, 215. Chlorine bleaching, 216. Chlorine, combustion in, 221. Chlorine, occurrence of, 209. Chlorine, oxides of, 226. Chlorine, preparation of, 210, 211. Chlorine water, 213. Chloroform, 550. Chlorophyll, 447. Chromium, 352. Chrome yellow, 352. 422 INDEX. Cinnabar, 374. Clay, constituents of, 259. Clays, ingredients of, 326. Climate and food, 566. Coal, 98. Coal, combustion of, 177. Coals, varieties of, 439. Cobalt, 348. Cohesion, 37. Collodion, 433. Coloring matters, 532. Combustion by nitric acid, 76. Combustion, chemistry of, 169. Combustion, early ideas of, 168. Combustion, general remarks on, 167. Combustion in chlorine, 221. Combustion, means of hastening, 180. Combustion of hydrogen, 170. Combustion, requisites for, 194. Combustion, results of, 179. Combustion, spontaneous, 192, 521. Combustion without oxygen, 193. Compound ethers (page 388), 548. Compounds and mixtures, difference between, 157. Compounds, chemical, composition of, 27. Compounds, naming of, 18. Copper, 366. Copper, nitrate of, 73. Copper, sulphate of, 367. Copper, test for, 368. Coral, 315. Corpulency, 568. Courtois, M., 228. Cream of tartar, 508. Creosote, 436. Crops, rotation in, 494. "Cry "of tin, 353. Cyanogen, 164. Cyanogen, preparation of, 165. D. Daguerre, 389. Davy, Sir Humphrey, 4, 154. Definite proportions, law of, 27. Deliquescence, 159. Dephlogisticated air, 48. Deville,M.,325. Dextrin, 454. Dextrin from starch, 455. Diamond, 100. Diastase, 472. Diffusion of gases, 120. Dimorphism, 234. Displacement, 104. Dissociation, 43. Distillation of liquors, 544. Dobereiner's lamp, 385. Drummond light, 189. Dyads, 44. Dynamite, 515. Eau de Cologne, 524. Efflorescence, 159. Egg, formation of the bird in the, 563. Electrolysis, 141. Element, definition of, 2. Elements, ancient view of, 3. Elements as found in nature, 6. Elements, atomicity of, 44. Elements, atomic weights of, 4, 26. Elements, classification of, 5. Elements, forms of, 5. Elements in organized bodies, sources of, 408. Elements, principal, 4. Elements, table of, 4. Emerald, 330. Emery, 326. Endosmose, 582. Epsom salt, 329. Equations explained, 33, 35. Etching on glass, 232. Ether, preparation of, 549. Ether, properties of, 547. Ethers, compound (page 388), 548. Ethers, how derived, 423. INDEX. 423 Ethylamine, 425. Ethylene, 419. Eudiometer, 144. Exosraose, 582. Explosions of oxygen and hydrogen, 190. F. Fahrenheit scale compared with the Centigrade, see Appendix, p. 418. Fat, uses of, in the system, 576. Fats, combustion of, 522. Fats, properties of, 519. Fatty acid series (see table on page 303), 508. Fermentation, acetous, 552. Fermentation, alcoholic, 537. Fermentation, varieties of, 535. Ferments, 536. Ferric hydrate, 338. Fertilizers, 496. Fibrin, vegetable, 467. Fire extinguishers, 187. Fire under water, 186. Fires, bad management at, 183. Fires, extinguishing, 185. Fishes and water-plants, 136. Flame, nature of, 176. Flame shown to be hollow, 173. Flame, structure of candle's, 172. Flames, oxidizing and deoxidizing, 174. Flints, liquor of, see Soluble glass. Fluorine, 232. Food and labor, 570. Food, classification of, by Liebig, 565. Food, heat, and building, 571. Food, two kinds of, 565. Fool's gold, 346. Forces, physical and chemical, 37. Forms of substances, how affected by heat, 9. Formula explained, 29. Formulae, graphic, 417. Franklin, anecdote of, 505. Fuel, sources of, in animals, 200. Fumes of burning charcoal, 124. Fuming sulphuric acid, 241. Fusel-oil, 545. Fusible metal, 279. G. Galena, extraction of silver from, 379. Galvanized iron, 334. Gas, illuminating, 154. Gas, manufacture of, 178. Gases and gravitation, 119. Gases and vapors, difference between, 50. Gases, diffusion of, 1 20. Gelatin, 564. Glass, annealing of, 264. Glass, coloring of, 263. Glass, etching on, 232. Glass, general remarks on, 262. Glass, soluble, 266. Glauber's salt, 303. Glazing, 268. Gluten, 467. Glycerin, 575. Glyceryl, 514. Gold, 382. Gold chloride, 383. Goodyear, anecdote of, 530. Gramme, value of, see Appendix, p. 415. Grape-sugar, 460. Graphite, 99. Grass-bleaching compared with chlo- rine-bleaching, 218. Grass-bleaching explained, 196. Green fire, 308. Grotto del Cane, 122. Guano, 499. Guano, tests of, 500. Gums, 453. Gun-cotton, 433. Gunpowder, 292. 424 INDEX. Gunpowder, explosion of, explained, 293. Gutta-percha, 529. Gypsum, 319. Gypsum in agriculture, 505. II. Hard soap, 518. Hare's blowpipe, 188. Harmonica chemica, 151. Hatcheling, 431. Heat, relations of, to forms of sub- stances, 9. Hematite, 338. Hibernation, 205. Hibernation, warmth in, 567. Homologues and isologues, 420. Honey, 465. Humus, 490. Hydrates, 80. Hydrocarbons, ethylene series of, 419. Hydrocarbons in petroleum, 443. Hydrocarbons of illuminating gas, 154. Hydrochloric acid, production of, 223. Hydrogen and respiration, 152. Hydrogen, arsenetted, 360. Hydrogen, combustibility of, 148. Hydrogen compared with carbonic anhydride, 146. Hydrogen, metallic nature of, 156. Hydrogen not a supporter of com- bustion, 150. Hydrogen peroxide, 155. Hydrogen, phosphoretted, 255. Hydrogen, preparation of, by iron and steam, 142. Hydrogen, preparation of, by zinc and sulphuric acid, 143. Hydrogen, sounds in, 153. Hydrogen, specific gravity of, 145. Hydrogen, sulphuretted, 248. Hydroxyl, 421. India rubber, 529. Indigo, 532. Ink, sympathetic, 349. Ink, writing, how made, 512. Instability of organic bodies, 413. Iodine a supporter of combustion, 230. Iodine, preparation of, 229. Iodine, production of, 228. Iridium, 387. Iron, abundance of, 337. Iron, galvanized, 334. Iron in the animal kingdom, 579. Iron, oxides of, 338. Iron, production of, from ores, 340. Iron, pure, 336. Iron, sulphides of, 346. Isologues and homologues, 420. Isomerism defined, 415. Isomerism explained, 416. Isomorphism, 328. K. Kelp, 228. Kerosene, unsafe, 445. Kirchhoff, 402. Kol-cannon, foot-note on p. 403. L. Lagoons of Tuscany, 269. Lakes, 327. Lamp, Dobereiner's, 385. Lampblack, 92. Lana philosophica, 331. Laughing-gas, 81. Lavoisier, 17, 48. Laws of chemical combination, 27, 30, 31. Lead, 369. Lead acetate, 373. Lead, oxides of, 370. Lead-pencils, 99. Lead-poisoning, 372. INDEX. 425 Lead-tree, 373. Leaves, chemistry of, 128, 130. Liebig's classification of food, 574. Light and locomotives, 391. Light, chemical influence of, 388. Light dissected, 393. Light, Drummond, 189. Light-pictures, 395. Lignite, 439. Lime, carbonate of, 315. Lime, chloride of, 322. Lime in the animal kingdom, 578. Lime-kiln, 311. Lime, phosphate of, 253. Lime, solubility of, 313. Limestone, 315. Lime-water, 125. Linen and cotton, 431. Liquor sanguinis, 579. Liter, value of, see Appendix, p. 415. Litharge, 370. Lunar caustic, 380. Lungs, carbonic anhydride from the, 125. Lungs not the body's furnace, 198. M. Madder, 532. Magnesia alba, 329. Magnesium, 329. Manganese, oxides of, 335. Manna, 46G. Manures, 495. Manures, animal, 498. Manures, volatile bodies in, 497. Manuring, green, 480. Marl, 493, 504. Marsh gas, 154. Marsh gas series, 420. Massicot, 370. Matches, manufacture of, 252. Mathematical calculations, 36. Matter, circulation of, in the three kingdoms, 583. Matter, constitution of, 19. Matter, expansion of, explained, 21. Matter, forms of, 11. Mercuric chloride, 376. Mercury, 374. Metal, fusible, 279. Metals, action of chlorine on, 214. Metals, action of nitric acid on, 73. Metals, atomicity of, 281. Metals, characteristics of, 270. Metals, classification of, 281. Metals, color of, 272. Metals, density of, 271. Metals, ductility of, 275. Metals, fusibility of, 276. Metals, malleability of, 274. Metals, specific gravity of, 271. Metals, tenacity of, 273. Metals, welding of, 277. Metamerism, 415. Meteorites, 339. Meter, value of, see Appendix, p. 415. Methylic alcohol, 437. Milk, 572. Milk-sugar, 459. Minerals, peculiarity of, 8. Minium, 370. Moire' metallique, 353. Molecular weights, law of, 30. Molecules, 20. Molecules and state of aggregation, 21. Molecules, compound and simple, 24. Mordants, 327, 533. Mordants, colors modified by, 534. Morphine, 531. Mortar, 314. Mother of vinegar, 552. Multiple proportions, law of, 31. Musical sounds of burning hydrogen, 151. N. Nascent state, 42. Nascent state illustrated by forma- tion of ammonia, 1G1. 426 INDEX. Neutral salts, 80. New elements, discovery of, 403. Nickel, 350. Nicotine, 531. Nihil album, 331. Nitrates, 75. Nitre, 291. Nitric acid, preparation of, 71. Nitric acid, properties of, 72. Nitric anhydride, 70. Nitric oxide, 83. Nitric peroxide, 88. Nitrogen, abundance of, G6. Nitrogen, chloride of, 227. Nitrogen in respiration, 68. Nitrogen in the air, 132. Nitrogen, oxides of, 69. Nitrogen, preparation of, 66. Nitrogen, properties of, 67. Nitrogen, sources of, in plants, 477. Nitroglycerin, 515. Nitrous anhydride, 86. Nitrous anhydride in nitric acid, 87. Nitrous oxide, 81. Nitrous oxide, properties of, 82. Nomenclature, 17, 79. Nordhausen sulphuric acid, 241. O. Oils and fats, 513. Oils, composition of, 514. Oils, varnish, 520. Oils, volatile, 524. Olefins, 419. Ores, 280. Organic bodies, molecules in, 412. Organic chemistry, definition of, 411. Organic chemistry, remarks on, 406. Organic substances, classification of, 418. Organic substances, constituents of, 407. Organic substances similarly com- posed, 41 4. Organized bodies, 406. Organo-metallic compounds, 426. Osmium, 387. Oxalic acid, decomposition of, 113. Oxidation a slow combustion, 195. Oxidation, degrees of, 62. Oxides, 61. Oxygen, abundance of, 46. Oxygen a supporter of combustion, 56. Oxygen, discovery of, 48. Oxygen essential to life, 60. Oxygen, experiments with, 57, 58, 59. Oxygen, preparation of, by various methods, 54. Oxygen, preparation of, from man- ganese dioxide, 51. Oxygen, preparation of, from mercu- ric oxide, 47, 49. Oxygen, preparation of, from potas- sium chlorate, 52. Oxygen, properties of, 55. Oxygen, source of, in plants, 475. Ozone, 63. Ozone, nature of, 65. Ozone, test for, 64. P. Paraffin series of hydrocarbons, 420. Paris green, 361. Pectin, 453. Perfume ethers (page 388), 548. Perissads, 44. Peroxide, 62. Petrified wood, see Silicified wood. Petroleum, composition of, 443. Petroleum, discovery of, 442. Petroleum, hydrocarbons in, 443. Petroleum, refining of, 444. Phlogiston, 48". Phosphoretted hydrogen, 255. Phosphorus, amorphous, 251. Phosphorus burned in oxygen, 58. Phosphorus, experiments with, 250. Phosphorus in animals, 577. INDEX. 427 Phosphorus in nature, 254. Phosphorus, oxides of, 257. Phosphorus, preparation of, from bones, 2u3. Phosphorus, properties of, 249. Photography, principles of, 395. Physics, or Natural Philosophy, 1. Plants, action of lime in cultivation of, 503. Plants, annual changes in, 485. Plants, ashes of, 482. Plants, food of, 481. Plants growing without earth, 476. Plants, mineral classification of, 483. Plants, silica in, 2GO. Plants, soil the food of, 486. Plants, source of carbon in, 474. Plants, water in, 484. Plaster casts, 320. Platinum, 384. Plumbago, 99. Potash, preparation of, 287. Potassium, 282. Potassium and water, action of, 285. Potassium carbonate, 288. Potassium hydrate, 286. Potassium hydrate, action of chlorine on, 226. Potassium hydro-carbonate, 290. Potassium nitrate, 291. Potassium permanganate, 335. Potassium, preparation of, 283. Potassium, properties of, 284. Pottery, 267. Priestley's discovery of oxygen, 48. "Prince Rupert's drops," 264. Protein substances, 470. Providence balancing the atmos- phere, 131. Proximate analysis, 427. Puddling iron, 342. Q. Quartz, composition of, 259. Quicklime, 311. Quicklime and water, 312. Quinine, 531. R. Radical, definition of, 164. Rat-poison, 249. Reciprocal proportions, law of, 31. Red fire, 308. Resins, 527. Resins, uses of, 528. Rochelle salt, 508. Rocks; changes in, 13. Rotten wood, 446. Ruby, Oriental, 326. S. Sal volatile, 307. Saleratus, 290. Salt cake, 301. Salt, common, 296. Salt, decomposition of, 297. Salt in the animal economy, 580. Salt, localities of common, 298. Saltpetre, 291. Salts, 80. Salt-works, 299. Scheele, 17. Scheele's green, 361. Sea, salt in the, 300. Sea- water, lime in, 318. Seed, growth of, 471. Sesquioxide, 62. Sewer-water, value of, 507. Silica, abundance of, 259. Silicified wood, 261. Silicon, 258. Silver, 378. Silver, nitrate of, 380. Silver, salts of, 380. Size of molecules, 20. Slag, 265. Slaked lime, 3 10, 3 12. Slit of spectroscope, use of, 400. Smalt, 348. Snow, experiment with, 135. 428 INDEX. Soap-bubbles of hydrogen with oxy- gen, 191. Soaps, 517. Soda ash, 301. Soda saltpetre, 305. Sodium, 294. Sodium bi-borate, 269. Sodium carbonate, 301. Sodium chloride, 296. Sodium hydrocarbonate, 302. Sodium sulphate, 303. Soft soap, 518. Soil, constitution-of, 489. Soil, origin of, 491. Soil, treatment of, 487. Soil, varieties of, 493. Soil, water in, 488. Solder, 278. Soot, 91. Specific gravity of metals, 271. Spectra, continuous, 398. Spectra, discontinuous, 399. Spectra of alkaline metals, 402. Spectra of heavy metals, 404. Spectroscope explained, 401. Spectrum analysis, 402. Spectrum, experiments with the, 394. Spectrum of white light, 393. Spongy platinum, 386. Spontaneous combustion, 192, 521. Stalactites, 317. Stalagmites, 317. Starch converted into sugar, 463. Starch, grains of, under the micro- scope, 450. Starch, iodide of, 452. Starch, occurrence of, 448. Starch, preparation of, 449. Starch, properties of, 451. Steel, Bessemer process for, 344. Steel burned in oxygen, 59. Steel, nature of, 343. Steel, tempering of, 345. Stephenson, anecdote of, 391. Stereopticon, 189. Stoichiometry, 36. Strychnine, 531. Suboxide, 62. Substitution in organic bodies, 421. Sucrose, 457. Sugar, cane, 458. Sugar, cheating in, 462. Sugar, grape, 460. Sugar, milk, 459. Sugar of lead, 373. Sugars in general, 456. Sugars, varieties of, 457. Sulphate of magnesium, 329. Sulphur, amorphous, 235. Sulphur, flowers of, 236. Sulphur, forms of, 234. Sulphur, occurrence in animals, 577. Sulphur, occurrence of, 233. Sulphur, properties of, 237. Sulphuretted hydrogen, 248. Sulphuretted oils, 525. Sulphuric acid, manufacture of, 242. Sulphuric acid, properties of, 244. Sulphuric acid, remedy for burns by, 246. Sulphuric acid, uses of, 247. Sulphuric anhydride, 241. Sulphurous anhydride, bleaching by, 240. Sulphurous anhydride, nature of, 238. Sulphurous anhydride, preparation of, 239. Sun, agency of the, 14, 129. Sun-bleaching explained, 196. Symbols, chemical, 4, 28. Symbols explained, 30. Sympathetic ink, 349. Synthesis, 16. T. Table of atomicity, p. 48. Table of classification of the metals based on atomicity, p. 205. Table of elementary bodies, their symbols and atomic weights, p. 13. INDEX. 429 Table of fusing points of metals, p. 201. Table of hydrocarbons, homologues and isologues, p. 301. Table of hydrocarbons, showing their relations to alcohols, acids, and ethers, p. 309. Table of hydrocarbons in petroleum, p. 324. Table of the olefin series of hydrocar- bons, p. 303. Table of perfume ethers, p. 388. Table of petroleum products, p. 325. Table of specific gravity of the met- als, p. 198. Table of tenacity of the metals, p. 199. Table of thermometers, Centigrade and Fahrenheit, see Appendix, p. 418. Table of weights and measures, see Appendix, p. 417. Tannic acid, 510. Tanning, 511. Tartar emetic, 363, 508. Tessie' du Motay, 54. Tetrads, 44. Thermometer, Centigrade and Fah- renheit compared, see Appendix, p. 418. Tin, 353. Tin, "cry of," 353. Tin salts, 354. Tin, sulphides of, 355. Triads, 44. Tri-nitro-cellulose, 433. Tuscany, lagoons of, 2G9. U. Ultimate analysis, 427. Ultramarine, 327. V. Varnish oils, 520. Vegetable parchment, 430. Vegetable refuse, 506. Vegetables, influence of light on, 390. Ventilation, 126. Verdigris, 366. Vermilion, 375. Vinegar, 551. Vinegar, adulteration of, 556. Vinegar, quick method of making, 555. Volatile oils, 524. Volume, combination by, 34. Vulcanized India rubber, 530. W. Water, air in, 133. Water as a chemical agent, 158. Water, chlorine, 213. Water, constituents of, 140. Water, decomposition of, 141. Water, formation of, from elements, 144. Water, hard and soft, 316. Water in the animal economy, 581. Water of ammonia, 163. Water of crystallization, 159. Water, silica in, 260. Wax, 523. Wells, carbonic anhydride in, 123. White-lead, 371. Will-o'-the wisp, 255. Windpipe, the, the smoke-pipe of the body, 202. Wines, acidity of, 541. Wines, amount of alcohol in, 542. Wines, cider, etc., 539. Wines, flavor of, 540. Wood, combustion of, 175. Wood, distillation of, 435. Wood made from sugar, 464. Wood-naphtha, 437. Wood, products from, on heating, 434. Wood, silicified, 261. Wood, sugar made from, 461. Wood-tar, 438. 430 Wood, uses of, 432. Woody fibre, 429. Wrought iron, 342. y. Yeast, 538. INDEX. Z. 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